Producing method for die coater and coating apparatus

The present invention relates to a coating apparatus provided with a die coater having at least 2 bars mounted thereon and to a method of producing the die coater, and specifically, relates to a coating apparatus provided with a die coater having at least 2 bars with an excellent cleanability mounted thereon and to a method of producing the die coater having at least 2 bars mounted thereon, wherein the coating apparatus causes few coating failures and achieves an excellent coating quality.

In the prior art, as a method for coating a continuously running belt-shaped support (hereinafter, also referred to as ‘support’) with a liquid coating composition (for example, liquid coating compositions for subbing, overcoating, and a backside layer) for surface treatment of materials such as photographic photosensitive materials, heat development recording materials, abrasion recording materials, magnetic recording media, glass plates, steel plate, etc., there are known methods such as dip coating methods, blade coating methods, air knife coating methods, wire bar coating methods, gravure coating methods, reverse coating methods, reverse roll coating methods, extrusion coating methods, slide coating methods, and curtain coating methods.

Among these, slide coating methods, extrusion coating methods, and curtain coating methods allow high speed coating, thin layer coating, and simultaneous multi-layer coating, and accordingly, are widely used in coating photographic photosensitive materials, heat development recording materials, and abrasion recording materials. Serving as coating apparatuses to be used in these coating methods, there are used slide type die coaters for slide coating methods, extrusion type die coaters for extrusion coating methods, and curtain type die coaters for curtain coating methods.

These die coaters are produced having at least two bars mounted thereon, and regarding the structure of the die coaters, in the case of a slide type die coater, for example, the die coater has at least 2 bars and is comprised of a slit section that is constructed of at least 2 bars and lets a liquid coating composition flow out, a pocket section for supplying the liquid coating composition uniformly in the lateral direction of the slit section, a sliding section on which the liquid coating composition having flowed out of the slit section flows, and a lip section for forming beads between the end of the sliding section and a support to coat the support with the beads of the liquid coating composition. The slit section, the pocket section, the sliding section, the lip section, and an outer wall that is continuous with the lip section, are portions that come in contact with the liquid coating composition.

As for performing coating of a liquid coating composition for a photographic photosensitive material containing silver halide grains or a heat development recording material by the use of a slide type die coater, an extrusion type die coater, or a curtain type die coater, it is known that a portion, of the various die coaters, which comes in contact with the liquid coating composition has the following problem.

Regarding an outer wall continuous with a lip section, when a flow rate is set at the start of coating and when coating is terminated, a liquid coating composition flows down along the outer wall continuous with the lip section, adheres to the outer wall, and then gets dry and solidifies, which makes cleaning after the termination of coating painstaking.

Tiny foreign materials and silver halide grains may adhere to the slit section, the pocket section, the sliding section, and the lip section. In the course of coating for a long time, tiny foreign materials and silver halide grains adhering to these sections turn into a core, then further foreign materials and silver halide grains adhere to the core, and thus such created an adhering deposit may grow. If the deposit grows to a certain extent in this way, the rate and the flow speed of a liquid coating composition vary at the deposit, which makes the flow of the liquid coating composition unstable, resulting in a coating failure and difficulty in production. It is understood that these foreign materials and silver halide grains appear, for example, in such a way that foreign materials adhering to dead spaces of joint sections and valves of pipes which are disposed in a complex liquid coating composition supply system extending from a liquid coating composition supply pipe to the exit of a slit section of a die coater are torn off by conveying the liquid coating composition, and silver halide deposits in the liquid coating composition to become grains in the course of coating of the liquid coating composition for a long time. Particularly, at a start of coating, a liquid coating composition is rapidly conveyed into a liquid coating composition supply system, which tears off tiny foreign materials adhering to the respective dead spaces of the liquid coating composition supply system, and then the foreign materials adhere to portions of the die coater where the die coater contacts with the liquid coating composition.

For coating for a long time, there are known the following solutions that prevent silver halide grains deposited in a liquid coating composition and tiny foreign materials from adhering to portions, of a die coater, which contact with the liquid coating composition, and allow stable coating and easy cleaning after termination of coating.

For example, there is known a technology in which a pocket section, a slit section, etc. of an extrusion type die coater are formed with a fluorine based resin so that cleaning and disassembling are easy (referring to Patent Documents 1 and 2, for example). Another technology is known in which the periphery of a slit section of an extrusion type die coater is lyophilized with a fluorine based resin to allow forming of a thin layer without a streak type unevenness (referring to Patent Document 3, for example). Still another technology is known in which the outer wall side surface of an extrusion type coater for coating base materials is covered with a fluorine based resin to prevent retention of a liquid coating composition at a start of coating and to achieve uniform layer thickness (referring to Patent Document 4, for example).

The technologies disclosed in the above stated Patent Documents 1 to 4 are so sophisticated as to allow it to prevent adherence of foreign materials by covering portions of a die coater, the portions coming in contact with a liquid coating composition, with a fluorine based resin, but these technologies have the following problem.

Usually, a die coater covered with a fluorine based resin at portions coming in contact with a liquid coating composition is produced through the following processes in brief. Bars that are components of the die coater are subjected to either sweeping treatment for cleaning of portions to be covered with the fluorine based resin or a heat treatment called ‘pre-idle heating’, and a heat treatment called ‘baking’ for sticking the fluorine based resin to a base material, thereafter the bars are subjected to grinding and polishing, and then at least two such bars are mounted to produce the die coater.

In a process of covering bars with a fluorine based resin, these heat treatments deteriorate the straightness of the bars, and when a die coater is produced having these bars mounted thereon, the gap of a slit section in the lateral direction of coating and the distance between the die coater and an object to be coated become uneven to lower the uniformity of thickness of a layer in the lateral direction of coating, which may have resulted in a fear that coating cannot be achieved.

As a coating layer thickness is required to be accurate, the straightness of a die coater is also required to have an accuracy of a few micrometers. In covering a bar with a fluorine based resin, if the bar has a coating width shorter than 1 m approximately, the influence of heat treatment in a resin covering process is negligible and will not be a problem. However, in the case of a bar used for a die coater having a coating width exceeding 1 m, the influence of heat treatment in a fluorine based resin covering process is so significant that although a die coater produced having bars covered with the fluorine based resin is allowed to prevent coating failures due to deposition of a liquid coating composition, but the die-coater is not allowed to attain uniformity of layer thickness in the lateral direction of coating, thus only permitting coating that does not require a quality with uniformity of the coating layer thickness.

[Patent Document 1]

TOKKAI No. H11-156265

[Patent Document 2]

TOKKAI No. 2001-269606

[Patent Document 3]

TOKKAI No. 2001-191004

[Patent Document 4]

TOKKAI No. 2001-276709

With the background stated above, an object of the invention is to provide a coating apparatus using a die coater with a width of 1 meter or longer and a method of producing the die coater, the die coater having portions that come in contact with a liquid coating composition and have been subjected to covering with a fluorine based resin to achieve products that are coated with a uniform coating thickness in the lateral direction of coating and have few coating failures can be achieved.

The above-described object has been attained with the following items.

1) A coating apparatus comprising a pocket section for extending a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition (coating liquid) to the pocket section, and a slit section for ejecting the liquid coating composition from the pocket section to an object to be coated, and employing a die coater having at least 2 bars mounted thereon, wherein at least one portion, of each bar, that forms a surface of the die coater and comes in contact with the liquid coating composition is covered with a fluorine based resin, and the straightness, in the lateral direction of coating, of the surface covered with the fluorine based resin of each bar ranges from 0.1 to 10 μm.

2) A coating apparatus comprising a pocket section for extending a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section for ejecting the liquid coating composition from the pocket section to an object to be coated, and employing a die coater having at least 2 bars mounted thereon, wherein at least one portion, of each bar, that forms a surface of the die coater and comes in contact with the liquid coating composition is covered with a fluorine based resin, and the surface roughness of the fluorine based resin covered portion of each is within a range of 0.01 μm<Ra<1 μm and 0.1 μm<R max <5 μm.

3) A coating apparatus comprising a pocket section for extending a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section for ejecting the liquid coating composition from the pocket section to an object to be coated, and employing a die coater having at least 2 bars mounted thereon, wherein at least one portion, of each bar, that forms a surface of the die coater and comes in contact with the liquid coating composition is covered with a fluorine based resin, the surface roughness of the fluorine based resin covered portion of each bar is within a range of 0.01 μm<Ra<1 μm and 0.1 μm<R max <5 μm, and the straightness of the fluorine based resin covered portion of the bar in the lateral direction of coating is within a range from 0.1 to 10 μm.

4) A coating apparatus comprising a pocket section for extending a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section for ejecting the liquid coating composition from the pocket section to an object to be coated, and employing a die coater having at least 2 bars mounted thereon, wherein at least one portion, of each bar, that forms a surface of the die coater and comes in contact with the liquid coating composition is covered with a fluorine based resin, and the portion of the bar to be covered with the fluorine based resin is removed in advance by grinding for the thickness of the fluorine based resin cover prior to the fluorine based resin covering, and thereafter, covered with the fluorine based resin.

5) A coating apparatus comprising a pocket section for extending a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section for ejecting the liquid coating composition from the pocket section to an object to be coated, and employing a die coater having at least 2 bars mounted thereon, wherein at least one portion, of each bar, that forms a surface of the die coater and comes in contact with the liquid coating composition is covered with a fluorine based resin, and the bars are subjected in advance to a thermal pretreatment at a temperature same as or higher than that of a heat treatment in a fluorine based resin covering process, thereafter to grinding, and then to covering with the fluorine based resin.

6) The coating apparatus according to item 5, wherein the grinding includes a first grinding for removing deformation caused by the thermal pretreatment and a second grinding for forming a final finish shape.

7) The coating apparatus according to item 5 or 6, wherein the bars are subjected to covering with the fluorine based resin, and thereafter to finish grinding.

8) The coating apparatus according to item 7, wherein the finish grinding makes the straightness of the surface of each portion covered with the fluorine based resin within a range from 0.1 to 10 μm.

9) The coating apparatus according to any one of items 5 to 8, wherein the bars are subjected to covering with the fluorine based resin, and thereafter to polishing on the surface of each portion subjected to the covering.

10) The coating apparatus according to any one of items 5 to 9, wherein the bars have a surface roughness of each portion subjected to the covering process within a range of 0.01 μm<Ra<1 μm and 0.1 μm<R max <5 μm.

11) The coating apparatus according to any one of items 5 to 10, wherein the bars are subjected to the thermal pretreatment, thereafter each portion thereof to be covered with the fluorine based resin is removed in advance by grinding for the thickness of the fluorine based resin prior to the covering, and then covered with the fluorine based resin.

12) The coating apparatus according to any one of items 1 to 11, wherein the die coater is comprised of at least two bars; the gap of at least one slit section formed by the bars has an outlet narrower than an inlet of a liquid coating composition and the gap d at the outlet is d≦5×10 −5 [m]; and the bars are components of the die coater that ejects a liquid coating composition in a layer form from the slit section in order to make the liquid coating composition collide, at a predetermined gap, with an object to be coated for coating, the object being disposed or conveyed with no contact with the outlet of the slit section.

13) The coating apparatus according to any one of items 1 to 11, wherein the bars are structure members of an extrusion type die coater that extrudes the liquid coating composition from at least one slit section formed by at least 2 bars onto a belt-shaped support that is continuously conveyed from upstream to downstream, then forms beads of the liquid coating composition between the vicinity of a liquid coating composition extruding part of the lip section and the support, and coats the beads on the support.

14) The coating apparatus according to any one of items 1 to 11, wherein the bars are structure members of a slide type die coater that extrudes the liquid coating composition from at least one slit section formed by at least 2 of the bars onto a belt-shaped support that is continuously conveyed from upstream to downstream, lets the liquid coating composition having been extruded flow down along a steep which is continuous with the outlet of the slit, then forms beads of the liquid coating composition between the belt-shaped support and a vicinity of an end part of the steep, and coats the beads on the belt-shaped support.

15) The coating apparatus according to any one of items 1 to 11, wherein the bars are structure members of a curtain type die coater that lets the liquid coating composition having been extruded from at least one slit section formed by at least two of the bars fall freely onto a belt-shaped support that is continuously conveyed from upstream to downstream, and thereby coats the liquid coating composition.

16) The coating apparatus according to any one of items 1 to 15, wherein the bars are structure members of a die coater having a width of 1 meter or larger.

17) The coating apparatus according to any one of items 11 to 16, wherein the belt-shaped support is in a state that a surface opposite to a coated surface thereof is supported by a backroll.

18) The coating apparatus according to item 13, wherein the belt-shaped support is supported by a support roll at a position near the die coater.

19) The coating apparatus, according to any one of items 1 to 18, wherein the liquid coating composition is a liquid coating composition for a photosensitive layer containing a silver component for a heat-developing photosensitive material or a liquid coating composition for a non-photoreceptive protective layer.

20) A method of producing a die coater comprising a pocket section that extends a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section that ejects the liquid coating composition from the pocket section to an object to be coated, the die coater having at least 2 bars mounted thereon, the bars having a surface coming in contact with the liquid coating composition and being components of the die coater and coated with a fluorine based resin at, at least, one portion of the surface, wherein the portion of each bar to be covered with the fluorine based resin is covered with the fluorine based resin for a thickness greater than the amount to be finish-grinded, then baked; and thereafter, the surface covered with the fluorine based resin is finish-grinded and/or polished to be finished with a straightness in the lateral direction of coating within a range from 0.1 to 10 μm and with a surface roughness of the portion having been subjected to covering with the fluorine based resin within a range of 0.01 μm<Ra<1 μm, and 0.1 μm<Rmax<5 μm.

21) A method of producing a die coater comprising a pocket section that extends a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section that ejects the liquid coating composition from the pocket section to an object to be coated, the die coater having at least 2 bars mounted thereon, the bars having a surface coming in contact with the liquid coating composition and being coated with a fluorine based resin at, at least, one portion of the surface, wherein each bar is subjected in advance to a thermal pretreatment at a temperature same as or higher than that of a heat treatment of a covering process of the fluorine based resin and thereafter to grinding; a portion of each bar to be covered with the fluorine based resin is covered with the fluorine based resin for a thickness greater than the amount to be finish-grinded, then baked; and thereafter, the surface covered with the fluorine based resin is finish-grinded and/or polished to be finished with a straightness in the lateral direction of coating within a range from 0.1 to 10 μm and with a surface roughness of the portion having been subjected to covering with the fluorine based resin within a range of 0.01 μm<Ra<1 μm, and 0.1 μm<Rmax<5 μm.

22) A method of producing a die coater comprising a pocket section that extends a liquid coating composition in the lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, and a slit section that ejects the liquid coating composition from the pocket section to an object to be coated, the die coater having at least 2 bars mounted thereon, the bars having a surface coming in contact with the liquid coating composition and being coated with a fluorine based resin at, at least, one portion of the surface, wherein each bar is subjected in advance to a thermal pretreatment at a temperature same as or higher than that of a heat treatment of a covering process of the fluorine based resin and thereafter to grinding; each portion to be covered with the fluorine based resin is removed by grinding for the thickness of the covering with the fluorine based resin prior to the covering; a portion of each bar to be covered with the fluorine based resin is covered with the fluorine based resin for a thickness greater than the amount to be finish-grinded, then baked; and thereafter, the surface covered with the fluorine based resin is finish-grinded and/or polished to be finished with a straightness in the lateral direction of coating within a range from 0.1 to 10 μm and with a surface roughness of the portion having been subjected to covering with the fluorine based resin within a range of 0.01 μm<Ra<1 μm, and 0.1 μm<Rmax<5 μm.

23) The method of producing a die coater according to item 21 or 22, wherein the grinding includes a first grinding for removing deformation caused by the thermal pretreatment and a second grinding for forming a final finish shape.

As stated above, in the case where portions, of bars constructing a die coater, coming in contact with a liquid coating composition are covered with a fluorine based resin, the straightness of the abovementioned portions of the bars in the lateral direction of coating cannot be maintained for a long time use. As a conclusion of an intensive study for solving the problem and on the cause thereof, the inventors estimated that the internal stress of the bars generated through a heat treatment in a covering process of the fluorine based resin and a machining stress generated through producing of the die coater having the bars mounted thereon get elicited and generate deformation, and thus deteriorate the straightness of the die coater. The inventors further estimated that the deterioration of straightness causes ununiformity of the gap of a slit in the lateral direction of coating and of the distance between the die coater and an object to be coated, thus degrading the uniformity of layer thickness in the lateral direction of coating.

The inventors studied intensively on this to reduce deformation caused through covering of a bar with a fluorine based resin. As a result, it proved that a uniform layer thickness in the lateral direction of coating is attained and few coating failures are caused with improved coating quality even for a long time use, by removing, prior to covering the bar, a residual machining stress generated through production of the bar and held by the bar, thereafter covering the bar with the fluorine based resin, then finishing the bar to a desired straightness and surface roughness, and using a die coater that is produced mounting the bars thereon. Thus, the invention is attained.

There is provided a coating apparatus employing a die coater and a method of producing the die coater, wherein the die coater has a large width of 1 m or larger and is covered with a fluorine based resin at a portion coming in contact with a liquid coating composition, thereby making it possible to obtain coated products having a uniform coating layer thickness in the lateral direction of coating and few coating failures. Coating failures have decreased, layer thickness distribution has become stable, and accordingly, the product quality has become stable with an increase in the fine quality rate. Further, the straightness is not degraded even for a long elapsed time, and coating with a stable coating layer thickness in the lateral direction is allowed.

Incidentally, “straightness” is defined by JIS B0182 and “surface roughness” is defined by JIS B0601.

FIG. 1 a is a schematic diagram of a slide coating system that performs coating by forming beads by the use of a slide type die coater;

FIG. 1 b is an enlarged schematic diagram of the slide type die coater system shown in FIG. 1 a;

FIG. 2 a is a schematic diagram of an extrusion coating system that performs coating by forming beads by the use of an extrusion type die coater;

FIG. 2 b is an enlarged schematic diagram of the extrusion type die coater shown in FIG. 2 a;

FIG. 3 is a schematic diagram of an extrusion coating system that performs coating of a support that is supported by a support roll, using an extrusion type die coater shown in FIGS. 2 a and 2 b;

FIG. 4 a is a schematic diagram of an extrusion coating system that uses another structure of extrusion type die coater and performs coating by colliding, across a predetermined gap from a slit section, a liquid coating composition with an object to be coated instead of forming beads;

FIG. 4 b is an enlarged schematic diagram of the extrusion type die coater shown in FIG. 4 a;

FIG. 5 is a schematic diagram of a curtain coating system using the slide type die coater shown in FIGS. 1 a and 1 b;

FIG. 6 is a schematic flowchart showing a method of producing a die coater having bars mounted thereon, the bars being covered with a fluorine based resin;

FIG. 7 is a schematic flowchart showing a method of producing a die coater having bars mounted thereon, the bars having been subjected to a thermal pretreatment, thereafter to grinding, and then to fluorine based resin covering; and

FIG. 8 is a schematic flowchart showing another method of producing a die coater having bars mounted thereon, the bars having been subjected to a thermal pretreatment, thereafter to grinding, and then to fluorine based resin covering.

The best mode of the invention will be described referring to FIGS. 1 a to 8 , but the invention is not limited to this.

FIGS. 1 a and 1 b are schematic diagrams showing a slide coating system that performs coating by forming beads by the use of a slide type die coater. FIG. 1 a is a schematic diagram of the slide coating system that performs coating on a holding section of a support, which is held by a back-roll at a surface opposite to one to be coated, in such a way that the slide type die coater forms beads. FIG. 1 b is an enlarged schematic diagram showing the slide type die coater system shown in FIG. 1 a.

In FIGS. 1 a and 1 b , numeral 1 represents the slide type die coater, 2 represents the back-roll, and 3 represents a belt-shaped support, which is continuously conveyed from upstream to downstream (in the direction shown by the arrow in the figure). The slide type die coater 1 is produced mounting respective bars 101 a to 101 d thereon. The quantity of bars is not fixed by the bars 101 a to 101 d , but can be increased or decreased depending on the quantity of layers to be coated. The back-roll is a conveying roll disposed on the surface side of the belt-shaped support 3 opposite to the coating surface side thereof, sandwiching the belt-shaped support 3 cooperating with the slide type die coater 1 . Since the cylindricality of the back-roll has a significant effect on the accuracy of the gap in the lateral direction of coating as well as the slide type die coater 1 , the back-roll is constructed of a metal with a large diameter of 200 mm or larger.

Numerals 102 a to 102 c represent slit sections that are arranged between the respective bars 101 a to 101 d which construct the slide type die coater and serving as an outlet of a liquid coating composition. The quantity of slit sections is variable depending on the quantity of bars such as the respective bars 101 a to 101 d constructing a slide type die coater, and is ordinarily 2 to 20 . The slide type die coater shown in FIGS. 1 a and 1 b is constructed by mounting 4 bars thereon, thus having 3 slit sections, and used for simultaneous multilayer coating.

Numerals 103 a to 103 c represent the inner walls of the respective slit sections 102 a to 102 c , while numerals 104 a to 104 c represent edge sections at the outlets of the respective slit sections 102 a to 102 c . Numerals 105 a to 105 c represent pocket sections formed at the respective slit sections 102 a to 102 c so that liquid coating compositions, the liquid coating compositions having been conveyed from respective supplying pipes 403 a to 403 c , are extruded from the respective slit sections 102 a to 102 c uniformly in the lateral direction. Numerals 106 a to 106 c represent the inner walls of the pocket sections 105 a to 105 c.

Numerals 107 a to 107 d represent sliding surfaces. Liquid coating compositions adjusted by adjusting pots 401 a to 401 c of a liquid coating composition supply system 4 are fed to the respective pocket sections 105 a to 105 c formed between the bars 101 a to 101 d by liquid conveying pumps 402 a to 402 c through the respective supply pipes 403 a to 403 c , then the liquid coating compositions are ejected from the respective sections 102 a to 102 c , flow down along the respective sliding sections 107 a to 107 c , and form beads 5 through a lip section 108 to be coated on the holding section of the support 3 that is conveyed in such a way that the surface thereof on the side opposite to the surface to be coated is held by the back-roll 2 .

Numeral 110 represents an outer wall that is continuous with the lip section 108 . Numerals 109 a to 109 c represent liquid coating composition supply flow paths for supplying the liquid coating compositions, which have been conveyed from the respective pipes 403 a to 403 c , to the respective pocket sections 105 a to 105 c.

Numeral 6 represents a pressure reducing chamber for stabilizing coating, the pressure reducing chamber being arranged under the slide type die coater 1 , wherein numeral 601 represents a suction pipe. Numeral 7 represents coating layers coated on the support 3 , and symbol W 1 represents a coating point where the slide type die coater 1 coats the liquid coating compositions on the support 3 , wherein the coating point W 1 is, in a typical case, preferably located at a position 0 to 20 degrees upward from the horizontal axis that goes through the back-roll.

When coating is performed for a long time, liquid coating compositions deposit on the lip section 108 and the outer wall 110 which is continuous with the lip section 108 , become dry, and solidify. Further, foreign materials and silver halide grains mixed in the liquid coating compositions deposit on the respective inner walls 106 a to 106 c of the pocket sections 105 a to 105 c , on the respective inner walls 103 a to 103 c of the slit sections 102 a to 102 c , and on the respective edge sections 104 a to 104 c at the outlets of the slit sections 102 a to 102 c . When deposits are carried out by the liquid coating compositions and coated on the belt-shaped support as they are, foreign material deposit failures occur.

Also, when foreign materials and silver halide grains mixed in the liquid coating compositions deposit on the respective inner walls 103 a to 103 c of the slit sections 102 a to 102 c , the edge sections 104 a to 104 c , the sliding surfaces 107 a to 107 c , and the lip section 108 , the flows of the liquid coating compositions at portions with the deposits are not normal and become streaks which cause streak failures.

Further, when a covering film created by dried liquid coating compositions adheres to the lip section 108 , beads forming becomes unstable, and accordingly, coating becomes unstable. When coating films created, by dried liquid coating compositions adhere to the outer wall 110 that is continuous with the lip section 108 , cleaning after terminating coating becomes painstaking. When adjusting the flow rates of liquid coating compositions or when cleaning the inside of the slit sections 102 a to 102 c prior to a start of coating, the liquid coating compositions flow down along the outer wall 110 , and get dry and solidify. Therefore, the outer wall 110 continuous with the lip section 108 needs cleaning such as rubbing off and scraping off such created solids for each coating.

Surfaces of the slide type die coater 1 shown in FIGS. 1 a and 1 b that contact a liquid coating composition according to the invention include the inner walls 103 a to 103 c of the slit sections 102 a to 102 c constructed of the respective bars 101 a to 101 d , the edge sections 104 a to 104 c , the inner walls 106 a to 106 c of the pocket sections 105 a to 105 c , the liquid coating composition supply flow paths 109 a to 109 c , the sliding sections 107 a to 107 c , the lip section 108 , and the outer wall 110 continuous with the lip section 108 . These portions in contact with the liquid coating compositions are portions to be covered with a fluorine based resin according to the invention.

That is, in the slide type die coater 1 produced mounting the respective bars 101 a to 101 d thereon, portions, of the respective bars 101 a to 101 d , coming in contact with a liquid coating composition are the portions to be covered with a fluorine based resin according to the invention.

FIGS. 2 a and 2 b are schematic diagrams of an extrusion coating system that uses an extrusion type die coater to form beads and perform coating. FIG. 2 a is a schematic diagram of the extrusion coating system that uses the extrusion type die coater to form beads and perform coating of a holding section of a support, the support having a surface, opposite to one to be coated, held by a back-roll. FIG. 2 b is an enlarged schematic diagram of the extrusion type die coater shown in FIG. 2 a.

Numeral 8 in FIGS. 2 a and 2 b represents the extrusion type die coater. The extrusion type die coater 8 is produced mounting respective bars 801 a to 801 c thereon. The quantity of bars is not fixed by the bars 801 a to 801 c , but can be increased or decreased depending on the quantity of coating layers.

Numerals 802 a and 802 b represent slit sections that are flow outlets of liquid coating compositions formed between the respective bars 801 a to 801 c that construct the extrusion type die coater 8 . The quantity of slit sections is variable depending on the quantity of bars such as the respective bars 801 a to 801 c constructing the extrusion type die coater, and typically in a range from 1 to 5. The extrusion type die coater 8 shown in FIGS. 2 a and 2 b is constructed of 3 bars, having 2 slit sections for simultaneous multilayer coating.

Numerals 803 a and 803 b represent inner walls of the respective slit sections 802 a and 802 b , numerals 804 a and 804 b represent edge sections at the outlets of the respective slit sections 802 a and 802 b , and numeral 805 a to 805 c represent lip sections. Numerals 806 a and 806 b represent pocket sections formed at the respective slit sections 802 a and 802 b in order to push out the liquid coating compositions from the respective slit sections 802 a and 802 b uniformly in the lateral direction, the liquid coating compositions having been conveyed from the respective supplying pipes 403 a and 403 b . Numerals 807 a and 807 b represent inner walls of the respective pocket sections 806 a and 806 b.

Numerals 808 a and 808 b represent liquid coating composition supply flow paths for supplying the liquid coating compositions, the liquid coating compositions having been conveyed from the respective supplying pipes 403 a and 403 b , to the respective pocket sections 806 a and 806 b . Numeral 809 represents an outer wall continuous with the lip section 805 a . The outer wall 809 is a portion that needs cleaning. Specifically, when adjusting the flow rates of liquid coating compositions or when cleaning the inside of the respective slit sections 802 a and 802 b prior to a start of coating, the liquid coating compositions flow down along the outer wall 809 , and get dry and solidify. Therefore, the outer wall 809 needs cleaning such as rubbing off and scraping off such created solids for each coating.

Liquid coating compositions adjusted by adjusting pots 401 a and 401 b of a liquid coating composition supply system 4 are fed to the respective pocket sections 806 a and 806 b formed between the bars 801 a to 801 c through the respective supplying pipes 403 a and 403 b by respective solution conveying pumps 402 a and 402 b , then the liquid coating compositions are extruded from the respective slit sections 802 a and 802 b , pass through the lip section 805 a , and form beads 9 to be coated on the holding section of the belt-shaped support 3 that is conveyed in such a way that the surface thereof on the side opposite to the surface to be coated is held by the back-roll 2 . Symbol W 2 represents a coating point where the coater 8 coats the support 3 with the liquid coating compositions, wherein the coating point W 2 is, in an ordinary case, preferably located at a position 0 to 90 degrees downward from the horizontal axis that goes through the back-roll. Other symbols represent the same as those in FIGS. 1 a and 1 b.

When coating is performed for a long time, liquid coating compositions deposit on the lip section 805 a and the outer wall 809 which is continuous with the lip section 805 a , become dry and solidify. Further, foreign materials and silver halide grains mixed in the liquid coating compositions deposit on the respective inner walls 807 a and 807 b of the pocket sections 806 a and 806 b , the respective edge sections 804 a and 804 b , and the respective inner walls 803 a and 803 b of the slit sections 802 a and 802 b . When deposits are pushed out by the liquid coating compositions and coated on the belt-shaped support as they are, foreign material deposition failures occur. Also, when foreign materials and silver halide grains mixed in the liquid coating compositions deposit on the respective inner walls 803 a and 803 b of the slit sections 802 a and 802 b , the respective edge sections 804 a and 804 b , and the lip sections 805 a to 805 c , the flows of the liquid coating compositions at the portions with deposits become different and turn into streaks which cause streak failures. Further, when a covering film created by a dried liquid coating composition adheres to the lip section 805 a , beads forming becomes unstable, and accordingly, coating becomes unstable. When a covering film created by a dried liquid coating composition adheres to the outer wall 809 that is continuous with the lip section 805 a , cleaning after terminating coating becomes painstaking.

Surfaces, of the extrusion type die coater shown in FIGS. 2 a and 2 b , that contact liquid coating compositions according to the invention include the respective inner walls 803 a and 803 b of the slit sections 802 a and 802 b , the respective edge sections 804 a and 804 b , the respective inner walls 807 a and 807 b of the pocket sections 806 a and 806 b , the liquid coating composition supply flow paths 808 a and 808 b , the lip sections 805 a to 805 c , and the outer wall 809 continuous with the lip section 805 a . These surfaces coming in contact with the liquid coating compositions are portions to be covered with a fluorine based resin according to the invention. That is, in the extrusion type die coater 8 produced mounting the respective bars 801 a to 801 d thereon, portions, of the respective bars 801 a to 801 d , coming in contact with a liquid coating composition are the portions to be covered with a fluorine based resin according to the invention.

FIG. 3 is a schematic diagram showing an extrusion coating system that performs coating of a support that is supported by a support roll, using an extrusion type die coater shown in FIGS. 2 a and 2 b.

Numeral 10 in the figure represents the support roll. Other symbols represent the same as those in FIGS. 2 a and 2 b . The only difference between the coating system shown in FIG. 3 and the coating system shown in FIGS. 2 a and 2 b is that the coating system uses a different method of supporting of the belt-shaped support from one shown in FIG. 2 a . Therefore, portions where liquid coating compositions deposit through a long time coating, portions where foreign materials adhere, surfaces in contact with the liquid coating compositions, and portions to be coated with a fluorine based resin are the same as those of the extrusion type die coater shown in FIGS. 2 a and 2 b.

FIGS. 4 a and 4 b are schematic diagrams of an extrusion coating system that uses another structure of extrusion type die coater and performs coating by colliding, across a predetermined gap from a slit section, a liquid coating composition with an object to be coated instead of forming beads. FIG. 4 a is a schematic diagram of the extrusion coating system that performs coating on a holding section of a support having a surface, opposite to a surface to be coated, held by a backroll, using another structure of extrusion type die coater without forming beads. FIG. 4 b is an enlarged schematic diagram of the extrusion type die coater shown in FIG. 4 a.

In FIGS. 4 a and 4 b , numeral 11 represents the extrusion type die coater. The extrusion type die coater 11 is produced having bars 111 a to 111 c mounted thereon. The quantity of bars is not fixed by the bars 111 a to 111 c , but can be increased or decreased depending on the quantity of coating layers.

Numerals 112 a and 112 b represent slit sections arranged between the respective bars 111 a to 111 c which construct the extrusion type die coater. Numerals 12 a and 12 b represent coating layers formed by ejecting liquid coating compositions from the respective slit sections 112 a and 112 b.

The quantity of slit sections is variable depending on the quantity of bars constructing the extrusion type die coater, and is typically in a range from 1 to 5. The extrusion type die coater shown in FIGS. 4 a and 4 b is constructed of 3 bars, having 2 slit sections for simultaneous multilayer coating.

Numerals 113 a and 113 b represent the outlet sides, of liquid coating compositions, of the respective slit sections 112 a and 112 b , and numerals 113 a 1 and 113 b 1 represent the inlet sides of, of the liquid coating compositions, of the respective slit sections 112 a and 112 b . Numerals 114 a and 114 b represent inner walls of the respective slit sections 112 a and 112 b on the respective outlet sides 113 a and 113 b of the liquid coating compositions, and numerals 114 a 1 and 114 b 1 represent inner walls of the respective slit sections 112 a and 112 b on the respective inlet sides 113 a 1 and 113 b 1 of the liquid coating compositions. Numerals 115 a and 115 b represent edge sections of the respective slit sections 112 a and 112 b , and numerals 116 a and 116 b represent lip sections. Numerals 117 a and 117 b represent pocket sections formed at the respective slit sections 112 a and 112 b to extrude the liquid coating compositions, the liquid coating compositions having been conveyed from the respective supply pipes 403 a and 403 b , out from the respective slit sections 112 a and 112 b uniformly in the lateral direction. Numerals 118 a and 118 b represent inner walls of the respective pocket sections 117 a and 117 b.

Numerals 119 a and 119 b represent liquid coating composition supply flow paths for supplying the liquid coating compositions, the liquid coating compositions having been conveyed from the respective supplying pipes 403 a and 403 b , to the respective pocket sections 117 a and 117 b . Numeral 120 represents an outer wall continuous with the lip section 116 a . The outer wall 120 is a portion that needs cleaning. Specifically, when adjusting the flow rates of liquid coating compositions or when cleaning the inside of the respective slit sections 112 a and 112 b prior to a start of coating, the liquid coating compositions flow down along the outer wall 120 , and get dry and solidify. Therefore, the outer wall 120 needs cleaning such as rubbing off and scraping off such created solids for each coating.

Surfaces, of the extrusion type die coater shown in FIGS. 4 a and 4 b , that contact with liquid coating compositions include the respective inner walls 114 a and 114 b of the slit sections 112 a and 112 b on the outlet side 113 a and 113 b of the liquid coating compositions, the respective inner walls 114 a 1 and 114 b 1 of the slit sections 112 a and 112 b on the inlet side 113 a 1 and 113 b 1 of the liquid coating compositions, the edge sections 115 a and 115 b , the respective lip sections 116 a and 116 b , the respective inner walls 118 a and 118 b of the pocket sections 117 a and 117 b , the respective liquid coating composition supplying flow paths 119 a and 119 b , and the outer wall 120 continuous with the lip section 116 a . These surfaces coming in contact with the liquid coating compositions are portions to be coated with a fluorine based resin. That is, in the extrusion type die coater 11 produced having the respective bars 101 a to 101 c mounted thereon, portions of the respective bars 111 a to 111 c coming in contact with a liquid coating composition are the portions to be covered with a fluorine based resin according to the invention.

The liquid coating compositions adjusted by adjusting pots 401 a and 401 b of a liquid coating composition supply system 4 are supplied to the respective pocket sections 117 a and 117 b arranged between the respective bars 111 a to 111 c through the respective supply pipes 403 a and 403 b by liquid conveying pumps 402 a and 402 b , then the liquid coating compositions are ejected from the respective slit sections 112 a and 112 b in a layer form so that the liquid coating compositions are collided with the holding section of the belt-shaped support 3 that is conveyed in such a way that the surface thereof on the side opposite to the surface to be coated is held by the back-roll 2 , and thus the liquid coating compositions are coated on the holding section of the belt-shaped support 3 .

Symbol D represents an outlet gap of a slit section. The outlet gap D can be properly adjusted depending on the physical properties of a liquid coating composition to be used and the thickness of a coating layer. The gap of the slit section is wider on the inlet side of the liquid coating composition and narrower on the outlet side, wherein the outlet gap D of the slit section is in a range of D≦5×10 −5 [m]. More preferably, D is in a range of 1×10 −5 [m]≦D≦4×10 −5 [m]. The outlet gap D is set in such a range so that the liquid coating composition is ejected in an extremely thin layer form that allows thin layer coating compared with known extrusion type die coaters.

In the case of the extrusion type die coater shown in FIGS. 4 a and 4 b , portions where foreign materials and silver halide grains deposit in the course of coating for a long time are the same as those of the extrusion type die coater shown in FIGS. 2 a and 2 b.

FIG. 5 is a schematic diagram of a curtain coating system using the slide type die coater shown in FIGS. 1 a and 1 b.

In FIG. 5 , numeral 13 represents layers formed in such a way that liquid coating compositions extruded out from the outlets of respective slit sections flow down along a sliding surface in a state the liquid coating compositions are laminated and fall with gravity. The layers 13 are coated on a belt-shaped support. Other symbols represent the same as those in FIGS. 1 a and 1 b.

In the case of the slide type die coater shown in FIG. 5 , surfaces in contact with liquid coating compositions, portions subjected to covering with a fluorine based resin, and portions where foreign materials and silver halide grains deposit through coating for a long time, are the same as those of the slide type die coater shown in FIGS. 1 a and 1 b . In the invention, the slide type die coater and the extrusion type die coaters shown in FIGS. 1 a to 5 are also referred to as a die coater to be a generic term.

In the various types of die coaters shown in FIGS. 1 a to 5 , a pocket section is usually designed in a large cross section for a low flow velocity so that a liquid coating composition is distributed in a uniform pressure in the lateral direction of coating. In general, foreign materials and silver halide grains in a liquid coating composition easily deposits on a surface of a die coater. Once they have deposited, the depositions turn into a core and grow, and then get torn by some trigger to be mixed in the liquid coating composition, causing a coating failure. Therefore, covering with a fluorine based resin to prevent deposition is effective in preventing occurrence of coating failures.

Since a slit section has a narrow gap, if foreign materials and silver halide grains in the liquid coating composition deposit on a surface even a little, the flow path is blocked to cause a streak-shape failure. Therefore, performing coating with fluorine based resin to avoid deposition is effective in preventing occurrence of coating failure.

When the straightness of a slit section is low, it is difficult to eject a liquid coating composition in the lateral direction of a die coater with a uniform pressure, thus the ejection amount of the liquid coating composition is unstable in the lateral direction, and the coating layer thickness in the lateral direction is not constant. Therefore, making the straightness small is effective in achieving a constant coating layer thickness in the lateral direction.

To prevent deposition of foreign materials and silver halide grains in a liquid coating composition on a lip section, it is quite effective to cover the lip section with a fluorine based resin as well as in the case of a slit section. Particularly at a lip section, which is on the lowest downstream side, when a liquid coating composition having come round beads and deposited gets dry and solidifies, beads cannot be formed stably, and accordingly, stable coating is not allowed. Therefore, it is extremely effective to cover with a fluorine based resin in preventing deposition to avoid coating failures.

If the straightness of a lip section is low, forming of beads is unstable in the lateral direction, and it is impossible to perform stable coating, by which the coating layer thickness in the lateral direction is not constant. Therefore, it is effective to make the straightness small in achieving a constant coating layer thickness in the lateral direction.

Since a liquid coating composition on a sliding surface flows down with gravity, the flow velocity is small, by which foreign materials and silver halide grains in the liquid coating composition tend to deposit as well as in a pocket section. Therefore, it is extremely effective to cover a fluorine based resin in preventing deposition to avoid coating failures.

When the straightness of a sliding surface is low, a liquid coating composition flows down on the sliding surface unstably, and it is impossible to perform stable coating, by which the coating layer thickness in the lateral direction is not constant. Therefore, it is effective to make the straightness small in achieving a constant coating layer thickness in the lateral direction.

An edge is also a part where foreign materials and silver halide grains in a liquid coating composition tend to deposit, and deposition, when occurred, makes a flow of the liquid coating composition unstable to cause a streak failure. Therefore, it is effective to cover with a fluorine based resin in preventing deposition to avoid coating failures.

When the straightness of an edge is low, the ejection amount of a liquid coating composition is unstable in the lateral direction of a slit, and it is impossible to perform stable coating, by which the coating layer thickness in the lateral direction is not constant. Therefore, it is effective to make the straightness small in achieving a constant coating layer thickness in the lateral direction.

When adjusting the flow rates of liquid coating compositions or when cleaning the inside of respective slit sections prior to a start of coating, the liquid coating compositions flow down along an outer wall that is continuous with a lip section, deposit, and get dry and solidify, which requires cleaning such as rubbing off and scraping off for each coating. Thus, the outer wall continuous with the lip section is a part which takes time to be cleaned. It is effective to cover a fluorine based resin on the outer wall continuous with the lip section in greatly reducing deposition of liquid coating compositions, which shorten the time for cleaning.

In the case of coating by a die coater that is produced having bars, the bars having been subjected to covering with a fluorine based resin at portions thereof coming in contact with a liquid coating composition, mounted thereon, the portions of the die coater in contact with a liquid coating composition have less dirt, but, through a long elapsed time, coating with a uniform coating layer thickness in the lateral direction of coating may not be achieved, which particularly tends to occur on a die coater having a large coating width not smaller than 1 m.

Although, in the case of covering portions of a bar, the portions coming in contact with a liquid coating composition, with a fluorine based resin, a heat treatment for cleaning of processing surfaces and a heat treatment called a baking treatment for sticking a fluorine based resin to a base material are performed at a temperature of 400 to 500° C., as a result of an intensive study by the inventors, it proved that deformation caused by an inner stress generated and accumulated through processing of the bar gets elicited and deteriorates the straightness of the bar, and a die coater produced having bars in this state mounted thereon has a low straightness thereof.

The present invention relates to a coating apparatus employing a die coater having at least two bars mounted thereon, and relates to a method of producing the die coater, wherein each bar is covered with a fluorine based resin at least at portions thereof coming in contact with a liquid coating composition including a pocket section for extending the liquid coating composition in the coating lateral direction of coating, a liquid coating composition supply inlet for supplying the liquid coating composition to the pocket section, a slit section for ejecting the liquid coating composition from the pocket section onto an object to be coated, and a wall continuous with a lip section.

In the invention, a covering process heat treatment is referred to, including a heat treatment for cleaning surfaces, to be covered, in the covering process with a fluorine based resin and a baking treatment.

As a first means for stable coating with a minimum possible deformation of a bar due to a heat treatment of a covering process with a fluorine based resin, it is effective to make the straightness of the bars within a range from 0.1 to 10 μm by grinding-removing the deformation caused by the covering process with the fluorine based resin. Further, covering each bar with the fluorine based resin in a thickness greater than that of grinding enables correction by grinding of the deformation of the bar caused by the baking treatment, and further enables this correction of the deformation caused by the baking treatment in such a manner that the deformation is removed by grinding only the fluorine based resin without grinding the bar, by which the residual grinding stress in the bar is reduced. Therefore, utilizing a die coater produced having such processed bars mounted thereon prevents the residual grinding stress in the bars from gradually getting elicited and prevents the straightness of the die coater from degrading even after a long elapsed time, and makes stability of the slit gap in the lateral direction of coating and the distance between the die coater and an object to be coated, thereby enabling coating excellent in the uniformity of the layer thickness in the lateral direction of coating. Further, stable coating is achieved also in the aspect that the portions coming in contact with a liquid coating composition are covered with a fluorine based resin to be protected from dirt even for a long time coating.

As a second means, a residual machining stress which is caused when a bar is produced and is latent in the bar is removed prior to the covering process. The inventors found that, as a means for removing the residual machining stress, it is effective to perform a thermal pretreatment at the temperature same as or higher than that of a covering process heat treatment, thereafter remove deformation by grinding, and then cover the bar with the fluorine based resin. It is difficult to determine the upper limit of the temperature of the thermal pretreatment because it varies with the material to be employed for the bar, but at least, it should be lower than the melting point of the material.

Deformation amount generated on the bar can be reduced by performing a thermal pretreatment, removing the generated deformation by grinding, thereafter cleaning the portions to be covered a with fluorine based resin by a heat treatment, covering the portions with the fluorine based resin, and performing a baking treatment. The smaller deformation amount requires a smaller amount of finish grinding after the baking treatment, and thus the residual grinding stress in the bar is reduced. Therefore, utilizing a die coater produced having such processed bars mounted thereon prevents the residual grinding stress in the bars from gradually getting elicited and prevents the straightness of the die coater from degrading even after a long elapsed time, and makes stability of the slit gap in the lateral direction of coating and the distance between the die coater and an object to be coated, thereby enabling coating excellent in the uniformity of the layer thickness in the lateral direction of coating. Further, stable coating is achieved also in the aspect that the portions coming in contact with a liquid coating composition are covered with a fluorine based resin to be protected from dirt even for a long time coating.

By performing the thermal pretreatment on the bar in advance at the same temperature or higher than that of the covering process heat treatment, then removing the caused deformation, and thereafter coating with the bar with fluorine based resin, deformation of the bar caused by the baking treatment can be reduced, even if the die coater has a large width not smaller than 1 m for which reduction of deformation has been difficult before. Particularly, a bar for a die coater with a large width ranging from 1 to 4 m is preferably suitable.

In the case of covering only a part (for example, only in the vicinity of a pocket section of a slit face) of a single surface (for example, a slit face) of a bar with a fluorine based resin, the inventors found that, as a means for having both a portion covered with a fluorine based resin and a portion not covered with the fluorine based resin on the same surface, it is effective to remove the material of the bar, by grinding prior to covering, at the portion to be covered with the fluorine based resin for the thickness of covering, and then cover the portion with the fluorine based resin.

In such a manner, grinding of the surface can be proceeded to the extent that no step remains between the portion covered with the fluorine based resin and the portion not covered, by which a stable flatness is obtained, permitting a stable coating. Since fluorine based resins are usually softer than metals, in the case where the roundness at an angular part such as an edge or lip of a die coater is required to be 5 mm or smaller, covering the angular part with a fluorine based resin is not suitable due to durability of the angular part, but it is allowed to omit covering of the vicinity of the angular part with the fluorine based resin in this case.

Further, after performing the first means and the second means, a surface having been covered with the fluorine based resin is subjected to finish grinding and/or polishing so that the surface is finished with the straightness in the lateral direction of coating within a range from 0.1 to 10 μm and the surface roughness of the portion covered with the fluorine based resin within a range of 0.01 μm<Ra<1 μm and 0.1 μm<Rmax<5 μm, thereby enabling stable coating.

There is no particular limitation on a fluorine based resin to be used to practice the invention, and For example polytetrafluoroethylene (PTFE), tetrafluoroethylene—soft-headed fluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene—hexafluoropropylene copolymer (a FEP), polychlorotrifluoroethylene copolymer (PCTFE), polyvinyl fluoride (PVF) and a polyvinylidene fluoride (PVDF) may be usable.

A method of producing a die coater of the invention will be described referring to FIGS. 6 to 8 .

FIG. 6 is a schematic flowchart showing a method of producing a die coater having bars mounted thereon, the bars being covered with a fluorine based resin.

Producing a die coater covered with a fluorine based resin at portions coming in contact with a liquid coating composition can be divided into a fluorine based resin covering process S 1 - 1 , a grinding process S 1 - 2 of grinding surfaces covered with the fluorine based resin, a polishing process S 1 - 3 of polishing the surfaces covered with the fluorine based resin, and a mounting process S 1 - 4 of mounting bars. Each process will be described below.

The fluorine based resin covering process S 1 - 1 comprises 1) a pre-treatment process of a bar, 2) a covering (painting, immersion, etc.) and drying process, 3) a baking process, and 4) a cooling process. A desired layer thickness can be attained through these four processes, and through a repeat of these processes if necessary.

The pre-treatment process of a bar includes 1) a foundation treatment process that makes the fluorine based resin covering surfaces of the bar rough by sandblast or the like prior to fluorine based resin covering in order to give excellent adherability and prevent peeling after the fluorine based resin covering, and 2) a sweeping treatment or a heat treatment for cleaning of the surfaces to be covered with the fluorine based resin. It is necessary that the temperature of the heat treatment for cleaning is the same as or lower than that for the baking treatment. If the temperature is higher than that for the baking treatment, it is possible that a greater deformation is caused than that caused by the baking treatment, by which the grinding amount for removing deformation increases and a grinding stress remains in the bar. In the invention, a covering process heat treatment is referred to, including a heat treatment for cleaning and a baking treatment performed after the fluorine based resin covering, wherein the temperature of the covering process heat treatment is usually within a range from 400 to 500° C., and possibly higher than 500° C. The temperature of the heat treatment for cleaning of resin covering surfaces and that for the baking treatment may be the same. The covering/drying process with a fluorine based resin is a process that performs covering a bar having been subjected to pre-process with the fluorine based resin by painting, immersion, etc. and performs drying. The covering thickness of the fluorine based resin is required to be greater than the amount of deformation of the bar in order to grinding-remove, after covering, bend and torsion of the bar due to the deformation thereof caused by the baking treatment after the fluorine based resin covering. Accordingly, the covering thickness of the fluorine based resin ranges from 0.1 to 1.0 mm. By grinding this thick fluorine based resin in an amount smaller the thickness thereof, the portions covered with the fluorine based resin can be finally formed in a required straightness, surface roughness, and shape. If the covering layer thickness is smaller than 0.1 mm, when grinding the surfaces covered with the fluorine based resin, the fluorine based resin cover may be lost before removing bend and torsion due to the deformation of the bar. If the covering layer thickness is greater than 1 mm, the thickness is greater than required, which may raise the cost depending on the type of the fluorine based resin.

The baking process is a process for sticking the fluorine based resin to the die coater. The temperature of the baking process in the fluorine based resin covering process is usually in a range from 400 to 500° C., and possibly higher than 500° C.

The cooling process cools the bar after the baking.

The finish grinding process S 1 - 2 , of the surfaces covered with the fluorine based resin, grinds and corrects the deformation caused by the baking treatment performed after the fluorine based resin covering, and finishes the straightness of the surfaces of the bar in the lateral direction of coating to a required straightness. The straightness of a surface of a die coater according to the invention ranges from 0.1 to 10 μm (per meter) in the lateral direction of coating. By making the straightness of surfaces in the lateral direction of coating within a range from 0.1 to 10 μm, a uniform coating layer is achieved. If the straightness is smaller than 0.1 μm, machining is difficult due to the limit on the grinding accuracy. If the straightness is greater than 10 μm, it is not preferable because the coating layer thickness becomes unstable.

In the invention, since the thickness of a fluorine based resin covering is made greater than the grinding amount for correcting the deformation caused by the baking treatment, in the case where finish grinding surfaces are entirely covered with the fluorine based resin, it is allowed to reduce machining stress that remains in the bar because a metal portion of the bar is not grinded.

The polishing process S 1 - 3 of polishing the surfaces covered with the fluorine based resin means polishing that makes the surface roughness of the surfaces covered with the fluorine based resin within a range of 0.01 μm<Ra<1 μm, and 0.1 μm<Rmax<5 μm. By attaining such a surface roughness, foreign materials and silver halide grains in a liquid coating composition are prevented from depositing and the flow of the liquid coating composition is made smooth even for a long time coating, thus preventing coating failure and stably obtaining uniform coating layers. A polishing machine may be used for polishing, and manual polishing using polishing powder is also allowed.

In the case where the surface roughness Ra is smaller than 0.01 μm, machining is difficult, and the straightness at the portions covered with the fluorine based resin may be deteriorated, which is not preferable. In the case where the surface roughness Ra is greater than 1 μm, surfaces are rough, by which the abovementioned foreign materials tend to deposit easily and the effect of the fluorine based resin covering is reduced, which is not preferable.

In the case where the surface roughness Rmax is smaller than 0.1 μm, machining is difficult, and the straightness at the portions covered with the fluorine based resin may be deteriorated, which is not preferable. In the case where the surface roughness Rmax is greater than 5 μm, surfaces are rough, by which the abovementioned foreign materials tend to deposit easily and the effect of the fluorine based resin covering is reduced, which is not preferable.

The bar mounting process S 1 - 4 mounts at least 2 bars having been subjected to the polishing process S 1 - 3 and produces a die coater.

Through the processes S 1 - 1 to S 1 - 4 , a die coater, according to the invention, that is covered with a fluorine based resin at portions coming in contact with a liquid coating composition is achieved.

FIG. 7 is a schematic flowchart showing a method of producing a die coater having bars mounted thereon, the bars having been subjected to a thermal pretreatment, thereafter to grinding, and then to fluorine based resin covering.

Producing of a die coater covered with a fluorine based resin at portions coming in contact with a liquid coating composition can be divided into the processes, namely, a thermal pretreatment process S 2 - 1 on a bar, a grinding process S 2 - 2 , a fluorine based resin covering process S 2 - 3 , a grinding process S 2 - 4 on the surfaces covered with the fluorine based resin, a polishing process S 2 - 5 on the surfaces covered with the fluorine based resin, and a bar mounting process S 2 - 6 . Each process will be described below.

The thermal pretreatment process S 2 - 1 on a bar is executed prior to the heat treatment of a fluorine based resin covering process, and performs heat treatment at a temperature same as or higher than that of the heat treatment of the fluorine based resin covering process to elicit deformation generated by an inner stress or a machining stress which are caused through producing the bar, thereby reducing the deformation caused by the heat treatment of the fluorine based resin covering process. The heat treatment of the fluorine based resin covering process means a heat treatment for cleaning of surfaces to be covered in the fluorine based resin covering process and a baking process. The temperature of the covering process heat treatment is usually within a range from 400 to 500° C., and sometimes higher than 500° C. It is difficult to determine the upper limit of the temperature of the thermal pretreatment because it varies with a material to be employed for the bar, but at least, it should be lower than the melting point of the material. By performing the thermal pretreatment, the deformation of the bar caused by the covering process heat treatment can be reduced.

The grinding process S 2 - 2 includes 1) a first grinding process for correction of deformation accompanying the elicitation of the inner stress caused in the thermal pretreatment process S 2 - 1 on the bar and the machining stress generated through producing the bar and 2) a second grinding process of forming a final shape. By performing the first grinding and the second grinding, only a slight amount of grinding in the finish grinding process is required after the fluorine based resin covering, thus avoiding removal of all the amount of the fluorine based resin cover by grinding. Thus, it is possible to make the fluorine based resin cover 0.1 mm thick or thinner. Also, it is possible to reduce the machining stress caused by this grinding, allowing it to reduce generation of deformation of the bar after a long elapsed time. The second grinding process of forming the final finished shape means a grinding process for forming the shape of a die coater in a design drawing.

In the fluorine based resin covering process S 2 - 3 , the thickness of a fluorine based resin film formed through the fluorine based resin covering can be as small as 0.1 mm or smaller, because almost no deformation is caused by baking after the fluorine based resin covering, which is achieved by the thermal pretreatment, and only finish grinding in a small amount of grinding is required after the fluorine based resin covering. However, in the case where the fluorine based resin cover is thinner than 0.03 mm, the fluorine based resin cover may be lost by grinding the surface of the fluorine based resin cover, which requires careful attention to be prevented. On the other hand, although the covering film thickness may be greater than 0.1 mm, then the covering film tends to be thicker than required, causing a higher cost depending on the type of the fluorine based resin. The preprocess, the baking process, and the cooling process in the fluorine based resin covering process S 2 - 3 are the same as those of the process shown in FIG. 6 .

In the following, the grinding process S 2 - 4 on the surfaces covered with the fluorine based resin, the polishing process S 2 - 5 on the surfaces covered with the fluorine based resin, and the bar mounting process S 2 - 6 are the same as the processes S 2 - 2 to S 2 - 4 shown in FIG. 6 .

It is possible to produce a die coater, according to the invention, that is covered with a fluorine based resin at portions coming in contact with a liquid coating composition through the processes S 2 - 1 to S 2 - 6 .

FIG. 8 is a schematic flowchart showing another method of producing a die coater having bars mounted thereon, the bars having been subjected to a thermal pretreatment, thereafter to grinding, and then to fluorine based resin covering.

In the method of producing a die coater shown in FIG. 8 , a pre-resin-covering grinding process for removing the material for the thickness of a fluorine based resin is added to the grinding process S 2 - 2 of the method shown in FIG. 7 . By grinding-removing the material, in advance prior to covering, at portions to be covered with a fluorine based resin, for the thickness of the fluorine based resin, and thereafter covering the grinded portions with the fluorine based resin to be thick, even if the covered surface is grinded, it is allowed to obtain a uniform surface having an excellent straightness without causing a step between a portion which is not covered and a portion which is covered, and further, retention of a liquid coating composition and deposition of foreign materials are prevented, which is an effective means. The rest of S 3 - 1 to S 3 - 6 are the same as those in FIG. 7 .

It is possible to produce a die coater, according to the invention, that is covered with a fluorine based resin at portions coming in contact with a liquid coating composition through the processes S 3 - 1 to S 3 - 6 .

By the method of producing a die coater, shown in FIGS. 6 to 8 , according to the invention, various die coaters, shown in FIGS. 5 to 8 , that perform wide web coating in a coating width ranging from 1 to 4 m have advantages including 1) reducing deformation that accompanies fluorine based resin covering, 2) enabling fluorine based resin covering of the portions, of the die coater, coming into contact with a liquid coating composition with accuracy, 3) achieving a stable straightness of the die coater due to being free from variation of the straightness of bars which construct a die coater even for a long elapsed time, and maintaining evenness of a slit gap in the lateral direction of coating and the distance between the die coater and an object to be coated, and 4) preventing foreign materials and silver halide grains in the liquid coating composition from depositing on the portions in contact with the liquid coating composition even for a long time coating. Thus, a coating apparatus is achieved that employs a die coater which attains an excellent coating quality with a uniform thickness in the lateral direction of coating and few coating failures while keeping the cleanability of known die coaters. The method of producing a die coater of the invention is effective for die coaters for performing wide web coating with a width of 1 m or larger, and particularly effective for die coaters for performing wide web coating with a width ranging from 1 to 4 m.

A support to be used in practicing the invention is not limited in type as long as a support has a belt shape and is conveyable, and for example, a paper sheet, a plastic film, and a metal sheet can be used. As paper sheets, resin coat papers and composite papers can be applied, for example. As plastic films, polyolefin film (for example polyethylene film, polypropylene film), polyester film (for example, polyethylene terephthalate film, 2,6-polyethylene naphthalate film), polyamide film (for example polyeter ketone film), cellulose acetate (for example cellulose triacetate) may be usable. As metal sheets, aluminum plates are representative. Further, there is no particular limit on the thickness of a support to be employed.

A liquid coating composition to be employed in practicing the invention is not limited particularly, and it is allowed to use, for example, liquid coating compositions for photographic photosensitive materials, thermal development recording materials, abrasion recording materials, magnetic recording media, steel plate surface treatment, and electrophotographic photoreceptors (including liquid coating compositions for subbing, overcoating, and a backside layer). Among these, particularly preferable are liquid coating compositions for photoreceptive layers which are liquid coating compositions for thermal development photoreceptive materials and contain a silver component, and liquid coating compositions for non-photoreceptive protective layers.

The present invention will now be described with reference to examples. However, the present invention is not limited thereto.