Method of decomposing thermosetting resin, apparatus and heat control program

1. Field of the Invention

This invention relates to a method of decomposing a thermosetting resin, and to an apparatus and a heat control program for carrying out the method.

2. Description of the Background

Discarded electric household appliances provide one example of waste matters comprising a thermosetting resin. In recent years, it has been increasingly requested to recycle discarded electric household appliances. With a view to responding to such requests, it is now extensively studied to discover methods of recycling discarded electric household appliances by examining each of their components. In the disposal of discarded refrigerators, for example, since foamed urethane resin is employed therein as a heat-insulating material, the recycle of the urethane resin is studied now.

As for the method of recycling foamed urethane resin, there have been proposed various methods in the past. For example, Japanese Patent Unexamined Publication H6-184513 sets forth a method wherein a thermosetting resin comprising soft or hard polyurethane foam is decomposed at a constant temperature ranging from 150 to 280° C. using aminoethanol as a decomposer.

However, this method is problematical in that it takes a lot of time for decomposing the polyurethane foam, e.g., 11 hours at a temperature of 190° C., 2 hours even at a higher temperature of 230° C., and that under some circumstances, it is impossible to completely decompose the thermosetting resin. The reason for this may be attributed to the fact that the decomposer is not necessarily fully effective. Specifically, when the thermal decomposition of the thermosetting resin is immediately started at this range of temperatures, the heating is initiated at a temperature which is higher than the boiling point of the decomposer, such as aminoethanol. As a result, the decomposer is forced to volatilize before it is sufficiently mixed with the thermosetting resin, thus making it impossible to perform the kneading of the decomposer with the thermosetting resin at a constant mixing ratio, thereby inviting a phenomenon where the decomposing reaction of the thermosetting resins is inhibited.

This invention has been accomplished under the circumstances as mentioned above, and therefore, an object of this invention is to provide a method of decomposing thermosetting resins, which makes it possible to shorten the time required to decompose thermosetting resins, and to completely decompose thermosetting resins.

Another object of this invention is to provide an apparatus for decomposing thermosetting resins using the aforementioned method.

A further object of this invention is to provide a control program for the method of decomposing thermosetting resins.

According to this invention, there is provided a method of decomposing a thermosetting resin by a decomposer, comprising the steps of:

pre-heating the thermosetting resin up to a pre-heating temperature T 0 ;

kneading the pre-heated thermosetting resin together with a decomposer, and concurrently heating a mixture comprising the thermosetting resin and the decomposer up to a kneading temperature T 1 , thereby allowing a reaction to take place between the decomposer and the thermosetting resin to obtain a kneaded matter wherein the decomposer becomes consumed; and

heating said kneaded matter to a maximum temperature T 2 to decompose the thermosetting resin; wherein:

said pre-heating temperature T 0 is not higher than the boiling temperature of said decomposer;

said kneading temperature T 1 is not lower than said pre-heating temperature T 0 but is lower than the thermal decomposition temperature of the thermosetting resin;

said maximum temperature T 2 is lower than the decomposition temperature of the thermosetting resin; and

said pre-heating of the thermosetting resin is performed under the following conditions of temperature T 0 and time t:

100° C.≦T0<260° C.

0.5 min≦t≦7 min.

According to this invention, there is also provided a decomposition apparatus for decomposing a thermosetting resin by the aforementioned method, wherein said apparatus comprises:

a chamber for accommodating the thermosetting resin;

a temperature controllable heating means for heating said chamber;

a decomposer supply means for feeding a decomposer to said chamber;

a monitoring means for detecting a quantity of residual decomposer left in said chamber; and

a temperature control means for controlling said heater on the basis of the quantity of residual decomposer.

According to this invention, there is also provided a control program for controlling heating of a thermosetting resin in a decomposition process of said thermosetting resin, wherein said program comprises the steps of:

instructing a computer to heat a chamber accommodating the thermosetting resin up to a temperature T 0 ;

instructing the computer to determine if said temperature T 0 of said chamber is in the range of 100 to 260° C., and if heating time is in the range of 0.5 min to 7 min;

instructing the computer, when it is determined that said temperature T 0 of said chamber is in the range of 100 to 260° C., and said heating time is in the range of 0.5 min to 7 min, to feed a decomposer to said chamber for a decomposition of the thermosetting resin;

instructing the computer to heat said chamber at a temperature of less than the thermal decomposition temperature of the thermosetting resin;

instructing the computer to detect the quantity of residual decomposer left in said chamber;

instructing the computer to determine if the quantity of residual decomposer is less than 10%;

instructing the computer, when it is determined that the quantity of residual decomposer is not less than 10%, to continue heating of said chamber while keeping the temperature of the thermosetting resin to less than the decomposition temperature of the thermosetting resin; and

instructing the computer, when it is determined that the quantity of residual decomposer is less than 10%, to raise a maximum temperature from a temperature T 1 at this moment up to T 2 which is higher than T 1 .

The invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph illustrating the conditions with respect to the temperature and time in the pre-heating step according to one embodiment of this invention;

FIG. 2 is a schematic view illustrating the extruder according to one embodiment of this invention;

FIG. 3 is a diagram schematically illustrating the construction of the decomposer supply means in the extruder shown in FIG. 2 ;

FIG. 4 is a flow chart of the program for controlling the temperature in the decomposition process of thermosetting resin according to this invention;

FIG. 5 is a graph illustrating the temperature history during the reaction in Example 1 of this invention; and

FIG. 6 is a graph illustrating the temperature history during the reaction in Example 2 of this invention.

It has been found as a result of intensive studies made by the present inventors that the chemical decomposition of a thermosetting resin by a decomposer can be more effectively carried out when the thermosetting resin is preheated prior to the addition of the decomposer to the thermosetting resin, thereby accomplishing the present invention. In the method of decomposing a thermosetting resin according to this invention, the thermosetting resin is at first preheated up to a pre-heating temperature T 0 . As a result of this preheating, the temperature of the thermosetting resin itself is raised to promote the fluidity of the thermosetting resin.

Then, a decomposer is added to the thermosetting resin, the resultant mixture being subsequently kneaded. In this case, under some circumstances, the kneading may be performed by raising the temperature of the mixture, thereby allowing the decomposer to be almost completely consumed. During this kneading step, the decomposer is attached to a carbonyl bond in the thermosetting resin, thereby forming an intermediate product. The treatment temperature of the thermosetting resin is further raised even after the generation of this intermediate product for performing the decomposition of the thermosetting resin.

Namely, the thermosetting resin is preheated in the preheating step so as to facilitate the kneading thereof with a decomposer to be subsequently added thereto. Generally, the decomposer is added to the thermosetting resin at an initial stage of the kneading step. Incidentally, when a decomposer is added to the thermosetting resin of room temperature as seen in the conventional method, it is difficult to effectively perform the kneading of thermosetting resin with the decomposer, thereby necessitating a lot of time for accomplishing the decomposition of the thermosetting resin. By contrast, according to this invention, since the thermosetting resin is preheated prior to the kneading, the kneading of thermosetting resin with a decomposer can be effectively performed.

Specifically, the preheating temperature T 0 , the kneading temperature T 1 and a maximum temperature T 2 according to this invention can be set in the following manner.

The preheating temperature T 0 should be not higher than the boiling temperature of a decomposer. Further, if the preheating temperature T 0 in the preheating step is represented on the x-axis, and the preheating time t is represented an the y-axis, the conditions for the preheating step can be set so as to satisfy the following conditions of temperature T 0 and time t:

100° C.≦T0<260° C.

0.5 min≦t≦7 min.

Namely, the preheating should be performed under the conditions which fall within the region defined by B in the graph of FIG. 1 . Specifically, the preheating should be performed by controlling the temperature and time thereof so as to make them fall within the aforementioned region.

If the preheating time is less than 0.5 min, it would become difficult to sufficiently preheat the thermosetting resin. On the other hand, if the preheating time exceeds 7 min, the resin may be hardened.

More preferably, the preheating step should be performed under the following conditions of temperature T 0 and time t:

100° C.≦T0<230° C.

0.5 min≦t≦7 min.

3.375≦0.0125T0+t≦8.25

Namely, according to the method of this invention, the preheating should preferably be performed under the conditions which fall within the region defined by A in the graph of FIG. 1 .

A decomposer which is capable of decomposing the thermosetting resin is added to this preheated thermosetting resin. Further, the kneading of the thermosetting resin together with the decomposer is performed by raising the temperature of the thermosetting resin up to the aforementioned temperature T 0 or more. Preferably, the temperature in the kneading step should be not higher than the boiling point of the decomposer and also not higher than the decomposition temperature of the thermosetting resin. In the case where plural kinds of decomposers are concurrently employed, the temperature T 1 should preferably be set such that it is lower than the boiling point of any of these decomposers. If the temperature T 1 is higher than the boiling point of any of these decomposers, any one of these decomposers may be volatilized before it is fully kneaded, so that it would become impossible to perform the kneading of the thermosetting resin with the decomposers at a constant mixing ratio. As a result, the decomposition reaction of the thermosetting resin would become insufficient.

As described above, the temperature T 1 should preferably be not higher than the decomposition temperature of the thermosetting resin. If the temperature T 1 is higher than the decomposition temperature of the thermosetting resin, the thermal decomposition reaction of the thermosetting resin itself would be initiated before the kneading between the thermosetting resin and the decomposer would take place substantially, resulting in the generation of hydrocarbon gas and hence obstructing the decomposition reaction of the thermosetting resin.

When thermosetting resins are heated under excessively high temperatures, the thermal decomposition of thermosetting resins is initiated, generating hydrocarbon gas. For this reason, the kneading temperature T 1 should preferably be set to not higher than 200° C. On the other hand, the lower limit of the kneading temperature T 1 should preferably be set to not lower than 100° C. When the kneading temperature T 1 is set to lower than 100° C., flon or halogen of halogenated hydrocarbon which are included in a foamed thermosetting resin may be preferentially reacted with the urethane bond of the thermosetting resin, thereby obstructing the decomposition of the thermosetting resin. Therefore, it is preferable for the purpose of avoiding these undesirable phenomena to eliminate these gases during the kneading step to be performed at a temperature of T 1 .

The temperature during the kneading step may be kept substantially constant, and the final temperature T 1 thereof may be substantially identical with the preheating temperature T 0 . When the temperature during the kneading step and the final temperature T 1 are selected to be identical with the preheating temperature T 0 ±15° C., the final temperature T 1 may be assumed as being substantially identical with the preheating temperature T 0 .

When the thermosetting resin is allowed to react with the decomposer under these conditions, the decomposer is consumed.

According to this invention, the kneading should preferably be performed while monitoring the quantity of residual decomposer. Further, the quantity of residual decomposer after finishing the kneading step should preferably be less than 10%. If the quantity of residual decomposer after finishing the kneading step is more than 10%, it would become difficult to sufficiently decompose the thermosetting resin in the subsequent decomposition step to be performed successively. The temperature at the time when the quantity of residual decomposer becomes less than 10% may be defined as the final temperature T 1 of the kneading step.

After the temperature of kneaded matter has reached the final temperature T 1 , the temperature of kneaded matter is further raised up to the maximum temperature T 2 to initiate the decomposition reaction of the thermosetting resin.

Therefore, it is preferable in this invention to control the heating on the basis of the quantity of residual decomposer on the occasion of raising the temperature from T 1 to the maximum temperature T 2 . The maximum temperature T 2 on this occasion is set higher than the final temperature T 1 of the kneading step. However, this maximum temperature T 2 should preferably be controlled to not higher than the thermal decomposition temperature of the decomposed products to be generated on this occasion. Incidentally, the maximum temperature T 2 may be higher than the boiling point of the decomposer. This will be explained hereinafter with reference to the following examples.

The following reaction formulas (1a) and (1b) illustrate the reactions in the kneading step and in the decomposition step, which will take place on the occasion of decomposing urethane resin as one example of thermosetting resin by alkanol amine as a decomposer according to this invention.

wherein R 1 and R 2 are respectively each a bivalent organic group, preferably alkyl group or aryl group;

R 3 , R 4 , R 6 and R 7 are respectively each a hydrogen atom or a monovalent organic group, preferably —CH 2 CH 2 OH;

R 5 is bivalent organic group, preferably an alkylene group; and

n and m are respectively a positive integer.

When urethane resin is to be decomposed by alkanol amine, the carbon atom of carbonyl group of the urethane bond in the urethane resin A is attacked by the nitrogen atom of alkanol amine B employed as a decomposer during the kneading step, thereby enabling the alkanol amine B to be attached to the urethane resin A, thus producing an intermediate product C as shown in the reaction formula (1a).

In the following decomposition step, when this intermediate product C is heated up to the maximum temperature T 2 , the intermediate product C is decomposed as shown in the reaction formula (1b) to produce decomposition products D. As seen from these reaction formulas, the intermediate product C to be produced through the bonding of alkanol amine as a decomposer to urethane resin is constituted by a compound which differs from the original alkanol amine added as a decomposer B. Therefore, the maximum temperature T 2 in the subsequent step, i.e., the decomposition step may be higher than the boiling point of the alkanol amine B employed as a decomposer.

The reaction formulas on the occasion of decomposing urethane resin by monoethanol amine (NH 2 CH 2 CH 2 OH), diethanol amine (HOCH 2 CH 2 NHCH 2 CH 2 OH) or triethanol amine (N(C 2 H 4 OH) 3 ) as a decomposer according to this invention are shown below.

As shown in the above reaction formulas, an intermediate product comprising urethane resin to which a decomposer is attached can be produced in the kneading step in every case.

Next, examples where compounds each having hydroxyl group are employed as a decomposer will be explained.

The following reaction formulas (2a) and (2b) illustrate the reactions in the kneading step and in the decomposition step, which will take place on the occasion of decomposing urethane resin by polyol as a decomposer according to this invention.

wherein R 1 and R 2 are respectively each a bivalent organic group, preferably an alkyl group or aryl group;

R 8 and R 9 are respectively each a bivalent alkyl group; and

n and m are respectively a positive integer excluding 0.

When urethane resin is to be decomposed by polyol, the oxygen atom of the hydroxyl group of the compound E having hydroxyl groups and employed as a decomposer is attached to the carbon atom of a carbonyl group of the urethane bond in the urethane resin A during the kneading step, thus producing an intermediate product F as shown in the reaction formula (2a).

In the following decomposition step, when this intermediate product F is heated up to the maximum temperature T 2 , the intermediate product F is decomposed as shown in the reaction formula (2b) to produce decomposition products G. As seen from these reaction formulas, the intermediate product F to be produced through the bonding of a compound having hydroxyl group to urethane resin is constituted by a compound which differs from the original compound E having hydroxyl group and employed as a decomposer. Therefore, the maximum temperature T 2 in the subsequent step, i.e., the decomposition step may be higher than the boiling point of the compound having hydroxyl group and employed as a decomposer.

The maximum temperature T 2 in the decomposition step should be T 2 >T 1 . Further, it is much desired in order to shorten the time required for the decomposition of thermosetting resin that the maximum temperature T 2 be not lower than the boiling point of the decomposer. Further, it is also preferable that the difference in temperature between the maximum temperature T 2 in the decomposition step and the final temperature T 1 in the kneading step be 20° C. or more.

On the other hand, the upper limit of the maximum temperature T 2 should preferably be not higher than 300° C. If the upper limit of the maximum temperature T 2 exceeds 300° C., a thermal decomposition reaction which is separate from the chemical decomposition reaction of thermosetting resin by the decomposer may be initiated to take place. As a result, hydrocarbon gas or a harmful gas such as dioxin may be generated.

As explained above, the method of decomposing thermosetting resins according to this invention comprises a preheating step, a kneading step and a decomposition step, each step being carried out at a predetermined temperature. These three steps can be performed within a single apparatus such as a kneader or a reactor, wherein the temperature is allowed to rise from the preheating temperature T 0 to the maximum temperature T 2 . The employment of a single apparatus is advantageous since the temperature can be controlled while observing the state of decomposed matters discharged from the outlet port of the apparatus.

Alternatively, three unit apparatuses which are connected sequentially may be employed. In this case, a first unit apparatus can be employed for preheating a thermosetting resin up to the temperature T 0 , a second unit apparatus can be employed for kneading the thermosetting resin at the final temperature T 1 after incorporating a decomposer into the thermosetting resin, and a third unit apparatus can be employed for decomposing the thermosetting resin by heating the thermosetting resin up to the maximum temperature T 2 . When a plurality of unit apparatuses are employed in this manner, the elimination of flon can be concurrently performed in the second unit apparatus.

Thermosetting Resins:

As for the thermosetting resin which can be decomposed according to this invention, preferable examples thereof include a resin having carbonyl groups, such as a resin having urethane bonds, a resin having urea bonds and unsaturated polyester, the most preferable example thereof being urethane resin. As for the urethane resin, it is possible to employ any kind of urethane resin containing urethane bonds, urea bonds, etc. Specific examples of urethane resins are soft urethane, hard urethane, semi-hard urethane, urethane elastomer and urethane rubber.

As for the examples of other kind of thermosetting resin to be decomposed, they include acid anhydride-cured epoxy resin, amine-cured epoxy resin, phenol-cured epoxy resin, urea resin, melamine resin, phenol resin, alkyd resin, polyimide resin, unsaturated polyester resin and cross-linked polyethylene.

Any of these thermosetting resins should preferably be pulverized before they are subjected to the preheating step. The following reaction formula (3) illustrates the reaction involved in the step of kneading acid anhydride-cured epoxy resin or unsaturated polyester together with alkanol amine employed as a decomposer. On the other hand, the following reaction formula (4) illustrates the reaction involved in the step of kneading urea resin together with alkanol amine.

wherein R 3 , R 4 , R 6 and R 7 are respectively each a hydrogen atom or a monovalent organic group, preferably —CH 2 CH 2 OH;

R 5 is a bivalent organic group, preferably an alkyl group;

R 1 , R 2 , R 10 and R 11 are respectively each a bivalent organic group, preferably an alkylene group or bivalent phenyl group; and

n and m are respectively a positive integer.

Even if the kind of thermosetting resin is altered, when the altered thermosetting resin is subjected to the decomposition process according to the method of this invention, an intermediate product can be generated in the step of the kneading thereof together with a decomposer.

Decomposer:

The decomposer is employed for assisting the decomposition of thermosetting resins to be decomposed. As for the specific examples of the decomposer, they include a single amine compound, a single compound having hydroxyl group, and a combination of amine compound with a compound having hydroxyl group.

As for the amine compound, linear aliphatic amines, cyclic aliphatic amines, aromatic amines and heterocyclic amines can be used. Specific examples of linear aliphatic amines include ethylene diamine, tetramethylene diamine, hexamethylene diamine, 2-ethylhexyl amine, monoethanol amine, diethanol amine, triethanol amine, iso-propanol amine, n-propyl amine, di-n-propyl amine, n-amyl amine, iso-butyl amine and methyldiethyl amine. Specific examples of cyclic aliphatic amines include cyclohexyl amine, piperazine and piperidine. Specific examples of aromatic amines include aniline, toluidine, xylilene diamine, benzyl amine and chloroaniline. Specific examples of heterocyclic amines include pyridine, picoline, N-methyl morpholine, ethyl morpholine, and pyrazole. These amines can be employed singly or in any combination of two or more.

As for the compounds having a hydroxyl group, specific examples thereof include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, polyoxyethylene glycol and polyoxypropylene glycol; trihydric alcohols such as glycerin; and polymers such as polyethylene glycol.

The mixing ratio of the aforementioned decomposers to the thermosetting resins may be of nonstoichiometric composition. More specifically, the mixing ratio of the thermosetting resins to the decomposers (thermosetting resin:decomposer) should preferably be in the range of 1:3 to 1:20 (based on weight). If the relative amount of the decomposers is too small, it would become difficult to sufficiently decompose the thermosetting resins. On the other hand, if the relative amount of the decomposers is too large, a lot of gas may be caused to generate due to the volatilization of the decomposers in the vicinity of the outlet port of apparatus. More preferably, the mixing ratio of the thermosetting resins to the decomposers (thermosetting resin:decomposer) should be confined within the range of 1:5 to 1:7 (based on weight).

Decomposition Apparatus:

FIG. 2 shows a decomposition apparatus according to one embodiment of this invention. The following is an explanation on this decomposition apparatus.

A thermosetting resin to be decomposed is placed in a hopper 3 and then, pulverized by a screw 4 . Incidentally, the screw 4 is driven by a motor 2 , which is controlled by a control board 7 .

A reaction vessel 20 for preheating, kneading and decomposing the thermosetting resin is partitioned into eight chambers (barrels) C 0 to C 7 . These barrels are provided with heat control means 6 - 0 to 6 - 7 , respectively, so as to make it possible to set any desired temperature. Each of the heat control means in this case may be constituted for example by a heater, a thermocouple, a cooling water supply tube, etc.

The thermosetting resin pulverized is fed via an inlet port 5 to a first barrel C 0 . The inner temperature of the first barrel is set to a preheating temperature T 0 by the heat control means 6 - 0 . Preheating of the thermosetting resin is performed in this barrel C 0 in this manner, i.e., this barrel C 0 is assigned for the preheating step.

Upon finishing the preheating, the thermosetting resin is transferred to a second barrel C 1 . This second barrel C 1 is designed such that a decomposer can be injected thereinto through a decomposer injection port 15 by a decomposer supply means 24 . This decomposer supply means 24 is controlled by a controller 21 , and comprises as shown in FIG. 3 a weighing instrument 10 , a tank 11 for storing the decomposer, a piping 12 , an injection pump 13 and a heater 14 for heating the piping 12 .

In the barrel C 1 , the kneading of the thermosetting resin and the decomposer is initiated. This kneading step can be performed in any of the barrels disposed on the downstream side of the barrel C 1 . The final temperature T 1 in this kneading step should be not lower than the aforementioned preheating temperature T 0 but lower than the decomposition temperature of the thermosetting resin. As already explained above, during this kneading step, the decomposer is consumed through the reaction between the thermosetting resin and the decomposer.

The monitoring of quantity of residual decomposer during this kneading step can be performed in such a manner that a GC (gas chromatography, a GC/MS (gas chromatography-mass spectrometer), etc. are attached to predetermined barrel portions, and data on the residual quantity of decomposer is fed back to the control board 7 . This control board 7 is enabled to control, on the basis of the residual quantity of decomposer, the temperature of barrels of later stage so as to raise it higher.

The resin mixture and decomposed matters existing inside the reaction vessel 20 are pushed out by the screw 1 toward a discharge nozzle 9 . Since this screw is extended along the length of the reaction vessel 20 , the contents placed in the reaction vessel 20 are enabled to be pushed up to the discharge nozzle 9 .

Namely, the mixture that has been kneaded inside the barrel CI is successively pushed out passing through the barrels disposed on the downstream side of the barrel C 2 .

As shown in FIG. 2 , the barrels C 2 to C 7 are provided with vents 16 - 1 to 16 - 5 and 17 , respectively. The last vent 17 of the final barrel C 7 is connected with a condenser 18 and with a vacuum pump 19 . This vacuum pump 19 is connected with an exhaust system 23 so as to make it possible to discharge flon gas, hydrocarbon gas, etc. that have been generated through the reactions in these barrels or generated from urethane resin. The decomposed matters are discharged from the nozzle 9 of the final barrel C 7 and placed in a receiving vessel 22 .

The heat control means 6 - 0 to 6 - 7 for controlling the temperature of the barrels C 0 to C 7 are designed to be controlled by the temperature controlling means (control board) 7 . Specifically, the barrel C 0 which is assigned to perform the preheating step is heated up to an inner temperature T 0 which is not more than the boiling point of the decomposer. Further, any desired barrel which is assigned to perform the kneading step is heated up to an inner temperature T 0 which is not more than the thermal decomposition temperature of thermosetting resin, and the temperature of the final barrel is set to the final temperature T 1 . Additionally, a barrel which is assigned to perform the decomposition step subsequent to the kneading step is set such that the maximum temperature becomes T 2 which is higher than the aforementioned final temperature T 1 .

As for the reactor, it is possible to employ an extruder which is capable of heating and extruding a thermosetting resin while enabling the thermosetting resin to be kneaded together with a decomposer. The temperatures of the extruder along the length thereof extending from the inlet port 5 to the discharge nozzle 9 are increased from T 0 to T 2 as described above. In this case, the extruder may be uniaxial or biaxial. Further, it is also possible to employ any desired kinds of device such as a continuous kneader or a monopump as long as they are capable of performing the heating and kneading of thermosetting resin. Since these kneaders are capable of performing a continuous decomposition reaction, they are suited for the decomposition of a large quantity of thermosetting resin.

The decomposition method of thermosetting resin according to this invention is performed while controlling the temperature of thermosetting resin under specific conditions.

FIG. 4 is a flow chart illustrating the flow of program for the control of temperature.

As shown in FIG. 4 , urethane is introduced into the hopper for preheating the urethane at a temperature T 0 . On this occasion, it is determined whether or not the temperature T 0 and the time are those falling within predetermined ranges. If it is determined that these conditions are not met, the preheating is continued until these conditions are met.

Subsequently, a decomposer is added to the thermosetting resin, and the kneading step is initiated. During this kneading step, the quantity of residual decomposer is monitored. The kneading is continued until the quantity of residual decomposer is reduced to less than 20%. When the quantity of residual decomposer is reduced to less than 10%, the temperature of the resin is further raised up to the maximum temperature T 2 to thereby allow the thermosetting resin to decompose.

As already explained above, by the apparatus shown in FIG. 2 , the preheating step is performed in the first barrel C 0 . In order to perform the control of temperature in this manner in the apparatus shown in FIG. 2 , the data on the temperature inside the barrel C 1 as well as on the time are fed back to the control board 7 . Additionally, the quantity of residual decomposer in any of barrels disposed on the downstream side of the barrel C 1 where the kneading step can be performed is fed back to the control board 7 . Thus, the control board 7 is operated, based on the data thus obtained, to control the temperatures of the entire barrels.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples and comparative examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

Decomposition of Urethane: