Composition to be used in paints

The present invention relates to an environmentally friendly, epoxy-resin-based anti-corrosive composition to be used in paints, which composition has high dry solids content and low viscosity and which can be applied to protect steel structures and/or concrete surfaces.

Epoxy-, alkyd- and polyurethane-based paints and combinations thereof are commonly used to protect steel structures and/or concrete surfaces against corrosion. In general, polyurethane-based paints require a primer. Their greatest disadvantage, however, is related to health factors. The dry solids content of the polyurethane paints is low, which results in a great amount of volatile substances (solvents) and limits the use of said paints. Even though epoxy paints have several good properties, such as good adhesion to steel, concrete and other substrates, good mechanical strength and chemical resistance, it is necessary to use weather-resistant alkyd, or in particular, polyurethane paint for topcoating, because the epoxy paint chalks, i.e. becomes matt, and often yellows when exposed to weather. The required film thicknesses are within the range of about 150 to 500 μm, which often requires 2 to 4 repeated treatments. Even though the epoxy paints have been developed to achieve thicker films with fewer treatments and a slight improvement in the weatherability has also been achieved, the use of polyurethane as a top coat cannot have been avoided so far. The amount of volatile organic content (VOC) still constitutes a problem for both epoxy and polyurethane paints.

High viscosity has also limited the use of previously known epoxy paints. A low ambient temperature has also imposed restrictions on their use in the open air. Quite recently, reduction in viscosity and improvement in weather resistance of the epoxy paints are achieved by modifying epoxy resins with acrylic monomers and oligomers. At the same time, the use of acrylic monomers and oligomers has considerably shortened drying times and exploitation times of the paints.

Further, silicone paints and silicate paints based on organic and inorganic silicon compounds have been known for a long time. Silicone paints resist well heat, up to 600° C., but they dry poorly and yellow easily. Zinc silicate paints have often been used as a primer for demanding anti-corrosive paintings.

Polysiloxane-based paints, based on silicon and oxygen compounds, have also been developed having excellent weather resistance and particularly improved UV light resistance even as compared with the polyurethanes. However, due to their high price, these polysiloxanes acting as binders are used as a sole binder in paints only in exceptional cases, such as in space technology where requirements are extremely high. The high price has forced paint manufacturers to use silicone and siloxane compounds instead of polysiloxanes for improving and modifying the properties of other binders.

An epoxy-based polysiloxane coating composition useful for corrosion prevention is known from WO 96/16109, the composition including a non-aromatic hydrogenated epoxy resin, a polysiloxane and an organo-oxysilane. As preferred non-aromatic epoxide resins are stated hydrogenated cyclohexane dimethanol and diglycidyl ethers of hydrogenated Bisphenol A-type. When the composition dries, the non-aromatic epoxy resin used forms a straightchain epoxy polymer and not a three-dimensional structure, which is possible in the solution of the present invention. Good weather resistance of the known composition is believed to be specifically due to the linear epoxy polymer. On the other hand, it has been found that the drying times of these compositions are relatively long.

A casting resin composition used for covering optoelectronic components is known from U.S. Pat. No. 5,492,981. Said US patent thus relates to a field of use which is different from the field of use of the present invention. For instance, the hardener type and the curing temperature cited in said patent publication indicate that the known composition in question is not related to paints in any manner whatsoever. The resin component of the casting resin composition according to the US patent contains 5 to 95% by weight of a condensation product which is an epoxy group containing polysiloxane formed of a silanol and an epoxyalkoxysilane at an elevated temperature. According to the publication, the resin component also contains 5 to 95% by weight of epoxy resin. The solution of the present invention, in turn, uses polysiloxane, which does not include epoxy groups, and separately epoxy silane and aliphatic epoxy resin.

The object of the invention is thus to provide a low-viscosity anti-corrosive paint composition which avoids the problems of the corresponding, known epoxy-based paint compositions. The present invention is based on the use of a combination of aliphatic epoxy constituents and specific polysiloxane-containing constituents. Now, it has been found that a paint composition having excellent properties is obtained by using epoxy silane, instead of organo-oxysilane (cf. WO 96/16109), together with an aliphatic epoxy resin. The composition of the invention has an advantage that it has low viscosity, whereby diluting is not generally needed, and that it dries quickly also at low temperatures, even at −5° C. The drying rate and curing at low temperatures of known epoxy compositions can be improved by specific accelerators, which, however, do not act at the same temperatures or they cause other problems, such as more intense yellowing than conventionally and matting (chalking) of a painted surface. These accelerators can also be toxic, for instance, phenol derivatives.

The compositions of the invention have a further advantage that it is possible to apply new coatings over the paints containing said compositions after a long time without that any adhesion or curling problems occur. They need not be coated with a separate weather-resistant topcoat either, film thicknesses can be reduced in many cases and the intervals between maintenance paintings can be prolonged, which in turn reduces costs.

The present invention relates to a composition to be used in paints, which is characterized by comprising a resin constituent which includes

i) a non-aromatic epoxy resin,

ii) a polysiloxane having the formula:

where R 1 is hydroxyl or an alkyl, aryl or alkoxy group having up to 6 carbon atoms, R 2 is a hydrogen or an alkyl or aryl group having up to 6 carbon atoms and n is a number selected so that the molar mass of the polysiloxane is within the range of 400 to 2000, and

iii) an epoxy silane which acts as a crosslinking agent between the epoxy and siloxane chains.

The invention also relates to a kit, which is characterized by comprising a container A, which contains a composition of the present invention, and a container B, which contains a hardening agent, whereby the container A and/or B may further contain conventional additives. The additives may include accelerators, water and other conventional additives.

FIG. 1 shows the charge in glass of several paint compositions subjected to a QUV test.

In the composition of the invention, the non-aromatic epoxy resin is preferably an aliphatic branched epoxy resin. A suitable branched aliphatic epoxy resin has the general formula:

where p is an integer between 0 and 3, s is an integer between 1 and 3, R 3 and R 4 represent independently C 1-6 alkyl or a group

where p and s are as defined above and R 5 is hydrogen, C 1-6 alkyl or a group

where p and s are as defined above.

The preferred branched aliphatic epoxy resins include

Polysiloxanes described in WO 96/16109 can be generally used as a polysiloxane constituent of the resin component in the compositions of the invention. Particularly preferable are substances under commercial names DC-3074 and DC-3037 available from the manufacturer Dow Corning, which are methoxy functional polysiloxanes. The amount of polysiloxane in the paint composition is 15 to 45% by weight.

Suitable epoxy silanes include those having the general formula:

where k is an integer between 0 and 4, l is an integer between 1 and 6, r is 0 or 1, m is an integer between 1 and 6 and Alk is an alkyl group having 1 to 6 carbon atoms. Particularly preferable epoxy silanes are glycidoxypropyl-trimethoxysilane having the formula

and β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane having the formula

In the composition of the invention the weight ratio between the epoxy silane, polysiloxane and non-aromatic epoxy resin is suitably 1:2-5:2-5.

In connection with the present invention, conventional hardening agents can be used as hardeners. Such hardeners include, for instance, aliphatic amines, aliphatic amine adducts, polyamidoamines, cycloaliphatic amines and adducts thereof, aromatic amines, Mannich bases and ketimines all of which may be substituted wholly or in part with aminosilanes. Amine hardeners useful for the present invention are described in WO 96/16109, for instance.

Organic tin compounds, such as dibutyl tin dilaurate (DBTL) or organic salts, for instance naphthanates, of some metals, such as cobalt, zinc, manganese, iron and lead, can be used as an accelerator in the compositions of the invention.

Water can be included in the compositions of the invention, either separately added or in the form of water present in the ingredients. The amount of water is about 1% by weight of the total weight of the paint.

The compositions of the invention may also include other commonly used paint ingredients, such as pigments, fillers, additives such as tixotropic substances, softeners, solvents, et cetera, to achieve the properties desired by the user.

Following advantages, for instance, are achieved by using epoxy silane instead of organo-oxysilane in the composition of the invention:

epoxy silane has properties improving paint adhesion, epoxy silane acts as a crosslinking agent between the epoxy and siloxane chains, when using epoxy silane in a siloxane reaction, the amount of alcohol liberated in the reaction in relation to the molecular weight is considerably lower than when using organo-oxysilane. Consequently, a higher dry solids content and a lower amount of volatile organic compounds (VOC) can be achieved. epoxy silane reduces the viscosity of the paint, epoxy silane also has a modifying effect on functional fillers, such as wollastonite, whereby strength and anti-corrosive properties improve.

The following examples illustrate the invention.