GB2068001A - Solvent Free Coating Compositions - Google Patents

Abstract

A solvent free or high solids coating composition is described, comprising an epoxide resin, a polyacrylate or polymethacrylate compound and a cycloaliphatic polyamine as curing agent, said composition having a pot life time of at least 120 minutes and an exothermicity peak during the curing reaction not exceeding 100 DEG C.

Description

SPECIFICATION Solvent Free Coating Compositions The present invention relates to solvent free coating compositions or in other terms to high solids coating compositions, comprising an epoxy resin, having more than one epoxy group per molecule, a polyacrylate or polymethacrylate compound, and a curing agent of the amine type.

Epoxide resins, particularly polyglycidylether of bisphenol A have a wide variety of uses in the field of paints and coating compositions, advantageously after having been submitted to a curing reaction in the presence of aliphatic or aromatic amines, anhydrides or still with polyacids. However the working of these compositions based on epoxide resins needs the use of important amounts of solvent to overcome production and application problems due to the viscosity of the epoxide resin itself. Moreover, the high prices and eventual scarcity of solvents which are derived from petroleum, as well as ecological problems risen by the evaporation of these solvents, have forced research people to develop either solvent free coatings or water based coating compostions. A typical example of solvent free paints is the powder coating.The equipment for the production and application of powder coating is however quite different from the conventional one for solvent based systems.

Therefore, it is of great importance for paint manufacturers to find out solvent free or high solids coating compositions which may be prepared and applied with a conventional equipment used for the solvent based compositions.

Rather than using volatile oil-solvent to reduce the viscosity of the epoxide resins, it has already been proposed to dilute these resins with liquid non-volatile reactive compounds such as unsaturated polyesters or polyacrylate and polymethacrylate compounds.

The most significative improvement with regard to viscosity is obtained with the compositions described in the US patent 4051195 which comprise an epoxide resin and a polyacrylate or polymethacrylate compound.

However, the gel time, after addition of the curing agent remains very short, since it ranges generally between 2 and 20 minutes. Said short period of time is due to the strong reactivity of the used curing agents which are the most often aliphatic polyamines. It has also been noticed that this reactivity is strong not only for the epoxide resin used alone, but it is still stronger for polyacrylate or polymethacrylate compounds used alone. Moreover, the use of such curing agents provides, during the curing reaction, very high exothermicity peaks, of about 1 70 to 2300C, that may be dangerous when important amounts of products are mixed together.Both the very short gel time at room temperature which results in an extremely short-pot life time i.e. the time between the moment of mixing of the curing agent and the time of the application of the resulting composition, and the exothermicity peaks, are factors which seriously restrict the use of such coating compositions.

It is also known in the art the use of cycloaliphatic polyamines as curing agent of epoxide resins used alone, in order to extend their pot life time, but however the viscosity of these compositions are still too high.

Solvent free coating compositions should fulfil some important conditions, among which it may be cited: low viscosity of the composition which is ready to use restricted increasing of viscosity during the time, that needs a sufficiently long period of time of stability before reaching a complete gelification of the composition and therefore a longer period of time for the easy working of said composition a low exothermicity peak during the curing of the composition in order to reduce the internal stresses of the cured resin.

An object of the present invention is to provide coating compositions which fulfil these conditions.

Another object of the present invention is to provide solvent free or high solids coating compositions comprising an epoxide resin, a polyacrylate or polymethacrylate compound and a curing agent such that the pot life time is at least 120 minutes and the exothermicity peak during the curing reaction does not exceed about 1800C and the viscosity of the composition is lower than 2500 centipoises during the pot life time.

The solvent free or high solids coating composition of the invention comprising an epoxide resin having more than one 1,2 epoxy group per molecule, a polyacrylate or polymethacrylate compound having more than one terminal acrylate or methacrylate group, and a curing agent is characterized in that the curing agent is a cycloaliphatic polyamine.

The terms "high solids coating composition" mean a composition having a solid matter content of at least 80% by weight and preferably of at least 90% by weight.

The Applicant has unexpectedly found that by using a cycloaliphatic polyamine as curing agent of synthetic resins comprising an epoxide resin and a polyacrylate or polymethacrylate compound, the period comprised between the moment of the introduction of the curing agent into the resin and the moment where the resin gelifies, that's to say the pot life time of the resin, is considerably increased. This pot life time is of at least 120 minutes.

The Applicant has also found that when a polyacrylate or a polymethacrylate compound is added to an epoxide resin in the presence of a cycloaliphatic amine as curing agent, not only the pot life time of the resin is extended, but still the exothermicity peak remains very low during all the period of gelification, these findings is all the more surprising as in case where a polyacrylate or polymethacrylate compound is added to the epoxide resin in the presence of an aliphatic amine as curing agent, the pot life time of the resin is reduced and the exothermicity peak is very high.

The pot life time typically depends on the evolution of the viscosity of the composition during the curing reaction. Generally, a resin will be easily worked inasmuch the viscosity does not exceed 2500 centipoises and preferably 1500 centipoises.

Moreover the Applicant has also found that the use of a cycloaliphatic polyamine as curing agent provides an exothermicity peak during the curing reaction, which is much lower, than with other curing agents, said peak generally not exceeding 1000C.

The cycloaliphatic polyamines have at least two aminoaliphatic groups which can react with the epoxy groups of the resin. The term "aminoaliphatic group" means an amino group wherein the nitrogen atom is neither a member of an aromatic ring nor directly linked to a carbon atom of an aromatic ring. Generally the amino group may be directly linked to a carbon atom of an aliphatic ring or indirectly linked by means of a mono or divalent carbonaceous radical.

As suitable examples of cycloaliphatic polyamines, it may be cited, 3,5,5-trimethyl-3 (aminoethyl)cyclohexylamine, also called isophorone diamine, N,N'-bis-(2 aminoethyl)piperazine, paramenthane-diamine, 1 ,3-bis-(aminoethyl)cyclohexane, 1,4 diaminocyclohexane, bis-(4 aminocyclohexyl)methane, bis-(4-amino-3 methylcyclohexyl)methane, 2,2'-bis-(4 aminocyclohexyl)propane or their isomers.

However, for reasons of easiness, liquid cycloaliphatic polyamines, such as isophorone diamine are preferred.

In order to realize the curing reaction under suitable conditions it is advantageous to use the cycloaliphatic diamines in such an amount that there is from 0.5 to 1.2 amine group per epoxy group and per terminal acrylate or methacrylate group.

Although the curing reaction may be carried out completely at room temperature, if desired, it may be carried out at a higher temperature, comprised between 30 and 1 800C, eventually in the presence of a catalyst such as triethylamine or salicylic acid or analogs, well known by the skilled in the art worker.

The epoxides resins used in the present invention are resins which contain more than one 1,2 epoxy group per molecule. They can be saturated or unsaturated, aliphatic, cycloaliphatic or heterocyclic and can be monomeric or polymeric in nature.

Preferably, the epoxide resins will contain glycidyl ether or ester groups, will be liquid rather than solid and will have weight per epoxide in the range of about 100 to about 2,000 and preferably of about 110 and about 500.

Useful epoxide resins are glycidyl polyethers of polyhydric phenols which are derived from an epihalohydrin, e.g. epichlorhydrin, and a polyhydric phenol. Examples of such polyhydric phenols include resorcinol, hydroquinone, bis (4hydroxyphenyl)-2,2-propane, or bisphenol A as it is commonly called, 4-4'-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1 ,1 -ethane, bis(4-hydroxyphenyl)- 1,1 -isobutane, bis(4hydroxyphenyl)-2,2-butane, bis(2dihydroxynaphthyl)methane, phloroglucinol and bis(4-hydroxyphenyl)sulfone. Additional polyhydric phenols are novolac resins containing more than two phenol, or substituted phenol, moieties linked through methylene bridges as well as halogenated, e.g., brominated and chlorinated, phenolic compounds.

Additional epoxide resins are glycidyl polyethers of polyhydric alcohols prepared by reacting a polyhydric alcohol with an epihalohydrin using an acidic catalyst, e.g., boron trifluoride, and subsequently treating the resulting product with an alkaline dehydrohalogenating agent. Included among the polyhydric alcohols that can be used in the preparation of these polyepoxides are glycerine, ethylene glycol, propylene glycol, diethylene glycol, hexanediol, hexanetriol, trimethylolpropane, trimethylolethane, pentaerythritol and the like.

Other epoxide resins are glycidyl esters of polycarboxylic acids which are derived from an epihalohydrin and a polycarboxylic and using procedures described in US patents 3,859,314 and 3,576,827 which are herein incorporated by reference. Examples of polycarboxylic acids include phthalic acid or its anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic anhydride, adipic acid, dimerized fatty acids, dibasic acids made from an unsaturated fatty acid and acrylic acid and the like.

The most preferred epoxide resins are glycidyl polyether of bisphenol A.

The polyacrylate and polymethacrylate ester of polyols useful in this invention are those esters which contain more than one terminal acrylate or methacrylate group. These esters are the acrylic and methacylic acid esters of aliphatic polyhydric alcohol such as, for example, the di- and polyacrylates and the di- and polymethacrylates of alkylene glycols, alkoxylene glycols, alicyclic glycols and higher polyols such as ethylene glycol, triethylene glycol, tetraethylene glycol, tetramethylene glycol, hexanediol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaetythritol and the like, or mixtures of these with each other or with their partially esterified analogs.

Typical compounds include but are not limited to trimethylolpropane triacrylate, trimethylolethane triacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, tetramethylene glycol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,6 hexa nediol dimethacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and the like.

Particularly preferred esters are 1 6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate.

Additional acrylate or methacrylate esters of polyols are the acrylate or methacrylate esters of epoxide resins wherein epoxide resins as used herein are considered to be polyols. These resins are described in US patent 3,377,406 incorporated by reference.

These acrylate or methacrylate esters of polyols are mixed with the hereabove described epoxide resins, in a weight ratio of about 5 to 100 parts ester per 100 parts epoxide resin, such as described in US patent 4051195 incorporated by reference.

The solvent free or high solids coating compositions of the present invention can be used instead of solvent based paints or powder coating paints. They can be used as anti-corrosive coating for metallic plates, back mirror coating, glass coating, concrete or wood coatings, or as mortar component and for other analog uses well known by the skiiled in the art worker.

The following examples are given in order to better illustrate the present invention but without limiting it in any way.

Example 1 The following solvent free resin was prepared by mixing 49.0 g of diglycidyl ether of bisphenol A 29.8 g of hexanediol diacrylate 21.9 g of isophorone diamine.

The amounts of each component are calculated so as to obtain 1 amine group per each terminal acrylate group and each epoxy group, and for a total weight sample of about 100 g.

The viscosity of the composition was determined just after having mixed the constituents. it was of 80 centipoises.

The viscosity was still determined at various moments which are defined with regard to the initial time to which is the time where the constituents were mixed.

Viscosity at to+120 minutes: 960 centipoises Viscosity at to+180 minutes: 2400 centipoises.

The exothermicity peak during the curing reaction was 36.50C. By way of comparison, other composition were prepared but with curing agent not conform to the present invention.

The amounts of the different constituents were calculated so as to obtain 1 amine group per each terminal acrylate group and each epoxy group, and so as to keep the same total weight of about 100 g for the sample in order not to false the determination of the exothermicity peak.

Composition A was obtained by mixing: 54.0 g of diglycidyl ether of bisphenol A 32.2 g of hexanediol diacrylate 1 3.8 g of triethylene tetramine 13 minutes after having mixed the constituents, the composition was cured and therefore was unapplicable. Moreover, the exothermicity peak during the curing reaction was 1450C.

Composition B was obtained by mixing 51.2 g of diglycidylether of bisphenol A 30.5 g of hexanediol diacrylate 18.3 g of xylene diamine The initial time to was the time where the constituents were mixed and the viscosity of the composition was determined at the following moments: to : 85 centipoises to+120 minutes : 3520 centipoises to+1 80 minutes : 8640 centipoises The exothermicity peak during the curing reaction was 440C. If the period of tirne during which this composition may be easily applied is longer than with composition A, on the other hand, after 120 minutes a solvent is needed because viscosity is too high.

Example 2 The following composition was prepared by mixing 50.0 g of diglycidylether of bisphenol A 29.8 g of hexanediol diacrylate 0.2 g of Modaflow (product sold by Monsanto Co) 20.0 g of TiO2 22.6 g of isophorone diamine.

Immediately after having mixed the constituents, this paint composition was applied on metallic plates. Curing was carried out during 30 minutes in an oven heated at 1200 C. The following properties were determined: Gloss: 72-84 according to the Lange 60 method Erichsen: > 7 mm Reverse impact strength according to ASTM D.2794: > 10kg/cm Two hours after having mixed the constituents, the viscosity of the composition was 1020 centipoises and a new application was carried out on another metallic plate. Curing was carried out during 30 minutes in an oven heated at 1 200C.

The obtained properties were similar to those hereabove determined.

Example 3 The following composition was prepared by mixing 70 g of diglycidylether of bisphenol A 30 g of diacrylate of 1,6 hexanediol 27 g of isophorone diamine One part of the composition had been used to coat the back of the mirror.

The other part, about 100 g, had been used to determine the pot life time of the composition together with the exothermicity peak during the curing reaction.

Pot life time: 210 minutes Exothermicity peak: 370C.

The mirror had been submitted to a Kesternich test, according to the method DIN 50018 which consists in submitting the coating to a saturated wet atmosphere in the presence of sulfurous anhydride.

It has been noticed a slight loss of adhesion on the sides of the mirror after 9 cycles of 24 hours each.

This mirror had also been submitted to the salt spray test according to the method DIN 53167 and to the R-H test according to the method ASTM D.2247.

For these both tests, no change had been noticed after 500 hours exposure.

Example 4 The following composition was mixed to 283 g of a mixture comprising sand and ballast in order to form a concrete.

23.3 g of diglycidyl ether of bisphenol A 4.1 g of benzyl alcohol 12.1 g of trimethylol propanetriacrylate 1.5 g of salycylic acid 10.5 g of isophorone diamine The pot life time was 90 minutes and the exothermicity peak during the curing reaction was 350C.

Example 5 The following composition was prepared by mixing 45.6 g of diglycidylether of bisphenol A 26.4 g of 1,6 hexanediol diacrylate 28.0 g of dimethyldicyclohexylmethane diamine The following results were obtained: Pot life time: 7 hours Exothermicity peak: 240C.

Claims (3)

Claims

1. Solvent free or high solids coating composition comprising an epoxy resin having more than one 1,2 epoxy group per molecule, a polyacrylate or polymethacrylate compound and a curing agent characterized in that the curing agent is a cycloaliphatic polyamine.

2. Coating composition according to claim 1 wherein the cycloaliphatic polyamine is used in an amount corresponding to 0.5 to 1.2 amine group per epoxy group and per terminal acrylate or methacrylate group.

3. Coating composition according to claim 1 and 2 wherein the aliphatic polyamine is selected from the group comprising 3,5,5-trimethyl-3 (aminoethyl)cyclohexylamine or isophorone diamine, N,N'-bis-(2-am inoethyl)piperazine, paramenthane diamine, 13-bis- (aminoethylcyclohexane, 1,4diaminocyclohexane, bis-(4aminocyclohexyl)methane, bis-(4-amino-3 methylcyclohexyl)methane, 2,2'-bis-(4- aminocyclohexyl)propane and their isomers.