KR20010005521A - Acrylic powder coating including high homopolymer glass transition temperature cyclic (meth)acrylate monomer as viscosity modifier - Google Patents

Abstract

The present invention relates to a powder coating composition. The powder paint coating composition of the present invention comprises a binder consisting of the following two components:

(a) one or more acrylate polymers derived from two or more monomers, wherein at least 15% by weight of these two or more monomers are cyclic acrylate monomers having a homopolymer glass transition temperature of at least about 75 ° C. Ingredients to make; And

(b) a component comprising one or more crosslinking agents.

Where they are applied on the surface and heated, the coatings crosslink to form a thin irreversible film.

Description

ACRYLIC POWDER COATING INCLUDING HIGH HOMOPOLYMER GLASS TRANSITION TEMPERATURE CYCLIC (METH) ACRYLATE MONOMER AS VISCOSITY MODIFIER} As a viscosity modifier, an acrylic powder coating comprising a cyclic acrylate and / or methacrylate monomer having a high homopolymer glass transition temperature

Constant improvements in form, application method, and process economics have introduced thermosetting powder coatings as a reliable and suitable finish. Many different techniques have been developed in the finishing industry dealing with various applications in polyester, epoxy polymer, and acrylic polymer chemistry. In particular, the outstanding outdoor durability and hardness of acrylic powder coatings have led to the boom in acrylic powder coatings as it has led to the use of thermosetting powders across important applications in the automotive industry.

Currently, acrylic powder coatings developed and used for thermosetting powder coatings are acrylic resin systems having glycidyl, hydroxy, or carboxyl functional groups. Typically, acrylics with glycidyl functional groups are cured by either long chain dicarboxylic acids or acid anhydrides, while acrylics with hydroxy functional groups can be crosslinked by blocked isocyanates and glycolurils. . Acrylics with carboxyl functionalities can be crosslinked by many different chemicals, e.g. epoxy and hydroxy alkylamides.

When making this coating, it is desirable to provide a coating that has a low melt temperature or can reach very low melt viscosities. The primary motivation for the former's properties is to reduce the energy cost of applying the coating to the substrate, and the primary motivation for the latter's properties is to provide as thin and uniform a coating as possible. It is to.

Literature on the use of acrylic powder coatings and / or viscosity modifiers can be found in the literature: Yeates et al. Rheology of Acrylic Powder Coatings, Journal of Coatings Technology, Vol. 68, no. 861, October 1996, US Pat. Nos. 4,131,572, 4,286,021, 4,023,977, 5,098,956, 3,787,340, 5,510,444, 5,492,955, 5,407,707, and 5,153,252.

Despite such teachings, there remains a need in the art for acrylic powder coatings that can be cured at relatively low temperatures and that can form a uniform and thin film upon curing.

The present invention relates to a coating composition. In particular, the composition is an acrylic powder coating comprising cyclic acrylate and / or methacrylate monomers having a high homopolymer glass transition temperature as a viscosity modifier. This modifier serves to lower the viscosity or lower the melting temperature of the final coating composition so that a thin, uniform film is obtained when the coating is cured.

The present invention provides a novel acrylic powder coating that can be cured at relatively low temperatures and that can form a uniform and thin film upon curing. In particular, the coating has an acrylate polymer derived from two or more monomers as a binder, wherein at least 15% by weight of the two or more monomers is a cyclic acrylate monomer having a homopolymer glass transition temperature of at least about 75 ° C. .

One embodiment of the present invention provides a powder paint coating composition comprising a binder consisting of the following two components:

(a) one of said components comprises one or more acrylate polymers derived from two or more monomers, wherein at least 15% by weight of said two or more monomers have a homopolymer glass transition temperature of at least about 75 ° C Cyclic acrylate monomers;

(b) the other of the components comprises one or more crosslinkers.

Here, when applied to a surface and heated, the coating crosslinks to form a thin irreversible film.

In a preferred embodiment, component (a) of the binder comprises a polymer of acrylate and / or methacrylate monomers and isobornyl methacrylates having hydroxy functional groups as ring acrylates and component (b) cross-polyisocyanate Includes a binder suitably; Or component (a) of the binder comprises a polymer of acrylate and / or methacrylate monomer and isobornyl methacrylate having a carboxyl functional group as ring acrylate and component (b) suitably comprises an epoxy crosslinker; Or component (a) of the binder comprises a polymer of acrylate and / or methacrylate monomers having isocylyl functional groups and isobornyl methacrylate as ring acrylates and component (b) is a crosslinking agent having carboxyl functional groups Include appropriately. In a further preferred embodiment, component (a) can also be derived from further ethylenically unsaturated monomers.

Another embodiment of the present invention includes a method of coating a substrate comprising coating a substrate as defined above and then heating the substrate to crosslink the binder to form a thin irreversible film.

In a preferred embodiment, the curing temperature is about 80 ° C to 220 ° C.

In addition, another embodiment of the present invention includes a surface having a coating comprising the final product prepared by the method described above.

It is an object of the present invention to provide a novel acrylic powder coating having excellent film formation and viscosity properties.

It is another object of the present invention to provide a coating method for coating a substrate with an acrylic powder coating and then curing the coating on the substrate.

Another object of the present invention is to provide a substrate having a thin acrylic powder coating film cured on the substrate.

Those skilled in the art will readily understand the objects and other objects mentioned above by reference to the detailed description of the preferred embodiments.

In describing the above preferred embodiment, some terms will be used for clarity. This term tends to include not only the foregoing embodiments but all technically relevant phrases used in the same method for the same purpose to achieve the same result.

The coating composition of the present invention comprises a binder consisting of the following two components:

(a) one of said components comprises one or more acrylate polymers derived from two or more monomers, wherein at least 15% by weight of said two or more monomers have a homopolymer glass transition temperature of at least about 75 ° C Cyclic acrylate monomers;

(b) the other of the components comprises one or more crosslinkers.

Here, when applied to a surface and heated, the coating crosslinks to form a thin irreversible film.

The first component above comprises an acrylate polymer. This polymer should be derived from two or more monomers, one of which is a cyclic acrylate monomer having a homopolymer glass transition temperature of at least about 75 ° C., more preferably at least 100 ° C., most preferably at least 115 ° C. . This cyclic acrylate monomer should be present in an amount of at least 15% by weight, more preferably about 15-50% by weight and most preferably about 15-30% by weight of the polymer component.

The cyclic acrylate monomers include isobornyl methacrylate, cyclohexyl methacrylate, trimethyl cyclohexyl acrylate and methacrylate, isobornyl acrylate, 4-t-butyl cyclohexyl methacrylate, and mixtures thereof It may be selected from, it is particularly preferred to have isobornyl methacrylate.

At least one of the other monomers preferably used for binder formation is acrylates and / or methacrylates having hydroxy functional groups, acrylates and / or methacrylates having glycidyl functionalities, acrylates having carboxyl functionalities and And / or methacrylates, or acrylates and / or methacrylates having carbamate functional groups. Specially contemplated mixtures of these materials within the scope of the present invention.

Suitable hydroxyalkyl acrylates or methacrylates include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and mixtures thereof. Preferred hydroxyalkyl acrylates are hydroxyethyl acrylates. If present, these monomers comprise from about 10 to 85%, more preferably from about 15 to 50%, most preferably from about 20 to 40% by weight of the acrylic polymer.

Suitable glycidyl functional group-containing acrylates or methacrylates include glycidyl acrylate or glycidyl methacrylate and mixtures thereof. If present, these monomers comprise from about 10 to 85%, more preferably from about 15 to 50%, most preferably from about 20 to 40% by weight of the acrylic polymer.

Suitable carboxyl group-containing acrylates or methacrylates are acrylic acid, methacrylic acid, fumaric acid, crotonic acid, itaconic acid, maleic acid, cinnamic acid, 2,3-bis- (para-methoxyphenyl) -acrylic acid, meta-phenyl Lene diacrylic acid, oleic acid and the like and mixtures thereof. If present, these monomers comprise from about 10 to 85%, more preferably from about 15 to 50%, most preferably from about 20 to 40% by weight of the acrylic polymer.

Suitable carbamate functional group-containing acrylates or methacrylates include hydroxypropyl carbamoyl acrylate and / or methacrylate. If present, these monomers comprise from about 10 to 85%, more preferably from about 15 to 50%, most preferably from about 20 to 40% by weight of the acrylic polymer.

In addition to the monomers disclosed above, the acrylic polymer may comprise other ethylenically unsaturated monomers having no functional groups. These monomers are present in an amount of about 0 to 75%, more preferably about 30 to 70%, and most preferably about 35 to 65% by weight of the acrylic polymer. These monomers include ethylenically unsaturated aromatic hydrocarbons and alkyl acrylates and / or methacrylates, where alkyl means groups having from 1 to 30 carbon atoms and mixtures thereof.

Examples of ethylenically unsaturated aromatic hydrocarbons include styrene, ortho-methyl styrene, para-methyl styrene, and mixtures thereof. Preferred comonomers are styrene, which is present in an amount of about 15 to 30% by weight, more preferably about 20 to 25% by weight of the acrylic polymer.

Examples of alkyl acrylates and / or methacrylates, where alkyl means groups having from 1 to 30 carbon atoms and mixtures thereof, include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate , n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, neopentyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylic Rate, 2-ethylhexyl acrylate, lauryl (n-dodecyl) acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, Isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, neopentyl meta Methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, lauryl (n-dodecyl) methacrylate, and mixtures thereof It is not limited to these.

Preferred alkyl acrylates include ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, and mixtures thereof. If present, such acrylate monomers are present in an amount of about 1 to 30 weight percent, more preferably about 5 to 15 weight percent of the acrylic polymer.

Preferred alkyl methacrylate monomers include methyl methacrylate, n-butyl methacrylate, ethyl methacrylate, and mixtures thereof. If present, such methacrylate monomer is present in an amount of about 25 to 60% by weight, more preferably about 30 to 45% by weight of the acrylic polymer.

In a preferred embodiment, the acrylate polymer is isobornyl methacrylate (20 wt%), hydroxyethyl acrylate (20 wt%), styrene (20 wt%), methyl methacrylate (35 wt%), and copolymer of n-butyl acrylate (5% by weight).

The polymers are prepared in the form of solutions, emulsions or suspensions in large quantities by methods known in the art such as free-radical polymerization. Preferably, this reaction is carried out in the presence of azo compounds such as azobisisobutyronitrile, free radical initiators such as benzoyl peroxide, tert-butyl peroxide, decanoyl peroxide and the like. Useful initiators are present in about 0.1-5% by weight of the total monomer. Also contemplated are methods for improving the reaction between monomers using heat within the scope of the present invention.

The second component of the binder includes one or more crosslinkers that react with the functional group (s) of the acrylic polymer. These compounds contain reactive groups capable of reacting with the functional groups of the base polymer at high temperatures. Preferably, the crosslinker is selected from compounds having the following functional groups: alkoxy groups, blocked isocyanate groups, carboxyl groups, epoxy groups, and hydroxyamide groups.

The crosslinker may be selected from the following compounds: dicyanamide, hydroxyalkylamide, hexamethoxy-melamine, tetramethoxymethylglycoluril, aliphatic dicarboxylic acid, 1,12-dodecanedionic acid acid), sebacic acid, 1,4-cyclohexanedicarboxylic acid, and caprolactam blocked isophorone diisocyanate and oligomers thereof, blocked toluene diisocyanate and oligomers thereof, triglycidyl isocyanurate, low molecular glycidyl Blocked isocyanates such as methacrylate copolymers and the like. The crosslinking agent is selected such that these functional groups and functional groups of the acrylic polymer are paired so that sufficient crosslinking is achieved upon thermal curing.

Preferred crosslinkers for thermosetting acrylic polymers having carboxyl functionalities include tetramethoxymethyl-glycoluril, triglycidyl isocyanurate, and hydroxyalkyl amides. Preferred crosslinking agents for thermosetting acrylic polymers having hydroxy functional groups are caprolactam blocked meta-tetramethyl xylene diisocyanate, methyl ethyl ketone blocked isophorone diisocyanate, blocked trimers of hexamethylene diisocyanate—but caprolactam blocked hexamethylene Not limited to diisocyanate trimers—or blocked diisocyanates such as caprolactam blocked isophorone diisocyanates. Preferred crosslinkers for thermosetting acrylic polymers having glycidyl methacrylate functional groups are 1,12-dodecanedioic acid, 1,3,5-triscarboxyethyl isocyanate, and 1,4 cyclohexane dicarboxylic acid.

In a preferred embodiment, the acrylate polymer has a hydroxy functional group, blocked polyisocyanate, and more preferred caprolactam blocked isophorone diisocyanate is selected depending on the application.

In practice, the binder is about 25 to 95 weight percent of the acrylic polymer and about 75 to 5 weight percent of the component comprising the crosslinker, more preferably about 50 to 90 weight percent of the acrylic polymer and about the component comprising the crosslinker. 50 to 10% by weight, most preferably about 70 to 90% by weight of the acrylic polymer and about 30 to 10% by weight of the component comprising the crosslinker.

In general, the two different components are stored in separate containers until they are used to prevent coordination between the functional groups of the acrylic polymer and the functional groups of the crosslinker.

Optionally, plasticizers, stabilizers, initiators, catalysts, antistatic agents, degassing additives such as benzoin, ultraviolet absorbers, fillers, extenders, and other conventional additives and mixtures thereof may be included in the binder composition. These additives may be added in about 0.1 to 30% by weight content of the final acrylic powder coating composition. These optional additives of the two component system are usually stored in a container comprising an acrylic polymer.

The composition of the present invention may further contain a flow control agent used to produce a smooth, uniform coating that is different from the high T _g cyclic (meth) acrylate monomer melt viscosity modifiers of the present invention. have. This flow control agent can be added at a content of about 0.1-30% by weight of the binder composition to remove surface defects such as inferior flow rates, orange peel effects, and cratering. Useful flow control agents include silicone oligomers, fluorescent polyolefins, polyvinyl butyral, polyacrylates and others known in the art. Flow regulators serve to reduce the surface tension of the coating system. On the other hand, the melt viscosity modifier of the present invention reduces the melt viscosity of the powder coating composition during the initial stages of the baking process.

The composition can be used as a transparent powder acrylic coating. In a preferred embodiment, however, the composition may comprise pigments and / or dyes. Examples of suitable pigments include titanium dioxide, carbon black, iron blue, phthalocyanine blue and green; Metal oxides, hydroxides, sulfides, sulfates, silicates, and chromates; Organic maroons, aluminum flakes, bronze powder, pearl essence, and various fillers or extenders such as talc, barite, Chinese clay, and diatomaceous earth. It will be obvious to those skilled in the art of organic coatings that the content of pigments can vary greatly depending on the desired effect. The content of pigments based on the weight of the coating composition ranges from about 1% by weight of the final composition to light, high-hiding pigments such as carbon black to heavy low potential pigments such as lead chromate. low-hiding pigments) in the range of about 50% by weight of the final composition. The method of adding a pigment to the powdered resin does not provide a uniform coating critically. Pigments may be present as discrete particles or added within the acrylic polymer, although the latter is preferred.

The powder coating composition may be prepared by dry mixing all the raw materials (e.g., two components of the binder, optional additives, and pigments) and then melt mixing in an internal mixer or extruder at a temperature of 80 ° C to 120 ° C. It will be appreciated that other methods may be chosen, such as liquid phase mixing. Thereafter, the homogeneous composition is cooled to room temperature and crushed by crushing or finely ground in a mill. Useful products are flow free powders having a particle size of about 500 microns or less, preferably about 50 to 250 microns. Powder compositions of the invention are physically or chemically stable for extended periods of up to two years at room temperature. The powder coating is preferably free of flow and resistant to silicification which forms agglomerates at the temperatures used.

The composition may be applied using a suitable sprayer known in the art as a dry coating on a substrate such as a metal material, and then 5-30 in an oven at about 80-220 ° C., more preferably about 100-140 ° C. Bake for a minute. The crosslinked film thus obtained has excellent mechanical strength, thermal stability, solvent resistance, adhesion, mechanical strength, and weather resistance.

The advantage obtained when using the composition of the present invention is that it is possible to lower the baking temperature required for curing on the substrate. On the other hand, compositions of the prior art typically require an enormous baking temperature of 150 ° C. for curing. The use of cyclic acrylate monomers having a homopolymer glass transition temperature of about 75 ° C. or higher can lower the film formation (curing) temperature by about 10 to 50 ° C., thus consequently obtaining a desired curing temperature of about 100 to 140 ° C. do. Reduction of the curing temperature has the effect of saving significant energy required when applying the coating composition on the substrate.

It is also believed that the coating composition may have a reduced viscosity that allows the formation of an extremely thin coating upon curing. This can have the effect of providing a very uniform and defect free coating. Conventional powder paint coatings could not be applied directly to smooth forms. This results in an "orange peel" type of tissue, which means ineffective flow following the powder application. The use of a cyclic acrylic monomer in the coating composition can help to prevent the orange peel effect, and obtain a high gloss uniform and thin film coating.

The invention is described in more detail in the following examples, which, however, are not intended to limit the invention.

Example 1

The following monomers are mixed in liquid form and dissolved in xylene solvent, and then 2% by weight of benzoyl peroxide catalyst is added thereto. Contents listed in the table below are weight ratios.

Monomer content Isobonyl methacrylate 20 Hydroxyethyl acrylate 20 Styrene 20 Methyl methacrylate 35 n-butyl acrylate 5

The catalyzed monomer solution is added to xylene heated at 140 ° C. for 4 hours under nitrogen conditions. After the addition of the monomers is finished, additional 0.12% by weight of benzoyl peroxide is added to the heated reactor. The polymerization is continued for an additional 3 hours. At the end of the polymerization reaction, the material is cooled, sprayed onto an aluminum sheet and the solvent removed to give a solid polymer resin (resin A).

The second vessel contains caprolactam-blocked isocyanates (Vestagon BF 15-40).

The resultant obtained after mixing 80% Resin A and 20% of the composition of the second vessel was subjected to a Gay's twin screw extruder with a barrel temperature profile of 80/90/100 at 130-150 rpm and 70 torque. Extrude). The extrudate is cooled to room temperature and comminuted to size (70-micron mesh Tyler screen). The extrudate is applied onto a steel panel with a dry film thickness of about 70 to 90 microns, then the panel is heated to 100 to 150 ° C. for about 5 to 30 minutes to thermally cure the coating composition for excellent mechanical strength, thermal stability, solvent A colorless transparent crosslinked film having resistance, adhesion, mechanical strength, and weather resistance is obtained.

Example 2

The procedure of Example 1 is repeated except that 50 wt% titanium dioxide is added before coating. The steel panel obtained has a white gloss.

The present invention has been described in detail herein with reference to preferred embodiments, and modifications and variations are possible without departing from the scope of the appended claims.

The present invention provides a novel acrylic powder coating that can be cured at relatively low temperatures and that can form a uniform and thin film upon curing.

Claims (21)

In powder paint coating composition, (a) one or more acrylate polymers derived from two or more monomers, wherein at least 15% by weight of these two or more monomers are cyclic acrylate monomers having a homopolymer glass transition temperature of at least about 75 ° C. Ingredients to make; And (b) a component comprising one or more crosslinking agents A coating composition comprising a binder, wherein the coating is applied on a surface and crosslinked when heated to form a thin irreversible film. The method of claim 1, And the cyclic acrylate monomer comprises a bicyclic alcohol of ethylenically unsaturated acrylic acid and / or methacrylic acid. The method of claim 2, The coating composition of the ethylenically unsaturated acrylic acid ring isobornyl methacrylate. The method of claim 1, At least one of said two or more monomers comprises a crosslinkable acrylate monomer and / or methacrylate. The method of claim 4, wherein The crosslinkable acrylate monomers and / or methacrylate monomers are acrylates and / or methacrylates having hydroxy functional groups, acrylates and / or methacrylates having glycidyl functional groups, and acrylates having carboxyl functional groups. And / or a coating composition selected from the group consisting of methacrylates, acrylates and / or methacrylates having carbamate functional groups, and mixtures thereof. The method of claim 4, wherein At least one of said two or more monomers comprises a further ethylenically unsaturated monomer. The method of claim 6, Said further ethylenically unsaturated monomer being an ethylenically unsaturated aromatic hydrocarbon, alkyl acrylate and / or methacrylate, wherein alkyl means a group containing from 1 to 30 carbon atoms-and a mixture thereof. Composition. The method of claim 7, wherein The further ethylenically unsaturated monomer is selected from the group consisting of styrene, methyl methacrylate, butyl acrylate, and mixtures thereof. The method of claim 3, The coating composition of said isobornyl methacrylate comprises about 15 to 50% by weight of said two or more monomers. The method of claim 9, The coating composition of said isobornyl methacrylate comprises about 15 to 30% by weight of said two or more monomers. The method of claim 1, A coating composition wherein the crosslinking agent of component (b) of the binder is selected from the group consisting of compounds comprising isocyanate, amide, carboxy, epoxy or amino functional groups and mixtures thereof. The method of claim 11, Wherein said acrylic polymer is derived from acrylates and / or methacrylates having hydroxy functional groups and said crosslinker comprises one or more blocked polyisocyanates. The method of claim 11, Wherein said acrylic polymer is derived from an acrylate and / or methacrylate having a carboxyl functional group and said crosslinker comprises a crosslinking agent having an epoxy functional group. The method of claim 11, Wherein said acrylic polymer is derived from acrylate and / or methacrylate having glycidyl functional groups and said crosslinking agent comprises a crosslinking agent having carboxyl functional groups. The method of claim 1, The composition further comprises an additive material selected from the group consisting of pigments, dyes, flow regulators, plasticizers, stabilizers, initiators, catalysts, antistatic agents, degassing additives, ultraviolet absorbers, fillers, extenders, and mixtures thereof. Coating composition. The method of claim 1, The acrylate monomer is selected from the group consisting of cyclohexyl methacrylate, trimethyl cyclohexyl acrylate and / or methacrylate, isobornyl acrylate, 4-t-butyl cyclohexyl methacrylate, and mixtures thereof Coating composition. The method of claim 1, The acrylate polymer of component (a) is a copolymer of isobornyl methacrylate, hydroxyethyl acrylate, styrene, methyl methacrylate, and n-butyl acrylate; Component (b) is a coating composition containing caprolactam blocked isocyanates. A method of forming a thin irreversible film coating on a substrate, (1) coating a powder paint coating composition comprising a binder consisting of the following two components on the substrate: (a) one or more acrylate polymers derived from two or more monomers, wherein at least 15% by weight of these two or more monomers are cyclic acrylate monomers having a homopolymer glass transition temperature of at least about 75 ° C. Ingredients to make; And (b) a component comprising one or more crosslinking agents; And (2) heating the substrate to crosslink the binder to form a thin irreversible film on the substrate How to include. The method of claim 18, Wherein said heating step occurs at a temperature of about 80 ° C to 220 ° C. The method of claim 19, Said heating step at a temperature of about 100 ° C to 140 ° C. In a substrate having a powder paint coating, (1) coating on said substrate a powder paint coating composition comprising a binder comprising the following two components: (a) one or more acrylate polymers derived from two or more monomers, wherein at least 15% by weight of these two or more monomers are cyclic acrylate monomers having a homopolymer glass transition temperature of at least about 75 ° C. Ingredients to make; And (b) a component comprising one or more crosslinking agents; And (2) heating the substrate to crosslink the binder to form a thin irreversible film on the substrate Substrate formed by a method comprising a.