JPS584069B2 - Netsukokaseifuntaiyoujiyushisoseibutsu - Google Patents

Description

[Detailed description of the invention] The present invention relates to a resin composition for thermosetting powder coatings.

Thermosetting powder coatings using polyhydric carboxylic acids as curing agents in acrylic resins or methacrylic resins having epoxy groups are already known.

This known thermosetting powder coating forms a coating film with excellent heat resistance and weather resistance, and the coating film is preferably formed at a lighting temperature in the range of 190 to 200°C, and the above-mentioned A decrease in hardness, mechanical properties, impact resistance, water resistance, chemical resistance, solvent resistance, stain resistance, etc. is observed in coating films formed at the following baking temperatures.

Therefore, it is necessary to increase the epoxy group concentration in the acrylic resin in order to obtain a sufficient crosslinking density, and to lower the molecular weight in order to improve the thermal fluidity that decreases accordingly.

As a result, the hardness, solvent resistance, and stain resistance of the coating film deteriorate.In order to solve this problem, polyvalent carboxylic acids, which are hardeners, have a high reactivity with epoxy groups and are difficult to dissolve in solvents. If a material with a difficult molecular structure is used, the smoothness, gloss, and sharpness of the coating film will decrease, making it difficult to maintain a balance with other properties.

In this way, a thermosetting powder coating using only a polycarboxylic acid as a curing agent for a resin having an epoxy group can be heated to 190°C.
It was difficult to maintain a balance between appearance and physical properties at a baking temperature below.

The purpose of the present invention is to improve the gloss, hardness, solvent resistance, and stain resistance of the coating film, and to improve the appearance (smoothness, gloss) of the coating film, which has conventionally been difficult to maintain a balance under low baking conditions. The object of the present invention is to provide a resin composition for a thermosetting powder coating that can maintain a balance with various performances of the present invention.

That is, the present invention provides a copolymerizable monomer containing 5 to 40% by weight of glycidyl acrylate and/or glycidyl methacrylate, or 10% by weight or less of a polymerizable monomer having one or more hygoxyl groups. A solid copolymer with a glass transition temperature of 5 to 100°C and a number average molecular weight of 3,000 to 30,000 obtained by copolymerizing a polymer mixture, a compound having two or more carboxyl groups or its acid anhydride, and an aminoplast resin. The aminoplast resin consists of a compound having a carboxyl group in an amount such that its acid anhydride provides 0.7 to 1.2 carboxyl groups per epoxy group in the solid copolymer, and the aminoplast resin is present in the solid copolymer. The present invention relates to a resin composition for a thermosetting powder coating, characterized in that the amount is 1 to 10 parts by weight per 100 parts by weight of the polymer.

Next, the constituent components of the resin composition for thermosetting powder coating of the present invention will be specifically explained.

The solid copolymer used in the present invention is obtained by copolymerizing a copolymerizable monomer mixture containing glycidyl acrylate and/or glycidyl methacrylate as essential components. When the resin composition of the invention is put into practical use, the coating film is crosslinked mainly by reacting with a polyhydric carboxylic acid compound or its acid anhydride,
Improves the chemical and physical properties of coatings, such as solvent resistance, chemical resistance, water resistance, hardness, Erichsen resistance, impact resistance, and stain resistance.

The amount of glycidyl acrylate and/or glycidyl methacrylate is 5 to 40% by weight in the copolymerizable monomer mixture.
If the amount is less than 5% by weight, sufficient crosslinking density cannot be provided and the chemical and physical properties of the coating film cannot be improved.

Moreover, if it exceeds 40% by weight, the crosslinking reaction will proceed before thermal melting is insufficient in the baking step after painting, and the smoothness of the surface of the coating film will be significantly impaired, which is not practical.

In the above copolymerizable monomer mixture, examples of polymerizable monomers having one or more hydroxyl groups to be used in combination with glycidyl acrylate and/or glycidyl methacrylate include 2-hydroxyethyl acrylate and 2-hydroxyethyl acrylate. -Hydroxypropyl, 1-methyl acrylate-
2-hydroxyethyl, 2-hydroxyethyl methacrylate, 1-methyl-2-hydroxyethyl methacrylate, polypropylene glycol monomethacrylate, glycerol monomethacrylate, 3-chloro-2 methacrylate
-Hydroxybubutyr is a typical example.0 Since the addition reaction between an epoxy group and a carboxyl group produces one ester bond and one hydroxyl group, the polymerizable monomer having the above-mentioned hydroxyl group is used. Even solid copolymers that have not been added to the solid copolymer react with the aminoplast resin to crosslink the coating film and fully satisfy the purpose of the present invention. By including it therein, the reaction between the hydroxyl group and the curing agent becomes easier, thereby achieving the object of the present invention.

However, if the polymerizable monomer having one or more human xyl groups exceeds 10% by weight in the comonomer mixture, a large amount of unreacted hydroxyl groups will remain in the coating film after crosslinking. This is undesirable as it reduces performance such as water resistance.

Other polymerizable monomers in the copolymerizable monomer mixture used to produce the solid copolymer include methyl methacrylate, ethyl methacrylate, n-butyl meccrylate, i-butyl methacrylate, and methacrylic acid. t-butyl, 2-ethylhexyl methacrylate, lauryl methacrylate, ethyl acrylate, n-butyl acrylate, i acrylate
-Esters of methacrylic acid or acrylic acid and alcohols having an alkyl group having 1 to 18 carbon atoms, such as butyl, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, etc., styrene, α-methyl Typical examples include styrene and styrene derivatives such as styrene, vinyltoluene, and para-t-butylstyrene.

These are used for modifying solid copolymers, but since they have a large effect on blocking resistance, thermal fluidity, film sharpness, gloss, and various physical properties, their selection should be made accordingly. The quantitative ratio should be determined depending on the intended use of the resin composition by fully understanding the characteristics of the resin composition.

For example, methyl methacrylate provides durability, transparency, and
Other methacrylic esters or acrylic esters provide durability, transparency, gloss retention, and flexibility to the coating, but if used in large amounts, they reduce the blocking resistance of the powder. .

Further, styrene and its derivatives give the coating film sharpness, gloss, and water resistance, but if used in large amounts, the gloss retention and yellowing resistance will deteriorate, so the amount is preferably 40% by weight or less.

The solid copolymer can be obtained by copolymerizing the above-mentioned copolymerizable monomer mixture, and can be easily obtained by known methods such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization.

In solution polymerization, the aforementioned copolymerizable monomer mixture is copolymerized in a single solvent or a mixed solvent.

In emulsion polymerization, the above-mentioned copolymerizable monomer mixture, water, molecular weight regulator, emulsifier, emulsification aid, and catalyst are mixed with vigorous stirring, and the mixture is heated at a temperature of 40 to 90°C for 1 hour.
Allow to react for ~8 hours.

The latex is precipitated by adding an at least partially water-soluble alcohol such as methanol, ethanol or isopropyl alcohol or an acid such as hydrochloric acid.

Suspension polymerization is considered to be a type of bulk polymerization, and usually consists of an aqueous solution containing a protective colloid (e.g., natural polymer or its derivative, aqueous synthetic polymer, poorly soluble inorganic salts, inorganic polymer, etc.) and phosphoric acid. salt (e.g., monosodium phosphate salt, dibasic sodium phosphate salt, etc.) with a small amount of an aqueous buffer solution containing the aforementioned copolymerizable monomer mixture, catalyst, and molecular weight modifier. This is done by mixing it into a solution.

The reactor is purged with inert gas and stirred rapidly to disperse the copolymerizable monomer mixture in the water.

When the temperature is maintained at 40-90°C for 1.5-8 hours, the reaction is completed and a pearl-like product is obtained.

Known catalysts can be used for the polymerization reaction, including organic peroxides (e.g. penzoyl peroxide, di-t-butyl peroxide, lauroyl peroxide, etc.),
Examples include inorganic peroxides (eg, ammonium persulfate, potassium persulfate, etc.), azo compounds (eg, azodiisobutyronitrile, etc.), and the like.

The solid copolymer produced in this way has a glass transition temperature of 5 to 100°C. However, if the glass transition temperature is lower than 5°C, the resin composition of the present invention becomes sticky and maintains a powdery state in practical use. If the temperature exceeds 100°C, the thermal fluidity will be poor and a smooth coating film will not be obtained.

The number average molecular weight of the solid copolymer is 3000 to 3000
0, but if it is less than 3000, the strength of the coating film, solvent resistance,
Performance such as stain resistance deteriorates, and if it exceeds 30,000, thermal fluidity becomes poor and a smooth coating film cannot be obtained.
Not suitable for the present invention.

Compounds having two or more carboxyl groups or their acid anhydrides include resinous polycarboxylic acids represented by succinic acid, adipic acid, Zn sinoic acid, etc., aromatic acids represented by phthalic acid, isophthalic acid, etc. polyhydric carboxylic acids,
Examples include vinyl resins polymerized with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, and alkyd resins with an acid value of 30 or more.

Examples of the acid anhydride include phthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride, and pyromellitic anhydride.

The required amount of such compounds having two or more carboxyl groups or their acid anhydrides is such as to provide from 0.7 to 12 carboxyl groups per epoxy group in the solid copolymer.

If the amount provides less than 0.7 carboxyl groups per epoxy group in the solid copolymer, the crosslinking density of the coating film will be insufficient, and the amount of remaining epoxy groups will increase, resulting in poor coating quality. This will not only lead to a decrease in performance such as weather resistance of the membrane, but also make the production of the resin composition of the present invention economically disadvantageous.

In addition, if the amount provides more than 1.2 carboxyl groups, the amount of carboxyl groups remaining in the coating film increases, resulting in a decrease in performance such as water resistance and weather resistance, which is not preferable.

Aminoplast resins include those obtained by addition condensation reaction of urea, melamine or guanamines with aldehydes (such as formaldehyde) or etherification by further reaction of these with alcohols, N-methylolated polyacrylamide or N- Examples include alkoxymethylated ones.

The aminoplast resin reacts with groups having active hydrogen (eg, hydroxyl groups, etc.) in the resin composition of the present invention to form crosslinks.

By using such aminoplast resins, it is possible to introduce molecular groove structures (for example, triazine rings, benzene rings, etc.) and bonds (for example, amide bonds, etc.) with a large collective force into the coating film components, thereby improving the durability of the coating film. stain resistance, solvent resistance, hardness,
Improve performance such as weather resistance.

In addition, it is relatively easy to obtain a compound with a large number of functional groups, and by using it, the crosslinking density of the coating film can be increased with a small amount, and the surface condition is less likely to deteriorate.

Furthermore, this aminoplast resin can react advantageously with a group having active hydrogen at a lower temperature than the reaction between an engineered poxy group and a carboxyl group, and a lower baking temperature can be achieved.

Such aminoplast resin is preferably used in an amount of 1 to 10 parts by weight per 100 parts by weight of the solid copolymer, and if it is less than 1 part by weight, the effect of use will not be sufficiently achieved.

Moreover, if the amount exceeds 10 parts by weight, the amount of low molecular weight substances produced as by-products due to the crosslinking reaction increases, which is undesirable because pinholes are likely to occur in the coating film.

The resin composition of the present invention may contain Lewis acids (for example, BF3, etc.), bases (for example, benzyldimethylamine, etc.), if necessary.
2-ethyl-5-methylimidazole, triethylamine, N-methylmorpholine, etc.), salts (e.g. boron trifluoride monoethylamine complex salt, triethanolamine borate A stannous chloride), organometallic compounds (e.g. octylic acid stannous A curing catalyst such as tin, tetrabutyl titanate, dibutyltin dilaurate, etc.) may be added.

Furthermore, if necessary, a modifying resin such as epoxy resin A alkyd resin or cellulose acetate butyrate may be added to the resin composition of the present invention.

Examples of epoxy resins used for this purpose include condensates of bisphenol A and shrimp chlorohydrin, condensates of novolak and shrimp chlorohydrin, diepoxy compounds having a polyether chain as a backbone, and alicyclic epoxy resins. The alkyd resin is useful for optimizing the adhesion to the undercoat, improving the corrosion resistance of the paint film, and providing the desired flexibility to the paint film.

Alkyd resins include oil or fatty acid modified alkyd resins and polyester resins (commonly referred to as oil-free polyester resins).

The amount used is preferably 40 parts by weight or less per 100 parts by weight of the solid copolymer.

If the amount exceeds 40 parts by weight, the blocking resistance of the resin composition of the present invention and the hardness, water resistance, and yellowing resistance of the coating film will decrease, which is not preferable.

Cellulose acetate butyrate can be added in an amount of 50 parts by weight or less per 100 parts by weight of the solid copolymer.

The cellulose acetate butyrate in this case has 2 to 25% by weight of acetyl groups, 25 to 55% by weight of butyryl groups, and 3% by weight or less of hydroxyl groups, and has a viscosity of A of 0.1 to 3 seconds (ASTMD formula 871-48 2B). measurement) is preferred.

The resin composition that is the object of the present invention can be obtained by mixing the above-mentioned constituent compositions in a conventional manner.

Mixing methods include dry blending, semi-dry blending, and melt blending, and can be carried out using a mixer such as a super mixer, extruder, hot kneader, or hot roller mill.

It is preferable to carry out the mixing at a temperature of 130° C. or lower; at a temperature exceeding 130° C., the curing reaction of the resin composition proceeds too much and it is often not possible to obtain a desired result.

When heating and mixing, it is necessary to select an appropriate mixing temperature and time so that the curing reaction does not progress too much and result in gelation.

When the resin composition of the present invention is put to practical use as a thermosetting powder coating, for example, inorganic pigments such as titanium oxide, iron oxide, silica sand, calcium carbonate, barium sulfate, various metal flakes such as aluminum flakes, carbon black, etc. After mixing and dispersing with organic pigments such as , phthalocyanine blue and green, and synthetic sheared, dye pigments, and if necessary, ordinary additives such as surface conditioners and stabilizers, it is made into powder using a pulverizer such as an atomizer. .

Further, it is easier to obtain a metallic feel in the coating film by adding the metal flakes after the resin composition is powdered and mixing and dispersing it by a dry blending method.

Painting is done using a conventional method such as electrostatic coating or fluidized dipping, and is baked in a baking oven at a temperature of 140 to 200°C for 5 to 60 minutes to make it smooth and improve its sharpness, gloss, and solvent resistance. It is possible to obtain a coating film with excellent properties, chemical resistance, stain resistance, and weather resistance.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

In the examples, "part J" means "part J" by weight.

Example 1 40 parts of methyl methacrylate, 1 part of n-butyl methacrylate
0 parts, 30 parts of styrene and 2 parts of glycidyl meccrylate
Solid copolymer 70 with a glass transition temperature of 69° C. and a number average molecular weight of 3600 obtained by suspension polymerization in a proportion of 0 parts
0 parts, 104 parts of decanedicarboxylic acid, 200 parts of titanium white (trade name rR-820, manufactured by Ishihara Sangyo Co., Ltd.), 14 parts of melamine-formaldehyde resin (trade name [Sumimar M-100, manufactured by Sumitomo Chemical Co., Ltd.]), and surface conditioning. After uniformly mixing 10 parts of the agent (trade name: Modaflow J manufactured by Monsanto) with a super mixer, 110 parts of
Mixing and dispersion treatment was carried out at ℃.

Furthermore, it was made into a fine powder using an atomizer and passed through a 150 mesh sieve to obtain a powder coating.

This powder coating was applied to a phosphate-treated iron plate by electrostatic coating so that the baked coating film had a film thickness of approximately 80 μm, and baked in a hot air baking oven at 180° C. for 20 minutes.

The performance of the coating film is shown in Table 1.

Example 2 30 parts of methyl methacrylate, 1 part of n-butyl methacrylate
700 parts of a solid copolymer with a glass transition temperature of 60°C and a number average molecular weight of 4200, obtained by suspension polymerization in the proportions of 0 parts of styrene, 30 parts of styrene, 20 parts of glycidyl methacrylate and 10 parts of 2-hydroxyethyl methacrylate. , 100 parts of sebacic acid, titanium white (trade name manufactured by British Titanium Products Co., Ltd. [Tioxide RCR-3J) 2
00 parts, melamine-formaldehyde resin solution (manufactured by Inu Nippon Ink Kagaku Kogyo Co., Ltd., trade name [Super Betsucomin J-8])
20J), 35 parts of epoxy resin (trade name "Epon-1004J" manufactured by Shell Chemical Co., Ltd.) and Example 1
The performance of the coating film obtained by converting, painting and baking 5 parts of the surface conditioner used in Example 1 in the same manner as in Example 1 was evaluated.
Shown in the table.

Example 3 35 parts of methyl methacrylate, 1 part of n-butyl methacrylate
A solid copolymer having a glass transition temperature of 57° C. and a number average molecular weight of 4500 obtained by suspension polymerization in the ratio of 0 parts of styrene, 20 parts of styrene, 30 parts of glycidyl methacrylate and 5 parts of 2-hydroxyethyl methacrylate 700 parts, decanedicarboxylic acid 136 parts, titanium white 20 used in Example 2
0 parts, 20 parts of epoxy resin, 28 parts of the melamine-formaldehyde resin used in Example 1, and 5 parts of the surface conditioner were made into a paint in the same manner as in Example 1, painted, and baked at 170°C for 20 minutes in a hot air baking oven. Table 1 shows the performance of the coating film obtained.

Comparative Example 1 Table 1 shows the performance of a coating film obtained under the same conditions as in Example 1, except that the melamine-formaldehyde resin in the powder coating in Example 1 was not used.

■Measured value at 60° by visual judgment ■Mitsubishi Yuji used ■Number of tapes remaining after peeling of 100 pieces of 1 mm square ■Dupont type 500 g, 1/2 inch diameter ■Immersed at 40℃ for 10 days ■Immersed in 5N acid aqueous solution for 2 days ■ Immersed in 5N alkaline aqueous solution for 2 days ■ 15W, 30 (1 irradiation height, 1 day irradiation at 030°C)
After applying the oil-based marker, it was left for 1 day and removed with ethanol.The evaluation ranged from very good (◎) to very poor (XX).
Based on the 5-step method.

Claims (1)

[Scope of Claims] 1. A glass transition temperature of 5 to 100°C obtained by copolymerizing a copolymerizable monomer mixture containing 5 to 40% by weight of glycidyl acrylate and (or glycidyl methacrylate)
and a solid copolymer with a number average molecular weight of 3,000 to 30,000, a compound having two or more carboxyl groups or its acid anhydride, and an aminoplast resin, in which the compound having a carboxyl group or its acid anhydride is a solid copolymer. characterized in that the amount provides 0.7 to 1.2 carboxyl groups per epoxy group in the incorporation and the aminoplast resin is in an amount of 1 to 10 parts by weight per 100 parts by weight of solid copolymer. A resin composition for thermosetting powder coatings. 2 5 to 40% by weight of glycidyl acrylate and/or glycidyl methacrylate and 1 hydroxyl group
A glass transition temperature of 5 to 100°C and a number average molecular weight of 3,000 to 30,000 obtained by copolymerizing a copolymerizable monomer mixture containing 10% by weight or less of a polymerizable monomer having
solid copolymer, a compound having two or more carboxyl groups or its acid anhydride, and an aminoplast resin; Hit). 7-1.2
1. A resin composition for a thermosetting powder coating, characterized in that the aminoplast resin is present in an amount of 1 to 10 parts by weight per 100 parts by weight of a solid copolymer.