JP2513662B2 - Resin composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is smooth and glossy, and flexibility of polyester resin is characteristic, and hardness, stain resistance and weatherability of acrylic resin are characteristic. The present invention relates to a polyester / acrylic / hybrid powder-type resin composition for powder-resistant coatings, which provides an excellent coating film.

(Prior Art) A resin composition for powder coating is obtained by melt-kneading a resin mixture comprising a polyester resin or an acrylic resin and respective curing agents at a temperature of 100 to 130 ° C. for 2 to 5 minutes. The resin composition used is well known.

Polyester resin composition forms a coating film that is smooth and glossy, and has flexibility and coating strength. Acrylic resin composition is smooth and glossy, that is excellent in hardness, stain resistance, and weather resistance. The feature is that it forms a coating film.

Therefore, it is the present situation that they are used by making the best use of their respective characteristics according to each application, but it is desired to develop a resin composition having two characteristics, and in recent years, polyester / acrylic hybrid Research on resin compositions for mold-type powder coatings has been actively conducted.

On the other hand, a resin composition for a polyester / acrylic / hybrid powder coating is a resin composition comprising a combination of a carboxyl group-containing polyester resin and a glycidyl group-containing acrylic resin (for example, Japanese Patent Publication No. 52-22006 and Japanese Patent Laid-Open No.
No. 6-136856) or a resin composition comprising a polyester resin and an acrylic resin having one or both of a hydroxyl group and a carboxyl group as a functional group and a curing agent that crosslinks and cures with the functional group (for example, Kosho 55-19
No. 45) etc. are known.

(Problems to be Solved by the Invention) However, the conventional polyester / acrylic / hybrid type powder coating resin composition is
The compatibility between the polyester and acrylic resins was poor, and therefore the coating film was inferior in smoothness.

It is an object of the present invention to provide a resin composition for polyester / acrylic / hybrid powder coatings, which is smooth and glossy and exhibits the features of both resin compositions.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies to eliminate the above-mentioned drawbacks, and as a result, have found that a reaction product obtained by reacting a polyester resin, an acrylic resin, the polyester resin, and the acrylic resin is used. The inventors have found that the compatibility of both resins is remarkably improved by using them, and arrived at the present invention.

That is, the present invention has a softening point of 60 to 150 ° C. and a hydroxyl value of 15 to 200 KOHmg / g of a polyester resin of 5 to 95 parts by weight,
A resin composition (A) consisting of 95 to 5 parts by weight of an acrylic resin having a softening point of 40 to 140 ° C. and a hydroxyl value of 10 to 200 KOHmg / g,
A resin composition for powder coating, comprising a curing agent (B) having a functional group capable of reacting with a hydroxyl group of the resin composition, wherein the resin composition (A) is a polyester resin and an acrylic resin. When it is dissolved in a solvent that is a good solvent for both polyester resin and acrylic resin, the resulting solution does not separate into layers and the insoluble content is less than 5 wt%. A gist of the present invention is a resin composition for a polyester / acrylic / hybrid powder coating material characterized by:

The polyester resin which is one component of the resin composition (A) has a softening point (by the ring and ball method) of 60 to 150 ° C., preferably 1
It has a hydroxyl value of 15-200KOHmg / g
(The unit is omitted below.), Preferably 20 to 50. If the softening point is less than 60 ° C, blocking occurs during storage and a sufficiently stable powder coating cannot be obtained. If it exceeds 150 ° C, the flowability of the resin decreases and a smooth coating film cannot be obtained. Further, if the hydroxyl value is less than 15, a sufficient crosslinking effect cannot be obtained and the coating film strength is poor, and if it exceeds 200, the curing reaction proceeds too much and a smooth and glossy coating film cannot be obtained.

Such a polyester resin can be produced by a known method such as a solvent method or a melting method using one or more kinds of carboxylic acid components and one or more kinds of alcohol components.

Examples of the carboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1 , 10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,2-dodecanedicarboxylic acid, 1,2-octadecanedicarboxylic acid, eicosanedicarboxylic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid, hexahydrophthalic acid, Polyhydric carboxylic acids such as tetrahydrophthalic acid, trimellitic acid and pyromellitic acid, or lower alkyl esters and anhydrides thereof, or hydroxycarboxylic acids such as malic acid, tartaric acid, 1,2-hydroxystearic acid and paraoxybenzoic acid. Can be used.

Examples of the alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol,
1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, spiroglycol, 1, 4-cyclohexanedimethanol, 2,2,4-trimethylpentane-1,3-diol, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, propylene oxide Additives and the like can be used.

The acrylic resin which is another component of the resin composition (A) has a softening point of 40 to 140 ° C., preferably 100 to 130 ° C., and a hydroxyl value of 10 to 200, preferably 30 to 70. . If the softening point is less than 40 ° C, a powder coating having good storage stability cannot be obtained, and if it exceeds 140 ° C, the flowability of the resin is deteriorated, and a smooth coating film cannot be obtained. Further, if the hydroxyl value is less than 10, a sufficient crosslinking effect cannot be obtained and the coating film strength is poor, 20
If it exceeds 0, the reaction with the curing agent proceeds too much and a smooth and glossy coating film cannot be obtained.

Such an acrylic resin is a known polymer such as solution polymerization, suspension polymerization, bulk polymerization, etc., using one or more kinds of aquatic group-containing monomers and one or more kinds of copolymerization monomers. It can be manufactured legally.

Examples of the hydroxyl group-containing monomer include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 2-hydroxy-2-phenylethyl acrylate, 2-hydroxy-2-phenylethyl methacrylate. , Allyl alcohol and the like can be used.

Examples of the copolymerization monomer include acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n.
-Butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, te
rt-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, dodecyl acrylate, dodecyl methacrylate, benzyl acrylate, benzyl methacrylate, glycidyl acrylate, glycidyl methacrylate, α-methylglycidyl acrylate, Use acrylic acid esters such as α-methylglycidyl methacrylate, β-methylglycidyl acrylate, β-methylglycidyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, or methacrylic acid esters. be able to.

Other copolymerizable monomers include, for example, fumaric acid dialkyl ester, itaconic acid dialkyl ester, styrene, vinyltoluene, α-methylstyrene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, vinyl. Oxazoline, vinyl acetate,
Vinyl propionate, lauryl vinyl ether, halogen-containing vinyl monomers, silicon-containing vinyl monomers and the like can be used.

The resin composition (A) contains a reaction product of the above polyester resin and the above acrylic resin,
When itself is dissolved in a solvent that is a good solvent for both the polyester resin and the acrylic resin that are components of the resin composition, the resulting solution does not undergo layer separation, and the insoluble content is less than 5 wt%, preferably 2 wt. It is less than%.

When a resin composition in which the solution is separated into layers is used, the compatibility of both resins is poor, and a coating film having a smooth and excellent gloss cannot be obtained. Further, when the resin composition (A) having an insoluble content of 5 wt% or more is used, the flowability of the resin composition is lowered and the smoothness and gloss of the coating film are impaired.

The good solvent here means a solvent capable of simultaneously dissolving both resins at room temperature, and specifically, for example, dioxane, tetrahydrofuran, tetrachloroethane, toluene, xylene, ethyl acetate, methyl ethyl ketone, methyl cellosolve or a mixture thereof. can give.

The resin composition (A) comprises a polyester resin and an acrylic resin in a weight ratio of 5 to 95:95 to 5, preferably 30 to 70:
Mixed in a ratio of 70 to 30, both polyester and acrylic resin melt, between the hydroxyl group of the polyester resin and the ester group of the acrylic resin, a condition in which a transesterification reaction can occur, for example, at a temperature of 180 to 280 ° C It can be produced by melting and stirring in a reaction vessel for 1 to 3 hours.

In the present invention, as the curing agent (B), any one can be used as long as it reacts with the hydroxyl group of the resin composition (A) and participates in cross-linking curing. For example, blocked isocyanate, melamine compound, acid anhydride, particularly From the viewpoints of coating film appearance and low temperature curability, blocked isocyanates are preferably used.

Examples of the blocked isocyanate include a prepolymer having an isocyanate compound or an isocyanate group, which is masked with a blocking agent, and the like. Examples of the isocyanate compound include isophorone diisocyanate,
Hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, or dimers thereof, uretdione ring which is a trimer, an isocyanate compound having an isocyanuric ring can be used, and as the prepolymer, for example, the above-mentioned isocyanate A prepolymer obtained by reacting a compound with ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, or the like can be used. Then, as the blocking agent, lactams, phenols, alcohols, oximes and the like can be used.

In addition, in the present invention, melamine resins such as hexamethoxymethylolmelamine and hexabutoxymethylolmelamine, acid anhydrides such as pyromellitic dianhydride, and the like can be used as the curing agent (B).

The amount of the curing agent (B) used is usually in the range of 0.5 to 1.5, particularly preferably about 1.0 in terms of equivalent ratio to the resin composition (A).

In addition to the performance of the coating film obtained from the resin composition comprising the resin composition (A) and the curing agent (B), the characteristics of the polyester resin or the characteristics of the acrylic resin, or
When the features of both polyester and acrylic resins are required, a polyester resin or an acrylic resin, or a polyester resin and an acrylic resin can be further added to the resin composition for powder coating of the present invention. .

The polyester resin and acrylic resin used here may be different from those used as the component of the resin composition (A) in the present invention, but are the same from the viewpoint of coating film performance and storage stability. Is preferable, and the same as that used in the resin composition (A) is particularly preferable.

The addition ratio of these resins to the resin composition (A) may be appropriately determined according to the required performance, but the weight ratio is preferably 30:70 to 70:30.

The resin composition for powder coating of the present invention, if necessary,
For example, an epoxy resin for improving the corrosion resistance, benzoin for suppressing the cracking of the coating film, and a curing catalyst for accelerating the curing reaction, a pigment, a leveling agent, an additive such as an antistatic agent can be blended. .

The resin composition for a powder coating material of the present invention is produced by a conventional method, for example, by dry blending each of the above components with a Henschel mixer, and then pulverizing and classifying the melt blended and cooled product with an extruder. can do.

(Function) From the resin composition (A), a coating film excellent in plasticity, which is a characteristic of a polyester resin, and hardness, stain resistance, and weather resistance, which are characteristic of an acrylic resin, is obtained. This is because A) is substantially composed of three components: (1) polyester resin, (2) acrylic resin, and (3) reaction product (grafted product) obtained by reacting polyester resin and acrylic resin. Therefore, polyester resin, It is speculated that the characteristics of acrylic resin were utilized individually.

It is speculated that the reason why the smooth and glossy coating film was obtained was that the graft product acted as a compatibilizing agent for both polyester and acrylic resins. Further, when a polyester resin, an acrylic resin, or a polyester resin and an acrylic resin are added to the resin composition (A), the features of the added resins are dominantly exhibited, respectively, as described above. It is presumed that the individual features were remarkably utilized.

(Examples) Next, the present invention will be specifically described with reference to Examples.

Reference Example-1 (Production Example of Polyester Resin) The raw materials shown in Table 1 were charged into a reaction vessel in an amount shown in Table 1 and an esterification reaction was carried out at 250 ° C. to remove a theoretical amount of water out of the system. After that, 0.02 mol of antimony triacid was added and the reaction was carried out at 270 ° C. to prepare a polyester resin having a high degree of polymerization of 100 to 120, and then trimethylolpropane shown in Table 1 was added to In addition to the amount shown in Table 1, 270
A depolymerization reaction was carried out at a temperature of ℃ to obtain a polyester resin (I) having a softening point of 123 ° C and a hydroxyl value of 31, and a polyester resin (II) having a softening point of 115 ° C and a hydroxyl value of 37.

Reference Example-2 (Production Example of Acrylic Resin) The monomers, polymerization initiators, and chain transfer regulators shown in Table 2 were mixed in the amounts shown in Table 2, and the mixture was added to xylene at 100 ° C. The mixture was added dropwise over a period of time and, after being kept under reflux for 1 hour, cooled, 0.05 mol of azobisisobutyronitrile was added, and the residual monomer was removed out of the system at 80 to 100 ° C. to complete the polymerization. Remove the solvent under reduced pressure,
An acrylic resin (I) having a softening point of 117 ° C. and a hydroxyl value of 50 and an acrylic resin (II) having a softening point of 108 ° C. and a hydroxyl value of 39 were obtained.

Reference Example-3 [Production Example of Resin Composition (A)] Polyester resin (I) and acrylic resin (I)
Mix by weight ratio 70:30, 50:50, and 30:70,
Charge into a reaction vessel and carry out a melt-stirring reaction at 240 ° C. for 1 hour. Mix in the ratio of 50:50 by weight and 220 ° C in the same manner as above.
The melt-stirring reaction was carried out for 2 hours to obtain 4 points in total of the resin composition (d).

In each of the solutions obtained by dissolving the resin composition of the above 4 points in dioxane in an amount of 30 wt%, layers were not separated and there was no insoluble matter.

Furthermore, polyester resin (I) and acrylic resin (I
The resin composition (e), (I) and () are mixed at a weight ratio of 70:30, and melt-stirring reaction is performed at 180 ° C. for 20 minutes and at 270 ° C. for 5 hours in the same manner as above. Two points of f) were obtained.

Of the solution obtained by dissolving 30 wt% of the above two resin compositions in dioxane, the resin composition (e) was layer-separated, and the resin composition (f) was not layer-separated, but the insoluble content was 15 wt. %
Met.

Examples 1 to 4 and Comparative Examples 1 to 5 The coating components shown in Table 3 were dry blended in the amounts shown in Table 3 by using a Henschel mixer, and then 100 by using a Cokneader PR-46 manufactured by Bus Co. The mixture was melt-kneaded at ˜115 ° C., solidified by cooling, pulverized and classified to obtain 9 kinds of powder coatings having a particle size of 105 μm or less.

These powder coatings were applied to a 0.8 mm layer of zinc phosphate-treated steel sheet by electrostatic spraying so as to have a film thickness of about 50 μm, and baked at 200 ° C. for 20 minutes.

The performance of the obtained coating film is also shown in the third grade. As is clear from Table 3, in Example 1, the same resin as that used in Example 1 was simply blended in the same mixing ratio. It shows that the coating film was smoother than that of Comparative Example 1, and the coating film was excellent in flexibility, which is a characteristic of the polyester resin, and excellent in stain resistance and weather resistance, which are characteristic of the acrylic resin.

Examples 2 to 4 are examples in which a polyester resin, an acrylic resin, or both resins are further added to the resin composition (A), and Example 2 has a coating film strength characteristic of the polyester resin. Example 3 shows that the acrylic resin has excellent stain resistance, and Example 4 shows that the polyester resin has excellent coating film strength and the acrylic resin has excellent stain resistance.

On the other hand, Comparative Example 2 shows that the compatibility between both resins is poor, and the resulting coating film is inferior in smoothness, gloss and other properties. Further, Comparative Example 3 shows that the flowability of the resin is lowered and the smoothness, gloss and other properties of the coating film are poor. Further, Comparative Examples 4 and 5 respectively show coating film performance of resin compositions comprising a polyester resin alone or an acrylic resin alone and a curing agent thereof,
Comparative Example 4 shows that the coating film made of the polyester resin is excellent in flexibility and coating film strength, but inferior in hardness, stain resistance and weather resistance, and Comparative Example 5 is made of the acrylic resin. It shows that the coating film is excellent in hardness, stain resistance and weather resistance, but inferior in flexibility and coating film strength.

(Effect of the Invention) From the resin composition for powder coating material of the present invention, a powder coating material which is smooth and glossy and can form a coating film having the characteristics of both polyester and acrylic resin can be obtained. further,
The resin composition for powder coating of the present invention, a polyester resin,
When acrylic resin or both of these resins are added,
It is possible to obtain a powder coating material which does not impair the characteristics of the coating film of the resin composition of the present invention and which exhibits the characteristics of the coating film of the added resin in a dominant manner.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C09D 167/00 PMX C09D 167/00 PMX

Claims (1)

(57) [Claims] 1. A powder coating resin composition comprising a resin composition (A) and a curing agent (B), wherein the resin composition (A) has a softening point of 60 to 150 ° C. and a hydroxyl value. 5 to 95 parts by weight of a polyester resin of 15 to 200 KOHmg / g and 95 to 5 parts by weight of an acrylic resin having a softening point of 40 to 140 ° C. and a hydroxyl value of 10 to 200 KOHmg / g, and an ester group of the acrylic resin Resin composition containing (a1) polyester resin, (a2) acrylic resin and (a3) grafted product of polyester resin and acrylic resin, which is obtained as a result of melting and stirring under the condition of partially transesterifying the hydroxyl groups of polyester resin. When the substance (A) was dissolved in dioxane, which is a good solvent for both the polyester resin and the acrylic resin, at 30 wt% at room temperature, the solution did not undergo layer separation, and
Polyester / acryl / hybrid type powder characterized in that the insoluble content is less than 5 wt% and the curing agent (B) has a functional group capable of reacting with the hydroxyl group of the resin composition (A) Paint resin composition.