JPH0372672B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved resin composition for powder coatings, and more particularly to a resin composition with a specific acid value obtained by reacting a polyester resin with a specific hydroxyl value with a polyfunctional organic carboxylic acid anhydride. had,
It forms a coating film that is excellent in appearance, mechanical strength, and corrosion resistance, and has a polyester resin with residual hydroxyl groups and a polyepoxy compound as essential components, and is also useful because it has excellent storage stability. The present invention relates to a resin composition. BACKGROUND ART Powder coatings made of carboxyl group-containing polyester resins and polyepoxy compounds have been used for a wide range of purposes because of their excellent mechanical strength, adhesion, and corrosion resistance. At this time, it is particularly important to use a carboxyl group-containing polyester resin obtained by reacting a polyester resin having hydroxyl groups with a polyfunctional organic carboxylic acid anhydride as the base polyester resin to be combined with the polyepoxy compound. It is described in the specification of Japanese Patent Publication No. 55-15506 and the specification of Japanese Patent Publication No. 58-29342 and is well known. However, as long as the techniques described in these known documents are followed, powder coatings are mainly based on polyester resins with relatively high acid values, mainly in the range of 40 to 70. Therefore, the storage stability of powder coatings is unavoidable, and reactions progress during storage, resulting in many coatings using such coatings having poor smoothness. Since a resin with almost no hydroxyl groups is used as the base polyester resin, it tends to have insufficient compatibility with polyepoxy compounds, and especially when increasing the pigment concentration, it is difficult to melt. Another drawback is that poor dispersion occurs during kneading, resulting in poor coating film smoothness or image clarity. However, in view of the various shortcomings in the prior art as described above, the inventors of the present invention conducted extensive research and found that a polyester resin having a hydroxyl value within a specific range, that is, a polyfunctional polyester having a valence of 3 or more, is used as an intermediate polyester. The specific acid value and softening point obtained by reacting a divalent or higher polyfunctional organic carboxylic acid anhydride (hereinafter also referred to as polycarboxylic acid anhydride) containing a polycarboxylic acid anhydride as an essential component. The present invention was completed based on the discovery that all of the above-mentioned drawbacks can be overcome by using a polyester resin having a polyester resin having hydroxyl groups remaining. That is, the present invention has a hydroxyl value of 12.5 to 70KOH.
mg/g (hereinafter, units are omitted) and has an acid value of 2 to 10 (a-1) (hereinafter,
Abbreviated as intermediate polyester. ) with a polycarboxylic anhydride (a-2), a polyester resin (A) having an acid value of 15 or more and less than 30, a hydroxyl value of 2 or more, and a softening point of 80 to 150°C
60 to 97 parts by weight as a base polyester resin component, and 3 to 40 parts by weight as a crosslinking curing agent component of a polyepoxy compound (B) having at least two epoxy groups in one molecule. It has good compatibility with the polyepoxy compound, which is composed of The present invention provides a resin composition for powder coatings that has excellent smoothness and sharpness. Here, the above-mentioned polyester resin (A), which is one essential component of the composition of the present invention, is obtained by reacting a polycarboxylic anhydride (a-2) with an intermediate polyester (a-1) having a hydroxyl group as described later. obtained, each having an acid value of 15 to less than 30, preferably 16 to 28, and a hydroxyl value of 2 or more, preferably 3 to 20, and a softening point of 80 to 150°C,
Preferably within the range of 90 to 130°C, it should be noted that by actively leaving hydroxyl groups,
It refers to a resin designed to be compatible with the polyepoxy compound (B). If the acid value is lower than 15, the resulting coating film will inevitably have insufficient mechanical strength;
If it is more than 30, the storage stability of the powder coating inevitably decreases, and the reaction progresses during storage, resulting in deterioration of the smoothness of the coating film. Undesirable. On the other hand, it is an essential condition that hydroxyl groups remain in the polyester resin (A), and if the hydroxyl value is lower than 2, it will inevitably be incompatible with the polyepoxy compound (B) described later. This is not preferable because it results in poor pigment dispersibility. As mentioned above, the polyester resin (A) is an intermediate polyester having a hydroxyl group (a-
1) and polycarboxylic anhydride (a-2), and there are no particular restrictions on the method of reaction between these two compounds (a-1) and (a-2). However, among them, the representative one is intermediate polyester (a
-1) with a polycarboxylic anhydride (a-2), or an intermediate polyester (a-1).
Examples include a method in which a polycarboxylic anhydride (a-2) is added to 1) and then further subjected to a condensation reaction. Here, the intermediate polyester (a-
1) has a hydroxyl value of 12.5 to 70, preferably 13 to 50, and an acid value of 2 to 10, preferably 3.
-8, and as long as it falls within this range, it may have a branched structure or a linear structure. There is no particular restriction on the method for preparing the intermediate polyester (a-1), and well-known and commonly used methods can be applied as they are, and as the acid component and the alcohol component, well-known and commonly used dibasic acids and/or Alternatively, polybasic acids, dihydric alcohols (glycols), and/or polyhydric alcohols can be used as they are, but typical acid components include terephthalic acid, isophthalic acid, phthalic acid, and methyl terephthalic acid. , trimellitic acid, pyromellitic acid and their anhydrides or adipic acid, sebacic acid, succinic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, methyl-tetrahydrophthalic acid, hexahydrophthalic acid, methyl-hexahydrophthalic acid and the like. On the other hand, typical alcohol components include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, and 1,6-butanediol.
Hexanediol, neopentyl glycol, isopentyl glycol, bishydroxyethyl terephthalate, hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, propylene oxide adduct of hydrogenated bisphenol A, trimethylolethane, trimethylol Examples include propane, glycerin, pentaerythritol, and 2,2,4-trimethylpentane-1,3-diol, but monoepoxy compounds can also be used as one of the glycols in the present invention. On the other hand, the polycarboxylic acid anhydride (a-2) to be reacted with the intermediate polyester (a-1)
As a divalent aromatic, aliphatic or alicyclic acid anhydride containing 30 to 100% by weight of a trivalent or higher polybasic organic carboxylic anhydride based on the total polycarboxylic anhydride, it is possible to apply. Among them, the most representative ones are terephthalic acid, isophthalic acid, phthalic acid,
These include acid anhydrides such as trimellitic acid, pyromellitic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, tetrahydrophthalic acid or hexahydrophthalic acid. The polyepoxy compound (B), which is another essential component of the composition of the present invention, refers to a compound having at least two epoxy groups in one molecule, and among these, particularly representative ones are: are diglycidyl ethers of bisphenol A or bisphenol F, glycidyl esters/ethers of oxybenzoic acid; polydiglycyl ethers of polyhydric alcohols such as diglycidyl ethers of ethylene glycol or glycidyl ethers of trimethylolpropane; Diglycidyl esters of dibasic acids such as glycidyl esters; or triglycidyl isocyanurates. Therefore, the resin composition for powder coating of the present invention contains the above-mentioned polyester resin (A) and polyepoxy compound (B) as essential components, and both of these essential components The usage ratio is 60 to 97 parts by weight of component (A): component (B).
40-3 parts by weight, preferably 65-96 parts by weight: 35-4
A ratio of parts by weight is appropriate. In order to further promote the crosslinking and curing reaction, a well-known catalyst can be appropriately added to the composition of the present invention, and it also prevents the formation of craters on the coating surface and further improves the smoothness. For this purpose, an acrylic acid long-chain alkyl ester polymer, a fluorine compound, or the like may be added as a flow control agent (flow agent). A powder coating can be prepared using the thus obtained composition of the present invention by any known method. By applying the resulting powder coating by a well-known method such as electrostatic spraying or fluidized dipping and then baking, a coating film with excellent performance can be obtained. Next, the present invention will be specifically explained using reference examples, examples, and comparative examples, and all parts and percentages are based on weight unless otherwise specified. Reference Example 1 [Preparation example of polyester resin (A)] A mixture consisting of 83 parts of ethylene glycol, 327 parts of neopentyl glycol, 435 parts of dimethyl terephthalate and 0.4 parts of zinc acetate was prepared by removing the methanol produced from the reaction system. While removing, the temperature was gradually raised to 210°C, and the same temperature was then maintained for 2 hours to continue the alcohol exchange reaction. Next, here is 6 of trimethylolpropane.
149 parts of terephthalic acid, 224 parts of isophthalic acid and 0.5 part of di-n-butyltin oxide were added, the temperature was raised to 240°C over 8 hours, and further dehydration condensation was carried out at the same temperature to form hydroxyl groups. An intermediate polyester (a-1) having a value of 14 and an acid value of 7 was obtained. After that, this polyester (a-1)
The temperature was lowered to 200°C, and then the trimellitic anhydride was heated to 29
When the mixture was reacted at the same temperature for 2 hours, the target resin (A) having an acid value of 23, a hydroxyl value of 5, and a softening point of 123°C was obtained. Hereinafter, this will be abbreviated as polyester (A-1). Reference Example 2 (same as above) The amounts of ethylene glycol, neopentyl glycol and dimethyl terephthalate were
The alcohol exchange reaction was carried out in the same manner as in Reference Example 1, except that the amounts were changed to 159 parts, 218 parts, and 452 parts. Then, the use of isophthalic acid was omitted, and the amounts of trimethylolpropane and terephthalic acid were changed to 20 parts and 20 parts, respectively. A dehydration condensation reaction was carried out in the same manner as in Reference Example 1, except that the amount was changed to 384 parts, to obtain an intermediate polyester (a-1) having a hydroxyl value of 30 and an acid value of 3. After that, the amount of trimellitic anhydride used was reduced to 45%.
The intermediate polyester was reacted in the same manner as in Reference Example 1 except that the acid value was 28,
A target resin (A) having a hydroxyl value of 16 and a softening point of 124°C was obtained. Hereinafter, this will be abbreviated as polyester (A-2). Reference Example 3 (same as above) The amounts of ethylene glycol, neopentyl glycol and dimethyl terephthalate were changed to 136 parts, 253 parts and 472 parts, respectively, and 1,
The alcohol exchange reaction was carried out in the same manner as in Reference Example 1, except that 29 parts of 6-hexanediol was also used, and then 33 parts of adipic acid was used instead of 20 parts of trimethylolpropane. A dehydration condensation reaction was carried out in the same manner as in Reference Example 2, except that the amount of terephthalic acid used was changed to 308 parts, to obtain an intermediate polyester (a-1) having a hydroxyl value of 45 and an acid value of 6. Ta. After that, this polyester (a-1)
The temperature was lowered to 200°C, and then 60°C of trimellitic anhydride was added.
240 g of water and kept at the same temperature for 2 hours, then
When the temperature was raised to ℃ and reacted at the same temperature for 3 hours, the acid value was 25, the hydroxyl value was 12, and the softening point was 119℃.
The desired resin (A) was obtained. Hereinafter, this will be abbreviated as polyester (A-3). Reference Example 4 [Preparation example of polyester resin for comparison] The same procedure as Reference Example 2 was carried out except that the amount of trimellitic anhydride used was changed to 102 parts, and the acid value was 57, the hydroxyl value was 0, and the softening A control polyester resin (A') having a temperature of 126°C was obtained. Hereinafter, this will be abbreviated as polyester (A'-1). Reference Example 5 (same as above) except that the amounts of ethylene glycol, neopentyl glycol, and dimethyl terephthalate were changed to 141 parts, 236 parts, and 440 parts, respectively.
The alcohol exchange reaction was carried out in the same manner as in Reference Example 1, and then the dehydration condensation was carried out in the same manner as in Reference Example 1, except that the amounts of trimethylolpropane, terephthalic acid, and isophthalic acid used were changed to 5 parts, 172 parts, and 235 parts, respectively. After the reaction, the hydroxyl value is 6,
A control intermediate polyester (a'-1) having an acid value of 20 was obtained. Afterwards, the amount of trimellitic anhydride used was reduced to 7
This is changed to the above polyester (a′-
The acid value was 24, the hydroxyl value was 4,
A control polyester resin (A') having a softening point of 118°C was obtained. Hereinafter, this will be abbreviated as polyester (A'-2). Reference Example 6 [Preparation example of polyester resin (A)] Except that the amounts of ethylene glycol, neopentyl glycol, and dimethyl terephthalate were changed to 127 parts, 261 parts, and 442 parts, respectively.
The alcohol exchange reaction was carried out in the same manner as in Reference Example 1, except that the amounts of trimethylolpropane and terephthalic acid used were changed to 19 parts and 378 parts.
A dehydration condensation reaction was carried out in the same manner as in Reference Example 2 to obtain an intermediate polyester (a-1) having a hydroxyl value of 27 and an acid value of 3. After that, the amount of trimellitic anhydride used was reduced to 37%.
parts, and also used 13 parts of phthalic anhydride, and both of these polycarboxylic anhydrides (a-
2) was changed to react with the above polyester (a-1) in the same manner as in Reference Example 1, and the acid value was 28, the hydroxyl value was 10, and the softening point was 125 ° C.
A desired polyester resin (A) was obtained. below,
This is abbreviated as polyester (A-4). Reference Example 7 [Preparation example of polyester resin (A)] 455.5 parts of dimethyl terephthalate (DMT),
The procedure was carried out in the same manner as in Reference Example 1, except that a mixture consisting of 145.7 parts of ethylene glycol (EG), 244.4 parts of neopentyl glycol (NG), and 0.4 parts of zinc acetate was used, and then terephthalic acid ( 385.4 parts of TPA) and 0.5 parts of di-n-butyltin dioxide were added and subjected to dehydration condensation to obtain an intermediate polyester (a-1) having a hydroxyl value of 12.5 and an acid value of 9. Next, this intermediate polyester (a-1)
The reaction was carried out in the same manner as in Reference Example 1, except that 27 parts of trimellitic anhydride was added to 1000 parts, to obtain a target polyester resin having an acid value of 24 and a hydroxyl value of 2. Hereinafter, this will be abbreviated as polyester resin (A-5). Reference Example 8 (same as above) A target polyester having an acid value of 28 and a hydroxyl value of 2 was produced in the same manner as Reference Example 7, except that the amount of trimellitic anhydride (TMA) used was changed to 36 parts. Resin was obtained. Hereinafter, this will be abbreviated as polyester resin (A-6). Reference Example 9 [Example of preparation of control polyester resin (A')] 455.2 parts of DMT, 145.6 parts of EG, 244.3 parts of NPG
A control intermediate polyester having a hydroxyl value of 12 and an acid value of 9 was obtained in the same manner as in Reference Example 7 except that TPA was changed to 385.9 parts. Next, the acid value was determined in the same manner as in Reference Example 7, except that the amount of TMA used was changed to 23.9 parts.
22 and a hydroxyl value of 5, a control polyester resin was obtained. Hereinafter, this will be abbreviated as polyester resin (A'-3). Reference example 10 (same as above) 455.2 parts of DMT, 145.3 parts of EG, 243.7 parts of NPG
A control intermediate polyester having a hydroxyl value of 10 and an acid value of 9 was obtained in the same manner as in Reference Example 7 except that TPA was changed to 387.9 parts. Next, a control polyester resin having an acid value of 28 and a hydroxyl value of 2 was obtained in the same manner as in Reference Example 7 except that the amount of TMA used was changed to 36 parts. This is abbreviated as polyester resin (A'-3). Examples 6 and 7 and Comparative Examples 3 and 4 Each component was mixed in the composition ratio shown in Table 1, and then made into a paint in the same manner as in Example 2, and then the coating film performance was compared. I considered it. The results are summarized in the same table. Examples 1 to 5 and Comparative Examples 1 and 2 Each component was mixed in the composition ratio as shown in Table 1, and then each mixture was melt-kneaded using "Conneader PR-46" manufactured by Buss, Switzerland. After pulverization, the amount that passed through 150 meshes was applied to a 0.8 mm thick zinc phosphate treated steel plate separately by electrostatic spraying to a film thickness of 50 to 60 μm, and then baked at 200° C. for 20 minutes. The coating film performance test results for each paint are summarized in the same table.

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【table】

Claims (1)

[Scope of Claims] 1 (A) A hydroxyl value of 12.5 to 70 KOHmg/g,
and an acid value of 15 KOH obtained by reacting a polyester resin (a-1) with an acid value of 2 to 10 KOH mg/g with a polyfunctional organic carboxylic acid anhydride (a-2).
mg/g or more and less than 30KOH mg/g, and the hydroxyl value is
60 to 97 parts by weight of a polyester resin containing 2KOHmg/g or more and having a softening point of 80 to 150°C; (B) 3 to 40 parts by weight of a polyepoxy compound having at least two epoxy groups in one molecule; A resin composition for powder coating, comprising as an essential component.