JPH05171106A - Production of polyester resin for coating and coating - Google Patents

Abstract

PURPOSE:To obtain a polyester resin for coating having good blocking resistance, solvent resistance and hardness by depolymerizing a straight-chain polyester resin with tri- or more polyhydric alcohol and/or tri- or more valent hydroxycarboxylic acid. CONSTITUTION:(A) 100 pts. wt. straight-chain polyester resin having >=10000 number-average molecular weight and synthesized from A1: an acid component consisting of 100-30mol% aromatic dicarboxylic acid and 0-70mol% aliphatic dicarboxylic acid component based on total acid components and A2: an alcohol component consisting of a dialcohol is blended with (B) 0.02-0.18 pts.wt., preferably 0.02-0.1 pts. wt. tri- or more polyhydric alcohol (B1) (e.g. trimethylol propane) and/or tri or more valent hydroxy carboxylic acid (B2) having each one or more OH group and COOH group, with the proviso that total number of these groups is >=3 (e.g. dimethylol propionic acid) and the blend is depolymerized under ordinary pressure, preferably at 200-300 deg.C to produce a branched polyester resin for coating, preferably having 5000-20000 number- average molecular weight.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polyester resin for paints which is excellent in solvent resistance, blocking property and the like, and which can form a coating film having good hardness and processability on the surface of ferrous or non-ferrous metal and the like. Regarding paints.

[0002]

2. Description of the Related Art Conventionally, the painting of home electric appliances involves processing steel sheets,
Although it was performed in a box shape after molding, in order to solve various problems such as rationalization of coating line, factory of productivity, pollution prevention, improvement of working environment, processing and molding are performed after coating flat steel sheet We have moved to the pre-coating method. The pre-coated steel sheet used in this method is processed into a complicated shape after painting, and thus requires high workability. On the other hand, among home electric appliances, refrigerators, washing machines and the like are required to have excellent coating film hardness, stain resistance and chemical resistance.

Conventionally, thermosetting acrylic resins have been mainly used for coating these home electric appliances, because acrylic resin coatings have excellent coating film hardness and stain resistance. However, acrylic resin paints have insufficient processability to be used for precoat coating, and in order to satisfy the processability, it is necessary to soften the composition of the acrylic resin, which is a coating that can withstand practical use. It is difficult to show hardness and stain resistance.

Further, the thermosetting polyester resin has been used for coil coating of color galvanized iron and the like, but it still has a drawback that workability and coating film hardness and stain resistance cannot be balanced. However, linear high-molecular-weight polyester resins obtained by polycondensing polyester resins under reduced pressure have a better balance of processability, coating film hardness, and stain resistance than ordinary polyester resins, and are used in refrigerators, washing machines, etc. It has also been put to practical use in the painting of home appliances.

[0005]

These linear high molecular weight polyester resins have few functional groups in the molecular chain, and the functional groups are located at both ends of the polymer chain. When it is cured with a curing agent, the coating film has a low crosslink density and the crosslink structure is not uniform. Therefore, the workability is better than that of a normal branched polyester resin having a cross-linked structure of a network structure. However, the polyester resin portion has a problem that the crosslinking reaction is insufficient and the coating film has poor blocking property, solvent resistance, hardness and the like.

By adding a large amount of curing agent and curing catalyst,
It is considered to balance the processability, hardness and stain resistance of the coating film, but there is a limit due to deterioration of coating stability and deterioration of coating film surface condition. Further, by increasing the degree of branching of the polyester resin, it is possible to improve blocking properties, solvent resistance, etc., but the workability is significantly reduced, and it is difficult to balance hardness, workability, and stain resistance. There is a point. Therefore, an object of the present invention is to provide a polyester resin for paints and a paint which are excellent in solvent resistance and blocking properties and which can form a coating film having good hardness and workability and which are suitable for steel sheets.

[0007]

That is, according to the present invention, 100 to 30 mol% of an aromatic dicarboxylic acid component and 0 to 70 mol% of an aliphatic dicarboxylic acid component are used as an acid component with respect to a total acid component, and a dialcohol is used. 100 parts by weight of a linear polyester resin having a number average molecular weight of 10,000 or more synthesized as an alcohol component is added to a polyhydric alcohol component having a valence of 3 or more and /
Alternatively, add 0.02 of trivalent or higher hydroxycarboxylic acid component.
The present invention relates to a method for producing a polyester resin for paint, which is characterized by depolymerizing at 0.18 parts by weight, and a paint containing the polyester resin obtained by the production method.

Examples of the aromatic dicarboxylic acid used for the linear polyester resin include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, lower alkyl esters thereof, acid anhydrides, etc., and one or more of them may be used. Can be used. As the aliphatic dicarboxylic acid, there are adipic acid, sebacic acid, azelaic acid, succinic acid, fumaric acid, maleic acid, hymic acid, 1,6 cyclohexanedicarboxylic acid, etc., and their lower alkyl ester, acid anhydride, etc. They may be used, or one or more of them may be used. The above-mentioned aromatic dicarboxylic acid and aliphatic dicarboxylic acid are 100 to 30 mol% of the former, preferably 100 to 40, based on all acid components.
The latter is used in a proportion of 0 to 70 mol%, preferably 0 to 60 mol%. 70 aliphatic dicarboxylic acid components
If it exceeds mol%, the hardness and stain resistance decrease.

As the dialcohol component used in the linear polyester resin, ethylene glycol, propylene glycol, 1,2-propanediol, 1,3-
Propanediol, 1,3-butanediol, 1,4-
Butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methylpentanediol, diethylene glycol, 1,4-
Cyclohexanedimethanol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2
-Butyl-2-ethyl-1,3-propanediol xylylene glycol or hydrogenated bisphenol A and ethylene oxide or propylene oxide adduct of bisphenol A, and the like, and one or more of them can be used.

The trihydric or higher polyhydric alcohol component used for depolymerization of the obtained linear polyester resin is an alcohol having three or more hydroxyl groups, such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol. can give. Moreover, the trivalent or more hydroxycarboxylic acid used in the same manner has at least one hydroxyl group and at least one carboxyl group, and three or more in total, and includes dimethylolpropionic acid and the like. Can be used. These polyhydric alcohols and / or polyhydric hydroxycarboxylic acids are added in an amount of 0.
02-0.18 parts by weight, preferably 0.02-0.15
Part by weight, particularly preferably 0.02 to 0.10 part by weight, is used. If it exceeds 0.18 parts by weight, the workability is remarkably deteriorated, and if it is less than 0.02 parts by weight, the improvement of coating film properties is insufficient. As the trihydric or higher polyhydric alcohol component or the trihydric or higher hydroxycarboxylic acid component used in the depolymerization of the present invention, it is preferable to use a hydroxycarboxylic acid such as dimethylolpropionic acid as a base material such as a metal. Since a carboxyl group, which also serves as an adhesion point, is introduced into the molecular chain, it is more preferable from the viewpoint of improving adhesion.

In the production of the polyester resin of the present invention, the above-mentioned dicarboxylic acid component and dialcohol component are preferably used by blending so that the acid / alcohol ratio is 1/1 to 1/3 (equivalent ratio). In the presence of a catalyst such as dibutyltin oxide, lead acetate, calcium acetate, N-butyl titanate, etc., the esterification or transesterification reaction is carried out at 200 to 300 ° C. according to the In the presence of a catalyst such as acid value antimony, acid value germanium, N-butyl titanate, preferably 10 m
mHg or less, particularly preferably 1 mmHg or less under reduced pressure, preferably 200 to 300 ° C., particularly preferably 23.
By performing a polycondensation reaction at 0 to 280 ° C., a linear polyester resin having a number average molecular weight of 10,000 or more is prepared. Here, when the number average molecular weight is less than 10,000, the molecular weight of the resin obtained by the subsequent depolymerization is low, and the processability is poor. The upper limit of the number average molecular weight is not particularly limited, but is usually about 50,000 or less. To 100 parts by weight of the obtained linear polyester resin, 0.02 to 0.18 parts by weight of the above-mentioned polyhydric alcohol component having a valence of 3 or more and / or a hydroxycarboxylic acid component having a valence of 3 or more is blended, and under normal pressure, The desired branched polyester resin can be obtained by carrying out depolymerization while maintaining at preferably 200 to 300 ° C, particularly preferably 210 to 250 ° C.

The branched polyester thus obtained preferably has a number average molecular weight of 5,000 to 20,000. If it is less than 5,000, the workability tends to be poor,
If it exceeds 20,000, the solid content of the coating tends to decrease, and the practicality tends to be poor. Since the branched polyester resin obtained by depolymerization has a low molecular weight, part of coating film performance such as processability may be deteriorated. In that case,
In order to further improve the coating film performance, the polycondensation reaction can be performed again to increase the molecular weight. In the present invention, the "number average molecular weight" is calculated by utilizing gel permeation chromatography and using a calibration curve of standard polystyrene.

The polyester resin obtained by the present invention contains aromatic hydrocarbon, aliphatic hydrocarbon,
A paint can be prepared by diluting with a solvent such as an ester or a ketone. The polyester resin obtained by the present invention is an amino resin obtained by reacting an amino compound such as melamine, urea or benzoguanamine with formaldehyde, obtained by etherifying the amino resin with a lower alcohol such as methanol, ethanol, propanol or butanol. It can be used as a thermosetting coating material in combination with an amino resin such as an etherified amino resin.
In this case, the polyester resin and the amino resin are preferably blended in a weight ratio of solids of preferably 95/5 to 60/40, particularly preferably 90/10 to 70/30. Further, if necessary, a pigment, a plasticizer, a colorant and an acid catalyst such as p-toluenesulfonic acid can be added. The coating material thus obtained can be coated on the surface of ferrous or non-ferrous metal by a known method such as spray coating or roll coating.

[0014]

[Function] A coating film using a linear high molecular weight saturated polyester resin is inferior in blocking property and solvent resistance because the functional group in the molecular chain is small and the functional groups are located at both ends of the polymer chain. Therefore, when it is cured together with a curing agent such as an etherified amino resin, the cross-linking density of the coating film becomes low, the cross-linking structure is non-uniform, and the cross-linking reaction becomes insufficient for the polyester resin portion. The polyester resin obtained by the present invention is obtained by depolymerizing a linear high molecular weight polyester resin with a trace amount of a polyhydric alcohol component having a valency of 3 or more and / or a hydroxycarboxylic acid component having a valency of 3 or more, and slightly depolymerizing the polyester molecular chain. By introducing the branch part,
Since the crosslink density of the polyester resin part is high,
Blocking properties, solvent resistance, chemical resistance, etc. can be improved. On the other hand, the degree of branching is much lower than that of a normal polyester resin, and it is branched by depolymerization,
Since the molecular weight distribution does not broaden, it has little effect on processability and other coating properties.

[0015]

The present invention will be described in detail below with reference to Examples.
The present invention is not limited to these. Less than,
The number average molecular weight is Hitachi 635 type HLC and gel pack (GELPACK) R440, R450, R as a column.
400M (both are trade names of Hitachi Chemical Co., Ltd.) were used in series connection, tetrahydrofuran was used as an eluent, a chromatogram was obtained, and then calculation was performed based on standard polystyrene.

Example 1 (A): 299 parts by weight of terephthalic acid (1.8 mol), 75 parts by weight of isophthalic acid (0.45 mol), 141 parts by weight of azelaic acid (0.75 mol), ethylene glycol 1
24 parts by weight (2.0 mol), neopentyl glycol 1
25 parts by weight (1.2 mol) and 0.1 part by weight of dibutyltin dioxide were subjected to an esterification reaction at 250 ° C. in the presence of an inert gas to remove water produced, and a polyester resin of oxidation 1.0 ( a) was obtained. (B): Polyester resin (a) 50 obtained in (A)
0.8 mmHg by adding 0.1 part by weight of antimony trioxide and 0.2 part by weight of triethyl phosphate to 0 part by weight.
Polycondensation reaction at 280 ° C. under reduced pressure to obtain a high molecular weight linear polyester resin (b) having a number average molecular weight of 20,000
Got (C): Polyester resin (b) 40 obtained in (B)
To 0 part by weight, 0.1 part by weight of dimethylolpropionic acid was added at 260 ° C., followed by keeping the temperature for 1 hour to carry out a depolymerization reaction to obtain a finely branched polyester resin having a number average molecular weight of 19000.

Example 2 The procedure of Example 1 (C) was repeated except that the amount of dimethylolpropionic acid used for depolymerization was changed to 0.16 parts by weight. A branched polyester resin was obtained.

Example 3 The procedure of Example 1 (C) was repeated except that the dimethylolpropionic acid used for depolymerization was 0.32 parts by weight, and the number average molecular weight was 16,000. A branched polyester resin was obtained.

Example 4 The procedure of Example 1 was repeated except that the amount of dimethylolpropionic acid used for depolymerization was changed to 0.48 part by weight in (C) of Example 1, and a fine powder having a number average molecular weight of 15,000 was used. A branched polyester resin was obtained.

Example 5 A finely branched polyester having a number average molecular weight of 14000 was operated in the same manner as in Example 1 except that 0.48 part by weight of trimethylolpropane was used for depolymerization in (C) of Example 1. A resin was obtained.

Example 6 The procedure of Example 1 was repeated except that the amount of dimethylolpropionic acid used for depolymerization was changed to 0.64 parts by weight in (C) of Example 1, and a fine powder having a number average molecular weight of 14,000 was used. A branched polyester resin was obtained.

Example 7 The same procedure as in Example 5 was carried out to carry out the depolymerization reaction, and then
The polycondensation reaction was performed again at 280 ° C. under a reduced pressure of 8 mmHg to obtain a finely branched polyester resin having a number average molecular weight of 18,000.

Comparative Example 1 Polyester having a number average molecular weight of 19000 was operated in the same manner as in Example 1 except that the amount of dimethylolpropionic acid used for depolymerization was changed to 0.04 part by weight in (C) of Example 1. A resin was obtained.

Comparative Example 2 A polyester resin having a number average molecular weight of 5000 was prepared in the same manner as in Example 1 except that 1 part by weight of dimethylolpropionic acid used for depolymerization was used in (C) of Example 1. Obtained.

Comparative Example 3 A branched polyester having a number average molecular weight of 3,500 was operated in the same manner as in Example 1 except that 8 parts by weight of dimethylolpropionic acid used for depolymerization was used in (C) of Example 1. A resin was obtained.

Comparative Example 4 The number average molecular weight 2 obtained in (B) in Example 1 was 2
0000 linear polyester resin (b).

Comparative Example 5 The linear polyester resin of Comparative Example 4 and the branched polyester resin of Comparative Example 3 were mixed at a ratio of Resin of Comparative Example 4 / Resin of Comparative Example 3 = 90/10 (weight ratio).

Comparative Example 6 The linear polyester resin of Comparative Example 4 and the branched polyester resin of Comparative Example 2 were mixed at a ratio of Resin of Comparative Example 4 / Resin of Comparative Example 2 = 70/30 (weight ratio).

The resin obtained in each of the examples and comparative examples was prepared into a resin solution having a heating residue of 40% by using Solvesso 150 (Esso Petroleum, trade name) / cyclohexanone = 50/50 (weight ratio). The resin liquid thus obtained was made into a paint with the following composition and tested. (1) White enamel coating formulation Polyester resin of Examples or Comparative Examples 300 parts by weight Melan 523 (trade name of methyl etherified melamine resin manufactured by Hitachi Chemical Co., Ltd.) 30 parts by weight Typake CR95 (titanium white manufactured by Ishihara Sangyo) 100 parts by weight Parts p-toluenesulfonic acid 1 part by weight thinner (Solvesso 150 / cyclohexanone = 5/5) 69 parts by weight

(2) Test plate preparation conditions Base material: Bonderite # 144 treated steel plate (manufactured by Japan Test Panel Co., thickness 0.5 mm) Coating: Applicator (dry film thickness 20 μm) Baking: 280 ° C. × 90 seconds

(3) Test method Mitsuzawa: According to JIS K5400. Pencil hardness: According to JIS K5400. Stain resistance: After applying blue, black and red magic ink (using an oil-based ink felt pen) on the test piece, 2 at 20 ° C
After leaving it for 4 hours, it was wiped off with ethanol and the degree of contamination was shown by relative evaluation. <Evaluation> 5 points ... No ink marks. 4 points ... Between 5 points and 3 points. 3 points ... Slight ink marks remain. 2 points ... Between 3 points and 1 point. 1 point ... Ink marks clearly remain.

Workability: The test piece was bent 180 °, and the crack at the bent portion was evaluated with a 20 times magnifying glass according to the following criteria. <Evaluation> 5 points ... No crack. 4 points ... Between 5 points and 3 points. 3 points ... Some cracks. 2 points ... Between 3 points and 1 point. 1 point: There is a crack on the entire surface.

Blocking resistance: 1 piece of gauze on the test piece
After placing a sheet and applying a load of 100 g / cm ² at 40 ° C. for 1 hour, the trace of gauze on the test piece was evaluated according to the following criteria. <Evaluation> ◎ ... No trace of gauze. ○: Gauze marks remain slightly. △: Gauze traces clearly remain. ×: Gauze traces clearly remain, and the adhered gauze does not peel off.

Solvent resistance: The test pieces were evaluated for the state of the coating film after rubbing 100 times in a rubbing test using xylol according to the following criteria. <Evaluation> ◎ ... No luster. ○: There is a slight luster. B: The coating film is largely removed, but the trace does not reach the base material. ×: Traces reaching the base material.

Alkali resistance: The test piece was treated with 5% by weight of Na.
The surface condition of the coating film after being immersed in an aqueous OH solution for 24 hours was evaluated according to the following criteria. <Evaluation> ◎ ... No luster. ○: There is a slight luster. △: Large luster. × ... Large bulge. The test results according to the above are shown in Table 1.

[0036]

[Table 1]

As is clear from Table 1, the finely branched polyester resin obtained by the present invention is excellent as a resin for thermosetting paints and has an excellent balance of coating film hardness, processability and stain resistance. At the same time, it has good blocking resistance, solvent resistance, and chemical resistance. On the other hand, Comparative Example 1
Indicates that the amount of branched components is small, but improvement in solvent resistance and the like is insufficient. Comparative Example 2 has a large amount of branching components, and has good blocking resistance, solvent resistance, etc., but processability is reduced. Comparative Example 3 is different from Comparative Example 2 in
Further, although the amount of branching components is large, the workability is significantly reduced. Comparative Example 4 is a case of a straight chain high molecular weight polyester resin, which has an excellent balance of processability, hardness, and stain resistance, but is inferior in blocking resistance, solvent resistance, and chemical resistance. Comparative Example 5 is a case where a linear high molecular weight polyester resin (Comparative Example 4) and a branched polyester resin having a large amount of branching components (Comparative Example 3) are combined, and solvent resistance and the like are improved, but blocking resistance is improved. The sex is insufficient and it cannot be balanced. Comparative Example 6 is a case where a linear high molecular weight polyester resin (Comparative Example 4) and a branched polyester resin having a small amount of branching components (Comparative Example 4) are combined, and the balance is still unbalanced.

[0038]

INDUSTRIAL APPLICABILITY According to the present invention, a polyester resin which is not only excellent in workability, coating film hardness and stain resistance, but also excellent in blocking resistance, solvent resistance and chemical resistance and which is useful for metal steel sheets. And paint can be obtained.

Claims (4)

[Claims] 1. An aromatic dicarboxylic acid component of 100 to 30 mol% and an aliphatic dicarboxylic acid component of 0 to all acid components.
100 parts by weight of a straight-chain polyester resin having a number average molecular weight of 10,000 or more synthesized by using 70 mol% as an acid component and dialcohol as an alcohol component, and a polyhydric alcohol component having a valence of 3 or more and / or
Tricarboxylic or higher hydroxycarboxylic acid component 0.02 to 0.1
A method for producing a polyester resin for paint, which comprises depolymerizing at 8 parts by weight. 2. The method for producing a polyester resin for coating according to claim 1, wherein the hydroxycarboxylic acid component having a valence of 3 or more is dimethylolpropionic acid. 3. A coating material containing the polyester resin obtained by the production method according to claim 1. 4. The coating composition according to claim 3, further comprising an amino resin.