JPS5829341B2 - Resin composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin composition for powder coatings that not only provides a coating film with excellent coating surface smoothness and weather resistance, but also has excellent storage stability.

Since powder coatings do not contain solvents, they are establishing a unique field in the paint industry as pollution-free and resource-saving paints, but compared to solvent-based paints, there are still many points that need to be improved in terms of performance.

Currently, thermosetting powder coatings are typified by acrylic, epoxy, and polyester paints, but none of them have been able to resolve the conflicting relationship between coated surface smoothness and storage stability.

In order to improve the smoothness of the painted surface, the melt viscosity of the resin is generally lowered by considering the resin composition or by lowering the molecular weight, but on the other hand, this lowers the softening point of the resin and causes it to become powdery during storage. There is a problem in that the body paint blocks or the curing reaction progresses during storage, making it impossible to obtain an initial smooth painted surface when a paint film is actually formed.

In particular, this problem is a major obstacle when curing polyester resins using epoxy compounds as curing agents, and a solution is strongly desired.

These problems are relatively small with polyester powder coatings that use commonly known bisphenol-type epoxy resins with an epoxy equivalent of 800 or more as a curing agent, but they use epoxy compounds with an epoxy equivalent of 500 or less as a curing agent. In this case, the storage stability is so poor that powder coating is difficult.

On the other hand, one of the advantages of polyester-based powder coatings is that they have good weather resistance, but when currently known epoxy resins with an epoxy equivalent of 800 or more (e.g., Epicoat 1004 manufactured by Shell Chemical Co., Ltd.) are used, the optimal blending conditions In order to make it (epoxy group/carboxyl group - 1/1 mole) polyester resin/Epikoat 1004 = about 1/1 mole, the weather resistance of the resulting coating film becomes extremely poor.

In order to improve weather resistance, it is better to reduce the amount of epoxy resin blended, but for epoxy resins with a high epoxy equivalent, lowering the amount will result in insufficient curing.

The only way to reduce the amount of epoxy resin blended under optimal blending conditions is to use a resin with a low epoxy equivalent as the epoxy resin.

However, many resins with low epoxy equivalents are in liquid form, and powder coatings obtained by blending them have poor storage stability, and such low epoxy value resins have higher reactivity than high epoxy value resins. Since curing proceeds before the coating film becomes fluid and smooth, there is a problem in that it is difficult to obtain a smooth coating surface, and improvements are strongly desired.

The inventors of the present invention have conducted various intensive studies in order to solve these problems and obtain a polyester powder coating that has excellent coating surface smoothness, weather resistance, and storage stability.
The inventors have discovered that a powder coating compounded with a polyester resin and an epoxy group-containing polyester resin can solve the above-mentioned problems, and have thus arrived at the present invention.

That is, the present invention has an acid value of 20 to 1501 and a softening point of 50 to 16.
A polyester resin [1] having a temperature of 0°C, a polyester resin having an acid value of 25 to 200 containing at least 30 moles of aromatic dicarboxylic acid as an acid component, and an epoxy compound having at least two epoxy groups in one molecule are combined into an epoxy resin. group/carboxyl group = 3/1 to 1.5/1 (mole ratio), and the reaction rate of carboxyl group is 25
This is a resin composition for a powder coating comprising an epoxy group-containing polyester resin having an epoxy group equivalent of 400 to 2,500 and a softening point of 40 to 160°C, which is obtained by reacting the resin composition so as to have an equivalent weight of 400 to 2,500.

The resin composition for powder coating of the present invention has an epoxy group equivalent of 400 to 2,500 and a softening point of 40 to 16 as an epoxy compound.
By using an epoxy group-containing polyester resin that has a temperature of 0°C, it not only provides a coating film with superior coating surface smoothness and weather resistance, but also has excellent storage stability compared to the case of using conventional epoxy compounds. It is something.

Acid value 20-150, softening point 50-160 in the present invention
℃ polyester resin CI) contains terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, and tetrahydrophthalic acid as polycarboxylic acid components. , divalent carboxylic acids such as hexahydrophthalic acid, trivalent or higher polyhydric carboxylic acids such as trimellitic acid, pyromellitic acid, ethylene glycol bis trimellitate, neopentyl glycol bis trimellitate, 1,6-hexanethiol bis trimellitate, etc. carboxylic acids.

It is desirable that the polyvalent carboxylic acid component is mainly composed of divalent carboxylic acid.

Polyhydric alcohol components include ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-
Bentanediol, neopentyl glycol, ■, 6-
hexanediol, 1,4-cyclohexane dimetatool, alkylene oxide adduct of bisphenol A,
Examples include dihydric alcohols such as alkylene oxide adducts of hydrogenated bisphenol A, and polyhydric alcohols of trihydric or higher hydricity such as chrycerin, trimethylolethane, trimethylolpropane, and pentaerythritol.

It is desirable that the polyhydric alcohol component is mainly dihydric alcohol.

These polyhydric carboxylic acid components and polyhydric alcohol components can be arbitrarily selected from the viewpoint of economic efficiency and physical properties of the coating film, but from the viewpoint of storage stability, weather resistance, moisture resistance, and strength of the coating film, It is desirable to mainly use aromatic polycarboxylic acids as the polycarboxylic acid component, and in particular, in order to maintain coating film strength such as impact resistance, at least 30 moles of the total polycarboxylic acid component should be used. Terephthalic acid is preferred.

The polyester resin CI) according to the invention may contain small amounts of hydroxycarboxylic acids such as P-oxybenzoic acid.

The polyester resin CI) of the present invention has an acid value of 20 to 150.
It is necessary to be within the range of .

If the oxidation value is less than 20, the reaction of the epoxy group-containing polyester resin with the epoxy group becomes insufficient, and a coating film having excellent physical properties cannot be obtained.

On the other hand, if the acid value exceeds 150, the amount of epoxy group-containing polyester resin to be blended increases, resulting in poor weather resistance of the storage-stable coating film.

Further, the softening point of the polyester resin [I] of the present invention is 50
It is necessary that the temperature is in the range of ~160°C.

If the softening point of the resin (I) is less than 50°C, the storage stability of the powder coating will be poor, and if the softening point of the resin [I] exceeds 160°C, it will be difficult to melt and mix it into a paint. Become.

In the present invention, the epoxy group-containing polyester resin having an epoxy equivalent of 400 to 2,500 degrees and a softening point of 40 to 160 degrees Celsius is combined with a polyester resin having an acid value of 25 to 200 and containing at least 30 moles of aromatic dicarboxylic acid as an acid component. It is obtained by reaction with an epoxy compound having at least two or more epoxy groups in the molecule.

The polyester resin mentioned here can be arbitrarily selected from each component of the polyester resin [I] described above, and considering economic efficiency and physical properties of the coating film, at least 30% of the total acid components
Preferably, the mole is terephthalic acid.

On the other hand, as for the epoxy compound having at least two or more epoxy groups in one molecule here, it is desirable that the epoxy equivalent is low.

This is because when a compound with a high epoxy equivalent is used, the amount of epoxy resin compounded increases, resulting in a decrease in weather resistance.

The epoxy equivalent of the epoxy compound used here is 50
It is preferably 0 or less, such as bisphenol A diglycidyl ether and its oligomer, hydrogenated bisphenol A diglycidyl ether and its oligomer, orthophthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, P -oxybenzoic acid glycidyl ester ether, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester,
Succinic acid diglycidyl ester, adipic acid diglycidyl ester, sebacate acid diglycidyl ester, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, ■, 4-butanediol diglycidyl ether, ■, 6-hexanethiol diglycidyl ether , trimellitic acid triglycidyl ester, triglycidyl isocyanurate, and the like.

Epoxy group-containing polyester resin of the present invention
The desired reaction ratio of a polyester resin having a polyester resin having a molecular weight of 5 to 200 and an epoxy compound having at least two or more epoxy groups in one molecule is epoxy group/carboxyl group -3/1 to 1.5/1 (mol). 1, so that the reaction rate of the carboxyl group is 25 to 85 equivalents.
It is preferable to carry out the reaction under temperature conditions of 20°C to 200°C.

When the reaction rate of carboxyl groups is less than 25 equivalents φ, the obtained powder coating will block during storage.

Moreover, if the equivalent weight exceeds 85 φ, a smooth coating film cannot be obtained.

The epoxy group-containing polyester resin composition of the present invention has an epoxy equivalent of 400 to 2,500, preferably 500 to 20.
It is in the range of 00.

When the epoxy equivalent is less than 400, defects such as poor storage stability of the obtained powder coating and poor coating surface smoothness occur, whereas when it exceeds 2500, curing is not performed sufficiently and impact resistance etc. The physical properties of the coating film deteriorate significantly.

Moreover, the epoxy group-containing polyester resin (6) of the present invention
has a softening point in the range of 40 to 160°C.

When the softening point is less than 40°C, the storage stability of the obtained powder coating is poor, and in some cases, pulverization becomes impossible.

In addition, when the softening point exceeds 160°C, it becomes difficult to melt and mix the resin when forming it into a paint.

In the resin composition for powder coating of the present invention, the ratio of the polyester resin CI) to the epoxy group-containing polyester resin (9) is 80/20 to 30/70 (weight ratio).

If the amount of the polyester resin CI) exceeds 800 parts by weight or less than 300 parts by weight, a powder coating composition that satisfies all of storage stability, coated surface smoothness and weather resistance cannot be obtained.

The resin composition for powder coatings of the present invention includes, as a curing catalyst, a tertiary nitrogen compound such as dimethylbenzylamine, a quaternary ammonium salt compound such as trimethylbenzyl ammonium chloride, choline chloride, bistetraethylammonium terekrate, and boron trifluoride ether vinegar. Known curing catalysts such as boron trifluoride compounds such as salts and alkali metal salts of phenols such as sodium phenoxide may be added.

The amount of catalyst used is 3% by weight or less based on the polyester resin I).

In addition to pigments such as titanium oxide, known additives such as silicon compounds and acrylic esters may be added to the resin composition for powder coatings of the present invention depending on the purpose and use.

Any known technique may be used to form the resin composition for powder coating of the present invention into a coating, but it is preferable to melt and mix it using a melt extruder, then crush it and pass through a 100-mesh sieve to obtain a powder coating. is preferred.

As mentioned above, the resin composition for powder coatings of the present invention has excellent storage stability, and the resulting coating film has excellent smoothness and impact resistance.

The present invention will be explained below using Examples.

In the examples, "parts" simply indicate parts by weight, and "饅" indicates parts by weight.

Each measurement item was measured according to the following method.

(1) Molecular weight The molecular weight was measured using a molecular weight measuring device using chloroform as a solvent.

(2) Softening point Measured according to JIS K-2351.

(3) Acid value Measured by the method of JIS K-5400 using chloroform as a solvent.

(4) Epoxy value Measured according to the dioxane method.

(5) Storage stability The powder coating was stored in a constant temperature room at 35℃ for one month, and the workability of the coating and the smoothness of the resulting coating surface changed compared to the initial coating. I checked visually to see if it was there.

(6) DuPont impact value Measured according to JISK-5460.

1 kg 4" force. (7) Smoothness of painted surface Based on visual judgment.

(8) Gloss 600 reflectance was measured.

(9) Weather resistance The product was left outdoors for 3 months and 6 months and changes in gloss were measured.

(10) Ester bond concentration in epoxy-containing polyester resin was determined using the following formula.

Ester bond concentration - (Nt/N1+N2+N5)Xl,
00 bits N1: 2X (average molecular weight of polyester resin/average unit molecular weight of polyester constituents) N2 + N3: Number of ether bonds and ester bonds in epoxy resin Production example 1 970 parts of dimethyl terephcrate, 316 parts of ethylene glycol, 530 parts of neopentyl glycol and 0.44 parts of zinc acetate were charged into a reaction vessel, and heated from 140°C to 22°C.
The transesterification reaction was carried out over a period of 3 hours until the temperature reached 0'C.

Next, 747 parts of isophthalic acid was added, and the temperature was raised from 200°C to 240'C over 12 hours to perform an esterification reaction.

Next, 96 parts of anhydrous trimellitic vinegar was added and a reaction was carried out at 2400C for 30 minutes.

As a result of compositional analysis such as NMR, the obtained polyester resin (4) was found to have an acid component of terephthalic acid/isophthalic acid/trimellitic acid = 48748/4 (mol) and a glycol component of ethylene glycol/neopentyl glycop L/= =5
0150 (mol), and is yellow-orange transparent and has a molecular weight of 28.
00, the softening point was 98°C, and the acid value was 52.

Polyester resins (B) to (2) having the compositions shown in Table 1 were produced in the same manner.

Production example 2゜Put 1000 parts of polyester resin (A) into a reaction container,
After heating to 170°C, 285 parts of terephthalic acid diglycidyl ester was added with stirring, and the mixture was heated to 160°C to 180°C.
The reaction was carried out at ℃ for 40 minutes.

The obtained epoxy group-containing polyester resin (a) had a softening point of 87°C, an epoxy equivalent of 1450, all the bonds contained in the molecule were ester bonds, and the reaction rate of carboxyl groups was 6.
0 equivalent φ.

Epoxy group-containing polyester resins (b) to (g) shown in Table 2 were produced in the same manner.

Example 1, 500 parts of polyester resin (B), 850 parts of epoxy group-containing polyester resin (a), 500 parts of titanium oxide (R-930 manufactured by 6 Hara Sangyo), 7 parts of Polyflow S (manufactured by Kyoeisha Yushi Kagaku Kogyo), benzoin After mixing 12 parts in a Henschel mixer, the mixture was heated to 100 to 130°C in a twin-screw extruder.
The mixture was melt-mixed, cooled, and then finely ground.

The obtained powder was passed through a 100-mesh sieve, and the material that passed through was used as a powder coating, and coated on a mild steel plate (JIS G-3141) with a film thickness of 50 to 80 mm using an electrostatic powder coating machine manufactured by Landsberg.
It was coated so as to have a thickness of .mu. and baked at 220.degree. C. for 20 minutes.

A coating film test was conducted on the obtained coated steel plate.

The physical property values of the coating film at this time are shown in Table 4 as initial values.

Separately, the obtained powder coatings were stored in a thermostatic chamber at 35° C. for one month, and a storage stability test was conducted to examine whether there would be any difference in the physical properties of the coating film.

The results are shown in Table 4. Example 2. ~5° In the same manner as in Example 1, polyester resins and epoxy group-containing polyester resins were made into paints in the proportions shown in Table 3, and the results are shown in Table 4.

Comparative example 1. ~8゜By the same method as in Example 1, a polyester resin and an epoxy group-containing resin were made into a paint in the proportions shown in Table 3.
The results are shown in Table 4.

Claims (1)

[Claims] 1 A polyester resin CI) having an acid value of 20 to 150 and a softening point of 50 to 160°C and an acid value of 25 to 200 containing at least 30 moles of aromatic dicarboxylic acid as an acid component.
An epoxy compound having at least two epoxy groups in one molecule and a polyester resin having an epoxy group/
Epoxy group equivalents obtained by blending carboxyl groups in the range of 11 to 1.5/1 (molar ratio) and reacting so that the reaction rate of carboxyl groups is 25 to 85 equivalents φ 400 to 2
500, and an epoxy-containing polyester resin composition having a softening point of 40 to 160°C.