JPS638995B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition for paint that can be baked at low temperatures. Recently, there has been a strong demand for labor-saving and energy-saving coatings for automobile repair, automobiles, industrial machinery, steel furniture, electrical appliances, etc. To solve these problems, it is necessary to lower the temperature range
It is desirable to cure at 80-100°C. In conventional amino alkyd resin paints,
Baking at 130-150℃ for 20-30 minutes is common.
Baking at 120°C for 20 minutes is the lower limit for maintaining practical properties. Conventional butyl etherified melamine resins generally have an average of 4.5 to 6.0 formaldehyde bonds and an average of 3 to 5 butyl ether groups per melamine nucleus, and these are used to form a coating with an alkyd resin and heated at 90°C. Under the baking conditions of 20 minutes, the hardness of the coating film is low and there are drawbacks such as stickiness remaining on the coating surface. The present invention solves these drawbacks. That is, the present invention provides an average of 3 to 5 bound formaldehydes per melamine core, and an average of 1 to 5 bound formaldehydes per melamine core.
The present invention relates to a resin composition for coatings containing a butyl etherified melamine resin (A) having 2.3 butyl ether groups and an alkyd resin (B). The butyl etherified melamine resin of component (A) has an average of 3 to 5 formaldehyde bonds per melamine nucleus. If the average number is less than 3, the resin will become cloudy, and if the average number exceeds 5, the curability will be poor. The butyl etherified melamine resin has an average of 1 to 2.3 butyl ether groups per melamine nucleus. If the average number is less than 1, the coating film will become brittle, and if the average number exceeds 2.3, the curing properties at low temperatures will be poor. In addition, the butyl etherified melamine resin of component (A) contains 0 to 0 free formaldehyde to the resin.
Preferably, it contains 1.5% by weight. If free formaldehyde exceeds 1.5% by weight, the odor becomes intense and the paint film tends to become soft. Conventionally, the butyl etherified melamine resin of component (A) is obtained using melamine, formaldehyde, and butyl alcohol. First, the reaction is, for example, 1 mole of melamine, 4 to 6.5 moles of formaldehyde, and 5 to 5 moles of butanol.
An addition reaction is carried out in the presence of a basic catalyst in a 10 mol solution, and then an acidic catalyst is added to carry out a condensation reaction and a butyl etherification reaction under acidic conditions at reflux temperature. Butyl etherification and condensation reaction may be performed simultaneously. If necessary, add 0.1 to 0.5 mole of melamine and heat at 80 to 150℃.
Preferably at 95-135°C for 0.5-5 hours, preferably 1
The amount of free formalin can be reduced by reacting for ~3 hours. After this, the amount of free formalin was reduced to 1.5% based on the resin solid content by a depressurization process.
% by weight or less. The alkyl resin used in combination with the melamine resin can be any commonly known alkyl resin and has a hydroxyl group. For example, coconut oil, soybean oil, castor oil, dehydrated castor oil, linseed oil, tung oil, safflower oil, tall oil or ethylene glycol, diethylene glycol, trimethylrolethane, with or without these fatty acids.
Trimethylolpropane, glycerin, 1,6-
Polyhydric alcohols such as hexanediol and pentaerythritol, polybasic acids such as phthalic acid, adipic acid, succinic acid, glutaric acid, isophthalic acid, sebacic acid, and tetrahydrophthalic acid, or their anhydrides, and monobasic acids as necessary. It can be obtained by condensation reaction at a temperature of ~240°C. The alkyd resin has a hydroxyl value of 50 to 200, particularly preferably 80 to 150. If the hydroxyl value is less than 50, curing will be insufficient, and if it exceeds 200, coating film properties such as water resistance will deteriorate. Other molecular weight 1000-5000, acid value 10 or less, viscosity (Gartna / 25℃ / heating residue 60%) Z ₂ ~
_Z6 is preferable. The mixing ratio of butyl etherified melamine resin (A) and alkyd resin is melamine resin/alkyd resin.
10/90 to 30/70 (solid content weight ratio) is preferable.
If it is less than 10/90, a sufficiently crosslinked coating film will not be obtained and curing will tend to be insufficient, and if it exceeds 30/70, the coating will tend to be brittle and have poor adhesion. If necessary, an external catalyst such as hydrochloric acid, p-toluenesulfonic acid, or phosphoric acid may be added to the resin composition of the present invention, and its catalytic effect becomes more pronounced during low-temperature curing. The paint resin composition of the present invention thus obtained is made into a paint by adding pigments, solvents, and other additives depending on the purpose. The coating method may be any method such as spraying, roll coating, or dipping. The present invention will be explained in detail below with reference to production examples and examples. In the examples, % and parts indicate weight % and parts by weight, respectively. Synthesis Example 1 Weigh 211 g of paraformaldehyde, 180 g of isoptanol, and 100 g of melamine into a flask equipped with a stirrer, reflux condenser, and thermometer and heat to 85-90℃.
Carry out the addition reaction for 30 minutes. Then melamine 26
g, 180 g of isobutanol, and 0.15 g of phthalic acid were added, and reflux dehydration was performed under acidic conditions for 2 hours. After this, it is concentrated under reduced pressure. The end point was 130°C at a vacuum degree of 200 torr. The heated residue of the concentrate thus obtained is adjusted to 60% with isobutanol. The viscosity at this time (25°C/Gardna) was V. Synthesis Example 2 Using the same equipment as Synthesis Example 1, 180g of paraformaldehyde, 360g of n-butanol, and melamine
Weigh out 100g and conduct the addition reaction at 90-95°C for 30 minutes. Add 0.1 g of phthalic acid and dehydrate under reflux for 1 hour and 45 minutes under acidic conditions. After this, add 26g of melamine.
and reflux dehydration for 30 minutes again. After this, it is concentrated under reduced pressure. The end point was 200 torr and 130°C without vacuum.
The heating residue of the concentrate thus obtained is 60%
was adjusted with xylene. The viscosity at this time (25°C/Gardana) was J. Synthesis Example 3 Using the same equipment as Synthesis Example 1, 211 g of paraformaldehyde, 360 g of n-butanol, and melamine
Weigh out 126 g and conduct an addition reaction at 90-95°C for 30 minutes. Add 0.1 g of phthalic acid and perform reflux dehydration under acidic conditions for 1 hour and 30 minutes. After this, concentrate under reduced pressure. The heating residue of the concentrate thus obtained is adjusted to 60% with xylene. The viscosity at this time (25°C/Gardana) was S. Synthesis Example 4 The method of Synthesis Example 1 was followed up to reflux dehydration.
Then, it is concentrated under normal pressure. The end point was when the temperature reached 105°C. 60% concentrate with imbutanol
adjusted to %. Viscosity at this time (Gardna/25℃)
was W. Synthesis Example 5 According to the method of Synthesis Example 3, concentration was carried out at normal pressure. The end point was when the temperature reached 130°C, and the heating residue was adjusted to 60% with xylene. The viscosity (Gardner/25°C) at this time was V. Example 1 30 parts of the butyl etherified methylolmelamine resin of Synthesis Example 1, alkyd resin (phthalkyd 213-
60, Hitachi Chemical Co., Ltd. product name, hydroxyl value 54,
Acid value 13) 70 parts, titanium white (Tiepeke R-840)
After weighing 100 parts and kneading it three times with three rolls, dilute the thinner (xylene/isobutanol = 70/30 weight ratio) with food cup #4 for 20 seconds at 25°C until the film thickness is 30-35μ. It was spray-painted onto a painted board (Bonderite-treated steel plate #144), left at room temperature for about 15 minutes, and then baked at 90°C for 20 minutes. The performance of the obtained coating film is shown in Table 3. Examples 2 to 3 and Comparative Examples 1 to 2 A coating film performance test was conducted in the same manner as in Example 1 except that the butyl etherified amino resin and the alkyd resin were formulated as shown in Table 2.

【table】

【table】

【table】

[Table] The test method is as follows. 1 Gloss: Measured with a 60° specular reflectance meter 2 Pencil hardness: Judged with Mitsubishi Pencil Uni 3 Cross cut: 1 x 1 mm squares on the coating surface
Make 100 pieces with a steel pen and peel off the sellotape 4 Erichsen value: JIS K 7777 5 Impact value: Dupont impact tester 1/2″-
Judgment in cm using 500g6 Solvent resistance: Rub the test plate with xylene 100 times and judge the surface condition of the coating film with the naked eye. ○: No abnormality. △: Slightly immersed. ×: Severely immersed. As is clear from the above, the coating resin composition of the present invention can be cured at low temperatures, has excellent coating properties, and has great practical effects.

Claims (1)

[Claims] 1. Butyl etherified melamine resin (A) having an average of 3 to 5 formaldehyde bonds and an average of 1 to 2.3 butyl ether groups per melamine nucleus.
and a resin composition for paint containing an alkyd resin (B). 2 Butyl etherified melamine resin (A) and alkyd resin (B) (A)/(B) is 10/90 to 30/70 (solid content weight ratio)
The resin composition for coating according to claim 1, containing the following. 3. The resin composition for paint according to claim 1 or 2, wherein the butyl etherified melamine resin contains 0 to 1.5% by weight of free formaldehyde based on the resin.