JPS59152964A - Epoxy resin powder coating - Google Patents

Abstract

PURPOSE:The titled coating that is obtained by using a solid bisphenol-A epoxy resin of a specific epoxy equivalent, thus being suitable for use as a primer in steel pipes, containers, cars and household electric appliances, because of its high flexibility and impact resistance. CONSTITUTION:The objective coating is obtained by using an epoxy resin which is prepared by reaction of (A) 100pts.wt. of a solid bisphenol-A epoxy resin of 500-1,300 epoxy equivalent with (B) 30-50pts.wt. of bisphenol A and satisfies the equation: 0<=(x+y+z)/(w+x+y)X100<=10 [w is epoxy content (equivalent/ 100g); x is diol content; y is hydrolyzable chlorine content (the amount on the reaction of bisphenol A with less than 0.1% of bisphenol A epoxy resin); z is the content of phenolic hydroxyls]. USE:Coating for bicycles and other vehicles.

Description

DETAILED DESCRIPTION OF THE INVENTION In particular, the present invention relates to a bisphenol A type epoxy resin powder coating having improved compatibility and impact resistance.

Powder coatings using solid bisphenol A type epoxy resins generally have excellent chemical resistance, adhesion, and surface hardness, but have the disadvantage of poor flexibility and impact resistance. As a result of various studies in search of the cause of these drawbacks, we found that the solid bisphenol A epoxy resin used for conventional powder coatings does not have all of its terminal groups as epoxy groups, such as diol groups, etc. Hydrolyzable chlorine, phenolic hydroxyl groups, etc. account for about 12 of the terminal functional groups.
It was found that this accounted for ~20%.

That is, commercially available solid bisphenol A epoxy resins are usually produced by a one-step method or a two-step method.

In the two-step method, a high molecular weight product is produced by reacting a predetermined amount of bisphenol A and epichlorohydrin at once in the presence of an alkali such as sodium hydroxide. It is thought that the reaction mechanism is as follows. Therefore, epichlorohydrin changes to glycidol,
It is thought that it reacts with phenolic hydroxyl groups to generate diols.

On the other hand, in the two-step method, an excess of epichlorohydrin is used relative to bisphenol A, and the reaction is performed in the presence of an alkali to once produce a low molecular weight epoxy resin.
Further, this is reacted with bisphenol A to increase the molecular weight. In this case, because there is an excess of epichlorohydrin when producing low molecular weight epoxy resin,
The proportion of glycidol decreases, and the amount of terminal diol produced decreases, but on the other hand, a large amount of hydrolyzable chlorine remains in the low molecular weight epoxy resin, and even if such a substance is further reacted with bisphenol A, However, in the high molecular weight product obtained, hydrolyzable chlorine still remains in the following form.

ph・0- CH2-CH-CH2ClH! Although the phenolic hydroxyl group remains unreacted, the amount thereof is small compared to hydrolyzable chlorine and diol.

In this way, the conventionally used solid bisphenol A
Type epoxy resins, whether produced by membrane or two-step processes, contain diol groups, hydrolyzable chlorine, and phenol groups in addition to epoxy groups as terminal functional groups. However, based on this recognition, if powder coatings are prepared using epoxy resins with a low content of terminal functional groups other than these epoxy groups, the disadvantages seen in conventional powder coatings may be avoided. It has been found that the flexibility and impact resistance are significantly improved.

Therefore, the present invention relates to an epoxy resin powder coating, and the epoxy resin powder coating has an epoxy equivalent of about 500 to 13.
00 solid bisphenol A type epoxy resin,
An epoxy resin that satisfies the following formula is used.

W: Epoxy group content (equivalent/100g) Such epoxy resin powder coating is
The coating film formed from it is strong, flexible, and has excellent impact resistance.

The solid bisphenol A type epoxy resin used in the present invention is represented by the following general formula, and has a molecular weight of about 500 to 130
0, preferably about 600 to 1100. Epoxy equivalents with lower epoxy equivalents can no longer be solid, or even if they are solid, they have significant blocking properties and are not suitable for powder coatings. On the other hand, if an epoxy equivalent having a larger value than this is used, the melt viscosity will increase, and the workability in preparing the paint will deteriorate.

Additionally, the content of other terminal functional groups represented by the above formula is 0
It should be in the range of 10% to 10%, preferably 0 to 5%. If the content of these other non-reactive terminal functional groups is higher than this, the crosslinking reaction at the terminal groups will not take place sufficiently and only a network structure similar to the uncured state will grow, increasing the crosslinking density. Therefore, the desired modification effect cannot be obtained.

The production of such epoxy resins with a low content of other terminal functional groups is possible, for example, with a hydrolyzable chlorine content of about 0.01 to 0.06
To a liquid bisphenol A type epoxy resin having an epoxy equivalent of about 250% by weight or less, less than 1 equivalent of alkali is added to 1 equivalent of the hydrolyzable chlorine,
100 parts by weight of an epoxy resin with a hydrolyzable chlorine content of less than 0.1% because it is obtained by bringing the two into contact under a temperature condition of about 100 to 130°C (see Japanese Patent Application No. 155,050/1982) About 30 to 50 parts by weight of bisphenol A to the
The reaction is carried out in the presence of an alkali such as sodium hydroxide, potassium hydroxide, or sodium carbonate, or an amine catalyst such as trialkylamine or tetraalkylammonium halide.

The epoxy resin produced in this way has a small content of terminal functional groups other than epoxy groups of 10% or less, and
It has a lower epoxy equivalent than commercially available epoxy resins at the same viscosity.

The preparation of powder coatings using such epoxy resins is carried out according to conventional methods. That is, a hardening agent, a filler, and other additives are blended into a solid epoxy resin, and the blend is thoroughly ground and mixed in a mixer, and then the mixture is mixed with a powder of about 80 to 120
℃ using a twin-screw intermeshing extruder, two-roll mixing machine, etc., and then a fine pulverizer to reduce the particle size suitable for powder coating, for example, about 30 to 70μ in the case of electrostatic coating. Grind to a certain extent.

As curing agents, commonly used curing agents include dihydrazides of dicarboxylic acids such as dicyandiamide, adipic acid, and sebacic acid, aromatic amines, acid anhydride adducts, and crosslinkable resins such as polyesters, polyacrylics, and polyphenolic acids. It is used as is. Further, tris(dimethylaminomethyl)phenol, iamidazoles, organic carboxylic acids, etc. can also be used to accelerate curing. Further, as additives, pigments such as Merck, titanium oxide, silicon oxide, and red oxide, Aeroseal, which improves the flowability and pinhole property of paint, acrylic resin, butyral resin, and the like are used.

Coating is performed by commonly used methods such as dipping, fluid dipping, and electrostatic coating for applications such as undercoating large, medium, or small diameter steel pipes, containers, automobiles, bicycles, other vehicles, and home appliances. be able to.

Note that the epoxy resin used in the present invention is not only used for powder coatings, but also suitably used as a resin fraction for solvent-based coatings, emulsion-based coatings, and the like.

Next, the present invention will be explained with reference to examples.

Silkworm example 1 Low hydrolyzable chlorine-containing bisphenol A type epoxy resin (epoxy equivalent: 189-529 milliequivalents/
'100111 JP-A-54-390Q8- Measured by the method described in α-diol 6 meq/100.9, hydrolyzable chlorine 0014% by weight -0
4 milliequivalents/100g, phenolic hydroxyl group not detected) 1
00 parts (weight, same below) and bisphenol A 3
3 parts were charged into a 500 ml noseparable flask, and triphenylphosphine 002 as a catalyst was added.
Added a section.

These mixtures are heated with stirring under nitrogen blanket,
The reaction was carried out at 150°C for 7 hours. As a result, 1 per epoxy
An epoxy resin having a t6oo and a viscosity (Gardner) of J- was obtained.

Reference Example 2 In Reference Example 1, 39.4 parts of bisphenol A was used. As a result, an epoxy resin having an epoxy equivalent of 81O1 and a viscosity (Gardner) of T was obtained.

Reference example 3 Bisphenol A type epoxy resin (epoxy equivalent 4'7
5-211 milliequivalents/100g, α-diol 20 milliequivalents/100g, hydrolyzable chlorine 0005 East weight%-01
4 milliequivalent/100.9, no phenolic hydroxyl group detected)
100 parts and 4.2 parts of bisphenol A in a volume of 50
0-2 separable flask, and further added 02 parts and 1 part of triphenylphosphine a.

These mixtures are heated with stirring under nitrogen blanket,
The reaction was carried out at 150°C for 7 hours. As a result, the epoxy
An epoxy resin with p620 and viscosity (Gardner) J was obtained.

Reference Example 4 Epicoat 1004 (Epoxy-f
%) 920 and viscosity S) were used.

Example 1 To 100 parts of the epoxy resin produced in Reference Example 1, 4 parts of dicyandiamide as a hardening agent and 50 parts of rutile titanium oxide as a filler were added.
This mixture was pulverized and mixed using a pulverizer, and then mixed for 10 minutes using two 8-inch rolls heated to 95°C. After cooling the kneaded material, it is pulverized in a no-mer mill, and the particle size is 1.
A powder containing 50 to 250 meshes as a main component was prepared.

Apply this powder paint to 180 to 200% using an electrostatic coating machine in advance.
A 9-inch iron plate (88-41, #120) heated to 0°C.
The film thickness is approximately 300 to 35 mm by applying the coating to Zander polishing) and post-curing for 10 minutes at 200℃.
A coating film of 0μ was obtained.

A coating film of the same type as this was evaluated for each of the following items.

Tensile Strength Bending strength: Tensile test dumbbells (No. TI52) were punched out from the film that was electrostatically coated on a two-plated forming iron plate, baked, and then peeled off, and the tensile strength was measured in accordance with JI8-6911. : Test piece (JISK-69
11; size 125 x 4 mtl) was prepared and the bending strength was measured. Impact resistance: A DuPont impact machine was taken off, and a 2 kg weight was dropped after hitting 5 parts of 8 inches. The results obtained were as follows: As shown in the table below, the tensile strength, bending strength, and impact resistance at low temperatures are clearly higher than that of Comparative Example 1, which used an epoxy resin with a content of other terminal functional groups exceeding 10%. It is excellent in this respect.

Example 2 In Example 1, instead of dicyandiamide as the curing agent, 9. '7 parts of adipic acid dihydrazide was used, and the crosstalk temperature was changed to 100°C and the post-cure temperature was changed to 210°C.

The evaluation results for the obtained coating film are shown in the table below, and it is clearly superior to that of Comparative Example 2 in terms of tensile strength, bending strength, and impact resistance at low temperatures.

Comparative Example 1 In Example 1, the epoxy resin produced in Reference Example 3 was used. The obtained evaluation results for &B are shown in the table below.

Comparative Example 2 In Example 2, the epoxy resin produced in Reference Example 3 was used. The evaluation results for the obtained coating films are shown in the table below.

Example 3 In Example 1, the epoxy resin produced in Reference Example 2 was used, and the crosstalk conditions were changed to 115° C. for 8 minutes.

The evaluation results for the obtained coating film are shown in the table below, and the tensile strength is clearly higher than that of Comparative Example 3, in which an epoxy resin with a content of other terminal functional groups exceeding 10% was used. It has excellent bending strength and impact resistance even at low temperatures.

Example 4 In Example 2, the epoxy resin produced in Reference Example 2 was used, and the amount of adipic acid dihydrazide used was 7
The crosstalk conditions were changed to 120°C and 8 minutes.

The evaluation results for the obtained coating film are shown in the table below, and it is clearly superior to that of Comparative Example 4 in terms of tensile strength, bending strength, and impact resistance at low temperatures.

Comparative Example 3 In Example 3, the epoxy resin of Reference Example 4 was used. The evaluation results for the obtained coating film are shown in the table below.

Comparative Example 4 In Example 4, the epoxy resin of Reference Example 4 was used. The evaluation results for the obtained coating films are shown in the following table.

Below margin

Claims (1)

[Scope of Claims] An epoxy resin powder coating comprising a solid bisphenol AW epoxy resin having an epoxy weight of about 500 to 1,300 and satisfying the following formula. W: Epoxy group @ M (equivalent weight/100.9)
Equivalent weight: 7100 g) 2 Hydrolyzable chlorine content: 0.1% Bisphenol A to unvortexed Bisphenol A epoxy resin
The epoxy resin powder coating according to claim 1, wherein an epoxy resin prepared by reacting is used. 3-bisphenol A type epoxy resin 10 The epoxy resin powder coating according to claim 2, wherein an epoxy resin in which about 30 to 50 parts of bisphenol A is reacted with ONN base is used.