JPS61204243A - Undercoating composition for polybutylene terephthalate resin - Google Patents

Abstract

PURPOSE:To provide the titled composition applicable easily and capable of giving a coating film having excellent appearance, by compounding a mixed resin composition with a specific epoxy resin, a melamine resin having a specific mineral spirit tolerance, and a cold-curing catalyst at specific ratios. CONSTITUTION:The objective composition can be produced by compounding (A) 100pts.wt. of a coating composition composed of (i) 100pts. of a mixed resin composition, (ii) 60-80pts. of an epoxy resin having an epoxy equivalent of 2,400-3,300 and (iii) 20-40pts. of a melamine resin having a mineral spirit tolerance of <=15 with (B) 1.0-2.5pts. of a cold-curing catalyst (e.g. morpholine, etc.).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an undercoat composition used for coating polybutylene terephthalate resin molded articles.

(Prior art) Polybutylene terephthalate (hereinafter abbreviated as PBT) resin molded products have recently become widely used in automobile parts because they have excellent toughness and heat resistance. It has become. When applying a topcoat to a PBT resin molded product for cosmetic purposes, it is usually done to improve the adhesion of the topcoat and hide material defects.
A primer coat is applied.

Conventionally, the coating method for such PBT resin molded products has been as follows:
After performing general degreasing cleaning treatment such as organic solvent wiping,
A two-coat, two-bake process has been used in which an undercoat for PBT resin is applied by air atomization and baked dry, and then, for example, a top coat for car body steel plates is applied by air atomization and baked dry.

Moreover, since the paint is usually painted using equipment with one booth and one oven, in order to complete the process with two coats and two bakes, the paint must be passed through the same equipment twice. I have been using a repurposed intermediate paint. Most of the conventional solid top coatings for car body steel plates are made of mixed compositions of fatty acid-modified polyester resins, oil-free polyester resins, and alkylated melamine formaldehyde resins, and metallic and some solid top coatings. uses a mixed composition of an acrylic resin and an alkylated melamine formaldehyde resin as the main resin component.

(Problems to be Solved by the Invention) Conventionally, in order to impart adhesion to a PBT resin molded product with a topcoat film, for example, an intermediate coating for car body steel plates was used and baking was carried out after drying. , a 2-coat, 2-bake process was absolutely necessary, in which a top coat was applied and then the baking process was dried.When using a conventional undercoat and wet-on-wet painting with a topcoat, the undercoat and topcoat Extreme inversion occurs at the contact surface with the paint, causing color mottling and blurring due to the bleeding phenomenon of the undercoat paint onto the topcoat film surface.
A normal paint film that could be tested was not obtained.

Furthermore, in order to paint one PBT resin molded product, it has to pass through the same equipment twice, which is undesirable from the viewpoint of production efficiency.

(Means for Solving the Problems) The present invention provides an undercoat composition for PBT resin that enables conventional topcoat paint for car body steel plates to be applied wet-on-wet on top of the wet film of undercoat paint. developed,
This makes it possible to perform two-coat, one-bake coating using wet-on-wet coating with an undercoat and a topcoat, thereby solving the above-mentioned conventional problems.

That is, in the present invention, 60 to 80 parts by weight of an epoxy resin having an epoxy equivalent of 2,400 to a, 3 o, and a mineral spirit tolerance (hereinafter abbreviated as MST) of 15 parts by weight to 100 parts by weight of the solid matter of the resin mixed composition. Wet-on-uret undercoat for polybutylene terephthalate resin, characterized by containing 20 to 40 parts by weight of the following melamine resin and 1.0 to 2.5 parts by weight of a medium-low temperature curing catalyst of 100 parts by weight of the paint. The present invention relates to a coating composition.

The PBT resin molded products to be coated with the undercoat composition of the present invention include molded products made of PBT resin and used as automobile parts.

The resin component of the resin mixture composition in the undercoat composition of the present invention has an epoxy equivalent of 2,400 to 8,8
A mixture of an epoxy resin in the range of 0.00 and a melamine resin with an MST of 15 or less is used. The epoxy resin functions to impart adhesion to the PBT resin to the undercoat paint due to the hydrogen bonding force of the hydroxyl groups within the molecule. The epoxy resin is obtained by the reaction of bisphenol A and echylolhydrin, and has an epoxy equivalent of 2,400 mma, ao
Bisphenol type epoxy resin of o is preferred. If the epoxy equivalent of the epoxy resin is less than 2,400, wet-on-wet painting workability, visual finish appearance, adhesion, moisture resistance, and solvent resistance are all poor, resulting in a, ao.

If it exceeds 20%, the air atomization coating workability will be poor and it will be difficult to form a normal coating film, which is not preferable. The amount of the epoxy resin is 60 to 80 parts by weight based on 100 parts by weight of the solid matter of the resin mixture composition of the undercoat.

If the amount is less than 60 parts by weight or more than 80 parts by weight, the wet-on-wet coating workability and visual finish appearance are poor and cannot be used.

Next, melamine resin, which is another resin component of the resin mixture composition of the undercoat, is used as a crosslinking agent for the epoxy resin, but a butylated melamine formalde resin having an MST of 15 or less is preferred. In addition, the amount of melamine resin is 100f solids of the resin mixture composition of the undercoat [Okibe Chu, 20-4
0 parts by weight.

The low temperature curing catalyst used in the present invention includes block type p-toluenesulfonic acid blocked with morpholine, aminomethylpurpanol, pyridine, etc.
Examples include chloroacetic acid, maleic ester, phosphoric ester, etc., and are used auxiliary to accelerate the curing of undercoat paints and improve solvent resistance. The amount of the low-temperature curing catalyst added is 1.0 to 2.5 parts by weight per 100 parts by weight of the paint. If it is less than 1.0 part by weight, the effect is small;
If the amount exceeds 1 part by weight, the storage stability becomes poor, which is not preferable.

In addition to the above-mentioned resin mixture composition, the undercoat composition of the present invention includes titanium dioxide, barium sulfate, calcium carbonate,
Talc, kaolin, bentonite, carbon black,
60 to 140 parts by weight of one or more conductive carbon and other various constitutional and coloring pigments may be used as necessary, based on 100 parts by weight of the solid matter of the resin mixture composition. can.

The undercoating paint of the present invention further contains one type of additive such as silicone and non-silicon surfactants, ultraviolet absorbers, antioxidants, light stabilizers, antistatic agents, conductive agents, and acrylic and amide waxes. Alternatively, two or more types can be used as necessary.

The solvent in the undercoat and the thinner used to adjust the coating viscosity must be selected taking into account the solubility of the resin mixture composition and wet-on-wet painting workability, but cellosolve acetate, xylene, toluene, butanol and Two or more solvents such as methyl isobutyl ketone are mainly used.

The undercoat paint of the present invention can be manufactured by the same method as conventional undercoat paints. That is, the pigment and a part of the resin face (resin solution) are mixed, dispersed using a sand mill, super mill, attritor, ball mill, or four-mill mill, etc., and then the remainder of the resin face and a solvent are added as appropriate, and finally, An undercoat paint is obtained by adding a low-temperature curing catalyst to the mixture and stirring uniformly.

There are no particular restrictions on the topcoat paint, but the following are conventionally used for car body copper plates: (1) aminoalkyd resin-based 1-coat, 1-bake type solid color, (2) aminoacrylic resin-based 2-coat, 1-bake type solid color, (3) Aminoacrylic resin-based one-foot, one-bake metallic color, (4) aminoacrylic resin-based two-coat, one-bake metallic color, etc. can be used as is as a top coat for PBT resin molded products.

The coating method is to first wash the PBT resin molded product with an organic solvent, then apply the undercoat of the present invention using an air atomization coating machine or an electrostatic air atomization coating machine, and then apply the above-mentioned coating on top using a wet-on-wet method. The top coat is applied using an air atomizer or an electrostatic air atomizer, and baked at 120 to 160° C. for 80 minutes to harden.

In addition, when applying the top coat with an electrostatic air atomizer or rotary electrostatic atomizer, since PBT resin does not have conductivity, it is possible to apply the top coat by incorporating conductive carbon into the undercoat. Paint application efficiency can be improved.

In the above description, the PBT resin molded product may be other than automobile parts, and other molded products can be coated in the same manner as described above.

(Effects of the Invention) As described above, the undercoat paint composition of the present invention has an epoxy equivalent of 2 to 4 in 100 parts by weight of the solid matter of the resin mixture composition.
00-8. 60 to 80 weight of δ00 epoxy resin, M
Contains 20 to 40 parts by weight of a melamine resin with an ST of 15 or less, and 1.0 to 2 parts by weight of a medium-low temperature curing catalyst per 100 parts by weight of the paint.
．． Because the composition contains 5 parts by weight, when painting PBT resin molded products, the undercoat and conventional topcoat can be applied wet-on-wet, which greatly simplifies the painting process and doubles production efficiency. Painting costs can be significantly reduced, including the reduction in personnel. In addition, the finished appearance of the coating film applied to the PBT resin molded product is the same as that of conventional products, and is the same as that of the steel plate for car bodies, resulting in a coating film with excellent appearance and quality. [Example] Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In the examples, parts indicate parts by weight, and parts by weight indicate parts by weight.

Examples 1-8. Comparative Examples 1 to IIs The resin mixture composition, low-temperature curing catalyst, and pigment composition shown in Table 1 were blended at the indicated blending ratio of 1009, thoroughly kneaded in a disilver, and then kneaded for 1 hour in a paint shaker. 28 types of mixed materials were obtained (however, the low-temperature curing catalyst was added after kneading in a paint shaker).
. To these kneaded materials, 60 parts of toluene, 20 parts of ethyl acetate
A mixed solvent consisting of 20 parts of H-butanol and 20 parts of H-butanol was added thereto, and the coating viscosity was adjusted to 20 seconds (20° C.) using a Ford Cobbuna 4 to produce undercoat paints for Examples 1 to 8 and Comparative Examples 1 to 15.

Details of each component shown in Table 1 are as follows.

Epoxy resin varnish I: Ebifu) 1009 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name, epoxy equivalent: 2,400
~8,800) 40% solution.

Epoxy resin varnish ■: Epicoat 10o7 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name, epoxy equivalent 1.750
~2.100) 50% solution.

Epoxy resin varnish I: Ebicoat 10o4 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name, epoxy equivalent: 900-1
000) 50 chi solution.

Epoxy resin varnish ■: Epicoat 1001 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name, epoxy equivalent: 450-5
00) 60% solution.

Oil-free polyester resin varnish: Glycerin 5.
0 parts, neopentyl glycol 22.0 parts, adipic acid 18.4 parts and isophthalic acid 22.9 parts at 280°C.
A polyester resin varnish was subjected to an esterification reaction for 6 hours, and after cooling, 86.7 parts of a mixed solvent of xylene and methyl isobutyl ketone (1:1) was added to make the solid content 60 parts.

Butylated melamine resin varnish I Newpan 128 (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name) 60% solution, MST4-1
0゜Butylated melamine resin varnish ■Newpan 208E (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name) 60% solution, Mi9T8
~15° Butylated melamine resin varnish I Newpan 208B (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name) 50 inches, MST 40 or more.

Low temperature curing catalyst: BYK-Catalyst 450 (manufactured by Sheep Mallinckrodt International, trade name)
.

Titanium dioxide: JR-602 (manufactured by Teikoku Kako Co., Ltd., trade name).

Yellow iron oxide: Mapico Yellow I, LXLO (Titan Kogyo)
Co., Ltd., product name).

Barium sulfur: Precipitated Burr 5S-50 (manufactured by Sakai Chemical Co., Ltd., trade name).

Next, a coating test, a coating film test, and a paint test were conducted on each of the above-mentioned undercoat paints according to the methods described below.

(Painting test) s omx a omx PBT resin with a thickness of 31111 (
After cleaning the board (manufactured by Toshiku Co., Ltd.) for 60 seconds with 1.1.1-trichloroethane vapor (74°C), apply the above-mentioned undercoat paint using an air atomization coating machine to a dry film thickness of 1.
Paint to a thickness of 5 to 20 μm, leave for 1 minute, then apply wet-on-wet amino alkyd resin 1 coat 1 bake type solid color "Melami AX Red" (
(manufactured by Nippon Oil & Fats Co., Ltd., product name) using an air atomization coating machine.
The coating was applied to a dry film thickness of 80 to 85 μm, and the standard baking conditions were 140° C. for 80 minutes to dry. Based on the results of this coating test, the wet-on-wet coating workability of the undercoat and topcoat paints was evaluated. The obtained results are also listed in Table 1.

The evaluation criteria are O (excellent), Δ (fair), × (poor), and xx (very poor).

(Coating film test) - The PBT resin test board obtained in the above process (however, for the test board for solvent resistance test, only the undercoat paint film) was visually inspected under the test conditions shown below for visual finish appearance, -sub-adhesion , moisture resistance, secondary adhesion after the moisture resistance test, and solvent resistance tests were conducted. The baking conditions for the test plates for adhesion and solvent resistance tests were 120°C for 80 minutes, 140°C for 80 minutes, and 160°C for 80 minutes, taking into account the temperature range in the actual painting line. It was set as a standard. The obtained results are also listed in Table 1.

The finished appearance was visually evaluated by visually evaluating the finish properties (smoothness, clarity, gloss, color mottling, etc.) of the topcoat film. Evaluation criteria are O (excellent), Δ (acceptable), × (poor), xx
(very poor).

-Secondary adhesion and moisture resistance test The secondary adhesion after the moisture test was determined by attaching cellophane tape to 100 squares where 11 lines were drawn vertically and horizontally at 1U intervals on the painted surface using a cutter knife.- Evaluation was made by counting the number of squares that remained between the material and the undercoat, or between the undercoat and the topcoat, and remained when they were removed. The evaluation standard is “0/100 (
0, excellent), 99/1oo~80/,. . (Δ, acceptable), 7
9/100~50/100 (x, poor), 49/100~
0/100 (xx, extremely poor).

Moisture resistance was evaluated by leaving the sample in a humidity tester adjusted to a temperature of 50±1° C. and a relative humidity of 98% or higher for 240 hours, taking it out, leaving it at room temperature for 1 hour, and then evaluating the degree of blistering. The evaluation criteria are ○ (excellent), Δ (fair), × (poor), xx (
significantly inferior).

Solvent resistance was evaluated from the state of dissolution by rubbing the primer coated surface 10 times with gauze sufficiently impregnated with cellosolve acetate. The evaluation criteria are O (excellent), Δ (fair), × (poor), and XX (remarkably poor).

(Paint test) Storage stability was evaluated by leaving the paint in an atmosphere of 50±1°C for 120 hours and evaluating the rate of increase in viscosity from the initial stage to that time. The evaluation criteria are ○ (excellent), Δ (acceptable), and × (poor).

As is clear from the test results in Table 1, the paints of Examples 1 to 8 satisfied all test items, but the paints of Comparative Examples 1 to 8
3 (conventional 2-foot, 2-bake type undercoat paint), regardless of the type of melamine resin, was extremely poor in wet-on-wet painting workability, which is important, and a satisfactory paint film could not be obtained, so we conducted a paint film test. has been omitted. Comparative example 4~
6 (type of epoxy resin) is when epoxy resins with different epoxy equivalents are used, and even if a low-temperature curing catalyst is added, the smaller the epoxy equivalent, the poorer the wet-on-wet painting workability, and the workability of wet-on-wet coating is inferior regardless of the epoxy equivalent. Solvent resistance was also poor. Comparative Example 7 (type of melamine resin) uses a melamine resin with a large MST, and the wet-on-wet coating workability was poor. Comparative Examples 8 to 10 (epoxy resin/melamine resin ratio) are cases where the ratio of epoxy resin and melamine resin is different, and outside a certain range of ratios, wet-on-wet painting workability was poor and solvent resistance was poor in all cases. . In Comparative Examples 11 to 15 (amount of low-temperature curing catalyst), the amount of low-temperature curing catalyst was too small and too large, and the former had poor solvent resistance, and the latter had poor storage stability and moisture resistance.

Patent applicant: Nissan Motor Co., Ltd. Same applicant: Nippon Oil & Fats Co., Ltd.

Claims (1)

[Claims] 1. 60 to 60 parts of epoxy resin having an epoxy equivalent of 2,400 to 3,300 in 100 parts by weight of solids of the resin mixed composition
80 parts by weight, 20 to 40 parts by weight of melamine resin with a mineral spirit tolerance of 15 or less, and paint 1
An undercoat coating composition for polybutylene terephthalate resin, characterized in that it contains 1.0 to 2.5 parts by weight of a low-temperature curing catalyst in 0.00 parts by weight.