JPS58176225A - Painting of ethylene/vinyl acetate copolymer-containing molding - Google Patents

Abstract

PURPOSE:To obtain a paint film excellent in adhesive strength, by forming hydroxyl groups on the surface of the titled molding and applying an isocyanato group-containing synthetic resin paint. CONSTITUTION:Hydroxyl groups are formed on the surface of a synthetic resin molding containing at least 40wt% ethylene/vinyl acetate copolymer, and then an isocyanato group-containing synthetic resin paint is applied to the surface. The molding consists essentially of an ethylene/vinyl acetate copolymer, and excels in flexibility and impact resistance and therefore elimination of the coating step of a primer becomes possible, with consequent cost down. A beautiful paint film good in water resistance and oil resistance and excellent in adhesive strength can be obtained, so that the painted product is useful as parts for electric appliances and devices or cars.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention The present invention relates to a method for coating a molded article containing an ethylene-vinyl acetate copolymer. More specifically, the ethylene-vinyl acetate copolymer is characterized in that hydroxyl groups are generated on the surface of the synthetic resin molded product containing the ethylene-vinyl acetate copolymer, and a synthetic resin coating having an isocyanate group is applied to the surface. Regarding the coating method for polymer-containing molded articles,
The purpose is to provide a coating material with excellent adhesion strength.

BACKGROUND OF THE INVENTION In recent years, synthetic resins or compositions thereof with excellent mechanical properties such as flexibility and impact resistance have been used for interior and exterior parts in the automobile industry and the like. Among these synthetic resins, ethylene-vinyl acetate copolymer not only has excellent processability and freedom of molded shape, but also is lightweight and inexpensive, so it is often included in its composition. It is used as a molded product.

However, in the case of an ethylene-vinyl acetate copolymer or a molded article containing the copolymer as a main component, the surface thereof is not only easily damaged but also easily stained. Furthermore, as automobiles become more fashionable, there is a demand for aesthetically pleasing surfaces to be coated with synthetic resin paints that are beautiful and have excellent durability, such as urethane paints.

However, ethylene-vinyl acetate copolymer has poor adhesion to synthetic resin paints such as urethane paints, so synthetic resins may be applied to the surface of molded products made of ethylene-vinyl acetate copolymer or compositions containing the copolymer. It is not possible to obtain a satisfactorily applied coating of paint.

As a method for satisfactorily applying a synthetic resin paint to the surface of a molded product of an ethylene monovinyl acetate copolymer or a composition containing the copolymer, a primer is applied to the surface of the molded product in advance, and a layer of the primer is coated on the surface of the molded product. Various methods have been developed for applying synthetic resin paint to the surface of. However, this method not only adds one step to the coating process of applying the primer, but also increases the cost because the primer itself is quite expensive. parable,
Even if a coated product with excellent adhesion and a beautiful surface is obtained by using this primer, the adhesion mechanism is not essentially based on chemical bonding as in the present invention, so it is not water resistant like car parts. In fields where oil resistance and oil resistance (gasoline resistance) are desired, it is possible to obtain a coated product with practically sufficient adhesion strength. As a result of various searches to obtain coatings coated with synthetic resin paints on molded articles of ethylene-vinyl acetate copolymers or compositions containing this copolymer with excellent It has been discovered that a coated product with excellent adhesion strength can be obtained by generating hydroxyl groups on the surface of a synthetic resin molded product containing at least 40% by weight and applying a synthetic resin coating having isocyanate groups to the surface,
We have arrived at the present invention.

Effects of the Invention According to the method of the present invention, the following effects (characteristics) are exhibited, so that it can be further used for the following purposes.

(1) Since the molded product is essentially an ethylene-vinyl acetate copolymer, it is flexible and has excellent mechanical properties such as impact resistance.

(2) Costs increase because the step of applying a primer is not necessary.

(3) Good water resistance and oil resistance.

(4) Not only is the adhesion strength excellent, but the coated product is also beautiful.

(5) Since it has the above-mentioned effects, it is promising as a part for electrical equipment and automobiles.

The reason why the coated product obtained by the present invention exhibits these effects is that the hydroxyl groups generated on the surface of the molded product and the isocyanate groups of the synthetic resin paint undergo a chemical reaction, resulting in a coated molded product with a strongly adhered coating film. The adhesion mechanism is essentially different from that obtained by applying a primer.

M Detailed Description of the Invention (A) Ethylene-vinyl acetate copolymer The ethylene-vinyl acetate copolymer used in the present invention is produced by copolymerizing ethylene and vinyl acetate using a free radical generator as a catalyst ( () and usually contains 0.5 to 40% by weight (preferably 1 to 30% by weight) of vinyl acetate.
If it is less than 5''X clear, the adhesion strength of the resulting molded product will be poor. On the other hand, if it exceeds 40% by weight, it will be too soft to be used as a molded product.

In addition, its melt index (JIS K-67
60, the temperature is 190'O and the load is 2.
Measured under the condition of 16 kf (hereinafter referred to as 1'M, I, J)
is generally 0.05 to 100,! i'/10 minutes (preferably 0.1 to 50,9/10 minutes). M,■
.

If it is less than o, osg/lo, moldability is poor.

On the other hand, if it exceeds 100 g/10 minutes, mechanical properties, thermal properties, etc. will be significantly deteriorated.

(B) Production of molded product In producing the molded product of the present invention, although it can be obtained by molding the ethylene-vinyl acetate copolymer, at least 40% by weight of ethylene-vinyl acetate copolymer is added.
A composition of a vinyl acetate copolymer and an olefin polymer described below may also be used. The olefin polymers include ethylene homopolymers, propylene homopolymers, random or block copolymers of ethylene and propylene, ethylene and/or propylene and other α-polymers having at most 7 carbon atoms. Copolymer with olefin (α
- The copolymerization ratio of olefin is at most 20% by weight). The molecular weight of these olefin polymers is generally from 20,000 to 1,000,000, preferably from 20,000 to 500,000, and particularly preferably from 50,000 to 300,000.

These olefin polymers are obtained by using a catalyst system (so-called Ziegler catalyst) obtained from a transition metal compound and an organoaluminium compound, and by supporting a chromium compound (for example, chromium oxide) on a carrier (for example, silica). They are obtained by homopolymerization or copolymerization of olefins using catalyst systems (so-called Phillips catalysts) or radical initiators (for example organic peroxides).

Furthermore, the present invention also includes modified polyolefins obtained by graft polymerizing these olefin polymers with a compound having at least one double bond (for example, an unsaturated carboxylic acid, a basic carboxylic acid, a vinyl silane compound). It will be done.

The production methods for these olefin polymers and modified polyolefins are well known.

These olefin polymers and modified polyolefins may be used alone or in combination of two or more. Furthermore, two or more of these olefin polymers and modified polyolefins may be used as a resin blend in any proportion.

In addition, depending on the intended use of the molded product, stabilizers against oxygen, heat and ultraviolet rays, metal deterioration inhibitors,
Additives such as flame retardants, colorants, electrical property modifiers, fillers, antistatic agents, lubricants, processability modifiers, and tack modifiers do not impair the properties of the compositions of the present invention. It may be blended as long as it is within the range.

The composition may be prepared by triblending using mixers commonly used in the olefinic polymer industry such as Henschel mixers, Banbury mixers, Niegoos, roll mills, and screw extruders. It can also be produced by melt-kneading using a mixer such as a blender. At this time, a more uniform composition can be obtained by triblending in advance and further melt-kneading the resulting mixture.

Various molded products may be produced from the composition thus produced by processing methods commonly used in the field of olefin polymers, such as extrusion molding, injection molding, and press molding.

At this time, it is necessary to carry out the process at a temperature higher than the temperature at which the composition obtained as described above melts. However, if the process is carried out at a considerably high temperature, the ethylene-vinyl acetate copolymer or olefin polymer (if used) may deteriorate, so it is necessary to carry out the process at a temperature below which decomposition occurs. Of course.

From the above, melt kneading and molding are usually 160 to 3
Implemented at 00'O.

(C) Surface Treatment In the present invention, in order to generate hydroxyl groups on the surface of the molded product obtained as described above, alcohol or a mixture of alcohol and water is added to caustic soda or caustic potash or the general formula [(1) It can be obtained by treatment using a solution in which alcoholade represented by the formula] is dissolved.

M(OR) (1) (In formula 11, M is sodium or potassium, and R is a hydrocarbon group having at most 6 carbon atoms. Among these alcoholades, R has 1 or 2 carbon atoms. Alcorado is preferable.

Moreover, as the alcohol, methyl alcohol and ethyl alcohol are preferable.

Alcoholic solutions of sodium methylate and sodium ethylate are preferred in the practice of this invention. By using an alkaline solution of caustic soda dissolved in alcohol or a mixed solution of alcohol and water,
The above-mentioned alcohol solution of Alcolade has a great treatment effect. Furthermore, by adding small amounts of hydrocarbon solvents such as toluene and xylene to these solutions, the treatment effect can be increased, allowing treatment with short rti+.

When carrying out this treatment, the treatment temperature is usually room temperature (2
0°C) to 50°C.

The generation of hydroxyl groups on the surface of the molded product by these treatments can be easily confirmed by measuring the surface infrared absorption of the molded product.

(D) Coating method The object of the present invention is achieved by uniformly coating the surface of the molded product obtained as described above with a paint having an isocyanate group to a thickness of 1 to 500 microns (when dry). can be achieved. The application method is not a special method; it is sufficient to apply a method that is generally used on the surface of metal or synthetic resin molded objects. Typical methods include applying with a spray gun, and applying with a brush. Examples include a coating method using a roll coater, and a coating method using a roll coater.

According to the coating method of the present invention, for example, in the case of urethane coating, it is possible to obtain a molded article that not only has excellent adhesion and gloss on the coated surface, but also has excellent weather resistance and gasoline resistance. It can be applied to automobile parts, etc.

It is also suitable for metallizing, laminating different materials, etc. on the coated film having isocyanate groups.

EXAMPLES EXAMPLES AND COMPARATIVE EXAMPLES The present invention will be explained in more detail with reference to Examples below.

In addition, in the Examples and Comparative Examples, the paint film peeling strength test was performed by cutting out a strip of 10 rIrM in width from the test piece, forcibly peeling off a portion of the paint film from one end of the test piece, and then peeling off the plastic film. Using a tensile tester used in tensile tests, etc., the tensile speed was 50 #/min and the peel angle was 18
The coating film was peeled off under the conditions of 0°C and 20C, and the peeling strength of the coating film at that time (.9/ow) was determined. Furthermore, gasoline resistance is confirmed by using an NT cutter at an angle of 30 mm on the coating surface.
A cross cut was made at a temperature of 20°C, and each test piece was immersed in gasoline at room temperature (about 20°C) for 24 hours, and changes in the coating surface were observed.

For water resistance, cross-cuts were made in the same way as the gasoline resistance test pieces, and after each test piece was immersed in 40°C lukewarm water for 240 hours, changes in the coating surface were observed. Furthermore, in the cellophane tape peeling test, 100 cross-shaped incisions were made on the specimen, a cellophane tape (manufactured by Chiban Co., Ltd.) was completely adhered to the sample using finger pressure, and the seven-cut tape was peeled off. , observed the results.

In the Examples and Comparative Examples, the ethylene-vinyl acetate copolymer, treatment liquid, etc. used had the following physical properties or composition ratios.

[Ethylene-vinyl acetate copolymer]

Vinyl acetate as ethylene-vinyl acetate copolymer
Weight% of ethylene-vinyl acetate copolymer [: M
, I, 20.17/10 min, hereinafter referred to as "EVA (]) I" and an ethylene-vinyl acetate copolymer containing 15% by weight of vinyl acetate [M, I, 12 g 710 min, hereinafter referred to as "EVA (2) ” was used.

[Low density polyethylene]

Density is o as low density polyethylene, 9x7g/crn
Low density polyethylene (M, 1.7.2g71
0 minutes, hereinafter referred to as "LDPE") was used.

[Processing liquid]

As the treatment liquid, a 15-th methyl alcohol solution of sodium methylate [hereinafter referred to as "treatment agent"], a 28-elb methyl alcohol solution of sodium methylate [hereinafter referred to as "
Processing solution (called August), 15% of sodium ethylate
Ethyl alcohol solution [hereinafter referred to as processing solution (0 month)],
15% methyl alcohol solution of caustic soda [hereinafter referred to as "treatment liquid (D)"], a mixed solution of 15% methyl alcohol of caustic soda and water [volume ratio 50:50] [:hereinafter referred to as 1 treatment liquid (E)'' A 154 methyl alcohol solution (containing 5% by weight of toluene) of sodium methylate (hereinafter referred to as "treatment liquid (F)") was used.

Examples 1 to 10, Comparative Example IEVA (1) (Examples 1 to 9, Comparative Example 1)
and 70 parts by weight + 7) EVA (2) and 30 parts by weight of LDPE (Example 10) were each injection molded using a 5 oz. injection molding machine at a resin temperature of 2.
00”C), flat plate (12ox15omm, thickness 21+
0++) was produced. Each of the obtained flat plates was immersed in the treatment liquid shown in Table 1 at the temperature shown in Table 1 for the time shown in Table 1. After soaking, rinse with running water for about 2 minutes, then soak in gear open at 70'O temperature for 30 minutes.
Drying was performed for minutes. After drying, a urethane paint (trade name: Heiurethane 5000HF, manufactured by Nihon Yushi Co., Ltd.) was applied uniformly to a thickness of about 80 microns using a spray gun for a paint film peeling test. In other tests, coatings were applied to a thickness of 30 microns. Each of the resulting applications was incubated at a temperature of 70°C in an open gear for 4 hours.
It was cured by heating for 0 minutes. After curing, it was left to stand at room temperature for 24 hours or more, and a cross-cut peel test and coating peel strength were measured. The results obtained are shown in Table 1. Note that the test pieces of Examples 1 to 10 were tested for gasoline resistance and water resistance.

In either case, no change was observed in the coating film.

Comparative Example 2 A test piece produced in the same manner as in Example 1 was treated with a toluene solution containing 5 parts of a treated product obtained by treating an ethylene-vinyl acetate copolymer with maleic anhydride as a primer, and the thickness was It was applied evenly to a thickness of 20 microns (when dry). After setting for 20 minutes at room temperature, urethane paint was applied in the same manner as in Example 1. Then, drying was performed in the same manner as in Example 1. When this coating was subjected to a stripping test, it did not peel off at all, and the coating peel strength was 450! It was 9/crn.

When a water resistance test was conducted, blistering occurred on the paint film, and when a gasoline resistance test was conducted, cross-cut areas were peeled off.

Patent applicant: Showa Denko Co., Ltd. Agent: Patent attorney Sei Kikuchi

Claims (1)

[Claims] At least 40% by weight of ethylene-vinyl acetate copolymer
1. A method for coating a molded article containing an ethylene-vinyl acetate copolymer, which comprises generating hydroxyl groups on the surface of the molded article containing an ethylene-vinyl acetate copolymer, and applying a synthetic resin coating having an isocyanate group to the surface.