JPS60248257A - Manufacture of plastic molded article - Google Patents

Abstract

PURPOSE:To obtain a coated film having excellent adhesiveness and satisfactory abrasion resistance due to high hardness by coating a resin which can be cross- linked and cured with ultraviolet rays on the surface of a plastic molded article, and irradiating ultraviolet rays on the surface while increasing gradually the intensity of light on the irradiated surface. CONSTITUTION:A resin (e.g., dipentaerythritol tetraacrylate) which can be cross- linked and cured with ultraviolet rays is coated on the surface of a plastic molded article of methacrylic resin, etc. to obtain a molded article 1 which is irradiated with ultraviolet rays to crosslink and cure said resin. In the manufacture of said plastic molded article, the ultraviolet rays are irradiated so that the intensity of light on the irradiated surface may be gradually increased. For example, high pressure mercury-arc lamps 2 and 2', 3 and 3', and 4 and 4' are used, and the distance between the high pressure mercury-arc lamp and the irradiated surface is gradually reduced. Consequently, the coated film is closely adhered to the base material of the molded article, and satisfactory abrasion resistance can be shown.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a plastic molded article having a crosslinked cured coating film with excellent adhesion to a plastic substrate.

[Technical background of the invention and its problems] In recent years, in place of solvent-based paints and inks, ultraviolet curable paints, ink hard coating agents, etc. have been widely used in terms of productivity and economic efficiency improvement due to quick drying properties. However, these crosslinked coatings cured by ultraviolet rays have a high polymerization shrinkage rate,
In general, the adhesion to the substrate is lower than that of solvent-based materials.

In particular, polyfunctional polyester (meth)acrylate, polyol (meth)acrylate), etc. are used as coating components.
In the field of using urethane (meth)acrylate etc. as a crosslinked cured resin material to significantly improve the surface hardness and scratch resistance of plastic molded products, there is a strong desire to improve the adhesion of crosslinked cured resin coatings. If the adhesion of the cross-linked cured resin film to the base material of the plastic molded product is poor, the cross-linked cured resin film may peel off from the surface of the molded product due to light impact, thermal cycles, moisture, etc., which may affect the performance of the product. This causes the value to decrease.

Until now, several proposals have been made as a method to eliminate the above-mentioned drawbacks, for example,
In order to improve the adhesion between the substrate (plastic) and the coating, JP-A No. 3072 discloses a method of subjecting the substrate to a specific pretreatment in the step before crosslinking and curing, and JP-A-50-12227.
In order to achieve the same objective, Japanese Patent No. 9 discloses a method in which active energy rays are irradiated from the side opposite to the coated side of a crosslinked cured resin material. However, the former method not only complicates the production process because it requires pretreatment when applying the crosslinked cured resin material to the base material.
Problems such as poor coating film smoothness tend to occur, and since the latter method involves irradiating actinic rays from one side, the target substrate must be colorless or transparent. It cannot be said to be a versatile method in terms of practicality, such as the need for limited materials.

Also, JP-A-51-20280 and JP-A-51-
Publication No. 20917 describes a method for obtaining a plastic molded article that does not easily retain crosslinking strain even when a crosslinked cured film is formed, but these methods significantly restrict the flow of molten resin during injection molding. This method has drawbacks such as difficulty in process control because it requires the use of a mold that is similar to the conventional injection molding method and special injection molding conditions.

[Object of the Invention] The object of the present invention is to eliminate the drawbacks mentioned above, namely, to provide a cross-linked cured product that exhibits excellent adhesion to the base material of plastic molded products, as well as high hardness and good scratch resistance. An object of the present invention is to provide a method for manufacturing a plastic molded product having a resin coating on its surface.

[Structure 1 of the Invention] The method of manufacturing a plastic molded article of the present invention comprises applying an ultraviolet crosslinking curable resin to the surface of the plastic molding, and then irradiating the resin with ultraviolet rays to crosslink and harden the resin. The method is characterized in that the ultraviolet rays are irradiated so as to sequentially increase the light intensity of the irradiated surface.

The plastic molded product of the present invention may be any known plastic molded product, and the shape of the plastic molded product may be any shape depending on its purpose, use, etc. For example, the shape may be plate-like, circular, or other shapes. Specific examples of this plastic molded product include plates, containers, instrument covers, lens covers, optical materials such as lenses, audio equipment, recording materials, etc. made of acrylic resin, styrene resin, polycarbonate, and the like.

Examples of the crosslinked curable resin used in the method of the present invention include formulas synthesized from adipic acid/trimethylolpropane/acrylic acid, succinic acid/trimethylolethane/acrylic acid, cepatic acid/pentaerythritol/methacrylic acid, etc. (■): (OH,,)n, R(ill:H2), iR (wherein, R
may be the same or different, at least three of them represent an acryloyloxy group and/or a methacryloyloxy group, and the remainder represents a hydrogen atom, a hydroxyl group, an amine group, or an alkyl group, and! +1 ””n
4 and J-m4 may be the same or different, and each is an integer of O to 2, and X is an integer of 1 to 1O. Polyether (meth)acrylate synthesized from 6-hexandriol/propylene oxide/acrylic acid, trimethylolpropane/ethylene oxide/methacrylic acid, trimethylolpropane/propylene oxide/acrylic acid, etc.; triethylene glycol diacrylate, neopentyl Glycol diacrylate, 1.4-
Butanediol diacrylate, 2-ethylhexyl acrylate, tetrahydrofurfuryl acrylate, 2
-Hydroxyethyl methacrylate, 1,4-butanedio-Jremonometaacrylate, ethylcarpitol acrylate, trimethylolethane triacrylate,
Monools or polyols such as pentaerythritol triacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate (
Meth)acrylate; Epoxy (meth) synthesized from diglycidyl etherified bisphenol A/acrylic acid, triglycidyl etherified glycerin/acrylic acid, etc.
Acrylates, urethane (meth)acrylates such as 2.13-)lylene diisocyanate diacrylate, isophorone diisocyanate dimethacrylate, etc.
Or oligomer etc. are mentioned.

Among these compounds, 30% by weight or more of compounds having three or more (meth)acryloyloxy groups in one molecule.
- and 70% by weight or less of a compound having one or two (meth)acryloyloxy groups in one molecule, the mixture having an average molecular weight per (meth)acryloyloxy group of 300 or less. It is particularly preferable that the adhesiveness between the crosslinked resin film and the plasma polymerized film is high and the plastic molded article of the present invention with excellent scratch resistance can be obtained.

In addition, among the above compounds having three or more (meth)acryloyloxy groups in one molecule, those having the general formula (): In the formula (1), n is an integer of 1 to 4, and X is at least 1 and clearly 3 or more. is the formula: CH2=C-C0O-R2- (wherein, R1 represents a hydrogen atom or a methyl group, and R2 is a single bond, an alkylene group having 1 to 8 carbon atoms, or an alkylene group having 1 to 8 carbon atoms)
Represents a polyoxyalkylene group having ~8 alkylene groups, with the remainder having 1 to 8 carbon atoms.
8 alkyl group, hydroxyl group, amine 7 group, formula: (-OR3~
H (wherein R3 may be the same or different and each represents an alkylene group having 1 to 8 carbon atoms,
is a positive integer): (OR4
) OH (in the formula, R6 and p have the same meanings as above)] A compound represented by the following is particularly preferable because it has excellent curability by ultraviolet irradiation in air. Specific examples of such compounds include dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate,
Examples include dipentaerythritol hexamethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol pentamethacrylate, tripentaerythritol hexaacrylate, tripentaerythritol heptacrylate, and the like.

1- When curing the crosslinked curable resin using ultraviolet rays, it may be possible to cure the resin by irradiating it for a long time even without a photopolymerization initiator. For example, benzoin ethyl ether, benzoin isopropyl ether, acetoin, butyroin, toluoin, benzyl, benzyl dimethyl ketal, jetoxyacetophenone, 4'-isopropyl-
A photopolymerization initiator such as 2-hydroxy-2-methylpropiophenone, l-hydroxycyclohexylphenylketone, benzophenone, p-chlorobenzophenone, Michler's ketone, etc. is added to the crosslinked curable resin.

As a method for applying the crosslinked curable resin to the base material of the plastic molded product, for example, spray coating, brush coating, cast coating, dip coating, etc. may be applied, and the surface smoothness of the coated surface may be adjusted as necessary. may be adjusted. The thickness of the coating layer is usually 0.5 gm or more, preferably in the range of 1 to 100 pL.

In the method of the present invention, when irradiating ultraviolet rays to a plastic molded product having a coating layer of crosslinked curable resin on the surface, actinic rays are irradiated so that the optical hardness of the irradiated surface increases sequentially to crosslink the crosslinked curable resin layer. Let it harden.

There are various methods for sequentially increasing the light intensity of active light on the irradiated surface of plastic molded product L. For example, as shown in Figure 1, using lamps with the same output, the distance between the lamp and the irradiated surface is increased. Examples include a method in which the lamps are successively made smaller, or a method in which the lamps are placed on a carrier (such as a conveyor) and passed through an ultraviolet furnace in which lamps of smaller to larger output are lined up.

The ultraviolet light source used in the present invention is preferably ultraviolet light with a wavelength of 1000 to 8000 A emitted from a light source such as a xenon lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, or an ultra-high-pressure mercury lamp.

EXAMPLES Below, the present invention will be explained in more detail by giving Examples and Comparative Examples.

[Examples of the Invention] The effects of the present invention will be explained in more detail below with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, "parts" represent "parts by weight."

Wow ILILL 10 parts dipentaerythritol hexaacrylate, 20 parts dipentaerythritol pentaacrylate, 4 parts dipentaerythritol tetraacrylate, 6 parts ethylcarpitol acrylate, 40 parts isopropyl alcohol, 20 parts methyl ethyl ketone, 2-hydroxy-2-methyl Q.
It was immersed at a speed of cm/sec and pulled up to form a coating layer.

Next, after leaving it for 5 minutes, 5 parts w of a high-pressure mercury lamp (Iwasaki Electric ■
A plastic molded article having a crosslinked and cured coating according to the present invention was obtained by irradiating ultraviolet rays from both sides at a conveyor speed of 3 m/min using a lamp arrangement as shown in FIG. In addition, as a light source, a pair of high-pressure mercury lamps (2,2°),
The intensity of the ultraviolet rays at the irradiation surfaces of (3, 3') and (4, 4') is 400 W/L, respectively, with a wavelength of around 3135 nm.
m2.800W/+a2, 1200W/m2.

In order to demonstrate the excellent effects of the plastic molded article according to the manufacturing method of the present invention, tests were conducted to evaluate the pencil hardness and hot water adhesion of the obtained molded article. Regarding hardness, JIS
A pencil hardness test was conducted on K-5400, and adhesion was determined by immersing the material in hot water at 80°C for 1 hour after cross-cutting, thoroughly wiping off water droplets on the surface, returning the material to room temperature, and attaching Sellotape to the sample. A peel test was conducted by crimping and peeling upward rapidly.

The results are shown in Table 1.

■■1 With the light source arranged as shown in Figure 2, (2,2°)
, (3,3°) and (4,4°) The UV intensity at the irradiation surface of the lamp is 800 W/ for all three pairs of light with a wavelength of 385 nm.
The evaluation test was conducted in the same manner as in Example 1 except that +w2 was used. The results are shown in Table 1.

1 Table 1 [Effects of the Invention 1 As detailed above, according to the manufacturing method of the present invention, the plastic molded product base material and the coating are extremely tightly adhered to each other, even when used in fields with severe usage conditions. No peeling of the coating occurs. Furthermore, the adhesion of this surface coating allows the plastic molded product to exhibit high hardness and excellent scratch resistance. Therefore, the plastic molded product obtained by the manufacturing method of the present invention can be applied to fields where the usage environment is harsh, such as head lens covers and window materials, and its practical value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the arrangement 2 of irradiation lamps according to the method of the present invention, and FIG. 2 is a diagram showing the arrangement of irradiation lamps according to a conventional example. (1)...Irradiation treated molded product (2), (2)', (3), (3)', (4)
, (4) '...High-pressure mercury lamp Figure 1 Figure 2

Claims (1)

[Claims] 1. In a method of manufacturing a plastic molded product in which an ultraviolet crosslinkable curable resin is applied to the surface of a plastic molded product and the resin is crosslinked and cured by irradiation with ultraviolet rays, the ultraviolet rays are applied so as to sequentially increase the light intensity on the irradiated surface. A method for producing a plastic molded product, characterized by irradiating the product with