JPS6135220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of polycarbonate molded articles. More specifically, the present invention relates to a surface treatment method for improving the surface hardness, scratch resistance, and ultraviolet deterioration resistance of polycarbonate molded articles.

Plastic has excellent moldability, light weight, and impact resistance, but on the other hand, it has drawbacks such as insufficient surface hardness and easy scratching, poor solvent resistance, and poor UV deterioration resistance when used outdoors. have.

In order to improve these drawbacks, after applying a paint with a binder made of a polymer containing 50% by weight or more of methyl methacrylate as a primer, a paint mainly consisting of a hydrolyzate of tetraalkoxysilane and alkyltrialkoxysilane was applied. There is a method of painting (see Japanese Patent Publication No. 50-39096), a method of applying a paint mainly containing methyl methacrylate, and then applying a paint mainly containing a hydrolyzate of organotrialkoxysilane after heat treatment (see Japanese Patent Publication No. 1983-39096). Showa 52-
136565 (see Publication No. 136565) have been proposed, but all of them have the disadvantage that they have poor weather resistance for outdoor use, and the adhesion of the paint film is lost after 300 to 500 hours of Sunshine Weather Meter irradiation, so they are not satisfactory. It wasn't something.

As a result of extensive research into improving the surface properties of polycarbonate molded products, which have excellent weather resistance and scratch resistance, the present inventor found that the surface properties were significantly improved by a two-step coating method using the specific paint described below. The present invention was completed based on the discovery that the weather resistance was also improved.

That is, the present invention provides polyalkyl acrylate or polyalkyl acrylate on the surface of a polycarbonate molded product.
A homopolymer of methacrylate with a weight average molecular weight of 10,000 to 50,000.
25wt% and UV absorber to the polymer
A paint containing 5wt% or more is applied, and after heat treatment, partial hydration of alkyltrialkoxysilane represented by the general formula R′Si(OR) ₃ (where R and R′ are alkyl groups having 1 to 4 carbon atoms) is applied. This is a method for surface treatment of polycarbonate molded articles, which is characterized by applying and curing a paint whose main component is a decomposition condensation product.

Examples of polycarbonate molded articles used in the present invention include molded articles of polycarbonate resins such as aromatic polycarbonates derived from bisphenol A and phosgene and aliphatic polycarbonates such as diethylene glycol bisallyl carbonate.

In the present invention, the paint to be first applied is made of a homopolymer of polyalkyl acrylate or polyalkyl methacrylate, and specific examples include polymethyl (meth)acrylate, polyethyl (meth)acrylate, polypropyl (meth)acrylate, etc.
Examples include acrylate, polybutyl (meth)acrylate, polyisobutyl (meth)acrylate, poly2-ethylhexyl (meth)acrylate, polyhydroxyethyl (meth)acrylate, and particularly preferred is a homopolymer of polymethylmethacrylate. .

The molecular weight of these polymers is the weight average molecular weight.
Must be in the range of 10,000 to 50,000. The reason for this is that the coefficient of thermal expansion of the polycarbonate molded product is larger than that of the cured film of the second paint, and this large difference means that the stress of peeling at the interface is large due to shrinkage and expansion, and this peeling stress It is considered that a condition for maintaining adhesion for a long period of time is to provide the first paint with the ability to absorb and reduce the amount of adhesion. For this purpose, it is considered that the molecular weight of the polymer used here is within the above range, thereby making it possible to absorb the peeling stress. If the molecular weight is less than 10,000, the scratch resistance will be low even if a second coating is applied;
If it exceeds 50,000, adhesion decreases and peeling occurs during long-term weather resistance tests, so both are not preferred.

Examples of the ultraviolet absorbent used in the present invention include benzophenone type, benzotriazole type, and salicylate type. Specific examples include 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,4-hydroxybenzophenone, and 2-hydroxybenzophenone.
Hydroxy-4-dodecyloxybenzophenone,
2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-4′-
octoxyphenyl)benzotriazole, p-
Examples include t-butylphenyl salicylate and phenyl salicylate.

In the present invention, the above-mentioned polymer is used after being dissolved in a suitable solvent. Examples of solvents include organic carboxylic acid-based, ester-based, ketone-based, alcohol-based,
One or more of ether, halogenated hydrocarbon, and aromatic hydrocarbon solvents are used. When using these solvents, it is necessary to select a solvent that is a good solvent for the ultraviolet absorber, dissolves the above-mentioned polymer, and does not impair the appearance of the polycarbonate molded product. or,
The concentration of the polymer contained in the solvent is preferably 5 to 25 wt%. If it is less than 5wt%, sufficient adhesion cannot be obtained and weather resistance is also poor. On the other hand, if it exceeds 25 wt%, a good coating film will not be obtained and the appearance will be poor, both of which are undesirable. The concentration of the ultraviolet absorber added is 5 wt% or more based on the polymer, more preferably 10 to 40 wt%, and if it is less than 5 wt%, sufficient weather resistance cannot be obtained. Moreover, if it exceeds 40wt%, the appearance of the coating film will be poor.

The second applied paint has the general formula R′Si(OR) ₃
(However, R and R' are alkyl groups having 1 to 4 carbon atoms.) The main component is a partially hydrolyzed condensate of alkyltrialkoxysilane.

Specific examples of the alkyltrialkoxysilane represented by the above general formula include methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, isopropyltrimethoxysilane, and methyltributoxysilane. The hydrolysis reaction of these silane monomers is carried out by adding a trace amount of acid and 1.5 to 5 molar equivalents (per mole of silane monomer) of water as a reaction catalyst. At this time, it is also possible to add a lower alcohol in order to alleviate the temperature rise due to heat generated during the hydrolysis reaction.

The formulation of the second paint using the partially hydrolyzed condensate of the alkyltrialkoxysilane obtained in this way uses quaternary ammonium as the curing catalyst.
Compounds, alkali metal hydroxides, organic acid salts of alkali metals, diaza-bicyclo-alkenes and their salts, etc. can be used, and formic acid,
Add an organic acid such as acetic acid, propionic acid, oxalic acid, etc. to a weakly acidic pH of 4 to 7, more preferably 5 to 5.
It is desirable to adjust within the range of 6. Further, in order to further improve the surface properties, it is also preferable to add a surface smoothing agent, an antioxidant, and a heat stabilizer.

As described above, the present invention imparts scratch resistance to the surface of a polycarbonate molded product by selecting the type, molecular weight, concentration, and amount of the ultraviolet absorber added in the first paint, and the siloxane in the second paint. Its performance is such that the adhesiveness of the cured film can be maintained even after 1500 hours of Sunshine Weathermeter irradiation. In order to further improve the accuracy of this coating film performance, it is necessary to select favorable conditions for the drying conditions of the first paint and the application and curing conditions of the second paint. As a method of applying the first paint and the second paint, methods such as dip, spray, spin, and flow can be adopted. The drying conditions for the first paint are 60 to 130
C. for 5 minutes or more is preferred. Further, the curing conditions for the second coating material depend on the heat resistance of the polycarbonate molded article, but it is generally appropriate to carry out the curing by heating at 90 to 130° C. for 10 minutes to 10 hours.

The present invention will be specifically described below with reference to Examples. All parts in the examples represent parts by weight.

Example 1 Weight average molecular weight (W) as the first paint
A solution of 15 parts of polymethyl methacrylate (23,000) dissolved in 10 parts of acetone, 30 parts of methyl ethyl ketone, 15 parts of methyl isobutyl ketone, 26 parts of isobutyl alcohol, and 4 parts of an ultraviolet absorber (2-hydroxy-4-octoxybenzophenone) was prepared. used.
As the second paint, 30 parts of a partially hydrolyzed condensate of methyltriethoxysilane was mixed with 50 parts of ethanol and acetic acid.
10 parts of catalyst and other components dissolved in 10 parts of catalyst were used. A 2 mm thick polycarbonate sheet was used as the plastic base material, and the first paint was dip coated on this sheet and heat treated at 100° C. for 10 minutes.
The polycarbonate thus obtained was colorless and transparent and had a polymethyl methacrylate layer of 4 to 6 microns. The adhesion between this first paint and the base polycarbonate sheet was determined using cellophane tape (Nitto Electric Industries Co., Ltd.'s Nitto Cellophane Adhesive Tape No. 1).
29) 100/10 in the goban eye peeling test
It was 0. Further, a second coating material was dip coated on this sheet and heat-cured at 120° C. for 60 minutes. The sheet thus obtained was colorless and transparent and had a cured film layer of 4 to 6 microns without any cracks in the coating. The adhesion between the cured film layer of the second paint and the coating layer of the first paint was 100/100 in a cross-cut peeling test using cellophane tape. In addition, taper wear test (wear ring CS-
The Δ haze% before and after (10F, 500g load, 100 cycles) was 3%, and there was no change even after immersion in 60°C hot water for 30 days. In addition, thermal cycle test (80℃
There was no change after 10 cycles of ×8Hrs→-20°C×16Hrs (1 cycle). On the other hand, Sunshine weather meter irradiation for accelerated weathering tests
Even after 2000 hours, the adhesion remained 100/100, the appearance was colorless and transparent, the yellowing characteristic of polycarbonate was prevented, and no cracks were observed.

Example 2 Weight average molecular weight (W) as the first paint
50,000 polymethyl methacrylate dissolved in 10 parts of acetone, 35 parts of methyl ethyl ketone, 18 parts of methyl isobutyl ketone, 24 parts of isobutyl alcohol, and 3 parts of ultraviolet absorber (2-hydroxy-4-octoxybenzophenone). used.
This was dip coated onto a polycarbonate sheet and heat treated at 100°C for 10 minutes. The sheet was colorless and transparent and had a 4-6 micron layer of polymethyl methacrylate. A second coating material similar to that in Example-1 was applied to this and cured. The performance of this coating film was 100/100 in terms of adhesion between the first paint and the substrate and between the second paint and the first paint. or,
ΔHaze% before and after taper wear test
%) was 2.5%. There was no change even after 30 days of immersion in 60°C warm water. There was no change even after 10 cycles of cooling and heating. On the other hand, even after 1500 hours of sunshine weather meter irradiation in the accelerated weathering test, the adhesion remained at 100/100 and there was no change in appearance.

Example 3 Same as Example-1, the ultraviolet absorber in the first paint was replaced with benzotriazole-based 2-(2'-hydroxy-4'-n-octoxyphenyl)benzoto
Everything else was the same as in Example-1 except that lyazole was replaced and the amount added was 4 parts. This result shows that the adhesion between the first paint and the polycarbonate base material and between the second paint and the first paint is both 100/10.
It was 0. Further, the ΔHaze% before and after the taper wear test was 3.2%. 60℃ warm water immersion for 30 days,
There was no change in the temperature during 10 cycles of the heating and cooling cycle test. On the other hand, even after 1500 hours of sunshine in weather meter irradiation, the adhesion remained at 100/100 and there was no change in appearance.

Comparative Example 1 A polycarbonate sheet was coated with the same second paint as in Example-1 without being coated with the first paint, and then heat-cured. The adhesion between the coating film of this second paint and the polycarbonate was 0/100 in the goban peel test.

Comparative Example 2 A polycarbonate sheet was coated in the same manner as in Example-1 except that no ultraviolet absorber was added to the first paint. The adhesion was 100/100 in the goban peel test, but the adhesion was 50/10 after 600 hours of Sunshine Weather Meter irradiation.
It was 0.

Comparative Example 3 In Example-1, the amount of ultraviolet absorber added in the first paint was changed to 0.5 part, and the difference from Example-1 was
The same procedure as in Example 1 was carried out except that 3.5 times the amount was replaced with isobutyl alcohol. The adhesion was 100/100 in the goban peel test, but the adhesion was 8 after 1000 hours of Sunshine Weather Meter irradiation.
It was 0/100.

Comparative Example 4 A polycarbonate sheet was coated in the same manner as in Example-2, except that 10 parts of polymethyl methacrylate having a weight average molecular weight (W) of 100,000 was used as the first paint. The adhesion was 100/100 in the goblin peel test, but cracks appeared in the cured film after 1000 hours of sunshine weather meter irradiation, and the adhesion was 90/100 after 1200 hours of irradiation.

Comparative Example 5 A polycarbonate sheet was coated in the same manner as in Example 2, except that 10 parts of polymethyl methacrylate with a weight average molecular weight (W) of 100,000 was used as the first paint in Example 2, and no ultraviolet absorber was added. I coated it. Adhesion is 100/ in the goban peel test.
However, the adhesion was 10/100 after 600 hours of sunshine weather meter irradiation.

Comparative Example 6 A polycarbonate sheet was coated with a formulation using 3 parts of the first paint, polymethyl methacrylate, in Example-2. The polymethyl methacrylate layer in this case was 1-1.5 microns.
A second paint was applied to this to form a cured film layer. This adhesion was 100/100 between the first paint film and the polycarbonate sheet as a base material, but it was 50/100 to 50/100 in a cross-cut peeling test after coating with the second paint. It was 90/100.

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Claims (1)

[Claims] 1. On the surface of the polycarbonate molded product, a homopolymer of polyalkyl acrylate or polyalkyl methacrylate with a weight average molecular weight of
A coating containing 5 to 25 wt% of a polymer of 10,000 to 50,000 and at least 5 wt% of an ultraviolet absorber to the polymer is applied, and after heat treatment, it is further coated with the general formula R'Si.
(OR) ₃ (wherein R and R' are alkyl groups having 1 to 4 carbon atoms) A polycarbonate characterized by applying and curing a coating material whose main component is a partially hydrolyzed condensate of alkyltrialkoxysilane. Surface treatment method for molded products.