JPS6236072B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating composition particularly excellent in scratch resistance and transparency. In general, plastic products such as polycarbonate, polymethyl methacrylate, polystyrene, polyvinyl chloride, ABS resin, etc. are used in large quantities due to their advantages such as lightness, ease of processing, and impact resistance. The use of plastic products in areas where abrasion resistance is required, as the low viscosity of plastic products can cause them to be easily scratched, seriously impairing their appearance or significantly impairing the inherent transparency of the resin. making it difficult. Therefore, the present invention aims to increase the surface hardness of such a base material to provide a transparent surface that will not be scratched by friction caused by sand grains or emery paper, and thereby to maintain the surface quality over a long period of time. The purpose is to maintain gloss. Conventionally, coating materials that increase the surface hardness of plastic substrates include organic materials such as melamine resin and high-hardness acrylic resin, inorganic materials such as silica applied to the surface of the substrate by vapor deposition, and Organic-inorganic materials typified by polyalkylsiloxanes obtained by hydrolyzing organic silane compounds are known. Among these organic materials, although they have a sand-falling hardness that allows sand grains to drop with an impact, they do not have sufficient strength in abrasion tests such as the emery test and the eraser test, which are considered to be more practical tests. On the other hand, although inorganic materials and organic-inorganic materials have sufficient hardness, they are not practical due to high material or molding costs. Therefore, the inventors of the present invention have arrived at the present invention as a result of various attempts to add inorganic materials to impart wear resistance to organic materials, which have good sand-fall hardness and sufficient economic efficiency. . In other words, inorganic materials that provide wear resistance must have high hardness, have a small difference in refractive index with organic materials in order to be used as a transparent coating material, and must be small enough that they do not scatter visible light themselves. Therefore, an alcohol dispersion of silica colloid was used. If the average particle size of the colloid is set to about 1000 Å, which is much smaller than the lowest wavelength of visible light, almost no scattering of visible light should occur, but in reality, silica colloids with an average particle size of 400 Å or more If silica colloid is used, the transparency of the coating film will be significantly reduced, so the average particle size of the silica colloid is 400 Å or less, preferably 50 to 250 Å. In addition, as an organic material, there are requirements that the silica colloid be well dispersed, that the difference in refractive index with silica be small, that it be highly transparent, have high film-forming ability, and be crosslinkable by heat or light. After examining various materials to meet these requirements, we found that butyral resin was the most suitable. Therefore, a coating liquid was obtained by mixing an alcohol dispersion of silica colloid and an organic solvent solution of Braral resin. However, in order to cure butyral resin sufficiently by heat alone within an economically practical heating time, it is necessary to apply a temperature of 180°C or higher, and at this temperature, most plastic substrates cannot be cured. softens or flows, and at this temperature, the butyral resin itself partially undergoes thermal decomposition, causing the coating film to turn yellow, reducing its transparency and
There is a major problem in that it spoils the appearance. Furthermore, it is economically unfavorable that high temperatures are required for heat curing. It is generally known that an acid catalyst is used to promote heat curing of butyral resin. Therefore, if an inorganic acid such as phosphoric acid is used, the coating solution will gel in a short time at room temperature, and the transparency of the coating film coated using this solution will also be low. However, when the catalyst of general formula (A) was used, gelation of the solution did not occur for more than three months, and a highly transparent coating film was obtained. (R is H ₁ or a C ₁ to C ₄ alkyl group, n is 0 or 1) What is very surprising is that when this type of catalyst is used, the coating film becomes smaller than when other catalysts are added. The resistance to abrasion caused by emery paper and eraser has improved dramatically, and its performance has improved to the point where it approaches that of inorganic coating materials. This fact has not been well known until now, and is an essentially important discovery in order to economically obtain a coating film that is transparent and has high scratch resistance. It is not clear what kind of reactions occur due to the addition of this type of catalyst, and which of them contributes to improved scratch resistance, but the scratch resistance of coatings that do not contain any silica colloid is The properties of the coating film that does not contain silica colloid do not change even when other catalysts or this type of catalyst are used; in other words, it is limited to curing of butyral resin only. Since there is no difference in the performance of the two types of catalysts when the catalyst is added, some type of bond is created between the terminal silanol group of the silica colloid and the hydroxyl group of the butyral resin, and the inorganic material silica It is expected that the colloid strongly binds to the butyral resin, which is an organic binder, and that this improves the abrasion resistance of the entire coating film. Such catalysts of general formula (a) include benzenesulfonic acid, P-toluenesulfonic acid, P-ethylbenzenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 1-butanesulfonic acid, etc. This is an example. If such a catalyst is used, it is expected that a strong bond will be formed between the butyral resin and the silica colloid to improve the scratch resistance, but if this is the case, the mixing ratio of the butyral resin and the silica colloid will also be affected. Naturally, it should be limited by the ratio of the number of reactive functional groups of both. In particular, the silanol groups of silica cause the hydroxyl groups of the butyral resin to be consumed simply by the cross-linking reaction between polymer chains, so apart from slightly lowering the abrasion resistance of the coating, there is no significant effect on the transparency or other aspects of the coating. However, when the number of silanol groups in silica becomes larger than the number of hydroxyl groups in butyral resin, a dehydration reaction occurs between the silica colloids that cannot bond to the butyral resin, and the silica particle size increases and the transparency of the coating film becomes remarkable. decreases rapidly. This range is 20 to 95 wt% of butyral resin and 80 to 5 wt% of silica colloid. The range in which the coating film has the highest abrasion resistance means that almost all of the silica colloid is bonded to the butyral resin, and there is an appropriate surplus of hydroxyl groups in the butyral resin, and these bind between the polymer chains of the butyral resin, which is the binder. In the case of crosslinking at density, this range is 30 to 85 wt% of butyral resin and 70 to 15 wt% of silica colloid.
It is. Butyral resin, silica colloid, and a curing catalyst represented by general formula (A) are sufficient for the performance required for general wear-resistant substrate treatment. However, with this composition alone, the sand-falling hardness is inferior to both glass and other coating compositions. Therefore, when a methylolated melamine resin in which some or all of the methylol groups are alkyl etherified is added to the above composition, the sand-falling hardness is also improved. At this time, in order to obtain a practically sufficient sand hardness, the amount of alkyl etherified methylol melamine added must be 0.1 to 0.1 to butyral resin in weight ratio.
In order to obtain a sand-falling hardness of 4/1, and even comparable to that of glass, the butyral resin must be 0.3 to 4/1, a sand-falling hardness comparable to that of glass, but without impairing the transparency of the coating film. The ratio is preferably 0.3 to 2.5/1 to the butyral resin. Furthermore, whether or not alkyl etherified methylol melamine is added, the amount of catalyst added must be 0.5 to 5 wt% based on the total organic solid content to obtain sufficient coating strength, and sufficient transparency. In order to provide the same, it is preferably 1.5 to 3 wt%. Next, the solvent or powder for dissolving or dispersing these solids is not particularly limited as long as it does not cause significant harm to the base material, but for example, methanol, ethanol, isopropanol, n-butanol, etc. It is preferable to use lower alcohols, cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, etc. alone or in combination. The amount of solvent or dispersant used can be selected appropriately depending on the required film thickness, coating method, etc.
Preferably, the butyral resin concentration in the solution is 5 to 15% by weight. The butyral composition thus obtained can be applied to a substrate by a conventional coating method such as spray coating, dip coating, brush coating, roller coating, or spinner coating.
After applying the coating composition to the substrate in this way, the temperature range of 80 to 150 °C, more preferably 100 °C
By heating and curing at a temperature range of ~130°C for 15 minutes to 2 hours, more preferably 30 minutes to 1 hour, a coating film with good surface hardness and transparency can be obtained. The thickness of the coating film is preferably 2 to 20 microns, more preferably 10 to 15 microns. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. Note that parts in the examples indicate parts by weight. The hardness was evaluated according to the following JIS standards. Sand hardness JIS T-8147, Pencil hardness JIS K-
5400, Eraser hardness A wear test was conducted under the following conditions, and the difference in scattering rate (haze difference) before and after the test was expressed in %. Load 500g/cm ² Slide distance 4cm Slide speed 35 reciprocations/min Number of slides 500
Type of eraser: Plastic eraser containing fine quartz powder (RABBIT, manufactured by CO.LTD, No. 1010) In addition, in order to investigate the wear resistance against materials even harder than erasers, we conducted a friction test using #1500SiC emery paper. It is called the emery hardness test. Examples 1 to 5, Comparative Examples 1 to 2 100 parts of isopropanol dispersion of silica colloid with an average particle size of 110 Å (silica content 30 wt%) and butyral resin (Sekisui Chemical's Eslex BM-
1) n-butanol solution (resin content 10wt)
%) and 70 parts of isopropanol, P-toluenesulfonic acid was added in various proportions in the range of 0 to 10 wt% based on the resin. The physical properties of the resulting coating films were compared by coating them on a polycarbonate plate by dipping to a dry film thickness of 10 μm and then heating and drying them at 130° C. for 1 hour. The results are shown in Table 1.

[Table] However, each value indicates the difference between the value (%) of the amount of haze measured with a haze meter after the end of each test and the value (%) of the amount of haze measured with a haze meter before the start of each test. The appearance represents the amount of haze before the start of the test. Examples 6 to 9, Comparative Example 3 Using an isopropanol dispersion of silica colloid with an average particle size of 150 Å (silica content 30 wt%) and an n-butanol solution of butyral resin (Sekisui Chemical Eslex BM-5), Silica-butyral stock solutions with different silica to resin ratios were prepared. At this time, the amount of n-butanol was adjusted so that the concentration of butyral resin in the solution was 6.5 wt%. A composition obtained by adding 1.5 wt% methanesulfonic acid to the butyral resin into this mixture was placed on a 3 mm thick polymethyl methacrylate plate so that the film thickness after drying was 10 μm. After coating by spinner method, the physical properties of the coating films obtained by heating and drying at 110° C. for 1 hour were compared. The results are shown in Table 2.

[Table] Examples 10 to 11, Comparative Example 4 Isopropanol dispersion of silica colloid with average particle diameters of 110 Å, 200 Å, and 500 Å (silica content
Benzenesulfonic acid or ethanesulfonic acid 2.5wt% to resin
The resulting composition was applied onto a 3 mm thick polymethyl methacrylic board so that the film thickness after drying was 10 μm, and then heated and dried at 110°C for 1 hour. The physical properties of the resulting coating film were compared. did. The results are shown in Table 3.

[Table] Examples 12 to 16, Comparative Example 5 100 parts of n-butanol dispersion of silica colloid with an average particle size of 120 Å (silica content 30 wt%),
Butyral resin (Sekisui Chemical Eslex BM-
1) Isopropanol solution (resin content 20wt)
%) to 150 parts of the mixture, butyl etherified methylol melamine resin (Super Betsukamine J820 manufactured by Nippon Reichhold - solid content 60 wt%) was divided into various types at a weight ratio of 0.1 to 4/1 to the butyral resin. and added to obtain a mixture. N-butanol was added to this mixture so that the solution concentration of butyral resin was 7 wt%, and further, P-
A coating composition was obtained by adding toluenesulfonic acid or phosphoric acid in an amount of 2.5 wt% based on the total organic solid content. After coating this composition on a 3mm thick polycarbonate plate so that the film thickness after drying is 10μ,
The physical properties of the coating films obtained by heating and drying at 130°C for 1 hour were compared. The results are shown in Table 4.

【table】

Claims (1)

[Scope of Claims] 1. 0.5 to 5 wt% of the general formula (A) based on the organic solvent solution of butyral resin, the alcohol dispersion of silica colloid, and the total organic solid content. (R is H or a _C1 - _C4 alkyl group, n is 0 or 1) A coating composition comprising a mixture with a curing catalyst represented by: 2. The coating composition according to claim 1, wherein the amount of butyral resin in the solid content contained in the mixture is 20 to 95 wt%, and the amount of silica is 80 to 5 wt%. 3. The coating composition according to claim 1 or 2, wherein the mixture further contains a crosslinking agent. 4. Claim 3, wherein the crosslinking agent is a methylolmelamine resin in which a part or all of the methylol groups are alkyl etherified, and the amount added is in the range of 0.1 to 4/1 to the butyral resin.
Coating composition as described in . 5. Claim 1, wherein the average particle size of the silica colloid in the alcohol dispersion is 50 to 400 Å.
The coating composition according to item 2, item 3, or item 4.