JPS636098B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves forming and coating an undercoat layer with good adhesion on the surface of a base material such as a plastic product or a paint-coated product thereof, and then applying a butyral resin-silica colloid thereon. The present invention relates to a surface hardness improvement method for improving surface hardness by coating a butyral resin-alkyl etherified methylolmelamine-silica colloid-based paint. Generally 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. This makes it difficult to use plastic products in areas where abrasion resistance is required. Therefore, in the present invention, the surface hardness of such a base material is increased to provide a transparent surface that is not scratched by friction caused by sand grains or emery paper, and thereby to maintain the gloss of the surface for a long time. It is intended to maintain. The present inventors previously investigated various paints for increasing surface hardness, and found that (A) butyral resin, (B) silica colloid, or (A) butyral resin, (B)
It was discovered and proposed that a paint containing colloidal silica and (C)alkyl etherified methylolmelamine as the main components provides excellent surface hardness. However, although such paints have very good adhesion to substrates such as glass, they tend to have poor adhesion to plastics such as polycarbonate and polymethyl methacrylate. The present inventors have developed a method that allows the above-mentioned coating material with excellent surface hardness to be used even on substrates that have poor adhesion to such butyral resin-silica colloid or butyral resin-alkyl etherified methylolmelamine-silica colloid based coatings. The present invention was achieved as a result of intensive research into methods for improving the adhesion. That is, the present invention provides a mixture of a polyhydric alcohol with a molecular weight of 100 to 8000 and a compound having at least two or more isocyanate groups in the molecule, or
100-8000 polyhydric alcohol and at least 2 in the molecule
more than one phenol, malonic acid diester, ε-
A mixture with a compound having an isocyanate group protected with an isocyanate group protecting agent such as caprolactam, or a solution of these diluted with a solvent such as tetrahydrofuran, ethyl acetate, or toluene, or a polyhydric alcohol with a molecular weight of 100 to 8000, and a molecule A mixture of a preliminary reaction product with a compound having at least two isocyanate groups in the molecule and a compound having at least two isocyanate groups in the molecule, or a polyhydric alcohol with a molecular weight of 100 to 8000 and a compound having at least two isocyanate groups in the molecule. A preliminary reaction product with a compound having two or more isocyanate groups and a compound having at least two or more isocyanate groups in the molecule protected with an isocyanate group protecting agent such as phenol, malonic acid diester, ε-caprolactam, etc. After coating the surface of the base material using a polyurethane primer such as a mixture or a solution of these diluted with a solvent such as tetrahydrofuran, ethyl acetate, or toluene, butyral resin is further applied on the layer formed by the undercoat components. This is a surface hardness improvement method by applying a component mainly containing - silica colloid or butyral resin - silica colloid - alkyl etherified methylol melamine. The base material to be coated in the present invention includes:
In particular, plastics such as polycarbonate, polymethyl methacrylate, and ABS resin, and their paint-coated products. In particular, the undercoat layer forming component and butyral resin used in the present invention - silica colloid or butyral resin -
Coatings based on silica colloid-alkyl etherified methylolmelamine have excellent transparency, so they can be used to protect the surfaces of transparent plastics such as polycarbonate and polymethyl methacrylate by providing wear resistance. It is effective for Among the undercoat layer forming components used in the present invention, the polyhydric alcohol is generally known as polyether polyol or polyester polyol, and the molecular weight thereof is 100 to 8,000, preferably 500 to 3,000. In addition, the isocyanate components include diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, 1.3
-Bis(isocyanatomethyl)cyclohexane, polymethylene polyphenylene isocyanate, etc. and these isocyanate groups can be converted into phenols, malonic acid diester, ε-caprolactam,
It is protected with oximes, etc. These polyhydric alcohols and isocyanate-containing compounds used in the present invention are already abundantly available as polyols for adhesives or paints, or as isocyanates or pre-reacted products thereof. . However, these general-purpose polyurethane resins for paints and adhesives are not only compatible with polymethyl methacrylate but also with resins such as polycarbonate, for which it is generally difficult to find a primer with excellent durability. What is the best way to make a top coat of a butyral resin-silica colloid system or a butyral resin-silica colloid-alkyl etherified methylol melamine system, which has almost no adhesion, adhere to the substrate without impairing its transparency? It is surprising that adhesiveness can be maintained for a long time even under harsh environments. In the present invention, the composition for forming an undercoat layer is generally a liquid, and if it has a low viscosity, it can be used without being diluted in any way. However, since they are often high viscosity liquids, it is preferable to apply them as a solution dissolved in a suitable solvent. Such a solvent is not particularly limited as long as it does not contain amino groups, hydroxyl groups, etc. that easily react with the isocyanate component in the undercoat layer forming composition. In particular, even if the solvent partially dissolves the surface of the substrate, it can be used as long as it does not harm the transparency and smoothness of the surface of the substrate after the undercoat layer has been applied and dried. Examples of such solvents include tetrahydrofuran, toluene, xylene, ethyl acetate, and butyl acetate, and these can be used alone or in combination depending on the type of substrate. It is also possible to add additives such as antioxidants and ultraviolet absorbers to this composition for forming an undercoat layer, if necessary. The copolymer solution for forming an undercoat layer thus obtained can be applied to the substrate by a conventional application method such as spinner coating, dip coating, or spray coating. Also, the thickness of the undercoat layer is 0.1
A range of ~5μ is preferred. After applying this composition for forming an undercoat layer to a base material, it is dried at a predetermined temperature, and after the surface is in a state where no finger marks are left even when touched with a finger,
A top coat paint of butyral resin-silica colloid system or butyral resin-alkyl etherified methylolmelamine-silica colloid system is applied to improve surface hardness. The butyral resin-silica colloid paint used in the present invention consists of a solution of butyral resin in an organic solvent that is compatible with alcohols and an average particle size of 50 to 400 Å.
Alcohol dispersion of silica colloid and the amount of solids contained in the resin mixture is 20 to 95 wt.
%, an organic sulfonic acid such as p-toluenesulfonic acid is added as a catalyst to a mixture in which the amount of silica is 80 to 5 wt% based on the resin. In addition, butyral resin-silica colloid-alkyl etherified methylol melamine is a mixture of the above-mentioned butyral resin and silica colloid, in which a methylolated melamine resin in which some or all of the methylol groups are alkyl etherified is added to the mixture. for butyral resin of
A composition obtained by adding an organic sulfonic acid such as p-toluenesulfonic acid in an amount of 0.1 to 4/1 and further adding 0.5 to 5 wt% of an organic sulfonic acid such as p-toluenesulfonic acid based on the total amount of butyral resin and alkyl etherified methylol melamine. shows. It is also possible to add small amounts of additives such as surface smoothing agents, antistatic agents, viscosity modifiers, antioxidants, and ultraviolet absorbers to these top coating compositions. The top coat paint prepared in this manner is applied to the surface of the substrate coated with the undercoat layer by a conventional coating method such as spinner coating, dipping coating, spray coating, roller coating, etc. at a temperature of 80 to 150°C. By heating and curing for 15 minutes to 2 hours, a coating film with good surface hardness and excellent adhesion to the substrate can be obtained. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited by these Examples. Note that parts in the examples indicate parts by weight. Adhesion was evaluated using the crosshatch test, in which 100 cuts of 1 mm square were made on the paint film with a steel knife, reaching the base material, and then cellophane tape (manufactured by Sekisui Chemical Co., Ltd.) was sufficiently applied on top of the cuts. After adhesion, the extent to which the coating film remains on the substrate when the cellophane tape is strongly peeled off in an upward 90° direction is expressed as "number of squares remaining without peeling/100". Ta. In addition, the surface hardness was evaluated in accordance with JIS T-8147 for falling sand hardness. Eraser hardness was measured by a wear test under the following conditions.
The difference in scattering rate (haze difference) before and after the test is expressed in %. Load: 500 g/cm ² Slide distance: 4 cm Slide speed: 35 reciprocations/min Number of slides: 500 times Type of eraser Plastic eraser containing fine quartz powder (RABBIT, manufactured by CO.LTD, No. 1010) Example 1 Undercoat layer solution and topcoat layer composition was prepared as follows. (1) Preparation of undercoat layer solution One-component polyurethane primer (manufactured by Nippon Polyurethane Industries Co., Ltd., Nipporan 2302, solid content
An undercoat layer solution was obtained by dissolving 10 parts of 35 wt% MEK solution in 165 parts of tetrahydrofuran. (2) Preparation of topcoat layer composition 100 parts of an isopropanol dispersion of silica colloid with an average particle size of 120 Å (silica content 30 wt%) and n-butanol of butyral resin (Eslex BM-1 manufactured by Sekisui Chemical Co., Ltd.) An overcoat layer composition was obtained by adding 2.5 wt % of p-toluenesulfonic acid based on the resin into a mixture of 300 parts of solution (resin content 10 wt %) and 70 parts of isopropanol. First, the undercoat layer solution prepared in (1) above was applied with a spinner to a 3 mm thick polycarbonate sheet whose surface had been washed with a neutral detergent, thoroughly washed with water, and air-dried, and then dried by heating at 130°C for 30 minutes in a hot air dryer.
Next, the topcoat layer solution prepared in (2) above was applied using a spinner to the polycarbonate plate coated with the undercoat layer obtained in this way, and then dried in a hot air dryer for 130 minutes.
It was heated and cured at ℃ for 1 hour. The thus obtained polycarbonate plate was transparent and smooth, had a haze rate of 0.8%, and a visible light transmittance of 90%. The difference between the haze rate after the sand drop test and the haze rate before the test was 23.2%, and the difference between the haze rate after the eraser test and the haze rate before the test was 5.7%. Also,
In evaluating the adhesion of the paint film, no peeling was observed in the crosshatch test, which was good at 100/100. This high adhesion makes this polycarbonate board
Even after being immersed in water at 100°C for 2 hours and ethyl alcohol at room temperature for 2 weeks, the properties were maintained, and the crosshatch test after these tests was also good at 100/100. Comparative Example 1 A polycarbonate sheet coated only with the top coat solution was obtained in the same manner as in Example 1, except that the undercoat solution was not applied. The appearance hardness of this polycarbonate sheet was similar to that of Example 1, but the evaluation of adhesion was 0/100. Also,
When this polycarbonate sheet was soaked in water at 100°C for 1 hour, part of the paint film naturally peeled off from the polycarbonate base material. Example 2 An undercoat layer solution and topcoat layer composition were prepared as follows. (1) Preparation of undercoat layer solution 10 parts of two-component polyurethane primer (Nitsuporan 3105, manufactured by Nippon Polyurethane Industries Co., Ltd.) and 1.5 parts of two-component polyurethane primer (Nitsuporan 3004, manufactured by Nippon Polyurethane Industries, Ltd.) and cured. An undercoating solution was obtained by dissolving 1.5 parts of the agent (Coronate L manufactured by Nippon Polyurethane Industries, Ltd.) in 500 parts of tetrahydrofuran. (2) Preparation of topcoat layer composition A topcoat layer composition was obtained in the same manner as in Example 1. A polycarbonate hard coat board was obtained in the same manner as in Example 1. The polycarbonate plate obtained in this way is transparent and smooth with a haze rate of
The visible light transmittance was 89.5%. Further, the increase in haze rate after the sand drop test was 22.8%, and the increase in haze rate after the eraser test was 6.2%.
In addition, in evaluating the adhesion of the coating film, no peeling was observed in the crosshatch test, which was good at 100/100.
This high adhesion makes this polycarbonate board
It was maintained even after being immersed in water at 100°C for 2 hours and in ethyl alcohol for 2 weeks at room temperature, and the crosshatch test after these tests was also good at 100/100. Examples 3-5 Undercoat solutions and topcoat layer compositions were prepared as follows. (1) Preparation of undercoat layer solution 10 parts of one-component polyurethane primer (Nitsuporan 2304, manufactured by Nippon Polyurethane Industry Co., Ltd.) was dissolved in 165 parts of tetrahydrofuran to obtain an undercoat layer solution. (2) Preparation of topcoat layer composition An isopropanol dispersion of silica colloid with an average particle size of 120 Å (silica content 30 wt%) 100
A mixture of 150 parts of n-butanol solution (resin content 20 wt%) of butyral resin (Eslex BM-1 manufactured by Sekisui Chemical Co., Ltd.) was mixed with butyl etherified methylol melamine resin (Super Betsukamine J820 manufactured by Nippon Reichhold - solid content content).
60wt%) to butyral resin 0.5 to 2.5/
Mixtures were obtained by adding at various ratios within a range of 1. Isopropanol was added to this mixture so that the solution concentration of the butyral resin was 7 wt %, and p-toluenesulfonic acid was further added at 2.5 wt % based on the total organic solid content to obtain an overcoat layer composition. A polycarbonate hard coat board was obtained in the same manner as in Example 1. The physical properties of each of these polycarbonate plates were compared and shown in Table 1. Comparative Example 2 A polycarbonate plate coated with only an overcoat layer was obtained in the same manner as in Example 4 except that the coating treatment of the undercoat layer solution was not performed. The physical properties of this polycarbonate plate are also shown in Table 1. 【table】

Claims (1)

[Claims] 1. When applying a surface hardness improving coating containing butyral resin and silica colloid to the surface of a substrate,
A surface hardness improvement method characterized by pre-treating the surface of a base material with a polyurethane primer. 2. The method according to claim 1, wherein the surface hardness improving paint is a paint containing a mixture of a butyral resin solution in an organic solvent and a silica colloid alcohol dispersion. 3. The method of claim 2, wherein the surface hardness improving coating further comprises an organic solvent solution of alkyl etherified methylolmelamine. 4. The method according to claim 1, characterized in that the base material is transparent plastic.