JP2010017644A - Method for forming surface-protective coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a cured surface-protective coating film, which has suitable surface hardness and is excellent in heat resistance, weather resistance and adhesiveness, on a plastic base material, wherein the method has productivity and cost effectiveness in combination. <P>SOLUTION: The method for forming the surface-protective coating film includes the steps of: applying a coating composition containing thermally curable silicone and a solvent to the surface of the plastic base material; drying the coating film of the applied coating composition; and heating/curing the dried coating film by using the latent heat of condensation of the vapor generated when an inactive liquid fluorine compound is heated. A coating liquid containing (A) organosilane triol and/or the partial condensate thereof, (B) colloidal silica and (C) the solvent can be used as the coating composition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a surface protective coating, and more particularly to a method for forming a cured silicone coating for surface protection on the surface of a substrate made of plastic.

  Plastics are used in various fields because they are lightweight, strong and easy to process. However, it has the above-mentioned advantages, but has disadvantages such as low surface hardness, inferior heat resistance, weather resistance, and solvent resistance.

  Various attempts have been made in the past in order to eliminate such drawbacks, and the surface hardness, heat resistance, weather resistance, solvent resistance, etc. can be improved by coating the plastic surface. Compositions have been developed. Among these, a coating solution of a silicone composition containing colloidal silica has been proposed as one having extremely excellent physical properties of the coating (see, for example, Patent Document 1). However, in the surface coating treatment using this composition, the heating time required for curing the coating is as long as 1 hour, and it may be difficult to use from the viewpoint of productivity.

  In addition, such a surface protection coating solution is diluted with a solvent in order to maintain good coating properties, and in order to maintain a good appearance of the resulting coating, the environment in the coating process (temperature Management of humidity and cleanliness) is important. In addition, the cost related to the management and maintenance of the coating environment occupies a large part of the cost of forming the surface protective coating, so environmental management is required from the viewpoint of cost reduction and further downsizing of the equipment. Therefore, it is required to shorten the time required for the coating process as much as possible.

  That is, in order to keep the appearance of the film good, it is important to strictly control the temperature, humidity and cleanliness in the coating process (silicone composition) coating process (coating process and solvent drying process). is there. If the temperature and humidity are not sufficiently controlled, the surface of the coating film is cooled to remove moisture from the coating liquid applied to the surface of the plastic substrate. Condensation. The condensed water droplets may cause fine dents after the solvent is dried, causing white turbidity due to irregular reflection of light on the surface of the cured film, which is extremely undesirable in appearance.

  In order to avoid such problems, it is important to manage the temperature and humidity in the environment of the coating process (coating environment) so that the cooling temperature due to the heat of vaporization of the solvent does not fall below the dew point. In addition, when the degree of cleanliness is not sufficiently managed, dust and dust are likely to adhere to the surface of the coating, which also leads to an extremely undesirable result in terms of the appearance of the coating.

Thus, in order to obtain a surface protective coating with good appearance and excellent adhesion, it is important to manage the temperature, humidity, and cleanliness of the coating environment, which requires a lot of cost to manage and maintain it. In addition, there is a problem that the entire coating equipment is enlarged. Therefore, it is required to reduce as much as possible the time required for a process that requires management of the environment (temperature, humidity and cleanliness) such as a coating process.
JP-A-56-125466

  The present invention has been made in order to solve such problems. A cured coating for surface protection having an appropriate surface hardness and excellent heat resistance, weather resistance, and adhesion on the surface of a plastic substrate. It is an object of the present invention to provide a method for forming a surface protective film, which is formed while achieving both high productivity and economy.

  The method for forming a surface protective coating of the present invention comprises a step of applying a coating composition containing a thermosetting silicone and a solvent to the surface of a substrate made of plastic, and a step of drying the coating film of the coating composition. And a step of heating and curing the dried coating film of the coating composition using a latent heat of condensation of vapor generated by heating a liquid fluorine-based inert compound.

  According to the present invention, the coating composition can be efficiently cured in a short time by heating the coating film of the coating composition using the condensation latent heat of the vapor of the heated liquid fluorine-based inert compound. And a surface protective film having sufficient surface hardness and excellent heat resistance, weather resistance and adhesion can be formed with high productivity. In addition, since the time required for maintenance and management of the environment (temperature, humidity and cleanliness), such as the coating process, can be shortened, the operating cost can be reduced. The required space (area and length) and the area and length of equipment for maintaining and managing the coating environment can be reduced, and space can be saved.

  Embodiments of the present invention will be described below. An embodiment of the present invention includes a step of applying a coating composition containing a thermosetting silicone and a solvent to the surface of a plastic substrate, and a step of evaporating the solvent of the coating composition to dry the coating film And a step of heating and curing the dried coating film using the condensation latent heat of vapor of a heated liquid fluorine-based inert compound (hereinafter referred to as fluorine-based inert liquid).

  First, the protective coating composition applied to the surface of the plastic substrate will be described. This protective coating composition contains a silicone of a type that is heat-cured by a dehydration condensation reaction between terminal silanol groups, (B) colloidal silica, and (C) a solvent.

Examples of the silicone that is heat-cured by a dehydration condensation reaction between terminal silanol groups include an organosilane triol represented by the formula (A): R ¹ Si (OH) ₃ and / or a partial condensate thereof.

In the formula, R ¹ represents a monovalent hydrocarbon group, and specific examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a vinyl group, and an allyl group. Of these, a methyl group is preferred. This partial condensate can be obtained, for example, by hydrolyzing an organotrialkoxylane in an aqueous dispersion of colloidal silica. The amount of the organosilane triol and / or its partial condensate as component (A) is preferably 5 to 45% by weight of the total protective coating composition. When the amount is less than 5% by weight, the flexibility of the coating is lowered and cracks are likely to occur. When the amount exceeds 45% by weight, the surface hardness of the coating is remarkably reduced.

  The (B) component colloidal silica is usually used in a form dispersed in an aqueous dispersion. Examples of such a dispersion include Snowtex (trade name: manufactured by Nissan Chemical Co., Ltd.), Ludox (trade name: DuPont). This colloidal silica may be either acidic or basic. The blending amount of the colloidal silica is preferably 5 to 45% by weight of the entire protective coating composition. When it is less than 5% by weight, the surface hardness of the coating is not sufficient, and the fast curability is also lowered. On the other hand, if it exceeds 45% by weight, the flexibility of the coating is lowered, and cracks are likely to occur due to heating and deformation.

  (C) As a solvent which is a component, C1-C4 aliphatic alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, are mentioned. Preferably isobutanol is used. In order to easily adjust the evaporation rate of the coating composition (coating liquid) and improve the adhesion, it is preferable to use ethylene glycol monoethyl ether acetate in combination with the aliphatic alcohol. It is preferable that the compounding quantity of a solvent shall be 40 to 60 weight% of the whole composition for protective coatings. When it is less than 40% by weight, the leveling property at the time of coating is poor, and cracks are likely to occur due to long-term heating. On the other hand, when it exceeds 60% by weight, a sufficient film thickness (3 to 10 μm) cannot be obtained at the time of coating, and the wear resistance is lowered.

  Such a protective coating composition is sufficiently cured without a curing catalyst. However, when it is desired to further shorten the curing time, the use of the curing catalyst is effective. However, when a quaternary ammonium salt-based compound such as tetramethylammonium hydroxide is used as a curing catalyst, water resistance and weather resistance may be adversely affected, so water resistance and weather resistance are required. It is necessary to use it carefully for the application.

  The blending amount of the curing catalyst is 0.1 to 5.0 with respect to 100 parts by weight of the solid content of the mixture of (A) the organosilane triol and / or its partial condensate and (B) colloidal silica. It is preferable to use parts by weight. When the amount is less than 0.1 part by weight, sufficient hardness of the coating cannot be obtained, and when the amount exceeds 5.0 parts by weight, the coating is unfavorably caused with the skin.

  The coating composition of the present invention can be obtained, for example, by the following method. That is, an appropriate hydrolysis catalyst (for example, acetic anhydride or glacial acetic acid) is added to a predetermined amount of organotrialkoxysilane and colloidal silica for condensation. If necessary, the produced alcohol and water are distilled off, a solvent containing an aliphatic alcohol is added, the pH is returned to neutrality, and aging is performed for several weeks. Finally, a coating solution is obtained by adding a curing catalyst to this solution as necessary.

  Next, the process of forming a surface protective film using such a coating composition will be described in order.

  First, it is preferable to degrease and clean the surface of a base material made of plastic such as polycarbonate or acrylic resin with isopropyl alcohol or the like, and then form a primer layer thereon. The coating composition is not directly applied to the surface of the substrate, but is applied on the primer layer, whereby the adhesion and adhesion of the surface protective coating can be improved. As the primer, a known primer such as an acrylic material such as polymethyl acrylate or polymethyl methacrylate can be used.

  The primer layer is formed by applying a primer to the surface of the plastic substrate, evaporating the solvent at room temperature, drying the coating film, and then curing by heating. The application of the primer and the evaporation / drying of the solvent are performed in a coating environment (clean room) in which the temperature, humidity and cleanliness are controlled. The temperature and humidity in such a coating environment (clean room) are managed and maintained at 25 ° C. and 35-50% RH, for example. Examples of the application method include a dipping method, a spray method, a flow coating method, and a roll coating method.

  The primer solvent can be dried using a far-infrared heater. By using a far infrared heater, the time required for evaporation and drying of the solvent can be shortened.

  As the heating means for curing the primer, a known heating means such as a hot air oven can be adopted, but a method of heating using the condensation latent heat of the vapor of the heated fluorine-based inert liquid can be adopted. preferable.

  Here, examples of the fluorine-based inert liquid include Fluorinert (trade name: manufactured by 3M) and GALDEN (trade name: manufactured by SOLVAY SOLEXIS). Since these fluorinated inert liquids have the following characteristics, they are suitable as a medium for heating the primer and the coating composition. That is, the fluorine-based inert liquid has high thermal stability and does not deteriorate even when heated for a long time, and also has a vapor density of about 20 times that of air and does not diffuse in the air. A vapor layer is formed. In addition, it is chemically stable and inert, hardly reacts with other substances, and has a low dissolving power and does not dissolve most organic and inorganic materials. Furthermore, since the surface tension is low and the surface of an object is easily wetted and spread, the liquid runs out quickly. Furthermore, since the heat of evaporation is small, when it is removed from the vapor layer, it dries immediately.

  In this way, the primer is heated and cured using the latent heat of condensation of the fluorine-based inert liquid vapor, and then allowed to cool at room temperature. Instead of cooling at room temperature, it is also possible to cool by spraying a fluorine-based inert liquid to remove heat of vaporization.

  Next, the above-described coating composition (coating liquid) is applied onto the cured primer, and the solvent is evaporated at room temperature to dry the coating film. As a coating method of the coating composition, a dipping method, a spray method, a flow coating method, a roll coating method, or the like can be used. In addition, the application of the coating composition and the evaporation / drying of the solvent are performed in a coating environment (clean room) in which the temperature and humidity are controlled (for example, the temperature is 25 ° C. and the humidity is 35 to 50% RH) and the cleanness is controlled. ). The solvent of the coating composition can be dried using a far infrared heater. By using a far infrared heater, the time required for evaporation and drying of the solvent can be shortened.

  After drying the coating film of the coating composition in this manner, the coating film is held in the heated fluorine-based inert liquid vapor and heated using latent heat (condensation latent heat) generated when the vapor condenses. To do. By this heating, curing occurs due to a dehydration condensation reaction between terminal silanol groups in the mixture of (A) component organosilane triol and / or its partial condensate and (B) colloidal silica, and sufficient surface hardness is obtained. The film which has is formed.

  In the embodiment of the present invention configured as described above, in the curing process of the coating film of the coating composition, the large latent heat of condensation released when the vapor of the heated fluorine-based inert liquid changes to a liquid state. Since the coating film is heated by using it, the curing reaction can be advanced efficiently by heating in a short time, surface protection with sufficient surface hardness and excellent heat resistance, weather resistance and adhesion A film can be formed with high productivity. In addition, the heating in the primer curing step can also be performed using the latent heat of condensation of the fluorine-based inert liquid vapor to further increase the productivity.

  In addition, since the primer and coating composition are heated in the curing process using the latent heat of condensation of the heated fluorine-based inert liquid vapor, an environment where the temperature, humidity and cleanliness are controlled is required. The time for the solvent drying step in the previous stage can be greatly reduced compared to the conventional method in which solvent drying is performed by hot air oven heating.

  That is, in the conventional method in which the primer and the coating composition are cured by heating in a hot air oven, if any solvent remains in the coating composition or the coating film of the primer, Although a smooth film is not formed due to volatilization of the solvent, heating using the condensation latent heat of the heated fluorine-based inert liquid vapor will adversely affect the formation of a smooth film even if the solvent is brought into the vapor. There is nothing. Therefore, there is an advantage that the time required for solvent drying can be shortened because it is not necessary to dry the solvent so completely.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to an Example. In the following examples and comparative examples, as a primer, SHP470 (trade name: manufactured by Momentive Performance Materials), which is a polymethyl methacrylate solution containing an ultraviolet absorber, is used as a coating composition. Used AS4700F (trade name: manufactured by Momentive Performance Materials). AS4700F is a coating solution containing a hydrolyzate of methyltrialkoxysilane and a partial condensate thereof, colloidal silica, and n-butanol and 2-propanol as a solvent. In addition, Fluorinert FC-3283 (trade name: manufactured by 3M, boiling point 128 ° C.) was used as the fluorine-based inert liquid. Furthermore, all the processes of the example and the comparative example were performed in a clean room in which the cleanliness was controlled.

Example 1
In a coating environment of 25 ° C. and 50% RH, the surface of a polycarbonate molding plate (length 150 mm × width 150 mm, thickness 3 mm) was washed with isopropyl alcohol, and then a primer was applied thereon by a flow coating method. The primer was then allowed to evaporate and dry for 20 minutes in the same controlled coating environment.

  Next, about 300 g of the fluorinated inert liquid was put into a 10-liter beaker and heated on a hot plate for chemical experiments to generate a vapor of the fluorinated inert liquid. Then, a polycarbonate molding plate coated with a primer and dried in a solvent was placed in this steam, and heated for 5 minutes using the condensation latent heat of the fluorine-based inert compound vapor to cure the primer.

  Next, the polycarbonate molded plate was taken out from the vapor of the fluorine-based inert liquid and cooled at 25 ° C. (room temperature) for 15 minutes.

  Next, in a coating environment of 25 ° C. and 50% RH, the coating composition was applied by a flow coating method onto the polycarbonate molded plate that had been subjected to the primer curing treatment. Then, it was placed in the same controlled coating environment for 20 minutes to evaporate and dry the solvent of the coating composition.

  Next, in the same manner as in the primer heating / curing step, a polycarbonate molded plate obtained by applying the coating composition and drying the solvent is put into the vapor of the fluorine-based inert liquid generated by heating. The coating composition was cured by heating for 25 minutes using latent heat (condensation latent heat) generated with a change in state (condensation). Thus, a surface protective film was formed on the surface of the polycarbonate molding plate via the primer layer (cured layer).

  FIG. 1A shows the process flow of Example 1 and the time (minutes) required for each process. As can be seen from this figure, the total process time in the coating environment requiring temperature and humidity control was 50 minutes, and the total time required for forming the surface protective film was 95 minutes.

Example 2
In a coating environment of 25 ° C. and 50% RH, a primer was applied by flow coating on a polycarbonate molded plate (150 mm long × 150 mm wide, 3 mm thick) whose surface was degreased and washed with isopropyl alcohol. The primer was then allowed to evaporate and dry for 20 minutes in the same controlled coating environment.

  Next, about 300 g of the fluorinated inert liquid was put into a 10 liter beaker and heated with a hot plate to generate a vapor of the fluorinated inert liquid. And the polycarbonate molding board which dried the solvent of the primer was put into this vapor | steam, and it heated for 5 minutes using the condensation latent heat of the vapor | steam of a fluorine-type inert liquid, and the primer was hardened.

  Next, the polycarbonate molding plate was taken out from the vapor of the fluorine-based inert liquid, brought into contact with the mist of the fluorine-based inert liquid at 25 ° C. for 1 minute, and then allowed to cool at 25 ° C. (room temperature) for 4 minutes.

  Next, in a coating environment of 25 ° C. and 50% RH, the coating composition was applied by a flow coating method onto the polycarbonate molded plate that had been subjected to the primer curing treatment. Then, it was placed in the same controlled coating environment for 20 minutes to evaporate and dry the solvent of the coating composition.

  Next, as in the heating / curing step of the primer, the polycarbonate molding plate coated with the coating composition and dried with the solvent is placed in the vapor of the fluorine-based inert liquid, and the condensation latent heat of the vapor of the fluorine-based inert liquid Was used for 25 minutes to cure the coating composition. Thus, a surface protective film was formed on the surface of the polycarbonate molding plate via the cured layer of the primer.

  FIG. 1B shows the process flow of Example 2 and the time required for each process. As can be seen from this figure, the total process time in the coating environment requiring temperature and humidity control was 50 minutes, and the total time required for forming the surface protective film was 85 minutes.

Example 3
In a coating environment of 25 ° C. and 50% RH, a primer was applied by flow coating on a polycarbonate molding plate (150 mm long × 150 mm wide, 3 mm thick) whose surface was degreased and washed with isopropyl alcohol. And it heated for 10 minutes with the far-infrared heater in the same controlled coating environment, and the solvent of the primer was dried.

  Next, about 300 g of the fluorinated inert liquid was put into a 10 liter beaker and heated with a hot plate to generate a vapor of the fluorinated inert liquid. And the polycarbonate molding board which dried the solvent of the primer was put into this vapor | steam, and it heated for 5 minutes using the condensation latent heat of the vapor | steam of a fluorine-type inert liquid, and the primer was hardened.

  Next, the polycarbonate molded plate was taken out from the vapor of the fluorine-based inert liquid, brought into contact with the mist of the fluorine-based inert liquid at 25 ° C. for 1 minute, and then left to cool at 25 ° C. (room temperature) for 4 minutes.

  Next, in a coating environment of 25 ° C. and 50% RH, the coating composition was applied by a flow coating method onto the polycarbonate molded plate that had been subjected to the primer curing treatment. And it heated for 10 minutes with the far-infrared heater in the same controlled coating environment, and dried the solvent of the composition for coating.

  Next, as in the heating / curing step of the primer, the polycarbonate molding plate coated with the coating composition and dried with the solvent is placed in the vapor of the fluorine-based inert liquid, and the condensation latent heat of the vapor of the fluorine-based inert liquid is obtained. Was used for 25 minutes to cure the coating composition. Thus, a surface protective film was formed on the surface of the polycarbonate molding plate via the cured layer of the primer.

  FIG. 1C shows the flow of the process of Example 3 and the time taken for each process. As can be seen from this figure, the total process time in the coating environment requiring temperature and humidity control was 30 minutes, and the total time required for forming the surface protective film was 65 minutes.

Comparative Example In a coating environment of 25 ° C. and 50% RH, a primer was applied by flow coating on a polycarbonate molded plate (150 mm long × 150 mm wide, 3 mm thick) whose surface was degreased and washed with isopropyl alcohol. The primer was then allowed to dry for 30 minutes in the same controlled coating environment.

  Subsequently, the polycarbonate molding board which dried the solvent of the primer was put into 125 degreeC hot-air oven, and it heated for 30 minutes, and the primer was hardened.

  Next, the polycarbonate molded plate was taken out from the hot air oven and cooled at 25 ° C. (room temperature) for 15 minutes.

  Next, in a coating environment of 25 ° C. and 50% RH, the coating composition was applied by a flow coating method onto the polycarbonate molded plate that had been subjected to the primer curing treatment. Then, it was placed in the same controlled coating environment for 30 minutes to dry the solvent of the coating composition.

  Subsequently, the polycarbonate molding board which dried the solvent of the coating composition was put into 125 degreeC hot-air oven, and it heated for 25 minutes, and the coating composition was hardened. Thus, a surface protective film was formed on the surface of the polycarbonate molding plate via the cured layer of the primer.

  FIG. 1D shows the process flow of this comparative example and the time taken for each process. As can be seen from this figure, the total process time in the coating environment requiring temperature and humidity control was 70 minutes, and the total time required for forming the surface protective film was 175 minutes.

  Next, with respect to the surface protective coatings formed in Examples 1 to 3 and Comparative Example, the appearance, wear resistance and adhesion by Taber abrasion test were measured and evaluated as shown below.

[appearance]
The cured film was returned to room temperature and the appearance was visually observed.

[Abrasion resistance by Taber abrasion test]
Using a Taber abrasion tester, the surface of the coating was abraded under the conditions of a wear wheel CS-10F, a load of 500 g and a wear frequency of 500 times, and ΔH was calculated from the haze value measured with a haze meter.

[Adhesion]
On the surface of the coating, 11 parallel lines were placed vertically and horizontally at intervals of 1 mm to cross-cut 100 squares, and a cellophane adhesive tape was affixed to the surface. Thereafter, the tape was peeled off, and the peeled state of 100 squares was observed. A state where all the squares were not peeled was regarded as good.

  Table 1 shows the measurement evaluation results. Table 1 shows the process time and the improvement rate of the coating environment (clean room) that needs to be managed in Examples 1 to 3 and the comparative example, and the time and the improvement rate required for all the processes. In addition, the improvement rate of the process time of the coating environment and the improvement rate of the time required for all the processes are all obtained on the basis of each time in the comparative example.

  From Table 1, in Examples 1-3, the time of the process of the coating environment (clean room) which needs management of temperature, humidity, and cleanliness, and the time required for all the processes of formation of a surface protective film can be shortened. Recognize. Moreover, in Examples 1-3, it turns out that it has sufficient surface hardness and abrasion resistance, and can form the surface protective film excellent in adhesiveness with sufficient productivity.

FIGS. 1A to 1D are diagrams showing the flow of steps and the time taken for each step in Examples 1 to 3 and Comparative Example of the present invention, respectively.

Claims (5)

Applying a coating composition containing a thermosetting silicone and a solvent to the surface of a plastic substrate;
Drying the coating film of the coating composition;
A step of heating and curing the dried coating film of the coating composition using the latent heat of condensation of steam generated by heating a liquid fluorine-based inert compound, and forming a surface protective film Method.   The coating composition contains (A) an organosilane triol and / or a partial condensate thereof, (B) colloidal silica, and (C) a solvent containing an aliphatic alcohol having 1 to 4 carbon atoms. The method for forming a surface protective film according to claim 1.   The method for forming a surface protective coating according to claim 1 or 2, wherein the step of drying the coating film of the coating composition includes a step of heating with a far infrared heater. Before the step of applying the coating composition,
A step of applying a primer composition to a surface of a substrate made of plastic, a step of drying a coating film of the primer composition, and a step of heating and curing the dried coating film of the primer composition. The method for forming a surface protective film according to any one of claims 1 to 3.   The step of heating and curing the coating film of the primer composition includes the step of heating and curing the coating film using the latent heat of condensation of the steam generated by heating the liquid fluorine-based inert compound. The method for forming a surface protective film according to claim 4.

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