Article with antifogging film and process for producing same

Abstract: An antifogging article includes a substrate and an antifogging film covering the substrate. This antifogging film contains a water-absorbing organic polymer and an inorganic substance and has a water repellent finishing on a surface of the antifogging film. Another antifogging article includes (1) a substrate, (2) a water-absorbing, antifogging film covering the substrate, and (3) a water-permeable, protective film covering the antifogging film. This antifogging film contains (a) a polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol% and (b) a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2. These antifogging articles are superior in antifogging property and abrasion resistance.

Description: BACKGROUND OF THE INVENTION The present invention relates to an article with an antifogging film, which is useful for windows, mirrors and the like in various fields such as architectural, industrial and automotive ones, and a process for producing the article. In recent years, there have been proposals of forming photocatalytic films on the substrate surface for providing hydrophilicity and antifogging property. Japanese Patent Laid-open Publication JP-A-5-253544 discloses a process for producing a plate-like member with deodorizing function by applying a glaze to a substrate and then by spraying an anatase-type TiO 2 powder to the glaze layer. JP-A-7-232080, which corresponds to U.S. Patents 6,027,797 and 5,853,866, discloses a multifunctional material with photocatalytic function, prepared by forming a binder layer on a substrate and then by forming a photocatalytic layer of photocatalytic particles on the binder layer. JP-A-9-59042 discloses a transparent substrate with an antifogging coating containing photocatalytic titania particles. JP-A-52-101680 discloses an antifogging agent containing polyacrylic acid, surfactant and a solvent (water and/or alcohol). Japanese Patent Examined Publication JP-B-5-67330, which corresponds to JP-A-1-38103, discloses a hydrophilic porous film and a process for producing the same. This film is made of a hydrophobic polymer. The external surface and the pore surfaces of the film are coated with a coating of a polyvinyl alcohol/vinyl acetate copolymer and then with a coating of a hydrophilic polymer. JP-A-10-212471 discloses an antifogging agent containing polyvinyl alcohol, tetramethoxysilane, and hydrochloric acid as a catalyst for polycondensation of these compounds. JP-A-11-84102 discloses an antifogging coating film and an optical article with this film. This antifogging coating film has (1) a water-absorbing film formed on a substrate and (2) a porous film formed on the water-absorbing film. JP-A-5-51471 discloses a laminate prepared by forming a curable coating film on a substrate. At least a surface layer portion of the substrate is made of a polymer having -P=N-skeleton. JP-A-6-157794 discloses an antifogging agent containing a polyvinyl acetal resin. JP-A-6-158031 discloses a first antifogging article prepared by forming on a substrate an antifogging layer of a polyvinyl acetal resin having a degree of acetalization of 2-40 mol%. This publication further discloses a second antifogging article prepared by forming a water-soluble resin layer on a substrate and then the antifogging layer. JP-A-9-136374 discloses an antifogging resin article prepared by forming on a resin substrate a first layer containing hydrophilic inorganic fine particles and a coupling agent and then by forming on the first layer a second layer made of a hydrophilic resin and/or a surfactant. SUMMARY OF THE INVENTION It is an object of the present invention to provide an antifogging article which is superior in antifogging property and abrasion resistance. It is another object of the present invention to provide a process for producing such antifogging article. According to the present invention, there is provided an antifogging article comprising: a substrate; a water-absorbing, antifogging film covering said substrate, said antifogging film comprising: (a) a polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol%; and (b) a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2; and a water-permeable, protective film covering said antifogging film. According to the present invention, there is provided a process for producing an antifogging article, comprising: (a) providing a substrate; (b) preparing a first coating liquid by adding a polyvinyl acetal resin and an alkylsilylisocyanate to a solvent, said polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol%, said alkylsilylisocyanate being represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2; (c) applying said first coating liquid to said substrate, thereby forming a first precursory film on said substrate; (d) drying said first precursory film into a water-absorbing, antifogging film; (e) applying a second coating liquid containing an alkylsilylisocyanate to said antifogging film, said alkylsilylisocyanate being represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2, thereby forming a second precursory film on said antifogging film; and (f) drying said second precursory film into a water-permeable, protective film. The antifogging article can be produced by the process. DESCRIPTION OF THE PREFERRED EMBODIMENTS The antifogging article is superior for a long time in antifogging property, wiping resistance and abrasion resistance, particularly when the antifogging film is coated with a water-permeable, protective film having a thickness of 3-10 nm. The antifogging film of the antifogging article is superior in strength, since a cross-linking can be formed by a reaction between hydroxyl group of the polyvinyl acetal resin and the isocyanate group of the alkylsilylisocyanate. The antifogging article can widely be used for automobiles and mirrors. Furthermore, the antifogging article can be produced by the process at relatively low drying temperatures. Therefore, it is possible to partially or entirely coat a substrate, to which a high temperature drying is not desirable, such as a glass plate already formed into a mirror or an automotive glass pane already bent and shaped, thereby producing the antifogging article. As stated above, the antifogging film of the antifogging article contains a first essential constituent, a polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol%. With this, the antifogging film becomes superior in antifagging property and transparency. If its degree of acetalization is greater than 10 mol%, the resulting antifogging film may become inferior in antifogging property. A second essential constituent of the antifogging film is a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2. The amount of the second constituent in the antifogging film is preferably of 1-5 wt%, based on the total weight of the first and second constituents. If it is less than 1 wt%, the antifogging film may become inferior in strength and wiping resistance. If it is greater than 5 wt%, the antifogging film may become inferior in antifogging property. In the process, the solvent for preparing the first coating solution (liquid) is preferably a mixture of water and at least one compound selected from (1) alcohols (particularly lower alcohols) such as methanol, ethanol, propanol, ethylene glycol, propylene glycol and hexylene glycol, (2) esters such as ethyl acetate, butyl acetate and amyl acetate, and (3) cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve. Of these, it is preferable to select a suitable one or mixture of at least two, in view of the evaporation rate of the first coating solution (liquid) and/or viscosity of the first precursory film. Furthermore, it is optional to add suitable amounts of a silane coupling agent (e.g., methacryloxypropyltrimethoxysilane) and a methyl silicone (e.g., dimethyl silicone) as a leveling agent. In the process, the manner of applying the first or second coating solution (liquid) is not particularly limited. For example, it can be selected from spin coating, dip coating, reverse coating, flexography, roller coating, curtain coating, nozzle coating, spraying and screen printing. In the process, the first precursory film is dried at a temperature of preferably 90-150°C for a period of time of preferably 30-60 minutes. With this, most of the solvent evaporates, and at the same time the hydrolysate or partial hydrolysate of the alkylsilylisocyanate becomes a matrix of the antifogging film. The antifogging film of the second antifogging article has a thickness of preferably about 3-10µm. If it is less than 3µm, the antifogging film may become inferior in antifogging durability. If it is greater than 10µm, the antifogging article may have an optical distortion in connection with the external appearance. In the process, it is possible to use an alkylsilylisocyanate rep resented by R 2 n SiR 1 4-n where R 1 , R 2 and n are defined as above, for preparing the water-permeable, protective film. In this film, the alkylsilylisocyanate can be in the form of its hydrolysate or partial hydrolysate. In the preparation of the second coating liquid, the alkylsilylisocyanate can be added to a solvent (e.g., ester or hydrocarbon). Furthermore, it is optional to add a leveling agent. The second precursory film can be dried at a relatively low temperature of 90-120°C for a period of time of 10-60 minutes. With this, most of the solvent may evaporate, and at the same time the hydrolysate or partial hydrolysate of the alkylsilylisocyanate may turn into a hardened film. The antifogging article is improved in scratch resistance and wiping resistance due to the use of the water-permeable, protective film. The water-permeable, protective film of the antifogging article has a thickness of preferably 3-10 nm in order to have a sufficient water permeability. If it is less than 3 nm, the antifogging article may become inferior in abrasion resistance and wiping resistance. If it is greater than 10 nm, water permeability of the film may become inferior. With this, the antifogging article may become inferior in antifogging property. In the process, the substrate is not limited to particular materials. It may be selected from glass, resin, metal and ceramic, as long as it does not deteriorate by the dryings. It is typically a glass plate, which can be selected from float glass plates for automotive, architectural and industrial uses, clear and various color glass plates of green, bronze and other colors, various functional glass plates, tempered glass plates, laminated glass plates, double-layered glass plates, and flat and bent glass plates. The glass plate may have a thickness of about 1.0-12 mm. In fact, it is preferably about 3.0-10 mm for architectural use and about 2.0-5.0 mm for automotive use. The following nonlimitative examples are illustrative of the present invention. Examples 1-1 to 1-4 are illustrative of the present invention. FIRST EVALUATION TEST (for reference) A first antifogging test was conducted in accordance with Japanese Industrial Standard (JIS) S 4030 as follows. In this test, a first step was conducted by retaining the test sample in water vapor of warm water of 43°C for 3 minutes, and then a second step was conducted by moving the test sample from the water vapor to an environment (temperature: 23°C; relative humidity: 63%) and then by blowing breath against the test sample, thereby completing one cycle. The first and second steps were conducted alternately to complete ten cycles. The test sample was judged to be satisfactory when the external appearance did not change after each first step and each second step, as shown by "Good" in the column of "external appearance" of Table 1. On the other hand, it was judged to be unsatisfactory when the external appearance changed, as shown by "Not Good" in the column of "external appearance" of Table 1. Furthermore, the test sample was judged to be satisfactory when no fogging was observed on the test sample even by blowing breath against the test sample after each first step and each second step, as shown by "Good" in the column of "fogging" of Table 1. On the other hand, it was judged to be unsatisfactory when fogging was observed, as shown by "Not Good" in the column of "fogging" of Table 1. A second antifogging test was conducted by a first step of allowing the test sample to stand still in a refrigerator of 4°C for 30 min and then by a second step of allowing the test sample to stand still at room temperature for 10 min to complete one cycle. The first and second steps were conducted alternately to complete ten cycles. The test sample was judged in the same manner as that of the first antifogging test. An abrasion resistance test was conducted in accordance with JIS L 3120-1961-1206 by moving a cotton canvas cloth on the test sample in a reciprocative manner under a load of 100 g/cm 2 at a rate of one reciprocation per second to complete 3,000 reciprocations. A water resistance test was conducted by immersing the test sample in water of room temperature (20-25°C) for 6 hr. The test sample was judged to be satisfactory when the external appearance of the test sample did not change after the water resistance test, as shown by "Good" in the column of "external appearance" of Table 1. It was judged to be unsatisfactory when the external appearance changed, as shown by "Not Good" in the column of "external appearance" of Table 1. Furthermore, the test sample was judged to be satisfactory when no fogging was observed on the test sample even by blowing breath against the test sample after the water resistance test, as shown by "Good" in the column of "fogging" of Table 1. It was judged to be unsatisfactory when fogging was observed, as shown by "Not Good" in the column of "fogging" of Table 1. EXAMPLE 1-1 At first, a polyvinyl acetal resin (degree of acetalization: 8 mol%; solid matter: 8%), KX-1 (trade name) of Sekisui Chemical Co., and an alkylsilylisocyanate coating agent, ORGATIX SIC-003 (trade name) of Matsumoto Seiyaku Co., were added to a solvent (i.e., a mixture of ethanol and water). This coating agent contained (1) methylsilyltriisocyanato in an amount of 10 wt% in terms of SiO 2 and (2) ethyl acetate as a solvent. The resulting mixture was stirred, thereby obtaining a first coating solution (solid matter concentration: 3 wt%). The amounts of the polyvinyl acetal resin and the alkylsilylisocyanate coating agent in the first coating solution were such that the weight ratio of the polyvinyl acetal resin to the hydrolysate or partial hydrolysate of alkylsilylisocyanate in the first film was 97.5 : 2.5. Then, a glass plate (substrate) having one masked major surface was dipped in the first coating solution. Then, the coated glass plate was dried at about 120°C for about 30 minutes, thereby forming a water-absorbing first film (thickness: 7.5µm) on the substrate. Separately, the above-mentioned alkylsilylisocyanate coating agent was added to ethyl acetate, thereby obtaining a second coating solution (solid matter concentration: 1 wt%). Then, the second coating solution was applied to the first film by dipping while the uncoated side of the glass plate was masked, followed by drying at about 120°C for about 30 minutes, thereby forming a moisture-permeable, protective, second film (thickness: 10 nm) on the first film. EXAMPLE 1-2 Example 1-1 was repeated except that the amounts of the polyvinyl acetal resin and the alkylsilylaisocyanate coating agent in the first coasting solution were changed to adjust the weight ratio of the polyvinyl acetal resin to the hydrolysate or partial hydrolysate of alkylsilylisocyanate in the first film to 99 : 1. The resulting first film was 8 µm in thickness. EXAMPLE 1-3 Example 1-1 was repeated except that the amounts of the polyvinyl acetal resin and the alkylsilylisocyanate coating agent in the first coating solution were changed to adjust the weight ratio of the polyvinyl acetal resin to the hydrolysate or partial hydrolysate of alkylsilylisocyanate in the first film to 95 : 5. The resulting first film was 7 µm in thickness. EXAMPLE 1-4 Example 1-1 was repeated except that the second film was adjusted to have a thickness of 4 nm. The first film was 7 µm in thickness. COMPARATIVE EXAMPLE 1-1 Example 1-1 was repeated except that the use of the alkylsilylisocyanate coating agent was omitted. The resulting first film was 7 µm in thickness. Numerous scratches were found on the test sample after 300 reciprocations of the after-mentioned abrasion resistance test (see Table 1). The first and/or second film exfoliated from the substrate after 10 times of the wiping of the after-mentioned wiping test. COMPARATIVE EXAMPLE 1-2 Example 1-1 was repeated except that the second film was adjusted to have a thickness of 2 nm. The first film was 7 µm in thickness. Numerous scratches were found on the test sample after 600 reciprocations of the abrasion resistance test (see Table 1). The first and/or second film exfoliated from the substrate after 30 times of the wiping of the wiping test. COMPARATIVE EXAMPLE 1-3 Example 1-1 was repeated except that the second film was adjusted to have a thickness of 20 nm. The first film was 7 µm in thickness. Fogging was observed by blowing breath against the test sample. COMPARATIVE EXAMPLE 1-4 Example 1-1 was repeated except that a polyvinyl acetal resin (degree of acetalization: not less than 70 mol%), ESREK KS-5 (trade name) of Sekisui Chemical Co. was used in place of KX-1. The resulting first film was 6µm in thickness. Fogging was observed by blowing breath against the test sample. COMPARATIVE EXAMPLE 1-5 Example 1-1 was repeated except that a polyvinyl alcohol resin was used in place of the polyvinyl acetal resin. The resulting first film was about 6 µm in thickness. The first and/or second film exfoliated from the substrate after 20 times of the wiping of the wiping test. Fogging was observed even by allowing the test sample to stand still for at least one day after the after-mentioned water resistance test. COMPARATIVE EXAMPLE 1-6 Example 1-1 was repeated except that the formation of the second film was omitted. The first film was 7 µm in thickness. Numerous scratches were found after 300 reciprocations of the abrasion resistance test. The first and/or second film exfoliated from the substrate after 20 times of the wiping of the wiping test. SECOND EVALUATION TEST The resulting test samples (the coated substrates) of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-6 were subjected to the following evaluation tests. The first antifogging test of First Evaluation Test was repeated. The second antifogging test of First Evaluation Test was repeated except that the second step was conducted by moving the test sample from the refrigerator to an atmosphere of 23°C and a relative humidity of 63%. The water resistance test of First Evaluation Test was repeated except that the test sample was immersed in water of room temperature (21-25°C). A wiping resistance test was conducted by wetting a cloth, then squeezing the excess water from the cloth, then wiping the test sample with the cloth fifty times in total. After each ten times of the wiping, breath was blown against the test sample. The test sample was judged to be satisfactory when no fogging was observed on the test sample even by blowing breath after fifty times of the wiping, as shown by "Good" in the column of "fogging" of Table 1. On the other hand, it was judged to be unsatisfactory when fogging was observed during the test, as shown by "Not Good" in the column of "fogging" of Table 1. The abrasion resistance test of First Evaluation Test was repeated except that the external appearance of the test sample and the existence of fogging on the test sample were checked after each 300 reciprocations of the canvas cloth. The test sample was judged to be satisfactory, when no abnormality of the test sample was found even after 3,000 reciprocations, as shown by "Good" in the column of "external appearance" of Table 1. It was judged to be unsatisfactory, when abnormality of the test sample was found, as shown by "Not Good" in the column of "external appearance" of Table 1. Furthermtore, the test sample was judged to be satisfactory when no fogging was observed even by blowing breath against the test sample even after 3,000 reciprocations, as shown by "Good" in the column of "fogging" of Table 1. It was judged to be unsatisfactory when fogging was observed, as shown by "Not Good" in the column of "fogging" of Table 1.

Claims: An antifogging article comprising: a substrate; a water-absorbing, antifogging film covering said substrate, said antifogging film comprising: (a) a polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol%; and (b) a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2; and a water-permeable, protective film covering said antifogging film. An antifogging article according to claim 1, wherein said protective film has a thickness of 3-10 nm. An antifogging article according to claim 1, wherein said antifogging film comprises 95-99 wt% of said polyvinyl acetal resin and 1-5 wt% of said hydrolysate or partial hydrolysate. An antifogging article according to claim 1, wherein said protective film comprises a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2. A process for producing an antifogging article, comprising: (a) providing a substrate; (b) preparing a first coating liquid by adding a polyvinyl acetal resin and an alkylsilylisocyanate to a solvent, said polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol%, said alkylsilylisocyanate being represented by the general formula R 2 n SiR 1 4-n where R 1 is an alkyl group having a carbon atom number of 1 or 2, R 2 is an isocyanate group, and n is 1 or 2; (c) applying said first coating liquid to said substrate, thereby forming a first precursory film on said substrate; (d) drying said first precursory film into a water-absorbing, antifogging film; (e) applying a second coating liquid containing an alkylsilylisocyanate to said antifogging film, said alkylsilylisocyanate being represented by the general formula R 2 n SiR 1 4-n where R 1 , R 2 and n are defined as above, thereby forming a second precursory film on said antifogging film; and (f) drying said second precursory film into a water-permeable, protective film. A process according to claim 5, wherein said first precursory film is dried at a first temperature of 90-150°C. A process according to claim 5, wherein said second precursory film is dried at a second temperature of 90-120°C. A process according to claim 5, wherein said solvent is a mixture of water and an at least one compound selected from the group consisting of alcohols, esters and cellosolves.

Inventors: MURATA NOBORU, YAMAMOTO HIDEKI, YAMAZAKI SEIJI, MURATA, NOBORU, YAMAMOTO, HIDEKI, YAMAZAKI, SEIJI, Murata, Noboru, Central Glass Company, Ltd., Yamamoto, Hideki, Central Glass Company, Ltd., Yamazaki, Seiji, Central Glass Company, Ltd.
Applicants: CENTRAL GLASS CO LTD, CENTRAL GLASS COMPANY, LIMITED
Application year: 2000
Main classification: C03C17
IPC codes: C03C17