GB1578283A - Process for dimsting transparent materials - Google Patents

Description

(54) PROCESS FOR DEMISTING TRANSPARENT MATERIALS (71) We, HOYA LENS CORPORA TION, a Corporation organized under the laws of Japan, of 25 Kowada, Itsukaichimachi, Nishitama-gun, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a process for preventing misting on the surface of a transparent material, especially an optical part such as a lens, mirror and prism or the window glass of a car or ship which consist of a transparent material such as glass or a plastic.More particularly, the invention provides a process for demisting transparent materials with a demisting agent consisting mainly of a copolymer obtained by subjecting 2- hydroxyethyl methacrylate (hereinafter referred to as "HEMA") to solution polymerization and then graft - polymerizing an allyl alcohol tribasic acid ester (hereinafter referred to as "AATE") onto the resulting polymer.

Further, the invention provides a process for demisting transparent materials with a demisting agent obtained by adding an organo silicon nonionic surface active agent to the above-mentioned copolymer.

The demisting agents used in the present invention can impart a demisting property to the surface of said transparent materials when they are coated onto the surface of the transparent materials, baked and then dried to form a durable demisting film on the surface.

In general, when the above-mentioned transparent materials are rapidly transferred into a wet atmosphere at a temperature of higher than dew point from an atmosphere at a temperature of lower than dew point, dew falls on the surface of the transparent materials and their transparency decreases. Further, these conditions are maintained until the materials are brought to ambient temperature and dewdrops are evaporated, as usually experienced.

Several processes have heretofore been proposed to prevent misting of transparent materials. One of the processes comprises coating a certain kind of demisting agent to impart a temporary demisting effect.

However, this process is unsatisfactory in durability since the effect is reduced on exposure to air of high humidity.

As a result of the present inventors' various studies, polymer compositions which can form a durable demisting film have now been found and an advantageous demisting process by the use of the compositions have been provided.

In general, the demisting film obtained by coating polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide, polyacrylic acid, etc.

produces its demisting effect by the hygroscopic and swelling properties of the materials. Therefore, such a demisting film has often been poor in durability since its hardness is reduced and its is injured or peeled off when it absorbs moisture and is swelled.

The present inventors have paid attention to the above-mentioned defect and considered not only hygroscopic and swelling properties but also "wetting" characteristic for water. They have now found polymer compositions which form demisting film in which dewdrops are instantaneously diffused on the surface of the transparent materials by "wetting", part of the moisture is absorbed and softening hardly occurs when the film absorbs moisture and is swelled.

The following passages describe preferred embodiment of the invention: The demisting agents used in the present invention are a copolymer obtainable by subjecting HEMA (which is a hydrophilic substance) to polymerization and then graft - copolymerizing an AATE such as triallyl cyanurate or triallyl isocyanurate as a modifier to improve chemical resistance and thermal resistance at SOC to 900C for 0.5 to 2 hours and a mixture of the abovementioned copolymer with an organo silicon nonionic surface active agent such as a silicone-alkylene oxide copolymer for improving the surface active properties and "wetting" characteristics.

The above-mentioned demisting agents are coated onto the surface of a transparent material, baked at 1000 to 200"C for 20 to 60 minutes to form a demisting film.When the demisting film thus obtained is tested according to the expiration method, no mist occurs. Also, even on exposure to a large amount of water vapor or dipping in water, the film is neither swelled nor peeled off. Its hardness is almost the same as that in a dry state, i.e., a pencil hardness of 4H (JIS K5400). Also, the film is not colored at all and the optical characteristics of the original transparent materials do not change at all.

HEMA is added to an organic solvent in a weight ratio of 1:1 to 1:4, and 0.5 to 5% by weight of an organic peroxide catalyst or an azo polymerization catalyst based on the weight of HEMA is added to the resulting solution. The mixture is subjected to solution polymerization at SOC to 1000C for about 1 hour. When the solution polymerization has proceeded to the stage where the viscosity of the reaction mixture becomes high, 5 to 15% by weight of AATE based on the weight of said HEMA and 3 to 5 times as much as the amount used in solution polymerization of said organic solvent are added to suppress the sudden increase of the viscosity. The mixture is subjected to graft polymerization at 50 to 90"C for 0.5 to 2 hours.Here, an increased amount of the catalyst and a rapid increase in temperature have an undesirable effect on the characteristics of the resulting demisting film. The thus obtained copolymer is coated onto the surface of a transparent material in a thickness of 1 to 100 L by the spin coating or dipping method. The resulting coating is heated at 100" to 2000C for 20 to 60 minutes to dry it.

Thus, a demisting film is formed. This film has considerably durable demisting effect.

However, the film is hygroscopic, and can not absorb excess moisture and is misted in the extreme case if a sudden change in temperature and/or humidity occurs. In this respect, a demisting agent which forms a more effective demisting film, in that not only its hygroscopic property but also its "wetting" characteristic has been improved, is prepared by adding the following modification.

To the copolymer obtained by subjecting said HEMA to solution polymerization, adding AATE to the polymer and then graft - polymerizing the mixture, 0.5 to 2% by weight of an organo silicon nonionic surface active agent is added to improve "wetting" of the finally obtained film for water. In this case, it is considered that the triazine ring of said AATE is effective in improving the thermal resistance of the surface active agent.

The mixture of the copolymer with the surface active agent is thoroughly stirred and coated onto the surface of a transparent material so that the optical characteristics of the material may not be impaired. The resulting coating is heated at 1000 to 200"C for 20 to 30 minutes to cure it. The demisting effect of the thus obtained demisting film is tested according to expiration method which comprises blowing on the film and then examining the mist with the naked eye. The film of the copolymer obtained by polymerizing said HEMA and then graft - polymerizing AATE has a satisfactory demisting effect, but has the above-mentioned defect in that eventually it can not absorb any more moisture and it is misted when excess water vapor is blown thereon.Nevertheless, the film can be used satisfactorily for usual demisting purposes and has a more durable demisting effect than that of prior art demisting films. Further, the film obtained by adding the surface active agent to said copolymer and then curing the mixture is hygroscopic and becomes easy to be wet on exposure to excess moisture. If water vapor is blown on the film, therefore, part of water vapor is absorbed by the film but the remainder is diffused over the whole surface of the film. Thereby, dew does not form on the surface of the film and mist does not occur. Also, owing to the smaller amount of moisture absorbed, the film is not softened by swelling. Therefore, the film is durable in that the surface hardness and adhesive property of the film are not reduced. Even if the film is washed with water, the effect of the film is not deteriorated.

The organic solvents which may be used in the present invention are exemplified by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and dimethylformamide.

Also, preferable examples of the organic peroxide catalysts used in the present invention are benzoyl peroxide, acetyl peroxide, lauroyl peroxide, tert - butyl peroxyisobutyrate, tert - butyl peroxyoctoate, tert - butyl peroxypivalate, and diisopropyl peroxydicarbonate.

Further, the azo polymerization catalysts used in the present invention are those wherein an azo group is bonded to nonaromatic carbon atoms each having different valencies, and preferably to a tertiary non-aromatic carbon atom, and are exemplfied by a,a' - azobisisobutyronitrile, azobiscyclohexanecarbonitrile and azobisisopropylnitrile.

Also, the organo silicon surface active agents used in the present invention are those represented by the general formula,

where R is hydrogen or a lower alkyl group.

The excellence of the demisting agents used in the process of the present invention has been confirmed by preparing many products in the above-mentioned manner and repeating tests. The following examples illustrate the present invention in more detail, but it is a matter of course that there are many embodiments of the invention using a combination of said raw materials other than the following examples.

Example 1 In 200 g of ethylene glycol monoethyl ether (hereinafter referred to as "2EE") was dissolved 100 g of 2 - hydroxyethyl methacrylate. To the resulting solution was added 2 g of a,a' - azobisisobutyronitrile (hereinafter referred to as "ABIN"). The mixture was well stirred and then polymerized at 650 to 700C for about 1 hour. At the gelation point, 10 g of triallyl isocyanurate (hereinafter referred to as "TAIC") was added and the mixture was further polymerized. As the viscosity of the reaction mixture increased, 1500 g of 2 EE as a solvent was added to obtain 1800 g of copolymer solution.

After cooling, this solution was coated onto the surface of an optical part and then cured by allowing the coated part in a drier at 150"C for 30 minutes.

When the demisting film thus obtained was tested according to the expiration method, no mist occurred. However, mist occurred on the exposure to excess water vapor.

Example 2 To 50 g of the copolymer solution obtained in Example 1 was added I g of an organo silicon nonionic surface active agent. The mixture was well stirred, and then coated onto the surface of plate glass and cured at 1500C for 20 minutes.

When the resulting film was tested according to the expiration method, no mist occurred. Also, even on exposure to excess water vapor, "wetting" phenomenon acted well and thereby no mist occurred. Further, on washing with water, it was confirmed that the demisting effect was durably maintained without being reduced.

Example 3 To 50 g of the copolymer solution obtained in Example I were added 0.5 g of an organo silicon nonionic surface active agent and 0.5 g of hexamethoxymethylmelamine (hereinafter referred to as "H MM"). The mixture was well stirred and coated onto the surface of glass and then cured at 1500C for 30 minutes.

When the resulting film was tested by the expiration method, no mist occurred. Also, even on exposure to excess water vapor, waterdrops were diffused by wetting and no mist occurred. Further, it was confirmed that the addition of HMM improved wettability of the film and increased the hardness of the film.

Example 4 In 200 g of dimethylformamide (hereinafter referred to as "DMF") was dissolved 100 g of HEMA, and 1.5 g of benzoyl peroxide was added. The mixture was reacted at 800 to 90"C for about 1 hour.

At the gelation point, 10 g of TAIC was added and the reaction was continued. As the viscosity of the reaction mixture increased, solvent DMF was suitably added to obtain about 1500 g of a copolymer solution.

To 50 g of this solution was added 0.8 g of an organo silicon nonionic surface active agent. The mixture was well stirred and coated onto the surface of glass and then cured at 1400C for 30 minutes.

When the resulting film was tested by the expiration method, no mist occurred. Also, even on exposure to water vapor, waterdrops were diffused by wetting and no mist occurred.

WHAT WE CLAIM IS: 1. A process for demisting transparent materials which comprises coating onto the surface of the transparent materials a copolymer obtained by subjecting 2 hydroxyethyl methacrylate to solution polymerization and then graft copolymerizing an allyl alcohol tribasic acid ester thereonto and then curing the resulting copolymer by heating it.

2. A process according to Claim 1, wherein an organo silicon nonionic surface active agent is further added to said copolymer.

3. A process according to Claim I or 2, wherein said allyl alcohol tribasic acid ester is selected from triallyl cyanurate and triallyl isocyanurate.

4. A process according to Claim 1 or 2, wherein the solution polymerization of the 2 - hydroxyethyl methacrylate is carried

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. tertiary non-aromatic carbon atom, and are exemplfied by a,a' - azobisisobutyronitrile, azobiscyclohexanecarbonitrile and azobisisopropylnitrile. Also, the organo silicon surface active agents used in the present invention are those represented by the general formula, where R is hydrogen or a lower alkyl group. The excellence of the demisting agents used in the process of the present invention has been confirmed by preparing many products in the above-mentioned manner and repeating tests. The following examples illustrate the present invention in more detail, but it is a matter of course that there are many embodiments of the invention using a combination of said raw materials other than the following examples. Example 1 In 200 g of ethylene glycol monoethyl ether (hereinafter referred to as "2EE") was dissolved 100 g of 2 - hydroxyethyl methacrylate. To the resulting solution was added 2 g of a,a' - azobisisobutyronitrile (hereinafter referred to as "ABIN"). The mixture was well stirred and then polymerized at 650 to 700C for about 1 hour. At the gelation point, 10 g of triallyl isocyanurate (hereinafter referred to as "TAIC") was added and the mixture was further polymerized. As the viscosity of the reaction mixture increased, 1500 g of 2 EE as a solvent was added to obtain 1800 g of copolymer solution. After cooling, this solution was coated onto the surface of an optical part and then cured by allowing the coated part in a drier at 150"C for 30 minutes. When the demisting film thus obtained was tested according to the expiration method, no mist occurred. However, mist occurred on the exposure to excess water vapor. Example 2 To 50 g of the copolymer solution obtained in Example 1 was added I g of an organo silicon nonionic surface active agent. The mixture was well stirred, and then coated onto the surface of plate glass and cured at 1500C for 20 minutes. When the resulting film was tested according to the expiration method, no mist occurred. Also, even on exposure to excess water vapor, "wetting" phenomenon acted well and thereby no mist occurred. Further, on washing with water, it was confirmed that the demisting effect was durably maintained without being reduced. Example 3 To 50 g of the copolymer solution obtained in Example I were added 0.5 g of an organo silicon nonionic surface active agent and 0.5 g of hexamethoxymethylmelamine (hereinafter referred to as "H MM"). The mixture was well stirred and coated onto the surface of glass and then cured at 1500C for 30 minutes. When the resulting film was tested by the expiration method, no mist occurred. Also, even on exposure to excess water vapor, waterdrops were diffused by wetting and no mist occurred. Further, it was confirmed that the addition of HMM improved wettability of the film and increased the hardness of the film. Example 4 In 200 g of dimethylformamide (hereinafter referred to as "DMF") was dissolved 100 g of HEMA, and 1.5 g of benzoyl peroxide was added. The mixture was reacted at 800 to 90"C for about 1 hour. At the gelation point, 10 g of TAIC was added and the reaction was continued. As the viscosity of the reaction mixture increased, solvent DMF was suitably added to obtain about 1500 g of a copolymer solution. To 50 g of this solution was added 0.8 g of an organo silicon nonionic surface active agent. The mixture was well stirred and coated onto the surface of glass and then cured at 1400C for 30 minutes. When the resulting film was tested by the expiration method, no mist occurred. Also, even on exposure to water vapor, waterdrops were diffused by wetting and no mist occurred. WHAT WE CLAIM IS:

1. A process for demisting transparent materials which comprises coating onto the surface of the transparent materials a copolymer obtained by subjecting 2 hydroxyethyl methacrylate to solution polymerization and then graft copolymerizing an allyl alcohol tribasic acid ester thereonto and then curing the resulting copolymer by heating it.

2. A process according to Claim 1, wherein an organo silicon nonionic surface active agent is further added to said copolymer.

3. A process according to Claim I or 2, wherein said allyl alcohol tribasic acid ester is selected from triallyl cyanurate and triallyl isocyanurate.

4. A process according to Claim 1 or 2, wherein the solution polymerization of the 2 - hydroxyethyl methacrylate is carried

out in the presence of 1 to 4 times the weight of the 2 - hydroxyethyl methacrylate of an organic solvent and 0.5 to 5% by weight of an organic peroxide catalyst or an azo polymerization catalyst based on the weight of the 2 - hydroxyethyl methacrylate at SOC to 1000C for about 1 hour.

5. A process according to Claim 1 or 2, wherein the graft - copolymerization is carried out by adding 5 to 15% by weight of the allyl alcohol tribasic acid ester based on the weight of the 2 - hydroxyethyl methacrylate and 3 to 5 times as much as the amount used in the solution polymerization of an organic solvent and heating the mixture at 50 to 90bC for 0.5 to 2 hours.

6. A process according to Claim 1 or 2, wherein said copolymer is coated onto the surface of transparent materials in a thickness of 1 to 100 ,u and then cured by heating it at 100C to 2000C for 20 to 60 minutes.

7. A process according to Claim 4 or 5, wherein said organic solvent is selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and dimethylformamide.

8. A process according to Claim 4, wherein said organic peroxide catalyst is selected from the group consisting of benzoyl peroxide, acetyl peroxide, lauroyl peroxide, tert - butyl peroxyisobutyrate, tert - butyl peroxyoctoate, tert - butyl peroxypivalate and diisopropyl peroxydicarbonate.

9. A process according to Claim 4, wherein said azo polymerization catalyst is selected from the group consisting of aa' azobisisobutyronitrile, azobiscyclohexanecarbonitrile and azobisisopropylnitrile.

10. A process as claimed in claim 1, substantially as described in any one of the examples.

11. A coated transparent article, produced by a process as claimed in any one of claims 1 to 10.

12. A transparent article having on a surface thereof a demisting coating of a crossed-linked 2 - hydroxy ethyl methacrylate/triallyl ester copolymer the backbone of which is derived from 2 hydroxyethyl methacrylate, optionally comprising a non-ionic organosilicon surface active agent.