CN1445262A

CN1445262A - High hydrophilic polytitanium siloxane compound induced by photocatalysis and its preparing method

Info

Publication number: CN1445262A
Application number: CN 03108949
Authority: CN
Inventors: 谢平波
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-04-12
Filing date: 2003-04-12
Publication date: 2003-10-01

Abstract

A high-hydrophilicity polytitanosiloxane compound is prepared from high-hydrophilicity polytitanosiloxane and photocatalyst through light radiating. The contact angle between its surface and water is 5-10 deg. After it is applied to the surface of substrate, the surface of substrate has high hydrophilicity, and excellent antifogging, anticharging and self-cleaning performance.

Description

Photocatalytic-induced highly hydrophilic polytitanium siloxane compound and preparation method thereof

The field to which the invention relates:

the invention relates to the field of photocatalytic and hydrophilic materials, and provides a photocatalytic highly hydrophilic coating film with high hydrophilicity, fog resistance, antistatic property and self-cleaning property, which can be applied to various occasions. An inorganic coating film mainly composed of titanium-oxygen-silicon (Ti-O-Si) bonds has good durability, weather resistance and high hydrophilicity. The prior art is as follows:

various studies have been conducted to prevent fogging of various surfaces, and there are two main principles of conventional anti-fogging technologies: the principle of hydrophilicity and the principle of hydrophobicity. The former makes water drop spread on various surfaces to form water film without affecting light scattering or refraction, while the latter makes water drop difficult to adhere on the surface and easy to fall off under various external forces to achieve the goal of fog prevention. However, both of the conventional methods have certain defects, such as short effective life, inconvenient use, etc. The principle of hydrophilicity is mainly based on the action of a surfactant, but the general surfactant has small molecular weight and is easy to dissolve and lose by water, and finally loses the hydrophilic effect, and the latter is mainly various organic silicon coatings which have weak adhesion with the surface and are easy to peel off. However, due to various needs for life, production, and the like, various long-acting antifogging products are continuously researched.

In recent years, there have been proposed methods for producing superhydrophilicity by photocatalyst under light induction, such as Japanese patent (W096/29375) and Chinese patent (application No.: 96193834.X, 99800525.8, 97197799.2, 01115626.0). They all use photocatalyst to excite to generate electron-hole pairs under the irradiation of ultraviolet light with band gap higher than that of the photocatalyst, so that water adsorbed in the form of hydroxyl (-OH) can be generated on the surface of the photocatalyst, resulting in high hydrophilicity, and the contact angle is close to 0 degree. This property of the photocatalyst disappeared quickly in the dark and its contact angle increased again, but when the light was re-irradiated, the contact angle decreased again to 0 degrees, indicating that the property was reproducible. However, if the sensitivity of inorganic compounds based solely on photocatalysts (e.g., chinese patent, application No. 96193834.X) to ultraviolet rays is low, strong ultraviolet rays are required to be irradiated for a long time to generate the inorganic compounds. Another solution is that the photocatalyst is carried by an inorganic adhesive based on polysiloxane, which utilizes the stability of polysiloxane, and this organosilicon compound is hard to be decomposed by the photocatalyst, but because polysiloxane has strong hydrophobicity, it has no hydrophilicity for a while after film forming, and the photocatalyst can only show hydrophilicity after being activated by light, and especially under the conditions of bad light condition and discontinuous light irradiation, it takes longer time for the photocatalyst contained therein to act to generate hydrophilicity. Limiting the use of this superior feature of the photocatalyst. The invention has the following main points:

the invention solves the existing problems, not only utilizes the photoinduced high hydrophilicity of the photocatalyst, but also the adhesive is the polytitanium siloxane with very excellent hydrophilicity, and the permanent or semi-permanent high hydrophilicity of the compound can be maintained no matter whether the light is irradiated or not.

Since the photocatalyst has a very strong oxidation-reduction action of an electron-hole pair generated under light irradiation, an organic compound having a C-C bond is easily decomposed, and a binder for supporting the photocatalyst generally requires an inorganic product, and a compound of fluoride, polysiloxane or cement is generally used. For the coating film, an organic silicon compound such as polysiloxane is generally used because of its relatively good coatability and stability. Since the silicon-oxygen-silicon bond (Si-O-Si) in the polysiloxane is inorganic, the polysiloxane is very stable and can stably exist under the condition of the oxidation-reduction reaction of the photocatalyst. However, this is not entirely suitable in the case of applications where a high degree of hydrophilicity is caused by a photocatalyst, because conventional polysiloxanes aregenerally hydrophobic, and even if the photocatalyst decomposes organic groups in the polysiloxane with the addition of the photocatalyst to cause hydroxyl groups to substitute for silicon-bonded alkyl groups, hydrophilicity can be gradually developed, but this is a long time course, and it takes a long time from the light irradiation to the development of hydrophilicity, and the hydrophilicity disappears after a certain period of time in the dark, and the repeated development of hydrophobicity, reactivation to produce hydrophilicity and long-term light irradiation are required, which requires the light irradiation to be as long and continuous as possible, which is not suitable for the requirement of continuity of antifogging property which may be developed at any time. Therefore, it is necessary to find an inorganic binder which cannot be destroyed by the photocatalytic effect, has strong hydrophilicity, and is easy to exert the high hydrophilicity of the photocatalyst. The titanium polysiloxane film is based on Ti-O-Si bond, and the pure inorganic compound has very good stability. And the prepolymer has excellent coating property and is convenient to use. The invention utilizes silane and titanium alkane compounds which can be hydrolyzed to generate hydrophilic polytitanium siloxane with more attached hydroxyl groups through a two-step polymerization process. When the photocatalyst is loaded, the main chain Ti-O-Si bond of the photocatalyst can not be decomposed due to the photocatalytic effect of the photocatalyst, but the photocatalyst enables more hydroxyl groups to be attached to the main chain by decomposing the carbon alkyl organic groups in the photocatalyst so as to generate better hydrophilicity.

The hydrolytic polymerization is a key step and is controlled to provide uniform distribution of the final polytitanium siloxane polymer, less reaction by-products and high hydrophilicity, silane materials including epoxy and acyloxy groups, specifically, N- (3-acryloyloxy) -3-aminopropyltrimethoxysilane, N- (3-acryloyloxy) -3-aminopropyltriethoxysilane, gamma-methacryloyloxypropyltrimethoxysilane, β - (3, 4-epoxycyclo-ethyl) trimethoxysilane, gamma-glycidyl ether epoxypropyltrimethoxysilane or the like can be used.

In the presence of water, the silane and the titanane will undergo hydrolysis to produce an alkylhydroxy group and a silylhydroxy group. R, R_m，R_nAll represent alkyl, (1), (2) and (3) represent the hydrolysis process of silane containing propylene acyloxy, general silane and titanium alkane respectively.

(2) (3) In this process, the alkane hydroxyl and the silicon hydroxyl respectively generated in the reactions (1), (2) and (3), and the titanium hydroxyl (underlined in the formula) have high activity, and will react with each other to lose the hydroxyl, and the hydrophilicity of the final product is not optimal. Therefore, the propylene acyloxy group is protected firstly, silane and titanium alkane are hydrolyzed firstly, and after the reaction of silicon hydroxyl and titanium hydroxyl is finished, a long-chain molecule with Ti-O-Si bond as the main is formed.

After which the acryloyloxy group is hydrolyzed again, most of the alkylhydroxy groups can be preserved and exhibit strong hydrophilicity.

In order to allow the post-hydrolysis of the acryloyloxy group, it is critical to introduce a titanate which hydrolyses very rapidly so that the acryloyloxy group does not hydrolyse until the hydrolysis of the titanate is complete, so that when all of the silane and titanate hydrolyses to form the final network most of the acryloyloxy groups hydrolyse. This ensures that the hydrophilicity is preserved.

However, if the rate of hydrolysis is too fast, the titanate will precipitate as titanium dioxide and to avoid this, the rate of hydrolysis of the titanate can be reduced by suitably controlling the solution to be acidic, suitably at a pH of 1 to 5. The pH can be adjusted by using hydrochloric acid, nitric acid, sulfuric acid, etc. If the acidity is too strong, an alkaline substance such as ammonia water may be used. There is no particular limitation thereto.

The amount of water added to the hydrolytic polymerization reaction is also an important control parameter during the hydrolytic polymerization reaction. If the amount of water added is too small, complete hydrolysis cannot be achieved, but if the amount of water added is too large, the rate of hydrolysis reaction of the titanate is too fast, and precipitation may occur. The amount of water added is the minimum stoichiometric amount of water required for the hydrolysis reaction of the acryloyloxysilane and tetrabutyl titanate to be complete.

After the above prepolymerization, the solution must be diluted to avoid polymerization into a gel by stepwise gelation. In order to preserve the coating for a long period of time, the coating should be kept in the acidic range: preferably, the pH of the solution is between 1 and 7, and more preferably, the pH of the solution is between 3 and 6.

In the present invention, the photocatalyst is a main factor for rapidly achieving high hydrophilicity of the hydrophilicity-inducing titanium silica compound, and there are many types of photocatalysts, but from the viewpoint of cost and product effect, anatase type titanium dioxide is preferably selected or the photocatalytic effect is made better, and titanium dioxide may be mainly used with other dopants for enhancing the photocatalytic property added, such as titanium dioxide-supported metals, such as iron, platinum, nickel, rhodium, etc., or a mixture of titanium dioxide and some metal oxides, such as tungsten oxide, iron oxide, molybdenum oxide, silicon oxide, etc. When added to form a coating, the photocatalyst may be in the form of a solid powder, or a sol, which is suitable from the viewpoint of ease of dispersion and uniformity of dispersion.

The prepared titanium polysiloxane and the photocatalyst are mixed uniformly to form a photocatalytic titanium polysiloxane compound, so that the titanium polysiloxane compound can be used in various occasions and can be coated on various substrates in the form of paint. For the convenience of coating, some auxiliaries such as leveling agents for coating materials, film-forming aids, hardening accelerators, pigments and the like may be added, and these auxiliaries may be various coating additives known at present. The addition of these auxiliaries is based on the principle that the basic hydrophilicity and the photocatalyst are not affected. Forming a coating compound that is more suitable for easier application to a variety of substrates and applications.

If the compound is finally formed into a film, various means such as spray coating, spin coating, flow coating, dip coating, blade coating and the like can be used. The coating method is not limited. After coating, when the solvent is evaporated, the prepolymer of the titanosiloxane may be crosslinked to form a film under various conditions, and firmly attached to the surface of the substrate. The curing process may be room temperature, or may be accelerated by heating to 100-160 ℃.

When the coating is coated, a coating film with strong hydrophilicity and a contact angle less than 25 degrees can be obtained immediately, and after ultraviolet irradiation, a polytitanium-silicon-oxide coating film with super hydrophilicity and a contact angle close to zero degrees can be obtained. If anatase type titanium dioxide is used, the excitation light may be any ultraviolet ray having a band gap higher than that of the anatase type titanium dioxide, and the light source may be derived from an ultraviolet lamp, a fluorescent lamp, or the sun, etc., and if it is applied to outdoor, the sunlight may be used as the excitation light. After the super-hydrophilicity is generated by excitation, the super-hydrophilicity of the compound can be stored for a long time, and the super-hydrophilicity can be excited again by weaker light even after being in the dark for a very long time. The polytitanium siloxane can also maintain strong hydrophilicity until super hydrophilicity is not temporarily produced.

The titanium silicalite can be used in a variety of applications and in a variety of substrates including plastic metal, wood, glass, ceramics, resins, paper, and the like on a variety of surfaces. All occasions needing antifogging and self-cleaning surfaces, such as windshields and rearview mirrors of various vehicles such as automobiles and the like; various indicators of the road; a billboard; glasses; bathroom mirrors; various photographic lenses, display windows, solar cells, water heaters and greenhouses; various window glasses; self-cleaning paint for external wall and various decorative ceramic tiles.

Example (b):

the present invention is illustrated in detail by the following examples and comparative examples. The percentages are, unless otherwise specified, the molar percentages of the various starting materials. The invention and layout is limited to the following examples. Variations may be made by those skilled in the art without departing from the spirit of the invention.

Example 1:

0.01 mol of gamma-methacryloxypropyltrimethoxysilane and 0.01 mol of butyl orthotitanate were mixed, and then 30 ml of absolute ethanol was added. The mixture was charged into a three-necked flask equipped with a stirrer, heating jacket, condenser, dropping funnel. Then 0.5 ml of concentrated hydrochloric acid was added dropwise. The solution was heated at 50 ℃ for 4 hours with constant stirring to homogenize the solution. To the above solution, 40 ml of ethanol was added, and then 10 ml of acidic water adjusted to pH 2 with hydrochloric acid was gradually added dropwise and heated at 60 ℃ for 6 hours to perform hydrolysis reaction. A prepolymer of the titanosiloxane was obtained.

The prepolymer of the resulting titanium polysiloxane was added in an amount of 30% by weight based on the solid content of the prepolymer, and an anatase type titanium dioxide photocatalyst (produced by nano group in river sea, Jiangsu province) was added. Stirring and mixing evenly to obtain the coating composition of the photocatalytic hydrophilic titanium polysiloxane prepolymer.

The resulting composition was diluted with ethanol to a concentration of 3% by weight, based on the final solid content.

A wet film with a thickness of 10 μm was coated on a glass plate by a wire bar coater, and after completion of solvent evaporation at room temperature. The mixture was placed in an oven and heated at 140 ℃ for 1 hour. Thus obtaining the hydrophilic photocatalytic titanium polysiloxane coating film. Referred to as coating film 1. The resulting coating film had a thickness of 0.5 μm.

Example 2

The other preparation steps were the same as in example 1 except that the addition ratio of the photocatalyst was adjusted to 5% by weight of the solid content of the polytitanium siloxane, and the composition was finally diluted to 1% by weight of the coating solution. Finally, a coating film 2 with the thickness of 0.1 micron is prepared. The coating film was colorless and transparent.

Example 3

A doped photocatalyst compound containing iron can be obtained by preparing a 20% aqueous suspension from nano-anatase titanium dioxide produced by Nana Material Ltd in Zhoushanhui, Zhejiang, and adding 0.8% ferric chloride thereto and evaporating water to dryness, instead of the titanium dioxide produced by Nana Material Ltd in Jiangsu river sea in example 1, the other preparation steps are the same as in example 1. A 0.5 micron coating film 3 was obtained. Comparative example 1

The procedure of example 1 was otherwise followed, except that tetrabutyl titanate was replaced with ethyl orthosilicate. A coating of polysiloxane was obtained and a 0.5 micron comparative coating film 1 was prepared on a glass plate. Comparative example 2

The same procedure as in example 1 was repeated except that methyltrimethoxysilane was used instead of gamma-methacryloxypropyltrimethoxysilane, to obtain a 0.5 μm comparative coating film 2.

Description of the drawings: FIG. 1 shows the change of contact angle with the time of illumination of comparative coating film 1 and comparative coating film 2 under the irradiation of a 20W ultraviolet lamp, for coating film 1. (1) The curves (2), (3) correspond to the contact angle as a function of the time of illumination for the comparative coating film 2, the comparative coating film 1, and the coating film of example 1, respectively. Fig. 2 is a graph showing the change in contact angle with time of the coating film 1 and the comparative coating film 2 in the dark. (1) The curves (2) correspond to the changes of the comparative coating film 2 and the coating film 1, respectively. Measurement of coating film properties:

the contact angle of the coating film with water was measured with a contact angle measuring instrument.

Contact angles of the respective coating films with water were first measured without ultraviolet irradiation, and it was found that the coating films prepared in examples 1, 2, and 3 had good hydrophilicity and the initial contact angles thereof were all 25 degrees or less. In contrast, comparative examples 1 and 2 were hydrophobic and had contact angles of 60 degrees or more.

Specific contact angle values are shown in table 1.

Coating film 1	Coating film 2	Coating film 3	Comparative coating film 1	Comparative coating film 5
Coating film 1	Coating film 2	Coating film 3	Comparative coating film 1	Comparative coating film 5	18°	22°	21°	65°	77°

When the coating film sample was irradiated with a 20 watt uv lamp and the contact angle with water was measured at intervals, the contact angle of example 1 was very fast approaching 0 degrees, and the contact angle of example 2 was very fast decreasing. The final contact angle of the comparative example can be close to 0 degrees after long-term ultraviolet irradiation. The contact angle of comparative example 1 decreased very slowly with the time of illumination, and remained above 70 degrees after three hours of illumination. The contact angle dropping speed of comparative example 2 was relatively fast compared to comparative example 1, but the contact angle at the initial stage of light irradiation was close to 70 degrees. May be considered hydrophobic. (results are shown in figure 1)

The samples were kept in the dark and the angle of contact was measured at intervals. It was found that the contact angle increased slowly in the dark, but the contact angle of example 1 increased only to twenty more degrees. While comparative example 1 rose to more than sixty degrees. The super-hydrophilic effect of example 1 was achieved for a period of more than 48 hours. (results are shown in FIG. 2) effects of the invention

The coating film is composed of the high hydrophilic polytitanium siloxane and the photocatalyst which can generate super hydrophilic property through light induction, so that the coating film can maintain the long-term hydrophilic effect and has good antifogging property, antistatic property and self-cleaning function. The defect that the super-hydrophilic effect of the traditional photocatalyst coating film needs a long time from the completion of preparation to the exertion of the effect is overcome. And because the main body of the coating film is formed by Ti-O-Si bonds, the coating film is very stable, the damage of the oxidation-reduction effect of the photocatalyst to the coating film is avoided, and the coating film has very excellent weather resistance and durability. Can be applied to various surfaces needing antifogging, antistatic and self-cleaning. Is an ideal functional coating. Can be conveniently applied to various occasions and has important practical value.

Claims

1. A compound product with durable hydrophilicity and higher hydrophilicity under photocatalysis is characterized by that its main component is formed from polytitanium siloxane resin and photocatalyst material.

2. The product of the titanium polysiloxane compound contained in claim 1, wherein the organosilane as the raw material in the synthesis of the titanium polysiloxane resin contains a silane material which can produce hydrophilic hydroxyl groups after hydrolysis.

3. A silane material capable of generating an amphiphilic hydroxyl group according to claim 2, wherein the silane material comprises a silane material having an epoxy group and an acyloxy group, and specifically, N- (3-acryloyloxy) -3-aminopropyltrimethoxysilane, N- (3-acryloyloxy) -3-aminopropyltriethoxysilane, γ -methacryloyloxypropyltrimethoxysilane, β - (3, 4-epoxycyclo-alkyl) ethyltrimethoxysilane, γ -glycidylether epoxypropyltrimethoxysilane, or the like, as long as they contain an epoxy group or an acyloxy group.

4. The compound of claim 1 wherein the titanium component of the polytitanium siloxane resin is derived from a titanate ester or titanate. Such as tetrabutyl titanate or the like, titanium tetrachloride, and the like. One or a combination of several of them.

5. The hydrophilic composite article according to claim 1, wherein the proportion of the polytitanium siloxane resin is 5 to 90% by weight.

6. The coated film according to claim 1 wherein the photocatalyst comprises TiO₂，SnO₂，ZnO，Fe₂O₃，WO₃，Sr(TiO₃) Etc. or a mixture thereof.

7. The photocatalyst according to claim 5, comprising anatase titanium dioxide.

8. The anatase titanium dioxide according to claim 6 having a particle size of 100 nm or less.

9. The anatase titanium dioxide of claim 7 further including other dopants based on titanium dioxide that enhance the charge separation upon photoexcitation. Including titanium dioxide supporting metals such as iron, platinum, nickel, rhodium, etc., and mixtures of titanium dioxide and certain strong acid type metal oxides such as tungsten oxide, iron oxide, molybdenum oxide, silicon oxide, etc.

10. The hydrophilic compound preparation of claim 1, which is composed of an inorganic compound having a titanium-silicon-oxide (Ti-O-Si) bond as a main component, wherein a part of the organic groups bonded to the titanium-silicon-oxide bond can be decomposed by a photocatalyst.