JPH0585714A - Production of alcohol-base silica sol which silica coating film can be formed by low temperature baking - Google Patents

Abstract

PURPOSE:To provide a non-glare treating liquid for silica coating method for CRT faces or the like so that a nonglare coating film having excellent characteristics can be formed by baking at lower temp. (room temp.-100 deg.C) which is very low compared with a convenitional method of forming a nonglare coating film which requires high temp. (150-200 deg.C) and long time baking conditions. CONSTITUTION:The production of the alcohol-base silica sol features in hydrolysis of lower alkyl silicate expressed by formula Si(OR)4 (wherein R is methyl or ethyl group) and methanol and/or ethanol with specified amt. of water and catalyst. With using this silica sol, a silica coating film can be formed by low temp. baking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alcoholic silica sol which can be applied to various objects to be coated and can be baked at an extremely low temperature to form a strong inorganic silica coat film. It is a thing.

[0002]

2. Description of the Related Art CRT is an application example of a film-forming silicate.
There is a so-called silica coating method non-glare treatment technology in which a non-glare coating (anti-glare coating, diffuse reflection coating) is formed by coating on the (cathode ray tube) or the face surface of a liquid crystal display device and baking. As is well known, for example, recent color picture tubes for displays (C
In the technical development of (RT), not only high resolution but also efforts have been made to improve the visibility and safety for display users. Reflecting these development trends, the performance requirements for non-glare treatment technology by the silica coating method on the display surface are increasing more and more.

Conventionally, the following has been reported regarding the non-glare treatment technique by the silica coating method.

(1) In Japanese Utility Model Publication No. 50-26277, the disadvantage of using an aqueous solution of an alkali salt of silicic acid (commonly called water glass) shown in Japanese Utility Model Publication No. 44-11150, that is, since it is an aqueous solution, it becomes fluid after spray coating. There is disclosed a technique for improving the drawback that a rough surface having a fine irregularity that is easy and diffusely diffused is not easily formed. More specifically, by spraying a mixed solution (non-aqueous) of silicon tetrachloride (SiCl ₄ ) and alcohols or esters on the surface of the cathode ray tube and heat-treating it, the external light is diffused and reflected on the surface of the cathode ray tube to make the image easier to see. For this purpose, a so-called non-glare-treated cathode ray tube in which a fine uneven coating is formed is proposed.

(2) In JP-A-60-109134, a treatment liquid consisting of hydrolyzed silicate ester, alcohol, water, and hydrochloric acid (and / or nitric acid) is preliminarily prepared in an amount of 40 to 40.
Disclosed is a method for producing a cathode ray tube having a light diffusing layer, which is characterized in that it is applied to a face surface of a cathode ray tube preheated to 90 ° C. and then heated and baked at 100 to 200 ° C. to form a light diffusing layer. In addition, the reason why the face surface of the cathode ray tube is preheated to 40 to 90 ° C. beforehand is that a good diffusion layer can be obtained by the treatment liquid and the adhesion force of the film after firing is increased. In the above cited publication, 0.0025 to 0.025 mol of ethyl silicate (specifically, ethyl silicate 40 which is a hydrolysis product) and 100 mol of the ethyl silicate with respect to 100 ml of a solvent such as ethanol as a treatment liquid. 12 times more water and a catalytic amount of hydrochloric acid are added. It is shown that the use of pre-hydrolyzed (in other words, oligomeric) silicate ester is superior to the characteristics of a monomeric silicon compound (for example, silicon tetrachloride). There is.

(3) JP-A-61-118932 discloses that Si (OR) _{4 is} formed on the outer surface of the front panel of a cathode ray tube.
Alcohol solution Si (O to or the addition of HNO _3, the
R) ₄ alcohol solution (where R represents an alkyl group) is spray-coated, and then baked at 80 to 150 ° C. The front panel surface is made of SiO ₂ and is transparent and antiglare. Discloses a method for producing a cathode ray tube having a fine uneven coating. The addition of HNO ₃ is for improving the adhesive strength of the formed film, and is unnecessary if other strengthening means is adopted for the film strength. Further, in the above cited publication, 80 to 150 ° C.
By low temperature firing of (panel surface temperature), Si-O-Si
It is also shown that an antistatic effect can be obtained because the silanol group of Si-OH can be left in a part of the siloxane structure of. In the above cited publication, as a specific spraying liquid, a solute is Si (OC ₂ H ₅ ) ₄ , a solvent is ethanol, and other components are water and HNO ₃ , and the spraying liquid is used as a front panel. It is shown that a silica coat film is formed by spray coating on the outer surface of the above and baking temperature of 80 to 150 ° C. (holding for 30 minutes).

(4) In Japanese Patent Laid-Open No. 63-160131, a solution containing a polyalkylsiloxane is applied on a face plate, and then a condensation reaction is performed to form a SiO ₂ film on the surface of the face plate. A method of manufacturing a cathode ray tube (CRT) is disclosed. It is recognized that the one disclosed in this reference is intended to improve the method disclosed in the above-mentioned JP-A-61-118932. That is, HNO _{3 is} used as the adhesion improver in JP-A-61-118932 (it is well known that an acid of this type generally promotes a hydrolysis reaction, that is, a silanol group formation reaction). However, sufficient adhesive force cannot be obtained by this alone. Therefore, in order to ameliorate this drawback, the reference discloses that the treatment liquid contains a polyalkylsiloxane having some siloxane bond. In the above cited publication, an alcohol solution comprising a polyalkylsiloxane (average degree of polymerization tetramer), an acid or alkali for promoting a hydrolysis reaction, water, and an alcohol is shown as a specific coating solution. It should be noted that polyalkylsiloxane has an average of 2
Preference is given to those from the trimer to the hexamer. Further, as specific firing conditions, 115 ° C. for 10 minutes, 11
The condition of 5 ° C. for 5 minutes is disclosed.

(5) Japanese Patent Laid-Open No. 2-118601 discloses
In the method for producing a screen having an antiglare observation surface, (a) a step of heating a glass support to a first temperature higher than room temperature (for example, 48 to 50 ° C.), (b) a lithium-stabilized silica sol aqueous solution And (c) exposing the surface and the coating of the support to a heat source for a short period of time to a second temperature higher than the first temperature (eg 65 ° C.) Raising step, (d) washing step,
(e) a drying step is disclosed. This reference discloses that the temperature of the surface of the support and the film formed thereon is exposed to a temperature higher than the first temperature for a short time (for example, skin heating at 60 ° C. for about 30 seconds is adopted. It is recognized that it is based on the finding that the optical and physical properties of the coating are revealed.
The cited publication explains that in the conventional method, baking at 150 to 300 ° C. was necessary to obtain a wear resistant coating.

As described above, various methods have been proposed as a method for forming an antiglare silica coating film on various coating objects, but these have the following drawbacks and are sufficiently satisfactory. Not something you can do. (i) That is, in JP-B-50-26277, which uses monomeric SiCl ₄ as the silicic acid compound, the treatment liquid is a hydrochloric acid acidic liquid, so that the treatment equipment (eg, spray nozzle) is corroded. However, it is not sufficient from the standpoint of film characteristics (for example, halogen ions have a great influence on the emission slump, which is the life of cathode ray tubes). Further, in JP-A-61-118932, which uses an alcohol solution of Si (OR) ₄ , which is actually a treatment liquid obtained by adding water and nitric acid, the treatment liquid is applied to the front panel surface of a cathode ray tube. After that, hydrolysis reaction, condensation reaction, gelation reaction (generation of silanol group,
Since a siloxane bond is formed and three-dimensionalization occurs, the reaction is non-uniform and unstable, and it is not possible to obtain a silica coat film that is sufficiently strong and has excellent characteristics. -160131). (ii) Further, as the silicic acid compound, an alcoholic solution of a silicic acid ester which is preliminarily hydrolyzed is used, and in practice, a treatment liquid obtained by adding water and an acid (or alkali) as a catalyst is used. JP-A-60-1091
No. 34 and JP-A No. 63-160131 apply the treatment liquid on a face plate and cause a part of the hydrolysis reaction, condensation reaction and gelation reaction on the applied surface, and therefore the same as described above. The reaction is uneven and unstable,
In particular, it is not possible to obtain a silica coat film that is sufficiently strong and has excellent characteristics when baked at a low temperature of 100 ° C. or less. Furthermore, a lithium-stabilized silica sol is used as an oligomeric pre-hydrolyzed silicate ester.
No. 8601 is an aqueous solution of an alkaline salt of silicic acid (commonly called water glass) of the same type as that disclosed in JP-B-44-11150 cited in JP-B-50-26277.
In this method, the formed film reacts with the moisture in the air to become cloudy and the surface is eluted, which is a problem because the method uses as a starting material.

[0010]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The inventors of the present invention have made extensive studies to solve the above-mentioned problems of the prior art.
In particular, a treatment liquid capable of forming a silica coat film having a strong adhesive force by heating (or firing) at a low temperature of 100 ° C. or lower was examined. As a result, the alcoholic silica sol itself prepared by hydrolyzing a lower alkyl silicate in an alcohol medium with a predetermined amount of water and a catalyst to a predetermined hydrolysis rate is a hard adhesive having excellent adhesive strength by low temperature heating (calcination). The inventors have found that a film of 1) can be formed and completed the present invention.

[0011]

The present invention will be summarized as follows.
The present invention has the general formula Si (OR) ₄ (1) (where R is
Represents a methyl group or an ethyl group. The present invention relates to a process for producing an alcoholic silica sol capable of forming a silica coat film by low temperature firing, which comprises hydrolyzing a lower alkyl silicate represented by the formula (1) in methanol and / or ethanol.

The technical constitution of the present invention will be described in detail below. As described above, the present invention was born from the problem of developing a treatment liquid that is optimal for keeping the firing step conditions as low as possible and for a short time in the silica coat method non-glare treatment. As the conditions for the firing step, it is assumed that the processing conditions are room temperature to 100 ° C., preferably 50 to 100 ° C., and low temperature and short time of 30 to 60 minutes. As a result of investigating various treatment liquids for forming a silica coat film, the above-mentioned alcoholic silica sol itself has a very excellent adhesive force on various objects to be coated under firing conditions of low temperature and short time. It was found that the silica coat film can be formed.

The treatment liquid used for the non-glare treatment by the silica coating method of the present invention is a lower alkyl silicate of the general formula (1) which is hydrolyzed in a methanol and / or ethanol medium and under a catalyst. The resulting alcoholic silica sol has a very small sol particle size (1 μm or less). In the present inventors, such an alcoholic silica sol has not been sufficiently clarified as to why it forms a hard silica coat film having excellent adhesiveness under the condition of low temperature and short time, but the sol particle Small particle size,
Therefore, it is considered that the surface area of the sol particles is very large and that many silanol groups (Si-OH) are present on the surface of each particle, which produces a strong adhesive force even at low temperature firing. The non-glare treatment liquid comprising the alcoholic silica sol of the present invention is (i) clearly different from the treatment liquid containing a monomeric monomer as a main component, as compared with the non-glare treatment liquid of the prior art, and (ii) This is also clearly different from an oligomeric silicon compound, specifically, a non-glare treatment liquid obtained by further adding water and a catalyst to an alcoholic silica sol of a silicic acid ester which has been previously hydrolyzed. The above-mentioned alcoholic silica sol applied to the silica coating method non-glare treatment of the present invention is at first glance similar to that of the prior art of (ii), but the non-glare treatment liquid of the present invention is applied on the object to be coated. At this time, it is not necessary to add water or a catalyst. The present invention is based on the surprising fact that an alcoholic silica sol itself having a small sol particle size gives a hard coating with strong adhesion by a low temperature and short time baking process. , It cannot be understood by conventional common sense.

The alcoholic silica sol applied to the silica coating method non-glare treatment of the present invention must be prepared under the above-mentioned reaction conditions. That is, the general formula
As the lower alkyl silicate of (1), R must be a methyl group or an ethyl group. Also, methyl alcohol and / or ethyl alcohol must be used as the reaction medium.

Next, the hydrolysis step will be described. In the present invention, an acid catalyst is generally used as a catalyst for hydrolysis with a focus on the relationship with the membrane characteristics. As such an acid catalyst, nitric acid, hydrochloric acid, acetic acid, sulfuric acid, etc. may be used.
In particular, nitric acid is relatively low (bp 86 ° C.), has a strong oxidizing power as compared with other acids, and has a property of not easily corroding iron and the like. Therefore, nitric acid is the most preferable acid catalyst because it promotes the oxidation of the film at the time of film formation, forms a strong film, is less likely to remain in the film, and can suppress the corrosion of the film forming apparatus. In the present invention, the hydrolysis reaction is performed until a hydrolysis rate of about 300 to 1500% is achieved. The term “hydrolysis rate” as used herein means that in the chemical reaction formula Si (OR) ₄ + 2H ₂ O → SiO ₂ + 4ROH, hydrolysis rate (%) = [(amount of water used for reaction (g) / (alkyl silicate) Of 100% SiO ₂ (g)) × 100. When the hydrolysis rate is less than 300%, the hydrolysis reaction does not proceed sufficiently. for,
The amount of Si-OR remaining in the liquid increases and the adhesive force decreases. On the other hand, when the content is 1500% or more, the hydrolysis proceeds to the contrary, and the silica sol particles formed in the liquid become large, so that the surface area becomes small and the adhesive force decreases.
More specifically, room temperature to 50 ° C. (preferably room temperature to 30) using 10 to 20 times the molar number of tetramethoxysilane or tetraethoxysilane and water and the catalyst.
The hydrolysis reaction may be carried out at a temperature of (° C.) for 1 hour or more (preferably 2 to 5 hours) under stirring. In this way Si
An alcoholic silica sol having a solid content concentration of 20% or less, preferably 1 to 10% as an O ₂ concentration is prepared.

A desired diluting medium can be used in order to use the alcoholic silica sol thus prepared as a treatment liquid for the non-glare treatment by the silica coating method. Diluents of this type include methanol, ethanol, n-propanol, 2-propanol, n-butanol,
Examples thereof include C _{1 to} C ₁₀ alcohols such as 2-butanol, esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone, and mixed solvents thereof. Incidentally, these diluents are added to the above-mentioned alcoholic silica sol to dilute it so that the SiO ₂ concentration is 10% or less, preferably 5% or less.

From the viewpoint of pot life, it is desirable to store the non-glare treatment liquid prepared by the silica coating method prepared as described above at room temperature or lower. In the non-glare treatment, an object to be coated, for example, a CRT face surface or a liquid crystal display surface is heated to 40 to 90 ° C., the non-glare treatment liquid is spray-coated thereon, and 60 to 1 after coating.
It may be baked at a temperature of 00 ° C for 30 to 60 minutes. As a result, a silica coat film having a strong adhesive force and a high surface hardness can be obtained.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples and application examples. (1) Preparation example of alcoholic silica sol (i) Methyl silicate-based alcoholic silica sol 61.5 g of tetramethoxysilane was placed in a 1-liter four-neck round bottom flask, 463.9 g of MeOH was added, and the liquid temperature was adjusted to 3
The liquid was made uniform by stirring while maintaining the temperature constant at 0 ° C. Next, an aqueous solution obtained by adding 3.0 g of HNO ₃ to 71.6 g of water was added, and the mixture was stirred at 30 ° C. for 5 hours. (ii) Ethyl silicate alcoholic silica sol 85.7 g of tetraethoxysilane was placed in a 1-liter four-neck round bottom flask, 356.7 g of MeOH was added, and the liquid temperature was adjusted to 3
The liquid was made uniform by stirring while maintaining the temperature constant at 0 ° C. Next, an aqueous solution obtained by adding 3.0 g of HNO ₃ to 154.6 g of water was added, and the mixture was stirred at 30 ° C. for 5 hours.

(2) Preparation example of silica coating non-glare treatment liquid (blending ratio is wt%) (i) Methyl silicate alcoholic silica sol ((1)-(i), Example 1) ... 50% IPA 50% (ii) Ethylsilicate alcoholic silica sol ((1)-(ii) above, Example 1) 50% IPA ………………………………………………………… 50% (iii) Ethyl silicate 40-1 (Note 1) (Comparative example 1) Four 60 g of ethyl silicate 40 mouth Round bottom flask 2
1 liter, MeOH 445.9 g was added, and the liquid temperature was adjusted to 30
The liquid was made uniform by stirring while maintaining the temperature constant at 0 ° C. next,
An aqueous solution obtained by adding 3.0 g of HNO ₃ to 91.1 g of water was added, and the mixture was stirred at 30 ° C. for 5 hours. Then IPA 600
g was added to make a sample. (iv) Methyl silicate 51 (Note 2) (Comparative Example 2) 47.1 g of ethyl silicate 51 was placed in a 4-neck round bottom flask 2 l, MeOH 455.6 g was added, and the liquid temperature was adjusted to 3
The liquid was made uniform by stirring while maintaining the temperature constant at 0 ° C. Next, an aqueous solution obtained by adding 3.0 g of HNO ₃ to 94.3 g of water was added, and the mixture was stirred at 30 ° C. for 5 hours. Then IPA 6
A sample was prepared by adding 00 g. (v) Ethyl silicate 40-2 (Note 3) (Comparative Example 3) Four-neck round bottom flask 2 containing 60 g of ethyl silicate 40
It was put in 1 and 800 g of IPA and 240 g of n-BuOH were added, and the mixture was stirred while keeping the liquid temperature constant at 30 ° C. to make the liquid uniform. Next, an aqueous solution obtained by adding 10 g of HCl to 90 g of water was added and stirred at 30 ° C. for 1 hour to prepare a sample. (Note 1) Tetraethoxysilane pentamer is the main component. (Note 2) Tetramethoxysilane tetramer is the main component. (Note 3) Tetraethoxysilane pentamer is the main component.

(3) Characteristics of Silica-Coated Nonglare Coating The above-mentioned silica-coated nonglare treatment liquid was applied to a test piece by the following procedure and baked, and then the coating characteristics were evaluated.
The results are shown in Table 1. (i) Test piece ... * 12 inch CRT (ii) Treatment method (a) Preheating * 60 ° C x 1.5 hours (in electric constant temperature dryer) (b) Spray conditions * Spray nozzle: Spraying System Japan 2-fluid nozzle, φ = 0.4mm * Distance ...... 25cm * Flow rate 10ml / min * Spray time ...... 60 seconds * Air pressure ...... 2.0Kg / cm ² (c) Firing condition * Use far infrared firing furnace * Temperature rising rate (60 → 100 ° C) …… 8 ° C / min * Baking …… 60 ° C or 100 ° C, 30 minutes (iii) Evaluation method (a) Measurement of gloss value Nippon Denshoku Industries Co., Ltd. VG-2P
-Measured according to JIS Z 8741 using D3. Measurement conditions Gs (60 °) (b) Eraser test LION No. A reciprocating friction test is conducted with an eraser tester using 50-30, the gloss value after 200 times is compared with the initial value (ΔG200), and the surface state is observed with the naked eye. Measurement conditions Load 1 kg (c) Pencil hardness test JIS K 5400 (6,14)
Measured according to the pencil scratch test. (d) Glitter Turn on the CRT and observe the glare on the surface of the CRT with the naked eye.

[0021]

[Table 1]

From Table 1, the examples are almost the same in terms of glare as compared with the comparative examples. However, a significant difference was found in the results of the eraser test and the pencil hardness test. In particular, the example shows a result which is almost the same as that of Comparative Example 3 at 180 ° C. for 30 minutes. The film hardness at the time of baking at 60 ° C. for 30 minutes in the example is
It can be used as a silica-coated non-glare film.

[0023]

EFFECTS OF THE INVENTION According to the present invention, it is possible to form a hard silica coat film which can be fired on a much lower temperature side than conventional ones and which has a strong adhesive force on various objects to be coated. A silica coating non-glare treatment liquid capable of achieving the above is provided.

Claims (4)

[Claims] 1. A method for hydrolyzing a lower alkyl silicate represented by the general formula Si (OR) ₄ (1) (wherein R represents a methyl group or an ethyl group) in methanol and / or ethanol. A method for producing an alcoholic silica sol capable of forming a silica coat film by low temperature firing. 2. The method for producing an alcoholic silica sol capable of forming a silica coat film by low temperature firing according to claim 1, wherein the hydrolysis rate is 300 to 1500%. 3. The method for producing an alcoholic silica sol capable of forming a silica coat film by low temperature firing according to claim 1, wherein the hydrolysis is carried out using an acid catalyst. 4. The method for producing an alcoholic silica sol capable of forming a silica coat film by low temperature firing according to claim 1, wherein the alcoholic silica sol has a solid content concentration of 1 to 10% as SiO ₂ .