JP2015194740A - Highly-durable low refractive index film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly-durable low refractive index film which has a low refractive index, is highly anti-reflective, and exhibits small refractive index variation even after being kept in a high-temperature high-humidity environment for a prolonged period of time.SOLUTION: A low refractive index film is obtained by coating a substrate or a layer formed on the substrate with a composition containing aggregates comprising fumed silica particles aggregated together and a hydrolysate of silicon alkoxide and then baking the coated product. The film has a porosity of 15-55%, a refractive index in a range of 1.15-1.39 immediately after baking, and a refractive index variation of no more than 8%.

Description

  The present invention relates to a low refractive index film used for display panels, solar cells, optical lenses, camera modules, sensor modules, and the like. More specifically, the present invention relates to a low refractive index film having a low refractive index and a high antireflection effect, and having excellent durability with little change in refractive index even when held at high temperature and high humidity for a long time.

  A low refractive index film formed on the surface of a transparent substrate such as glass or plastic is a reflection of incident light on display panels such as cathode ray tubes, liquid crystals, organic EL, solar cells, optical lenses, glass for showcases, etc. It is used as an antireflection film for preventing the above. For example, an antireflection film for improving visibility is provided on the display surface side of the display panel, and in the field of solar cells, the reflection of incident sunlight is prevented to increase the light absorption rate. In addition, measures such as forming a low refractive index film as an antireflection film on the surface of a glass substrate are taken.

As a film for preventing such reflection, conventionally, a single layer film made of MgF ₂ , cryolite or the like formed by a vapor phase method such as a vacuum deposition method or a sputtering method has been put into practical use. In addition, a multilayer film formed by alternately laminating a low refractive index film such as SiO ₂ and a high refractive index film such as TiO ₂ or ZrO ₂ on a base material has a high antireflection effect. It has been known. However, gas phase methods such as vacuum deposition and sputtering have problems in terms of manufacturing cost because the equipment is expensive. In addition, the method of forming a multilayer film by alternately laminating a low refractive index film and a high refractive index film is not practical because the manufacturing process is complicated and takes time and labor.

  Therefore, recently, a coating method such as a sol-gel method has attracted attention in terms of manufacturing cost and the like. However, in the sol-gel method, in general, a sol-gel solution is prepared and applied to a transparent substrate such as glass, and then a film is formed by drying, baking, or the like. As compared with a film formed by a vapor phase method such as a vacuum deposition method, a desired low refractive index cannot be obtained, and various problems such as poor adhesion to a substrate and generation of cracks remain.

  As a low refractive index film using such a sol-gel method, a silica sol (a) in which silica particles having a predetermined average particle diameter are dispersed, an alkoxysilane hydrolyzate, a metal alkoxide hydrolyzate, and a metal salt are included. Disclosed is a low-refractive-index antireflection film comprising at least one component (b) selected from the group, which is applied to a substrate with a coating solution containing the organic solvent in a desired ratio and then cured. (For example, refer to Patent Document 1). In this film, in particular, by using the silica particles at a specific ratio, it is said that minute irregularities are formed on the surface of the film, and a good antireflection effect is obtained to lower the refractive index.

  Patent Document 2 discloses an antireflection film in which a silica layer made of an organosilicon compound formed using an organic silicone as a raw material is formed on the surface of an antireflection laminate formed on a substrate. . The silica layer provided in the antireflection film has a low refractive index, and it is said that the refractive index hardly changes even when used for a long time or under high temperature and high humidity conditions.

  Further, Patent Document 3 includes a low refractive index in which microparticles are formed between microparticles by containing inorganic microparticles and polymers having microvoids formed therein in a desired ratio and by stacking at least two inorganic microparticles. An antireflective coating having a layer is disclosed. In this antireflection film, microvoids are formed in the fine particles and between the fine particles. As a result, the porosity of the low refractive index layer is high, a very low refractive index is obtained, and the inorganic fine particles are adhered by the polymer. It is said that the strength of the low refractive index layer is also excellent.

JP-A-8-122501 (Claim 1, paragraph [0008], paragraph [0020]) JP 2002-103507 A (Claims 1 to 6, paragraph [0008]) JP 11-326601 A (Claim 1, paragraph [0006])

  However, in the conventional film disclosed in Patent Document 1, silica sol in which silica particles obtained by a so-called wet method are dispersed is used. Therefore, there is a problem that it is difficult to sufficiently lower the refractive index, and a higher antireflection effect cannot be obtained. In addition, since the surface of the coating film is made of silica particles to form a minute irregular surface, it exhibits hydrophilicity, and therefore, when used as an antireflection film, problems such as adhesion of dirt occur. In particular, in the case of a low refractive index film for solar cells that are used outdoors and exposed to harsh conditions for a long time, high durability is also required when used under severe conditions such as high temperature and high humidity. .

  Moreover, the film shown in the above-mentioned conventional patent document 2 has a high initial refractive index of 1.40 to 1.46, and the antireflection effect is not sufficient. Moreover, although the said low reflection glass article shown by the said patent document 3 is said to have a low reflectance etc., it is a space | gap with which the micro void in the particle | grains was closed, and it generate | occur | produced inside in high temperature high humidity It is difficult for moisture to escape, and the refractive index of the film may change due to moisture. Thus, various problems remain in the technical field of forming a low refractive index film by a sol-gel method or the like.

  An object of the present invention is to provide a low refractive index film having a low refractive index and a high antireflection effect, and having excellent durability with little change in refractive index even when held at high temperature and high humidity for a long time.

  According to a first aspect of the present invention, a composition containing an aggregate in which fumed silica particles are aggregated and a hydrolyzate of silicon alkoxide is applied to a base material or a layer formed on the base material, followed by firing. A low refractive index film obtained by the above process, the porosity is in the range of 15 to 55%, the refractive index immediately after the film formation is in the range of 1.15 to 1.39, and the following formula (1) The calculated refractive index change rate is 8% or less.

Change rate of refractive index (%) = (refractive index of film B / refractive index of film A−1) × 100 (1)
However, in the formula (1), the film A is a film immediately after film formation, and the film B is 2000 hours after film formation in high temperature and high humidity (temperature 80 ° C., relative humidity 85% RH). The membrane after holding.

  The second aspect of the present invention is an invention based on the first aspect, and is characterized in that the average primary particle size of the fumed silica particles in the film is in the range of 5 to 50 nm.

  The third aspect of the present invention is an invention based on the second aspect, and the silica particle portion occupying in the silica structure composed of the fumed silica particles and the hydrolyzate of silicon alkoxide in the film is 50 to 50%. It is 99 mass%.

  A fourth aspect of the present invention is an invention based on the first to third aspects, and is characterized in that the contact angle of the film surface is 85 to 125 °.

  The low refractive index film according to the first aspect of the present invention is a composition comprising a base material or a layer formed on the base material, and an aggregate of fumed silica particles and a hydrolyzate of silicon alkoxide. Is a low refractive index film obtained by applying and baking, the porosity is in the range of 15 to 55%, the refractive index immediately after the film formation is in the range of 1.15 to 1.39, High anti-reflection effect, little change in refractive index, high durability in long-time use under harsh conditions.

  The low refractive index film of the second aspect of the present invention is more excellent in terms of film transparency and antireflection effect because the average primary particle diameter of the fumed silica particles in the film is in the range of 5 to 50 nm. Effect.

  In the low refractive index film of the third aspect of the present invention, the silica particle portion in the silica structure composed of the fumed silica particles and the hydrolyzate of silicon alkoxide in the film is controlled in the range of 50 to 99% by mass. Therefore, cracks that are likely to occur after firing are greatly suppressed.

  Since the low refractive index film of the fourth aspect of the present invention has a contact angle of 85 to 125 ° on the film surface, in addition to the antireflection effect and durability described above, the film surface also has water repellency and antifouling properties. Excellent.

  Next, the form for implementing this invention is demonstrated.

  The low refractive index film of the present invention has a porosity of 15 to 55% and a refractive index immediately after film formation of 1.15 to 1.39. The void means, for example, a portion where voids are formed in the film due to the shape of the particles constituting the film, the particle size distribution, etc., and the porosity means the ratio of the void to the entire film. .

  The reason why the porosity is limited to the above range in the present invention is that when the porosity is less than 15%, the refractive index does not fall below the predetermined value, and a sufficient antireflection effect of the film cannot be obtained. On the other hand, if the upper limit is exceeded, the hardness decreases and the film becomes brittle, which causes inconveniences in terms of impact resistance and the like. On the other hand, by controlling the porosity to the above desired range, a desired low refractive index can be achieved and a high antireflection effect can be exhibited. Among these, the porosity is preferably in the range of 20 to 55%. The reason why the desired low refractive index can be achieved by controlling the porosity to a desired range is presumed that the film contains moderately low-refractive-index air than the material constituting the film. Is done. Even if the porosity is controlled within the above range, it is difficult to make the refractive index of the film below 1.15 at present. Further, the low refractive index film of the present invention has a very high durability with a change rate of the refractive index calculated from the following formula (1) of 8% or less.

Change rate of refractive index (%) = (refractive index of film B / refractive index of film A−1) × 100 (1)
However, in the formula (1), the film A is a film immediately after film formation, and the film B is 2000 hours after film formation in high temperature and high humidity (temperature 80 ° C., relative humidity 85% RH). The membrane after holding.

  Therefore, even if it is used for applications such as solar cells used under severe conditions such as outdoors, the refractive index is in the initial state (after film formation, temperature 23 ° C. ± 5 ° C., humidity 65% RH ± 20 %, And a state within 48 hours after film formation, hereinafter referred to as immediately after film formation), can maintain a high antireflection effect over a long period of time without significant change. Normally, when water droplets or the like adhere to the film surface due to high humidity conditions, the phenomenon of whitening of the film occurs from that location, which may greatly change the refractive index and transparency of the film. When there is a desired void penetrating to the film surface as in the low refractive index film of the invention, a vapor escape path is created, and the whitening can be prevented without the vapor staying inside the film. Therefore, the low refractive index film of the present invention is presumed to have excellent durability even under such severe conditions.

  For reasons described later, the film contains a hydrolyzate of fumed silica particles and silicon alkoxide, and the average primary particle size of the fumed silica particles is preferably in the range of 5 to 50 nm. A range of 30 nm, particularly 8 to 24 nm is particularly preferable. The average primary particle size of the fumed silica particles in the film means the smallest unit particle diameter that can be confirmed in the film. Moreover, it is preferable that the ratio of the silica particle part which occupies for the silica structure comprised by the hydrolyzate of the fumed silica particle and silicon alkoxide in a film | membrane is 50-99 mass%. The reason is that if the ratio of the silica particle portion in the silica structure composed of the hydrolyzed product of fumed silica particles and silicon alkoxide in the film is less than the lower limit value, cracks will occur during the film formation process, particularly during firing. On the other hand, if the upper limit is exceeded, problems such as poor adhesion to the substrate or the like and the film becoming brittle may occur. Among these, it is especially preferable that it is 70-95 mass%. Moreover, it is preferable that the contact angle of the film | membrane surface is 80-125 degrees. Thereby, the water repellency and antifouling property of the coating surface can be improved at the same time. If the contact angle is too small, problems such as adhesion of dirt may occur when used in an external environment as an antireflection film, while if too large, problems such as poor film adhesion may occur. .

  Such a low refractive index film is formed by, for example, applying the composition by a wet coating method onto a base material or a layer formed on the base material using a composition described later, and baking the composition. Can do. As an example of a composition suitable for forming the low refractive index film, for example, a hydrolyzate of a specific silicon compound and silica sol (E) in which fumed silica particles are dispersed in a liquid medium (dispersion medium) are used. Examples thereof include a composition for forming a low refractive index film prepared by mixing at a predetermined ratio. The hydrolyzate mentioned here is a product produced by hydrolysis (condensation) of silicon alkoxide (A) represented by the following chemical formula (2).

Si (OR) ₄ (2)
(In the formula (2), R represents an alkyl group having 1 to 5 carbon atoms.)

  The reason why the hydrolyzate of the silicon alkoxide (A) is used in the composition is to maintain the speed of reactivity and the hardness of the film obtained from the composition. For example, a hydrolyzate of a silicon alkoxide having an alkyl group having 6 or more carbon atoms has a slow hydrolysis reaction, takes a long time for production, and decreases the hardness of a film obtained by applying the obtained composition. There is a case.

  Specific examples of the silicon alkoxide (A) represented by the above formula (2) include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane. Examples include methoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane. Among these, tetramethoxysilane is preferable because a film having high hardness can be obtained.

  In addition, the hydrolyzate is formed by mixing the silicon alkoxide (A) with a fluoroalkyl group-containing silicon alkoxide (F) represented by the following formula (3) at a predetermined ratio and hydrolyzing (condensing) these. What was made to contain can also be contained.

CF ₃ (CF ₂ ) _n CH ₂ CH ₂ Si (OR ¹ ) ₃ (3)
(However, Formula (3) R1 represents an alkyl group having ¹ to 5 carbon atoms, and n represents an integer of 0 to 8).

  By using this hydrolyzate, the refractive index of the film can be further reduced, and the water repellency and antifouling property of the coating surface can be further improved. Specific examples of the fluoroalkyl group-containing silicon alkoxide (F) represented by the above formula (3) include trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane, and tridecafluoro. Examples include octyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, and the like. Of these, trifluoropropyltrimethoxysilane is preferred because of its high hydrolysis reactivity and ease of reaction control.

  The mixing ratio of the hydrolyzate of the silicon alkoxide (A) and the fluoroalkyl group-containing silicon alkoxide (F) is 1: 0.6 to 1.6 (A: F) by mass ratio. It is preferable to do this. Here, the reason why the mass ratio between the silicon alkoxide (A) and the fluoroalkyl group-containing silicon alkoxide (F) is preferably in the above range is that the fluoroalkoxy group-containing silicon alkoxide (F) is compared with the silicon alkoxide (A). This is because if the mass ratio is too small, it is difficult to obtain the effect of reducing the refractive index of the formed film. Moreover, if the mass ratio of the fluoroalkoxy group-containing silicon alkoxide (F) to the silicon alkoxide (A) is too large, the film adhesion and the film hardness may decrease. Among these, the ratio of silicon alkoxide (A) to fluoroalkyl group-containing silicon alkoxide (F) is particularly preferably 1: 0.65 to 1.3 (A: F) in terms of mass ratio.

  To produce a hydrolyzate of silicon alkoxide (A) represented by the above formula (2), or a hydrolyzate of silicon alkoxide (A) and a fluoroalkoxy group-containing silicon alkoxide (F) represented by the above formula (3). These are hydrolyzed (condensed) in an organic solvent. Specifically, in the case of a hydrolyzate of silicon alkoxide (A), hydrolysis of silicon alkoxide (A) and fluoroalkoxy group-containing silicon alkoxide (F) with respect to 1 part by mass of silicon alkoxide (A) In the case of a product, preferably 0.5 to 2.0 parts by mass of water (B), an inorganic acid, or 1 part by mass of the total amount of silicon alkoxide (A) and fluoroalkyl group-containing silicon alkoxide (F) The organic acid (C) is mixed in a proportion of 0.005 to 0.5 parts by mass and the organic solvent (D) is mixed in a proportion of 1.0 to 5.0 parts by mass, and the silicon alkoxides (A) or silicon alkoxides (A) are mixed. And a fluoroalkyl group-containing silicon alkoxide (F). Here, the reason why the ratio of water (B) is preferably within the above range is that the refractive index may not be sufficiently lowered when the ratio of water (B) is less than the lower limit. On the other hand, if the upper limit is exceeded, problems such as gelation of the reaction solution may occur during the hydrolysis reaction. In addition, the adhesion with the substrate may be reduced. Among these, the ratio of water (B) is particularly preferably 0.8 to 3.0 parts by mass. As the water (B), it is desirable to use ion-exchanged water, pure water or the like in order to prevent impurities from being mixed.

  Examples of the inorganic acid or organic acid (C) include inorganic acids such as hydrochloric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, oxalic acid, and acetic acid. Of these, it is particularly preferable to use formic acid. Inorganic acid or organic acid (C) functions as an acidic catalyst for accelerating the hydrolysis reaction. However, formic acid is used as the catalyst, so that it is easy to form a film having a lower refractive index and excellent transparency. It is. Compared with the case where other catalysts are used, the effect of preventing the promotion of non-uniform gelation in the film after film formation is higher. The reason why the ratio of the inorganic acid or the organic acid (C) is preferably in the above range is that the ratio of the inorganic acid or the organic acid (C) is less than the lower limit value, so that the reactivity is poor and the water repellent property is low. On the other hand, the reactivity is not affected even when the upper limit is exceeded, but problems such as corrosion of the base material due to residual acid may occur. Among these, the ratio of the inorganic acid or the organic acid (C) is particularly preferably 0.008 to 0.2 parts by mass.

  As the organic solvent (D), alcohol, glycol ether or glycol ether acetate is preferably used. The reason why it is preferable to use these alcohols, glycol ethers or glycol ether acetates as the organic solvent (D) is to improve the coating properties of the composition, and also includes, for example, silicon alkoxide (A) and a fluoroalkyl group-containing compound. This is because these are easily mixed when using a hydrolyzate of silicon alkoxide (F). Examples of the alcohol include methanol, ethanol, propanol, isopropyl alcohol (IPA) and the like. As glycol ethers, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, propylene glycol monoethyl ether, dipropylene glycol monoethyl ether Etc. As glycol ether acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monoethyl ether Examples include acetate and dipropylene glycol monoethyl ether acetate. Of these, the hydrolysis reaction is easy to control, and good coating properties can be obtained during film formation, so ethanol, IPA, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether or propylene glycol monomethyl ether Acetate is particularly preferred. Further, the reason why the ratio of the organic solvent (D) is preferably within the above range is that when the ratio of the organic solvent (D) is less than the lower limit value, the reaction solution is likely to be gelled during the hydrolysis reaction, resulting in low refraction. This is because it is difficult to obtain a film excellent in water repellency at a high rate. In addition, the adhesion to the substrate may be reduced. On the other hand, if the upper limit is exceeded, problems such as a decrease in the reactivity of hydrolysis occur, and a film having a low refractive index and excellent water repellency cannot be obtained. Among these, the ratio of the organic solvent (D) is particularly preferably 1.5 to 3.5 parts by mass.

As the silica sol (E), a sol in which fumed silica particles having an average particle diameter of 5 to 50 nm and a specific surface area (BET value) of 50 to 400 m ² / g are dispersed in a liquid medium is used. It is preferable to do this. Silica sols include sols in which so-called wet silica (colloidal silica) obtained by neutralization of an aqueous solution of sodium silicate with an acid or alkali metal salt is dispersed, but flames of volatile silicon compounds such as silicon halide compounds It is preferable to use a sol obtained by dispersing a so-called dry silica (fumed silica) obtained by a spray flame method in which hydrolysis is performed. Examples of such fumed silica include “AEROSIL200 (registered trademark)” manufactured by Nippon Aerosil Co., Ltd. The reason why it is preferable to use a silica sol in which fumed silica is dispersed is, for example, that the water repellency of the coating surface in the film after film formation is further improved as compared with the case in which a silica sol in which colloidal silica is dispersed is used. Because it can. The reason is presumed to have an aggregate structure with higher hydrophobicity than sols such as colloidal silica. In addition, by setting the average particle size and specific surface area (BET value) of the silica particles in the silica sol within the above range, the average primary particle size of the silica particles contained in the formed film is controlled to the above desired range. This is because it is easy to obtain a film having higher transparency and lower refractive index. The reason why the average particle diameter and specific surface area (BET value) of the silica particles are preferably in the above range is that, if the average particle diameter is less than the lower limit value, the average primary particle diameter of the silica particles contained in the formed film is the above-mentioned. This is because the lower limit of the above may not be satisfied and problems such as the refractive index of the formed film not being sufficiently lowered may occur. On the other hand, if the average particle size exceeds the upper limit value, the average particle size of the silica particles contained in the formed film exceeds the above upper limit value, and the transparency of the formed film may deteriorate. The average particle size of fumed silica particles referred to here is the average particle size of secondary particles in which several to several tens of primary particles are aggregated, and is measured using a dynamic light scattering type particle size distribution device. The volume-based median diameter. The specific surface area (BET value) refers to a value obtained by using a calculated value by the BET three-point method measured by adsorbing nitrogen gas.

  In addition, in silica sol in which silica particles obtained by a so-called wet method are dispersed, it is difficult to form voids in the formed film. On the other hand, fumed silica particles have an aggregate that aggregates in a bead-like manner after production, whereby nanometer-sized pores are formed in the aggregate. Then, gaps are formed between the aggregated particles in the film whose packing property is deteriorated due to the irregular aggregated shape, and pores are more easily formed. As a result, the refractive index inside the film tends to decrease, and high antireflection performance can be obtained. In the sol in which fumed silica particles are dispersed, the primary particles are formed by high-density silica particles. Although pores exist in the agglomerate of fumed silica particles, these pores communicate with each other and are not closed voids as in Patent Document 3 described above. In the case of closed voids, there is a problem that moisture generated inside is difficult to escape under high temperature and high humidity, but since the pores between the aggregates are connected to the outside, moisture can be released and Problems such as a change in refractive index due to the remaining moisture are less likely to occur. For these reasons, it is preferable to use a silica sol in which fumed silica is dispersed.

  Moreover, before mixing the silica sol (E) with the hydrolyzate, it is preferable that an aggregate in which silica particles are aggregated in a bead shape in the composition after preparation is preferably stirred as described below. It can be prepared to be contained in a size of 20 to 150 nm. Thus, the effect of reducing the refractive index of a film | membrane is heightened more by including a silica particle as an aggregate of a predetermined magnitude | size. Further, when the size of the aggregate is less than the lower limit, applicability may be deteriorated due to thickening of the composition, and when the upper limit is exceeded, the transparency of the formed film may be deteriorated. The size of the aggregate refers to a volume-based median diameter measured using the dynamic light scattering particle size distribution apparatus. The bead shape is an irregular bead shape, and is not limited to a shape in which particles are connected in a straight line, for example. The aggregate includes the above-described secondary particles and agglomerated particles in which the secondary particles are further entangled and aggregated. Rely on forming particles.

In the low refractive index film-forming composition, the hydrolyzate and the silica sol (E) is a SiO ₂ minutes in the hydrolyzate when the 1 part by mass, SiO ₂ minutes of the silica sol (E) is It is preferably prepared by mixing so as to be 1 to 99 parts by mass. This is because if the ratio of silica sol (E) is less than the lower limit, the refractive index of the formed film is difficult to decrease, whereas if it exceeds the upper limit, the transparency and hardness of the formed film may decrease. In addition, the adhesion to the substrate may be reduced. Among these, it is particularly preferable that the ratio of the silica sol (E) is such that the SiO ₂ content of the silica sol (E) is ₂ to 30 parts by mass with respect to 1 part by mass of SiO ₂ in the hydrolyzate.

  In order to prepare this composition for forming a low refractive index film, first, an organic solvent (D) is added to the silicon alkoxide (A), and the mixture is preferably stirred at a temperature of 30 to 40 ° C. for 5 to 20 minutes. A first solution is prepared by When the hydrolyzate of the silicon alkoxide (A) and the fluoroalkyl group-containing silicon alkoxide (F) is contained, the silicon alkoxide (A) and the fluoroalkyl group-containing silicon alkoxide (F) are Before adding to an organic solvent (D), it measures and mixes so that it may become the above-mentioned predetermined ratio. On the other hand, water (B) and inorganic acid or organic acid (C) are mixed, and the second liquid is prepared separately by stirring preferably at a temperature of 30 to 40 ° C. for 5 to 20 minutes. Since tetramethoxysilane used as the silicon alkoxide (A) is highly toxic, it is desirable to use an oligomer obtained by polymerizing this monomer for about 3 to 6 in advance.

  Next, the first liquid prepared as described above is preferably maintained at a temperature of 30 to 80 ° C., the second liquid is added to the first liquid, and the mixture is stirred for 30 to 180 minutes while maintaining the temperature. . As a result, a hydrolyzate of the silicon alkoxide (A) or a hydrolyzate of the silicon alkoxide (A) and the fluoroalkoxy group-containing silicon alkoxide (F) is produced. And the said composition for low refractive index film formation is obtained by mixing this hydrolyzate and the silica sol (E) in which a fumed silica particle disperse | distributes to a liquid medium in the above-mentioned predetermined ratio.

In addition, when preparing the silica sol (E), the liquid medium (dispersion medium) in which the fumed silica particles are dispersed is an organic material used for the production of the hydrolyzate in terms of the mixing property and coating property of the composition. It is preferable to use the same kind as the solvent (D), or one compatible with the same. Examples of the dispersion medium other than the organic solvent (D) which are compatible with the organic solvent (D) include alcohols such as butanol, ketones such as acetone and methyl ethyl ketone, ethylene glycol, propylene glycol, hexylene glycol and the like. Examples include glycols, N-methylpyrrolidone, and dimethylformamide. The ratio of fumed silica particles in the silica sol (E) is the concentration of SiO ₂ in the silica sol (E) is preferably adjusted so that 5 to 30 mass%. If it is less than the lower limit, there may be a problem that the refractive index of the film does not sufficiently decrease, and if it exceeds the upper limit, a problem such as a decrease in transparency and hardness of the formed film may occur.

  In addition, after adding the fumed silica particles to the dispersion medium, the mixture is sufficiently dispersed by stirring for 15 to 90 minutes at a rotational speed of 5000 to 20000 rpm using a homomixer before mixing with the hydrolyzate. Is desirable. Fumed silica powder with a small particle size often forms aggregates containing secondary particles in which the particles are aggregated in a bead-like manner or agglomerates after production. By carrying out, the magnitude | size of the said aggregate can be adjusted to 20-150 nm preferably in the composition after preparation. If the dispersion step is not performed under the above conditions, the size of the aggregate is out of the above range, so that the refractive index of the film does not sufficiently decrease as described above, or the transparency and hardness of the film decrease. May cause problems. In addition, if the dispersion step is excessively performed, fumed silica particles are not dispersed, and a large aggregate is formed, which may cause a problem such as precipitation, which is not preferable. In addition to the method of using the homomixer, the method of controlling the size of the aggregate includes, for example, a method of using zirconia beads, shaking with a paint shaker, and sufficiently dispersing. Moreover, the reason why it is preferable to perform these treatments before mixing with the hydrolyzate is that when the hydrolyzate is mixed and then subjected to a strong agitation or dispersion step by shaking, the hydrolysis reaction of the silicon alkoxide rapidly increases. This is because problems such as progress and composition instability may occur.

  A method for forming a low refractive index film using the thus prepared composition for forming a low refractive index film will be described. The wet coating method for applying the low refractive index film-forming composition to a substrate or the like is not particularly limited, and examples thereof include a spin coating method, a die coating method, and a spray method. After coating, it is preferably dried at a temperature of 50 to 100 ° C. for 5 to 60 minutes using a hot plate or an atmosphere firing furnace, and then preferably 100 to 300 ° C. using a hot plate or an atmosphere firing furnace. Bake at a temperature of 5 to 120 minutes to cure. The film formed in this manner achieves a very low refractive index of 1.15 to 1.39 as described above by generating appropriate voids inside the film and exhibiting the desired porosity described above.

  If the drying temperature is less than the lower limit value, the solvent in the film does not volatilize, and a problem such as film unevenness and cracks may occur due to a sudden temperature rise during firing. If it exceeds, defects such as unevenness during drying may occur in the film. In addition, if the drying time is less than the lower limit, the solvent in the film remains without volatilizing, and problems such as film unevenness and cracks may occur during firing. There is no problem, but problems such as increased costs may occur. On the other hand, when the firing temperature is lower than the lower limit, there may be a problem such as poor adhesion due to insufficient curing of the film or insufficient hardness. On the other hand, if the upper limit is exceeded, there may be a problem such as an increase in refractive index due to a decrease in the void structure in the film. Also, if the firing time is less than the lower limit, there may be problems such as poor adhesion due to insufficient curing of the film and insufficient hardness, on the other hand, there is no problem with the film even if the upper limit is exceeded, Problems such as increased costs may occur.

  The low refractive index film of the present invention thus obtained is an antireflection film used for preventing reflection of incident light in display panels such as cathode ray tubes, liquid crystals, organic EL, solar cells, glass for showcases, etc. Alternatively, it can be suitably used for forming an intermediate film or the like using a difference in refractive index used for a sensor, a camera module or the like.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1-1>
First, tetramethoxysilane (TMOS) is prepared as the silicon alkoxide (A), trifluoropropyltrimethoxysilane (TFPTMS) is prepared as the silicon alkoxide (F) containing a fluoroalkyl group, and the mass of the silicon alkoxide (A) is 1. The fluoroalkyl group-containing silicon alkoxide (F) was weighed so that the ratio (mass ratio) was 0.6, and these were put into a separable flask and mixed to obtain a mixture. Propylene glycol monomethyl ether acetate (PGMEA) in an amount of 1.0 part by mass relative to 1 part by mass of the total amount of silicon alkoxide (A) and fluoroalkoxy group-containing silicon alkoxide (F) is used as the organic solvent (D). The first liquid was prepared by adding and stirring at a temperature of 30 ° C. for 15 minutes. In addition, as silicon alkoxide (A), the oligomer which superposed | polymerized the monomer about 3-5 previously was used.

  In addition to the first liquid, ion-exchanged water (B) in an amount of 1.0 part by mass with respect to 1 part by mass of the total amount of silicon alkoxide (A) and fluoroalkoxy group-containing silicon alkoxide (F). Then, formic acid in an amount of 0.01 parts by mass was introduced into the beaker as an organic acid (C), mixed, and stirred at a temperature of 30 ° C. for 15 minutes to prepare a second liquid. Next, after maintaining the prepared first liquid at a temperature of 55 ° C. in a water bath, the second liquid was added to the first liquid and stirred for 60 minutes while maintaining the temperature. Thereby, a hydrolyzate of the silicon alkoxide (A) and the fluoroalkyl group-containing silicon alkoxide (F) was obtained.

The hydrolyzate obtained above and fumed silica particles having an average particle size of 40 nm and a specific surface area (BET value) of 200 m ² / g obtained by the gas phase method (dry method) shown in Table 1 (Japan) Aerosil Co., Ltd. trade name: "AEROSIL 200 (R)") silica sol (E) was dispersed, and SiO ₂ minutes in the silica sol (E) with respect to SiO ₂ minutes 1 part by weight of the hydrolyzate is 2 parts by weight The composition was obtained by mixing at a ratio and stirring. The average particle size of the fumed silica particles refers to the average particle size of secondary particles in which several to several tens of primary particles are aggregated, and is based on a volume basis measured using a dynamic light scattering particle size distribution device. Is the median diameter. The specific surface area (BET value) is a value obtained by using a value calculated by the BET three-point method measured by adsorbing nitrogen gas.

  In addition, before mixing the silica sol (E) with the hydrolyzate, a homomixer (primix) is used so that the aggregate size in which the fumed silica particles aggregate in a bead shape in the prepared composition is 100 nm. For 25 minutes at a rotational speed of 14,000 rpm and sufficiently dispersed.

  Subsequently, the prepared composition was applied to the surface of a glass substrate as a substrate by a spin coating method to form a coating film. Then, the glass substrate on which the coating film is formed is dried for 10 minutes at a temperature of 50 ° C. using an atmosphere firing furnace, and then cured by baking for 30 minutes at a temperature of 130 ° C. using an atmosphere firing furnace. Thus, a film having a thickness of about 80 nanometers was formed.

<Examples 1-2, 1-3 and Comparative Example 1-1, Comparative Example 1-2>
A composition was prepared by changing the ratio of water (B) when the mixture of silicon alkoxide (A) and fluoroalkoxy group-containing silicon alkoxide (F) was 1 part by mass as shown in Table 1 below. Except for this, a film was formed in the same manner as in Example 1-1.

<Examples 2-1 and 2-2 and Comparative Example 2-1 and Comparative Example 2-2>
The ratio of the organic acid (C) when the mixture of the silicon alkoxide (A) and the fluoroalkoxy group-containing silicon alkoxide (F) was 1 part by mass was changed and dispersed as shown in Table 1 below. The type of fumed silica particles was changed to fumed silica particles having an average particle size of 45 nm and a specific surface area (BET value) of 170 m ² / g (trade name: “AEROSIL R974 (registered trademark)” manufactured by Nippon Aerosil Co., Ltd.). And the ratio of the silica sol (E) was changed so that the SiO ₂ content of the silica sol (E) relative to 1 part by mass of SiO ₂ in the hydrolyzate was the ratio shown in Table 1 below. Except for this, a film was formed in the same manner as in Example 1-1.

<Examples 3-1 to 3-5 and Comparative Examples 3-1 to Comparative Example 3-3>
The ratio of the organic solvent (D) when the mixture of the silicon alkoxide (A) and the fluoroalkoxy group-containing silicon alkoxide (F) is 1 part by mass, the type of the organic solvent (D), the inorganic acid or the organic acid (C) The ratio of the inorganic acid or organic acid (C) was changed as shown in Table 1 below, and the temperature of the water bath when adding the second liquid to the first liquid was changed to 63 ° C. A composition was prepared in the same manner as in Example 1-1 except that the composition was prepared. In Example 3-1, only the temperature of the water bath at the time of preparing the composition was changed. In the table, “PGME” represents propylene glycol monomethyl ether.

<Examples 4-1 and 4-2 and Comparative Example 4-1 and Comparative Example 4-2>
The proportion of the fluoroalkyl group-containing silicon alkoxide (F) when the mass of the silicon alkoxide (A) is 1, and the mixture of the silicon alkoxide (A) and the fluoroalkyl group-containing silicon alkoxide (F) is 1 part by mass. When the ratio of water (B), the ratio of organic acid (C), and the ratio of organic solvent (D) were changed to the ratio shown in Table 2 below, the ratio of silica sol (E) was The silica sol (E) has been changed so that the SiO ₂ content of the decomposed product is 1 mass part of SiO _{2 in the} ratio shown in Table 2 below, and the type of dispersed fumed silica is changed in terms of the average particle size. 37nm, specific surface area (BET value) of 260m ² / g fumed silica particles (Nippon Aerosil Co., trade name: "AEROSIL R106 (R)"), except that the preparation of the composition was changed to, the real To form a film in the same manner as in Example 1-1.

<Example 5-1>
First, tetramethoxysilane (TMOS) is prepared as silicon alkoxide (A), and propylene glycol monomethyl ether acetate (PGMEA) in an amount of 1.5 parts by mass with respect to 1 part by mass of silicon alkoxide (A) is used as an organic solvent. A first liquid was prepared by adding as (D) and stirring at a temperature of 30 ° C. for 15 minutes. In addition, as silicon alkoxide (A), the oligomer which superposed | polymerized the monomer about 3-5 previously was used.

  Separately from the first liquid, ion exchange water (B) in an amount of 1.0 part by mass and organic acid (in an amount of 0.02 part by mass) with respect to 1 part by mass of silicon alkoxide (A). C) was put into a beaker, mixed, and stirred at a temperature of 30 ° C. for 15 minutes to prepare a second liquid. Next, after maintaining the prepared first liquid at a temperature of 55 ° C. in a water bath, the second liquid was added to the first liquid and stirred for 60 minutes while maintaining the temperature. This obtained the hydrolyzate of the said silicon alkoxide (A).

  And the composition was obtained by stirring and mixing the said hydrolyzate with silica sol (E) similarly to Example 1-1. Before mixing the silica sol (E) with the hydrolyzate, the homogenizer is used at a rotational speed of 16000 rpm so that the size of the aggregate in which the fumed silica particles aggregate in a bead shape is 90 nm. Stir for 25 minutes and disperse well. That is, this composition was prepared without adding a fluoroalkyl group-containing silicon alkoxide (F).

  Subsequently, a film having a thickness of about 80 nanometers was formed on a glass substrate as a substrate in the same manner as in Example 1-1.

<Example 5-2>
A film was formed in the same manner as in Example 5-1, except that the composition was prepared using tetraethoxysilane (TEOS) instead of tetramethoxysilane (TMOS) as the silicon alkoxide (A).

<Example 5-3>
A film was formed in the same manner as in Example 5-1, except that the composition was prepared by changing the type of inorganic acid or organic acid (C) as shown in Table 2 below.

<Example 5-4>
The type of dispersed fumed silica particles is fumed silica particles having an average particle size of 42 nm and a specific surface area (BET value) of 210 m ² / g (trade name: “AEROSIL RX300 (registered trademark)” manufactured by Aerosil Japan). was changed to and the proportion of silica sol (E), SiO ₂ minutes of silica sol (E) with respect to SiO ₂ minutes 1 part by weight of the hydrolyzate is changed so that the ratio shown in Table 2 below composition A film was formed in the same manner as in Example 5-1, except that the product was prepared.

<Example 5-5>
The type of the organic solvent (D) was changed as shown in Table 2 below, and the type of dispersed fumed silica particles having an average particle size of 42 nm and a specific surface area (BET value) of 210 m ² / g The fumed silica particles (trade name: “AEROSIL RX300 (registered trademark)” manufactured by Nippon Aerosil Co., Ltd.) and the ratio of silica sol (E) to silica sol (E with respect to 1 part by mass of SiO ₂ in the hydrolyzate) The composition was prepared by changing so that the SiO ₂ content in (1) would be the ratio shown in Table 2 below, and controlling the size of the aggregates contained in the prepared composition to be 150 nm. Except for this, a film was formed in the same manner as in Example 5-1. In the table, “PGME” represents propylene glycol monomethyl ether.

<Example 5-6>
The type of inorganic acid or organic acid (C) was changed as shown in Table 2 below, and the type of dispersed fumed silica particles was 34 nm in average particle size and 150 m in specific surface area (BET value). ^A film was formed in the same manner as in Example 5-1, except that the composition was prepared by changing to ² / g fumed silica particles (product name: “AEROSIL RX200 (registered trademark)” manufactured by Nippon Aerosil Co., Ltd.). did.

<Example 5-7>
The type of dispersed fumed silica particles is fumed silica particles having an average particle diameter of 37 nm and a specific surface area (BET value) of 260 m ² / g (trade name: “AEROSIL R106 (registered trademark)” manufactured by Nippon Aerosil Co., Ltd.). it was changed to the ratio of the silica sol (E), the SiO ₂ minutes of silica sol (E) with respect to SiO ₂ minutes 1 part by weight of the hydrolyzate was changed to be the ratio shown in Table 2 below, and A film was formed in the same manner as in Example 5-1, except that the composition was prepared by controlling the size of the aggregates contained in the prepared composition to be 20 nm. The size of the aggregate was controlled by using a zirconia bead having a diameter of 0.5 mm instead of the homomixer and shaking for 15 hours with a paint shaker to sufficiently disperse the aggregate.

<Examples 5-8 to 5-10>
Instead of tetramethoxysilane (TMOS) as a silicon alkoxide (A), tetraethoxysilane (TEOS) is used, and a silicon alkoxide (F) containing a fluoroalkyl group with respect to 1 part by mass of silicon alkoxide (A) The ratio shown in Table 2 and mixing in the same procedure as in Example 1-1, and the ratio of water (B), the ratio of organic acid (C), and the ratio of organic solvent (D) Example 5-1 except that the composition was prepared by changing to the ratio shown in Table 2 below with respect to 1 part by mass of the mixture of alkoxide (A) and fluoroalkoxy group-containing silicon alkoxide (F). A film was formed in the same manner.

<Comparative Example 5>
Instead of fumed silica particles obtained by the vapor phase method (dry method), colloidal silica particles having an average particle size of 20 nm and a specific surface area (BET value) of 130 m ² / g obtained by the wet method (Nissan Chemical Industries) The ratio of the SiO ₂ content of silica sol (E) shown in Table 2 below to 1 part by mass of SiO ₂ in the hydrolyzate using silica sol (E) in which product name: “ST-O”) is dispersed. A film was formed in the same manner as in Example 5-1, except that the composition was prepared by changing the type of the organic solvent (D).

<Comparative Example 6-1>
Instead of fumed silica particles obtained by the vapor phase method (dry method), colloidal silica particles having an average particle size of 20 nm and a specific surface area (BET value) of 130 m ² / g obtained by the wet method (Nissan Chemical Industries) A composition was prepared in the same manner as in Example 5-1, except that silica sol (E) in which a product name “ST-O”) was dispersed was used. A film was formed in the same manner as in Example 5-1, except that the firing temperature was 500 ° C. and the firing time was 180 minutes.

<Comparative Example 6-2>
A film was formed in the same manner as in Example 1-1 except that the firing temperature was 50 ° C. and the firing time was 10 minutes.

<Comparison test and evaluation>
For the films obtained in Example 1-1 to Example 5-10 and Comparative Example 1-1 to Comparative Example 6-2, the porosity, contact angle, refractive index, average primary particle diameter of silica particles in the film, The ratio of the silica particle part in the silica structure in the film was evaluated. These results are shown in Tables 3 and 4 below.

  (i) Porosity: A cross section (10 mm × 10 mm) of the formed film was observed with a TEM (Transmission Electron Microscope; JEOL Ltd., model name: JEM-2010F), and silica particles and silicon alkoxides were observed. The area occupied by the whole of the cross section of the film of the void portion that appears dark in the visual field excluding the portion formed by the hydrolyzate was analyzed by an image, and the value was defined as the porosity.

  (ii) Contact angle: Using a contact angle measuring device (model number: Drop Master 700, manufactured by Kyowa Interface Science Co., Ltd.), the contact angle when ion-exchanged water is dropped on the coating surface is analyzed by the θ / 2 method. Value.

  (iii) Refractive index: Measured using a spectroscopic ellipsometer (manufactured by J.A. Woollam Japan, model number: M-2000), and the value is 633 nm in the analyzed optical constant.

  In addition, in order to evaluate the durability of the film, the film A immediately after film formation for each Example and Comparative Example, and the film after being held for 2000 hours under conditions of a temperature of 80 ° C. and a relative humidity of 85% RH after the film formation. The refractive index of B was measured. Further, from the measured refractive index of the film A and the refractive index of the film B, the rate of change of the refractive index when held for 2000 hours under the above-described high temperature and high humidity condition was calculated from the following formula (1). The results are shown in Tables 3 and 4 below. Note that the refractive index of each film is a value measured at a film temperature of 25 ° C. The film A immediately after film formation refers to a film that has been stored in a standard state (temperature 23 ° C. ± 5 ° C., humidity 65% RH ± 20% and has not passed 48 hours).

    Rate of change (%) = (refractive index of film B / refractive index of film A−1) × 100 (1)

  (iv) Average primary particle diameter of silica particles: The particle diameter of 50 primary particles was measured from the TEM image when the cross section of the film was observed with the TEM, and the average value was the average primary particle diameter of the silica particles in the film. It was.

(v) Ratio of silica particle part: The value calculated from the following formula (4) was defined as the ratio of the silica particle part in the silica structure in the film. Note that equation (4) "composition" in except the solvent and the like, refers to the total amount of the hydrolyzate of the silica particles and silicon alkoxide in the composition, expressed in SiO ₂ minutes terms.

  As is clear from Tables 3 and 4, when Example 1-1 to Example 5-10 and Comparative Example 1-1 to Comparative Example 6-2 are compared, Example 1-1 to Example 5-10 are Compared with the films of Comparative Example 1-1 to Comparative Example 6-2, the refractive index is very low, indicating that the antireflection effect is high. It can also be seen that it has a desired contact angle and is excellent in water repellency and antifouling properties. In Comparative Example 1-2, when preparing the composition, water exceeding an appropriate amount was added, so that the hydrolysis reaction could not be controlled, and solids were generated in the hydrolyzate, and the composition was suspended. Since the viscosity increased along with this, a film having a desired thickness could not be formed. Moreover, in Comparative Example 2-1, when preparing the composition, the proportion of the organic acid (C) is too small so that the hydrolysis reaction does not proceed sufficiently, and the film has a low refractive index and sufficient antireflection effect. Was not obtained. In Comparative Example 2-2, when the composition was prepared, the proportion of the organic acid (C) was too large to form the film itself. In Comparative Example 3-3, the film itself could not be formed because the liquid was suspended when the composition was prepared. In Comparative Example 4-2, when the composition was prepared, an excessive amount of silica sol (E) was added, so that the unevenness of the film was increased, and the refractive index and the like could not be evaluated.

  Further, in Comparative Examples 3-1 and 4-1, in which the porosity is not controlled within a desired range, the refractive index after holding for a long time under high temperature and high humidity conditions changes greatly, and the change rate is 8%. Exceeded. In particular, in Comparative Example 6-2 in which the porosity exceeds a predetermined value, the film becomes brittle, the durability is lowered, and the rate of change is also high. In Comparative Example 1-1, Comparative Example 3-2, Comparative Example 5 and Comparative Example 6-1, the change rate showed a small value, but the refractive index itself immediately after the film formation showed a high value. On the other hand, in Examples 1-1 to 5-10, the refractive index immediately after the film formation is very low, and the change in the refractive index after being held for a long time under high temperature and high humidity conditions is small. It was confirmed that the properties were excellent.

  The low refractive index film of the present invention is an antireflection film used to prevent reflection of incident light in a display panel such as a cathode ray tube, a liquid crystal, an organic EL, a solar cell, a glass for a showcase, or a sensor or camera module. For example, it can be used for an intermediate film using a difference in refractive index.

Claims (4)

Low refractive index obtained by applying and baking a composition containing an aggregate of fumed silica particles and a hydrolyzate of silicon alkoxide on a substrate or a layer formed on the substrate. A membrane,
The porosity is in the range of 15-55%,
The refractive index immediately after film formation is in the range of 1.15 to 1.39,
A low refractive index film having a refractive index change rate calculated from the following formula (1) of 8% or less.
Change rate of refractive index (%) = (refractive index of film B / refractive index of film A−1) × 100 (1)
However, in the formula (1), the film A is a film immediately after film formation, and the film B is 2000 hours after film formation in high temperature and high humidity (temperature 80 ° C., relative humidity 85% RH). The membrane after holding.   The low refractive index film according to claim 1, wherein the average primary particle diameter of the fumed silica particles in the film is in the range of 5 to 50 nm.   The low-refractive-index film according to claim 2, wherein the silica particle portion in the silica structure composed of the fumed silica particles and the hydrolyzate of the silicon alkoxide in the film is 50 to 99 mass%.   The low refractive index film according to any one of claims 1 to 3, wherein a contact angle of the film surface is 85 to 125 °.