JP5241199B2 - Method for producing fibrous hollow silica fine particles and substrate with antireflection coating - Google Patents

Description

  The present invention relates to a fibrous hollow silica fine particle dispersion and fibrous hollow silica fine particles. The present invention also relates to a composition for forming an antireflection coating containing the fibrous hollow silica fine particles and a substrate with an antireflection coating.

  The display surface of a display device such as a cathode ray tube display (CRT) or a liquid crystal display (LCD) desirably suppresses reflection of light emitted from an external light source in order to ensure a certain level of visibility. As a method of suppressing this reflection, a method of forming a transparent low refractive index layer on the surface of the transparent display device is conventionally known.

The method for forming the low refractive index layer is generally roughly divided into a vapor phase method and a coating method.
The vapor phase method includes a physical method such as a vacuum deposition method and a sputtering method, and a chemical method such as a CVD method. Examples of the coating method include a roll coating method, a gravure coating method, a slide coating method, a spray method, a dipping method, and a screen printing method.

  In the case of the vapor phase method, a high-quality transparent thin film can be formed, while atmosphere control in a high vacuum system is required. Moreover, since a special heating apparatus or ion generation acceleration apparatus is required, there is a problem that the cost inevitably increases. Furthermore, it is difficult to form a transparent thin film having a large area or to form a transparent thin film uniformly on the surface of a film having a complicated shape.

  On the other hand, in the case of the spray method among the application methods, there is a problem that the utilization efficiency of the coating liquid is poor and the film formation conditions are not easily controlled. In the case of the roll coating method, gravure coating method, slide coating method, dipping method, screen printing method, etc., the utilization efficiency of raw materials is good and the mass production and equipment cost are excellent. In the case of the method, the quality of the obtained transparent thin film may be inferior to the case of the gas phase method.

  As the coating method, for example, a coating liquid composed of a polymer containing fluorine atoms in the molecule is applied to the surface of the substrate and dried to form a low refractive index layer, or ionizing radiation or A method of forming a low refractive index layer by applying a coating liquid comprising a monomer containing a functional group that is cured by heat to the surface of the substrate, drying, and then curing the monomer by UV irradiation or heat is known. It has been.

  As another method for forming the low refractive index layer, the refractive index of the entire coating film is decreased by making bubbles having a refractive index of 1 smaller than the wavelength of visible light and containing the bubbles inside the coating film. The method is known.

Patent Document 1 and Patent Document 2 disclose a low refractive index layer in which hollow fine particles such as hollow silica having cavities therein are dispersed in a binder containing an inorganic component obtained from a hydrolyzed polycondensate of alkoxysilane. Has been. This low refractive index layer has the same effect as a low refractive index layer having a large number of microvoids, and the microvoids are protected by a hard outer shell such as silica. Have. However, while a hard coating film is formed with a binder containing an inorganic component, there is a problem in that the mechanical strength of the coating film, particularly the scratch resistance, is inferior because it is brittle against external impacts. Furthermore, a harder coating film can be obtained than the case of the coating film alone due to the aggregation effect of the hollow silica particles. However, since the brittleness increases, it is difficult to realize a coating film having a low refractive index and excellent mechanical strength. And when the addition amount of the silica particles is increased to some extent, there is a problem that the aggregation of the silica particles occurs and the mechanical strength of the coating film decreases at a stretch.

Therefore, an antireflection coating having a low refractive index and excellent mechanical strength is required.
Regarding the hollow silica particles, hollow silica particles having a particle size of about 0.1 to 300 μm are known (for example, see Patent Documents 3 and 4). In Patent Document 5, active silica is precipitated from an aqueous alkali metal silicate solution on a core made of a material other than silica, and the material is removed without destroying the silica shell, thereby forming a dense silica shell. A method for producing hollow particles is disclosed.

  Further, Patent Document 6 discloses a micron-sized spherical silica particle having a core-shell structure in which the outer peripheral portion is a shell, the center portion is hollow, and the shell is denser on the outside and has a coarser concentration gradient structure on the inside. Is disclosed.

  Further, the present inventors have previously proposed composite oxide fine particles having a low refractive index obtained by completely covering the surface of porous inorganic oxide fine particles with silica or the like (for example, Patent Documents). 7).

  Patent Document 8 discloses a group of inorganic oxide particles in which inorganic oxide particles are connected in a chain form with an average connection number of 2 to 30 as hollow silica particles having a shape other than a spherical shape. In addition, an invention relating to a substrate with a hard coat layer comprising a group of inorganic oxide fine particles, which is porous and / or hollow particles having a cavity inside is disclosed, and the composition of the particles is silica. The case is described.

In the hollow silica particles, since the silica particles in the coating are spherical, the coating strength cannot be expressed unless a specific amount is blended.
Patent Document 9 includes an inorganic compound as a constituent component, is fibrous, has a hollow structure, has a number average length (L) of 10 to 1000 μm, and a number average diameter (D) of 0.1 to 30 μm. A fibrous hollow inorganic compound particle characterized in that the aspect ratio (L) / (D) is 5 to 100 and the number average outer diameter of the hollow holes is in the range of 30 to 95% of the number average diameter. The case where the composition of the particles is silica is described. The fibrous hollow inorganic compound particles gradually develop the coating strength in proportion to the amount of the compound, so that not only a coating with a stable strength is obtained, but also a crack is difficult to occur. can get.

However, silica particles having a low refractive index and excellent film forming properties have not been obtained.
Japanese Patent Laid-Open No. 2001-167637 JP 2002-225866 A JP-A-6-330606 Japanese Patent Laid-Open No. 7-013137 Special Table 2000-500113 JP-A-11-029318 JP 7-133105 A JP 2005-186435 A JP 2005-289932 A

  An object of the present invention is to provide a dispersion in which fibrous hollow silica fine particles having a low refractive index and excellent film-forming properties are dispersed in a dispersion medium, and a composition for forming an antireflection coating containing the silica fine particles. .

  As a result of intensive studies to solve the above-mentioned problems of the prior art, the present inventor is not a structure in which the fine particles are connected, but is a fibrous hollow silica fine particle composed of one particle, and the length of the major axis is on the order of nm. The present inventors have found that the fibrous hollow silica fine particles as described in 1) have a low refractive index and excellent film-forming properties, and have completed the present invention.

  That is, the fibrous hollow silica fine particle dispersion of the present invention has an average particle diameter in the range of 5 to 500 nm, is fibrous, and is formed by dispersing fibrous hollow silica fine particles having a hollow structure in a dispersion medium. It is characterized by.

The fibrous hollow silica fine particles preferably satisfy the following conditions (a), (b), (c) and (d).
(A) The average particle size is in the range of 5 to 500 nm,
(B) The ratio of the major axis to the minor axis (major axis / minor axis) is in the range of 1.5 to 10,
(C) The specific surface area according to the BET method is in the range of 5 to 600 m ² / g,
(D) The refractive index is in the range of 1.20 to 1.40.

The fibrous hollow silica fine particles of the present invention are characterized by satisfying the above conditions (a), (b), (c) and (d).
The method for producing the fibrous hollow silica fine particle dispersion of the present invention comprises:
Step (I): The ratio of the major axis to the minor axis (major axis / minor axis) is in the range of 1.5 to 10, and the acid-soluble inorganic oxide fine particles are dispersed as a core particle in a dispersion medium, thereby the core particle. Obtaining a dispersion;
Step (II): adjusting the pH of the core particle dispersion to 8 to 13,
Step (III): coating the surface of the core particle with (1) silica, or (2) an inorganic oxide capable of generating the same component as silica and the core particle,
Step (IV): After step (III), part or all of the elements constituting the core particles are removed to obtain porous fibrous silica fine particles, and step (V): the porous fibrous silica A method for producing a fibrous hollow silica fine particle dispersion, comprising a step of further coating the surface of the fine particles with silica in this order.

The method for producing the fibrous hollow silica fine particle dispersion of the present invention comprises:
Step (i): The ratio of major axis to minor axis (major axis / minor axis) is 1.5 to 10, and acid-soluble inorganic oxide fine particles are dispersed as a core particle in a dispersion medium to prepare a core particle dispersion. Obtaining step,
Step (ii): adjusting the pH of the core particle dispersion to 8 to 13,
Step (iii): A step of growing the core particles by adding a polymerizable silicon compound while maintaining the temperature of the core particle dispersion at 60 to 250 ° C.
Step (iv): A step of removing a part or all of the elements constituting the core particles by adding an acidic solution to obtain a porous fibrous silica fine particle dispersion,
Step (v): a step of further adding a polymerizable silicon compound to the porous fibrous silica fine particle dispersion; and step (vi): the porous fibrous silica fine particle dispersion containing the polymerizable silicon compound. It includes a step of heat treatment at a temperature of 100 ° C. to 270 ° C. in this order.

The acid-soluble inorganic oxide fine particles are preferably fine particles selected from the group consisting of fibrous alumina fine particles, fibrous calcium oxide fine particles, and fibrous iron oxide fine particles.
The composition for forming an antireflective coating according to the present invention comprises the fibrous hollow silica fine particles, a component for forming an antireflective coating, and a dispersion medium.

  The substrate with an antireflection coating of the present invention is a substrate with an antireflection coating in which an antireflection coating is formed on a resin substrate, and the antireflection coating forms the antireflection coating with the fibrous hollow silica fine particles. Ingredients are contained. Moreover, the base material with an antireflection coating of the present invention may be provided with the antireflection coating on a resin base via a hard coat layer.

  The fibrous hollow silica fine particle of the present invention is a material having a low refractive index (for example, a refractive index in the range of 1.20 to 1.40), and is excellent in film forming property due to its structure. Further, a dispersion liquid in which the fine particles are dispersed in a dispersion medium is suitably used for forming an antireflection coating.

Furthermore, according to the composition for forming an antireflection coating containing the fine particles, a smooth film can be formed on the substrate, and the aesthetic appearance of the film after curing is excellent.
The antireflection substrate containing the fine particles is an excellent antireflection substrate having a low refractive index.

  According to the production method of the present invention, a dispersion liquid in which fine fibrous hollow silica fine particles having an average particle diameter in the range of 5 to 500 nm are dispersed in a dispersion medium can be practically prepared.

[Fibrous hollow silica fine particles and fibrous hollow silica fine particle dispersion]
The fibrous hollow silica fine particle dispersion of the present invention has an average particle diameter in the range of 5 to 500 nm, is fibrous, and is obtained by dispersing fibrous hollow silica fine particles having a hollow structure in a dispersion medium. It is said. This fibrous hollow silica fine particle dispersion is a sol having a fibrous hollow silica fine particle as a dispersoid, and can also be referred to as a fibrous hollow silica sol.

  The average particle diameter of the fibrous hollow silica fine particles is usually in the range of 5 to 500 nm, preferably in the range of 10 to 200 nm, and more preferably in the range of 30 to 80 nm. When the average particle diameter is within the above range, the fibrous hollow silica fine particles are easily dispersed, for example, in an antireflection coating forming component to be described later. Therefore, the antireflection coating or the antireflection coating with a film thickness of 100 nm to 0.5 μm is used. It is suitable for forming an attached substrate. When the average particle size is less than 5 nm, the effect of the present invention is not impaired, but it is not easy to prepare by the production method according to the present invention. Further, when the average particle diameter exceeds 500 nm, a flat and uniform film may not be formed depending on the film thickness of the antireflection coating containing the fibrous hollow silica fine particles.

  The fibrous hollow silica fine particles have a fibrous (or needle-like) shape, and are distinguished from the spherical silica particles in terms of structure. In the present invention, the fibrous hollow silica fine particles are silica having a ratio of a major axis to a minor axis (major axis / minor axis) measured by an image analysis method of the fibrous hollow silica fine particles in a range of 1.5 to 10. Refers to fine particles. When the ratio of the major axis to the minor axis (major axis / minor axis) is 1.5 or more, it is clearly not spherical in appearance.

  The ratio of the major axis to the minor axis (major axis / minor axis) is usually in the range of 1.5 to 10, preferably in the range of 2.0 to 8.0, more preferably 2.5 to 5.0. It is in the range. When the ratio of the major axis to the minor axis (major axis / minor axis) is within the above range, the composition for forming an antireflection coating containing fibrous hollow silica fine particles exhibits excellent film-forming properties. When the ratio of the major axis to the minor axis (major axis / minor axis) is less than 1.5, the film forming property of the composition tends to be lowered. When the ratio of the major axis to the minor axis (major axis / minor axis) exceeds 10, the effect of the present invention is not impaired, but such fibrous hollow silica fine particles are prepared by the production method according to the present invention. Is not easy.

The average particle diameter and the ratio of the major axis to the minor axis (major axis / minor axis) are values when measured by the method (image analysis method) described in Examples described later.
BET specific surface area of the fibrous hollow fine silica particles according to the present invention is usually in the range of 5~600m ² / g, preferably in the range of 15~400m ² / g, more preferably 20~250m ² / The range of g.

When the specific surface area by the BET method is within the above range, it is preferable in that the film forming ability is good. When the specific surface area by the BET method is less than 5 m ² / g, silica fine particles having no hollow structure may be contained. Moreover, when the specific surface area by BET method exceeds 600 m < ² > / g, the void | hole inside microparticles | fine-particles tends to become small and a refractive index becomes large.

In addition, the specific surface area by the said BET method is a value at the time of measuring by the method as described in the Example mentioned later.
Since the fibrous hollow silica fine particles according to the present invention have a hollow structure, the refractive index tends to be smaller than silica fine particles not having a hollow structure. In general, the refractive index of silica is usually in the range of 1.45 to 1.46, although it depends on the production method. On the other hand, the refractive index of the fibrous hollow silica fine particles according to the present invention is usually in the range of 1.20 to 1.40. This shows that the fibrous hollow silica fine particles according to the present invention are fibrous hollow silica fine particles having a pore structure in the particles.

  The range of the refractive index of the fibrous hollow silica fine particles according to the present invention is preferably in the range of 1.25 to 1.39, more preferably in the range of 1.28 to 1.38. The refractive index of the fibrous hollow silica fine particles depends on the average particle diameter of the core particles and the amount of (1) silica or (2) silica and the inorganic oxide that can produce the same components as the core particles. Adjusted.

  When the refractive index is within the above range, it is preferable in terms of the reflectance of the coating. When the refractive index is less than 1.20, the effect of the present invention is not impaired, but in order to make the refractive index less than 1.20, the proportion of the pore structure in the fine particles must be increased. However, it is not easy to prepare by the manufacturing method according to the present invention. In addition, the strength of the fine particles themselves may be adversely affected. When the refractive index exceeds 1.40, it may be difficult to achieve the antireflection effect of the antireflection coating or the substrate with the antireflection coating as planned by the present invention.

In addition, the said refractive index is a value at the time of measuring by the method as described in the Example mentioned later.
As the dispersion medium used in the fibrous hollow silica fine particle dispersion according to the present invention, water or an organic solvent is usually used. Examples of the organic solvent include, for example, alcohols such as methanol, ethanol, isopropanol and butanol, ketones such as acetone, MEK and MIBK, esters such as ethyl acetate and butyl acetate, aromatics such as toluene and xylene, Examples thereof include ethers such as methyl cellosolve and ethyl cellosolve. These organic solvents can be used alone or in admixture of two or more. Alternatively, a mixed solvent of these organic solvents and water may be used. In the case where the fibrous hollow silica fine particle dispersion is applied to the composition for forming an antireflection coating, it is practical to use an organic solvent whose volatility does not interfere with the formation of the antireflection coating. desirable.

  The solid content concentration of the fibrous hollow silica fine particles in the dispersion medium is usually in the range of 5 to 50% by mass, preferably in the range of 10 to 40% by mass, and more preferably in the range of 20 to 30% by mass. It is. When the solid content concentration is less than 5% by mass, the concentration is practically too dilute, and thus a concentration treatment may be necessary. Moreover, when solid content concentration exceeds 50 mass%, since it becomes easy to produce aggregation between silica fine particles, practicality may fall.

[Method for producing fibrous hollow silica fine particle dispersion]
In the method for producing a fibrous hollow silica fine particle dispersion of the present invention, the step (I): the ratio of the major axis to the minor axis (major axis / minor axis) is in the range of 1.5 to 10, and the inorganic oxidation is acid-soluble. A step of dispersing fine particles as core particles in a dispersion medium to obtain a core particle dispersion, step (II): a step of adjusting the pH of the core particle dispersion to 8 to 13, step (III): the core particles (1) Silica, or (2) Step of coating silica and inorganic oxide capable of producing the same components as the core particles, Step (IV): After the step (III), the core particles are constituted Remove some or all of the elements
A step of obtaining porous fibrous silica fine particles and a step (V): a step of further covering the surface of the porous fibrous silica fine particles with silica in this order.

  As the inorganic oxide fine particles used as the raw material of the core particles, since it is necessary to remove the inorganic oxide fine particles with an acid in a later step, acid-soluble inorganic oxide fine particles are used. The kind of inorganic oxide fine particles soluble in acid is not particularly limited as long as it has a fibrous shape with a major axis / minor axis ratio of 1.5 to 10, but it is removed by acid. In view of ease of treatment, fibrous inorganic oxide fine particles such as fibrous alumina fine particles, fibrous calcium oxide fine particles, or fibrous iron oxide fine particles are preferable. However, the silica fine particles are excluded from the inorganic oxide fine particles used as the raw material for the core particles. Of the acid-soluble inorganic oxide fine particles, the use of fibrous alumina fine particles is recommended for practical use.

  As the fibrous alumina fine particles, for example, fibrous alumina obtained by a production method described in JP-A-60-166220, JP-A-4-42809 or the like may be used, and commercially available fibrous alumina is used. It doesn't matter.

The ratio of the major axis to the minor axis (major axis / minor axis ratio) of the acid-soluble inorganic oxide fine particles used as a raw material is selected according to the size of the target fibrous hollow silica fine particles. It exists in the range of 1.5-10, Preferably it exists in the range of 2.0-8.0, More preferably, it exists in the range of 2.5-6.0.
The major axis / minor axis ratio of the fibrous hollow silica fine particles, which is the dispersoid of the fibrous hollow silica fine particle dispersion according to the present invention, is approximately equal to the major axis / minor axis ratio of the inorganic oxide fine particles used as a raw material. It is desirable to select the major axis / minor axis ratio of the inorganic oxide fine particles used as a raw material in accordance with the application of the fibrous hollow silica fine particle dispersion. In general, the larger the long diameter / short diameter ratio of the fibrous hollow silica fine particles, the more the fibrous hollow silica fine particles tend to have better film-forming properties.

  Further, the average particle size of the inorganic oxide fine particles used as a raw material is also selected according to the size of the target fibrous hollow silica fine particles, but is usually in the range of 5 nm or more and less than 500 nm, preferably It is the range of 10-300 nm, More preferably, it is the range of 30-250 nm.

The method for producing a fibrous hollow silica fine particle dispersion of the present invention includes a step of obtaining a nuclear particle dispersion by dispersing the inorganic oxide fine particles as core particles in a dispersion medium.
As a method for dispersing the inorganic oxide fine particles as core particles in a dispersion medium, a known method such as a method using a homogenizer is applied.

  As the dispersion medium, usually pure water or a mixed solvent of water and a water-soluble organic solvent is used. As an example of a water-soluble organic solvent, ethanol etc. can be mentioned practically. In order to promote dispersibility, a surfactant or the like may be added as a dispersion aid.

The solid content concentration of the fibrous inorganic oxide in the dispersion medium is usually in the range of 5 to 50% by mass, preferably in the range of 10 to 40% by mass, more preferably 20 to 30% by mass. It is a range. If the solid content concentration is less than 5.0% by mass, the efficiency in the process may not be practical. When the solid content concentration exceeds 50% by mass, it is not easy to obtain a good dispersion state.

  The method for producing a fibrous hollow silica fine particle dispersion of the present invention includes a step of adjusting the core particle dispersion to pH 8-13, preferably pH 9-12, more preferably pH 10-11.

  When the pH is less than 8, the aggregation of the core particles tends to occur and is unstable, which is not preferable. When the pH is higher than 13, the solubility of silica is large, which is not preferable for the coating treatment with silica or the like performed in a later step.

  When the core particle dispersion is acidic, the pH is adjusted by subjecting the core particle dispersion to ion exchange treatment with a basic anion exchanger or the like, and adding an alkali component as necessary.

  Examples of the alkali component used in the above method include hydroxides of alkali metal elements such as sodium hydroxide, potassium hydroxide or lithium hydroxide, or ammonia, tetramethylammonium hydroxide, N-methyl-2-pyrrolidone or trimethylamine. Can be mentioned. Moreover, these alkali components can be used individually by 1 type or in mixture of 2 or more types.

  The anion exchanger can be used as long as it has anion exchange ability, and examples thereof include chelate resins, ion exchange membranes, ion exchange filters, in addition to strong or weakly basic anion exchange resins. Is done. These anion exchangers can be used singly or in combination of two or more. The amount of the anion exchanger used is appropriately adjusted according to the pH.

The case where the pH adjusting method is applied to acidic alumina sol is exemplified below.
First, the acid which is a stabilizer of acidic alumina sol is removed by the anion exchanger, and when passing through the isoelectric point (pH 7 to 9) of alumina, the alumina fine particles aggregate. On the alkali side, the alumina and the alkali component react to produce an aluminum salt. The aluminate ions in the aluminum salt are removed by the anion exchanger to regenerate the alkali component. This reaction between the alkali component and alumina is repeated, and the alumina fine particles are peptized into colloidal particles (fine particles).

  In this method, even if the amount of the alkali component relative to alumina is small, the alkali component is regenerated and repeatedly acts on the alumina, so that the alumina fine particles can be sufficiently peptized. Moreover, since the aluminate contained in the resulting alumina sol is very small, that is, the content of the salt in the sol is small, the colloidal particles sufficiently form an electric double layer, and the stability of the sol is increased. .

When the core particle dispersion is alkaline, treatment such as ion exchange is usually unnecessary.
The method for producing a fibrous hollow silica fine particle dispersion of the present invention comprises a step of growing core particles by adding a polymerizable silicon compound at a temperature of 60 to 250 ° C. to the core particle dispersion after pH adjustment. Including.

The temperature at which the polymerizable silicon compound is added is usually in the range of 60 to 250 ° C, preferably in the range of 70 to 220 ° C, and more preferably in the range of 70 to 210 ° C. If the temperature is less than 60 ° C., the growth of the core particles is slow, which may not be practical. Moreover, when the said temperature exceeds 250 degreeC, there exists a tendency for reaction of polymerizable silicon compounds to advance easily.

  Examples of the polymerizable silicon compound include alkali silicates or silicic acid solutions obtained by dealkalizing dilute aqueous solutions of alkali silicates with a cation exchange resin, sodium metasilicate, sodium orthosilicate, silicon alkoxide or derivatives thereof. Can be mentioned. Specific examples include alkoxysilanes such as tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, triphenylmethoxysilane, vinyltrimethoxysilane, and trivinylmethoxysilane.

These silicon compounds can be used individually by 1 type or in mixture of 2 or more types.
Among these silicon compounds, silicic acid liquid (or acidic silicic acid liquid), alkaline silicate aqueous solution (sodium silicate aqueous solution or potassium silicate aqueous solution), tetraethoxysilane, or the like is particularly preferable.

For example, even when a polymerizable silicon compound is added to the acidic alumina sol, silica is not polymerized in the acidic region, so that the surface of the alumina particles cannot be coated with silica.
The amount of the polymerizable silicon compound used is usually in the range of 0.1 to 45 parts by weight, preferably in the range of 3 to 43 parts by weight, more preferably 5 to 5 parts by weight with respect to 100 parts by weight of the core particles. The range is 35 parts by mass. If the amount is less than 0.1 parts by mass, the particles are disintegrated during dealumination and target low refractive index particles cannot be obtained. When the amount exceeds 45 parts by mass, the silica layer occupies a large proportion of the particles even after dealumination treatment, and the proportion of voids becomes too small, so that the refractive index of the particles becomes too large and the antireflection effect decreases. There is a case.

  When the polymerizable silicon compound is added to the core particle dispersion liquid whose pH has been adjusted, a compound capable of generating the same component as the fibrous inorganic oxide fine particles that are core particles may be added together. I do not care. For example, when the core particle is alumina, sodium aluminate can be added together with the polymerizable silicon compound. This is added for the purpose of promoting the removal effect when the core particles are removed in a later step.

  The amount of the compound containing the same component as the core particle is preferably in the range of 0.1 to 0.5 mol in terms of oxide with respect to 1 mol of silica of the polymerizable silicon compound to be added. When the addition amount is less than 0.1 mol, the promoting effect tends not to be observed. When the addition amount exceeds 0.5 mol, there are cases where components removed in a later step are excessive and an appropriate particle shape cannot be maintained.

  In the method for producing a fibrous hollow silica fine particle dispersion of the present invention, an acidic solution or the like is then added to remove part or all of the elements constituting the core particles, and a porous fibrous silica fine particle dispersion is obtained. A obtaining step.

Porous fibrous silica fine particles are prepared by removing part or all of the elements constituting the core particles from the core particles having the silica coating layer.
As a method for removing a part or all of the elements constituting the core particles, a part or all of the elements constituting the core particles are dissolved and removed by adding a mineral acid or an organic acid to the core particle dispersion. Examples thereof include a method or a method in which the nuclear particle dispersion is brought into contact with a cation exchange resin and removed by ion exchange.

The solid content concentration of the core particles in the core particle dispersion having the silica coating layer varies depending on the treatment temperature, but is in the range of 0.1 to 50% by mass, particularly 0.5 to 25% by mass in terms of oxide. It is preferable that it exists in. When the concentration is less than 0.1% by mass, the silica coating layer may be dissolved. Further, since the concentration is low, the processing efficiency tends to decrease. On the other hand, if the concentration exceeds 50% by mass, it tends to be difficult to remove the desired amount of the elements constituting the core particles with a small number of times. In general, inorganic oxide fine particles soluble in an acid other than silica can be dissolved and removed by addition of an acid. On the other hand, in the case of silica, since the solubility in acid is low, for example, even when a low molecular weight silica component is eluted by addition of an acid, silica is immediately precipitated. The structure of the fibrous silica fine particles is maintained. Note that the porous fibrous silica fine particles obtained by removing some or all of the elements constituting the core particles include a case where the inside has a hollow structure in addition to the porous structure.

The method for producing a fibrous hollow silica fine particle dispersion of the present invention includes a step of further adding a polymerizable silicon compound to the obtained dispersion of porous fibrous silica fine particles.
By further covering the porous fibrous silica fine particles with silica, the surface of the silica fine particles having a porous structure is blocked to obtain fibrous hollow silica fine particles.

Here, as the polymerizable silicon compound used as the silica coating, a polymerizable silicon compound similar to the polymerizable silicon compound described above can be used.
The addition amount of the polymerizable silicon compound is usually in the range of 0.1 to 30 parts by mass, preferably in the range of 1 to 20 parts by mass, more preferably 100 parts by mass of the porous fibrous silica fine particles. It is the range of 3-15 mass parts. The temperature at the time of addition of the polymerizable silicon compound is preferably in the range of 10 to 90 ° C. When the amount of the polymerizable silicon compound used is less than 0.1 parts by mass, the surface of the porous fibrous silica fine particles is not sufficiently blocked, and the silica fine particles are unlikely to become fibrous hollow silica fine particles having a hollow structure. When the amount of the polymerizable silicon compound used exceeds 30 parts by mass, in the fibrous hollow silica fine particles, the proportion of the layer provided by the polymerizable silicon compound is relatively increased, and the proportion of voids is decreased. Characteristics based on the hollow structure, for example, effects such as a reduction in refractive index are less likely to occur.

After completion of the addition of the polymerizable silicon compound, a fibrous hollow silica fine particle dispersion in which the fibrous hollow silica fine particles are dispersed in a dispersion medium is obtained by heat treatment.
The said heat processing temperature is 100 to 270 degreeC normally, it is preferable that it is 130 to 240 degreeC, and it is more preferable that it is 150 to 230 degreeC.

  When heated within the above temperature range, the condensation reaction between the porous silica particle surface and the polymerized organosilicon compound proceeds further, so that the porous silica particle surface is sufficiently blocked and a hollow structure is formed inside the particle. The Since air exists in such a hollow structure sufficiently sealed from the outside, it can exhibit a refractive index lower than that of silica.

When the dispersion medium is removed from the fibrous hollow silica fine particle dispersion, fibrous hollow silica fine particles are obtained.
Further, in the dispersion liquid, Al, Na, and Cl may remain as impurities in addition to the fibrous hollow silica fine particles and the dispersion medium.

When the fibrous hollow silica fine particle dispersion according to the present invention comprises an aqueous solvent, an organosol can be produced by substituting with an organic solvent. A conventionally known method can be employed as the substitution method. When the boiling point of the organic solvent is generally higher than that of water, it can be obtained by adding an organic solvent and performing distillation. When the boiling point of the organic solvent is low, it can be obtained by the ultrafiltration membrane method disclosed in Japanese Patent Application Laid-Open No. 59-8614 filed by the present applicant. The concentration of the resulting organosol from 10 to 50% by weight in terms of SiO ₂ is preferred. In addition, this organosol can be used after being appropriately diluted or further concentrated.

[Antireflection coating composition]
The composition for forming an antireflective coating according to the present invention is characterized by containing the fibrous hollow silica fine particles, a component for forming an antireflective coating, and a dispersion medium.

  As a component for forming an antireflection coating, any of known thermosetting resins or thermoplastic resins can be employed. Specifically, polyester resin, polycarbonate resin, polyamide resin, polyphenylene oxide resin, thermoplastic acrylic resin, vinyl chloride resin, fluororesin, vinyl acetate resin or silicone rubber or other thermoplastic resin, or urethane resin, melamine resin, silicon Examples thereof include thermosetting resins such as resins, butyral resins, reactive silicone resins, phenol resins, epoxy resins, unsaturated polyester resins, and thermosetting acrylic resins. Further, two or more kinds of copolymers or modified products of these resins may be used.

  These resins may be emulsion resins, water-soluble resins or hydrophilic resins. Further, in the case of a thermosetting resin, it may be an ultraviolet curable type or an electron beam curable type, and may contain a curing catalyst.

  In the present invention, it is particularly preferable to use a thermosetting resin or an ultraviolet curable type because a substrate with an antireflection coating having a high hardness tends to be obtained even if the amount of the inorganic oxide fine particles is small.

  It is also possible to use a hydrolyzable organosilicon compound as a component for forming an antireflection coating. Specific examples include a partial hydrolyzate of alkoxysilane obtained by adding water and an acid or alkali as a catalyst to a mixture of alkoxysilane and alcohol.

  As the hydrolyzable organosilicon compound, the general formula RnSi (OR ') 4-n [R and R' are each independently a hydrocarbon group such as an alkyl group, an aryl group, a vinyl group, an acrylic group, and n = 0, 1, 2, or 3. Can be used. In particular, tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, and tetraisopropoxysilane are preferably used. These antireflection coating forming components are used singly or in combination of two or more.

In the composition for forming an antireflection coating according to the present invention, the component for forming an antireflection coating is preferably 10 to 400 parts by mass with respect to 100 parts by mass of the fibrous hollow silica fine particles.
The solvent used in the composition for forming an antireflection coating is not particularly limited as long as it easily volatilizes and does not adversely affect the resulting antireflection coating. Specifically, alcohols such as methanol, ethanol, isopropanol and butanol, ketones such as acetone, MEK and MIBK, esters such as ethyl acetate and butyl acetate, aromatics such as toluene and xylene, methyl cellosolve and ethyl Examples include ethers such as cellosolve. These organic solvents are used alone or in admixture of two or more.

  For example, a coloring agent such as a dye or a pigment may be added to the coating liquid for forming an antireflection coating according to the present invention as long as the object of the present invention is not impaired. The amount of the solvent used is not particularly limited as long as it is in a suitable range for the formation of the antireflection coating, but usually 100 parts by mass in total of the fibrous hollow silica fine particles and the components for forming the antireflection coating. The range is 10 to 10,000 parts by mass.

The antireflection coating is formed by applying the antireflection coating forming composition on a resin substrate or a hard coat layer.
The method for applying the composition for forming an antireflective coating on the resin substrate or the hard coat layer is not particularly limited, and a known method such as a dipping method, a spray method, a spinner method, or a roll coating method can be used. Can be mentioned. An antireflection coating can be formed by drying after application.

  When the component for forming an antireflection coating is a thermosetting resin, curing of the hard coat layer described above may be promoted by heat treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, or the like. Moreover, when the hydrolyzable organosilicon compound is contained in the component for forming an antireflection coating, hydrolysis and polycondensation of the hydrolyzable organosilicon compound may be promoted by heat treatment.

The content of the fibrous hollow silica fine particles in the antireflection coating is usually 90% by mass or less, preferably 50% by mass or less. The lower limit is usually about 20% by mass.
When the content of the fibrous hollow silica fine particles, which are low refractive index components, exceeds 90% by mass, the strength of the antireflection coating and the adhesion to a substrate such as a hard coat layer may be insufficient, resulting in lack of practicality. is there. If it is less than 20% by mass, the refractive index of the film increases and the reflectance increases, which is not practical.

The thickness of the antireflection coating is usually 50 to 300 nm, preferably 80 to 200 nm.
When the thickness of the antireflection coating is less than 50 nm, the strength of the film, the antireflection performance, etc. may be inferior. If the thickness of the antireflection coating exceeds 300 nm, cracks may occur in the film, resulting in a decrease in film strength, and the film may be too thick, resulting in insufficient antireflection performance.

  The refractive index of the antireflection coating varies depending on the mixing ratio of the fibrous hollow silica fine particles, which are low refractive index components, and the antireflection coating forming component, but is usually in the range of 1.28 to 1.50, preferably It exists in the range of 1.35-1.45, More preferably, it exists in the range of 1.36-1.42.

When the refractive index of the antireflection coating exceeds 1.50, the antireflection performance may be insufficient depending on the refractive index of the substrate. It is not easy to obtain an antireflection coating having a refractive index of less than 1.28.

[Base material with antireflection coating]
The substrate with an antireflection coating according to the present invention is a substrate with an antireflection coating in which an antireflection coating is formed on a resin substrate, and the antireflection coating comprises the fibrous hollow silica fine particles and the antireflection coating. It contains a film-forming component. The antireflection coating according to the present invention may be a substrate with an antireflection coating in which the antireflection coating is provided on the resin substrate via a hard coat layer.

  Examples of the resin substrate in the substrate with an antireflection coating according to the present invention include a plastic sheet, a plastic film, and a plastic panel. Examples of the material constituting the resin substrate include polycarbonate, acrylic resin, PET, and triacetyl cellulose (TAC).

The hard coat layer in the present invention contains inorganic particles and a film-forming component.
Here, as inorganic particles, particles of oxides such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , particles of composite oxides such as SiO ₂ · Al ₂ O ₃ , SiO ₂ · ZrO ₂ , and surface Oxide particles coated with resin, composite oxide particles, metal colloidal particles such as gold, silver and platinum, carbon material particles such as carbon black and graphite, inorganic compounds such as magnesium fluoride and sodium aluminum fluoride Particles are used.

The shape of the inorganic particles is not particularly limited, but spherical particles are suitable because they can be densely arranged in a base material. Among these, SiO ₂ , SiO ₂ .Al ₂ O ₃ , S
Silica-based particles such as iO ₂ / ZrO ₂ are suitable because it is easy to obtain spherical particles and a hard coat layer having excellent adhesion between the hard coat layer and the substrate can be formed.

  Further, the surface of the inorganic particles may be treated with a silane coupling agent. When the said process is performed, there exists a tendency for the dispersibility with respect to the below-mentioned resin to improve. The average particle diameter of such inorganic particles is not particularly limited as long as the relationship with the thickness of the hard coat layer described later satisfies a specific relationship, and is usually 0.2 to 20 μm, and more preferably 1 to What is in the range of 10 micrometers is suitable.

  When the average particle diameter of the inorganic particles is less than the lower limit of the above range, the dispersibility of the inorganic particles is reduced or the particles are too small with respect to the thickness of the hard coat layer, so that the finally obtained reflection with a hard coat layer There is a tendency for the strength of the protective coating to be insufficient. In addition, if the average particle diameter exceeds the upper limit of the above range, the adhesion with the component for forming a hard coat layer to be described later is reduced, cracks are likely to occur, and if the thickness is larger than the thickness of the hard coat layer Unevenness may remain on the surface of the antireflection coating formed on the hard coat layer, resulting in uneven surface hardness.

  The hard coat layer contains a component for forming a hard coat layer from the viewpoints of adhesion to the base material and coating properties. As the hard coat layer forming component, a resin component is suitable. As such a resin component, specifically, any of known thermosetting resins and thermoplastic resins can be employed as coating resins. Specifically, polyester resins, polycarbonate resins, polyamide resins can be used. , Polyphenylene oxide resin, thermoplastic acrylic resin, vinyl chloride resin, fluorine resin, vinyl acetate resin or silicone rubber or other thermoplastic resin, or urethane resin, melamine resin, silicon resin, butyral resin, reactive silicone resin, phenol resin, Examples thereof include a thermosetting resin such as an epoxy resin, an unsaturated polyester resin, or a thermosetting acrylic resin. Further, two or more kinds of copolymers or modified products of these resins may be used.

  These resins may be emulsion resins, water-soluble resins or hydrophilic resins. Further, in the case of a thermosetting resin, it may be an ultraviolet curable type or an electron beam curable type, and may contain a curing catalyst.

  In the present invention, it is particularly preferable to use a thermosetting resin or an ultraviolet curable type because a substrate with an antireflection coating having a high hardness tends to be obtained even if the amount of the inorganic oxide fine particles is small.

The thickness (Th) of the hard coat layer is not particularly limited, but in the present invention, the ratio between the average particle diameter (Dp) of the inorganic particles and the thickness (Th) of the hard coat layer to be formed ( Dp /
Th) is usually in the range of 0.2 to 1.0, preferably in the range of 0.5 to 0.98.

  Of the inorganic particles described above, when silica-based particles are used, a transparent hard coat layer can be obtained. Since the silica-based particles have a low refractive index and a small difference in refractive index from the refractive index of the hard coat layer forming component, a substrate with an antireflection coating excellent in transparency and haze can be obtained. Specifically, silica-based particles, organopolysiloxane-based particles and the like disclosed in JP-A-63-110016 and JP-A-11-228699 are preferably used as the silica-based particles. Since the organopolysiloxane-based particles contain organic groups in the particles, the dispersibility with respect to the resin used as the component for forming the hard coat layer is good. For this reason, the hard-coat layer excellent in adhesiveness can be formed.

In order to obtain a hard coat layer having transparency, the refractive index difference between the refractive index of the inorganic particles and the refractive index of the component for forming the hard coat layer is usually 0.2 or less, more preferably 0.1 or less. To do. When the refractive index difference exceeds 0.2, visible light scattering tends to be remarkable, and the transparency of the hard coat layer and the finally obtained antireflection coating may be lowered.

  Further, if necessary, the hard coat layer may contain particles made of high hardness polystyrene, polycarbonate, or the like together with inorganic particles. Such particles made of polystyrene or polycarbonate can be blended in the hard coat layer without being used in combination with inorganic particles. Such a hard coat layer can be formed by applying a coating liquid containing hard coat layer forming components and inorganic particles, and optional components such as colored particles.

  Further, the coating liquid may contain a solvent that dissolves the hard coat layer forming component and can easily volatilize. When the hard coat layer forming component is a thermosetting resin, a curing agent can be blended in the coating solution as necessary.

  A hard coat layer can be formed by applying such a coating solution to a substrate by a known method such as a dipping method, a spray method, a spinner method, or a roll coating method, and drying. When the hard coat layer forming component is a thermosetting resin, the hard coat layer can be formed by further curing. When the component for forming the hard coat layer is a thermoplastic resin, the hard coat layer can be formed by further heat treatment at a temperature lower than the softening point of the base material as necessary.

[Example]
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these Examples.

[Measurement method or analysis method used in Examples and Comparative Examples]
About the measuring method or analysis method in an Example and a comparative example, it is as follows.
[1] Measurement of ratio of major axis to minor axis by image analysis method Using a transmission electron microscope (H-800, manufactured by Hitachi, Ltd.), the sample silica sol was photographed at a magnification of 250,000 times to obtain a photographic projection drawing. It was. In the photographic projection view, 50 particles were arbitrarily selected, and the maximum diameter (DL) of each particle and the diameter (DS) orthogonal thereto were measured. The major axis was DL and the minor axis was DS, and the ratio of the major axis to the minor axis (DL / DS) was calculated. The average value was taken as the ratio of the major axis to the minor axis of the sample.

[2] Average particle size measurement by dynamic light scattering method The sample was diluted with 0.58% by mass aqueous ammonia, adjusted to pH 11 and silica concentration of 0.1% by mass, and averaged using the following particle size distribution measuring device. The particle size was measured.

(Particle size distribution measuring device)
Model number NICOMP 380, manufacturer PARTICLE SIZING SYSTEMS Co. Ltd., Measurement principle: Dynamic light scattering method (homodyne / particle size distribution), Light source: 5 mW
He-Ne laser (standard), detector: photomultiplier tube for photocounting, correlator: 32-bit digital autocorrelator (with DSP), measuring cell: four-plane transmission type angular cell (disposable), temperature control method: Peltier element (Computer control), setting range: 5 ° C. to 80 ° C., measurement particle size distribution range: 1 nm to 5 μm, measurement object: colloidal particles.

[3] Measurement of Refractive Index of Particle (1) A sample (sol) was taken in an evaporator and the dispersion medium was evaporated.
(2) The sample obtained by evaporating the dispersion medium was dried at 120 ° C. to obtain a powder.
(3) A standard refractive index liquid having a known refractive index was dropped onto a glass substrate in a few drops, and silica particles were mixed therewith to obtain a mixed liquid.
(4) The operation of (3) above was performed with various standard refractive index liquids, and the refractive index of the standard refractive index liquid when the mixed liquid became transparent was defined as the refractive index of the silica particles.

[4] Specific surface area measurement by BET method 50 ml of silica sol was adjusted to pH 3.5 with HNO ₃ , 40 ml of 1-propanol was added, and the mixture was dried at 110 ° C. for 16 hours. This dried solid was pulverized in a mortar and baked in a muffle furnace at 500 ° C. for 1 hour to obtain a measurement sample. Using this measurement sample, the specific surface area of the silica sol was measured by a nitrogen adsorption method (BET method).
As the measuring device, a specific surface area measuring device (manufactured by Yuasa Ionics, model number Multisorb 12) was used.
Hereinafter, specific surface area measurement by the BET method will be described in detail.

First, 0.5 g of a measurement sample was put in a measurement cell, and degassing was performed at 300 ° C. for 20 minutes in a mixed gas stream of 30% by volume of nitrogen and 70% by volume of helium. Then, the sample was kept at the liquid nitrogen temperature in the above mixed gas stream, and nitrogen was adsorbed on the sample in an equilibrium manner. Next, the sample temperature was gradually raised to room temperature while flowing the above mixed gas, the amount of nitrogen desorbed during that time was detected, and the specific surface area (SA1) of silica sol was measured with a calibration curve prepared in advance.
The average particle diameter (D1) of the silica sol was calculated from the following formula (1).

D1 = 6000 / (ρ × SA1) (1)
D: Average particle diameter (nm)
ρ: Sample density (g / cm ³ )
SA1: Specific surface area (m ² / g)
In addition, the average particle diameter in a following example and a comparative example means the value measured by said [2] dynamic light-scattering method unless there is particular description.

[Raw material 1]
Acidic alumina fine particle dispersion (product name: Cataloid (registered trademark) AS-3, manufactured by Catalytic Chemical Industry Co., Ltd., fibrous, average particle size: 200 nm, specific surface area: 200 m ² / g, major axis / minor axis ratio = 5
. 0, acetic acid content 0.3 mass%, pH 4.0, alumina solid content 7 mass%)
[Silica coating]
While stirring 1710 g of the acidic alumina fine particle dispersion of the raw material 1 and 540 g of pure water at room temperature, 60 g of a 1% by mass sodium hydroxide aqueous solution was added. Thereafter, 600 cc of a strongly basic anion exchange resin (manufactured by Mitsubishi Kasei, DAIAION, SA-20A) was gradually added, and stirring was continued for 20 hours. After the stirring, the ion exchange resin was removed, and 2100 g of a stable alkaline alumina fine particle dispersion (pH 10.0) was prepared.

  Next, 60 g of an aqueous sodium silicate solution (silica concentration: 5 mass%) was added to 2100 g of the prepared alkaline alumina fine particle dispersion, and further heated to 150 ° C. and 1200 g of 1 mass% silicic acid solution was added over 5 hours. Stirring was continued for another hour while maintaining the temperature at 150 ° C., and then the solution was cooled to room temperature. Subsequently, the sample was washed with an ultrafiltration membrane (Asahi Kasei, SIP-1013) while adding pure water. After washing, it was concentrated to obtain 2400 g of a silica-coated alumina fine particle dispersion having a solid content of 5% by mass. The average particle diameter of the silica-coated alumina fine particles as the dispersoid of this dispersion was 201 nm.

[Dealuminization]
1002 g of concentrated hydrochloric acid aqueous solution (concentration: 35.5% by mass) was added dropwise to 2400 g of the silica-coated alumina fine particle dispersion to adjust the pH to 1.0, thereby performing dealumination treatment. Subsequently, while adding 10 L of concentrated hydrochloric acid aqueous solution (concentration 35.5% by mass) and 5 L of pure water, ultrafiltration was performed until the pH reached 3, and the dissolved aluminum salt was separated.

[Concentration, dilution, sealing treatment and heat treatment]
After removing alumina, 800 g of the silica fine particle dispersion was concentrated to a solid content of 5% by mass. Thereafter, 30 g of an aqueous ammonia solution (concentration: 15% by mass) and 50 g of methanol were added to 80 g of the dispersion to dilute to a solid content concentration of 2.5% by mass. Next, it heated up to 80 degreeC with the apparatus heat retention tank with a stirrer, and 6 g of tetraethyl orthosilicate solutions (methanol solvent) with a silica conversion density | concentration of 5 mass% were added over 16 hours.

Then, after removing the solvent with a rotary evaporator, ammonia was added to adjust the pH to 10. Thereafter, heat treatment was performed at 150 ° C. for 1 hour to obtain 20 g of a fibrous hollow silica fine particle dispersion. The silica fine particles, which is a dispersoid in the obtained fibrous hollow silica fine particle dispersion, had a refractive index of 1.34, and thus was found to have a hollow structure.
Table 1 shows the analysis results for the obtained fibrous hollow silica fine particle dispersion.

[Synthesis Example 1]
Commercially available aluminum oxide powder (specific surface area: 110 m ² / g, average particle diameter of powder: 0.6
μm, main crystal form: δ form, hydrochloric acid content (value converted to HCl): 0.4% by mass) and 400 g of pure water were mixed and stirred at room temperature with strong acid cation exchange resin. (Mitsubishi Kasei Co., DIAION, SK-1B) After gradually adding 400 cc and stirring for 20 hours, the ion exchange resin was removed to obtain 500 g of acidic alumina fine particle dispersion. The average particle diameter of the alumina fine particles dispersed in this alumina fine particle dispersion was 50 nm, and the major axis / minor axis ratio was 5.0. This alumina fine particle dispersion was concentrated to give an acidic alumina fine particle dispersion having a solid content of 20% by mass.

[Silica coating]
While stirring 200 g of acidic alumina fine particle dispersion (solid content concentration 20% by mass) obtained in Synthesis Example 1 and 180 g of pure water at room temperature, 20 g of 1% by mass sodium hydroxide was added thereto, and a strongly basic anion was added. 200 cc of an exchange resin (Mitsubishi Kasei, DAIAION, SA-20A) was gradually added and stirring was continued for 20 hours. Then, the ion exchange resin was removed to obtain 360 g of a stable alkaline alumina fine particle dispersion (pH 10.1). .

  After adding 20 g of an aqueous sodium silicate solution (silica concentration: 5% by mass) to this alumina fine particle dispersion, the mixture was heated to 200 ° C. and 400 g of a 1% by mass silicic acid solution was added over 5 hours, and the temperature was maintained at 200 ° C. While further stirring was continued for 1 hour, the mixture was cooled to room temperature. Subsequently, the resultant was washed while adding pure water with an ultrafiltration membrane (Asahi Kasei, SIP-1013) and then concentrated to obtain 220 g of a silica-coated alumina fine particle dispersion having a solid content of 20% by mass. The average particle diameter of the silica-coated alumina fine particles dispersed in this silica-coated alumina fine particle dispersion was 52 nm.

[Dealuminization]
The silica-coated alumina fine particles were diluted with water, and 100 g of concentrated hydrochloric acid aqueous solution (concentration 35.5% by mass) was added dropwise to 800 g of a dispersion having a solid content concentration of 5% to adjust the pH to 1.0. Aluminum treatment was performed. Subsequently, while adding 10 L of concentrated hydrochloric acid aqueous solution (concentration 35.5% by mass) and 5 L of pure water, ultrafiltration was performed until the pH reached 3, and the dissolved aluminum salt was separated.

[Concentration, dilution, sealing and heat treatment]
After removing alumina, 800 g of the silica fine particle dispersion was concentrated to a solid content of 5% by mass.
Thereafter, 30 g of an aqueous ammonia solution (concentration: 15% by mass) and 50 g of methanol were added to 80 g of the dispersion to dilute to a solid content concentration of 2.5% by mass. Next, it heated up to 80 degreeC with the apparatus heat retention tank with a stirrer, and 6 g of tetraethyl orthosilicate solutions (methanol solvent) with a silica conversion density | concentration of 5 mass% were added over 16 hours.

  Then, after removing the solvent with a rotary evaporator, ammonia was added to adjust the pH to 10. Next, heat treatment was performed at 150 ° C. for 1 hour to obtain 20 g of a fibrous hollow silica fine particle dispersion. The silica fine particles, which are the dispersoid in the obtained fibrous hollow silica fine particle dispersion, had a refractive index of 1.37, and thus were confirmed to have a hollow structure. Table 1 shows the analysis results for the obtained fibrous hollow silica fine particle dispersion.

[Silica coating]
Acid alumina fine particle dispersion prepared in the same manner as in Synthesis Example 1 (solid content concentration: 20% by mass, average particle size: 50 nm, major axis / minor axis ratio: 5.0), 1000 g, 2950 g of pure water, and 1% by mass of water Potassium oxide (50 g) was added, and while further stirring at 50 ° C., 1000 cc of a strongly basic anion exchange resin (manufactured by Mitsubishi Kasei, DAIAION, SA-10A) was gradually added thereto, followed by stirring for 20 hours. Subsequently, after cooling to room temperature, the ion exchange resin was removed to obtain 3600 g of an alkaline alumina fine particle dispersion (pH 10.7). After adding 20 g of a sodium silicate aqueous solution (silica concentration: 5 mass%) to this alkaline alumina fine particle dispersion, the mixture was heated to 80 ° C. and 1200 g of a 5 mass% silicic acid solution was added over 10 hours. To obtain 1050 g of a silica-coated alumina fine particle dispersion having a solid content of 20% by mass. The average particle diameter of the silica-coated alumina fine particles dispersed in this silica-coated alumina fine particle dispersion was 55 nm.

[Dealuminization]
100 g of concentrated hydrochloric acid aqueous solution (concentration: 35.5% by mass) was added dropwise to 800 g of the silica-coated alumina fine particle dispersion to adjust the pH to 1.0, thereby performing dealumination treatment. Subsequently, while adding 10 L of concentrated hydrochloric acid aqueous solution (concentration 35.5% by mass) and 5 L of pure water, ultrafiltration was performed until the pH reached 3, and the dissolved aluminum salt was separated.

[Concentration, dilution, sealing and heat treatment]
After removing alumina, 800 g of the silica fine particle dispersion was concentrated to a solid content of 5% by mass. Thereafter, 30 g of an aqueous ammonia solution (concentration: 15% by mass) and 50 g of methanol were added to 80 g of the dispersion to dilute to a solid content concentration of 2.5% by mass. Next, it heated up to 80 degreeC with the apparatus heat retention tank with a stirrer, and 6 g of tetraethyl orthosilicate solutions (methanol solvent) with a silica conversion density | concentration of 5 mass% were added over 16 hours.

  Then, after removing the solvent with a rotary evaporator, ammonia was added to adjust the pH to 10. Next, heat treatment was performed at 150 ° C. for 1 hour to obtain 20 g of a fibrous hollow silica fine particle dispersion. The silica fine particles, which are the dispersoid in the obtained fibrous hollow silica fine particle dispersion, had a refractive index of 1.36, and thus were confirmed to have a hollow structure. Table 1 shows the analysis results for the obtained fibrous hollow silica fine particle dispersion.

[Silica coating]
2000 g of commercially available acidic alumina fine particle dispersion (manufactured by Catalyst Chemical Industry, solid content concentration: 10% by mass, average particle size: 20 nm, major axis / minor axis ratio: 5.0, crystal form: pseudoboehmite type) and 5990 g of pure water To this, 10 g of 1 mass% sodium hydroxide was added, and then 2000 cc of a strongly basic anion exchange resin (Mitsubishi Kasei, DAIAION, SA-30A) was gradually added and stirred for 20 hours. Thereafter, the ion exchange resin was removed to obtain 7200 g of an alkaline alumina fine particle dispersion (pH 10.5). Example 3 After adding 30.3 g of an aqueous sodium silicate solution (silica concentration: 5% by mass) to this alumina fine particle dispersion, heating to 98 ° C. and adding 1600 g of a 5% by mass silicic acid solution over 10 hours, Example 1 In the same manner as above, 1002 g of 10% by mass silica-coated alumina fine particle dispersion was obtained as an oxide. The average particle diameter of the silica-coated alumina fine particles dispersed in this silica-coated alumina fine particle dispersion was 22 nm.

[Dealuminization]
100 g of concentrated hydrochloric acid aqueous solution (concentration: 35.5% by mass) was added dropwise to 800 g of the silica-coated alumina fine particle dispersion to adjust the pH to 1.0, thereby performing dealumination treatment. Subsequently, while adding 10 L of concentrated hydrochloric acid aqueous solution (concentration 35.5% by mass) and 5 L of pure water, ultrafiltration was performed until the pH reached 3, and the dissolved aluminum salt was separated.

[Concentration, dilution, sealing and heat treatment]
After removing alumina, 800 g of the silica fine particle dispersion was concentrated to a solid content of 5% by mass. Thereafter, 30 g of an aqueous ammonia solution (concentration: 15% by mass) and 50 g of methanol were added to 80 g of the dispersion to dilute to a solid content concentration of 2.5% by mass. Next, it heated up to 80 degreeC with the apparatus heat retention tank with a stirrer, and 6 g of tetraethyl orthosilicate solutions (methanol solvent) with a silica conversion density | concentration of 5 mass% were added over 16 hours.

  Then, after removing the solvent with a rotary evaporator, ammonia was added to adjust the pH to 10. Next, heat treatment was performed at 150 ° C. for 1 hour to obtain 20 g of a fibrous hollow silica fine particle dispersion. The silica fine particles, which are the dispersoid in the obtained fibrous hollow silica fine particle dispersion, had a refractive index of 1.34, and thus were confirmed to have a hollow structure. Table 1 shows the analysis results for the obtained fibrous hollow silica fine particle dispersion.

Isopropanol / containing 2% of a fibrous hollow silica fine particle dispersion (solid content concentration 20% by mass) prepared in Example 4 and an ultraviolet curable resin (Unidec 17-824, manufactured by Dainippon Ink Co., Ltd.)
A butanol mixed solution (isopropanol / butanol mixing ratio = 1/1 (wt / wt)) was mixed, and a solid content concentration of 4% by weight (100 parts by mass of UV curable resin was added to 100 parts by mass of fibrous hollow silica fine particles). ) Was prepared.

  This composition for antireflection coating formation was designated 5 applied to a polarizing film (NPF105DU manufactured by Nitto Denko Corporation) with a bar coater of 5, and after drying, irradiated with 80 W / cm ultraviolet rays (high pressure mercury lamp) to form a substrate with an antireflection coating (the thickness of the antireflection coating is 50 nm) ) When the reflectance at a wavelength of 550 nm of the obtained substrate with antireflection coating was measured with a spectrophotometer (manufactured by JASCO Corporation), the reflectance was 1.0% and the pencil hardness was H.

  The fibrous hollow silica fine particles according to the present invention have a particularly low film forming property and a low refractive index. Therefore, a fibrous hollow silica fine particle dispersion obtained by dispersing the silica fine particles in a dispersion medium can suitably form an antireflection coating or an antireflection coating substrate. In addition, the antireflection coating or the antireflection coating substrate containing the fibrous hollow silica fine particles according to the present invention is used for ensuring the visibility of display surfaces of cathode ray tube display devices (CRT), liquid crystal displays (LCD) and the like. It can be used suitably.

Claims (6)

  A process for producing fibrous hollow silica fine particles satisfying the following (a) to (d), comprising the following steps (I) to (V) in this order;
(A) The average particle size is in the range of 5 to 500 nm.
(B) The ratio of the major axis to the minor axis (major axis / minor axis) is in the range of 1.5-10.
(C) Specific surface area according to BET method of 5 to 600 m ² In the range of / g,
(D) the refractive index is in the range of 1.20 to 1.40;
Step (I): The ratio of the major axis to the minor axis (major axis / minor axis) is in the range of 1.5 to 10, and the acid-soluble inorganic oxide fine particles are dispersed as a core particle in a dispersion medium, thereby the core particle. Obtaining a dispersion;
Step (II): adjusting the pH of the core particle dispersion to 8 to 13,
Step (III): (1) silica, or (2) silica and the nucleus
Coating with an inorganic oxide capable of producing the same components as the particles;
Step (IV): After step (III), removing a part or all of the elements constituting the core particles to obtain porous fibrous silica fine particles, and
Step (V): a step of further coating the surface of the porous fibrous silica fine particles with silica.   A process for producing fibrous hollow silica fine particles satisfying the following (a) to (d), comprising the following steps (i) to (vi) in this order;
(A) The average particle size is in the range of 5 to 500 nm.
(B) The ratio of the major axis to the minor axis (major axis / minor axis) is in the range of 1.5-10.
(C) Specific surface area according to BET method of 5 to 600 m ² In the range of / g,
(D) the refractive index is in the range of 1.20 to 1.40;
Step (i): The ratio of major axis to minor axis (major axis / minor axis) is 1.5 to 10, and acid-soluble inorganic oxide fine particles are dispersed as a core particle in a dispersion medium to prepare a core particle dispersion. Obtaining step,
Step (ii): adjusting the pH of the core particle dispersion to 8 to 13,
Step (iii): While maintaining the temperature of the core particle dispersion at 60 to 250 ° C., polymerizable silicon
Growing the core particles by adding a compound;
Step (iv): A step of removing a part or all of the elements constituting the core particles by adding an acidic solution to obtain a porous fibrous silica fine particle dispersion,
Step (v): a step of further adding a polymerizable silicon compound to the porous fibrous silica fine particle dispersion, and
Step (vi): a step of heat-treating the porous fibrous silica fine particle dispersion containing the polymerizable silicon compound at a temperature of 100 ° C. to 270 ° C.   3. The fiber according to claim 1, wherein the acid-soluble inorganic oxide fine particles are fine particles selected from the group consisting of fibrous alumina fine particles, fibrous calcium oxide fine particles, and fibrous iron oxide fine particles. For producing hollow hollow silica fine particles.   A composition for forming an antireflective coating, comprising fibrous hollow silica fine particles obtained by the production method according to any one of claims 1 to 3, a component for forming an antireflective coating, and a dispersion medium.   The fibrous hollow silica obtained by the manufacturing method in any one of Claims 1-3 which is a base material with an antireflection film by which an antireflection film is formed on the resin base material, A substrate with an antireflection coating, comprising fine particles and an antireflection coating forming component.   6. The substrate with antireflection coating according to claim 5, wherein the antireflection coating is provided on a resin substrate via a hard coat layer.