TWI414811B - Method for producing a layered material containing a layer of inorganic particles - Google Patents

Abstract

The invention provides a method for producing layered material comprising layer with inorganic particles on a substrate, which comprises the following processes (1)-(3) of process (1): adding coagulant to a dispersion liquid (A) comprising a liquid medium and inorganic particles dispersed therein to obtain a coagulation liquid (B) with at least partial of the inorganic particles coagulated; process (2): coating above-mentioned coagulation liquid (B) on the substrate; and process (3): removing liquid medium from the coated coagulation liquid (B) and forming a film made up of inorganic particles on the substrate.

Description

Method for producing laminated body having inorganic fine particle layer

The present invention relates to a method for producing a laminate having an inorganic fine particle layer, and more particularly to a method for producing a laminate having an inorganic fine particle layer, which can produce an antireflection film laminate having excellent antireflection properties at low cost. The method is used as a method of effective application.

In various displays such as LCD, PDP, CRT, organic EL, inorganic EL, and FED, such external light of sunlight and fluorescent light is reflected on the surface, causing reflection and glare, resulting in a problem of reduced visibility.

The reason for the above problem is that the refractive index of the surface of the display changes rapidly, and in order to alleviate such a change, a technique of forming an antireflection film composed of a material having a lower refractive index than a material constituting the surface of the display on the surface of the display is known. Theoretically, it is known that the refractive index of the material constituting the surface of the display, that is, the refractive index of the substrate is n2, and the refractive index of the antireflection film formed on the substrate is n1, which satisfies the relationship of n1=(n2) ^0.5 . The principle of 0. Since the substrate is an acrylic resin, n2 = about 1.5, and therefore an antireflection film composed of a material having an n1 = 1.2 or so is preferable. However, since the refractive index of magnesium fluoride which is a material of the low refractive index film is about 1.38, sufficient antireflection effect cannot be obtained even if an antireflection film formed of such a material is used.

An antireflection film which is known as a superior antireflection effect is an antireflection film which uses hollow microparticles having voids inside. When the inside of the particle is hollowed out, the refractive index of the particle is lowered, and as a result, a low refractive index film can be formed, and a high antireflection effect can be obtained (see Patent Document 1).

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-201443

However, if the aforementioned hollow fine particles are used, the cost will increase.

The present invention provides a method for producing an antireflection film laminate having excellent antireflection properties at a low cost, and a method for producing a laminate having a substrate and an inorganic fine particle layer.

The present invention relates to a method for producing a laminate comprising a film composed of inorganic fine particles on a substrate, and a method for producing a laminate comprising the following steps (1) to (3): Step (1): Containing a liquid a step of adding a coagulant to the dispersion (A) of the inorganic fine particles dispersed in the liquid medium to obtain a coagulating liquid (B) in which at least a part of the inorganic fine particles contained in the dispersion (A) is agglomerated; Step (2): a step of applying the agglomerating liquid (B) to a substrate; and (3): forming a liquid medium from the substrate by removing a liquid medium from the coated coagulating liquid (B) a step of forming a film of microparticles;

According to the method of the present invention, an antireflection film laminate having excellent antireflection properties can be produced at low cost.

The anti-reflection film of the present invention is disposed on the surface or inside of various displays such as LCD, PDP, CRT, organic EL, inorganic EL, FED to prevent light from being reflected outside the surface of the display or from the inside of the display or As the light generated by the luminescent layer is reflected inside the display, the light transmittance is lowered and the brightness of the display is lowered.

One aspect of the present invention is a method for producing a laminate in which a film composed of inorganic fine particles is laminated on a substrate. In the present invention, the substrate is preferably a transparent substrate, and it can be suitably selected from a transparent plastic film or sheet having moderate mechanical rigidity and a transparent glass depending on the product. Specific examples of the plastic film or the sheet include polyethylene terephthalate, polyethylene, polypropylene, cellophane, cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate. Film or sheet of acetylcellulose butyrate, polymethyl methacrylate, and the like. A film or sheet composed of cellulose triacetate and polyethylene terephthalate is preferred because of its excellent transparency and no optical anisotropy.

In the method of the present invention, a laminate in which a film composed of inorganic fine particles is laminated on a substrate is produced, but in order to form a film composed of inorganic fine particles, a liquid medium and an inorganic substance dispersed in the liquid medium are used. Dispersion of microparticles (A). Examples of the inorganic fine particles include fine particles such as cerium oxide, titanium oxide, aluminum oxide, zinc oxide, tin oxide, calcium carbonate, barium sulfate, talc, and kaolinite.

In the method of the present invention, a flocculating agent is added to the dispersion (A), and a coagulating liquid (B) obtained by agglomerating at least a part of the inorganic fine particles contained in the dispersion (A) is coated. On the surface of the substrate, in order to ensure the stability of the coacervate when the coagulating solution (B) is applied to the substrate, the dispersion (A) used is charged and the inorganic microparticles are passed through the charge in the liquid medium. The stable and dispersed colloid is ideal. The colloid may be a hydrophilic colloid or a hydrophobic colloid. When the liquid medium is water, the dispersion (A) is preferably a hydrophilic colloid, and since the particle size distribution is small, it is particularly preferable to use colloidal silica.

In the liquid medium of the dispersion (A), water or a volatile organic solvent can be used. When the inorganic fine particles are dispersed in a colloidal form in the dispersion (A), pH adjustment or addition of an electrolyte or a dispersant can be performed. Further, in order to uniformly disperse the inorganic fine particles, a method such as stirring by a stirrer, ultrasonic dispersion, ultrahigh pressure dispersion (ultrahigh pressure homogenizer) or the like can be applied. The concentration of the inorganic fine particles in the dispersion (A) is not particularly limited, but is preferably from 1 to 20% by weight from the viewpoint of coatability to the substrate of the dispersion (A).

In the particle size distribution diagram of the horizontal axis particle diameter and the vertical axis frequency obtained by measuring the dispersion liquid by the laser diffraction scattering method, the particle diameter shown by the highest peak Ra is present in 0.01. In the range of up to 1 μm, in the cumulative particle size distribution map obtained by the laser diffraction diffraction method, the number of particles having a particle diameter of D ₉₀ or less is 90% of the total particle number. The particle diameter D _{90 is} preferably 1 μm or less. The highest peak Ra is the highest peak in the particle size distribution map. The particle diameter shown by the highest peak Ra of the dispersion (A) is preferably in the range of 0.05 to 0.5 μm from the viewpoint of uniformity of the formed coating film.

In the step (1) of the present invention, a coagulant is added to the dispersion (A) to obtain a coagulating liquid (B) in which at least a part of the inorganic fine particles in the dispersion (A) is agglomerated.

The aggregating agent is a substance having an effect of aggregating inorganic fine particles dispersed in a liquid medium. When the dispersion (A) is in a colloidal state, the inorganic fine particles are aggregated by the addition of the electrolyte. Examples of the electrolyte include citrate, tartrate, sulfate, acetate, nitrate, chloride, bromide, iodide, thiocyanate, sodium carboxymethylcellulose, and sodium alginate. (sodium alginate) and so on. Further, a nonionic polymer such as polyvinyl alcohol or methyl cellulose having an action of agglomerating inorganic fine particles and a monomer such as acrylic acid, acrylamide, sodium acrylate or dimethyl methacrylate may be used. A polymer agglomerating agent composed of a polymer. Further, when the pH can be adjusted by adding an acid or a base to agglomerate the inorganic fine particles in the dispersion, such an acid or a base also corresponds to a coagulant.

When the dispersion (A) is a hydrophilic colloid, the inorganic fine particles can be agglomerated as a coagulant by using a dehydrating agent or a dehydrating agent in combination with an electrolyte. Here, the dehydrating agent has an effect of removing hydration water from the surface of the inorganic fine particles in the hydrophilic colloid, and is preferably an alcohol such as methanol, ethanol, propanol or isopropanol.

The condensed liquid (B) obtained in the step (1) of the present invention is obtained by adding a coagulant to the dispersion (A), and the condensed liquid (B) is obtained by laser-stacking the coagulant In the particle size distribution map of the horizontal axis particle diameter and the vertical axis frequency obtained by the scattering method, it is preferable to exhibit a peak Rb having a particle diameter of 20 times or more which shows the particle diameter of the highest peak Ra. By using such a condensed liquid (B), an antireflection film having excellent antireflection properties can be formed. The condensed liquid (B) is preferably a condensed liquid having a peak Rb having a particle diameter of 100 times or more, more preferably 50 times or more of the particle diameter shown by the highest peak Ra in the particle size distribution map.

The step (2) of the present invention is a step of applying the condensed liquid (B) to a substrate, and the step (3) is: removing the liquid medium from the coated condensed liquid (B), the substrate A step of forming a film composed of the aforementioned inorganic fine particles. The condensed liquid (B) may be applied to one side of the substrate or may be coated on both sides. The condensed liquid (B) can be applied to a substrate by using a roll coater, a reverse roll coater, a gravure coater, or a knife coater. ), a coating device such as a bar coater. The surface on which the condensed liquid (B) is applied to the substrate is preliminarily applied, corona treatment, ozone treatment, plasma treatment, flame treatment, cathode ray treatment, anchor coating (Anchor Coat) treatment, washing treatment, and the like. The pretreatment is ideal. In addition, as the substrate, a substrate having an antistatic layer containing a hard coat layer composed of an ultraviolet curable resin or the like and conductive fine particles as a surface layer can be applied to the surface layer. Cloth condensate (B). In the step (3), the liquid medium is removed from the condensed liquid (B) applied to the substrate, but usually removed by volatilizing the liquid medium. The temperature (drying temperature) at this time is usually from room temperature to 200 °C. In the case where the condensed liquid (B) is applied to both surfaces of the substrate to form a film composed of inorganic fine particles on both surfaces of the substrate, the film may be formed on one surface of the substrate, and the film may be further formed on the other surface. form.

According to the inventors' estimation, in the film of the inorganic fine particles formed on the substrate by such a method, voids are formed by contacting the inorganic fine particles with each other. Since this void system exhibits a refractive index which is substantially the same as the refractive index (refractive index of 1.0) of air, the film system having such a void has a low refractive index.

In the method of the present invention, the film thickness of the inorganic fine particles formed on the substrate is preferably in the range of 50 to 150 nm, more preferably in the range of 80 to 130 nm. In particular, the laminated body produced is used as a display. When the anti-reflection member of the element is used, the film of the inorganic fine particles constitutes the outermost layer of the display, and in the case of preventing the reflection of external light, if the interference effect of the reflected light is considered, the film thickness of the inorganic fine particles is in the above range. It is ideal inside. The film thickness of the inorganic fine particles can be controlled by the concentration of the selected particle condensed liquid (B) and the coating method. Further, the film thickness of the inorganic fine particles is an average value of the measured values of the thickness of 10 or more points measured in the thickness direction cross section of the film.

In one aspect of the present invention, the inorganic fine particles contained in the dispersion (A) are preferably inorganic fine particles (C) having an average particle diameter Da of from 1 to 300 nm. By using the dispersion of the dispersed inorganic fine particles (C), an inorganic fine particle film having excellent uniformity can be formed. Further, the average particle diameter of the inorganic fine particles (C) is a value measured by a BET method or a laser diffraction scattering method.

In other aspects of the present invention, the inorganic fine particles contained in the dispersion (A) are 55 to 90% by weight of inorganic fine particles (C) and 10 to 45% by weight of the average particle diameter in the range of 30 to 300 nm. It is preferable that the mixture of the inorganic fine particles (D) having an average particle diameter of 1 to 20 nm (only a total amount of the inorganic fine particles (A) and the inorganic fine particles (B) is 100% by weight). By using such a dispersion (A), a film of excellent strength can be formed. Further, the average particle diameter of the inorganic fine particles (D) is a value measured by a method of transylvanic or dynamic light scattering.

As the dispersion (A), when a dispersion of a mixture of the inorganic fine particles (C) or the inorganic fine particles (C) and the inorganic fine particles (D) is used, a coagulant is added to the dispersion (A). In the particle size distribution map of the horizontal axis particle diameter and the vertical axis frequency obtained by measuring the condensed liquid by the laser diffraction scattering method, the condensed liquid (B) is 20 times or more larger than the particle diameter of the highest peak Ra. The total volume of the aggregated particles of the particle diameter is preferably 1% or more of the total volume of the inorganic fine particles in the condensed liquid (B). By using such a coagulating liquid, an antireflection film having excellent antireflection properties can be formed.

In still another aspect of the present invention, the inorganic fine particles contained in the dispersion (A) are preferably chain-shaped inorganic fine particles (E). The chain-like inorganic fine particles are usually spherical particles in which three or more chain-shaped inorganic fine particles are connected. By using the dispersion (A) in which the chain-like inorganic fine particles (E) are dispersed, an antireflection film having excellent antireflection properties can be formed.

In other aspects of the present invention, the inorganic fine particles contained in the dispersion (A) are 55 to 90% by weight of the chain-like inorganic fine particles (E) and 10 to 45% by weight of the average particle diameter is 1 to 20 nm. A mixture of the inorganic fine particles (F) in the range (exceptably, the total amount of the inorganic fine particles (E) and the inorganic fine particles (F) is 100% by weight). By using such a dispersion (A), a film of excellent strength can be formed. By using the antireflection film formed by the dispersion (A), the inorganic fine particles (F) are present on the surface and the gap of the chain-like inorganic fine particles (E), and the effect of connecting and fixing the inorganic fine particles (E) is achieved. It can be a film with excellent strength. Further, the average particle diameter of the inorganic fine particles (F) is a value measured by a Sears method or a dynamic light scattering method.

In the dispersion (A), when a dispersion containing the above-mentioned chain-like inorganic fine particles (E) or a mixture of chain-like inorganic fine particles (E) and inorganic fine particles (F) is used as the dispersion (A) The condensed liquid (B) obtained by adding a coagulant is shown in the particle size distribution map of the horizontal axis particle diameter and the vertical axis frequency measured by the laser diffraction scattering method, and shows the particle diameter of the highest peak Ra. The total volume of the aggregated particles having a particle diameter or more is preferably 5% or more of the total volume of the inorganic fine particles in the condensed liquid (B). By using such a coagulating liquid, an antireflection film having excellent antireflection properties can be formed.

In the aggregated particles formed by adding a flocculating agent to the dispersion liquid (A) containing the chain-like inorganic fine particles (E), it is difficult to fill the voids between the spherical particles forming the chain-like inorganic fine particles (E) due to the mutual connection of the chains. It should be easy to form an anti-reflection film with a moderate void.

In the dispersion (A) used in the present invention, a resin binder can be added to the extent that the antireflection effect is not impaired. Further, after the inorganic fine particle film is formed on the substrate, a resin adhesive may be laminated on the film, or a resin adhesive may be impregnated into the film. Further, the inorganic fine particle film formed on the substrate by the method of the present invention can further form an antifouling layer composed of a fluorine-containing compound.

The laminate obtained by the present invention can be used as an optical member such as a polarizing plate, a diffusion plate, a light guide plate, a brightness improving film, or a reflective polarizing plate, by appropriately selecting a substrate. Further, a plastic film or a sheet and an glass which form an antireflection film may be bonded to the surface of each of the above optical members.

(Example)

Hereinafter, the present invention will be described in further detail by way of examples, but the invention is not limited thereto. The substrate was a cellulose triacetate film made of Fuji Photo Film. The reflectance of the film surface was 4.0%, and the transmittance was 93.0%. Further, the evaluation of the examples was carried out in the following manner.

(1) Particle size distribution: The particle size distribution system was measured by a flow cell method using a laser diffraction/scattering type particle size distribution measuring apparatus LA-910 manufactured by Horiba, Ltd. At the time of the measurement, the concentration of isopropanol in the liquid medium was the same as the concentration of isopropanol of the dispersion (B).

(2) Reflectance: The relative specular intensity of the incident angle of 5 was measured using a spectrophotometer UV-3150 manufactured by Shimadzu Corporation. A black tape was attached to the back of the film at the time of measurement.

(3) Transmittance: The total light transmittance was measured using a spectrophotometer UV-3150 manufactured by Shimadzu Corporation.

(Example 1)

Niobic acid ST-XL (average particle diameter 40 to 60 nm, solid partial concentration: 40% by weight; liquid medium: water) 25.00 g, which is prepared by Nissan Chemical Co., Ltd. as inorganic fine particles (C), Niobic acid ST-XS (average particle size 4 to 6 nm, solid partial concentration: 20% by weight; liquid medium: water) 12.50 g, pure water 100.00 g, which is made by Nissan Chemical Co., Ltd. as inorganic fine particles (D), The dispersion (A) was obtained. To the dispersion (A), 112.50 g of isopropyl alcohol as a coagulant was added and mixed to obtain a condensed liquid (B). The composition of the condensed liquid (B) is 12.5 g of inorganic fine particles, 125 g of water, and 112.5 g of isopropyl alcohol, and the weight ratio of the inorganic fine particles (C) to the total of the inorganic fine particles (C) and the inorganic fine particles (D) is 80. The weight ratio of % and inorganic fine particles (D) is 20%. Further, regarding the sample (A') prepared by diluting the dispersion (A) with pure water, the average particle diameter was measured by a laser diffraction scattering method, and it was found that the highest peak Ra was 0.08 μm and the D ₉₀ was 0.10 μm. The sample (B') prepared by diluting the condensed liquid (B) with a mixed solvent of water: isopropyl alcohol = 125: 112.5 (weight ratio), and measuring the average particle diameter by a laser diffraction scattering method, 86 μm is applied to show the peak and the peak Rb can be seen. In the sample (B'), the aggregated particle volume of the particle diameter of 100 times or more of Ra was 85.2%.

This condensed liquid (B) was applied onto a cellulose triacetate film using a coating bar, and dried at 60 ° C to form an antireflection film. The minimum reflectance in the visible light range of the obtained antireflection film was 0.5%, and the maximum transmittance was 96.0%, and the antireflection performance was quite excellent. Further, the film thickness of the antireflection film estimated from the reflectance measurement results was 110 nm.

(Example 2)

Chain-like phthalic acid gel PS-M manufactured by Nissan Chemical Co., Ltd. as a chain-like inorganic fine particle (E) (average particle diameter 111 nm measured by dynamic light scattering method, solid portion concentration: 20% by weight; liquid medium: Water) 62.50g and chain-like phthalic acid gel PS-S manufactured by Nissan Chemical Co., Ltd. (average particle diameter 106nm measured by dynamic light scattering method, solid partial concentration: 20% by weight; liquid medium: water) 6.25g It is a mixture of citric acid ST-XS (average particle diameter 4 to 6 nm, solid partial concentration: 20% by weight; liquid medium: water) 25.00 g and pure water 81.25 g manufactured by Nissan Chemical Co., Ltd. of inorganic fine particles (F). The dispersion (A) was obtained. In the dispersion (A), 75.00 g of isopropyl alcohol as a coagulant was added and mixed to obtain a condensed liquid (B). The composition of the condensed liquid (B) is 18.75 g of inorganic fine particles, 156.25 g of water, and 75 g of isopropyl alcohol, and the total weight of the chain-like inorganic fine particles (E) and inorganic fine particles (F), and chain-like inorganic fine particles (E) The weight ratio was 73%, and the weight ratio of the inorganic fine particles (F) was 27%. Further, regarding the sample (A') prepared by diluting the dispersion (A) with pure water, the average particle diameter was measured by a laser diffraction scattering method, and it was found that the highest peak Ra was 0.12 μm and the D ₉₀ was 0.15 μm. The sample (B') prepared by diluting the condensed liquid (B) with a mixed solvent of water: isopropyl alcohol = 156.25:75 (weight ratio), and measuring the average particle diameter by a laser diffraction scattering method, was found at 77. The μm shows the peak and the peak Rb is visible. In the sample (B'), the aggregated particle volume of the particle diameter of 100 times or more of Ra was 90.1%.

This condensed liquid (B) was applied onto a cellulose triacetate film using a coating bar, and dried at 60 ° C to form an antireflection film. The minimum reflectance in the visible light range of the obtained antireflection film was 0.1%, and the maximum transmittance was 95.8%, and the antireflection performance was quite excellent. Further, the film thickness of the antireflection film estimated from the reflectance measurement results was 120 nm.

(Comparative Example 1)

25.00 g of phthalic acid gel ST-XL as inorganic fine particle (C), 12.50 g of citric acid gel ST-XS as inorganic fine particle (D), and 212.50 g of pure water were mixed to obtain a solid content content ratio and examples. The dispersion liquid (A) having the same solid content of the condensed liquid (B) of 1. The weight ratio of the inorganic fine particles (C) is 80% and the weight ratio of the inorganic fine particles (D) is 20% based on the total weight of the inorganic fine particles (C) and the inorganic fine particles (D). This dispersion (A) was applied onto a cellulose triacetate film using a coating bar, and dried at 60 ° C to form an antireflection film. The minimum reflectance in the visible light range of the obtained antireflection film was 1.6%, the maximum transmittance was 93.7%, and the antireflection performance was poor. Further, the film thickness of the antireflection film estimated from the reflectance measurement results was 110 nm.

(Comparative Example 2)

62.50g of phthalic acid gel PS-M as chain inorganic fine particles (E), 6.25g of phthalic acid gel PS-S which is also used as chain inorganic fine particles (E), and tannic acid as inorganic fine particles (F) 20.00 g of gum ST-XS and 156.25 g of pure water were mixed to obtain a dispersion (A) having a solid content ratio of the solid content of the condensed liquid (B) of Example 2. The weight ratio of the chain-like inorganic fine particles (E) is 73% and the weight ratio of the inorganic fine particles (F) is 27%, based on the total weight of the chain-like inorganic fine particles (E) and the inorganic fine particles (F). This dispersion (A) was applied onto a cellulose triacetate film using a coating bar, and dried at 60 ° C to form an antireflection film. The minimum reflectance in the visible light range of the obtained antireflection film was 0.8%, the maximum transmittance was 94.6%, and the antireflection performance was poor. Further, the film thickness of the antireflection film estimated from the reflectance measurement results was 70 nm.

Claims (11)

A method for producing a laminate, comprising the steps of (1) to (3): the step (1) of a step of adding a coagulant to the dispersion (A) of the inorganic fine particles dispersed in the liquid medium to obtain a coagulating liquid (B) in which at least a part of the inorganic fine particles contained in the dispersion (A) is agglomerated; 2) a step of applying the agglomerating solution (B) to a substrate; and the step (3) comprises forming a liquid medium from the coated coagulating liquid (B), and forming a composition of the inorganic fine particles on the substrate. a step of the film, wherein the dispersion (A) satisfies the following requirement (A1), and the condensed solution (B) satisfies the following requirement (B1): the necessary condition (A1) is based on the dispersion (A) In the particle size distribution diagram obtained by the diffraction diffraction method, the particle diameter shown by the highest peak Ra is in the range of 0.01 to 1 μm, and the accumulation of the dispersion is measured by the laser diffraction scattering method. particle size distribution, the particles having a particle diameter D ₉₀ of the cumulative sum of the number of particles is 90% full The particle diameter D ₉₀ of 1μm or less; necessary conditions (B1) based on the aggregated liquid (B) obtained by the particle size distribution measured by laser diffraction scattering method, the particle size of the display shown to have the highest Ra A peak Rb of 20 times or more of the particle diameter is present. The method of claim 1, wherein the inorganic fine particles contained in the dispersion (A) have an average particle diameter Da in the range of 1 to 300 nm. The method of claim 1, wherein the inorganic fine particles contained in the dispersion (A) are 55 to 90% by weight of inorganic fine particles (C) and 10 to 45 in an average particle diameter of 30 to 300 nm. A mixture of inorganic fine particles (D) having an average particle diameter in the range of 1 to 20 nm by weight (however, the total amount of the inorganic fine particles (C) and the inorganic fine particles (D) is 100% by weight). The method of claim 2, wherein, in the condensed liquid (B), the aggregated particle volume having a particle diameter of 20 times or more of the particle diameter showing the highest peak Ra is a total of The total volume of the inorganic fine particles in (B) is 1% or more. The method of claim 1, wherein the inorganic fine particles contained in the dispersion (A) are chain-like inorganic fine particles (E). The method of claim 1, wherein the inorganic fine particles contained in the dispersion (A) are 55 to 90% by weight of chain-like inorganic fine particles (E) and an average particle diameter of 10 to 45% by weight is A mixture of inorganic fine particles (F) in the range of 1 to 20 nm (except that the total amount of the inorganic fine particles (E) and the inorganic fine particles (F) is 100% by weight). The method of claim 5, wherein, in the condensed liquid (B), the aggregated particle volume having a particle diameter of 20 times or more of the particle diameter showing the highest peak Ra is a total of The total volume of the inorganic fine particles in (B) is 5% or more. The method of claim 1, wherein the dispersion (A) is a hydrophilic colloid. The method of claim 1, wherein the dispersion (A) is a citric acid gel. The method of claim 1, wherein the aggregating agent is a dehydrating agent. The method of claim 10, wherein the dehydrating agent is an alcohol.