JPH1077416A5 - - Google Patents

Description

[0001]
[Technical Field to which the Invention Belongs]
The present invention relates to a method for producing a dispersion composition in which an inorganic layered compound is dispersed in a medium, the dispersion composition obtained by the production method, and a laminate obtained from the dispersion composition.

[0007]
[Means for solving the problem]
The present inventors conducted extensive research to solve the above-mentioned problems and arrived at the present invention. Specifically, the present invention relates to a method for producing a dispersion composition comprising an inorganic layered compound and a medium, in which a mixture of an inorganic layered compound and a medium is passed through a capillary tube at high speed, split, and then reunited to cause the components to collide with each other, wherein the maximum pressure in the capillary tube is 100 kgf/cm2 or ^higher . It also relates to a dispersion composition obtained by this production method and its uses. Molded articles or laminates obtained using the dispersion composition of the present invention have extremely excellent transparency, with a haze of 15 or less. In the present invention, treating the inorganic layered compound and the medium in a high-pressure dispersion device under pressure conditions of 100 kg/cm2 or ^higher results in a composition with excellent transparency when processed into a molded article or laminate. Furthermore, excellent control of the orientation of the inorganic layered compound results in excellent gas barrier properties, anti-fogging effects, and favorable refractive index anisotropy.

[0010]
From the viewpoint of film-forming or moldability when made into a film, the particle size of the inorganic layered compound measured by the method described below is usually preferably 5 μm or less. From the viewpoint of the transparency of the dispersed resin composition, this particle size is preferably 2 μm or less, and when used in applications where transparency is important, such as food packaging, this particle size is more preferably 1 μm or less.

[0015]
The medium used in the present invention is not particularly limited, but preferably used is one that is at least partially dissolved or uniformly dispersed when the dispersion composition of the present invention is formed.For example, resins and monomers having polymerizable functional groups can be mentioned.Such resins include polyvinyl alcohol and its analogs, vinyl alcohol resins such as ethylene-vinyl alcohol copolymers, polysaccharides such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, amylose, amylopectin, pullulan, curdlan, xanthan, chitin, chitosan, cellulose, and their chemically modified products, microbial polyesters such as poly-3-hydroxybutyrate and 3-hydroxybutyrate-3-hydroxyacrylate copolymers, biodegradable aliphatic polyesters such as polylactic acid, silane coupling agents, titanium coupling agents, polyethylene (low density, high density), polyolefin resins such as ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, polypropylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ionomer resin, etc.; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyhydroxybenzoic acid, etc.; amide resins such as nylon-6, nylon-6,6, metaxylenediamine-adipic acid condensation polymer, polymethyl methacrylimide, diethylenetriamine-adipic acid copolymer and salts thereof, etc.; aramid resins acrylic resins such as polymethyl methacrylate, polyacrylic acid, sodium polyacrylate, poly-2-hydroxyethyl acrylate, poly-2-hydroxyethyl methacrylate, polyacrylamide, ethylene-acrylic acid copolymers and salts thereof; styrene or acrylonitrile resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene copolymer, polyacrylonitrile; hydrophobic cellulose resins such as cellulose triacetate and cellulose diacetate; halogen-containing resins such as polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, and polytetrafluoroethylene; Examples of suitable resins include engineering plastic resins such as organic resins, polycarbonate resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyphenylene oxide resins, polymethylene oxide resins, and liquid crystal resins; and resins having hydrogen-bonding groups or ionic groups in the molecule, such as polystyrene sulfonic acid, sodium polystyrene sulfonate, polyvinylpyridine and its salts, polyethyleneimine and its salts, polyallylamine and its salts, polyvinylpyrrolidone, polyvinylsulfonic acid and its salts, polyvinylthiol, polyethylene glycol, polypropylene glycol, and polyglycerin. Here, the term "hydrogen-bonding group" refers to a group having at least one hydrogen atom directly bonded to an atom other than carbon (heteroatom). Examples of such hydrogen-bonding groups include hydroxyl groups, amino groups, thiol groups, carboxyl groups, sulfonic groups, and phosphate groups. Furthermore, the term "ionic group" refers to a group having at least one "positive or negative" charge that is localized to such an extent that it can be hydrated with water molecules in water. Examples of such ionic groups include carboxylate groups, sulfonate ion groups, phosphate ion groups, ammonium groups, and phosphonium groups.

[0025]
When the dispersion composition of the present invention is in the form of a dispersion, the concentration of the total solids (inorganic layered compound, resin, monomer, etc.) including the inorganic layered compound is not particularly limited. Of course, lowering the total solids concentration facilitates dispersion, but this has disadvantages such as excessive drying capacity when coating the dispersion, so it is desirable to keep the total solids concentration as high as possible. The concentrations of the medium and inorganic layered compound are usually 1 to 70 wt%, preferably 3 to 20 wt%, and more preferably 4 to 10 wt%. The inorganic layered compound/resin (or monomer having a polymerizable functional group) composition in a molded article or laminate formed using the dispersion composition is as follows: The volume ratio of inorganic layered compound/resin (ratio at the time of "charging") is usually in the range of 1/100 to 100/1, preferably 5/95 to 50/50, and more preferably 10/90 to 30/70. Furthermore, a volume ratio in the range of 5/95 to 30/70 is advantageous in terms of flexibility as a film or molded product. If the volume ratio (volume fraction) of the inorganic layered compound/resin is less than 1/100, the properties that the inorganic layered compound should impart (e.g., gas barrier properties) tend to decrease. On the other hand, if the volume ratio exceeds 100/1, film-forming or moldability tends to decrease. Furthermore, from the viewpoint of suppressing deterioration of physical properties due to bending when formed into a molded product or laminate, a volume ratio of 7/93 or more is preferred. On the other hand, from the viewpoint of suppressing the flexibility of the layer made of the dispersion composition of the present invention or peelability from the substrate, a volume ratio of 17/83 or less is preferred. That is, a volume ratio of (inorganic layered compound/resin) in the range of 7/93 to 17/83 is particularly preferred from the viewpoint of flexibility, suppression of peelability from the substrate, and suppression of deterioration of physical properties due to bending. Such a volume ratio can be determined by dividing the numerator (weight of the inorganic layered compound) and denominator (weight of the medium) of the weight ratio when these components are "charged" by their respective densities. The density of the medium (particularly a resin, such as polyvinyl alcohol) generally varies slightly depending on the crystallinity, but the volume ratio can be calculated, for example, assuming that the crystallinity of polyvinyl alcohol is 50%.

[0026]
In the present invention, haze (cloudiness) is used as an index of transparency, and this haze is determined by subtracting the value measured when the entire substrate is immersed in a medium having the same refractive index as the substrate from the measured value measured when a molded article in which the dispersion composition of the present invention is formed into a film on a substrate, or a laminate in which the dispersion composition is coated on a substrate, has a dry film of the dispersion composition as the outermost layer. When the appearance of the molded article or laminate of the present invention is taken into consideration, particularly in packaging applications, the haze is preferably 25% or less, more preferably 20% or less, and particularly preferably 15% or less.

[0027]
The dispersion composition of the present invention may contain various solvents for the purpose of adjusting coating properties and viscosity, and may also contain additives as needed. Examples of additives include pigments, surfactants, mildew inhibitors, preservatives, crosslinking agents, antifoaming agents, and antioxidants. Examples of pigments include anti-rust pigments for primers, such as strontium chromate, zinc chromate, zinc phosphate, red lead, zinc white, basic sulfates, and basic carbonates. Examples of coloring pigments include phthalocyanine blue, phthalocyanine green, quinacridone, indanthrone, isoindolinone, perylene, anthrapyrimidine, benzimidazolone, carbon black, titanium dioxide, graphite, yellow iron oxide, and red iron oxide. Examples of metal foil pigments include aluminum foil, bronze foil, tin foil, gold foil, silver foil, copper foil, titanium metal foil, stainless steel foil, nickel foil, chromium foil, and alloy foils of the above metals, as well as plastic-coated metal foils. Examples of luster pigments include mica foil and foil-like phthalocyanine blue. Examples of extender pigments include calcium carbonate, gypsum, clay, and talc.

[0033]
The dispersion composition of the present invention is characterized by being processed using a high-pressure dispersion device. Various methods can be used for the order of blending. For example, when the medium is a resin aqueous solution or resin dispersion, the resin is first added to water to dissolve and disperse it, and then the inorganic layered compound is added and dispersed. Other methods include adding the inorganic layered compound and the resin in that order, or mixing the inorganic layered compound dispersion with the resin aqueous solution or dispersion. Any blending order can be used. Multiple types of resins and inorganic layered compounds can be used, and each raw material can be added multiple times. The method for mixing the inorganic layered compound and the medium prior to processing with the high-pressure dispersion device is not particularly limited. A mixing kettle with a jacket on the outer wall that can pass a heat medium such as hot water or steam for temperature control is preferred. Furthermore, to prevent bubble entrapment and ensure uniform dispersion, a kettle with a baffle inside is often used. For the same reason, it is preferable to position the dispersion blade slightly off-center (eccentrically) rather than at the center of the kettle. However, in order to obtain a dispersion composition having a relatively high solids concentration and good dispersion, a composition containing a mixed inorganic layered compound and a medium is used, and high-speed stirring at 4,000 to 7,000 rpm is carried out in a vessel whose internal pressure is reduced to 200 mmHg or less to prevent the incorporation of bubbles, which is an effective method of achieving high shear force.

[0034]
Next, the composition obtained by mixing the inorganic layered compound and the medium is treated in a high-pressure dispersion device. The high-pressure dispersion device used in the present invention is a device that creates special conditions such as high shear and high pressure by passing the composition obtained by mixing the inorganic layered compound and the medium through a narrow tube at high speed. When treating with a high-pressure dispersion device, for example, the maximum pressure condition inside the device is 100 kgf/ ^cm2 or more in a narrow tube with a tube diameter of 1 to 1000 μm . In addition, at this time, it is preferable that the maximum speed reach 100 m/sec or more and the heat transfer rate reach 100 kcal/hr or more.

[0036]
The dispersion composition of the present invention can itself be formed into a molded article by a cast film-forming method or the like. The method for producing a laminate is not particularly limited, and the composition is used for at least one layer of the laminate, particularly an intermediate. To obtain a laminate, a method is typically used in which a water-containing composition is dried and formed into a film (such as a cast film-forming method) and then laminated to a substrate, or a method is used in which a water-containing composition is coated on a substrate. Methods for obtaining a laminate using a film obtained by drying the dispersion composition include coextrusion, melt coating, extrusion lamination, and dry lamination. These laminates can be molded into films, sheets, tubes, cups, bottles, and the like. Conventional molding methods, such as T-die molding, inflation molding, injection molding, blow molding, and stretch-blow molding, can be used by thermal melting. Furthermore, the film or sheet can be subjected to commonly performed stretching processes, such as uniaxial stretching, zone stretching, flat sequential stretching, flat simultaneous biaxial stretching, and tubular simultaneous stretching. Examples of methods for obtaining a laminate by coating include roll coating methods such as a direct gravure method, a reverse gravure method, a microgravure method, a two-roll beat coating method, and a bottom-feed three-roll reverse coating method, as well as a doctor knife method, a die coating method, a dip coating method, a bar coating method, and a coating method that combines these methods.

[0037]
The thickness of the layer formed from the dispersion composition of the present invention can be appropriately selected depending on the desired properties of the laminate and is not particularly limited. Usually, the dry thickness is preferably 30 μm or less, more preferably 10 μm or less. There is no particular limit on the lower limit, but in order to obtain the desired effect, it is preferably 1 nm or more, more preferably 10 nm or more, particularly preferably 100 nm or more.

[0038]
The substrate to be used to form a laminate together with the dispersion composition of the present invention is not particularly limited, and may be in any form, such as a film, sheet, bottle, or tray. Known or common materials such as resin, paper, aluminum foil, wood, cloth, and nonwoven fabric can be used depending on the purpose and application. In particular, when the substrate is in a film form, it may be unstretched or may be uniaxially or biaxially stretched. Of course, known undercoating or corona treatment may be performed, and these surface treatments may be performed on substrates in not only film form but also other forms, as long as they do not impair the object of the invention.

[0040]
Molded articles or laminates obtained from the dispersion composition of the present invention are used in a variety of applications, including packaging, liquid crystal displays, and greenhouse horticulture. For example, they can be used as retardation films that utilize the birefringence of inorganic layered compounds, or as gas/low-molecular diffusion barrier films and molded articles that utilize the low-molecular diffusion retardation effect of the layered structure. When used as a gas barrier film for food or pharmaceutical packaging, the film can be printed or further laminated with another film to produce a molded article. Furthermore, the dispersion composition obtained by the present invention can be molded into a liquid crystal display device by processing it using a high-pressure dispersion device, using the method and application described in JP-A-06-082779, in which synthetic hectorite is used as the inorganic layered compound and an aqueous polyvinyl alcohol resin medium. Such liquid crystal display devices have excellent transparency and film-forming properties due to the control of the fine dispersion state and orientation of the inorganic layered compound. Furthermore, by compounding a resin between layers of the inorganic layered compound, the in-plane refractive index differs from the refractive index in the thickness direction, resulting in a molded article or laminate with almost no in-plane refractive index anisotropy and large refractive index anisotropy in the thickness direction, and excellent birefringence and viewing angle characteristics. Furthermore, the dispersion composition obtained by the present invention can be used for greenhouse horticulture applications using the method and application described in JP-A-08-53558, which uses synthetic hectorite as the inorganic layered compound and an aqueous polyvinyl alcohol medium, and is processed using a high-pressure dispersion device. The molded article or laminate using the dispersion composition obtained by the production method of the present invention can obtain a film with excellent immediate and sustained anti-fogging effect and excellent adhesive strength of the coating film, due to the combination of the fine dispersion structure of the inorganic layered compound and the resin as a binder.

[0041]
The methods for measuring the various physical properties used in the present invention will be explained below.
[Method for determining average particle size]
Methods for determining the average particle size of inorganic particles in a dispersion composition include diffraction/scattering, dynamic light scattering, electrical resistance change, and image processing after microscopy. Dynamic light scattering is difficult to evaluate when inorganic particles coexist with a medium consisting of multiple components because the apparent liquid viscosity changes from that of a single medium. Electrical resistance change methods are limited by the electrolyte concentration of the composition, and image processing after microscopy has resolution issues, making each method difficult to use. The diffraction/scattering method is relatively preferred when the medium has substantially little scattering (i.e., transparency) and particle-related scattering is dominant, since it can obtain information only on the particle size distribution of inorganic particles regardless of the number of medium components.

[0042]
[Measurement of particle size distribution and average particle size using diffraction/scattering methods]
Measurement of particle size distribution and average particle size using the diffraction/scattering method is performed by calculating the particle size distribution that is most consistent with the diffraction/scattering pattern obtained when light is passed through the dispersion composition using Mie scattering theory or the like. Commercially available instruments include Coulter's laser diffraction/light scattering particle size analyzers LS230, LS200, and LS100; Shimadzu's laser diffraction particle size analyzers SALD2000, SALD2000A, and SALD3000; Horiba's laser diffraction/scattering particle size analyzers LA910, LA700, and LA500; and Nikkiso's Microtrack SPA and Microtrack FRA. The dispersion composition of the present invention is preferably measured without dilution. In the case of a liquid with excessive scattering and low light transmittance, the dispersion composition can be measured without dilution by shortening the optical path length (for example, in the case of Horiba's LA910, the optical path length can be significantly shortened using a batch cell, paste cell, etc.). Furthermore, this measurement method cannot separate and identify inorganic particles if the interparticle distance is less than the wavelength of the light source, so multiple particles that are close to each other and separated by a certain distance (e.g., submicron or less) (with a resin or other material interposed between them) are recognized as a single particle. Therefore, this method can evaluate not only poor dispersion due to particle aggregation, but also poor dispersion caused by the presence of a resin or other material interposed between particles.

[0043]
[Aspect ratio determination method]
The aspect ratio (Z) is a ratio calculated from the relationship Z = L/a. Here, L is the particle size (volume-based median diameter) of the inorganic layered compound in the dispersion composition, calculated by the particle size measurement method using the diffraction/scattering method described above, and a is the unit thickness of the inorganic layered compound. This "unit thickness a" is a value determined based on measurements of the inorganic layered compound alone, such as by powder X-ray diffraction, as described below. More specifically, as shown in the graph of Figure 2, in which the horizontal axis represents 2θ and the vertical axis represents the intensity of the X-ray diffraction peak, the "unit thickness a" is the distance calculated based on the Bragg equation (nλ = 2D sin θ, n = 1, 2, 3...) from the angle θ corresponding to the lowest-angle peak among the observed diffraction peaks (for details of powder X-ray diffraction, see, for example, "Guide to Instrumental Analysis (a)" edited by Jiro Shiokawa, p. 69 (1985), published by Kagaku Dojinsha). When a dispersion composition containing only a resin medium is subjected to powder X-ray diffraction, the interplanar spacing d of the inorganic layered compound in the resin medium can be determined. More specifically, as shown in the graph of FIG. 3, in which the horizontal axis is 2θ and the vertical axis is the intensity of the X-ray diffraction peak, the spacing corresponding to the lowest-angle peak among the diffraction peaks observed on the low-angle (larger spacing) side from the diffraction peak position corresponding to the above-mentioned "unit thickness a" is taken as "interplanar spacing d"(a<d). As shown in the graph of FIG. 4, when the peak corresponding to the above-mentioned "interplanar spacing d" overlaps with a halo (or background) and is difficult to detect, the area excluding the baseline on the lower-angle side of 2θd is taken as the peak corresponding to the "interplanar spacing d". Here, "θd" is the diffraction angle equivalent to "(unit length a) + (width of a single resin chain)" (for details on how to determine this interplanar spacing d, see, for example, Shuichi Iwao et al., "Clay Dictionary," pp. 35 et seq. and 271 et seq., 1985, Asakura Shoten Co., Ltd.). Thus, the "integrated intensity" of the diffraction peak (corresponding to the interplanar spacing Sd) observed in powder X-ray diffraction of the dispersed resin composition is preferably 2 or more (even 10 or more) relative to the integrated intensity of the reference diffraction peak (corresponding to the interplanar spacing a). Typically, the difference between the interplanar spacing d and the "unit thickness a," i.e., the value k = (d - a) (when converted to "length"), is equal to or greater than the width of a single resin chain constituting the dispersed resin composition (k = (d - a) ≥ width of a single resin chain). This "width of a single resin chain" can be calculated by simulation or the like (see, for example, "Introduction to Polymer Chemistry," pp. 103-110, 1981, Kagaku Dojin), and is 4-5 angstroms for polyvinyl alcohol (2-3 angstroms for water molecules). Although the aspect ratio Z = L/a is not necessarily equal to the "true aspect ratio" of the inorganic layered compound in the dispersed resin composition, it is valid to use this aspect ratio Z to approximate the "true aspect ratio" for the following reasons. Specifically, it is extremely difficult to directly measure the "true aspect ratio" of the inorganic layered compound in the dispersed resin composition. On the other hand, if the interplanar spacing d determined by powder X-ray diffraction of the dispersed resin composition and the "unit thickness a" determined by powder X-ray diffraction measurement of the inorganic layered compound alone satisfy the relationship a<d, and the value of (d-a) is equal to or greater than the width of a single resin chain in the dispersed resin composition, then the resin is intercalated between the layers of the inorganic layered compound in the dispersed resin composition. Therefore, it is fully valid to approximate the thickness of the inorganic layered compound in the dispersed resin composition with the "unit thickness a," i.e., to approximate the "true aspect ratio" in the dispersed resin composition with the "aspect ratio Z" of the inorganic layered compound in the dispersion liquid. As mentioned above, it is extremely difficult to measure the true particle size in a dispersed resin composition, but the particle size of the inorganic layered compound in the resin can be considered to be quite close to the particle size of the inorganic layered compound when the medium is a resin/solvent. However, since it is considered highly unlikely that the particle size L in the dispersion determined by the diffraction/scattering method exceeds the long diameter Lmax of the inorganic layered compound, the true aspect ratio (Lmax/a) is theoretically very unlikely to be lower than the "aspect ratio Z" used in the present invention (Lmax/a<Z). From the above two points, the definition of the aspect ratio Z used in the present invention is considered to be sufficiently valid. In the present invention, "aspect ratio" or "particle size" means the "aspect ratio Z" defined above or "particle size L determined by the diffraction/scattering method."

[0045]
[Oxygen permeability]
The molded article or laminate of the present invention has oxygen barrier properties when formed into a thin film by drying a dispersion composition using an inorganic layered compound, and has an oxygen permeability at 23°C and 95% RH of 30 cc/m2 day ^atm or less per μm, preferably 20 cc/ ^m2 day atm or less. The molded article or laminate not only has excellent oxygen barrier properties, but also has remarkably excellent barrier properties against other gas molecules, such as helium, nitrogen, carbon dioxide, water, and low-molecular-weight aroma components such as limonene and menthol.

[0046]
[Effects of the Invention]
Molded articles and laminates made using the dispersion composition of the present invention exhibit excellent transparency and also have excellent gas and water vapor barrier properties, making them suitable for a variety of applications, including food packaging. Furthermore, molded articles and laminates made using the dispersion composition of the present invention can also be used in applications that require metals or inorganic materials, such as aluminum foil or glass, from the perspective of barrier properties, and also have excellent transparency. Needless to say, the dispersion resin composition of the present invention is superior to these materials in terms of the opacity of metals and the brittleness of ceramics. Furthermore, the production method of the present invention also provides benefits such as shortening the stirring time during liquid preparation and producing a highly concentrated, uniform dispersion. In addition, the composition can be used in a wide range of applications, including liquid crystal display devices with excellent viewing angle characteristics and greenhouse horticulture applications with excellent anti-fogging properties.

Claims (8)

A method for dispersing a composition obtained by mixing an inorganic layered compound and a medium by passing the composition through a thin tube at high speed, dividing the mixture, and then reuniting the mixture to cause the components to collide with each other, wherein the maximum pressure in the thin tube is 100 kgf/cm ² The method for producing a dispersion composition comprising an inorganic layered compound and a medium, characterized in that: A dispersion composition obtained by dispersing a composition obtained by mixing an inorganic layered compound and a medium through a capillary tube at high speed, dividing the mixture, and then reuniting the mixture to cause the components to collide with each other, wherein the maximum pressure in the capillary tube is 100 kgf/cm ² A dispersion composition comprising an inorganic layered compound and a medium, characterized in that: 3. The dispersion composition according to claim 2, wherein the medium is a resin, a resin dissolved or dispersed in a solvent, a monomer having a polymerizable functional group, or a monomer having a polymerizable functional group dissolved or dispersed in a solvent. 4. The dispersion composition according to claim 3, wherein the volumetric blending ratio of the inorganic layer compound to the resin or the monomer having a polymerizable functional group is in the range of 100/1 to 1/100. 3. The dispersion composition according to claim 2, wherein the inorganic layered compound has an aspect ratio of 200 or more and 3,000 or less. 3. The dispersion composition according to claim 2, wherein the particle size of the inorganic layered compound dispersed in the medium is 1 μm or less. A laminate using a dried film prepared using the dispersion composition according to claim 2 as an outermost layer, the laminate having a haze of 15% or less. A laminate comprising a layer obtained using the dispersion composition according to any one of claims 2 to 6. In the case of a film obtained by using the dispersion composition, the oxygen permeability per 1 μm of thickness at 23° C. and 95% RH is 30 cc/m ² A laminate characterized in that the temperature is 1000°C or less.