KR102747045B1 - Composite materials - Google Patents

Abstract

The object of the present invention is to provide a thinned layered material having good dispersibility and a large effect of improving physical properties when blended with a silicone resin or the like. The present invention is a composite material in which the surface of a thinned layered material is covered with a coating material, wherein the coating material is a polysiloxane compound having an organic group, and the content of the coating material is 0.1 to 100 parts by mass with respect to 100 parts by mass of the thinned layered material. The average thickness of the thinned layered material is preferably 1200 nm or less, and the average area of the thinned layered material is preferably 0.1 ㎛ ² to 500 ㎛ ² .

Description

Composite materials

The present invention relates to a composite material in which the surface of a thin layered material is coated with a polysiloxane compound having an organic group.

Exfoliated graphite, such as graphene, obtained by exfoliating graphite, which is a layered material, is used as a conductive additive for electrodes of secondary batteries (see, for example, Patent Document 1), conductive ink (see, for example, Patent Document 2), filler for resins or elastomers (see, for example, Patent Documents 3 to 4), gas barrier materials (see, for example, Patent Documents 5 to 6), etc. Since layered materials become thinner when exfoliated and have a smaller number of layers, they are more likely to coagulate, which causes the problem of being difficult to disperse in a matrix, and there have been cases where sufficient physical properties were not obtained. In order to improve coagulation and dispersibility in solvents, etc., exfoliated graphite whose surface is coated with a polymer such as polyvinyl alcohol (see, for example, Patent Document 7) has been studied, but the effect of improving dispersibility when mixed with silicone resins, etc. was not sufficient. In addition, a method of treating the surface of a layered material with a silane coupling agent to improve dispersibility in a resin is also known (see, for example, Patent Document 8), but since the silane coupling agent is relatively expensive, an inexpensive method is desired.

Japanese Patent Publication No. 2016-060887 US20170179490 WO2011/086391 WO2013/165677 US20140272350 WO2016/115377 US20160200580 Japanese Patent Publication No. 2015-040211

The object of the present invention is to provide a thin layered material having good dispersibility and a large property improvement effect when mixed with silicone resin or the like.

The present inventors have conducted a preliminary study on the above-mentioned problem and have found that the problem can be solved by covering the surface of a flaky layered material with a specific material, thereby completing the present invention. That is, the present invention is a composite material in which the surface of a flaky layered material is covered with a covering material, wherein the covering material is a polysiloxane compound having an organic group, and the content of the covering material is 0.1 to 100 parts by mass with respect to 100 parts by mass of the flaky layered material.

In addition, the present invention provides a resin composition containing the composite material and a synthetic resin.

〔Layered material with thin layers〕

The layered material, which is the raw material of the thin layered material used in the present invention, has a layered structure in which unit layers formed by strong bonds such as covalent bonds or ionic bonds are laminated mainly through weak van der Waals forces. The layered material may include graphite, boron nitride, transition metal dichalcogenides, group 13 chalcogenides, group 14 chalcogenides, bismuth chalcogenides, layered metal halides, layered transition metal oxides, layered perovskite oxides, clay minerals, or layered silicates.

Graphite is a layered compound with a unit layer made of carbon. Graphite includes, in addition to graphite, expanded graphite, which is made by expanding the interlayers of graphite, and oxidized graphite, which is made by oxidizing graphite with an oxidizing agent.

Boron nitride is a layered material containing nitrogen and boron as constituent elements, such as boron nitride (BN) and carbon boron nitride (BCN).

Transition metal dichalcogenides are layered materials composed of transition metals and chalcogens, and are represented by the formula MX ₂ , where M is a transition metal and X is a chalcogen. Transition metals include titanium, zirconium, hafnium, vanadium, niobium, chromium, molybdenum, tungsten, technetium, rhenium, nickel, tin, palladium, or platinum. Chalcogens include sulfur, selenium, or tellurium. Examples of transition metal dichalcogenides include TiS ₂ , TiSe ₂ , TiTe ₂ , HfS ₂ , HfSe ₂ , HfTe ₂ , VTe ₂ , VSe ₂ , NbS ₂ , NbSe ₂ , NbTe ₂ , MoS ₂ , MoSe ₂ , MoTe ₂ , WS ₂ , WSe ₂ , WTe ₂ , TcS ₂ , ReSe ₂ , ReS ₂ , ReTe ₂ , TaS ₂ , TaSe ₂ , TaTe ₂ , PtTe ₂ , etc.

Group 13 chalcogenides are layered materials composed of group 13 elements such as gallium or indium and chalcogens, and include GaS, GaSe, GaTe, and InSe.

Group 14 chalcogenides are layered materials composed of group 14 elements germanium, tin, or lead and chalcogens, and examples include GeS, SnS ₂ , SnSe ₂ , and PbO.

Bismuth chalcogenides are layered materials composed of bismuth and chalcogens, and examples include Bi ₂ , Se ₃ , and Bi ₂ Te ₃ .

Layered metal halides are layered materials composed of metal elements and halogens, and examples include MgBr ₂ , CdCl ₂ , CdI ₂ , AgF ₂ , AsI ₃ , and AlCl ₃ .

Layered transition metal oxides are layered materials composed of oxides or oxyacids of transition metals such as titanium, manganese, molybdenum, niobium, and vanadium, and examples include MoO ₃ , Mo ₁₈ O ₅₂ , V ₂ O ₅ , LiNbO ₂ , K ₂ Ti ₂ O ₅ , K ₂ Ti ₄ O ₉ , and KTiNbO ₅ .

Layered _metal phosphates are layered phosphates of titanium, zirconium, selenium _, tin, zirconium, aluminum, etc., and examples include Ti( _HPO4 ) ₂ , Ce( _HPO4 ) ₂ , Zr( _HPO4 ) ₂ , _AlH2P3O10 , etc.

Examples of _{layered perovskite} oxides _{include KCa2Nb3O10 , KSr2Nb3O10} , _{and KLaNb2O7} .

Clay minerals or layered silicates include smectites such as montmorillonite, nontronite, and saponite; kaolin, pyrophyllite, talc, vermiculite, micas, brittle micas, chlorite, sepiolite, parigolskite, imogolite, allophene, hisingerite, magadiite, and kanemite.

The thinned layered material used in the present invention is a material in which the above layered material is thinned, and refers to a material having a layered structure in which unit layers of the layered material are laminated from 1 layer to several thousand layers. The thinned layered material has a greater effect on improving physical properties as the number of layers decreases and the thickness decreases, but it becomes easier to aggregate. In view of this point and economic efficiency, the average thickness in the present invention is preferably 0.3 nm to 1,200 nm, more preferably 1.5 nm to 400 nm, and most preferably 3 nm to 200 nm.

The present invention is preferably applied to a flaky layered material having high cohesion and being difficult to disperse in resins and the like. Examples of such flaky layered materials include flaky graphite and flaky boron nitride. Among them, the present invention is preferably applied to flaky graphite and flaky boron nitride.

In the present invention, the thickness of the flaky layered material is the thickness in the vertical direction with respect to the laminated surface of the flaky layered material, and the average thickness is the average value of the thicknesses of 30 or more flaky layered materials. The thickness of the flaky layered material can be measured, for example, using an SEM image of the flaky layered material taken by a scanning electron microscope. Meanwhile, the thickness of the flaky layered material is the thinnest when it is composed of only one unit layer, and the thickness varies depending on the flaky layered material and is approximately 1 nm. For example, among the flaky layered materials of graphite, a material composed of one unit layer is called graphene, and its thickness is theoretically about 0.335 nm.

If the area of the flaky layered material is small, there are cases where a sufficient property improvement effect is not obtained, so the area of the flaky layered material is preferably large. However, if it is too large, a great deal of effort is required for flakyization, so the average area of the flaky layered material in the present invention is preferably 0.1 µm ² to 500 µm ² , more preferably 0.5 µm ² to 300 µm ² , and even more preferably 1.0 µm ² to 130 µm ² . The area of the flaky layered material in the present invention is the projected area when the flaky layered material is viewed from a plane, and the average area is the average value of the areas of 50 or more flaky layered materials. The area of the flaky layered material can be measured, for example, by dropping a dilute dispersion of the flaky layered material onto a filter paper and using an image of the flaky layered material captured by a microscope.

The method for flaking a layered material is not particularly limited, and the layered material may be flaked by applying shear force, ultrasonic vibration, cavitation, etc. to the layered material using a known device. Such devices include medium-stirring mills such as a sand mill, an attritor, and a bead mill; ball- or rod-driven mills such as a rotary mill, a vibration mill, and a planetary mill; a jet mill, a roll mill, a hammer mill, a pin mill, a high-pressure emulsifier, and an ultrasonic emulsifier. As high-pressure emulsifiers, examples thereof include a through-hole type high-pressure emulsifier and an impact type high-pressure emulsifier. The through-hole type of the through-hole type high-pressure emulsifier includes a single nozzle type, a slit nozzle type, etc. The collision type of the collision type high-pressure emulsifier includes a type in which a liquid containing a raw material collides with a flat surface such as a valve or a spherical surface such as a ball, a type in which liquids containing raw materials collide, etc.

When thinning a layered material, either a wet thinning method using a solvent or a dry thinning method not using a solvent can be used, and can be selected according to the thinning method of each device.

Solvents used in the wet thinning method are preferably alcohol solvents such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, and methoxyethanol, because they are unlikely to be electrostatically charged; ketone solvents such as acetone and methyl ethyl ketone; heterocyclic solvents such as pyridine, piperidine, morpholine, tetrahydrofuran, and dioxane; ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate; dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and water.

When flaking a layered material, a water-soluble salt may be used in combination. In the flaking process, the water-soluble salt in the solid state functions as a medium that promotes flaking, and the water-soluble salt dissolved in the solvent acts between the layers of the layered material to promote flaking. After flaking, the water-soluble salt can be easily removed by washing with water. Preferable water-soluble salts include sodium chloride, potassium chloride, magnesium chloride, sodium sulfate, potassium sulfate, calcium sulfate, and sodium acetate.

〔Polysiloxane compound having organic group〕

In the present invention, the polysiloxane compound having an organic group is a general term for a polymer or oligomer having a siloxane bond (Si-O-Si bond) as a main skeleton and an organic group bonded to a silicon atom. Examples of the organic group of the polysiloxane compound having an organic group used in the composite material of the present invention include an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, a cycloalkenyl group, an aryl group, an aralkyl group, and the like, and these organic groups may have a substituent such as a hydroxyl group, an ether group, an ester group, an epoxy group, a (meth)acryloxy group, a carbonyl group, a carboxyl group, an amino group, a thiol group, or a thioether group. As the organic group, a methyl group, an ethyl group, a butyl group, a vinyl group, a 2-cyclohexylethyl group, a 2-cyclohexenylethyl group, a phenyl group, a 2-phenylethyl group, a 2-phenylpropyl group, a 2-norbornenylethyl group, a 3-hydroxypropyl group, a 2-(3,4-epoxycyclohexyl)ethyl group, a 3-glycidoxypropyl group, a 3-acryloxypropyl group, a 3-methacryloxypropyl group, a 3-(polyoxyalkylene)propyl group, and the like are preferable because the raw materials are easily available, and a methyl group, an ethyl group, a vinyl group, and a phenyl group are preferable. Furthermore, from the viewpoint of dispersibility in the resin, the organic group of the polysiloxane compound having an organic group is preferably an aryl group such as a phenyl group, and an aralkyl group such as a 2-phenylethyl group, and a 2-phenylpropyl group. The organic group may be just one type or may be a combination of two or more types. In the case of a combination of two or more types, from the viewpoint of dispersibility in the resin, it is preferable that one type is an aryl group or an aralkyl group. When the organic group has a phenyl group, the content of the phenyl group in the compound is preferably 5 to 70 mass%, more preferably 6 to 70 mass%, and most preferably 8 to 60 mass%. The content of the phenyl group in the compound can be calculated from the content in the repeating unit constituting the polysiloxane compound and the content ratio of the repeating unit. On the other hand, when the organic group has an aryl group or aralkyl group other than a phenyl group, only the benzene ring portion is included in the content of the phenyl group. When polysiloxane compounds having two or more types of organic groups with different phenyl group contents are used in combination, the phenyl group content is a mass average value taking into account the mass ratio of the polysiloxane compounds having the organic groups used. A polysiloxane compound having an organic group may have all of the substituents of silicon substituted with organic groups, or, if the number of organic groups is a minority, some of the organic groups may be substituted with hydrogen atoms, halogen atoms, hydroxyl groups, alkoxy groups, etc.

Since a polysiloxane compound having an organic group is likely to volatilize if its molecular weight is low, the polysiloxane compound having an organic group preferably has at least 5 silicon atoms, and more preferably 10 or more silicon atoms. The molecular shape of the polysiloxane compound having an organic group may be any of linear, cyclic, branched, basket-shaped, ladder-shaped, etc., or a combination thereof, and the polysiloxane compounds having an organic group may have a molecular shape in which they are connected by a hydrocarbon group or the like.

〔Composite Materials〕

The composite material of the present invention has a surface of a flaky layered material covered with a polysiloxane compound having an organic group. In the present invention, the polysiloxane compound having an organic group may cover a part of the surface of the flaky layered material or may cover the entire surface, but it is preferable that it covers at least a majority of the surface. Furthermore, the polysiloxane compound having an organic group may cover the surface of the flaky layered material continuously or intermittently.

In the composite material of the present invention, the content of the polysiloxane compound having an organic group is 0.1 to 100 parts by mass per 100 parts by mass of the flaky layered material. When the content of the polysiloxane compound having an organic group is less than 0.1 parts by mass, the covering by the polysiloxane compound having an organic group may become insufficient, and when it is more than 100 parts by mass, not only is the increasing effect corresponding to the amount used not obtained, but when the composite material of the present invention is added to a resin or the like and used, the physical properties of the resin or the like may be adversely affected. The content of the polysiloxane compound having an organic group is preferably 0.2 to 70 parts by mass, more preferably 0.5 to 60 parts by mass, and most preferably 1 to 50 parts by mass per 100 parts by mass of the flaky layered material.

〔Method for manufacturing composite materials〕

Examples of methods for coating a thin layered material with a polysiloxane compound having an organic group include a method in which a polysiloxane compound having an organic group and the thin layered material are dispersed and mixed in a solvent and then coated (hereinafter referred to as a mixing coating method), a method in which a hydrolyzable silane compound is added to an aqueous dispersion of the thin layered material, the hydrolyzable silane compound undergoes a hydrolysis/condensation reaction (so-called sol-gel reaction) and the resulting polysiloxane compound having an organic group is coated (hereinafter referred to as a sol-gel coating method), etc.

<Mixed Covering Method>

Since the flaky layered material tends to aggregate and form secondary particles, simply immersing the flaky layered material in a solution or dispersion of a polysiloxane compound having an organic group is insufficient for covering. Therefore, it is preferable to cover by disintegrating the secondary particles of the flaky layered material in a solution or dispersion of a polysiloxane compound having an organic group, or to add a polysiloxane compound having an organic group to a dispersion obtained by disintegrating the secondary particles of the flaky layered material. In order to disintegrate the secondary particles of the flaky layered material, it is necessary to apply shear force, ultrasonic vibration, cavitation, or the like to the liquid containing the flaky layered material using a dispersion device. Dispersing devices for this purpose include a high-speed rotating shear-type agitator such as a homomixer; a medium stirring mill such as a sand mill, an attritor, or a bead mill; a vessel-driven mill using balls or rods as a medium such as a rotary mill, a vibrating mill, or a planetary mill; Examples of the high-pressure emulsifier include a colloid mill, a high-pressure emulsifier, and an ultrasonic emulsifier. Examples of the high-pressure emulsifier include a penetrating high-pressure emulsifier and an impaction-type high-pressure emulsifier. The penetrating type of the penetrating-type high-pressure emulsifier includes a single nozzle type, etc. The impact type of the impaction-type high-pressure emulsifier includes a type that collides a liquid containing raw materials with a flat surface such as a valve or a spherical surface such as a ball, a type that collides liquids containing raw materials, etc. When a strong shear force is applied to a thinned layered material, the number of layers, thickness, particle size, etc. of the thinned layered material may be reduced compared to before coating.

In the case where a polysiloxane compound having an organic group is added to a dispersion obtained by disintegrating secondary particles of a thin layered material in a mixed coating method, since the polysiloxane compound having an organic group is easily dissolved and dispersed, the dispersion device used for disintegration can be used as is after disintegrating the thin layered material.

The solvent used in the mixed coating method is not only a solvent capable of dissolving an organic group-containing polysiloxane compound, but also a solvent that cannot dissolve an organic group-containing polysiloxane compound as long as it is a solvent capable of dispersing an organic group-containing polysiloxane compound using a dispersion device. The solvent may be selected by considering ease of removal, safety (toxicity, flammability, electrostatic properties, etc.). Examples of the solvent used in the mixed coating method include alcohol solvents such as methanol, ethanol, isopropanol, and methoxyethanol; ketone solvents such as acetone and methyl ethyl ketone; and water. The ratio of the thinned layered material to the solvent or the solution of the polysiloxane compound having an organic group varies depending on the pulverizing device, but is preferably about 200 to 5,000 parts by mass of the solvent or the solution of the polysiloxane compound having an organic group per 100 parts by mass of the thinned layered material.

After mixing the flaky layered material and the polysiloxane compound having an organic group, the solvent is removed to obtain the composite material of the present invention. The method for removing the solvent is not particularly limited, and a method such as heat drying, reduced pressure drying, spray drying, freeze drying, or a combination of these methods may be applied. Before removing the solvent, if necessary, an excess of the polysiloxane compound having an organic group and a part of the solvent may be removed by filtration or centrifugation, and then the remaining solvent may be removed. The composite material of the present invention may be pulverized or granulated if necessary.

<Sol-gel coating method>

In the case of the sol-gel coating method, after the secondary particles of the thinned layered material are decomposed using water as a solvent, a hydrolyzable silane compound is subjected to a sol-gel reaction. As a dispersion device used for decomposition, the dispersion device exemplified in the mixed coating method can be exemplified. In the case of the sol-gel coating method, as in the case of the mixed coating method, if a strong shear force is applied to the thinned layered material by cleavage, the number of layers, thickness, particle size, etc. of the thinned layered material may be reduced compared to before coating.

A hydrolyzable silane compound is a silane compound having a group that generates a silanol (Si-OH) group by hydrolysis, and the silanol group dehydrates and condenses to generate a siloxane group. The hydrolyzable silane compound can be selected by considering the structure of the polysiloxane compound having the hydrolyzable group and the organic group in addition to the organic group introduced into the polysiloxane compound having the organic group.

The hydrolyzable groups of the hydrolyzable silane compound include alkoxysilyl groups such as a methoxysilyl group, an ethoxysilyl group, a propoxysilyl group, and a methoxyethoxysilyl group; halosilyl groups such as a chlorosilyl group and a bromosilyl group; acyloxysilyl groups such as an acetyloxysilyl group; and aminosilyl groups such as a dimethylaminosilyl group and a cyclohexylaminosilyl group. Among them, alkoxysilyl groups are preferable because they cause less corrosion to equipment, the hydrolysis reaction is fast, and they are easy to obtain industrially, and a methoxysilyl group and an ethoxysilyl group are more preferable.

In the present invention, the hydrolyzable silane compound is classified according to the number of organic groups and hydrolyzable groups: a silane compound having three organic groups and one hydrolyzable group is called an M-type silane compound, a silane compound having two organic groups and two hydrolyzable groups is called a D-type silane compound, a silane compound having one organic group and three hydrolyzable groups is called a T-type silane compound, and a silane compound having four hydrolyzable groups is called a Q-type silane compound. The structure of a polysiloxane compound having an organic group obtained by a sol-gel reaction is greatly affected by the number of hydrolyzable groups of the hydrolyzable silane compound used. For example, when only a D-type silane compound is used, a polysiloxane compound having a high molecular weight and a linear organic group is obtained, and when only a T-type silane compound is used, a polysiloxane compound having a basket-shaped organic group is obtained. As a hydrolyzable silane compound used in the sol-gel coating method, a D-type silane compound is preferable because it can form a film of a polysiloxane compound having an organic group of high molecular weight on a thin layered material, and when using a combination of different types of hydrolyzable silane compounds, at least one is preferably a D-type silane compound. Preferable D-type silane compounds include dimethyldimethoxysilane, dimethyldiethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane.

In the sol-gel coating method, a sol-gel reaction occurs by adding a hydrolyzable silane compound to water in which secondary particles are disintegrated and dispersed in the state of primary particles, and a film of a polysiloxane compound having an organic group is formed on the surface of the flaky layered material. The water used may be water alone, or water containing a water-soluble solvent such as methanol, ethanol, or isopropanol. In addition, the water used may contain, as a catalyst, inorganic acids such as hydrochloric acid, phosphoric acid, or sulfuric acid; organic acids such as formic acid, acetic acid, oxalic acid, citric acid, methanesulfonic acid, or benzenesulfonic acid; or inorganic bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia, in order to promote the reaction. The temperature of the sol-gel reaction varies depending on the type of the hydrolyzable silane compound, the type and amount of the catalyst, etc., but is preferably 5 to 50°C, and more preferably 8 to 30°C.

After the sol-gel reaction is completed, filtering and washing are performed as needed, and then drying is performed. The drying method is not particularly limited, and methods such as heat drying, reduced pressure drying, spray drying, and freeze drying, or a combination of these methods may be applied. In addition, the composite material of the present invention may be pulverized and granulated as needed.

In the composite material of the present invention, since the surface of the flaky layered material is coated with a polysiloxane compound having an organic group, agglomeration of the flaky layered material does not occur and dispersibility with respect to a substrate is significantly improved. As a result, the effects of improving physical properties by the flaky layered material, such as conductivity, heat dissipation, mechanical properties (impact resistance, bending strength, compressive strength, etc.), etc., can be improved. The composite material of the present invention can be suitably used for applications such as additives for resins such as synthetic resins, elastomers, paints, etc.; conductive additives for battery electrodes, etc.

〔Resin composition〕

The resin composition of the present invention contains the composite material of the present invention and a synthetic resin. Synthetic resins that can be preferably used in the resin composition of the present invention include phenol resins, epoxy resins, melamine resins, urea resins, alkyd resins, PET resins, PBT resins, polycarbonate resins, polyacetal resins, modified polyphenylene ether resins, polyurethanes, polyimides, polyimideamides, polyetherimides, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl acetate, fluorine-based resins, ABS resins, AS resins, acrylic resins, silicones, and the like. The composite material of the present invention has particularly good dispersibility for silicone resins.

When the resin of the resin composition of the present invention is a thermoplastic resin, the composite material of the present invention may be blended by a process of mixing the resin and the additive, similarly to other additives, and when it is a thermosetting resin, the composite material of the present invention may be blended with an uncured resin and then the resin may be cured. For example, in the case of a resin composition containing the composite material of the present invention and a silicone resin, the composite material of the present invention may be blended with another additive in an uncured silicone resin composition and then cured by a method such as heating. Examples of the uncured silicone resin composition include an addition-curing composition containing a polysiloxane compound having a hydrosilyl group (SiH group), a polysiloxane compound having a vinyl group (CH ₂ = CH- group), and a hydrosilylation catalyst; a condensation-curing composition containing a polysiloxane compound having a methylsilyl group (Si-CH ₃ group) and a peroxide catalyst; Examples thereof include a condensation-curable composition comprising a polysiloxane compound having a methylsilyl group, a polysiloxane compound having a vinylsilyl group, and a peroxide catalyst; a moisture-curable composition comprising a hydrolysis-condensation-type polysiloxane compound; and a photocurable composition comprising a polysiloxane compound containing a (meth)acrylic group.

The amount of the composite material of the present invention added varies depending on the type of resin or the required physical properties, but is preferably 1 to 150 parts by mass of the composite material of the present invention per 100 parts by mass of the synthetic resin, and more preferably 2 to 100 parts by mass.

In the resin composition of the present invention, a resin composition using a silicone resin as the resin is preferable. Since such a resin composition has excellent heat resistance, it can be suitably used as, for example, a sealing material for semiconductors, a heat-radiating sheet, etc.

Example

The present invention is described in more detail below by examples and comparative examples. However, the present invention is not limited in any way by the following examples, etc.

In the examples below, the average thickness of the thinned layered material is the average value of the thickness of 30 randomly selected thinned layered materials, which was measured using SEM images taken by a scanning electron microscope. In addition, the average area of the thinned layered material is the average value of the area of 50 randomly selected thinned layered materials, which was measured using an image taken by a microscope after dropping a thin dispersion of the thinned layered material on a filter paper.

〔Manufacturing Example 1〕

According to Example 1 described in International Publication No. WO2013/172350, a thin layered material A1 was prepared from natural graphite. That is, 74 parts by mass of 1-butyl-3-methylimidazolium hexafluorophosphate and 26 parts by mass of polyethylene glycol (product of Fujifilm Wako Purenyaku, product name: Polyethylene Glycol 20000) were mixed and dissolved by heating, and 10 parts by mass of natural graphite (product of Fujifilm Wako Purenyaku) was dispersed. 0.6 g of this dispersion was collected in a 0.5 cm3 vial, the vial was capped, and then the dispersion was irradiated with 2450 MHz microwaves at 170°C for 30 minutes using a microwave synthesis device (Initiator+ manufactured by Biotege Japan). Thereafter, the dispersion was filtered, washed with acetone, and dried by heating in an oven, thereby obtaining a thin layered material A1 derived from natural graphite. The average thickness and average area of the thin layered material A1 were 123 nm and 11.6 μm ² , respectively.

〔Manufacturing Example 2〕

Except that expanded graphite (product of Ito Kokuen Kogyo Co., Ltd., product name: EC1500) was used instead of natural graphite, the same operation as in Manufacturing Example 1 was performed to obtain a flaky layered material A2 derived from expanded graphite. The average thickness and average area of the flaky layered material A2 were 30 nm and 1.4 μm ² , respectively.

〔Manufacturing Example 3〕

Except that boron nitride (Aldrich Corporation) was used instead of natural graphite, the same operation as in Manufacturing Example 1 was performed to obtain a boron nitride-derived flaky layered material A3. The average thickness and average area of the flaky layered material A3 were 183 nm and 10.3 μm ² , respectively.

〔Examples 1 to 9 and Comparative Example 1〕

The above-mentioned thin layered material, the following covering material, and the solvent were placed in a bead mill (Kotobuki Kogyo, product name: UAM-015) at the mass ratios shown in Table 1, the secondary particles of the thin layered material were crushed, and the solvent was removed by heating and drying under reduced pressure to manufacture composite materials of Examples 1 to 9 and Comparative Example 1.

In Table 1, the numbers in parentheses represent the mass ratio, and MEK in the solvent represents methyl ethyl ketone. Comparative Example 1 is an experimental example using polyvinyl alcohol as a coating material, but because it is powdery and insoluble in methyl ethyl ketone, only water was used as a solvent.

<Covering material>

B1: Diphenylsiloxane-dimethylsiloxane copolymer

(Phenyl group content: 31 mass%, product of Gelest, trade name: PDM-1922)

B2: Phenylmethylsiloxane-dimethylsiloxane copolymer

(Phenyl group content: 10 mass%, product of Gelest, trade name: PMM-1015)

B3: Phenylmethylsiloxane polymer

(Phenyl group content: 56 mass%, product of Gelest, trade name: PMM-0021)

B4: Silanol-terminated diphenylsiloxane-dimethylsiloxane copolymer

(Phenyl group content: 26 mass%, product of Gelest, trade name: PDS-1615)

B5: Vinyl-terminated diphenylsiloxane-dimethyl siloxane copolymer

(Phenyl content: 22 mass%, AB Specialty Silicones product, trade name: Andisil SF2430CV)

C1: Polyvinyl alcohol (Kurare Co., Ltd. product, product name: PVA217)

〔Example 10〕

70 parts by mass of the flaky layered material A1 and 1,400 parts by mass of water were subjected to secondary particle disintegration treatment of the flaky layered material using a bead mill (manufactured by Kotobuki Kogyo, product name: UAM-015). 147 parts by mass of the dispersion of the flaky layered material, 4 parts by mass of dimethyldiethoxysilane, 1.2 parts by mass of diphenyldimethoxysilane, and 0.05 parts by mass of 85% phosphoric acid were placed in a glass container and stirred at 10°C for 3 hours and then at 30°C for an hour to produce a composite material of Example 10. Meanwhile, the phenyl group content of the polysiloxane compound having an organic group of Example 10 was 25 mass%.

〔Production of resin composition〕

10 parts by mass or 30 parts by mass of the composite material or the flaky layered material shown in Table 2 and 100 parts by mass of an addition-curing silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KE-109E-A/B) were mixed using a planetary stirring and defoaming device. The mixture was heated at a temperature of 100°C and a pressure of 5 MPa for 1 hour, and cured by heat press to produce resin sheets of Examples 11 to 21 and Comparative Examples 2 to 5 as resin compositions in the form of sheets having a thickness of 2 mm.

〔Dispersiveness Assessment〕

The manufactured resin sheet was cut using a cryo microtome, the central part of the cut surface was photographed using a microscope, and the number of aggregates and the aggregate ratio per 300 ㎛ × 300 ㎛ were measured using image analysis software. Meanwhile, the number of aggregates is the number of cases where particles having an area of 40 ㎛ ² or more were aggregates, and the aggregate ratio is the ratio (%) of the total aggregate area to the total particle area. A greater number of aggregates and a larger aggregate ratio indicate a greater proportion of aggregates. The results are shown in Table 2.

The resin sheets of Comparative Examples 4 and 5 are examples using the flaky layered material A1, the resin sheets of Examples 11 to 19 and Comparative Examples 2 to 3 are examples using a composite material derived from the flaky layered material A1, the resin sheet of Example 20 is an example using the flaky layered material A2, and the resin sheet of Example 21 is an example using a composite material derived from the flaky layered material A3. The resin sheets of Examples 11 to 19, in which the flaky layered material A1 was coated with a polysiloxane compound having an organic group, have improved dispersibility compared to the uncoated Comparative Examples 4 to 5. The resin sheets of Comparative Examples 2 to 3, which were coated with polyvinyl alcohol, have lower dispersibility than the uncoated resin sheets of Comparative Examples 4 to 5, and it can be seen that the dispersibility greatly differs depending on the coating material.

〔Mechanical properties evaluation〕

The manufactured resin sheet was processed into a dumbbell shape (No. 2), and the tensile strain was measured in accordance with JIS K6251 (Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties). The results are shown in Table 3.

〔Evaluation of electrical characteristics〕

The surface resistance value was measured according to JIS K7194 (resistivity test method by the four-probe method for conductive plastics). The results are shown in Table 3.

The resin sheets of Examples 13 to 18, in which the surface of the graphite-based flaky layered material was coated with a polysiloxane compound having an organic group, had a larger tensile strain and a lower surface resistivity than the resin sheets of Comparative Example 3 coated with polyvinyl alcohol and Comparative Example 5 without coating. This is presumed to be due to the influence of the dispersibility in the resin.

The resin sheet of Example 21, in which the surface of a boron nitride-based thin layered material was coated with a polysiloxane compound having an organic group, exhibited a greater tensile strain than the resin sheet of Comparative Example 6, which was not coated. This is presumed to be due to the effect of dispersibility in the resin. Although no difference was observed in surface resistivity, it is presumed to be due to the originally low conductivity of boron nitride.

According to the present invention, the dispersibility of the thin layered material in a resin or the like is improved, and the properties of the obtained resin composition, such as toughness, elasticity, and impact resistance, are significantly improved.

Claims (5)

A composite material in which the surface of a flaky layered material is covered with a coating material, wherein the flaky layered material is graphite, boron nitride, a transition metal dichalcogenide, a group 13 chalcogenide, a group 14 chalcogenide, a bismuth chalcogenide, a layered metal halide, a layered transition metal oxide, or a layered perovskite oxide, the average thickness of the flaky layered material is 1.5 nm to 400 nm, the average area of the flaky layered material is 0.1 ㎛ ² to 500 ㎛ ² , the coating material is a polysiloxane compound having an organic group, and the content of the coating material is 0.1 to 100 parts by mass with respect to 100 parts by mass of the flaky layered material. In the first paragraph,
A composite material wherein a polysiloxane compound having an organic group is a polysiloxane compound having a phenyl group, and the phenyl group content is 5 mass% to 70 mass%. A resin composition containing the composite material described in claim 1 or claim 2 and a synthetic resin. In the third paragraph,
A resin composition in which the synthetic resin is a silicone resin. delete