JP2008303233A - Highly conductive filler, and highly conductive silicone composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly conductive filler obtaining a cured object of high conductivity, when compounded in an addition reaction-cured type silicone composition, and a highly conductive silicone composition compounded therewith. <P>SOLUTION: This highly conductive filler is a filler compounded in the addition reaction-cured type silicone composition, and is silver powder surface-treated with a compound having a polar group selected from a group comprising a hydroxy group, an alkoxy group and a carboxy group, and an aliphatic unsaturated group. The highly conductive silicone composition is the addition reaction-cured type silicone composition compounded with the highly conductive filler. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a highly conductive filler excellent in conductivity formed by surface treatment of silver powder and a highly conductive silicone composition containing the same.

  Resin materials containing conductive fillers composed of various metal powders such as silver powder, gold powder, and nickel powder as coating agents, electromagnetic shielding materials, and die bonding agents for semiconductor chips that require electrical conductivity in use. Among metal powders, silver powder is widely used because of its excellent electrical conductivity.

  The silver powder is manufactured by, for example, an electrolytic method, a pulverizing method, an atomizing method, a chemical manufacturing method, or the like. The electrolytic method is a method of obtaining silver powder by electrolyzing an aqueous solution of silver nitrate and precipitating it on the cathode, and the pulverization method is a method of obtaining silver powder with a stamp mill, ball mill, vibration mill, hammer mill, etc. In this method, molten silver heated to 1000 ° C or higher is sprayed into water or an inert gas to obtain silver powder. In the chemical production method, an aqueous silver nitrate solution is reduced with a reducing agent such as hydrazine, formaldehyde, or ascorbic acid. This is a method for obtaining silver powder.

  Examples of the shape of the silver powder include a spherical shape, a granular shape, a dendritic shape, a flake shape, and an indefinite shape, and the flake shape is preferably used for obtaining high conductivity.

  The flaky silver powder is added with higher fatty acids such as oleic acid and stearic acid to prevent silver powder from agglomerating when pulverizing the silver powder with a ball mill or stamp mill. The surface has been treated.

  Epoxy resin-based compositions and silicone-based compositions are used as the composition for blending silver powders treated with such higher fatty acids. Among them, addition reaction curing using a curing reaction by addition reaction is used. The silicone composition of the mold is excellent in productivity because it is cured in a short time by heating, and is widely used because no by-product is generated during curing (see, for example, Patent Document 1).

However, it is known that when the composition is highly filled with silver powder, it is known that the conductive performance is improved. However, the workability in the manufacturing process is reduced and the cost is easily increased, and the upper limit of the blending amount is limited. It was. For this reason, a conductive composition having a lower resistance value has been demanded in response to the recent demand for higher conductivity, but a conventional silver powder cannot provide a sufficient conductive effect.
Japanese Patent Laid-Open No. 3-170581

  An object of the present invention is to provide a highly conductive filler that gives a highly conductive cured product when blended with an addition reaction curable silicone composition, and a highly conductive silicone composition containing the same.

  As a result of intensive studies to achieve the above object, the inventors of the present invention compounded silver powder into an addition reaction curable silicone composition by surface treatment with a compound having an aliphatic unsaturated group and a polar group. In some cases, it was found that a highly conductive cured product was obtained, and the present invention was made.

  That is, the highly conductive filler of the present invention is a highly conductive filler blended in an addition reaction curable silicone composition, and the highly conductive filler is any one of a hydroxyl group, an alkoxyl group, or a carboxyl group. It is characterized by comprising a silver powder surface-treated with a compound having a polar group and an aliphatic unsaturated group.

  In addition, the highly conductive silicone composition of the present invention is characterized in that the above highly conductive filler is blended with an addition reaction curable silicone composition.

  According to the said structure, when a highly conductive filler is mix | blended with an addition reaction-curable silicone composition, highly conductive hardened | cured material is obtained.

  Hereinafter, embodiments of the present invention will be described in detail.

  The highly conductive filler is a filler blended in an addition reaction curable silicone composition, and is obtained by surface-treating silver powder with a compound having an aliphatic unsaturated group and a polar group.

  As the silver powder, pure silver or a silver alloy is used. As the silver alloy, one containing 50 wt% or more, preferably 70 wt% or more of silver can be used. For example, silver-copper alloy, silver-palladium alloy, silver-zinc alloy, silver-tin alloy, silver-magnesium alloy And silver-nickel alloys.

  The compound for treating the surface of the silver powder may be a compound having a polar group of any one of a hydroxyl group, an alkoxyl group or a carboxyl group and an aliphatic unsaturated group, preferably an unsaturated fatty acid or an organosilicon compound. is there.

Examples of the unsaturated fatty acids, _{e.g., C n H 2n-1 COOH} (n is 6 to 28, preferably a number from 10 to 24) such as oleic acid, nervonic acid as represented by, _{C n} of linoleic acid H _2n-3 COOH (n is 6 to 28, preferably 10 to 24), C _n H _2n-5 COOH such as linolenic acid (n is 6 to 28, preferably 10 to 24) Which is the number of

  Examples of the organosilicon compound include alkenyl group-containing alkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (methoxyethoxy) silane, acryl groups such as methacryloxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, or the like. Examples include alkoxysilanes such as methacryl group-containing alkoxysilanes.

  These can be used individually by 1 type or in mixture of 2 or more types.

  Since these compounds have any one of hydroxyl groups, alkoxy groups, or carboxyl groups, when the surface of the silver powder is treated with this compound, the compounds are likely to adhere to the surface of the silver powder. Therefore, when a highly conductive filler obtained by surface-treating silver powder with this compound is added to an addition reaction curable silicone composition, the aliphatic unsaturated group in the compound and the addition reaction curable silicone The addition reaction proceeds with the hydrogen atom (Si-H group) bonded to the silicon atom of the cross-linking agent that is a constituent of the composition, whereby the silicone composition is cured, and then the highly conductive cured product. Is obtained.

  As a method for surface-treating silver powder, for example, when the silver powder is pulverized by ball milling, stamp milling, vibration milling, hammer milling, etc., the compound having the above aliphatic unsaturated group and polar group is added. And a method of coating and treating the surface of the silver powder. In this case, it is preferable that the compounding quantity of the compound which has an aliphatic unsaturated group and a polar group is 0.01-10 weight part with respect to 100 weight part of silver powder. When the blending amount is less than 0.01, aggregation of silver powders easily occurs, and furthermore, desired high conductivity is difficult to obtain. On the other hand, if it exceeds 10 parts by weight, the effect of high conductivity is not so changed, which is uneconomical.

  Examples of the shape of the highly conductive filler include granular, dendritic, flaky, and indeterminate shapes. When this filler is blended into the composition to obtain a highly conductive cured product, the flaky shape is preferable.

  The average particle size of the highly conductive filler is preferably 50 μm or less, and more preferably in the range of 0.01 to 20 μm. When the average particle diameter exceeds 50 μm, the dispersibility is deteriorated, and this filler is liable to settle when blended in the composition. The average particle diameter can be obtained by, for example, a laser beam diffraction method.

The specific surface area of the highly conductive filler is preferably not more than ^{50 m} 2 / g, more preferably 0.1 to 10 m ² / g. When it exceeds 50 m < ² > / g, when adding a highly conductive filler to a silicone composition, there exists a possibility that a dispersibility may worsen. The specific surface area can be determined by the BET method.

  The highly conductive filler can be blended in the addition reaction curable silicone composition. The addition reaction curable silicone composition contains at least the following components (A) to (C), and the above-described highly conductive filler is added to the composition as the component (D). Thus, a highly conductive silicone composition can be obtained.

  That is, the highly conductive silicone composition of the embodiment includes (A) a polyorganosiloxane having an average of 0.2 or more alkenyl groups bonded to silicon atoms in one molecule, and (B) bonded to silicon atoms in one molecule. A polyorganohydrogensiloxane having two or more hydrogen atoms, (C) a platinum-based catalyst, and (D) a highly conductive filler.

  Hereinafter, the components (A) to (D) will be described in detail.

[(A) component]
Component (A) is a base polymer, and in order to sufficiently cure the composition, an average of 0.2 or more, preferably 0.5 or more, more preferably an average of alkenyl groups bonded to silicon atoms in one molecule. Have an average of 2 or more. The molecular structure may be linear, cyclic or branched, but is preferably linear from the viewpoint of rubber physical properties after curing, and may be used alone or in combination of two or more.

  Examples of the alkenyl group bonded to the silicon atom include a vinyl group, an allyl group, a butenyl group, a petenyl group, and a hexenyl group, and a vinyl group is preferable. The alkenyl group may be bonded to the silicon atom at the end of the molecular chain, or may be bonded to the silicon atom in the middle of the molecular chain, or may be bonded to both. From the viewpoint of physical properties of rubber, it is preferably bonded to at least a silicon atom at the molecular chain terminal, particularly a silicon atom at both molecular chain terminals.

  Examples of organic groups bonded to silicon atoms other than alkenyl groups include alkyl groups such as methyl, ethyl and propyl groups, cycloalkyl groups such as cyclopentyl and cyclohexyl groups, phenyl groups, tolyl groups and xylyl groups. Or a group having 1 to 12 carbon atoms such as a halogenated hydrocarbon group in which these hydrogen atoms are partially substituted by chlorine atoms, fluorine atoms, etc., preferably alkyl groups and aryl groups. More preferably a methyl group or a phenyl group.

  (A) The viscosity in 25 degreeC of a component is 0.1-1000 Pa.s, Preferably it is 0.5-100 Pa.s. When the viscosity is less than 0.1 Pa · s, the mechanical strength after curing tends to decrease. On the other hand, when it exceeds 1000 Pa · s, the fluidity of the composition is lowered and the workability is deteriorated.

[Component (B)]
The component (B) is a cross-linking agent and has 2 or more, preferably 3 or more hydrogen atoms bonded to silicon atoms in one molecule. This hydrogen atom may be bonded to the silicon atom at the end of the molecular chain, may be bonded to the silicon atom in the middle of the molecular chain, or may be bonded to both.

As the component (B), an average composition formula:
R ² _d H _e SiO _{[4- (d + e)] / 2}
What is shown by is used.

In the formula, R ² is a substituted or unsubstituted monovalent hydrocarbon group excluding an aliphatic unsaturated hydrocarbon group. R ² includes, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a hexyl group, a cyclohexyl group, and an octyl group; Aryl groups such as; aralkyl groups such as benzyl and phenylethyl groups; and those in which some or all of the hydrogen atoms in these groups are substituted with halogen atoms such as fluorine, chlorine, bromine or cyano groups, Examples include chloromethyl group, bromoethyl group, trifluoropropyl group, cyanoethyl group. Among them, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group from the viewpoint of ease of synthesis and cost. An alkyl group having 1 to 4 carbon atoms such as a methyl group is preferable, and a methyl group is more preferable.

  d and e are positive numbers satisfying 0.5 ≦ d ≦ 2, 0 <e ≦ 2, and 0.5 <d + e ≦ 3, respectively, preferably 0.6 ≦ d ≦ 1.9, 0 .01 ≦ e ≦ 1.0 and 0.6 ≦ d + e ≦ 2.8.

  The molecular structure of the component (B) may be linear, branched, cyclic or three-dimensional network, and may be used alone or in combination of two or more.

  (B) The viscosity in 25 degreeC of a component is 1-1000 mPa * s, Preferably it is 10-500 mPa * s.

  The blending amount of the component (B) is 0.2 to 10 moles of hydrogen atoms bonded to the silicon atoms of the component (B) with respect to a total of 1 mole of alkenyl groups bonded to the silicon atoms of the component (A). The amount is preferably 0.5 to 5 mol. If the amount is less than 0.2 mol, the composition is not sufficiently cured. On the other hand, if it exceeds 10 moles, the expected rubber properties cannot be obtained.

[Component (C)]
(C) component is a component which accelerates | stimulates hardening of a composition.

  As the component (C), a known catalyst used in hydrosilylation reaction can be used. For example, platinum black, secondary platinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and olefins or vinyl siloxane, platinum bisacetoacetate, or the like can be given.

  The blending amount of the component (C) may be an amount necessary for curing, and can be appropriately adjusted according to a desired curing rate. Usually, it is in the range of 0.1 to 1000 ppm, preferably in the range of 0.5 to 500 ppm in terms of platinum element with respect to the total amount of the composition.

[(D) component]
The highly conductive filler of component (D) is a component that imparts excellent conductivity to the composition, and as described above, any polar group of a hydroxyl group, an alkoxyl group, or a carboxyl group, and aliphatic unsaturation A silver powder is surface-treated with a compound having a group.

  (D) The compounding quantity of component is 50-2000 weight part with respect to 100 weight part of (A) component, Preferably it is 100-1500 weight part. If the blending amount is less than 50 parts by weight, desired high conductivity cannot be obtained after curing. On the other hand, when it exceeds 2000 parts by weight, the fluidity of the composition is lowered, and the workability is easily deteriorated.

  The highly conductive silicone composition comprises the above components (A) to (D) as basic components, and, as necessary, as other optional components, reaction inhibitors, colorants, difficulty for adjusting the curing rate. A flame-imparting agent, a heat resistance improver, a plasticizer, reinforcing silica, an adhesion-imparting agent, and the like may be added as long as the object of the present invention is not impaired.

  Examples of the method for producing a highly conductive silicone composition include a method of kneading the components (A) to (D) and other optional components with a kneader at room temperature. As the kneading machine, a known apparatus can be used, and examples thereof include a planetary mixer, a three-roller, a kneader, a Shinagawa mixer, etc. equipped with a heating means and a cooling means, if necessary, and used alone or in combination. be able to. In addition, the addition order of each component is not specifically limited.

  The viscosity of the highly conductive silicone composition is preferably 100 to 1,000,000 mPa · s at 25 ° C., more preferably 500 to 100,000 mPa · s.

  Examples of a method for curing the highly conductive silicone composition include a method of curing by heating at room temperature or 50 to 200 ° C. for 60 to 120 minutes, and it is preferable to heat for rapid curing. The cured product is rubbery and is preferably hard rubbery.

The volume resistivity after curing is 1 × 10 ⁻² Ω · cm or less, preferably 5 × 10 ⁻³ Ω · cm or less. When the volume resistivity exceeds 1 × 10 ⁻² Ω · cm, the conductive performance becomes insufficient and the application is likely to be limited.

  Therefore, a highly conductive silicone composition provides a low-resistance rubber-like cured product after curing. For example, a coating agent or paint for a substrate requiring conductivity, an electromagnetic shielding material, or a die bonding agent for a semiconductor chip. It is suitable as.

  The present invention will be described in detail with reference to examples. The conductive silicone compositions obtained in Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1. The characteristics shown in Table 1 are values measured at 25 ° C. The average particle diameter is a value measured by a laser diffraction method, and the specific surface area is a value measured by a BET method.

[Volume resistivity after curing]
The obtained conductive silicone composition was poured into a mold to a thickness of 2 mm and heated at 150 ° C. for 1 hour to obtain a sheet-like cured product. The volume resistivity of the cured product was measured by a constant current application method.

[Example 1]
(A) Polymethylhydrosiloxane having a viscosity of 5000 mPa · s at 25 ° C., 100 parts by weight of polydimethylorganosiloxane blocked at both ends of the molecular chain with vinyldimethylsiloxy groups, and (B) 50 mol% hydrogen groups in the side chain Gensiloxane 2.3 parts by weight, (C) vinylsiloxane complex of chloroplatinic acid (5 ppm as platinum element), (D-1) flaky silver powder surface-treated with oleic acid (average particle size 5.4 μm, 300 parts by weight of a specific surface area of 0.8 m ² / g) was kneaded with three rolls to obtain a conductive silicone composition.
The properties of this composition were measured and the results are shown in Table 1.

[Example 2]
(A) Polymethylhydrosiloxane having a viscosity of 5000 mPa · s at 25 ° C., 100 parts by weight of polydimethylorganosiloxane blocked at both ends of the molecular chain with vinyldimethylsiloxy groups, and (B) 50 mol% hydrogen groups in the side chain 2.3 parts by weight of Gensiloxane, (C) vinyl siloxane complex of chloroplatinic acid (5 ppm as platinum element) (D-3) flaky silver powder surface-treated with methacryloxypropyltrimethoxysilane (average particle size 5 .3 μm, specific surface area 0.78 m ² / g) 300 parts by weight were kneaded with three rolls to obtain a conductive silicone composition.
The properties of this composition were measured and the results are shown in Table 1.

[Comparative Example 1]
(A) Polymethylhydrosiloxane having a viscosity of 5000 mPa · s at 25 ° C., 100 parts by weight of polydimethylorganosiloxane blocked at both ends of the molecular chain with vinyldimethylsiloxy groups, and (B) 50 mol% hydrogen groups in the side chain 2.3 parts by weight of Gensiloxane, (C) vinyl siloxane complex of chloroplatinic acid (5 ppm as platinum element) (D-2) flaky silver powder surface-treated with stearic acid (average particle size 5.2 μm, ratio 300 parts by weight of a surface area of 0.83 m ² / g) was kneaded with three rolls to obtain a conductive silicone composition.
The properties of this composition were measured and the results are shown in Table 1.

[Comparative Example 2]
(A) Polymethylhydrosiloxane having a viscosity of 5000 mPa · s at 25 ° C., 100 parts by weight of polydimethylorganosiloxane blocked at both ends of the molecular chain with vinyldimethylsiloxy groups, and (B) 50 mol% hydrogen groups in the side chain Genosiloxane 2.3 parts by weight, (C) chloroplatinic acid vinylsiloxane complex (5 ppm as platinum element), (D-4) flaky silver powder surface-treated with hexyltrimethoxysilane (average particle size 5. 3 parts by weight of 4 μm and a specific surface area of 0.8 m ² / g) were kneaded with three rolls to obtain a conductive silicone composition.
The properties of this composition were measured and the results are shown in Table 1.

  As is clear from Table 1, as (D) component, (D-1) silver powder treated with oleic acid or (D-3) silver powder treated with methacryloxypropyltrimethoxysilane was blended In the example, since the compound for surface treatment of the silver powder has a polar group and an aliphatic unsaturated group, a cured product having a low resistance can be obtained as compared with the comparative example.

Claims (6)

A highly conductive filler blended in an addition reaction curable silicone composition,
The highly conductive filler is made of silver powder surface-treated with a compound having a polar group of any one of a hydroxyl group, an alkoxyl group or a carboxyl group, and an aliphatic unsaturated group. Agent.   The highly conductive filler according to claim 1, wherein the compound having the polar group and the aliphatic unsaturated group is an unsaturated fatty acid. The unsaturated fatty acid is C _n H _2n-1 COOH (n is a number from 6 to 28), C _n H _2n-3 COOH (n is a number from 6 to 28) or C _n H _2n-5. The highly conductive filler according to claim 2, which is represented by COOH (n is a number of 6 to 28).   The highly conductive filler according to claim 1, wherein the compound having the polar group and the aliphatic unsaturated group is an organosilicon compound.   A highly conductive silicone composition comprising the highly conductive filler according to any one of claims 1 to 4 in an addition reaction curable silicone composition. The highly conductive silicone composition according to claim 5, wherein the volume resistivity after curing is 1 × 10 ⁻² Ω · cm or less.