JP2020139094A - Method for producing organosiloxane polymer sheet - Google Patents

Abstract

To provide a method for producing an organosiloxane polymer sheet having heat resistance, adhesiveness, thermal conductivity or electrical insulation in a short time at a relatively low temperature.SOLUTION: The method for producing an organosiloxane polymer sheet includes: a kneading step of kneading a condensation type organosiloxane prepolymer and a thermally conductive filler having a thermal conductivity of 2.0 W m-1 K-1 or more in an amount of 34 pts.mass or more based on 100 pts.mass of the organosiloxane prepolymer to obtain a kneaded product; and a sheet molding step of molding the kneaded product under a reduced pressure atmosphere at a temperature of 40-250°C to obtain a sheet.SELECTED DRAWING: None

Description

The present invention relates generally to a method for producing an organosiloxane polymer sheet, and specifically to a method for producing an organosiloxane polymer sheet having heat resistance, adhesiveness, thermal conductivity or electrical insulation.

With the recent high integration, miniaturization, and thinning of semiconductors, the demand for heat resistance and electrical insulation resistance of members such as adhesive layers used together with semiconductors is increasing. It is also important to control the heat, such as how to efficiently dissipate the heat generated from the substrate. In response to such a demand for an adhesive layer, an organosiloxane polymer having high heat resistance produced by using a polydimethylsiloxane-based polymer has been proposed. In particular, the organosiloxane prepolymer using an oligomer containing a phenyl group has high heat resistance and can be used in an environment of 200 ° C. or higher. A heat-resistant thermally conductive elastic sheet can be produced by blending the organosiloxane prepolymer with a thermally conductive filler to form a sheet.

Such an elastic sheet is generally processed by curing a film-shaped molded body sheeted by a calendar roll or the like through a continuous firing furnace of several meters to several tens of meters and winding it as a roll. .. It is highly productive and has a great price advantage, providing the market with low cost heat dissipation sheets. However, in this molding method, the curing time of the resin as the base material is limited to several minutes to 30 minutes at the longest. For a resin having a curing time longer than that, a continuous firing furnace of 20 m or more is required, which causes a problem in productivity from the viewpoint of equipment and is not general purpose. In particular, in calendar roll molding, it becomes difficult to maintain the transfer accuracy when the process becomes long, and in the case of a wide sheet, the film thickness accuracy at both ends deteriorates, and the equipment becomes large and expensive.

Since the above-mentioned organosiloxane polymer having high heat resistance needs to form an inorganic bond having a high binding energy, it is necessary to cause a long-term condensation reaction at a high temperature, and a curing time of 2 to 3 hours is usually obtained at 200 ° C. or higher. Needs. Although various curing catalysts have been proposed, it is still difficult to complete the condensation reaction in about several minutes to 30 minutes, and it is not easy to apply general-purpose calendar roll molding. In addition, the organosiloxane prepolymer is usually delayed in curing when fine particles having a particle size of μm or less, such as carbon black used for imparting conductivity and alumina fine particles used in blending a heat dissipation sheet, are blended. It does not solidify at the curing temperature or curing time, and it is often difficult to deal with it even if a curing agent is used.

As a method for rapidly curing the condensed organosiloxane prepolymer, a method using a metal catalyst, metal alkoxides, a polymerization initiator, or the like has been proposed.

Japanese Unexamined Patent Publication No. 2011-137140 (Patent Document 1) describes that a metal compound of zinc and hafnium or a metal alkoxide is used in combination.

Japanese Patent Application Laid-Open No. 2012-107123 (Patent Document 2) describes thermosetting containing an organic polymer having a specific hydrolyzable silyl group and a cationic polymerization initiator for the purpose of obtaining excellent curability and the like. The sex resin composition is described.

Further, in Japanese Patent Application Laid-Open No. 2017-122181 (Patent Document 3), in a condensation-curable silicone composition, organic peroxide curing with an organic peroxide is used in combination at the time of curing for the purpose of improving deep curability. It is stated that.

Japanese Unexamined Patent Publication No. 2011-137140 Japanese Unexamined Patent Publication No. 2012-107123 Japanese Unexamined Patent Publication No. 2017-122181

However, in Patent Document 1, although the curing temperature is relatively low for the condensation type curing reaction, the curing time requires 10 hours or more, which makes mass production difficult.

In Patent Document 2, the productivity is improved to 80 ° C. × 1.5 hours, but there is a problem in heat resistance because a cationic polymerization initiator is compounded.

Further, even in the condensation-curable silicone composition in Patent Document 3, heat resistance tends to be sacrificed because it is necessary to incorporate a functional group that reacts with an organic peroxide into the condensation-type organosiloxane prepolymer.

In sheet processing technology such as adhesive sheets, heat dissipation sheets, and insulating sheets, continuous production of the above-mentioned calendar rolls and the like is the mainstream, and a short processing process in consideration of productivity is required. In addition to calendar roll processing, molding by casting method or screen printing method is also conceivable, but since it is necessary to inject into a mold and adjust the viscosity that can be printed, there are restrictions on the amount of filler compounded, resulting in high thermal conductivity and conductivity. It becomes a big restriction when developing the conversion and proper adhesiveness.

Therefore, an object of the present invention is to provide a method for producing an organosiloxane polymer sheet having heat resistance, adhesiveness, thermal conductivity or electrical insulation in a short time and at a relatively low temperature.

Method for producing the organosiloxane polymer sheet according to the present invention, condensed organosiloxane prepolymer and 34 parts by mass or more of the thermal conductivity with respect to organosiloxane prepolymer 100 parts by 2.0W ^· m -1 · K ^{- A} kneading step in which ^one or more thermally conductive fillers are kneaded to obtain a kneaded product, and a sheet molding in which the kneaded product is pressure-molded at a temperature of 40 to 250 ° C. in a reduced pressure atmosphere to obtain a sheet. Includes steps.

In the method for producing an organosiloxane polymer sheet according to the present invention, the kneaded product preferably contains 50 parts by mass or more of a thermally conductive filler with respect to 100 parts by mass of the organosiloxane prepolymer.

In the method for producing an organosiloxane polymer sheet according to the present invention, the reduced pressure in the sheet molding step is preferably 95 kPa or less.

In the method for producing an organosiloxane polymer sheet according to the present invention, it is preferable that the thermally conductive filler has a thermal conductivity of 25 W · m ^-1 · K ^-1 or more.

In the method for producing an organosiloxane polymer sheet according to the present invention, in the sheet molding step, the sheet is formed by pressure molding the kneaded product under a reduced pressure atmosphere with a molding die heated to a temperature of 40 to 250 ° C. It is preferably a step of obtaining.

In pressure molding using a molding die, even when a thin film having a film thickness of 0.1 mm or less is produced, for example, compared with the case of pressure molding using a calendar roll thickness, the casting method, or the screen printing method, A highly viscous kneaded product with a large amount of filler can be used, and the film thickness accuracy can be improved by increasing the dimensional accuracy of the molding die.

In the method for producing an organosiloxane polymer sheet according to the present invention, in the sheet molding step, a release film having a moisture permeability of 1 × 10 ⁻¹⁵ mol · m / (m ² · s · Pa) or more is used as a kneaded product. It is preferably interposed between the molding dies.

In the method for producing an organosiloxane polymer sheet according to the present invention, in the sheet molding step, the sheet is pressure-molded by a calendar roll heated to a temperature of 40 to 250 ° C. under a reduced pressure atmosphere. It is preferably a step of obtaining.

As described above, according to the present invention, it is possible to provide a method for producing an organosiloxane polymer sheet having heat resistance, adhesiveness, thermal conductivity or electrical insulation in a short time and at a relatively low temperature.

Method for producing the organosiloxane polymer sheet according to the present invention, condensed organosiloxane prepolymer and 34 parts by mass or more of the thermal conductivity with respect to organosiloxane prepolymer 100 parts by 2.0W ^· m -1 · K ^{- A} kneading step in which ^one or more thermally conductive fillers are kneaded to obtain a kneaded product, and a sheet molding in which the kneaded product is pressure-molded at a temperature of 40 to 250 ° C. in a reduced pressure atmosphere to obtain a sheet. Includes steps. The present invention will be described in detail below.

<Condensation type organosiloxane prepolymer>
The condensed polysiloxane prepolymer used in the kneading step of the present invention preferably uses linear polydimethylsiloxane having silanol groups at both ends as a main raw material. In the production of a general heat-condensation type organosiloxane prepolymer, one having an average molecular weight of about 500 to 100,000 is used properly depending on the application. If the molecular weight is low, a hard polydimethylsiloxane polymer can be obtained, and if the molecular weight is high, a highly flexible polydimethylsiloxane polymer can be obtained. However, if the molecular weight is too low, the number of reactive groups increases and the number of volatile components during the condensation reaction increases, making it unsuitable for pressure molding. On the other hand, when the molecular weight is high, the viscosity of the produced polydimethylsiloxane polymer is high and it is difficult to mix the filler. Therefore, the molecular weight range is preferably 3,000 to 80,000, more preferably 10,000 to 50,000, and even more preferably 20,000 to 40,000 as the number average molecular weight.

The condensed organosiloxane prepolymer preferably contains a phenyl group. The phenyl group has a high heat transfer power, and by incorporating it into the structure of the organosiloxane prepolymer, heat transfer during pressure molding is improved and curing is promoted. In addition, the effect of improving the heat resistance is also high, and it becomes possible to improve the heat resistance of the molded organosiloxane polymer sheet.

Further, in order to form a sheet in a short time while improving heat resistance and adhesiveness, the condensed organosiloxane prepolymer is composed of a polydimethylsiloxane having a silanol group (1) or an alkoxy group (2) at the end. It is preferably a prepolymer obtained by subjecting a silane monomer (3) or a silane oligomer (4) having an alkoxy group to a condensation reaction.

<Both-terminal silanol polydimethylsiloxane>
The PDMS used as a raw material for both-terminal silanol polydimethylsiloxane is preferably represented by the chemical formula (1). In the production of the condensed organosiloxane prepolymer, a number average molecular weight Mn of about 500 to 100,000 is used. Although the molecular weight distribution index (Mw / Mn) is not specified, it is preferable to use PDMS having a molecular weight distribution index (Mw / Mn) of 1.5 or less because the curing time can be significantly shortened and the molding time can be further shortened. From the viewpoint of the flexibility of the molded sheet, it is desirable to have a large molecular weight distribution index, but in press molding using a molding mold, it is also necessary to remove the mold after molding, and if solidification does not proceed to some extent by primary curing, molding processing Is difficult. From the viewpoint of heat resistance, the number average molecular weight is more preferably 5,000 to 50,000, and when it is produced as a base material for a sheet in which heat resistance and flexibility are desired, PDMS having a number average molecular weight of 30,000 or more is used as a raw material. It is desirable to do.

<Both ends alkoxypolydimethylsiloxane>
The PDMS used as a raw material for both-terminal arcosikipolydimethylsiloxane is preferably represented by the chemical formula (2).

Polydimethylsiloxane having an alkoxy group at both ends of the chemical formula (2) has a high curing promoting effect, and the number average molecular weight is preferably 3,000 to 30,000. R _{1 in the} molecule is an alkyl group having 1 to 3 carbon atoms, and those selected from the methyl group, the ethyl group, the n-propyl group, and the isopropyl group are all the same, but are partially or all different. May be. R ₁ is most preferably an ethyl group from the viewpoint of reactivity, safety and reaction control. X is oxygen or an alkylene group having 2 or less carbon atoms, which may be the same or different.

<Alkoxysilane>
In the production of organosiloxane prepolymers that require heat resistance, alkoxysilanes that can react with the above-mentioned both-terminal silanol polydimethylsiloxane and exhibit inorganic properties are used. A condensed organopolysiloxane prepolymer is formed by reacting the terminal silanol group of polydimethylsiloxane with the alkoxy group of silanes. By using an alkoxysilane oligomer having a plurality of alkoxy groups, the number of cross-linking points can be increased and the reaction can be accelerated.

Further, since a part of the alkoxy group remains after the reaction, it is possible to form a strong bond with the object to be bonded and impart adhesiveness. This effect is also exhibited on the surface of the filler, leading to prevention of hydrolysis of the filler and improvement of kneadability.

If silanes having a phenyl group are used, the heat resistance of the obtained condensed organopolysiloxane is improved and the thermal conductivity is also improved. Examples of the phenyl group-containing silane compound used include phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane. It is desirable to use phenyltrimethoxysilane in consideration of reactivity, and it is desirable to use phenyltriethoxysilane in consideration of reaction stability and safety. For silanes having two phenyl groups, diphenyldimethoxysilane can be used. The same effect or more can be obtained by using an alkoxysilane oligomer containing a phenyl group.

The general formula of the alkoxysilane monomer is shown in the chemical formula (3). In the formula, R ₂ and R ₃ are alkyl groups or phenyl groups having 1 to 4 carbon atoms, and are methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group. It is selected from. From the viewpoint of reactivity, a methyl group is preferable, and from the viewpoint of stability and safety, an ethyl group is preferable. An integer of 0 to 3 is entered in q, and an integer of (4-q) is entered in p. R ₂ and R ₃ may all be the same or different.

The alkoxysilane oligomer is shown in the chemical formula (4). In the formula, R ₄ is an alkyl group having 1 to 4 carbon atoms, which is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group and a tert-butyl group. From the viewpoint of reactivity, a methyl group is preferable, and from the viewpoint of stability and safety, an ethyl group is preferable. R ₄ may all be the same or different from each other.

<Reaction catalyst>
Metal-based catalysts and alkoxides can be used in the synthesis of the condensed organopolysiloxane. Examples of the metal catalyst include tin, zinc, zirconium, and platinum-based metal compounds. Titanium-based metal alkoxides are desirable from the viewpoint of stability and reactivity. In addition, aluminum-based and zirconium-based alkoxides can also be used. In addition, it can be produced by using an acid / basic catalyst or the like.

<Preparation of condensed organosiloxane prepolymer>
The condensed organosiloxane prepolymer can be prepared by a condensation reaction of the above-mentioned structural formula (1) or (2) or a mixture thereof with a silane monomer (3) and a silane oligomer (4). In the reaction, a metal catalyst, metal alkoxides, etc. are used for dehydration and dealcohol condensation. The reaction is carried out in an inert gas atmosphere for the purpose of controlling hydrolysis, and is carried out by heating to 80 ° C. to 120 ° C. The obtained heat-resistant condensed organosiloxane prepolymer is a transparent viscous liquid.

<Thermal conductive filler>
The condensed organosiloxane prepolymer of the present invention needs to be blended with a filler. The filler used is preferably a filler having high thermal conductivity, and for example, fillers such as α-alumina, aluminum nitride, boron nitride, and magnesium oxide can be used. The scaly filler such as boron nitride may have a large difference in thermal conductivity in the thickness direction and the plane direction, but at least 2.0 W · m ^-1 · K ^-1 or more is effective. Further, when electrical conductivity may be imparted, carbon or a metal-based filler can also be used.

The above filler has excellent heat transfer properties and can rapidly transfer the heat required for the condensation reaction of the condensed organosiloxane prepolymer to the hybrid polymer. The heat of the press machine is transmitted to the filler densified by pressurization and quickly transferred to the inside of the kneaded product, so that the condensation reaction can proceed quickly. The filler used is preferably one having a thermal conductivity of 25 W · m ^-1 · K ^-1 or more.

The thermally conductive filler preferably has reactive functional groups present on the surface interacting with the organosiloxane prepolymer. This is because the organosiloxane prepolymer is a condensed type and reacts remarkably with hydroxyl groups and alkoxy groups, so that the reaction with the filler surface easily occurs to form a sheet shape. However, when the number of functional groups is excessive, the reaction between the organosiloxane prepolymer and the filler is suppressed, and the reaction of the organosiloxane prepolymer is inhibited, which is not preferable.

The scaly filler has properties that impart electrical insulation and gas barrier properties, and when blended, it can exhibit superior properties. It also has the effect of increasing the elongation, which is the mechanical characteristic of the sheet. Further, the filler may be surface-treated. In particular, in the case of a filler having irregularities on the surface having a large specific surface area, the air residue after kneading can be reduced by smoothing the surface to some extent by surface treatment.

Further, by mixing a plurality of fillers having different types and shapes of fillers and particle diameters, the filling of the fillers can be made more precise. The particle size depends on the target sheet film thickness, but it is desirable to combine a particle size having an average particle size of several tens of μm and a particle size of several μm to several hundred nm. As for the shape, by combining fillers having different shapes, such as those having a polyhedron shape and those having a scaly shape, densification progresses and high thermal conductivity can be exhibited.

The filler needs to be blended in an amount of 34 parts by mass or more with respect to 100 parts by mass of the condensed organosiloxane prepolymer, and it is desirable to blend 50 parts by mass or more. Molding is possible even if it is less than that, but it is difficult to mold in a short time because sufficient heat cannot be transferred to the condensed organosiloxane prepolymer. On the other hand, the compounding of 1500 parts by mass or more with respect to 100 parts by mass of the condensed organosiloxane prepolymer is difficult to form into a film during pressure molding, although it depends on the type of filler and the kneading method, and is mechanical as a sheet. It is difficult to obtain strength.

<Kneading of condensed organosiloxane prepolymer and thermally conductive filler>
As a method of kneading the condensed organosiloxane prepolymer and the filler, a primary mixer or the like can be used as long as it is a low-blending product. For high-blend products, a mortar-type kneader or kneader that can be kneaded with a strong share, a single-screw or twin-screw kneading extruder, a three-roll mill with a ceramic roll, and an open roll (two). It is desirable to use a roll) or the like. When emphasizing mass productivity, kneading with a roll mill is also possible.

It is desirable to knead in a reduced pressure atmosphere. Most ceramic fillers form secondary particles and have many bubbles, and it is difficult to obtain denseness only by mechanical kneading. By using a planetary mixer with vacuum degassing or a kneading extruder with a vacuum vent, it is possible to remove the remaining air in the kneaded product and suppress appearance defects such as hole holes after molding. be able to. Further, by being densified by pressurization, effects such as improvement of thermal conductivity and improvement of mechanical properties can be obtained.

<Formation of condensed organosiloxane prepolymer kneaded product>
The pressure molding may be performed by press molding only on the top plate and the bottom plate, or by using a molding die, or by calendar molding using a calendar roll. Pressurization requires constant pressure pressurization, heating of the press plate or roll, and decompression of the molding atmosphere.

Since the organosiloxane prepolymer is a thermal condensation type, it needs to be molded at 40 ° C. or higher by heating in order to cause a condensation reaction. The temperature of the pressure molding is more preferably a temperature in the range of 50 to 180 ° C, and even more preferably a temperature in the range of 80 to 180 ° C.

Pressurization is necessary to densify the heat conductive filler and transfer heat to the entire molded body quickly and evenly, and it is preferable to pressurize at 30 kN or more.

In order to remove water and alcohol generated in the condensation reaction from the condensed organosiloxane prepolymer, it is necessary to carry out under a reduced pressure atmosphere. The reduced pressure atmosphere is preferably 95 kPa or less.

This processing method can also be used when producing an adhesive sheet having adhesiveness with a reduced amount of filler for the purpose of developing adhesiveness rather than thermal conductivity. The filler is densified by pressure molding, and mechanical properties such as elastic modulus and elongation can be improved as an adhesive sheet. In particular, when a scale-shaped filler is used, the long side surfaces of the filler tend to line up parallel to the stretching direction of the condensed organosiloxane prepolymer kneaded product under pressure, and 200% or more, and in some cases 300% or more. It becomes possible to develop the elongation of the sheet.

The conditions for press molding are not limited, but due to the characteristics of the condensed organosiloxane prepolymer kneaded product, it is desirable to mold in a multi-stage system and carry out the bumping treatment. That is, the heating / stretching step of the hybrid prepolymer kneaded product, the bubble removal by the bumping treatment, the pressure molding step, the bubble removal by the bumping treatment, and the pressure molding step are performed. When the size of the molded sheet is large, air bubbles may be removed by the bumping treatment two or more times. It is effective to carry out the bumping treatment for removing air bubbles under reduced pressure. The bumping treatment is generally used for the purpose of efficiently removing the air existing in the mold. However, since the hybrid prepolymer generates water and alcohol due to the condensation reaction during curing, the bumping treatment is performed. Is extremely effective. However, if the residual bubbles are sufficiently removed by the vacuum vent type kneading extruder, the mortar type kneader, or the like, the bumping treatment is not always necessary.

<Molding mold>
The molding die can be made of pure iron, steel, cast iron, tungsten carbide, or aluminum or resin depending on the pressure conditions. In particular, it is possible to use a resin mold for molding an adhesive sheet or the like having a low amount of filler, and acrylic resin or the like is advantageous because the adhesion reaction of the condensed organosiloxane prepolymer is unlikely to occur. Since the molded surface is often worn by the heat conductive filler when the sheet is press-molded, it is effective to use a plating process or a release film. A fluorine-based resin type is also effective.

<Release film>
In heat press molding, it is desirable to use a release film. By molding using a release film for the molding mold, it is possible to reduce mold wear and foreign matter contamination as much as possible. When an organosiloxane prepolymer kneaded product is interposed in a release film and pressure is applied to prepare a sheet, it can be molded together with the release film, so there is no need to attach a release film in a subsequent process when shipping as a product. It is possible to significantly reduce the time.

As the release film, any film such as a fluorine film or a silicone film that has sufficient heat resistance that does not cause deterioration or wrinkles at a temperature of 120 ° C. or higher and has undergone a release treatment can be used. When the sheet area to be molded is large, the volatile components of water and alcohol generated by the condensation reaction of organosiloxane cannot be removed, and gas residue (bubbles) may be generated in the central part, so that the release film is gas permeable. It is preferable to use a film having a high rate. Examples of the film having a high gas permeability include a polymethylpentene resin film processed into a porous state. The release film is preferably used on at least one side, and more preferably on both sides. Specifically, it is preferable to use a release film having a moisture permeability of 1 × 10 ^-15 mol · m / (m ² · s · Pa) or more on both sides. Further, a porous body may be sandwiched between the release film and the molding die for the purpose of improving the release of volatile components. Examples of the material of the porous body include ceramics and metals.

The film thickness of the sheet is determined by the size of the die, but by inserting a spacer of a certain size between the upper and lower plates of the press, the film thickness can be arbitrarily produced. By using a plurality of spacers, it is possible to secure a predetermined film thickness, and a desired sheet film thickness can be produced with one mold. Further, the use of the spacer reduces the wear of the mold, and the use of the spacer as a consumable item makes it possible to significantly reduce the running cost.

The film thickness of the sheet molding can be adjusted by combining a plurality of spacers having a constant film thickness between the upper and lower molding dies during press molding. Furthermore, by inserting a thin slit in this spacer, when the chamber is released from the decompressed state, the inside of the molding mold under the press pressure is released from the decompressed state, so that the sheet is broken or the release film is released. It is possible to suppress the occurrence of shape defects such as slamming.

<Adhesive sheet>
The sheet formed by appropriately blending a heat conductive filler with the condensed organosiloxane prepolymer according to the present invention in a semi-cured state can be used as an adhesive sheet. Adhesive sheets have a wide range of uses, such as joining dissimilar materials such as ceramics and metals, manufacturing heat-resistant laminated boards, and joining LED packages.

The high level of electrical insulation, which is important in applications such as laminated boards, can be achieved by adding boron nitride as a heat conductive filler to be blended. The condensed organosiloxane prepolymer according to the present invention has high electrical insulation properties, but by adding boron nitride, it is possible to exhibit even higher electrical insulation properties. The scaly filler is expected to have the effect of improving the gas barrier property and the electrical insulation property, but the effect is particularly remarkable for the nanofiller of μm or less.

The adhesive sheet needs to have adhesive strength after the primary molding, and the primary molded sheet needs to be peelable from the release film. The adhesive sheet is intended to be used for joining dissimilar materials with different linear expansion coefficients such as metal, glass, and ceramics, and because it needs to function as an adhesive sheet in a cold impact environment of -40 to 250 ° C, it is 200% or more after curing. Growth is needed.

<Heat-resistant heat conductive sheet>
The sheet in which the heat conductive filler is highly blended in the condensed organosiloxane prepolymer according to the present invention can be applied to a product group called a heat radiating sheet (heat conductive sheet). In recent years, there has been a remarkable demand for high heat resistance of heat radiating sheets due to high integration, thinning, densification, and examination of practical application of SiC power modules. Further, in order to increase the thermal conductivity, there is a demand for a property that can maintain flexibility even if a high amount of filler is added.

Since the condensed organosiloxane prepolymer is a viscous liquid in a state before curing, it is possible to add a high amount of filler, and it is possible to provide a heat-resistant sheet having high thermal conductivity. 50 to 1500 parts by mass of a thermally conductive filler can be blended with 100 parts by mass of the prepolymer, and it is possible to exhibit the characteristics of 2 to 8 W · m ^-1 · K ^{-1 in} thermal conductivity. ..

The present invention can be summarized as follows.

(1) The method for producing an organosiloxane polymer sheet according to the present invention has a thermal conductivity of 2.0 Wm- ^{1 of} 34 parts by mass or more with respect to 100 parts by mass of the condensed organosiloxane prepolymer and the organosiloxane prepolymer. -The sheet is formed by a kneading process in which a thermally conductive filler of K- ¹ or higher is kneaded to obtain a kneaded product, and the kneaded product is pressure-molded at a temperature of 40 to 250 ° C. in a reduced pressure atmosphere. Includes a sheet forming step to obtain.

(2) In the method for producing an organosiloxane polymer sheet according to the present invention, the kneaded product preferably contains 50 parts by mass or more of a thermally conductive filler with respect to 100 parts by mass of the organosiloxane prepolymer.

(3) In the method for producing an organosiloxane polymer sheet according to the present invention, the reduced pressure in the sheet molding step is preferably 95 kPa or less.

(4) In the method for producing an organosiloxane polymer sheet according to the present invention, it is preferable that the thermally conductive filler has a thermal conductivity of 25 W · m ^-1 · K ^-1 or more.

(5) In the method for producing an organosiloxane polymer sheet according to the present invention, in the sheet molding step, the kneaded product is pressure-molded in a reduced pressure atmosphere by a molding die heated to a temperature of 40 to 250 ° C. It is preferable that the step is to obtain a sheet by.

(6) In the method for producing an organosiloxane polymer sheet according to the present invention, a release film having a moisture permeability of 1 × 10 ⁻¹⁵ mol · m / (m ² · s · Pa) or more is mixed in the sheet molding step. It is preferably interposed between the wrought product and the molding die.

(7) In the method for producing an organosiloxane polymer sheet according to the present invention, in the sheet forming step, the kneaded product is pressure-molded by a calendar roll heated to a temperature of 40 to 250 ° C. under a reduced pressure atmosphere. It is preferable that the step is to obtain a sheet by.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Unless otherwise specified, "parts" and "%" in the examples are based on mass (parts by mass,% by mass).

The organosiloxane polymer sheets of Examples 1 to 7 and Comparative Examples 1 to 4 were produced as follows.

First, a hybrid prepolymer (solution A) was prepared as follows. First, the reaction vessel equipped with the stirrer, thermometer, and dropping line was sufficiently filled with nitrogen gas. At this time, as the nitrogen gas, a nitrogen gas produced by a nitrogen gas production apparatus (UNX-200 manufactured by Japan Unix Co., Ltd.) was used.

FM9927 (PDMS-1; number average molecular weight (Mn) = 32,000, molecular weight distribution index (Mw / Mn) = 1.09) manufactured by JNC as a polydimethylsiloxane having silanol groups at both ends, manufactured by Tokyo Kasei Kogyo Co., Ltd. Phenyltriethoxysilane (Ph-1; molecular weight = 240.37) and tetra (2-ethylhexyl) titanate (Organix TA-30; molecular weight = 564.75) manufactured by Matsumoto Fine Chemicals Co., Ltd. were placed in a reaction vessel, and a propeller stirrer was used. A hybrid prepolymer (solution A) was obtained by stirring the mixture at a liquid temperature of 80 ° C. for 3 hours. During the reaction, nitrogen gas continued to flow.

The molar ratio of PDMS-1 (FM9927) to Ph-1 (phenyltriethoxysilane) is PDMS-1: Ph-1 = 1: 2, and the molar ratio of PDMS-1 to Organix TA-30 is PDMS-1. : TA-30 = 1: 0.1.

A hybrid prepolymer (solution B) was prepared in the same manner as in solution A. The raw materials used are as follows.

FM8826 (PDMS-2; number average molecular weight (Mn) = 20,000, molecular weight distribution index (Mw / Mn) = 1.06) manufactured by JNC as a polydimethylsiloxane having a triethoxysilyl group at both ends, Shinetsu Chemical Industry Co., Ltd. Diphenyldimethoxysilane (Ph-2; KBM-202SS, molecular weight = 244.36), 35 g of water diluted 20-fold with ethanol, phenyltriethoxysilane (Ph-1; manufactured by Tokyo Kasei Kogyo Co., Ltd., molecular weight = 240. 37), Tetra (2-ethylhexyl) titanate manufactured by Matsumoto Fine Chemicals Co., Ltd. (Organix TA-30; molecular weight = 564.75). Each raw material was placed in a reaction vessel and stirred at a liquid temperature of 80 ° C. for 10 hours using a propeller stirrer to obtain a hybrid prepolymer (liquid B). During the reaction, nitrogen gas continued to flow.

The molar ratio of PDMS-2 (FM8826) to Ph-1 (phenyltriethoxysilane) was PDMS-2: Ph-1 = 1: 2, and the molar ratio of PDMS-2 (FM8826) and Ph-2 (diphenyldimethoxysilane). The ratio is 1: 1 and the molar ratio of PDMS-2 (FM8826) to Organix TA-30 is PDMS-2: TA-30 = 1: 0.1.

The above-mentioned liquid A and liquid B are placed in a container at a mass ratio of 9: 1 (liquid A: liquid B), stirred and defoamed by a sinky rotation / revolution mixer ARE310, and mixed as the main agent. A liquid hybrid prepolymer (C) was obtained.

A mixture of boron nitride (SP-2 manufactured by Denka Co., Ltd.) and silicon oxide (R972 manufactured by Nippon Aerosil Co., Ltd.) was prepared as a filler. Boron nitride filler (SP-2) is a flaky, thermal conductivity, in the longitudinal direction is 110W · ^{m -1} · ^K -1, in the thickness direction was 2W · ^{m -1} · ^K -1. The thermal conductivity of the silicon oxide filler (R972) was 1.3 W · m ^-1 · K ^-1 .

The hybrid prepolymer (C) was weighed in a deep agate mortar with the mass of liquid C, the mass of filler, and the mixing ratio of filler shown in Table 1, and the filler was appropriately added and kneaded with a pestle. Then, additional kneading was performed using a tabletop three-roll mill to obtain a filler-blended hybrid prepolymer kneaded product.

The obtained kneaded product was molded by the molding method, mold release film, degree of vacuum, molding temperature, and curing time shown in Table 1.

When the molding method was "vacuum heating press" or "vacuum heating press", a vacuum heating press device (250t press machine manufactured by Toho Oil Bottle) was used. A release film was laid on a preheated 20 cm × 20 cm × 5 mm deep iron mold, and 10 g of an organosiloxane prepolymer kneaded product was placed on the release film. Furthermore, a release film was put on and the kneaded product was sandwiched between the release films. As for the pressing conditions, using a metal spacer with a slit, the top plate temperature and the bottom plate temperature were set to the molding temperatures shown in Table 1, the atmosphere was set to the vacuum degree shown in Table 1, and the pressure was 3 kgf / cm ² . After performing the bumping treatment for 30 seconds, the bumping treatment is performed again at 6 kgf / cm ² for 30 seconds, and the pressure is applied at 9 kgf / cm ^{2 so} that the total press treatment time becomes the "curing time" in Table 1. Was done. In Comparative Example 4, the processing was performed so that the total time of the press processing exceeded 20 minutes. In this way, the primary molding of the sheet having a film thickness of 0.3 mm was carried out.

When the molding method was "heat press" and no depressurization was performed, a heat press device without a vacuum chamber was used. A mold release film is laid on a preheated 20 cm x 20 cm x 5 mm depth iron mold, 10 g of the hybrid prepolymer kneaded product is placed on it, and the mold release film is put on the mold release film. I sandwiched it with a film. As for the pressing conditions, the top plate temperature and the bottom plate temperature were set to the molding temperatures shown in Table 1 using a metal spacer with slits, and after 10 kgf / cm ² × 5 minutes and 50 kgf / cm ² × 5 minutes, The press treatment was performed for 100 kgf / cm ² × 5 minutes. In this way, the primary molding process of the sheet having a film thickness of 0.3 mm was carried out.

When the molding method is "pressure stretching", 10 g of the hybrid prepolymer kneaded product is sandwiched between release films and stretch-molded using a pressure stretching machine so that the thickness gradually increases to 0.3 mm at room temperature and atmospheric pressure. , It was fired at the molding temperature and the curing time shown in Table 1 using a blower type firing furnace.

As the release film, Mitsui Chemicals Tohcello Co. polymethylpentene resin (TPX) film (trade name: Opyuran 50μm thickness, moisture permeability ^{1 × 10 -15 mol · m /} (m 2 · s · Pa)) or Teflon A (registered trademark) film (moisture permeability 0 mol · m / (m ² · s · Pa)) was used.

Regarding the gas permeability of the release film, the water permeability was measured using an HL788 gas permeability measuring device (prototype model) manufactured by GL Sciences Co., Ltd. The measurement conditions are as follows.
Transmission area: 25 cm ² (φ56.5 mm)
The humidifying gas and the drying gas were adjusted so that the water content was 2.5% at a total flow rate of 15 to 20 ml / min.
GC analysis column
Column1: Moleculaer Sieve13x 60/80 1/8 ”x 0.5t × 3m Sirico Steel
Column2: Gaskuropack 54 60/80 1/8 ”× 0.5t × 2m Sirico Steel
GC condition setting Column temperature: 100 ℃ PDD temperature: 120 ℃ TCD temperature: 120 ℃ TCD current: 120mA
Gas flow rate: Column1: 20ml / min Column2: 20ml / min Discharge gas: 30ml / min
Gas partial pressure: PRIMARY: 500KPa Column1: 195KPa Column2: 95KPa

Table 2 shows the evaluation of the curability and appearance (remaining bubbles) of each Example and Comparative Example. The evaluation of curability is "◎" when cured within 5 minutes, "○" when cured within 5 minutes to 10 minutes, "△" when cured within 10 minutes to 20 minutes, and 20 minutes. If it exceeds, it is listed in Table 2 as “x”. Comparative Example 4 did not cure even if the total pressing time exceeded 20 minutes. In addition, "curing" is a state in which there is no sheet adhesion residue on the release film when it is peeled off from the release film. For the evaluation of the remaining air bubbles, the presence or absence of air bubbles was visually confirmed by observing the state of the surface after depressurizing the sheet.

As shown in Table 2, in the comparative example in which the amount of the heat conductive filler having a thermal conductivity of 2.0 W · m ^-1 · K ^-1 or more is small, the heat transfer is insufficient and the amount of the hybrid prepolymer which is a curing component is not sufficient. Therefore, the release film did not peel off because it did not cure by press molding for a short time.

Further, in the comparative example of heat-stretching, it was not cured unless the firing time was long, and even if it was cured, bubble residue was observed. In the comparative example in which heat pressing was performed under atmospheric pressure conditions, a large number of bubble traces were visible on the sheet, and curing was insufficient even if a long processing time was taken.

Next, the organosiloxane polymer sheets of Examples 8 to 11 were produced as follows.

First, the above-mentioned liquid A and liquid B are placed in a container at a mass ratio of 3: 1 (liquid A: liquid B), stirred and defoamed by a sinky rotation / revolution mixer ARE310, and a hybrid prepolymer mixed liquid is used. (Liquid D) was obtained.

Aluminum nitride / alumina mixed fillers (FN-005P, FN-008P manufactured by Furukawa Denshi Co., Ltd.) were prepared as fillers. The thermal conductivity of aluminum nitride is 150 to 160 W · m ^-1 · K ^-1 , and the thermal conductivity of alumina is 25 ~ 35 W · m ^-1 · K ^-1 .

With the D liquid mass, filler mass, and filler mixing ratio shown in Table 3, weigh the organosiloxane prepolymer mixed liquid (D liquid) into a Fritche motor grinder P-2 (agate mortar type) as a mortar type kneader, and fill the filler. Was appropriately added and kneaded to obtain a filler-blended hybrid prepolymer kneaded product.

The obtained kneaded product was molded by the molding method, mold release film, degree of vacuum, molding temperature, and curing time shown in Table 3.

When the pressure at the time of molding was "decompression", a vacuum heating press device (250t press machine manufactured by Tojo Oil Co., Ltd.) was used. A release film was laid on a preheated 20 cm × 20 cm × 5 mm deep iron mold, and 10 g of an organosiloxane prepolymer kneaded product was placed on the release film. Furthermore, a release film was put on and the kneaded product was sandwiched between the release films. As for the pressing conditions, using a metal spacer with a slit, the top plate temperature and the bottom plate temperature were set to the molding temperatures shown in Table 4, the atmosphere was set to the vacuum degree shown in Table 3, and the pressure was 3 kgf / cm ² . After pressurizing for 30 seconds, bumping treatment is performed, then bumping treatment is performed again at 6 kgf / cm ² for 30 seconds, and then pressure treatment is performed at 9 kgf / cm ² for the total time of the press treatment. The press treatment was performed so as to have the "curing time" in Table 3. In this way, a primary molded sheet having a film thickness of 0.3 mm was obtained.

The measurement result of the moisture permeability of the release film is that 1 × 10 ^-15 mol ・ m / (m ²・ s ・ Pa) of polymethylpentene resin (TPX) film (trade name: Opulan 50 μm thickness) manufactured by Mitsui Kagaku Tohcello Co., Ltd. ), AGC Co., Ltd. FLUON ETFE film (100 μm thickness), which is a high-performance fluororesin film, is 0 mol · m / (m ² · s · Pa), and silicone-treated RF · OPP40cs001 (manufactured by I'm Co., Ltd.) The 0 mol · m / (m ² · s · Pa) and EXPEEK (manufactured by Kurashiki Spinning Co., Ltd.) 25 μm film was 0 mol · m / (m ² · s · Pa).

For the primary molded sheet, one side of the film is peeled off from the mold, placed in a blower firing furnace, dried at 120 ° C. for 3 hours, and then the other release film is peeled off to form a Teflon (registered trademark) film. The film was further baked at 180 ° C. for 2 hours and at 200 ° C. for 2 hours to be completely cured to obtain a heat conductive sheet.

Table 4 shows the evaluation of the curability and appearance (remaining bubbles) of each Example and Comparative Example.

As shown in Table 4, the sheet was cured in Example 11 in which the release film was not used, but metal powder was mixed. Mixing metal powder may reduce the insulation characteristics and may deteriorate the surface of the mold and shorten the life, which is not preferable.

From the above results, in the method for producing an organosiloxane polymer sheet according to the present invention, it is possible to produce a sheet having high thermal conductivity as a heat dissipation sheet at a low temperature and in a short time. This is because the densification of the heat conductive filler accompanying press molding accelerates the condensation reaction of the condensed organosiloxane prepolymer, and an elastic sheet in which the heat conductive filler is densified can be produced.

It should be considered that the embodiments and examples disclosed above are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims, not the above description, and includes all modifications within the meaning and scope equivalent to the scope of claims.

The condensation type organopolysiloxane polymer sheet of the present invention provides a cured product having excellent adhesiveness, heat resistance (flexibility), and heat resistance maintenance characteristics, and is required for semiconductors, LEDs, etc. It is useful as a heat-resistant adhesive sheet used for ceramic bonding and the like.

Claims (7)

The condensed organosiloxane prepolymer and a thermally conductive filler having a thermal conductivity of 2.0 Wm- ¹ K- ¹ or more of 34 parts by mass or more with respect to 100 parts by mass of the organosiloxane prepolymer are kneaded. The kneading process to obtain the kneaded product and
A method for producing an organosiloxane polymer sheet, which comprises a sheet molding step of obtaining a sheet by pressure molding the kneaded product at a temperature of 40 to 250 ° C. under a reduced pressure atmosphere. The method for producing an organosiloxane polymer sheet according to claim 1, wherein the kneaded product contains 50 parts by mass or more of the thermally conductive filler with respect to 100 parts by mass of the organosiloxane prepolymer. The method for producing an organosiloxane polymer sheet according to claim 1 or 2, wherein the reduced pressure atmosphere in the sheet molding step is 95 kPa or less. The method for producing an organosiloxane polymer sheet according to any one of claims 1 to 3, wherein the thermally conductive filler has a thermal conductivity of 25 W · m ^-1 · K ^-1 or more. The sheet molding step is a step of obtaining a sheet by pressure molding the kneaded product in a reduced pressure atmosphere with a molding die heated to a temperature of 40 to 250 ° C., according to claims 1 to 4. The method for producing an organosiloxane polymer sheet according to any one of the above. In the sheet molding step, a release film having a moisture permeability of 1 × 10 ^-15 mol · m / (m ² · s · Pa) or more is interposed between the kneaded product and the molding die. Item 5. The method for producing an organosiloxane polymer sheet according to Item 5. The sheet molding step is a step of obtaining a sheet by pressure molding the kneaded product with a calendar roll heated to a temperature of 40 to 250 ° C. in a reduced pressure atmosphere, from claims 1 to 4. The method for producing an organosiloxane polymer sheet according to any one of the above.