JP5323432B2 - Molded body for heat conduction - Google Patents

Description

  The present invention relates to a heat conductive molded body and a composition suitable as a heat conductive member typified by a heat conductive sheet, used to transmit heat from a heat generating component inside an electric / electronic device to a heat radiating component, More specifically, it does not generate halogen gas when burned while having high flame retardancy, and it is flexible and does not generate low-molecular-weight siloxane during use. The present invention relates to a body and a heat conductive non-silicone liquid rubber composition.

  In recent years, electric and electronic devices have been made lighter, thinner, and faster, and the heat generation density of internal electronic components has increased. Therefore, these heats can be dissipated efficiently and the electronic components can be cooled. This is an important issue for the normal operation of parts. These electronic components that require cooling by receiving heat from their own heat and / or surrounding heat generation components (hereinafter simply referred to as heat generation components) are usually heat dissipation components such as heat sinks and heat sinks (hereinafter referred to as heat generation components). It is cooled by dissipating the heat to the atmosphere or the housing. At that time, a heat conductive member such as a heat conductive grease or a heat conductive sheet is applied or pasted between the heat generating / heat radiating parts in order to eliminate the air layer and efficiently transfer heat.

  Among these, in the heat conductive sheet, in order to efficiently transfer the heat from the heat generating component to the heat radiating component, it adheres to the surface of each component without interposing an air layer when pasted between both components. The only softness and its own thermal conductivity are important properties.

  In addition, as such a heat conductive sheet, a polymer such as silicone rubber, acrylic rubber, and thermoplastic elastomer is used as a matrix, and a metal such as aluminum, copper, silver, aluminum oxide, zinc oxide is used as a heat conductive filler there. A polymer composition having increased thermal conductivity by blending powders of substances having high thermal conductivity such as ceramics such as silicon nitride, boron nitride and aluminum nitride, and carbon-based materials such as diamond and carbon fiber The formed body is generally used.

  When the thermal conductivity is increased by blending a thermally conductive filler, there is a problem that the flexibility inherent to the polymer is impaired as the blending amount increases. That is, there is a trade-off relationship between the blending amount of a filler such as a heat conductive filler and the flexibility of the composition. In order to solve this problem, a sheet in which a plasticizer, oil, or the like is added to a polymer such as a thermoplastic elastomer has been proposed in order to obtain flexibility of a molded article even when a large amount of filler is blended. (See Patent Documents 1 and 2.)

  However, when plasticizers and oils are added, they may bleed out due to their use in high temperature environments, long-term use, or heat cycles, causing bleeding out. Addition of a plasticizer / oil or the like is inherently undesirable because the oil / plasticizer may be transferred to a contacted object due to contact (for example, a housing).

  On the other hand, as a technique for obtaining a flexible composition even when a large amount of filler is blended, a technique of using a liquid polymer and crosslinking it has been proposed. (See Patent Documents 3 to 4.)

  Incidentally, flame retardancy is one of the characteristics required for such a heat conductive sheet. This is important from the viewpoint of ensuring safety against fire when used as a member inside electric / electronic devices, and in particular, in the member used for home appliances, the safety standard UL-94 (Underwriter Laboratories, Inc. Standard No. 94 “flammability testing”) is often required to have high flame retardancy such as V-0 in the flame retardancy evaluation in the 20 mm vertical combustion test. In the heat conductive sheet, a thin sheet of 2 mm or less is preferably used in order to reduce the thermal resistance when conducting heat from the heat generating part to the heat radiating part. It is even more difficult to obtain a flammability evaluation, and flame retardancy is one of the important issues in thermal conductive sheets in addition to thermal conductivity and flexibility.

  In general, it is effective to add a flame retardant to a composition used in a molded body for flame retardant of a polymer composition / molded body. Conventionally, halogen-based flame retardants such as bromine compounds and chlorine compounds are used. High flame retardant performance has been obtained by blending.

  However, when a composition containing a halogen-based flame retardant is used, harmful halogen-based gas is generated when the composition / molded body burns. It is not preferable also from the point of consideration for.

  Examples of effective flame retardants other than halogen-based ones include phosphorus-based flame retardants containing organic phosphorus compounds such as red phosphorus and phosphoric acid esters and polyphosphoric acid. However, red phosphorus generates harmful phosphine gas under high temperature and humidity conditions, and organophosphorus compounds degrade the sheet used by hydrolysis, and metals such as copper that exist in the surrounding environment. In particular, the use of phosphorus-based flame retardants in the field of electrical and electronic equipment is not preferable as in the case of halogen-based flame retardants.

  Examples of the flame retardant other than the halogen-based and phosphorus-based flame retardant include metal hydroxides such as aluminum hydroxide and magnesium hydroxide. Metal hydroxide has a composition in which a hydroxyl group (OH) is bonded to a metal ion, and it decomposes into metal oxide and water when heated, but it suppresses combustion by the endotherm associated with this decomposition. It has a function to make it. For this reason, there are no concerns such as the above-mentioned halogen-based and phosphorus-based flame retardants that generate harmful gases when combusted and adversely affect other surrounding components during use, and are safe and environmentally friendly. In recent years, the tendency to use metal hydroxide as a flame retardant has been increasing. (See Patent Documents 5 to 6.)

  However, the metal hydroxide-based flame retardant has a drawback that the blending amount is higher than the halogen-based and phosphorus-based flame retardants, and a large amount of the metal hydroxide-based flame retardant is required to obtain particularly high flame resistance. In the composition blended with the metal hydroxide type flame retardant, since the reduction of flexibility and other mechanical properties and molding processability occur as described above regarding the filling of the heat conductive filler. It has become an issue when using.

  In particular, the composition used in the molded article for heat conduction often contains a large amount of heat conductive filler in order to obtain high heat conductivity, and when a large amount of metal hydroxide flame retardant is added, In general, the flexibility of the composition is impaired and in some cases the molding of the composition becomes impossible. Therefore, in the heat conductive sheet, in order to obtain high flame retardancy, the actual situation is that it relies on the above halogen flame retardant or phosphorus flame retardant. (See Patent Documents 4 and 7.)

  On the other hand, an invention in which a metal hydroxide filler such as aluminum hydroxide or magnesium hydroxide is used as a flame retardant and heat conductive filler is disclosed. Although this is inferior in thermal conductivity compared with the case where a metal oxide, metal nitride, metal powder or the like is added to impart thermal conductivity, it achieves both thermal conductivity and flame retardancy. It can be said to be one means. (See Patent Documents 8 and 9.)

  By the way, as a composition for a heat conductive sheet, a composition using a silicone polymer such as silicone rubber as a matrix is suitably used. This is because when a silicone polymer is used as a matrix, a flexible composition can be obtained more easily than when other polymers are used. Since a composition having high flame retardancy can be obtained easily (even if the amount of the flame retardant is small) compared to the case of using it, the amount of heat conductive filler added can be increased, and flexibility and heat conductivity can be increased. It is because it has the advantage that it is easy to line up flame retardancy. (See Patent Document 10.)

  As described above, the thermally conductive composition using a silicone polymer as a matrix has excellent characteristics from the viewpoints of thermal conductivity, flexibility, and flame retardancy, but on the other hand, problems derived from the silicone polymer itself have been pointed out. Yes.

  In other words, the silicone monomer and / or low molecular weight silicone molecules generated by decomposition of the polymer remaining in the silicone polymer volatilize as siloxane gas, which causes a contact failure by forming an oxide film inside the electronic device. It is. For this reason, it is desired to use a polymer other than the silicone polymer as a matrix, particularly in use in the field of electric / electronic equipment.

  In view of this point, a composition for heat conduction using a polymer other than a silicone polymer as a matrix and a molded body using the same have been proposed.

  In particular, Patent Document 11 discloses a composition for heat conduction in which generation of siloxane gas is reduced by using a non-silicone polymer as a matrix. However, since a silane-based substance is used for the cross-linking agent, the amount is less than when a silicone polymer is used, but it is also not preferable because siloxane is generated.

  On the other hand, it is often desired that the heat conductive sheet has adhesiveness to the heat radiating component and / or the heat generating component. This is not necessary if the parts that sandwich the thermal conductive sheet are tightened with screws, etc., and the thermal conductive sheet is used in a state where pressure is applied so that both parts are sufficiently adhered to each other. It is not necessarily used under such conditions, and the thermal conductive sheet itself is often required to have adhesiveness. For this reason, depending on the case, it may be used by separately applying an adhesive to the heat conductive sheet. However, it goes without saying that adding an adhesive application step in this way is not preferable in terms of cost and complexity of the manufacturing process.

JP 2001-310974 A JP 2002-121354 A Japanese Patent Laying-Open No. 2005-048124 JP 2006-022263 A Japanese Patent Laid-Open No. 15-31431 JP 2007-056067 A JP 2005-226007 A JP-A-14-138205 JP 2005-105028 A Japanese Patent No. 0318257 JP 2008-56723 A

In view of the above situation, the present invention, using a non-silicone polymer as a matrix, a high flame retardancy and has a flexible, yet moderate tack suitable thermally conductive molded article for electric and electronic equipment fields having It is intended to provide.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have blended a predetermined amount of a crosslinking agent and a large amount of metal hydroxide with a predetermined non-silicone liquid rubber material, and thereby a predetermined composition. It is found that a liquid rubber composition having high flame retardancy and thermal conductivity, flexibility and adhesiveness that achieves the above-mentioned problems can be obtained after crosslinking, and the present invention is completed. It came to.

That is, according to the present invention, the following molded body for heat conduction and a heat conductive liquid rubber composition are obtained.
(1) (B) at least 1 to 8 parts by weight of an organic peroxide crosslinking agent and (C) 200 to 600 parts by weight of a metal hydroxide filler with respect to 100 parts by weight of (A) liquid ethylene / propylene copolymer rubber. preparative a composition ing by blending, a molded article yield stress was molded liquid or pasty composition in the range of 0.1~1000Pa measured by E-type viscometer, cyclohexane extraction As a result, the Asker C hardness is 40 or less and the average particle size of the metal hydroxide filler is crosslinked so that the gel fraction x determined by the following (formula 1) is in the range of 26 to 52. (D ₅₀ ) is in the range of 0.5 to 30 μm, the molded body has an adhesiveness of 8 or more in a ball tack test based on JIS Z 0237, and the molded body is subjected to UL-94 20 mm combustion test. Evaluation Thermally conductive molded article for flame retardancy level is V-0 to be.
Gel fraction (x) = (mass insoluble in cyclohexane out of the mass of rubber contained in the molded product) / (rubber mass contained in the molded product) × 100 (Equation 1)
( 2 ) Further, the volume fraction (X _D ) of the thermally conductive filler (D) selected from other than the metal hydroxide in the entire composition is within the range represented by the following (formula 2). The heat conductive molded article according to claim 1 , wherein the molded article is used for heat conduction.
X _D + X _C ≦ 0.7 (Expression 2)
(In the formula, X _C represents the volume ratio of the (C) metal hydroxide filler in the entire composition.)
( 3 ) The molded article for heat conduction according to (1) , wherein the molded article has an adhesiveness of 8 to 15 or more in a ball tack test based on JIS Z 0237.
( 4 ) The heat conductive molded article according to (1) or (2), which is a heat conductive sheet.

A composition containing at least (A) a liquid ethylene / propylene copolymer rubber, (B) an organic peroxide crosslinking agent (C) and a metal hydroxide filler according to the present invention has a gel fraction of 26 to 52 (%). The molded product obtained by crosslinking in such a manner can achieve flame retardancy and thermal conductivity at the same time by blending a large amount of metal hydroxide, and can be made very soft with an Asker C hardness of 40 or less. It can be used as a heat dissipation member that does not volatilize low molecular siloxane.

  First, the non-silicone liquid rubber composition according to the present invention and its use will be specifically described.

(A) Liquid ethylene / propylene copolymer rubber In the present invention, (A) a liquid ethylene / propylene copolymer rubber and an organic peroxide cross-linking agent that do not contain any silane-based material that is a siloxane generation source are used. No contact failure due to generation of siloxane. In addition, by using a liquid rubber material, a composition containing a large amount of filler such as (C) metal hydroxide filler in order to impart high flame retardancy and high thermal conductivity can be used. By adjusting the addition amount to an appropriate amount, the molded article after cross-linking can be kept flexible. Also, since the resulting molded product is a cross-linked rubber molecule, it is used in a high temperature environment or for a long period of time, unlike when plasticizer / oil is added to a solid rubber material to give flexibility. Is excellent in that no bleeding or bleeding out of plasticizer / oil occurs.

  The (A) liquid ethylene / propylene copolymer rubber used in the present invention is obtained by copolymerizing a non-conjugated polyene as a third component in addition to the ethylene / propylene component, and (A1) liquid ethylene / propylene / non-conjugated. Polyene copolymer rubber can be used, but is particularly suitable in the present invention because the crosslinking reaction can be efficiently advanced by adding a non-conjugated polyene component.

  (A1) The non-conjugated polyene component of the liquid ethylene / propylene / non-conjugated polyene copolymer rubber is mainly derived from at least one non-conjugated polyene represented by the following general formula (1) or (2) It is preferable to include as. This is because a double bond is included at the terminal, so that a crosslinking reaction is more likely to occur.

(Wherein R ¹ and R ³ represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms)

  The (A1) liquid ethylene / propylene / nonconjugated polyene copolymer rubber used in the present invention contains a diene component other than that represented by the above formula such as a chain nonconjugated diene and a cyclic nonconjugated diene. There is no particular limitation as long as the physical properties of the present invention are not impaired.

The liquid ethylene / propylene copolymer rubber preferably satisfies at least one of the following (1) to (4).
(1) The ratio of ethylene units to propylene units contained (ethylene units / propylene units) is 40/60 to 95/5. (2) The iodine value is 0.5 to 50 (g / 100 g). (3) The intrinsic viscosity measured in decalin at 135 ° C. is 0.01-2 dl / g. (4) The molecular weight distribution (Mw / Mn) measured by GPC is 3-50.

  As the liquid ethylene / propylene / non-conjugated polyene copolymer rubber, for example, liquid EPT (product name) manufactured by Mitsui Chemicals, Inc. can be used. Moreover, it is compoundable based on description of Unexamined-Japanese-Patent No. 2008-56723.

(B) Organic peroxide cross-linking agent (B) The organic peroxide cross-linking agent introduces a cross-linking structure between molecules by itself decomposing and generating radicals, but is not limited to rubber materials. It is widely used in situations where a crosslinked structure is introduced into various polymers. For this reason, many types according to materials and processing conditions are easily available, and it is easy to select an appropriate one according to the composition and processing conditions.

(B) Organic peroxide crosslinking agents include hydroperoxides, diacyl peroxides, peroxide esters, dialkyl peroxides, ketone peroxides, peroxyketals, peroxycarbonates, and the like. Among them, dialkyl peroxides typified by dicumyl peroxide and peroxyketals typified by 1,1-bis (t-butylperoxy) 3,3,5 trimethylcyclohexane are particularly preferable. . Moreover, these organic peroxide crosslinking agents can be diluted with a diluent or the like.

  In the present invention, (B) the organic peroxide crosslinking agent is used in an amount of 1 to 8 parts by weight, preferably 2 to 5 parts by weight, based on 100 parts by weight of the (A) liquid ethylene / propylene copolymer rubber. Preferably it is 2.5-4 mass parts. The blending amount is equivalent to the cross-linking agent. When a diluted cross-linking agent is used, it is necessary that the mass of only the cross-linking agent component falls within this numerical range.

  (B) If the blending amount of the organic peroxide crosslinking agent is less than 1 part by mass, the degree of crosslinking of the liquid rubber composition is low, so it cannot be handled as a molded product in the form of a paste or putty or molded. When the body is used as a heat conductive sheet, problems such as the uncrosslinked component ooze out due to the application of heat (50 ° C. or higher). On the other hand, when 8 parts by mass or more is blended, the flexibility that is the object of the present invention is impaired.

In particular, according to the number average molecular weight Mn of the (A) liquid ethylene / propylene / non-conjugated polyene copolymer rubber, the blending amount m of the cross-linking agent is within the range of mass parts represented by m according to (Formula 1a). Is preferred.
2000 / Mn <m <5000 / Mn (Formula 1a)
This is because the smaller the molecule, the higher the crosslinking density, and the higher the molecular weight, the lower the crosslinking density.

  In the present invention, a crosslinking aid such as triallyl isocyanurate (TAIC) or trimethylolpropane trimethacrylate may be further added in combination with the crosslinking agent. The crosslinking aid is an aid for efficiently proceeding with the crosslinking reaction, and can be added in the present invention in order to efficiently proceed the crosslinking reaction as in normal use. Care is required so as not to impair the flexibility, and the blending amount is preferably 10 parts by mass or less with respect to 100 parts by mass of (A) liquid ethylene / propylene rubber.

(C) Metal hydroxide filler Examples of the metal hydroxide used in the present invention include magnesium hydroxide and aluminum hydroxide. These may be used alone or in combination of two or more. good. The metal hydroxide used here preferably has an average particle diameter (d ₅₀ value) measured by a laser diffraction method, a dynamic light scattering method, or the like, preferably 0.5 to 30 μm, more preferably 8 to 30 μm. In the particle size distribution, either a dispersion showing a monodisperse peak, or a particle distribution showing a plurality of dispersion peaks and a plurality of peaks can be used. The particles having different monodispersions can be obtained by mixing two or more kinds of particles each having a predetermined monodisperse amount, but the latter is desirable for making a more flexible composition.

On the other hand, in order to obtain flexibility and high thermal conductivity, a larger filler particle size is preferable. However, in the present invention, it is not preferable to use aluminum hydroxide having a d ₅₀ value of 30 μm or more because the surface condition after molding tends to be rough and the flame retardancy tends to decrease.

  Further, for compatibility with (A) liquid ethylene / propylene copolymer rubber, the (C) metal hydroxide filler is more preferably surface-treated with a fatty acid and / or a coupling agent. Examples of the fatty acid include stearic acid, margaric acid, palmitic acid, oleic acid, and the like, and one or more types can be selected from these. Moreover, a silane coupling agent, a titanium coupling agent, an aluminate coupling agent etc. are mentioned as a coupling agent, One or more types can be selected and used from these. However, among these, it is particularly preferable to use a titanium coupling agent, and in a composition using the same, the processability is good, and the molded product obtained by crosslinking the composition has particularly good flame retardancy and flexibility. can get.

  Although there is no restriction | limiting in particular about the processing amount of these surface treating agents, Generally the processing amount of 0.1-5% is used with respect to powder, and this is adjusted with the average particle diameter etc. of the metal hydroxide to process. .

  In the present invention, (C) 100 to 1000 parts by mass of (C) metal hydroxide filler is added to 100 parts by mass of (A) liquid ethylene / propylene copolymer rubber, thereby providing high flame retardancy, high thermal conductivity and flexibility. A molded article having properties can be obtained. When it is 100 parts by mass or less, the flame retardancy is insufficient, and when it is 1000 parts by mass or more, the hardness of the molded body becomes too high. The content of (C) metal hydroxide filler with respect to 100 parts by mass of (A) liquid ethylene / propylene copolymer rubber is preferably 200 to 600 parts by mass, and more preferably 250 to 450 parts by mass.

  In the present invention, the shape of the molded body is not particularly limited and can be used after being molded into a shape according to the application. However, when the thickness of the molded body is reduced, the flame retardant targeted by the present invention is used. Care must be taken because the properties are easily impaired. Therefore, particularly when the molded body of the present invention is used at a thickness of 2.0 mm or less, the blending amount of the (C) metal hydroxide filler is desirably 200 parts by mass or more, and similarly 1.5 mm or less. The thickness is preferably 250 parts by mass or more, the thickness of 1.0 mm or less is preferably 300 parts by mass or more, and the thickness of 0.5 mm or less is preferably 350 parts by mass or more.

  However, when a flame retardant aid is added separately, the blending amount of these (C) metal hydroxide fillers can be reduced.

  On the other hand, in the present invention, a flexible molded article having an Asker C hardness of 40 or less is preferably obtained. However, in applications that require flexibility having an Asker C hardness of 30 or less, the amount of (C) the metal hydroxide filler is included. Is preferably 600 parts or less.

(D) Thermally conductive filler In the present invention, high thermal conductivity is obtained at the same time that high flame retardancy is obtained by blending a large amount of (C) metal hydroxide filler. By blending (D) a thermally conductive filler selected from those other than hydroxides, a composition further excellent in thermal conductivity can be obtained.

  As such (D) thermally conductive filler, for example, metals such as aluminum, copper, silver, etc., ceramics such as aluminum oxide, zinc oxide, silicon nitride, boron nitride, and aluminum nitride, and high thermal conductivity such as diamond are used. Examples thereof include powders of substances having the same. Among these, it is more preferable to use an insulating material for use in the electric / electronic equipment field. Moreover, these may mix | blend individually by 1 type, and may mix and use 2 or more types.

The blending amount in the case of blending (D) a thermally conductive filler, the volume fraction X _D in the total composition is preferably blended such that the range expressed by the following equation (2). However, X _C denotes a volume fraction of total composition of (C) metal hydroxide filler.
X _D + X _C ≦ 0.7 (Expression 2)
If the blending amount is more than this, the hardness of the composition becomes high and the flexibility is impaired, so that it is unsuitable in the present invention.

  (D) It is more preferable to use a thermally conductive filler that is spherical or closer to spherical. This is because the irregular shape (angular shape) tends to extremely increase the viscosity when blended with the liquid rubber, the blending is often difficult, and the flexibility of the molded body is easily impaired.

(D) The d ₅₀ value of the thermally conductive filler is not particularly limited, but is more preferably 5 to 100 μm. Even when a single average particle size is used, two or more different average particle sizes are used. Although what you have may be mixed and used, the latter is more preferable for flexibility. Moreover, it is more preferable that the surface treatment is performed similarly to the (C) metal hydroxide filler.

(Other additives)
Moreover, in the liquid rubber composition of the present invention, if necessary, a crosslinking aid, a processing aid, a dispersant, an anti-aging agent, a light stabilizer, a flame retardant aid (excluding those containing halogen and phosphorus), Coloring agents, defoaming agents, and the like may be added within a range that does not impair the intended characteristics of the present invention. The blending amount is preferably 100 parts by mass or less, more preferably 10 parts by mass or less with respect to 100 parts by mass of the (A) liquid ethylene / propylene copolymer rubber.

(Preparation of composition and method for obtaining molded article)
In the present invention, (A) a liquid ethylene / propylene copolymer rubber, (B) a crosslinking agent, (C) a metal hydroxide filler (and (D) a thermally conductive filler as necessary) A rubber composition having a yield stress measured at 20 ° C. using an E-type viscometer of 0.1 to 1000 Pa, preferably 5 to 500 Pa, more preferably 50 to 400 Pa, is crosslinked to form a molded product. Get. When the viscosity of the composition is within the above range, the moldability of the composition is good, and the crosslinked composition can have appropriate flexibility and tackiness. If the viscosity of the composition is 0.1 Pa · sec or less, the strength of the molded article after crosslinking is weak and brittle, and if it is 1000 Pa · sec or more, the flexibility of the composition after crosslinking is impaired.

  The liquid rubber composition used in the present invention can be prepared by the same method as for ordinary liquid rubber. That is, it is a closed-type mixing stirrer such as a planetary mixer, or rolls such as a three roll or an open roll, a rotation and revolution mixer, and the like. (A) Non-silicone liquid rubber, (B) cross-linking agent, (C) metal hydroxide (and (D) thermally conductive filler) may be kneaded in a lump, or either one may be blended first. You may mix | blend the other after kneading | mixing. However, since (B) the crosslinking agent has a small blending amount and is preferably dispersed uniformly, after (A) the non-silicone liquid rubber and (B) the crosslinking agent are mixed and homogenized in advance, (C) metal water It is more preferable to blend an oxide filler (and (D) a thermally conductive filler).

  In addition, the liquid rubber composition of the present invention is likely to generate heat and temperature due to mixing and stirring depending on the viscosity. Depending on the type of organic peroxide crosslinking agent used, decomposition may proceed even at relatively low temperatures, so care must be taken not to raise the temperature during mixing and stirring. Cooling may be desirable in some cases. .

  The liquid rubber composition in the present invention obtained as described above can be molded and crosslinked by a known method, and can be used as, for example, a heat conductive sheet. That is, it can be molded by a technique such as injection, pressing, transfer, or casting. Moreover, although a crosslinking reaction can be normally advanced by applying a heat | fever, it is also possible to use an electron beam or an ultraviolet-ray.

The cross-linked molded body obtained by the above method has a gel fraction x in the range of 26 to 52 (%). If it is 5% or less, it is difficult to keep the shape as a molded body, and uncrosslinked components may ooze out when heat is applied. On the other hand, if it is 60% or more, the amount of cross-linking increases and the hardness increases, which is not suitable for the purpose of the present invention.

  By the way, the gel fraction of the cross-linked molded product is relatively low within the above range in the case where the blending amount of (C) metal hydroxide filler (and (D) thermally conductive filler) is high. To. This is because the hardness of the molded body tends to increase as the filler content increases. On the contrary, when the filler content is low, the gel fraction of the molded body is desirably relatively high within the above range.

  In addition, the gel fraction here shall be measured with the method shown below.

About 0.1 g (m ₁ (g)) of a molded product obtained by crosslinking the composition is immersed in about 100 g of cyclohexane (purity of 95% or more) and held at room temperature (20 ° C.) for 24 hours or more. Next, once cyclohexane is discarded and replaced with fresh cyclohexane, the mixture is further maintained for 24 hours to extract uncrosslinked rubber components. Thereafter, the molded body is gently taken out and vacuum-dried at 80 ° C. for 16 hours or more by a vacuum dryer. The mass m ₂ (g) of the molded body after drying was measured, and the mass ratio y (= the mass other than the liquid rubber component / the mass of the entire composition) other than the liquid rubber component in the original composition obtained in advance. From the mass), the gel fraction x is determined from the following equation.
x (%) = (mass insoluble in cyclohexane out of the mass of rubber contained in the molded product) / (mass of rubber contained in the molded product) × 100
= (Crosslinked rubber) / (total rubber) × 100
= (M ₂ − (m ₁ × y)) / (m ₁ − (m ₁ × y)) × 100

(Adhesive)
Further, it is desirable that the surface of the molded body has a tackiness of 8 or more , preferably 8 to 15 based on JIS Z 0237. This is important because when the molded body of the present invention is brought into contact with the heat-generating component and / or the heat-radiating component, the molded body is closely contacted only with the molded body and the position does not shift due to vibration or the like.

  The molded body of the present invention is preferably a highly flame-retardant molded body having a flame retardancy level of V-0 evaluated in a UL-94 20 mm combustion test.

(Application of molded products)
The molded article of the present invention obtained by the above method is a molded article for heat conduction. The molded article for heat conduction of the present invention is particularly formed into a sheet shape, and is used as a heat conductive sheet between the heat-generating component and the heat-dissipating component inside the electric / electronic device to efficiently conduct heat. Can be suitably used.

  Specifically, it can be used for personal computers including notebook computers, mobile phones, audio devices, digital cameras, digital videos, illuminations, displays having a heat source such as a liquid crystal screen, and electronic devices for automobiles.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

(Examples 1-11 , Reference Example 1 )
(A) Liquid ethylene / propylene copolymer rubber, (B) crosslinking agent, (C) metal hydroxide, (D) thermally conductive filler and other additives in the proportions (parts by mass) shown in Table 1. Weighed. First, (A) a liquid ethylene / propylene copolymer rubber and (B) a crosslinking agent are mixed with a hybrid mixer AR-250 (manufactured by Keyence Corporation), and then (C) a metal hydroxide filler and (D). A thermally conductive filler and other compounding agents were blended and mixed.
The mixed composition is poured into a predetermined mold and cross-linked by holding at 150 ° C. for 20 minutes in a 100-ton press, and sheets of 10 mm, 2.0 mm, 1.0 mm, and 0.5 mm are respectively formed. Molded.

(Evaluation test)
The following evaluation tests were performed using the sheets of Examples 1 to 11 and Reference Example 1 . The results are shown in Tables 1-2.
-Thermal conductivity Thermal conductivity (W / mK) was measured at 20 ° C with a rapid thermal conductivity meter QTM-500 (manufactured by Kyoto Electronics Industry Co., Ltd.) using a 10 mm thick sheet.
Hardness Using a 10 mm thick sheet, the hardness was measured at 20 ° C. using an Asker C hardness meter (manufactured by Kobunshi Keiki Co., Ltd.).

・ Flame retardance About 2.0mm, 1.0mm and 0.5mm sheets, 20mm vertical combustion test specified in UL-94 was conducted, and flame retardancy evaluation was V-0. "

-Generation of siloxane Measure the occurrence of low molecular weight siloxane when 1-5 g of a small test piece cut out from a cross-linked sheet is held at 100 ° C. Is indicated by ×.

(Comparative Examples 1-5)
Except for changing the composition contents shown in Table 3 were prepared and evaluated test sample as described in Example 1-11. The results of the evaluation test are also shown in Table 3.

(material)
The materials in Tables 1 to 3 are as follows.
(A) Liquid ethylene / propylene copolymer rubber Liquid EPT rubber a; Liquid ethylene / propylene / non-conjugated polyene copolymer rubber, manufactured by Mitsui Chemicals, Mn = 920
Liquid EPT rubber b; liquid ethylene / propylene / non-conjugated polyene copolymer rubber, manufactured by Mitsui Chemicals, Mn = 1980
(B) Organic peroxide crosslinking agent
1,1-bis (t-butylperoxy) 3,3,5 trimethylcyclohexane, trade name: Perhexa C, manufactured by NOF Corporation diluted to 70% by mass with liquid paraffin (B ′) silane crosslinking agent SiH group-containing compound represented by C ₆ H ₅ Si (—OSi (CH ₃ ) ₂ H) ₃ (C) Metal hydroxide filler Aluminum hydroxide a; Trade name: B153T, manufactured by Nippon Light Metal Co., Ltd., d50 = 15 μm, titanium coupling agent treated aluminum hydroxide b; trade name: B703T, manufactured by Nippon Light Metal Co., Ltd., d50 = 2 μm, titanium coupling agent treated magnesium hydroxide a; trade name: Kisuma 5A, Kyowa Chemical Industry Co., Ltd. ), D50 = 1 μm, stearic acid treatment (D) thermally conductive filler spherical alumina; trade name: AW50-74, other auxiliary manufactured by Micron Co., Ltd. ; Triallyl isocyanurate, product name: tike, Nippon Kasei Chemical Co., Ltd.
Flame retardant aid: Zinc stannate, trade name: Flamtard S, manufactured by DK Fine Co., Ltd.

As shown in Tables 1 and 2, in the sheets of Examples 1 to 11 and Reference Example 1 , the thermal conductivity is 0.7 w / mK or more, high thermal conductivity, Asker C hardness of 39 or less, and at least Flame retardancy evaluation V-0 in the vertical combustion test of UL-94 at a thickness of 2.0 mm V-0 flame retardance, and no low molecular siloxanes are generated.
On the other hand, as shown in Table 3, the comparative example 1 was not cured and could not be molded. In Comparative Example 2, the flexibility and flame retardancy were poor. In Comparative Example 3, the flame retardancy was inferior. In Comparative Example 4, the flexibility was inferior. In Comparative Example 5, harmful low molecular siloxane was generated.

Claims (4)

(A) At least (B) 1 to 8 parts by weight of an organic peroxide crosslinking agent and (C) 200 to 600 parts by weight of a metal hydroxide filler are blended with 100 parts by weight of the liquid ethylene / propylene copolymer rubber. a composition ing and, a molded article yield stress was molded liquid or pasty composition in the range of 0.1~1000Pa measured by E-type viscometer, cyclohexane extraction, the following Crosslinked so that the gel fraction x determined by (Equation 1) is in the range of 26 to 52 , the Asker C hardness is 40 or less,
(C) The average particle diameter (d ₅₀ ) of the metal hydroxide filler is in the range of 0.5 to 30 μm ,
The molded body has an adhesiveness of 8 or more in a ball tack test based on JIS Z 0237,
The molded object for heat conduction whose flame retardance level evaluated by a UL-94 20mm combustion test is V-0 .
Gel fraction (x) = (mass insoluble in cyclohexane out of the mass of rubber contained in the molded product) / (rubber mass contained in the molded product) × 100 (Equation 1) Furthermore, (D) thermally conductive filler selected from other than the metal hydroxide was blended so that the volume ratio (X _D ) in the entire composition was within the range represented by the following (formula 2). The molded article for heat conduction according to claim 1 .
X _D + X _C ≦ 0.7 (Expression 2)
(In the formula, X _C represents the volume ratio of the (C) metal hydroxide filler in the entire composition.) The thermal conductive molded article according to claim 1 or 2 , wherein the molded article has an adhesiveness of 8 to 15 in a ball tack test based on JIS Z 0237. It is a heat conductive sheet, The molded object for heat conduction of any one of Claims 1-3 characterized by the above-mentioned.