KR20050076147A - Flexible heat conducting foam body - Google Patents

Abstract

The present invention relates to a flexible thermally conductive foam body, which is placed between a heating element such as an electronic device and a heat sink such as a heat sink or a metal chassis to prevent overheating of the electronic device, thereby allowing the electronic device to operate smoothly and compressively. A thermally conductive polymer foam body, particularly a polymer foam sheet, which is impregnated and dried by a water-soluble suspension containing the thermally conductive fine particles as a main component to provide a continuous porous soft thermally conductive foam body in which the thermally conductive fine particles are implanted in a matrix. . According to the present invention, the continuous porous type flexible thermally conductive foam body is an economical and highly efficient thermally conductive sheet containing high density of thermally conductive fine particles by a simple process without significantly impairing the flexibility and compressibility of the foam. Can be obtained.

Description

Flexible heat conducting foam body

The present invention relates to a flexible thermally conductive foam body, which is placed between a heating element such as an electronic device and a heat sink such as a heat sink or a metal chassis to prevent overheating of the electronic device, thereby allowing the electronic device to operate smoothly and compressively. The present invention relates to a thermally conductive polymer foam sieve.

As the field of electronic devices, especially computers and displays, which are accelerating the pace of development in recent years, has been increasingly integrated and enlarged, smooth processing of heat generation problems of electronic devices has emerged as an important problem affecting the life of equipment. For example, as Moore's Law doubled the density every 18 months, the heat generation problem is getting bigger and the cooling capacity is increased. However, no matter how large the cooler's capacity, if the CPU's heat does not flow smoothly to the heatsink, the CPU's cooling will not be smooth, causing expensive electronic devices to fail. In addition, as the display area becomes larger and heat generation increases, especially in the case of PDP, cooling of the panel by smooth heat flow becomes an important factor for the stability of the device.

In the case of assembly electronics, as well as in the cooling of individual components, the components that are the heating element (s) form irregularities so that a flexible and compressible thermally conductive sheet capable of contacting this form is required.

The prior art discloses a thermally conductive sheet having fluidity in order to provide bonding between the heat generating device and the heat sink. U.S. Patent No. 6,496,373 to Kevin Light-Cheung discloses a compressible thermally conductive interface that is cured as it flows by heating using a combination of an epoxy component + adhesive + wax containing a rubber component + a hardener. 3M Korean Patent Publication No. 2001-0104214 discloses a sheet made of a crystalline resin containing short fibers as a resin filled with a thermally conductive filler that flows at a T _m or more. While such sheets must be properly heated to flow in order to achieve bondability, it is difficult to adjust the double-sidedness that must also be maintained to some extent.

In addition, 3M Korean Patent No. 2002-0002257 discloses a thermally conductive sheet obtained by slicing and laminating a rubber material filled with a thermally conductive material. Mochida Korean Patent Publication No. 2001-0110652 discloses a heat dissipation sheet in which a silicon substrate filled with a thermally conductive material and different adhesives are laminated on both sides. The use of an elastic material as the sheet material can improve the bond between the heating element and the heat sink due to the elasticity of the material. However, there is a limitation in adapting to excessive irregularities or changes in thickness, and it is not easy to remove bubbles formed at the interface. not.

Bunyan US Pat. No. 6,432,497 discloses a thermally conductive adhesive tape having an adhesive filled with a thermally conductive material on both sides of a substrate. 3M Korean Patent Publication No. 2002-0070449 discloses a sheet filled with a thermally conductive filler in a substrate + binder component (silicone or urethane, rubber or acrylic adhesive). Such adhesives have variability in shape due to tackiness, but are not easy to handle, difficult to maintain in shape, and are not easy to adjust to excessive unevenness or change in thickness and maintain shape.

Mochida Korean Patent Publication No. 2003-6964 discloses a heat dissipation sheet which is cured by impregnating a heat dissipation gel filled with a thermal conductive material or a heat dissipation grease in a sponge-type substrate having continuous pores in order to improve the shape retention. . However, the sponge acts as a matrix and helps to maintain its shape, but in order to obtain sufficient heat dissipation effect, the heat-resistant gel or heat-dissipating grease must be sufficiently impregnated at low viscosity and hardened to prevent leakage, thereby impairing the flexibility of the sheet. Not only is it difficult to obtain sufficient thermal conductivity, but it is expensive because expensive heat sinks or additional manufacturing processes are used.

The present invention is to provide a thermally conductive sheet excellent in flexibility and compressibility, excellent in form bonding between the heating element device and the heat sink, thermal conductivity is good, and the manufacturing process is simple and economically manufactured, and there is no handling problems such as leakage of liquid It is for. In particular, the present invention is to provide a thermally conductive sheet suitable for being placed and used between the display panel and the chassis so that the heat of a large display panel such as LCD or PDP can be discharged to the chassis.

According to the present invention, there is provided a continuous pore-type flexible thermally conductive foam body in which the thermally conductive fine particles are impregnated with a water-soluble suspension having a main component and dried to implant the thermally conductive fine particles into the matrix. The foam sieve is preferably a foam sheet. The thermally conductive foam of the present invention comprises the steps of 1) preparing a water-soluble suspension by adding and stirring a suspension aid and a thermally conductive fine powder containing a surfactant in water; 2) impregnating the aqueous suspension into a sheet of continuous pore type; And 3) drying to evaporate the water absorbed in this step. Impregnation of step 2) may be accomplished by immersing the continuous porous sheet in the aqueous suspension or spraying the aqueous suspension onto the continuous porous sheet. In order to sufficiently impregnate the suspension bath may be impregnated under reduced pressure.

Continuous porous flexible foam sheets or blocks of resin are well known. The flexible foam sheet is well known polyolefin series, PVC (polyvinyl chloride), EVA (ethyl vinyl acetate), polyisocyanate series, melamine resin series, rubber series and the like. Quinel, U.S. Patent No. 4,163,085, describes in detail a foam sheet based on polyolefins by mixing polyolefins with rubber components or other synthetic resins. Kosma U.S. Patent No. 5,859,076 describes foam preparation of silane grafted polyolefins. US Patent 4334971 to Manke describes melamine-based elastic foams. The foam sieve used as the compressible matrix used in the present invention can be variously selected from the prior art by the compatibility of the endurance temperature and the thermally conductive fine particles is not particularly limited by the prior art.

The thermally conductive fine particles or powders used in the present invention include granules or powders, and are used in the future mixed with the powders. Metal fine particles such as gold, silver, copper, zinc, molybdenum, tin, titanium, aluminum, and fine particles of oxides, carbides, nitrides or carbonitrides of carbon fine or metal or metalloid. For example, oxides such as alumina, silica and magnesia, nitrides such as silicon nitride, aluminum nitride and boron nitride, carbides such as silicon carbide and aluminum carbide. The size of the particles is not particularly limited but is preferably 0.1 to 200 mu m to obtain a suspension. Different particle sizes or mixtures of different thermally conductive particles are also possible. Although the stability of the suspension is not particularly required, it is preferred to add a surfactant (or wetting agent) to maintain the suspension in the range where work is required. Surfactants include, for example, ethoxylated alkylphenols and / or sulfonate surfactants, for example polyethoxylated alkylphenols, ammoniumalkylarylethersulfates, polyethoxylated sorbitan fatty acid esters, dialkylsulfosuccinates Nate, alkyl sulfate, alkylbenzene sulfonate, organosilicon, N, N-dialkyl taurate, more specifically lignin sulfonate, polyoxyethylene nonylphenyl ether, polyethoxylated alcohol, naphthalene sulfonate,, polycar Carboxylate polyoxyethylene lauryl ether, polyoxyethylene octylphenyl ether, polyoxyethylene cetyl ether, polyoxyethylene styryl ether, polyoxyethylene lauryl amine, polyoxyethylene stearyl amine, dodecylbenzenesulfonic acid sodium salt , Dioctylsulfosuccinate acid sodium salt, and the like, and mixtures thereof are used.

When the thermally conductive particles of the present invention are dried after the impregnation treatment, they are fixed to the foam matrix by intermolecular forces of Van der Waals. It is desirable to add suspended adhesives such as polyurethane latexes or acrylic latexes or silicone suspensions, or solution adhesives such as polyurethane adhesives, if necessary, in order to increase the bonding force. Some crosslinking may also be added to increase the adhesion. Suspension aids may be added to aid in suspension. When using an adhesive with acrylic latex, an acri monomer may be used as a suspending aid. As the polyurethane-based adhesive, a cross-linking agent is a polyfunctional isocyanate.

The amount of particles in the suspension bath is set in consideration of the workability of the impregnation. The workability of the impregnation is determined by the viscosity of the suspension bath, preferably about 100 to 800 mPa. Preferably it is about 30 to 80% by weight in the total bath on the basis of weight%. Surfactants containing wetting agents, preferably up to 7% by weight, and adhesives including crosslinking agents, preferably up to 15% by weight may be added.

Impregnation can be accomplished in a variety of ways. It is most common to soak in suspension baths. Alternatively, the spray gun may be sprayed. Impregnation and drying can be repeated several times. The drying temperature after the impregnation treatment is preferably 70 to 130 ° C. Not only hot air drying but also drying by vacuum drying or microwave can be performed. The drying temperature can be further increased for curing the adhesive or for further crosslinking of the foam sieve.

A pressure sensitive adhesive may be applied to one side or both sides of the continuous porous type flexible thermal conductive foam sheet. The pressure-sensitive adhesive is an acrylic adhesive, a polyurethane adhesive or a silicone-based adhesive. Such adhesives may be filled with the above thermally conductive material. Acrylic adhesives are homo, nasal or terpolymer or crosslinked of acrylates and / or acrylamides such as alcohol esters such as acrylic acid, methacrylic acid, butyl acrylate. Silicone-based adhesives are, for example, polymethylsiloxane gums or resin suspensions. Polyurethane-based pressure sensitive adhesives are of organic solvent type and water dispersion type. Such pressure-sensitive adhesives may be applied to and applied on both sides of the thermally conductive foam sheet. If a release paper is attached on the pressure-sensitive adhesive is easy to handle it is preferable. Instead of such an adhesive, a silicone gel filled with a thermally conductive material disclosed in Japanese Patent Laid-Open No. 10-189838 can be used.

The heat conductive sheet of the present invention is a heat dissipation solution filled with a heat conductive material in order to overcome the difference in thermal conductivity caused by the gap between the heat generating element and the heat sink after the mounting between the heat generating element and the heat sink, or to improve the adhesion of the interface. For example, silicone grease or silicone gel may be additionally injected. At this time, in order to facilitate the injection of the heat dissipating liquid it can be sealed between the heating element and the heat sink and apply a low pressure. The heat dissipation liquid can be held in liquid form or cured with time or heating.

The present invention will be described by the following examples.

Example 1

A 10 mm thick melamine foam sheet was immersed in a bath of strongly stirred suspension with the following composition.

100 parts water

Boron nitride diameter 5 ㎛ 100 parts

10 parts of acryl latex (50% polyacrylic ester)

Dodecylbenzenesulfonate part 2

5 parts polyoxyethylene stearylamine

0.3 part of acrylic ester

After removing the immersed foam sheet and left for 5 minutes and dried at 90 ℃ for 90 minutes and summarized the measured value as follows.

After treatment

Density (kg / m ³ ) 13 73

Thermal Conductivity (W / mK)

          Compression Ratio 0% 0.01 0.7

          Compression Ratio 30% 1.3

Compression Ratio 60% 1.7

Example 2

A 10 mm thick polyurethane foam sheet was immersed in the bath of suspension prepared as follows.

100 parts water

Silicon Carbide Diameter 5㎛ 80parts

Polyurethane latex (polybutyl adipate diol + isophorone diisocyanate

Based polymer content 40%) 10 parts

Crosslinking agent (polyfunctional diisocyanate,

       DESMODUR RFE, Bayer Manufacturing) 0.3part

Dodecylbenzenesulfonate part 2

5 parts polyoxyethylene stearylamine

After removing the immersed foam sheet and left for 5 minutes, dried at 120 ℃ for 40 minutes and summarized the measured value as follows.

After treatment

Density (kg / m ³ ) 15 70

Thermal Conductivity (W / mK)

          Compression Ratio 0% 0.01 0.6

          Compression 30% 1.1

Compression Ratio 60% 1.5

Example 3

After dipping the foam sheet treated in Example 2 and drying at 120 ° C. for 40 minutes, the measured values are summarized as follows.

After treatment

Density (kg / m ³ ) 15 108

Thermal Conductivity (W / mK)

          Compression Ratio 0% 0.01 0.8

          Compression 30% 1.4

Compression Ratio 60% 1.8

The continuous porous type flexible thermally conductive foam body according to the present invention impregnates the thermally conductive fine particles with a high density by a simple process (including repeated immersion and drying) without significantly impairing the solubility and compressibility of the foam. This provides an economical and high efficiency heat dissipation sheet.

Claims (15)

A continuous pore-type flexible thermally conductive foam body in which thermally conductive fine particles are impregnated with a water-soluble suspension having a main component and dried to implant thermally conductive fine particles into a matrix. 2. The flexible thermally conductive foam sieve of claim 1, wherein the foam sieve is a foam sheet and the foam sheet is used for flat panel display cooling. The flexible foam sheet according to claim 2, wherein the flexible foam sheet is a polyolefin-based, PVC (polyvinyl chloride), EVA (ethylvinylacetate), polyisocyanate-based, melamine resin-based, or rubber-based continuous porous flexible foam body. . 4. The flexible thermally conductive foam body of claim 3, wherein the thermally conductive fine particles are metal fine particles, carbon fine particles or fine particles of oxides, carbides, nitrides or carbonitrides of metals or metalloids. The method of claim 4, wherein the thermally conductive fine particles are gold, silver, copper, zinc, molybdenum, tin, titanium, aluminum, alumina, silica, magnesia, silicon nitride, aluminum nitride, boron nitride, A continuous pore-type soft thermally conductive foam body selected from the group consisting of silicon carbide, aluminum carbide powder or mixtures thereof. 6. The flexible thermally conductive foam body according to claim 4 or 5, wherein the thermally conductive fine particles have a size of 0.1 to 200 mu m. The continuous porous type flexible thermal conductive foam body according to claim 6, wherein a pressure-sensitive adhesive is applied to one or both surfaces of the continuous porous type flexible thermal conductive foam sheet. The continuous porous type flexible thermal conductive foam body according to claim 7, wherein primers are applied to both surfaces of the continuous porous type flexible thermal conductive foam sheet and the pressure-sensitive adhesive is applied. The flexible porous conductive foam body according to claim 8, wherein a release paper is attached on the pressure-sensitive adhesive. 7. The continuous porous type flexible thermally conductive foam body according to claim 6, wherein at least one of ethoxylated alkylphenol and sulfonate is used as a surfactant of the suspension. The method according to claim 6, wherein the suspension has a viscosity of 100 to 800 mPa, the thermally conductive particles 30% to 80% by weight in the total bath and less than 7% by weight of the surfactant including the wetting agent, 15% by weight of the adhesive including a crosslinking agent A continuous pore-type soft thermally conductive foam body consisting of the following and remaining water. According to claim 6, After the heat is mounted between the heat sink and the heat sink after the heat conductivity due to the difference in thermal conductivity caused by the gap between the heating element and the heat sink or to improve the bonding of the interface is filled with a heat conductive material filled Soft thermally conductive foam sieve additionally injected between remaining pores.  12. The flexible thermally conductive foam body of claim 11, wherein the suspension comprises polyurethane latex or acrylic latex, or a polyurethane adhesive in solution. 1) adding a suspension aid and thermally conductive fine powder to water to prepare a water-soluble suspension; 2) impregnating the aqueous suspension into a sheet of continuous pore type; And 3) drying the water absorbed in the step to dry the evaporated water. The continuous porous soft thermal conductive foam of claim 13, wherein the impregnation of step 2) is performed by dipping the continuous porous sheet into the aqueous suspension or spraying the aqueous suspension onto the continuous porous sheet. ) Method of manufacturing sieve.