JP6550599B2 - Composite sheet - Google Patents

Description

  The present invention relates to a technique for dissipating heat from an electronic component that generates heat (hereinafter referred to as a heat generating component) in a housing such as an electronic device or a precision device.

  In recent years, the heat generation density from heat-generating components has rapidly increased with the advancement of the performance of electronic devices such as mobile phones and laptop computers, and the heat diffusion technology in these electronic devices has become essential. In particular, small mobile devices have many opportunities to directly touch the human body, and the temperature rise on the outer surface of the housing has become a serious problem.

  Low temperature burns are one of the problems caused by the temperature rise on the outer surface of the mobile device housing. Low temperature burns are a type of burn that occurs when a human body is exposed to a temperature higher than the body temperature for a long time. At 44 ° C., there is a report that a burn occurs in 6 hours, and every time it rises by 1 ° C., the time to reach a burn is halved.

  In comparison to ordinary burns, cold burns usually delay the onset of symptoms by the parties, and often the skin suffers severe damage when noticed. Recently, there are many cases of low-temperature burns when a small notebook computer is used on a knee for a long time. In the future, with the trend toward smaller and more mobile devices, it is the most important task to keep the temperature of the device surface as low as 1 ° C.

  As a method for preventing the temperature rise on the surface of the device, Patent Document 1 discloses that a sheet in which a graphite sheet and a heat insulating material are laminated is installed between a heat generating component and a housing. The composite sheet 50 is shown in FIG.

  A component 11 is mounted on the substrate 10. The heat conductive layer 12 and the heat insulating layer 13 are stacked on the component 11. The housing 14 is located thereon.

  The heat generated in the component is spread by the heat conduction layer 12 and is not transmitted to the housing 14 by the heat insulation layer 13. As a result, heat is transferred to the entire heat conduction layer 12 and heat is transferred to the housing as a whole.

  As a result, even if the housing 14 is touched with a hand, it does not sense local heat.

JP, 2009-111003, A

  However, in the structure of Patent Document 1, inorganic fiber glass wool or rock wool, natural wool heat insulating material, cellulose heat insulating material, or the like is used as the composite sheet, but sufficient heat insulating performance cannot be obtained. It was. In particular, as the heat insulating material is made thinner as the product becomes thinner, the heat insulating performance thereof is reduced, and heat is concentrated and transmitted to the housing.

  Therefore, we use as a composite sheet an airgel sheet in which an inorganic or organic fiber is impregnated with an airgel having an extremely low thermal conductivity of 0.012 to 0.022 W / mK while being non-vacuum, and The use of a graphite sheet having excellent thermal conductivity was considered.

  However, since the airgel is porous, there has been a problem that when the graphite sheet and the adhesive are bonded to each other, the adhesive layer penetrates into the airgel, so that the heat insulating property is lowered (the thermal conductivity is increased).

  Therefore, the subject of this application is providing the thin composite sheet excellent in the heat insulation performance.

  In order to solve the above problems, a graphite sheet disposed on the electronic component side, an airgel layer disposed on the housing side, a composite sheet in which the graphite layer and the airgel layer are fixed with an adhesive layer, and the area of the airgel layer is And a composite sheet which is smaller than the area of the graphite layer and located in a portion corresponding to the electronic component.

  Moreover, the mounting structure which provided the said composite sheet of the said description between the said electronic component and the said housing | casing is used. Further, an electronic device having the mounting structure inside is used.

  According to the present invention, there is provided a composite sheet capable of exhibiting a sufficient heat insulation effect even in a narrow space in a housing of an electronic device and effectively reducing heat transfer from a heat-generating component to the housing, and an electronic device including the same. can do.

(A) Cross-sectional view of heat insulation structure of Embodiment 1, (b) Partial enlarged view of (a), (c) Partial enlarged cross-sectional view of a heat insulator, (d) A diagram for explaining an evaluation method (A)-(b) Cross section of the heat insulation structure of Embodiment 2 Sectional view of the heat insulating structure of the third embodiment (A) to (d) sectional views of the heat insulating structure of the fourth embodiment (A)-(b) Sectional drawing of the heat insulation structure of Embodiment 5. Cross sectional view showing a conventional heat insulation structure

Embodiment 1
FIG. 1A shows a cross-sectional view of the internal structure of an electronic device using the composite sheet 50 of the first embodiment. FIG. 1B shows an enlarged cross-sectional view of the adhesive layer 15 portion of the composite sheet 50 of the first embodiment. The enlarged sectional view of the heat insulation layer 13 is shown in FIG.1 (c).

  The electronic device comprises a housing 14, a composite sheet 50, a component 11 and a substrate 10. The composite sheet 50 is composed of the heat insulating layer 13, the adhesive layer 15, and the heat conductive layer 12. Those not described are the same components as in the prior art. It is preferable that the adhesive layer 15 has a gap 20. I will explain later.

  The role of the composite sheet 50 is to spread the heat generated in the component 11 (high temperature portion) in the horizontal direction by the heat conduction layer 12 and not to transfer the heat to the housing 14 (low temperature portion) by the heat insulating layer 13 is there.

  In the heat insulation layer 13 of FIG. 1 (c), the nanofibers 32 and the airgel 33 are mixed and held between the fibers 21 in the fiber sheet 31. In addition, the fiber 21 is not essential, and if it is easy to maintain the shape. The nanofibers 32 are also not essential, and if this is the case, the powder applied by the airgel 33 is unlikely to be detached.

  Preferably, an adhesive layer 15 is present between the housing 14 and the heat insulating layer 13. The heat insulating layer 13 can be firmly fixed, and the heat insulating layer 13 can be prevented from being chipped or broken.

<Thermal conduction layer 12>
As the heat conductive layer 12, a metal plate or the like can be used, and among them, a graphite sheet or a rubber sheet containing graphite made of graphite and rubber is preferable. That is, it is preferable to use a graphite layer. This sheet has a good thermal conductivity in the horizontal direction and can spread heat. Moreover, the ratio of the thermal conductivity between the horizontal direction and the vertical direction is large, and heat can be spread mainly in the horizontal direction.

  The graphite sheet is, for example, a thin sheet obtained by processing a polymer film having a thickness of 50 μm or less as a raw material at a high temperature of over 2500 ° C., pressurization, and reducing atmosphere. The composition is nearly 100% carbon. For this reason, this graphite sheet is a graphite plate laminated in parallel with a basal plane which is a plane constituted by a six-membered ring of carbon. The thickness of the graphite sheet is about 0.1 mm.

Further, the front and back surfaces of the graphite sheet are substantially parallel to the surface (basal surface) formed by the six-membered ring of carbon. The thermal conductivity of the parallel graphite sheet is 1000 W / mk or more, the thermal conductivity of the graphite sheet in the vertical direction is 5 W / mk or less, the specific gravity is 2.25 g / cm ³ or less, and the electrical conductivity. And Young's modulus are 10 ⁶ S / m or more and 750 GPa or more, respectively.
<Method of producing graphite>
An aromatic polyimide sheet material having a thickness of 25 μm to 75 μm was prepared as a starting material. First, 1 kg of sheet material was weighed and filled in a carbon crucible. Next, the crucible filled with the sheet material was placed in a heating electric furnace, and the air in the electric furnace was replaced with nitrogen gas. After substituting with nitrogen gas, it was heated at a heating rate of 100 ° C./h and held at the maximum temperature for 1 hour, and then naturally cooled to room temperature. In addition, in the case of heating, it heated, flowing nitrogen gas.

  Here, the maximum temperature during heating was 1500 ° C. to 2500 ° C.

  As such a polymeric material, aromatic polyimide, polyamide imide, polyamide, polyoxadiazole, polybenzimidazole and the like can be mentioned.

  Among these, it is desirable to use aromatic polyimide as the polymer material. The thermal conductivity of the resulting graphite is better than when other materials are used.

  In addition to the graphite sheet, a rubber sheet containing graphite may be used. The rubber sheet containing graphite contains a resin having a rubber component in addition to carbon. The graphite used is a powder of the above graphite sheet. This powder, graphite filler, about 40% by weight, EPDM (Esprene, manufactured by Sumitomo Chemical Co., Ltd.), about 60% by weight, peroxide cross-linking agent, and stearic acid are mixed, and an 8-inch two-roll The mixture was thoroughly kneaded by a kneader to prepare a mixture, and the graphite filler powder in the mixture was oriented in the surface direction. C. for 10 minutes to proceed the vulcanization. It has thermal conductivity and high thermal conductivity in the planar direction.

<Adiabatic layer 13>
It is preferable to use an airgel containing fibers as the heat insulating layer 13. That is, it is preferable to use an airgel layer. The airgel has a property that the thermal conductivity is smaller than the thermal conductivity 0.028 W / mK of air, and has a thermal conductivity of about 0.013 W / mK to 0.025 W / mK.

  The airgel 33 is a foam containing approximately 85 to 95 Vol% of air, and the size of the hole of the foam is smaller than 68 nm, which is considered as the mean free path of air, so that low heat conduction is achieved.

  Moreover, the airgel 33 is a foam with very little silica as solid content. Therefore, the skeleton has a fragile nature, and once broken, it will reduce its volume significantly.

  The heat insulating layer 13 is composed of a fiber sheet 31 as a base material and an airgel 33 containing nanofibers 32.

<Composition>
It is preferable that the airgel 33 (silica xerogel or silica airgel) containing the nanofibers 32 is supported at a ratio of 50 to 98% with respect to the air layer in the fiber sheet 31 with respect to the volume of the air layer. 80 to 98% is more preferable, and 90 to 98% is particularly preferable.

  In this state, the composite sheet 50 can be handled easily and has excellent heat insulation performance. If the volume fraction is less than 50%, convection cannot be sufficiently suppressed and the thermal conductivity may increase. On the other hand, when the volume fraction exceeds 98%, the flexibility of the fibrous composite sheet becomes insufficient, and the handleability decreases.

<Fiber sheet 31>
The form of the fiber sheet 31 of the substrate may be any resin fiber such as glass wool, rock wool, polyester, or a composite fiber containing a plurality of these, and can be selected based on the heat-resistant temperature and incombustibility during use. However, since cellulose and pulp fibers are decomposed by a process using an acid during hydrophobization, it is necessary to hydrophobize with alkoxysilane or hexamethyldisilazane.

  When the airgel 33 is in a sol state, when the fiber sheet 31 is combined, the fiber sheet 31 having high affinity with the sol such as glass wool or cellulose fiber has good wettability, and the fiber sheet 31 and xerogel are combined. It is easy to make it.

<Nanofiber 32>
As the nanofiber 32, a nanofiber having a hydroxyl group on the surface, such as cellulose nanofiber or silica nanofiber, having a fiber diameter of 30 nm or less is used.

  The particle diameter of the fine particles desorbed by the aerogel 33 is 7 to 9.5% of 0.1 to 10 μm (average particle diameter is 0.1 to 10 μm), and the fiber diameter of the nanofiber 32 is 30 nm or less By using (the average fiber diameter is also 30 nm or less), it becomes easy to suppress the detachment of fine particles of 0.1 μm or more when the three-dimensional network of the nanofibers 32 is formed.

  If the fiber diameter of the nanofiber 32 is 30 nm or less and the nanofiber content is 1 to 10 wt% with respect to the volume of the airgel 33, the nanofiber 32 is combined with the airgel 33. The gap size of is approximately 5 to 70 nm in size.

  Therefore, it is considered that the airgel 33 fine particles of 0.1 μm or more are difficult to be detached from the gaps of the nanofibers 32. This is assumed considering that when the airgel 33 has a secondary particle diameter of 20 to 30 nm and a continuous structure of the particles uniformly forms a three-dimensional structure, pores having a size of 5 to 67 nm are formed. It is a structure.

  Moreover, the thing of a fiber diameter size of 5-100 nm is good. When the thickness is smaller than 5 nm, desorption of the airgel 33 fine particles can be prevented. If it is thicker than 100 nm, the thermal conductivity is greatly affected. If the thickness is 5 to 50 nm, the airgel 33 can be prevented from being detached, and the thermal conductivity is less affected. The thickness of 5 to 30 nm is more preferable because the airgel 33 can be prevented from being detached and the thermal conductivity is hardly affected.

Further, in the first embodiment, the use of nanofibers 32 of 30 nm or less in particular has the effect of minimizing the thermal conductivity of the nanofibers 32 and not increasing the thermal conductivity of the composite sheet 50.

  When 1 to 10 wt% of nanofibers 32 is added, the heat conduction of composite sheet 50 in the first embodiment is approximately 1, because the solid heat conduction component of general fiber sheet 31 is about 0.001 to 0.003 W / mK. The rate increases by about 4 to 12% of about 0.025 W / mK.

  In general fibers, among the three components of thermal conductivity, the solid thermal conductivity component, the convective component, and the radiation component, the solid thermal conductivity component is very small, and generally, the total of the thermal conductivity of the fiber is three components. Among about 0.03 to 0.08 W / mK, the solid thermal conductivity component is about 0.001 to 0.003 W / mK.

  It is considered that the addition of the nanofiber 32 increases the solid heat conduction component and the radiation component. However, the radiation component can be almost neglected unless the temperature is high, such as 100 ° C. or higher, and it can be regarded as only an increase in solid heat conduction component. Therefore, the total thermal conductivity of the composite sheet 50 is significantly increased by the addition of the nanofibers 32, although there is a slight increase in the thermal conductivity of 0.001 to 0.003 W / mK even when the nanofibers 32 are added. There is nothing.

  These nanofibers 32 are contained in an amount of 1 to 10% by weight with respect to the airgel 33, and a network of nanofibers 32 having a mesh size smaller than that of the airgel 33 having a particle size of about 0.1 to 10 μm is formed. Suppresses detachment of fine particles. Further, the hydroxyl group on the surface of the nanofiber 32 and the airgel 33 can be chemically and firmly bonded by dehydration condensation.

  Further, when the nanofiber 32 is added up to 50 weight percent, contact heat resistance between the nanofibers 32 and contact heat resistance between the airgel 33 and the nanofiber 32 are generated, so that the heat insulation performance of the composite sheet 50 is deteriorated. There is no significant impact.

<Aerogel 33>
In addition, the airgel 33 has an average pore size of 10 to 67 nm, a pore volume of 3.5 to 8 cc / g, and a specific surface area of 500 to 900 m 2 / g. It has pores smaller than the average free path of air 68 nm.

The average pore is preferably 10 to 50 nm, more preferably 10 to 30 nm. The pore volume is preferably 5 to 8 cc / g, more preferably 6 to 8 cc / g. Bulk density 90~250kg / ^{m 3,} the bulk density is preferably ^{120~180kg / m 3, 140~150kg / m} 3 and more preferably. In order to ensure heat insulation, the thermal conductivity is required to be 0.025 W / mK or less.

  If the average pore size, the specific surface area and the bulk density of the airgel 33 are in the above-mentioned ranges, the heat insulation is excellent, so that the composite sheet is suitable.

  Water glass (sodium silicate aqueous solution) is used as a starting material for producing the airgel 33, and the preparation is made of the silica concentration of the water glass, the type and concentration of the acid used during gelation, and the gelation conditions (temperature, time, pH). It can control by adjusting). Moreover, it can control by adjusting the quantity of a silylating agent, the quantity of a solvent, temperature, and time as hydrophobization conditions. The drying conditions can be controlled by adjusting the drying temperature, time, and the like.

  In the water glass as the raw material of the airgel 33, the silica weight may be adjusted to 5 to 20% by weight with respect to the total weight of the sol, preferably 10 to 20% by weight, and 15 to 20% by weight. More preferably.

  If the concentration of silica is 6% by weight or less, the strength of the wet gel skeleton may be insufficient because the concentration of silica is low. Also, if the concentration of silica exceeds 20%, the gelation time of the sol solution may be rapidly accelerated and it may become impossible to control.

  The same structure as the above-mentioned airgel 33 may be used for the silica airgel. What was produced by atmospheric pressure drying is preferable, but may be produced by supercritical drying.

<Method of Manufacturing Heat Insulating Layer 13>
The manufacturing method of the heat insulation layer 13 is demonstrated. The manufacturing method comprises the following steps. The sodium in the water glass which is a raw material of the airgel 33 is removed. Thereafter, a sol preparation step is performed to adjust the pH to gelation. An impregnation step is performed in which the sol is impregnated into the nanofiber 32 and the fiber sheet 31 of the base material before gelation. A curing step is performed to obtain a strong skeleton of silica that can withstand the capillary force applied to the inner wall of the gel when the solvent is dried. In order to prevent the hydroxyl groups present on the inner wall of the gel from dehydrating and condensing during drying and shrinking, a hydrophobizing step is performed in which the surface of the airgel 33 is hydrophobized with a silylating agent or functional silane. A drying step is performed to remove the solvent present in the fibrous composite sheet.

  Here, the functional silane is a group of silicon compounds composed of chlorosilanes, alkoxysilanes and silazanes, and is also a silylating agent. In this case, alkoxysilane is particularly preferable in view of compatibility with solvents such as alcohols, ketones and straight-chain aliphatic hydrocarbons. The silylating agent is an organosilicon compound capable of replacing active hydrogen in an organic compound with a Si atom. The active hydrogen is replaced with Si atoms.

<Sol preparation process>
The water glass aqueous solution used in Embodiment 1 may be prepared to be 5 to 20% by weight, preferably 10 to 20% by weight, and more preferably 15 to 20% by weight. When the concentration of silica in the aqueous solution is less than 5%, the strength of the wet gel skeleton may be insufficient because the concentration of silica is low. On the other hand, if the concentration of silicic acid exceeds 20%, the gelation time of the sol solution may be rapidly increased and may not be controlled.

  The water glass is used after removing sodium contained in the water glass when the airgel 33 is manufactured. The water glass used is No. 1 water glass (silica concentration 35 to 38% by weight), No. 2 water glass (silica concentration 34 to 36%), No. 3 water glass (silica concentration 28 to 30%) (Japanese Industrial Standard (JIS Any of K1408)) may be used. However, in order to form a three-dimensional network of silica densely and uniformly, it is preferable to use No. 1 water glass having a high silica concentration.

  In order to remove sodium in the water glass aqueous solution, sodium contained in the water glass is removed using an acid ion exchanger. The water glass is mixed with a proton ion exchange resin, and the aqueous glass solution is stirred until the pH reaches 1 to 3 to remove sodium. Thereafter, a base is added to adjust the gelable pH = 5 to 8. The base is generally ammonia, ammonium hydroxide, sodium hydroxide or aluminum hydroxide, with preference given to ammonia for ease of preparation.

  Alternatively, a sol may be prepared by forming sodium as a salt using an acid and then washing the formed hydrogel to remove the salt. At that time, an acid of 10 to 30% by weight of the water glass is added, and the gel is washed until the electrolyte disappears after curing.

  At this time, the acid used is hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, chloric acid, chlorous acid, hypochlorous acid or other inorganic acids, acidic aluminum phosphate And acidic phosphates such as acidic magnesium phosphate and acidic zinc phosphate, and organic acids such as acetic acid, propionic acid, oxalic acid, succinic acid, citric acid, malic acid and adipic acid. Hydrochloric acid is preferred from the viewpoint of the gel skeleton strength of the resulting silica xerogel.

  As a solution used for washing, a water-soluble solvent such as pure water, methanol, ethanol, or propanol may be used.

  Alternatively, a colloidal silica solution (pH = 10 to 11) which has already been grown may be used without using water glass containing sodium as a starting material, and the above acid may be added to the solution to adjust the gel. A uniform hydrogel can be produced in the same manner by adjusting to pH = 5-8. The amount of the acid catalyst added at that time depends on the pH value to be adjusted. In the case of hydrochloric acid, the amount of the 12N hydrochloric acid aqueous solution is preferably 0.5 to 5.0% with respect to 100% by weight of the hydrogel. -2.5% is more preferable.

<Impregnation process>
Next, 1 to 50% by weight of nanofibers 32 based on the weight of the sol is added to the prepared sol, and dispersed using a stirrer or the like. The nanofiber 32 having a large specific gravity may be precipitated at the bottom if left standing in a sol for a long time after stirring.

  The nanofibers 32 used are silica nanofibers 32 or cellulose nanofibers 32 having a hydroxyl group and having a fiber diameter of 50 nm or less. Moreover, you may add both these fibers.

  Next, in order to impregnate the sol in which the nanofibers 32 are dispersed into the fiber sheet 31, composite is formed by immersing the fiber sheet 31 in the sol containing 50 to 95 vol% of the nanofibers 32 with respect to the air layer of fibers. .

  The fiber sheet 31 to be used is a sheet having a fiber diameter of 1 to 50 μm and a ratio of air occupied in a unit volume of 80 to 99%, more preferably 90 to 99%.

  The form of the fiber sheet 31 may be glass fiber, rock wool, resin fibers such as polyester, and composite fibers containing a plurality of these, and can be selected in consideration of the heat resistance temperature and non-combustibility during use. In addition, since cellulose and pulp fibers are decomposed by a process using an acid during hydrophobization, it is necessary to hydrophobize with alkoxysilane or hexamethyldisilazane.

<Cure curing process>
After impregnating the fiber sheet 31 with the sol containing the nanofibers 32, the polycondensation of the silica colloid in the sol and the growth of secondary particles are promoted in order to make the strength sufficient to withstand the capillary force applied during drying. There is a need. After the sol in the impregnated fiber sheet 31 is gelled, the water in the sheet does not volatilize at 70 to 95 ° C., preferably 80 to 95 ° C., more preferably 90 to 95 ° C., and the weight of silica particles is increased. Promote condensation and growth of secondary particles.

  The curing time is 2 to 24 hours, preferably 6 to 24 hours, and more preferably 12 to 24 hours. Alternatively, the necessary curing time can be shortened by curing in high temperature and high pressure in order to shorten the curing time.

Hydrophobing process
The silylating agent used when the silica nanofibers 32 are added is represented by the general formula R1R2 ₂ SiCl or R1 _n Si (OR ₂ ) _4-n (wherein R1 and R2 are independent of each other) A straight-chain alkyl, cyclic alkyl or phenyl, alkoxysilane). Hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDS) are also suitable.

  Here, the silylating agent replaces active hydrogen such as hydroxyl group, amino group, carboxyl group, amide group, mercapto group, etc. in the organic compound with silicon.

On the other hand, when using cellulose nanofibers 32, when hydrochloric acid is generated in the hydrophobization solution, the cellulose is decomposed. For this reason, R1 _n Si (OR ₂ ) _4-n (wherein R1 and R2 are independently C1-C6 linear alkyl, cyclic alkyl or phenyl) or hexamethyldisilazane (HMDS). Perform hydrophobization using.

R1R22SiCl is preferably trimethylchlorosilane (TMCS), and R1nSi (OR ₂ ) _4-n is preferably trimethylmethoxysilane.

  When HMDSO is used, HCl can be added in a molar ratio of 0.02 to 2.0 with respect to the amount of HMDSO charged to generate TMCS, which is an active species in the reaction system. In that case, the concentration of the aqueous hydrochloric acid solution is preferably 1 to 12 N, and more preferably 10 to 12 N.

  100-800% is preferable with respect to the pore volume of a hydrogel, and, as for the preparation amount of a silylating agent, 100-300% is more preferable.

  The hydrophobization reaction is performed in a solvent if necessary, and is generally performed at 20 to 100 ° C, preferably 30 to 60 ° C. When the reaction temperature is less than 20 ° C., the silylating agent may not be sufficiently diffused to be sufficiently hydrophobized.

  As the solvent to be used, alcohols such as methanol, ethanol and 2-propanol, ketones such as acetone and methyl ethyl ketone, and linear aliphatic hydrocarbons such as pentane, hexane and heptane are preferable. Since the gel before hydrophobization is hydrophilic while the silylating agent is a hydrophobic solvent, an alcohol which is an amphiphilic solvent or an amphiphilic solvent to efficiently react the silylating agent of the active species with the hydrogel It is preferred to use ketones.

  The hydrophobization time is preferably 2 to 24 hours, more preferably 2 to 12 hours.

<Drying process>
Next, in order to volatilize the solvent contained in the impregnated sheet after hydrophobization, it is dried at 100 to 150 ° C. for 2 to 5 hours. At that time, when the heat resistance temperature of the base fiber sheet 31 is lower than the drying temperature, alcohols such as methanol, ethanol and 2-propanol, ketones such as acetone and methyl ethyl ketone, pentane and hexane are substituted, It is good to substitute by the solvent which has a boiling point below the heat-resistant temperature of resin fiber, and to make it dry.

  Unlike the composite sheet of the conventional example, the composite sheet 50 obtained through each of the above steps is freed of fine particles due to the formation of a network of nanofibers 32 smaller than the particle size of the airgel 33 and the effects of dehydration condensation between the airgel 33 and the nanofibers 32. It is possible to suppress separation, and to suppress detachment of the fine particles of the airgel 33 from the cross section even when arbitrarily cut and used, and to maintain the heat insulation performance semipermanently.

  Moreover, in the above, although the nanofiber 32 and the fiber sheet 31 were used, the base materials other than this may be used, and only one of them may be used.

<Adhesive layer 15>
Consider the case where the graphite sheet or the rubber sheet containing graphite is used as the heat conductive layer 12 and the airgel 33 is used as the heat insulating layer 13.

<Water-based adhesive>
The adhesive layer 15 is preferably a water-based adhesive. An adhesive using water as a dispersing agent, an adhesive using water as a solvent, or an adhesive containing water is preferable.

  This is because the airgel 33 of the heat insulating layer 13 is water-repellent, repels an aqueous adhesive, and does not enter the airgel 33. If you enter, the thermal insulation performance falls. The graphite of the heat conductive layer 12 is also water repellent, and the same can be said. Water glass or the like can be used.

  Since the graphite sheet and the airgel 33 are water-repellent, they are positioned between the heat insulating layer 13 (aerogel 33) and the heat conductive layer 12 (graphite) using water-based water glass (a sodium silicate concentrated aqueous solution) having a certain degree of viscosity. Then, heat is applied to 100 ° C. or more to vaporize water, whereby the water glass adhesive layer 15 is foamed and becomes an inorganic layer mainly composed of silica and solidified. Accordingly, a foamed layer can be formed without entering the hole of the airgel 33, and the graphite sheet and the airgel 33 can be bonded.

One example will be described. As a water glass paste for forming the adhesive layer 15, silica particles (true spherical particles having an average particle diameter of 2 μm) and sodium silicate (a molar ratio of silicon dioxide and sodium oxide (SiO ₂ / Na ₂ O) of about 2.5) are used. Solution) and potassium silicate (an aqueous solution having a molar ratio of silicon dioxide to potassium oxide (SiO ₂ / K ₂ O) of about 2).

The molar ratio (SiO ₂ / Na ₂ O) of silicon dioxide and sodium oxide of sodium silicate is about 2 to 4 and preferably about 2.5 because it affects the coating properties. The molar ratio of silicon dioxide and potassium oxide potassium silicate (SiO ₂ / K 2 _O) for also affects the coatability and water-resistant as well, often about 1-4, preferably about 2.

  When adjusting the paste, stirring was performed twice at 1500 rpm for 3 minutes in a rotating / revolving vacuum mixer.

In particular, water glass in which the heat insulating layer 13 is made of the same silicic acid based material as the airgel 33 has good adhesion and does not reduce the heat insulation of the airgel 33.
<Foam adhesive>
Further, the adhesive is preferably an adhesive that finally generates a void 20 (FIG. 1B). An adhesive that foams is preferable. Since the gap 20 remains, heat conduction from the heat conductive layer 12 to the heat insulating layer 13 is hindered. Further, the air gap 20 acts elastically with respect to a change in the distance between the component 11 and the housing 14. Therefore, even if the distance between the housing 14 and the component 11 changes, the heat insulation structure can be followed for a long time.

  Further, the air gap 20 on the surface of the adhesive layer 15 also serves as a space for air in the heat insulating layer 13. Also, the air gap 20 should not penetrate the adhesive layer 15. This is because the heat insulating layer 13 and the heat conducting layer 12 transfer heat through the air in the penetrating portion. The air gap 20 is preferably a sealed space in which air can not flow in and out. However, the void 20 on the surface of the adhesive layer 15 may not be sealed. The voids 20 should be homogeneously distributed in the adhesive layer 15, and the size thereof should be at least one-quarter or less of the thickness of the adhesive layer 15. The gaps 20 are not connected to each other, and a through hole is not formed. Eliminate heat transfer. Preferably, 1/8 or less is good. The air gaps 20 can be prevented from sticking to each other and becoming a large air gap 20. Heat conduction in the large gap 20 can be inhibited.

  Further, instead of water glass, a water-based adhesive in which a resin elastomer is dispersed may be used as the adhesive layer 15 to heat and foam water.

  Furthermore, in order to provide the void 20, the adhesive layer 15 in which the adhesive is made to absorb water may be used. An acrylic adhesive which absorbs water is inserted between the graphite and the airgel 33, and heated and pressurized to 100 ° C. or higher. Water is vaporized and foamed in the pressure-sensitive adhesive layer, thereby making it possible to form the adhesive layer 15 including bubbles.

<Assembly>
As a first step, water glass of the adhesive layer 15 is applied to the graphite that is the heat conductive layer 12. In the second step, the temperature is increased to 80 ° C. at which the foaming is not caused. As a third step, the heat conductive layer 12 and the heat insulating layer 13 are bonded together via the adhesive layer 15. As a 4th process, the composite sheet 50 is produced by heating to 100 degreeC or more and foaming and hardening.

By this manufacturing method, the composite sheet 50 in which the heat insulating layer 13 and the heat conductive layer 12 are bonded by the adhesive layer 15 is obtained. The composite sheet 50 is used by being sandwiched between the component 11 and the housing 14.
<Evaluation>
It evaluated by the structure of FIG.1 (d). The metal block 52 was placed on the hot plate 53, and the composite sheet 50 was placed thereon. The temperature of the upper surface of the composite sheet 50, the temperature immediately above the metal block 52 was measured by the thermocouple 51. Further, the temperature at the interface between the metal block 52 and the heat conductive layer 12 was measured with a thermocouple 51. Heat was applied from the hot plate 53 with the part 11 as the metal block 52.

The heat insulation layer 13 used the airgel 33 described above and a thickness of 1 mm. The adhesive layer 15 was made of two types of epoxy resin and water glass, and had a thickness of 30 μm. As the heat conductive layer 12, the above-described graphite sheet having a thickness of 0.1 mm was used. The airgel 33 is 5 to 20 times thicker than the graphite sheet that is the heat conductive layer 12. Furthermore, 7 to 15 times are preferable.
It is a ratio that can spread heat and insulate heat efficiently in a limited space.

  The area of the composite sheet 50 is 50 × 80 mm, and the same applies to the heat insulating layer 13, the adhesive layer 15, and the heat conductive layer 12.

  The other conditions were the same, and evaluation was made with two samples in which only the adhesive layer 15 was changed. The results are shown in Table 1. It can be seen that heat is not transferred onto the composite sheet 50 in the case of the water glass (example) in the adhesive layer 15 than in the epoxy resin (comparative example). Although the difference is only about 2 degrees, this difference is large when the housing 14 is touched for a long time by hand.

  This is because in the case of the epoxy resin, the resin penetrates into the airgel 33 and the heat insulation performance of the airgel 33 is degraded. In the case of water glass, the water glass does not soak into the airgel 33, and the heat insulation performance of the airgel 33 does not deteriorate.

（実施の形態２）
図２（ａ）、図２（ｂ）にて、実施の形態２を説明する。図２（ａ）、図２（ｂ）は、図１（ａ）に対応する図である。断熱構造の断面図である。実施の形態１との相違点は、熱伝導層１２の構造にある。その他は、実施の形態１と同じである。

Second Embodiment
The second embodiment will be described with reference to FIGS. 2 (a) and 2 (b). 2A and 2B correspond to FIG. 1A. It is sectional drawing of a heat insulation structure. The difference from the first embodiment is the structure of the heat conductive layer 12. Others are the same as in the first embodiment.

  In FIG. 2A, two first heat conductive layers 121 and second heat conductive layers 122 are laminated as heat conductive layers. Each is bonded by an adhesive layer 15. The first heat conductive layer 121 is in a sufficiently wide range (four times or more of the upper surface of the component), and the second heat conductive layer 122 is one area larger than the same area as the upper surface of the component (within twice the upper surface of the component). . The heat at the top of the part 11 is the highest and the heat is the most uneven. At this point, another heat conductive layer 12 is disposed. The heat can be spread efficiently. The heat insulation performance is better than the first embodiment.

  In FIG. 2B, the third heat conductive layer 123 is further laminated on the component 11 between the first heat conductive layer 121 and the second heat conductive layer 122 via the adhesive layer 15. Each heat conductive layer has a larger area as it goes upward. It is easy to spread the heat. Furthermore, the heat insulation performance is increased.

  Although there are a plurality of adhesive layers 15, the adhesive can be changed for each. The materials of Embodiment 1 are preferably used for the first heat conductive layer 121, the second heat conductive layer 122, the third heat conductive layer 123, the adhesive layer 15, and the heat insulating layer 13.

Third Embodiment
A third embodiment will be described with reference to FIG. FIG. 3 is a diagram corresponding to FIG. It is sectional drawing of a heat insulation structure. The difference from the first embodiment is that the first heat conductive layer 121 and the fourth heat conductive layer 124 are stacked.

  In FIG. 3, the first thermally conductive layer 121 and the fourth thermally conductive layer 124 are provided on the upper and lower sides of the heat insulating layer 13 via the adhesive layer 15. The heat spreads and shuts off with these three layers, and the heat insulation performance is improved. However, each layer may be thinned to reduce the layer thickness. Even in the case of the same thickness, the heat insulation performance is better than in the case of FIG. 1 (a).

  Each of the three layers has a sufficiently larger area than the component 11. There is more than 4 times the area.

  Although there are a plurality of adhesive layers 15, the adhesive can be changed for each. It is preferable that the material of Embodiment 1 be used for the first heat conductive layer 121, the fourth heat conductive layer 124, the adhesive layer 15, and the heat insulating layer 13.

Embodiment 4
A fourth embodiment will be described with reference to FIGS. 4 (a) to 4 (c). FIG. 4A to FIG. 4C are diagrams corresponding to FIG. It is sectional drawing of a heat insulation structure. The difference from Embodiment 1 is that there is no heat insulation layer 13 on the entire surface. Therefore, at least the side surface of the heat insulating layer 13 is covered with the adhesive layer 15.

  In FIG. 4A, the heat insulating layer 13 is located above the adhesive layer 15. The upper surfaces of the heat insulating layer 13 and the adhesive layer 15 are the same surface.

  By this structure, the heat insulating layer 13 is protected by the adhesive layer 15, and the heat of the component 11 is prevented from being transmitted to the housing 14 in a short distance. Further, since the heat insulating layer 13 is not adhesive, the adhesion between the heat insulating layer 13 and the housing 14 is poor, and heat is not transmitted to the housing 14 more.

  Since the top surfaces of the heat insulating layer 13 and the adhesive layer 15 are the same surface, it is easy to insert the electronic sheet into the single sheet-like composite sheet 50. The same applies to FIGS.

  In FIG. 4 (b), the heat insulating layer 13 is located below the adhesive layer 15. The lower surfaces of the heat insulating layer 13 and the adhesive layer 15 are the same surface.

  By this structure, the heat insulating layer 13 is protected by the adhesive layer 15, and the heat of the component 11 is prevented from being transmitted to the housing 14 in a short distance. The heat insulating layer 13 is surrounded and protected by the adhesive layer 15 and the heat conduction layer 12.

  In FIG. 4C and FIG. 4D, the heat insulating layer 13 is located inside the adhesive layer 15. The heat insulating layer 13 does not appear on the upper and lower surfaces of the adhesive layer 15.

  With this structure, the heat insulating layer 13 is completely covered with the adhesive layer 15, and the heat insulating layer 13 is protected. Furthermore, in FIG. 4D, this structure prevents the heat transmitted to the case 14 by the adhesive layer 15 from the side surface of the heat insulating layer 13.

  The heat of the component 11 is spread horizontally by the heat conducting layer 12. In this example, heat transfer was prevented only in the upper part of the component 11 having the highest heat. The other part was thermally insulated by the adhesive layer 15.

  In particular, in the case where the heat insulation layer 13 is the airgel shown above, the generation of powder and the like can be prevented. The failure of the thermal barrier is protected. Furthermore, it is an area | region smaller than the heat conductive layer 12, and the usage-amount can be restrained.

  It is preferable to use the material of Embodiment 1 for the heat conductive layer 12, the adhesive layer 15, and the heat insulating layer 13.

Fifth Embodiment
The fifth embodiment will be described with reference to FIGS. 5 (a) to 5 (b). FIG. 5A to FIG. 5B are diagrams corresponding to FIG. It is sectional drawing of a heat insulation structure. The difference from Embodiment 1 is that there is no heat insulation layer 13 on the entire surface. Therefore, at least the side surface of the heat insulating layer 13 is covered with the adhesive layer 15.

  In FIG. 5A and FIG. 5B, the heat insulating layer 13 penetrates the adhesive layer 15. It appears on the upper and lower surfaces of the adhesive layer 15. The upper and lower surfaces of the heat insulating layer 13 and the adhesive layer 15 are the same surface.

  This structure reduces the probability of the heat of the component 11 being transferred to the housing 14 through the adhesive layer 15. As a result, the heat of the part 11 is not more transferred to the housing 14.

  In FIG. 5B, the shape of the heat insulating layer 13 is further different in FIG. 5A. The housing 14 side is large and the component 11 side is small.

  With this structure, the heat transmitted to the housing 14 through the adhesive layer 15 is blocked by the side surface of the heat insulating layer 13.

  The heat of the component 11 is spread in the horizontal direction by the heat conductive layer 12. In this example, heat transfer was prevented only in the upper part of the component 11 having the highest heat. Other portions were insulated with the adhesive layer 15.

  This structure is good when the heat insulating layer 13 is expensive, when powder or the like is likely to be generated, or when the strength is weak. That is, the heat insulating layer 13 is protected by the adhesive layer 15.

It is preferable to use the material of Embodiment 1 for the heat conductive layer 12, the adhesive layer 15, and the heat insulating layer 13.
(Note)
The above embodiments can be combined as needed.

As described above, according to the present invention, composite heat insulation can be sufficiently exhibited even in a narrow space in the housing of the electronic device, and heat transfer from parts accompanied with heat generation to the outer surface of the housing can be effectively reduced. A body and an electronic device including the body can be provided.

DESCRIPTION OF SYMBOLS 10 Board | substrate 11 Component 12 Thermal conductive layer 13 Thermal insulation layer 14 Housing | casing 15 Adhesive layer 20 Space | gap 21 Fiber 31 Fiber sheet 32 Nanofiber 33 Aerogel 50 Composite sheet 51 Thermocouple 52 Metal block 53 Hot plate 121 1st thermal conductive layer 122 2nd Heat conduction layer 123 third heat conduction layer 124 fourth heat conduction layer

Claims (8)

A graphite layer disposed on the electronic component side,
An airgel layer disposed on the housing side,
A composite sheet in which the graphite layer and the airgel layer are fixed by an adhesive layer,
The area of the airgel layer is smaller than the area of the graphite layer, located in a portion corresponding to the electronic component ,
A composite sheet in which all side surfaces of the airgel layer are covered with the adhesive layer. The upper surface of the airgel layer is not covered with the adhesive layer,
The lower surface of the airgel layer is double if sheet according to claim 1, wherein that covered by the adhesive layer. The upper surface of the airgel layer is not covered with the adhesive layer,
The composite sheet according to claim 1, wherein a lower surface of the airgel layer is not covered with the adhesive layer. A graphite layer disposed on the electronic component side,
An airgel layer disposed on the housing side,
A composite sheet in which the graphite layer and the airgel layer are fixed with an adhesive layer,
The area of the airgel layer is smaller than the area of the graphite layer, located in a portion corresponding to the electronic component,
The side surface of the airgel layer is covered with the adhesive layer,
The upper surface of the airgel layer is covered with the adhesive layer,
Lower surface, Ifuku if sheet such covered by the adhesive layer of the airgel layer. A graphite layer disposed on the electronic component side,
An airgel layer disposed on the housing side,
A composite sheet in which the graphite layer and the airgel layer are fixed by an adhesive layer,
The area of the airgel layer is smaller than the area of the graphite layer, located in a portion corresponding to the electronic component,
The side surface of the airgel layer is covered with the adhesive layer,
The upper surface of the airgel layer is covered with the adhesive layer ,
The composite sheet according to claim 1, wherein a lower surface of the airgel layer is covered with the adhesive layer. A graphite layer disposed on the electronic component side,
An airgel layer disposed on the housing side,
A composite sheet in which the graphite layer and the airgel layer are fixed with an adhesive layer,
The area of the airgel layer is smaller than the area of the graphite layer, located in a portion corresponding to the electronic component,
The side surface of the airgel layer is covered with the adhesive layer,
The upper surface of the airgel layer is a bottom than the area size Ifuku case sheet of the airgel layer. The mounting structure which provided the said composite sheet of any one of Claims 1-6 between the said electronic component and the said housing | casing. The electronic device which has the mounting structure of Claim 7 inside.

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