JP5896201B2 - Adhesive composition and adhesive tape - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive tape having good thermal conductivity and flame retardancy, and excellent adhesion, and for fixing members in various fields such as electronic parts, OA equipment parts, home appliance parts, etc. In particular, the present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive tape that are useful for fixing heat-generating LEDs.

  In recent years, remarkable progress in electronics technology has led to higher integration and higher performance of electrical, electronic, and OA equipment, which has been prone to problems caused by internal high temperatures and heat storage. Adhesive members used for fixing internal components In addition, high thermal conductivity is required to prevent high temperature and heat storage. Moreover, in order to prevent the risk of ignition even when excessive temperature increase or heat storage occurs, the adhesive member is also required to have high flame retardancy. In recent years, electronic devices and OA devices are becoming lighter, thinner, and smaller, and it is necessary to dissipate heat in a limited heat-dissipating space. In particular, LED light sources used for image display backlights tend to generate heat. When the mounting density is increased in order to ensure the luminance of the display portion, the amount of heat generation is further increased. Therefore, high heat dissipation and flame retardancy are required.

As an adhesive composition having thermal conductivity and flame retardancy, for example, a thermally conductive flame-retardant pressure-sensitive adhesive (see Patent Document 1) containing a flame retardant and a thermally conductive filler in an acrylic polymer,
It has a (meth) acrylate polymer and a metal hydroxide, has a specific range of the toluene-insoluble fraction of the (meth) acrylate polymer and the molecular weight of the toluene-soluble component, and 100 mass of the (meth) acrylate polymer. A pressure-sensitive adhesive composition in which the blending ratio of the metal hydroxide to 80 parts is 80 to 160 parts by mass is disclosed (see Patent Document 2).

  These pressure-sensitive adhesives have flame retardancy and thermal conductivity. However, in order to improve flame retardancy and thermal conductivity when applied to electronic devices and OA devices that are becoming lighter and thinner, flame retardants and Increasing the amount of thermally conductive filler added significantly reduced the adhesive strength, making it difficult to apply to various parts fixing applications.

JP 2002-294192 A JP 2002-285121 A

  The problem to be solved by the present invention is to provide a pressure-sensitive adhesive having excellent adhesiveness that does not easily drop off when fixing a component even if a large amount of inorganic filler is added to achieve good thermal conductivity and flame retardancy. It is to provide a composition.

  In the present invention, the pressure-sensitive adhesive composition contains an acrylic copolymer containing (meth) acrylate as a main monomer component and an inorganic filler, and the acrylic copolymer has 2 carbon atoms as a monomer component. It contains a (meth) acrylate monomer having a carboxy group at the molecular chain end through the saturated hydrocarbon group as described above, and the content of the inorganic filler is 200 parts by mass or more with respect to 100 parts by mass of the acrylic copolymer. The adhesive composition can realize excellent adhesiveness even when a large amount of inorganic filler is added, and can achieve both good flame retardancy and thermal conductivity and suitable adhesiveness.

  Since the pressure-sensitive adhesive composition of the present invention has excellent adhesiveness even if a large amount of inorganic filler is added in order to achieve good flame retardancy and thermal conductivity, high reliability is required for component fixing, In addition, the present invention can be suitably applied to fixing electronic components such as various electronic devices and OA devices that are becoming lighter and thinner in recent years. Among these, the amount of heat generation is large, and it can be particularly suitably used for fixing an LED light source used for an image display backlight or the like that requires a high mounting density in order to ensure the luminance of the image display unit.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition containing an acrylic copolymer containing (meth) acrylate as a main monomer component and an inorganic filler, wherein the acrylic copolymer is used as a monomer component. It contains a (meth) acrylate monomer having a carboxy group at the molecular chain end via a saturated hydrocarbon group having 2 or more carbon atoms, and the content of the inorganic filler is 200 mass with respect to 100 mass parts of the acrylic copolymer. It is a pressure-sensitive adhesive composition of at least part.

(Acrylic copolymer)
The acrylic copolymer constituting the pressure-sensitive adhesive composition of the present invention comprises (meth) acrylate as a main monomer component, and a vinyl monomer that undergoes a cross-linking reaction with a cross-linking agent via a saturated hydrocarbon group having 2 or more carbon atoms. It consists of the (meth) acrylate monomer which has group at the molecular chain terminal.

  In a conventional pressure-sensitive adhesive, when a large amount of an inorganic filler is blended in order to realize good thermal conductivity and flame retardancy, the flowability of the pressure-sensitive adhesive is lowered and initial adhesiveness is lowered. Therefore, in order to compensate for this, the flowability of the pressure-sensitive adhesive can be reduced by reducing the molecular weight of the acrylic copolymer, reducing the content of the crosslinking point monomer and the amount of crosslinking agent added, and reducing the cohesive strength of the pressure-sensitive adhesive. It is possible to improve. However, when the fluidity of the acrylic copolymer is improved by the above-described method, the performance as a binder is insufficient in the state where the inorganic copolymer is contained in a large amount and the volume of the acrylic copolymer is small. When stress is applied to the film, it peels between the acrylic copolymer and the inorganic filler, and the physical properties of the adhesive deteriorate. Therefore, the acrylic copolymer needs to have both cohesion and fluidity. In the pressure-sensitive adhesive composition of the present invention, an inorganic filler is added to the acrylic copolymer by using a (meth) acrylate monomer having a carboxy group at the molecular chain end via a saturated hydrocarbon group having 2 or more carbon atoms. Even if it is contained in a large amount, both cohesion and fluidity can be achieved. A (meth) acrylate monomer having a carboxy group at the end of a molecular chain via a saturated hydrocarbon group having 2 or more carbon atoms is excellent in fluidity at a crosslinking point because of a long side chain. In addition, since the (meth) acrylate monomer having a carboxy group at the molecular chain terminal via a saturated hydrocarbon group having 2 or more carbon atoms has a low glass transition temperature, the temperature at which the loss tangent peak of the pressure-sensitive adhesive layer is low is low. Thus, an adhesive composition having excellent fluidity can be realized. Furthermore, since the (meth) acrylate monomer having a carboxy group at the molecular chain end via a saturated hydrocarbon group having 2 or more carbon atoms has little steric hindrance, the terminal carboxy group and the crosslinking agent can easily react with each other. Cohesive force can be obtained. Thus, since the cohesiveness and fluidity of the pressure-sensitive adhesive can be compatible without reducing the cohesive strength of the resin by using the (meth) acrylate monomer, the pressure-sensitive adhesive composition of the present invention contains a large amount of filler. Even if contained, it exhibits excellent adhesive properties.

（式（１）中、Ｒ_１は水素又はメチル基であり、Ｒ_２はアルキル基又は水酸基を側鎖に含んでもよい炭素数２以上のアルキレン基であり、Ｘ_１はカルボキシ基又はジカルボン酸残基であり、ｎは１〜２である。） Examples of the (meth) acrylate monomer having a carboxy group at the molecular chain end through a saturated hydrocarbon group having 2 or more carbon atoms include a (meth) acrylate monomer represented by the following formula (1).

(In Formula (1), R ₁ is hydrogen or a methyl group, R ₂ is an alkylene group having 2 or more carbon atoms which may contain an alkyl group or a hydroxyl group in the side chain, and X ₁ is a carboxy group or a dicarboxylic acid residue. And n is 1 to 2.)

  In addition, the said dicarboxylic acid residue represents the residue of the dicarboxylic acid in the structure which one carboxy group of dicarboxylic acid couple | bonded with the molecular chain terminal, For example, it forms with the dicarboxylic acid represented as HOOC-R-COOH. The dicarboxylic acid residue is -OOC-R-COOH. As the dicarboxylic acid constituting the dicarboxylic acid residue, a dicarboxylic acid in which R is directly bonded, or a dicarboxylic acid having a divalent aliphatic hydrocarbon group or an aromatic hydrocarbon group as R can be appropriately used. However, dicarboxylic acids having an aliphatic hydrocarbon group, particularly a chain aliphatic hydrocarbon group, are preferred because steric hindrance is unlikely to occur. Specific examples of suitable dicarboxylic acids include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. It can be illustrated.

Among the (meth) acrylates represented by the above formula (1), R ₂ is preferably an alkylene group having 2 to 18 carbon atoms, and particularly preferably an alkylene group having 2 to 5 carbon atoms. X ₁ is preferably a carboxy group. Specifically, for example, β-carboxyalkyl (meth) acrylate, ethylene oxide (EO) modified succinic acid (meth) acrylate, propylene oxide (PO) modified succinic acid (meth) acrylate and the like can be exemplified. Among these, β-carboxyethyl acrylate can be particularly preferably used.

  The content of the (meth) acrylate monomer having a carboxy group at the molecular chain end through a saturated hydrocarbon group having 2 or more carbon atoms is 0.5 to 10% by mass in the monomer component constituting the acrylic copolymer. It is preferable that it is 1-5 mass%. By setting the content of the (meth) acrylate monomer having a carboxy group at the end of the molecular chain through a saturated hydrocarbon group having 2 or more carbon atoms within the above range, a crosslinking point can be easily formed, It becomes easy to improve cohesion force and initial adhesiveness.

  As the (meth) acrylate used as the main monomer component, various (meth) acrylates used for the pressure-sensitive adhesive can be used, and among them, alkyl (meth) acrylates having 1 to 12 carbon atoms in the alkyl group can be preferably used. Examples of the alkyl (meth) acrylate having 1 to 12 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, Examples include monomers such as n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and one or more of these are used. It is done. Among these, alkyl (meth) acrylates having 4 to 8 carbon atoms in the alkyl group, particularly 2-ethylhexyl acrylate, are preferable because they can easily secure adhesiveness even when a filler is added.

  The content of the alkyl (meth) acrylate having 1 to 12 carbon atoms is preferably 60% by mass or more, and more preferably 80% by mass or more in the monomer component constituting the acrylic copolymer. Especially when using 2-ethylhexyl acrylate, it is preferable that 80 mass% or more of all the C1-C12 alkyl (meth) acrylates are 2-ethylhexyl acrylate, and it is 90 mass% or more. More preferred.

  As the monomer component constituting the acrylic copolymer, various vinyl monomers can be used as monomer components other than those described above. As such a vinyl monomer, a carboxy group-containing monomer can be preferably used. Examples of the carboxy group-containing vinyl monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, phthalic acid, and phthalic anhydride. 1 type, or 2 or more types, such as crotonic acid, can be used. Of these, acrylic acid and methacrylic acid can be preferably used because they easily adjust the cohesiveness of the acrylic copolymer.

  The content of the carboxy group-containing vinyl monomer is preferably 10% by mass or less, more preferably 0.5 to 10% by mass, and more preferably 1 to 5% in the monomer component constituting the acrylic copolymer. More preferably, it is mass%. By containing in the said range, it is easy to improve the cohesive force, holding force, and adhesiveness of an adhesive.

  Other vinyl monomers include vinyl acetate, sulfonic acid group-containing monomers such as 2-acrylamido-2-methylpropanesulfonic acid, (meth) acrylates having 1 to 3 carbon atoms, (meth) acrylates having 13 or more carbon atoms, Known vinyl monomers such as isobornyl (meth) acrylate and styrene may be used.

  The content in the case of using other vinyl monomers is preferably 10% by mass or less, more preferably 5% by mass or less, in the monomer component constituting the acrylic copolymer. By containing in the said range, it is easy to adjust the cohesive force, holding force, and adhesiveness of an adhesive to a suitable range.

  The acrylic copolymer can be obtained by copolymerization by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Polymerization is initiated by peroxides such as benzoyl peroxide and lauryl peroxide, thermal initiation methods using azo-based thermal polymerization initiators such as azobisisobutylnitrile, acetophenone, benzoin ether, benzyl ketal In addition, an initiation method by ultraviolet irradiation using an acylphosphine oxide-based, benzoin-based or benzophenone-based photopolymerization initiator, or a method by electron beam irradiation can be arbitrarily selected.

  The acrylic copolymer polymerized within the above range has a weight average molecular weight in terms of polystyrene of gel permeation chromatography of 300,000 to 800,000, more preferably 400,000 to 700,000. When the weight average molecular weight is 300,000 or more, the cohesive force of the pressure-sensitive adhesive is easily secured, and the adhesiveness at high temperature is easily improved. Moreover, it is easy to improve the dispersibility of a heat conductive filler, the applicability | paintability of an adhesive, and initial stage adhesiveness because a weight average molecular weight shall be 800,000 or less.

(Inorganic filler)
The inorganic filler used for this invention can use the inorganic filler which has heat conductivity and a flame retardance, for example, can use a metal hydroxide, a metal oxide, a metal, ceramics, etc. Specifically, as the thermally conductive filler, for example, aluminum hydroxide, magnesium hydroxide, aluminum oxide, silicon oxide, magnesium oxide, zinc oxide, titanium oxide, zirconium oxide, iron oxide, silicon carbide, boron nitride, nitriding Examples thereof include aluminum, titanium nitride, silicon nitride, titanium boride, carbon, nickel, copper, aluminum, titanium, gold, and silver. Examples of the flame retardant filler include aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, basic magnesium carbonate, dolomite, hydrotalcite, calcium hydroxide, barium hydroxide, tin oxide hydrate, Hydrate of inorganic metal compounds such as borax, zinc borate, zinc metaborate, barium metaborate, zinc carbonate, magnesium carbonate-calcium carbonate, calcium carbonate, barium carbonate, magnesium oxide, molybdenum oxide, zirconium oxide, tin oxide, oxidation Examples include antimony and red phosphorus. These inorganic fillers may be subjected to surface treatment such as silane coupling treatment or stearic acid treatment in order to improve dispersibility in the acrylic copolymer.

  These inorganic fillers may be appropriately selected and used as necessary, but among these, in applications that require thermal conductivity and flame retardancy, thermal conductivity and flame retardance are difficult. It is preferable to use a flammable filler. In particular, in LED fixing applications, it is particularly preferable to use a metal hydroxide such as aluminum hydroxide or magnesium hydroxide as the heat conductive flame retardant filler. These metal hydroxides can impart thermal conductivity and flame retardancy. Among the metal hydroxides, aluminum hydroxide is particularly preferable because a thermal decomposition reaction takes place from about 250 ° C. and exhibits a flame retardant effect before the resin is remarkably melted.

  The shape of the inorganic filler may be either a regular shape or an irregular shape, such as a polygonal shape, a cubic shape, an elliptical shape, a spherical shape, a needle shape, a flat plate shape, a scale shape, or a combination thereof. Etc., and these may be agglomerated fillers. As for the size of the inorganic filler, it is preferable that the average of the maximum width and length, for example, in the case of particles, the average particle size is 0.5 to 50 μm. More preferably, it is 1-30 micrometers. In addition, the magnitude | size and shape of a filler are suitably selected by the thickness of the adhesive tape obtained. It is desirable that the maximum width and length of the inorganic filler be smaller than the thickness of the adhesive tape.

  The amount of the inorganic filler added to the pressure-sensitive adhesive composition is 200 parts by mass or more, preferably 200 parts by mass to 100 parts by mass of the acrylic copolymer in order to realize good thermal conductivity and flame retardancy. It is 280 mass parts, More preferably, it is 230-250 mass parts. Even if the pressure-sensitive adhesive composition of the present invention contains the large amount of the inorganic filler, suitable adhesiveness can be realized.

(Tackifying resin)
A tackifier resin may be used in the heat conductive adhesive of the present invention for the purpose of improving adhesive properties. As tackifying resins, known aliphatic petroleum resins, aromatic petroleum resins, alicyclic petroleum resins, etc., rosin resins, rosin ester resins, disproportionated rosin resins, polymerized rosin resins, polymerized rosin esters Resins, rosin resins such as rosin phenol, terpene resins, terpene phenol resins and the like can be used. Further, two or more kinds of tackifying resins can be used in combination.

  As addition amount of tackifying resin, 20 mass parts or less are preferable with respect to 100 mass parts of acrylic copolymers. More preferably, it is 10 parts by mass or less. By setting it as the said range, it will become easy to acquire a favorable tackifying effect and initial stage adhesiveness. Moreover, it is also preferable not to use a tackifying resin for applications that require particularly high flame retardancy, for example, high flame retardancy such as UL94V-0 and VTM-0.

  Moreover, it is preferable to use tackifying resin with a high flash point, and it is especially preferable to use resin with a flash point of 200 degree | times or more as tackifying resin. When a tackifying resin having a flash point of 200 degrees or more is used, it becomes easy to particularly effectively exhibit a flame retardant effect produced by thermal decomposition of the flame retardant filler during combustion.

(Crosslinking agent)
In the pressure-sensitive adhesive composition of the present invention, a crosslinking agent is used for improving cohesive strength. As the cross-linking agent, an epoxy-based cross-linking agent can be preferably used in order to react with the carboxy group of β-carboxyethyl acrylate. Examples of the epoxy crosslinking agent include 1.3-bis (N, N-glycidylaminomethyl) cyclohexane (Tetrad C manufactured by Mitsubishi Gas Chemical Company), 1.3-bis (N, N-glycidylaminomethyl) benzene (Mitsubishi Gas). Known epoxy crosslinking agents such as Tetrad X) manufactured by Kagaku Co., Ltd. can be used.

  As an index of the degree of cross-linking, the value of the gel fraction for measuring the insoluble content after the pressure-sensitive adhesive layer is immersed in toluene for 24 hours is used. The gel fraction after crosslinking of the pressure-sensitive adhesive composition of the present invention is preferably 25% to 60%. More preferably, it is 30% to 50%. In addition, the value of a gel fraction refers to the insoluble part of resin which deducted the addition amount of the inorganic filler. By adopting the range, even when stress is applied to the pressure-sensitive adhesive layer after crosslinking, peeling between the acrylic copolymer and the inorganic filler hardly occurs, and it is easy to obtain good pressure-sensitive adhesive properties. Easy initial adhesion.

  Moreover, the pressure-sensitive adhesive composition of the present invention may appropriately use additives such as an anti-aging agent, a colorant, and a dispersant as long as the thermal conductivity, flame retardancy, and pressure-sensitive adhesive properties are not significantly impaired.

  The pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition of the present invention preferably has a temperature at which the loss tangent peak is -40 ° C or higher and -10 ° C or lower. By setting it as the said range, even if it mix | blends many inorganic fillers, it will become easy to make the fluidity | liquidity and cohesion of an adhesive compatible. The peak temperature of loss tangent is 5 mm thick. The test piece is an adhesive layer, a rheometer viscoelasticity tester Ares 2kSTD is attached to a parallel plate with a diameter of 7.9 mm, and the test piece is sandwiched. This is a value measured by a frequency 1 Hz frequency dispersion method.

(Adhesive manufacturing method)
As a manufacturing method of the pressure-sensitive adhesive composition of the present invention, after manufacturing an acrylic copolymer by the above-described manufacturing method, an organic solvent such as ethyl acetate, hexane, or MEK is used for adjusting the tackifier resin and viscosity as necessary. Add and mix while dissolving the tackifying resin and take out the resulting resin composition. Next, the obtained resin composition and the inorganic filler and other additives are mixed using a low-speed stirrer such as a planetary mixer until the resin composition, the inorganic filler and other additives are uniform, and an adhesive composition Get.

[Adhesive tape]
The pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive composition. The pressure-sensitive adhesive tape of the present invention may be a pressure-sensitive adhesive tape having a base material or a pressure-sensitive adhesive tape comprising only a pressure-sensitive adhesive layer having no base material. The pressure-sensitive adhesive tape having a base material has good handleability and processability, and the pressure-sensitive adhesive tape consisting only of the pressure-sensitive adhesive layer having no base material is easy to obtain effects of thermal conductivity and flame retardancy. What is necessary is just to select suitably according to the use etc. to make.

  When it is set as the adhesive tape which has a base material, a film, a nonwoven fabric, metal foil, etc. can be used as a base material as a base material. Among them, the film substrate is preferably used because it is excellent in handleability and the like. Examples of the film substrate include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene film, polypropylene film, cellophane, diacetyl cellulose film, and triacetyl cellulose. Film, acetylcellulose butyrate film, polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film, ethylene-vinyl acetate copolymer film, polystyrene film, polycarbonate film, polymethylpentene film, polysulfone film, polyether ether ketone film , Polyethersulfone film, polyetherimide film, polyimide film, Tsu Seo resin film, nylon film, mention may be made of resin film base material such as an acrylic resin film.

  When the adhesive composition is bonded to one side of the substrate, it becomes a single-sided adhesive tape, and when the adhesive is bonded to both sides of the substrate, it becomes a double-sided adhesive tape. It is necessary to select the material and thickness of the base material in consideration of not inhibiting thermal conductivity and flame retardancy. In particular, as a base material for a double-sided pressure-sensitive adhesive tape, a PET film is preferable from the viewpoints of productivity and availability in addition to performance aspects such as strength, insulation, flame retardancy, smoothness and uniform thickness. The PET film surface is preferably subjected to corona treatment or easy adhesion treatment in order to improve the anchoring property of the pressure-sensitive adhesive.

  In the case of a resin film, the thickness of the substrate is preferably 3 μm to 50 μm, more preferably 6 to 25 μm. By setting it as the said range, favorable handleability and workability can be obtained, without inhibiting heat conductivity and a flame retardance.

  The thickness of the pressure-sensitive adhesive layer is preferably 10 μm to 150 μm as a coating thickness after drying once. By setting it as the said range, it is easy to ensure adhesive physical property suitably, and it becomes easy to dry the dilution solvent in the adhesive at the time of manufacture, and it becomes easy to improve productivity.

  The thickness of the adhesive tape is preferably 20 μm to 300 μm, particularly in the case of a double-sided adhesive tape. More preferably, it is 50 micrometers-250 micrometers. When the pressure-sensitive adhesive tape exceeds 150 μm, a thick film can be formed by a method such as laminating a pressure-sensitive adhesive layer through two coating steps. If a base material is bonded between each adhesive layer at the time of lamination | stacking, it will become a double-sided adhesive tape which has a base material. In the case of a single-sided tape, the thickness of the pressure-sensitive adhesive layer plus the thickness of the base material is the pressure-sensitive adhesive tape thickness.

When the base material is not used, the pressure-sensitive adhesive tape is manufactured by applying the pressure-sensitive adhesive composition to a support such as a release liner with a constant thickness using a roll coater or die coater, drying the diluted solvent with a dryer, etc. It can manufacture by the method of bonding the release liner of. When a release liner that has been subjected to a release treatment on both sides is used, the pressure-sensitive adhesive composition can be applied to the release liner and dried in the same manner as described above, and then wound into a roll.
When using a base material, a single-sided adhesive tape can be manufactured by apply | coating an adhesive composition to a release liner like the above, and drying and then bonding to the one side of a base material. Furthermore, a double-sided pressure-sensitive adhesive tape can be produced by applying a thermally conductive pressure-sensitive adhesive to a release liner and bonding the dried liner to the other side of the substrate.

  As the inorganic filler in the pressure-sensitive adhesive composition, the pressure-sensitive adhesive tape and double-sided pressure-sensitive adhesive tape of the present invention using the heat-conductive flame-retardant pressure-sensitive adhesive composition using a heat-conductive flame-retardant filler are particularly used for backlights for liquid crystal image display, etc. It can be particularly suitably used for fixing the LED light source used in the above. The LED light source can be fixed to a heat conductive material, for example, a metal material such as aluminum, thereby realizing more suitable heat dissipation.

  When the adhesive tape using the heat conductive flame retardant filler is used for fixing the LED light source, the thermal conductivity of the adhesive tape is preferably 0.6 W / m · k or more. In addition, flame retardancy is reported by Underwriters Laboratories Inc. According to the company standard, the performance is preferably UL94V-2 or VTM-2 or higher, particularly preferably UL94V-0 or VTM-0 or higher. Furthermore, as adhesive properties, it is preferable that the adhesive strength is 5 N / 20 mm width or more, and the holding power is a performance of holding for 24 hours when a load of 100 g is applied in the shear direction in an area of 5 mm width × 30 mm length.

  Examples will be specifically described below, but the present invention is not limited thereto.

[Example 1]
(1-1) Preparation of acrylic copolymer In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 96.4 parts by mass of 2-ethylhexyl acrylate, 2.4 parts by mass of β-carboxyethyl acrylate Part, 1.2 parts by mass of acrylic acid and 98 parts by mass of ethyl acetate were added, and the temperature was raised to 75 ° C. while blowing nitrogen under stirring. Thereafter, 2 parts by mass (solid content 5% by mass) of an azobisisobutyronitrile solution previously dissolved in ethyl acetate was added. Then, after holding for 8 hours at 75 ° C. with stirring, the contents were cooled and filtered through a 200 mesh wire mesh. An acrylic polymer solution having a nonvolatile content of 50% by mass, a viscosity of 8000 mPa · s, and a weight average molecular weight of 500,000 was obtained.

(1-2) Adjustment of pressure-sensitive adhesive composition Heat conductive flame retardant aluminum hydroxide (Hijilite H32, Showa Denko Co., Ltd., average particle size: 8 μm) as an inorganic filler in a container of a planetary mixer 240 parts by mass are added to 100, and then the resulting pressure-sensitive adhesive composition is added. The mixture was stirred for 30 minutes to uniformly mix the aluminum hydroxide and the pressure-sensitive adhesive composition. Ethyl acetate was added to adjust the solid content to 70% to obtain a heat conductive flame retardant pressure-sensitive adhesive composition having a viscosity of 4000 mPa · s.

(1-3) Adjustment of pressure-sensitive adhesive tape An epoxy-based crosslinking agent (Tetrad C, manufactured by Mitsubishi Gas Chemical Company) 2% ethyl acetate solution is difficult to heat-conductive to the heat-conductive flame-retardant pressure-sensitive adhesive composition obtained in (1-2). 2.1 parts of 100 parts of the acrylic copolymer solid content in the flammable pressure-sensitive adhesive composition are blended and stirred with a dissolver stirrer for 30 minutes. The obtained pressure-sensitive adhesive composition is applied to a release liner with a roll coater so as to have a thickness of 60 μm after drying, and dried in an 80 ° C. dryer for 3 minutes. The obtained pressure-sensitive adhesive sheet was laminated on both sides of a 6 μm-thick PET film having a corona treatment on the surface to prepare a double-sided pressure-sensitive adhesive tape having a thickness of 125 μm. A double-sided pressure-sensitive adhesive tape was obtained by curing in a 40 ° C. dryer for 48 hours for the crosslinking reaction of the crosslinking agent.

[Example 2]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that aluminum hydroxide Showa Denko Hygielite H32 (average particle size 8 μm) was 260 parts by mass with respect to the pressure-sensitive adhesive composition solid content 100 as the inorganic filler.

[Example 3]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that aluminum hydroxide Showa Denko Hygielite H32 (average particle size 8 μm) was 220 parts by mass with respect to the pressure-sensitive adhesive composition solid content 100 as the inorganic filler.

[Example 4]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that aluminum hydroxide Showa Denko Hygielite H32 (average particle size 8 μm) was used as the inorganic filler in an amount of 200 parts by mass with respect to 100 of the pressure-sensitive adhesive composition solid content.

[Example 5]
As a tackifier, terpene resin (PX1250 manufactured by Yasuhara Chemical Co., Ltd.) is 15 parts by mass with respect to the acrylic copolymer solid content 100, and polymerized rosin pentaerythritol (Halitac PCJ manufactured by Harima Chemicals Co., Ltd.) is 5 masses with respect to the acrylic copolymer solid content 100. A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except that the parts were blended. In addition, the compounding of the tackifier was performed by the adjustment method of the below-mentioned adhesive composition.

[Adjustment of adhesive composition]
As a tackifier, 15 parts by mass of terpene resin (PX1250 manufactured by Yasuhara Chemical Co., Ltd.) and 100% polymerized rosin pentaerythritol (Haritama PCJ manufactured by Harima Kasei Co., Ltd.) as a tackifier was added to the obtained acrylic copolymer. Add 5 parts by weight of polymer solids 100, 15 parts by weight of hexane as dilution solvent, 5 parts by weight of ethyl acetate, and stir for 60 minutes to dissolve the tackifier. Adhesive with 50% solids and a viscosity of 2000 mPa · s A composition was obtained. The obtained pressure-sensitive adhesive was adjusted by the method described in the above-mentioned (1-2) Preparation of pressure-sensitive adhesive composition.

[Example 6]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 5 except that the terpene resin (PX1250 manufactured by Yasuhara Chemical Co., Ltd.) was used as a tackifier at 5 parts by mass with respect to the acrylic copolymer solid content 100.

[Example 7]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except that the coating thickness after drying the pressure-sensitive adhesive was 112 μm, a 25 μm-thick PET film was used as the substrate, and the thickness of the tape was 250 μm.

[Example 8]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 7 except that aluminum hydroxide Showa Denko Hygielite H32 (average particle size 8 μm) was 260 parts by mass with respect to the pressure-sensitive adhesive composition solid content 100 as the inorganic filler.

[Example 9]
The pressure-sensitive adhesive composition obtained in the same manner as in Example 1 was used, and after drying the pressure-sensitive adhesive, it was applied to a release liner so that the coating thickness was 125 μm. A release liner was bonded to obtain a double-sided pressure-sensitive adhesive tape.

[Comparative Example 1]
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 5 except that aluminum hydroxide (Hijilite H32 manufactured by Showa Denko KK, average particle size: 8 μm) was 150 parts by mass with respect to the solid content of the pressure-sensitive adhesive composition as an inorganic filler. .

[Comparative Example 2]
Double-sided adhesive as in Example 5 except that β-carboxyethyl acrylate was not used in preparation of the acrylic copolymer, and 97.7 parts by mass of 2-ethylhexyl acrylate and 2.3 parts by mass of acrylic acid were added. I got a tape.

  About the adhesive tape created as an Example and a comparative example, the gel fraction, thermal conductivity, a flame retardance, 90 degree peel adhesive force, and retention strength were evaluated by the method shown below.

[Gel fraction]
Samples obtained by cutting the adhesive tapes obtained in the above Examples and Comparative Examples into 40 mm × 50 mm were weighed with a balance, immersed in toluene, and allowed to stand at room temperature for 24 hours. After immersion, the sample was taken out, dried at 105 ° C. for 1 hour with a drier, cooled at room temperature, and the weight of the sample was measured. The weight of the sample after immersion in toluene was divided by the weight of the sample before immersion in toluene, and the proportion of insoluble matter was determined as a percentage.

[Thermal conductivity]
The pressure-sensitive adhesive tapes obtained in the above examples and comparative examples were laminated to 500 μm so as not to entrain air. The outermost surface was bonded with a PET film having a thickness of 6 μm. The obtained sample was cut into 5 cm × 15 cm to prepare a measurement sample. The obtained measurement sample was measured using a Kyoto Electronics Industrial thermal conductivity measuring device QTM-500 and a thin film method measurement software QTM-5W.

[Flame retardance]
The adhesive tapes obtained in the above examples and comparative examples were obtained from Underwriters Laboratories Inc. The test was conducted according to the standard of UL94VTM. In addition, since the adhesive tape which does not have a base material cannot form a cylinder shape, it tested according to the specification of the company UL94V.
The flame retardancy class was determined according to the following table.

[90 ° peel adhesion]
An aluminum foil having a thickness of 50 μm was bonded to one side of the pressure-sensitive adhesive tape obtained in the above examples and comparative examples, and cut into a width of 20 mm. Adhesion when the other adhesive surface is affixed to an aluminum plate under a reciprocating pressure of 2 kg roller in a reciprocating atmosphere at 23 ° C and 50% RH, and left for 1 hour and then peeled off at a rate of 300 mm / min in the 90 ° direction. The force was measured.

[Retention force]
The sample which made the adhesive tape obtained in the said Example and comparative example 5 mm width x 30 mm length was affixed on the one end of the 500-micrometer-thick aluminum plate. The other adhesive surface was affixed to an aluminum plate in an atmosphere of 23 ° C. and 50% RH, affixed under a pressure condition of one reciprocation and one reciprocation of a 5 kg roller, and allowed to stand for 1 hour. After standing, a load of 100 g was applied in the shear direction in an atmosphere at 85 ° C., and the time until the sample peeled off and dropped was measured. When the sample did not fall after 24 hours, the test was terminated and it was described as 24 hours or longer (> 24).

  As is clear from Tables 1 and 2 above, the pressure-sensitive adhesive compositions of the present invention of Examples 1 to 9 can realize excellent adhesion even when a large amount of inorganic filler is added, and have good flame retardancy and It was possible to achieve both thermal conductivity and suitable adhesiveness. On the other hand, the pressure-sensitive adhesive compositions of Comparative Examples 1 and 2 did not sufficiently exhibit the characteristics of the inorganic filler or had poor adhesion.

Claims (6)

A pressure-sensitive adhesive composition containing an acrylic copolymer containing (meth) acrylate as a main monomer component and an inorganic filler, wherein the acrylic copolymer is a saturated hydrocarbon having 2 or more carbon atoms as a monomer component It contains a (meth) acrylate monomer having a carboxy group at the molecular chain end via a group, and the content of the inorganic filler is 200 parts by mass or more with respect to 100 parts by mass of the acrylic copolymer. Adhesive composition. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic copolymer contains, as monomer components, an alkyl (meth) acrylate having an alkyl group having 1 to 14 carbon atoms and a carboxy group-containing vinyl monomer. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the inorganic filler is contained in a range of 200 parts by mass to 280 parts by mass with respect to 100 parts by mass of the acrylic copolymer . The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the acrylic copolymer has a weight average molecular weight in the range of 300,000 to 800,000 . The adhesive tape which has an adhesive layer which consists of an adhesive composition in any one of Claims 1-4. The liquid crystal image display part by which the LED light source unit was fixed to the heat conductive material with the adhesive tape of Claim 5.