JP2013028753A - Biaxially stretched thermoplastic resin film for highly thermoconductive pressure-sensitive adhesive tape substrate and highly thermoconductive pressure-sensitive adhesive tape made of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched thermoplastic resin film for a highly thermoconductive pressure-sensitive adhesive tape substrate that exhibits high adhesive properties and high thermoconductivity via a pressure-sensitive adhesive layer when used as a pressure-sensitive adhesive tape, and to provide a highly thermoconductive pressure-sensitive adhesive tape made of the same.SOLUTION: The biaxially stretched thermoplastic resin film comprises a fibrous carbon material, where the fibrous carbon material has an average fiber diameter of 0.05-5 μm, an average aspect ratio of at least 15, and a thermoconductivity in the film thickness direction of at least 0.28 W/(m K), wherein: the content of the fibrous carbon material in the film is more than 1 wt.% and not more than 20 wt.%; and the film has a centerline average roughness Ra of at least 4 nm and at most 100 nm.

Description

  The present invention relates to a biaxially stretched thermoplastic resin film for a highly heat conductive pressure-sensitive adhesive tape substrate and a high heat conductive pressure-sensitive adhesive tape comprising the same, and more particularly, a high heat conductive pressure-sensitive adhesive tape substrate having high heat conductivity even when an adhesive layer is interposed. The present invention relates to a biaxially stretched thermoplastic resin film and a high thermal conductive adhesive tape comprising the same.

In recent years, with the increase in the amount of heat generated by devices, the heat dissipation technology has become a major issue. As such heat dissipation technology, for example, heat generated from electrical elements and devices (hereinafter collectively referred to as devices) that generate large amounts of heat, such as CPUs, MPUs, power transistors, LEDs, and laser diodes, are thermally conductive sheets. A design for releasing heat dissipation parts such as a heat sink and a metal cover through an adhesive sheet called “etc.” has been studied, and various heat conductive sheets have been proposed.
For example, the thermal conductive sheet is required to have high thermal conductivity and electrical insulation so that no leak current or the like is generated between the thermal conductive sheet and the heat radiating member. As a high thermal conductive adhesive sheet for solving these problems, for example, a thin ceramic substrate is proposed in Patent Document 1, and it is proposed to adhere to a heat dissipation component via a thermoplastic resin layer.

Patent Document 2 proposes a composite film in which a graphite film is used as a high thermal conductive material, a protective layer is provided to protect the surface of the soft graphite film, and an adhesive layer is further laminated.
On the other hand, when a ceramic sheet or a graphite sheet is used as a high thermal conductivity material, there is a problem that although the thermal conductivity is increased, the flexibility is poor or the substrate is difficult to be thinned.

Further, in Patent Document 3, a bonding material containing a large amount of a thermally conductive filler in the resin has been studied. Although the thermal conductivity is improved when the amount of the metal filler is increased in order to increase the thermal conductivity, the adhesiveness is improved. In view of the fact that when the form of the bonding material is paste-like, the viscosity of the paste needs to be increased as the amount of the metal filler increases, and the workability is reduced. By doing so, it has been proposed that high adhesion and high thermal conductivity can be provided in a well-balanced manner. On the other hand, in order to use such a method, a thermosetting resin is used as the matrix resin, and a curing step is required.
Therefore, while using a thermoplastic and flexible film such as a widely used polyester film as the base material of the heat conductive sheet, a high heat conductive pressure-sensitive adhesive tape having high adhesiveness and high heat conductivity is obtained with high productivity. There is a need to provide.

JP 2007-173338 A JP 2008-80672 A JP 2003-221573 A

  The object of the present invention is to solve the problems of the prior art, and when used as a pressure-sensitive adhesive tape, biaxially stretched heat for a highly heat-conductive pressure-sensitive adhesive tape substrate that can exhibit high adhesiveness and high heat conductivity via the pressure-sensitive adhesive layer. An object of the present invention is to provide a plastic resin film and a high thermal conductive pressure-sensitive adhesive tape comprising the same.

  As a result of intensive investigations to solve the above problems, the present inventors have incorporated a fibrous carbon material having a small fiber diameter and a high aspect ratio into a thermoplastic resin film without forming voids after stretching. It can be contained in the film, and as a result, it exhibits high thermal conductivity without increasing the filler content, and at the same time has a certain electrical insulating property, and is also a thermally conductive film containing filler. However, since the film surface is smoother than before, it has been found that when forming an adhesive layer having a uniform adhesive force, the thickness can be reduced, and a high thermal conductive adhesive tape having high adhesiveness and high thermal conductivity can be provided. The present invention has been completed.

  That is, an object of the present invention is to provide a biaxially stretched thermoplastic resin film containing a fibrous carbon material, wherein the fibrous carbon material has an average fiber diameter of 0.05 to 5 μm and an average aspect ratio of 15 or more. The content of the carbonaceous material exceeds 1% by weight and is 20% by weight or less, the center line average roughness Ra of the film is 4 nm or more and 100 nm or less, and the thermal conductivity in the film thickness direction is 0.28 W / ( m · K), which is achieved by a biaxially stretched thermoplastic resin film for a highly thermally conductive pressure-sensitive adhesive tape substrate.

  In the biaxially stretched thermoplastic resin film for a highly heat-conductive adhesive tape substrate of the present invention, the thermoplastic resin constituting the film is polyester, and the polyester constituting the film is polyethylene terephthalate or polyethylene naphthalene dicarboxylate. The aspect which comprises any one of being at least 1 sort of these and film thickness being 5 micrometers or more and 100 micrometers is also included preferably.

  The present invention also includes a high thermal conductive pressure-sensitive adhesive tape having an adhesive layer on at least one side of the biaxially stretched thermoplastic resin film for a high heat conductive pressure-sensitive adhesive tape substrate of the present invention. It is also included that the layer thickness is 1 μm or more and 100 μm or less, and that the adhesive layer contains an acrylic or epoxy adhesive.

  ADVANTAGE OF THE INVENTION According to this invention, when using as an adhesive tape, the biaxially stretched thermoplastic resin film for base materials of a high heat conductive adhesive tape which can express high adhesiveness and high heat conductivity through an adhesive layer, and high heat conductive adhesive which consists of it Tape can be provided with high productivity.

<Biaxially stretched thermoplastic resin film>
The biaxially stretched thermoplastic resin film of the present invention contains a fibrous carbon material and is used as a base material for a high thermal conductive pressure-sensitive adhesive tape. The average fiber diameter of the fibrous carbon material is 0.05 to 5 μm, the average aspect ratio is 15 or more, and the content of the fibrous carbon material is more than 1 wt% and 20 wt% or less. The centerline average roughness Ra of the film in the present invention is 4 nm or more and 100 nm or less, and the thermal conductivity in the film thickness direction is 0.28 W / (m · K) or more.

Hereinafter, each structural component which comprises the biaxially stretched thermoplastic resin film of this invention is demonstrated.
<Fibrous carbon material>
The fibrous carbon material in the present invention is not particularly limited as long as it is a fibrous carbon material and satisfies the thermal conductivity and surface roughness characteristics defined by the present invention, preferably carbon nanofibers, Examples include carbon nanotubes. These carbon materials not only have extremely high thermal conductivity, but also have excellent thermal stability, dimensional stability, chemical stability, mechanical strength, etc., and can improve the film forming property. Are particularly preferably used.
The fibrous shape in the present invention includes not only a cylindrical shape but also a kamaboko shape and a plate shape.

  The average fiber diameter of the fibrous carbon material in the present invention is 0.05 to 5 μm. When the average fiber diameter of the fibrous carbon material is in the above numerical range, the thermal conductivity and the film-forming property are simultaneously excellent. With regard to the high thermal conductivity characteristics, when the fibrous carbon material is contained in the polyester film and biaxially stretched, the use of the fibrous carbon material having such a small fiber diameter makes it difficult for voids to occur, and the fibrous carbon material. It is considered that the thermal conductivity of itself is efficiently expressed without being impaired even in the state of the film.

  When the average fiber diameter of the fibrous carbon material is too small, the thermal conductivity is inferior, and the fibrous carbon material is difficult to disperse, so that the film forming property tends to be lowered. On the other hand, if the average fiber diameter is too large, voids are likely to be formed at the interface between the fiber and the matrix resin due to stretching, and the thermal conductivity is lowered. Tend to. From such a viewpoint, the average fiber diameter of the fibrous carbon material is more preferably 0.05 to 3 μm, further preferably 0.05 to 1 μm, and particularly preferably 0.05 to 0.2 μm.

The average aspect ratio of the fibrous carbon material in the present invention is 15 or more, preferably 20 or more, more preferably 40 or more, and particularly preferably 100 or more. When the average aspect ratio of the fibrous carbon material is in the above numerical range, the thermal conductivity and the film forming property are simultaneously excellent. If the average aspect ratio is too small, the thermal conductivity tends to decrease.
The upper limit of the average aspect ratio of the fibrous carbon material is not particularly limited, but is preferably 10,000 or less, more preferably 1000 or less, still more preferably 500 or less, and particularly preferably 200 or less.
Here, the average aspect ratio of the fibrous carbon material is expressed by average fiber length / average fiber diameter, and the average aspect ratio in the case of a plate shape is expressed by average long diameter / average thickness. In the case of a semi-cylindrical shape, an average fiber diameter can be obtained by measuring a linear portion of the outer edge of the semicircular cross section.
These average fiber diameters and average fiber lengths can be determined from the average values of 50 measured using a scanning electron microscope.

The true density of the fibrous carbon material in the present invention is preferably 2.0 to 2.5 g / cc. When the true density is in the above numerical range, the effect of improving thermal conductivity can be increased.
The average fiber length of the fibrous carbon material in the present invention is not particularly limited as long as it satisfies the above aspect ratio, but is preferably 0.75 to 4000 μm, more preferably 3 to 2000 μm, still more preferably 5 to 500 μm, Especially preferably, it is 5-100 micrometers.
The fibrous carbon material may be subjected to a surface treatment as necessary. Such surface treatment includes surface activation treatment for enhancing dispersibility in the film.

  In the present invention, the content of the fibrous carbon material in the film is more than 1% by weight and 20% by weight or less based on the weight of the film. In the present invention, by containing a fibrous carbon material having a small average fiber diameter and a high aspect ratio in the film, generation of voids in the biaxially stretched thermoplastic resin film is suppressed. High thermal conductivity can be exhibited without increasing the thickness, and at the same time, a certain electrical insulation can be provided, and the film forming property and the film surface property are also excellent.

On the other hand, when the content of the fibrous carbon material is increased, the thermal conductivity tends to be improved, but the film forming property, the film surface property, and the electrical insulating property tend to be poor. From such a viewpoint, the upper limit of the fibrous carbon material is preferably 15% by weight or less, more preferably 12% by weight or less. The lower limit of the fibrous carbon material is preferably 2% by weight or more, more preferably 3% by weight or more, and further preferably 5% by weight or more.
Moreover, when using together heat conductive fillers other than the fibrous carbon material mentioned later with a fibrous carbon material, you may reduce the quantity of a fibrous carbon material within this range.

(Carbon nanofiber / carbon nanotube)
The carbon nanotube is an allotrope of carbon, in which a plurality of carbon atoms are bonded and arranged in a cylindrical shape, and the average fiber diameter is preferably 0.1 μm or less.
Arbitrary carbon nanotubes can be used as the carbon nanotubes. Examples of carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes, and those in which they are coiled.
Single-walled carbon nanotubes are composed of single-walled graphite-like carbon atoms, and multi-walled carbon nanotubes are composed of two or more layers of graphite-like carbon atoms concentrically, and any carbon nanotube may be used. Further, carbon nanohorns having a shape in which one side of the carbon nanotube is closed, a cup-shaped nanocarbon material having a hole in its head, a carbon nanotube having holes in both sides, and the like can also be used.

The average fiber diameter of the carbon nanofiber is preferably 0.1 μm or more and 0.9 μm or less, and vapor grown carbon fiber is exemplified.
The carbon nanofibers and carbon nanotubes may be purified by washing, centrifugation, filtration, oxidation, chromatography, or the like, or may be unpurified. Further, the carbon nanofibers and the carbon nanotubes may be dispersed in a state where they are separated one by one in the film, or may be dispersed in a state where a plurality of carbon nanofibers and carbon nanotubes are bundled.

<Thermal conductive filler other than fibrous carbon material>
The biaxially stretched thermoplastic resin film of the present invention may further contain a thermally conductive filler different from the fibrous carbon material. By simultaneously containing the fibrous carbon material described above and a thermally conductive filler other than the carbon material, the thermal conductivity of the film can be further enhanced by a synergistic effect, and the effect of improving the thermal conductivity is further increased. be able to.
Furthermore, when it contains a heat conductive filler, it is preferable that content of a heat conductive filler is 1 to 40 weight% on the basis of the weight of a film. When content of a heat conductive filler exists in the said numerical value range, the heat conductive improvement effect can be made higher, maintaining film forming property. The content of the heat conductive filler is more preferably 5 to 30% by weight, still more preferably 10 to 20% by weight. When a plurality of types of thermally conductive fillers are used at the same time, the total content of these may be in the above numerical range.
Examples of such a thermally conductive filler include graphite, aluminum oxide, silicon oxide, boron nitride, aluminum nitride, and other ceramic materials, and those having a particle shape are preferable.

<Thermoplastic resin>
The thermoplastic resin constituting the film of the present invention is not particularly limited, and various types can be used. Among them, sheet formability by melt extrusion or the like, and extension in the in-plane direction by heat stretching, among others. A thermoplastic resin having excellent properties is preferred. In the present invention, the thermoplastic resin also includes a thermoplastic elastomer resin.
These thermoplastic resins include polyolefin resins and copolymers thereof (polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate. Copolymers, ethylene-α-olefin copolymers such as ethylene-propylene copolymers), polylactic acid resins, polyester resins and copolymers thereof (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalene dicarboxylate, Liquid crystalline polymer), aliphatic polyamides and copolymers thereof, aromatic polyamides and copolymers thereof, and the like.

Furthermore, polyimides and copolymers thereof, polyamideimides and copolymers thereof, polymethacrylic acids and copolymers thereof (polymethacrylates such as polymethyl methacrylate), polyacrylic acids and copolymers thereof, Polyacetals and copolymers thereof, fluororesins and copolymers thereof (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polystyrenes and copolymers thereof (styrene-acrylonitrile copolymers, ABS resins, etc.), polyacrylonitrile And copolymers thereof, polyphenylene ethers (PPE) and copolymers thereof (including modified PPE resins), polycarbonates and copolymers thereof, polyphenylene sulfides and copolymers thereof, polysulfones and copolymers thereof Coalescence, polyethersulfone and its Copolymers, polyether nitriles and their copolymers, polyether ketones and copolymers thereof, polyetheretherketones and copolymers thereof include polyketones and copolymers thereof, and the like.
Among these, preferred thermoplastic resins include polyester resins and copolymers thereof, and among them, at least one of polyethylene terephthalate or polyethylene naphthalene dicarboxylate is preferred. By using these polyesters, the film-forming property is excellent, and the balance between the film-forming property and the thermal conductivity can be improved.

(polyester)
When polyester is used as the thermoplastic resin, specifically, it is a polymer obtained by polycondensation of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative.
Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid and sebacic acid. Examples of the diol component include ethylene glycol and trimethylene glycol. 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol. Among the polyesters obtained by polycondensation of these dicarboxylic acid components and diol components, polyethylene terephthalate and polyethylene naphthalene dicarboxylate are preferable, and polyethylene-2,6-naphthalene dicarboxylate is particularly preferable from the viewpoint of heat resistance.

The polyester of the present invention may be a homopolymer, or may be a copolymer or a mixture of two or more polyesters. The subordinate component in the copolymer or mixture is preferably 20 mol% or less, more preferably 10 mol% or less, still more preferably 5 mol% or less, based on the total acid component.
As copolymerization components, diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, etc. Of the dicarboxylic acid component.

  Such polyester can be produced by applying a known method. For example, it can be produced by a method in which a diol component, a dicarboxylic acid component and, if necessary, a copolymerization component are esterified, and then a reaction product obtained is subjected to a polycondensation reaction to obtain a polyester. Alternatively, these raw material monomer derivatives may be transesterified, and then the resulting reaction product may be subjected to a polycondensation reaction to obtain a polyester.

  The intrinsic viscosity of the polyester is preferably 0.40 dl / g or more, more preferably 0.40 dl / g or more and 0.80 dl / g or less at 35 ° C. in o-chlorophenol. When the intrinsic viscosity is less than 0.40 dl / g, cutting may occur frequently during film formation, or product strength after molding may be insufficient. On the other hand, when the intrinsic viscosity exceeds 0.80 dl / g, the productivity during polymerization tends to decrease.

<Film centerline average roughness Ra>
In the biaxially stretched thermoplastic resin film of the present invention, the center line average roughness Ra of the film is 4 nm or more and 100 nm or less. Although it contains a certain amount of fiber-shaped carbon material, it has a flatter surface than before, so the thickness required to obtain a uniform adhesive force when providing an adhesive layer can be reduced, and high adhesion and high thermal conductivity It is possible to provide a highly heat conductive pressure-sensitive adhesive tape having the property.
The center line average roughness Ra of the film is preferably 5 nm to 85 nm, more preferably 5 nm to 50 nm, and still more preferably 5 nm to 20 nm.
In order to obtain such surface properties, the average fiber diameter of the fibrous carbon material and the content thereof may be set in the above-mentioned range. Further, when a thermally conductive filler other than the fibrous carbon material is used, the content thereof Is used within the above-mentioned range.

<Thermal conductivity in the film thickness direction>
The thermal conductivity in the thickness direction of the biaxially stretched thermoplastic resin film of the present invention is 0.28 W / (m · K) or more. The thermal conductivity is preferably 0.30 W / (m · K) or more, more preferably 0.31 W / (m · K) or more. The upper limit of the thermal conductivity in the thickness direction is preferably 0.50 W / (m · K) or less, more preferably 0.48 W / (m · K) or less, and still more preferably 0.45 W / (m · K) or less, particularly preferably 0.42 W / (m · K) or less.
By having such a thermal conductivity in the thickness direction of the film, the thermal conductivity is excellent, so that heat generated from the devices of the heat source can be sufficiently dissipated to the heat radiating member when used as an adhesive tape. On the other hand, although higher heat conductivity is preferable, it is necessary to increase the content of the fibrous carbon material in order to obtain higher heat conductivity, and the film surface may become too rough.

  The biaxially stretched thermoplastic resin film of the present invention preferably has a thermal conductivity in the plane direction of 0.95 W / (m · K) or more and 20 W / (m · K) or less. When the thermal conductivity in the surface direction is within the range, the effect of improving the film forming property and thermal conductivity can be increased. If the thermal conductivity in the plane direction is less than the lower limit, it may be difficult to efficiently perform thermal conduction and thermal diffusion in the in-plane direction, and the effect of improving thermal conductivity may be reduced. On the other hand, when it is going to obtain the heat conductivity of the surface direction exceeding 20 W / (m * K), film forming property may become scarce. From such a viewpoint, the thermal conductivity in the plane direction is more preferably 1.0 W / (m · K) or more and 10 W / (m · K) or less, and further preferably 1.0 W / (m · K) or more and 5 W. / (M · K).

In order to obtain such thermal conductivity characteristics, the shape and content of the fibrous carbon material, film forming conditions, and the like may be appropriately adjusted. Moreover, the thermal conductivity tends to be further increased by using a thermally conductive filler other than the fibrous carbon material.
Here, the thermal conductivity in the present invention is the thermal conductivity λ (W from the following formula (1) from the thermal diffusivity α determined by the laser flash method, the specific heat capacity Cp measured according to JIS K7123, and the density ρ. / Cm · K) and is expressed as a unit converted value.
Thermal conductivity λ = α · Cp · ρ (1)
The thermal conductivity in the thickness direction can be obtained by cutting a film sample into 25 mmφ and measuring the thickness direction as a measurement direction.

<Film thickness>
The thickness of the biaxially stretched thermoplastic resin film of the present invention is preferably 5 μm to 100 μm, more preferably 10 μm to 90 μm, and still more preferably 20 μm to 80 μm. If the film thickness is less than the lower limit, the handleability and strength as an adhesive tape substrate may not be sufficient. On the other hand, when the film thickness exceeds the upper limit, the thermal conductivity function may be deteriorated.

<Electrical insulation layer>
The biaxially stretched thermoplastic resin film of the present invention has sufficient electrical insulation properties even without providing an electrical insulation layer, but is preferably 3 μm or less as long as the high thermal conductivity of the film itself is not impaired. May have an electrical insulation layer laminated on one or both sides of the film within a range of 2 μm or less.
The electrical insulation layer preferably has a level of electrical insulation required for various applications. For example, the volume resistivity is preferably at least 1E13 (Ω · cm) or more, more preferably 1E14 (Ω · cm). ) That's it.
When the electrical insulating layer having a thickness exceeding the upper limit is provided on both surfaces of the film, the thermal resistance of the layer increases, and the presence of the electrical insulating layer may hinder the flow of heat.
Examples of the resin constituting the electrical insulating layer include the same materials as those used for the highly thermally conductive biaxially stretched thermoplastic resin film of the present invention.

<Adhesive layer>
The biaxially stretched thermoplastic resin film of the present invention is preferably provided with an adhesive layer on at least one side, more preferably on both sides. By releasing the heat generated from the devices to heat dissipation parts such as heat sinks and metal covers via the high thermal conductive adhesive tape having an adhesive layer, the interface between the devices and the high thermal conductive adhesive tape or the high thermal conductive adhesive tape and It becomes easy to conduct heat without hindering the flow of heat at the interface with the heat dissipation component.
The thickness of the adhesive layer is preferably 1 μm or more and 100 μm or less, and more preferably 1 μm or more and 50 μm or less per layer. By setting the thickness of the adhesive layer to the above numerical range, the thermal conductivity as an adhesive tape is excellent. If the thickness exceeds the upper limit, the thermal resistance of the layer increases, and the heat flow tends to be hindered.
In the present invention, since the biaxially stretched thermoplastic resin film contains a large amount of fibrous material, the film surface has high flatness, so that the adhesive layer can be formed thin, and the adhesive layer has a uniform adhesive surface. The thermal resistance due to the layer can be reduced.

As the resin constituting the adhesive layer, the same materials as those used in the highly thermally conductive biaxially stretched thermoplastic resin film of the present invention, copolymer materials and / or modified materials thereof, and acrylics widely used as adhesives Examples thereof include an adhesive material and an epoxy-based adhesive material, and it is preferable to use an amorphous material having a melting point lower than that of the resin constituting the high thermal conductivity biaxially stretched thermoplastic resin film or not showing the melting point.
For the purpose of increasing the thermal conductivity of the layer, the above-mentioned fibrous carbon material or thermal conductive filler may be added to the adhesive layer, but if the content of these is too large, the adhesive performance may be reduced. When formed by coextrusion with a biaxially stretched thermoplastic resin film, the film forming property may be lowered. Therefore, the pressure-sensitive adhesive layer does not substantially contain a fibrous carbon material or a heat conductive filler (preferably 1% by weight or less, more preferably 0.5% by weight or less, and further preferably 0.1% by weight or less. Embodiment) is preferred.

<Film manufacturing method>
The method for obtaining the biaxially stretched thermoplastic resin film of the present invention is specifically described below, but is not particularly limited to the following examples.
The biaxially stretched thermoplastic resin film of the present invention is a biaxially stretched sheet obtained by melt-kneading a thermoplastic resin, a fibrous carbon material, and an agent to be further added as necessary, using an extruder, melt-extruding, and then solidifying and forming the sheet. It can manufacture by extending | stretching to a direction and can manufacture using a well-known film forming method.

  As an example, after the thermoplastic resin is dried as necessary, the resin composition is melted in an extruder at a temperature of the melting point of the resin to (melting point + 70) ° C. Here, the fibrous carbon material to be mixed with the thermoplastic resin may be added and mixed in advance in the step of producing the resin (for example, the polymerization step), or the resin (generally handled as a polymer chip). It may be added before drying and mixed well, or may be added and mixed after drying. When adding and mixing after drying, it may be before adding to the extruder, or may be added to the resin and mixed in the extruder.

  Subsequently, the sheet-like molded product extruded from the die is cooled and solidified with a cooling drum having a surface temperature of 10 to 60 ° C. to obtain an unstretched film. The unstretched film is heated by, for example, roll heating or infrared heating, and then sequentially or Simultaneously, biaxial stretching is performed. For example, in the case of sequential biaxial stretching, first, a longitudinally stretched film is obtained by stretching in the machine axis direction (which may be referred to as a longitudinal direction, a longitudinal direction, or MD). Such longitudinal stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The longitudinal stretching temperature is preferably higher than the glass transition temperature (Tg) of the thermoplastic resin, and more preferably 20 to 40 ° C. higher than Tg.

The longitudinal draw ratio is preferably in the range of 1.1 to 3.0 times, more preferably in the range of 1.3 to 2.8 times, and still more preferably in the range of 1.5 to 2.8 times. It is a range. When the longitudinal stretch ratio is too low, the strength as a heat conductive film may not be sufficient, and the thickness unevenness of the film may deteriorate and a good film may not be obtained. Further, the orientation of the thermoplastic resin tends to be low, and thereby the effect of improving the thermal conductivity tends to be low. On the other hand, when the longitudinal draw ratio is too high, crystallization and orientation are promoted by the fibrous carbon material, and tend to tear in the longitudinal direction. Further, the film tends to break during film formation, and the effect of improving the film forming property tends to decrease.
The obtained longitudinally stretched film is subsequently stretched in the direction perpendicular to the machine axis direction (transverse direction, width direction, sometimes referred to as TD), and then subjected to heat fixation and thermal relaxation treatment in sequence. Although it is set as a biaxially oriented film, this process is performed while running the film.

The transverse stretching treatment is carried out while starting from a temperature 20 ° C. higher than the glass transition temperature (Tg) of the thermoplastic resin and increasing the temperature to a temperature lower by 120 to 30 ° C. than the melting point (Tm) of the thermoplastic resin. The transverse stretching start temperature is preferably (Tg + 40) ° C. or lower. The maximum transverse stretching temperature is preferably a temperature lower by (100 to 40) ° C. than Tm. When the transverse stretching start temperature is too low, the film is easily broken. When the maximum transverse stretching temperature is lower than (Tm−120) ° C., the thermal shrinkage rate of the obtained film increases, and the uniformity of physical properties in the width direction tends to be lowered. On the other hand, when the maximum transverse stretching temperature is higher than (Tm-30) ° C., the film becomes too soft, and the film tends to be easily broken during film formation, and the productivity improvement effect is lowered.
Although the temperature increase in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually increased stepwise. For example, the transverse stretching zone of the stenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone.

  The transverse draw ratio is preferably in the range of 2.1 times to 4.0 times, more preferably in the range of 2.5 times to 3.8 times, and still more preferably in the range of 2.8 times to 3.5 times. It is a range. When the transverse draw ratio is too low, the productivity improvement effect tends to be low, and the thermal conductivity improvement effect tends to be low. In addition, the strength of the film tends to be low, and the thickness unevenness of the film is deteriorated, so that a good film may not be obtained. On the other hand, when the transverse stretching ratio is too high, the film tends to break during stretching. Further, the film tends to break during film formation, and the effect of improving the film forming property tends to decrease.

  In the present invention, it is a particularly preferable production method to simultaneously adopt the specific longitudinal stretch ratio and lateral stretch ratio ranges as described above. By adopting such stretching conditions, it is possible to appropriately orient the film and the fibrous carbon material, and to further enhance the effect of improving thermal conductivity. Moreover, by setting the longitudinal stretch ratio to be lower than the lateral stretch ratio, it is possible to suppress film breakage during lateral stretching and to further improve the film-forming property.

The biaxially stretched film is then heat set. By performing the heat setting treatment, the dimensional stability of the obtained film under high temperature conditions can be enhanced. The heat setting treatment is preferably (Tm-100 ° C) or more, more preferably (Tm-70) ° C to (Tm-40) ° C.
For example, when polyethylene naphthalene dicarboxylate is used as the thermoplastic resin, it is preferably carried out in the range of 220 ° C to 250 ° C. In addition, after heat setting treatment, heat relaxation treatment of 1 to 3% at a temperature condition of 150 ° C. to 250 ° C., heat treatment (anneal treatment) at 150 to 250 ° C. for 5 minutes or more in an offline process, and cooling at 50 to 80 ° C. Annealing treatment or the like may be performed. The upper limit of the annealing treatment time is not particularly limited, but if it is too long, the film physical properties may be lowered, and therefore it is preferably at most 1 hour.

When a coating layer is further formed on at least one surface of the biaxially stretched thermoplastic resin film thus obtained, the film surface is subjected to corona surface treatment, flame treatment, plasma treatment as a preliminary treatment for improving coatability. Or a chemically inert surfactant may be used in combination with the composition.
As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method and the like can be used alone or in combination.

<High thermal conductive adhesive tape>
In the present invention, it is preferable to form an adhesive layer on at least one side, preferably both sides, of the biaxially stretched thermoplastic resin film of the present invention and use it as a high thermal conductive adhesive tape. Since the high thermal conductive pressure-sensitive adhesive tape of the present invention is formed using a film having a smoother film surface than a conventional high thermal conductive film, even if the thickness of the pressure-sensitive adhesive layer is reduced, uniform adhesive force can be obtained. It has excellent high thermal conductivity.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited thereto. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

1. Average fiber diameter and average aspect ratio of fibrous carbon material Using a field emission scanning electron microscope (Hitachi S-4700), the fiber diameter and fiber length of 50 fibrous carbon materials were measured at a magnification of 10,000 times, and the respective averages were measured. The average fiber diameter and average aspect ratio (average fiber length / average fiber diameter) were determined from the values.

2. The thickness of each layer of the film The sample was cut into 1 cm in the longitudinal direction and 3 cm in the width direction, and cut perpendicularly to the width direction using a razor blade. The cross section of the sample was observed and photographed using an optical microscope, and the thickness of each layer was measured from the photograph.

3. Film forming property The film was evaluated as follows according to the number of times the film was cut when 10,000 m was formed by a continuous film forming machine.
○: No break (0 times)
Δ: 1 to 2 times ×: 3 times or more

4). Thermal conductivity Using a xenon flash analyzer (manufactured by NETZSCH; LFA447), the thermal diffusivity α (cm ² / sec) in the thickness direction was measured, and the specific heat capacity Cp (J / g · K) and density ρ (g / Cc), the thermal conductivity λ (W / cm · K) in the thickness direction was obtained by λ = α · Cp · ρ, and evaluation was performed using the values obtained by unit conversion.
The thickness-direction thermal diffusivity α was measured by cutting a film sample to 25 mmφ. The surface direction was measured by slitting a film sample to a width of 3 mm and winding the sample around a cylindrical wood having a diameter of 2 mm so that the diameter became 10 mmφ.
The density ρ can be obtained by measuring with a density gradient tube method using an aqueous calcium nitrate solution.
The specific heat capacity Cp is a value measured according to JIS K 7123.

5. Centerline average roughness (Ra)
In accordance with JIS-B0601, B0651, using a three-dimensional surface roughness meter (trade name: SURF CORDER SE-3CK, manufactured by Kosaka Laboratory Ltd.), stylus tip R2 μm, scanning pitch 2 μm, scanning length 1 mm, scanning The center line average roughness Ra was measured under the conditions of 100 pieces and a cutoff of 0.25 mm.

6). Volume resistivity (Evaluation of electrical insulation)
In accordance with JIS C2151, the volume resistance (Rv) at a voltage of 100 V was measured using a digital ultrahigh resistance / microammeter manufactured by Advantest Corporation, and the volume resistivity (ρv) was calculated by the following formula.
ρv = 18.84 × Rv

7). Substrate temperature On the biaxially oriented film (5 cm square) obtained in the following examples and comparative examples, a commercially available acrylic adhesive was applied on both sides to be 15 μm, and four 3 W LED chips were placed on one side. The other side was bonded to a 5 cm square 1.5 mm thick aluminum plate.
After 2 hours had passed since the LED was turned on, the temperature of the central portion of the CEM-3 substrate was measured.

<Example 1>
Polyethylene-2,6-naphthalenedicarboxylate resin is used as the polyester, and a fibrous carbon material with an aspect ratio of 167 (multi-walled carbon nanotube, MWNT7 manufactured by Hodogaya Chemical Co., Ltd. (average fiber diameter 0.06 μm, average fiber length 10 μm)) Was added to a content of 2% by weight based on the film weight, and the resin composition was supplied to an extruder and melt-kneaded at 290 ° C.
The melt-kneaded resin was extruded through a die slit and then cooled and solidified on a casting drum set at a surface temperature of 60 ° C. to prepare an unstretched film.
This unstretched film was led to a roll group heated to 140 ° C., stretched 1.5 times in the longitudinal direction (longitudinal direction), and cooled by a roll group at 60 ° C. Subsequently, the film was stretched by 3.0 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 150 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 235 ° C. in a tenter, the mixture was uniformly cooled, and cooled to room temperature to obtain a 25 μm biaxially stretched polyester film. The obtained film characteristics are shown in Table 1.
In addition, since the biaxially stretched polyester film surface is smooth, a 15 μm-thick adhesive layer was formed on the film in the same manner as the sample preparation for the substrate temperature, and the surface was observed. It was smooth like the above, and no roughening due to the fibrous carbon material was observed.

<Example 2>
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the same fibrous carbon material as in Example 1 was used and the carbon fiber content was changed to 5% by weight. The obtained film characteristics are shown in Table 1.

<Example 3>
A biaxially stretched polyester film was obtained by the same method as in Example 1 except that the same fibrous carbon material as in Example 1 was used and the carbon fiber content was changed to 10% by weight. The obtained film characteristics are shown in Table 1.

<Example 4>
Using the same fibrous carbon material as in Example 1 for the heat conductive layer, the carbon fiber content was changed to 5% by weight, and another polyethylene-2,6-naphthalenedicarboxylate resin was used for the electrical insulating layer. The mixture was supplied to an extruder and melt kneaded at 290 ° C.
Each of the melt-kneaded resins is laminated in two layers (high thermal conductive layer thickness: electrical insulating layer thickness = 96: 4), and the same method as in Example 1 except that the extruded state is maintained while maintaining such a laminated state. A biaxially stretched polyester film was obtained. The obtained film characteristics are shown in Table 1.

<Example 5>
A biaxially stretched polyester film was prepared in the same manner as in Example 2 except that the film stretching ratio was 2.8 times in the longitudinal direction (longitudinal direction) and 3.0 times in the direction perpendicular to the longitudinal direction (lateral direction). Got. The obtained film characteristics are shown in Table 1.

<Example 6>
A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that the thickness of the biaxially stretched polyester film was 75 μm. The obtained film characteristics are shown in Table 1.

<Example 7>
Example except that the type of fibrous carbon material was changed to VGCF-H (carbon nanofiber (vapor-grown carbon fiber) average fiber diameter 0.15 μm, average fiber length 6 μm, aspect ratio 40) manufactured by Showa Denko KK A biaxially stretched polyester film was obtained by the same method as 2. The obtained film characteristics are shown in Table 1.

<Example 8>
Polyethylene terephthalate resin is used as the polyester, the melting temperature is changed to 280 ° C., the longitudinal roll temperature is changed to 80 ° C., and the subsequent cooling roll temperature is changed to 20 ° C., the transverse stretching heating temperature is set to 120 ° C., and the heat fixing temperature is set to 220 ° C. A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that the temperature was changed to ° C. The obtained film characteristics are shown in Table 1.

<Example 9>
In addition to the fibrous carbon material, artificial graphite (SCMG-AF manufactured by Showa Denko KK) was further added biaxially in the same manner as in Example 2 except that the content was 15% by weight based on the film weight. A polyester film was obtained. The obtained film characteristics are shown in Table 1.
Although the film smoothness is somewhat lower than in Example 1, when the surface of the 15 μm-thick adhesive layer was formed on the film by the same method as the sample preparation for the substrate temperature, the surface of the adhesive layer was smooth. No roughness due to the fibrous carbon material was observed.

<Example 10>
In addition to the fibrous carbon material, boron nitride having an average particle size of 5 μm (BN Powder PT-180 manufactured by Momentive Performance Materials Japan GK) was added to a content of 15% by weight based on the film weight. A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that. The obtained film characteristics are shown in Table 1.

<Comparative Example 1>
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the content of the fibrous carbon material was changed to 1% by weight. The obtained film characteristics are shown in Table 1.

<Comparative example 2>
An unstretched film was obtained in the same manner as in Example 1 except that the content of the fibrous carbon material was changed to 30% by weight. However, the unstretched film could not be stretched and a biaxially stretched polyester film could not be obtained.

<Comparative Example 3>
Biaxially stretched polyester film by the same method as in Example 3 except that the type of fibrous carbon material was changed to Rahema R-A301 (carbon fiber average fiber diameter 8 μm, average fiber length 200 μm, aspect ratio 25) manufactured by Teijin Ltd. Got. The obtained film characteristics are shown in Table 1.
Surface roughness due to the fibrous carbon material was observed on the film surface, and when a 15 μm thick adhesive layer was formed on the film by the same method as the sample preparation for substrate temperature, the surface was observed. Surface roughness due to the fibrous carbon material was observed.

<Comparative example 4>
Example 1 except that alumina spherical particles having an average particle diameter of 5 μm (alumina beads CB-A05S manufactured by Showa Denko KK) were added instead of the fibrous carbon material so as to have a content of 30% by weight based on the film weight. A biaxially stretched polyester film was obtained by the same method. The obtained film characteristics are shown in Table 1.

<Comparative Example 5>
Instead of fibrous carbon material, boron nitride having an average particle size of 5 μm (BN powder PT-180 manufactured by Momentive Performance Materials Japan GK) was added to a content of 15% by weight based on the film weight. Obtained a biaxially stretched polyester film by the same method as in Example 1. The obtained film characteristics are shown in Table 1.

PEN: Polyethylene-2,6-naphthalene dicarboxylate PET: Polyethylene terephthalate CNT: Multi-walled carbon nanotube CNF: Carbon nanofiber (vapor-grown carbon fiber)
BN: Boron nitride CF: Carbon fiber Al ₂ O ₃ : Alumina spherical particles

  ADVANTAGE OF THE INVENTION According to this invention, when using as an adhesive tape, the biaxially stretched thermoplastic resin film for base materials of a high heat conductive adhesive tape which can express high adhesiveness and high heat conductivity through an adhesive layer, and high heat conductive adhesive which consists of it Tape can be provided with high productivity.

Claims (7)

  The biaxially stretched average fiber diameter including the fibrous carbon material is 0.05 to 5 μm, and the average aspect ratio is 15 or more. In the thermoplastic resin film, the fibrous carbon material has a content of the fibrous carbon material of 1. It exceeds 20% by weight and is 20% by weight or less, the center line average roughness Ra of the film is 4 nm or more and 100 nm or less, and the thermal conductivity in the film thickness direction is 0.28 W / (m · K) or more. A biaxially stretched thermoplastic resin film for a highly thermally conductive pressure-sensitive adhesive tape substrate.   The biaxially stretched thermoplastic resin film for a highly thermally conductive pressure-sensitive adhesive tape substrate according to claim 1, wherein the thermoplastic resin constituting the film is polyester.   The biaxially stretched thermoplastic resin film for a highly thermally conductive pressure-sensitive adhesive tape substrate according to claim 2, wherein the polyester constituting the film is at least one of polyethylene terephthalate or polyethylene naphthalene dicarboxylate.   The biaxially stretched thermoplastic resin film for a highly thermally conductive pressure-sensitive adhesive tape substrate according to any one of claims 1 to 3, wherein the film thickness is 5 µm or more and 100 µm.   The high heat conductive adhesive tape which has an adhesive layer in the at least single side | surface of the biaxially stretched thermoplastic resin film for high heat conductive adhesive tape base materials in any one of Claims 1-4.   The high thermal conductive pressure-sensitive adhesive tape according to claim 5, wherein the pressure-sensitive adhesive layer has a thickness of 1 μm to 100 μm.   The high thermal conductive adhesive tape according to claim 5 or 6, wherein the adhesive layer contains an acrylic or epoxy adhesive.