JP4938466B2 - Electronic mounting board, light reflective heat conductive coverlay film - Google Patents

Description

  The present invention relates to a functional composite filler having high light reflectivity and thermal conductivity and suitable for coating on various substrates and a resin composition thereof, for example, a light reflection film used for a backlight of a liquid crystal display, an LED, It is preferably applied to the use of a mounting substrate on which a laser diode or the like is mounted.

  With the recent increase in the size of liquid crystal displays, etc., there is a growing need for improving the brightness of the backlight, but as a result, more heat is generated in the backlight part than before, and this heat dissipation measure Is an urgent need. For example, as a light reflecting film provided on the back side of a direct type backlight, a plastic film having a large number of holes (for example, Reference 1) is often used, but in a portion directly under a cold cathode tube, In particular, a large temperature rise is observed, and this heat dissipation measure is becoming important.

  In addition, in a wiring board on which a light emitting element such as an LED or a laser diode is mounted, it is necessary to form a path that can effectively dissipate heat generated by the light emitting element.

On the other hand, with respect to the functional compounding technique on the filler surface, a technique for forming a plating layer on the surface of fine particles by, for example, an electrolytic plating method using a barrel plating apparatus has been proposed. (For example, Reference 2)
Regarding heat dissipation measures for the light reflecting film, for example, by laminating a layer having high thermal conductivity (hereinafter referred to as a heat conducting layer) on the surface opposite to the surface facing the light source of the film, the film was accumulated inside the film. It is considered that this can be realized by transferring heat to the heat conductive layer and further transporting it in the plane or in the thickness direction of the heat conductive layer.

  The heat conductive layer is preferably laminated with a thickness of at least several μm from the viewpoint of securing the amount of transport heat, and a method of laminating a metal foil having a high thermal conductivity via an adhesive layer or a high heat in which a filler having a high thermal conductivity is dispersed. A method of laminating a conductive resin layer is preferable.

  However, the method of laminating the metal foil has problems such as the occurrence of warpage due to the difference from the thermal expansion coefficient of the light reflecting film and the inhibition of heat conduction through the adhesive layer, and the method of laminating the heat conductive resin layer However, when the light reflectance of the layer does not have a sufficiently high value, there has been a problem that the light reflectance of the surface of the light reflecting film facing the light source is remarkably lowered.

Further, as a heat dissipation measure for a wiring board for mounting a light emitting element, a method of pattern-laminating a heat conductive resin layer functioning as a heat conduction path on the surface of the wiring board on the light emitting element mounting surface side is conceivable. However, in these wiring boards, it is often necessary to increase the light reflectivity of the substrate surface on which the light emitting element is mounted from the viewpoint of improving the light utilization efficiency. It was difficult to achieve both.
JP 2002-137350 A JP 2006-037228 A

The object of the present invention is to solve the problems of the prior art described above, and to provide a functional composite filler having high light reflectivity and thermal conductivity and suitable for coating on various substrates, and a resin composition comprising the same. It is an object of the present invention to provide a light-reflective heat-conductive coverlay film and an electronic mounting substrate used .

The present invention is as follows.
1. At least the side surface of the pitch-based graphitized carbon fiber filler having an average fiber diameter of 0.1 to 30 μm, an aspect ratio of 2 to 100, an average fiber length of 0.2 to 1000 μm, and a true density of 2.0 to 2.5 g / cc is a thickness. A light-reflective heat-conductive filler coated with a light-reflective layer of 0.01 to 10 μm and a binder resin, and the mixing ratio of the light-reflective heat-conductive filler is 5 to 80 in the total solid component A light-reflective heat-conductive resin layer having a thickness of 5 to 1000 μm, which is made of a light-reflective heat-conductive resin composition, is laminated on one side of an electrically insulating plastic film having a thickness of 1 to 100 μm and the other side A light-reflective heat-conductive coverlay film obtained by laminating an electrically insulating adhesive layer on the substrate.
2. 2. The light-reflective heat-conductive coverlay film according to 1 above, wherein the electrically insulating plastic film is a film having a thickness of 2 to 20 μm made of polyparaphenylene terephthalamide (PPTA).
3. An electronic mounting board comprising the light reflective heat conductive coverlay film of 1 or 2 and a wiring pattern of a mounting board laminated on an electrically insulating adhesive layer surface of the coverlay film.
4). At least the side surface of the pitch-based graphitized carbon fiber filler having an average fiber diameter of 0.1 to 30 μm, an aspect ratio of 2 to 100, an average fiber length of 0.2 to 1000 μm, and a true density of 2.0 to 2.5 g / cc is a thickness. A light-reflective heat-conductive filler coated with a light-reflective layer of 0.01 to 10 μm and a binder resin, and the mixing ratio of the light-reflective heat-conductive filler is 5 to 80 in the total solid component A light-reflective heat-conductive resin layer having a thickness of 5 to 1000 μm made of a light-reflective heat-conductive resin composition in weight% is placed on a wiring pattern of a mounting substrate via an electric insulating layer and / or an electric insulating adhesive layer. Electronic mounting board laminated on
5). 4. The electronic mounting board as described in 4 above , wherein the electrically insulating adhesive layer and / or electrically insulating adhesive layer is formed by laminating an electrically insulating adhesive layer on one surface of an electrically insulating plastic film having a thickness of 1 to 100 μm .

  Next, embodiments of the present invention will be described in detail.

  The light reflective thermally conductive filler used in the present invention is obtained by laminating a light reflective layer on the surface of a pitch-based graphitic carbon fiber having a very high thermal conductivity.

  Pitch-based graphitized carbon fibers are made of pitch hydrocarbons made of cyclic hydrocarbons such as petroleum and coal, and after undergoing spinning, infusibilization, carbonization firing, and extremely high temperature graphitization treatment, graphitized carbon Various performances as a fiber appear. Although graphitized carbon fiber is not a single crystal, it contains graphite crystals with a number of network structures. The characteristics derived from these crystals include higher electrical conductivity, thermal conductivity, and elasticity than PAN-based carbon fibers. And has a low thermal expansion coefficient comparable to that of ceramics.

  The thermal conductivity of graphite crystals is not as good as that of diamond, but is superior to metals such as silver and copper. Since it is a hexagonal crystal, it has anisotropy, and in particular, a value exceeding 600 W / m · K can be expressed in the hexagonal network direction of the graphite crystal.

  Therefore, these pitch-based graphitized fibers can be combined with resin materials and other types of materials to increase their thermal conductivity and conductivity, and to improve thermal dimensional stability and mechanical rigidity.

  The pitch-based graphitized carbon fiber used in the present invention preferably has a thermal conductivity in the fiber axis direction of at least 200 W / (m · K) or more, more preferably 300 W / (m · K) or more, and more It is preferably 400 W / (m · K) or more, and most preferably 500 W / (m · K) or more.

  In order to develop such a high thermal conductivity in the carbon fiber, it is preferable that the content of graphite crystals in the carbon fiber (hereinafter referred to as graphitization rate) is high, and that the crystallite size is large. It is preferable to realize conduction. This is due to the fact that the heat conduction in the carbon fiber is mainly carried by the phonon conduction.

  Regarding the graphitization rate, it is preferable that the true density of the pitch-based graphitized carbon fiber is in the range of 2.0 to 2.5 g / cc as a reflection value.

  Regarding the crystallite size, the crystallite size (Lc) in the c-axis direction of the graphite crystal (hexagonal network surface) in the carbon material is preferably in the range of 20 to 100 nm.

More preferably, the crystallite size (La) in the ab axis direction of the graphite crystal (hexagonal network surface) in the carbon material is preferably in the range of 30 to 200 nm.
These crystallite sizes can be obtained by the X-ray diffraction method. The Gakushin method is used as an analysis method, and the crystallite size is obtained by using diffraction lines from the (002) plane and the (110) plane of the graphite crystal. Can do.

  Thus, in order to obtain a carbon material with a very high graphitization rate, raw materials such as PAN and rayon are not so preferable as described above, and cyclic hydrocarbons having condensed heterocyclic rings, that is, pitch-based raw materials are used. It is preferable to use a liquid crystal mesophase pitch among them.

  As for the form of the carbon material, a spherical or indefinite shape can be used. Especially when a mesophase pitch is used, the growth surface of the graphite crystal is oriented almost in one direction to obtain extremely high thermal conductivity. It is more preferable that it is a fibrous shape that enables the above.

  From these things, the pitch-based graphitized carbon fiber using the pitch as a raw material is optimal as the carbon material used in the present invention.

  Examples of raw materials for such pitch-based carbon fibers include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch, and the like. In particular, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferred.

  In particular, an optically anisotropic pitch, that is, a mesophase pitch is preferable. These may be used singly or in appropriate combination of two or more, but the use of mesophase pitch alone can increase the graphitization rate in the graphitization treatment, and consequently The thermal conductivity of the carbon fiber can be improved, which is a preferred embodiment.

  The softening point of the raw material pitch can be determined by the Mettler method, and is preferably in the range of 230 ° C. or higher and 340 ° C. or lower. If the softening point is lower than 230 ° C., fusion between fibers or large heat shrinkage occurs during infusibilization. If the temperature is higher than 340 ° C., the pitch is thermally decomposed in the spinning process, which tends to make the spinning molding difficult. Furthermore, under high temperature spinning conditions, gas components are generated, bubbles are generated inside the spun fibers, leading to strength deterioration, and yarn breakage is likely to occur.

  The raw material pitch is spun by a known melt spinning method or melt blowing method, and then the pitch-based graphitized carbon, which has a relatively short fiber length by various processes of infusibilization, carbonization firing, milling, sieving, and graphitization, and is optimal as a filler Become fiber.

  Below, the process regarding pitch-type graphitized carbon fiber manufacture using a melt blow method is demonstrated as an example.

  First, the shape of the spinning nozzle is not particularly limited, but those having a ratio of the nozzle hole length to the hole diameter of less than 3 are preferably used, and more preferably about 1.5.

  There are no particular restrictions on the nozzle temperature during spinning, and there is no problem as long as the temperature can maintain a stable spinning state. If the viscosity of the raw material pitch is in an appropriate range, the spinning state is stabilized, that is, the pitch viscosity during spinning is 0.1 to 20 Pa · S, preferably 8 to 16 Pa · S, more preferably 10 to 14 Pa · S. The temperature may be S.

  The pitch fibers drawn out from the nozzle holes are shortened by blowing a gas having a linear velocity of 100 to 10000 m per minute heated to 100 to 370 ° C. in the vicinity of the thinning point. As the gas to be blown, air, nitrogen, argon or the like can be used, but air is preferable from the viewpoint of cost performance.

  The pitch fibers are collected on a wire mesh belt, become a continuous mat, and are further cross-wrapped to form a web having a predetermined basis weight (weight per unit area).

  The web made of pitch fibers thus obtained has a three-dimensional randomness due to the interlace of the fibers. These webs can be infusibilized by known methods.

  Infusibilization is achieved by applying heat treatment for a certain time at a temperature of about 200 to 300 ° C., for example, using air or a mixed gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine or bromine to air. . Considering safety and convenience, it is desirable to carry out in air.

  The infusible pitch fiber is then fired in a temperature range of 700 to 900 ° C. in a vacuum or in an inert gas such as nitrogen, argon or krypton. Usually, the calcination is performed at low pressure using nitrogen at low cost.

  The web made of infusibilized and fired pitch fibers is further milled and sieved in order to further shorten the fibers and to obtain a predetermined fiber length. For milling, a pulverizer or cutting machine such as a Victory mill, a jet mill, or a high-speed rotary mill is used. In order to perform milling efficiently, a method of cutting fibers in a direction perpendicular to the fiber axis by rotating a rotor to which blades are attached at high speed is appropriate.

  The average fiber length of the fibers generated by milling is controlled by adjusting the number of rotations of the rotor, the angle of the blade, and the like, and can be classified by a combination of the coarseness of the sieve through a sieve.

  The fiber after the milling and sieving is heated to 2300-3500 ° C. and graphitized to obtain a final pitch-based carbon short fiber. Graphitization is performed in a non-oxidizing atmosphere in an Atchison furnace or the like.

  The pitch-based graphitized carbon fiber filler used in the present invention preferably has a structure in which the graphene sheet is closed by observing the shape of the filler end face with a transmission electron microscope. When the end surface of the filler is closed as a graphene sheet, generation of extra functional groups and localization of electrons due to the shape do not occur, so that the concentration of impurities such as water can be reduced.

  Note that the graphene sheet is closed means that the end of the graphene sheet itself constituting the carbon fiber is not exposed at the end of the carbon fiber, the graphite layer is curved in a substantially U shape, and the curved portion is the end of the carbon fiber. It is in the state exposed to the part.

  The pitch-based graphitized carbon fiber filler used in the present invention has a substantially flat observation surface with a scanning electron microscope. Here, “substantially flat” means that the surface does not have severe unevenness like a fibril structure, and when there is intense unevenness on the surface of the filler, the surface area increases upon kneading with the matrix resin. It is desirable that the surface irregularities be as small as possible, since this causes an increase in the viscosity accompanying this and lowers the moldability.

  The pitch-based carbon fiber filler described above can be easily obtained by performing graphitization after milling.

  The fiber diameter of the pitch-based graphitized carbon fiber thus obtained is 1 to 30 μm as an average fiber diameter (D1) observed with an optical microscope, more preferably 3 to 20 μm, and further preferably 5 to 15 μm. When the fiber diameter is larger than 30 μm, adjacent fibers are likely to be fused in the infusibilization step. When the fiber diameter is less than 1 μm, the surface area per weight of the pitch-based carbon fiber filler is increased, and the fiber surface is substantially Even if it is flat, the formability may be lowered in the same manner as a fiber having irregularities on the surface, which may be inappropriate in practice. The percentage of the fiber diameter dispersion (S1), which is the dispersion of the fiber diameter with respect to the average fiber diameter (D1) observed with an optical microscope, is preferably in the range of 5 to 18%. More preferably, it is 5 to 15% of range.

  In addition to pitch-based graphitized carbon fibers using the melt blow spinning method described so far, pitch-based graphitized carbon fibers usable in the present invention include pitch-based graphitized carbon fibers obtained by melt spinning. . However, it is more preferable to use the pitch-based graphitized carbon fiber of this method because the melt blow spinning method is more excellent in the productivity and quality (surface properties, appearance, etc.) of the pitch-based graphitized carbon fiber.

  On the other hand, as a pitch-based graphitized carbon fiber whose fiber diameter is smaller and finer than the pitch-based graphitized carbon fiber described so far, for example, in WO 04/031461 pamphlet, a carbon material as a core material, A composite fiber is prepared by a blend spinning method (or conjugate spinning method) using an olefin-based material or the like as a matrix material, and the matrix material is dissolved and removed as a post-treatment, so that a final fiber of about 0.1 to 1 μm is obtained. A technique for obtaining fine graphitized pitch-based carbon fibers having a diameter with high productivity is disclosed, and these can also be suitably used.

  Overall, the average fiber diameter of the pitch-based graphitized carbon fibers preferably used in the present invention is in the range of about 0.1 to 30 μm.

  The aspect ratio represented by the ratio of average fiber length / average fiber diameter is preferably in the range of about 2-100. This is because when the aspect ratio is less than 2, it is difficult to utilize the characteristics of the fiber shape, and when it exceeds 100, the bulk density is lowered, and high-density filling becomes difficult.

  The aspect ratio is more preferably in the range of 2 to 60, still more preferably in the range of 3 to 30, and most preferably in the range of 3 to 15.

  On the other hand, the average fiber length of the pitch-based graphitized carbon fiber is preferably 1000 μm or less. When it exceeds 1000 μm, the bulk density is greatly lowered, and it becomes difficult to increase the dispersion ratio in the binder resin. The average fiber length is more preferably 500 μm or less, and still more preferably 300 μm or less. On the other hand, the lower limit of the average fiber length is about 0.2 μm.

  In the present invention, it is a great feature that a layer having high light reflectivity (hereinafter referred to as a light reflection layer) is formed on the surface including at least the side surfaces of these pitch-based graphitized carbon fibers.

  In the present invention, the light reflecting layer is laminated on the long-fiber carbon fiber (the coating forming method for the long-fiber carbon fiber is exemplified in, for example, Japanese Patent Application Laid-Open No. 2005-082876), and then cutting. A method of obtaining a light-reflective heat-conductive filler by performing a process such as milling (pulverization) can also be used, but in the present invention, a light-reflective layer is formed particularly on short fiber-like carbon fibers. In this case, the light reflecting layer can be formed not only on the side surface of the carbon fiber but also on the end surface portion. Thus, it can be said that it is very preferable that the light reflecting layer is laminated on the entire surface including the end face of the carbon fiber from the viewpoint of further increasing the light reflectance of the carbon fiber.

  The thickness of the light reflecting layer is preferably about 0.01 to 10 μm. If the thickness is less than 0.01 μm, the light reflectivity is insufficient, and if it exceeds 10 μm, the adhesion to the carbon fiber may be lowered, or heat conduction may be hindered as a heat resistance component, which is not preferable. In addition, the thickness of the light reflection layer is more preferably 0.03 to 5 μm, and further preferably 0.05 to 3 μm.

  The light reflecting layer is preferably, for example, a layer made of a metal and / or ceramic film and / or metal and / or ceramic fine particles.

  As metal species used as these films and / or fine particles, metals such as silver, nickel, cobalt, platinum, titanium, lead, tin, tungsten, aluminum, zinc, gold, copper, iron, chromium, and alloys thereof and two kinds thereof The above composite fine particles (for example, silver-coated copper powder) are preferably used, and silver is particularly preferably used among them.

As ceramics, ceramics composed of ceramics, such as titanium oxide, aluminum oxide, magnesium oxide, aluminum oxynitride, silicon oxide, barium titanate, aluminum nitride, boron nitride, silicon nitride, etc. can be used. Of these, titanium oxide, barium titanate, and aluminum oxide are particularly preferably used.
As the fine particles, it is preferable to use particles that are as spherical as possible from the viewpoint of efficiently performing compounding to carbon fibers by the mechanochemical method described later. The particle size is preferably about 0.01 to 10 μm, more preferably 0.3 to 3 μm. From the same point of view, a resin material in which fine particles of these metals and ceramics are dispersed in a high proportion (approximately 70% by weight or more) can be used almost synonymously.

  As a method of laminating the light reflecting layer composed of these films and / or fine particles on the surface of the carbon fiber, as exemplified by the barrel plating apparatus of the above-mentioned Patent Document 2, in a fluid using a rotating field or other flow field. Film formation method by electrolytic plating method on fine particles of particles, wet plating method such as electroless plating, physical vapor deposition method such as vacuum deposition, sputtering, ion plating, laser ablation method, chemical vapor deposition method such as plasma CVD, etc. And a mechanochemical method in which fine particles are bonded together based on mechanical impact, a method using a rotary flow device (for example, “Ominitex” manufactured by Nara Machinery Industry Co., Ltd.), etc. A method such as plating or a mechanochemical method is particularly preferably used.

  A typical example of a wet plating method using a flow field is a barrel plating method. In barrel plating, for example, a plating solution and a material to be processed are placed in a rotatable polygonal cylindrical container (barrel), and the electrode provided in the barrel and the material to be processed come into contact with the rotation of the barrel. In this method, a plating film is formed on the material to be treated. However, the formation of a liquid flow field suitable for electrolytic plating on fine particles can be realized not only by the above-described method of rotating the barrel but also by other methods, for example, forced turbulence generation using a special high-speed stirrer, etc. Etc. can also be used.

  As for the composition of the plating bath, as an example of silver, as a monovalent silver compound as a raw material of silver, silver oxide, silver sulfate, silver citrate, silver nitrate, silver chloride, silver iodide, silver methanesulfonate, etc. These are used after being dissolved in a dilute acid solution or the like, if necessary, and then adjusting the PH value to an appropriate range. Further, polyethylene glycol, polyoxyalkyl ether, polyoxyethylene or the like may be added as a surface conditioner for the purpose of increasing the surface gloss of the film.

  When laminating the light reflecting layer, surface treatment may be applied to the carbon fiber surface as necessary for the purpose of improving the adhesion to the carbon fiber surface. Such surface treatment includes various coating treatments (dipping coating, spray coating, electrodeposition coating, various plating, plasma CVD, etc.), ozone treatment, plasma treatment, corona treatment, ion implantation treatment, electrolytic oxidation treatment, acid / alkali and other chemicals. Treatment, etc., coating of resin, inorganic substance, metal oxide, metal and their fine particles on the surface of carbon fiber, surface activation by introduction of hydrophilic functional groups and metal elements, and introduction of hydrophobic groups It is possible to control surface roughness by surface inactivation and etching.

  Now, a light reflective heat conductive composition obtained by dispersing these light reflective heat conductive fillers will be described.

  The light-reflective heat-conducting composition comprises at least a light-reflective heat-conductive filler and a resin binder, and further contains 5 to 80% by weight of the light-reflective heat-conductive filler in the total solid component of the composition. It is made by mixing in the range. If the mixing ratio is less than 5% by weight, the effect of increasing the thermal conductivity is insufficient, and if it is 80% by weight or more, problems may occur in dispersibility and fluidity as a composition, which is not preferable. The mixing ratio is more preferably 10 to 60% by weight, still more preferably 15 to 40% by weight.

  As the resin binder, either a thermoplastic resin or a curable resin can be used. In addition, a resin material having tackiness (adhesiveness) can also be used depending on the application.

  Specifically, acrylic resin (methacrylate, acrylate), epoxy resin, silicone resin, polyimide resin, urethane resin, melamine resin, polyester resin (including unsaturated polyester), polyester acrylate resin, silicone polyimide resin, epoxy silicone resin, Acrylic rubber fine particle-dispersed epoxy resin and the like are preferable, but there is no particular limitation. In the case of a curable resin, it is possible to crosslink and cure the resin with moisture, heat, ultraviolet rays, etc. in the air after adding a reaction initiator, a curing agent or the like as necessary.

  If necessary, other kinds of fillers, dispersants, surfactants, solvents and the like can be mixed in the composition as necessary.

  As other types of fillers, the fine metals of the above exemplified metals and ceramics are preferably mentioned, and two or more types may be mixed as necessary.

  Now, these light-reflective heat conductive resin compositions can form a light-reflective heat conductive resin layer by coating on a suitable base | substrate, for example. The light-reflective heat-conductive resin layer is coated on a substrate that can be peeled later or sandwiched between two substrates, and after forming the layer, the substrate is peeled off to provide a self-supporting light reflecting layer. It can also be made as a heat conductive sheet. In addition, such a self-supporting light-reflective heat-conducting sheet is manufactured without peeling the substrate as necessary, such as when it is an adhesive sheet, and the substrate is peeled off during actual use. Such a method is also preferably used.

  The coating can be performed by various known techniques, and examples thereof include gravure coating, knife coating, die coating, slit die coating, bar coating, screen printing, and ink jet method. In addition, according to a technique such as screen printing or ink jet, a pattern can be formed only at a necessary portion on the substrate.

  The light-reflective heat-conductive resin composition includes a dispersant for the purpose of enhancing the dispersibility of fine particles, various organic solvents and other solvents for the purpose of adjusting the viscosity to be suitable for coating, and a light-reflective heat-conductive resin. Silicone oil and other leveling agents, surfactants and the like may be added for the purpose of enhancing the surface smoothness of the layer.

  The thickness of the light reflective heat conductive resin layer is preferably about 5 to 1000 μm. If the thickness is less than 5 μm, the heat transfer capacity of the heat conductive resin layer is often insufficient, and if it exceeds 1000 μm, the uniform formation and adhesion of the layer are reduced, and the flexibility and flexibility of the layer are reduced. This is not preferable because the number of cases increases.

  The thickness of the resin layer is more preferably 20 to 700 μm, still more preferably 30 to 500 μm, and most preferably 40 to 300 μm.

  Moreover, although the value of the light reflectance of a light-reflective heat conductive resin layer is so preferable that it is high, in this invention, it is preferable that it is at least 20% or more as an average reflectance in a 400-700 nm visible region. The light reflectance is more preferably 50% or more, still more preferably 65% or more, and most preferably 80% or more.

  The thermal conductivity of these light reflective heat conductive layers can be measured by a known method. Among them, the probe method, the hot disk method, and the laser flash method are preferable, and the probe method is particularly simple and preferable. The higher the thermal conductivity value of the light-reflective heat conductive layer, the better. However, in the present invention, it is preferably at least 1 W / (m · K) or more. The thermal conductivity is more preferably 2 W / (m · K) or more, further preferably 3 W / (m · K) or more, and most preferably 5 W / (m · K) or more.

  These light-reflective heat conductive layers of the present invention can be laminated on an appropriate substrate to form a heat conduction path (heat radiation path) on the substrate and improve the light reflectivity of the formed portion. it can.

  For example, by coating and laminating the surface opposite to the surface facing the cold cathode tube of the light reflecting film of the direct-type backlight unit of the liquid crystal display, the heat accumulated in the light reflecting film due to the heat generation of the cold cathode tube Can be efficiently dissipated. As the light reflecting film, a porous film, that is, a plastic film having a large number of pores inside and exhibiting high light reflectivity based on light scattering in the pores is currently used. . More specifically, polyester-based (polyethylene terephthalate, polyethylene naphthalate, etc.) or olefin-based (polyethylene, polypropylene, etc.) porous films are preferably used, and it is particularly preferable to use these films as substrates in the present invention. .

  Further, for the purpose of improving the adhesion between the light reflection film and the light reflective heat conductive layer, the surface treatment of the light reflection film is also preferably performed. Examples of these surface treatments include plasma treatment, ozone treatment, various coupling agent treatments, and thin-film coating of various resin materials such as epoxy resins.

  The light-reflective heat conductive layer is formed in the shape of, for example, an adhesive tape, an adhesive tape, etc., so that the frame (made of metal or resin) placed on the back side of the light-reflective film in the backlight unit and the light reflection It can also be used for adhesion to film and adhesive fixation. In this case, an air layer is not interposed between the light reflecting film and the frame, and a more efficient heat dissipation path can be formed.

  Furthermore, the light-reflective heat conductive layer may be uniformly laminated on the entire surface of the light-reflective film. For example, the light-reflective heat conductive layer may correspond to a region directly below the cold cathode tube, and may be laminated in a pattern only on a portion where the temperature is high. good. Examples of a method for forming a laminate in such a pattern include, for example, a method for performing screen printing based on a predetermined pattern, a method for performing etching according to a light irradiation pattern after forming a layer, using a photosensitive resist resin as a binder resin, Examples of the method include creating the shape of the above-mentioned pressure-sensitive adhesive tape, adhesive tape, and the like, and locally sticking to a predetermined portion.

Well light reflective heat conductive layer of the present invention, even if the implementation substrate, in particular LED, the mounting substrate for the light emitting elements such as laser diodes, are laminated through an electrically insulating layer on the metal wiring pattern of the device mounting surface As a result, a heat radiation path (heat diffusion, heat transport) for efficiently radiating the heat generated from the device can be formed in the device mounting surface, and at the same time, it can also function as a heat sink (heat release mechanism to the gas phase). Furthermore, since the light reflectivity of the surface of the mounting substrate can be improved, the light emitted from the light emitting element can be extracted to the external space more efficiently.

  The electrical insulating layer preferably has a necessary level of electrical insulation (for example, a volume resistance of 10E9 Ω · m or more, more preferably 10E12 Ω · m or more, and further preferably 10E15 Ω · m or more). Moreover, it is preferable to have heat resistance, chemical stability, and thin leaf property that can withstand various device mounting processes.

  As such an electrical insulation layer, various solder resists, various epoxy resins, electrical insulation resins such as polyester resins, adhesive layers made of them, and electrical insulation plastic films are preferably used.

  More preferably, the electrical insulating layer is preferably a layer having a high thermal conductivity, and an electrical insulating filler made of aluminum oxide, silicon oxide or other ceramics may be added for the purpose of improving thermal conductivity. Preferably done.

  The thinness of the electrical insulating layer, that is, the thickness is preferably in the range of about 1 to 100 μm. If it is less than 1 μm, it is difficult to ensure electrical insulation, and if it exceeds 100 μm, the thermal resistance increases and heat dissipation is hindered. The thickness of the electrical insulating layer is more preferably 2 to 40 μm, still more preferably 2 to 20 μm, and most preferably 2 to 10 μm.

  In the case of using a plastic film for the electrical insulating layer, in addition to the above required characteristics, for example, a thin film having a thickness of several μm is preferable because sufficient rigidity and strength can be ensured, for example, from polyparaphenylene terephthalamide (PPTA). The film is preferably used. This film is very preferable as an electrical insulating layer used in the present invention because sufficient electrical insulation and mechanical rigidity can be obtained even with a thickness of only a few μm.

Now the method for laminating the light reflective heat conductive layer on the implementation substrate, on the example, if implemented solder resist layer are layered in a predetermined pattern on a substrate and coverlay layer, by screen printing or other techniques A pattern printing method can be mentioned. The formation pattern may be the same as the solder resist layer or the coverlay layer, or may be a finer pattern.

  As another method, for example, a self-supporting sheet-like material is used as the light-reflective heat conductive layer, and after coating and laminating an electrically insulating adhesive layer on one side of the sheet, it can be cut into a predetermined shape pattern as necessary. After punching out, a method of stacking on a mounting substrate and performing adhesive fixing can be used.

  If a plastic film is used, a light-reflective heat conductive layer is laminated on one side of the film and an electrically insulating adhesive layer is formed on the other side in advance. A method of laminating on a substrate and performing adhesive fixation is preferably used.

The implementation substrate can be used known ones, for example, a rigid wiring board according to fiberglass / epoxy composite wires is made of such as copper, a flexible wiring board using the heat resistant film of polyimide or the like, a metal layer And a composite substrate (metal core substrate or the like) formed by alternately laminating and resin layers.

Examples are shown below, but the present invention is not limited to these techniques.
(1) Average fiber diameter of pitch-based graphitized carbon fiber:
The graphitized pitch-based carbon fiber was photographed with 10 fields of view at 400 times under an optical microscope, and the dimensions were determined from the enlarged photographic image.
(2) Average fiber length of pitch-based graphitized carbon fiber:
The pitch-based carbon fiber that had undergone graphitization was obtained by photographing 10 arbitrary views under an optical microscope. The magnification was appropriately adjusted according to the fiber length.
(3) True density of pitch-based graphitized carbon fiber:
It calculated | required using the specific gravity method.
(4) Crystal size:
Obtained by X-ray diffraction, the crystal size in the thickness direction of the hexagonal mesh surface is obtained using diffraction lines from the (002) plane, and the crystal size in the growth direction of the hexagonal mesh surface is obtained by using diffraction lines from the (110) plane. Asked. In addition, the request was made in accordance with the Gakushin Law.
(5) Thermal conductivity of pitch-based graphitized carbon fiber:
The resistivity of the fiber after graphitization treatment prepared under the same conditions except for the pulverization step was measured, and the relationship between the thermal conductivity and the electrical resistivity disclosed in JP-A-11-117143 is represented by the following formula (1 )
[Equation 1]
C = 1272.4 / ER-49.4 (1)
Here, C represents the thermal conductivity (W / m · K) of the fiber after graphitization, and ER represents the electrical specific resistance μΩm of the same fiber.
(6) Thermal conductivity of light reflective heat conductive composition and light reflective heat conductive layer:
Measurement was performed by a probe method using a thermal conductivity measuring device “QTM-500” manufactured by Kyoto Electronics. The composition was coated on a reference plate to a thickness of about 300 μm and dried or solidified under predetermined conditions as a sample.
(7) Light reflectivity of light reflective heat conductive composition, light reflective heat conductive layer, light reflective film:
Using a spectrophotometer (UV-3101PC manufactured by Shimadzu Corporation) equipped with an integrating sphere, the average reflectance in the wavelength range of 400 to 700 nm was determined. The reflectance was measured at a wavelength interval of 5 nm, and the value when the reflectance of a standard BaSO ₄ white plate was 100% was used.
In addition, about the composition, what coated to about 300 micrometers thickness on the 100-micrometer-thick polycarbonate film, and dried or solidified on predetermined conditions was made into the sample.
[Experimental Example 1] (Preparation of pitch-based graphitized carbon fiber)
A pitch made of a condensed polycyclic hydrocarbon compound was used as a main raw material. The optical anisotropy ratio was 100%, and the softening point was 283 ° C. Using a spinneret having a diameter of 0.2 mm, heated air was ejected from the slit at a linear velocity of 5000 m / min, and the pitch pitch carbon fibers having an average fiber diameter of 15 μm were drawn by pulling the melt pitch. The spun fibers were collected on a belt to form a mat, and a web made of pitch-based carbon fibers having a basis weight of 320 g / m ² by cross-wrapping.

  The web was infusibilized by increasing the temperature from 175 ° C. to 280 ° C. in air at an average temperature increase rate of 7 ° C./min. After firing the infusible web at 800 ° C. in a nitrogen atmosphere, milling or the like is performed, fibers having an average fiber length of about 50 μm (hereinafter referred to as carbon fiber A), fibers having an average fiber length of about 200 μm (hereinafter referred to as “fiber”). Sieve into carbon fiber B). Thereafter, it was graphitized by heat treatment at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere. The average fiber diameter was 9.7 μm. The percentage of the fiber diameter dispersion to the average fiber diameter was 14%. The true density was 2.18 g / cc.

  Using a transmission electron microscope, the pitch-based graphitized carbon fiber was observed at a magnification of 1,000,000 times and magnified on a photograph at 4 million times. It was confirmed that the graphene sheet was closed on the end face of the pitch-based graphitized carbon fiber. Further, the surface of the pitch-based graphitized carbon fiber observed with a scanning electron microscope at a magnification of 4000 times was smooth with no large irregularities.

  The crystallite size in the c-axis direction of the graphite crystal obtained by the X-ray diffraction method of the pitch-based graphitized carbon fiber was 33 nm. The crystallite size in the ab axis direction was 57 nm.

Moreover, the single yarn was extracted from the graphitized web heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical specific resistance was measured. However, it was 2.2 μΩ · m. The thermal conductivity obtained using the following formula (1) was 530 W / m · K.
[Equation 2]
C = 1272.4 / ER-49.4 (1)
(ER indicates the electrical resistivity, and the unit here is μΩ · m)
[Experimental example 2] (Formation of light reflecting layer on carbon fiber surface)
The surface of the pitch-based graphitized carbon fiber (carbon fiber A, carbon fiber B) prepared in Experimental Example 1 was coated with silver as a light reflective layer. Electrolytic plating using a liquid flow field was used for the silver coating.

  Prior to the electrolytic plating, the carbon fiber surface was subjected to a surface treatment with ozone using an ozone treatment apparatus manufactured by Iwasaki Electric Co., Ltd.

  The plating solution used was composed of 3 g / L silver oxide, 1 g / L polyethylene glycol having a molecular weight of 5000, and the like. The plating solution 9L and carbon fiber 50 g were put in a tabletop super vibration α-1 type stirring tester manufactured by Nippon Techno Co., Ltd., and five copper foils were immersed in the plating solution at regular intervals as a cathode. As an anode, a tin plate is immersed in a container containing a plating solution, and the vibration motor of the stirring tester is driven to generate a violent turbulent flow field around the cathode, while maintaining a predetermined input current. A silver film was formed on the surface of each of the carbon fibers A and B by electrolytic plating. The silver film had an average thickness of about 2 μm, and the film was uniformly formed on the entire surface including the end face portion of the carbon fiber.

[ Reference Example 12]
30% by weight of carbon fiber A prepared in Experimental Example 2, 15% by weight of silver fine particles having an average particle diameter of about 3 μm (“SPN-20J” manufactured by Micron Co., Ltd.), a solder resist agent made of polyester acrylate resin (product of Toyobo Co., Ltd.) Name “SR-610C”) 53 wt% and photosensitizer 2 wt% were vacuum degassed while mixing for 30 minutes using a planetary mixer to produce a light reflective heat conductive composition.
The heat conductivity of this light reflective heat conductive composition was 1.7 W / (m · K), and the light reflectivity was 58%. It should be noted that the layer made of the present light-reflective heat-conducting composition could be made a high heat-resistant layer by performing predetermined curing using ultraviolet rays.

[ Reference Example 13]
30% by weight of carbon fiber B prepared in Experimental Example 2, 20% by weight of silver fine particles having an average particle diameter of about 3 μm (“SPN-20J” manufactured by Micron Co., Ltd.), a solder resist agent made of polyester acrylate resin (product of Toyobo Co., Ltd.) The name “FR-200C”) 48 wt% and photosensitizer 2 wt% were vacuum degassed while mixing for 30 minutes using a planetary mixer to produce a light-reflective thermally conductive composition.
The heat conductivity of this light reflective heat conductive composition was 5.4 W / (m · K), and the light reflectivity was 73%. It should be noted that the layer made of the present light-reflective heat-conducting composition could be made a high heat-resistant layer by performing predetermined curing using ultraviolet rays.

[ Reference Example 14] (Preparation of light reflective film)
On one side of a 100 μm thick white reflective film based on polyethylene terephthalate (Teijin DuPont Films Co., Ltd., light reflectivity 97%), hydrolysis / condensation product of aminopropyltrimethoxysilane is composed of 1 methoxy 2-propanol and ethanol. Using a precursor solution diluted with a mixed solvent, coating was performed with a Meyer bar at a dry thickness of about 50 nm, followed by drying at 120 ° C. for 3 minutes and thermosetting.
Next, after diluting the light-reflective thermally conductive composition prepared in Reference Example 12 with a mixed solvent of methyl isobutyl ketone and 1 methoxy 2-propanol, the film surface on which the silane condensation layer was formed was dried with a Meyer bar. After coating with a thickness of 50 μm and solvent drying at 120 ° C. for 1 minute, the layer is cured by irradiating UV light with an integrated light quantity of 2000 mJ / cm ² , and a light reflective heat conductive layer is laminated on one side of the white reflective film A formed light reflective film was obtained.
The light reflectance of the film surface opposite to the surface on which the light-reflective heat conductive layer of this light-reflective film was laminated was 97%, which was equivalent to the light reflectance of the non-laminated white reflective film.

[ Reference Comparative Example 1]
Reference Example 12 and Reference Example 14 except that the step of forming a silver film on the pitch-based graphitized carbon fiber exemplified in Experimental Example 2 was omitted and the pitch-based graphitized carbon fiber prepared in Experimental Example 1 was used as it was. In exactly the same manner, a heat conductive resin composition and a light reflective film on which a heat conductive resin layer was formed were obtained.
The thermal conductivity of this thermally conductive resin composition was 1.6 W / (m · K), which was not significantly different from Reference Example 12, but the light reflectance was an extremely low value of 8%.
Furthermore, the light reflectance of the surface opposite to the surface on which the heat conductive resin layer of the light reflective film is laminated (the surface opposite to the cold cathode tube) is 95%, which is lighter than that of the non-laminated white reflective film. The reflectivity decreased by 2%.

[Example 15] (Creation of light-reflective coverlay film and creation of electronic mounting substrate)
On one side of a polyparaphenylene terephthalamide film (trade name “Aramika” manufactured by Teijin Advanced Film Co., Ltd., light reflectance 9%) having a thickness of about 9 μm, the light reflective heat conductive composition prepared in Reference Example 13 is knife After coating with a coater with a thickness of about 200 μm, the layer was cured by irradiating with an ultraviolet ray with an integrated light quantity of 2000 mJ / cm ² to form a light reflective heat conductive resin layer.
Subsequently, on the other side of the polyparaphenylene terephthalamide film, an epoxy resin-silica hybrid adhesive (product name “COMPOSELLAN AD10” manufactured by Arakawa Chemical Industries, Ltd.) was diluted with methyl ethyl ketone and then coated with a Meyer bar to a dry thickness of 8 μm. And dried at 60 ° C. for 1 hour to laminate and form an incompletely cured adhesive layer to obtain a light-reflective thermally conductive coverlay film.
The light reflectance of the surface of the coverlay film on which the light-reflective heat-conductive resin layer is formed is 67%, and the light reflectance is increased by 58% compared to the unformed polyparaphenylene terephthalamide film. did.
The implementation substrate, patterning the copper wiring using glass / epoxy laminate board was made in the outermost surface for white LED chip array implementation.
The light-reflective thermally conductive coverlay film is punched out in a shape corresponding to the mounting pattern of the white LED chip and other components, and the adhesive layer forming surface of the film is relative to the mounting substrate surface on which the copper wiring is made. In this direction, after pattern matching, lamination was performed, and press bonding at 120 ° C. for 2 hours was performed to obtain a target electronic mounting substrate.

[Comparative Example 2]
Reference Example 13 and Example 15 except that the step of forming a silver film on the pitch-based graphitized carbon fiber exemplified in Experimental Example 2 was omitted and the pitch-based graphitized carbon fiber prepared in Experimental Example 1 was used as it was. The heat conductive resin composition and the heat conductive coverlay film in which the heat conductive resin layer was formed were obtained in exactly the same manner.
The thermal conductivity of this thermal conductive resin composition was 5.2 W / (m · K), which was not significantly different from Reference Example 13, but the light reflectance was an extremely low value of 11%.

  The light-reflective heat-conductive resin composition and light-reflective heat-conductive layer created using the light-reflective heat-conductive filler of the present invention are heat dissipation measures for light-reflective films used in backlight units of liquid crystal displays, It can be widely used in applications that require advanced heat dissipation measures, such as the formation of heat dissipation paths on the surface of electronic mounting boards on which light emitting elements are mounted.

Claims (5)

At least the side surface of the pitch-based graphitized carbon fiber filler having an average fiber diameter of 0.1 to 30 μm, an aspect ratio of 2 to 100, an average fiber length of 0.2 to 1000 μm, and a true density of 2.0 to 2.5 g / cc is a thickness. A light-reflective heat-conductive filler coated with a light-reflective layer of 0.01 to 10 μm and a binder resin, and the mixing ratio of the light-reflective heat-conductive filler is 5 to 80 in the total solid component A light-reflective heat-conductive resin layer having a thickness of 5 to 1000 μm, which is made of a light-reflective heat-conductive resin composition, is laminated on one side of an electrically insulating plastic film having a thickness of 1 to 100 μm and the other side A light-reflective heat-conductive coverlay film obtained by laminating an electrically insulating adhesive layer on the substrate. The light-reflective thermally conductive coverlay film according to claim 1, wherein the electrically insulating plastic film is a film having a thickness of 2 to 20 μm made of polyparaphenylene terephthalamide (PPTA). 3. An electronic mounting substrate comprising: the light-reflective thermally conductive coverlay film according to claim 1; and a wiring pattern of the mounting substrate laminated on the electrically insulating adhesive layer surface of the coverlay film. At least the side surface of the pitch-based graphitized carbon fiber filler having an average fiber diameter of 0.1 to 30 μm, an aspect ratio of 2 to 100, an average fiber length of 0.2 to 1000 μm, and a true density of 2.0 to 2.5 g / cc is a thickness. A light-reflective heat-conductive filler coated with a light-reflective layer of 0.01 to 10 μm and a binder resin, and the mixing ratio of the light-reflective heat-conductive filler is 5 to 80 in the total solid component A light-reflective heat-conductive resin layer having a thickness of 5 to 1000 μm made of a light-reflective heat-conductive resin composition in weight% is placed on a wiring pattern of a mounting substrate via an electric insulating layer and / or an electric insulating adhesive layer. Electronic mounting board laminated on The electronic mounting substrate according to claim 4, wherein the electrically insulating adhesive layer and / or the electrically insulating adhesive layer is formed by laminating an electrically insulating adhesive layer on one surface of an electrically insulating plastic film having a thickness of 1 to 100 μm.