JP2005139298A - Anisotropic epoxy resin cured product and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epoxy resin cured product having high thermal conductivity and a low coefficient of thermal expansion in a specific direction. <P>SOLUTION: The anisotropic epoxy resin cured product is formed from a liquid crystalline epoxy resin having a mesogenic group in a molecular chain thereof and an epoxy resin composition containing a photopolymerization initiator. The mesogenic group is oriented in a specific direction in the anisotropic epoxy resin cured product. The anisotropic epoxy resin cured product has a thermal conductivity of 0.4-30 W/(m×K) and a coefficient of thermal expansion of -10×10<SP>-6</SP>-50×10<SP>-6</SP>[/K] in the direction that the mesogenic group is oriented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermally conductive anisotropic epoxy resin cured product that conducts heat generated from an electronic component or the like and reduces defects caused by thermal stress, and a method for producing the same.

  2. Description of the Related Art In recent years, in electronic devices, high-density mounting of semiconductor packages, high integration of LSIs, high speeds, and the like have been performed with high performance, miniaturization, and weight reduction. As a result, the heat generated in various electronic components increases, and therefore, a heat dissipation measure that effectively dissipates heat from the electronic components to the outside has become a very important issue. As such heat dissipation measures, heat conduction members made of heat dissipation materials such as metals, ceramics, and polymer chain compositions are used for heat dissipation members such as printed wiring boards, semiconductor packages, housings, heat pipes, heat dissipation plates, and heat diffusion plates. A molded product is applied.

  Among these heat dissipation members, thermally conductive epoxy resin cured products made of epoxy resin are excellent in electrical insulation, mechanical properties, heat resistance, chemical resistance, adhesion, low density, etc. It is widely used mainly in the electric and electronic fields as laminates, sealing materials, adhesives and the like.

As the epoxy resin composition constituting the thermally conductive epoxy resin cured product, one in which a thermally conductive filler having high thermal conductivity is blended in an epoxy resin is known.
When higher heat conductivity is required, a heat conductive epoxy resin composition or a heat conductive epoxy resin molded body in which a special heat conductive filler is blended with an epoxy resin has been proposed. As this type of thermally conductive filler, surface-modified aluminum oxide, spherical cristobalite, inorganic filler having a specific particle size, and the like are known (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). In addition, an insulating composition is known in which thermal conductivity is improved by polymerizing a liquid crystalline epoxy resin having a mesogenic group (see, for example, Patent Document 4). This insulating composition is characterized in that a high thermal conductivity of 0.4 W / (m · K) or more can be obtained without blending a thermally conductive filler.

  On the other hand, electronic parts such as a semiconductor package and a printed circuit board are integrally formed by bonding or adjoining various kinds of different materials such as resin, metal, and ceramics. In these electronic components and the like, when the ambient environmental temperature changes, thermal stress is generated at each material and material interface. In general, the thermal expansion coefficient of a metal such as copper used for a wiring material of an electronic component is small, and the thermal expansion coefficient of a cured epoxy resin is large. Therefore, due to the difference in thermal expansion coefficient, in electronic parts such as printed circuit boards made of epoxy resin, cracks, separation at the interface with different materials, disconnection of wiring, short circuit, etc. A problem occurs due to a problem.

  However, since recent electronic components have increased in calorific value as their performance increases, the cured epoxy resin obtained from the composition described in the background art has insufficient thermal conductivity. Yes.

  Moreover, the hardened | cured material obtained by hardening | curing the composition which consists of a liquid crystalline epoxy resin of patent document 4 is obtained by thermosetting an epoxy resin composition, and can control the advancing speed of hardening reaction. Have difficulty.

Furthermore, in order to use the epoxy resin composition forming the cured epoxy resin as an adhesive or a sealing material, it is necessary to heat electronic components such as elements and substrates in order to achieve thermal curing of the composition. In addition, there is a possibility that a malfunction may occur in an electronic component using a material that is altered or decomposed by heat or a material having a large thermal stress.
Japanese Patent Publication No. 6-51778 (Table 1) JP 2001-172472 A (Table 2) JP 2001-348488 A (Table 1) JP-A-11-323162 (Claim 1 etc.)

  The present invention has been made paying attention to the problems existing in the background art as described above. The object is to provide a cured anisotropic epoxy resin that exhibits excellent thermal conductivity and reduces defects in thermal stress.

  In order to achieve the above object, in the cured anisotropic epoxy resin according to claim 1, in the cured epoxy resin formed from the epoxy resin composition, the epoxy resin composition is in a molecular chain. The gist is that the composition includes a liquid crystalline epoxy resin having a mesogenic group and a photopolymerization initiator, and the mesogenic group is aligned in a certain direction in the cured product.

  In the cured anisotropic epoxy resin of the invention according to claim 2, in the invention according to claim 1, the thermal conductivity in the direction in which the mesogenic groups are oriented is 0.4 to 30 W / (m · K). ).

In the cured anisotropic epoxy resin of the invention according to claim 3, in the invention according to claim 1, the coefficient of thermal expansion in the direction in which the mesogenic groups are oriented is −10 × 10 ⁻⁶ to 50 × 10. ^-6 [/ K].

  A cured anisotropic epoxy resin according to a fourth aspect of the present invention is the cured product according to any one of the first to third aspects, wherein the cured product has a sheet shape and extends along the thickness direction thereof. The gist is that the groups are oriented.

  In the method for producing a cured anisotropic epoxy resin according to claim 5, the epoxy resin cured formed from an epoxy resin composition containing a liquid crystalline epoxy resin having a mesogenic group in a molecular chain and a photopolymerization initiator. In the manufacturing method of the product, the mesogenic groups are oriented in a certain direction in the cured product, and the manufacturing method includes a step of preparing an epoxy resin composition, and a mesogen of an epoxy resin contained in the epoxy resin composition. The gist consists of a step of aligning the groups in a certain direction and a step of photopolymerizing the epoxy resin composition while maintaining the state in which the mesogenic groups are aligned.

The present invention has the following effects.
According to the cured anisotropic epoxy resin of the invention described in claim 1, since the mesogenic group is oriented in a certain direction, it has a very high thermal conductivity and a very small thermal expansion coefficient in that direction. be able to.

  According to the anisotropic epoxy resin cured product of the invention described in claim 2, since the thermal conductivity in the specific direction is 0.4 to 30 W / (m · K), heat is more effectively conducted or It becomes possible to dissipate.

According to the cured anisotropic epoxy resin of the invention described in claim 3, since the thermal expansion coefficient in the specific direction is 50 × 10 ⁻⁶ / K or less, copper used for wiring materials for electronic components The difference between the thermal expansion coefficient of such a metal and the thermal expansion coefficient of the cured epoxy resin is reduced, and problems due to thermal stress can be reduced.

According to the cured anisotropic epoxy resin of the invention described in claim 4, it can be applied to a sheet-like application that requires excellent thermal conductivity and low thermal expansion in the thickness direction. .
According to the method for producing a cured anisotropic epoxy resin of the invention according to claim 5, the epoxy resin composition is cured by photopolymerization with the mesogenic groups in the epoxy resin composition oriented in a certain direction. Therefore, it can be cured at a relatively low temperature. In addition, when the epoxy resin composition is cured by photopolymerization, light is selectively irradiated to the epoxy resin composition, and only the portion irradiated with the light is cured, so that the desired shape is anisotropic. A cured epoxy resin product can be obtained.

Hereinafter, the best mode for carrying out the present invention will be described in detail.
The cured anisotropic epoxy resin according to the present invention comprises a liquid crystalline epoxy resin having a mesogenic group in the molecular chain and an epoxy resin composition containing a photopolymerization initiator, and the mesogenic group is oriented in a certain direction. It is characterized by.

  FIG. 1 shows an embodiment in which the anisotropic epoxy resin cured product of the present invention is embodied as an anisotropic epoxy resin sheet 1. In this embodiment, the epoxy resin sheet 1 is obtained by curing a liquid crystal epoxy resin having a mesogenic group in a molecular chain and an epoxy resin composition containing a photopolymerization initiator into a sheet shape. In the present embodiment, the mesogenic groups contained in the molecular chain of the liquid crystalline epoxy resin are oriented so that the major axis direction is along the thickness direction of the epoxy resin sheet 1 (Z-axis direction in FIG. 1). . Thereby, the epoxy resin sheet 1 exhibits excellent thermal conductivity in the thickness direction, and the thermal expansion in the thickness direction is reduced.

  Next, the epoxy resin composition will be described. Examples of the epoxy resin contained in the epoxy resin composition of the present invention include a bisphenol type epoxy resin, a novolac type epoxy resin, a naphthalene type epoxy resin, a triphenolalkane type epoxy resin, a biphenyl type epoxy resin, a cyclic aliphatic type epoxy resin, and the like. And the hydrogenated products thereof. Furthermore, it is essential that at least a part of the epoxy resin is a liquid crystalline epoxy resin having a mesogenic group in the molecular chain. By orienting mesogenic groups in a certain direction in the epoxy resin composition, it is possible to improve the thermal conductivity in the aforementioned direction of the cured anisotropic epoxy resin and reduce the thermal expansion coefficient. In general, heat conduction in an insulator such as a polymer material is caused by scattering of phonons, and it is considered that the phonons are easily scattered along the molecular chain direction. As described above, by aligning the long axis of the mesogenic group in the epoxy resin along a certain direction, the molecular chain of the entire epoxy resin is also oriented in a certain direction, and as a result, the thermal conductivity in that direction is reduced. It is thought to improve. The mesogenic group is rigid and highly linear. In the cured epoxy resin, such rigid mesogenic groups are aligned in a certain direction, so that the cured product becomes difficult to extend in that direction, and thermal expansion is considered to be suppressed.

The mesogenic group refers to a functional group exhibiting liquid crystallinity, specifically, biphenyl, cyanobiphenyl, terphenyl, cyanoterphenyl, phenylbenzoate, azobenzene, azomethine, azoxybenzene, stilbene, phenylcyclohexyl, biphenylcyclohexyl, phenoxy. Examples include phenyl, benzylidene aniline, benzyl benzoate, phenyl pyrimidine, phenyl dioxane, benzoyl aniline, tolan and derivatives thereof. The liquid crystalline epoxy resin used in the present invention only needs to have at least one mesogenic group in one molecular chain, and may have two or more mesogenic groups. Moreover, the connection part and terminal part of a some mesogen group are comprised by the flexible structure part called a bending chain (spacer). Examples of the flexible structure include an aliphatic hydrocarbon group, an aliphatic ether group, an aliphatic ester group, and a siloxane bond.

  Such a liquid crystalline epoxy resin has a property of being in a liquid crystal state in which mesogenic groups are regularly arranged in a certain temperature range. This liquid crystallinity can be confirmed by a polarization inspection method using an orthogonal polarizer, and a liquid crystalline epoxy resin in a liquid crystal state exhibits a unique strong birefringence. Examples of the liquid crystal state include a nematic phase, a smectic phase, a cholesteric phase, and a discotic phase. Among them, the liquid crystal state of the liquid crystalline epoxy resin used in the present invention is particularly preferably a nematic phase and a smectic phase in which the long axis of the molecular chain is aligned in a certain direction, but is not limited thereto. The nematic phase refers to a liquid crystal state in which the center of gravity of liquid crystal molecules is not ordered but its major axis is aligned in a certain direction. The smectic phase refers to a liquid crystal state in which the major axis directions of liquid crystal molecules are aligned in a certain direction and the liquid crystal molecules are arranged in layers. It is expected that the higher the regularity of the liquid crystal structure, the higher the thermal conductivity.

  Furthermore, as the liquid crystalline epoxy resin used in the present invention, an epoxy resin having homeotropic orientation in which the mesogenic group is oriented perpendicularly to the surface of the epoxy resin sheet 1 in the present embodiment in a predetermined temperature range. May be used. An anisotropic epoxy resin cured product obtained by curing an epoxy resin composition containing an epoxy resin having such a self-orientation property while maintaining the orientation state exhibits high thermal conductivity in the orientation direction.

In addition to the liquid crystalline epoxy resin, the epoxy resin composition may contain an epoxy resin that does not contain a mesogenic group in the molecular chain.
Furthermore, a photopolymerization initiator is blended in the epoxy resin composition for the purpose of reaction-curing the above-described epoxy resin. It does not limit about the kind and quantity of a photoinitiator to be used, photocuring conditions, etc. In addition to photopolymerization initiators, amine curing agents, acid anhydride curing agents, phenol curing agents, latent curing agents, polymercaptan curing agents, polyaminoamide curing agents, isocyanates, block isocyanates, etc. These curing agents may be used alone or in combination of two or more.

  Generally, the amount of the photopolymerization initiator in the photopolymerization of the epoxy resin composition is very small compared to the case of using a curing agent such as an amine curing agent. It is possible to increase the proportion of groups. Therefore, when the epoxy resin composition is cured by photopolymerization, a larger number of mesogenic groups are oriented in a certain direction in the resulting cured epoxy resin, and higher thermal conductivity is exhibited in the orientation direction. It becomes possible to do. Moreover, since photopolymerization is used as a curing method, the epoxy resin composition can be cured at a relatively low temperature. Thereby, for example, when an epoxy resin composition is used as an adhesive or a sealant, it is possible to avoid exposing an electronic component to be applied to high heat that causes a problem for a long time.

The type of photopolymerization for curing the epoxy resin composition is not particularly limited, but photocationic polymerization is particularly preferable.
Particularly preferred as the photopolymerization initiator used in the present invention is a compound capable of releasing a substance that initiates photopolymerization of an epoxy resin by receiving energy rays such as light. Here, energy rays such as light include visible light, ultraviolet light, infrared light, X-rays, α rays, β rays, γ rays, and the like. Particularly preferred photopolymerization initiators include onium salts having a structure represented by the following general formula (1).

[R ² _a R ³ _b R ⁴ _c R ⁵ _d Q] ^{+ m} [MX _{n + m} ] ^−m (1)
In the above formula, the cation is an onium ion, Q is S, Se, Te, P, As, Sb, Bi, O, I, Br, Cl or ^{-N = N, R 2, R} 3, R 4 And R ⁵ are the same or different organic groups, a, b, c and d are each an integer of 0 to 3, and (a + b + c + d) is equal to the valence of Q. M is a metal or metalloid constituting the central atom of the halide complex [MX _{n + m} ], for example, B, P, As, Sb, Fe, Sn, Bi, Al, Ca, In, Ti, Zn, Sc, V, Cr, Mn, Co and the like. X is a halogen atom such as F, Cl, Br, etc., m is the net charge of the halide complex ion, and n is the valence of M.

This onium salt is a compound that releases a Lewis acid by receiving light.
Specific examples of the anion [MX _{n + m} ] in the general formula (1) include tetrafluoroborate (BF ₄ ⁻ ), hexafluorophosphate (PF ₆ ⁻ ), hexafluoroantimonate (SbF ₆ ⁻ ), hexa Examples thereof include fluoroarsenate (AsF ₆ ⁻ ) and hexachloroantimonate (SbCl ₆ ⁻ ).

An onium salt having an anion represented by the general formula [MX _n (OH) ⁻ ] can also be used. Further, perchlorate ion (ClO ₄ ⁻ ), trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ), fluorosulfonate ion (FSO ₃ ⁻ ), toluenesulfonate ion, trinitrobenzenesulfonate anion, trinitrotoluenesulfonate Onium salts having other anions such as anions can also be used. Among such onium salts, aromatic onium salts are particularly effective as photopolymerization initiators.

  Said photoinitiator can be used individually by 1 type or in combination of 2 or more types. Moreover, you may use the radical photoinitiator which decomposes | disassembles by receiving energy rays, such as light, and generate | occur | produces a radical together with said photoinitiator.

  In order to further improve the thermal conductivity of the cured anisotropic epoxy resin, an appropriate amount of a thermally conductive filler can be added to the epoxy resin composition. Thermally conductive fillers include metals, metal oxides, metal nitrides, metal carbides, metal hydroxides, metal-coated resins, carbon fibers, glass fibers, graphitized carbon fibers, natural graphite, artificial graphite, and spherical graphite particles , Mesocarbon microbeads, whisker-like carbon, microcoiled carbon, nanocoiled carbon, carbon nanotube, carbon nanohorn, and the like. Examples of the metal include silver, copper, gold, platinum, and zircon. Examples of the metal oxide include aluminum oxide and magnesium oxide. Examples of the metal nitride include boron nitride, aluminum nitride, and silicon nitride. Examples of the metal carbide include silicon carbide. Examples of the metal hydroxide include aluminum hydroxide and magnesium hydroxide.

  Furthermore, for the purpose of improving the wettability between such a heat conductive filler and an epoxy resin, reinforcing the interface between the heat conductive filler and the epoxy resin, and promoting dispersibility in the epoxy resin composition, The conductive filler may be subjected to ordinary coupling agent treatment.

The amount of these thermally conductive fillers is not specified, but is preferably less than 100 parts by weight, more preferably less than 50 parts by weight, and even more preferably less than 10 parts by weight with respect to 100 parts by weight of the epoxy resin. Is preferred. When the blending amount is 100 parts by weight or more with respect to 100 parts by weight of the epoxy resin, the curability and moldability of the cured anisotropic epoxy resin are deteriorated, or the epoxy resin composition is thermally conductively filled. When mixing the agent, there is a risk of bubbles being mixed. In applications where weight reduction is required, the epoxy resin composition preferably contains substantially no thermally conductive filler. “Contains substantially no thermally conductive filler” means that the amount of the thermally conductive filler is preferably 5 parts by weight or less, more preferably 1 part by weight or less, based on 100 parts by weight of the epoxy resin. Preferably, it means that no thermally conductive filler is contained.

  In addition, the epoxy resin composition includes a curing agent, a curing accelerator, a curing retarder, a photopolymerization initiation aid, a photosensitizer, a reinforcing material, a low stress agent such as rubber or elastomer, a pigment, a dye as necessary. , Fluorescent brighteners, dispersants, stabilizers, UV absorbers, energy quenchers, antistatic agents, antioxidants, thermal stabilizers, lubricants, reactive diluents, plasticizers, solvents, etc. can also be added It is.

Next, the anisotropic epoxy resin cured product will be described in detail.
An anisotropic epoxy resin cured product obtained by curing an epoxy resin composition containing an epoxy resin having a mesogenic group in the molecular chain is a liquid crystal in which the mesogenic group is at least partially aligned in a certain direction in the cured state. It is preferable that the phase is fixed. More preferably, the epoxy resin composition is heated as necessary so that the mesogenic groups are at least partially aligned to a liquid crystal state at the start of curing of the epoxy resin composition.

  Furthermore, the thermal conductivity λ of the cured anisotropic epoxy resin containing a liquid crystalline epoxy resin having a mesogenic group in the molecular chain is extremely high in that direction because the long axis of the mesogenic group is aligned in a certain direction. Become. The anisotropic epoxy resin cured product of the present invention is 0.4 to 30 W / (m · K), preferably 0.6 to 20 W / (m · K), more preferably 0.7 in at least one direction. It has a thermal conductivity λ of -10 W / (m · K). If the thermal conductivity λ is less than 0.4 W / (m · K), it may be difficult to effectively transmit the heat generated from the electronic component to the outside. On the other hand, it is difficult to obtain a cured anisotropic epoxy resin having a thermal conductivity λ exceeding 30 W / (m · K) in view of the physical properties of the epoxy resin.

In addition, the thermal expansion coefficient of the cured anisotropic epoxy resin containing a liquid crystalline epoxy resin having a mesogenic group in the molecular chain is determined by the orientation of the major axis of the mesogenic group in a certain direction (this embodiment). In the molecular chain direction of the epoxy resin). The anisotropic epoxy resin cured product of the present invention is preferably -10 × 10 ⁻⁶ to 50 × 10 ⁻⁶ [/ K], more preferably −5 × 10 ⁻⁶ to 40 × 10 ^{− in} at least one direction. ^{6 It} has a thermal expansion coefficient of [/ K]. If this thermal expansion coefficient is 50 × 10 ⁻⁶ [/ K] or more, it may be difficult to reduce thermal stress generated in an electronic component or the like. On the other hand, it is difficult to obtain an anisotropic epoxy resin molded product having a thermal expansion coefficient smaller than −10 × 10 ⁻⁶ [/ K] in view of the physical properties of the epoxy resin.

  As described above, the cured anisotropic epoxy resin of the present invention has anisotropy related to thermal conductivity and thermal expansion coefficient, indicating high thermal conductivity and a very small thermal expansion coefficient in a specific direction. Become. Therefore, it is useful in a printed wiring board, a semiconductor package, a housing, a heat pipe, a heat radiating plate, a heat diffusing plate, a sealing material, an adhesive and the like in an electronic device that requires thermal conductivity and low thermal expansion.

  The cured anisotropic epoxy resin of the present invention can be formed from the epoxy resin composition into various shapes such as a sheet shape, a film shape, a block shape, a granular shape, and a fibrous shape. Moreover, epoxy resin hardened | cured material can also be used as a sealing material or an adhesive agent. In that case, after applying the epoxy resin composition before curing to the application target, orienting the mesogenic groups in the composition in a certain direction, the composition is cured by irradiating with ultraviolet rays, It can function as a sealing material or an adhesive.

When the anisotropic epoxy resin cured product is formed into a sheet shape as in the embodiment shown in FIG. 1, the orientation of the long axis direction of the mesogen group is aligned with the thickness direction of the sheet, thereby increasing the thickness direction. The thermal conductivity in can be improved. Thereby, application to a circuit board material, a heat dissipation sheet, a semiconductor package, a heat dissipation plate, a heat diffusion plate, an adhesive sheet and the like that are sheet-like and require thermal conductivity in the thickness direction is possible.

  Moreover, when shape | molding an anisotropic epoxy resin hardened | cured material in a sheet form, the thickness becomes like this. Preferably it is 0.005-5 mm, More preferably, it is 0.05-3 mm, Most preferably, it is 0.1-1 mm. When the thickness is less than 0.005 mm, workability when applied to an application target such as a heating element may be deteriorated. On the other hand, when the thickness exceeds 5 mm, not only is photopolymerization by ultraviolet irradiation difficult, but the thermal conductivity may be deteriorated.

  Next, the manufacturing method of anisotropic epoxy resin hardened | cured material is demonstrated. The method for producing a cured cured epoxy resin of the present invention comprises the steps of preparing the above-described epoxy resin composition, aligning the mesogenic groups in the composition in a certain direction, and maintaining the orientation of the mesogenic groups. And the step of photopolymerizing the composition with ultraviolet rays or the like.

  As a method of aligning the mesogenic groups of epoxy resins that have mesogenic groups in the molecular chain to develop anisotropy, use the property that liquid crystal molecules are aligned along the scratches by providing finer scratches on the alignment film than rubbing. And a method of aligning liquid crystal molecules by applying a surfactant or the like to the alignment film. A method of orienting mesogenic groups by an external force such as a flow field, a shear field, a magnetic field, or an electric field is also possible. Among these alignment methods, an alignment method using a magnetic field is preferable because the alignment direction can be easily controlled. Moreover, these alignment methods can also be used together as needed. For example, by combining the application of a magnetic field and the use of an alignment film, the effect of alignment can be further enhanced, and the direction and degree of alignment on the surface and inside of the cured epoxy resin product can be controlled.

  When orienting mesogenic groups by a magnetic field, in the method for producing a cured anisotropic epoxy resin, the step of orienting mesogenic groups in the composition in a certain direction is performed by applying a magnetic field in a certain direction to the epoxy resin composition by a magnetic field generator. The step of applying is included. By applying a magnetic field in a certain direction by a magnetic field generator to an epoxy resin composition containing a liquid crystalline epoxy resin having a mesogenic group in the molecular chain, the mesogenic group in the molecular chain of the epoxy resin is parallel to the magnetic field lines. It can be oriented in the direction or the vertical direction.

  Examples of the magnetic field generator include a permanent magnet, an electromagnet, a superconducting magnet, and a coil. Among these magnetic field generators, a superconducting magnet is preferable because a magnetic field having a practical magnetic flux density can be generated.

  The magnetic flux density of the magnetic field applied to the epoxy resin composition is preferably 0.2 to 20 Tesla (T), more preferably 0.5 to 15 T, and most preferably 1 to 10 T. When this magnetic flux density is less than 0.2T, the mesogenic group in the epoxy resin composition cannot be sufficiently oriented, and an anisotropic epoxy resin cured product having excellent thermal conductivity cannot be obtained. On the other hand, a magnetic field having a magnetic flux density exceeding 20T is difficult to obtain in practice. When the range of the magnetic flux density is 0.2 to 20 T, the mesogenic group in the epoxy resin composition can be sufficiently oriented, and thus an anisotropic epoxy resin cured product having excellent thermal conductivity can be obtained. And practical.

As a method for orienting mesogenic groups in a certain direction, it is also effective to use an epoxy resin having mesogenic groups having a property of homeotropic alignment in a predetermined temperature range. By heating an epoxy resin composition containing such an epoxy resin to a predetermined temperature, the epoxy resin composition is transferred to a phase in which mesogenic groups are homeotropically aligned, and the epoxy resin composition is photopolymerized while maintaining the homeotropic alignment. Let Thereby, for example, in the embodiment of FIG. 1, it is possible to obtain an anisotropic epoxy resin cured product oriented so that the major axis direction of the mesogen group coincides with the thickness direction of the epoxy resin sheet 1.

Even in the case of using an epoxy resin having a mesogenic group having a property of homeotropic alignment in a molecular chain, a magnetic field and an alignment film can be used in combination.
There is no particular limitation on the ultraviolet ray generation source that irradiates ultraviolet rays for initiating photopolymerization of the epoxy resin composition. However, when the orientation of the mesogen groups in the epoxy resin composition is performed by a magnetic field, the ultraviolet ray generation source is preferably disposed at a place where the magnetic flux density is 0.01 Tesla or less. There are no particular restrictions on the method of guiding the ultraviolet light from the ultraviolet light source to the epoxy resin composition to which a magnetic field is applied, but the method of directly irradiating the ultraviolet light from the light source, the method of irradiating it with reflection on the mirror, and the irradiation through the focusing lens And a method of guiding and irradiating with a fiber.

  Next, an embodiment in which the cured anisotropic epoxy resin of the present invention is embodied as a sheet-shaped anisotropic epoxy resin molded body will be described in detail with reference to FIGS.

  First, a method for forming a mesogen group of an epoxy resin having a mesogen group in the molecule by orienting it in the thickness direction (Z-axis direction in FIG. 1) of the anisotropic epoxy resin sheet 1 will be described. As shown in FIG. 2, a cavity 12 a corresponding to a desired sheet shape is formed inside the mold 12. The upper part of the mold 12 is opened or formed of a material that transmits a sufficient amount of ultraviolet rays to cure the epoxy resin composition. A pair of upper and lower permanent magnets 13 are disposed above and below the mold 12 as a magnetic field generator. Thereby, the magnetic force lines M1 of the magnetic field generated by the permanent magnet 13 coincide with the thickness direction of the cavity 12a. An ultraviolet ray generation source 15 is disposed at a location not affected by the magnetic field generated by the permanent magnet 13, and a fiber 16 extends between the cavity 12 a and the upper magnet 13 from the ultraviolet ray generation source 15. Ultraviolet rays generated from the ultraviolet ray source 15 pass through the fiber 16 and irradiate the cavity 12a. First, the cavity 12a is filled with an epoxy resin composition 11 containing a liquid crystalline epoxy resin having a mesogenic group in the molecular chain and a photopolymerization initiator. If necessary, the epoxy resin composition 11 in the cavity 12a is maintained in a desired liquid crystal state or molten state by a heating device (not shown). Next, a magnetic field having a predetermined magnetic flux density is applied to the epoxy resin composition 11 in the cavity 12 a by the permanent magnet 13. Note that the magnetic field may be applied before filling the epoxy resin composition. At this time, the direction of the magnetic lines of force M1 coincides with the thickness direction of the sheet-like epoxy resin composition 11, so that the mesogenic group of the liquid crystalline epoxy resin having a mesogenic group in the molecular chain is replaced with the sheet-shaped epoxy resin composition. It can be oriented along the thickness direction of the object 11. While maintaining this orientation state, the epoxy resin composition 11 is irradiated with ultraviolet rays from the tip of the fiber 16. Thereby, the epoxy resin composition is cured by photopolymerization, and the cured product is taken out from the mold 12. As a result, the mesogenic group of the epoxy resin is oriented in the thickness direction of the sheet, and thus an anisotropic epoxy resin sheet 1 having high thermal conductivity and a low coefficient of thermal expansion can be obtained in the thickness direction of the sheet. .

In the above method, the magnetic field is used to orient the mesogenic groups of the epoxy resin in the thickness direction of the anisotropic epoxy resin sheet 1, but in order to orient the mesogenic groups in the same manner, the homeotropic region is used in a predetermined temperature range. A method utilizing the self-orientation property of an epoxy resin having a mesogenic group having the property of orientation is also possible. The apparatus used in this method has the same configuration as the apparatus used in the above-described method except that it does not have a magnetism generator, that is, the permanent magnet 13. First, the cavity 12a is filled with an epoxy resin composition 11 including a liquid crystalline epoxy resin having a mesogenic group having a property of homeotropic alignment in a predetermined temperature range in a molecular chain and a photopolymerization initiator. Next, by maintaining the epoxy resin composition 11 in the cavity 12a within a predetermined temperature range, the epoxy resin contained in the composition is transferred to a liquid crystal phase in which mesogenic groups are homeotropically aligned. The epoxy resin composition 11 is irradiated with ultraviolet rays from the tip of the fiber 16 while maintaining the state in which the mesogenic group is homeotropically oriented. Thereby, the epoxy resin composition is cured by photopolymerization, and the cured product is taken out from the mold 12. Thereby, the mesogenic group of the epoxy resin is homeotropically oriented, that is, the long axis of the mesogenic group is oriented along the thickness direction of the sheet, and in the thickness direction of the sheet, high thermal conductivity and low thermal expansion coefficient The anisotropic epoxy resin sheet 1 which has can be obtained.

  Alternatively, the mesogenic group of the epoxy resin having a mesogenic group in the molecular chain may be oriented in the direction along the surface of the anisotropic epoxy resin sheet 1 (for example, the X-axis direction or the Y-axis direction in FIG. 1). Is possible. The apparatus used in this case is configured in the same manner as the apparatus shown in FIG. 2 except for the arrangement of the pair of permanent magnets 13 as shown in FIG. In the apparatus shown in FIG. 3, a pair of permanent magnets 13 are arranged opposite to both sides of the mold 12 so that the lines of magnetic force M2 are parallel to the bottom surface of the cavity 12a of the mold 12. First, the cavity 12a is filled with an epoxy resin composition 11 containing a liquid crystalline epoxy resin having a mesogenic group in the molecular chain and a photopolymerization initiator. If necessary, the epoxy resin composition 11 in the cavity 12a is maintained in a desired liquid crystal state or molten state by a heating device (not shown). Next, a magnetic field is applied to the epoxy resin composition 11 in the cavity 12 a by a pair of permanent magnets 13. At this time, since the magnetic lines of force M2 are parallel to the surface of the sheet-like epoxy resin composition 11, the mesogenic groups of the epoxy resin can be oriented in the direction along the surface of the epoxy resin composition 11. While maintaining this alignment state, the epoxy resin composition 11 is irradiated with ultraviolet rays from the fiber 16. Thereby, the epoxy resin composition 11 is cured by photopolymerization, and the cured product is taken out from the mold 12. As a result, the mesogenic group of the epoxy resin having a mesogenic group in the molecular chain is oriented in a direction along the surface of the sheet, and thus has a high thermal conductivity and a low thermal expansion coefficient in the direction along the surface of the sheet. The epoxy resin sheet 1 can be obtained.

In addition, the said embodiment can also be changed and comprised as follows.
The pair of permanent magnets 13 are arranged so as to sandwich the mold 12, but one of the pair of permanent magnets 13 may be omitted.

The S pole and the N pole of the pair of permanent magnets 13 are arranged so as to face each other, but may be arranged so that the S poles or the N poles face each other.
The magnetic lines M1 and M2 are linear, but may be curved. The pair of permanent magnets 13 are arranged so that the magnetic lines of force M1, M2 extend in one direction, but a plurality of permanent magnets may be arranged so that the magnetic lines of force M1, M2 extend in two or more directions. . Further, the magnetic lines of force M1, M2 or the mold 12 may be rotated.

-You may irradiate an ultraviolet-ray directly from the said ultraviolet-ray generation source 15 without using the said fiber 16. FIG.
In place of the fiber 16, a mirror or a lens may be used to guide ultraviolet rays.

  Hereinafter, the embodiment will be described more specifically with reference to examples and comparative examples.

(Example 1)
The epoxy resin represented by the following formula (1), benzoate type epoxy resin having a mesogenic group in the molecular chain (referred to as epoxy resin A) 98 wt%, diphenyliodonium hexafluoroarsenate (1 wt%) as a photopolymerization initiator 2 as photopolymerization initiation aid
An epoxy resin composition 11 is prepared by mixing 2-dimethoxy-2-phenyl-acetophenone (0.5 wt%) and isopropylthioxanthone (0.5 wt%). The epoxy resin A transitions to a smectic phase having the property of homeotropic alignment at 87 ° C. during the temperature rising process, transitions to a nematic phase having no property of homeotropic alignment at 143 ° C., and isotropic phase at 162 ° C. To be transferred to. Next, the prepared epoxy resin composition 11 is filled in the cavity 12a of the mold 12 heated to 120 ° C. and melted to form a smectic phase having a property of homeotropic alignment of the epoxy resin A contained in the composition. Transferred. While maintaining the phase state, the epoxy resin composition 11 is cured by irradiating ultraviolet rays having an illuminance of 0.2 W / cm ² from the ultraviolet ray source 15 through the fiber 16 for 5 minutes without applying a magnetic field. An anisotropic epoxy resin sheet 1 having a thickness of 0.5 mm was produced.

（実施例２）
実施例１と同一のエポキシ樹脂組成物１１を、温度１５５℃に加熱した型のキャビティ１２ａに充填して溶融させ、エポキシ樹脂Ａをホメオトロピック配向する性質を有さないネマティック相に転移させた。その後、磁束密度５テスラの磁場中にて、照度０．２Ｗ／ｃｍ^２の紫外線を５分間照射することにより、エポキシ樹脂組成物１１を硬化させ、厚み０．５ｍｍの異方性エポキシ樹脂シート１を作製した。尚、磁力線の方向はシート状の厚み方向とした。
（実施例３）
表１に示すように磁束密度を１０テスラに変更した以外は実施例２と同様の方法で異方性エポキシ樹脂シート１を作製した。
（実施例４）
エポキシ樹脂として、下記式（２）で示される、分子鎖内にメソゲン基を有するベンゾエート型エポキシ樹脂（エポキシ樹脂Ｂとする）９８ｗｔ％、光重合開始剤としてジフェニルヨードニウムヘキサフルオロアルセネート １ｗｔ％、光重合開始助剤として２，２- ジメトキシ- ２- フェニル- アセトフェノン ０．５ｗｔ％、イソプロピルチオキサントン ０．５ｗｔ％の混合物を調製した。エポキシ樹脂Ｂは昇温過程において、１１０℃でホメオトロピック配向する性質を有さないネマティック相に転移し、１６５℃で等方相に転移するものである。次に、エポキシ樹脂組成物１１を、温度１４０℃に加熱した型１２のキャビティ１２ａに充填して溶融させ、エポキシ樹脂Ｂをホメオトロピック配向する性質を有さないネマティック相に転移させた。その後、磁束密度５テスラの磁場中にて、照度０．２Ｗ／ｃｍ^２の紫外線を５分間照射することによりエポキシ樹脂組成物１１を硬化させ、厚み０．５ｍｍの異方性エポキシ樹脂シート１を作製した。尚、磁力線の方向はシート状の厚み方向とした。

(Example 2)
The same epoxy resin composition 11 as in Example 1 was filled in a mold cavity 12a heated to a temperature of 155 ° C. and melted, and the epoxy resin A was transferred to a nematic phase having no homeotropic alignment property. Thereafter, the epoxy resin composition 11 is cured by irradiating ultraviolet rays with an illuminance of 0.2 W / cm ² for 5 minutes in a magnetic field having a magnetic flux density of 5 Tesla, and the anisotropic epoxy resin sheet 1 having a thickness of 0.5 mm. Was made. The direction of the lines of magnetic force was the sheet-like thickness direction.
(Example 3)
An anisotropic epoxy resin sheet 1 was produced in the same manner as in Example 2 except that the magnetic flux density was changed to 10 Tesla as shown in Table 1.
Example 4
The epoxy resin represented by the following formula (2), benzoate type epoxy resin having a mesogenic group in the molecular chain (referred to as epoxy resin B) 98 wt%, diphenyliodonium hexafluoroarsenate 1 wt% as a photopolymerization initiator, light A mixture of 0.5 wt% of 2,2-dimethoxy-2-phenyl-acetophenone and 0.5 wt% of isopropylthioxanthone was prepared as a polymerization initiation aid. Epoxy resin B transitions to a nematic phase having no property of homeotropic alignment at 110 ° C. and transitions to an isotropic phase at 165 ° C. in the temperature rising process. Next, the epoxy resin composition 11 was filled in the cavity 12a of the mold 12 heated to a temperature of 140 ° C. and melted, and the epoxy resin B was transferred to a nematic phase having no homeotropic alignment property. Thereafter, the epoxy resin composition 11 is cured by irradiating ultraviolet rays having an illuminance of 0.2 W / cm ² for 5 minutes in a magnetic field having a magnetic flux density of 5 Tesla, and the anisotropic epoxy resin sheet 1 having a thickness of 0.5 mm is obtained. Produced. The direction of the lines of magnetic force was the sheet-like thickness direction.

（実施例５）
実施例４で用いたものと同一のエポキシ樹脂組成物１１から、表１に示すように磁束密度を１０テスラに変更した以外は実施例４と同様の方法で異方性エポキシ樹脂シート１を作製した。
（比較例１）
前記エポキシ樹脂Ａと、硬化剤として４，４’‐ジアミノ‐１，２‐ジフェニルエタンとを、１：０．５のモル比で混合したエポキシ樹脂組成物１１を、温度１５５℃に加熱した型１２のキャビティ１２ａに充填して溶融させた後、磁場を印加せずに、１５５℃で、３０分間にわたって熱硬化させた。それにより、厚み０．５ｍｍの異方性エポキシ樹脂シート１を作製した。
（比較例２）
比較例１と同一のエポキシ樹脂組成物１１を、温度１５５℃に加熱した型１２のキャビティ１２ａに充填して溶融させ、エポキシ樹脂Ａをホメオトロピック配向する性質を有さないネマティック相に転移させた後、磁束密度５テスラの磁場中にて、１５５℃で、３０分間にわたって熱硬化させた。それにより、厚み０．５ｍｍの異方性エポキシ樹脂シート１を作製した。尚、磁力線の方向はシート状の厚み方向とした。
（比較例３）
比較例１と同一のエポキシ樹脂組成物１１から、表１に示すように磁束密度を１０テスラに変更した以外は比較例２と同様の方法で、異方性エポキシ樹脂シート１を作製した。（比較例４）
実施例１と同一のエポキシ樹脂組成物１１を、温度１５５℃に加熱した型１２のキャビティ１２ａに充填して溶融させ、エポキシ樹脂Ａをホメオトロピック配向する性質を有さないネマティック相に転移させた。その後、磁場を印加せずに、照度０．２Ｗ／ｃｍ^２の紫外線を５分間照射することによりエポキシ樹脂組成物１１を硬化させた。それにより、厚み０．５ｍｍの異方性エポキシ樹脂シート１を作製した。

(Example 5)
An anisotropic epoxy resin sheet 1 was produced from the same epoxy resin composition 11 used in Example 4 by the same method as in Example 4 except that the magnetic flux density was changed to 10 Tesla as shown in Table 1. did.
(Comparative Example 1)
A mold in which the epoxy resin composition 11 prepared by mixing the epoxy resin A and 4,4′-diamino-1,2-diphenylethane as a curing agent in a molar ratio of 1: 0.5 is heated to a temperature of 155 ° C. Twelve cavities 12a were filled and melted, and then thermally cured at 155 ° C. for 30 minutes without applying a magnetic field. Thereby, an anisotropic epoxy resin sheet 1 having a thickness of 0.5 mm was produced.
(Comparative Example 2)
The same epoxy resin composition 11 as in Comparative Example 1 was filled in the cavity 12a of the mold 12 heated to a temperature of 155 ° C. and melted, and the epoxy resin A was changed to a nematic phase having no homeotropic alignment property. Then, it was heat-cured at 155 ° C. for 30 minutes in a magnetic field having a magnetic flux density of 5 Tesla. Thereby, an anisotropic epoxy resin sheet 1 having a thickness of 0.5 mm was produced. The direction of the lines of magnetic force was the sheet-like thickness direction.
(Comparative Example 3)
An anisotropic epoxy resin sheet 1 was produced from the same epoxy resin composition 11 as in Comparative Example 1 by the same method as in Comparative Example 2 except that the magnetic flux density was changed to 10 Tesla as shown in Table 1. (Comparative Example 4)
The same epoxy resin composition 11 as in Example 1 was filled in the cavity 12a of the mold 12 heated to a temperature of 155 ° C. and melted, and the epoxy resin A was changed to a nematic phase having no homeotropic alignment property. . Then, the epoxy resin composition 11 was hardened by irradiating the ultraviolet-ray of illumination intensity 0.2W / cm < ² > for 5 minutes, without applying a magnetic field. Thereby, an anisotropic epoxy resin sheet 1 having a thickness of 0.5 mm was produced.

  In the epoxy resin compositions 11 in Examples 1 to 5 and Comparative Examples 1 to 4, the weight content of the mesogen group portion relative to the entire epoxy resin composition was determined. Moreover, about the epoxy resin sheet 1 obtained in Examples 1-5 and Comparative Examples 1-4, the thickness direction of each sheet | seat 1 is measured with the laser flash method thermal constant measuring apparatus (LF / TCM-FA8510B Rigaku Corporation). The thermal diffusivity and specific heat were measured, and the density of each sheet 1 was measured by an underwater substitution method. The thermal conductivity λ in the thickness direction of each epoxy resin sheet 1 was calculated from the obtained measured values (thermal conductivity = thermal diffusivity × specific heat × density). Furthermore, the thermal expansion coefficient in the thickness direction of those epoxy resin sheets 1 was measured with a thermomechanical analyzer (TMA-50 manufactured by Shimadzu Corporation). Table 1 shows the thermal conductivity λ and the thermal expansion coefficient in the thickness direction of the sheets obtained in Examples 1 to 5 and Comparative Examples 1 to 4. Table 1 also shows the thermal expansion coefficient in the direction along the surface of the sheet in order to show the anisotropy of the sheet.

表１の結果から明らかなように、実施例１では分子鎖内にメソゲン基を有する液晶性エポキシ樹脂が、表面に対して垂直方向に配向するホメオトロピック配向性を有する液晶相を発現する条件を維持したまま、エポキシ樹脂組成物１１を光重合させたことにより、厚さ方向の熱伝導率λが０．４３Ｗ／（ｍ・Ｋ）と高い値を示した。

As is apparent from the results in Table 1, in Example 1, the liquid crystal epoxy resin having a mesogenic group in the molecular chain has a condition for expressing a liquid crystal phase having homeotropic alignment aligned in a direction perpendicular to the surface. The epoxy resin composition 11 was photopolymerized while being maintained, so that the thermal conductivity λ in the thickness direction was as high as 0.43 W / (m · K).

  In Examples 2 to 4, after the liquid crystalline epoxy resin having a mesogenic group in the molecular chain is transferred to a low-viscosity nematic liquid crystal phase by heating and melting, the mesogenic group is aligned in one direction by a magnetic field. An anisotropic epoxy resin sheet having a thermal conductivity λ in the vertical direction of 0.4 W / (m · K) or more and having excellent thermal conductivity was obtained.

  Furthermore, in the epoxy resin sheets of Examples 1 to 4, the thermal expansion coefficient in the thickness direction showed a negative value. This means that these epoxy resin sheets shrink rather than expand due to heat. However, the absolute values of these thermal expansion coefficients are extremely small. Therefore, it can be seen that these epoxy resin sheets have reduced thermal expansion and small thermal shrinkage.

On the other hand, in Comparative Example 1, since an amine-based curing agent that needs to be used in a large amount is used as the curing agent, the weight content of the mesogenic group portion relative to the entire epoxy resin composition is low, and the orientation of the mesogenic group by a magnetic field Not done. Therefore, the thermal conductivity λ in the thickness direction was a low value of 0.30 W / (m · K), and the thermal expansion coefficient was a high value of 104 × 10 ⁻⁶ / K.

  In Comparative Examples 2 and 3, since the mesogenic group is oriented by applying a magnetic field, the thermal conductivity is higher than that of Comparative Example 1. However, as in Comparative Example 1, since an amine-based curing agent that needs to be used in a large amount is used as the curing agent, the weight content of the mesogen group portion relative to the entire epoxy resin composition is low. Therefore, a sufficiently high thermal conductivity has not been obtained.

In Comparative Example 4, a photopolymerization initiator is used, but since the mesogenic groups are not oriented in one direction as a whole, the thermal conductivity λ in the thickness direction is as low as 0.31 W / (m · K). The coefficient of thermal expansion was as high as 144 × 10 ⁻⁶ / K. Thus, in Comparative Examples 1-4, the thermal conductivity λ in the thickness direction is less than 0.4 W / (m · K), and the thermal conductivity is insufficient.

The technical idea that can be grasped from the above embodiment will be described below.
The anisotropic epoxy resin cured product according to claim 1, wherein the liquid crystalline epoxy resin having a mesogenic group in the molecule contains a mesogenic group having a property of homeotropic alignment within a predetermined temperature range. Epoxy resin cured product.

  The method for producing a cured anisotropic epoxy resin according to claim 5, wherein the step of orienting the mesogenic groups of the epoxy resin contained in the epoxy resin composition in a certain direction applies a magnetic field to the epoxy resin composition. The manufacturing method of anisotropic epoxy resin hardened | cured material performed by doing.

-In the manufacturing method of the said anisotropic epoxy resin hardened | cured material, the magnetic flux density of the said magnetic field is a manufacturing method of anisotropic epoxy resin hardened | cured material which is 0.2-20 Tesla.
In the method for producing a cured anisotropic epoxy resin according to claim 5, the liquid crystalline epoxy resin having a mesogenic group in the molecule contains a mesogenic group having a property of homeotropic alignment within a predetermined temperature range, The step of orienting the mesogenic groups of the epoxy resin contained in the epoxy resin composition in a certain direction is performed by maintaining the epoxy resin composition in the predetermined temperature range and orienting the mesogenic groups homeotropically, A method for producing a cured anisotropic epoxy resin.

The perspective view which shows the sheet-like anisotropic epoxy resin hardened | cured material in embodiment of this invention. Schematic which shows the manufacturing apparatus of the anisotropic epoxy resin sheet of this invention. Schematic which shows another manufacturing apparatus of the anisotropic epoxy resin sheet of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Anisotropic epoxy resin sheet, 11 ... Epoxy resin composition

Claims (5)

An epoxy resin cured product formed from an epoxy resin composition, the epoxy resin composition comprising:
A liquid crystalline epoxy resin having a mesogenic group in the molecular chain;
A photopolymerization initiator,
An anisotropic epoxy resin cured product in which the mesogenic group is oriented in a certain direction in the cured product.   The anisotropic epoxy resin hardened | cured material of Claim 1 whose heat conductivity in the direction where the mesogen group is orientated is 0.4-30W / (m * K). Thermal expansion coefficient in the direction mesogenic groups are oriented, -10 × a ^{10 -6 ~50 × 10 -6 [/} K], the anisotropic cured epoxy resin according to claim 1.   The cured anisotropic epoxy resin according to any one of claims 1 to 3, wherein the cured epoxy resin has a sheet shape and mesogenic groups are oriented along the thickness direction thereof. A method for producing a cured epoxy resin formed from an epoxy resin composition comprising a liquid crystalline epoxy resin having a mesogenic group in a molecular chain and a photopolymerization initiator, wherein the mesogenic group is in a certain direction in the cured product. Oriented, and the manufacturing method comprises:
Preparing an epoxy resin composition;
A step of orienting the mesogenic groups of the epoxy resin contained in the epoxy resin composition in a certain direction;
The manufacturing method which consists of the process of photopolymerizing an epoxy resin composition, maintaining the state which orientated the mesogen group.

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