Resin sheet

Abstract

To provide a new resin sheet which enables easy production of a resin sheet excellent in heat resistance.SOLUTION: A resin sheet 10 is obtained by crosslinking a resin composition containing a thermoplastic resin and a filler by irradiation with an electronic beam, and has dynamic elastic modulus E' at 250°C of 1 MPa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resin sheet. [Background technology]

[0002] Demand for heat-resistant films is expanding as materials for electronic components such as printed wiring boards, semiconductor packages, and cable coverings, as well as sealing films and release films, and there is a demand for further improvement in performance and functionality as well as cost reduction. For example, films made from high-melting-point resins such as polymethylpentene (PMP) and polytetrafluoroethylene (PTFE) have excellent heat resistance but are expensive.

[0003] Patent Document 1 discloses a heat-resistant polyamide film having a dynamic modulus of elasticity of 0.5 MPa or more at 300°C, which is obtained by crosslinking a polyamide resin composition containing an aliphatic polyamide resin, an electron beam crosslinking aid, a heat stabilizer, and a crosslinkable olefin resin having a functional group reactive with polyamide, by electron beam irradiation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-350536 Summary of the Invention [Problem to be solved by the invention]

[0005] When a resin composition containing a crosslinking coagent such as triallyl isocyanurate (TAIC) is crosslinked by electron beam irradiation, it is difficult to control the progress of crosslinking. For example, excessive crosslinking may occur during kneading of the resin composition, making it difficult to produce a resin sheet that uniformly exhibits excellent physical properties such as heat resistance at low cost and with high productivity.

[0006] An object of the present invention is to provide a novel resin sheet that can be easily manufactured to have excellent heat resistance. [Means for solving the problem]

[0007] The present invention employs the following configuration. [1] A resin sheet characterized in that a resin composition containing a thermoplastic resin and a filler is crosslinked by electron beam irradiation, and has a dynamic elastic modulus E' at 250°C of 1 MPa or more. [2] The resin sheet according to [1], wherein the melting point of the thermoplastic resin is 100°C or lower. [3] The resin sheet according to [1] or [2], wherein the melting point of the thermoplastic resin is 60°C or lower. [4] The resin sheet according to any one of [1] to [3], wherein the thermoplastic resin contains an ethylene-based polymer or an olefin-based thermoplastic elastomer. [5] The resin sheet according to any one of [1] to [4], wherein the thermoplastic resin contains an ethylene-vinyl acetate copolymer. [6] The resin sheet according to [5], wherein the ethylene-vinyl acetate copolymer has a vinyl acetate content of 25 to 45% by mass. [7] The resin sheet according to any one of [1] to [6], wherein the filler contains magnesium hydroxide. [8] The resin sheet according to any one of [1] to [7], wherein the thermal conductivity in the plane direction of the resin sheet is 3 W / m·K or more. [9] The density of the resin sheet is 2 g / cm 3 The resin sheet according to any one of [1] to [8] below.

[10] The resin sheet according to any one of [1] to [9], wherein, when the dynamic modulus of elasticity of the resin sheet measured under conditions of 100°C and 10 Hz is E'(100), and the dynamic modulus of elasticity of the resin sheet measured under conditions of 250°C and 10 Hz is E'(250), the rate of change in dynamic modulus of elasticity ((E'(100)-E'(250)) / E'(100)*100) is 70% or less. [Effects of the Invention]

[0008] According to the present invention, a novel resin sheet that can be easily produced as a resin sheet having excellent heat resistance is provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view showing an example of a resin sheet. [Figure 2] 1 is a graph showing the results of DMA measurement at 1 Hz of a resin sheet of an example. [Figure 3] 1 is a graph showing the results of DMA measurement at 10 Hz of a resin sheet of an example. DETAILED DESCRIPTION OF THE INVENTION

[0010] A resin sheet according to one embodiment of the present invention is obtained by crosslinking a resin composition containing a thermoplastic resin including an ethylene-based polymer and a filler by electron beam irradiation, and has a dynamic modulus of elasticity E' at 250°C of 1 MPa or more.

[0011] The resin sheet of this embodiment may have electrical insulation properties, which are expressed, for example, by a breakdown voltage, and the breakdown voltage measured by a short-circuit test method in accordance with JIS C 2110 is preferably 1 KV / mm or more.

[0012] <Thermoplastic resin> The resin sheet contains the thermoplastic resin, so that the resin sheet can maintain its sheet shape and has flexibility and adhesion to the object to which it is applied. The thermoplastic resin is not particularly limited as long as it can impart flexibility to the resin sheet before and after crosslinking by electron beam irradiation.

[0013] The resin sheet can be produced, for example, by molding (heat-pressure molding) a resin composition described below for producing the resin sheet, and then crosslinking the resin composition by electron beam irradiation. In this case, the thermoplastic resin preferably has a melting point lower than the heating temperature (molding temperature) at which the resin composition is molded. By molding the resin composition at a temperature higher than the melting point of the thermoplastic resin, a resin sheet with higher uniformity can be obtained.

[0014] The melting point of the thermoplastic resin is preferably 100° C. or lower, and more preferably 90° C. or lower, and may be, for example, 80° C. or lower, 70° C. or lower, or 60° C. or lower. By using a thermoplastic resin having a melting point equal to or lower than the upper limit, a resin sheet with higher uniformity can be obtained. The lower limit of the melting point of the thermoplastic resin is not particularly limited. For example, thermoplastic resins with a melting point of 35° C. or higher are more easily available or produced. In one embodiment, the melting point of the thermoplastic resin may be, for example, any one of 35 to 90° C., 35 to 80° C., and 35 to 70° C. However, these are only examples of the melting points of the thermoplastic resin, and there may be cases where the thermoplastic resin does not have a clear melting point.

[0015] The melt flow rate (sometimes referred to herein as "MFR") of the thermoplastic resin is preferably 1 to 40 g / 10 min, and may be, for example, 5 to 40 g / 10 min, or 10 to 40 g / 10 min. When the MFR of the thermoplastic resin is equal to or greater than the lower limit, the flexibility of the resin sheet relative to the object to which it is applied is increased, and when the resin sheet is used to cover an object to which it is applied, such as a heating element, the object can be easily covered with the resin sheet. When the MFR of the thermoplastic resin is equal to or less than the upper limit, the shape of the resin sheet can be more stably maintained. In this specification, unless otherwise specified, MFR means a value measured in accordance with JIS K 6922-1.

[0016] Preferable examples of the thermoplastic resin include ethylene-based polymers and olefin-based thermoplastic elastomers. When radicals are generated in the polymer chain of the thermoplastic resin by electron beam irradiation, it is preferable that the radicals move along the polymer chain or bond with each other to generate crosslinking points. From this viewpoint, a thermoplastic resin with low crystallinity and high flexibility is preferable.

[0017] Examples of ethylene-based polymers include polyethylene, ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-vinyl acetate copolymer (EVA), etc. Examples of polyethylene (PE) include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and metallocene-catalyzed linear low-density polyethylene (mLLDPE).

[0018] Examples of olefin-based thermoplastic elastomers include hydrogenated block copolymers obtained by hydrogenating a block copolymer consisting of at least one polymer block primarily composed of a vinyl aromatic compound and at least one polymer block primarily composed of a conjugated diene compound. Examples of hydrogenated block copolymers include hydrogenated styrene-isoprene block copolymer (SEPS) and hydrogenated styrene-butadiene block copolymer (SEBS). Ethylene-vinyl acetate copolymer (EVA), which has a high vinyl acetate content, can also be used as a thermoplastic elastomer.

[0019] Because ethylene-vinyl acetate copolymer has a lower melting point than other resins, the resin sheet containing ethylene-vinyl acetate copolymer has excellent moldability before being crosslinked by electron beam irradiation. Furthermore, its heat storage latent heat function provides superior heat dissipation. Furthermore, ethylene-vinyl acetate copolymer has flexibility, impact resistance, and adhesiveness, so when the resin sheet containing ethylene-vinyl acetate copolymer is used to cover an object such as a heating element, the resin sheet easily adheres to the object. Furthermore, because ethylene-vinyl acetate copolymer has polarity, it can be combined with a flame retardant (e.g., magnesium hydroxide), making it easy to impart flame retardancy to the resin sheet.

[0020] In the ethylene-vinyl acetate copolymer, the ratio of the amount (parts by mass) of structural units derived from vinyl acetate to the total amount (parts by mass) of structural units (sometimes referred to herein as the "vinyl acetate content") is preferably 10 to 40% by mass, and may be, for example, 20 to 40% by mass or 30 to 40% by mass. The vinyl acetate content may also be 25 to 45% by mass. When the ratio (vinyl acetate content) is equal to or greater than the lower limit, the flexibility and adhesion of the resin sheet to its application object are improved. For example, when the resin sheet is used to cover an application object such as a heating element, the resin sheet can easily cover the heating element and easily adhere to the application object. When the ratio is equal to or less than the upper limit, the workability during production of the resin sheet is improved.

[0021] The resin sheet may contain only one type of thermoplastic resin, or two or more types. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0022] The thermoplastic resin contained in the resin sheet is preferably ethylene-vinyl acetate copolymer (EVA) in that the effects of the present invention are more pronounced. For example, the proportion of EVA in the thermoplastic resin is preferably 50% by mass or more, more preferably 80% by mass or more, and may be 100% by mass.

[0023] In the resin sheet, the ratio of the content (parts by mass) of the thermoplastic resin to the total mass (parts by mass) of the resin sheet ([content (parts by mass) of thermoplastic resin in resin sheet)] / [total mass (parts by mass) of resin sheet]×100) is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. When the ratio is equal to or greater than the lower limit, the effect obtained by the resin sheet containing the thermoplastic resin is further enhanced. In the resin sheet, the ratio of the content (parts by mass) of the thermoplastic resin to the total mass (parts by mass) of the resin sheet is preferably 45% by mass or less, more preferably 40% by mass or less. When the ratio is equal to or less than the upper limit, the effect obtained by the resin sheet containing components other than the thermoplastic resin is further enhanced. In one embodiment, the ratio may be, for example, any one of 20 to 45 mass%, 25 to 45 mass%, and 30 to 45 mass%, or any one of 20 to 40 mass%, 25 to 40 mass%, and 30 to 40 mass%, although these are just examples of the ratio. The ratio is usually the same as the ratio of the content (parts by mass) of the thermoplastic resin to the total content (parts by mass) of components that do not vaporize at room temperature in the resin composition described below ([content (parts by mass) of thermoplastic resin in resin composition)] / [total content (parts by mass) of components that do not vaporize at room temperature in the resin composition]×100).

[0024] In this specification, "room temperature" means a temperature that is neither particularly cold nor hot, that is, an ordinary temperature, and examples thereof include temperatures of 15 to 25°C.

[0025] <Filler> The filler improves moldability and heat resistance. Examples of the filler include plate-like fillers and granular fillers. The resin sheet may contain only one type of filler or two or more types of fillers. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0026] The filler is not particularly limited, but examples thereof include metal compounds such as metal hydroxides, metal oxides, metal nitrides, and metal carbides, as well as simple metals and alloys. The metal elements contained in the metal compound filler are not particularly limited, but examples thereof include magnesium (Mg), calcium (Ca), titanium (Ti), zirconium (Zr), iron (Fe), zinc (Zn), boron (B), aluminum (Al), and silicon (Si).

[0027] In the resin sheet, the ratio of the filler content (volume parts) to the total volume (volume parts) of the resin sheet ([filler content (volume parts) of resin sheet)] / [total volume (volume parts) of resin sheet]×100) is preferably 10% by volume or more, and may be, for example, 15% by volume or more, 20% by volume or more, or 25% by volume or more. When the ratio is equal to or more than the lower limit, the effect obtained by using the filler is further enhanced. In the resin sheet, the ratio of the content (volume part) of the filler to the total volume (volume part) of the resin sheet is preferably 80% by volume or less, and may be, for example, 70% by volume or less, 60% by volume or less, or 50% by volume or less. When the ratio is equal to or less than the upper limit, the effect obtained by using a thermoplastic resin crosslinked by electron beam irradiation is further enhanced.

[0028] <Filler plate> The resin sheet may contain the plate-like filler. The plate-like filler in the resin sheet is likely to be oriented in the same direction as the surface direction of the resin sheet or in a direction close to the surface direction of the resin sheet. Therefore, the thermal conductivity of the resin sheet in the surface direction is particularly high, and the heat dissipation ability in the surface direction is also high. In this specification, the "direction parallel to the surface" may be referred to as the "plane direction", not only in the case of a resin sheet. Furthermore, the card-house-like filler (a filler in which plate-like fillers are aggregated to form secondary particles) is a filler other than the plate-like filler.

[0029] The aspect ratio of the plate-like filler ([particle diameter of plate-like filler] / [thickness of plate-like filler]) is preferably 10 to 50, and may be, for example, any of 10 to 30 and 30 to 50. When the aspect ratio of the plate-like filler is within this range, the effect obtained by the resin sheet containing the plate-like filler is further enhanced.

[0030] As the particle diameter of the flake-like filler, for example, the maximum length of a line segment connecting two different points on the periphery of the flake-like filler can be used. As the thickness of the flake-like filler, for example, the maximum distance between the main surfaces of the flake-like filler can be adopted. As the aspect ratio of the flake-like filler, for example, the average value of the aspect ratios of 50 randomly selected flake-like fillers can be used.

[0031] The average particle size of the platy filler is preferably 5 μm or more, and may be, for example, 6.5 μm or more or 8 μm or more. When the average particle size of the platy filler is equal to or more than the lower limit, the effect obtained by using the platy filler is further enhanced. There is no particular upper limit to the average particle size of the flake-like filler. For example, flake-like fillers with an average particle size of 40 μm or less are more readily available. In one embodiment, the average particle size of the flake-like filler may be, for example, any one of 5 to 40 μm, 6.5 to 35 μm, and 8 to 30 μm, although these are just examples of the average particle size of the flake-like filler.

[0032] In this specification, not limited to the case of a plate-like filler, unless otherwise specified, the "average particle size" means the particle size at 50% accumulation of particles (D50) when the particle size distribution of particles is measured on a volume basis by a laser diffraction particle size distribution measurement method.

[0033] The thermal conductivity of the flake-like filler may be, for example, any one of 5 W / m·K or more, 10 W / m·K or more, 25 W / m·K or more, and 40 W / m·K or more. The upper limit of the thermal conductivity of the flake-like filler is not particularly limited. For example, flake-like fillers with a thermal conductivity of 400 W / m·K or less are more readily available. In one embodiment, the thermal conductivity of the flake-like filler may be, for example, any one of 5 to 400 W / m·K, 10 to 400 W / m·K, 25 to 400 W / m·K, and 40 to 400 W / m·K, although these are just examples of the thermal conductivity of the flake-like filler.

[0034] The thermal conductivity of fillers, including plate-like fillers, can be measured, for example, by preparing a sintered body of the filler and measuring it using a known thermal conductivity measuring device such as a laser flash method or a hot disk method, or by measuring it using a thermal property microscope or the like.

[0035] Examples of the material for the plate-like filler include metal nitrides such as boron nitride and metal oxides such as aluminum oxide.

[0036] The resin sheet may contain only one type of flake filler, or two or more types. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0037] The plate-like filler is preferably made of boron nitride (BN) or aluminum oxide (Al2O3) (i.e., a boron nitride filler or an aluminum oxide filler). A resin sheet containing such a plate-like filler has high heat dissipation properties and better flexibility. For example, when the resin sheet is used to cover an object such as a heating element, the object can be easily covered with the resin sheet.

[0038] The plate-like filler is preferably made of boron nitride (BN) (i.e., a boron nitride filler). A resin sheet containing such a plate-like filler has the above-mentioned preferable properties, and furthermore, since its relative dielectric constant is lowered, it has further preferable properties as described below.

[0039] In the resin sheet, the ratio of the content (volume parts) of the plate-like filler to the total volume (volume parts) of the resin sheet ([content (volume parts) of the plate-like filler in the resin sheet)] / [total volume (volume parts) of the resin sheet]×100) is preferably 10% by volume or more, and may be, for example, 15% by volume or more, 20% by volume or more, or 25% by volume or more. When the ratio is equal to or more than the lower limit, the effect obtained by using the plate-like filler is further enhanced. In the resin sheet, the content (volume part) of the plate-like filler relative to the total volume (volume part) of the resin sheet is preferably 35% by volume or less, and may be, for example, 30% by volume or less, 25% by volume or less, or 20% by volume or less. When the content is equal to or less than the upper limit, the effect obtained by using a filler other than the plate-like filler, such as the granular filler, is further enhanced. In one embodiment, the ratio may be, for example, any one of 10 to 35 volume%, 15 to 35 volume%, 20 to 35 volume%, and 25 to 35 volume%, any one of 10 to 30 volume%, 15 to 30 volume%, 20 to 30 volume%, and 25 to 30 volume%, any one of 10 to 25 volume%, 15 to 25 volume%, and 20 to 25 volume%, or 10 to 20 volume%, although these are just examples of the ratio.

[0040] <Granular filler> The resin sheet has improved heat resistance and moldability due to the inclusion of the granular filler. The granular filler in the resin sheet is widely distributed in both the surface direction and thickness direction of the resin sheet, and as described below, the size of the granular filler is small. When the granular filler is used in combination with a plate-like filler, the granular filler acts as a connecting filler and maintains contact with the plate-like filler in both the surface direction and thickness direction of the resin sheet, thereby connecting the plate-like fillers together. In this case, the thermal conductivity is increased in both the surface direction and thickness direction of the resin sheet, and heat dissipation is improved. In particular, the resin sheet contains a plate-like filler and a connecting filler, and thus the thermal conductivity in the thickness direction is increased, and heat dissipation is improved.

[0041] The average particle size of the granular filler is preferably 2 μm or less, so that when the granular filler is used in combination with the flake-like filler, the flake-like filler particles are sufficiently connected to each other by the granular filler. In order to enhance such effects, the average particle size of the particulate filler is preferably 1.5 μm or less, and may be, for example, either 1.2 μm or less or 0.9 μm or less. The lower limit of the average particle diameter of the granular filler is not particularly limited. For example, granular fillers having an average particle diameter of 0.5 μm or more are more readily available, and the use of such granular fillers can more easily improve the performance of the resin sheet (particularly, the heat dissipation properties as a connecting filler). In one embodiment, the average particle size of the particulate filler may be, for example, any one of 0.5 to 2 μm, 0.5 to 1.5 μm, 0.5 to 1.2 μm, and 0.5 to 0.9 μm, although these are just examples of the average particle size of the particulate filler.

[0042] The shape of the granular filler is not particularly limited, but when used in combination with a plate-like filler, the granular filler preferably has a flat shape, and more preferably is plate-like. Having a flat surface, particularly a plate-like shape, of the granular filler increases the contact area between the granular filler and the plate-like filler. As described above, the surface direction of the plate-like filler tends to be oriented in the same direction as the surface direction of the resin sheet or in a direction close to the surface direction of the resin sheet. Therefore, even if the granular filler has a flat surface, the more the overall shape of the granular filler deviates from a plate shape, the smaller the contact area between the granular filler and the plate-like filler tends to be. However, by having an average particle diameter of 2 μm or less, sufficient contact between the granular filler and the plate-like filler is maintained.

[0043] The granular filler is preferably non-agglomerated (not agglomerated). The lower the content of the granular filler, which is an agglomerate, in the resin sheet, the more flexible the resin sheet becomes. For example, when the resin sheet is used to cover an object such as a heating element, the object can be easily covered with the resin sheet.

[0044] The thermal conductivity of the particulate filler may be, for example, any one of 5 W / m·K or more, 10 W / m·K or more, 25 W / m·K or more, and 40 W / m·K or more. There is no particular upper limit to the thermal conductivity of the granular filler. For example, granular fillers with a thermal conductivity of 400 W / m·K or less are more readily available. In one embodiment, the thermal conductivity of the particulate filler may be, for example, any one of 5 to 400 W / m·K, 10 to 400 W / m·K, 25 to 400 W / m·K, and 40 to 400 W / m·K, although these are just examples of the thermal conductivity of the particulate filler.

[0045] Examples of the material of the particulate filler include metal hydroxides such as magnesium hydroxide.

[0046] The surface of the granular filler may or may not be treated with a surface treatment agent. By using a surface-treated granular filler, for example, the affinity between the granular filler and a resin such as a thermoplastic resin is improved, and the flexibility of the resin sheet is improved, thereby increasing the adhesion of the resin sheet to the object to which it is applied. Examples of surface treatments for particulate fillers include surface treatments with fatty acids or organic silicon compounds (silane coupling agents).

[0047] The resin sheet may contain only one type of particulate filler, or two or more types. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0048] The particulate filler is preferably made of magnesium hydroxide (Mg(OH)2) (i.e., a magnesium hydroxide filler). Since magnesium hydroxide is also a flame retardant, a resin sheet containing such a particulate filler has high flame retardancy in addition to high heat dissipation properties.

[0049] The resin sheet to which flame retardancy has been imparted, such as the resin sheet containing magnesium hydroxide filler, can meet, for example, grade V-0, V-1 or V-2 of the UL94 standard.

[0050] When a plate-like filler and a granular filler are used in combination in the resin sheet, the ratio of the granular filler content to the plate-like filler content ([parts by volume of granular filler in resin sheet] / [parts by volume of plate-like filler in resin sheet]×100) is preferably 60% by volume or more, and may be, for example, 65% by volume or more, 70% by volume or more, 90% by volume or more, or 200% by volume or more. When the ratio is equal to or greater than the lower limit, the effect obtained by using the granular filler is further enhanced. In the resin sheet, the ratio of the granular filler content to the plate-like filler content is preferably 300% by volume or less, and may be, for example, 250% by volume or less, 140% by volume or less, 110% by volume or less, or 80% by volume or less. When the ratio is equal to or less than the upper limit, the effect obtained by using a filler other than the granular filler, such as the plate-like filler, is further enhanced. In one embodiment, the ratio is preferably 60 to 300% by volume, and may be, for example, any of 65 to 300% by volume, 70 to 300% by volume, 90 to 300% by volume, and 200 to 300% by volume, any of 60 to 250% by volume, 65 to 250% by volume, 70 to 250% by volume, and 90 to 250% by volume, any of 60 to 140% by volume, 65 to 140% by volume, 70 to 140% by volume, and 90 to 140% by volume, any of 60 to 110% by volume, 65 to 110% by volume, 70 to 110% by volume, and 90 to 110% by volume, or any of 60 to 80% by volume, 65 to 80% by volume, and 70 to 80% by volume. However, these are just examples of the ratios.

[0051] In the resin sheet, the ratio of the granular filler content (volume parts) to the total volume (volume parts) of the resin sheet ([granular filler content (volume parts) of the resin sheet)] / [total volume (volume parts) of the resin sheet]×100) is preferably a numerical range that satisfies the ratio of the granular filler content to the plate-like filler content described above, and is, for example, preferably 6% by volume or more, and may be, for example, any of 9.8% by volume or more, 14% by volume or more, 20% by volume or more, and 25% by volume or more. When the ratio is above the lower limit, the effect obtained by using the granular filler is further enhanced. In the resin sheet, the content (volume part) of the granular filler relative to the total volume (volume part) of the resin sheet is preferably 49% by volume or less, and may be, for example, 33% by volume or less or 21% by volume or less. When the content is equal to or less than the upper limit, the effect obtained by using a filler other than the granular filler, such as the plate-like filler, is further enhanced. In one embodiment, the ratio may be, for example, any one of 6 to 49 volume%, 9.8 to 49 volume%, 14 to 49 volume%, 20 to 49 volume%, and 25 to 49 volume%, any one of 6 to 33 volume%, 9.8 to 33 volume%, 14 to 33 volume%, and 20 to 33 volume%, or any one of 6 to 21 volume%, 9.8 to 21 volume%, and 14 to 21 volume%, but these are just examples of the ratio.

[0052] <Other ingredients> The resin sheet may contain other components that do not fall under either the thermoplastic resin or the filler, as long as the effects of the present invention are not impaired. The other components can be selected arbitrarily depending on the purpose and are not particularly limited.

[0053] The resin sheet may contain only one type of other component, or two or more types. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0054] Examples of the other components include additives known in the art. Examples of the additives include antioxidants, antistatic agents, viscosity reducers, thickeners, infrared absorbers, ultraviolet absorbers, and antiblocking agents.

[0055] In the resin sheet, the ratio of the total content (parts by mass) of the thermoplastic resin and the filler to the total mass (parts by mass) of the resin sheet (([content of thermoplastic resin in resin sheet (parts by mass)] + [content of filler in resin sheet (parts by mass)]) / [total mass of resin sheet (parts by mass)] × 100) is preferably 80% by mass or more, more preferably 90% by mass or more, and may be, for example, any one of 95% by mass or more, 97% by mass or more, and 99% by mass or more. Meanwhile, the ratio is 100% by mass or less. The ratio is usually the same as the ratio of the total content (parts by mass) of the thermoplastic resin and the filler to the total content (parts by mass) of components that do not vaporize at room temperature in the resin composition described below (([content (parts by mass) of thermoplastic resin in resin composition)] + [content (parts by mass) of filler in resin composition)]) / [total content (parts by mass) of components that do not vaporize at room temperature in the resin composition] × 100).

[0056] <Thickness of resin sheet> The thickness of the resin sheet is preferably 10 μm or more, and may be, for example, 15 μm or more, or 20 μm or more. When the thickness of the resin sheet is equal to or more than the lower limit, the functionality (for example, heat dissipation) of the resin sheet is further improved. On the other hand, the thickness of the resin sheet is preferably 2000 μm or less, and may be, for example, 1500 μm or less or 1000 μm or less. When the thickness of the resin sheet is equal to or less than the upper limit, the handleability (for example, flexibility) of the resin sheet becomes higher. In one embodiment, the thickness of the resin sheet may be, for example, any one of 10 to 2000 μm, 15 to 1500 μm, and 20 to 1000 μm, although these are just examples of the thickness of the resin sheet. As will be described later, the thickness of the resin sheet is preferably adjusted depending on the thickness of the object to which the resin sheet is to be applied.

[0057] <Thermal conductivity in the surface direction of the resin sheet> The thermal conductivity of the resin sheet in the plane direction is preferably 2 W / m K or more, more preferably 3 W / m K or more, and may be, for example, 4 W / m K or more. The resin sheet having a thermal conductivity equal to or greater than the lower limit has high heat dissipation properties in the plane direction. There is no particular upper limit to the thermal conductivity of the resin sheet in the plane direction. For example, a resin sheet having a thermal conductivity of 15 W / m·K or less can be more easily manufactured. In one embodiment, the thermal conductivity of the resin sheet in the plane direction may be, for example, any one of 2 to 15 W / m·K, 3 to 15 W / m·K, and 4 to 15 W / m·K. Not limited to the resin sheet, the thermal conductivity in the plane direction of a resin sheet is more specifically the thermal conductivity of the resin sheet in a direction parallel to one surface or the other surface of the resin sheet.

[0058] The thermal conductivity in the plane direction of the resin sheet can be measured by the hot disc method in accordance with ISO 22007-2, for example, using a hot disc method thermal property measuring device (e.g., "TPS 2500 S" or "TPS 500 S") manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0059] The thermal conductivity in the plane direction of the resin sheet can be adjusted, for example, by adjusting the type of thermoplastic resin and its content in the resin sheet; the type of filler and its content in the resin sheet; the thickness of the resin sheet, etc.

[0060] <Resin sheet density> The density of the resin sheet is 2 g / cm 3 It is preferable that the density is 1.7 g / cm or less, for example. 3 The following may be used. Various electronic devices configured with such a resin sheet are suitable for use in, for example, portable electronic devices because they are lightweight and suppress heat generation. Furthermore, it is possible to reduce fuel consumption and CO2 emissions during transportation. The lower limit of the density of the resin sheet is not particularly limited. 3 The resin sheet described above can be more easily realized. In one embodiment, the density of the resin sheet is, for example, 1 to 2 g / cm 3 , and 1 to 1.7 g / cm 3 However, these are just examples of the density of the resin sheet. The density of the resin sheet can be adjusted by, for example, adjusting the types and contents of the components contained in the resin sheet.

[0061] The density of the resin sheet can be measured by a known method, for example, in accordance with JIS K 7112:1999 or JIS K 0061:2022 (density gradient tube method).

[0062] <Electron beam irradiation of resin sheet> The resin sheet is crosslinked by electron beam irradiation. In this case, the resin sheet is preferably irradiated with electron beams at an absorbed dose of 20 to 300 kGy. The acceleration voltage of the electron beam irradiation is preferably 100 to 300 kV. By irradiating the resin sheet with electron beams, the resin sheet is partially crosslinked, improving the heat resistance of the resin sheet. Furthermore, if the resin sheet has high adhesion before electron beam irradiation, the crosslinking increases the dynamic modulus of elasticity, reducing adhesion and improving releasability and repairability.

[0063] When the absorbed dose of electron beam irradiation is equal to or greater than the lower limit, the crosslink density of the resin sheet can be further improved. When the absorbed dose of electron beam irradiation is equal to or less than the upper limit, excessive electron beam irradiation of the resin sheet can be prevented.

[0064] When the acceleration voltage of the electron beam irradiation is equal to or greater than the lower limit, the crosslink density of the resin sheet can be further improved. When the acceleration voltage of the electron beam irradiation is equal to or less than the upper limit, excessive electron beam irradiation of the resin sheet can be prevented.

[0065] The atmosphere during electron beam irradiation is not particularly limited, but may be air or an inert gas atmosphere such as nitrogen.

[0066] <Dynamic elastic modulus of resin sheet> A resin sheet obtained by crosslinking a resin composition by electron beam irradiation has a dynamic modulus of elasticity E' of 1 MPa or more at 250°C. This makes it possible to obtain excellent heat resistance even in a resin sheet with a low specific gravity that uses an inexpensive resin.

[0067] The dynamic modulus of elasticity E' of the resin sheet at a temperature of 250°C can be measured in accordance with JIS K 7244-4. Specifically, the dynamic modulus of elasticity E' can be measured, for example, using a dynamic viscoelasticity measuring device. In this case, for example, the dynamic modulus of elasticity E' can be measured using a sample with a width of 4 mm in a tensile mode in a temperature range of 25°C to 250°C under conditions of a displacement of 10 μm, a vibration frequency of 1 Hz or 10 Hz, and a temperature rise rate of 3°C / min.

[0068] The dynamic modulus of elasticity E' of the resin sheet can be more easily adjusted by, for example, adjusting the type and content of the components contained in the resin sheet, the thickness of the resin sheet, the absorbed dose of electron beam irradiation, etc. The resin sheet after electron beam irradiation may have a dynamic modulus of elasticity E' of 1 MPa or more in a temperature range of 25° C. to 250° C. The upper limit of the dynamic modulus of elasticity E' is not particularly limited, and examples include 10 MPa, 20 MPa, 50 MPa, and 100 MPa.

[0069] Furthermore, when the dynamic storage modulus of the resin sheet measured at 100°C and 10 Hz is E'(100), and the dynamic storage modulus measured at 250°C and 10 Hz is E'(250), it is preferable that the rate of change in storage modulus ((E'(100)-E'(250)) / E'(100)*100) is 70% or less. This results in small changes in modulus even with temperature changes, allowing for stable use (less susceptible to disturbances).

[0070] Furthermore, if the dynamic modulus of elasticity of the resin sheet measured under conditions of 100°C and 1 Hz is E'(100), and the dynamic modulus of elasticity measured under conditions of 250°C and 1 Hz is E'(250), it is preferable that the rate of change in the dynamic modulus of elasticity ((E'(100)-E'(250)) / E'(100)*100) is 70% or less. This means that the change in the dynamic modulus of elasticity is small even when the temperature changes, allowing for stable use (less susceptible to disturbances).

[0071] <Resin composition and method for producing same> The resin sheet of the present embodiment can be produced, for example, by crosslinking a resin composition containing the thermoplastic resin, the filler, and, if necessary, the other components, by electron beam irradiation.

[0072] The resin composition may contain a solvent in addition to the above-mentioned components. The resin composition containing a solvent may have improved handleability. In this specification, unless otherwise specified, the term "solvent" refers not only to a component capable of dissolving a solute in a solution, but also to a component that serves as a dispersion medium in a dispersion liquid.

[0073] The solvent is preferably an organic solvent, and more preferably an organic solvent that can be removed by vaporization when the resin composition is heated. The content of the solvent in the resin composition can be selected arbitrarily depending on the purpose, and is not particularly limited.

[0074] The resin composition may be produced by adjusting the types and contents of the components contained so that the resin sheet contains the desired components (constituent materials) in the desired amounts. For example, the ratio of the contents of the components that do not vaporize at room temperature in the resin composition is usually the same as the ratio of the contents of the components in the resin sheet.

[0075] The resin composition can be produced by blending the thermoplastic resin, the filler, and, if necessary, the other components, and, if necessary, the solvent. The order of addition of the components when blending is not particularly limited, and two or more components may be added simultaneously. The method for mixing the components during blending is not particularly limited, and may be appropriately selected from known methods. The temperature and time for adding and mixing each component are not particularly limited as long as the components do not deteriorate, and can be adjusted appropriately.

[0076] The resin composition may be, for example, a kneaded product obtained by kneading the thermoplastic resin, the filler, and, if necessary, the other components.

[0077] <Molding of resin sheets> The resin sheet may be, for example, one obtained by molding the resin composition before being irradiated with an electron beam. Even when the resin sheet is irradiated with an electron beam, the shape of the resin sheet before being irradiated with an electron beam is maintained. By molding the resin composition before being irradiated with an electron beam, a resin sheet having a desired shape can be easily formed.

[0078] The resin composition can be molded by a known method. For example, when molding under vacuum conditions, the resin composition can be molded by a vacuum hot press. When molding under normal pressure, the resin composition can be molded by a melt extrusion film-forming method. The shape of the resin sheet is not particularly limited, and examples include a flat shape, a curved shape, etc. Fig. 1 shows an example of a resin sheet 10 having flat surfaces 11 and 12. In this case, the left-right direction of the figure is the surface direction, and the up-down direction is the thickness direction.

[0079] The molding temperature (pressurizing temperature) of the resin composition is preferably higher than the melting point of the thermoplastic resin, and may be, for example, any of a temperature 15°C or higher than the melting point of the thermoplastic resin, a temperature 35°C or higher than the melting point of the thermoplastic resin, and a temperature 55°C or higher than the melting point of the thermoplastic resin. When the molding temperature is equal to or higher than the lower limit, the resin sheet can be obtained with higher uniformity. The upper limit of the molding temperature is not particularly limited. For example, if the molding temperature is equal to or lower than a temperature 150° C. higher than the melting point of the thermoplastic resin, excessive heating can be avoided.

[0080] The pressure during molding of the resin composition is not particularly limited as long as the effect of pressurization is sufficient, but is preferably 3 MPa or more, and may be, for example, 8 MPa or more or 13 MPa or more. When the pressure is equal to or more than the lower limit, a resin sheet with higher uniformity can be obtained. The upper limit of the pressure is not particularly limited. For example, if the pressure is 20 MPa or less, excessive pressure can be avoided.

[0081] The molding time (pressure time) of the resin composition is not particularly limited as long as the effect of pressure is sufficiently obtained, and can be set arbitrarily depending on, for example, the pressure during molding, but is preferably 0.5 minutes or more. By setting the molding time to be equal to or greater than the lower limit, a resin sheet with higher uniformity can be obtained. There is no particular upper limit to the molding time. For example, if the molding time is 10 minutes or less, excessive pressure can be avoided.

[0082] The resin composition is preferably molded under reduced pressure, more preferably under vacuum conditions, for example, a pressure of 0.05 MPa or less. By molding under reduced pressure in this manner, a resin sheet with higher uniformity can be obtained.

[0083] <Resin sheet> The resin sheet of this embodiment has significantly improved heat resistance when irradiated with an electron beam, and can be used for, for example, gaskets, packing, sealing sheets, release sheets, molding sheets, and the like.

[0084] The resin sheet of this embodiment can be produced from a thermoplastic resin containing an ethylene-based polymer and a resin composition containing a filler, and therefore has a low specific gravity. It is also possible to produce a halogen-free resin sheet (containing no halogens such as fluorine or chlorine). Fluorine resins have excellent heat resistance, but are expensive and require careful handling of organic fluorine compounds. The resin sheet of this embodiment can be used to replace fluororesin sheets.

[0085] As a release sheet, it can be placed between the material to be processed and a processing member such as a hot plate when producing molded products or laminates made by bonding different materials, and can be used to prevent the material from sticking. The sealing sheet can be used for sealing electronic materials, other products, materials, etc., and for sealing housings, etc.

[0086] When the resin sheet is used as a heat dissipation sheet, by covering the surface of a heat generating body such as a CPU, a new heat dissipation structure can be configured in various electronic devices, and heat generation in the various electronic devices can be suppressed.

[0087] As described above, the resin sheet has high thermal conductivity and heat dissipation properties in both the planar and thickness directions, and is also highly flexible, making it an excellent heat dissipation sheet. [Example]

[0088] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below. The raw materials and ingredients used in the examples and comparative examples are shown below.

[0089] [Thermoplastic resin] Thermoplastic resin (a1): Ethylene-vinyl acetate copolymer (EVA) (Mitsui Dow Polychemicals "Evaflex (registered trademark) EV150"; melting point: approximately 60°C; MFR: 30 g / 10 min; density: 0.96 g / cm 3 , vinyl acetate content 33% by mass The MFR of the EVA is a value measured in accordance with JIS K 7210:1999 under a temperature condition of 190° C. and a load of 2.16 kg.

[0090] [Plate-shaped filler] Plate-shaped filler (b1): Plate-shaped boron nitride filler (Tokuyama Corporation "K03", average particle size 9 μm, density 2.3 g / cm 3 , thermal conductivity 60W / m·K, aspect ratio 30, relative dielectric constant 4) [Granular filler] Granular filler (c1): Magnesium hydroxide filler surface-treated with higher fatty acid (Kyowa Chemical Industry Co., Ltd., "KISUMA (registered trademark) 5B", magnesium hydroxide content 95% by mass or more, higher fatty acid content 5% by mass or less, average particle diameter 0.83 μm, thermal conductivity 8 W / m K) Granular filler (c5): Magnesium hydroxide filler (Kyowa Chemical Industry Co., Ltd. "KISUMA (registered trademark) 8", average particle size 1.38 μm, thermal conductivity 8 W / m·K)

[0091] <Manufacturing of resin sheets> A pellet-shaped resin composition was prepared by melt-kneading thermoplastic resin (a1) (500 g), plate-like filler (b1) (250 g), granular filler (c1) (75 g), and granular filler (c5) (675 g) using a twin-screw extruder. Furthermore, the obtained resin composition was sandwiched between a pair of hot plates and molded by vacuum hot pressing at a pressure of 15 MPa for 1 minute while heating at 120°C under vacuum conditions of a pressure of 0.02 MPa or less, to obtain a single-layer resin sheet (thickness 1 mm).

[0092] The resin sheet contains 33.3% by mass of thermoplastic resin (a1), 16.7% by mass of flake filler (b1), 5.0% by mass of granular filler (c1), and 45.0% by mass of granular filler (c5). The total flake filler content is 11.6% by volume, and the granular filler content is 34.4% by volume.

[0093] The resin sheet was irradiated with electron beams at an absorbed dose of 150 kGy in Example 1, with an absorbed dose of 300 kGy in Example 2, and without electron beam irradiation in Comparative Example 1.

[0094] <Measurement of dynamic elastic modulus> The dynamic modulus of elasticity E' of the resin sheet obtained above was measured in accordance with JIS K 7244-4 using a dynamic viscoelasticity measuring device ("DMA7100" manufactured by Hitachi High-Tech Science Corporation) in a tensile mode in a temperature range of 25°C to 250°C using a 4 mm wide sample, under conditions of a displacement of 10 μm, a vibration frequency of 1 Hz or 10 Hz, and a heating rate of 3°C / min. The results of the measurement at a vibration frequency of 1 Hz are shown in Figure 2, and the results of the measurement at a vibration frequency of 10 Hz are shown in Figure 3.

[0095] As shown in Figures 2 and 3, the resin sheet of Comparative Example 1 showed a significant decrease in dynamic modulus at temperatures above the melting point of EVA, whereas the resin sheets of Examples 1 and 2 suppressed the decrease in dynamic modulus at temperatures above the melting point of EVA, and the dynamic modulus E' at 250°C was 1 MPa or more.

[0096] The resin sheet of Example 1 had a dynamic elastic modulus E' at 250°C of 3 MPa or more at a vibration frequency of 1 Hz and 4 MPa or more at a vibration frequency of 10 Hz. The resin sheet of Example 2 had a dynamic elastic modulus E' at 250°C of 8 MPa or more at a vibration frequency of 1 Hz and 10 MPa or more at a vibration frequency of 10 Hz.

[0097] <Change in dynamic modulus of elasticity> The dynamic modulus change rate ((E'(100)-E'(250)) / E'(100)*100) was calculated from the dynamic modulus measured under the above conditions. As a result, for the resin sheet of Example 1, the dynamic modulus change rate at 1 Hz was 69.7%, and the dynamic modulus change rate at 10 Hz was 69.6%, both of which were below 70%. Furthermore, for the resin sheet of Example 2, the dynamic modulus change rate at 1 Hz was 55.2%, and the dynamic modulus change rate at 10 Hz was 55.2%, both of which were below 70%.

[0098] <Measurement of thermal conductivity in the surface direction of a resin sheet> The thermal conductivity of the resin sheet obtained above in the plane direction was measured using a hot disc method thermal property measuring device ("TPS 500 S" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) At this time, two resin sheets were sandwiched between insulating materials, and a sensor with a diameter of 7 mm was inserted between these resin sheets to measure the thermal conductivity of the resin sheet. The thermal conductivity of the resin sheet obtained above in the plane direction was 3 W / m·K.

[0099] <Measurement of resin sheet density> The density of the resin sheet obtained above was measured in accordance with JIS K 7112:1999. The density of the resin sheet obtained above was 1.6 g / cm 3 and 2 g / cm 3 It was less than.

[0100] <Measurement of dielectric breakdown voltage> The dielectric breakdown voltage of the resin sheet obtained above was measured in accordance with JIS C 2110. The dielectric breakdown voltage of the resin sheet obtained above was 1.6 KV / mm, which was 1 KV / mm or more. [Industrial Applicability]

[0101] The resin sheet of the present invention can be used to form a heat dissipation material for electronic components and a cushion film used in the manufacturing process of electronic components. [Explanation of symbols]

[0102] 10...resin film, 11...one side, 12...other side.

Claims

1. A resin sheet characterized in that a resin composition containing a thermoplastic resin and a filler is crosslinked by electron beam irradiation, and has a dynamic elastic modulus E' at 250°C of 1 MPa or more.

2. The resin sheet according to claim 1 , wherein the melting point of the thermoplastic resin is 100° C. or lower.

3. The resin sheet according to claim 1 , wherein the melting point of the thermoplastic resin is 60° C. or lower.

4. The resin sheet according to claim 1 , wherein the thermoplastic resin comprises an ethylene-based polymer or an olefin-based thermoplastic elastomer.

5. The resin sheet according to claim 1, wherein the thermoplastic resin comprises an ethylene-vinyl acetate copolymer.

6. The resin sheet according to claim 5, wherein the ethylene-vinyl acetate copolymer has a vinyl acetate content of 25 to 45% by mass.

7. The resin sheet according to claim 1 , wherein the filler comprises magnesium hydroxide.

8. The resin sheet according to claim 1 , wherein the resin sheet has a thermal conductivity of 3 W / m·K or more in a plane direction.

9. The density of the resin sheet is 2 g / cm ３ The resin sheet according to claim 1, wherein:

10. When the dynamic modulus of elasticity of the resin sheet measured under conditions of 100 ° C. and 10 Hz is E' (100), and the dynamic modulus of elasticity measured under conditions of 250 ° C. and 10 Hz is E' (250), the rate of change in the dynamic modulus of elasticity ((E' (100) - E' (250)) / E' (100) * 100) is 70% or less. The resin sheet according to claim 1.

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