JP5308204B2 - Heat dissipation sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-dissipating sheet that is formed of a thermoplastic liquid crystal polymer, exhibits high heat-dissipating properties and is excellent in processability, mechanical strengths and the like. <P>SOLUTION: The heat-dissipating sheet includes a liquid crystal polymer, where the liquid crystal polymer is a thermoplastic liquid crystal polymer and the ratio (&lambda;xy/&lambda;z) of a thermoconductivity &lambda;z in the thickness direction to a thermoconductivity &lambda;xy in the plane direction of the heat-dissipating sheet is 6-60. Such heat dissipating sheet is obtained by extrusion molding a thermoplastic liquid crystal polymer while stretching it. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a heat dissipating sheet which is formed using a thermoplastic liquid crystal polymer and has high heat dissipating properties, as well as excellent workability and mechanical strength.

Conventionally, metals and ceramics having high heat dissipation characteristics have been used as heat dissipation sheets. However, these metals and ceramics are not only difficult to be multilayered, but also have the disadvantage that ceramics are brittle.
Therefore, a heat radiating sheet using a resin material has been studied from the viewpoint of not only multilayering but also being able to overcome fragility.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2007-9084), a polyamide resin, a polyacetal resin, a polyphenylene ether resin, a polycarbonate resin, an ABS resin, a polyolefin resin, a polystyrene resin, a methacrylic resin, One or more kinds of thermoplastic resins selected from thermoplastic elastomers are 1% by weight or more and less than 20% by weight, and the core part and zinc oxide which is needle-like crystals extending in four axial directions different from the core part are 80% by weight. A heat-dissipating resin sheet in which a resin composition consisting of more than 99% and 99% by weight or less is formed into a sheet shape is disclosed.

JP 2007-9084 A (Claims)

  However, in the heat-dissipating resin sheet used in Patent Document 1, not only a specific shape of zinc oxide is required, but also because the ratio of zinc oxide to the resin is high, breakage of the film occurs when the film is stretched, Mechanical strength may be reduced.

Accordingly, an object of the present invention is to provide a sheet which is formed from a liquid crystal polymer and has excellent heat dissipation even when the filler content is reduced.
Another object of the present invention is to provide a heat dissipating sheet that can achieve both workability and heat resistance.

Still another object of the present invention is to provide a heat dissipating sheet that is not only excellent in dimensional stability but also has low hygroscopicity.
Another object of the present invention is to provide a heat dissipating sheet that is excellent in mechanical strength and has a low dielectric constant and a low dielectric loss tangent.

  As a result of intensive studies to solve the above-described problems of the prior art, the present inventors have given anisotropy to the thermal conductivity in the plane direction and the thickness direction of the liquid crystal polymer sheet, so that The heat dissipation can be promoted and the heat dissipation characteristics can be improved, and the obtained liquid crystal polymer sheet is useful as a heat dissipation sheet even if the filler content is reduced (particularly, without the filler). As a result, the present invention has been completed.

That is, the present invention is a heat dissipation sheet composed of a liquid crystal polymer, wherein the liquid crystal polymer is a thermoplastic liquid crystal polymer, and the thermal conductivity λxy in the planar direction with respect to the thermal conductivity λz in the thickness direction of the heat dissipation sheet. The ratio (λxy / λz) is 6 to 60, and concavo-convex transfer processing is performed in the thickness direction of the sheet , and the depth of the concave portion of the concavo-convex portion is 1/10 to 3/5 of the thickness of the original film. der Ru.

  The heat dissipation sheet may have a plane direction thermal conductivity λxy of 1.0 W / mK or more, a relative dielectric constant at 1 GHz of 4.0 or less, and a dielectric loss tangent at 1 GHz of 0.005 or less. Also good.

Such a heat-dissipating sheet may be formed by molding extrusion molding such as inflation (for example, extrusion molding with stretching treatment), and in the case involving stretching processing, the product of the stretching ratio in the MD direction and the TD direction of extrusion molding. May be 3 or more. Moreover, the shear rate of extrusion molding may be 200 sec ⁻¹ or more.

  Such a heat-radiating sheet may be subjected to uneven transfer processing in the thickness direction of the sheet, or may be heat-treated at a melting point of the liquid crystal polymer or higher.

The heat dissipating sheet of the present invention is not only excellent in heat dissipating property, but also formed from a thermoplastic liquid crystal polymer, so that it has excellent workability and high heat resistance.
Moreover, in the heat-radiating sheet of the present invention, not only is it excellent in mechanical strength, but even if the filler content is reduced (particularly, even if the filler is not included), excellent heat-dissipating properties can be realized.
Furthermore, the heat dissipating sheet of the present invention is not only excellent in dimensional stability but also can exhibit excellent heat dissipating properties even if it has low hygroscopicity.

  In particular, the heat dissipating sheet of the present invention is excellent in dielectric characteristics in a wide frequency band (especially, a high frequency band of 1 GHz or more), so that not only the signal transmission speed in electronic equipment can be increased, but also the heat generation amount itself. Can be suppressed.

It is the schematic for demonstrating the uneven | corrugated transfer process to the thermoplastic liquid crystal polymer film by a stamper. It is the schematic for demonstrating the process of heat-processing with respect to a thermoplastic liquid crystal polymer film.

[Heat dissipation sheet]
The heat dissipating sheet of the present invention is a heat dissipating sheet composed of a thermoplastic liquid crystal polymer, formed from a liquid crystalline polymer that can be melt-molded as described below, and controlling the molecular orientation of the liquid crystalline polymer, The ratio of the thermal conductivity λxy in the planar direction to the thermal conductivity λz in the thickness direction is in a specific range.

(Thermoplastic liquid crystal polymer)
The thermoplastic liquid crystal polymer is not particularly limited as long as it is a liquid crystalline polymer that can be melt-molded. For example, a thermoplastic liquid crystal polyester or a thermoplastic liquid crystal in which an amide bond is introduced is used. Examples thereof include polyester amide.

  The thermoplastic liquid crystal polymer may be a polymer in which an isocyanate-derived bond such as an imide bond, a carbonate bond, a carbodiimide bond, or an isocyanurate bond is further introduced into an aromatic polyester or an aromatic polyester amide.

  Specific examples of the thermoplastic liquid crystal polymer used in the present invention include known thermoplastic liquid crystal polyesters and thermoplastic liquid crystal polyester amides derived from the compounds (1) to (4) listed below and derivatives thereof. Can be mentioned. However, it goes without saying that there are suitable ranges for combinations of various raw material compounds in order to form a polymer liquid crystal.

(1) Aromatic or aliphatic dihydroxy compounds (see Table 1 for typical examples)

(2) Aromatic or aliphatic dicarboxylic acids (see Table 2 for typical examples)

(3) Aromatic or aliphatic hydroxycarboxylic acids (see Table 3 for typical examples)

(4) Aromatic diamine, aromatic hydroxyamine or aromatic aminocarboxylic acid (see Table 4 for typical examples)

  Representative examples of the liquid crystal polymer obtained from these raw material compounds include copolymers having the structural units shown in Tables 5 and 6.

  Of these copolymers, a polymer containing at least p-hydroxybenzoic acid and / or 6-hydroxy-2-naphthoic acid as a repeating unit is preferable, and in particular, (i) p-hydroxybenzoic acid and 6-hydroxyoxy- A polymer containing a repeating unit with 2-naphthoic acid, (ii) 6-hydroxy-2-naphthoic acid, at least one aromatic diol selected from the group consisting of 4,4′-dihydroxybiphenyl and hydroquinone, and terephthalate A polymer containing a repeating unit with at least one aromatic dicarboxylic acid selected from the group consisting of acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid is the most preferred embodiment.

  For example, when the thermoplastic liquid crystal polymer contains at least a repeating unit of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the repeating unit (A) of p-hydroxybenzoic acid and the repeating unit (B) of The molar ratio (A) / (B) with 6-hydroxy-2-naphthoic acid is desirably about (A) / (B) = 10/90 to 90/10 in the liquid crystal polymer, more preferably , (A) / (B) = about 50/50 to 85/15, and more preferably (A) / (B) = about 60/40 to 80/20.

  Further, the thermoplastic liquid crystal polymer is at least one aromatic diol selected from the group consisting of 6-hydroxy-2-naphthoic acid, 4,4′-dihydroxybiphenyl and hydroquinone, terephthalic acid, isophthalic acid and 2,6 -When it contains a repeating unit with at least one aromatic dicarboxylic acid selected from the group consisting of naphthalenedicarboxylic acid, the molar ratio of each repeating unit in the liquid crystal polymer is the repeating unit of 6-hydroxy-2-naphthoic acid (C) : The aromatic diol (D): The aromatic dicarboxylic acid (E) = 30-80: 35-10: 35-10, more preferably (C) :( D) :( E ) = 35 to 75: 32.5 to 12.5: 32.5 to 12.5, more preferably (C) :( D) (E) = 40~70: 30~15: may be about 30 to 15.

  Moreover, it is preferable that the molar ratio of the repeating structural unit derived from aromatic dicarboxylic acid and the repeating structural unit derived from aromatic diol is (D) / (E) = 95 / 100-100 / 95. Outside this range, the degree of polymerization does not increase and the mechanical strength tends to decrease.

  The optical anisotropy at the time of melting referred to in the present invention can be recognized by, for example, placing a sample on a hot stage, heating and heating in a nitrogen atmosphere, and observing the transmitted light of the sample.

  The thermoplastic liquid crystal polymer preferably has a melting point (hereinafter referred to as Mp) in the range of 260 to 360 ° C, more preferably Mp of 270 to 350 ° C. In addition, Mp is calculated | required by measuring the temperature where a main endothermic peak appears with a differential scanning calorimeter (Mettler DSC).

  The thermoplastic liquid crystal polymer may include a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyarylate, polyamide, polyphenylene sulfide, polyester ether ketone, and fluororesin within a range not impairing the effects of the present invention. It may be added.

(Filler)
Furthermore, the heat-dissipating sheet includes fillers (for example, highly conductive fillers) and various additives (for example, plasticizers, light stabilizers, weathering stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, combustion retardants, Dyes, pigments, lubricants, viscosity modifiers, and the like). Such fillers may be fibrous, powdery, plate-like, or any.

  Moreover, as the material, inorganic fillers such as glass, silica, carbon, oxalate, zirconia, aluminum nitride, aluminum oxide and boron nitride; metal fillers such as stainless steel, aluminum, titanium, iron, nickel, copper; Examples thereof include organic fillers such as polyamide, fluororesin, polyester, acrylic resin, liquid crystal polymer, and polyimide.

  The content of the filler may be, for example, about 1 to 20% by weight, preferably about 3 to 17% by weight, and more preferably about 5 to 15% by weight, based on the entire heat radiating sheet. The filler can be mixed or combined with the polymer by a known or conventional method depending on its shape.

[Production method of heat dissipation sheet]
In the case of forming a heat radiation sheet in which the ratio of the thermal conductivity λxy in the planar direction to the thermal conductivity λz in the thickness direction is within a specific range from the thermoplastic liquid crystal polymer used in the present invention, for example, the thermoplastic liquid crystal polymer is It can be formed by extrusion (T-die method, inflation method, etc.).

(Extrusion molding)
In extrusion molding, it may be accompanied by stretching treatment. For example, in extrusion molding by the T-die method, the melt sheet extruded from the T-die is not only in the mechanical axis direction of the film (hereinafter abbreviated as MD direction), You may extend | stretch simultaneously with respect to both the direction (henceforth TD direction) orthogonal to this, or the melt sheet | seat extruded from T-die is once extended | stretched to MD direction, and then extended to TD direction. Also good.

  In addition, in the extrusion molding by the inflation method, a predetermined draw ratio (corresponding to a stretching ratio in the MD direction) and a blow ratio (corresponding to a stretching ratio in the TD direction) with respect to a cylindrical sheet melt-extruded from a ring die. May be stretched.

  The stretch ratio of such extrusion molding may be, for example, about 1.0 to 10, preferably about 1.2 to 7, more preferably about 1. as the stretch ratio (or draw ratio) in the MD direction. About 3-5 may be sufficient. Further, the draw ratio (or blow ratio) in the TD direction may be, for example, about 1.5 to 20, preferably about 2 to 15, and more preferably about 2.5 to 10.

  And the product which multiplied each draw ratio of MD direction and TD direction is 3 or more (for example, about 3.3-20), preferably 3.5 or more (for example, about 3.8-15), More preferably, it may be 4 or more (for example, about 4.3 to 12).

Further, the die shear rate that the thermoplastic polymer undergoes in the die region during melt extrusion from the die (sometimes simply referred to as shear rate) is 200 seconds ⁻¹ or more (for example, about 200 to 5000 sec ^-1), preferably be selected from about 210 to 4000 sec ^-1.

These stretching ratios and shredding speeds are closely related to each other in controlling the thermal conductivity. For example, the product obtained by multiplying the respective stretching ratios in the MD direction and the TD direction is 11 or more. In this case, the film may be formed at a shredding speed of 700 sec- ¹ or less (for example, about 300 to 700 sec- ¹ , preferably about 350 to 650 sec- ¹ ).

(Uneven transfer process)
Further, the heat radiating sheet may be subjected to uneven transfer processing in the sheet thickness direction. In this unevenness transfer processing, first, an original sheet is obtained by extrusion or the like, and a stamper on which unevenness is formed is heated and pressed on at least one surface of the original sheet, and then the stamper is peeled off, The unevenness formed on the stamper can be transferred to the original sheet.

  The stamper may be pressed by using a heating roller or by pressing in a sheet form. The stamper has a large number of uneven portions, and the uneven pattern may be a one-dimensional array in which groove-shaped uneven portions are arrayed, or a two-dimensional array such as a lenticular lens. Alternatively, it may be a three-dimensional array such as a fly-eye lens or a flat lens in which fine cones such as a cone and a pyramid are arranged in the XY direction.

For example, as shown in FIG. 1, in the concavo-convex portion of the cross section in the thickness direction of the stamper (S), the height (t _R ) of the convex portion is 1 of the thickness (t _B + t _R ) of the raw film (F). It may be about / 10 to 3/5, preferably about 1/5 to 1/2. Further, in the concavo-convex portion, the width of the concavo-convex portion may be the same or different, and each is, for example, about 1/10 to 3/5, preferably about 1/5 to 1/2 of the thickness of the raw film. May be.

  The heating temperature of the stamper (or the surface temperature of the heating part) may be performed at a melting point (Mp) of the liquid crystal polymer of about −60 ° C. to Mp−20 ° C., preferably about Mp−40 ° C. to Mp−25 ° C.

Moreover, the pressure applied stamper against raw film, 10~200kgf / cm ² approximately at a surface pressure conversion, preferably may be about 15~150kgf / cm ^2, 5~400kgf / cm in linear pressure converted Or about 10 to 300 kgf / cm.

(Heat treatment)
Moreover, you may heat-process with respect to the raw material sheet | seat or the sheet | seat which performed the stamper process above melting | fusing point (Mp) of a liquid crystal polymer (for example, about Mp-Mp + 30 degreeC, Preferably about Mp + 10-Mp + 20 degreeC).

  For example, such heat treatment may be performed by thermocompression bonding a raw sheet and a support such as a metal foil to form a laminate, and the laminate may be heat-treated. For example, such heat treatment may be performed continuously as shown in FIG. That is, in a state where the long original sheet 2 unwound from the unwinding roll 1 and the sheet-like support 4 unwound from the unwinding roll 3 are overlapped, they are fed into the heating roll 5 and bonded by thermocompression bonding. Thus, the laminated body 10 is manufactured, and this laminated body 10 is sent to the first heat treatment apparatus 6 and heat-treated. Thereafter, the laminate 10 is peeled off by two upper and lower peeling rolls 7, 7 to separate the heat-treated thermoplastic liquid crystal polymer film 2 and the support 4, and the heat-treated thermoplastic liquid crystal polymer film. 21 can be obtained. In addition, after performing heat processing, you may perform the annealing process for eliminating internal distortion further.

(Extension process)
The thermoplastic liquid crystal polymer film may be stretched as necessary. The stretching method itself is known, and either biaxial stretching or uniaxial stretching may be adopted, but biaxial stretching is preferred because it is easier to control the degree of molecular orientation. For stretching, a known uniaxial stretching machine, simultaneous biaxial stretching machine, sequential biaxial stretching machine or the like can be used.

[Heat dissipation sheet]
In the heat dissipation sheet of the present invention formed as described above, the molecular orientation is controlled inside the heat dissipation sheet, and the ratio of the thermal conductivity λxy in the planar direction to the thermal conductivity λz in the thickness direction (λxy / λz) is 6 to 60, preferably 6 to 30. By having such a ratio, heat can be radiated uniformly over the entire film.

Moreover, the heat dissipation sheet of the present invention may have a thermal conductivity λxy in the planar direction of 1.0 W / mK or more (for example, about 1 to 30 W / mK), preferably 1.2 W / mK or more.
Furthermore, the heat dissipation sheet of the present invention has a thermal conductivity λxy in the planar direction and a thermal conductivity λxy in the thickness direction and a sum (λxy + λz) of 1.05 W / mK or more (for example, about 1.1 to 30 W / mK), preferably 1.15 W / mK or more may be sufficient.

  The heat-dissipating sheet of the present invention is excellent in dielectric characteristics. For example, the relative dielectric constant at 1 GHz is 4.0 or less (for example, about 1.8 to 3.6), preferably 2.5 to 3. It may be about 4. By having such a relative dielectric constant, it is possible to reduce a transmission loss of an electric signal.

  The dielectric loss tangent at 1 GHz may be 0.005 or less (for example, about 0.0001 to 0.004), preferably about 0.001 to 0.003. By having such a dielectric loss tangent, it is possible to reduce power and noise, and to reduce the amount of generated heat.

  The thickness of the heat dissipating sheet can be appropriately set according to the application as long as the thermal conductivity in the thickness direction and the planar direction can be controlled. For example, the thickness is 500 μm or less (for example, about 5 to 450 μm), preferably 10 It may be about ˜400 μm, more preferably about 15 to 300 μm.

Moreover, as above-mentioned, when receiving the uneven | corrugated transfer process, the uneven | corrugated | grooved part may be formed in at least one surface of the heat dissipation sheet. The shape of such an uneven portion is formed in a state where the shape of the stamper is transferred. As a result, in the heat radiating sheet to which such concavo-convex portions are transferred, as shown in FIG. 1, in the concavo-convex portions, the depth (t _R ) of the concave portions is equal to the thickness (t _B + t _R ) of the raw film. It may be about 1/10 to 3/5, and preferably about 1/5 to 1/2, that is, a layer (t _B ) having a concavo-convex portion with respect to a layer (t _B ) having no concavo-convex portion. The ratio of _{R 1} ) (t _R / t _B ) may be about 1/9 to 2/3, and preferably about 1/4 to 1/2.

Moreover, in the concavo-convex part, the width (W _B ) of the concave part and the width (W _R ) of the convex part may be the same or different, and each is, for example, about 1/10 to 3/5 of the thickness of the original film. Preferably, it may be about 1/5 to 1/2. Further, the ratio (W _R / W _B ) of the width (W _R ) of the convex portion to the width (W _B ) of the concave portion is about 1/5 to 5/1, preferably about 1/4 to 4/1. May be.

  As long as it has such a thermal conductivity ratio, for example, inside the heat-dissipating sheet, (i) liquid crystal polymer molecules arranged mainly in the plane direction and liquid crystal polymer molecules arranged mainly in the non-plane direction And (ii) the heat-dissipating sheet may include a layer in which liquid crystal polymer molecules are mainly arranged in a plane direction, or (iii) heat dissipation. The adhesive sheet may include both a layer in which liquid crystal polymer molecules are mainly arranged in a planar direction and a layer in which liquid crystal polymer molecules are mainly arranged in a non-planar direction.

  For example, in the case of (i), a heat dissipating sheet in which a plate-like or powdered filler is mixed with a thermoplastic liquid crystal polymer corresponds, and in the case of (ii), a heat dissipating sheet that has been subjected to a stretching treatment corresponds to (iii) In this case, a heat-radiating sheet that has been subjected to a heat transfer process with a concavo-convex transfer process or a support on one side is applicable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by this Example. In the following examples and comparative examples, various physical properties were measured by the following methods.

[Thermal conductivity]
Rigaku Co., Ltd. Laser flash method thermal constant measuring device LF / TCM FA8510B was used and measured at a measurement temperature of 20 ° C. The measurement in the planar direction was performed with a dedicated attachment.

(Inflation method)
The die shear rate which the thermoplastic liquid crystal polymer melted at the time of forming the inflation film receives in the die region was defined by the following equation. Q represents the resin discharge rate (mm ³ / sec), R represents the die diameter (mm), and d represents the die slit interval (mm).
Die shear rate (second ⁻¹ ) = (6 × Q) / (π × R × d ² )

[Sheet thickness]
The thickness of the heat dissipation sheet was measured using a Digimatic indicator manufactured by Mitutoyo Corporation. For the measurement, sample fragments (50 cm long × 50 cm wide) were collected from the heat-dissipating sheet, 100 points were randomly measured for each sample, and the average value was used as the sheet thickness.

[Dielectric properties]
The dielectric constant was measured by a resonance perturbation method at a frequency of 1 GHz. Connect a 1 GHz cavity resonator (Kanto Electronics Co., Ltd.) to a network analyzer (Agilent Technology “E8362B”), and insert a minute material (width: 2 mm x length: 90 mm) into the cavity resonator. The dielectric constant and dielectric loss of the material were measured from the change in resonance frequency before and after insertion.

( Reference Example 1)
A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27), is kneaded with a single-screw extruder to obtain a die diameter. From a circular inflation die of 33.5 mm and a die slit interval of 350 μm, melt extrusion at a die shear rate of 2775 seconds −1 was performed under the conditions of a longitudinal draw ratio (Dr) of 1.8 and a transverse draw ratio (Bl) of 5.6. A film with a thickness of 25 μm was obtained. Table 7 shows the physical properties of the obtained film.

( Reference Example 2)
A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27), is kneaded with a single-screw extruder to obtain a die diameter. It was melt-extruded at a die shear rate of 991 sec-1 from an annular inflation die having a pitch of 46.0 mm and a die slit interval of 500 μm, under the conditions of a longitudinal stretch ratio (Dr) of 2.2 and a lateral stretch ratio (Bl) of 4.1. A film with a thickness of 50 μm was obtained. Table 7 shows the physical properties of the obtained film.

( Reference Example 3)
A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27), is kneaded with a single-screw extruder to obtain a die diameter. From a circular inflation die of 75.0 mm and a die slit interval of 1000 μm, melt extrusion was performed at a die shear rate of 414 sec−1, and under conditions of a longitudinal draw ratio (Dr) of 2.0 and a transverse draw ratio (Bl) of 6.6. A film with a thickness of 75 μm was obtained. Table 7 shows the physical properties of the obtained film.

( Reference Example 4)
A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27), is kneaded with a single-screw extruder to obtain a die diameter. It was melt-extruded at a die shear rate of 225 seconds −1 from an annular inflation die having a die slit interval of 1000 μm at 51.0 mm and a longitudinal draw ratio (Dr) of 2.2 and a transverse draw ratio (Bl) of 3.6. A film having a thickness of 175 μm was obtained. Table 7 shows the physical properties of the obtained film.

(Example 1 )
A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27), is kneaded with a single-screw extruder to obtain a die diameter. It was melt-extruded at a die shear rate of 991 sec-1 from an annular inflation die having a die slit spacing of 500 μm at a length of 33.5 mm and a longitudinal draw ratio (Dr) of 2.2 and a transverse draw ratio (Bl) of 4.1. A film with a thickness of 50 μm was obtained. Next, with respect to the obtained film, projections and depressions were formed such that the width (WB) of the protrusions formed on the film was 25 μm, the width (WR) of the depressions was 15 μm, and the height (tR) of the protrusions was 10 μm. Using a stamper, uneven transfer was performed at a surface pressure of 20 kg / cm 2 and a heating temperature of 260 ° C. to obtain a film having a thickness of 50 μm. Table 7 shows the physical properties of the obtained film.

( Reference Example 5 )
Using the apparatus of FIG. 1, the film obtained in Example 3 was unwound from the unwinding roll 1, and a stainless foil having a thickness of 40 μm (thermal expansion coefficient (S): 16 × 10 −6 cm / cm / ° C.) was used. As a support, a heat resistant rubber roll 51 and a heated metal roll 52 are attached to a continuous hot roll press device, and are pressure-bonded at a pressure of 20 kgf / cm 2 in a heated state at 260 ° C., and a thermoplastic liquid crystal polymer film / stainless foil at a speed of 6 m / min. A laminate 10 having the structure as described above was produced.

Subsequently, the laminated body 10 is supplied to the hot-air circulating heat treatment furnace 6 having a furnace length of 2 m controlled at 280 ° C. at a rate of 6 m / min and continuously heat-treated, and then the support body 10 is peeled off at the top and bottom. The film was peeled off with rolls 7 and 7 to obtain a thermoplastic liquid crystal polymer film 21 continuously.
Thereafter, the heated thermoplastic liquid crystal polymer film 21 is further supplied to the hot-air circulating heat treatment furnace 8 having a furnace length of 2 m controlled at 195 ° C. at a rate of 6 m / min for annealing treatment to obtain a film having a thickness of 75 μm. It was. Table 7 shows the physical properties of the obtained film.

(Reference Comparative Example 1)
A thermoplastic liquid crystal polymer having a melting point of 280 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (molar ratio: 73/27), is kneaded with a single-screw extruder to obtain a die diameter. From a circular inflation die of 51.0 mm and a die slit interval of 1000 μm, melt extrusion was performed at a die shear rate of 162 sec− ¹ , and under conditions of a longitudinal draw ratio (Dr) of 2.0 and a transverse draw ratio (Bl) of 1.4. A film having a thickness of 175 μm was obtained. Table 7 shows the physical properties of the obtained film.

  As shown in Table 7, in Examples 1 to 6, the ratio (λxy / λz) of the thermal conductivity λxy in the planar direction to the thermal conductivity λz in the thickness direction of the heat radiating sheet falls within the range of 6 to 60. In addition, in particular, the sum of λxy and λz was 1.15 W / mK or more, and the thermal conductivity of the entire radioactive sheet was excellent.

  Although not included in the category of the prior art, in Reference Comparative Example 1 described as a reference example for comparing the characteristics of the present invention, the thermal conductivity λxy in the planar direction with respect to the thermal conductivity λz in the thickness direction is used. The ratio (λxy / λz) is out of the range of 6 to 60, the thermal conductivity λxy in the plane direction is low, and the sum of λxy and λz is only 0.86 W / mK. The heat conductivity was inferior.

  Since the heat radiating sheet of the present invention is formed from a thermoplastic liquid crystal polymer, it has high heat radiating properties and is excellent in workability, mechanical strength, dimensional stability, chemical resistance, and gas barrier properties. Also, since it has both high heat resistance and low hygroscopicity, it can be suitably used as heat dissipation parts for various computers, OA equipment, AV equipment, etc., automotive semiconductors, industrial semiconductors, especially heat dissipation sheets. It is possible to efficiently dissipate heat generated from an electronic component or a circuit board on which the electronic component is mounted.

  The heat-dissipating sheet of the present invention can also be used as a circuit board material for electrical and electronic products as described above, and in particular, printed wiring circuit board materials for LEDs that are becoming thinner and smaller. As such, it can be used effectively.

  As described above, the preferred embodiments of the present invention have been described. However, various additions, modifications, or deletions are possible without departing from the spirit of the present invention, and such modifications are also included in the scope of the present invention. It is.

Claims (9)

A heat dissipating sheet composed of a liquid crystal polymer,
The liquid crystal polymer is a thermoplastic liquid crystal polymer;
The ratio (λxy / λz) of the thermal conductivity λxy in the planar direction to the thermal conductivity λz in the thickness direction is 6 to 60, and the uneven transfer process is performed in the thickness direction of the sheet, and the depth of the concave portion of the uneven portion is Is a heat-dissipating sheet whose thickness is 1/10 to 3/5 of the thickness of the original film. In Claim 1, The width | variety (WB) of a recessed part and the width | variety (WR) of a convex part are respectively 1/10-3/5 of the thickness of a raw film, The heat-radiating sheet.   The heat-radiating sheet according to claim 1 or 2, wherein a thermal conductivity λxy in a planar direction is 1.0 W / mK or more.   The heat dissipation sheet according to any one of claims 1 to 3, wherein a relative dielectric constant at 1 GHz is 4.0 or less.   The heat-radiating sheet according to any one of claims 1 to 4, wherein a dielectric loss tangent at 1 GHz is 0.005 or less.   The heat-radiating sheet according to any one of claims 1 to 5, wherein the heat-radiating sheet is formed by extrusion with a stretching process, and a product of stretching ratios in the MD direction and the TD direction is 3 or more. The heat-radiating sheet according to claim 6, wherein the shear rate of extrusion molding is 200 sec ⁻¹ or more.   The heat-radiating sheet according to claim 6 or 7, wherein the extrusion molding is inflation molding.   The heat-radiating sheet according to any one of claims 1 to 8, which has been heat-treated at a temperature equal to or higher than a melting point of the liquid crystal polymer.

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