JP6205877B2 - High heat-resistant liquid crystal polymer film and production method thereof - Google Patents

Description

  The present invention relates to a high heat-resistant liquid crystal polymer film having extremely excellent heat resistance, a method for producing the same, a metal layer-clad laminated film including the high heat-resistant liquid crystal polymer film, and an electronic circuit board.

  Conventionally, a material obtained by reinforcing a thermosetting resin such as an epoxy resin with a woven fabric or a nonwoven fabric made of glass fiber has been used as an electronic circuit board material. However, such a material has to be a rigid board. On the other hand, in recent years, a flexible substrate has been demanded, and polyimide is mainly used as the material thereof. However, polyimide exhibits hygroscopicity, and there is a problem that dimensional accuracy and electrical characteristics are deteriorated under high humidity.

  Recently, lead-free solder has been used for electronic circuit boards due to environmental problems. However, since reflow of lead-free solder requires a high temperature of 260 to 280 ° C., a general resin cannot be used as a substrate material.

  Therefore, techniques for improving the heat resistance of the resin material have been studied.

  For example, Patent Documents 1 to 5 disclose techniques for improving heat resistance and strength by irradiating a composition of polyester such as PBT (polybutylene terephthalate), acrylic resin, or styrene resin with ionizing radiation. .

  Further, as described above, since the electronic circuit board material is required to have low hygroscopicity and heat resistance, attention has been focused on the liquid crystal polymer. A liquid crystal polymer is a general term for polymers exhibiting liquid crystallinity in a molten state or a solution state, and has high moisture resistance and excellent heat resistance in addition to high solvent resistance, dimensional stability, electrical insulation and dielectric properties.

  As a technique for improving the heat resistance of an engineering plastic such as a liquid crystal polymer, Patent Document 6 discloses a method of irradiating an engineering plastic with 1 kGy to 10 MGy of ionizing radiation in a specific oxygen concentration atmosphere. Patent Document 7 discloses a molded product obtained by crosslinking a composition of a liquid crystal polymer by irradiating it with ionizing radiation.

  In addition, Patent Documents 8 to 10 describe a method of performing heat treatment under specific conditions in order to improve the wear resistance of the liquid crystal polymer.

JP 2001-348442 A JP 2002-155154 A JP 2003-82132 A JP 2003-128741 A JP 2003-327713 A Japanese Patent No. 3790865 JP-A-3-167208 Japanese Patent No. 3882213 Japanese Patent No. 3655464 Japanese Patent No. 3878741

  As described above, various techniques for improving the heat resistance of a resin that can be used as a material for an electronic circuit board have been studied.

  Recently, however, solder having a higher melting point has been used and solder mounting has been performed even at high temperatures such as around 340 ° C., so that higher heat resistance is required for electronic circuit board materials. It has become to. The conventional resin material cannot be used in the soldering process under such a high temperature.

  For example, in the techniques of Patent Documents 1 to 5 and Patent Document 7, a resin polymer is crosslinked by irradiating a composition containing a crosslinking agent such as triallyl isocyanurate having a plurality of carbon-carbon double bonds with ionizing radiation. However, the crosslinking agent often has a plurality of highly reactive functional groups, and the blending of the composition causes moisture to enter the composition or the composition to exhibit hygroscopicity. When such a composition is exposed to a high temperature, there is a problem that the internal moisture rapidly vaporizes and foams, resulting in a reduction in product quality. The purpose of ionizing radiation irradiation in these techniques is to react a crosslinking agent, and the irradiation dose is about several hundred kGy at most.

  In addition, the invention described in Patent Document 6 relates to engineering plastics, and there are examples of liquid crystal polymers as engineering plastics, but the resins actually tested are polyetheretherketone (PEEK) and tetrafluoroethylene-based polymers ( PTFE) only. In addition, although an extremely wide range of 1 kGy to 10 MGy is described as the ionizing irradiation dose to be irradiated, in the first place, the problem is to crosslink the resin with a low dose of irradiation, and the ionizing irradiation actually applied The radiation dose is only 50 kGy.

  Furthermore, the heat resistance at a high temperature exceeding 340 ° C. is not sufficient only by simply heat-treating the liquid crystal polymer as in the techniques of Patent Documents 8 to 10.

  Therefore, the present invention provides a highly heat-resistant liquid crystal polymer film that exhibits heat resistance even at a high temperature of 340 ° C. or higher, a method for producing the same, a metal layer-clad laminated film including the highly heat-resistant liquid crystal polymer film, and an electronic circuit board. With the goal.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been known that the heat resistance is increased by irradiating the resin with ionizing radiation, and that when the irradiation amount is too large, the molecular cleavage becomes dominant and the strength is reduced. On the other hand, when a liquid crystal polymer is irradiated with ionizing radiation of 2000 kGy or higher, which is an unprecedented amount of irradiation, a unique phenomenon is found in which the storage elastic modulus increases at a high temperature of 340 ° C. or higher. Completed the invention.

  The high heat-resistant liquid crystal polymer film according to the present invention is obtained by irradiating the raw liquid crystal polymer film with ionizing radiation of 2000 kGy or more, and the temperature-storage in which the horizontal axis represents the temperature and the vertical axis represents the measured storage elastic modulus value. In the elastic modulus curve graph in the range of 300 ° C. or higher and 400 ° C. or lower, there is a point that the storage elastic modulus value with respect to the temperature rises from decreasing to increasing.

The storage elastic modulus at 350 ° C. of the high heat-resistant liquid crystal polymer film according to the present invention can be 1.0 × 10 ⁷ Pa or more, more preferably 2.0 × 10 ⁷ Pa or more. In general liquid crystal polymer films, the storage elastic modulus continues to decrease as the temperature rises, but the high heat-resistant liquid crystal polymer film according to the present invention has a unique characteristic that the storage elastic modulus increases at a high temperature of 340 ° C. or higher. Has characteristics.

  The high heat-resistant liquid crystal polymer film according to the present invention is preferably not crosslinked by a crosslinking agent and / or does not contain a crosslinking agent. When a cross-linking agent is blended, water is inevitably mixed in. However, such water causes foaming by rapidly vaporizing at a high temperature. Moreover, the high heat-resistant liquid crystal polymer film according to the present invention exhibits heat resistance even at a high temperature of 340 ° C. or higher, even if it is not crosslinked by a crosslinking agent.

  The linear expansion coefficient in the planar direction of the highly heat-resistant liquid crystal polymer film according to the present invention is preferably 10 ppm / ° C. or more and 25 ppm / ° C. or less. For example, when a metal layer is laminated on the high heat-resistant liquid crystal polymer film according to the present invention, if the linear expansion coefficient in the plane direction is adjusted within the range, the difference from the linear expansion coefficient with the metal layer is small, and the line Warpage caused by the difference in expansion coefficient is reduced.

  In the high heat-resistant liquid crystal polymer film according to the present invention, the ratio of the linear expansion coefficient in one direction of the plane direction to the linear expansion coefficient in the direction orthogonal to the direction is 0.4 or more and 2.5 or less. It is preferable. If the ratio is adjusted within a predetermined range, the disadvantages peculiar to liquid crystal polymer films such as little anisotropy in the plane direction and easy tearing in one direction are suppressed.

  In the high heat-resistant liquid crystal polymer film according to the present invention, the linear expansion coefficient in the Z direction (thickness direction) is reduced by 6 ppm / ° C. or more as compared with the raw material liquid crystal polymer film not irradiated with ionizing radiation. In a general liquid crystal polymer film, the linear expansion coefficient in the Z direction cannot be reduced unless it depends on the filler composition, etc. The linear expansion coefficient in the Z direction is easily reduced. Further, the reduction of the linear expansion coefficient in the Z direction increases the connection reliability in the thickness direction when the electronic circuit board is formed, and also suppresses the warp when laminated with a metal layer or the like.

  The thickness of the high heat resistant liquid crystal polymer film according to the present invention is preferably 10 μm or more and 500 μm or less. If the thickness is less than 10 μm, there may be a problem in strength and the application range may be limited. On the other hand, since the liquid crystal polymer film has a large coefficient of linear expansion in the Z direction, if it is too thick, there may be a problem in connection reliability in the thickness direction. Therefore, the thickness is preferably 500 μm or less.

  The high heat-resistant liquid crystal polymer film of the present invention preferably contains a filler. By selecting an appropriate filler, it is possible to further improve the heat resistance and to make the linear expansion coefficient within a predetermined range.

  The method for producing a high heat-resistant liquid crystal polymer film according to the present invention includes a step of irradiating a raw liquid crystal polymer film with ionizing radiation of 2000 kGy or more.

  In the method of the present invention, the irradiation dose of ionizing radiation is more preferably 5000 kGy or more. According to the experimental findings by the present inventors, when the ionizing radiation dose is 5000 kGy or more, an improvement in the storage elastic modulus at 340 ° C. or higher is more clearly recognized, and a polymer film having further excellent heat resistance is more reliably obtained. Can be manufactured.

  In the method of the present invention, for the same reason as described above, it is preferable to use a raw material liquid crystal polymer film that is not crosslinked with a crosslinking agent and / or does not contain a crosslinking agent.

  The metal layer-clad laminated film according to the present invention is characterized in that a metal layer is laminated on the high heat-resistant liquid crystal polymer film according to the present invention.

  The electronic circuit board according to the present invention includes the metal layer-clad laminated film according to the present invention.

  The high heat-resistant liquid crystal polymer film according to the present invention has a storage elastic modulus that increases at a high temperature of 340 ° C. or higher, whereas a normal thermoplastic resin continues to decrease as the temperature increases. It exhibits very unique properties and has extremely excellent heat resistance. Therefore, the high heat-resistant liquid crystal polymer film according to the present invention can withstand high melting point solder mounting and solder repair that require a high temperature of 340 ° C. or higher.

  In addition, the linear expansion coefficient in the Z direction of the liquid crystal polymer film is a factor that greatly affects the connection reliability in the thickness direction when an electronic circuit board is used. Much effort has been made to lower the coefficient by several ppm / ° C. On the other hand, in the present invention, the linear expansion coefficient in the Z direction is reduced by a very easy method.

  Therefore, the present invention is industrially excellent as a technique relating to a high heat-resistant liquid crystal polymer film useful for electronic circuit board materials and the like.

FIG. 1 is a temperature-storage modulus curve graph of an I-type liquid crystal polymer film not irradiated with ionizing radiation or irradiated with 1500 kGy ionizing radiation. FIG. 2 is a temperature-storage modulus curve graph of an I-type liquid crystal polymer film irradiated with 2500-10000 kGy of ionizing radiation. FIG. 3 is a temperature-storage modulus curve graph of a type II liquid crystal polymer film not irradiated with ionizing radiation or irradiated with ionizing radiation of 1000 kGy or 1500 kGy. FIG. 4 is a temperature-storage modulus curve graph of a type II liquid crystal polymer film irradiated with 2500-10000 kGy of ionizing radiation.

  The high heat-resistant liquid crystal polymer film according to the present invention is obtained by irradiating the raw liquid crystal polymer film with ionizing radiation of 2000 kGy or more, and the temperature-storage in which the horizontal axis represents the temperature and the vertical axis represents the measured storage elastic modulus value. In the elastic modulus curve graph in the range of 300 ° C. or higher and 400 ° C. or lower, there is a point that the storage elastic modulus value with respect to the temperature rises from decreasing to increasing.

  Conventionally, polymer films have been irradiated with ionizing radiation of several hundreds kGy, and cross-linking between polymers using a cross-linking agent, or cross-linking of polymers directly, while excessive ionizing radiation was applied. Then, it was known that the decomposition of the polymer becomes more dominant than the cross-linking and the film strength and the like are lowered. On the other hand, the present invention has been completed based on the new finding that the heat resistance is remarkably improved by irradiating the liquid crystal polymer film with high energy ionizing radiation, which has not been considered in the past, of 2000 kGy or more. Is.

  That is, the high heat-resistant liquid crystal polymer film according to the present invention has a temperature-storage elastic modulus curve graph in which the temperature is plotted on the horizontal axis and the storage elastic modulus value measured on the vertical axis is plotted in the range of 300 ° C. or higher and 400 ° C. or lower. The storage modulus value with respect to the temperature rise has a unique property that there is a point where the value changes from decreasing to increasing.

  In the present invention, “storage modulus” is a value obtained from measurement of dynamic viscoelasticity. The measurement of dynamic viscoelasticity is performed by applying a sinusoidal strain to the measurement object and detecting the stress that has passed through the measurement object, and the storage elastic modulus and the loss elastic modulus are obtained as the measurement values. The storage elastic modulus refers to energy (elastic modulus) stored in the system, and the loss elastic modulus refers to energy lost in the system.

  The reason why dynamic viscoelasticity is adopted in the present invention is that the variation is small and the measurement in the high temperature range is easy. The reason for using the storage elastic modulus obtained from the measurement of dynamic viscoelasticity as a main index is that the storage elastic modulus has a certain correlation with the tensile elastic modulus.

  As described above, the storage elastic modulus is an index of the tensile elastic modulus at the measurement temperature. Therefore, in the temperature-storage elastic modulus curve graph in which the horizontal axis represents the temperature and the vertical axis represents the measured storage elastic modulus value, normal thermoplasticity In the case of a resin film, the storage elastic modulus continues to decrease with increasing temperature. On the other hand, in the case of the high heat-resistant liquid crystal polymer film according to the present invention, there is a point that the storage elastic modulus value with respect to the temperature rise changes from the decrease to the increase in the high temperature range. In the high heat-resistant liquid crystal polymer film according to the present invention having such unique properties, crosslinking is caused between radicals generated after the ester group in the liquid crystal polymer molecule is once cleaved by irradiation with high-energy ionizing radiation. However, it was impossible to analyze what structural change occurred in the liquid crystal polymer, and unfortunately, the structure could not be specified.

  In the present invention, “there is a point where the storage elastic modulus value from the decrease to the increase with respect to the temperature increase” means that the temperature is plotted on the horizontal axis and the measured storage elastic modulus value is plotted on the vertical axis. In other words, in the range of 300 ° C. or higher and 400 ° C. or lower, in other words, there is a point where the differential value of the curve changes from negative to positive through 0, and the storage elastic modulus at 400 ° C. is the minimum value of the storage elastic modulus. It is less than the rate value.

  The liquid crystal polymer includes a thermotropic liquid crystal polymer exhibiting liquid crystallinity in a molten state and a rheotropic liquid crystal polymer exhibiting liquid crystallinity in a solution state. In the present invention, any liquid crystal polymer can be used, but a thermotropic liquid crystal polymer is preferably used because of excellent heat resistance and flame retardancy.

  Among the thermotropic liquid crystal polymers, thermotropic liquid crystal polyester (hereinafter simply referred to as “liquid crystal polyester”) is, for example, an aromatic compound mainly composed of aromatic dicarboxylic acid and monomers such as aromatic diol and aromatic hydroxycarboxylic acid. Polyester, which exhibits liquid crystal properties when melted. Typical examples thereof include type I [Formula (1)] synthesized from parahydroxybenzoic acid (PHB), phthalic acid, and 4,4′-biphenol, PHB and 2,6-hydroxynaphthoic acid. Type II [Formula (2)] synthesized from the above, Type III [Formula (3)] synthesized from PHB, terephthalic acid, and ethylene glycol. Among the above, since the I-type liquid crystal polyester and the II-type liquid crystal polyester are more excellent in heat resistance, it is preferable to use the I-type liquid crystal polyester and / or the II-type liquid crystal polyester in the present invention.

  In the above formula (1), isophthalic acid is preferable as phthalic acid.

  A normal liquid crystal polymer is insoluble or hardly soluble in a general solvent. In the present invention, insoluble means that the solvent at 25 ° C. required to dissolve 1 g of the substance (liquid crystal polymer) is 10,000 mL or more, and hardly soluble means that the solvent is 1,000 mL or more, It means less than 10,000 mL. Further, as a solvent for dissolving the liquid crystal polymer, fluorine-containing phenol solvents such as pentafluorophenol, tetrafluorophenol, 3,5-bistrifluoromethylphenol are known, but such solvents are special and very expensive. In addition, it is not a general solvent because it has a large environmental load and cannot be used industrially. In addition, there are liquid crystal polymers that have a structure soluble in aprotic polar solvents such as N-methyl-pyrrolidone and parachlorophenol, and are soluble in aprotic polar solvents, but alloys with other resins such as polyimide, etc. Thus, the characteristics derived from the liquid crystal polymer have been reduced. In the present invention, a liquid crystal polymer that is insoluble or hardly soluble in a solvent is used.

  The raw material liquid crystal polymer film used in the present invention preferably does not contain a crosslinking agent. The cross-linking agent generally has a plurality of highly reactive functional groups and exhibits hydrophilicity. Therefore, when the cross-linking agent is blended, it causes water mixing and absorption. When water is contained in a film used for solder reflow or the like, the water is rapidly vaporized to foam and the quality of the film is deteriorated. Therefore, the liquid crystal polymer film used as a raw material in the present invention and the high heat-resistant liquid crystal polymer film according to the present invention preferably do not contain a crosslinking agent and are not crosslinked by the crosslinking agent.

  However, the crosslinking agent may be included as long as it does not cause foaming at a high temperature of 340 ° C. or higher. For example, in producing the raw material liquid crystal polymer film, the amount of the crosslinking agent used relative to the entire raw material is 5% by mass or less, and the raw liquid crystal polymer film and the entire high heat resistant liquid crystal polymer film according to the present invention are unreacted. The remaining crosslinking agent is preferably 2% by mass or less. The amount of the crosslinking agent used is more preferably 2% by mass or less, further preferably 1% by mass or less, and particularly preferably 0.5% by mass or less. The residual amount of the crosslinking agent is preferably 1% by mass or less, more preferably 0.5% by mass or less, and particularly preferably 0.1% by mass or less. Moreover, although these minimums are not specifically limited, Naturally it is preferable that it is 0 mass%.

  Or when using a crosslinking agent, it is preferable to use a thing with low hydrophilicity. Examples of the low hydrophilic crosslinking agent include acrylate crosslinking agents such as dicyclopentanyl acrylate, benzyl acrylate, and phenoxyethyl acrylate; vinyl crosslinking agents such as divinylbenzene and vinyl silicone.

  The raw material liquid crystal polymer film used in the present invention is not particularly limited as long as it can be said to be a film. For example, as long as ionizing radiation irradiation is possible, the thickness and width are not particularly limited, and a long one may be used. The thickness of the raw material liquid crystal polymer film can be, for example, 10 μm or more and 500 μm or less.

  The raw material liquid crystal polymer film used in the present invention may contain a filler. The filler that can be used in the present invention is not particularly limited, and either an organic filler or an inorganic filler can be used. As fillers, for example, mineral fillers composed of talc, mica, wollastonite, attapulgite, shirasu balloon, montmorillonite, activated clay, zeolite, sepiolite, zonotolite, etc .; copper, gold, silver, lead, iron, tungsten, stainless steel, aluminum, Metal filler made of nickel, alloy (Fe—Ni, Fe—Si, Fe—Si—Al, Fe—Si—Cr, Fe—Co, Fe—Si—B—Cr, etc.); silica Silicon filler composed of graphite, charcoal, carbon fiber, activated carbon, etc .; metal oxide filler composed of ferrite, zinc oxide, alumina, calcium oxide, magnesium oxide, titanium oxide, cerium oxide, etc .; barium sulfate , Gold consisting of potassium titanate, calcium carbonate, etc. Metal salt filler; organic filler made of aromatic polyamide, polyimide, etc. can be mentioned.

  What is necessary is just to select the kind of filler by the characteristic. That is, the properties of the filler are imparted to the liquid crystal polymer film, and the defects of the film consisting only of the liquid crystal polymer can be improved by the filler, so the filler is selected according to the purpose. Specifically, for example, according to the purpose such as improvement of elastic modulus, thermal conductivity, electrical conductivity, shielding / reflection of electromagnetic waves, improvement of defects derived from liquid crystal polymer such as anisotropy and high linear expansion coefficient, fillers Can be selected. Depending on the purpose, only one filler may be selected, or two or more fillers may be used in combination.

  The shape of the filler is not particularly limited, and a plate-like filler, a granular filler, a rod-like (needle-like) filler, an amorphous filler, or the like can be used.

  The plate-like filler has a shape having a face part facing each other and a side part between the face parts. For example, the average aspect ratio of the surface portion is 1 or more and 4 or less, and the average ratio of the major axis of the surface portion to the thickness is 10 or more. The surface portion may be curved.

  The particulate filler is spherical or substantially spherical. For example, the average ratio between the longest part and the shortest part is 1 or more and 2 or less.

  A rod-like (needle-like filler) means a rod-like material regardless of whether or not the surface is confirmed. For example, the average length of the length portion is about 0.5 μm or more and 300 μm or less, the average major axis of the cross section is about 0.05 μm or more and 15 μm or less, and generally the ratio of the length to the major axis of the cross section Means 5 or more.

  An amorphous filler has no uniform shape and includes various shapes.

  In addition, the shape in the definition of a filler is an enlarged photograph by a scanning electron microscope (SEM) or the like, and means a shape that can be confirmed by more than half of the fillers in the screen. Moreover, the average aspect ratio, average length, etc. in the definition of a filler shall mean the average value of 100 or more fillers which can be observed with the same enlarged photograph.

  The average particle size of the filler used in the present invention is preferably a small particle size of 5 μm or less, more preferably 1 μm or less, as determined from the particle size distribution measurement measured on a volume basis. However, for the average particle diameter, a commercially available filler is used, and when there is a catalog value, the catalog value may be referred to.

  The blending amount of the filler may be appropriately adjusted. For example, it is 1 part by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the liquid crystal polymer constituting the raw liquid crystal polymer film or the high heat-resistant liquid crystal polymer film according to the present invention. It is preferable to set it as a range, and it is more preferable to set it as 5 to 30 mass parts.

  In the present invention, the raw material liquid crystal polymer film is irradiated with ionizing radiation of 2000 kGy or more.

  In the present invention, the term “ionizing radiation” is a general term for high-energy radiation that ionizes atoms and molecules, and includes fast charged particles such as electron beams and α rays, particle beams such as fast neutrons, and short wavelengths. Examples include high energy ultraviolet rays, X-rays, and γ rays. In the present invention, it is preferable to use an electron beam from the viewpoint of safety. Further, “1 kGy”, which is a unit of irradiation dose imparted from ionizing radiation to the raw material liquid crystal polymer film, indicates that 1 J of energy was absorbed per 1 kg of the raw material liquid crystal polymer film. Such irradiation amount can be adjusted by the irradiation apparatus used. As a matter of course, the ionizing radiation is irradiated as uniformly as possible in the plane direction of the raw liquid crystal polymer film.

The dose of ionizing radiation to be irradiated is preferably 2500 kGy or more, more preferably 5000 kGy or more, and further preferably 10,000 kGy or more. When the irradiation amount is 5000 kGy or more, particularly in the case of an I-type liquid crystal polymer film, the storage elastic modulus at 350 ° C. is 1.0 × 10 ⁷ Pa or more, and the film has extremely excellent heat resistance in a high temperature range. On the other hand, if the irradiation dose is too large, the mechanical strength of the film may be excessively lowered. Therefore, it is preferably 75000 kGy or less, more preferably 50000 kGy or less, and further preferably 25000 kGy or less.

  As described above, it is not always clear what structural change occurs in liquid crystal polymer molecules by irradiation with ionizing radiation. However, at least as described above, the storage elastic modulus starts to increase in the high temperature range, and the linear expansion coefficient in the Z direction (thickness direction of the film) decreases. Therefore, irradiation with high doses of ionizing radiation causes Z direction. Cross-linking may also occur between the liquid crystal polymer molecules.

  Specifically, irradiation with a high dose of ionizing radiation lowers the linear expansion coefficient in the Z direction by 6 ppm / ° C. or more as compared with a raw material liquid crystal polymer film not irradiated with ionizing radiation. In general, it is extremely difficult to reduce the linear expansion coefficient in the Z direction of the liquid crystal polymer film, but in the present invention, it can be easily reduced by irradiation with a high dose of ionizing radiation. Further, if the linear expansion coefficient in the Z direction of the liquid crystal polymer film can be reduced, for example, when used for an electronic circuit board, advantages such as an increase in connection reliability in the thickness direction can be obtained.

Further, the heat resistance of the high heat-resistant liquid crystal polymer film according to the present invention is extremely high, and can withstand solder repair that requires a high temperature of 340 ° C. or higher. Specifically, the storage elastic modulus at 350 ° C. is preferably 1.0 × 10 ⁷ Pa or more, and more preferably 2.0 × 10 ⁷ Pa or more.

Furthermore, the high heat-resistant liquid crystal polymer film according to the present invention is extremely unique in that the storage elastic modulus is increased at a high temperature of 340 ° C. or higher, and the storage elastic modulus at 370 ° C. is higher than the storage elastic modulus at 350 ° C. Excellent heat resistance. Specifically, the storage elastic modulus at 370 ° C. is preferably 1.0 × 10 ⁷ Pa or more, more preferably 2.0 × 10 ⁷ Pa or more, and 5.0 × 10 ⁷ Pa or more. More preferably it is.

  In addition, the linear expansion coefficient in the plane direction of the highly heat-resistant liquid crystal polymer film according to the present invention is preferably 10 ppm / ° C. or more and 25 ppm / ° C. or less, and the linear expansion coefficient in one direction of the plane direction It is preferable that the ratio with the linear expansion coefficient in the orthogonal direction is 0.4 or more and 2.5 or less. When the linear expansion coefficient and the ratio are within the above range, for example, when laminated with a metal layer, the difference in linear expansion coefficient with the metal layer is relatively small, and warpage can be reduced.

  The direction in which the linear expansion coefficient in the planar direction is measured is not particularly limited, but after the liquid crystal polymer film is melt-extruded, it is stretched in the direction (TD direction) perpendicular to the extrusion direction (MD direction) to reduce anisotropy. In some cases, the linear expansion coefficient in the MD direction is usually the smallest in the plane direction. However, when the draw ratio is increased, the linear expansion coefficient in the TD direction is minimized and the MD direction may be maximized. Thus, since the linear expansion coefficient is maximized or minimized in the MD direction or the TD direction in the plane direction of the liquid crystal polymer film, the linear expansion coefficient is preferably measured in the MD direction and the TD direction.

  According to experimental findings by the present inventors, at least the linear expansion coefficient in the planar direction hardly changes even when ionizing radiation is irradiated. Also, the film thickness is not substantially changed by the radiation of ionizing radiation. Therefore, in order to adjust the linear expansion coefficient in the planar direction, the ratio, and the thickness of the highly heat-resistant liquid crystal polymer film according to the present invention, the liquid crystal polymer film as a raw material may be adjusted.

  The metal layer-clad laminated film according to the present invention is characterized in that a metal layer is laminated on the high heat-resistant liquid crystal polymer film according to the present invention.

  The material of the metal layer may be appropriately selected according to the use of the metal layer-clad laminated film, but when used for an electronic circuit board, for example, copper, copper alloy, nickel, nickel alloy, gold, silver, etc. In view of versatility, copper or a copper alloy is preferable.

  The thickness of the metal layer to be laminated may be selected as appropriate, and may be, for example, about 0.1 μm or more and 2 mm or less.

  The method for laminating the high heat-resistant liquid crystal polymer film and the metal layer according to the present invention is not particularly limited. For example, it may be bonded by an adhesive or may be bonded by thermocompression bonding. In addition, the metal layer may be laminated by a plating method such as wet plating, vapor deposition, sputtering, or the like. More preferably, thermocompression bonding is preferably performed taking advantage of the properties of the liquid crystal polymer that is a thermoplastic resin.

  The metal layer-clad laminated film according to the present invention can be used as an electronic circuit board by etching at least a part of the metal layer. The electronic circuit board is very useful as it can withstand high temperature solder mounting at about 340 ° C. or more and 400 ° C. or less because the heat resistance of the high heat resistance liquid crystal polymer film according to the present invention is extremely excellent.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Examples 1 to 4 and Comparative Examples 1 and 2
A commercially available 50 μm-thick liquid crystal polymer film (product name “BIAC (registered trademark) BA” manufactured by Primatec Co., Ltd.), which is made of type I liquid crystal polymer and contains 10% by mass of silica having a diameter of 20 to 100 μm as a filler. The sample was cut into 310 mm × 210 mm, and repeatedly irradiated with an electron beam with an acceleration voltage of 200 kV in a nitrogen atmosphere until the total irradiation amount reached 1500 kGy, 2500 kGy, 5000 kGy, 7500 kGy, or 10000 kGy. For comparison, a film not irradiated with an electron beam was also produced.

Examples 5-8 and Comparative Examples 3-5
A commercially available 50 μm-thick liquid crystal polymer film (product name “BIAC (registered trademark) BC” manufactured by Primatec Co., Ltd.) made of type II liquid crystal polymer and containing no filler is cut into 310 mm × 210 mm, and an acceleration voltage is 200 kV in a nitrogen atmosphere. Were repeatedly irradiated until the total irradiation amount became 1000 kGy, 1500 kGy, 2500 kGy, 5000 kGy, 7500 kGy, or 10000 kGy. For comparison, a film not irradiated with an electron beam was also produced.

Test Example 1: Measurement of storage elastic modulus In accordance with Japanese Industrial Standard JIS-K7244, MD of each of the above films was measured by a tensile method using a viscoelasticity measuring apparatus (product name “Rheogel-E4000” manufactured by UBM). The storage modulus in the direction was measured from room temperature to 400 ° C. at a vibration frequency of 1 Hz, a strain of 0.1%, and a heating rate of 5 ° C./min. Temperature of I-type liquid crystal polymer film not irradiated with ionizing radiation or irradiated with ionizing radiation of 1500 kGy-Storage elastic modulus curve graph is shown in FIG. 1 and temperature of type I liquid crystal polymer film irradiated with ionizing radiation of 2500-10000 kGy- A storage elastic modulus curve graph is shown in FIG. 2, a temperature-storage elastic modulus curve graph of a type II liquid crystal polymer film irradiated with ionizing radiation or irradiated with ionizing radiation of 1000 kGy or 1500 kGy is shown in FIG. 3, and ionization of 2500 to 10,000 kGy is performed. FIG. 4 shows a temperature-storage modulus curve graph of the type II liquid crystal polymer film irradiated with radiation. In addition, Tables 1 and 2 show numerical values of storage elastic modulus at 350 ° C. or 370 ° C. of each liquid crystal polymer film.

  1-4 and the results of Tables 1 and 2, a liquid crystal polymer film not irradiated with an electron beam (Comparative Examples 1 and 3) and a liquid crystal polymer film with an electron beam irradiation amount of 1000 kGy or 1500 kGy (Comparative Examples 2, 4, and 5) ) As the measurement temperature increases, the storage elastic modulus continues to decrease temporarily. Moreover, it melted at 350 ° C. or 370 ° C.

  On the other hand, when the electron beam of 2500 to 10000 kGy is irradiated (Examples 1 to 8), an inflection point at which the storage elastic modulus value that has continued to decrease as the measurement temperature rises starts to rise is clearly recognized, Even at 350 ° C. and 370 ° C., it did not melt and showed a clear storage modulus.

  Thus, it was demonstrated that the liquid crystal polymer film according to the present invention has remarkably improved heat resistance in a high temperature range of 340 ° C. or higher by irradiation with high energy ionizing radiation.

Test Example 2: Measurement of mechanical strength Based on ASTM D882, the tensile strength and tensile elongation of the film at room temperature were measured. Specifically, using a Tensilon universal material testing machine (Orientec Co., Ltd.), a 10 mm × 100 mm strip test piece was pulled at a speed of 10 mm / min, and the load and elongation rate at the time of breaking were measured. Tables 1 and 2 show the ratio of the measured values of each electron beam irradiated liquid crystal polymer film when the measured value of the electron beam unirradiated liquid crystal polymer film is 100. From this value, it is possible to grasp how many percent of each intensity is retained even by electron beam irradiation.

  As shown in the results of Tables 1 and 2, it was conventionally thought that when excessive ionizing radiation was applied to the resin film, the decomposition became dominant and the mechanical strength was reduced. However, in the case of a liquid crystal polymer film, high energy of 2000 kGy or more. It was revealed that the mechanical strength did not decrease much even when ionizing radiation was irradiated in an amount.

Test Example 3: Measurement of linear expansion coefficient (CTE) The MD direction, TD direction, and Z direction lines of the liquid crystal polymer film irradiated with the electron beam obtained above and the liquid crystal polymer film irradiated with an electron beam of 5000 kGy or 10000 kGy The expansion coefficient was measured.

  Specifically, using a thermomechanical analyzer (TMA: Thermal Mechanical Analysis, manufactured by Seiko Electronics Co., Ltd.), the temperature of each liquid crystal polymer film was raised to 230 ° C. at 40 ° C./min, and the strain was removed. The sample length was measured while lowering the temperature to 30 ° C. at 10 ° C./min, and the linear expansion coefficient was calculated from the displacement of 50 to 100 ° C. In the measurement of the linear expansion coefficient in the MD direction and the TD direction, a test piece of 20 mm × 4 mm was cut out from the center of the film, placed on a TMA probe with a chuck distance of 10 mm, and a 5 g load was applied for measurement. In the measurement of the linear expansion coefficient in the Z direction, 40 test pieces cut out with a diameter of 5 mm were placed on the probe and measured by applying a weight of 20 g. The results are shown in Table 3.

  As described above, it can be said that the linear expansion coefficient in the plane direction hardly changes even when the liquid crystal polymer film is irradiated with ionizing radiation.

  On the other hand, in general liquid crystal polymer films, no matter how the stretching conditions are devised, the liquid crystal polymer molecules do not align in the Z direction, so the linear expansion coefficient in the Z direction remains high, but when irradiated with ionizing radiation It was found that the linear expansion coefficient in the Z direction decreases according to the irradiation amount. Therefore, it can be said that the high heat-resistant liquid crystal polymer film according to the present invention is excellent in that the difference in linear expansion coefficient between the planar direction and the Z direction is reduced.

Claims (14)

The ratio of the linear expansion coefficient in one direction of the plane direction to the linear expansion coefficient in the direction orthogonal to the direction is 0.4 or more and 2.5 or less, and
In the temperature-storage modulus curve graph in which the temperature is plotted on the horizontal axis and the measured storage modulus value is plotted on the vertical axis, the storage modulus value with respect to the temperature rises from a decrease to an increase in the range of 300 ° C. to 400 ° C. A high heat-resistant thermotropic liquid crystal polymer film characterized by the presence of dots. The high heat-resistant thermotropic liquid crystal polymer film according to claim 1, wherein the thermotropic liquid crystal polymer is represented by the following formula (1), (2) and / or (3).
The high heat resistant thermotropic liquid crystal polymer film according to claim 1 or 2 , which has a storage elastic modulus at 350 ° C of 1.0 x 10 ⁷ Pa or more. The high heat-resistant thermotropic liquid crystal polymer film according to claim 1 or 2 , wherein the storage elastic modulus at 350 ° C is 2.0 x 10 ⁷ Pa or more. The high heat-resistant thermotropic liquid crystal polymer film according to any one of claims 1 to 4 , which is not crosslinked by a crosslinking agent and / or does not contain a crosslinking agent. The high heat resistant thermotropic liquid crystal polymer film according to any one of claims 1 to 5 , wherein a linear expansion coefficient in a planar direction is 10 ppm / ° C or more and 25 ppm / ° C or less. The high heat resistant thermotropic liquid crystal polymer film according to any one of claims 1 to 6 , which has a thickness of 10 µm or more and 500 µm or less. The high heat-resistant thermotropic liquid crystal polymer film according to any one of claims 1 to 7 , which contains a filler. A method for producing a high heat-resistant thermotropic liquid crystal polymer film,
A step of irradiating ionizing radiation or 2000kGy the raw thermotropic liquid crystal polymer film seen including,
The ratio of the linear expansion coefficient in one direction of the plane direction of the high heat resistant thermotropic liquid crystal polymer film to the linear expansion coefficient in the direction orthogonal to the direction is 0.4 or more and 2.5 or less, A method for producing a highly heat-resistant thermotropic liquid crystal polymer film. The manufacturing method of the high heat resistant thermotropic liquid crystal polymer film of Claim 9 which makes ionizing radiation dose 5000 kGy or more. The method for producing a high heat-resistant thermotropic liquid crystal polymer film according to claim 9 or 10 , wherein the raw material thermotropic liquid crystal polymer film is not crosslinked by a crosslinking agent and / or does not contain a crosslinking agent. The linear expansion coefficient in the Z direction of the high heat-resistant thermotropic liquid crystal polymer film is 6 ppm / ° C or less lower than that of the raw material thermotropic liquid crystal polymer film not irradiated with ionizing radiation. The manufacturing method of the high heat resistant thermotropic liquid crystal polymer film as described in 1 .. A metal layer-clad laminated film, wherein a metal layer is laminated on the high heat resistant thermotropic liquid crystal polymer film according to any one of claims 1 to 8 .   An electronic circuit board comprising the metal layer-clad laminated film according to claim 13.