JP2006054239A - Biaxially oriented polyester film for flexible printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film for a flexible printed circuit board that has a highly flat circuit forming surface and is excellent in dimensional stability to heat and a traveling property. <P>SOLUTION: The biaxially oriented polyester film for the flexible printed circuit board formed with an applied layer on one surface of a base material layer composed of polyethylene-2, 6-naphthalene dicarboxylate satisfies all of the following characteristics:(1) The 10-point average height Rz on the surface of the base material layer of the film is 2-30 nm, (2) The 10-point average height Rz on the surface of the applied layer of the film is 50-150 nm, and (3) The heat shrinkage factor of the film in both lengthwise and widthwise directions when the film is heated to 200°C for 10 minutes is ≤1.5%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biaxially oriented polyester film for flexible printed circuit boards. More specifically, the present invention relates to a biaxially oriented polyester film for a flexible printed circuit board having a highly flat surface on which a circuit is formed and excellent thermal dimensional stability and runnability.

  A flexible circuit is an electric circuit disposed on a flexible substrate, and is formed by attaching a metal foil to a film to be a substrate or performing etching after plating or the like. The substrate on which the circuit is formed is further subjected to heat treatment, circuit component mounting, and the like, and is put to practical use as a component of an electric or electronic device.

  Conventionally, as a film for a flexible circuit board, a polyimide (hereinafter sometimes abbreviated as “PI”) film because of its good adhesion to a circuit and heat resistance when soldering when mounting circuit components. Is commonly used. On the other hand, polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”) films are inexpensive and are used in some flexible circuit board films because of their good chemical resistance and insulation properties. .

  In recent years, portable electric and electronic devices such as notebook personal computers and mobile phones have been rapidly spread, and miniaturization of these portable devices has been actively performed. However, there is a demand to have functions equivalent to or higher than those provided by conventional models even if the size is reduced, and accordingly, miniaturization and higher density of circuits have been required.

  While such advanced technology is required, the price competition due to the recent popularization of portable devices is intensifying, but the price of PI films that have been used as flexible circuit board films is high. As long as this is used, there is a limit to reducing the price of portable devices.

  In addition to being expensive, PI film has high hygroscopicity and large dimensional change during moisture absorption, so neglecting moisture conditioning of the film during processing may cause a decrease in adhesive strength with metal. Humidity is essential and is an obstacle to improving production efficiency. Furthermore, if different materials such as polyimide are included in the polyester, the recycling of the film may become complicated. In addition, if the PI resin dissolving solvent used when manufacturing the PI film remains in the film, there may be a problem in the quality of the circuit board.

  On the other hand, PET film is inexpensive as a flexible circuit board film and suitable for lowering the price, but its use has been limited in terms of heat resistance. For example, in the heat treatment in the membrane switch processing process, the dimensional change of the film becomes a problem, and soldering in circuit component mounting is performed at a high temperature, so the surface flatness of the film may deteriorate. As a densified circuit board film, it cannot be used.

  Also, due to advances in soldering technology when mounting circuit components, it is possible to lower the soldering temperature in recent reflow solders compared to conventional flow solders, but PET films still lack heat resistance. . On the other hand, with PI films, solder heat resistance is an excessive quality.

  For these reasons, a search for a plastic film that replaces the PI film has been conducted, and among the heat-resistant plastic films, a relatively inexpensive polyethylene-2,6-naphthalenedicarboxylate film is attracting attention. became.

  The use of a polyethylene-2,6-naphthalene dicarboxylate film as a film for a flexible circuit board has been proposed in, for example, JP-A-62-293991, JP-A-11-168267, and JP-A-2001-191405. ing. However, in the conventionally proposed polyethylene-2,6-naphthalene dicarboxylate film, since a lubricant is contained in the film from the viewpoint of runnability, it is desired to increase the density desired for recent circuits, In order to form a fine circuit having a line / space spacing of 25 μm / 25 μm or less, the surface flatness is insufficient, and the thin metal layer in contact with the concave portion of the film is not etched in the circuit component mounting process. Problems such as failure may occur. On the other hand, a film containing no lubricant is not practical because the film running property is not sufficient and the productivity is lowered.

  Moreover, in the printed wiring board, in order to improve the adhesiveness when the polymer film as a substrate and a circuit are bonded together, irregularities may be imparted to the surface of the polymer film called an anchor effect. In order to give unevenness to the film surface, a step of roughening the film surface is provided, and the roughened surface is about 3 to 5 μm in terms of Rz value. Therefore, since a substrate having a thin metal layer formed on a polymer film having the surface roughness has an uneven surface, the surface is formed when the line / space value of the formed circuit exceeds 30/30 μm. Roughness is not a problem, but when a circuit with a line width of 30/30 μm or less, particularly 25/25 μm or less is formed, insulation failure between wirings is a serious problem. This is because, when a circuit line, which is such a high-density thin line, is etched, it becomes easier to be affected by irregularities on the substrate surface. Therefore, at present, there is a demand for a polymer film suitable for a flexible circuit board capable of forming a circuit having a line / space value of 25/25 μm or less.

JP-A-62-93991 JP-A-11-168267 JP 2001-191405 A

  The present invention provides a biaxially oriented polyester film for a flexible printed circuit board having a high flatness on the surface on which a circuit is formed and excellent thermal dimensional stability and running property in order to solve the above-mentioned problems of the prior art. The purpose is to do.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have extremely high flatness on the surface on which the circuit is formed, the thermal contraction rate at 200 ° C. × 10 minutes is in a specific range, and the coating layer surface By using a biaxially oriented polyester film having an average surface roughness in a specific range, a fine pitch circuit having a line / space spacing of 25 μm / 25 μm or less is formed on an FPC board formed from the film. The present inventors have found that this is excellent in electrical resistance characteristics and is suitable for increasing the density of a circuit, and have reached the present invention.

Thus, according to the present invention, in the biaxially oriented polyester film in which the coating layer is provided on one side of the base material layer made of polyethylene-2,6-naphthalenedicarboxylate,
(1) Ten-point average roughness Rz on the substrate layer surface of the film is 2 to 30 nm.
(2) Ten-point average roughness Rz on the coating layer surface of the film is 50 to 150 nm.
(3) The heat shrinkage rate at 200 ° C. × 10 minutes is achieved by a biaxially oriented polyester film for a flexible printed circuit board that simultaneously satisfies the characteristics represented by 1.5% or less in both the longitudinal direction and the width direction of the film. . Moreover, the biaxially oriented polyester film for flexible printed circuit boards of this invention has a temperature expansion coefficient ((alpha) t) in 30-100 degreeC as 20 ppm / degrees C or less as a preferable aspect, and a total light transmittance is 85% or more. Also included are those having at least one of a haze of 1.5% or less and a coating layer containing a polymer binder and fine particles having the same refractive index as that of the polymer binder. .

According to the present invention, the biaxially oriented polyester film for a flexible printed circuit board according to the present invention is a copper-clad laminate for a flexible printed circuit board, in which a copper foil or a conductive paste is further laminated on the base material layer surface, the copper The insulation resistance value of the circuit pattern when DC100V is continuously applied to the circuit pattern formed using a flexible printed circuit board made of a tension laminate in an environment of 85 ° C. and 85% RH is expressed by the following formula (I). Also included are those provided with at least one of flexible printed circuit boards characterized by satisfying.
R ₁₀₀₀ / R ₀ ≧ 0.7 (I)
(In the formula, R ₁₀₀₀ represents an insulation resistance value (unit: MΩ) after continuous application of DC ₁₀₀ V for 1000 hours, and R ₀ represents an initial value of insulation resistance (unit: MΩ).)

  According to the present invention, the film surface on the circuit forming side is extremely smooth, the thermal shrinkage at 200 ° C. × 10 minutes is in a specific range, and the average roughness of the surface of the coating layer is in the specific range. Useful as a film for high-density FPC boards because of its excellent electrical resistance characteristics when a fine pitch circuit with a line / space spacing of 25 μm / 25 μm or less is formed on an FPC board formed from a biaxially oriented polyester film Moreover, the copper-clad laminate for flexible printed circuit boards and a flexible printed circuit board which consist of this film can be provided, and the industrial value is very high.

Hereinafter, the present invention will be described in detail.
<Polyester>
In the present invention, the polyester constituting the base layer of the biaxially oriented polyester film is made of polyethylene-2,6-naphthalenedicarboxylate.

  In such polyethylene-2,6-naphthalenedicarboxylate, 2,6-naphthalenedicarboxylic acid is used as the main dicarboxylic acid component, and ethylene glycol is used as the main glycol component. Here, “main” means at least 90 mol%, preferably at least 95 mol% of all repeating units in the polymer constituting the base layer of the biaxially oriented polyester film of the present invention.

  The polyethylene-2,6-naphthalenedicarboxylate in the present invention may be a single copolymer, a copolymer with other polyesters, or a mixture of two or more polyesters. The other component in the copolymer or mixture is preferably 10 mol% or less, more preferably 5 mol% or less, based on the total number of moles of the repeating structural unit.

  In the case of a copolymer, a compound having two ester-forming functional groups in the molecule can be used as a copolymer component constituting the copolymer. For example, oxalic acid, adipic acid, phthalic acid, sebacic acid, Dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid Dicarboxylic acid such as acid, oxycarboxylic acid such as p-oxybenzoic acid, p-oxyethoxybenzoic acid, or trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, bis Ethylene oxide adducts of E Nord sulfone, ethylene oxide adduct of bisphenol A, diethylene glycol, can be preferably used dihydric alcohols such as polyethylene oxide glycol.

  These compounds may be used alone or in combination of two or more. Of these, the acid component is preferably isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, p-oxybenzoic acid, and the glycol component is trimethylene glycol. , An ethylene oxide adduct of hexamethylene glycol, neopentyl glycol, and bisphenol sulfone.

  Further, the polyethylene-2,6-naphthalene dicarboxylate in the present invention is obtained by blocking part or all of the terminal hydroxyl group and / or carboxyl group with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Alternatively, it may be one obtained by copolymerizing an extremely small amount of an ester-forming compound such as glycerin or pentaerythritol within a range in which a substantially linear polymer is obtained.

  Polyethylene-2,6-naphthalenedicarboxylate in the present invention is a conventionally known method, for example, a method of directly obtaining a low polymerization degree polyester by reaction of dicarboxylic acid and glycol, or a lower alkyl ester of dicarboxylic acid and glycol. In the presence of a polymerization catalyst after reacting with one or more of the compounds including, for example, sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt. It can be obtained by a method of conducting a polymerization reaction. Polymerization catalysts include antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or partial hydrolysates thereof, and titanyl ammonium oxalate. , Titanium compounds such as potassium titanyl oxalate and titanium trisacetylacetonate can be used.

  When polymerization is performed via a transesterification reaction, a phosphorus compound such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, or normal phosphoric acid is usually added for the purpose of deactivating the transesterification catalyst before the polymerization reaction. Is done. A preferable content of the phosphorus compound is 20 to 100 ppm by weight in polyethylene-2,6-naphthalenedicarboxylate as a phosphorus element. When the content of the phosphorus compound is less than 20 ppm, the transesterification reaction catalyst is not completely deactivated, the thermal stability is poor, and the mechanical strength may be lowered. On the other hand, when the content of the phosphorus compound exceeds 100 ppm, the thermal stability may be poor and the mechanical strength may be reduced.

  Polyethylene-2,6-naphthalenedicarboxylate may be chipped after melt polymerization, and further subjected to solid phase polymerization under heating under reduced pressure or in an inert gas stream such as nitrogen.

  The intrinsic viscosity of polyethylene-2,6-naphthalenedicarboxylate in the present invention is preferably 0.40 dl / g or more at 35 ° C. in o-chlorophenol, and is 0.40 to 0.90 dl / g. More preferably it is. If the intrinsic viscosity is less than 0.40 dl / g, process cutting may occur frequently. If the intrinsic viscosity is higher than 0.9 dl / g, melt extrusion is difficult because of high melt viscosity, and the polymerization time is long and uneconomical.

  The polyethylene-2,6-naphthalene dicarboxylate of the present invention may contain a colorant, an antistatic agent, an antioxidant, and a catalyst within the range not impairing the object of the present invention.

<Biaxially oriented polyester film>
The biaxially oriented polyester film of the present invention has a configuration in which a coating layer is provided on one side of a base material layer made of the above-described polyethylene-2,6-naphthalenedicarboxylate. The base material layer made of polyethylene-2,6-naphthalenedicarboxylate of the present invention is substantially free of inert particles in order to obtain extremely high surface flatness.

<Coating layer>
The coating layer of the present invention contains a polymer binder, fine particles and an aliphatic wax. Since the biaxially oriented polyester film of the present invention has a circuit forming surface, that is, the surface flatness of the substrate layer is extremely high, the substrate layer alone has poor film running properties. It is necessary to have running performance. Further, the biaxially oriented polyester film of the present invention preferably has good optical properties expressed by total light transmittance and haze, and the polymer binder, fine particles and aliphatic wax have the following constitutions, respectively. Is preferred.

  The polymer binder and the fine particles preferably have the same refractive index. Here, “same” in the present invention refers to substantially the same refractive index, and means that the refractive index difference between the polymer binder and the fine particles is 0.04 or less. The difference in refractive index between the two is more preferably 0.02 or less, still more preferably 0.01 or less, and particularly preferably 0.005 or less. When the difference in refractive index exceeds the upper limit, light is greatly scattered due to the difference in refractive index at the boundary between the polymer binder and the fine particles, the haze of the coating layer is increased, and the transparency as a biaxially oriented polyester film is deteriorated. There is.

  The polymer binder used for the coating layer of the present invention is a polyester resin and an acrylic resin mixture having an oxazoline group and a polyalkylene oxide chain from the viewpoint of imparting good adhesion to the base material layer. The polymer binder is preferably soluble or dispersible in water, but water-soluble one containing some organic solvent can also be preferably used.

  The thickness of the coating layer of the present invention is preferably 0.01 to 0.2 μm, more preferably 0.02 to 0.1 μm.

<Polymer binder>
As the polyester resin constituting the polymer binder, a polyester obtained from the following polybasic acid component and diol component can be used. Such polyvalent base components include terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid , Dimer acid, and 5-sodium sulfoisophthalic acid. As the polyester resin constituting the polymer binder, it is preferable to use a copolyester using two or more kinds of polybasic acid components. Examples of the diol component include ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, and poly (ethylene oxide). ) Glycol and poly (tetramethylene oxide) glycol.

  The glass transition point of the polyester resin of the polymer binder is preferably 40 to 100 ° C, more preferably 60 to 80 ° C. Within this range, excellent adhesion and excellent scratch resistance can be obtained. When the glass transition temperature is less than the lower limit, the films tend to be blocked with each other. When the glass transition temperature exceeds the upper limit, the coating film is hard and brittle, and the scratch resistance may be deteriorated.

  As an acrylic resin having an oxazoline group and a polyalkylene oxide chain used as components of the polymer binder, for example, an acrylic resin comprising a monomer having an oxazoline group as shown below and a monomer having a polyalkylene oxide chain is used. Can do.

  Examples of the monomer having an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2 -Isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline can be exemplified, and one or a mixture of two or more can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. By using an acrylic resin having an oxazoline group, the cohesive force of the coating layer is improved, and the adhesion with an adjacent layer is further strengthened. Furthermore, the abrasion resistance with respect to the metal roll in the processing process in a film forming process can be provided.

  Examples of the monomer having a polyalkylene oxide chain include those obtained by adding polyalkylene oxide to an ester bond portion of acrylic acid or methacrylic acid. Examples of the polyalkylene oxide chain include polymethylene oxide, polyethylene oxide, polypropylene oxide, and polybutylene oxide. The repeating unit of the polyalkylene oxide chain is preferably 3 to 100. By using such an acrylic resin having a polyalkylene oxide chain, the compatibility between the acrylic resin and the polyester resin that forms the polymer binder of the coating layer is improved as compared with the acrylic resin not containing the polyalkylene oxide chain. Can improve transparency. If the repeating unit of the polyalkylene oxide chain is less than 3, the compatibility between the polyester resin and the acrylic resin is poor and the transparency of the coating layer is poor. If it exceeds 100, the moisture and heat resistance of the coating layer is lowered, and the humidity and temperature are high. This is not preferable because the adhesion with adjacent layers deteriorates.

  As the other copolymerization component, for example, monomers exemplified below can be copolymerized with the acrylic resin. That is, alkyl acrylate, alkyl methacrylate (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc.); Hydroxy group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; Epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether; acrylic acid, methacrylic acid, itaconic acid, malein Monomers having a carboxy group or a salt thereof such as acid, fumaric acid, crotonic acid, styrenesulfonic acid and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); acrylic Amide, methacrylamide, N-alkyl acrylamide, N-alkyl methacrylamide, N, N-dialkyl acrylamide, N, N-dialkyl methacrylamide (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N-dialkoxyacrylamide, N, N-dialkoxymethacrylamide (As the alkoxy group, methoxy group, ethoxy group, butoxy group, isobutoxy group, etc.), acryloylmorpholine, N-methylolacrylamide, N-methylolmethacrylamide, N-phenylacrylamide, N-phenylmethacrylamide Monomers having an amide group such as; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinyl methyl ether, vinyl ethyl ether, vinyl trialkoxysilane, alkyl Maleic acid monoester, alkyl fumaric acid monoester, alkylitaconic acid monoester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate and butadiene.

  When the polymer binder forming the coating layer is formed from a polyester resin and an acrylic resin having an oxazoline group and a polyalkylene oxide chain, the content of the polyester resin in the polymer binder is 5 to 95% by weight. It is preferable that it is 50 to 90 weight% especially. The content of the acrylic resin having an oxazoline group and a polyalkylene oxide chain forming the coating layer in the polymer binder is preferably 5 to 95% by weight, and particularly preferably 10 to 50% by weight. When the polyester resin exceeds 95% by weight, or the acrylic resin having an oxazoline group and a polyalkylene oxide chain is less than 5% by weight, the cohesive force of the coating layer decreases and the adhesion to the adjacent layer becomes insufficient. There is. Further, when the acrylic resin exceeds 95% by weight or the polyester resin is less than 5% by weight, the adhesion with the adjacent layer may be similarly lowered.

  The content of the polymer binder is preferably in the range of 40 to 99.4% by weight of the coating layer. If it is less than 40% by weight, the cohesive force of the coating film becomes low and the adhesion to the polyester film may be insufficient. If it exceeds 99.4% by weight, sufficient slipping and scratch resistance cannot be obtained. There is a case.

  The polymer binder of the coating layer in the present invention usually has a refractive index in the range of 1.50 to 1.60.

<Fine particles>
As fine particles constituting the coating layer in the present invention, it is preferable to use composite inorganic particles of silica and titania. The composite inorganic particles of silica and titania can be arbitrarily adjusted in refractive index, and the refractive index can be easily adjusted. Since the refractive index of the polymer binder is in the range of 1.50 to 1.60, the refractive index of the fine particles is also preferably in the range of 1.50 to 1.60, similar to the polymer binder.

  The average particle diameter of the fine particles is preferably in the range of 40 to 120 nm. If the average particle size is larger than 120 nm, the particles are likely to fall off, and if it is smaller than 40 nm, sufficient lubricity and scratch resistance may not be obtained. The content of the fine particles is preferably in the range of 0.1 to 10% by weight of the coating layer. If it is less than 0.1% by weight, sufficient lubricity and scratch resistance cannot be obtained, and if it exceeds 10% by weight, the cohesive force of the coating film may be lowered and the adhesion may be deteriorated.

<Aliphatic wax>
It is preferable that an aliphatic wax is contained in the coating layer since the film surface can be lubricated, and the content is preferably 0.5 to 30% by weight, more preferably 1 to 10% by weight of the coating layer. is there. If this content is less than 0.5% by weight, the slipperiness of the film surface may not be obtained. On the other hand, if it exceeds 30% by weight, the adhesion to the polyester film substrate layer may be insufficient. Specific examples of the aliphatic wax include plant waxes such as carnauba wax, candelilla wax, rice wax, wood wax, jojoba oil, palm wax, rosin-modified wax, olicuric wax, sugar cane wax, esparto wax, and bark wax. , Animal waxes such as beeswax, lanolin, whale wax, ibota wax, shellac wax, mineral waxes such as montan wax, ozokerite, ceresin wax, petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam, Fischer Tropus wax And synthetic hydrocarbon waxes such as polyethylene wax, oxidized polyethylene wax, polypropylene wax, and oxidized polypropylene wax. In particular, carnauba wax, paraffin wax, and polyethylene wax are particularly preferable because of easy adhesion to adjacent layers and good lubricity. These are preferably used as water dispersions because they can reduce the environmental burden and are easy to handle.

<Additives>
The coating layer may contain other fine particles to the extent that the transparency is not affected, in order to further improve the lubricity and scratch resistance. Examples of the other fine particles include calcium carbonate, magnesium carbonate, calcium oxide, zinc oxide, magnesium oxide, silicon oxide, sodium silicate, aluminum hydroxide, iron oxide, zirconium oxide, barium sulfate, titanium oxide, tin oxide, and trioxide. Examples thereof include inorganic fine particles such as antimony, carbon black, and molybdenum disulfide, and organic fine particles such as acrylic crosslinked polymer, styrene crosslinked polymer, silicone resin, fluororesin, benzoguanamine resin, phenol resin, and nylon resin. Among these, for the water-insoluble solid substance, it is preferable to select fine particles whose specific gravity does not exceed 3 in order to avoid sedimentation in the aqueous dispersion.

<Metal layer>
In the present invention, a metal layer can be further laminated on the base material layer surface of the biaxially oriented polyester film, and the obtained metal layer laminate can be used for a flexible printed circuit board. As this metal layer, metal foil, such as copper foil and aluminum foil, or electrically conductive paste is mentioned. Such a metal foil can be obtained by a general method such as one produced by rolling or one produced by electrolysis. In addition, the conductive paste is obtained by adding conductive fine powder such as silver, copper, carbon, etc., to a highly viscous resin ink. Among these metal foils or conductive pastes, copper foil is particularly preferable, and by using a copper-clad laminate in which the copper foil is laminated on a biaxially oriented polyester film, the productivity of the process when manufacturing a flexible printed circuit board is increased. be able to.

The thickness of the metal layer in the present invention is preferably 5 μm to 100 μm.
Examples of a method for laminating these metal layers include a method using an adhesive and a method of directly melting and sealing the surface layer of the polyester film base layer. The adhesive is not particularly mentioned, but a curable resin is preferable from the viewpoint of heat resistance. Suitable curable resins include epoxy resins, phenol resins, acrylic resins, polyimide resins, polyamide resins, polyisocyanate resins, polyester resins, polyphenyl ether resins, alicyclic olefin polymers, and the like.

  Moreover, other components can be mix | blended with an adhesive agent as needed. Compounding agents include UV absorbers, soft polymers, fillers, heat stabilizers, weathering stabilizers, anti-aging agents, leveling agents, antistatic agents, slip agents, antiblocking agents, antifogging agents, dyes, pigments, natural Examples thereof include oils, synthetic oils, waxes, emulsions, fillers, curing agents, flame retardants, and the like, and the blending ratio thereof is appropriately selected within a range not impairing the object of the present invention.

  In addition, the method for laminating the metal layer of the present invention may be a method in which a metal foil is directly formed on a base film without using an adhesive by plating or sputtering.

<Surface roughness of substrate layer surface>
The biaxially oriented polyester film of the present invention has a 10-point average roughness Rz of 2 to 30 nm on the substrate layer surface. The ten-point average roughness Rz on the substrate layer surface is more preferably 3 to 29 nm, and particularly preferably 4 to 28 nm. If Rz is less than the lower limit, the slipperiness of the film is poor, and when the film is wound on a roll, transfer and folding wrinkles due to air accumulation occur and flatness is impaired. On the other hand, when forming a fine circuit in which the line / space spacing is 25 μm / 25 μm or less when Rz exceeds the upper limit, the metal layer of the film recess is not etched in the portion to be etched, and as a minute metal scrap When a voltage is applied for a long period of time, it remains in an island shape, causing an insulation failure (migration) between wirings.

  In order to achieve the above-mentioned surface roughness, it is necessary that the base material layer made of polyethylene-2,6-naphthalenedicarboxylate does not contain inert particles including coarse particles of 1.0 μm or more, and 0.50 μm. It is more preferable not to contain the above inert particles.

  As for the surface roughness of the base material layer surface in the present invention, the ten-point average roughness Rz is preferably 2 to 30 nm, and the three-dimensional surface roughness SRa is preferably 10 nm or less. The three-dimensional surface roughness SRa is more preferably 8 nm or less, and particularly preferably 5 nm or less. On the other hand, the lower limit of the three-dimensional surface roughness SRa is preferably as small as possible, but is preferably 0 nm. Here, the ten-point average roughness Rz is attributed to the average particle diameter of coarse particles, while the three-dimensional surface roughness SRa is attributed to the average particle diameter and number of coarse particles and inert particles. In order to make the three-dimensional surface roughness SRa within such a range, it is preferable not to contain inert particles including coarse particles of 1.0 μm or more.

  The three-dimensional surface roughness SRa is measured using a non-contact type three-dimensional roughness meter (trade name “ET30HK” manufactured by Kosaka Laboratory) with a semiconductor laser having a wavelength of 780 nm, a measurement length of 1 mm, a sampling pitch of 2 μm, and a cutoff of 0.25 mm The measurement is performed under the measurement conditions of the vertical direction (film continuous film forming direction) magnification of 100,000 times, the horizontal direction (continuous film forming direction and vertical direction) magnification of 200 times, and the number of scanning lines of 100.

<Surface roughness of coated layer>
The biaxially oriented film of the present invention has a ten-point average roughness Rz of 50 to 150 nm on the coating layer surface. The ten-point average roughness Rz on the coating layer surface is more preferably 60 to 140 nm. When Rz is less than the lower limit, sufficient slipperiness cannot be obtained, winding becomes difficult, and wrinkles are formed on the film, so that wrinkles and irregularities are partially generated in the flexible circuit, resulting in poor flatness. On the other hand, if Rz exceeds the upper limit, the slipperiness is excellent but the transparency is lowered, and the fine particles in the coating layer may fall off. The surface roughness of the coating layer surface of the present invention is achieved by the average particle size and content of fine particles in the coating layer.

<Heat shrinkage>
The biaxially oriented polyester film of the present invention has a heat shrinkage rate at 200 ° C. for 10 minutes of 1.5% or less in both the longitudinal direction and the width direction of the film. In the biaxially oriented polyester film of the present invention, the lower limit of the heat shrinkage rate at 200 ° C. × 10 minutes is preferably −1.5% or more in both the longitudinal direction and the width direction of the film. The thermal shrinkage is more preferably -1.0 to 1.0%, particularly preferably -0.5 to 0.5%. In the present invention, unless otherwise specified, the longitudinal direction is a traveling direction when a film is continuously formed, and may be referred to as a film forming direction, a longitudinal direction, and an MD direction. In the present invention, the width direction is a direction orthogonal to the longitudinal direction in the film in-plane direction, and may be referred to as a transverse direction or a TD direction. If the thermal shrinkage at 200 ° C. × 10 exceeds the above-mentioned range, the dimensional change of the film at the time of curing after bonding the metal layers and the dimensional change of the film in the drying process after printing are large. In some cases, warping may occur, or wrinkles or irregularities may partially occur in the flexible circuit after soldering when mounting circuit components, resulting in poor flatness.

  In order to achieve the above-mentioned heat shrinkage rate, the lower the draw ratio, the better, but on the other hand the temperature expansion coefficient increases, so the draw ratio is 2.0 to 5.0 times in both the longitudinal direction and the width direction. A range is preferable. The stretching temperature is preferably 120 to 180 ° C. The higher the heat setting temperature, the better the heat shrinkage rate. However, when the temperature is too high, the film is loosened and the temperature expansion coefficient is increased. Furthermore, it is preferable to perform a heat treatment relaxation treatment for the purpose of further reducing the heat shrinkage rate, and it is preferable to carry out at a temperature of 160 to 240 ° C.

<Temperature expansion coefficient>
The biaxially oriented polyester film of the present invention preferably has a temperature expansion coefficient (αt) of 20 ppm / ° C. or less in the process of 30 to 100 ° C. The lower limit of the temperature expansion coefficient in the present invention is preferably 1 ppm / ° C. Moreover, the temperature expansion coefficient in this invention becomes like this. More preferably, it is 2-19 ppm / degrees C, More preferably, it is 3-18 ppm / degrees C. When the temperature expansion coefficient is less than the lower limit or exceeds the upper limit, the thermal deformation of the film may be deteriorated during the FPC processing step, and problems such as warpage of the FPC substrate may occur. The temperature expansion coefficient in the present invention is 30 to 100 ° C. in a temperature dimensional change curve obtained by measuring at a rate of temperature increase of 10 ° C./min from 30 ° C. to 180 ° C. using a thermomechanical analyzer (TMA). The coefficient of thermal expansion is obtained from the slope.

  In order to achieve the above-mentioned temperature expansion coefficient, the stretching ratio is preferably in the range of 2.0 to 5.0 times in both the longitudinal direction and the width direction in order to achieve both the thermal expansion coefficient and the thermal contraction rate. . The stretching temperature is preferably 120 to 180 ° C. The higher the heat setting temperature, the better the heat shrinkage rate. However, when the temperature is too high, the film is loosened and the temperature expansion coefficient is increased.

<Total light transmittance>
The total light transmittance of the biaxially oriented polyester film of the present invention is preferably 85% or more. The total light transmittance in the present invention is more preferably 87% or more, and particularly preferably 90% or more. When the total light transmittance is less than the lower limit, the transparency of the film is deteriorated, and it may be difficult to use such as illuminating with a light emitting diode from the lower part of the substrate of the FPC and making the illumination visible on the upper part of the substrate. Within the range of the total light transmittance of the present invention, the upper limit is preferably as high as possible, but is preferably less than 100%. Such total light transmittance is achieved by not containing inert particles in the base material layer of the biaxially oriented polyester film, and adjusting the polymer binder and fine particles in the coating layer.

<Haze>
The biaxially oriented polyester film of the present invention preferably has a haze of 1.5% or less. The haze in the present invention is more preferably 1.0% or less, and particularly preferably 0.5% or less. When the haze exceeds the upper limit, the transparency is deteriorated, and it may be difficult to use the FPC by illuminating it with, for example, a light emitting diode from the lower part of the FPC board. If it is the range of the haze of this invention, it is so preferable that a minimum is small, However Preferably it is 0%. Such haze is achieved by not containing inert particles in the base material layer of the biaxially oriented polyester film, and by adjusting the polymer binder and fine particles in the coating layer.

<Water absorption rate>
The water absorption rate of the biaxially oriented polyester film of the present invention is preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.6 or less. When the water absorption rate exceeds the upper limit, when used in a high humidity environment, the film tends to absorb moisture, resulting in a decrease in insulation performance, or corrosion of metal parts of the circuit.

<Film thickness>
The thickness of the biaxially oriented polyester film of the present invention is preferably in the range of 12 to 250 μm, more preferably 25 to 200 μm, and particularly preferably 38 to 150 μm. When the film thickness is less than the lower limit, the insulation performance of the film is insufficient, and the bending rigidity may be insufficient as a circuit board film. On the other hand, when the thickness of the film exceeds the upper limit, the film has insufficient bending resistance, and when an external force is applied, the film may be cracked or may not return in a broken state.

<Insulation resistance value>
The present invention also includes a preferred embodiment of a flexible printed circuit board using a copper clad laminate in which a copper foil or a conductive paste is further laminated on the base layer surface of the biaxially oriented polyester film. Such a flexible printed circuit board is preferably formed with a fine circuit pattern having a line / space interval of 25 μm / 25 μm or less, and a fine line pattern having a line / space interval of 20 μm / 20 μm or less. A circuit pattern is preferably formed. The flexible printed circuit board according to the present invention forms such a fine circuit pattern, and the insulation resistance value of the flexible printed circuit when a DC voltage (DC) of 100 V is continuously applied in an environment of 85 ° C. and 85% RH is expressed by the following formula. It is preferable to satisfy (I). If R ₁₀₀₀ / R ₀ is less than 0.7, the circuit may not be used as a flexible printed circuit board that has insufficient long-term electrical characteristics and requires long-term insulation characteristics.
R ₁₀₀₀ / R ₀ ≧ 0.7 (I)
(In the formula, R ₁₀₀₀ represents an insulation resistance value (unit: MΩ) after continuous application of DC ₁₀₀ V for 1000 hours, and R ₀ represents an initial value of insulation resistance (unit: MΩ).)

In order to achieve R ₁₀₀₀ / R ₀ in the range of the present invention, it is necessary that the ten-point average roughness Rz on the substrate layer surface of the biaxially oriented polyester film is within the range of the present invention. Since the substrate layer surface is extremely flat, even when a fine circuit having a line / space spacing of 25 μm / 25 μm or less is formed, the unevenness of the film surface is extremely small. This is because the etching is continuously formed, and defective etching portions that cause insulation failure (migration) between the wirings, that is, metal scraps remaining without being etched are not generated.

<Film forming method>
The biaxially oriented polyester film of the present invention is obtained by melt-extruding the above-described polyethylene-2,6-naphthalenedicarboxylate into a film shape and cooling and solidifying it with a casting drum to form an unstretched film. ) Stretched biaxially at a magnification of 2.0 to 5.0 times in the longitudinal and transverse directions at ° C, and desired by heat setting at a temperature of (Tm-100) to (Tm-5) ° C for 1 to 100 seconds Film can be obtained. Stretching can be performed by a generally used method such as a method using a roll or a method using a stenter. The stretching may be performed simultaneously in the longitudinal direction and the transverse direction, or may be sequentially performed in the longitudinal direction and the transverse direction. In the case of sequential stretching, the coating layer is formed by applying an aqueous coating liquid to a uniaxially oriented film stretched in one direction, stretching in the other direction as it is, and heat fixing. As a coating method, a roll coating method, a gravure coating method, a roll brush method, a spray method, an air knife coating method, an impregnation method, a curtain coating method, or the like can be used alone or in combination. Here, Tg represents the glass transition temperature of the polymer, and Tm represents the melting point of the polymer.

  Furthermore, when performing a relaxation | loosening process, it is effective to perform heat processing in the temperature of (X-80) -X degreeC of a film. Here, X represents the heat setting temperature. As a relaxation treatment method, the film is cut off at both ends of the film in the middle of the heat setting zone until it is wound on a roll after heat setting, and the take-off speed is reduced with respect to the film supply speed. A method of heating with an IR heater between rolls, a method of transporting a film on a heated transport roll and reducing the speed of the transport roll after the heated transport roll, while transporting the film on a nozzle that blows hot air after heat fixing, A method of reducing the take-off speed over the supply speed, or a method of reducing the speed of the transport roll by transporting the film onto a heating transport roll after winding with a film forming machine, or heating in a heating oven or IR heater There is a method to reduce the roll speed after the heating zone from the roll speed before the heating zone while transporting the zone. Of may be used a method, it is preferable to perform relaxation by the deceleration rate of the take-off side of the speed from 0.1 to 10% with respect to the speed of the supply side.

  In particular, the coating layer of the present invention contains fine particles, and the ten-point average roughness Rz on the film coating layer surface side is within the range of the present invention, so that the film-forming property at the time of producing the film is improved.

Hereinafter, the present invention will be described in more detail by way of examples, but various physical property values and characteristics in the present invention are measured and defined as follows. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.
(1) Film thickness About the obtained biaxially oriented polyester film, 10-point film thickness was measured at 30 g of needle pressure using an electronic micrometer (trade name “K-312A type” manufactured by Anritsu Corporation). The average value was defined as the film thickness.

(2) Surface roughness / ten-point average roughness Rz
Using an atomic force microscope (trade name “Nano Scope III AFM” manufactured by Digital Instruments, J scanner), Rz calculated under the following conditions was measured.
Probe Single-bond silicon sensor scan mode Tapping mode Number of pixels 256 × 256 data point scan speed 2.0 Hz
Measurement environment Room temperature, scanning range in air 10μm × 10μm

(3) Heat shrinkage rate The obtained biaxially oriented polyester film samples were marked at intervals of 30 cm, heat-treated for 10 minutes in an oven at a temperature of 200 ° C. without applying a load, It measured and the thermal contraction rate R was computed by the following formula in the film continuous film forming direction (MD direction) and the direction (TD direction) perpendicular | vertical to the film forming direction.
R (%) = {(L1-L2) / L1} × 100
Here, L1 is the distance between the marks before heat treatment, and L2 is the distance between the marks after heat treatment.

(4) Water absorption Measured according to JIS K7209.

(5) Temperature expansion coefficient (αt)
A film is set on a TMA / SS 120C manufactured by Seiko Instruments Inc. with a sample width of 3 mm and a space between chucks of 15.05 mm, and under a load of 80 g / mm ² , from room temperature (30 ° C.) to 180 ° C. (in the case of PET) The temperature was measured at a temperature increase rate of 10 ° C./min up to 150 ° C.). In the obtained temperature dimension change curve, the thermal expansion coefficient was determined from the slope of 30 to 100 ° C.

(6) Total light transmittance, haze Using the obtained biaxially oriented polyester film, the total light transmittance Tt (%) and scattered light transmittance Td (%) were determined according to JIS standard K6714-1958, and haze ( (Td / Tt) × 100) (%) was calculated.

(7) Electrical insulation Copper foil is laminated on the surface of the base material layer of the obtained biaxially oriented polyester film, and as shown in FIG. 1, a circuit pattern made of a comb pattern having a pattern length 3 of 10 mm is formed by etching. , 85 ° C. and 85% RH in a constant temperature and humidity machine and left for 24 hours. Thereafter, a voltage of 100 V DC was applied, 100 V DC was continuously applied under the same environment, and the resistance value was continuously monitored. The R ₁₀₀₀ / R ₀ value was calculated when the initial insulation resistance value was R ₀ (unit: MΩ) _and the insulation resistance value after 1000 hours was R ₁₀₀₀ (unit: MΩ), and evaluation was performed according to the following criteria. The pattern width 1 and the inter-line space 2 shown in FIG. 1 were both measured at 25 μm.
○: R ₁₀₀₀ / R ₀ is 0.7 or more Δ: R ₁₀₀₀ / R ₀ is 0.5 or more and less than 0.7 ×: R ₁₀₀₀ / R ₀ is less than 0.5

(8) Film flatness A polyester film and a general-purpose vinyl chloride resin are bonded to each other with an adhesive made of a plasticizer, and pressure-bonded using a pressure-bonding roll under conditions of a temperature of 160 ° C., a pressure of 30 kg / cm ² , and a time of 30 minutes. . The sample size was 25 cm × 25 cm, and the curled state at the four corners was observed in a state where the sample was placed on a surface plate for 100 hours in an atmosphere of 85% relative humidity and 65 ° C. The average of the amount of warping (mm) at the four corners was measured. Evaluation was performed according to the following criteria. ○ is a pass.
○: Warpage amount less than 10 mm ×: Warpage amount of 10 mm or more

(9) Thickness of coating layer A small piece of film is embedded in an epoxy resin (trade name “Epomount” manufactured by Refine Tech Co., Ltd.), and the total thickness of the embedded resin is 50 nm using a Microtome 2050 manufactured by Reichert-Jung. The film was observed with a transmission electron microscope (“LEM-2000” manufactured by JEOL Ltd.) at an acceleration voltage of 100 KV and a magnification of 100,000 times, and the thickness of the coating layer was measured.

(10) Average particle diameter The same operation as the measurement of the coating layer thickness was performed, the particle diameter of 100 particles was measured, and the average value was defined as the average particle diameter.

(11) Comprehensive evaluation In response to the above evaluation results, the results of the planarity, thermal dimensional stability and water absorption of the biaxially oriented polyester film were comprehensively evaluated. ◎ and ○ are acceptable.
A: Very good (all the above results are good and there is a particularly excellent part)
○: Good (all the above results are good)
Δ: Slightly poor (some of the above results are somewhat unsatisfactory)
×: Defect (Any of the above results has a fatal defect)

[Resin composition in coating layer and blending ratio of each component]
Table 1 shows the composition and blending ratio of the coating layers used in the examples. Here, the following components were used as the components constituting the coating layer.

  Polyester resin: Acid component is composed of 63 mol% of 2,6-naphthalenedicarboxylic acid / 32 mol% of isophthalic acid / 5 mol% of 5-sodium sulfoisophthalic acid, and glycol component is composed of 90 mol% of ethylene glycol / 10 mol% of diethylene glycol. (Tg = 76 ° C., average molecular weight 12000). In addition, polyester was manufactured as follows according to the method of Example 1 of Unexamined-Japanese-Patent No. 06-116487. That is, 42 parts of dimethyl 2,6-naphthalenedicarboxylate, 17 parts of dimethyl isophthalate, 4 parts of dimethyl 5-sodium sulfoisophthalate, 33 parts of ethylene glycol and 2 parts of diethylene glycol were charged into a reactor. 05 parts were added, the temperature was controlled at 230 ° C. in a nitrogen atmosphere, and the resulting methanol was distilled off to conduct a transesterification reaction. Subsequently, the temperature of the reaction system was gradually raised to 255 ° C., and the pressure inside the system was reduced to 1 mmHg to carry out a polycondensation reaction to obtain a polyester resin.

  Acrylic resin: composed of 30 mol% methyl methacrylate / 2 mol% 2-isopropenyl-2-oxazoline / 10 mol% polyethylene oxide (n = 10) methacrylate / 30 mol% acrylamide (Tg = 50 ° C.). The acrylic was produced as follows according to the method described in Production Examples 1 to 3 of JP-A-63-37167. That is, 302 parts of ion-exchanged water was charged into a four-necked flask and heated to 60 ° C. in a nitrogen stream, and then 0.5 parts of ammonium persulfate and 0.2 part of sodium hydrogen nitrite were added as a polymerization initiator. Furthermore, a mixture of monomers, 23.3 parts of methyl methacrylate, 22.6 parts of 2-isopropenyl-2-oxazoline, 40.7 parts of polyethylene oxide (n = 10) methacrylic acid, and 13.3 parts of acrylamide. The solution was added dropwise over 3 hours while adjusting the liquid temperature to 60 to 70 ° C. After completion of dropping, the reaction was continued with stirring while maintaining the same temperature range for 2 hours, and then cooled to obtain an acrylic aqueous dispersion having a solid content of 25%.

Fine particles: Silica and titania composite inorganic particles (average particle size: 100 nm) were used. The fine particles were produced as follows according to the methods described in the production examples and examples of JP-A-7-2520. A glass reaction vessel with an inner volume of 4 liters equipped with a stirring blade was charged with 140 g of methanol, 260 g of isopropanol, and 100 g of aqueous ammonia (25% by weight) to prepare a reaction solution, and stirred while maintaining the temperature of the reaction solution at 40 ° C. did. Next, 542 g of silicon tetramethoxide (Si (OMe) ₄ , trade name “Methyl silicate 39” manufactured by Colcoat Co., Ltd.) 542 g was charged into a 3 liter Erlenmeyer flask, and 195 g of methanol and 0.1 wt. 28 g of an aqueous hydrochloric acid solution (35% hydrochloric acid manufactured by Wako Pure Chemical Industries, Ltd. diluted with water to 1/1000) was added and stirred for about 10 minutes. Subsequently, a solution obtained by diluting 300 g of titanium tetraisopropoxide (Ti (O-i-Pr) ₄ , trade name “A-1 (TPT)”) manufactured by Nippon Soda Co., Ltd. with 634 g of isopropanol was added, and transparent. A homogeneous solution (co-condensate of silicon tetraalkoxide and titanium tetraalkoxide) was obtained. Each of 1699 g of the homogeneous solution and 480 g of aqueous ammonia (25% by weight) were simultaneously added dropwise to the reaction solution over 2 hours while initially decreasing the dropping speed and gradually increasing the speed toward the end. After completion of the dropping, the obtained cohydrolyzate was filtered, the organic solvent was dried at 50 ° C., and then dispersed in water to obtain fine particles having a concentration of 10% by weight and a refractive index of 1.56.

  Wax: Carnauba wax (trade name “Cerosol 524” manufactured by Chukyo Yushi Co., Ltd.) was used.

  Wetting agent: Polyoxyethylene (n = 7) lauryl ether (trade name “Naroacty N-70” manufactured by Sanyo Chemical Co., Ltd.) was used.

[Example 1]
Using 100 parts of dimethyl naphthalene-2,6-dicarboxylate and 60 parts of ethylene glycol as a transesterification catalyst, 0.03 part of manganese acetate tetrahydrate, and gradually increasing the temperature from 150 ° C. to 238 ° C. for 120 minutes A transesterification reaction was performed. On the way, when the reaction temperature reached 170 ° C., 0.024 part of antimony trioxide was added, and after the transesterification reaction, trimethyl phosphate (135 ° C. in ethylene glycol, 0.11 to 0.16 MPa for 5 hours) was added. The solution heat-treated under pressure: 0.023 parts in terms of trimethyl phosphate was added. Thereafter, the reaction product is transferred to a polymerization reactor, heated to 290 ° C., and subjected to a polycondensation reaction under a high vacuum of 27 Pa or less, and has an intrinsic viscosity of 0.61 dl / g and substantially no particles. Polyethylene-2,6-naphthalenedicarboxylate was obtained.

  The polyethylene-2,6-naphthalenedicarboxylate pellets were dried at 170 ° C. for 6 hours, then fed to an extruder hopper, melted at a melting temperature of 305 ° C., and filtered through a stainless steel fine wire filter having an average opening of 17 μm. The film was extruded through a 3 mm slit die on a rotary cooling drum having a surface temperature of 60 ° C. and rapidly cooled to obtain an unstretched film. The unstretched film thus obtained was preheated at 120 ° C., and further heated by a 900 ° C. IR heater 15 mm above between low-speed and high-speed rolls and stretched 3.1 times in the longitudinal direction. The coating for the coating layer was applied to one side of the film after the longitudinal stretching with a roll coater so that the coating thickness after drying was 0.1 μm.

  Subsequently, it was supplied to a tenter and laterally at 145 ° C. 3. Stretched 2 times. The obtained biaxially oriented film was heat-fixed at a temperature of 240 ° C. for 40 seconds to obtain a biaxially oriented polyester film having a thickness of 50 μm. The properties of the obtained film are shown in Table 2. According to this example, a film excellent in surface flatness, dimensional stability, low water absorption, transparency, and electrical insulation (electric resistance characteristics) of the base material layer surface could be obtained.

[Example 2]
After winding the biaxially oriented polyester film obtained in Example 1 on a roll, the biaxially oriented polyester was subjected to a relaxation treatment at a treatment temperature of 220 ° C. and a relaxation rate of 0.5% using an IR heater heating zone. A film was obtained. The properties of the obtained film are shown in Table 2. By this example, a film excellent in surface flatness, dimensional stability, low water absorption, transparency and electrical insulation on the surface of the base material layer could be obtained. Among them, the dimensional stability was particularly excellent.

[Comparative Example 1]
A polyethylene-2,6-naphthalene dicarboxylate used in Example 1 was kneaded with 0.1% by weight of spherical silica particles having an average particle size of 0.35 μm, and the draw ratio was 3.7 in the machine direction. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched 3.8 times in the transverse direction and no coating layer was provided. The properties of the obtained film are shown in Table 2. Since the obtained film contained a lubricant in the base material layer, the surface flatness of the base material layer surface was inferior, and the electrical insulation was insufficient. Further, the obtained biaxially oriented polyester film was opaque.

[Comparative Example 2]
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the coating layer was not provided. The properties of the obtained film are shown in Table 2. Since the obtained film did not have a coating film layer, the film running property was insufficient, and further, film wrinkles were generated and the electrical insulation was inferior.

[Comparative Example 3]
96 parts of methyl terephthalate, 58 parts of ethylene glycol, 0.038 part of manganese acetate and 0.041 part of antimony trioxide were charged into the reactor, respectively, and the ester exchange reaction was carried out while distilling methanol under stirring until the internal temperature reached 240 ° C. After the transesterification reaction was completed, 0.097 parts of trimethyl phosphate was added. Subsequently, the temperature of the reaction product was raised, and finally polycondensation was performed under conditions of 280 ° C. under high vacuum to obtain a chip of polyethylene terephthalate having an intrinsic viscosity ([η]) of 0.64.

Next, this polyethylene terephthalate chip was dried at 170 ° C. for 3 hours, then supplied to a twin-screw extruder, melt-kneaded at 280 ° C., and rapidly cooled and solidified to obtain a master chip.
The polyethylene terephthalate pellets were dried at 160 ° C. for 3 hours, then supplied to an extruder hopper, melted at a melting temperature of 295 ° C., and rapidly cooled and solidified on a cooling drum maintained at 20 ° C. to obtain an unstretched film. The unstretched film is stretched 3.5 times in the longitudinal direction at 95 ° C., and then the coating film thickness after drying the above coating layer coating agent is 0.1 μm on one side of the film after longitudinal stretching. The film was stretched 3.8 times in the transverse direction at 110 ° C. and heat-set at 230 ° C. to obtain a biaxially stretched polyester film having a thickness of 100 μm. The properties of the obtained film are shown in Table 2. In addition to being inferior in electrical insulation, the film had a large thermal shrinkage rate and lacked dimensional stability.

[Comparative Example 4]
A 50 μm film of “Kapton; Type H” manufactured by Toray DuPont was used. The properties of the obtained film are as shown in Table 2. Although the heat shrinkage ratio is very excellent, in addition to being inferior in surface flatness and transparency, the film flatness is inferior in an atmosphere under high humidity due to high water absorption.

  The biaxially oriented polyester film obtained by the present invention is excellent in surface flatness, thermal dimensional stability, runnability, and has excellent electrical insulation properties and excellent electrical resistance characteristics when used as a flexible printed circuit board. A fine pitch of the circuit pattern can be achieved, and it is suitably used for flexible printed circuit board applications.

It is the figure which illustrated the circuit pattern used for evaluation of the electrical insulation of this invention.

Explanation of symbols

1 Pattern width 2 Space between lines 3 Pattern length 4 DC power supply

Claims (6)

In the biaxially oriented polyester film in which the coating layer is provided on one side of the base material layer made of polyethylene-2,6-naphthalenedicarboxylate,
(1) Ten-point average roughness Rz on the base material layer surface of the film is 2 to 30 nm.
(2) Ten-point average roughness Rz on the coating layer surface of the film is 50 to 150 nm.
(3) Biaxially oriented polyester for flexible printed circuit boards characterized in that the thermal shrinkage rate at 200 ° C. × 10 minutes simultaneously satisfies the characteristics represented by 1.5% or less in both the longitudinal direction and the width direction of the film the film.   The biaxially oriented polyester film for flexible printed circuit boards according to claim 1, wherein the coefficient of thermal expansion (αt) at 30 to 100 ° C is 20 ppm / ° C or less.   The biaxially oriented polyester film for flexible printed circuit boards according to claim 1 or 2, wherein the total light transmittance is 85% or more and the haze is 1.5% or less.   The biaxially oriented polyester film for flexible printed circuit boards according to any one of claims 1 to 3, wherein the coating layer contains a polymer binder and fine particles having the same refractive index as that of the polymer binder.   A copper-clad laminate for a flexible printed circuit board, wherein the biaxially oriented polyester film according to claim 1 is further laminated with a copper foil or a conductive paste on the surface of the base material layer. The insulation resistance value of the circuit pattern when DC100V is continuously applied to the circuit pattern formed using the flexible printed circuit board made of the copper clad laminate according to claim 5 in an environment of 85 ° C and 85% RH. Satisfy | fills following formula (I), The flexible printed circuit board characterized by the above-mentioned.
R ₁₀₀₀ / R ₀ ≧ 0.7 (I)
(In the formula, R ₁₀₀₀ represents an insulation resistance value (unit: MΩ) after continuous application of DC ₁₀₀ V for 1000 hours, and R ₀ represents an initial value of insulation resistance (unit: MΩ).)

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