JP2011096847A - Supporting material polyester film for interlayer insulation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film suitable for a supporting material to form an interlayer insulating film material to be used for a multilayer printed wiring board manufactured with a build-up method responding to a request for ultra-fine and high-density wiring. <P>SOLUTION: A polyester film is used as a supporting material for coating a thermosetting resin to form an interlayer insulating film. This supporting material polyester film for interlayer insulation is formed as a co-extrusion laminated polyester film formed of at least a double-layered polyester film, wherein an average roughness Ra at the center surface of one polyester film is 30 nm or less and an average roughness Rz of ten points is 200 nm or less, while an average roughness Ra at the center surface of the other polyester film is 10 to 50 nm, slackening degree of the film is 15 mm/m or less, and thickness of the film is in the range of 20 to 100 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polyester film used as a support for forming a film-like insulating layer used in a build-up type multilayer printed wiring board in which circuit-formed conductor layers and insulating layers are alternately stacked.

  In recent years, build-up printed wiring boards in which a plurality of insulating layers are stacked are attracting attention in the field of multilayer printed wiring boards that provide mounting circuits corresponding to higher functionality and higher density of electronic devices.

  The build-up method using a build-up printed wiring board is a new process for forming a multi-layered conductor layer by forming insulating layers one by one, creating a conductor pattern, and connecting the layers. The core technology of the innovative build-up method is the use of vias for connecting interlayers (small-diameter holes), and the miniaturization of the holes that connect multilayer wiring boards in three dimensions has progressed. The number of holes can be greatly increased. As a result, fine line technology and thinning technology for conductor / insulating layer thickness have also progressed, and furthermore, vias can be opened at different positions for each layer, so that interlayer connection holes can be arranged rationally, which is a great advantage in pattern design Brought about.

  Insulating layers used for multilayer printed wiring boards are made of glass cloth impregnated with epoxy-based polyimide resin, or ceramic-based materials. Because it is an important parameter that influences the electrical characteristics such as the characteristic impedance, it is necessary to select such a material. Specifically, a material having a dielectric constant as low as possible is selected, and various proposals are also available. Has been made. In addition, since the insulating layer is formed on the film support with a uniform thickness, it is preferable to meet the demands for miniaturization and high performance, and a material that can be applied is used. Yes.

  The insulating layer is formed by applying a thermosetting resin as an insulating layer to a film-like support as an interlayer insulating material for miniaturization and high performance, and curing the support film with the film. A method has been proposed for forming a roll. However, with regard to the film that is a support for forming a film-like insulating layer, specific proposals are made despite the great influence on the surface properties of the insulating layer and the productivity when forming the insulating layer. The situation has not been made. In particular, when the insulating layer is applied, it is difficult to process the insulating resin to be applied with a constant thickness when the film has a large amount of sag.

JP 2005-154727 A JP 2005-39247 A JP 2008-251971 A

  The present invention has been made in view of the above circumstances, and its solution is a film-like interlayer insulation used for a multilayer printed wiring board manufactured by a build-up method to cope with miniaturization and high density of wiring. It is to provide a suitable polyester film as a support for forming the material.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is a polyester film used as a support for applying a thermosetting resin that forms an interlayer insulating layer, and is a coextruded laminated polyester film comprising at least two polyester layers. The center average roughness Ra of one polyester film surface is 30 nm or less, the ten-point average roughness Rz is 200 nm or less, and the center average roughness Ra of the other polyester film surface is 10 to 50 nm. The sag amount is 15 mm / m or less, and the thickness of the film is 20 to 100 μm.

  According to the present invention, a material suitable as a support film for interlayer insulation can be provided, and its industrial value is high.

Hereinafter, the present invention will be described in detail.
The support for forming the film-like interlayer insulating material of the present invention is usually composed of a biaxially oriented polyester film, which is a so-called coextrusion method using two or three or more melt extruders. Is a film having a laminated structure of two layers or three or more layers.

  The polyester film of the present invention has at least two layers, and in order to obtain the desired surface roughness to the polyester used for each surface layer, it is necessary to use raw materials in which different particles are blended. it can.

  The polyester used in the present invention is preferably obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN) and the like.

  The polyester used in the present invention may be a homopolyester or a copolyester. In the case of a copolyester, it is a copolymer containing 30 mol% or less of the third component. Examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acids (for example, P-oxybenzoic acid). Or 2 or more types are mentioned, As a glycol component, 1 type, or 2 or more types, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4- cyclohexane dimethanone neopentyl glycol, is mentioned.

  The film of the present invention has a specific surface roughness in order to achieve both the surface property of the interlayer insulating layer formed on the polyester film and the roll winding property of the laminated film on which the insulating layer is formed. preferable. In order to achieve this, for example, particles having an average particle diameter of 0.1 to 10 μm, preferably 0.2 to 10 μm are contained. If the average particle size is less than 0.1 μm, the surface roughness of the film is low, the slipping property of the film is poor, and the product may not be obtained in a roll state after forming the interlayer insulating layer. On the other hand, when the average particle diameter exceeds 10 μm, the surface roughness of the interlayer insulating layer is increased, which may adversely affect the circuit density.

  The content of the particles in the film is usually 0.1 to 10.0% by weight, preferably 1.0 to 5.0% by weight. If the content of the particles is less than 0.1% by weight, the slipperiness of the film tends to deteriorate, and if the content exceeds 10.0% by weight, the surface roughness of the film becomes too large and the flatness is impaired. May be.

  Examples of such particles include silicon oxide, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, titanium oxide, kaolin, talc, carbon black, silicon nitride. , Boron nitride, and crosslinked polymer fine powder as described in JP-B-59-5216 are not limited thereto, as long as the gist of the present invention is not impaired.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film in the present invention as necessary.

  The greatest feature of the present invention is that the amount of sag (planarity) of the film is 15 mm / m or less, preferably 7.5 mm / m or less. When an insulating coating is applied to a film having a sagging amount exceeding 15 mm / m, it is difficult to perform a process for making the coating thickness constant. For example, the gap between the coater head and the film affects the coating thickness. When the film width is 1460 mm or more and the amount of sag exceeds 15 mm / m, the coater head and the film can only partially contact each other. It cannot be countered by condition adjustment. This is undesirable because it has the same effect in all coating systems.

  In the present invention, the center line average roughness (Ra) of one surface of the polyester film is 10 to 50 nm, preferably 20 to 30 nm. When the center line average roughness Ra is less than 10 nm, the slipperiness of the film and the so-called air leakage between the films tend to deteriorate, and a product cannot be obtained in a roll state after forming the interlayer insulating layer. Further, when the center line average roughness Ra exceeds 50 nm, the surface roughness of the polyester film of the interlayer insulating layer is transferred to the surface of the interlayer insulating layer when wound in a roll shape, which becomes a defect of the interlayer insulating layer. .

  The polyester film itself of the present invention is peeled off after the interlayer insulating layer is bonded to the core substrate as an adhesive sheet, and the role is finished, but the interlayer insulation bonded to the core substrate after the polyester film is peeled off Affects the surface of the layer.

  The center line average roughness (Ra) of the surface of the polyester film on which the thermosetting resin is applied and the interlayer insulating layer is formed (the side opposite to the surface where Ra is in the range of 10 to 50 nm) is 30 nm or less. It is preferably 20 nm or less, and the ten-point average roughness (Rz) is 200 nm or less, preferably 100 nm or less. When the centrality average roughness Ra exceeds 30 nm or the ten-point average roughness Rz exceeds 200 nm, the surface roughness of the interlayer insulating layer increases, which causes a problem in increasing the circuit density.

  The thickness of the polyester film of the present invention is in the range of 20-100 μm, preferably 25-50 μm. If the film thickness is less than 20 μm, wrinkles occur when an insulating material is applied, which is not preferable. When the film thickness exceeds 100 μm, the amount of polyester used increases, which is not preferable in terms of cost.

  The curable resin used for the interlayer insulating layer in the present invention can be used without particular limitation as long as it can form a layer on the support and has sufficient insulation, for example, epoxy resin-based, acrylic-based , Polyimide resin system, polyimide amide resin system, polycyanate resin system, polyester resin system, thermosetting polyphenylene ether resin system, and the like. Further, two or more of these may be used in combination, or a multilayer structure may be used.

  A method of forming an interlayer insulating layer on a support is a known method in which a resin composition varnish in which the above-described thermosetting resin or the like is dissolved is applied, and then the solvent is dried by heating to simultaneously cure the resin. Can be created.

  In the present invention, a cured resin layer serving as an interlayer insulating layer is provided as a laminated film on a support made of a polyester film, and the laminated film is rolled. When making it into a roll shape, it does not matter whether it can be stored as it is, in a state where a protective film for protecting the surface of the cured resin is bonded, or in a roll state. However, by protecting with a protective film, it is possible to prevent the adhesion and scratches of dust etc. to the surface of the resin composition layer. It is preferable to add a step of bonding.

  The protective film is not particularly limited as long as it has a function of protecting the surface of the interlayer insulating layer, and a plastic film such as polyethylene, polypropylene, or polyester is used.

  The thickness of the interlayer insulating layer formed of the polyester film is not less than the thickness of the conductor layer. Since the thickness of the conductor layer of the circuit board is usually in the range of 5 to 70 μm, the thickness of the resin composition layer is preferably 10 to 100 μm.

  The film having an interlayer insulating layer obtained in the present invention is laminated on the core substrate by peeling off the protective film of the interlayer insulating layer as an adhesive film when patterning the conductive layer to form a circuit. Structure of core base material / interlayer insulating layer / polyester film support, or structure of polyester film support / interlayer insulation / core base material / interlayer insulating layer / polyester film support in which both sides of the core base material are sandwiched between interlayer insulating layers The core substrate and the interlayer insulating layer are adhered to each other by heating, and the support made of the polyester film is peeled off.

  As a method of adhering the interlayer insulating layer to the core substrate, a method of laminating on the circuit board under reduced pressure by a vacuum laminating method is suitably used. The laminating method may be a batch method or a continuous method using a roll. Further, the adhesive film and the circuit board may be heated (preheated) as necessary before lamination.

The lamination conditions are bonding temperature (lamination temperature) of preferably 70 to 140 ° C., preferably the crimping pressure ^{1~11kgf / cm 2 (9.8 × 10} 4 ~10 7 .9 × 10 4 N / m 2) And laminating under reduced pressure with an air pressure of 20 mmHg (26.7 hPa) or less.

  The vacuum lamination can be performed using a commercially available vacuum laminator.

  The circuit board in the present invention mainly includes a conductor layer (circuit) patterned on one or both sides of a substrate such as a glass epoxy, metal substrate, polyester substrate, polyimide substrate, BT resin substrate, thermosetting polyphenylene ether substrate, or the like. The one formed. Also included in the circuit board of the present invention is a multilayer printed wiring board in which conductor layers and insulating layers are alternately formed and a conductor layer (circuit) is patterned on one or both sides. The surface of the conductor circuit layer is preferably roughened by blackening or the like in advance from the viewpoint of adhesion of the insulating layer to the circuit board.

  Thus, after laminating the adhesive film on the circuit board, when the support film is peeled off, the insulating film can be formed on the circuit board by peeling and thermosetting. The conditions of heat curing are selected in the range of 20 to 180 minutes at 150 to 220 ° C, more preferably 30 to 120 minutes at 160 to 200 ° C. If the support film is not peeled off after the insulating layer is formed, it is peeled off here.

  Next, a hole is made in the insulating layer formed on the circuit board to form a via hole and a through hole. Drilling can be performed by a known method such as drilling, laser, plasma, or a combination of these methods, if necessary. However, drilling by a laser such as a carbon dioxide laser or YAG laser is the most common. Is the method.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.

  First, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the extending | stretching temperature orthogonal to the 1st step | paragraph extending | stretching direction is 70-170 degreeC normally, and a draw ratio is 3.0-7 times normally, Preferably it is 3.5-6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  The simultaneous biaxial stretching method can also be adopted for the production of the polyester film in the present invention. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is as follows: The area magnification is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Furthermore, a so-called coating stretching method (in-line coating) in which the film surface is treated during the above-described polyester film stretching step can be applied. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with stretching and the thickness of the coating layer can be reduced according to the stretching ratio, producing a film suitable as a polyester film. it can.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  In this invention, it does not necessarily limit about the curing conditions at the time of forming a coating layer on a polyester film, For example, when providing a coating layer by the coating extending | stretching method (in-line coating), it is 170-280 degreeC normally. The heat treatment may be performed for 3 to 40 seconds, preferably 200 to 280 ° C. for 3 to 40 seconds.

  Moreover, you may use together heat processing and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of the coating extending | stretching method (in-line coating) or offline coating.

  The polyester film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage of producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction, The polycondensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded.
The measuring method used in the present invention is as follows.

(1) Film thickness It calculated | required with the micrometer.

(2) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(3) Measurement of average particle size (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(4) Surface roughness (Ra)
The center line average roughness Ra (μm) is defined as the surface roughness. It calculated | required as follows using the Kosaka Laboratory Co., Ltd. surface roughness measuring machine (SE-3F). That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-section curve in the direction of the center line, the center line of the extracted portion is the x axis, and the direction of the vertical magnification is the y axis. When represented by (x), the value given by the following equation is represented by [μm]. The center line average roughness was represented by the average value of the center line average roughness of the extracted portion obtained from 10 cross section curves obtained from the sample film surface. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.
Ra = (1 / L) ∫ 0 L | f (x) | dx

(5) Ten point average roughness (Rz)
Elevation of the peak from the highest to the fifth in the cross-section curve of the section extracted by the reference length (2.5 mm) from the cross-section curve obtained by the surface roughness measuring machine (SE-3F) manufactured by Kosaka Laboratory Ltd. And the average value of the altitude of the bottom of the valley from the deepest to the fifth. The ten-point average roughness was represented by the average value of the ten-point average roughness of the extracted portion obtained from 10 cross-section curves obtained from the sample film surface. The radius of the stylus used at this time is 2.0 μm, the load is 30 mg, and the cutoff value is 0.08 mm.

(6) Measurement of amount of sag The film unwound from the roll film is placed on two parallel rolls placed horizontally in the air. Here, the interval between the rolls is 1.5 m, and the tension applied to the film is 40 g / mm 2. Measure the distance from the plane formed by connecting two parallel rolls to the film surface submerged in the entire area, and divide the value by dividing the (maximum value-minimum value) by the film width (mm / m).

(Manufacture of polyester)
Production Example 1 (Polyethylene terephthalate A)
100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate are placed in a reactor, the temperature is raised by heating, methanol is distilled off, transesterification is performed, and 4 hours are required from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, after adding 0.04 part of ethylene glycol slurry ethyl acid phosphate and 0.03 part of antimony trioxide, the temperature reached 280 ° C. and the pressure reached 15 mmHg in 100 minutes. It was 0.3 mmHg. After 4 hours, the system was returned to atmospheric pressure to obtain polyethylene terephthalate A1 having an intrinsic viscosity of 0.61.

Production Example 2 (Polyethylene terephthalate B)
100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate are placed in a reactor, the temperature is raised by heating, methanol is distilled off, transesterification is performed, and 4 hours are required from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of ethylene glycol slurry ethyl acid phosphate, 0.03 part of antimony trioxide and 0.01 part of silica particles having an average particle size of 3.4 μm were added, and then the temperature was 280 ° C. and the pressure was increased in 100 minutes. The pressure reached 15 mmHg, and the pressure was gradually reduced thereafter to finally reach 0.3 mmHg. After 4 hours, the system was returned to normal pressure to obtain polyethylene terephthalate B having an intrinsic viscosity of 0.61.

Production Example 3 (Polyethylene terephthalate C)
In the same manner as in Production Example 1, except that 0.01 parts of synthetic calcium carbonate particles having an average particle diameter of 0.70 μm are added instead of 0.01 parts of silica particles having an average particle diameter of 3.4 μm, polyethylene is added. Terephthalate C was obtained.

Production Example 4 (Polyethylene terephthalate D)
In the same manner as in Production Example 1, except that 0.01 parts of synthetic calcium carbonate particles having an average particle diameter of 0.27 μm are added instead of 0.01 parts of silica particles having an average particle diameter of 3.4 μm, polyethylene is added. Terephthalate D was obtained.

Production Example 5 (Polyethylene terephthalate E)
In the same manner as in Production Example 1, except that 0.01 parts of synthetic calcium carbonate particles having an average particle diameter of 1.50 μm are added in place of 0.01 parts of silica particles having an average particle diameter of 3.4 μm, polyethylene is added. Terephthalate E was obtained.

(Manufacture of polyester film)
The above polyesters A to E are mixed raw materials of the A layer and the B layer at the blending ratio shown in Tables 1 and 2 below, and each is supplied to two twin-screw extruders and melted at 285 ° C. On the other hand, it is co-extruded on a casting drum cooled to 20 ° C. in a two-layer / two-layer configuration so that the thickness ratio of A layer / B layer = 50% / 50%, and solidified by cooling to obtain a non-oriented sheet. It was. Next, the film is stretched 3 to 5 times in the longitudinal direction at 100 ° C., then subjected to a preheating step in the tenter and subjected to 4 to 5 times transverse stretching at 120 ° C., and then subjected to heat treatment at 200 to 230 ° C. for 10 seconds. Thereafter, 10% relaxation was applied in the width direction at 180 ° C. to obtain polyester films having thicknesses shown in Tables 1 and 2.

(Applying resin composition varnish to polyester film: Formation of interlayer insulation layer)
The resin composition varnish produced by the following method was applied to the surface of the B layer of the polyester film obtained in Examples 1 to 4 and Comparative Examples 1 to 8 with a die coater for the resin thickness after drying to be 70 μm. It apply | coated and dried at 80-120 degreeC (average 100 degreeC), and the interlayer insulation layer which made the polyester film the support body was produced.

Table 3 shows the surface and processing characteristics of the polyester film obtained by the above method.
<< Epoxy resin composition >>
20 parts of liquid bisphenol A type epoxy resin (“Epicoat 828EL” manufactured by Japan Epoxy Resin Co., Ltd.), 20 parts of brominated bisphenol A type epoxy resin (YDB-500 manufactured by Toto Kasei Co., Ltd.), cresol novolac type epoxy resin (epoxy) Equivalent 215, softening point 78 ° C., Dainippon Ink Chemical Co., Ltd. Epiklone N-673) 20 parts, terminal epoxidized polybutadiene rubber (Nagase Kasei Kogyo Co., Ltd. Denarex R-45EPT) 15 parts are stirred in MEK. The solution was dissolved while heating, and brominated phenoxy resin varnish (non-volatile content 40% by weight, bromine content 25% by weight, solvent composition, xylene: methoxypropanol: methyl ethyl ketone = 5: 2: 8, YPB- manufactured by Toto Kasei Co., Ltd. 40-PXM40) 50 parts, 2,4-diamino as epoxy curing agent 6- (2-Methyl-1-imidazoliethyl) -1,3,5-triazine / isocyanuric acid adduct 4 parts, 2 parts of finely pulverized silica, 4 parts of antimony trioxide and 5 parts of calcium carbonate A composition varnish was prepared.

《Practical properties》
<Inspection of coating appearance of the obtained film>
The resin composition varnish was applied on a polyester film, and the coating appearance of the obtained interlayer insulating layer was visually inspected.
○: Extremely flat and rich in practicality △: Slightly lacking in flatness, but practical ×: Inferior flatness and lack of practicality Of the above criteria, those above Δ are not problematic for practical use It is a usable level.

<Roll appearance>
The resin composition varnish was applied on a polyester film, and in the production of a film having an interlayer insulating layer, the appearance of the product roll of the film was visually observed and evaluated. The results are shown in Table 3. In particular, the deviation of both end faces of the roll was observed.
(Roll appearance is good) ◎>○>△> × (Roll appearance is bad)
Among the above criteria, those above Δ are levels that can be used without any problem in actual use.

<Surface characteristics>
The surface corresponding to the polyester film of the obtained interlayer insulating layer was observed, and the presence / absence of protrusions affecting the electrical characteristics and the surface characteristics of the uniformity of the protrusions were evaluated as follows. The results are shown in Table 3.
◎: Projection uniformity, no large projections that adversely affect electrical characteristics are observed ○: Projection uniformity is slightly inferior, and some large projections are seen △: Uniformity at a level that can be used practically without problems X: Protrusions that are inferior in the uniformity of the protrusions and have an adverse effect on the electrical characteristics are observed. Among the above judgment criteria, those above Δ are levels that can be used without problems in actual use.

《Cost advantage》
The obtained characteristics and the cost evaluation related to the production such as yield are evaluated as follows, and the results are shown in Table 3.
◯: Advantage in terms of cost Δ: Slightly inferior in cost ×: Inferior in cost Among the above criteria, those above Δ are at a level that can be used without problems in actual use.

  The film of this invention can be utilized suitably as a support body for apply | coating the thermosetting resin which forms an interlayer insulation layer.

Claims (1)

A polyester film used as a support for applying a thermosetting resin that forms an interlayer insulating layer, a coextruded laminated polyester film comprising at least two polyester layers, the center of one polyester film surface The average roughness Ra is 30 nm or less, the ten-point average roughness Rz is 200 nm or less, the center average roughness Ra of the other polyester film surface is 10 to 50 nm, and the sag amount of the film is 15 mm / m or less. A support polyester film for interlayer insulation, wherein the thickness of the film is 20 to 100 μm.