JP2015174357A - Multilayer polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer polyester film which is a polyester film base material to be used suitably when a ceramic multilayer capacitor is produced, hardly causes a shape change by the heat when used in mold release treatment, and is capable of allowing a high-quality green sheet to be produced even when used for producing a thin-film green sheet.SOLUTION: The multilayer polyester film has a multilayer structure of at least three layers, 1.6395 or higher refractive index (nMD) in the longitudinal direction, and 0.005-0.030 μm surface roughness (Ra) on both sides.

Description

  The present invention relates to a laminated polyester film that can be suitably used, for example, as a base material for a release film used as a base material for manufacturing a ceramic multilayer capacitor.

  In recent years, as the ceramic multilayer capacitor has been reduced in size and capacity, the thickness of the green sheet tends to become thinner. As the green sheet becomes thinner, the influence of the surface properties of the polyester film, which is the supporting base material, on the properties of the green sheet is increasing, and a polyester film designed to have a smoother surface property is required. There is a situation (Patent Document 1).

  With the further thinning of the green sheet, especially when trying to mold a green sheet having a thickness (after drying) of 1 μm or less, in the drying process when performing release treatment on the polyester film substrate for green sheet molding, The shape that local shape change (local vertical wrinkles) of the polyester film substrate due to heat during drying tends to affect the quality of the green sheet product, and was not a problem with conventional polyester films Even if it is a change, a situation has arisen in which the change in shape becomes a problem in green sheet molding.

  Specifically, when a release layer is provided on a polyester film, a phenomenon occurs in which, in the drying process, intermittently recessed portions appear in the film surface due to heat applied to the film surface. This phenomenon does not appear in the polyester film manufacturing stage, and a defect occurs only when the release layer is laminated in the next process. Therefore, it is difficult to predict in advance whether or not the defect has occurred.

  Furthermore, as a type of film flatness failure, a wrinkle-like flatness failure called heat wrinkle is generally exemplified. In this case, the tension applied to the film is adjusted when a release layer is laminated on the film. In some cases, an improvement effect can be expected to some extent. However, in the case of local shape change (local vertical wrinkles), which is regarded as a problem, problems occur in the film plane and the phenomenon occurs intermittently, so the improvement effect by adjusting the tension during release layer lamination However, there is a difficulty that can hardly be expected.

  As a result, when a green sheet is formed using a release film whose base material is a polyester film having a local shape change, the variation in the thickness of the obtained green sheet increases. Furthermore, when a multilayer ceramic capacitor is manufactured using a green sheet with a large variation in thickness, the electrical characteristics of the obtained capacitor tend to increase in the variation in dielectric characteristics, which can be fatal, such as a decrease in product yield. Lead to a serious malfunction.

JP 2003-291291 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is a polyester film substrate that can be suitably used during the production of a ceramic multilayer capacitor, and the shape change due to heat during the release treatment is small. An object of the present invention is to provide a laminated polyester film capable of producing a high-quality green sheet even when used when producing a thin film green sheet.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above-described problems can be easily solved by a polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is a laminated polyester film having a laminated structure of at least three layers, the refractive index (nMD) in the longitudinal direction of the polyester film is 1.6395 or more, and the surface roughness ( Ra) exists in the range of 0.005-0.030 micrometer, It exists in the laminated polyester film characterized by the above-mentioned.

  According to the laminated polyester film of the present invention, there is provided a laminated polyester film capable of producing a high-quality green sheet even when used when producing a thin film green sheet because deformation due to heat at the time of mold release is small. And its industrial value is high.

  The laminated polyester film of the present invention is required to be a multilayer film having at least 3 layers. The laminated polyester film referred to in the present invention is a polyester film extruded by a so-called extrusion method that is melt-extruded from an extrusion die, and is oriented in the biaxial direction of the vertical direction and the horizontal direction as necessary. It is.

  In the present invention, the polyester is 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, are mentioned.

  In the present invention, it is preferable to blend particles in the polyester layer mainly for the purpose of imparting slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and magnesium phosphate. , Particles of kaolin, aluminum oxide, titanium oxide and the like. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  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.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.01-1 micrometer. When the average particle diameter is less than 0.01 μm, the particles are likely to aggregate and dispersibility may be insufficient. On the other hand, when the average particle diameter exceeds 3 μm, the surface roughness of the film becomes too rough and There may be a problem when a release layer is applied in the process.

Furthermore, the particle content in the polyester layer is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% by weight,
In some cases, the slipperiness of the film is insufficient. On the other hand, when the amount exceeds 5% by weight, the transparency of the film may be insufficient.

  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 of producing the polyester constituting each layer, but preferably a polycondensation reaction may be carried out 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 the laminated polyester film in the present invention, it is an essential requirement to use two kinds of particles having different average particle diameters for the surface layer. In the present invention, an example in which calcium carbonate particles having an average particle diameter of 0.7 μm and heat-resistant organic particles having an average particle diameter of 0.4 μm are combined will be described. However, it is not limited to these.

  In the laminated polyester film of the present invention, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments and the like can be added to the laminated polyester film as necessary.

  The thickness of the laminated polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 5 to 250 μm, preferably 12 to 188 μm.

  Next, production examples of the laminated polyester film in the present invention will be specifically described, but the present invention is not limited to the following production examples.

  First, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a plurality of dies 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 4.5 times, preferably 3.0 to 4 times. Subsequently, the extending | stretching temperature orthogonal to the extending | stretching direction of the 1st step is 70-170 degreeC normally, and a draw ratio is 3.0-6.0 times normally, Preferably it is 3.5-5.5 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 10% 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. Moreover, when the final draw ratio in the direction is out of the above range, the refractive index (nMD) in the longitudinal direction as claimed in the present invention may not be achieved.

  The simultaneous biaxial stretching method can also be adopted for the production of the laminated 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, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be employed.

  The release layer constituting the release film in the present invention preferably contains a curable silicone resin in order to improve the release property. A type having a curable silicone resin as a main component may be used, or a modified silicone type by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used.

  As the type of the curable silicone resin, any of the curing reaction types such as an addition type, a condensation type, an ultraviolet curable type, an electron beam curable type, and a solventless type can be used. Specific examples include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X-62-2461, X manufactured by Shin-Etsu Chemical Co., Ltd. -62-1387, KNS-3051, X-62-1496, KNS320A, KNS316, X-62-1574A / B, X-62-7052, X-62-7028A / B, X-62-7619, X-62 -7213, manufactured by Momentive Co., Ltd. YSR-3022, TPR-6700, TPR-6720, TPR-6721, TPR6500, TPR6501, UV9300, UV9425, XS56-A2775, XS56-A2982, UV9430, TPR6600, TPR6604, TPR6605, SM3200, SM3030, Toray Dowco DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, SRX357, SRX211, SD7220, LTC750A, LTC760A, SP7259, BY24-468C, SP7248S, BY24-452, SP7265S, SP7265S , LTC1000M, LTC1050L, SYLOFF7900, SYLOFF7198, SYLOFF22A, Asahi Kasei Wacker's Dehesive 430, Dehesive 440, and the like. Further, a release control agent may be used in combination to adjust the release property of the release layer.

In the present invention, the curing conditions for forming the release layer on the laminated polyester film are not particularly limited. For example, when the release layer is provided by a coating stretching method (in-line coating), usually, 170 to The heat treatment may be performed at 280 ° C. for 3 to 40 seconds, preferably 200 to 280 ° C. for 3 to 40 seconds. On the other hand, when providing a release layer by off-line coating, heat treatment is usually performed at 80 to 200 ° C. for 3 to 40 seconds, preferably 100 to 180 ° 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. In addition, a conventionally well-known apparatus and an energy source can be used as an energy source for hardening by active energy ray irradiation. The coating amount of the release layer from the viewpoint of coating property, usually 0.005~1g / ^{m 2,} preferably in the range from 0.005 to 0.5 / ^{m 2.} If the coating amount is less than 0.005 g / m ² , the coating property may be less stable and it may be difficult to obtain a uniform coating film. On the other hand, when the coating is thicker than 1 g / m ² , the coating layer adhesion and curability of the release layer itself may be lowered.

  Further, inorganic particles may be contained for the purpose of improving the fixing property and slipperiness of the release layer, and specific examples include silica, alumina, kaolin, calcium carbonate, titanium oxide, barium salt and the like.

  Further, an antifoaming agent, a coating property improver, a thickener, an organic lubricant, organic polymer particles, an antioxidant, an ultraviolet absorber, a foaming agent, a dye and the like may be contained as necessary. In the case of the coating stretching method (in-line coating), the above-mentioned series of compounds is used as a solvent-free or organic solvent dispersion, and a coating solution with a solid content concentration adjusted to about 1 wt% to 100 wt% as a guide is applied to the laminated polyester film. It is preferable to produce a release film in the manner of applying to the substrate.

  In a range not exceeding the gist of the present invention, a small amount of an organic solvent may be contained in the coating solution for the purpose of improving the dispersibility of the coating solution, improving the film forming property, and the like. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

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

  Regarding the release film in the present invention, a coating layer such as an adhesive layer, an antistatic layer and an oligomer precipitation preventing layer may be provided on the surface where the release layer is not provided, as long as the gist of the present invention is not impaired. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. Since the coating can be performed simultaneously with the film formation, the production can be handled at a low cost, and therefore in-line coating is preferably used.

  The in-line coating is not limited to the following, but for example, in the sequential biaxial stretching, the coating treatment can be performed particularly before the lateral stretching after the longitudinal stretching is finished. When the coating layer is provided on the polyester film by in-line coating, it is possible to apply at the same time as the film formation, and the coating layer can be processed at a high temperature in the heat treatment process of the polyester film after stretching. Performances such as adhesion to various surface functional layers that can be formed on the layer and heat-and-moisture resistance can be improved. Moreover, when coating before extending | stretching, the thickness of an application layer can also be changed with a draw ratio, and compared with off-line coating, uniform coating can be performed with a thin film. That is, a film suitable as a polyester film can be produced by in-line coating, particularly coating before stretching.

  Moreover, the coating layer of the film of the present invention comprises a surfactant, an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, organic particles, inorganic particles, an antioxidant, an ultraviolet absorber, a foaming agent, It may contain additives such as dyes and pigments. These additives may be used alone or in combination of two or more as necessary.

As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, amides such as N-methylpyrrolidone Can be mentioned.
These organic solvents may be used in combination of two or more as required.

  Moreover, you may use together heat treatment and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of offline coating or in-line coating as needed. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, the laminated polyester film constituting the release film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  The present inventor considered that the inconvenience occurred because the microscopic film orientation crystallinity was non-uniform as a cause of the local shape change appearing after the heat treatment step. Therefore, the refractive index (nMD) in the longitudinal direction of the film in the laminated polyester film of the present invention needs to satisfy 1.6395 or more, preferably 1.6410 or more, more preferably 1.6420, for any measurement location. That's it. As used herein, “about an arbitrary measurement location” means that anywhere on the film is measured. When the refractive index (nMD) in the longitudinal direction is less than 1.6395, the local shape of the polyester base material due to heat during drying in the drying step when performing release treatment on one surface of the laminated polyester film Changes occur and negatively affect the quality of green sheet products.

Further, in the present invention, it is preferable that the refractive index (nMD) in the longitudinal direction is satisfied and the refractive index (nTD) in the width direction is 1.6850 or less.

  By satisfying the above range at the same time, it was found that even after the heat treatment step, there is no local shape change and a polyester film with good film flatness can be obtained, and the present invention has been completed. It was.

  As a specific means for satisfying the above range, in the production conditions at the time of producing the polyester film in the present invention, for example, the transverse draw ratio is increased from 4.5 times to 5.0 times and the main crystal temperature is changed from 200 ° C. By setting the temperature within the range of 225 ° C., it becomes possible to produce a film with more uniform film orientation crystallinity.

  The center line average roughness (Ra) of the film surface in the laminated polyester film of the present invention needs to satisfy 0.030 μm or less, preferably 0.020 μm or less, more preferably 0.015 μm or less, The thickness (after drying) can be sufficiently adapted for forming a thin film green sheet having a thickness of 1 μm or less. When Ra on the surface of the film exceeds 0.030 μm, problems such as repelling of the slurry occur at the time of ceramic slurry coating. The lower limit of Ra on the surface of the laminated polyester film is set to 0.005 μm in consideration of workability during film handling.

  In the present invention, as a method for bringing the Ra of the film surface of the laminated polyester film to a range of 0.030 μm or less, for example, a coating layer is provided on the laminated polyester film in advance to flatten the film surface, and then release The method of coating a layer etc. are mentioned.

  In the laminated polyester film of the present invention, after the release layer is provided, the residual adhesion rate of the release layer suppresses the migration or transfer of the release component to the surface of the opposite substrate to be bonded. Therefore, 90% or more is preferable, and more preferably 95% or more. When the residual adhesive rate is less than 90%, the amount of the release component transferred to the surface of the counterpart substrate that comes into contact with the release surface of the release film increases. For example, the adhesive strength between sheets decreases when the green sheets are laminated, or the pressure-sensitive adhesive. In layer protection applications, problems such as a decrease in adhesive strength may occur.

  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. In the examples and comparative examples, “parts” means “parts by weight”. The measuring method used in the present invention is as follows.

(1) 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.

(2) Measurement of average particle diameter (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.

(3) Surface roughness (Ra) of laminated polyester film
It measured according to JIS-B-0601-1994 using the surface roughness measuring machine "SE-3F" by Kosaka Laboratory. However, the cut-off value was 80 μm and the measurement length was 2.5 mm.

(4) Tensile test (Strong elongation)
Using Intesco tensile tester Intesco model 2001 type, temperature 2
A sample film having a length of 50 mm and a width of 15 mm is pulled at a speed of 200 mm / min in a room adjusted to 3 ° C. and a humidity of 50% RH, and the following values are obtained from the tensile stress-strain curve.
(4-1) The tensile fracture strength is calculated by the following formula.
σ = F / A
(In the above formula, σ is the tensile fracture strength (kg / mm ² ), F is the load at the time of fracture (kg), and A is the original cross-sectional area (mm ² ) of the test piece)
(4-2) Tensile fracture elongation is calculated by the following formula.
E = (L−L0) ÷ L0 × 100
(In the above formula, E means tensile fracture elongation (%), L means distance between gauge points at break (mm), and L0 means original distance between gauge points (mm))

(5) Heat shrinkage rate A sample measured in advance is subjected to heat treatment for 5 minutes in a hot air circulating thermostatic chamber at 150 ° C. without tension, and the length of the sample after heat treatment is measured to obtain the following formula: It calculated in.
Heat shrinkage rate = (length before heat treatment−length after heat treatment) ÷ length before heat treatment × 100

(6) Refractive index of laminated polyester film Atago Abbe refractometer (SL-NA-B) was used. Methylene iodide is mounted, the sample film is closely attached to the prism with the measurement surface facing down, and the refractive index in the longitudinal direction (nMD) and the refractive index in the width direction are obtained using a monochromatic light sodium D line (589 nm) as a light source. (NTD) was measured at 10 locations in the film width direction. About nMD, the minimum value at the time of measuring 10 places was adopted.

(7) Winding property The film roll winding property at the time of manufacturing a polyester film was evaluated according to the following evaluation criteria.
○: Good winding property Δ: Slightly insufficient slipping property of film, winding property is slightly inferior ×: Insufficient slipping property of film, misalignment, etc. The roll used was a plastic core with a product width of 1370 mm, a product winding length of 12600 m, and a winding core used of 6 inches.

(8) Coating property of green sheet slurry On the surface of the polyester film, 100 parts of a curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical Co., Ltd.), a curing agent (manufactured by Shin-Etsu Chemical Co., Ltd. “ A release agent consisting of 1 part of CAT-PL-8 "and 2200 parts of methyl ethyl ketone / toluene mixed solvent (mixing ratio 1: 1) was applied so that the coating amount after drying was 0.1 g / m ² A film was obtained.
On the release surface of this release film, 100 parts of barium titanate (Fuji Titanium Industry Co., Ltd .: average particle size 0.7 μm), polyvinyl butyral resin (Sekisui Chemical Co., Ltd. “S-REC BM-S”) ”) 30 parts of plasticizer (dioctyl phthalate), 200 parts of a toluene / ethanol mixed solvent (mixing ratio: 6: 4) was applied, and the coating amount after drying was 0.5 g / m ^2. It applied so that it might become, and the green sheet was obtained. At this time, the coating property of the green sheet was evaluated according to the following evaluation criteria.
○: Slurry repelling and coating unevenness do not occur Δ: Fine slurry repelling and coating unevenness occur ×: Slurry repelling and coating unevenness remarkably occur

(9) Peelability of green sheet Using the green sheet obtained in (8), after forming the green sheet so that the thickness (after drying) is 1 μm, the release film and the green sheet The peelability was determined according to the following criteria.
<Criteria>
○: Smoothly peelable Δ: Slightly heavy peelability ×: Difficult to peel off or too light peeling Δ: Above is a level that is practically acceptable.

(10) Green sheet thickness variability The green sheet thickness obtained in item (8) was evaluated for variability, and the determination was made according to the following criteria.
<Criteria>
○: Green sheet thickness variation is 3% or less ×: Green sheet thickness variation is 3% or more ○ is a level where there is no practical problem.

(11) Comprehensive evaluation Regarding the sample film, winding property, green sheet coatability, green sheet peelability, and green sheet thickness variability were determined according to the following criteria.
<Criteria>
○: All evaluation items of winding property, green sheet coating property, green sheet peeling property, and green sheet thickness variation property are ○. Δ: winding property, green sheet coating property, green sheet peeling property, green sheet. At least one evaluation item of thickness variability is Δ. X: At least one evaluation item of winding property, green sheet coating property, green sheet peelability, and green sheet thickness variability is ×. It is a level with no problem.

<Manufacture of polyester>
Production Example 1 (Polyester 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. Was finally reduced to 0.3 mmHg. After 4 hours, the system was returned to normal pressure to obtain polyester A having an intrinsic viscosity of 0.61.

Production Example 2 (Polyester B)
A polyester B having an intrinsic viscosity of 0.61 was obtained in the same manner as in Production Example 1 except that 1.0 part of synthetic calcium carbonate particles having an average particle size of 0.7 μm was added.

Production Example 3 (Polyester C)
In Production Example 1, the particles used are produced in the same manner as in Production Example 1 except that 1.0 part of divinylbenzene-crosslinked polystyrene particles having an average particle size of 0.4 μm is added, and polyester C having an intrinsic viscosity of 0.61 is obtained. It was.

Example 1:
Polyester A, B, and C blended in proportions of 53%, 17%, and 30%, respectively, are used as the surface layer raw material, and polyester A = 100% raw material is supplied to the two vented extruders as the intermediate layer raw material. Then, it was supplied to an extruder with a vent, melt extruded at 290 ° C., and then cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an amorphous film. Next, the film was stretched 3.35 times in the machine direction at a film temperature of 85 ° C. using the roll peripheral speed difference, and then this longitudinally stretched film was led to a tenter and stretched 4.85 times at 120 ° C. in the transverse direction, to 220 ° C. After the heat treatment, the film was rolled up on a 6-inch plastic core to obtain a laminated polyester film roll having a thickness of 31 μm, a film width, 1370 mm, and a winding length of 12600 m. The properties of the obtained film roll are shown in Table 1 below.

Example 2:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the laminated polyester film F1 was changed to the laminated polyester film F2.

Example 3:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the laminated polyester film F1 was changed to the laminated polyester film F3.

Example 4:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the laminated polyester film F1 was changed to the laminated polyester film F4.

Comparative Example 1:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the laminated polyester film F1 was changed to the laminated polyester film F5.

Comparative Example 2:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the laminated polyester film F1 was changed to the laminated polyester film F6.

Comparative Example 3:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the laminated polyester film F1 was changed to the laminated polyester film F7.
Tables 1 and 2 show the properties of the release films obtained in the above Examples and Comparative Examples.

  The film of the present invention can be suitably used particularly as a base material for producing a ceramic multilayer capacitor.

Claims (1)

It is a laminated polyester film having a laminated structure of at least 3 layers, the refractive index (nMD) in the longitudinal direction of the polyester film is 1.6395 or more, and the surface roughness (Ra) on both sides of the film is 0.005 to 0. A laminated polyester film having a thickness of 0.030 μm.