JP2008279704A - Polyester film for molding and simultaneously transferred foil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film with enough heat resistance, moldability and transferring properties. <P>SOLUTION: A biaxially oriented polyester film in which both faces of a layer consisting of a polyester composition comprising 40-90 wt.% copolymerized polyester in which 70-95 mol% of dicarboxylic acid component is terephthalic acid, 5-30 mol% thereof is 2,6-naphthalene dicarboxylic acid, 10-60 mol% of glycol component is 1,4-butane diol and 40-90 mol% of thereof is ethylene glycol, is laminated with a layer consisting of a polyethylene terephthalate copolymer, is characterized in that the mean value in the longitudinal direction and in the transverse direction of the film after treated at 170°C for 3 minutes is 2-15%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a polyester film for molding simultaneous transfer foil having excellent moldability and transferability. More specifically, in injection molding having a high squeezing rate, the heat resistance against heating before molding, the surface of an object to be transferred The present invention relates to a polyester film as a base film for an in-mold molding simultaneous transfer foil having excellent molding followability to shape and transferability.

  Conventionally, a polyester film such as polyethylene terephthalate or a film of vinyl chloride resin is used as a base film as a molding simultaneous transfer foil for transfer printing at the same time as molding in injection molding or the like, and a release layer is provided on the surface of the base film. A laminated film having a printed layer applied thereon is used. Such a laminated film is separated between the release layer surface and the print layer surface after molding transfer. That is, after molding transfer, the printed layer is adhered to the surface of the molded product and taken out as a product, and the release layer is removed after molding while remaining on the base film.

  The required properties of these films include moldability, heat resistance, transferability, dimensional stability, thickness uniformity, etc. Among them, recently, household appliances, automobile interior parts, kitchenware, cosmetic containers, For the purpose of use in large plastic molded products such as toys, the squeezing rate at the time of molding is increasing, and the moldability to follow them is required. In this process, since the squeezing rate is high, the film is heated at a high temperature before molding. At that time, the film does not melt, and the film deforms when the air layer expands in the mold and the film space. Therefore, it is required to have heat resistance that can sufficiently withstand the above. Conventionally, as a film used for such applications, a polyester film having a specific degree of plane orientation (Patent Document 1), a polyester film obtained by mixing and melting polybutylene terephthalate and polyethylene terephthalate (Patent Document 2), and the like have been proposed. Not all the above problems could be solved.

JP 7-237283 A Japanese Patent Laid-Open No. 10-17683

  This invention is made | formed in view of the said actual condition, The solution subject is to provide the polyester film which has sufficient heat resistance, a moldability, and transferability.

  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 that 70 to 95 mol% of the dicarboxylic acid component is terephthalic acid, 5 to 30 mol% is 2,6-naphthalenedicarboxylic acid, and 10 to 60 mol% of the glycol component is 1,4-butanediol. , A biaxially oriented polyester film in which a layer made of a polyethylene terephthalate copolymer is laminated on both sides of a layer made of a polyester composition containing 40 to 90% by weight of a copolymer polyester containing 40 to 90% by weight of ethylene glycol, In the polyester film for molded simultaneous transfer foil, the average value in the vertical and horizontal directions of the heat shrinkage of the film after 3 minutes treatment at 170 ° C. is 2 to 15%.

Hereinafter, the present invention will be described in detail.
The polyester film of the present invention is a laminated film composed of at least three layers having an inner layer and layers on both sides thereof, and all layers are extruded by a so-called coextrusion method in which co-extrusion is performed from a die of an extruder. The product is obtained as stretched and heat treated. Hereinafter, the coextruded three-layer film will be described. However, the present invention is not limited to the three-layer film as long as the gist of the present invention is not exceeded, and may be a multilayer of four layers or more.

  In the present invention, the polyethylene terephthalate copolymer constituting the layers in contact with both surfaces of the inner layer is usually a polyester comprising 85 to 95 mol% of ethylene terephthalate. In this polyester, the components that can be copolymerized as the third component include acid components such as 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, and the like. Mellitic acid, pyromellitic acid and the like can be mentioned, and among them, it is preferable to use isophthalic acid as a copolymerization component. Examples of the alcohol component that can be copolymerized include diol components such as butylene glycol, propylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol, and polyalkylene glycol. . These can be used alone or in combination of two or more.

  In the present invention, the copolyester constituting the inner layer is that 70 to 95 mol% of the acid component is terephthalic acid, 5 to 30 mol% is 2,6-naphthalenedicarboxylic acid, and 10 to 60 mol% of the glycol component is 1 , 4-butanediol, refers to a copolyester in which 40 to 90 mol% is ethylene glycol.

  Moreover, the inner layer of the film of the present invention is composed of a polyester composition containing 40 to 90% by weight of the copolymerized polyester, and contains one or more polyesters other than the copolymerized polyester. The bifunctional acid component of the polyester other than the copolyester is mainly an aromatic dicarboxylic acid or an ester-forming derivative thereof, and terephthalic acid, 2,6-naphthalenedicarboxylic acid, or an ester-forming derivative thereof is terephthalic acid. Examples thereof include dimethyl acid and dimethyl 2,6-naphthalenedicarboxylate. Among these, terephthalic acid and dimethyl terephthalate are preferable. Examples of the glycol component include ethylene glycol, butylene glycol, propylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, and among these, ethylene glycol is preferable. Further, the polyester may be a polyester using one kind of aromatic dicarboxylic acid or an ester-forming derivative thereof and one kind of alkylene glycol as a starting material, and is a copolymer containing two or more kinds of components. Also good. In addition to the above, the components to be copolymerized include, for example, diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, and isophthalic acid, trimellitic acid, and pyromellitic An acid etc. are mentioned.

  As a method for obtaining the inner layer of the film of the present invention, a method in which a copolymerized polyester and another polyester are blended and melt-kneaded is preferably used. The content of the copolymerized polyester in the present invention is 40 to 90% by weight, preferably 50 to 90% by weight, and more preferably 60 to 90% by weight. If it is less than 40% by weight, it is not preferable because the film is torn or the molding followability is impaired at the time of molding with a high shrinkage rate. On the other hand, if it exceeds 90% by weight, the heat resistance is impaired, and the film is melted and broken in the step of heat-treating the film before molding at a high temperature. In addition, breakage occurs frequently at the time of film production, and the stretchability is remarkably deteriorated, resulting in a decrease in productivity.

  The copolymer polyester constituting the inner layer of the present invention comprises 70 to 95 mol% of the acid component, terephthalic acid component, 5 to 30 mol% of 2,6-naphthalenedicarboxylic acid component, preferably 75 to 90 mol% of terephthalic acid. 10-25 mol% is composed of a 2,6-naphthalenedicarboxylic acid component. Outside this range, the dimensional stability of the film deteriorates and the film shrinks during injection molding, which deteriorates the appearance of the molded product.

  Further, 10 to 60 mol% of the glycol component of the copolyester constituting the inner layer is 1,4-butanediol component, 40 to 90 mol% is ethylene glycol component, preferably 20 to 50 mol% is 1,4-butane. The diol component, preferably 50 to 80 mol%, is composed of an ethylene glycol component. Outside this range, molding followability is impaired, and the film is torn during vacuum molding, which is not preferable.

  The polyester film of the present invention is preferably blocking resistance, to improve workability in the winding process or printing process during film production, etc., to roughen the surface of the film and impart appropriate slipperiness to the film, At least the polyester constituting the B layer which is the outermost layer of the polyester film contains organic or inorganic fine particles having an average particle size of about 0.1 to 5.0 μm as a lubricant, for example, 0.01 to 2.0% by weight. It is preferable to make it contain in a ratio. The fine particles to be contained may be a single component, or two or more components may be used simultaneously. Specific examples of such fine particles include inorganic particles such as calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, lithium phosphate, magnesium phosphate, calcium phosphate, lithium fluoride, aluminum oxide, silicon oxide, kaolin, acrylic resins, Examples thereof include, but are not limited to, precipitated particles obtained by granulating organic particles such as guanamine resin and catalyst residues.

  The method of blending each particle with the raw material polyester is not particularly limited, and for example, a method of adding each particle to the polyester polymerization step or a method of melt-kneading the raw material polyester and each particle is suitable. In addition, various stabilizers, lubricants, antistatic agents, and the like can be added as appropriate.

  The average value of the vertical direction and the horizontal direction of the heat shrinkage ratio (S) after 3 minutes treatment at 170 ° C. of the polyester film of the present invention is 2 to 15%, preferably 2 to 10%. If S is less than 2%, the moldability deteriorates, and if it exceeds 15%, the film shrinks greatly during heating in the molding process, which is not preferable for operation.

  In the present invention, the tensile breaking elongation (EB) at 100 ° C. of the polyester film is preferably 160% or more, more preferably 180% or more, particularly preferably 200% or more, and the tensile breaking strength (FB) is 75 MPa or less, 70 MPa or less, particularly 60 MPa or less is desirable. When EB is less than 180% or FB exceeds 70 MPa, troubles such as film breakage may occur particularly during deep drawing with a high squeezing rate.

  The degree of plane orientation (ΔP) of the polyester film of the present invention is preferably in the range of 0.020 to 0.180, and more preferably in the range of 0.030 to 0.160. If ΔP is less than 0.020, the strength of the film tends to decrease and the flatness tends to deteriorate. On the other hand, if ΔP exceeds 0.160, the moldability may be insufficient.

  In the present invention, the melting point (Tm1) of the layer in contact with both surfaces of the inner layer is preferably in the range of 180 ° C to 270 ° C, and more preferably in the range of 190 ° C to 260 ° C. The melting point (Tm2) of the C layer in the intermediate layer is preferably in the range of 140 ° C to 220 ° C, and more preferably in the range of 150 ° C to 210 ° C. When Tm1 is less than 180 ° C, heat resistance and transfer suitability tend to be inferior, and when Tm2 exceeds 220 ° C, formability tends to be inferior.

  The thickness of the polyester film of this invention is 10-150 micrometers normally, Preferably it is 30-130 micrometers, More preferably, it is 50-100 micrometers. Moreover, the ratio for which the thickness of an inner layer accounts to the thickness of the whole film is 78 to 95% normally, Preferably it is the range of 85 to 95%. If it is less than 78%, the flexibility is impaired, and the molding followability may be lowered or the film may be broken during injection molding. On the other hand, when it exceeds 95%, the lamination thickness in the width direction tends to be non-uniform.

  In the present invention, a coating layer may be provided in order to impart adhesion, antistatic properties, and slipperiness of the polyester film. Examples of the components constituting the coating layer include resins and copolymers such as polyester, polyamide, polystyrene, polyacrylate, polycarbonate, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and polyurethane. You may contain 1 type of this resin, or 2 or more types of resin simultaneously.

  Examples of the method for applying the coating solution to the film include a forward rotation roll coater, a reverse roll coater, a gravure coater, a knife coater, a blade coater, a rod coater, an air doctor coater, a curtain coater, a fountain coater, a kiss coater, and a kiss roll. A coating apparatus such as a coater, a bead coater, and a dip coater, a coating method such as a screen coating, a cast coating, and an impregnation machine LB method can be adopted, but is not limited thereto. The coating layer may be provided within the film production process, or may be applied after the film production. The method of apply | coating within a film manufacturing process is especially preferable at the point of the uniformity of application | coating thickness, or production efficiency.

  As a method of coating in the film manufacturing process, a coating solution is applied to an unstretched sheet, and biaxially stretched sequentially or simultaneously, applied to a uniaxially stretched film, and further in a direction perpendicular to the previous uniaxially stretched direction. There are a method of stretching, a method of applying to a biaxially stretched film, and a method of stretching in the transverse and / or longitudinal direction.

  The thickness of the coating layer is usually in the range of 0.005 to 1.0 μm, and preferably in the range of 0.01 to 0.5 μm. If the coating thickness exceeds 1.0 μm, continuity during film production is deteriorated, which is not preferable. On the other hand, when the coating thickness is less than 0.005, there is a tendency that coating leakage and coating spots are likely to occur.

  Next, although the manufacturing method of the polyester film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  That is, using the above-mentioned polyester raw material, using a plurality of extruders, a multi-layer multi-manifold die or a feed block, laminating each polyester, extruding a multi-layer molten sheet from the die, and using a cooling roll By cooling and solidifying, an unstretched sheet in a substantially amorphous state is obtained. 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. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  Next, the obtained unstretched sheet is stretched biaxially and biaxially oriented. That is, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 20 to 100 ° C., preferably 30 to 90 ° C., and the stretching ratio is usually 2.0 to 6.0 times, preferably 2.5 to 5.0 times. Next, stretching is performed in a direction orthogonal to the first-stage stretching direction. The stretching temperature is usually 40 to 130 ° C, preferably 40 to 120 ° C, and the stretching ratio is usually 2.5 to 5.5 times, preferably 3.0 to 5.0 times. In addition, although the method of extending | stretching one direction in two steps or more can also be used, it is desirable for the final draw ratio to enter into the above-mentioned range also in that case. Further, the unstretched sheet can be simultaneously biaxially stretched so that the area magnification is 5 to 35 times.

  The film thus obtained is preferably heat treated at 150 to 220 ° C. for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. In particular, it is preferable to perform 1 to 15% relaxation in the lateral direction. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  According to the present invention, in an injection molding process with a high squeezing rate, a polyester film for in-mold molding simultaneous transfer foil that is excellent in heat resistance by heating before molding, molding conformability to the surface shape of the transfer target, and transferability. The industrial value of the present invention is high.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In addition, the measurement and evaluation method of various physical properties of a film are shown below.

(1) Breaking strength (FB) and elongation at break (EB) of the film
Using a tensile tester with a thermostat (2001 type) manufactured by Intesco, set the thermostat at 100 ° C, set a film with a width of 15 mm on the tester so that the gap between chucks is 50 mm, and leave for 2 minutes. Then, it pulled at a speed of 200 mm / min, and calculated from the following equation from a tensile stress-strain curve.
FB (kg / mm ² ) = F / A
(In the above formula, F represents the load (kg) at break, and A represents the cross-sectional area (mm ² ) of the original film. The average value was obtained by measuring five points in the longitudinal and lateral directions of the film)

EB (%) = 100 × (L−L ₀ ) / L ₀
(In the above formula, L represents the length (mm) of the film at break, and L ₀ represents the length (mm) of the original film. The average value is obtained by measuring five points in the longitudinal and lateral directions of the film. Was)

(2) Degree of plane orientation of film (ΔP)
It was performed at 23 ° C. using an Atago Abbe refractometer, using a monochromatic light sodium D line (589 nm) as a light source. In the measurement, the maximum value (nγ) of the refractive index in the film plane, the refractive index (nβ) in the orthogonal direction and the refractive index (nα) in the thickness direction of the film were measured, and ΔP was calculated from the following equation.
ΔP = (nγ + nβ) / 2−nα

(3) Melting point of film (Tm1 and Tm2)
It measured using the Perkin-Elmer differential thermal scanning calorimeter DSC7 type. The DSC measurement conditions are as follows. That is, the temperature of the endothermic peak accompanying melting obtained when the sample was heated from 0 ° C. to 300 ° C. at a rate of 20 ° C./min was defined as Tm. Of the melting peak temperatures obtained by the above method, the melting point (Tm2) of the inner layer is the melting peak temperature obtained in the measurement, and the melting point (Tm1) of the layer in contact with both sides of the inner layer is obtained after the peak temperature of Tm2. The melting peak temperature obtained.

(4) Heat shrinkage rate of film (S)
The sample was treated for 3 minutes in an oven maintained at 170 ° C. under no tension, the sample length before and after that was measured, and S was calculated according to the following equation.
S (%) = 100 × (L ₀ −L) / L ₀
(In the above formula, L ₀ represents the length (mm) of the film before the heat treatment, and L represents the length (mm) of the film after the heat treatment. Sought)

(5) Lamination thickness of film It performed by observation of the film cross section with a transmission electron microscope (TEM). That is, a small piece of a film sample was embedded in a resin in which an epoxy resin was mixed with a curing agent and an accelerator, and a section having a thickness of 200 nm was prepared with an ultramicrotome to obtain an observation sample. The obtained sample was observed with a transmission electron microscope (H-9000) manufactured by Hitachi, Ltd. In the cross section, the interface is observed by light and darkness almost parallel to the film surface. The distance from the interface to the film surface was averaged for one transmission electron micrograph and the surface layer thickness was calculated. However, the acceleration voltage was set to 300 kV, and the magnification was set in the range of 1 to 100,000 times according to the surface layer thickness. At least 50 photographs were taken, and 10 points were deleted from the thicker measurement value, 10 points were deleted from the thinner one, and 30 points were averaged to obtain a measurement value.

(6) Suitability as a film for molding simultaneous transfer foil A release layer, a printing layer, and an adhesive layer are formed on a polyester film, and a mold having a length of 300 mm, a width of 200 mm, and a maximum depth of 25 mm is used. After fixing, the film was pre-heated with an IR heater, and pre-molded by vacuum or pressure molding in the mold. The heat resistance of the film was evaluated according to the condition of the film by preheating and preforming.
◯: Can be preheated and molded with a uniform thickness in premolding △: Can be preheated and can follow the premolding, but there is a locally extremely thin film ×: During preheating Film tear due to film melting, film expansion due to film softening, and film tear due to local occurrence of extremely thin parts during pre-molding

(7) Moldability as film for molding simultaneous transfer foil After pre-molding by the method of (6) above, resin was injection molded and simultaneous molding transfer was performed. The moldability was evaluated according to the following criteria depending on the appearance of the obtained molded product, the state of the printed pattern, and the state of distortion.
○: Appearance of the molded product is good, and there is no printing leakage or distortion. Δ: There is almost no printing leakage or distortion, but wrinkle transfer marks on the molded product are generated due to local deformation of the film by resin injection. : Film breakage due to film softening at the time of resin injection, wrinkle transfer marks, printing leakage and distortion occur in molded products

Example 1:
<Manufacture of polyester (1)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, amorphous silica particles having an average particle size of 2.3 μm were added as an ethylene glycol slurry to the reaction mixture which had been substantially transesterified, and 0.04 part of ethyl acid phosphate was added. Then, 0.04 part of antimony trioxide was added and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure to produce polyester (1). The content of amorphous silica particles in the polymer was 0.5% by weight.

<Manufacture of polyester (2)>
In the production of the polyester (1), instead of 100 parts by weight of dimethyl terephthalate, 78 parts by weight of dimethyl terephthalate and 22 parts by weight of dimethyl isophthalate were used, and the method was the same as for polyester (1) except that no particles were added. Polyester (2) was obtained.

<Production of copolymerized polyester (A)>
Dimethyl terephthalate 75 mol%, 2,6-naphthalenedicarboxylate dimethyl 25 mol%, ethylene glycol 50 mol%, 1,4-butanediol 50 mol%, tetrabutyl titanate 0.005 parts were charged in a reactor, and the reaction start temperature. The reaction temperature was gradually raised along with distillation of methanol, and the temperature was raised to 225 ° C. after 3 hours. Furthermore, a polycondensation reaction was performed by a conventional method. In this reaction, the temperature was gradually increased and the pressure was gradually decreased from the normal pressure. After 2 hours, the temperature was 280 ° C. and the pressure was 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure.

<Manufacture of polyester film>
60 parts by weight of the polyester (1) and 40 parts by weight of the polyester (2) are uniformly blended, and 80 parts by weight of the copolyester (A) and 20 parts by weight of the polyester (1) are uniformly blended. The two outer layers are melt-kneaded with separate extruders set at 280 ° C, and these polymers are merged and laminated in a feed block and electrostatically applied with a rotary cooling drum set at 30 ° C from a slit die. Rapid cooling and solidification was performed using a cooling method to obtain a laminated unstretched sheet. The obtained sheet was stretched 3.3 times at 70 ° C. in the longitudinal direction and 3.5 times at 100 ° C. in the transverse direction, and further subjected to heat treatment at 185 ° C. for 15 seconds, and in the cooling zone at the heat treatment outlet. A laminated polyester film having an outer layer / inner layer / outer layer thickness of 3 μm / 69 μm / 3 μm was obtained while relaxing 5%. The properties of the obtained film are shown in Table 1 below.

Example 2:
In Example 1, except that the copolymerized polyester (A) is dimethyl terephthalate 85 mol%, dimethyl 2,6-naphthalenedicarboxylate 15 mol%, ethylene glycol 70 mol%, 1,4-butanediol 30 mol%. In the same manner as in Example 1, a laminated polyester film having a thickness of each layer of 3/69/3 (μm) was obtained. The properties of the obtained film are shown in Table 1.

Example 3:
Uniform blend of 60 parts by weight of polyester (1) and 40 parts by weight of polyester (2), both outer layers, 60 parts by weight of copolyester (A) and 40 parts by weight of polyester (1) are blended uniformly. A laminated polyester film having a thickness of each layer of 3/69/3 (μm) was obtained in the same manner as in Example 1 except that the resulting layer was used as the inner layer. The properties of the obtained film are shown in Table 1.

Example 4:
Uniform blend of 35 parts by weight of polyester (1) and 65 parts by weight of polyester (2) in both outer layers, 80 parts by weight of copolyester (A) and 20 parts by weight of polyester (2) A laminated polyester film having a thickness of each layer of 3/69/3 (μm) was obtained in the same manner as in Example 1 except that the resulting layer was used as the inner layer. The properties of the obtained film are shown in Table 1.

Comparative Example 1:
In Example 1, a laminated polyester film having a thickness of 3/69/3 (μm) was obtained in the same manner as in Example 1 except that both outer layers were 100 parts by weight of polyester (1). The properties of the obtained film are shown in Table 1.

Comparative Example 2:
In Example 1, the thickness of each layer was the same as in Example 1, except that the inner layer was uniformly blended with 20 parts by weight of copolymerized polyester (A) and 80 parts by weight of polyester (1). A laminated polyester film having a thickness of 3/69/3 (μm) was obtained. The properties of the obtained film are shown in Table 1.

Comparative Example 3:
In Example 1, except that the copolymer polyester (A) is 90 mol% dimethyl terephthalate, 10 mol% dimethyl 2,6-naphthalenedicarboxylate, 95 mol% ethylene glycol, and 5 mol% 1,4-butanediol. In the same manner as in Example 1, a laminated polyester film having a thickness of each layer of 3/69/3 (μm) was obtained. The properties of the obtained film are shown in Table 1.

Comparative Example 4:
With an extruder set at 280 ° C. separately, with 60 parts by weight of polyester (1) and 40 parts by weight of polyester (2) uniformly blended as both outer layers and 100 parts by weight of copolymerized polyester (A) as inner layers. While melt-kneading, laminating these polymers and extruding them into a sheet, an attempt was made to produce a biaxially oriented film in the same manner as in Example 1, but a satisfactory film was obtained because of poor stretchability and frequent film breaks. I couldn't.

Comparative Example 5:
Uniform blend of 20 parts by weight of polyester (1) and 80 parts by weight of polyester (2), both outer layers, 80 parts by weight of copolyester (A) and 20 parts by weight of polyester (2) are uniformly blended An attempt was made to produce a biaxially oriented film by the same method as in Example 1 except that the inner layer was used as an inner layer. However, as in Comparative Example 6, the film was poor in stretchability and frequent film breakage, and a satisfactory film could not be obtained. It was.

  The polyester film of the present invention is a base film for in-mold molding simultaneous transfer foil that has excellent heat resistance in molding processing, molding follow-up to the surface shape of the transfer target, and transferability in injection molding with a high squeezing rate. It can be suitably used.

Claims (1)

70-95 mol% of the dicarboxylic acid component is terephthalic acid, 5-30 mol% is 2,6-naphthalenedicarboxylic acid, 10-60 mol% of the glycol component is 1,4-butanediol, and 40-90 mol% is ethylene. A biaxially oriented polyester film in which a layer made of a polyethylene terephthalate copolymer is laminated on both sides of a layer made of a polyester composition containing 40 to 90% by weight of a copolyester that is glycol, after treatment at 170 ° C. for 3 minutes A polyester film for molded simultaneous transfer foil, wherein the average value of the heat shrinkage of the film in the vertical direction and the horizontal direction is 2 to 15%.