JP5225828B2 - Polyester film for in-mold transfer foil - Google Patents

Description

  The present invention provides a molded product with excellent thermal dimensional change, excellent printability, easy elongation at low stress, good moldability, and excellent low gloss in the printing process for shallow drawing to drawing applications. The present invention relates to a polyester film for in-mold transfer foil.

  Conventionally, a polyester biaxially stretched film has been used as a base film for a transfer foil used after printing and molding (see, for example, Patent Document 1 and Patent Document 2). Further, it has been proposed to scratch a polyester biaxially stretched film having an intrinsic viscosity and density within a specific range and use it as a film for matte transfer foil (see Patent Document 3).

  Further, as a deep drawing film, it is proposed to use a polyester film having a molding stress within a specific range, that is, to use a copolymer polyester film having a lower molding stress than biaxially stretched polyethylene terephthalate. (See Patent Document 4).

  Further, it has been proposed to use a polyester film polymerized from a monomer composition containing two or more glycol components selected from butanediol and the like as a film for process such as molding.

  On the other hand, in the molding application, the diaphragm in the molding process varies greatly depending on various applications, such as cellular phones and electrical products, which have a narrow diaphragm during molding and those with a large diaphragm during molding such as automobiles. The drawing in this forming process is classified into shallow drawing, medium drawing, and deep drawing, and a suitable base film is selected and used according to the intended application.

  Release layer, pattern printing, adhesive layer, etc., coating process and printing process are affected by drying temperature and tension, causing thermal dimensional change due to stretch deformation and width shrinkage in base film, resulting in printing misalignment and harmful flatness deterioration Therefore, the base film is required to have certain thermal dimensional stability and mechanical characteristics. However, the transfer foil laminated using this base film also has high mechanical strength, so the deformation stress is high at the time of in-mold molding, the followability with the mold is poor, and the printing is not clear. There is a problem that phenomenon and molding breakage are likely to occur.

  The base film for deep drawing is processed at a low temperature such as 80 to 100 ° C., which does not hinder the elongation deformation in consideration of this point, because the base material itself has soft characteristics in terms of film design. In many cases, the pattern to be painted is one-step full surface printing such as woodgrain, and it is used for transfer foils that do not interfere with the quality of the pattern even if some thermal dimensional change or elongation deformation occurs. Yes.

  However, in many applications from shallow to medium apertures, the pattern to be painted is often printed in multiple colors, such as three to seven colors, and stretched and deformed under the influence of drying temperature and processing tension due to such high temperatures. And width shrinkage, printing deviation and flatness (single tarmi, etc.) are deteriorated, resulting in a fatal defect in the quality of the transfer foil.

  For this reason, the substrate film for shallow drawing to medium drawing is given mechanical strength so as to suppress elongation deformation in the vertical direction in coating and printing. However, the transfer foil obtained using such a base film also has high mechanical strength, so the deformation stress is high at the time of in-mold molding, the followability with the mold is poor, and the printing is clear. There is a problem that chipping phenomenon and molding tearing are likely to occur.

Further, as a means for giving a low gloss feeling to a molded product, a method using a transfer foil having a matte resin layer formed in advance, which can reduce the processing step, is desirable. It has been thought that the number of processing steps can be further reduced if it can be blended. However, when a matting agent is blended into the base film, there are problems that the continuity during film formation is poor and molding breaks that occur when used as a transfer foil, which is difficult to realize. .
Japanese Patent Laid-Open No. 7-196821 JP 7-237283 A JP 2007-181978 A JP 2004-9596 A JP-A-6-210799 JP 2000-344909 A Japanese Patent Publication No. 60-11628 Japanese Patent No. 3090911 JP 2002-97261 A

  The present invention has been made in view of the above-mentioned circumstances, and the problem to be solved is that in a printing process for shallow drawing to medium drawing use, the thermal dimensional change is good, the printability is excellent, and the film is easily stretched and molded with low stress. Another object of the present invention is to provide a polyester film capable of obtaining a molded article having good properties and excellent low gloss.

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

  That is, the gist of the present invention is that the heat shrinkage rate in the film longitudinal direction at 180 ° C. for 5 minutes is 3.0% or less, the heat shrinkage rate in the film transverse direction is 0.5% or less, and the film at 25 ° C. The 5% elongation stress in the longitudinal direction is 90 to 120 MPa, the 100% elongation stress at 25 ° C. is 200 MPa or less in both the longitudinal and transverse directions of the film, and the average surface roughness (Ra) of the film is 0.30 to 0.70 μm. It exists in the polyester film for in-mold transfer characterized by the above-mentioned.

Hereinafter, the present invention will be described in more detail.
The polyester film used in the present invention is a polyester obtained using aromatic dicarboxylic acid or its ester and glycol as main starting materials, and 80% or more of the repeating structural units are ethylene terephthalate units or ethylene- A polyester having 2,6-naphthalate units. And you may contain other 3rd components on the conditions which do not deviate from said range. As the aromatic dicarboxylic acid component, for example, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid, etc.) ) Etc. can be used. As the glycol component, in addition to ethylene glycol, for example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used. Can be used.

  Examples of the polymerization catalyst include antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds, and titanium compounds. Titanium compounds include, for example, tetraalkyl titanates, tetraaryl titanates, titanyl oxalate salts, titanyl oxalate, chelate compounds containing titanium, titanium tetracarboxylates, and specifically tetraethyl titanate, tetrapropyl titanate, tetraphenyl Examples thereof include titanate or a partial hydrolyzate thereof, titanyl ammonium oxalate, potassium titanyl oxalate, titanium triacetylacetonate and the like.

  In addition, it is preferable to add inorganic particles, organic salt particles and crosslinked polymer particles to the polyester film of the present invention. Inorganic particles that can be used include calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, Examples thereof include lithium fluoride. On the other hand, examples of the organic salt particles include calcium oxalate, terephthalate such as calcium, barium, zinc, manganese, and magnesium. Examples of the crosslinked polymer particles include divinylbenzene, styrene, acrylic acid, methacrylic acid, acrylic acid or a methacrylic acid vinyl monomer homopolymer or copolymer. In addition, organic particles such as polytetrafluoroethylene, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin may be used.

  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 average particle size of the particles used in the present invention is usually preferably 3 to 8 μm. When the average particle size is less than 3 μm, the ability to form protrusions on the surface may be insufficient. On the other hand, when the average particle size exceeds 8 μm, breakage occurs frequently when the film is stretched, and the product is stable. May not be collected.

  Furthermore, the particle content in the polyester is usually 0.1 to 5% by weight, preferably 0.2 to 3% by weight. When the particle content is less than 0.1% by weight, the number of protrusions on the film is not sufficient, and the appearance of the molded product with low gloss may be rough, whereas 5% by weight When adding exceeding it, when extending | stretching a film, a fracture | rupture etc. occur frequently and a product cannot be extract | collected stably.

  The average roughness Ra of the polyester film of the present invention needs to be in the range of 0.30 to 0.70 μm. When Ra is less than 0.30 μm, the molded article has insufficient low gloss, and a film having excellent low gloss cannot be obtained. Moreover, in order to make it larger than 0.70 micrometer, it is necessary to mix | blend a large amount of coarse particles, and when extending | stretching a film, fracture | rupture etc. occur frequently and a product cannot be extract | collected stably.

  The method for adding particles to the polyester 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, 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, heat stabilizers, lubricants, antistatic agents, fluorescent brighteners, dyes, pigments, and the like are added to the polyester film in the present invention as necessary. be able to. Depending on the application, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber, may be contained.

  The polyester film of this invention can use the polyester raw material with little oligomer content as a method of suppressing a surface oligomer. Such a raw material is obtained by solid-state polymerization in which a polyester chip obtained by a usual melt polycondensation reaction is kept at 180 ° C. to 240 ° C. for about 1 hour to 20 hours under reduced pressure or under the flow of an inert gas. Can do. A single-layer polyester film may be formed by mixing only this raw material or this raw material and a normal raw material, or a multilayer structure of two or more layers, and this raw material is used only for the surface layer opposite to the transfer layer. May be. In the case of a multilayer structure, normal polyethylene terephthalate may be used for the inner layer, and for simultaneous molding transfer, for the purpose of improving moldability, copolymerized polyester or polybutylene containing isophthalic acid and terephthalic acid as a copolymerization component. Terephthalate may be used.

  The polyester film used as the base material of the present invention may be either a single layer or a multilayer structure, but if it is a multilayer structure, it is possible to design differently for the inner layer and the outer layer, for example, containing particles only in the fill surface layer This can reduce manufacturing costs.

  The total thickness of the polyester film for transfer foil of the present invention is not particularly limited because it is appropriately selected according to the use for which the polyester film for transfer foil of the present invention is used, but the mechanical strength, handling properties, productivity, etc. From the viewpoint, it is preferably 12 to 100 μm.

  In the present invention, from the viewpoint of heat resistance, molding processability, and dimensional stability, the melting peak temperature Tm measured with a differential scanning calorimeter is preferably in the range of 220 to 260 ° C, more preferably 230 to 255 ° C. Range. When Tm is less than 220 ° C, heat resistance and dimensional stability tend to be inferior, so that wrinkles are generated in the printing process, the film surface after molding is swollen, and the design of the design pattern is impaired. Problems may occur. On the other hand, when Tm exceeds 260 ° C., moldability and productivity tend to deteriorate.

  In the present invention, the secondary transition temperature Tg obtained from the differential scanning calorimeter is preferably 50 ° C to 90 ° C, more preferably 55 ° C to 80 ° C. When Tg is 50 ° C. or lower, heat resistance tends to be inferior, and when it exceeds 90 ° C., formability tends to be inferior.

  In the present invention, the heat shrinkage rate in the longitudinal direction of the film after heat treatment at 180 ° C. for 5 minutes is 3.0% or less, and that in the transverse direction is required to be 0.5% or less, preferably, The vertical direction is 2.5% or less, and the horizontal direction is 0.3% or less. When the thermal contraction rate in the longitudinal direction is larger than 3.0%, the flatness (single tarmi) considered to be affected by the thermal contraction difference in the width direction is deteriorated. On the other hand, if the thermal contraction rate in the horizontal direction exceeds 0.5%, the width shrinkage becomes large, and a printing misalignment problem occurs in the width direction.

  From the viewpoint of processability to a transfer foil, the film of the present invention needs to have a 5% elongation stress in the range of 90 to 120 MPa in the longitudinal tensile test at 25 ° C., preferably in the range of 95 to 115. is there. If the 5% elongation stress is lower than 90 MPa in the tensile test in the longitudinal direction, film elongation occurs in a processing step such as printing, which causes problems such as printing misalignment in the longitudinal direction. On the other hand, if the 5% elongation stress in the vertical direction exceeds 120 MPa, the mechanical strength of the base film finished on the transfer foil is maintained, so that the deformation stress during in-mold molding is also high, and good moldability is ensured. It becomes difficult.

  From the viewpoint of moldability, the film of the present invention has a 100% elongation stress of 200 MPa or less, preferably 180 MPa or less in both the longitudinal and lateral directions at 25 ° C. in the tensile test. If the 100% elongation stress exceeds 200 MPa in the vertical and horizontal directions at 25 ° C., the deformation stress also increases at the time of in-mold molding, and the followability with the so-called mold deteriorates and the decorative printed surface becomes clear. This is not preferable because a chipping phenomenon and molding breakage are likely to occur.

  The basis for specifying the 5% elongation stress is that the elongation deformation rate in the longitudinal direction that occurs in the coating process and the printing process is substantially less than 3%. Is. In addition, with 100% elongation stress, when the molding elongation rate was converted from the thickness change after shallow drawing to middle drawing, the deformation rate was in the range of 70 to 130%. It has been identified. In addition, although these measurement temperatures vary depending on the application, in general, a high temperature test in consideration of film temperature such as drying temperature (80 to 180 ° C.) and molding temperature (120 to 160 ° C.) in coating or printing. The law can be considered. However, in this method, crystallization proceeds in the process of raising the film temperature, and it is difficult to know the exact mechanical characteristics of the polyester film for transfer foil. Therefore, the measurement temperature is measured with the mechanical characteristics at room temperature (JIS C 2318). Compliant).

  The film of the present invention is preferably used as a base film having an antistatic layer having both antistatic ability and blocking prevention ability.

Details of the antistatic agent will be described below.
When an anionic antistatic agent having a low molecular weight is used as the antistatic agent, the antistatic agent is transferred to the surface of the transfer layer where the release layer is coated while the polyester film is wound into a roll, and the release layer is coated. The antistatic agent is transferred to the adhesive layer when the transfer layer is rolled up after processing, and the adhesive cannot exhibit the desired performance. In order to prevent such transfer of the antistatic agent, a high molecular weight anionic compound is preferably used. In the case of a cationic antistatic agent, it is desirable to use a high molecular weight cationic compound.

The surface specific resistance of the antistatic layer is usually 1 × 10 ¹³ Ω / □ or less, preferably 1 × 10 ¹² Ω / □ or less. If the surface specific resistance exceeds 1 × 10 ¹³ Ω / □, the antistatic performance is inferior, and problems in the process may not be improved.

  The antistatic layer preferably has little or no transfer of the antistatic agent as described above, but at the same time, it is desirable that blocking with the adhesive of the transfer layer does not occur. As a guideline that does not cause blocking, the peel strength of the pressure-sensitive adhesive tape (Cellotape (registered trademark)) from the pressure-sensitive adhesive layer is preferably 2.4 N / cm or less, more preferably 2.0 N / cm or less, and particularly preferably 1 0.7 N / cm or less. If this value exceeds 2.4 N / cm, the effect of improving the blocking property may not be obtained.

  Examples of the antistatic agent satisfying such characteristics include a compound having a quaternary ammonium base. This refers to a compound having a component containing a quaternary ammonium base in the main chain or side chain in the molecule. Examples of such constituents include, for example, a pyrrolidinium ring, an alkylamine quaternized product, a copolymer of these with acrylic acid or methacrylic acid, an N-alkylaminoacrylamide quaternized product, a vinylbenzyltrimethylammonium salt, 2-hydroxy 3-methacryloxypropyltrimethylammonium salt etc. can be mentioned. Further, these may be combined or copolymerized with other resins. In addition, examples of anions that serve as counter ions for these quaternary ammonium salts include ions such as halogen, alkyl sulfate, alkyl sulfonate, and nitric acid.

  In the present invention, the compound having a quaternary ammonium base is preferably a polymer compound. When the molecular weight is too low, the antistatic agent is transferred from the antistatic layer to the adhesive layer, and a desired adhesive effect is not obtained, or it adheres to a heating roll or a mold during transfer. In order not to cause such a problem, it is desirable that the number average molecular weight of the compound having a quaternary ammonium base is usually 1000 or more, more preferably 2000 or more, particularly 5000 or more. On the other hand, when such a compound has a molecular weight that is too high, problems such as excessively high viscosity of the coating solution may occur. In order not to cause such a problem, the number average molecular weight is preferably 500,000 or less.

  In order to reduce the peel strength of the adhesive tape from the adhesive to 2.4 N / cm or less, not only the selection of the antistatic agent is important, but in order to reduce the peel strength, a polyolefin resin and / or a fluorine-based resin is used. It is effective to mix the resin actively. As the polyolefin-based resin and the fluorine-based resin, it is preferable to blend those having little transfer, preferably no transfer, like the antistatic agent.

  The coating layer in the present invention is preferably provided by in-line coating. In-line coating is a method of coating within the process of producing a polyester film. Specifically, it is a method of coating at any stage from melt-extrusion of polyester to biaxial stretching, heat setting and winding. is there. Usually applied to either a substantially amorphous unstretched sheet obtained by melting and quenching, a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction), or a biaxially stretched film before heat setting. To do. In these, the method of extending | stretching to a horizontal direction after apply | coating to a uniaxially stretched film is excellent. According to such a method, since film formation and coating / drying can be performed simultaneously, there is a merit in manufacturing cost, thin film coating is easy to perform stretching after coating, and heat treatment performed after coating is not limited. Since the high temperature is not achieved by this method, the coating film and the polyester film are firmly adhered.

  The thickness of a coating layer is 0.001-10 micrometers normally as thickness after drying, Preferably it is 0.010-5 micrometers, More preferably, it is 0.015-2 micrometers. When the thickness of the coating layer is less than 0.001 μm, the antistatic effect may not be sufficiently improved. When the thickness of the coating layer exceeds 10 μm, so-called blocking may occur in which the coating layer acts like an adhesive and the films wound up on the roll adhere to each other.

  According to the present invention, in a printing process from shallow drawing to medium drawing, the thermal dimensional change is good, the printing property is excellent, the elongation is easy with low stress, the moldability is good, and the glossiness is excellent. The polyester film which can obtain a product can be provided, and the industrial value of the present invention is high.

  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.

(1) Melting peak temperature (Tm)
Accompanied by melting obtained when a temperature difference of about 5 mg of a polyester resin is raised from 0 ° C. to 300 ° C. at a rate of 20 ° C./minute using a differential scanning calorimeter “MDSC 2920 type” manufactured by TA Instruments Inc. The temperature of the endothermic peak was Tm.

(2) Second order transition temperature (Tg)
Using a differential scanning calorimeter “MDSC2920 type” manufactured by TA Instruments Inc., about 5 mg of polyester resin is heated from 0 ° C. to 300 ° C. at a rate of 20 ° C./min, and held at 300 ° C. for 5 minutes. After that, the glass was rapidly cooled to 0 ° C. or lower, and then the transition point accompanying the glass transition observed when the temperature was raised from 0 ° C. to 300 ° C. at 300 ° C. at 20 ° C./min was defined as Tg.

(3) Surface resistivity (Ω / □)
Yokogawa, Hewlett-Packard's inner electrode 50mm diameter, outer electrode 70mm diameter concentric circular electrode 16008A (trade name) is placed on the sample in an atmosphere of 23 ° C, 50% RH, and a voltage of 100V is applied. The surface resistivity of the sample was measured using 4329A (trade name), a high resistance meter manufactured by the same company.

(4) Average roughness (Ra)
The center line average roughness Ra (nm) 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 [nm]. 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) ∫ L 0 | f (x) | dx

(5) 5% elongation stress Using an Intesco tensile tester Intesco Model 2001, a sample film having a length of 50 mm and a width of 15 mm at a temperature of 25 ° C. is subjected to a tensile test at a speed of 200 mm / min. The stress at 5% elongation in the longitudinal direction was determined.

(6) 100% elongation stress By the measuring method of said (5), the sample piece was pulled to the vertical direction and the horizontal direction, and the stress at the time of 100% elongation was calculated | required.

(7) Elongation at break The sample piece was pulled in the vertical direction and the horizontal direction by the measurement method of (5) above, and the elongation at break of the sample piece was determined.
(8) Heat shrinkage rate of 180 ° C. Using a hot air circulating furnace (manufactured by Tajii Mfg. Co., Ltd.), the film in a non-tension state is heat-treated for 5 minutes in an atmosphere of 180 ° C. Was measured by the following formula and expressed as an average value for each of five samples.

Thermal contraction rate (%) = (L ₀ −L ₁ ) × 100 / L ₀
In the above formula, L ₀ represents the sample length (mm) before the heat treatment, and L ₁ represents the sample length (mm) after the heat treatment. However, when L ₀ is smaller than L ₁ (when the film expands), the value of the thermal contraction rate is represented by − (minus).

(9) Printability <Print misalignment>
A roll-shaped film sample was unwound at a tension of 8 MPa, subjected to four-color gravure printing, and then dried at 180 ° C. for 30 seconds to prepare a pattern printing film. The printing misalignment of the resulting pattern printing film was visually observed and judged according to the following criteria.
A: No occurrence of printing misalignment (elongation and shrinkage of the film) is observed. O: Slight printing misalignment is observed, but is practically usable level. X: Printing misalignment is observed, and practically unusable. failure)

<Flatness (single tarmi)>
The pattern printing film prepared in the above manner was drawn out to a length of 2 m from the roll shape, visually observed for the flatness of one piece, and judged according to the following criteria.
◎: The flatness of the piece tarmi is hardly observed on the pattern printed film. ○: The piece tarmi is slightly observed but is practically usable. (failure)

(10) Formability The pattern printing film prepared in the above (8) was continuously formed at a rate of 100 pieces / min into a cylindrical shape having a bottom diameter of 50 mm and a depth of 5 mm using a male and female mold. The state of the obtained sample was visually observed and judged according to the following criteria.
A: 95 or more out of 100 films are uniformly formed without tearing of the film. O: 80 or more of 100 films are uniformly formed without generating a film tear. X: 21 out of 100 films. Film tear occurs at more than one piece, and many defective parts are observed (failed)

(11) Low gloss feeling of transfer molded product The method of JIS Z-8741 using a gloss meter VG-107 type manufactured by Nippon Denshoku Co., Ltd. at the bottom of the film obtained in (10) above. The glossiness was measured according to the above. The reflectance of the sample was determined based on the reflectance of the black standard plate at an incident angle and a reflection angle of 60 degrees, and the gloss was determined.
◎: 0 or more and less than 20 ○: 20 or more and less than 30 ×: 30 or more

Next, the polyester raw material used in the following examples will be described.
<Polyester 1>
Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, a polyester chip containing no lubricant particle size and having an intrinsic viscosity of 0.66 dl / g by a conventional melt polymerization method was produced.

<Polyester 2>
By using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, and using an alkyl methacrylate-styrene copolymer having an intrinsic viscosity of 0.66 dl / g and an average particle size of 4.5 μm by a conventional melt polymerization method. A polyester chip containing 10 parts of organic particles was produced.

<Polyester 3>
Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, 0.60 part of amorphous silica having an intrinsic viscosity of 0.66 dl / g and an average particle diameter of 2.5 μm by a conventional melt polymerization method A polyester chip was produced.

<Polyester 4>
Using diphthalic acid components as isophthalic acid and terephthalic acid, and polyhydric alcohol components as ethylene glycol, raw material chips polymerized by a conventional melt polycondensation method were produced. The isophthalic acid content in the dicarboxylic acid component of this raw material was 22 mol%.

Example 1:
Polyester 1 and polyester 2 are blended at a weight ratio of 1: 9, melted in an extruder, supplied to the outer layer A of the laminated die, polyester 1 is supplied to the inner layer of the laminated die, and each extruder is fed. The extrusion amount ratio of the outer layer A and the inner layer B is supplied at a ratio of 1: 4, and a two-layer / three-layer laminated polyester resin composed of the outer layer A / inner layer B / outer layer A is extruded into a film shape at 35 ° C. An unstretched film cast on a cooling drum and rapidly solidified was produced. Next, after preheating with an 80 ° C. heating roll, the film is stretched 3.2 times in the vertical direction between 95 ° C. rolls using an infrared heating heater and a heating roll, and then charged to a thickness of 5 μm with a gravure coater on one side of the film. Then, the film edge is gripped with a clip, guided into a tenter, stretched 4.2 times in the transverse direction while heated at a temperature of 110 ° C., and subjected to a heat treatment at 250 ° C. for 10 seconds and at the same time width A polyester film having a thickness of 50 μm was obtained by 10% relaxation in the direction.
The properties of the obtained film were as shown in Table 1. From this result, printing misalignment and flatness were good, the moldability was satisfactory, and the result was excellent in low gloss.

Example 2:
In Example 1, a polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the raw material composition supplied to the outer layer A was changed to a weight ratio of polyesters 1 and 2 of 7: 3.

Comparative Example 1:
In Example 1, polyester 2 and polyester 4 are blended at a weight ratio of 1: 4, melted in an extruder, supplied to a single-layer die, extruded into a film, and cast on a cooling drum at 35 ° C. Then, it was cooled and solidified to produce an unstretched film. Next, after preheating with a heating roll at 80 ° C., using an infrared heater and a heating roll in combination, the film is stretched 3.0 times in the vertical direction between 85 ° C. rolls, and then charged to a thickness of 5 μm with a gravure coater on one side of the film. After performing the prevention coating, the film end is held by a clip and guided into a tenter, and stretched 3.5 times in the horizontal direction while being heated at a temperature of 100 ° C., and subjected to a heat treatment at 195 ° C. for 10 seconds, A polyester film composed of a single layer film having a thickness of 50 μm was obtained by relaxing 3% in the width direction at 170 ° C. The properties of the obtained film were as shown in Table 1. From this result, the print misalignment in the longitudinal direction and the misalignment in the width direction due to the width shrinkage, which are considered to be caused by the lack of the 5% elongation stress in the vertical direction, are conspicuous. Furthermore, since the vertical shrinkage was somewhat large, a slight deterioration in flatness was observed. In terms of moldability, a good molded product was obtained without any problem of mold breaking.

Comparative Example 2:
In Comparative Example 1, the thickness was adjusted to 50 μm in the same manner as in Comparative Example 1 except that only the vertical magnification was increased from 3.0 to 3.5 and the relaxation in the width direction was changed from 3% to 4%. A polyester film was obtained. Although the printability of the obtained film improved, flatness deterioration was observed due to an increase in the vertical shrinkage rate. As for the moldability, a good molded product was obtained without any problem as in Comparative Example 1.

Comparative Example 3:
In Example 1, a 50 μm thick polyester film was prepared in the same manner as in Example 1 except that the stretching in the longitudinal direction was 3.8 times, heat treatment was performed at 230 ° C. for 10 seconds, and then 3% was relaxed in the width direction at 190 ° C. Obtained. Although the printing deviation of the obtained film was very good, many breaks occurred in the formability, and the molded article was partially observed to have a defect of lack of clear printing at the corner.

Comparative Example 4:
A polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the raw material composition supplied to the outer layer A in Example 1 was changed to 7: 3 by weight ratio of polyesters 1 and 3. The obtained film was inferior in low gloss, and the target film excellent in low gloss could not be obtained.

Comparative Example 5:
In Example 1, the raw material composition supplied to the outer layer A is only polyester 2, and the raw material composition supplied to the intermediate layer B is the same as in Example 1 except that the polymerization ratio of 1, 3 in polyester is 5: 5. A film with a thickness of 50 μm was obtained. Although a film could not be formed for a long time and a stable quality sample could not be obtained, only the average roughness was measured from a small sample.

  The film of the present invention can be suitably used as an in-mold transfer film.

Claims (1)

The heat shrinkage rate in the film longitudinal direction at 180 ° C. for 5 minutes is 3.0% or less, the heat shrinkage rate in the film transverse direction is 0.5% or less, and the 5% elongation stress in the film longitudinal direction at 25 ° C. In-mold transfer characterized in that it is 90 to 120 MPa, 100% elongation stress at 25 ° C. is 200 MPa or less in both the longitudinal and lateral directions of the film, and the average surface roughness (Ra) of the film is 0.30 to 0.70 μm. Polyester film.