JP4815662B2 - Biaxially stretched polyester film for molding - Google Patents

Description

【００６８】
【表２】

なお、表中の記号は次の通りである。
ＰＥＴ：ポリエチレンテレフタレート
ＰＥＮ：ポリエチレンナフタレート
ＰＰＴ：ポリプロピレンテレフタレート
ＴＰＡ：テレフタル酸
ＮＰＡ：ナフタレンジカルボン酸
ＩＰＡ：イソフタル酸
ＥＧ：エチレングリコール
ＰＧ：１，３-プロパンジオール
Ｔmeta：ヒートセット温度
Ｆ１００応力：１００％伸張時応力（２５℃）
ＭＤ：フィルム長手方向
ＴＤ：フィルム幅方向
【００６９】
表１の結果からわかるように、実施例１〜４で得られた成形用二軸延伸ポリエステルフィルムは、耐環境性、寸法安定性、印刷性、成形性のいずれにも優れるフィルムであった。
一方、比較例１〜２で得られたポリエステルフィルムは、成型品とした時フィルムの波打ちおよび印刷物のズレが生じ、成形性が劣るフィルムであり、いずれのフィルムも成形用二軸延伸ポリエステルフィルムとしては好ましくなかった。
【００７０】
【発明の効果】
本発明の成形用二軸延伸ポリエステルフィルムは、耐環境性、寸法安定性、印刷性、成形性に優れ、成形用の二軸延伸ポリエステルフィルムとして好適なものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyester film that is suitably used as a processing sheet that is adhered and bonded to the surface of an article (molded article) made of metal, wood, paper, resin, or the like. More specifically, the present invention relates to a biaxially stretched polyester film for molding that is suitable as a surface material for furniture, building materials (wall materials, etc.), housing equipment, home appliances, electronic equipment, and as a printing substrate.
[0002]
[Prior art]
As a conventional sheet for processing, a polyvinyl chloride film is typical and has been preferably used from the viewpoint of excellent workability. On the other hand, the polyvinyl chloride film has problems such as generation of toxic gas when the film burns due to fire or the like and bleeding out of the plasticizer, and a new material has been demanded according to recent needs for environmental resistance.
[0003]
In order to solve these requirements, a method using a transparent polyester film is effective. However, conventional polyester films have good heat resistance, but are insufficient in elongation required for molding processing. Was not suitable and improvement was desired.
[0004]
For example, Japanese Patent Publication No. 6-4276 proposes a membrane switch film using a polyethylene naphthalate film, and a film having good dimensional stability is obtained. However, these techniques have insufficient molding processability, and are not suitable for a switch having a so-called click feeling that requires a pressing depth.
[0005]
[Problems to be solved by the invention]
Therefore, the object of the present invention is to solve the problems of the prior art and not only to be environmentally friendly, but also to have excellent processability such as in-mold molding and emboss molding, and to achieve dimensional stability at high temperatures. It is to provide a biaxially stretched polyester film for molding excellent in properties.
[0006]
[Means for Solving the Problems]
The above object is a polyester film comprising a polyester mainly composed of an ethylene terephthalate unit and / or an ethylene naphthalate unit, wherein the polyester film has a melting point of 245 ° C. or more, a plane orientation coefficient (fn), a film length 190 ° C. heat shrinkage in the direction {SrMD (%)} and 190 ° C. heat shrinkage in the width direction {SrTD (%)} simultaneously satisfy the following formulas I to III, and the heat set temperature (Tmeta) is from 222 to 240. ℃ For in-mold molding of key tops This can be achieved by forming a biaxially stretched polyester film.
0.02 ≦ fn ≦ 0.15 Formula I
0 ≦ SrMD ≦ 3 Formula II
0 ≦ SrTD ≦ 3 Formula III
[0007]
The biaxially stretched polyester film for molding of the present invention preferably satisfies the following conditions.
(A) 100% elongation stress {F100MD (MPa)} in the film longitudinal direction at 25 ° C., 100% elongation stress {F100TD (MPa)} in the film width direction and film thickness {d (μm)} Satisfy Formulas IV to VII at the same time.
F100MD ≦ 150 Formula IV
F100TD ≦ 150 Formula V
6000 ≦ F100MD × d ≦ 25000 Formula VI
6000 ≦ F100TD × d ≦ 25000 Formula VII
[0008]
(B) The breaking elongation in the film longitudinal direction and the breaking elongation in the film width direction at 25 ° C. are both 170% or more.
(C) Heat set temperature (Tmeta) is 180-240 degreeC.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0010]
The polyester in the present invention is a general term for high molecular weight substances constituted by ester bonds.
[0011]
Examples of the dicarboxylic acid component used for the ester bond include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid and the like. Aliphatic dicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, cyclohexyne dicarboxylic acid and other alicyclic dicarboxylic acids, p-oxybenzoic acid and the like An oxycarboxylic acid or the like can be used. Among these, in the polyester in the present invention, the ratio of terephthalic acid and naphthalenedicarboxylic acid is preferably 95 mol% or more from the viewpoint of heat resistance and productivity.
[0012]
On the other hand, examples of the glycol component include aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and neopentylglycol, alicyclic glycols such as cyclohexanedimethanol, and aromatics such as bisphenol A and bisphenol S. Glycol, diethylene glycol and the like can be used. These dicarboxylic acid components and glycol components may be used in combination of two or more.
[0013]
Furthermore, as long as the effects of the present invention are not inhibited, a copolymerized polyester obtained by copolymerizing a polyfunctional compound such as trimellitic acid, trimesic acid, or trimethylolpropane can also be used.
[0014]
In addition, it is preferable to use a blend of two or more of the above polymers in order to improve processability. Of these, polyesters mainly composed of polyethylene terephthalate units and / or ethylene naphthalate units are particularly preferred from the viewpoint of heat resistance and processability.
[0015]
The melting point of the polyester film in the present invention is preferably 245 ° C. or higher, more preferably 245 ° C. to 270 ° C., particularly preferably 248 ° C. to 270 ° C. from the viewpoint of heat resistance and workability. In particular, if the melting point is less than this range, the heat resistance is inferior. Here, the melting point of the polyester film is an endothermic peak temperature at the time of melting the polymer, which is detected at the time of the first temperature rise (1st run) of the so-called differential scanning calorimeter measurement method (DSC).
[0016]
As the polyester film of the present invention, a biaxially stretched polyester is desirably used from the viewpoint of heat resistance, dimensional stability, scratch resistance, and antifouling properties. Such a biaxial stretching method may be either simultaneous biaxial stretching or sequential biaxial stretching. At this time, simultaneous biaxial stretching is particularly preferable from the viewpoint of suppressing thickness unevenness.
[0017]
The polyester film of the present invention can have a laminated structure as shown in, for example, JP-A-9-24588 using different types of polyester. The form of the laminated film is not particularly limited, and examples thereof include A / B, B / A / B, and C / A / B lamination.
[0018]
The total thickness of the biaxially stretched polyester film for molding of the present invention is preferably 10 to 500 μm, and more preferably 20 in terms of moldability, covering properties to the substrate, protecting the surface of the substrate, and design properties. It is -300 micrometers, Most preferably, it is 20-200 micrometers.
[0019]
In the present invention, from the viewpoint of improving moldability, printability, aesthetics, and dimensional stability, the plane orientation coefficient (fn), the 190 ° C. heat shrinkage rate in the longitudinal direction of the film {SrMD (%)}, and the width direction It is necessary that the 190 ° C. heat shrinkage rate {SrTD (%)} simultaneously satisfies the following formulas I to III.
[0020]
0.02 ≦ fn ≦ 0.15 Formula I
0 ≦ SrMD ≦ 3 Formula II
0 ≦ SrTD ≦ 3 Formula III
In the formula I, the range of the plane orientation coefficient (fn) is preferably 0.05 to 0.15, particularly preferably 0.10 to 0.15 from the viewpoint of moldability. The plane orientation coefficient (fn) is calculated from the following equation using the longitudinal refractive index (Nx), the width refractive index (Ny), and the thickness direction refractive index (Nz) of the film measured using an Abbe refractometer or the like. Value.
[0021]
fn = (Nx + Ny) / 2−Nz
At this time, when the longitudinal direction and the width direction of the film are not clear, the plane orientation coefficient is obtained by setting the refractive index in the thickness direction to Nx, Ny, and Nz, respectively, in the main axis direction of orientation, the direction perpendicular to the main axis direction of orientation, and the thickness direction. Can do.
[0022]
In Formula II and Formula III, the range of 190 ° C. heat shrinkage (SrMD) in the film longitudinal direction and 190 ° C. heat shrinkage (SrTD) in the width direction is preferably 0 to 2%, particularly preferably 0 to 1%. It is. If it is outside the above range, problems such as deformation of the printed pattern after molding occur, which is not preferable from the viewpoint of dimensional stability.
[0023]
In the biaxially stretched polyester film for molding of the present invention, from the viewpoint of moldability, 100% elongation stress {F100MD (MPa)} in the longitudinal direction of the film at 25 ° C. {100% elongation stress {F100TD ( MPa)} and the film thickness {d (μm)} preferably simultaneously satisfy the following formulas IV to VII.
F100MD ≦ 150 Formula IV
F100TD ≦ 150 Formula V
6000 ≦ F100MD × d ≦ 25000 Formula VI
6000 ≦ F100TD × d ≦ 25000 Formula VII
[0024]
More preferably, F100MD of formula IV and F100TD of formula V are 140 MPa or less, particularly preferably 130 MPa or less. More preferably, F100MD × d of formula VI and F100MD × d of formula VII are in the range of 7000 to 20000, particularly preferably in the range of 8000 to 18000.
[0025]
From the viewpoint of formability, the breaking elongation in the longitudinal direction of the film and the breaking elongation in the width direction at 25 ° C. are preferably 170% or more, more preferably 200% or more, and particularly preferably 250% or more. When the breaking elongation is less than 170%, it is not preferable because the elongation is insufficient and molding failure such as film peeling tends to occur.
[0026]
Furthermore, the heat set temperature (Tmeta) of the film is preferably in the range of 180 to 240 ° C. Especially preferably, it is 200-240 degreeC. If the heat set temperature is less than this range, the dimensional stability is likely to deteriorate, and if it is higher than this range, film tearing is likely to occur, which is not preferable from the viewpoint of productivity. The heat set temperature (Tmeta) is a heat treatment that exists in the vicinity of the peak temperature (melting point) in the endothermic melting curve detected at the first temperature rise (1st run) of differential scanning calorimetry (DSC). It is the temperature of the resulting sub-endothermic peak.
[0027]
Further, the thickness unevenness of the film is preferably 15% or less, particularly preferably 10%, from the viewpoints of printability and workability.
[0028]
In the film of the present invention, the surface wetting tension is preferably 50 mN / m or more, and more preferably 56 mN / m or more, from the viewpoints of printability, workability, and adhesion to the film.
[0029]
Films with a wetting surface tension of 50 mN / m or more can be achieved by applying an appropriate surface treatment, such as corona discharge treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, chemical treatment, physical Although it can be achieved by a surface treatment such as a general surface roughening treatment or a surface coating treatment, any surface treatment can be employed as long as it does not impair the effects of the present invention, and it is not particularly limited. Among these, corona discharge treatment is preferable because it is a simple and effective technique.
[0030]
Various coatings may be applied to the film of the present invention, and the coating compound, method, and thickness are not particularly limited as long as the effects of the present invention are not impaired.
[0031]
In the present invention, from the viewpoint of aesthetics after printing, the 60-degree specular gloss of the film is preferably 60% or more, particularly preferably 90% or more.
[0032]
The film of the present invention has a carboxyl end group amount of preferably 20 to 60 equivalents / ton, more preferably 30 to 50 equivalents / ton from the viewpoint of improving the adhesion between the film and the base material and processability. Is good.
[0033]
In the present invention, in order to further improve the adhesion and film formation stability, the intrinsic viscosity of the polyester is preferably 0.50 dl / g or more, more preferably 0.55 dl / g or more, and particularly preferably 0.60 dl / g. What is more than g is used. An intrinsic viscosity of less than 0.50 dl / g is not preferable because the adhesiveness decreases.
[0034]
Although it does not specifically limit as a catalyst at the time of manufacturing polyester used by this invention, An alkaline earth metal compound, a manganese compound, a cobalt compound, an aluminum compound, an antimony compound, a titanium compound, a titanium / silicon composite oxide, a germanium compound, etc. Can be used. Of these, titanium compounds, titanium / silicon composite oxides, and germanium compounds are preferable in optimizing the catalytic activity, taste characteristics, and the amount of the catalytic metal.
[0035]
For example, when a titanium / silicon catalyst is added as a catalyst in a polymerization process for producing a polyester, a terephthalic acid component and an ethylene glycol component are reacted, and then a titanium / silicon composite oxide and a phosphorus compound are added. A method in which a polycondensation reaction is performed at a high temperature under reduced pressure until a certain diethylene glycol content is obtained to obtain a polyester having a specific catalytic metal amount and phosphorus amount is preferably employed.
[0036]
Although the phosphorus compound added as a heat stabilizer is not specifically limited, Phosphoric acid, phosphorous acid, etc. are preferable.
[0037]
In the polyester film of the present invention, the beautifulness of the molded product, weather resistance, and discoloration resistance of printing are extremely good, and the remaining amount of catalyst metal in the film (M: unit mmol%) and the remaining amount of phosphorus element ( It is preferable that the relationship of P: millimol% satisfies the following formula. 0.3 ≦ M / P ≦ 5
Further, when the value of M / P is 3 or less, both the productivity and thermal stability of the film are improved, which is particularly preferable.
[0038]
The method for producing the polyester film of the present invention is not particularly limited. For example, after drying the polyester as necessary, the polyester film is supplied to a known melt extruder, extruded into a sheet from a slit die, and electrostatically applied. After being brought into close contact with the casting drum by a method such as the above, cooling and solidifying to obtain an unstretched sheet, the unstretched sheet is stretched. Such a stretching method may be either simultaneous biaxial stretching or sequential biaxial stretching. In short, the unstretched sheet is stretched and heat-treated in the longitudinal direction and the width direction of the film to obtain a film having a desired degree of plane orientation. The method is adopted. Among these methods, a tenter method is preferable in terms of film quality, and a sequential biaxial stretching method of stretching in the width direction after stretching in the longitudinal direction, after stretching in the width direction, A sequential biaxial stretching method of stretching or a simultaneous biaxial stretching method of stretching the longitudinal direction and the width direction almost simultaneously is desirable.
[0039]
The stretching ratio of such biaxial stretching is 1.6 to 4.2 times in each direction, preferably 1.7 to 4.0 times. In this case, either of the stretching ratios in the longitudinal direction and the width direction may be increased or the same. The stretching speed is desirably 1000% / min to 200000% / min, and the stretching temperature can be any temperature as long as it is not less than the glass transition temperature of the polyester and not more than [glass transition temperature + 100 ° C.]. The film is preferably stretched in the range of 80 to 170 ° C. Furthermore, the film is heat-treated after biaxial stretching, and this heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. The heat treatment temperature can be any temperature of 120 ° C. or higher and 245 ° C. or lower, but is preferably 120 to 240 ° C. Moreover, although the heat processing time can be made arbitrary, Preferably it is good to carry out for 1 to 60 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction. Furthermore, re-stretching may be performed once or more in each direction, and then heat treatment may be performed.
[0040]
The polyester may contain particles arbitrarily selected from known internal particles having an average particle diameter of 0.01 to 10 μm, external particles such as inorganic particles and / or organic particles. Here, if particles having an average particle diameter exceeding 10 μm are used, defects of the film are likely to occur, which is not preferable from the viewpoint of transparency and design properties. Examples of such particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay, hydroxyapatite and the like, and styrene, silicone, acrylic acid, etc. Organic particles or the like having a component as a component can be used. Among these, inorganic particles such as dry, wet and dry colloidal silica and alumina, and organic particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components are preferably used. Two or more of these internal particles, inorganic particles and / or organic particles may be used in combination as long as the properties are not impaired.
[0041]
Furthermore, the addition amount of these particles is preferably in the range of 0.01 wt% to 50 wt%. If it is 0.01 weight% or less, film winding will become difficult and it is unpreferable on handling. On the other hand, if it exceeds 50% by weight, coarse projections, deterioration of transparency and film forming property and the like are caused.
[0042]
The biaxially stretched polyester film for molding of the present invention is used as a film application that exists in close contact with a raw material such as a resin, that is, as a film for molding. For this molding, for example, it is used in close contact with a material such as metal, wood, paper, resin, etc., and is used in a mold at the time of injection molding and bonded to the surface at the time of injection molding Specifically, it is represented for injection molding and transfer in-mold molding.
[0043]
A film molded with a material such as resin may be commercialized as it is affixed to the surface of a molded product made of resin, etc., or a film is used as a mold release material or transfer material for commercialization. It may be peeled off before As the latter case, for example, the material is laminated and integrally formed on the printing surface side of the film printed with ink, and after the ink is cured by UV irradiation or the like and the printing is transferred to the material molded product side, The method of peeling off a film and making it into a product is mention | raise | lifted. In addition, as the transfer in-mold molding, for example, a resin is poured onto a sheet processed into a film / release layer / top layer (hard coat layer) / printing layer / adhesive layer, and the sheet is in close contact with the sheet. There is a method of producing a printed product by simultaneously performing printing and member molding by peeling the film / release layer after the product is manufactured.
[0044]
Similarly, it is also suitable for molding applications such as injection mold decoration. Here, as a resin used for transfer in mold, injection mold decoration, or the like, a resin such as ABS, acrylic, polycarbonate, or the like is preferably used because of good adhesion and adhesion to the film.
[0045]
In addition, when producing a molded article provided with a pattern layer or a colored layer (called a printed layer) by printing on the surface, the film may be bonded after forming the printed layer on the molded article side, Moreover, you may bond together, after forming a printing layer in the film side. The bonding may be thermal bonding or bonding via an adhesive.
[0046]
Examples of the adhesive used here include urea resin adhesives, melamine resin adhesives, phenol resin adhesives, α-olefin resin adhesives, polyester adhesives, and adhesives based on mixtures of aqueous polymers and isocyanates. , Epoxy adhesive, solution type vinyl acetate resin adhesive, emulsion type vinyl acetate resin adhesive, acrylic emulsion adhesive, hot melt adhesive, cyanoacrylate adhesive, polyurethane adhesive, chloroprene rubber adhesive Agent, nitrile rubber adhesive, SBR adhesive, modified rubber emulsion adhesive, ethylene copolymer resin adhesive, resorcin adhesive, natural rubber adhesive, cellulose adhesive, starch paste, dextrin Etc.
[0047]
The biaxially stretched polyester film for molding of the present invention can be used for molding after being subjected to various surface treatments such as embossing and printing. For example, after printing on the film, it is bonded to a steel plate, bent, and compressed. And can be suitably used as a transparent surface material for furniture, building materials (wall materials, etc.), housing equipment, home appliances, and electronic devices, and as a printing substrate.
[0048]
【Example】
Next, the effects of the present invention will be described with reference to examples, but the present invention is not limited to these examples. First, the characteristic value measurement method and evaluation method will be described below.
[0049]
[Measurement method and evaluation method of characteristic values]
The characteristic values in the present invention are determined by the following measuring method.
[0050]
(1) Melting point (Tm), heat set temperature (Tmeta)
Using a differential scanning calorimeter DSCII type manufactured by Seiko Instrment Co., Ltd., the peak temperature of the endothermic melting curve when 5 mg of the sample was heated from room temperature at a heating rate of 10 ° C./min was defined as the melting point (Tm). . The sub-endothermic peak temperature resulting from the heat treatment was defined as the heat set temperature (Tmeta).
[0051]
(2) Intrinsic viscosity
The polyester was dissolved in orthochlorophenol and measured at 25 ° C.
[0052]
(3) Plane orientation coefficient (fn)
Using an Abbe refractometer manufactured by Atago Co., Ltd., the refractive index of the film was measured using sodium D line (wavelength 589 nm) as a light source. The longitudinal refractive index nγ within the film plane, the transverse refractive index nβ and the refractive index nα in the thickness direction perpendicular to it are obtained by the following formula:
fn = (nγ + nβ) / nα
Thus, the plane orientation coefficient (fn) was determined.
[0053]
(4) Thermal contraction rate (Sr)
A sample having a distance between marked lines of 200 mm in the film longitudinal direction (MD) and a sample having a distance between marked lines of 200 mm in the film width direction (TD) were prepared, and each was cut into an elongated film sample having a width of 10 m. A film sample is suspended in the length direction, a load of 1 g is applied in the length direction, heated for 30 minutes using hot air at 190 ° C., the length between the marked lines is measured, and the amount of film shrinkage is measured. It was obtained as a percentage (%) as a ratio to the dimension. When the film was stretched, it was indicated by minus (−), the thermal shrinkage rate in the MD direction was SrMD, and the thermal shrinkage rate in the TD direction was SrTD.
[0054]
(5) Stress at 100% elongation, elongation at break
A sample having a length of 150 mm and a width of 10 mm was cut out from the biaxially stretched film (the sample length direction was the film longitudinal direction or width direction), and this sample was subjected to a tensile tester manufactured by Orientec Co., Ltd., with an initial length of 50 mm and a tensile speed of 300 mm / Measured under the conditions of 25 ° C. and 100% elongation stress and elongation at break in each direction were determined from the obtained load-strain curve.
[0055]
(6) Dimensional stability
The (4) MD direction and TD direction were determined by the following criteria from the values of 190 ° C. × 30 minutes heat shrinkage rate (◯, Δ: pass, ×: fail, the same applies to the following evaluations).
○: SrMD, SrTD, both values are ± 2% or less.
Δ: One of SrMD and SrTD is in the range of −2% ≦ SrMD ≦ 2% and −2% ≦ SrTD ≦ 2%.
X: The value of either SrMD or SrTD exceeds ± 3%.
[0056]
(7) Printability
After heat-treating the film at 100 ° C. for 30 minutes, four-color silk printing was performed. After printing each color, drying was performed at 80 ° C. for 30 minutes. Based on the printing accuracy and sharpness at this time, printability was determined according to the following criteria.
○: Vivid, and printing misregistration of each color is not seen at the visual level.
Δ: A slight shift in printing or the like is observed at a level visually observed with the eyes close to a distance of about 20 cm, but the appearance is generally good at a level observed at a distance of 20 cm or more.
×: Printing misalignment in each color is observed, and printing is uneven and the appearance is remarkably bad.
[0057]
(8) Formability
After printing on one side of the film, ABS resin heated to 245 ° C. was poured into the film (injection molding) to produce a key top with a height of 2 mm whose surface was covered with the film. The molding state of the film at this time was visually observed and judged according to the following criteria.
○: Appearance is very good.
Δ: Although slight wrinkles can be observed, it is at a level where there is no practical problem.
X: Breakage is observed in the film. Or a big wrinkle enters and an external appearance is remarkably bad.
[0058]
(9) Comprehensive evaluation
In terms of practicality as a film for molding, dimensional stability, printability, and moldability were evaluated as “Excellent”, “Slightly inferior” as “Δ”, and Inferior as “x”.
[0059]
Next, the effects of the present invention will be described with reference to examples.
[0060]
Example 1
A magnesium compound and an antimony compound are used as a polymerization catalyst, phosphoric acid, silicon oxide particles having a particle size of 1.0 μm (0.08% by weight) are added, and polyethylene terephthalate (intrinsic viscosity 0.65 dl / g, melting point 257 ° C.) Was polymerized. The obtained polyester was dried under reduced pressure at 180 ° C. for 4 hours. After drying, it was supplied to a melt extruder. The polyester was extruded into a sheet form from a slit-shaped die, brought into close contact with a mirror surface cooling drum by electrostatic application (3.0 kV), and solidified by cooling to obtain an unstretched sheet. This unstretched sheet is first preheated at 105 ° C. for 7 seconds, then stretched 2.8 times in the longitudinal direction with a roll heated to 115 ° C., further preheated at 95 ° C. for 6 seconds, and then heated in a 120 ° C. heating zone. After stretching 2.9 times in the width direction, 5% relaxation was performed in the width direction at 245 ° C. for 5 seconds to obtain a biaxially stretched polyester film for molding having a thickness of 100 μm. One side of the obtained film was subjected to corona discharge treatment and evaluated.
[0061]
(Example 2)
The same 50 parts by weight of polyethylene terephthalate as in Example 1 and polyethylene naphthalate (polymerization with addition of phosphoric acid using magnesium compound and antimony compound as a catalyst, intrinsic viscosity 0.69 dl / g, melting point 270 ° C.) were blended and dried. Then, it was supplied to an extruder to form a film. Example 1 except that after preheating at 110 ° C. for 6 seconds, stretching 2.5 times at 120 ° C. in the longitudinal direction, after preheating at 100 ° C. for 6 seconds, and stretching 2.9 times at 130 ° C. in the transverse direction. Similarly, a biaxially stretched polyester film for molding having a thickness of 50 μm was obtained.
[0062]
(Example 3)
Biaxially stretched polyester for molding having a thickness of 25 μm in the same manner as in Example 1 except that the same polyethylene terephthalate as in Example 1 was used, preheated at 97 ° C. for 4 seconds, and stretched 3.0 times in the longitudinal direction at 98 ° C. A film was obtained.
[0063]
Example 4
80 parts by weight of polyethylene terephthalate and polypropylene terephthalate used in Example 1 (polymerization with addition of phosphoric acid using titanium compound as a catalyst, intrinsic viscosity 0.9 dl / g, carboxyl end group 10 equivalents / ton, M / P = 5 ) 20 parts by weight were blended, dried under reduced pressure at 150 ° C. for 5 hours, and supplied to an extruder to form a film. A biaxially stretched polyester film for molding having a thickness of 50 μm was obtained in the same manner as in the example except that after preheating at 85 ° C. for 4 seconds, the film was stretched 3.1 times at 85 ° C. in the longitudinal direction.
[0064]
(Comparative Example 1)
A biaxially stretched polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 2.
[0065]
(Comparative Example 2)
Using magnesium compound and antimony compound as catalyst, phosphoric acid and silicon oxide particles (0.2% by weight) are added, and 11 mol% of isophthalic acid copolymerized polyethylene terephthalate (inherent viscosity 0.62 dl / g, carboxyl end group 25 equivalents / Ton, M / P = 6). The obtained polyester was dried and supplied to an extruder to form a film. After preheating at 90 ° C for 6 seconds, stretched 3.3 times at 95 ° C in the longitudinal direction, after preheating at 110 ° C for 6 seconds, stretched 3.4 times at 125 ° C in the width direction, and at 195 ° C, A biaxially stretched polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that 3% relaxation in the width direction and heat treatment for 5 seconds were performed.
[0066]
Tables 1 and 2 summarize the quality evaluation results of the above-described biaxially stretched polyester film for molding.
[0067]
[Table 1]

[0068]
[Table 2]

The symbols in the table are as follows.
PET: Polyethylene terephthalate
PEN: Polyethylene naphthalate
PPT: Polypropylene terephthalate
TPA: terephthalic acid
NPA: Naphthalenedicarboxylic acid
IPA: Isophthalic acid
EG: Ethylene glycol
PG: 1,3-propanediol
Tmeta: Heat set temperature
F100 stress: 100% elongation stress (25 ° C)
MD: Film longitudinal direction
TD: Film width direction
[0069]
As can be seen from the results in Table 1, the biaxially stretched polyester films for molding obtained in Examples 1 to 4 were excellent in environmental resistance, dimensional stability, printability, and moldability.
On the other hand, the polyester film obtained in Comparative Examples 1 and 2 is a film in which the waviness of the film and the deviation of the printed matter occur when it is made into a molded product, and the formability is inferior, and any film is a biaxially stretched polyester film for molding. Was not preferred.
[0070]
【Effect of the invention】
The biaxially stretched polyester film for molding of the present invention is excellent in environmental resistance, dimensional stability, printability, and moldability, and is suitable as a biaxially stretched polyester film for molding.

Claims (3)

A polyester film comprising a polyester mainly comprising an ethylene terephthalate unit and / or an ethylene naphthalate unit, wherein the polyester film has a melting point of 245 ° C. or more, a plane orientation coefficient (fn), and a film longitudinal direction of 190 ° C. Heat shrinkage rate {SrMD (%)} and 190 ° C. heat shrinkage rate in the width direction {SrTD (%)} satisfy the following formulas I to III simultaneously, and the heat set temperature (Tmeta) is 222 to 240 ° C. A biaxially stretched polyester film for in-mold molding of key tops .
0.02 ≦ fn ≦ 0.15 Formula I
0 ≦ SrMD ≦ 3 Formula II
0 ≦ SrTD ≦ 3 Formula III 100% elongation stress {F100MD (MPa)} in the film longitudinal direction at 25 ° C., 100% elongation stress {F100TD (MPa)} in the film width direction and film thickness {d (μm)} are expressed by the following formulas IV to The biaxially stretched polyester film for in-mold molding of a key top according to claim 1, which simultaneously satisfies VII.
F100MD ≦ 150 Formula IV
F100TD ≦ 150 Formula V
6000 ≦ F100MD × d ≦ 25000 Formula VI
6000 ≦ F100TD × d ≦ 25000 Formula VII The biaxially stretched polyester film for in-mold molding of a key top according to any one of claims 1 to 2, wherein both the breaking elongation in the film longitudinal direction and the breaking elongation in the film width direction at 25 ° C are 170% or more.