TWI605077B - Polyester film, laminate and method for manufacturing polyester film - Google Patents

Description

Polyester film, laminate, and method for producing polyester film

The present invention relates to a novel polyester film having a specific range of stress and elastic modulus at the time of elongation and a method for producing the same. Further, the present invention relates to a laminate comprising the aforementioned polyester film.

The polyester film is excellent in heat resistance, chemical resistance, insulation, and the like, and is used in a wide range of fields such as a film for packaging, a film for magnetic tape, a film for optical use, and a film for electronic parts.

In recent years, a laminate type lithium ion battery exterior material or a press through package has been obtained by cold molding a laminate comprising a resin film or a metal foil.

The laminate for performing the above cold forming is generally a nylon film (Ny) / Al foil / unstretched polypropylene film (CPP), or polyethylene terephthalate (PET) / Ny / Al foil In the structure of the /CPP or the like, the laminate containing the Al foil is provided with a nylon film in order to impart ductility to enable cold forming.

However, the lamination of the laminate film not only causes an increase in cost, but also causes the heat resistance of the polyamide film to be inferior to that of the polyester film, so that there is a problem that the physical properties are lowered due to thermal deterioration under high temperature and high humidity. In addition, by Since it is hygroscopic, there is a problem that the size changes due to moisture absorption, and the obtained packaging bag has a problem that curling may occur.

On the other hand, the polyester film is harder and brittle than the nylon film, and is generally produced by a tenter type sequential stretching method, so that the anisotropy is large, and thus it is difficult to impart ductility to the metal laminated on the polyester film. Foil. However, a polyester film which can constitute a laminate having excellent cold moldability has been proposed. For example, in Patent Documents 1 and 2, a lithium battery having a specific stress in a longitudinal direction and a width direction of the film is disclosed. Polyester film for pool packaging. In addition, in recent years, a laminated body used as a laminate type lithium ion battery exterior material or a blister package or the like has a structure in which a nylon film is not used in the outer layer, and only a polyester film of PET/Al/CPP is used. By.

In the laminate including the resin film and the metal foil, it is important to impart ductility to the metal foil by the resin film when performing cold forming. Therefore, the resin film must be uniformly elongated in all directions. When the physical properties of the resin film in four directions of MD, 45°, TD, and 135° are changed, it is difficult to uniformly elongate in all directions during cold forming. That is, there is a direction in which the resin film is easily elongated and a direction in which it is difficult to elongate, resulting in breakage of the metal foil during cold forming or peeling or pinhole in the resin film. When this problem occurs, the molded body cannot function as a package or the like, and there is a concern that the package (content) is damaged. Therefore, the resin film must be changed as much as possible in the physical properties of each other.

The factors affecting the moldability at the time of cold forming include the flexibility of the resin film. When the resin film has low flexibility, it will be subjected to a strong load during elongation of cold forming, and pinholes or delamination may occur. The opposite of, When the flexibility of the resin film is too high, the effect of protecting the laminate including the metal foil as a substrate is poor, and the physical properties of the obtained laminate are lowered. Therefore, it is important that the resin film has flexibility that is not too high and does not become too low.

Further, one of the other physical properties that affect the moldability at the time of cold forming is the thickness of the resin film. When the laminate of the polyester film having a varying thickness is laminated, the relatively thin portion of the polyester film is broken to cause pinholes, or the delamination is raised. Therefore, it is also important that the polyester film used in the cold forming is uniformly controlled throughout the film.

In recent years, the use of a resin film and a laminate thereof in a lithium ion battery exterior material has been required to further reduce the thickness of the resin film in accordance with the demand for further increase in output, size, and cost of the battery. In general, the thicker the thickness of the resin film, the easier it is to ensure the uniformity of the thickness. However, since the thickness is thinner (especially, the thickness is 25 μm or less), the uniformity of the thickness is worse, so that the influence on the moldability is more remarkable.

In view of the development of a polyester film, it is expected that the change in physical properties in the four directions is small, the flexibility is in an appropriate range, and the uniformity of thickness is excellent, and the cold formability is excellent even if the thickness is changed. Resin film, but such a film has not yet been developed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2004-362953

[Patent Document 2] Japanese International Publication No. 2015/125806

An object of the present invention is to provide a polyester film which can suppress fluctuations in physical properties in the above four directions, has appropriate flexibility, and is excellent in thickness uniformity, thereby imparting good adhesion to a laminated metal foil. It is excellent in ductility and heat resistance, and is suitable for cold forming applications.

In order to solve the above-mentioned problems, the inventors of the present invention have intensively studied, and have found that it is possible to suppress variations in physical properties in the above four directions by adjusting the stretching ratio and the temperature during stretching to a specific range. The polyester film which is excellent in flexibility and uniform in thickness, has completed the present invention.

That is, the gist of the present invention is as follows.

(1) A polyester film characterized in that any direction on the surface of the film is set to 0°, and directions in four directions of 45°, 90°, and 135° are clockwise with respect to the direction. The stress at 5% elongation, the difference between the maximum value and the minimum value of these stresses is 50 MPa or less, and the difference between the maximum value and the minimum value of the stress at 15% elongation in each of the four directions described above. When it is 70 MPa or less, the modulus of elasticity of the polyester film in the above four directions is in the range of 2.0 to 3.5 GPa in either direction.

(2) The polyester film according to (1), wherein the dry heat shrinkage ratio in the above four directions is in the range of 0 to 10%.

(3) The polyester film according to (1) or (2), which is thick in the above four directions The average value of degrees is 30 μm or less.

The polyester film according to any one of (1) to (3), wherein the standard deviation of the thickness in the four directions is 0.4 μm or less.

(5) A laminate comprising the polyester film according to any one of the above (1) to (4), and a metal foil.

(6) A laminated body obtained by laminating a metal foil, an adhesive layer, and the polyester film according to any one of (1) to (4).

(7) A method for producing a polyester film, which is a method for producing a polyester film according to any one of the above (1) to (4), which is to make a machine direction (MD) The stretching ratio (DR _MD ) and the stretching ratio (DR _TD ) in the transverse direction ( _TD ) satisfy the following modes (a) and (b), and the unstretched sheets are biaxially stretched sequentially or simultaneously.

0.70≦DR _MD /DR _TD ≦0.90 (a)

12.5≦DR _MD ×DR _TD ≦15.5 (b)

(8) The method for producing a polyester film according to (7), wherein the stretching is sequential biaxial stretching, and the unstretched sheet is stretched in the machine direction (MD) at a temperature ranging from 65 to 105 °C. The first stretch of the first stretched film is obtained, and the first stretched film is stretched in the transverse direction (TD) in a temperature range of 90 to 160 ° C to obtain a second stretch of the second stretched film.

(9) The method for producing a polyester film according to (7) or (8), wherein the biaxially stretched film is heat-treated in a temperature range of from 160 to 210 °C.

The polyester film of the present invention not only stretches in four directions The stress balance is excellent, and the flexibility is moderate. Therefore, the metal foil is laminated on the polyester film of the present invention, so that the metal foil has good ductility and is drawn by cold forming. In the case of the type (especially deep drawing or drawing), the metal foil is not broken, peeled, pinhole or the like, and a high-quality product (molded body) having high reliability can be obtained.

In addition, even if the thickness of the polyester film of the present invention is 25 μm or less, the stress balance in the four directions is excellent, and the uniformity of the thickness is excellent, so that the polyester film is laminated with the metal foil. The laminated body can be miniaturized by cold forming, which is also advantageous in terms of cost.

In the conventional polyester film, since the cold moldability is poor, it is necessary to laminate a resin film having a ductility such as a polyamide film when the laminate is formed. However, the polyester film of the present invention has sufficient a laminate film without a polyimide film. Since the cold formability is excellent, the laminating step and the miniaturized product can be shortened, and a laminate having excellent economic efficiency can be provided.

Further, according to the production method of the present invention, by adjusting the draw ratio of MD and TD and the temperature at the time of stretching to a specific range, it is possible to efficiently and efficiently produce a polyester film having the above-described excellent characteristics.

A‧‧‧ center point

X‧‧‧Test specimen for stress measurement when the polyester film is stretched in the reference direction (0° direction)

Fig. 1 is a view showing a collection position of a sample for measuring the stress at the time of elongation of the polyester film.

Fig. 2 is a view showing a method of measuring the thickness of a polyester film.

The invention is described in detail below.

The polyester resin constituting the polyester film of the present invention may, for example, be a polyester resin composed of a dicarboxylic acid component and a main alcohol component or a polyester resin composed of a hydroxycarboxylic acid component.

Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, sodium 5-sulfonate isophthalate, oxalic acid, succinic acid, and adipic acid. , azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, Cyclohexanedicarboxylic acid and the like.

Further, examples of the diol component include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and a ring. Ethylene oxide adduct of hexane dimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, bisphenol A or bisphenol S, and the like.

Examples of the hydroxycarboxylic acid component include ε-caprolactone, lactic acid, and 4-hydroxybenzoic acid.

The polyester resin constituting the polyester film of the present invention (hereinafter sometimes referred to as "the polyester resin (R) of the present invention)" may be a homopolymer or a copolymer composed of the above components, and may be a small amount. The ground contains trifunctional compounds such as trimellitic acid, trimellitic acid, pyromellitic acid, trimethylolpropane, glycerin, and neopentyl alcohol.

Further, the polyester resin (R) of the present invention may be used in combination of two or more kinds of homopolymers or copolymers composed of the above components.

Among them, the polyester resin (R) of the present invention has an ultimate viscosity before being supplied to the method for producing the polyester film of the present invention, preferably from 0.65 to 0.88, more preferably from 0.67 to 0.84. When the ultimate viscosity of the polyester resin (R) is In the above range, the polyester film of the present invention can be obtained by the production method of the present invention to be described later. When the ultimate viscosity of the polyester resin (R) is not within the above range, it tends to be difficult to obtain a film which satisfies the stress balance and the elastic modulus when stretched in four directions prescribed by the present invention.

When the ultimate viscosity of the polyester resin (R) of the present invention is adjusted to the above range, the temperature or time during the polymerization may be adjusted, and solid phase polymerization may be carried out in addition to the melt polymerization.

The ultimate viscosity of the polyester resin (R) of the present invention is obtained by dissolving 0.25 g of a polyester resin in 50 ml of phenol/tetrachloroethane = 5/5 (mass ratio) and using a Ubbelohde Viscometer. Determined at 25 ° C.

More specifically, the polyester resin (R) of the present invention preferably contains a polybutylene terephthalate resin (A) and a polyethylene terephthalate resin (B). In the polyester resin (R) of the present invention, the ratio of the polybutylene terephthalate resin (A) to the polyethylene terephthalate resin (B) is preferably 90% by mass or more, more preferably It is 95% by mass or more.

In the present invention, the polybutylene terephthalate resin (A) is mainly composed of terephthalic acid and 1,4-butanediol, and other components may be copolymerized therein. As the copolymerization component, the above-exemplified dicarboxylic acid component or diol component can be used.

In the present invention, when a copolymer is used as the polybutylene terephthalate resin (A), the type of the copolymerization component may be appropriately selected, but the ratio of the copolymerization component is a dicarboxylic acid component or a diol component. It is preferably 20 mol% or less, and more preferably 10 mol% or less. Regarding the polybutylene terephthalate resin (A), when the ratio of the copolymerization component exceeds 20 mol%, the fusion The point may be lower than the range described later, and as a result, the crystallinity may be lowered, and the heat resistance of the polyester film may be lowered.

In the polyester film of the present invention, the polybutylene terephthalate resin (A) preferably has a melting point of from 200 to 223 ° C, more preferably from 210 to 223 ° C. When the melting point is less than 200 ° C, the heat resistance of the polyester film is lowered.

The polyethylene terephthalate resin (B) of the present invention contains terephthalic acid and ethylene glycol as main polymerization components, and can copolymerize other components therein. As the copolymerization component, the above-exemplified dicarboxylic acid component or diol component can be used.

Further, the ratio of the copolymerization component is preferably 20 mol% or less of the acid component and the alcohol component, and more preferably 10 mol% or less.

The polyethylene terephthalate resin (B) preferably has a melting point of 225 to 260 ° C, more preferably 240 to 260 ° C. When the melting point is less than 225 ° C, the heat resistance of the polyester film is lowered.

The mass ratio (A/B) of the polybutylene terephthalate resin (A) to the polyethylene terephthalate resin (B) in the polyester resin of the present invention is preferably 5/95 to 40/ 60, more preferably 5/95 to 30/70, and even more preferably 5/95 to 25/75.

Since the aliphatic chain contained in the unit skeleton of the butylene terephthalate resin (A) has two more carbon atoms than the polyethylene terephthalate resin (B), the molecular chain is High mobility and high flexibility. By mixing the polybutylene terephthalate resin (A) with the polyethylene terephthalate resin (B), the flexibility of the obtained polyester film can be improved. That is, the higher the mass ratio of the polybutylene terephthalate resin (A) in the above range, the more It can enhance the softness of the polyester film. On the other hand, when the mass ratio of the polybutylene terephthalate resin (A) is less than the above range, the obtained polyester film will lack flexibility, resulting in an increase in the modulus of elasticity. Further, when the mass ratio of the polybutylene terephthalate resin (A) is higher than the above range, the obtained polyester film exhibits a characteristic of a strong polybutylene terephthalate resin (A). It becomes too soft to lower the elastic modulus, and heat resistance sometimes decreases.

The polyester resin (R) of the present invention preferably contains two kinds of poly pairs in addition to the above-mentioned polybutylene terephthalate resin (A) and polyethylene terephthalate resin (B). Ethylene phthalate resin (B), that is, a polyethylene terephthalate resin (Bc) containing a copolymerization component, and a polyethylene terephthalate resin substantially free of a copolymerization component ( Bh). In the polyester resin (R) of the present invention, the ratio of the polyethylene terephthalate resin (Bc) to (Bh) is preferably 90% by mass or more, and more preferably 95% by mass or more.

The polyethylene terephthalate resin (Bc) containing a copolymerization component is preferably polyethylene terephthalate copolymerized from isophthalic acid, and polyterephthalic acid containing a copolymerization component. The melting point of the ethylenediester resin (Bc) is preferably from 220 to 225 ° C, more preferably from 210 to 225 ° C. When the melting point is less than 200 ° C, the heat resistance of the polyester film is lowered.

When the polyester resin (R) of the present invention contains polyethylene terephthalate resin (Bc) and (Bh), the mass ratio (Bc/Bh) of (Bc) to (Bh) is preferably 5/. 95 to 40/60, more preferably 5/95 to 30/70, still more preferably 5/95 to 25/75.

There is no specific method for polymerizing a polyester resin such as the above polybutylene terephthalate resin (A) and polyethylene terephthalate resin (B). The definition is, for example, a transesterification method or a direct polymerization method. Examples of the transesterification catalyst include oxides or acetates of Mg, Mn, Zn, Ca, Li, and Ti. Further, examples of the polycondensation catalyst include oxides of Sb, Ti, and Ge, and acetates.

Since the polyester after polymerization contains acetaldehyde or tetrahydrofuran such as a monomer or an oligomer or a by-product, solid phase polymerization can be carried out at a temperature of 200 ° C or higher under reduced pressure or under an inert gas flow.

In the polymerization of the polyester resin, additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like may be added as needed. Examples of the antioxidant include a hindered phenol compound and a hindered amine compound. Examples of the heat stabilizer include a phosphorus compound, and examples of the ultraviolet absorber include a diphenylketone compound and benzene. And triazole compounds and the like. In addition, when the polyester resin contains two or more kinds of resins as in the case of the polybutylene terephthalate resin (A) and the polyethylene terephthalate resin (B), the reaction for suppressing such reactions is suppressed. The inhibitor is preferably a phosphorus compound.

Next, the characteristic values of the polyester film of the present invention will be described. The polyester film of the present invention is an index which is excellent in stress balance at the time of elongation in secondary processing, and must satisfy the following (1) and (2) at the same time. That is, the polyester film of the present invention must satisfy: (1) about setting any direction on the surface of the film to 0°, and winding four of 45°, 90°, and 135° clockwise with respect to the direction. The stress at 5% elongation in each direction of the direction, the difference between the maximum value and the minimum value of these stresses is 50 MPa or less; (2) in the stress at 15% elongation in each of the four directions described above, such stress The difference between the maximum value and the minimum value is 70MPa or less.

The difference between the maximum value and the minimum value (ΔF5) of the stress (F5) when 5% elongation in 4 directions, and the maximum value and minimum value of the stress (F15) when the elongation is 15% in 4 directions When the difference (?F15) exceeds the above range, the stress balance of the polyester film in all directions is poor, and it is difficult to obtain uniform moldability. In the case of a polyester film having a non-uniform moldability, for example, when a laminate having a metal foil laminated thereon is cold-formed, sufficient ductility cannot be imparted to the metal foil (that is, the polyester film is difficult to follow the metal foil), so that metal is likely to be generated. Fracture of the foil, or defects such as peeling, pinholes, and the like.

The ΔF5 must be 50 MPa or less, preferably 35 MPa or less, more preferably 25 MPa or less, still more preferably 15 MPa or less. The ΔF15 must be 70 MPa or less, preferably 60 MPa or less, more preferably 50 MPa or less, still more preferably 35 MPa or less.

In general, when a film is produced by a tenter sequential stretching method, the film is obtained in the form of a roll of a film wound into a cylinder, but the roll width of the obtained film roll is usually about 2 to 8m. The resulting film roll is then subjected to slit processing and shipped in the form of a roll width of about 1 to 3 m. In the tenter type sequential stretching method, since the both ends of the film are sandwiched by the fastener, the stress difference at the time of elongation is likely to occur in the vicinity of the central portion of the roll width of the film roll and the end portion. .

However, according to the production method of the present invention, in the obtained polyester film, ΔF5 can be set to 15 MPa or less and ΔF15 can be set to 35 MPa or less in the vicinity of the center portion of the film roll.

In addition, the polyester film should be stretched at 5% in 4 directions. The force (F5) is preferably from 80 to 130 MPa, more preferably from 85 to 125 MPa, even more preferably from 90 to 120 MPa, from the viewpoint of cold formability after the formation of the laminate. Further, the stress (F15) at 15% elongation is preferably from 80 to 160 MPa, more preferably from 90 to 155 MPa, still more preferably from 95 to 150 MPa from the viewpoint of cold formability after the formation of the laminate.

In the polyester film of the present invention, when the stress in the above four directions does not satisfy the above range at 5% and 15% elongation, sufficient cold moldability cannot be obtained.

The stress of the film of the present invention in the above four directions was measured as follows. First, after adjusting the polyester film for 2 hours at 23 ° C × 50% RH, as shown in Fig. 1, the reference direction of the film (0° direction) is arbitrarily specified with any point A on the film as a center point. ), and in the clockwise direction (b), the direction of 90° (c), and the direction of 135° (d) from the reference direction (a) to the clockwise direction, the four directions are used as the measurement direction, and then The strip shape from the center point A to each measurement direction was 100 mm, and the direction perpendicular to the measurement direction was 15 mm, and this was used as a sample. For example, as shown in Fig. 1, a sample X (length 100 mm × horizontal length 15 mm) is cut out from the center point A in a range of 30 mm to 130 mm in the 0° direction. For other directions, the sample was cut in the same manner. For these samples, a tensile tester (AG-1S manufactured by Shimadzu Corporation) equipped with a dynamometer for measuring 1 kN and a sample jig was attached, and the stress at 5% elongation was measured at a tensile speed of 500 mm/min ( F5) and stress at 15% elongation (F15). The measurement was performed for each direction in each sample number 5, and the average value was calculated as the stress value in each direction. Then, the difference between the maximum value and the minimum value of the stress values in four directions is obtained.

Regarding the above-mentioned reference direction (0°), when the MD in the stretching step can be discriminated at the time of film production, it is preferable to use MD as the reference direction.

Next, the polyester film of the present invention, as an index indicating flexibility having a suitable cold formability, must have an elastic modulus in the above four directions in the range of 2.0 to 3.5 GPa in either direction, and preferably. It is in the range of 2.2 to 3.4 GPa and is in the range of 2.4 to 3.3 GPa.

In the polyester film of the present invention, when the stress equalization in the above four directions simultaneously satisfies (1) and (2), and the elastic modulus in the above four directions is within the above range, the effect of the present invention can be attained. . That is, the metal foil is laminated on the polyester film of the present invention, so that the metal foil has good ductility, and is formed by cold forming (especially deep drawing or When the molding is pulled out, the metal foil is not broken, peeled, pinhole, or the like, and a highly reliable product (molded body) having high reliability can be obtained. When the polyester film has a modulus of elasticity of less than 2.0 GPa in any of the above four directions, the flexibility becomes excessive. On the other hand, when the polyester film has a modulus of elasticity exceeding 3.5 GPa in any of the above four directions, the flexibility is lowered. Further, when any one of the elastic moduli in the four directions of the polyester film is outside the range of the present invention, even if the stress balance in the four directions is satisfied while satisfying (1) and (2), it is impossible to Good ductility is imparted to the metal foil, which will lower the cold formability.

The elastic modulus of the polyester film of the present invention measured in the above four directions is measured by using a tensile tester (AG-1S manufactured by Shimadzu Corporation) when the stress in the four directions is measured.

Further, the polyester film of the present invention preferably exhibits a dry heat shrinkage ratio in the above four directions as an index indicating flexibility suitable for cold formability, and is preferably in the range of 0 to 10%. Preferably, it is in the range of 2 to 9.5%, and more preferably in the range of 2.5 to 9.0%. When the dry heat shrinkage ratio of the polyester film in the above four directions is within the above range, it is preferably in a range suitable for crystallization, and has flexibility suitable for cold formability.

When the polyester film exceeds 10% of the dry heat shrinkage ratio in the above four directions, crystallization may not proceed sufficiently, and the flexibility may become excessive. On the other hand, when the dry heat shrinkage rate of the polyester film in the above four directions is less than 0%, the crystallization proceeds excessively, and the flexibility may be lowered. In any case, cold formability is reduced.

The dry heat shrinkage ratio of the polyester film of the present invention in the above four directions was measured as follows.

According to the method of collecting the sample used for the measurement of the stress at the time of elongation, the polyester film is cut into a long strip so as to be 100 mm in each measurement direction from the center point A and 10 mm in the direction perpendicular to the measurement direction. Shape to collect samples.

The sample was conditioned for 2 hours (dimming 1) at 23 ° C × 50% RH, exposed to dry air at 160 ° C for 5 minutes, and then conditioned again at 23 ° C × 50% RH for 2 hours (conditioning 2 ). The length of the sample after the humidity control 1 and the length of the sample after the humidity control 2 were measured, and the dry heat shrinkage ratio was determined by the following formula. The measurement was carried out in the number of samples of 5, and the average value was taken as the dry heat shrinkage ratio.

Dry heat shrinkage rate (%) = {(sample length after humidity control 1 - sample length after humidity control 2) Degree) / sample length after conditioning 1} × 100

In the polyester film of the present invention, as an index indicating that the thickness accuracy (the uniformity of the thickness) is extremely high, a reference point is set on the film, and a plurality of measurement points are respectively set in the four directions from the reference point. The standard deviation of the measured value at the time of measuring the thickness at each measurement point is preferably 0.4 μm or less, more preferably 0.3 μm or less, still more preferably 0.28 μm or less.

When the standard deviation of the thickness accuracy (the uniformity of the thickness) of the polyester film is 0.4 μm or less, the variation in thickness is extremely small. For example, even if the thickness is 15 μm or less, the laminate bonded to the metal foil is deep. In the case of drawing and cooling, no defects such as peeling or pinholes are generated, and good moldability can be obtained.

A polyester film having a standard deviation of less than 0.4 μm and having a low thickness precision, especially when the thickness is small, when bonded to a metal foil, sufficient ductility cannot be imparted to the metal foil, resulting in deformation of the peeling layer or pinhole. Significantly, sometimes good formability cannot be obtained.

The above evaluation method of thickness accuracy is performed as follows. After the polyester film was conditioned at 23 ° C × 50% RH for 2 hours, as shown in Fig. 2, the reference direction (0° direction) of the film was arbitrarily specified with the arbitrary position on the film as the center point A. And from the reference direction (a) clockwise direction of 45° (b), 90° direction (c), and 135° direction (d), in each of the four directions, a total of four Straight lines L1 to L4 of 100 mm. The thickness at 10 points was measured by a length meter (HEIDENHAIN-METRO MT1287 manufactured by Haidenhain Co., Ltd.) at intervals of 10 mm from the center point on each straight line. Then calculate the average thickness of the 40 points measured on the four lines Value and use this as the thickness. Further, the standard deviation was calculated using the measured value of the thickness of 40 points. In the above-mentioned reference direction, when the MD in the stretching step can be discriminated at the time of film production, it is preferable to use MD as a reference direction.

In the present invention, the average thickness and the standard deviation may be based on a point (point A) of any one of the polyester films, and the manufacturing method according to the present invention, even at the end and the center of the obtained film roll The polyester film wound in the vicinity of the portion may also have an average thickness and a standard deviation within the above range.

The average thickness of the polyester film of the present invention is preferably 30 μm or less, more preferably 26 μm or less, still more preferably 16 μm or less. The polyester film of the present invention is suitable as a laminate which is bonded to a metal foil, and is suitable for use in cold forming, but is used in a tenter which is described later by using a stretching condition which satisfies specific conditions. In the axial stretching, even in the case of a film having a small thickness, the stress balance in the four directions is excellent, and the thickness accuracy (the uniformity of the thickness, etc.) in the above four directions is extremely high.

When the average value of the thickness of the polyester film exceeds 30 μm, moldability is lowered, and it is sometimes difficult to use it in a small battery exterior material, and there is also a concern that the cost is relatively unfavorable.

The thinner the polyester film, the more difficult it is to impart sufficient ductility to the metal foil. That is, the thinner the thickness, the more easily the thickness accuracy of the obtained film is lowered, and the more the stress during elongation is more likely to fluctuate, so that the cracking of the polyester film or the metal foil becomes remarkable due to the press-fitting force of cold forming. On the other hand, the polyester film of the present invention can be successfully provided in the above four directions by using a specific production method to be described later, in particular, even if the thickness is 26 μm or less. A polyester film excellent in stress balance and high in uniformity in thickness. The lower limit of the average value of the thickness of the polyester film of the present invention is not particularly limited, but is usually about 2 μm. When the average value of the thickness is less than 2 μm, the adhesion to the metal foil tends to be insufficient when it is bonded to the metal foil.

In the polyester film of the present invention, in order to improve the windability of the obtained polyester film in the production method of the present invention to be described later, particles may be added to the film. The particles to be blended in the polyester film are not particularly limited as long as they can impart smoothness, and examples thereof include cerium oxide, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Inorganic particles such as magnesium, kaolin, alumina, and titanium oxide. Further, heat-resistant organic particles such as a thermosetting urea resin, a thermosetting phenol resin, a thermosetting epoxy resin, or a benzoguanamine resin can also be used. Further, in the production step of the polyester resin, a precipitated particle obtained by precipitating and finely dispersing a part of the metal compound such as a catalyst 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, and a flat shape can be used. Further, there are no particular restrictions on the hardness, specific gravity, color, and the like. These particles may be used in combination of two or more kinds as needed.

On at least one side of the polyester film of the present invention, a coating layer of one or more layers may be laminated. For example, a coating layer capable of imparting electrolyte resistance, acid resistance, alcohol resistance, abrasion resistance, electrostatic resistance, printability, and adhesion can be mentioned.

Further, in terms of easy handling for improving the adhesion of the substrate to the aluminum foil, the polyester film may be surface-treated to exhibit an easy-to-attach effect.

Wherein, the polyester film of the present invention is used for lifting Preferably, the coating layer has a puller layer at least on one side. By having a pull-up layer and laminating a laminate of the polyester film of the present invention and a metal foil, the adhesion between the polyester film and the metal foil can be improved, and the ductility can be more effectively imparted to the metal foil during cold forming. Therefore, not only the metal foil can be easily broken, but also the effect of suppressing the peeling can be effectively exhibited.

The main component of the puller layer may, for example, be a water-soluble or water-dispersible polyurethane compound, an acrylic compound or a polyester compound, and is preferably an anionic water-dispersible polyurethane resin. The hardener of the puller layer may, for example, be a melamine compound or an isocyanate compound. Oxazoline compound.

The thickness of the puller layer is preferably from 0.01 to 0.5 μm. When the thickness of the puller layer is thinner than 0.01 μm, the adhesion is lowered. When the thickness of the puller layer is thicker than 0.5 μm, there is no significant change in the easy adhesion, which may cause the film roll to be rubbed or agglomerated, resulting in back transfer of the puller layer, or when the film is unwound. The damage of the puller layer or even the breakage of the film is missing, and the cost side is also disadvantageous.

In order to form the pull-up layer, as a method of applying the aqueous solution or the aqueous dispersion of the above compound, any known method can be selected, and for example, a bar coating method, an air knife coating method, a reverse roll coating method, or a gravure roll coating method can be applied.

If necessary, a lubricating material for blocking agglomeration or a wetting material for improving coating properties may be added to the puller layer without affecting the adhesion.

Hereinafter, the manufacturer of the polyester film of the present invention will be described in detail. law. The polyester film of the present invention which satisfies the above characteristic values can be obtained by the polyester film of the present invention.

Hereinafter, a method for producing a polyester film composed of a polyester resin (R) containing a polybutylene terephthalate resin (A) and a polyethylene terephthalate resin (B) will be described as an example. The polyester film of the present invention can be produced by a sheet forming step and a subsequent stretching step.

In the sheet forming step, the polyester resin (R) is formed into a sheet shape to obtain an unstretched sheet.

The polyester resin (R) can be prepared in accordance with a generally known method. For example, the raw material containing the polybutylene terephthalate resin (A) and the polyethylene terephthalate resin (B) can be put into an extruder equipped with a heating device, and at 270 to It is obtained by melt-kneading at 300 ° C for 3 to 15 minutes. The melt-kneaded resin composition was extruded in a T-die and cooled and solidified by a die-casting roll whose temperature was adjusted to 50 ° C or lower, whereby an unstretched sheet of a sheet-like formed body was obtained.

The average value of the thickness of the unstretched sheet is not particularly limited, and is generally preferably from about 15 to 250 μm, more preferably from 50 to 235 μm. By setting the average value of the thickness of the unstretched sheet within the above range, stretching can be performed more efficiently.

In the stretching step, the stretched film can be obtained by subjecting the unstretched sheet to biaxial stretching in the machine direction (MD) and the transverse direction (TD) sequentially or simultaneously.

Synchronous biaxial stretching can be exemplified by using a tenter to hold both ends of the unstretched film, stretching in the MD direction, and stretching to the TD. The method of biaxial stretching of MD and TD is carried out step by step.

On the other hand, in the sequential biaxial stretching, it is preferred to stretch in at least one direction of MD and TD by a tenter, whereby a more uniform film thickness can be obtained. The sequential biaxial stretching using a tenter is: (1) by stretching the unstretched sheet through a plurality of rolls having different rotation speeds, and then stretching the film by a tenter. TD stretching method; (2) stretching the unstretched sheet to the MD by a tenter, and then stretching the stretched film to TD by a tenter. The method of the above (1) is particularly preferable from the viewpoint of physical properties, productivity, and the like of the obtained film. The sequential biaxial stretching using a tenter is advantageous in terms of productivity, equipment, and the like because it is stretched by the roll to the MD, and since it is stretched by the tenter to the TD, the film thickness is controlled. Etc.

In the production method of the present invention, in the stretching step, it is necessary to satisfy the following (a) and (b) at the same time as the MD stretching ratio (DR _MD ) and the TD stretching ratio (DR _TD ). It is important that the unstretched sheets are biaxially stretched sequentially or simultaneously.

0.70≦DR _MD /DR _TD ≦0.90 (a)

12.5≦DR _MD ×DR _TD ≦15.5 (b)

When the above-mentioned (a) and (b) are not satisfied, the obtained polyester film is inferior in stress balance in four directions, and it is difficult to obtain the polyester film of the present invention.

That is, when the draw ratio (DR _MD /DR _TD ) is less than 0.70, the TD magnification becomes a high magnification with respect to the MD magnification, so the stress value of the polyester film in the stress-strain curve of TD becomes high, And become low elongation. On the other hand, when the draw ratio ratio (DR _MD /DR _TD ) exceeds 0.90, the MD magnification becomes a high magnification with respect to the TD magnification, so the stress value of the MD of the polyester film in the stress-strain curve becomes high, And become low elongation. Further, since the stress-strain curves in the 45° direction and the 135° direction are also affected, as a result, it is difficult to obtain the difference between the maximum value and the minimum value of the stress at the time of elongation specified by the present invention (ΔF5, ΔF15). The polyester film of the condition.

Further, when the surface magnification (DR _MD × DR _TD ) is less than 12.5, the surface magnification is too low and the stretching is insufficient, so that the polyester film cannot obtain sufficient molecular alignment. On the other hand, when the surface magnification (DR _MD × DR _TD ) exceeds 15.5, the surface magnification is too high, so that the polyester film cannot be uniformly stretched in all directions during stretching, and as a result, it is difficult to simultaneously satisfy the requirements of the present invention. The condition of the difference between the maximum value and the minimum value (ΔF5, ΔF15) of the stress at the time of elongation.

The draw ratio ratio (DR _MD /DR _TD ) and the area magnification (DR _MD ×DR _TD ) must satisfy (a) and (b) as described above, and it is preferable to set the DR _MD to 3.0 to 3.7, The best is set to 3.1 to 3.6.

In the case of sequential biaxial stretching, it is preferred to carry out the first stretching of the first stretched film by stretching the unstretched sheet in the longitudinal direction (MD) in a temperature range of 65 to 105 ° C, more preferably It is carried out at a temperature ranging from 70 to 100 °C. Next, the first stretched film is preferably stretched in the transverse direction (TD) in a temperature range of 90 to 160 ° C to obtain a second stretch of the second stretched film, more preferably at 100 to 150 ° C. Performed within the temperature range. The temperature in the stretching step can be set and controlled while preheating, for example, by a preheating roll or a preheating zone of a tenter.

By the temperature range of the first stretching and the temperature of the second stretching When the degree range is set within the above range, the polyester film of the present invention can be obtained with certainty. Then, it is preferable that both the first stretching and the second stretching are in the above temperature range, and the temperature is gradually increased along the pulling direction of the film.

Further, the simultaneous biaxial stretching and the sequential biaxial stretching using a tenter are preferably performed after the stretching to perform a relaxation heat treatment. The temperature in the relaxation heat treatment is preferably from 160 to 210 ° C, more preferably from 170 to 210 ° C. The temperature in the relaxation heat treatment can be set and controlled in the preheating zone of the tenter. Further, the relaxation rate in the relaxation heat treatment is preferably from 2 to 9%, more preferably from 3 to 7%.

The means for setting the temperature at the time of stretching or relaxing heat treatment to the above range includes a method of blowing hot air to the surface of the film, a method of using a far infrared ray or a near infrared ray heater, and a method of combining the same. In the present invention, it is preferred to include a method of blowing hot air.

Further, in the case of obtaining a polyester film of the present invention having at least one side of the film surface and having an easy-to-adhere layer, it is preferably carried out by the same stretching method and stretching conditions as described above. In order to form an easy-adhesion layer on the surface of the film, in the above production method, it is preferred to apply an easy-to-adhere layer-forming aqueous coating agent to the polyester film after the MD has been stretched. Then, it is preferred to apply the film together with the aqueous coating agent to TD stretching (in-mold coating) under the same stretching conditions as described above. The coating amount of the aqueous coating agent is preferably adjusted so that the thickness of the easy-adhesion layer formed on the surface of the stretched film becomes 0.01 to 10 μm.

Further, the laminate of the present invention comprises a polyester film and a metal foil. Representative examples of the laminate of the present invention include the present invention. A polyester film and a laminate of metal foil laminated on the film. In this case, the polyester film of the present invention may be laminated in such a manner as to be in direct contact with the metal foil, or may be laminated in a state in which another layer such as an adhesive layer is interposed. In particular, in the present invention, it is preferred to laminate the laminate of the film/metal foil/sealant film of the present invention in this order. At this time, an adhesive layer may be interposed between the layers or an adhesive layer may be interposed.

Since the polyester film of the present invention can impart good ductility to the metal foil, it is not necessary to laminate another resin film having ductility such as a polyamide film.

The metal foil may, for example, be a metal foil (including an alloy foil) containing various metal elements (aluminum, iron, copper, nickel, etc.), and in particular, a pure aluminum foil or an aluminum alloy foil may be used. It is preferable that the aluminum alloy foil contains iron (aluminum-iron-based alloy, etc.), and the other components are within a known content range defined by JIS or the like within a range that does not impair the moldability of the laminate. It can contain any component.

The thickness of the metal foil is not particularly limited, and is preferably from 15 to 80 μm, particularly preferably from 20 to 60 μm, from the viewpoint of moldability.

The sealant film constituting the laminate of the present invention is preferably a thermoplastic resin having heat sealability such as polyethylene, polypropylene, olefin copolymer or polyvinyl chloride. The thickness of the sealant film is not limited, and is usually preferably from 20 to 80 μm, particularly preferably from 30 to 60 μm.

[Examples]

The invention will be described in detail below by way of examples. However, the invention is not limited to the following examples. The properties of the polyester film and the laminate were measured by the following methods.

Further, the obtained film roll was divided into three equal parts in the width direction. The film roll located at the center is set to "a", and the film roll on the right side when viewed from the upstream side in the moving direction of the film is set to "b", and is located on the left side when viewed from the upstream side in the moving direction of the film. The film roll is set to "c".

(1) Stress, modulus of elasticity, dry heat shrinkage rate in four directions of 5% elongation of polyester film and 15% elongation

The stress, the modulus of elasticity, and the dry heat shrinkage rate in four directions when the polyester film is 5% stretched and 15% stretched, the reference direction (0° direction) is MD, and the method described above is used. Measured and calculated.

At this time, samples were taken from the film roll "a" and the film roll "b" and measured. In the film reels "a" and "b", a film collected from a position half the volume is used, and the center point in the width direction is set to the center point A as shown in Fig. 1.

The values in the film reel "b" were measured only in the examples and comparative examples shown in Table 7.

(2) Average thickness and standard deviation of polyester film

The average thickness and standard deviation of the polyester film were measured and calculated by the above methods.

At this time, samples were taken from the film roll "a", the film roll "b", and the film roll "c", and were measured. In the film reels "a" and "b", a film collected from a position half the volume is used, and a center point in the width direction is set as a center point A as shown in Fig. 2 . In the film reel "c", use from the end of the roll The film collected in the vicinity was set to a position of 20 cm from the end on the left side when viewed from the upstream side in the moving direction of the film, and was set as the center point A as shown in Fig. 2 .

(3) Cold formability

After the obtained laminate was conditioned at 23 ° C × 50% RH for 1 hour or more, an Erichsen tester (No. 5755, manufactured by Yasuda Seiki Co., Ltd.) was used according to JIS Z2247 at 23 ° C × 50% RH. The steel ball punch is pressed to the laminated body at a predetermined pressing depth to obtain an Aison value. The size of the laminate of the sample was 10 cm in length and 10 cm in length. The Aison value was measured every 0.5 mm, and the measurement was performed for each sample number 5, and the average value was calculated.

When the Aristotle value is 6.5 mm or more, especially when it is 7 mm or more, it is judged to be suitable for deep drawing.

As the polyester resin (R), the following polyester resin was used.

A-1: polybutylene terephthalate (NOVADURAN 5010S manufactured by Mitsubishi Engineering Plastic Co., Ltd., ultimate viscosity: 1.10)

A-2: polybutylene terephthalate (NOVADURAN 5505S manufactured by Mitsubishi Engineering Plastic Co., Ltd., ultimate viscosity: 0.92)

Bh-1: polyethylene terephthalate (UT-CBR, Nippon Ester, ultimate viscosity: 0.67)

Bh-2: polyethylene terephthalate (NEH2050, manufactured by Nippon Ester, ultimate viscosity: 0.78)

Bh-3: polyethylene terephthalate copolymerized from isophthalic acid (MA-1342, manufactured by Nippon Ester Co., Ltd., ultimate viscosity: 0.63)

Bh-4: polyethylene terephthalate copolymerized from isophthalic acid (SA-1345, manufactured by Nippon Ester Co., Ltd., ultimate viscosity: 0.78)

Example 1 (Production of polyester film)

The above A-1 and Bh-1 were mixed at a mass ratio (A-1/Bh-1) 5/95, and as a polyester resin (R), coagulation and oxidation were added so that the ceria content became 0.05% by mass. The base metal (GS-BR-MG, manufactured by Nippon Ester Co., Ltd.) was melted at 280 ° C, extruded from the T-die outlet at a residence time of 5 minutes, quenched and solidified, and the thickness after stretching was 25 μm. An unstretched film was obtained.

The unstretched film is then stretched one by one. First, it was heated to 85 ° C by a longitudinal stretching machine using a heating roll, and stretched 3.4 times to MD, followed by transverse stretching at 120 ° C, and 4.25 times to TD. In this stretching, the draw ratio ratio (DR _MD /DR _TD ) was 0.80, and the area magnification (DR _MD ×DR _TD ) was 14.5.

Next, the relaxation heat treatment temperature was set to 190 ° C, the relaxation rate of TD was set to 6.0%, and after a gentle heat treatment for 4 seconds, the film was cooled to room temperature to obtain a polyester film having a thickness of 25 μm. The obtained polyester film was taken up in a roll shape.

(production of laminate)

Then, a two-liquid polyurethane adhesive (TM-K55/CAT-10L, manufactured by Toyo Morton Co., Ltd.) was applied to the obtained polyester film so as to have a coating amount of 5 g/m ² , and dried at 80 ° C. 10 seconds. An aluminum foil (AA size 8079P, thickness 50 μm) was attached to the adhesive-coated surface. Then, the same type of adhesive was applied to the aluminum foil side of the aluminum foil adhered to the polyester film under the same conditions, and an unstretched polypropylene film (GHC manufactured by Mitsui Chemicals Tohcello Co., Ltd., thickness: 50 μm) was bonded thereto at 40 ° C. The aging treatment was carried out for 72 hours to prepare a laminate.

Examples 2 to 67 and Comparative Examples 1 to 34

In addition to the type and mass ratio of the polyester resin used as the polyester resin (R), the draw ratio of MD and TD, the stretching temperature, the relaxation heat treatment temperature, the relaxation rate, and the thickness after stretching, it is changed to Other than those described in Tables 1 to 7, the same procedure as in Example 1 was carried out to obtain a polyester film. When the thickness after stretching is changed, the supply amount of the polyester resin (R) extruded from the T-die outlet is changed.

Using the obtained polyester film, a laminate was obtained in the same manner as in Example 1.

The composition, production conditions, and characteristic values of the polyester films obtained in Examples 1 to 67 and Comparative Examples 1 to 34 and the cold formability of the obtained laminate were as shown in Tables 1 to 7.

From these results, it is clear that in Examples 1 to 67, since the draw ratio ratio (DR _MD /DR _TD ) and the area magnification (DR _MD ×DR _TD ) are within the range prescribed by the present invention, The difference between the maximum value and the minimum value of the stress of the polyester film when 5% elongation in four directions is 50 MPa or less, and the difference between the maximum value and the minimum value of the stress at the time of 15% elongation is 70 MPa or less, and is 4 The elastic modulus in each direction is in the range of 2.0 to 3.5 GPa. Further, the standard deviation of the thickness in four directions is 0.4 μm or less, and the uniformity of thickness is also excellent.

Further, it is clear from the embodiment shown in the seventh table that even if the end portion of the wound width of the film roll that is wound up satisfies the above characteristic value, the entire width of the film roll can be satisfied. The polyester film of the characteristic value of the invention.

Further, the laminate obtained by using the polyester film which satisfies the characteristic value specified in the present invention has a high Aison value, and has a uniform ductility in all directions after cold forming. That is, the polyester film of each of the examples has excellent cold formability without causing breakage of the aluminum foil, peeling, pinhole, or the like at the time of cold forming.

On the other hand, in Comparative Examples 1 to 33, since the draw ratio ratio (DR _MD /DR _TD ) or the area magnification (DR _MD ×DR _TD ) when the polyester film was obtained was not within the range specified by the present invention, Therefore, the obtained polyester film does not satisfy the above characteristic values of the present invention. Further, in Comparative Example 34, the polyester resin constituting the polyester film had a high ultimate viscosity and the relaxation heat treatment temperature was too low, so that the obtained polyester film did not satisfy the above-described characteristic value of the present invention. Therefore, the laminate obtained by using the polyester films of Comparative Examples 1 to 34 had a low Aison value and did not have uniform ductility in all directions after cold forming. Therefore, at the time of cold forming, breakage of the aluminum foil, peeling, pinholes, and the like occur, and the cold moldability is poor.

The drawings in this case all indicate their test methods, which are not representative

In this case, the technical features of the invention are requested in the scope of patent application, so there is no designated representative figure in this case.

Claims (8)

A polyester film for use in cold forming, characterized in that it is set to 0° in any direction on the surface of the film, and is wound in a clockwise direction of 45°, 90°, and 135° with respect to the direction. The stress at 5% elongation in each direction of the direction, the difference between the maximum value and the minimum value of these stresses is 50 MPa or less, and the stress at 15% elongation in each of the four directions is the maximum value of these stresses. The difference in minimum value is 70 MPa or less, and the elastic modulus of the polyester film in the above four directions is in the range of 2.0 to 3.5 GPa in either direction, and the average value of the thickness of the polyester film in the above four directions is 30 μm or less. The polyester film according to claim 1, wherein the dry heat shrinkage ratio in the above four directions is in the range of 0 to 10%. The polyester film according to claim 1 or 2, wherein the standard deviation of the thickness in the four directions is 0.4 μm or less. A laminate comprising a polyester film and a metal foil according to any one of claims 1 to 3, which is used for cold forming. The laminate according to claim 4, wherein the metal foil has a thickness of 15 to 80 μm. The laminate according to claim 4, wherein the laminate is provided with a metal foil, an adhesive layer, and a polyester film according to any one of claims 1 to 3. By. A method for producing a polyester film, which is a method for producing a polyester film according to any one of claims 1 to 3, which is to make a stretching ratio in a machine direction (MD) (DR _MD ) and the transverse (TD) stretching ratio (DR _TD ) satisfy the following modes (a) and (b), and the unstretched sheet is subjected to sequential biaxial stretching at a temperature range of 65 to 105 ° C. The unstretched sheet is stretched in the machine direction (MD) to obtain the first stretch of the first stretched film, and the first stretched film is stretched in the transverse direction (TD) in a temperature range of 100 to 150 °C. The second stretch of the second stretched film was obtained, and the temperature was gradually increased along the pulling direction of the film, 0.70 ≦ DR _MD /DR _TD ≦ 0.90 (a) 12.5 ≦ DR _MD × DR _TD ≦ 15.5 (b). The method for producing a polyester film according to claim 7, wherein the biaxially stretched film is heat-treated in a temperature range of from 160 to 210 °C.