JP2021119237A - Polyester film, laminate, and production method for polyester film - Google Patents

Abstract

To provide a polyester film which imparts extensibility to a metal foil by resin, thereby capable of suppressing breakage of the metal foil, delamination between the resin film and the metal foil, and occurrence of pinhole even under various conditions such as draw depth, pressure, velocity during cold forming and which is suitable for cold forming application.SOLUTION: There is provided a polyester film, in which about stresses at the time of 5% elongation and stresses at the time of 15% elongation in each of four directions of 45°, 90° and 135° in a clockwise direction to 0° being an arbitrary direction on a film surface, stresses (A) measured at tensile speed of 100 mm/min and stresses (B) measured at tensile speed of 1000 mm/min satisfy the following conditions (1) and (2). Condition (1): the stresses at the time of 5% elongation in each of four directions are 70 to 120 MPa together with the stresses (A) and the stresses (B), and a difference between both stresses in each of four directions [the stresses (A)-the stresses (B)] are 15 MPa or less. Condition (2): the stresses at the time of 15% elongation in each of four directions are 90 to 180 MPa together with the stresses (A) and the stresses (B), and a difference between both stresses in each of four directions [the stresses (A)-the stresses (B)] are 10 MPa or less.SELECTED DRAWING: None

Description

The present invention relates to a novel polyester film having a stress during elongation in a specific range and a method for producing the same. Furthermore, the present invention relates to a laminate containing the polyester film.

Polyester films are used in a wide range of fields such as packaging films, magnetic tape films, optical films, and electronic component films because they are excellent in heat resistance, chemical resistance, and insulating properties.

In recent years, laminated lithium-ion battery exterior materials, press-through packs, and the like have been obtained by cold-molding a laminate composed of a resin film or a metal foil.
The laminate for cold molding is generally a nylon film (Ny) / aluminum foil (Al foil) / unstretched polypropylene film (CPP) or a polyethylene terephthalate film (PET) / Ny / Al foil /. A structure such as CPP is adopted, and a nylon film is laminated on the laminate containing the Al foil in order to impart ductility and enable cold molding.
However, in addition to the fact that the laminated body is directly linked to an increase in cost due to the lamination of the nylon film, the nylon film is inferior in heat resistance to the polyester film, so that the physical properties are deteriorated due to thermal deterioration under high temperature and high humidity. There is a problem, and since it is hygroscopic, there is a problem that the dimensions change due to hygroscopicity, and there is a problem that the obtained packaging bag may be curled.

On the other hand, the polyester film is harder and more brittle than the nylon film, and is generally manufactured by the tenter type sequential stretching method, so that it has a large anisotropy and imparts ductility to the metal foil laminated on the polyester film. It was difficult to do. However, a polyester film capable of forming a laminated body having excellent cold moldability has been proposed. For example, in Patent Documents 1 and 2, the stress during elongation in the longitudinal direction and the width direction of the film is defined in a specific range. The polyester film for packaging a lithium battery is disclosed. In recent years, as a laminate used for a laminated lithium-ion battery exterior material, a press-through pack, etc., a structure such as PET / Al foil / CPP in which only a polyester film is used as an outer layer without using a nylon film. Has been adopted.

When cold-molding a laminate in which a metal foil is laminated on a resin film, it is important to impart malleability to the metal foil by the resin film. Since the resin film has a direction in which it is easily stretched and a direction in which it is difficult to stretch, the metal foil is broken during cold molding, delamination between the resin film and the metal foil occurs, and pinholes occur. When such a problem occurs, the obtained molded body cannot function as a package or the like, which may lead to damage to the packaged body (contents) or the like. In cold molding, the mold shape and molding depth are also diverse, so stable moldability that can be adapted to various machining conditions (for example, various pressures and speeds during draw molding) can be achieved. There is a demand for a polyester film to have.

In this way, even under various cold molding conditions, the resin film can impart spreadability to the metal foil, causing the metal foil to break, causing delamination between the resin film and the metal foil, and pinholes. Although the development of a polyester film is eagerly desired as a resin film having good cold moldability and preventing the occurrence of such a film, the current situation is that such a film has not yet been developed. ..

Japanese Unexamined Patent Publication No. 2004-362953 International Publication No. 2015/125806

According to the present invention, the resin film can impart ductility to the metal foil even under various processing conditions such as drawing depth, pressure, and speed during cold molding, and the metal foil may break or the resin film may be formed. It is an object of the present invention to provide a polyester film which can prevent delamination with a metal foil or pinholes and is suitable for cold molding use.

As a result of diligent studies to solve the above problems, the present inventor has found that a polyester film in which stress in the four directions measured under two kinds of measurement conditions satisfies a specific range is suitable for various cold molding conditions and is a metal. We have found that it is possible to impart malleability to a foil, and have arrived at the present invention.
That is, the gist of the present invention is as follows.
[1] The stress at 5% elongation and the stress at 15% elongation in each of the four directions of 45 °, 90 °, and 135 ° clockwise with respect to the arbitrary direction of the film surface as 0 °. A polyester film, wherein the stress (A) measured at a tensile speed of 100 mm / min and the stress (B) measured at a tensile speed of 1000 mm / min satisfy the following conditions (1) and (2).
Condition (1): The stress at 5% elongation in each of the four directions is 70 to 120 MPa for both the stress (A) and the stress (B), and the difference between the two stresses in each of the four directions [stress]. (A) -Stress (B)] is 15 MPa or less.
Condition (2): The stress at the time of 15% elongation in each of the four directions is 90 to 180 MPa for both the stress (A) and the stress (B), and the difference between the two stresses in each of the four directions [stress]. (A) -Stress (B)] is 10 MPa or less.
[2] The polyester film according to [1], wherein the density is 1.360 to 1.400 g / cm ^3.
[3] The polyester film according to [1] or [2], wherein the average value of the thicknesses in the four directions is 30 μm or less.
[4] A laminate containing the polyester film and metal leaf according to any one of the above [1] to [3].
[5] A laminate obtained by laminating a metal foil, an adhesive layer, and the polyester film according to any one of [1] to [3] in this order.
[6] The method for producing the polyester film according to any one of [1] to [3] above, wherein the unstretched sheet is sequentially biaxially stretched in the vertical direction (MD) and the horizontal direction (TD). In simultaneous biaxial stretching,
The lateral (TD) stretching is performed in three stages, the film width W ₀ before the lateral stretching, the film width W ₁ after the first lateral stretching, and the film width after the second lateral stretching. W _{2 and the film width W 3} after the third-stage lateral stretching satisfy the following (a).
In addition, the stretching ratio (DR _MD ) in the vertical direction (MD) and the total stretching ratio (DR _TD = W ₃ / W ₀ ) in the horizontal direction (TD) satisfy the following (b) and (c). A method for producing a polyester film, which comprises biaxial stretching.
W _2- W ₁ <W _1- W ₀ <W _3- W ₂ (a)
0.70 ≤ DR _MD / DR _TD ≤ 0.90 (b)
12.5 ≤ DR _MD x DR _TD ≤ 15.5 (c)
[7] In sequential biaxial stretching,
The unstretched sheet is stretched in the longitudinal direction (MD) to obtain a longitudinally stretched film, which is subjected to longitudinal stretching in a temperature range of 65 to 105 ° C.
The method for producing a polyester film according to [6], wherein the longitudinally stretched film is stretched laterally (TD) in a temperature range of 90 to 160 ° C.
[8] The method for producing a polyester film according to [6] or [7], wherein the film after biaxial stretching is heat-treated in a temperature range of 160 to 210 ° C.

In the polyester film of the present invention, the stress at the time of elongation in the four directions measured under two kinds of measurement conditions satisfies a specific range, so that the laminate obtained by laminating the metal foil on the polyester film of the present invention is a metal foil. Has good ductility, and when drawing molding (especially deep drawing molding or overhang molding) by cold molding under various conditions and specifications, the metal foil breaks and the metal foil and the polyester film are separated. It is possible to obtain a highly reliable high-quality product (molded body) without causing lamination, pinholes, or the like.
Since the conventional polyester film is inferior in cold moldability, it is necessary to laminate a stretchable resin film such as a nylon film when forming a laminate. However, the polyester film of the present invention is made of nylon. Since it has sufficiently excellent cold moldability without laminating films, it is possible to shorten the laminating process and obtain a miniaturized product, and it is possible to provide a laminated body having excellent economic efficiency. can.
Further, according to the production method of the present invention, by adjusting the stretching ratio of MD and TD and the temperature at the time of stretching within a specific range, the polyester film having the above-mentioned excellent properties can be efficiently produced. Can be manufactured well.

It is a figure which shows the sampling position of the sample for measuring the stress at the time of elongation of a polyester film. It is a figure which shows the method of measuring the thickness of a polyester film.

Hereinafter, the present invention will be described in detail.
Examples of the polyester resin constituting the polyester film of the present invention include a polyester resin composed of a dicarboxylic acid component and a diol component, and a polyester resin composed of a hydroxycarboxylic acid component.

The dicarboxylic acid components include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedic acid, and dimer. Examples thereof include acids, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid and cyclohexanedicarboxylic acid.

The diol components include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, and polypropylene glycol. , Polytetramethylene glycol, ethylene oxide adducts of bisphenol A and bisphenol S, and the like.

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

The polyester resin constituting the polyester film of the present invention (hereinafter, may be abbreviated as "polyester resin (R) in the present invention") may be a homopolymer composed of the above components or a copolymer, and further, trimellitic acid. It may contain a small amount of a trifunctional compound component such as trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol.
Further, as the polyester resin (R) in the present invention, two or more kinds of homopolymers and copolymers composed of the above components may be used in combination.

Among them, the polyester resin (R) in the present invention preferably has an ultimate viscosity of 0.65 to 0.88 before being used in the method for producing a polyester film of the present invention, and more preferably 0.67 to 0.84. Those are preferable. When the ultimate viscosity of the polyester resin (R) is within the above range, the polyester film of the present invention can be obtained by the production method of the present invention described later. If the ultimate viscosity of the polyester resin (R) is not within the above range, it tends to be difficult to obtain a film that satisfies the stress balance and elastic modulus at the time of elongation in four directions specified in the present invention.
In order to adjust the ultimate viscosity of the polyester resin (R) in the present invention to be within the above range, the temperature and time at the time of polymerization may be adjusted, and solid-phase polymerization may be performed in addition to melt polymerization. ..

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

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

In the present invention, the polybutylene terephthalate resin (A) contains terephthalic acid and 1,4-butanediol as a main polymerization component, and may be copolymerized with other components. As the copolymerization component, the dicarboxylic acid component and the diol component exemplified above can be used.
In the present invention, when a copolymer is used as the polybutylene terephthalate resin (A), the type of the component to be copolymerized may be appropriately selected, but the ratio of the copolymerization component is 20 for both the dicarboxylic acid component and the diol component. It is preferably mol% or less, and more preferably 10 mol% or less. When the proportion of the copolymerization component of the polybutylene terephthalate resin (A) exceeds 20 mol%, the melting point may be lower than the range described later, and as a result, the crystallinity is lowered and the heat resistance of the polyester film is lowered. Sometimes.

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

The polyethylene terephthalate resin (B) in the present invention contains terephthalic acid and ethylene glycol as main polymerization components, and may be copolymerized with other components. As the copolymerization component, the dicarboxylic acid component and the diol component exemplified above can be used.
The proportion of the copolymerization component is preferably 20 mol% or less, and more preferably 10 mol% or less for both the acid component and the alcohol component.

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

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

Compared with the polyethylene terephthalate resin (B), the polybutylene terephthalate resin (A) has two more carbon atoms in the aliphatic chain contained in the unit skeleton, so that the molecular chain has high mobility and high flexibility. By mixing the polybutylene terephthalate resin (A) with the polyethylene terephthalate resin (B), the resulting polyester film has increased flexibility. That is, the higher the mass ratio of the polybutylene terephthalate resin (A) within the above range, the more flexible the polyester film is. On the other hand, when the mass ratio of the polybutylene terephthalate resin (A) is lower than the above range, the obtained polyester film has poor flexibility and a high elastic modulus. Further, when the mass ratio of the polybutylene terephthalate resin (A) is higher than the above range, the obtained polyester film strongly exhibits the characteristics of the polybutylene terephthalate resin (A), becomes too flexible, and has a low elastic modulus. In addition, heat resistance may decrease.

The polyester resin (R) in the present invention contains two types of polyethylene terephthalate resin (B), that is, copolymerization, in addition to the above-mentioned one containing the polybutylene terephthalate resin (A) and the polyethylene terephthalate resin (B). It is preferable that the polyethylene terephthalate resin (Bc) containing the component and the polyethylene terephthalate resin (Bh) containing substantially no copolymerization component are contained. Above all, in the polyester resin (R) of the present invention, the ratio of the polyethylene terephthalate resin (Bc) and (Bh) is preferably 90% by mass or more, and more preferably 95% by mass or more.

As the polyethylene terephthalate resin (Bc) containing a copolymerization component, polyethylene terephthalate obtained by copolymerizing isophthalic acid is preferable, and the melting point of the polyethylene terephthalate resin (Bc) containing a copolymerization component is 200 to 225 ° C. It is preferably 210 to 225 ° C., more preferably 210 to 225 ° C. If the melting point is less than 200 ° C., the heat resistance of the polyester film is lowered.

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

The method for polymerizing the polyester resin such as the polybutylene terephthalate resin (A) and the polyethylene terephthalate resin (B) described above is not particularly limited, and examples thereof include a transesterification method and a direct polymerization method. Examples of the transesterification catalyst include oxides of Mg, Mn, Zn, Ca, Li and Ti, acetates and the like. Examples of the polycondensation catalyst include oxides of Sb, Ti, and Ge, acetates, and the like.

Since the polymerized polyester contains monomers, oligomers, by-products such as acetaldehyde and tetrahydrofuran, solid-phase polymerization may be carried out at a temperature of 200 ° C. or higher under reduced pressure or an inert gas flow.

In the polymerization of the polyester resin, additives such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents and the like can be added, if necessary. Antioxidants include, for example, hindered phenol compounds and hindered amine compounds, heat stabilizers include, for example, phosphorus compounds, and ultraviolet absorbers include, for example, benzophenone compounds and benzotriazole compounds. And so on. Further, when the polyester resin contains two or more kinds of resins so as to contain the polybutylene terephthalate resin (A) and the polyethylene terephthalate resin (B), as a reaction inhibitor that suppresses the reaction between them. It is preferable to add a phosphorus-based compound.

Next, the characteristic values of the polyester film of the present invention will be described. It is essential that the polyester film of the present invention simultaneously satisfies the following conditions (1) and (2) as an index showing that it has properties that can be applied to various cold molding processes. That is, in the polyester film of the present invention, the stress at 5% elongation in each of the four directions of 45 °, 90 °, and 135 ° clockwise with respect to the arbitrary direction on the film surface is set to 0 ° and the above. Regarding the stress at the time of 15% elongation in each of the four directions, the stress (A) measured at a tensile speed of 100 mm / min and the stress (B) measured at a tensile speed of 1000 mm / min are the following (1) and (2). It is essential to meet the conditions of.
That is, as the condition (1), the stress at 5% elongation in each of the four directions is 70 to 120 MPa for both the stress (A) and the stress (B), and the stresses of both stresses in each of the four directions. The difference [stress (A) -stress (B)] is 15 MPa or less.
Above all, the stress at the time of 5% elongation in each of the four directions is preferably 80 to 120 MPa for both the stress (A) and the stress (B), and more preferably 85 to 115 MPa.
Then, as the condition (2), the stress at the time of 15% elongation in each of the four directions is 90 to 180 MPa for both the stress (A) and the stress (B), and the stresses of both stresses in each of the four directions. The difference [stress (A) -stress (B)] is 10 MPa or less.
Above all, the stress at the time of 5% elongation in each of the four directions is preferably 90 to 170 MPa, more preferably 95 to 160 MPa for both the stress (A) and the stress (B).

In the polyester film of the present invention, the values measured by the two types of measuring methods are within a specific range for the stress during elongation, and the difference between the values measured by the two types of measuring methods is within the specific range. Therefore, it is possible to cope with cold molding of various mold shapes and molding depths, and for example, it is possible to adapt to various pressures and speeds at the time of drawing molding. Further, even under various processing conditions, the polyester film easily follows the metal foil, and it is possible to impart sufficient ductility to the metal foil.
If at least one of the above conditions (1) and (2) is not satisfied, the above effects cannot be achieved in various cold molding processes, and the metal foil breaks during cold molding. Or, delamination between the resin film and the metal foil occurs, and pinholes occur.

Further, since the polyester film of the present invention is excellent in stress balance in all directions, the above-mentioned effects of the present invention can be sufficiently exhibited. That is, the difference (ΔF5) between the maximum value and the minimum value (ΔF5) of the stress (F5) at the time of 5% elongation in four directions in the stress (A) is preferably 50 MPa or less, particularly preferably 35 MPa or less, and 25 MPa. It is more preferably 15 MPa or less, and further preferably 15 MPa or less. Further, the difference (ΔF15) between the maximum value and the minimum value (ΔF15) of the stress (F15) at the time of 15% elongation in four directions in the stress (A) is preferably 70 MPa or less, particularly preferably 60 MPa or less, and 50 MPa. It is more preferably 35 MPa or less, and further preferably 35 MPa or less.
The difference (ΔF5) between the maximum value and the minimum value (ΔF5) of the stress (F5) at the time of 5% elongation in four directions in the stress (B) is preferably 50 MPa or less, particularly preferably 35 MPa or less, and 25 MPa. It is more preferably 15 MPa or less, and further preferably 15 MPa or less. Further, the difference (ΔF15) between the maximum value and the minimum value (ΔF15) of the stress (F15) at the time of 15% elongation in four directions in the stress (B) is preferably 70 MPa or less, particularly preferably 60 MPa or less, and 50 MPa. It is more preferably 35 MPa or less, and further preferably 35 MPa or less.
When the difference between the maximum value and the minimum value of these stresses exceeds the above range, the polyester film has a poor stress balance in all directions, and it tends to be difficult to obtain uniform moldability.

Generally, when a film is produced by a tenter type sequential stretching method, the film is obtained in the form of a film roll wound into a cylinder, and the winding width of the obtained film roll is usually about 2 to 8 m. Then, the obtained film roll is slit processed and shipped as a product having a winding width of about 1 to 3 m. In the tenter-type sequential stretching method, since both ends of the film are gripped by clips and stretched, a difference in stress during stretching tends to occur between the vicinity of the center and the ends of the winding width of the film roll.
However, according to the production method of the present invention, the difference in stress during elongation of the film wound around the end portion and the center portion of the obtained film roll is unlikely to occur, and the polyester film wound around the end portion of the film roll is less likely to occur. Also, the values of stress (A) and stress (B) are within the above range.
Then, according to the production method of the present invention, among the obtained polyester films, those near the central portion of the film roll can have ΔF5 in stress (A) and stress (B) of 15 MPa or less, and ΔF15. Can be 35 MPa or less.

The stress in the four directions in the film of the present invention is measured as follows. First, after adjusting the humidity of the polyester film at 23 ° C. × 50% RH for 2 hours, as shown in FIG. 1, the reference direction (0 ° direction) of the film is arbitrarily set with an arbitrary point A on the film as a center point. The measurement direction is defined in four directions of 45 ° direction (b), 90 ° direction (c) and 135 ° direction (d) clockwise from the reference direction (a), and 100 mm in each measurement direction from the center point A. The sample is cut into strips of 15 mm in the direction perpendicular to the measurement direction. For example, as shown in FIG. 1, in the 0 ° direction, a sample X (length 100 mm × width 15 mm) is cut out in a range of 30 mm to 130 mm from the center point A. Cut the sample in the same way in the other directions.
For these samples, a tensile tester (AG-1S manufactured by Shimadzu Corporation) equipped with a load cell for 1 kN measurement and a sample chuck was used, and the stress (A) was extended by 5% at a tensile speed of 100 mm / min. The stress at time (F5) and the stress at 15% elongation (F15) are measured, respectively. Regarding the stress (B), the stress at 5% elongation (F5) and the stress at 15% elongation (F15) are measured at a tensile speed of 1000 mm / min, respectively.
For both stress (A) and stress (B), measurements are performed with 5 samples in each direction, an average value is calculated, and the stress value is used in each direction. Then, the difference between the maximum value and the minimum value of the stress values in the four directions is obtained.
The reference direction (0 °) is preferably MD when the MD in the stretching step during film production is known.

Next, the polyester film of the present invention preferably has a density of 1.360 to 1.400 g / cm ³ , and more preferably 1.370 to 1.385 g / cm ³ .
Density is an indicator of the flexibility of a polyester film. If the resin film has low flexibility, a strong load is applied when the cold molding is stretched, which may cause delamination or pinholes with the metal foil. On the contrary, if the flexibility of the resin film becomes too large, the effect of protecting the laminate containing the metal foil as a base material is weakened, and the obtained laminate has deteriorated mechanical properties. For this reason, the resin film preferably has flexibility that is neither too high nor too low.
If the density of the polyester film ^{is less than 1.360 g / cm 3} , the flexibility becomes too large and the physical properties of the resulting laminate deteriorate. On the other hand, when the density of the polyester film ^{exceeds 1.400 g / cm 3} , the flexibility becomes low, a load is applied during the elongation of cold molding, and good ductility cannot be imparted to the metal foil, resulting in cold. Moldability tends to decrease.

The density of the polyester film of the present invention is measured by using the density gradient tube method described in JIS K-7112. The measurement is performed three times each, and the average value is calculated and used as the density.

Further, the polyester film of the present invention preferably has an average thickness of 30 μm or less, more preferably 26 μm or less, and further preferably 20 μm or less. The polyester film of the present invention is preferably a laminate to be bonded to a metal foil, and is preferably used for cold molding. However, biaxial stretching using a tenter as described later is specific. By carrying out under stretching conditions that satisfy the conditions, a polyester film having a specific stress value specified in the present invention can be obtained even if the film has a small thickness.
If the average thickness of the polyester film exceeds 30 μm, the moldability is lowered, it may be difficult to use it as a small battery exterior material, and there is a possibility that it is disadvantageous in terms of cost.
The average value of the thickness of the polyester film is measured and calculated as follows. After adjusting the humidity of the polyester film at 23 ° C. × 50% RH for 2 hours, as shown in FIG. 2, the center point A is set at an arbitrary position on the film, and the reference direction (0 ° direction) of the film is arbitrarily specified. , Draw a total of four 100 mm straight lines L1 to L4 in four directions of 45 ° direction (b), 90 ° direction (c), and 135 ° direction (d) clockwise from the reference direction (a). The thickness at 10 points at 10 mm intervals from the center point on each straight line is measured with a length gauge (HEIDENHAIN-METRO MT1287 manufactured by Heidenhain Co., Ltd.). Then, the average value of the thickness of 40 points obtained by measuring on the four straight lines is calculated, and this is used as the average value of the thickness.

In the production method of the present invention described later, the polyester film of the present invention may have particles added to the film in order to improve the takeability of the obtained polyester film. The particles to be blended in the polyester film are not particularly limited as long as they are particles capable of imparting slipperiness. For example, silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, etc. Inorganic particles such as kaolin, aluminum oxide, and titanium oxide can be mentioned. Further, heat-resistant organic particles such as a thermosetting urea resin, a thermosetting phenol resin, a thermosetting epoxy resin, and a benzoguanamine resin may be used. Further, during the production process of the polyester resin, precipitated particles in which a part of a metal compound such as a catalyst is precipitated and finely dispersed can also be used.
The shape of the particles used is not particularly limited, and any of spherical, lumpy, rod-shaped, flat-shaped, and the like may be used. Further, the hardness, specific gravity, color and the like are not particularly limited. Two or more kinds of these particles may be used in combination, if necessary.

One or more coat layers may be laminated on at least one side of the polyester film of the present invention, depending on the intended purpose. For example, a coat layer capable of imparting electrolytic solution resistance, acid resistance, alcohol resistance, scratch resistance, charge resistance, printability, and adhesiveness can be mentioned.
Further, as an easy-adhesion treatment for improving the adhesiveness between the base material and the aluminum foil, the polyester film may be surface-treated to exhibit the easy-adhesion effect.

Above all, the polyester film of the present invention preferably has a primer layer on at least one side as a coat layer for improving adhesiveness. By having the primer layer, the laminate in which the polyester film and the metal foil of the present invention are laminated improves the adhesiveness between the polyester film and the metal foil, and when cold-molded, more effectively spreads the metal foil. Since it can be applied, the metal foil is less likely to break, and it is also effective in suppressing delamination.

Examples of the main component of the primer layer include a water-soluble or water-dispersible polyurethane compound, an acrylic compound, and a polyester compound, and an anionic water-dispersible polyurethane resin is preferable. Examples of the curing agent for the primer layer include melamine compounds, isocyanate compounds, and oxazoline compounds.

The thickness of the primer layer is preferably 0.01 to 0.5 μm. If the thickness of the primer layer is less than 0.01 μm, the adhesiveness is lowered. When the thickness of the primer layer is thicker than 0.5 μm, no significant change is observed in the improvement of easy adhesion, etc. Rather, brushing or blocking occurs in the film roll, and the primer layer shows-through and the primer at the time of film unwinding occurs. There are adverse effects such as layer damage and film cutting, which is disadvantageous in terms of cost.

Any known method can be selected as a method for applying an aqueous solution or an aqueous dispersion of the above compound in order to form a primer layer. For example, a bar coating method, an air knife coating method, or a reverse roll coating method can be selected. , The gravure roll coat method can be applied.

If necessary, a lubricant for preventing blocking or a wetting material for improving coatability may be added to the primer layer as long as it does not affect the adhesiveness.

Hereinafter, the method for producing the polyester film of the present invention will be described in detail. The polyester film of the present invention satisfying the above-mentioned characteristic values can be obtained by the production method of the present invention.
A method for producing a polyester film made 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 molding step and a subsequent stretching step.

In the sheet molding step, an unstretched sheet is obtained by molding the polyester resin (R) into a sheet shape.

The polyester resin (R) can be prepared according to a known method. For example, it can be obtained by putting a raw material containing a polybutylene terephthalate resin (A) and a polyethylene terephthalate resin (B) into an extruder equipped with a heating device and melt-kneading at 270 to 300 ° C. for 3 to 15 minutes. .. An unstretched sheet, which is a sheet-shaped molded product, can be obtained by extruding the melt-kneaded resin composition with a T-die and cooling and solidifying it with a casting drum or the like whose temperature is adjusted to 50 ° C. or lower.

The average value of the thickness of the unstretched sheet is not particularly limited, but is generally preferably about 15 to 250 μm, and more preferably 50 to 235 μm. The unstretched sheet can be stretched more efficiently when the average thickness is within the above range.

In the stretching step, the unstretched sheet is biaxially stretched sequentially or simultaneously in the longitudinal direction (MD) and the transverse direction (TD) to obtain a stretched film.
Examples of the simultaneous biaxial stretching include a method of simultaneously biaxially stretching MD and TD by grasping both ends of the unstretched film using a tenter and stretching the unstretched film to MD and at the same time to TD.
On the other hand, in the sequential biaxial stretching, it is preferable to stretch the MD and TD in at least one direction with a tenter, which makes it possible to obtain a more uniform film thickness. Sequential biaxial stretching using a tenter is a method of (1) stretching to MD by passing an unstretched sheet through a plurality of rolls having different rotation speeds, and then stretching the stretched film to TD by a tenter, (2). ) After stretching the unstretched sheet to MD with a tenter, there is a method of stretching the stretched film to TD with a tenter. The method (1) is particularly preferable in terms of physical characteristics, productivity and the like of the obtained film. Sequential biaxial stretching using a tenter is advantageous in terms of productivity, equipment, etc. because the MD is stretched by a roll, and is advantageous in controlling the film thickness, etc., because the TD is stretched by the tenter.

In the production method of the present invention, in the stretching step, it is necessary to perform three-step stretching so that the amount of increase in the film width after stretching is different at the time of stretching in the lateral direction (TD), which is an important point. .. The film width W ₀ before stretching, the film width W ₁ after the first stage stretching, the film width W ₂ after the second stage stretching, and the film width W ₃ after the third stage stretching are as follows ( It is necessary to satisfy a).
W _2- W ₁ <W _1- W ₀ <W _3- W ₂ (a)
Further, unstretched sheets are sequentially added so that the draw ratio of _MD (DR MD) and the total draw ratio of _TD (DR TD = W ₃ / W ₀ ) simultaneously satisfy the following (b) and (c). Alternatively, it is necessary to stretch biaxially at the same time.
0.70 ≤ DR _MD / DR _TD ≤ 0.90 (b)
12.5 ≤ DR _MD x DR _TD ≤ 15.5 (c)
The total amount of film width increase due to the three-step lateral stretching ((W _1- W ₀ ) + (W _2- W ₁ ) + (W _3- W ₂ ) = W _3- W ₀ ) is calculated before the lateral stretching. The film width _{divided by W 0} ((W _3- W ₀ ) / W ₀ = W ₃ / W _0- W ₀ / W ₀ ) corresponds to _{DR TD -1.}
By satisfying all of the above (a), (b) and (c), the obtained polyester film has stress values in four directions satisfying a specific range and has an excellent stress balance in four directions. Can be.

That is, when stretching in the lateral direction (TD), the amount of increase in film width after stretching in the first to third steps does not satisfy the above relationship (a), or stretching in the lateral direction (TD) is performed in one step. In the case of performing in two steps, the difference (variation) between the stress (A) and the stress (B) measured at different tensile velocities cannot be reduced, and the stress values in the four directions are within a specific range. Cannot be.
It is preferable that the time for performing the first-step stretching, the second-step stretching, and the third-step stretching are all substantially the same. For example, assuming that the stretching time of the first stage is T1, the stretching time T2 of the second stage and the stretching time T3 of the third stage are preferably in the range of 0.8 × T1 to 1.2 × T1.

Further, in order to carry out the stretching of the lateral stretching (TD) in three stages, it is possible by stretching using a tenter and adjusting the rail width so as to be different in each step. Further, it is preferable to adopt a sequential biaxial stretching method.

Further, when the draw ratio (DR _MD / DR _TD ) is less than 0.70, the TD ratio is higher than the MD ratio, so that the polyester film has a higher stress value in the stress-strain curve of TD. , Low elongation. On the other hand, when the draw ratio (DR _MD / DR _TD ) exceeds 0.90, the MD magnification is higher than the TD magnification, so that the polyester film has a high stress value in the stress-strain curve of MD. It has low elongation.

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 orientation. 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.

The stretch ratio (DR _MD / DR _TD ) and the surface magnification (DR _MD × DR _TD ) need to satisfy (b) and (c) as described above, and among them, DR _MD is 3.0. It is preferably ~ 3.7, and more preferably 3.1 to 3.6.

When the sequential biaxial stretching is performed, the unstretched sheet is stretched in the longitudinal direction (MD) to obtain a longitudinally stretched film, and the longitudinal stretching is preferably performed in a temperature range of 65 to 105 ° C., particularly 70 to 100 ° C. It is preferable to carry out in the temperature range of. Next, the transverse stretching in which the longitudinally stretched film is stretched in the transverse direction (TD) is preferably performed in a temperature range of 90 to 160 ° C., and more preferably in a temperature range of 100 to 150 ° C. The temperature in the stretching step can be set and controlled while preheating in, for example, a preheating roll or a preheating zone of a tenter.

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

By setting the temperature during stretching and the temperature during relaxation heat treatment within the above ranges, the polyester film of the present invention can be reliably obtained, and the density is 1.360 to 1.400 g / cm ^3. Can be done. Then, it is preferable to raise the temperature sequentially along the taking-up direction of the film in the above temperature range for both longitudinal stretching and transverse stretching.

As a means for setting the temperature at the time of stretching or relaxation heat treatment within the above range, there are a method of blowing hot air on the film surface, a method of using a far-infrared ray or a near-infrared ray heater, a method of combining them, and the like. Preferably includes a method of blowing hot air.

Further, when obtaining the polyester film of the present invention having an easy-adhesion layer on at least one side of the film surface, it is preferable to carry out the same stretching method and stretching conditions as described above. In order to form the easy-adhesion layer on the film surface, it is preferable to apply the water-based coating agent for forming the easy-adhesion layer to the polyester film after stretching to MD in the above manufacturing method. Then, it is preferable that the film is subsequently stretched to TD together with an aqueous coating under the same stretching conditions as described above (in-line coating). The amount of the water-based coating agent applied is preferably adjusted so that the thickness of the easy-adhesion layer formed on the film surface after stretching is 0.01 to 0.5 μm.

The laminate of the present invention includes a polyester film and a metal foil. A typical example of the laminate of the present invention is the polyester film of the present invention and a laminate containing a metal foil laminated on the film. In this case, the polyester film of the present invention and the metal foil may be laminated so as to be in direct contact with each other, or may be laminated with another layer such as an adhesive layer interposed therebetween. In particular, in the present invention, a laminate in which the film of the present invention / the metal foil / the sealant film is laminated in this order is preferable. In this case, an adhesive layer may or may not be interposed between the layers.
Since the polyester film of the present invention can impart good ductility to the metal foil, it does not require the lamination of other ductile resin films such as nylon film.

Examples of the metal foil include metal foils (including alloy foils) containing various metal elements (aluminum, iron, copper, nickel, etc.), and pure aluminum foils or aluminum alloy foils are particularly preferably used. The aluminum alloy foil preferably contains iron (aluminum-iron alloy, etc.), and other components are known as specified in JIS, etc., as long as the moldability of the laminate is not impaired. Any component may be contained as long as it is within the content range.
The thickness of the metal foil is not particularly limited, but is preferably 15 to 80 μm, and more preferably 20 to 60 μm from the viewpoint of moldability and the like.

As the sealant film constituting the laminate of the present invention, it is preferable to use, for example, a thermoplastic resin having heat-sealing properties such as polyethylene, polypropylene, an olefin-based copolymer, and polyvinyl chloride. The thickness of the sealant film is not limited, but is usually preferably 20 to 80 μm, and more preferably 30 to 60 μm.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the present invention is not limited to the following examples. The characteristics of the polyester film and the laminate were measured by the following methods.
The obtained film roll was divided into three equal parts in the width direction. The central film roll was designated as "a", the film roll on the right when viewed from the upstream side in the film flow direction was designated as "b", and the film roll on the left when viewed from the upstream side in the film flow direction was designated as "c".

(1) Stress in four directions when the polyester film is stretched by 5% and stretched by 15% (stress (A), stress (B))
The stresses (stresses (A) and stresses (B)) in the four directions at the time of 5% elongation and 15% elongation of the polyester film are the methods described above, with the reference direction (0 ° direction) being MD. Measured and calculated.
At this time, a sample was taken from the film roll “a” and measured. In the film roll “a”, a film collected at a position corresponding to half of the winding amount was used, and the center point in the width direction was set as the center point A shown in FIG.

(2) Density of Polyester Film The density of the polyester film was measured by the above method.

(3) Average Thickness of Polyester Film The average thickness of the polyester film was measured by the above method.
At this time, a sample was taken from the film roll “a” and measured. In the film roll “a”, a film collected at a position corresponding to half of the winding amount was used, and the center point in the width direction was set as the center point A shown in FIG.

(4) Cold moldability After adjusting the humidity of the obtained laminate at 23 ° C. × 50% RH for 1 hour or more, using an Ericssen testing machine (No. 5755 manufactured by Yasuda Seiki Seisakusho Co., Ltd.) based on JISZ2247, 23 At ° C. × 50% RH, a steel ball punch was pressed against the laminate at a predetermined pressing depth, and the Elixin value was determined. At this time, the pushing speed of the steel ball punch was set to 15 mm / min. The size of the laminated body as a sample was 10 cm in length and 10 cm in width, the Elixin value was measured every 0.5 mm, the measurement was carried out with 10 samples, and the average value was calculated.
When the Elixin value is 6.5 mm or more, especially when it is 7 mm or more, it is judged that it is suitable for deep drawing molding.

The following polyester resin was used as the polyester resin (R).
A-1: Polybutylene terephthalate (NOVADURAN 5010S manufactured by Mitsubishi Engineering Plastics Co., Ltd., ultimate viscosity: 1.10)
A-2: Polybutylene terephthalate (NOVADURAN 5505S manufactured by Mitsubishi Engineering Plastics Co., Ltd., ultimate viscosity: 0.92)
B-1: Polyethylene terephthalate (UT-CBR manufactured by Nippon Esther Co., Ltd., ultimate viscosity: 0.67)
B-2: Polyethylene terephthalate copolymerized with isophthalic acid (MA-1342 manufactured by Nippon Ester Co., Ltd., ultimate viscosity: 0.63)

Example 1
(Making polyester film)
As the polyester resin (R), the above A-1 and B-1 are mixed at a mass ratio (A-1 / B-1) of 5/95, and agglomerated silica master (GS-BR-MG manufactured by Nippon Ester Co., Ltd.) is silica. The unstretched film was added so that the content was 0.05% by mass, melted at 280 ° C., extruded from the T-die outlet with a residence time of 5 minutes, rapidly cooled and solidified, and the thickness after stretching was 25 μm. Got
Then, the unstretched film was sequentially stretched. First, it was heated to 85 ° C. using a heating roll with a longitudinal stretching machine, stretched 3.4 times to MD, and then lateral stretching was started at 120 ° C., and after the first step stretching, the amount of increase in film width was increased. The ratio of ((W _1- W ₀ ) / W ₀ ) is 1.12, and the ratio of the amount of increase in film width after the second stage stretching ((W _2- W ₁ ) / W ₀ ) is 0.71. In addition, the total stretching ratio (DR _TD = W ₃ / W ₀ ) 4 so that the ratio of the amount of increase in film width after stretching in the third step ((W _3- W ₂ ) / W _{0) is 1.41.} .25 times stretched. In this stretching, the stretching ratio (DR _MD / DR _TD ) was 0.80, and the surface magnification (DR _MD × DR _TD ) was 14.5. In addition, the stretching time of each stage was assumed to be the same.
Next, the relaxation heat treatment temperature was set to 190 ° C., the relaxation rate of TD was set to 6.0%, the relaxation heat treatment was performed for 4 seconds, and then the film was cooled to room temperature to obtain a polyester film having a thickness of 25 μm. The obtained polyester film was wound into a roll.

(Preparation of laminate)
Next, a two-component polyurethane adhesive (TM-K55 / CAT-10L manufactured by Toyo Morton Co., Ltd.) was applied to the obtained polyester film so that the coating amount was 5 g / m ^2, and dried at 80 ° C. for 10 seconds. did. An aluminum foil (AA standard 8079P, thickness 50 μm) was attached to the adhesive-coated surface. Next, the same type of adhesive was applied to the aluminum foil side of the aluminum foil bonded 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 to 40 ° C. Aging treatment was carried out for 72 hours in the atmosphere of the above to prepare a laminated body.

Examples 2-45, Comparative Examples 1-26
Except that the type, mass ratio, stretching ratio of MD and TD, stretching temperature, relaxation heat treatment temperature, relaxation rate, and thickness after stretching were changed as shown in Tables 1 to 6 of the polyester resin used as the polyester resin (R). , The same method as in Example 1 was carried out to obtain a polyester film. When changing the thickness after stretching, the supply amount of the polyester resin (R) extruded from the T-die outlet was changed. In Comparative Examples 2, 3, 16 and 17, the total stretching time of the transverse stretching is the same as the total stretching time of the transverse stretching of Example 1, but the transverse stretching is carried out in two stages, and each step is performed. Was stretched so that the stretching times of the above were equal.
Using the obtained polyester film, a laminate was obtained in the same manner as in Example 1.

Tables 1 to 6 show the constitution, production conditions and characteristic values of the polyester films obtained in Examples 1 to 45 and Comparative Examples 1 to 26, and the cold moldability of the obtained laminate.

As is clear from these results, in Examples 1 to 45, the amount of increase in film width, the draw ratio (DR _MD / DR _TD ), and the surface magnification (DR _MD × DR) in the three-step stretching in the lateral direction (TD). _{Since TD} ) was within the range specified in the present invention, the obtained polyester film had a stress at 5% elongation in four directions of 70 mm / min in both the tensile speed of 100 mm / min and the tensile speed of 1000 mm / min. It is in the range of ~ 120 MPa, the difference in stress due to the difference in measurement method is 15 MPa or less, and the stress at the time of 15% elongation in four directions is the measurement method of tensile speed 100 mm / min and tensile speed 1000 mm / min. In each case, the stress difference was in the range of 90 to 180 MPa, and the stress difference due to the difference in the measuring method was 10 MPa or less.
The laminate obtained by using a polyester film satisfying the characteristic values specified in the present invention has a high Elixin value and has uniform ductility in all directions when cold-molded. rice field. That is, the polyester film of each example had excellent cold moldability without breaking the aluminum foil, causing delamination, pinholes, etc. during cold molding.
On the other hand, in Comparative Examples 1 to 26, the amount of increase in film width, the draw ratio (DR _MD / DR _TD ), and the surface magnification (DR _{MD) in the three-step stretching in the lateral direction (TD) when obtaining the polyester film.} Since × DR _TD ) is not within the range specified in the present invention, the obtained polyester film does not satisfy the above-mentioned characteristic values of the present invention. Therefore, the laminates obtained by using the polyester films of Comparative Examples 1 to 26 had a low Elixin value and did not have uniform ductility in all directions when cold-molded. .. Therefore, during cold molding, the aluminum foil is broken, delamination, pinholes, and the like occur, and the cold moldability is inferior.

A Center point X Sample for measuring stress during elongation in the reference direction (0 ° direction) of polyester film

Claims (8)

The tensile speed is set to 0 ° in any direction on the film surface, and the stress at 5% elongation and the stress at 15% elongation in each of the four directions of 45 °, 90 °, and 135 ° clockwise with respect to that direction are the tensile speeds. A polyester film characterized in that the stress (A) measured at 100 mm / min and the stress (B) measured at a tensile speed of 1000 mm / min satisfy the following conditions (1) and (2).
Condition (1): The stress at 5% elongation in each of the four directions is 70 to 120 MPa for both the stress (A) and the stress (B), and the difference between the two stresses in each of the four directions [stress]. (A) -Stress (B)] is 15 MPa or less.
Condition (2): The stress at the time of 15% elongation in each of the four directions is 90 to 180 MPa for both the stress (A) and the stress (B), and the difference between the two stresses in each of the four directions [stress]. (A) -Stress (B)] is 10 MPa or less. The polyester film according to claim 1, wherein the density is 1.360 to 1.400 g / cm ^3. The polyester film according to claim 1 or 2, wherein the average value of the thicknesses in the four directions is 30 μm or less. A laminate containing the polyester film and metal leaf according to any one of claims 1 to 3. A laminate obtained by laminating a metal foil, an adhesive layer, and the polyester film according to any one of claims 1 to 3 in this order. The method for producing a polyester film according to any one of claims 1 to 3, wherein the unstretched sheet is subjected to sequential biaxial stretching or simultaneous biaxial stretching in the longitudinal direction (MD) and the transverse direction (TD).
The lateral (TD) stretching is performed in three stages, the film width W ₀ before the lateral stretching, the film width W ₁ after the first lateral stretching, and the film width after the second lateral stretching. W _{2 and the film width W 3} after the third-stage lateral stretching satisfy the following (a).
In addition, the stretching ratio (DR _MD ) in the vertical direction (MD) and the total stretching ratio (DR _TD = W ₃ / W ₀ ) in the horizontal direction (TD) satisfy the following (b) and (c). A method for producing a polyester film, which comprises biaxial stretching.
W _2- W ₁ <W _1- W ₀ <W _3- W ₂ (a)
0.70 ≤ DR _MD / DR _TD ≤ 0.90 (b)
12.5 ≤ DR _MD x DR _TD ≤ 15.5 (c) In sequential biaxial stretching,
The unstretched sheet is stretched in the longitudinal direction (MD) to obtain a longitudinally stretched film, which is subjected to longitudinal stretching in a temperature range of 65 to 105 ° C.
The method for producing a polyester film according to claim 6, wherein the longitudinally stretched film is stretched laterally (TD) in a temperature range of 90 to 160 ° C. The method for producing a polyester film according to claim 6 or 7, wherein the film after biaxial stretching is heat-treated in a temperature range of 160 to 210 ° C.

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