JP2017121774A - Biaxially oriented polyester film for metal sheet lamination molding - Google Patents

Abstract

[PROBLEMS] To provide a biaxially oriented polyester film for metal plate lamination molding which has sufficient adhesiveness even when laminated at a low temperature, excellent molding processability after lamination, and excellent gold color development. A laminated film having a layer A forming one surface layer and a layer B, wherein the layer A has a heat of fusion of 10 J/g or less in DSC and a plane orientation coefficient of 0.000 or more and 0 .050 or less, the layer B is a polyester layer having a melting point of 210° C. or more and 245° C. or less, and an X-ray diffraction intensity ratio Xb of 0.50 or more; At least one layer of Layer B contains 0.05 to 50% by weight of a colorant based on the weight of the layer containing the colorant, and the a* value of the film is -30 to 20, b by a color difference meter. * A biaxially oriented polyester film for metal plate lamination molding, having a value of 20 to 70. [Selection figure] None

Description

  The present invention relates to a biaxially stretched polyester film for metal plate lamination molding. More specifically, the present invention relates to a biaxially stretched polyester film for metal plate laminating molding, which can be easily thermally bonded to a metal plate, particularly a tin plate, and is excellent in gold color development.

  Metal cans are generally painted to prevent corrosion on the inner and outer surfaces, but in recent years polyester has been used as a method to obtain rust prevention without using organic solvents for the purpose of simplifying processes, improving hygiene, and preventing pollution. Coating with a thermoplastic resin film such as a film is performed (Patent Document 1). In other words, food cans and beverage cans that are subjected to severe molding such as drawn cans and thinned drawn cans after laminating a thermoplastic resin film to a metal plate such as tin-free steel or aluminum Has been used.

In addition to the method of using an adhesive, for example, a method of bonding a polyester film directly to an adherend by applying thermal adhesion to a polyester film, and further using a polyester film as a base material. There is a method of imparting thermal adhesiveness by forming a laminated structure of a layer and a layer having thermal adhesiveness. Among these, the method of forming a laminated structure having a thermal adhesive layer is excellent in that both adhesiveness and strength can be achieved.
However, for example, when laminating to tinplate, since the melting point of the tin plating layer is low, it must be laminated at a low temperature. For this reason, the film may be peeled off or torn when performing a molding process after lamination.

  Patent Document 2 describes a laminated polyester film that can be thermally bonded to tinplate via a thermally adhesive polyester layer. However, this film is for three-piece metal can lamination that is not subjected to molding after metal lamination. When the laminate is laminated at a low temperature, the film may be peeled off or torn as described above. There is a fear. Therefore, there is a demand for a polyester film for metal plate laminating molding that can be laminated at a low temperature and has sufficient moldability at the same time.

  Moreover, as a film for laminating a metal plate, a canned polyester film (Patent Document 3) mainly composed of ethylene phthalate or a colored polyester film (Patent Document 4) composed of ethylene phthalate and butylene terephthalate has been used. It has been proposed to impart a gold color to give the appearance a high-class appearance, but these have been insufficiently laminated at low temperatures, so that they have been difficult to laminate on tinplate.

Japanese Patent Laid-Open No. 04-105922 JP 2003-080654 A JP 2001-301025 A JP 2004-148627 A

  The object of the present invention is to eliminate the problems of the prior art, have sufficient adhesiveness even when laminated at a low temperature, have excellent moldability after lamination, and have excellent gold colorability. The object is to provide a biaxially stretched polyester film for processing.

As a result of intensive studies to solve the above-mentioned problems, the present inventors used a copolyester having a small orientation after stretching, imparted thermal adhesiveness to at least one surface of the film, and colored at least one layer. It has been found that by containing an agent, it can be laminated on tinplate at a low temperature and is excellent in subsequent processability, and the present invention has been completed.
That is, the present invention employs the following configuration in order to solve the above problems.

２．層Ａの下記式で表されるＸ線回析強度比Ｘａと上記Ｘｂとの差Ｘａ−Ｘｂが０．２０〜０．７０である、上記１に記載の金属板貼合せ成形加工用二軸延伸ポリエステルフィルム。

３．層Ａにおける共重合ポリエステルが、共重合成分としてナフタレンジカルボン酸またはイソフタル酸を１６〜３０モル％含有する共重合ポリエチレンテレフタレートである、上記１または２に記載の金属板貼合せ成形加工用二軸延伸ポリエステルフィルム。
４．フィルムの融解サブピーク温度（Ｔｓｍ）が１８０℃以上２１５℃以下である、上記１〜３のいずれか１に記載の金属板貼合せ成形加工用二軸延伸ポリエステルフィルム。
５．着色剤が、アンスラキノン系、イソインドリノン系、ベンズイミダゾロン系、キノフタロン系、縮合アゾ系からなる群から選ばれる少なくとも１種類からなる、上記１〜４のいずれか１に記載の金属板貼合せ成形加工用二軸延伸ポリエステルフィルム。 1. A laminated film having a layer A and a layer B forming one surface layer;
Layer A is a copolyester layer having a heat of fusion of 10 J / g or less in DSC and a plane orientation coefficient of 0.000 or more and 0.050 or less,
Layer B is a polyester layer having a melting point of 210 ° C. or more and 245 ° C. or less, and an X-ray diffraction intensity ratio Xb represented by the following formula of layer B of 0.50 or more,
The colorant is contained in at least one of the layer A and the layer B in an amount of 0.05 to 50% by weight based on the weight of the layer containing the colorant, and the a * value by the color difference meter of the film is −30 A biaxially stretched polyester film for metal plate laminating molding, having a b * value of 20 to 70.

2. The biaxial for metal plate laminating and forming process according to 1 above, wherein the difference Xa-Xb between the X-ray diffraction intensity ratio Xa represented by the following formula of layer A and Xb is 0.20 to 0.70: Stretched polyester film.

3. The biaxial stretching for metal plate lamination molding processing according to 1 or 2 above, wherein the copolymer polyester in layer A is copolymer polyethylene terephthalate containing naphthalene dicarboxylic acid or isophthalic acid as a copolymer component in an amount of 16 to 30 mol%. Polyester film.
4). The biaxially stretched polyester film for metal plate laminating molding according to any one of 1 to 3 above, wherein the melting subpeak temperature (Tsm) of the film is 180 ° C. or higher and 215 ° C. or lower.
5. The metal plate sticking according to any one of the above 1 to 4, wherein the colorant is at least one selected from the group consisting of anthraquinone, isoindolinone, benzimidazolone, quinophthalone, and condensed azo. Biaxially stretched polyester film for combined molding.

  The biaxially stretched polyester film for metal plate lamination molding processing of the present invention has sufficient adhesiveness even when laminated at a low temperature, has excellent molding processability after lamination, and is excellent in gold color development. Therefore, it can use suitably for uses, such as a drink can and a food can using a metal plate, especially metal plates with low processing temperature, such as tinplate.

The present invention will be described in detail below.
<Layer A>
(Copolymer polyester for layer A)
The copolymerized polyester constituting the layer A in the present invention may be any of copolymerized polyethylene terephthalate and copolymerized polyethylene-2,6-naphthalate as long as it satisfies the plane orientation characteristics described later, and among them, copolymerized polyethylene terephthalate. Is preferred.
The copolymer component of the copolymer polyester may be an acid component or an alcohol component. Acid components include aromatic dicarboxylic acid components other than main acid components such as isophthalic acid component, orthophthalic acid component, terephthalic acid component, 2,6-naphthalenedicarboxylic acid component, adipic acid component, azelaic acid component, sebacic acid component Examples of the alcohol component include an aliphatic diol component such as a diethylene glycol component, a triethylene glycol component, a neopentyl glycol component, and a 1,6-hexanediol component, and 1,4. -An alicyclic diol component such as a hexamethylene dimethanol component can be mentioned. These may be used alone or in combination of two or more. Among these, an isophthalic acid component, a 2,6-naphthalenedicarboxylic acid component, a diethylene glycol component, and a 1,4-hexamethylene dimethanol component are preferable.

  The copolymerization amount of such a copolymer component is preferably 16 to 30 mol% based on 100 mol% of all acid components of the copolymer polyester. Thereby, it is excellent in adhesiveness. If the copolymerization amount is less than 16 mol%, the crystallinity of the copolyester becomes high, and these crystals and orientations are obtained by a heat treatment at a temperature exceeding the melting point of layer A to relax the crystals and orientations of layer A caused by stretching. Is not sufficiently relaxed, the adhesiveness is impaired. On the other hand, if the amount is too large, the heat resistance tends to decrease.

(Heat of fusion)
The layer A in the present invention has a heat of fusion of about 10 J / g or less, preferably 8 J / g or less, more preferably 5 J / g when a weight of about 10 mg in DSC is raised at a rate of 20 to 20 ° C./min. g or less. This heat of fusion represents the degree of crystallinity of layer A. If the heat of fusion exceeds the upper limit, the thermal adhesiveness decreases due to the crystallization of layer A, which is a thermal adhesive layer, and the initial adhesive strength is insufficient, Since it will peel off after a process, it is not preferable. The heat of fusion of layer A is not particularly limited as long as it is within such a range, but the lower limit of the heat of fusion is preferably 0 J / g or more, and more preferably in the range exceeding 0 J / g. The above is the heat of fusion of layer A in the film before being laminated to the metal plate.

In order to achieve such a requirement, as the above-mentioned copolymer polyester, an amorphous or low-crystalline polyester (a copolymer having a large amount of copolymerization) can be used. What is necessary is just to heat-set at the temperature close | similar to melting | fusing point of copolyester, or the temperature beyond it, to melt the layer A, and to reduce crystallinity.
In the present invention, it is preferable to use a copolyester having a crystalline property (having a melting point) rather than a completely amorphous polyester, because it is easy to handle, such as the temperature at which the polymer is dried can be increased. The copolymer polyester has a melting point of 15 ° C. or more, preferably 20 ° C. or more lower than the melting point of the polyester constituting the layer B described later.

(Plane orientation coefficient)
The layer A of the biaxially stretched polyester film of the present invention has a film longitudinal direction (the film forming machine axis direction; hereinafter, sometimes referred to as a longitudinal direction, a film forming direction or an MD direction), and a transverse direction (longitudinal direction). And the direction perpendicular to the thickness direction, hereinafter referred to as the width direction or the TD direction) and the refractive index in the thickness direction (hereinafter referred to as the thickness direction perpendicular to the film surface, sometimes referred to as the z direction). The plane orientation coefficient (Ns) obtained from is 0.000 or more and 0.050 or less. Thereby, it is excellent in adhesiveness. If the plane orientation coefficient (Ns) is too large, the adhesion tends to be inferior. From this viewpoint, the plane orientation coefficient (Ns) is preferably 0.000 or more and 0.030 or less, and particularly preferably 0.000 or more and 0.020 or less. The above is the plane orientation coefficient of layer A in the film before being laminated to the metal plate. Here, the plane orientation coefficient is represented by a value obtained by calculation according to the following formula (1) using the refractive index of each direction component of the film measured by the Abbe method.
Ns = (nMD + nTD) / 2−nZ (1)
(Where nMD is the refractive index in the MD direction of the film, nTD is the refractive index in the TD direction of the film, and nZ is the refractive index in the thickness direction perpendicular to the film surface. (Refractive index)
The plane orientation coefficient of the film can be said to be an index representing the orientation state of the molecular chains in the film. When the upper limit is exceeded, the adhesion to the metal plate is reduced due to the orientation of the molecular chains of the layer A accompanying stretching.

<Layer B>
(Polyester for layer B)
The melting point of the polyester constituting the layer B in the present invention is 210 ° C. or higher and 245 ° C. or lower. The lower limit of the melting point is preferably 215 ° C or higher, more preferably 220 ° C or higher. When the melting point is less than the lower limit, there is a possibility that the metal plate is fused to the roll when the metal plate is bonded, which is not preferable. The upper limit of the melting point is preferably 243 ° C. or lower, more preferably 240 ° C. or lower, particularly preferably 237 ° C. or lower. When the melting point exceeds the upper limit, many orientations remain at the time of bonding the metal plates, and the film is torn during the molding process, which is not preferable.
It may be a copolymer or a blend as long as the melting point condition is satisfied. The copolymerized polyester may be any of copolymerized polyethylene terephthalate, copolymerized polybutylene terephthalate, and copolymerized polyethylene-2,6-naphthalate. Among them, copolymerized polyethylene terephthalate is preferable.

  The copolymer component of the copolymer polyester may be an acid component or an alcohol component. Acid components include aromatic dicarboxylic acid components other than main acid components such as isophthalic acid component, orthophthalic acid component, terephthalic acid component, 2,6-naphthalenedicarboxylic acid component, adipic acid component, azelaic acid component, sebacic acid component Examples of the alcohol component include an aliphatic diol component such as a diethylene glycol component, a triethylene glycol component, a neopentyl glycol component, and a 1,6-hexanediol component, and 1,4. -An alicyclic diol component such as a hexamethylene dimethanol component can be mentioned. These may be used alone or in combination of two or more. Among these, an isophthalic acid component, a 2,6-naphthalenedicarboxylic acid component, a diethylene glycol component, and a 1,4-hexamethylene dimethanol component are preferable.

<Colorant>
The layer A and / or the layer B in the present invention contains 0.05 to 50% by weight of a colorant based on the weight of the layer containing the colorant. This makes it easy to develop suitable gold color development. Moreover, it is excellent in moldability. If the content is too small, suitable color development cannot be achieved and the gold color developability is poor. From this viewpoint, 0.1% by weight or more is preferable, and 0.3% by weight or more is more preferable. On the other hand, too much is excessively expensive and uneconomical. From this viewpoint, it is preferably 25% by weight or less, more preferably 10% by weight or less, still more preferably 5.0% by weight or less, and particularly preferably 3.0% by weight or less.
The colorant may be contained in both layer A and layer B. In that case, the content in the layer A is preferably 0.5 to 4.0% by weight, more preferably 1.0 to 3.0% by weight based on the weight of the layer A, and the content in the layer B is Preferably it is 0.1-1.5 weight% based on the weight of the layer B, More preferably, it is 0.2-1.0 weight%.

  In another preferred embodiment, the layer A contains a colorant, and the layer B contains no colorant or a small amount (for example, 1.0% by weight or less, preferably 0.5% based on the weight of the layer B). When the weight is less than or equal to% by weight, the layer A becomes an adhesion layer with the metal plate, and therefore, there is an effect that the colorant hardly deposits on the surface after lamination. On the other hand, the layer B contains a colorant, and the layer A contains no colorant or a small amount (for example, 3.0% by weight or less, preferably 1.5% by weight or less based on the weight of the layer A). If it makes it, there exists an effect which is hard to reduce adhesiveness. In the present invention, the aspect in which the colorant is contained in the layer A among the above is preferable.

In the present invention, the colorant is not limited as long as a specified hue can be obtained, but a yellow colorant is preferable from the viewpoint of easily obtaining a specified hue.
As the colorant, at least one organic pigment selected from the group consisting of anthraquinone, isoindolinone, benzimidazolone, quinophthalone, and condensed azo is preferably used. In order to adjust the color tone, other components may be used in combination as the colorant, but those having good heat resistance are preferred, and those that are recognized as safe in terms of food hygiene are preferred for their use. .
The colorant may be contained in the raw material resin polymerization step, and a high-concentration master chip is produced using, for example, a twin screw extruder, and mixed with a chip not containing the colorant to obtain a desired colorant. You may obtain the resin composition containing the coloring agent of a density | concentration. Further, for example, using a screw feeder, the colorant may be directly contained in the extruder in the film forming process as powder.

<Other ingredients>
In layer A and layer B in the present invention, other additives such as a lubricant (organic particles, inorganic particles, organic-inorganic composite particles, etc.), fluorescent whitening, and the like, as long as the object of the present invention is not impaired. An agent, antioxidant, heat stabilizer, ultraviolet absorber, antistatic agent, and the like can be added.

<Film thickness and layer structure>
The thickness of the biaxially stretched polyester film of the present invention can be appropriately changed as necessary, but is preferably in the range of 6 to 75 μm, more preferably in the range of 10 to 75 μm, and particularly preferably in the range of 15 to 50 μm. If the thickness is less than 6 μm, blurring or the like tends to occur during the molding process, while those exceeding 75 μm are excessive quality and uneconomical.

The thickness of the layer A is preferably 1 μm or more and 40 μm or less, and this improves the adhesiveness. Further, when the layer A contains a colorant, it becomes easier to develop a more suitable color. From this viewpoint, it is more preferably 2 μm or more, more preferably 25 μm or less, and further preferably 20 μm or less. The thickness of the layer B is preferably 5 μm or more and 35 μm or less, and when the layer B contains a colorant, this makes it easier to develop a more suitable color. More preferably, it is 8 micrometers or more, More preferably, it is 12 micrometers or more, More preferably, it is 30 micrometers or less.
Further thickness ratio of layer A and layer _{B (T} A / T B: However, _{T A} is the thickness of the layer A, _{T B} is the thickness of layer B) is, adhesion and rust resistance from point 1 / 7-1 A range of / 2 is preferred.

<Other layers and surface treatment>
The biaxially stretched polyester film of the present invention is a laminated film in which the layer A forms one surface layer and the layer B, and the layer A is an adhesive layer bonded to a metal plate. As long as it does not inhibit, other layers can be laminated as required. For example, another layer A or other resin layer including polyester may be provided on the surface of the layer B opposite to the layer A. Further, another resin layer may be provided between the layer A and the layer B. In the present invention, a particularly preferred embodiment is a two-layer structure of layer A and layer B. When layer B forms the other surface in this way, the effect that layer B is brought into contact with the laminate roll during lamination can be exhibited. Further, any surface may be subjected to corona treatment or plasma treatment. In addition, a primer layer can be used for the purpose of further improving the adhesion to the metal plate.

<Film manufacturing method>
The manufacturing method of the biaxially stretched polyester film for metal plate laminating molding processing of the present invention is not particularly limited, and an unstretched laminated sheet may be first prepared by a conventionally known film forming method and then stretched in two directions.
The copolyester prepared for layer A is sufficiently dried and then melted in the extruder at a temperature not lower than the glass transition point or a melting point to (melting point + 70) ° C. At the same time, the polyester prepared for layer B is sufficiently dried and then supplied to another extruder and melted at a temperature of melting point to (melting point + 70) ° C. Subsequently, a laminated unstretched laminated sheet is manufactured by a method of laminating both molten resins inside the die, for example, a simultaneous lamination extrusion method using a multi-manifold die. According to this simultaneous lamination extrusion method, the melt of the resin that forms one layer and the melt of the resin that forms another layer are laminated inside the die and formed into a sheet shape from the die while maintaining the laminated form. The

Then, the unstretched film can be produced by a method of sequentially or simultaneously biaxially stretching and heat setting. When forming a film by sequential biaxial stretching, the unstretched laminated sheet is heated by roll heating, infrared heating or the like, first stretched in the longitudinal direction, and then stretched transversely by a stenter. At this time, the stretching temperature is 20 to 50 ° C. higher than the glass transition point (Tg) of the polyester, the longitudinal stretching ratio is 2.5 to 3.6 times, and the transverse stretching ratio is 2.6 to 3.9 times. It is preferable that The heat setting temperature is preferably selected so as to adjust the film quality so that the plane orientation coefficient of the layer A is 0.000 or more and 0.050 or less in the range of 150 to 240 ° C.
As the metal plate to which the biaxially stretched polyester film for metal plate laminating molding processing of the present invention is bonded, particularly as a metal plate for can manufacturing, a plate of tin, tin-free steel, aluminum or the like is suitable. Since the biaxially stretched polyester film can be bonded at a low temperature, a tin plate that requires bonding at a low temperature is preferable.

<Characteristics of film>
(Hue)
The biaxially stretched polyester film of the present invention has an a * value of −30 to 20 and a b * value of 20 to 70 by a color difference meter of the film. The a * value is preferably -20 to 10. The b * value is preferably 40 to 70. When the a * value is lower than −30 or exceeds 20, a desired appearance cannot be obtained when bonded to a metal plate. If the b * value is less than 20, the colorability is poor, and good gold color developability cannot be obtained after metal lamination. If the b * value exceeds 70, the colorant content is increased, and the dispersion state of the colorant deteriorates. Membrane properties are likely to deteriorate. By setting the a * value and the b * value within this range, it is possible to impart a gold color with a high-quality appearance after metal lamination.

(Melting sub-peak temperature (Tsm))
The biaxially stretched polyester film of the present invention preferably has a melting subpeak temperature (Tsm) of 180 ° C. or higher and 215 ° C. or lower. The lower limit of the melting subpeak temperature (Tsm) is more preferably 185 ° C. or higher, and further preferably 190 ° C. or higher. Further, the upper limit of the melting subpeak temperature (Tsm) is more preferably 210 ° C. or lower, and further preferably 205 ° C. or lower. By adjusting the heat setting temperature and the film having a melting sub-peak in such a temperature range, the initial adhesive force can be further increased, and the subsequent molding processability and the adhesive force after processing can be further increased.

(X-ray diffraction intensity ratio of layer B)
The layer B in the present invention has an X-ray diffraction intensity ratio Xb represented by the following formula of 0.50 or more.

Thereby, excellent moldability is obtained while having sufficient strength as a biaxially stretched film. If Xb is low, the moldability tends to decrease. From this viewpoint, Xb is preferably 0.55 or more, more preferably 0.60 or more, further preferably 0.65 or more, and particularly preferably 0.70 or more. From this point of view, it is not a problem that Xb is high, but if it is too high, the strength tends to decrease, and it may be unfavorable because it tends to cause thickness unevenness when forming a biaxially stretched film. . From this viewpoint, Xb is preferably 0.95 or less, more preferably 0.92 or less, and still more preferably 0.90 or less.
In order to make the Xb of the layer B within the above range, the stretching ratio and the stretching temperature may be adjusted. For example, when the draw ratio is increased (decreased), Xb tends to be decreased (increased).

(Difference in X-ray diffraction intensity ratio between layer A and layer B)
In the present invention, the difference Xa-Xb between the X-ray diffraction intensity ratio Xa of the layer A represented by the following formula and the X-ray diffraction intensity ratio Xb of the layer B described above is in the range of 0.20 to 0.70. It is preferable that it exists in.

Thereby, the further excellent effect is show | played about the adhesiveness at the time of low temperature lamination, and a moldability. If the difference is too small, the effect of improving adhesiveness tends to be low. On the other hand, if the difference is too large, the effect of improving the moldability tends to decrease. From this viewpoint, the Xa-Xb is more preferably 0.22 to 0.68, further preferably 0.25 to 0.65, and particularly preferably 0.25 to 0.45.
Said X-ray diffraction intensity ratio Xa and Xb can obtain the said aspect by adjusting suitably copolymerization amount and extending | stretching conditions, for example, The direction which makes an oriented crystal high is the direction where X total diffraction intensity ratio becomes small. It is.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Amount of polyester component
^{From the 1} H-NMR measurement, the components of the polyester, the copolymer components, and the amounts of each component were specified.

(2) Heat of fusion of layer A Layer A was scraped from the film sample, about 10 mg of layer A was enclosed in an aluminum pan for measurement, and attached to a differential scanning calorimeter (TA Instruments, DSCQ100). The temperature was raised to 290 ° C. at a rate of 20 ° C./min, and the heat of fusion was measured.

(3) Melting point of layer B About 10 mg of layer B was sealed in an aluminum pan for measurement and attached to a differential scanning calorimeter (TA Instruments, DSCQ100), and 290 ° C at a rate of 20 ° C to 20 ° C / min. The temperature was raised to 290 ° C. for 3 minutes and then taken out, immediately transferred onto ice and quenched. This pan was again attached to the differential calorimeter, and the temperature was raised from 20 ° C. to 20 ° C./min, and the melting point Tm (unit: ° C.) was measured.

(4) Plane orientation coefficient About the obtained film, according to JIS-K7105, using the Abbe refractometer (light source: sodium D line 589 nm, mount liquid: methylene iodide), the refractive index in each direction is measured on the surface on the layer A side. It was measured. From the obtained refractive index, a plane orientation coefficient Ns was calculated according to the following formula (1).
Ns = (nMD + nTD) / 2−nZ (1)
(In the formula, nMD represents the refractive index in the MD direction of the film, nTD represents the refractive index in the TD direction of the film, and nZ represents the refractive index in the thickness direction perpendicular to the film surface.)
In addition, when measurement of the refractive index by an Abbe refractometer is difficult or impossible because the thickness of the layer A in the laminated film is too thin, the same total thickness as the total thickness of the example under the same film forming conditions as the example. A single layer film composed of the composition of layer A is prepared, the refractive index of the single layer film is measured as described above, and the obtained plane orientation coefficient can be used as the plane orientation coefficient Ns of layer A in the laminated film. .

(5) Melting sub-peak temperature (Tsm)
About 20 mg of film was sealed in an aluminum pan for measurement and attached to a differential scanning calorimeter (TA Instruments, DSCQ100), and a DSC curve was drawn at a heating rate of 20 ° C./min. The lower endothermic peak was taken as the melting subpeak temperature. In addition, when the melting sub-peak was close to the crystal melting peak and was not clear as a peak, the point where the second derivative curve of the DSC curve was 0 was defined as the sub-peak temperature.

(6) Thermal adhesiveness A polyester film sample was laminated on one side of a tin plate having a thickness of 0.25 mm so that the layer A was on the metal plate side and heat-sealed at 220 ° C. For the film adhered to the tin plate, the adhesive strength of the bonded portion was evaluated as follows.
◯: Can be thermally bonded (does not peel off from tinplate if traced with fingers)
Δ: Can be thermally bonded, but may be peeled off from the tinplate when traced with fingers ×: Cannot be thermally bonded (peeled off from the tinplate immediately after bonding)

(7) Formability Processed by laminating a film with tin according to the method of (6) above, it is cut into a 150 mm diameter disc shape, deep drawn in four stages using a drawing die and punch, and a 55 mm diameter side surface. A seamless container (hereinafter abbreviated as “can”) was prepared. The processing conditions of these cans were observed and evaluated according to the following criteria.
○: The film was processed without any abnormality, and no peeling or breakage of the film or generation of pinholes was observed.
(Triangle | delta): Generation | occurrence | production of very slight film peeling, a fracture | rupture, or a pinhole was recognized.
X: Peeling, breakage, and generation of pinholes are observed.

(8) Hue (gold color development)
Based on JIS Z8722, using an automatic color difference meter (SE-Σ90 type) manufactured by Nippon Denshoku Industries Co., Ltd., the a * value and b * value of one sample of 5 cm square were measured. evaluated. In the measurement, a white plate attached to the apparatus was used as a film presser, and the measurement was performed by a reflection method.
A: a * value is −20 to 10, b * value is 40 to 70
○: a * value is −30 to 20, b * value is 20 to 70 (however, not in the range of ◎)
×: a * value and b * value outside the above range

(9) X-ray diffraction intensity Using CuK-α ray as an X-ray source, conditions of divergence slit 0.2 mm, scattering slit 10 mm, light receiving slit 10 mm, scan speed 0.25 ° / min, incident angle 0.07 degree The following X-ray diffraction intensity was measured by a multiple peak separation method, and the X-ray diffraction intensity ratios Xa and Xb were calculated by the above formula.

  For the X-ray diffraction intensity, the area of the diffraction peak on each crystal plane is obtained, and this area is taken as the X-ray diffraction intensity. When a colorant or other additive is included, the obtained strength is divided by the resin weight ratio so as to obtain the strength per resin weight.

(10) Thickness unevenness In the width direction of the film, a slit sample of 30 mm width × product roll width length (for example, 2 m) is collected, and the thickness at each width direction position is 1 cm intervals with a continuous electronic micrometer manufactured by Anritsu Corporation. The difference between the maximum thickness and the minimum thickness of the sample in the measurement range was determined as thickness spots, and the value was evaluated according to the following criteria.
◎: Less than 1.0 μm ○: 1.0 μm or more, less than 2.0 μm ×: 2.0 μm or more

[Example 1]
A copolymer containing 18 mol% of isophthalic acid copolymerized polyethylene terephthalate as the copolyester constituting the layer A and containing 1.6% by weight of isoindolinone yellow as the colorant based on the weight of the layer A As a raw material for forming the layer A, 12 mol of isophthalic acid copolymerized polyethylene terephthalate is used as the polyester constituting the layer B, and lump silica having an average particle size of 1.5 μm is used as the lubricant in an amount of 0.0. The material containing 1% by weight is used as a raw material for forming the layer B, and after drying and melting each independently, the thickness ratio of the obtained film is as shown in Table 1 from the adjacent die. Were coextruded at 280 ° C. and rapidly cooled and solidified to obtain an unstretched laminated film. Subsequently, this unstretched laminated film was longitudinally stretched 2.9 times at 100 ° C., then transversely stretched 3.1 times at 120 ° C., and subsequently fixed at 215 ° C. to obtain a biaxially stretched polyester film. The total thickness of the film was 20 μm. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was carried out except that isophthalic acid 8 mol% copolymerized polyethylene terephthalate was used as the copolyester constituting layer B, and the heat setting condition was 220 ° C. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Example 3]
The same procedure as in Example 1 was performed except that the thickness ratio was as shown in Table 1. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Example 4]
The same operation as in Example 1 was performed except that the heat setting condition was 210 ° C. The evaluation results of the obtained polyester film are shown in Table 1.

[Example 5]
The same procedure as in Example 1 was conducted except that 20 mol% of isophthalic acid copolymerized polyethylene terephthalate was used as the copolyester constituting the layer A. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Example 6]
The same operation as in Example 1 was performed except that the heat setting condition was 195 ° C. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Example 7]
The same operation as in Example 1 was performed except that the longitudinal draw ratio was 3.6 times, the transverse draw ratio was 3.6 times, and the heat setting condition was 220 ° C. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Example 8]
The same operation as in Example 1 was performed except that the longitudinal draw ratio was 2.7 times and the transverse draw ratio was 2.7 times. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Comparative Example 1]
The same procedure as in Example 1 was conducted except that the copolymer polyester constituting layer A was 16 mol% copolymerized polyethylene terephthalate of isophthalic acid. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Comparative Example 2]
It carried out like Example 1 except having used polyethylene terephthalate as polyester which constitutes layer B. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Comparative Example 3]
The same operation as in Example 1 was performed except that the heat setting condition was 170 ° C. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

[Comparative Example 4]
The same procedure as in Example 1 was performed except that no colorant was added to layer A. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

  In Table 1, IAn represents n mol% of isophthalic acid copolymerized polyethylene terephthalate. PET indicates polyethylene terephthalate.

  The biaxially stretched polyester film for metal plate laminating molding of the present invention has sufficient adhesiveness even when laminated at a low temperature, and is excellent in molding processability after lamination and also excellent in gold colorability. It can be suitably used for applications such as beverage cans and food cans using metal plates, particularly metal plates with low processing temperatures such as tinplate.

Claims (5)

A laminated film having a layer A and a layer B forming one surface layer;
Layer A is a copolyester layer having a heat of fusion of 10 J / g or less in DSC and a plane orientation coefficient of 0.000 or more and 0.050 or less,
Layer B is a polyester layer having a melting point of 210 ° C. or more and 245 ° C. or less, and an X-ray diffraction intensity ratio Xb represented by the following formula of layer B of 0.50 or more,
The colorant is contained in at least one of the layer A and the layer B in an amount of 0.05 to 50% by weight based on the weight of the layer containing the colorant, and the a * value by the color difference meter of the film is −30 A biaxially stretched polyester film for metal plate laminating molding, having a b * value of 20 to 70.

The difference Xa-Xb between the X-ray diffraction intensity ratio Xa represented by the following formula of layer A and the above Xb is 0.20 to 0.70. Axial stretched polyester film.

  The biaxial for metal plate lamination molding processing according to claim 1 or 2, wherein the copolymer polyester in layer A is copolymer polyethylene terephthalate containing naphthalene dicarboxylic acid or isophthalic acid as a copolymer component in an amount of 16 to 30 mol%. Stretched polyester film.   The biaxially stretched polyester film for metal plate laminating molding according to any one of claims 1 to 3, wherein a melting subpeak temperature (Tsm) of the film is 180 ° C or higher and 215 ° C or lower.   The metal according to any one of claims 1 to 4, wherein the colorant comprises at least one selected from the group consisting of anthraquinone, isoindolinone, benzimidazolone, quinophthalone, and condensed azo. Biaxially stretched polyester film for board lamination molding.