JP7398041B2 - Film for laminating metal plates - Google Patents

Description

The present invention relates to a film for laminating metal plates.

Metal cans are generally coated with paint to prevent corrosion on the inside and outside surfaces, but recently a method to achieve rust prevention without using organic solvents has been developed to simplify processes, improve hygiene, and prevent pollution. As one of the advances, coating with thermoplastic resin film has been attempted. That is, studies are underway on a method of laminating a thermoplastic resin film onto a metal plate such as tinplate, tin-free steel, aluminum, etc., and then producing cans by drawing or the like.

On the other hand, gold-colored paint is still widely used to give cans a luxurious appearance, and proposals have been made to replace this with colored film laminates, but there are many problems. For example, Patent Document 1 discloses a colored polyester film containing ethylene terephthalate as a main component, but the high melting point of the film makes it difficult to laminate it with good adhesion to a metal plate, and it is difficult to form it. There was a problem in that it could only be used for shallow squeeze cans with low elasticity, and could not be applied to applications that require a high degree of molding, such as beverage cans, which are the most widely used type. In addition, in the case of a single-layer film made of colored polyester resin, depending on the colorant, the colorant may easily bleed out during retort sterilization after can manufacturing, which not only impairs the appearance, but also makes it safer, especially when laminated on the inner surface of the container. There could be sexual problems. Further, in Patent Document 2, at least one type of organic pigment selected from the group consisting of anthraquinone type, isoindolinone type, benzimidazolone type, quinophthalone type, condensed azo type, and pteridine type is used as the coloring agent. However, due to the low heat resistance of the organic pigment, there were problems such as discoloration during heat molding and bleed-out of the colorant during retort sterilization treatment after can formation.

Therefore, in the conventional technology, there has been no material that has film formability, high moldability, discoloration during heat molding, gold color development after retorting, and colorant bleedout resistance.

Japanese Patent Application Publication No. 2001-301025 Japanese Patent Application Publication No. 2006-142654

The purpose of the present invention is to have excellent film forming properties, to exhibit excellent molding processability when laminated to a metal plate and subjected to can manufacturing processes such as drawing, and to prevent discoloration when heated and formed, and to develop a golden color after retorting. An object of the present invention is to provide a film for laminating metal plates, which can be used to manufacture metal cans and has excellent properties and resistance to colorant bleed-out.

According to the research conducted by the present inventors, it has been found that the above-mentioned problems can be achieved by the following configurations 1 to 9.
1. A film made of a polyester composition containing a pigment, which has an a ^* value of -30 to 20 and a b ^* value of -10 to 70 as measured by a color difference meter, and has a pigment-containing oxygen atmosphere from room temperature to A film for laminating metal plates, characterized in that the weight loss rate when the temperature is raised to 300°C at a heating rate of 10°C/min is less than 1.5% by mass.
2. The metal plate according to the above 1, wherein the weight loss rate of the pigment when heated from room temperature to 300°C at a heating rate of 10°C/min in a nitrogen atmosphere is in the range of 0.1 to less than 1.5% by mass. Laminating film.
3. 1. The film for metal lamination as described in 1 above, wherein the pigment is at least one selected from the group consisting of acetoacetanilide azo pigments and quinacridone organic pigments.
4. 3. The film for laminating metal plates as described in 3 above, in which at least two types of pigments having different structures are used in combination.
5. The film is a laminated film consisting of a polyester A layer and a polyester B layer in contact with the polyester A layer, in which the main resin component forming the polyester A layer is polyethylene terephthalate (a), and the main resin component forming the polyester B layer is polybutylene. Polyester layer B contains 0 to 70% by weight of terephthalate (b1) and 30 to 100% by weight of polyethylene terephthalate (b2), and 0.1 to 100% of a colorant is added to the total 100 parts by weight of the polymer consisting of the resin component of layer B. 5. The film for laminating metal plates according to any one of 1 to 4 above, containing 5.0 parts by weight.
6. 5. The film for laminating metal plates as described in 5 above, wherein the polyester A layer has a thickness of 0.5 to 5 μm, and the polyester B layer has a thickness of 5 to 50 μm.
7. 5. The film for laminating metal plates as described in 5 above, wherein the polyester A layer is used as the outermost layer.
8. The film for laminating metal plates according to any one of 1 to 7 above, which has a color difference ΔE* of 3.0 or less before and after heat treatment at 230° C. for 1 minute.
9. 9. The film for laminating metal plates according to any one of 1 to 8 above, which is used for molding after being laminated to a metal plate.

The film for laminating metal plates of the present invention has excellent film formability, exhibits excellent molding processability when laminated to metal plates and performs can manufacturing processes such as drawing, and has excellent discoloration properties when heated and formed. It is possible to obtain a film for laminating metal plates in which gold color development after retorting and colorant bleed-out are also suppressed.

The film for laminating metal plates of the present invention is suitable for use by laminating to the can bodies and lids of metal cans, such as those for soft drinks and food cans.

The present invention will be explained in detail below.
The film for laminating metal plates of the present invention is a film made of a polyester composition containing a pigment, and has an a* value of -30 to 20 and a b* value of -10 to 70 as measured by a color difference meter. is a film for laminating metal plates, which has a weight loss rate of less than 1.5% by mass when the pigment is heated from room temperature to 300°C at a heating rate of 10°C/min in an oxygen atmosphere; It may be a layered film or a laminated film consisting of at least two layers: a surface layer (layer A) and a base layer (layer B). A laminated film consisting of at least two layers, a surface layer (layer A) and a base layer (layer B), is preferable because the functions can be separated into each layer and the effects of the present invention can be more easily expressed.

The polyester forming the polyester composition in the present invention can be of any known type, and preferred examples include polyethylene terephthalate having ethylene terephthalate as its main repeating unit, polybutylene terephthalate having butylene terephthalate as its main repeating unit, and combinations thereof. can. Hereinafter, polyethylene terephthalate and polybutylene terephthalate will be explained in detail as representative examples of polyester.

[polyethylene terephthalate]
The polyethylene terephthalate in the present invention is a polyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component. Polyethylene terephthalate is not limited to a homopolymer, and may be copolymerized with other components as long as the effects of the present invention are not impaired, and copolymerization facilitates improving moldability.

The copolymerization component of polyethylene terephthalate in the present invention may be an acid component or an alcohol component. Examples of the copolymerized dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalene dicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; and alicyclic acids such as cyclohexane dicarboxylic acid. Examples include group dicarboxylic acids and their ester-forming derivatives. Examples of the diol component to be copolymerized include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more.

The ratio of the copolymerization components is preferably such that the resulting polymer has a melting point in the range of 210 to 256°C, preferably 215 to 256°C, and more preferably 220 to 256°C. If the melting point of the polymer is less than the lower limit, the heat resistance will be poor, and if the polymer melting point exceeds the upper limit, the crystallinity of the polymer will be too high and moldability will be impaired.

The intrinsic viscosity of polyethylene terephthalate is preferably 0.50 to 0.80, more preferably 0.54 to 0.70, particularly preferably 0.57 to 0.65. If the intrinsic viscosity is less than the lower limit, it is difficult to obtain a film with mechanical strength that can be used in practical use, and if it exceeds the upper limit, moldability is likely to be impaired.

In addition, unless otherwise specified, the melting point of the polyester in the present invention is the melting point obtained by a method of determining the melting peak using a differential scanning calorimeter DSC (TA Instruments Q100) at a heating rate of 20° C./min. The sample amount is approximately 20 mg. Further, unless otherwise specified, the intrinsic viscosity of the polyester in the present invention is a value determined from a value measured at 35° C. after dissolving it in o-chlorophenol.

By the way, when it is necessary to particularly increase heat resistance, homopolyethylene terephthalate is preferable, for example, when the proportion of the copolymer component is 0.3 mol% or less, further 0.2 mol% or less, especially 0.1 mol% or less. Certain homopolyethylene terephthalates are preferred.

[Polybutylene terephthalate]
The polybutylene terephthalate in the present invention is a polyester containing terephthalic acid as a dicarboxylic component and 1,4-butanediol as a diol component. This polyester is preferably one that has been subjected to a solid phase polycondensation reaction after a melt polymerization reaction.

The polybutylene terephthalate in the present invention is not limited to a homopolymer, and other components may be copolymerized as long as the effects of the present invention are not impaired, and the copolymerized component may be a dicarboxylic acid component or a diol component.

In the present invention, the copolymerized dicarboxylic acid component of polybutylene terephthalate includes aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalene dicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and cyclohexane. Examples include alicyclic dicarboxylic acids such as dicarboxylic acids. Among these, isophthalic acid, 2,6-naphthalenedigalbonic acid, and adipic acid are preferred. Examples of copolymerized diol components include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more.

The proportion of the copolymerized components depends on the type thereof, but is such that the resulting polymer has a melting point in the range of 180 to 223°C, preferably 200 to 223°C, and more preferably 210 to 223°C. If the melting point of the polymer is below the lower limit, the crystallinity of the polyester will be low, resulting in a decrease in the heat resistance of the film.

The intrinsic viscosity of polybutylene terephthalate in the present invention is preferably 0.60 to 2.00, more preferably 0.80 to 1.70, particularly preferably 0.85 to 1.50. If the intrinsic viscosity is less than the lower limit, it will be difficult to obtain a film with mechanical strength that can be used for practical purposes, and if it exceeds the upper limit, the productivity of the polyester resin and film will decrease.

[Layer structure]
As mentioned above, the film for laminating metal plates of the present invention may be a single layer or a laminated film consisting of at least two layers: a surface layer (layer A) and a base layer (layer B).

In the case of a single layer, the resin component is preferably the aforementioned polyethylene terephthalate or a mixture of polyethylene terephthalate and polybutylene terephthalate. When it is a mixture of polyethylene terephthalate and polybutylene terephthalate, the weight ratio of polyethylene terephthalate and polybutylene terephthalate is preferably 100:0 to 30:70, more preferably 70:30 to 30:70, particularly 60:40 to 40. :60 is preferable. By blending polybutylene terephthalate, the shortest half crystallization time can be shortened and the appearance after retort treatment can be prevented from turning into a milky white color in spots.

When the film for laminating metal plates of the present invention is a laminated film consisting of at least two layers, a surface layer (layer A) and a base layer (layer B), the surface layer (layer A) may be made of the above-mentioned polyethylene terephthalate. Preferably, the other base material layer (layer B) is preferably made of polyethylene terephthalate or a mixture of polyethylene terephthalate and polybutylene terephthalate as explained in the case of the single layer described above, and particularly preferably a mixture of polyethylene terephthalate and polybutylene terephthalate. preferable. When it is a mixture of polyethylene terephthalate and polybutylene terephthalate, the ratio is preferably 100:0 to 30:70, more preferably 70:30 to 30:70, particularly preferably 60:40 to 40:60. By blending polybutylene terephthalate, the shortest half crystallization time can be shortened and the appearance after retort treatment can be prevented from turning into a milky white color in spots.

In addition, when using a mixture of polyethylene terephthalate and polybutylene terephthalate, it is preferable from the viewpoint of molding processability that the mixture is homogeneously kneaded in a molten state before film formation, and that a portion of the mixture is subjected to a transesterification reaction at that time.

[Colorant]
As mentioned above, the polyester composition forming the film for laminating metal plates of the present invention contains a colorant. Pigments are preferred as the colorant in the present invention.

If the film for laminating metal plates of the present invention is colored yellow, when it is laminated to a metal plate, the metal plate will have a gold shine due to the luster of the metal, giving a high-class feel to the metal can. can do. Therefore, the colorant is preferably a yellow pigment. Pigments have excellent coloring power and transparency, but many have poor heat resistance, and may bleed out during retort sterilization treatment after can manufacturing.

Therefore, the present inventors conducted extensive research on colorants in films for use with metal plates. At that time, I thought that it would be better to use a colorant with excellent heat resistance, so I selected a colorant that has a small weight loss rate when heated from room temperature to 300℃ at a heating rate of 10℃/min in a nitrogen atmosphere. However, even with a colorant having excellent heat resistance and a weight loss rate of less than 1.5% by mass, the desired effect could not be obtained. Therefore, no correlation was observed between the heat resistance and retort resistance of the colorant.

However, when we also checked the weight loss rate when the colorant pigment was heated from room temperature to 300°C at a heating rate of 10°C/min in an oxygen atmosphere, we found that the weight loss rate was less than 1.5% by mass. Then, they discovered that they exhibited excellent retort resistance and arrived at the present invention. The weight loss rate when the colorant is heated from room temperature to 300° C. at a heating rate of 10° C./min in an oxygen atmosphere is less than 1.3% by mass, preferably less than 1.0% by mass.

As the colorant having a low weight loss rate under an oxygen atmosphere, pigments are preferably used, particularly acetoacetanilide azo pigments and quinacridone organic pigments. The acetoacetanilide azo pigment is a pigment represented by the following structural formula (1), and the quinacridone organic pigment is a pigment represented by the following structural formula (2).

When using an acetoacetic acid anilide azo pigment or a quinacridone organic pigment, it is preferable to use yellow and red pigments in order to obtain a golden color when bonded to a metal plate. As a specific coloring agent, at least one selected from the group represented by the following structural formulas (3) to (6) can be preferably exemplified.

The method of blending the colorant in the present invention is not particularly limited, and it may be blended in the manufacturing process of the raw resin, for example, in the polymerization process, or it may be blended into the finished raw resin using a melt kneader or the like. , by producing master chips of raw resin containing a high concentration of colorant in advance using, for example, a twin-screw extruder, and mixing them with chips of raw resin that does not contain colorant or contains colorant at low concentration. , a resin composition containing a desired concentration of colorant may be obtained. In particular, a method using a master chip is preferable because it is easy to disperse the colorant uniformly and the content of the colorant is easy to adjust. Alternatively, the colorant may be directly incorporated in powder form into an extruder in the film forming process using, for example, a screw feeder.

The content of the colorant in the film for laminating metal plates of the present invention is 0.1 to 5.0 parts by weight, preferably 0.3 to 5.0 parts by weight, based on 100 parts by weight of the resin component forming the layer containing the colorant. Preferably, it is 1.0 part by weight. By containing the colorant in such a range, it is easy to achieve a good color tone while suppressing bleed-out.

[Color]
The film for laminating metal plates of the present invention has a color tone with an a ^* value of -30 to 20 and a b ^* value of -10 to 70, preferably an a ^* value of -15 to 15, and a b* value measured by a color difference meter. ^* Has a tone with a value between 5 and 45. By setting the a ^* value and the b ^* value within these ranges, it is possible to impart a gold coloring property that gives a luxurious appearance after metal lamination. For example, if the b* value is less than the lower limit, colorability is poor and good gold coloring cannot be obtained after metal lamination. The color measurement is based on JIS Z-8722, and is a value measured by a white plate reflection method using a spectroscopic automatic color difference meter.

[Polymerization catalyst]
When polymerizing the polyester resin used in the film for laminating metal plates of the present invention, it is preferable to add a polycondensation reaction catalyst or a transesterification reaction catalyst as a polymerization catalyst. Examples of transesterification reaction catalysts include calcium compounds, manganese compounds, germanium compounds, titanium compounds, etc., and preferable examples of polycondensation reaction catalysts include antimony compounds, aluminum compounds, germanium compounds, and titanium compounds. Among these, titanium compounds such as titanium acetate and titanium tetrabutoxy are preferred because they can minimize the amount of catalyst.

[Stabilizer]
In order to obtain good thermal stability and color, the polyester resin used in the film for laminating metal plates of the present invention preferably contains a stabilizer, such as a phosphoric acid stabilizer such as trimethyl phosphate. It is preferable to add.

[Fine particles]
The film for laminating metal plates of the present invention preferably contains fine particles in order to improve the handling properties, particularly the winding properties, in the film manufacturing process. The fine particles preferably have an average particle size of 2.5 μm or less, more preferably 0.01 to 1.8 μm. The fine particles are preferably contained in an amount of 0.01 to 1 part by weight, more preferably 0.01 to 0.5 part by weight, per 100 parts by weight of the polymer. As the fine particles, either inorganic fine particles or organic fine particles may be used, but inorganic fine particles are preferably used. Examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, and barium sulfate. Examples of organic fine particles include crosslinked polystyrene particles and crosslinked silicone resin particles.

The average particle size of the fine particles is preferably 2.5 μm or less, and if the average particle size of the fine particles exceeds 2.5 μm, the coarse particles (for example, particles of 10 μm or more) in the portion deformed by the molding process become the starting point and become pinned. This may cause holes or even breakage in some cases. Particularly preferable fine particles from the viewpoint of pinhole resistance are monodisperse fine particles having an average particle size of 2.5 μm or less and a particle size ratio (major axis/breadth axis) of 1.0 to 1.2. Examples of the fine particles include true spherical silica, true spherical titanium dioxide, true spherical zirconium, and true spherical crosslinked silicone resin particles.

[laminate]
The film for laminating metal plates of the present invention is a laminated film consisting of at least two layers, a surface layer (layer A) and a base layer (layer B), in order to prevent colorant from bleeding out during retort sterilization treatment after can manufacturing. is preferred. In the case of a laminated film, it is necessary to laminate the A layer to the metal plate so that it becomes the outermost layer. Furthermore, in order for layer A to exhibit the effect of preventing colorant bleed out from layer B, the thickness of layer A is 0.5 to 5.0 μm, preferably 2 μm or more, and more preferably an upper limit of 5 μm. It is.

The film for laminating metal plates of the present invention preferably has a thickness of 6 to 55 μm, more preferably 8 to 45 μm, particularly preferably 10 to 30 μm. If the thickness is less than 6 μm, breakage is likely to occur during molding, and if it exceeds 55 μm, the quality is excessive and uneconomical, which is undesirable.

As a metal plate to which the metal plate laminating film of the present invention is laminated, particularly a metal plate for can manufacturing, plates made of tin plate, tin free steel, tin nickel steel, aluminum, etc. are suitable. The polyester film can be attached to the metal plate by, for example, the method (a) or (b) below.
(a) A metal plate is heated to a temperature higher than the melting point of the film, the films are bonded together, and then cooled to amorphize the surface layer (thin layer) of the film in contact with the metal plate and bring them into close contact.
(a) Primer-coat the film with adhesive in advance and attach this side to the metal plate. As the adhesive, known resin adhesives such as epoxy adhesives, epoxy-ester adhesives, and alkyd adhesives can be used. Further, by dispersing a white pigment or a yellow pigment in this adhesive, a film having a colored appearance can be obtained.

[Production method]
The polyester used in the film for laminating metal plates of the present invention can be produced by a conventionally known method. For example, terephthalic acid, ethylene glycol, and a copolymer component are subjected to an esterification reaction, and then the resulting reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester, or dimethyl terephthalate, ethylene glycol, and a copolymer component are subjected to a transesterification reaction. It can be produced by a method in which a copolymerized polyester is produced by subjecting the resulting reaction product to a polycondensation reaction. If necessary, other additives such as optical brighteners, antioxidants, heat stabilizers, and antistatic agents may be added.

The film for laminating metal plates of the present invention can be manufactured using the above-mentioned polyester according to a conventionally known extrusion film forming method (in the case of a laminated film, a coextrusion film forming method).

Taking the case of a laminated film as an example, the following explanation will be made. First, each of the polyester raw materials mentioned above is dried as necessary, and then each polyester is The molten sheet is extruded through a slit-shaped die, and is cooled and solidified with a cooling roll to obtain an unstretched sheet. In this case, in order to improve the flatness of the sheet, it is necessary to increase the adhesion between the sheet and the rotating cooling drum, and an electrostatic application adhesion method or a liquid application adhesion method is preferably employed. In the present invention, both may be used in combination if necessary.

Although the film for laminating metal plates of the present invention may be an unstretched film, it is preferably a biaxially oriented film. Therefore, a method for forming a biaxially oriented film will be explained. The obtained unstretched film is biaxially oriented by stretching in two directions. That is, first, the unstretched sheet is stretched in the longitudinal direction using a roll or tenter type stretching machine. The stretching temperature is 50 to 100°C, preferably 60 to 90°C, and the stretching ratio is 2.8 to 5.0 times, preferably 3.0 to 4.5 times. Next, stretching is performed in the width direction using a tenter type stretching machine. The stretching temperature is 60 to 110°C, preferably 70 to 10°C, and the stretching ratio is 3.0 to 5.0 times, preferably 3.5 to 4.5 times. Further, it is preferable to subsequently carry out a heat treatment at a temperature in the range of 130 to 220° C. with a relaxation of not more than 20%, and in this way a biaxially stretched film can be obtained.

The present invention will be further explained below with reference to Examples. In addition, the characteristics of the film were measured and evaluated by the following methods.
(1) Weight loss rate of colorant (1-1) Under oxygen atmosphere Using a thermogravimetric analyzer TGA (Q50 manufactured by TA Instruments), under an oxygen atmosphere (flow rate 60 mL/min) at a heating rate of 10 °C/min from 30 °C. After the temperature was changed to 300°C, the temperature was further held at 300°C for 30 minutes, and the weight loss rate of the pigment was determined. Note that the sample amount was 10 mg of pigment.
(1-2) Under a nitrogen atmosphere Using a thermogravimetric analyzer TGA (TA Instruments Q50), the temperature was changed from 30°C to 300°C at a temperature increase rate of 10°C/min under a nitrogen atmosphere (flow rate 60mL/min), and then The weight loss rate of the pigment was determined by holding at 300° C. for 30 minutes. Note that the sample amount was 10 mg of pigment.
(2) Melting point The melting peak temperature of the film was determined using a differential scanning calorimeter DSC (TA Instruments Q100) at a heating rate of 20° C./min. Note that the sample amount was approximately 20 mg.
(3) Intrinsic viscosity Measured using o-chlorophenol at a temperature of 35°C.
(4) Gold color development Based on JIS Z-8722, the a ^* value and b ^* value of one 5 cm square sample were measured using an automatic color difference meter (SE6000) manufactured by Nippon Denshoku Industries, and the film was evaluated according to the following criteria. The gold color development was evaluated. Incidentally, during the measurement, a white plate attached to the apparatus was used as a film holder, and the measurement was carried out by the reflection method.
◎: a ^* value is -15 to 15, b* value is 5 to 45
○: a ^* value is -30 to 20, b ^* value is -10 to 70
△: a ^* value is -30 to 20, b ^* value is outside the above range
×: A ^* value and b ^* value outside the above range (5) Retort resistance The film was retort sterilized at 125°C for 90 minutes, and L ^* , a ^* , b were determined in the same manner as in (4) for the film before and after treatment. ^* was measured. Furthermore, the color difference (ΔE*) was calculated and evaluated using the following formula.
ΔE ^* = {(ΔL*) ² + (Δa*) ² + (Δb*) ² } ^1/2
ΔL* = difference in L* of film before and after processing
Δa* = difference in a* of film before and after treatment
Δb* = difference in b* of the film before and after processing ○: ΔE ^* is 5 or less △: ΔE ^* is more than 5 and less than 10 ×: ΔE ^* is 10 or more Nippon Denshoku also measured the haze of the film before and after retort processing. It was measured using an industrial haze meter NDH4000 model, and the amount of change in haze (ΔHz) before and after the retort treatment was calculated.
ΔHz = (Haze after retort treatment) - (Haze before retort treatment)
○: ΔHz is 10 or less △: ΔHz is more than 10 and less than 15 ×: ΔHz is 15 or more (6) Heat resistance (dry heat)
The film was subjected to dry heat treatment at 230° C. for 1 minute, and L ^* , a ^* , and b ^* were measured in the same manner as in (4) for the film before and after the treatment. Furthermore, the color difference (ΔE ^* ) was calculated and evaluated using the above formula in the same manner as in (5).
○: ΔE* is 3 or less
△: ΔE* is more than 3 and less than 5 ×: ΔE* is 5 or more

[Examples 1 to 12]
The polyester compositions of layer A and layer B shown in Table 1 were dried by a conventional method, and then separately melted at 280°C for layer A and 270°C for layer B, containing pigments with the color index numbers shown in Table 2. After that, two layers were laminated using a feed block, extruded from a die, and cooled and solidified to produce an unstretched film.
Next, this unstretched film was longitudinally stretched at 85°C to 3.2 times in the film forming direction, then laterally stretched at 105°C to 3.8 times in the direction perpendicular to the film forming direction, and heat-set at 200°C. A biaxially oriented laminated film was obtained. The thickness of the obtained biaxially oriented laminated film was 20 μm.

[Comparative example 1]
A biaxially oriented laminated film was obtained by forming a film in the same manner as in Example 1, except that the colorant was changed to a monoazo salt pigment having the color index number shown in Table 2.

[Comparative example 2]
A biaxially oriented laminated film was obtained by forming a film in the same manner as in Example 1, except that the colorant was changed to a pteridine pigment having the color index number shown in Table 2.

The evaluation results are shown in Tables 1 and 2.

In Table 2, those in which the colorant of Comparative Examples 1 and 2 was used had low gold color development, retort resistance, and heat resistance.

The film for laminating metal plates of the present invention has excellent film formability, exhibits excellent molding processability when laminated to metal plates and performs can manufacturing processes such as drawing, and has excellent discoloration properties when heated and formed. Since it has excellent gold color development after retorting and colorant bleed-out resistance, it is suitable for use in bonding to the can bodies and lids between metals, such as those for soft drinks and food cans.

Claims (8)

A biaxially oriented film made of a polyester composition containing a pigment, the film comprising:
The a ^* value of the biaxially oriented film measured with a color difference meter is -30 to 20, the b ^* value is -10 to 70,
The weight loss rate of the pigment when heated from room temperature to 300°C at a heating rate of 10°C/min in an oxygen atmosphere is less than 1.5% by mass,
The pigment contains an acetoacetanilide azo pigment ,
A biaxially oriented film for laminating metal plates to create a gold color with the metallic luster of metal plates. The metal plate according to claim 1, wherein the weight loss rate of the pigment when heated from room temperature to 300°C at a heating rate of 10°C/min in a nitrogen atmosphere is in the range of 0.1 to less than 1.5% by mass. Biaxially oriented film for lamination. The biaxially oriented film for laminating metal plates according to claim 1 or 2, wherein at least two types of pigments having different structures are used in combination. The biaxially oriented film is a laminated film consisting of a polyester A layer and a polyester B layer in contact with this,
The main resin component forming the polyester A layer consists of polyethylene terephthalate (a),
The main resin components forming the polyester B layer are 0 to 70% by weight of polybutylene terephthalate (b1) and 30 to 100% by weight of polyethylene terephthalate (b2), and the polyester B layer is composed of the resin components of the B layer with a total weight of 100%. The biaxially oriented film for laminating metal plates according to any one of claims 1 to 3, which contains 0.1 to 5.0 parts by weight of a coloring agent. The biaxially oriented film for laminating metal plates according to claim 4, wherein the polyester A layer has a thickness of 0.5 to 5 μm, and the polyester B layer has a thickness of 5 to 50 μm. The biaxially oriented film for laminating metal plates according to claim 4 or 5, wherein the polyester A layer is used as the outermost layer. The biaxially oriented film for laminating metal plates according to any one of claims 1 to 6, which has a color difference ΔE ^* of 3.0 or less before and after heat treatment at 230°C for 1 minute. The biaxially oriented film for laminating metal plates according to any one of claims 1 to 7, which is used for molding after being laminated to metal plates.