JP2006015718A - Laminated film for metal lamination molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated film for metal lamination molding which has excellent molding processability and is excellent in post-retort appearance, gold coloring properties, coloring agent bleed-out resistance and the like. <P>SOLUTION: The laminated film is made by laminating a polyester layer A and a polyester layer B, the polyester layer A comprises a resin composition which consists of 30-70 wt.% of polybutylene terephthalate and 30-70 wt.% of polyethylene terephthalate, and the polyester layer B comprises a colored resin composition which comprises 100 pts.wt. of a resin composition consitsting of 30-70 wt.% of polybutylene terephthalate and 30-70 wt.% of polyethylene terephthalate, and incorporated therewith 0.1-5.0 pts.wt. of a coloring agent, wherein the shortest half-crystallization time of the laminated film is 1-100 s, and an a* value and a b* values measured by a color-difference meter are -30 to 20 and 20 to 70, respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminated film for metal laminating and forming processing, and more particularly excellent in film forming properties, and exhibits excellent forming workability when performing canning processing such as drawing by bonding to a metal plate. The present invention relates to a laminated film for metal lamination molding capable of producing a metal can excellent in appearance, gold color development and the like, for example, a beverage can and a food can.

  Metal cans are generally painted to prevent corrosion on the inner and outer surfaces, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, developed a method to obtain rust resistance without using organic solvents. As one of them, coating with a thermoplastic resin film has been attempted. That is, a method for making a can by drawing or the like after laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, or aluminum has been studied.

  On the other hand, in order to give a high-quality appearance to the can, a paint that develops a gold color is still widely used, and proposals have been made to replace it with a laminate of a colored film, but there are many problems. For example, in Japanese Patent Application Laid-Open No. 2001-301025, a colored polyester film having ethylene terephthalate as a main constituent is disclosed. However, since the melting point of the film is high, a laminate capable of obtaining good adhesion on a metal plate is disclosed. There is a problem that it is difficult and can only be used as a shallow can with low moldability, and cannot be applied to a use with a high degree of molding such as the most widely used beverage can. Japanese Patent Application Laid-Open No. 2003-26823 discloses a colored polyester film having good thermal laminating properties and moldability by copolymerizing PET to lower its melting point and lower crystallization. There has been a problem that the film that has been melted and amorphized is crystallized during retort sterilization to become white and impair the appearance. Furthermore, in the case of a single layer film made of colored polyester resin, depending on the colorant, not only does the colorant easily bleed out during retort sterilization after iron making, and the appearance is impaired, especially when laminating on the inner surface of the container There could be a problem with sex.

JP 2001-301025 A JP 2003-26823 A

Therefore, none of the conventional techniques satisfy all of high moldability, good appearance after retorting, gold color development, and colorant bleedout resistance.
The object of the present invention is a metal laminating process that can produce metal cans, such as beverage cans, food cans, etc., which have excellent moldability and excellent post-retort appearance, gold color development and colorant bleedout resistance. It is to provide a laminated film.

  That is, the present invention is a laminated film formed by laminating a polyester A layer and a polyester B layer, and the polyester A layer is composed of 30 to 70% by weight of polybutylene terephthalate and 30 to 70% by weight of polyethylene terephthalate. And a polyester B layer containing 0.1 to 5.0 parts by weight of a colorant per 100 parts by weight of a resin composition comprising 30 to 70% by weight of polybutylene terephthalate and 30 to 70% by weight of polyethylene terephthalate It is composed of a composition, the shortest half crystallization time of the laminated film is 1 to 100 seconds, and the a * value measured by a color difference meter is −30 to 20, and the b * value is 20 to 70. This is a laminated film for metal lamination molding.

  ADVANTAGE OF THE INVENTION According to this invention, the laminated | multilayer film for metal lamination | stacking shaping | molding processes provided with the outstanding moldability, the appearance after retort, gold color development property, and a coloring agent bleed-out resistance can be obtained.

Hereinafter, the present invention will be described in detail.
[Polyester A layer]
In the present invention, the polyester A layer is composed of a resin composition comprising 30 to 70% by weight of polybutylene terephthalate and 30 to 70% by weight of polyethylene terephthalate. Preferably, the polyester A layer is 40 to 60% by weight of polybutylene terephthalate. And polyethylene terephthalate 40 to 60% by weight.

  In the polyester A layer, when the polybutylene terephthalate is less than 30% by weight or the polyethylene terephthalate is more than 70% by weight, the shortest crystallization time of the resin composition exceeds 100 seconds, and the appearance after the retort treatment is milky white spots. Is likely to occur.

  In the polyester A layer, when the polybutylene terephthalate exceeds 70% by weight and the polyethylene terephthalate is less than 30% by weight, the shortest half crystallization time of the resin composition is less than 1 second, and the crystallinity is increased so that the film forming property is increased. Getting worse.

[Polyester B layer]
The polyester B layer is composed of a resin composition comprising 30 to 70% by weight of polybutylene terephthalate and 30 to 70% by weight of polyethylene terephthalate and a colored resin composition comprising a required amount of a colorant. It comprises a polyester resin composition comprising 40 to 60% by weight of butylene terephthalate and 40 to 60% by weight of polyethylene terephthalate and a colored resin composition comprising a required amount of colorant.

  In the polyester B layer, when the polybutylene terephthalate is less than 30% by weight or the polyethylene terephthalate is more than 70% by weight, the shortest crystallization time of the resin composition exceeds 100 seconds, and the appearance after retorting is milky white spots. Is likely to occur.

  In the polyester B layer, when the polybutylene terephthalate exceeds 70% by weight and the polyethylene terephthalate is less than 30% by weight, the shortest half crystallization time of the resin composition is less than 1 second, and the crystallinity is increased so that the film-forming property is increased. Getting worse.

  The required amount of colorant in the present invention is 0.1 to 5.0 parts by weight, preferably 0.3 to 1.0 parts by weight, based on 100 parts by weight of the polyester resin composition. This will be described later.

[Polybutylene terephthalate]
In the present invention, polybutylene terephthalate is a polyester composed of a terephthalic acid component and a 1,4-butanediol component.

  For this purpose, the copolymerization component may be copolymerized within a range in which the effects of the present invention are not impaired, for example, within a range of 30 mol% or less, further, for example, 20 mol% or less per total dicarboxylic acid component or total diol component. The copolymer component may be a dicarboxylic acid component or a diol component.

  Examples of the dicarboxylic acid component that can be used as the copolymerization component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. An alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid can be exemplified. Of these, isophthalic acid, 2,6-naphthalenedigalbonic acid or adipic acid is preferred.

  Examples of the diol component that can be used as a copolymerization component 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.

  When a copolymerization component is used, the copolymerization ratio is such that the melting point of the resulting polymer is preferably in the range of 180 to 223 ° C, more preferably 200 to 223 ° C, and particularly preferably 210 to 223 ° C. When the melting point of the polymer is less than 180 ° C., the crystallinity as polyester is low, and as a result, the heat resistance of the film is lowered. The melting point of polybutylene terephthalate homopolymer is 223 ° C.

[polyethylene terephthalate]
The polyethylene terephthalate in the present invention is a polyester mainly composed of a terephthalic acid component and an ethylene glycol component.

  For this purpose, the copolymerization component may be copolymerized within a range in which the effects of the present invention are not impaired, for example, within a range of 30 mol% or less, further, for example, 20 mol% or less per total dicarboxylic acid component or total diol component. The copolymer component may be a dicarboxylic acid component or a diol component.

  Examples of the dicarboxylic acid component that can be used as the copolymerization component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. An alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid can be exemplified. Of these, isophthalic acid, 2,6-naphthalenedigalbonic acid or adipic acid is preferred.

  Examples of the diol component that can be used as a copolymerization component 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.

  When the copolymer component is used, the copolymerization ratio is such that the melting point of the resulting polymer is preferably 210 to 256 ° C, more preferably 215 to 256 ° C, and particularly preferably 220 to 256 ° C. When the polymer melting point is less than 210 ° C., the heat resistance is poor. When the polymer melting point exceeds 256 ° C., the crystallinity of the polymer is too large, and the moldability is impaired. The polymer melting point is measured by differential scanning calorimetry using a differential scanning calorimeter (mDSC manufactured by TA Instruments) to obtain a melting peak at a heating rate of 20 ° C./min. The sample amount is about 20 mg.

  About the raw material polyester used in order to manufacture the laminated | multilayer film of this invention, the intrinsic viscosity of polybutylene terephthalate becomes like this. Preferably it is 0.60-2.00, More preferably, it is 0.80-1.70, Most preferably, it is 0.8. 85 to 1.50. An intrinsic viscosity of less than 0.6 is not preferable because a film having mechanical strength that can be used practically cannot be obtained. It is preferable that it is 2.0 or less from the surface of productivity of a raw material polyester resin and a film. The intrinsic viscosity of polyethylene terephthalate is preferably 0.50 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to 0.65. If the intrinsic viscosity is less than 0.50, a film having mechanical strength that can be practically used cannot be obtained, and if it exceeds 0.80, the molding processability is impaired. The intrinsic viscosity of the copolyester is measured at 35 ° C. after being dissolved in o-chlorophenol.

[Production method of polyester]
Polyethylene terephthalate and polybutylene terephthalate can be produced by applying conventionally known methods. Polyethylene terephthalate is produced, for example, by a method in which terephthalic acid, ethylene glycol, and, if necessary, a copolymerization component are esterified, and then a reaction product obtained is polycondensed to form a copolymerized polyester. Can do. It may be produced by a method in which dimethyl terephthalate, ethylene glycol and, if necessary, a copolymer component are subjected to an ester exchange reaction, and then a reaction product obtained is subjected to a polycondensation reaction to obtain a copolymer polyester.

  Polybutylene terephthalate is produced, for example, by a method in which terephthalic acid, tetramethylene glycol and, if necessary, a copolymerization component are esterified, and then the resulting reaction product is polycondensed to form a copolymerized polyester. can do. It may be produced by a method in which dimethyl terephthalate, tetraethylene glycol and, if necessary, a copolymer component are transesterified, and then the resulting reaction product is polycondensed to give a copolymer polyester.

[Colorant]
The polyester B layer is composed of a colored resin composition containing 0.1 to 5.0 parts by weight, preferably 0.3 to 1.0 parts by weight of a colorant with respect to 100 parts by weight of the resin composition.
When the colorant is less than 0.1 parts by weight, good color developability cannot be obtained, and when the colorant exceeds 5.0 parts by weight, the dispersion state of the colorant is deteriorated and the film forming property is lowered.

  As the colorant, an anthraquinone-based, isoindolinone-based, benzimidazolone-based, quinophthalone-based, or condensed azo-based organic pigment can be used, preferably an isoindolinone-based, benzimidazolone-based Any organic pigment of the quinophthalone type is used. Among them, isoindolinone-based organic pigments such as isoindolinone yellow; benzimidazolone-based organic pigments such as benzimidazolone yellow are preferable. One type of organic pigment may be used, or two or more types may be used. For the colorant, other components may be used in combination to adjust the color tone, but those having good heat resistance are preferred, and those that are recognized as safe for food hygiene are preferred. .

  The colorant may be added in the raw resin polymerization step, or a high concentration master chip is prepared by a twin screw extruder or the like and mixed with a colorant-free chip to a desired concentration. You may adjust. For example, you may use the method of using a screw feeder and adding a coloring agent directly with a powder to the polymer extruder of a film forming process.

[Fine particles]
In the laminated film of the present invention, fine particles having an average particle size of 2.5 μm or less, preferably 0.01 to 1.8 μm, are added to 100% by weight of polyester in order to improve handling properties, particularly winding properties in the film production process. The content is preferably 0.005 to 1% by weight, more preferably 0.01 to 0.5% by weight.

  These fine particles may be inorganic or organic, but are preferably inorganic. Examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, and barium sulfate, and examples of organic fine particles include crosslinked polystyrene particles and crosslinked silicone resin particles. In any case, it is desirable that the average particle size is 2.5 μm or less. When the average particle size of the fine particles exceeds 2.5 μm, coarse particles (for example, particles of 10 μm or more) deformed by the molding process are used as starting points, which may cause pinholes and may break in some cases.

  Particularly preferable fine particles in terms of pinhole resistance are monodispersed fine particles having an average particle size of 2.5 μm or less and a particle size ratio (major axis / minor axis) of 1.0 to 1.2. Examples of such fine particles include true spherical silica, true spherical titanium dioxide, true spherical zirconium, and true spherical crosslinked silicone resin particles.

  In the present invention, the polyethylene terephthalate and polybutylene terephthalate constituting the polyester composition of the polyester A layer are preferably melt-kneaded before film formation. Moreover, it is preferable that the polyethylene terephthalate and polybutylene terephthalate constituting the polyester composition of the polyester B layer are also melt-kneaded before film formation.

[Minimum semi-crystallization time]
In the present invention, the shortest half crystallization time of the film is 1 to 100 seconds, preferably 5 to 80 seconds, and particularly preferably 5 to 50 seconds. When the shortest half crystallization time is less than 1 second, the crystallinity is excessively increased and the film forming property is deteriorated. On the other hand, when the shortest crystallization time exceeds 100 seconds, the appearance after the retort treatment changes to a milky white color.

  The shortest half crystallization time referred to here is the half crystallization time measured in the temperature range where crystallization of the resin occurs, and the shortest half crystallization time in the temperature range. Using a measuring device (manufactured by Kotaki Seisakusho Co., Ltd., MK-801 type), the transmitted light due to the optically anisotropic crystal component that increases with crystallization of the sample placed between the orthogonal polarizing plates is measured at each sample temperature ( This is the shortest time among the values at each sample temperature at which the time required for the crystallinity to be ½ was calculated using the following Abramy equation.

  A sample (sample weight: 8 mg) was heated in nitrogen at a temperature of the maximum melting point of the resin + 50 ° C. for 1 minute in a melting furnace incorporated in the apparatus, immediately moved to a sample, immersed in a crystallization bath, 10 The measurement is started so that the sample temperature becomes an equilibrium measurement temperature within 2 seconds.

  The maximum melting point here is one or more endothermic peaks when the temperature is increased at a rate of temperature increase of 20 ° C./min by a differential scanning calorimeter (TA Instruments DSC type). The highest temperature among the temperatures indicating the depth. The depolarized intensity method is described in a new experimental chemistry course (Maruzen) and polymer chemistry Vol. 29. No. As described in 139, 323 and 336 (Polymer Society), this is an effective method for measuring a fast crystallization rate.

  In consideration of the time required for the sample to reach thermal equilibrium, the time when 10 seconds passed after moving the sample into the crystallization bath was measured as t = 0 seconds. The depolarized transmission intensity measured at t = 0 seconds is Io, the depolarized transmission intensity is plotted against Log, and the depolarized transmission intensity at the point where the crystallization temperature curve starts to become a straight line is defined as Ig.

  In the present invention, the amount of terminal COOH of polyethylene terephthalate and polybutylene terephthalate is largely related to the shortest half crystallization time of the film. When the COOH terminal amount of polybutylene terephthalate is 10 to 70 equivalent / ton and the COOH terminal amount of polyethylene terephthalate is 10 to 50 equivalent / ton, the shortest crystallization time can be controlled within the range of the present invention. On the other hand, if this method is not used, for example, if the residence time when the polymer is melted is increased or the residence temperature is increased, the polymer deteriorates due to thermal decomposition, which is not preferable.

  If the COOH terminal amount of polybutylene terephthalate is less than 10 equivalents / ton, the shortest half crystallization time becomes too long, and the film-forming property of the film due to the deterioration of the polymer tends to be lowered, and the appearance after the retort treatment Is not preferable because it changes to milky white in the form of spots. On the other hand, when the COOH terminal amount exceeds 70 equivalents / ton, the shortest semi-crystallization time becomes too short, causing crystallization during the film forming process, particularly during the stretching process, and local thickness unevenness and width variation. This is not preferable because the film forming property is likely to deteriorate.

  When the COOH terminal amount of polyethylene terephthalate is less than 10 equivalents / ton, the shortest half crystallization time becomes too long, and the film-forming property of the film due to the deterioration of the polymer tends to be lowered, and the appearance after the retort treatment is It is not preferable because it changes to milky white in the form of spots. On the other hand, when the COOH terminal amount exceeds 50 equivalents / ton, the shortest half crystallization time becomes too short, causing crystallization during the film forming process, particularly during the stretching process, and local thickness variation and width variation. This is not preferable because the film forming property is likely to deteriorate.

The COOH terminal amount was measured by adding 20 mg of benzyl alcohol to 100 mg of sample, heating at 200 ° C. for 4 minutes in a nitrogen atmosphere, cooling to room temperature, and using phenol red as an indicator. As 0.02N sodium hydroxide benzyl alcohol solution is added dropwise, and the following formula is obtained from the titration amount until indicator discoloration.
COOH terminal amount (equivalent / ton) = titer (cc) × 200

[Color tone]
The laminated film of the present invention needs to have a color tone having an a * value of −30 to 20 and a b * value of 20 to 70 as measured by a color difference meter, and an a * value of −20 to 10 and b. * More preferably, the value is 40 to 70. The a * value and the b * value are numerical values measured by a white plate reflection method using a spectroscopic automatic color difference meter based on JIS Z-8722.

  By setting the a * value and the b * value within this range, it is possible to provide a gold color with a high-quality appearance after metal lamination. When the b * value is less than 20, the colorability is poor, and good gold colorability cannot be obtained after metal lamination. On the other hand, when it exceeds 70, the dispersion state of the colorant is deteriorated, and the film-forming property tends to be lowered.

[Color difference]
The laminated film of the present invention has a color difference ΔE * before and after retorting at 125 ° C. for 90 minutes, preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less. In particular, the heat resistance of the colorant added to the film is important in order to use it suitably under high temperature or retort. For example, use a colorant whose thermal mass change rate at 300 ° C. is 5% or less. Is preferred.

  The laminated film of the present invention has a color difference ΔE * before and after being subjected to a dry heat treatment at 200 ° C. for 1 minute, preferably 3 or less, more preferably 2 or less. If the color difference before and after the dry heat treatment at 200 ° C. for 1 minute exceeds 3, the colorant is denatured due to heat applied during film formation or lamination, and the desired film color developability cannot be obtained.

[Haze change]
In the laminated film of the present invention, the haze change (ΔHz) before and after retorting at 125 ° C. for 90 minutes is preferably 10 or less, more preferably 7 or less, more preferably 5 or less, particularly preferably 3 or less. is there. If the amount of change in haze (ΔHz) before and after retorting for 90 minutes at 125 ° C exceeds 10, the film changes to a milky white spotted pattern after retort sterilization after sticking to metal and making a can. Damage.

[Thickness]
The thickness of the polyester A layer is preferably 1 to 7 μm, and the thickness of the polyester B layer is preferably 5 to 50 μm. In order for the polyester A layer to exhibit the effect of preventing pigment bleed out from the polyester B layer, the thickness of the polyester A layer is preferably 1 μm or more, more preferably 2 μm or more. When the thickness of the polyester A layer is less than 1 μm, there is no effect of preventing the bleeding out of the pigment. Further, if the thickness of the polyester B layer is less than 5 μm, good color developability cannot be obtained, which is not preferable. Furthermore, the total thickness of the laminated film of the present invention is preferably 6 to 55 μm, more preferably 8 to 45 μm, and particularly preferably 10 to 30 μm. If the total layer thickness is less than 6 μm, tearing tends to occur at the time of molding, while those exceeding 55 μm are undesirable because they are excessive quality and uneconomical.

[Production method]
In order to obtain the laminated film of the present invention, it is important to use a colorant having high heat resistance as a colorant to be added to the film, particularly for use under high temperature or retort. As the colorant, it is preferable to use an organic pigment having a thermal mass change rate at 300 ° C. of 5% or less. As such a colorant, an anthraquinone-based, isoindolinone-based, benzimidazolone-based, quinophthalone-based, condensed azo-based organic pigment can be used, among which an isoindolinone-based organic pigment, For example, isoindolinone yellow; benzimidazolone-based organic pigments such as benzimidazolone yellow are preferable. In the present invention, an organic pigment selected from the group consisting of these compounds can be used. One type of organic pigment may be used, or two or more types may be used.

  A conventionally known film forming method can be adopted as the film forming method itself of the laminated film of the present invention. First, after drying each above-mentioned polyester raw material as needed, it is supplied to a melt extruder, extruded from a slit-shaped die into a sheet, and 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 improve the adhesion between the sheet and the rotary 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 together as necessary.

  The laminated film of the present invention may be an unstretched film, but is preferably a biaxially oriented laminated film. Next, a method for forming a laminated film when the laminated film of the present invention is a biaxially oriented laminated film will be described. The obtained unstretched film is stretched biaxially and biaxially oriented. That is, first, the unstretched sheet is stretched in the longitudinal direction by 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, the film is stretched in the width direction by a tenter type stretching machine. The stretching temperature is 60 to 110 ° C., preferably 70 to 100 ° C., and the stretching ratio is 3.0 to 5.0 times, preferably 3.2 to 4.5 times. Further, heat treatment is performed at a temperature in the range of 130 to 220 ° C. under relaxation within 20% to obtain a biaxially oriented laminated film.

[metal]
The laminated film of the present invention is used by being bonded to a metal, particularly a metal plate. In particular, the polyester A layer is preferably used so as to be the outermost layer. The laminated polyester of the present invention is preferably laminated to a metal plate so that the polyester A layer is the outermost layer in order to prevent bleeding out of the colorant during retort sterilization treatment after ironmaking.

As the metal plate, a plate of tin, tin-free steel, tin-nickel steel, aluminum or the like is appropriate. The lamination film can be bonded to the metal plate by, for example, the following methods (a) and (b).
(A) The metal plate is heated to the melting point of the film or higher, and the films are bonded together and then cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is amorphized and adhered.
(A) The film is preliminarily coated with an adhesive, and this surface is bonded to a metal plate. As the adhesive, a known resin adhesive such as an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used. Moreover, it can also be set as the film which has a colored appearance by disperse | distributing a white pigment or a yellow pigment to this adhesive agent.

Hereinafter, the present invention will be further described with reference to examples. The film characteristics were measured and evaluated by the following methods.
(1) Melting point According to a method for obtaining a melting peak temperature at a heating rate of 20 ° C./min using a DSC2920 Modulated DSC manufactured by TA Instruments. The sample amount is about 20 mg.

(2) Intrinsic viscosity After the film was dissolved in o-chlorophenol, the filler such as titanium oxide was removed by a centrifuge and measured at a temperature of 35 ° C. In addition, an intrinsic viscosity is a value of an unstretched film.

(3) COOH terminal amount Using a COOH automatic measuring device manufactured by Seiwa Giken, 20 mg of benzyl alcohol was added to 100 mg of sample, heated at 200 ° C. for 4 minutes in a nitrogen atmosphere, cooled to room temperature, and phenol red as an indicator. A 0.02N sodium hydroxide benzyl alcohol solution is dropped, and it is determined from the titration amount until indicator discoloration using the following formula.
COOH terminal amount (equivalent / ton) = titer (cc) × 200

(4) Shortest half crystallization time Using a polymer crystallization rate measuring apparatus MK-801 manufactured by Kotaki Seisakusho, measurement is performed in the range of 40 to 150 ° C. with 8 mg of sample.

(5) Deep drawing workability A sample film is bonded to both sides of a 0.25 mm thick tin-free steel heated to 230 ° C., cooled with water, then cut into a 150 mm diameter disk, and using a drawing die and punch Then, deep drawing is performed in four stages, and a 55 mm diameter side seamless container (hereinafter abbreviated as a can) is created. The following observations and tests are conducted on these cans and evaluated according to the following criteria.
○: The film is processed without any abnormality, and no whitening or breakage is observed in the film.
(Triangle | delta): Whitening is recognized by the can upper part of a film.
X: Film breakage is observed in a part of the film.

(6) Hue measurement of film Based on JIS Z 8722, using an automatic color difference meter (SE-Σ90 type) manufactured by Nippon Denshoku Industries Co., Ltd., the a * value and b * value of one 5 cm square sample were measured. The film color developability is evaluated based on the standard. In the measurement, a white plate attached to the apparatus is used as a film presser and the measurement is performed by a reflection method.
A: a * value is -30 to 20, b * value is 20 to 70
Δ: a * value is −30 to 20, b * value is less than 20 or more than 70 ×: a * value is less than −30 or more than 20, and b * value is less than 20 or more than 70

(7) Retort resistance of film The film is subjected to retort sterilization at 125 ° C. for 90 minutes, and L *, a *, and b * are measured in the same manner as in (6) for the film before and after the treatment. Further, the color difference (ΔE *) is calculated from the following formula and evaluated.
ΔE * = {(ΔL *) ² + (Δa *) ² + (Δb *) ² } ^1/2
ΔL * = difference of L * of film before and after treatment Δa * = difference of a * of film before and after treatment Δb * = difference of b * of film before and after treatment ○: ΔE * is 5 or less Δ: ΔE * Is more than 5 and less than 10 x: ΔE * is 10 or more Further, the haze of the film before and after the retort treatment is measured by a Nippon Denshoku Haze meter NDH2000 type, and the amount of change in haze (ΔHz) before and after the retort treatment is calculated. .
ΔHz = (haze after retorting) − (haze before retorting)
○: ΔHz is 10 or less Δ: ΔHz exceeds 10 and less than 15 ×: ΔHz is 15 or more

(8) Colorant bleed-out resistance Retort treatment is performed in the same manner as in (7) above, and the polyester resin layer at the bottom of the deep-drawn can is lightly wiped with gauze, and the degree of gauze coloring is examined.
○: Gauze is not colored.
Δ: Gauze was slightly colored.
X: The gauze was remarkably colored yellow.

[Examples 1 to 3]
The polyester compositions of layer A and layer B shown in Table 1 are dried by a conventional method, individually melted at 270 ° C., then laminated into two layers using a feed block, extruded from a die, cooled and solidified, and unstretched A film was created.
Next, the unstretched film was longitudinally stretched 3.2 times at 68 ° C., then transversely stretched 3.7 times at 78 ° C., and heat-set at 185 ° C. to obtain a biaxially oriented laminated film. The thickness of the obtained film was 12 μm.

[Comparative Example 1]
In Example 3, a film was formed in the same manner except that the layer thicknesses of the A layer and the B layer were changed as shown in Table 1, and a biaxially oriented laminated film was obtained.

[Comparative Example 2]
The polyester compositions of layer A and layer B shown in Table 1 are dried by a conventional method, melted individually at 280 ° C., then laminated into two layers using a feed block, extruded from a die, and cooled and solidified. A stretched film was prepared.
Next, this unstretched film was longitudinally stretched 3.2 times at 105 ° C., then stretched 3.2 times at 120 ° C., and heat-set at 210 ° C. to obtain a biaxially oriented laminated film. The thickness of the obtained film was 15 μm.

[Comparative Example 3]
In Example 2, a film was formed in the same manner except that the polyester composition of the A layer was changed as shown in Table 1, and a biaxially oriented laminated film was obtained. In the transverse stretching process during film formation, cutting frequently occurred and the film forming property was poor.

[Comparative Example 4]
In Example 2, a film was formed in the same manner except that the polyester composition of the A layer was changed as shown in Table 1, and a biaxially oriented laminated film was obtained. In the transverse stretching process during film formation, cutting frequently occurred and the film forming property was poor.

[Comparative Example 5]
In Example 1, except that the polyester composition of the B layer was changed as shown in Table 1, film formation was performed in the same manner to obtain a biaxially oriented laminated film. In the transverse stretching process during film formation, cutting frequently occurred and the film forming property was poor.

[Comparative Example 6]
In Example 1, except that the polyester composition of the B layer was changed as shown in Table 1, film formation was performed in the same manner to obtain a biaxially oriented laminated film. In the longitudinal stretching process during film formation, the width variation was large, cutting frequently occurred, and the film forming property was poor.

  As is clear from the results in Table 2, the can using the laminated film for metal lamination molding of the present invention has excellent deep drawing workability, appearance after retort, gold color development, colorant bleedout resistance. Is excellent.

  The laminated film for metal laminating molding of the present invention is used for laminating metal plates used for laminating metal plates constituting soft drink cans, food cans, etc., in particular, can bodies and lid parts of metal cans. It can be suitably used as a laminated film.

Claims (8)

  A laminated film formed by laminating a polyester A layer and a polyester B layer, wherein the polyester A layer is composed of a resin composition comprising 30 to 70% by weight of polybutylene terephthalate and 30 to 70% by weight of polyethylene terephthalate. The B layer is composed of a colored resin composition containing 0.1 to 5.0 parts by weight of a colorant per 100 parts by weight of a resin composition comprising 30 to 70% by weight of polybutylene terephthalate and 30 to 70% by weight of polyethylene terephthalate. The shortest half crystallization time of the laminated film is 1 to 100 seconds, the a * value measured by a color difference meter is -30 to 20, and the b * value is 20 to 70. Laminated film for molding process.   The laminated film for metal lamination molding according to claim 1, wherein the polyester A layer has a thickness of 1 to 7 µm and the polyester B layer has a thickness of 5 to 50 µm.   The laminated film for metal lamination molding according to claim 1 or 2, wherein the polyester A layer is used as an outermost layer.   The metal bonding according to any one of claims 1 to 3, wherein the colorant is at least one organic pigment selected from the group consisting of isoindolinone-based organic pigments, benzimidazolone-based organic pigments, and quinophthalone-based organic pigments. Laminated film for molding process.   The laminated film for metal lamination molding according to any one of claims 1 to 3, wherein the colorant is an isoindolinone-based organic pigment.   The laminated film for metal lamination molding according to any one of claims 1 to 5, wherein a haze change amount ΔH before and after retorting at 125 ° C for 90 minutes is 10 or less.   The laminated film for metal lamination molding according to any one of claims 1 to 6, wherein the color difference ΔE * before and after retorting at 125 ° C for 90 minutes is 5 or less.   The laminated film for metal lamination molding according to any one of claims 1 to 7, wherein a color difference ΔE * before and after a dry heat treatment at 200 ° C for 1 minute is 3 or less.