JP5894308B2 - Colored biaxially stretched polyester film for metal plate lamination - Google Patents

Description

  The present invention relates to a colored biaxially stretched polyester film for metallized sheet laminated molding. More specifically, it is excellent in concealment, exhibits excellent molding processability when it is molded into a can after being bonded to a metal plate, and has excellent ink adhesion, and is a biaxial coloring plate for metal plate lamination molding processing. The present invention relates to a stretched polyester film.

  Metal cans are generally painted to prevent internal and external corrosion. In recent years, coating with a thermoplastic resin film such as a polyester film has been performed as a method for imparting rust prevention without using an organic solvent for the purpose of simplifying the process, improving hygiene, and preventing pollution. In other words, it is used for food cans and beverage cans where a thermoplastic resin film is laminated on a metal plate such as tin, tin-free steel, aluminum, etc. and then subjected to severe molding such as drawn cans and thinned drawn cans. Has been. The cans used for these applications have been manufactured by performing thinning drawing and ironing with stricter processing conditions from the viewpoint of cost reduction.

  When such a strict molding process is performed, the resin film is also thinned as the metal plate is thinned. The outer surface of food cans and beverage cans is generally printed to enhance design, but in cans molded from resin film-coated metal plates, white is used to conceal the color of the metal plate as the printing ground. Or what laminated | stacked the resin film containing the pigment of various colors on the metal plate is used. When such a laminated metal plate is subjected to severe processing, the thickness of the resin is significantly reduced, and the absolute amount in the thickness direction of the added pigment is reduced, so that sufficient concealment of the base cannot be obtained. A problem occurs. In addition, if a large amount of pigment is added to the resin film in advance in anticipation of a reduction in the resin thickness due to such a strict thinning process, the strength of the resin film will decrease, and the resin film will be easily scratched or damaged during processing. Furthermore, a phenomenon in which the resin film is cracked and peeled off occurs, and it is extremely difficult to improve the concealing property and to keep the strength of the coated resin film high.

  For example, a method of laminating a biaxially stretched polyester film on a metal plate and using it as a can-making material has been proposed (Japanese Patent Laid-Open Nos. 11-342577 and 2000-37836). During molding, the resin film is scraped or scratched, and in extreme cases, breakage occurs. In addition, a method of laminating an unstretched polyester film on a metal plate and using it as a can-making material has been proposed (Japanese Patent Laid-Open No. 11-348218). There is a problem that it is easy to cut and the productivity is poor.

Japanese Patent Laid-Open No. 11-342577 JP 2000-37836 A Japanese Patent Laid-Open No. 11-348218

  The present invention has been made in view of the above, and its purpose is to provide excellent concealment to the underlying metal plate even when used in a can that requires severe processing as described above. Metal plate lamination molding process that exhibits excellent moldability without causing film to be scraped, wrinkled or peeled off when molded into cans It is to provide a colored biaxially stretched polyester film.

According to the study by the present inventors, the above problem is made of a copolyester having an intrinsic viscosity of 0.66 to 0.85 and a melting point of 215 to 230 ° C., and the content of the color pigment is 10% by weight or less. A back layer comprising a surface layer (A layer) and a copolyester having an intrinsic viscosity of 0.46 to 0.66 and a melting point of 235 to 245 ° C., and the content of the color pigment is more than 10% by weight and 50% by weight or less A colored biaxially stretched polyester film comprising two layers (B layer), the melting point and intrinsic viscosity of the copolymer polyester of the A layer and B layer satisfy the following formulas (1) to (2), and polyester Achieved by a colored biaxially stretched polyester film (Claim 1) for metal plate laminating and forming that performs ironing, characterized in that the film has a breaking strength of 100 MPa or more and the B layer is bonded to the surface of the metal plate. Is It has been found.
TmB-TmA ≦ 20 ° C. --- (1)
IVA-IVB ≧ 0.15 −−− (2)
However, TmA and IVA represent the melting point and intrinsic viscosity of the copolyester of the A layer, respectively, and TmB and IVB represent the melting point and intrinsic viscosity of the copolyester of the B layer, respectively.

Moreover, the colored biaxially stretched polyester film for metal plate lamination molding processing of the present invention includes the following aspect 2 as a preferred embodiment.
2. Item 2. The colored biaxially stretched polyester film for metal plate lamination molding processing according to Item 1, wherein the copolymer polyester constituting the A layer and the B layer is isophthalic acid copolymerized polyethylene terephthalate.

  The colored biaxially stretched polyester film for metal plate laminating and forming of the present invention is excellent in concealment, and when it is molded into a can after being laminated to a metal plate, it can be scraped into a film on the can wall, scratched or peeled off. It exhibits excellent molding processability that does not occur, and also has good ink adhesion to the can after molding.

The present invention will be described in detail below.
The copolymer polyester constituting the A layer and the B layer in the present invention may be either a polyethylene terephthalate copolymer or a polyethylene-2,6-naphthalate copolymer as long as it satisfies the melting point requirement described later. However, a polyethylene terephthalate copolymer is preferable.

  The copolymer component of the copolymer polyester may be an acid component or an alcohol component. Examples of acid components include aromatic dicarboxylic acids other than the main acid components such as isophthalic acid, phthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid. Examples of the alcohol component include aliphatic diols such as 1,6-hexanediol, and alicyclic diols such as 1,4-hexamethylenedimethanol. These may be used alone or in combination of two or more. Of these, isophthalic acid and sebacic acid are preferable from the viewpoint of the effects of the present invention, and isophthalic acid is particularly preferable.

  In the case of layer A, the copolymerization ratio of such copolymerization components needs to be such that the melting point of the copolymerized polyester is in the range of 215 to 230 ° C, preferably 220 to 230 ° C. If the melting point is less than 215 ° C., the heat resistance is inferior, and it is not preferable because it cannot withstand the heating in printing after canning. On the other hand, if the temperature exceeds 230 ° C., the adhesion with the ink when printing after canning is deteriorated, which is not preferable.

  In the case of the B layer, it is necessary that the copolymer polyester has a melting point in the range of 235 to 245 ° C. If the melting point is less than 235 ° C., the heat resistance is inferior. On the other hand, if the melting point exceeds 245 ° C., the crystallinity of the copolyester becomes high and the molding processability is impaired, which is not preferable. The B layer is not printed because it is bonded to the metal plate when the colored biaxially stretched polyester film is bonded to the metal plate, so there is no problem even if the melting point exceeds 230 ° C.

  The above-mentioned copolymer polyester constituting the A layer or the B layer may be only a copolymer polyester as each resin material, or may be a resin material comprising a blend of a copolymer polyester and a homopolyester. Among these, from the viewpoint of moldability when molding into a can, only the copolymer polyester is used as the resin material for the A layer, and the resin material consisting of a blend of the copolymer polyester and homopolyester is used for the B layer. Embodiments are preferred.

  When only the copolymer polyester is used as the resin raw material, one type of copolymer polyester having the above melting point may be used, or two or more types of copolymer polyesters having different types of copolymer components or different copolymerization amounts may be used. You may adjust so that melting | fusing point after film formation may become this range.

  Moreover, you may adjust so that melting | fusing point after film formation may become this range by using the resin raw material which consists of a blend of copolyester and homopolyester as a resin raw material. By using homopolyester as one of the resin raw materials, the copolyester constituting the layer can be controlled to a block copolymerized state rather than a random copolymerized state, and then molded into a can after being bonded to a metal plate When processing, the orientation of the layer is increased, so that molding processability is easily improved.

  When using a resin raw material comprising a blend of a copolyester and a homopolyester as the resin raw material, the homopolyester content should be in the range of 15 wt% or more and 35 wt% or less based on the total amount of the polyester constituting the layer. preferable. The homopolyester is preferably homopolyethylene terephthalate.

  When the raw material of the copolyester constituting the A layer or the B layer is two or more types of copolyester or a blend of copolyester and homopolyester, the melting point peak of each layer may be one. preferable.

  Furthermore, the biaxially stretched polyester film of the present invention is bonded to a metal plate in order to realize good workability that does not cause scratching, scratching or peeling even if it is subjected to molding under severe conditions. At this time, it is necessary to bond them under the condition that the crystal components are completely melted. For this reason, the upper limit of the melting point difference between the A layer and the B layer needs to be 20 ° C. or less, preferably 15 ° C. or less.

When the melting point difference exceeds 20 ° C., the A layer is fused to the laminate roll when it is bonded to the metal plate under the temperature condition where the crystalline components of the film are completely melted, which is not preferable.
Here, the melting point of the copolyester was measured for each layer of the film. About 20 mg of a sample was taken, and a melting peak was obtained while raising the temperature at a rate of temperature rise of 20 ° C./min using a TA Instruments Q100 DSC. Depending on the method.

  Next, the intrinsic viscosity of the copolyester (polymer portion) constituting the A layer in the present invention needs to be in the range of 0.66 to 0.85, preferably in the range of 0.70 to 0.85. . In the present invention, since the polyester constituting the A layer is a copolymer polyester having the above-mentioned melting point, if it is not a copolymer polyester having a high intrinsic viscosity, severe processing conditions are required when it is molded into a can after being bonded to a metal plate. It is difficult to perform the molding process. When this intrinsic viscosity is less than 0.66, the can is easily damaged when it is molded into a can under severe processing conditions, and surface defects are likely to occur. On the other hand, those exceeding 0.85 are uneconomical because not only are the excessive quality but also the productivity of the raw material copolyester is lowered.

  Here, the intrinsic viscosity of the copolyester of layer A was measured in a 35 ° C. solution after dissolving the copolyester composition used for film formation in o-chlorophenol and then removing the color pigments with a centrifuge. This is the value obtained. When the raw material of the copolyester constituting the layer A is two or more types of copolyester or a blend of copolyester and homopolyester, the intrinsic viscosity of each raw material to be blended is measured. The weight average may be in such a range.

  In addition, the intrinsic viscosity of the copolyester (polymer portion) constituting the B layer in the present invention needs to be in the range of 0.46 to 0.66, preferably in the range of 0.48 to 0.64. When the intrinsic viscosity is less than 0.46, not only is the film easily broken when stretched, but the resulting film is likely to break when it is molded into a can after being bonded to a metal plate. . On the other hand, when the intrinsic viscosity exceeds 0.66, since the pigment is contained in a high concentration, aggregation of the pigment is likely to occur, and not only the quality is excessive, but also the productivity of the raw material copolyester is lowered.

  Here, the intrinsic viscosity of the copolyester of layer B is measured in a 35 ° C. solution after dissolving the copolyester composition used for film formation in o-chlorophenol and then removing the color pigments with a centrifuge. This is the value obtained. When the raw material of the copolyester constituting the B layer is two or more types of copolyester or a blend of copolyester and homopolyester, the intrinsic viscosity of each raw material to be blended is measured. The weight average may be in such a range.

  Furthermore, the biaxially stretched polyester film of the present invention is unique to the A layer in order to achieve good moldability without being scratched, scratched or peeled off even if it is molded under severe conditions. The viscosity needs to be 0.15 or more, preferably 0.18 or more larger than the intrinsic viscosity of the B layer.

  Next, the content of the color pigment in the A layer in the present invention needs to be 10% by weight or less. When the content of the color pigment exceeds 10% by weight, the resulting film tends to be damaged when it is molded into a can after being bonded to a metal plate, resulting in increased surface defects. Therefore, it is not preferable. On the other hand, the content of the color pigment in the B layer needs to be more than 10% by weight and 50% by weight or less, preferably 20 to 50% by weight, more preferably 30 to 50% by weight. When the content of the color pigment is less than the lower limit, the concealability is poor, which is not preferable. On the other hand, when the content of the color pigment exceeds the upper limit, not only the effect of improving the concealability is saturated, but the film becomes brittle and easily breaks during stretching, and the obtained film is formed into a metal plate. After being bonded to each other, breakage is likely to occur when the can is molded. The coloring pigment contained in the A layer and the B layer may be either inorganic or organic, but is preferably inorganic. Preferred examples of the inorganic pigment include alumina, titanium dioxide, calcium carbonate, barium sulfate and the like, and titanium dioxide is particularly preferable.

  The copolymer polyester constituting the A layer and the B layer has other additives such as a fluorescent whitening agent, an antioxidant, a heat stabilizer, as necessary, as long as the object of the present invention is not impaired. An ultraviolet absorber, an antistatic agent, etc. can be added. In particular, in order to improve whiteness, a fluorescent whitening agent is effective.

  The biaxially stretched polyester film of the present invention must have a breaking strength of 100 MPa or more in both the film longitudinal direction (sometimes referred to as the longitudinal direction or MD direction) and the width direction (sometimes referred to as the transverse direction or TD direction). In particular, it is preferably 120 MPa or more. When the breaking strength is less than 100 MPa, it is not preferable because cutting tends to occur when the film is produced, and productivity is lowered.

  Here, the breaking strength of the biaxially stretched polyester film was determined from the obtained biaxially stretched polyester film by using a tensile tester (trade name “Tensilon” manufactured by Toyo Baldwin Co., Ltd.). A sample having a direction of 150 mm × longitudinal direction of 10 mm was taken and fixed in a normal temperature atmosphere with a chuck set at an interval of 100 mm, and then the load was measured with a load cell attached to a tensile tester at a speed of 100 mm / min. And the load at the time of a fracture | rupture was read, and the fracture strength (MPa) was calculated by dividing by the sample cross-sectional area before tension.

Next, the thickness of the biaxially stretched polyester film of the present invention can be appropriately changed as necessary, but the total thickness is preferably in the range of 6 to 75 μm, and more preferably in the range of 10 to 75 μm, particularly 15 to 50 μm. . If the thickness is less than 6 μm, scraping or the like is likely to occur during the molding process, while those exceeding 75 μm are excessive quality and uneconomical.
The colored biaxially stretched polyester film for laminating and forming a metal plate of the present invention comprises only the above-mentioned surface layer (A layer) and the above-mentioned back layer (B layer), and the back layer (B layer) is a metal plate. Bonded to the surface.
Furthermore, the thickness ratio between the A layer and the B layer (X _A / X _B : where X _A is the thickness of the A layer, and X _B is the thickness of the B layer) is 1/7 to from the viewpoint of moldability and concealability A range of 1/3 is appropriate.

The manufacturing method of the colored biaxially stretched polyester film for metal plate laminating processing of the present invention described above is not particularly limited. First, an unstretched laminated sheet is prepared by a conventionally known film forming method, and then stretched in two directions. do it.
For example, after sufficiently drying the copolyester prepared for the A layer, it is melted in the extruder at a temperature of the melting point to (melting point + 70) ° C. At the same time, the copolyester 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 copolyester, the longitudinal stretching ratio is 2.5 to 3.6 times, and the transverse stretching ratio is 2.6 to 3.7 times. It is preferable to set it as the range. The heat setting temperature is preferably selected in order to adjust the film quality in the range of 150 to 230 ° C. according to the melting point of the copolyester.

As the metal plate to which the colored biaxially stretched polyester film for metal plate laminating molding processing of the present invention is bonded, particularly as a metal plate for can making, a plate of tin, tin-free steel, aluminum or the like is suitable. The lamination to the metal plate can be performed, for example, by the following method.
Heat the metal plate above the melting point of the copolyester of the B layer, and place the B layer side on the metal plate surface so that the entire layer of the film is in an amorphous state. Cool and adhere to maintain the state. At this time, if the film is partially amorphized, the can wall portion is likely to be scraped during molding.

  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.

(Melting point)
About 20 mg of a sample was taken for each layer of the film, and the melting point of the copolyester was measured by a method of obtaining a melting peak while raising the temperature at a rate of temperature increase of 20 ° C./min using a TA Instruments Q100 DSC.

(Intrinsic viscosity)
The copolyester composition used for film formation was dissolved in o-chlorophenol, and then the color pigments and the like were removed with a centrifuge, and the measurement was performed with a 35 ° C. solution. The unit is dl / g.

(Breaking strength)
The film breaking strength was determined by using a tensile tester (trade name “Tensilon” manufactured by Toyo Baldwin Co., Ltd.), and samples obtained from the obtained copolymer polyester film of 150 mm in the longitudinal direction × 10 mm in the width direction and 150 mm in the width direction × 10 mm in the longitudinal direction, respectively. The sample was collected and fixed in a normal temperature atmosphere with a chuck set at an interval of 100 mm, and then the load was measured with a load cell attached to a tensile tester at a speed of 100 mm / min. And the load at the time of a fracture | rupture was read, and it divided | segmented by the sample cross-sectional area before tension | pulling, and calculated the breaking strength (MPa) of a film longitudinal direction and each film width direction.

(Molding processability)
A polyester film sample was laminated by thermal fusion on one side of tin-free steel having a thickness of 0.18 mm and a width of 1 m (amount of chromium metal: 120 mg / m ² , chromium hydroxide amount: 15 mg / m ² as chromium). During the lamination, the polyester film was placed so that the back layer (B layer) was on the metal plate side.
The obtained film-laminated metal plate was punched out into a blank having a diameter of 160 mm, and then a drawn can having a can bottom diameter of 100 mm was formed such that the film-coated surface was on the outer surface side of the can. Then, a redraw can with a can bottom diameter of 80 mm was made by redraw. Furthermore, this redrawn can was made into a drawn and ironed can having a can bottom diameter of 65 mm by a composite process in which the ironing process was performed simultaneously with the stretch process. In this combined processing, the distance between the redrawing portion and the ironing portion that is the upper end of the can is 20 mm, the shoulder radius of the redrawing die is 1.5 times the plate thickness, and the clearance between the redrawing die and the punch is the plate thickness The machining conditions were set so that the clearance of the ironing part was 50% of the original plate thickness.
Molding processability was evaluated according to the following criteria based on the occurrence of scraping and wrinkling of the polyester film layer on the can wall of the can body 30 thus obtained.
A: No occurrence of shaving or scratching is observed.
○: Some cans are scraped or scratched, but there is no practical problem.
(Triangle | delta): The shaving and damage which are a problem practically are recognized by some cans.
X: Scraping, scratching and peeling that are practical problems are observed in a considerable number of cans.

(Concealment)
The L * value representing the whiteness defined by the CIE 1976 (L *, a *, b *) color space of the film sample was placed under the film using a Nippon Denshoku SE6000 spectrocolorimeter. Measured and evaluated for concealment according to the following criteria.
A: L * value: 85 or more Excellent concealability.
○: L * value: 80 or more and less than 85 Good concealability is exhibited.
Δ: L * value: 75 or more and less than 80 The concealability is slightly inferior.
X: L * value: less than 75 The concealability is inferior.

(Film formation stability)
The film forming property when the film was formed was observed and evaluated according to the following criteria.
○: Breakage does not occur and film formation is extremely stable. Uncut for more than 4 days.
Δ: Cutting sometimes occurs, and film formation is unstable.
Cutting frequency (once per 4 days) or more, less than (once per day) ×: Many breaks occur and substantially stable film formation is impossible. Cutting frequency (once / day) or more

(Ink adhesion)
Ink adhesion was evaluated by the DuPont impact test.
A known thermosetting ink and a thermosetting finish varnish were applied to a can body made of a metal plate to which a biaxially stretched film sample was bonded, and then baked and cured in a baking oven. The obtained can was opened, and the can body portion was flattened to obtain a test piece. The obtained test piece was set in a DuPont impact tester so that the inner surface side of the side wall faced up and the impact core hit a position 90 mm from the ground contact portion. The hitting core weighed 300 g and had a tip sphere diameter of 3/8 inch, and was processed so that the outer surface side of the can became convex by dropping from a height of 50 mm on the basis of the position where the test piece was set.
A cellophane tape (manufactured by Nichiban Co., Ltd., product name) having an area of 18 mm × 40 mm with the apex of the convex portion as the center was adhered to the outer surface of the can after processing, and the work was peeled off at 180 °. This measurement was performed at two locations for each of the five cans obtained. The total area from which the ink was peeled was evaluated according to the following criteria. ○ and Δ are acceptable ranges.
○: Peeling area is less than 20% Δ: Peeling area is 20% or more and less than 40% ×: Peeling area is 40% or more

[Examples 1 to 10, Comparative Examples 1 to 8]
Using the rutile type titanium oxide as the coloring pigment, the A layer copolyester and the B layer copolyester shown in Table 1 are dried and melted independently, and then co-extruded from adjacent dies, rapidly solidified and unstretched. A laminated film was obtained. Next, the unstretched film was longitudinally stretched 3 times at 100 ° C., then transversely stretched 3 times at 120 ° C., and then heat-set at 180 ° C. to obtain a biaxially stretched polyester film. The total thickness of the film was 17 μm, and the thicknesses of the A layer and B layer were 4 μm and 13 μm, respectively. The evaluation results of the obtained polyester film are shown in Table 2.

[Comparative Example 9]
An unstretched laminated film was obtained in the same manner as in Example 1 except that the total thickness of the unstretched film was 17 μm. The thicknesses of the A layer and the B layer were 4 μm and 13 μm, respectively. Table 2 shows the evaluation results of the obtained unstretched laminated film.

[Comparative Example 10]
The same procedure as in Example 1 was carried out except that a 70/30 (weight ratio) blend of the copolymerized polyester and polybutylene terephthalate shown in Table 1 was used as the polyester for the B layer. The evaluation results are shown in Table 2. The B layer had two melting points, and one of them had a melting point of less than 235 ° C., so that the moldability was not sufficient.

[Examples 11 to 13]
Rutile titanium oxide is used as the color pigment, and the copolymerized polyester for layer A shown in Table 3 and the copolymeric molar ratio of isophthalic acid 12 mol% copolymerized polyethylene terephthalate and homopolyethylene terephthalate shown in Table 3 are as shown in Table 3. The polyesters blended in this manner were dried and melted independently, and then coextruded from adjacent dies and rapidly solidified to obtain an unstretched laminated film. Next, the unstretched film was longitudinally stretched 3 times at 100 ° C., then transversely stretched 3 times at 120 ° C., and then heat-set at 180 ° C. to obtain a biaxially stretched polyester film. The total thickness of the film was 17 μm, and the thicknesses of the A layer and B layer were 4 μm and 13 μm, respectively. Table 4 shows the evaluation results of the obtained polyester film.

[Example 14]
Same as Example 13 except that the color pigment concentration of the B layer and the total thickness of the biaxially stretched polyester film are 17 μm and the thicknesses of the A layer and the B layer are 2.5 μm and 14.5 μm, respectively. Thus, a biaxially stretched polyester film was obtained. Table 4 shows the evaluation results of the obtained polyester film.

  The colored biaxially stretched polyester film for metal plate laminating molding of the present invention is excellent in concealment, and even if it is molded into a can under severe conditions after being laminated to a metal plate, it can be scraped into a film on the can wall, Expresses excellent molding processability without causing scratches and peeling, and also has good ink adhesion to the can after molding, so it is suitably used for metal cans such as beverage cans and food cans. can do.

Claims (2)

A surface layer (A layer) comprising a copolyester having an intrinsic viscosity of 0.66 to 0.85 and a melting point of 215 to 230 ° C., and having a color pigment content of 10% by weight or less, and an intrinsic viscosity of 0.46 to A colored biaxially stretched polyester comprising two layers of a back layer (B layer) comprising a copolyester having a melting point of 0.66 and a melting point of 235 to 245 ° C. The melting point and intrinsic viscosity of the copolymer polyester of the A layer and the B layer satisfy the following formulas (1) to (2), the breaking strength of the polyester film is 100 MPa or more, and the B layer is a metal A colored biaxially stretched polyester film for laminating and processing a metal plate, which is laminated on a plate surface.
TmB-TmA ≦ 20 ° C. --- (1)
IVA-IVB ≧ 0.15 −−− (2)
However, TmA and IVA represent the melting point and intrinsic viscosity of the copolyester of the A layer, respectively, and TmB and IVB represent the melting point and intrinsic viscosity of the copolyester of the B layer, respectively.   The colored biaxially stretched polyester film for metal plate laminating molding according to claim 1, wherein the copolymer polyester constituting the A layer and the B layer is isophthalic acid copolymer polyethylene terephthalate.