COLORED BIAXIALLY STRETCHED POLYESTER FILM FOR METAL PLATE ATTACHMENT AND FORMING PROCESSING

Abstract

A colored biaxially stretched polyester film for metal plate attachment and forming processing, includes three layers: opposite surface layers (layers A) that contain substantially no coloring pigment and are made of a copolyester having an intrinsic viscosity of 0.65 to 0.80 and a melting point (TmA) of 230 to 260 C.; and a core layer (layer B) that has a coloring pigment content of more than 10 wt % and 50 wt % or less and is made of a copolyester having an intrinsic viscosity of 0.55 to 0.70 and a melting point (TmB) of 230 to 260 C. The film has a surface roughness within a range of 10 to 40 nm, and (TmBTmA) is 4 C. or less.

Claims

1. A colored biaxially stretched polyester film for metal plate attachment and forming processing, comprising three layers: opposite surface layers (layers A) that are made of a copolyester having an intrinsic viscosity of 0.65 to 0.80 and a melting point of 230 to 260 C. and contain substantially no coloring pigment; and a core layer (layer B) that is made of a copolyester having an intrinsic viscosity of 0.55 to 0.70 and a melting point of 230 to 260 C. and has a coloring pigment content of more than 10 wt % and 50 wt % or less, the colored biaxially stretched polyester film being characterized in that the film has a surface roughness within a range of 10 to 40 nm, and the melting points of the copolyesters of the layers A and the layer B satisfy the following equation (1):
TmBTmA4 C. (1) wherein TmA represents the melting point of the copolyester of the layers A, and TmB represents the melting point of the copolyester of the layer B.

2. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 1, wherein the copolyesters forming the layers A and the layer B are each an isophthalic acid-copolymerized polyethylene terephthalate.

3. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 1, wherein the copolyester forming the layers A or the layer B includes only a copolyester as a resin raw material.

4. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 1, wherein the copolyester forming the layers A or the layer B includes a blend of a copolyester and a homopolyester as resin raw materials.

5. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 1, wherein the film is for being attached to a surface of a metal plate that serves as an outer surface of a container.

6. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 2, wherein the copolyester forming the layers A or the layer B includes only a copolyester as a resin raw material.

7. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 2, wherein the copolyester forming the layers A or the layer B includes a blend of a copolyester and a homopolyester as resin raw materials.

8. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 2, wherein the film is for being attached to a surface of a metal plate that serves as an outer surface of a container.

9. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 3, wherein the film is for being attached to a surface of a metal plate that serves as an outer surface of a container.

10. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 4, wherein the film is for being attached to a surface of a metal plate that serves as an outer surface of a container.

11. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 6, wherein the film is for being attached to a surface of a metal plate that serves as an outer surface of a container.

12. The colored biaxially stretched polyester film for metal plate attachment and forming processing according to claim 7, wherein the film is for being attached to a surface of a metal plate that serves as an outer surface of a container.

Description

EXAMPLES

[0049] Hereinafter, the invention will be described in detail with reference to examples. However, the invention is not limited to these examples. Incidentally, the characteristic values were measured by the following methods. In addition, unless otherwise noted, part and % in the examples are by weight.

(Melting Point)

[0050] The melting point of a copolyester was measured by the following method. About 20 mg of a sample was taken from each layer of a film, and, using TA Instruments Q100 DSC, and the melting peak was determined while heating at a heating rate of 20 C./min.

(Intrinsic Viscosity)

[0051] A copolyester (composition) used for film production was dissolved in o-chlorophenol, then the coloring pigment and the like were removed by a centrifugal separator, and measurement was performed from the solution at 35 C. The unit is dl/g.

(Surface Roughness (Ra))

[0052] Measurement was performed using a non-contact three-dimensional surface roughness meter (manufactured by Zygo Corporation: New View 5022) under the following conditions: measurement magnification: 25, measurement area: 283 m213 m (=0.0603 mm.sup.2). The center plane average roughness (Ra) was determined using the built-in surface analysis software Metro Pro of the roughness meter and defined. as the surface roughness (Ra). Incidentally, the measurement was performed five times at different measurement points on each side, and their average was defined as the center plane average roughness (Ra).

(Forming Processability)

[0053] A sample film was attached to one side of a tin-free steel plate having a thickness of 0.25 mm heated to a temperature equal to or higher than the melting points of the copolyesters of the layers A and the layer B, water-cooled, then cut out into a 150-mm-diameter disc shape, and deep-drawn in four stages using a drawing die and a punch, thereby preparing a 55-mm-diameter container having no seam on the side surface. With respect to this can, from the occurrence of chipping and scratching of the polyester film layer on the can wall, the forming processability was evaluated based on the following criteria. [0054] Good: The film is processed without any abnormality, and no microcracking or chipping of the film is seen. [0055] Poor: Microcracking and chipping are seen in the film.

(Concealability)

[0056] An L* value that indicates the whiteness of a film sample the CIE 1976 (L*, a*, b*) color space was measured using Spectrocolorimeter SE 6000 manufactured by Nippon Denshoku Industries Co., Ltd., without placing anything under the film, and the concealability was evaluated based on the following criteria. [0057] Excellent: value: 85 or more; This indicates excellent concealability. [0058] Good: L* value: 80 or more and less than 85; This indicates good concealability. [0059] Fair: L* value: 75 or more and less than 80; Concealability is slightly poor. [0060] Poor: L* value: less than 75; Concealability is poor.

(Film Production Stability)

[0061] The film production properties in the production of a fair were observed and evaluated based on the following criteria. [0062] Good: No breakage occurs, allowing for extremely stable film production. No cutting occurs for at least four days. [0063] Fair: Cutting sometimes occurs, and film production is unstable. Cutting frequency is (once/four days) or more and less than (once/day) or more. [0064] Poor: Breakage frequently occurs, and stable film production is substantially impossible. Cutting frequency is (1 once/day) or more.
(Appearance after Heat Treatment)

[0065] A can having good forming processability was maintained in an oven at 235 to 255 C. for 90 seconds, and then the appearance of the can was evaluated based on the following criteria. [0066] Good: No appearance defects are seen on the film surface of the can. [0067] Poor: The film surface of the can is roughened, and appearance defects are seen.
(Handleability during Winding Up)

[0068] A produced film, 1,000 mm in width and 10,000 m in length, was wound up into a roll. The appearance of the wound-up roll was observed and evaluated based on the following criteria. [0069] Good: Film misalignment is not seen at the ends of the roll, and the roll surface is not wrinkled. [0070] Poor: Film misalignment is seen at the ends of the roll, or the roll surface is wrinkled.

Examples 1 to 2 and Comparative Examples 1 to 3

[0071] The copolyester for layers A and the copolyester for a layer B using rutile-type titanium dioxide as a coloring pigment shown in Table 1 were each independently dried and melted, then co-extruded from adjoining dies, and rapidly cooled and solidified to give an unstretched laminate The copolyester for layers A has added thereto, as inert particles, perfectly spherical silica particles having the average particle size and concentration shown in Table 1. Next, the unstretched film was longitudinally retched at 100 C. to 3 times the original length, then transversely stretched at 130 C. to 3 times the original length, and subsequently heat-set at 165 C. to give a biaxially stretched polyester film. The total thickness of the film was 20 m, and the thicknesses of the layers A and the layer B were 5 m (each layer A is 2.5 m thick) and 15 m, respectively. The evaluation results of the obtained polyester films are shown in Table 2.

Examples 3 to 4, Comparative Examples 4 to 5

[0072] The same procedure as in Example 1 was performed, except that the 50/50 (weight ratio) blend of a copolyester and polybutylene terephthalate shown in Table 1 was used as the polyester for layers A, and the pigment concentration and the average particle size, kind, and concentration of inert particles were as shown in Table 1. The evaluation results are shown in Table 2.

TABLE-US-00001 TABLE 1 Surface Layers (Layers A) Core Layer (Layer B) Copolyester Coloring Copolyester Coloring Film Melt- Pigment Inert Particles Melt- Pigment Surface ing Intrinsic Concen- Concen- ing Intrinsic Concen- Rough- Point Vis- tration Average Particle tration Piont Vis- tration ness Polyester ( C.) cosity (wt %) Size-Kind (wt %) Polyester ( C.) cosity (wt %) (nm) Example 1 PET-IA4.0 248 0.71 0 2.0 m-Perfectly 0.1 PET-IA3.2 250 0.60 18.0 17 spherical silica Example 2 PET-IA4.0 248 0.71 0 2.0 m-Perfectly 0.1 PET-IA3.6 249 0.65 18.0 16 spherical silica Example 3 PET-IA4.5/ 241 0.72 0 1.5 m-Perfectly 0.01 PET-IA6 243 0.62 18.0 11 PBT spherical silica Example 4 PET-IA6/ 239 0.71 0 2.0 m-Perfectly 0.3 PET-IA6 243 0.59 18.0 25 PBT spherical silica Comparative PET-IA6 243 0.63 0 2.0 m-Perfectly 0.1 PET-IA6 243 0.58 23.4 17 Example 1 spherical silica Comparative PET-IA12 228 0.65 0 2.0 m-Perfectly 0.1 PET-IA12 228 0.56 23.4 17 Example 2 spherical silica Comparative PET-IA6 243 0.65 0 2.0 m-Perfectly 0.1 PET-IA6 243 0.54 23.4 17 Example 3 spherical silica Comparative PET-IA6/ 239 0.69 5.3 2.0 m-Perfectly 0.1 PET-IA6 243 0.59 23.4 55 Example 4 PBT spherical silica Comparative PET-IA7.2/ 238 0.70 0 0.1 m-Perfectly 0.1 PET-IA4.0 248 0.60 22.0 4 Example 5 PBT spherical silica PBT: Polybutylene terephthalate

TABLE-US-00002 TABLE 2 Forming processability Appearance Handleability Cracking, Film after at the Chipping, Production Heat Time of Overall Scratching Concealability Stability Treatment Winding Up Evaluation Example 1 Good Excellent Good Good Good Good Example 2 Good Excellent Good Good Good Good Example 3 Good Excellent Good Good Good Good Example 4 Good Excellent Good Good Good Good Comparative Example 1 Poor Excellent Poor Poor Good Poor Comparative Example 2 Poor Excellent Good Good Good Poor Comparative Example 3 Poor Excellent Poor Poor Good Poor Comparative Example 4 Poor Excellent Fair Good Good Poor Comparative Example 5 Good Excellent Good Poor Poor Poor

[Industrial Applicability]

[0073] The colored biaxially stretched polyester film for metal plate attachment and forming processing of the invention has excellent concealability and exhibits excellent forming processability such that even when the film is forming-processed into a can, for example, under severe conditions after being attached to a metal plate, the film on the can wall portion is not chipped, scratched, or peeled off. Further, the can after forming has excellent appearance. Therefore, the film is suitable for metal cans, such as beverage cans, food cans, and aerosol cans, for example.