Biaxially drawn colored polyester film for laminating metal sheet

Abstract

[Problem] To provide a biaxially drawn colored polyester film for laminating and forming metal sheet that: exhibits excellent formability such that even under severe processing or high-temperature heat treatments, the film is prevented from chipping or cracks during forming into a can etc.; and yields formed articles such as cans that have excellent concealability, appearance, and printability. [Solution] The invention is arrived at using a biaxially drawn colored polyester film for laminating and forming metal sheet. Said film comprising at least two layers of: a surface layer (layer A) mainly composed of a polyester having a melting point TmA of 230 to 260 C., layer A having a coloring pigment with an amount of 10 wt % or less, a polymer component with intrinsic viscosity of 0.46 or more, and a water contact angle of 70 to 120 on an outer surface; and a substrate layer (layer B) mainly composed of a polyester having a melting point TmB of 230 to 260 C. and a coloring pigment, layer B having a polymer component with intrinsic viscosity of 0.46 or more and the coloring pigment with an amount of more than 10 wt % and 50 wt % or less; wherein |TmBTmA| is 4 C. or less.

Claims

1. A biaxially drawn colored polyester film comprising at least two layers of: a surface layer (layer A) mainly composed of a polyester having a melting point of 230 to 260 C., layer A having a polymer component with intrinsic viscosity of 0.46 or more, optionally having a coloring pigment with an amount of 0.05 wt % or less, and having a water contact angle on an outer surface of 70 to 120; and a substrate layer (layer B) mainly composed of a polyester having a melting point of 230 to 260 C. and a coloring pigment, layer B having a polymer component with intrinsic viscosity of 0.46 or more and the coloring pigment with an amount of more than 10 wt % and 50 wt % or less; wherein the melting points of the polyesters of layer A and layer B satisfy the following expression (1):
|TmBTmA|4 C.(1) wherein TmA represents the melting point of the polyester of layer A, and TmB represents the melting point of the polyester of layer B.

2. The biaxially drawn colored polyester film according to claim 1, wherein the polyester constituting layer B is a copolyester having a melting point of 230 to 250 C.

3. The biaxially drawn colored polyester film according to claim 1, wherein the polyester constituting layer A is a copolyester having a melting point of 230 to 250 C.

4. The biaxially drawn colored polyester film according to claim 1, wherein the polyesters constituting layer A and layer B each are a copolyester having a melting point of 230 to 250 C., and an isophthalic acid-copolymerized polyethylene terephthalate.

5. The biaxially drawn colored polyester film according to claim 1, wherein layer A contains 0.2 to 2.0 wt % of a wax based on the weight of layer A.

6. The biaxially drawn colored polyester film according to claim 5, wherein the wax is a polyethylene wax having a dropping point of 120 to 140 C.

7. The biaxially drawn colored polyester film according to claim 1, wherein the film is laminated on a surface of a metal sheet that will become the outer surface of a container.

8. The biaxially drawn colored polyester film according to claim 2, wherein the polyester constituting layer A is a copolyester having a melting point of 230 to 250 C.

9. The biaxially drawn colored polyester film according to claim 1, wherein the amount of the coloring pigment in layer A is not greater than 0.01 wt %.

10. The biaxially drawn colored polyester film according to claim 1, wherein layer A does not comprise the coloring pigment.

11. The biaxially drawn colored polyester film according to claim 1, wherein thickness of the biaxially drawn colored polyester film is 6 microns to 75 microns.

12. The biaxially drawn colored polyester film according to claim 1, wherein thickness of the biaxially drawn colored polyester film is 15 microns to 50 microns.

13. The biaxially drawn colored polyester film according to claim 1, wherein the coloring pigment in layer B comprises inorganic material.

14. The biaxially drawn colored polyester film according to claim 1, wherein the coloring pigment in layer B comprises titanium dioxide.

15. The biaxially drawn colored polyester film according to claim 1, wherein the coloring pigment in layer B comprises organic material.

16. The biaxially drawn colored polyester film according to claim 1, wherein a polyester composition for layer A is prepared by adding wax to the polyester, and the composition is melted in an extruder at a temperature ranging from the melting point of the polyester to (melting point of the polyester+70) C.

17. The biaxially drawn colored polyester film according to claim 1, wherein layer A contains 0.2 to 3.5 wt % of a wax based on the weight of layer A.

18. The biaxially drawn colored polyester film according to claim 1, wherein layer A contains 0.5 to 3.3 wt % of a wax based on the weight of layer A.

19. The biaxially drawn colored polyester film according to claim 1, wherein layer A contains 0.8 to 3.0 wt % of a wax based on the weight of layer A.

20. The biaxially drawn colored polyester film according to claim 1, wherein layer A contains 0.9 to 2.5 wt % of a wax based on the weight of layer A.

Description

EXAMPLES

(1) Hereinafter, the invention will be described in detail with reference to examples. However, the invention is not limited only to these examples. The characteristic values were measured by the following methods. In addition, unless otherwise particularly noted, part and % in the examples means part by weight and wt %.

(2) (Melting Point)

(3) The melting point of a polyester was measured by taking about 20 mg of a sample from each layer of a film and determining the melting peak while the temperature was raised at a temperature rising rate of 20 C./minute using TA Instruments Q100 DSC.

(4) (Dropping Point)

(5) The dropping point was measured in accordance with DIN 51801/2 ( C.) using an Ubbelohde dropping point instrument.

(6) (Intrinsic Viscosity)

(7) The intrinsic viscosity is obtained by dissolving a resin composition collected from the extruder in o-chlorophenol, and then removing the coloring pigment and the like by a centrifuge, and performing measurement in a solution at 35 C. The unit is dl/g.

(8) (Water Contact Angle)

(9) The contact angle was measured using a contact angle meter manufactured by Kyowa Interface Science Co., Ltd. A film sample was place in an environment of a temperature of 25 C. and a humidity of 50% for 24 hours or more. Then, 5 mg of distilled water was dropped on the film, and a photograph was taken after 20 seconds from the horizontal direction. An angle formed on the water droplet side by the film and the tangent of the water droplet is taken as the contact angle.

(10) (Formability)

(11) A sample film was laminated on one side of a tin-free steel sheet having a thickness of 0.230 mm heated to a temperature equal to or higher than the melting point (approximately, melting point+10 C.) of the polyester of layer B (the surface laminated on the metal sheet) for a two-layer structure sample, or equal to or higher than the melting point (approximately, melting point+10 C.) of the polyester of layer A, which is the surface laminated on the metal sheet for a three-layer structure sample. After water cooling, the laminate sheet was cut into a 150-mm-diameter disc and subjected to five-stage drawing and ironing using a 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 cracks of the polyester film layer on the can wall, the formability was evaluated based on the following criteria.

(12) [Chipping]

(13) Excellent: No film chipping is observed.

(14) Good: Film chippings are slightly observed.

(15) Fair: Small chippings are observed in the film.

(16) Poor: Large chippings are observed in the film.

(17) [Cracks]

(18) Excellent: No crack is observed in the film.

(19) Good: Minute cracks are observed in the film.

(20) Fair: Small cracks are observed in the film.

(21) Poor: Large cracks are observed in the film.

(22) (Concealability)

(23) Using the can body obtained as above, the can barrel was visually observed, and the concealability was evaluated based on the following criteria.

(24) Excellent: Color of the metal sheet base cannot be seen at all. This sample exhibits excellent concealability.

(25) Good: Substantially color of the metal sheet base cannot be seen at all. This sample exhibits good concealability.

(26) Fair: The color of the metal sheet base can be slightly seen. Concealability is slightly poor.

(27) Poor: The color of the metal sheet base can be seen. Concealability is poor.

(28) (Film Forming Stability)

(29) The film forming stability during film forming was observed and evaluated based on the following criteria.

(30) Good: No film breakage occurs, allowing for extremely stable film forming. No breakage occurs for at least four days.

(31) Fair: Breakage sometimes occurs, and film forming is unstable. Breakage frequency is (once/four days) or more and less than (once/day).

(32) Poor: Breakage frequently occurs, and stable film forming is substantially impossible.

(33) Breakage frequency is (once/day) or more.

(34) (Appearance After Heat Treatment)

(35) A can having good formability 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.

(36) Good: No appearance defects are observed on the film surface of the can.

(37) Poor: The film surface of the can is roughened, and appearance defects are observed.

(38) (Printability)

(39) A biaxially drawn film sample was laminated on a metal sheet and a can was manufactured using the sheet. To the can barrel, well-known thermosetting ink and thermosetting finishing varnish were applied and then baked and cured in a baking oven. The can obtained was cut open, and the can barrel portion was drawn flat to prepare a test piece. The test piece obtained was set to a Du Pont impact tester such that the test piece was placed with the side wall inner surface facing upward, and an impact shaft would hit at a point in the test piece corresponding to a can height of 90 mm from the tread portion of the can. The impact shaft weighed 300 g and its tip sphere had a diameter of inches. The impact shaft was allowed to fall from a height of 50 mm so that the outer surface side of the can was formed to protrude outward.

(40) To thus-formed outer surface side of the can, a piece of cellophane tape (manufactured by Nichiban Co., LTD.) was attached and peeled off twice. For each of five cans obtained, this measurement was performed at two points per can. The total area from which the ink was peeled off was evaluated based on the following criteria.

(41) Good and Fair represent tolerable ranges.

(42) Good: The peeled area was less than 20%.

(43) Fair: The peeled area was 20% or more and less than 40%.

(44) Poor: The peeled area was 40% or more.

Examples 1 to 10 and Comparative Examples 1 to 7

(45) The polyester composition for layer A and the polyester composition for layer B show in Table 1 were separately dried and melted at 270 C. for layer A and at 280 C. for layer B. Then, the compositions were laminated by means of a three-layer feed block into a three-layer structure of A/B/A, co-extruded from an adjacent die, and rapidly cooled and solidified to give an undrawn laminate film. Next, this undrawn film was longitudinally drawn at 100 C. at a draw ratio of 3, then laterally drawn at 130 C. at a draw ratio of 3, and subsequently heat-set at 165 C. to give a biaxially drawn polyester film.

(46) As a coloring pigment, rutile titanium dioxide (average particle size: 0.5 m) was used. As a wax, a polyethylene wax having a dropping point of 135 C. was used. The evaluation results of the biaxially drawn polyester films obtained are shown in Table 2.

Examples 11 to 20 and Comparative Examples 8 to 14

(47) A biaxially drawn polyester film was obtained in the same manner as in Example 1 except that the composition was laminated into two-layer structure of A/B by means of a two-layer feed block. The evaluation results of the biaxially drawn polyester films obtained are shown in Table 2.

(48) TABLE-US-00001 TABLE 1 Surface Surface layer (layer A) layer Copolyester Coloring thickness Melting pigment Wax Total (single point Concentration Concentration Layer structure thickness layer) Type ( C.) (wt %) (wt %) Ex. 1 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 0.3 Ex. 2 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 1.0 Ex. 3 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 2.2 Ex. 4 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 3.3 Ex. 5 3 layers A/B/A 20 2.8 PET-IA4.0 248 0 1.2 Ex. 6 3 layers A/B/A 20 2.4 PET-IA4.5//PBT 241 0 1.0 Ex. 7 3 layers A/B/A 20 2.4 PET-IA6//PBT 239 0 0.9 Ex. 8 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 1.0 Ex. 9 3 layers A/B/A 20 2.5 PET 256 0 1.0 Ex. 10 3 layers A/B/A 20 2.5 PET-IA4.0 248 5.0 1.0 Ex. 11 2 layers A/B 20 2.5 PET-IA4.0 248 0 0.3 Ex. 12 2 layers A/B 20 2.5 PET-IA4.0 248 0 1.0 Ex. 13 2 layers A/B 20 2.5 PET-IA4.0 248 0 2.2 Ex. 14 2 layers A/B 20 2.5 PET-IA4.0 248 0 3.3 Ex. 15 2 layers A/B 20 2.8 PET-IA4.0 248 0 1.2 Ex. 16 2 layers A/B 20 2.4 PET-IA4.5//PBT 241 0 1.0 Ex. 17 2 layers A/B 20 2.4 PET-IA6//PBT 239 0 0.9 Ex. 18 2 layers A/B 20 2.5 PET-IA4.0 248 0 1.0 Ex. 19 2 layers A/B 20 2.5 PET 256 0 1.0 Ex. 20 2 layers A/B 20 2.5 PET-IA4.0 248 5.0 1.0 C Ex. 1 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 0.0 C Ex. 2 3 layers A/B/A 20 2.5 PET-IA4.0 248 0 4.0 C Ex. 3 3 layers A/B/A 20 2.0 PET-IA6 243 0 0.7 C Ex. 4 3 layers A/B/A 20 4.0 PET-IA12 228 0 1.5 C Ex. 5 3 layers A/B/A 20 2.5 PET-IA6 243 0 1.5 C Ex. 6 3 layers A/B/A 20 2.5 PET-IA6//PBT 239 11.0 2.3 C Ex. 7 3 layers A/B/A 20 2.0 PET-IA7.2//PBT 238 0 2.3 C Ex. 8 2 layers A/B 20 2.5 PET-IA4.0 248 0 0.0 C Ex. 9 2 layers A/B 20 2.5 PET-IA4.0 248 0 4.0 C Ex. 10 2 layers A/B 20 2.0 PET-IA6 243 0 0.7 C Ex. 11 2 layers A/B 20 4.0 PET-IA12 228 0 1.5 C Ex. 12 2 layers A/B 20 2.5 PET-IA6 243 0 1.5 C Ex. 13 2 layers A/B 20 2.5 PET-IA6//PBT 239 11.0 2.3 C Ex. 14 2 layers A/B 20 2.0 PET-IA7.2//PBT 238 0 2.3 Surface layer (layer A) Substrate layer (layer B) Polymer Polymer Water portion Copolyester Coloring portion contact intrinsic Melting pigment intrinsic angle viscosity point Concentration viscosity dL/g Type ( C.) (wt %) dL/g Ex. 1 73 0.57 PET-IA3.2 250 18.0 0.57 Ex. 2 79 0.57 PET-IA3.2 250 18.0 0.57 Ex. 3 100 0.57 PET-IA3.2 250 18.0 0.57 Ex. 4 119 0.57 PET-IA3.2 250 18.0 0.57 Ex. 5 83 0.54 PET-IA3.6 249 18.0 0.65 Ex. 6 80 0.56 PET-IA6 243 18.0 0.62 Ex. 7 78 0.60 PET-IA6 243 18.0 0.59 Ex. 8 79 0.57 PET-IA3.2 250 30.0 0.51 Ex. 9 80 0.57 PET 256 18.0 0.57 Ex. 10 79 0.57 PET-IA3.2 250 18.0 0.57 Ex. 11 73 0.57 PET-IA3.2 250 18.0 0.57 Ex. 12 79 0.57 PET-IA3.2 250 18.0 0.57 Ex. 13 100 0.57 PET-IA3.2 250 18.0 0.57 Ex. 14 119 0.57 PET-IA3.2 250 18.0 0.57 Ex. 15 83 0.54 PET-IA3.6 249 18.0 0.65 Ex. 16 80 0.56 PET-IA6 243 18.0 0.62 Ex. 17 78 0.60 PET-IA6 243 18.0 0.59 Ex. 18 79 0.57 PET-IA3.2 250 30.0 0.51 Ex. 19 80 0.57 PET 256 18.0 0.57 Ex. 20 79 0.57 PET-IA3.2 250 18.0 0.57 C Ex. 1 60 0.57 PET-IA3.2 250 18.0 0.57 C Ex. 2 130 0.57 PET-IA3.2 250 18.0 0.57 C Ex. 3 75 0.45 PET-IA6 243 23.4 0.58 C Ex. 4 88 0.57 PET-IA12 228 23.4 0.56 C Ex. 5 89 0.64 PET-IA6 243 23.4 0.45 C Ex. 6 102 0.64 PET-IA6 243 23.4 0.59 C Ex. 7 117 0.59 PET-IA4.0 248 22.0 0.60 C Ex. 8 60 0.57 PET-IA3.2 250 18.0 0.57 C Ex. 9 130 0.57 PET-IA3.2 250 18.0 0.57 C Ex. 10 75 0.45 PET-IA6 243 23.4 0.58 C Ex. 11 88 0.57 PET-IA12 228 23.4 0.56 C Ex. 12 89 0.64 PET-IA6 243 23.4 0.45 C Ex. 13 102 0.64 PET-IA6 243 23.4 0.59 C Ex. 14 117 0.59 PET-IA4.0 248 22.0 0.60 Ex. 1: Example 1, C Ex. 1: Comparative Example 1

(49) TABLE-US-00002 TABLE 2 Film Appearance Formability forming after heat Chipping Cracks Concealability stability treatment Printability Ex. 1 Fair Excellent Good Good Good Good Ex. 2 Good Excellent Good Good Good Good Ex. 3 Excellent Excellent Good Good Good Fair Ex. 4 Excellent Excellent Good Good Good Fair Ex. 5 Good Excellent Good Good Good Good Ex. 6 Good Excellent Good Good Good Good Ex. 7 Good Excellent Good Good Good Good Ex. 8 Good Excellent Excellent Fair Good Good Ex. 9 Excellent Fair Good Fair Good Good Ex. 10 Fair Excellent Good Good Good Good Ex. 11 Fair Excellent Good Good Good Good Ex. 12 Good Excellent Good Good Good Good Ex. 13 Excellent Excellent Good Good Good Fair Ex. 14 Excellent Excellent Good Good Good Fair Ex. 15 Good Excellent Good Good Good Good Ex. 16 Good Excellent Good Good Good Good Ex. 17 Good Excellent Good Good Good Good Ex. 18 Good Excellent Excellent Fair Good Good Ex. 19 Excellent Fair Good Fair Good Good Ex. 20 Fair Excellent Good Good Good Good C Ex. 1 Poor Excellent Good Good Good Good C Ex. 2 Excellent Excellent Good Good Good Poor C Ex. 3 Poor Poor Good Poor Good Good C Ex. 4 Poor Excellent Good Good Good Good C Ex. 5 Poor Poor Good Poor Good Good C Ex. 6 Poor Poor Good Fair Good Fair C Ex. 7 Good Excellent Good Good Poor Fair C Ex. 8 Poor Excellent Good Good Good Good C Ex. 9 Excellent Excellent Good Good Good Poor C Ex. 10 Poor Poor Good Poor Good Good C Ex. 11 Poor Excellent Good Good Good Good C Ex. 12 Poor Poor Good Poor Good Good C Ex. 13 Poor Poor Good Fair Good Fair C Ex. 14 Good Excellent Good Good Poor Fair Ex. 1: Example 1, C Ex. 1: Comparative Example 1

(50) In Table 1, PET represents a homopolyethylene terephthalate, and PET-IAx represents an x mol % isophthalic acid-copolymerized polyethylene terephthalate. PET-IAx//PBT is a 50/50 (weight ratio) blend of an x mol % isophthalic acid-copolymerized polyethylene terephthalate and a polybutylene terephthalate.

INDUSTRIAL APPLICABILITY

(51) The biaxially drawn colored polyester film for laminating and forming metal sheet of the present invention has excellent concealability and exhibits excellent formability such that even under severe conditions, for example, of forming into a can after lamination on a metal sheet, the film does not cause chipping or cracking on the can wall portion, and further the film has an excellent appearance after forming into a can and excellent printability. Thus, the film is suitably used for metal cans, such as beverage cans, food cans, and aerosol cans and particularly for the outer surface of these cans.