JP2015214046A - Coloring biaxial drawing polyester film for laminate molding processing of metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coloring biaxial drawing polyester film for laminate molding processing of a metal plate exhibiting excellent molding processability without scraping, generating flaw or peeling during molding processing to a can or the like even with severe processing or conducting a heat treatment at high temperature and capable of providing a molded article such as can having excellent concealing property and appearance.SOLUTION: There is achieved by a coloring biaxial drawing polyester film for laminate molding processing of a metal plate consisting of three layers of double surface layers (A layer) consisting of copolymer polyester containing substantially no coloring pigment and having an intrinsic viscosity of 0.65 to 0.80 and the melting point (TmA) of 230 to 250°C and a core layer (B layer) consisting of polymer polyester having the content of the coloring pigment of over 10 wt.% and 50 wt.% or less, intrinsic viscosity of 0.55 to 0.70 and the melting point (TmB) of 230 to 250°C, and having (TmB-TmA) of 4°C or less.

Description

  The present invention relates to a colored biaxially stretched polyester film for metallized sheet laminated molding. More specifically, it has excellent concealability, expresses excellent moldability when being molded into a container such as a can after being bonded to a metal plate, and has excellent appearance after molding. The present invention relates to a biaxially 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, food cans, beverage cans and aerosol cans that are severely molded, such as drawn cans and thinned drawn cans, after laminating a thermoplastic resin film to a metal plate such as tinplate, tin-free steel, and aluminum Has been used. 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 anticipation of this problem, if a large amount of pigment is added to the resin film in advance, the strength of the resin film will decrease, the resin film will be easily scratched or damaged during processing, and the resin film will crack and peel off. It is difficult to improve the concealability and 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.

  In order to solve such a problem, International Publication No. 2013/002323 describes a colored biaxial structure comprising a surface layer composed of a high-polymerization degree copolyester and a back layer composed of a copolyester containing a high concentration colorant. Stretched laminated films have been proposed. Certainly, according to this film, it is possible to achieve both concealability and strength of the resin film.

  However, in recent years, heat treatment has been performed in the middle of a series of can-making processes in order to relieve stress associated with strain applied to the film of the laminated metal plate and reduce film damage in the subsequent forming process. In this heat treatment, a higher heat treatment temperature is required for coexistence with the enamel rater value that confirms the presence or absence of coating film defects in the polyester film for inner coating of the can. Occurrence of poor appearance of the film has become a new issue, and the solution is desired.

Japanese Patent Laid-Open No. 11-342577 JP 2000-37836 A Japanese Patent Laid-Open No. 11-348218 International Publication No. 2013/002323 Pamphlet

  The present invention has been made in view of the above. The purpose of the present invention is that even when severe processing or high-temperature heat treatment is performed as described above, the film may be scraped or formed when forming into a can after bonding. A colored biaxially stretched polyester film for metal plate laminating molding processing that exhibits excellent molding processability that does not stick or peel off, and that can be formed into a molded product such as a can having excellent concealability and appearance. It is to provide.

  According to the study by the present inventors, it has been found that the above-described problem can be achieved by the following configuration.

1. Both surface layers (A layer) which are made of a copolyester having an intrinsic viscosity of 0.65 to 0.80 and a melting point of 230 to 250 ° C., and have an intrinsic viscosity of 0.55 to 0 .70, a colored biaxially stretched polyester film comprising three layers of a core layer (B layer) which is made of a copolyester having a melting point of 230 to 250 ° C. A colored biaxially stretched polyester film for metal plate laminating molding, wherein the copolymer polyester of the A layer and B layer satisfies the following formula (1).
TmB-TmA ≦ 4 ° C. --- (1)
However, TmA shows melting | fusing point of copolymer polyester of A layer, and TmB shows melting | fusing point of copolymer polyester of B layer.
2. 2. The colored biaxially stretched polyester film for metal plate laminating molding according to the above 1, wherein the copolymer polyester constituting the A layer and the B layer is isophthalic acid copolymerized polyethylene terephthalate.
3. The colored biaxially stretched polyester film for metal plate lamination molding processing according to 1 or 2 above, wherein the copolymer polyester constituting the A layer or the B layer is composed only of the copolymer polyester as a resin raw material.
4). The colored biaxially stretched polyester film for metal plate laminating and molding according to 1 or 2 above, wherein the copolymer polyester constituting the A layer or the B layer is a blend of a copolymer polyester and a homopolyester as a resin raw material.
5. The colored biaxially stretched polyester film for metal plate lamination molding processing according to any one of the above 1 to 4, wherein the film is bonded to the surface of the metal plate that is the container outer surface.

  The colored biaxially stretched polyester film for metal plate laminating and molding of the present invention has excellent concealment properties, and when it is molded into a can after being laminated to a metal plate, it is scraped into a film on the can wall, scratched or peeled off. Excellent molding processability that does not occur is exhibited, and the appearance of a molded article such as a can after molding is also good.

The present invention will be described in detail below.
The colored biaxially stretched polyester film for metal plate laminating molding processing of the present invention is a laminated film composed of three layers of both surface layers (A layer) and a core layer (B layer). The surface layer (A layer) and the core layer ( The copolymer polyester constituting the B layer) 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. Coalescence is preferred.

  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, and isophthalic acid is particularly preferable.

  In the case of layer A, the copolymerization ratio of the copolymerization component needs to be such that the melting point (TmA) of the copolymerized polyester is in the range of 230 to 250 ° C, preferably 238 to 250 ° C. If the melting point is less than 230 ° C., the heat resistance is inferior, and the chipping occurs due to the heat generated during the molding process. On the other hand, when the temperature exceeds 250 ° C., the crystallinity of the copolyester is increased, and molding processability is impaired.

  In the case of the B layer, it is necessary that the copolymer polyester has a melting point (TmB) of 230 to 250 ° C., preferably 242 to 250 ° C. If the melting point is less than 230 ° C., the heat resistance is inferior, and the chipping occurs due to the heat generated during the molding process. On the other hand, when the temperature exceeds 250 ° C., the crystallinity of the copolyester is increased, and molding processability is impaired.

The copolymer polyester constituting the A layer and the B layer is composed of a copolymer polyester and a homopolyester, as long as the melting point after film formation is in the above-mentioned range, Blends may be used. Among these, the former method is preferable from the viewpoint of forming processability when forming into a can and stability of film quality, and it is particularly preferable to use only copolymer polyester as a resin raw material for both the A layer and the B layer. On the other hand, according to the latter method using homopolyester as one of the resin raw materials, the copolymerized polyester constituting the layer can be controlled to a block copolymerized state rather than a random copolymerized state, and is applied to a metal plate. When forming into a can after combining, it is preferable because the orientation of the layer is increased, and thus the forming processability is easily improved.
When using the resin raw material which consists of a blend of copolyester and homopolyester as a resin raw material, it is preferable that content of homopolyester is the range of 30 to 60 weight% on the basis of the total amount of the polyester which comprises this layer.

Furthermore, the biaxially stretched polyester film of the present invention is a laminated metal plate film in order to realize good workability that does not cause scratching, scratching, peeling, etc. on the can wall even when subjected to molding under severe conditions. Heat treatment is performed in the middle of a series of can-making processes in order to relieve the stress associated with strain applied to. For this reason, the melting point difference (TmB−TmA) between the A layer and the B layer needs to be 4 ° C. or less. If this difference in melting point exceeds 4 ° C., when the heat treatment is performed, the residual stress at the time of can molding is relaxed (shrinks) in the B layer, the A layer melts and flows, and the appearance of the film surface is poor. This is not preferable.
Here, the melting point of the copolyester is measured by using a TA Instruments Q100 DSC and obtaining a melting peak at a heating rate of 20 ° C./min. The sample amount is about 20 mg.

  Next, the intrinsic viscosity of the copolyester (polymer part) constituting the layer A in the present invention needs to be in the range of 0.65 to 0.80, preferably in the range of 0.71 to 0.77. . In the present invention, if the polyester constituting the A layer is not a copolyester having a high intrinsic viscosity, severe heat treatment is performed at a higher temperature in the heat treatment step, so that the appearance after the heat treatment is deteriorated. When this intrinsic viscosity is less than 0.65, the fluidity of the film changes in the heat treatment step, and the appearance tends to deteriorate. On the other hand, those exceeding 0.80 are not economical because not only the quality is excessive but also the productivity of the raw material copolyester is lowered.

  Further, the intrinsic viscosity of the copolymerized polyester (polymer portion) constituting the B layer needs to be in the range of 0.55 to 0.70, and preferably in the range of 0.59 to 0.67. When the intrinsic viscosity is less than 0.55, not only is the film easily broken during stretching, but the resulting film is easily bonded to a metal plate and then molded into a can. . In addition, in the heat treatment step, the fluidity of the film changes and the appearance tends to deteriorate. On the other hand, when it exceeds 0.70, it is necessary to contain a high concentration of color pigment in the B layer as will be described later. Since productivity of polymerized polyester also falls, it is not preferred.

  Here, the intrinsic viscosity of the copolyester of the A layer and the B layer was measured in a 35 ° C. solution after dissolving the resin raw material used for film formation in o-chlorophenol and then removing the color pigment and the like with a centrifuge. This is the value obtained. In addition, when using the blend of copolyester and homopolyester as a resin raw material, the intrinsic viscosity of each resin raw material to blend is measured, and the weight average should just be in this range.

  Next, the A layer in the present invention needs to contain substantially no color pigment. “Substantially free of color pigment” as used herein means, for example, a small amount for the purpose of imparting surface smoothness to particles such as titanium dioxide (which is a color pigment and also has a function as a lubricant). Means that it may contain 0.05% by weight or less, preferably 0.03% by weight or less, more preferably 0.01% by weight or less, and it is particularly preferred that no color pigment is contained. When the layer A contains a colored pigment substantially, when the resulting film is bonded to a metal plate and then molded into a can, the can wall is damaged due to severe processing conditions. This is not preferable because it tends to occur and the number of surface defects increases. In addition, the film becomes brittle and film breakage tends to occur during film stretching.

  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 15 to 40% by weight, particularly preferably 15 to 30% by weight. When the content of the color pigment is 10% by weight or less, the hiding property is inferior, and when it exceeds 50% by weight, not only the effect of improving the hiding property is saturated but also the film becomes brittle and breaks during film stretching. This is not preferred because it tends to occur, and the resulting film tends to break when it is molded into a can after being bonded to a metal plate. The color pigment contained in 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.

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, especially 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.
Further, the thickness ratio between the A layer and the B layer (X _A / X _B : X _A is the total thickness of the A layer, and X _B is the thickness of the B layer) is 0.25 from the viewpoint of molding processability and concealability. ~ 0.43 is suitable.

The manufacturing method of the colored biaxially stretched polyester film for metal plate laminating molding 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

  Next, the unstretched laminated sheet 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, in particular, a plate made of tin, tin-free steel, aluminum or the like is suitable. Bonding to the metal plate is performed, for example, by heating the metal plate to a temperature equal to or higher than the melting point of the film, cooling after bonding the film, and amorphizing and fusing the surface layer portion of the film in contact with the metal plate. Can do. In this case, the polyester film for covering the inner surface of the can is also bonded to the other surface of the metal plate and fused at the same time.

Thus, after the polyester film for can outer surface coating and the polyester film for inner surface of the can are bonded to both surfaces of the metal plate, it is formed into a metal can or the like by drawing or the like.
At this time, heat treatment is performed in the middle of a series of can-making processes in order to reduce the film damage in the subsequent forming process by relaxing the stress accompanying the strain applied to the film of the film laminate metal plate. The

  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.

(Molding processability)
The sample film was bonded to one side of a 0.25 mm thick tin-free steel heated to the melting point of the copolyesters of the A layer and B layer, cooled with water, cut into a 150 mm diameter disk, and a drawing die and punch Was deep-drawn in four stages to produce a 55 mm diameter side seamless container. With respect to this can, molding processability was evaluated according to the following criteria, depending on the state of occurrence of shaving and wrinkling of the polyester film layer on the can wall.
○: The film is processed without abnormality, and no microcracks or film scraping is observed. ×: Microcracks or chipping is observed on the film.

(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) x: Breaking occurs frequently and substantially stable film formation is impossible. Cutting frequency (once / day) or more

(Appearance after heat treatment)
For cans having good moldability, the appearance of the cans after being held in an oven at 235 to 255 ° C. for 90 seconds was evaluated according to the following criteria.
○: No appearance failure is observed on the surface of the can film X: The appearance of the appearance failure is recognized because the surface of the can film is rough

[Examples 1-2, Comparative Examples 1-3]
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 130 ° C., and then heat-set at 165 ° C. to obtain a biaxially stretched polyester film. The total thickness of the film was 20 μm, and the thicknesses of the A layer and the B layer were 5 μm (both layers A were 2.5 μm) and 15 μm, respectively. The evaluation results of the obtained polyester film are shown in Table 2.

[Examples 3-4, Comparative Examples 4-5]
The same procedure as in Example 1 was carried out except that a 50/50 (weight ratio) blend of the copolyester and polybutylene terephthalate shown in Table 1 was used as the polyester for layer A and the pigment concentration was as shown in Table 1. . The evaluation results are shown in Table 2.

  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, Because it exhibits excellent molding processability without causing scratches and peeling, and also has an excellent appearance after can molding, it can be suitably used for metal cans such as beverage cans, food cans, and aerosol cans. Can do.

Claims (5)

Both surface layers (A layer) which are made of a copolyester having an intrinsic viscosity of 0.65 to 0.80 and a melting point of 230 to 250 ° C., and have an intrinsic viscosity of 0.55 to 0 .70, a colored biaxially stretched polyester film comprising three layers of a core layer (B layer) which is made of a copolyester having a melting point of 230 to 250 ° C. and the content of the color pigment is more than 10 wt% and not more than 50 wt% A colored biaxially stretched polyester film for metal plate laminating molding, wherein the copolymer polyester of the A layer and B layer satisfies the following formula (1).
TmB-TmA ≦ 4 ° C. --- (1)
However, TmA shows melting | fusing point of copolymer polyester of A layer, and TmB shows melting | fusing point of copolymer polyester of B layer.   2. 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 copolymerized polyethylene terephthalate.   The colored biaxially stretched polyester film for metal plate laminating molding according to claim 1 or 2, wherein the copolymer polyester constituting the A layer or the B layer comprises only a copolymer polyester as a resin raw material.   The colored biaxially stretched polyester film for metal plate laminating molding according to claim 1 or 2, wherein the copolymer polyester constituting the A layer or the B layer comprises a blend of a copolymer polyester and a homopolyester as a resin raw material.   The colored biaxially stretched polyester film for metal plate laminating molding according to any one of claims 1 to 4, wherein the film is bonded to a surface of the metal plate that is a container outer surface.