JP6982273B2 - Colored biaxially stretched polyester film for metal plate bonding molding processing - Google Patents

Description

The present invention relates to a colored biaxially stretched polyester film for metal laminating plate laminating molding processing.

Metal cans are generally painted to prevent corrosion of the inner and outer surfaces. In recent years, a thermoplastic resin film such as a polyester film has been coated as a method for imparting rust prevention without using an organic solvent for the purpose of simplifying the process, improving hygiene, preventing pollution, and the like. That is, it is used for food cans, beverage cans and aerosol cans that are subjected to strict molding processing such as squeezed cans and thinned squeezed cans after laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel or aluminum. Used for. From the viewpoint of cost reduction, the cans used for these purposes have come to be manufactured by subjecting them to thinning drawing or ironing with stricter processing conditions.

When such a strict molding process is applied, 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 the design, but in cans molded from a resin film-coated metal plate, white is used to conceal the color of the metal plate as the printing base. Alternatively, a resin film containing pigments of various colors laminated on a metal plate is used. When such a laminated metal plate is subjected to strict processing, the thickness of the resin becomes significantly thin, and the absolute amount of the added pigment in the thickness direction decreases, so that there is a problem that sufficient concealment cannot be obtained. appear. If a large amount of pigment is added to the resin film in anticipation of this problem, the strength of the resin film will decrease, the resin film will be easily scraped or scratched during processing, and the resin film will crack and peel off. It is difficult to improve the concealing property, keep the strength of the coated resin film high, and secure sufficient molding processability.

For example, a method of laminating a biaxially stretched polyester film on a metal plate and using it as a can-making material (Patent Document 1) has been proposed, but the resin film is scraped or damaged when it is molded by performing stricter processing. Or, in extreme cases, breakage occurs. Further, a method of laminating an unstretched polyester film on a metal plate and using it as a can-making material (Patent Document 2) has been proposed, but since the unstretched film is very brittle, it is cut when forming a film or handling it. There is a problem that it is easy and the productivity is poor.

In order to solve such a problem, Patent Document 3 describes a surface layer made of a copolyester having a high melting point and a high degree of polymerization and containing a wax, and a back layer made of a copolyester containing a high concentration colorant. A colored biaxially stretched laminated film comprising the above has been proposed. Certainly, according to this film, it is possible to achieve both concealing property and molding processability of the resin film.

However, after the laminated metal plate is formed into a can, a wide variety of printing is applied to the outer surface side of the can. Then, the end of the can body is molded into the final shape of the can by a molding tool. At this time, if the adhesion between the printed ink and the film is insufficient, the ink peels off, which causes a problem of impairing the appearance.

Japanese Unexamined Patent Publication No. 11-342577 Japanese Unexamined Patent Publication No. 11-348218 Japanese Unexamined Patent Publication No. 2017-30231

In recent years, the plate thickness has been reduced for the purpose of cost reduction, and the can manufacturing process has been improved accordingly, resulting in a stricter can manufacturing process and an increasing load on the film. In addition, since a wide variety of prints are applied to the surface of the can, adhesion with ink is also required.

The present invention has been made in view of the above, and an object thereof is that the film is scraped or scratched when the film is formed into a can after bonding even when severe processing or heat treatment at a high temperature is performed as described above. A colored biaxially stretched polyester film for metal plate laminating molding processing that can obtain molded products such as cans that exhibit excellent molding processability that does not stick and have excellent hiding power, appearance, and printability. To provide.

According to the research of the present inventors, it was found that the above-mentioned problems are achieved by the following configurations.
1. 1. Mainly composed of polyester having a melting point of 230 to 260 ° C., the intrinsic viscosity of the polymer portion is 0.46 or more, the content of the coloring pigment is 10% by weight or less, and polyethylene wax is 0.01 to 0.25. The surface layer (layer A) having a weight% of 10 points and an average roughness of 10 points in the range of 350 to 700 nm, and
A base material mainly composed of polyester having a melting point of 230 to 260 ° C. and a coloring pigment, the intrinsic viscosity of the polymer portion is 0.46 or more, and the content of the coloring pigment is more than 10% by weight and 50% by weight or less. A colored biaxially stretched polyester film composed of at least two layers with a layer (B layer).
A colored biaxially stretched polyester film for metal plate laminating molding processing in which the melting points of the polyesters of the A layer and the B layer satisfy the following formula (1).
｜ TmB-TmA ｜ ≦ 4 ℃ ――― (1)
(However, TmA indicates the melting point of the polyester of the A layer, and TmB indicates the melting point of the polyester of the B layer.)
2. 2. The colored biaxially stretched polyester film for metal plate laminating molding processing according to 1 above, wherein the polyester constituting the B layer is a copolymerized polyester having a melting point of 230 to 252 ° C.
3. 3. The colored biaxially stretched polyester film for metal plate laminating molding processing according to 1 or 2 above, wherein the polyester constituting the layer A is a copolymerized polyester having a melting point of 230 to 252 ° C.
4. 2. Coloring for metal plate laminating molding processing according to 1 above, wherein the polyesters constituting the A layer and the B layer are both copolymerized polyester having a melting point of 230 to 252 ° C. and both are isophthalic acid copolymerized polyethylene terephthalate. Axial stretched polyester film.
5. The colored biaxially stretched polyester film for metal plate laminating molding processing according to 4 above, wherein the wax is a polyethylene wax having a drip point of 120 to 140 ° C.
6. The colored biaxially stretched polyester film for metal plate bonding molding processing according to any one of 1 to 5 above, wherein the film is bonded to the surface of the metal plate on the outer surface of the container.

The colored biaxially stretched polyester film for metal plate bonding molding processing of the present invention has excellent molding processability that is less likely to cause cracks because it is scraped by the film on the can wall portion when it is molded into a can or the like after being bonded to a metal plate. Furthermore, the concealing property after molding, the appearance of molded products such as cans, and the printability are also good.

Hereinafter, the present invention will be described in detail.
The colored biaxially stretched polyester film for metal plate laminating molding processing of the present invention is a laminated film composed of at least two layers of a surface layer (A layer) and a base material layer (B layer).

The surface layer (layer A) is mainly made of polyester having a melting point of 230 to 260 ° C. Here, "mainly" means that the polyester is, for example, 80% by weight or more, preferably 85% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more based on the weight of the A layer. Is shown.

The base material layer (B layer) is mainly composed of polyester having a melting point of 230 to 260 ° C. and a coloring pigment. Here, "mainly" means that the total of the polyester and the coloring pigment is, for example, 80% by weight or more, preferably 85% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight, based on the weight of the B layer. Indicates that it is% or more.

When the melting points of the polyesters of the A layer and the B layer are in the above range, the molding processability is excellent. If it is lower than the lower limit of the melting point, film scraping occurs during molding, while if it is higher than the upper limit of the melting point, cracks occur.

Further, the biaxially stretched polyester film of the present invention is composed of at least two layers of A layer and B layer, for example, a two-layer structure of A layer / B layer and a three-layer structure of A layer / B layer / A layer. And so on. Further, as long as the object of the present invention is not impaired, a layer other than the A layer and the B layer may be provided. At that time, at least one surface of the film is made to be the A layer.

The polyester constituting the surface layer (A layer) and the base material layer (B layer) may be a homopolyester or a copolymerized polyester as long as the above melting point requirements are satisfied. As the homopolyester, homopolyethylene terephthalate is preferably mentioned. The copolymerized polyester may be a polyethylene terephthalate copolymer, a polyethylene-2,6-naphthalate copolymer, or a blend of these or the above homopolyester and polybutylene terephthalate. Among them, polyethylene terephthalate. Copolymers are preferred.

(Homo polyester)
In the present invention, as the polyester constituting the A layer and / or the B layer, a polyester having a melting point of more than 250 ° C and a melting point of 260 ° C or less can be preferably mentioned. By adopting such polyester, the effect of suppressing film scraping during molding is particularly excellent in the molding processability. If the melting point is higher than the upper limit, the formability is inferior in terms of not being able to follow the stretching during can making, and cracks occur in the film. On the other hand, when the melting point is lower than the lower limit, the effect of improving the film scraping suppression tends to be low. From this point of view, the melting point is more preferably 251 to 260 ° C, still more preferably 253 to 258 ° C, and particularly preferably 254 to 257 ° C.

Examples of such polyesters include homopolyesters, preferably homopolyethylene terephthalates, copolymerized polyesters having a relatively high melting point (the amount of copolymerization is relatively small) in the above melting point range, and preferably copolymerized polyethylene terephthalates. .. In particular, homopolyethylene terephthalate is preferable from the viewpoint of suppressing film scraping. Here, the homopolyethylene terephthalate does not exclude the inclusion of a diethylene glycol component that is inevitably contained. In addition, examples of the copolymerization component of the copolymerized polyester having a relatively high melting point include the copolymerization component in the copolymerized polyester described later, and the type and amount of the copolymerization component may be adjusted so as to be within the above melting point range. Just do it.

It is preferable that the polyester constituting both the A layer and the B layer is a polyester having a melting point of more than 250 ° C. and a melting point of 260 ° C. or lower as described above, so that the above-mentioned effect is more satisfactorily exhibited.

(Copolymerized polyester)
In the present invention, as the polyester constituting the A layer and / or the B layer, a copolymerized polyester having a melting point of 230 to 250 ° C. can be preferably mentioned. By adopting such polyester, it is excellent in the effect of suppressing both film cracking and film scraping during molding processability in a well-balanced manner. If the melting point is higher than the upper limit, cracks in the film tend to occur easily. On the other hand, if it is too lower than the lower limit, film scraping occurs due to heat generation during molding.

The copolymerization component of the copolymerized polyester may be an acid component or an alcohol component. Examples of the acid component 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 an aliphatic diol such as 1,6-hexanediol and an alicyclic diol such as 1,4-hexamethylenedimethanol. These can 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 the A layer, the copolymerization ratio of the copolymerization component of the copolymerized polyester as described above may be such that the melting point (TmA) of the copolymerized polyester is in the range of 230 to 250 ° C., preferably 235 to 250. The ratio is in the range of ° C., more preferably 238 to 250 ° C., still more preferably 238 to 249 ° C. If this melting point is low, the heat resistance is inferior, and scraping occurs due to heat generation during molding, which is not preferable. On the other hand, if it is higher than this, the crystallinity of the copolymerized polyester tends to be high, the effect of improving the molding processability is low, and cracks are likely to occur.

Similarly, in the case of the B layer, the melting point (TmB) of the copolymerized polyester may be set to a ratio in the range of 230 to 250 ° C., preferably 235 to 250 ° C., more preferably 238 to 250 ° C., still more preferably 242. The ratio is in the range of ~ 250 ° C. If this melting point is lower than the lower limit, the heat resistance is inferior, and the B layer tends to flow and deform due to heat generation during the molding process, and thus defects are likely to occur. Further, when the B layer is on the film surface, scraping occurs. On the other hand, when the melting point is higher than the upper limit, the crystallinity of the copolymerized polyester tends to be high, the effect of improving the molding processability is low, and cracks are likely to occur.

It is preferable that the polyester constituting both the A layer and the B layer is the above-mentioned copolymerized polyester having a melting point of 230 to 250 ° C., so that the above-mentioned effect is more satisfactorily exhibited.

The copolymerized polyester constituting the A layer and the B layer can be a copolymerized polyester and a homopolyester as long as the melting point after film formation is within the above range, even if only the copolymerized polyester is used as the resin raw material. Blends may be used. Among these, the former method is preferable from the viewpoint of molding processability and film quality stability when molding into a can, and it is particularly preferable to use only a copolymerized polyester as a resin raw material for both the A layer and the B layer.

When a resin raw material composed of a blend of a copolymerized polyester and a homopolyester is used as the resin raw material, the content of the homopolyester is preferably in the range of 30 to 60% by weight based on the total amount of polyester constituting each layer.

Further, the biaxially stretched polyester film of the present invention is added to the film of the laminated metal plate in order to realize good processability that the can wall portion is not scraped and cracks are not generated even if the molding process is performed under severe conditions. Heat treatment is performed in the middle of a series of can manufacturing processes for the purpose of relieving the stress caused by the strain. Therefore, the melting point difference | TmB-TmA | between the A layer and the B layer needs to be 4 ° C. or less. If this melting point difference exceeds 4 ° C, the residual stress during can molding is relaxed (shrinked) in the B layer when heat treatment is applied, and it melts and flows in the A layer, resulting in a poor appearance of the film surface. Therefore, it is not preferable.

(Intrinsic viscosity)
Next, the intrinsic viscosity of the polymer portions of the A layer and the B layer in the present invention needs to be 0.46 or more, preferably 0.49 or more, and more preferably 0.52 or more. When this intrinsic viscosity is low, the film breaks more often when the film is stretched, and breaks are likely to occur when the obtained film is bonded to a metal plate and then molded into a container. A high intrinsic viscosity is preferable from the viewpoint of molding processability, but an excessively high intrinsic viscosity may cause problems such as a decrease in productivity, and from such a viewpoint, for example, 0.80 or less is preferable. More preferably, it is 0.75 or less.

Here, the intrinsic viscosity (IV) of the copolymerized polyesters of the A layer and the B layer is determined by dissolving the raw material copolymerized polyester composition used for film formation in o-chlorophenol and then removing the coloring pigment and the like by a centrifuge. The value (IVa) obtained by measuring with a solution at 35 ° C. was substituted into the following equation (2) to obtain the value in terms of weight of the resin content.
IV = IVa / (1-C) --- (2)
Here, C refers to the color pigment concentration of each layer.

(Polyethylene wax)
In the present invention, the surface layer (layer A) needs to contain 0.01 to 0.25% by weight of polyethylene wax, more preferably in the range of 0.02 to 0.23% by weight, 0.03. The content is more preferably in the range of ~ 0.15% by weight. Is in the range of. When the content is less than the lower limit, the lubricity of the film surface is insufficient, and the film is liable to be scraped or scratched during the molding process in which a stricter load is applied to the film. If the content exceeds the upper limit, the adhesion to the ink printed on the film surface is impaired, and ink peeling occurs in the subsequent steps, which is not preferable. The polyethylene wax can be used without particular limitation as long as it has a composition mainly composed of a polyethylene main chain, and examples thereof include polyethylene oxide, linear polyethylene, branched polyethylene, and mixtures thereof. However, linear polyethylene having excellent heat resistance in the film forming process is preferable. The dropping point of the polyethylene wax is preferably 120 to 140 ° C. Within this range, polyethylene wax is easily exposed on the film surface in the can manufacturing process, the lubricity of the film surface is improved, and it is scraped and scratched during the molding process in which a stricter load is applied to the film. Sticking is less likely to occur. More preferably, it is 125 to 140 ° C.

(Surface roughness)
When the polyester film in the present invention has a two-layer structure of A layer / B layer, the ten-point average roughness on the A layer side has a three-layer structure of A layer / B layer / A layer. The ten-point average roughness on the A layer side of any one of them needs to be in the range of 350 to 700 nm, more preferably in the range of 400 to 690 nm, and further preferably in the range of 410 to 685 nm. When the ten-point average roughness is less than the lower limit, shaving occurs due to friction with a metal tool during molding, which is not preferable. In addition, the adhesion to the ink is also impaired, which is not preferable. If the ten-point average roughness exceeds the upper limit, the film starting from the particles contained in order to increase the roughness is scraped and cracks occur, which is not preferable. In order to achieve the above-mentioned surface roughness, the A layer is preferably inert particles having an average particle size of 1.0 to 3.0 μm, and more preferably 1.2 to 1.8 μm. preferable. The inert particles are preferably contained in an amount of 0.01 to 0.5% by mass, more preferably 0.05 to 0.3% by mass, and 0.08 to 0 to 0, based on the mass of the A layer. It is more preferably contained in an amount of .2% by mass.

The inert particles contained in the layer A are not particularly limited as long as they can stably exist in the polymer, and those known per se can be adopted, for example, polystyrene, polyacrylic acid methyl ester, polyacrylic acid ethyl ester. , Polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, and polymer of each monomer selected from divinylbenzene, or copolymer, polytetrafluoroethylene, polyacrylonitrile, benzoguanamine, organic material such as silicone, silica. , Kaolin, talc, graphite and other inorganic substances are preferably used.

By designing the surface roughness of the film so as to be within the above range and adding wax so as to be within the above range, the lubricating action derived from the wax and the contact area with the molding tool derived from the surface roughness are obtained. Molding workability is satisfied by the reduction of. Further, by setting the surface roughness within the above range, the adhesion of the ink is ensured by the anchor effect between the film and the ink.

(Coloring pigment)
In the present invention, the B layer contains a coloring pigment, and the content of the coloring pigment needs to be more than 10% by weight and 50% by weight or less based on the weight of the B layer, and a more preferable content is 15 to 40. It is in the range of% by weight, particularly preferably 15 to 30% by weight. When the content of the coloring pigment is 10% by weight or less, the hiding property is inferior, and when the content exceeds the upper limit, not only the effect of improving the hiding property is saturated, but also the film becomes brittle and the film breaks during stretching. It is not preferable because it becomes easy and cracks and breaks are likely to occur when the obtained film is bonded to a metal plate and then molded into a can. The coloring pigment contained in the B layer may be either inorganic or organic, but an inorganic pigment is preferable. As the inorganic pigment, alumina, titanium dioxide, calcium carbonate, barium sulfate and the like are preferably exemplified, and titanium dioxide is particularly preferable.

The color pigment may or may not be contained in the A layer as long as the object of the present invention is not impaired. When it is contained, it shall be 10% by weight or less based on the weight of the A layer. When the content of the coloring pigment in the A layer exceeds the upper limit, cracks are likely to occur in the can wall portion when the film is bonded to a metal plate and then molded into a can or the like, if severe processing conditions are involved. It is in. In addition, the film becomes brittle and tends to break easily when the film is stretched. From this point of view, it is more preferably 5% by weight or less, further preferably 3% by weight or less, and particularly preferably 1% by weight or less. Further, as the most preferable embodiment in the present invention, there is an embodiment in which the A layer does not substantially contain a coloring pigment. The term "substantially free of colored pigments" as used herein means that particles such as titanium dioxide (which is a colored pigment and at the same time also acts as a lubricant) are provided with a small amount, for example, A for the purpose of imparting surface smoothness. It means that it may be contained in an amount of 0.05% by weight or less, preferably 0.03% by weight or less, more preferably 0.01% by weight or less based on the weight of the layer, and particularly preferably no coloring pigment. .. By doing so, it is possible to further suppress the occurrence of cracks in the can wall portion even in the molding process accompanied by the severe processing conditions as described above, and it is possible to further reduce the surface defects. Further, it is possible to further suppress the film from becoming brittle, and it is possible to further suppress the film breakage during film stretching.

(Other additives)
In addition, in the A layer and the B layer, other additives such as a fluorescent whitening agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, and an antistatic agent are used as necessary, as long as the object of the present invention is not impaired. Agents and the like can be added. In particular, when improving the whiteness, a fluorescent whitening agent is effective.

(Thickness)
Next, the thickness of the biaxially stretched polyester film of the present invention can be appropriately changed as needed, but the total thickness is preferably in the range of 6 to 75 μm, and particularly 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 molding, while if the thickness exceeds 75 μm, the quality is excessive and it is uneconomical.

Furthermore, the thickness ratio between the A layer and the B layer (X _A / X _B : where X _A is the total thickness of the A layer and X _B is the total thickness of the B layer) is suitable for the surface contact angle, molding processability, and the like. From the viewpoint of the balance of concealment, 0.13 to 0.43 is preferable, 0.15 to 0.40 is more preferable, and 0.16 to 0.35 is more preferable.

(Production method)
The method for producing the colored biaxially stretched polyester film for the metal plate laminating molding process of the present invention described above is not particularly limited, and an unstretched laminated sheet is first prepared by a conventionally known film forming method, and then stretched in two directions. do it.

For example, a polyester composition obtained by adding polyethylene wax and inert particles to polyester for the A layer is prepared, sufficiently dried, and then melted in an extruder at a temperature of melting point to (melting point +50) ° C. Here, the melting point is the melting point of the polyester used. At the same time, a polyester composition obtained by adding a coloring pigment to polyester for the B layer is prepared, sufficiently dried, and then supplied to another extruder and melted at a temperature of melting point to (melting point +50) ° C. Subsequently, a laminated unstretched laminated sheet is manufactured by a method of laminating both molten resins inside the die, for example, a simultaneous laminating extrusion method using a multi-manifold die. According to such a simultaneous laminated extrusion method, the melt of the resin forming one layer and the melt of the resin forming another layer are laminated inside the die and formed into a sheet from the die while maintaining the laminated form. To.

Next, the unstretched laminated sheet can be manufactured by a method of sequentially or simultaneously biaxially stretching and heat-fixing. In the case of forming a film by sequential biaxial stretching, the unstretched laminated sheet is heated by roll heating, infrared heating or the like to first stretch in the vertical direction, and then laterally stretched by a stenter. At this time, the stretching temperature is set to a temperature 20 to 50 ° C. higher than the glass transition point (Tg) of the polyester (preferably the polyester of layer A), and the longitudinal stretching ratio is 2.0 to 5.0 times, preferably 2.2 to 2. 4.0 times, more preferably 2.5 to 3.6 times, lateral stretching ratio 2.5 to 5.0 times, preferably 2.6 to 4.0 times, more preferably 2.6 to 3. The range should be 7 times. The heat-fixing temperature is preferably selected in the range of 150 to 240 ° C., preferably 150 to 230 ° C., in order to adjust the film quality according to the melting point of the polyester.

(Use)
The colored biaxially stretched polyester film for metal plate bonding molding processing of the present invention is suitably used for applications in which the metal plate is bonded to the outer surface of the container. This is because the inner surface of the container is not usually required to have printability.

As the metal plate to which the colored biaxially stretched polyester film for laminating molding processing of the present invention is bonded, particularly the metal plate for can making, a plate such as tinplate, tin-free steel, or aluminum is suitable. For bonding to a metal plate, for example, the metal plate is heated to a temperature higher than the melting point of the film (the melting point of polyester constituting the layer in contact with the metal plate in the film), the film is bonded and then cooled, and the film is in contact with the metal plate. This can be done by a method of decrystallizing and fusing the layers of. In this case, the polyester film for covering the inner surface of the can can also be attached to the other surface of the metal plate and fused at the same time. If the film has a two-layer structure of A layer / B layer, the B layer is in contact with the metal plate, and if the film has a three-layer structure of A layer / B layer / A layer, any one of them. The A layer of the above comes into contact with the metal plate. Similarly, in the case of other laminated configurations, it is sufficient that the A layer forms the film surface layer opposite to the metal plate, and the surface layer on the side opposite to the A layer forming the surface layer in the film is formed. The layer is on the side to be bonded to the metal plate.

In this way, the polyester film for covering the outer surface of the can and the polyester film for the inner surface of the can are bonded to both sides of the metal plate, and then formed into a metal can or the like by several steps of squeezing and ironing. At this time, heat treatment is performed in the middle of a series of can manufacturing processes in order to reduce the stress due to the strain applied to the film of the film-laminated metal plate and to reduce the film damage in the subsequent molding process. To. The present invention is excellent in appearance even if the heat treatment is applied.

(Characteristic value)
[crack]
The sample film has a two-layer structure that is equal to or higher than the melting point of the polyester of the B layer (metal plate bonding surface) (approximately melting point + 10 ° C.), and a three-layer structure is that of the A layer polyester that is the metal plate bonding surface. It is attached to one side of tin-free steel with a plate thickness of 0.230 mm heated to above the melting point (approximately melting point + 10 ° C), cooled with water, cut into a disk shape with a diameter of 150 mm, and squeezed in 5 stages using a die and a punch. To create a sideless seamless container with a diameter of 55 mm. For this can, the state of cracks in the polyester film layer on the can wall is evaluated.

The cracks in the colored biaxially stretched polyester film for the metal plate laminating molding process of the present invention are preferably such that small cracks are observed in the film depending on the state of occurrence of cracks in the polyester film layer on the can wall of 1000 cans. , More preferably, no cracks are observed in the film.

[Ink adhesion]
Known thermosetting ink (MC QL R-3 Red-3, manufactured by DIC Corporation) and thermosetting finishing varnish (manufactured by DIC Corporation, 6WB117) are placed in a can made of a metal plate to which a biaxially stretched film sample is attached. ) Was applied to the can body, and then baked and cured at 200 ° C. for 30 seconds in an oven. 700 of the obtained cans were cut open and the can body was flattened to form a test piece. The surface on which the ink of the obtained test piece was printed was scanned with a pencil hardness tester (PS-310 manufactured by Maruhishi Kagaku Kikai Seisakusho Co., Ltd.) under a load of 500 g at a speed of 10 mm / min, and ink peeling occurred. Do not measure the maximum pencil hardness and judge according to the following criteria.

The ink adhesion of the colored biaxially stretched polyester film for the metal plate laminating molding process of the present invention is preferably H in pencil hardness, more preferably 2H, and further preferably 3H or more.

[Concealment]
Using the can body obtained above, the can body is visually observed and the concealment property is evaluated according to the following criteria.
The hiding power of the colored biaxially stretched polyester film for the metal plate laminating molding process of the present invention preferably shows good hiding power with almost no visible color of the metal plate base, and more preferably no color of the metal plate base. It is invisible and shows excellent concealment.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. Each characteristic value was measured by the following method. Further, the parts and% in the examples mean parts by weight and% by weight, respectively, unless otherwise specified.

(Melting point)
The melting point of the copolymerized polyester was measured using TA Instruments Q100 DSC by a method of obtaining a melting peak at a heating rate of 20 ° C./min. As the sample, 5 mg of the polyester composition scraped from each layer of the film is used as the sample.

(Drip point)
The drip point was measured using a Ubbelohde drip point meter according to DIN 51801/2 (° C.).

(Intrinsic viscosity)
0.3 g of the polyester composition scraped from each layer of the film is dissolved in 25 ml of o-chlorophenol, cooled once, colored pigments and the like are removed by a centrifuge, and the solution is heated to 35 ° C. using an Ostwald viscosity tube. It was calculated from the solution viscosity measured under the conditions.

(Surface roughness)
After aluminum vapor deposition on the surface of the film on the surface layer (A layer) side using a vacuum vapor deposition device (JEE-4X manufactured by JEOL Ltd.), the surface is surfaced with an objective 50 using a laser microscope (VK-X100 manufactured by KEYENCE CORPORATION). The 10-point average roughness (R _ZJIS ) was measured 5 times, and the average value was taken as the 10-point average roughness.

(Color pigment concentration)
The concentration of the colored pigments in the A and B layers is such that about 1 to 2 g of the polyester composition scraped from each layer of the film is placed in a ceramic crucible and heated at 600 ° C. for 6 hours or more in an electric dryer, and then the ash content remaining in the crucible. The weight was calculated by dividing by the weight of the original polyester composition. The color pigment concentration of the entire film was calculated by the same method using 1 g of the formed biaxially stretched polyester film.

(Thickness of each layer of film)
The sample was cut out in the longitudinal direction and 2 cm in the width direction, fixed in an embedding capsule, and then embedded in an epoxy resin. Then, the embedded sample is cut vertically in the width direction by a microtome (Supercut manufactured by Reichert-Jung) to obtain a thin film section having a thickness of 50 μm. Using a scanning electron microscope (Hitachi 4300SE / N), observation and photography were performed at an acceleration voltage of 20 kV, the thickness of each layer was measured from the photograph, and the average thickness of 5 points was obtained.

(Moldability)
The sample film has a two-layer structure that is equal to or higher than the melting point of the polyester of the B layer (metal plate bonding surface) (approximately melting point + 10 ° C.), and a three-layer structure is that of the A layer polyester that is the metal plate bonding surface. It is attached to one side of tin-free steel with a plate thickness of 0.230 mm heated to above the melting point (approximately melting point + 10 ° C), cooled with water, cut into a disk shape with a diameter of 150 mm, and squeezed in 5 stages using a die and a punch. To create a sideless seamless container with a diameter of 55 mm. The moldability of this can was evaluated according to the following criteria based on the state of scraping and cracking of the polyester film layer on the can wall.

[Shave]
The molding processability was evaluated according to the following criteria based on the state of occurrence of scraping of the polyester film layer on the can wall of 1000 cans.
⊚: The incidence of scraping and peeling is less than 0.1%.
◯: It was scraped to 0.1 to 0.5% of the can, and peeling occurred, but there was no practical problem.
X: Shaving and peeling, which are practically problematic, are observed in 0.1 to 0.5% cans.
XX: Shaving and peeling, which are practically problematic, are observed in cans exceeding 0.5%.

[crack]
◯: No cracks were found on the film.
Δ: Small cracks are observed in the film.
X: Large cracks are observed in the film.

(Ink adhesion)
The ink adhesion was evaluated by a pencil hardness test.
Known thermosetting ink (MC QL R-3 Red-3, manufactured by DIC Corporation) and thermosetting finishing varnish (manufactured by DIC Corporation, 6WB117) are placed in a can made of a metal plate to which a biaxially stretched film sample is attached. ) Was applied to the can body, and then baked and cured at 200 ° C. for 30 seconds in an oven. 700 of the obtained cans were cut open and the can body was flattened to form a test piece. The surface on which the ink of the obtained test piece was printed was scanned using a tensile coating film hardness tester (~~~) at a speed of 10 mm / min under a load of 500 g, and the maximum pencil hardness at which ink peeling did not occur. Was measured and judged according to the following criteria.
◎: Pencil hardness is 3H or more ○: Pencil hardness is 2H
Δ: Pencil hardness is H
×: Pencil hardness is F or less

(Concealment)
Using the can body obtained above, the can body was visually observed and the concealing property was evaluated according to the following criteria.
⊚: The color of the metal plate background is not visible at all, showing excellent concealment.
◯: The color of the metal plate background is almost invisible, showing good concealment.
X: The color of the metal plate background is visible, and the concealing property is inferior.

(Appearance after heat treatment)
For a can having good moldability, the appearance of the can after holding it in an oven at 235 to 255 ° C. for 90 seconds was evaluated according to the following criteria.
◯: No appearance defect was observed on the film surface of the can.
X: The film surface of the can is rough and poor appearance is observed.

[Examples 1 to 12, Comparative Examples 1 to 11]
The polyester composition for A layer and the polyester composition for B layer shown in Table 1 are dried independently. ・ Both A layer and B layer are melted at 280 ° C., and then a three-layer feed block is used to form a three-layer structure of A / B / A. It was laminated, co-extruded from an adjacent die, and rapidly cooled and solidified to obtain an unstretched laminated film. Next, this unstretched film was longitudinally stretched 3.0 times at 100 ° C., then transversely stretched 3.0 times at 130 ° C., and then heat-fixed at 165 ° C. to obtain a biaxially stretched polyester film.

A rutile-type titanium oxide (average particle size 0.5 μm) was used as the coloring pigment. Further, as the wax, a linear polyethylene wax having a dropping point of 135 ° C. was used. Table 2 shows the evaluation results of the obtained biaxially stretched polyester film.

[Example 13]
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the film was laminated in a two-layer structure of A / B by a two-layer feed block. Table 2 shows the evaluation results of the obtained biaxially stretched polyester film.

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

The colored biaxially stretched polyester film for bonding and molding of a metal plate of the present invention has excellent concealing properties, and even if it is molded into a can under severe conditions after being bonded to a metal plate, it can be scraped into a film on the can wall. It exhibits excellent molding processability without cracking, and also has excellent appearance after can molding and excellent printability. Therefore, it is particularly suitable for metal cans such as beverage cans, food cans, and aerosol cans. It can be suitably used for the outer surface of these cans.

Claims (6)

Mainly composed of polyester having a melting point of 230 to 260 ° C., the intrinsic viscosity of the polymer portion is 0.46 or more, the content of the coloring pigment is 10% by weight or less, and the content of polyethylene wax is 0.01 to 0.01. The surface layer (layer A) having a viscosity of 0.25% by weight and an average roughness of 10 points in the range of 350 to 700 nm,
A base material mainly composed of polyester having a melting point of 230 to 260 ° C. and a coloring pigment, the intrinsic viscosity of the polymer portion is 0.46 or more, and the content of the coloring pigment is more than 10% by weight and 50% by weight or less. A colored biaxially stretched polyester film composed of at least two layers with a layer (B layer).
A colored biaxially stretched polyester film for metal plate laminating molding processing in which the melting points of the polyesters of the A layer and the B layer satisfy the following formula (1) (however, the melting point of the polyester of the A layer is 245 ° C. or less and B (Except when the melting point of the polyester in the layer is 245 ° C or lower) .
｜ TmB-TmA ｜ ≦ 4 ℃ ――― (1)
(However, TmA indicates the melting point of the polyester of the A layer, and TmB indicates the melting point of the polyester of the B layer.) The colored biaxially stretched polyester film for metal plate laminating molding processing according to claim 1, wherein the polyester constituting the B layer is a copolymerized polyester having a melting point of 230 to 252 ° C. (However, the melting point of the polyester of the A layer is 245. Except when the temperature is below ° C and the melting point of the polyester in layer B is below 245 ° C) . The colored biaxially stretched polyester film for metal plate laminating molding processing according to claim 1 or 2, wherein the polyester constituting the A layer is a copolymerized polyester having a melting point of 230 to 252 ° C. (However, the melting point of the polyester of the A layer). Is 245 ° C. or lower, and the melting point of the polyester in the B layer is 245 ° C. or lower) . The coloring for metal plate laminating molding processing according to claim 1, wherein the polyester constituting the A layer and the B layer is both a copolymerized polyester having a melting point of 230 to 252 ° C. and both are isophthalic acid copolymerized polyethylene terephthalates. Biaxially stretched polyester film (except when the melting point of the polyester of the A layer is 245 ° C. or lower and the melting point of the polyester of the B layer is 245 ° C. or lower) . The colored biaxially stretched polyester film for metal plate laminating molding processing according to claim 4, wherein the wax is a polyethylene wax having a drip point of 120 to 140 ° C. The colored biaxially stretched polyester film for metal plate bonding molding processing according to any one of claims 1 to 5, wherein the film is bonded to the surface of the metal plate on the outer surface of the container.