TWI606922B - Film for coating steel plate - Google Patents

Description

Coated steel sheet

The present invention relates to a film for coated steel sheets.

The present application claims priority based on Japanese Patent Application No. 2013-87173, filed on April 18, 2013 in Japan, the disclosure of which is incorporated herein.

In recent years, a can obtained by performing a drawing process and an extension process on a resin film-coated steel sheet in which a resin film is laminated on both sides of a steel sheet is used, and the drawing process is simultaneously performed after the drawing process. The can is coated with a resin film having a high height such as a can obtained by thinning. Among these cans, a resin film excellent in workability composed of a copolymer of ethylene terephthalate and ethylene isophthalate is used. Since the film of the copolymer of ethylene terephthalate and ethylene isophthalate is excellent in the fragrance protection of the content, the cans are widely used as cans for beverages and foods. However, when a film of a copolymer of ethylene terephthalate and ethylene isophthalate is used in a can for beverages or foods, there is a case where the film is insufficient in corrosion resistance to the contents, and the steel sheet is corroded. . Moreover, when the resin film-coated steel sheet applied to the beverage or the food can is coated with the resin in the film without the alignment, when the resin film is coated with the steel sheet, the film is heated near the melting point of the resin. It grows into a brittle and large-sized resin crystal, and has a disadvantage that cracks are likely to occur in the resin film.

As a method for overcoming such a drawback, as disclosed in Patent Document 1, it has been proposed that a lower layer which is in contact with a steel sheet is a mixture of polyethylene terephthalate and polybutylene terephthalate, and the upper layer a film composed of polyethylene terephthalate or a lower layer that is in contact with the steel sheet A mixture of a copolymer of ethylene terephthalate and ethylene isophthalate and polybutylene terephthalate, and the upper layer is a film composed of polyethylene terephthalate. However, if the lower layer is a mixture of polyethylene terephthalate and polybutylene terephthalate, and the upper layer is made of a film composed of polyethylene terephthalate, there is a film for The adhesion of the steel sheet is insufficient, and when the distillation treatment is performed after the extension molding, the film is peeled off from the steel sheet. Further, if the lower layer is a mixture of a copolymer of ethylene terephthalate and ethylene isophthalate and a mixture of polybutylene terephthalate, the upper layer is composed of polyethylene terephthalate. In the film composed of the diester, the adhesion of the film to the steel sheet is insufficient, and when the distillation treatment is performed after the extension molding, the film shrinks and is peeled off from the steel sheet, and the steel sheet is corroded.

Further, as shown in Patent Document 2, it has been proposed that the lower layer which is in contact with the steel sheet is a mixture of polybutylene terephthalate and a copolymer of ethylene terephthalate and ethylene isophthalate. The resulting mixture, the intermediate layer is polybutylene terephthalate, and the upper layer is a film composed of a copolymer of ethylene terephthalate and ethylene isophthalate. However, when a copolymer of ethylene terephthalate and ethylene isophthalate is used as the upper layer, the film may be whitened during the distillation treatment, and the appearance may be deteriorated.

Further, Patent Document 2 proposes that the lower layer that is in contact with the steel sheet is a mixture of polybutylene terephthalate and a copolymer of ethylene terephthalate and ethylene isophthalate. The upper layer is a film composed of polybutylene terephthalate. However, if a mixture of polybutylene terephthalate and a copolymer of ethylene terephthalate and ethylene isophthalate is used as the lower layer, after the resin film-coated steel sheet is drawn, When the distillation treatment is carried out, there is a case where the film shrinks and is peeled off from the steel sheet, and the steel sheet is corroded.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-213104

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-1447

An object of the present invention is to provide a film for coated steel sheets which is excellent in corrosion resistance and which is difficult to produce peeling of a film from a steel sheet even after distillation treatment after extension molding.

Such an object is achieved by the present invention described in the following (1) to (9). Further, the wetting tension according to JIS K6768 refers to the wetting tension measured according to the method described in JIS K6768.

(1) A film for a coated steel sheet, comprising: a first resin layer that is in contact with the steel sheet, wherein the surface of the first resin layer that is in contact with the steel sheet has a wet tension of 34 mN/m or more according to JIS K6768, The melting point of the resin constituting the first resin layer is 140 to 280 °C.

(2) The film for coated steel sheets according to the above aspect, wherein the first resin layer contains a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol, and crystallizing Polyester.

(3) The film for a coated steel sheet according to the above aspect, wherein the first resin layer contains 1 to 50% by weight of ethylene glycol or terephthalic acid, based on the entire first resin layer. And a copolymer obtained by copolymerization of cyclohexane dimethanol and 50 to 99% by weight of a crystalline polyester.

(4) The film for coated steel sheets according to the above (2), wherein the copolymer has 1 to 50 mol% as a constituent monomer component with respect to the alcohol unit of the entire copolymer. Cyclohexane dimethanol.

(5) The film for coated steel sheets according to any one of the above (2), wherein the crystalline polyester is polybutylene terephthalate.

(6) The film for a coated steel sheet according to any one of the above aspects, wherein the film for a coated steel sheet has a second surface on a side opposite to a surface in contact with the steel sheet of the first resin layer. Resin layer.

(7) The film for coated steel sheets according to the above aspect, wherein the second resin layer contains a crystalline polyester and is copolymerized with ethylene glycol, terephthalic acid, and cyclohexane dimethanol. The resulting copolymer.

(8) The film for a coated steel sheet according to the above aspect, wherein the second resin layer contains 70 to 99% by weight of the crystalline polyester and the entire second resin layer. 1 to 30% by weight of a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol.

(9) The film for coated steel sheets according to the above (7), wherein the crystalline polyester is a polymer Butylene terephthalate.

According to the present invention, it is possible to provide a film for coating a steel sheet which is excellent in corrosion resistance and which is difficult to be produced by peeling off the film even after the distillation treatment after the extension molding.

[Formation of Carrying Out the Invention]

Hereinafter, an example of the film for coated steel sheets of the present invention will be described in detail.

(first resin layer)

The film for coated steel sheets according to the present invention includes a first resin layer on a surface in contact with the steel sheet. The first resin layer is tied to a surface that is in contact with the steel sheet, and is excellent in adhesion to the steel sheet to prevent corrosion of the steel sheet.

The melting point of the resin constituting the first resin layer is 140 to 280 °C. When the melting point of the resin is within this range, the resin does not easily flow during the distillation treatment, and the film for covering the steel sheet can be prevented from being peeled off from the steel sheet. The resin constituting the first resin layer has a melting point of 140 to 280 ° C, and is not particularly limited, but is preferably 170 to 280 ° C, more preferably 200 to 280 ° C. When the melting point of the resin constituting the first resin layer is within the above range, the effect of preventing the film for covering the steel sheet from being peeled off from the steel sheet can be more remarkably exhibited.

Moreover, the wettability of the surface which contact|connects the steel plate of the said 1st resin layer is 34 mN / m or more. When the wetting tension is within this range, the adhesion between the film for covering the steel sheet and the steel sheet is improved, and the film for covering the steel sheet can be prevented from being peeled off from the steel sheet.

The wet tension of the surface in contact with the steel sheet of the first resin layer is not particularly limited as long as it is 34 mN/m or more, and is preferably 36 mN/m or more, and more preferably 38 mN/m or more. With this, The effect of preventing the film for coated steel sheets from being peeled off from the steel sheet can be exhibited more remarkably.

Further, the wet tension is measured in accordance with the method described in JIS K6768.

In other words, the film for a coated steel sheet of the present invention has a melting point of 140 to 280 ° C for the resin constituting the first resin layer and a wet tension of 34 mN for the surface of the steel sheet of the first resin layer. Above m, the resin does not easily flow during the distillation treatment, and is excellent in adhesion to a steel sheet. Therefore, the film-form film for coated steel sheets of the present invention is not easily peeled off from the steel sheet, and is excellent in corrosion resistance.

Preferably, the resin constituting the first resin layer has a melting point of 170 to 280 ° C and a wet tension of a surface in contact with the steel sheet of the first resin layer is 36 mN/m or more, and more preferably constitutes the first resin layer. The melting point of the resin is 200 to 280 ° C, and the wettability of the surface in contact with the steel sheet of the first resin layer is 36 mN/m or more. Therefore, the effect of preventing the coating film for coated steel sheets from being peeled off from the steel sheet, which is excellent in corrosion resistance, can be exhibited more remarkably.

Moreover, it is preferable that the first resin layer contains a crystalline polyester, and more preferably a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol. When the first resin layer contains a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol with a crystalline polyester, it is less likely to generate crystals in the first resin layer during heating. The whitening of the film for coated steel sheets at the time of the distillation treatment is suppressed. Further, it is possible to suppress peeling of the film from the steel sheet due to shrinkage of the film at the time of distillation treatment.

Further, the ratio of the copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol to the crystalline polyester is not particularly limited, and preferably contains 1 with respect to the entire first resin layer. ~50% by weight of a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol with 50 to 99% by weight of a crystalline polyester, more preferably ethylene glycol or terephthalic acid The copolymer obtained by copolymerization of cyclohexane dimethanol is 1 to 15% by weight, and the crystalline polyester is 85 to 99% by weight. When the ratio of the copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, or cyclohexane dimethanol to the crystalline polyester is within the above range, the first resin layer can be further suppressed in the first step. The crystals during heating in the resin layer are grown, and the whitening of the film for coated steel sheets during the distillation processing can be further suppressed. Further, peeling of the film from the steel sheet due to film shrinkage at the time of distillation treatment can be further suppressed.

Further, in the case where the first resin layer contains a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol, the copolymer is preferably an alcohol unit based on the entire copolymer. It has 1 to 50 mol% of cyclohexanedimethanol as a constituent monomer component, and more preferably 5 to 40 mol%. When the content of the cyclohexanedimethanol which is a monomer component is less than the lower limit, the first resin layer may be crystallized, and the film for covering the steel sheet may be insufficient in adhesion to the steel sheet. In addition, when the content of the cyclohexanedimethanol which is a monomer component is more than the above-mentioned upper limit, the film for coated steel sheets may be whitened during the distillation process, and the appearance may become a problem.

In the case where the first resin layer contains a crystalline polyester, the crystalline polyester is not particularly limited, and is preferably polybutylene terephthalate or polyethylene terephthalate. The ester, polyethylene naphthalate, polytrimethylene terephthalate, polybutylene naphthalate or the like is preferred, and polybutylene terephthalate is more preferred. Thereby, the compatibility of the copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol with the crystalline polyester is improved, the corrosion resistance of the film is improved, and corrosion of the steel sheet can be prevented.

Further, the thickness of the first resin layer is not particularly limited, but is preferably 2 μm or more and 40 μm or less. More preferably, it is 5 μm or more and 35 μm or less. When the thickness of the first resin layer is less than the lower limit, the first resin layer may be cut during the drawing and the film for covering the steel sheet may be peeled off from the steel sheet. When the thickness of the first resin layer is thicker than the upper limit value, the film for covering the steel sheet becomes thick, and the shrinkage force of the film increases during the distillation treatment after the drawing process, and the film is peeled off from the steel sheet. The situation. Also, there will be a case where the cost becomes high.

Further, it is preferable that the anti-caking agent is further dispersed in the first resin layer. In the case of the anti-caking agent, it is preferred to use spherical glass, spherical acrylic resin, ultra high molecular weight polyethylene, polytetrafluoroethylene, globular vermiculite, fatty acid ester, talc, calcium carbonate, diatomaceous earth. More preferably, an aliphatic ester is used. By dispersing the anti-caking agent, the coefficient of friction between the films can be reduced at the time of film formation, and the film can be made slippery, and the winding wrinkles of the wound original roll of the film can be prevented.

Further, the content of the anti-caking agent is not particularly limited, and is preferably the first resin layer. 1 to 10% by weight, more preferably 0.5 to 5% by weight. When the content of the anti-caking agent is within the above range, the coefficient of friction between the films can be reduced at the time of film formation and the film can be made slippery, and the winding wrinkles of the wound original roll of the film can be prevented.

(second resin layer)

Moreover, it is preferable that the film for a coated steel sheet according to the present invention has a second resin layer on the side opposite to the surface in contact with the steel sheet of the first resin layer. The second resin layer is a layer laminated on the first resin layer, and in particular, the steel sheet can be protected from damage caused by corrosive contents.

Further, the second resin layer preferably contains a crystalline polyester, and more preferably further contains a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol. The second resin layer contains a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol, and a crystalline polyester, so that crystals are less likely to be generated in the second resin layer during heating. Further, whitening of the film for coated steel sheets during distillation processing can be suppressed. Further, it is possible to suppress peeling of the film from the steel sheet due to shrinkage of the film during the distillation processing.

Further, the ratio of the copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol to the crystalline polyester is not particularly limited, and preferably contains 1 with respect to the entire second resin layer. ~30% by weight of a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol with 70 to 99% by weight of crystalline polyester, more preferably 20 to 30% by weight of B A copolymer obtained by copolymerization of a diol, terephthalic acid or cyclohexane dimethanol and 70 to 80% by weight of a crystalline polyester. When the ratio of the copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol to the crystalline polyester is within the above range, the second resin layer is present in the entire first resin layer. In the middle, the crystal growth during heating can be further suppressed, and whitening of the film for coated steel sheets during the distillation processing can be further suppressed. Further, peeling of the film from the steel sheet due to film shrinkage at the time of distillation processing can be further suppressed.

Further, in the case where the second resin layer contains a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol, the copolymer is preferably an alcohol unit based on the entire copolymer. Containing 1 to 50 mol% of cyclohexanedimethanol as a constituent monomer component, more preferably 5 to 40 Moer%. When the content of the cyclohexanedimethanol which is a monomer component is less than the lower limit, the second resin layer may be crystallized, and the adhesion of the film for the steel sheet to the steel sheet may be insufficient. In addition, when the content of the cyclohexanedimethanol which is a monomer component is more than the above-mentioned upper limit, the film for coated steel sheets may be whitened during the distillation process, and the appearance may become a problem.

In addition, in the case where the second resin layer contains a crystalline polyester, the crystalline polyester is not particularly limited, and polybutylene terephthalate, polyethylene terephthalate, and poly are preferable. Ethylene naphthalate, polyethylene terephthalate, polybutylene naphthalate, etc., more preferably polybutylene terephthalate. Therefore, the compatibility of the copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol with the crystalline polyester is improved, the corrosion resistance of the film is improved, and corrosion of the steel sheet can be prevented.

Further, the thickness of the second resin layer is not particularly limited, but is preferably 2 μm or more and 40 μm or less, and more preferably 5 μm or more and less than 25 μm. When the thickness of the second resin layer is less than the lower limit, the corrosion resistance may be insufficient and the steel sheet may be corroded. When the thickness of the second resin layer is thicker than the upper limit, the steel sheet may be coated. The film becomes thicker and the cost increases.

Further, it is preferable to further disperse the anti-caking agent in the second resin layer. In the case of the anti-caking agent, it is preferred to use spherical glass, spherical acrylic resin, ultra high molecular weight polyethylene, polytetrafluoroethylene, globular vermiculite, fatty acid ester, talc, calcium carbonate, diatomaceous earth. More preferably, an aliphatic ester is used. By dispersing the anti-caking agent, the coefficient of friction between the films can be reduced at the time of film formation, and the film can be made slippery, and the winding wrinkles of the wound original roll can be prevented.

The content of the anti-caking agent is not particularly limited, but is preferably 1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the second resin layer. When the content of the anti-caking agent is within the above range, the coefficient of friction between the films can be reduced at the time of film formation and the film can be made slippery, and the winding wrinkles of the wound original roll of the film can be prevented.

The method for producing a film for a coated steel sheet according to the present invention is not particularly limited. For example, a resin for a first resin layer and a resin for a second resin layer may be co-extruded by a T-die extruder. in The film can be produced by cooling to a normal temperature on a cooling roll.

The thickness of the entire film for a coated steel sheet is not particularly limited, but is preferably 10 μm or more and 50 μm or less, more preferably 15 μm or more and less than 35 μm. When the thickness of the entire film for a coated steel sheet is less than the lower limit, the corrosion resistance of the film may be insufficient and the steel sheet may be corroded. The thickness of the entire film for the coated steel sheet is thicker than the upper limit. There will be a situation where the cost will become higher.

In the case where the film for a coated steel sheet according to the present invention contains the second resin layer, the ratio of the thickness of the first resin layer to the thickness of the second resin layer is not particularly limited, and is greater than the thickness of the entire film for covering the steel sheet. Preferably, the thickness of the first resin layer is 5 to 30%, and the thickness of the second resin layer is 70 to 95%. More preferably, the thickness of the first resin layer is 10 to 25%, and the thickness of the resin layer 2 is 75~90%. When the ratio of the thickness of the first resin layer to the thickness of the second resin layer is within the above range, whitening of the film during the distillation treatment can be suppressed, and the film for coated steel sheet can be prevented from being peeled off from the steel sheet during the distillation processing.

[Examples]

Hereinafter, the present invention will be described in detail by way of examples and comparative examples, but the invention is not limited to the examples described below.

Each resin was mixed according to the blending formula shown in Table 1, and co-extruded using a T-die extruder (helical diameter: φ40 mm, L/D: 28) to prepare a film having a total thickness of 30 μm.

(Example 1)

According to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol (Eastman Chemical Japan Co., Ltd., product number: Easter GN071), a pair As a first resin layer, butyl phthalate (manufactured by Mitsubishi Engineering Plastics Co., Ltd., product number: NOVADURAN 5020) was placed in an extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer was extruded under a T die (mold temperature: 250 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

(Example 2)

According to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol (Eastman Chemical Japan Co., Ltd., product number: Easter GN071), a pair As a first resin layer, butyl phthalate (manufactured by Mitsubishi Engineering Plastics Co., Ltd., product number: NOVADURAN 5020) was placed in an extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. Further, according to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was mixed. Polybutylene terephthalate (manufactured by Mitsubishi Engineering Plastics Co., Ltd., product number: NOVADURAN 5020) was used as the second resin layer, and then placed in an extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer and the second resin layer were co-extruded in a T-die (die temperature: 250 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

(Example 3)

According to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol (Eastman Chemical Japan Co., Ltd., product number: Easter GN071), a pair Ethylene phthalate (manufactured by Mitsubishi Chemical Corporation, product number: Novapecks GM700Z) was used as the first resin layer, and then placed in an extruder (cylinder temperature: 300 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. Further, according to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was mixed. Polybutylene terephthalate (manufactured by Mitsubishi Engineering Plastics Co., Ltd., product number: NOVADURAN 5020) was used as the second resin layer, and then placed in an extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer and the second resin layer were co-extruded in a T-die (die temperature: 300 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

(Example 4)

According to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol (Eastman Chemical Japan Co., Ltd., product number: Easter GN071), a pair Ethylene phthalate (manufactured by Mitsubishi Chemical Corporation, product number: Novapecks GM700Z) was used as the first resin layer, and then placed in an extruder (cylinder temperature: 300 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. Further, according to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was mixed. Polyethylene terephthalate (manufactured by Mitsubishi Chemical Corporation, product number: Novapecks GM700Z) was used as the second resin layer, and then placed in an extruder (cylinder temperature: 300 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer and the second resin layer were co-extruded in a T-die (die temperature: 300 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

(Comparative Example 1)

A copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol as a first resin layer (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was placed in an extruder (cylinder) Temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. Further, according to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was mixed. Polybutylene terephthalate (manufactured by Mitsubishi Engineering Plastics Co., Ltd., product number: NOVADURAN 5020) was used as the second resin layer, and then placed in an extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer and the second resin layer were co-extruded in a T-die (mold temperature: 250 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

(Comparative Example 2)

A copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol as a first resin layer (Eastman Chemical Japan Co., Ltd., product number: Easter) GN071) Put into the extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. Further, according to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was mixed. Polyethylene terephthalate (manufactured by Mitsubishi Chemical Corporation, product number: Novapecks GM700Z) was used as the second resin layer, and then placed in an extruder (cylinder temperature: 300 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer and the second resin layer were co-extruded in a T-die (die temperature: 300 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

(Comparative Example 3)

The polypropylene (manufactured by Sumitomo Chemical Co., Ltd., product number: Noblen FS2011DG2) as the first resin layer was placed in an extruder (cylinder temperature: 250 ° C). Further, according to the blending formula shown in Table 1, a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid or cyclohexane dimethanol (manufactured by Eastman Chemical Japan Co., Ltd., product number: Easter GN071) was mixed. Polybutylene terephthalate (manufactured by Mitsubishi Engineering Plastics Co., Ltd., product number: NOVADURAN 5020) was used as the second resin layer, and then placed in an extruder (cylinder temperature: 250 ° C). The copolymer described above has 33 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The first resin layer and the second resin layer were co-extruded in a T-die (mold temperature: 250 ° C), and then cooled and solidified by a cooling roll (temperature: 25 ° C) to obtain a film.

<melting point determination>

The resin constituting the first resin layer was mixed according to the blending formula shown in Table 1, and then placed in a twin-screw extruder (cylinder temperature: Examples 1 and 2, Comparative Examples 1 and 3 were 250 ° C, and Examples 3 and 4) Comparative Example 2 (300 ° C) was molded into a strand by a strand mold (mold temperature: Example 1, 2, Comparative Example 1, 3 was 250 ° C, Examples 3 and 4, and Comparative Example 2 was 300 ° C). After the molding, the resin was cooled, solidified in a water tank (temperature: 25 ° C), and pelletized by a granulator. The pellets of the produced resin were dried at 65 ° C for 12 hours. The melting point of the resin constituting the first resin layer was measured by scanning differential scanning calorimetry (DSC), and when the temperature was raised at a temperature elevation rate of 5 ° C /min, the endothermic peak was the observed temperature of the resin. Further, the resin having no endothermic peak is amorphous.

<wetting tension test>

The first resin layer was measured in accordance with the method described in JIS K6768.

<Distillation resistance test>

In the case of T ° C (the resin constituting the first resin layer is crystalline, T is a temperature at which the melting point is +20 ° C, and when the resin constituting the first resin layer is amorphous, T is 240 ° C), 5 MPa. Conditions: The coated steel sheet with a total thickness of 30 μm is heated by a film. The chrome-plated steel sheet was pressed for 1 minute and then to a thickness of 250 μm to prepare a laminated steel sheet.

The laminated steel sheet was cut into a size of MD 150 mm × TD 150 mm to prepare an evaluation sample A, which was heated at the temperature of T ° C for 3 minutes, and then immersed and cooled in water at 20 ° C for 1 minute.

Next, the evaluation sample A was punched into a dumbbell shape of the test piece type 2 described in JIS K7127. Then, a Tensilon universal testing machine (Tensilon universal testing machine: RTG-1310 manufactured by Orientec Co., Ltd., thermostat: TCF-R3T-F manufactured by Orientec Co., Ltd.) equipped with a thermostatic bath was used to make the marking line at 125 ° C. After the elongation (25 mm) was 10%, the line between the marks was cut out and used as the evaluation sample B.

The evaluation sample B was subjected to a distillation treatment for 120 minutes under the conditions of 120 ° C and 1 MPa by an autoclave (manufactured by K.K., Ltd., K-21) to visually confirm whether or not the film for chrome-coated steel sheets was peeled off from the steel sheet. . Four samples were tested, and those who could not be confirmed in all of them were evaluated as "no peeling".

<Whitening resistance test>

In the case of T ° C (in the case where the resin constituting the first resin layer is crystalline, T is a temperature at which the melting point is +20 ° C, and the resin constituting the first resin layer is amorphous, T is 240 ° C) A chrome-plated steel sheet having a thickness of 250 μm and a film for covering a steel sheet having a total thickness of 30 μm were bonded, and then water-cooled at 25° C. to form a laminated steel sheet. The laminated steel sheet was heat-treated at 120 ° C for 30 minutes using an autoclave (manufactured by K.K., Ltd., model: K-21) to confirm the presence or absence of white turbidity of the film for coated steel sheets. The evaluation of whitening was performed according to the following criteria.

○: There is no white turbidity in all.

△: There is white turbidity in a part.

×: There is white turbidity in all.

<Extension forming evaluation>

In the case of T ° C (in the case where the resin constituting the first resin layer is crystalline, T is a temperature at which the melting point is +20 ° C, and the resin constituting the first resin layer is amorphous, T is 240 ° C) A chrome-plated steel sheet having a thickness of 250 μm and a film for covering a steel sheet having a total thickness of 30 μm were bonded, and then water-cooled at 25° C. to form a laminated steel sheet. The laminated steel sheet was stretched at 100 °C. The depth/diameter of the laminated steel sheet was taken as the elongation ratio, and the moldability was evaluated in accordance with the following evaluation criteria.

◎: Even if it is 2.0 or more, the plate body of the laminated steel plate is not broken.

○: The plate body of the laminated steel sheet was broken in the range of 1.0 or more and less than 2.0.

△: The plate of the laminated steel sheet was broken in a range of 0.5 or more and less than 1.0.

<Evaluation of corrosion resistance>

After the distillation resistance test, the surface of the steel sheet coated with the film for the coated steel sheet of the sample B was visually observed, and the corrosion resistance was evaluated according to the following evaluation criteria.

○: Corrosion in the absence of steel sheets.

△: Corrosion of a steel plate in a part.

×: Corrosion of the steel plate is comprehensive.

The film for coated steel sheets of each of the examples and the comparative examples was evaluated by the evaluation method as described above, and the results are shown in Table 1.

[Industrial use possibilities]

According to the present invention, it is possible to provide a film for coating a steel sheet which is excellent in corrosion resistance and which is not easily peeled off by a film even after the drawing treatment. Therefore, the present invention can be suitably used in the "film for coating a steel sheet" and is extremely important industrially.

Claims (8)

A film for a coated steel sheet, comprising: a first resin layer that is in contact with the steel sheet, wherein a surface of the first resin layer that is in contact with the steel sheet has a wetting tension of 34 mN/m or more according to JIS K6768, and is configured. The resin of the first resin layer has a melting point of 140 to 280 ° C; and the first resin layer contains 1 to 50% by weight of a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol. , with 50 to 99% by weight of crystalline polyester. The film for coated steel sheets according to the first aspect of the invention, wherein the copolymer has 1 to 50 mol% of cyclohexanedimethanol as a constituent monomer component with respect to the alcohol unit of the entire copolymer. The film for coated steel sheets according to claim 1, wherein the crystalline polyester is polybutylene terephthalate. The film for a coated steel sheet according to the first or second aspect of the invention, wherein the film for a coated steel sheet is provided with a second resin layer on a side opposite to a surface in contact with the steel sheet of the first resin layer. The film for coated steel sheets according to claim 4, wherein the second resin layer contains a crystalline polyester and a copolymer obtained by copolymerizing ethylene glycol, terephthalic acid, and cyclohexane dimethanol. The film for coated steel sheets according to claim 4, wherein the second resin layer contains 70 to 99% by weight of crystalline polyester and 1 to 30% by weight based on the entire second resin layer. A copolymer obtained by copolymerization of ethylene glycol, terephthalic acid, and cyclohexane dimethanol. The film for coated steel sheets according to claim 5, wherein the crystalline polyester is polybutylene terephthalate. The film for coated steel sheets according to claim 6, wherein the crystalline polyester is polybutylene terephthalate.