CA2114511C - Metal sheet covered with polyester resin film for drawn and stretch formed can - Google Patents
Metal sheet covered with polyester resin film for drawn and stretch formed can Download PDFInfo
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- CA2114511C CA2114511C CA002114511A CA2114511A CA2114511C CA 2114511 C CA2114511 C CA 2114511C CA 002114511 A CA002114511 A CA 002114511A CA 2114511 A CA2114511 A CA 2114511A CA 2114511 C CA2114511 C CA 2114511C
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- polyester resin
- metal sheet
- resin film
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
- B32B15/09—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyesters
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/02—Physical, chemical or physicochemical properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/18—Layered products comprising a layer of metal comprising iron or steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/20—Layered products comprising a layer of metal comprising aluminium or copper
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
- B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/16—Tin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/20—Zinc
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/22—Nickel or cobalt
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/24—Aluminium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/30—Iron, e.g. steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2367/00—Polyesters, e.g. PET, i.e. polyethylene terephthalate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2439/00—Containers; Receptacles
- B32B2439/40—Closed containers
- B32B2439/66—Cans, tins
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2439/00—Containers; Receptacles
- B32B2439/70—Food packaging
Landscapes
- Laminated Bodies (AREA)
Abstract
The invention is concerned with a metal sheet covered with a polyester resin film having a biaxially oriented structure. The polyester resin film comprises an innermost layer of polyester resin which is directly in contact with the metal sheet surface or indirectly in contact therewith by laying a thermosetting resin layer between the polyester resin film and the metal sheet, and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150. Such a metal sheet covered with a polyester resin film is suitable for applications in which excellent formability and excellent corrosion resistance after severe forming are required, especially for drawn and stretch formed cans having high can height.
Description
The. present invention relates to a metal sheet covered with a polyester resin film, which is used as a material for container for foodstuff or beverage and which has excellent formability and excellent corrosion resistance after severe forming, wherein the planar orientation coefficient of the innermost layer of polyester resin film, directly contacted with the metal sheet surface or indirectly contacted therewith by laying a thermosetting resin layer between the polyester resin film and the metal sheet, is different from that of the outermost (the farthest from the metal sheet surface) layer of polyester resin film on the metal sheet.
Such a metal sheet covered with a polyester resin film is suitable for applications where excellent formability and excellent corrosion resistance after severe forming are required, especially for drawn and stretch formed cans having high can height.
Recently, a technique for the production of a drawn and stretch formed can (which is also called a drawn thin redrawn can, or DTR can) has been developed. This DTR
can is characterized by an average decreased ratio in the thickness of the can wall to the original thickness of the employed metal sheet which is about 10 to 30$.
However, DTR cans are not widely used for foodstuff and beverage, because the precoated lacquer film peels off the surface of the metal sheet such as tin free steel, or many cracks arise in coated lacquer film under severe forming such as drawn and stretch forming, even if tin free steel having excellent lacquer adhesion is used as a film covering base metal sheet.
A
Such a metal sheet covered with a polyester resin film is suitable for applications where excellent formability and excellent corrosion resistance after severe forming are required, especially for drawn and stretch formed cans having high can height.
Recently, a technique for the production of a drawn and stretch formed can (which is also called a drawn thin redrawn can, or DTR can) has been developed. This DTR
can is characterized by an average decreased ratio in the thickness of the can wall to the original thickness of the employed metal sheet which is about 10 to 30$.
However, DTR cans are not widely used for foodstuff and beverage, because the precoated lacquer film peels off the surface of the metal sheet such as tin free steel, or many cracks arise in coated lacquer film under severe forming such as drawn and stretch forming, even if tin free steel having excellent lacquer adhesion is used as a film covering base metal sheet.
A
2~~.~5~~
Recently, various methods for lamination of a polyester resin film on a metal sheet with or without adhesive described in U.S. Patent Nos. 4,517,255 and 4,614,691, Laid-Open Japanese Patent Application No. Hei 1-249331 and Japanese Patent Application No. Hei 2-154098 have been developed as alternative methods of lacquer coating.
U.S. Patent No. 4,517,255 relates to a process for lamination of a crystalline polyester resin film onto a metal sheet by heating the metal sheet above the melting temperature of the polyester resin film and thereafter immediately quenching the laminate. In this process, the crystalline polyester resin film is sufficiently adhered to the metal sheet with an amorphous non-oriented polyester resin layer which is formed due to the change of a part of the crystalline polyester resin film as a result of the heating step. However, the polyester resin film laminated metal sheet according to this patent is not used for DTR
cans, since DTR cans require a heat treatment at about 180 to 220°C for curing the printing ink coated on the outside ~' of the DTR cans and the amorphous non-oriented polyester resin layer is rapidly recrystallized and the recrystallized amorphous non-oriented polyester resin layer lacks impact resistance. When the impact stress (such as falling from a shelf) is given to a can body from the outside of the can body, micro-cracks arise in the polyester resin film at the pushed out area that is the reverse inside area of the can body, resulting in corrosion of the exposed metal in these areas.
In addition, the upper limit of the planar orientation coefficient of the laminated polyester resin f ~._ _ film is not defined in U.S. Patent No. 4,517,255, so that in the event the planar orientation coefficient of the laminated polyester resin film is greater than 0.150 (even if only in the outermost layer of the film) many cracks arise in the laminated polyester resin film under forming the laminate into a DTR can having high can height.
Therefore, the laminate according to U.S. Patent No.
4,517,255 cannot be employed as a material for DTR cans.
U.S. Patent 4,614,691, Laid-Open Japanese Patent Application No. Hei 1-249331 and Japanese Patent Application No. Hei 2-154098 relate to the lamination of a biaxially oriented polyester resin film precoated with a small amount of a resin containing in its molecular structure at least one radical such as epoxy radical onto a metal sheet heated to below or above the melting temperature of the polyester resin film. In Laid-Open Japanese Patent Application No. Hei 1-249331 and Japanese Patent Application No. Hei 2-154098, a polyester resin film having specified characteristics is laminated onto the metal sheet. However, in these applications, many cracks arise in the laminated polyester resin film under severe w forming or the laminated polyester resin film lacks impact resistance, because the planar orientation coefficients of the outermost layer of polyester resin film and of the innermost layer of polyester resin film indirectly ' contacted with the metal sheet surface by laying a resin layer between the polyester resin film and the metal sheet are not controlled within a preferable range.
It is therefore an object of the present invention to provide a metal sheet covered with a polyester resin film having excellent formability and excellent f.,..
a . a mn n corrosion resistance after severe forming and which can be used in the manufacture of DTR cans having high can height.
The object of the present invention is accomplished by controlling the planar orientation coefficients in the innermost layer of polyester resin film which is directly or indirectly in contact with the metal sheet surface and the outermost layer of polyester resin film.
According to one aspect of the invention, there is provided a metal sheet covered with a polyester resin film having a biaxially oriented structure, wherein the polyester resin film comprises an innermost layer of polyester resin which is directly in contact with a surface of the metal sheet and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150.
The present invention also provides, in another aspect thereof, a metal sheet covered with a polyester resin film having a biaxially oriented structure, wherein the polyester resin film comprises an innermost layer of polyester resin which is indirectly in contact with a surface of the metal sheet by laying a layer of thermosetting resin between the polyester resin film and the metal sheet, and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150.
According to a still further aspect of the invention, there is provided a metal sheet covered with a polyester resin film having a biaxially oriented i an ~5n structure, wherein the polyester resin. film comprises an innermost layer, which is indirectly in contact with a surface of the metal sheet precoated with a thermosetting resin by laying a layer of the thermosetting resin between the polyester resin film and the metal sheet, and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150.
The metal sheet covered with a polyester resin film according to the present invention has excellent corrosion resistance after severe forming. Therefore, it can be used not only for DTR cans having high can height, but also for deeply drawn cans, DRD cans and can ends where a tab for easy opening is attached. In these applications, the cans are exposed to hot steam for sterilization after being packed with foodstuffs or beverages such as fruit juice, coffee drink, meat and fish. For example, fruit juice is packed in a can immediately after sterilization at a temperature of 90 to 100°C. Coffee drink, meat or fish is sterilized in hot steam at above 100°C in a retort after being packed in a can. Furthermore, the metal sheet according to the present invention can be used for screw cap and crown cap.
In these applications, color printing ink or lacquer coating is often applied on the outside of the cans before or after forming. In these cases, the laminated polyester resin film in the present invention maintains excellent adhesion and excellent impact resistance, even after reheating for curing color printing ink or lacquer and subsequent treatment in hot water or hot steam.
Recently, various methods for lamination of a polyester resin film on a metal sheet with or without adhesive described in U.S. Patent Nos. 4,517,255 and 4,614,691, Laid-Open Japanese Patent Application No. Hei 1-249331 and Japanese Patent Application No. Hei 2-154098 have been developed as alternative methods of lacquer coating.
U.S. Patent No. 4,517,255 relates to a process for lamination of a crystalline polyester resin film onto a metal sheet by heating the metal sheet above the melting temperature of the polyester resin film and thereafter immediately quenching the laminate. In this process, the crystalline polyester resin film is sufficiently adhered to the metal sheet with an amorphous non-oriented polyester resin layer which is formed due to the change of a part of the crystalline polyester resin film as a result of the heating step. However, the polyester resin film laminated metal sheet according to this patent is not used for DTR
cans, since DTR cans require a heat treatment at about 180 to 220°C for curing the printing ink coated on the outside ~' of the DTR cans and the amorphous non-oriented polyester resin layer is rapidly recrystallized and the recrystallized amorphous non-oriented polyester resin layer lacks impact resistance. When the impact stress (such as falling from a shelf) is given to a can body from the outside of the can body, micro-cracks arise in the polyester resin film at the pushed out area that is the reverse inside area of the can body, resulting in corrosion of the exposed metal in these areas.
In addition, the upper limit of the planar orientation coefficient of the laminated polyester resin f ~._ _ film is not defined in U.S. Patent No. 4,517,255, so that in the event the planar orientation coefficient of the laminated polyester resin film is greater than 0.150 (even if only in the outermost layer of the film) many cracks arise in the laminated polyester resin film under forming the laminate into a DTR can having high can height.
Therefore, the laminate according to U.S. Patent No.
4,517,255 cannot be employed as a material for DTR cans.
U.S. Patent 4,614,691, Laid-Open Japanese Patent Application No. Hei 1-249331 and Japanese Patent Application No. Hei 2-154098 relate to the lamination of a biaxially oriented polyester resin film precoated with a small amount of a resin containing in its molecular structure at least one radical such as epoxy radical onto a metal sheet heated to below or above the melting temperature of the polyester resin film. In Laid-Open Japanese Patent Application No. Hei 1-249331 and Japanese Patent Application No. Hei 2-154098, a polyester resin film having specified characteristics is laminated onto the metal sheet. However, in these applications, many cracks arise in the laminated polyester resin film under severe w forming or the laminated polyester resin film lacks impact resistance, because the planar orientation coefficients of the outermost layer of polyester resin film and of the innermost layer of polyester resin film indirectly ' contacted with the metal sheet surface by laying a resin layer between the polyester resin film and the metal sheet are not controlled within a preferable range.
It is therefore an object of the present invention to provide a metal sheet covered with a polyester resin film having excellent formability and excellent f.,..
a . a mn n corrosion resistance after severe forming and which can be used in the manufacture of DTR cans having high can height.
The object of the present invention is accomplished by controlling the planar orientation coefficients in the innermost layer of polyester resin film which is directly or indirectly in contact with the metal sheet surface and the outermost layer of polyester resin film.
According to one aspect of the invention, there is provided a metal sheet covered with a polyester resin film having a biaxially oriented structure, wherein the polyester resin film comprises an innermost layer of polyester resin which is directly in contact with a surface of the metal sheet and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150.
The present invention also provides, in another aspect thereof, a metal sheet covered with a polyester resin film having a biaxially oriented structure, wherein the polyester resin film comprises an innermost layer of polyester resin which is indirectly in contact with a surface of the metal sheet by laying a layer of thermosetting resin between the polyester resin film and the metal sheet, and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150.
According to a still further aspect of the invention, there is provided a metal sheet covered with a polyester resin film having a biaxially oriented i an ~5n structure, wherein the polyester resin. film comprises an innermost layer, which is indirectly in contact with a surface of the metal sheet precoated with a thermosetting resin by laying a layer of the thermosetting resin between the polyester resin film and the metal sheet, and which has a planar orientation coefficient of 0.000 to 0.100, and an outermost layer of polyester resin having a planar orientation coefficient of 0.010 to 0.150.
The metal sheet covered with a polyester resin film according to the present invention has excellent corrosion resistance after severe forming. Therefore, it can be used not only for DTR cans having high can height, but also for deeply drawn cans, DRD cans and can ends where a tab for easy opening is attached. In these applications, the cans are exposed to hot steam for sterilization after being packed with foodstuffs or beverages such as fruit juice, coffee drink, meat and fish. For example, fruit juice is packed in a can immediately after sterilization at a temperature of 90 to 100°C. Coffee drink, meat or fish is sterilized in hot steam at above 100°C in a retort after being packed in a can. Furthermore, the metal sheet according to the present invention can be used for screw cap and crown cap.
In these applications, color printing ink or lacquer coating is often applied on the outside of the cans before or after forming. In these cases, the laminated polyester resin film in the present invention maintains excellent adhesion and excellent impact resistance, even after reheating for curing color printing ink or lacquer and subsequent treatment in hot water or hot steam.
f- LI~I~~I
In the present invention, it is preferable to use a polyester resin film having a melting temperature of 210 to 250°C and selected from the homo-polyester resins, co-polyester resins and polyester resins blended with at least one homo-polyester resin and/or co-polyester resin.
Preferably, the homo-polyester resin is polyethylene terephthalate or polybutylene terephthalate, and the co-polyester resin is a copolymer of ethylene terephthalate and ethylene isophthalate or a copolymer of butylene terephthalate and butylene isophthalate.
In the present invention, it is impossible to use non-oriented polyester resin film, because such a film has high friction coefficient to tools used for the production of DTR cans and has poor permeability resistance to the corrosive content. In particular, the formability of the metal sheet covered with such a film into DTR cans is remarkably poor and DTR cans which are packed with corrosive contents are corroded in a relatively short period of time. Moreover, as mentioned above, the impact resistance is lacking in this film so that the film cannot be used for DTR cans.
Therefore, the use of a polyester resin film having a biaxially oriented structure and the control of the planar orientation coefficient of the innermost layer (hereinafter referred to as Layer B) of polyester resin film directly or indirectly in contact with the metal sheet surface and the outermost layer (hereinafter referred to as Layer A) of polyester resin film are essential in the present invention.
In some cases, additives such as antioxidants, stabilizers, pigments, antistatic agents and corrosion _s_ ~3.~.~~~.~.
inhibitors can be added during the manufacturing process of the polyester resin film used in the present invention.
The planar orientation coefficient which is defined as the degree of the orientation of Layer A or Layer B of the laminated polyester resin film can be determined by the following method. Firstly, the laminated polyester resin film is removed from the metal sheet by dipping the laminate into a hydrochloric acid solution ~~
which only dissolves the metal sheet. After rinsing in water and drying the film, the refractive indexes in the lengthwise, widthwise and thickness directions of either side layer (Layer A and Layer B) of the polyester resin film are measured with a refractmeter. Thereafter, the planar orientation coefficient is determined according to the following equation:
A=(B+C)/2-D
where A represents the planar orientation coefficient of the polyester resin film:
B represents the refractive index in the lengthwise direction of the polyester resin film;
C represents the refractive index in the widthwise direction of the polyester resin film: and D represents the refractive index in the thickness direction of the polyester resin film.
The refractive indexes measured by the method described above show an average value within 5 Eun from the outermost layer (of either side of the resin film) in the polyester resin film used for the measurement of the refractive indexes. Therefore, it is possible to divide f r a l r~r.~~ r t the planar orientation coefficient in Layer A from that in Layer B.
Generally, in the production of polyester resin film laminated metal sheets, the polyester resin film is laminated onto a metal sheet heated to about the melting temperature of the polyester resin film. Therefore, the planar orientation coefficient of the innermost polyester resin layer contacted with the heated metal sheet drops after lamination due to the disappearance of the biaxially oriented structure according to the melting of the resin.
Furthermore, when the metal sheet is heated to higher temperature, or the laminate is quenched in a shorter period of time immediately after lamination, the additional heat applied to the metal sheet is conducted to the polyester resin film and a greater proportion of the biaxially oriented structure of the resin film disappears, and then the planar orientation coefficient of the laminated film decreases in accordance with the distance from the surface contact with the metal sheet. Therefore, the planar orientation coefficient of the innermost polyester resin layer contacted with the surface of the ' heated metal sheet is the lowest value and it increases in the polyester resin film with the distance from the contacted surface with the heated metal sheet.
Additionally, the use of a laminating roll heated to a higher temperature (below the melting temperature of the polyester resin) similarly affects the disappearance of the biaxially oriented structure of the polyester resin film.
Indeed, the amount of heat applied to the metal sheet is conducted to the laminating roll through the intermediate of the polyester resin film: however, the conduction of the ~
'~(I~SII
heat is inhibited and a considerable amount of heat is accumulated in the polyester resin film by heating of the laminating roll, and the more the polyester resin film is heated, the more biaxially oriented structure of the polyester resin film disappears. Accordingly, it is considered that the slope of the planar orientation coefficient is formed in the laminated polyester resin film and the gradient of the slope can be controlled by means of the temperature of the metal sheet and of the laminating roll, and the period of time between lamination and quenching.
In the present invention, when the planar orientation coefficient in Layer B of the laminated polyester resin film is below 0.000, quite a few of the amorphous non-oriented polyester resin has formed in the whole laminated polyester resin film. Thus, when the laminate is formed into DTR cans and is heated to a temperature at about 180 to 220°C required.for curing and the printing ink is applied on the outside of it, the amorphous non-oriented polyester resin in the film is rapidly recrystallized and the polyester resin film may crack on impact. In addition, since the amorphous non-oriented polyester resin layer does not have enough permeability resistance to corrosive content, the laminate covered with such a polyester' resin film cannot be used as raw material for a DTR can.
The amount of amorphous non-oriented resin in the laminated polyester resin film is decreased with the increase of the planar orientation coefficient in Layer B
and the adhesive strength of the laminated polyester resin film to the surface of the metal sheet is also decreased.
_ g _ A
a r When the planar orientation coefficient in Layer B is above 0.100, the adhesion of the laminated. polyester resin film to the surface of the metal sheet is not good enough to form the laminate into a DTR can and the laminated .polyester resin film peels off the surface of the metal sheet under severe forming. The reason is that the amount of the amorphous non-oriented polyester resin, enough for the excellent adhesive strength but not more than enough for the poor impact resistance, has not formed in the polyester resin layer directly or indirectly contacted with the metal sheet. Therefore, it is preferable in the present invention that the planar orientation coefficient in Layer B be maintained in the range of 0.000 to 0.100, more preferably 0.005 to 0.050.
It is undesirable in the present invention that the planar orientation coefficient in Layer A of the laminated polyester resin film be below 0.010, since a considerable proportion of the biaxially orientated structure in the whole film has been lost in the polyester resin film having such a low planar orientation coefficient measured in Layer A, so that the polyester resin film laminated metal sheet cannot uniformly be formed into a DTR
can having high can height due to increase of the friction coefficient in Layer A to tools used for the production of the DTR can and the surface of the metal sheet of the polyester resin film laminated metal sheet is chapped by severe forming. Furthermore, a DTR can made of the polyester resin film laminated metal sheet having such a low planar orientation coefficient of Layer A is remarkably corroded by corrosive content in a long storage period of 1 time after being packed with corrosive content, since the r ~.- . ~1~4~1~.
, a permeability resistance of the whole laminated polyester resin film becomes poor with decrease in the planar orientation coefficient measured in Layer A. In addition, with the decrease of the planar orientation coefficient measured in Layer A, the amount of amorphous non-oriented polyester resin increases in the whole polyester resin film, then susceptibility to the impact stress of the film becomes good.
On the other hand, in the case where the planar orientation coefficient in Layer A of the laminated polyester resin film is above 0.150, many cracks arise in the laminated polyester resin film when forming the laminate into a DTR can having a high can height, independently of the planar orientation coefficient of Layer B, because the biaxially oriented polyester resin film having such a high planar orientation coefficient cannot extend well. Therefore, it is essential in the present invention that the planar orientation coefficient in Layer A be maintained within a range of 0.010 to 0.150, preferably 0.030 to 0.120.
Furthermore, it is preferable in the present invention that the planar orientation coefficient in Layer A be larger than that in Layer B, in order to produce a ..
stable metal sheet covered with polyester resin film.
As described above, the metal sheet covered with polyester resin film having the aforesaid controlled planar orientation coefficient is excellent in formability, scratch resistance, corrosion resistance and impact resistance after severe forming. However, the metal substrate of the laminate may be corroded or the laminated polyester resin film may be peeled off the surface of the ~l~.~a~~-metal substrate when the laminate is in contact with a more corrosive content. In such a case, the provision of a thermosetting resin (adhesive resin) layer between the polyester resin film and the metal sheet prevents the corrosion of the metal substrate since the permeability resistance of the thermosetting resin layer to corrosive content is remarkably superior to that of the thermoplastic polyester resin film. Known resins can be used as an adhesive in the present invention; however, it is preferable to apply a thermosetting resin having a molecular structure containing at least one radical selected from the group consisting of an epoxy radical, a hydroxyl radical, an amide radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical, on one side of the polyester resin film or on at least one side of the metal sheet.
The main features for the production of the polyester resin laminated metal sheet according to the present invention are as follows:
1. Control of the planar orientation coefficient in Layer B to 0.000 to 0.100 by laminating a biaxially oriented polyester resin film having a planar orientation coefficient of 0.010 to 0.150 onto a metal sheet heated to about a melting temperature of the polyester resin film and by melting part of the polyester resin film in contact with a metal sheet surface.
2. Use of the above mentioned biaxially oriented polyester resin film of which the side to be contacted with the metal sheet is precoated with a thermosetting resin in the same laminating manner described above.
, 3. Lamination of the above mentioned biaxially oriented polyester resin film onto the metal sheet of which the side to be contacted with the polyester resin film is precoated with a thermosetting resin in the same laminating manner described above.
4. Use of a double-layered polyester resin film in the same laminating manner described above and, more particularly, a film comprising an upper film layer (farthest from the metal sheet surface) having a melting temperature of 210 to 250°C and a lower film layer (directly or indirectly in contact with the metal sheet surface) having a melting temperature of 190 to 230°C.
In the present invention, the surface of the metal sheet employed should preferably be covered with a hydrated chromium oside layer in order to obtain excellent adhesion of the laminated polyester resin film to the metal sheet. Therefore, the metal sheet employed should be selected from the group consisting of a tin free steel having a double layer composed of an upper layer of hydrated chromium oxide and a lower layer of metallic chromium, a steel sheet plated with at least one metal selected from the group consisting of tin, nickel and zinc and covered with a mono layer of hydrated chromium oxide or the above-described double layer and a sheet of aluminum or an aluminum-alloy (containing 0.3 to 1.4 weight manganese, 0.7 to 4.8 weight ~ magnesium, 0.24 to 0.29 weight ~ zinc, and 0.16 to 0.24 weight ~ copper) covered ~
with a mono layer of hydrated chromium oside. The optimum range of the hydrated chromium oxide is 3 to 50 mg/m2 as chromium, more preferably 7 to 25 mg/m2. If~the amount of the hydrated chromium oxide is below 3 mg/m2 or above 50 a [IHsll mg/m2 as chromium, the adhesion of the laminated polyester resin film becomes noticeably poor in severely formed areas. In respect of the corrosion resistance after the forming and the adhesion of the laminated polyester resin film, it is preferable that the amount of the metallic chromium ranges from 10 to 200 mg/m2, and more preferably, from 50 to 150 mg/m2, in the double layer of tin free steel or a steel sheet plated with tin, nickel or zinc, in order to facilitate high speed production.
In the present invention, the method for heating the metal sheet to a temperature at which the polyester resin film is laminated is not critical. However, from the standpoint of a continuous and steady production of the polyester resin film laminated~metal sheet according to the present invention at high speed, conduction heating with a roll heated by induction heating, as well as induction heating and resistance heating are suitable because the metal sheet can rapidly be heated and the temperature of the heated metal sheet can easily be controlled.
Furthermore, it is also preferable that the heating with rolls heated with hot steam be used as an auxiliary method for preheating the metal sheet to be laminated.
The following non-limiting examples illustrate the invention.
Example 1 A biaxially oriented copolyester resin film i having the characteristics set forth hereinbelow under (A) was laminated at 235°C on. both sides of a tin free steel having a thickness of 0.17 mm, a temper of DR-10 and covered with a hydrated chromium oxide layer, in an amount lit f S
of 14 mg/m2 as chromium with a metallic chromium content of 110 mg/m2.
After the planar orientation coefficients in Layer A and Layer B of the copolyester resin film in the obtained copolyester resin film laminated metal sheet were determined according to the method described above, the copolyester resin film laminated tin free steel was formed into a DTR can having high can height under the conditions set forth hereinbelow under (B) and then dome, neck-in and flange forming was applied in turn to the DTR can.
(A) Characteristics of the polyester resin film employed Thickness : 20 ~tm Composition of the polyester resin film Ethylene glycol : 100 mole ~
' Terephthalic acid : 88 mole $
Isophthalic acid : 12 mole ~
Planar orientation coefficient : 0.125 Melting temperature : 230°C
(B) Conditions for forming a DTR can (1) Drawing process Diameter of blank : 187 mm Drawing ratio : 1.50 (2) Redrawing process First redrawing ratio : 1.29 ~
Second redrawing ratio : 1.24 Third redrawing ratio : 1.20 Radius in the corner of dies used for redrawing : 0.4 mm Load for prevention of wrinkles in the drawing process : 6000 kg i (3) Average decreased ratio in the thickness of DTR can body -20 ~ to the thickness of the employed metal sheet.
Example 2 A coextruded biaxially oriented copolyester resin film having the characteristics set forth hereinbelow under (A) was laminated at 232°C on both sides of the same tin free steel used in Example 1. After the planar orientation coefficients of Layer A and Layer B of the laminated copolyester resin film were determined, the copolyester resin film laminated tin free steel was formed into a DTR
can under the same conditions as in Example 1.
(A) Characteristics of the polyester resin film employed 1) Upper layer Thickness : 15 Eun Composition of the resin film Ethylene glycol : 100 mole ~
Terephthalic acid : 88 mole $
Isophthalic acid : 12 mole ~
Planar orientation coefficient : 0.122 Melting temperature : 230°C
2) Lower layer i Thickness : 5 ~.un Composition of the resin film -copolyester resin 55 weight ~
composed of Ethylene glycol : 100 mole ~
Terephthalic acid : 94 mole ~
Isophthalic acid : 6 mole ~
a l I ~ISII
-polybutylene terephthalate : 45 weight ~
Planar orientation coefficient : 0.080 Melting temperature : 226°G
Example 3 A clear copolyester resin film having the same composition and planar orientation coefficient as in Example 1 and a white-colored copolyester resin film made of the same resin composition and according to the same method as described in Example 1, except that it was pigmented with 16 weight ~ of titanium dioxide, were simultaneously laminated at 250°C on either side of the same tin free steel as in Example 1. After the planar orientation coefficients in Layer A and Layer B of the laminated clear copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1. (The side laminated with white-colored copolyester resin film defined the outside of the DTR can.) Example 4 The copolyester resin film having the same composition as in Example 1 which was precoated with 0.5 g/m2 of epoxy-phenolic resin was laminated at 245°C on both sides of the same tin free steel as in Example 1. After i the planar orientation coefficients in Layer A and Layer B
of the laminated copolyester resin film were determined, the laminate was formed into a DTR can under the same condition as in Example 1.
Example 5 .
Both sides of an aluminum-alloy sheet (JIS 3004) was coated with 0.3 g/m2 of the same epoxy-phenolic resin as in Example 4 and dried at 118°C. Thereafter, the same r...
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coextruded biaxially oriented copolyester resin film as in Example 2 and the same white-colored copolyester resin film as in Example 3 were laminated at 230°C on either precoated side of the aluminum-alloy sheet. After the blanar orientation coefficients in Layer A and Layer B of the laminated clear copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1, except that the load for prevention of wrinkles in the drawing process was 2,000 kg.
(The side laminated with white-colored copolyester resin film defined the outside of the DTR can.
Comparative Example 1 A polyethylene terephthalate film having a thickness of 25 dun, planar orientation coefficient of 0.165 and melting temperature of 260°C was laminated at 280°C on both sides of the same tin free steel as in Example 1.
After the planar orientation coefficients in Layer A and Layer B of the laminated polyethylene terephthalate film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1.
Comparative Example 2 The same copolyester resin film used in Example 1 i was laminated at 210°C on both sides of the same tin free steel as in Example 1. After the planar orientation coefficients in Layer A and Layer B of the laminated copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1.
Comparative Example 3 The same copolyester resin film used in Example 1 was laminated at 305°C on both sides of the same tin free ~1~ 411 steel as in 'Example 1. After the planar orientation coefficients in Layer A and Layer B of the laminated copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1.
The characteristics of the DTR cans in Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated according to the following methods. The degree of cracks arising in the laminated polyester resin film and the degree of peeling-off of the polyester resin film in the formed areas, especially in the upper wall part and neck-in and flange formed area of the DTR can, were evaluated with the naked eye. The results are shown in Table 1.
(1) Degree of exposed metal surface of the inside of the DTR can The degree of exposed metal surface was evaluated according to a current value shown between an anode of the metal surface exposed through the cracks in the polyester resin film of the DTR can which was filled with a 3~ sodium chloride solution and a cathode of a stainless steel rod inserted in the DTR
can at the constant voltage of 6.3 V.
(2) Resistance to hot steam The resistance to hot steam was evaluated according to the degree of peeling-off of the laminated polyester resin film in the flange formed part of the DTR can after treatment of the obtained DTR can in hot steam, having a temperature of 125°C
in a retort for 30 minutes.
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(3) Heat resistance The heat resistance was evaluated according to the degree of cracks in the laminated polyester resin film, the discoloration and peeling-off of the laminated polyester resin film in the formed - area of the third redrawn can after the heat treatment at 200°C, corresponding to the temperature for curing of the printing ink to be coated on the outside of the DTR can.
(4) Corrosion resistance The corrosion resistance was evaluated according ' to the degree of corrosion on the inside of the DTR can which was filled with a 3~ acetic acid solution and then stored for 3 months at 50°C.
The degree of corrosion was divided into 5 ranks evaluated with the naked eye, namely, 5 was excellent, 4 was good, 3 was fair, 2 was poor and 1 was bad.
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In the present invention, it is preferable to use a polyester resin film having a melting temperature of 210 to 250°C and selected from the homo-polyester resins, co-polyester resins and polyester resins blended with at least one homo-polyester resin and/or co-polyester resin.
Preferably, the homo-polyester resin is polyethylene terephthalate or polybutylene terephthalate, and the co-polyester resin is a copolymer of ethylene terephthalate and ethylene isophthalate or a copolymer of butylene terephthalate and butylene isophthalate.
In the present invention, it is impossible to use non-oriented polyester resin film, because such a film has high friction coefficient to tools used for the production of DTR cans and has poor permeability resistance to the corrosive content. In particular, the formability of the metal sheet covered with such a film into DTR cans is remarkably poor and DTR cans which are packed with corrosive contents are corroded in a relatively short period of time. Moreover, as mentioned above, the impact resistance is lacking in this film so that the film cannot be used for DTR cans.
Therefore, the use of a polyester resin film having a biaxially oriented structure and the control of the planar orientation coefficient of the innermost layer (hereinafter referred to as Layer B) of polyester resin film directly or indirectly in contact with the metal sheet surface and the outermost layer (hereinafter referred to as Layer A) of polyester resin film are essential in the present invention.
In some cases, additives such as antioxidants, stabilizers, pigments, antistatic agents and corrosion _s_ ~3.~.~~~.~.
inhibitors can be added during the manufacturing process of the polyester resin film used in the present invention.
The planar orientation coefficient which is defined as the degree of the orientation of Layer A or Layer B of the laminated polyester resin film can be determined by the following method. Firstly, the laminated polyester resin film is removed from the metal sheet by dipping the laminate into a hydrochloric acid solution ~~
which only dissolves the metal sheet. After rinsing in water and drying the film, the refractive indexes in the lengthwise, widthwise and thickness directions of either side layer (Layer A and Layer B) of the polyester resin film are measured with a refractmeter. Thereafter, the planar orientation coefficient is determined according to the following equation:
A=(B+C)/2-D
where A represents the planar orientation coefficient of the polyester resin film:
B represents the refractive index in the lengthwise direction of the polyester resin film;
C represents the refractive index in the widthwise direction of the polyester resin film: and D represents the refractive index in the thickness direction of the polyester resin film.
The refractive indexes measured by the method described above show an average value within 5 Eun from the outermost layer (of either side of the resin film) in the polyester resin film used for the measurement of the refractive indexes. Therefore, it is possible to divide f r a l r~r.~~ r t the planar orientation coefficient in Layer A from that in Layer B.
Generally, in the production of polyester resin film laminated metal sheets, the polyester resin film is laminated onto a metal sheet heated to about the melting temperature of the polyester resin film. Therefore, the planar orientation coefficient of the innermost polyester resin layer contacted with the heated metal sheet drops after lamination due to the disappearance of the biaxially oriented structure according to the melting of the resin.
Furthermore, when the metal sheet is heated to higher temperature, or the laminate is quenched in a shorter period of time immediately after lamination, the additional heat applied to the metal sheet is conducted to the polyester resin film and a greater proportion of the biaxially oriented structure of the resin film disappears, and then the planar orientation coefficient of the laminated film decreases in accordance with the distance from the surface contact with the metal sheet. Therefore, the planar orientation coefficient of the innermost polyester resin layer contacted with the surface of the ' heated metal sheet is the lowest value and it increases in the polyester resin film with the distance from the contacted surface with the heated metal sheet.
Additionally, the use of a laminating roll heated to a higher temperature (below the melting temperature of the polyester resin) similarly affects the disappearance of the biaxially oriented structure of the polyester resin film.
Indeed, the amount of heat applied to the metal sheet is conducted to the laminating roll through the intermediate of the polyester resin film: however, the conduction of the ~
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heat is inhibited and a considerable amount of heat is accumulated in the polyester resin film by heating of the laminating roll, and the more the polyester resin film is heated, the more biaxially oriented structure of the polyester resin film disappears. Accordingly, it is considered that the slope of the planar orientation coefficient is formed in the laminated polyester resin film and the gradient of the slope can be controlled by means of the temperature of the metal sheet and of the laminating roll, and the period of time between lamination and quenching.
In the present invention, when the planar orientation coefficient in Layer B of the laminated polyester resin film is below 0.000, quite a few of the amorphous non-oriented polyester resin has formed in the whole laminated polyester resin film. Thus, when the laminate is formed into DTR cans and is heated to a temperature at about 180 to 220°C required.for curing and the printing ink is applied on the outside of it, the amorphous non-oriented polyester resin in the film is rapidly recrystallized and the polyester resin film may crack on impact. In addition, since the amorphous non-oriented polyester resin layer does not have enough permeability resistance to corrosive content, the laminate covered with such a polyester' resin film cannot be used as raw material for a DTR can.
The amount of amorphous non-oriented resin in the laminated polyester resin film is decreased with the increase of the planar orientation coefficient in Layer B
and the adhesive strength of the laminated polyester resin film to the surface of the metal sheet is also decreased.
_ g _ A
a r When the planar orientation coefficient in Layer B is above 0.100, the adhesion of the laminated. polyester resin film to the surface of the metal sheet is not good enough to form the laminate into a DTR can and the laminated .polyester resin film peels off the surface of the metal sheet under severe forming. The reason is that the amount of the amorphous non-oriented polyester resin, enough for the excellent adhesive strength but not more than enough for the poor impact resistance, has not formed in the polyester resin layer directly or indirectly contacted with the metal sheet. Therefore, it is preferable in the present invention that the planar orientation coefficient in Layer B be maintained in the range of 0.000 to 0.100, more preferably 0.005 to 0.050.
It is undesirable in the present invention that the planar orientation coefficient in Layer A of the laminated polyester resin film be below 0.010, since a considerable proportion of the biaxially orientated structure in the whole film has been lost in the polyester resin film having such a low planar orientation coefficient measured in Layer A, so that the polyester resin film laminated metal sheet cannot uniformly be formed into a DTR
can having high can height due to increase of the friction coefficient in Layer A to tools used for the production of the DTR can and the surface of the metal sheet of the polyester resin film laminated metal sheet is chapped by severe forming. Furthermore, a DTR can made of the polyester resin film laminated metal sheet having such a low planar orientation coefficient of Layer A is remarkably corroded by corrosive content in a long storage period of 1 time after being packed with corrosive content, since the r ~.- . ~1~4~1~.
, a permeability resistance of the whole laminated polyester resin film becomes poor with decrease in the planar orientation coefficient measured in Layer A. In addition, with the decrease of the planar orientation coefficient measured in Layer A, the amount of amorphous non-oriented polyester resin increases in the whole polyester resin film, then susceptibility to the impact stress of the film becomes good.
On the other hand, in the case where the planar orientation coefficient in Layer A of the laminated polyester resin film is above 0.150, many cracks arise in the laminated polyester resin film when forming the laminate into a DTR can having a high can height, independently of the planar orientation coefficient of Layer B, because the biaxially oriented polyester resin film having such a high planar orientation coefficient cannot extend well. Therefore, it is essential in the present invention that the planar orientation coefficient in Layer A be maintained within a range of 0.010 to 0.150, preferably 0.030 to 0.120.
Furthermore, it is preferable in the present invention that the planar orientation coefficient in Layer A be larger than that in Layer B, in order to produce a ..
stable metal sheet covered with polyester resin film.
As described above, the metal sheet covered with polyester resin film having the aforesaid controlled planar orientation coefficient is excellent in formability, scratch resistance, corrosion resistance and impact resistance after severe forming. However, the metal substrate of the laminate may be corroded or the laminated polyester resin film may be peeled off the surface of the ~l~.~a~~-metal substrate when the laminate is in contact with a more corrosive content. In such a case, the provision of a thermosetting resin (adhesive resin) layer between the polyester resin film and the metal sheet prevents the corrosion of the metal substrate since the permeability resistance of the thermosetting resin layer to corrosive content is remarkably superior to that of the thermoplastic polyester resin film. Known resins can be used as an adhesive in the present invention; however, it is preferable to apply a thermosetting resin having a molecular structure containing at least one radical selected from the group consisting of an epoxy radical, a hydroxyl radical, an amide radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical, on one side of the polyester resin film or on at least one side of the metal sheet.
The main features for the production of the polyester resin laminated metal sheet according to the present invention are as follows:
1. Control of the planar orientation coefficient in Layer B to 0.000 to 0.100 by laminating a biaxially oriented polyester resin film having a planar orientation coefficient of 0.010 to 0.150 onto a metal sheet heated to about a melting temperature of the polyester resin film and by melting part of the polyester resin film in contact with a metal sheet surface.
2. Use of the above mentioned biaxially oriented polyester resin film of which the side to be contacted with the metal sheet is precoated with a thermosetting resin in the same laminating manner described above.
, 3. Lamination of the above mentioned biaxially oriented polyester resin film onto the metal sheet of which the side to be contacted with the polyester resin film is precoated with a thermosetting resin in the same laminating manner described above.
4. Use of a double-layered polyester resin film in the same laminating manner described above and, more particularly, a film comprising an upper film layer (farthest from the metal sheet surface) having a melting temperature of 210 to 250°C and a lower film layer (directly or indirectly in contact with the metal sheet surface) having a melting temperature of 190 to 230°C.
In the present invention, the surface of the metal sheet employed should preferably be covered with a hydrated chromium oside layer in order to obtain excellent adhesion of the laminated polyester resin film to the metal sheet. Therefore, the metal sheet employed should be selected from the group consisting of a tin free steel having a double layer composed of an upper layer of hydrated chromium oxide and a lower layer of metallic chromium, a steel sheet plated with at least one metal selected from the group consisting of tin, nickel and zinc and covered with a mono layer of hydrated chromium oxide or the above-described double layer and a sheet of aluminum or an aluminum-alloy (containing 0.3 to 1.4 weight manganese, 0.7 to 4.8 weight ~ magnesium, 0.24 to 0.29 weight ~ zinc, and 0.16 to 0.24 weight ~ copper) covered ~
with a mono layer of hydrated chromium oside. The optimum range of the hydrated chromium oxide is 3 to 50 mg/m2 as chromium, more preferably 7 to 25 mg/m2. If~the amount of the hydrated chromium oxide is below 3 mg/m2 or above 50 a [IHsll mg/m2 as chromium, the adhesion of the laminated polyester resin film becomes noticeably poor in severely formed areas. In respect of the corrosion resistance after the forming and the adhesion of the laminated polyester resin film, it is preferable that the amount of the metallic chromium ranges from 10 to 200 mg/m2, and more preferably, from 50 to 150 mg/m2, in the double layer of tin free steel or a steel sheet plated with tin, nickel or zinc, in order to facilitate high speed production.
In the present invention, the method for heating the metal sheet to a temperature at which the polyester resin film is laminated is not critical. However, from the standpoint of a continuous and steady production of the polyester resin film laminated~metal sheet according to the present invention at high speed, conduction heating with a roll heated by induction heating, as well as induction heating and resistance heating are suitable because the metal sheet can rapidly be heated and the temperature of the heated metal sheet can easily be controlled.
Furthermore, it is also preferable that the heating with rolls heated with hot steam be used as an auxiliary method for preheating the metal sheet to be laminated.
The following non-limiting examples illustrate the invention.
Example 1 A biaxially oriented copolyester resin film i having the characteristics set forth hereinbelow under (A) was laminated at 235°C on. both sides of a tin free steel having a thickness of 0.17 mm, a temper of DR-10 and covered with a hydrated chromium oxide layer, in an amount lit f S
of 14 mg/m2 as chromium with a metallic chromium content of 110 mg/m2.
After the planar orientation coefficients in Layer A and Layer B of the copolyester resin film in the obtained copolyester resin film laminated metal sheet were determined according to the method described above, the copolyester resin film laminated tin free steel was formed into a DTR can having high can height under the conditions set forth hereinbelow under (B) and then dome, neck-in and flange forming was applied in turn to the DTR can.
(A) Characteristics of the polyester resin film employed Thickness : 20 ~tm Composition of the polyester resin film Ethylene glycol : 100 mole ~
' Terephthalic acid : 88 mole $
Isophthalic acid : 12 mole ~
Planar orientation coefficient : 0.125 Melting temperature : 230°C
(B) Conditions for forming a DTR can (1) Drawing process Diameter of blank : 187 mm Drawing ratio : 1.50 (2) Redrawing process First redrawing ratio : 1.29 ~
Second redrawing ratio : 1.24 Third redrawing ratio : 1.20 Radius in the corner of dies used for redrawing : 0.4 mm Load for prevention of wrinkles in the drawing process : 6000 kg i (3) Average decreased ratio in the thickness of DTR can body -20 ~ to the thickness of the employed metal sheet.
Example 2 A coextruded biaxially oriented copolyester resin film having the characteristics set forth hereinbelow under (A) was laminated at 232°C on both sides of the same tin free steel used in Example 1. After the planar orientation coefficients of Layer A and Layer B of the laminated copolyester resin film were determined, the copolyester resin film laminated tin free steel was formed into a DTR
can under the same conditions as in Example 1.
(A) Characteristics of the polyester resin film employed 1) Upper layer Thickness : 15 Eun Composition of the resin film Ethylene glycol : 100 mole ~
Terephthalic acid : 88 mole $
Isophthalic acid : 12 mole ~
Planar orientation coefficient : 0.122 Melting temperature : 230°C
2) Lower layer i Thickness : 5 ~.un Composition of the resin film -copolyester resin 55 weight ~
composed of Ethylene glycol : 100 mole ~
Terephthalic acid : 94 mole ~
Isophthalic acid : 6 mole ~
a l I ~ISII
-polybutylene terephthalate : 45 weight ~
Planar orientation coefficient : 0.080 Melting temperature : 226°G
Example 3 A clear copolyester resin film having the same composition and planar orientation coefficient as in Example 1 and a white-colored copolyester resin film made of the same resin composition and according to the same method as described in Example 1, except that it was pigmented with 16 weight ~ of titanium dioxide, were simultaneously laminated at 250°C on either side of the same tin free steel as in Example 1. After the planar orientation coefficients in Layer A and Layer B of the laminated clear copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1. (The side laminated with white-colored copolyester resin film defined the outside of the DTR can.) Example 4 The copolyester resin film having the same composition as in Example 1 which was precoated with 0.5 g/m2 of epoxy-phenolic resin was laminated at 245°C on both sides of the same tin free steel as in Example 1. After i the planar orientation coefficients in Layer A and Layer B
of the laminated copolyester resin film were determined, the laminate was formed into a DTR can under the same condition as in Example 1.
Example 5 .
Both sides of an aluminum-alloy sheet (JIS 3004) was coated with 0.3 g/m2 of the same epoxy-phenolic resin as in Example 4 and dried at 118°C. Thereafter, the same r...
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coextruded biaxially oriented copolyester resin film as in Example 2 and the same white-colored copolyester resin film as in Example 3 were laminated at 230°C on either precoated side of the aluminum-alloy sheet. After the blanar orientation coefficients in Layer A and Layer B of the laminated clear copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1, except that the load for prevention of wrinkles in the drawing process was 2,000 kg.
(The side laminated with white-colored copolyester resin film defined the outside of the DTR can.
Comparative Example 1 A polyethylene terephthalate film having a thickness of 25 dun, planar orientation coefficient of 0.165 and melting temperature of 260°C was laminated at 280°C on both sides of the same tin free steel as in Example 1.
After the planar orientation coefficients in Layer A and Layer B of the laminated polyethylene terephthalate film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1.
Comparative Example 2 The same copolyester resin film used in Example 1 i was laminated at 210°C on both sides of the same tin free steel as in Example 1. After the planar orientation coefficients in Layer A and Layer B of the laminated copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1.
Comparative Example 3 The same copolyester resin film used in Example 1 was laminated at 305°C on both sides of the same tin free ~1~ 411 steel as in 'Example 1. After the planar orientation coefficients in Layer A and Layer B of the laminated copolyester resin film were determined, the laminate was formed into a DTR can under the same conditions as in Example 1.
The characteristics of the DTR cans in Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated according to the following methods. The degree of cracks arising in the laminated polyester resin film and the degree of peeling-off of the polyester resin film in the formed areas, especially in the upper wall part and neck-in and flange formed area of the DTR can, were evaluated with the naked eye. The results are shown in Table 1.
(1) Degree of exposed metal surface of the inside of the DTR can The degree of exposed metal surface was evaluated according to a current value shown between an anode of the metal surface exposed through the cracks in the polyester resin film of the DTR can which was filled with a 3~ sodium chloride solution and a cathode of a stainless steel rod inserted in the DTR
can at the constant voltage of 6.3 V.
(2) Resistance to hot steam The resistance to hot steam was evaluated according to the degree of peeling-off of the laminated polyester resin film in the flange formed part of the DTR can after treatment of the obtained DTR can in hot steam, having a temperature of 125°C
in a retort for 30 minutes.
~.li~~~~.
(3) Heat resistance The heat resistance was evaluated according to the degree of cracks in the laminated polyester resin film, the discoloration and peeling-off of the laminated polyester resin film in the formed - area of the third redrawn can after the heat treatment at 200°C, corresponding to the temperature for curing of the printing ink to be coated on the outside of the DTR can.
(4) Corrosion resistance The corrosion resistance was evaluated according ' to the degree of corrosion on the inside of the DTR can which was filled with a 3~ acetic acid solution and then stored for 3 months at 50°C.
The degree of corrosion was divided into 5 ranks evaluated with the naked eye, namely, 5 was excellent, 4 was good, 3 was fair, 2 was poor and 1 was bad.
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Claims (16)
1. A metal sheet directly covered with a polyester resin film having a biaxially oriented structure, wherein the polyester resin film comprises an innermost layer of polyester resin which is indirectly in contact with a surface of said metal sheet precoated with a thermosetting resin by laying a layer of said thermosetting resin between said polyester resin film and said metal sheet, and which has a melting temperature of 190 to 230°C and a planar orientation coefficient of 0.000 to 0.100, and an outermost layers of polyester resin having a melting temperature of 210 to 250°C and a planar orientation coefficient of 0.010 to 0.150.
2. A metal sheet according to claim 1, wherein said innermost layer of polyester resin has a planar orientation coefficient of 0.005 to 0.050.
3. A metal sheet according to claim 1, wherein said outermost layer of polyester resin has a planar orientation coefficient of 0.030 to 0.120.
4. A metal sheet according to claim 1, wherein said metal sheet is covered on both sides thereof with said polyester resin film.
5. A metal sheet according to claim 4, wherein said polyester resin is selected from the group consisting of homo-polyester resins, co-polyester resins and polyester resins blended with a least arm homo-polyester or co-polyester resin.
6. A metal sheet according to claim 4, wherein said polyester resin is selected from the group consisting of homo-polyester resins, co-polyester resins and polyester resins blended with a least one homo-polyester resin and at least one co-polyester resin.
7. A metal sheet according to claim 5 or 6, wherein said homo-polyester resin is polyethylene terephthalate or polybutylene terephthalate.
8. A metal sheet according to claim 5 or 6, wherein said copolyester resin is a copolymer of ethylene terephthalate and ethylene isophthalate or a copolymer of butylene terephthalate and butylene isophthalate.
9. A metal sheet according to claim 1, wherein said polyester resin film is a white-colored polyester resin film.
10. A metal sheet according to claim 1, wherein said polyester resin film is a white-colored polyester resin film comprising a titanium dioxide pigment in an amount of 2 to 20 weight %.
11. A metal sheet according too claim 1, wherein the outermost layer of polyester resin has a planar orientation coefficient which is larger than that of the innermost layer of polyester resin.
12. A metal sheet according to claim 1, wherein the termosetting resin has a molecular structure containing at least one radical selected from the group consisting of an epoxy radical, a hydroxyl radical, an amide radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical.
13. A metal sheet according to claim 1, wherein said metal sheet is covered with a double layer consisting of an upper layer of hydrated chromium oxide and a lower layer of metallic chromium, said double layer being disposed between said metal sheet and said layer of thermosetting resin.
14. A metal sheet according to claim 13, wherein said metal sheet is a steel sheet or a steel sheet plated with at least one metal selected from the group consisting of tin, nickel and zinc.
15. A metal sheet according to claim 1, wherein said metal sheet is covered with a mono layer of hydrated chromium oxide disposed between said metal sheet and said layer of thermosetting resin.
16. A metal sheet according to claim 15, wherein said metal sheet is a steel sheet plated with tin or an aluminum alloy sheet.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9400928A GB2285952B (en) | 1994-01-19 | 1994-01-19 | Metal sheet covered with polyester resin film for drawn and stretch formed can |
| FR9400708A FR2715344B1 (en) | 1994-01-19 | 1994-01-24 | Metal sheet covered with a polyester resin film, for boxes formed by stamping and drawing. |
| CA002114511A CA2114511C (en) | 1994-01-19 | 1994-01-28 | Metal sheet covered with polyester resin film for drawn and stretch formed can |
| NL9400154A NL194788C (en) | 1994-01-19 | 1994-02-01 | Metal plate coated with a polyester resin film for a deep-drawn look. |
| DE4403174A DE4403174C2 (en) | 1994-01-19 | 1994-02-02 | Metal sheet coated with a polyester resin film |
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9400928A GB2285952B (en) | 1994-01-19 | 1994-01-19 | Metal sheet covered with polyester resin film for drawn and stretch formed can |
| FR9400708A FR2715344B1 (en) | 1994-01-19 | 1994-01-24 | Metal sheet covered with a polyester resin film, for boxes formed by stamping and drawing. |
| CA002114511A CA2114511C (en) | 1994-01-19 | 1994-01-28 | Metal sheet covered with polyester resin film for drawn and stretch formed can |
| NL9400154A NL194788C (en) | 1994-01-19 | 1994-02-01 | Metal plate coated with a polyester resin film for a deep-drawn look. |
| DE4403174A DE4403174C2 (en) | 1994-01-19 | 1994-02-02 | Metal sheet coated with a polyester resin film |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2114511A1 CA2114511A1 (en) | 1995-07-29 |
| CA2114511C true CA2114511C (en) | 2004-03-16 |
Family
ID=27508537
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002114511A Expired - Lifetime CA2114511C (en) | 1994-01-19 | 1994-01-28 | Metal sheet covered with polyester resin film for drawn and stretch formed can |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA2114511C (en) |
| DE (1) | DE4403174C2 (en) |
| FR (1) | FR2715344B1 (en) |
| GB (1) | GB2285952B (en) |
| NL (1) | NL194788C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6045905A (en) * | 1996-03-29 | 2000-04-04 | Mitsubishi Polyester Film Corporation | Polyester film for laminating metal can end substrate surface |
| KR100219340B1 (en) * | 1996-08-29 | 1999-09-01 | 미키 히로후미 | Laminate and container made of the same |
| US6150012A (en) * | 1996-10-23 | 2000-11-21 | Unitika Ltd. | White film to be laminated to metal surface and method of producing same |
Family Cites Families (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS549632B2 (en) * | 1974-02-04 | 1979-04-26 | ||
| US4517255A (en) * | 1982-07-15 | 1985-05-14 | Toyo Kohan Co., Ltd. | Method for production of metal sheet covered with polyester resin film |
| DE3232755C2 (en) * | 1982-09-03 | 1984-06-28 | Inmont GmbH, 5300 Bonn | Zinc dust primer system for deformable phosphated or chromated sheet steel |
| US4614691A (en) * | 1984-10-01 | 1986-09-30 | Toyo Kohan Co., Ltd. | Method for production of metal sheet covered with polyester resin film |
| DE3436412A1 (en) * | 1984-10-04 | 1986-04-17 | Toyo Kohan Co., Ltd., Tokio/Tokyo | Process for the lamination of metal sheeting with polyester film |
| ATE137997T1 (en) * | 1984-11-09 | 1996-06-15 | Raychem Corp | PROTECT ITEMS |
| JPS61149341A (en) * | 1984-12-25 | 1986-07-08 | Toyo Kohan Co Ltd | Manufacture of polyester resin film-covered metal plate |
| JPS6422530A (en) * | 1987-07-17 | 1989-01-25 | Toray Industries | Polyester film for pasting to metal |
| GB8724240D0 (en) * | 1987-10-15 | 1987-11-18 | Metal Box Plc | Laminated metal sheet |
| JPS63118336A (en) * | 1987-10-27 | 1988-05-23 | Matsushita Electric Works Ltd | Production of metallic foil-clad laminate |
| JPH01249331A (en) * | 1988-03-31 | 1989-10-04 | Toyo Kohan Co Ltd | Manufacture of metallic sheet coated with polyester resin superior in processability |
| US5094924A (en) * | 1988-10-19 | 1992-03-10 | Kenzo Matsui | Polyester resin film laminated steel sheet for drawn and ironed can |
| DE3836858A1 (en) * | 1988-10-19 | 1990-05-10 | Toyo Kohan Co Ltd | Steel sheeting coated with a polyester resin film, in particular for drawn-and-ironed cans, and process for the production thereof |
| JP2897129B2 (en) * | 1988-12-02 | 1999-05-31 | 工業技術院長 | Conductive paper, thermoplastic conductive paper and heat-fusible conductive paper |
| GB2234704B (en) * | 1989-07-28 | 1993-04-14 | Toyo Kohan Co Ltd | Method for producing steel sheet laminated with a polyester resin film |
| JPH0755552B2 (en) * | 1989-09-18 | 1995-06-14 | 東洋製罐株式会社 | Deep drawing can manufacturing method |
| CA2000356C (en) * | 1989-11-09 | 1995-08-22 | Atsuo Tanaka | Copolyester resin film laminated metal sheet and method for production thereof |
| GB2242159B (en) * | 1990-03-19 | 1994-02-02 | Toyo Kohan Co Ltd | Copolyester resin film-metal sheet laminates |
-
1994
- 1994-01-19 GB GB9400928A patent/GB2285952B/en not_active Expired - Lifetime
- 1994-01-24 FR FR9400708A patent/FR2715344B1/en not_active Expired - Lifetime
- 1994-01-28 CA CA002114511A patent/CA2114511C/en not_active Expired - Lifetime
- 1994-02-01 NL NL9400154A patent/NL194788C/en not_active IP Right Cessation
- 1994-02-02 DE DE4403174A patent/DE4403174C2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE4403174A1 (en) | 1995-08-03 |
| FR2715344B1 (en) | 1996-04-12 |
| NL194788C (en) | 2003-03-04 |
| GB2285952B (en) | 1997-06-25 |
| NL9400154A (en) | 1995-09-01 |
| DE4403174C2 (en) | 1999-02-11 |
| NL194788B (en) | 2002-11-01 |
| FR2715344A1 (en) | 1995-07-28 |
| GB2285952A (en) | 1995-08-02 |
| CA2114511A1 (en) | 1995-07-29 |
| GB9400928D0 (en) | 1994-03-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20140128 |