CA1339459C - Method for producing steel sheet laminated with a polyester resin film - Google Patents
Method for producing steel sheet laminated with a polyester resin filmInfo
- Publication number
- CA1339459C CA1339459C CA000606025A CA606025A CA1339459C CA 1339459 C CA1339459 C CA 1339459C CA 000606025 A CA000606025 A CA 000606025A CA 606025 A CA606025 A CA 606025A CA 1339459 C CA1339459 C CA 1339459C
- Authority
- CA
- Canada
- Prior art keywords
- resin film
- copolyester resin
- steel sheet
- copolyester
- acid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
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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
- 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
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
-
- 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
- B32B15/04—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
- 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
- B32B2255/00—Coating on the layer surface
- B32B2255/06—Coating on the layer surface on metal layer
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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
- B32B2307/00—Properties of the layers or laminate
- B32B2307/70—Other properties
- B32B2307/714—Inert, i.e. inert to chemical degradation, corrosion
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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
- B32B2309/00—Parameters for the laminating or treatment process; Apparatus details
- B32B2309/08—Dimensions, e.g. volume
- B32B2309/10—Dimensions, e.g. volume linear, e.g. length, distance, width
- B32B2309/105—Thickness
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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
- B32B2311/00—Metals, their alloys or their compounds
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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
- B32B2367/00—Polyesters, e.g. PET, i.e. polyethylene terephthalate
Abstract
A steel sheet covered with a copolyester resin film is produced by laminating thereon a precoated copolyester resin film consisting of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester resin produced by the esterification of at least one saturated polycarboxylic acid with at least one saturated polyalcohol. The copolyester resin film is precoated on one side uniformly with a small amount of a resin composite containing in its molecular structure at least one radical such as an epoxy radical or hydroxyl. The steel sheet is then heated to the temperature of the melting point of said copolyester resin film ~ 50° C, and the precoated side of said copolyester resin film is applied to both surfaces.
This steel sheet laminated with copolyester resin film is suitable for some applications in which severe formability is required, such as deeply drawn cans formed by multiple drawings, drawn and partially ironed cans, and drawn and stretch-formed cans.
This steel sheet laminated with copolyester resin film is suitable for some applications in which severe formability is required, such as deeply drawn cans formed by multiple drawings, drawn and partially ironed cans, and drawn and stretch-formed cans.
Description
39 ~ 59 FIELD OF THE INVENTION
The present invention relates to a method for producing a surface treated steel sheet covered with a copolyester resin film. The method comprises laminating the copolyester resin film, precoated on one side with a resin composite containing in its molecular structure at least one radical such as epoxy radical or hydroxyl, to both sides of a surface-treated steel sheet such as tin-free steel and electrotinplate which has been heated to a temperature of the melting point of said copolyester resin film + 50~C.
The side of said copolyester resin film precoated with said resin composite contacts the surface-treated steel sheet.
BACKGROUND OF THE INVENTION
At present, metal sheets such as electrotinplate, tin-free steel and aluminum sheets are widely used for can stock after coating with lacquer one or several times. The lacquer coating is disadvantageous from the standpoint of energy cost because a long time is required for curing the lacquer and a large volume of solvent discharged during lacquer curing must be burned in another furnace in order to prevent air pollution.
*
Recently, the lamination of thermo,; _stic resin film on a metal sheet was attempted in order to avert these problems. For example, the methods shown in Laid-Open Japanese Patent Application No. Sho 53-141786, Japanese Patent Publication No. Sho. 60-47103, Laid-Opqn Japanese Patent Application Nos. Sho. 60-168643, Sho 61-29736 and Sho 81-149341 have been already known.
Laid-Open Japanese Patent Application No. Sho 53-141786 relates to a metal can produced from a metal sheet covered with polyolefin resin film by using an adhesive-containing polyolefin resin modified with a carboxyl radical. However, this polyolefin film laminated metal sheet cannot be used for a material for can stock because the metal sheet can be corroded by the packed contents as a result of the laminated polyolefin resin film having poor permeability resistance. Furthermore, even if the polyolefin resin film laminated metal sheet is used as a material for can stock, cans having a satisfactory appearance cannot be obtained because the laminated polyolefin resin film is melted during heating at the 160~
to 200~C temperatures required for curing printing ink or coated lacquer.
1~39459 Japanese Patent Publication No. Sho 60-47103 relates to a process for lamination of a crystalline polyester resin film to a metal sheet by heating the sheet to above the melting point of said polyester resin film and thereafter immediately quenching the laminate. In this patent, the crystalline polyester film is sufficiently adhered to the metal sheet by an amorphous non-oriented polyester resin film which is formed at the interface of the crystalline polyester film and the metal sheet as a result of the heating step. However, when the polyester laminated metal sheet according to said patent is reheated to the temperature of 160~ to 200~ C for 10 to 30 minutes required for curing the printing ink or lacquer placed on the other side of the metal sheet before forming, adhesion of the polyester resin film becomes noticeably poor because the amorphous non-oriented polyester resin film is recrystallized upon reheating. Therefore, the filiform corrosion resistance becomes also poor.
Laid-Open Japanese Patent Application No. Sho 60-168643 relates to a thermoplastic resin film laminated steel sheet for a drawn and ironed can (DI can) and the production method therefor. In said patent, the side of the steel sheet to be employed for the inside of the DI can is laminated with a thermoplastic resin film, such as polyethylene terephthalate resin film without any adhesives and the side of the steel sheet to be employed for the outside of the DI can is plated with a ductile metal such as tin, nickel or aluminum. The steel sheet according to said patent has the same defects as those in Japanese Patent Publication No. Sho 60-47103; i.e, as a result of the reheating to the temperature of 160~ to 200~ C for 10 to 30 minutes required for curing the printing ink or lacquer on the outside of the DI can, the adhesion of the polyester resin becomes noticeably poor.
Laid-Open Japanese Patent Application Nos. Sho 61-20736 and Sho 61-149341 relate to lamination of a precoated biaxially oriented polyester resin film to a metal sheet heated to below the melting point of said polyester resin film. The film is precoated with a special adhesive such as an epoxy resin containing a curing agent. In said patents, an amorphous and non-oriented polyester resin layer as shown in Japanese Patent Publication No. Sho 60-47103 and Laid-Open Japanese Patent Application No. Sho 60-168643 is not formed, because-the lamination of biaxially oriented polyester resin film to the metal sheet is carried out below the temperature of the melting point of said polyester resin film. Therefore, the corrosion resistance and the 13394~9 adhesion of polyester resin film to the metal sheet does not deteriorate, even if it is reheated at the temperature of 160~ to 200~C for the time required for curing printing ink and lacquer. However, if said laminated metal sheet is used for some applications in which more severe formability, such as a deep drawn can having a drawing ratio higher than 2.0, many cracks occur in the polyester resin film.
Accordingly, it is a first objective of the present invention to provide a surface-treated steel sheet covered with copolyester resin film having excellent adhesion of copolyester resin film to said steel sheet and excellent corrosion resistance in a severely formed part such as a deeply drawn can, a drawn and partially ironed can, or a drawn and stretch-formed can having high can height above 2.0 in drawing ratio, even after reheating to cure overcoated color printing ink or lacquer.
It is the second objective of the present invention to provide a method for the continuous lamination at high speed of copolyester resin film on both sides of a surface-treated steel sheet.
1339~a9 BRIEF DESCRIPTION OF THE INVENTION
The first objective of the present invention can be accomplished by the formation on a surface treated steel sheet of double coating layers consisting of: an outer layer of a copolyester resin film produced by stretching and heat setting of a copolyester resin consisting of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester which is produced by esterification of at least one saturated polycarboxylic acid with at least one saturated polyalcohol; and an inner layer of thin resin composite containing in its molecular structure at least one radical, such as an epoxy radical or hydroxyl, on both sides of the surface treated steel sheet.
The second objective of the present invention can be accomplished by continuously laminating, at high speed, said copolyester resin film, precoated with said resin composite, onto both sides of a surface-treated steel sheet heated to the temperature of the melting point of said copolyester film +50~C, with the precoated side of the copolyester resin film in contact with the steel sheet 1339~9 The present invention is characterized by the lamination of the copolyester resin film to both sides of the surface-treated steel sheet heated to the temperature of the melting point of said copolyester resin film ~ 50~ C, said film having been precoated with the thin resin composite which contacts the surface of the steel sheet.
The copolyester resin film laminated steel sheet according to the present invention can be used in applications wherein excellent corrosion resistance is required after severe forming, such as deeply drawn cans, drawn and partially ironed cans, and drawn and stretch-formed cans having high can height and high drawing ratio.
In these applications, the cans are exposed to hot water or hot steam for sterilization after packing foods such as fruit juices, coffee beverages, meats and fish, except for carbonated beverages and beer. For example, fruit juices are immediately packed in the can after sterilization at a temperature of 90~ to 100~ C and coffee drinks, meats and fish are sterilized by hot steam at a temperature above 100~ C in a retort after being packed in the can.
In these applications, color printing or lacquer coating on one or both sides of the steel sheet used for the outside or inside of these cans is often carried out before or after forming. In these cases, the laminated copolyester resin film in the present invention is not peeled off in the severely formed areas even after reheating for curing the color printing ink or lacquer and subsequent treatment by hot water or hot steam.
Generally, the present invention relates to a method for producing a surface-treated steel sheet laminated with a copolyester film onto a film which comprises the steps of (1) producing a copolyester resin film from a copolyester resin consisting essentially of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester resin produced by the esterification of at least one saturated polycarboxylic acid and at least one saturated polyalcohol, (2) precoating said copolyester resin film on one side with a resin composite containing in its molecular structure at least one radical selected from the group consisting of an epoxy radical hydroxyl, an amide radical, an ester radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical, (3) heating a surface-treated steel sheet to the temperature of the melting point of said copolyester film +50 ~C, and (4) laminating said copolyester resin film onto both sides of said steel sheet wherein the side of said copolyester resin film precoated with said resin composite contacts said steel sheet.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the copolyester resin film employed is prepared by processing according to known methods a copolyester resin 1~3~59 consisting of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester resin which is produced by the esterification of at least one saturated polycarboxylic acid with at least one saturated polyalcohol selected from the following polycarboxylic acids and polyalcohols.
Saturated polycarboxylic acids are selected from phthalic acid, isophthalic acid, terephthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, diphenyl carboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid and trimellitic acid anhydride.
- 9a -13~g~9 Saturated polyalcohols are selected from ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexane dimethanol, trimethylol propane and pentaerythritol.
In some cases, additives such as antioxidants, stabilizers, pigments antistatic agents and corrosion inhibitors are added during the manufacturing process of the copolyester resin film used for the present invention.
In the present invention, the use of copolyester resin film which is biaxially stretched and then heat set is especially desirable from the viewpoint of corrosion resistance, compared with non-stretched copolyester resin film.
The thickness of the copolyester resin film used in the present invention should be 5 to 50 ~m, preferably 10 to 30 ~m. If the thickness of the employed copolyester resin film is below 5 ~m, good corrosion resistance after severe forming of the steel sheet according to the present invention is not obtained and the continuous lamination of thin copolyester resin film to the metal sheet becomes noticeably difficult.
The use of copolyester resin film having a thickness above 50 ~m is not economically suitable for the film to be laminated to the surface treated steel sheet, because the copolyester resin film used for the present invention is expensive as compared with epoxy phenolic lacquers widely used in the can industry.
In the present invention, the softening temperature and the melting temperature of the copolyester resin film are also important factors. The softening temperature is defined as the temperature at which the insertion of the needle into the copolyester resin film starts at a heating rate of 10~C/min. in the thermal mechanical analyzer (TMA 100) made by Seiko Denshi Kogyo Co. The melting temperature is defined as the temperature at which the endothermic peak is obtained at a heating rate of 10~C/min. in the differential scanning calorimeter (SS10) made by Seiko Denshi Kogyo Co.
In the present invention, a copolyester resin film having a softening temperature of 170 to 235~C and a melting temperature of 210 to 250~C should be used. A
13~3~59 copolyester resin Lilm having a softening temperature of above 235~ C becomes poor in formability, and many cracks occur in the severely formed copolyester resin film. On the other hand, if a copolyester resin film having a softening temperature below 170~ C is used, the efficiency in the production process of deeply drawn cans becomes noticeably poor because the copolyester resin film soften as a result of the reheating require to cure color printing ink lacquer applied to the outside or the inside of the drawn can which is done at a higher temperature than the softening temperature of the film.
The use of a copolyester resin film having a melting temperature above 250~ C is not suitable in the present invention because such rigid copolyester resin films show poor formability. If a copolyester resin film having a melting temperature below 210~ C is applied to the surface-treated steel sheet, many cracks are observed in the resin film after severe forming, because the mechanical property of those copolyester resin films deteriorates upon the reheating require to cure the color printing ink or lacquer applied to the outside or the inside of the can.
Furthermore, the mechanical properties of the copolyester resin film are also very important factors from the ~i339459 standpoint of formability o he copolyester resin film.
Specifically, an elongation at break of the copolyester resin film, which is determined at the speed of 100mm/min.
at 25~ C in an ordinary tensile testing machine, should be within the range of 150 to 400 %. If a copolyester resin film having below 150% of elongation at break is used in the present invention, many cracks arise in the film after severe forming, because the formability of said film becomes noticeably poor. On the other hand, if a copolyester resin film having above 400 % of elongation at break is used in the present invention, the film is easily damaged by severe forming because the thickness of this copolyester resin film becomes non-uniform during extrusion; in particular, the film can be easily cut off in the biaxial stretching process.
In the present invention, one side of the copolyester resin film described above is precoated with 0.1 to 5.0 g/m2 of a resin composite containing in its molecular structure at least one radical selected from the group consisting of an epoxy radical, hydroxyl, an amide radical, an ester radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical. Epoxy resin, phenol resin, nylon resin, polyester resin, modified vinyl resin, urethane resin, acryl resin and urea resin are examples of such resin composites.
~9~59 It is desirable in the present invention that the resin composite be coated on the one side of the copolyester resin film as uniformly and thinly as possible because the bonding strength of the resin composite layer to the surface-treated steel sheet and the copolyester resin film becomes gradually poorer with an increase in the thickness of the precoated resin composite. However, it is very difficult to uniformly coat an amount below 0 1 g/m2 of resin composite on the copolyester resin film. Furthermore, when the amount of the resin composite is below 0.1 g/m2 or above 5.0 g/m2~
the bonding strength of resin composite layer to the surface treater steel sheet and the copolyester resin film becomes noticeably poor in severely formed areas.
It is preferable in the present invention that the resin composite be diluted with a solvent and then coated by a roller or spray method in order to form a uniform and thin resin composite layer on the copolyester resin film. The temperature for drying the resin composite diluted by a solvent which is coated on the copolyester resin film is also one of the important factors in the present invention. If the temperature is below 60~C, a long time is required for the removal of solvent and the resin composite layer 1~394S9 becomes tacky. When the drying temperature is above 150~ C, the chemical reaction of resin composite coated on the copolyester resin film is accelerated, and then the bonding strength of resin composite layer to the steel sheet becomes noticeably poor.
It is suitable in the present invention that the drying time of the resin composite solution coated on the copolyester resin film be from 5 to 30 seconds at a temperature of 60~ to 150~ C. If the drying time is less than 5 seconds, the solvent is not sufficiently removed. On the other hand, long time drying of more than 30 seconds results in poor productivity.
In the present inventlon, a solvent having low boiling point should be used for the dissolution of resin composite because it is easily removed by heating at 60~ to 150~ C, although the solvent is not otherwise specially limited. In some cases, a color agent such as a dye may be added to the resin composite dissolved in a solvent.
As described above, it is suitable in the present invention for the resin composite to be coated on the copolyester resin film and, after dissolution of the low 1339~9 boiling solvent for the coated film to be dried at 60~ to 150~ C for 5 to 30 seconds.
The surface-treated steel sheet should be selected from the group consisting of a double layer tin-free steel having an upper layer of hydrated chromium oxide and a lower layer of metallic chromium, electrotinplate covered with the double layer as described above and electrotinplate covered with hydrated chromium oxide, because the steel sheet according to the present invention is contemplated for use as sanitary food cans. The optimum range of hydrated chromium oxide and metallic chromium in a tin-free steel is 5 to 25 mg/m2 as chromium and 10 to 150 mg/m2 as chromium, respectively. If the amount of hydrated chromium oxide is below 5 mg/m or above 25 mg/m2 as chromium, the bonding strength to the copolyester resin film precoated with said resin composite becomes noticeably poor in severely formed areas. Although the corrosion resistance in the formed part becomes gradually poorer with a decrease in the amount of metallic chromium, even the tin-free steel having about 10 mg/m of metallic chromium can be used for some applications where mild corrosion resistance is required. The electrotinplate used in the present invention should be cathodically treated in an electrolyte for producing an 133!~59 ordinary tin-free steel or treated by immersion into a solution containing about 30 g/liter of sodium dichromate in water. By said cathodic treatment, a double layer consisting of an upper layer of hydrated chromium oxide and a lower layer of metallic chromium is formed on electrotinplate. It is suitable in the present invention that the amount of hydrated chromium oxide and metallic chromium on electrotinplate be almost the same as that in tin-free steel. However, it is more preferable that the amount of metallic chromium be 10 to 50 mg/m2 in order to facilitate high speed production.
In the case of immersion treatment of electrotinplate into sodium dichromate solution, a thin layer of hydrated chromium oxide having almost constant amount ~1 to 4 mg/m2 as chromium) is formed on electrotinplate. The thin hydrated chromium oxide on electrotinplate is necessary for excellent adhesion of the copolyester resin film precoated with said resin composite in severely formed areas. If electrotinplate is not treated by immersion into sodium dichromate solution, the adhesion of the copolyester resin film precoated with resin composite becomes gradually poorer during storage in an atmosphere having high humidity. If hydrated chromium oxide having above ~ mg/m2 as chromium is formed on elect-rotinplate by ~ 1339459 cathodic treatment in sodium dichromate solution, adhesion of the copolyester resin film precoated with resin composite becomes noticeably poor in the severely formed areas. It is considered that the difference in the adhesion of the copolyester resin film to electrotinplate depends on the quality of the hydrated chromium oxide. Namely, the hydrated chromium oxide fonned by cathodic treatment in an electrolyte for producing a tin-free steel has better adhesion to said copolyester resin film compared with that by an immersion treatment into sodium dichromate solution.
It is suitable in the present invention that the amount of plated tin in electrotinplate be 0.5 to 5.6 g/m2.
If the amount of plated tin is less than 0.5 g/m2, the effect of plated tin on the corrosion resistance is hardly apparent, despite further plating process. An amount of above 5.6 g/m2 of tin is not economically preferable.
The temperature of the surface-treated steel sheet heated just before the lamination of the copolyester resin film precoated with resin composite, which is also one of the important factors in the present invention, should be maintained in the range of the melting point of said copolyester resin film +50~ C. If the temperature is above 1~39~9 the melting point + 50~ C, corrosion resistance becomes noticeably poor because the copolyester resin film is deteriorated by heating. The copolyester resin film used in the present invention cannot be easily recrystallized at the heating temperature required for curing the color printing ink or lacquer applied on the steel sheet, although a non-oriented amorphous copolyester resin layer is formed by heating. Therefore, the steel sheet according to the present invention maintains excellent corrosion resistance, even if it is heated at 160~ to 200~ C. If the lamination of the copolyester resin film precoated with resin composite to the surface treated steel sheet is carried out below the melting point of the copolyester resin film - 50~ C, the copolyester resin film is easily peeled off from the surface of the surface-treated steel sheet.
In the present invention, the method for heating the surface-treated steel sheet to which the copolyester resin film is laminated is not especially limited. However, from the standpoint of continuous and stable production of steel sheets according to the present invention at high speed, conduction heating by a roller heated by induction heating, induction heating and/or resistance heating which are used for reflowing electrotinplate in the production .. . ..
13~34~9 process of electrotinplate is suitable as the method for heating the surface-treated steel sheet to be laminated, because the surface-treated steel sheet can be rapidly heated and the temperature of the heated steel sheet can be easily controlled. Furthermore it is also preferable in the present invention that heating by roller heated by hot steam or heating in an electric oven be used as an auxiliary method for preheating~the surface-treated steel sheet to be laminated.
The surface temperature of laminating roller is also one of the important factors in the present invention.
The surface temperature of the laminating roller should be controlled in the range of 80~ to 180~ C. At below 80~ C, an air bubble occurs easily between the copolyester resin film precoated with resin composite and the surface-treated steel sheet during the lamination of the copolyester resin film to the steel sheet. On the other hand, at a temperature of the laminating rolls above 180~ C, production of the steel sheet according to the present invention at high speed is prevented, because the copolyester resin film readily adheres to the laminating roller. As the laminating roller, the use of a chromium plated roller, a ceramic roller or a rubber roller is preferable in the present invention. In the use of a rubber roller, a roller made ~3'~9~59 with silicon rubber or fluorine rubber, which is an excellent in heat conductivity and heat resistance, should be selected.
The present invention is explained in further detail by reference to the following examples.
A cold rolled steel strip having a thickness of 0.21 mm and a width of 300 mm was electrolytically degreased in a solution of 70 g/liter of sodium hydroxide and then pickled in a solution of 100 g/liter of sulfuric acid. The steel strip, after being rinsed with water, was cathodically treated by using an electrolyte containing 60 g/liter of CrO3 and 3 g/liter of NaF in water under 20 A/dm of cathodic current density at an electrolyte temperature of 50~ C. The thus treated steel strip was rinsed with hot water having a temperature of 80~ C and dried.
After that, a biaxially oriented copolyester resin film produced from a condensation of ethylene glycol and polycarboxylic acid consisting of 80 mole % of terephthalic _ .
13~9 459 a~ia and 20 mole % of isophthalic acid having a thickness of 25 um, softening temperature of 176~ C, melting temperature of 215~ C, and elongation at break of 330%, which was precoated with resin composite by the following condition (A), was continuously laminated on both surfaces of thus treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated material:
Epoxy resin having an epoxy equivalent of 3000 -80 parts Resol product from paracresol - 20 parts Drying temperature of precoated resin composite: 100~ C
Drying time of precoated resin composite: 10 seconds Amount of resin composite after drying at 100~ C:
0.2 g/m (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 185~ C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max. 154~ C
Method for cooling the laminate: Gradual cooling The same steel strip pretreated as in Example 1 was cathodically treated in an electrolyte containing 80 g/liter of CrO3, 0.8 g/liter of HBF4 and 0.5 g/liter of H2SO4 in water under 50 A/dm2 of cathodic current density at an electrolyte temperature of 60~ C. The thus treated steel sheet was rinsed with hot water having a temperature of 80~ C and dried.
After that, a biaxially oriented copolyester resin film produced from a condensation polymerization of ethylene glycol and polycarboxylic acid consisting of 85 mole % of terephthalic acid and 15 mole % of isophthalic acid having a thickness of 25 ~m, softening temperature of 192~ C, melting temperature of 239~ C and elongation at break of 210%, which had been precoated with resin composite by the following condition (A), was continuously laminated on both sides of the thus treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 3000 -70 parts Resol product from paracresol - 30 parts Drying temperature of precoated resin composite: 120~ C
Drying time of precoated resin composite: 7 seconds Amount of resin composite after drying at 120~ C:
0.6 g/m (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 219 ~C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max. 176~ C
Method for cooling the laminate: Gradual cooling 1~39~S9 The same steel strip pretreated as in Example 1 was electroplated with 1.7 g/m2 of tin by using an electrolyte containing 10 g/liter of SnSO4, 20 g/liter of phenolsulfonic acid (60% aqueous solution) and 5 g/liter of ethoxylated ~-naphthol sulfonic acid in water under 5 A/dm of cathodic current density at an electrolyte temperature of 40~ C. After rinsing with water, the tin plated steel sheet was cathodically treated by using an electrolyte containing 30 g/liter of CrO3 and 0.3 g/liter of H2SO4 in water under 50 A/dm of cathodic current density at an electrolyte temperature of 50~ C. The thus treated electrotinplated was rinsed with hot water having a temperature of 80~ C and dried.
After that, a biaxially oriented copolyester resin film produced from a condensation polymerization of ethylene glycol and polycarboxylic acid consisting of 90 mole ~ of terephthalic acid and 10 mole ~ of isophthalic acid having a thickness of 16 ~m, softening temperature of 212~ C, melting temperature of 241~ C and elongation at break of 172%, which had been precoated with resin composite by the following condition (A), was continuously laminated on both sides of 13~g4~9 the thus treated steel strip under the followi..~- condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 2500 -70 parts Polyamide resin (Trade name: Versamide 115) - 30 parts Drying temperature of precoated resin composite: 80~ C
Drying time of precoated resin composite: 15 seconds Amount of resin composite after drying at 80~ C: 1.5 g/m2 (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 255~ C
Material of laminating roller: Fluorine rubber Surface temperature of laminating roller: Max. 128 ~ C
Method for cooling the laminate: Gradual cooling 133g4~9 The same steel strip pretreated as in Example 1 was electroplated with 2.8. g/m2 of tin by using an electrolyte containing 80 g/liter of SnSO4, 60 g/liter of phenolsulfonic acid (60% aqueous solution) and 5 g/liter of ethoxylated ~-naphthol sulfonic acid in water under 15 A/dm2 of cathodic current density at an electrolyte temperature of 45~ C. After reflowing of tin and rinsing with water, the tin plated steel sheet was treated by immersion into 30 g/liter of sodium dichromate solution for 3 seconds at a temperature of 45~ C. The thus treated electrotinplate strip was rinsed with water and dried.
After that, the same biaxially oriented copolyester resin film as in Example 1 precoated with resin composite by the following condition (A) was laminated on the thus treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated resin composite;
Copolyester resin (Trade name Vylon 200) -75 parts Urethane resin (Trade name Coronate L) - 25 parts Drying temperature of precoated resin composite: 80~C
Drying time of precoated resin composite: 20 seconds Amount of resin composite after drying at 80~C: 2.0 g/m2 (B) Conditions for lamination of coPolyester resin film precoated bY under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 215~C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max. 165~C
Method for cooling the laminate: Gradual cooling . 29-133~ iS9 The same steel strip pretreated as in Example 1 was electroplated with metallic chromium by using a Sargent bath containing 250 g/liter of CrO3 and 2.5 g/liter of H2SO4 in water under 30 A/dm2 of cathodic current density at a bath temperature of 55~ C. After rinsing with water, a chromium plated steel strip was cathodically treated by using an electrolyte containing 30 g/liter of CrO3 and 1.2 g/liter of NH4F in water under 20 A/dm of cathodic current density at an electrolyte temperature of 40~ C and then rinsed with hot water having a temperature of 80~ C and dried.
After that, a copolyester resin film produced from a condensation polymerization of ethylene glycol and carboxylic acid consisting of 96 mole % of terephthalic acid and 4 mole % of isophthalic acid having a thickness of 30 ~m, softening temperature of 235~ C, melting temperature of 250~ C and elongation at break of 155~ precoated with resin composite by the following condition (A) was continuously laminated on both surface of the treated aluminum strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film 13394~9 Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 3000 -80 parts Urea resin - 20 parts Drying temperature of precoated resin composite: 135~ C
Drying time of precoated resin composite: 10 seconds Amount of resin composite after drying at 135~ C:
1.5 g/m (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 245~ C
Material of laminating roller- Silicon rubber Surface temperature of laminating roller: Max. 160~ C
Method for cooling the laminate: Rapid cooling 13394~9 A biaxially oriented polyethylene terephthalate film (Trademark Lumirror made by Toray Co. Ltd.) having a thickness of 25 ~m, softening temperature of 240~C, melting temperature of 257~C and elongation at break of 125% precoated with the same resin composite as shown in condition (A) of Example 1 was continuously laminated on both surfaces of the same treated steel strip as in Example 1 under the same condition (B) as in Example 1.
A biaxially oriented polyethylene terephthalate film (Tradename Enblett made by Unichika Co. Ltd.) having a thickness of 25 ~m, softening temperature of 238~C, melting temperature of 257~C and elongation at break of 138~ precoated with the same resin composite as shown in condition (A) of Example 2 was continuously laminated on both sides of the same treated steel strip as in Example 2 under condition (B) of Example 2.
A non-oriented polyethylene terephthalate film (Trademark Tetoron made by Teijin Co. Ltd.) having a 1339~59 thickness of 30 ~m, softening temperature of 242~ C, melting temperature of 254~ C and elongation at break of 110%
precoated with the same resin composite as shown in condition (A) of Example 3 was continuously laminated on both surface of the same treated electrotinplate strip as in Example 3 under condition (B) of Example 3.
The same copolyester resin film as in Example 2 precoated with the same resin composite as shown in the condition (A) of Example 2 was continuously laminated on both sides of the same treated steel strip as in Example 1 under the same condition (B) of Example 2, except for the temperature of the treated steel strip just before the lamination.
Temperature of the treated steel strip just before the lamination: 175~ C
The same polyethylene terephthalate film as in Comparative Example 1 was laminated on the same treated steel strip as in Example 5 without the resin composite adhesive under the following conditions:
Conditions for the lamination of polyethylene terephthalate film Temperature of the treated steel strip just before the lamination: 280~ C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max.
105~ C
Method for cooling the laminate: Rapid cooling The adhesion of polyester resin film in the resultant steel sheet was evaluated by the following testing methods, after the measurement of the coating weight on the resultant steel sheet by the X-ray fluorescent method. The results are shown in the Table.
(1) Degree of cracks in polyester resin film after forming The resultant steel sheet was cut to a circular blank having a diameter of 140 mm by a punch press after heating for 10 minutes at 190~ C. The blank was deeply drawn to form a cup at a drawing ratio of 2.55. After that, 1% of sodium chloride solution was filled in the drawn cup.
The degree of cracks of polyester resin film in the formed part was evaluated by a current value flowing between an anode of the steel exposed through cracks of polyester resin film in said drawn cup and a cathode of stainless steel rod inserted in said drawn cup at constant voltage of 6.3 volts.
The present invention relates to a method for producing a surface treated steel sheet covered with a copolyester resin film. The method comprises laminating the copolyester resin film, precoated on one side with a resin composite containing in its molecular structure at least one radical such as epoxy radical or hydroxyl, to both sides of a surface-treated steel sheet such as tin-free steel and electrotinplate which has been heated to a temperature of the melting point of said copolyester resin film + 50~C.
The side of said copolyester resin film precoated with said resin composite contacts the surface-treated steel sheet.
BACKGROUND OF THE INVENTION
At present, metal sheets such as electrotinplate, tin-free steel and aluminum sheets are widely used for can stock after coating with lacquer one or several times. The lacquer coating is disadvantageous from the standpoint of energy cost because a long time is required for curing the lacquer and a large volume of solvent discharged during lacquer curing must be burned in another furnace in order to prevent air pollution.
*
Recently, the lamination of thermo,; _stic resin film on a metal sheet was attempted in order to avert these problems. For example, the methods shown in Laid-Open Japanese Patent Application No. Sho 53-141786, Japanese Patent Publication No. Sho. 60-47103, Laid-Opqn Japanese Patent Application Nos. Sho. 60-168643, Sho 61-29736 and Sho 81-149341 have been already known.
Laid-Open Japanese Patent Application No. Sho 53-141786 relates to a metal can produced from a metal sheet covered with polyolefin resin film by using an adhesive-containing polyolefin resin modified with a carboxyl radical. However, this polyolefin film laminated metal sheet cannot be used for a material for can stock because the metal sheet can be corroded by the packed contents as a result of the laminated polyolefin resin film having poor permeability resistance. Furthermore, even if the polyolefin resin film laminated metal sheet is used as a material for can stock, cans having a satisfactory appearance cannot be obtained because the laminated polyolefin resin film is melted during heating at the 160~
to 200~C temperatures required for curing printing ink or coated lacquer.
1~39459 Japanese Patent Publication No. Sho 60-47103 relates to a process for lamination of a crystalline polyester resin film to a metal sheet by heating the sheet to above the melting point of said polyester resin film and thereafter immediately quenching the laminate. In this patent, the crystalline polyester film is sufficiently adhered to the metal sheet by an amorphous non-oriented polyester resin film which is formed at the interface of the crystalline polyester film and the metal sheet as a result of the heating step. However, when the polyester laminated metal sheet according to said patent is reheated to the temperature of 160~ to 200~ C for 10 to 30 minutes required for curing the printing ink or lacquer placed on the other side of the metal sheet before forming, adhesion of the polyester resin film becomes noticeably poor because the amorphous non-oriented polyester resin film is recrystallized upon reheating. Therefore, the filiform corrosion resistance becomes also poor.
Laid-Open Japanese Patent Application No. Sho 60-168643 relates to a thermoplastic resin film laminated steel sheet for a drawn and ironed can (DI can) and the production method therefor. In said patent, the side of the steel sheet to be employed for the inside of the DI can is laminated with a thermoplastic resin film, such as polyethylene terephthalate resin film without any adhesives and the side of the steel sheet to be employed for the outside of the DI can is plated with a ductile metal such as tin, nickel or aluminum. The steel sheet according to said patent has the same defects as those in Japanese Patent Publication No. Sho 60-47103; i.e, as a result of the reheating to the temperature of 160~ to 200~ C for 10 to 30 minutes required for curing the printing ink or lacquer on the outside of the DI can, the adhesion of the polyester resin becomes noticeably poor.
Laid-Open Japanese Patent Application Nos. Sho 61-20736 and Sho 61-149341 relate to lamination of a precoated biaxially oriented polyester resin film to a metal sheet heated to below the melting point of said polyester resin film. The film is precoated with a special adhesive such as an epoxy resin containing a curing agent. In said patents, an amorphous and non-oriented polyester resin layer as shown in Japanese Patent Publication No. Sho 60-47103 and Laid-Open Japanese Patent Application No. Sho 60-168643 is not formed, because-the lamination of biaxially oriented polyester resin film to the metal sheet is carried out below the temperature of the melting point of said polyester resin film. Therefore, the corrosion resistance and the 13394~9 adhesion of polyester resin film to the metal sheet does not deteriorate, even if it is reheated at the temperature of 160~ to 200~C for the time required for curing printing ink and lacquer. However, if said laminated metal sheet is used for some applications in which more severe formability, such as a deep drawn can having a drawing ratio higher than 2.0, many cracks occur in the polyester resin film.
Accordingly, it is a first objective of the present invention to provide a surface-treated steel sheet covered with copolyester resin film having excellent adhesion of copolyester resin film to said steel sheet and excellent corrosion resistance in a severely formed part such as a deeply drawn can, a drawn and partially ironed can, or a drawn and stretch-formed can having high can height above 2.0 in drawing ratio, even after reheating to cure overcoated color printing ink or lacquer.
It is the second objective of the present invention to provide a method for the continuous lamination at high speed of copolyester resin film on both sides of a surface-treated steel sheet.
1339~a9 BRIEF DESCRIPTION OF THE INVENTION
The first objective of the present invention can be accomplished by the formation on a surface treated steel sheet of double coating layers consisting of: an outer layer of a copolyester resin film produced by stretching and heat setting of a copolyester resin consisting of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester which is produced by esterification of at least one saturated polycarboxylic acid with at least one saturated polyalcohol; and an inner layer of thin resin composite containing in its molecular structure at least one radical, such as an epoxy radical or hydroxyl, on both sides of the surface treated steel sheet.
The second objective of the present invention can be accomplished by continuously laminating, at high speed, said copolyester resin film, precoated with said resin composite, onto both sides of a surface-treated steel sheet heated to the temperature of the melting point of said copolyester film +50~C, with the precoated side of the copolyester resin film in contact with the steel sheet 1339~9 The present invention is characterized by the lamination of the copolyester resin film to both sides of the surface-treated steel sheet heated to the temperature of the melting point of said copolyester resin film ~ 50~ C, said film having been precoated with the thin resin composite which contacts the surface of the steel sheet.
The copolyester resin film laminated steel sheet according to the present invention can be used in applications wherein excellent corrosion resistance is required after severe forming, such as deeply drawn cans, drawn and partially ironed cans, and drawn and stretch-formed cans having high can height and high drawing ratio.
In these applications, the cans are exposed to hot water or hot steam for sterilization after packing foods such as fruit juices, coffee beverages, meats and fish, except for carbonated beverages and beer. For example, fruit juices are immediately packed in the can after sterilization at a temperature of 90~ to 100~ C and coffee drinks, meats and fish are sterilized by hot steam at a temperature above 100~ C in a retort after being packed in the can.
In these applications, color printing or lacquer coating on one or both sides of the steel sheet used for the outside or inside of these cans is often carried out before or after forming. In these cases, the laminated copolyester resin film in the present invention is not peeled off in the severely formed areas even after reheating for curing the color printing ink or lacquer and subsequent treatment by hot water or hot steam.
Generally, the present invention relates to a method for producing a surface-treated steel sheet laminated with a copolyester film onto a film which comprises the steps of (1) producing a copolyester resin film from a copolyester resin consisting essentially of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester resin produced by the esterification of at least one saturated polycarboxylic acid and at least one saturated polyalcohol, (2) precoating said copolyester resin film on one side with a resin composite containing in its molecular structure at least one radical selected from the group consisting of an epoxy radical hydroxyl, an amide radical, an ester radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical, (3) heating a surface-treated steel sheet to the temperature of the melting point of said copolyester film +50 ~C, and (4) laminating said copolyester resin film onto both sides of said steel sheet wherein the side of said copolyester resin film precoated with said resin composite contacts said steel sheet.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the copolyester resin film employed is prepared by processing according to known methods a copolyester resin 1~3~59 consisting of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester resin which is produced by the esterification of at least one saturated polycarboxylic acid with at least one saturated polyalcohol selected from the following polycarboxylic acids and polyalcohols.
Saturated polycarboxylic acids are selected from phthalic acid, isophthalic acid, terephthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, diphenyl carboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid and trimellitic acid anhydride.
- 9a -13~g~9 Saturated polyalcohols are selected from ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexane dimethanol, trimethylol propane and pentaerythritol.
In some cases, additives such as antioxidants, stabilizers, pigments antistatic agents and corrosion inhibitors are added during the manufacturing process of the copolyester resin film used for the present invention.
In the present invention, the use of copolyester resin film which is biaxially stretched and then heat set is especially desirable from the viewpoint of corrosion resistance, compared with non-stretched copolyester resin film.
The thickness of the copolyester resin film used in the present invention should be 5 to 50 ~m, preferably 10 to 30 ~m. If the thickness of the employed copolyester resin film is below 5 ~m, good corrosion resistance after severe forming of the steel sheet according to the present invention is not obtained and the continuous lamination of thin copolyester resin film to the metal sheet becomes noticeably difficult.
The use of copolyester resin film having a thickness above 50 ~m is not economically suitable for the film to be laminated to the surface treated steel sheet, because the copolyester resin film used for the present invention is expensive as compared with epoxy phenolic lacquers widely used in the can industry.
In the present invention, the softening temperature and the melting temperature of the copolyester resin film are also important factors. The softening temperature is defined as the temperature at which the insertion of the needle into the copolyester resin film starts at a heating rate of 10~C/min. in the thermal mechanical analyzer (TMA 100) made by Seiko Denshi Kogyo Co. The melting temperature is defined as the temperature at which the endothermic peak is obtained at a heating rate of 10~C/min. in the differential scanning calorimeter (SS10) made by Seiko Denshi Kogyo Co.
In the present invention, a copolyester resin film having a softening temperature of 170 to 235~C and a melting temperature of 210 to 250~C should be used. A
13~3~59 copolyester resin Lilm having a softening temperature of above 235~ C becomes poor in formability, and many cracks occur in the severely formed copolyester resin film. On the other hand, if a copolyester resin film having a softening temperature below 170~ C is used, the efficiency in the production process of deeply drawn cans becomes noticeably poor because the copolyester resin film soften as a result of the reheating require to cure color printing ink lacquer applied to the outside or the inside of the drawn can which is done at a higher temperature than the softening temperature of the film.
The use of a copolyester resin film having a melting temperature above 250~ C is not suitable in the present invention because such rigid copolyester resin films show poor formability. If a copolyester resin film having a melting temperature below 210~ C is applied to the surface-treated steel sheet, many cracks are observed in the resin film after severe forming, because the mechanical property of those copolyester resin films deteriorates upon the reheating require to cure the color printing ink or lacquer applied to the outside or the inside of the can.
Furthermore, the mechanical properties of the copolyester resin film are also very important factors from the ~i339459 standpoint of formability o he copolyester resin film.
Specifically, an elongation at break of the copolyester resin film, which is determined at the speed of 100mm/min.
at 25~ C in an ordinary tensile testing machine, should be within the range of 150 to 400 %. If a copolyester resin film having below 150% of elongation at break is used in the present invention, many cracks arise in the film after severe forming, because the formability of said film becomes noticeably poor. On the other hand, if a copolyester resin film having above 400 % of elongation at break is used in the present invention, the film is easily damaged by severe forming because the thickness of this copolyester resin film becomes non-uniform during extrusion; in particular, the film can be easily cut off in the biaxial stretching process.
In the present invention, one side of the copolyester resin film described above is precoated with 0.1 to 5.0 g/m2 of a resin composite containing in its molecular structure at least one radical selected from the group consisting of an epoxy radical, hydroxyl, an amide radical, an ester radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical. Epoxy resin, phenol resin, nylon resin, polyester resin, modified vinyl resin, urethane resin, acryl resin and urea resin are examples of such resin composites.
~9~59 It is desirable in the present invention that the resin composite be coated on the one side of the copolyester resin film as uniformly and thinly as possible because the bonding strength of the resin composite layer to the surface-treated steel sheet and the copolyester resin film becomes gradually poorer with an increase in the thickness of the precoated resin composite. However, it is very difficult to uniformly coat an amount below 0 1 g/m2 of resin composite on the copolyester resin film. Furthermore, when the amount of the resin composite is below 0.1 g/m2 or above 5.0 g/m2~
the bonding strength of resin composite layer to the surface treater steel sheet and the copolyester resin film becomes noticeably poor in severely formed areas.
It is preferable in the present invention that the resin composite be diluted with a solvent and then coated by a roller or spray method in order to form a uniform and thin resin composite layer on the copolyester resin film. The temperature for drying the resin composite diluted by a solvent which is coated on the copolyester resin film is also one of the important factors in the present invention. If the temperature is below 60~C, a long time is required for the removal of solvent and the resin composite layer 1~394S9 becomes tacky. When the drying temperature is above 150~ C, the chemical reaction of resin composite coated on the copolyester resin film is accelerated, and then the bonding strength of resin composite layer to the steel sheet becomes noticeably poor.
It is suitable in the present invention that the drying time of the resin composite solution coated on the copolyester resin film be from 5 to 30 seconds at a temperature of 60~ to 150~ C. If the drying time is less than 5 seconds, the solvent is not sufficiently removed. On the other hand, long time drying of more than 30 seconds results in poor productivity.
In the present inventlon, a solvent having low boiling point should be used for the dissolution of resin composite because it is easily removed by heating at 60~ to 150~ C, although the solvent is not otherwise specially limited. In some cases, a color agent such as a dye may be added to the resin composite dissolved in a solvent.
As described above, it is suitable in the present invention for the resin composite to be coated on the copolyester resin film and, after dissolution of the low 1339~9 boiling solvent for the coated film to be dried at 60~ to 150~ C for 5 to 30 seconds.
The surface-treated steel sheet should be selected from the group consisting of a double layer tin-free steel having an upper layer of hydrated chromium oxide and a lower layer of metallic chromium, electrotinplate covered with the double layer as described above and electrotinplate covered with hydrated chromium oxide, because the steel sheet according to the present invention is contemplated for use as sanitary food cans. The optimum range of hydrated chromium oxide and metallic chromium in a tin-free steel is 5 to 25 mg/m2 as chromium and 10 to 150 mg/m2 as chromium, respectively. If the amount of hydrated chromium oxide is below 5 mg/m or above 25 mg/m2 as chromium, the bonding strength to the copolyester resin film precoated with said resin composite becomes noticeably poor in severely formed areas. Although the corrosion resistance in the formed part becomes gradually poorer with a decrease in the amount of metallic chromium, even the tin-free steel having about 10 mg/m of metallic chromium can be used for some applications where mild corrosion resistance is required. The electrotinplate used in the present invention should be cathodically treated in an electrolyte for producing an 133!~59 ordinary tin-free steel or treated by immersion into a solution containing about 30 g/liter of sodium dichromate in water. By said cathodic treatment, a double layer consisting of an upper layer of hydrated chromium oxide and a lower layer of metallic chromium is formed on electrotinplate. It is suitable in the present invention that the amount of hydrated chromium oxide and metallic chromium on electrotinplate be almost the same as that in tin-free steel. However, it is more preferable that the amount of metallic chromium be 10 to 50 mg/m2 in order to facilitate high speed production.
In the case of immersion treatment of electrotinplate into sodium dichromate solution, a thin layer of hydrated chromium oxide having almost constant amount ~1 to 4 mg/m2 as chromium) is formed on electrotinplate. The thin hydrated chromium oxide on electrotinplate is necessary for excellent adhesion of the copolyester resin film precoated with said resin composite in severely formed areas. If electrotinplate is not treated by immersion into sodium dichromate solution, the adhesion of the copolyester resin film precoated with resin composite becomes gradually poorer during storage in an atmosphere having high humidity. If hydrated chromium oxide having above ~ mg/m2 as chromium is formed on elect-rotinplate by ~ 1339459 cathodic treatment in sodium dichromate solution, adhesion of the copolyester resin film precoated with resin composite becomes noticeably poor in the severely formed areas. It is considered that the difference in the adhesion of the copolyester resin film to electrotinplate depends on the quality of the hydrated chromium oxide. Namely, the hydrated chromium oxide fonned by cathodic treatment in an electrolyte for producing a tin-free steel has better adhesion to said copolyester resin film compared with that by an immersion treatment into sodium dichromate solution.
It is suitable in the present invention that the amount of plated tin in electrotinplate be 0.5 to 5.6 g/m2.
If the amount of plated tin is less than 0.5 g/m2, the effect of plated tin on the corrosion resistance is hardly apparent, despite further plating process. An amount of above 5.6 g/m2 of tin is not economically preferable.
The temperature of the surface-treated steel sheet heated just before the lamination of the copolyester resin film precoated with resin composite, which is also one of the important factors in the present invention, should be maintained in the range of the melting point of said copolyester resin film +50~ C. If the temperature is above 1~39~9 the melting point + 50~ C, corrosion resistance becomes noticeably poor because the copolyester resin film is deteriorated by heating. The copolyester resin film used in the present invention cannot be easily recrystallized at the heating temperature required for curing the color printing ink or lacquer applied on the steel sheet, although a non-oriented amorphous copolyester resin layer is formed by heating. Therefore, the steel sheet according to the present invention maintains excellent corrosion resistance, even if it is heated at 160~ to 200~ C. If the lamination of the copolyester resin film precoated with resin composite to the surface treated steel sheet is carried out below the melting point of the copolyester resin film - 50~ C, the copolyester resin film is easily peeled off from the surface of the surface-treated steel sheet.
In the present invention, the method for heating the surface-treated steel sheet to which the copolyester resin film is laminated is not especially limited. However, from the standpoint of continuous and stable production of steel sheets according to the present invention at high speed, conduction heating by a roller heated by induction heating, induction heating and/or resistance heating which are used for reflowing electrotinplate in the production .. . ..
13~34~9 process of electrotinplate is suitable as the method for heating the surface-treated steel sheet to be laminated, because the surface-treated steel sheet can be rapidly heated and the temperature of the heated steel sheet can be easily controlled. Furthermore it is also preferable in the present invention that heating by roller heated by hot steam or heating in an electric oven be used as an auxiliary method for preheating~the surface-treated steel sheet to be laminated.
The surface temperature of laminating roller is also one of the important factors in the present invention.
The surface temperature of the laminating roller should be controlled in the range of 80~ to 180~ C. At below 80~ C, an air bubble occurs easily between the copolyester resin film precoated with resin composite and the surface-treated steel sheet during the lamination of the copolyester resin film to the steel sheet. On the other hand, at a temperature of the laminating rolls above 180~ C, production of the steel sheet according to the present invention at high speed is prevented, because the copolyester resin film readily adheres to the laminating roller. As the laminating roller, the use of a chromium plated roller, a ceramic roller or a rubber roller is preferable in the present invention. In the use of a rubber roller, a roller made ~3'~9~59 with silicon rubber or fluorine rubber, which is an excellent in heat conductivity and heat resistance, should be selected.
The present invention is explained in further detail by reference to the following examples.
A cold rolled steel strip having a thickness of 0.21 mm and a width of 300 mm was electrolytically degreased in a solution of 70 g/liter of sodium hydroxide and then pickled in a solution of 100 g/liter of sulfuric acid. The steel strip, after being rinsed with water, was cathodically treated by using an electrolyte containing 60 g/liter of CrO3 and 3 g/liter of NaF in water under 20 A/dm of cathodic current density at an electrolyte temperature of 50~ C. The thus treated steel strip was rinsed with hot water having a temperature of 80~ C and dried.
After that, a biaxially oriented copolyester resin film produced from a condensation of ethylene glycol and polycarboxylic acid consisting of 80 mole % of terephthalic _ .
13~9 459 a~ia and 20 mole % of isophthalic acid having a thickness of 25 um, softening temperature of 176~ C, melting temperature of 215~ C, and elongation at break of 330%, which was precoated with resin composite by the following condition (A), was continuously laminated on both surfaces of thus treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated material:
Epoxy resin having an epoxy equivalent of 3000 -80 parts Resol product from paracresol - 20 parts Drying temperature of precoated resin composite: 100~ C
Drying time of precoated resin composite: 10 seconds Amount of resin composite after drying at 100~ C:
0.2 g/m (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 185~ C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max. 154~ C
Method for cooling the laminate: Gradual cooling The same steel strip pretreated as in Example 1 was cathodically treated in an electrolyte containing 80 g/liter of CrO3, 0.8 g/liter of HBF4 and 0.5 g/liter of H2SO4 in water under 50 A/dm2 of cathodic current density at an electrolyte temperature of 60~ C. The thus treated steel sheet was rinsed with hot water having a temperature of 80~ C and dried.
After that, a biaxially oriented copolyester resin film produced from a condensation polymerization of ethylene glycol and polycarboxylic acid consisting of 85 mole % of terephthalic acid and 15 mole % of isophthalic acid having a thickness of 25 ~m, softening temperature of 192~ C, melting temperature of 239~ C and elongation at break of 210%, which had been precoated with resin composite by the following condition (A), was continuously laminated on both sides of the thus treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 3000 -70 parts Resol product from paracresol - 30 parts Drying temperature of precoated resin composite: 120~ C
Drying time of precoated resin composite: 7 seconds Amount of resin composite after drying at 120~ C:
0.6 g/m (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 219 ~C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max. 176~ C
Method for cooling the laminate: Gradual cooling 1~39~S9 The same steel strip pretreated as in Example 1 was electroplated with 1.7 g/m2 of tin by using an electrolyte containing 10 g/liter of SnSO4, 20 g/liter of phenolsulfonic acid (60% aqueous solution) and 5 g/liter of ethoxylated ~-naphthol sulfonic acid in water under 5 A/dm of cathodic current density at an electrolyte temperature of 40~ C. After rinsing with water, the tin plated steel sheet was cathodically treated by using an electrolyte containing 30 g/liter of CrO3 and 0.3 g/liter of H2SO4 in water under 50 A/dm of cathodic current density at an electrolyte temperature of 50~ C. The thus treated electrotinplated was rinsed with hot water having a temperature of 80~ C and dried.
After that, a biaxially oriented copolyester resin film produced from a condensation polymerization of ethylene glycol and polycarboxylic acid consisting of 90 mole ~ of terephthalic acid and 10 mole ~ of isophthalic acid having a thickness of 16 ~m, softening temperature of 212~ C, melting temperature of 241~ C and elongation at break of 172%, which had been precoated with resin composite by the following condition (A), was continuously laminated on both sides of 13~g4~9 the thus treated steel strip under the followi..~- condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 2500 -70 parts Polyamide resin (Trade name: Versamide 115) - 30 parts Drying temperature of precoated resin composite: 80~ C
Drying time of precoated resin composite: 15 seconds Amount of resin composite after drying at 80~ C: 1.5 g/m2 (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 255~ C
Material of laminating roller: Fluorine rubber Surface temperature of laminating roller: Max. 128 ~ C
Method for cooling the laminate: Gradual cooling 133g4~9 The same steel strip pretreated as in Example 1 was electroplated with 2.8. g/m2 of tin by using an electrolyte containing 80 g/liter of SnSO4, 60 g/liter of phenolsulfonic acid (60% aqueous solution) and 5 g/liter of ethoxylated ~-naphthol sulfonic acid in water under 15 A/dm2 of cathodic current density at an electrolyte temperature of 45~ C. After reflowing of tin and rinsing with water, the tin plated steel sheet was treated by immersion into 30 g/liter of sodium dichromate solution for 3 seconds at a temperature of 45~ C. The thus treated electrotinplate strip was rinsed with water and dried.
After that, the same biaxially oriented copolyester resin film as in Example 1 precoated with resin composite by the following condition (A) was laminated on the thus treated steel strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film Composition of precoated resin composite;
Copolyester resin (Trade name Vylon 200) -75 parts Urethane resin (Trade name Coronate L) - 25 parts Drying temperature of precoated resin composite: 80~C
Drying time of precoated resin composite: 20 seconds Amount of resin composite after drying at 80~C: 2.0 g/m2 (B) Conditions for lamination of coPolyester resin film precoated bY under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 215~C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max. 165~C
Method for cooling the laminate: Gradual cooling . 29-133~ iS9 The same steel strip pretreated as in Example 1 was electroplated with metallic chromium by using a Sargent bath containing 250 g/liter of CrO3 and 2.5 g/liter of H2SO4 in water under 30 A/dm2 of cathodic current density at a bath temperature of 55~ C. After rinsing with water, a chromium plated steel strip was cathodically treated by using an electrolyte containing 30 g/liter of CrO3 and 1.2 g/liter of NH4F in water under 20 A/dm of cathodic current density at an electrolyte temperature of 40~ C and then rinsed with hot water having a temperature of 80~ C and dried.
After that, a copolyester resin film produced from a condensation polymerization of ethylene glycol and carboxylic acid consisting of 96 mole % of terephthalic acid and 4 mole % of isophthalic acid having a thickness of 30 ~m, softening temperature of 235~ C, melting temperature of 250~ C and elongation at break of 155~ precoated with resin composite by the following condition (A) was continuously laminated on both surface of the treated aluminum strip under the following condition (B).
(A) Conditions for precoating of resin composite to the copolyester resin film 13394~9 Composition of precoated resin composite:
Epoxy resin having an epoxy equivalent of 3000 -80 parts Urea resin - 20 parts Drying temperature of precoated resin composite: 135~ C
Drying time of precoated resin composite: 10 seconds Amount of resin composite after drying at 135~ C:
1.5 g/m (B) Conditions for lamination of copolyester resin film precoated by under condition (A) Method for heating the treated steel strip:
Roller heated by induction heating Temperature of the treated steel strip just before lamination: 245~ C
Material of laminating roller- Silicon rubber Surface temperature of laminating roller: Max. 160~ C
Method for cooling the laminate: Rapid cooling 13394~9 A biaxially oriented polyethylene terephthalate film (Trademark Lumirror made by Toray Co. Ltd.) having a thickness of 25 ~m, softening temperature of 240~C, melting temperature of 257~C and elongation at break of 125% precoated with the same resin composite as shown in condition (A) of Example 1 was continuously laminated on both surfaces of the same treated steel strip as in Example 1 under the same condition (B) as in Example 1.
A biaxially oriented polyethylene terephthalate film (Tradename Enblett made by Unichika Co. Ltd.) having a thickness of 25 ~m, softening temperature of 238~C, melting temperature of 257~C and elongation at break of 138~ precoated with the same resin composite as shown in condition (A) of Example 2 was continuously laminated on both sides of the same treated steel strip as in Example 2 under condition (B) of Example 2.
A non-oriented polyethylene terephthalate film (Trademark Tetoron made by Teijin Co. Ltd.) having a 1339~59 thickness of 30 ~m, softening temperature of 242~ C, melting temperature of 254~ C and elongation at break of 110%
precoated with the same resin composite as shown in condition (A) of Example 3 was continuously laminated on both surface of the same treated electrotinplate strip as in Example 3 under condition (B) of Example 3.
The same copolyester resin film as in Example 2 precoated with the same resin composite as shown in the condition (A) of Example 2 was continuously laminated on both sides of the same treated steel strip as in Example 1 under the same condition (B) of Example 2, except for the temperature of the treated steel strip just before the lamination.
Temperature of the treated steel strip just before the lamination: 175~ C
The same polyethylene terephthalate film as in Comparative Example 1 was laminated on the same treated steel strip as in Example 5 without the resin composite adhesive under the following conditions:
Conditions for the lamination of polyethylene terephthalate film Temperature of the treated steel strip just before the lamination: 280~ C
Material of laminating roller: Silicon rubber Surface temperature of laminating roller: Max.
105~ C
Method for cooling the laminate: Rapid cooling The adhesion of polyester resin film in the resultant steel sheet was evaluated by the following testing methods, after the measurement of the coating weight on the resultant steel sheet by the X-ray fluorescent method. The results are shown in the Table.
(1) Degree of cracks in polyester resin film after forming The resultant steel sheet was cut to a circular blank having a diameter of 140 mm by a punch press after heating for 10 minutes at 190~ C. The blank was deeply drawn to form a cup at a drawing ratio of 2.55. After that, 1% of sodium chloride solution was filled in the drawn cup.
The degree of cracks of polyester resin film in the formed part was evaluated by a current value flowing between an anode of the steel exposed through cracks of polyester resin film in said drawn cup and a cathode of stainless steel rod inserted in said drawn cup at constant voltage of 6.3 volts.
(2) Stretch formability of polyester resin film The resultant steel sheet was cut to a size of 10 cm (width~ x 30 cm (length) after reheating for 10 minutes at 190~ C. After that, the sample was stretched by cold rolling in the transverse direction to the cold rolling direction of steel strip after coating palm oil on both sides of the sample. The limiting reduction ratio in which cracks in polyester resin film on the sample is observed was determined by the following equation after cold rolling of several times.
R (%) = x 100 to where R = limiting reduction ratio (%) to = thickness of the sample before cold rolling (mm) t = thickness of the sample after cold rolling (mm) ~ ~ o U~ o ~, . c~J _ ~ o ~In a O 1~ L L c~
~ --~ o ~ ~ C~
O ~ ~ ~ ~C'~ ~ ~ ~ ~_ ~ e O O r-- --I L
~ O ~~ O ~ ~ O ~ O~,~
e x r-O
O t~~ -- ~ L. C'~C'~ ~- 0 e x x O ~ ~ L~
~ ~ o u~
. ~ ~ u~ o t - u~ . o L~
e x O ~
o ~ ~ ~ ~C~ O
u~ o a~ In In ~ O U~ O m_I o X O ~ ~O~ ~
L. ~ ~C~J~ O ~a o o e O ~ -. O ~ ~D ~ O ~._ X a~ 7 0 ~ e L. _ C~ ~ O
,C a~
~~ o o t~
X t-- o 'o' O X
~~) o -1 e 0 ~ u~ ~ cn o o X o ~ N 0~ ~ e ~ ~ ~ o e o --~ o ~ -- u~ o o ~~ ~:
x o - ~~ ~' - ~ ~
0~ o_ ~ _ e ~ ~ ~ ~
~ ~ 1~ O
~_. L. E u~ c ~ ~ -- ~~ ~ tJ~ t~
O C~ e ~~
a~ ~ .C ,C O ~ ~ ~ _ al ~ E
e I ~ ~
o ~ _ L- O
V
V .C V C~
~ v ~ o c _ ~ O ~ e ~ ~ ~ o ~ ._, ~
R (%) = x 100 to where R = limiting reduction ratio (%) to = thickness of the sample before cold rolling (mm) t = thickness of the sample after cold rolling (mm) ~ ~ o U~ o ~, . c~J _ ~ o ~In a O 1~ L L c~
~ --~ o ~ ~ C~
O ~ ~ ~ ~C'~ ~ ~ ~ ~_ ~ e O O r-- --I L
~ O ~~ O ~ ~ O ~ O~,~
e x r-O
O t~~ -- ~ L. C'~C'~ ~- 0 e x x O ~ ~ L~
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. ~ ~ u~ o t - u~ . o L~
e x O ~
o ~ ~ ~ ~C~ O
u~ o a~ In In ~ O U~ O m_I o X O ~ ~O~ ~
L. ~ ~C~J~ O ~a o o e O ~ -. O ~ ~D ~ O ~._ X a~ 7 0 ~ e L. _ C~ ~ O
,C a~
~~ o o t~
X t-- o 'o' O X
~~) o -1 e 0 ~ u~ ~ cn o o X o ~ N 0~ ~ e ~ ~ ~ o e o --~ o ~ -- u~ o o ~~ ~:
x o - ~~ ~' - ~ ~
0~ o_ ~ _ e ~ ~ ~ ~
~ ~ 1~ O
~_. L. E u~ c ~ ~ -- ~~ ~ tJ~ t~
O C~ e ~~
a~ ~ .C ,C O ~ ~ ~ _ al ~ E
e I ~ ~
o ~ _ L- O
V
V .C V C~
~ v ~ o c _ ~ O ~ e ~ ~ ~ o ~ ._, ~
Claims (11)
1. A method for producing a surface-treated steel sheet laminated with a copolyester film onto a film which comprises the steps of (1) producing a copolyester resin film from a copolyester resin consisting essentially of 75 to 99 mole % of polyethylene terephthalate and 1 to 25 mole % of a polyester resin produced by the esterification of at least one saturated polycarboxylic acid and at least one saturated polyalcohol, (2) precoating said copolyester resin film on one side with a resin composite containing in its molecular structure at least one radical selected from the group consisting of an epoxy radical, hydroxyl, an amide radical, an ester radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical, (3) heating a surface-treated steel sheet to the temperature of the melting point of said copolyester film ~
50° C, and (4) laminating said copolyester resin film onto both sides of said steel sheet wherein the side of said copolyester resin film precoated with said resin composite contacts said steel sheet.
50° C, and (4) laminating said copolyester resin film onto both sides of said steel sheet wherein the side of said copolyester resin film precoated with said resin composite contacts said steel sheet.
2. The method according to claim 1 wherein the polyester resin is produced by the esterification of at least one saturated polycarboxylic acid selected from the group consisting of phthalic acid, isophthalic acid, terephthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, diphenylcarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid and trimellitic acid anhydride with at least one saturated polyalcohol selected from the group consisting of ethylene glycol, 1,4-butanediol, 1,5-pentane diol, 1,6-hexanediol, propylene glycol, polytetramethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexane dimethanol, trimethylol propane and pentaerythritol.
3. The method according to claim 1 wherein the copolyester resin film has a thickness of 5 to 50 um, a softening temperature of 170° to 235° C, a melting temperature of 210° to 250° C and an elongation at break of 150 to 400%.
4. The method according to claim 3 wherein said copolyester resin film has a biaxially oriented structure.
5. The method according to claim 1 wherein the resin composite precoated on the copolyester resin film is dried at a temperature of 60° to 150° C for 5 to 30 seconds.
6. The method according to claim 5 wherein the amount of said resin composite precoated on said copolyester resin film is 0.1 to 5.0 g/m2 after drying.
7. The method according to claim 1 wherein said surface treated steel sheet is a sheet or strip of steel or electrotinplate covered with double layer consisting of an upper layer of hydrated chromium oxide and a lower layer of metallic chromium or electrotinplate covered with hydrated chromium oxide.
8. The method according to claim 6 wherein the tin coating weight in said electrotinplate is 0.5 to 5.6 g/m 2.
9. The method according to claim 7 wherein the amount of hydrated chromium oxide is 5 to 25 mg/m2 as chromium and the amount of metallic chromium is 10 to 150 mg/m2 in said double layers, respectively.
10. The method according to claim 6 wherein the amount of hydrated chromium oxide on said electrotinplate is 1 to 4 mg/m2 as chromium.
11. The method according to claim 1 wherein the lamination is carried out by using a roller having a surface temperature of 80° to 180° C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000606025A CA1339459C (en) | 1989-07-18 | 1989-07-18 | Method for producing steel sheet laminated with a polyester resin film |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000606025A CA1339459C (en) | 1989-07-18 | 1989-07-18 | Method for producing steel sheet laminated with a polyester resin film |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1339459C true CA1339459C (en) | 1997-09-16 |
Family
ID=4140365
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000606025A Expired - Lifetime CA1339459C (en) | 1989-07-18 | 1989-07-18 | Method for producing steel sheet laminated with a polyester resin film |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1339459C (en) |
-
1989
- 1989-07-18 CA CA000606025A patent/CA1339459C/en not_active Expired - Lifetime
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