FR2653703A1 - METALLIC SHEET LAMINATE WITH COPOLYESTER RESIN FILM AND PROCESS FOR PRODUCING THE SAME - Google Patents

Abstract

Disclosed is the production of a metal foil laminated with a film of copolyester resin. It consists in laminating a film of biaxially oriented copolyester resin to one side or both sides of a surface-treated metal foil, which has been heated to the melting point of said film + -50 ° C, just before laminating this film. This film has been coated beforehand with a composite resin containing at least one radical, such as an epoxy or hydroxyl radical. The face of said film coated beforehand with the composite resin is in contact with the metal foil surface treated. Application: Production of a metal foil laminated with a film of copolyester resin, exhibiting excellent workability.

Description

The present invention relates to a metal sheet laminated with

  a copolyester resin film having excellent workability and its production process. The method comprises laminating a biaxially oriented copolyester resin film having specified characteristics pre-coated with a small amount of a composite resin, the composite resin containing at least one radical such as an epoxy radical or a radical hydroxyl, on one of the faces or

  two sides of a metal sheet which has been treated

  surface, which has been heated to the melting point of the

  copolyester resin film 50 C just before stratifica-

  of the copolyester resin film. The face of the copolyester resin film previously coated with the composite resin is in contact with the treated metal sheet

surface.

  Currently, metal foils, such as galvanic tinplate, tin-free steel and aluminum foil, are widely used as raw materials for metal cans after having been coated, at least once, with a varnish. This coating of varnish is disadvantageous from the point of view of energy, a long time being required for the crosslinking of the varnish and large volumes of solvent evacuated during the process of crosslinking the varnish to be burned in another oven to avoid a

air pollution.

  Recently, the lamination of a thermoplastic resin film on a metal foil has been attempted to avoid these problems. See, for example, Japanese Patent Application Laid-Open No. Sho 53-141,786, Japanese Patent Publication No. Sho 60-47,103, Japanese Patent Applications Laid-Open Nos. Sho 60168 643, Sho 61-20 736

and Sho 61-149 341.

  The Japanese patent application being inspected

  N Sho 53-141 786 discloses a can produced from a metal foil coated with a polyolefin resin film using an adhesive containing a carboxyl-modified polyolefin resin. However, this metal foil laminated with a polyolefin film can not be used as a raw material for the production of the canisters, since the conditioned contents can cause corrosion of the metal foil due to the poor permeability resistance of the resin film. laminated polyolefin Further, even if the metal foil laminated with a polyolefinic resin film is used as a raw material for the production of metal cans, metal cans having a satisfactory appearance can not be obtained because the laminated polyolefinic resin film is melted during the course of the process. heating at temperatures of 160 to 200 C. These temperatures are required for the crosslinking of the ink

  of printing or coating varnish.

  Japanese Patent Publication No. Sho 60-47103 relates to a method of laminating a crystalline polyester resin film to a metal sheet by heating the sheet to a temperature above the melting point of said polyester resin film, and then immediate tempering of the laminate. In this patent, the crystalline polyester film is sufficiently fixed to the metal foil by a resin film

  amorphous and undirected polyester which is formed

  facing the crystalline polyester film and the metal sheet as a result of the heating step. However, when the metal sheet laminated with a polyester film is reheated to a temperature of 160 to C for a time of 10 to 30 minutes, as is required for the crosslinking of the printing ink or the applied varnish on the other side of the metal foil before shaping, the adhesion of the polyester resin film deteriorates. This is due to the recrystallization, by heating, of the non-oriented amorphous polyester resin layer. As a result, the resistance to corrosion is

also deteriorates.

  The Japanese patent application being inspected

  N Sho 60-168 643 relates to a sheet of steel laminated with a thermoplastic resin film

  for a drawn-stamped canister

  wise (box D + I), as well as its production process.

  In said patent, the face of the steel sheet to be used

  for the inside of the metal box D + I is strati-

  It is bonded with a film of a thermoplastic resin, such as polyethylene terephthalate, in the absence of any adhesive. The face of the steel sheet to be used for the outside of the metal box D + I is plated with a ductile metal, such as tin, nickel

or aluminum.

  The steel sheet conforming to said patent has the same defects as those of the sheets of the Japanese patent published under N Sho 60-47 103, that is to say that as a result of the new heating at a temperature of 200 C for 10 to 30 minutes required for the crosslinking of the printing ink and varnish on the outside of the D + I can, the adhesion of the

  polyester resin film deteriorates noticeably.

  Japanese Patent Application Laid-open Nos. Sho 6120 736 and Sho 61-149 341 relate to the lamination of a previously coated biaxially oriented polyester resin film to a metal foil heated to a temperature below the point melting said polyester resin film. The film is pre-coated with a special adhesive, such

  an epoxy resin containing a crosslinking agent.

  In said patents, an amorphous and non-oriented polyester resin layer, as disclosed in Japanese Patent Publication No. 60-47103 and Japanese Patent Application Laid-open No. Sho 60-168,643, No. is not formed. This is due to the fact that the biaxially oriented polyester resin film is laminated to the metal foil at a temperature below the melting point of said polyester resin film. As a result, the corrosion resistance and adhesion of the polyester resin film to the metal sheet does not deteriorate, even if the sheet is heated again at temperatures of 160 to C for the time required for the crosslinking of printing ink and varnish. However, if said laminated metal sheet is used for some applications, requiring greater workability, as in the case of a deep drawn can, having a draw ratio greater than 2.0, many cracks occur in

the polyester resin film.

  Recently, the use of a polyester resin film having specified characteristics has been proposed to improve the workability of the laminated metal sheet with a polyester resin film (Japanese Patent Application Laid-Open) N Sho 64-22,530 and Japanese Patent Application N Sho 63-75,837). However, when these metal sheets laminated with a polyester resin film are formed in processes such as deep drawing or high speed bending, many cracks occur or the laminated polyester resin film shows peeling in the area. shaping

said polyester resin film.

  Accordingly, the first object of the present invention is to convert a surface-treated metal sheet coated with a copolyester resin film having excellent corrosion resistance into a shaped part under severe conditions. , such as a deep drawn can, a stamped and partially drawn can, and a deep drawn and drawn can, at a draw ratio greater than 2.0, even after a new heating to cause the crosslinking of a colored printing ink or a varnish constituting the

siding.

  The second object of the present invention is to provide a high speed continuous laminating process of a copolyester resin film on one or both sides of the surface-treated metal sheet. The first object of the present invention can be achieved by forming a film consisting of an outer layer and an inner layer on the surface of a metal layer. The outer layer consists of a copolyester resin film having specific characteristics and is produced by stretching and thermosetting a copolyester resin film comprising 99 mole percent polyethylene terephthalate and 25 mole percent polyester resin. produced by esterification of at least one polycarboxylic acid saturated with at least one saturated polyhydric alcohol. The inner layer comprises a thin composite resin containing in its molecular structure at least one radical, such as an epoxy radical or a hydroxyl radical. The composite layer is present on one or both sides of the treated metal sheet

surface.

  The second object of the present invention can be achieved by high speed continuous lamination of the copolyester resin film pre-coated with the composite resin, on one or both sides of a surface-treated metal foil which has been heated to the point of melting 50 C of the copolyester resin film, the previously coated surface of the copolyester resin film being in contact with the metal sheet. The specific characteristics mentioned above are: (1) the melting temperature; (2) the refractive index as a function of the thickness of the film; (3) the refractive index as a function of the planar dimensions of the film; and (4) the amount and average particle diameter of the added lubricant,

when a lubricant is added.

  The sheet laminated with a copolyester resin film having excellent workability in accordance with the present invention can be obtained by

  the adjustment of all these factors to the ranges

  timings, as described below.

  The metal sheet laminated with a film

  copolyester resin in accordance with the present invention.

  It can be used in applications in which excellent corrosion resistance is required after severe shaping. Examples are deep-drawn metal cans, stamped and partially drawn metal cans, stamped and drawn high-pitched metal cans, which have been subjected to a high draw ratio, and molded metal cans. upper parts of the metal boxes to which a tab has been fixed for easy opening. In this application, the metal cans are brought into contact with hot water or hot steam for sterilization after conditioning of foods, such as fruit juices, coffee drinks, meat and meat. fish. For example, fruit juices are immediately packaged in the canister after sterilization, at a temperature of 90 to 100 C. Coffee beverages, meat and fish are sterilized by hot steam at a higher temperature at 100 C in an autoclave after conditioning in the can. In addition, the metal sheet according to the present invention can be used to

  screw caps and capsules ..

  In these applications, a coating with a colored printing ink or a varnish on one side or the

  two sides of the metal foil used for the ex-

  The inside or inside of these metal boxes is often done before or after shaping. In these cases, the laminated copolyester resin film of the present invention does not exhibit peeling in the severely shaped areas, even after further heating for the crosslinking of the colored printing ink or varnish and subsequent treatment with hot water or

hot steam.

  Other features and benefits of the

  present invention will emerge from the detailed description

  which follows, made with reference to the accompanying drawing in which: The single figure shows graphically the relationship between the refractive index of a given copolymer and the degree of elongation possible before rupture of the copolymer film. The present invention relates to a laminated metal sheet, the metal sheet being laminated with a copolyester resin film having specified characteristics, comprising 75 to 99 mole% polyethylene terephthalate and 25 to 1 mole% polyester resin produced by esterification of polyethylene terephthalate. at least one saturated polycarboxylic acid with at least one saturated polyhydric alcohol selected from the following polycarboxylic acids and polyalcohols. The saturated polycarboxylic acids are selected from phthalic acid, isophthalic acid, terephthalic acid, succinic acid, azelaic acid, adipic acid, sebacic acid, diphenylcarboxylic acid, acid, and the like. 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid and anhydride

of trimellitic acid.

  The saturated polyalcohols are chosen from ethylene glycol, 1,4-butanediol and 1,5-pentanediol.

  1,6-hexanediol, propylene glycol, polytetramethyl

  ethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexane dimethanol,

  trimethylolpropane and pentaerythritol.

  In addition, in the present invention, the use

  A biaxially oriented copolyester resin film having all of the following factors within a certain optimum range is required from the point of view of corrosion resistance after severe shaping. These factors are: (1) the melting temperature; (2) the refractive index as a function of the thickness of the film; (3) the refractive index as a function of the planar dimensions of the film; and (4) the amount and average particle diameter of the lubricant added, when a lubricant is added thereto. In certain cases, additives such as antioxidants, stabilizer, pigments, antistatic agents and corrosion inhibitors are added during the implementation of the production process of the product.

copolyester resin film.

  The melting temperature of the copolyester resin film used is defined as the temperature at which the maximum endothermic reaction is achieved at a heating rate of 10 C / minute in the differential scanning calorimeter (SS10) produced by Seiko Denski Kogyo Co. It is preferred that a copolyester resin film having a melting temperature of about 210 to about 250 ° C be used. The use of a resin copolyester film having a melting temperature greater than 250 ° C is not suitable in the present invention since these rigid copolyester resin films have poor workability. A copolyester resin film having a melting temperature of less than 210 ° C is not practical, its mechanical properties deteriorating during the new heating required for the crosslinking of the colored printing ink or the varnish applied to the outside or

  inside the canister.

  The refractive indices, the second and third factors mentioned, are measured using a polarized monochromatic light in a refractometer

from Abbe to 25 C.

  In the copolyester resin film, orientated

  In the biaxial approach used in the present invention, the refractive indices in the thickness direction and all directions in the plane must be in the range of from about 1, 5000 to about 1.5500, and range of about 1.6000 to

  about 1.6600. These refractive indices vary slightly

  according to the conditions used for stratification

  copolyester resin film to the metal foil, as well as conditions of the new heating necessary for crosslinking the colored printing ink or varnish applied to the laminated metal sheet with a copolyester resin film. The degree of variation of the refractive index of said copolyester resin film also depends on the draw conditions and the thermosetting conditions for the production of a thin and wide copolyester resin film. For example, if the laminating temperature of the copolyester resin film is higher

  high, the refractive index of the copolyes resin film

  laminate is lower. The refractive index of the copolyester resin film produced at a lower draw and thermoset at a higher temperature is lower. On the other hand, the refractive index obtained at a higher draw and a thermoset at a lower

temperature is increased.

  As described above, the refractive index of the copolyester resin film depends on the conditions of production of the copolyester resin film, the lamination conditions and the conditions of the new heating. In the present invention, it is necessary that the refractive indices, in the direction of thickness and in all directions in the plane of the copolyester resin film, be adjusted respectively in the range of about 1.5000 to about 1.5500 and in the range of about 1.6000 to about 1.6600, after

  stratification to the surface-treated metal sheet.

  It is preferred that the index of refraction in all directions in the plane of the copolyester resin film be maintained in the range of 1.6100 to about 1.6500 after lamination to obtain a metal sheet laminated with a film of copolyester resin exhibiting

  excellent workability.

  Copolyester resin films having refractive indices beyond the optimum range described above are not practical for certain applications in which severe processability is required. Many cracks may occur in said copolyester resin film or the laminated copolyester resin film may exhibit chipping in the severely shaped area as a result of

  deterioration of workability.

  The Japanese patent application being inspected

  No. Sho 64-22,530 and Japanese Patent Application Laid-Open No. Sho 63-75,837 disclose a metal sheet laminated with a polyester resin film having excellent workability. The first patent application shows that a polyester resin film having excellent workability is obtained by adjusting the coefficient

  planar orientation in the range of 0.130 to 0.160.

  This planar orientation coefficient, which is defined as the degree of the planar coefficient of the polyester resin film, is determined using a refractometer and is represented by the following equation:

A = (B + C) / 2-D

  wherein A represents the planar orientation coefficient of the polyester resin film, B represents the refractive index, in the length direction, of the polyester resin film, C represents the refractive index, in the direction of the width, of the polyester resin film, and D represents the refractive index, in the

  direction of thickness, polyester resin film.

  Typically, a thin, broad film of polyester resin is continuously produced by stretching in the length and width directions of the extruded thick polyester resin film. As a result, the characteristics at the center of the broad film of polyester resin are different from those near the edges, in particular the mechanical property and the coefficient of thermal expansion in the oblique direction at the edges of the

wide film.

  Even though the planar orientation coefficient at the center of the broad film of polyester resin is identical to that at the edges, the characteristics in the center are different from those at the edges because the planar orientation coefficient calculated by the equation described above is defined without taking into consideration the refractive index in the oblique direction of the polyester resin film. The last patent application shows

  that a polyester resin film having an excellent

  is obtained by adjusting the melting temperature, the softening temperature and the elongation at break respectively in the

  intervals of 210 to 250 C, 175 to 235 C and 150 to 400%.

  Recently, it has been found that the elongation at break is related to the index of refraction in the plane of the copolyester resin film, as shown in FIG. In particular, the elongation at break decreases if the index of refraction in the plane falls below a value less than 1.6100. Even with a refractive index of less than 1.6100 in the plane, the copolyester resin film to be laminated to the metal sheet has an elongation at break greater than 150% and excellent workability. The corrosion resistance of the metal foil covered by this copolyester resin film becomes low in the areas which have been shaped under severe conditions because the amorphous and non-oriented parts in this resin film

  copolyester increase if the refractive index decreases.

  In addition, the progressive decrease in elongation at break when the refractive index is greater than 1.6200 depends on the increase in the degree of orientation.

  in the copolyester resin film.

  Even if a copolyester resin film having an elongation at break greater than 150% with a refractive index of 1.6700 in the plane is laminated on the metal sheet, a metal sheet laminated with a copolyester resin film having excellent ability shaping is not always obtained. This is because the elongation at break of said film of

  copolyester resin decreases after lamination.

  As a result, a metal sheet laminated with a copolyester resin film having excellent workability is not always obtained by using the copolyester resin film according to Japanese Patent Application No. Sho 63-75,837. , the characteristics of the copolyester resin film variant

  following the stratification and annealing conditions.

  This problem has been solved by the present invention by adjusting the characteristics of the film of

  copolyester resin used, before and after lamination.

  In accordance with the present invention, in a metal sheet laminated with a copolyester resin film, where severe processability is required, it is essential that the mechanical property, the thermal property and the chemical property of the resin film copolyester used be uniform in

the whole of this film.

  Accordingly, the copolyester resin film used in the present invention is characterized by the restriction in the range of refractive indices in the thickness direction and all directions in the direction of thickness.

  plan, as described above.

  In order to produce a copolyester resin film having excellent workability in all positions of the copolyester resin broad film, it is necessary that the extruded copolyester resin film be thick.

  is stretched biaxially at a lower, comparative rate

  to that obtained with a conventional film of ethylene terephthalate. For example, it is desirable to stretch the extruded copolyester resin film at a rate of 2.7 to 3.7 times in the length direction and at a rate of about 3.0 to 3.8 times in the direction of the width, and that the temperature is set in the range of approximately

at about 230 C.

  In addition, the amount and the particle diameter of a lubricant in the copolyester resin are

  important factors when a lubricant is used.

  At least one lubricant selected from silica (SiO2), alumina, titanium dioxide, calcium carbonate, barium sulfate and an organic silicon compound is usually added during the process of producing the copolyester resin film and it is desirable to use a lubricant having an average particle size of less than 2.5 μm, preferably 0.5 to 2.0 μm. It is impractical to use a lubricant having a particle diameter greater than 2.5 Dm, since this lubricant acts as a starting point for the development of many cracks in the laminated copolyester resin film during severe shaping. In general, the amount of lubricant added to the copolyester resin film is determined by the windability of the copolyester resin film produced and the workability of the laminated metal sheet with the copolyester resin film. If the lubricant is not added to the copolyester resin film, it is not possible to uniformly wind the copolyester resin film produced. Usually, the addition of a lubricant having a large particle diameter is effective in small amounts. On the other hand, a lubricant having a small particle diameter should be added in a larger amount. For example, silica having an average particle diameter of 2.3 gm is effective by adding 0.001 to 0.05 wt%, based on the weight of the copolyester resin. In the case of a silica having an average particle diameter of 0.3 Sm, the addition of 0.05 to 5% by weight, based on the weight of

  the copolyester resin is necessary.

  The copolyester resin films for use outside of metal cans, containing a colored inorganic pigment such as titanium dioxide (TiO 2 powder), instead of coating with a white enamel on the metal sheet laminated with a Colorless copolyester resin film, then cross-linking of the white enamel applied. It is desirable that the amount of color pigment added to the copolyester resin film be in the range of 2 to 20% by weight, based on the weight of the copolyester resin. If the amount of colored pigment is less than 2% by weight, one aspect

  satisfactory is not obtained. The copolyes resin film

  It is not suitable for the present invention to contain a colored pigment in an amount of greater than 20% by weight, the processability of said film becoming substantially poor. Measurement of the refractive indices of the copolyester resin film containing a colored pigment is not possible because the polarized monochromatic light used for the measurement does not pass through the pigmented film. Accordingly, it is necessary to produce the copolyester resin film containing a colored pigment under the same conditions as those encountered for the colorless copolyester resin film having the refractive indices.

described above.

  The thickness of the copolyester resin film used in the present invention should be in the range of 5 to 50 μm, preferably 10 to 30 μm. If the thickness of the copolyester resin film used is less than 5 gm, the excellent corrosion resistance after severe shaping of the laminated metal sheet with the copolyester resin film is not obtained and continuous lamination of a film of thin copolyester resin to the treated metal sheet

  surface becomes clearly difficult. In addition, the use

  of the copolyester resin film having a thickness greater than 50 μm is not suitable from the point of view

  for stratification on a metal foil

  only surface treated because the copolyester resin film

  used for the present invention is expensive, compared with

  extensively with widely used epoxy-phenolic varnishes

  in the can-metal industry.

  One side of the chosen copolyester resin film

  according to the different characteristics described above.

  above is precoated with 0.1 to 5.0 g / m 2 of a composite resin containing at least one radical chosen from

  the group comprising an epoxy group, a hydroxyl group or

  the, an amide radical, an ester radical, a carboxyl radical, a urethane radical, an acryl radical and an amino radical. A phenolic resin, a nylon resin, a polyester resin, a modified vinyl resin, a urethane resin, an acrylic resin and a resin derived from urea are examples of these composite resins. It is desirable that the composite resin be applied to one side of the copolyester resin film in such a uniform manner and in as thin a layer as possible. The reason for this is the gradual deterioration of the bond strength of the composite resin layer to the surface-treated metal sheet and the copolyester resin film with increasing thickness of the previously applied composite resin. However, it is very difficult to uniformly coat the copolyester resin film with the composite resin in amounts of less than 0.1 g / m 2. Further, when the amount of the composite resin is less than 0.1 g / m 2 or greater than 0 g / m 2, the bond strength of the composite resin layer to the surface-treated metal sheet and the resin film Copolyester becomes markedly poor in areas that have undergone severe shaping. It is preferred that the composite resin be diluted with a solvent and then applied by a roll coating process or a sputtering method to form a uniform and thin layer of composite resin on the copolyester resin film. The drying temperature of a solvent-diluted composite resin, which is applied to one side of the copolyester resin film, is 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 the solvent and the formed composite resin layer becomes sticky. When the drying temperature is above 150 ° C, the chemical reaction of the composite resin applied to the copolyester resin film is accelerated and the bond strength of the composite resin to the surface-treated metal sheet becomes significantly poor. It is preferred that the drying time of the composite resin solution applied to the copolyester resin film be in the range of 5 seconds at a temperature of 60-150 ° C. If the drying time is less than 5 seconds, the solvent is not sufficiently removed. On the other hand, drying times greater than 30 seconds result in productivity

poor.

  A solvent having a low boiling point is preferred for the dissolution of the composite resin, which solvent is easily removed by heating at a temperature of 60 to 150 C. The solvent is not subject to any other particular limitation. In some cases, a coloring matter, such as a colorant, may be added

  to the composite resin dissolved in the solvent.

  The surface-treated metal sheet should be selected from the group consisting of tin-free steel sheet having two layers consisting of an upper layer of chromium oxide hydrate and a lower layer of metallic chromium, a metal sheet of 'tinning

  galvanic layer covered by the double layer described above.

  a galvanic tin plating sheet coated with hydrated chromium oxide and an aluminum foil treated in a solution containing a chromate, a phosphate or a zirconium salt which is usually used for the treatment of aluminum canisters stretched and stamped, the metal foil of the present invention being intended to be used for the production of cans. The optimum range of hydrated chromium oxide and metallic chromium in tin-free steel ranges from 5 to 25 mg / m 2 in the form of chromium.

  hydrate and from 10 to 150 mg / m2 as metallic chromium

  that, respectively. If the amount of chromium oxide hydrate is less than 5 mg / m 2 or greater than 25 mg / m 2 as chromium, the binding force to the copolyester resin film pre-coated with said composite resin becomes substantially poor in areas having has undergone severe shaping. Although the corrosion resistance in the machined portion becomes progressively lower with a decrease in the amount of chromium metal, even a tin-free steel containing about 10 mg / m 2 of metallic chromium can be used for some applications. when moderate resistance to corrosion is required. The galvanic tinplating sheet is to be cathodically treated in an electrolyte to produce a standard tin-free steel or to an immersion treatment in an aqueous solution containing about 30 g / l of dichromate

  sodium. By the implementation of said cathodic treatment

  that a double layer comprising a top layer of chromium oxide hydrate and a lower layer of metallic chromium is formed on the galvanic tinplating sheet. It is desirable that the amount of chromium oxide hydrate and metallic chromium on the galvanic tinplate is substantially the same as that in the tin-free steel sheet. However, it is preferable that the amount of chromium metal be in the range of 10 to 50 mg / m 2 in order to

  facilitate high speed production.

  In the case of immersion treatment of a galvanic tinplating sheet in a solution of sodium dichromate, a thin layer of chromium oxide hydrate, in a substantially constant amount (1 to 4 mg / m 2 in the form of

  of chromium) is formed on the galvanic tinplate.

  The thin hydrated chromium oxide on the galvanic tinplate is required for excellent adhesion of the copolyester resin film pre-coated with said composite resin in the severely shaped areas. If the galvanic tinplate is not treated by immersion in a solution of sodium dichromate,

  adhesion of the previously coated copolyester resin film

  This composite resin gradually becomes weaker during storage in a high humidity atmosphere. If the chromium oxide hydrate, in an amount greater than 5 mg / m2 in the form of chromium,

  is formed on the galvanic tinplate by means of a

  cathodic effect in a solution of sodium dichromate,

  adhesion of the previously coated copolyester resin film

  the composite resin becomes significantly poor in the areas that have undergone severe shaping. It is believed that the difference in adhesion of the copolyester resin film to a galvanic tinplate depends on the quality of the chromium oxide hydrate. Chromium oxide

  hydrate formed by cathodic treatment in an electrolytic

  te, for the production of a tin-free steel, has a better adhesion to the copolyester resin film

  previously coated with the composite resin, comparative-

  to that obtained by immersion treatment in

  a solution of sodium dichromate.

  It is desirable in the present invention that the amount of tin plated in the galvanic tinplate is in the range of 0.5 to 5.6 g / m 2. If the amount of plated tin is less than 0.5 g / m 2, the effect of plated tin on the corrosion resistance is hardly apparent, despite the implementation of the subsequent plating process. An amount

  tin content greater than 5.6 g / m2 is not economical.

  The temperature of the surface-treated metal sheet, heated just prior to lamination of the copolyester resin film pre-coated with the composite resin, is also an important factor. This temperature must be maintained at the melting point of said copolyester resin film 50 C. If the temperature is above the melting point +50 ° C., the corrosion resistance becomes markedly poor, the copolyester resin film deteriorating during subsequent heating.

after stratification.

  The copolyester resin film used in the present invention can not be easily recrystallized by the heating temperature required for the crosslinking of the colored printing ink or varnish applied to the

  sheet metal, although a layer of copolyes resin

  Unoriented amorphous ter is formed by heating. As a result, the metal foil retains excellent corrosion resistance, even if it is heated to a temperature of 160 to 200 C. If the lamination of the copolyester resin film pre-coated with the composite resin to the surface-treated metal foil is at a temperature below the melting temperature of the copolyester resin film -50 C, the copolyester resin film easily shows a flaking of the

  surface of the metal sheet treated on the surface.

  In the present invention, the method of heating the surface-treated metal sheet to which the copolyester resin film is laminated is not limited. However, from the point of view of a continuous and stable production of high speed metal foil, it is suitable to carry out heating by means of an inductively heated and / or resistive cylinder which is used for the reflow of the galvanic tinplating sheet in the galvanic tinplating sheet production process, as a method of heating the surface-treated metal sheet to be laminated. This is because the surface-treated metal sheet can be heated quickly and the temperature of the heated metal sheet can be easily adjusted. In addition it is also preferable to perform heating by cylinders heated by hot steam or to heat for preheating of the sheet

  surface-treated metal to be laminated.

  The surface temperature of the laminating cylinder is also an important factor. The surface temperature of the laminating cylinder should be in the range of 80 to 180 ° C. At a temperature below 80 ° C, air bubbles can easily occur between the copolyester resin film pre-coated with the composite resin. and the surface-treated metal sheet, when the copolyester resin film is laminated to the metal sheet. On the other hand, at temperatures above 180 C, the production of the high speed foil is hampered because the copolyester resin film readily adheres to the lamination roll. The use of a laminating cylinder of ceramic material or chromium-plated rubber is preferable. A cylinder made of silicone rubber or fluorinated rubber, which has a thermal conductivity and a heat resistance

excellent, must be chosen.

  Usually, the copolyester resin film is laminated to the surface-treated metal under the conditions described above, and then the metal foil

  laminated with the copolyester resin film is progressing

  or quickly cooled down. In some applications

  When more severe workability is required, it is preferable to subject the laminated metal sheet with a copolyester resin film to

  a -post-cooking at a temperature included in

  value ranging from -80 ° C melting point of the copolyester resin film for a time of 5 to 1000 seconds, to improve the workability of the laminated metal sheet with a copolyester resin film. Heating for crosslinking the colored printing ink or the lacquer applied to the laminated metal foil with a copolyester resin film, prior to shaping, is also effective for measuring the workability of the laminated metal foil with a film of copolyester resin. The heating performed for the crosslinking of the colored printing ink or lacquer applied to the laminated metal foil with a copolyester resin film, after shaping, is also effective to improve the workability of the laminated metal foil with a resin film

copolyester.

  It is considered that this effect depends on the relaxation of the residual voltage of the layered copolyester by the post-heating. When this post-heating is applied to the laminated metal foil with a copolyester resin film, prior to shaping, the laminated copolyester resin film does not exhibit peeling of the surface of the metal foil and cracks in the copolyester resin film laminate are practically

  none in areas that have undergone severe shaping.

  The present invention is explained in more detail with reference to the following examples. These examples

  do not limit the scope of the invention.

EXAMPLE 1

  A cold-rolled steel strip having a thickness of 0.21 mm and a width of 300 mm was degreased electrolytically in a 70 g / l sodium hydroxide solution and then pickled in an aqueous solution. sulfuric acid at 100 g / l. The steel strip, after rinsing with water, was subjected to a cathodic treatment using an electrolyte containing 60 g / l of CrO 3 and 3 g / l of NaF in water, at a density of cathodic current of 20 A / dm 2, at an electrolyte temperature of 50 C. The treated steel strip was rinsed with

  hot water having a temperature of 80 C and was dried.

  Then a copolyester resin film, orientated

  biaxially produced by condensation polymerization of ethylene glycol and a carboxylic acid comprising moles% terephthalic acid and 15 mole% sebacic acid having the characteristics mentioned in (A), which had been previously coated with a composite resin under the following conditions (B), was laminated continuously on both surfaces of the strip

  of treated steel under the following conditions (C).

  (A) Characteristics of copolyester resin film used Thickness: 25 gm Melting temperature: 229 C Refractive index, in the thickness direction: 1.5311 Refractive index in all planar directions: 1.6411 minimum: 1.6210 Type of Lubricant Added: Silica (SiO2) Average Particle Diameter of Added Lubricant: 2.0 gm Lubricant Quantity: 0.07 wt.%, Based on the weight of the copolyester used. (B) Conditions for pre-coating the copolyester resin film with the composite resin Composition of the previously coated material: Epoxy resin having an epoxy equivalent of 3000: 80 parts Resolate produced from the paracresol: 20 parts Drying temperature of the pre-coated composite resin: Pre-coated composite resin drying time: 10 seconds Composite resin quantity after drying: 0.2 g / m 2 (C) Conditions for laminating the film

  of copolyester resin coated prior

  under the conditions (B) Process for heating the treated steel strip: Induction heated cylinder Temperature of the treated steel strip just before lamination: 200 C Material of the laminating cylinder: silicone rubber Surface temperature of the cylinder of

stratification: 180 C max.

  Cooling method after lamination: rapid cooling Post-heating of the laminate: 215 C

for 1 minute.

EXAMPLE 2

  Two types of biaxially oriented copolyester resin films produced by condensation polymerization of ethylene glycol and a carboxylic acid comprising 88 mole% terephthalic acid and 12 mole% isophthalic acid having the characteristics mentioned in (A), which were previously coated with a composite resin under the following conditions (B), were simultaneously laminated on each side of the same treated steel strip as in Example 1, under the conditions

(C) following.

  (A) Characteristics of copolvester resin film used Clear film Thickness: 25 gm Melting point: 229 C Refractive index, in the thickness direction: 1.5405 Refractive index in all planar dimensions: maximum: 1, 6500 Minimum: 1.6305 Type of Lubricant Added: Silica (SiO2) Average Particle Diameter of Added Lubricant: 1.5 nm Amount of lubricant added, 0.12% by weight, based on the weight of copolyester resin used Film white color Thickness: 20 Mm Melting point: 229 C Type of colored pigment: TiO2 Average particle size of the added colored pigment: 0.3 Yr Quantity of colored pigment added: 15% by weight, based on the weight of the copolyester resin used (B) Conditions for pre-coating the copolvester resin film with the composite resin Composition of the previously coated material: Epoxy resin having an epoxy equivalent of 3000: 70 parts Resol produ it from paracresol: parts Drying temperature of the previously coated composite resin:

120 C

  Drying time of the pre-coated composite resin: 5 seconds Quantity of composite resin after drying: 1.1 g / m 2 (C) Conditions for the lamination of a previously coated copolyester resin film under the conditions (B) heating of the treated steel strip: Induction heated cylinder Temperature of the treated steel strip just before lamination: 230 C Temperature of the treated steel strip just before lamination: 230 C Material of the laminating cylinder: silicone rubber Surface temperature of the cylinder of

stratification: 210 C max.

  Process for cooling after lamination: rapid cooling Post-heating of the laminate: 210 C

for 5 minutes.

EXAMPLE 3

  The same steel strip, pretreated as in Example 1, was electroplated with 2.8 g / m 2 tin using an electrolyte containing g / l SnSO 4, 60 g / l phenolsulfonic acid (60% aqueous solution) and 5 g / l of α-naphtholsulphonic acid in water, at a cathodic current density of A / dm 2, at a temperature of the electrolyte of 40 C. After remelting the Tin and water rinse, the tin-plated steel strip was treated using an electrolyte containing 30 g / l CrO 3 and 0.3 g / l H 2 SO 4 in water, under a cathodic current density of A / dm 2, at a temperature of the electrolyte of 50 C. The galvanic tin plating thus treated was rinsed with

water and dried.

  Then a copolyester resin film, orientated

  biaxial composition, produced by condensation polymerization of ethylene glycol and a polycarboxylic acid comprising 88 mole% terephthalic acid and 12 mole% sebacic acid having the characteristics mentioned in (A), which had been previously coated with the resin under the following conditions (B), was laminated continuously on both surfaces of the steel strip as well as

  treated under the following conditions (C).

  (A) Characteristics of copolyester resin film used Thickness: 25 μm Melting temperature: 243 C Refractive index, in the thickness direction: 1.5218 Refractive indexes in all planar dimensions: maximum: 1.66312 minimals : 1,6228 Type of lubricant added: silica (SiO2) Average particle diameter of the lubricant added: 0.3 pm Amount of lubricant added: 0.81% by weight, based on the weight of the

copolyester resin used.

  (B) Conditions for pre-coating the copolvester resin film with the composite resin Composition of the pre-coated composite resin: Epoxy resin having an epoxy equivalent of 2500: 75 parts Resolate produced from the paracresol: parts Drying temperature of the pre-coated composite resin: C Drying time of the previously coated composite resin: 15 seconds Quantity of composite resin after drying: 1.2 g / m2 (C) Conditions for the layering of a

  pre-coated polyester resin film

  (B) Process for heating the treated steel strip: resistance heating Temperature of the treated steel strip just before lamination: 228 C Material of the laminating cylinder: silicone rubber Surface temperature of the laminating cylinder: 200 C Process for cooling after stratification, progressive cooling Posterior heating of the laminate: 220 C for 30 seconds

EXAMPLE 4

  The same steel strip, pretreated as in Example 1, was electroplated with 1.5 g / m 2 of tin using an electrolyte containing g / l of SnSO 4, 20 g / l of phenolsulfonic acid (60% aqueous solution) and 4 g / l of ethoxylated α-naphthol in water at a cathodic current density of 3 A / dm 2 at an electrolyte temperature of 45 ° C. After rinsing with In the water, the tin-plated steel strip was treated by immersion in a solution of sodium dichromate at 1 g / l for 3 seconds at a temperature of 45 ° C. The galvanic tin plating thus treated was rinsed at

water and dried.

  Then a copolyester resin film, orientated

  biaxial composition, produced by condensation polymerization of ethylene glycol and a polycarboxylic acid comprising moles% of terephthalic acid and 20 mole% of sebacic acid, having the characteristics indicated in A, which had been previously coated with the same composite resin that in Example 3, was laminated continuously on both surfaces of the steel strip thus treated,

under the following conditions (C).

  (A) Characteristics of copolyester resin film used Thickness: 25 μm Melting temperature: 215 C Refractive index, in the thickness direction: 1.5100 Refractive index in all planar dimensions: maximum: 1.6211 minimum : 1,6110 Type of lubricant added :: TiO2 Average particle diameter of the lubricant added: 0.5 gm Amount of lubricant added: 0.52% by weight, based on the weight of the

copolyester resin used.

  (B) Conditions for film lamination

  copolvester resin coated prior-

  under the conditions (B) of the Example Process for heating the treated steel strip: resistance heating Temperature of the treated steel strip just before lamination: 234 C Material of the laminating cylinder: fluorinated rubber Surface temperature of the laminating cylinder: 180 C Process for cooling after stratification: rapid cooling Posterior heating of the laminate: 190 C

for 30 seconds.

EXAMPLE 5

  An aluminum strip (JIS 3004) having a thickness of 0.23 mm was subjected to cathodic degreasing in a g / l sodium carbonate solution. After rinsing with water, the aluminum strip was immersed in a solution of Alodine 401-41 at 5% (of the chromatephosphate type) produced by Nippon Paint Co., Ltd., for 20 seconds at 45.degree. was rinsed with water

and dried.

  Then, the same biaxially oriented copolyester resin film as that mentioned in (A) in Example 1, which had been previously coated with the same composite resin as in (B) in Example 1, was laminated continuously on both surfaces of the aluminum strip thus treated, under the same conditions as

  under the conditions (C) of Example 1.

COMPARATIVE EXAMPLE 1

A biaxially oriented copolyester resin film produced by condensation polymerization of ethylene glycol and a polycarboxylic acid comprising mole% terephthalic acid and 15 mole% sebacic acid, having the characteristics mentioned in (A). ), which had been pre-coated with the same composite resin as in Example 1, was laminated continuously on both surfaces of the same treated steel strip as in Example 1, under the same conditions as in C) in

Example 1

  (A) Characteristics of copolyester resin film used Thickness: 25 Lm Melting point: 229 C Refractive index, in the thickness direction, 1.5334 Refractive index in all planar dimensions: maximum: 1.6473 minimum : 1.6022 Type of lubricant added: silica (SiO2) Average particle diameter of the lubricant added: 2.0 pm Amount of lubricant added: 0.07% by weight, based on the weight of the

copolyester resin used.

COMPARATIVE EXAMPLE 2

  A biaxially oriented copolyester resin film produced by condensation polymerization of ethylene glycol and a polycarboxylic acid comprising 88 mole% terephthalic acid and 12 mole% isophthalic acid, having the characteristics mentioned in ( A), which had been pre-coated with the same composite resin as in Example 1, was laminated continuously on both surfaces of the same treated steel strip as in Example 1, under the same conditions as in (C) in

Example 1

  (A) Characteristics of the copolyester resin film used Thickness: 25 gm Melting point: 229 C Refractive index, in the thickness direction: 1.5110 Refractive indexes in all planar dimensions: maximum: 1.6720 minimals Type of Lubricant Added: Silica Average Particle Diameter of Added Lubricant: 2.0 gm Amount of lubricant added: 0.07 wt.%, Based on the weight of resinol copolyester used.

COMPARATIVE EXAMPLE 3

  A biaxially oriented copolyester resin film produced by condensation polymerization of ethylene glycol and a polycarboxylic acid comprising 83 mol% terephthalic acid and 17 mol% isophthalic acid, having the characteristics indicated in (A). ), which had been pre-coated with the same composite resin as in Example 3, was laminated continuously on both surfaces of the same treated steel strip as in Example 3, under the same conditions as in C) in

Example 3

  (A) Characteristics of copolvester resin film used Thickness: 25 Am Melting temperature: 212 C Refractive index, in the thickness direction: 1.5442 Refractive indexes in all directions in the plane: maximum: 1, 6041 Minimum: 1.5986 Type of Lubricant Added: Silica Average Particle Diameter of Added Lubricant: 2.3 μm Amount of lubricant added: 0.07% by weight, based on the weight of the lubricant

copolyester resin used.

COMPARATIVE EXAMPLE 4

  A biaxially oriented copolyester resin film produced by condensation polymerization of ethylene glycol and a carboxylic acid comprising 85 mol% terephthalic acid and 15 mol% sebacic acid, having the characteristics indicated in (A). ), which had been pre-coated with the same composite resin as in Example 3, was laminated continuously on both surfaces of the same treated steel strip as in Example 4, under the same conditions as in B) in

Example 4

  (A) Characteristics of the copolyester resin film used Thickness: 25 Mm Melting temperature: 215 C Refractive index, in the thickness direction: 1.5311 Refractive indices in all directions in the plane: maximum: 1, 6331 minimum: 1.6098 Type of lubricant added: silica Average particle size of the lubricant added: 2.9 Dm Amount of lubricant added: 0.05% by weight, based on the weight of the lubricant

copolyester resin used.

COMPARATIVE EXAMPLE 5

  The same copolyester resin film, oriented

  biaxially, as in Example 1, which had been pre-coated with the same composite resin as in Example 1, was laminated continuously on both surfaces of the same treated aluminum strip as in Example 5, under the same conditions as in Example 1, except that the temperature of the treated aluminum strip,

  just before stratification, was equal to 162 C.

  The workability and corrosion resistance of the resulting foil were evaluated by the following test methods, after measuring the coating weight on the resulting foil by an X-ray fluorescence process.

are mentioned in the Table.

  (1) Deep drawing forming ability The resulting foil was cut

  punch press to form a circling piece.

  cutting die with a diameter of 158 mm. The die cut piece was deep drawn to form a cylindrical cup at a draw ratio of 2.92. The workability of the resulting foil was evaluated by the degree of cracking of the copolyester resin film and the degree of peeling of the copolyester resin film in the shaped area, and then divided into 5 classes. 5 was excellent, 4 was good, 3 was average,

  2 was mediocre and 1 was bad.

  (2) Impact bending workability The resulting metal sheet was cut to dimensions of 30 mm x 50 mm. The sample was previously bent by means of a rod having a diameter of 3 mm, then was folded by dropping a load weighing 2.3 kg from a height of 30 cm. The workability, by bending of the resulting metal foil, was evaluated by the degree of cracking of the resin film.

  copolyester in the folded area by means of a microscope.

  Then it was divided into the 5 classes described above.

above.

  (3) Resistance to corrosion after stamping

  The resultant foil was cut off

  punch press to form a circling piece.

  punching die with a diameter of 85 mm. The die cutter was deep drawn to form a cylindrical cup at a draw ratio of 2.15. The drawn cup was filled with Coca Cola and stored at 20 C. After three months, iron absorption was measured using

an atomic absorption process.

  It goes without saying that the present invention has been described only for explanatory purposes, but in no way limiting, and that many modifications can be added thereto.

without leaving his frame.

TABLE 1

  Example Example Example Example Example Example Example Example Example Example

  1 2 3 4 5 Compara- Compara- Compara- Compara- Compara- Compara-

  uif 1 tif 2 tif 3 tif 4 tif 5 Base metal Steel Steel Steel Steel A1 Steel Steel Steel A1 Sn Sn Sn Sn Jo. '2,81,5 2,8 1,5 Cr Cr Cr CrOX crOX + pO + f Cr Crro Cr crx + po e HH Coating weight 0,120 0,120 0, 015 0,008 0,120 0,120 0,015 0,008 9,' Crox Crox Crox Cr x CrOx Crox CrOx Crox a, a) 005 005.10 0.003,1 00 003 ee (g / m 2 0.015 0.015 0.010 0.003 0.015 0.015 0.010 0.003 'IR in the direction u of the thickness 1.5300 1, 5395 1.5190 1.5160 1.5290 1.5520 1.5180 1.5390 1.5330 1.5311

4 4-4151

At o '[.

  o 'H IR max. in the plan 1,6395 1,6510 1,6358 1,6115 1,6390 1,6311 1, 6790 1,5960 1,6300 1,6389 hr! IR min. in plan 1,6180 1,6311 1,6300 1,6005 1,6175 1,5900 1,6411 1,5900 1,6081 1,6195 Deep drawing forming capability S 5 5 5 5 4 1 2 5 1 se È Ability to IH shaping by impact bending 5 5 5 5 5 1 5 1 5 5

Resistance to corrosion

  Fe Fe Fe Fe A1 Fe Fe Fe Fe Fe (Fe uptake, A1) 0.02 0.01 0 0 0 30.6 106.3 50.6 2.60 fication

  Notes: * 1 IR stands for refractive index.

  Cr is the metal Cr and CrOx is Cr as hydrated decbromide oxide.

  * 3 The absorption of Fe and Al is given in ppm.

Claims (17)

  1. Sheet metal laminated with a film   copolyester resin, characterized in that   takes: (i) a biaxially oriented copolyester resin film having a melting point of about 210 ° C to about 250 ° C, a refractive index of about 1.5000 to about 1.5500 depending on the thickness of said film and a refractive index of about 1.6000 to about 1.6600 along its directions in the plane, (ii) a composite resin applied to one side of said copolyester resin film, which contains at least one radical selected from the group comprising epoxy, hydroxyl, amide, ester, carboxyl, urethane, acryl and amino groups, and (iii) a surface-treated metal sheet, the face of said copolyester resin film coated with said composite resin being laminated to said treated metal sheet; surface, at least one side of said surface-treated metal sheet being   laminated with said copolyester resin film.   The laminated film with copolyester resin film according to claim 1, further characterized in that it comprises a lubricant in said copolyester resin film characterized by a diameter of particles less than 2.5 Hm.   3. Sheet laminated with a copolyester resin film according to claim 1, characterized in that it has a refractive index, following a   direction in the plane, from about 1.6100 to about 1.6500.   A laminated film with a copolyester resin film according to claim 1, characterized in that said copolyester resin film comprises about 75 to about 99 mole percent polyethylene terephthalate and about 1 to 25 mole percent polyester resin produced by 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-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and trimellitic acid anhydride, with at least one saturated polyhydric alcohol selected from the group consisting of ethylene glycol, 1,4-butanediol, 1,5 pentanediol,   1,6-hexanediol, propylene glycol, polytetramethyl   ethylene glycol, trimethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol,   trimethylolpropane and pentaerythritol.   5. Metal sheet laminated with a film   copolyester resin according to claim 1,   characterized in that the copolyester resin film has a   thickness from about 5 to about 50 μm.   6. Metal sheet laminated with a film   copolyester resin according to claim 1,   characterized in that the composite resin is present in an amount of about 0.1 to about 5.0 g / m 2 of said copolyester resin.   7. Metal sheet laminated with a film   copolyester resin according to claim 1,   characterized in that the surface-treated metal sheet is selected from the group consisting of a tin-free steel having a double layer of a top layer of chromium oxide hydrate and a lower layer of metallic chromium, a sheet metal galvanic tinning covered by said double layer, a galvanic tin-plated sheet coated with chromium oxide hydrate and a treated aluminum foil in the solution,   containing a chromate, a phosphate or a zirconium salt.   8. Metal sheet laminated with a film 2653703   copolyester resin according to claim 7,   characterized in that the hydrated chromium oxide is present in an amount, in the form of chromium, of about 5 to about mg / m 2 of said treated metal sheet and the chromium metal is present in an amount of about 10 to about 150 mg / m 2 of said treated metal sheet in said double layer.   9. Metal sheet laminated with a film   copolyester resin according to claim 7,   characterized in that the treated metal sheet is a galvanic tinplate and said galvanic tinplate is coated with a tin layer in an amount of about 0.5 to about 5.6 g / m 2 of said sheet treated metal.   10. Metal sheet laminated with a film   copolyester resin according to claim 8,   characterized in that the amount of chromium oxide hydrated on the galvanic tinplate is in the range   from about 1 to about 4. mg / ml as chromium.   Metal sheet laminated with a copolyester resin film according to claim 1, characterized in that the copolyester resin film contains about 2 to about 20% by weight of an inorganic pigment. 12. Metal sheet laminated with a film   copolyester resin according to claim 11,   characterized in that the inorganic pigment is titanium dioxide.   13. Process for producing a metal foil   laminated with a copolyester resin film, which is   characterized in that it consists of: (i) pre-coating one side of a copolyester resin film with a composite resin containing at least one radical selected from the group consisting of epoxy, hydroxyl, amide, ester, carboxyl, urethane radicals acryl and amino, said copolyester resin film having a melting point of about 210 to about 250 C and a refractive index of about 1.5000 to about 1.5500 depending on the thickness of said film and a refractive index from about 1,6000 to about 1,6600 in planar directions, (ii) heating a surface-treated metal sheet to a temperature in the range defined by the melting point of said 50 C copolyester resin film and (iii) contacting the face of said treated copolyester resin film with said composite resin with at least one side of said surface-treated metal sheet so as to laminate said copoly resin film ster on this metal foil.   The method of claim 13, further characterized by adding to the copolyester resin film a lubricant characterized by a   particle diameter less than about 2.5 Dm.   The method of claim 13, characterized in that the composite resin is applied to the copolyester resin film in an amount of from about 0.1 to about 5.0 g / m 2 of said copolyester resin film, said method further comprising drying at a temperature of about 60 to about 150 ° C   said composite resin applied.   16. The method of claim 15, wherein the composite resin is dried at a temperature of about 60 to about 150 C for a time. from about 5 to about 30 seconds.   The method according to claim 15, characterized in that the treated metal surface is selected from the group consisting of a tin-free steel carrying a double layer comprising an upper layer of chromium oxide hydrate and a lower layer of metallic chromium, a galvanic tinplating sheet covered by said double layer, said galvanic tin-plated sheet coated with chromium oxide hydrate and an aluminum sheet treated in a solution containing a chromate, a phosphate or a zirconium salt, the heating being carried out at a temperature within the range defined by the melting point of said copolyester resin film 50 C, and cooling being effected quickly or gradually.