HRP930107A2 - Laminated metal sheets - Google Patents

Description

The field of technology

This invention relates to the production process of laminated sheets.

Technical problem

The application of polymeric materials to sheets, such as metal strips, is a well-known and well-documented technique. The laminates produced have many applications such as use for making barrels and containers for storing food products and beverages, and for the edge parts of lids with valves for aerosol cans.

In many applications, a layer of polymer is applied to both major surfaces of the sheet. In general, most known polymer films of the same or similar composition to the opposite surface of the sheet or to the description of the application of polymer films whose compositions are different from the composition of the opposite sheet, where each of the two different polymers is applied to the sheet in separate stages, more often than simultaneously.

Although metal laminates, which have similar coatings on both sides of the sheet or strip, have some advantages, they can be used for all purposes. Thus, for example, while polyester coatings, which are described in GB 2125746, have an exceptional formability, they are not fully applicable for heat-sealed finishes, they are difficult to pigment to an acceptable level of opacity at an affordable cost and change the external appearance over time.

State of the art

Polypropylene or polyethylene coatings, such as those described in e.g. GB 1324952 and EP 0062385, show acceptable corrosion resistance when it comes to sheets, but are relatively soft, easily damaged, have a low melting point and a relatively low surface gloss.

No single polymer can satisfy all the different physical properties intended for use in metal/polymer laminates intended for use in storage drums. Therefore, it has been found that it is much more convenient to use a combination of different polymers in a simple polymer/metal/polymer laminate and to use the properties of each polymer appropriately.

In many cases, it is desirable to use different polymers applied to the two surfaces of the sheet and thus enable the application of different properties of different polymers.

From the point of view of economy, it is better to apply coatings of different polymers to sheets in a simultaneous process, thereby reducing labor costs. The simultaneous application of two different polymers can be achieved by applying an adhesive that is applied in two different polymer films, and then by simultaneously applying these films to the sheet. Alternatively, the desired polymer films can be simultaneously coated in one process on two surfaces of the metal strip.

However, the first method is undesirable due to the requirement to use solvent-based materials that may contain biologically described chemicals, such as isocyanates, and also entails a long list of drugs. The second method, which requires coextrusion of polymer melts, can impair the exceptional properties of biaxially oriented polyester materials, such as polyethylene terephthalate (PET), since such biaxially oriented materials cannot be extruded and retain their outstanding properties.

Thermal deposition of biaxially oriented PET on metal tape is known, e.g., from GB 2123746. Similarly, thermal deposition of polypropylene films on metal tape is described, e.g., in GB 1324952 and US 3679513, while thermal deposition of polyethylene films on metal tape is described eg in EP 0062385 and US 4452375. However, the conditions described in these documents for the thermal deposition of polymer films with such different properties are not suitable for the simultaneous thermal deposition of a polyester film, especially a biaxially oriented polyethylene terephthalate film, on one side of a metal strip, while simultaneously on the other side of the metal strip, he thermally applies a film containing polyolefin or polyamide with a thickness economically and technically suitable for making storage barrels.

Description of the solution to the technical problem with practical examples

We found that simultaneous thermal deposition of a polyester film on one side of the sheet and a film containing polyolefin or polyamide on the other side of the sheet can be easily achieved by measuring the softness characteristics of the different polymers on each side of the sheet, providing an intermediate layer of non-crystalline polyester having certain specific physical properties between the sheets and polyester layer, which is desired to adhere to the sheet, and by applying polymer films to the sheet by the process of thermal applications, whereby in the first stage, the polymer films are applied to the sheet at the original temperature that does not damage the outer surface of the films when passing through the bath for application, and in the next step the resulting laminate is indirectly heated again to a second higher temperature, which conditions the polymer films to react with the sheet with a solid union.

According to the first aspect of this invention, a production process for polymer/metal/polymer laminates with simultaneous application is provided, wherein this process includes the application of a polyester film (A) containing an inner layer A1) of mainly non-crystalline polyester, the softening temperature of which is below 150ºC, and the melting point above 150ºC but below 240ºC, on one of the main surfaces of the sheet, and the inner layer (A2) of linear polyester, whose melting point is above 220ºC, and the simultaneous application of film (B) containing polyolefin, which implies the bonding of acid-modified polyolefin resin containing carboxylic or anhydride groups, to the second main surface of the sheet, whereby the sheet is heated to a temperature T1 at which the polymer film softens and comes into indirect contact with the sheet, with the temperature T1 being lower than the temperature at which the outer surface of the film containing the polyolefin is damaged during application and the resulting laminate is heated again to temperature T2, which allows both polymer films (A ) and (B) react with each other with the appropriate binder and sheet surface.

According to another aspect of this invention, a polymer/metal/polymer laminate is provided, which consists of a sheet, on each large surface of which there is a polymer film that is simultaneously thermally applied to the sheet, whereby one of the films, applied to one large surface of the sheet, represents a polyester film (A) containing an inner layer (A1), usually of non-crystalline linear polyester, with a softening temperature above 150ºC but below 240ºC, and an outer layer (A2) of linear polyester whose melting point is above 220ºC, and a polymer film (B), applied to the other a large surface area of sheet containing polyolefin with a binder acid-modified polyolefin resin with carboxylic acid or anhydride groups.

The polyolefin-containing film (B) may be a single-layer film of a binder resin which is acid-modified and contains carboxylic acid or anhydride groups, or it may be a multilayer film or anhydride groups, or it may be a multilayer film containing an outer layer (B2) of polyolefin or polyamide attached to inner (or binding) layer (B1) of binding resin, as already defined.

In a further solution of this invention, the composite film (B) may also contain a polyethylene or polyamide layer (B4) attached to the mentioned outer layer (B2) by means of an intermediate layer (B3) of the binding resin defined by the layer (B1).

More conveniently, composite films (A) and (B) represent films prepared by coextrusion.

Using the process of this invention, a metal/polymer laminate can be obtained by applying biaxially oriented polyester materials, such as polyethylene terephthalate to one side of the sheet and a polyolefin or polyamide coating to the other side of the sheet. Using this procedure, both polymer coatings can be applied simultaneously without solvents containing adhesives that are undesirable for the environment.

The process of this invention takes place in several stages. In the first stage, the metal is preheated to a temperature T1 of 120 to 240ºC, and at least between 140 and 220ºC, so that the outer surface of the film (B) does not reach the temperature of its melting point in the coating bath, and preferably does not even reach its temperature softening.

In the second stage, the films and metal are brought together in a coating bath to establish a close and uniform contact without wrinkling. In this stage, the contact layers are the inner layer (A) of amorphous polyester and metal, and on the opposite side of the metal and the inner surface of the polyolefin or polyamide film (B).

In the third stage, the resulting laminate is heated again, preferably by induction heating of the metal core to a temperature T2 that is higher than 250ºC, but below the thermal or oxidative decomposition temperature of the outer surface of the film (B) containing polyolefin or polyamide, or the temperature at which the outer the layer physically decomposes when it is suddenly filled with water. If desired, heating with infrared radiation can also be applied.

In conditions where the outer surface of the polyester film (A) is kept below its melting point, but with the metal core above the melting point of the polyester, a rapid interaction occurs between the metal, the inner polyester layer (A1) and the polyolefin layer (B). To achieve this effect, the laminate is kept above 200ºC for 1 to 30 seconds, and best at approx. 250ºC for 2 seconds and then the laminate is quickly and evenly rinsed with water to a temperature below the softening point of the resin which has the lowest softening temperature.

We have found that by ensuring that the outer surface of the biaxially oriented polyester film (A) remains below its melting point, we can achieve the excellent properties of the biaxially oriented polyester, ie polyethylene terephthalate. The temperature in the post-coating zone can be varied in order to control the properties, especially the formability, which is particularly required for polyester coatings. this control can be done particularly well if induction heating is used to reheat the laminate after the application bath. In order to measure the temperature of polyester, it is best to use a suitable pyrometer. Likewise, devices for detecting changes from biaxially oriented to crystalline non-oriented or amorphous polyester can be used to define the critical state of the polyester film (eg X-ray diffractometer).

The exact temperature T1 to which the sheet must be heated before application depends on the thickness of the films that are applied, as well as on the chemical nature of said films. In this way, temperatures of approx. 120º and above, usually 140ºC, are suitable for cast polypropylene film of 20 microns, and up to 230ºC for polypropylene film thicknesses of 200 microns.

Temperatures from 140 to 270ºC are suitable for coextruded biaxially oriented polyethylene terephthalate.

Films containing polyamide can withstand slightly higher metal temperatures than cast polypropylene, and oriented polypropylene requires higher temperatures than cast polypropylene, typically 200ºC for a 20 micron ml.

The temperature T2 applied to reheat the laminate above the coating bath is usually in the range of 230 to 270ºC. The actual temperature that must be applied depends on the dwell time until immersion in water temperatures above 270ºC lead to physical damage to the polyolefin film when it comes into contact with the cooling water and lead to melting of the polyethylene terephthalate films. The temperature at the lower limit of the mentioned area is controlled in order to achieve a satisfactory strength of the connection between the sheet and the polymer films that are stuck to the sheet for a very short time during which the laminate is heated to the desired temperature. Economic procedures usually require a downtime of approx. just 3 seconds.

The metal substrate on which polymer films are applied is usually in the form of a metal strip made of steel or aluminum or their alloys, which are further used in the packaging industry.

The measurement range is usually 0.05 mm to 0.4 mm for steel and 0.02 to 0.4 mm for aluminum.

The steel may be tin-plated, preferably by a passive common chromium treatment, or electroplated with nickel or zinc, black iron sheet, or phosphated black iron sheet, which is usually chromate-washed after phosphating.

The best steel treatment is electrolytic chromium plating of steel (ECCS) with a double layer of metallic chromium and chromium oxide. With such steels, the amounts of metallic chromium and oxides can vary greatly. Usually, the content of metallic chromium is in the range of 0.10 to 0.20 gm/m2, and the content of chromium oxide is from 0.005 to 0.05 gm/m2. ECCS was carried out on precipitation systems containing catalysts based on sulfur or fluorine.

The composite polyester film (A) can most conveniently be obtained by coextrusion before application to the metal strip. Composite polyester film (A) contains a thinner inner layer (A) of mostly non-crystalline (i.e. amorphous) linear polyester with a softening temperature below 150ºC and a melting point around 150ºC but below 240ºC, and a thicker outer layer (A2) with a melting point of 220ºC and preferably it has an intrinsic viscosity of 0.5 to 1.1, most preferably 0.6 to 0.8.

It is most advantageous that the outer layer (A2) is a biaxially oriented polyester, such as polyethylene terephthalate. It is most favorable for the inner layer (A1) to be a linear copolyester, for example an amorphous copolymer of approximately 80% mol% ethylene terephthalate and 20 mol% ethylene isophthalate. Copolyesters of terephthalic acid and two alcohols, eg ethylene glycol and cyclohexane-dimethanol, are also suitable for the inner layer (A1).

Typically, the biaxially oriented polyester in the outer layer (A2) has a crystallinity greater than 30%, preferably 40 to 50%.

The crystallinity of the polyester material can be determined by X-ray diffraction methods, as described in GB 1566422, or by density measurement and the formula

Vc = (P - Pa) · (Pc - Pa)-1

Vc is the volume fraction of crystallinity,

P is the density of the sample,

So the density of the amorphous material is,

Pc is the density of the crystalline material

P can be measured in a density column using a mixture of zinc chloride/water or n-heptane/carbon tetrachloride.

A biaxially oriented film which can be used as an outer layer can be formed by drawing an amorphous extruded polymer in the longitudinal direction at temperatures above the glass transition temperature of that polymer by a factor of 2.2 to 3.8 and similarly in the transverse direction by a factor of 2.2 to 4, 2. When the applied coatings are to be used for deep-drawn metal vessels, the orientation is generally reduced to drawing by a factor of about 2.5 in both longitudinal and transverse directions.

The best set temperature of biaxial PET film is in the range of 215 to 220ºC. A lower heating temperature can also be used, but this is usually accompanied by an increased tendency to shrink during application.

Usually, the inner layer (A1) should be continuous with a thickness of 2 to 4 microns. The ratio of the thickness of the outer polyester layer (A2) to the inner polyester layer (A1) is between 12 and 4, whereby the total thickness of the combined layers is from 12 to 25 microns.

If necessary, the polyester layers can contain anti-blocking agents, such as synthetic silicon dioxide, the average particle size of which is 0.5 to 5 microns.

Also, if necessary, the outer polyester layer (A2) can be colored with common pigments such as titanium dioxide.

The basic function of the inner polyester layer (A1) is to adhere to the metal surface by the action of heat at temperatures below the melting point, so that the inner layer can retain its amorphous structure after orientation and hot film coating. In addition, the inner polyester layer (A1) must be bonded to the metal at temperatures consistent with the simultaneous lamination of the opposite side of the tape with a coating containing polyamide or polyolefin. These requirements are set with the condition that the inner layer of polyester (A1) has a softening point in accordance with the temperatures required for laminating a wide range of polyolefin or polyamide based coatings. Therefore, the softening temperature must be lower than 150ºC, and especially not higher than 130ºC.

The film containing the polyolefin (B) and the binder resin layer (B1) in the composite film (B) is an acid-modified polyolefin resin containing carboxylic acid or anhydride groups. Typical acids for preparing such acid-modified polymers are ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid and itaconic acid. Typical anhydrides used for the same purpose are ethylenically unsaturated carboxylic anhydrides, such as maleic.

The acid groups may be present as ethylene polymers, eg ethylene/acrylic acid (EAA) and ethyl/methacrylic acid (EMMA). The acid concentration is usually 5 to 15%.

Acid modification of acid-modified polymers can be obtained, for example, by cleavage of maleic anhydride to polyolefins, such as polypropylene, polyethylene ethylene-propylene or ethylene-vinyl acetate copolymer. Cleavage can be achieved by a process such as the reaction of maleic anhydride with a polyolefin in solution in an organic solvent with a free radical catalyst such as dibenzyl peroxide. Alternatively, some active center can be introduced into the polymer by, for example, high-energy radiation, such as gamma radiation, and then reacting the resulting substance with an anhydride.

It is most suitable that the bonding resin contains from 0.05% to 0.5%, and even better from 0.1 to 0.25% acid modification, measured by infrared absorption analysis at 1790cm-1, resin pre-dried at 200ºC to make the acid functional group translated into an anhydride.

The anhydride cleavage modified polyolefin can be diluted with the unmodified polyolefin to produce a binder resin with an acid cleavage content (ie, cleavage level) of 0.02 to 0.6%, preferably 0.2±0.5%. The unmodified polyolefin for the diluent can be the same polyolefin that was used to produce the acid modified polyolefin, or it can be a different polyolefin. Thus, for example, some acid-modified low-density polyethylene (LDPE) or linear low-density polyethylene (LLDE) can be diluted with polypropylene, or acid-modified polypropylene can be diluted with polypropylene or ethylene propylene copolymer.

The purpose of the inner layer (B1) of bonding resin is to bind the outer layer (B2) of polyolefin or polyamide to the metal surface. It is more convenient, when the outer polyolefin layer (B2), that the polyethylene base of the binding resin of the inner layer (B1) is polyethylene and ethylene copolymer. It is more convenient, when the outer layer is a polyethylene layer (B2), a polypropylene homopolymer or an ethylene-propylene copolymer, that the base of the binding resin of the inner layer (B1) is polypropylene or an ethylene-propylene copolymer. When the outer layer (B2) is polyamide, the binding resin layer can be based on polyethylene or polypropylene.

It is best that for a layer of bonding resin based on polypropylene, the mass flow rate of the bonding resin melt is 3 to 30 g/10 min, measured at 230ºC by the ASTM D 1238 method.

Especially suitable bonding layers of bonding resin are based on ethylene-propylene copolymer or a mixture of linear low-density polyethylene (LLDPE) with polypropylene.

A particularly suitable acid-modified olefinic copolymer is ethylene vinyl acetate modified with maleic anhydride.

For the bonding resin layer (B1) in the composite polymer film (B), it is best to have a thickness of 1 to 10 microns.

In a further solution of this invention, a polyamide or polyoledine layer (B4) can also be adhered to the outer layer (B2) using the next layer of bonding resin (B3), as defined for the bonding layer (B1). If necessary, each of the layers (B1) to (B4) can be painted in the usual way, for example with titanium dioxide. It is more convenient for the color to be in layer (B2) or in layers (B2) and (B4). Conveniently, the outer polyolefin or polyamide layer may contain an anti-blocking agent, such as synthetic silicon dioxide with a particle size of 0.5 to 5 microns.

In this description, the actual viscosity is measured at 25ºC in o-chlorophenol solutions at a concentration of 5 g/l. The following examples further illustrate this invention.

Examples 1 to 42

Polymer/methane/polymer laminates were prepared by the lamination process carried out in the device schematically shown in Figure 11 or Figure 12, in the attached drawings. The metal strip M is preheated to the appropriate temperature T1 by the heater 1. The temperature T1 is usually in the range of 120 to 220ºC. Polyester film A is fed from feed roller 2, and the film contains polyolefin from feed roller 4, which is laminated on opposite sides of the preheated metal strip between lamination rollers 6 and 8, the diameter of which is usually 100-400 mm. Lamination is usually carried out using a holding force of 200-400 N/m between the laminating rollers.

With a close and uniform grip, lamination establishes contact without wrinkling the metal strip and polymer films. Behind the laminating rollers, the obtained laminate is reheated using the induction heater 10 to the temperature T2 at which both polymer films A and B react with each other creating a bond with the metal strip. The temperature T2 is usually in the range of 230 to 270ºC. The metal-polymer laminate is held at temperature T2 or at a temperature slightly below T2 for a short time, usually no longer than 2 seconds, and then rapidly and evenly immersed in water to a temperature below the melting point of the polyolefin-containing film (B). Immersion can be carried out in any of the usual ways, but it is mainly carried out by passing the laminate through a bath of water 12, which is shown in Figure 11, or by passing the laminate through a water curtain 14, which is seen in Figure 12.

In principle, the procedure shown in Figure 11 is better, in which the lamination is carried out vertically. The vertical movement of the metal strip through the lamination stage enables a higher speed of immersion, and the immersion itself is better and more uniform.

Figure 11 also shows a schematic diagram of the temperature profile in the process whose device is shown in Figure 11.

Table 1 lists the types of polymers laminated to the metal strip, as well as the thicknesses of each layer. Lamination conditions and the results obtained are shown in table 2.

The polyester film A applied to the metal strip may be in the form of a single layer film (as in Examples 11 to 14 provided for comparison). In these cases, the nature of the polymer is listed in Table 1 in column A1. Alternatively, the polyester film A may be a composite film consisting of an inner layer A1 and an outer layer A2 and is usually prepared by coextruding the corresponding polymer films. Such films represent films in accordance with the present invention.

The polyolefin film can have only one single layer B1, as in the case of the laminate shown in Figure 1, or it can contain a number of layers B1, B2, B3, B4, which are usually prepared by coextruding the corresponding polymer films.

Figure 1 shows a polymer/metal/polymer laminate having a composite polyester film A1/A2 applied to one side of a metal strip M with a single layer of polyolefin-containing film applied to the opposite side of the film. The laminates presented in examples 1 to 3, 17 and 18 have this structure.

Figure 2 shows a polymer/metal/polymer laminate containing a composite polyester film A1/A2 on one side of the metal strip and a composite film containing polyolefin B1/B2 on the other side. Laminates from diameters 4 to 8, 15, 16 and 19 to 24 have this structure. Examples 9 and 10 have this structure, but also contain two additional outer layers B3 and B4 on this side of the metal strip which is coated with polyolefin.

Figure 3 shows a polymer/metal/polymer laminate where both polymer films A and B have one layer each. The films of examples 11 and 12 have this team of layers.

The metal/polymer laminate structures from examples 1 to 10 and 15 to 23 are suitable for production in accordance with this invention. Table 2 shows examples of the behavior of laminates in different conditions and of various laminate structures shown in table 1.

Table 2 shows that if the temperature of the metal strip during lamination rises to too high a value, the polyolefin coatings stick to the rollers (Case D, E, F and I). In addition, if the temperature is too low and there is no polyester inner layer (A1) according to the invention, the polyester layer will not adhere properly to the metal strip (case G and H).

Table 1: Composition of metal-polymer laminates.

[image] Explanation to table 1:

Polyester A:

In examples 1 to 10, 15, 17-22 and 23, non-crystalline (i.e. amorphous) polyester was used, which is an 80:20 copolymer of terephthalate and ethylene isophthalate. The softening temperature of polyester was below 150ºC and the melting point was 210ºC. The intrinsic viscosity of the polyester was 0.6 to 0.7.

In Example 16, the amorphous polyester was a copolymer of terephthalic acid and ethyl glycol and cyclohexane dimethanol. The softening temperature of polyester was below 150ºC, and the melting point of polyester was 180ºC. The intrinsic viscosity of polyester was around 0.9 and below 1.1.

Bonding resin 1:

An ethylene propylene random copolymer modified by maleic anhydride grafting with a degree of grafting of about 0.2 to 0.05.

Bonding resin 2:

Polyethylene modified by maleic anhydride grafting with a grafting level of approximately 0.08±0.05.

Bonding resin 3:

Ethylene/acrylic acid copolymer (EAA) which usually has 6% or 9% acrylic acid.

Bonding resin 4:

Ethylene/methacrylic acid copolymer (EMAA) typically has 9% or 12% methacrylic acid.

Bonding resin 5:

Maleic anhydride graft modified ethylene vinyl acetate copolymer with a grafting level of approximately 0.08%±0.05.

Bonding resin 6:

A graft-modified polypropylene copolymer with maleic anhydride having a grafting level of approximately 0.2±0.05%.

Bonding resin 7:

Maleic anhydride graft-modified ethylene-propylene block copolymer with a grafting level of approximately 0.2±0.05.

FIVE:

Polyethylene terephthalate.

Biaxial PET:

Biaxially oriented polyethylene terephthalate with a melting point of 255ºC.

Polyamide:

Nylon 6.

Metal strip M:

It can be ECCS (marked with E), aluminum or some of its alloys (marked with A), tin plate (marked with T) or black iron sheet (marked with B).

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Remark

Cases A, B and C illustrate the materials and processes described in the present invention that have been applied successfully.

Cases D, E and F illustrate the limitations imposed by polyolefin coatings on lamination temperature. Polyester is successfully laminated in D-F.

Cases G, H and I: Combinations with already described material that show incompatibility at low (G, H) and high (I) lamination temperatures and require lamination of polyolefin and biaxially oriented PET films.

Examples 25 to 51 (see Table 3)

These examples illustrate a number of components for metal packaging containers, as well as their closures, which can be successfully made from polymer/metal/polymer laminates produced in accordance with the present invention. Illustrations of typical shapes of common products are shown in Figures 4 to 10 of the attached drawings.

Table 3 contains the nature of the metal strip (M), the types of polymer films (A) and (B) that are laminated to it and for each application the composition of the polymer film for the outer coating (C) of the product and the composition of the polymer film for the inner coating (D) are listed. products.

The laminates described in examples 25 to 31 were processed by conventional methods into lids for containers for food products which are shown in Figure 4 of the attached drawings.

The laminates described in Examples 32 to 34 and 51 were formed by conventional deep drawing into containers (drawn - again deep drawing into containers), such as those shown in Figure 5 of the attached drawings.

The laminates described in examples 35 to 38 were processed by conventional methods into lids for beverage containers, as shown in Figure 6 of the attached drawings.

The laminates described in Examples 39 and 40 were processed in the usual manner into iron pans with deep drawn walls such as those shown in Figure 7 of the accompanying drawings.

The laminates described in Examples 41 to 43, 44, 45 and 46 to 50 were processed in a conventional manner into aerosol containers, aerosol domes and aerosol cones, such as those shown in Figures 8, 9 and 10 of the accompanying drawings.

The ECCS used in Examples 25-29, 31-36 and 41-51 is a commercial product of British Steel Corporation and undergoes its ECC treatment in chromic acid containing a sulfuric acid catalyst (type 1). The ECC treatment applied to the steel in Example 30 was chromic acid containing HBF4 as a catalyst (type 2).

The aluminum used in Examples 37-40 was treated in a chromic acid - phosphoric acid medium in an aluminum strip mill after cold rolling and cleaning.

The tin plates used in Example 22 had a tin coating of 0.5 g/m 2 and 2.8 g/m 2 .

Table 3.

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The properties of the polymer film coatings laminated on the products from examples 25 to 51 were verified by subjecting the products to various tests including the following:

Double hemming

The lids of the containers with a diameter of 73 mm are formed from laminate and bent. The lids are butt-welded to the body of the container using a conventional device for edging the lids. The coating was tested for fibrillation, scraping and damage. The lid was checked by immersing it in acidified copper sulfate for 2 minutes and visual inspection for copper deposits.

The ability to shape

Formability is checked by coating the coating after the vessel has already been formed, The coating is checked as described for double lining.

Protection

Protection is assessed by accelerated tests simulating the packaging of aggressive products for 6 to 12 months, evaluating enamel values and determining duration with various specific products.

Common accelerators:

- acetic acid (1.5%), sodium chloride (1.0%) in water,

- citric acid (0.63%), sodium chloride (1.0%),

- malic acid (0.42%), water up to pH 4.

Usual test conditions:

- retort at 121ºC, one hour,

holding for 24 hours,

The components or containers were inspected after the test and the corrosion compared to conventionally coated containers.

Assessing the value of enamel:

- sodium chloride solution,

- 6.4 V,

- monitor current,

- 2 mA acceptable limit

Closing the lid

Polymer coated caps are soldered or riveted in the case of a valve dome to the body of the vessel without trim pieces. The containers were filled with the product and pressed. Weight loss was measured to compare the rate of content loss to conventional parts having trim parts. If this speed is lower than usual, the covers are considered acceptable.

Certain advantages in the properties of the products from examples 25 to 51 are listed in the following presentation.

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Claims (19)

1. A process for the production of a polymer/metal/polymer laminate by simultaneous lamination, characterized by the fact that it includes the application to one of the main surfaces of the sheet of a polyester film composition (A) containing an inner layer (A1), mainly of non-crystalline polyester, whose softening temperature is below 150ºC, and a melting point above 150ºC but below 240ºC, and an inner layer (A2) of linear polyester whose melting point is above 220ºC, and the simultaneous application of a film (B) containing polyolefin, which implies the bonding of an acid-modified polyolefin resin containing carboxylic acid or anhydride groups , to the second main surface of the sheet, whereby the sheet is heated from the temperature T1 at which the polymer film softens and comes into indirect contact with the sheet, with the temperature T1 being lower than the temperature at which the outer surface of the polyolefin-containing film is damaged during application; the resulting laminate is reheated to a temperature T2 that allows both polymer films (A) and (B) to react with each other with the appropriate binder and sheet surface. 2. The method according to claim 1, characterized in that the temperature T1 is in the range of 120 to 240ºC. 3. The method according to claim 1 or 2, characterized in that the laminate is reheated by induction. 4. The method according to claim 1 or 2, characterized in that the laminate is heated again with infrared heaters. 5. The process according to any of the preceding claims, characterized in that the temperature T2 is in the range of 230 to 270ºC. 6. The method according to claim 5, characterized in that the laminate is heated to a temperature between 230 and 270ºC and then held at 220ºC for at least 1 second before being rapidly cooled. 7. The process according to claim 6, characterized in that the laminate is heated to a temperature of 270ºC, and then held at 240ºC for 2 seconds before sudden cooling: 8. The method according to claim 6 or 7, characterized in that the laminate is cooled quickly and uniformly, preferably by immersion in a bath with water or linear cooling with water. 9. The method according to any of the preceding claims, characterized in that the polyester of the inner layer (A) is a copolymer of ethylene terephthalate and ethylene isophthalate, or a copolymer obtained from terephthalate acid and two alcohols, usually ethylene glycol and trichlorohexane-dimethanol. 10. The method according to claim 9, characterized in that the molar ratio of ethylene terephthalate and ethylene isophthalate is 80:20. 11. The method according to any of the preceding claims, characterized in that the outer layer (A2) is biaxially oriented polyester. 12. The method according to any of the preceding claims, characterized in that the outer layer (A2) is polyethylene terephthalate or, even better, biaxially oriented polyethylene terephthalate. 13. The method according to claim 11 or 12, characterized in that the polyester of the outer layer (A2) has a crystallinity greater than 30%, or even better from 40 to 50%. 14. The method according to any of the preceding claims, characterized in that the film (B) containing the polyolefin is actually a monolayer, or is a composite film consisting of an inner layer (B1) of a binding resin such as propylene modified with maleic anhydride, ethylene-propylene copolymer modified with maleic anhydride or ethylene-vinyl acetate copolymer modified with maleic anhydride. 15. The method according to claim 14, characterized in that the content of maleic anhydride in the polymer is from 0.05 to 0.5%, and preferably from 0.1 to 0.25%. 16. The method according to claims 1 to 13, characterized in that the film (B) containing the polyolefin is really a monolayer, or is a complex film consisting of an inner layer (B1), a binding resin such as an ethylene-acrylic acid copolymer or a copolymer ethylene-methacrylic acid, and it is best if it contains from 5 to 15% by weight. acid. 17. The method according to any of the preceding claims, characterized in that the film (B) containing polyolefin is actually a composite film consisting of an inner layer (B1) of binding resin and an outer layer (B2) of polyolefin or polyamide adhered to the inner layer ( B1). 18. The method according to claim 17, characterized in that the film containing polyolefin also has a polyolefin or polyamide layer (B4) which adheres to the layer (B2) via the intermediate layer (B3) of the binding resin, wherein this binding resin is defined in either which of requirements 1 to 4 to 17. 19. The method according to any of the preceding claims, characterized in that the sheet is actually steel electrolytically coated with chromium with a double layer of metallic chromium and chromium oxide.