Untitled record

Method for the production of film-coated metal strips or sheets for the production of cans or similar containers It is already known to use a solution of plasic masses in suitable solvents as a lacquer for coating sheet metal, which is used for the production of packaging, such as B. IConservendosell u. Like., Are determined.

It is also known. finished molded cans and can ends subsequently coated with such a protection paint. This protective lacquer is to prevent the corrosion of the iron or aluminum or the like. Existing sheet metal material and serve as a substitute for the expensive tin.

Experience has shown that the protection by a paint coating, even if it is applied relatively strong, is insufficient. The resulting coating of the liquid paint is namely never tight, which is related to the application of the paint or surface tension during the drying process.

Another method which has been mentioned is the production of films intended to be used instead of paper for packaging purposes. It is suggested, paper, cardboard or a metal foil! using adhesives and applying pressure to a plastic film. However, this method is only suitable for joining two thin layers of approximately the same thickness, wherein the mechanical stress of packaging films is much lower than the stress on sheet metal, as occurs, for example, in the manufacture of cans, in particular in deep-drawing operations. Although this method is sufficient for wrapping paper or cardboard with a plastic film, it is entirely unsuitable for the production of onion can sheets.

In a further known method thermoplastic material is applied in powder form and using heat and pressure with the substrate, such as. As fabric, paper, wood and metal connected. In this process, the Metallbledie must be perforated so that the plastic powder enters the holes and in this way a connection between the two Kunststoftlagen is achieved. If only one surface of the sheet is to be coated, it is proposed to incorporate into the sheet screw holes or holes or slots with a conical cut to connect the plastic layer on the surface.

It can be seen from these proposals that it is very difficult to fix powdery plastic adherent to a metallic sheet and that further provided for this method with plastic sheet for consu dendosenherstellung is practically out of the question. In addition, it is not possible by this method, to bring the flowing from a container powdery mass by rolling on a small layer thickness, as is required in tin cans.

The method according to the invention now makes it possible to firmly connect a film which meets all the requirements both as a protective coating and as a gasket to a metal strip or sheet in a simple manner without the use of an Elel bonder.

According to the invention, a pre-applied stretched thermoplastic resin film without adhesive is bonded by rolling at a temperature close to the softening point to a previously roughened and correspondingly preheated metal strip or sheet. For the present purpose, various thermoplastics come into question, such as. B. polyisobutylene or acrylic and methacrylic acid polymers. The first named polyisobutylene has proved to be particularly suitable. These films are very dense because they are manufactured in the Walzverfallren and accordingly go much better protection against corrosion of most of an iron band or 4lech ordering Verpadungsmateri than, as is possible by a LackschllutzaIlstrich.

For sealing purposes, it is possible to use a thermoplastic film which swells when liquid is taken up. In this case, the gasket will be particularly good and effective in the pleats of the packaging bags, containers or cans. The films can be applied on one or two sides.

If, for special reasons, only one side is protected, the late! R in the packaging, eg. As the cans. the inner surface forms, then the other side (outer surface of the box) by other coatings, for. By calcination.

In the new process, the use of a particular adhesive is eliminated by bonding the finished pre-stretched thermoplastic film to the roughened metal sheet at a temperature close to the softening point.

In order to achieve an intimate solid and permanent connection between the film and sheet or strip, according to the invention, the sheet or strip is roughened before applying the film. This roughening can already take place during the rolling of the sheet by using rollers with a correspondingly roughened surface during the last rolling passes. This rough on can also be effected in other ways or additionally by sand blasting or other means.

The firm connection between film and metal sheet or band is achieved in that the film is pressed in the plastic state in the roughened surface. The plastic mass penetrates so deep into the pores or grooves of the roughened surface that a firm and durable connection of Kmistoffolie takes place with the metal strip.

Further, the film is stretched before application by means of pressure rollers on the metal strip or sheet. This is necessary to prevent damming of sheet material in front of the pressure rollers and thus to permit thin rolling of the films at all. As is known, rubber-like films can not be rolled down under a film thickness of 0.5 mm. By means of the rolling process according to the invention, it is possible to apply films with substantially lower thicknesses to the sheet or strip.

It has been found by experimentation that it is correct not to heat the pressure rollers, but rather the metal strip or sheet before applying the film, to a temperature which is at or above the softening point of the film.

The following will be on. Hand of the drawing explains the new procedure. 1 shows a schematic embodiment of a device for carrying out the new method, FIG. 2 shows a section through a piece of a building with a film according to the invention on a greatly enlarged scale.

According to Fig. I is a metal strip. z. As iron strip 1, withdrawn from a tape roll 2 and passed through a muffle furnace 3, which heats the tape over the softening point of the film. As stated above, channel the iron band already be roughened in the cold rolling mill, or it can be roughened subsequently, and optionally also between the tape roll 2 and the open 3, the Aufrauhvorrichtimg can be turned on. The heated iron strip passes over guide rollers 4 and through the two pressure rollers 5 to a take-up reel 6. The thermoplastic film 7 is withdrawn from a Trommel8, passed over two drums 9 and IO and then fed to the pressure rollers 5 together with the iron strip.

The Tromineln 9 and IO operate a stretching device for the film 7. For this purpose can act on the two drums 9 and 10 brakes. This is shown schematically in the drawing at the Trommelg by a jaw brake II. It is advantageous, however, to drive the drums g and IO slower relative to the pressure rollers 5, wherein in turn the two drums g and IO rotate under different speed, ie In this way, the film 7 can be stretched to a fraction of its original strength before it passes with the belt or sheet between the pressure rollers 5. Furthermore, a smoothing roller I2 is arranged in front of the pressure rollers, which smoothes out any wrinkles that may still be present in the film.

If, with the drafting system shown in FIG. 1, the film is applied very thinly to the strip or sheet, reinforcement of the film at the later folding (sealing) points may be desired. This can be achieved in a simple manner in that the edges of the expiring of the drum 8 slide 7 are beaten or beaded before running onto the drum g, so that the film has twice the thickness at the edges. The pressure rollers 5 must of course be recessed at the ends so that they do not press on the reinforced edges of the film. Optionally, a reinforcement of the film edges can also be effected by using spherical Tro, mmelng and IO, which have after the end faces to a smaller diameter than in the middle.

FIG. 2 shows a cross section through the product obtained with the device according to FIG. The iron band I is roughened on one side, as indicated at I3, so that point-like or channel-shaped depressions arise. A firm connection of the film 7 with the iron hand 1 is achieved by pressing in the film in the plastic state into the recesses of the rough surface 13. The film coating can be double-sided and single-sided. In the latter case, the other side (outside of the package) is protected in any manner, for example by a tin coating I4, against corrosion.

The film applied according to the invention has three functions: it serves as a protective cover, fe urn as a sealant for the grooves in the bottom and lid of the container or the box and finally as a sealant for the longitudinal seam of the container or can body. With the film can be coated according to the invention, the whole band or sheet surface, so that the film also serves as a protective coating and at the folds as a sealant. Of course, the film can also be applied only in strips, so that it either serves only as a protective coating or only as a sealant.

The new method makes it possible to use a finished commercial film and apply them by special, above measures so on metal strip or sheet, that the synthetic resin layer has a correspondingly low and controllable strength (less than 5 mm) and this so intimately and firmly is associated with the metal that this metal can withstand the highest stresses in further processing, especially in drawing operations in the manufacture of food cans. In contrast to the previously known methods, the film can be applied in a sufficiently low thickness smooth and without wrinkling, the Folirenstärke can be varied as desired to extremely thin and wiflschaftlich portable Auflagedi bridges. The plastic film serves primarily as a reliable corrosion protection, since it does not like pvc coatings has pores, but receives a dense surface by rolling. It is guaranteed in this way an absolute protection of the base metal.

At the same time, the plastic film also serves as a sealant for longitudinal seam and the flare on the bottom and lid of the container or can. It is consequently mcht more than ever necessary to solder the longitudinal seam and flare on the bottom and lid with tin or insert special seals, since the plastic film itself acts to seal when heated, so that containers and cans with sheet produced by the new process much more economical can be made.