Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1998-03-10
2000-07-04
Stemmer, Daiel
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156219, 1562726, 1563082, 156322, 156324, 156555, B32B 3108
Patent
active
06083336&
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus and a process for coating metal sheets with plastic films.
The coating of metal surfaces with plastics finds numerous applications for various products such as electrical equipment or packaging, for example. In the food industry, for example, foodstuffs are packaged in containers (cans), the metal body guaranteeing the stability of the packaging vessel and the plastic coating providing for food-compatible separation of the metal from the foodstuffs. A film applied additionally to the outer faces of metal containers is able, furthermore, to accommodate information and advertising by virtue of being printed.
A problem which naturally occurs with these applications is that of applying the plastic coating to the metal substrate with a sufficient adhesive strength. A number of process variants have already been developed for this purpose in accordance with the prior art. Among these, particular importance attaches to the processes in which a prepared plastic film is applied over a large area to the metal and is bonded to it. Here, fundamental forces of adhesion are responsible for the adhesion of the plastic to the metal. In this case sufficient adhesion is achieved in particular by means of an adhesive interlayer or by melting the plastic film onto the metal.
EP-0 312 309 describes, for example, a process for coating metal films with polypropylene. Features of this process are that the polypropylene film is bonded to the metal by melting and that rapid and uniform cooling takes place after the melting operation. This influences the crystallization process within the polypropylene. However, there is no possibility with this process to direct the surface texture of the laminate in a desired direction. This is highly disadvantageous, since the nature and appearance of the surface represent important properties of the product.
In connection with the coating of metals with apolar substrates such as polypropylene, for example, a surface treatment is additionally of advantage. Suitable such treatments include cleaning processes, which remove disruptive substances from the film, and mechanical pretreatments, such as roughening or chemical activation, for example. In the case of coating with polyolefins, moreover, flame treatment of the film is employed in particular. Chemical activation of polypropylene melt films can be carried out by treatment with ozone. Good control of the intensified adhesion and a good activation effect are also offered by pretreatment by means of so-called corona discharge. In this type of treatment, spontaneous gas discharges occur in a non-homogeneous high-voltage alternating field which is generated over the film. It is assumed that this produces substances such as peroxides, for example, which then lead to chemical activation of the plastic surface. Nevertheless, effective coating of the metal sheets with plastic film remains technically problematic. For instance, in the case of thin polyolefinic films, there are often instances of blocking in the course of corona pretreatment. In addition, the corona pretreatment produces an adhesion-promoting surface tension which, however, becomes reduced over the course of time (days or weeks) and may then, following application of the film to the metal sheet, lead to adhesion problems.
The object addressed by the invention is to provide an improved apparatus and an improved process for laminating plastic films onto metal sheets and, in so doing, to achieve improved adhesion values, in particular, and to be able to control the surface texture.
This object is achieved by an apparatus which consists of a feed for the metal sheet, an oven for preheating the metal sheet, at least one feeding unit with laminating rolls for films that are to be applied, optionally a further downstream oven for the conjoint heating of metal sheets and the film atop them, at least two downstream texturing or smoothing rolls, and optionally a printing mechanism.
This arrangement makes it possible to apply the film with firstly with very good
REFERENCES:
patent: 3616198 (1971-10-01), Saito
patent: 4250274 (1981-02-01), Damico et al.
patent: 5158831 (1992-10-01), Schirmer
patent: 5234516 (1993-08-01), Okamura et al.
BASF Coatings AG
Stemmer Daiel
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