Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2001-05-24
2004-06-22
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S195100, C428S458000, C428S480000, C428S035800, C428S035900, C428S035700, C427S223000, C427S224000, C427S314000, C427S322000, C427S331000, C427S372200, C427S412100, C427S412500, C215S235000, C215S252000, C215S329000, C215S341000, C215S347000, C215S352000, C215S349000
Reexamination Certificate
active
06753088
ABSTRACT:
FILED OF THE INVENTION
The invention relates to a method for at least locally providing an article coated with an organic coating with a layer of readily deformable sealing material (a so-called compound), which involves a layer of an intermediate of said compound being applied to the coating layer, after which the article is temporarily kept at an elevated temperature in order to form the compound from its intermediate
BACKGROUND OF THE INVENTION
At many points in industrial applications it is necessary to be able to connect such an article and another article to one another in, for example, a vacuum-tight manner. A known example of this are the generally known screw tops on glass jars which are designed to contain food. In order to extend the shelf life of these foods it is then essential for the lid to be able to be seal the jar in a gas-and-vacuum-tight manner, said sealing also being able to withstand a pasteurization or sterilization treatment of the contents of the jar.
Since the mating rims of lid and jar are not always fashioned so as to provide a completely smooth seal, the absolute seal is achieved with the aid of an interposed layer of the readily deformable sealing material, the compound. Processable intermediates of such compounds are commercially available in various types and chemical compositions, many of these compounds having a composition based on PVC. After application of the processable intermediate to the article in question the intermediate is cured to produce the compound itself. Particularly for use with screw tops it is required for the applied layer of compound to have good adhesion to the article to which it is applied. If said adhesion is inadequate, the layer of compound, particularly when used in screw tops, will curl up or shear off, and a good seal is no longer guaranteed.
As a rule, articles provided with a compound layer are first coated with an organic coating. This can be the case, for example, with screw tops made of steel. Whilst a steel lid can be protected against corrosion by applying a metallic top layer, preference is nevertheless given in many cases to the additional application of a coating. This may be desirable, for example, to protect the taste of the contents of a jar or to allow the inside of the lid to be provided with pictures or text. Good adhesion of a compound to a coating layer in many cases is found to constitute a problem that cannot readily be solved. In particular this is the case if the article is coated with organic coating based on a PET (polyethylene terephthalate).
SUMMARY OF THE INVENTION
The invention provides a solution for this generally experienced problem. The invention then, with the method assumed to be known, consists in the coating layer of the article comprising a polyethylene terephthalate and the compound being chosen from the group consisting of urethanes, amides, mixtures thereof and heteropolymers thereof, and in the free surface of the coating layer prior to the application of the intermediate of the compound, at least at the location where this intermediate is applied, being briefly subjected to a processing operation from the group of equivalent processing operations comprising a flame treatment in the course of which the coating layer does not melt.
It should be noted that the layer of compound in many cases has been formed by a special treatment of an intermediate of the compound as applied to the article. For example, said intermediate will have to be cured after having been applied, for example by a solvent or a dispersant being driven off therefrom with the aid of a thermal treatment.
It was found, surprisingly, that the additional subjection of the coating layer to the proposed processing operation has the effect, with PET polymers, that the surface of the coating layer has acquired a very greatly improved potential for adhesion to the compound. Surprisingly, said improvement is found to occur, in particular, with compounds of the abovementioned type. The adhesion of PVC-based compounds is as a rule not improved, in many cases even deteriorates, after the treatment described.
It is also noteworthy that an effect is involved here which comes about due to the type of processing operation in the form of a flame treatment, and that, for example, an increase in temperature on its own will not, as a rule, achieve a comparable effect. In some other thermal processes in individual cases somewhat similar other conditions are apparently effected, as a result of which, for example in the case of heating with the aid of a plasma, a positive effect is also observed with some PET coatings. Very good results on virtually all customary PET coatings are however obtained according to the invention if the operation of subjecting the free surface of the coating layer to a processing operation is effected with the aid of a flame which is obtained by burning a stoichiometric mixture of propane and combustion air.
It should be noted that flame treatments and the conditions under which these are carried out are generally known for the purpose of acting on free surfaces. Reference can be made, for example, to the publication “Gas Flame Technology” by Cliff Bartley and P. B. Sherman, published by the English company Sherman Treaters. There the effect of the flame treatment on a free surface is ascribed to the action on the surface of free radicals, ions, neutral compounds and electrons formed in the flame. It will be evident that it is possible, by varying process parameters, to obtain a group of physicochemical processing operations which are equivalent in terms of the end result. Flame treatments are known for increasing the surface tension. This proves not to be a determining factor for the adhesion of compounds, however.
In the case of exposure to an open flame it is possible to proceed in various ways. However, it was found to be preferable for the article and a flame, obtained by combustion of propane, to be moved with respect to one another while in contact with one another. It should be noted in this context that in many cases an end product such as a lid is fabricated from strip material which after a pretreatment is converted into a final form by punching and further mechanical treatment. In the case of coated steel screw tops, for example, it is possible for a steel strip first to be coated and to undergo the flame treatment described, after which blanks are punched from said strip which are then made into screw tops which finally are provided with an annular layer of compound in their base.
As stated previously, the compound layer will be formed firstly by an intermediate of the compound being applied, said intermediate then being cured to produce the compound proper. According to the invention, said curing to produce the compound can be effected by the article, after application of the intermediate, being kept for at least 40 sec at a temperature of between 200 and 230° C. and then being cooled. Obviously, in the case of a strip-like article a highly feasible option is to carry out thermal treatment by passing the strip through a continuous furnace.
Although the novel method is applicable to coated articles whose substrate may comprise widely diverse materials, such as plastics, the invention proves to be particularly advantageous when applied to articles comprising a metal substrate. In particular, a suitable application was found if the metal substrate consists of a metallically coated steel plate. Possible applications are tin plate or steel plate with an ECC coating (electrolytic chromium/chromium oxide coating).
The above referred to a coating layer on the article, but with many applications it will be preferable for said coating layer itself to consist of a plurality of layers. For example, an under layer may be chosen which ensures good adhesion to, for example, a metal substrate, whilst a top layer may be chosen because of its inert characteristics with respect to materials with which the article must come into contact. For example, if the article is a lid of a tin for food or drinks, the t
Belvroy Renauld Robert
Van Veenen Jan Willem
Chen Vivian
Corus Technology BV
Stevens Davis Miller & Mosher LLP
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