Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1993-08-25
1995-09-19
Barry, Chester T.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156378, 156289, 1563084, 156367, 1563796, B32B 3100
Patent
active
054512867
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method of welding an embossing and/or welding and/or parting seam in one or more layers of material containing heat-weldable, especially thermoplastic plastic material, by means of indirect heating of the plastics in a welding press, by using a welding electrode arranged against one side of the material, said welding electrode in particular being an upper electrode of a welding profile and pattern mating the welding to be performed, where the temperature of the welding electrode is kept constant and preferably below the softening point of the plastic material.
The invention relates furthermore to a welding press for carrying out the method and comprising a welding plane and a fixing plane, where the welding plane is provided with a welding electrode of a welding profile and pattern mating the welding to be carried out and the temperature of which can be kept constant within a temperature range of approximately 20.degree. C. and approximately 250.degree. C., and where at least one plane can be moved towards and away from the other plane.
BACKGROUND ART
Heat contact welding is traditionally used for embossing, welding, cutting, and producing of bending lines in thermoplastic material, said welding involving a direct or an indirect heating or an HF-welding when it is a question of welding plastic materials presenting a sufficiently high dielectric loss, such as in case of PVC.
The HF-welding is advantageous in only using a single electrode, i.e. the welding electrode, whereas the heating of the material is caused by the dielectric losses in the material with the result that the method is very easy and convenient to perform and does not require a production of exactly mating and accordingly expensive electrodes. The HF-generator of the machine is, however, very expensive and involves a high consumption of energy. The method has gradually been extensively used especially for welding PVC.
A heat contact welding involving an indirect heating of the plastics employs usually a welding electrode and a counter electrode, where both electrodes are heated, the welding electrode being heated to a temperature about the softening temperature of the plastics and the counter electrode being heated to a temperature exceeding the melting temperature of the plastics. The welding electrode includes the particular welding profile acting directly on the possibly Teflon-coated top side of the plastics, whereas the counter electrode is plane and shielded from the plastics by means of a separation tape of a higher melting point than the plastics. The latter method has been extensively used for welding thin sheets, but can only be used to a limited extent for welding thick sheets and materials because the heat must be conducted through the plastics in order to reach the welding spot, and accordingly the top side of the plastics is heated more than the welding spot, which causes problems of heat damages of the plastics outside the welding seams. In order to obtain high production rates, attempts have been made at operating at temperatures being as high as possible, but such procedures only made the situation worse because the high temperatures and high amounts of heat, especially in the bottom tool, involved a considerably increased risk of the sheets being damaged. A consequence of the unintended heating is that the sheets turn soft and form bulges, especially in connection with even very short breaks. Attempts have been made at solving this problem by establishing suitable screening devices and cooling devices, but these devices did not provide satisfactory results when thick sheets were involved.
The above problems have become particularly topical because of the present requirements for restricting the use of PVC so as to reduce the environmental damages. Accordingly, a demand has arisen for using other types of plastics, especially polyolefines. These types of plastics cannot, however, like PVC be welded by way of HF-welding in a satisfactory manner, and accordingly it is necessary to
REFERENCES:
patent: 2714416 (1955-08-01), Fener
patent: 3484325 (1969-12-01), Pendleton
patent: 4416713 (1983-11-01), Brooks
Barry Chester T.
Weldan A/S (Evald A. Nyborg A/S)
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