Adhesive bonding and miscellaneous chemical manufacture – Surface bonding means and/or assembly means therefor – Presses or press platen structures – per se
Patent
1996-05-30
1999-01-05
Sells, James
Adhesive bonding and miscellaneous chemical manufacture
Surface bonding means and/or assembly means therefor
Presses or press platen structures, per se
100295, 139425R, 442229, B30B 1502, D03D 1500
Patent
active
058557334
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a press pad for use in a laminating press for the production of laminate sheets, such as decorative laminates and printed circuit boards, using low pressure and high pressure single daylight and multi daylight presses.
Background Art
As shown in FIG. 4 of the drawings appended hereto, in a single daylight laminating press, a laminate sheet 1 to be pressed between two platens 2 of the press is located between two metal caul plates 3 and two press pads 4. The press pads 4 are each located between one of the caul plates 3 and one of the platens 2. The press pads 4 are usually a little larger than the dimensions of the platen 2 to allow for clamping.
The purpose of the press pads 4 is to compensate for density variations in the laminate sheet 1 and thereby ensure that an equal pressure is applied to all parts of the sheet 1. In addition, the press pads 4 compensate for any unevenness in the surfaces of the platens 2 of the press itself and any flexure or bowing of the platens 2 when under pressure. Again, this assists in the production of a flat even density laminate. Thus, it is important for a press pad to be resilient and have a natural springiness to permit it to compensate for the aforementioned density variations and the surface unevenness of the press platens but also to allow it to relax after each pressing operation and recover its form to enable it to be used again. The capacity a press pad has to re-form itself after each pressing is an important characteristic to ensure a reasonable working life and to avoid unnecessary downtime of a press whilst the press pads are replaced.
However, because the purpose of the press is to apply heat to the laminate sheet whilst it is under pressure, it is important that the press pad also conducts the heat supplied by the press platens to the laminate sheet. Working temperatures for such presses are usually in a range up to 220.degree. C.
Typically, therefore, a conventional press pad is a densely woven combination of high temperature resistant non-asbestos yarns and metal wire. The metal wire is included to give good heat transmission through the pad to the laminate sheet. In contrast, the non-metal yarn is required to give the pad the springiness and resilience required to enable the pad to relax after each pressing operation. The relative proportion of the two types of material is a consideration when devising a press pad for a particular purpose. Usually a compromise must be reached between the heat transference and the resilience required in each case.
The metal wires used are typically copper or brass wire whereas the temperature resistant yarns are usually made from aromatic polyamide fibres such as those manufactured and marketed by Du Pont Inc under the trade marks KEVLAR and NOMEX. Whilst metal wires can be woven per se, it is also common for metal strands to be wrapped around heat resistant yarns and for heat resistant yarns to be wrapped around metal strands. Metal wires may also be sheathed with textile fibres.
A conventional press pad for use in a high pressure daylight press is described in EP 0 493 630 A1. Here, the press pad is made from a woven textile of aromatic polyamide and metal threads.
Another press pad is described in EP 0 488 071 A2. This also is made from a combination of heat resistant organic fibres, such as aramide fibres, phenol fibres, polyetheretherketone fibres, and polyphenylsulfone fibres, and heat resistant inorganic fibres such as carbon fibres, glass fibres and metallic fibres.
One of the problems encountered with these conventional press pads is that in use, the metal threads eventually flatten the weave structure to such an extent that the press pad is unable to relax after each pressing operation and the pad loses its resilience and springiness.
Another problem with conventional press pads is that once a pad has been used for pressing a particular size and format of laminate sheet, it is generally not possible to use the pad again with sheets of a larger size or differen
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Boyes Peter
Douglas Melvyn
Payne John Lynn
Marathon Belting Limited
Sells James
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