Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1997-08-20
1999-05-04
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
2643282, 26432815, 26432816, B29C 3502, B29C 3302, B29C 4573
Patent
active
059002042
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The automatic pressure gelation technique (APG) for moulding articles with thermosetting resins is well known and consists essentially of the supply of liquid curable resins under pressure into a mould and ensuring that the pressurised liquid supplied from outside the mould remains in contact with the liquid resin in the mould whilst it gels or solidifies from the furthest point or points from mould entry and or the last point to fill back to the mould entry. By ensuring this applied pressure is maintained on the liquid resin system and the gel progression follows this pattern excellent void and shrinkage free mouldings are obtained by compensating for polymerisation shrinkage with further liquid supplied from the external pressurised source.
This process is well proved in practice for the manufacture of both complex and simple shaped mouldings alike. The process can be used for long production runs of mouldings of high quality with very low rates of rejection. The production of such moulding has been described in Patents EP 0 333 456B1 and U.S. 5,064,585 and in these consists essentially of filling moulds that have temperature within the mould set in the range of from around 120.degree. C. to 160.degree. C. at the point of entry to 130.degree. C. to 170.degree. C. at the furthest point from entry where the furthest point is always the higher and with the ideal temperature at points furthest from resin entry being approximately 10.degree. C. higher than the temperatures at the entry point. Such positive temperature gradients had been stated to be important in order to obtain excellent mouldings from epoxy/anhydride curing compositions which are particularly suited to this process. The temperatures had been chosen to achieve a linear gradient in the moulding operation to ensure the desired gel sequence as stated
However, there is a great need to speed this moulding process to achieve the maximum possible use of capital equipment such as moulds and press machines, to reduce labour cost per unit and to approach or to exceed the speed of producing the equivalent item made by thermoplastic injection or dough or sheet moulding compound matched tool moulding. The conditions taught under the patents referenced above do not permit this speed of production with the desired type of resin system.
In order to increase the speed of the process, higher temperatures can be used. However using the known process where a temperature gradient is maintained the temperature gradient at the hotter end of the mould cannot be increased too much as this will result in decomposition of the resin hardener system.
SUMMARY OF THE INVENTION
We have now found that by eliminating the temperature gradient, or even reversing it so that the entry point is at a higher temperature than the furthest point from entry, a decrease in the moulding cycle time can be achieved without decomposition of the resin and without changing the desired gel sequence. The net result is that for any given temperature at the furthest point from entry and for any given resin system, the speed of the process is increased.
Accordingly, the present invention provides a process for making a cured plastics moulding by introducing a curable resin composition to a heated mould and supplying further resin under pressure to compensate for shrinkage of the composition which comprises heating the curable resin composition either before entry or as quickly as possible on entry into the mould, or both, to a temperature which permits the satisfactory filling of the mould before gelation and subsequent progressive gel from the point furthest from entry back to the point of mould entry, and wherein the entry parts of the mould are heated to a temperature at least as high as the temperature of the final fill point of the mould.
The temperatures actually employed may be any which allow the desired sequence of gelation to take place provided degradation of the resin system itself does not occur. Thus for very reactive systems of whatever composition e.
REFERENCES:
patent: 3777000 (1973-12-01), Kusenberg et al.
patent: 5064585 (1991-11-01), Cooper et al.
patent: 5194197 (1993-03-01), Munk et al.
Derwent Abst. 76-93552X (1976).
Derwent Abst. 88-124216 (1988).
Patent Abstr. of Japan, vol. 12, No. 416, (1988).
Patent Abst. of Japan, vol. 17, No. 623, (1993).
Badcock William Walter Charles
Lucchi Marco
Wombwell Paul Terrence
Ciba Specialty Chemicals Corporation
Crichton David R.
Heitbrink Jill L.
Levine Jacob M.
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