Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1994-07-20
1995-07-11
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
2643289, 425544, 425DIG228, B29C 4546, B29C 4502
Patent
active
054318548
DESCRIPTION:
BRIEF SUMMARY
The present invention firstly relates to a method for pressing a plastic, which cures by means of a reaction, from a displacement chamber via at least one injection channel and a gate into a mould cavity, said method at least comprising the following steps: displacement chamber; vicinity of the gate of the mould cavity.
The term plastic which cures by means of a reaction is used to designate plastics such as, for example, thermosetting plastics and photopolymerisable plastics, multicomponent plastics and the like. These are plastics which cure by supplying heat or light or after mixing with a chemical compound. Examples of such plastics are generally known to those skilled in the art. The plastics which cure by means of moisture or air can also be mentioned in this context. Usually however thermosetting plastics are used.
The abovementioned method is generally known and is used for the production of diverse mouldings from plastics which cure by means of a reaction. The encapsulation of integrated circuits in thermosetting plastics, and the production of car components from such plastics, can, for example, be considered in this context.
In this respect reference is made to U.S. Pat. No. 3,911,075. In said specification a method is described, in which method a first thermosetting polymeric material is used as the plastic which cures by means of a reaction. Further a cheap second thermosetting polymeric material is used as the pressing auxiliary. By pressing the two polymeric materials together from a displacement chamber, through an injection channel and a gate into a mould cavity, the passages up to the gate are filled with the relatively cheap thermosetting polymeric material.
Pressing of plastics which cure by means of a reaction into a mould cavity is, as a consequence of the properties of these plastics, usually a batchwise method, because the curing reaction is frequently exothermic and is a reaction which goes to completion. For example, thermosetting plastics are plastics which melt by supplying heat thereto and then cure by means of an exothermic reaction. As a consequence thereof, thermosetting plastics have a relatively short storage time and must also be stored cool. Comparable storage problems arise in the case of plastics which cure by means of light, air or moisture. Although multicomponent plastics, which cure by mixing the various components with one another, have fewer storage problems, the curing reaction usually goes to completion after mixing.
Plastics which cure by means of a reaction are usually placed in a determined amount, for example in pill form, together with a, e.g. thermosetting, pressing auxiliary, in a displacement chamber which is connected via injection channels to the gates of the mould cavities. The plastic and pressing auxiliary are then pressed with the aid of a plunger or the like through the injection channels and the gates into the mould cavities. With this method it can be advantageous, for example in the case of thermosetting plastics, to heat the plunger or the displacement chamber. The plastic itself can also be preheated.
Once the mould cavities have been filled with the plastic, said cavities must be kept under pressure during curing of the plastic, in order to prevent bubble formation as a result of any entrapped air or moisture which may be present. This is done by pressurising the pressing auxiliary.
By using a pressing auxiliary a number of significant disadvantages of using only the plastic which cures by a reaction are overcome. A relatively large amount of cured plastic, which remained behind in said channels and in the displacement chamber after curing, is saved.
The materials used as pressing auxiliaries are in the state of the art limited to thermosetting plastics (e.g. U.S. Pat No. 3,911,075). These plastics have proven to be quite useful although they still possess a number of important disadvantages. Thermosetting materials usually have an exceptionally good adhesive strength to the mould (mould cavity, the injection channels and the displacement c
REFERENCES:
patent: 3483287 (1969-12-01), Davis
patent: 3870449 (1975-03-01), Stringfellow
patent: 3911075 (1975-10-01), Boesch et al.
patent: 5043199 (1991-08-01), Kubota et al.
"3P" Licensing B.V.
Heitbrink Jill L.
Jaskiewicz Edmund M.
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