Plastic moulding and a process for production thereof

Details Plastic moulding and a process for production thereof Plastic moulding and a process for production thereof

2000-05-18

2001-07-03

Dixon, Merrick (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Edge feature

C264S259000, C264S261000, C264S266000, C264S271100, C264S265000, C264S260000, C156S299000, C156S242000, C156S212000, C156S294000, C156S297000

Reexamination Certificate

active

06254968

ABSTRACT:

This invention relates to a plastic moulding and also to a process for production of said plastic moulding.
BACKGROUND OF THE INVENTION
A plastic moulding is described in GB 2 271 956 A. In the latter it is a matter of providing a field that is lined with an elastic layer with a plastic substrate in such a way that in the course of the production process the elastic layer is not compressed and does not lose its elasticity in this manner. The plastic substrate is therefore applied onto the field of the plastic moulding exhibiting the elastic layer in the form of a melt cake which is then press-moulded by the closing of two mould halves. The neighbouring fields of the plastic moulding, on the other hand, in which no elastic layer is located, are injected in conventional manner under high pressure. Nothing is said in GB 2 271 956 A about the material of the plastic substrate in the two fields.
JP 08 281 704 also describes a plastic moulding with at least one blank field next to at least one laminated field; the material of the plastic substrate in both fields, however, is the same.
SUMMARY OF THE INVENTION
It is an object of the present invention to configure a plastic moulding in such a way that it is less costly overall.
This object is achieved by means of a plastic moulding that comprises a plastic substrate with several fields, at least one of said fields being laminated with a covering material and at least one other of said fields being blank, whereby
a) the plastic substrate of the blank field consists of a plastic which is injected under high pressure, and
b) the plastic substrate of the laminated field consists of a plastic which is introduced under relatively low pressure and at low rate of flow, wherein the plastic substrate of the blank field is produced from a high-quality plastic and that of the laminated field is produced from a lower-quality plastic.
With the present invention it is recognized for the first time that the material of the plastic substrate in the blank field and in the laminated field does not have to be the same. Rather it is sufficient to produce the plastic substrate of the blank field from a high-quality plastic; the plastic substrate of the laminated field, on the other hand, can be produced from a lower-quality and therefore less costly plastic. By virtue of this configuration it is possible for appreciable cost savings to be achieved, since only for the blank fields, in which the plastic substrate remains visible on the visible side of the finished plastic moulding, is use made of a costly plastic material, whereas for the laminated fields, which often constitute a major part of the plastic moulding and which have a plastic substrate that is concealed on the visible manner of the finished plastic moulding by the covering material, an inexpensive plastic material finds application.
An advantageous further development of this plastic moulding comprises, several fields which are laminated with optionally differing covering materials, between which a blank connecting field is present in each instance. This blank connecting field may be of extremely narrow design. By virtue of the blank connecting field the edge of the covering material is held securely. Above all in the case of differing covering materials, an optically pleasing exterior is created.
A particularly durable and high-quality design of a plastic moulding includes the protruding edge of the covering material of the laminated field being extrusion-coated by the plastic substrate of the adjoining blank field. This blank field may also be a blank connecting field as set forth in the preceding paragraph, which is adjoined by another field which is laminated with optionally differing covering material. By virtue of this further development a detachment of the covering material from the plastic substrate in the edge region of the laminated field is reliably prevented during the lifespan of the plastic moulding.
In the case of the subject-matter of GB 2 271 956 A which was mentioned in the introduction, production of the plastic moulding is effected in such a way that the elastic layer is inserted into the corresponding recess in a moulding cavity, the edges not being secured separately. The slides which, according to
FIG. 10
of this printed publication, separate the various moulding cavities from one another do not grip the edges of the elastic layer, so the latter are not fixed. In the course of production of the plastic moulding this can result in the covering material slipping or warping in the moulding cavity.
It is therefore a further object of the present invention to configure a process for production of a plastic moulding in such a way that warping and displacement of the covering material during the production process are ruled out.
This object is achieved by virtue of a process for producing a plastic moulding, in which
a) the covering material in the moulding cavity pertaining to a moulding tool is firstly brought into a shape already corresponding to that which it exhibits on the finished plastic moulding;
b) after this the material of the plastic substrate of the laminated field is introduced as a deformable melt cake in almost unpressurized manner into the moulding cavity pertaining to the laminated field and at low rate of flow;
c) after this the melt cake in the moulding cavity pertaining to the laminated field is press-moulded and distributed;
d) after this the melt of the plastic substrate of the blank field is injected under high pressure into the corresponding moulding cavity pertaining to the moulding tool,
wherein
e) after process step a) the edges of the covering material of the laminated field are fixed in such a way that the moulding cavity pertaining to the laminated field is tightly separated from the moulding cavities of the other fields;
d) the edges of the covering material are released after sufficient solidification of the melt cake.
With the process according to the invention the edges of the covering material are accordingly fixed by a separate measure. Only when either the melt cake in the moulding cavity pertaining to the laminated field has sufficiently solidified or when the edges of the covering material within the solidifying melt of the neighbouring blank field have been sufficiently fixed are the edges released, at which point the plastic moulding is entirely finished. Accordingly, at no time can the edges of the covering material move freely or be displaced; the covering material cannot warp or form creases.
In the case of the variant of the process according to the invention that is specified above, firstly the plastic substrate of the laminated field and subsequently the plastic substrate of the blank field are produced. In this case, the melt cake can be applied into the moulding cavity pertaining to the laminated field, distributed in relatively flat manner over the base area of the die. By this means the rates of flow in the course of press-moulding of the melt cake are further reduced and consequently warpage of the covering material is further avoided.
Particularly cost-effective is the process in which press-moulding of the melt cake in the moulding cavity pertaining to the laminated field is effected by the closing of the moulding tool which is clamped on a normal press.
A variant of the first production process aspect, according to the invention, is a process for producing a plastic moulding, in which
a) the covering material in the moulding cavity pertaining to a moulding tool is firstly brought into a shape already corresponding to that which it exhibits on the finished plastic moulding;
b) in a later process step the material of the plastic substrate of the laminated field is introduced as a deformable melt cake under relatively low pressure and at low rate of flow into the corresponding moulding cavity pertaining to the moulding tool;
c) after process step b) the melt cake is distributed in the moulding cavity by press-moulding,
d) the melt of the plastic substrate of the blank field is injected under high pressure into the corresp

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