GB2124539A

GB2124539A - Moulding disc records

Info

Publication number: GB2124539A
Application number: GB08220345A
Authority: GB
Inventors: Hermann Strausfeld
Original assignee: EMI Electrola GmbH
Current assignee: EMI Electrola GmbH
Priority date: 1982-07-13
Filing date: 1982-07-13
Publication date: 1984-02-22
Also published as: DE3323045A1

Abstract

An anti-stringing device suitable for use with a mould cavity (1) which receives a thermoplastics material, includes means for causing the device to assume a start position wherein its rod (5) is inserted into the unfilled mould cavity and is disposed opposite and in close proximity to a thermoplastics material injection orifice (4), and means (6) for progressively retracting the rod (5) during filling of the cavity, until the rod attains a position whereby it substantially merges with the opposite wall of the cavity when the cavity is full. <IMAGE>

Description

SPECIFICATION Improvements relating to disc record production This invention relates to the production of predetermined, discrete portions of thermoplastics material suitable for use in the manufacture of disc records.

A disc record is commonly produced by pressing of a flowable thermoplastics material between two stamper plates bearing a negative impression of the information track the record is to carry. In manufacture it is important that a sufficient portion of material has been placed between the plates to permit a complete disc record to be moulded and to allow an excess to produce a border or flash, by means of which the record can be gripped and also ensuring the completeness of the disc record.

The thermoplastics material must have a flowable consistency prior to moulding of the record, which consistency can be achieved by heating the thermoplastics material to a suitable temperature. A sufficient portion or shot of the material can be produced prior to the pressing by injecting the material into a suitably sized mould.

The mould shape can additionally be selected to enhance flow of the material during subsequent pressing of the disc record. However, this extra step of forming a shot can introduce irregularities in consistency of the material, for example air pockets. Another common problem encountered is termed stringing. The initial injected material adheres to the mould cavity walls and as the mould fills parts of this initial material are stretched to produce a thin filament or string, which is subsequently pressed back into the shot surface when the mould is completely full. The occurrence of these strings can produce defects in the final disc record when the shot is subsequently pressed. Consequently, the problem of stringing can lead to an increase in disc records having an unacceptable fault level.

It is an object of this invention to produce an anti-stringing device suitable for use with a thermoplastics material mould cavity.

According to one aspect of the invention there is provided an anti-stringing device suitable for use with a mould cavity to receive a thermoplastics material, including means for causing the device to assume a start position whereby a member is inserted into the unfilled mould cavity and is disposed opposite and in close proximity to a thermoplastics material injection orifice, and means for progressively retracting the member during filling of the cavity from said orifice, until said member attains a position whereby it substantially merges with a wall of said cavity when the cavity is full.

Preferably the mould cavity is suitable for the production of shots prior to pressing of disc records, and the member is a rod.

For a better understanding of the present invention and to show how the same can be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:~ Figure 1 illustrates in section a mould cavity including an anti-stringing device, a member of the device being in a start position.

Figure 2 illustrates in section a mould cavity including an anti-stringing device, the member of the device merging with a cavity wall.

Referring to the drawings, a mould cavity 1, suitable for production of thermoplastic shots utilized in manufacture of disc records, is defined by an upper plate 2 and a lower plate 3. An injection orifice 4 provides entry to the cavity for thermoplastic material 7 to be moulded. A rod member 5 forms part of an anti-stringing device, which also includes a feed device 6 having a rack and pinion mechanism to insert and retract the rod member 5 from cavity 1.

Initially the rod member is inserted to a position in which it is disposed opposite the orifice and in close proximity to it. This is the starting position of the anti-stringing device and thermoplastics material is then injected through the orifice. As this occurs the rod is progressively retracted by the feed device as the cavity fills up. When the cavity has been completely filled, the rod has been retracted to a position wherein it substantially merges with the side wall of the cavity as illustrated in Figure 2. After the mould cavity is split to remove the shot formed therein the rod 5 can be returned to its starting position to await the following injection of thermoplastics material.

In this manner, the amount of stringing occurring during formation of the shot can be reduced, consequently reducing the occurrence of defects in disc records pressed from the shot.

It will be understood that the embodiment illustrated shows an application of the invention in one form only. In practice the invention may be applied to many different configurations of mould for example or feed device; the detailed embodiments being straightforward for those skilled in the art to implement.

Claims

1. An anti-stringing device suitable for use with a mould cavity to receive a thermoplastic material, including means for causing the device to assume a start position whereby a member is inserted into the unfilled mould cavity and is disposed opposite and in close proximity to a thermoplastics material injection orifice, and means for progressively retracting the member during filling of the cavity from said orifice, until said member attains a position whereby it substantially merges with a wall of said cavity when the cavity is full.

2. A device according to Claim 1 in which said mould cavity is suitable for the production of shots (as hereinbefore defined) prior to the production of disc records.

3. A device according to either preceding claim in which said member is a rod.

4. A device according to any preceding claim in which said means for progressively retracting said member includes a rack and pinion mechanism.

5. An anti-stringing device substantially as herein described with reference to the accompany drawings.