The present invention relates to a method for producing legible identifying data in the label portion of disc-shaped information carriers which are provided with a groove spiral for the storage of scannable signals, the method being particularly applicable to discs formed in a preliminary stage in the manufacture of records, e.g. discs used to produce record stampers.
Information carriers are understood to be, for example, lacquer foils, such as matrices, which serve to duplicate recorded information, by means of a stamping or pressing process, i.e. in the manufacture of audio or video records.
Records are legibly or visually identified by printed paper labels at their center. These labels, in addition to containing a text information about the contents of the side of the record, also contain numerical identifications, such as stock numbers and license information. In the conventional manufacturing process for records, these labels are inserted into the pressing mold before the record is pressed and are irremovably sealed with the record material during the pressing process.
This process stresses the paper both thermally and mechanically; it must thus meet unusual requirements. It must contain only a few volatile components, in the paper and printing dye, the printing dyes must not come off, and the paper must have a particularly high tensile strength so that it will not tear during the pressing process due to shear forces in the record material.
It is furthermore necessary, when a record receives labels on both sides, to apply the labels with the paper fibers running in the same direction because otherwise a bending moment results which warps the record. In exceptional cases it is also the custom to effect the labelling by glueing the labels onto the finished record after the pressing process is completed.
A subsequent direct printing of the record surface in the label portion by means of a screen printing process is known particularly for foil-shaped pressed records. These thin plastic foils, which are generally less than 0.3 mm thick, would principally not be able to withstand, without warping, labelling with paper labels, particularly a one-sided labelling. Thus allowances must be made for the time-consuming screen printing process and the danger of subsequent damage or soiling of the finished foil by the dyes.
Finally, it is also known to effect the numerical identification during the galvanic fabrication of the matrices, mainly so as to legibly identify the galvanically made objects. This identification consists of a catalog number constituted by a sequence of numbers and letters. The matrix contains a negative representation of this identification number and the number is then transferred to the record mass during pressing. This number cannot be read too easily on the record, but serves as a distinguishing feature to the person skilled in the art. Thus this same number is also printed on the label, for example, and provides an opportunity for checking the musical content of the record against the text of the label.
The drawbacks of the known identification techniques are summarized as follows:
1. Paper labels can be used only with thicker records, not with foils of less than 0.3 mm thickness.
2. Paper labels must be manually or mechanically placed into the pressing mold with great precision.
3. The subsequent glueing constitutes an additional process step which also brings with it the danger of subsequent damage or soiling of the record.
4. Screen printing is an additional process step requiring a relatively long drying period and involves the danger of soiling of the finished audio grooves by dyes.
5. Engraved letters applied to the galvanically produced items in the conventional technique are difficult to read in the stamped surface and, due to the depth of the engraving, it would interfere with the movement of foil-type carriers during playback.