DISC-SHAPED, OPTICALLY READABLE INFORMATION CARRIER

Abstract: The invention relates to a disc-shaped, optically readable information carrier (10) made of plastic material. The disc (10) has a distance member (16) projecting from one side in the form of at least three point-shaped raised portions distributed uniformly in the circumferential direction.

Description: Disc-shaped, optically readable information carrier The present invention relates to a disc-shaped, optically readable information carrier made of plastic material, one side of which has an information- containing microstructure and the other side of which has a distance member which projects from the plane of the side and is located radially inside the microstructure . In the production of CD discs, the newly pressed disc products are normally stacked in an intermediate station before they go through further stages of manufacture, such as metallizing, labelling, lacquering etc. In order to prevent the disc products lying one on another in the stack from adhering to each other when they are to be lifted individually from the stack, each disc has on one side a distance member in the form of an annular raised portion located radially inside the information-containing microstructure and on the side opposite the microstructure. In this way, a narrow gap is formed between the disc products, which allows air to penetrate between the latter so that mutual adhesion is prevented. It has been found that this annular raised portion leads to certain phenomena of stress and shrinkage in the plastic material when the disc element hardens directly after pressing. This ring and the stress and shrinkage phenomena it causes can in certain cases impart to the finished CD impaired optical characteristics and a less aesthetically pleasing appearance by virtue of the fact that there is an annular discontinuity on the disc side when visually readable printing on this side goes right in towards the centre hole of the disc. In order to essentially eliminate this disadvantage in every respect, it is proposed according to the present invention that the continuous, annular raised portion is replaced by a small number of (at least three) point-shaped, uniformly distributed raised portions. In this connection, it has been found that, in addition to the necessary air gap between the discs in the stack being brought about, the previous stress and shrinkage phenomena virtually disappear also, which results in the optical and aesthetic characteristics of the disc being improved. Further features of the disc-shaped, optically readable information carrier according to the invention are indicated in the dependent patent claims below. The invention is described in greater detail below with reference to the appended drawing, in which: Fig. 1 is a plan view of a CD disc provided with point- shaped raised portions according to the present invention, and Fig. 2 is an enlarged cross-sectional view along the line II-II in Fig. 1, showing a further enlarged detail of a raised portion on the disc element. Fig. 1 shows an optically readable, disc-shaped information carrier 10, such as what is known as a compact disc or CD. The disc 10 is injection-moulded in a known manner in a plastic material, for example polycarbonate, and provided with an information- containing microstructure on one side 12. On the opposite side 14 of the disc 10, a small number of unobtrusive, point-shaped raised portions 16 are formed (six in the embodiment shown) , distributed uniformly in the circumferential direction. The raised portions 16 are positioned concentrically with the centre hole 18 of the disc 10 and located radially inside the microstructured region of the disc. These raised portions 16 constitute a basic distance element for keeping newly pressed, stacked CDs slightly apart so as thus to prevent the discs adhering to one another when they are to be lifted individually off the stack. Suitably, there are six point-shaped raised portions 16, but there can be fewer (at least three) or more. As shown in the enlarged detail in Fig. 2, the raised portion 16 can suitably be in the form of a truncated cone, with a base diameter of roughly 0.8 mm, a top diameter of roughly 0.6 mm and a height of roughly 0.2 mm or another dimension depending on the desired separation of the discs. It has been found that it is possible to eliminate shrinkage and stress phenomena which occurred previously in connection with a continuous annular raised portion as the distance element, which had a negative effect on the optical characteristics of the finished disc and to some extent on its appearance in the form of streaks caused by displaced air from the mould cavity for the circular distance ring.

Claims: Patent Claims 1. Disc-shaped, optically readable information carrier made of plastic material, one side (12) of which has an information-carrying microstructure, and the other side (14) of which has a distance member (16) which projects from the plane of the side and is located radially inside the microstructure, characterized in that distance member (16) is in the form of at least three point-shaped raised portions distributed uniformly in the circumferential direction. 2. Information-carrier according to Claim 1, characterized in that the raised portions (16) are each in the form of a truncated, circular-cylindrical cone. 3. Information carrier according to Claim 1 or 2 , characterized in that there are three to twelve raised portions (16) , preferably roughly six. 4. Information carrier according to Claim 2 or 3 , characterized in that the base of the cone has a diameter of roughly 0.8 mm, while the plane top surface has a diameter of roughly 0.4 mm. 5. Information carrier according to any one of Claims 1-4, characterized in that the height of the raised portions is roughly 0.2 mm.

Inventors: NAEPPI JARMO, ZETTERGREN ULF, NAEPPI, JARMO, ZETTERGREN, ULF
Applicants: NAEPPI JARMO, TOOLEX ALPHA AB, ZETTERGREN ULF, NAEPPI, JARMO, ZETTERGREN, ULF
Application year: 1999
Main classification: G11B7
IPC codes: G11B7