WO2006115410A2

WO2006115410A2 - Die assembly and/or stamper

Info

Publication number: WO2006115410A2
Application number: PCT/NL2006/050080
Authority: WO
Inventors: Herm Adrianus Tijl; Marcelis Johannes Van Rijt
Original assignee: Axxicon Moulds Eindhoven B.V.
Priority date: 2005-04-11
Filing date: 2006-04-11
Publication date: 2006-11-02
Also published as: NL1028737C2; WO2006115410A3

Abstract

Die assembly and stamper possibly in combination. This is used in particular for the manufacture of disc-shaped data carriers. To prevent the end edge of a data carrier manufactured in this way from having a greater thickness than the central part, it is proposed either to make one of the die parts of the die assembly facing the mould cavity thicker or to make the stamper used near the edge boundary which is of annular design thicker. Compensation will then automatically be made for differences in thickness. Injection-moulded parts obtained in this way are particularly suitable for producing optical data carriers made up of two disc parts or disc parts that are provided with a thin spin-coated layer or disc parts to which a thin foil has been bonded.

Description

Die assembly and/or stamper

The present invention relates to a die/stamper assembly comprising a first die part and a second die part to be mated with it, wherein each die part represents a boundary of a mould cavity defined between said first and second die parts, wherein a stamper is mounted in said boundary in one of the die parts, wherein the outer boundary of said stamper and mould cavity is a ring. Such an assembly is generally known in the art and is used for the manufacture by means of injection moulding of optical data carriers such as CDs, DVDs and such like. Ongoing efforts are devoted to storing more and more data per unit of surface area on the data carrier. As a result ever more stringent requirements are being placed on the precision of the optical data carrier.

It will be observed that the free extremity of an optical data carrier is somewhat thicker relative to the rest of the data carrier. This increase in thickness can vary on both sides of the data carrier from a few μ to a few tens of μm. This increase in thickness near the peripheral edge is not caused by imprecision in the die/stamper assembly. Ih other words, measured diametrically in the direction of closure of the die, the distance between the first and second die parts or the die part and the stamper is always constant.

Such an increase in thickness is no longer acceptable in light of.the constantly higher requirements of optical data carriers. The aim of the present invention is to provide an optical data carrier, wherein the thickness near the peripheral edge is essentially the same as the thickness at any other location on the optical data carrier.

This aim is realised in a die/stamper assembly as described above in that, when mating said die parts with a stamper fitted at the outer boundary, the distance between the free surface of the stamper and the opposed boundary of the mould cavity in said other die part is 1-100 μm less than the same dimension measured at a distance of 2 mm from said ring.

It is assumed that the difference in thickness is caused in that solidification of the liquid plastic material starts near its end edge. As a result, the thickness near the end edge or peripheral edge is greater than at other locations on the disc-shaped data carrier. The invention proposes to make a correction such as to address the thicker end edge. This means that, seen in a diametric direction from the centre, there is a decrease in the gap near the end edge between the stamper and the opposed die part which define the mould cavity. Such a reduction of the gap can be achieved in a number of ways.

Firstly, it is possible to make one of the face sides near the end edge thereof "thicker". Ih other words, the end edge of the relevant die part is curved slightly outwards, ^" i.e. higher than the base surface. This can be implemented in one of the die parts or both die parts. This can be achieved by making the relevant die parts thicker, but it is also possible, for example, to fit a separate ring which acts as a thickening.

Another option, which may or may not be used in combination with the above, is, when using a stamper, to make the stamper thicker near the end edge of the disc-shaped data carrier which is injected later. This is not necessarily also the end edge of the stamper because the end edge of the stamper projects beyond the mould cavity. More particularly, this can be a displaceable venting ring mounted on the opposite die part, with this venting ring being displaceable independently of the central die part.

The thickness of the resulting data carrier is preferably 0.6 or 1.2 mm. The invention also relates to a method of manufacturing a disc-shaped data carrier comprising the provision of a first disc part with data and the provision of a second disc part with data and the attachment of the disc parts to each other with the data always facing inwards, wherein the provision of said disc parts involves injection moulding. With suϋh disc-shaped data carriers, mainly in the form of DVDs or HD-DVDs, remaining within the international standards for the overall thickness is a problem. This means that the adhesive layer used for bonding together the two disc parts has to be particularly thin. If, however, the peripheral edges of the disc parts are thicker, it is not possible to comply with these standards.

By opting for the solution described above in accordance with the invention it is possible to prevent the peripheral edge from having a thickness which is significantly different from the rest of the disc part, as a result of which a comparatively thin adhesive layer is sufficient and the thickness standards can be met.

The invention can also be implemented in a disc part in which a thin layer is applied to the data side by means of spin coating or by bonding a film to it, as is done with a BIu- ray disc.

The first die part is preferably flat.

The invention will now be described in greater detail with reference to an illustrative embodiment shown in the drawing in which: Figure 1 shows diagrammaticaUy a side view of a die assembly for manufacturing optical data carriers;

Figure 2 shows the detail II from Figure 1;

Figure 2a shows a variant of the detail II from. Figure 1; Figure 3 shows a variant of the detail according to Figure 2; and

Figure 4 shows a further variant of the detail according to Figure 1.

In Figure 1 a die assembly as a whole is labelled 1. This comprises a first die part 2 and a second die part 3. The second die part 3 consists of a central part 4 and a venting ring 5 displaceable relative to it. The first die part 2 is provided with a stamper 7 attached thereto. The mould cavity 6 is bounded between the stamper 7 and the face side of the central second die part 4 and the inner boundary of the venting ring 5. Plastic can be injected into the mould cavity in a manner which is not illustrated in further detail.

Although the die assembly is shown in Figure 1 to close in a vertical direction, a horizontally acting configuration can also be used. Figure 2 illustrates the detail π from Figure 1. This shows that the first die part 2 near the free peripheral end thereof has a thickening. This thickening 11 deviates from tangent 10 to the rest of the face side of the first die part 2. It will be appreciated that the drawing in Figure 2 is not to scale and is considerably exaggerated in the interest of promoting understanding of the invention. As a result of the thickening 11 , the stamper 7 will also be mounted with a slight curve near the free extremity. There will be a difference in dimension between a and b, i.e. the distance (a) between the stamper and the face side of the second die part 3 (or the central part 4) and at a location which is, for example, 2 mm (c) from the outer periphery and is labelled (b), differs. It is evident that with appropriate sizing of the difference in dimension b-a, i.e. setting the dimension of the thickening 11 appropriately, the above-described phenomenon of a thickened peripheral edge of the optical data carrier injection-moulded using such a die assembly is no longer observed.

In the variant in accordance with Figure 2a, the venting ring 5 does not contact the stamper but rather the opposed part of die 2.

Figure 3 shows a variant of the invention. In this, the face side of die part 2 is completely flat. In other words, the face side of the first die part is no different from what is known in the art. In this case, however, the stamper is provided with a thickening 15 over a length f near the peripheral edge. The furthest left part of this thickening is not of importance to the injected product because this ends up against the venting ring. The thickest part is labelled- d, while the nominal dimension is labelled e. The difference between d and e is illustrated by means of the centre line 14. In practice, this difference is approximately 10 μm. The distance between d and e is comparable to the distance c from Figure 2 and is preferably less than 2 mm. The shape of the stamper outside the mould cavity is unimportant for the present invention.

Figure 4 shows a further variant in which the central part 4 of the second die part exhibits a thickening 21 relative to the basic dimension 20.

It will be appreciated that the various options described above can be used in combination. The deviation relative to a straight line in such a case will be less.

These and further variants are obvious after reading the above description and lie within the scope of the accompanying claims.

Claims

1. Die/stamper assembly, comprising a first die part (2) and a second die part (3) to be ^• mated with it, wherein each die part represents a boundary of a mould cavity (6) defined between said first and second die parts, wherein a stamper (7) is mounted in said boundary in one of the die parts, wherein the outer boundary of said stamper and mould cavity is a ring, characterised in that when mating said die parts (2, 3) with the stamper (7) fitted at the outer boundary the distance (a) between the free surface of the stamper and the opposed boundary of the mould cavity in said other die part is 1-100 μm less than the same distance (b) measured at a distance of 2 mm (c) from said ring.

2. Die assembly comprising a first die part (2) and a second die part (3) to be mated with it, wherein each die part comprises a boundary of a mould cavity (6) defined between said first and second die parts, wherein the outer boundary of said mould cavity is a ring, characterised in that when mating said die parts at the outer boundary of said mould cavity the distance between the free surface of the mould cavity and the opposed boundary of the mould cavity in said other part is 1-100 μm less than the same distance measured at a distance (c) of 2 mm from said ring.

3. Assembly according to Claim 1 or 2, wherein one of said die parts is provided with a venting ring (5) configured around it and displaceable relative to it.

4. Assembly according to any one of the preceding claims, wherein the dimensional difference (a-b) is approximately 10 μm.

5. Stamper (7) to be used in a die assembly for manufacturing disc-shaped data carriers, where said stamper comprises a disc-shaped part with an annular outer boundary, characterised in that the thickness of the stamper (d) at the outer boundary is 1-100 μm greater than its thickness (e) at a distance (f) of 20 mm from said outer boundary.

6. Method of manufacturing a disc-shaped data carrier comprising the provision of a first disc part with data and the provision of a second disc part with data and the attachment of said disc parts to each other with the data always facing inwards, wherein the provision of said disc parts involves injection moulding, characterised in that a die/stamper assembly according to Claim 1 is used when injection-moulding one of said disc parts.