NL1012111C2 - Injection moulding tool, especially for making optical data discs, has ring between tool sections moved by piston cylinder units that apply less force as these sections get closer to each other - Google Patents

Abstract

The ring between the tool sections (2, 3) is moved in the tool opening direction by fluid operating piston cylinder units that apply less force to the ring as the tool sections get closer to each other. An injection moulding tool (1) comprises two tool sections defining the mould cavity, one of the tool sections being provided with a ring that surrounds the cavity and can be moved relative to the section in the tool opening/closing direction. The means provided for moving the ring in the tool opening direction comprise fluid operating piston-cylinder units. The fluid operating system is designed to move the ring in the opening direction with relatively great force when the tool sections are spaced apart, but applies less force to the ring as the tool sections get closer to each other. An independent claim is also included for a mould tool section provided with the above piston-cylinder system.

Description

Injection mold assembly.

The present invention relates to an injection mold assembly comprising two mold parts bounding between a mold cavity, one of these mold parts being provided with a ring which delimits the circumference of that mold cavity, relative to that mold part in the closing / opening direction of those mold parts, wherein means are provided for driving said ring in the opening direction of said mold parts, said means comprising fluid-actuated piston-cylinder assemblies.

Such a device is known from EP-0557147-A. In the prior art, such injection molds are used, for example, for spraying optical information carriers such as CDs, DVDs, etc. During the spraying there is a so-called stamper on which the digital optical information is applied or on which the groove pattern is present. It is to be understood that the invention is not limited to an injection mold using such a stamper.

Plastic is injected after or during the closing of the mold, i.e. when the mold parts move towards each other. At the end of the closing stroke, a wave movement is caused by the closing impact. As a result, the opposite circumferential ends of the respective mold parts tend to move slightly apart for a short time. The same movement is found when the injection of the plastic is ended. These movements are very slight and nevertheless, with the increased pressure prevailing within the mold cavity, it is possible for a small amount of plastic to exit the mold cavity and cause "flash" there. Often such membranes are not acceptable and must be removed by hand. In addition, they lead to contamination of the various parts of the mold.

In order to prevent this, it has been proposed in the prior art to provide a so-called vent ring. This is movable relative to the relevant mold part, so that small movements can be accommodated between the mold parts. On the other hand, it is possible to realize venting of the mold cavity during the closing movement. In the prior art, such a vent ring was driven out by spring force. This 1012111 2 spring force was such that under normal operating conditions sufficient outward movement is always ensured, without excessive force being exerted on the ring during the closing movement. After all, if this force becomes too great, because heavy springs are used, impact of both the ring and the opposite surface of the other mold part will occur.

It has been found in practice that it is quite possible to design such a resilience such that under normal operating conditions the movement of the vent ring is optimal without adversely affecting the service life of the opposite mold part.

During the start-up phase of the injection process, i.e. during the first injections, the part inside the vent ring will gradually warm up. Over time, the heat in question will be transferred to the vent ring and a thermally stable whole will be created. However, during the heating-up phase, the part of the mold located inside the ring is warmer than the ring itself. Since the ring must be movable relative to the mold, but on the other hand, plastic must not be allowed to enter the gap between the ring and the mold, the tolerance between the interior of the ring and the mold is very small. It has been found that clamping of the ring takes place during the heating-up phase. On the one hand, it can no longer be guaranteed that the ring will come out sufficiently and, on the other hand, skewing has been observed, with all the consequences when closing the mold halves.

The aim of the present invention is to prevent this drawback, whereby on the one hand it must be ensured under all circumstances that the ring moves outwards, but on the other hand force imposed on the ring when closing the mold is not so high that damage to the contact surfaces between the ring and the opposite mold part.

This object is achieved with an injection mold assembly described above, in that the fluid actuation is such that, with spaced-apart mold parts, that ring is driven with a relatively great force in the opening direction and when approaching those mold parts, a comparatively smaller force at that ring is opened in the opening direction.

By replacing the spring construction with constant force by fluid-operated piston-cylinder assemblies, the force 101 2 1 t 1 3 on the bleed ring can be determined depending on the circumstances. It is thus possible to apply a higher force to the vent ring during the heating phase. It is also possible (whether or not in combination with the above) to have the force for bringing out the ring when opening the mold relatively large, and then to reduce this force or to remove it only completely. closing the mold. Therefore, the above-mentioned damage to the opposite surfaces of the vent ring and the other mold part will not occur. As indicated above, it is possible to combine the fluid-actuated piston-cylinder assemblies with the spring-loaded construction known in the art. Therefore, it is possible that during normal operation, that is, after all parts are at the usual operating temperature, the spring provides compression, but that the fluid provides support during critical start-up.

European application 0557147 refers to a fluid-actuated ring 148 which, however, is not intended to solve the above problem and the operation thereof therefore deviates from what is proposed according to the invention.

According to the invention, all this can of course be controlled with an appropriate control.

Preferably, the medium used to move the vent ring outward is compressed air. This is generally present with injection molding machines and on the one hand the necessary resilience is obtained, while on the other hand the magnitude of the resilience and the time during which it is applied are well controllable.

It will be understood that operation can also take place in other ways, such as by hydraulic or electric means.

The piston-cylinder assemblies described above can be implemented in many ways.

It is thus possible to design the ring itself as a piston. In addition, it is possible to provide a piston in the ring which opposes a part of the relevant mold part. Further variations are simple for those skilled in the art to design after taking note of the inventive idea described above.

1012111 4

Some embodiments of the construction according to the invention will be shown below. Show:

Fig. 1 is a schematic sectional view of an injection mold assembly according to the present invention in opened position; FIG. 2 the injection mold assembly of FIG. 1 in closed position;

Fig. 3-6 detail A in fig. 1 and 2, but executed according to the invention in different variants.

In Fig. 1, a mold assembly is indicated in its entirety by 1. Parts of interest to the understanding of the present invention have been omitted or are not discussed further herein.

The mold assembly 1 consists of a fixed mold part 2 and a movable mold part 3. The assembly is arranged in an injection molding machine well known in the art, with which the movement in question is imposed.

The mold assembly 1 shown here is particularly suitable for injection molding optical information carriers with not too large series. For this purpose, a so-called stamper 4 is arranged in the mold part 3. This is provided with the digitally readable information (pits and / or grooves / lands). A punch 5 is arranged in the heart of the mold assembly, with which (part of) the opening in the optical information carrier is realized after injection molding.

The fixed mold part 2 is provided with an aerosol 6.

As can be seen from the detail in Fig. 4, which is the same for all the embodiments described above, the movable mold part is provided with grooves 12. An aeration ring which can occur in all kinds of variants is provided with a groove 13. From Fig. 4 it is clear how the rammer is received between the fixed mold part 2 and the movable mold part 3. In this case, vent gap 19 remains in principle free for the discharge of gases when closing the mold. In the prior art construction as shown in Figs. 1 and 2, the vent ring is indicated by 8. This is driven upwards by means of a spring 9 and an intermediate pressure sleeve 10. The end position of vent ring 8 shown in Fig. 1 is determined by stop 8.

The tolerance between the interior of vent ring 8 and the adjacent surface of the mold part 2 is small, in the order of magnitude of p, s.

Fig. 2 shows the mold in closed position. It appears from this that 1012111 é 5 vent ring 4 is pressed inwards by the opposite part of mold part 3. This movement is against the force of spring 9.

As indicated above, due to the small tolerance between the interior of the ring and the mold part 2 when tensioning from the mold part 2, problems arise which can cause clamping of the ring. However, the small tolerances as indicated above are necessary to prevent plastic from entering between the breather ring 11 and the mold part during injection molding, thereby completely preventing functioning, i.e. moving the ring 11 back and forth altogether.

In order to avoid these heating problems, various constructions are shown in FIGS. 3-6.

A first variant is shown in Fig. 3. The breather ring, which is somewhat shortened compared to the embodiment according to Fig. 1, is indicated by 18. The lower part has now been replaced by a pressure plate 19 which rests on the pressure sleeve 10 and spring 9 present as example 15. An air supply is indicated by 22. The stop for determining the "highest" position of vent ring 18 is indicated by 21. Different seals are realized by means of grooves and O-rings 20.

The embodiment shown here is particularly easy to realize because the parts 9 and 10 can in principle be adopted unchanged. In the critical start-up phase with unacceptable temperature differences, the driving out of ring 18 can be assisted by the supply of compressed air through line 22. In addition, it is possible to make the spring 9 flatter or even omit it altogether. In the latter case, compressed air must be supplied through line 22 25 under all circumstances. However, it is possible in a simple manner to vary the pressure of the compressed air supplied. On the one hand, a variation may exist depending on the temperature differences between vent ring 18 and the environment and, on the other hand, a variation may exist depending on the position of the mold parts 2 and 3. After all, once vent ring 18 has been moved out, there is no longer a need for a proportional exert high pressure thereon such that movement outwards is guaranteed. As a result, in a second stage, i.e. the closing stage of the mold, a lower pressure will suffice.

With the aid of the construction according to the invention it is possible to further reduce the tolerance f10 12 111 6 between the breather ring and mold part 2, because after all the fluid such as compressed air always ensures that the ring is pressed outwards. This results in less pollution and less burr formation. The first means that longer cycles without cleaning are possible. The second means that less or no post-processing of the product produced by injection molding is necessary.

A further variant is shown in Fig. 4. The vent ring indicated there with 28 has a greater height. As a result, the danger of tilting the vent ring 28 is smaller. The stop which determines the extreme position of the vent ring 28 is indicated by 31. The air supply with 32. With this variant, some further steps are required to modify existing molds. The previously shown spring and pressure sleeve have been removed and replaced by a filling sleeve 27. Sealing takes place with the aid of O-rings 26. As a result of the application of pressure, ring 28 will move outwards.

Fig. 5 shows an embodiment in which the vent ring is indicated by 38. It has a considerable height, but in its interior there is a piston 39, which is sealed by means of an O-ring 40 with respect to the cylindrical bore in the venting ring 38. The supply of compressed air is indicated by 42. Piston 39 closes on a filling sleeve 37. The stop which determines the end position of vent ring 38 is indicated by 41.

Fig. 6 shows a further variant of the construction according to the invention. This is currently the most preferred option, but is economically only feasible for new-build dies. The breather ring is indicated in its entirety by 48 and the associated stop with 51. Below this is placed a pressure pin 25 and this is in turn engaged by a piston 49. This is with the aid of toroidal O-ring 50 with respect to the environment sealed. The air supply is indicated by 52.

It will be understood that the above-described construction is distributed circumferentially in a number of places to provide an even pressing force on the relevant vent ring. Depending on the application, one of the variants described above may be preferred, with those skilled in the art immediately understand that further detail changes of the inventive idea are possible without going beyond the scope of the application.

101 2111

Claims (8)

Injection mold assembly (1) comprising two mold parts (2, 3) bounding between them, one of said mold parts being provided with a bounding the circumference of said mold cavity, relative to that mold part in the closing / opening direction of said mold parts ring (18, 28, 38, 48), wherein means are provided to drive said ring in the opening direction of said mold parts, said means comprising fluid-actuated piston-cylinder assemblies, characterized in that said fluid actuator 10 is , that in the case of spaced-apart mold parts, that ring is driven with a relatively large force in the opening direction and, when approaching those mold parts, a relatively smaller force is exerted on that ring in the opening direction. Injection mold assembly according to claim 1, characterized in that said fluid actuation comprises a compressed air control. Injection mold assembly according to any one of the preceding claims, characterized in that a number of piston-cylinder assemblies is arranged along the circumference of said ring distributed in the respective mold part. Injection mold assembly according to one of the preceding claims, characterized in that a pressure pin is arranged between said ring and said piston-cylinder assembly. Injection mold assembly according to any one of the preceding claims, characterized in that said ring is arranged in a groove and sealing means are present acting between said groove and said ring, said groove being provided with a fluid connection. Injection mold assembly according to any one of the preceding claims, characterized in that said ring is provided with a number of openings distributed along its periphery, in which a piston is arranged, and provided with a fluid supply. Injection-mold assembly according to any one of the preceding claims, characterized in that said means comprise spring means. Mold part, characterized in that it is provided with piston-cylinder assemblies according to one of the preceding claims. 10 1 2111