Patent Application
20060163762
The present invention relates to the field of injection molding technique. It in particular relates to a method and a device for machining of a disc shaped information- and/or structure carrier (stamper) for injection molding forms, in particular for CD's or DVD's, which comprises a central, substantially cylindrical opening for fastening.
For the production of optically readable information carriers like Audio CD's, CD-ROM's, Video-CD's or DVD's, injection molding tools are used, which, by means of two opposite, in direction towards each other relatively movable mirror blocks form a cavity (cavity of the injection molding form). Usually, on one of the mirror blocks, a thin disc shaped stamper is removably fastened, which stamper during injection molding of the information carrier being formed embosses the information or at least structure comprising traces. This information and/or structure carrier is thus a 3D-template or embossing form or dye template, in which either the groove structure for embedding of the dye in case of writable media is provided as a negative, or in which the full information, which is optically read, in case of only readable media, is provided by means of additional structuring of the grooves as a negative. The negative data provided in the stamper are taken over by the formed article during the injection molding process in the plastic material.
The stamper is held in the injection molding tool by means of a so-called stamper holder. The stamper to this end comprises a central opening, in which the stamper holder at least partially intrudes. The stamper holder thus is a substantially ring shaped element, which, after the stamper has been put onto the mirror block, is introduced through its opening and is fixed on the mirror block, wherein the fastening is provided by means of interaction of the outer diameter of the stamper holder with the inner diameter of the opening of the stamper. This fastening may either be provided by form closure by means of holding noses or ribs on the stamper holder, or by force closure by means of vacuum directly on the mirror block, wherein in the latter case the stamper holder substantially provides the centring function.
Due to the increasingly high read- and write speeds, which have to be achieved with data carriers produced this way, also the requirements in respect to eccentricity (ECC) are increasing. The eccentricity is defined as the difference between the two axes of the central hole of the data carrier and the information grooves of the data carrier. In specifications, typically the following measures have to be kept
The total eccentricity is given by the sum of the deviations of stamper, tolerances of the device as well as widenings of the central opening of the stamper (among others wear due to lateral forces during use or during mounting).
The accuracy of the inner diameter of the central opening of the stamper, which typically is made of nickel or a nickel alloy in a photochemical process, is thus decisive for eccentricity. The central opening of the stamper is made by punching. During punching of this opening, different punching regions are generated due to technical reasons of the material. At the entrance edge of the punching tool, a radius or a slight flattening or truncation is generated, and at the exit edge a small ridge or even chipped spots. In between there is a substantially cylindrical region.
In particular the size and the direction of the radius/truncation which is formed in the entrance region can only be controlled with much difficulty and it varies in dependence of the punching stamp, the hardness of the stamper, the temperature and the speed during punching, on protective lacquers, etc. All these effects are detrimental to a precise centring of the central diameter of the central opening of the stamper.
Correspondingly there is a need to be able to, without too much effort, provide a very precise inner diameter of the stamper and to keep the eccentricity on a minimum.
It is thus one object of the invention to provide a process as well as a device for the more precise formation of a central opening of an information and/or structure carrier for injection molding tools, in order to keep the eccentricity of a data carrier (CD, DVD) produced using such information and/or structure carrier on a minimum.
In particular a method for machining of a disc-shaped information- and/or structure carrier for injection molding tools shall be provided, which information- and/or structure carrier comprises a central, substantially cylindrical opening, wherein the information and/or structure carrier is of the type which is fastened within the injection molding form by means of a holding device with at least partially penetrates the opening, and in which the information and structure, respectively is provided substantially concentrically to this opening on a surface facing the cavity of the injection molding form.
One solution to this object is achieved in that the substantially cylindrical opening is provided with a chamfer on at least one side at the edge towards a surface. In other words, an already existing central opening of the information- and/or structure carrier normally produced in a punching process is post-processed in that one of the edges between the surface and the cylindrical circumferential surface of the central opening is made conical.
One of the essential elements of the invention thus resides in the fact, primarily not to improve the punching process, but to get rid of the problems generated during punching in a post-processing step. To this end a post-processing is used, which allows holding through the central opening, effecting a self-centring of the information- and/or structure carrier during fastening in the injection molding form, and which correspondingly improves the value of the eccentricity. Surprisingly it is thus very simply possible to get rid of the uncontrollable variabilities generating during the punching process by means of a simple and reliable step of post-processing.
According to a first preferred embodiment the edge is provided with a chamfer by means of removal of material either circumferentially or in sections. The removal of material prevents that substantial modifications in the material structure take place, which may lead to tensions and correspondingly to additional eccentricities or wear and tear.
The chamfer or conical taper may be provided on the edge between the cylindrical opening and the surface facing away from the cavity of the injection molding form of the information- and/or structure carrier. In this case the self-centring effect for example takes place if the information and/or structure carrier is held on the mirror block by means of a vacuum fastening. A fastening effect on the mirror block is however not achieved unless additional means are provided.
Preferentially however, the chamfer is alternatively or in addition to that provided on the edge between the cylindrical opening and the surface carrying the information or structure, respectively. Like this a correspondingly structured stamper holder, can, without giving rise to tensions or material dislocations, be introduced into this conical taper and can on the one hand fasten the information- and/or structure carrier on the mirror block and on the other hand it can also optimally centre it.
According to a further preferred embodiment the information- and/or structure carrier is a stamper for the production of an optical data carrier, in particular of a CD or DVD, and the injection molding form is an injection molding tool for the making of disc-shaped information carriers, in particular in the form of CD's and or DVD's. The injection molding tool for the formation of a cavity comprises a first and a second mirror block, which are located opposite to each other, and which for opening and closure of the form are movable relative to each other, comprising preferentially additionally a form ring, which concentrically encloses the first mirror block and which borders the cavity to its outer edge and which is movable relative to the first mirror block.
Preferentially the stamper has a thickness (h) in the range of 0.2-0.5 mm, preferentially in the range of 0.25-0.35 mm. Normally the stamper is made of pure nickel or a nickel alloy.
According to a further preferred embodiment the chamfer is machined circumferentially (by means of removal of material) and the conical taper or chamfer with the normal to the stamper encloses an angle of 5-60°, preferentially of 7-20°, and particularly preferably of 10-15°. The depth of the chamfer for example is in the range of 0.1-0.3 mm, preferentially in the range of 0.15-0.25 mm. The ratio of the depth of the chamfer to the thickness of the stamper for example is in the range of 0.1-0.9, preferentially of 0.25-0.5, and particularly preferably of 0.6-0.7. The extension of the chamfer in radial direction (width) preferably is 0.03-0.1 mm, particularly 0.05-0.08 mm.
According to a further preferred embodiment of the method according to the invention, the production of the chamfer takes place by means of a cutting head with several, substantially conically oriented cutting edges, in particular in the form of a countersink, or with a conical grinding surface, which is guided into the opening of the structure- and/or information carrier in a concentrical and controlled manner until reaching a defined limit-stop, and in that the chamfer is produced by means of removal of material, wherein particularly preferably the removal of material takes place manually, i.e. the rotation of the cutting head is provided manually. It is however also possible to provide this by using a motor.
The method can be carried out in a particularly simple manner if a device as follows is used: a device for the machining of a disc-shaped information- and/or structure carrier for the injection molding forms, comprising first means for the controlled fastening of the information and/or structure carrier, and comprising a grinding- and/or cutting tool which by second means can be introduced into the central opening of the fastened information- and/or structure carrier in a concentrical manner. Thereby, by means of a rotation of the grinding- and/or cutting tool, the substantially cylindrical opening is provided with a chamfer on at least one side at the edge to a surface, i.e. the edge is preferably provided with a circumferential chamfer.
A first preferred embodiment of the device is characterised in that the first means are given as a cutting plate, in which holding means for the information- and/or structure carrier are provided, wherein preferentially these holding means are given by magnets and/or positioning ribs (for example at least partially circumferential around the outer edge of the stamper), and/or vacuum aspiration devices.
A further preferred embodiment of the device according to the invention is characterised in that the second means are given as a guiding column attached to the first means either tightly or rotatably, which penetrates through the central opening in a concentrical manner and perpendicular to the surface of the information- and/or structure carrier, and wherein the grinding- and/or cutting tool is provided with a corresponding, substantially cylindrical opening or bore in the tip, in which the guiding column, if need be with interposing friction reducing bearings, preferably in the form of a ball cage, is introduced such that the grinding- and/or cutting tool is rotatable concentrically to the central opening.
Alternatively, so to speak in a kinematic exchange, it is possible to provide a device, which is characterised in that the second means are provided as a guide column penetrating through the central opening in a concentrical manner, which is fastened to the grinding- and/or cutting tool tightly or rotatably and coaxially, and in that the first means are provided with a corresponding substantially cylindrical opening or bore perpendicular to the surface of the information- and/or structure carrier, if need be with interposition of friction reducing bearings, preferably in the form of a ball cage, in which the guide column is introduced such that the grinding- and/or cutting tool is rotatable concentrically to the central opening.
Preferably the cutting tool is a countersink and/or a deburring sink, which particularly preferably comprises at least three, preferably four to eight cutting edges. Further more the grinding- and/or cutting tool is preferably designed such as to be manually actuated for removal of material.
Further preferred embodiments are described in the appended claims.
The invention shall be illustrated in the following by means of the examples in conjunction with the drawings. The examples merely serve to illustrate the invention and shall not be constructed for limiting the scope of the invention as defined in the dependent claims. The figures show:
a)-c) different cut outs according to circle A as given in
In
The injection molding tool 10 which is shown in open state comprises as central parts a first (left) mirror block 11, a second (right) mirror block 12, and a form ring (venting ring) 20, enclosing the first mirror block 11 concentrically, which together, if the form is closed, form the cavity 25. Each of the mirror blocks 11, 12 is mounted in a concentrically enclosing centring ring 13, 14, respectively. The information is embossed or formed during the injection into the molded form (the CD/DVD) by means of a stamper 19, which is provided as a thin disc on the surface of the form of the second mirror block 12 and adjacent to it, and which is held in the centre by means of a bush-type stamper holder 18. For the connection of the injection molding tool 10 to the nozzle 28 of the injection molding machine a sprue bush 17 is provided penetrating to the centre of the second mirror block 12 to the sprue bush 17 extending to the cavity 25, which sprue bush opens conically towards the outer side.
Opposite to the sprue bush 17 there is provided concentrically and located within each other and relatively movable (indicated by means of the double arrows) an injector sleeve 16, a punch 15 and a sprue ejector 23. With the sprue ejector 23 the sprue 22 (for illustration displayed in the centre of the open form) remaining in the inner bore of the sprue bush 17 can be ejected. With the punch 15, the central opening is punched in the injection molded CD or DVD, respectively. With the ejector sleeve 16 the finished CD can finally be ejected after opening of the cavity 25.
The form ring 20 is mounted movably in the centering ring 13, and is pressed towards the second mirror block 12 by means of springs. By means of a pneumatically driven operating element 24 it can be discharged. The form ring 20 does not directly abut with the inner side to the outer side of the first mirror block 11, but it is separated therefrom by means of a ball cage 21, which is concentrically provided on a set-off provided on the outer side of the first mirror block 11. The ball cage 21 substantially has the form of a hollow cylinder. It thus acts as a sliding bearing for the form ring 20 made of steel and the first mirror block 11 also made of steel.
The two halves of the injection molding form 10 are mounted movable relative to each other by means of guiding columns 26 (normally four such columns), wherein for easy relative mobility these guiding columns 26 are bearing mounted by means of ball cages 27 in corresponding recesses. The mirror blocks 11 and 12, respectively, as well as if need be also the venting ring 20 comprise means for tempering or may also be provided with vacuum, and this is schematically indicated for the venting ring 20 by the inlet for media 29.
In connection with such an injection molding tool 10, by means of the circular cut out A, as given in
The
In
a) shows the possibility, to substantially only centre the stamper 19 by the stamper holder 18 and to actually effect the fixation on the mirror block 12 by means of a vacuum aspiration. To this end the mirror block 12 is provided with at least one vacuum channel 30, which is open towards the surface of the mirror block 12 via the aspiration openings 31. The stamper 19 with its lower surface 57, which is not provided with a 3-dimensional structure or information, rests on the surface of the mirror block 12, and is held on the mirror block if a vacuum is provided in the channel 30.
The outer diameter D of the stamper holder 18 is for example 22 mm, wherein a tolerance in the range of +0.0 mm and −0.005 mm/−0.01 mm, respectively, is admitted. The inner diameter of the central opening 56 of the stamper is also designed to be 22 mm, wherein however, for reasons of safety (the diameter of the central opening may under no circumstances be smaller than the outer diameter of the stamper holder 18 within the limits of the tolerances) here the tolerances are designed to be in a region of +0.01 mm and −0.0 mm. Thereby an allowance 32 in the region of the central opening 56 is produced which is in the range of 0.005-0.020 mm, and which finally does not allow a qualitatively high valued eccentricity.
Even if the stamper is provided with an accurate central opening 56 due to this allowance 32 the whole stamper and correspondingly also the information which is provided concentrical to the central opening 56 on the surface 55 of the stamper can be shifted within the limits of this tolerance, contributing thus to the eccentricity of the finally produced data carrier. The problem of this solution is also that in the mirror block 12 vacuum channels 30 have to be provided for fastening of the stamper. Since however in the mirror block 12 for tempering there is also necessity for channels for the tempering medium, difficult conditions are given in the mirror block 12 due to the requirement of the channels 30.
An alternative is given in
A further possibility is given in
In other words the chamfer 37, e.g. at a height h of the stamper of 0.3 mm is provided over a depth k of 0.2 mm, wherein this chamfer 37 has a width n in radial direction of 0.06 mm. Due to the preceding machining of the upper edge, i.e. the edge between the inner circumferential surface of the central opening 56 of the stamper and the information carrying surface 55 of the stamper 19, there is no generation of tensions during mounting, and the final eccentricity can thus be improved. In addition to that due to the reciprocal conical shape of the stamper holder 18 and the stamper 19 a reciprocal centering effect during mounting is provided leading to an optimal eccentricity furthermore.
In
In the context with the chamfer 37 described in conjunction with the
Preferably therefore a post-processing is used in which material is removed in a gentle manner. This is typically in a chipping manner, and either using a grinding tool or a cutting tool, wherein the latter for example may be a countersink, which can only be introduced into the central opening of the stamper until reaching a limit stop.
A particularly useful tool for the post-processing of the stamper according to the invention is given in
A device according to
At least partially in a central bore of the cutting plate in addition to that there is provided a guide column 42 and it is fastened by means of a screw 45 from the bottom. The guide column 42 is perpendicular to the cutting plate 41.
The stamper 19 is put onto the cutting plate 41 in that its central opening 56 is imposed on the guide column 42. Subsequently the cutting tool 48, which on its tip is provided with central or which is adapted to the guide column 42, is put onto the guide column 42 and moved downwards. The cutting tool 48 is mounted around the guide column 42 rotatably by means of a ball cage 46. It comprises a central cutting core 51, about which on its upper end a handle 49 is provided and is fastened with a pin 50. On its lower end the central cutting core 51 is provided with the already mentioned central bore for taking up the guide column 42, and the ball cage 46 is mounted in this central bore by means of a pin 47. On the tip the cutting head 52 is given, in that several cutting edges 53, specifically in this case there is six of them (there is also more than that or less than that possible) are provided. The cutting head 52 is similar to a cutting head, as it is used in the context of countersinks.
The desired chamfer 37 can now manually be produced on the stamper 19 in a highly controlled manner, if the cutting tool 48 is introduced into the central opening 56 under rotation and concomitant removal of material. By means of the guide column 42 an optimal centring and guidance is provided, and at the same time due to the design of the tip 52 and the limit stop on the cutting plate 41 it is made sure that the chamfer 37 has the desired depth k.
In Detail for example the following dimensions were chosen: diameter of the cutting plate 41: b=150 mm; diameter of the cutting core 51: a=25 mm; height of the cutting plate 41: c=25 mm; height of the mounted cutting tool 48: d=130 mm; diameter of the handle 49: e=30 mm. The control measure of the cutting head 52 on the height 0.3 mm is: f=22.09 mm; the diameter at the tip of the cutting head 52 is: g=21.99 mm; the depth of the chamfer is: 1=ca. 0.2 mm.
In summary the following advantages are provided due to the post-processing of the stamper 19 and the use of the described tool, respectively:
| Number | Date | Country | Kind |
|---|---|---|---|
| 0129/05 | Jan 2005 | CH | national |
