DE2709342A1 - PROCESS FOR PRESSING A LEVEL PRECISION MOLDED PART MADE OF THERMOPLASTIC PLASTIC AND PRESSING DIE FOR IT - Google Patents

Description

DR. ING. K. WCKSnriIOKF

DH. E. ψ. PBCHIUA NN DII. ING. D. BJTHIlKNS ΓΙ PL ·. ING. R. COKTTZ

PiTIItIiSWlLTI

8COO JUKCHKN OO 8CI1WE IIF.HSTRASSE S TtLin »« Οββ »60 2031 TBLKX S 24 070

TBLKO ΗΛΜΜΚΙ raOTECTFATBKT ΜΟΚΟ! »

1A-48 908

Applicant: RHÖNB-POULENC INDUSTRIES

22, avenue Montaigne, 75 Paris France

Title: Method for pressing a flat precision molded part made of thermoplastic material and a press die therefor

709836/0956

UU. IN O. K. WUKSTHOFF DR. E.v. PKCIIM ANN DR. ING. D. HKIIRKNS

DIPL. ING. R. GOKT7,

PATENT LAWYERS

8OUO M iINCHEN OO StIIlVKIOEHSTHASSE 2 TRLFTON (089) 60 20 91 TRLRX Λ 24 070

TKI-KOITAMMK ι PHOTKCTPATENT M UNOD EN

1A-48 908

2 7 09 3 4?

Description of the patent application

The invention relates to a method for pressing a flat precision molded part made of thermoplastic material , in particular of information carriers such as sound or image disks according to the preamble of the main claim and a press die for performing the method.

The reproduction or pressing of precision molded parts, in particular of plate-shaped information carriers made of thermoplastic material with spiral-shaped modulated Recording grooves, the geometric changes of which in the vertical and / or horizontal direction are the variations or reproduce changes (fluctuations) in the original recording medium has long been known; the production takes place by pressing or embossing a thermoplastic plastic mass, which is between two press punches, provided with metallic press dies for the molded part to be reproduced, is gelled. In the case of a plate-shaped The information carrier then becomes the mechanical one for the audio or visual reproduction of the signals or signs Image scanned with appropriate devices.

The overall process for the production of precision molded parts, In particular, information carriers such as audio or video disks generally comprise two clearly differentiated from one another Sections, namely the production of the press die

709836/0956 COPY

and the actual pressing. The press die is usually produced in several stages. With records for example, the recording on a magnetic tape (for example, 16 tracks) becomes after mixing on two-track stereo tape with a record cutter on a lacquer film, e.g. made of a cross-linked epoxy resin layer on a metal support, overdid and engraved the recording grooves with a cutting stylus and in a vertical position and modulated in the horizontal direction. Then the lacquer film is metallized with the help of silver nitrate, to make the surface conductive and to strengthen the silver coating in an electroplating bath by depositing nickel, In this way, a positive film or matrix called "father" is obtained, which is then placed in a further electroplating bath reinforced with a nickel coating and then removed. This mother die or electroplating is made with regard to the The complexity of the procedural measures is monitored acoustically and corrected with the cutting stylus if necessary. The mother matrix then again contains a galvanic coating, which is removed, and the actual (negative) press die represents. This press die is brought into shape and centered and placed on a press ram, which is supplied with and Discharge of flowable heating and cooling media is provided.

Obviously, this first stage in the manufacture of the press die is lengthy and cumbersome and must be meticulous be led; further disadvantages are that the disturbances possible in each individual process step and errors add up on the finished press die and sometimes make it unsuitable for the Require reproduction or pressing of information carriers or cumbersome and time-consuming controls. These methods are well known.

709836/0956 ' ³ ~

COPY

- ^r _e 27093A2

The second section in the production of an information carrier comprises the pressing or embossing itself. According to a first embodiment, a previously weighed and hand-arranged extruded disc made of thermoplastic material is compressed between the press dies provided with the press dies. The effective closing pressure of the press is at least 150 kg / cm. The temperature of the press ram depends on the type of Preßgemisches from and is generally from 150 to 180 ⁰ C, the heating time generally from 15 to 30 seconds. Subsequently, until cooled to room temperature, the disk or plate under the same pressure and finally removed from the mold and finished.

According to another embodiment, a predetermined amount of the plastic is injected between the two press dies and then proceed as just described.

This second manufacturing stage, which occurs during manufacture most records has the following serious disadvantages:

a) It comes with annoying and space-consuming material and

b) high closing pressure worked;

c) there are significant thermal energy losses in the course of the heating-cooling cycle;

d) the process is difficult to automate;

e) the proportion of manual labor is considerable;

f) long cooling time under the press;

g) unavoidable encrustation of the lines for the heating and cooling medium for the ram that is on the information carrier as a result of the fluctuations in heat exchange in the press rams leads to errors and also requires frequent cleaning of the lines for the flowable heat exchangers power;

709836/0956

COPY

h) after cooling, tensions occur in the information carrier, which can lead to breakages or deformations;

i) the components of the compression molding process and the thermoplastic resin in powder or granular form must first premixed and then treated again by means of extrusion or extrusion or blow molding before the molding compound can be introduced into the platen press; this requires an additional long time before the actual plate pressing and time-consuming work steps as well as a considerable amount of material are necessary.

Furthermore, the industry has switched to pressing Plastics with relatively low softening temperature, relatively poor mechanical properties and after compression molding low dimensional stability in order to be able to reproduce or reproduce the original (e.g. sound or Image) to achieve more work cycles (per unit of time).

From FR-PSs 2 163 380 and 2 244 788 there is also a method for reproducing or pressing plate-shaped Information carriers made of plastic known, in which the resin is heated and gelled by the fact that the metallic press die with the help of distributed in an insulating layer ;. Thermal energy is heated by dielectric loss is generated with the aid of a high-frequency generator (dielectric heating or heating); the insulating layer is arranged between the press die and the plate which makes up the press ram. However, this procedure continues assume that metal matrices are produced, the disadvantages of which are known.

As a result, there is a need in the industry for a simple one Manufacturing process for information carriers and, more generally, for precision molded parts, with the help of which they are faithful

*warmth-

709836/0956
COPY

27093A2

Reproductions can be obtained at high production rates.

The invention is based on the object of an improved and simplified method for producing a reproduction a substantially flat precision molded part with a relatively small and constant thickness, which a related has on the thickness flat surface relief and consists of a thermoplastic material, as well as this provide required press die.

This task is achieved with the help of the method described in more detail in the claims and the press die developed for it solved.

The invention relates to a method for pressing a flat precision molded part made of thermoplastic material, of relatively small and constant thickness, which has a relatively flat surface relief in relation to the thickness, in which the plastic is heated and gelled by means of dielectric heating and between two press dies for precision ion molded parts are pressed and then cooled under low pressure, the press dies being made of a plastic, which is thermally and mechanically stable at the pressing temperature and under the pressing pressure.

_{According to the invention, products of different shapes and dimensions such as records, optical discs, supports for printed circuits and other electronic components f} insulating parts for electrical devices are referred to as "substantially flat precision molded part of relatively low and constant thickness with a surface relief that is relatively flat in relation to the thickness." such as intermediate parts of capacitors, transformers of capacitors, optical products such as contact lenses or adhesive shells, lenses for optical apparatus, plastic glasses for glasses, optical surfaces with

709836 / 09S6,

Microprisms or microbumps, i.e. optical gratings (e.g. magnifying transparencies).

The industry places extremely strict requirements on accuracy and faithful reproduction of such products the surface relief of the original template; this is especially true for records, optical disks and optical ones Bars; the faithful reproduction of this relief determines the technical quality or goodness of the product. Generally the thickness of such products becomes no more than 5 cm, and the ratio of the height of the relief to the thickness less than 1: 4.

Thermoplastic plastics in the sense of the description are solid plastics in the form of powders, granules or foils that gel when heated and then form a mass that can be deformed with a slight Eteuck, which becomes solid or hard again on return to room temperature with or without crosslinking of the macromolecular structure . The thermoplastics have a loss factor of 10 ~ ¹ to

-4
10 at the frequencies used and in the range of working temperatures.

The plastic compounds based on polyvinyl chloride can be used, Copolymers of vinyl chloride and vinyl acetate and their mixtures, preferably mixtures that 99 wt .- # polyvinyl chloride and 1 to 30 wt .- # copolymer Contained from vinyl chloride and vinyl acetate; aliphatic polyolefins such as polyethylene, polypropylene and mixtures thereof; aromatic poly-oC-olefins such as polystyrene and polymers from acrylic monomers; Polymers obtained by condensation of polycarboxylic acids with polyols such as polyethylene glycol terephthalate, Polymers obtained by condensation of polycarboxylic acids and polyamines such as polyhexamethylene diamine adipate, still in the thermoplastic state

709836/0 956 ~ ⁷ ~

non-crosslinked polymers in which a crosslinking reaction takes place when heated. These include, for example the masses described in FR-PS 1 555 564, solid masses based on epoxy resins and corresponding hardeners, etc.

The resin compositions can contain the usual additives such as lubricants, plasticizers, stabilizers and Fillers. According to another embodiment, the filler mass contains a pore former, which is used in the implementation of the process results in the formation of a precision molded part foamed thermoplastic material with a density of 0.05 to 0.9 causes.

According to a preferred embodiment, the plastic compound lies as granules with a particle size of 0.05 to 0.5 mm; this enables the ones supplied by the manufacturer To use plastic resins immediately after the addition of the usual additives, without these first undergoing a shaping process would have to be subjected.

In the context of the description, a device is referred to as a high-frequency generator which is located in the space between an electric field of high frequency in the range from 1 MHz to 5 × 10 MHz, preferably in the range from 10 to 1000 MHz under a voltage of 100 to 10 000 V, preferably from 300 to 5000 V generated. Such devices are generally known.

As a "press die made of mechanically and thermally resistant Plastic "is the negative representation of the precision molded part, obtained by compression molding or embossing of the precision molded part or one of its positive representations. The press die consists of a plastic, not at the application or processing temperature

709836/0956 - 8 -

is degraded and does not deform mechanically inelastic at the applied temperature and pressure According to a first embodiment, the press die is made by pouring a liquid mass onto the to be reproduced Precision molded part and subsequent curing or crosslinking of the plastic obtained. As a liquid plastic mass for example:

1) Organopolysiloxane compositions which cure to give elastomers at room temperature and above; these masses are preserved by mixing hydroxylated and / or alkoxylated diorganopolysilocanes, finely divided fillers, crosslinking agents based on organosilicon compounds selected from the group of the alkyl silicates and polysilicates as well as organohydrogenpolysiloxanes and catalysts such as metal salts of carboxylic acids, organic tin compounds and metal chelates (FR-PS 1 126 411, 1 179 969, 1 189 216, 2 027 834 and FR-OS 2 221 492);

2) Organopolysiloxane compositions that when heated to temperatures above 50 ° C, generally to temperatures in the range of Cure 80 to 160 ° C to form elastomers; these crowds will be obtained by mixing diorganopolysiloxanes containing vinyl groups, optionally finely divided fillers, organosilicon plastics optionally containing vinyl groups, crosslinking agents of the organohydrogenpolysiloxane type and Platinum compounds as catalysts (FR-PSs 1 314 679, 1 511 598, 2 058 988).

According to another embodiment, the press die is made by impression of the precision molded part to be reproduced or one of its positive representations obtained under elevated pressure and at elevated temperature with The help of a plastic that contributes thermally and mechanically is resistant to the maximum pressures and temperatures used. For this purpose, fluorine-containing plastics come into question, such as poly-

709836/0956 _ ₉ _

tetrafluoroethylene, polytrifluoromonochlorethylene and copolymers from tetrafluoroethylene and ethylene and a.m.

In general, the choice of plastic material depends on the press dies and their shape depend on a number of technical parameters, namely:

a) the nature of the thermoplastic molding compound and its dielectric properties in the temperature interval from room temperature to the maximum pressing temperature,

b) the flowability of the molten molding compound,

c) the shape and dimensions of the precision molding to be reproduced,

d) the theological behavior of the material from which the press dies are made in the working temperature range,

e) the dielectric properties of the material of the press dies in comparison with those of the molding compound and

f) Voltage and frequency of the electric field used.

When carrying out the method according to the invention, the press dies and the molding compound are heated by means of dielectric Loss. The invention is not limited to greater heating or heating of the molding compound; Indeed this mode of operation represents a preferred embodiment. However, the press dies can also be substantially heated will, as long as they do not suffer irreversible deformations at the maximum temperature they then reach, which would be detrimental to the quality of the reproduction or the precision molded part; the molding compound. is in in this case gelled by the thermal energy obtained by means of dielectric loss in their own volume, increased by

709836/0956

- 10 -

the thermal energy transferred from the heated press dies or is handed in.

For the sake of simplicity, a rough approximation is based on the assumption that the use in dielectric terms the means according to the invention leads to a connection of volumes with parallel surfaces, as is shown schematically in the appended Drawing is reproduced. In this, 1 denotes the press dies, 2 denotes the thermoplastic / molding compound, 3 denotes the Metal press ram and 4 the high frequency generator. Under these conditions, the dielectric loss is increased Power distributed or converted into heat in a component volume of the overall arrangement by the following general Equation (I)

(I) P -Qi-) ts> t tg <f

in which P is the power loss in watts, V is the voltage in volts between the parallel surfaces of the given volume, C is the capacity of the volume in Farads, tD is the frequency in Hertz, i is the dielectric constant of the volume and tgö is the dissipation factor at the frequency \ P means reproduced.

In equation (I), the capacitance depends on the dimensions of the volume and is represented by the formula

ο 6 / S

in which L and C are as defined above, S is the surface of the

2
Volume in cm and e the distance between the parallel surfaces of the volume under consideration in cm.

Taking into account the circumstances or data of the practical problem to be solved, those skilled in the art can select and define the conditions to which the

- 11 709836/0956

different parts of the overall device should suffice, depending according to whether the molding compound and / or the press dies should preferably be heated. Appropriately, one does use of tables of numbers as provided by the plastics manufacturers or by the Tables in "Insulation Materials for Design and Engineering Practice" by Clark.Ed John Wiley, 1962.

In its most general form, the method of the invention encompasses the following features:

1) the use of dies obtained as indicated above. Usually two such press dies are used by corresponding reproduction (replica) of two parts of the precision molding that is to be reproduced, manufactured in such a way that they form a cavity when they are placed on top of one another (opposed), which is the precision molded part is equivalent to; the two outer surfaces of the two press dies are formed lying in parallel planes, so that the dies can be placed between the flat plates of the ram afterwards.

According to a variant, the press dies are made from a metallic negative preform of the precision molded part obtained by covering it with a 0.1 to 5 mm thick film of the plastic of the press die and then as above specified, the relief and shape of the part to be reproduced can be removed by means of compression molding. The press dies obtained in this way are then finished in final operations, i.e. deburred, ground etc.

According to a further embodiment of the method according to the invention, the press dies with lines for a circumferential Provided coolant and also with the press plates

- 12 709836/0956

firmly connected. Yet another embodiment provides that the press dies are independent of the press plates and with or without a metal support or base on one in the plastics processing industry in general known carousel can revolve and that before a certain number of work step places such as pressing, cooling while pressing, opening the mold, removing the molding, cleaning and cooling the mold, charging the mold and closing the mold.

2) The two press dies, which together make up the mold, are preferably made with evenly distributed thermoplastic Plastic filled in the form of a powder, as granules or as a film in the form of a preform. On it will the mold closed and the electric field for heating or heating generated during a period of 10 to 100 s, with an effective pressure on the thermoplastic from 0.5 to 20 kg / cm, preferably from 1

up to 10 kg / cm is exercised. Developed by the dielectric heating in the plastic temperature is in the range of 100 to 300 ° C, preferably in the range of 150 to 220 ⁰ C.

According to a modification, further powder layers or plastic films of a different nature can be provided in the form depending on the desired effect. For example In this way, an inner film reinforced with glass fibers can be arranged between two outer films, around which to improve the mechanical strength * of the molded part obtained,

3) Cooling is expediently to a temperature not below 30 ° C, the mold is closed and below

an effective pressure not exceeding 20 kg / cm and preferably

in the range of 1 to 10 kg / cm.

♦ or. Stiffness

- 13 -

709836/0956

Surprisingly, it is found that the use of such low pressures as mentioned above enables a perfectly faithful reproduction of the precision molding even if the surface relief has a low height of the order of / µm, while according to the prior art for this purpose had to work with higher or stronger pressures. It is also surprising to find that the press dies provided according to the invention enable a faithful and very precise reproduction of the precision molded part, although the mechanical rigidity of the dies is very low in the case of crosslinked and flexible elastomers and low in the case of non-crosslinked plastics Comparison with the metallic press dies of the prior art and at the maximum temperature reached by the dies, the negative reliefs of which can be mechanically deformed by the flowing gelled thermoplastic molding compound. If records are pressed in the manner according to the invention, no disturbance or impairment of the sound reproduction is observed, for example. It is also surprising to find that the precision molded parts produced according to the invention have no internal stresses or surface tensions, in contrast to precision molded parts produced with the aid of known methods; in the case of the latter, these stresses are detected by reheating the cooled precision molded part on a complete base to a temperature of 50 to 80 ^° C. for 1 to 4 hours. In the case of a precision molded part produced according to the invention, no deformation whatsoever is observed during such a treatment. The following examples serve to explain the invention in more detail; unless otherwise stated, all parts are by weight.

- 14 709836 / 095B

- Ί / f -

example 1

Manufacture of press dies

A) Production of press dies from a silicone elastomer for the production of records *

First one was made with a cutting stylus in the usual way engraved mother die made of hardened epoxy resin and carefully washed with distilled water and dried. With the help of this master die, a cylindrical hollow shape with a flat bottom was created in a rigid block made of machined polyvinylchloride with the master die placed on the flat solid bottom of the mold and was centered and the engraving, i.e. the tone grooves, were inside the form; the diameter the shape was 10 mm larger than the diameter of the master die.

A homogeneous mixture of the following components was then prepared in a conventional mixer with a rotary stirrer:

<C «3 -dihydroxy-dimethylpolysiloxane oil, viscosity

3500 cP / 25 ° C 100 parts

Quartz powder with average particle size h / around 90 parts ethyl silicate 4 parts

Dibutyltin dilaurate 0.5 parts

The mixture was degassed in vacuo for 15 minutes at room temperature and then poured into the above mold with a layer thickness of 1 cm between the upper surface of the mother die and the free area of the mixture; the whole was left to stand overnight at room temperature to allow vulcanization to effect the elastomer. Then the obtained solid die and the mold were separated from each other and the latter used for a further production process.

709836/0956

- 15 -

Λ «

The second press die produced in the same way together with the first press die formed a cavity according to the desired record; the external volume of the two press dies taken together was uniform and constant thickness of 21.2 mm. The press dies produced in this way were placed opposite one another on the Press plates of a printing press arranged and centered; the press plates themselves were equipped with inlet and outlet lines for cooling media provided and connected to the high frequency generator.

B) Production of press dies from silicone elastomers partially reinforced with glass fibers

The procedure was as in A) using the same elastomer composition, with the modification that in the following way was worked in two stages:

First of all, silicone elastomer compound was filled into the cylindrical mold up to a layer thickness of over 0.5 mm above the Poured in relief. This mass was allowed to harden as in A).

of which 2

Separated / was a glass fabric with a surface weight of 400 g / m, which was impregnated with the above silicone compound for plastic application * (sized) corresponding to a ratio of glass to plastic = 40 %. This impregnated fabric was then placed in several layers on the already poured plastic in such a way that the layer thickness between the filled (leveled) relief of the mother matrix and the free surface was 1.0 cm; in addition, care was taken that no air bubbles remained in the composite material. Then it was left to harden overnight at room temperature and finally worked and finished as in A). With the help of this way of working will be

♦ prepared

709836/0956 - 16 -

Press dies obtained that have better dimensional stability and are better suited for higher press pressures and which also have lower dielectric loss, whereby the means of dielectric loss in the molding compound distributed energy can be localized when the high-frequency field is applied.

C) Production of press dies from fluorine-containing polymer

A commercially available copolymer was used to produce the two press dies for the production of records made of tetrafluoroethylene and ethylene (PTFE and PFA from Du Pont de Nemours) and poured into a mold, one inside of which has the positive one labeled "Father" above Image of the intended record, obtained by electroplating, was. The work was carried out under a pressure of 150 kg / cm and at a temperature of 3A5 ° C; the minimum thickness of the received The press die was 2 mm. The two press dies were then placed on the plates of a press as described under A) fixed.

Example 2

Pressing records

The press dies produced according to Example 1 B) were used to produce records with a diameter of 27 cm and a thickness of 1.2 mm. The press plates were attached to the terminals of a high frequency generator (manufactured by the company
HFI, Maisons-Alfort, France) connected:

Electric field frequency: 27.12 MHz

Power: 15 kW

- 17 709836/0956

Composition of the molding or molding compound:

Polyvinyl chloride with viscosity number AFNOR 78

and mean particle diameter 0.118 mm 90 parts

Copolymer of vinyl acetate and vinyl chloride containing 15 wt .- # vinyl acetate units, viscosity number AFNOR 58 and mean part diameter 0.115mm 10 parts

Dioctyl phthalate 10 parts

Soot Microlithe CT (from Ciba-Geigy) 1 part

Tin octoate (trade name Stavinor Z 8015 B

from Rousselot) 6 parts

For the preparation of this composition, the solid components were mixed in a Pape Meyer mixer to a temperature of 55 ° (Subsequently, the liquid components were added and the inner temperature to 90 ⁰ C allowed to rise;., Finally, the contents of the mixer was shed.

After opening the press dies arranged on the press, 100 g of molding compound were poured onto the lower press die and distributed evenly. The press was then closed with a thrust on the closing piston of 2100 kg, corresponding to an effective pressure on the molding compound of 3 kg / cm. A high-frequency field was then applied between the press plates for 30 seconds at a voltage of 8000 V and with a strength of 3 A, while the pressure was kept constant. It was then allowed to ^{cool to 30 °} C. under constant pressure for 60 s. In this way, a pressed record was obtained with a sound reproduction that was true to the original. To demonstrate the dimensional stability and the absence of mechanical stresses, the plate was treated as follows: on a metal support plate 1 was held in an oven, then taken out, brought the temperature of the Heizschrankes at 50 ° C, the sheet under the h at 40 ⁰ C. same conditions

- 18 709836/0956

gen, i.e. put in for 1 hour, taken out again and

continued in this way up to a temperature of 80 ⁰ C

first
ren; at this temperature there was a slight deformation of the plate, which had an adverse effect on the sound reproduction. By this good dimensional stability up to 8O ⁰ C records the observed changes or deformations usually prepared at conventionally been avoided, which are observed when one lays the conventional plates on a conventional heat source.

Example 3

The procedure was as in Example 2 with a molding compound of the following composition:

Vinyl chloride homopolymer, viscosity number AFNOR 95, mean particle diameter 0.120 mm 100 parts

Dioctyl phthalate 10 parts

Carbon black (commercial product Noir Microlithe CT from Ciba

Geigy) 1 part

Dibutyltin dilaurate (commercial product Stavinor MS

6032 by Rousselot) 6 parts

The molding compound was produced as in Example 2. The electric field (high frequency) was applied for 30 s and then proceed according to example 2; the pressed record was characterized by very good mechanical quality and sound off.

example k

The procedure was as in Example 3 with the modification that the molding composition did not contain any dioctyl phthalate. The electric Field was applied for 45 minutes and then as above

- 19 709836/0956

proceed as described. The finished pressed record was characterized by very good sound reproduction and mechanical quality.

Example 5

In this example, the press dies produced according to Example 1 and the molding compound according to Example 2 were used. The finished record had the same good properties as the record according to Example 2.

Example 6

The press dies according to Example 1 A) and otherwise under the conditions of Example 2 were used with the following modifications: the molding compound was obtained by stacking molding compounds in the following manner. First, two disks or plates corresponding to the inner shape of the press dies were cut out of a form with a layer thickness of 300 μm consisting of polyvinyl chloride with a viscosity number 80 (70 parts), a copolymer of polyvinyl acetate and polyvinyl chloride with 15 % vinyl acetate units (30 parts) and an additive to improve the Shock resistance MBS (3 parts). A first / slice of the film was placed on the lower die. Then 30 g of powder consisting of were evenly distributed

Vinyl chloride homopolymer with viscosity number AFNOR 78 and average particle diameter 0.118 mm 90 parts

Copolymer of vinyl acetate and vinyl chloride with 15% by weight of vinyl acetate units, viscosity number AFNOR 58 and mean particle diameter 0.115 mm 6 parts

Dioctyl phthalate 10 parts

Commercial azodicarbonamide 0.5 parts

Soot 1 part

produced as a dry mixture according to example 2 distributed on the first sheet of film. Then came the second sheet of foil

709836/0956

- 20 -

placed and finally the whole as described in Example 2 pressed. A record was obtained with less Weight and apparent density 0.9, which was characterized by very good sound reproduction.

* (Volume weight)

709836/0956

Le

rft

e i t e

Claims (7)

Expectations 1 , ι method for pressing a flat precision molded part made of thermoplastic material, of relatively small and constant thickness, which has a relatively flat surface relief based on the thickness, in particular of sound and image plates and optical grids, in which a powder, foils - Or granular thermoplastic material heated between two press dies using dielectric heating and gelled and then pressed and cooled, characterized in that with press dies made of a plastic that is thermally and mechanically resistant at the pressing temperature and the pressing pressure and from the group of cross-linked Elastomers based on organopolysiloxanes and fluorinated polymers is selected, pressed and the press dies and / or the thermoplastic material are dielectrically heated. 2. The method according to claim 1, characterized in that with compression dies, which in addition to a crosslinked elastomer based on an organopolysiloxane 1 to 50 wt. -96, in particular 20 to 40 wt. -96 have glass fibers, is pressed. 3. The method according to claim 1 or 2, characterized geke η η that with a high frequency field of 1 to 5 χ 10 ³ MHz ₉ preferably from 10 to Λ0 NHz and an electrical voltage of 100 to 10,000 V ₉ preferably from 300 to 5000 V is heated. 709836/0958 4. The method according to any one of claims 1 to 3, characterized in that during pressing and cooling a pressure of 0.5 to 20 kg / cm, preferably 1 to 10 kg / cm, is maintained. 5. The method according to any one of claims 1 to 4, characterized characterized that with a pressing temperature of 100 b: is tet. from 100 to 30O ⁰ C, preferably from 150 to 220 ° C. 6. Press die for the production of a flat precision molded part Made of thermoplastic material, of relatively small and constant thickness, which is a relative to the thickness has flat surface relief, in particular of clay and video plates and optical grids, consisting of a at the pressing temperature and the pressing pressure thermally and mechanically resistant plastic from the group of cross-linked Elastomer compounds based on organopolysiloxanes and fluorinated Polymers. 7. Press die according to claim 6, characterized in that gee k e η η, that in addition to the crosslinked elastomer composition based on an organopolysiloxane from 1 up to 50% by weight, preferably 20 to 40% by weight, of glass fibers. 709836/0966