The invention concerns a pressing cushion (1, 11, 31, 32, 33) having a cushioning (2, 12) that is elastic in its thickness direction and having connecting threads (8, 25), going back and forth between the surfaces of the cushioning, that are configured at least partially as thermally conductive threads. The pressing cushion (1, 11, 31, 32, 33) is characterized in that connecting threads (8, 25) are provided which have a sewn profile or form knitted stitches.

The invention concerns a pressing cushion for use in laminating presses, having a cushioning that is elastic in the thickness direction and having connecting threads, going back and forth between the surfaces of the pressing cushion, that are configured at least partially as thermally conductive threads whose thermal conductivity is better than that of the cushioning.
The manufacture of layered materials, for example decoratively coated particle boards, is performed in laminating presses that can be configured as low- or high-pressure multiplaten presses or short-cycle presses. To ensure that the pressure of the press plates is transferred uniformly onto the pressed material over its entire surface, pressing cushions are inserted between the pressed material and the press plates. The pressing cushions must be capable of withstanding high pressures as well as the temperatures that occur in such presses, and they must be capable of transferring the heat proceeding from the press plates quickly and without major losses onto the pressed material. It is also desirable to be able to process pressed materials in different formats in succession with one pressing cushion.
The known pressing cushions can be divided into two groups. The one group involves layered designs. For example, DE-A-26 27 442 describes a pressing cushion in which a matted nonwoven fabric is coated on both sides with a silicone elastomer. EP-A-0 235 582 discloses a pressing cushion in which a silicone elastomer film is coated on both sides with a parting film. U.S. Pat. No. 3,723,3320 discloses a pressing cushion made of a silicone film that can additionally be equipped with a parting film.
Pressing cushions that are made of or contain a textile thread system in the form of a fabric are known in many embodiments, especially as regards the materials used therein. DE-B-23 19 593 discloses a pressing cushion whose basis is a metal sieve fabric that is enclosed in a matrix made of a silicone elastomer. The pressing cushion according to DE-A-23 38 749 has a glass fiber fabric in which individual or all threads are impregnated or coated with a plastic, for example a silicone elastomer, so that these threads form the cushioning. The teaching of DE-A-26 50 642 is similar. EP-A-0 493 630 proposes a pressing cushion made of a textile fabric in which the fabric is composed of aromatic polyamide threads and metal threads as thermally conductive threads. DE-U-295 18 204 discloses a pressing cushion in which one portion of the threads has a silicone elastomer and a further portion can be configured as metal wire. DE-U-94 18 984.6 describes a pressing cushion in which the threads can be made of a wide variety of materials, in particular of rubber, silicone elastomer, or metal, and combinations thereof. Lastly, DE-U-297 21 495 and DE-U-297 21 494 depict pressing cushions made of a fabric in which the individual threads are interwoven and configured in a particular fashion.
With the first group of pressing cushions, satisfactory thermal conductivity cannot be achieved. With the second group of pressing cushions, compromises must be made between thermal conductivity and dimensional stability, so that an optimum result in terms of those properties cannot always be obtained.
It is therefore the object of the invention to configure a pressing cushion in such a way that the thermal conductivity and dimensional stability can be adjusted within wide limits, and that in terms of the cushioning as well, a wide range of possible variations exists for designing the pressing cushion in accordance with requirements.
According to the present invention, this object is achieved in that connecting threads are provided which have a sewn profile or form knitted stitches. The basic idea of the invention is thus for at least a portion of the connecting threads, preferably all of the connecting threads, not to be interwoven with the cushioning, but rather for the connection to be made by sewing (which is also to be understood as quilting or embroidering) or knitting. It has been found that a strong overall structure having high dimensional stability can be achieved thereby. It is moreover possible, by way of the proportion of thermally conductive threads among the connecting threadsxe2x80x94and the connecting threads can also all be configured as thermally conductive threadsxe2x80x94and by way of the nature and quantity of the stitches, to adapt the thermal conductivity to the particular requirements within wide limits. A greater freedom in terms of configuring the cushioning also results. In this context, xe2x80x9cthermally conductive threadsxe2x80x9d are to be understood as those threads which, because of their presence, improve the thermal conductivity of the pressing cushion in the thickness direction. If further connecting threads are present in addition to the stitch-forming connecting threads, these threads can be configured entirely or partially as thermally conductive threads, either in combination with thermally conductive threads of the stitch-forming connecting threads or indeed alone, if the stitch-forming connecting threads do not contain thermally conductive threads in the aforesaid sense. The overall result is to make available a structure for the pressing cushion that offers a substantially greater breadth of variation in terms of the aforesaid properties than has been attainable with the previously known fabric configurations.
The cushioning can be configured as a single-ply cushioning layer. There also exists the possibility, however, of configuring the cushioning with multiple plies and configuring at least one of the plies elastically in the thickness direction, all of the plies being interconnected by connecting threads.
As a detail, the elastic ply or at least one of the elastic plies can have or be made of cushion threads that are elastic in the thickness direction.
As an embodiment of this basic idea, the cushion threads can extend next to one another in the same direction in the particular ply; the cushion threads can be present as a layer or can be part of a fabric or of a knitted material. In this context, multiple plies having cushion threads can also be arranged one on top of another. It is advantageous in this case if the cushion threads of the plies extend in different directions, for example diagonally, transversely, or longitudinally, so that they cross one another.
The cushion threads can be made, for example, of an elastomeric material, such as silicone elastomer or fluorosilicone elastomer. They can, however, also be structured, in a manner known per se, in such a way that they each have a core thread made, for example, of metal wire that is surrounded by an elastomeric thread material, for example silicone elastomer. In addition, the cushion threads can also be at least partially surrounded by metal wire, for example in overbraided, wound, or stranded form, as is evident for example from DE-U-295 18 204 and DE-U-297 21 495. The elastomeric thread sheath can also, for example, be constituted from elastomeric threads that are wound or stranded around the core thread.
Instead of or in combination with cushion threads, the elastic ply or at least one of the elastic plies can also be made of an elastomer film. The film can be equipped with the elements that improve thermal conductivity, for example powders, threads, or fibers made of metal such as aluminum, bronze, stainless steel, copper, or brass. For reinforcement, the elastomer film can also contain a textile support that can be present as a fabric, thread layer, or knitted fabric.
In addition, the elastic ply or at least one of the elastic plies can also be configured as an elastic woven fabric or knitted fabric, or as a fiber batt, or as a combination of the aforesaid textiles.
The elastic ply or at least one of the elastic plies can, however, also be made of foamed material; the foamed material can contain the elements that improve thermal conductivity. Another possibility consists in providing a nonwoven ply; the nonwoven ply can have metal fibers in order to improve thermal conductivity. It is also possible, however, instead or in combination, to provide a fabric, thread layer, or a knitted material, the respective ply being made partially or entirely of metal threads. Combinations of the aforesaid plies are also possible, for example a combination of fabric, thread layer, or knitted material with a nonwoven ply.
If the pressing cushion is of multiple-layer configuration, it may also be advantageous if at least one of the plies is of incompressible configuration, being made for example as a metal foil or of foil strips.
As regards the thermally conductive threads, metals with good thermal conductivity, for example aluminum, bronze, stainless steel, copper, or brass, are suitable. The thermally conductive threads can, as wires or strands, be made entirely of these metals or can continuously contain them. It is possible in this context to configure the thermally conductive threads as plastic threads, for example from high-strength plastics such as aramid or polyimide, with a metal content.
Provision is also made, according to the invention, for thermally conductive threads and thermally non-conductive threads to alternate as weave threads [sic], the thermally non-conductive threads having a greater tensile strength than the thermally conductive threads, for example being made of aramid or polyimide.
Lastly, the invention provides for the pressing cushion to have edge thickenings, which can be achieved by the use of additional threads or ribbons, or forming loops at the edge. Folding the edges over and then sewing them up also yields such edge thickenings. This results in an equalization of pressure all the way into the edge regions.
The invention is illustrated in more detail, with reference to exemplary embodiments, in the drawings, in which:

Thomas Josef Heimbach Gesellschaft mit beschrankter Haftung and Co.


Amorphous polymers, including homopolymers and co-polymers, containing residues of vinyl cyclohexane and/or substituted vinyl cyclohexane are described. The polymers of the present invention have a syndiotactic configuration in which the quantity of diads is greater than 50.1% and less than 74%. The polymers of the invention have high transparency, low birefringence and high heat defection temperature, and can be used to prepare molded articles (e.g., optical data storage media and lenses) and films.

The present invention relates to polymers and co-polymers based on vinyl cyclohexane (VCH) with predominantly syndiotactic configuration and a process for their manufacture and their use as optical material. The materials may be processed into moulded bodies by extrusion or injection moulding and are particularly suitable as substrate for optical data storage media such as compact discs, video discs, re-writable optical discs.
Transparent plastics such as aromatic polycarbonate, polymethyl methacrylate or polystyrene may be used as substrate for optical data storage media. Addition co-polymers comprising ethylene and a norbornene derivative or a tetracyclododecene derivative and hydrogenated products of ring-opened metathesis polymers comprising norbornene or tetracyclododecene are also considered.
None of the current substrate materials may, however, be used without restriction for very high data storage densities ( greater than 5, particularly  greater than 10 Gbytes related to a disc of 120 mm diameter). Very low birefringence and water absorption, high heat deflection temperature, accompanied by adequate mechanical properties and low melting viscosity, are simultaneously required for this purpose.
Although aromatic polycarbonates have very good mechanical properties and heat deflection temperature, their birefringence and water absorption are too high.
The birefringence of polystyrene is too high and its heat deflection temperature too low.
The water absorption of polymethyl methacrylate is too high and its dimensional stability too low. The birefringence of addition co-polymers comprising ethylene and a non-polar norbornene or tetracyclododecene is low and they have virtually no water absorption.
These materials are very expensive to produce, however. The materials may only be produced in optically pure quality with great difficulty. The presence of gel contents also reduces their applications as optical materials. Considerable technical outlay is involved in separating the catalysts and co-catalysts.
Optical materials comprising a hydrogenation product of a polymer comprising an alkenyl-aromatic hydrocarbon compound or a co-polymer thereof are described in GB 933,596 (=DE-AS 1 131 885), EP-A 317 263, U.S. Pat. Nos. 4,911,966 and 5,178,926. There is no reference to the configuration.
Hermann Staudinger was the first to describe the hydrogenation of polystyrene in 1929. More recent patent literature concerns the basic micro-structure of polyvinyl cyclohexane and/or hydrogenated polystyrene. The prior art is that amorphous vinyl cyclohexane polymers have an atactic configuration and crystalline VCH (vinyl cyclohexane) polymers either isotactic or syndiotactic configuration (EP-A 0 322 731, EP-A 0 423 100, U.S. Pat. Nos. 5,654,253; 5,612,422; WO 96/34896). Isotactic PVCH (polyvinyl cyclohexane) is produced in the presence of Ziegler catalysts and has a high melting point (J. Polym. Sci., A2, 5029 (1964). EP-A 0 322 731 describes that vinyl cyclohexane polymers with syndiotactic configuration by hydrogenation of syndiotactic polystyrene are crystalline, wherein the quantity of the diads is at least 75% and the quantity of the pentads at least 30%. WO 94/21694 describes a process for producing hydrogenated poly(alkenyl-aromatic) polymers and poly(alkenyl-aromatic)/polydiene block co-polymers. Syndiotactic polystyrene is mentioned in general terms.
Processes which lead to isotactic, syndiotactic and atactic hydrogenated polystyrene which have the material properties known hitherto are described in WO 94/21694, U.S. Pat. No. 5,352,744, wherein specific catalysts are used. Processes for the hydrogenation of atactic polystyrene to produce atactic hydrogenated polystyrene by the use of specific catalysts are described in U.S. Pat. Nos. 5,654,253; 5,612,422; WO 96/34896.
Atactic polymers are regular polymers. By definition they have the possible configurative base units in equal quantities, with ideal-random distribution from molecule to molecule (TUPAC). They are distinguished by the same number of iso-and syndiotactic diads. An amorphous material with only one glass stage with no crystalline content is described.
The present invention provides a polymer or co-polymer based on vinyl cyclohexane, wherein olefins, acrylic acid derivatives, maleic acid derivatives, vinyl ethers or vinyl esters may be used in production as co-monomers, with syndiotactic configuration, characterized in that the quantity of diads is greater than 50.1% and less than 74%. The polymers based on vinyl cyclohexane are amorphous polymers.
The polymers according to the invention are distinguished by, high transparency, low birefringence and high heat deflection temperature and may therefore be used as substrate material for optical data storage media. Because of its crystallinity the known, isotactic PVCH is unsuitable for optical applications.
The invention provides hydrogenated products of polystyrene which lead to an amorphous hydrogenated polystyrene with an excess of the racemic (syndiotactic) diads.
The vinyl cyclohexane polymer of this invention is a new amorphous polymer with a defined stereostructure which is distinguished by the predominant occurrence of the racemic diads configuration and may be efficiently produced by the process described.
A polymer based on vinyl cyclohexane is preferred with the repeating structural unit of formula (I)
in which
R1 and R2 independently of each other stand for hydrogen or C1-C6 alkyl, preferably C1-C4 alkyl, and
R3 and R4 independently of each other stand for hydrogen or for C1-C6 alkyl, preferably C1-C4 alkyl, particularly methyl and/or ethyl, or R3 and R4 jointly stand for alkylene, preferably C3 or C4 alkylene (fused 5 or 6-membered cycloaliphatic ring),
R5 stands for hydrogen or C1-C6 alkyl, preferably C1-C4 alkyl,
R1, R2 and R5 independently of each other stand in particular for hydrogen or methyl.
Apart from the stereoregular head-to-tail linkage, the linkage may have a small content of head-to-head linkage. The amorphous, predominantly syndiotactic polymer based on vinyl cyclohexane may be branched via centres and may have a stellar structure for example.
The following may preferably be used in the polymerization of the starting polymer (optionally substituted polystyrene) and be co-incorporated into the polymer as co-monomers: olefins with in general 2 to 10 C atoms, such as for example ethylene, propylene, isoprene, isobutylene, butadiene, C1-C8, preferably C1-C4 alkyl esters of acrylic and/or methacrylic acid, unsaturated cycloaliphatic hydrocarbons, e.g. cyclopentadiene, cyclohexene, cyclohexadiene, optionally substituted norbornene, dicyclopentadiene, dihydrocyclopentadiene, optionally substituted tetracyclododecenes, nucleus-alkylated styrenes, xcex1-methylstyrene, divinyl benzene, vinyl esters, vinyl acids, vinyl ethers, vinyl acetate, vinyl cyanides such as for example acrylonitrile, methacrylonitrile, maleic anhydride and mixtures of these monomers.
The amorphous vinyl cyclohexane polymer according to the invention has a syndiotactic diad content, determined by two-dimensional NMR spectroscopy, of 50.1 to 74%, preferably of 52-70%. Methods for microstructure elucidation using 13C-1H correlation spectroscopy of the methylene carbon atoms of a polymer backbone are generally known and are described by A. M. P. Ros and O. Sudmeijer for example (A. M. P. Ros, O. Sudmeijer, Int. J. Polym. Anal. Charakt. (1997) 4, 39).
The signals of crystalline isotactic and syndiotactic polyvinyl cyclohexane are determined by means of two-dimensional NMR spectroscopy. The methylene-carbon atom (in the polymer backbone) of the isotactic polyvinyl cyclohexane splits into two separated proton signals in the 2-D CH correlation spectrum and exhibits the pure isotactic diad configuration. In contrast, for the carbon atom C 1, syndiotactic polyvinyl cyclohexane exhibits only one signal in the 2-D CH correlation spectrum. The amorphous syndiotactically rich polyvinyl cyclohexane according to the invention has an integral intensity excess of the syndiotactic diads compared to the isotactic diad configuration.
The birefringence determined on these materials, measured with the aid of the rheo-optical constant CR, isxe2x88x920.3 GPaxe2x88x921, which is more than one power of ten lower than that for polycarbonate (CR=+5.4 GPaxe2x88x921). The method for measuring the rheo-optical constant is described in EP-A 0621 297. The plane-parallel 150 to 1000 xcexcm sample bodies required for this may be produced by melt compression moulding or film casting. Compared with polycarbonate the material may be regarded as birefringence-free. It has a high heat deflection temperature, low water absorption, accompanied by adequate mechanical properties, and is therefore an ideal material for very high optical data storage densities ( greater than 10 Gbytes on a disc of 120 mm diameter).
In general the vinyl cyclohexane (co)polymers have absolute molecular weights Mw weight average of 1000-10000000, preferably of 60000-1000000, most particularly preferably 70000-600000, determined by light scatter.
In general the homopolymers based on vinyl cyclohexane according to the invention have a glass temperature  greater than 140xc2x0 C., preferably  greater than 145xc2x0 C., determined by DSC.
The co-polymers may be present both randomly and as block co-polymers.
The polymers may have a linear chain structure and also have branch points by co-units (e.g. graft co-polymers). The branch centres contain stellar or branched polymers for example. The polymers according to the invention may have other geometrical shapes of the primary, secondary, tertiary, optionally quaternary polymer structure; helix, double helix, pleated sheet etc. and/or mixtures of these structures may be mentioned.
Block co-polymers contain di-blocks, tri-blocks, multi-blocks and stellar block co-polymers.
The VCH (co)polymers are produced by polymerizing derivatives of styrene with the corresponding monomers radically, anionically, cationically or by metal complex initiators and/or catalysts and then partially or completely hydrogenating the unsaturated aromatic bonds (cf WO94/21694, EP A 322 731 for example). They are distinguished by the predominant occurrence of the syndiotactic configuration of the vinyl cyclohexane units of the present invention.
The VCH (co)polymers may be further produced, for example, by hydrogenation of aromatic polystyrenes and/or their derivatives in the presence of a catalyst, wherein an ether which has no xcex1-hydrogen atom on a carbon atom adjacent to the ether function, or a mixture of such ethers or a mixture of at least one of the said ethers with solvents suitable for hydrogenation reactions is used as solvent.
The reaction is generally conducted at volume concentrations of the ether component with respect to the entire solvent of 0.1% to 100%, preferably 1% to 60%, most particularly preferably 5% to 50%. The ether component may be designated as a co-catalyst.
In general the process leads to a virtually complete hydrogenation of the aromatic units. Usually the degree of hydrogenation is xe2x89xa780%, preferably xe2x89xa790%, most particularly preferably xe2x89xa799%, particularly 99.5 to 100%. The degree of hydrogenation may be determined by NMR or UV spectroscopy for example.
The starting polymers are generally known (WO 94/21 694 for example).
Ethers of formula (I):
in which
R1, R2, R3 and R4 independently of each other stand for C1-C8 alkyl, which is straight-chain or branched, or for C5-C6 cycloalkyl optionally substituted by C1-C4 alkyl or
two of the groups R1, R2, R3 and R4 form a ring with 3 to 8, preferably 5 or 6 carbon atoms,
are preferably used as solvent.
Methyl-t-butyl ether, ethyl-t-butyl ether, propyl-t-butyl ether, butyl-t-butyl ether, methyl-(2-methyl-2-butyl)ether, (tert. amyl-methyl ether), 2-ethoxy-2-methylbutane (ethyl-tert.-amyl ether) are particularly preferred.
The quantity of catalyst used depends on the process conducted; this may be continuous, semi-continuous or discontinuous.
The ratio of catalyst to polymer is generally 0.3-0.001, prefer ably 0.2-0.005, particularly preferably 0.15-0.01, for example, in the discontinuous process.
The polymer concentrations, related to the overall weight of solvent and polymer, are generally 80 to 1, preferably 50 to 10, particularly 40 to 15 wt. %.
The starting polymers are hydrogenated according to generally known methods (WO 94/21 694, WO 96/34 895, EP-A-322 731 for example). A plurality of known hydrogenation catalysts may be used as catalysts. Preferred metal catalysts are quoted in WO 94/21 694 or WO 96/34 896 for example. Any catalyst known, for hydrogenation reactions may be used as catalyst. Suitable catalysts are ones with a large surface (such as 100-600 m2/g) and small average pore diameter (20-500xc3x85 for example). Catalysts with a small surface (such as xe2x89xa710 m2/g) and large average pore diameters, which are characterized in that 98% of the pore volume have pores with pore diameters greater than 600xc3x85 (approx. 1000-4000xc3x85 for example) (cf. U.S. Pat. Nos. 5,654,253, 5,612,422, JP-A 03076706 for example) are also suitable. Raney nickel, nickel on silicon dioxide or silicon dioxide/aluminium oxide, nickel on carbon as carrier and/or precious metal catalysts such as Pt, Ru, Rh, Pd are used in particular.
The reaction is generally carried out at temperatures between 0 and 500xc2x0 C., preferably between 20 and 250xc2x0 C., particularly between 60 and 200xc2x0 C.
The solvents which may conventionally be used for hydrogenation reactions are described in DE-AS 1 131 885 for example (see above).
The reaction is generally carried out at pressures of 1 bar to 1000 bar, preferably 20 to 300 bar, particularly 40 to 200 bar.
The polymers or copolymers based on vinyl cyclohexane according to the invention are outstandingly suitable for producing optical data storage media, preferably with data storage densities  greater than 5, particularly  greater than 10 Gbytes, related to a disc of 120 mm diameter.
The following may be quoted as examples of optical data storage media:
Magneto-optic disc (MO-disc)
Mini-disc (MD)
ASMO (MO-7) (xe2x80x9cAdvanced storage magnetoopticxe2x80x9d)
DVR (12 Gbyte Disc)
MAMMOS (xe2x80x9cMagnetic Amplifying magneto optical systemxe2x80x9d)
SIL and MSR (xe2x80x9cSolid immersion lensxe2x80x9d and xe2x80x9cmagnetic superresolutionxe2x80x9d)
CD-ROM (Read only memory)
CD, CD-R (recordable), CD-RW (rewritable), CD-I (interactive), Photo-CD
Super Audio CD
DVD, DVD-R (recordable), DVD-RAM (random access memory); DVD 32 digital versatile disc
DVD-RW (rewritable)
PC+RW (Phase change and rewritable)
MMVF (multimedia video file system)
Because of their outstanding optical properties the polymers according to the invention are also particularly suitable for producing optical materials, e.g. for lenses, prisms, mirrors, colour filters etc. Also as media for holographic reproductions (e.g. cheque, credit cards, identity cards, three-dimensional holographic images). The materials may be used as transparent media for inputting three-dimensional structures, for example comprising focussed coherent radiation (LASER) particularly as three-dimensional data storage media or for the three-dimensional representation of objects.
The material may conventionally be used in place of or in conjunction with glass up to service temperatures of 145xc2x0 C. Exterior applications for the transparent materials are roofing, window panes, films, glazing of glasshouses, in the form of twin-wall sheets for example. Further applications are covers to protect mechanically sensitive systems with high transparency at the same time, e.g. in the photovoltaics field, particularly solar cells or solar collectors. The plastics according to the invention may be coated with other materials, particularly with nanoparticles to increase scratch resistance, metals and other polymers.
Examples of domestic applications are transparent packing materials with low water permeability, household articles produced by extrusion or injection moulding, e.g. pots and containers. Also domestic appliances and transparent lampshades.
As temperature-resistant rigid foams the plastics may be used for insulation in the building and technology field (house and appliance insulation, for refrigerators for example) and replace polystyrene and polyurethane foam for example. The high long-term service temperature is an advantage.
Because of the low density (d less than 1) and weight-saving which results therefrom the materials are particularly suitable for applications in the motor vehicle, aviation and aerospace industry for instrument panels, transparent covers of instrument systems and of light sources, on-board glazing and insulating material.
The materials are insulators for electric current and are therefore suitable for producing capacitors (e.g. dielectrics), electronic circuits and equipment housings. Further applications in the electrical industry are based in particular on the combination of high optical transparency with high heat deflection temperature, low water absorption in conjunction with light from suitable emitting sources. The materials are therefore suitable for producing light-emitting diodes, laser diodes, matrices for organic, inorganic and polymeric electroluminescent materials, opto-electrical signal receiving equipment, data transmission systems by replacing glass fibre (e.g. polymer optical fibres), transparent materials for electronic display media (screens, displays, projection equipment) e.g. of liquid crystal substrates.
The materials are suitable for applications in medical technology for transparent extruded or injection moulded articles for sterile and non-sterile analytical vessels, Petri dishes, microfilter plates, microscope slides, hoses, breathing tubes, contact lenses, spectacle lenses and containers of infusion solutions or drug solutions for example, extruded and injection moulded articles for applications in contact with blood, particularly for producing syringes, cannulas, catheters, short and long-term implants (e.g. artificial lenses), flexible tubes for blood, membranes for blood detoxification, dialyzers, oxygenators, transparent plasters, stored blood containers and suture materials.