EP3927540B1 - Press pad for use in a hydraulic single- or multi-level heat press, as well as press pad/press plate unit and press pad/heating plate unit - Google Patents

Description

Introduction

The invention relates to a press pad for use in a hydraulic single or multi-level heating press. In addition, the invention relates to a press pad/press plate unit and a press pad/heating plate unit.

State of the art

The coating of wood-based panels, such as plywood, chipboard, MDF, HDF or multiplex panels is usually done with high-grade cellulose paper impregnated with amino resin. These papers can be printed with different decors or be single-colored. The amino resins consist of pre-condensed melamine/formaldehyde resins or mixed resins of melamine and urea or phenol and cresol. The pre-condensed resins are in a liquid phase, which is why paper webs are thoroughly saturated in special impregnation channels with drying and cooling zones. In the heated drying zone, the polycondensation of the resins is stimulated again at a temperature between approx. 150°C and 170°C and interrupted in a subsequent cooling zone, depending on the desired degree of condensation. The paper webs obtained in this way have a low water content and are solid and therefore transportable for further processing in a press installation, in particular in the form of a hydraulic single-daylight or multi-daylight heating press.

The impregnated decor papers are now used with the appropriately selected wood-based panels in a hydraulic heating press, which can have one or, alternatively, multiple tiers. The precondensed amino resins first become liquid under pressure and temperature, with the viscosity of the liquid resins increasing again as a result of further molecular crosslinking and finally a solid surface being formed. To create the surface, metallic press plates with structured, matt or shiny surfaces are brought into contact with the decorative papers or the amino resins. The press plates are usually chrome-plated to protect the surface against abrasion and damage. The chrome layer also has the function that after the coating process (lamination) a perfect separation from the resin layer can take place. Metallic press plates can be made, for example, from brass, the alloy MS64 or the materials AISI 410 or AISI 630 exist, with steel sheets being preferred today due to their greater hardness and longer service life.

Depending on the area of application, the wood-based panels have different bulk densities and therefore also require different pressing pressures. When manufacturing floor panels (flooring panels) from HDF material (High Density Fibreboard), the specific pressing pressures are particularly high and amount to approx. 400 N/cm ² to 600 N/cm ² , since the raw densities of the panels are around 800 N/cm cm ³ to 1000 N/cm ³ . The raw panels themselves have a very low cushioning effect of their own and also have thickness tolerances that have to be compensated for during the coating process. In principle, all panel materials have greater or lesser thickness tolerances. Further tolerances result from the respective press system itself, in particular the press plates and the heating plates present in it.

If the aforementioned tolerances are not compensated for, there will be considerable surface defects in the formation of the surfaces of the coated wood-based panels. For this reason, the press systems are always equipped with appropriate press cushions, in particular those in the form of pressure-compensating fabrics or mats. The press pads are fixed between the heating plates and the press plates. They must be thermally stable, ie they must not decompose even at temperatures between 200°C and 230°C, they must have good resilience or restoring force and high thermal conductivity. The even distribution of pressure and the rapid flow of heat during the coating process are particularly important factors. As previously mentioned, under pressure and heat, the aminoplast resin reflows, giving off formaldehyde and water in vapor form. Since the resin is located between the metallic press plate and the wood-based panel, the system is hermetically sealed and the corresponding vapors have to diffuse into the paper web and the panel surface in the short time specified by the clocking of the press systems. If this does not happen because the pressure is uneven, the gas bubbles remain trapped in the resin layer and are later visible as milky, cloudy spots on the surface. Boards with such defects are then no longer suitable for further use. Due to the high heating plate temperatures (approx. 200°C to 230°C), the selection of suitable materials for the press pads is comparatively small. In recent decades, an elastomeric material based on silicone rubber has proven to be suitable, with blend materials and copolymers made from silicone rubber and fluorosilicone rubber or fluororubber also being used. The prior art press pads are typically constructed as fabrics containing elastomeric material Threads or as coated mats with an inner, mostly metallic supporting fabric.

From the EP 1 136 248 A a press pad having a fabric is known which contains a copolymer consisting of a silicone and a fluorosilicone rubber. The copolymer is incorporated into the press cushion in the form of coated threads that are used as warp or weft threads. In order to increase the thermal conductivity, metallic additives can be added to the elastomer material.

The EP 0 735 949 A1 describes a press pad which has a silicone elastomer in one thread system and metal threads in the other thread system. The threads containing the silicone elastomer can be designed as sheath-core threads, with the thread core being made of wire and the thread sheath being made of the silicone elastomer, for example.

At the one from the DE 20 2012 005 265 U known press pads, certain threads are designed as thermally conductive threads which, because they run as perpendicularly as possible to the press pad surfaces, are intended to enable more direct heat transfer.

In addition, are from the EP 1 300 235 A and the DE 23 19 593 A in each case a press cushion made of metal fabric, which is then coated essentially over the entire surface with a silicone rubber. According to the teaching of EP 1 300 235 A the metal threads lying on a surface of the press pad, in particular their loops or loops, are exposed by squeegeeing during the coating process in order in this way to achieve metallic contact between the press pad and the heating plate or press plate. Particles can also be added to the silicone elastomer to increase thermal conductivity. A disadvantage in this context is the fact that the addition of the particulate additives to the elastomer matrix has a negative effect on its elasticity and also its resilience properties.

The known press pads often have the disadvantage of material fatigue, in particular with regard to their restoring force or spring effect. The known silicone elastomers, but also alternatively used press pads with threads made of aromatic polymers, in particular polyamides, show such aging processes at permanent temperatures above approx. 200°C to 230°C. The press pads therefore have to be replaced relatively early, which results in downtimes of the press systems and increased environmental pollution, especially since the press pads made of the known materials or material mixtures are very poorly recyclable are. Especially when coating floor panels, press pads are required that have a high resilience value over a long period of use and a very high heat transfer. So far, when coating HDF boards for flooring ("laminate"), it has not been possible to change the board format with the known press pads, since the pads are heavily compressed in the selected board format and a later change to a larger format leaves marks on the pressed material. In addition, press pads according to the invention can also be used in so-called high-pressure press systems in which, for example, so-called high-pressure laminates, for example in the form of base materials for printed circuit boards, are produced by pressing under heat. A press cushion for such an application, which consists of a high-temperature-resistant plastic fleece and a PTFE film bonded thereto, is made of DE 200 11 432 U known. Due to the long cycle times in such pressing processes, metals are not required for this high-pressure cushion.

US 3980016A , DE2402931A1 and GB 1249825A describe press pads according to the preamble of claim 1.

Task

The object of the invention is to provide a press pad that is characterized by a very high elastic resilience, which is maintained over as long a period of time as possible without tiring, as well as a high level of thermal conductivity.

Solution

According to the invention, this object is achieved, starting from a press pad of the type mentioned at the outset, by a large number of metallic spring elements which are connected to the supporting structure and distributed in or on it.

Metallic spring elements have two advantages over elastomer materials or aromatic polymer materials: On the one hand, they can have a very high modulus of elasticity, ie high spring stiffness, due to the metal material. This means that the restoring forces are already very large even with comparatively small deflections, ie deformations, of the spring elements. Examples of metals with a high modulus of elasticity and high elongation at break are steel, especially spring steel. In principle, however, other metal materials such as copper alloys (eg beryllium copper) can also be used. Despite the large spring constants, metallic springs retain their restoring properties over very long periods of time, so that the press pads according to the invention have a correspondingly long service life.

On the other hand, metallic spring elements have very good thermal conductivity, so that the heat transfer through the press pad according to the invention is positively influenced, especially in comparison with press pads that have large proportions of an elastomeric material that is characterized by its comparatively poor thermal conductivity properties.

The invention thus allows for the first time the use of a press cushion component which is equally advantageous both with regard to its thermal conductivity properties and with regard to its spring properties (resilience). In the prior art, in order to optimize both properties (thermal conductivity and resilience), different components, such as e.g. elastomer materials for resilience and metal materials, in particular metal threads, for good thermal conductivity were always used. According to an exemplary embodiment, which is not part of the claimed invention, the support structure can be formed by a metallic plate, preferably a pressing plate or a heating plate of the single or multi-daylight heating press. In the two last-mentioned cases of connecting the spring elements to a press plate or a heating plate, a unit is created from the press plate and spring elements or heating plate and spring elements. The spring elements are preferably glued and/or soldered and/or welded and/or positively connected to the respective plate, for example by inserting spring sections into corresponding recesses or openings in the plate.

In the case of the present invention, the support structure can be in the form of a textile fabric. In particular, the textile fabric can be designed as a knitted or crocheted fabric or nonwoven or woven fabric, with at least some of the threads that form the textile fabric being made of metal or containing metal, the metal being made in particular of brass, copper, bronze, steel, in particular stainless steel, can be formed.

In addition, a combination of a metal plate and a textile fabric to form the support structure is also an option. In this variant, the spring elements are preferably connected to the textile fabric and/or the metal plate. In addition, a suitable connection between the textile fabric and the metallic plate is required, for example in the form of gluing or welding or soldering or a positive connection between threads of the textile fabric and the plate, e.g. threads of the textile fabric being guided through openings or recesses in the metallic plate.

Plate springs or helical springs or leaf springs or wave springs can preferably be used as metallic spring elements.

According to a preferred embodiment of the invention, it is proposed to connect the spring elements to threads of the textile fabric, in particular to connect them in a form-fitting manner, preferably to arrange them at crossing points of warp threads and weft threads. For this purpose, the spring elements can have openings through which threads of the textile fabric, in particular the aforementioned warp and weft threads, are passed. A particularly preferred embodiment is formed by a press cushion in which the spring elements each have four openings, two of which have a warp thread and the other two have a weft thread. The crossing points of the respective threads can be designed particularly advantageously in this way.

In order to achieve the best possible homogeneity of the spring properties of the press pad, the spring elements should be arranged equidistantly from one another, in particular in crossing rows, further in particular along the weft and/or warp threads of a fabric serving as the supporting structure. This results in a kind of matrix structure and a particularly simple arrangement of the spring elements.

Further developing the invention, it is provided that the spring elements can be partially embedded in an elastomeric material, preferably in a silicone elastomer or a fluorosilicone elastomer or a blend polymer or copolymer of the two aforementioned elastomers. Sections or parts of the spring elements on both opposite sides of the press pad preferably form part of the surface of the press pad. In this way, a particularly good heat transfer is achieved since the transfer of heat on both surfaces of the press pad is created by metallic contact surfaces of the press pad to the press plate or to the heating plate. It is particularly advantageous in this connection if the spring elements extend through the press pad completely over its entire thickness in order to optimize the conduction of heat.

In connection with a combination of metallic spring elements with an elastomeric material, it can be useful to add particles to the elastomeric material to increase the thermal conductivity of the press pad. These are, in particular, particles made of a metal or a mineral, with these particles preferably being in the form of nanoparticles.

example

Figur 1

eine schematische Ansicht eines erfindungsgemäßen Presspolsters,

Figur 2

einen vertikalen Schnitt durch ein Federelement aus Figur 1,

Figur 3

eine schematische Ansicht eines weiteren erfindungsgemäßen Presspolsters,

Figur 4

einen vertikalen Schnitt durch das Presspolster aus Figur 3,

Figur 5

einen vertikalen Schnitt durch eine Einetagen-Heizpresse gemäß dem Stand der Technik,

Figur 6

einen vertikalen Schnitt durch eine erfindungsgemäße PresspolsterHeizplatten-Einheit und

Figur 7

einen vertikalen Schnitt durch eine erfindungsgemäße PresspolsterPressblech-Einheit.

The invention is explained in more detail below using exemplary embodiments that are illustrated in the figures. It shows:

figure 1

a schematic view of a press pad according to the invention,

figure 2

a vertical section through a spring element figure 1 ,

figure 3

a schematic view of another press pad according to the invention,

figure 4

Make a vertical cut through the press pad figure 3 ,

figure 5

a vertical section through a single-daylight heating press according to the prior art,

figure 6

a vertical section through a press pad heating plate unit according to the invention and

figure 7

a vertical section through a press pad press plate unit according to the invention.

An embodiment in the figure 1 is shown includes a press pad 1 'according to the invention for use in a hydraulic single or multi-daylight heating press. As in the prior art, it is provided to arrange the press pad 1 between a heating plate and a pressing plate of a single or multi-level heating press in order to compensate for thickness tolerances present in the pressing plate or the heating plate and at the same time to transfer the heat emitted by the heating plate to the pressing plate make possible.

The press pad 1 according to the invention comprises a planar support structure 2 and a multiplicity of spring elements 3. The planar support structure 2 is in the form of a fabric which comprises two thread systems 4, 5, namely warp threads 6 and weft threads 7. The warp threads 6 and the weft threads 7 are in the form of wire strands made of brass and are woven together to form a plain weave. The warp threads 6 accordingly run alternately over and under the weft threads 7 and vice versa.

The spring elements 3 of the press pad 1 are designed in the form of metal disk springs 8 . When used in a single or multi-daylight heating press, the disc spring 8 is in an undeformed state with only a circular, circumferential, upper edge 9 with a heating plate of a single or multi-daylight heating press and with a likewise circular, circumferential, lower edge 10 with a pressing plate a single or multi-level heating press in contact, with the two edges 9, 10 each forming a circular contact line 11, 12. However, a reverse orientation of the Spring element 3 conceivable, in which the upper edge 9 is in contact with the press plate and the lower edge 10 with the heating plate.

Furthermore, the cup springs 8 have beveled (conical) side sections 15 which bring about a reduction in a diameter of the first contact line 11 compared to a diameter of the second contact line 12 . A section through a plate spring 8 is in the figure 2 shown and illustrates a truncated cone shape.

During a pressing process in a single or multi-level heating press, the spring element 3 is deformed in such a way that a planar, upper contact surface 13 is formed. At the same time, a planar, lower contact surface 14 is formed. In this case, one of the contact surfaces 13, 14 is in contact with the heating plate when used in a single or multi-level heating press, while the other contact surface 13, 14 is in contact with the pressing plate. The disc spring 8 thus essentially assumes the shape of a hollow cylinder during the pressing process.

In an edge area 16, the disk springs 8 are provided with four openings 17, which are arranged at an angle of 90° to one another on a circle and, to simplify production, can also be open towards the circular outer edge of the disk spring 8 in order to insert the weft threads 7 or Warp threads 6 do not have to be "threaded through" with one thread end but can be "threaded in" from the side. A thread 6, 7 of a thread system 4, 5 is passed through two opposite openings 17 in the spring elements 3, while the remaining two openings 17 are provided for receiving a thread 6, 7 of the corresponding other thread system 4, 5. A crossing point 18 of a warp thread 6 and a weft thread 7 essentially corresponds to a central axis 19 of the spring element 3. The plate springs 8 are arranged equidistantly in the press pad 1 and form rows in the press pad 1 crossing at an angle of 90°. The press pad 1 is therefore easy to roll up and transport.

Due to an increased, compared to a diameter 20 of the warp threads 6 and weft threads 7, a non-stressed (force-free) length 21 of the plate springs 8, an upper contact surface of the press cushion 1 is formed by the totality of the upper contact surfaces 9 of the individual plate springs 8, while a lower contact surface of the press cushion 1' is determined by the totality of the lower contact surfaces 10 of the individual plate springs 8. This can ensure that different thicknesses in the heating plate and/or the pressing plate are compensated for by means of a resilient effect of the disc springs 8, with a degree of the resilient effect changing by means of a change in an outer diameter 22, an inner diameter 23, a material thickness 24 and the unstressed Vary length 21 of the plate spring 8 and can thus be adapted to the specific requirements in the single or multi-level heating presses. The warp threads 6 and the weft threads 7 therefore do not come into contact with the pressing plate or the heating plate. As a result of the thermally conductive property of the plate springs 8, which extend very directly, ie over a short distance, through the press plate, the heat emitted by the heating plate is transferred well to the press plate.

A further exemplary embodiment of the press pad 1' according to the invention is shown in FIG figure 3 shown. The press pad 1 'also includes a flat support structure 2 in the form of a fabric and a variety of metallic spring elements 3. In contrast to in the figure 1 illustrated press pad 1 ', the press pad 1' according to figure 2 a coating 25 on both sides of a heat-stable elastomeric material. That in the figure 1 The press pad 1' shown is therefore essentially embedded in the elastomeric material. In order to ensure that the contact between the heating plate and the pressing plate continues only with the spring elements 3, the coating 25 is removed in the area of each spring element 3, as well as in FIG figure 4 is recognizable. A lower surface and a lower surface 26 of the press pad 1 ′ are therefore partially formed by the spring elements 3 .

A one-daylight heating press 27 according to the prior art is in figure 5 shown. The single-daylight heating press 27 comprises two heating plates 28 and two pressing plates 29. According to the present invention, as already provided in the prior art, a press pad 1′, 1 according to the invention is to be arranged between a heating plate 28 and a pressing plate 29 of the single-daylight heating press 27. A wood material board 30 to be coated is inserted between the two press plates 29 and is covered with a decorative paper not shown in the figure. The decorative paper is bonded to the wood-based panel 30 by means of the heat emitted by the single-daylight heating press 27 and the pressure exerted on the wood-based panel 30 .

An embodiment of a press pad heating plate unit 31 according to the invention, which is shown in FIG figure 6 is shown, includes a press pad 1, 1 'according to the invention and a heating plate 28 of a single or multi-stage heating press. In this case, the press pad 1, 1' is glued to the heating plate 28 in such a way that a single component is formed.

An exemplary embodiment of a press cushion press plate unit 32 according to the invention is shown in FIG figure 6 shown. In contrast to the press pad-heating plate unit 31, the press pad 1′, 1 according to the invention is not connected to a heating plate 28, but to a press plate 29 of a single or multi-level heating press, for example glued, and thus also forms a single component.

Reference List

1'

press pad

1

press pad

2

supporting structure

3

spring element

4

thread system

5

thread system

6

warp thread

7

weft thread

8th

disc spring

9

upper edge

10

lower edge

11

contact line

12

contact line

13

upper contact surface

14

lower contact surface

15

side section

16

edge area

17

breakthrough

18

crossing point

19

central axis

20

diameter

21

relaxed length

22

outer diameter

23

inner diameter

24

material thickness

25

coating

26

surface

27

Single Day Heating Press

28

hotplate

29

press plate

30

wood-based panel

31

Press pad heating plate unit

32

Press pad press plate unit

Claims (10)

1. A press pad (1, 1') for use in a hydraulic single or multi-level hot press, the press pad (1, 1') comprising:

   a flat support structure (2); and a plurality of metal spring elements (3) connected with the flat support structure (2) and arranged distributed therein or thereon,

   characterized in that the flat support structure (2) is a flat contexture, in particular a knitted material, or a woven material or a fleece material or a fabric, wherein at least a portion of threads (6, 7) that form the flat contexture is made from metal or includes metal, wherein the metal is composed particularly of brass, copper, bronze, steel, particularly stainless steel.
2. The press pad (1, 1') according to claim 1, characterized in that the flat support structure (2) is formed by a metal plate and a flat contexture, wherein the metal spring elements (3) are connected with the flat contexture and the metal plate.
3. The press pad (1, 1') according to claim 1 or 2, characterized in that the metal spring elements (3) are disc springs (8) or coil springs or leaf springs or corrugated springs.
4. The press pad (1, 1') according to one of the claims 1 to 3, characterized in that the metal spring elements (3) are connected with threads (6, 7) of the flat contexture, particularly by form locking, wherein the metal spring elements (3) are preferably arranged at intersection points of warp threads and weft threads of the flat contexture.
5. The press pad (1, 1') according to claim 4, characterized in that the metal spring elements (3) include cut outs (17), wherein the threads (6, 7) of the flat contexture are run through the cut outs (17).
6. The press pad (1') according to claim 5, characterized in that the metal spring elements (3) respectively include at least four cut outs (17), wherein a respective warp thread is run through two cut outs (17) and a respective weft thread is run through another two cut (17) outs of the at least four cut outs (17).
7. The press pad (1, 1') according to one of claims 1 to 6, characterized in that the metal spring elements (3) are arranged equidistant from one another, particularly in intersecting rows, particularly along the weft threads and/or the warp threads.
8. The press pad (1, 1') according to claim 1, characterized in that the metal spring elements (3) are partially embedded in an elastomeric material, preferably in a silicon elastomeric material or a fluor silicon elastomeric material, or a blend polymer or a copolymer of the both aforesaid elastomeric material, wherein the metal spring elements (3) respectively form a portion of a surface of the press pad (1, 1') at opposite sides of the press pad (1, 1').
9. The press pad (1, 1') according to claim 8, characterized in that particles that increase heat conductivity, particularly particles made from a metal or a mineral, are included in the elastomeric material, and wherein the particles are preferably nano particles.
10. A press pad - press plate unit or a press pad - heating plate unit, comprising a press pad (1, 1') according to at least one of claims 1 to 9.

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