WO2004054788A1

WO2004054788A1 - Knitted press pad

Info

Publication number: WO2004054788A1
Application number: PCT/EP2003/050919
Authority: WO
Inventors: Guido Heirbaut; Pol Speleers
Original assignee: N.V. Bekaert S.A.
Priority date: 2002-12-18
Filing date: 2003-12-02
Publication date: 2004-07-01
Also published as: AU2003298337A1

Abstract

A press pad for use in a laminating press comprises a knitted textile fabric, which comprising metal fibers. The fibers are present in the textile fabric by means of yarns, comprising metal staple fibers or metal filament fibers.

Description

KNITTED PRESS PAD

Field of the invention.

The present invention relates to press pads to be used in laminating presses for production of e.g. laminated wood plates or veneer plates.

Background of the invention.

The present invention relates to press pads, to be used to eliminate unevenness in the surface of the press plates of laminating press, and to distribute the pressure and thermal energy of the presses over the pressed surface in an essentially even way. Such press pads may be inserted between the presser plate and the caul plate of the presses. This caul plate contacts the laminate product. Such press pads may also be inserted between the press and the laminate itself.

In order to provide sufficient performance, such press pads have to fulfill certain requirements.

A pad has to have sufficient resiliency and springiness to compensate the thickness variations, and to recover to its original form after pressure. The latter requirement is to allow multiple uses during its working life.

A pad has to be able to distribute the pressures used by the press plate equally over its surface. Usually slight deviations of pressure over the press plate occur due to slight variations on the surface of the pressure platen. In order to be able to compensate variations sufficiently, the press pad typically has to have a thickness of more than 2mm, or even more than 3mm.

Since heat is to be conducted from the press to the laminate or the caul plate of the press, which contacts the laminate itself, the press pad is to have a significant thermal conductivity. However the press pad is to be resistant to temperature and pressures during pressure application. Pressures of more than 60 kg/cm² under a temperature of more than 200°C are to be envisaged.

Typically, woven press pads are used. EP488071 makes reference to a woven press pad, which consists of thermal resistant fibers. Other press pads are known from several patent applications, such as WO01/76861, WO02/02304 and WO02/26480.

These woven press pads are very dense in order to be able to conduct thermal energy sufficiently, to provide the resiliency and springiness to compensate the thickness variations, and to recover to its original form after pressure being applied. Due to the density of the woven fabric, such press pads are very heavy, difficult to manipulate and relatively expensive.

Knitted Press pads are known from US6413889 and US6342457. The knitted press pad comprises metal treads or wires which function as thermal bridges between caul plate and laminated product. A drawback of the presently known press pads is that the metal wires or strands used, if any, tends to break after a certain period of use of the pad. Due to fatigue ruptures, the wires or strands break, usually at locations where the wire or strand is bend, e.g. due to the weaving or knitted structure used. These ruptures cause a decrease in amount of thermal energy being transported from the press plate to the laminated product. The lifetime of such pads may be minimized by such ruptures.

Further, the new designs of laminated products require higher pressures to be used by the presses. The presently known press pads tend to fail under such increasing pressures.

Finally, in case the presently known press pads contact the laminated product or surface itself, a recess showing the profile of the edges of the laminated product is noticed in the pad. When consecutively, a laminate is to be produced, having an other profile, the used press pad is to be replaced by an unused one. If not, the profile of the former product can be seen in the new laminate product.

Summary of the invention.

The present invention has as a subject to provide a press pad which does not show the drawbacks of the presently known press pads known in prior art. The present invention has as a subject to provide an alternative press pad, which meet the requirements for press pads such as resiliency, springiness, thermal conductivity and thickness. The present invention has as an other subject to provide a press pad which is less heavy. It is an other subject of the present invention to provide a press pad which can be used for different laminate profiles without the necessity to change the pad, even when the highest applicable pressures are used. The present invention has as an other subject to provide a press pad with a longer life time in use in a laminating press.

According to the present invention, a press pad comprises a textile fabric, which fabric is a knitted fabric. The press pads as subject of the invention is characterized in that it comprises metal fibers. Metal fibers are to be understood as either metal staple fibers having a variable staple length, or metal filament fibers having an endless long length. The metal fibers have an equivalent diameter of more than 1μm, preferably more than 4μm, and having an equivalent diameter of less than 150μm, such as less than 100μm or less than 75μm, e.g. less than

60μm or even less than 50μm. As an example, a metal fiber having an equivalent diameter of 8μm, 12μm, 14μm or 25μm or even 35μm is given.

"Equivalent diameter" is to be understood as the diameter of an imaginary circle, of which the surface area of a radial cross section is equal to the surface area of a cross section of the fiber. In order to incorporate the metal fibers in the knitted fabric, yarns comprising metal fibers are used to provide the textile fabric. Such yarns can be spun yarns, comprising metal staple fibers, or multifilament yarns, comprising metal filament fibers. In case of spun yarns, the yarns can be provided using the presently known spinning techniques, such as e.g. ring spinning, core spinning, wrap spinning, false twist spinning, friction spinning, dref spinning, rotor or open end spinning. Preferably, the yarns, either spun or multifilament yarns, are multiple plied yarns, comprising two or more single yarns.

The fineness of the yarns comprising metal fibers is preferably in the range of 50 Tex to 333 Tex. Each radial cross section of a yarn comprising metal fibers, which yarn used to provide a press pad as subject of the invention, comprises preferably at least 55 or even more individual metal fibers.

The use of yarns comprising metal fibers as subject of the invention provide a press pad of which thermal conductors, being yarns comprising metal fiber, does not have the negative property of having fatigue ruptures during excessive use of the pad in a laminating press, e.g. during long press runs of under extreme high pressures used.

Although the inventors do not want to be bound by any theory, it is believed that this avoiding of ruptures is due to the fact that metal fibers present in a yarn are not subjected to such severe forces as compared to metal wires or threads, at the heads of the loops in which they are present.

Apparently, metal fibers present in a yarn does not suffer from tensions due to the difference in bending radii between inner and outer surface of material present in the head of the loop. It is believed that due to the relative freedom of the metal fibers in the yarns, the fibers at the outer side of the head of the loop, may slightly shift or reposition in the yarn, in order to reduce the tension force to which they are subjected. This seems not to be the case when metal wires or threads are used to make heads of the loops. When a metal wire or thread is bend in order to make a head of a loop, the difference in bending radius between inner and outer side of the head of the loop causes mechanical tension inside the wire or tread. This tension is function of the diameter of the wire or thread. This tension assists the repetitive compression force due to the use of the press pad, to cause ruptures of the metal wire of threads.

The term "loop" is to be understood as the curvature of the yarn which describes a stitch of the knitted fabric. Such loop, and thus such stitch, comprises a head, two legs, connected to this head, and two feet, each connected to one of the legs.

In spite of the fineness of the metal fibers, it was noticed that the thermal conductivity of the press pad comprising metal fibers could meet the thermal conductivity of the presently known press pads. Even more, as press pads comprising mainly metal fibers or even consisting out of metal fibers can be provided, the thermal conductivity of the press pad as subject of the invention can be improved strongly.

Even in case a press pad consisting out of metal fibers is provided, this press pad has a weight being within the acceptable ranges.

It was found that the press pads as subject of the invention have improved elastic properties in the direction perpendicular to its plane. It is also an advantage that possibly the use of polyurethane to provide resilience and elasticity can be avoided. The use of polyurethane usually results in less thermal insulation and a pore efficient heat transfer between both sides of the press pads during use as separation material between e.g. caul plate and laminate.

It is understood that, next to yarns comprising metal fibers, possibly also other yarns may be used to provide a press pad as subject of the invention. Preferably, the yarns not comprising metal fibers comprise temperature resistant fibers such as aramide fibers, POLY (P- PHENYLENE-2-6- BENZOBISOXAZOLE) fibers, glass fibers or carbon fibers.

The yarns comprising metal fibers, may further comprise temperature resistant fibers such as aramide fibers, POLY (P-PHENYLENE-2-6-

BENZOBISOXAZOLE) fibers, glass fibers or carbon fibers. Preferably, at least 25% by weight of the yarns comprising metal fibers is provided by metal fibers.

According to the present invention, metal fibers may be provided out of a metal or metal alloy, such as e.g. copper, aluminum, titanium, nickel, copper alloys such as brass or bronze, nickel alloys, iron or iron alloy, such as steel or stainless steel alloys, e.g. Fe-Cr-AI alloys or Fe-Ni-Cr alloys. Preferably stainless steel alloys out of the AISI 300 series or AISI 400 series such as AISI 302, AISI 316 or AISI 444 are used.

Such metal fibers may be provided by any metal fiber production process known in the art. Preferably, bundle drawn metal fibers are used.

It was found that preferably 25% by weight of the fiber material, used to provide a preferred press pad according to the present invention, is provided by metal fibers. Possibly the press pad as subject of the invention comprises more than 30% by weight or even more than 40% by weight of metal fibers. Most preferred however, more than 75% by weight of the press pad are metal fibers. Possibly the press pad consist out of metal fibers.

Preferably, the knitted fabric has a fabric density of more than 5 % or even more than 10%. As the press pad as subject of the invention is obtained by knitting, the fabric density is usually and preferred less than

25%. "Fabric density" is to be understood as the weight of a particular volume of the fabric, divided by the weight of an identical volume which would consist of the material out of which the fabric is provided, and this expressed in %. Surprisingly it was found that, in spite of the relatively low density of the knitted fabric, the thermal conductivity of the pads as subject of the invention are equal or even better than compared with the commercially available pads at present. This especially when the press pad as subject of the invention consists of metal fibers.

The thickness of the knitted fabric preferably is more than 1.5mm, most preferably more than 2.5mm.

A press pad as subject of the invention may be provided as a single bed or double bed knitted fabric, comprising metal fibers, using warp or weft knitting techniques. It is preferred that the knitted fabric is provided using a double-bed knitting structure, either warp or weft knitted. Most preferably, weft knitted fabrics are used.

Knitting machine used to provide a press pad as subject of the invention, have machine gauges ranging preferably from 2 to 20. A "machine gauge" number is to be understood as the number of needles present per inch of needle bed. Most preferably, lower gauges are used, e.g. between 2 and 14 needles per inch, such as gauges 2, 2.5, 3, 4, 5, 6, 7,

8, 9, 10, 11, 12, 13 or 14.

Taking now more in particular the knitted fabric into consideration, it was found that, in order to provide preferred embodiments of a press pad as subject of the invention, the yarns providing the links between the first and the second side of the knitted fabric are to comprise the metal fibers.

A skilled man understands that a textile fabric, also a knitted fabric, always has two side. More in particular, depending on the parts of the stitches seen on the side, a side of a knitted fabric is referred to as a front, right or face side, or a back, left or reverse side. As known in the art, a front side, a right side or a face side of a knitted fabric, is defined as a side of the knitted fabric on which the legs of the stitches are seen.

A back side, a left side or a reverse side of a knitted fabric, is defined as a side of the knitted fabric on which the heads and feet of the stitches are seen.

Depending on the knitting structure used to provide the knitted fabric, the knitted fabric has two right sides, two left sides or a left and a right side.

As both sides of the knitted fabric are to be connected one to the other, independent of the type of sides, at least one yarn, but usually more than one yam, makes links between the two sides. Such yarn which is partially present at the first and partially at the second side, is hereafter referred to as "link-yarn". It was found that, in order to obtain preferred embodiments of the press pad as subject of the invention, at least one of the link-yarns are to comprise metal fibers. Most preferably a significant part of the fibers providing the link-yarns are to be metal fibers, or even consist of metal fibers. Preferably, at least 50% by weight of the link- yarns is provided by such metal fibers, most preferably, link-yarns consists of metal fibers. Link-yarns may be present at both sides of the press pad by making tuck stitches, by making knitted stitches, or by making tuck stitches and knitted stitches at these sides of the press pad.

Further it was found that preferably sufficient number of links between the first and second side of the knitted fabric are to be present in order to obtain a preferred embodiment of the press pad as subject of the invention.

It was found that preferably, the total weight of the link-yarns of the knitted fabric represents more than 20% of the total weight of the knitted fabric, even more preferred, more than 25% or even more than 50%. Possibly the whole weight of the knitted fabric is provided by link-yarns, as is e.g. the case when a rib fabric, purl fabric or interlock fabric is used.

Additional to the yams used to provide the links, also other yarns may be present on one or both of th sides of the knitted fabric. At both sides of the knitted fabric identical or different yams may therefor be used. They may differ in yarn thickness, yarn construction or fibers used to provide the yarn. Preferably all metal fiber yarns are used.

In order to obtain the best resiliency and springiness, combined with an improved thermal conductivity, it was found that a double-bed weft knitted structure is to be preferred. Possibly, at least 25% of the stitches may be made by the yarns providing the links are tuck stitches. In case of double bed knitted fabrics, in addition to link-yarns, and to yarns only present at one side of the fabric, the knitted fabric may also comprise so-called "inlay-yarns". Such inlay-yams are present between both sides of the fabric, but are not present at the first, nor at the second side of the fabric. Since they are not present at both sides, they are not to be seen as link-yams, however their presence may improve the resiliency and springiness.

The surface weight of pads as subject of the invention is preferably more than 1500g/m², e.g. in the range of 1500 g/m² to 5000 g/m². The pads as subject of the invention show no significant impression of the laminate profile when high pressures are used during laminating process.

Therefor, different laminates with different profiles may be produces using the same press pad as subject of the invention.

The method to produce a laminated product as subject of the invention comprises the steps of

• providing a lamination press having heatable pressing tooling;

• providing layers to be laminated under heat and pressure; • providing a press pad as subject of the invention between the heatable pressing tooling and the layers to be laminated;

• transferring heat and pressure from the heatable pressing tooling to the layers to be laminated. In such a way, a laminated product is provided.

The press pads as subject of the invention may be used to produce laminated products such as e.g. laminated wood plates, veneer plates, chip board, flax board, polymer-faced chipboard or flax board, paper, plastic, textile or combinations thereof. The press pad may be used to be inserted between press plates and caul plates of a press, or the pad may be used to contact the laminated product surface itself, being inserted between press plate and the laminated product. The presses using the press pad may be mono- or multi-daylight presses

Brief description of the drawings.

The invention will now be described into more detail with reference to the accompanying drawings wherein

- FIGURE 1 shows a knitting structure of knitted products used to provide a press pad as subject of the invention.

- FIGURES 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h and 2i together show a knitting structure of knitted products used to provide a press pad as subject of the invention, each figure being one step of the knitting structure. - FIGURES 3a, 3b, 3c, 3d, 3e and 3f together show a knitting structure of knitted products used to provide a press pad as subject of the invention, each figure being one step of the knitting structure.

- FIGURES 4a, 4b, 4c, 4d, 4e, 4f, 4g and 4h together show a knitting structure of knitted products used to provide a press pad as subject of the invention, each figure being one step of the knitting structure.

- FIGURE 5 and FIGURE 6 being knitting structures of knitted products used to provide a press pad as subject of the invention.

- FIGURE 7 shows schematically the test setup of a comparative thermal conductivity test. - FIGURE 8 shows the thermal conductivity of a press pad as subject of the invention, compared to press pads known in the art.

- FIGURE 9 shows schematically a press using a press pad as subject of the invention.

Description of the preferred embodiments of the invention.

FIGURE 1 shows schematically the knitting structure of a knitted fabric, which can be used to provide a press pad as subject of the invention.

The knitting structure consists of four knitting actions, referred to as 101, 102, 103 and 104. On a double bed weft knitting machine the needles 100 of the first needle bed 110 and second needle bed 120 are positioned in such a way that each needle of the first needle bed 110 facing a needle of the second needle bed 120.

During the first knitting action 101, on the first needle bed 110, a stitch is made on each second needle 112, whereas no stitches are made on every first needle 111. After having made a stitch on a needle 112 of needle bed 110, the knitting yarn 131 is to make a tuck stitch on every first needle 121 of the second needle bed 120. No stitches are made on every second needles 122 of needle bed 120.

During the second consecutive knitting action 102, a knitting yarn 132 makes a stitch on every needle 121 of the second needle bed 120, on which a tuck stitch was made during knitting action 101, and makes a tuck stitch on every needle 112 of needle bed 110 on which a stitch was made during knitting action 101.

During the third knitting action 103, on the first needle bed 110, a stitch is made on each first needle 111, whereas no stitches are made on every second needle 112. After having made a stitch on a needle 111 of needle bed 110, the knitting yarn 133 is to make a tuck stitch on every second needle 122 of the second needle bed 120. No stitches are made on every first needles 121 of needle bed 120.

During the fourth and last consecutive knitting action 104, a knitting yarn 134 makes a stitch on every needle 122 of the second needle bed 120, on which a tuck stitch was made during knitting action 103, and makes a tuck stitch on every needle 111 of needle bed 110 on which a stitch was made during knitting action 103.

The yarns 131 , 132, 133 and 134 may be different, however for the present embodiment, a spun, 100% metal staple fiber yarn was used, having a fineness of 5.5 Nm, being 181 Tex. The needles of needle bed 110 and the needles of needle bed 120 are on a distance 140 of 0.21 cm from each other in the same needle bed. This means that the knitting machine has a gauge equal to 12, meaning that in each needle bed, 12 needles are counted per inch of the needle bed.

A knitted fabric of 3mm thickness and having a weight of 2.5 kg/m² is so obtained. This means that the knitted fabric has a density of approximately 10.4%, since a steel volume of 1 m² by 3mm thickness has a weight of 24kg.

All yarns 131, 132, 133 and 134 are to be understood as link-yarns, since they all are present at the first and at the second side of the fabric. This due to the fact that they make stitches (normal or tuck stitches) at both sides of the fabric.

An alternative knitting structure is shown in FIGURES 2a to 2i. Both needle beds 210 and 220 of a weft knitting double bed machine are positioned in such a way that each needle of the first needle bed 210 is positioned between two needles of the second needle bed 220. The set of needles of needle bed 210 are grouped in a group of first needles 211, a group of second needles 212 and a group of third needles 213, alternating in the bed 210. The set of needles of needle bed 220 are grouped in a group of first needles 221, a group of second needles 222 and a group of third needles 223, alternating in the bed 220. Each first needle 211 of bed 210 is positioned between a needle of the second group 222 and a needle of the third group 223 of needle bed 220.

The knitting structure has nine knitting actions named 201, 202, 203, 204, 205, 206, 207, 208 and 209, each represented in one of the figures 2a to 2i.

During the first knitting action 201 of FIGURE 2a, a link yarn 231 makes a stitch on a needle of the group of first needles 220 and a needle of the firsts needle group 221 consecutively.

During the second knitting action 202 of FIGURE 2b, a yarn 232, present at only one side of the fabric makes a stitch on each needle of the group of third needles 223.

In third knitting action 203 of FIGURE 2c, a yarn 233, present at the other side of the fabric makes a stitch on each needle of the group of third needles 213.

During the fourth knitting action 204 of FIGURE 2d, a link yarn 234 makes a stitch on a needle of the group of second needles 212 and a needle of the second needle group 222 consecutively.

During the fifth knitting action 205 of FIGURE 2e, a yarn 235, present at only one side of the fabric makes a stitch on each needle of the group of first needles 221. In the sixth knitting action 206 of FIGURE 2f, a ya 236, present at the other side of the fabric makes a stitch on each needle of the group of first needles 211.

During the seventh knitting action 207 of FIGURE 2g, a link yarn 237 makes a stitch on a needle of the group of third needles 213 and a needle of the third needle group 223 consecutively.

During the eighth knitting action 208 of FIGURE 2h, a yarn 238, present at only one side of the fabric makes a stitch on each needle of the group of second needles 222. In the last knitting action 209 of FIGURE 2i, a yarn 239, present at the other side of the fabric makes a stitch on each needle of the group of second needles 212.

The fabric is provided using for each yam 231 to 239 a yarn comprising

360 metal filament fibers of stainless steel AISI 316L, each filament having an equivalent diameter of 14μm. The knitted product was provided on a gauge 12 machine, providing a fabric having a weight of 4.35 kg/m² and having a thickness of 3mm. This results in a density of 18%.

The percentage in weight of the link yarns (231, 234 and 237) is 55 % of the total weight of the knitted fabric.

An other alternative knitting structure is shown in FIGURES 3a to 3f. An embodiment of a press pad as subject of the invention comprises a knitted fabric having link-yarns incorporated in the weft knitted structure using only tuck stitches. The needle bars 310 and 320 of the weft knitting machine are positioned in such a way that each needle of the first needle bed 310 facing a needle of the second needle bed 320. On each needle bed, the needles are grouped in two needle groups 311 and 312, and 321 and 322. In each needle bed, the needles alternate. The needles 311 of the first group of needles of the first needle bed 310 are facing the first needle group 321 of the second needle bed 320. During a first knitting action 301 shown in FIGURE 3a, a link-yarn 331 is alternately provided to a first needle 311 and a second needle 322. On all of these needles, the link-yarn 331 makes a tuck stitch. During the second knitting action 302 shown in FIGURE 3b, a yarn 332 makes a stitch on all second needles 312 of the first needle bed 310. During the third knitting action 303 shown in FIGURE 3c, a yarn 333 makes a stitch on all first needles 321 of the second needle bed 320. During a fourth knitting action 304 shown in FIGURE 3d, a link-yarn 334 is alternately provided to a second needle 312 and a first needle 321. On all of these needles, the link-yarn 334 makes a tuck stitch. During the fifth knitting action 305 shown in FIGURE 3e, a yarn 335 makes a stitch on all first needles 311 of the first needle bed 310. During the sixth knitting action 306 shown in FIGURE 3f, a yarn 336 makes a stitch on all second needles 322 of the second needle bed 320.

An alternative knitting structure for the embodiment as shown in FIGURES 3a to 3f, is shown in FIGURES 4a to 4h. Again, the needle bars 410 and 420 of the weft knitting machine are positioned in such a way that each needle of the first needle bed 410 facing a needle of the second needle bed 420. On each needle bed, the needles are grouped in four needle groups respectively 411, 412, 413 and 414, and 421 422,423 and 424. In each needle bed, the needles alternate. The needles 411 of the first group of needles of the first needle bed 410 are facing the first needle group 421 of the second needle bed 420. The knitting structure comprises eight knitting actions.

During a first knitting action 401 shown in FIGURE 4a, a link-yarn 431 is alternately provided to a second needle 412 and a fourth needle 424. On all of these needles, the link-yarn 331 makes a tuck stitch. During a second knitting action 402 shown in FIGURE 4b, a link-yarn 432 is alternately provided to a fourth needle 414 and a second needle 422. On all of these needles, the link-yarn 431 makes a tuck stitch. During the third knitting action 403 shown in FIGURE 4c, a yarn 433 makes a stitch on all first needles 411 and third needles 413 of the first needle bed 410. During the fourth knitting action 404 shown in FIGURE 4d, a yarn 434 makes a stitch on all first needles 421 and third needles 423 of the second needle bed 420.

During a fifth knitting action 405 shown in FIGURE 4e, a link-yarn 435 is alternately provided to a first needle 421 and a third needle 413. On all of these needles, the link-yarn 435 makes a tuck stitch.

During a sixth knitting action 406 shown in FIGURE 4f, a link-yarn 436 is alternately provided to a first needle 411 and a third needle 423. On all of these needles, the link-yarn 436 makes a tuck stitch. During the seventh knitting action 407 shown in FIGURE 4g, a yarn 437 makes a stitch on all second needles 412 and fourth needles 414 of the first needle bed 410.

During the eighth knitting action 408 shown in FIGURE 4h, a yam 438 makes a stitch on all second needles 422 and fourth needles 424 of the second needle bed 420.

An other alternative knitting structure is shown in FIGURE 5. A double bed warp knitting machine has a front needle bed 501 and a rear needle bed 502. The needles of the bed are positioned such a way that each needle of the first needle bed 501 facing a needle of the second needle bed 502. Each needle in the front bed is provided with a yarn 503. As schematically shown in FIGURE 5, during a first knitting action, the yarns 503 make a stitch on front bed needle 504. During the successive knitting action 512, the yarn 503 is provided to the needle 505 being on the rear bed, positioned left of needle 504, where it makes a stitch. During knitting action 513, the yam is provided again to the needle 504 and makes a stitch. During knitting action 514, the yarn is provided to the needle 506 of the rear bed at the right side of needle 504, where it makes a stitch. In such a way, and using a yarn being three two-folded spun yarns out of AISI 316L metal fibers, each two folded yarn comprising two single yarns having a fineness of 90 tex, a warp knitted fabric is obtained having a density of 12.5%, a thickness of 2.65mm and a surface weight of 2.7kg/m².

As an alternative for the three above-mentioned fabrics, yarn comprising 30 % weight of POLY (P-PHENYLENE-2-6- BENZOBISOXAZOLE) fibers and 70% of weight of metal fibers may be used.

An other alternative knitting structure is shown in FIGURES 6a to 6f. An embodiment of a press pad as subject of the invention comprises a knitted fabric having link-yarns incorporated in the weft knitted structure using only stitches. The needle bars 610 and 620 of the weft knitting machine are positioned in such a way that each needle of the first needle bed 610 facing a needle of the second needle bed 620. On each needle bed, the needles are grouped in two needle groups 611 and 612, and 621 and 622. In each needle bed, the needles alternate. The needles 611 of the first group of needles of the first needle bed 610 are facing the first needle group 621 of the second needle bed 620.

During a first knitting action 601 shown in FIGURE 6a, a link-yarn 631 is alternately provided to a first needle 611 and a second needle 622. On all of these needles, the link-yarn 631 makes a stitch. During the second knitting action 602 shown in FIGURE 6b, a yarn 632 makes a stitch on all second needles 612 of the first needle bed 610.

During the third knitting action 603 shown in FIGURE 6c, a yarn 633 makes a stitch on all first needles 621 of the second needle bed 620. During a fourth knitting action 604 shown in FIGURE 6d, a link-yarn 634 is alternately provided to a second needle 612 and a first needle 621. On all of these needles, the link-yarn 634 makes a tuck stitch.

During the fifth knitting action 605 shown in FIGURE 6e, a yarn 635 makes a stitch on all first needles 611 of the first needle bed 610. During the sixth knitting action 606 shown in FIGURE 6f, a yarn 636 makes a stitch on all second needles 622 of the second needle bed 620. The fabric is provided using for each link-yarn 631 and 634 a yarn comprising metal staple fibers of stainless steel AISI 316L, each yarn being a two-ply yarn having metrical number Nm 11/2 (= 181 Tex) . The bundle drawn fibers have an equivalent diameter of 12μm. For each yarn 632,633, 635 and 636, being present at only one side of the press pad, two yarns comprising metal staple fibers of stainless steel

AISI 316L, each yarn being a two-ply yarn having metrical number Nm 11/2 (= 181 Tex) . The bundle drawn fibers have an equivalent diameter of 12μm. The knitted product was provided on a gauge 12 machine, providing a fabric having a weight of 1.8 kg/m² and having a thickness of 2.5mm.

This results in a density of 9%.

As an example, the product of the second embodiment was subjected to a comparative test on thermal conductivity. As shown in FIGURE 7 press pad 701 was placed between two metal plates 702. This "sandwich" was loaded on one side with a heat source 703 of 200°C. at the other side of the sandwich, the temperature increase was measured in function of time using a temperature sensor 704.

As shown in FIGURE 8, a woven Cu-silicon fabric 802 and a woven kevlar®/Cu filament fabric 803, which are state of the art, are compared with a pad 801 as subject of the invention as described in FIGURE 2. In table I, the measured temperatures T in °C of the sensor 804 is shown in ordinate, in function of the time t (seconds) in abscissa.

The curve of pad 801 according to the present invention clearly show the improved temperature transfer.

As shown in FIGURE 9, the press pad 903 may be used as an insert between the heated press plates 901 and caul plates 902 of a laminating press 900. When the press is closed, the layers of the product 904 to be laminated using pressure and heat, is pressed between the two caul plates 902 of the press 900. The press pad 903 distributes the pressure of the press plates 901 over the whole surface of the caul plates 902, and transfers the pressure and the thermal energy of the heated press plates 901 to the caul plates 902, and so to the product 904. As an alternative, the pad 903 may contact the product 904 itself. No caul plates 902 are present then.

Possibly, more than one layer of products 904 are pressed simultaneously. Several products 904 can be provided, comprising several layers of e.g. paper, plastic, textile or wood or combinations thereof. The laminated product provided may be e.g. chipboard, flax board, melamine-faced chip or flax board, veneer plates or laminated wood boards.

Claims

1. A press pad comprising a textile fabric, said textile fabric being a knitted fabric, characterized in that, said knitted fabric comprises metal fibers.

2. A press pad according to claim 1 , wherein said metal fibers have an equivalent diameter of more than 1μm, said metal fibers having an equivalent diameter of less than 150μm.

3. A press pad according to any one of claims 1 to 2, wherein said textile fabric comprises yarns comprising metal staple fibers.

4. A press pad according to any one of claims 1 to 2, wherein said textile fabric comprises yarns comprising metal filament fibers.

5. A press pad according to any one of claim 1 to 4, wherein said textile fabric has a first and a second side, said textile fabric comprising link-yarns being present at said first and said second side and providing links between said first and said second side, at least one of said link-yarns comprising said metal fibers.

6. A press pad according to claim 5, wherein at least 20% of the weight of said textile fabric are provided by said link-yarns

7. A press pad according to any of claim 5 to 6, wherein at least 50% by weight of said link-yarns are provided by metal fibers.

8. A press pad according to any one of claim 5 to 7, wherein said link-yarns are incorporated in said knitted textile fabric using tuck stitches.

9. A press pad according to any one of claim 5 to 7, wherein said link-yams are incorporated in said knitted textile fabric using knitted stitches.

10. A press pad according to any one of claim 5 to 7, wherein said link-yarns are incorporated in said knitted textile fabric using tuck stitches and knitted stitches.

11. A press pad according to any one of claim 1 to 10, wherein at least 25% by weight of said textile fabric is provided by metal fibers.

12. A press pad according to claim 11 , wherein said textile fabric consists of metal fibers.

13. A press pad according to any one of claim 1 to 12, wherein said knitted fabric is provided using a double-bed knitting structure.

14. A press pad according to any of claim 1 to 13, wherein said textile fabric is a weft knitted textile fabric.

15. A press pad according to any one of claim 1 to 14, wherein said textile fabric has a density of more than 5%.

16. A press pad according to any one of claim 1 to 15, wherein said textile fabric has a density of less than 25%.

17. A press pad according to any one of claim 1 to 16, wherein said textile fabric has a thickness of more than 1.5mm.

18. A press pad according to any one of claim 1 to 17, wherein said press pad has a weight of more than 1500g/m².

19. A press pad according to any of claim 1 to 18, wherein said metal fibers are stainless steel fibers.

20. The use of a press pad as in any one of claim 1 to 19 for production of laminated products.

21. The use of a press pad as in claim 20 for production of veneer plates.

22. The use of a press pad as in claim 20 for production of chipboard.

23. The use of a press pad as in claim 20 for production of flax board.

24. The use of a press pad as in claim 20 for production of plastic faced chip board or flax board.

25. The use of a press pad as in claim 20 for production of textile laminated products.

26. The use of a press pad as in claim 20 for production of paper.

27. a method to produce a laminated product comprising the steps of • providing a lamination press having heatable pressing tooling;

• providing layers to be laminated under heat and pressure;

• providing a press pad as in one of the claims 1 to 19 between said heatable pressing tooling and said layers to be laminated;

• transferring heat and pressure from said heatable pressing tooling to said layers to be laminated;