WO2002020258A1

WO2002020258A1 - Method and apparatus for the manufacture of patterned board

Info

Publication number: WO2002020258A1
Application number: PCT/SE2001/001874
Authority: WO
Inventors: Per Eiritz
Original assignee: Valmet-Karlstad Aktiebolag
Priority date: 2000-09-04
Filing date: 2001-09-04
Publication date: 2002-03-14

Abstract

The present invention relates to a method of and an apparatus for making a patterned board product. A wet fibrous web (w) is supplied directly from a forming section of a boardmaking machine to an imprinting press nip (12) having at least one roll (8) with a surface that has raised (8E) and/or recessed (8B, 8C) portions to form a patterned surface (8A) on the roll. A heater (58) is provided for heating at least the patterned surface (8A) of the roll (8). The wet web (w) is dewatered in the press nip (12) during the pressing of the heated patterned surface (8A) of the roll (8) into the web (w) to form to form a reverse image of the pattern therein. The web (w) is dried to a desired dryness, while the heated patterned surface (8A) of the roll (8) is maintained in contact with the imprinted pattern (2B, 2E) in the web (w), so as to achieve a patterned stiff board product, which may have one imprinted side and one plain side. In a subsequent bonding section, a facing (4) or another imprinted web (2') may be bonded to the produced imprinted web (2).

Description

METHOD AND APPARATUS FOR THE MANUFACTURE OF PATTERNED BOARD

TECHNICAL FIELD

The present invention relates to a method of making a patterned board product, in particular a corrugated board product. The method includes running a fibrous web through a heated imprinting nip comprising at least one roll provided with a surface that has raised and/or recessed portions that form a patterned surface on the roll such that, in the nip, a pattern is formed on at least one side of said fibrous web. The invention also relates to an apparatus for perforaiing the method.

PRIOR ART

Corrugated board/corrugated paperboard has been known for a long time as a packaging and construction material. New applications and fields of use are still found in spite of the fact that the material has been known since the middle of the nineteenth century. In a global perspective, the use increases continuously. Above all, you can see an increased use of corrugated board/paperboard having comparatively small corrugations, so called mini-flute and micro-flute, respectively, with corrugations having a maximal height of about 1 mm. Also in other product segments there is an increased demand for corrugated board.

The technique for the manufacture of corrugated board has in principle been the same for many decades. Ready-made board is used as starting material, which is conveyed through a special series of devices, see for instance US 5,894,681. At least one corrugated layer, so called fluted paper, is manufactured in said series of devices, which layer is brought together with at least one (single faced corrugated fiberboard), in most cases two surface layers (single wall corrugated fiberboard). At the manufacture of double wall corrugated board and triple wall corrugated fiberboard, respectively, several fluted papers are used, which are brought together between the facings in a manner known per se. The corrugated layer/fluted paper is manufactured by means of rolls in the form of dented wheels, the teeth of which are engaging each other in such a way that the fiberboard layer, which is introduced between the teeth, will get a fluted shape. The peaks are glue coated subsequent to the corrugation, generally by means of a smooth roll, against which the corrugated fiberboard layer is brought, whereafter a facing layer is pressed against the corrugated layer to adhere thereto. This can also be made on the one or the other side, and with several parallel corrugation layers, in order to obtain further strength. The basic principle is, however, always the same one. After glue coating and bonding, the corrugated fiberboard is conveyed into a heating device for final drying/setting. Thereafter, the corrugated fiberboard can be cut into suitable lengths before storing and further treatment.

It should be understood that the additional machine equipment, which has been described above for the manufacture of corrugated fiberboard, entails a considerable investment cost as well as maintenance costs. Further, it should be noted that in order to achieve the desired result of the corrugation rolls, a high precision must be maintained, so that necessary co-operation between the rolls is obtained.

DISCLOSURE OF THE INVENTION

A purpose of the present invention is to eliminate the above mentioned drawbacks, at least to some extent. This is achieved by means of a method of making a patterned board product that includes running a fibrous web through an imprinting press nip having at least one roll with a surface that has raised and/or recessed portions to form a patterned surface on the roll. The patterned surface is preferably a corrugated surface. At least the patterned surface of at least one roll is heated and the heated patterned surface is pressed into the fibrous web to form a reverse image of the pattern therein. According the invention, the web is supplied in a wet condition directly from a forming section of a boardmaking machine to the press nip. The wet web is dewatered in the press nip during pressing of the heated patterned surface of the at least one roll into the web. The web is dried to a desired dryness while the heated patterned surface of the at least one roll is maintained in contact with the imprinted pattern in the web, so as to achieve a patterned stiff board product.

In the context of this patent application, the phrase "directly from a forming section of a boardmaking machine to the press nip" should not be understood as excluding the possibility of web treatment between the forming section and the imprinting press nip. Instead, the phrase should be understood as meaning that the web has not yet been finally dewatered and that it still retains a substantial part of its original water content from the forming section when it reaches the imprinting press nip.

Similarly, the purpose of the invention is achieved by means of a machine for making a patterned board product, comprising a press having two press members that define an imprinting press nip. At least one of the press members is a roll with a surface that has raised and/or recessed portions to form a patterned surface on the roll. The machine further comprises a heater for heating at least the patterned surface of the roll, and means for running a fibrous web through the imprinting press nip to press the heated patterned surface into the fibrous web to form to form a reverse image of the pattern therein,. The machine additionally comprises a forming section of a boardmaking machine for wet forming the fibrous web, and a press section. The press section includes, in addition to the press with the two press members and the imprinting press nip, the means for running the fibrous web through the imprinting press nip. The means for running the fibrous web through the imprinting press nip is arranged to supply the wet fibrous web from the foraiing section directly to the imprinting press nip. In the imprinting press nip, the fibrous web is dewatered by pressing and the heated patterned surface is pressed into the fibrous web. The heater is arranged and adapted to heating the patterned surface to effect drying of the fibrous web to a desired dryness while the heated patterned surface of said roll is maintained in contact with the imprinted pattern in the web, so as to achieve a patterned stiff board product. The means for running the fibrous web through the imprinting press nip may be a press felt.

Thanks to this solution one can eliminate a great part of the machine equipment, which today is necessary for the manufacture of corrugated board by instead integrating the manufacture of the pattern/corrugation with the drying of the wet fibrous web. Thus, a drastic reduction of the tied-up capital can be obtained with the invention. Further, you gain the advantage that the fiber bonding in the finished corrugated sheet can be very strong, as a quick and large supply of heat is provided, which in favorable cases leads to achieving the softening temperature of the fiber, whereby strong fiber bonds are obtained. Thus, the invention can also result in reduction of the material consumption.

BRIEF DESCRIPTION OF DRAWINGS

Below, the invention will be described more in detail with reference to the enclosed drawings, of which:

Fig. 1 shows a preferred embodiment of the invention to manufacture embossed fiberboard, Fig. 2a shows portions, in cross section, of a product, which has been manufactured with a series of devices according to Fig. 1, Fig. 2b shows portions, in cross section of an other compound board product. Fig. 3 shows an alternative series of devices for the manufacture of corrugated fiberboard according to the invention, Fig. 4 shows a product, which has been manufactured by means of a series of devices according to Fig. 1, Figs. 5 A, B show portions of a roll intended for the manufacture of the corrugated portion of the corrugated fiberboard according to the invention, Fig. 6 shows a conceivable design of a shoe press roll for the use in connection with the invention, Fig. 7 shows the pressure curve in a roll according to Fig. 6, Fig. 8 shows a first alternatively designed surface of a patterned roll according to the invention, Fig. 9 shows a second alternatively designed surface of a patterned roll according to the invention, and Fig. 10 is a schematic drawing of a forming portion and of the press portion according to the invention.

DETAILED DESCRIPTION

In Fig. 1, a fibrous web w is shown, which runs from the right to the left in the figure. In the upstream part of the fibrous web (to the right in the figure), the dry solids content is about 30-40 %. A shoe press unit 8, 10 with an extended nip 12 is shown. The shoe press unit consists of an upper, heated roll 8, which on its surface is provided with raised and/or recessed portions, e.g. corrugations/grooves 8 A, which run transverse the direction of the device, i.e. parallel to the longitudinal direction of the roll. At the bottom there is an enclosed shoe press roll 10, which in a manner known per se is provided with a flexible jacket 10A, which in operation is pressed against the heated roll 8 by means of a shoe unit 11 (shown schematically). As is shown in Fig. 1, also the press felt 13 suitably runs through the nip 12 between the paper web w and the flexible jacket 10 A. Further, there is shown a glue coating unit 16 cooperating with a counter- roll 14. The glue coating unit 16 consists of a roll 18 rotating in a longitudinal container device 20, to which glue is continuously supplied through a refill device 22. The glue coating roll 18 is rotatably arranged in the glue bath in the container 20, so that glue can continuously be supplied to its surface during rotation. The glue coating roll 18 is positioned so that its periphery contacts the peak of the corrugations on top of the fibrous web 2 after the passage through the nip 12. A cover layer 4, generally a so called facing, is brought together with the glue coated, corrugated fiberboard 2 between two press rolls 24, 26. The cover layer or facing 4 is fed over a guide roll 28. A heating unit 30, which is arranged on the lower portion 2C of the two layers 2, 4, supplies heat for drying and setting of the layer, which have been glued together. Above the heating unit 30 there is a press unit consisting of a number of pressing roll units 36, 38, 40, which press against the upper layer 4 via a fabric 32. The fabric 32 runs around said pressing roll units 36, 38, 40 and also at least one guide roll 34.

The method according to the invention functions in the following way. A fibrous web w is formed in a known manner in a forming section E of a boardmaking machine, see Fig. 10, and is supplied in a wet condition directly from the forming section to a press section P. Optionally, the web w may be dewatered by a suitable pressing unit to a dry solids content of about 30%. The web w is then run through an imprinting press nip 12 having at least one roll 8 with a surface that has raised 8E and/or recessed 8B, 8C portions to form a patterned surface 8 A on the roll. At least the patterned surface 8 A of the at least one roll 8 is heated and the heated patterned surface 8 A is pressed into the fibrous web w to form to form a reverse image of the pattern therein. The imprinting nip 12 is preferably formed between a shoe press roll 10 with a flexible jacket 10A and a concave shoe 11 cooperating with the patterned roll 8 to form an extended press nip. In the imprinting press nip 12, the wet web w is dewatered against the press felt 13 during the pressing of the heated patterned surface 8 A of the at least one roll 8 into the web w. The web w is dried to a desired dryness, while the heated patterned surface 8 A of the at least one roll 8 is maintained in contact with the imprinted pattern 2B, 2E in the web w so that a patterned stiff board product is achieved. The patterned surface 8 A on the roll 8 preferably comprises raised 8E and/or recessed 8B, 8C portions so as to imprint a pattern of grooves 2E and ridges 2B, respectively, in the fibrous web while the fibrous web is dewatered. The grooves and ridges preferably extend in a cross machine direction. The pattern 2B, 2E that is imprinted in the web will thus comprise corrugations 2B that are formed when the upper side of the fibrous web is pressed against corrugations/grooves 8A in the heated roll 8.

In the imprinting nip, the fibrous web w may be shaped so as to have an imprinted side 2D and a substantially plain side 2C.

When the fibrous web w reaches the nip, it should have a dry solids content of 20-45 %, preferably 25-40 % and more preferred 30-40 %.

According to a most preferred embodiment an impulse technique is used, whereby the shoe press roll 10 for instance can be designed as is shown in Fig. 6. At the impulse drying, the fibrous web is heated under high pressure in the nip to a temperature above evaporation, so that the obtained vapor carries liquid out of the web, whereby a very high dewatering can be achieved. As the web w exits the imprinting nip 12, the dry solids content of the web 2 suitably exceeds 70 %, preferably exceeds 80 % and more preferred exceeds 90 %.

Due to the supply of intensive heat in connection with the dewatering, a very strong fiber bonding can also be obtained, especially if combined with the a high lignin content in the fibers of the fibrous web w. The web 2, formed in this way with substantially smooth bottom side 2A and a patterned upper side consisting of corrugations 2B, is then carried to a guide roll 14, which co-operates with the glue unit 16 in such a way that the glue coating 6 is obtained on the peaks of the corrugations. This is achieved in a manner known per se, as the glue coating roll 18 rotates with its periphery contacting the peaks of the corrugations. The glue coated, corrugated web 2 is then brought into contact with a top layer 4, which is provided against the glue coated peaks between rolls 24, 26. Then the glue 6 and the patterned or corrugated board are set/dried in the heating unit 30 as a felted pressing device 36, 38, 40 is pressing from above. As is indicated in Fig. 1, one or several additional drying devices 15 A, 15B can be provided directly after the exit from the nip 12 in order to increase the dry solids content further.

A great advantage with the embodiment according to the invention is that the heated counter-roll 8 due to its patterned surface 8 A provides a large area for heat transfer. As high web speeds in connection with the manufacture of fiberboard and paper are desirable today, this is an important advantage. The increased exposure surface in the nip 12 permits a larger heat transfer than what is possible with a conventional smooth roll surface. Thus, besides the fact that patterns can be formed directly in the wet web, one gains the synergetic effect that the heat-transferring surface in the nip is increased drastically.

A compound product may be obtained by coating the raised portions 2B of the imprinted fibrous web 2 with glue, and then bonding an additional fibrous web 4, 2' to the imprinted side 2D to form a compound stiff board product. The additional web may be a facing 4. The additional web can also have an imprinted side 2D', and preferably the two webs are bonded to each other in such a way that the imprinted sides 2D, 2D' are facing each other to form a compound stiff board product having two substantially plain sides.

In Fig. 2 a it is shown that in the nip 12 there is shaped a patterned board layer 2 consisting of transverse ridges 2B and transverse grooves 2E, respectively, which are kept together by a continuous bottom layer 2A. According to the preferred embodiment the ridges 2B are unbroken, so that they form continuous ridges across substantially the entire fibrous web. The bottom surface 2C is substantially smooth, which is achieved by the felt 13 (and also the jacket) having a substantially smooth outer surface. Fig. 2 a also shows that a facing 4 has been connected with the patterned layer 2 by means of glue applied on top of the ridges 2B. The board produced in this way can be considered to correspond to a single wall corrugated fiberboard, which according to a traditional production method consists of two facings and an intermediate fluted layer. Thus, the single layer 2, which is formed according to a method of the invention, may be regarded to be equivalent to a single wall corrugated board.

As can be seen in Fig. 2 b, a compound product can also be obtained by bonding two imprinted webs 2, 2' and a facing 4 to one another in such a way that the imprinted sides 2D, 2D' of the imprinted webs 2, 2' face in the same direction and form an intermediary board product having an exposed imprinted side 2D and a substantially plain side 2C, while the facing 4 covers the exposed imprinted side 2D to form a compound stiff board product.

In Fig. 3 a production unit is shown, which comprises two press units, the first unit, which is exactly like the one shown in Fig. 1, being shown with the same reference numbers as in Fig. 1. The other unit, which is mirror-inverted relative to Fig. 1, is shown with a '-reference. The construction and function of the two units 8, 10, 16; 8', 10', 16' is generally the same as described in connection with Fig. 1 and will therefore not be explained in detail. It should be appreciated that the left unit 8¹, 10', 16' of the figure by means of its wet web w' provides a web 2' with an embossed upper side 2B', the pattern of which is formed by the surface 8A' of the heated roll 8\ According to the embodiment which is shown in Fig. 4 the surfaces of the respective heated rolls 8, 8¹ are similar, thus producing two exactly identical layers 2, 2'. The two layers are, however, offset in phase in relation to each other, so that after glueing 16, 16' and bonding in two parallel rolls 24, 26, they are arranged in such a way that the ridges 2B, 2B' of one layer are glued into the grooves 2E, 2E' of the other layer (see Fig. 4). Thus, the roll units with the patterned rolls 8, 8' are arranged in such a way that the embossed surfaces 2D, 2D' of the two layers 2, 2' are directed towards each other when they are brought together. In this way a board product with good strength is manufactured.

Fig. 5 shows a schematic front view of a portion of a counter-roll 8. As can be seen in said figure the pattern of the surface 8A of the roll consists of ridges 8E and grooves 8B, respectively, which extend in parallel to the longitudinal direction of the roll. It should be appreciated that the pattern, which is shown in cross section (see Fig. 5B), can vary with respect to depth t, bottom width b and top width a, as is desired for the final product. In Fig. 5 there is shown that the bottom width b is smaller than the top width a, i.e. a>b. According to more preferred embodiments the rule is, however, that b>a, for instance in order to manufacture a product according to Fig. 4. As can be understood from Figs. 2 and 4, respectively, the distance between ridges and grooves, respectively, is made different depending on whether a product according to Fig. 2 or Fig. 4 shall be manufactured. With a product according to Fig. 4, the distance between the grooves 8B in the roll can thus be made larger compared to a product according to Fig. 2, but a final product with comparable strength properties is obtained.

In Fig. 6 a conceivable embodiment of a shoe press unit 10, 8 according to the invention is shown in cross section, wherein the principles for impulse technique are utilized. An enclosed shoe press 10 is shown co-operating with a patterned counter-roll 8, so that a long nip 12 is formed therebetween. The fibrous web w and a press felt 13 move through the nip 12. The shoe press 10 comprises a support beam 42A, 42B, 42C in the form of an I-beam consisting of a waist 42A and a lower T-piece 42B and an upper T- piece 42C. In the upper surface 44 of the upper T-piece 42C, there is a recess 46. In the recess 46 there is a lower pressing device 48 and a shoe 11, the shoe 11 being fixed on top of the lower pressing device 48. The shoe 11 is provided with an outwardly facing, concave surface 11A. This concave surface 11 A co-operates with a flexible jacket 10A, which is attached to end walls 52 and which is sealingly surrounding the shoe press. Above the shoe press roll 10 and cooperating with the same there is a counter-roll 8, the surface of which is patterned and manufactured of a material with good thermal conductivity, suitably of steel. Further, it is shown that the counter-roll 8 is provided with a heating device 58, which in a suitable manner, for instance radiation and/or flames, is heating the outer surface 8A of the counter-roll 8. The heating device 58 extends along the entire width of the roll 8 but surrounds only a minor part of its periphery and is arranged somewhere in the area of its downward side of the roll. The roll 8 can suitably also be heated from inside, for instance by vapor.

As can be seen from the figure the pressing device 48 for the shoe 11 is a single row (but also a known twin row pressing system can be used). It has been suggested that, for impulse drying, a reversed pressure curve should be aimed at, i.e. a higher pressure is created across the fibrous web near its entry into the shoe press than at its exit. In case it is deemed suitable to utilize a reversed pressure curve, such one could be obtained for instance by a single-row pressing device according to Fig. 6 by placing the press plane 50 eccentrically in relation to the center C of the concave edge line 11 A of the shoe, so that a so called tilting of the shoe is obtained.

FI and F2, respectively, (Fig. 7) are Active forces (in exchange of the single-row real force) which act in an end portion each of the shoe according to Fig. 6, wherein FI indicates the force at the end where the paper web is entering the shoe and F2 thus indicates the force at the exit.

The press plane 50 is defined by the axis of rotation 54 of the counter-roll and the center axis 56 of the I-beam of the shoe press roll. The jacket 10A of the shoe press roll 10A and the sealing end walls, in which it is fixed, rotate about an axis 51 being displaced a distance B against the dry end of the paper machine in relation to the press plane 50. It is suitable that the center 56 of the beam is displaced along a circular arc 58 in relation to the rotation center 51 of the end walls and that the center of said circular arc 58 is arranged in or in the vicinity of the rotation center 54 of the counter-roll 8.

By adapting the displacement Z to suitable values (see our application SE 9902318-6) the desired pressure profile is obtained, as is shown in Fig. 7.

In Figs. 6 and 7 there is shown a conceivable device for impulse drying, which utilizes an extended nip with a reversed pressure curve. It produces a reversed pressure curve, which brings about that the fibrous web w, at its entry into the nip 12, is exposed to an initially high pressure while it is effectively heated by the hot embossed surface 8A of the counter-roll. In this way, a very rapid heating of the liquid content in the fibrous web is achieved, which liquid is partly evaporated. The vapor thus obtained moves out of the fibrous web against the press felt 13 carrying with it remaining liquid, whereby a very efficient dewatering is achieved. Thereafter, the pressure is reduced successively in the nip 12, which in turn leads to an increased evaporation, which carries away further liquid from the fibrous web, so that sufficient dryness is obtained at its exit to maintain the pattern in accordance with the principles of the invention described above. (A person skilled in the art understands, however, that in many cases it is preferred to use a twin row pressing system to obtain a reversed pressure curve. Such a solution is usually somewhat more expensive, but in return easier to control/optimize.)

In Fig. 8 there is shown a first alternatively design of a pattern in the surface 8 A of the counter-roll, the pattern being square and formed by means of intersecting recesses 8B, preferably N- or U-shaped, which are placed helically in the surface of the roll 8, suitably by milling.

In Fig. 9 there is shown an patterned surface consisting of circular recesses 8C, which are symmetrically arranged in the surface 8 A of the roll. The circular recesses have in cross section suitably the shape of a truncated cone with a flat bottom 8D and inclined side surfaces 8E.

In Fig. 10 a conceivable foπning section F and a conceivable press section P according to the invention are shown schematically, the shoe press 10 with the embossed counter- roll 8 being included as a last unit in the press section.

The machine according to the invention comprises a press having two press members 8, 10 that define an imprinting press nip 12. At least one of the press members is a roll 8 with a surface that has raised 8E and/or recessed 8B, 8C portions to form a patterned surface 8A on the roll. The machine has a heater 58 for heating at least the patterned surface 8 A of the roll 8, and means 13 for running a fibrous web w through the imprinting press nip 12 to press the heated patterned surface 8A into the fibrous web w to form to form a reverse image of the pattern therein. The means 13 for running a fibrous web through the nip may be a felt 13. The machine further comprises a forming section F of a boardmaking machine for wet forming the fibrous web w and a press section P. The press section includes, in addition to said press with the two press members 8, 10 and the imprinting press nip 12, the means 13 for running the fibrous web w through the imprinting press nip 12. The means 13 are arranged to supply the wet fibrous web w from the forming section F directly to the press nip for dewatering the fibrous web w by pressing, and for pressing the heated patterned surface 8A into the fibrous web w. The heater 58 is arranged to heat the patterned surface 8Ato effect drying of the fibrous web w to a desired dryness while the heated patterned surface 8A of said roll 8 is maintained in contact with the imprinted pattern 2B, 2E in the web w, so as to achieve a patterned stiff board product.

The pattern in said roll 8 may have a depth t of 0.5 to 5 mm, preferably 0.5 to 3 mm, more preferred 0.7 to 2 mm.

In a preferred embodiment, the pattern in the roll 8 comprises grooves 8B, which preferably are substantially N- or U-shaped. If the pattern comprises grooves, the grooves 8B should preferably run substantially parallel to the longitudinal direction of the roll 8. It is also preferable that the grooves 8B are substantially continuous from one end of the roll 8 to the other.

Preferably, the grooves 8B of said roll 8 have a bottom width a, which is smaller than the distance b between two adjacent grooves 8B at the bottom of the grooves, so that b>a.

It is also possible that there are intersecting grooves.

The pattern in the patterned roll 8 may comprise rotation symmetrical recesses 8D, 8E, preferably in the shape of truncated cones.

The press section is followed by a bonding section 16, 24, 26, 30, 32, 34, 36, 38, 40 for bonding another web 4, 2' to said imprinted web 2. The bonding section may be preceded by a drying unit 15 A.

The invention is not limited to the above description but can be varied within the scope of the following patent claims. Thus, a person skilled in the art realizes that a single layer, manufactured according to the invention and comprising corrugations/patterns on one side can be used as such, without providing any facing, in certain applications. Further, a man skilled in the art realizes that a plurality of different arrangements of layers according to the invention can be brought together in different ways to create different properties in the laminated product. It is also realized that more than one additional drying device can be used after the forming of the layer in the extended nip to obtain desired dryness prior to glue coating. Also other techniques than impulse drying can be used. The most important thing is that sufficient dewatering and forming, respectively, is obtained in the nip, which in some applications (among other things depending on the dryness at entry, the length of the nip, the size of the surface transferring heat in the nip, temperature) can possibly be achieved by means of an extended nip with "conventional" pressure profile. Further, it is realized that the invention is not limited to any special type of forming section F but in principle any forming section intended for fiberboard may be used.

Further, it is realized that many different types of pattern can be used, which differ from those described as examples in the figures. Further, many different manufacturing methods can be utilized to produce the pattern in the surface 8 A of the roll but in many cases milling (for recesses/grooves) and drilling (for rotation symmetric holes), respectively, are preferred.

Claims

1. A method of making a patterned board product, including running a fibrous web (w) through an imprinting press nip (12) having at least one roll (8) with a surface that has raised (8E) and/or recessed (8B, 8C) portions to form a patterned surface (8 A) on the roll, heating at least the patterned surface (8 A) of said at least one roll (8), and pressing the heated patterned surface (8 A) into the fibrous web (w) to form to form a reverse image of the pattern therein, characterized by supplying the fibrous web (w) in a wet condition directly from a foπning section of a boardmaking machine to the press nip (12), dewatering the wet web (w) in the press nip (12) during the pressing of the heated patterned surface (8 A) of said at least one roll (8) into the web (w), and drying the web (w) to a desired dryness, while maintaining the heated patterned surface (8 A) of said at least one roll (8) in contact with the imprinted pattern

(2B, 2E) in the web (w), so as to achieve a patterned stiff board product.

2. A method according to claim 1, characterized by forming the raised (8E) and/or recessed (8B, 8C) portions of the patterned surface (8A) on the roll (8) so as to imprint a pattern of grooves (2E) and ridges (2B), respectively, in the fibrous web, the grooves and ridges preferably extending in a cross machine direction.

3. A method according to claim 1, characterized by foraiing said press nip (12) between said roll (8) provided with the patterned surface (8A) and a shoe press roll (10) with a flexible jacket (10A) and a concave shoe (11) cooperating with the patterned roll (8) to form an extended press nip.

4. A method according to claim 1, characterized by using impulse technique in said nip (12).

5. A method according to claim 1, characterized by running to the nip (12) a fibrous web (w) having a dry solids content of 20-45 %, preferably 25-40 % and more preferred 30-40 %.

6. A method according to claim 1, characterized in that the dry solids content of the web (2) on exiting the nip (12) exceeds 70 %, preferably exceeds 80 % and more preferred exceeds 90 %.

7. A method according to claim 1, characterized by shaping the fibrous web (w) to have an imprinted side (2D) and a substantially plain side (2C).

8. A method according to claim 7, characterized by coating the raised portions (2B) of said imprinted fibrous web (2) with glue, and then bonding an additional fibrous web (4, 2') to the imprinted side (2D) to form a compound stiff board product.

9. A method according to claim 8, characterized in that said additional web is a facing (4).

10. A method according to claim 8, characterized in that also said additional web has an imprinted side (2D¹), and preferably bonding the two webs to each other in such a way that the imprinted sides (2D, 2D') are facing each other to form a compound stiff board product having two substantially plain sides.

11. A method according to claim 8, characterized by bonding two imprinted webs (2, 2') and a facing (4) to one another in such a way that the imprinted sides (2D, 2D') of the imprinted webs (2, 2') face in the same direction and form an intermediary board product having an exposed imprinted side (2D) and a substantially plain side

(2C), while the facing (4) covers the exposed imprinted side (2D) to form a compound stiff board product.

12. A machine for making a patterned board product, comprising a press having two press members (8, 10) defining an imprinting press nip (12), at least one of the members being a roll (8) with a surface that has raised (8E) and/or recessed (8B, 8C) portions to form a patterned surface (8A) on the roll, a heater (58) for heating at least the patterned surface (8A) of the roll (8), and means (13) for running a fibrous web (w) through the imprinting press nip (12) to press the heated patterned surface (8 A) into the fibrous web (w) to form to form a reverse image of the pattern therein, said machine being characterized by further comprising: a forming section (F) of a boardmaking machine for wet forming the fibrous web (w), and a press section (P), said press section including in addition to said press with the two press members (8, 10) and the imprinting press nip (12), the means (13) for running the fibrous web (w) through the imprinting press nip (12), said means (13) supplying the wet fibrous web (w) from the forming section (F) directly to the press nip for dewatering the fibrous web (w) by pressing, and for pressing the heated patterned surface (8A) into the fibrous web (w), said heater (58) heating the patterned surface (8 A) to effect drying of the fibrous web (w) to a desired dryness while the heated patterned surface (8 A) of said roll

(8) is maintained in contact with the imprinted pattern (2B, 2E) in the web (w), so as to achieve a patterned stiff board product.

13. An apparatus according to claim 12, characterized in that the pattern in said roll (8) has a depth (t) of 0.5 to 5 mm, preferably 0.5 to 3 mm, more preferred 0.7 to 2 mm.

14. An apparatus according to claim 12, characterized in that the pattern in said roll (8) comprises grooves (8B), which preferably are substantially N- or U-shaped.

15. An apparatus according to claim 14, characterized in that said grooves (8B) run substantially parallel to the longitudinal direction of the roll (8).

16. An apparatus according to claim 12, characterized in that the pattern in said roll (8) comprises rotation symmetrical recesses (8D, 8E), preferably in the shape of truncated cones.

17. An apparatus according to claim 14, characterized in that said grooves (8B) are substantially continuous from one end of the roll (8) to the other.

18. An apparatus according to claim 17, characterized in that there are intersecting grooves (2E).

19. An apparatus according to claim 12, characterized in that said press section is followed by a bonding section (16, 24, 26, 30, 32, 34, 36, 38, 40) for bonding another web (4, 2') to said imprinted web (2).

20. An apparatus according to claim 19, characterized in that the bonding section is preceded by a drying unit (15 A).

1. An apparatus according to claim 14, characterized in that the grooves (8B) of said roll (8) have a bottom width (a), which is smaller than the distance (b) between two adjacent grooves (8B) at the bottom of the grooves, so that (b)>(a).