EP3711970B1 - Method for refining a construction plate - Google Patents

Description

The invention relates to a method for finishing a provided building board, in particular made of MDF, HDF or a wood-based material-plastic mixture with an upper side and a lower side, wherein a relief is embossed at least into the upper side, which consists of at least one strip-shaped depression with a depth running in a longitudinal direction.

Such a procedure is known, for example, from WO 2017/164806 A1 This process is used to refine a floor panel by pressing a bevel into the side edges starting from the top.

The EP 1 820 640 B1 The well-known building boards are divided into individual panels after finishing and used, for example, as floor or wall and ceiling panels and are often provided with a wood, stone or fantasy decor with a superimposed, three-dimensional surface. The divided panels have connecting elements (tongue and groove) and are usually equipped with locking elements for locking adjacent panels in a horizontal and vertical direction (so-called click panels). The overlay of the decor and the three-dimensional surface creates a realistic optical and tactile impression of the imitated material.

It is known, particularly in the case of floor panels, that they are coated at least on the top side and have a structure adapted to the decor. Such a structure is referred to as an embossed register structure. The decor is either a paper layer laminated onto the carrier board or a layer of color printed directly onto the carrier board. The decor is also provided with a wear-resistant layer. For this purpose, either abrasion-resistant paper layers, so-called overlays, or, after curing, abrasion-resistant lacquer or resin layers are used. The decor-synchronous structure is a three-dimensional surface structure and is embossed into the surface of the panel using a correspondingly three-dimensionally structured press plate. The thermal and pressure-activatable components of the coating melt and run and fill the three-dimensional structural embossing as it cures. The structure usually has a height of up to 500 µm. The number and depth of the structures are limited by the available amount of activatable components, the bulk density of the carrier and the pressing force.

With laminate flooring, the abutting edges where neighboring floor panels meet are problematic. Depending on the incidence of light, even the smallest differences in height cause visually unsightly shadows that negatively affect the overall appearance of a floor. The core is made of wood-based material, which also makes the panels sensitive to moisture. Liquid spilled on the floor must be wiped away as quickly as possible to prevent the liquid from penetrating the connecting joint between the abutting edges. If water penetrates, the wood fibers in the carrier board can swell and cause irreversible damage, as the swelling pressure of the wood destroys the structure and/or partially hydrolyses the adhesive. For this reason, it is important that special attention is paid to the later abutting edges when the panels are manufactured. Neighboring panels should be able to lie firmly against one another, a visually uniform appearance should result with a floor of laid panels, and precautions must be taken to ensure that spilled liquid cannot immediately flow into the connecting joints.

The EP 3 059 020 A1 discloses a method for producing a wood-based panel provided with a decorative layer, which provides for treating at least a portion of its surface with water-containing steam, sanding the moistened surface and then providing it with at least one decorative layer.

The US 4,579,767 A discloses a hardboard in which a tile mirror simulated by longitudinal and transverse recesses is embossed and which is coated in such a way that tiles are imitated. A large number of individual tiles are reproduced on each hardboard. Several hardboards can be placed next to one another.

From the WO 2016/180643 A1 It is known to produce panels with recesses in the edge areas of the usable surface by embossing at least two parallel grooves with a web between them into a large-format wood-based panel and dividing the embossed panel into individual smaller panels with a saw cut through the web. The process described places extreme mechanical stress on the impregnated materials (decorative and overlay) as they are extremely deformed or overstretched during structuring. This is unfavourable for such brittle materials and can lead to cracks and damage to the surfaces. Microcracks in the surface can remain undetected for a long time, but they can allow moisture to penetrate into the core of the panel and destroy the panel.

The EN 10 2006 052 555 B3 describes a method for producing a panel with a structured surface, in which a carrier plate is provided with an elastic coating, the carrier plate is separated into strips and a surface structure is embossed into the coated surface of the strips. Finally, the strips are profiled and separated into panels.

From the EP 2 905 135 A2 A method for producing a panel is known in which groove-shaped depressions are embossed into the top of a carrier plate using a calender roller. For this purpose, the roller has circumferential elevations on its casing. Alternatively or additionally, the roller can have at least one elevation on its casing that runs parallel to the axis of rotation.

The DE 197 18 770 A1 discloses a method and a system for producing structured wood-based panels. In order to maintain the adhesive properties and strength properties of the panels, the cold wood-based panels are sprayed with water on one or both surfaces and then run through a heated vapor deposition section. This is followed by structuring on one or both sides.

Based on this problem, the process described at the beginning should be improved so that the embossing of the depression is simplified and the embossed relief is clearly contoured. However, the essential manufacturing steps should remain as unchanged as possible in order to be able to use existing equipment. There should be no increase in costs or a slowdown in the production process.

In order to avoid the aforementioned disadvantages, the invention provides that in order to produce the relief, the building board is heated to a temperature of 80 to 100°C and then the at least one depression is embossed to a depth of at least 0.5 mm by means of at least one calender roller heated to a temperature of 100 to a maximum of 150°C, the calender roller having structural elements corresponding to the desired relief. The structural elements preferably run in the circumferential direction and are formed by a ring placed on the cylinder jacket of the calender roller.

If at least one further recess is embossed in the transverse direction at an angle of preferably 90° transversely to the at least one recess running in the longitudinal direction, individual panels can later be cut out of the large-format building board, which have recessed edges on both the long sides and the transverse sides.

The embossed recesses lower the top side at the side edges. The abutting edges of adjacent panels are therefore lower than the top side. In such a case, a height offset cannot cause any shadows that are visually noticeable because all the butt joints are lowered. By profiling the edges accordingly, a firm connection can be achieved between adjacent panels, effectively preventing liquid from penetrating the butt joint too quickly.

The depressions running in the longitudinal and transverse directions can be produced by means of several calender rolls. Preferably, the depressions running in the longitudinal and transverse directions are embossed by means of a single calender roll.

In order for the depressions to be visually perceptible, they must have a minimum depth of 0.5 mm. The material must not be damaged or even destroyed when the relief is embossed. To achieve this, the building board and the calender roller are heated. The building board can be heated using steam. Depending on the material from which the building board is made, a so-called "spring-back effect" can occur, which leads to a change in the contour of the embossed depression. The displaced material springs back. In order to still achieve the required structure depth, the height of the structuring of the calender roller in the circumferential direction is 20 to 40% greater than the depth of the depression to be embossed. Preferably, the height can be 25 to 35%, in particular 30% greater than the depth of the depressions to be embossed in the longitudinal direction.

Since a linear pressure is applied in a calender press, if the depressions are embossed in the longitudinal and transverse directions with the same calender roll, the height of the structural element must be even higher for the transverse structuring. It is 40 to 60%, preferably 45 to 55%, in particular 50% more than the depression to be embossed in the transverse direction.

If a fibreboard, in particular an MDF or HDF board, is used as a construction board, it is intended that its density profile (progression of the density over the cross-section of the board) is compared to a usual density profile, as it is known, for example, from the EP 3 023 261 B1 known, is lowered. When the fiber cake is pressed into a building board of the desired thickness, the greatest bulk density is found in the area of the top and bottom of the board. Due to the heat input during pressing, a pressed skin forms on the top and bottom, which is also called a "rotting layer".

The preferred construction board is an HDF board with a pressed skin on the top. This pressed skin can have a thickness of 0.3 to 0.5 mm.

The bulk density of the building board in the covering layer forming the upper side is preferably between 800 and 950 kg/m ³ .

A building board made from a wood-based material-plastic mixture can also be used. Regardless of the material used for the building board, it is advantageous if it has a filler content of up to 70% based on the total weight. Calcium carbonate or substances with comparable properties can be used as fillers.

In order to improve the embossing result, a tempering agent can be applied to the top of the construction board before embossing. This tempering agent is preferably aqueous melamine resin and is preferably made deformable by means of an elasticizing agent. Acrylates, polyols, caprolactam, etc. can be considered as elasticizing agents. The tempering agent is dried after application.

It can also be planned to apply an elastic primer to the top of the construction board before embossing, which can be white in color to create a surface that is easy to print on. At least the recess can be printed with a single-color or multi-color decoration using a digital printer. Preferably, the entire top is printed with a decoration. Instead of using a white color for the primer, any other color can be used if necessary. It is important that the primer withstands the plastic deformation during the subsequent embossing.

The first embossing step is carried out using at least one calender roll. This has the advantage that the embossing step can be integrated into the production line. The embossing can then take place immediately after the pressing of the wood-based panel in a continuous press, in which the previously scattered fiber cake is formed into a Plate of desired thickness has been pressed. This optimizes production.

After completion of the structure, which consists of at least a primer, the decoration and, if necessary, an abrasion-resistant layer, the construction board is laminated in a short-cycle press under high pressure and high temperature in relation to the environment, and in a second embossing step, at least one strip-shaped depression is embossed again in order to achieve the formation of the side walls, if possible without changing the position of the bottom wall in depth. During the coating, the side walls formed in the first embossing step are "rounded" so that the second embossing step converts these rounded areas back into a flat, straight surface.

In order to be able to align the construction board during the subsequent processing steps, markings can be printed on the bottom walls of at least one recess, which can consist of lines, circles, dots, crosses or other graphic symbols. Lines are preferably used. These markings can be used to align the construction board for the second embossing step and other subsequent processing steps using a camera system.

The repeated embossing into the recess in the second embossing step is preferably carried out in a short-cycle press in which strip-shaped elevations are applied to the press plate.

In the first and/or second embossing step, a structure can be embossed into the upper side that runs at least partially synchronously with the decoration, which in technical terms is called "embossed register".

After the large-format panel has been completed, it is cut along the embossed recesses and divided into individual panels. Saw cuts are preferably made in the middle of the recesses running lengthwise and crosswise and the individual panels are then profiled on their side edges so that several panels can be connected to one another without glue.

A calender roller for embossing at least one strip-shaped depression into at least the upper side of a provided building board made of a wood-based material, in particular MDF or HDF, or a wood-based material-plastic mixture essentially consists of a cylinder body arranged about an axis of rotation and at least one structural element running in the circumferential direction, which is essentially complementary (congruent) to the depression to be embossed and has a height that protrudes radially from the lateral surface of the cylinder body.

The height of the structural element is 20 to 40%, preferably 25 to 35%, particularly preferably 30% more than the depth of the recess to be embossed.

In order to be able to emboss depressions in the building board in the longitudinal direction and in the transverse direction with a single calender roller, a structural element running in the axial direction (transverse direction) is provided on the cylinder body, which is designed to be essentially complementary (congruent) to the depression to be embossed in the transverse direction of the board and has a height that protrudes radially from the outer surface of the cylinder body.

The height of the structural element(s) running in the axial direction (transverse direction) is 40 to 60%, preferably 45 to 55%, in particular 50% greater than the depth of the recess to be embossed in the transverse direction.

Preferably, the structural elements are linear and extend to each other at an angle of 90°.

The structural elements can have any cross-section. They are preferably designed with a U, V, W, Y or comparable cross-section.

Preferably, a plurality of structural elements running parallel to one another are arranged at least in the circumferential direction. The structural elements can also be distributed over several calender rolls.

The temperature of the calender roll can be raised or lowered compared to the ambient temperature. The calender roll can therefore be heated or cooled. In the process according to the invention, however, the calender roll is heated to a temperature of 100 to 150 °C.

Figur 1 -

eine perspektivische Teildarstellung einer großformatigen Bauplatte;

Figur 2 -

die Draufsicht auf die Bauplatte nach Figur 1;

Figur 3 -

eine schematische Teildarstellung vor dem zweiten Prägeschritt;

Figur 4 -

eine vergrößerte Teildarstellung während des zweiten Prägeschrittes;

Figur 5 -

eine schematische Teildarstellung während des ersten Prägeschrittes;

Figur 6 -

eine schematische Darstellung der in der Kurztaktpresse befindlichen Bauplatte;

Figur 7 -

eine weitere schematische Teildarstellung während eines ersten Prägeschrittes;

Figur 8 -

eine schematische Teildarstellung während eines ersten Prägeschrittes, bei dem sowohl in Längsrichtung als auch in Querrichtung Vertiefungen geprägt werden;

Figur 9 -

ein Rohdichteprofil einer MDF-Platte.

An embodiment of the invention will be described in more detail below with the help of a drawing. They show:

Figure 1 -

a perspective partial view of a large-format building board;

Figure 2 -

the top view of the building board after Figure 1 ;

Figure 3 -

a schematic partial representation before the second embossing step;

Figure 4 -

an enlarged partial view during the second embossing step;

Figure 5 -

a schematic partial representation during the first embossing step;

Figure 6 -

a schematic representation of the building board in the short-cycle press;

Figure 7 -

another schematic partial representation during a first embossing step;

Figure 8 -

a schematic partial representation during a first embossing step, in which depressions are embossed both in the longitudinal direction and in the transverse direction;

Figure 9 -

a density profile of an MDF board.

The starting point is a large-format MDF or HDF board with a length of 2,800 or 1,860 mm, a width of 2,070 mm and a thickness of 6 to 14 mm, which is divided into smaller boards (panels) after finishing. The gross density is lower than a standard HDF board. To form a weak top layer that can be plastically deformed, the top layer peaks were lowered by at least 40 kg/m ³ compared to the standard. Good results were achieved with a reduction of up to 60 kg/m ³ . The bulk density is in the range of 850 to 950 kg/m ³ . An example of the bulk density profile of an MDF board is shown in Figure 9.

In order to be able to emboss depressions 5, 6 into the top side 2 of the construction board 1, the board is first heated to a temperature between 80 and 100°C using steam. Then 10 to 50 g/m ³ , preferably 30 g/m ³ of aqueous melamine resin is applied as a curing agent. This can be a standard impregnating resin with a solids content of 50 to 65% by weight, preferably 60% by weight. In addition to water, other additives such as hardeners, wetting agents and the like can be present in the solution. The liquid melamine resin is made deformable by means of elasticizing agents. Acrylates, polyols, caprolactam, etc. can be used as elasticizing agents. Alternatively, UF resin or mixtures of UF and melamine resin can be used as a curing agent. It is either a postforming resin or a standard impregnating resin that has been made more elastic by adding flexibilizing agents (e.g. 1,4-butanediol, caprolactam, polyglycol, etc.). Subsequent addition of the elasticizing agent should be in a range of about 3 to 7% by weight.

The building board 1 pretreated in this way is passed under one or more calender rollers 20 arranged one behind the other, heated to a temperature of 100 - 150°C, with embossing rings arranged parallel to one another, which serve as the first structural elements 205, and a web running in the axial direction Q, which serves as the second structural element 206. In a first embossing step, depressions 5, 6 with a depth Tu of at least 0.5 mm are embossed into the top side 2 over the at least two structural elements 205 in the longitudinal direction L and over the second structural element 206 in the transverse direction Q. The transverse direction Q related to the building board 1 is identical to the axial direction Q related to the calender roller 20. The line pressure of the structural elements 205 is up to 300 N/mm and the surface temperature is up to 220°C under certain circumstances. In this first embossing step, the tempering agent on the top side 2 is at least partially implemented, thus at least partially hardens and thereby increases the bulk density. The depressions 5, 6 can be formed in a stepped manner, for example by using several calender rollers 20 with different embossing rings as structural elements 205 and, for example, initially 0.3 mm and then a further depth of at least 0.5 mm is embossed. Between the structural elements 205, 206, a structure can be engraved in the casing 22 of the calender roller 20, which is then embossed into the top side 3 next to the depressions 5, 6 in the first embossing step. If the building board 1 can show a so-called "spring-back" during embossing, the height of the structural elements 205, 206 must be greater than the depth of the relief to be embossed.

Before the first embossing step, the top side 2 is primed with a white base color that is also elastic. The base color can be applied in one or more layers. After embossing, a decoration 3 is printed onto the base 11 using digital printing, whereby the color dots of the digital printer are reproduced not only on the flat top side 2, but also on the side walls 5.1, 5.2 and the bottom wall 5.3 of the strip-shaped depressions 5, 6, so that the depressions 5, 6 are completely decorated. The decoration 3 can be single-colored or multi-colored and is applied in such a way that it runs at least partially synchronously with the previously embossed structure. At the same time as the decoration 3, markings 7 are printed onto the bottom wall 5.3. The markings 7 can be circles 7.1, crosses 7.2, lines 7.3 and strokes 7.4 or other geometric figures. Using these markings 7, the construction plate 2 can be aligned via a camera system for further processing steps.

After the decorative printing, which does not necessarily have to be digital but can also be done using an analogue process, a counter layer 8 is placed on the underside 9 of the construction board 1 and an overlay paper 4 is placed on the decorative 3. Instead of an overlay paper 4, a liquid overlay can also be applied using a roller application, into which corundum is mixed or sprinkled. The counter layer 8 can also be applied in liquid form.

This structure is then fed to a short-cycle press 30, the upper press plate 31 of which is provided with strip-shaped elevations 32. Via the markings 7 and a camera system, the building plate 1 is aligned so that the elevations 32 once again dip into the embossed depressions 5, 6 during the subsequent pressing of the structure and once again emboss the side walls 5.1, 5.2 of the depressions 5, 6 that were rounded during the coating of the top side 2 in order to set parallel and flat side walls 5.1, 5.2 in a second embossing step, without changing the depth Tu of the depressions 5, 6 or the position of the bottom walls 5.3.

How Figure 4 shows, the elevations 32 in the transition area from the side walls 5.1, 5.2 to the bottom wall 5.3 are larger than the width of the recesses 5, 6 in order to securely form the lower edges of the recesses 5, 6.

The pressing time in the second embossing step is between 10 and 30 seconds, preferably 12 to 15 seconds, during which the resins melt and bond with the construction board 1. Due to the temperature of the pressing plates 31, 33, a surface temperature of 120° to 180°C is established on the pressed part during the pressing process. The pressure progression starts from a pressure build-up phase, then moves to a holding phase and then a pressure reduction phase. The embossing depth Tu is controlled in the sense of a path.

The at least one calender roller 20 is integrated into the printing system or is located immediately upstream of it. For a sensible design, at least two depressions 5, 6 in the longitudinal direction L and two in the transverse direction Q must be embossed in the first embossing step so that the side edges of the divided panels are all lowered.

In Figure 5 the calender roller 20 is shown schematically, which embosses depressions 5 running in the longitudinal direction L into the building board 1. This calender roller 20 is driven to rotate about an axis of rotation A. Several spaced-apart rings are placed on its casing 22 or have been produced by milling from solid material, which serve as structural elements 205 and protrude in the radial direction R from the casing surface 22 by a height Hu. This height Hu is 20 to 40% greater than the depth Tu of the depression 5 to be embossed. The calender roller 20 can be tempered. The temperature can be raised or lowered compared to the ambient temperature.

The embossing of the recesses 6 in the transverse direction Q can be carried out with a separate calender roll 20, as shown in Figure 7 is shown, or with a calender roll 20 which has both the structural elements 205 and at least one web running in the axial direction or transverse direction Q as a structural element 206. This linear structural element 206 runs at an angle α _S of 90° to the structural elements 205. The height H _A of the structural elements 206 running in the axial direction Q is 40 to 60% greater than the depth T _L of the depressions 6 to be embossed in the transverse direction, because a linear pressure is applied in a calender press. The height H _A is preferably 45 to 55%, and in particular 50% greater than the depth T _L .

At least one plank length should be shown on the circumference of the calender roller 20, whereby "plank length" is understood to mean the length of the planks shown on a panel. "Plank length" and the length of the panel can be the same, but do not have to be. Different plank lengths can be achieved by varying the diameter of the calender roller 20 or by using multiple lengths on the calender roller.

Structural elements 205, 206 with a rectangular cross-section are shown. However, they can also have a U, V, W, Y or similar cross-section.

List of reference symbols

1

Building board

2

Top

3

decor

4

abrasion-resistant layer / overlay

5

Deepening

5.1

Side wall

5.2

Side wall

5.3

Floor wall

6

Deepening

7

mark

7.1

Circle

7.2

Cross

7.3

line

7.4

line

8

Countermove

9

bottom

20

Calender roll

21

Cylinder body

22

Coat

30

Short-cycle press

31

upper press plate

32

strip-shaped elevation

33

lower press plate

205

Structural element

206

Structural element

α

angle

αS

angle

A

Rotation axis

HU

Height

HA

Height

L

Longitudinal direction

Q

Axial directionQ Transverse direction

R

radial direction

TU

depth

Claims (10)

1. A method for refining a provided construction plate (1) made of a wood-based material, in particular MDF, HDF or a wood-based material/plastic mix with an upper side (2) and a lower side (9), wherein a relief is embossed at least into the upper side (2), said relief being composed of at least a first strip-shaped depression (5) extending in a longitudinal direction (L) and/or in a transverse direction (Q) with a depth (T), the depression (5) being embossed to the depth (T) of at least 0.5mm by means of at least one calendar roller (20), the calendar roller (20) comprising structural elements (205, 206) that correspond to the desired relief, characterised in that, in order to create the relief, the construction plate (1) is heated to a temperature of 80 to 100°C and the depression (5) is subsequently embossed, wherein the at least one calendar roller is heated to a temperature of 100 to maximum 150°C
2. The method according to claim 1, characterised in that at least one further second depression (6) extending at an angle (α) of preferably 90° transverse to the first depressions (5) is embossed.
3. The method according to one of the preceding claims, characterised in that the height Hu of the structural element (205) of the calendar roller (20) is 20 to 40%, preferably 25 to 35%, in particular 30%, greater in the circumferential direction than the depth T_L of the depression (5) to be embossed in the longitudinal direction (L).
4. The method according to claim 3, characterised in that the height H_A of the structural element (205) in the axial direction of the calendar roller (20) is 40 to 60%, preferably 45 to 55%, in particular 50%, greater than the depth T_L of the depression (6) to be embossed in the transverse direction (Q).
5. The method according to one of the preceding claims, characterised in that a tempering agent is applied to the upper side (2) before embossing, which is preferably an aqueous melamine resin, which is preferably made deformable in particular by an elasticizer, and that deformability is achieved by heating the upper side (2) prior to embossing, wherein heating prior to embossing is done by means of steam.
6. The method according to one of the preceding claims, characterised in that a single-colour or multicoloured decor (16) is printed onto the upper side (2) and at least the depressions (5) in the longitudinal direction (L) by means of a digital printer (15).
7. The method according to one of the preceding claims, characterised in that, once the structure is completed, the construction panel (1) is laminated in a short-cycle press at a high pressure and at a high temperature, and in a second embossing step, it is embossed into the strip-shaped depressions (5, 6) to achieve the exact design of the side walls (5.1, 5.2).
8. The method according to claim 7, if dependent on claim 6, characterised in that a structure is embossed in the upper side (2) in one of the embossing steps, said structure extending at least partially synchronously to the decor (3).
9. The method according to one of the preceding claims, characterised in that the construction panel (1) is divided into individual panels by separating them in and along the depressions (5,6).
10. The method according to one of the preceding claims, characterised in that the calendar roller (20) comprises a plurality of structural elements (205) arranged parallel to each other is provided in at least the circumferential direction.

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