The invention relates to a method for the production of an impregnate provided with markings, wherein a resin is impregnated into a marked fibrous material web, after which the impregnate is dried. The invention further relates to a wood or fibre-based board that is coated with such an impregnate,, a high-pressure laminate containing the impregnate and the use of the impregnate as a coating of a con- crete casting mould, in particular.

A fibre-based impregnate is used as a moisture-barrier coating of plywood or other such fibre-based boards in floor and wall panels of spaces that are exposed to humidity, in bases and other structures in outdoor locations and, particularly, in casting moulds that receive wet concrete and other moist and hardening masses. The coating prevents wetting and swelling of the board and also protects the board mechanically against blows and wearing. In casting moulds, the coating should prevent the mass from adhering to the board and protect the mould so that it endures several instances of use.

In plywood concrete moulds protection is required in particular by the inner surface of the mould, which is exposed to the moisture of the cast concrete and mechanical stress. However, in practice, both the inner and outer surfaces of the moulds are provided with similar protective coatings. Namely, the coating is applied to the board material, of which the moulds are built, whereby it is insignificant, which side of the board becomes the inner surface of the mould and which one becomes its outer surface.

It is common to include information, such as advertising, instructions, warnings or manufacturer's identification data on the surfaces of the structures to be protected. Thus, the outer surface of the concrete casting mould can be provided, e.g., with the logo of the user as a constantly repeating pattern. Present technology com- prises flexographic printing of the base paper of the impregnate, winding the printed paper web and transferring the roll to an impregnating machine. It has not been possible to combine flexographic printing with impregnation on the on-line principle. As a subcontractor has been needed for printing the paper, it has been difficult to manufacture the printed impregnate, and the manufacturing costs have been high.

Thus, the problem to be solved is to simplify the manufacturing process of the impregnate provided with markings, so that the impregnate can be manufactured quicker, with less working phases and lower costs. Particularly, in concrete casting moulds, wherein for the reasons mentioned, the impregnate also becomes the inner surface of the mould, the impregnate should also endure, without significant damages, the mechanical and other stresses resulting from the casting. As a solution, the invention provides a manufacturing method of the impregnate, which is characterized in that laser marking is made on a moving fibrous material web to produce the markings, after which the laser-marked web is impregnated and dried.

When applying the method according to the invention, the fibrous material web can preferably be marked by an impregnating machine on the on-line principle, so that having the printing made by a subcontractor with related costs and delays is avoided. A particular advantage of the laser marking is the possibility to simply and quickly change the logo or other figure or mark that constitutes the invention, which makes it possible to make different markings on impregnates that go to different clients. Printing inks or other colouring agents are not needed in the method of the invention. For the usability of the invention, it is also essential that, accord- ing to observations, the laser marking does not considerably weaken the impregnating ability of the web. The resin is absorbed into the laser-marked spots of the web almost as well as into those not marked, and the impregnation does not weaken the visibility or recognizability of the markings or the mechanical properties of the coating that is formed by the impregnate or the high-pressure laminate that contains the impregnate.

The laser-marked fibrous material, such as a paper web, can be impregnated effectively by conveying the moving web through a basin that contains resin, so that the web is immersed in the resin. The impregnation basin can preferably be followed by a roll nip, which adjusts the amount of resin in the impregnated web. In impregnation, a one or multi-phase roll application of resin, a combination of roll application and immersing in the basin, or pressure impregnation can also be considered. The web is most preferably dried with hot air in a fluidized-bed drier. The web to be impregnated in the invention can be kraft paper, into which resin is absorbed, so that the amount of resin is typically about 30-70% of the weight of the finished impregnate. Alternatively, however, an extruded plastic layer can also be included in the impregnate or a multilayer coating material can be manufactured, wherein the plastic layer is situated between two paper layers that are impregnated with resin. Such structures are described in the patent specification WO2006/010788.

According to the invention, the marking, impregnation and drying of the web are preferably carried on continuously on-line without interrupting the movement of the web. However, off-line marking and impregnation carried out separately thereafter are also feasible within the invention.

The paper or paper web in the invention not only refers to various fairly thin <150gm ² fibre-based materials, but also to thicker (≥ 150 g/m ² ) paperboards and cardboards, which are suitable for laser marking and impregnation.

According to the invention, the web to be impregnated can comprise paper, which is manufactured from unbleached or bleached chemical pulp. For the coatings of fibre-based boards in concrete casting moulds or the like, as well as for the high- pressure laminates, unbleached kraft pulp is used, in particular, whereby the laser markings can be distinguished in the impregnate either as darker or lighter than their surroundings. It is also possible for the marking to be visible as differences in opacity or shades. A CO ₂ laser head can be used to produce a dark mark, which is based on the oxidation occurring on the surface of the web. However, the CO ₂ laser, suitably with a power density of 0.005-0.02 J/mm ² , can also be used to pro- vide on unbleached brown paper a marking, which can be distinguished by its lighter colour and the generation mechanism of which is not known with certainty, but which, without limiting the invention, is presumably, based on a reaction of Hg- nin. The laser marking differs from conventional printing processes in that no ink or other colouring agent is brought onto the paper. A typical marking in casting moulds, wall and floor panels and other applications of the invention comprises the logo, name or other symbol of a company, which is repeated on the surface of the impregnate at regular intervals. Conventional markings also include information about the manufacturer or manufacturing lot and time of manufacturing or technical instructions for the user of the end product. However, the invention does not set limitations on the markings that are to be included in the impregnate. For example, it would be possible to change a partially bleached, brownish paper surface by laser marking so as to simulate wood with its grains and annual rings. In addition to the method described above, the invention relates to a board consisting of wood or fibre-based material, such as plywood, which is coated with an impregnate manufactured according to the method. The board is characterized in that the impregnate contains markings, which are produced by laser marking and which can be distinguished from their surroundings due to their lighter or darker colours.

The invention also relates to a high-pressure laminate, which is characterized in including an impregnate manufactured according to the invention, whereby the surface of the laminate comprises markings, which are provided by laser marking and which can be distinguished from their surroundings due to their lighter or darker colours.

The invention further comprises a special application concerning the use of the impregnate provided with laser markings as a coating material of a concrete casting mould, which is constituted by wood or fibre-based board, such as plywood, on at least the outer surface of the mould that is visible on the outside and, preferably, also on its inner surface that comes into contact with the concrete.

In the following, the invention is described in detail, first, with reference to the appended drawing, wherein

Fig. 1 shows a continuous process of manufacturing the impregnate that is pro- vided with laser markings;

Fig. 2 shows a top view of the laser marking of a paper web in the process according to Fig. 1 (direction U-Il); and

Fig. 3 shows a concrete casting mould according to the invention, which is formed from plywood that is coated with the impregnate manufactured according to Fig. 1 ; Fig. 4 is the cross section IV-IV of the coated plywood of Fig. 3; and

Fig. 5 is the cross section of the high-pressure laminate that contains the impregnate according to the invention that is manufactured according to Fig. 1.

Figs. 1 and 2 show the continuous on-line manufacturing process of the impregnate that is provided with markings made by laser, wherein a paper web 1 is marked by a laser head 2, the impregnation is carried out with resin 3 in an impregnation basin 4, the amount of resin is adjusted in a roll nip 5 and the impregnated web is dried in a fluidized-bed drier 6. The base paper 1 of the impregnate comprises brown kraft paper, which is conveyed from a roll and the weight of which is 30-350 g/m ² , preferably within 40-250 g/m ² . The laser head 2 is placed on the route of the kraft paper web 1, producing on the web a marking 7 as a constantly repeating pattern, according to Fig. 2. The marking 7 can be the logo of the company or other similar figure, also a word mark, such as the name of the product or the company. In addition to or instead of this, the marking can be a manufacturing lot marking that runs in the longitudinal direction of the web or a time tagging that changes in real-time or the marking of length of the web (a metric marking). Other informational markings or identifiers, such as 2D identifiers, are also feasible within the invention. In the appended black-and-white drawing, the markings 7 are dark, corresponding to a real situation, since the laser marking is based on the oxidation of the surface of paper 1. However, the markings 7 that are made on the brown kraft paper are more preferably whitened spots, which on the basis of tests can be made by the CO ₂ laser, its power density being 0.005-0.02 J/mm ² . In the light of the tests, the use of protective gas in the marking is not necessary.

After the marking stage, the moving web is immersed into the liquid resin 3 in the impregnation basin 4, which is, e.g., phenolic resin. Other resins used in the invention include amino, polyester, epoxy, vinyl ester, polyurethane and polyimide res- ins, a condensation polymer such as allyl resin, or a mixture thereof. After rising from the basin 4, the web saturated with absorbed resin is conveyed to the roll nip 5, which adjusts the amount of resin by extruding the excess resin from the web. In the impregnate intended for the coating of the concrete casting moulds, the resin most preferably comprises about 70% of the weight of the dried impregnate 8.

Finally, the web that is saturated by resin moves to the fluidized-bed drier 6, where it is dried with hot air on both sides. A suitable temperature in the drier is about 200-230 O. Blowing with hot air dries the resin so that the impregnate 8 thus obtained is adhesive-resistant and it can be stored by cutting and stacking into sheets or by winding. However, it is preferable for the drying not to complete the cross-linking reaction of the resin but to leave reactive groups in the resin, which complete the cross-linking, when the impregnate 8 is laminated by pressing it to the base material, such as plywood board 10 (cf. Fig. 4) or to other impregnate layers 8' (cf. Fig. 5). The impregnate 8 that is laser-marked according to the invention has been examined, and it has not been observed that the marking should have adverse effects on the properties of the impregnate. The marked spots of the web are essentially as good in absorbing resin as those outside the markings, and the markings do not weaken the quality of the coated plywood or the like or the functioning of the impregnate coating in concrete casting. Neither does the impregnation impede the visibility of the markings on the web.

Rg. 3 shows a concrete casting mould 9, which consists of a rectangular plywood frame. Fig. 4 shows the cross section of the plywood board 10 that is used for the mould. According to the figures, the board 10 is coated on both sides with the laser-marked impregnate 8 that is manufactured according to Figs. 1 and 2. Adher- ing of impregnates 8 to the plywood board 10 is carried out by pressing them at a pressure of about 10-20 bar. Thus, both the outer surface of the moufd 9 that is visible on the outside and its inner surface are patterned with the figure 7, which is produced by the laser and which is preferably lighter than the basic shade of the mould. Fig. 5 shows the cross section of a high-pressure laminate 11 according to the invention, which is formed by five impregnate layers 8, 8' that are pressed together. The uppermost and lowest layers 8 of the laminate 11 are laser-marked impregnates that are manufactured by the process according to Fig. 1 , whereas the intermediate layers 8' are otherwise similar impregnates, although unmarked. The markings 7 are thus situated in the stacks opposite the laminate 11. In practice, the number of impregnate layers can vary from a few (2-5) to several dozen (e.g., 20-30), and the compression pressure that adheres them to each other can be about 50-100 bar.

Examples CO ₂ laser marking equipment was installed in a Pilot impregnating machine, wherein the kraft paper to be impregnated was marked on a moving web. The power density being 0.005-0.2 J/mm ² , the laser could neither carve a groove nor essentially evaporate the material. The laser made markings of a size of 6.5 x 6.5 mm on the brown paper. The marked spot was lighter than its surroundings. The laser marking was made on-line immediately after unwinding the raw paper and before impregnating with resin and air-drying.

By means of the test, it was ensured that the laser marking would not impede the impregnation process. The paper was examined on the spots of the laser mark- ings ("laser on") and outside the same ("without laser"). The results are shown in the following tables 1-2.

Table 1

Marking on the felt side of the paper Power 85%, power density 0.013 J/mm ²

Without laser Laser on

Grammage of paper gsm 83.4 82.9

Weight of impregnate- gsm 195.8 194.4

Amount of resin gsm 112.4 111.5

Percentage of resin % 57.4 57.3

Table 2

Marking on the wire side of paper Power 85%, power density 0.013 J/mm ²

Without laser Laser on Grammage of paper gsm 83.4 82.5

Weight of impregnate gsm 210.4 204.7

Amount of resin gsm 127.1 122.2

Percentage of resin % 60.4 59.7

On the basis of the results, it could be stated that the marking considerably influ- ences neither the grammage of the paper nor the uptake capability of the resin.

The basic analyses of a concrete casting film were made at the laser marking:

- Bull's eye and concrete casting tests, which measure the degree of maturing of the resin

- Water cooking, which measures the behaviour of the coating in casting - Water vapour test and water transmission, typical tests to assess the quality of the coating

- Assessment of the hardness of the surface by a lattice method. In laboratory tests, it was not observed that the laser marking should have an adverse effect on the behaviour of the coating in casting.

It is obvious to those skilled in the art that the applications of the invention are not limited to the above examples but may vary within the appended claims. For ex- ample, the marking device can consist of not only the CO ₂ laser printing head but also of another type of a laser. Nor are the applications of the invention limited to the concrete casting moulds, but other typical applications of fibre-based impregnates can also be considered, such as the floor and wall coatings of the boot spaces of trailer lorries, delivery vans, railway wagons or similar means of trans- port, the floor and wall coatings of industrial halls and storage spaces, open storage areas, loading platforms, racks and other working tops etc. The applications of the high-pressure laminates according to the invention include the back plates of furniture components that are provided with markings and decorative laminates that are provided with background markings. Furthermore, the marking does not have to cover the web throughout its width but information about or identifiers related to the time or place of manufacture or the manufacturer can be marked, e.g., on the edge of the web only.