METHOD FOR THE PRODUCTION OF MULTILAMINAR WOOD SHEETS THAT REPRODUCES THE GRAIN OF NATURAL WOOD ESSENCES

Abstract

 A method for producing a multilaminar wood sheet with patterns comprises the steps of: depositing a printing mixture on one or more base wood sheets to be printed; controlling penetration and diffusion of the printing mixture on said one or more base wood sheets to be printed by applying a set pressure value to the printing mixture, thus obtaining one or more printed wood sheets; forming a block of sheets comprising a plurality of printed wood sheets; cutting the block of sheets to obtain the multilaminar wood sheet.

Description

[0001] The invention relates to a method for producing a multilaminar wood sheet, in particular a multilaminar wood sheet that simulates the natural grain and pores of wood.

Background of the invention

[0002] As known, in the wood industry, multilaminar wood sheets are increasingly used for veneering.

[0003] In order to make the multilaminar wood sheets, the trunks of low-grade types of trees are peeled in a circular manner. The sheets obtained are preferably but not necessarily bleached and subsequently dyed (to obtain dyed sheets) using a dye bath with water-soluble dyes. The dyed sheets are dried and then glued onto one another to obtain a parallelepiped-shaped block. They are then pressed in a mould and when the glue has dried, the block of wood that is thus obtained is cut to obtain multilaminar wood sheets.

[0004] In order to improve the faithfulness of reproduction of natural wood veining, modifications have been made to the process described above using different methods; in particular, it has been found to be possible to obtain an improvement by modifying the surface of the dyed sheets by decorating the dyed sheets by dyeing.

[0005] One method for making prior art decorated multilaminar wood sheets is disclosed in document EP 1 275 481 B1.

[0006] In order to control the penetration and the diffusion of the colour in the production of multilaminar wood sheets decorated according to this method, it is necessary to keep the temperature of the printing mixture at a substantially constant value, which depends both on the features of the sheet of wood to be printed and on the chemical and physical properties, for example the pH, of the colouring agent used. In particular, this temperature varies in a range comprised between 30° and 90°C depending on the pH of the dye.

[0007] More in detail, it is known to maintain the temperature of the printing mixture in a range comprised between 50° and 90°C to obtain good penetration of the colouring agent into the wood. To obtain a blander penetration effect, the temperature is maintained in a range between 30 and 50°C.

[0008] Known methods, although they enable multilaminar wood sheets to be obtained that are able to simulate partially the natural grain of most types of wood existing in nature, do have some drawbacks.

[0009] One drawback of the prior art is the impossibility of obtaining penetration of the colouring agent into the sheet of wood that is greater than 0.1 mm. In fact, even by increasing the temperature of the printing mixture to 90°C, the colouring agent is unable to penetrate to a depth greater than 0.1 mm into the sheet of wood, not enabling the natural pores and grain of wood to be reproduced faithfully.

[0010] Another drawback of the prior art is the complexity thereof. In fact, the need to continuously control the temperature of the printing mixture that has to be maintained at a constant temperature to enable the colouring agent to penetrate into the sheets of wood complicates the production process.

Summary of the invention

[0011] The object of the present invention is to provide a method for producing multilaminar wood sheets that overcomes the drawbacks of the prior art.

[0012] Another object is to provide a method for producing decorated multilaminar wood sheets that enables the colouring agent to penetrate more than 0.1 mm into the printed sheet of wood.

[0013] Still another object is to provide a method that improves and simplifies making a multilaminar wood sheet with patterns.

[0014] A still further object of the present invention is to make multilaminar wood sheets that reproduce with great accuracy the grain of natural wood, reducing waste and speeding up the process.

[0015] Such objects and still other objects are achieved by a method as specified in the first claim attached to this description.

Short description of the drawings

[0016] The invention can be better understood with reference to the attached drawings that illustrate one embodiment thereof by way of non-limiting example in which:

Figure 1 is a block diagram showing some steps of the method according to the present invention;

Figure 2 shows a side view of a roller printing system that is usable for printing a pattern on sheets of wood;

Figure 3 illustrates the printing depth reached in a sheet of wood printed with a printing mixture having 80 mPas viscosity, applying pressure of 2 kg/cm²;

Figure 4 illustrates the surface of a multilaminar sheet obtained with the method according to the present invention.

Detailed description of the invention

[0017] The present invention provides a method for producing multilaminar wood sheets with patterns, in particular multilaminar wood sheets that simulate grain and pores of natural wood.

[0018] As illustrated in figure 1, the method comprises the steps S1-S3 that can be performed along a work line.

[0019] The method comprises a printing step S 1 of printing on one or more base wood sheets, obtaining one or more printed wood sheets.

[0020] The base wood sheets to be printed can comprise one or more sheets of stripped wood obtained by stripping and cutting the trunk.

[0021] The base wood sheets can comprise one or more sheets of bleached wood obtained by stripping a subsequently bleaching a trunk.

[0022] The base wood sheets can comprise one or more sheets of dyed wood, in particular sheets of dyed wood with the basic colour that it is desired to give to the multilaminar wood sheet to be produced.

[0023] The base wood sheets can comprise one or more sheets of bleached and dyed wood.

[0024] The printing step S 1 deposits a printing mixture onto a surface of one or more base wood sheets to create a basic pattern on this surface. During the printing step S1, penetration and diffusion of the printing mixture into one or more base wood sheets is controlled.

[0025] The penetration and the diffusion of the printing mixture are controlled by applying a set printing pressure value to a set printing mixture. In particular, the printing pressure is applied during depositing of the printing mixture to the surface of the base wood sheet. The applied printing pressure can be comprised between 0.5 kg/cm² and 30 kg/cm², more in particular, printing pressure is comprised between 1 kg/cm² and 10 kg/cm². The penetration of the printing mixture is proportional to the printing pressure.

[0026] Controlling the printing pressure enables the penetration of the printing mixture into the sheet of wood to be controlled, in fact, less applied printing pressure is matched by less penetration of the printing mixture, whereas greater printing pressure is matched by greater penetration. In particular, printing pressure is the same over the entire surface of the sheet.

[0027] Varying the printing pressure can lead to penetration of the mixture to a depth comprised between 0.01 and 0.4 mm, in particular between 0.1 and 0.3 mm. Some tests have shown that applying a printing pressure of 20 kg/cm² leads to a penetration depth of about 0.3 mm, with a printing mixture at greater viscosity (300 mPas), whereas pressure of 1 kg/cm² permits penetration to a depth of about 0.15 mm, with a printing mixture with reduced viscosity (75 mPas).

[0028] The printing mixture used in the printing step S1 comprises a mixture of micronized pigments and a polymer binder. The mixture can be water-based.

[0029] The micronized pigments have a D₅₀ that is less than or the same as 1 µm. In other words, the printing mixture comprises micronized pigments with a median diameter of the particles that is less than or the same as 1 µm. The pigments are of an organic or inorganic nature.

[0030] The printing mixture is obtained using a dyeing system based on 8 pigments, like, for example: PY 74, PR 254, PB 15:3; PBK 7, PW 6, PO 5, PV23, PG7.

[0031] As indicated above, the printing mixture comprises a polymer binder, in particular a water-soluble polymer binder.

[0032] The polymer binder is a styrene-acrylic polymer in water emulsion with neutral pH.

[0033] After the printing step S1, the method entails a drying step Sr, in which the polymer binder present in the printing mixture present on the printed wood sheets is subjected to physical drying, for example in a dryer at a temperature of about 80° C. Drying occurs without using cross-linking catalysts.

[0034] Drying can also occur at ambient temperature, but drying with supply of heat is preferable, which enables fast drying of the printing mixture to be obtained in a time of the order of just a few minutes.

[0035] During the printing step S1, the penetration and diffusion of the printing mixture in one or more base wood sheets can be controlled by controlling the viscosity of the printing mixture. In particular, with the same applied printing pressure, an increase in the viscosity of the printing mixture leads to a decrease in the depth of penetration of the printing mixture into each printed wood sheet, whereas a decrease in the viscosity leads to an increase in the depth of penetration of the printing mixture.

[0036] The penetration of the printing mixture is inversely proportional to the viscosity of the printing mixture.

[0037] The viscosity of the printing mixture can be comprised between 50 and 400 mPas. It is possible to modify the viscosity of the printing mixture by modifying the quantity and type of polymer binder used. Further, it is possible to modify the viscosity by modifying the water content present in the binder.

[0038] With the same viscosity, the penetration of the printing mixture increases as the pressure increases and decreases as the pressure applied during the printing step decreases.

[0039] The method further comprises a step S2 that forms a block of sheets by superimposing the printed sheets, each glued, in particular on both sides. The block of superimposed sheets is placed in a suitable shaped mould and is then pressed.

[0040] Physical drying of the polymer binder without the use of cross-linking catalysts is indispensable for making correct gluing of the sheets possible.

[0041] In fact, the inventors of this application have discovered that, by using cross-linking catalysts, a film forms on the surface of each sheet that cannot be permeated by the adhesives that are usable to glue the sheets, making effective gluing substantially impossible, whilst by drying the polymer binder without the use of cross-linking catalysts, the film that forms on the surface of the sheets is permeable to the adhesives that are usable for gluing, making effective gluing of the sheets possible.

[0042] After formation of the block of sheets has been completed, in particular after the glue has been left to harden, the method entails a cutting step S3 of cutting the block of sheets to obtain one or more multilaminar wood sheets.

[0043] Cutting can occur along different cutting planes depending on specific needs and the pattern that it is desired to be obtained.

[0044] In the printing step S1, the temperature of the printing mixture can be about 5°C or more. For example, the printing temperature can be comprised between 10°C and 20°C.

[0045] The printing step S1 is performed by a printer 1, in particular a printer that implements rotogravure printing technology, using a pressure roller 2 and a printing roller 3. The printing roller 3 is a photo-engraved roller that is able to apply the printing mixture to the base wood sheet according to a desired pattern.

[0046] At the same time as depositing the printing mixture, the pressure roller 2 applies the printing pressure at a set value on the basis of the penetration of the printing mixture that it is desired to be obtained.

[0047] The pressure can be controlled by dynamometers.

[0048] Printing pressure not only enables the penetration of the printing mixture along a direction perpendicular to the surface of the base wood sheet to be controlled, but also the diffusion of the printing mixture to be controlled, in particular the undesired diffusion that occurs along directions that are transverse to the thickness of the base wood sheet.

[0049] Applying pressure thus enables controlled and precise penetration to be obtained as it is devoid of undesired diffusion of the printing mixture, which results in more thorough and precise simulation of the grain of natural wood in multilaminar wood sheets.

[0050] In addition, even fast drying of the polymer binder, for example of siccative type, improves the quality of the print obtained, preventing the undesired diffusion of the printing mixture.

[0051] Accordingly, the diffusion of the printing mixture can be controlled by controlling the viscosity of the mixture and the pressure applied by the rollers to the base wood sheets.

[0052] In the light of what has been set out above, it is clear that the method according to the present invention achieves the set objects.

[0053] In fact, the method, owing to the application of the printing pressure, enables the printing mixture to penetrate the printed wood sheets to a depth of more than 0.1 mm.

[0054] The method disclosed improves the creation of a multilaminar wood sheet. In fact, again owing to the application of the printing pressure, it is possible to obtain a multilaminar wood sheet with patterns provided with the desired features without the need to adjust the temperature of the printing mixture, accelerating the process, thus reducing the steps of the process and the checks to be performed. Reducing steps and checks also leads to a process that is less affected by variables that are difficult to control and thus to a reduction in rejects.

[0055] Lastly, owing to the control of the printing pressure and of the viscosity of the printing mixture, the aesthetic performance and reproducibility of the end product are greater than those of known technology.

Claims

1. Method for producing a multilaminar wood sheet with patterns having shapes and arrangements defined on the faces of said multilaminar wood sheet, said method comprising the steps of:

a. printing a basic pattern on a surface of one or more base wood sheets to be printed, said printing comprising depositing a printing mixture and controlling penetration and diffusion of said printing mixture on said one or more base wood sheets to be printed, obtaining one or more printed wood sheets;

b. forming a block of sheets comprising a plurality of printed wood sheets;

c. cutting said multilaminar wood sheet from said block of sheets;

said controlling the penetration and diffusion of said printing mixture in said one or more base wood sheets to be printed being characterized in that it comprises applying a printing pressure of preset value to said printing mixture during said printing.

2. Method according to claim 1, wherein said controlling the penetration and diffusion of said printing mixture further comprises controlling viscosity of said printing mixture.

3. Method according to claim 1 or 2, wherein said printing mixture comprises at least one pigment with D₅₀ less than or equal to 1µm and a polymer binder.

4. Method according to any one of the preceding claims, wherein said at least one micronized pigment comprises one or more pigments chosen from a group comprising PY 74, PR 254, PB 15:3; PBK 7, PW 6, PO 5, PV23, PG7.

5. Method according to claim 3 or 4 comprising, after said printing, drying said polymer binder present in said printing mixture without using cross-linking catalysts.

6. Method according to claim 5, wherein said drying occurs by supplying heat.

7. Method according to claim 6, wherein said drying occurs by using a flow of hot air at a temperature of about 80° C.

8. Method according to one of claims 3 to 7, as appended to claim 2, wherein said controlling said viscosity of said printing mixture comprises modifying a quantity of said polymer binder.

9. Method according to claim 7, wherein said polymer binder comprises a styrene-acrylic polymer in a water emulsion with neutral pH.

10. Method according to any one of the preceding claims, wherein said applying said printing pressure occurs during said depositing said printing mixture.

11. Method according to any one of the preceding claims, wherein said printing pressure is comprised in a range from 0.5 kg/cm² to 30 kg/cm², said penetration of said printing mixture being proportional to said printing pressure.

12. Method according to any one of the preceding claims, wherein said penetration of said printing mixture is comprised between 0.01 and 0.4 mm.

13. Method according to any one of claims 2 to 11, wherein said viscosity of said printing mixture is comprised between 50 and 400 mPas.

14. Method according to any one of the preceding claims, wherein said one or more base wood sheets comprise at least one of: a peeled wood sheet, a bleached wood sheet, a dyed wood sheet, a dyed bleached wood sheet.

Drawing