WO2017105355A1

WO2017105355A1 - Method of manufacturing a decorative panel

Info

Publication number: WO2017105355A1
Application number: PCT/TR2015/050248
Authority: WO
Inventors: Ilter EREN; Ercan CELIK; Yigit TUNA
Original assignee: Kastamonu Entegre Agac Sanayi Ve Ticaret Anonim Sirketi
Priority date: 2015-12-15
Filing date: 2015-12-15
Publication date: 2017-06-22

Abstract

The present invention provides a methodology for forming a dye sublimation image of high printing quality on surfaces of wood based panels. The disclosed method produces a durable, clear, sharp image on wood based panel surface, which improves much of its physical and technical performance like sharpness of contours of design, color authenticity and tone consistency of used colors. In order to achieve these advantages, the present invention discloses a method wherein, the image on a transfer paper produced by digital inkjet printer with sublimable dyes is applied by pressure on the top of polyethylene coated wood based panel.

Description

METHOD FOR MANUFACTURING A DECORATIVE PANEL

FIELD OF THE INVENTION

The present invention relates to a new method of sublimation heat transfer printing on wood based panels. The image on the decorative paper is printed onto wood based panel by sublimation of dyes whereas, the images in prints are produced by a digital inkjet printer.

The present finding relates in general to print transfers using sublimation dyes, and in particular to a method of using prints produced by digital inkjet printers. Such prints are applied with a short cycle press apparatus on wood based panels, covered with polyurethane and hot coat lacquer.

BACKGROUND OF THE INVENTION

In order to fulfill the demand of customized wood based panels of customers, various methods and apparatus are used in the wood based panel industry. Digital printing is one of these methods, which is usually applied directly on the board followed by some lacquering or coating process for the purpose of surface protection.

Among the diverse printing systems, the "sublimation heat transfer printing" method reaches an extensive use in various sectors, such as textile or industrial sectors where the print is used on various surfaces such as, glass, metallic, ceramics or wood objects. Such method requires a mutual contact between the surface of the material to be printed which is coated with a special coating and the surface of the transfer paper already printed by a digital inkjet printer. Said wood based panel and transfer paper are pressed between two plates of pressure equipment which is heated up to the temperature whereas the effect of sublimation is reached, and the ink penetrates on the surface to be printed.

There are many printing techniques used to print images on surfaces such as wood, ceramic, metal or plastics. Most known methods are dye-sublimation digital printing, inkjet printing or color video print systems.

Color video print system is used due to its advantages to achieve advantages of enhancing efficiency, simplifying structure and operation, reducing cost and power consumption. But the print quality is not satisfactorily in comparison with other techniques.

Inkjet printer system has limited colors of the inks since each drop of ink is limited to a color. An inkjet print is composed of droplets of ink layered and scattered to simulate continuous tones, therefore the print quality is not consistent. Dye-sublimation printing system has many advantages over inkjet printing. Such as dye- sublimation printing system has a continuous-tone technology, where each dot can be of any desired color. This dyeing system produces true continuous tones appearing much like a genuine photograph and the prints are dry and ready to handle as soon as they exit the printer. The whole printing cycle is extremely clean as there are no liquid inks to clean up. These factors make dye-sublimation printing system is a more reliable technology over inkjet printing with more satisfactorily print qualities.

Digital printing is the most common method of printing in industrial applications due to advantages mentioned above. Sublimation dyes can be used in digital printing technology although they are known as sensitive to heat and pressure. There are many digital printing machines like; Epson, Mutoh or Mimaki. The most preferred one used in this invention, is Mimaki for its ease of use and fast and complete dye transferring properties.

Dye sublimation printing is a thermal process whereby color dyes are transferred from an ink ribbon into, the surface of a special substrate which is then laminated during the final stage of the process. This is a computer printing system which employs a printing process that uses heat to transfer dye onto materials such as plastic, card, paper or fabric. The dye makes the transition between the solid and gas states without going through a liquid stage. According to this technique images are firstly printed on sublimation paper and then the printed images are transferred to surfaces under pressure and heat at a proper time range. For this purpose sublimation dyes are used as coloring agents. Some studies should be carried out to determine appropriate heat, pressure and time parameters in accordance to the thickness of the surface, the printing is applied.

Sublimation dyes which are very popular in printing applications, are readily available in the market as inkjet ink, toner for laser printers or as ribbons for the thermal-transfer printing. Some dye-sublimation printers use cyan magenta yellow over-coating colors, which differs from the more recognized cyan magenta yellow and black colors in that the black is eliminated in favor of a clear over-coating. This over-coating is also stored on the ribbon and as a thin overcoating layer, protects the print from discoloration from UV light and the air.

US5643387 is related to printing images produced by color video printer on surfaces, mainly ceramic surfaces, which are capable of receiving and retaining dyes those are able to sublime. The application of the process on wood and wood based panels is missing.

EP 1650052 application relates to a process on sublimation heat transfer printing on various surfaces by using reduced pressure or vacuum chamber. According to this method the material to be printed and the print paper are placed between two plates of the equipment and one of these plates is enough to be heated in order to enable the sublimation heat transfer printing. Reduced pressure applied in this process renders this method of printing application non- feasible due to enhanced cost manufacturing caused by energy consumption and equipment needed.

US 20030192136 application is related to a methodology for forming permanent, abrasion- resistant images in sheet plastics which are imaged utilizing a dying process applied at elevated pressure and temperatures known as "dye-sublimation method". But it lacks of delivering a method of qualified printings on wood surfaces.

These known processes have not resulted in commercially successful imaged articles on wood surfaces. Moreover, many of the known dye sublimation printing methodologies previously applied to solid surfaces are so sensitive to variations in pressure, temperature, time, or other manufacturing variables, which resulted in unacceptable images or destroyed substrates. It still remains that, precise, vibrant durable images on wood panels is a challenging goal of the wood imaging industry to obtain smooth and defect free surfaces.

By using sublimation heat transfer printing method, uniformity of colors on the surface of the printed article is obtained, but satisfying penetration of the inks inside the substrates of the same articles is not always obtained. Especially the ink that applied to wood surfaces by known methods cannot be resorbed by wood totally.

There still exists a need to improve the known techniques and overcome the technical problems to obtain highly qualified wooden printed surfaces, which enables the maximum of dye transfer in process. A new method is needed for forming durable, clear, sharp images on solid panels by means of dye sublimation process that results in distortion-free application.

In the present invention, a new dye sublimation imaging method is applied on wood surface which completely obviate the unwanted results like; adhesion of the dye carrier to the substrate during imaging, distorted or shrunk images, under qualified surfaces or easily degraded images on surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Cross section view of wood panel with enhanced gloss. (Lacquered board panel)

FIG. 2 Short Cycle Press apparatus for sublimation heat transfer printing

FIG.3 View of pre-press steps for sublimation heat transfer printing followed by sublimation heat transfer printing method

Wherein;

1- Sublimation transfer paper

2- Digital inkjet printer

3- Printed transfer paper 4- Polyethylene polymer film

5- Wood panel having enhanced gloss (Lacquered board panel)

6- Polymer film coated wood panel

7- Press plates

8- Upper press block

9- Bottom press block

10- Pistons

11- Short-cycle (heat transfer) press

12- Overall media of pressed plate with PE film

13- Final product

14- Top coat lacquer

15- Base coat lacquer

16- Polyurethane hot melt layer

17- Melamine decorative paper

18- Medium Density Fiber Board (MDF)

DETAILED DESCRIPTION OF THE INVENTION

The principal object of the present invention is to provide an alternative method to transfer an image quickly and completely on hard surfaces such as wood based panels, especially on panels, having enhanced gloss mentioned as lacquered board panel.

The present inventor has discovered that prints produced by inkjet printers can be adequately transferred to wood panel surfaces having an appropriate coating to absorb the sublimable dyes therein. A favorable copy is obtained when proper heat and pressure are applied during a proper time period. With this method, maximum and unspoiled transfer of sublimable dye on surfaces is obtained which led to highly qualified board surfaces.

The present invention reveals a new method for manufacturing a decorative board panel. In this method, the transfer paper (1), wherein the image is applied by using digital printing (2), is placed on the polymer film coated wood panel (6) and pressed together under elevated temperature and pressure conditions so as to allow the sublimation dye to penetrate the polymer layer and the board upper coatings which enables the maximum of transfer and protection of coating layer.

Accordingly a new method of transferring an image is applied with a transfer paper and sublimable dyes onto a dye absorbent surface, wherein said surface is protected by covering with a polymer film which is capable of transferring the sublimable dye to dye absorbent surface.

In previously applied method, the printed paper was directly applied by means of pressure on panels to be transferred. However the images cannot be totally transferred to the panel surface and occasionally the images or colors are dithered, which is an unwanted phenomenon on the production line.

The invention comprises of general use of normal prints created with the use of sublimable dyes on sublimation transfer paper (1) by a typical digital inkjet printer (2), such as Mutoh or Mimaki, in order to obtain printed transfer paper (3) as a media ready to be used on the sublimation heat transfer printing process.

Referring to FIG. 2 which illustrates pre-press steps of the process, the additional materials also used in this process are multi-layer UV & moisture cured lacquered board panel (5) and polyethylene polymer film (4), which is used with the aim of covering of lacquered board panel (5). The present invention involves therefore a novel use of polymer film as a semi-permeable membrane which enhances the penetration of sublimable dyes on wood panels and so protecting the gloss characteristics of board surface.

Lacquered board panel characteristics can be seen on FIG. 1 consists of multilayers. For forming such a panel, firstly a layer of melamine decorative paper (17) is set on fiber board (MDF,PB) (18) to obtain melamine based layer which cannot absorb dye. Over this layer, a polyurethane hot melt polymer layer (16) is applied, subsequently upper side of the panel is coated with acrylic based, base coat lacquer (15) and upon this a top coat lacquer (14) is applied. The thicknesses of these layers are ranging between 30-80 micrometer (μιτι) preferably 50-60 micrometer. The polyurethane and acrylic based layers are known as absorbing surface layers that absorb sublimation dyes.

Once the printed transfer paper (3) and lacquered board panel (5) covered with the polymer film (4) the obtained wood based panel (6) is ready for the sublimation heat transfer printing. The required press parameters are set in the temperatures ranging between 120 to 220°C preferably 170 to 200°C and most preferably 190 °C at press plate (which is directly applied to the surface. The pressure applied on the surface ranges between 20 to 50 kg/cm², preferably 30 to 40 kg/cm² and the time interval of pressure and heat application on surface ranges between 10 - 80 sec. Having set said parameters wood based panel and the sublimation transfer paper are fed into the short-cycle press (11) as seen in FIG. 2 and 3.

Referring in particular to FIG. 2 showing the press components, whereas upper press block (8) which is pushed by pistons (10) compresses the wood based panel and the transfer paper with the help of bottom press block (9). In the meantime, recirculating heat transfer fluid inside the press blocks provides the required isothermal conditions. With press parameters mentioned above which provides the effective conditions of the present invention dyes undergo the effect of phase change called as "sublimation" and the cured lacquer coating on the wood based panel captures the already sublimed dyes. Once the pressing process has been completed, upper press block (8) moves back to its initial position by means of pistons. As can be seen in FIG. 3, the overall media of pressed plate with polyethylene film (12) shown is ready to be taken out of the short-cycle press (11). When the latest is discharged, the printed transfer paper (3) and the polyethylene film (6) are already adhered to each other and mutually to the board during the process, which are to be removed to obtain the final product (13) of decorative panel.

By application of the present invention method the transfer paper containing sublimation dye is pressed onto with the four different layers. These layers are top coat layer (14), base coat layer (15), polyurethane based layer (16) and melamine decorative paper layer (17). Additionally a polyethylene layer is applied on the surface of lacquered board panel (5). During the process the penetration is enhanced by the polyethylene film as semi permeable membrane media which enables to produce printings with sharp contour and saturated original colors. This method is comprised of preparation of required transfer paper and wood based panel for the application and hot press operation technique by working principle of short press cycle.

In the present invention, short-cycle press has two main elements as upper plate and lower plate. In the process, the panel is placed on the lower plate and upper plate presses the panel with the help of lower plate in a required temperature and time range.

Three different crucial parameters, which are temperature, pressure and time, can be modified during the operation according to the needs of the process to obtain printings of required quality. In addition to these parameters the thickness of polymer based films can be varied to achieve the best result with regard to sublimation and surface smoothness. To achieve best conditions for the best results the parameters were varied accordingly, which are to be seen in experimental part and tables.

Accordingly, the UV cured wood based panel which is in the present invention exemplarily lacquered board panel, that is covered with polyethylene film is first taken to the press loading unit, and then sublimation dye paper placed above. Afterwards, the board is static charged to fix the decorative transfer paper and loaded inside the press. With the appropriate combination of the press parameters, the dye inside the paper penetrates in to the wood based panel lacquer.

During this process heat is applied to a temperature range that the ink of drawings of the print paper undergoes the effect of sublimation. Thereby the sublimed dyes deposit itself on the surface of the material to be printed. The action of the sublimation heat transfer printing takes place under the conditions of increased pressure and temperature.

In order to understand the invention and to see how it may be carried out in practice, several specific embodiments are given below.

In one embodiment, the method of the present invention comprises following steps;

a. A transfer paper is printed by using sublimation dyes with an inkjet printer,

b. Lacquered board panel covered with a polymer film, preferably with polyethylene film, is provided c. In step a) prepared transfer paper is put on the top of in step b. prepared coated lacquered board panel

d. Heat and pressure is applied for appropriate time period,

e. The transfer paper with polyethylene film adhered on it, is removed from the top of the lacquered board panel.

The present inventor assumes that, the polymer film is serving as a semi-permeable membrane enhancing the penetration of sublimable dyes while protecting the gloss characteristics of wood based panel surface. Specifically used polyethylene film layer's thickness ranges between 15- 100 μιτι, preferably 15-50 μιτι and most preferably 25 μιτι.

In a further embodiment, the lacquered board panel has a transparent, smooth surface for the completeness of dye transfer on wood based panel. The lacquered board panel surface enables obtaining smooth decorative surfaces by avoiding orange peel like appearance.

The lacquered board panel is made of different layers formed by known techniques. Said layers are comprising a wood panel or Medium Density Fiber board (MDF, PB) (18) coated successively with melamine decorative layer (17), polyurethane hot melt layer (16), base coat lacquer layer (15) and top core lacquer layer (14) on top. Said lacquer layers are preferably acrylic based polymeric layers. The underside of the wood panel or MDF, PB panel (18) is preferably coated with melamine decorative paper (17).

In a further embodiment, a short-cycle press is used during heating a nd pressing step, which is a conventionally used pressure equipment in the wood based panel manufacturing sector.

To show the invention of the method; examples are given below. These examples are given to make the present invention illustrative. EXAMPLES:

EXAMPLE 1: Process for acquiring polyethylene coated wood based panel

1. A decorative transfer paper is prepared by using sublimation dyes with inkjet printer

2. Lacquered board panel is prepared by UV curing of melamine and polyacrylate coated MDF. 3. Lacquered board panel's top surface is coated with polyethylene polymer film.

4. Short-cycle press equipment's upper plate temperature is set at 190 °C.

5. Lacquered board panel which is obtained at step 2 is put on the bottom press plate.

6. Decorative transfer paper with sublimable dyes on it, prepared at step 1, is put on the lacquered board panel 7. Upper press plate and bottom press plate are pressed together with 30 kg/cm² pressure applied on lacquered board panel and hold for 20-25 sec.

8. The press plated drawn apart and polyethylene layer with stuck decorative paper is striped from top surface of the lacquered board panel to have the final product.

The polymer film used for coating lacquered board panel's top surface has a thickness of 15-50 μιτι, preferably 25 μιτι.

EXAMPLE 2: Process for acquiring uncoated wood based panel

The same procedure of Example 1 except step 3 is applied. The lacquered board panel is not coated with polyethylene polymer film.

TEST METHODS:

Compared test results of example 1 and 2 are given in Table 1 and 2.

1. Gloss Test

For determination of the gloss difference of coated and uncoated panels, gloss test is performed by using Gloss meter.

By this method, the reflected gloss of the test panel is measured and the obtained result is compared with a reference as a numerical value.

This test is performed in compliance of TS EN 14323 standards.

Results of Gloss Test

Gloss is measured by using 20° geometrical method. If the result is equal or higher than the 70 unit value, 20° geometrical method is used. 70 unit value corresponds to high reflected gloss. Gloss degree of the sample corresponding to reference sample is given on Table 1 and 2. It can be seen that, the gloss of coated panel is higher compared to uncoated panels results. The colors of decorative figures of the coated panel are sharp, consistent and much clearer.

2. Scratch Resistance Test

For determination of the scratch resistance of wood panel, panel sample having 100 mm x 100 mm dimensions is prepared, cleaned with acetone and fixed on the table. Two perforators with a distance of 1-2 mm are put on the panel surface and 1 N pressure is applied. The pressure is enhanced up to 4 N. increasing 0.5 N in each level.

The pressure is applied on the surface for 2 hours. After releasing the pressure 24 hours waited and observed scratch is measured and evaluated.

This test is performed in compliance of TS EN 14323 standards.

Results of Scratch Resistance Test

According to pressure applied on the surface of the panel the scratch dimension formed on the panel is reported and compared with other test results.

According to test results at Table 1 and 2, it can be seen that, the coated panel samples are much more resistant to scratch. The most preferred conditions according to tables are, the samples that are formed by using 190 °C, 30 kg/cm² pressure applied in 20-25 seconds.

3. Surface Resistance to Micro scratching Test

This test is intended to be carried out on a part of finished panel for determination of the mechanical performance of panel with regard to resistance to micro scratching.

For this purpose, the test panel surface is fixed on table. A circular scrub material fixed on a holder impacts on the panel surface with a defined load. Table and holder move to each other with defined frequencies. The panel surface is exposed to the scrub material for predetermined number of rubs.

This test is performed in compliance with TSE-CEN-TS 16611 procedure A standards.

Results of Surface Resistance to Micro scratching Test

The changes of the panel surface are determined by gloss measurement and visual assessment. The gloss change is calculated for the test surfaces according to formula;

AR'= ¾^ * 100 (%),

Wherein,

R: gloss value

AR': gloss value difference R : mean gloss va lue at initia l state;

R'F: gloss value after finishing the test;

According to test results shown at Table 1 and 2, su rface resistance of the polyethylene film coated panel to micro scratching is en hanced compared to uncoated pa nels. The best results are obtained with the samples which are produced under the conditions of 190 °C and 30 kg/cm² pressure applied for 20-25 seconds.

The test measu rements are performed under 30 kg/cm² pressu re. Below this pressu re the polyethylene layer is not sufficiently ad hered on the decorative paper to affect subli mation transfer. Over this pressu re the polyethylene polymer is stuck on the panel as difficult to remove and some parts of the decorative panel is da maged . Ta ble 1 and 2 a re the resu lts of examples obtained from the samples that a pplied 30 kg/cm² pressu re.

Table 1. Test Results of Polymer Coated Lacq uered Boa rd Panel

in this condition partially the polymer film stuck onto panel surface

-test results cannot be obtained due to damaged polyethylene film Table 2. Test Results of Uncoated Lacquered Board Panel.

-test results cannot be obtained due to damaged polyethylene film

Claims

1. A method of transferring an image prepared from a transfer paper and sublimable dyes onto a dye absorbent surface of wood based panel, wherein said wood based panel's surface is covered with a polymer film capable of transferring said sublimable dye to the said wood based panel's surface.

2. A method according to claim 1, wherein said wood based panel is preferably UV cured lacquered board panel.

3. A method according to claim 1, wherein said polymer film is polyethylene, polypropylene or polyester film, preferably polyethylene film.

4. A method according to claim 3, wherein said polymer film has a thickness of 15-100 μιτι. preferably 15-50 μιτι, most preferably 25 μιτι.

5. A method according to claim 1, wherein said absorbent surface is comprised of acrylic based polymer layers on the top and polyurethane layer underneath.

6. A method according to claiml, wherein said wood based panel comprises melamine decorative paper under said absorbent surfaces.

7. A method according to claim 1, wherein said images on transfer paper are prepared with sublimable dyes applied preferably by means of digital inkjet printer.

8. A method according to claim 1, wherein said transferring of an image comprises the steps; i: coating the wood based panel with polyethylene film

ii: placing the transfer paper with an image on the wood based panel,

iii: heating and pressing the printed transfer paper and polyethylene film layer coated wood based panel together.

9. A method according to claim 8, wherein in step iii applied pressure is carried out between 20-50 kg/cm², preferably 30-40 kg/cm², most preferably 30 kg/cm².

10. A method according to claim 8, wherein in step iii applied heating is carried out at temperatures between 120-220 °C, preferably 170-200 °C, more preferably 190 °C.

11. A method according to claim 8, wherein in step iii applied heating and pressure proceeds between 10-80 seconds, preferably 20-25 seconds.

12. A process to prepare a printed wood based panel according to preceding claims comprising the steps;

i) providing a lacquered board panel, ii) coating said lacquered board panel with a polymer film,

iii) preparing a transfer paper with an image by a digital inkjet printer using sublimable dyes, iv) in step iii prepared transfer paper with image is set on the lacquered board panel, v) the image is printed applying 20-50 kg/m² pressure, at temperatures between 120-220 °C in 10-80 seconds,

vi) stripping the transfer paper and polymer film from lacquered board panel's surface.

13. A process according to claim 12 comprising the steps;

i) providing a lacquered board panel,

ii) coating said lacquered board panel with a polyethylene film,

iii) preparing a transfer paper with an image by a digital inkjet printer using sublimable dyes, iv) in step iii prepared transfer paper with image is set on the lacquered board panel, v) the image is printed applying 30 kg/cm² pressure, at 190 °C in 20-25 seconds,

vi) stripping the transfer paper and polyethylene film from lacquered board panel's surface.

14. A process according to claim 12 wherein said process is carried out with a press apparatus preferably with a short cycle press apparatus.