Abstract:
A method for producing a panel is disclosed. The method includes the step of applying steam on a dry powder layer on a core. Thereafter is a heat and pressure applied to the powder layer in order to bond the powder together.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Application No. 61/349,950, filed on May 31, 2010. The entire contents of U.S. Provisional Application No. 61/349,950 are hereby incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure generally relates to a method for producing a fibre-based building panel, preferably a floor panel, and to a building panel produced by said method. 
       BACKGROUND 
       [0003]    A new type of panel called Wood Fiber Floor (WFF) is disclosed in WO2009/065769, which shows both products and methods to produce such a panel. Further methods and production equipments are disclosed in WO2009/124704. 
         [0004]    The WFF floor panels are produce by applying a dry powder mix on a HDF core. The powder mix is bonded together under heat and pressure to form a decorative surface layer. 
         [0005]    In order to stabilize the dry powder mix the production methods in WO2009/065769 or in WO2009/124704 (see page 15, line 15-21;  FIG. 3 ) uses spraying of pure water or water with additives. 
         [0006]    The entire contents of WO2009/065769 and WO2009/124704 are hereby incorporated by reference herein, and with a specific reference to page 15, line 15-21 and FIG. 3 of WO2009/124704. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    An objective of embodiments of the disclosure is to provide production methods that are more effective than the present known technology. Another objective is to produce panels with a more uniform colour or a more controlled colour variation and/or pattern. 
         [0008]    When pressing a surface layer out of powder mix—such as a WFF mixture disclosed in WO2009/065769 or in WO2009/124704—one problem is to avoid that the powder mixture completely or partly blows off when the board is handled in the line before pressing and/or blow out of the press when the air is evacuated due to the closing of the press. 
         [0009]    The known solutions to stabilize the powder by using spraying of water has the disadvantage that it is difficult to control the distribution of the water and to avoid water drops unintentionally falling down on the powder layer from the spraying unit. 
         [0010]    An uneven water distribution and/or unintentional water drops normally have a negative effect of the visual as well as technical properties of the product. Furthermore, a waiting time to let the water penetrate into the powder before entering the press slow down the press cycle and to total out put from the production line is lowered. 
         [0011]    A first aspect of the disclosure is a method of manufacturing a panel comprising a core ( 1 ) and a decorative surface layer ( 4 ) comprising the steps of:
       Applying a dry powder layer ( 2 ) on a core ( 1 ); and   Applying steam to the powder layer.       
 
         [0014]    The steam is preferably a water steam, most preferably a substantially pure water steam, even though the steam may comprise one or more additives. Examples of additives are wetting agents, releasing agents and/or colour additives. 
         [0015]    The dry powder layer is preferably a mix of fibres, preferably wood fibres, and binder(s). The powder layer may also include wear resistant particles, preferably aluminium oxide. The core is preferably a wood fibre based core, preferably an HDF panel. 
         [0016]    A second aspect of the disclosure is a method of manufacturing a panel comprising a core ( 1 ) and a surface layer ( 4 ) with a designed pattern comprising the steps of:
       Applying a dry powder layer ( 2 ) on a core ( 1 ); and   Creating a pattern by applying steam to parts of the powder layer or applying steam unevenly (e.g., over all of the powder layer, but in different amounts) over the powder layer.       
 
         [0019]    The steam in the first and the second aspect is preferably a water steam, most preferably a substantially pure water steam, even though the steam may comprise one or more additives. The steam may be a mist or the gas phase of water (water vapour), preferably a saturated vapour and most preferably a saturated vapour mainly comprising water. 
         [0020]    Preferred embodiments of the first and second aspects of the disclosure are disclosed below. 
         [0021]    A third aspect of the disclosure is a panel produced according to any one the aspects above. 
         [0022]    The methods above may be used to any production of a building panel in which a dry powder layer is applied to a core. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The disclosure will in the following be described in connection to exemplary embodiments and in greater detail with reference to the appended exemplary drawings, wherein: 
           [0024]      FIG. 1  Illustrates a production line and a method according to an embodiment of the disclosure; 
           [0025]      FIGS. 2   a - b  Illustrate a method for creating a design according to an embodiment of the disclosure; 
           [0026]      FIG. 3  Illustrates a method for creating a design according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0027]    In  FIG. 1  an embodiment of a production line is disclosed for producing a panel  5  with a decorative layer  4 . A dry powder mix  2  is applied by scattering on a core  1 , preferably an HDF core. The powder mix is stabilized by applying steam  3  before the powder mix is bonded together by applying heat and pressure in, for example, a press  9 . If a pattern is desired, the steam may in one embodiment, be applied through a template  6 , preferably rotating. In a preferred embodiment also a balancing layer  7  is applied to the core. 
         [0028]    In the methods according to the present disclosure preferably the same scattering and pressing units as disclosed in WO2009/065769 or in WO2009/124704 are used. 
         [0029]    In one embodiment the steam is applied by using a steam box  8 , a box with one or more outlets at the bottom for steam, positioned above the transportation belt. The box preferably extends across the panel with a uniform width. An even moisture distribution is applied over the surface of the scattered powder layer  2 , when the board pass under the steam box. Since the steam penetrate into the powder very effectively it is possible to immediately move the board into the press and close the press  9 . 
         [0030]    A suitable steam box is either fed by an external steam generator or the steam is generated in the steam box itself. It is suitable that that the steambox is equipped with one or several layers of nets for example mesh and/or sheets with holes to even out the steam concentration close to the powder layer. 
         [0031]      FIGS. 2   a  and  2   b  shows how an uneven distribution of moisture  21 , obtained by applying steam  3  through, e.g., a nozzle  25 , can be used for design effect purpose. Different amount of moisture  21  in different parts of a single colour powder, but not yet pressed, surface gives a visual colour difference of the different parts. By controlling where on the surface the moisture content is higher a wanted design effect  22  can be generated (see  FIG. 2   b ) in the pressed surface  24  of the panel even if only one unicolored powder layer is applied on the core  1 . 
         [0032]    By controlling the relative movement between a core  1  with the powder mix layer  2  and one or several steam outlets a controlled variation of the content of moisture  21  in the powder can be achieved. This variation of moisture content will after pressing be visible as color differences  22  on the ready surface  24 . 
         [0033]    One or several of the steam outlets could be fixed on a robot arm and their position in relation to the scattered board could then be controlled in all directions. 
         [0034]    The steam outlets  41  could be positioned in a rotating device, preferably a steam pipe  40 , to generate a controlled moisture variation  42  in the powder layer  2 , see  FIG. 3 . 
         [0035]    As a non-limiting example, the steps for producing a WFF board could be as follows:
       1) Place a balancing layer, e.g. a paper impregnated with a thermosetting resin or a mixture of wood powder and thermosetting resin is placed on a transportation belt. A typical balancing layer is two sheets of DKB 140 paper.   2) Place a wood fibre board, typically an about 10 mm thick HDF board with a density of typically about 900 kg/m3, on top of the balancing layer.   3) Moving the balancing layer and board in a speed of 1-10 m/min (a typical value is about 3 m/min) under a scattering machine were a premade mixture of wood fibres, binders, hard particles and pigments are scattered on top of the board. The powder applied can be in the range of about 100-1000 g/m2. Typical value is about 700 g/m2.   4) Moving the board, with a balancing layer on the backside and a scattered powder layer on the top side, through a steam box with even steam concentration in the speed of 1-10 m/min (typical value is about 3 m/min) where steamed water, with or without additives, penetrates into the powder and stabilize it to improve further handling and to avoid that the powder blows out when the press is closing. Typical amount of moisture applied by the steam box is 3 g/m2.   5) Bringing the board with a balancing layer on the backside and a scattered and steam stabilized powder layer on the top side into the press.   6) Closing the press, and curing the thermosetting resin in the balancing layer and the powder layer under heat and pressure. Typical press parameters are 30 seconds pressing (range is, for example, 8-60 seconds). 40 bars pressure (range is, for example, 30-60 bars) may be applied on the board. Temperature of typically about 170 degrees C. (range is, for example, 150-220 degrees C.) on the top and bottom press plates. The pressing surfaces of the press plates can be even or have structure. Structure depth typically about 0.5 mm (range for example about 0-1.5 mm)       
 
         [0042]    In an alternative example also one or more paper sheets are applied after step 4. 
         [0043]    An Example of a Production of a WFF Board with a Designed Pattern by Controlled Uneven Moisture Distribution:
       1) Place a balancing layer, e.g. a paper impregnated with a thermosetting resin or a mixture of wood powder and thermosetting resin is placed on a transportation belt. A typical balancing layer is two sheets of DKB 140 paper.   2) Place a wood fibre board, typically an about 10 mm thick HDF board with a density of typically about 900 kg/m3, on top of the balancing layer.   3) Moving the balancing layer and board in a speed of about 1-10 m/min (typical value is about 3 m/min) under a scattering machine were a premade mixture of wood fibres, binders, hard particles and pigments are scattered on top of the board. The powder applied can be in the range of about 100-1000 g/m2. Typical value is about 700 g/m2.   4) Moving the board, with a balancing layer on the backside and a scattered powder layer on the top side, under one or several steam outlets that also might move sideways and open and close during the board passing time, in the speed of about 1-10 m/min (typical value is about 3 m/min) where steamed water, with or without additives, penetrates into the powder in an uneven but controlled way to obtain a variation in the moisture content in the powder layer.   5) Bringing the board with a balancing layer on the backside and a scattered and steam stabilized powder layer on the top side into the press.   6) Closing the press, and curing the thermosetting resin in the balancing layer and the powder layer under heat and pressure. The different moisture content resulting in a visible design effect in the ready pressed board. Typical press parameters are about 30 seconds pressing (range is, for example, about 8-60 seconds). About 40 bars pressure (range is, for example, 30-60 bars) may be applied on the board. Temperature of typically about 170 degrees C. (range is, for example, about 150-220 degrees C.) on the top and bottom press plates. The pressing surfaces of the press plates can be even or have structure. Structure depth typically value about 0.5 mm (range for example about 0-1.5 mm)       
 
         [0050]    In an alternative example also one or more paper sheets are applied after step 4.