WO2013113589A1

WO2013113589A1 - Method for producing coated wood fiber material plates

Info

Publication number: WO2013113589A1
Application number: PCT/EP2013/051172
Authority: WO
Inventors: Detlef Krug; Marco MÄBERT; Detlef Kleber; Thorsten Pauen
Original assignee: Institut Für Holztechnologie Dresden Gemeinnützige Gmbh
Priority date: 2012-01-30
Filing date: 2013-01-23
Publication date: 2013-08-08
Also published as: DE102012100718B4; DE102012100718A1

Abstract

The invention relates to a method for producing coated wood fiber material plates by means of fleece forming and hot pressing of the fleece, characterized in that after the fleece forming and before the hot pressing of the fleece, a solvent-free liquid or solid coating system is applied on the fleece and/or on the die of the hot press or a transfer means occurs such that the pressing of the fleece to the wood fiber material plate and the coating of the resulting wood fiber material plate occur together in one work step.

Description

Process for the preparation of coated

Wood fiber material plates

The invention relates to a process for the production of coated wood fiber material boards and the products produced by the process. Wood fiber material boards within the meaning of the invention are to be understood as meaning wood material products which are produced from a wood fiber fleece by pressing the fleece as an essential process step determining the material properties. Thus, in addition to medium-density wood fiber boards, also referred to as MDF, high-density wood fiber boards, also referred to as HDF, and coarse chipboard, also referred to as OSB and plate-shaped products and moldings to understand it.

Furthermore, the field of application is also to be understood as meaning fibrous material products which, in part or in the place of wood, have other natural or synthetic fibers and are produced according to the method principle described above.

Such products are produced in various qualities and provided in particular for certain applications with a surface coating. The coating of Wood fiber material boards and moldings, also abbreviated as wood fiber boards, is associated with the state of the art with sometimes expensive additional process steps in the production. The coating of plates and moldings takes place in wood fiber boards, for example, by laminating with Dekorfinishfolien or plastic films, by pressing melamine or phenol impregnated papers, painting with liquid coating materials and painting with powder coating materials, wherein the coating materials according to the prior art on the pressed and pretreated wood fiber board are applied.

From the plastics processing, the in-mold coating process is known, in which the workpiece to be provided with the coating is introduced into a mold in which the coating material is located. Subsequently, the finished to the coating workpiece in the mold is pressed together with the coating material, so that the coating material covers the workpiece and takes on the outside of the contour and possibly structure of the mold.

A method of this type for the discontinuous production of coated moldings is known from DE 10 2005 017 141 A1. A method for producing a workpiece is disclosed, in particular for the production of a trim piece for interior decoration in a motor vehicle, wherein a base body is provided with a high gloss surface forming layer. The material forming the layer is applied to a highly polished surface of a tool part and the base body is connected to the layer on the side facing away from the high-gloss surface. A process for the continuous production of coated plates is known from DE 199 33 100 A1. It will be a procedure for Powder coating of plate or sheet-shaped workpieces, in particular of building materials or wood materials disclosed, wherein a resin powder is applied to the workpiece and liquefied under the action of heat and pressure using a double belt press, brought to solidification or cured.

The in-mold coating process for the production of coated wood fiber material panels according to the prior art has the common disadvantage that several technical process steps between the formed uncoated substrate when leaving the press and the start of surface finishing must be carried out to the wood fiber material product Finishes finished surfaces. In particular, it is necessary to grind the surface of the pressed uncoated substrate and preformat for transport. Furthermore, there are expenses due to the transport between the substrate production and the coating. When using liquid coating materials, environment polluting solvents emit during application.

Furthermore, a multi-stage application technology is widespread, wherein melamine or phenol impregnated papers for subsequent coating with transparent or colored paints in moldings or liquid and solvent-containing coating materials after a pretreatment, such as multiple primer, intersection and subsequent painting, are used.

The well-known in the art coating of wood and wood fiber materials with powdery coating materials is described as difficult because insulating substrate properties hinder the effect of the electric field forces and complex substrate preparations are required to increase the conductivity. On this basis, it is an object of the invention to provide a process for the production of coated Holzfaserwerkstoffpiatten available, in which the Holzfaserwerkstoffpiatten are coated efficiently and can be produced with as few production steps. Furthermore, it is an object of the invention to be able to influence the surface properties of the coating and the product targeted and reproducible and to achieve an improvement in the properties of the wood fiber material latte.

The object is solved by the features of a method according to claim 1. Further developments are specified in the dependent claims.

The object of the invention is achieved in particular by a process for the production of coated Holzfaserwerkstoffpiatten, which is characterized in that after a web formation and before a hot pressing of the web, a solvent-free liquid or solid coating system, particularly advantageous by a powder coating order on the fleece and / or on the shape of the hot press or transfer means such that the pressing of the web to the wood fiber material plate and the coating of the resulting wood fiber material plate done together in one step.

In the context of the invention, a solvent-free liquid or solid coating system is understood to mean paints, inks or additives in the broader sense which have no or substantially no solvents. These coating systems are also referred to as 100% systems. In the case of solvent-free liquid coating systems, the conversion of liquid into solid takes place by means of the pressure and the temperature during the pressing process, whereas the powder coating systems usually have the effect that the solid particles are at least partially melted, melt together and then solidify. Under a coating system is to be understood that this must be neither chemically nor particulate homogeneous. This means that a coating system according to the invention can consist of various components and particles.

The concept of the invention can also be described by the term Lackdirektbeschichtung. In the conventional production of wood fiber material panels takes place after the web formation a pre-pressing, preheating _. , Hot pressing, Formatting, Conditioning, Grinding, Coating, Fixmaßsteilteilen and packaging the wood fiber material panels instead.

The inventive method of manufacturing the wood fiber material plates takes place in contrast to the conventional method of preparation after web formation and optionally the pre-pressing and preheating of the web of the coating application and in particular the powder application to the web or the shape of the hot press instead of hot pressing, formatting, conditioning, the Fixmaßaufteilung and the packaging of the wood fiber boards done. Under the hot pressing in the context of the invention thus the pressing process is understood, which produces the product wood fiber material board or optionally the wood fiber material molding from the intermediate product wood fiber fleece. In this pressing process, the otherwise customarily provided additional pressing process for powder coating or in-mold coating is integrated according to the invention.

It should be noted that in the process according to the invention by hot pressing temperatures of more than 150 ° C to 250 ° C are used, whereas in the classical in-mold coating significantly lower temperatures are used. With regard to the order of the coating system and in particular of the powder coating, there are various alternatives which are advantageous in different aspects.

The powder coating is applied either directly to the nonwoven or to the mold or to a transfer medium, such as transfer sheets or the like, before the nonwoven is subjected to the forming and coating hot pressing operation together with the powdered finish.

In the case of liquid coating systems, the application to the nonwoven takes place, for example, by spraying or brushing on. An advantage of these systems is the utilization of the cold tack of these coating systems, whereby an application against gravity from below is advantageously possible. A particularly advantageous embodiment of the invention is that the powder coating is applied to the fleece top and / or fleece underside in the continuous or discontinuous production of wood fiber material boards.

A preferred development of the invention is that the powder coating is actively penetrated into the web. This is done either with the application, for example by blowing the powder into the fleece or after application, for example by shaking or ultrasonic treatment. The aim of this step is to achieve a better penetration of the powder coating in the outer layers of the web and thus improve the properties of the edge regions of the wood fiber material plate by a three-dimensional design of a paint fiber matrix.

However, this effect of the penetration of the outer layers is also initially achieved by applying the coating system to the mold or the circulating belt of the press. Due to the enormous difference in particle size between the fibers of the nonwoven fabric with a high porosity of the nonwoven and the powder coating particles or paint droplets, which are in the powder coating, for example in the range of 0.01 mm to 0.1 mm, the trickling or shaking of the particles allowed by the transport of the fleece.

The layer thickness of the powder coating applied to the nonwoven is up to one millimeter, preferably 0.02 mm to 0.25 mm being used.

Particularly advantageously, the method is further developed if the surfaces of the hot press for the nonwoven to produce a structured surface of the coating on the wood fiber material plate are structured. Thus, rough, dull or decorated surfaces without additional process steps are producible bar. Powder coatings based on free-radically curing unsaturated binders or liquid systems are preferably used as the coating. In particular polyester-based powder coatings are advantageously usable. Radically curing coating materials, such as, for example, unsaturated polymers based on polyester, acrylate, such as polyester acrylates, polyether acrylates, oligoether acrylates, epoxy acrylates, am in-modified acrylates, urethane acrylates and vinyl ether urethane and other systems, are generally advantageously usable.

Further powder coatings which can be used with advantage are thermosetting coating materials, such as polyesters, epoxies, acrylates, polyurethanes, hybrids and amines. Likewise, thermoplastic coating materials can advantageously be used with the invention.

Particularly advantageously, the coating application and, in particular, the application of powder coating takes place on the circulating belt of a continuously operating belt press. Alternatively, the coating is applied to the form of a discontinuously operating press.

According to a preferred embodiment of the invention, an electrically conductive layer is integrated into the coating. Alternatively, the powder coating with electrically conductive particles, which are also referred to as additives, offset such that the powder coating layer itself is electrically conductive.

The inventively produced wood fiber material panels can be used as floor elements or moldings with specific decor or specific decorative elements and as panels for interior design. Further application examples of the method are the coating of furniture component panels with specific surface structures, as décor, gloss or structure and the production of panels with furniture surfaces that can be repolished. The production of plates and moldings with conductive primer for a separate electrostatic coating and the production of plates and moldings with a fire protection equipment are further advantageous fields of application of the wood fiber material boards produced according to the invention.

As particular advantages of the method according to the invention are emphasized that adhesion problems in the coating of wood materials with powdered coating materials can be avoided as a result of insulating substrate properties as well as complex substrate preparations for increasing the conductivity. In connection with the powder coating eliminates the demand for a powder-coated electrostatically conductive substrate for powder coating in the products produced according to the design, since the coating has already taken place within the production process of the wood fiber material board. When using powder coatings and solvent-free liquid coating systems, there is also no solvent release, since the powder coating itself is solvent-free. Also, no multi-stage application technology with pre-treatment, multiple primer and intermediate steps, such as painting, by direct coating during substrate production is required.

The process of powder coating is also a process reliable process and the products have good resistance to chemicals and weathering with appropriate binders. Also, higher layer thicknesses are possible, whereby an increase in the fire protection class can be achieved. Furthermore, new optical and haptic qualities and a high mechanical resistance result.

Further advantages result from the fact that several technical intermediate steps between the produced and coated substrate and the beginning of the surface finishing by the direct coating omitted. In particular, no transport costs arise between the substrate production and the coating. Of particular note is that no surface finish is required in the manufacture of panels, resulting in a significant cost and material savings potential.

There are also technologically new opportunities for products and product qualities for the wood fiber material panels and moldings. In addition to reducing the specific costs of the wood fiber material panels, the investment costs for new plants are reduced by saving on plant components for unnecessary treatment steps.

A particular advantage of the method and the resulting properties of the wood-based panel is that the powdered coating articles penetrate into the outer zones of the nonwoven. The outer porous zones of the fleece are penetrated with the particles of the powder coating and a three-dimensional matrix of the coating forms, wherein a gradient of the particle density sets from outside to inside. During the hot pressing process, the powder coating particles melt and combine with each other, whereby the outer fibers of the nonwoven fabric are positively integrated into this matrix and the coating with the nonwoven virtually invisibly connects. After the hot pressing process, a strength-increasing effect of the outer layer of coating material is achieved.

Thus, the advantages of producing plate-shaped

Wood fiber materials associated with the advantages of solvent-free painting, with additional synergistic effects are achieved, leading to new strengths and surface structures of the products produced.

A further advantage of the invention is that surface structures that can be achieved with the coating depend on the selected surface structure of the molding or press surface and thus there is great freedom of design. Structured, matt or high-gloss surfaces can be produced depending on the nature of the mold surface, wherein for high-gloss surfaces, subsequent polishing of the powder coating surface can also be provided.

The use of weather-resistant powder coatings enables the application of the products outdoors. The treatment according to the invention also leads to an improvement in the physical, in particular the static properties of the molded part. As a result, parts with a smaller thickness can be produced, which leads to a material saving. 1

Thus, overall expanded market opportunities result from novel products such as panels for furniture, floors or elements of the interior as well as molded parts with high design freedom in the shaping.

Further details, features and advantages of embodiments of the invention will become apparent from the following description of Äúführungsbeispielen with reference to the accompanying drawings. Show it;

Fig. 1: schematic cross section of a wood fiber material board

Fig. 2; schematic cross section of a wood fiber material plate with integrated electrically conductive layer.

In Figure 1, a schematic cross section of a wood fiber material plate is shown before the forming presses in the hot press.

The fleece 1 is shown horizontally in part as a band and consists of adhesive-coated fibers 3. The porosity of the fleece 1 is chosen so that powder paint particles 5 applied in the edge regions 2 can penetrate into the interior of the fleece 1. A powder coating layer 4 forms on the nonwoven 1 and, moreover, powder coating particles 5 also penetrate into the nonwoven 1 as a function of their size and surface properties and the porosity of the nonwoven 1. In the subsequent hot pressing process, the nonwoven fabric 1 is compressed to the wood fiber material board and the adhesive-coated fibers 3 are joined together. At the same time, the powder coating particles 5 melt and combine with each other with partial sheathing of the fibers 3 to form a matrix with properties resulting from the properties of the fibers 3 and the properties of the powder coating particles 5. Depending on the properties of the powder coating used, additional interactions occur between the powder coating and the fibers 3. FIG. 2 shows a schematic cross-section of a wood-fiber material panel with an integrated electrically conductive layer. The electrically conductive layer 8 is formed from metal particles or metallized particles and applied to the nonwoven 1 between two powder coating layers 4. Thus, the electrically conductive layer 6 is electrically insulated outwardly covered by the outer powder coating layer and on the other hand, the matrix composite of powder coating layer 4 and fleece 1 is optimally achieved by the inner powder coating layer. Optionally, it is provided to provide and generate penetration areas of the electrically conductive layer 8 within a plane in order to achieve a secure bonding of the outer and inner powder coating layers 4.

The mode of action of the method is determined by the fact that the curing of the powder coating is determined by the action of a temperature over a defined time. The moisture in the plate tends to leak from the plate at a certain temperature. How quickly the moisture escapes and when the process is complete depends on the bulk density of the plate. The higher the density, the slower the moisture is released. The aim of the coating of finished MDF boards is to realize the moisture leakage, when the powder coating is melted and flows, because the emergence of moisture holes, also called pinholes, can close again. This difficult system tuning, which until now has only been solved insufficiently in the state of the art, is circumvented by the method to be patented because the coating and outgassing simultaneously take place during hot pressing over the narrow sides of the plate,

An advantage of coating the mold or the belt press is that the incipient hardening of the coating, also referred to as crosslinking, forms a barrier layer which prevents surface disturbances due to outgassing or alignment of fibers. The uncrosslinked or uncured coating at the boundary layer to the later substrate allows a chemical and / or physical 1

Connection and thereby leads to an ideal adhesion of the coating to the molding or to the plate.

Another advantage, especially in powder coating is that high layer thicknesses can be achieved in a lungsgang order to be able to compensate for flow during the pressing process and thus to ensure a flawless surface.

An advantageous embodiment of the method consists in the possibility of forming a hardened lacquered and at the same time conductive product surface through the use of special lacquers and / or lacquer constructions, for example with conductive metallic fillers. This would, if component and / or design required necessary, allow a further layer structure with electrostatic spraying. This requirement may be present, for example, when vehicle components have to be manufactured in the vehicle color and the powder coating layer is necessary as a functional primer. This embodiment of the method results in extended application possibilities. The exemplary embodiments are advantageously supplemented by the use of solvent-free liquid coating systems, wherein coating system droplets penetrate into the edge regions of the nonwoven instead of the powder coating particles.

LIST OF REFERENCE SIGNS

1 fleece

2 edge area of the fleece

3 fiber

Coating, lacquer layer, powder coating layer

5 powder coating particles, coating system droplets

6 electrically conductive layer

Claims

1 . A process for the production of coated wood fiber material plates with web formation and hot pressing of the web (1), characterized in that after the web formation and before the hot pressing of the web (1) a solvent-free liquid or solid Besch ichtungssystem on the web (1) and / or on the shape of the hot press or a transfer agent is such that the pressing of the nonwoven (1) to the wood fiber material plate and the coating of the resulting wood fiber material board done together in one step,

2. The method according to claim 1, characterized by the following method steps

web formation

prepresses

preheat

Coating system order

hot pressing

Formatting and

Condition.

3. The method according to claim 1 or 2, characterized in that the coating system coating takes place on the fleece top and / or fleece underside in the continuous or discontinuous production of wood fiber material boards,

4. The method according to claim 3, characterized in that the coating system is penetrated during or after the coating system application in the fleece (1).

5. The method according to claim 1 or 2, characterized in that the

Apply coating system order on a circulating belt of a continuous belt press.

6. The method according to claim 1 or 2, characterized in that the

Apply coating system order takes the form of a discontinuous press.

7. The method according to any one of claims 1 to 6, characterized in that the continuous or discontinuous hot pressing of the nonwoven fabric (1) after the Besch coating system with structured surfaces to produce a structured surface of the coating (4) takes place on the wood fiber material board.

8. The method according to any one of claims 1 to 7, characterized in that as coating system, a powder coating is used.

9. The method according to any one of claims 1 to 8, characterized in that in the coating (4) an electrically conductive layer (6) is integrated.