EP1817145B1 - Light-coloured to white wooden material panels - Google Patents

Description

The present invention relates to light to white wood-based panels, which are MDF, HDF or particle board, which are mass-colored with a white pigment and optical whitening agents are added.

In the field of wood-based panels, the market for so-called medium-density fiberboards (MDF panels) and high-density fibreboards (HDF panels) is growing rapidly. The production volumes have more than tripled in the last ten years.

MDF and HDF boards can be processed like conventional chipboard. Due to their uniform structure, they are also suitable for the production of profiled parts and are therefore becoming increasingly popular in furniture construction. Thus, for example, furnishings for rooms and for decorative purposes (for example, in trade fair construction), but also higher-quality furniture made from these plates and then, in order to preserve the wood-like structure visible, only colorless or coated with overlay.

Naturally, these boards, depending on the type of wood used, a more or less pronounced brown color, which is of little aesthetic value for an application in the furniture sector

By mass coloring with those from the WO-A-04135276 known pigment and dye-containing colorant preparations can be compensated for the inherent color of the wood fibers. In this way, colorful, completely colored, lightfast and therefore aesthetically high-quality MDF boards are obtained, which are suitable for the production of durable articles, for example of furniture for the living area.

However, bright or even white wood-based panels, in particular MDF panels, have not been available so far. Especially for the production of furniture and interior decoration objects, e.g. but for kitchen or bathroom these plates would be of particular interest.

Although the production of white paper by bleaching of the paper pulp and addition of white pigments or white fillers, blue colorants and optical brighteners has long been known and, for example, in Paper Trade Journal, 145, pp. 26-27 (1961 ), but it has not been expected by those skilled in the art that white wood-based panels, especially MDF panels, are accessible in this manner.

For example, the wood fibers used in the production of MDF boards contain substances which are sensitive to oxidation and thus to discoloration (for example lignin), which are no longer present in the paper pulp. In addition, MDF boards are made at much higher temperatures (about 200 ° C) than paper, which adds to the brownish inherent color of the wood fibers a process-related browning due to the oxidation and thermal decomposition of wood constituents. In addition, the light exposure of a MDF board incorporated in furniture is significantly longer and more intense than the usual papers and causes a not inconsiderable yellowing.

The invention therefore an object of the invention to provide light or white wood-based panels available.

This object is achieved by bright to white wood-based panels, which are MDF, HDF or chipboard, characterized in that the curing to white wood-based panels are mass-colored with a white pigment and optical brighteners are added.

The invention also includes such light to white wood-based panels made of bleached wood fibers and wood-based panels of the invention made from wood fibers which have been first bleached oxidatively and then reductively.

The wood-based panels according to the invention are distinguished by their brightness or their white color. Depending on the combination of measures taken, the desired whiteness can be easily adjusted. Especially white plates are e.g. by bleaching the wood fibers and mass-coloring with a dispersion of a white pigment which additionally contains optical brighteners. Bright plates with a lower degree of whiteness are also accessible merely by bleaching the wood fibers or by mass coloration with a white pigment.

The wood-based panels according to the invention are MDF or HDF boards or chipboards. Particularly preferred are MDF boards.

MDF and HDF boards are usually produced in a continuous process. This washed, water-moist, small chopped pieces of wood (wood chips) are first preheated to about 80 ° C and then in a digester under a pressure of 2 to 5 bar and a temperature of 100 to 150 ° C geweicht. In the adjoining refiner, the chips are then shredded. The refiner consists of two metal discs with radial relief, which rotate close to each other in the opposite direction. The fibers leave the refiner via the so-called blowline. Here, the glue is usually applied. As binders are usually urea-formaldehyde resins, reinforced in part with melamine, or for moisture-resistant Sheets urea-melamine-formaldehyde resins used. Isocyanates are also used as binders. The binders are usually applied to the fibers together with the desired additives (eg hardener, paraffin dispersion, colorant). The glued fibers then pass through a dryer in which they are dried to humidities of 8 to 15 wt .-%. Occasionally, the dried fibers are coated only later in special continuously operating mixers.

In chipboard production, the gluing of the previously dried chips takes place in continuous mixers.

The glued fibers or chips are then poured into mats, optionally cold precompressed and pressed in heated presses at temperatures of 170 to 240 ° C to plates.

In the production of an embodiment of the bright wood-based panels according to the invention are bleached wood fibers (hereinafter is not differentiated between the terms "wood fibers" and "chips", but should the term "wood fibers" include "chips") used.

In the chemical bleaching of wood fibers, the coloring impurities of the wood are destroyed or rendered ineffective by oxidizing and / or reducing chemicals. For oxidative bleaching, e.g. Hydrogen peroxide, ozone, oxygen and salts of organic and inorganic peracids, such as peracetates, percarbonates and perborates, especially their alkali metal salts, in particular sodium salts, wherein the percarbonates and hydrogen peroxide are preferred. For the reductive bleaching, e.g. reducing sulfur compounds, such as dithionites, disulfites, sulfites or sulfur dioxide, sulfinic acids and their salts, in particular the alkali metal salts and especially the sodium salts, and hydroxycarboxylic acids, such as citric acid and malic acid, suitable. Preferred reducing agents are the disulfites and sulfites, in particular sodium hydrogen sulfite, as well as malic and citric acid.

For the wood-based panels according to the invention, wood fibers which have been firstly oxidatively and then reductively bleached are particularly preferred.

Most preferably, the oxidative bleaching is carried out with percarbonates or hydrogen peroxide and the reductive bleaching with sulfites, malic or citric acid.

Technically, the bleaching is advantageously carried out so that aqueous, 5 to 40 wt .-% wood fiber dispersions continuously in countercurrent towers at temperatures of 90 to 150 ° C and pushers up to 3 bar with aqueous solutions or dispersions of the bleaching agents. Usually, it is carried out in the presence of complexing agents, such as EDTA, to avoid the degradation of the bleaching agents by transition metal ions.

In a preferred embodiment of the wood-based panels according to the invention, the bleaching of the fibers is carried out in particular in MDF / HDF boards during board production. The bleaching agents can be added to the wood chips in the preheater or in the cooker. Preferably, complexing agents are also added.

In principle, all fibrous materials to be obtained from plants can serve as the base material for the wood-based panels according to the invention. Thus, e.g. in addition to the wood fibers commonly used fibers that are to win from palm trees, suitable. Preferred base materials are light wood species, especially spruce or pine, but darker woods such as beech can also be used.

In a particularly preferred embodiment of the wood-based panels according to the invention, the use of bleached wood fibers with a mass coloration is combined with a white pigment. As a result, the whiteness can be significantly improved. However, the mass coloration with the white pigment can also be carried out alone. In this case, bright plates are also obtained.

The term "white pigments" according to the invention includes both inorganic pigments, which are preferred, such as titanium dioxide (rutile, CI Pigment White 6), calcium carbonate and calcium / magnesium mixed carbonates (eg dolomite), zinc oxide, zinc sulfide, lithopone and sodium aluminum silicate , as well as white-coloring, highly light-scattering plastic emulsions and dispersions. Particularly preferred white pigment is titanium dioxide. Of course, mixtures of white pigments can be used.

The white pigments are preferably used in the form of aqueous dispersions in which they are finely divided, since they can be introduced via the blowline, separately from or together with the glue, directly into the MDF / HDF production process.

These pigment dispersions may contain other customary auxiliaries, in particular wetting and dispersing agents, defoamers and biocides, but also anti-settling agents, water retention agents and rheology modifiers and are preferably prepared by wet milling of all components, for example in a stirred ball mill.

Recommended levels of the white pigment in the finished wood material board are generally from 0.5 to 15% absolutely dry, preferably 1 to 6% bone dry (atro =% wt .-% based o n tro ckene fiber).

A further increase in the whiteness can be achieved by adding optical brighteners, which compensate for their bluish fluorescence (complementary color) graying and yellowing.

Suitable are, in principle, all blue emitting fluorescent dyes, more commercially accessible products such as Ultraphor ^® (BASF), Leucophor ^® (Clariant) or Tinopal ^® (Ciba), linked from the chemical substance classes of the stilbenes, distyrylbiphenyls, coumarins, naphthalimides and double bonds benzoxazole and benzimidazole systems.

The optical brighteners can be introduced in the form of aqueous dispersions or solutions together with the white pigments and the glue in the MDF / HDF manufacturing process.

If an optical brightener is used, its concentration in the finished wood-based panel is generally from 0.01 to 1% atro, preferably from 0.08 to 0.2% atro.

Very particular preference is given to wood-based panels according to the invention in which all features (bleached wood fiber, white pigments and optical brighteners) are combined, since the individual contributions are potentiated by synergy effects to a maximum overall degree of whiteness.

It is procedurally particularly advantageous to prepare the white pigments and the optical brightener together in a single aqueous dispersion, which is added to the glue liquor before it is injected by the blowline in the MDF / HDF manufacturing process.

Any resulting from the inventive measures changes in the physical properties of the pressed wood-based panel can be controlled by choosing the glue quality and amount of glue.

Examples Production of MDF boards according to the invention

As a measure of the whiteness of the plates produced by colorimetric measurement according to CIELAB the brightness difference .DELTA.L was determined as compared to an MDF plate made analogously from unbleached wood fibers and without the addition of white pigments and optical brighteners as standard.

Comparative Example 1

1. a) In a 5I vessel with anchor stirrer and thermostat-compensating heating 70 g of wood pulp (spruce) and 1 g of ethylenediaminetetraacetic acid were heated (Trilon B ^®, BASF) in 3 liters of water with stirring to 70 ° C. After addition of 7 g of sodium percarbonate was stirred at 70-75 ° C for 1 h. Then 7 g of sodium dithionite were added and finally stirred at 70-75 ° C for a further 30 min.
   The Holzstoffmaische was separated after cooling to room temperature through a sieve of mesh size 1 mm from the liquid constituents and briefly washed out with running water and durchgewalgt. The spread filter material was then dried at 60 ° C in a convection oven for 3 days.
2. b) The bleached wood fibers from step a) were mixed in a paddle mixer and sprayed with the glue batch listed in Table 1.

Table 1 glue batch Urea-melamine-formaldehyde resin, 69 wt .-% in water 100.0 parts by weight. Paraffin dispersion, 60% strength by weight in water 4.1 parts by weight. water 49.2 parts by weight. Solid resin content of the liquor 45% Solid resin / atro fibers 14% Fleet on 100 kg of atro fibers 31.1 kg

The ennobled fibers were then poured into a mat, precompressed cold and pressed at 190 ° C to a plate.

Comparative Example C1

Analogous to the procedure described in Comparative Example 1b), an MDF board was produced from the unbleached wood fibers.

Comparative Example 2

Analogous to Comparative Example 1b), an MDF board was produced from unbleached wood fibers (spruce), the wood chips containing the white pigment titania containing the white pigment listed in Table 2 being sprayed. Table 2 glue batch Urea-melamine-formaldehyde resin. 69 wt .-% in water 100.0 parts by weight. Paraffin dispersion, 60% strength by weight in water 4.1 parts by weight. Titanium dioxide preparation, 70% strength by weight in water 39.4 parts by weight. water 9.8 parts by weight. Solid resin content of the liquor 45% Solid resin / atro fibers 14% Titanium dioxide / atro fibers 5.6% Fleet on 100 kg of atro fibers 31.1 kg

In Table 3, the obtained whiteness (expressed in the brightness difference .DELTA.L), based on the comparative example V1 as a standard, compiled. Table 3 example .DELTA.L 1 12 2 10 V1 -

Comparative Example 3

Wood chips from spruce wood were added during the MDF production process in the digester of an MDF pilot plant with a 40 wt .-% aqueous sodium disulfite solution, corresponding to 7.5% sodium hydrogen sulfite atro fibers.

The MDF production process was continued as usual with a throughput of 21 kg / h, the wood chips were fiberized by the refiner, and the obtained fibers were continuously glued by the blowline with the glue batch listed in Table 4. Table 4 glue batch Urea-melamine-formaldehyde resin, 66.5% by weight in water 100.0 parts by weight. Paraffin dispersion, 60% by weight, in water 4.0 parts by weight. water 33.8 parts by weight. Solid resin content of the liquor 48% Solid resin / atro fibers 14% Fleet on 100 kg of atro fibers 29.2 kg

The glued wood fibers were dried in the subsequent continuous dryer to a residual moisture content of about 9 wt .-% and then poured discontinuously to a mat, cold precompressed and at 190 ° C with a pressing time factor of 15 s / mm to a 16 mm thick plate pressed.

Comparative Example V2

Analogous to the procedure described in Comparative Example 3, but without the addition of sodium disulfite, an MDF board was produced.

In Table 5, the obtained whiteness (expressed in the brightness difference ΔL), based on the comparative example V2 as a standard listed. Table 5 example .DELTA.L 3 4 V2 -

Comparative Example 4

Wood chips from spruce wood were sprayed in a mixer with a 40 wt .-% aqueous sodium disulfite solution, corresponding to 4.5% sodium hydrogen sulfite atro fibers sprayed. These chips were then placed in the digester of an MDF pilot plant fed. The MDF production process was continued as usual with a throughput of 21 kg / h, the chips were defibered by the refiner, and the sustaining fibers were continuously glued by the blowline with the glue formulation containing white pigment titania as shown in Table 6. Table 6 glue batch Urea-melamine-formaldehyde resin, 66.5% by weight in water 100.0 parts by weight. Paraffin dispersion, 60% strength by weight in water 4.0 parts by weight. Titanium dioxide preparation, 70% strength by weight in water 47.5 parts by weight: Solid resin content of the liquor 44% Solid resin / atro fibers 14% Fleet on 100 kg of atro fibers 31.8 kg

The glued wood fibers were dried in the subsequent continuous dryer to a residual moisture content of about 9 wt .-% and then poured discontinuously to a mat, cold precompressed and at 190 ° C with a pressing time factor of 15 s / mm to a 16 mm thick plate pressed.

Comparative Example C3

Analogously to the procedure described in Comparative Example 4, but without the addition of the white pigment (replacement of the titanium dioxide preparation by the same amount of water), an MDF board was produced.

In Table 7, the obtained whiteness (expressed in the brightness difference ΔL), based on the comparative example V3 as a standard listed. Table 7 example .DELTA.L 4 6 V3 -

Comparative Example 5

Wood chips from beech wood were added during the MDF production process in the digester of an MDF pilot plant with a 40 wt .-% aqueous sodium disulfite solution, corresponding to 6% Natriumhydrogensulfit atro fibers. The MDF production process was continued as usual with a throughput of 30 kg / h, the chips were defibered by the refiner, and the obtained fibers were coated by the blowline continuously with the glue batch listed in Table 8 Table 8 glue batch Urea-melamine-formaldehyde resin, 66.5% by weight in water 100.0 parts by weight. Paraffin dispersion, 60% by weight in water 4.0 parts by weight. water 47.5 parts by weight. Solid resin content of the liquor 44% Solid resin latro fibers 14% Fleet on 100 kg of atro fibers 31.8 kg

The glued wood fibers were dried in the subsequent continuous dryer to a residual moisture content of about 9 wt.% And then poured discontinuously into a mat, cold precompressed and pressed at 190 ° C with a pressing time factor of 15 s / mm to a 16 mm thick plate ,

Comparative Example 6

Analogous to the procedure described in Comparative Example 5, but using the white pigment titanium dioxide, an MDF board was produced using the glue formulation shown in Table 6.

Example 7

Analogously to the procedure described in Comparative Example 5, but using the white pigment titanium dioxide in combination with optical brightener, an MDF board was produced using the glue formulation listed in Table 9. Table 9 glue batch Urea-melamine-formaldehyde resin, 66.5% by weight in water 100.0 parts by weight. Paraffin dispersion, 60% strength by weight in water 4.0 parts by weight. Titanium dioxide preparation, 50 wt.% In water, containing 2 wt .-% of a commercially available optical brightener 47.5 parts by weight. Solid resin content of the liquor 44% Solid resin / atro fibers 14% Titanium dioxide / atro fibers 5% optical brightener / atro fibers 0.2% Fleet on 100 kg of atro fibers 31.8 kg

Comparative Example V4

Analogous to the procedure described in Comparative Example 5, but without the addition of sodium bisulfite, an MDF board was produced.

In Table 10, the obtained whiteness (expressed in the brightness difference ΔL), based on the comparative example V4 as a standard listed. Table 10 example .DELTA.L 5 3 6 6 7 7 V4 -

Claims (3)

1. A light to white wood-base board which is an MDF board, HDF board or particleboard, wherein the light to white wood-base board has been beater dyed with a white pigment and optical brighteners have been added thereto.
2. The wood-base board according to claim 1, which is produced from bleached wood fibers.
3. The wood-base board according to claim 1 or 2, which is produced from wood fibers which have been first oxidatively and then reductively bleached.