WO2006042651A1

WO2006042651A1 - Light-coloured to white wooden material panels

Info

Publication number: WO2006042651A1
Application number: PCT/EP2005/010848
Authority: WO
Inventors: Andres Carlos Garcia Espino; Juliane Krüsemann; Manfred Siegler; Norbert Jäger
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-10-14
Filing date: 2005-10-08
Publication date: 2006-04-27
Also published as: DE102004050278A1; US20070256804A1; JP2008516793A; CN100546783C; EP1817145B1; CN101039784A; BRPI0515996A; EP1817145A1

Abstract

Light-coloured to white wooden material panels are produced from bleached wood fibres and/or vat-dyed with a white pigment.

Description

Light to white wood-based panels

description

The present invention relates to light to white wood-based panels made of bleached wood fibers and / or mass colored with a white pigment.

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 closing to get the wood-like structure visible, only colorless coated or coated with overlay.

Naturally, these plates, depending on the type of wood used, have a more or less pronounced brown color, which is of little aesthetic value for use in the furniture sector.

By mass coloration with the known from WO-A-04/35276 pigment and colorant containing colorant preparations, the intrinsic color of the wood fibers can be compensated. In this way it is possible to obtain colorful, completely colored, light-fast and therefore aesthetically high-quality MDF boards which are suitable for producing long-lasting articles, e.g. of furniture for the living area, are suitable.

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. For kitchen or bath, however, these plates would be of particular interest.

Although the production of white paper by bleaching the paper pulp and adding white pigments or white fillers, blue colorants and optical brighteners has long been known and described, for example, in Paper Trade Journal, 145, pp. 26-27 (1961), it has become Experts do not expect that white wood-based panels, especially MDF panels, are accessible in this way. 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 produced at much higher temperatures (about 2OfJ ⁰ C) than paper, which in addition to the brown inherent color of wood fibers enters a process-related browning, which is due to the oxidation and thermal decomposition of wood ingredients. 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

Accordingly, light to white wood-based panels were found, which are made of bleached wood fibers.

In addition, light to white wood-based panels were found, which are mass-colored with a white pigment.

Furthermore, bright to white wood-based panels were found, which are mass dyed with a dispersion of a white pigment, which additionally contains optical brighteners.

Finally, bright to white wood-based panels were found, which are made of bleached wood fibers and are mass-colored with a white pigment.

Last but not least, bright to white wood-based panels were produced, which are made of bleached wood fibers and are colored with a dispersion of a white pigment which contains optical brighteners.

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 wer¬ the 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 may be MDF or HDF boards or chipboards. Particularly preferred are MDF boards.

MDF and HDF boards are usually produced in a continuous process. Here, washed, water-moist, small chopped pieces of wood (Hack¬ schnitzel) are first preheated to about 80 ⁰ C and then in a digester under a Pressure of 2 to 5 bar and a temperature of 100 to 150 ° C soaked. 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. Urea-formaldehyde resins, some of which are reinforced with melamine, or urea-melamine-formaldehyde resins used for damp-resistant boards, are usually used as binders. 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 also subsequently coated 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, where appropriate cold precompressed and pressed in heated presses at temperatures of 170 to 24O ⁰ C to plates.

Bleached wood fibers are differentiated in the production of one embodiment of the light wood-based panels according to the invention (hereinafter, the term "wood fibers" and "chips" are not differentiated; rather, the term "wood fibers" is also intended to include "chips").

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, the percarbonates and hydrogen peroxide being preferred. For the reductive lead, there are 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 Äpfel¬ acid suitable. Preferred reducing agents are the disulfites and sulfites, in particular sodium hydrogen sulfite, and malic and citric acids.

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.

The process is in bleaching expediently so before that aqueous, 5 to 40 wt .-% strength wood fiber dispersions continuously men in Gegenstromtür- at temperatures from 90 to 150 ⁰ C and pressures up to 3 solutions bar with aqueous Lö¬ or dispersions of the bleaching agent treated. 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 the case of 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 wood species 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 decisively improved. However, the mass coloration with the white pigment can also be carried out alone. In this case, bright plates are also obtained.

According to the invention, the term "white pigment" 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, lithopones and Sodium-aluminum silicates, 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 also 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 directly into the MDF / HDF production process via the blowline, separately from or together with the glue. These pigment dispersions may contain further customary auxiliaries, in particular wetting and dispersing agents, defoamers and biocides, but also antisettling 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 concentrations of the white pigment in the finished Holzwerkstoffplat¬ te are usually at 0.5 to 15% atro, preferably at 1 to 6% atro (% atro = wt .-% based on dry fiber).

A further increase in the whiteness can be achieved by the addition of optical Aufhel¬ learning compensated by their bluish fluorescence (complementary color) Vergrau¬ ments 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 separately or together with the white pigments and the glue in the MDF / HDF production 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 size liquor before it is injected by the blowline in the MDF / HDF production process.

Any resulting from the inventive measures changes in the physical properties of the pressed wood-based panel can be controlled by selecting 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, the brightness difference .DELTA.L was determined as a standard by coloristic measurement according to CIELAB in comparison to a MDF board produced analogously from unbleached wood fibers and without the addition of white pigments and optical brighteners.

example 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 (Trilon ^® B _1, BASF) were heated in 3 liters of water with stirring to 70 ⁰ C. After addition of 7 g of sodium percarbonate was stirred at 70-75 ⁰ C for 1 h. Then 7 g of sodium dithionite were added and finally stirred at 70-75 ⁰ C for a further 30 min.

After cooling to room temperature, the wood pulp mash was separated from the liquid constituents via a sieve with a mesh size of 1 mm and briefly washed out with running water and blown through. The spread filter material was then dried at 60 ⁰ C in a convection oven for 3 days.

b) The bleached wood fibers from step a) were mixed thoroughly in a paddle mixer and sprayed with the glue batch listed in Table 1.

Table 1

The glued fibers were then poured into a mat, cold precompressed and pressed at 190 ° C to a plate. Comparative Example C1

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

Example 2

Analogously to example 1 b), an MDF board of unbleached wood fibers (spruce) was prepared, wherein the wood fibers were sprayed with the glue mixture containing the white pigment titanium dioxide listed in table 2.

Table 2

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 3

Wood chips from spruce were added during the MDF production process in the digester of an MDF pilot plant with a 40 wt .-% aqueous Natriumdisul- fit solution, corresponding to 7.5% sodium hydrogen sulfite atro fibers. The MDF The production process was continued as usual with a throughput of 21 kg / h, the wood chips were defibered by the refiner, and the resulting fibers were coated by the blowline continuously with the glue formulation listed in Table 4.

Table 4

The glued wood fibers were dried in the subsequent continuous Trock¬ ner to a residual moisture content of about 9 wt .-% and then poured discontinuously to a mat, cold precompressed and at 190 ⁰ C with a pressing time factor of 15 s / mm to a 16 mm pressed thick plate.

Comparative Example V2

An MDF plate was prepared analogously to the procedure described in Example 3, but without addition of sodium disulfite.

Table 5 shows the whiteness achieved (expressed in the difference in brightness ΔL), based on comparative example C2 as standard.

Table 5

Example 4

Wood chips from spruce wood were sprayed in a mixer with a 40% strength by weight aqueous sodium disulphite solution, corresponding to 4.5% sodium hydrogen sulphite fibers. These chips were then fed into the digester of an MDF technology plant. The MDF production process was as usual with a Throughput of 21 kg / h continued, the wood chips were zerfa¬ sert by the refiner, and the sustaining fibers were by the blowline continuously with the glue listed in Table 6, the white pigment containing titanium dioxide glued glue¬.

Table 6

The glued wood fibers were dried in the subsequent continuous drier to a residual moisture content of about 9 wt .-% and then poured discontinuously to a mat, cold precompressed and at 19O ⁰ C with a pressing time factor of 15 s / mm to a 16 mm pressed thick plate.

Comparative Example C3

Analogously to the procedure described in 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.

Table 7 shows the whiteness achieved (expressed in the difference in brightness ΔL), based on comparative example V3 as standard.

Table 7

Example 5

Beech wood chips were added during the MDF production process in the digester of an MDF pilot plant with a 40% strength by weight aqueous sodium disulfide solution, corresponding to 6% sodium hydrogen sulfite-free 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 continuously glued by the blowline with the glue batch listed in Table 8.

Table 8

Example 6

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

Example 7

Analogously to the procedure described in 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

Comparative Example V4

An MDF plate was prepared analogously to the procedure described in Example 5, but without addition of sodium disulfite.

In Table 10, the obtained whiteness (expressed in the brightness difference ΔL), based on the comparative example V4 as a standard listed.

Table 10

Claims

claims

1. Light to white wood-based panels made from bleached wood fibers.

2. wood-based panels according to claim 1, wherein the wood fibers are first bleach oxidative and then reductive.

3. wood-based panels according to claim 1 or 2, wherein the wood fibers have been bleached during the plate-making.

4. Light to white wood-based panels, mass-colored with a white pigment.

5. wood-based panels according to claim 4, which are mass-colored with a dispersion of a Weißpig¬ ment, which additionally contains optical brightener.

6 wood-based panels according to claims 1 to 4, which are made of bleached Holzfa¬ fibers and mass-colored with a white pigment.

7. wood-based panels according to claims 1 to 5, which are made of bleached Holzfa¬ fibers and mass-colored with a dispersion of a white pigment containing optical brighteners.

8. wood-based panels according to claims 1 to 7, characterized in that it is MDF, HDF or chipboard.