DE102004050278A1 - Light to white wood-based panels - Google Patents

Abstract

Wood-based panels made from bleached wood fibers and / or mass-dyed with a white pigment.

Description

The The present invention relates to wood-based panels made of bleached Wood fibers are produced and / or mass dyed with a white pigment.

in the The field of wood-based materials is the market for so-called medium-density fiberboard (medium density fibreboard, MDF boards) and high-density fiberboard (high-density fibreboard, HDF plates) is growing rapidly. Production volumes have more than exceeded in the last 10 years tripled.

MDF and HDF disks can like traditional ones Particle boards are processed. Due to their uniform structure But they are also suitable for the production of profiled parts and therefore strengthen their position in furniture construction by. For example, furnishings for rooms and for decorative Purposes (for example, in exhibition construction), but also higher-quality furniture made these plates and then to the wood-like structure Visible, only colorless or with overlay coated.

Own by nature these plates, depending on the type of wood used, one more or less pronounced brown color, the for an application in the furniture sector only of low aesthetic Is worth.

By mass coloring with the pigment and dye-containing colorant preparations known from WO-A-04/35276 can the self-coloring the wood fibers are compensated. In this way are colorful, completely colored, lightfast and therefore aesthetically to obtain high quality MDF boards, which are more durable Article, e.g. of furniture for the Living area, are suitable.

Bright or white Wood-based panels, especially MDF panels, have so far been however, not available. Especially for the manufacture of furniture and interior decoration objects e.g. for kitchen or bathroom these would be Plates but of particular interest.

Though is the production of white Paper by bleaching the paper pulp and adding white pigments or white fillers, blue colorants and optical brighteners have long been known and e.g. in Paper Trade Journal, 145, pp. 26-27 (1961), it However, experts have not expected that white wood-based panels, in particular MDF panels, accessible in this way are.

So contain the wood fibers used in the production of MDF boards still oxidation and thus discoloration sensitive Substances (for example lignin) which are no longer present in the paper pulp are. In addition, will MDF panels far higher Temperatures (about 200 ° C) produced as paper, resulting in the brown inherent color of the wood fibers additionally a process-related browning occurs on the oxidation and thermal decomposition of wood constituents is due. In addition, the light exposure of an incorporated in furniture MDF board much longer and more intense than the usual ones Papers and causes a not inconsiderable yellowing.

Of the The invention was therefore based on the object, light or white wood-based panels available too put

Accordingly, were Wood-based panels found that are made from bleached wood fibers are.

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

Farther were found wood-based panels with a dispersion of a white pigment mass colored are, in addition contains optical brightener.

Finally were Wood-based panels found that are made from bleached wood fibers are and with a white pigment mass colored are.

Not Finally, wood-based panels were found that were bleached Wood fibers are made and with a dispersion of a white pigment mass colored which contains optical brighteners.

The Wood-based panels according to the invention are characterized by their brightness or their white color out. Depending on the combination of measures taken, the desired whiteness can be easily adjusted become. Especially white Plates are e.g. by bleaching the wood fibers and mass coloring with a dispersion of a white pigment, the additional contains optical brightener, receive. Bright plates with lower whiteness are already through sole bleaching of the wood fibers or by mass coloration with a white pigment accessible.

at the wood-based panels according to the invention Can it be MDF or HDF boards or to act particleboard. Particularly preferred are MDF boards.

MDF and HDF boards are becoming common produced in a continuous process. Here are washed, water-moist, small chopped pieces of wood (wood chips) first to about 80 ° C preheated and then in a digester under a pressure of 2 to 5 bar and one Temperature of 100 to 150 ° C softened. In the subsequent Refiner the wood chips are then shredded. The refiner consists of two metal discs with radial relief, which are tight to turn on each other in the opposite direction. Leave the fibers the refiner over the so-called blowline. Here, the glue is usually applied. As a binder become common Urea-formaldehyde resins, sometimes reinforced with melamine, or for moisture-resistant panels Urea-melamine-formaldehyde resins used. Also isocyanates are in use as binders. The binders are usually together with the desired Additives (e.g., hardeners, Paraffin dispersion, colorant) applied to the fibers. The glued fibers then pass through a dryer, in which they are dried to moistures of 8 to 15 wt .-%. isolated The dried fibers are only subsequently in special continuously glued on working mixers.

at The chipboard is glued to the previously dried Chips in continuous mixers.

The glued fibers or chips will be afterwards poured into mats, optionally cold precompressed and in heated presses at temperatures from 170 to 240 ° C pressed into plates.

at the production of an embodiment the bright invention Wood-based panels are bleached wood fibers (hereafter is not differentiated between the terms "wood fibers" and "chips", rather the term "wood fibers" should also include "chips").

at The chemical bleaching of wood fibers becomes the coloring Accompanying substances of the wood by oxidizing and / or reducing Chemicals destroyed or rendered ineffective. For the oxidative bleaching is suitable 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, with the percarbonates and hydrogen peroxide being preferred are. For the reductive bleaches are e.g. reducing sulfur compounds, such as dithionites, disulfites, sulfites or sulfur dioxide, sulfinic acids and their salts, especially the alkali metal salts and especially the Sodium salts, and hydroxycarboxylic acids, like citric acid and malic acid, suitable. Preferred reducing agents are the disulfites and sulfites, in particular Sodium hydrogen sulfite, as well as apple and citric acid.

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

All the oxidative bleaching is particularly preferred with percarbonates or hydrogen peroxide and the reductive bleaching with sulfites, apples or citric acid carried out.

process engineering you go on bleaching expediently so before that one aqueous, 5 up to 40 wt.% Wood fiber dispersions continuously in countercurrent towers Temperatures from 90 to 150 ° C and To press up to 3 bar with aqueous solutions or Treated dispersions of bleach. The usual way is in the presence complexing agents, such as EDTA, worked to reduce the bleaching agent by transition metal ions to avoid.

at a preferred embodiment the wood-based panels according to the invention is the bleaching of the fibers especially in MDF / HDF boards while the plate making made. The bleach can do the Wood chips in the preheater or added in the digester. Preferably also be Added complexing agent.

When Base material can for the Wood-based panels according to the invention in principle all fibrous materials to be extracted from plants serve. Thus, e.g. in addition to the usual used wood fibers fibers that can be extracted from palm trees, suitable. Preferred base materials are light wood species, in particular Spruce or pine, but darker wood species, like beech, used.

at a particularly preferred embodiment the wood-based panels according to the invention is the use of bleached wood fibers with a mass coloring with a white pigment combined. This can be done the whiteness decisively improve. The mass coloration with the white pigment however, it can be done on its own. In this case will be also received bright plates.

Of the Term "white pigment" includes according to the invention both the preferred inorganic pigments which are preferred, such as Titanium dioxide (rutile, C.I. Pigment White 6), calcium carbonate and calcium / magnesium mixed carbonates (e.g., dolomite), zinc oxide, zinc sulfide, lithopones and sodium aluminum silicateates, as well as white-coloring, highly light-scattering plastic emulsions and dispersions. Especially preferred white pigment is titanium dioxide. Of course can also mixtures of white pigments be used.

The White pigments are preferably in the form of aqueous dispersions, in which they are finely distributed, used as they so on the Blowline, separately or together with the glue, introduced directly into the MDF / HDF manufacturing process can be.

These Pigment dispersions can more usual Auxiliary agents, in particular wetting and dispersing agents, defoamers and Biocides, but also anti-settling agents, water retention agents and rheology modifiers included and are preferably by wet grinding of all components e.g. produced in a stirred ball mill.

recommended Concentrations of white pigment in the finished wood-based panel are usually at 0.5 up to 15% atro, preferably at 1 to 6% atro (% atro =% based on dry fiber).

A further increase in whiteness let yourself by the addition of optical brighteners reach through their bluish Fluorescence (complementary Color) compensate for 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 brightener can in the form of aqueous dispersions or solutions separately or together with the white pigments and the glue in introduced the MDF / HDF manufacturing process become.

Becomes an optical brightener used, so is its concentration in the finished wood board generally at 0.01 to 1% atro, preferably at 0.08 to 0.2% atro.

All such wood-based panels according to the invention are particularly preferred all features (bleached wood fiber, white pigments and optical brighteners) combined, as the individual contributions through synergy effects too a maximum overall brightness be potentiated.

there it is procedurally particularly advantageous, the white pigments and the optical brighteners together in a single aqueous dispersion to prepare added to the glue fleet before being injected through the blowline into the MDF / HDF manufacturing process becomes.

any from the inventive measures resulting changes the physical properties of the pressed wood board can by Choice of glue quality and Leimmenge are controlled.

manufacturing of MDF boards according to the invention

As a measure of the whiteness of the plates produced by colorimetry by CIELAB the brightness difference .DELTA.L is determined as standard 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 51 vessel with anchor stirrer and thermostat-compensating heating 70 g of wood pulp (spruce) and 1 g of ethylenediaminetetraacetic acid (Trilon B ^®, BASF) were heated 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 wood pulp mash was separated after cooling to room temperature over a sieve of mesh size 1 mm from the liquid components and washed out briefly under running water and durchgewalgt. The spread filter material was then dried at 60 ° C in a convection oven for 3 days.
• b) The bleached wood fibers from step a) were in a Mixing paddle mixer and with the glue formulation listed in Table 1 sprayed.

Table 1

The glued fibers were then poured into a mat, cold pre-compressed and at 190 ° C pressed to a plate.

Comparative Example C1

Analogous the procedure described in Example 1b) became an MDF board Made of unbleached wood fibers.

Example 2

Analogous Example 1b) was an MDF board made of unbleached wood fibers (Fichte), whereby in wood fibers with the in table 2 listed, the white pigment Titanium dioxide-containing glue batch were sprayed.

Table 2

In Table 3 shows the degrees of whiteness achieved (expressed in the Brightness difference ΔL), based on the comparative example V1 as a standard, compiled.

Table 3

Example 3

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

Manufacturing process was as usual continued with a throughput of 21 kg / h, the wood chips were defibered by the refiner, and the obtained fibers were passed through the blowline continuously with the glue formulation listed in Table 4 glued.

Table 4

The glued wood fibers were in the subsequent continuous dryer to a rest moisture of about 9 wt .-% dried and then poured discontinuously to 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 V2

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

In Table 5 is the whiteness achieved (expressed in the brightness difference ΔL), based on the comparative example V2 as standard listed.

Table 5

Example 4

wood chips from spruce wood were mixed in a mixer with a 40 wt .-% aqueous sodium disulfite solution, according to 4.5% sodium hydrogen sulfite atro fibers, sprayed. These wood chips were subsequently in the stove of an MDF pilot plant fed. The MDF production process was as usual with a throughput of 21 kg / h continued, the wood chips were fiberized through the refiner, and the sustaining fibers were through the blowline continuously with that listed in Table 6, the white pigment Glueing containing titanium dioxide glue.

Table 6

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

Comparative Example C3

Analogous to the procedure described in Example 4, but without the addition of the white pigment (replacement of the TiO ₂ preparation by the same amount of water), an MDF board was prepared.

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

Table 7

Example 5

wood chips beechwood were used during of the MDF production process in the digester of an MDF pilot plant with a 40 wt .-% aqueous sodium disulfite solution, corresponding 6% sodium hydrogen sulfite atro fibers, added. The MDF manufacturing process was as usual continued with a throughput of 30 kg / h, the wood chips were defibered by the refiner, and the obtained fibers were passed through the blowline continuously with the glue formulation listed in Table 8 glued.

Table 8

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

Example 6

Analogous the procedure described in Example 5, but with use of white pigment Titanium dioxide was an MDF plate using the table 6 listed Glue batch made.

Example 7

Analogous the procedure described in Example 5, but with use of white pigment Titanium dioxide in combination with optical brightener was an MDF plate using of the listed in Table 9 Glue batch made.

Table 9

Comparative Example V4

Analogous the procedure described in Example 5, but without addition of sodium disulfite, an MDF board was made.

In Table 10 shows the degrees of whiteness achieved (expressed in the Brightness difference ΔL), based on the comparative example V4 as standard listed.

Table 10

Claims (8)

Wood-based panels made of bleached wood fibers are made. Wood-based panels according to claim 1, wherein the Wood fibers first oxidative and then bleached reductive. Wood-based panels according to claim 1 or 2, at which the wood fibers during the blanks have been bleached. Wood-based panels with a white pigment mass colored are. Wood-based panels according to claim 4, which are provided with a Dispersion of a white pigment mass colored are, in addition contains optical brightener. Wood-based panels according to claims 1 to 4, made of bleached wood fibers and with a white pigment mass colored are. Wood-based panels according to claims 1 to 5, made of bleached wood fibers and with a dispersion a white pigment mass colored which contains optical brighteners. Wood-based panels according to claims 1 to 7, characterized in that it are MDF, HDF or chipboard.