Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N1/00—Pretreatment of moulding material

Definitions

• the present invention relates to the manufacture of a a wood replacement product, such as consist of a composite resin material organic and wood fiber, in the density range medium. These are materials that come under the form of plates to be cut and which is called in the profession a "medium density fiberboard", or "MDF", from the Anglo-Saxon expression.
• MDF medium density fiberboard
• Wood fibers have undeniable advantages for the manufacture of composite materials from compositions in which they are mixed with organic resins hardening by polymerization. They provide much better cohesion than fillers in powder. They also have the advantage of being largely available inexpensively from sawmill residues and factories for the manufacture of carpentry articles in real wood.
• the manufacturing MDF composites especially in the case of a industrial manufacturing, involves compositions and conditions that are different from the ones we apply for light products or for very dense materials in which wood fibers are little more than a charge among others.
• Wood fibers are generally used there calcined and in combination with organic resins of the family of aminoplasts, especially those melamine-formaldehyde and / or urea-formaldehyde resins, in proportions such as when the basic composition is spread out in a felt then hardened, which is done hot under mechanical pressure, at a temperature sufficient to cause polymerization of the resin binder (s), it leads to usable MDF material plates, better, replacing wood or reconstituted wood plates more classic.
• organic resins of the family of aminoplasts especially those melamine-formaldehyde and / or urea-formaldehyde resins
• composites of this type find many applications in the industry, where they are generally intended to replace wood in its applications common, especially for the manufacture of furniture and other equipment of premises and decoration, but also for making boxes, panels and miscellaneous items. It follows that they must be equally easier than natural wood to cut, hole, glue, screwing, planing, abrading, polishing, etc. However, even if we can try, compared to natural wood, to do better in certain properties such as resistance to chemical agents, impact or scratch resistance, fire resistance etc. they still exhibit the major drawback of not accepting painting subsequent superficial for consumption reasonable.
• the invention is based on the selection of specific coloring agents in combination with the composition of the material to be cured and the conditions of its implementation.
• the subject of the invention is a manufacturing process a wood replacement product, presenting in cutting plates and made of a composite material organic resin from the aminoplast family and wood fibers, in the range of medium densities, which characterized in that, to ensure the coloring of the material in its mass in various shades, and especially in pastel tones, it consists in causing the hardening, by hot polymerization under pressure mechanical, of a composition comprising a coloring agent organic in addition to organic resin and fibers wood, this composition being subjected beforehand to a hot drying step in an oxidizing atmosphere.
• the dyes can advantageously be of the type cationic. However it is better to choose them from dyes cataloged basic or those cataloged direct, with a preference for the latter that they are not of the cationic type.
• the coloring agent possibly itself constituted by a mixture of several compatible chemical compounds, is present in the composition in an effective proportion both to remove the shade from the fibers of wood that he would have in his absence and to confer his clean shade to final hardened material.
• this proportion is advantageously included in the range of 0.1 to 3% by weight of the weight of dry matter of the total composition, and preferably between 0.1 and 1%.
• the coloring agents useful according to the invention exist on the market. They are offered there for completely different applications, namely dyeing textile fibers in natural or synthetic fabrics.
• the invention relates not only to the process, but also on the corresponding composition and on the plate materials obtained.
• the wood fibers are incorporated into the composition to be cured in the form of a so-called thermo-mechanical pulp, resulting from the drying of crushed wood waste.
• excess wood waste is reduced to sawdust or shavings then sieved or otherwise sorted to keep only those whose dimensions are of the order of 5 to 40 mm. Then after a possible cleaning in itself classic, they went into oven for humidification and softening treatment by water vapor which takes place at a temperature in the range of 150 to 170 ° C. They are ejected from it through a rotary disc mill that shreds them into fibers whose length does not exceed 1 to 2 mm on average.
• the chemical composition of the wood is as follows, by weight: Average Cellulose 43 - 47% 45% Hemicellulose 25 - 35% 30 % Lignin 16 - 24% 20% Volatile matter 2 - 8% 5%
• sawdust from wood fibers is intimately mixed in the composition with the resin added with coloring agent from the drying step prior to the actual hardening step.
• the resin is as it is classic a resin belonging to the family of aminoplast resins, and capable of hardening by polycondensation of the resin on itself and possibly also by reaction with others constituents added to the composition.
• the resin used here is a urea-formaldehyde resin or a melamine-urea-formaldehyde resin. In general, it is not it does not have to be modified by another polymer. On the other hand, urea-formaldehyde copolymers are often preferred. and melamine formalin.
• the resin comprises 75% urea and 25% melamine, in combination with formaldehyde in the stoichiometric proportions.
• a paste is thus obtained which is deposited in regular thickness on a sieve band which passes over vacuum pumps, so as to compact the dough retained on the sieve to form a felt.
• the operation leads to a felt compact where the wood fibers are distributed so homogeneous and where cohesion is already ensured between them and the resin added with dye.
• the rate humidity is only around 8 to 10%. They are lowered for example by 12% at the end of the drying stage 9% after additional drying at room temperature involved in the compaction step.
• the composition has a slightly acid, unlike the starting paste.
• the pH is between 8.5 and 10, and at the end of drying, it is close to 5.
• the felt thus obtained in a continuous strip is cut into individual plates before being subjected to a baking which hardens by polymerization.
• This cooking takes place hot and under pressure, each plate being compressed between two plates of a mechanical press which simultaneously heat it to a temperature of the order of 170 ° C, more generally between 160 ° C and 180 ° C .
• the pressure is of the order of 290 bars, and more generally between 30 and 10 kg / cm 2 .
• the plates finally obtained, colored in the mass, are ready to be marketed after a rectification of the edges.
• their chemical compositions consist, in weight proportions of dry matter, of: On average Wood fibers 80 - 90% 83% Organic resin 8 - 12% 10% Paraffin oil 1 - 2% 1.5% Organic dye 0.1 - 1% 0.5%
• Coloring agents incorporated in these compositions according to the invention at a dose between 0.1 and 1% by weight of the total weight of the material composition dry (depending on the intensity of coloring desired in the mass of the final plate), are all dyes organic which only belong to two categories of the SDC classification, namely that of the so-called compounds basic, or that of so-called direct coloring agents.
• the dyes recommended according to the invention have been developed for used for dyeing textile fibers, mainly cotton fibers, which are free of lignin and exclusively made of cellulose. So it was unpredictable that the coloring agents of this family can be effective in coloring composite materials to based on wood fibers, to the point of imposing the color dye by making the natural color disappear coming from the wood fibers that the material would have in their absence.
• the dyes have their coloring power preserved throughout composition processing, even though the conditions of its implementation make it undergo variations in pH temperatures and high temperatures, whether during the drying stage or during the hardening stage thermo-mechanical proper.
• the cellulose contained in the wood fiber is in the form of microfibers, or fibrils, showing amorphous regions and others the addition of water vapor during the treatment results in an increase in amorphous regions.
• Organic compounds constituting dyes so-called basic are much less likely than dyes direct to react with cellulose fibers but they have the advantage of having a strong electrophilic affinity, hence their capacity to form hydrogen bridges linking them by Van des Walls' forces in the amorphous regions of the fibrils.
• the invention has the advantage of allowing the manufacture of wooden plates to be cut which present in the mass, variable shades at will, and in particular in pastel shades, which you could't imagine build on previous technical knowledge without inventive work.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)
• Dry Formation Of Fiberboard And The Like (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9511535

Family Applications (1)

Country Status (2)

Cited By (3)

Citations (3)

• 1997
  • 1997-09-22 FR FR9712032A patent/FR2768645A1/fr active Pending
• 1998
  • 1998-09-22 EP EP98402324A patent/EP0903208A1/de not_active Withdrawn

Patent Citations (3)

Also Published As

Similar Documents

Legal Events