Method for making lignocellulosic board

Method for manufacturing lignocellulose board

BACKGROUND OF THE INVENTION The present invention relates to a method for preparing lignocellulose particles, flexible boards, and board precursors in sheet form for the manufacture of finished products.

The manufacture of composite board products from wood-derived raw materials is well known. Examples are medium density fiberboard (MDF), high density fiberboard, oriented wood wool board, particle board and so on. Such boards are most commonly bonded by condensation resins such as urea, melamine or resol formaldehyde resins. A new trend is to use agricultural fibers as raw materials, because agriculture produces excellent fibers whose sources can be quickly regenerated, thereby reducing the pressure on wood raw materials and logistics supply constraints. In this case, because the nature of the agricultural fiber surface and composition, particle shape and specific surface area put forward more stringent requirements on the adhesive, isocyanate becomes an ideal adhesive.

In the case of all lignocellulose composite board products, plywood, paper products and solid wood, especially soft materials and edge hard materials, water is the most important factor in their degradation.

Therefore, lignocellulosic products are required to be treated to make them highly water resistant.

This requirement can be through pretreatment of granular lignocellulosic materials used as raw materials for board production, or veneers used for plywood production, or by pretreatment of composite boards themselves such as particle board or MDF, pulp and paper products, and solid wood. Post-processing to achieve. DE4223604A discloses the use of one or more water-insoluble polymers, copolymers, oligomers, prepolymers or monomers (especially isocyanate thermosetting resin) dissolved in an organic solvent (especially gasoline) to impregnate fiberPrimematerial.

Minor improvements can also be specified, such as improved mechanical properties, fire resistance, elimination of formaldehyde and resistance to microbes or insects.

There is always a need for improved methods of manufacturing products from lignocellulose materials.

SUMMARY OF THE INVENTION According to the first aspect of the present invention, a method for manufacturing a finished product from a lignocellulose material selected from the group consisting of lignocellulose particles or fibers, soft boards, and sheet-like board precursors is provided. The method includes the following steps: (a) Impregnating the lignocellulose material with an impregnating composition, said impregnating composition comprising:

(i) mineral oil; and (ii) liquid thermosetting resin and, if necessary, its catalyst; it is in the form of a dispersion of liquid resin in mineral oil; and (b) compressed and impregnated while heating The lignocellulosic material, the mineral oil is injected into the lignocellulosic material and polymerized with thermosetting resin to form a finished product.

When the lignocellulose material is lignocellulose particles or fibers, the method of the present invention preferably includes another step (c): (c) before step (a) or preferably before step (b), finely pulverizing The thermosetting resin in the form of dry powder and its catalyst, if necessary, are applied to the lignocellulose material so that the thermosetting resin in the form of a finely pulverized dry powder adheres to the surface of the lignocellulose material.

The lignocellulose material can be: A lignocellulose particles or fibers, such as particles, chips, shavings, wood or agricultural fibers, such as tows or fibers of annual or biennial crop residues, pulp, etc.; B soft board , Its meaning does not have to be a board that has been impregnated or bonded with an adhesive such as thermosetting resin. An example is a low-density board, that is, a board with a density of 180~400kg/m3 (including 180 and 400kg/m3), which is usually formed by a wet method; C is a plate precursor in the form of a sheet, which means Adhesive pad of lignocellulose material, which has not been resinized with adhesives such as thermosetting resins. An example of this is the medium density fiber mat for the production of medium density fiberboard. It is best to form the medium density fiberboard after the initial pre-compression of the medium density fiber, but it can also be formed before the final high pressure of the medium density fiber.

It should be noted that the impregnation composition must not contain a solvent, which gives the method some advantages, including the fact that it can be carried out without removing the solvent before step (b).

The thermosetting resin used in step (a) must be a liquid thermosetting resin so that it can be impregnated into the lignocellulose material to form a dispersion of the resin in mineral oil.

The thermosetting resin used in step (a) is preferably an isocyanate thermosetting resin or a precursor thereof, and more preferably a resin derived from diphenylmethane-4,4'-diisocyanate (MDI).

The thermosetting resin in the form of finely pulverized dry powder used in step (c) is preferably a novolac resin based on phenol and formaldehyde.

The preferred amount of liquid thermosetting resin used in step (a) is 1%-20% (including the end value) of the mass of the dry lignocellulose material, more preferably 2%-10% (including the end value) .

The preferred amount of mineral oil is 5% to 30% (including the end value) of the dry lignocellulose material, more preferably 10% to 20% (inclusive of the end value).

The amount of the thermosetting resin in the form of finely pulverized dry powder used in step (c) can be 0%-20% (including the end value) of the mass of the dry lignocellulose material, preferably 3%-10% (including End value inclusive).

Preferably, before step (a), the lignocellulosic material is dried to a desired percentage moisture content, preferably with a moisture content of 5% to 20% by mass (inclusive).

In step (a), the lignocellulosic material can be impregnated with the impregnating composition in any suitable manner, for example, by spraying or applying the impregnating composition on the lignocellulosic material, or by impregnating the impregnating composition in conventional mixing equipment. The composition is mixed with the lignocellulose material in the form of particles or fibers, or, when the lignocellulose material is a soft board or sheet-like board precursor, the impregnation is combined through any coating, spraying or dipping process The object is applied to one or both sides of the board or the board precursor.

In step (b), the impregnated lignocellulose material can be in a suitable press or mold at a temperature of 120°C to 250°C (inclusive), preferably up to 220°C and a pressure of 2 to 70 kg /cm2 (including the end value), preferably 10~60kg/cm2 (including the end value), 5 seconds to 20 seconds (including the end value) per 1mm thickness is compressed and heated, so that the mineral oil is immersed in the lignin Cellulosic material and polymerize the thermosetting resin or resin present.

The impregnation composition may also contain various optional components such as: (iv) preservatives such as fungicides, fungicides or insecticides, etc., and the preferred amount is 0.25%-10% (including end) of the impregnation composition by mass. Value); (v) wax or dry particulate wax that dissolves in the impregnation composition at high temperature; (vi) other additives selected from flame retardants, ultraviolet light absorbers, dyes and antioxidants.

According to a second aspect of the present invention, there is provided a method for preparing an impregnated lignocellulose material from a lignocellulose material selected from the group consisting of lignocellulose particles or fibers, soft boards, and sheet-like board precursors, and The prepared impregnated lignocellulose material is used to manufacture a finished product, and the method includes the following steps: (a) impregnating the lignocellulose material with an impregnation composition, the impregnation composition comprising: (i) mineral oil; And (ii) liquid thermosetting resin and, if necessary, its catalyst; it is in the form of a dispersion of liquid resin in mineral oil. When the lignocellulose material is lignocellulose particles or fibers, before or after step (a), the method may include additional steps, step (c): (b) before or after step (a) The thermosetting resin in the form of a finely pulverized dry powder and, if necessary, a catalyst thereof is applied to the lignocellulose material so that the thermosetting resin in the form of a finely pulverized dry powder adheres to the surface of the lignocellulose material.

DESCRIPTION OF EMBODIMENTS The gist of the present invention is a method of manufacturing a finished product from a lignocellulose material selected from lignocellulose particles or fibers, soft boards, and sheet-like board precursors.

Lignocellulosic material refers to any plant material formed by photosynthesis.

The lignocellulose material can first be lignocellulose particles or fibers, for example, raw materials for manufacturing composite board products such as particle board, particle board, medium density fiber board, oriented wood wool board, and the like. The raw material can be wood or another type of particles, uniform fibers or small fiber bundles, tows, shavings or chips taken from short fiber segments of agricultural fiber raw materials. The agricultural fiber raw materials are such as annual or biennial crops. , Especially crop waste such as hemp, sisal, cotton stalk, wheat or other grains, straw, bamboo, jute, lye reeds, palm leaves, flax, peanut shells, grain shells and so on.

In addition, the lignocellulose material may be in the form of a low-density soft board, that is, a soft board with a density of 180 to 400 kg/m3, which is usually made by the so-called wet process or the hard board represented by Temple-InlandFibre Products or Masonite Corporation Operations. Produced by the plate method.

Also, the lignocellulosic material may be in the form of a sheet-like board precursor, preferably a pre-pressed mat of MDF fibers that has not been subjected to final high-pressure processing.

The flexible board or board precursor must be such that the oil can penetrate into the flexible board or board precursor during the subsequent compression and the liquid thermosetting resin is intimately dispersed therein, so that a finished product with suitable characteristics can be produced.

Natural plant fibers or particles, or their final products are composed of hemicellulose, cellulose and lignin. The increase in the moisture content of these materials can cause swelling because the cell wall polymers of said materials contain hydroxyl groups or other oxygen-containing groups, which attract water through hydrogen bonds. Hemicellulose is the most hygroscopic. It is the water that swells the cell wall and causes the material to swell until the cell wall is saturated with water. This obviously leads to degradation and swelling and dimensional instability as a result of microbial attack, which in the case of composite panels may cause it to break. This phenomenon occurs in all lignocellulose material groups described in the present invention.

It is known that chemical modification of lignocellulosic materials is performed mainly by using anhydrides and the synergistic resin infiltration of the materials with isocyanate resin. The chemical modification of cellulose serves to reduce the hydrogen bonding phenomenon by reducing the number of hydroxyl groups present. However, the gist of the present invention is to reduce the water contact with these lignocellulose material groups by inserting a hydrophobic cohesive film, which is formed of mineral oil/thermosetting resin.

Therefore, the gist of the present invention is to impregnate the lignocellulose material with an impregnating composition that must contain mineral oil and a liquid thermosetting resin dispersed therein.

The oil must be mineral oil, preferably low-viscosity paraffin oil or inert naphthenic mineral oil.

An example of a suitable mineral oil is: Waksol-F, provided by the Carbon-Tar Division of Sasol Chemical Industries Co., Ltd. in South Africa. It is a mineral oil derived from coal with a flash point of 107.5°C, a water content of 0.05% and wax The content is 10-15%, the wax dissolves in the oil at high temperature, and the pour point of the wax is 30-40°C. The density of this oil is 0.9g/cm3.

Parprol 22 from Engen (Mobil Chemicals), South Africa, is a low-viscosity, honey-colored, petroleum-derived paraffin processing oil with or without wax. Parprol 22 has a density of 0.859g/cm3 and a viscosity of 20.6cSt (1cSt=1×10-6m2/S) at 40°C. The carbon structure group analysis and percentage are aromatic 3, cycloalkane 28, and alkane 69. The sum value is 0.01mgKOH/g, and the flash point is 196°C.

Shell Base Oil, model MVI (P1300), has a polycyclic aromatic compound content of 2.9%, a sulfur percentage of 2%, and a total acid value of 0.1 mgKOH/g.

Other examples are Quendilla 19, a processing oil; or Transcal N, a low-viscosity heat transfer oil, both of which are provided by BP.

Generally speaking, for cost reasons, paraffin oil is preferred to naphthenic oil. Mineral oils within the scope of the present invention are processing oils for waterproofing lignocellulosic materials. They are inert and do not crosslink with thermosetting resins, that is, isocyanates or novolac resins that may be used because of their chemical properties. There are no available hydroxyl groups or other active groups in the composition.

The impregnation composition must also contain a liquid thermosetting resin and, if necessary, its catalyst.

The thermosetting resin is preferably an isocyanate thermosetting resin.

Isocyanates are compounds containing -N=C=O groups and are characterized by the general formula: R(NCO)x, where x is variable and represents the number of NCO groups, and R represents a suitable group.

Examples of organic isocyanates include aromatic isocyanates such as meta and para phenylene diisocyanates, toluene-2,4- and 2,6-diisocyanates, diphenylmethane-4,4'-diisocyanate, diphenylmethane -2,4 diisocyanate, chlorophenylene-2,4 diisocyanate, diphenylene-4,4'-diisocyanate, 4,4'-diisocyanate-3,3'-dimethyl biphenyl , 3-Methyldiphenylmethane-4,4'-diisocyanate and diphenyl ether diisocyanate, 2,4,6-triisocyanato toluene and 2,4,4'-triisocyanato diphenyl ether. Mixtures of isocyanates can be used, such as toluene diisocyanate isomers such as the commercially available mixtures of 2,4- and 2,6-isomers and also dimerization resulting from the phosgenation of aniline/formaldehyde condensates. And a mixture of polyisocyanates. Such mixtures are well known in the art and include crude phosgenation products of polyphenyl polyisocyanates containing methylene bridges, including diisocyanates, triisocyanates, and more with any phosgenation by-products. High-functionality polycyanate ester.

Preferred compositions are those in which the isocyanate is an aromatic diisocyanate or higher functionality polyisocyanate, especially polyphenyl polyisocyanate containing methylene bridges of diisocyanates, triisocyanates and higher functionality polyisocyanates The crude mixture. Methylene bridged polyphenyl polyisocyanates are well known in the art, and are sometimes referred to as polymeric methylene bridged polyphenyl diisocyanates (MDI) with isocyanate functionality of 2.5 to 3, and others The product is sometimes referred to as crude MDI with higher functionality. They are prepared by the phosgenation of the corresponding polyamine mixture, which is obtained by the condensation of aniline and formaldehyde.

Specific examples of suitable isocyanates are those with an (NCO) percentage content preferably exceeding 20%, more preferably exceeding 25%. These isocyanates promote the latent state or reduce activity due to the high number of NCO groups and provide maximum hydroxyl binding capacity. Examples are Desmadur VKS or Desmadur VK from the Bayer company, which are mixtures of aromatic polyisocyanates such as diphenylmethane-4,4-diisocyanate and polymeric substances. These substances and similar substances are those referred to in the industry as the MDI class. Another material used is diisocyanate-diphenylmethane, a more specific example is Suprasec DNR-5005 (it is polymerized MDI), or Suprasec 2020 (it is monomeric MDI), both of which have available NCO The percentages are 30.7% and 29%, respectively, which are polymerized MDI and monomeric MDI with standard functionality. Suprasec resin is supplied by ICI. Another example of crude MDI is Voronate M229 provided by Dow Chemical Company.

Another suitable diisocyanate is toluene diisocyanate, and its other name is tolylene diisocyanate abbreviated as TDI, such as Desmadur L 75 from Bayer.

It must be noted that the term "isocyanate thermosetting resin" is used to include the resin itself and those components that can be referred to as the resin precursor, such as MDI and TDI.

Another example of wood esterification is the use of ethyl isocyanate, which reacts with hydroxyl to form urethane (urethane) according to the following formula:

The isocyanate resin reacts with the hydroxyl groups on the cellulose and hemicellulose molecules of the lignocellulose material to form wood esters. In this way they form a chemical bond instead of a cohesive bond. The isocyanate helps to bind the mineral oil to the lignocellulose matrix.

Other examples of suitable thermosetting resins are as follows: epoxy resins such as the Epikote series provided by Shell Chemicals or Araldite PY340.2 provided by Ciba-Geigy, using 80°C latent heat trigger catalysts such as those provided by Anchor Chemicals Catalyzed by boron trifluoride or aromatic polyamines such as Ancamine SRX. Methyl methacrylate, acrylic acid or methacrylate esters, use a suitable catalyst.

The preferred amount of liquid thermosetting resin is 1%-20% (inclusive) of the mass of the dry lignocellulose material, more preferably 2%-10% (inclusive).

The preferred amount of mineral oil is 5%-30% (inclusive) of the mass of the dry lignocellulose material, more preferably 10%-20% (inclusive).

It should be noted that the quality of the liquid thermosetting resin and mineral oil used is based on the quality of the dry lignocellulose material. In this regard, in the method of the present invention, it is ideal to apply mineral oil and liquid thermosetting resin to the lignin fiber that has been dried to a desired percentage moisture content, usually 5% to 20% by mass (inclusive).Primematerial. Therefore, the dry lignocellulosic material means a lignocellulosic material with a percent moisture content of 5% to 20% by mass (inclusive). In addition, as mentioned earlier, mineral oil is used in the presence of anhydrous or non-aqueous solvents for mineral oil. This eliminates the need to remove solvent before further processing.

When the lignocellulose material is lignocellulose particles or fibers, the method of the present invention preferably includes step (c), which is before step (a) or before step (b), the finely pulverized dry powder form The thermosetting resin and its catalyst if necessary are applied to the lignocellulose material in order to make the thermosetting resin adhere to the surface of the lignocellulose material.

The thermosetting resin is preferably a novolac resin based on phenol and formaldehyde, for example, a phenol resin whose molar ratio of phenol to formaldehyde exceeds the same level, or a phenol resin modified with a nut oil extract or a long-chain alkyl group with a nut oil. Phenolic resins used with prepolymers, they may contain catalysts such as hexamethylenetetramine. These products generate a source of formaldehyde when thermally decomposed, which causes the condensation of the polymer to form a three-dimensionally stable, hard and hard water-insoluble network with minimal shrinkage.

Examples of suitable novolac resins are CH113 from BP Chemicals, J3100L from BP Chemicals, or Schennectady SA891 or PRP3337 from Polyresin Products of South Africa, all of which are long-flow novolac resins.

The preferred amount of the thermosetting resin in the form of finely pulverized dry powder is 0%-20% (inclusive) of the mass of the dry lignocellulose material, more preferably 3%-10% (inclusive).

The dipping composition may also contain preservatives such as fungicides, fungicides or insecticides, especially termiticides. The preferred amount of preservatives is 0.25%-10% of the mass of the dipping composition. Examples of biocides are complexes of boron, atrazine, thiazole or carbamate, and examples of termiticides are zinc or copper naphthenates, synthetic pyrethrins, oil-compatible high-boiling tar acids, Pentachlorophenol or tert-butyl tin oxide-hexachlorobenzene.

The impregnation composition may also contain other additives listed below.

Fire retardants or flame retardant chemicals can be added to the impregnation composition to add advantages. There is considerable compatibility with other components in the impregnation composition, and the flame retardant used is selected based on its solubility in the selected solvent. Examples are Flyrol FR2-LV [it is tris(1,3-dichloroisopropyl) phosphate] provided by Akzo Chemicals and FlyrolDMMP (dimethylmethalphosphenate with a phosphorus content of 25% and an acid value of 1.3 mgKOH/g ). The flame retardant also functions as an effective viscosity inhibitor. The flame retardant is added at a ratio of 0.25% to 5% of the mass of the impregnating composition.

The impregnation composition of the present invention may also include wax dissolved in the impregnation composition.

The first step of the method of the present invention is to impregnate the lignocellulosic material with the impregnation composition. This can be achieved in any suitable way.

For example, when the lignocellulosic material is in the form of particles or fibers, the impregnation composition can be applied to the particles or fibers by a fine atmospheric spray in the discharge line, and then, optionally, the fine air spray is applied downstream of the discharge line. Thermosetting resin in the form of pulverized dry powder.

In addition, and again when the lignocellulosic material is in the form of particles or fibers, the impregnating composition can be fed into the mixer and mixed with the particles or fibers, for example using conventional mixing equipment such as a ribbon blender , Screw type or paddle type blender, and then optionally post-add the thermosetting resin in the form of finely pulverized dry powder.

In addition, as another way, when the lignocellulose material is a soft board or board precursor, the impregnating composition can be applied to one or both sides of the board or board precursor by a curtain coater, a roll coater or a sprayer. Surface. It must be ensured that the impregnation is carried out within the entire thickness of the board or board precursor. This can be achieved by subjecting the board or board precursor to appropriate pressure and temperature conditions to promote the penetration and close impregnation of the impregnating composition before the resin is fully polymerized. Guaranteed.

During this processing, the plate or plate precursor can then be compressed into a flat plate or profile.

The second step of the method of the present invention is to compress the impregnated lignocellulose material with simultaneous heating in a suitable press or flat or tangible mold, so that the existing oil is injected into the particles or fibers or board or board precursor And polymerize any resin that exists to form a finished product.

For example, the lignocellulosic material can be used in a suitable press or mold at a temperature of 120°C to 250°C (inclusive), preferably 130°C to 220°C (inclusive), and a pressure of 2 to 70kg/ m3 (including the end value) is hot pressed.

As mentioned above, the optional third step of the method of the present invention is to apply the thermosetting resin in the form of a finely pulverized dry powder and, if necessary, its catalyst before step (a) or preferably before step (b) Lignocellulose particles or fibers. The method to achieve this has been described above.

The use of mineral oil-containing impregnating compositions has several advantages. First, the mineral oil acts as an isolation layer for the liquid thermosetting resin, so that the liquid thermosetting resin can be dispersed in the form of finely divided, very fine droplets. Because mineral oil is not volatile, this increases the safety of the resin system and prevents droplets from escaping into the atmosphere.

In addition, a very low percentage of liquid thermosetting resin can be applied to the lignocellulose material while still maintaining a uniform and reliable distribution, and there is no need to add any water or other things that may affect the final product when heated and pressurized. Of solvents.

In addition, mineral oil functions as a water repellent to prevent water penetration, and also prevents water from penetrating the treated lignocellulose material due to capillary action.

Finally, when the thermosetting resin in the form of a finely pulverized dry powder is used, the oil ensures that it can firmly adhere to the surface of the lignocellulose material.

As an example to illustrate the effect of using the impregnation composition, the MDF made by the method of the present invention shows a water swelling rate of less than 3% and a water absorption rate of less than 6% after 24 hours of water immersion. The water swelling rate of the treated material is 30% and the water absorption rate is 70%.

The following are examples of the method of the present invention.

Example 1

Prepare the impregnation composition as follows:

In the absence of solvents, liquid MDI is dispersed in mineral oil. With this impregnation composition, 1200 g of wood chips were impregnated.

Thereafter, 90 g of novolac resin, PRP3337 from Polyresin Products, was applied to the impregnated wood chips. PRP3337 is a long-flowing, moderately active novolak resin in the form of a finely pulverized (200 mesh or finer) dry powder. The novolak resin particles adhere to the impregnated wood chips.

Thereafter, the wood chips impregnated and impregnated with resin are compressed at a temperature of 210°C and a pressure of about 25 kg/m3, and the hot pressing time is about 8 minutes per mm thickness to form a board with a density of 975 kg/cm2.

The panels formed in this way can be used for applications exposed to humid environments.

In Example 2, a soft board with a density of 225 kg/m3 and a thickness of 14 mm was dried in a dryer to a moisture content of 2% by mass.

The impregnation combination of 5% by mass of MDI Suprasec 5005 provided by ICI or Desmodur VKS provided by Bayer in 75% by mass of WaksolF (a low-viscosity mineral oil derived from coal) provided by Sasol Chemicals The material was applied to the soft board by a curtain coater at a rate of 1.5kg/m3, applying 66% to the top surface of the board and 34% to the bottom surface of the board.

After that, the plates were compressed between the forming press plates at a pressure of 50 kg/cm2 and a temperature of 180°C to form a waterproof door panel with a thickness of 4 mm and a density of 1170 kg/m3.