CS234437B1 - Agglomerated boards and method of their production - Google Patents

Abstract

Agglomerated boards based on lignocellulose mass and a synthetic binder consisting of aminoaldehyde resin, amino compound, hardener, hydrophobicizing agent and optionally additives from the group of fungicides, flame retardants, fillers, pigments and dyes. These agglomerated boards are characterized by very low formaldehyde leakage, maximum 5 mm per 100 g of board, and are particularly suitable for furniture production and interior design of buildings.

Description

Wood-based agglomerated boards are commonly manufactured in a continuous process from disintegrated wood. A solution of hardenable resin is sprayed onto the dried chipboard. The material is layered to the basic dimensions of the board and pressed under high heat and pressure into a solid board. These materials are mainly used in construction and furniture manufacturing.

The most commonly used binder for agglomerated boards is urea-formaldehyde resin, the advantage of which is its availability, low price and advantageous processing properties. A significant disadvantage of cured urea-formaldehyde resin is its susceptibility to hydrolysis at elevated temperatures and humidity, with the release of formaldehyde. Therefore, particle boards with this binder release formaldehyde for a long time. If the boards are used indoors in larger quantities, the formaldehyde content in the air very often reaches a value exceeding the maximum permissible concentration set by hygiene regulations.

In order to reduce formaldehyde emissions from particleboard, a number of different modifications have been proposed, concerning both the binder and the particleboard. First of all, the molar ratio of formaldehyde to urea in the resin was reduced, and thus the content of free and releasable formaldehyde was reduced, namely by so-called urea modification. However, this modification is only possible to a certain extent, and further undesirable changes in some properties of the resin occur, such as impaired solubility, stability and especially reactivity /K*Ernst, Holz ais Roh- u· Werkstoff, 1982, 40, 249/ Modifications with other amino compounds or other substances that are capable of binding formaldehyde, e.g. ketones, phenols, sulfites, encounter similar problems or are not economical. Furthermore, procedures are known in which e.g. ammonia or urea is added to the basic resin during application, or is applied separately by spraying the particleboard material ZDAS 2,553 459/ However, the greater addition of these substances to the ^urea -formaldehyde resin causes, in addition to a decrease in reactivity, a large decrease in the viscosity of the binder, which seeps into the chipboard mass and loses its cohesion*, ultimately significantly reducing the mechanical and physical properties of the chipboard*. A certain improvement in the quality of the boards in terms of formaldehyde release can also be achieved by technological changes in their production*, for example* by optimizing the pressing conditions*, which, however, usually has an adverse impact on the production economy*. To reduce formaldehyde emissions, additional treatments of the boards* have been proposed, especially by the action of gaseous ammonia or by spraying an ammonium carbonate solution*, where the released formaldehyde reacts to non-volatile hexamethylenetetramine*. These treatments*, requiring additional equipment*, often have only a short-term effect. Additional surface treatments of chipboard, such as coatings*, lamination, etc.*, are costly and not always effective.

The above-mentioned shortcomings are eliminated by the present invention* It describes hygienically harmless single-layer or multi-layer agglomerated boards based on lignocellulose mass and synthetic binder with very low formaldehyde leakage* which are particularly suitable for the production of furniture and the creation of building interiors* It also relates to a method of producing these boards* The essence of the invention lies in the fact* that the agglomerated boards consist of 80 to 95 parts by weight of lignocellulose mass* 5 to 15 parts by weight of a hardened binder based on a mixture of 75 to 92 parts by weight of dry matter of aminoaldehyde resin and 8 to 25 parts by weight of amino compound* Furthermore, they contain 0*01 to 1 parts by weight of a hardener from the group of hydrolyzable salts of inorganic and organic acids and/or organic acids themselves* 0*1 to 2 parts by weight of a hydrophobicizing agent*, for example paraffin* and up to 12 parts by weight of water* The board optionally contains 0*05 to 10 parts by weight* of additives from the group of fungicides*, flame retardants*, fillers*, pigments and dyes. The starting aminoaldehyde resin is prepared by condensation of an amino compound*, especially urea and/or dicyandiamide and/or melamine* or* their derivatives* with formaldehyde with a molar ratio of amino groups and aldehyde groups of 1*6 to 1*8*. After the addition of the amino compound*, preferably urea*, a molar ratio of these groups of 1*8 to 2*5* is achieved, preferably 1*94 to 2*2*. Salts of inorganic and organic acids include chlorides*, sulfates, nitrates*, phosphates and oxalates of divalent and/or trivalent metals*, e.g.* magnesium*, zinc*, aluminum*, iron and/or ammonium*, individually or in mixtures thereof*.

The method of manufacturing the agglomerated boards mentioned consists in*

234 437 that a catalyzed binder is continuously applied to the disintegrated lignocellulose mass. In the case of a multilayer board, the binder has a different composition for the inner layer and the outer layers. The binder is made up of an aqueous solution or dispersion of amino resin, amino compound, hardener and hydrophobicizing agent in an amount of 9 to 12 g per 1 m of surface area of the disintegrated mass, calculated in dry matter. It is prepared by simultaneous or gradual mixing and application of the individual components. The semi-finished product is then formed, pressed and cured in the usual way under a pressure of 0.7 to 3.5 MPa and a temperature of 140 to 180°C. This produces hygienically harmless agglomerated boards with formaldehyde emissions of no more than 5 mg per 100 g of these boards.

As already mentioned, the biggest obstacle to reducing the molar content of formaldehyde in the amino resin, and thus also to reducing free and hydrolyzable formaldehyde, has been the decrease in its reactivity. For example, reducing the molar content of formaldehyde in a urea-formaldehyde resin below 1.25 per 1 mole of urea will result in impaired hardenability, so that a longer pressing time is required for sufficient hardening of such a binder in a particle board. Partial improvement in this direction can be achieved by modifying the starting materials and technological changes / ^e-202 405/. When reducing the molar content of formaldehyde to 1.1, the physical properties of the binder are completely different from conventional binders and the pressed particle boards do not have the necessary mechanical properties /M. Kellner, M. Sedliačik, Dřevo, 1983, 38, 26/.

The loss of reactivity of urea-formaldehyde resin by modification with additional urea is seemingly in contradiction with the results of the study of the kinetics of condensation of urea-formaldehyde addition compounds. It is known that of the functional groups present in the reaction solution, the amino group is the most reactive. The observed decrease in the reactivity of the modified resin has several causes. The basic urea-formaldehyde resin, prepared by alkali-acid condensation to the required condensation degree, can be modified with additional urea without loss of solubility only in an alkaline medium. In this case, the addition of free and labilely bound formaldehyde to urea occurs mainly to form low-molecular methylol compounds, which are stabilized by intramolecular side bonds. As a result, the reactivity of the resin decreases. The urea-modified resin contains only a small amount of free formaldehyde. The loss of reactivity of the resin is also caused by a decrease in the efficiency of the catalyst, most often ammonium chloride, whose function is to

234,437 in the release of hydrochloric acid by the reaction of ammonium salt with formaldehyde

According to this invention, the decrease in resin reactivity is limited by preventing the addition of formaldehyde to the modifying urea. Therefore, a urea-formaldehyde resin with the lowest possible formaldehyde content is used as the basic binder component, and a relatively high amount of urea» or other amino compounds» is added only before use. At the same time, the addition of a suitable catalyst and the selection of optimal processing conditions create the conditions for condensation reactions» leading to complete hardening of the material with the participation of lignocellulosic material. In this case, most of the reactive groups and bonds of the resin are converted into stable methylene bridges» which create a solid connection between the wood material and the resin» which ultimately results in a significantly reduced ability to hydrolyze and release formaldehyde.

The basic aminoformaldehyde resin according to this invention is most often a urea-formaldehyde resin, optionally modified with another amino compound, with a molar ratio of NHg groups to CHO groups in the range of 1.6 to 1.8. The addition of urea or another amino compound is chosen so that a sufficient amount of reactive amino groups is available. At the same time, a higher addition of this component contributes to an increase in the dry matter and thus to maintaining the necessary viscosity of the binder. The fact that this addition adjusts the molar ratio of NHg/CHO groups in the binder to 2 and above seems to be in conflict with the theoretical possibility of the formation of a hardenable condensate. However, the fact that hardening occurs with the contribution of hydroxyl and other reactive groups of cellulose, hemicelluloses and lignin of the wood mass is proven by the properties of the agglomerated boards according to this invention. Favorable conditions for the formation of these boards are provided by the catalytic system used, where in addition to conventional ammonium salts, hydrolyzable metal salts can also be used. salts acting independently of the free formaldehyde content. In addition, suitably selected thermal processing conditions also play a role. The amount of catalyzed binder applied to the disintegrated lignocellulose mass is also an important factor. This amount, based on the surface area of 2 chips, is 9 to 12 g per 1 m2, calculated in dry matter. The applied mass is layered into a chip mat so that the bulk density of the pressed chipboard is greater than 680 kg/m2 and of the lightweight chipboard greater than 460 kg/m2, which guarantees the achievement of first-class quality of the agglomerated board.

234,437

The basic material of the agglomerated boards according to the present invention is either chips prepared for this purpose from wood raw material on special chipping machines or chips, sawdust, shavings and shavings, which are waste material from other wood processing and which can be further ground and sorted into suitable fractions. The treated and dried chip mass should have 2 to 5% moisture. Waste from lignocellulose single-leaved trees, mainly flax husks, is also used for agglomerated boards.

The starting aminoaldehyde resin is prepared by condensation of amino compounds with aldehydes. Among amino compounds, urea and its derivatives such as thiourea, methylurea, phenylurea, ethyleneurea, hydroxyethyleneurea, ethyleneurea, acetylenedurea, biuret and others are mainly used. Dicyandiamide and its derivatives are also considered, e.g. cyanamide, dicyandiamide, guanidine, biguanide, and also melamine and its derivatives such as amelin, guanamines, etc. In addition to the above amino compounds, other nitrogenous compounds of amide, imide, amine and lactam nature can be used, such as formamide, acetamide, adipamide, toluenesulfamide, maleimide, phthalimide, caprolactam, etc. The second condensation component is most often formaldehyde, glyoxal, acetaldehyde, benzaldehyde, fural, etc. are also considered.

The aminoaldehyde resin is prepared by conventional alkaline-acid condensation, preferably of urea with formaldehyde, with the optional addition of another amino compound, e.g. melamine, in an initial molar ratio of NH^/CHO groups of 0.95 to 1.1 to a condensation stage characterized by viscosity or solubility in water. -9 and subsequent alkaline condensation with a modifying urea or another amino compound so that the final ratio of the said groups is 1.6 to 1.8. A suitable type of such a basic resin^, a thermosetting urea-formaldehyde resin is shown in 202405.

As another binding component, i.e. an amino compound added before application, urea or its derivative is preferably considered, dicyandiamide or melamine and other compounds mentioned above are also suitable.

Suitable hardeners are ammonium and metal salts of inorganic and organic acids, especially acids with a pK lower than 4, such as hydrochloric, sulfuric, nitric, phosphoric, sulfurous, oxalic, citric, maleic, formic, etc. Among the metal salts, the salts of groups II, III, and VIII of the periodic table are preferred, especially salts of magnesium, calcium, zinc, aluminum, and iron.

234,437

Paraffin is commonly used as a hydrophobicizing agent, either in a molten state or in the form of an aqueous dispersion. It is also possible to add fungicidal substances to the binder, e.g. sodium pentachlorophenolate, substances reducing flammability, e.g. hydrated alumina, borates, phosphates, sulfates and common fillers, pigments and dyes, which positively affect the properties of agglomerated boards.

According to this invention, the production of hygienically safe boards is generally carried out in the following manner. Disintegrated lignocellulose material prepared in a conventional manner is dried to up to 5% moisture content (in some cases, flax husks are dried only after the binder has been applied). A solution of catalyzed binder with additives in an amount of 9 to 2 g calculated in dry matter per 1 m of chip area is applied to the thus prepared material in applicators. A lower application rate is used for softwoods and a higher rate for hardwoods. The binder consumption per unit depends on the thickness and specific weight of the disintegrated material. It is determined according to Klauditz from the relation ₈ « -gi“|29_«. (g/lOOg) where n·····, the binder layer in g per 1 M ² jh . ...et>is the weight of the chips in kg/m ; d ,,·,· the average thickness of the chips in mm*

The applied disintegrated mass is further formed, possibly compacted, and pressed at a temperature of 145 to 180°C and a pressure of 0.7 to 3.5 MPa. Pressing is carried out in a single-deck or multi-deck press or in an extruder. When formulating the adhesive mixture, the different curing conditions of the middle and surface layers are taken into account, i.e., maximum curing in the middle layer and as much as possible suppression of hydrolytic conditions in the surface layer of the pressed chipboard. The pressing time depends on the pressing temperature, humidity, geometry and type of chipboard, and also on the format of the pressed board. The pressing time is expressed by the product of the thickness of the pressed board in mm and the pressing factor, which, depending on the selected conditions and processing method, is within the limits of 0.25 to 0.5 minutes per 1 mm of board thickness for the production of chipboards according to the present invention. After pressing, the board is formatted, conditioned, thickness-leveled and shipped in the usual way.

These chipboards allow for wide application as a large-scale structural or insulating material, especially in the production of furniture and the interior design of residential and public buildings, wherever these materials are not constantly exposed to increased humidity.

The subject matter of the present invention is further illustrated by examples.

Example 1 234 ⁴³⁷

Production of single-layer particle board.

The quantity of individual components based on 1 m of particleboard with a density of 715 kg/μιθ at a humidity of 8 wt. %i in kg:

chips, average thickness 0.4 mm.

density 450 kg/m,

moisture 4 wt. %; 627.0 urea formaldehyde resin, molar ratio 1.66, dry matter content 65 wt. %; 100.0 urea 9.0 ammonium chloride 0.5 water 14.0 paraffin emulsion, 25 percent 16.0 total molar ratio of NH^/CHO groups 2.0

The prepared binder including the paraffin emulsion is applied to the chips, in the technological flow the chip mass is further layered into carpets and pressed at a pressing temperature of 160°C with a pressing factor of

0.33 minutes per 1 mm of chipboard thickness.

Features of the manufactured particle board:

bending strength in MPa 27.4 tensile strength perpendicular to the plane of the board in MPa 0.77 swelling after 2 hours in water at a temperature of 20°C in wt.% 3.3 bulk density in kg/m 740 released formaldehyde determined according to

ČSN 49 2657 in mg per 100 g of particleboard 3.5

Example 2

Production of three-layer or multi-layer chipboard.

Quantity of individual components based on 1 m of chipboard with a density of 715 kg/m at a humidity of 8% by weight, in kg:

middle layers of chips, average thickness 0.4 mm,

O bulk density 450 kg/m, moisture 4 wt.%; 394.0 surface layers

233.0 urea-formaldehyde resin, molar ratio 1.66,

dry matter content 65 wt.%; 58.0 41.0 urea 4.04 3.7 ammonium chloride 0.8 0.06 water 7.0 6.0 paraffin emulsion, 25 percent 10.0 6.0 total molar ratio of NH^/CHO groups 1.96 2.0

The chip material applied with a binder is layered in a ratio of middle layer: surface layers 63:37 into a chip carpet, which is pressed at a pressing temperature of 170°C with a pressing factor of

0.266 minutes per 1 mm of chipboard thickness

Features of the manufactured particle board:

bending strength in MPa 23 _r 0 tensile strength perpendicular to the plane of the board in MPa 0.628 swelling after 2 hours, in water at a temperature of 20°C in wt.% 5.1 bulk density in kg/m 720 released formaldehyde determined according to

ČSN 49 2657 in mg per 100 g of particleboard 3.8

Example 3

Production of particleboard by extrusion method

Amount of individual components based on 100 kg of wood chips, in kg:

chips, average thickness 0.8 mm, bulk density 450 kg/m , moisture 4 wt.%; 102.0 urea-formaldehyde resin, molar ratio 1.66, dry matter content 65 wt.%; 7.7 urea 0.53 ammonium chloride 0.1 water 1.4 total molar ratio of NH^/CHO groups in the binder 1.96

Properties of the produced particle board: the board was extruded on a Kreibaum line at a pressing temperature of 170°C and a displacement of 0.80 m per minute, the thickness of the lightweight board was 25 mm; bending strength in MPa 5.8 swelling after 2 hours in water at 20°C in wt.% 3.2

234 437 bulk density in kg/m 470 released formaldehyde determined according to

ČSN 49 2657 in mg per lOOg of particle board 4 _t 2

Example 4

Production of the sheath plate* o

Quantity of individual components in kg per 1 m of board:

mixture of sorted flax husks and sorted sawdust in max* ratio; 30, moisture up to 6% by weight*%; 566.0 urea-formaldehyde resin, molar ratio 1.66, dry matter content 65% by weight*%; 100.0 urea 6.0 ammonium chloride 0.5 water 12.0 paraffin emulsion, 25 percent 5.0 total molar ratio of NH^/CHO groups 1.87

The individual binder components are mixed and applied to the sheath material. Paraffin emulsion, or melted paraffin, is applied separately.* Boards are pressed from the applied sheath at a pressing temperature of 140 to 150°C with a pressing factor of 0.5 to 0.55 minutes per 1 mm of the thickness of the pressing.* The pressed board met the quality parameters according to ČSN 49 2614.* The amount of released formaldehyde, determined according to ČSN 49 2657, was 4.8 mg per 100 g of sheath board.*

The conditions given in the basic examples can be calculated according to the thickness and volumetric weight of the lignocellulose material particles used according to the above-mentioned Klauditz relationship* For softwoods it is more advantageous to choose a layer of 9 to 10 g/m2 and for hardwoods 11 to 12 g/m2 of binder per area of the agglomerated material*

The amount of amino compound added to the binder is related to the total molar ratio of NHg/CHO groups: for single-layer boards, the most preferable molar ratio is in the range of 1.96 to 2.0, for multilayer boards for the middle layers in the range of 1.95 to 1.98, for the surface layers in the range of 2.0 to 2.05*

For particle boards with special requirements for resistance to microorganisms and insects, 1 to 2% by weight of substances with fungicidal and insecticidal effects is added to the binder mixture* To increase resistance10

234 437 fire resistance of particle boards, 25 to 50% by weight of substances that retard the combustion process may be added to the mixture. However, substances added to the binder mixture must not disrupt the condensation reaction of the binder by buffering it and must not reduce the concentration of hydrogen ions in the binder solution below pH 3, which leads to hydrolytic degradation of the condensed resin, thereby increasing the amount of formaldehyde released and reducing the mechanical and physical properties of the particle boards.

The following examples illustrate the above variations in the preparation of particle boards in order to improve their other properties*

Example 5

Production of single-layer chipboard with increased resistance to moisture and microorganisms*

Quantity of individual components in kg per 1 m of chipboard:

chips, average thickness Of4mm, bulk density 450 kg/m , moisture 4% by weight*; 627.0 mixed urea-melaminoformaldehyde or urea-dicyandiamidoformaldehyde resin with a molar ratio of NHg/CHO groups 1.8, dry matter content 65% by weight*; 100.0 urea 5.0 ammonium chloride 1.5 water 16.0 sodium pentachlorophenolate 1.8 paraffin emulsion, 25 percent J.6.0 total molar ratio of NHg/CHO groups 2.0

The individual components of the binder and additives are mixed together and applied to the chip material, which is further processed as in example 1,

Example 6

Production of single-layer particleboard with reduced flammability*

Quantity of individual components in kg per 1 m of chipboard:

chips, average thickness 0.4 mm, bulk density 450 kg/m

234 437 moisture 4 wt.%; 627.0 mixed resin as in example 5 100.0 urea 3.0 secondary ammonium phosphate 5.0 ammonium sulfate 5.0 micronized gypsum 10.0 water 20.0 paraffin emulsion, 25 percent 16.0 total molar ratio of NHg/CHO groups (excluding ammonium phosphate and sulfate groups) 1.905

The individual components, binders and additives, are mixed together and applied to the chip material, which is processed as in example 1.

Example 7

Production of single-layer particleboard with reduced flammability.

Quantity of individual components in kg per 1 m of chipboard;

chips as in example 1 627.0 urea-formaldehyde resin as in example 1 100.0 dicyandiamide 9.0 potassium oxalate 15.0 oxalic acid 0.5 water 45.0 paraffin emulsion, 25 percent 16.0 total molar ratio of NHg/CHO groups 2.0

The individual components of the binder and additives are mixed together and applied to the chip material, which is processed as in example 1. Dicyandiamide must be dissolved in hot water in advance.

Claims (4)

1 »Agglomerated boards of single or multilayer based on lignocellulosic material and synthetic binder with very low formaldehyde leakage, especially suitable for furniture and interior building construction characterized by consisting of 80 to 95 parts by weight of lignocellulosic material, 5 to 15 parts by weight cured binder based on a mixture of 75 to 92% by weight of the aminoaldehyde resin solids and 8 to 25% by weight of the amino compound, 0.01 to 1 parts by weight of a curing agent from the group of hydrolyzable salts of inorganic and organic acids up to 2 parts by weight of a hydrophobizing agent, for example paraffin, up to 12 parts by weight of water and, optionally, 0.05 to 10 parts by weight, parts of fungicide additives, flame retardants, fillers, pigments and dyes; 2 * Agglomerated plates according to item 1; characterized in that the starting aminoaldehyde resin is prepared by condensation of an amino compound, in particular urea and / or dicyandiamide and / or melamine, or derivatives thereof with formaldehyde having a molar ratio of amino groups to aldehyde groups of 1.6 to 1.8 and after addition of an amino compound, preferably urea a molar ratio of these groups of 1.8 to 2.5, preferably 1.94 to 2.2, is achieved. Agglomerated plates according to claim 1 _, characterized in that the salts of inorganic and organic acids include chlorides, sulphates, nitrates, phosphates and oxalates of divalent and / or trivalent metals, for example magnesium, zinc, aluminum, iron and / or ammonium, individual or mixtures thereof · 4. A process for the production of agglomerated boards according to claim 1, characterized in that a cured binder is applied to the disintegrated lignocellulosic mass in the case of a multilayer board of different composition for the inner layer and the outer layer consisting of an aqueous solution or dispersion. 9 to 12 g / m < 2 > surface area of the disintegrated mass calculated on the dry basis, prepared by simultaneous or sequential mixing and application of the individual components, and further forming the formed product, compacting and curing at 145-180 [deg.] 7 to 3.5 MPa