DK170753B1 - Process for making pressed materials - Google Patents

Abstract

Compression materials are prepared by compressing substrates with binders which contain polyisocyanates, compounds having at least two hydrogen atoms which are reactive towards isocyanates, alkylene carbonates and, if desired, further additives.

Description

DK 170753 B1

The invention relates to a process for preparing pressed materials using polyisocyanate binders or mixtures of polyisocyanates and other binders and simultaneously using additives 5 consisting of polyether or polyester polyols as well as any mixtures thereof and alkylene carbonates.

Pressed materials, e.g. particle boards, compound sheets or other moldings are usually prepared such that inorganic or organic feedstock, e.g. a lot of 10 wood shavings, wood fibers or other lignocellulosic material, are hot pressed with various adhesives or binders. In the wood material industry, which is the largest in the field of pressed materials, away from it are still used as the main binders, e.g. aqueous dispersions or solutions of urea / formaldehyde (aminoplast) or phenol / formaldehyde (phenoplast) resins.

It is also known to use polyisocyanates or polyisocyanate solutions as binders for pressed sheets instead of formaldehyde resins (DE Publication 207, 1.271984, 1.492.507, 1.653.177 and 2.109.686).

The use of polyisocyanates as binders, since 1973, has become increasingly industrial, improving the stability and wettability of products and increasing their mechanical strengths. In addition, polyisocyanates as binders have far-reaching process technical advantages, as described in DE Publication No. 2,109,686.

The large industrial manufacture of materials bonded with polyisocyanates, especially lignocellulosic materials, e.g. however, unlike 30 aminoplastic resins, wood chipboard is hampered by the non-tackiness or cold-sticking ability of the glued chips. Even with a cold compression (cold pressing) of the polyisocyanates glued, but still moist material parts, no sufficiently stable or self-supporting moldings can be obtained, as is necessary for many production plants. In this way, a universal use of polyisocyanates in the preparation DK 170753 B1 2 of pressed materials is very difficult.

The particle blanks spread on strips, pressed sheets and the like are transferred during transport to the hot press for additional strips, sheets, rollers and the like are pushed off, and these substrates are removed. In order for this to be possible without destroying the chipboard blanks or without disturbing the edge zones, the chip blanks are cold-compressed. In the case of pre-compressed moldings, their surface chips must also be interconnected so that the air which passes out between the chip forms and the enclosed hot-pressing plates does not tear any chips (ie no mud blowing ”of the surfaces takes place). There are continuous and tactile working presses which load the chips for 10-60 seconds with specific pressures 15 of up to 40 bar.

The invention has for its object to develop a method which eliminates the disadvantage of the lack of cold adhesive of the polyisocyanate binders while preserving the favorable flowability of the glued chips which is necessary for an impeccable spread of the moldings.

This object is achieved in a surprisingly simple manner by those skilled in the art by the method of the invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a process for preparing pressed materials by pressing layers of raw materials and / or particulate raw materials with polyisocyanate-based binders, the process being characterized in that the binder contains, as components, polyisocyanates, compounds having at least two hydrogen atoms which are reactive. to isocyanates, having a molecular weight of 400 to 10,000, alkylene carbonates and optionally additional additives, whereby 100 parts by weight of the polyisocyanate, 10-250 parts by weight, preferably 20-80 parts by weight, of the compounds having at least two hydrogen atoms reactive to isocyanates having a molecular weight of 400 to 10,000 are used and the ratio of these compounds to the alkyl carbonate is in range DK 170753 B1 3 from 0.5: 1.0 to 10.0: 1.0 parts by weight.

Preferred embodiments of the invention consist in the alkylene carbonate being propylene carbonate, the compounds having at least two hydrogen atoms reactive to isocyanates having a molecular weight of 400-10,000 being hydroxyl group-containing polyethers or polyesters having a molecular weight of 400-10,000. contains aromatic polyisocyanates, the aromatic polyisocyanates are mixtures of diphenyl-methane diisocyanates and polyphenyl-polymethylene-polyisocyanates obtained by aniline-formaldehyde condensation and subsequent phosgenation, and the binder contains, as additional additives, aqueous condensates. of urea, melamine, phenol and tannin or any mixtures thereof with formaldehyde and sulfite liquor.

According to the invention, a cold adhesive of the chips is obtained with the aforementioned binders from e.g. lignocel-20 Lulose-containing raw materials.

Accordingly, it will also be possible to exploit the advantages offered by the polyisocyanates as binders to pressed materials on such production lines on which the cold adhesive properties of the chip molds are indispensable. Of particular economic utility is the ability to shorten the pressing time in the hot press using the method of the invention. The cold-adhesive properties of the chips glued with the present binders present additional advantages. Disturbances in the peripheral area of the dispersed particulate matter are reduced or avoided.

30 With the lower edge losses, the economic utilization of the raw sheets is increased. This is also of interest to plants that do not necessarily require cold-sticking chipboard blanks.

Both the combination of polyols with polyisocyanates as binders (DE Publication No. 2,538,999, DE Publication No. 2,403,656) and additions of alkylene carbonate, e.g. propylene carbonate, for polyisocyanate (US Patent No. 4,359,507, Elastomers Plastics: 16 (1984) No. 3) is sufficiently described.

However, for an economically appropriate use of such binders, it is necessary that the fluids be applied to the chips in an optimum fine atomized state. In the case of e.g. high viscous polyols, this is done by colloidal solution of the polyol components in a liquid medium, e.g. water (DE Publication No. 2,538,999). Alkylene carbonates can again be used in the present form due to their low viscosity (e.g. propylene carbonate) or the polyisocyanate is also added.

However, the behavior of the thus-glued chips does not differ in any way from the behavior of only the pure polyisocyanate binders with the glued chips. In addition, the addition of 15 hydroxyl group-containing compounds leads more or less rapidly to the corresponding polyurethanes. A suitable use under the conditions which e.g. is common in the wood material industry (storage of the glued raw material for up to 60 minutes at partly higher temperatures), 20 is therefore not expected.

Therefore, it has been found to be much more surprising to those skilled in the art that additions of the present polyols and alkylene carbonate to polyisocyanate binders or mixtures of polyisocyanates with other binders in amounts of 25 to 10-250 parts by weight, based on 100 parts by weight of binder, preferably 20-80 parts by weight, causing cold stickiness of such glued raw materials while maintaining good flowability. The addition of polyol and alkylene carbonate is in the ratio of 0.5: 1.0 to 10.0: 1.0 parts by weight, preferably from 1.0: 1.0 to 3.0: 1.0 parts by weight. The storage of the raw materials glued according to the invention is not adversely affected while maintaining the cold tack, as compared to raw materials which are only glued with polyisocyanate.

In addition, by adding the above-mentioned polyols and alkylene carbonates, it is possible, to a considerable extent, to reduce the pressing times of the pressed materials in the hot press while maintaining the physical and mechanical properties of the finished sheets depending on the pressing temperature.

Speaking as alkylene carbonates come liquid cyclic alkylene carbonates (cyclic alkylene esters of carboxylic acids), preferably propylene carbonate and / or butylene carbonate.

According to the invention, polyisocyanates are used as follows: 1. Aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates, e.g. those described by W. Siefken in Justus Liebigs Annalen der Chemie, 10 562, pages 75-136, for example those of formula Q (NCO) n wherein n means 2-4, preferably 2, and Q means an aliphatic hydrocarbon group having 2-18, preferably 6-10 hydrocarbons, a cycloaliphatic hydrocarbon group of 4-15, preferably 5-10 hydrocarbons, an aromatic hydrocarbon group of 6-15, preferably 6-13 hydrocarbons, or an araliphatic hydrocarbon group of 8-15, preferably 8-13 carbon atoms, e.g. 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1, 3- and -1,4-diisocyanate and any mixtures of these isomers, 1- isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (DE disclosure no.

U.S. Patent No. 1,202,785, U.S. Patent No. 3,401,190), 2,4- and 2,5-hexahydrotoluylene diisocyanate, and any mixtures of these isomers, hexahydro-1,3- and / or 1,4-phenylene diisocyanate, 2,4'- and / or 1,4-phenylene diisocyanate, 2,4- and 2,6-toluylene diisocyanate, and any mixtures of these isomers, diphenylmethane-2,4'- and / or -4,41-diisocyanate and naphthylene -1,5-diisocyanate.

In addition to the present invention, for example: triphenylmethane-4,4 ', 4 "triisocyanate, polyphenyl-polymethylene-polyisocyanates, which are obtained by aniline-formaldehyde condensation and subsequent phosgenation and are described, for example, in GB Patent Nos. 874,430 and 848,671, m- and p-isocyanate-tophenylsulfonyl isocyanates according to U.S. Patent No. 3,454,606, perchlorinated aryl polyisocyanates, for example, described in DE Specification No. 1,157,601 ( U.S. Patent No. 3,277,138), carbodiimide group-containing polyisocyanates, as described, for example, in U.S. Pat.

No. 1,092,007 (U.S. Patent No. 3,152,162) and in U.S. Patent Nos. 2,504,400, 2,537,685, and 2,552,350, norbornane diisocyanates according to U.S. Patent 3,492,330, allophanate group-containing polyisocyanates, such as f. eg. is disclosed in GB Patent No. 994,890, BE Patent No. 761,626 and NL Patent Application No. 7,102,524, isocyanurate group-containing polyisocyanates such as e.g. is disclosed in U.S. Patent No. 3,001,973, to DE

1,022,789, 1,222,067 and 1,027,394, as well as in DE Publication No. 1,929,034 and 2,004,048, urethane group-containing polyisocyanates, such as e.g. are described in BE Patent No. 752,261 or in U.S. Patent Nos. 3,394,164 and 3,644,457, acylated urea group-containing polyisocyanates according to DE Patent No. 1,230,778, biuret group-containing polyisocyanates, such as e.g. are disclosed in US Patent Nos. 3,124,605, 3,201,372 and 3,124,605, and in GB Patent No. 889,050, ester group-containing polyisocyanates, such as e.g. are disclosed in GB Patent Nos. 965,474 and 1,072,956, in US Patent No. 3,567,763 and in DE Patent Nos.

25 1,231,688, reaction products of the above-mentioned isocyanates with acetals according to U.S. Pat. No. 1,072,385 and polymeric fatty acid ester-containing polyisocyanates according to U.S. Pat.

It is also possible to use the isocyanate group-containing distillation residues formed by the technical isocyanate preparation, optionally dissolved in one or more of the above polyisocyanates. In addition, it is possible to use any mixtures of the above polyisocyanates. Aromatic polyisocyanates are preferred.

In particular, the technically readily available polyisocyanates, e.g. 2,4- and 2,6-toluylene diisocyanate DK 170753 B1 7 as well as any mixtures of these isomers ("TDI"), polyphenyl-polymethylene-polyisocyanates, which can be prepared by aniline-formaldehyde condensation and subsequent phosgenation ("crude MDI" "), and carbodiimide group, urethane group, allophanate group, isocyaurate group, urea group or biuret group containing polyisocyanates (" modified polyisocyanates "), in particular such modified polyisocyanates derived from 2,4- and / or 2.6 -toluylene diisocyanates or of 4,4 - and / or 2,4'-diphenylmethane diisocyanate.

The compounds having at least two hydrogen atoms reactive to isocyanates having a molecular weight of generally 400-10,000 are preferably hydroxyl group-containing compounds, especially compounds containing 2-8 hydroxyl groups, especially those having a molecular weight of 1000-8000, preferably 15 1500-4000, preferably at least 2, in rule 2-8, but preferably polyesters and polyethers containing 2-4 hydroxyl groups which are known per se for the production of homogeneous and cellular polyurethanes.

The hydroxyl group-containing polyesters which are available are e.g. reaction products of polyhydric, preferably divalent and optionally additional trivalent alcohols with polyhydric, preferably divalent, carboxylic acids. Instead of free polycarboxylic acids, the corresponding polycarboxylic acid anhydrides or corresponding lower alcohol alcohol polycarboxylic acid or mixtures thereof can also be used to prepare the polyesters. The polycarboxylic acids may be of aliphatic, cycloaliphatic, aromatic and / or heterocyclic nature and optionally substituted by e.g. halogen atoms and / or unsaturated.

30 Examples of such carboxylic acids and derivatives thereof may be mentioned succinic acid, adipic acid, cork acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, anhydride anhydride, anhydride, anhydride, anhydride, anhydride, anhydride, anhydride, fumaric acid, dimerized and trimerized unsaturated fatty acids, optionally in admixture with monomeric unsaturated fatty acids such as oleic acid, terephthalic acid dimethyl ester and terephthalic acid bis-glycol ester.

Speaking as polyhydric alcohols come e.g. ethylene glycol, propanediol- (1,2) and - (1,3), butanediol- (1,4) and- (2,3), hexanediol- (1,6), octanediol- (1,8) , neopentyl glycol, 1,4-bis-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol, glycerol, trimethylolpropane, hexanetriol- (1,2,6), butanthriol- (1,2,4), trimethylolethane, pentaerythritol, quinitol , mannitol and sorbitol, formitol, 1,4,3,6-dianhydrosorbitol, methyl glycoside, in addition diethylene glycol, triethylene glycol, tetraethylene glycol and higher polyethylene glycols, dipropylene glycol and higher polypropylene glycols, and dibutylene glycol and higher polybutylene glycols. The polyesters may contain, in part, terminal carboxyl group. Also polyesters of lacquers, e.g. e-caprolactone, or of hydroxycarboxylic acids, e.g. ω-hydroxycaproic acid, are useful.

Polyethers containing at least 2, usually 2-8, preferably 2-3, hydroxyl groups which are also present are 20 such as are known per se and are prepared e.g. by polymerization of epoxides such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, or of epichlorohydrin or tetrahydrofuran with itself, e.g. in the presence of Lewis catalysts such as BF 3, or by the addition of these epoxides, preferably ethylene oxide and propylene oxide, optionally in admixture or in succession, to starting components with reactive hydrogen atoms such as water, alcohols, ammonia or amines, e.g. ethylene glycol, propane-diol- (1,3) or - (1,2), trimethylolpropane, glycerol, sorbitol, 4,4'-dihydroxy-diphenylpropane, aniline, ethanolamine or ethylenediamine. Speaking of the invention also come sucrose polyesters, such as e.g. are described in DE-B no.

1,176,358 and No. 1,064,938, and polyether started on formitol or formose (DE-A No. 2,639,083). Often, 35 such polyethers are preferred, as predominantly (up to 90% by weight), based on all OH groups present in the polyether.

DK 170753 B1 9 contains primary OH groups. Also polybutadiene containing OH groups are suitable according to the invention. Of course, mixtures of the polyesters and polyethers can be used.

Optionally, compounds having at least 5 two hydrogen atoms that are reactive to isocyanates and having a molecular weight of 32-399 are also used.

By this is meant compounds containing hydroxyl groups and / or amino groups and / or thiol groups and / or carboxyl groups, preferably compounds containing hydroxyl groups and / or amino groups which serve as chain extenders or crosslinking agents. These compounds usually have from 2-8, preferably 2-4, hydrogen atoms which are reactive to isocyanates.

Also in this case, mixtures of 15 different compounds having at least two hydrogen atoms reactive to isocyanates having a molecular weight of 32-399 can be used.

Examples of such compounds are e.g. detailed in DE Publication No. 3,430,285, pages 20 19-23.

Optionally used as auxiliary means: a) Catalysts of the kind known per se, e.g. tertiary amines such as triethylamine, tributylamine, N-methylmorpholine, N-ethyl-morpholine, N, N, N ·, N1-tetramethyl-ethylenediamine, pentamethyl-diethylenetriamine, and higher homologue (DE Publication Nos. 2,624,527 and 2,624,528 ), 1,4-diazabicyclo- (2,2,2) -octane, N-methyl-N'-dimethylamino-ethylpiperazine, bis- (dimethylaminoalkyl) -piperazine (DE Publication No. 2,636,787), N, N- dimethylbenzylamine, N, N-dimethylcyclohexylamine, Ν, Ν-diethylbenzylamine, bis (N, N-diethylaminoethyl) adipate, Ν, Ν, Ν ', Ν'-tetramethyl-1,3-butane-diamine, N, N -dimethyl- / 3-phenylethylamine, 1,2-dimethylimidazole, 2-methylimidazole, monocyclic and bicyclic amidines (DE Publication No. 1,720,633), bis- (dialkylamino) -35 alkyl ethers (U.S. Patent No. 3,330,782, DE disclosure no. 030.558, DE disclosure no.

DK 170753 B1 10,804,361 and 2,618,280) as well as amide group (preferably form amide groups) containing tertiary amines according to DE Publication No. 2,523,633 and 2,732,292). Speaking as catalysts, Mannich bases 5 of secondary amines such as dimethylamine and aldehydes, preferably formaldehyde, or ketones such as acetone, and phenols are also known per se.

Tertiary amines containing hydrogen atoms active against isocyanate groups such as catalysts are e.g.

10 triethanolamine, triisopropanolamine, N-methyl diethanolamine, N-ethyl-diethanolamine, Ν, Ν-dimethylethanolamine, their reaction products with alkylene oxides such as propylene oxide and / or ethylene oxide, and secondary tertiary amines of DE Publication No. 2,732,292.

In addition, as catalysts, silamines with carbon-silicon bonds, such as e.g. is disclosed in DE Patent No. 1,229,290 (similar to U.S. Patent No. 3,620,984), e.g. 2,2,4-trimethyl-2-silamorpholine and 1,3-dethylaminomethyl-tetramethyl-diisoxane.

In addition, as catalysts, nitrogen-containing bases such as tetraalkylammonium hydroxides also comprise alkali metal hydroxides such as sodium hydroxide, alkali metal phenolates such as sodium phenolate, or alkali metal alcohols such as sodium methylate. Also hexahydrotriazines can be used as catalysts (DE Publication No. 1,709,043) as well as amide group-containing (preferably formamide groups) tertiary amines according to DE Publication No. 2,523,633 and 2,732,292). Speaking as catalysts are also known per se known Mannich bases of secondary amines, such as dimethylamine, and aldehydes, preferably formaldehyde, or ketones such as acetone, and phenols.

According to the invention, organic metal compounds, especially organic tin compounds, can also be used as catalysts. In view of organic tin compounds, in addition to sulfur-containing compounds such as di-n-octyl-tin-mercaptide (DE disclosure No. 1,769,367, U.S. Patent DK 170753 B1 11, No. 3,645,927), preferably tin (II) - salts of carboxylic acids such as tin (II) acetate, tin (II) octoate, tin (II) ethyl hexoate and tin (II) laurate, and tin (IV) compounds, e.g. dibutyltindilaurate.

Of course, all of the above catalysts can be used as mixtures.

Further examples of catalysts which can be used in accordance with the invention as well as details on the mode of action of the catalysts are described in Kunststoff-Handbuch, Vol. VII, 10 published by Vieweg and Hochtlen, Carl-Hanser-Verlag, Munich 1966, e.g. on pages 96-102.

The catalysts are usually used in an amount of between approx. 0.001 and 10% by weight, based on the amount of polyisocyanate.

15 b) Surfactant additives such as emulsifiers and foam stabilizers. Speaking as emulsifiers, for example. the sodium salts of castor oil sulfonates or salts of fatty acids with amines such as oleic acid diethylamine or stearic acid diethanolamine. Also, alkali metal or ammonium salts of sulfonic acids such as dodecylbenzosulfonic acid or dinaphthylmethanedisulfonic acid, or of fatty acids such as ricinolic acid, or of polymeric fatty acids may be used as surfactant additives.

Substances which are the subject of the invention are lignocellulose-containing raw materials which can be bonded with the binders according to the invention, e.g. wood, bark, cork, bagasse, straw, flax, bamboo, alpha grass, rice husks, sisal and coconut fiber. However, according to the invention, of course, pressed materials can also be prepared from other organic (e.g.

30 plastic wastes of any kind) and / or inorganic raw materials (e.g. expanded mica or silicate spheres). The material may thereby be in the form of granules, chips, fibers, balls or flour and have a moisture content of e.g. 0-35% by weight, preferably 4-20% by weight.

According to the invention, it is possible, but less preferred, to apply separately the components of the binder combination DK 170753 B1 12 (polyisocyanate, polyether or polyester polyol and alkylene carbonate) to the material to be bonded. It is preferred to use the polyether or polyester polyol with the alkylene carbonate in admixture with the polyisocyanate as the binder.

According to the invention, the organic and / or inorganic material to be bonded is added to the binder in an amount of approx. 0.5 to 20 wt.%, Preferably 2 to 12 wt.%, Based on the total mass of the mold body, and pressed, usually under the influence of pressure and heat (e.g. 70-250 ° C and 1-250 bar ) for sheets or three-dimensional shaped moldings.

By analogy, multilayer sheets or moldings can also be made from veneer, paper or tissue, the layers 15 being treated with the binder as described above and then pressed, usually at elevated temperature and elevated pressure. Preferably, temperatures of 100-250 ° C are observed, especially preferably 130-200 ° C. The initial pressure is preferably between 5 and 150 bar; during the press procedure 20, the pressure thereon usually drops to about 0.

The binders to be used in accordance with the invention may also be combined with the aqueous solutions used so far in the predominantly aqueous solutions of condensation products of formaldehyde with urea and / or melamine 25 and / or phenol, but also with other hitherto less common binding and impregnating agents. for example. on the basis of polyvinyl acetate or other plastic latexes, sulphite liquor or tannin, thereby maintaining a mixing ratio of the materials of this invention to these additional binders 30 between 1:20 and 20: 1, preferably between 1: 5 and 5: 1 and wherein the polyisocyanate mixtures and the additional binders can be used either separately or in admixture.

Embodiments 35 In the following examples, the following polyols are used as starting components: DK 170753 B1 13

Polyether ethervolvol I - prepared from 1,2-propanediol and propylene oxide with an OH number of 284 and a viscosity of 75 mPas at 25 ° C.

Polymer ether polyvol II - prepared from 1,2-propanediol and propylene oxide and ethylene oxide with an OH number of 185 and a viscosity of 130 mPas at 25 ° C.

Polyether ether vol. III - prepared from ethylenediamine and 10 propylene oxide with an OH number of 60 and a viscosity of 660 mPas at 25 ° C.

Example 1 2800 g of tire industrial chips (u = 15.0 wt% a.a.) 15 and 6400 g of intermediate layer (u = 10.0% a.a.) are sprayed with, respectively. 5% by weight a.a. of a binder according to the invention consisting of a mixture of 70 wt% crude diphenylmethane-4,4'-diisocyanate, NCO content 30 wt%, 10 wt% polyether polyol I, 10 wt% polyether polyol II and 10 wt -% propylene carbonate.

20 Three-layer plate molds are dispersed therefrom, which at certain intervals are pressed both cold and hot under pressure.

Example 2

Analogous to Example 1, however, the binder of the invention consists of 70% by weight of crude diphenylmethane-4,4'-diisocyanate, NCO content of 30% by weight, and a mixture of 20% by weight of polyether polyol III with 10% by weight of propylene carbonate, the spraying of the chips with the isocyanate and the polyol / alkylene carbonate mixture taking place separately. The pressing is made analogously to Example 1.

Example 3 4200 g of tire industrial chips (u = 12.0% a.a.) are sprayed with 13% by weight a.a. of a binder of the invention 35 consisting of a mixture of 80 wt.% crude diphenylmethane-4,4'-diisocyanate, NCO content 30 wt.%, 12 wt.% polyether-polyol II and 8 wt. gt. -% propylene carbonate. From this, one-layer plate molds are spread which are pressed analogously to Example 1.

Example 4 5 Analogous to Example 3, however, one half of the binder according to the invention consists of a mixture of 70 wt% crude diphenylmethane-4,4 'diisocyanate, NCO content 30 wt%, 20 wt% polyether polyol I and 10 wt.% propylene carbonate, and the other half consists of a commercially available 10 E1 urea-formaldehyde resin. Spray per half 3% by weight on the chips. The pressing is done analogously to Example 1.

In accordance with Examples 1-4, cold-pressed plate moldings all exhibit a cold tackiness of the molds in comparison with chips treated with polyisocyanate only. Also in the hot pressing, the examples of the present invention exhibit clear advantages over the comparison experiment with the same test conditions.

Table I

Example PIade crude density Cross tensile kg / m3 strength MPa 1) 25 V20 V100

Comparative experiment with 5% by weight 680 0.94 0.27 a.a. "Desmodur PU 30 1520 A" (crude MDI with an NCO content of 30.5 wt% and a viscosity of 300 mPa * s / 25c) 35 ----- 1 680 1.13 0.33 2 680 1, 09 0.34 3 850 0.82 40 4 650 0.84% aa = wt% calculated on absolutely dry wood.

1) Test according to DIN 68.763.

Claims (7)

A process for preparing pressed materials by pressing layers of raw materials and / or particulate raw materials with polyisocyanate-based binders, characterized in that the binder contains, as components, polyisocyanates, compounds having at least two hydrogen atoms which are reactive to isocyanates, having a molecular weight of 400 to 10,000, alkylene carbonates and optionally additional additives, 100 parts by weight of the polyisocyanate, 10-250 parts by weight, preferably 20-80 parts by weight, of the compounds having at least two hydrogen atoms reactive to isocyanates having a molecular weight of 400 to 10,000 are used, and the ratio of these compounds to the alkylene carbonate is in the range of 0.5: 1.0 to 10.0: 1.0 parts by weight. Process according to claim 1, characterized in that the alkylene carbonate is propylene carbonate. Process according to claims 1 and 2, characterized in that the compounds having at least two hydrogen atoms, which are reactive to isocyanates, are hydroxyl-containing polyethers or polyesters having a molecular weight of 400-10.000. Process according to claim 3, characterized in that the alkylene carbonate is present as a mixture 25 with the polyether or polyester. Process according to claims 1-4, characterized in that the binder contains aromatic polyisocyanates. 6. A process according to claims 1-5, characterized in that the aromatic polyisocyanates are mixtures of diphenylmethane diisocyanates and polyphenyl polymethylene polyisocyanates obtained by aniline-formaldehyde condensation and subsequent phosgenation. Process according to claims 1-6, characterized in that the binder contains as additional additives aqueous condensation products of urea, flour amine, phenol and tannin or any mixtures thereof with formaldehyde and sulfite liquor.