CH619975A5 - Process for producing shaped articles - Google Patents

Description

The invention relates to a process for the production of moldings, in particular sheets.

Composite panels and flat panels or other moldings and the like are usually produced in such a way that a mass of wood chips, wood fibers or other ligno-cellulose material is hot-pressed with binders, in particular solutions of hearts of urea / formaldehyde or phenol / formaldehyde. The pressing temperatures are usually about 150 to 220 ° C, because otherwise sufficient adhesion cannot be achieved in an acceptable time even at the high pressing pressures of 20 to 70 kg / cm2 that are usually used.

It is known to use isocyanate solutions instead of urea / formaldehyde or phenol / formaldehyde resins as binders for particle board.

From DE-OS No. 1 653 177 (Deutsche Novopan) a process for the production of clamping plates is known which is essentially characterized by the use of solutions of isocyanates in organic solvents for gluing. However, the DE-OS contains a brief reference to the preparation of emulsions by mixing an isocyanate liquid or solution with urea-formaldehyde, melamine-formaldehyde and phenol-formaldehyde resin glues. These resin glues are concentrated syrups. The emulsification can occur due to the combination of the viscosity, density and compatibility properties of the resin glue. The DE-OS contains no references to aqueous emulsions of isocyanates which do not contain these known resins. The binders known from DE-OS No. 1 633 177, which consist of an emulsion of a mixture of isocyanate with urea-form aldehyde, melamine-formaldehyde or phenol-formaldehyde resin, are less water-resistant than those according to the invention used binder.

The process according to the invention is characterized in that a mass of ligno-cellulose material mixed with a binder is hot-pressed, the binder comprising an aqueous emulsion of an organic polyisocyanate which contains a nonionic surface-active agent which is free from hydroxyl, amino and carboxyl groups , having.

The lignocellulosic materials that can be used in the present process include wood chips, wood fibers, shavings, wood wool, cork and bark, sawdust and similar waste products from the wood processing industry and / or fibers from other natural products containing lignocellulose, for example bagasse, straw, flax residues and dried rushes, reed grasses and grasses. In addition, inorganic flakes or fibrous materials, such as, for example, glass fibers, mica or asbestos, can also be mixed with the lignocellulose materials.

Suitable organic polyisocyanates are diisocyanates, in particular aromatic diisocyanates, and isocyanates of higher functionality.

Examples of organic polyisocyanates which can be used in the process according to the invention are aliphatic diisocyanates, such as hexamethylene diisocyanate, aromatic diisocyanates, such as m- and p-phenylene diisocyanate, tolylene-2,4- and -2,6-diisocyanate , Diphenylmethane-4,4'-diisocyanate, chlorophenylene-2,4-diisocyanate, naphthylene-1,5-diisocyanate, diphenylene-4,4'-diisocyanate, 4,4'-diisocyanato-3,3 ' -dimethyldiphenyl, 3-methyldiphenylmethane-4,4'-diisocyanate and diphenyl ether diisocyanate, cycloalophatic diisocyanates, such as cyclohexane-2,4- and -2,3-diisocyanate, 1-methylcyclohexyl-2,4- and -2,6-diisocyanate and mixtures thereof and bis- (isocyanatocyclohexyl) methane, and triisocyanates such as 2,4,6-triisocyanatotoluene and 2,4,4'-triisocyanatodiphenyl ether.

Mixtures of isocyanates can also be used, such as, for example, a mixture of tolylenediisocyanate isomers, for example the commercially available mixtures of the 2,4- and 2,6-isomers, and also the mixtures of di- and higher polyisocyanates which are obtained by phosgene

3rd

619 975

tion of aniline / formaldehyde condensates. Such mixtures are generally known to the person skilled in the art; these include the crude phosgenation products, which contain mixtures of methylene-bridged polyphenyl polyisocyanates, including diisocyanates, triisocyanates and higher polyisocyanates, together with any by-products of phosgenation.

Preferred polyisocyanates which can be used according to the invention are aromatic diisocyanates or polyisocyanates with higher functionality, in particular crude mixtures of methylene-bridged polyphenyl polyisocyanates which contain diisocyanates, triisocyanates and polyisocyanates with higher functionality. Polyphenyl polyisocyanates containing methylene bridges are generally known and correspond e.g. the general formula:

NCO

Jn-1

Surface-active agents or emulsifiers correspond, for example, to the formula:

R0 (CH2CH20) "C0NHX

wherein R represents an alkyl group having 1 to 4 carbon atoms, n is an integer such that the compound contains an average of at least five oxyethylene groups per molecule, and X represents the remainder of a di- or polyisocyanate and contains at least one free isocyanate group. R means, for example, ethyl, propyl or butyl, but preferably methyl. Preferably n has an average value of 5 to 120, in particular 10 to 25.

X represents the remainder 1 obtained by removing an isocyanate group from any di- or polyisocyanate. If the diisocyanate is, for example, a tolylene diisocyanate, X corresponds to the formula:

wherein n is at least 1 and has an average of more than 1 in the case of raw mixtures. These compounds can be prepared by phosgenating corresponding mixtures of polyamines, which are obtained by condensation of aniline and formaldehyde. For the sake of simplicity, crude mixtures of methylene-bridged polyphenyl polyisocyanates which contain diisocyanates, triisocyanates and polyisocyanates with higher functionality are referred to below as MDI.

Particularly preferred organic isocyanates which can be used according to the invention are prepolymers which have isocyanate end groups and are prepared by reacting an excess of a diisocyanate or a polyisocyanate with higher functionality with a polyester having hydroxyl end groups or polyether having hydroxyl end groups, and products which are obtained by reacting an excess of Diisocyanate or polyisocyanate with higher functionality with a monomeric polyol or a mixture of monomeric polyols, such as ethylene glycol, trimethylolpropane and butanediol, can be obtained. However, because of their slower reaction with water, a desirable property to be discussed, prepolymers containing isocyanate end groups that are made using hydrophobic polyols such as castor oil are of particular value.

One class of prepolymers that can be used with isocyanate groups includes the prepolymers that have isocyanate groups <MDI.

The aqueous emulsion of organic polyisocyanate which is used in the process according to the invention preferably contains, as a surface-active agent, a condensate of ethylene oxide molecules which contains no terminal hydroxyl, amino or carboxyl groups. These include, for example, condensates of ethylene oxide with alkylphenols, long-chain alcohols or amides, the terminal hydroxyl group in each case, for example, being etherified or esterified. i

The reaction products of diisocyanates and polyisocyanates with higher functionality with monoalkyl ethers of polyethylene glycols are of particular value. These special

CH-

NCO

The radical X preferably contains only one isocyanate group.

Examples of isocyanates from which X can be derived are the di- and polyisocyanates mentioned above.

Surface-active urethanes of the formula given above can be prepared by reacting an alcohol of the formula R0 (CH2CH20) nH with a di- or polyisocyanate which contains at least two isocyanate groups, using at least one mole of isocyanate per mole of alcohol. An excess of isocyanate is preferably used.

The reaction can be carried out by adding the alcohol to the di- or polyisocyanate while stirring until the liquid is clear, whereupon the reaction is continued at room temperature. The reaction can be accelerated by heating to temperatures up to 100 ° C.

To prepare the emulsions used according to the invention, a surface-active agent of the above type can be prepared in situ in the di- or polyisocyanate. If an emulsion of a diisocyanate of the formula X (NCO) is to be prepared, a small amount of the poly-ethoxy alcohol of the formula R0 (CH2CH20) nH can be added to a large excess of the diisocyanate of the formula X (NCO) 2 and the emulsifier are formed in situ in the isocyanate.

If a prepolymer is used as the polyisocyanate, the formation of the prepolymer and the formation of a surface-active agent can take place in situ simultaneously or in two separate steps, after which the prepolymer and the surface-active agent can be mixed with water to produce the emulsion of the prepolymer. Emulsification is facilitated by first mixing the prepolymer and the surfactant with about a quarter of their own weight in water and then diluting them with further water as required.

Thus, if the polyisocyanate present in the emulsion is one from the class of the preferred prepolymers mentioned above, namely a prepolymer from MDI, the emulsion of the prepolymer can be prepared by one of the following three methods:

1. Reaction of the MDI with the required amount of polyol to produce the prepolymer, subsequent reaction with a small amount of the polyethoxy alcohol of the formula CH30 (CH2CH20) nH and finally emulsification by stirring with water.

619 975

4th

2. Reaction of the MDI with the required small amount of the polyethoxy alcohol of the formula CH30 (CH2-CH20) nH, subsequent reaction with the amount of polyol which is required to prepare the prepolymer, and finally emulsification.

3. Simultaneous implementation of the MDI with the required amounts of polyol and polyethoxy alcohol and subsequent emulsification in water.

In these three processes, the surfactant is thus prepared in situ in the polyisocyanate. The "surfactant in this case corresponds to the formula R0 (CH2CH20) nX, where X is the rest of the polyisocyanate and R is an alkyl group with 1 to 4 carbon atoms.

Preferred surfactants are derived from a poly-ethoxy compound of the formula R0 (CH2CH20) nH, '' '' wherein R is methyl and n has an average value of 10 to 25. Typical examples of the polyethyleneoxy compounds are methoxypolyethylene glycol with a molecular weight of 300 to 1000.

The surface-active agent can of course be produced separately and a small amount of it can be dissolved in the mixture forming the prepolymer or in the pre-formed prepolymer.

The prepolymers can be prepared by any known method, for example by heating the components together or by allowing the components to react with one another at room temperature, optionally in the presence of a catalyst.

The emulsions of the prepolymers which are obtained by the methods described are oil-in-water emulsions.

Another type of surfactant that can be used corresponds to the formula:

^ .C0O (CH2CH2O) mR1

r-x-nhcochcT

^ -COO (CH2CH2 0) "R '

wherein X represents the residue of an organic isocyanate, R1 represents an alkyl group having 1 to 4 carbon atoms, n tu and m are integers such that the sum of m + n is at least 10, and R, which is only present when X is the Represents the residue of a diisocyanate or a polyisocyanate of higher functionality, an isocyanate group or a group of the formula: is

^^ - C00 (CH2CH20) mR1 -NHCOCH <^

^ C00 (CH2CH20) nR1

where R1 is preferably methyl and the sum of m and n is preferably between 20 and 80.

If X represents the remainder of a monoisocyanate, R is absent.

For example, X may be the residue of any of the isocyanates listed above.

These surfactants or emulsifiers can be prepared by reacting an isocyanate with a bis (alkoxypolyethenoxy) ester of malonic acid and can, if desired, be prepared in situ in the isocyanate.

Preferred emulsions for use in the process according to the invention are those which contain 99 to 25 parts by weight of water and 1 to 75 parts by weight of organic polyisocyanate, in particular 75 to 50 parts by weight of water and 25 to 50 parts by weight organic polyisocyanate. A preferred amount of the surfactant is from 5 to 15 parts by weight based on 100 parts by weight of the di- or polyisocyanate.

The emulsions can be prepared by customary methods, preferably by mixing the surface-active agent with the organic polyisocyanate and mixing this mixture with water. However, in certain cases the non-ionic surface-active agent can also be prepared in situ in the polyisocyanate and, if desired, the product obtained can be diluted with further polyisocyanate, mixed with water and the whole thing stirred to obtain the desired emulsion.

The lignocellulosic material is expediently mixed with the binder by fine spraying with the aqueous emulsion, so that the lignocellulosic material is well covered. It has been found that aqueous emulsions of the organic polyisocyanates with a concentration up to 65% have a viscosity which is sufficiently low for spraying, while the solutions of urea / formaldehyde and phenol / formaldehyde resins which are usually used in the production of clamping plates and the like Materials used are generally not sprayable at concentrations above 40%. The invention thus provides a working method in which less water is present than was previously thought possible, so that less water needs to be removed during the hot operation or the subsequent conditioning. Alternatively, the ligno-cellulose material does not need to be dried to the extent previously thought to be normal before it is mixed with the binder. Emulsification and spraying can be facilitated by using warm water and / or warm organic polyisocyanate.

It has also been found that the hot pressing operation using the method according to the invention is successful at temperatures below 100 ° C. (for example at 90 to 95 ° C.) instead of the usual 150 to 220 ° C., as is the case when using urea / formaldehyde and Phenol / formaldehyde resin must be applied. The use of such low temperatures saves energy, improves the environmental conditions and prevents the formation of smoke and vapors. The method is also advantageous because it avoids the destructive influence of steam pressures that arise inside plates or molded articles at higher temperatures, which is particularly important in the production of laminates with impermeable coverings. A better solidification can therefore be achieved during the pressing, because it is no longer necessary to provide a permeability sufficient for the escape of steam.

Of course, it is also possible to work at the usual higher temperatures; in certain circumstances, this may indeed be desirable, since this results in shorter curing times and the chipboard produced can be removed more easily from the press plates. This fact can be significant if plates are to be produced without a surface covering.

According to a preferred embodiment of the invention, the lignoellulose material is mixed with an aqueous emulsion of an organic polyisocyanate, preferably an isocyanate-terminated prepolymer, of a crude mixture of methylene-bridged polyphenyl polyisocyanates, which contains a stabilizing amount of the nonionic surfactant, which is free of hydroxyl, Is amino and carboxyl groups, and which contains 75 to 50 parts by weight of water to 25 to 50 parts by weight of the organic polyisocyanate, whereupon it is optionally dried at 20 to 40 ° C. to remove part of the water, and the sprayed raw material is then hot-pressed at a temperature below 200 ° C., in particular below 100 ° C., for example at 90 to 95 ° C., in order to bring about the cohesion.

In this way, composite panels or moldings can be produced economically.

55

5

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In practice, delays between the operations of making the emulsion, spraying the lignocellulosic mass and hot pressing the sprayed material are inevitable, and delays also arise from correcting processing errors and making operational adjustments. The reaction between the isocyanate and the water of the emulsion expediently proceeds so slowly that a delay of about 2 hours between the preparation of the emulsion and the hot pressing can be accepted. The rate of the reaction can be slowed down to produce an emulsion that has an acceptable processing time using less surfactant or less effective agent, but each of these measures adversely affects and also causes the stability of the binder and the distribution of the isocyanate over the lignocellulosic material Difficulty spraying. It is therefore preferred to reduce the reaction rate by using an isocyanate-terminated prepolymer which is derived from a hydrophobic polyol of the type already mentioned and / or by adding an inert hydrophobic diluent to the emulsion, which can also be advantageous in this respect , as this improves the water-repellent properties of the resulting particle board and makes it easier to remove the particle board from the press plates. Suitable diluents are aromatic and aliphatic fatty hydrocarbons and esters, which may contain a halogen substituent. Examples include: mineral oil and paraffin cake (impure paraffin wax), didodecyl phthalate, tris (ß-chloropropyl) phosphate and in particular chlorinated paraffin waxes. These diluents, which are not reactive to isocyanate groups, can be added during the preparation of the prepolymer or shortly before the emulsification.

example 1

320 g of wood chips were dried to a moisture content of 6% and placed in an open mixing vessel. While being circulated, the binder was sprayed on by means of a hand-operated simple spray device, the amount used being monitored by determining the weight loss. The sprayed schnitzel continued to move for 1 minute; then they were spread evenly over the area of 18 x 18 cm in a molded box. The mass was then pressed together by hand as much as possible after an appropriate size top plate had been placed, creating a loosely solidified mat of s chips about 4.5 cm to 5 cm thick. The mat was then placed on metal plates,

the surface of which had been treated with a release agent and transferred to a hydraulic press in which it was subjected to a pressure of 50 kg / cm 2 between the plates at a temperature of 90 to 95 ° C. for 5 minutes. The specific weight was limited to about 0.7 by means of a spacer plate of 1.4 cm. After removing the plates, they were conditioned to adjust the water content to about 10%, the physical examinations were carried out in the representative-i-iative area of the resulting plates of 15 × 15 cm.

A comparison was made with emulsifiable MDI and an emulsifiable MDI prepolymer from:

, MDI

Oxypropylated Glyceri, MW 1,000 methoxypolyethylene glycol (Methoxy PEG), MG 650

100 parts 30 parts

10 parts executed. Each sample was emulsified by mixing with half the weight of water and then with the same weight of water to produce 40% solids emulsions.

40 g of these emulsions were sprayed onto 320 g wood chips in the manner indicated above.

Both plates showed good hardening after removal from the press; no visible vapors or gases were evolved at this temperature and no swelling was observed when the plates were removed from the press.

A similar pair of experiments were carried out using half the amounts of the emulsions so that they give only 2.5% solids as a binder based on the weight of the chips.

The physical properties determined by tests according to British Standard 1811 Part 2 are shown in the following table. Mean:

EMDI = emulsifiable MDI

EMDIPP = emulsifiable MDI prepolymer

attempt

2.5% EMDI

2.5% EMDIPP

5% EMDI

5%

EMDIPP

Panel density (kg / m3)

650

679

731

720

Thickness (mm)

14.1

13.7

14.1

13.5

Moisture content

9.6

8.6

10.0

9.6

when trying

Increase in thickness

(%)

24.6

52.9

18.6

18.5

2 hour immersion

Increase in length

(%)

0.65

0.85

0.45

0.50

in water

Weight gain

(%)

99.4

108.4

57.3

64.2

Increase in thickness

(%)

38.1

53.8

22.2

21.8

24 hour immersion

Increase in length

(%)

0.8

0.9

0.7

0.7

in water

Weight gain

(%)

113.6

127.4

75.6

79.7

-

Tension (stress), MN • irr2

14

16.2

24.6

21.3

Bending properties

Deformation (strain),

%

1.74

1.71

3.39

3.58

Module, MNm ~ 2

1060

1240

960

760

Tensile liability kN-m ~ 2

260

330

460

570

(Tensile adhesion)

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6

The stability of the emulsion was such that it could be used at 20 to 22 ° C for up to 112 hours; it was possible to obtain completely satisfactory plates even if the freshly sprayed chips were kept at 20 to 22 ° C for 1 hour before they were pressed into the plate.

By adding a catalyst to the emulsion it is possible to accelerate the hardening, which either allowed a shorter operation at 90 to 95 ° C or a work at a lower temperature; for example, 1% dimethylhexadecylamine based on the weight of the EMDIPP was added to the emulsion, reducing its stability so that it had to be sprayed within 2 minutes. The sprayed schnitzel then had to be pressed within 5 minutes, but the plate was cured in 3 minutes at 95 ° C or in 5 minutes at 70 ° C.

An improvement in water resistance can be expected if additional water-repellent agents are added in a similar way to the systems already used for the conventional fiberboard bound with urea / formaldehyde or phenol / formaldehyde.

Example 2

Four emulsifiable MDI prepolymers (I) to (IV), which are obtained by mixing 100 parts of MDI, 10 parts of methoxy-PEG (MW 650) and the following polyols:

in (I) 30 parts of oxypropylated glycerin, OH number 160 in (II) 9 parts of oxypropylated glycerin, OH number 540 in (III) 9 parts of a polyester, OH number 540, from adipic acid, diethylene glycol and glycerin in (IV) 30 parts of castor oil, OH number 160, were emulsified with water in a weight ratio of 1: 1.

The NCO content of each emulsion was determined after 2 hours at 22 ° C using the usual method by adding an excess of di-n-butylamine to a 40% aqueous emulsion and then back titrating with hydrochloric acid. The following loss of activity of the individual emulsions resulted:

Emulsion of (I) 55%

Emulsion of (II) 30%

Emulsion of (III) 24%

Emulsion of (IV) 17%

These results show that the more hydrophobic the polyol used in the preparation of the prepolymer, the longer the processing time of an emulsion.

It was also found that emulsions which were prepared from 7 parts of an emulsifiable prepolymer and 12 parts of water and corresponding emulsions which were used as diluents «Cereclor S45» (branded product), i.e. a chlorinated paraffin wax, showed the following loss of activity:

Castor oil prepolymer 27.3%

Castor oil prepolymer + 4 parts «Cereclor S45» 18.9%

Prepolymer of hydrogenated castor oil 22.9%

Prepolymer of hydrogenated castor oil + 4

Parts «Cereclor S 45» 13.7%

Prepolymer made from oxypropylated glycerin

(OH number 540) 30.4%

Prepolymer made from oxypropylated glycerin

(OH number 540) + 4 parts «Cereclor S45» 17.2%

Prepolymer made from oxypropylated glycerin

(OH number 540) + 7 parts «Cereclor S45» 13.5%

These results show that when a paraffin wax is added to an aqueous emulsion of a prepolymer, the processing time of the emulsion is extended.

Example 3

A prepolymer was prepared by adding 100 parts of MDI

30 parts of castor oil (first pressing), OH number 160,

and

10 parts methoxy PEG (MG 650)

mixed, warmed to 80 ° C overnight and then cooled. Two emulsions (a) and (b) were prepared by mixing the following ingredients.

"(a) 4 parts of the castor oil prepolymer indicated above and 10 parts of water; and

(b) 6 parts of a mixture of 4 parts of the above-mentioned castor oil prepolymer with 2 parts of "Cereclor S45" and 10 parts of water.

'Two chipboard samples were then prepared by spraying separately 102 parts of wood chips with 2% moisture content with circulation with the above-mentioned emulsions, which were sufficiently thin to allow good atomization. Each batch of treated chips was sprinkled into a frame placed on a stationary plate to form a cake, which was covered with an aluminum plate after the frame was removed. Both metal plates are waiting to be treated with a wax-based release agent. The cakes "were pressed together in a hydraulic press at a plate temperature of 175 ° C. under a pressure of 135 kg / cm2. A spacer plate was inserted to limit the thickness to 19 mm; the amount of chips treated was chosen so that that the clamping plate had a final density of about 680 kg / m3, the pressing time was 4.75 minutes, and when the pressure was released, it became clear that the hardening of the plate made with the addition of "Cereclor S45" to the binder was better than that of the plate (a), which showed a certain tendency to stick, especially in the case of the use of steel plates.

The plates were then cooled and conditioned and finally tested, with the following results.

a b

Density, kg / m3

704

713

Water swelling after 2 hours,%

23.0

18.0

Water swelling after 24 hours,%

26.0

21.6

German V20 test, kN / m2

703

822

German VI 00 test, kN / m2

157

190

Example 4

A batch of wood chips of the same type with a moisture content of 2% was sprayed with an emulsion consisting of:

6 parts of a mixture of the castor oil prepolymer according to Example 3 (4 parts) with "Cereclor S45" (2 parts) and 6 parts of water, and then were

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5 parts of a 2 (Kfigen paraffin cake emulsion sprayed on density, kg / m1 690

and the treated schnitzel then in the above-mentioned water swelling after 2 hours, r'r 13.5

Processed way. The cooled conditioned plates water swell after 24 hours S '<22.0

were tested and the following results were obtained: V20, kN / m2 790

C.

Claims (10)

619 975 PATENT CLAIMS 1. A process for the production of moldings, characterized in that a mass of ligno-cellulose material mixed with a binder is hot-pressed, the binder comprising an aqueous emulsion of an organic polyisocyanate which contains a nonionic surface-active agent which is free of hydroxyl , Amino and carboxyl groups. 2. The method according to claim 1, characterized in that the organic polyisocyanate is a crude mixture of methylene-bridged polyphenyl polyisocyanates, which contains diisocyanates, triisocyanates and higher-functionality polyisocyanates. 3. The method according to claim 1, characterized in that the organic polyisocyanate is a prepolymer having isocyanate end groups, such as by reacting an excess of a diisocyanate or a higher-functionality polyisocyanate with a hydroxyl-terminated polyester or hydroxyl-terminated polyether or with a monomeric polyol or a mixture of monomeric polyols is available. 4. The method according to claim 1 or 3, characterized in that the organic polyisocyanate is a prepolymer having isocyanate end groups, as can be obtained using a hydrophobic polyol. 5. The method according to any one of claims 1 to 4, characterized in that the surface-active agent of the formula: R0- (CH2CH20) n-C0NHX in which R represents an alkyl group having 1 to 4 carbon atoms, n is an integer such that the compound contains on average at least 5 oxyethylene groups, and X represents the remainder of a di- or polyisocyanate and contains at least one free isocyanate group. 6. The method according to any one of claims 1 to 5, characterized in that the emulsion contains 99 to 25 parts by weight of water to 1 to 75 parts by weight of organic polyisocyanate and a stabilizing amount of a non-ionic surfactant that is free of Is hydroxyl, amino and carboxyl groups. 7. The method according to claim 5 or 6, characterized in that the amount of surfactant is 5 to 15 parts by weight, based on 100 parts by weight of the organic isocyanate. 8. The method according to claim 1, characterized in that Lignoeellulosematerial is sprayed with an aqueous emulsion of an organic polyisocyanate, which emulsion contains a stabilizing amount of a non-ionic surfactant, which is free of hydroxyl, amino and carboxyl groups, and 75 to 50 parts by weight of water to 25 to 50 parts by weight of the organic polyisocyanate contains that the mass is optionally dried at 20 to 40 ° C to remove part of the water, and that then the sprayed lignified raw material at a Hot pressed temperature below 200 ° C. 9. The method according to claim 8, characterized in that the organic polyisocyanate is a prepolymer having isocyanate end groups of a crude mixture of methylene-bridged polyphenyl polyisocyanates. 10. The method according to any one of claims 1 to 9, characterized in that the emulsion contains an inert hydrophobic diluent.