DE2703271C3 - Preparation of aqueous isocyanate emulsions - Google Patents

Description

20th

30th

35

The uses of isocyanates as a chipboard binder is known (see e.g. H.-J. D ep pe and K .. E r η s t, Holz als Roh- und Material, Volume 29, p. 45, 1971). Binders based on diphenylmelhan-4,4'-diisocyanate are particularly known. as Solvent-free liquid products can be used in the processing plants commonly used in the wood industry insert.

However, it is a disadvantage, especially at low dosages, that binders are based Difficult to distribute isocyanates evenly on the chip material. This allows the technological properties of the finished chipboard are worsened in terms of the strength wedge. Even It is disadvantageous that devices or machine parts contaminated with isocyanate cannot easily be treated with water let it clean. It is known to use organic solvents to dilute isocyanates. Suitable solvents, such as dichloromethane and others, are, however, others for toxicological reasons Solvents, such as acetals, are practically inapplicable due to their flammability.

It ist.there in DE-OS 26 10 552 the proposal has been made to use isocyanates as binders (adhesives) for lignocellulose-containing particles come into question to use as an aqueous emulsion.

However - according to the result of the experiments dealt with in the DE-OS - the isocyanates must be used themselves and the emulsifying auxiliaries are subject to special requirements. As (poly) isocyanates prepolymers are preferred, i. H. Implementation projects of actual polyisocyanates with polyester or Polyether polyols that still have isocyanate end groups have used. Nonionic products are used as emulsifiers or surface-active agents used, which should also be free of hydroxyl, amino or carboxylic acid residues.

As the DE-OS admits, it is also specially hydrophobic due to the use of considerable amounts Polyols that are used to produce the above-mentioned prepolymers are not possible. To obtain emulsions, which have a sufficient shelf life; from Example 2 of DE-OS it rather follows that the loss of isocyanate groups in the emulsion in the course of two hours at room temperature in the most favorable Fall about 14 to 17%, in less favorable cases over 50%.

For those skilled in the field of the production of wood-based materials it follows that such a Binder is of no practical value because the tech-

50

55

60 nisch necessary waiting times between the preparation of an emulsion and the pressing, which are given by the capacity of the storage container for glue and glued chips, cannot be achieved.

It is therefore the object of the invention to provide isocyanate emulsions of the type mentioned Do not have disadvantages or to a much lesser extent, d. H. the creation of storable aqueous Polyisocyanate emulsions.

The invention relates to a process for the production of aqueous polyisocyanate emulsions which are sufficiently storable, which is characterized in that the polyisocyanates in the presence of an emulsifier on the Based on a polyglycol with a molecular weight of about 4,000 to 20,000 dispersed in water or emulsified, the OH groups in the emulsifier making up 10 to 40% of the NCO groups.

The result of the invention is surprising because - not least from the DE-OS mentioned - it is known that especially aromatic isocyanates react quickly with water; are storable pure isocyanate emulsions has not yet been described.

Examples of organic polyisocyanates which are used in the process of the invention are aromatic isocyanates, especially diisocyanates such as m- or p-phenylene diisocyanate, Toluylene-2,4- or -2,6-diisocyanate, diphenylmethane-4,4'-diisoeyanate, Chlorophenylene-2,4-diisocyanate, naphthylene-1,5-diisocyanate, diphenylene-4,4'-diisocyanate. 4,4-diisocyanal-S ^ '- dimethyldiphenyl, 3-methyldiphenylmethane-4,4'-diisocyanate, Diphenylether diisocyanate, or triisocyanates, such as 2,4,6-triisocyanatotoluene or 2,4,4'-triisocyanalodiphenyl ether. They are known by phosgenation of appropriate amines Way received. Mixtures of isocyanates are, for example, the commercially available mixtures of 2,4- or 2,6-isomers of toluene diisocyanate, as well as the mixture of di- and higher polyisocyanates, which have been produced by phosgenation of aniline-formaldehyde condensals. Such mixtures are well known in practice and they include the crude phosgenation products, which mixtures of polyphenyl polyisocyanates containing methylene bridges, including diisocyanate, triisocyanate and contain higher polyisocyanates along with the phosgenation by-products.

Preferred polyisocyanates which can be emulsified according to the invention are those in which the Isocyanate an aromatic diisocyanate or polyisocyanate with higher functionality, especially crude mixtures of methylene bridges Polyphenyl polyisocyanates, which are diisocyanates, triisocyanates or polyisocyanates with higher functionality contain. Polyphenyl polyisocyanates having methylene bridges are generally known, and they have the general formula

CH,

W CH ₂ -

NCO

NCO

NCO

11 -

where η is more than 1 and, in the case of crude mixtures, is an average of more than 1. These compounds are made in a known manner by

Phosgenation of appropriate mixtures of polyamines produced by condensation of aniline and Formaldehyde. It is common to be raw Mixtures of polyphenyl polyisocyanates containing methylene bridges, which diisocyanate, tnisocyanate and polyisocyanates with higher functionality included, to be referred to as MDl.

Less suitable organic isocyanates which can be emulsified according to the invention are isocyanate radicals comprising prepolymers made by reacting an excess of diisocyanate or a higher functionality polyisocyanate with a hydroxyl terminated polyester or hydroxyl-terminated polyethers, as well as products that are soft by reacting an excess of diisocyanate or polyisocyanate of higher functionality with monomeric! Polyol or a mixture from monomeric polyols such as ethylene glycol, trimethylolpropane and butanediol are.

However, it is possible that such prepolymers (prepolymers) in the course of the invention Forming manufacturing process in small quantities.

Higher molecular weight polyglycols, especially polyethylene glycols, Polypropylene glycols, as well as mixed glycols with molecular weights between 4000 and 20,000, preferably between 6,000 and 12,000, are suitable emulsifiers for the production of emulsions of polyisocyanates. The emulsions produced are over a storage period of z. B. 1 to 10 hours to be regarded as stable. The emulsions contain e.g. B. 5 to 70 percent polyisocyanate, 2 to 20 percent emulsifier and the rest water. You will be in the for Emulsions are obtained in the customary manner by stirring the constituents with suitable devices.

To distinguish the invention from what is already known, it must be in connection with the In the preparation of the emulsions, the following should be noted:

It can therefore be assumed that the finished emulsions contain at least some of the polyglycol as a reaction product Mil parts of the isocyanate contain, but the emulsified particles then counteract the influence z. B. the hydrolysis are relatively protected by water.

example

A typical emulsion is made from 30 parts of diphenylmethane-4,4'-dii '; ocyanate, 10 parts of polyethylene glycol and 60 parts of water are obtained in the following way:

The polyethylene glycol (average molecular weight 9000) is dissolved in 60 parts of water and stirred into the Diphenylmethane-4,4'-diisocyanate solution is stirred in. The emulsification by means of a high-speed stirrer takes about 10 to 30 seconds.

The stability of the isocyanate emulsion can be determined by known methods, e.g. B. measured by titration against bromophenol blue. For this purpose, samples of the emulsion are taken at certain time intervals, excess dibutylamine solution is added and the amine that has not been consumed is back-titrated with methanolic hydrochloric acid. The ratio mval dibutylamine / g diisocyanate is selected as the index »R«.

The R values of the aqueous isocyanate emulsion are measured continuously and the decrease in the mean /? Values (in% of the initial value) is plotted as the ordinate against the time as the abscissa.

Tabel

Λ-values R

Time (hours)

Isocyanate

,. ,. _ mval dibutylamine

Code R = ^ -.

g diisocyanate

To evaluate the stability, the /? Value of pure isocyanate is determined and set equal to 100%.

R ₀

Ro.2S

R 1.25
20th

7.162
7.190
7.129

7.249
7,072
7.155

7.194
7.196
7.269
6,997
7.048
7.070

6,959
6,971
6.976
6,959
7.033
6,999

6,930
6.871
6.889

7.160
7.159
7.220
7.038
6,969
6,997
6.897

0.25

1.25

2.00

3.00

4.00

5.00

100 99.99

100.84 98.30 97.33 97.72 96.33

The figure and table show the decrease in isocyanate content at a temperature of 23 ° C as a function of time (0 to 5 hours). Between the Isocyanate content and storage time, there is the following empirical relationship:

K = 100 - 0.793 time (in hours)%

The isocyanate content only decreases by an average of 0.793% per hour. The hatched area around the regression degrees indicates their confidence level for 95% reliability. The two outside Curves enclose 95% scatter of the individual measurements.

This investigation proves sufficient storage stability within the practical processing times the emulsion.

Chipboard was manufactured with the polyisocyanate emulsion and its technological application was tested.

Application examples

Spruce chips that have been produced under pilot plant conditions and have a humidity level of approx. 4% are in a conventional gluing device with those mentioned in the following examples Adhesive mixtures treated. A 50% paraffin emulsion is used as a water repellent In all cases, the amount is 1% solid wax on absolutely dry chips. For setting a moisture content of the resinified shavings of approx. 12% is the necessary amount of water before the resination on the chips sprayed.

The preparation of the adhesive emulsion takes place after

the procedure described in the example. The adhesive emulsion is distributed on the chips by means of a mixer so that 2 to 4% isocyanate on absolutely dry wood reach. As a comparison, the experiment with nichlemulgierlem Isocyanate carried out.

The chips pretreated in this way are shaped into a chip cake in a test pouring system. the Press temperature is 165 ° C with a press time of

4 minutes and a specific pressure of 2.5 N / mm ² . Because of the tendency of the isocyanates to stick, release papers are used. The thickness of the manufactured chipboard is 18.5 mm, the density approx. 610 kg / m3.

The panels are tested in accordance with DIN 52 360-65.

Isocyanate calc. 100% on absolutely dry chips Pure Isücyanat (comparison) 4% Isocyanate emulsified 4% 2% 3% 2% 3% PiaUenpfüfung 26.70 24.70 Flexural strength (N / mm ² ) 19.80 32.40 5.00 20.50 22.60 7.50 Shear strength V 20 (kp / cm ² ) 2.50 4.50 2.20 3.80 6.20 3.00 Shear strength V 100 (kp / cm ² ) 0.47 1.50 1.10 1.00 2.50 1.20 Swelling after 2 h (%) 2.20 1.70 8.50 1.70 1.50 7.80 Swelling after 24 h (%) 13.00 10.00 11.30 9.10

The results show that, with the same amount of glue used, the measures on which the invention is based a better mechanical strength is achieved and the sensitivity to water is significantly reduced.

1 sheet of drawings

Claims (2)

Patent claims: 1. Process for the preparation of aqueous polyisocyanate emulsions. characterized, that the polyisocyanates in the presence of an emulsifier based on a polyglycol with a molecular weight of about 4000 to 20,000 dispersed or emulsified in water, wherein the OH groups in the emulsifier make up 40% or less of the NCO groups. 2. The method according to claim 1, characterized in that the OH groups in the emulsifier 10% or make up fewer of the NCO groups.