DK148359B - PROCEDURE FOR MANUFACTURING Aqueous POLYISOCYANATE EMULSIONS FOR LIMITING CHIPBOARDS - Google Patents

Description

140359 i

The invention relates to a process for preparing aqueous polyisocyanate emulsions for bonding particleboard, of the kind specified in the claim.

The use of isocyanates as particle board binder is known (see, e.g., H.-J. Deppe and K. Ernst, Holz als Roh und Werkstoff, year 2 £, page 45, 1971). Particularly known are binders based on diphenylmethane-4,4'-diisocyanate.

Solvent free liquid products may be used which can be used in the processing plants customary in the wood industry.

However, it is a disadvantage, especially at low doses, that binder based on isocyanates is difficult to dispense regularly on the chip material. Thereby, the technological properties of the finished chipboard in terms of strength can be impaired. It is also a disadvantage that appliances or machine parts contaminated with isocyanate are not easily cleansed with water. It is well known that organic solvents can be used to dilute isocyanates. However, suitable solvents such as dichloromethane and others are practically unusable for toxicological reasons and other solvents such as acetals are practically unusable due to the fire hazard.

Accordingly, in DE Publication 2,610,552, 25, cf. DK-ans. No. 1073/76, proposed to use the isocyanates considered as binders for lignocellulosic particles in the form of an aqueous emulsion.

However, in this connection - as can also be seen from the results of the experiments mentioned in the publication specification - 30 have to make special requirements both for the isocyanates themselves and for the emulsifiers used. Preferably, as (poly) isocyanates, prepolymers are used, i.e. reaction products of actual polyisocyanates with polyester or polyether polymers, which prepolymers still exhibit isocyanate end groups. As emulsifiers or surfactants, nonionic products are used which must also be free of hydroxyl, amino or carboxylic acid groups.

5 However, as is apparent from the disclosure, despite the use of significant amounts of special hydrophobic polyols, in the preparation of said prepolymers, it is also not possible to prepare emulsions which exhibit a sufficient durability; In addition, from Example 2 of the disclosure, it appears that the loss of isocyanate groups in the emulsion during the two cases at least two hours at room temperature is most advantageously 14 to 17 0, and in the less favorable case above 50 °.

It will thus be apparent to those skilled in the art which comprise the manufacture of wood materials, that such a binder is of less practical value, because of the technically necessary lag times between the preparation of an emulsion and the compression, given the capacity of the storage container for glue and glued particle material are not obtained.

It is therefore the object of the invention to provide a process for the preparation of isocyanate emulsions which do not exhibit the disadvantages stated or exhibit only a slight extent, i.e. to disclose a process for preparing 25 more stock-stable, aqueous emulsions of polyisocyanates.

The process according to the invention is characterized by the characterizing part of the claim. Surprisingly, it has been found that the aqueous polyisocyanate emulsions prepared according to the invention exhibit greater storage stability than the known polyisocyanate emulsions.

148359 3

Preferably, as an emulsifier, a polyglycol is used, to which is added 1 to 30 wt Si of a polypeptide, calculated on the polyglycol.

The result of the invention is surprising because, not least from the disclosed DE publication specification, it is known that precisely aromatic isocyanates react rapidly with water; storage stable isocyanate emulsions have not been described so far.

It is admittedly known from US Patent No. 3,428,592 to 10 aqueous polyisocyanate emulsions which contain as a dispersion phase a solution of an aromatic polyisocyanate in an organic solvent. In addition to the fact that the aqueous polyisocyanate emulsions produced by the process of the invention contain no organic solvents, the known polyisocyanate emulsions are used for a completely different purpose, namely, for impregnating paper.

Examples of organic polyisocyanates which can be used in the process of the invention are aromatic isocyanates, especially diisocyanates such as m- and p-phenylene diisocyanate, tolylene-2,4- and 2,6-diisocyanates, diphenylmethane-4,4'- diisocyanate, chlorophenylene-2,4-diisocyanate, naphthylene-1,5-diisocyanate, diphenylene-4,4'-diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, 3-methyldiphenylmethane 4,4'-diisocyanate and diphenyl ether diisocyanate, and tri-isocyanates, such as 2,4,6-triisocyanatotoluene and 2,4,4'-tri-isocyanatodiphenyl ether. They are prepared, inter alia, by phosgenation of corresponding amines in a known manner. Mixtures of isocyanates may e.g. are commercially available in the form of mixtures of 2,4- and 2,6-isomers of the tolylene diisocyanate 30 as well as the mixtures of di- and higher polyisocyanates prepared by the phosgenation of aniline-formaldehyde condensates. Such mixtures are generally known in practice, and they comprise the crude phosgenation products which contain 4 148359 mixtures of methylene bridge-containing polyphenyl polyisocyanates including diisocyanate, triisocyanate and higher polyisocyanates together with the phosgenation by-products.

Preferred polyisocyanates which can be used according to the invention are those in which the isocyanate is an aromatic di isocyanate or higher functionality polyisocyanate, especially crude mixtures of methylene bridged polyphenyl polyiso. cyanates containing diisocyanates, triisocyanates or polyisocyanates with higher functionality. Methylene-bridged polyphenyl polyisocyanates are well known in the art and exhibit the general formula O 2 - O - (Jp) -

NCO NCO NCO

J n-1 where n is greater than 1 and, in the case of crude mixtures, represents an average value greater than 1. These compounds are prepared by phosgenation of similar mixtures of polyamines produced by condensation of aniline and formaldehyde. It is customary to designate crude mixtures of methylene bridge-containing polyphenyl polyisocyanates containing diisocyanate, triisocyanate and higher functionality polyisocyanates, such as MDI.

Less suitable isocyanates which can be used according to the invention are isocyanate group-containing prepolymers prepared by reaction of an excess of diisocyanate or of a higher functionality polyisocyanate with a polyester or polyether having terminated hydroxyl groups and products obtained by reaction of an excess of diisocyanate or higher functionality polyisocyanate with monomeric polyol or a mixture of monomeric polyols such as ethylene glycol, trimethylolpropane and butanediol.

Admittedly, it is possible that during the preparation according to the invention, such prepolymers are formed in small amounts.

High molecular weight commercial polyglycols, especially polyethylene glycols, polypropylene glycols, and mixed glycols of molecular weights of 4000 to 20,000, preferably from 6000 to 12,000, are suitable emulsifiers for preparing emulsions of polyisocyanates. The emulsions produced are considered to be stable over a storage period of e.g.

1 to 10 hours. The emulsions contain e.g. 5 to 70¾ polyisocyanate, 2 to 20¾ polyglycol and other water. They are prepared in the usual way for emulsions by stirring the ingredients with suitable apparatus.

20 Polyvinyl alcohols with the specified molecular weight range are available on the market and require no further explanation.

They are preferably added to the emulsifying water at a corresponding concentration and allow a high emulsification rate.

He obtains particularly suitable emulsions when using as an emulsifier polyglycol and an additional 1 to 30 weight percent of a polypeptide calculated relative to the polyglycol.

Aqueous emulsions of isocyanates occur which, in comparison with those obtainable according to the claim, exhibit an increased useful life and are also cheaper because only a small amount of emulsifier is required for their preparation. In general, an amount of approx. 0.5-5% emulsifier, calculated in relation to the total emulsion weight, sufficient to produce an emulsion whose titratable content of isocyanate groups over 10 hours is not reduced by more than approx. 5%.

Polypeptides of the invention are e.g. gelatin, bone glue and the like of protein extractable products. These are available on the market and need no further explanation. They are preferably added to the emulsifying water at similar concentration and allow a high emulsification rate. In general, the content of polyglycol in the emulsion is 1-10%, while 0.1-1% polypeptide is used.

In general, an amount of approx. 0.5-5% polyvinyl alcohol, calculated on the total weight of the emulsion, sufficient to prepare an emulsion whose titratable content of isocyanate groups is not reduced by more than about 10 hours. 2%. The table set forth in Example 2 below shows this.

In order to separate the invention from the prior art, in the context of the preparation of the emulsions, one must briefly refer to the following:

Since it is known that hydroxyl group-containing compounds react with isocyanates, the amounts of glycol or PVA must be selected, taking into account the respective molecular weights and content of reactive groups, that the hydroxyl groups present in the emulsifier constitute only a fraction, e.g. not more than 10 to a maximum of 40% of the available isocyanate groups, as required. The minimum amount of 30 can be deduced from the technical emulsification of the mixtures.

148359 7

It must then be assumed that the finished emulsions contain the emulsifier, at least partly as a reaction product with parts of the isocyanate, but that the emulsified particles nevertheless also contain relatively unchanged components of the polyisocyanate which are protected against the effect e.g. from hydrolysis with water.

EXAMPLE 1

A typical emulsion is prepared from 30 parts of diphenylmethane-4,4'-diisocyanate, 10 parts of polyethylene glycol and 60 parts of 10 water as follows:

The polyethylene glycol (average molecular weight 9,000, for example, under the trade name "Pluriol E 9000" obtainable product from BASF AG) is dissolved in 60 parts of water, and in the stirring solution, diphenyl-methane-4.4 is stirred. diisocyanate (eg "Kauranate CE 5043" from BASF AG). Emulsification using a fast-moving agitator (for example, the Tornado or Turrax brand) requires approx.

10-30 seconds.

The stability of the isocyanate emulsion can be measured using 20 known methods, e.g. by titration against bromophenol blue. For this purpose, samples of the emulsion are taken at specified time intervals and these are mixed with excess dibutylamine solution and unused amine is titrated back with methanolic hydrochloric acid. As the characteristic "R" 25, the ratio mval dibutylamine / g diisocyanate is selected.

Number R = mv / all dibutylamine and diisocyanate

To assess the stability, the R value of pure isocyanate is determined, the aqueous isocyanate emulsion is continuously measured and the reduction of determined R values in each case (in% of the initial value; plotted as ordinates against time as abscissa), cf. .

8 148359 TABLE 1 R.. R- R Time Isocyanate in values (hours) (¾) R 7,162 7,160 0 100 5 U 7,190 7,129

Rn 9C. 7,249 7,159 0.25 99.99 U'- 7,072 7,155 10 R, 7,194 7,220 1.25 100.84 7,196 7,269 R 6,997 7,038 2.00 98.30 Z 7,048 15 7,070 R, 6,959 6,969 3.00 97.33 J 6,971 6,976 R ^ 6,959 6,997 4,00 97,72 20 7,033 6,999 R- 6,930 6,897 5,00 96,33 6,871 6,889 The figure and Table 1 show the reduction of the isocyanate content at a temperature of 23 ° C. time dependence (0-5 hours). Between the isocyanate content and the storage time, there is the following empirical correlation: Y = 100 - 0.793 · time (in hours)% 30, so the isocyanate content decreases only on average 0.793? hour. The shaded area around the regression degree indicates the confidence interval for a significance. at 95¾. The two outside curves enclose 95¾ of the scattering range of the individual measurements.

148359 9

This study documents a sufficient storage stability of the emulsion within the processing times used in practice.

The polyisocyanate emulsion produced particleboard, 5 and their technological use was investigated in Example 4.

EXAMPLE 2

A typical emulsion was prepared from 30 parts of technical diphenylmethane-4,4'-diisocyanate (MDI) and 70 parts of 5¾ aqueous 10 emulsifier solution as follows:

A 5% aqueous solution of the polyvinyl alcohol is prepared, e.g. a polyvinyl alcohol of the trade name "Denka Poval B 17" dissolves hot in water. The emulsification using a fast-moving agitator requires approx. 10-30 se-15 customers.

To determine the stability of the emulsion, the isocyanate content at the time of preparation is set to 100? □ and the reduction is continuously measured. Thus, at the described 5% emulsion within 7 hours, only a reduction of 1.5¾ adhesive content occurs.

The following tables show an overview of the determined isocyanate content for an emulsion of 30 parts of diphenyl methane-4,4'-diisocyanate with 70 parts of 5¾ aqueous emulsifier solution or with 70 parts of 4¾ aqueous emulsifier solution.

10 148359

TABLE

30 parts MDI 30 parts MDI

70 parts 535 emulsif. 70 parts 4¾ emulsion solution

Hours Isocyanate (35) Isocyanate (35) 5 100 100 0.5 99.9 99.4 1 99.5 98.5 2 99.7 99.8 3 99.0 98.3 10 4 99.4 98, EXAMPLE 3 A typical emulsion is prepared from 38 parts of technical diphenylmethane-4,4'-diisocyanate (MDI) and 62 parts of 3,535. aqueous emulsifier solution as follows:

A 3,535 solution of 0.5 parts of gelatin and 3 parts of a polyglycol (for example, with the trade name "Pluri-20ol") is prepared in hot water. In 62 parts of the cooled solution, 38 parts of diphenylmethane-4,4'-diisocyanate are stirred. The emulsification using a fast-moving agitator requires approx.

10-15 seconds.

To determine the stability of the emulsion, the isocyanate content at the time of preparation is set to 10035 and the reduction is continuously measured. Thus, within the described 3835 emulsion within 7 hours, only a reduction of 2,635 adhesive content is obtained.

148359 11

The following table gives an overview of the determined isocyanate content for an emulsion of 38 parts of diphenylmethane-4,4'-diisocyanate with 62 parts of 3.5¾ aqueous emulsifier solution.

5 TABLE

Hours of Isocyanate (¾) 0 100.0 0.5 99.8 1 99.5 10 2 99.0 3 98.6 4 98.4 5 97.8 6 97.6 15 7 97.4 EXAMPLE 4 - (Application Example for example 1)

Spruce shavings made under technical conditions and having a moisture content of approx. 4%, is treated in a conventional adhesive (Drais mixer) with the adhesive mixtures indicated in the following 20 examples. As a hydrophobic agent, a 50K paraffin emulsion is used, the amount being in all cases IS solid wax relative to absolutely dry (atro) chips. For setting a moisture content of the resin treated chips of approx. 12S 25 the required amount of water is sprayed before the resin treatment on the chips.

The preparation of the adhesive emulsion is carried out according to the method described in Example 1. The adhesive emulsion is distributed by means of a mixer such on the chips that there is 2-4S isocyanate on dry wood. By comparison, the test is performed with non-emulsified isocyanate.

12 148359

The thus-prepared chips are formed in an experimental sprinkler system for a chip cake. The pressing temperature is 165 ° C at a pressing time of 4 minutes and a specific o pressure of 2.5 N / mm. Due to the adhesive tendency of the isocyanates, separator paper is used. The thickness of the. manufactured chipboard is 18.5 mm, the density approx.

610 kg / rn ^.

Examination of the plates is carried out in accordance with DIN 52 360-65.

Isocyanate ber. 100¾ Pure isocyanate Isocyanate on dry shavings comparison emulsified

Plate examination 2¾ 3¾ 4¾ 2¾ 3¾ 4¾ Bending breaking strength (N / mm ^) 19.80 22.40 26.70 20.50 22.60 24.70

Tensile strength V 20 (kp / cm 2) 2.50 4.50 5.00 3.80 6.20 7.50 15 Tensile strength V 100 0.47 1.50 2.20 1.00 2.50 3.00

Swelling after 2 hours (¾) 2.20 1.70 1.10 1.70 1.50 1.20

Swelling after 24 hours (¾) 13.00 10.00 8.50 11.30 9.10 7.80

The results show that at the same amount of adhesive, using the precautions of the invention 20, a better mechanical strength is obtained and that the sensitivity to water clearly decreases.

EXAMPLE 5 - (Application Example for Example 2)

With the described emulsion prepared on the basis of 5¾ emulsifier solution, chipboards were usually prepared in the usual way and their technological applicability was investigated.

148359 13

Isocyanate ber. 100? Ό on absolutely dry (atro) chips 2% 3? 4%

Plate examination according to DIN 32 360-65 Bending breaking strength (N / mm ^) 20.2 23.2 24.2

Transverse tensile strength V 20 (kp / cm 2) .3.5 5.6 7.6

Transverse tensile strength \ l 100 (kp / cm) 0.1 0.9 2.3

Swelling after 2 hours (%) 2.5 2.3 1.8 10 Swelling after 24 hours (¾) 11.9 10.7 9.4 EXAMPLE 6 - (Application Example for Example 3)

With the emulsion described in Example 3, which was prepared by means of 5% emulsifier solution, chipboard was prepared in the usual way and their technological applicability was investigated.

Isocyanate ber. 100? Ό on absolutely dry (atro) chips 2% 3? Ό 4? Ό

Plate study fair according to DIN 52 360-65 Bending breaking strength (N / mm ^) 21.2 23.4 26.2

Transverse tensile strength V · 20 (kg / cm 2) 3.1 5.9 7.9 ·

Transverse tensile strength V 100 (kp / cm 2) 0.2 1.4 2.4

Swelling after 2 hours (¾) 2.4 2.4 2.2

Swelling after 24 hours (%) 12.0 9.0 8.4