DK147599B - METHOD OF HEAT PRESSING CELLULOS MATERIAL WITH ISOCYANATE AS A BINDING AGENT - Google Patents

Description

147599

The present invention relates to a process for making sheets or molds by hot pressing a mass of lignocellulosic material mixed with an organic polyisocyanate as a binder.

Plates or moldings are generally prepared by hot pressing a mass of wood chips, wood fibers or other lignocellulosic materials mixed with binders, especially solutions of urea-formaldehyde or phenol-formaldehyde resins. Pressure temperatures are usually approx. 150 to 220 ° C, as otherwise no adequate adhesion will occur within an acceptable time, even at the high pressures (20-70 kg / cm) normally used.

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From British Patent Specification No. 1,148,016, it is known to use emulsions prepared by mixing a liquid isocyanate or isocyanate solution with urea, melamine and phenol-formaldehyde resin glue. The resins contain free hydroxyl groups which are reactive with isocyanate and are therefore not surfactants. Such binders have the disadvantage of being less water resistant than an isocyanate used as the sole binder.

From US Patent No. 3,781,238, it is known to use stable polyurethane emulsions which do not contain free isocyanate groups as coatings but not as binders for lignocellulosic materials.

British Patent No. 1,290,301 discloses highly miscible blocked isocyanate polymers containing substantially no free NCO groups, but containing carboxyl groups in the form of quaternary ammonium salts or alkali metal salts and OH groups which confer the polymeric water-soluble properties. These compounds can be used as coatings and adhesives, but the aqueous solution must be heated to create a crosslinked resin.

Liquid isocyanates or isocyanate solutions are known to be used as chipboard binders in place of urea molds for maldehyde or phenol-formaldehyde resins and emulsions of isocyanates with these resins.

If liquid isocyanate is used as the only binder, the relatively high viscosity of the isocyanate results in less efficient distribution over the large volume of wood chips when using a spraying or spreading technique. The use of solvents improves distribution but introduces environmental hazards due to the flammability of suitable solvents and atmospheric pollution caused by evaporation of the solvents during the hot pressing, thereby exposing workers to the danger of poison.

Emulsions of isocyanates with the usual resin adhesives which, among other things, lose to some extent, depending on the amount of resin adhesive used, the advantages of the finished product's resistance to the effects of water obtained by using isocyanates alone.

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The present invention alone retains the advantages of using isocyanate binders alone and yet facilitates the distribution of the binder without causing the dangers accompanying a solvent-based system.

The process of the invention is characterized in that the organic polyisocyanate is applied to lignocellulosic material: ten forms of an oil-in-water emulsion containing 5-15 parts by weight, calculated on 100 parts by weight of the organic isocyanate, of a surfactant of the formula R0 (CHoCHoO) CONHX, 2 n, where R is an alkyl group of 1-4 carbon atoms, n is on average from 5 to 120, and X is the residue of a di- or polyisocyanate and contains at least one free isocyanate group and wherein the emulsion contains from 1 to 75 parts by weight organic isocyanate per 100 parts by weight total of organic isocyanate and water.

lignocellulosic material which can be used in the process includes wood shavings, wood fibers, shavings, wood wool, cork and bark, sawdust and similar waste products from the woodworking industry and / or fibers from other natural products which are lignocellulosic products, e.g. bagasse, straw, flax residue and dried pipes, reeds and grasses. In addition, with the lignocellulosic materials, inorganic flake or fibrous materials may be mixed, e.g. fiberglass, mica or asbestos.

Organic polyisocyanates include diisocyanates, especially aromatic diisocyanates and isocyanates with higher functionality.

Examples of organic polyisocyanates which can be used for the process of the invention are aliphatic isocyanates such as hexa methylene diisocyanate, aromatic isocyanates such as m- and p-phenylenedi isocyanate, 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'-diisocyanate-3,3'-dimethyl diphenyl , 3-Methyldiphenylmethane-4,4'-diisocyanate and diphenyl ether diisocyanate, cycloalphatic diisocyanates such as cyclohexane-2,4- and -2,3-diisocyanate, 1-methylcyclohexyl-2,4- and -2,6- diisocyanate and mixtures thereof and o 4 147599

Bis- (isocyanatocyclohexyl) methane and triisocyanates such as 2,4,6-triisocyanatotoluol and 2,4,4'-triisocyanatodiphenyl ether.

Mixtures of isocyanates may be used, e.g. a mixture of thiolene diisocyanate isomers, such as the industrially available mixtures of 2,4- and 2,6-isomers, and also the mixture of di- and higher polyisocyanates prepared by the phosgenation of condensates of aniline and form aldehyde. Bite Mixtures are well known and include the crude phosphorylation products containing Mixtures of polyphenyl polyisocyanates with methyleneBro including diisocyanate, triisocyanate and higher polyisocyanates together with any phosgenation by-products.

Preferred polyisoeyanates for use in the invention are those in which the isocyanate is an aromatic diisocyanate or higher functionality polyisocyanate, especially crude Mixtures of polyphenyl polyisocyanates with methyleneBro containing diisocyanates, triisocyanate and polyisoeyanates with higher functionality. Polyphenyl polyisocyanates with methyleneBro are well known and have the general formula: -f-OHg - - | --CH2-- |

Y r V

ICO ICO n_i ICO

where n is 1 or more and in the case of the crude Mixtures represent an average of more than 1. Be is prepared by phosgenation of similar Mixtures of polyamines obtained by condensation of aniline and formaldehyde. For convenience, crude Mixtures of polyphenyl polyisocyanates with methyleneBro containing diisocyanate, triisocyanate and polyisoeyanates with higher functionality are hereinafter referred to as MBI.

Particularly preferred organic isocyanates which can be used in accordance with the invention include prepolymer with terminated isocyanate prepared by reaction of an excess of a diisocyanate or higher functionality polyisocyanate with a polyester with terminated hydroxyl or polyether with terminated hydroxyl and products obtained from excess diisocyanate or higher functionality polyisocyanate with a monomeric polyol or Mixture 5 147599 of monomeric polyols such as ethylene glycol, trimethylolpropane or butanediol. 4f of particular value because of their slower reaction with water, a desirable property discussed below, however, are prepolymers with terminated isocyanate prepared using hydrophobic polyols such as castor oil.

One class of terminal isocyanate prepolymer that can be used are MDI prepolymer polymers.

Of particular value are the reaction products of diisocyanates and polyisocyanates with higher functionality with the surfactants with R0 (CHoCH2 O) CONHX. λ λ n

Examples of R include ethyl, propyl and butyl, preferably methyl.

Sufficient oxyethylene groups (C 2 CE 2 O) must be present in the surfactant urethane for an average of 5 - 120 such groups per molecule.

Group X is the residue that would be left after one isocyanate = group was removed. The group X may be the residue of any diisocyanate or higher polyisocyanate, and if the diisocyanate e.g. is a tolylene diisocyanate, the residue X will be

ECO

The group X preferably contains an isocyanate group.

Isocyanates from which the group X can be derived include the di- and polyisocyanates mentioned above.

These surfactant urethanes can be prepared by reacting an alcohol of formula Ε0 (0Η20Ξ20) H with an isocyanate having at least two isocyanate groups, using at least one molar amount of isocyanate for each molar amount of alcohol. Preferably, an excess of the isocyanate is used.

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The reaction can be carried out by adding the alcohol to the isocyanate with stirring until clarity and allowing the reaction to proceed at room temperature. The reaction can be accelerated by heating to temperatures up to 100 ° 0.

In order to obtain the emulsions used according to the invention, the surfactant of the above type can be prepared in situ in the isocyanate. Thus, if it is desired to prepare an emulsion of an isocyanate of formula X (UCO) 2, a small amount of the polyethylene oxy alcohol RCKCHCHCHCHO 2 H can be added to a large excess of the isocyanate X. (EO0) 2 and the emulsifier is formed in situ in the isocyanate .

In the cases where the polyisocyanate is a prepolymer, the formation of the prepolymer and an in situ surfactant can be carried out simultaneously or as two separate steps, and the prepolymer and the surfactant can then be mixed with water to form the emulsified prepolymer. Emulsification is facilitated by initially mixing the prepolymer and the surfactant with approx. 1/4 of its weight of water and then dilute with more water as needed.

Thus, the hair polyisocyanate present in the emulsion must be of the class of preferred prepolymers mentioned above, namely a prepolymer of MDI, the emulsion of the prepolymer can thus be prepared by any of the following three methods: (1) Reaction of MDI with the required amount of polyol to form the prepolymer followed by reaction with a small amount of the polyethene oxy alcohol CH 2 O () nH followed by emulsification by stirring with water.

(2) Reaction of MDI with the required small amount of polyethylene oxy = the alcohol CH 2 O (CH 2 CH 2 O) nH followed by reaction with the amount of poly =. etc., which is necessary: to give the prepolymer, followed by emulsification.

(5) Reaction of MDI with the required amounts of polyol and polyethylene oxy = alcohol simultaneously followed by emulsification in water.

In the above three methods, the preparation of the in situ surfactant is carried out in the polyisocyanate, the surfactant having the general formula R0 (CH2CH2O) nX where X is the residue of the isoeyanate and R is an alkyl group having from 1 to 4 carbon atoms. .

Preferred surfactants are those derived from the polyethylene = oxy compound R0 (CH2CH2O) nH, where R is methyl and n is an average of 10 to 25. Typical examples of the polyethylene oxy compounds are methoxy polyethylene glycols having a molecular weight of 300 to 1000.

Of course, the surfactant can be prepared separately and a small amount dissolved in the prepolymer-forming mixture or in the pre-formed prepolymer.

Formation of the prepolymers can be carried out in any of the known ways, i.e. by heating the components together or by reacting them at ambient temperature, optionally in the presence of catalysts.

The emulsions of the prepolymers prepared by the methods described above are oil-in-water emulsions.

The emulsions can be prepared in conventional ways, preferably by mixing the emulsifier with the organic polyisoeyanate and mixing this mixture with water. In some cases, the nonionic surfactant may alternatively be prepared in situ in the polyisocyanate, and this product, optionally diluted with additional polyisoeyanate, is mixed with water and the whole stirred to form the desired emulsion. In order to carry out the process according to the invention, the lignocellulosic material with the binder is suitably mixed by spraying it nicely with the aqueous emulsion so as to obtain good coverage. It has been found that aqueous emulsions of the organic polyisocyanates have sufficiently low viscosity to be sprayed at strengths of up to $ 65, while the solutions of urea-formaldehyde and phenol-formaldehyde resin usually used for the production of particle board and similar materials , usually not sprayable in strengths over $ 40. Thus, the invention provides a means of working with less water than has hitherto been possible, so that it is only necessary to expel less water during the hot pressing step or subsequent conditioning. Alternatively, the lignocellulosic material needs to be dried to the normal extent before mixing with the binder. Use of hot water and / or organic polyisocyanate can facilitate emulsification and spraying.

It has further been found that the hot pressing step of the process according to the invention can be effectively carried out at temperatures below 100 ° 0 (e.g., at 90-95 ° C) instead of the usual 150-220 ° C used with urea. -formaldehyde and phenol-formaldehyde resins. - The use of these lower temperatures saves energy, reduces environmental discomfort and eliminates smoke. It is also advantageous because it avoids the bursting effect of vapor pressure developed inside sheets or molded articles made at higher temperatures, which is especially important in the manufacture of laminates having impervious surface coatings, therefore improved consolidation can be achieved during the pressing step. it is no longer necessary to leave enough permeability for steam to evade.

Of course, the more usual higher temperatures can still be used and may in fact be desirable in certain circumstances as they provide shorter curing times and tend to promote improved release of the chipboard from the press plates. This latter consideration may be of importance where boards without surface coatings are to be manufactured.

Accordingly, in a preferred embodiment, the invention discloses a process for making sheets or molded articles consisting of spraying lignocellulosic material with an aqueous emulsion of an organic polyisocyanate, preferably a prepolymer of terminal isocyanate, of a crude mixture of polyphenyl polyisocyanates, said aqueous emulsion containing a stabilizing amount of a non-ionic surfactant free of hydroxy, amino and carboxylic acid groups having 75-50 parts by weight of water together with 25-50 parts by weight of the organic polyisocyanate, optionally dry at 20 -4Q ° C to remove part of the water and hot-press the sprayed pre-treated raw material at a temperature below 200 ° C and especially below 100 ° C, especially 90-95 ° C, to effect cohesion.

In this way, highly bonded sheets or molded bodies are obtained economically.

In practice, there will inevitably be periods of delay between stages in the preparation of emulsion, spraying of the lignocellulosic material and hot pressing of the sprayed material, and delays also occur in correcting processing errors and in making operational settings. Conveniently, the reaction between the isocyanate and the water of the emulsion is sufficiently slow that a delay of e.g. 2 hours between preparation of the emulsion and hot pressing. The rate of reaction may be slowed to obtain an emulsion with an acceptable working time, by using less surfactant or by using a less effective agent, but both of these pathways adversely affect the stability of the binder and the distribution of the isocyanate over the lignocellulosic material and also causes spraying difficulties. Therefore, it is advantageous to decrease the reaction rate by using a prepolymer with terminal isocyanate derived from a hydrophobic polyol, as already mentioned, and / or by including in the emulsion an inert hydrophobic diluent which also provides advantages in improving the water repellent nature of the obtained chipboard and by supporting the release of the chipboard from the pressing plates. Suitable diluents are fatty hydrocarbons, aromatic and aliphatic as well as esters optionally containing a halogen substituent. Examples include mineral oil and slack wax (impure paraffin wax), didodecyl phthalate, tris-P-chloropropyl phosphate and especially chlorinated paraffin wax species. These diluents which do not react with isocyanate groups can be added during the preparation of the prepolymer or just before the emulsification.

Example 1 320 g of wood chips were dried to a moisture content of $ 6. They were placed in an open bowl mixer, and while being rolled over, binder liquid was sprayed in by means of a simple hand operated syringe, the amount supplied being controlled by reference to the weight loss. Stirring of the sprayed shavings was continued for 1 minute, then sprinkled evenly over the 18 x 18 cm area in a molding box. The pulp was then compressed manually as much as possible after applying a surface of similar size, so that a loosely compressed mat of chips was produced approx. 4.5-5 cm thick. The mat was transferred to release-treated metal sheets and placed in a hydraulic press where it was compressed using a pressure of 50 kg / cm 2 between sheets at 90-95 ° C for 5 minutes. A clearance of 1.4 cm "was used to limit the room weight to about 0.7. After removal, the plates were conditioned to obtain the water content of about $ 10 and physical testing was performed on the representative 15 x 15 cm central portion. of the resulting sheet pieces.

A comparison was made between emulsifiable DMI and emulsifiable DMI prepolymer of MDI 100

Oxypropylated glycerine MW 1000 30

Methyl oxyp o lyethyl methyl glyco 1 (methoxy PEG ·) MW 650 10

Each was emulsified by mixing with half its weight of water followed by its own weight of water to make emulsions with a content of $ 40 solids.

40 g of these emulsions were used for spraying 320 g portions of wood shavings as described above.

The plates both exhibited good curing after removal from the press, and at this temperature no visible vapor or smoke was produced and no swelling was observed in the removal of the plates from the press.

A similar pair of tests was carried out using half the emulsions so that only 2 1/2% of solids appeared as a binder, based on the weight of the chips.

Physical properties of samples described in BS 1811 part 2 were as follows:

EMDI = emulsifiable MDI

EMDIPP - emulsifiable MDI prepolymer

Il · 147599

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HO * CO ·> LO λ • 'C "~ LO O O

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83 0 H {> 5 Η P

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The stability of the emulsion was such that it could be used for up to 1/2 hour at 20-22 ° C, and it was possible to obtain a fully satisfactory plate, although the freshly sprayed chips were balded at 20-22 ° C 1 hour before being compressed into a board.

By including a catalyst in the emulsion, it is possible to accelerate the curing and thereby enable either a shorter time at 90-95 ° C or to operate at a lower temperature. For example, to include 1 $ dimethylhexadeoylamine, based on the weight of EMDIPP in the emulsion, the stability was reduced so that it had to be sprayed over 2 minutes and the sprayed chips had to be pressed within 5 minutes, but the board was cured for 3 minutes at 95 ° C. or in 5 minutes at TO ° C.

Pore improvement in water resistance can be expected by including additional water repellents in a manner similar to those already used with the usual urea-formaldehyde and phenol-formaldehyde bonded particle boards.

Example 2

Eire emulsifiable MDI prepolymers (1) to (4) prepared by admixing MDI (100 parts), methoxy PEG-MW 650 (10 parts) and the following polyols: oxypropylated glycerine, OH value 160 (30 parts) in (1) oxypropylated glycerine, OH value 540 (9 parts) in (2) a polyester, OH value 540, derived from adipic acid = diethylene glycol and glycerine (9 parts) in (3) and castor oil, OH value 160 (30 parts) in (4) was emulsified with water in the 1: 1 weight ratio.

The ICO content of each emulsion was determined after 2 hours at 22 ° C using the standard method of adding excess di-n-butylamine to a $ 40 aqueous emulsion followed by back titration with hydrochloric acid. The loss of activity of each emulsion was as follows: emulsion derived from (1) - $ 55 emulsion derived from (2) - $ 30 emulsion derived from (3) - $ 24 emulsion derived from (4) - $ 17.

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These results show that the more hydrophobic polyol used to prepare the prepolymer, the greater the processing time of the emulsion.

The loss of activity of the emulsions derived from 7 parts of an emulsifiable prepolymer and 12 parts of water and the corresponding emulsions containing a chlorinated paraffin wax as diluent "Cereclor S45" (registered trademark) were as follows:

Castor Oil Eor Polymer - $ 27.3

Castor Oil Eor polymer + 4 parts "Cereclor S45" - $ 18.9

Hydrogenated Eor Polymer Castor Oil - $ 22.9

Eor polymer of hydrogenated castor oil + 4 parts "Cereclor S45" - $ 13.7

Oxypropylated glycerine Eor polymer (OH value 540) - $ 30.4.

Oxypropylated glycerine Eor polymer (OH value 540) + 4 parts "Cereclor S45" - $ 17.2

Oxypropylated glycerine Eor polymer (OH value 540) + 7 parts "Cereclor S45" - $ 13.5

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

Example 5

A prepolymer was prepared by admixing 100 parts of MDI

30 parts of castor oil (first extruder) OH 160. and 10 parts of methoxy PEG MW 650 heat to 80 ° C overnight and then cool. Two emulsions (a) and (b) were prepared by admixing: (a) 4 parts of the above castor oil prepolymer and 10 parts water, and (b) 6 parts of the castor oil prepackle (4 parts) mixture and " Cereclor S45 "(2 parts) and 10 parts water.

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Two particle board samples were then prepared by taking 102 parts of wood chips containing 2% moisture and spraying separately under upheaval with the aforementioned emulsions sufficiently liquid to provide good atomization. Each batch of treated shavings was sprinkled in a frame placed on a sheet to form a cake which, after removing the mold, was covered with an aluminum sheet, both metal sheets having been treated with a wax-based release agent. The cakes were compressed in a hydraulic press with plates at 175 ° C using a pressure of 135 kg / cm. A spacer plate was mounted to limit the compression to 19 mm. 680 kg / m. The pressing time was 45 minutes and when the pressure was removed, the adhesives of the plate using "Cereclor S45" in the binder were better than the adhesives of the item (a) which showed some tendency to adhere especially to the steel plate.

The manufactured sheets were allowed to cool and condition and then tested. The results were as follows: a b

Space weight kg / m in 704 713

Swelling in water 2 hours fo 23.0 18.0

Swelling in water 24 hours before 26.0 21.6

German V20 sample KN / m ^ 703 822

German Y100 sample KH / m ^ 157 190

Example 4

A portion of the same type of wood shavings with 2% moisture was sprayed with an emulsion made from 6 parts of a mixture of castor oil prepolymer as used in Example 3 (4 parts) and "Cereclor S45" (2 parts) and 6 parts water. then 5 parts of 20 µm of uncleaned paraffin wax emulsion were sprayed and the treated chips were then sprinkled and processed as before. One cooled conditioned board was tested and the results were as follows: 2

Space weight kg / m 690