WO1997009360A1

WO1997009360A1 - Aqueous binder mixtures with low free-formaldehyde content for producing derived timber products

Info

Publication number: WO1997009360A1
Application number: PCT/EP1996/003796
Authority: WO
Inventors: Anton Meier; Christel Hittinger; Hermann Schatz; Gunter Lehmann; Tilmann Reiner; Manfred Niessner
Original assignee: Basf Aktiengesellschaft
Priority date: 1995-09-05
Filing date: 1996-08-29
Publication date: 1997-03-13
Also published as: DE19532719A1

Abstract

Disclosed are aqueous binder mixtures suitable for producing derived timber products and containing (A) an aqueous aminoplast resin consisting of (a1) melamine, (a2) 0.8 to 6 mol urea per mol melamine, (a3) 2 to 20 mol formaldehyde per mol melamine and (a4) 0 to 1 mol of another compound that can react with formaldehyde in an addition reaction or condensation reaction and is different from phenol or a condensation-polymerizable phenol derivative, per mol melamine, and (B) 0.55 to 0.75 mol urea per mol of the total amount of urea used as components (a2) and (B), with the proviso that the molar ratio of the melamine (component (a1)) to the total amount of urea (components (a2) and (B)) is 1:3.5 to 1:13 and that the molar ratio of formaldehyde (component (a3)) to the -NH2 groups in components (a1), (a2) and (B) is 0.2:1 to 0.7:1.

Description

Aqueous binder mixtures with a low free formaldehyde content for the production of wood-based materials

description

The present invention relates to aqueous binder mixtures which are suitable for the production of wood-based materials containing

A) an aqueous aminoplast resin

al) melamine, a2) 0.8 to 6 mol of urea per mol of melamine a3) 2 to 20 mol of formaldehyde per mol of melamine and a4) 0 to 1 mol of a further compound which react with formaldehyde in an addition reaction or condensation reaction can, the compound being different from phenol or a polycondensation phenol derivative, per mole of melamine, and

B) 0.55 to 0.75 mol of urea per mole of the total amount of urea used as components (a2) and (B), with the proviso that

the molar ratio of the amount of melamine used (component a1) to the total amount of urea (components (a2) and (B)) is 1: 3.5 to 1:13 and the molar ratio of formaldehyde (component a3) to those in the Components (a1), (a2) and (B) present -NH ₂ groups is 0.2: 1 to 0.7: 1.

Furthermore, the invention relates to processes for their production, their use as binders for the production of wood-based materials, and wood-based materials which can be obtained using these binder mixtures.

Binders based on aqueous aminoplast resins made from urea and formaldehyde, which are suitable for gluing shredded wood, for example wood chips and wood fibers, to the corresponding wood materials, for example wood chipboard or wood fiber boards, are generally known ( see Ulimanns Encyklopadie der Technische Chemie, 4th edition, volume 7, pp. 413 to 422). Usually, the binders are applied to the shredded wood in the manufacture of the wood-based materials, after which they are pressed together at elevated temperatures, the binder hardening. The aminoplast resins should have good processing properties and should enable the economical production of wood-based materials with good usage properties. Important processing properties are high reactivity and low viscosity with a high solids content at the same time, so that short working cycles, in particular short pressing times, are sufficient to process wood chips which have been wetted with the glue resins into high-quality chipboard. In addition, it should be possible to store the glue resins over a long period of time without changing their properties.

Important mechanical properties of the wood-based materials are good mechanical properties such as good tensile strength and insensitivity to moisture and especially water vapor.

Wood-based materials with good mechanical properties and, in particular, good water resistance can be obtained from those amino resins which, in addition to formaldehyde and urea, have also been produced using melamine or phenol, the melamine-containing aminoplast resins (MUF resins) compared to the phenol-containing resins have the advantage that the wood materials made from them do not darken (cf. loc. eit. p. 417)

Mixtures of aqueous MUF resins and urea are known from DE-A 34 42 454. The MUF resins are produced by condensing a mixture of formaldehyde, urea and melamine, into which the formaldehyde has been introduced partly or completely in the form of a concentrated aqueous solution with urea, under weakly basic conditions. It is recommended that up to about 50% of the urea, based on the total amount of urea, be added to these resins after the condensation. There is no information on the molar ratio of formaldehyde to amino groups in the urea and melamine used and on the molar ratio of melamine to urea.

Example 3 of this document describes a size resin which is prepared by adding 65% urea to an aqueous MUF resin, based on the total amount of urea contained in the finished size resin. The molar ratio of urea to melamine is 3.08: 1 and the ratio of formaldehyde to amino groups is 0.67.

The glue resins obtained according to this teaching have a satisfactory level of application technology, as far as their processing properties and the use properties of the derived timber products are concerned. Your free form content However, aldehyde is still too high and does not meet today's requirements.

The glue resins should have the lowest possible free formaldehyde content, because such glue resins release formaldehyde only to a small extent when they are processed into wood-based materials and the formaldehyde emission of the wood-based materials produced with these glue resins is also reduced.

It was therefore an object of the present invention to find binders made of melamine, urea and formaldehyde which are suitable for the production of wood-based materials and which have a good application-related profile and in particular only a low content of free formaldehyde.

Accordingly, the aqueous binders defined at the outset were found.

The aqueous binders according to the invention contain an aqueous aminoplast resin as component (A)

al) melamine, a2) 0.8 to 6, preferably 1 to 4 mol of urea per mol of melamine a3) 2 to 20, preferably 2 to 11 mol of formaldehyde per mol of melamine and a4) 0 to 1 mol, preferably 0 to 0.2 mol of a further compound which can react with formaldehyde in an addition reaction or condensation reaction which is different from phenol or a phenol derivative capable of polycondensation, per mol of melamine

The melamine (component a1) and the urea (component a2) are suitably used in solid form.

The formaldehyde (component a3) is usually used in the form of a 30 to 50% strength by weight aqueous solution or in the form of paraformaldehyde.

Component (a4) are compounds which react with formaldehyde in a condensation or addition reaction which are different from phenol or a polycondensation-capable phenol derivative. Phenol derivatives capable of polycondensation are generally aromatic alcohols which can react with formaldehyde in a condition or addition reaction, for example those described in Ulimann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A19, pp. 371 to 384 for the production of phenolic resins.

In order to improve the water dilutability of the binder mixtures, sulfites, disulfites and hydrogen sulfites can be used, which preferably contain alkali metals and the ammonium ion as cations.

In addition, come as (component a4) urea derivatives, e.g. Ethylene urea, ethylene diurea and dipropylene tris urea as well as guanamines e.g. Benzoguanamine, amides, e.g. Epsilon-caprolactam, alcohols, e.g. Ethylene glycol into consideration.

The starting materials (a1), (a2) and (a4) can also be used as a mixture with formaldehyde (component a3) or as formaldehyde adducts or formaldehyde condensates.

Component (a2) (urea) is preferably used in the form of a concentrated aqueous solution with formaldehyde, which is known from DE-A 24 51 990 and EP-A 0 083 427. These solutions of 2.0 to 6.0, preferably 3.5 to 4.5, mol of formaldehyde per mole of urea preferably have a solids content of 50 to 85, particularly preferably 60 to 80,% by weight. They contain urea and formaldehyde partly in monomeric form, partly in the form of reaction products such as methylolureas or low molecular weight condensation products.

These solutions are preferably adjusted so that they have a total formaldehyde content of 30 to 60% by weight, preferably 40 to 55% by weight and a total urea content of 15 to 40, preferably 20 to 30% by weight. They generally contain, in addition to free formaldehyde and mono- and polymethylolurea compounds which contain only one unit derived from urea, preferably less than 10% by weight of urea-formaldehyde condensation products or addition products which contain more than one derived from urea Unit included.

The preparation of component (A) is generally carried out in such a way that components (al) to (a4) in an aqueous solution, at 60 to 100, preferably from 75 to 95 ° C. and a pH of 7, 5 to 10, preferably 8.2 to 9.0 is allowed to react until the solution has a viscosity of 150 to 2000, preferably 150 to 1000 mPa s, after which the solution is allowed to cool until it becomes a Temperature of 10 to 80, preferably from 40 to 75 ° C. The concentration of the starting materials (al to (a4) in the aqueous solution is generally 30 to 80, preferably 55 to 75, very particularly preferably from 60 to 70% by weight.

Otherwise, the condensation is carried out in a manner known per se. More details are e.g. Ullmann's Encyclopedia of Technical

Chemistry, 4th edition, volume 7, pp. 403 to 415 and DE-A 34 42 454.

Immediately after cooling to 10 to 80, preferably 40 to 75 ° C or at a later time, e.g. immediately before the processing of the binders, the reaction product of components (a1) to (a4) is mixed with urea.

The urea (component B) is preferably added in pure solid form or in the form of a 40 to 80, preferably 60 to 70% by weight aqueous solution.

The manner of mixing is not critical and is conveniently carried out by stirring the urea (component B) into the reaction product.

The amount of component (B) is preferably 0.55 to 0.75 per mole of the total amount of urea used as components (a2) and (B).

The molar ratio of the amount of melamine used (component a1) to the total amount of urea used (components (a2) and (B)) is 1: 3.5 to 1:13 and preferably 1: 3.5 to 1: 6.

The molar ratio of the amount of formaldehyde used (component a3) to the —NH ₂ groups present in components (a1), (a2) and (B) is 0.2: 1 to 0.7: 1 and preferably 0.4: 1 to 0.7: 1. The units derived from components (a1), (a2) and (a4), which may be in the form of

Reaction products of formaldehyde (component a3) with components (al), (a2) and (a4) are used as starting materials (for example methylolurea). The amount of -NH groups also relates to the amount of -NH ₂ groups that were originally present in components (a2) and (a4) before they were reacted with formaldehyde.

The binder mixtures obtainable by the process according to the invention are preferably adjusted to a pH of 7 to 10, preferably 8.5 to 9.5 and can be stored for more than 6 weeks at a storage temperature of approximately 20 ° C. without their physical and application properties noticeably changing.

To adjust the pH, the generally customary bases such as alkali or alkaline earth metal hydroxides, preferably in the form of their aqueous solutions, tertiary amines, for example tri- (C (- to C ₆ -alkyl) amines such as tributylamine and triethylamine and tertiary Ci bis C _δ -alkanolamines, for example triethanolamine, methyldiethanolamine can be used.

The binder mixtures generally have a solids content (in accordance with DIN 12 605) of 50 to 75, preferably 60 to 70% by weight and a viscosity of 10 to 2000, preferably 10 to 1000, mPas.

Binder mixtures which have the high solids contents mentioned can easily be obtained by the production process described if starting materials with correspondingly high solids contents are selected. It is therefore usually not necessary to increase the solids content by distilling off water.

The binder mixtures can, if appropriate, be mixed with other customary auxiliaries and additives.

To stabilize them and to improve the mechanical properties of the wood-based materials produced with the binders, polyhydric alcohols, sugars and water-soluble polymers built up from monomers such as acrylamide, ethylene oxide, N-vinylpyrrolidone, vinyl acetate or copolymerizable mixtures of these monomers can be added to the binder mixtures become. However, they generally do not contain effective amounts of phenol or condensable phenol derivatives.

The reactivity of the binder mixtures during curing can be increased by adding a hardener such as alkali carbonate, for example potassium carbonate or alkaline earth carbonate, for example calcium carbonate, in amounts of 2 to 8, preferably 4 to 6,% by weight, based on the amount of the binder is added. Other hardeners which can be added to the binder mixtures immediately before or during processing are ammonium salts such as ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium phosphates, strong carboxylic acids such as formic acid and oxalic acid and mineral acids such as sulfuric acid. Furthermore, pesticide compositions, for example commercially available insecticides or fungicides, can be added to the binder mixtures.

The binder mixtures are particularly suitable as binders for the production of composite materials made from comminuted plastic or textile fibers and, in particular, wood-based materials such as plywood, wooden beams made of plywood or plywood and, above all, wood fiber boards and chipboard (see Ullmanns Encyklopadie der Technischen Chemie, 4 Edition, 1976, Volume 12, pp. 709 to 727) made of shredded wood.

The wood-based materials are manufactured using the methods generally known in this field. The gluing is advantageously carried out by pressing the comminuted wood provided with the binder mixtures at temperatures of 120 to 250 ° C. Under these conditions, the aminoplast resin hardens quickly and wood materials with good mechanical properties are obtained that are largely insensitive to the effects of moisture. In particular, the binder mixtures contain only a very low content of free formaldehyde, as a result of which the formaldehyde emission of the binders when they are processed into wood-based materials and that of the finished wood-based materials can be significantly reduced.

example 1

A mixture of 1.72 kg melamine, 3.99 kg of an aqueous solution of 50 wt .-% formaldehyde and 25 wt .-% urea and 2.34 kg of a 40 wt .-% aqueous formaldehyde solution was at a pH -Value from 8.5 to 9 (the pH was adjusted with sodium hydroxide solution) until the mixture had a viscosity of 500 mPa s and then cooled to 60 ° C. 1.95 kg of urea were then added, the mixture was cooled to room temperature and the pH was adjusted to 9.5 with sodium hydroxide solution.

Urea: melamine ratio: 3.6: 1

Ratio of formaldehyde: NH ₂ groups: 0.70: 1

Free formaldehyde content: <0.1% Comparative Example 1

A mixture of 1.64 kg of melamine, 4.34 kg of an aqueous solution of 50% by weight of formaldehyde and 25% by weight of urea and 2.37 kg of a 40% by weight aqueous formaldehyde solution was at a pH -Value from 8.5 to 9 (the pH was adjusted with sodium hydroxide solution) until the mixture had a viscosity of 650 mPa s and then cooled to 60 ° C. Then 1.64 kg of urea were added, the mixture was cooled to room temperature and the pH was adjusted to 9.5 with sodium hydroxide solution.

Urea: melamine ratio: 3.5: 1

Ratio of formaldehyde: NH ₂ groups: 0.80: 1

Free formaldehyde content: 0.35%

Comparative Example 2 (analogous to Example 3 in DE-A 34 42 454)

A mixture of 1.27 kg of melamine, 2.59 kg of an aqueous solution of 50% by weight of formaldehyde and 25% by weight of urea and 1.39 kg of a 40% by weight aqueous formaldehyde solution was at a pH -Value from 8.5 to 9 (the pH was adjusted with sodium hydroxide solution) until the mixture had a viscosity of 650 mPa s and then cooled to 60 ° C. Then 1.22 kg of urea were added, the mixture was cooled to room temperature and the pH was adjusted to 9.5 with sodium hydroxide solution.

Urea: melamine ratio: 3.1: 1

Ratio of formaldehyde: NH ₂ groups: 0.67: 1

Free formaldehyde content: 0.25%

The information given in the examples on the viscosities relates to measurements according to DIN 53 018. The viscosity is then measured in a rotary viscometer at 20 ° C. and a shear rate of 500 s ^_1 .

The free formaldehyde content was determined according to de Jong, as described in Z. Anal. Chem. Volume 281 from 1976, pages 17 to 21 is described. The free formaldehyde is reacted under weakly alkaline reaction conditions with an amount of sulfite which is greater than the amount of formaldehyde, an adduct of formaldehyde and sulfite being formed. Then the closed sulfite titrated at a weakly acidic pH, then the sulfite-formaldehyde adduct formed is hydrolyzed and the sulfite released is determined by titration with iodine.

Claims

claims

1. Containing aqueous binder mixtures which are suitable for the production of wood-based materials

A) an aqueous aminoplast resin

al) melamine, a2) 0.8 to 6 mol of urea per mol of melamine a3) 2 to 20 mol of formaldehyde per mol of melamine and a4) 0 to 1 mol of a further compound which react with formaldehyde in an addition reaction or condensation reaction can, the compound of phenol or a polycondensation-capable phenol derivative being different, per mole of melamine, and

2. Aqueous binder mixtures according to claim 1, wherein component (a4) is an alkali metal hydrogen sulfite and / or an alkali metal sulfite.

3. Aqueous binder mixtures according to claim 1 or 2, wherein the molar ratio of the amount of melamine used (component al) to the total amount of urea used (components (a2) and (B)) is 1: 3.5 to 1: 6 .

4. Aqueous binder mixtures according to claims 1 to 3, wherein the molar ratio of the amount of formaldehyde used

(Component a3) to -NH ₂ groups present in components (a1), (a2) and (B) is 0.4: 1 to 0.7: 1. 5. A process for the preparation of aqueous binder mixtures according to claims 1 to 4, characterized in that an aqueous solution of the components (al),

(a2), (a3) and (a4), where these components can also be used in the form of their reaction products with formaldehyde (component a3), at 60 to 100 ° C. and at a pH of 7,

Allow 5 to 10 to react with each other until the solution has a viscosity of 150 to 2000 mPa.s, after which this solution is allowed to cool and then mixed with component (B).

6. Use of the aqueous aminoplast resins according to claims 1 to 5 as binders for the production of wood materials.

Wood materials obtainable using the aqueous aminoplast resins according to claims 1 to 4.