NO310880B1 - Mixture suitable as binders for the preparation of lignocellulosic moldings, process for the preparation of mixtures suitable as adhesive resins and the use of the mixtures - Google Patents

Abstract

Mixtures of: (A) an aqueous condensation product comprising (a) 1 mol melamine and (b) 3 to 11 mol formaldehyde, and (B) a total urea quantity of 0.8 to 13 mol, in which up to 25 % of this total quantity may be contained as component (c) in the resin (A). These mixtures are suitable as adhesive resins.

Description

The present invention relates to a mixture which is suitable as a binder for the production of lignocellulosic moldings, and which consists of

(A) an aqueous condensation resin of

(a) 1 mole of melamine,

(b) 3-11 moles of formaldehyde,

(c) 0-0.5 mol aromatic or partially aromatic

hydroxy compounds

(d) 0-0.1 mol additional aminoplast-forming

components,

and

(B) a total amount of urea of from 0.8 to 13 moles, being up to

25% of this total amount can be added during manufacture

ling of (A).

Furthermore, the invention relates to a method for the production of such mixtures as well as their use for the production of lignocellulose-containing shaped bodies.

It has long been known that wood and other lignocellulosic components can be glued with urea-formaldehyde resins which harden under acidic conditions. For many purposes, however, the water resistance of such adhesive compounds is not sufficient. One therefore often has to resort again to the alkaline-curing phenol-formaldehyde resins. However, these have the disadvantage that they are more expensive, that they finish curing more slowly, that they still contain free phenol, take on a dark color and also exhibit a high alkali content, which causes difficulties with varnishes and coatings, and it can be feared so-called "blooms" of the alkali.

These disadvantages can be partially avoided by using melamine-containing urea-formaldehyde resins, which for reinforcement can additionally contain certain proportions of phenol. In order for a lignocellulosic molded body that has been produced with such a resin to no longer contain any free phenol, a condensate of phenol and formaldehyde and possibly an alkali (hydrogen) sulphite is produced in a separate work operation, to which urea is then added the melamine-formaldehyde resin at a suitable point. Such resins harden under acidic conditions, require somewhat shorter curing times than phenolic resins and also provide waterproof bonding. The disadvantages of these, however, are the expensive multi-stage production, the high price of the melamine and the still relatively long curing time compared to pure urea-formaldehyde resins, which increase the production costs of chipboard or other lignocellulosic products that are bonded to them.

EP-A 25 245 discloses melamine-modified aminoplast resins which are obtained by mixing urea-formaldehyde resins with melamine-urea-formaldehyde resins or by mixing melamine-formaldehyde resins with urea-formaldehyde resins.

DE-A 24 55 420 describes a method for the production of melamine-urea-formaldehyde resins by condensing melamine with urea-formaldehyde pre-condensates.

From EP-P 54 755, a method for the production of melamine-formaldehyde wet resins is known, where the melamine-formaldehyde condensates are added to a urea solution to increase the storage stability.

According to the teachings of US-A 4,123,579, wet resins of melamine-formaldehyde condensates are, after condensation, added with smaller amounts of urea to improve flowability.

In DE-A 34 42 454 it is recommended to prepare urea-melamine-formaldehyde condensation products in such a way that the formaldehyde is used in the form of an aqueous solution with urea for the reaction with the melamine. It can be used here up to approx. 50% by weight of the total amount of urea that is needed, during, before or after the condensation, also in a form other than the formaldehyde solution. A certain part of the urea compound remains unbound before it has to serve as a formaldehyde scavenger.

All known resins, however, allow several improvements in terms of their applicability as a binder only insofar as, under certain conditions, they meet the requirements for good moisture resistance in the moldings with good firmness as well as simple and cost-effective production of the resins in each case.

The purpose of the present invention has been to find improved aqueous resins which are suitable as binders, based on melamine, urea and formaldehyde.

The present invention comprises a mixture which is suitable as a binder in the production of lignocellulose-containing shaped bodies,

where it consists of

(A) aqueous condensation products of

(a) 1 mole of melamine and

(b) 3-11 moles of formaldehyde,

and

(B) from 0.8 to 13 moles of urea, with up to 25% of this

total amount of urea can be added during production

of the condensation products (A).

Furthermore, the invention also describes a method for producing mixtures suitable as adhesive resins,

where it

(A) in aqueous medium at pH values of from 7.5 to 10.0 and

temperatures of from 50 to 100°C are converted

(a) 1 mole of melamine,

(b) 3-11 moles of formaldehyde,

(c) 0-0.5 moles of phenol and

(d) 0-0.1 mol additional aminoplast-forming

components,

and

(B) then a total amount of urea of from 0.8 is added

to 13 mol at temperatures of from 20 to 80°C, in that

up to 25% of this total amount can be present at the time of conversion (A).

In conclusion, the invention includes the use of mixtures according to one of claims 1-6 as binders in the production of lignocellulose-containing shaped bodies.

According to this, the initially defined mixtures have been found.

The aqueous condensation products (component A) are obtained by reacting 1 mol of melamine (a) with (b) 3-11 mol, preferably 3.6-9.5 mol, particularly preferably 4-7 mol, of formaldehyde.

Melamine is usually used in solid form. Formaldehyde is usually used in the form of concentrated aqueous solutions, for example as a 40% by weight aqueous solution or as paraformaldehyde. It is also possible to use a concentrated aqueous solution of formaldehyde and urea, if part of the urea compound is already added during the condensation.

Furthermore, the aqueous condensation products (A) can contain up to 0.5 mol per moles of melamine of an aromatic or partially aromatic hydroxy component (c). Such components are primarily mono- or polyvalent phenols, for example resorcin, hydroquinone or preferably phenol, and likewise polynuclear compounds such as for example α- or β-naphthol or partially aromatic dihydroxy compounds such as 2,2-bis(4-hydroxyphenyl )-propane (bisphenol A), 1,1-bis-(4-hydroxyphenyl)-ethane or 1,1-bis-(4-hydroxyphenyl)-isobutane. Phenol is preferably added in the form of phenol-formaldehyde precondensates, which can for example be obtained according to DE-A-

31 25 874, or also in free form.

Furthermore, modified urea compounds such as ethylene urea, ethylene diurea or dipropylene triurea, or guanamine such as benzoguanamine or amides such as caprolactam, can be added as aminoplast-forming components (d) in quantities of up to 0.1 mol in the preparation of (A).

The conversion is advantageously carried out by mixing 1 mol of melamine with 3-11 mol of formaldehyde and up to 25% of the total quantity required of urea, at a temperature of 20-40°C, and heating to a temperature of between 70 and 100°C, preferably 75-95°C. The pH value should be between 7.8 and 9.5, preferably between 8.2 and 9.0. Under these conditions, it condenses until the viscosity of the mixture, measured with a plate-plate viscometer, is between 10 and 1000 mPa.s, particularly preferably 10-500 mPa.s. It is then cooled until from

10 to 80°C, preferably from 40 to 75°C.

Component (B), a total amount of urea of from 0.8 to 13 mol, preferably from 1.3 to 4.5 mol, is then added to the condensation product (A), as up to 25% of this total amount can already be added during the preparation of the resin (A).

The urea compound is preferably added in solid form or in aqueous solution. In the case where up to 25% of the total amount of urea is already added during the production of the condensation product (A), the urea compound can also be added in the form of a concentrated aqueous solution of urea and formaldehyde.

According to the preferred embodiment, the urea compound as a total amount is mixed with the resins (A) after completion of their condensation. The method of addition is not critical. The urea compound can be stirred into the resin (A) or the resin (A) can be stirred into a urea solution. Mixing of both components can take place at room temperature or in such a way that the resin, which still has a temperature of up to 80°C, is mixed with the urea compound. The finished resin mixture can then be cooled to room temperature. The pH value in the cooled resin must be between 8.5 and 10.0. It is recommended that only part of the urea compound is then added already during the production of component (A), if more than 4 mol of formaldehyde is added per moles of melamine.

For setting the pH values, you can use the alkaline compounds that are usually common, such as alkali and alkaline earth hydroxides in the form of their aqueous solutions, tertiary amines such as, for example, tributylamine or triethylamine, and tertiary alkanolamines, such as e.g. e.g. triethanolamine or methyldiethanolamine.

The method according to the invention is usually carried out so that the solids content in the resin amounts to 50-70% by weight, based on the aqueous resin mixture. However, it is also possible to increase the solids content by distilling off water at 30-45°C in a vacuum.

The viscosity of the aqueous resins obtained is at 20°C in the range 10-800 mPa.s, preferably between 20 and 500 mPa.s, at a solids content of approx. 60%, so that these products are very easy to handle even with higher solids content. They can be particularly easily pumped, mixed with hardener and sprayed. They can also be distributed very easily on the substrate, which gives further advantages when processing them.

The products are usually storage-stable for several weeks at 20°C.

It is also possible to incorporate further additives in amounts of up to 10% by weight in these resins. It can e.g. involve alcohols such as ethylene glycol, diethylene glycol or saccharides. Likewise, water-soluble polymers based on acrylamide, ethylene oxide, N-vinylpyrrolidone, vinyl acetate and copolymers with these monomers can be used.

The resins according to the invention are excellently suitable as binders for the production of lignocellulose-containing shaped bodies such as, for example, chipboard, plywood or fiberboard.

Such molded bodies can, for example, be produced by pressing 5-30% by weight of solid resin, based on lignocellulosic material, at temperatures of from 120 to 250°C under pressure. In addition, hardeners such as, for example, ammonium chloride, ammonium sulphate, ammonium nitrate, ammonium phosphates, formic acid, sulfuric acid or other inorganic or organic acids can also be used. Usually, the hardeners are mixed with the aqueous binder ("glue bath") and then sprayed onto the chips.

The mixtures according to the invention are also suitable for manufacturing

of shaped bodies such as beams, which are obtained by surface-gluing wooden parts.

An advantage of the aqueous mixtures according to the invention is, in addition to the simple method of preparation by which, in contrast to the usual methods, a co-condensation of the urea compound can be avoided, that compared to ordinary resins of comparable composition, a improvement of the processing technical properties, in such a way that, with comparable melamine proportions, an improved moisture resistance and shorter gelling times and consequently higher processing speeds are achieved. With the same good processing properties compared to ordinary resins, the proportion of expensive melamine can be reduced. In this way, the economics of the production of molded bodies from lignocellulosic materials can be improved overall.

Examples

A 40% by weight aqueous solution was used as the formaldehyde solution. The pH values were adjusted with aqueous sodium hydroxide solution.

The viscosities were measured at 20°C with a plate-plate viscometer. The fine solids contents were determined by drying for 2 hours at 120°C in a drying cabinet with circulating air. The gelation times were measured after adding 8 parts of 20% ammonium sulphate solution to 100 parts of glue at 100°C.

Example 1

600 g of formaldehyde solution and 264 g of melamine were heated to 95°C and condensed for 120 minutes at pH 8.6. The viscosity of the mixture was 150 mPa.s (measured at 20°C). It was then cooled to 75°C, and 272 g of urea was added. After cooling to 20°C, the following values were measured: Viscosity 65 mPa.s, solids content 58.7%, gelation time 50 seconds.

Example 2

528 g of formaldehyde solution and 222 g of melamine were heated to 95°C and condensed for 120 minutes at pH 8.8. The viscosity of the mixture was 110 mPa.s (measured at 20°C). It was then cooled to 75°C, and 246 g of urea was added. After cooling to 20°C, the following values were measured: Viscosity 60 mPa.s, solids content 58.8%, gelation time 58 seconds.

Example 3

539 g of formaldehyde solution and 234 g of melamine were heated to 95°C and condensed for 120 minutes at pH 8.7. The viscosity of the mixture was 100 mPa.s (measured at 20°C). It was then cooled to 75°C, and 245 g of urea was added. After cooling to 20°C, the following values were measured: Viscosity 40 mPa.s, solids content 59.4%, gelation time 55 seconds.

Example 4

1200 g formaldehyde solution, 495 g melamine and 24 g urea were heated to 95°C and condensed for 120 minutes at pH 8.5. The viscosity of the mixture was 130 mPa.s (measured at 20°C). It was then cooled to 75°C, and 540 g of urea was added. After cooling to 20°C, the following values were measured: Viscosity 60 mPa.s, solids content 58.6%, gelation time 58 seconds.

Example 5

648 g of formaldehyde solution, 222 g of melamine and 45 g of urea were heated to 95°C and condensed for 120 minutes at pH 8.5. It was then cooled to 75°C, and 255 g of urea was added. After cooling to 20°C, the following values were measured: Viscosity 30 mPa.s, solids content 57.3%, gelation time 56 seconds.

Example 6 (Comparison example)

556 g of formaldehyde solution, 264 g of melamine and 111 g of urea were heated to 95°C and condensed for 60 minutes at pH 8.6. The viscosity of the mixture was 490 mPa.s (measured at 20°C). It was then cooled to 75°C, and 140 g of urea was added. After cooling to 20°C, the following values were measured: Viscosity 150 mPa.s, solids content 57.9%, gelation time 80 seconds.

Example 7 (Comparison example according to DE-OS 34 42 450)

A mixture of 445 g of a concentrated aqueous solution of 50 wt% formaldehyde, 25 wt% urea and 25 wt% water, 246 g melamine and 104 g water was heated to 95°C and condensed for 55 minutes at pH 8.6. The viscosity of the reaction mixture was 1220 mPa.s (20°C). It was then cooled to 75°C, and 140 g of urea was added. After cooling to 20°C, the resin had a viscosity of 420 mPa.s, a solids content of 66.5% by weight and a gel time of 76 seconds.

Application example

With the resin according to examples 1-7, glue soups were produced for the production of chipboards. To this was added 100 g of resin with 8 g of a 20% by weight aqueous ammonium sulfate solution, and the solids content in the glue soup was adjusted to 51.8% by weight by adding water. Particle boards with a thickness of 19 mm were produced, the solid resin content of each of the chips being 12% by weight and the pressing time 114 seconds at 210°C.

The chipboard properties are listed in the table below.

Claims (7)

1. Mixture that is suitable as a binder in the production of lignocellulose-containing shaped bodies, characterized in that it consists of (A) aqueous condensation products of (a) 1 mol melamine and (b) 3-11 mol formaldehyde, and (B) from 0.8 to 13 moles of urea, being up to 25% thereof total amount of urea can be added during production of the condensation products (A). 2. Mixtures according to claim 1, characterized in that the total quantity of urea has been added after completion of the condensation of the condensation products (A). 3. Mixture according to claim 1 or 2, characterized in that it contains condensation products (A) which additionally contain up to 0.5 mol of an aromatic or partially aromatic hydroxy component. 4. Mixture according to one of claims 1-3, characterized in that it contains condensation products (A) which additionally contain up to 0.1 mol of a further aminoplast-forming component. 5. Mixtures according to one of claims 1-4, characterized in that they can be obtained by (A) condensation of (a) 1 mol of melamine, (b) 3-11 mol of formaldehyde, (c) 0-0.5 mol of phenol and (d) 0-0.1 mol of additional aminoplast - forming components, in aqueous medium at pH values of from 7.5 to 10.0 and temperatures of from 50 to 100°C, and (B) then adding a total amount of urea of from 0.8 to 13 mol, being up to 25% of this total amount can be added when making condensation the products (A). 6. Process for the production of mixtures suitable as adhesive resins, characterized in that (A) 1 mol of melamine is reacted in an aqueous medium at pH values of from 7.5 to 10.0 and temperatures of from 50 to 100°C , (b) 3-11 mol formaldehyde, (c) 0-0.5 mol phenol and (d) 0-0.1 mol additional aminoplast-forming components, and (B) then adding a total amount of urea of from 0.8 to 13 mol at temperatures of from 20 to 80°C, in that up to 25% of this total amount can be present at the time of conversion (A). 7. Use of mixtures according to one of claims 1-6 as binders in the production of lignocellulose-containing moldings.