SK86096A3 - Binders for the production of lignocellulose-containing mouldings - 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

Technical field

The present invention relates to a composition suitable as a binder for the production of lignocellulose-containing moldings consisting of (A) an aqueous condensation resin of (a) 1 mol of melamine, (b) 3 to 11 mol of formaldehyde, (c) 0 to 0.5 ml of aromatic or (d) 0 to 0.1 moles of other aminoplast forming components; and (B) urea in a total amount of 0.8 to 13 moles, up to 25% of this total amount being added in the manufacture of (A).

The invention further relates to a process for the production of such compositions as well as to their use for the production of lignocellulose-containing moldings.

BACKGROUND OF THE INVENTION

It has long been known that wood and other lignocellulose-containing components can be glued with urea-formaldehyde resins which are cured under acidic conditions. However, the water resistance of such bonded joints is not sufficient for many purposes. It is therefore necessary to frequently return to the alkali cured phenol-formaldehyde resins. However, these have the disadvantage that they are more expensive, slower to cure, still contain free phenol, darken and, inter alia, have a high alkali content, thereby creating veneering and coating difficulties and worrying about alkali flowering.

This disadvantage can be partially eliminated by the use of a melamine-containing urea-formaldehyde resin, which may contain some phenol for stiffening. In order to ensure that no free phenol is present in the lignocellulose-containing molding produced from such a resin, a condensate of phenol and formaldehyde and optionally (hydrogen) potassium sulphite is produced in a separate process step, which in a suitable place adds urea-melamine resin to the resin. formaldehyde. Such resins cure under acidic conditions, require a slightly shorter cure time than phenolic resins, and also provide water-resistant bonding. However, their disadvantage is the costly, multi-stage production, the high cost of melamine and, in comparison with the pure urea-formaldehyde resins, always a relatively long curing time, which increases the manufacturing costs of the particle board or other glued lignocellulose-containing products.

EP-A 25245 discloses melamine-modified aminoplast resins obtained by mixing melamine-formaldehyde resins with melamine-urea-formaldehyde resins or by mixing melamine-formaldehyde resins with urea-formaldehyde resins.

DE-A 2455420 describes a process for producing melamine-urea-formaldehyde resins by condensation of melamine with urea-formaldehyde precondensates.

EP-P 54755 discloses a process for the preparation of melamine-formaldehyde-impregnating resins in which melamine-formaldehyde condensate with urea solution is mixed to increase storage stability.

According to US-A 4123579, impregnating resins from melamine-formaldehyde condensates are mixed after condensation to improve flowability with small amounts of urea.

DE-A 3442454 recommends the production of urea-melamine-formaldehyde condensation products by using formaldehyde in the form of an aqueous urea solution for the reaction with melamine. Up to about 50 wt. of the total urea required during, before or after condensation also in a form other than formaldehyde solution. Some of the urea remains unbound and thus serves as a formaldehyde scavenger.

All known resins, however, require further improvement in terms of their usefulness as binders to meet the requirements for good moisture resistance as well as for simple and inexpensive resin production.

SUMMARY OF THE INVENTION

The object of the present invention was to provide an improved aqueous resin based on melamine, urea and formaldehyde suitable as a binder.

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

Furthermore, the aqueous condensation products (A) may contain up to 0.5 moles of aromatic or partially aromatic hydroxy component (c) per mole of melamine. Particularly suitable as such components are mono- or polyhydric phenols, for example resorcinol, hydroquinone or preferably phenol, as well as polynuclear compounds such as [alpha] or [beta] -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. The phenol is preferably added in the form of phenol-formaldehyde precondensates, which can for example be obtained according to DE-A 3125874, but also in free form.

In addition, modified ureas such as ethylene urea, ethylenediurea or dipropylene triurea, or guanamine such as benzoguanamine or amides such as caprolactam may be added as aminoplast-forming components (d) in amounts up to 0.1 mol in production (A).

The reactions are preferably carried out by mixing 1 mol of melamine with 3 to 11 mol of formaldehyde and up to 25% of the amount of urea required at a temperature of 20 to 40 ° C together and heating to a temperature between 70 to 100 ° C, preferably 75 to 95 ° C The pH must be between 7.8 and 9.5, preferably between 8.2 and 9.0. Under these conditions, the condensation is continued until the viscosity of the mixture, as measured by the plate-to-plate viscosimeter, is in the range 10 to 1000 mPas, particularly preferably 10 to 500 mPas. It is then cooled to 10 to 80 ° C, preferably to 40 to 75 ° C.

Thereafter, the condensation product (A) is mixed with component (B) in a total amount of urea of from 0.8 to 13 mol, preferably from 1.3 to 13 mol.

4.5 mol, up to 25% of which may be added already during the production of the resin (A).

The urea addition is preferably carried out in solid form or also in aqueous solution. If up to 25% of the total amount of resin is added already in the production of the condensation product (A), the urea can also be added in the form of a concentrated aqueous solution of urea and formaldehyde.

According to a preferred embodiment, the urea as a whole is mixed after completion of the condensation of the resin (A) with the resin. The type of addition is not essential. The urea may be admixed with the resin (A) or the resin (A) may also be mixed into the urea solution. The mixing of both components can be carried out at room temperature or also by mixing up to 80 ° C of the warm resin with urea. The solid resin mixture can then be cooled to room temperature. The pH of the cooled resin must lie between

8.5 and 10.0. It is recommended to add part of the urea already in the production of component (A) only if more than 4 moles of formaldehyde are used per mole of melamine.

Conventional alkaline compounds such as alkali or alkaline earth metal hydroxides, in the form of their aqueous solutions, tertiary amines such as tributylamine or triethylamine and tertiary alkanolamines such as e.g. triethanolamine, methyldiethanolamine.

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

The viscosity of the obtained aqueous resin lies at 10 to 800 mPas at 20 ° C, preferably from 20 to 500 mPas at a solids content of about 60%, so that these products can also be easily handled at higher solids content. They can be easily pumped, mixed with hardener and sprayed. They are also very easy to separate on the substrate, which brings with it an additional processing advantage.

The products are generally stable for several weeks when stored at 20 ° C.

In addition, it is possible to incorporate further additives in amounts of up to 10% by weight. into this resin. This may be e.g. o alcohols such as ethylene glycol, diethylene glycol or carbohydrates. Water-soluble polymers based on acrylamide, ethylene oxide, N-vinylpyrrolidone, vinyl acetate as well as copolymers with these monomers can also be used.

The resins according to the invention are particularly suitable as binders for the production of lignocellulose-containing moldings such as particle boards, plywood or fiber boards.

Such moldings may, for example, be produced in such a way that 5 to 30 wt. The solid resin, based on the lignocellulosic material, is pressed at temperatures of 120 to 250 ° C under pressure. At the same time, hardeners such as ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium phosphate, formic acid, sulfuric acid or other inorganic or organic acids can also be used. Usually the hardener is mixed with an aqueous binder (sizing bath) and then sprayed onto the chips.

In addition, the mixtures according to the invention are also suitable for the production of moldings such as prisms which can be obtained by gluing the wooden parts by flat bonding.

It is advantageous on the aqueous compositions according to the invention in addition to a simple preparation process, in which the urea condensation is not used in comparison with the available processes, that an improvement in the processing properties is achieved over known resins of comparable composition. gelation time and hence higher processing speeds. With good processing properties over the available resins, the proportion of expensive melamine can be reduced. This improves the cost-effectiveness of producing lignocellulose-containing moldings.

DETAILED DESCRIPTION OF THE INVENTION

A 40% aqueous solution is used as the formaldehyde solution.

The pH is adjusted with an aqueous sodium hydroxide solution.

The viscosity is measured at 20 ° C with a plate-to-plate viscosimeter. The solids content is determined by drying at 120 ° C for two hours in a ventilated oven. The gelling time is measured by adding 8 parts of a 20% ammonium sulfate solution to 100 parts of the size.

Example 1

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

Example 2

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

Example 3

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

Example 4

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

Example 5

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

Example 6 (comparative example)

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

Example 7 (comparative example according to DE-OS 3442450)

A mixture of 445 g of a concentrated aqueous solution of 50 wt. % formaldehyde, 25 wt. % urea and 254 wt. 246 g of melamine and 104 g of water are heated to 95 ° C and condensed for 55 min at pH 8.6. The viscosity of the reaction mixture is 1220 mPas (20 ° C). It is then cooled to 75 ° C and 140 g of urea are added. After cooling to 20 ° C, the resin exhibits a viscosity of 420 mPas, a solids content of 66.5% by weight. and a gel time of 76 seconds.

Example of use

Sizing baths for the manufacture of particle boards are produced with the resins according to Examples 1 to 7. Therefore, 100 g of resin is mixed with 8 g of 20 wt. % aqueous ammonium sulfate solution and the solids content of the sizing bath was adjusted to 51.8 wt. 19 mm thick chipboards are produced, with a solids content per chip of 12% by weight, a pressing time of 114 seconds at 210 ° C.

Table properties.

chip boards are listed in the following

table

Resin according to Art. 1 2 3 4 5 6 7 gelling time (s) 50 58 55 58 56 80 87 shear strength V 20 (N / mm ² ) 3.06 2.73 2.61 3.57 3.81 2.78 2.61 cross-sectional strength V 100 (N / mm ² ) ¹ ) 0.44 0.52 0.51 0.54 0.63 0.39 0.30 swelling after 24 h p) 14.9 n, i 12.2 13.1 12.9 18.8 16.9 Perforator value (mg HCHO / 100 g atro plate) 4.9 5.0 5.2 5.1 6.3 4.9 5.2

to DIN 68763 ² ) to DIN EN 120

Claims (8)

A composition suitable as a binder for the production of lignocellulose-containing moldings consisting of (A) an aqueous condensation resin of (a) 1 mol of melamine, (b) 3 to 11 mol of formaldehyde, and (B) 0.8 to 13 moles of urea, up to 25% of which may be added to produce the condensation product (A). Compositions according to claim 1, wherein the total amount of urea is added after completion of the condensation of the condensation product (A). A composition according to claim 1 or 2, comprising condensation products (A) which additionally contain up to 0.5 moles of aromatic or partially aromatic hydroxy component. A composition according to any one of claims 1 to 3, comprising a condensation product (A) which additionally contains up to 0.1 mol of other aminoplast-forming components. Compositions according to any one of claims 1 to 4, obtainable by (A) condensation of (a) 1 mol of melamine, (b) 3 to 11 mol of formaldehyde, (c) 0 to 0.5 mol of phenol and (d) 0 to 0, 1 mole of other aminoplast forming components, in an aqueous medium at pH values of 7.5 to 10.0 and temperatures of 50 to 100 ° C, (B) by addition of a total amount of urea of 0.8 to 13 mol, up to 25% of this total amounts may be added in the production of the condensation product (A). 6. A process for the preparation of suitable mixtures as the size of resins, characterized in that (A) in a suitable medium at a pH of 7.5 to 10.0 and temperatures of 50 to 100 DEG C. is reacted with (a) 1 mol of melamine, (b) 3 to 11 moles of formaldehyde, (c) 0 to 0.5 moles of phenol, and (d) 0 to 0.1 moles of other aminoplast forming components; and (B), and then a total amount of urea of from 0.8 to 13 moles is added at temperatures from 20 to 80 ° C, up to 25% of this total amount being processed in reaction (A). Use of the mixtures according to any one of claims 1 to 6 as a binder in the production of lignocellulose moldings. A lignocellulose molding, comprising as a binder mixtures according to any one of claims 1 to 6.