NO149815B - PROCEDURE FOR POLYCONDENCE OF Aqueous URINANTS / - OR MELAMINE / FORMALDEHYDE-RESIN BINDING AGENTS WITH THE CONNECTING OF CELLULOSE PRODUCTS, AND THE BINDING MATERIAL FOR USE IN PROMOTION - Google Patents

Description

The invention relates to a method for polycondensation of aqueous urea/- or melamine/formaldehyde resin binders while simultaneously bonding together water-permeable cellulose products, as well as a binder for use in carrying out the method.

From US patent no. 3,697,355 it is known to use alkali metal halide, especially sodium chloride together with urea-formaldehyde-resin binder when bonding cellulose products. With this known technique, the halide salt can replace solid resin binder substances in a weight

amount of 1:1.

In one embodiment of this known technique can

the used halide salt in solid, dissolved or slurry form is added to the vessel in which the urea-formaldehyde resin has just been prepared. In such an embodiment, sodium chloride can be used in an amount that replaces up to a maximum of 13% of the resin substances, as larger amounts of sodium chloride do not dissolve in the resin.

If sodium chloride is to replace larger quantities of resinous substances by said known technique, e.g. up to approx. 30%, according to this US patent this requires a two-step process in which the sodium chloride is first sprayed as a separate aqueous solution onto the cellulose product to be bonded, which product is then dried, after which the resin binder is applied.

In the aforementioned known technique, the halide salt used as mentioned can maximally replace the same amount of solid resin substance by weight. Furthermore, the halide salt has no increasing effect on the production rate, which can still be reduced with a high content of halide salt, and further, the halide salt has

addition to the resin binder has an undesirable effect on the specific gravity.

By using acid-curing catalysts, the production rate can be increased, but beyond a certain limit this takes place while simultaneously reducing the properties of the bonded material. Addition of the known caralysers in large quantities makes it possible to carry out the polycondensation even at room temperature (despite the addition of delay agents such as ammonia or hexamethylenetetramine), but thereby the durability of the binder at room temperature is simultaneously reduced, which leads to a hardening prior to introduction 1 the press and the known disadvantages associated with such a phenomenon.

The examples in the present description provide a direct comparison with US Patent No. 3,697,355 and show that the results obtained with a mixture of sodium chloride and urea-formaldehyde monomers cannot be obtained by pure addition of sodium chloride. Particularly in example 3 in the present description, sample 1 corresponds to US patent no. 3,697,355 and sample 2 corresponds to the present invention. Sample 2 has a very low gel time and a higher degree of production than example 1. Such degrees cannot be achieved by simple addition of sodium chloride alone.

In example 4 in the present description, sample 2 corresponds to US patent no. 3,697,355 and sample 3 to the present invention. In this example, the higher substitution achieved by the present invention is shown. In sample 3, a quantity of reactive additive is added in similar amounts to the sodium chloride shown in sample 2. In sample 3 there is a resin substitution of 1:2, while in sample 2 there is a resin substitution of 1:1. Despite the high substitution, the same mechanical properties are achieved in the chipboards. In example 5 in the present description, sample 2 corresponds to US patent 3,697,355, while sample 3 corresponds to the present invention. In this example, it is shown that at a higher level of substitution, the formulation according to US patent 3,697,355 (sample 2) cannot produce a chipboard in one step according to methods well known in the field, but rather requires a two-step method. According to the present invention, a higher degree of substitution is achieved in just one step.

The term additive used above and in the following is to be understood as the combination of a) and b) as defined in the requirements.

The advantages of the invention in relation to US patent no. 3,697,355 can be summarized as follows:

1) Greatly increased production speed.

2) Higher substitution (replacement) of the resin, opp

to 30% in one step, instead of using extra steps.

According to US patent no. 3,826,770, solutions of urea and formaldehyde, as well as inorganic salt, are used,

and an amino resin is not used as a binder.

The main differences between the latter American patent and the present invention are: According to the American patent, urea ormaldehyde condensation products are not stabilized.

According to the American patent, the stickiness of the binder is reduced (see e.g. column 2 lines 19 and 20).

According to the invention, additives are used in combination

with normal amino-resin ks to bind water-impregnated ligno-cellulosic material, whereby the following advantages are achieved:

1) The additive enables the use of smaller amounts of binder, whereby savings are achieved. 2) Binder according to the invention enables shorter pressing cycles. 3) The additive does not reduce the stickiness of the adhesive mixture, which is very important when producing chipboard.

The invention therefore relates to a method for the polycondensation of aqueous urea/- or melamine/formaldehyde resin binders while simultaneously bonding together water-permeable cellulose products, in particular bonding to chipboard, whereby the cellulose products are applied with a binder containing common catalysts for the polycondensation of amino resins and a water-soluble alkali metal halide, and the polyton densification is carried out at elevated temperature and pressure, the method being characterized by the application of a binder in which the alkali metal halide a) is incorporated in the form of an aqueous solution, in which is dissolved an organic material b) consisting of urea and formaldehyde or a combination of a non-resinous urea/formaldehyde co-condensation product and urea, the dry matter weight ratio between

a) and b) amount to 0.1 - 1.5 parts by weight of a) per part by weight b), which aqueous solution possibly contains 0.1 - 2.0% by weight of a surface-active agent, and since the components a) and b) are present in the binder in a total amount of dry matter of 1 - 30% by weight of the

solid amino resin substances.

Furthermore, the invention relates to a binder for carrying out the above-mentioned method, comprising an aqueous urea/- or melamine/formaldehyde resin, for the polycondensation of amino resins, common catalysts and a water-soluble alkali metal halide, the binder being characterized in that the alkali metal halide a) is incorporated into the binder in the form of an aqueous solution in which an organic material b) consisting of urea and formaldehyde is dissolved, or of a combination of a non-resinous urea/formaldehyde condensation product and urea, the dry matter weight ratio between a) and b) being 0.1 - 1.5 parts by weight a) per weight part b), which aqueous solution optionally contains 0.1 - 2.0% by weight of a surface-active agent, and the components a) and b) are present in the binder in a total dry matter amount of 1 - 30% by weight of the solid amino resin substances .

It is preferred that sodium chloride is used as the alkali metal halide and formaldehyde and urea as the organic material.

Method according to the invention leads to increased production speed compared to a method that makes use of the same resin binder without addition or with only sodium chloride as an addition.

Furthermore, the method according to the invention results in a saving of resin binder, as it has been shown that the weight amount of solid resin substances in the binder can be reduced by up to twice the dry matter weight amount of the additives used. These advantages are shown in the examples below.

This is a synergistic effect between the binder's alkali metal halide and its organic material, the effect achieved being greater than the sum of the effects obtained by using the aforementioned components separately.

It should be noted that, among other things, due to the above-mentioned synergistic effect between the binder's halide salt and its organic material, it is natural to consider the binder as a whole, and this also applies to the calculations made below regarding the binder's resin-substituting and -saving effect. However, if the binder's organic material is theoretically included as resin substances in the total binder, there is a significant resin saving compared to, for example, the above-mentioned known technique which is also shown in the examples below.

When the binder according to the invention is used in relatively small amounts of, for example, 3 - 10%, without the above-mentioned advantages in terms of production speed and resin savings, an improvement is also achieved in the case of bonded end products in properties compared to the products produced by the above-mentioned known methods. When the binder is used in larger quantities such as 30%, no such additional improvement of the final product's properties is observed.

At higher temperatures, the production rate can be increased to values that would never be achieved with the simple addition of acid-curing catalysts without reducing the properties of the combined product. At the same time, the present method has the advantage that the binder used is only

such as at high temperatures and therefore essentially only increases the production rate at the temperature of the press. This avoids unwanted hardening phenomena at room temperature.

The additive used in the present method is added to the resin binder at the same time as other well-known chemicals for the binder, such as ammonium chloride or sulfate, ammonia or paraffin emulsion during the actual use of the binder to bind the cellulose product together.

Regardless of the quantities in which the binder is used in the present method, it is thus a question of spraying the cellulose product in a single step by a method known per se.

Finally, the present method is associated with the advantage that the amount of free formaldehyde in the manufacture of the cellulose products is significantly reduced as a result of the reduced amount of resin binder used, and the manufactured products such as boards or plates are practically odorless.

The invention can be used with all types of cellulose products which are mixed with resin binders of the type in question, e.g. cellulose products for the production of chipboard using flat presses or calenders, or wood veneer, such as plywood production. The quality of boards and plates produced by the present method has been checked weekly over a period of 6 months, without any decrease in the properties being observed. This shows that no polymer degradation occurs and that the aging properties of the boards and plates correspond to the properties of them, which are produced in the usual way.

The invention shall be explained in more detail by means of the following examples.

Example 1

A constant amount of urea-formaldehyde-resin (BASF 285) was reacted with the additive under controlled temperature and pressure conditions, the additive varying depending on the proportions of the components that form the additive solution. The additive was not used alone, but in addition to the usual known catalyst which usually consists of ammonium chloride, which may or may not contain hexamethylenetetramine.

In the following table I, the synergistic effect of the binder's organic and inorganic components is clearly shown.

Sample 1, which is to be considered a mild sample, and which does not contain the binder according to the invention, but as catalyst only contained the known ammonium chloride, had at 100°C

one gel time of 90 seconds.

Sample 2 contained, apart from ammonium chloride, also a certain amount of urea-formaldehyde and it has a slightly increased catalytic effect with a gel time at 100°C of 85 seconds.

Sample 3 contains, apart from ammonium chloride, also a certain amount of sodium chloride, but no urea-formaldehyde, and it shows a slightly increased catalytic effect at 100°C with a gel time of 80 seconds.

Sample 4 contained, apart from ammonium chloride, a mixture of urea-formaldehyde and sodium chloride, the total amount of the added mixture being equal to the amount of the individual components added in samples 2 and 3. Samples 4, 5 and 6 showed an increased catalytic effect due to the synergistic ratio of the components used and the obtained gel times at 100°C amounted to 60, 35 resp. 28 seconds.

The difference between samples 4, 5 and 6 was a consequence of the different proportions of the organic components used compared to the inorganic components of the additive solution. It was determined that sample 6, which contained a higher amount of organic material, also has the greatest catalytic effect.

The tests listed in Table I are consistent with common practice for gel time measurements made with binder alone, but similar results are obtained when the binder is used in practice when binding together cellulose products where a shorter gel time means greater production strength.

The results shown in Table I are not due to different water content in the samples, which is shown in Table Ia below, where the amount of water is kept constant.

Example 2

This example illustrates the advantages listed above

which is obtained in chipboard production, when the additive according to the invention is added to the resin binder.

Three cases are illustrated below, in which the same total amount of resin binder solution is used. Differences existed with regard to the different amounts of the different components in the solution used, as indicated in Table II below. Comparisons have been made with two resin binders with different concentrations of organic

nic component in the additive, and a binder usually used in industry, i.e. the same resin binder as above,

but without additives and without sodium chloride. It should be noted that columns A in table II relate to the solution used for spraying fine wood flour which was used to produce the outer surface of the chipboard, while columns B relate to the solution used to produce the core of the chipboard.

In this example, the chipboard was produced according to the Bison system, i.e. during continuous layer formation under controlled conditions, which are kept constant in all the cases shown.

20 liters of binder solution as stated for samples IA, 2A

and 3A were each sprayed with 100 kg of wood flour to the surface with a moisture content of 1-2%, while 13 liters of binder solution as specified for samples IB, 2B and 3B were each sprayed on

100 kg wood shavings for the core with a moisture content of 1%:

The quality of the chipboards produced in this way had no notable differences in the three cases (cf. the results in table II). In samples 2 and 3, the quality is slightly reduced, while the density is also lower, which, as is known in the area, usually results in a poorer quality. The difference in quality, however, falls within the accuracy of the method and is of no importance for ordinary chipboards. The results fall in all cases within the requirements according to German

standard DIN 52 360 to 52 365.

The use of resin binder containing additive led to a reduction in the pressing time as stated below: Sample 1: 9.25 seconds per mm of unsanded (sandblasted) chipboard.

Test 2: 8.0 0 seconds per mm of the non-sanded or sandblasted chipboard.

Test 3: 7.00 seconds per mm of the non-sandblasted chipboard.

Sample 3, which contained the largest amount of organic component in relation to the inorganic component, showed the best results.

The results show that by using the additive it is possible to reduce the pressing time when producing the chipboard, and that at the same time it is possible by using this additive to reduce the use of resin, with an amount of up to 17.3%

(sample 2) or up to 22% (sample 3). If the organic material of the additive is theoretically included in the binder-forming resin material, compared to sample 1, 8 parts of sodium chloride in samples 2A and 3A replace respectively 16.3 parts and 13 parts of resin substances, while in samples 2B and 4B 14 parts of sodium chloride replace respectively 33.3 parts and 27.7 parts resin-substance f is, i.e. exchange ratio significantly higher than 1:1.

Example 3

This example illustrates the increase in speed

respectively the degree of chipboard production that is achieved when a binder according to the invention is used, (ie with a mixture of sodium chloride and urea-formaldehyde monomers present) compared to the speed resp. degree obtained by simple addition of sodium chloride (without urea-formaldehyde monomers).

The results obtained are indicated in the following table III in which sample 1, apart from the usual additives that are added to the resin mixture for the production of chipboard, only contained sodium chloride, and which has a gel time of 80 seconds, while sample 2 had the same additives as sample 1, however in addition also urea-formaldehyde monomers, as well as the same amount of sodium chloride, and had a gel time of 28 seconds. It should be noted that this difference in gel time is not due to a lower water content in sample 2, compared to sample 1, as a sample with the same compositions as sample 2, with the amount of water increased to 58 parts by weight, showed a gel time of 30 seconds.

Chipboards were produced under the same conditions

in a Bison plant without separation of the cellulosic materials into core and surface layers prior to the mixing machine. Of sample 1, 230 kg were sprayed on 130 kg of dry cellulose particles, which resulted in a content of solid resin substances (including sodium chloride) of 7.9% based on the dry wood. Correspondingly, 230 kg of sample 2 was sprayed on 160 kg of dry cellulose particles, which resulted in a solid resin substance content of 7.3% based on dry wood. The degree of production or -speed-

the heat for the chipboards was 10 seconds per mm, in the case of sample 1, and in 7 seconds per mm in the case of sample 2. The achieved mechanical properties according to DIN 52 360 to 52 365 were essentially the same in the two cases, with deviations as mentioned above in connection with example 2 falling within the accuracy of the measurement methods and the results obtained in all cases falling within the requirements according to the aforementioned DIN standards.

Example 4

This example shows the high substitution substitution) of urea-formaldehyde resin using the additive compared to the lower substitution obtained using only sodium chloride without the addition of urea

and formaldehyde monomers, as chipboards were formed which in both cases have equivalent mechanical properties.

This particularly explains the case where the substitution in the case of sodium chloride with respect to the resin was 1:1, while in the case of mixing sodium chloride with urea and formaldehyde the resin substitution was 1:2. After pulverization, a supply of wood shavings was treated with the corresponding compositions indicated in the following Table IV.

In the A samples, fine wood flour was sprayed, which was used to form the outer surfaces of the chipboards, while the B samples concern spraying from wood shavings that were used in the core of the chipboards. The same amounts of composition were sprayed on the same amount of wood as indicated below:

Sample IA: 170 kg of the composition was sprayed on 650 kg

dry wood flour, i.e. 10% resin solids based

on the dry wood flour.

Sample IB: 240 kg of the composition was sprayed on 1857 kg of dry wood shavings, i.e. 7% resin solids based

on the dry wood shavings.

Sample 2A: 170 kg of the composition was sprayed on 650 kg

dry wood flour, i.e. 9% resin solids based on

the dry wood flour.

Sample 2B: 240 kg of the composition was sprayed on 1857 kg of dry wood shavings, i.e. 6.3% resin solids based on

the dry wood shavings.

Sample 3A: 170 kg of the composition was sprayed on 650 kg

dry wood flour, i.e. 8% resin solids based on

the dry wood flour.

Sample 3B: 240 kg of the composition was sprayed on 1857 kg of wood shavings, i.e. 5.6% resin solids based on the dry wood shavings.

Sample 1 served as blank without resin substitution. The samples differed from each other in that in sample 2

only a substitution of the resin dry matter took place with sodium chloride (known technique), while in sample 3 (with the additive) a resin substitution took place with a mixture of sodium chloride and urea-formaldehyde monomers.

In sample 2, 19.5 parts solid resin was replaced with 19.5 parts sodium chloride.

In sample 3, 39 parts solid resin substances were replaced with 19.5 parts solid additives (ie sodium chloride, urea and formaldehyde).

In sample 2 there was thus a substitution of 1:1,

while in sample 3 there was a substitution of 1:2.

If the additive's organic material is theoretically included in the binder-formed resin material, compared to sample 1, 4.6 parts of sodium chloride in sample 3A replace 11.1 parts of resin substances, while in sample 3B 9.2 parts of sodium chloride replace 22.2 parts of resin substances, i.e. exchange ratio significantly higher than 1:1, which is obtained according to sample 2A

and 2B.

The chipboards produced had the same mechanical properties, even though sample 3 had a lower dry matter content. in'

in all three cases, chipboards were produced according to the Bison system, i.e. with continuous layer formation under controlled conditions, which were kept constant:

The properties (quality) of the manufactured chipboards are listed in the following table IV.

Example 5

The novelty of the present invention is evident from the fact that when high degrees of substitution are desired,

it is absolutely necessary to use the additive to spray the stock in one step, as this is done with all types of systems used for chipboard production.

When only sodium chloride is added to the resin without the addition of urea and formaldehyde monomers, apart from the fact that the rate is low as shown in the previous examples already mentioned, a separate spraying of the wood shavings with sodium chloride with subsequent drying of the wood mixture and further spraying with adhesive. This requires the use of additional devices which are expensive and reduce production.

An extra step is necessary because of sodium chloride's low solubility in water, since sodium chloride must be used in a solids quantity equal to the quantity of solids from the substituted resin. In order to replace (substitute) larger amounts of resin, too much water is needed in the mixture, which cannot be dried in one step in the press within the normal pressing times.

The additive can very well be used as a substitute

of higher amounts of resin without using too much water,

and as the manufacturing (production) is possible in one step, as is normally done in chipboard manufacturing without the production steps changing at all. This is possible due to the fact that the solubility of urea and formaldehyde in water is higher than that of sodium chloride and therefore less water is used, and also because the substitutions are achieved by adding only half the amount of substituted material, calculated as solid material.

At the same degree of high substitution (35 <%> in the present example), the use of the additive results in a shorter gel time and therefore a higher production rate (mixture 3). By using only sodium chloride without the addition of urea and formaldehyde monomers, a much longer gel time is obtained, as the added substituents in this case act as retarders instead of as catalysts (mixture 2). All the mentioned points appear from the mixture in the following table V. In this table, three mixtures are shown: Mixture 1 is considered a blank test, in which the resin is used without any substituents (substitutes).

Mixture 2 contains only sodium chloride replacing resin and

mixture 3 contains additive, i.e. a mixture of sodium chloride and urea-formaldehyde monomers.

The percentage of substituted resin amounts to i

mixtures 2 and 3 each time 35%. In mixture 3, 37.5 parts of additive solid was added, which replaces 68.5 parts of solid resin, while in mixture 2, 68.5 parts of sodium chloride were added, which replaces the same amount of resin, i.e. 68.5 parts of resin. This shows that according to the invention a substitution of 1:1.8 was achieved, while the use of only sodium chloride gives a substitution of 1:1.

The total amount of the resin solution in mixture 3 containing the additive was kept at the same value as in mixture 1. This was not possible in the case of mixture 2, in which only sodium chloride was added due to the large amount of water required in the mixture due to the high resin substitution.

The gel time of the blank sample was 60 seconds. In the mix

3 which contained the additive, a lower gel time of 40 seconds is obtained, which enabled higher production rates resp. -speeds. In mixture 2, in which only sodium chloride was used, the gel time was 110 sec., as the added components acted as retarders rather than as catalysts.

Column A refers to it in all three cases

solution used for spraying fine wood flour, which was used to produce the chipboard's outer surface, while column B in all three cases refers to the solution used for spraying wood shavings, which was used to produce the chipboard's core.

Using resin mixtures, as indicated in the three cases in Table V, chipboards were produced. The production method used involved the Bison system, and the conditions were kept constant in all three cases:

The quality of the chipboards produced corresponded

DIN standards 52.360 to 52.365 and they have no differences in cases 1 and 3. In case 2, which only contains sodium chloride instead of the additive, the properties of the produced chipboard could not be measured, because the formed boards had already expanded at the normal pressing time. This shows that the sodium chloride used itself does not give a high degree of substitution in the order of 35% when it is used for the production of chipboards with only a single spraying step according to the method known per se.

Example 6

This example illustrates the synergistic relationship

which was determined when a mixture of sodium chloride together with a non-resinous condensation product of urea and formaldehyde monomers was added to the resin preparation. The results thus obtained are set out in the following table IV, where sample 1 apart from the usual additives which were added to the resin preparation for the production of chipboard only contained sodium chloride, and which had a gel time of 49 seconds. Sample 2 contained a urea-formaldehyde condensate and had

a gel time of 51 seconds, and samples 3 and 4 both contained sodium chloride and a urea-formaldehyde condensate, the sum of which corresponded to the amount of sodium chloride used in sample 1, all calculated as 100% solids. The two samples 3 and 4 had a shorter gel time than samples 1 and 2, and the two samples 3 and 4 in particular had a gel time of 42 seconds.

Example 7

This example illustrates the synergistic relationship

which was determined when a mixture of potassium chloride together with a condensation product of urea and formaldehyde monomers was added to the resin preparation. The results obtained are given in the following Table VII, in which sample 1 is a blank containing water instead of the additive.

Sample 2 contained potassium chloride and sample 3 contained a mixture of potassium chloride and a condensate of urea and formaldehyde monomers.

Sample 1 had a gel time of 93 seconds, sample 2 has a weak catalytic effect with a gel time of 82 seconds, sample 3

which contains the additive, however, showed a surprisingly high catalytic effect with a gel time of 42 sec.

Example 8

This example relates to the production of a

veneered chipboard. It particularly highlights the fact that the additive can also be used for gluing flat boards (plates) such as e.g. for the production of plywood, laminated boards, veneered boards

(board) or other fibre-layer boards, resp. tray. In this case, a Tianna-type veneer sheet of 0.6 mm thickness and 10% moisture content was glued to both surfaces of a 15 mm thick sanded chipboard, 185 x 305 cm in size, and a moisture content of 9%. The glue was distributed using a glue distribution device on the chipboard.

The plates were pressed under a pressure of 7 kp/cm at a temperature of 120°C. Two samples are indicated. In sample 1, the normal adhesive preparation was used, while in sample 2, an additive was used. The preparations are indicated in the following table VIII.

While the plates produced with the preparation according to sample 1 required a pressing time of 2 minutes, the plates produced with the preparation according to sample 2 only required a pressing time of 1.7 minutes. The adhesive preparation used during the application of additive for the production of veneered chipboards had the following properties: Increase in production speed around 15% Adhesive savings 26%

Example 9

This example illustrates the synergistic relationship

which was observed when a mixture of sodium chloride and urea and formaldehyde monomers was added to a resin preparation based on a melamine-formaldehyde resin. The resin used is Kauramin 542 from the company BASF.

The results thus obtained are listed in the following table IX:

Test 1 is a blind test. Sample 2 contained, apart from the usual resin preparation, ammonium chloride and ammonia as well as sodium chloride. Sample 3 contained, apart from the usual resin preparations, ammonium chloride and ammonia, as well as urea and formaldehyde. All these samples had the same gel time of 65 sec. Sample 4 contained, apart from the usual resin preparations, ammonium chloride and ammonia, as well as urea, formaldehyde and sodium chloride, the total sum of the added mixture being equal to the amount of the individual components added in samples 2 and 3. Sample 4 is therefore an example of the use of the additive and it actually had a much shorter gel time of 48 seconds.

Similar results could be obtained when, in the above-mentioned examples, sodium or potassium chloride was replaced by lithium chloride or fluorides, bromides or iodides of sodium, potassium or lithium.

Claims (2)

1. Process for the polycondensation of aqueous urea/- or melamine/formaldehyde resin binders during the simultaneous bonding of water-permeable cellulose products, especially bonding to chipboard, whereby the cellulose products are applied with a binder containing common catalysts for the polycondensation of amino resins and a water-soluble alkali metal halide, and the polycondensation. carried out at elevated temperature and pressure, characterized by the application of a binder in which the alkali metal halide a) is incorporated in the form of an aqueous solution, in which is dissolved an organic material b) consisting of urea and formaldehyde or of a combination of a non-resin agent urea for formaldehyde condensation product and urea, the dry substance weight ratio between a) and b) being 0.1 - 1.5 parts by weight of a) per part by weight b), which aqueous solution optionally contains 0.1 - 2.0% by weight of a surface-active agent, and the components a) and b) are present in the binder in a total dry matter amount of 1 - 30% by weight of the solid amino resin substances. 2. Binder for carrying out the method according to claim 1 comprising an aqueous urea/- or melamine/formaldehyde resin, common catalysts for the polycondensation of amino resins, and a water-soluble alkali metal halide, characterized in that the alkali metal halide a) is incorporated into the binder in the form of an aqueous solution, in which an organic material b) consisting of urea and formaldehyde is dissolved, or of a combination of a non-resinous urea/formaldehyde condensation product and urea, the dry matter weight ratio between a) and b) being 0.1 - 1, 5 parts by weight a) per weight part b), which aqueous solution optionally contains 0.1 - 2.0% by weight of a surface-active agent, and the components a) and b) are present in the binder in a total amount of dry matter of 1 - 30% by weight of the solid amino-resin substances f is .