DK159065B - APPLICATION OF A HARDENER BASED ON AMMONIUM SALTS OF STRONG ACIDS FOR THE SURFACE ADJUSTMENT OF TREASURY MATERIALS WITH URINE FORMALDEHYD GLUE AND PROCEDURE FOR THE PREPARATION OF SUCH FLAT-LIMITED TREATED MATERIALS - Google Patents

Abstract

1. Use of a curing agent based on an ammonium salt of a strong acid and, if required, urea, which curing agent contains form 10 to 50% by weight of a sheet silicate, from 0.3 to 3% by weight of a starch powder or from 10 to 50% by weight of a dextrin and from 0.1 to 2% by weight of xanthan, the percentages being based on its dry components, for urea/formaldehyde or melamine/urea/formaldehyde resin glue liquors which are used for gluing the surfaces of woodworking materials.

Description

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The invention relates to the use of a hardener or curing agent for glue resin floats of urea-formaldehyde and melamine-urea formaldehyde, which are used in the surface sizing of wood materials, and a new method 5 for the production of flat-glue wood materials.

Without the surface gluing of wood materials, it is primarily about gluing veneer wood on particle board, so that on the basis of it, for example. can manufacture panels, furniture parts or doors. In addition, it is also understood that the gluing of sheets on chipboard or the gluing of veneer on solid wood.

It is known in the art that one can prepare the glue resin floats for surface sizing of wood materials of aqueous resin solutions of urea-formaldehyde or melamine-urea-formaldehyde and a hardener. The hardener is usually added in the form of a solution.

It can also be added as a dry substance and dissolved in the glue resin solution.

As a hardener, mixtures of several 20 components are usually employed. As the main component, the actual curing substance serves. It is e.g. ammonium salts of acids, ammonium chloride or ammonium sulfate. Another component serves as a reaction retardant for the curing reaction. For this purpose, e.g. urea or hexamethylenetetramine. Finally, as a third component, a so-called extender is applied, e.g. flour or similar organic substances.

For the most part, the curing solutions are not stable and over time, the chemistry separates over time. This is again the main reason for a number 2

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disadvantages and difficulties encountered in the surface sizing of wood.

As a result, there are already considerable difficulties when passing through the glue application machine. Since the main part of the glue application machine consists of two rollers running in opposite directions, between which there is an adjustable gap through which the glue float in the form of a curtain runs on the surfaces to be supplied with glue, the glue float frequently forms a bead in the roller-10 gap. Therefore, the surfaces are provided with glue in an irregular manner and with different thicknesses. To prevent this, a substantial supply of labor, including control measures and resetting of the rollers, is necessary.

15 If the adhesive application in its places is too high, the adhesive in these places blows through the veneer tree and forms spots on the surface. But even during normal application with the usual glue floats, a glue passage takes place. To prevent this, you can add flour to the 20 float, which in turn supports an irregular application.

Such glue stains are particularly undesirable in expensive and therefore woody species used, such as oak, teak or mahogany, because the stains in this case can no longer be abraded. However, when a grinding is possible, one must expect an increased labor supply. In addition, the dimensions of the wood materials are thereby changed.

Depending on the penetration of the glue fleet into the tree, the veneered tree leaves bend too much and form wave formations.

30 This can be counteracted by spraying water on veneer-3

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however, the pressing times are extended due to the resulting glue thinning.

Finally, it should be noted that the service life of the fleet at a temperature of 20 ° C is usually approx. 1.5 hours.

5 Then the glue float becomes too viscous and it has to be cooked again.

It is the object of the invention to provide a hardener which does not suffer from the stated disadvantages so as to reduce the difficulties encountered in the surface sizing of wood materials.

This object is achieved by using the hardener according to the invention.

The use according to the invention, which is of the kind specified in the preamble of claim 1, is peculiar to that of the characterizing part of claim 1.

It has further been found that the preparation of flat-glued wood materials by urea-formaldehyde or melamine-urea-formaldehyde resins is particularly advantageous when carrying out the curing of the adhesive resins with the hardener, the use of which has been described above. , addressing the disadvantages set forth above.

A hardener which contains a poly- (meth) acrylamide instead of xanthan, and which is also used in the surface bonding of wood materials, is the subject of the previous German application P 33 43 670.3.

In addition, the older German patent application P 33 16 352.9 discloses a method for bonding solid wood by means of aminoplast or phenoplast adhesive resins, 50 whereby the adhesive resins and / or curing agent mixtures 4

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By surface gluing of wood materials in the sense of the invention, as already stated, the gluing of foils and veneers on chipboard and solid wood is to be understood.

Urea-formaldehyde and melamine-urea-formaldehyde resins within the scope of the invention are the usual binders used in the manufacture of wood materials.

They are commercially available in the form of aqueous solutions or powders and contain urea and / or melamine formaldehyde condensates. Also mixed condensates and 10 condensates which may contain additional constituents, e.g. phenol or other aldehydes are common. The preparation and use thereof is well known in the art and is of no significance to the invention.

The necessary ammonium salts of strong acids are generally derived from such one or more base acetic acid rs which exhibit a value of pK 2 which is less than 2.5, preferably less than 1.5. Examples include hydrochloric acid, sulfuric acid, hydrobromic acid, benzenesulfonic acid or phosphoric acid. The ammonium salts 20 of hydrochloric acid and sulfuric acid are preferred.

The layer silicates referred to are understood to be silicates in which the [SiO 2] tetrahedra are bonded to layers. Such compounds, also known as phyllosilicates, are e.g. quinals, bentonite or montmorillonite.

25 Starch flour is the processed form of the naturally occurring polysaccharide starch. As a starch flour, for example. apply potato starch, rice starch or rye starch.

For dextrins which can be used instead of starch 5

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flour, is understood to be the degradation products of starch arising from incomplete hydrolysis with dilute acids, by heat or by enzymatic degradation.

Such dextrins are preferred, which are derived from corn starch or potato starch.

Xanthan is a polysaccharide that can be prepared by biosynthesis using microorganisms. The molecular weight thereof generally lies at approx. 2,000,000.

The main chain of the xanthan molecule consists of D-glucose units 10 in the form of β-D-glucopyranose rings> (1,4) -glycosidically linked to each other. Thereby, every other glucose building block of the chain carries a side chain consisting of two β-D-mannopyranose units and one β-D-glucoronic acid unit.

Xanthan causes thixotropy in aqueous medium. By thixotropy, it is understood that the effect of the very high viscosity of liquid substances at an earlier stage is greatly reduced, whereby the viscosity after the termination of the displacement forces 20 increases again, depending on the time. In the context of the invention, however, it is to be understood by this designation that the effect is that the viscosity after the termination of the stress resulting from the shear forces is immediately increased again. This effect is generally characterized by the term. "Intrinsic".

It is known to add various polysaccharides as auxiliaries to aminoplast or phenoplast adhesive resins.

Thus, DE-C-853 929 and SE-A-370 546 are disclosed

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6 the addition of alginates. However, these products are used in the same manner as the cellulose ethers disclosed in United States Patent No. 2,613,167 as a thickener or as a protective colloid and exhibit no thixotropic action.

According to the technical teachings disclosed in EP-A-96797, the chips in the manufacture of particle board materials for reducing formaldehyde emission before or after or simultaneously with the binder application 10 must be treated with an aqueous liquid containing agents for binding formaldehyde and a polysaccharide which produces thixotropy. As an advantageous polysaccharide, D-galacto-D-mannan has been mentioned.

However, on the basis of this proposal, it could not be deduced that the use of polysaccharides which produce thixotropy in aqueous medium would also confer advantages in addition to the specified special curing agents for surface gluing of wood materials.

In addition, it has been found that precisely the use of the 20 known D-galacto-D-mannans in the present case would produce adverse results. For using similar adhesive floats which contain a cured emide moiety exhibiting D-galactose-D-mannans as thixotroping agent, these adhesive floats have an increased tendency for wire drawing. This means that additional glue floats are still dripping, e.g. by interrupting the adhesive application, whereby such interruption always occurs when e.g. a chipboard has passed through the glue application machine. Thereby the machines are soiled during the 30 following workflows; the necessary cleaning work loads the waste water. In addition, reference should be made to the occurring losses of glue floats.

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It is therefore very surprising and not to foresee that these problems could be avoided precisely by the addition of the polysaccharide xanthan to the curing agents used in the invention.

5 The proportion of the individual curing agent components can be varied over a wide range. Thus, e.g. the following concentration ranges possible (in each case calculated in relation to the dry constituents of the curing agent): ammonium chloride or sulfate 5 to 30% by weight 10 urea 0 to 60% by weight quinals 10 to 50% by weight potato starch 0.3 to 3% by weight (or corn dextrin) 10 to 50 wt.% xanthan 0.1 to 2 wt.% The curing powders used according to the invention can be used in the form of aqueous solutions or suspensions. Advantageously, mixtures which are in the range between 70 parts of powder and 30 parts of water and 40 parts of powder and 60 parts of water are used.

A glue barge typical of the process of the invention, in addition to urea-formaldehyde or melamine-formaldehyde resin, contains 5 to 50% by weight of the dry matter content of the curing agent, calculated as curing agent powder.

Thus, it is prepared to contain between 5 and 50 parts of curing powder in relation to 100 parts of dry solids. After mixing, it is ready for use and can be applied to the glue application machine.

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In connection with the method according to the invention, considerably shorter press times occur than is usual. In addition, a flawless embedding of the veneer, i.e. it does not bend too much and no glue is observed.

Finally, the adhesive float exhibits a significantly longer service life.

The following examples will further explain the invention.

The parts listed in the examples are parts by weight.

EXAMPLE 1

A curing powder was mixed with the following powdery ingredients: 12.5 parts of ammonium chloride 37.5 parts of urea 15 21.0 parts of quinals 0.8 parts of potato starch 0.3 parts of xanthan

This mixture was stirred with 50 parts of water to a suspension and allowed to stand for 2 hours at a temperature of 20 ° C.

The suspension thus obtained was stable and showed no sedimentation phenomena.

Eighteen parts of this curing suspension were mixed with 150 parts of an adhesive solution. As a glue solution, a urea-formaldehyde condensate with a molar ratio of urea: formaldehyde = 1: 1.85, a viscosity of 900 mPa.s measured at 20 ° C and a content of free formaldehyde of 1.6 wt. The solids content thereof was 65% by weight Si.

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The adhesive float thus produced exhibited a gelation time of 50 minutes measured at 40 ° C.

With this great one glued a paper foil to a chipboard. The adhesive application on the particle board was 60 g / m2 (constant over the entire plate surface) applied with a adhesive application machine (this consisted of 2 rollers, between which the adhesive ran out in the form of a wide surface). The film was glued at a temperature of 110 ° C for a period of 35 seconds.

No penetration of the glue could be observed through the 10 sheets. The duration of use of the adhesive float in the running machine was 4 hours at 20 ° C.

EXAMPLE 2 15 parts of a hardener suspension according to Example 1 were mixed with an adhesive resin solution for an adhesive float.

The glue resin solution consisted of a urea-formaldehyde condensation product with a solids content of 70% by weight. The molar ratio of urea: formaldehyde was 1: 2.10, the viscosity was 7200 mPa.s, measured at 20 ° C, and the content of free formaldehyde was 3.1% by weight. The gelation time of this glue float was 40 minutes measured at 40 ° C. An oak veneer tree with a leaf thickness of 0.6 mm was glued at a temperature of 110 ° C on a chipboard for a period of 40 seconds. For this purpose, the glue application machine described in Example 1 was used. The adhesive application on the particle board was 25 60 g / m2. Despite this low amount of adhesive per flat unit achieved a very regular distribution. The application time for the glue float on the machine was measured for 5 hours at 20 ° C.

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EXAMPLE 3

comparison Example

A hardener suspension according to Example 1, but without xanthan, was used analogously to Example 2 for a 5 glue float together with a glue resin solution. The gelation time of the glue float was 40 minutes measured at 40 ° C.

This adhesive float was glued to an oak veneer with a leaf thickness of 0.6 mm on a chipboard. The bonding took place analogously to Examples 1 and 2 at a temperature 10 of 110 ° C for a period of 40 seconds. The average adhesive application on the particle board was at 80 g / m2 and, despite all precautionary measures, was highly irregular with differences in volume of + 20 g / m2. After the adhesion, a breakthrough of the glue was noted, which could be detected by white spots and mirror positions in the veneer. The mirror positions could not be painted. In addition, it was observed that the glue float settles. The fillers are already settling in the short period of 10 minutes, so that intensive stirring 20 was necessary throughout the glueing process. The time of use of the adhesive float on the applicator was approx. 1 hour.

EXAMPLE 4

This example was carried out analogously to Example 1. However, instead of 37.5 parts of urea, 25 parts of urea were now used. In addition, instead of 0.8 parts of potato starch, 40 parts of corn dextrin was now used.

The same advantageous results were obtained as in Example 1.

Claims (2)

Use of a curing agent based on ammonium salts of strong acids and, optionally, urea, which cures 10 to 50% by weight of a layer silicate, 0.3 to 35% by weight of a starch flour or 10% by weight of a starch flour or 10 to 50 wt.% of a dextrin and 0.1 to 2 wt.% xanthan, for urea-formaldehyde or melamine-urea-formaldehyde glue resin floats used in the surface sizing of wood materials. 2. A process for producing flat-glueed wood materials using urea-formaldehyde or melamine-urea-formaldehyde glue resins, characterized in that the curing of the glue resins is carried out with a curing agent based on ammonium salts of strong acids and optionally urea, whereby the curing agent, calculated in relation to its dry constituents, contains 10 to 50% by weight of a layer silicate, 0.3 to 3% by weight of a starch flour or 10 to 50% by weight of a dextrin and 0.1 to 2% by weight xanthan.