NO314407B1 - Process for the preparation of aqueous aminoplastic resins, the resins thus obtained, their use and wood materials obtained by the use - Google Patents

Abstract

The invention concerns a process for preparing aqueous aminoplastic resins which are suitable as binders for producing derived timber products. The process is characterized in that: a) 1 mole melamine; b) a concentrated aqueous solution of 0.5 to 5 moles urea and 3 to 6 moles formaldehyde per mole of urea, in which urea and formaldehyde can also be present in the form of their reaction products, c) 0.01 to 0.5 moles phenol or a phenol derivative which can be polycondensed, d) 0 to 9 moles formaldehyde, and e) 0 to 1 mole of a further compound which can be polycondensed are reacted with one another at 50 to 100 DEG C and a pH of 7.5 to 10.0 until the solution attains a viscosity of 10 to 1500 mPa.s, after which this solution is left to cool, and f) is mixed with 0.55 to 0.75 moles urea per mole of the total amount of urea used as components (b) and (f).

Description

The present invention relates to a method for the production of aqueous aminoplast resins which are suitable as binders in the production of wood materials.

Furthermore, the invention relates to aqueous aminoplast resins which can be obtained by means of this method, the use of these as binders for the production of wood materials, as well as wood materials which can be obtained by using these aminoplast resins.

Binders based on aqueous phenol-formaldehyde resins which are suitable for gluing chopped wood, such as wood chips, to the appropriate wood products, such as wood chipboards, are generally known. In the production of the wooden materials, a glue resin bath consisting of the binder and a hardener is usually applied to the wooden parts, after which the parts are pressed together at elevated temperatures, as the binder then hardens. However, the mechanical properties of these wooden materials are not sufficient for many applications if the wooden materials are exposed to moisture or water for a long time.

This disadvantage can be eliminated if part of the urea in the formaldehyde/urea resins is replaced with melamine and phenol.

From DE-A 3 442 454, mixtures of melamine ("M")-urea ("U")-phenol {"P")-formaldehyde ("F") resins (MUPF resins) and urea are known. The MUPF resins are produced by condensing a mixture of formaldehyde, melamine and phenol, where the formaldehyde has been partially or completely brought into the form of a concentrated aqueous solution with urea, under slightly alkaline conditions. After condensation, these resins can be added approx. 50% of the urea, calculated on the total amount of urea.

In EP-A 273 794, a method for the production of MUPF resins is described, according to which a mixture of a phenol/formaldehyde precondensate, which contains formaldehyde and phenol in a ratio of 1.5 to 3.5, is condensed, a further precondensate which contains formaldehyde and urea in a ratio of 1.8:1 to 3:1, as well as melamine, and then mixes the condensation product with urea. According to this teaching, the proportion of urea that is added to the MUPF resins before condensation amounts to 70%, calculated on the total quantity of urea.

DE-A 3 125 874 relates to a method for the production of aqueous MUPF resins, and the method is characterized by first preparing a precondensate of phenol, formaldehyde and possibly an alkali hydrogen sulphite, as well as a further precondensate of formaldehyde and urea in a molar ratio of up to 1 ,5 : 1 or less, and further condenses these two precondensates together with formaldehyde and melamine. The MUPF resin can optionally be mixed with urea.

The older German application P 4 401 562.3 relates to binders based on melamine/phenol/formaldehyde condensation resins in which urea is optionally condensed. These resins are mixed after condensation with urea. A maximum of 25% of the total amount of urea that the mixture contains is used during the condensation, while the rest is added afterwards.

The known MUPF resins do indeed show an improved level of properties compared to the formaldehyde/urea resins, which concerns the mechanical properties and the water resistance of the wood materials produced from them, but there is still a lot left in relation to what is desirable when it comes to these and other properties. For example, the resin processors are interested in resins with a higher reactivity and a higher solids content, which harden faster when processed into wood materials. This means shorter work cycles and thus enables a more economical production of the wood materials. Added to this is the fact that melamine and phenol are expensive compared to the other substances used. Binders are therefore desired that contain a smaller proportion of these components, without the wood materials produced from them becoming worse in terms of the level of properties.

It was therefore the task of the present invention to find improved binders suitable for the production of wooden materials, based on melamine, urea and formaldehyde, which do not exhibit the aforementioned defects and which in particular harden quickly when processed into wooden materials.

In accordance with this, a method was found for the production of aqueous aminoplast resins which are suitable as binders for the production of wood materials and which are characterized by allowing

a) 1 mole of melamine,

b) a concentrated aqueous solution of 0.5 to 5 mol urea and 3 to 6 mol formaldehyde per mol of urea, since urea and formaldehyde can also be present in the form of their reaction products, c) 0.01 to 0.5 mol of phenol or a phenol derivative capable of undergoing a polycondensation,

d) 0 to 9 moles of formaldehyde, and

e) 0 to 1 mole of a further compound which is i

able to be polycondensed,

react with each other at 50 to 100°C and at a pH value of 7.5 to 10.0, until the solution has achieved a viscosity of 10 to 1500 mPa-s, after which this solution is allowed to cool, and f) adds 0.55 to 0.75 mol urea per moles of the total amount of urea used as components (b) and (f).

In the method according to the invention, the melamine (component a) is preferably used in solid form.

The concentrated aqueous solutions of urea and formaldehyde (component b) are known from DE-B 2 451 990 and EP-A 0 083 427. These solutions of 3.0 to 6.0, preferably 3.5 to 4.5 mol of formaldehyde per mol of urea preferably has a solids content according to DIN 12 605 from 50 to 85, preferably from 60 to 80% by weight. They contain urea and formaldehyde partly in free form, in the form of methylolurea types and in the form of low-molecular condensation products.

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

As component (c), in addition to phenol, such phenol derivatives that are capable of polycondensation are taken into consideration, where the properties of the condensation resins when they are used in comparison with those that are only made up of phenol, do not change to a significant extent. Suitable phenol derivatives are, for example, homologues of phenol, e.g. (C-^- to Cg-)-alkylphenols, such as the inexpensive cresols, xylenols, naphthols, 2,2-bis(4-hydroxyphenyl)-propane (<®>bisphenol A), 1,1-bis-( 4-hydroxyphenyl)-ethane or 1,1-bis(4-hydroxyphenyl)-isobutane, hydroquinone, and resorcin.

Instead of or in addition to the phenol or derivatives of phenol, a reaction product of phenol and/or a phenol derivative and formaldehyde can also be used. These turnover products are likewise generally known (see Ullmann's Encyclopedia of Industrial Chemistry, 5th ed., vol. A 19, p.

371-384). Above all, aqueous solutions of resoles which exhibit a solids content of from 30 to 80 and preferably from 50 to 70% by weight and a viscosity according to DIN 53 018 from 10 to 5000, preferably from 50 to 500 mPa■s are taken into consideration.

The resols usually contain phenol and/or a phenol derivative and formaldehyde in a ratio of 0.1:1 to 3:1 and preferably 0.3:1 to 1:1.

It is particularly advantageous to use the phenol or phenol derivative in the form of a reaction product with formaldehyde, e.g. a resol, where 0.35 to 0.02 mol of an alkali metal hydrogen sulphite and/or alkali metal sulphite per moles of the phenol. Such resins and their production are for example described in DE-A 3 125 874.

Formaldehyde (component d) is preferably used in the form of a 30 to 40% by weight aqueous solution.

As further compounds capable of polycondensation (component e) come urea derivatives, e.g. ethylene urea, ethylene diurea, dipropylene triurea and dipropylene triurea, as well as guanamine, e.g. benzoguanamine, amides, e.g. e-caprolactam, alcohols, e.g. ethylene glycol, in consideration.

The components (a) to (e) are allowed to react at 60 to 100, preferably at 75 to 95°C, and at a pH value of from 7.5 to 10, preferably from 8.2 to 9.0, until the solution has obtained a viscosity of from 10 to 1500, preferably from 10 to 500 mPa-s, after which the solution is allowed to cool down until it has reached a temperature of from 10 to 80°C, preferably from 40 to 75°C.

Otherwise, the condensation can be carried out in a manner known per se. Further details can be found, e.g. in Ullman's Encyklopådie der technischen Chemie, 4th ed., vol. 7, pp. 403-415, and in DE-A 3,442,454.

Immediately after cooling to 20 to 80°C or at a later time, the reaction product of components (a) to (e) is mixed with urea.

Urea (component f) is preferably added in solid form or in the form of a 40 to 80, preferably 60 to 70, wt% aqueous solution.

The way in which the mixture is carried out is not critical and is carried out in a practical way so that the urea is mixed into the turnover product.

In the method according to the invention, the components (a) to (e) are preferably used in such amounts that for

a) 1 mol of amine is used

b) a concentrated aqueous solution of 0.5 to 2.0, particularly preferably 0.7 to 1.5 mol of urea and 3 to 5 mol, particularly preferably 3.5 to 4.5 mol of formaldehyde per moles of urea, as urea and formaldehyde can also be present in

form of their reaction products,

c) 0.05 to 0.2 mol of phenol or a phenol derivative capable of undergoing a polycondensation,

d) 0 to 4 moles of formaldehyde, and

e) 0 to 0.2 mol of a further compound capable of polycondensation.

The amount of component (f) is preferably 0.55 to 0.75 mol per moles of the total amount of urea used as components (b) and (f).

Preferably used per mol {-NH2)-groups of the (-NH2)-groups originally occurring in the urea as component (b) and in the melamine (component a) 0.9 to 1.3, preferably 1.2 to 1.0, mol formaldehyde . However, only the formaldehyde used in free form or in the form of a urea/formaldehyde adduct or condensate is taken into account. The bound formaldehyde in a conversion product of phenol or a phenol derivative is not taken into account in this case.

The aminoplast resins which can be obtained by the method according to the invention are preferably set to a pH value of from 8 to 10, preferably from 8.5 to 9.5, and can be stored at a storage temperature of 20°C for approx. 3 to 6 months without the physical and application technical properties undergoing any significant change.

For setting the pH values, the generally common bases can be used, such as alkali or alkaline earth hydroxides, preferably in the form of their aqueous solutions, tertiary amines, e.g. tri-(C 1 - to C 8 -alkyl) amines, such as tri-butylamine and triethylamine, as well as tertiary C 1 - to C 8 -alkanol amines, e.g. triethanolamine, methyldiethanolamine.

The aminoplast resins generally have a solids content from 50 to 75, preferably from 55 to 65% by weight, and a viscosity from 10 to 1000, preferably 10 to 500 mPa-s.

Aminoplast resins exhibiting the aforementioned high solids content can be easily obtained according to the described production methods if starting materials with a correspondingly high solids content are selected. It is therefore not necessary in most cases to increase the solids content by evaporation.

The aminoplast resins can optionally be mixed with further common auxiliaries and additives.

In order to stabilize and to improve the mechanical properties of the wood materials produced with the aminoplast resins, the aminoplast resins can be added to polyalcohols, sugars and water-soluble polymers, made up of monomers such as acrylamide, ethylene oxide, N-vinylpyrrolidone, vinyl acetate or copolymerizable mixtures of these monomers.

The reactivity of the aminoplast resins during curing can be increased by additionally adding a hardener in amounts from 0.1 to 2% by weight, calculated on the binder's solids content. Suitable curing agents are ammonium salts, such as ammonium chloride, ammonium sulphate, ammonium nitrate, ammonium phosphates, strong carboxylic acids, such as formic acid and oxalic acid, mineral acids, such as sulfuric acid, and p-toluenesulfonic acid.

Furthermore, the aminoplast resins can be mixed with pest control agents, e.g. insecticides or fungicides of the usual commercial type.

The aminoplast resins are particularly suitable as binders for the production of wood materials such as veneers, wooden beams which are made up of laminated wood, or carpentry boards, and above all wood fiber boards and chipboards (see Ullmann's Encyklopådie der technischen Chemie, 4th ed., 1976, vol. 12, pp. 709-727) of finely divided wood.

The production of the wooden materials takes place according to the methods that are generally known in this field. The gluing takes place in a favorable way by pressing the finely divided wood with the aminoplast resin at temperatures from 120 to 250°C. Under these conditions, the aminoplast resin hardens quickly, and wooden materials with good mechanical properties and which are highly resistant to the effects of moisture are obtained.

The chipboards produced with the aminoplast resins according to the invention exhibit good mechanical properties, e.g. a high transverse tensile strength, and they are resistant to moisture.

The aminoplast resins according to the invention are particularly distinguished by a high reactivity. When processing the resins into wood materials, they harden faster than ordinary binders. This property enables the pressing time required for the production of the aminoplast resin/wood compound to be shortened without the final strength of the bonded material being affected. In this way, an economical production of wooden materials is made possible.

The indications given in the examples regarding the viscosities are based on measurements according to DIN 53 018. The viscosity is measured according to this standard on an aqueous solution which is set to a solids content of 65% by weight, in a rotary viscometer at 20°C and a velocity gradient of 500 seconds-1 .

The mentioned solids contents refer to measurements according to DIN 12 605, with 1 g of substance being dried in a weighing glass with a diameter of 35 mm according to DIN 12 605 at a temperature of 100°C for 2 hours.

Example 1

A mixture of 855 g of a 40% aqueous formaldehyde solution (equivalent to 11.4 mol), 531 g (5.6 mol) of phenol and 116 g (0.92 mol) of sodium sulphite was heated to 60°C, after which the mixture warmed up without additional heat input to approx. 100°C. The mixture was cooled to 90°C and held at this temperature until the reaction product showed a viscosity of 370 mPa-s. It was then cooled to room temperature.

A mixture of 62.5 g of the phenol/formaldehyde condensate (equivalent to 0.48 mol of formaldehyde, 0.23 mol of phenol and 0.04 mol of sodium sulphite), 184 g (1.46 mol) of melamine, 127 g of a 40% aqueous formaldehyde solution (equivalent to 1.69 mol) and 418 g of a solution of 50 wt% formaldehyde (equivalent to 6.97 mol), 25 wt% urea (equivalent to 1.74 mol) and 25 wt% water were heated for 90 minutes to 90°C at a pH value of 8.6, and then cooled to 50°C, after which it was mixed with 283 g (4.71 mol) of urea. The viscosity was 360 mPa«s and the solids content 65% by weight.

Example 2

A mixture of 34.6 g of the phenol/formaldehyde condensate (see Example 1, corresponding to 0.27 mol of formaldehyde, 0.13 mol of phenol and 0.02 mol of sodium sulphite), 200 g (1.58 mol) of melamine, 203 g of a 40% aqueous formaldehyde solution (equivalent to 2.71 mol) and 355 g of a solution of 50% by weight formaldehyde (equivalent to 5.92 mol), 25% by weight urea (equivalent to 1.48 mol) and 25% by weight of water, was heated for 90 minutes to 90°C at a pH value of 8.6 and then cooled to 50°C, after which it was mixed with 222 g (3.70 mol) of urea. The viscosity was 152 mPa-s and the solids content 63% by weight.

Example IV (comparative example)

A mixture of 62.5 g of the phenol/formaldehyde condensate (see example 1, corresponds to 0.48 mol of formaldehyde, 0.23 mol of phenol and 0.04 mol of sodium sulphite), 184 g (1.48 mol) of melamine, 423 g of a 40% aqueous formaldehyde solution (equivalent to 5.64 mol) and 275 g of an aqueous urea/formaldehyde resin of the usual commercial type as described in DE-A 3 125 874, of 38% by weight formaldehyde (equivalent to 3.02 mol ) and 38 wt% urea

{equivalent to 1.74 mol) was heated for 90 minutes to 90°C at a pH value of 8.6 and then cooled to 50°C, after which it was mixed with 283 g (4.71 mol) of urea. The viscosity was 250 mPa-s and the solids content 57% by weight.

The reactivity of an aminoplast resin is higher the shorter its gelation time. While in the comparative example a gelation time of 87 seconds was determined, in the examples according to the invention it was respectively 57 seconds (example 1) and 55 seconds (example 2).

To determine the gelation time, in each case 100 parts of the aminoplast resins were mixed with 10 parts of a 20% by weight aqueous ammonium sulfate solution and heated to 100°C. The time required for gelation of a mixture is a measure of the reactivity of the mixture.

Claims (7)

1. Process for the production of aqueous aminoplast resins which are suitable as binders in the production of wood materials, characterized by allowing a) 1 mol of melamine, b) a concentrated aqueous solution of 0.5 to 5 mol of urea and 3 to 6 mol of formaldehyde per mol of urea, since urea and formaldehyde can also be present in the form of their reaction products, c) 0.01 to 0.5 mol of phenol or a phenol derivative capable of undergoing a polycondensation, d) 0 to 9 mol of formaldehyde, and e) 0 to 1 mole of an additional compound which is i able to be polycondensed, react with each other at 50 to 100°C and at a pH value of 7.5 to 10.0, until the solution has achieved a viscosity of 10 to 1500 mPa-s, after which this solution is allowed to cool, and f) adds 0.55 to 0.75 mol urea per moles of the total amount of urea used as components (b) and (f). 2. Method according to claim 1, characterized in that one uses the phenol or the phenol derivative which is able to be polycondensed in the form of a reaction product with formaldehyde. 3. Method according to claim 1 or 2, characterized in that an alkali metal hydrogen sulphite and/or an alkali metal sulphite is additionally condensed into the reaction product of phenol and formaldehyde. 4. Method according to claims 1 to 3, characterized in that one per mol (-NH2) groups of those in the urea in component (b) and in the melamine (component (a) originally occurring (-NH2) groups, use 0.9 to 1.3 mol of formaldehyde. 5. Aqueous aminoplast resins, characterized in that they can be obtained according to the methods in claims 1 to 4. 6. Use of the aqueous aminoplast resins according to claim 5 as binders for the production of wood materials. 7. Wood materials, characterized in that they have been obtained using the aqueous aminoplast resins according to claim 5.