SK9597A3 - Process for preparing aqueous aminoplastic resins - 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

Process for preparing aqueous aminoplast resins

Technical field

The invention relates to a process for the production of aqueous aminoplast resins which are suitable as binders for the production of wood materials. The invention also relates to aqueous aminoplast resins which are obtainable by the process according to the invention, to their use for the production of wood materials and also to wood materials w which are obtainable by using these resins.

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BACKGROUND OF THE INVENTION

Binders based on aqueous urea-formaldehyde resins which are suitable for sizing pulverized wood, such as wood chips, to the corresponding wood construction materials such as particle board are generally known. · As a rule, the sizing resin bath is applied to wood particles in the manufacture of wood construction materials. which consists of a binder and a hardener, the product is subsequently compressed at elevated temperatures to cure the binder. However, the mechanical properties of such wood construction materials are not sufficient for many purposes if such materials are exposed to moisture or water for an extended period of time.

This deficiency will be remedied by replacing one part of the urea in the formaldehyde urea resin with melamine and phenol.

DE-A 34 42 454 discloses mixtures of melamine (M) urea (U) phenol (P) formaldehyde (F) resin (MUPF resin) and urea. MUPF resins are prepared by condensing under a slightly basic condition a mixture of formaldehyde, melamine and phenol to which formaldehyde has been added partially or completely in the form of a concentrated aqueous urea solution. Up to about 50%, based on the total urea, may be added to these resins after condensation.

EP-A 273 794 discloses a process for producing MUPF resins by condensing a mixture of phenolfermaldehyde precodensate containing formaldehyde and phenol in a ratio of 1.5 to 3.5 with another precondensate containing formaldehyde and urea in a ratio of 1 8: 1 to 3: 1 as well as melamine and the condensation product are then mixed with urea. The proportion of urea added to the MUPF resins before condensation is 70% based on the total amount of urea.

DE-A 31 25 874 discloses a process for the manufacture of MUPF aqueous resins in which a precondensate is first produced comprising phenol, formaldehyde and optionally an alkali metal bisulfite and another precondensate consisting of formaldehyde and urea in a molar ratio of not more than 2.5 Both pre-condensates are further condensed together with formaldehyde and melamine. The MUPF resin may optionally be mixed with urea.

The earlier German patent application P 44 01 562.3 relates to binders based on melamine phenol formaldehyde condensation resins to which urea is optionally condensed. This resin is stirred off after condensation with urea. A maximum of 25% of the total amount of urea present in the mixture is added during the condensation, while the rest is added additionally.

Compared to the known formaldehyde urea resins, although MUPF resins exhibit improved mechanical properties and water resistance of the wood materials produced therefrom, further improvements are desirable with respect to these and other properties. For example, resin processors are interested in resins having a higher reactivity and a higher solids content, which cure more rapidly when processing wood materials. This would allow shorter work cycles and thus more economical production of wood materials. In addition, melamine and phenol are expensive compared to other starting materials. Binders are therefore desirable which contain less of these components without compromising the properties of the wood materials produced therefrom.

It is therefore an object of the invention to find improved binders suitable for the production of wood-based materials, based on melamine, urea, phenol and formaldehyde, which do not exhibit the aforementioned drawbacks and, in particular, rapidly cure in the manufacture of wood-based materials.

SUMMARY OF THE INVENTION

The process according to the invention for the preparation of aqueous aminoplast resins as binders for the production of wood-based materials consists in allowing them to react with one another

(a) 1 mol of melamine;

(b) a concentrated aqueous solution consisting of 0,5 to 5 mol of urea and 3 to 6 mol of formaldehyde per 1 mol of urea in which, where appropriate, urea and formaldehyde are in the form of their reaction products,

c) 0.01 to 0.5 moles of phenol or phenol derivative capable of polycondensation,

d) 0 to 9 mol of formaldehyde,

e) 0 to 1 mol of another compound capable of polycondensation at a temperature of 50 to 100 ° C and a pH of 7.5 to 10.0 until a viscosity of 10 to 1500 mPa.s is reached, then the solution is allowed to cool; and

f) is mixed with 0.55 to 0.75 mol of urea per mole of the total amount of urea according to (b) and (f).

In the process according to the invention, melamine is preferably added as component a) in solid form.

Concentrated aqueous solutions of urea and formaldehyde (component b) are known from DE-B 24 51 990 and EP-A 0 083 427. These solutions of 3.0 to 6.0, preferably of 3.5 to 4.5 mole of formaldehyde per mole of urea preferably have a solids content according to DIN 12 605 of 50 to 85, preferably 60 to 80 wt. They contain urea and formaldehyde partly in free form, in the form of methyl ureas and in the form of low molecular weight condensation products.

Preferably, these solutions are adjusted to have a total formaldehyde content of 30 to 60, preferably 40 to 55 wt. and a total urea content of 15 to 40, preferably 20 to 30 wt. Preferably, in addition to the free formaldehyde and the mono- or polymethylolurea compounds, they contain only one urea-derived unit, preferably less than 10% by weight. urea-formaldehyde condensation products containing more than one urea-derived unit.

Particularly suitable as component (c) are, in addition to phenol, those condensable phenol derivatives whose common use does not substantially alter the set of properties of the condensation resins as compared to resins consisting solely of phenol. Suitable phenol derivatives are, for example, phenol homologues, for example alkylphenols having 1 to 6 carbon atoms in the alkyl moiety, such as cost-effective cresols, xylenols, naphthols, 2,2-bis (4-hydroxyphenyl) propane ( ^R Bisphenol A), 1,1- bis- (4-hydroxyphenyl) ethane; or 1,1-bis- (4-hydroxyphenyl) isobutane, hydroquinone and resorcinol.

Instead of phenol or derivatives thereof, a reaction product consisting of phenol and / or a derivative thereof and formaldehyde may also be used. These reaction products are also generally known (e.g., Ullman's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A 19, pp. 371-384). Particularly suitable are aqueous solutions of resols having a solids content of 30 to 80, preferably 50 to 70% by weight. and according to DIN 53 018 a viscosity of 10 to 5000, preferably 50 to 500 mPa.s.

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.

Particularly preferably, phenol or a derivative thereof is used in the form of a reaction product with formaldehyde, for example resol, which contains 0.35 to 0.2 moles of alkali metal bisulfite and / or alkali metal sulfite per mole of phenol. Such resins and their preparation are described, for example, in DE-A 31 25 874.

The formaldehyde (component d) is preferably used in the form of 30 to 40 wt. aqueous solution.

Like other polycondensation-capable compounds (component e), suitable are urea derivatives, for example ethylene urea, dipropylene tri-urea, such as guanamines for example benzoguanamine, amides, for example ε-caprolactam, alcohols, for example ethylene glycol.

The components a) to e) are reacted at a temperature of 60 to 100, preferably 75 to 95 ° C and a pH of 7.5 to 10, preferably 8.2 to 9.0, until the solution has a viscosity of 10 to 1500, preferably 10 to 500 mPa · s, then the solution is allowed to cool to 10 to 80 ° C, preferably 40 to 75 ° C.

Otherwise, the condensation is allowed to proceed in the usual manner. Details are known in the literature (e.g., Ullmann's Encyclopedia der technischen Chemie, 4th edition, Volume 7, pp. 403-415 and DE-A 34 42 454).

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

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

The mixing method is not critical and is practically carried out by mixing the urea into the reaction product.

In the process according to the invention, components (a) to (e) are used in such an amount that

(a) 1 mol of melamine,

b) a concentrated aqueous solution consisting of 0.5 to 5 mol, 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 mol of urea, in which: urea and formaldehyde may be in the form of their reaction products,

c) 0.01 to 0.2 moles of phenol or phenol derivative capable of polycondensation,

d) 0 to 4 mol of formaldehyde,

e) 0 to 0.2 mol of another compound capable of polycondensation.

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

It is preferably employed per mole of the -NH ₂ groups initially present in the urea component (b) and in the melamine component (a) of 0.9 to 1.3, preferably 1.2 to 1.0 mol of formaldehyde. However, only formaldehyde used in the free form or in the form of a urea-formaldehyde adduct or condensate is respected. Formaldehyde bound in the reaction product of a phenol or phenol derivative is not taken into account.

The aminoplast resins obtainable by the process of the invention are adjusted to a pH of 8 to 10, preferably 8.5 to 9.5, and are stored at 20 ° C for 3 to 6 months without appreciable changes in physical and utility properties.

In general, conventional bases such as alkali metal or alkaline earth metal hydroxides, preferably in the form of their solutions, tertiary amines, for example C 1 -C 6 trialkylamines, such as tributylamine and triethylamine, as well as tertiary alkanolamines, can be used to adjust the pH. having 1 to 6 carbon atoms, for example triethanolamine and methyldiethanolamine.

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

Aminoplast resins which exhibit these high solids contents can be readily obtained by the manufacturing processes described, if a composition having a correspondingly high solids content is chosen. Therefore, it is usually unnecessary to increase the solids content by densification.

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The aminoplast resins may optionally be mixed with others

I _from l _χ '' usual auxiliary agents and additives.

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

The curing reactivity of the aminoplast resins can be increased by adding an additional curing agent in an amount of 0.1 to 2% by weight, based on the solids content of the binder. Suitable hardeners are ammonium salts such as ammonium chloride, sulfate and nitrate, ammonium phosphates, strong carboxylic acids such as formic and oxalic acids, mineral acids such as sulfuric acid and p-toluenesulfonic acid.

In addition, pest control agents such as commercially available insecticides or fungicides can be added to the aminoplast resins.

Aminoplast resins are particularly suitable as a binder for the manufacture of wood-based materials such as plywood, beams and table tops made of laminated wood, and in particular wood fiber and particle board (Ullmann's Encyclopedia der technischen Chemie, 4th edition, vol. 12, p. 12). 709-727 (1976).

Wood materials are produced by methods generally known in the art. Suitably, the sizing is carried out by compressing the ground wood mixed with the aminoplast resin at a temperature of 120 to 250 ° C. Under these conditions, the aminoplast resin cures rapidly and wood materials with good mechanical properties are obtained which are largely insensitive to moisture.

Particle boards made with the amiplastic resins according to the invention show good mechanical properties and are resistant to moisture.

The aminoplast resins according to the invention are distinguished by an extremely good reactivity. When processed into wood materials, they cure faster than conventional binders. This property makes it possible to reduce the pressing time required to produce the aminoplast and wood bundle without affecting the final strength of the bundle. This enables more economical production of wood materials.

The viscosity data given in the examples is the result of a measurement according to DIN 53 018. The viscosity of an aqueous solution having a solids content of 65% by weight is measured. in a rotary viscometer at 20 ° C with a speed gradient of 500 / s.

The stated solids contents refer to measurements according to DIN 12 605, whereby 1 g of substance is dried in a weighing pan with a diameter of 35 mm according to DIN 12 605 for two hours at 100 ° C.

The invention is illustrated by the following non-limiting examples.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

A mixture of 855 g of a 40% aqueous formaldehyde solution (corresponding to 11.4 moles), 531 g (5.6 moles) of phenol and 116 g (0.92 moles) of sodium sulfite was heated to 60 ° C, followed by heating without further heat. power input is heated to 100 ° C. The mixture is cooled to 90 ° C and kept at this temperature until the reaction product shows a viscosity of 370 mPa.s. It is then cooled to room temperature.

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A mixture of 62.5 g of phenol-formaldehyde condensate (corresponding to 0.48 mol of formaldehyde, 0.23 mol of phenol and 0.04 mol of sodium sulfite), 184 g (1.46 mol) of melamine, 127 g of a 40% aqueous solution of formaldehyde (corresponding to 1, 69 mol) and 418 g of a 50 wt. % formaldehyde (corresponding to 6.97 mol), 25 wt. % urea (corresponding to 1.74 mol) and 25 wt. of water is heated by heating at 90 ° C for 90 minutes at 90 ° C, then cooled to 50 ° C and then mixed with 283 g (4.71 mol) of urea. The viscosity is 360 mPa.s and the solids content is 65% by weight.

Example 2

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

Example IV (comparative)

A mixture of 62.5 g of phenol-formaldehyde condensate (see Example 1 corresponding to 0.48 mol of formaldehyde, 0.23 mol of phenol and 0.04 mol of sodium sulfite), 184 g (1.46 mol) of melamine, 423 g of a 40% aqueous solution of formaldehyde (corresponding to 5.64 moles) and 275 g of a commercially available solution of urea and formaldehyde resin as described in DE-A 31 25 874, which contains 38 wt. % formaldehyde (corresponding to 3.02 mol) and 38 wt. of urea (corresponding to 1.74 mol) was maintained at 90 ° C for 90 minutes, then cooled to 50 ° C and mixed with 283 g (4.71 mol) of urea. The viscosity is 250 mPa.s and the solids content is 57% by weight.

The reactivity of the aminoplast resin is greater the shorter its gel time. While a gel time of 87 seconds was found in the comparative example, the examples of the invention were 57 seconds (Example 1) and 55 seconds (Example 2).

To determine the gel time, 100 parts of an aminoplast resin are mixed with 10 parts of 20 wt. of an aqueous solution of ammonium sulphate and heated to 100 ° C. The time it takes for the mixture to gel is a measure of the reactivity.

Industrial usability.

Aminoplast resins for the production of wood materials with a shorter cure time, which allows shorter production times and increased productivity of the production of wood materials such as particle board.

Claims (7)

PATENT CLAIMS Process for the production of aqueous aminoplast resins as binders for the production of wood materials, characterized in that it is reacted with one another (a) 1 mol of melamine; (b) a concentrated aqueous solution consisting of 0,5 to 5 mol of urea and 3 to 6 mol of formaldehyde per 1 mol of urea in which, where appropriate, urea and formaldehyde are in the form of their reaction products, c) 0.01 to 0.5 moles of phenol or phenol derivative capable of polycondensation, (d) 0 to 9 mol of formaldehyde, (e) 0 to 1 mol of another compound capable of polycondensation at a temperature of 50 to 100 ° C and a pH of 7.5 to 10.0 until a viscosity of 10 to 1500 mPa.s is reached, followed by cooling the solution; (f) mixed with 0,55 to 0,75 mol of urea per mol of total urea referred to in (b) and (f). Process according to claim 1, characterized in that the phenol or the phenol derivative capable of polycondensation is used in the form of a reaction product with formaldehyde. Method according to claim 1 or 2, characterized in that an additional alkali metal bisulfite and / or alkali metal sulfite is condensed into the reaction product of the phenol with formaldehyde. The process according to claims 1 to 3, characterized in that per 1 mol of the -NH 2 groups initially present in the urea component (b) and in the melamine component of the formaldehyde. 5. Aqueous aminoplast resins 1 to 4. 6. Amino-plastic resins of year 1 to 4 as binders on (a), 0.9 to 1.3 moles obtainable by the process according to the claim obtainable by the process for the manufacture of wood materials are used. Wood materials characterized in that they can be produced using the aminoplast resins according to claims 1 to 5.