WO2013144226A1

WO2013144226A1 - Melamine-reinforced uf glues containing up to 0.9% of melamine for the production of medium-density fiberboards

Info

Publication number: WO2013144226A1
Application number: PCT/EP2013/056563
Authority: WO
Inventors: Michael Finkenauer; Konrad Roschmann; Ralph Lunkwitz; Stephan WEINKÖTZ
Original assignee: Basf Se; Basf Schweiz Ag
Priority date: 2012-03-29
Filing date: 2013-03-27
Publication date: 2013-10-03
Also published as: DE112013001771A5; PL233957B1; AR090594A1; PL409754A1

Abstract

The invention relates to a method for producing melamine-urea-formaldehyde resins containing up to 0.9% of melamine by reacting a) urea containing 0 to 10 wt% of one or more compounds A, together with formaldehyde and melamine, in the presence of a base at a pH value of 7.5 to 11, a temperature of 20 to 120°C, and a pressure of 0.1 to 10 bar, b) then carrying out the reaction in the presence of an acid optionally containing urea that comprises 0 to 10 wt% of one or more compounds A, at a temperature of 60 to 180°C and a pressure of 0.1 to 10 bar, and c) then adding urea containing 0 to 10 wt% of one or more compounds A, stage b) being carried out at a pH value of 4 to 5.9.

Description

Melamine-reinforced UF glues with up to 0.9% melamine for the production of medium density fiberboard

description

The present invention relates to a process for the preparation of melamine-urea-formaldehyde resins (MUF = melamine-urea-formaldehyde [Engl.]) By reacting formaldehyde, urea and melamine in three stages. From WO-A-2009/080798 a continuous process for the preparation of melamine-urea-formaldehyde resins (MUF) with a melamine content of 0.1 to 15 wt .-% is known in which in step a) a mixture of Amino compound (urea or melamine) prepared with aqueous formaldehyde solution, then in step b) added a catalyst and in step c) in a continuously operated reactor, eg a tubular reactor, is condensed. In an optional step d) then another amino compound, the same as in step a) or another, can be added. In order to produce MUF glues with a melamine content of up to 0.9% by weight in this process, the amino compound in step a) must be urea and the amino component in step d) must be melamine. The addition of melamine at a late stage in the production of MUF sizing is disadvantageous since such sizing cures more slowly. The negative effect of subsequently added melamine is known, for example, from G. E. Troughton, S. Chow, Holzforschung, 1975, pages 214 to 217. The production of MUF glues with up to 0.9 wt .-% melamine, in which the melamine is already present during the condensation phase (step c) is not possible by this method. From US-A-4 536 245 MUF resins having a low formaldehyde emission rate are known which contain 0.15 to 40% by weight of melamine and a molar ratio of formaldehyde to urea of 1.3: 1 to 0.9 Have: 1. However, for a substantial reduction in formaldehyde emission, at least 4% melamine is needed. The preparation of the MUF resins is carried out in a process consisting of a 1st stage with methylolation of urea and formaldehyde and possibly melamine in an alkaline medium, a second stage with condensation at a pH of 6 to 8.3 and Addition of urea and melamine and a 3rd stage with a scavenger, z. B. urea.

A disadvantage of this process is the amount of melamine for substantially reducing the formaldehyde emission.

The present invention was therefore based on the object to remedy the aforementioned disadvantages. Accordingly, a new and improved process for preparing melamine-urea-formaldehyde resins having up to 0.9% melamine by reaction has been developed a) urea containing 0 to 10 wt .-% of one or more compounds A, formaldehyde and melamine in the presence of a base at a pH of 7.5 to 1 1, a temperature of 20 to 120 ° C and a Pressure from 0.1 to 10 bar,

b) subsequent reaction in the presence of an acid which optionally contains urea with 0 to 10 wt .-% of one or more compounds A, at a temperature of 60 to 180 ° C and a pressure of 0.1 to 10 bar and

c) subsequent addition of urea containing 0 to 10% by weight of one or more compounds A,

which is characterized in that b) is carried out at a pH of 4 to 5.9, and the use of these resins as binders and lignocellulose-containing moldings containing this binder.

The present invention can be carried out as follows: In a) urea containing 0 to 10 wt .-% of one or more compounds A (hereinafter referred to as "urea / urea mixture"), formaldehyde and melamine in any order or and at a pH of 7.5 to 1 1, preferably 8 to 10.5, more preferably 8.5 to 10 implement. Adjustment of the pH may be accomplished by adding base at one or more times during this reaction. As a rule, the pH is adjusted at the beginning of the reaction and readjusted if necessary by addition of base. Urea / urea mixture and formaldehyde can also be used as formaldehyde-urea / urea mixture precondensate.

In a preferred embodiment, formaldehyde can be initially charged with a base in a) and then urea / urea mixture can be added.

In a further preferred embodiment, in a) a mixture of formaldehyde and a base can be added to the initially charged urea / urea mixture. In both preferred embodiments, in a) the melamine can be introduced into the reaction mixture at any time.

The reaction in a) is generally carried out at temperatures of 20 to 120 ° C, preferably 20 to 1 10 ° C, more preferably 20 to 95 ° C, in particular 60 to 90 ° C and a pressure of 0.1 to 10 bar , preferably 0.5 to 5 bar, more preferably 0.9 to 1, 5 bar, in particular at atmospheric pressure (atmospheric pressure). Preferably, the formaldehyde, the base or the mixture of formaldehyde and base is heated to the aforementioned temperatures before combining with urea / urea mixture and melamine. Subsequently, the further reaction of the reaction mixture in b) in the presence of an acid at a pH of 4 to 5.9, preferably 4.1 to 5.5, particularly preferably 4.2 to 5.3, in particular 4.5 to 5.2 and at temperatures of 60 to 180 ° C, preferably 90 to 180 ° C, more preferably 100 to 150 ° C, in particular 1 10 to 140 ° C and a pressure of 0.1 to 10 bar, preferably 0.5 to 5 bar, more preferably 0.9 to 1, 5 bar, in particular at atmospheric pressure (atmospheric pressure) are performed. In this case, can be adjusted by the reaction time, the temperature and the pressure, the viscosity of the reaction mixture, which is usually betweenl 0 and 5000 Pas, preferably between 100 and 2000 mPas, more preferably between see see 200 and 800 mPas, measured on an Anton Pair of viscometers MCR 51 with a plate-cone measuring system at room temperature (Thomas Mezger, The Rheology Manual, Hannover, Vincentz, 2000, page 203 and DIN EN ISO 3219: 1994-10)

If desired, one or more portions of urea / urea mixture can be added during b) at any given time, the amount of urea / urea mixture added during b) generally being selected such that, based on the total amount of urea / urea mixture to 20 wt .-%, preferably 0 to 15 wt .-%, particularly preferably 0 to 10 wt .-% is. Thereafter, the further reaction of the reaction mixture in c) after addition of a base at a pH of 6.5 to 1 1, preferably 7 to 10, particularly preferably 7.5 to 9.5, in particular 8 to 9, with the addition of Urea / urea mixture at temperatures of 30 to 120 ° C, preferably 40 to 100 ° C, more preferably 45 to 95 ° C, in particular 50 to 90 ° C and a pressure of 0.1 to 10 bar, preferably 0.5 to 5 bar, more preferably 0.9 to 1, 5 bar, in particular at atmospheric pressure (atmospheric pressure) are performed. Optionally, as a rule, the diluent may be partially removed, such as water, in vacuo, followed by an additional addition of urea / urea mixture at the abovementioned temperatures and pressures. The addition may be carried out by mixing the urea and, if appropriate, the compound A in solid form or as a solution under the reaction mixture or else the resin in a urea solution, which optionally contains compound A, stirred. The mixing of the two components can be carried out at room temperature or in such a way that the still up to 80 ° C warm resin is mixed with the urea. Thereafter, the mixture according to the invention can be cooled to room temperature. The pH of the cooled mixture is preferably adjusted to a pH between 8 and 10.

The process according to the invention is usually carried out in such a way that the solids content of the MUF resins 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 water at 30 to 60 ° C under reduced pressure to a content of 60 to 80 wt .-%.

The process of the invention can also be carried out in interconnected reactors, for. B. in a stirred tank cascade. In this case, for example, step a) in the first reactor, step b) in the second and step c) can be carried out in the third reactor.

The molar ratio of formaldehyde to the total amount of urea and optionally compound A in a) is generally from 1.5: 1 to 4: 1, preferably from 2: 1 to 3: 1, more preferably from 2: 1 to 2.6: 1 The molar ratio of formaldehyde to melamine in a) is generally 3000: 1 to 50: 1, preferably 2500: 1 to 100: 1, particularly preferably 2250: 1 to 150: 1.

The molar ratio of formaldehyde to Nh groups [F: (2xU + 3xM)] in a) is generally 0.8: 1 to 2: 1, preferably 1: 1 to 1, 5: 1, particularly preferably 1: 1 to 1, 3: 1. In this case, the connection A is counted as U.

The amount of optional addition of urea / urea mixture in b) can be made by one, two or more additions. The amount of urea / urea mixture is usually chosen so that a molar ratio of formaldehyde to total amount of urea and compound A of 1, 4: 1 to 4: 1, preferably 1, 8: 1 to 3: 1, especially preferably 1, 8: 1 to 2.6: 1.

The amount of addition of urea / urea mixture in c) can be made by one, two or more additions. The amount of urea / urea mixture is usually chosen so that a molar ratio of formaldehyde to total amount of urea and compound A of 0.7: 1 to 1, 5: 1, preferably 0.75: 1 to 1, 2 : 1, more preferably 0.8: 1 to 1, 05: 1, most preferably 0.8: 1 to 0.89: 1 results. Suitable formaldehyde is paraformaldehyde or aqueous 5 to 70 wt .-% strength formaldehyde solutions, such as aqueous solutions, preferably 30 to 60 wt .-% aqueous solutions, particularly preferably as 45 to 55 wt .-% aqueous solutions.

Urea is used either in solid form or as an aqueous solution, preferably as an aqueous solution, the concentration of urea in the solution being between 30 and 85%, preferably between 40 and 80%, particularly preferably between 50 and 75%.

The formaldehyde (F) and the urea (U) can also be used at least partially in the form of aqueous formaldehyde-urea solutions and / or aqueous formaldehyde-urea precondensate solutions. The pH of the aqueous formaldehyde solution, aqueous formaldehyde-urea solution and / or aqueous formaldehyde-urea precondensate solution is advantageously from 4 to 5.5, in particular from 4.5 to 5.

The concentration of the aqueous solution of formaldehyde and urea is advantageously from 50 to 80% by weight and the weight ratio of urea to formaldehyde is preferably between 10:90 and 70:30, in particular between 20:80 and 55:45, particularly preferably between 30: 70 and 50:50. This solution may contain small amounts of addition and low molecular weight condensation products of urea and formaldehyde. Further, an aqueous formaldehyde-urea precondensate solution prepared by reacting urea and formaldehyde at a pH greater than 7 can be used. The weight ratio of urea to formaldehyde is advantageously between 10:90 and 70:30, preferably between 20:80 and 55:45, in particular between 30:70 and 50:50. The concentration of the aqueous formaldehyde-urea precondensate solution is preferably 50 to 80%.

The urea can, regardless of whether it is used as a solid urea, urea solution, as formaldehyde-urea solution or as a formaldehyde-urea precondensate solution, partially replaced by compounds A, which can react with formaldehyde. Suitable compounds A are modified ureas such as ethyleneurea, ethylene diurea or dipropylene triurea, or guanamines such as benzoguanamine or amides such as caprolactam in amounts of 0 to 10% by weight, preferably 0 to 8% by weight, particularly preferably 0 to 5% by weight. % based on the total amount of urea. This means 100 to 90% by weight of urea and 0 to 10% by weight of compound A, preferably 100 to 92% by weight of urea and 0 to 8% by weight of compound A, particularly preferably 100 to 95% by weight. Urea and 0 to 5 wt .-% of compound A, ie pure urea (100 wt .-%) or mixtures of urea and compound A (> 100 to 90 wt .-% urea and <0 to 10 wt .-% of compound A ), which together add up to 100% by weight.

Suitable melamine melamine powder or liquid or powdered melamine-formaldehyde resins (MF resins) or melamine-urea-formaldehyde resins (MUF resins) are preferably MF and MUF resins, more preferably powdery MF and MUF resins , very particularly preferably powdery MF resins. If MF or MUF resins are used as melamine

Source used, then the amounts of formaldehyde and urea contained therein are taken into account in the calculation of the molar ratios.

Melamine-formaldehyde resin powders are typically prepared by spray-drying aqueous melamine-formaldehyde condensation products.

Suitable diluents are alcohols such as C 1 to C 4 alkanols, such as methanol, ethanol, n-propanol, isopropanol, propanol isomer mixtures, n-butanol, isobutanol, sec-butanol, tert-butanol, butanol isomer mixtures , Water and mixtures thereof, preferably water or 1 to 99% strength by weight aqueous alcohols of the C 1 to C 4 alkanols, more preferably water.

Suitable bases are all general alkaline compounds such as inorganic bases, for example alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, alkali metal or alkaline earth metal or organic amines, for example tertiary amines such as tributylamine, triethylamine, or tertiary alkanolamines such as triethanolamine, methyldiethanolamine, or their Mixtures, preferably aqueous alkali metal hydroxides and triethanolamine, particularly preferably sodium hydroxide solution.

Suitable acids are organic acids such as formic acid, acetic acid, maleic acid or inorganic acids such as nitric acid, sulfuric acid, preferably organic acids, particularly preferably formic acid.

The melamine-urea-formaldehyde resins according to the invention generally have a melamine content of. (Greater than or equal to) 0.05% by weight and .largecircle. (Lower than or equal to) 0.9% by weight, based on the total mass of the resin, ie 0.05 to 0.9 wt .-%, preferably 0.1 to 0.7 wt .-%, particularly preferably 0.2 to 0.5 wt .-%.

Optionally, the melamine-urea-formaldehyde resins of the present invention may be formulated with urea-formaldehyde condensation products having a formaldehyde to urea weight ratio of from 2: 1 to 0.85: 1 and / or urea in solid or aqueous form Solution be mixed. The solids content of the urea-formaldehyde condensation product is usually 50 to 80%. The solids content can be determined by weighing the liquid resin (eg about 1 g) in a flat sheet metal dish and then drying and re-weighing at 120 ° C. for two hours (M. Dunky, P. Niemz, Holzwerkstoffe und Leime, Springer, Berlin , 2002, page 458). The blending is usually carried out with urea-formaldehyde condensation products advantageously in a weight ratio of inventive melamine-urea-formaldehyde resin to urea-formaldehyde condensation products of 99: 1 to 10:90, in particular 95: 5 to 50:50. The blending with urea is generally carried out in a ratio of Me- lamin-urea-formaldehyde resin to urea or urea solution in a ratio of 99: 1 to 70:30, in particular 98: 2 to 80:20.

Further additives can be incorporated into these resins in amounts of up to 10% by weight. This may be e.g. to act alcohols such as ethylene glycol, diethylene glycol or saccharides. Likewise, water-soluble polymers based on acrylamide, ethylene oxide, N-vinylpyrrolidone, vinyl acetate and copolymers can be used with these monomers. Fillers may be added to the resins, such as cellulosic fibers, or mixtures thereof. In addition, they may contain carbonates, or mixtures thereof.

In order to improve the dilutability of the melamine-urea-formaldehyde resins with water, it is possible to use sulfites, disulfites and hydrogen sulfites which as cations preferably contain alkali metals such as lithium, sodium or potassium, preferably sodium or potassium, particularly preferably sodium or ammonium. These may be used in an amount of 0.01 to 10% by weight, preferably 0.05 to 1% by weight, based on the weight of the liquid resin.

The resins according to the invention are generally stable in storage at 20 ^° C. for several weeks. The resins according to the invention are suitable as binders, in particular for the production of moldings containing nocellulose, such as, for example, chipboard, fiberboard or Oriented Strand Board (OSB) boards. In addition, the mixtures according to the invention are suitable for the surface bonding of wood, for example for the production of plywood, single-layer and multilayer boards and glulam. Particularly suitable resins of the invention for the production of MDF (medium-density fiberboard), especially when the gluing is done in the blowline. In the blowline process, after the wood has been defibered in the refiner, the resin is injected into the fiber stream, which moves at high speed. subse- The glued fibers are dried (M.Dunky, P.Niemz, Holzwerkstoffe und Leime, Springer, Berlin, 2002, page 145).

The reactivity of the binder mixtures during curing can be increased by adding, immediately before processing, additionally a hardener such as ammonium salts, ammonium sulfate, ammonium nitrate, ammonium phosphates or carboxylic acids such as formic acid and oxalic acid or Lewis acids such as aluminum chloride or acidic salts such as aluminum sulfate or mineral acids such as sulfuric acid or mixtures thereof are added. The hardeners can be mixed with the aqueous binder ("glue liquor") and then sprayed onto chips or fibers, for example, or the hardeners can be applied to the substrate separately from the binder.

The lignocellulose-containing moldings according to the invention, for example chipboard, OSB boards or medium-density fiberboard (MDF), can be prepared, for example, by compressing 5 to 30% by weight of solid resin, based on lignocellulose-containing material, under pressure at from 120 to 250 ^° C. under pressure. In addition, hardeners can be used as described above. Under these conditions, the aminoplast resin usually hardens quickly and gives wood-based materials with good mechanical properties. An advantage of the melamine-urea-formaldehyde resins according to the invention is, in addition to the simple method of preparation, that an improvement in the processing properties is achieved over conventional resins of comparable composition, in particular, the resins of the invention are characterized by low swelling values and high strengths at low formaldehyde emissions. Another advantage is the low melamine content.

Examples Example 1

Glue with 0.33% melamine and F: U = 1.01 (melamine component = MF resin powder)

1 138 g (18.6 mol) of 49% strength aqueous solution of formaldehyde were heated to 87 ° C and adjusted with 10% sodium hydroxide solution to a pH of 7.7, within 30 min 495 g (8.24 mol ) Urea was added, then 1 1, 5 g of a melamine resin powder (prepared from formaldehyde solution and melamine by alkaline condensation and subsequent

Spray-drying, contains 60% by weight of melamine and 40% by weight of formaldehyde) and stirred for 15 minutes at 87 ° C. and a pH of 7.0 to 6.8. After heating to 92 ° C, a pH of 5.0 was set with formic acid, condensed at 95 ° C until a viscosity of 550 mPas was reached (viscosity measurement of a sample taken at RT), then with 10% Sodium hydroxide solution adjusted to a pH of 8.5, cooled to 85 ° C and added within 18 min 302 g (5.02 mol) of urea. After that, i. Vak. At 60 ° C, distilled off 230 g of water and added within 18 min at 50 ° C, a further 309 g (5.14 mol) of urea. 2031 g of glue were obtained with the following physical properties: Dry content 66.9% (measured by weight difference after 2 h at 120 ° C in a drying oven)

Viscosity 561 mPas (at a shear rate of 250 s ^_1 )

pH 8.2.

Example 2

Glue with 0.33% melamine and F: U = 1, 01 (melamine component = solid melamine) 1 148 g (18.8 mol) of a 49% aqueous formaldehyde solution were heated to 87 ° C and with 10% sodium hydroxide solution adjusted to pH 7.7, added within 30 min 495 g (8.24 mol) of urea, then 6.7 g (0.053 mol) of melamine was added and stirred for 15 min. After heating to 92 ° C, a pH of 5.0 was set with formic acid, condensed at 95 ° C until a viscosity of 550 mPas was reached (viscosity measurement see Example 1), then with 10% sodium hydroxide solution on a pH 8.5, cooled to 85 ° C and added within 18 min 302 g (5.02 mol) of urea. After that, i. Vak. At 60 ° C, distilled off 230 g of water and added within 18 min at 50 ° C, a further 309 g (5.14 mol) of urea. 2031 g of glue were obtained with the following physical properties:

- dry content 67% (measured by weight difference after 2 h at 120 ° C in a drying oven)

Viscosity 532 mPas (at a shear rate of 250 s ^_1 )

pH 8.2. The melamine content of the resin is 0.33% by weight; the molar ratio F: U is 1.01

Comparative Example 1 (according to US Pat. No. 4,536,245, Example No. 1)

Glue with 3.9% melamine and F: U = 1, 01

Preparation according to Example 1, US-A-4536245

Comparative Example 2

Glue without melamine and F: U = 1.01

1 148 g (18.8 mol) of a 49% aqueous formaldehyde solution were heated to 87 ° C and adjusted with 10% sodium hydroxide solution to a pH of 7.7, within 30 min 495 g (8.24 mol ) Urea was added and stirred for 15 min. After heating to 92 ° C, a pH of 4.8 was set with formic acid, condensed at 95 ° C until a viscosity of 550 mPas was reached (viscosity measurement see Example 1), then with 10% sodium hydroxide solution to a pH Value of 8.5, cooled to 85 ° C and added within 18 min 302 g (5.02 mol) of urea. After that, i. Vak. distilled off at 60 ° C 235 g of water and within 18 min at 50 ° C, a further 309 g (5.14 mol) of urea was added. 2019 g of resin were obtained with the following physical properties:

Dry content 66.9% (measured by weight difference after 2 h at 120 ° C in a drying oven)

- viscosity 528 mPas (at a shear rate of 250 s ^_1 )

pH 8.2.

Production of particle boards in the laboratory a) Mixing of the starting materials

500 g of spruce chips were placed in a mixer. Subsequently, a glue liquor of 100 parts and 4 parts of a 52% aqueous ammonium nitrate solution and 10 parts of water was applied. The amount of glue liquor was chosen so that the degree of gluing was 10%. The degree of gluing is the quotient of the mass of dry matter glue and the mass of dry matter wood. b) pressing the glued chips

The glued chips were cold pre-compacted in a 30x30cm-form. It was then pressed in a hot press (pressing temperature 200 ° C, pressing time 200 s). The thicknesses of the plates were 15.7 mm each.

Examination of wood materials Density

The density was determined 24 hours after preparation according to EN 1058. Querzugsfestigkeit

The determination of the transverse tensile strength is in accordance with EN 319.

source values

The determination of the swelling values after 24 h water storage was carried out according to EN 317

Formaldehyde emission (perforator method)

The determination of the formaldehyde emission was carried out according to EN 120 Melamine molar ratioDensity of transverse tensile strengthSource value perforator content F: U [kg / m ³ ] speed [N / mm ² ] after 24 h value [mg F /

[%] [%] 100 g]

Example 1 0.33 1, 01 585 0.60 20 5.5

Example 2 0.33 1, 01 582 0.61 19 5.3

Comparison 3.9 1, 01 588 0.49 20 5.5 Example 1

Comparative 0 1, 01 584 0.55 25 6.1 Example 2

Claims

claims

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine by reaction

a) urea containing 0 to 10 wt .-% of one or more compounds A, formaldehyde and melamine in the presence of a base at a pH of 7.5 to 1 1, a temperature of 20 to 120 ° C and a Pressure of 0.1 to 10 bar, b) subsequent reaction in the presence of an acid which optionally contains urea with 0 to 10 wt .-% of one or more compounds A, at a temperature of 60 to 180 ° C and a pressure of 0 , 1 to 10 bar and c) subsequent addition of urea containing 0 to 10% by weight of one or more compounds A,

characterized in that b) is carried out at a pH of 4 to 5.9.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to Claim 1, characterized in that the melamine-urea-formaldehyde resins according to the invention have a melamine content of greater than or equal to 0.05% by weight. % and less than or equal to 0.9 wt .-% based on the total mass of the resin.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 2, characterized in that b) is carried out at a pH of 4.1 to 5.5.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 3, characterized in that the process is carried out in interconnected reactors.

A process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to any one of claims 1 to 4, characterized in that the molar ratio of formaldehyde to urea in a) 1, 5: 1 to 4: 1 ,

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 5, characterized in that the molar ratio of formaldehyde to melamine in a) is 3000: 1 to 50: 1.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 6, characterized in that the molar ratio of formaldehyde to NH ₂ groups [F: (2xU + 3xM)] in a ) Is 0.8: 1 to 2: 1.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 7, characterized in that the molar ratio is optionally increased by adding one or more compounds A of formaldehyde to urea in b) 1, 4: 1 to 4: 1. Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of claims 1 to 8, characterized in that the molar ratio of formaldehyde to urea in c) 0.7: 1 to 1, 5: 1 amounts to

A process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to any one of claims 1 to 9, characterized in that as compound A modified ureas from the group ethylene urea, ethylene diurea or Dipropylentriharnstoff, or guanamines such as benzoguanamine or amides such as caprolactam.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 10, characterized in that the acids used are organic acids from the group of formic acid, acetic acid or maleic acid or inorganic acids from the group Nitric acid or sulfuric acid, preferably organic acids from the group of formic acid, acetic acid or maleic acid, particularly preferably formic acid, is used.

Process for the preparation of melamine-urea-formaldehyde resins with up to 0.9% melamine according to one of Claims 1 to 11, characterized in that the alkali compounds such as inorganic bases, for example alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, Alkali or alkaline earth metal carbonates or organic amines, for example tertiary amines such as tributylamine, triethylamine, or tertiary alkanolamines, such as triethanolamine, methyldiethanolamine, or mixtures thereof, preferably aqueous alkali metal hydroxides and triethanolamine, particularly preferably sodium hydroxide used

Use of the melamine-urea-formaldehyde resins prepared according to one of claims 1 to 12 with up to 0.9% melamine as a glue.

Use of the melamine-urea-formaldehyde resins prepared according to one of claims 1 to 12 with up to 0.9% melamine as a glue for the production of lignocellulose-containing moldings such as chipboard, OSB boards or medium-density fiberboard (MDF).

A process for the production of lignocellulose-containing moldings, characterized in that 5 to 30 wt .-% solid resin, based on lignocellulose-containing material, optionally with the use of a curing agent at press temperatures of 120 to 250 ^° C under pressure is pressed.