FI113274B - Binders for the preparation of lignocellulosic molding pairs - Google Patents

Abstract

Mixtures of: (A) an aqueous condensation product comprising (a) 1 mol melamine and (b) 3 to 11 mol formaldehyde, and (B) a total urea quantity of 0.8 to 13 mol, in which up to 25 % of this total quantity may be contained as component (c) in the resin (A). These mixtures are suitable as adhesive resins.

Description

, 113274

Binders for making lignocellulosic molded articles

The present invention relates to a mixture useful as a binder in the preparation of lignocellulosic molded articles comprising (A) an aqueous condensation resin containing (a) 1 mol of melamine, 10 (b) 3 to 11 mol of formaldehyde, (c) 0 to 0, 5 moles of aromatic or partially aromatic hydroxy compounds, (d) 0 to 0.1 moles of other amino-plastic forming components, and 15 (B) of urea in a total of 0.8 to 13 moles, up to 25% of this total A) during the manufacture of the resin.

The invention further relates to a process for the preparation of such compositions and their use for the preparation of lignocellulosic shaped articles.

It has long been known that wood and others ·; The lignocellulosic components may be glued to the urea / formaldehyde resin under acidic conditions. resins. The water resistance of such adhesive joints is not dry, ·. : 25 is not enough in all cases. For this reason, it is necessary to · · often use alkaline curing phenol / formaldehyde !!! formaldehyde resins. However, their downsides are the high cost, »» slow cure, residual free phenol, darkening, and high alkali content, which complicate · * 3 0 plywood and coating and can even occur in so-called.

"alkaline flowering".

| These drawbacks can be partially avoided by the use of melamine-containing urea / formaldehyde resins, which may still contain phenol in a certain concentration as a reinforcement. In order to remove the free phenol from the lignocellulose-containing mold formed with such a resin, a condensate is prepared from phenol and formaldehyde and optionally from alkali (hydrogen) sulfite in a separate step which is then added at the appropriate point to the urea / melamine / formaldehyde resin. Such resins cure under acidic conditions, have a slightly shorter cure time than phenolic resins, and also provide a waterproof adhesive. Their drawbacks, however, are laborious, multi-step manufacturing, the high cost of melamine and the relatively long cure time compared to pure urea / formaldehyde-10 resins, which increases the cost of manufacturing chipboard and other lignocellulosic products glued thereto.

EP-A 25 245 discloses melamine-modified amino-plastic resins obtained by mixing urea / formaldehyde resins and melamine / urea / formaldehyde resins or by mixing melamine / formaldehyde resins and urea / formaldehyde resins.

DE-A 2 455 420 discloses a process for the preparation of melamine / urea / formaldehyde resins by condensation of melamine and urea / formaldehyde precondensates and the like.

EP-P 54 755 discloses a process for the preparation of melamine / formaldehyde absorption resins in which; urea solution is added to the melamine / formaldehyde condensates to improve storage stability.

According to the teachings of US-A-4 123 579, small amounts of urea are added to condensates of methylene-formaldehyde after condensation to improve flowability.

DE-A 3 442 454 recommends the preparation of urea / melamine: 30 minine / formaldehyde condensation products by using formaldehyde in the form of an aqueous solution of urea in reaction with melamine. In this case, up to about 50% by weight of the urea size required may be used in other forms than before, after or after the condensation of the formaldehyde solution.

113274 3 Certain parts of urea remain unbound and may act as a formaldehyde retaining agent.

However, all known resins which are intended to be used as binders need to be improved as they do not always fully meet the requirements for the water resistance and strength of the molded bodies and the simple and inexpensive manufacture of resins.

It has been an object of the present invention to provide improved aqueous resin binders based on melamine, urea and formaldehyde.

Accordingly, the compositions defined in the introduction have been invented.

The aqueous condensation products (component A) are obtained by reacting 1 mol of melamine (a) and (b) with 3 to 11 mol, preferably 3.6 to 9.5 mol, particularly preferably 4 to 7 mol, of formaldehyde.

Melamine is usually used in solid form. Formaldehyde is usually used in the form of concentrated aqueous solutions, e.g. 40% by weight aqueous solution or paraformaldehyde. A concentrated aqueous solution of formaldehyde and urea may also be used if part of the urea is added already during condensation.

; In addition, the aqueous condensation products (A) may: contain up to 0.5 moles of melamine per mole of the aromatic or partially aromatic hydroxy component (c).

! Among such components are in particular mono- or polyvalent phenols such as resorcinols, hydroquinone or preferably phenol as well as polynuclear compounds such as alpha or beta-naphthol or partially aromatic dihydroxy compounds such as 2,2-bis (4-hydroxy). -siphenyl) propane (bisphenol A), 1,1-bis- (4-hydroxyphenyl) ethane, or 1,1-bis- (4-hydroxyphenyl) isobutane.

(Phenol is preferably added in the form of phenol / formaldehyde precondensates which may be obtained, e.g., according to DE-A 3 125 874, or in its free form.

113274 4

In addition, modified ureas such as ethylene-urea, ethylenediurea or dipropylene triurea, or Guana-amines such as benzoguanamine or amides such as capro-5-lactam may be added as constituents (d) in amounts up to 0.1 mol in the preparation of products (A).

The reaction is preferably carried out by stirring at 20 to 40 ° C with 1 mole of melamine and 3 to 11 moles of formaldehyde and up to 25% of the total amount of urea required and heating to 70-100 ° C, preferably 75 to 95 ° C. The pH should then be between 7.8 and 9.5, preferably between 8.2 and 9.0. Under these conditions, condensation is carried out until the viscosity measured on the wafer / wafer viscometer is between 10 and 1000 mPa · s, particularly preferably between 10 and 500 mPa · s. It is then cooled to 10-80 ° C, preferably 40-75 ° C.

Component (B), i.e. urea, is then added to the condensation product (A) in a total amount of 0.8-13 moles, preferably 1.3-4.5 moles, so that up to 25% of this total amount can already be added to the resin (A). : in this context.

The urea is preferably added in solid form or also as an aqueous solution. If up to 25% of the total urea is added during the preparation of the condensation products (A), the urea may also be added in the form of a concentrated aqueous solution of urea and formaldehyde.

According to a preferred embodiment, all of the urea is mixed with the condensation of the resins (A)

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30 at the end. The method of insertion is not critical. The urea may be placed under the resin (A) or the resin (A) may also be mixed with the urea solution. Both components can be mixed. stirring at room temperature or by mixing • a resin with a temperature of up to 80 ° C and 35 urea. The finished resin mixture can then be cooled to room temperature. . * to the temperature. The pH of the cooled resin should be between 8.5 and 10.0. It is advisable to add some urea already during the preparation of component (A) if more than 4 moles of formaldehyde are used per mole of melamine.

Commonly used alkali compounds such as alkali and alkaline earth hydroxides in the form of their aqueous solutions, tertiary amines such as tributylamine or triethylamine, and tertiary alkanolamines such as triethanolamine, methyldiethanolamine may be used for pH adjustment.

The process of the invention is usually carried out with a resin solids content of 50 to 70% by weight based on the aqueous resin mixture. However, it is also possible to increase the solids content by removing water by distillation at 30-45 ° C under vacuum.

The resulting aqueous resins have a viscosity at 20 ° C of between 10 and 800 mPa.s, preferably between 20 and 500 mPa.s, at a solids content of about 60%, so that these products are easy to handle even at high solids contents. They are particularly easy to pum-20 strain, mix with hardener and spray. They are also particularly easy to spread on the substrate »and this gives further machining advantages.

The products are generally stored for several weeks at 20 ° C.

I 25 In addition, it is possible to blend these additives with up to 10% by weight of other additives. In this case, the lii may be, for example, alcohols such as ethylene glycol, diethylene glycol or saccharides. Similarly, water-soluble polymers based on acrylamide, ethylene oxide, N-vinylpyrrolidone, vinyl acetate and copolymers with these monomers can be used.

The resins of the invention are excellent binders in the manufacture of lignocellulosic shaped articles such as chipboard, plywood or fibreboard.

113274 6 Such moldings can be made, for example, by compressing from 5 to 30% by weight of a lignocellulosic material at a temperature of 120 to 250 ° C and at a pressure. Additionally, hard-5 teas such as ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium phosphates, formic acid, sulfuric acid or other inorganic or organic acids may be used. Typically, the hardeners and the aqueous binder ("adhesive solution") are mixed and the mixture is then sprayed onto the chips.

The compositions of the invention are also suitable for the production of moldings such as beams obtained by surface gluing of wood parts.

The advantages of the aqueous compositions being processed include, in addition to a simple manufacturing process which allows for the elimination of urea cocoa-condensation in comparison with conventional resins of the same composition, an improvement in the machining properties, in particular with the same proportion of melamine. improved water resistance and shorter gel times and thus higher processing speeds. While retaining machining properties: as good as traditional resins,>; Reduce the proportion of expensive melamine. Thus one can; improves the formation of lignocellulosic materials. . : 25 in the economy of manufacturing molded parts-. ·. suutta.

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Examples> · »·

A 40% w / w aqueous solution was used as the formaldehyde solution.

The pH was adjusted with aqueous sodium hydroxide solution.

The viscosity was measured at 20 ° C with a wafer / wafer viscometer. The solids content was determined on a dry basis for two hours at 120 ° C in a convection oven.

To measure the gel time at 100 ° C, 8 parts: 20% ammonium sulfate solution was added to 100 parts of glue.

113274 7

Example 1

600 g of formaldehyde solution and 264 g of melamine were heated to 95 ° C and condensed for 120 minutes at pH 8.6. The mixture had a viscosity of 150 mPa · s (measured as 5 n at 20 ° C). It was then cooled to 75 ° C and 272 g of urea was added. After cooling to 20 ° C, the following values were measured: viscosity 65 mPas, solids content 58.7%, gel time 50 seconds.

Example 2 528 g of formaldehyde solution and 222 g of melamine were heated to 95 ° C and condensed for 120 minutes at pH 8.8. The mixture had a viscosity of 110 mPa · s (measured at 20 ° C). It was then cooled to 75 ° C and 246 g of urea was added. After cooling to 20 ° C, the following values were measured: viscosity 60 mPa.s, solids content 58.8%, gel time 58 seconds.

Example 3

539 g of formaldehyde solution and 234 g of melamine were heated to 95 ° C and condensed for 12 hours at pH 8.7. The mixture had a viscosity of 100 mPa.s (measured as na at 20 ° C). It was then cooled to 75 ° C and 245 g of urea was added. After cooling to 20 ° C, the following values were measured: viscosity 40 mPa.s, solid; · Content 59.4%, gel time 55 seconds.

. : 25 Example 4 * I »

1200 g of formaldehyde solution, 495 g, were heated! melamine and 24 g of urea at 95 ° C and condensed for 120 ° C at pH 8.5. The mixture had a viscosity of 130 mPa.s (measured at 20 ° C). It was then cooled to 30-75 ° C and 540 g of urea was added. After cooling to '20 ° C, the following values were measured: viscosity: 60 mPa.s, solids content 58.6%, gel time 58 seconds.

Example 5 358 g of a formaldehyde solution, 222 g of methylamine and 45 g of urea were heated to 95 ° C and condensed from 120 to 113274 lbs at pH 8.5. It was then cooled to 75 ° C and 255 g of urea was added. After cooling to 20 ° C, the following values were measured: viscosity 30 mPa.s, solids content 57.3%, gel time 56 seconds.

5 Example 6 (Comparative Example)

556 g of formaldehyde solution, 264 g of methylamine and 111 g of urea were heated to 95 ° C and condensed for 60 minutes at pH 8.6. The mixture had a viscosity of 490 mPa.s (measured at 20 ° C). It was then cooled to 10 75 ° C and 140 g of urea was added. After cooling to 20 ° C, the following values were measured: viscosity 150 mPa.s, solids content 57.9%, gel time 80 seconds.

Example 7 (Comparative Example according to DE 15 3 442 450)

A mixture of 445 g of concentrated aqueous solution containing 50% by weight of formaldehyde, 25% by weight of urea and 25% by weight of water, 246 g of melamine and 104 g of water was heated to 95 ° C and condensed to pH 20 for 55 minutes. at 8.6. The reaction mixture had a viscosity of 1220 mPa.s (20 ° C). It was then cooled to 75 ° C and 140 g of urea were added. After cooling to 20 ° C, the viscosity of the resin was 420 mPa.s, solids content 66.5% by weight; and a gel time of 76 seconds.

. : 25 Application example

From resins of Examples 1-7, solutions were prepared by glue to prepare particle boards. The adhesive solutions were prepared by adding 8 g of 20% w / w aqueous ammonium sulfate solution to 100 g of resin and adjusting the lye; · * 30 solids to 51.8% by weight with the addition of water. 19mm thick particle boards were made with a solids content of 12% by weight based on absolute dry particleboard and a compression time of 114 seconds at 210 ° C.

35 The properties of the particle board are shown in the table below.

113274 9

Table

Resin from example number 1234567

Gel Time (s) 50 58 55 58 56 80 87

Shear strength V 20 (N / mm 2) 3.06 2.73 2.61 3.57 3.81 2.78 2.61

Tensile strength V 100 (N / mm 2) 11 0.44 0.52 0.51 0.54 0.63 0.39 0.30

Swelling after 24 hours (1) 14.9 11.1 12.2 13.1 12.9 18.8 16.9 Puncture value (mg HCHO / 100 g absolute 4.9 5.0 5.2 5.1 6.3 4, 9 5.2 dry boards) 1) according to DIN 68763 5 2) according to DIN EN 120 • t · * · · »·» · · #

Claims (8)

113274 A composition useful as a binder in the manufacture of molded articles containing lignocellulose, characterized in that it comprises (A) an aqueous condensation resin containing (a) 1 mole of melamine and (b) 3 to 11 moles of formaldehyde, and (B) 0 , 8 to 13 moles of urea, whereby up to 25% of this total amount of urea can be added in the preparation of condensation products (A). Mixtures according to claim 1, characterized in that the urea is completely added to the condensation products (A) upon completion of the condensation. Mixture according to claim 1 or 2, characterized in that it contains condensation products (A), which additionally contain up to 0.5 moles of an aromatic or partially aromatic hydroxy component. Mixture according to one of Claims 1 to 3, characterized in that it contains condensation products (A), which additionally contain up to 0.1 mol of another amino-forming component. Mixture according to any one of claims 1 to 4. . known to be obtained by · ·: 25 (A) condensation »>» (a) 1 mole of melamine, I !! (b) 3 to 11 moles of formaldehyde, (III) * (c) 0 to 0.5 moles of phenol, and (d) 0 to 0.1 moles of other amino-forming constituents in an aqueous medium at pH 7, 5 to 10.0 and • · »at 50 to 100 ° C, and: (B) subsequently adding a total of 0.8 to 13 moles of urea, whereby up to 25% of this total may be added to (A). in the manufacture of condensation products i * * * '* 35. • »» 113274 A process for the preparation of suitable mixtures as adhesive resins, which comprises reacting (A) in an aqueous medium at a pH of 7.5 to 10.0 and at a temperature of 50 to 100 ° C (a) 1 mol of melamine, (b) 3- 11 moles of formaldehyde, (c) 0 to 0.5 moles of phenol, and (d) 0 to 0.1 moles of other amino-forming components, and (B) subsequently adding urea in a total amount of 0.8 to 13 moles at 20 to 80 ° C, up to 25% of this total amount may be present during reaction (A). Use of the compositions according to any one of claims 1 to 6, characterized in that they are used as a binder for the preparation of lignocellulosic shaped bodies. 8. Lignocellulose-containing moldings, characterized in that they contain the binders according to any one of claims 1 to 6 as binder. »> 1 * ·» · 113274