SE505134C2 - Use of certain organic melamine salts as additives to urea-formaldehyde adhesives and binders - Google Patents

Description

505 134 10 15 20 25 30 35 2 It is also well known that melamine in powder form can be added to an adhesive mixture with a UF resin. If about 20 parts by weight of melamine to 100 parts by weight of UF glue are used, an increased water strength is achieved, but the quality of the glue joint is lower than with a MUF glue.

The main object of the present invention is to find products which can be used as additives to an adhesive mixture based on a urea-formaldehyde resin and which increase the water resistance of adhesive joints in wood-based products glued or bonded with the mixture to at least the same level as a MUF adhesive. .

According to the present invention, it has been found that the addition of certain melamine salts to a mixture based on urea-formaldehyde resin gives the desired increase in the water strength of the adhesive joint, which makes it possible to use UF glued products also outdoors. The invention thus makes it possible to replace expensive MF or MUF adhesives with cheaper UF adhesives. Additives according to the invention make it possible to manufacture products with higher water strength of adhesive joints without any significant deterioration of the adhesive joint in other respects. The effect of the additives according to the invention can be achieved with much smaller amounts of melamine salts compared to the amount of melamine in MUF glue and the amount of powder melamine that has been used as an additive to UF glue, as mentioned above.

Thus, the present invention relates to the use of certain melamine salts as defined in the appended claims.

The melamine salts as additives to increase the water strength of UF adhesive joints are salts of melamine and certain organic acids, namely saturated aliphatic mono- and dicarboxylic acids with 1-4 carbon atoms or citric acid or phthalic acid.

The salts thus include salts of melamine and formic acid, butyric acid, isobutyric acid, oxalic acid, acetic acid, propionic acid, malonic acid, succinic acid, citric acid and phthalic acid. Salts of melamine and formic acid, acetic acid, oxalic acid, citric acid or phthalic acid are preferably used. In particular, salts of melamine and acetic acid or formic acid, because of their higher solubility in UF adhesives, are preferred over other melamine salts. As mentioned in the introduction, a hardener, commercially available is ammonium chloride. to cure the adhesive mixtures. Various hardeners have been proposed over the years and among them also some salts which according to the present invention are used to increase the water strength. Thus, GB patent 524,350 proposes the use of melamine and some salts of melamine and organic acids and inorganic acids, including formate, acetate and oxalate as hardeners for urea-formaldehyde resins, ie to accelerate the curing.

The main object of using the salts of the present invention is to increase the water strength of the adhesive joint and the salts are therefore used in amounts which are effective for this purpose. at least 6% by weight of melamine, based on the UF resin Usually, an amount of the salt corresponding to dry matter gives a noticeable increase in water strength. The upper limit is set mainly for economic reasons to get an adhesive with the advantages an MF-MUF adhesive applies to water strength and quality of the adhesive joint in general, but Salt amounts corresponding to or at a more economical price. to 25% by weight of melamine can be used and usually the amount is in the range from 6 to 20% by weight, calculated as melamine in the salt on the dry matter of the UF resin. The amount is preferably in the range from 8 to 16% by weight and most preferably in the range from 10 to 14% by weight, calculated as melamine in the salt of the dry matter of the UF resin.

The salts used in the present invention can be readily prepared according to conventional known methods for the preparation of salts of acids and amines. Melamine can, for example, be dissolved in water and reacted with the acid at elevated temperature, for example about 90-100 ° C, the salt precipitates on cooling to room temperature. The salts are then added to the UF adhesive mixture.

The salts of melamine and organic acids are used according to the invention for any urea-formaldehyde adhesive or binder, which usually has a molar ratio of F: U of from 1.4 to 1.7, a dry matter of 50 to 70% by weight viscosity of from 400 to 2000 mPa.s at 20 ° C.

The salts are added to the UF adhesive or to the UF adhesive mixture by simple mixing. Since the salts according to the invention and in addition to a water strength-increasing effect also give a curing effect, it is not necessary to add an additional hardener, even if one such as ammonium chloride, citric acid or monoammonium phosphate can used. In such a case, the hardener is incorporated into the adhesive mixture in conventional amounts, usually of from 0.5 to 2% by weight based on 65% dry matter UF resin, or in lower amounts.

An adhesive mixture usually also contains an organic or inorganic filler, for example wheat flour, maize flour or wood flour or gypsum or kaolin, as previously mentioned, in amounts of 3 to 20% by weight based on the dry matter of the UF resin.

The adhesive mixture containing additives according to the invention is used for gluing or assembling wood-based products such as plywood, chipboard, veneer, etc., but especially for plywood according to per se known manufacturing methods.

The melamine salts according to the invention can advantageously be used as additives to adhesive or binder mixtures based on urea-formaldehyde resins for the manufacture of products intended for outdoor use.

The invention is further illustrated in the following examples which, however, are not intended to limit the scope of the invention. Parts and percentages refer to parts by weight and 'percentage by weight. unless otherwise stated. All viscosity values in the examples are measured with Brookfield viscometer at 20 ° C with spindle 4 and 20 rpm.

Example 1 500 g of a UF resin with a dry content of 65%, a viscosity of 1200 mPa.s at 20 ° C and a molar ratio of formaldehyde to urea of 1.6 were mixed with 50 g of melamine acetate and 7 g of ammonium chloride as hardener. The glue mixture was applied to beech veneer with the dimensions 40 x 40 cm and a thickness of 2.2 mm.

The glue spread was 250 g / m2. A plywood of ES such veneers was pressed in a hot press at 125 ° C for 8 minutes.

The procedure in European Standard No 314 was followed and test pieces were cut from the plywood and placed in boiling water for 6 hours. The test pieces were tested in a tensile test equipment where the strength of the adhesive joint was registered.

All five test pieces passed the cooking test without delaminations (without openings in the glue joint). The tensile strength was good, 1.82 N / mmz. Example 2 A similar sample was made but without the addition of melamine salt according to the invention. 500 g of the same UF resin as in Example 1 were mixed with 7 g of ammonium chloride. A piece of plywood was prepared in the same way as in Example 1 and the test pieces were placed in boiling water, but after only 20 minutes all the glue joints had opened. This example shows how sensitive a UF adhesive joint is to water and high temperatures. The polymer chain is destroyed by water at high temperatures.

Example 3 In this example, a MUF resin was used instead of a UF adhesive. 500 g of a MUF adhesive with a dry content of 66% and a melamine content of 22%, based on the dry matter, were mixed with 9 g of ammonium chloride as hardener and 25 g of wheat flour as filler.

The same type of wood and the same procedure as in Example 1 were used. After 6 hours in boiling water, two of the five test pieces showed some delamination and the tensile strength was 1.25 N / mm2. Compared with the test results from Example 1, the MUF adhesive gave less good results than the UF adhesive with melamine acetate.

Example 4,500 g of a UF resin with a molar ratio of formaldehyde to urea of 1.4 (dry matter 65%, viscosity 900 mPa.s) were mixed with 70 g of melamine formate and 20 g of cornmeal as filler. A book plywood was manufactured as in Example 1.

After 8 hours in boiling water, no delamination was seen in the test pieces and the tensile strength was 1.95 N / mm 2.

Example 5 A similar sample as in Example 4 was made with melamine oxalate instead of melamine formate. A test piece of five showed some delamination and the tensile strength was 1.44 N / mml.

Example 6 500 g of a UF resin having a molar ratio of 1.7, dry matter 65% and viscosity 900 mPa.s at 20 ° C were mixed with 50 g of melamine citrate, 1.5 g of citric acid as hardener and 40 g of wheat flour as filler to increase the viscosity of the adhesive mixture. The viscosity was measured at 3400 mPa.s at 22 ° C. The adhesive mixture was applied to poplar veneer with the dimension 40 x 40 cm and thickness 1.8 mm. The glue spread was 280 505 134 10 15 20 25 6 g / m2. The press temperature was 120 ° C and the press time 7 minutes.

After 6 hours in boiling water no delamination was seen and the tensile strength was 1.25 N / mm2.

The tensile strength was lower than when beech was used because the strength of poplar is lower.

Example 7 500 g of the same UF resin as in Example 4 were mixed with 100 g of melamine and 10 g of NH 4 Cl and 20 g of cornmeal. A plywood was made as in Example 1.

After 6 hours in boiling water, two test pieces showed strong Four other pieces showed some delamination and four delamination and could not be used for tensile testing. showed no delamination. The tensile strength was 0.95 N / mm =.

This example shows that the addition of melamine to a UF adhesive increases the water resistance but not up to the level of a MUF adhesive.

Example 8 100 g of a UF resin with a dry content of 65% and with a viscosity of 1800 mPa.s at 20 ° C were mixed with 14 g of melamine formate and 5 g of corn flour.

The glue mixture was spread on a 40 x 40 cm piece of plywood with a glue spread of 120 g / m2. An oak veneer with a thickness of 0.7 mm was applied and pressed for 3 minutes at 110 ° C. Five test pieces were boiled for 6 hours and all the pieces showed fully satisfactory strength.

Claims (7)

10 15 20 505 134 7 Patent claims Use of salts of melamine and an organic acid selected from the group of saturated aliphatic mono- and dicarboxylic acids having 1 to 4 carbon atoms, citric acid and / or phthalic acid as addition to urea-formaldehyde resin or adhesive mixtures containing said resin to increase the water strength of the adhesive joint in wood-based products glued with these resins or adhesive mixtures. Use according to claim 1, wherein the salt is a salt of melamine and formic acid. Use according to claim 1, wherein the salt is a salt of melamine and acetic acid. Use according to claim 1, 2 or 3, wherein the salt is used in amounts of 6 to 25% by weight, calculated as the melamine component in the salt on the dry matter of the UF resin. Use according to claim 4, wherein the salt is used in amounts of 8 to 16% by weight calculated as the melamine content of the salt on the dry matter of the UF resin. Use according to any one of the preceding claims, wherein the wood-based product of plywood. Use according to one of the preceding claims, for glued or bonded products intended for outdoor use.