SE450385B - PROCEDURE FOR PREPARING A NON-STICKING CARBAMIDE FORMAL HEARTS - Google Patents

Description

450 385 2 mechanical) to feed the impregnated fiber to the press.

It is also impossible to perform impregnation before the fibers have dried. Since the resin cures quickly, only dry fibers can be impregnated (ie they must have passed the dryer), since transport of the impregnated fiber through a dryer causes gelation to occur before the material reaches the press and gives a fibreboard with poor mechanical properties.

In order to solve the above-mentioned problems, according to the invention, a process of the above kind is carried out, which is mainly characterized by the steps of treating a formaldehyde source with a strong organic base to regulate its pH value to a value between 7.0 and 8. 0, addition of urea until the formaldehyde / urea molar ratio is between 1.90 and 2.55, heating to boiling point, adjusting the pH to 5.0 - 6.5 with an acid, preferably formic acid, interrupting the polymerization reaction by means of an inorganic base when the product has reached the desired viscosity, adding an additional amount of urea to the product while it is cooling, the molar ratio of formaldehyde to urea being between 1.58 and 1.70, and adjusting the pH to 8.0 - 8.5, whereby a resin is obtained which has a dry content of 64 - 66% and a viscosity of 150 - 500 mPa-s at 2500.

According to the invention, the strong organic base is preferably selected from the group consisting of triisopropanolamine, triethylamine and diethylamine.

According to the invention, inorganic salts selected from the group consisting of alkali metal halides, alkaline earth metal halides and alkali metal sulfates are further added during the preparation to improve the stability properties.

It is also possible to replace a part of the urea (1 - 15%) with corresponding stoichiometric amounts of a product with similar chemical behavior, preferably melamine and dicyandiamide.

The following resin properties are obtained from the resin prepared according to the process of the invention: - low viscosity, within the above range; - non-sticky; stable at room temperature for more than two months. 450 385 3 If desired, the resin can be used for the preparation of impregnation preparations with different amounts of accelerators and retarders, allowing mixtures with different gelation times to be formed and thus enabling impregnation of the fiber before or after drying, as desired.

The fibers of lignocellulosic material, impregnated with a suitably catalyzed urea-formaldehyde resin, are transported by air or mechanical systems to a hot table press (heated by steam, fuel oil or high frequency electric current), where they are subjected to pressure and heat for advancement. position of a fiberboard.

The properties of the urea-formaldehyde resin should be the right ones so that proper impregnation of the fiber is obtained with the least possible resin consumption while the fiberboard gets the right mechanical properties. The behavior of the fiber, which is the product to be impregnated, in relation to resin absorption differs from the previously known behavior of curling iron or sawdust (production of fibreboards with urea-formaldehyde bark or glue) and the behavior of plywood (production of plywood with urea-formaldehyde resins or adhesives).

The combination of properties of the resin required for it to be used for proper impregnation of the fiber is obtained by appropriately combining certain factors during resin production, these factors being above all the molar ratios of formaldehyde to urea in the initial and final the stages of the resin, the pH and the temperature of the reaction and the final viscosity of the resin.

In order to similarly improve certain properties (resin stability time, mechanical properties of the finished fibreboard), inorganic salts can be used in the preparation of the resin, such as alkali metal or alkaline earth metal halides or alkali metal sulfates in amounts which may vary within the limits: by weight inorganic salt O'l7:> weight of dry resin:> 'o'O2 The gel time of the catalyzed resin should be correct, so as to avoid premature gelation during transport (or in some cases transport and drying) to the press and to keep the pressing time as short as possible, so that maximum economic yield can be obtained from the press while maintaining the right quality of the bonded fibreboard thus obtained.

The resin is catalyzed before the impregnation step, usually using strongly acidic ammonium salts, but also weakly acidic products can be used.

The fiber can be impregnated with the resin in the dry or wet state. In both cases, measuring equipment is required to regulate the ratios of fiber to resin. The normal weight ratio is as follows: Weight amount of dry resin = 0.07 - 0.11 Weight amount of dry fiber As a formaldehyde source in the preparation of the resins according to the invention, any commercially available products can be used, such as aqueous solutions with different cones. concentrations of formaldehyde or urea formaldehyde or paraformaldehyde precondensate.

The above precondensates generally have the following properties: Active urea + formaldehyde concentration: 60 - 85% Molar ratio of formaldehyde: urea: 4: 1 to 6: 1 These precondensates have the advantage that they contain a high concentration of formaldehyde while being very stable bila (over 6 months), and their production greatly simplifies the production of urea-formaldehyde resins.

Example 1 To 100 kg of a urea-formaldehyde precondensate with a molar ratio of formaldehyde urea of 5 and an active urea + formaldehyde concentration of 70% (50% formaldehyde and 94 urea) at pH 7.5 was added in cooling 32 kg urea, so that the molar ratio of formaldehyde urea became 1.92: 1, and the mixture was heated to boiling point.

The mixture was boiled under reflux for 35 minutes, and the pH was adjusted to 8.0 with triisopropanolamine.

Similar effects would be obtained with other bases, such as tri- 450 385 ethylamine and diethylamine.

Thereafter, the pH was adjusted to 6.0 with formic acid, the pH and viscosity being checked at regular intervals.

The polymerization reaction was quenched by the addition of sodium hydroxide when the viscosity of the mixture was 400 mPa-S at 25 ° C. The mixture was then cooled to 6500 and an additional 20 kg of urea was added to control the formaldehyde: urea molar ratio to 1.59: 1. After this addition, the product was cooled: iii 20 ° C, and the pia value was finally adjusted: iii 8.0 with sodium hydroxide.

The resin thus obtained (125 kg) had a dry content of 65% and a viscosity of 225 mPa-s at 25 ° C. Example 2 The pH of 120 kg of a 50% strength by weight aqueous solution of formaldehyde was adjusted to 8.0 with triisopropanolamine. and while heating, 57 kg of urea were added so that the molar ratio of formaldehyde urea became 2.1, and the mixture was heated to boiling point. The mixture was boiled under reflux for 20 minutes, and the pH was then adjusted to 5.5 with formic acid, the pH and viscosity being checked at regular intervals.

The polymerization reaction was stopped by the addition of sodium hydroxide when the viscosity of the mixture was 70 mPa-s at 25 ° C.

The mixture was then cooled to 65 ° C, and an additional 20 kg of urea was added to control the molar ratio of formaldehyde urea to 1.55: 1. The product was cooled after this addition. The excess water was removed by distillation in vacuo, and the resin was cooled to 2000. The pH was adjusted to 8.0. The resin thus obtained (175 kg) had a dry content of 65% and a viscosity of 225 mPa-s at 25 ° C.

Example 5 The pH of 150 kg of a 56.6% by weight solution of formaldehyde in water was adjusted to 8.0 using triisopropanolamine. In the cold, 47 kg of urea were added so that the molar ratio of formaldehyde: urea became 2.54: 1, and the mixture was heated to boiling point. The mixture was boiled under reflux for 55 minutes, and then the pH was adjusted to 5.0 with formic acid, the pH and viscosity being checked at regular intervals.

The polymerization reaction was stopped by the addition of sodium hydroxide when the viscosity of the mixture was 20 mPa-s at 25 ° C.

The mixture was then cooled to 6500 and an additional 18 kg of urea was added so that the molar ratio of formaldehyde urea became 1.70: 1. The product was cooled after this addition. The excess water was removed by distillation in vacuo, and the resin was cooled to 2000. The pH was adjusted to 8.0.

The resin thus obtained (about 151 kg) had a dry content of 65% and a viscosity of 225 mPa-s at 25 ° C.

Ekemgel 4 100 kg of an urea-formaldehyde precondensate with a molar ratio of formaldehyde urea of 5 and an active urea + formaldehyde concentration of 80% (57% formaldehyde and 25% urea) were heated to 65 ° C. The pH was adjusted to 8.0 by the addition of triethylamine.

Then 6 kg of potassium chloride were dissolved in the precondensate with the amount of water (18 kg) required to keep the final dry content of the resin at its normal value of 65%, the added amount of inorganic salt being such that the molar ratio of inorganic salt formaldehyde was 0.042: 1.

When the potassium chloride was completely dissolved (temperature 60%), 26 kg of urea were added so that the formaldehyde formaldehyde urea became 2.54: 1, and the mixture was heated to boiling point.

The mixture was boiled under reflux, and the pH and viscosity were checked at regular intervals. The pH was maintained at 6.0 with formic acid.

The polymerization reaction was stopped by the addition of sodium hydroxide when the viscosity of the mixture was 400 mPa-s.

The mixture was then cooled to 6500 and an additional 18 kg of urea was added so that the molar ratio of formaldehyde: urea was adjusted to 1.70: 1. After this addition, the product was cooled to 2006, and the pH was finally adjusted to 8.0.

The resin thus obtained (168 kg) had a dry content of 65% and a viscosity of 225 mPa-s at 25 ° C.

Claims (3)

450 385 7 PATENT REQUIREMENTS A process for the preparation of a non-stick urea formaldehyde resin starting from a formaldehyde source which is treated with a strong organic base for regulating its pH to between 7.0 and 8.3, characterized in that said formaldehyde source is selected from the group consisting of (a) a urea formaldehyde precondensate having a formaldehyde molar ratio of urea from 4: 1 to 5: 1; (b) a 50% by weight solution of formaldehyde in water and (c) a 36.5% by weight solution of formaldehyde in water and that the following steps are carried out after said treatment, namely that urea is added until the molar ratio of formaldehyde: urea is from 1, 90 to 2.35: 1, that heating takes place to the boiling point, that the pH value is adjusted to 5.0-6.3 with formic acid, that the polymerization reaction is stopped with an inorganic base when the product has reached the viscosity value 350-H50 mPa.s if the formaldehyde source is (a), the viscosity value HO-100 mPa.s if the formaldehyde source is (b) and the viscosity value 15-25 mPa.s if the formaldehyde source is (c), that an additional amount of urea is added to the product while it cools so that the final molar ratio formaldehyde: urea becomes between 1.38 and 1.70, and that the pH is adjusted to a value from 8.0 to 8.5, whereby a resin is obtained which has a dry content of 614-661, and a viscosity of 150-300 mras at 25 ° C. 2. A process according to claim 1, characterized in that the strong organic base is selected from the group consisting of triisopropanolamine, triethylamine and diethylamine. 3. A process according to claim 1, characterized in that the stability properties of the resin are improved by adding during its preparation inorganic salts selected from the group consisting of alkali metal halides, alkaline earth metal halides and alkali sulphates. Process according to Claim 1, characterized in that 1 to 15% of the urea are replaced by a product with a similar chemical behavior, preferably melamine and dicyandiamide.