DE1933303A1 - Curing accelerator for aminoplasts - Google Patents

Abstract

The curing accelerator is a zinc salt or aluminium salt of non-reducing acids, having a pH value below 2.9 in 0.1 N-solution at 25 degrees C. The salt solution has a pH value above 4. The salts are soluble in water or org. solvents, and are used in amount 0.02 to 1.5 wt.% with respect to weight of solids of aminoplast. The salts may be zinc chloride or Al-salts in form of complex cpds. the complexants used may be NH3, pyridine dimethylformamide or formaldehyde. Moulding cycles are reduced to half the time normally required to obtain void-free mouldings.

Description

"Method for curing aminoplasts" is the subject of the present invention is a method to accelerate the hardening process in aminoplasts Addition of suitable hardening accelerators. Press manufactured with it; show crowds good flowability, even after prolonged storage.

Another area of application is the area of impregnation resins.

It is known that when acids are used as hardeners for aminoplasts, if the resin does not cure directly, the flow behavior of the resin produced molding compounds is strongly influenced. Even weakly dissociated acids already cause an undesirable decrease in fluidity during storage of the Molding compound. Acid salts and substances behave in an analogous manner; Solution acid is set free. With neutral reacting substances, too those with a strong dipole and with alkaline reacting substances will not cure quickly achieved.

The aim is now to use hard substances that are only respond as spontaneously as possible at press temperature and accelerate the hardening process without this during processing, during the drying process or during storage a noticeable one Weather hardening with deterioration in processing properties or the flow properties. It is also true in the production of molding compounds possible to add solid substances to the dried raw mass together with other additives a # work, from which substances are then set free at the curing temperature that are effective as harders. Most of the time, however, this process deteriorates the surface quality and a decrease in the mechanical properties of the Pressed parts connected.

It is therefore generally advantageous to use such hardening substances which either dissolve in the resin itself or are added to the resin as an aqueous solution can be. It is necessary that a certain pH range of the resin is achieved after adding the hardener. This is especially true for the production of molding compounds. If the pH falls below a certain value, this affects the flow behavior the molding compound produced with it and the shelf life is lost. If the upper limit is exceeded, the hardening speed decreases sharply, so that rapid hardening is no longer achieved.

There has now been a method of accelerating the hardening process of aminoplasts by adding hardening accelerators and subsequent processing and thermal curing found, which is characterized in that the Aminoplast resin as hardening accelerator from 0.02 to 1.5% by weight, based on the solids content of the resin, zinc or aluminum salts soluble in water or organic solvents non-reducing acids, which in 0.1N solution at 250 C have a pH of c 2.9 have added, the solution of the salts having a pH value> 4 got to.

The salts mentioned have a strong tendency to complex and react as Lewis acids nift aminoplasts while buffering the free acid, causing it is possible to set the required pH range. It is advantageous e.g. Add zinc nitrate and zinc sulfate as an aqueous solution to the medicine. Other salts e.g. zinc chloride or aluminum sulfate, are already too acidic in aqueous solution, but are in the form of their numerous complex compounds e.g. with ammonia, pyridine, Dimethylformamide, formaldehyde, etc.

Endless. The best effectiveness in terms of rapid curing can be achieved with zinc nitrate and zinc sulfate.

It is already known that zinc sulfite is used as a hardening accelerator for aminoplasts'. However, this salt has been used as a hardening accelerator for aminoplasts either incorporated as a solid substance into the dried molding compound or as a complex, e.g.

dissolved in ammonia, added to the resin. This zinc sulfite complex but results even with the known use of 1.8% by weight, based on the solids content of the resin, no rapid curing yet.

An increase in the curing rate when using the complex compounds However, this can be achieved again by adding zinc nitrate or zinc sulfate.

Aminoplasts in the context of the invention are urea and melamine resins, as well as their derivatives or homologs, which by polycondensation of urea, thiourea, Guanidine dicyandiamide, resp.

Melamine, ammeline, benzoguanamine etc. or their derivatives with formaldehyde, Paraformaldehyde or substances that have decomposed into formaldehyde, e.g. trioxane, or others aldehydes and ketones known as condensation components, e.g. acetaldehyde and Acetone can be obtained. This also includes mixed resins made from these Products, as well as mixtures or mixed resins of aminoplasts with phenolic resins.

The above resins can be used as fillers for further processing all suitable substances are considered, e.g. cellulose, ceilulose pulp, cellulose powder, regenerated cellulose, cellulose ester, cellulose ether, cotton, wood flour, sisal fiber, Plastic staple fiber, silicate fiber, glass fiber, asbestos, silica, talc, kaolin, Rock flour, etc. or pigments, e.g.

Zinc oxide, zinc sulfide, shear pat, titanium dioxide, chalk and other dyes.

The pH of the saline solution used as a hardening accelerator, which can be used in any concentration, but preferably 20 to 25%, must not be less than 4.

The processing time of the resin-hardener mixture should not be longer than 1 hour. Drying in a drying cabinet at approx. 8000 resp. drying in a hot air dryer at an initial temperature of approx. 800C, where the inlet temperature depends on the total amount of material to be dried is.

With urea resins, resins made from urea derivatives and homologues as well Corresponding mixed resins are concentrations of the curing accelerator of 0.2 up to 1.5% by weight based on the solids content of the resin used, preferably 0.5 to 0.7 wt.%, Required, with a pH range of the resin after the addition of the Cure accelerator of 6-7, preferably 6.4-6.6, gives.

For melamine resins, resins made from flelamine derivatives and homologues as Corresponding mixed resins are hardening accelerator concentrations of 0.02 Up to 0.5% by weight, based on the solids content of the resin used, preferably 0.05 to 0.2 wt.%, Required, with a pH range of the heart after addition of the curing accelerator of 7 - 8, preferably -7.2 --7.6 results.

The advantage of the molding compounds produced according to the invention is that that the press time, which is required for the production of bubble-free moldings, in comparison to molding compounds containing zinc sulfate as a hardening accelerator can be made to shorten by half. This is a rapid hardening and a shelf life of 6 months with good patency.

The mechanical and electrical properties of the invention The molding compounds produced corresponded to DIN regulations. For characterization the molding behavior of the molding compounds in relation to the hardening speed and fluidity, the following methods were used; 1. Determination of the curing rate At 155 ° C. and a pressure of 534 kpjcm2, the pressure increased by 15 seconds each time Pressing time, starting with 15 seconds, 10 pressed parts (cover plate 75-75, 2 mm) pressed and subjected to a color test. The urea resin molding compound served as a color ribbon an 18% strength by weight solution of Nigrosin NBL (Color Index 865) in water. The storage time of the samples in the initially boiling dye bath lasted 30 minutes. The more or less strong staining served as a measure of the hardening, for one Characteristic value series from 1 to 9 was determined empirically. Corresponds to the highest characteristic value strongest discoloration and lowest degree of hardening. The characteristic value for the untreated Sample was set at 1 for comparison. The melamine resin molding compound was the rhodamine color test applied. A 1% strength by weight solution of Rhodamine B (color index 749) in a 1% strength by weight sulfuric acid, boiling time 10 minutes.

2. Determination of the flowability in a commercially available "flow test" device the different molding compounds were tested under the same conditions. As a measure the flow length of the rods and the corresponding flow time were used for the flowability. Temperature 1560C, tablet weight

0.8 g, pressure 75 kp / cm Example 1 415 g of one produced in a known manner Urea-formaldehyde resin with a solid resin content of 40% by weight and a pH value of 8.5 are mixed with 6.83 cm3 of aqueous zinc nitrate solution, which by dissolving of 31.4 g Zn (NO3) 2. 6 H20 in water and make up to a volume of 100 cm3 will be produced. The resin-hardener mixture is immediately made with 130 g of pulp and 1.2 g zinc stearate dried in a drying cabinet at 800C. The fine grinding takes place in a ball mill with 4 wt.% Lithopone, based on the weight of the dry material, after which then 0.4 wt.% Zinc stearate, also based on the weight of the Dry goods, is incorporated.

Example 2 Analogously to Example 1, a molding compound is produced in the urea resin 6.83 cm3 aqueous zinc sulfate solution is added, which is carried out by Dissolve 35.6 g of ZnS04. 7 H2 ° in water and fill up to a volume of 100 cm3 is produced.

Example 3 Analogously to Example 1, a molding compound is produced in to which 13 cm3 solution of the hardening accelerator is added to the urea resin, the by dissolving 15 g of ZnCl2 in dimethylformamide and making up to volume of 100 cm3.

Example 4 Analogously to Example 1, a molding compound is produced in which first made the urea resin a crystal slurry of a prepared in a known manner Zinc sulfite complex hardener is added.

Such a mass is used as a comparison mass in Tables 1 and 2 and is listed there under No. 1. According to the invention, tin nitrate is then additionally used added as hardening accelerator.

Preparation of the amount by weight of crystal slurry required in Example 4: 3 g ZnSO3. 2 H20 are suspended in 5 g of water and mixed with 5 g of 25% by weight ammonia added and dissolved with warming (solution A). Solution B contains 1 g of hexamethylenetetramine, 5 g of water and 7 g of 30% strength by weight aqueous formaldehyde solution. Then becomes solution A stirred into solution B.

Addition of aqueous zinc nitrate solution: 4.88 cm3 of the hardening accelerator solution from example 1.

Example 5 Analogously to Example 1, 12.5 kg of moist raw material are produced.

First the material is placed in a drying cabinet at 800C for 1 hour (weight loss about 10) and then in a hot air dryer at an inlet temperature of approx. 115 0C and an initial temperature of approx. 800C. The manufacture of the The molding compound is carried out as in Example 1. This is followed by compaction at about 400C and grinding to machine grain.

A corresponding molding compound with a zinc sulfite complex hardener is used as a reference mass and is listed in Tables 1 and 2 under No. 2.

Table 1 Nigrosintest molding compound, bubble-free after sec. according to the characteristic value after seconds of pressing time Pressing time 15 30 45 60 90 Example 1 7.0 5.0 4.0 3.0 2.5 30 Example 2 8.5 6.0 5.0 4.0 2.5 30 Example 3 9.0 -6.5 5.0 4.0 3.0 45 Example 4 9.0 6.0 4.5 3.5 2.5 45 Comparative molding compound 9.0 8.0 6.5 5.0 3.0 60 number 1 (see example 4) Example 5 7.5 5.5 4.0 3.0 2.5 30 Comparative molding compound 9.0 7.0 5.0 3.5 2.5 45 No. 2 (see example 5) Table 2 Flow behavior of the molding compound: flow path (mm) Flow time (sec) Molding compound according to Outgoing hot storage Storage at room temperature value 5 days 40 ° 3 months 6 months mm sec mm sec mm sec mm sec Example 1 63 10 56 11 54 13 42 17 Example 2 66 8 63 11 63 9 30 20 Example 3 60 15 51 18 50 18 35 21 Example 4 58 15 53 17 50 20 47 22 Comparative molding compound 1 64 15 63 15 60 18 55 20 (see example 4) Example 5 64 8 55 11 62 12 45 15 Comparative molding compound 2 63 18 51 18 61 16 40 20 (see example 5) Example 6 460 b of a melamine-formaldehyde resin produced in a known manner with a solid resin content of 40% by weight and a pH of 9.6 are mixed with 1.54 cm 3 of aqueous zinc nitrate solution which is produced according to Example 1. The resin-hardener mixture is intimately mixed with 115 g of ellstoff in a kneader. The molding compound is produced in the same way as in Example 1.

The rate of hardening is determined by the rhodamine test.

Table 3 contains the characteristics of the color test of a molding compound without or with curing accelerator according to Example 6.

Table 3 Pressing time (sec) at 155 ° C 30 45 60 90 Characteristic value without hardening accelerator 8.5 8.0 4.5 2.0- according to Example 6 6.5 5.5 3.5 2.0 The curing accelerators according to the present invention can also be used in conjunction with known curing accelerators.

Claims (7)

Claims 1. Method for accelerating the hardening process of aminoplasts by adding hardening accelerators and subsequent processing and thermal curing, characterized in that one is used as a curing accelerator the aminoplast resin 0.02 to 1.5 wt.%, Based on the solid content of the resin, in Zinc or aluminum salts that are not soluble in water or organic solvents reducing acids that have a pH value of <2.9 in o, 1 N solution at 25 ° C, adds, the solution of the salts must have a pH value> 4. 2. The method according to claim 1, characterized in that one aqueous solution of zinc nitrate or zinc sulfate is used. 3. The method according to claim 1, characterized in that one zinc chloride and the aluminum salts are used in the form of their complex compounds. 4. Process according to Claims 1 and 3, characterized in that ammonia, pyridine, dimethylformamide or formaldehyde are used as complexing agents. 5. Process according to Claims 1 to 4, characterized in that When hardening urea resins, the hardener is used in a proportion of 0.2 to 1.5 % By weight, preferably 0.5 to 0.7% by weight, based on the solid content of the resin, is used, so that the resin has a pH of 6-7i, preferably 6.4 to 6.6. 6. The method according to claims 1 to 4, characterized in that that when curing melamine resins, the curing accelerator is used in one proportion from 0.02 to 0.5% by weight, preferably 0.05 to 0.2% by weight, based on the remainder of the resin, so that the resin has a pH of 7-8, preferably 7.2 - has 7.6. 7. The method according to claims 1 to 6, characterized in that known hardening accelerators are additionally used.