SU57440A1 - The method of obtaining cast urea-formaldehyde artificial resin - Google Patents

Description

The manufacture of molded urea-formaldehyde products for handicraft haberdashery products (buttons), brooches, bracelets, clothing, etc., is known, although it has not yet achieved a wide production scale. The known methods of making such products are mainly as follows.

Urea and formaldehyde are condensed to form a gummy product. The obtained resin is subjected to deep dehydration by packing under vacuum. The viscous, dehydrated product is poured into molds and subjected to prolonged (up to several weeks) careful heating, during which the product is polished, acquiring a hardness that allows it to be machined. .

The most difficult point in this process is dehydration, since the urea-formaldehyde resin cheese is a colloidal solution of UNIFIED substances in water, which is very difficult to remove without causing premature gelatinization.

The second no less difficult point in the process described is the curing of cast urea-formaldehyde products, since this requires careful observance of the temperature and uniform heating. Otherwise, the product cracks, bubbles form or, in case of insufficient dehydration, the product becomes cloudy.

It was found that if you go the way opposite to that described, that is, to strengthen the process of gelatinization (syneresis), you can also get cast products that are suitable for the crafts of various haberdashery, optical glasses, etc.

It was possible to carry out the process according to the following scheme:

1. Condensation of urea and formaldehyde in the presence of catalysts that promote the formation of methylol or methylene derivatives of urea at the beginning of the reaction and ultimately giving resinous products capable of rapid polymerization and syneresis.

2. Filling in the form of the obtained resin (in the form of a colloidal solution of resinous products in water).

3. Exposure in closed forms at a temperature of 30-40 ° for 3-10 days (depending on the temperature of exposure, the depth of condensation, as well as the volume of the fill).

4. Removal of hardened and separated water, as a result of syneresis, of the product and drying it in air for 2-5 days (depending on the size).

5. Drying at 35-40 ° for 5-10 days (depending on size).

6. Gradual warming of the dried clear product at 70-80 ° for 6-24 hours and slow cooling to relieve tension.

The whole process (both syneresis and drying) can be carried out entirely at normal temperature, but this takes a lot of time and the product, although it reaches the final specific gravity and becomes completely transparent, but does not have sufficient hardness and water resistance.

It is established that if the process of syneresis is carried out at an elevated temperature (45-55 °) for 3.5-8 days, then products with a low specific gravity are formed opaque or with opaque vein inclusions.

To give the product an opal surface, add to the liquid product before pouring into the molds insignificant amounts of milk (tenths of a percent).

Example. 100 weight. including crystalline urea is dissolved in 200 weight. including formalin (35%), 7.66 weight. including hexamine dissolved in 30 wt. including formalin (35%). Both solutions are mixed and 1.25-2.5. "./G of zinc chloride (50% aqueous solution) is added. The solution is heated to reflux.

At 75-80 ° a white voluminous precipitate of urea methylol is formed, which dissolves with further heating. Boiling is maintained for

10-15 minutes until the precipitate completely dissolves, followed by rapid cooling. The cooled product, which is a viscous, clear, colorless solution (which is colored if necessary), is poured into molds with tightly closed, imis stoppers to avoid premature evaporation of water. The dynamics of Ph change in the resin manufacturing process is as follows: the mixture before injection of zinc chloride has a Ph of 7.5-8.5, after the introduction of zinc chloride Ph -5-5.5 and after the end of condensation Ph 4.0-4.8.

The molded product is placed in a chamber with a temperature of 35-40. After 10-24 hours, the product gelates and represents a jelly-like, slightly cloudy mass. After the next 20-25 hours, the product becomes very cloudy and begins to separate the water. After the next 40–0 hours, the product already separates the water strongly and there is a noticeable large shrinkage. By this time, the amount of separated water is 15-20% of the weight of the fill, which indicates the end of the process in sealed forms.

Water is drained (Ph water 3.2-3.5), the product is easily removed from the mold and dried in air at room temperature. During air drying, the product shrinks dramatically, loses weight (by 35-40% compared to the weight of the fill) and gradually changes from transparent to dairy; hardness increases dramatically. Air drying lasts until the product reaches a specific weight that remains almost unchanged for -1.5 days. This specific gravity is in the range of 1.35-1.38. Duration of drying in air for 3-8 days (depending on thickness). At the end of air drying, the product is transferred to a chamber with a temperature of 35-40 °, where it becomes completely transparent, reaches a specific gravity of 1.41 and has a hardness sufficient for mechanical processing. To speed up the process of syneresis to the resins before pouring can be

various accelerators of gelatinization and syneresis were added, and partial dehydration of the resin by refluxing with molds can also be used.

To speed up the drying, it can be carried out on water-removing agents (sulfuric acid, phosphoric anhydride, calcium chloride, etc.). To facilitate the drying of larger castings, as well as to accelerate it, drying can be carried out in an environment of plasticizers, softened, their surface of the hardened product (glycerin, triacetin, etc.).

The subject matter of the invention.

Claims (2)

1. A method of producing molten urea-formaldehyde artificial resins, without using a vacuum drying method, by using gelatinization from aqueous emulsions of resinous products obtained from the reaction mixture through methylol and methylene derivatives of urea, characterized in that the resin is poured into molds and kept in the latter in the closed state for several days at a temperature of 30-40 ° in order to carry out the processes of gelatinization and syneresis, after which the separated water is drained and the resin is removed from the molds and dried by known methods. 2. Modification of the method according to claim 1, characterized in that, in order to obtain opaque or with separate veins of cast resins, the latter are kept in molds from 3.5 to 8 days at a temperature of 44 degrees.