SU470967A3 - The method of obtaining products from foam - Google Patents

Description

(54) METHOD OF OBTAINING PRODUCTS FROM FOAMS

new or electronic. The most suitable are electron beams, the dose of which is 2.5-60 Mrad, preferably 40-50 Mrad.

In addition to polymer granules, flame retardant additives, colorants, fillers, lubricants or other polymers may be included in the composition for the manufacture of foam products, and polyisobutylene may also be used in the formulation.

Heating of the pre-foamed granules is carried out in a closed form. In this form, they are designed so that, when heated, a gaseous or liquid substance, such as air or water, may come out of them.

The most advantageous method is to use perforated walls or those in which nozzles with small holes are inserted in the walls, through which the heating medium can enter the mold and air can escape from the mold.

You can get a molded product without applying pressure, but you get low-quality products.

But to the proposed method, molded foam products are obtained by compressing in the form of pre-foamed granules of olefin polymers, some of the molecules of which have a reticular structure, 5-70% of their initial volume before, during or after heating. In this case, at least one wall of the form must be movable.

It is most advisable that the expanded granules be first heated and then compressed.

Especially good products are obtained if the granules are compressed from two sides of the mold to the center of the hollow space of the mold.

However, it is possible to compress the granules from several sides, first from two sides and then from the bottom or top of the form.

When compressed, the granules deform to such an extent that polyhedrons are formed, which fuse the surface.

The pre-foamed granules are heated in a mold to a temperature at which they are sintered. This temperature depends on the chemical structure of the polymer, the degree of formation of molecules with a network structure and additives.

It is most advantageous to heat the granules to a temperature at which at least 25% of the components that are at a comet temperature (25 ° C) in a crystalline state melt at approximately 90–140 ° C.

Hot gases, vapors or liquids are used as the heating medium. Good results are obtained if forms filled with expanded granules are immersed in a liquid in which the polymer does not dissolve, for example, water, glycerin or aqueous saline solutions.

The simplest method is to introduce hot steam into the mold as a heating medium.

In addition, the expanded granules are heated in forms using infrared rays or chickens to blow hot air.

Insignificant amounts of a substance having high dielectric noterium, for example, water or an aqueous saline solution, are sometimes added to the granules, and when this substance is introduced into the form, it is heated in a high frequency field. It is advisable to enter the heating medium through one side surface of the form and remove it through the opposite one.

For the manufacture of molded products

complex configuration sometimes heating

the medium is introduced into the form from several sides and

output from one side, for example through the bottom

forms.

In the case of a continuous process, the heating medium is circulated through the mold. Heating can also be stopped; it can also be done with probes or perforated pipes embedded between the foam granules so that heating is also carried out inside the mold. Such heating is applied in the case of large molded articles.

Probes are removed before squeezing the pellets.

During sintering, the product is cooled to a temperature below the melting point of the crystals, preferably below 40 ° C.

Items obtained after removal from

forms can be heated again so that

they foam even more

get a product with a lower bulk density.

It is also possible to crush the molded articles and heat the resulting particles again under pressure in the mold.

But the proposed method is used to obtain other products from foams based on polymers of olefins, a bulk weight of 15-30 kg / m-, which was not possible when they were obtained using known synthetic methods. These products have a particularly high elasticity and a slight deformation during compression.

Manufactured according to the proposed method, psioplasts can be used in various consumption areas: for upholstery, packaging, thermal and acoustic insulation in construction, for the manufacture of floats and toys.

For example 1. Pre-foamed granules with a diameter of 20 mm and a bulk weight of 16 g / l of a copolymer consisting of 83 wt. % ethylene and 17 wt. % tert, butyl ester of acrylic acid is subjected to irradiation with a dose of 60 Mrad in an electron accelerator. After this, the proportion of the molecules of the network structure is 84%. These granules are laminated into a non-perforated metal mold, which is closed and one wall of which is mobile, and is compressed to approximately 50% of the original volume. The closed mold is immersed for 10 minutes in water heated to. They get sploppy, homogeneous, very

elastic and highly elastic, capable of stretching penollasts with a bulk weight of 32 g / l. Such a molded product can be used as an upholstery material.

If a copolymer consisting of 90 wt.% Is used as the copolymer. % copolymer described at the beginning of example 1, and 10 weight. % polyisobutylene with mol. weighing 150,000, a particularly resilient fine cell foam is obtained under similar conditions of irradiation and processing.

Example 2. A copolymer consisting of 80 wt. % ethylene and 20 wt. % of vinyl acetate is mixed under pressure heating with a low-boiling hydrocarbon mixture. The hot mixture is squeezed through a pinless nozzle and crushed.

After grinding, foamed granules with a bulk weight of 35 g / l and a diameter of 10 mm are obtained. These granules are subjected to electron irradiation with a dose of 50 Mrad and receive granules in which the polymer has 68-70 weight. % of the molecules of the network structure.

The granules are placed in a metallic form having perforated walls, which is then closed. The form is heated for 30 minutes in a steam autoclave to 125 ° C. The granules are then compressed to 30% of the original volume and cooled in this state.

A solid, partially breathable foam with very good mechanical and elastic properties is obtained, which is suitable, for example, as a shock absorbing material for packaging or as an insulating material.

If the granules compress only 5% of the original volume, then a product is obtained in which the granules are sintered over a relatively small surface area.

Example 3. Pre-foamed foam granules obtained from a copolymer consisting of 75 wt. % ethylene and 25 wt. % n-butyl ester of acrylic acid with a diameter of 10-15 mm, and a bulk weight of 21 g / l is subjected to x-ray irradiation until part of the polymer molecules having a network structure reaches a value of 75 weight. % The granules treated in this way are placed in a metal mold having openings through which steam enters the mold for 2 minutes under a pressure of 0.5 MPa. Then, the foamed granules are compressed to 50% of the original volume and, in this form, cooled for 15 minutes at room temperature. A solid, elastic, homogeneous foam product with a bulk weight of 42 g / l is obtained.

Example 4. Pre-foamed granules of a mixture consisting of 60 wt. % polypropylene and 40 wt. The% poly (n-butobutylene) with a molecular weight of 150000, with a diameter of 5-8 mm, the bulk density of which is 13.9 g / l, is subjected to electron irradiation with a dose of 40 Mrad. Thereafter, the cell walls of the granules consist of a polymer, in which a part of the molecules with a reticular structure is 52 wt. %

The granules are placed in a perforated metal mold in which polytetrafluoroethylene fabric is embedded and placed in it for 120 mpn at 150 ° C, created by hot air.

Then the granules are compressed in such a way that their volume decreases by 40% from

original bulk volume. A homogeneous molded article is obtained, having a volume weight of 35 g / l, closed cells, and which can be used as an insulating material, for example, to insulate liquid vessels that are heated to 120 ° C.

Example 5. Pre-foamed granules with closed polyethylene cells. (specific gravity 0.928, melt index

0.1-0.3) 5-10 mm in size, having a bulk density of 17.2 g / l and consisting of a polymer in which 50% of the molecules have a network structure, are placed in a metal mold with holes lined perforated, made from polytetrafluoroethylene plates, n incubated for 10 minutes at, created by hot air. Then the granules are compressed to half the original bulk volume.

A foam is obtained with a volume weight of 34.4 g / l with properties that are typical of an elastic foam, namely, high compressibility, good elasticity, and high elasticity of rebound.

This foam can be used for insulating, sealing, for example, for making floats, gaskets, and upholstery materials, as pzol is a solid material in refrigeration engineering and construction.

Example 6. A metal form consisting of hexagonal perforated restrictive surfaces, 60X60X XO cm in size, is filled with foamed granules with an average diameter of 8-15 mm and saturated

weighing 17 g / l.

Granules are obtained in the following mixture: 78 wt. % copolymer consisting of 77.2 wt. % ethpl n 22.8% tert, butyl ester of acrylic acid; 19 wt. % polyisobutylene with mol. weighing 150,000 and 3 weight. % talc.

Mesh molecules make up 85% of the total polymer molecules that make up the granules.

In the form of the upper and lower bounding surfaces, they can be moved (can move to the middle of the form).

The top plate of the form is connected to the housing through which water can be introduced,

then entering through the holes in the plats into the internal hollow space of the mold.

In the course of 5 minutes, water heated to 92 ° C is introduced into the internal space of the mold through the upper plft. Water after

as she moistens the granules, comes out through the side