RU2094128C1 - Apparatus for continuous electrostatic cleaning of low-molecular polydimethylsiloxane rubber and method of cleaning - Google Patents

Abstract

FIELD: rubber industry. SUBSTANCE: apparatus for cleaning silica-stabilized polydimethylsiloxane rubber from ionic and suspended impurities contains negative and positive electrodes in the form of coaxially arranged metal pipes, positive electrode acting part of casing and negative electrode having on its surface a dielectric structure in the form of film-electrocarton corrugation. Rubber is cleaned by passing it through nonuniform electrostatic field between the two electrodes. Rubber to be cleaned is fed from below upward between outer positive electrode and film-electrocarton corrugation covering negative electrode, while concentrate moves over corrugation downward forming paste-like deposit. EFFECT: enhanced efficiency of cleaning process. 2 cl, 2 dwg , 1 tbl

Description

 The invention relates to devices, equipment and method for purification of liquid low molecular weight polydimethylsiloxane rubber stabilized with silica, and can be used in the synthetic rubber industry, and purified rubber is used in a number of intensively developing fields of technology: microelectronics, radio electronics, optics, fiber optics, medicine.

 Known is an electric dielectric fluid cleaner, including a housing and precipitation electrodes made in the form of round metal plates with slots, some of which form channels for the passage of liquid, while others are provided with partitions for dielectric material, and the electrodes and partitions form pollution accumulator cells (ed. St. USSR N 691199, class B 03 C 5/00).

 The disadvantage of the cleaner is the design complexity. A known method of purification of highly concentrated viscous dielectric liquids from fine impurities by pumping it through an electrostatic field between the negative and positive electrodes and at the same time pumping immiscible with the buffer buffer dielectric fluid with a lower viscosity and its subsequent filtration over the liquid being cleaned (ed. St. USSR N 994012, class . B 03 C 5/00).

 This method is also difficult to use and in the selection of a buffer fluid with a certain viscosity and dielectric constant.

The technology for producing low molecular weight polydimethylsiloxane rubbers SKTN (GOST 13835-73) provides for the use of caustic potassium KOH as a catalyst for the polymerization of a mixture of dimethylcyclosiloxanes, and finely dispersed silica in an amount of up to 0.5% (aerosil or white carbon black U-333) is used to deactivate the catalyst rubber acquires opalescence or turbidity and contains a significant amount of ionic impurities of alkali metals (the content of sodium and potassium is 10 ^-2 10 ^-3 %). The insufficient degree of purity of SKTN industrial rubber makes it difficult to use in electronics, lighting, and medicine.

A known method of purification (clarification) of liquid silicone rubber, selected as a prototype, which consists in treating the polymer with a chemical compound having a higher surface activity and not miscible with the polymer, in particular hydroxyorganofluorosiloxane, to form an emulsion followed by separation of the layers (ed. St. USSR N 1367414.cl. C 08 C 3/02 chipboard dated 15.9.87.). The method can significantly increase the degree of purity of the rubber: the transmittance is 99-100% of the content of ionic impurities of sodium and potassium 10 ^-4 10 ^-5 % The disadvantage of this method of cleaning rubber SKTN is low productivity, the complexity of the process technology. This limits its use only to laboratory practice.

 The aim of the invention is to simplify the technology of continuous cleaning of low molecular weight polydimethylsiloxane rubber and to increase the productivity of the process and the degree of purity.

 The goal is achieved by the fact that the authors developed a device for continuous electrostatic cleaning of low molecular weight polydimethylsiloxane rubber from ionic and mechanical impurities, containing negative and positive electrodes made in the form of coaxially arranged metal pipes, with the positive electrode acting as a body and a surface-developed electrode installed on the negative electrode dielectric structure of film-cardboard.

 The method for cleaning low molecular weight polydimethyloxane rubber involves passing it through an electrostatic inhomogeneous field between the negative and positive electrodes, the rubber being cleaned is fed upward between the external positive electrode and the corrugation from the film-electrocardboard by stringing it on the negative electrode, and the impurity concentrate moves down the corrugation, forming a paste-like precipitate.

 In FIG. 1 shows a device for continuous electrostatic cleaning of low molecular weight polydimethylsiloxane rubber (electrostatic separation unit).

The device contains coaxially arranged stainless steel metal pipes, which are:
1. central negative electrode;
2. external positive electrode;
3. dielectric sedimentation structure in the form of corrugation made of film electrocardboard.

 The essence of the method lies in the fact that when a strong inhomogeneous electric field (voltage at the electrodes of 20-30 kV) is applied to the finely dispersed suspension, the particles contained in the liquid are polarized, forming electric dipoles. An external field brings the particles into motion-electrophoresis. Electrophoretic movement of particles of the same name in one direction leads to their accumulation at one of the electrodes, whereby favorable conditions for coagulation are created.

 On the central negative electrode 1. i.e. in the zone of high field strength, a dielectric structure made of film-electric cardboard is developed over the surface.

 Film-electrocardboard, manufactured according to TU 16.803.138-80, is a composite material based on electrical insulation board of the EPV brand, bonded with PET-E polyethylene terephthalate film. In the proposed device used film-electric cardboard with a thickness of 0.3 mm

 The rubber being cleaned is fed from the bottom up through the gap between the external positive electrode and the corrugation. Particles of impurities, as the fluid moves through the system, migrate to the central negative electrode 1 and concentrate in the corrugation, forming a concentrate in it in the form of a suspension, the density of which is higher than the density of the purified rubber. The concentrate easily moves along the corrugation made of film-electric cardboard down, nevertheless being kept close to it due to the forces of the electric field and therefore not mixing with the rubber being cleaned. The concentrate flowing down from the corrugation is collected in the lower part of the element, where, due to the increasing concentration of dispersed particles in it, they coagulate with the formation of a pasty precipitate, which still has sufficient fluidity to remove.

 Thus, a certain electrohydrodynamic regime is established in the element, in which continuous regeneration of the sedimentary corrugation occurs.

 Technologically, the installation for cleaning low molecular weight polydimethylsiloxane rubber (SKTN) includes two units: an electrostatic separation unit (BER) and a power and control unit (BPU).

BER is the main part of the installation and is intended for rubber cleaning according to the stated principle of the developed device. The set capacity of the installation (10 t / g of refined rubber) determined the need for assembling the BER from 6 similar elements connected in parallel with removable end caps (flanges) equipped with valves. On the flanges there are input elements for a high voltage cable and a cable for a measuring and locking device. For better periodic release of the precipitation structure of the plant from retained contaminants, it is possible to tilt the BER at an angle of 45 ^o relative to the vertical axis.

 The control unit provides power to the unit with high rectified voltage (up to 30 kV), express control of the degree of cleaning of rubber SKTN, as well as the necessary blocking of the unit's high-voltage circuits in emergency situations.

 In FIG. 2 shows a diagram of an installation for cleaning rubber SKTN. The rubber from the tank 1 is pumped into the collection vessel 3 using the gear pump 2. When the valve 7 is opened, the BER 4 active zone is filled with rubber, and then the valve 7 is closed. The power supply unit 5 is turned on and the voltage on the electrodes is set to (20-25) kV. The rubber is held in the BER core for 1 hour. Then, the valve 8 is opened to discharge the cleaned rubber into the collection 6. The first portions of the cleaned rubber are discarded and combined with the original. The purity of the purified products is controlled using a pointer device BPU. As the purified rubber exits the apparatus, the collection 3 is periodically replenished with the original rubber. Using a tap 9, the impurity concentrate is drained into a collection tank.

 The table shows the results of the cleaning of a number of batches of rubber SKTN grade B, obtained from the Kazan plant of synthetic rubber. The light transmittance of rubber before and after purification was determined by an SF-26 spectrophotometer at a wavelength of 546 mm and a layer thickness in the cell of 10 mm with respect to the comparison cell with distilled water. The content of sodium and potassium impurities in the rubber was determined by atomic emission analysis at 100-fold enrichment.

As can be seen from the data in the table, the cleaning method of rubber SKTN brand B using a device for continuous cleaning can increase the transmittance from 17.5-51% to 99-100% and reduce the content of ionic impurities of sodium and potassium from 10 ^-2 -10 ^-3 % to (1-8) • 10 ^-5 % The yield of purified rubber is 95-98%
The installation for cleaning rubber is compact (size 1.5 x 1.5 x 4.0) m, easy to operate, allows continuous cleaning and provides high performance cleaning process (10 t / g or more of purified rubber). In addition, you can increase the productivity of the installation by increasing the number of elements in the BER to 20 pcs. The cleaning process at the installation is environmentally friendly, the waste during cleaning, which is rubber with a high content of silicon dioxide, can be used as the basis for casting compounds of the KTZ type (NUO.037.016.TU).

Claims (2)

 1. A device for continuous electrostatic cleaning of low molecular weight polydimethylsiloxane rubber from ionic and mechanical impurities, containing negative and positive electrodes forming an electric field, characterized in that the electrodes are made in the form of coaxially arranged metal pipes, the positive electrode being made in the form of a housing, and on the negative The electrode has a surface-developed dielectric structure in the form of a corrugation made of film-electric cardboard.  2. The method of continuous cleaning of low molecular weight polydimethylsiloxane rubber from ionic and mechanical impurities by passing it through an electrostatic field between the negative and positive electrodes, characterized in that the electrostatic field is inhomogeneous, the rubber being cleaned is fed from the bottom up between the external positive electrode and corrugation made of film-electrocardboard strung onto the negative electrode, and the impurity concentrate is moved down the corrugation and removed from the housing.

Images