SU686627A3 - Method of producing linked polyolefins - Google Patents

Description

(54) METHOD FOR OBTAINING STILABLE POLYOLEFINES

The invention relates to a method for producing by grafting a silane compound, crosslinking invented thermoplastics, such as olefinic polymers or copolymers, olefinic elastomers or thermoplastic rubbers (TPR), which are mainly used for coating longitudinally worn material, such as electric cables and wires, pipes and etc. A known method of crosslinking organic polymers by grafting alkoxysilane compounds and digging in the presence of moisture 1, such as trimethoxyvinylsilane, tr ethoxyvinylsilane, grafted onto a micromolecule of a polyolefin. The grafting of these silane compounds occurs, for example, during the extrusion process under the influence of radical-forming compounds, mainly peroxides, and high temperature (160-250 C7. In this process, the silane, peroxide and target additives are mixed with the polyethylene granulate under conditions at which free radicals are formed. Thus, the surface coating of the polyolefin occurs, and then in the extruder the material is homogenized, and finally, the granulation of the pretreated material. A sample of polyolefin, which contains a crosslinking catalyst, and the material is fed to a molding on an extruder, for example, to coat electrical cables or wires. The disadvantage of this method is the use of conventional extrusion systems, which easily leads to local pre-crosslinking due to the inhomogeneous peroxide distribution. gel particles are particularly disadvantageous if the material is intended for electrical purposes, measures in the cable industry, where it is very important to obtain continuous Insulation for cables and wires that must meet certain electrical and mechanical requirements and, therefore, the quality of the extrudate is of paramount importance. The method is rather laborious, multistage. Storage of graft components, crosslinking under the influence of moisture, is limited. The extrudability of the material used significantly degrades, because the material has small traces of moisture, which leads to high costs, and a rough surface is formed, which leads to products subjected to electrical voltage, to the output of the system.

The purpose of the invention is to improve the quality of the extrudate.

The goal is achieved by the fact that in the known; in the process of producing cross-linking JX polyolefins by mixing them with alkene (Cr, -C5) -trialkoxy- (C) -silane and target additives followed by inoculation of the silane in an extruder at 1 ÷ 250s, mixing is carried out at 6O-10O C for 320 minutes in a mixer with a stirrer rotating speed of 500-3000 rpm.

Individual particles of powder, grits, granules or other loose polyolefin material are mixed and heated as a result of friction and / or additional heating from the outside. During this heating (or in front of it), the silane compound is added in liquid form to the temperatures below the melting region of the crystallite (60-100 ° C), as well as the necessary for grafting and additive, such as peroxides, for example, which activates the main material. At the end of the diffusion process, the mixture is cooled and the cooled material is poured into closed containers prior to grafting.

Before the grafting process, for example in an extruder, the crosslinking chemicals are homogeneously distributed in the granules or powder. The danger of peroxide pre-crosslinking according to the proposed method is small; the entire length of the extruder is provided for grafting, thereby achieving higher productivity.

Due to the exclusion of a special extruder for grafting and granulation, the proposed method is known. Homogenization employed materials such as silane, peroxide activators, for example, polyfunctional monomers such as triallyl cyanurate, divinylbenzene, etilendimetikrilat, triallylphosphite, etc., As well as condensation catalysts are dibutyl tin dilaurate or salts of heavy metals of long chain fatty acids should be virtually one pre-fabricated stage of manufacture, and it is possible to dry the base material of polyethylene or ethylene copolymer with other comonomers, such as ethylene vinyl acetate, butylene, etc., without large ones . This drying, for example, at 50-80 C,

significantly reduces the risk of pre-crosslinking and leads to an improvement in the quality of the npHJvieHHeMoro material. The diffusion of the silane, as well as the crosslinking chemicals, starts slowly at first, and at 70-90 seconds, the diffusion rate can be set rather high. Accordingly, the resulting reduced pressure in the system can be compensated for by supplying an inert gas. The diffusion process itself can be controlled by the current consumption of the mixing device, so that during the diffusion phase the current consumption increases due to the lower lubricating effect of the grain surface.

To main material together

Q with silane, peroxide, activatoria etc. Antioxidants can be added, especially those that have little effect on the course of a radical reaction, as a monomer, respectively

2 oligomer 2,2,4-trimethyldihydroquinone, and during radical reactions also as silane are grafted onto an olefin molecule, for example, stabilizers known under the trade names Apoh HB, Flectol H, Agerite

 Resin D. These antioxidant additives have a beneficial effect on the course of the grafting process, better oxidation stability is achieved, since they are more homogeneous distributed in the base material and grafted onto the molecules of the main material, do not evaporate.

If, after the end of the diffusion mixing process, the base material is cooled and packaged in closed vessels, the antioxidate should be kept separately and added to the base material only before grafting, since the peroxide

5 and antioxidants deactivate each other, respectively, interfere with their activity and thereby reduce the effectiveness of the vaccination, on the other hand, to obtain a perfect extrude, cable or tubular sheath, it is necessary to add the antioxidant during the inoculation, for example, in the form of an antioxidant dressing with 8% of antioxidant. Due to this, undesirable side reactions are excluded. E. Reactions, for example, peroxide premixing.

The storage time of the product is up to 10 weeks or more. Antioxidant dressing at the same time. May also contain a dye or crosslinking catalyst, which reduces the sensitivity to moisture during storage of the granulate. Dosing of the charge makes it possible to influence the quality of the melt, the viscosity and the degree of crosslinking. The homogeneous distribution of the silane and additives in the base material can be achieved due to the fact that individual particles of the bulk basic material are induced to move with a large amount of energy in the Le mix, which is a closed device and in which the agitator rotates at a high speed of 500-3000 rpm if the rotational speed of the bag is set so that the required temperature is reached by collision and friction of the flowable material. Due to the high velocity of the particles, the particles do not agglomerate. The molten surfaces of the base material lead to a further increase in the rate of diffusion of the crosslinking agent. Diffusion of additives can be carried out at a much lower mixing rate due to the fact that the mixer is heated, i.e. the temperature required for diffusion is established by external heat. It is advisable to use silane as a solvent for the remaining additives in the proposed process in liquid form. In this way, a solution of peroxides, a catalyst and an antioxidant in silane is obtained. This solution can be added to the circulating 1.1y at a high speed in the mixer of the base granule or powder or first, i.e. the material is still at room temperature or as soon as the temperature of the base material in the rapidly rotating mixer due to collisions and friction of the circulating particles increases to about 8 ° C. It is preferable to keep the base material in the mixer under vacuum and introduce the crosslinking agent into the vacuum space. If the crosslinking agent is added in a liquid state, it will evaporate and at the same time diffuse even more easily into the base material. The catalyst additive can be introduced in such a way that a polyolefin-catalyst charge is obtained in the mixer with a content of 0.5-10% by weight of the catalyst, preferably 1%, and the polyolefin granulate is mixed with the calculated amount of tin dibutyldylaurate. The additive of the obtained dressing is introduced either directly into the extruder or into a high-speed mixer after the silane-peroxide mixture is completely diffused. in the main material. By this method, close contact between the catalyst and silane is excluded, which further has a positive effect on the processability and the degree of final crosslinking. High molecular weight polyethylene with a melt index of 2 is preferably used as the base material. This reduces the amount of silane in the peroxide and, moreover, in the manufacture of stitched shells (coatings), the danger of eccentric movement of the wire as well as insulation runoff is avoided. temperatures of about 220 ° C. With low melt viscosity, decomposition products resulting from the decomposition of peroxide are easy; may cause blistering. In this regard, it is advisable to inject as little peroxide as possible and use 1,3-bis- (tert-butylperoxyisopropyl) -benzene as a material. The amount of peroxide can be further reduced if a semi-functional monomer is added to the Base Material. In this way, the yield of radicals can be increased and the formation of decomposition products is limited to a minimum. It is also advantageous to add substances to the base material that act as a trap for methyl radicals without reducing the total yield of radicals. Highly condensed aromatic compounds are suitable for this. Additives to the base material based on ethylene-propylene rubbers, for example in the amount of 5-20 hours, can increase the melt viscosity, so that the risk of bubbles in the extruded material is further reduced. There are a number of organosilanes with unsaturated organic substituents, which are a prerequisite for grafting silane onto the base material molecules. But the measure for the crosslinking rate in the presence of water and in the absence or presence of a catalyst is the sensitivity to hydrolysis of the functional groups, i.e. their transformation into silanogroups. It is known that vinyltriacetoxysilane is experiencing a particularly rapid, this transformation, i.e. already in the presence of traces of HgO. With this high rate of hydrolysis, it is possible to achieve crosslinking at an acceptable rate also without a catalyst and in water. In the known methods for crosslinking organic polymers with a grafted cilane for initiation, it is recommended in the process of grafting peroxide or other radical-forming substances. Most peroxides, especially dicumyl peroxide (DCT), have a high crosslinking efficiency, i.e. C-Cc-ccc vaccination does not prevail. Therefore, processing in this case is difficult. According to this tricinum in the proposed method, it is advisable to be gripped to initiate the process of grafting peroxide with low efficiency of crosslinking, for example, peroxide of esters. These peroxides, for example, tert-butyl per-2-ethylhexa- nate or also tert-butyl perbenzoate, when thermally produced, give radicals that show only a small crosslinking efficiency, but can still occur in the process of crosslinking. Especially suitable is a tert-butyl peroxy isononate, which is added in an amount of 0.05-0.5% by weight, calculated on the main polymer. Peroxide mixtures, for example, a mixture of 1,8-bis- (tert-butylperoxyisopropyl) -benzene and tert-butylperoxy-isonanate, are used as initiators for crosslinking. When silane is grafted, for example, on polyethylene macromolecules, a relatively strong drop in the melt index occurs, i.e. due to the grafting process, the current properties of the polyethylene melt are deteriorated, but extrudability is often sufficient just after the grafting process. The strong drop in the melt index hinders the free mobility of polyethylene macromolecules, since the melt relaxation ability after molding is limited, especially under extrusion conditions that lead to a significant orientation of the macromolecules. It is necessary for the melt index to be reduced by grafting. Slightly. This is achieved by using small amounts of low molecular weight polyethylene, an extruder head with a small orientation and a choice of suitable extrusion conditions, such as high output mass and a slight stretching of the tube. Pre-heated wire and staged cooling are also used. The rate of crosslinking of the obtained materials depends on the amount of catalyst and water temperature, while the maximum degree of crosslinking is determined solely by the amount of grafted silane, the distribution of silane addition. There are precisely small traces to activate the stitching. So, it is not consumed completely, but is supplied during silanol condensation reactions, the resulting product, such as an electrical cable or wire, or a wire coated with the proposed material is not left in the WATER bath to achieve the Final degree of crosslinking, and after a short period contact with water (only 10 min.) it can be wound on a drum. Then the required degree of cross-linking for such projects is established on its own over time. With known words, the extrusion time in the cooling trays before winding is sufficient to activate the siloxane crosslinking mechanism. If crosslinking of the material after rolling onto the drum occurs in a water bath, in order to improve the crosslinking capacity of the liquid containing the catalyst and to prevent the occurrence of dry spots on the inner windings, it is advisable to add a wetting agent to the water to reduce surface tension. However, with this method of introducing the liquid required for crosslinking, it is not possible to control the amount to be introduced by diffusion of the liquid. Water or liquids that split protons are used as moisture. Preferably, crosslinking is carried out with water-based additives, the water that is chemically or physically bound being split off at elevated temperatures. In this way, the amount of aoda required for crosslinking can be accurately measured. By taking into account the number of crosslinking sites in the thermoplastic material, as well as the stoichiometric conversion factors, it is possible to determine the required amount of water splitting additives relatively accurately. Depending on the molecular weight of the water-splitting substance, it is preferable to add 0.05-5.0 parts, based on 100 parts of the main polymer, water-containing additives. This is possible because during the crosslinking process, which is a chemical condensation reaction of silanol groups, one molecule can form at each crosslinking site, which can cause a new crosslinking reaction, so that only catalytic amounts are necessary. high temperatures: about, after the end of the vaccination process. It is also possible to add water-splitting additives with a catalyst to the graft polymer. Inorganic compounds containing hydrated water substances, such as alumina hydrates, gypsum, etc., are used as water splitting agents. Organic materials are also known which, at certain temperatures, detach water, for example, cyclohexanedione hemihydrate, as well as structurally aneshogic compounds or also short-chain polyvini, fine alcohols, such as oligomers of vinyl alcohol or α-hydroxycarboxylic acids, y-hydroxycarboxylic acids and derivatives of these acids. Any condensation reaction can also be carried out in the process, where a third inert substance C and water are formed from the two substances A and B during a chemical reaction, and the substance c does not affect the crosslinking or the properties of the extrudate. Free fatty acids and their metal salts are simultaneously crosslinking catalysts and catalysts for water splitting at certain temperatures.

Water-containing substances do not affect extrusion. The extrusion temperature is chosen so that dehydration is directly achieved. In this way, during the chemical reaction, water arises inside the mixture and the crosslinking reaction proceeds under the influence of the added catalysts. Therefore, the HgO method is in the extrudate evenly distributed in the molecular dispersed form, so that uniform cross-linking is achieved, which is important for the electrical and mechanical properties of the cable. If there are no catalysts in the mixture, then the crosslinking under the influence of the released water occurs more slowly. Without a catalyst, crosslinking lasts about 10 to 20 times longer than with a catalyst, the time to complete crosslinking is 30-80 hours. The stitching inside the cable is completed before the cable is inspected or dispensed. The maximum degree of crosslinking does not depend on the catalyst, which determines only the rate of crosslinking, nor on the amount of water liberated in the cable, but solely on the amount of silane grafted.

As mentioned above, hydroxycarboxylic acids can be used as water splitting materials. The removal of water from the α-hydroxycarboxylic acid derivatives gives rise to acrylic acid derivatives, which are related in structure with known crosslinking activators from a number of methacrylic acid esters. At the same time, along with the possibility of introducing precisely dosed quantities of water necessary for the crosslinking process, it is possible at the same time to obtain an activator of sashvka, to save peroxide.

Example 1. Use the following components, wt.%:

Polyethylene100

2,2,4-trimethyldihydroquinolin 0, 4

Tert-butyl peroxy isononanO 2

1,3-Bis- (tert-butylperoxyisopropyl) -benzene0.02

Vinyltrimethoxysilane 2,6 Triallyl cyanurate 0.1 1% -filling (tin dibutyl dialylurinate in polyethylene) 5.0

5 In a heating mixer, at 1700 rpm, 14.25 kg of polyethylene are mixed with the appropriate amount of vinyltrimethyloxysilane in which all the additives have been dissolved, with the exception of tin-dibutyldyl uurinate and 2,2,4-trimethyl-dihydroquinoline. Upon reaching a material temperature of 95 ° C, the material is fed into a water-cooled mixer at a speed of 650 rpm. When 750 g of 1% refilling is introduced and the resulting product is packaged in plastic bags.

A 1% dressing of dibutyl dilaurinate tin is obtained by mixing in a mixer 14.850 kg of a polyethylene pellet o O, 150 kg of dibutyl dilaurinate tin at 1700 rpm for

2-5 min. Tin dibutyldilurinate diffuses very quickly into polyethylene, so that after about 5 minutes it can be cooled with water during throttling at 650 rpm. The catalyst charge is in the form of a granular granulate.

To increase the storage capacity of the mixed material, 2,2,4-trimethyldihydroquinoline (antioxidant)

stored separately in the form of a 5% refill with 8% antioxidant in a special container. An antioxidant is added before grafting, so that it contains 0.4% in the finished product.

Ready granulate with metered

catalyst and antioxidant refills are extruded from an extruder with the following temperatures, (° С) by zones

2180

3210

4230 Head 230 Mouthpiece 230

The mass temperature is

220 ° C, residence time 2.5 minutes at 25 rpm. In a smooth extrusion according to ASTM D 1238-57 T, a melt index of 0.5 g / 10 min was measured. The degree of crosslinking according to IEC extraction solvent was 70% after 2 hours of crosslinking in water at 100 ° C.

PRI mme R 2. Use the following components, Bes.%:

Polyethylene100

2,2,4-trimethyldihydroquinolin 0, 4

Tert-butyl peroxy isononate 0, 12