CS257130B1 - Polyethylene of low density for manufacturing pressure pipes with allowable stress great or equal to 3,2 mpa - Google Patents

Abstract

Low density polyethylene for pressure production tubes with permissible tension g 3.2 MPa, with a melt index of <0.6 g / 10 min, resistance against stress corrosion at least 400 h, by oxidation stable min., tensile strength at least 14 MPa and at least between the slip] 11 MPa, with a carbon black content of 2.0 to 2.5% by weight. and their distribution of the classification number podium a maximum of 13 and a maximum of 3 and a content antioxidant at most 0.3% by weight. on the the weight of the polymer

Description

257130 4

The invention of the gfl relates to low-density polyethylene for producing 3.2 MPa pressure pipes.

The so-called low density polyethylene used for the production of pressure pipes has not been known in the prior art. A disadvantage of these types of low density polyethylenes is that they can prepare pressure pipes with permissible tension up to 2.5 MPa, characterized by an acceptance test at a test voltage of 6.9 MPa and 20 ° C and a qualitative 100-hour test at a test voltage of 2.5 MPa. and 70 ° C, CSN 64 3041. The possibility of increasing the permissible tension of the pressure tubes using such low density polyethylene is limited by their physical and mechanical properties. Above all, it is a large dispersion of the melt index, the content of the additive, the unsuitable dispersion of carbon black characterized by the background and the classification number according to ČSN 64 3010, such as resistance to corrosion under tension in the environment of benzoactive substrates ČSN 64 0766, oxidation stability according to ČSN 64 3010, tensile strength at slip strength and honey at tensile strength at break.

These drawbacks are eliminated by the polyethylene low density for the production of pressure tubes with a permissible tension of - 3.2 MPa, the principle of which is that its tannin flow index is 0.6 g / 10 min. preferably 0.2 to 0.4 g / 10 min. density <0.94 g / cm3, corrosion resistance under intermediate benzoactive substances at least 400 h oxidation stability at least 40 min. according to CSN 64 3010, a tensile strength of at least 14 MPa and a tensile strength at the yield of at least 10.5 MPa, a carbon black content of 2.0 to 2.5% by weight. based on the polymer weight with the dispersion according to the classification number not more than 13 and at most 3 according to ČSN 64 3010 with a maximum content of 0.3% by weight. antioxidant. Base polymer with a melt flow index of 0.3 g / 10 min. is prepared by high-pressure polymerization of ethylene and blended with the black concentrate in a granular form periodically in a mixer chamber, using both kneading and mixing effects. The mixing cycle takes 10 to 20 minutes. with a piston pressure of 0.3 MPa, with the material temperature reaching up to 180 ° C. After mixing, the black composition is discharged into a hopper of the extruder, which is heated to 60-90 ° C, wherein the temperatures of the individual rollers from the hopper to the die are from 150 to 190 ° C and the nozzle is at a temperature of 150-165 ° C. of the polymer before the lance is 16 to 22 MPa, before the nozzle is 8 MPa. The extruded polymer strands are chopped into granules with a mower at 600 to 1000 rpm.

The granules are entrained by a stream of water on a de-centric dryer and thawed on a vibrating suture. Such a polymer is used for the production of tubes. The black concentrate is prepared in a mixer by mixing the base polymer with the seed and stabilizer so that the mixing temperature increases only slowly, with a high shear strain to achieve a fine soot dispersion. Black concentrate granulation is performed as in the preparative composition. The advantages are that the pressure tubes prepared from such a polymer have higher strength characteristics, which make it possible to reduce their wall ridge for the same operating pressures of the media to be conveyed, increasing their flow rate. A further advantage is the savings of polymer material in the production of 13% pressure pipes.

Low density polyethylene was prepared with a melt index of 0.6 g / 10 min. density 0.932 g / cm3, corrosion resistance of tension in the environment of benzoactive substances 300 h, oxidation stability 40 min., breaking tensile strength of 13.1 MPa, tensile strength between bars 10.1 MPa carbon black content 2.6% , a carbon black dispersion of background 4, a carbon black dispersion according to the classification number 14 and a content of 4, 4'-thiobis (2-tert-butyl-5-methylphenol) antioxidant of 0.2% by weight. weight of polymer. From this polymer, pipes of 25 mm / 3.5 mm were prepared by extrusion with a thread diameter of 0 32 mm. The prepared tubes were tested for resistance to internal pressure overpressure of 3.2 MPa. Taking the hour test at a permissible stress of 7.8 MPa and 20 ° C failed, the tubes were broken at 0.2 h; 0.25 h and 0.4 h. Qualitative 100-hour test at 2.9MPa and 70 ° G permissible strain, tubes failed at time 48, 84 and 75h. Example 2

Low density polyethylene was prepared with a melt flow index of 0.33 g / 10 min, a goose density of 0.931 g / cm 3, corrosion resistance of the tension in the benzoactive environment 432 h, oxidation stability of 58 min, tensile breaking strength of 15.93 MPa , a tensile strength between the slip of 11.2 MPa, a carbon black content of 2.2% by weight, a background dispersion of 2, a carbon black dispersion of the number 7 and the antioxidant 4,4'-thiobis (2- tert-butyl 5-methylphenol) 0.27 wt. to the weight of the polymer as follows. A base polymer was prepared with a melt index of 0.3 g / 10 min by high pressure polymerization of ethylene and blended with the black concentrate in the mixer chamber for 20 min. at a piston pressure of 0.3 MPa to a material temperature of 175 ° C. After mixing, the black composition was discharged from the extruder hopper heated to 80 degrees Celsius, with the individual belt temperature of the hopper to the nozzle 180.180, 190, 190 and the nozzle 165 ° C.

Claims (2)

Low density polyethylene for the production of pressure pipes with a permissible stress of 3.2 MPa resistant to stress corrosion and weathering, characterized in that its melt flow index is g0.6 g / 10 min, preferably 0.2 to 0 , 4 g / 10 min., Density <0.94 g / cm ³ , corrosion resistance under tension in the environment of tenzoactive substances is at least 400 h and oxidation stability at least 40 min., BACKGROUND OF THE INVENTION The tensile strength at break is at least 14 MPa and the yield strength at least 10.5 MPa, the carbon black content is 2.0 to 2.5 pens. wt. % by weight of the polymer having a dispersion according to the classification number of not more than 13 and a background of not more than 3 with a content of not more than 0.3% by weight; of an antioxidant to the weight of the polymer.