Method for producing ready-to-use soft PVC films or profiles

Abstract

The extrusion of polymer compositions based on polyvinyl chloride (PVC) and in particular to a method in which polymer compositions are produced that have an elongation at break of at least 200%, a tensile strength of at least 10 N/mm2 with a specific energy input SEI of 0.03 to 0.20 kWh/kg and in particular 0.04 to 0.16 kWh/kg. The method is expediently carried out such that a plasticizer is added in a plurality of portions to the non-composed polyvinyl chloride and mixed into said polyvinyl chloride. The method thereby offers a fast and simple possibility of producing products from finished soft PVC, the production of said products requiring only a single processing device in the form of an extruder.

Claims

1. A method for extruding a homogeneous polymer composition, which has a degree of gelation of 60% to 100%, an elongation at break of at least 200%, and a tensile strength of at least 10 N/mm.sup.2, from an uncompounded polyvinyl chloride, wherein the quantity of energy introduced into the polymer composition within the method, as indicated by the specific energy input (SEI), is 0.03 to 0.20 kWh/kg.

2. The method as claimed in claim 1, wherein the uncompounded polyvinyl chloride is polyvinyl chloride prepared by suspension polymerization.

3. The method as claimed in claim 1, wherein said extrusion apparatus is a planetary roller extruder, an annular extruder, a multiscrew extruder or a Buss kneader.

4. The method as claimed in claim 1, wherein the amount of energy introduced by the extrusion apparatus may be introduced both in the form of mechanical energy and in the form of thermal energy and that at the end of the extrusion apparatus a product temperature is reached of at least 150 C. up to at most 190 C.

5. The method as claimed in claim 1, wherein the homogeneous polymer composition has a residual thermal stability, determined according to DIN 53 381-1 at 180 C., of at least 60 minutes.

6. The method as claimed in claim 1, wherein the extrusion apparatus used for the extrusion comprises a pair of substantially isomorphous, elongate rotors which fit into the cavity and are disposed next to one another for interpenetrating movement.

7. The method as claimed in claim 6, wherein each of the rotors has a length L in the range of 32-60 times its diameter D.

8. The method as claimed in claim 6, wherein the polyvinyl chloride is admixed with a first portion of plasticizer at an L/D ratio in the range from 1 to 8 and with a second portion of plasticizer at an L/D ratio of 10 to 20.

9. The method as claimed in claim 1, the polymer composition consisting substantially of (A) 30 to 80 wt % of polyvinyl chloride, (B) 0.5-5 wt % of a stabilizing additive, (C) 0-40 wt % of a solid constituent, and (D) 5-40 wt % of a plasticizer, liquid at room temperature, for the polyvinyl chloride, where the figures in wt % are based in each case on the total weight of the polymer composition, and where the method comprises the steps of (I) feeding polyvinyl chloride (A) in uncompounded form into an extrusion apparatus having at least one rotor, which has at least three kneading and/or mixing zones and is capable of both transporting and mixing the mixture, (II) feeding the polyvinyl chloride (A) and stabilizing additive (B) into the extrusion apparatus through a first inlet, which is disposed in the vicinity of the drive unit and adjacent to a first conveying segment section of the at least one rotor; (III) feeding the plasticizer to the polyvinyl chloride mixed with the stabilizing additive through at least two inlets at a distance from one another, the plasticizer being added in at least two portions each of about 20-80 wt %, based on the total weight of the plasticizer, to the polyvinyl chloride, there being a kneading and/or mixing zone disposed between the addition of the individual portions, (IV) working the plasticizer/polyvinyl chloride mixture at a temperature of or above the glass transition temperature of the polyvinyl chloride, the temperature of the mixture not exceeding 150 C., until the plasticizer has been incorporated substantially completely into the polyvinyl chloride, (V) optionally feeding the solid constituent to the polyvinyl chloride mixed with the plasticizer in a section at which at least 80 wt % of the total amount of the plasticizer has been incorporated into the polyvinyl chloride, (VI) optionally devolatilizing and extruding the mixture through the extrusion die.

10. The method as claimed in claim 9, wherein the solid constituent is added to the polyvinyl chloride, mixed with the plasticizer, in a section at which at least 95 wt % of the plasticizer has been kneaded into the polyvinyl chloride.

11. The method as claimed in claim 9, wherein the polyvinyl chloride is admixed in step (V) with at least 80 wt %.

12. The method as claimed in claim 9, wherein the mixture of plasticizer and PVC is brought to a temperature of at least 30 C. below the glass transition temperature (Tg) of the polyvinyl chloride.

13. The method as claimed in claim 9, wherein the amount of the solid constituent in the polymer composition is 0.01 to 35 wt %.

14. The method as claimed in claim 9, wherein the solid constituent is incorporated into the polyvinyl chloride only after the plasticizer has been incorporated substantially completely into the polyvinyl chloride.

15. The method as claimed in claim 9, wherein the individual portions for the feeding of the plasticizer to the polyvinyl chloride, mixed with the stabilizing additive, in step (III) account for about 30 to 70 wt % based on the total weight of the plasticizer.

16. The method as claimed in claim 15, wherein the plasticizer is added in two portions to the polyvinyl chloride, with the portion added first making up 553 wt % and the portion added thereafter 453 wt % of the total amount of the plasticizer.

Description

COMPARATIVE EXAMPLES 1 TO 5

Dry Blend and Extruder Method According to the Prior Art

(1) PVC can in general not be processed without plasticizers, without thermal degradation of the PVC and hence the formation of hydrochloric acid occurring.

(2) In a first step according to the method for producing dry blends in accordance with the prior art, PVC, plasticizers, additives, and fillers are introduced into a simple mixing apparatus which is operated at a high speed and which is capable of heating the mixture by means of friction. The composition for this purpose consists of 56% of a premix of S-PVC and stabilizing additives, 35% of plasticizers, and 9% of fillers and pigments. With the aid of the mixing apparatus, the mixture is heated to 110 to 120 C. and treated in the mixer until a dry, free-flowing powder has formed. Within this step the plasticizer migrates into the PVC grain. It is important that here the migration of plasticizer has fully concluded. Incomplete migration prevents the attainment of good mechanical values on processing. The specific energy input (SEI) required for this step is between 0.05 and 0.10 kWh/kg for the dry blends described.

(3) Following this treatment, the dry blend obtained is transferred to a cooling apparatus and cooled to a temperature of less than 40 C.

(4) The dry blend thus obtained is then passed to an extrusion apparatus where it is heated by friction or convection until a homogeneous and processable melt is obtained. This is normally the case at temperatures of 160 to 195 C. The melt is then devolatilized and extruded. Employed for this purpose were common extrusion apparatuses, such as a single-screw extruder (comparative example 1), a contrarotating twin-screw extruder (comparative example 2), a corotating twin-screw extruder (comparative example 3), a Buss kneader (comparative example 4) and a planetary roller extruder (comparative example 5). In this processing step an SEI of about 0.1 to 0.25 kWh/kg is required. Necessary overall for the production of the dry blends, therefore, are SEI values of 0.15 to 0.30 kWh/kg. The results of the investigations carried out in this context are reported in table 1 below.

(5) The tensile strengths and elongations at break in table 1 and in the examples below were determined in accordance with DIN EN 12311-2; method B. The degree of gelation was by means of a DSC 821e (Mettler-Toledo) by the method of Potente H. Determination of the Degree of Gelation of PVC with DSC, Kunststoff-German Plastics, 1987, 77 (4), pp. 401-404. For this purpose, for each measurement, 10 mg of chopped material were heated from 25 to 220 C. at a heating rate of 20 C./min. The fraction of the melting endotherm occurring at lower temperatures relative to the sum of both melting endotherms is then reported as degree of gelation in percent.

(6) TABLE-US-00001 TABLE 1 Mechanical properties Degree Tensile Elongation of Comparative Processing Overall strength at break gelation example apparatus SEI [N/mm.sup.2] [%] [%] 1 Single-screw 0.26 19 350 85 extruder 2 Contrarotating 0.15 20 350 85 twin-screw extruder 3 Corotating 0.16 19 350 90 twin-screw extruder 4 Buss kneader 0.15 19 350 90 5 Planetary roller 0.14 20 350 85 extruder

(7) From table 1 it can be seen that with the methods available, flexible PVC products having suitable properties can be produced. As a result of the intermediate stage of producing a dry blend, however, such production requires an overall energy input (SEI) of at least 0.14 kWh/kg.

INVENTIVE EXAMPLES 1 TO 22

(8) In the inventive examples, the constituents were supplied continuously and throughout the implementation of the experiment in accordance with their corresponding proportions. In order to simplify the experiments, however, the PVC and also the stabilizing additives were premixed cold. The separate addition of the additives is readily possible by adapting the extrusion apparatus.

(9) In addition to the mechanical parameters determined in the comparative examples, the residual thermal stability as well was determined for the PVC products produced by the method according to the invention. This was done by reference to DIN 53 381-1, with the measurements being carried out at 180 C.

Example 1

(10) The feed section was cooled with water in order to prevent clogging. All barrel temperatures were set to a temperature of 140 C. The screw speed was set at 160 revolutions per minute. The throughput was 15 kg/h. The extruder used was a ZE25A UT corotating twin-screw extruder from Berstorff with an L/D ratio of 44.

(11) 100% of the PVC mixed with the stabilizing additive was supplied in the feed section of the extruder. 58 wt % of the phthalate plasticizer was then supplied at a temperature of 80 C. at an L/D ratio of 6 downstream of the feed area for the PVC. The mixture was then mixed, kneaded and further heated. Then 42 wt % of the phthalate plasticizer was added at an L/D ratio of 16 downstream of the feed area. The PVC plasticizer mixture was mixed further, kneaded, and heated.

(12) Downstream relative to the mixture of PVC and plasticizer, fillers and pigments were added at an L/D ratio of 24. The fillers and pigments were incorporated into the PVC by mixing and kneading. The completed mixture was then devolatilized by application of a vacuum of 100 mbar absolute pressure at an L/D ratio of 36 downstream of the feed section. The final sections of the extruder are designed for development of pressure for the flat extrusion die. The specimen producible in this way featured an SEI of only 0.057 kWh/kg, an elongation at break of 320%, and a tensile strength of 15.5 N/mm.sup.2. The specimen obtained was weldable.

Example 2

(13) Example 2 was carried out as for example 1, with the difference that the screw speed of the extruder was set at 100 rpm. The product produced in this way had an SEI of 0.05 kWh/kg, an elongation at break of 350%, and a tensile strength of 20 N/mm.sup.2.

Example 3

(14) Example 3 was carried out as for example 1, with the difference that the rotary speed of the screw was set at 330 rpm. The product obtained had an SEI of only 0.092 kWh/kg, an elongation at break of 350%, and a tensile strength of 19 N/mm.sup.2. However, the product obtained was not weldable.

Example 4

(15) Example 4 was carried out as for example 1, with the differences that the screw speed was set at 320 rpm and the throughput was increased to 30 kg/h. The product produced accordingly featured an SEI of 0.06 kWh/kg, an elongation at break of 370%, and a tensile strength of 16.5 N/mm.sup.2. The product was weldable.

Example 5

(16) Example 5 was carried out as for example 1, with the differences that the screw speed was set at 310 rpm, the throughput was increased to 30 kg/h, and no filler was added. The product produced in this way featured an SEI of only 0.082 kWh/kg, an elongation at break of 350%, and a tensile strength of 20 N/mm.sup.2. The specimen was weldable.

Examples 6 and 7

(17) Example 6 was carried out as for example 1, with the differences that the screw speed of the extruder was set at 210 rpm, the throughput was set at 18 kg/h, and the fillers and pigments were added at the L/D ratio of 1. The product obtained by means of this method featured an SEI of 0.060 kWh/kg, an elongation at break of 338%, and a tensile strength of 15.1 N/mm.sup.2. The product was weldable.

(18) Example 7 was carried out as for example 6, with the difference that the fillers and pigments were added only at an L/D ratio of 20. A product produced by this method featured an SEI of 0.060 kWh/kg, an elongation at break of 350%, and a tensile strength of 19 N/mm.sup.2. The product was likewise weldable.

(19) A key difference between the products of examples 6 and 7 lies in the residual thermal stability, which is reduced from 110 min to 94 min. A method wherein the fillers are dispersed into the PVC before the plasticizer therefore results in a greater final temperature in comparison to a method wherein the fillers are not added until a later point in time. The mechanical properties of example 6 are likewise less favorable than for example 7.

Examples 8 to 11

(20) Examples 8 to 11 were varied by modifying the feed temperature of the plasticizer in a temperature range from 20 to 125 C. The other operational parameters correspond to those from example 7. All of the products produced had an SEI in the range from 0.06 to 0.065 kWh/kg, an elongation at break of about 350%, and a tensile strength of about 19 N/mm.sup.2. Each of the specimens produced was weldable. Increasing the temperature of the plasticizer resulted in a reduction in the required motor force of the extruder and, accordingly, in a reduced SEI through the extruder motor.

Example 12

(21) Example 12 was carried out with method parameters corresponding to example 7. However, the amount of the fillers and pigments, in comparison to example 7, was reduced from about 18 wt % to about 9 wt %, and E-PVC rather than S-PVC was used. At an SEI of 0.067 kWh/kg, however, example 12 failed to furnish a product having useful properties in respect of elongation at break and tensile strength. It is assumed that this is attributable to the very fine structure of E-PVC (particle size about 1 m).

Examples 13 to 15

(22) These examples were likewise carried out in the same way as for example 7, though in contrast to example 7 no fillers and pigments were added and the ratio of the addition of phthalate plasticizer in the first portion to the addition of the plasticizer in the second position was varied. The ratio of the first plasticizer portion to the second plasticizer portion was 31:69 in example 13, 64:36 in example 14, and 75:25 in example 15.

(23) The products produced in line with this method featured an SEI of 0.135 kWh/kg, an elongation at break in the range from 320 to 380%, and a tensile strength in the 20 to 22 N/mm.sup.2 range. Each of the products produced was weldable. It was found that by metering in a higher proportion of plasticizer at an L/D ratio of 6, the material produced is protected more effectively from overheating in the first mixing section. This has a positive effect on the durability of the finished product. By adding a greater amount of plasticizer at an L/D ratio of 6, the mechanical properties deteriorated in example 15. The best ratio found for the addition of plasticizer was 58 wt % and 42 wt % on addition at an L/D ratio of 6 and 16, respectively.

Examples 16 to 18

(24) These examples were carried out as for example 1, but the temperature of the barrels was set at 120 C. (example 16), 140 C. (example 17), and 160 C. (example 18), the plasticizer was preheated to 80 C., and the screw speed was set at 180 rpm. Changing the temperature in the barrels has a direct effect on the temperature of the PVC at the end of the extrusion operation. The products produced had useful mechanical properties if a product temperature (T(max)) of more than 160 C. was attained (example 18). Temperatures below this figure, in contrast, yielded significantly less favorable mechanical properties (examples 16 and 17).

Examples 19 to 22

(25) In these examples the effect of screw speed on the products obtained was investigated. The method parameters of these investigations correspond to those of examples 8 to 11, with the differences that the temperature of the plasticizer was 80 C. and the screw speed was varied in the range from 210 to 420 rpm. The change in the screw speed has direct consequences for the temperature of the PVC at the end of the extrusion operation and for the SEI. Products which attained a melt temperature (T(max)) of 160 C. achieved useful mechanical properties. On exceedance of a melt temperature of 195 C., however, there is a deterioration in the weldability of the products.

(26) The compositions, parameters and results of the investigation of the examples described above are set out in table 2 below.

(27) TABLE-US-00002 TABLE 2 Plast. Screw Energy PVC Plast. 1 Plast. 2 temperature Fillers & speed consumption T(max) Example [kg] [kg/h] [kg/h] [ C.] pigments [rpm] [kW] [ C.] 1 8.47 3.00 2.21 80 1.32 160 1.1 184 2 8.47 3.00 2.21 80 1.32 100 0.9 180 3 8.47 3.00 2.21 80 1.32 330 1.9 191 4 16.94 6.00 4.40 80 2.63 320 2.3 189 5 10.63 4.14 3.23 80 0.00 310 2.2 184 6 8.92 3.60 2.70 80 3.27@1 210 1.4 174 L/D 7 8.92 3.60 2.70 80 3.27@20 210 1.4 173 L/D 8 10.17 3.60 2.70 20 1.58 210 1.5 176 9 10.17 3.60 2.70 50 1.58 210 1.5 177 10 10.17 3.60 2.70 100 1.58 210 1.4 178 11 10.17 3.60 2.70 125 1.58 210 1.4 180 12 10.17 3.60 2.70 80 1.58 210 1.2 180 13 11.60 2.00 4.40 80 0.00 210 2.80 196 14 11.60 4.10 2.30 80 0.00 210 2.80 196 15 11.60 4.80 1.60 80 0.00 210 2.75 195 16 8.47 3.0 2.21 80 1.32 180 1.4 138 17 8.47 3.0 2.21 80 1.32 180 1.4 154 18 8.47 3.0 2.21 80 1.32 180 1.3 174 19 10.17 3.6 2.7 80 1.58 210 1.7 156 20 10.17 3.6 2.7 80 1.58 280 1.9 164 21 10.17 3.6 2.7 80 1.58 350 2.4 175 22 10.17 3.6 2.7 80 1.58 420 2.8 182 Mechanical properties Residual Tensile Elongation thermal SEI strength at break stability Example [kWh/kg] [N/mm.sup.2] [%] Degree of gelation [%] [min] 1 0.057 15.5 320 90 110 2 0.050 20 350 85 110 3 0.092 19 350 90 110 4 0.060 16.5 370 95 110 5 0.082 20 350 85 110 6 0.060 15.1 338 85 94 7 0.060 19.0 350 95 110 8 0.065 19.0 352 95 110 9 0.065 19.0 350 95 110 10 0.060 19.0 350 95 110 11 0.060 18.7 348 95 110 12 0.067 n.a. n.a. n.a. 62 13 0.135 345 21 95 100 14 0.135 380 22 95 110 15 0.135 320 20 95 140 16 0.075 5.3 58 37 125 17 0.075 8.5 113 58 105 18 0.068 16.1 328 88 138 19 0.076 9.2 132 68 105 20 0.081 14.5 328 76 145 21 0.103 17.6 365 95 145 22 0.119 15.5 368 100 145