Method for producing semifinished plasticized PVC products

Abstract

The present invention relates to the extrusion of polymer compositions based on polyvinylchloride (PVC) as a semifinished PVC product, in particular as pellets, and in particular to a method in which homogeneous polymer compositions with an elongation at break of 0 to 270%, a tensile strength of at least 1 N/mm2 and a degree of gelation of 5 to 80% are produced by using a specific energy input SEI of 0.03 to 0.09 kWh/kg. The method according to the invention is expediently conducted by a plasticizer being added in a number of portions to the non-compounded polyvinylchloride and mixed in with it. The method according to the invention thereby offers a quick and easy possible way of producing semifinished plasticized PVC products, in particular as pellets, the production of which only requires a single processing device in the form of an extruder.

Claims

1. A method for extruding a polymer composition to form an extruded homogeneous polymer comprised of (A) 30 to 80 wt % of polyvinyl chloride, (B) 0.5 to 5 wt % of a stabilizing additive, (C) 0 to 40 wt % of a solid constituent, and (D) 5 to 40 wt % of a plasticizer, liquid at room temperature, for the polyvinyl chloride, where the figures in wt % are based in each case on a total weight of the polymer composition, where the method comprises (I) feeding polyvinyl chloride in an uncompounded form and the stabilizing additive into an extrusion apparatus through a first inlet, wherein the extrusion apparatus has a drive unit, has at least one rotor, and has at least three kneading and/or mixing zones, wherein the first inlet is disposed in a vicinity of the drive unit and adjacent to a first conveying segment section of the at least one rotor; (II) 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 a total weight of the plasticizer, to the polyvinyl chloride, there being at least one of the kneading and/or mixing zones disposed between the addition of the individual portions, (III) 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, (IV) optionally feeding the solid constituent to the polyvinyl chloride mixed with the plasticizer in a section at which at least 80 wt % of a total amount of the plasticizer has been incorporated into the polyvinyl chloride, (V) optionally devolatilizing the mixture, and (VI) extruding the mixture through an extrusion die of the extrusion apparatus, wherein the extruded homogeneous polymer has a degree of gelation of 5% to 80%, an elongation at break of 0 to 270%, and a tensile strength of at least 1 N/mm.sup.2, and wherein quantity of energy introduced into the polymer composition by the extrusion apparatus during the method, as indicated by the specific energy input (SEI), is 0.03 to 0.09 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 the extrusion apparatus comprises a pair of substantially isomorphous, elongate rotors which fit into a cavity of the extrusion apparatus and are disposed next to one another for interpenetrating movement.

4. The method as claimed in claim 3, wherein each of the rotors has a length L in a range of 32-60 times a diameter D thereof.

5. The method as claimed in claim 3, 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.

6. 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.

7. The method as claimed in claim 1, 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.

8. The method as claimed in claim 1, wherein the polyvinyl chloride is admixed in step (IV) with at least 80 wt % of the total amount of the solid constituent.

9. The method as claimed in claim 1, 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.

10. The method as claimed in claim 1, wherein individual portions for the feeding of the plasticizer to the polyvinyl chloride, mixed with the stabilizing additive, in step (II) account for about 30 to 70 wt % based on the total weight of the plasticizer.

11. The method as claimed in claim 10, 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.

12. The method as claimed in claim 1, wherein the amount of the solid constituent in the polymer composition is 0.01 to 35 wt %.

13. The method as claimed in claim 1, wherein the solid constituent is incorporated into the polyvinyl chloride only after the plasticizer has been incorporated substantially completely into the polyvinyl chloride.

14. 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, by means of heating elements, and that at the end of the extrusion apparatus a product temperature is reached of at least 130 C. up to at most 170 C.

15. 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 90 minutes.

16. The method as claimed in claim 1, wherein the extruded homogeneous polymer composition is present in the form of granules.

Description

EXAMPLES

Comparative Example: 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. 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.

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

(3) 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 in order to produce granules. Employed for this purpose were common extrusion apparatuses, such as a single-screw extruder, a contrarotating twin-screw extruder, a corotating twin-screw extruder, a Buss kneader and a planetary roller extruder. For the production of granules from the dry blend an SEI of about 0.06 to 0.15 kWh/kg is required depending on the extrusion apparatus used. Overall, therefore, for the production of granules in accordance with the prior art, SEI values of 0.11 to 0.25 kWh/kg are needed (SEI for dry blend+SEI for granule production). It follows from this that in accordance with the prior art, as a result of the intermediate stage of producing a dry blend, a total energy input (SEI) of at least 0.11 kWh/kg is required in order for granules to be produced.

Inventive Examples 1 to 4

(4) 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 produce a granule. 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.

Example 1

(5) The feed section was cooled with water in order to prevent clogging. All barrel temperatures were set to a temperature of 120 C. The screw speed was set at 180 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.

(6) 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.

(7) 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 produced in this way featured an SEI of only 0.075 kWh/kg, an elongation at break of 58%, and a tensile strength of 5.3 N/mm.sup.2. The degree of gelation was 37%.

Example 2

(8) Example 2 was carried out as for example 1, with the difference that the barrel temperature was set at 140 C. The product produced in this way had an SEI of 0.075 kWh/kg, an elongation at break of 113%, and a tensile strength of 8.5 N/mm.sup.2. The degree of gelation was 58%.

Examples 3 and 4

(9) Examples 3 and 4 were carried out as for example 1, with the differences that the screw speed of the extruder was set at 210 and 280 rpm, respectively, the throughput was set at 18 kg/h, and the fillers and pigments were added at the L/D ratio of 20. The products obtained by means of this method featured an SEI of 0.076 and 0.081 kWh/kg, respectively, an elongation at break of 132 and 328%, respectively, and a tensile strength of 9.2 and 14.5 N/mm.sup.2, respectively.

(10) The tensile strength and elongation at break are determined, in the examples, in accordance with DIN EN 12311-2; method B. The degree of gelation was with the aid 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 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 expressed as the degree of gelation in percent.

(11) Additionally to the mechanical parameters, the residual thermal stability as well was determined for the PVC granules produced. For this purpose, DIN 53 381-1 was referenced, with the measurements being carried out at 180 C.

(12) The compositions, parameters and results of the investigation of the examples described above are set out in table 1 below.

(13) TABLE-US-00001 TABLE 1 Plast. Screw Energy PVC Plast. 1 Plast. 2 temperature Fillers & speed consumption Example [kg] [kg/h] [kg/h] [ C.] pigments [rpm] [kW] 1 8.47 3.0 2.21 80 1.32 180 1.4 2 8.47 3.0 2.21 80 1.32 180 1.4 3 10.17 3.6 2.7 80 1.58 210 1.7 4 10.17 3.6 2.7 30 1.58 280 1.9 Mechanical properties Residual Tensile Elongation Degree of thermal T(max) SEI strength at break gelation stability Example [ C.] [kWh/kg] [N/mm.sup.2] [%] [%] [min] 1 138 0.075 5.3 58 37 125 2 154 0.075 8.5 113 58 105 3 156 0.076 9.2 132 68 105 4 164 0.081 14.5 328 76 145