DE2153143A1 - PROCESS FOR EXTRUSION OF HIGHLY VISCOSE THERMOPLASTICS USING SINGLE SCREW EXTRUDER - Google Patents

Description

I ¹ AREWKT'KE HOECHST AKTIENGESELLSCHAFT ^ IOOI 4 O

formerly Master Lucius? v. Brüning

Patent application - HOE 71 / F 282 u, H

Date: October 25, 1971 - DPh.HS / sch

Process for the extrusion of high-viscosity thermoplastics using a single-screw extruder

The invention relates to a method for extruding plastics with very high melt viscosities and lower temperature dependence these melt viscosities on single-screw extruders at a peripheral screw speed of at least 13 m / min and one that is fed to the extrudate via the screw mechanical energy not exceeding 0.25 kWh / kg.

When processing high-molecular, very high-viscosity plastics on standard single-screw extruders, i.e. with three-zone ode = r Short compression screws, the extrudate will overheat significantly even at medium screw speeds. As a result of the high viscosity of these melts, which is only slightly reduced even when the temperature is increased, a A very high proportion of the mechanical energy supplied to the screw is converted into heat via viscous friction. This overheating can be so great that it leads to thermal damage through degradation or decomposition of the plastic. While the throughput, i.e. the amount of extrudate conveyed in the unit of time, increases roughly proportionally to the screw rotation speed, the temperature rises disproportionately. For this reason, very high molecular weight plastics could be used on single-screw extruders Previously common design can only be extruded at low screw speeds and thus uneconomical.

There has now been a process for the extrusion of high viscosity thermoplastics found by means of single-screw extruder, which is characterized is that the thermoplastic raw material is placed in an extruder

309818 / 0A ₂₄ ^,

Schnockonujnf ang "sge £» ehv / indities of more than 13 m / .U ^; η predic '.. et v.nu preheated, after going through a compression axis, in a fine, flat screw channel, which is at most one eighth of the screw length, over the warmth there reacted shear foam is suddenly plasticized and then, after passing through a decompression zone, relaxed, mixed, homogenized, conveyed and discharged in a deeply cut screw caudal with low shear, the total energy flow through the extruder drive into the extrudate being at most 0.25 kWh / kg

A is particularly suitable for the method according to the invention

Extruder whose screw is ^ divided into five zones, wherein the channel depth D and the length of the Ψ zones are related to the screw length L to the Schneckendurchmessei *. the

The screw length L is 15-30 times, preferably 20-25 times the screw diameter.

1 “Feed zone with constant channel depth

Channel depth = 0.10 - 0.22 D

Length = 0.20 - 0.40 L

2. Compression zone

Length = 0.10 - 0.30 l

3. Plasticizing or shear zone with
ψ constant channel depth

Channel depth - 0.03 - 0.08 D.

Length = 0.08 - 0.125 L

4. Decompression zone

Length = 0.02 - 0.05 L

5. Ejection zone with constant channel depth

Channel depth = 0.08 - 0.125 D

Length = 0.25 - 0.60 L

ORIG | _NAL

3098 1 8 / CK2A

Screws with a constant pitch of 1 D have proven their worth, ί.ε can a. bei au "?: i work with other cream corner slopes,

The process is particularly suitable for processing very high molecular weight plastics with weight-vibrated l-molecular weight cn of ICO 000 and significantly above. It is suitable for the extrusion of high molecular weight Kio ~

rlipolyütjijOone rait molecular weights over 100,000 resp.

ziii '.- icco 1, IFI 190/5 under 2 g / 10, min (DIN 53 735 E). Except Granules can also be processed into powder without difficulty ",

In the method according to the invention, the released plastic is drawn into the first zone and obscenely compressed and preheated in this zone and the compress. In the following plasticizer: * One v / ird it is sheared in a narrow screw channel at high speed, with a relatively large proportion of the mechanical energy supplied via the screw being converted into heat by friction, so that the plastic can be replaced in a short time without any significant exchange plasticized by heat via screw and cylinder Y / ird. Because dor soon this zone, the extrudate passes quickly in the subsequent Dekompressionszonc and from this into the discharge zone. In the last two zones, the melt is mixed, homogenized and finally conveyed out of the cylinder with significantly reduced shear.

For proper implementation of the method according to the invention it is necessary that the discharge zone is completely covered with melt is filled. If the counterpressure of the tool is not sufficient for this, it is advantageous to place it between the end of the extruder and the tool to install a throttle section of known design. If particularly high demands are placed on the homogeneity of the extrudate, the ejection zone can also be stranded with a known mixing element.

Fig. 1 shows a five-zone screw, as it is for the orfindungsgeiaäß Procedure is suitable.

8AD ORlGINAt 309818/0424

For comparison, FIG. 2 shows a conventional core progressive three-zone screw.

In the two figures, the reference numbers have the following meaning:

1 feed zone

2 compression zone

3 shear or plasticizing zone

4 decompression zone

5 discharge zone

6 screw flight

7 pitch of the screw

8 screw shaft

The following two examples show the advantage of the invention Process with regard to excess temperature and throughput compared to extrusion with a conventional three-zone screw.

«AD OHIGiNAL

309818/042 /.

2153U3

example 1

Low-pressure polyethylene powder, density 0.945 g / cm, melt index MFI 190/5, determined according to DIN 53 735 E, of 1.2 g / 10 min, viscosity number according to ISO R 1191 «3.0 corresponding to a weight average Molecular weight of about 125,000, was effective on a single screw extruder, screw diameter D = 60 mm Screw length - 25 D, extruded according to the invention. For comparison the same polyethylene was extruded on the same extruder with a conventional three-zone screw. The dimensions of the two screws are listed in Table 1.

Tabel

according to the invention with a five-zone screw

comparison

with dceizone

slug

Screw diameter D effective screw length

Feed zone length channel depth

Compression zone length

Shear zone length channel depth

Decompression zone length

Ejection zone length channel depth

Screw pitch screw flight width

60 mm D. 25th D. mm 7, 5 10, 0

7.0 D.

2.0 D 4.0 mm

0.5 D

8.0 D. 4.9 mm 1.0 D. 7.0 mm

60 ram 25 D

8 D 10.1 mm

7.0 D.

10.0 D. 4.0 mm 1.0 D. 7.0 mm

3098 18/0424

A throttle valve was flanged to the end of the cylinder to regulate the back pressure. The set cylinder temperature the discharge zone and the throttle valve was 190 C. The temperature of the extrudate was measured with a thermocouple at the cylinder outlet measured. Table 2 shows the throughputs achieved and the excess temperatures determined (difference between extrudate temperature and set cylinder temperature) and the mechanical energy N supplied via the screw, based on the Throughput Q, for two screw rotation speeds each other juxtaposed.

Table 2

according to the invention 100 comparison 100 70 18.9 70 18.9 Screw rotation speed
RPM 13.2 84.5 13.2 71.5 Circumferential speed of the screw
speed rpm 58 29 47.5 53 Throughput Q kg / h 21.5 0.236 42 0.268 Overtemperature ⁰ C 0.22 0.265 N / Q kWh / kg

Example 2

The low-pressure polyethylene extruded according to the invention according to Example 1 was granulated. The determination of the melt index and viscosity number of the granules showed no deviations from this the values of the powder.

The granulate was again on a single screw extruder, Screw diameter 90 mm, effective screw length 24 D, according to the invention and for comparison, with a conventional three-zone screw extruded. A throttle valve was flanged to the end of the cylinder to regulate the back pressure. The cylinder temperature the discharge zone and the throttle valve were set at 190 ° C. The temperature of the extrudate was measured with a melt thermometer measured at the cylinder outlet. In Table 3 are the

309818/0 4 Ik

2153H3

of both screws, the speed of rotation, the throughputs achieved, the excess temperatures determined and the Mechanical energy supplied via the screw affects the throughput related, N / Q, compiled.

Tabel

according to the invention
with five-zone screw

Comparison with three-zone snail

Slice diameter D effective screw length

Feed zone length channel depth

Ko. '-. Ipressionszone length

Shear zone length channel depth

Decompression zone

Ejection zone length channel depth

Snail slice gixng Snail slice width

Screw rotation speed rpm

Circumferential screw speed m / min

40

kg / h

Throughput Q excess temperature C 90 mm
24 D

7.0 D.
13.3 mm

5.0 D

2.0 D. 4.5 mm 1.0 D. 9.0 D. 7.1 mm 1.0 D. 12.0 mm

60

90 mm 24 D

6.0 D 13.5 mm

6.0 D.

12.0 D. 3.6 well 1.0 D. 12.0 nuij

60

kWh / kg

11.3 17.2 11.3 17.2 110 163 71 102 32 37 56 88 0.215 0.225 0.295 0.350

30981 8/0424

Claims (4)

- β - 2153.U3 Patent to s ρ r ti c h e: 1.! Ancestors for the extrusion of high-viscosity thermoplastics using Fin-V, / screw extruder, characterized in that the thermoplastic Raw material in an extruder with a screw circumference speeds of over 13 m / min compressed and preheated, after passing through a compression zone, in. "a maximum one eighth of the screw length is a flat screw channel Abruptly plasticized by the shear work converted into heat there and then, after going through a Decompression zone, in a deep-cut snail canal is relaxed, mixed, homogenized, conveyed and discharged at low shear, whereby the total energy input through the extruder drive into the extrudate is at most 0.25 kWh / kg. 2. Single-screw extruder for carrying out the process according to Claim 1, characterized in that the screw of the extruder in a feed, a compression, a plasticizing or shear, a decompression and an ejection zone, where the length L of the screw is 15 to 30 times, preferably 20-25 times, the screw diameter D should be and the catchment zone has a constant canal depth of «0.10 - 0.22 D and a length of 0.20-0.40 L, the compression zone a length of 0.10-0.30 L, the plasticizing or shear zone a constant canal depth of = 0.03 - 0.08 D and a length of «= 0.08 - 0.125 L, the decompression zone has a length of = 0.02 - 0.05 L and the discharge zone has a constant channel depth of = 0.08 - 0.125 D and a length of 0.25 - 0.60 L. 3. Extruder according to claim 2, characterized in that the extruder screw in addition mixing elements in the discharge zone having. 4. Extruder according to claim 2 and 3, characterized in that a throttle section is arranged between the end of the extruder and the tool is. 3098 18/042 /.