DE1955720A1 - Process for the production of uniform moldings from a thermoplastic polymer - Google Patents

Description

It is known that articles of daily use or molded articles are made from A thermoplastic polymer can be obtained by first bringing the polymer to a temperature above its melting point is heated. This melted Polymer is then extruded through a suitable die into the desired shape, which upon cooling becomes solid The object results in «The device designed for the conventional extrusion process is based on the principle that the polymer must be melted before the deforming or shaping step is carried out.

009824/1771

BATH ORIGINAL

This method is indeed applicable but results zn diffi culties, which depend on the molecular weight of the particular polymer "For example, solid polyethylene rai.t molecular weights ranging from about 10" to about 000 5c500.000 commercially available. Polyethylene having a molecular weight of up to about 500,000 can be easily molded by conventional extrusion molding techniques without any problems. Polyethylenes with molecular weights above about 50O ₈ OOO, have not been used on a larger scale because they can not be verarbeitst gen satisfactorily in conventional Strangpreßverrichtun =. These higher molecular weight polyethylenes have not found widespread use, although they have some excellent physical properties such as high toughness and resistance to stress cracking. demonstrate. These higher molecular weight polyethylenes have an extremely high viscosity in the melt and therefore require a great deal of mechanical work in order to make the molten polyethylene flow. By applying such a large amount of mechanical work to the molten polyethylene, the molecules of the high molecular weight polymer are torn apart. The mechanical rupture of the polyraerene molecules has an adverse effect on the physical properties and therefore on the behavior of the finally formed polyethylene product.

- 2 -

009824/1775

Only recently has it been reported in the literature that molten polyethylenes with molecular weights of? .50 "OOO" to 1,500,000 can be extruded in commercially available devices using a specially designed screw (SOCIETY PLASTIC EH & IIEERS JOURNAL, Hai 1968, vol. 24, pp. 45-48) This more recent development is presented about 7 years after the report on the excellent properties of high molecular weight polyethylenes found in MODERN PLASTICS, November 1961, pp. 131-156 presented some of the procedural problems that occur with hoahr-> c-1 ekularan polyethylenes,

You & Alternative cure application Onea great effort ai * nitichanischer work oda :: d ^ r 7erw9mr. R ig a specially RK: designed device ₅ as "he vsrher wu ^mentioned: de:. 'St d sr addition of a xiiear .i.gerniolekularej.'i polyethylene from the high molecular weight polyethylene For example (.ir..e Polyätixyl.enraasse Hur pipe production in the "trade e ?? -} old, made from about 40 '," ί · polyethylene with ainen? Molsku3 He weight of 1,500,000 and about 60 · '/> Polyethylene: nit fc .-. no Molecular weight of about 6000. and a small amount of additives, the production of a similar mass for the formation of pipe or in the araeri'is.-rn.ßch «m patent specification" 5 ^ 19 728 by G-serge Q, Joris umq

^009824/1775 BADOR ₁ QlNA,

William L. Reiner dated November 23, 1965. That Mixing two polyethylenes with different molecular weights allows the formation of polyethylene moldings, which to a certain extent the superior properties of relatively high molecular weight polyethylene while improving processability will.

Another alternative to using a large amount of mechanical work or using a specially designed device or mixing different polyethylenes is to operate the extruder at higher temperatures. The high viscosity of molten polyethylenes having high molecular weights in excess of about 500,000 can be lowered somewhat by maintaining the melt at higher temperatures. However, it is thereby greatly increasing the temperature'lch erforder-to self-ze achieve a small reduction in viscosity.

This approach is unsatisfactory because the energy requirements are exceptionally high and besides an upper temperature limit exists. This temperature limit is the temperature at which the polymer molecules literally move break apart. This temperature is ther-

00 9-8 24/1776 ^ÖAD original

called mixed decomposition temperature. For many of these difficult to process thermoplastic polymers, the difference between the thermal decomposition temperature and the melting point is too small to produce any appreciable decrease in the viscosity of the molten polymer. The preceding discussion was conducted with a view to polyethylene; However, similar difficulties exist with other thermoplastic polymers. The molecular weight above which the problems mentioned occur is different for each έ special class of polymer.

The invention provides an improved method of extruding a unitary body of a desired shape from difficult to process thermoplastic polymers at a relatively high rate of production
without compromising the superior physical properties of the difficult-to-process polymers.

The invention therefore relates to a method for
Production of uniform moldings from a thermoplastic polymer which, under the conditions of ASTM test method D 1238-65 T, has no measurable melt index

shows.

«. 5 -

OQ9824 / 1775 BAD original

This process is characterized in that the thermoplastic polymer is in the form of solid, discrete particles introduces the solid, discrete particles into an extruder equipped with a corresponding extrusion die of the polymer at a temperature below the melting point of the polymer through the extruder in the press matriae transported by heating under pressure inside the press die at a temperature below the decomposition temperature of the polymer into a homogeneous one Melt transferred and pressed through the die at the same temperature and then the extrudate to a temperature cools below the melting point of the polymer.

According to the improved process of the present invention, the polymer particles are formed in one at a temperature below of the melting point of the polymer held mold by pressure to the desired molded body or object deformed. Thereafter, the temperature of the object or molded body in the die to a value above the Melting point of the polymer, but below the temperature at which thermal decomposition occurs, heated and maintaining the temperature until the particles melt. The shape obtained is then under the Melting temperature cooled.

0O8924 / 177S

Thermoplastic polymers that are difficult to process are polymers that have high viscosities in the molten state and show a tendency to thermal and / or mechanical during processing to form suitable molded articles Suffering shear degradation · This degradation lowers the molecular weight of the polymer and increases it Way worsens the physical properties and thus the desired behavior of the final product.

In the accompanying drawing, FIG. 1 A denotes the simplified one Cross-section of a typical extrusion press operated under conventional working conditions a continuous shaped body such as a pipe. Figure 1B is the simplified cross-section of an extruder for the formation of a continuous molded body, like a pipe under the working conditions according to the invention is operated.

The differences between conventional extrusion and the methods of the invention are using oilers Figures 1 A and 1 B, Figure 1 A for the conventional method of extruding an article, wio of a plastic pipe. Tablets 1 made of thermoplastic Polymers as defined here

- 7 _

009824/1775

introduced into the funnel-shaped addition port 3. That mixture falls under the effect of gravity into the channel of the compression screw rotating within the extrusion cylinder 5 2 and is pressed forwards by the rotating worm gear · While it is moving further the tablets are crushed into a powder and heated by the heating devices 7 and by the heat that by crushing the tablets when they break of the powder and advancing the solid and molten polymer is generated. As the crushed tablets move through the extrusion cylinder 5, they are converted into a melt. In this way the comminuted tablets will be complete at any point in the extrusion cylinder melted. The melt flows through a wire mesh 10 and then to the press die 9. The wire mesh 10 increases the back pressure in the extrusion cylinder 5. As the melt flows through the die 9, it is through the cooler 8 is cooled. The melt is cooled to a temperature below its melting temperature. The in This special process produced molded body is a plastic pipe 6. The temperatures within the The extrusion cylinder and the die are indicated by thermocouples 4.

BATH ORIGINAL 0O982A / 177S

The extrusion process according to the invention is shown in FIG. 1B. Solid particles of thermoplastic polymer 21 are placed in a funnel-shaped filler neck 23. The mixture falls under the action of gravity into the channel of the screw conveyor 22 rotating within the extrusion cylinder and is pressed forward by the rotating screw flights. As the particles move forward, the temperature of the particles is increased by the heat generated by the mechanical work of moving the particles forward. However, this frictional heat is insufficient to melt the particles. The still solid particles enter the die 29, where they are pressed into the desired shape. Air in the spaces between the particles is forced backwards along the screw 22 and exits through the hopper 23. The heat for melting the particles is supplied by the heating device 27 in that the temperature of the particles within the press die is increased above the melting temperature of the polymer, but to a value below the thermal decomposition temperature.

The homogeneous molten mass is passed through the die 29 pressed. A cooler 28 reduces the temperature of the homogeneous molten mass to a value below that

.003824 / 1776

Melting temperature of the polymer. The molded body formed in this special process is a plastic pipe 26. The temperatures in the extrusion cylinder and the die are indicated by thermocouples 24.

A comparison of the conventional extrusion method and
the extrusion process according to the invention, as described in connection with FIG. 1 A and 1 B, shows the differences between the two methods and the advantages resulting therefrom. These sub-periods and advantages are presented in the following sections.

Usually the tablets 1 consist of thermoplastic polymers which have been used to manufacture a plastic pipe 6 from high molecular weight polyethylene using conventional extrusion molding processes, from about
40 i> polyethylene with a molecular weight of 1,500,000 and $ 60> polyethylene with a molecular weight of 6.0Q0
as well as small amounts of additives. To produce these tablets, it is necessary to mix the two polyethylenes and then press the mixture into tablets.

According to the invention, particles are made from only one thermoplastic Polymers 21 introduced into the extruder.

- 10 -

ßAD ORIGINAL

089824/1775

The use according to the invention of only a single polyethylene therefore avoids the steps of mixing and pressing that were necessary for the manufacture of those previously used for extrusion Tablets used by tubes were necessary.

In conventional extrusion, the tablets are moved forward by a compression screw 2. After a melt has formed from the comminuted tablets, the polymer is meshed by the compression screw, compressed and transported to the compression die 9. The molten polymer is therefore exposed to a strong mechanical stress caused by mixing, pressing, conveying and passing through the wire mesh 10 _{or the like}

According to the invention, the small particles are made of thermoplastic Polymers 21 by a screw conveyor 22 forward sbev / egt. '/ Year during the entire passage of the particles due to the extrusion cylinder 25, the particles do not ground melted. and never the mechanical welding. Stresses exposed, like exe by -eino compression screw be generated. The molecular weight of the polymer is therefore never significantly reduced by mechanical degradation .

- 11 -

008824/1776

In conventional extrusion processes, the polymer is melted for a considerable period of time because the polymer in the cylinder 5 near the addition funnel 3 has melted is and is held in the melt until it is located just before it emerges from the press die 9. In addition, the adjustment of the temperature of the melt is between the melting point of the polymer and the thermal decomposition temperature for some polymers difficult because the temperature range is relatively narrow. Another complication is that the The amount of mechanical force acting on the melt is primarily determined by the friction which is applied to the melt Pressing the melt through the cylinder 5, the wire mesh 10 and the press die 9 has to be overcome, less than the amount of mechanical force required to generate the heat necessary for melting and to keep the polymer in the molten state. Therefore, when the temperature control is poor, occurs thermal decomposition of the polymer. This decomposition results in poorer physical properties of the Plastic pipe to express,

In contrast, the polymer is also in accordance with the invention only for a short time in the press die above its melting temperature. Furthermore, the regulation

- 12 -

00 9824/1775 ßAD ORIGiNAu

the heat supplied to the polymers is not difficult because the mechanical work used and therefore the heat generated is kept to a minimum. _{According to the} invention, thermal decomposition is therefore avoided and the physical properties of the plastic pipe 26 are consequently improved.

When using the method according to the invention, such as As shown in Figure 1B, a screw conveyor 22 is used. Commonly used extrusion processes will a sealing screw 2 is used, as shown in Figure 1A. The last-mentioned screw is the Aisle depth in the loading zone 11 is greatest and remains constant, it gradually decreases in the transition zone 12, in order to pass into the constant flight depth of the homogenizing zone at the front end of the screw. At the Fördersohnecke 22 the flight depth is constant because the diameter of the screw core does not change. A screw conveyor is preferred when an extrusion process having the features of the invention is used.

Compression in the term "compression screw" is intended to mean the ratio of the volume of a tendon flight in the feed zone to the volume of a screw flight in the homogenizing zone. Typical compression ratios as used in the extrusion of polyethylenes

- 13 -

001824/1776

are between 3: 1 and 4: 1. The screw conveyor 22 in FIG. 1B has a compression ratio of 1: 1, which means that there is no compression caused by a change in the volume of the screw flights

As indicated in FIG. 1B, however, the cross-sectional area of the hollow part of the die 29 is less than the cross-sectional area of the flight depth of the screw 22. This reduction in the cross-sectional area generates a pressure in the press die, which ensures a clean melting and the formation of a homogeneous one molten mass contributesc \ Jeraa. the ratio of the two cross-sections is 1.0, there would be no reduction in the cross-sectional areas. Effective pressure would therefore not be generated and proper melting would not take place. The ratio of the two cross-sectional areas must therefore be less than 1.0. On the other hand, if the ratio of the two areas were 0.175, then the pressure drop would be so great that the particles were melted by the formation of frictional heat and the process according to the invention could no longer be carried out. The ratio of the cross-sectional areas must therefore be less than 1.0, but more than 0.175 and preferably between 0.9 and 0.2,

-U-

. BATH

009824/1775

The friction occurring between the surface of the screw conveyor and the particles also affects the aforementioned reduction in the ratio of the cross-sectional areas. While the use of compression screws, the surface of which is plated with chrome, is a standard method for reducing the friction and improving the corrosion resistance when extruding molten polymers, the friction between the polymer and the surface of a screw conveyor is regarded as insignificant in conventional process management Friction between the polymer and the surface of the screw conveyor is important and must be considered. If the cross-sectional areas are reduced by a ratio of 0.465 and a screw conveyor with a polished steel surface is used, it is not possible to extrude a pipe according to the method according to the invention. On the other hand, with the same reduction in the aspect ratio, that is, with an aspect ratio of 0.46.5 and the use of a screw conveyor, the surface of which is plated with { chrome, it is possible to extrude pipes according to the invention. The friction exerted on the flow of particles through a screw conveyor with a highly polished steel surface may be sufficient to generate enough heat to melt the solid particles. on the other hand

- 15 -

008824/1776

that extends to the flow of particles through a screw conveyor, the surface of which is chrome-plated, the friction exerted is not sufficient to generate such heat to melt the solid particles.

The friction which is generated by the surface of the press die in contact with the polymer, also affects the aforementioned reduction in the ratio of the cross-sectional areas. By on the surface the friction occurring in the press die, sufficient pressure must be generated to ensure a clean fusing together of the particles: however, the resistance must not be so great that the particles or the molten mass can be prevented from moving through the Freßmatrize. In the event of a reduction in the planning ratio of 0.465 and using a screw conveyor, the surface of which is plated with chrome preferably a press die is used, the surface of which is in contact with the polymer is plated with chromium or coated with a fluorocarbon polymer is.

The problem of the high viscosities of molten, difficult to process thermoplastic polymers can be solved illustrate when looking at the melt index of polyethylenes

- 16 -

009824/1775

6A ORIGINAL

considered. Polyethylenes with molecular weights between about 10,000 and about 250,000 have a wide melt index range of about 250.0 to 0.20, as determined by the standard test method Λ3ΤΜ D 1238-65. However, a polyethylene with a molecular weight of 1,500,000 does not have a melt index that can be measured according to the standard test method ASiPM D 1238-65. The melt index describes the flow behavior of an ethylene polymer at a specific temperature under a specific pressure. Wbwa. the melt index of a polymer is low, its melt viscosity or the flow resistance of the melt is high. The flow resistance of the melt is the resistance of the molten polymers to the flow in the production of desired shaped bodies; polymers with a higher melt index therefore flow more easily in the hot, molten state than those with a lower melt index. Using conventional methods, melt index is an extremely important property for the fabricator because all mold forming processes involve melting the plastic and moving the molten material to fill a given cavity, such as a mold, or deform it into a given shape . In summary, it can be stated that thermoplastic polymers which have no measurable melt index under the conditions of the test method according to ASTM D 1236-65 T show no measurable flow.

- 17 -

09.124 / 1776

In order to indicate which polymers are difficult to process by conventional extrusion processes due to shear degradation and / or thermal decomposition and high viscosities, the polymer and the molecular weight must
of the polymer. For every polymer there is a molecular weight below which the polymer is easy to process and above which the polymer
Difficult to work with »Below are polymers
and the corresponding molecular weights above which both the problem of decomposition and high viscosities occur.

Polymer Molecular weight
about about Polyethylene 500,000 Polypropylene 400,000 Polystyrene 50,000 polyester 70,000 Polyamides 90,000 Polyvinyl chloride 50,000

You for the application of the method according to the invention suitable size of polymer particles can be varied within a wide range. For example be Polyethylenes with molecular weights of 1,000,000 or more commonly sold in the form of finely divided pulvar. These finely divided powders can according to the invention without

- 18 -

009 824/1775 Bad originai »

tr ■ -

any further processing apply. Larger particles can also be used. So became particles which pass a sieve with 32 meshes (corresponding to a mesh size of 0.465 mm) in a satisfactory manner Way used according to the invention.

Examples of extrusion are more specific below Pipes and rods described using the measures of the invention. Although in the described If only tubes or rods try to be extruded, the measures according to the invention can also be used in the formation of others desired shaped body can be used.

Examples

Table 1 compares the physical properties of pipes made from thermoplastic polymers which have been produced by conventional methods and those which have been produced according to the invention. The pipe no. 1 which is available commercially is made of polyethylene in tablet form, about $ 40> polyethylene \ contains the molecular weight of 1.5 million and about $ 60> polyethylene with a molecular weight of 6000 as well as small amounts of additives. Its pressure resistance (bursting pressure) at various temperatures and heat resistance properties are shown in Table 1. Pipe no.

- 19 -

009024/177 5 ΘΛΟ

using a hatred of the same composition how tube 1 was extruded according to the method according to the invention had the same despite its thinner wall thickness Pressure resistance at 23.3 ° C and 43.3 ° C like pipe no. 1 · In addition, pipe no. 2 - again despite a change in the wall thickness - less heat deformation as No. 1 tube after being held at a temperature of 149 ° C for 1/2 hour.

The reason why No. 2 pipe with a smaller wall thickness than No. 1 pipe has the same pressure resistance as pipe No. 1 showed that the polymer in tube No. 2 was deformed by the method of the present invention was subject to less mechanical and / or thermal decomposition. Tube # 1 was used during his Formation melted in the extrusion cylinder and, as already discussed, severe mechanical stresses subject.

Tube no. 1 had a uniform wall thickness because the rate of addition of polymers! into the extruder was kept at the optimum value to ensure uniform wall thickness. The optimal one Addition rate of polymers according to the invention / experience that ensures a uniform wall thickness can be determined through additional tests.

- 20 -

00 9824/1775 ^BAD

No. 3 pipe made of polyethylene having a molecular weight of 2,000,000 to 4,000,000 according to the invention had a pressure resistance at various temperatures superior to that of No. 2 or 1 pipe. This superior pressure resistance was obtained even though the wall thickness of pipe Hr. 3 was less than the wall thickness of pipe Hr * 1. In addition, pipe No. _β 3 by the action of heat showed a significantly lower change in length as a tube Nrο 2, as shown in Table 1 below.

The pipe produced from polyethylene with a molecular weight of 1,500,000 by the process according to the invention had higher compressive strength (bursting pressures) than pipe no 'at various temperatures. 1 or # 2 tube. As expected, however, the physical properties of # 4 tube were not as good as those of # 3 tube, which was obtained from far higher molecular weight polyethylene.

# 2, # 3, and # 4 tubes were extruded in a standard 1.9 cm (3/4 inch) screw press having a length to diameter ratio of 20 tons. It was powered by a one and a half horsepower engine. The speed of rotation of the screw was adjustable from 10 to 112 Upra. Your throughput was provided by the manufacturer

- 21 -

^009824/1778

2.72 to 3.63 kg / h (6-8 lbs per hour) stated. It was a chrome plated screw conveyor with a compression ratio of 1: 1 used. The screw flight depth was 3.8 am (0.150 inch).

As the results of the heat resistance test, Table 1 a minimum and maximum value of the percentage change in diameter and length are given for some pipes. This minimum and maximum of the percentage change means that the change in the specified dimension did not take place uniformly. In other words, changed For pipe no. 1, the pipe diameter at any point along the pipe length is 4 #. This was the slightest er-: increase in diameter over the entire subject to the test Pipe length. In addition, there was an increase in diameter at another point on the tested pipe length around 18.9 #. This value represented the greatest increase in diameter along the entire length of the pipe. The other changes that occurred in the pipe diameter were between the two specified values. Similar changes in diameter were observed for tube # 4 during changes in length could be observed in pipe no.

Table 1 also shows the throughput rates of the screw press specified. The throughput rate, expressed as weight

- 22 -

039824/17 7 * 5

Measured per inch and length per inch when extruding No. 2 pipe is given as the base value of 1.0. When extruding pipe no. 3 and no. 4 from high molecular weight polyethylenes that are difficult to process, both heat values are related to the corresponding throughput values for pipe no. Thus, in pipe in the specified weight per minute flow rate was 1.17 # 3 times higher than in the extrusion of pipe No. _e 2. the throughput reported in length per minute was 1.25 times greater than when extruding tube No. 2. As shown in Table 1, when extruding difficult-to-process, high-| molecular polyethylenes in most cases achieved higher throughput rates than when extruding an easy-to-process polyethylene mixture.

- 23 -

0Ö9824 / 1775

Tabel

Pipe Wr.

method used

polymer used, molecular weight

Wall thickness of the tube with 1.9 cn

Outside Diirchrvj knife in mm * (inch)

Pressure resistance (bursting pressure) at various temperatures kg / cm ^z (psi) 23.3 ° C (74 ⁰ P) 43.3 ° CMiO ⁰ P) 87.8 ° C (190 ° P)

conventional extrusion

40 i> 1.500.00O MGPA

and low levels of additives

(0.06) -invention device extrusion-

as for pipe no.1

⁽³⁾

39.37 (560) 31.64 (450) 16.17 (230) 39.37 (560)
31.64 (450)

2,000,000 to 4,000,000 /, χ MG. P.Ä '. ⁽¹⁾

(0.054 to 0.059) -

40.42 (575) 33.75 (480) 20.39 (290)

1,500,000 MGPA

39 , 72 (565) 33 , 04 (470) 17th , 58 (250 ") CO cn cn K) σ

Table 1 (port setting)

"■ 4 cn

Rohr Mr.

Hiteebestistentjν fceita test ^4;

? C change d. Diameter

i- change in length

Throughput rate of the extruder

Weight per min

Minimum + maximum +18.9

Minimum -36.0 maximum -58.0

ic

Length per min.

- 5.5

-20.0

(5)

1.0 1.0

- 6.5

- 4.0 %

(5)

(5)

1.17
1.25

Minimum - $ 7.5, Maximum - £ 15.0

- 8.4 1o

0.985 1.09

cn on

(1) M.G.P.Ä. = Molecular weight of the polyethylene

(2) For tube 3 and 4, determine the molecular weight by the solution viscosity in tetralin at 135 ° C

(3) At the two lower temperatures, the pressure was exerted on the pipe, which was in the Water bath had been kept at the respective temperature. At the highest temperature the pipe was held for half an hour.

(4) The measurement was made after the pipe had a was held in the oven at 149 ° C (300 ° F) for half an hour.

(5) No noticeable change.

(6) All throughput rates apply to 42 Upnu. The throughput rate in the extrusion of tube no. 2 was assumed to be 1.0 and the other throughputs in relation to this fourth were taken to be 1.0.

In Table 2 are process conditions of extrusion molding for the application of the method according to the invention for forming a tube or a rod from several different polymers. The operating temperature values show that the temperature of the powder in the Extrusion cylinder was below the melting temperature of the polymer used. The rods and tubes obtained had a smooth surface. The achieved extrusion speed

- 26 -

000824/1775 bathroom original

cLU'kelten were high bit, very high and in some cases had extremely high values ». i) The tubes 2, 3 and 4 given in Table 1 were produced essentially at the temperatures given in Table 2.

- 27 -

009824/1775

attempt I. 3 ro used Ti
! ¹ Iu JL ti Γ ¹ Γα -ύ '* ύ «■ -." Ό " ¹ J ■" V_j IA *'
«* W Μ« W * ι.Λ. ι «· βΜ va, ^ -j _ν . V. , »· ■ J- * - abbtslle 2 Operating temperatures ⁰ C ( ⁰ F) front back
rer Ab- Ab cut jpress Per Extrv; - high δ » high ! Jr. 00 Polymer Schmelstem- die cut d.Stran ^ -d.Strang 37.8 duct rate , 4 temperature of
Polymers Press (100) ⁰ C ( ⁰ P) 65.6 extreme (150) high i 5 Polyethylene 40? ' 1,500,000 176.7 pipe very ^ Pipe mix M.G.P.X. (4) and 140.6 (350) 37.8 high ^ _n extreme 6th 59 # 6000 M.S.P.Ä. (4) ⁽²⁸⁵⁾ (100) and 1 '/ additives 93.3 ro very O 7th (200) 37.8 σ high O 2 extremely high 1,500,000 ^ ² ^ 140.6 176.7 (100) Rod extreme? co 8th molecular (285) (350) 93.3 high OD Polyethylene (200) 148.9 * ■ » extremely high 2,000,000 to / ρΛ 140.6 176.7 (300) pipe high molecular 4,000,000 ^K4Li (285) (350) 165.6 - » Polyethylene (330) 60.0 -J
-J Nylon 11 NB ^{w <} 180.0 265.6 (140) Rod cn (356) (510) 93.3 37.3 or (200) (100) pipe Nylon 6 NB ^ ¹ ^ 215.0 226.7 93.3 37.8 pipe (419) (440) (200) (100) high Polypropylene 300,000 ^ 154.4 176.7 37.8 37.8 pipe (310) (350) (100) (100) cc
& Polyvinyl 91,000 ^ 82.2 148.9 60.0 Rod O chloride (180) (300) (140) or 00 Polyvinyl 91,000 ^ ^5; 82.2 148.9 pipe D. chloride / 4 (180) (300) pipe M ** Pipe mix I.

(2) determined by the solution viscosity in tetralin at 135 ° C

(3) According to the manufacturer

(4) M.G.P.A. β molecular weight of polyethylene.

Table 3 shows how the type of screw, the type of surface of the screw and the type of die inner surface, which are in contact with the polymers, affect the flow of the particles of the polymer or the melt. When using the screw press already described without using one attached to the cylinder Die, so that the particles do not flow through a die, no flow of the polymers is achieved when a compaction screw is used is used with a highly polished steel surface. Experiment 9 illustrates this. In this attempt some polymer particles were melted even though no heat was applied to the extrusion barrel. To removing said compression screw and replacing this screw with a highly polished screw conveyor Steel lobby surface became free flowing of particles obtained without melting, as shown in Experiment 10. In experiment 11, however, the experiment 10 corresponds to the Exception that a die is now attached to the end of the cylinder and the particles are therefore caused by the heated

- 29 -

-fl-Of 024/1778

BATH

trize must flow, no flow of the polymer is achieved. Even the replacement of the highly polished screw conveyor according to experiment 11 with a chrome-plated screw leads does not cause the polymers to flow. This is shown in experiment 12. The replacement for that used in Experiment 12 Highly polished steel molding device through a die coated with a fluorocarbon polymer caused the polymers to flow. This result is listed in experiment 13. This series of tests shows that a screw conveyor with a low friction surface, like a chrome-plated surface »and. a press matrix, the surface of which is in contact with the polymer has little resistance to the flow of the polymer, such as one coated with a fluorocarbon / hydrogen polymer provided surface represents the preferred combination of elements for extrusion.

- 30 -

Ö0Ü24 / 1775 ßADORIGINAL Table III

O
O
CD
CO

7 screw type

search

No.

(2)

without heat supply to the

Press die

9 compaction screw

10

Auger

with heat supply to

PreSmatrize

11 screw conveyor

12 screw conveyor

13 screw conveyor

Compaction Surface Usage Surface pitting behavior ^ ■■

Ratio of the screw of a layer of the

, Die die

highly polished steel

highly polished steel no

highly polished steel

with chrome yes plating

with chrome- yes

plating

no flowing of the particles, some melting in the cylinder;

Flow of particles; no melting

highly polished no flowing steel

hochnolier- no flowing steel

Fluorocarbon flow
fabric-polymer it

(1) The same results were obtained using polyethylene having a molecular weight of 1,500,000 or 2,000,000 to 4,000,000. ^δ

(2) Extrusion barrel inner diameter: 19.17 mm (0.755 inch); Outside diameter of Fordsrsefenacks 19.025mm (0.749 inch). The same result was obtained using a chronpiav-; x ^ rten screw conveyor with an outside diameter of 19.126 mm (0.753 inch) erzie) -.,

Claims (6)

Claims 1 »Process for the production of uniform moldings a thermoplastic polymer, which under the conditions of the test method according to ASTM-D 1238-65 T. shows measurable melt index, characterized in that the thermoplastic polymer introduced in the form of solid, discrete particles into an extrusion press provided with a corresponding press die, the solid, discrete particles of the polymer at a temperature below the melting point of the Conveying polymer through the extruder into the press die by heating under pressure inside the press die converted into a homogeneous melt at a temperature below the decomposition temperature of the polymer and at the same temperature presses through the die and then the extrudate to a temperature below the melting point of the polymer cools. 2. The method according to claim 1, characterized geke η η - draws that the polymer is polyethylene with a molecular weight of more than 500,000, polypropylene n with a molecular weight of more than 400,000, poly- - 32 - 0 0 9824/1775 ^BAD original styrene with a molecular weight of more than 50,000, polyester with a molecular weight of more than 70,000, Polyamides with a molecular weight greater than 90,000 and polyvinyl chloride with a molecular weight greater than used as 50,000. 3. The method according to claim 1 or 2, characterized in that the transport of the polymer particles through the extruder into the die with the help of a screw conveyor, the surface of which is small Exerts frictional drag on the flow of particles. 4. The method according to claim 3 »characterized in that one has a screw conveyor with chrome-plated Surface and a press die used, the surface of which is in contact with the polymer plated with chromium or with a fluorohydrocarbon polymer is covered » 5. The method according to claim 1 to 4, characterized in that the extrusion is carried out with a ratio of the cross-sectional area of the cavity of the press die to the cross-sectional area of the flight depth of the screw of less than 1.0 and more than 0.175. - 33 - * flil2 * / 177S BAD 6. The method according to claim 5, characterized in that a ratio of the cross-sectional areas between 0.9 and 0.2 is selected. - 34 - 6AD ORlQiNAu ÖÖ9824 / 1775