DE2033007A1 - Process for the production of open cell foams from ethylene copolymers - Google Patents

Description

Badische Anilin- & Soda-Fabrik AG

Our mark OoZ. 26 845 Ks / Wnz 6700 Ludwigshafen, 2.7.I97O

Process for the production of open-cell foams from ethylene

copolymers

The invention relates to a method for producing open-cell Foams made from ethylene copolymers by extrusion of homogeneous mixtures of partially crosslinked ethylene polymers and low-boiling blowing agents.

Several processes have already become known for the production of open-cell foams from ethylene polymers. Open-cell foams are to be understood as meaning foams in which the individual cells are not separated from one another by cell membranes, but are connected to one another. For example, it is known from Austrian Patent 280 609 to produce open-cell foams from ethylene copolymers by mixing the copolymers in the presence of crosslinking agents containing sulfur or sulfur compounds at temperatures above the eristallite melting point of the copolymers with low-boiling blowing agents at pressures above the vapor pressure of the blowing agent lie at the mixture temperature, the homogeneous mixture cools down to a temperature which lies between the Eristallitschmelzpunkt and 20 ⁰ C below, and the homogeneous mixture relaxes. However, the open-cell foams produced by this process do not have a uniform cell structure because the open cells are not evenly distributed and the cell size varies. The density of the extruded foam tape is lower in the outer zone than in the middle ο the foams also contain voids in some cases »

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The object of the invention was to show a method by which one can produce open-cell foams that are free from There are cavities, a uniform cell structure and a uniform one Have density.

The invention relates to a process for producing open-cell foams from ethylene copolymers by mixing of copolymers of ethylene and vinyl esters and / or esters of unsaturated carboxylic acids in the presence of crosslinking agents with low-boiling blowing agents at temperatures above the crystallite melting point of the polymers and Pressures that are above the vapor pressure of the propellant at the mixture temperature lying, cooling the homogeneous mixture on

ο
a temperature which is between 15 C above the crystallite melting point and 20 G below and pressing out the homogeneous mixture in a zone of lower pressure. The process according to the invention is characterized in that the polymer is crosslinked to such an extent that the elongation at break of the crosslinked polymer is reduced by 20 to 60 ^ compared to that of the uncrosslinked polymer and the homogeneous mixture at a temperature which is between 15 ⁰ G above the crystallite melting point of the Polymerisates and 2O ⁰ G is below, can dwell for at least 10 minutes in a zone in which there is a pressure that prevents the mixture from foaming. The advantage of the process according to the invention over the aforementioned process of the prior art is that void-free foams are obtained which have a uniform cell structure and a uniform density.

Copolymers of ethylene with vinyl esters and / or esters of unsaturated copolymers which are copolymerizable with ethylene are suitable for the process Carboxylic acids, The copolymers contain at least 60 percent by weight of ethylene as polymerized units. Suitable Comonomers are, for example, vinyl esters of acids with 2 to 5 carbon atoms or esters of unsaturated acids, which have 3 to 5 carbon atoms and are derived from alcohols with 1 to 20 carbon atoms ,. The foams are mostly made up

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Copolymers of ethylene with vinyl acetate or acrylic acid esters manufactured. However, ethylene copolymers are of particular importance to which, in addition to the esters mentioned, 1 to 20 percent by weight of an unsaturated acid, such as acrylic acid, Methacrylic acid, crotonic acid, fumaric acid or maleic acid, polymerized included * For the production of softer open-cell Foams are mainly copolymers of ethylene into consideration, the 5 to 20 percent by weight acrylic acid and 5 to 20 percent by weight of acrylic acid tert -butyl ester is polymerized contain.

In order to produce open-cell foams from the copolymers mentioned, it is necessary that the elongation at break of the polymers is reduced by crosslinking prior to foaming. also called gel content - is determined by treating the polymer for 24 hours in decalin at HO ⁰ G, filtering off the undissolved material and drying it. The amount of deSj / polymer which is insoluble in decalin is referred to as the gel content of the polymer. The elongation at break can be reduced with several crosslinking agents belonging to different substance classes. As a rule, the same degree of crosslinking gives different values for the elongation at break. For the process according to the invention, however, it is crucial that the elongation at break of the crosslinked polymer is reduced by 20 to 60% compared to that of the uncrosslinked polymer. The values for the elongation at break of the crosslinked base material , measured in accordance with DIN 53 571, are generally between 200 and 500 io _r, preferably between 250 and 400 fo _t

The polymers mentioned are particularly advantageous with Metal oxides of main groups Ϊ «and II as well as with metal oxides the IIο subgroup of the periodic system networked. Of the Metal oxides that come in bed are particularly suitable as zinc oxide and barium oxide. For crosslinking, the polymers are mixed with a metal oxide and the mixture is heated to temperatures

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"10: to 1OO ⁰ C above the Kr is all it melting point is of the polymers are" The crosslinking reaction is usually performed in? present a low-boiling propellant at pressures which prevent foaming of the mixture it is also possible. to mix an already crosslinked copolymer with the blowing agent »Although the crosslinking reduces the elongation at break of the polymer, the flowability of the polymer melt is retained. 0.5 to 7 parts by weight of metal oxide are used per 100 parts by weight of copolymer The degree of crosslinking of the polymer is 5 to 50 #.

The copolymers can also be mixed with mixtures of sulfur, a metal oxide of main group II or subgroup des Periodic table, fatty acids and optionally vulcanization accelerators be networked. The oxides can be in. Combination with each other or in combination with other oxides are used »Of the fatty acids, the saturated and unsaturated carboxylic acids come into consideration, which have 10 to 20 carbon atoms contain mainly oleic acid, palmitic acid and stearic acid. Under vulcanization accelerators, the Connections are understood that can be used to speed up the Vulcanization of rubber used (cf. Kunststofflexikon, 4ο edition, Carl Hanser-Verlag, Munich, 1967, page 377), e.g. Thiazole compounds, thiuram disulfides, thiuram tetrasulfides as well as piperidine or guanidine compounds. Based on 100 parts by weight of copolymer, 0.2 to 3 parts by weight are used Sulfur, 0.5 to 7 parts by weight metal oxide, 0.2 to 2 parts by weight Fatty acid and 0.1 to 5 parts by weight vulcanization accelerator an ο

However, it is also possible to use the copolymers in their absence of sulfur with thiuram disulfides and thiuram tetrasulfides to network. In this case, it is used per 100 parts by weight Copolymer 0, -5 to 7 parts by weight of the Ttiiuramdi or Thiuram tetrasulfide ο Possible - especially tetraalkyl - or dialkyldiaryl-thiuramdi- or tetra-sulfides with alkyl

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groups which preferably contain 1 to 5 carbon atoms. Tetramethylthiuram disulfide, tetraethylthiuram disulfide are advantageous, Dipentamethylene thiuram tetrasulfide and dimethyldiphenylthiuram disulfidο Foams with particularly advantageous properties are obtained if the thiuramdi or -tetrasulfide also adds fatty acids and / or oxides of divalent metals »When crosslinking with sulfur and / or vulcanization accelerators the gel content of the foams is 10 to 70 percent by weight, preferably 30 to 60 percent by weight O

A reduction in the elongation at break of the ethylene polymers can can also be achieved by crosslinking the ethylene polymers with isocyanates. The ethylene copolymers are mixed in with this Temperatures above the crystallite melting point of the polymer with polyisocyanates in the presence of a blowing agent. Man mainly uses aliphatic and aromatic diisocyanates, such as hexamethylene-1,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, Naphthylene-1,5-diisocyanate and tolylene-2,4-diisocyanate. The ethylene copolymers are mixed with 0.5 to 5 percent by weight of polyisocyanates based on the weight of the copolymer. The gel content of the ethylene copolymers is between 10 and 70 percent by weight.

The elongation at break of Äthylencopolymerisaten can also be decreased by exposing the polymers to an ionizing radiation, the irradiation preferably with Elektronenstrahleno The degree of crosslinking of the polymers is 1Q to 70 ^ ₀

The blowing agents used for the ethylene copolymers are hydrocarbons, halogenated hydrocarbons or chlorofluorocarbons into consideration, whose boiling points 25 to 150 ° C below the melting point of the copolymer. Under enamel » point should be understood here as the crystallite melting point. Suitable blowing agents are, for example, aliphatic or olefinic Hydrocarbons with 3 to 7 carbon atoms, such as propane, n-butane, -

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i-butane, pentane or propene, butene and pentene. Of particular importance as a blowing agent have isobutane or hydrocarbons having 5 to 7 carbon atoms and at least 2 pendent methyl groups whose boiling points are between -10 and +60 ⁰ C, ZOB, neopentane, and 2,2-dimethylbutane. Of the halogenated hydrocarbons, only those with 1 or 2 carbon atoms, such as methyl chloride, ethyl chloride and dichloromethane, are suitable. Suitable chlorofluorocarbon compounds are dichlorodifluoromethane, difluorotrichloroethane, monofluorochloromethane, 1.2 _s 2-trifluorotrichloroethane and 1,1,2,2-tetrafluorodichloroethane »

Based on the ethylene copolymer, 15 to 35 are used P weight percent propellant ,, The amount of propellant depends depending on the desired density of the foamed ethylene copolymer and the pressure ™ and temperature conditions during processing »In some cases it is advantageous to Use propellant mixtures. It is also possible to use solid propellants, which are formed at the mixing temperature decompose gaseous products; to use as propellant, ZoBo azodicarbonamide, azoisobutyric acid dinitrile or aromatic sulfohydrazides. For the production of foams With a particularly fine cell structure, mixtures of ethylene polymer, crosslinking agents and blowing agents can be used Nucleating agents are added. Fine powdered silicates such as talc, for example, are suitable, which is most useful in quantities from 1 to 3 percent by weight, based on the copolymer, is used. In addition to the polymer, the mixtures can contain crosslinking agents and propellants and other components, such as fillers, dyes, flame retardants, antistatic agents ^ stabilizers, Contain lubricants or other polymers. Other polymers include, for example, polyethylene and polypropylene and polyisobutylene into consideration. These polymers can be used in amounts of up to 40 percent by weight, based on the Copolymer to add the mixtures.

To produce the foams, nraii mixes the ethylene copolymers with a crosslinking agent and a blowing agent. It is expedient to work at temperatures which are 10 to 100 ⁰ C,

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■ preferably 30 to 90 ° C, above the crystallite melting point of the polymers are «The mixtures are under Pressures kept above the propellant pressure of the propellant lie at the mixing temperature, so that the propellants are always in the liquid state under the mixing conditions. This prevents the mixture from foaming in this zone (1o zone). The vapor pressure is under propellant pressure of the blowing agent over the molten copolymer to understand »The mixes are usually in continuous working mixing devices. Of these, extruders (screw presses) have proven particularly useful. However, the mixtures can also operate batchwise Devices, ZcB. in pressure vessels with agitator, getting produced.

The expandable mixture of crosslinked Gopolymerisat and blowing agent is cooled down before foaming to temperatures below, are between 15 ⁰ C above the crystallite melting point of the polymer and 20 ⁰ C lower, preferably 5 ⁰ C above the crystallite and 1O ⁰ C. The goal part of the process according to the invention occurs only if this mixture is allowed to dwell for at least 10 minutes in a second zone in which there is a pressure which prevents the mixture from foaming. The temperature of the mixture must be between 15 ^° C. above the crystallite melting point of the polymer and 20 ^° C. below. Shorter residence times result in foams whose cell structure is not uniform. The residence time of the mixture in the 2nd zone is usually 30 to 120 minutes. ·

The homogeneous mixtures are then released into a zone (3rd zone) in which there is a pressure which is below the blowing agent pressure in the 3rd zone, so that the mixture foams. Most appropriate to relax the homogeneous mixture in an alternate forming under atmospheric pressure zone, the temperature of this zone should generally be less than 5O ⁰ G.

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FIG. 1 shows a semi-continuous gate direction, polymer and crosslinking agent are introduced through the opening (3) into an extruder (1) equipped with a rotatable screw (2). The polymer is melted and partially crosslinked. The propellant is added under pressure through the opening (4) and mixed in. Before the melt is pressed out through the nozzle (5), it is ^{cooled to temperatures between 15 °} C. above the crystallite melting point of the polymer and 20 ^° G below it and then transferred into a cylinder (6) which is connected to a heat exchanger ( 7) is surrounded »The cylinder (6) is completely or partially filled with the melt, which is kept at a temperature in the specified range. After a certain dwell time, the initially closed outlet nozzle (9) is opened, nozzle (5) is closed and the homogeneous mixture pressed into the atmosphere with the aid of the press punch (8), the continuously emerging strand foams up.

However, it is also possible to use one instead of the cylinder (6) use a second extruder. So that the extrusion of the mixture during the extrusion of the melt from the cylinder (6) does not occur must be interrupted, you can connect several cylinders in parallel and fill a cylinder from the extruder with melt, while the homogeneous mixture is being pressed out of another cylinder and possibly in a third one the melt lingers. The advantage of the procedure occurs, however not on if the expandable homogeneous melt in the cylinder (6) is mechanically moved, e.g. stirred *

With a constant gel content of the blowing agent-containing melt the open-cell portion of the foam by changing the temperature in the cylinder (6) and by changing the dwell time can be influenced to a large extent at the corresponding temperature. If the temperature and the residence time are increased, then the number of open cells of the foam increases. Table 1 illustrates the relationship between elongation at break and percentage of the open cells in the foam produced for a terpolymer

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t and with

sat, which has a crystallite melting point of 95 C. 3 percent by weight of zinc oxide is crosslinked at various melt temperatures in the extruder. The melt contains 15 percent by weight Isobutane, the residence time in the cylinder (6) of the device according to Figure 1 is 1 1/2 hours.

Table 1

Top tempera
tur in the extru
dermix zone Gel content Elongation at break ge
measure at RT
¥ 1 part of the
open cells
in the foam [$] 1 160 8th 450 50 2 165 12th 410 65 3 170 VJl 380 75 4th 175 17th 360 80-100 5 180 20th 320 100

Elongation at break of the uncrosslinked copolymer; $ 600

The proportion of open cells is determined by differential weighing of the dry and alcohol-soaked samples. the end the weight difference can be used to calculate the volume of alcohol consumed and from this the proportion of open cells in the foam can be determined will.

Table 2 shows the influence of the temperature of the homogeneous mixture in the cylinder (6) on the distribution of the closed and open cells in the foam. A mixture of a terpolymer of ethylene, 5 percent by weight of acrylic acid and 10 percent by weight of tert-butyl acrylate, which has a melting point of 95 ° C and an elongation at break of 600 $> , is mixed with 3 percent by weight of zinc oxide in an extruder (1) of the device according to FIG 1 mixed at 175 ⁰ C with 15 weight percent isobutane and transferred to a pressure vessel, in which the melt in the various specified in Table 2. _v doors temperature dwells 1 1/2 hours. The higher the temperature of the homogeneous mixture in the cylinder (6), the higher the ■:

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Percentage of open cells in the foam,

Table 2

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temperature
in the nozzle the miscr
(9) fc lung
M.
1 1 Share of Ze
a) closed 95 60 97 30 ' 100 20 - 0 105 - 0 115 Too hot for
Foam fälH illen IfoJ
b) open 40 70 80-100 100 Foaming,
; together

As Table 3 shows, the residence time of the homogeneous mixture in a pressure vessel, in which the foaming of the mixture is prevented, surprisingly, at a temperature of 100 G As already mentioned, the longer the homogeneous, the more open cells the foam contains Mixture lingers in the cylinder (6).

Dwell time (h)

Table 3

Proportion of cells
a) closed b) open

1/2 1

1 1/2 2

70 50

10 - 20 5

30 50

80-90 95

The process according to the invention gives foams whose The proportion of open cells is between 15 and 100 ^ ,, foams, that have less than $ 40 open cells are used as sealing material, Packaging inserts and container insulation used. Since these foams also have a They can represent a gas and liquid barrier for everyone

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the purposes are applied, 'for which one is also closed-cell Used foams. ,

Foams more open than 40 ° i cells have become increasingly softer and already allow gas and Jlüssigkeitsdurch "- gang. These foams are mainly used in the upholstery and sponge sector.

The density of the foams is between 20 and 60 g / lo It is however, it is also possible to produce foams with higher densities by the process according to the invention.

The invention is explained in more detail with the aid of the following examples » The parts given in the examples are parts by weight, the percentages percentages by weight "

example 1

100 parts of a terpolymer consisting of 85 percent by weight of ethylene, 5 percent by weight of acrylic acid and 10 percent by weight of terto-butyl acrylate are added in a twin-screw extruder with 3 parts by weight of talc, 3 parts of dry zinc oxide with a particle size of <Ί00 / u and 15 percent by weight of isobutane, based on the copolymer 175 ⁰ G mixed. The homogeneous gel is conveyed into a storage cylinder (6) in which there is a pressure that prevents the mixture from foaming. The melt is cooled ^{to 100 °} C. in the cylinder (6). After a dwell time of 1 1/2 hours, the homogeneous gel is relaxed through a slot nozzle with internal dimensions 12 × 0.5 cm. A foam tape is obtained with a cross section of 200 cm. The foam has a gel content of 17 percent, a density of 25 g / l and 90 <fo open cells. The elongation at break of the crosslinked polymer is about 60 $ that of the uncrosslinked. The foam is used for the production of packaging inserts.

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Comparative example 1

The procedure described in Example 1 is followed, but the procedure is in the absence of zinc oxides. No foam is obtained because the product collapses after foaming,

Comparative example 2

The procedure is as described in Example 1, but the melt is only cooled to 115 ^° C. "The product collapses immediately after the expansion process"

Comparison example 3

The procedure is as described in Example 1, with the exception that the cylinder (6) of the device according to FIG. 1 is removed. A foam is obtained, with its cell structure Is penetrated by cavities. The center of the foam tape has a hard core.

Example 2

100 parts of tert of a terpolymer of 80 parts of ethylene, 10 parts of acrylic acid and 10 parts -Butylacrylsäureester having a melting point of 90 ⁰ C are dry blended with 3 parts of talc, 2,5 parts of zinc oxide and 2 parts of calcium oxide. 25 of the mix kg are plasticized in an extruder, and 5 kg of a blowing agent mixture _for which the device is injected according to Figure 1 under pressure through the opening (4) and of 60 parts of isobutane and 40 parts of η-butane, mixed homogeneously ,, The The melt is then ^{cooled to 92 °} C. and conveyed through the nozzle (5) into a pressure vessel (6) in which the foaming of the melt is prevented. After an 'hour' residence time in the pressure vessel (6), the homogeneous mixture is relaxed through a round nozzle. Diameter is 4 mm. A foam strand is obtained which has an open area of 50 $. The elongation at break of the crosslinked polymer is about 50 $. that of the. Starting polymer ,, - -.

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If the procedure is as described in Example 2, but the melt is not left to linger in a pressure vessel, but instead the homogeneous mixture is extruded after cooling to 97 ^° C., the foam largely collapses immediately after it has been released,

Example 3

25 parts of a Äthylenhomopolymerisates having a density of 0.918 g / cm and a melt index of 1.5, and 75 parts of a copolymer of 84 $ ethylene, 8 $ acrylic acid and 8 $ n-butyl acrylate, having a melting point of 92 ⁰ C , are dry mixed with 2 parts of talc, 3 parts of zinc oxide and 2 parts of carbon black. This mixture is processed in a twin-screw extruder with 20 parts of a mixture of 40% isopentane and 60 % isobutane to form a homogeneous gel. The temperature in the mixing zone is 17O ⁰ C. The blowing agent-containing melt is cooled to 100 ⁰ C and fed into a pressure vessel. After a residence time of 11/2 hours in the pressure vessel, the homogeneous mixture is relaxed through a slot nozzle. One obtains a foam that $ 90> open cells and a density of 25 g / l has. The elongation at break of the crosslinked terpolymer is 40% of the elongation at break of the uncrosslinked polymer. The foam is used for the under-wallpaper insulation.

Comparative example 5

One proceeds as in Example 3, but cools the melt instead of 100 to 74 ⁰ C., one obtains a geschlosaen- cell foam.

Example 4

80 parts of a copolymer of 88 # ethylene and 12 # vinyl acetate with 20 parts of polyisobutylene of a viscosity from 1.3 10, 3 parts of talc, 2 parts of titanium dioxide, 2.5 parts

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Zinc oxide and 25 parts of isobutane plasticized in a single screw extruder with a downstream dwell extruder. The melt is ^{cooled to 95 °} C. and pressed into a pressure vessel in which there is a pressure that prevents the mixture from foaming. After a residence time of 1 1/2 hours, the melt is pressed out of the pressure vessel through a nozzle with the aid of a piston. A foam profile is obtained which has 95 ° 1 ° open cells. The Eeißdehnung the non-crosslinked polymer is $ 550, which the 20 fo networked polymer $ 250>.

Example 5

In a twin-screw extruder a mixture of 100 parts of 1 homogenised at a temperature of 175 ⁰ G a Äthylenterpolymerisates from 85 io ethylene, 9 $ acrylic acid and 6 $ acrylic acid tert-butyl ester, 1.5 parts of sulfur, 5.0 parts of barium oxide, Part of stearic acid, 0.8 part of dibenzothiazole disulfide and 3 parts of talc with 25 parts of isobutane. The expandable mixture is cooled to a temperature which corresponds to the crystallite melting point of the terpolymer (95 ^° C.) and transferred into a cylinder which is designed as a heat-insulated pressure chamber. After a residence time of 1 hour, the homogeneous mixture is expanded through a slot nozzle with dimensions of 150 8 mm. To obtain a foam tape, the 90% open cells, a density of 25 g / l and a gel fraction of 55 i> has. the

sates is reduced by 45 # compared to the non-networked one. The foam is used as an insert for sound-absorbing partition walls.

Example 6

100 parts of a terpolymer of 80 parts of ethylene, 10 parts of n-Butylaorylat and 10 parts of free acrylic acid are DiphenylBethan-4 diieocyanat in a twin screw extruder old 2 parts "4 ^f, 3 parts Talkuia and 20 parts of a * Treibeittelgemischea, the aue 50 parts of isobutane, 30 parts isopentane and

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20 parts ή-hexane ", mixed. The -tre ibmitte Ihaltige melt is ^{cooled in the extruder to 10O 0} C and conveyed into a pressure vessel, in which a pressure prevails, de'r is above the vapor pressure of the propellant. After a dwell time of 2 hours, the homogeneous mixture is relaxed. This gives a foam which was 90 $ open cells has and has a gel content of 30 io. the elongation at break of the crosslinked terpolymer is compared to that of the uncrosslinked decremented by $ 40 the foam is used to produce small cushion parts. used for furniture construction.

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Claims (1)

- 16 - O.Z. 26 845 Process for the production of open-cell foams from ethylene polymers by mixing copolymers of ethylene and vinyl esters and / or esters of unsaturated carboxylic acids in the presence of crosslinking agents with low-boiling blowing agents at temperatures above the crystallite melting point of the polymers and pressures above the vapor pressure of the blowing agent at the mixing temperature are, the homogeneous mixture to a temperature comprised between 15 ⁰ C above the Eristallitschmelzpunkts and 20 ⁰ C below, and extruding the homogeneous mixture niedri cooling in a zone * Geren pressure, characterized in that as far crosslinks the polymers, that-the elongation at break of the crosslinked polymer compared to that of the uncrosslinked polymer is ^{reduced by 20 to 60 0} Jo and the homogeneous mixture at a temperature which is between 15 ⁰ C above the crystallite melting point of the polymer and 20 ⁰ C below, at least 10 minutes in one Can linger zone in which there is pressure that prevents the mixture from foaming. Badische Anilin- & Soda-Fabrik AG- Sign. 10 9 8 8 3/1 5 1 9