DE2407359A1 - METHOD OF MANUFACTURING DISCONTINUOUS FIBRILS - Google Patents

Description

PATENT LAWYERS

DR. ING. A. VAN DERWERTH DR. FRANZ LEDERER

21 HAMBURG 90 8 MUNICH 80

WILSTO RFER STR 32 TEL. (040) 770861 LUCILE-GRAHN-STR. 22 TEL. COS 111 47 29

Munich, January 28, 1974 Cas S.75 / 9-59 Comb.

SOLYAT & CIE.

33 rue du Prince Albert, Brussels, Belgium

Method of manufacturing discontinuous librils

The invention relates to a method for producing discontinuous fibrils by sudden relaxation of a liquid two-phase mixture of molten polymer and solvent which is at an elevated pressure and temperature.

There are already working methods for the production of continuous, f! brilliant structures or rovings. Such continuous structures are very difficult as such, mainly because of their extremely large volume and the The speed with which they are produced. This is the reason that you can turn them into economical Way to be able to use, first subjected to a dismemberment,

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which reduces their dimensions, but for their physical Properties is harmful and entails high fixed assets and significant energy consumption. For this Processes have already been developed to obtain discontinuous fibrils directly. In the Belgian patent specification 787 032 of the applicant is a working method for production of discontinuous fibrils, in which the two-phase mixture immediately before it the sudden Relaxation is subjected, is dispersed in an additive fluid. Applicant's Belgian patent 787 033 is a working method for the production of discontinuous i'ibrillen described in which the formed by the sudden relaxation of the two-phase mixture, fibrillated Structure is chopped up at the same moment of its formation by a cross flow of a fluid.

Although the technology for the production of discontinuous 5'ibrillen were greatly improved by these ways of working, they nevertheless had some serious disadvantages. The first Disadvantage is that very large amounts of additional fluid to bring about sufficient chopping or disintegration must be applied.

A second disadvantage is that the manufactured in this way, discontinuous i'ibrillen are not sufficiently regular for the greater part of the applications: their lengths show deviations that are too large in relation to the mean value.

A third disadvantage is that these procedures do not reproducible the production of discontinuous Allow fibrils with a given length, which are intended for a given application, and in particular not of very short fibrils.

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Surprisingly, a method for the production of discontinuous fibrils found which do not have these disadvantages.

The invention therefore relates to a process for the production of discontinuous fibrils due to sudden relaxation of a liquid two-phase mixture, which is molten polymer and contains solvent and is at elevated temperature and pressure, the solvent being instantaneous evaporated and the polymer solidified, this process is characterized in that the liquid two-phase mixture by ejecting through an opening at great speed is relaxed to form a discharge cone and that the discharge cone is atomized ..

Under the designation "discontinuous iTbrillen" are in the Description to understand elongated, fibrillated structures, which are formed by very thin individual threads with a thickness in the order of magnitude are formed by microns and below each other. Forming a three-dimensional network are connected. These Fibrils, which are flaky in appearance, are generally elongated in shape. Their length varies from about 0.5 mm to 5 cm, and their diameter approximately from 0.01 to 5 mni. The specific surface of such products is very high: it is above 1 m / g, and in many cases above 10 m / g. Such fibrils are an excellent starting material for the production of non-woven textiles (fleeces) and synthetic papers according to methods known per se.

The inventive method can employ any Polymers are carried out, which for the formation of two-phase mixtures - which will be explained in more detail later - in the Location is.

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In general, all polymers which can be spun into threads are suitable for the process according to the invention. Examples include: polyolefins, polyamides, thermoplastic polyesters, polyurethanes, vinyl polymers, e.g. B. Polymers based on vinyl chloride, vinyl acetate or vinylidene fluoride, and acrylic polymers, e.g. B. Polymers of acrylonitrile or methyl acrylate.

However, it is preferred to use crystalline polymers whose degree of crystallinity, as measured by X-ray diffraction, is above of 10% and preferably above 20%. The stretching, which the very thin fibrils form Filaments are subject to the immediate evaporation of the solvent, given them because of the sudden release The solvent vapors have an oriented structure when formed from a crystalline polymer, and thus noticeable better mechanical properties.

The best results are obtained with crystalline polyolefins. Among them, most commonly used are polymers having a substantially linear structure which are at least 50 mol% of one contain alpha-olefins with 2 to 6 carbon atoms. Examples this includes high density polyethylene and isotactic polypropylene, which are readily commercially available, as well isotactic polybutene- (i) and isotactic poly-4-methylpentene, which are manufactured on a much smaller scale.

The solvent, which is the other component of the two-phase mixture, is generally selected depending on the type of polymer used as well as the following criteria. It should preferably not normally dissolve the polymer: it must not dissolve more than 50 g / l and preferably not more than 10 g / l polymer under normal temperature and pressure conditions (20 ^° C. and 1 atm). Second, it is beneficial

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if its boiling point is lower than the temperature at which the polymer can be plastically deformed: it should maintain a boiling point at normal pressure of more than 20 ^° C. and preferably more than 40 ^° C. below the deformation temperature of the polymer it must enable the formation of a liquid two-phase mixture - as will be explained in more detail below - under the temperature and pressure conditions which allow its immediate evaporation and solidification of the polymer.

Among the numerous solvents that can be used, the following may be mentioned in particular: aliphatic ^ hydrocarbons, e.g. B. n-butane, n-pentane, η-hexane, n-heptane and n-octane and their isomers, cycloaliphatic hydrocarbons, e.g. 3. Cyclohexane and methylcyclohexane, aromatic hydrocarbons, e.g. B. benzene, toluene and xylene, haloalkanes, z, - B. chloromethanes, chlorofluoromethanes, chloroethanes and chlorofluoroethanes, alcohols, ketones, esters, amides, nitriles and ethers.

When a polymer selected from crystalline polyolefins is used, the present invention uses a solvent preferably that selected from aliphatic and cycloaliphatic hydrocarbons containing 4 to 8 carbon atoms will, e.g. B. hexane and cyclohexane technical grade.

The expression "liquid two-phase mixture" used in the description is explained in more detail below.

When looking at a mixture of polymer and a suitable solvent with a suitable concentration of polymer, which is at a temperature above the melting temperature of the polymer, applies a very high pressure, observed that the mixture is in the form of a single, homogeneous, liquid phase. If you then keep everything constant

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progressively lower the pressure under other conditions one that the only, homogeneous, liquid phase of a certain pressure, which varies with the respective case, is due to the Occurrence of a system with two liquid phases is cloudy, this system being replaced by a liquid, continuous, polymer rich phase is formed in which droplets of a liquid, polymer! poor phase are dispersed. The pressure value, wc this phenomenon can easily be observed experimentally for different values of temperature and concentration Polymer.

In the method according to the invention, it is sufficient to select the pressure of the mixture subjected to the sudden relaxation in such a way that that they are in the form of a liquid two-phase mixture is present. The same goes for the temperature and the concentration of polymer.

A convenient way of doing it!) It divides in, a liquid single phase mixture under constant conditions of polymer concentration, temperature and pressure, then one To carry out pre-expansion of the mixture under constant conditions, to bring about the appearance of the two-phase system, and then the sudden relaxation a short time later perform.

The temperature of the liquid subject to sudden relaxation Zv / eiphasengemisches must be such that the in latent form by the solvent and the molten polymer stored heat is sufficient to ensure complete evaporation of the solvent after the sudden relaxation; the temperature must therefore be above a minimum value. However, it must not exceed a maximum value, otherwise the The amount of heat consumed by the complete evaporation of the solvent is not sufficient to maintain a sufficient temperature starting to induce subsidence, whereby the immediate solidification

of the polymer is brought about. Furthermore, the temperature must also be sufficiently high for the formation of the liquid two-phase mixture from solvent and molten polymer. After all, of course, it has to be below the critical temperature of the solvent.

In general, working at a temperature between 100 ^° C. and 300 ^° C. and preferably between 125 ^° C. and 250 ^° C. is preferred.

The polymer concentration of the liquid two-phase mixture is also selected so that the preparation of this mixture, complete evaporation of the solvent and solidification of the polymer is possible. It varies depending on the strong cheeses on the physical properties of the polymer and the solvent. Generally it is between 1 and 500 g per kg of the mixture. However, the use of mixtures is preferred, which 10 to 300 g of polymer per kg of solvent and in particular contain 50 to 200 g / kg. In addition to polymers and solvents, which can also be present on their own or can themselves be mixtures, the liquid Two-phase mixture also includes conventional additives for polymers such as antioxidants, light stabilizers, antistatic Contain agents, surfactants / reinforcing agents, fillers, pigments, dyes and nucleating agents, provided that that this does not result in the formation of the mixture, the immediate evaporation of the solvent and the solidification of the polymer affect.

For each special case, a solvent which fulfills the characteristics given above should therefore be selected and then selected the polymer concentration, the pressure and the temperature of the liquid two-phase mixture, which is the sudden relaxation is subject to be selected. Such a determination can easily be made experimentally taking into account the above

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specified numerical values. The procedural conditions are the same as were carried out on liquid two-phase mixtures, which according to the prior art for Production of continuous strands of fibrin applied became.

In the process according to the invention, the liquid two-phase mixtures are subjected to sudden relaxation, d. H. the pressure suddenly becomes of the very high value at which they are initially relaxed to a value close to atmospheric pressure. This pressure after relaxation lies preferably below 3 kg / cm absolute. The duration of the Relaxation is very brief, preferably less than 1 second.

One of the essential features of the invention is to carry out the relaxation by the liquid two-phase mixture is ejected through an opening at high speed in such a way that a liquid from which is subjected to the tension Two-phase mixture formed discharge cone is generated. Because of the large difference that exists between the initial pressure of the liquid two-phase mixture and the pressure after relaxation, it is generally sufficient to use the liquid two-phase mixture through an appropriately sized opening, which is the connection between the container in which the two-phase mixture is before relaxation, and the container in which the discontinuous fibrils and the Solvent vapors are absorbed and which is at a pressure close to atmospheric pressure, ensures.

At the outlet of the opening, the mixture causes because of its high Velocity the appearance of a so-called "free jet", see John H. Perry, Chemical Engineers' Handbook, 1963, section ^ Page 18. Since the ejection takes place at high speed, it is a free jet with a turbulent flow. According to the theory of free jets with turbulent

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Flow forms at the outlet of the opening an ejection cone in which the liquid two-phase mixture is approximately the same speed as in the opening. However, the liquid is located in the discharge cone Two-phase mixture no longer in equilibrium as a result of the pressure reduction. If you don't atomize the discharge cone, before the free jet has started to spread, the solvent evaporates and forms a very large volume of gas. At the same time, the polymer solidifies, creating a brilliant structure which is shaped like a pear the influence of the solvents, which escape, spreads, and then in the form of a continuous, fibrillated Strand pulls together.

All of these phenomena are shown schematically in FIG. 1 of the drawing, in which, in section, a large Velocity of two-phase liquid mixture ejected into the atmosphere through a circular opening is shown.

The height of the discharge cone is at most about 5 times the diameter, if it is a circular opening and 5 times the thickness if it is an endless slot. The cross-sectional shape of the opening can be arbitrary however, it is preferred, for reasons of simplicity, openings to be used with a circular cut. The section of the opening must have such dimensions that the mean speed of the liquid two-phase mixture in the opening is above 50 m / sec and preferably above 75 m / sec. The best results are obtained when the speed is above 100 m / sec. Generally such Speeds achieved with openings whose diameter (or their hydraulic diameter in the case of openings with non-circular cross-section) between 0.1 and 3 mm and preferably is between 0.5 and 1.2 mm, and their ratio of

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Length / diameter between 0.1 and 10 and preferably between 0.5 and 2.

The second essential feature of the invention is to atomize the discharge cone in such a way that it is in droplets of liquid two-phase mixture, each droplet causing the formation of a discontinuous fibril. It is essential that the atomization of the discharge cone takes place at a point where the solvent has not yet had time to Has found vaporizing, d. H. very close to the opening. In this way, liquid two-phase mixture, which is still the possesses initial morphology, atomized. The distance from the opening at which the atomization is carried out lies below 0.25 mm, preferably below 0.10 mm. the best results are obtained when there is practically an eontakt here is present.

Numerous means or devices can be used to atomize the discharge cone. For example, as with the classic atomizers, use a fluid under pressure. However, this embodiment has the disadvantage that it is random and does not result in fibrils of regular dimensions. It is therefore preferred according to the invention to use atomization to ensure the discharge cone by mechanical devices.

Numerous embodiments can be used to carry out the atomization of the discharge cone can be applied by mechanical devices. One embodiment is the flow of the liquid Two-phase mixture by a high frequency device, ζ. Β. a device controlled by a piezoelectric quartz, to cut through. Another embodiment consists in placing the discharge cone on a rotating at high speed To fling disc so that the cone is under the influence of the

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Centrifugal force is atomized with the aid of a device, which of the device used in the so-called "atomization ±) ungstrocknen" is analogous, see John H. Perry, Chemical Engineers' Handbook, 1963, Section 20, page 58.

A third embodiment, which is preferred according to the invention, consists in cutting the ejection cone at high frequency with a device which is oriented in the transverse direction with respect to the direction of flow acts. According to a first modification of this embodiment, a rotating device can be used for this purpose, which rotates about an axis parallel to the direction of the flow, and is provided with any cutting blades which extend radially so that the ejection cone is pierced sufficiently close to the opening. Preferably the number is Cutting blades high to increase the frequency of cutting.

According to a second, preferred variant of this embodiment can- the eotation device formed by a toothed wheel which is moving with great speed around one to the direction of the river, which pours out of the relief opening, parallel axis or an axis perpendicular to this direction.

When the toothed wheel rotates in a direction parallel to the direction of the aforementioned flow, it is advisable to arrange it so that his teeth one after the other opposite the relaxation opening walk past. Preferably each tooth should be consecutive Completely cover the relaxation opening and then release it completely.

The shape of the teeth can be any, and they can be radial or inclined. The choice of the characteristics of the toothed wheel can be made by Attempts are made to determine the for each type of polymer used To determine parameters which lead to fibrils of excellent quality.

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The toothed wheel can also rotate at great speed around an axis perpendicular to the direction of the flow pouring out of the relief opening. In this case, the toothed wheel must have a thickness which is at least equal to the largest dimension of the Relaxation opening is, and preferably its axis of rotation should undercut the axis of the relaxation opening. In this way the toothed wheel works in the same way as a milling cutter, and the discharge cone is successive through the ridges Pierce teeth.

Regardless of the variant of this embodiment used, it is advantageous to ensure an increased frequency of severing or piercing. This is generally above 5000 impacts / sec and preferably above 10,000 impacts / sec. The best results are obtained when the frequency is above 50,000 impacts / sec. It is therefore advantageous to give the devices used a high rotational speed: above 10,000 rpm and preferably above 25,000 rpm. Such rotational speeds can be achieved with the aid of special electric motors or with the aid of turbines. Furthermore, they can be controlled with the help of devices such as frequency regulators. Such high speeds make it possible to limit the number of cutting edges or teeth of the devices used and thus to keep their diameter at an acceptable value.

With the different devices described above, it is possible to vary the length of the fibrils as desired by the various parameters, such as the speed of rotation of the devices used, the number of cutting edges or teeth, the profile and depth of the teeth is / are changed. Kit of such devices also allows short fibrils of excellent quality and predetermined, constant length to manufacture.

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In using the three devices described above, it has been found that it is imperative that the impact or
Impact between the cutting edges or the teeth and the flow from the expansion opening takes place at the level of the discharge cone. Indeed, it has been found that if the impact occurs at a greater distance from the opening than the height reached by the ejection cone, e.g. B. more than 8 times the opening diameter, the piercing or cutting is carried out on already solidified polymer, which is
compacted under the influence of this impact or impact, with little useful, dense sequins being formed. These
Sequins are no longer fibrillated at all, are no longer formed by very thin individual threads that form a three-dimensional network, and they no longer have a large, specific surface.

It has been found that when the type of polymer used and the relaxation conditions of the liquid two-phase mixture are changed, the height of the discharge cone is within a large
Limits can vary, but with an amount equal to that
5 times the diameter or the strength of the relief opening is not exceeded.

To make constant production with good quality,
it has been found that the distance between the relief opening and the puncture point should always be as small as possible
should.

As already described above, the process according to the invention enables the economical production of discontinuous, even very short fibrils, which have excellent fluidity exhibit. The use of such short fibrils is particularly useful in the field of partial or total manufacture Synthetic paper by conventional papermaking processes advantageous because of the great relief in the

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Conversion into aqueous suspension and the equipment.

The various, erfindungsgeinäße procedures for Chopping are explained in more detail below with reference to the drawing; the figures represent:

Fig. 1 is a schematic view of a section showing the ejection of a liquid two-phase mixture represents at high speed through a circular opening;

Fig. 2 is a schematic partial sectional view of a device which is used to carry out the method under Use of a cutting wheel is suitable, which rotates around an axis parallel to the direction of the relief opening leaving river turns;

3 shows a schematic partial sectional view of a device, which is suitable for carrying out the method using a toothed Eades, which rotates about an axis parallel to the direction of the flow leaving the relief opening;

FIG. 4 is a partial bottom view of that shown in FIG Contraption;

5 shows a schematic partial sectional view of a device, which is suitable for carrying out the method using a toothed Eades that rotates about an axis perpendicular to the direction of flow leaving the relief port;

FIG. 6 is a partial view of the profile of the device of FIG. 5.

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In each figure, the expansion nozzle is designated by the reference number and the rotating means for piercing by the reference numeral 2 marked. These figures are self-explanatory so that a detailed description is not necessary.

The invention is illustrated below with the aid of practical exemplary embodiments explained in more detail.

example 1

A liquid two-phase mixture of high density polyethylene (product of Solvay & Cie. Under the trade name ELTEX A 1050) and technical hexane was prepared. The mixture contained 15% by weight polymer. His temperature was 200 ⁰ C

and its pressure 60 kg / cm.

The mixture was subjected to sudden relaxation to form an ejection cone by passing it through an opening circular cross-section 1 mm in diameter and 1 mm in length. The relaxation was in an enclosure at atmospheric Pressure carried out.

The atomization of the discharge cone was carried out with the aid of a rotating device, which is driven by a toothed wheel rotating around an axis parallel to the direction of the flow leaving the "relaxation opening," such as this is shown schematically in FIGS.

The conditions of chopping were as follows:

- Number of teeth on the toothed wheel = 48

- Diameter of the toothed wheel = 80 mm

- Depth of the teeth «= 6 mm

- Distance nozzle-toothed wheel = 0.05 mm

- Speed of rotation of the toothed wheel = 60,000 rpm

When working under these conditions, fibrils were using a practically uniform length of 3.7 ™> · obtained.

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Example 2

The procedure of Example 1 was repeated exactly. the However, chopping conditions were as follows:

- Number of teeth on the toothed wheel = 80

- Diameter of the toothed wheel = ^ O mm

- Depth of the teeth = 4 mm

- Distance nozzle-toothed wheel = 0.05 εη »ί

- Speed of rotation of the toothed wheel = 60,000 rpm

When working under these conditions, fibrils were using obtained a practically uniform length of 2.2 mm.

example $

The procedure of Example 1 was repeated. However, the atomization of the discharge cone was carried out with the aid of a rotating device causes polygamy was formed by a toothed wheel that revolves around an axis perpendicular to the direction of the Relaxation opening turned out of the flow, as shown schematically in the i'ig. 5 and 6 is shown. The conditions of chopping were as follows:

- Number of teeth on the toothed wheel - = 120

- Diameter of the toothed wheel = 80 mm

- Thickness of the toothed wheel = 1.2 mm

- Depth of the teeth = 1.2 mm

- Distance between nozzle and comb of teeth = 0 mm (contact)

- Speed of rotation of the toothed wheel = 60,000 rpm

When working under these conditions, fibrils were using a uniform length of 1.4 mm.

Example 4

The procedure of Example 3 was repeated. The conditions of chopping, however, were the following:

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- Number of teeth on the cutted wheel = 80

- Diameter of the toothed wheel = 50 mm

- Thickness of the toothed wheel = 1.2 mm

- depth of teeth »= 1.2 mm - distance between nozzle and crest of teeth = 0 mm (contact)

- Speed of rotation of the toothed wheel = 60,000 rpm

When working under these conditions, fibrils were using a uniform length of 2 mm.

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Claims (12)

Claims 1. Process for the production of discontinuous fibrils by suddenly releasing a molten polymer
and solvent-containing two-phase mixture, which is at elevated pressure and elevated temperature, so that the solvent evaporates instantly and that
Polymers are solidified, characterized in that the liquid two-phase mixture is ejected
is expanded through an opening at high speed to form a discharge cone and that the discharge cone is atomized. 2. The method according to claim 1, characterized in that that the speed of the liquid two-phase mixture in the opening is adjusted to above 50 m / sec. 3. The method according to claim 1, characterized in that that an opening is used which has a circular section and a diameter between 0.1 and 3 mm and a length / diameter ratio between 0.1 and 10 has. 4. The method according to claim 1, characterized in calibration n e t that the discharge cone is at a distance from the opening is atomized from below 0.25 mm. 5. Method according to claim 1, characterized in that it is marked e t that the ejection cone is atomized at a distance from the opening of below 0.10 mm. 6. The method according to claim 1, characterized in that the discharge cone by mechanical devices is atomized. 409838 / 094B 7. The method according to claim 1, characterized in that that the ejection cone is pierced with high frequency by a device which in the transverse direction to 'The direction of the river works. 8. The method according to claim 7, characterized in that that the ejection cone is pierced by a device which rotates about an axis parallel to the direction of the river turns. 9. The method according to claim 7, characterized in that that a device is used which is provided with radial cutting edges. 10. The method according to claim 7 *, characterized in that that a device is used which is formed by a toothed wheel. 11. The method according to claim 10, characterized in that it is marked e t that the toothed wheel is arranged in such a way that its teeth pass one after the other in front of the relaxation opening. 12. The method according to claim 7i, characterized in that that the discharge cone is pierced by a device which is about an axis perpendicular to the direction of the river turns, and that the device is formed by a toothed wheel. 8 3 8/0940