FI57452C - FOERFARANDE FOER FRAMSTAELLNING AV SYNTHETIC FIBER FOER PAPPER - Google Patents

Description

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JgSA lBJ ("} UTLÄGGININCSSKRIFT 54 ^ v ^ (51) K» .ik? / Jnta3 D 01 D 5/11 SUO MI — FI N LAN D (21) Ptttnttihtkcrmis - Ptt «ntin * eknlng 753215 (22) Htkemlipiivl - AraSknlngad 1 ^ + · 11 · 7 5 (23) Alkupilvt — Glltigh «tadag 1 ^ .11.75 (41) Tullut JulklMkil - Bllvlt offmcllg 20.05.76

National Board of Patents and Registration (44) N «ht *» «k.lpwoo J. kuLjullulam pvm. -, Q

Patent- och regicterttyreiaan Anastan utlagd och utUkriftan pubiicand 30.04.80

(32) (33) (31) pyrd «« y «tuoltaut — Baglrd priorlm 19.11.7U

Italy-Italy (IT) 2959 ^ A / 7U

(71) Montedison S.p.A., 31, Foro Buonaparte, Milan, Italy-Italy (lT) (72) Giovanni Di Drusco, Milan, Deoscaride Zaffagnini, S. Biagio (Ferrara),

The present invention relates to a process for the production of synthetic fibrils or microfibers suitable for the production of paper, which process comprises the production of synthetic fibers for the production of paper. solutions, emulsions, or dispersions of thermoplastic polymers are extruded through a nozzle under conditions such that sudden evaporation of the liquid medium occurs in the extrusion zone, and the extruded polymer is decomposed, after exiting the nozzle, by a gas-vapor-vapor stream. -type nozzle and encounters the extruded polymer at high speed and at an angle to the extrusion direction.

In the manufacture of microfibers, the so-called the evaporation spinning method compresses solutions, emulsions, or suspensions of thermoplastic polymers in one or more liquid media through a nozzle under conditions of pressure and temperature such that the liquid flashes close to the nozzle to the outside of the die, a more or less continuous three-dimensional network with a surface area (specific surface area) greater than 1 m2 / g is formed.

2 57452

Evaporative spinning methods using homogeneous polymer solutions or emulsions of polymers, solvents and non-solvents (such as water) or dispersions of molten polymer in solvents and / or non-solvents are described, for example, in British Patents 891,931 and 1,262,531. in patents 3 U02 231, 3 081 519, 3 227 78U, 3 277 791 *, 3 770 856, 3 7 ^ 0 383 and 3 808 091, in the Belgian patent 789 808, in the French patent 2 176 858 and in the German application 2 3 ^ 3 5 ^ 3.

According to a more recent method, disclosed in the applicant's Finnish patent application 521/73, filed February 21, 1973, individual fibrils of the above type are obtained by direct application of a polyolefin solution extruded under "evaporation" conditions by a high-velocity gas jet which the direction forms an angle with respect to the direction of the solution.

An analogous method, but using biphasic liquid mixtures made from a molten polymer and a solvent, is disclosed in British Patents 1,355,912 and 1,355,913.

Finally, German application 2,339 OUU discloses a process for the preparation of fibrils, which process comprises extruding a polyolefin solution at a high temperature and applying a gas jet to the extruded solution at an angle of less than 30 ° at specified speed ratios.

According to these methods, a high velocity gas or steam jet has an oblique effect on the extruded polymer composition and these methods have been found to be the most suitable of all available methods for making synthetic microfibers for pulp production due to their simple equipment and ability to use all thermoplastic polymers.

The ability to use these methods on a commercial scale to provide fibrous products that are morphologically acceptable and economically competitive with cellulose is essentially related to the proper use of a gas jet for polymer solutions, emulsions, or dispersions. Several methods of use have already been proposed for this purpose. One of them is disclosed in the above-mentioned Finnish patent application 521/73 and comprises the use of a jet stream coaxially with an extrusion nozzle of a polymer solution.

Another solution is disclosed in the aforementioned British Patent 1,355,913, which uses a two-phase polymer / solvent mixture. The method comprises directing a flow into a tube having a shrinking portion, a throttling portion and optionally an expanding portion, wherein the encounter of the gas jet and the biphasic mixture is allowed to occur in either the shrinking portion of the tube or the throttling portion of the tube.

In both cases, the solutions presented are economically unsatisfactory due to the small amount of gas used due to the low yield of fibrous product.

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The uneconomical nature of the presented methods tends to increase with the use of high-velocity gas streams (especially if such a gas stream is formed of steam), which, however, are preferred to use.

The applicant has now found that it is possible in the above-mentioned methods to improve the yield of the fibrous product and at the same time to obtain advantageous properties.

The process according to the invention is characterized in that the polymer solutions, emulsions or dispersions are extruded into the expanding part of the nozzle.

A preferred embodiment of the invention is characterized in that the polymer solution, emulsion or dispersion is extruded into the zone of the expanding part where the medium reaches its maximum velocity according to the thermodynamic conditions upstream of the expanding part of the nozzle.

It is also preferred that the polymer solution, emulsion or dispersion be extruded at or in the immediate vicinity of the end of the expanding portion of the nozzle.

By the term "shrinkable-expandable-type nozzle" is meant any nozzle or tube comprising a successively shrinkable portion, a throttling portion and an expanding portion. The throttling part of such a nozzle is also called a "critical point" if the compressible medium is expanded, the pressure in the throttling part being higher than the pressure prevailing in the expanding part.

An example of a nozzle of the shrinkable-expandable type, which is generally used to create the above conditions in a gaseous medium and which can also be used in the process of this invention, is a nozzle known as "De Laval".

The conditions which form the basis of the present invention can be used for the treatment of homogeneous polymeric solutions as well as dispersions, suspensions and emulsions and, in general, heterogeneous mixtures of polymers in liquid solvents and / or non-solvents.

The polymer composition can be extruded at any point in the expanding portion of the nozzle where the gaseous medium expands, but in order to obtain homogeneous fibrils of suitable dimensions, it is preferred to extrude it to approximately the end of this expanding portion.

For the reasons already mentioned above, it is correspondingly advantageous for the gas jet velocity to be at or near this end point the highest possible velocity, which can be achieved on the basis of the gas jet temperature and pressure in the nozzle orifice. This can be achieved by dimensioning the nozzle appropriately as a function of the initial thermodynamic state and flow conditions of the medium used.

The solutions in question can be obtained by simple thermodynamic calculations or direct experiments.

When operating under the above conditions, it is possible, among other things, to use a very high velocity gas jet from the speed of sound at the critical point of the nozzle to multiple values at the end of the nozzle.

For each type of polymeric solution, emulsion or dispersion, there is an optimal gas jet rate depending on the polymer used and the solvent or liquid carrier as well as the thermodynamic properties of such a solution, emulsion or dispersion.

In general, it is preferred that the polymer solution or dispersion be extruded through a plurality of nozzles arranged around the expanding portion of the nozzle through which the medium flows.

As the gaseous medium, it is possible to use all gaseous substances or substances in the gaseous state disclosed for similar purposes in Italian patent 9 ^ 7 919, including solvents and liquid media containing the extrudable polymer composition, in gaseous form, provided that they are in such a state that - the material to be extruded - their temperature is lower than the dissolution and / or softening temperature of the polymer / residual solvent system in the polymer.

Steam is preferably used, especially when dry.

An example of a preferred solvent to be used as the gaseous medium is n-hexane in the form of superheated steam.

The conditions of use which form the basis of this invention are applicable to the treatment of any fibrous thermoplastic polymer, such as olefins, acrylonitrile, acrylates, vinyl chloride, vinyl acetate and styrene cm-copolymers, copolymers of these monomers, copolymers of such monomers, and such homopolymers.

The drawing shows an apparatus for applying the method of the present invention.

In this device, the nozzle 1, through which the gas jet flows in the direction indicated by the arrow 6 and having a convergent part 2, 3, and expanding the constricted part of the U, and the nozzles 5 to feed the polymer solution, emulsion, or dispersion of the arrow 7 direction to said expanding parts. The diameters of all these nozzles 5 may be uniform or their diameter may be larger in the vicinity of the expanding part it to allow a partial expansion of the polymer solution or dispersion before it comes into contact with the gas jet.

One surprising phenomenon when utilizing a gas jet according to the present invention is that no prior expansion of the polymer solution or dispersion is required to obtain suitable fibrous products.

In the device according to the drawing, the nozzles 5 form an angle of about 90 ° with respect to the longitudinal axis of the nozzle 1. However, the nozzles 5 can also be mounted at a different angle with respect to said axis, the angle being preferably between 5 57452 and 5-90 °.

The following examples are intended to illustrate the present invention without limiting it.

Example 1 This example deals with the preparation of polyethylene fibers using a solution of the polymer in n-hexane and a gas stream of dry saturated steam using the apparatus shown in the drawing.

For this, a solution containing 100 grams of high density polythene (M.I. = 1 +, 5) in one liter of solution was used, at a temperature of 180 ° C and a pressure difference to the outside air of 1 atmosphere.

The vapor pressure used at the inlet of the constricted portion of the nozzle was 18 kp / cm 2 and the temperature was 205 ° C. The steam flow rate was 300 kg / h.

The nozzle had a circular orifice (critical point) with a diameter of 6.5 mm and the diameter of the nozzle at the largest point (end point) of the expanding part was 15.1 + 2 mm.

The distance between the throttling part and the end point was 31.8 mm.

Under these conditions, the vapor pressure at the end of the approximately expanding portion was slightly, i. some mm Hg higher than normal atmospheric pressure and the steam had a maximum velocity of 900 m / sec, which corresponded to the conditions upstream of the critical point.

The vapor expansion corresponded to an enthalpy decrease of 115 kcal / kg.

The polymer solution was fed at a total flow rate of 960 kg / h through eight cylindrical nozzles placed symmetrically around the end of a shrink-expand-nozzle. The diameter of each nozzle was 2 nm.

After one hour of use, 120 kg of fibrils with a length of 3-h mm and an apparent diameter of 1 + 0 micrometers and an area of 7 m / g were obtained.

Steam consumption was 2.5 kg per kilogram of fibrils.

Example 2 A solution of the polyethylene of Example 1 in n-hexane at the same temperature and pressure and using the same hourly feeds was used.

The gas flow used was steam heated to 200 ° C with a pressure of 2.7 kp / cm and a flow rate of 300 kg / h.

A nozzle as shown in the drawing was used with a critical part diameter of 7.3 mm and a maximum cross-sectional diameter in the expanding part of the nozzle of 8.7 mm, where the steam was in the superheated state at a pressure slightly above normal pressure and the maximum steam velocity was 607 m / sec. The distance between the narrowest and widest parts was 22.1+ mm. The diameter of the nozzles used to extrude the polymer solution was 2 mm.

After one hour of use, 120 kg of fibrils with a length of 6 57452 2 1 + -5 mm, an apparent diameter of 1 + 0 micrometers and an area of 8 m / g were obtained. Steam consumption was 2.5 kg per kilogram of fibrils.

Example 3 This example relates to the preparation of fibrils from an emulsion formed from a solution of polypropylene in n-pentane and water. The polypropylene used had an M.I. of 10. The polypropylene content of the emulsion was 50 grams per liter of emulsion.

The weight ratio of N-pentane to water in the emulsion was 1. An apparatus as shown in the drawing was used in which the critical point of the gas flow nozzle was 11.5 mm, the maximum diameter of the expanding part of the nozzle at the end point was 11.7 mu and the distance between the critical and maximum diameter was about 21 nm.

The emulsion was extruded at a temperature of 155 ° C and a pressure of 21, U kp / cn? through eight cylindrical nozzles mounted symmetrically around the end point (maximum point) of the shrink-expandable-type nozzle, each nozzle having a diameter of 2 mm.

The emulsion was fed through these eight nozzles at a total flow rate of 2200 kg / h »The steam flow rate was 300 kg / h. The steam used was dry saturated steam with a pressure at the inlet of the shrinking part of the nozzle of 2 o 6 kp / cm and a temperature of 200 C.

Under these conditions, the vapor pressure at the end of the expanding portion of the nozzle was slightly, i. some mn Hg higher than normal atmospheric pressure and the steam had a maximum velocity of 715 m / sec which corresponded to the conditions upstream of the critical point.

After one hour of use, 150 kg of fibrils with a length of 1.5-2.5 nm, an average (apparent) diameter of 20 micrometers and an anine surface area of 2, 1 m / g were obtained. The steam consumption was 2 kg / kg per fiber.

Example 1+ This example relates to the preparation of fibrils from a two-phase polymer composition, wherein the second phase consists of molten polyethylene (MI = 5) and contains liquid n-hexane and the second phase consists of liquid n-hexane containing polyethylene in solution, the first phase being uniformly dispersed. -wound to the latter phase. Such a two-phase composition was obtained by heating a solution of polyethylene in n-hexane at a temperature of 200 ° C and a pressure of 17 k / cm. Under these temperature and pressure conditions, the biphasic composition was extruded through the eight nozzles of the apparatus shown in Example 1 at a total flow rate of 1200 kg / h. The gas flow used was steam at a temperature of 205 ° C and a pressure of 18 kp / cm at the inlet of the shrinking part of the nozzle, at a flow rate of 300 kg / h.

7 57452 The vapor pressure at the end of the expanding portion of the nozzle where the impact on the extruded polymer composition occurred was slightly higher than the normal atmospheric pressure and the gas flow had a maximum velocity of about 900 m / sec.

During one hour of use, 150 kg of fibrils with a length of 2-2.5 nm, an apparent diameter of about 25 micrometers and a specific surface area of 8 m / g were obtained. Steam consumption was 2 kg per kilogram of fibrils.

Claims (3)

8 57452 Claims; A process for the production of synthetic fibrils or microfibers suitable for the production of paper, which comprises extruding solutions, emulsions or dispersions of fiber-forming thermoplastic polymers through a nozzle (5) under conditions such that extrusion is extruded after extrusion, , with a gas or vapor stream passing through a nozzle (1) of the shrinkable-expanding type, e.g. De Laval type, and encountering the extruded polymer at high speed and at an angle to the extrusion direction, characterized in that the polymer solutions, emulsions or dispersions are extruded into the expanding part (U) of the nozzle (l). Method according to Claim 1, characterized in that the polymer solution, emulsion or dispersion is extruded into the zone of the expanding part (U) in which the medium reaches its maximum velocity under the thermodynamic conditions upstream of the expanding part of the nozzle. Process according to Claim 1, characterized in that the polymer solution, emulsion or dispersion is extruded at or in the immediate vicinity of the end point of the expanding part of the nozzle (M. k. Method according to one of Claims 1 to 3, characterized in that through nozzles (5) arranged around the expanding part (i +) of the nozzle (1) through which the medium flows.