JPS6020483B2 - Manufacturing method of synthetic fiber for paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing fibrils or microfibers made from thermoplastic polymeric materials suitable for use in the production of synthetic paper.

More particularly, the present invention provides for the production of said microwoven fabric by the technique of flash spinning a solution, emulsion or suspension of a polymer in a solvent in a gaseous or gaseous state and under the action of a fluid at high velocity. This relates to improvements related to manufacturing.

"Flash spinning" generally refers to the instantaneous or Near-instantaneous evaporation occurs, whereby the polymer precipitates in the form of numerous fibrils interconnected to form a more or less continuous three-dimensional network of fibers with a surface area (specific area) of 1 g/g or more. means the method of extrusion as occurs in

Flashew spinning methods using homogeneous polymers or emulsions of polymers in organic solvents, solvents and non-solvents (such as water) or dispersions of molten polymers in solvents and/or non-solvents are known, for example, from the UK. Patent No. 891943 and No. 1262531; U.S. Patent No. 340223
No. 1, No. 3081519, No. 3227784, No. 3
No. 770856, No. 3740383 and No. 3808
No. 091; Belgian Patent No. 789,808; French Patent No. 217 Plaque and German Patent No. 2,343,543.

According to a more recent method described in Tokusho No. 48-22,577, single fibrils of the type described above are produced by extruding a solution of a poly-IJ olefin in a "flash" state against the direction of the solution. It is obtained directly when subjecting to the disturbance action of a high-velocity gas jet with an angular direction. A similar process, but carried out starting from a two-phase liquid mixture of molten polymer and solvent, is described in GB 1355912 and GB 1355913.

Finally, in German Patent Publication No. 2 339 044, a polyolefin solution is extruded at high temperature and the extruded solution is heated at an angle of less than 30 degrees and at a special speed ratio.
A method of manufacturing fibrils is described that consists of impacting with a fluid jet.

The method of applying a high-velocity gas or steam jet at an angle onto an extruded polymer composition has been shown in paper due to both the simple equipment required and its applicability to any thermoplastic polymer. It has been found to be the most suitable of those conventionally available for producing synthetic microfibers to be used in producing pulp for commercial purposes. The feasibility of carrying out the process on a commercial scale in order to obtain textile products which are morphologically suitable and economically competitive with cellulose is primarily due to the fluidity of the polymer solutions, emulsions or dispersions used. Suitable methods of operating jets have already been proposed. One such method is described in Japanese Patent Application No. 48-22-577 mentioned above and consists in using a fluid in the form of a jet coaxial with the polymer solution extrusion nozzle. The use of a two-phase polymer/solvent mixture is proposed in the aforementioned British Patent No. 1,355,913.

It directs the fluid into a duct consisting of a convergent section, a narrow section and sometimes a diverging section in sequence, causing a collision between the fluid jet and the two-phase mixture in the converging or narrow section of the duct. consists of extruding the two-phase mixture into one of the parts. In both cases, the solutions proposed give unsatisfactory results from an economic point of view due to the low yield of textile products in terms of fluid consumption.

The uneconomical nature of the proposed method tends to increase when high fluid velocities are used (especially when the fluid is water vapor) and it is advantageous to obtain further benefits. The inventor has realized that in the above-described process the textile production can be significantly improved and at the same time fibrils of suitable properties, particularly homogeneity, can be obtained by using a fluid jet under special conditions. This condition involves expanding a fluid jet through a (convergence-diffusion type) nozzle (or duct) and dispersing the polymer solution, emulsion in a flash condition at an angle towards the expanding fluid jet in the diffusion section of said nozzle. Or it consists of extruding a dispersion.

The invention therefore involves extruding a solution, emulsion or dispersion of a fiber-forming thermoplastic polymer in a liquid medium through a nozzle under conditions such that the liquid soot immediately evaporates around the extrusion; At the periphery of the extrusion, the polymer solution, emulsion or dispersion is impinged on the polymer solution, emulsion or dispersion by a high velocity gaseous fluid jet in a direction angular to the direction of extrusion. Synthetic resin fibrils suitable for use in the manufacture of paper, characterized in that they are extruded in the diffusing section of an acquisition-diffusion type nozzle, which is initially expanded through and then subjected to a coalescing solution, emulsion or dispersion. Or to provide a method for producing microfibers.

According to a preferred embodiment of the invention, the extrusion of the polymer solution, emulsion or dispersion takes place in the band of the diffusion section, where the fluid jet is directed at a maximum temperature consistent with the thermodynamic conditions upstream of the fluid of the diffusion section. Reach the speed.

A further preferred condition is for the fluid to expand in the distal zone of the diffusion section of the nozzle in the vicinity of which it reaches its maximum velocity; It consists of extruding an emulsion or dispersion.

"Convergent-divergent nozzle" means any shape of nozzle or pipe consisting of, in order, a convergent section, a narrow section, and a diverging section.

The narrow section of the nozzle is used as a "limit section" when expanding a compressible fluid by making the pressure in the narrow section (critical pressure) higher than the pressure present downstream in the diffusing section.
is defined as An example of a nozzle of the drinking-diffusion type which is commonly used in the technology of clouding gaseous fluids and which can also be used for the purposes of the present invention is the nozzle known under the name "De Laval".

The conditions which constitute the object of the invention are applicable to the treatment of homogeneous polymer solutions as well as dispersions, suspensions, emulsions and in general heterogeneous mixtures of polymers and liquid solvents and/or non-solvents. The polymer composition can be extruded at any location in a nozzle diffusion section (as the fluid expands); Preferably, it is extruded near the end section of the diffusion section.

For similar reasons as already mentioned above, it is preferable to have a fluid jet in or near such end section at a maximum velocity compatible with the upward flow of the temperature and pressure conditions of the nozzle constriction.

This can be accomplished by suitably sizing the nozzle as a function of the initial thermodynamic state of the fluid utilized and downstream conditions.

The solution to the problem can be obtained simply by thermodynamic calculations or sometimes directly by experiment.

By operating in the manner described above, it becomes possible to utilize a range from the speed of sound in the marginal section to values several times higher in the terminal section.

For each type of polymer solution, emulsion or dispersion, the polymer, the solvent or liquid carrier used and the solution
There are selected velocity values for the fluid jet depending on the thermodynamic properties of the emulsion or dispersion.

It is preferred to use several extrusion nozzles of the polymer solution, emulsion or dispersion, generally arranged circularly around the nozzle diffusion section.

As a fluid, it is extruded in vapor form if conditions are such that when it impinges on the extrudate it is at a temperature below the decomposition and/or softening temperature of the polymer/residual solvent system in the polymer. It is possible to use the gaseous or vaporous substances described for a similar purpose in Italian Patent No. 94791, including solvents or liquid soots present in the polymer composition.

Especially if the condition is dry, use steam as much as possible.

An example of a solvent that can be advantageously utilized as a fluid in the state of superheated steam is n-hexane.

The operating conditions of the present invention are homopolymers of olefins, acrylonitrile, acrylates, vinyl chloride, vinyl acetate, styrene, copolymers formed by such monomers, and mixtures of such homopolymers and copolymers. It can be applied to the treatment of solutions, dispersions, etc. of fiber-forming thermoplastic polymers such as. The drawing shows an apparatus for carrying out the method of the invention. In this device, 1 is a nozzle through which the fluid jet passes in the direction indicated by arrow 6, 2 is a tapered part of the nozzle, 3 is a narrow part of the nozzle, 4 is a diffusing part, 5 is a solution of polymer in the direction of arrow 7; A nozzle for supplying the emulsion or dispersion and guiding it to the diffusion section.

The nozzle 5 can have a fairly uniform diameter or, although this is not necessary, can have a larger diameter in the vicinity of the diffusion section 4. This is to allow some expansion of the polymer solution or dispersion before impinging the fluid. In fact, a surprising feature of the fluid application conditions according to the invention is that no pre-expansion of the polymer solution or dispersion is required to obtain a suitable fibrous product.

In the device of the figures, the nozzle 5 forms an angle of about 90° with respect to the longitudinal axis of the nozzle, but it can also be arranged at different angles with respect to such axis, preferably between about 50 and 90°. be.

Next, the present invention will be specifically explained with reference to Examples. However, the present invention is not limited to these examples.
Example 1 This example concerns the production of polyethylene fibrils starting from a solution of the polymer in n-hexane using anhydrous saturated steam as the fluid and operating with the apparatus shown in the drawings.

For this, a solution containing high-density polyethylene (M.
It is used at a temperature of 0.00 and a different pressure to the outside of 14 atm. The steam used at the inlet of the intake section of the nozzle has a pressure of 18k9/lump gauge and a temperature of 205qo.

The steam flow rate is 300k9/h. The nozzle has a circular narrow part (critical) with a diameter of 6.5 ribs and 15.42
The largest (terminal) portion in the diffuser section is shown with the diameter of a willow.

The distance between the narrow part and the end part is 31.8 willows.

Under these conditions, the water vapor pressure near the end of the tapered section is slightly higher than atmospheric pressure (i.e., a few Hg).
and the water vapor corresponds to a maximum velocity upstream of the critical part consistent with that condition and equal to 900/sec. Water vapor expansion corresponds to an enthalpy drop of 115 Kcal'k9.

The polymer solution is fed at a total flow rate of 960 k9/h through eight cylindrical nozzles, each having a diameter of 2 sails, arranged symmetrically in the end part of the convergence-diffusion nozzle.

After 1 hour of operation, 120 of the fibrils with a length of 3-4 willow, an apparent diameter of 40 microns and a surface area of 7.
k9 is obtained.

Water vapor consumption is 2.5k9'k9 fibrils.

Example 2 A solution of polyethylene in n-hexane is used as in Example 1 under the same temperature, pressure and hourly capacity conditions.

Steam at a pressure of 2.7k9/k9, superheated to a temperature of 20p and at a flow rate of 300k9/h is used as fluid.

The equipment used was of the type shown in the drawings, with a critical diameter of 7.3 in the skin and 8.3 in the diffusion part of the nozzle.
It has a nozzle characterized by a maximum part diameter of 7 willows.

In its largest part the water vapor is in a superheated state, at a pressure slightly above about atmospheric pressure and at a maximum velocity of 607 m/s. The distance between the smallest part and the largest part is 22.4
It's on the side. The extrusion nozzle for the polymer solution has a diameter of 2 mm. After 1 hour of operation, one of the fibrils with a length of 4 to 5 mm, an apparent diameter of 40 microns, and a surface area of 8 mm.
20k9 is obtained and the water vapor consumption is 2.5k9/k9 of fibril. Example 3 This example demonstrates the production of fibrils starting from an emulsion formed by a solution of polypropylene in n-bentane and water.

The polypropylene used was M. 1. =10. The concentration of polypropylene in the emulsion is 1:50 for the emulsion. The weight ratio of n-pentane/water in the emulsion is 1.

The apparatus used was that shown in the drawings and featured a critical diameter of 11.5 skin, a distal maximum diameter of 15.7 in the diffusing section of the nozzle, and a critical and maximum diameter of approximately 21. It has a nozzle for fluid featuring a distance between.

The emulsion was deposited at a temperature of 155° C. and a pressure of 21.4 k9/gauge at a temperature of 8° C., each having a diameter of 2 ribs, arranged symmetrically around the distal (maximum) portion of the harvesting-diffusing nozzle.
extrude through cylindrical nozzles.

The emulsion is fed through 8 cylindrical nozzles at a flow rate of 2200k9/h. The steam flow rate is 300 kg/h. 6k of anhydrous steam at the inlet of one ridge of the nozzle
A fluid with a gauge pressure of o' and a temperature of 200 qo is used. Under these conditions, the water vapor pressure at the distal end of the diffusion section of the nozzle is slightly higher than atmospheric pressure (i.e., several orders of Hg), and the water vapor is consistent with that condition upstream of the critical section and at 715 m/s. corresponds to a maximum speed equal to .

After 1 hour of operation, approximately 150 k9 of fibrils are obtained with a skin length of 1.5 to 2.5 microns, a mean (apparent) diameter of 20 microns and a surface area (specific area) of 4.1 microns.

Water vapor consumption is 2k9 per lk9 of fibril.

Example 4 This example shows that one phase was formed by molten polyethylene (M.1.=5) containing liquid n-hexane and the other phase was formed by liquid n-hexane containing polyethylene in the dissolved state. The invention relates to producing fibrils starting from a two-phase polymer composition in which the former phase is homogeneously dispersed in the latter phase.

The two-phase composition consists of 1 solution of polyethylene in n-hexane containing 100 parts of polymer per solution.
000 and a pressure of 17k9/average gauge. Under such temperature and pressure conditions, the two-phase composition is extruded through the eight nozzles of the apparatus described in Example 1 with a total flow rate of 1200 k9'h. At the inlet of the intake part of the nozzle, steam at a temperature of 205°C and a pressure of 18°C is used as the fluid at a flow rate of 300K9'h. The pressure of the water vapor in the diffuser section at the end of the nozzle where impingement occurs with the extruded polymer composition is slightly above atmospheric and the fluid is approximately 900 m
/corresponds to the maximum speed of sand. After 1 hour operation, 2-2.5
Approximately 150k9 of fibrils are obtained having a willow length, an apparent diameter of about 25 microns and a surface area of 8/8 microns.

Water vapor consumption is 2k9 per fipril of lk9.

The embodiments of the present invention are summarized as follows.

{1} The polymer solution, emulsion or dispersion is extruded in the band of said branch section where the fluid reaches a maximum velocity compatible with the thermodynamic conditions upstream of the diffusion section of the slurry.

[2] The polymer solution, emulsion or dispersion is extruded at or near the end of the diffusion section of the nozzle.

'3' The polymer solution or dispersion is extruded through a number of nozzles arranged around the diffusion portion of the fluidic/zole.

[Brief explanation of the drawing]

The drawing is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention. 1... Nozzle, 2... Drinking part of the nozzle,
3... Narrow part of the nozzle, 4... Diffusion part of the nozzle, 5... Nozzle that supplies a polymer solution, emulsion or dispersion and leads it to the branching part. , 6...
...Arrow indicating the direction in which the fluid jet passes, 7...
- an arrow indicating the direction in which the polymer solution, emulsion or dispersion passes through the nozzle 5;

Claims (1)

[Claims] 1. A solution, emulsion or dispersion of a fiber-forming thermoplastic polymer in a liquid medium is extruded through a nozzle under conditions where the liquid medium flashes in the extrusion zone and passes through a convergent-diffusing nozzle in the direction of extrusion. A convergent-diffusion nozzle is a de Laval type nozzle in which an extruded polymer is fragmented after exiting the nozzle by a high-velocity gas or vapor jet stream that impinges at an angle to form a polymer solution, emulsion or dispersion. A method for producing synthetic resin fibrils or microfibers for paper production, characterized in that the liquid is extruded into the diffusion section of the De Laval type nozzle.