NO140770B - PROCEDURES FOR THE PREPARATION OF POLYOLEFIN FIBERS BY FLASHING A MIXTURE CONTAINING WATER AND POLYOLEFIN DISSOLVED OR SWELLED IN AN ORGANIC LIQUID - Google Patents

Description

The present invention relates to the production of fibres, which

have such a quality that they are suitable for the production of paper or a similar non-woven web.

Different methods for the production of such fibers have previously been proposed, whereby a mixture of a synthetic fiber-forming polymer is "flashed" in an evaporable liquid.

When the mixture is flashed, it is expanded through a nozzle at high pressure into a zone of low pressure, and where-

at the temperature of the liquid for the expansion is such that the liquid boils during the expansion, i.e. that at least part of the liquid evaporates at the reduced pressure. Procedures

whereby a solution of the polymer in a solvent is flashed to thereby form fibers, is described in U.S. Pat. patent 3,081,519, British patent 1,262,531 and German specification 19 50 609. Methods by which a dispersion of molten polymer in water is flashed are described in U.S. Pat. patent 3,402,231 and French patent 1,350,931.

In order to obtain a fiber of better quality than that obtained according to previously known methods, it has been proposed to flash an "emulsion" containing the polymer, a solvent for the polymer and water. Such proposals appear in British patent no. 1,323,174, German explanatory document 21 44 409 and Norwegian patent no. 137,243. In these earlier emulsion flash methods, the liquid being flashed contains water as a continuous phase, in which are dispersed droplets of the solvent forming a dispersed phase.

It is an object of the present invention to provide a method for the production of polyolefin fibres, which is either excellent in terms of simplifying paper production, or which results in excellent paper. We have found that the fibers obtained by flashing a polyolefin emulsion, solvent and water are better when the solvent is the continuous phase and water is the disperse phase, than when water is the continuous phase and the solvent is the disperse phase.

An inverse (water-in-oil) emulsion, where water constitutes the disperse phase, is usually more difficult to form than the emulsions that usually occur most often in emulsion technology, which constitute oil-in-water emulsions, and we have found that it is possible to form and flash water-in-oil emulsions containing a polyolefin, and that flashing an inverse emulsion produces very good fibers.

It is a surprising effect when flashing a water-in-oil emulsion containing a polyolefin that the product is obtained as relatively separate fibers rather than continuous threads. With most previous methods, continuous threads are produced which are unwanted as a fiber product with which one wants

manufacture non-woven webs.

The present method first comprises preparation

of a mixture containing:

(i) a polyolefin,

(ii) an organic liquid capable of dissolving or swelling the polymer and

(iii) water,

and second, flash the mixture at a temperature at least sufficiently high so that the polyolefin swells from the liquid, from a zone of high pressure to a zone of lower pressure, whereby the organic liquid evaporates and the polyolefin precipitates in the form of fibers , which can be refined relatively easily, and from which paper webs can be produced using conventional techniques. The present method is characterized by the fact that the water is mixed with the polyolefin and the organic liquid, so that the water is dispersed as small droplets in a continuous phase containing polyolefin

net and the organic liquid.

Preferably, the polyolefin is dissolved in the liquid, so that the mixture,

which is obtained in the first stage of the process and which is flashed in the second stage, a<y> consists of an emulsion, which contains the water as dis-

pers phase and the solution as the continuous phase.

For reasons not yet fully understood, it has been found that the fibers produced according to the present process tend to possess superior properties compared to fibers produced by flashing a corresponding mixture, where the polymer solution constitutes the dispersed phase in water.

An in-depth comparison of characteristics is given below, but that

can be briefly stated that by comparing the fibers from nearby

process with fibers produced by flashing a similar mixture with water as the continuous phase, then fi-

crene according to the present method higher surface area,

higher drainage factor, increased strength properties and they result in paper sheets with usually superior properties. These improved fiber properties are not only surprising, but highly significant, as such fiber properties are important to have for a pulp that is to be suitable for papermaking. Higher surface area gives increased whiteness and lightness to the fiber as well as better adsorption properties. Improved strength properties, e.g. breaking strength, tear strength, impact resistance etc. also make these fibers more competitive with natural cellulose pulp.

According to the present method, it is also possible to obtain such improved fibers which have a relatively low content of polymer pieces and fiber bundles. A low quantity level of polymer pieces and fiber bundles is important when using the fibers for several paper grades, e.g. printing paper, as the roller pressure during the paper-making process transforms these pieces and bundles into transparent spots in the paper.

The polyolefin used in the method according to the present invention is preferably a thermoplastic fiber-forming polyolefin. (The term fibre-forming means a polymer which is capable of forming fibers using conventional spinning techniques). It is preferred to use crystalline or partially crystalline polyolefins, such as low-pressure polyethylene (Ziegler-Natta), isotactic or partially isotactic polypropylene and ethylene-propylene copolymers. Polybutenes and polymethylpentenes are further examples of polyolefins which can be used in the method according to the present invention.

It is preferred to use those polyolefins which have a limiting viscosity number above 0.7 dl/g, which for polyethylene corresponds to

has a viscosity branch average molecular weight of over 30,000 to 40,000.

The polyolefins used in carrying out the present method can be in the form of dried powder or pellets, or preferably as a wet cake, slurry or solution of polyolefin in the reaction solvent, as obtained after polymerization.

Generally, any substituted or unsubstituted aliphatic, aromatic or cyclic hydrocarbon which is a solvent for the polymer at higher temperatures and pressures, which hydrocarbon is relatively inert under operating conditions, and which preferably has a boiling point at atmospheric pressure less than the softening point of the polymer, and which is essentially immiscible in water, or which forms a polymer solution which is essentially immiscible with water, is used as the organic liquid according to the present method. The solvent can exist as a liquid or gas at room temperature and atmospheric pressure. It is preferred that the solvent is a liquid at standard conditions with regard to pressure and temperature, otherwise the system after the flash zone must be pressurized. Typical solvents that can be used are aromatic hydrocarbons (eg benzene and toluene); aliphatic hydrocarbons, (eg butane, pentane, hexane, heptane, octane and their isomers and homologues); alicyclic hydrocarbons, (eg cyclohexane); chlorinated hydrocarbons, (eg methylene chloride, carbon tetrachloride, chloroform, ethyl chloride and methyl chloride); higher alcohols; esters; ethers; ketones; nitriles; amides; fluorinated compounds, (eg fluorohydrocarbons; nitromethane); and mixtures of the above-mentioned solvents or other solvents.

The polymer-solvent-water mixture according to the present invention can be prepared according to the water concentration using one of many methods. One can start with a polymer solution in solvent, as this comes from a solution polymerization process, either with the same polymer concentration in the solvent, diluted or concentrated, and then adding water to the solution or vice versa. In such a method, hot water is usually used to prevent precipitation of the polymer. Alternatively, one can start with a slurry of polymer particles in the solvent, and then similar to that produced by a slurry polymerization process, and the appropriate amount of water is added to the slurry or vice versa. A further alternative would be to start with a dry polymer powder or polymer granulate, or a wet cake, and then one that can be produced in some step of the 16s removal agent in the polymer plant, and whereby appropriate amounts of solvent and water are mixed with the dry polymer in one way or another.

As explained later, it is advantageous for solvent to be present for the addition of water because the addition of water to the solvent and not vice versa will help ensure that the solvent or polymer solution will form the continuous phase of the mixture to be manufactured. The latter embodiment is important when using a quantity of water which is close to the limit where inversion occurs,

ie close to the point where the amount of water is the amount where it will form the continuous phase. When the amount of water is significantly below the limit where inversion occurs, and then especially below 30% by volume of the mixture, then any conventional method of mixing or adding materials can be used.

The polymer concentration in relation to the solvent is not critical, and the solvent is present in an amount greater than 100% by weight of the polymer and sufficient to

provide a viscosity at the dissolution temperature used such that the dissolution can be easily handled, ie the viscosity is less than 500 poise. Typically, the polymer concentration will vary from 2 to 30% by weight of the solvent plus polymer, and preferably from 5 to 15% by weight.

One of the functions of water is to reduce the temperature of the fibrous mass in the zone immediately following the nozzle. The addition of water increases the total vapor pressure of the system, and thus lowers the boiling point. It is

practical to use water in an amount of at least approx. 1% by volume,

and then preferably over 10% by volume of the solvent-water mixture. By this reduction of the mixture's boiling point, the temperature of the fiber-containing mass, which is formed by flashing, is reduced, and the properties of the fiber obtained are suitable for paper production.

Another function of the water is that it serves as a carrier for

a hydrophilic water dispersant for the fibers to be formed. It has been found that it is most advantageous for the water-dispersing agent to be present during flashing and precipitation of the fibrous polymer. While the presence of the water-dispersing agent is beneficial to the fibers produced according to the present process, the best agents are those believed to be undesirable in a water-in-oil emulsion. Nevertheless, the presence of hydrophilic water dispersants in the flashing composition is preferred. An equivalent amount of the same agent added in a later step to the already formed fibers does not give the same degree of refinement to the fibers. Therefore, the water must be present in an amount that is sufficient

to carry the amount of the hydrophilic agent used so that the fibrous polymer obtains the desired level of water dispersibility, preferably as a solution thereof.

Additional water beyond this minimum amount, as required for

to carry the agent, can be used to give a suitable viscosity to the aqueous solution or dispersion agent, i.e. the aqueous solution of the water dispersant should not be so viscous that problems are created during handling or incorporation into the polymer solution as a dispersed phase. The water can also help reduce the viscosity of the mixture to a level less than that of the polymer solution itself,

and this thus allows higher polymer concentrations. Generally, the viscosity of the aqueous solution and/or mixture should be less than approx. 500 poise at the temperature used.

A further function of the water is that it provides energy (enthalpy) to support the evaporation of the solvent during flashing, as it is not desirable to have such a high temperature that there is sufficient energy in the solvent itself to cause its complete evaporation. However, the amount of water should not be so large that an unnecessary amount of heat is required to achieve the desired flash temperature, i.e. once a quantity of water, which has a suitable viscosity, has been determined, additional water can be used to a certain extent as it helps to reduce the viscosity of the mixture as well as support the solvent evaporation, but the additional amount of water should not be too great.

The amount of water required to complete the aforementioned functions is always less than the amount at which an inversion occurs, i.e. where water becomes the continuous phase of the mixture. A condition that is necessary to ensure that the organic liquid or solution forms a continuous phase is that the proportion of water in the mixture is quite low. If the proportion of water is more than approx. 70%, then it is very difficult to form a water-in-oil emulsion, even at somewhat lower proportions of water, i.e. more than 60% water, then any usual method of mixing will tend to result in an oil-in-water emulsion. When the quantity ratio of water becomes smaller, it becomes easier to form a water-in-oil emulsion. In mixtures where water will tend to be more stable as the continuous phase, it is desirable to use special mixing techniques to cause the water to become the least stable discontinuous phase. Suitable techniques are known within emulsion technology, and are described in e.g. volume 8 of Kirk-Othmer's "Encyclopaedia of Chemical Technology", 2nd revised edition.

A preferred method of ensuring a water-in-oil emulsion when the proportion of water is sufficient for either water or the organic liquid to form the continuous phase is to add the water to the liquid at a slow pace, and then slowly enough that the even at the point of addition there will be no local excess of water in relation to organic liquid and already formed emulsion, and the mixture is agitated so that the water breaks up into small drops when it is added. One can keep the addition of water steady by measuring the electrical conductivity of the organic liquid, and controlling the conductivity so that the addition under certain agitation conditions is such that the conductivity remains less than twice the original conductivity.

As a useful rule, it can be said that it is desirable to apply

such a special mixing technique when the water makes up approx. 30% by volume or more of the mixture. Especially when the amount of water used is approx. 30% by volume or more, then it is desirable to first form a solution of the polymer and the solvent, and then add water to this solution with vigorous stirring. In this context, the term "polymer solution" is understood to mean the swelt or dissolved mixture obtained by mixing the solvent with the polymer at a usually higher temperature.

It is further desirable that the entire mixture be subject to continuous agitation both during and after the addition of water. The mixing vessel or the mixing apparatus can be designed so that even and powerful agitation can be achieved, e.g. by suitable design of the vessel, guide plates and stirring devices. Very careful agitation must be avoided as this can cause phase inversion.

One prefers to carry out the mixing process while both the water

and the polymer solution are relatively hot. It is desirable to

keep the polymer solution at a temperature above the melt dissolution temperature, and the water to be added should have a temperature sufficiently high so that the mixture remains above said melt dissolution temperature during and after the addition of water. This method of operation will help to avoid phase inversion during water addition.

If the water and polymer solution phases are allowed to separate during or after the addition of the water, then a phase inversion can occur. It is therefore desirable to add the water at a rate that will prevent phase separation, and for the same purpose to maintain vigorous agitation during and after the addition of water.

As previously mentioned, the water will preferably be added successively at a rate so that it is quickly and evenly mixed with the polymer solution. That is to say, the water should not be added faster than it disperses as small droplets in the continuous polymer release phase.

When the mixture contains approx. 30% or less water, then a water-in-oil emulsion is preferably formed, and it is not even necessary to add the water to the organic liquids.

At low water concentrations, one can even mix the two liquids and then agitate them, or one can add the solution (or a slurry of polymer particles in organic liquid) to the water.

In the following examples 1-6, where the water concentration only

was 16%, thus no special mixing method was used.

In series no. li example 7, where the water concentration was 40%,

the water was added successively to the solution. The water concentrations in the order of 40 - 50% are actually preferred for the present method, but care must still be taken to ensure that the water constitutes the discontinuous phase.

According to a continuous flash method, part of the mixture thus formed is flashed through a nozzle, and further amounts of polymer solution and water can be continuously added with agitation to the remaining mixture, and then in previously mentioned amounts, to retain the water as the continuous phase in the mixture.

One of the characteristic features of the present invention is that it has been found that it is not necessary to form a stable "emulsion", and thus the need to use emulsifiers has been eliminated. However, the present invention describes the use of agents in the composition to promote the water dispersibility of the fibrous polymer formed by flashing. These agents are preferably water-soluble or partially water-soluble materials with a high molecular weight. However, they can also constitute materials which are soluble or partially soluble in the solvent. Some of these agents may technically be classified as "emulsifiers", but they are used only in an amount sufficient to provide the necessary degree of dispersibility and usually not in amounts required to form a stable emulsion. Due to the fact that the water dispersants must be somewhat hydrophilic, in reality they are not of the type that one would normally use to form a water-in-oil emulsion, i.e. that one would normally use a hydrophobic (lipophilic) emulsifier with a relatively low HLB (hydrophilic-lipophilic balance) to form a water-in-oil emulsion. The amount of water dispersant used can be from approx. 0.1 to approx. 15% by weight of the polymer, preferably from approx. 0.1 to approx. 5% by weight. The preferred water dispersant is a polyvinyl alcohol which has a degree of hydrolysis greater than approx. 77%, and which are preferably greater than approx.

85%, and which has a viscosity (in a 4% aqueous solution at 20°C) greater than approx. 2 centipoise. The polyvinyl alcohol is preferably added with the water at the time the mixture is formed. Other typical water dispersants that can be used are cationic guar, cationic starch, potato starch, methyl cellulose and "Lytron 820" (a styrene-maleic acid copolymer).

The components of the mixture can be added to some suitable container which can be heated to a higher temperature and higher pressure. Usually an autoclave is used. However, it is important that the container used is equipped with a mixing or stirring device, so that the mixture can be kept in a constant state of agitation due to the fact that a stable emulsion is not formed, and the mixture will quickly separate into two distinctly separated phases.

The ingredients were then heated to a suitable temperature and agitated to form a mixture in which water occurs as a discontinuous or dispersed phase in a continuous phase of polymer solution. The temperature used is preferably above the melt dissolution temperature of the polymer in the solvent used. The melting temperature of any polymer in a solvent is determined by adding a low concentration of the polymer (eg 0.1 and 1.0% by weight) to the solvent in a small bottle which is then sealed and placed in a oil bath. The temperature of the oil bath is increased slowly (e.g. 10°C/hour) until the last trace of polymer disappears. This temperature is the melt dissolution temperature. In certain cases it may be desirable to work at a temperature below the melt melting temperature, in which case the polymer should be present at least in a swollen state.

The maximum temperature used must be less than the critical temperature of the solvent and/or the decomposition temperature of the polymer. However, it is preferred to use somewhat lower temperatures. When it comes to polyethylene and polypropylene, it is preferred to work between 120°C

and 180°C and then preferably between 130°C and 160°C.

The applied pressure in the container, which contains the heated mixture, is preferably essentially self-pressure. Pressures significantly higher than the self-pressure are not required, and for a particular nozzle design this can result in poor fiber formation. It may be desirable to use an inert gas, such as nitrogen, during the flash process to thereby maintain the velocity of the mixture through the nozzle at a fairly constant level.

Flashing is preferably carried out through a nozzle (eg

by definition has an elongated dimension) rather than a sharp-edged nozzle, (which by definition does not have an elongated dimension) because it has been found that it is highly undesirable to impart shear forces to the mixture (especially the polymer component thereof) immediately before flashing. Such shear forces support fiber formation and improve fiber properties for papermaking. The nozzle may be circular or non-circular in cross-section.

The flashing is carried out by allowing the mixture consisting of polymer, solvent and water to pass through the nozzle into a zone of lower pressure. Preferably, the pressure in the zone with lower pressure is essentially atmospheric or less, as higher pressure will also result in a higher temperature in the fiber-shaped product during manufacture. Generally, the pressure of the emulsion for this flashes to the zone with the lower pressure should be below approx. 3.50 kg/cm 2 , and then preferably below approx. l, AND

2

Kg/cm .

The flashing is mainly carried out adiabatically, although this condition can vary somewhat.

During flashing, the polymer is precipitated as a bundle of fibers ("noodle"), which constitutes an Ib's aggregation of fibers that are sometimes continuous.

According to a preferred embodiment of the present invention, low-pressure steam (pressure less than about 1.4 kg/cm 2 ) is added to the fibrous bundle in the subsequent flashing zone to drive off the remainder of the solvent from the fibrous tuber. This can be done in a container or preferably in a line that follows immediately after the nozzle.

The fiber-shaped bundle is collected in a suitable receiving container, and then preferably one that allows separation of the evaporated solvent.

In industrial operation, the fibrous bundle is thinned

with water to a suitable consistency that is less than approx. 5% by weight and preferably less than 2% by weight, after which the whole is allowed to pass as an aqueous slurry through a disc refiner to thereby produce a fiber form that is optimally suitable for paper production. The refining of the fiber-shaped noodle causes a division into the individual fibers, and the refining can also be used to control the length of the fibers. Multiple passes through the refiner are usually undesirable. However, the disc refinement of the fibrous noodle is not important.

After refining, the fibers can be diluted to a suitable consistency, and synthetic paper webs are produced from this, either as such or mixed with ordinary cellulose fibers for paper production. Alternatively, the fibers can be dewatered, pressed into balls, stored and transported to the final consumer.

While the foregoing description illustrates a batch process whereby the mixture of polymer, solvent and water is prepared in a suitable vessel, it is also possible to prepare the mixture on a continuous basis by mixing the polymer solution with superheated water continuously in a series-connected mixing device ,

and then exactly for the flashing through the mouthpiece.

A determination of whether the water is present as a discontinuous phase or a continuous phase can be made in the following way. The mixture is formed at the appropriate temperature and pressure and with the degree of agitation that would normally be used. Electrodes, which consist of two conducting metals separated by a distance of approx. 12 mm or more, is immersed in the liquid mixture. The electrodes are connected to the poles of a battery, and the induced signal is registered by a recording instrument which is connected in series with the electrodes. The signal obtained is directly proportional to the conductivity of the mixture. A trace amount of an ionizable material, such as sodium chloride, can be used in the water to support its conductivity. Where the water forms the discontinuous phase, you get a very low conductivity or no conductivity at all, i.e. approx. the same conductivity as the polymer-solvent phase of the mixture.

It can thus be seen that by forming the desired water-discontinuous mixture, the degree of agitation for the mixture is desirably high enough to keep the conductivity of the mixture at approx. the same conductivity as the polymer solution phase has. By preparing such mixtures, where the desired water concentration is so high that a water continuous system is preferred,

in a similar way, the water is added to the polymer solution in such a successive degree that the conductivity of the mixture is kept at approx. the conductivity of the polymer solution phase.

Other suitable methods for determining whether an oil-in-water or a water-in-oil emulsion type is obtained are described on pages 146 and 147 of Volume 8 of the Kirk-Othmer Encyclopedia of Chemical Technology, Second Revised Edition, 1965.

EXAMPLE 1

The solution container used in this example was a

3620 1, glass-lined tank, equipped with guide plates, and which was also equipped with a centrally arranged 7.5 HP agitator with two 4-blade turbine-type inverters. The lower turbine was 685 mm from peak to peak, and the upper turbine was 4 92 mm from peak to peak. The converter went on during the entire drive.

272 1 water, containing 1% by weight polyvinyl alcohol (Monsanto Gelvatol, viscosity of 4-6 CP and 87.7-89% hydrolyzed) based on the weight of the polyethylene to be used, was added to the tank, after which 45.4 kg high density polyethylene with a limit viscosity number of 1.4 dl/g and a melt index of 5.5 (Mitsui 2200P). The vessel was closed and 1360 L of n-hexane was added. The volume ratio between water and hexane in the mixture was 1:5, and the polyethylene concentration was 40 g per liters of hexane. The contents of the container were then heated to 130 - 135°C and to a pressure of 8.43 kg/cm<2>.

A valve in the bottom of the container was then opened and the mixture discharged through a 76.4 mm (3") line, which is 127 mm long, to a Valtek angle-type control valve with an outlet port which has a diameter of -9.5 mm and a length of 7 mm. A nipple-shaped plug in the outlet of the valve forms a circular hole with the wall for the outlet. The valve is cut with about a quarter opening. The mixture flows through the annular opening, which forms flash nozzle, at a rate of 180 g polyethylene per minute. The mixture was flashed into a 25.4 mm diameter conduit. At a distance of approximately 153 mm from the nozzle, low-pressure steam (0.70 kg/cm ) inserted into the 25.4 mm (1") line to drive the solvent that was not previously flashed from the fibrous tuber. At a distance of approx. 460 mm from the nozzle, the 25.4 mm (1") line entered a steam separator vessel, whereby the steam was removed from the top of the vessel. Hot dilution water, i.e., water at 85°C, was added at the top of the water separator vessel with a rate of about 22.6 L per minute The water and fibrous pulp fall to the bottom of the water separation vessel and was fed at a temperature of 80 - 90°C and at a consistency of about 1% to a Jones double disc raffinbr (320 mm diameter discs) which was equipped with brush type discs (Jones type 1, 1, 1.5, + 10°).The discs were run at 2117 rpm with a clearance of 0.101 + 0.101 mm. The fibers were subjected to a total of four passes through the refiner, the second pass being carried out at a raw material temperature of 40 - 50° C. An additional 1% by weight of "Gelvatol 20-30" polyvinyl alcohol (which was based on weight of the polyethylene) was added to the feed tank and the feed was passed through the refiner a fifth time with the plates set t of 0.254 + 0.101 mm. The polyethylene fibers show the following fiber fractionation when examined according to TAPPI standard T2 33 su 64:

The fibers have a drainage factor of 0.24 seconds/g.

A part of the obtained fibers was used for the production of hand sheets according to TAPPI standard T-205 m-58 with modified wet pressing (2 8.1 kg/cm ) and a heat bonding step (121°C at minimal pressure). Another part of the fibers was mixed 50/50 with bleached orr kraft pulp with a Canadian Standard Freeness of 410 cm 3 , and from this, mock sheets were produced using the same procedure. The received hand sheets were examined and the results are shown in the table below:

A further portion of the polyethylene fibers was mixed with a bleached or kraft pulp having a Canadian Standard Freeness of 410 cm 3 to produce a ground pulp containing 40 wt.% polyethylene fibers and 60 wt.% kraft fibers. The resulting mixture was "Jordan" refined to give a ground pulp with a Canadian Standard Freeness of 250 cm, from which a paper was further produced on a paper machine. The paper machine was run to produce two levels of heat bonding (107° and 135°c on the sheet). The obtained paper webs had the following characteristics:

In the preceding example and subsequent examples, the basis weight, thickness, tear strength, folding and density of the hand sheet were determined using TAPPI standard T-220. As for the sheets produced on the paper machine, the basis weight was determined using TAPPI standard T-410, the thickness using TAPPI standard T-411, the tear strength using TAPPI standard T-410, the folding using TAPPI standard T -511 and the density using TAPPI standard T-426. The tensile strength, elongation, TEA (tensile energy absorption) and break length for both hand sheets and paper machine sheets were determined using TAPPI standard T-494. The stiffness of both sheets was determined using TAPPI standard T-489-70. Elrepho No. 8 brightness for both sheets was determined using TAPPI standard T-525. The smoothness of both sheets was determined using TAPPI Routine Control Method No. 285. The oil absorption was determined for both sheets using TAPPI Routine Control Method No. 26 (1966). Opacity and dispersion coefficient were determined for both sheets using TAPPI standard T-425. Other tests are indicated using the machine used to perform tests, all of which are well known in the paper industry. The drainage factor, which is to a large extent brought into accordance with the hydrodynamic surface area of the fibres, and which stands in a closer relation to the drainage characteristics of the fibers to be used in paper production than the gas adsorption surface area, was mainly determined according to TAPPI test T2 21 OS- 63 with a slight modification in the calculation method. In short, approx. 10 g from a fiber sample weighed and dispersed in water. The slurry is then added to the standard sheet mold and water is added up to the mark. The slurry is stirred using four up-and-down strokes from the standard stirrer, which is then removed. the water temperature in the mold is measured and the drainage valve is opened. The time between opening the valve and the first suction sound is noted. The procedure is repeated with only water (no fiber) in the sheet form, and the temperature and drainage time are noted. The drainage factor in seconds per grams are then calculated as follows:

where

DF = drainage factor, seconds/gram

D = drainage time with the mass in the mold, seconds

d = drainage time without mass in the mold, seconds VT = water viscosity at temperature T

W = the weight of the fibers used in the test, grams

The quantity (— T- 1) is quickly tabulated in the aforementioned TAPPI test T221 OS-63. This amount is multiplied by 0.3, which is empirically determined for the fibers present.

EXAMPLE 2

The procedure from example 1 was repeated except for the following:

a) The polyethylene concentration was 80 g/litre; b) the mixture was allowed to flow through the nozzle at a rate of 250 g per minute; and

c) the refining conditions were as follows:

1) The first flow through occurred at 80 - 90°C with a plate clearance of 0.101 mm; 2) the second flowed through at 40 - 50°C and with a plate clearance of 0.101 mm.

No additional polyvinyl alcohol was added.

The fibers obtained showed the following fiber fraction:

The drainage factor of the fibers was 0.46 seconds/gram.

Hand sheets were made as in Example 1, a group containing 100% polyethylene fibers and a group made from a 50/50 blend with bleached kraft pulp as described in Example 1. The properties were as follows:

A part of the fibers was mixed with the bleached kraft pulp described in example 1 (40 wt.% polyethylene fibers, 60 wt.% kraft pulp), and from this a paper web was produced on a paper machine at two levels for hot bond as in example 1- The properties of the path obtained were as follows:

EXAMPLE 3

The procedure from example 1 was repeated except for the following:

a) The polyethylene concentration was 80 g/litre; b) the mixture was forced through the nozzle at a rate of 150 g per minute; and c) the refining conditions were as follows: 1) The first pass was made at 80 - 90°C with a disk clearance of 0.055 + 0.101 mm; 2) the second and up to the sixth pass were made at 20°C and with a disc clearance of 0.055 + 0.101 mm. No additional polyvinyl alcohol was added.

The fibers obtained had the following fiber fraction:

The drainage factor for the fibers was 1.10 seconds/gram.

Hand sheets were made as in; example 1, whereby one group contained 100% polyethylene fibers and another group was made from a 50/50 mixture with the bleached orr-kraft pulp described in example 1. The properties were as follows:

A part of the fibers was mixed with the bleached kraft pulp described in example 1 (40% by weight polyethylene fibers and 60% by weight kraft pulp) and from this a paper

tap on a paper machine at two levels hot binding as in example

1. The properties of the path obtained were as follows:

EXAMPLE 4

In this example, the vessel used in the preparation of the mixture for flashing was a "Benco Model 575", and then a 4.54 L reactor equipped with a 10.5 kg/cm <2>steam jacket,

an inlet and outlet for nitrogen, and a centrally arranged air-driven agitator shaft with a mechanical sealing device. A 101 mm (4") diameter, 6-blade pitched blade turbine (Bench Scale Equipment Co.) was located approximately 127 mm from the bottom of the container on the rod, and a high shear propeller was located approximately 87 mm below the turbine. The container was fitted with four equidistant vertical baffles. The container was fitted with an electrode consisting of a piece of metal wire, sealed at one end by a short glass rudder. The other end of the wire was pulled through a 300 mm long stainless steel tube (6.3 mm or 1/4" outer diameter), and the glass tube and the metal tube were connected. The electrode was placed in the container so that the wire was above the water level in the mixture described later. The wire was attached to an ohm-meter lead in series with the battery. The stainless steel sleeve, which was separated from the wire at a distance of approx. 15 mm due to insulation of the entire length of the wire, was connected to the other pole. The signal was determined from just salt water to approx. 140 millivolts, while the signal for n-hexane alone was approx. 0 - 1.0 millivolts. Extending from the bottom of the container was an 18.9 mm (3.4") rudder with a ball valve located 50.8 mm below the bottom of the container. Immediately adjacent to the ball valve was a nozzle. The nozzle consisted of a 104 mm long brass plug with a centrally drilled hole with 3.5 mm diameter.

The mouthpiece plug was inserted into the 18.9 mm wide rudder, which

continued for a distance of 300 mm past the nozzle, and which discharged into the atmosphere. The container was filled with 500 ml of water;

2,500 ml of n-hexane; 100 g polyethylene (Mitsui 22COP, which is described in example 1), 2 g "Gelvatol" 20-30" polyvinyl alcohol and 20 drops of a 25% aqueous sodium chloride solution.

the holder was closed, flushed with nitrogen and the contents heated to between 145 - 150°C. Hereby, the agitator ran at a speed of 650 rpm. The content was kept at 145 -

150°C for approx. 1 1/2 hours to ensure complete polymer-up-

solution. The conductivity of the mixture was between 0.4 - 1.2

millivolts, which showed that the water constituted a discontinuous

honest phase. The ball valve was then opened, and the mixture was allowed to flow through the nozzle while the pressure was kept con-

stant in the container when nitrogen is added. The fiber

the formed product was collected on a wire net. The fibers were refined by passing them at room temperature through a "Sprout Waldron" single disc refiner with 300 mm plates (Sprout Waldron Fattern C-29-78-B) operated at 2,800 rpm.

at a plate clearance of 0.0508 mm, and with a total of 4 through-

runs.

The fiber fraction obtained was as follows:

The fibers' drainage factor was 4.3 seconds/g.

The hand sheets were produced as in example 1, whereby one group contained 100% polyethylene fibres, and whereby the other was produced from a 50/50 mixture with bleached orr-kraft pulp, which is described in example 1. The properties were as follows:

EXAMPLE 5

Example 4 was repeated except that polyvinyl alcohol was not included in the mixture. The conductivity of the mixture was the same as in Example 4. Stirring was only stopped briefly to examine the electrode, whereupon the conductivity quickly increased to approx. 100 millivolts. This indicated phase separation. After resuming stirring, the conductivity quickly returned to 0.4 to 1.2 millivolts. The mixture was maintained at 140°C

for half an hour, after which it was allowed to flow through the nozzle under a constant pressure of 11.5 kg/cm . The produced fibers could not be refined, nor could hand sheets be made from them because they had been treated with 1% by weight, calculated on

the fibers, "Gelvatol 20-30" polyvinyl alcohol, and whose mixing was carried out in an aqueous slurry. After the treatment, the fibers were refined as indicated in example 4, and they showed the following fiber fraction:

The fibers had a drainage factor of 16.5 seconds/gram.

Hand sheets were produced according to the method from example 1, whereby a group was produced from 100% polyethylene fibres,

and the other was made from a 50/50 mixture with the bleached ore kraft pulp described in Example 1. The properties were as follows:

EXAMPLE 6

The procedure from example 4 was repeated by using polypropylene with an intrinsic viscosity number of 1.7 dl/g ("

Hercules Profax 6301"). In one run the mixture contained

500 ml of water; 2500 ml of n-hexane; 200 g polypropylene and 2 g "Gelvatol 20-30" polyvinyl alcohol. This mixture was heated to 140°C and held at this temperature for one hour for the flashing. A second series was similar to the first series, except

given that the polypropylene was used in an amount of 100 g.

A third series was similar to the second, except that the mixing temperature was increased to 175-180°C for flashing. In all cases, a fiber-shaped product was obtained.

EXAMPLE 7, COMPARATIVE EXAMPLE

2 series were run to compare the fibrous products produced according to the present invention (experimental series no. 1)

with the fiber-containing product that was produced under the same fiber

manufacturing conditions, but whereby a flash mixture was used where the water is in the continuous phase (experimental series no. 2).

In both of these serial experiments, a 10 liter container was used, which was equipped with a steam jacket, and which had an inlet and an outlet for nitrogen, an electrode for measuring the conductivity, and which centrally featured a vertical agitator rod with a mechanical sealing. An upwardly pumping inclined blade turbine with a diameter of 102 mm was arranged on the rod 51 mm from the bottom of the container. Two single-bladed propellers with a diameter of 102 mm were arranged on the pole, respectively. 153 mm and 254 mm above the bottom of the container. A downward pumping turbine with a diameter of 102 mm and a downward pumping turbine with a diameter of 76 mm were arranged on the rod respectively. 356 mm and 460 mm above the bottom of the container. Three vertical baffles were placed radially equidistant by extending inward from the container wall.

This design ensures agitation of the entire mixture, and areas with little agitation, which could support the creation of a continuous water phase, are avoided.

Starting from the bottom of the container, there was a rudder with a diameter of 18.9 mm, on which was arranged an 18.9 mm ball valve, which was located 51 mm below the bottom of the container. Immediately adjacent to the ball valve was a nozzle, which contained a brass plug 28 mm long, and in which was a centrally drilled hole of 1.78 mm diameter. The mouthpiece plug was inserted into a rudder, which was 18.9 mm in diameter and 204 mm long, and which extended into a flash tank maintained at atmospheric pressure.

In both series of experiments, the materials forming the flash mixture were the same, namely 4800 ml of n-hexane, 384 g of polyethylene (Mitsui Hyzex 5000P, intrinsic viscosity number 2.0), 3200 ml of water and 7.7 g of "Gelvatol 20-30" polyvinyl alcohol (88% hydrolyzed, molecular weight 10,000). However, the method of making this flash mixture of these materials was different in the two serial experiments.

In serial experiment no. 1, i.e. the invention example, the container was first filled with the solvent and polymer. The container was then sealed and flushed with nitrogen, after which the contents were heated to approx. 144°C. At this temperature the mixture was held and the agitator was run at 1000 rpm. for about. 2 hours to ensure complete polymer dissolution. Then became PVA dissolved in the water in a separate container, and this solution was heated to approx. 144°C. The heated solution was then emptied under pressure into the container containing the heated polymer solution at a rate of approx. 500 ml per minute. This slow and successive rate of addition caused the water to remain the dispersed phase in the mixture. During charging of the PVA-containing water, the agitator in the container containing the polymer solution was maintained at 1000 rpm. Agitation of this mixture was continued for 15 minutes, after which the conductivity of the mixture was measured and found to be essentially 0 millivolts. This showed that the water was a discontinuous phase in the mixture.

In serial experiment no. 2, i.e. the comparative example, the formulation of the flash mixture was carried out according to the same procedure as stated in example 4, i.e. that the used container from serial experiment no. 1 was filled with all material at room temperature, after which this mixture was heated and agitated at the same speed as was used in serial experiment no. 1, and whereby polymer dissolution and dispersion of the PVA-containing water were intended. After agitation at between 110 and 140°C

for 2 hours the mixture was measured and found to be over 100 millivolts. This showed that the water was the continuous phase and the polymer solution the discontinuous phase.

In each of serial tests 1 and 2, the mixture, which was formed as described, was then heated at 144°C and flashed at this temperature and at a pressure of 11.25 kg/cm 2 using the method of Example 4. The flashed material was refined using the equipment described in Example 4, except that the refiner plates used were "Sprout Waldron pattern P-29-76-B". The refining was carried out at a consistency in water of approx. 3%. The clearance between the plates was as follows: first penetration, 6.4 mm; second pass-through, 0.6 mm; third piercing, 0.3 mm; fourth and further penetrations, 0.05 mm. The flashed material from each serial trial was refined in this manner until the fiber product achieved a "Classified Fiber Length" (CDL)

of approx. 1.2 mm. A portion of the products from each serial trial was then further refined using this method to produce a fiber product with a "Classified Fiber Length"

(CFL) of approx. 0.8 mm. The properties of these fibrous products and the hand sheets produced therefrom (as described in Example 1) were measured and compared as follows:

By comparing the fiber properties and the handsheet properties of the fiber products from trial series 1 and 2, which were refined to essentially the same "Classified Fiber Length", one will easily see that the fiber products, which have been produced according to the invention (trial 1), are markedly superior compared to those produced by flashing a similar mixture where the water is in a continuous phase (experiment 2). The drainage factor of the fiber products produced according to the present invention is significantly higher, and the same applies to the strength properties of the hand sheets made from these fiber products Fiber bundles and polymer bundles in such products were found to be at an acceptably low level.

Claims (12)

1. Process for the production of polyolefin fibers, preferably polyethylene and polypropylene fibers, by first forming a mixture containing water, the polyolefin and an organic liquid capable of dissolving or swelling the polymer, and then flashing the mixture at a temperature of 120-160°C from a zone of high pressure to a zone of lower pressure, whereby the organic liquid evaporates and the polyolefin is precipitated as fibers, characterized by mixing the water with the polyolefin and the organic liquid in such a way that the water is dispersed as small droplets in a continuous phase zone contain the polyolefin and the organic liquid. 2. Method according to claim 1, characterized in that the polyolefin is first dissolved in a solvent and that the water is then dispersed in the solution. 3. Method according to claim 1 or 2, characterized in that water is added to the mixture in an amount less than 30% by volume of the mixture. 4. Method according to claim 2, characterized in that water is added to the mixture in an amount of 30% by volume or more of the mixture and sufficient for the water to form the continuous phase, and that a solution of the polyolefin in the organic liquid is agitated while adding the water to the solution at low speed. 5. Method according to one of the preceding claims, characterized in that one further at least partially water-soluble dispersant for the fibers to be formed is added to the mixture, in a quantity ratio of 0.1 to 15% by weight of polyolefins. 6. Method according to claim 5, characterized in that the dispersant is essentially hydrophilic. 7. Method according to claim 6, characterized in that the dispersant is polyvinyl alcohol. with a degree of hydrolysis greater than 77% and with a viscosity in a 4% aqueous solution at 20°C greater than 2 centi-poise. 8. Method according to one of the preceding claims, characterized in that the polyolefin is an at least partially crystalline polymer, and that this occurs in an amount between 2 and 30% by weight of the solvent plus polyolefins. 9. Method according to claims 1-8, characterized in that said polyolefin is a polyethylene or polypropylene which has an intrinsic viscosity number greater than 0.7 dl/g, and that said polyolefin occurs in an amount between 5 and 15% by weight of the solvent. 10. Method according to one of the preceding claims, characterized in that the solvent has a boiling point, at the pressure in the lower pressure zone which is lower than the melting temperature range for the polyolefin. 11. Procedure according to one of the preceding claims. characterized in that the mixture is flashed in the second step at a temperature that is above the melt dissolution temperature of the polyolefin, which is less than the critical temperature for the solvent, and which is less than the decomposition temperature for the polyolefin, and that the flashing is carried out by self-pressure or a higher pressure. 12. Procedure according to one of the preceding claims. characterized in that: A. a solution is formed consisting of: (1) an at least partially crystalline polyolefin, and (2) an essentially water-insoluble organic solvent for the polyolefin in an amount between 70% and 98% of the total weight of the polyolefin and the solvent; B. water is added to said solution at a temperature above the melt dissolution temperature for said polyolefin, and then in an amount between 30 and 70% by volume of the mixture, while the solution is under sufficient agitation to disperse the water in it as a dispersed phase; C. the thus formed mixture is maintained under agitation at a temperature above said melt dissolution temperature and at self-pressure or higher pressure; and D. the mixture is allowed to flow through a nozzle to a zone of lower pressure.