JPH04281007A - Production of fibrillated polyethylene fiber - Google Patents

Abstract

PURPOSE:To obtain the title fiber having good strength and opening property and suitable for nonwoven fabric, etc., using a solvent having low ozone break ing ability by releasing a high-temperature and high-pressure solution containing polyethylene and a specific halogenated hydrocarbon-containing solvent from a spinnning inlet into ordinary temperature and ordinary pressure area under specific conditions. CONSTITUTION:When fibrillated polyethylene fiber is produced by preparing a high-temperature and high-pressure solution consisting of polyethylene and a solvent containing a halogenated hydrocarbon, passing the solution through a pressure-reduced orifice, pressure-reducing chamber and spinning inlet and releasing the solution into ordinary temperature and ordinary pressure area, a solution consisting of a solvent containing 1,1-dichloro-2,2,2-trifluoroethane or 1,2-dichloro-1,2,2-trifluoroethane or mixture thereof as a halogenated hydrocarbon, cyclohexene as another hydrocarbon and 5-25wt.% polyethylene is prepared at a temperature exceeding minimum point T and pressure not lowre than a cloud point pressure in a cloud point curve plotted by temperature as axis of abscissa and pressure as axis of ordinates. Then, pressure-reducing chamber is kept to a pressure in cloud point or below to provide the objective fiber.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to a method for producing polyethylene fibrillated fibers using an improved flash spinning process. Furthermore, the present invention relates to an improved flash spinning process that produces polyethylene fibrillated fibers of extremely high quality using solvents that have a significantly lower ability to deplete the earth's ozone layer. Furthermore, the present invention relates to a manufacturing method for obtaining polyethylene fibrillated fibers with excellent strength and spreadability for use in nonwoven fabric sheets using halogenated hydrocarbons with reduced ozone depletion ability.

0002

BACKGROUND OF THE INVENTION Fibrillated polyolefin fibers have been produced by flash spinning. In this flash spinning method, a polyolefin is added to an organic solvent, which can also be called a liquefied gas, and a polyolefin solution is prepared under high temperature and pressure.Then, the pressure of the solution is lowered through a vacuum orifice to cause phase separation, and it becomes opaque. This method is a well-known spinning method in which the octopus solution is further spouted into an atmosphere at room temperature and pressure through a spinneret to form fibrillated fibers.

[0003] That is, as a known technique, USP 3,08
No. 1,519, USP No. 3,227,794, US
No. P3,227,784, USP3,467,744
No. 3,564,088, USP 3,75
No. 6,441, EP-285670Al No. 6,441, EP3
21567Al bulletin, etc. or Special Publication No. 40-28125
No. 42-19520, etc., or Japanese Patent Publication No. 62
-33816, Japanese Unexamined Patent Publication No. 63-50512, etc.

The fibers obtained by this flash spinning method are used either as fibrids (short fibers) in synthetic pipes or as continuous fibrillated fibers in nonwoven sheets. . The product produced by the process to which the present invention is directed is fibrillated fibers that are turned into nonwoven sheets. This nonwoven fabric sheet is a so-called synthetic paper, and its main characteristics are that it is water resistant, strong, light, and does not fluff. This has been highly praised around the world, and we have produced products such as air mail envelopes, floppy disk sleeves, oxygen absorber bags, desiccant bags, medical sterilization bags, building insulation condensation prevention cloth, nuclear power generation work clothes, asbestos work clothes, etc. It has become indispensable for improving the safety and welfare of society. In order to produce products that meet the needs of society, fibrillated fibers that have high strength and are well opened are essential. This is because without such fibers, a dense, breathable, and uniform sheet cannot be obtained.

[0005] The present invention is also intended to respond to such social demands. Specific products include Tyvek manufactured by DuPont in the United States and Luxer manufactured by the present applicant. By the way, the following requirements are required for the solvent used in the flash spinning method for producing the above-mentioned useful fibers, as described in US Pat. No. 3,081,519. That is, (1) the boiling point is at least 25°C lower than the melting point of the polymer used, (2) it is inert to the polymer during spinning, and (2) the polymer is inert at temperatures and pressures suitable for preparing the spinning solution. ■Below the boiling point of the solvent, the polymer must be
It has been disclosed that (2) the polymer phase separates immediately during spinning to form a phase consisting mostly of polymer, and that the polymer phase contains almost no solvent.

Specific examples of solvents include aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as butane, pentane, hexane, heptane, and octane, and isomers and homologues thereof, and alicyclic hydrocarbons such as cyclohexane. group hydrocarbons,
Or unsaturated hydrocarbons, halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform, ethyl chloride, methyl chloride, alcohols such as ethanol, methanol, hexafluoroisopropanol, esters, ethers, ketones, nitriles, amides, trichlorofluoro methane,
Fluorinated chlorinated aliphatic hydrocarbons such as 1,1,2-trichloro-1,2,2-trifluoroethane, sulfur dioxide,
Carbon disulfide, nitromethane, water and various liquid mixtures of the above are known.

[0007] These solvents are optimal depending on the spinning method used and the polymer used. In particular, as a polyolefin spinning method, trichlorofluoromethane, which has excellent polymer solubility and spinnability, and is nonflammable and nontoxic,
A spinning method using 1,2-trichloro-1,2,2-trifluoroethane or the like is preferred. Among these, the spinning method using trichlorofluoromethane is the most excellent.

[0008]

However, in recent years, fully halogenated hydrocarbons in which all hydrogen has been replaced with chlorine and fluorine have been classified as specific fluorocarbons (chlorofluorocarbons, or CFCs).
Due to its high ozone-depleting ability, its production was banned by 2000 AD. Naturally, trichlorofluoromethane, which is a specific fluorocarbon, 1,
Flash spinning methods for polyolefins using 1,2-trichloro-1,2,2-trifluoroethane and the like are no longer available.

[0009] Against this background, a new spinning method has been proposed as a flash spinning method that preferably does not use trichlorofluoromethane, which is a specific fluorocarbon. That is,
JP-A-2-139408 discloses a flash spinning method using a mixture of methylene chloride and a partially substituted halogenated hydrocarbon;
, 1-dichloro-2,2,2-trifluoroethane, 1
,2,-dichloro-1,2,2-trifluoroethane,
1,1-dichloro-2,2-difluoroethane, 1,2
A spinning method using -dichloro-1,1-difluoroethane, 1,1-dichloro-1-fluoroethane, etc. is further described in EP-0407953A2 for polypropylene. A method of spinning using trifluoroethane, 1,2-dichloro-1,2,2-trifluoroethane, etc. has been proposed.

However, the disclosed method for spinning polyethylene fibrillated fibers has serious problems. That is, the polyethylene fibrillated fibers obtained by the above-described spinning method have low fiber strength and poor opening properties, making them impractical, and some of them cannot even be spun. As mentioned earlier, the characteristics of nonwoven fabric sheet products made from fibers obtained by flash spinning are that they must be light, strong, uniform, dense, and breathable. It is the basis of social utility.

[0011] Therefore, the proposed flash spinning method for polyethylene, which does not destroy ozone, cannot be said to have sufficient utility. If the strength of the fibrillated fiber is low, the strength of the product will also be low, and it is used in airmail envelopes, floppy disk sleeves, medical sterilization bags, building insulation condensation prevention cloth, nuclear power generation work clothes, asbestos work clothes, etc. Not only is it difficult to do this, but the spinning process also causes fibers to break, fuzz, and fibrits to form. As a result, lint is generated, making it difficult to use for dust-free paper, floppy disk sleeves, medical sterilization bags, nuclear reactor power generation work clothes, asbestos work clothes, etc., which do not want to generate lint at all.

In addition, if the opening properties are not good, the fibers will not spread out in a net shape and the sheet will be uneven, and the pore diameter of the ventilation holes, which is the lifeblood of a nonwoven fabric sheet made of fibrillated fibers, will vary, causing oxygen absorber bags, drying It can no longer be used for medicine bags, medical sterilization bags, building insulation condensation spun cloth, nuclear power generation work clothes, asbestos work clothes, etc. An object of the present invention is to provide an improved and socially useful flash spinning method that can produce fibrillated fibers with high strength and excellent opening properties using a solvent with low ozone-depleting ability. It is in.

[0013]

[Means for Solving the Problems] The present inventors have devised a method to create fibers that have performance comparable to or superior to polyethylene fibrillated fibers produced by conventional flash spinning methods, while using a solvent with low ozone depleting ability. The present invention was achieved through intensive research to see if it could be obtained. That is, a high-temperature, high-pressure solution consisting of polyethylene and a solvent containing a halogenated hydrocarbon is made, passed through a vacuum orifice, a vacuum chamber, and a spinneret, and then released into a normal temperature and pressure range to produce fibrillated polyethylene.
In the method for producing fibrillated fibers, 1,1-dichloro-2,2,2-trifluoroethane or 1,2-dichloro-1,2,2-trifluoroethane or a mixture thereof is used as the halogenated hydrocarbon. Using a solvent consisting of cyclohexene as another hydrocarbon, a solution consisting of the solvent and 5 to 25 wt% polyethylene was plotted below on a cloud point curve with temperature and pressure as the horizontal and vertical axes, respectively. Polyethylene fibrillation, characterized in that the temperature is adjusted to a temperature exceeding the temperature Tα at which the minimum point of the convexity is formed and the pressure is above the cloud point pressure, and then the pressure in the decompression chamber is reduced to the pressure below the cloud point pressure. It is a method of manufacturing fibers.

Preferably, a high-temperature, high-pressure solution consisting of a solvent containing polyethylene and a halogenated hydrocarbon is prepared, passed through a vacuum orifice, a vacuum chamber, and a spinneret, and discharged into a normal temperature and pressure range to form fibrillated polyethylene. In the above method for producing fibrillated fibers, 1,1-dichloro-2,2,
2-trifluoroethane or 1,2-dichloro-1,2
, 2-trifluoroethane or a mixture thereof is 75 wt%
~90wt%, cyclohexene from 25wt% to 10w
t% of the polyethylene fibrillated fiber.

More preferably, a high-temperature, high-pressure solution consisting of polyethylene and a solvent containing a halogenated hydrocarbon is prepared,
In the above method of manufacturing fibrillated polyethylene fibers by passing through a vacuum orifice, vacuum chamber, and spinneret and releasing into a room temperature and normal pressure region, when introducing a high temperature and high pressure solution into the vacuum chamber, This is a method for producing polyethylene fibrillated fibers, characterized in that the temperature of the solution is set from 10° C. below the critical temperature of the solvent constituting the solution to 10° C. above the critical temperature.

Preferably, a high-temperature, high-pressure solution consisting of a solvent containing polyethylene and a halogenated hydrocarbon is prepared, passed through a vacuum orifice, a vacuum chamber, and a spinneret, and discharged into a room temperature and pressure range to form fibrillated polyethylene. - In the above method for producing fibrillated fibers, the pressure in the vacuum chamber is 5 kg/cm2 lower than the cloud point pressure on the cloud point curve.
This is a method for producing polyethylene fibrillated fibers, characterized in that the pressure in the vacuum chamber is within a range from below to 30 kg/cm2.

By this method, the present inventors were able to obtain fibrillated fibers with significantly higher strength and good spreadability, unlike conventionally known methods, although using a solvent with low ozone depleting ability. Ta. 1,1-cyclo-2,2,2-trifluoroethane (
HCFC-123 (hereinafter referred to as HCFC-123) and 1,2-dichloro-1,2,2-trifluoroethane (hereinafter referred to as HCFC-123a) are specified worldwide as alternative CFCs to trichlorofluoromethane. well known. Therefore, this HCFC-123 and -123
Anyone wonders if it is possible to use a for flash spinning instead of trichlorofluoroethane.

However, these HCFC-123 and -123
When a is used for flash spinning, the polymer solubility is completely insufficient, and as it is, even flash spinnability cannot be examined. Therefore, HCFC-123 and -123
A huge amount of research has been done to apply a to flash spinning. The basic principle of flash spinning is to phase-separate a high-temperature, high-pressure polymer solution under reduced pressure to form an opaque liquid consisting of at least two phases, polymer and solvent, before spinning. Therefore, the temperature and pressure at the cloud point, which indicates phase separation, is extremely important as the liquid changes from transparent to opaque.

a. Cloud Point Curve Cloud point is expressed as the temperature and pressure at which the liquid changes from transparent to opaque. Since cloud point is usually measured visually, it varies somewhat depending on the measurement method. The transparency and opacity of the liquid also vary depending on the temperature, pressure, polymer concentration of the liquid, and the types of polymer and solvent that make up the system. Furthermore, it varies somewhat depending on the solution preparation method, measurement time, light source, etc. Therefore, although there is some variation, observations can be made with good reproducibility if the measurement method is fixed.

In polymer chemistry, a diagram plotting this cloud point on temperature/pressure coordinates is called a cloud point curve. The suitability of the solvent for flash spinning can be determined by the position of this cloud point curve on the temperature/pressure coordinate plane. With HCFC-123 and -123a alone, this cloud point curve was not observed even at considerably high pressures, and polyethylene could not be dissolved.

However, by combining it with cyclohexene, it was possible to bring the cloud point curve to a position suitable for flash spinning as shown in FIG.
It was also found that the position of the cloud point curve changes depending on the composition ratio of 123 or -123a and cyclohexene. As shown in Figure 1, the positions of the cloud point curves are different when the weight composition ratio is 85:15 and 80:20, and when the weight composition ratio is 80:20, it is approximately 50 kg/
It is about cm2 below. This indicates that the thermodynamic properties of the polymer solutions are different depending on the composition ratio.

By the way, the cloud point curve, which is an important factor in the present invention, is measured using the apparatus shown in FIG. That is, two optical windows 7 are provided at the lower end of an autoclave-type container (volume 250 cm@3) 1, so that the interior can be observed through light. The length of the optical path through which the light passes is 176 mm because the thickness of the glass of the optical window 7 is 88 mm per piece, and there are two pieces.
mm, and the thickness of the solution is 50 mm, etc., totaling 226 mm.
It becomes mm. This autoclave-type container 1 has a built-in stirrer 3, and is heated for approximately 500 r until the polymer is almost dissolved.
Stir the inside of the container at pm. The structure of the stirrer 3 is that two stirring blades are installed, and a cylindrical guide plate is welded to the outside of the stirring blades.
It looks like two blades are housed in a metal cylinder. Further, two scrapers are welded to the outside of the cylinder, facing 180 degrees to the cylinder core, so as to thoroughly stir the entire liquid and create a downward flow within the container. Further, a thermocouple 5 for temperature detection and a diaphragm pressure gauge 6 are provided so as to be in direct contact with the solution in the container. or,
Piping 4 (1 in Figure 2) is used for the N2 gas introduction pipe for degassing the gas inside the container and pushing out the liquid inside the container.
Although this is shown here, there are actually two). Furthermore, a pressure intensifier 10 for pressurizing the liquid in the container and a pipe 14 for draining or pushing out the liquid are provided. Each pipe is equipped with a needle valve. The entire container is covered with a cast aluminum heater, and the temperature is controlled by a control circuit.

[0023] To measure the cloud point, first, the polymer and solvent are weighed and supplied into a container so that the polymer concentration becomes a predetermined concentration and the inside of the container becomes a liquid seal. In the example in Figure 1, HCFC-123 is 85 wt% and cyclohexene is 1 wt%.
234.0g (87.5wt%) of solvent mixed with 5wt%
%) to polyethylene (density: 0.96 g/cc, MI:
0.78) was weighed and supplied to the container. It is then heated and as the liquid expands,
The pressure inside the container increases. In the example of Figure 1, the heating rate is 3.0
℃/min. In this way, the polymer begins to partially dissolve in the solvent when it reaches near the polymer melting point. In this state, prepare a polymer solution. By this time, the hydraulic pressure was 500k.
g/cm2, so the hydraulic pressure is 500kg/cm
2 When it gets close, drain the liquid and lower the pressure.

Next, the cloud point is measured. Find the cloud point by changing temperature and pressure. The cloud point is determined by observing changes in the amount of light through an optical window or by measuring with a photocell, etc., and when the visual field becomes dark or the amount of light suddenly decreases, that point is determined as the cloud point. In this way, while increasing the temperature, the liquid drain and pressure intensifier are controlled and measurements are made up to nearly 240°C. In the example of FIG. 1, the temperature increase rate during measurement was 1.3° C./min. This measurement should be done quickly as the polymer will deteriorate.

b. Singular point Tα on the cloud point curve FIG. 1 shows the cloud point curves of HCFC-123 and cyclohexene obtained in this way. As can be seen from FIG. 1, the cloud point pressure on the low temperature side decreases as the temperature rises. The cloud point pressure reaches a minimum point at a certain temperature, and then increases as the temperature further increases. The minimum point of this cloud point curve is defined as a singular point Tα. In the example of Figure 1, HCF
The weight mixing ratio of C-123 and cyclohexene is 85
:15 and the polymer concentration is 12.5%, the temperature Tα at the singular point is 197°C, and the pressure Pα at the singular point is 194 kg/cm.
It was 2.

The existence of this singularity Tα is surprising;
This was discovered for the first time by the present inventors. This singularity T
As a result of investigating the behavior of α, it was found that in the temperature increase method, the cloud point pressure forms the minimum point as shown in Figure 1, and in the temperature decrease method, the cloud point pressure does not change much at temperatures below the singular point Tα, and remains almost constant at the singular point. Tα
turns out to be an inflection point of the curve. Furthermore, when measuring by changing the temperature increase rate, temperature decrease rate, and pressure change, it was confirmed that the cloud point in the region on the low temperature side below the singular point Tα changes somewhat, but the position of the singular point Tα was found to be always constant. In the temperature increase method, it was discovered that the curve always forms a small point, which is a characteristic value representing phase equilibrium in a polymer solution of polyethylene and a solvent consisting of HCFC-123 or -123a and cyclohexene.

It is still unclear why such a singular point Tα appears, but according to observation, the state of light transmission is different in the region on the low temperature side before the singularity Tα and the region on the high temperature side after it. It is assumed that the structure of the liquid is different. More surprisingly, it has been found that the state of flash spinning changes before and after this singular point Tα, and that satisfactory fibrillated fibers cannot be obtained at temperatures below the singular point Tα. That is, the fibrillated fibers obtained by reducing the pressure from the solution at a temperature below the singular point Tα and turning it opaque, and then spinning it out from a spinneret have extremely poor spreadability and cannot be made into a nonwoven sheet. It was impossible. On the other hand, fibrillated fibers spun at a temperature above the singular point Tα had good spreadability and high strength, and could be made into a good nonwoven fabric sheet.

Specifically, Tables 1 and 2 show the results. HCFC-123/cyclohexene = 85 in Table 1:
In No. 15, Tα:Pα is 197°C: 194 kg/cm, and it can be seen that there is a large difference in quality between spinning at 188°C (Comparative Example 1) and spinning at 201°C (Example 1). The fibrillated fiber spun at 188°C (Comparative Example 1) is not suitable for practical use. Similarly, HCFC-123/cyclohexene = 80 in Table 2
:20, Tα:Pα is 190℃: 140kg/cm
2, there is a big difference between spinning at 180°C (Comparative Example 2) and spinning at 201°C (Example 6).

As a matter of course, the position of the singular point Tα is
Varies depending on the composition of the solvent. HCF as shown in Figure 1
The weight mixing ratio of C-123 and cyclohexene is 80:2
When the polymer concentration was 12.5%, the temperature Tα at the singular point was 190° C., and the pressure Pα at the singular point was 140 kg/cm 2 . In this way, as the content of cyclohexene increases, the position of the singular point Tα moves to the lower temperature side and the pressure thereof also decreases. When the content of cyclohexene exceeds 25 wt%, the singular point Tα moves to the low temperature side, making observation difficult. Further, when the temperature decreases below 10 wt%, the singular point Tα becomes extremely high temperature and Pα also becomes extremely high pressure. In this region, it is difficult to prepare the solution and spinning cannot be performed. Moreover, when the content of cyclohexene exceeds 25 wt%, the singularity point T
Not only will it be difficult to observe α, but the position of the cloud point curve will move too far to the low pressure side. Regions where the cyclohexene content is lower than 10 wt% and 25
The area exceeding wt% is not the area of the present invention.

c. Critical temperature The critical point of a solvent is a physical property value unique to the solvent, and is determined by the physicochemical properties of the solvent. In flash spinning, the spinning condition range is within the range of the singular point Tα or higher in the phase diagram represented by the cloud point curve. However, it has been found that there is a range in which even better fibrillated fibers can be stably obtained if spinning is performed within a more limited range. As a result of further research, it was discovered that the critical point Tc of the solvent is an extremely heavy element. That is, as a result of carrying out various spinning operations, it was found that when spinning was carried out near the critical point Tc of the solvent, high-quality fibrillated fibers with excellent spreadability and high strength could be obtained.

As can be seen from Table 1, the singularity Tα is 194
from 201°C (Example 1) to 225°C (Example 5)
) Good fibrillated fibers have been obtained. Furthermore, better fibrillated fibers are obtained at temperatures from 206°C to 219°C. This difference is also obvious in the spinning state, and the number of beads in the gas stream at the exit of the spinning nozzle is greater in Examples 2 to 4 than in Example 1. This also corresponds to the spinning speed. The critical temperature of a mixture of HCFC-123 and cyclohexane in a weight ratio of 85:15 is estimated to be 211°C based on the molar ratio, and within a range of ±10°C around the critical temperature Tc, it has excellent spreadability and strength. It can be seen that there is a range that provides fibrillated fibers.

As another example, the results of flash spinning using an 80:20 weight ratio mixture of HCFC-123 and cyclohexene as the solvent are shown in Table 2. in this case,
The singular point Tα is 190°C, and Pα is 140 kg/cm
It was 2. Furthermore, the critical temperature of the solvent is 215° C. based on molar ratio estimation. The same results as in the case of a mixed solvent with a weight ratio of 85:15 were shown.

[0033] Regarding the critical point of a single solvent, many measurement examples are referred to in papers, books, etc. However, there is no such value for mixed solvents. The solvent system targeted by the present invention is nearly nonpolar, and it is expected that there will be almost no interaction between the mixed solvents. In such a case, it was assumed that there would be no large deviation as it is proportional to the molar fraction, and this was adopted in the present invention. Actual measurements are required to ensure accuracy.

From Tables 1 and 2, it is clear that the spinning temperature is at the singular point Tα
It was found that the above results produced fibrillated fibers of good quality, and that flash spinning, especially at the point where the temperature reached the critical temperature, gave even more excellent fibrillated fibers. The reason for this is not clear, but as can be seen from the spinning speed, the gasified jet flow exiting the spinneret is clearly a supersonic flow. This is also evidenced by the fact that the gas jet flow immediately after exiting the spinneret nozzle has a bead-like shape with a supersonic flow. This indicates that the flow is choked within the nozzle of the spinneret, and after passing through that region, it becomes a gas flow, and the enthalpy of the solvent is converted into gas velocity, increasing the speed. The sound velocity of the fluid is at its lowest near the critical point of the solvent, and it is presumed that this is most convenient for polymer fiber formation.

The reason why there is a range of suitable spinning conditions is that, from the viewpoint of the PVT (pressure, volume, temperature) characteristics of the solvent, changes in temperature and pressure are small and gentle with respect to changes in volume near the critical point. That is, even if the volume changes somewhat, the temperature and pressure do not change much. We assume that this is related to this characteristic. d. As mentioned above, quench depth flash spinning is characterized by changing the phase of the polymer solution to form an opaque solution before spinning. Therefore, we invented a unique phase change method and achieved that goal. In the process, we discovered a region where even better fibrillated fibers could be consistently obtained. After studying the spinning method in more detail, we invented a new and improved spinning method.

By spinning in a temperature range exceeding the singular point Tα on the cloud point curve and at the critical point of the solvent, and by setting ΔP shown in FIG. 3 to an appropriate value, it has excellent fiber opening properties. It was found that high-quality fibrillated fibers with high strength could be stably obtained. Here, △P is called quench depth. Quench depth refers to the depth from cloud point pressure to spinning point pressure. FIG. 3 shows a model of the quench depth. The change from the solution preparation point to the spinning point is an isentropic change. Therefore, the change shown in the model diagram is impossible, and the temperature also changes. However, the temperature in the vacuum chamber corresponding to the spinning point pressure is not easy to detect in an autoclave experiment, and since the polymer hardly changes in volume, the temperature does not decrease much even with an isentropic change. Due to the heat content of this polymer, the temperature does not appear to change much. In fact, even in continuous spinning machines, the temperature in the vacuum chamber is equal to the solution temperature before the vacuum orifice.
It only decreased by ~10°C, which is not that much of a difference. Therefore, it can be shown as a model as shown in FIG. Table 3 shows how the quench depth ΔP affects the performance of fibrillated fibers.

As can be seen from Table 3, the quench depth △P
It can be seen that optimizing the fibers results in better and superior quality fibrillated fibers. It is not clear why this happens, but it is related to the phase structure developed by phase separation of the polymer. The reason for this is the comparative example No. When the quench depth ΔP is small as in No. 4, the fibers are extremely fine and fluffy. This indicates that the size of the polymer phase structure developed by phase change is extremely small. On the contrary, quench depth △P
Comparative example No. with a large 5 consists of extremely coarse fibers. This indicates that the size of the phase structure developed by the phase change is large.

Comparative Example No. In Comparative Example No. 4, the single filaments were fine and the spreadability was poor, and the strength was low, so it was difficult to say that it was an extremely good quality fibrillated fiber. In case of No. 5, the single yarn becomes too coarse and it is difficult to say that this is an extremely good product. The speed of phase change is said to depend on the thermodynamic potential of the location. It is thought that the pressure depth from the cloud point pressure corresponds to this thermodynamic potential, so it is estimated that the larger the quench depth ΔP, the faster the rate of change, and the more fully developed the structure becomes, the larger the size.

[0039] Thus, the quench depth △P is an extremely important factor, and it is
This is a unique property of the system of a, cyclohexene, and polyethylene. In this way, we have discovered, for the first time, a method for producing fibrillated fibers with good spreadability and high strength that can be put to practical use using a solvent with extremely low ozone depletion ability.

However, fibrillated fibers that are stable, have excellent opening properties, and have high strength can be obtained by using a solvent with low ozone-depleting ability. This industrial significance is of immeasurable value. 1,1-dichloro-2,2,2- used
trifluoroethane or/and 1,2-dichloro-1,
The 2,2-trifluoroethane may be a pure product or a mixture thereof. What you need to be careful about is the amount of water; the less the better.

[0041] The higher the purity of cyclohexene, the better; preferably, the purity is 80% or more. In particular, the water content is desirably 200 ppm or less. The most preferable polyethylene is high-density polyethylene, which has a density of 0.9.
It is 4 g/cc or more. Further, it is preferable that the copolymerization component is 15% or less and that the above-mentioned density is maintained. Additionally, commonly known polymer additives, such as heat stabilizers, light stabilizers, lubricants, nucleating agents, crosslinking agents, plasticizers, fillers, etc., may be included in the polymer.

The apparatus used in the present invention may be equipped with a solution adjusting device and a spinning device consisting of a vacuum orifice, a vacuum chamber, and a spinneret. At the tip, fibrillated fibers are opened and
There is a dispersion device, a moving conveyor device that converts the spread and dispersed fibrillated fibers into a sheet, and a winder that winds up the formed sheet. The sheet forming section is housed in a sealed box, and the solvent gas inside the box is collected. The solvent adjustment device may be an autoclave device or an extruder. Alternatively, a conventionally known device can also be used.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Examples] The contents of the present invention will be explained below with reference to Examples. This example is intended to specifically illustrate the content of the present invention, and is not intended to limit the scope of the claims of the present invention. The solution adjustment point used in the examples indicates the temperature and pressure conditions under which the polymer solution was created, and this term was used because it can be expressed as a point on a cloud point curve diagram. Similarly,
The term "spinning point" is used because it indicates the pressure conditions when a polymer solution is depressurized, undergoes a phase change, becomes an opaque liquid, and is spun out from a nozzle, and can be expressed as a dot on a cloud point curve diagram. What needs attention here is the temperature at the spinning point. The change from the solution preparation point to the spinning point can be roughly regarded as an isentropic change. Then, the liquid temperature should definitely drop. However, in the case of an autoclave experiment, this accurate detection is not possible because spinning is completed in a relatively short time. Furthermore, polymers can be considered to have little temperature variation. As a result, it can be assumed that the apparent temperature does not change much. Therefore, for convenience, the temperature is expressed as a model in FIG. 3 assuming that it does not change, but the present invention is not limited to this.

The number of free fibrils mentioned in the examples is a measure of the spreadability of fibrillated fibers, and if this value is 300 or more, a dense, uniform, uneven nonwoven fabric sheet can be obtained. On the other hand, if it is less than 100, the sheet will be non-uniform and extremely mottled, making it completely unusable. A value between 100 and 300 is somewhat unreasonable for advanced applications, but can be used satisfactorily for general applications that do not require very high performance.

[0048] The spreadability scale in Examples is: "○" means the number of free fibrils is 300 or more, "△-○" means 100 to 300, and "x" means 100 or less. be. The number of free fibrils was measured as follows. Fibrillated fibers have a structure in which a large number of fine short fibers (single threads) are connected in a network. The greater the number of individual fibers at the same denier, the better the fibrillated fibers are. The number of free fibrils is measured using a spread yarn obtained by colliding a spun gas jet with fibers still in it against a copper plate tilted at approximately 45° at a position approximately 25 mm from the tip of the spinneret. Gently pinch the sampled spread thread between the glass plates and place it through the objective lens 1.
While moving an optical microscope with a 6x magnification and a 10x eyepiece in the fiber width direction, count the number of single filaments in the field of view, and calculate the number of free fibrils per 100 denier. .

[0049]

[Example 1] Internal volume 550cm3 and pressure resistance 300kg/
In a cm2 autoclave, melt index (MI
) 0.78, density 0.96 g/cc, 439 g of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 77.4 g of cyclohexene, and closed the lid. After that, turn on the heater while rotating the stirrer to heat the HCFC-123.
:Polymer 1 consisting of cyclohexene=85:15 solvent
A solution for flash spinning of 2.5 wt% was made.

[0050] The solvent is always kept in a liquid-sealed state, and the pressure is 30°C.
The polymer solution was adjusted while draining when the temperature approached 0 kg/cm2. Finally, the temperature was 201℃,
The pressure was set at 243 kg/cm2. Next, the stirrer was stopped, and 248 kg/cm2 of N2 gas was introduced from the pressure accumulator, and while the solution was directly pressurized with this gas, the discharge valve at the bottom of the autoclave was quickly opened to perform spinning.

[0051] At this time, at the end of the autoclave's release valve, a part having the following dimensions: a decompression orifice, a decompression chamber, a nozzle, and a circular through hole whose central axis coincides with the nozzle,
A spinneret incorporating this order was attached. That is, a vacuum orifice with an inner diameter of 0.65 mmφ and a length of 5 mm, a vacuum chamber with an inner diameter of 8 mmφ and a length of 40 mm and an introduction angle of 60° from the vacuum chamber to the nozzle, and a vacuum chamber with an inner diameter of 0.5 mmφ and a length of 0. .5mm nozzle, inner diameter 3 coaxial with nozzle center axis
．． This is a part that has a through hole with a diameter of 0φ and a length of 3.0 mm.

The solution was then spun into the atmosphere by passing through the spinneret. At this time, the pressure in the decompression chamber was 179 kg/
cm2. Therefore, the solution adjustment point is 201℃, 2
43 kg/cm2, and the spinning point is 179 kg/cm2. The fibers were opened by applying them to a copper plate tilted at about 45° at a position about 25 mm away from the spinneret. The performance of the obtained fiber was that it had excellent opening properties, and the number of free fibrils was 18.
It was 8. Furthermore, the strength was 5.3 g/d, and the spinning speed determined from the denier was 200 m/s.

[0053] At this time, the singular point Tα is 197°C, and Pα is 19
It was 4 kg/cm2. Fibrillated fibers of excellent quality could be produced by spinning from a transparent liquid phase in a temperature range exceeding the singularity point.

[0054]

[Comparative Example 1] Using the same apparatus as in Example 1, a solution was prepared in the same manner as in Example 1, and spinning was carried out under the following conditions. That is, a polymer solution having the same solvent composition as in Example 1 and a concentration of 12.5 wt % was prepared at a solution adjustment point of 188° C. and 235 kg/cm 2 , and spun at a spinning point of 170 kg/cm 2 . The performance of the obtained fibers was poor in opening properties and the number of free fibrils was 4.
8, making it practically unusable. For reference, when the strength was measured, it was only 4.1 g/d. Furthermore, when the spinning speed was determined from the denier, it reached only 181 m/s, which was significantly different from the present invention. As described above, fibrillated fibers that can be used for practical purposes could not be obtained using a method different from that of the present invention.

[0055]

[Examples 2, 3, 4 and 5] Next, spinning was carried out by changing the conditions of the solution adjustment point. The polymer solution, spinning equipment and method are the same as in Example 1. Table 1 shows Example 1 and Comparative Example 1.
Shown with As is clear from this, fibrillated fibers with excellent spreadability and high strength were obtained in the temperature range from 201° C. to 225° C., which exceeds the singular point Tα.

Furthermore, in Examples 2 to 4 at 206°C to 219°C, fibrillated fibers with even better performance than Example 1 at 201°C were obtained. The number of free fibrils was 412 in Example 2, 458 in Example 3, and 42 in Example 4.
It had reached 3. It was also found that the strength was further improved. On the other hand, in Example 5, the number of free fibrils was 4.
95, but the strength was slightly low at 5.1 g/d. It also looked a little fluffy.

The critical temperature of HCFC-123 is 184°C and that of cyclohexene is 287°C. H.C.F.
The polymerization mixing ratio of C-123 and cyclohexene was 85:
15, so the mole fraction is 0.752:0.248, respectively.
Therefore, the critical point of the mixed solvent is 209°C. The temperature range more suitable for flash spinning is the critical temperature ±10°C. Very good fibrillated fibers have been obtained in this temperature range. It can be seen that the more preferred method of the invention provides highly superior fibrillated fibers.

[0058]

[Examples 6, 7, 8 and 9] Furthermore, spinning was carried out by changing the solvent composition. That is, in the same autoclave as in Example 1, 73.8 g of high-density polyethylene and 413 g of HCFC-123 and 103 g of cyclohexene were placed in the same autoclave as in Example 1.
g was added, and after the lid was placed, electricity was applied to the heater while rotating the stirrer to heat it, to prepare a solution for flash spinning of 12.5 wt % polymer consisting of a solvent of HCFC-123: cyclohexene = 80:20. . Other spinning equipment and methods are the same as in Example 1. The results are shown in Table 2. As is clear from Examples 6, 7, 8, and 9, fibrillated fibers with excellent spreadability and high strength were obtained in the temperature range from the solution adjustment point temperature of 201°C to 224°C. Further, from Example 7 with a solution adjustment point temperature of 206°C to a temperature of 224°C.
In Example 9 at 0.degree. C., fibrillated fibers with extremely excellent spreadability and strength were obtained.

The polymerization mixing ratio of HCFC-123 and cyclohexene is 80:20, so the molar fractions of each are 0.
683:0.317, and the critical point of the mixed solvent is 216
℃. The better temperature range for flash spinning is the critical temperature ±10°C, similar to Examples 2, 3, and 4. In this way, even more excellent fibrillated fibers were obtained within the critical temperature range of ±10°C. From this, it can be seen how superior the more preferred method of the present invention, which involves spinning near the critical temperature.

[0060]

[Comparative Example 2] A solution was prepared using the same apparatus and method as in Example 6, and spinning was carried out under the following conditions. That is, a polymer solution having the same solvent composition as in Example 6 and a concentration of 12.5 wt % was prepared at a solution adjustment point of 180° C. and 191 kg/cm 2 , and spun at a spinning point of 127 kg/cm 2 . The performance of the obtained fiber was that the number of free fibrils reached only 75, and it was of no practical value. For reference, when the strength was measured, it was only 3.9 g/d. Also, when calculating the spinning speed from the denier, it only reaches 172 m/s,
This was a significant departure from the invention. As described above, by a method different from that of the present invention, it was not possible to obtain fibrillated fibers that could be put to practical use.

[0061]

[Comparative Example 3] A solution was prepared using the same apparatus as in Example 6 and in the same manner, and spinning was carried out under the following conditions. That is, a polymer solution having the same solvent composition as in Example 6 and having a concentration of 12.5 wt % was adjusted at a solution adjustment point of 231° C. and 222 kg/cm 2 and spun at a spinning point of 158 kg/cm 2 . The spinning condition was unstable and the nozzle was sometimes clogged. The resulting fiber had a poor appearance without measuring its performance, and the polymer was clearly thermally degraded. The strength is also low at 4.0 g/d. From this, it is necessary that the temperature at the solution adjustment point be below the temperature at which the polymer does not deteriorate due to heat, that is, below 230°C.

[0062]

[Examples 10 and 11, Comparative Examples 4 and 5] Furthermore, in order to investigate the effect of quench depth during spinning, spinning was performed with different spinning and solution adjustment points. The polymer solution equipment and method are the same as in Example 3. Examples 3 and 1 shown in Table 3
As is clear from 0 and 11, the quench depth △P: 1
Quench depth △P from 1kg/cm2: 26kg/
Fibrillated fibers with excellent spreadability and high strength in the cm2 region were obtained.

On the other hand, quench depth △P: 5~
In Comparative Examples 4 and 5, which were out of the range of 30 kg/cm2, the fibrillated fibers were of good quality, but in Example 3,
Compared to No. 10 and No. 11, the yarn was not so great. It is clear that the quench depth ΔP affects the performance of fibrillated fibers, and it is clear that there is a suitable quench depth ΔP. This is also seen when looking at the spinning speed, indicating that good fibers cannot be obtained even if the spinning speed is too high or too slow. As described above, by using the even more preferred method of the present invention, extremely excellent fibrillated fibers can be obtained.

[0064]

[Effect of the invention] By using the flash spinning method of the present invention, the ozone layer surrounding the earth is not destroyed.
Furthermore, socially useful fibrillated fibers can be easily obtained without adversely affecting global warming. By utilizing the present invention, it is possible to produce fibrillated fibers that are far superior in opening properties and have high strength compared to conventionally known flash spinning methods that do not destroy the ozone layer, making it possible to greatly contribute to society.

[Brief explanation of the drawing]

FIG. 1 is an example of a cloud point curve of a polymer solution of the present invention. The position of temperature Tα and pressure Pα of the singular point and the transparency of the liquid are shown. The symbol "○" in the figure indicates HCFC-123/cyclohexene = 85:15, and the symbol "△" indicates HCFC-123.
2 shows a cloud point curve of a solvent composition of /cyclohexene=80:20. In addition, the polymer has a melt index of 0.7
8. Density: 0.96 g/cc and the polymer concentration of the solution is 1
It is 2.5wt%.

FIG. 2 is a schematic diagram of an autoclave apparatus with an optical window for measuring the cloud point and singularity of the polymer solution of the present invention.

FIG. 3 is an explanatory diagram of the quench depth according to the present invention, and ΔP shown in the diagram is the quench depth.

[Explanation of symbols]

1 Autoclave with optical window 2 Tightening bolt 3 Stirrer 4 Valve 5 Temperature detection terminal 6 Diaphragm pressure detection terminal 7 Optical window 8 Light source 9 Photo receiver 10　Liquid pressure booster 11-13 Valve

Claims (3)

[Claims] Claim 1: A high-temperature, high-pressure solution consisting of polyethylene and a solvent containing a halogenated hydrocarbon is prepared, passed through a vacuum orifice, a vacuum chamber, and a spinneret, and released into a room temperature and pressure range to form fibrillated polyethylene fibrils. In the method for producing synthetic fiber, 1 as a halogenated hydrocarbon.
, 1-dichloro-2,2,2-trifluoroethane or 1,2-dichloro-1,2,2-trifluoroethane or a mixture thereof and cyclohexene as another hydrocarbon, A solution consisting of the solvent and 5 to 25 wt% of polyethylene is heated to a temperature higher than the temperature Tα at which the downwardly convex minimum point is formed on a cloud point curve in which the horizontal and vertical axes represent temperature and pressure, respectively. A polyethylene product characterized in that the pressure is adjusted at a pressure higher than the cloud point pressure, and then the pressure in the decompression chamber is lowered to the pressure lower than the cloud point pressure.
Method for producing fibrillated fibers. 2. The solvent containing a halogenated hydrocarbon is 1,1-dichloro-2,2,2-trifluoroethane, 1,2-dichloro-1,2,2-trifluoroethane, or a mixture thereof. A method for producing polyethylene fibrillated fibers according to claim 1, characterized in that a solvent consisting of 75 wt% to 90 wt% and cyclohexene 25 wt% to 10 wt% is used. 3. When a high-temperature, high-pressure solution is introduced into the vacuum chamber, the temperature of the solution is set from 10° C. below the critical temperature of the solvent constituting the solution to 10° C. above the critical temperature. A method for producing polyethylene fibrillated fibers according to claims 1 and 2. [Claim 4] The pressure in the vacuum chamber is 30 kg/cm2 from 5 kg/cm2 below the cloud point pressure of the cloud point curve. The method for producing polyethylene fibrillated fibers according to claims 1, 2, and 3, characterized in that the pressure in the vacuum chamber is in the range of below 2 cm2.