JP2865447B2 - Manufacturing method of polyolefin network fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing polyolefin reticulated fibers using an improved flash spinning method. Further, the present invention relates to an improved flash spinning method capable of obtaining extremely high quality polyolefin network fibers using a solvent having a very low ability to destroy the ozone layer surrounding the earth. Furthermore, the present invention relates to a production method for obtaining a polyolefin network fiber excellent in strength and openability used for a nonwoven fabric sheet by using a halogenated hydrocarbon having reduced ozone destruction ability. In other words, the present invention relates to an improved flash spinning method capable of obtaining a high-quality polyolefin network fiber using a nontoxic and nonflammable solvent which can be used extremely safely.

[0002]

2. Description of the Related Art A method for producing polyolefin network fibers is flash spinning. In this flash spinning method, a polyolefin is added to an organic solvent also referred to as a liquefied gas, the polyolefin solution is adjusted under high temperature and high pressure, and then the pressure of the solution is temporarily reduced through a reduced pressure orifice to cause phase separation, thereby forming opaque. The spinning method is a well-known spinning method in which the solution is further jetted through a spinneret into an atmosphere under normal temperature and normal pressure to form reticulated fibers.

[0003] That is, as known technologies, USP 3,081,519, USP 3,227,794, USP 3,227,784, USP
No. 3,467,744, USP 3,564,088, USP 3,756,441
Publication, EP-285670A1 Publication, EP-321567A1 Publication, EP
-357364A2, JP-B-40-28125, JP-B42-19520
JP-A-62-33816, JP-A-63-50512, and the like.

[0004] Fibers obtained by the flash spinning method are used as fibrids (short fibrous materials) in synthetic pulp on one side, and as continuous mesh fibers on non-woven fabric sheets on the other side.

[0005] The product produced by the process to which the present invention is directed is a reticulated fiber to be a nonwoven sheet. This non-woven fabric sheet is a so-called synthetic paper, and is a product that has water resistance, is strong, light, and does not lint. This is highly valued in the world, such as airmail envelopes, floppy disk sleeves, oxygen absorber bags, desiccant bags, medical sterilization bags, building insulation and dew condensation prevention cloth, reactor power generation work clothes and asbestos work clothes, safety protection Work clothes, etc., are indispensable for improving social safety and welfare. Especially as work clothes for ensuring safety, non-woven fabric sheets are made of non-woven fabrics made of polyolefin network fibers that are resistant to chemicals, lint-free, impermeable to fine dust, breathable, and resistant to friction. It is missing and has become socially essential.

[0006] In order to provide a product that satisfies the demands of society, a high strength and well-opened reticulated fiber is essential.
This is because a dense and air-permeable uniform sheet cannot be obtained unless such fibers are used.

The present invention is also for responding to such a social demand. Specific products obtained from such reticulated fibers include Tyvek (DuPont, USA)
And Luxer manufactured by the present applicant.

[0008] USP 3,081,519 includes solvents used in the flash spinning method for producing useful fibers as described above.
The following requirements are required, as described in Japanese Patent Publication No. That is, the boiling point is at least 25 ° C. lower than the melting point of the polymer used, it is inert to the polymer during spinning, and at a temperature and pressure suitable for adjusting the spinning solution, the solvent of the polymer is used. What is necessary is that, below the boiling point of the solvent, only 1% or less of the polymer is dissolved, and the phase is immediately separated during spinning to form a phase substantially consisting of a polymer, and the polymer phase contains almost no solvent.

Specific examples of the solvent include aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as butane, pentane, hexane, heptane and octane, and isomers and homologs thereof, and alicyclics such as cyclohexane. Group hydrocarbons, or unsaturated hydrocarbons, methylene chloride, carbon tetrachloride, chloroform, ethyl chloride, halogenated hydrocarbons such as methyl chloride, ethanol, methanol, alcohols such as hexafluoroisopropanol, esters, ethers, ketones, nitriles, Amido, trichlorofluoromethane, fluorinated chlorinated aliphatic hydrocarbons such as 1,1,2-trichloro-1,2,2-trifluoroethane, sulfur dioxide, carbon disulfide, nitromethane, water, and the above various liquid mixtures Etc. are known.

[0010] From these solvents, the most suitable one is selected according to the spinning method used and the polymer used. In particular, as a method for spinning a polyolefin, a spinning method using trichlorofluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, which is excellent in polymer solubility and spinnability, and which is nonflammable and non-toxic, is used. It is suitable. Among them, the spinning method using trichlorofluoromethane is most excellent.

In flash spinning, it is absolutely necessary that the solvent be at least low-toxic and flame-retardant in order to gasify the solvent. There is a demand for a solvent having a low boiling point, a new oily property that does not thermally decompose even at a high temperature and is sufficient to dissolve the polyolefin. The most suitable solvent is trichlorofluoromethane, and there is no solvent that surpasses this. Actually, only the method using trichlorofluoromethane is actually commercialized.

Many hydrocarbons or halogenated hydrocarbons have been disclosed as flash spinning solvents. But
In flash spinning, the solvent must be gasified. Then, it is recovered by an operation such as cooling and compression. Therefore, the conversion of the three-dimensional network fiber into a nonwoven fabric is performed in a large closed space. Otherwise, gas cannot be recovered. The size of the closed space is, for example, 2000 m ³ . Filling such a huge space with combustible gas is extremely dangerous and practically impossible.

Further, a corona discharge device or a high voltage static eliminator is built in the closed space, and can serve as an ignition source of combustible gas. Combustible gas cannot be used from this point. Furthermore, in the closed space, there are various kinds of machines such as a wire mesh conveyor, a corona charging device, and a spinning head for forming a nonwoven fabric, and a worker is forced to enter the closed space for repair and maintenance. Cases inevitably arise.
In addition, the outlet of the formed nonwoven fabric sheet is a non-contact seal, and the gas in the closed space constantly leaks to the work place. Therefore, if the flash spinning solvent is toxic,
You will not be able to use it. For these reasons, the only solvent that can be used in the flash spinning method is non-flammable and non-toxic trichlorofluoromethane.

However, recently, it has been discovered that all halogenated hydrocarbons in which all hydrogen has been replaced by chlorine and fluorine have a very high ozone depleting ability as specific freon (also referred to as chlorofluorocarbon or CFC). Production was banned by 2,000 C.E. for protection. Naturally, the production of specific fluorocarbons such as trichlorofluoromethane and 1,1,2-trichloro-1,2,2-trifluoroethane is banned and cannot be obtained.
As a result, the flash spinning method of polyolefin using trichlorofluoromethane cannot be used, which has a great impact on society.

[0015] From such a background, a new spinning method without using trichlorofluoromethane, which is a preferable specific fluorocarbon, has been proposed as a flash spinning method.

That is, JP-A-2-139408 discloses that a partially substituted halogenated hydrocarbon such as methylene chloride, for example, chlorofluoromethane, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, 1,1,2-tetrafluoro-2-chloroethane, 1,1-difluoro-
A method of flash spinning using a mixture with 1-chloroethane and the like is disclosed in JP-A-2-160909, and 1,1-dichloro-2,2,2-trifluoroethane, 1,2-dichloro-1, 2,2-trifluoroethane, 1,1-dichloro-2,2-difluoroethane, 1,2-dichloro-1,1-difluoroethane, 1,1-dichloro-1-
A spinning method using fluoroethane or the like is further described in EP-0407953.
A2 discloses a method of spinning polypropylene with 1,1-dichloro-2,2,2-trifluoroethane, 1,2-dichloro-1,2,2-trifluoroethane, and the like. EP-357364A2 proposes a spinning method using methylene chloride and carbon dioxide gas.

However, the disclosed spinning method includes:
There are significant deficiencies when spinning with polyolefins. That is, Japanese Patent Application Laid-Open No. 2-1394 using methylene chloride.
JP 08 and EP-357364A2 cannot be practically used. Because methylene chloride is carcinogenic. Solvents with such toxicity cannot be used for flash spinning. Japanese Patent Application Laid-Open No. 2-160909, which proposes the use of CFC-11 instead of trichlorofluoromethane (CFC-11), discloses only 1,1-dichloro-1-fluoroethane (HCFC-
Only 141b) dissolves high-density polyethylene, which is a typical example of polyolefin, and the other CFC-11 alternative fluorocarbons do not dissolve high-density polyethylene at all. Rather, hydrocarbons proposed as co-solvents are the main solvents, and the alternative chlorofluorocarbons are merely boiling point regulators. Looking at these cosolvents, it is inevitable to use yabari methylene chloride from the viewpoint of flame retardancy or nonflammability. Further, 1,1-dichloro-1-fluoroethane (HCFC-141b) is remarkably inferior in thermal stability and has an ozone depletion ability exceeding 0.1, so that it cannot be detected.

Thus, what has been proposed so far is:
Only methylene chloride is practically usable, but this has to be avoided due to its toxicity. Even if it can be used, the polyolefin network fiber obtained by the above-mentioned spinning method cannot be put to practical use because of its low fiber strength and poor openability.

As described above, the feature of the nonwoven fabric sheet product made of the fiber obtained by the flash spinning method is that a light, strong, uniform and dense breathable sheet is essential. This is the basis of social utility. If the strength of the reticulated fiber is low, the strength of the product itself is also low, and it can be used for airmail envelopes, floppy disk sleeves, medical sterilization bags, building insulation heat-condensation prevention cloth, reactor power generation work clothes, asbestos work clothes, etc. Naturally, the fiber is cut, fuzzed, and fibrid is generated during the spinning process. As a result, lint is generated, and dust-free paper
It cannot be used at all for floppy disk sleeves, medical sterilization bags, reactor power generation work clothes and asbestos work clothes. If the spreadability is not good, the fibers do not spread in a net-like manner and become a sheet with many spots, and the diameter of the vent hole, which is the life of the nonwoven fabric sheet made of the mesh-like fibers, varies, and a bag of oxygen scavenger, desiccant bag, It cannot be used at all for sterilization bags for buildings, cloth for preventing thermal insulation and dew condensation, work clothes for nuclear power plants and work clothes for asbestos.
Therefore, the proposed method of flash spinning polyolefin that does not destroy ozone cannot contribute to the improvement of social welfare and safety.

An object of the present invention is to provide a method for flash-spinning an improved socially useful polyolefin, which can obtain a high-strength and excellent openable reticulated fiber by using a solvent having a low ozone-depleting ability. Is to provide. Furthermore,
It is an object of the present invention to provide an improved flash-spinning method which provides excellent reticulated fibers using a solvent which is less flammable, less toxic, and has a lower ozone depleting ability. In addition, it is an object of the present invention to provide an improved flash spinning method capable of spinning without greatly changing a conventional flash spinning apparatus.

[0021]

SUMMARY OF THE INVENTION The present inventors have obtained how to obtain a fiber having a performance comparable or surpassing that of a conventional flash-spun polyolefin network fiber using a solvent having a low ozone depleting ability. Or extensive research has led to the present invention.

That is, the method for producing a polyolefin network fiber according to the present invention comprises preparing a high-temperature and high-pressure solution comprising a polyolefin and a solvent containing a halogenated hydrocarbon, passing the solution through a reduced-pressure orifice, a reduced-pressure chamber, and a spinneret. A process for producing a fibrilated polyolefin reticulated fiber which comprises releasing 1,1- as a halogenated hydrocarbon.
Dichloro-2,2,2-trifluoroethane or 1,2
Using a solvent comprising dichloro-1,2,2-trifluoroethane or a mixture thereof and bromochloromethane as another halogenated hydrocarbon, said solvent comprising 5 to 25% by weight of polyolefin. The solution is adjusted at a temperature not less than the temperature Tα at the point where the temperature and pressure are represented by the horizontal axis and the vertical axis, respectively, and at the point where the minimum point of the convex point is formed on the cloud point curve, and at the cloud point pressure. The pressure of the chamber is set to a pressure equal to or lower than the cloud point pressure.

As a solvent containing a halogenated hydrocarbon,
95% to 60% by weight of 1,1-dichloro-2,2,2-trifluoroethane or 1,2-dichloro-1,2,2-trifluoroethane or a mixture thereof, and 5% to 40% by weight of bromochloromethane It is preferable to use a solvent consisting of

According to this method, the present inventors can obtain a polyolefin network fiber having a remarkably high strength and a good opening property, unlike a conventionally known method, while using a solvent having a low ozone depleting ability. Was completed.

1,1-dichloro-2,2,2-trifluoroethane (hereinafter referred to as HCFC-123) and
Dichloro-1,2,2-trifluoroethane (hereinafter referred to as HCFC-123a) is well known worldwide as a substitute for trichlorofluoromethane, which is a specific fluorocarbon. Therefore, anyone wonders if HCFC-123 and -123a could be used for flash spinning instead of trichlorofluoroethane.

However, the HCFC-123 and -123a
When used for spinning, the polymer solubility is completely insufficient.
As it is, it is not possible to investigate even the flash spinnability
No. That is, the phase equilibrium measurement shown in FIGS.
Polyolefin for HCFC-123 and -123a
The solubility of high-density polyethylene,
At this time, it did not dissolve at all in the temperature range up to 230 ° C. Pressure
800kgf / cm out of practical range^TwoDo not dissolve
won. The pressure within the practical range is 500kgf / cm ^TwoBelow
Means that the polymer melts even when the
The mer phase only separated completely and floated.

In flash spinning, it is a prerequisite for spinning to produce a uniform one-phase solution. If this is phase-separated and a uniform phase-separated structure is not developed, a uniform, high-strength, high-spreading mesh fiber cannot be obtained. Therefore, a solvent having no solubility for high-density polyethylene, which is a typical polyolefin, cannot be used as a flash spinning solvent. Further, a known HC disclosed in JP-A-2-160909 is disclosed.
The method using FC-123 and -123a is mostly flammable. If not flammable, the boiling point will be too high or the pressure for dissolution will be too high to use as a flash spinning solvent. So HCFC-123 and -123a
A great deal of research has been done to apply this to flash spinning.

As described above, flash spinning is based on the premise that an organic solvent which becomes a gas at normal temperature and normal pressure is used. That is, the polyolefin is dissolved under high temperature and high pressure, and then the pressure is once reduced to change the phase from a transparent liquid to an opaque liquid, and then the opaque polymer solution is blown through a spinneret into an atmosphere at normal temperature and normal pressure. At this time, the organic solvent is gasified to form a supersonic gas jet. The polymer is solidified and stretched by the gas jet, and becomes a fiber having high strength.

Accordingly, the properties to be possessed as a flash spinning solvent have been disclosed as described above, but when examined in more detail, they are as follows.

At room temperature and pressure, the polymer is not dissolved at all, and the polymer is dissolved at a temperature exceeding the melting point of the polymer and at a high pressure far exceeding the normal pressure.

A phase change from a transparent liquid to an opaque liquid by a temperature exceeding the melting point of the polymer and not causing thermal deterioration. In particular, in the case of flash spinning, LCST (Lower Critical Solution Temperature,
It is essential to use a polymer solution having a lower critical solution temperature) phase diagram. The LCST phase diagram is detailed in a general polymer chemistry textbook or a polymer solution theory textbook.
Naturally, the flash spinning solvent must also have an LCST phase diagram. Of course, it has an LCST type phase diagram, and its phase change must occur instantaneously. This property is important because flash spinning changes the phase from transparent to opaque with pressure.

At the moment of leaving the spinneret, it must be gasified. This means that it must have a boiling point near normal temperature and normal pressure. That is, the organic solvent must have a low boiling point.

The change before and after the spinneret is almost an isentropic change. Thus, the spinneret outlet is spontaneously a boiling liquid / gas mixture. If used as it is, it will not be used because it will be a wet mesh fiber. However, since the polymer has heat, the heat is used to gasify the liquid to form a dry reticulated fiber. This means that the heat of evaporation of the organic solvent must be adequate.

Organic solvents must have good thermal stability because they are exposed to high temperatures above the melting point of the polymer.

Since a large-capacity closed space is filled with electric equipment serving as an ignition source in the closed space, it must be nonflammable or nonflammable.

[0036] Since humans often come into contact with the gas filled in the enclosed space, it must be non-toxic.

Since the entire flash spinning apparatus becomes a high-pressure apparatus, it is necessary that the flash spinning apparatus has low corrosivity. Of particular importance are low boiling point, LCST type polymer solutions, non-flammable and non-toxic.

To date, a great number of polyolefin flash spinning solvents are known. However, in addition to trichlorofluoromethane (hereinafter abbreviated as CFC-11), the above 4
There is no proposal which partially satisfies the conditions, that is, low boiling point, LCST type polymer solution, nonflammability and non-toxicity. The alternative CFCs are representative of polyolefins and are not solvents for high density polyethylene when viewed in terms of the most widely marketed high density polyethylene for flash spun nonwovens. The alternative chlorofluorocarbon is merely a boiling point modifier when combined with another organic solvent, or merely a combustion suppressant. In addition, some of the alternative CFCs have a fear of carcinogenicity and cannot be used.

The present inventors have conducted numerous experiments to find a flash spinning solvent which satisfies at least the four conditions of low boiling point, LCST type polymer solution, non-flammable and non-toxic. As a result, they have found that an organic solvent composed of bromochloromethane (chlorobromomethane, methylenechlorobromide, CH ₂ BrCl) and HCFC-123 or / and HCFC-123a satisfies the above four conditions.

A. Toxicity Regarding toxicity, refer to the American Conference of Governance (ACGIH).
mental Industrial Hygienists) TLV (Threshold Limi
ts Values of Airbone Contaminants) is the indicator. Chlorobromomethane is 200 ppm, HCFC-123 and
HCFC-123a is said to have low toxicity as an alternative chlorofluorocarbon. The flash spinning solvent of the present invention composed of these solvents is at least over 200 ppm and is not completely non-toxic but has low toxicity. Be aware of gas leakage and location ventilation,
If the working area is maintained at a controlled concentration and a person touches it with an air line mask or the like, human health will not be harmed. This is the first time such a less toxic flash spinning solvent has been found with a flash spinning solvent other than trichlorofluoromethane (CFC-11).

B. Flammability In terms of flammability, bromochloromethane has an extremely high combustion suppression effect. In addition, the material itself is nonflammable. HC
Both FC-123 and HCFC-123a are nonflammable. This is the first time that such a low-toxic and nonflammable flash spinning solvent has been found.

C. Boiling point The boiling point is preferably 60 ° C. or lower in view of gasification at normal temperature and normal pressure. More preferably, it is 50 ° C. or lower. This boiling point is a function of the solvent composition and can be adjusted freely. The flash spinning solvent of the present invention can also be brought to a desirable boiling point by changing the mixing ratio of bromochloromethane and HCFC-123 and / or HCFC-123a.

D. Cloud Point Curve The solvent used in the present invention becomes an LCST-type polymer solution when a polyolefin is dissolved therein. As described above, the basic principle of flash spinning is that spinning is performed by depressurizing a high-temperature and high-pressure polymer solution to cause phase separation to form an opaque liquid comprising at least two phases of a polymer and a solvent.
Therefore, the temperature and pressure of the cloud point that can be determined by changing from a transparent liquid to an opaque liquid are extremely important. This cloud point is also the point at which phase separation occurs. The cloud point is represented by the temperature and pressure at which the liquid changes from transparent to opaque. The cloud point is usually measured visually and varies somewhat with 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 the polymer and the solvent constituting the system.
Further, the method for preparing the solution, the measurement time, the light source, and the like are slightly changed. Therefore, although there is some variation, if the measurement method is fixed, observation can be performed with good reproducibility. In polymer chemistry, a diagram in which the cloud point is stitched to the temperature / pressure coordinates is called a cloud point curve.
The suitability for flash spinning of the solvent can be determined from the position of the cloud point curve on the temperature / pressure coordinate plane.

In the case of bromochloromethane alone, this cloud point curve exists at a low pressure where it can be formed in the temperature range of flash spinning, and cannot be observed unless the temperature is considerably increased. The present inventors also attempted measurement, but the polymer and the solvent were thermally degraded and could not be actually observed. However, HCFC-123 and / or HC
By combining with FC-123a, it was possible to bring the cloud point curve to a position suitable for flash spinning. FIG. 1 shows an example of high-density polyethylene as the polyolefin. Furthermore, naturally, chlorobromomethane and HCFC
It was also confirmed that the position of the cloud point curve changed depending on the composition ratio with -123 and / or HCFC-123a. This indicates that the thermodynamic properties of the polymer solution change depending on the solvent composition ratio.

By the way, the cloud point curve which is an important factor in the present invention is measured by the apparatus shown in FIGS.
FIG. 2 is an explanatory view of the entire apparatus, and FIG. 3 is an explanatory view of an optical cell container for measuring a cloud point. That is, two optical windows 2 are provided in an optical cell container (dimensions, 40 mmφ × 83 mm length, volume of about 100 cm ² ) 1 so that the inside can be observed through light. The length of the optical path through which the light passes is 9 mm for the glass 14 of the optical window 2, 18 mm because two are provided, and the thickness of the solution is 40 mm, so the total length is 58 mm. The optical cell container 1 has a built-in stirring blade 13 for stirring the inside of the container at about 180 rpm until the polymer is almost dissolved. The structure of the stirring blade 13 is such that two stirring blades are installed, and the axis corresponding to the optical window is formed in a U-shape so as not to disturb the optical observation. Further, a thermometer 4 is inserted so as to be in direct contact with the solution in the optical cell container. The pressure gauge 5 is provided in the middle of the pipe 9 and detects the pressure in the optical cell container. In order to adjust the liquid pressure in the optical cell container, a plunger-type pressure regulator is provided via a pipe 9. Further, a pipe 10 for venting gas in the optical cell container and pushing out the liquid in the container is provided. Further, the entire optical cell container is covered with an aluminum casting heater, and the temperature is controlled by a control circuit.

In the method for measuring the cloud point, first, a polymer and a solvent are weighed so that the polymer concentration becomes a predetermined concentration and the inside of the container becomes a liquid seal, and then supplied to the container. Preparation of the polymer solution was performed on the basis of volume% for the purpose of simplifying the experiment.
That is, the solvent was adjusted by measuring with a measuring cylinder so as to have a predetermined volume ratio and mixed. Volume changes due to mixing were ignored. The conversion to the molar ratio used the solvent density at normal temperature and normal pressure.
If the polymer is high-density polyethylene, the specified volume%
Into a graduated cylinder, and the conversion to weight% used a density of 0.96 g / cm ³ . Then, heating is performed, and as the liquid expands, the internal pressure of the container increases. In most cases, the heating rate was 4.5 ° C./min. The liquid state is about 50kg.
After reaching f / cm ² and a temperature of about 105 ° C., the pressure was not adjusted until the polymer was completely dissolved. In this way, when the temperature reaches around the melting point of the polymer, the polymer starts to partially dissolve in the solvent. The polymer solution is adjusted in this state.

Next, measurement of the cloud point is started. Find cloud point by changing temperature and pressure. The cloud point is determined by observing a change in the amount of light through an optical window or by using a photocell or the like, and when the visual field becomes dark or the light amount sharply decreases, the point is regarded as the cloud point. In this way, while increasing the temperature, the pressure was adjusted using a plunger type pressure controller, and the cloud point was measured.

FIG. 1 shows a cloud point curve of HCFC-123 and bromochloromethane thus obtained. As can be seen from FIG. 1, the cloud point on the low temperature side increases as the temperature increases.
Cloud point pressure decreases. Then, a minimum point is formed at a certain temperature, and then the cloud point pressure 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 FIG. 1, when the weight mixture composition ratio of HCFC-123 and bromochloromethane is 69:31 and the polymer concentration is 11.9% by weight, the singular point temperature Tα is 152 ° C. and the singular point pressure Pα is 116 kgf.
/ Cm ² . Here, the notation of the singular point Tα will be described. Originally, a singular point should be expressed in terms of temperature and pressure. To be precise, it should be a singular point (Tα, Pα).
Abbreviated as α.

The existence of this singular point Tα is surprising,
The present inventors have discovered for the first time. This singular point T
As a result of examining the behavior of α, it was found that the minimum point of the cloud point curve was formed as shown in FIG. Furthermore, when the measurement was performed while changing the temperature rising rate, the temperature decreasing rate, the amount of change in pressure, and the like, it was confirmed that the cloud point in the low temperature region below the singular point Tα slightly changed. Also, the position of the singular point Tα is slightly changed by the temperature rise method and the temperature fall method,
This turned out to be the difference in how the temperature was transmitted. It was confirmed that the singular point Tα was always constant if the measurement method was always constant. And, in the temperature rise method, it is always a minimum value at a constant value, and it is a characteristic value representing a phase equilibrium in a polymer solution of a solvent composed of HCFC-123 or -123a and bromochloromethane and a high-density polyethylene. discovered.

It is still unclear why such a singular point Tα appears. However, according to observations, light is emitted in a low-temperature area before the singular point Tα and in a high-temperature area after the singular point Tα. It is presumed that the transmission state of the liquid is different and the structure of the liquid is different. Even more surprisingly, it has been found that the state of flash spinning changes around this specific point Tα, and that a satisfactory reticulated fiber cannot be obtained at a temperature below the specific point Tα. That is, below the temperature of the singular point Tα, the solution is decompressed from the solution to change to opaque, and then the reticulated fiber obtained by spinning out from the spinneret has a remarkably inferior openability, making it a very nonwoven sheet. There was nothing. They contained fluff and fine lumps like pulp, and a non-woven fabric sheet characterized by lint-free could not be used at all. On the other hand, the reticulated fibers spun at a temperature equal to or higher than the singular point Tα had good spreadability and high strength, and were excellent in nonwoven sheets.

As a matter of course, the position of the singular point Tα is
It varies depending on the composition of the solvent. That is, as the content of bromochloromethane increases, the position of the singular point Tα moves to the lower temperature side and the pressure thereof also decreases. When the content of bromochloromethane exceeds 40 wt%, the singular point Tα moves to the low temperature side, making observation difficult. Furthermore, the position of the cloud point curve moves too much to the low pressure side, making flash spinning difficult. Also, 5
When the amount falls below wt%, the singular point Tα becomes considerably high, and at the same time, Pα becomes extremely high. In this region, it is difficult to adjust the solution and spinning cannot be performed. For this reason, the region where the bromochloromethane content is lower than 5 wt% and
The region exceeding 40 wt% is not a target region of the present invention.

Thus, a method for producing, for the first time, a practically usable reticulated fiber having good spreadability and high strength by using a solvent having an extremely low ozone destruction ability has been found. Needless to say, a network fiber which is always stable, has excellent openability and high strength can be obtained by using a solvent having a low ozone depleting ability. This industrial significance has enormous value.

The 1,1-dichloro-2,2,2-trifluoroethane or / and 1,2-dichloro-1,
2,2-trifluoroethane may be a pure product or a mixture thereof. It should be noted that the lower the water content, the better, more preferably 10 ppm or less. The bromochloromethane used is preferably a pure product. It should be noted that the lower the water content, the better, and more preferably 10 ppm or less. Further, bromochloromethane is liable to be thermally degraded when exposed to a high temperature, so it is better to use a heat stabilizer. Examples of the heat stabilizer include 1,4-dioxane and 1,2-butylene oxide.

As the polyolefin, polyethylene,
Examples include polypropylene and polymethylpentene-1.
Polyethylene is most preferably high density polyethylene,
The density is 0.94 g / cc or more. Furthermore, the copolymer component is
It is preferable to maintain the above density at 15 wt% or less.
The polypropylene preferably contains about 85% by weight or more of isotactic polypropylene, and may contain about 15% by weight or less of other polypropylene or copolymer components such as ethylene and butene. Further, commonly known polymer additives, that is, heat stabilizers, light stabilizers, lubricants, nucleating agents, crosslinking agents, plasticizers, fillers and the like may be contained in the polymer.

The apparatus used in the present invention may be provided with a solution adjusting device and a spinning device including a decompression orifice, a decompression chamber, and a spinneret. Above that, there are a device for opening and dispersing the reticulated fibers, a conveyor device for moving the opened and dispersed reticulated fibers into a sheet, and a winding machine for winding the formed sheet. The sheet forming section is housed in a closed box, and the solvent gas in the box is recovered. The solution adjusting device may be an autoclave device or an extruder. Alternatively, a conventionally known device can be used.

[0056]

The present invention will be described below with reference to examples. This example is intended to specifically show the content of the present invention, and does not limit the scope of the claims of the present invention. The term “solution adjustment point” used in the examples indicates the temperature and pressure conditions when a polymer solution was produced, and can be indicated by a point on a cloud point curve diagram. Also,
The spin point indicates the pressure condition of the decompression chamber when the polymer solution is depressurized, undergoes phase change to an opaque liquid, and is spun from the nozzle, and can be represented by a point on a cloud point curve diagram, and thus the term is used. What should be noted here is the temperature at the spinning point. The change from the solution adjustment point to the spinning point can be considered roughly as an isentropic change. Then, the liquid temperature should always drop. However, in the case of an autoclave experiment, since the spinning is completed in a relatively short time, this accurate detection cannot be performed. In addition, the polymer can be considered to have little change in temperature. As a result, it can be assumed that the apparent temperature does not change much. Therefore, for the sake of convenience, FIG. 3 shows a model representation that the temperature does not change, but the present invention is not limited to this.

The number of free fibrils appearing in the examples is a measure of the spreadability of the fibrillated fibers, and if this value is 300 or more, a dense, uniform, non-uniform nonwoven sheet can be obtained. On the other hand, if it is less than 100, the sheet will be non-uniform and extremely uneven, and will not endure practical use at all. Those between 100 and 300 are more advanced
Although it is somewhat unreasonable, it can be used satisfactorily for general purposes that do not require very high performance.

The scale of evaluation of the spreadability in the examples is “○”.
If so, the number of free fibrils is 300 or more, if "△-△", it is between 100 and 300, and if "x", it is 100 or less.
"X" indicates that it cannot be used. The number of free fibrils was measured as follows. The fibrillated fiber has a structure in which many fine short fibers (single yarns) are connected in a network. The greater the number of individual fibers in comparison with the same denier, the better the fibrillated fibers are opened. The number of free fibrils is measured using a spun yarn obtained by colliding the spouted gas jet with the fibers contained in a copper plate tilted at about 45 ° to a position about 25 mm from the tip of the spinneret while containing the fibers. . The sampled spread yarn is gently sandwiched between glass plates, 1.6 times the objective lens and 10 eyepieces.
While moving the optical microscope at × 1 in the fiber width direction, the number of single yarns in the field of view is counted, and the number is converted into 100 denier to obtain the number of free fibrils.

[Example 1] With an internal volume of 550 cm ³ and a pressure resistance of 300 kgf
/ Cm ² autoclave, melt index (MI) 0.
78, 80.3 g of high-density polyethylene having a density of 0.96 g / cc (polymer concentration, 11.9 wt%) and 1,1-dichloro-2,2,2
412 g of 2-trifluoroethane (HCFC-123) and 183 g of bromochloromethane (hereinafter abbreviated as BCM) were added, and after covering the lid, the heater was energized and heated while rotating the stirrer. = 69.3: A solution for flash spinning with a polymer concentration of 11.9 wt%, consisting of 30.7 (wt%) solvent.

The dissolution is always performed in a liquid-sealed state, and the pressure is 300 k
gf / cm^TwoWhen approaching the vicinity, polymer is dissolved while draining.
The liquid was adjusted. Finally, the temperature is 193 ° C and the pressure is 196kgf
/cm ^TwoAnd Next, stop the stirrer and remove 201 kgf from the accumulator.
/cm^TwoN_TwoIntroduce gas and pressurize the solution directly with this gas
While opening the discharge valve at the bottom of the autoclave quickly.
Free spinning was performed. At this time, the release valve of the autoclave
The vacuum orifices, vacuum chambers, nozzles and
Parts having a circular through hole whose center axis coincides with the nozzle
Was installed in this order. That is,
Decompression orifice with inner diameter of 0.65mmφ and length of 5mm, inner diameter of 8mm
The angle of introduction from the decompression chamber with a diameter of 40 mm to the nozzle is 60 °
A decompression chamber with a 0.5 mm inside diameter and a 0.5 mm long nose
The inner diameter is 3.0mmφ and the length is 3.0mm, which is coaxial with the center axis of the nozzle.
It is a component having a through hole. And through this spinneret
The solution was released to the atmosphere and spun. Reduced at this time
The pressure in the pressure chamber is 131kgf / cm^TwoMet. Therefore, the solution adjustment
The point is 193 ℃, 196kgf / cm^TwoThe spinning point is 131kgf / cm^TwoTona
You.

The fiber was opened by contacting a copper plate inclined at about 45 ° at a position about 25 mm away from the spinneret. The performance of the obtained fiber is excellent in openability and the number of free fibrils is
453. Further, the strength was 7.2 g / d, and the spinning speed determined from denier was 180 m / s. At this time, the pressure corresponding to the solution preparation point temperature in the cloud point curve was 163 kgf / mm.
Further, the boiling point and T of the solvent used are calculated from the mole fraction.
The LV was about 41 ° C. and about 280 ppm, respectively. However,
The TLV of HCFC-123 was temporarily set to 350 ppm. This value is based on the PAF (Program for Alternative Flu
orocarbon Toxicity Testing)-Determined by the I Plan.

The reticulated fibers thus obtained were of very good quality and were most suitable for flash-spun nonwoven sheets.

[0063]

According to the present invention, compared to the conventionally known flash spinning method which does not destroy the ozone layer, reticulated fibers having remarkably excellent opening properties and high strength can be easily produced. Can contribute to society.
By using the flash spinning method of the present invention, socially useful reticulated fibers can be easily obtained without destroying the ozone layer surrounding the earth and without adversely affecting global warming.

According to the present invention, particularly, a polyolefin network fiber excellent in opening property and excellent in strength can be stably obtained, and from this network fiber, flash spinning having high uniformity and consequently great social utility is obtained. Nonwoven sheets are easily made.

In addition, the present inventors have found a flash spinning method using a non-flammable solvent having a low level of toxicity comparable to non-flammable and non-toxic, which is an excellent property of the conventional CFC. This is a flash spinning method that not only satisfies the protection of the global environment but also is extremely excellent in terms of occupational safety and health. Furthermore,
Since the solubility of the polyolefin was comparable to that of the conventionally known method, the apparatus manufactured by the conventional method can be used without any special modification. This economic effect is extremely large. Therefore, the social value of the present invention is immense.

[Brief description of the drawings]

FIG. 1 is an example of measurement of a cloud point curve of a polymer solution of the present invention. This cloud point curve shows the cloud point of the solvent composition of HCFC-123: BCM = 69: 31 (weight ratio). The figure shows a transparent region (one liquid phase) and an opaque region (two liquid phases). The polymer is a high-density polyethylene having a melt index of 0.78 and a density of 0.96 g / cc, and the polymer concentration of the solution is 11.9 wt%.

FIG. 2 is a schematic view of an optical cell container-based measuring device for measuring the cloud point of a polymer solution.

FIG. 3 is a schematic view of an optical cell container used for cloud point measurement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical cell container 2 ... Optical window 3 ... Motor 4 ... Thermometer 5 ... Pressure gauge 6 ... Valve 7 ... Light source 8 ... Light receiver 9 ... Piping 10 ... Piping 11 ... Plunger type pressure regulator 12 ... Valve 13 ... Stirring Feather 14 ... glass

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D01F 6/04 D01D 5/11

Claims (2)

(57) [Claims] 1. A high-temperature and high-pressure solution comprising a polyolefin and a solvent containing a halogenated hydrocarbon is prepared, passed through a reduced-pressure orifice, a reduced-pressure chamber, and a spinneret, and discharged into a room-temperature and normal-pressure region to produce a fibrillated polyolefin. In a method for producing a reticulated fiber, 1,1 as a halogenated hydrocarbon is used.
-Dichloro-2,2,2-trifluoroethane or 1,
Using a solvent comprising 2-dichloro-1,2,2-trifluoroethane or a mixture thereof and bromochloromethane as another halogenated hydrocarbon, the solvent and 5 to 25% by weight of polyolefin are removed. The resulting solution is adjusted above the cloud point pressure and above the temperature Tα at the point where the temperature and pressure form the downward convex minimum point in the cloud point curve with the horizontal axis and the vertical axis respectively. A method for producing a polyolefin network fiber, wherein the pressure in the decompression chamber is set to a pressure equal to or lower than the cloud point pressure. 2. A solvent containing a halogenated hydrocarbon,
95% to 60% by weight of 1,1-dichloro-2,2,2-trifluoroethane or 1,2-dichloro-1,2,2-trifluoroethane or a mixture thereof, and 5% to 40% by weight of bromochloromethane The method for producing a polyolefin network fiber according to claim 1, wherein a solvent comprising: