JPH0367100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ultra-high molecular weight polymer fine powder, and more specifically, ultra-high molecular weight polyethylene or polyacrylonitrile is used as a raw material, which is dissolved in a solvent and then spun and stretched to obtain high strength and high strength. In carrying out the method for producing elastic modulus fibers or films, it is necessary to obtain homogeneous, high-performance fibers or films that can be easily dispersed and dissolved in a solvent, can be easily subjected to spinning or extrusion, or can be easily subjected to subsequent drawing processing. This invention relates to an ultra-high molecular weight coalesced fine powder from which a film can be obtained. In the following description, the case of obtaining high-strength, high-modulus fibers will be mainly explained, but it can be similarly used as a raw material for high-strength, high-modulus films.

For example, when trying to manufacture fibers using an ultra-high molecular weight polymer as a raw material, the first consideration is to adopt the conventional general-purpose melt spinning method, but depending on the properties of the material, In some cases, during the heating process using conventional methods, thermal decomposition or thermal discoloration may occur before melting begins, making it impossible to achieve the intended purpose. For example, synthetic polymers such as polyvinyl alcohol and polyacrylonitrile cannot be melt-spun as substantially pure polymers, and ultra-high molecular weight materials such as polyethylene, polypropylene, polyester, and nylon cannot be melt-spun as substantially pure polymers. It is technically impossible to perform melt-spinning without physical decomposition.

In response to this situation, a technique has been developed in which spinning is carried out without the above-mentioned decomposition with the help of a suitable solvent (Japanese Patent Application Laid-Open No. 107506/1983). According to the invention, the ultra-high molecular weight polymer can be dissolved in a solvent and processed in a liquid state, making it possible to carry out the spinning operation at a temperature sufficiently lower than the decomposition temperature of the ultra-high molecular weight polymer. Ta. According to the above disclosure, polyolefins (polyethylene, polypropylene, ethylene propylene copolymer, polyoxymethylene, polyethylene oxide, etc.), polyamides (various types of nylon), polyesters (polyethylene terephthalate, etc.), acrylic polymers (polyacrylonitrile, etc.) ), vinyl polymers (polyvinyl alcohol, polyvinylidene fluorite, etc.), etc. are the targets of spinning. For example, taking polyolefins as an example, nonane, decane, undecane, dodecane, tetralin, decalin, etc. are suitable solvents. Can be adopted.
To explain further by giving a specific example, the molecular weight is, for example,
By spinning a decalin solution of polyethylene or polypropylene with an ultra-high molecular weight of 1.5 to 3 million at 130 to 140°C and cooling it in air or liquid, it has a gel-like appearance and contains a large amount (for example, 97 to 98%) of decalin. Once the filament is wound up, further unrolled and hot stretched, molecular orientation is formed and the decalin is evaporated, producing a filament of extremely high strength. The above-mentioned filaments are generally called gel fibers, and have extremely high expectations in this field because of their properties of high strength, high elastic modulus, and high toughness.

By the way, when carrying out the above-mentioned spinning method using the same equipment as the conventional melt spinning method, the most important thing is to prepare a gel with a uniform concentration. Therefore, the current method is to mill a mixture of ultra-high molecular weight polymers and solvents at a temperature close to the decomposition temperature of the ultra-high molecular weight polymers and mix them for a long time, but this method still allows the polymers to be uniformly dispersed in the solvent.・It is not easy to dissolve. In particular, in order to obtain fibers with high strength, high elastic modulus, and high toughness, it is necessary to use polymers with large molecular weights, so uniformly dissolving them in a solvent is much more difficult than expected. Moreover, due to the rapid increase in viscosity during dissolution, air bubbles are mixed in during the kneading process, which tends to further promote non-uniformity. If a non-uniform solution containing aggregates of polymer particles or bubbles that remain without being dispersed or dissolved is used, spinning and drawing properties are significantly inhibited, and the product fiber becomes inferior.

In order to avoid these problems, multiple melting tanks are installed for primary melting and secondary melting.
A method has also been proposed in which the dissolution is carried out in multiple stages over a long period of time, and the solution thus obtained is supplied to a screw extruder while being heated for spinning, and some results are expected. However, since the dispersion and solubility of ultra-high molecular weight polymers as mentioned above are extremely low, even this method cannot be said to be fully satisfactory.Furthermore, the solution is extremely viscous, so it is difficult to obtain fine particles. The inclusion of air bubbles cannot be avoided, and further negative factors include an increased burden on equipment due to the installation of multiple dissolution tanks and a decrease in molecular weight due to heated supply.

The present inventors have focused on these circumstances and have conducted various studies in an attempt to establish a technique that can easily prepare a uniform gel-like material that has good dispersibility and solubility in solvents. The present invention was completed as a result of such research, and consists of a fine powder made of ultra-high molecular weight polyethylene or polyacrylonitrile with a weight average molecular weight of 5 x 10 ⁵ or more, in which one powder particle Weight per hit is 5x
The gist is that it is 10 ^-5 mg or less, particularly 3 x 10 ^-5 mg or less.

The ultra-high molecular weight polymer used in the present invention has a weight average molecular weight of 5×10 ⁵ or more, preferably 1×
It is necessary to use an ultra-high molecular weight substance of 10 ⁶ or more,
Preferred polymers have a weight average molecular weight of 1×10 ⁶ or more,
More preferred are polyethylene having a weight average molecular weight of 2×10 ⁶ or more and polyacrylonitrile having a weight average molecular weight of 1×10 ⁶ or more. As a solvent for dispersing and dissolving the ultra-high molecular weight polymer, it exerts a dissolving action on the above polymer when heated, and becomes a non-solvent for the above polymer when cooled (for example, at room temperature). For example, for polyethylene, aliphatic, aromatic or alicyclic hydrocarbons with a boiling point of 100°C or higher such as octane, nonane, decane or their isomers, Higher branched or linear hydrocarbons, petroleum fractions with a boiling point of 100℃ or higher,
Preferred examples include toluene, xylene, naphthalene, decalin, tetralin, and hydrogenated derivatives thereof, as well as various halogenated hydrocarbons.

Next, regarding the concentration of the ultra-high molecular weight polymer to be dissolved in various solvents, it is not a good idea to uniformly determine the optimum value because the optimum value will vary depending on the influence of the following factors. In other words, the three factors are the appropriateness of the solvent for a specific ultra-high molecular weight polymer, the molecular weight of the polymer,
As for spinning temperature, the better the suitability, the higher the optimum concentration will shift, and the higher the molecular weight of the polymer, the lower the optimum concentration will shift.
Furthermore, when the spinning temperature is low, the optimum concentration becomes lower.

Based on the criteria selected and determined in this way, a gel-like solution for melt spinning is prepared by dissolving an ultra-high molecular weight polymer in a solvent at a constant concentration. A fine powder with an individual particle weight of 1 x 10 ^-5 mg or less must be used as the molecular weight polymer. The weight of the particles is determined by randomly sampling raw material fine powder, measuring its weight, and measuring the number of particles in it, but the average particle weight must not exceed 5 × 10 ^-5 mg. , even if it can be uniformly dispersed in the selected solvent,
A satisfactory homogeneous gel-like solution cannot be obtained. For example, when melt spinning is performed by supplying a solvent dispersion of ultra-high molecular weight polymer fine powder to the raw material input hopper of a spinning machine, the process of continuous heating and dissolution within the screw takes a long time, and complete and uniform dissolution cannot be achieved. If this is not done, the solution sent to the spinneret becomes non-uniform, leading to poor spinning. Moreover, there is a phenomenon in which some fine powder settles and adheres to the screw surface within the extruder of the spinning machine, which may cause concentration unevenness during the continuous heating and dissolving process, which may affect the operational stability of spinning and drawing and the quality of the product fiber. becomes significantly worse. However, the average weight of the fine powder is 5×
If less than 10 ^-5 mg is used, the above-mentioned poor dissolution and uneven solution concentration during dissolution by heating will not occur, and spinning and drawing can be carried out extremely smoothly and efficiently, and high-quality products can be obtained. Fiber can be obtained. The reason why such a remarkable effect can be obtained by ultrafinely pulverizing an ultra-high molecular weight polymer is not necessarily clear, but it is believed that pulverization increases the specific surface area and improves dispersibility due to lower bulk density. This is thought to be because they synergistically produced good results. The method for obtaining such a fine powder is not particularly limited, but the following method is exemplified as a preferable method. That is, an ultra-high molecular weight polymer is dissolved under heating in a solvent that exerts a dissolving action on the polymer under heating and becomes a non-solvent for the polymer under cooling, Next, the solution is slowly cooled to form a spherulite gel (preferably a monospherulite gel) of the polymer that occludes the solvent, and the weight per particle is reduced by freeze-drying the spherulite gel. It is possible to easily obtain a fine polymer powder having a molecular weight of 5×10 ^-5 mg or less.

In addition, when dispersing the above fine powder in a solvent,
It is also possible to use additives such as dispersants if necessary, but the amount of these additives depends on the strength of the product fiber,
Needless to say, it should be suppressed to a level that does not impede toughness, etc.

Although the specific method of performing melt spinning using the ultra-high molecular weight polymer fine powder as described above is not particularly limited, the most preferable method is to uniformly disperse the fine powder in a selected solvent, and then perform spinning. This is a method in which the raw material is supplied to the feed hopper of the machine, continuously heated and melted in the screw, and sent toward the spinneret to be continuously spun. Since the exposure time is short and the amount of heat received by the polymer is constant, it becomes easy to standardize the spinning and drawing processes, and the quality of the product fiber becomes extremely stable.

The present invention is constructed as outlined above, and has extremely good dispersion and solubility in solvents, so
A series of steps from dissolution to spinning or extrusion molding can be carried out efficiently in a relatively short time, and since the gel-like solution can be obtained in an extremely uniform state, the spun or extruded filament or film can also be extremely homogeneous. Become something. Therefore, the subsequent stretching and solvent removal steps can be carried out extremely smoothly, and high quality and uniform product fibers or stretched films can be produced with high productivity.

Next, Examples and Comparative Examples of the present invention will be shown.

Example 1 Polyethylene fine powder having a weight average molecular weight of 2×10 ⁶ (average particle weight 5×10 ⁻⁵ mg) was mixed with decalin to obtain a uniform dispersion having a polyethylene concentration of 3% by weight. This dispersion liquid was supplied at room temperature to the raw material input hopper of a screw-type melt spinning device, and melt spinning was performed in the same manner as in the usual melt spinning method [extruder temperature: 150°C, spinning head temperature: 156°C,
Discharge rate: 20g/min, spinneret: 0.8mm (φ) - 8mm
(L)18(H)]. The discharged solution was cooled using a conventional quenching device to obtain gel fibers containing the solvent. Spinning was carried out continuously for 30 hours, during which time no yarn breakage or yarn unevenness was observed, and the spinning operation was extremely stable. The strength of the fiber obtained by drawing this yarn is 43g/
d, initial modulus is 1360g/d, elongation is 5%
It had extremely excellent strength and toughness.

Comparative Example 1 Polyethylene (average molecular weight: 2 x 10 ^-5 ) with particle average weights of 6 x 10 ^-3 mg and 6 x 10 ^-4 mg were dispersed in decalin to prepare a dispersion liquid with a concentration of 3% by weight. . Using this dispersion, melt spinning was carried out under the same conditions as in Example 1. When 6 x 10 ^-3 mg of fine polyethylene powder was used, undissolved polyethylene powder adhered to the wall surface of the skewer and Immediately after starting, spinning became impossible. Further, in the case of using 6×10 ^-4 mg of polyethylene fine powder, spinning could be carried out to some extent, but the concentration of the spun product became uneven in some areas, and yarn breakage occurred frequently during the drawing process.

Example 2 and Comparative Example 2 Weight average molecular weight is 1×10 ⁵ (average particle weight 4.2×
10 ^-5 mg) of polyethylene fine powder (A) and polyethylene fine powder (B) with a weight average molecular weight of 5 × 10 ⁵ (average particle size 3.5 × 10 ^-5 mg) were added to decalin, respectively, and a 3% concentration of A homogeneous dispersion was prepared. Each of the obtained dispersions was fed to a screw-type spinning machine at room temperature, and the strength of each fiber obtained by spinning and drawing under the same conditions as in Example 1 was that of polyethylene fine powder (A) [Comparative Example 2]. The strength of the one using polyethylene fine powder (B) [Example 2] was as low as 26 g/d, while the strength of the one using polyethylene fine powder (B) [Example 2] was 41 g/d.
The g/d was extremely excellent.

Example 3 Polyacrylonitrile fine powder having a weight average molecular weight of 3.0×10 ⁶ (average particle weight 3×10 ⁻⁵ mg) was mixed with dimethylformamide to prepare a uniform dispersion having a concentration of 7% by weight. This dispersion was supplied to the raw material input hopper of the screw type melt spinning device at room temperature, extruder temperature: 180℃, spinning head temperature: 186℃.
Solution spinning was carried out at a spinneret temperature of 180°C and a discharge rate of 6 g/min. 0.8mm as a spinneret
(φ)-8mm(L)-4(H) was used. The discharged liquid was cooled in an alcohol-dry ice air gap at -40°C to obtain gel fibers. The spinning operation during this period was extremely smooth, and the gel fibers obtained were uniform and even, and the drawing process could be carried out without any problem.

Example 4 Polyethylene fine powder having a weight average molecular weight of 2×10 ⁶ (average particle weight 5×10 ⁻⁵ mg) was mixed with decalin to obtain a uniform dispersion liquid having a polyethylene concentration of 3%. This dispersion was supplied to the raw material input hopper of a screw-type melt extrusion device at room temperature and dissolved, and then passed through a slit die (width 4 cm, slit thickness 0.3 mm) through a 160 mm
It was extruded at an average extrusion speed of 5 m/min at 0.degree. C. and taken off with a cooled roller at a speed of 20 m/min. Continuously run the sheet containing enough of this solvent in the longitudinal direction of the sheet.
While heating at 110°C and removing the solvent, it was stretched 10 times and rolled up. When this sheet was further stretched in the longitudinal direction at 145°C, the longitudinal strength was 31 g/
d. A high-strength film having an initial modulus of 910 g/d, uniform in the thickness direction and longitudinal direction, and having sufficient length could be obtained.

Comparative Example 3 Weight average molecular weight is 2×10 ⁶ and average particle weight is 6
An attempt was made to prepare a film in the same manner as in Example 4, except that two types of polyethylene powders of ×10 ⁻³ mg and 6×10 ⁻⁴ mg were used. In the case of a polymer with an average particle weight of 6 × 10 ^-3 mg, ejection irregularities in the longitudinal direction that could be visually determined were observed at the stage of being extruded from the nozzle.
In addition, thickness unevenness appeared in the width direction as well, which was thought to be caused by density unevenness, and the film often broke at the thinner parts, making it impossible to wind the film satisfactorily. In addition, in the case of a polymer with an average particle weight of 6 x 10 ^-4 mg, it was possible to stretch up to the first stage, but breakage often occurred in the second stage. Microscopically, even in the portion that was wound in a short period of time, the thickness unevenness in the width and longitudinal directions was severe, and a satisfactory film could not be obtained.

Claims (1)

[Claims] 1 Fine powder made of polyethylene or polyacrylonitrile with a weight average molecular weight of 5 x 10 ^-5 or more, and the weight of each powder particle is 5 x 10 ^-5
An ultra-high molecular weight polymer fine powder for producing high-strength, high-modulus fibers or films, which is characterized by having a molecular weight of less than mg.