JPS6022010B2 - Method for preparing high molecular weight polyethylene molding dope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing a molding dope for producing high modulus, high strength fibers, films, etc. from high molecular weight polyethylene.

Recently, many methods have been proposed and implemented to improve the performance of polymeric materials.

For example, "Future Trend Survey Report on Japan's Knowledge-Intensive Industries, Trends in Technological Innovation in Polymer Materials" (Japan Industrial Technology Promotion Association, March 1982). There is a method in which a gel obtained from a dilute solution of so-called ultra-high molecular weight polyethylene, which has a molecular weight of 1,000,000, is subjected to high-stretching to form fibers and films with highly oriented molecular chains. It is attracting attention as a technology that can achieve performance dozens of times higher than that of ordinary molded products.
Science, vol. 15, pp. 505-514, 198 Wang;
Pau Smith, Piet J-jim Stra;).
umalofMaterialsScience,50
5-514, 15 (1980)]. The technical key to this method is that polyethylene with an extremely high average molecular weight is used, and it has been found that gel formation and stretchability, as well as the physical properties of the resulting fibers and films, are better as the average molecular weight is higher. [For example, Ball Smith, Peter Jahn Lemstra, Journal of Polymer Science, Polymer Physics Edition, 1st Male Sparrow, pp. 1007-1009, 1981
Pau I Smith, Piet J.戊ms け a;J
om female l ofPoMmerScieMe, Polym
erPhysics Edition, 191007-1
009 (1981)]. The polymer concentration in the solution has been investigated up to 2% by weight, and the results have shown that the thinner the solution, the better from the viewpoint of gel stretchability [Paul Smith, Peter Jahn-Lemstra and Henke et al.
C. Bouich, Journal of Polymer Science; Physics Edition, Volume 19, 877-
Shigeso Page (1 Hei 1), Pa. Smith, Piet J.
・Lemstra and Henk C. Bmeij;J
oumal of PolymerScience;P
hysics Edition, 19,877 ~ Nevus (
1981)]. However, from the viewpoint of productivity, it is desired that the solution concentration be higher. Generally, the moldability of polymers tends to deteriorate as the average molecular weight of the raw materials increases.

In particular, in the case of ultra-high molecular weight polyethylene, although it is a thermoplastic polymer, its melt viscosity is extremely high, so processing such as melt-grade yarn or melt molding is extremely difficult. It is the next best measure to reduce viscosity. However, even in this case, it is by no means easy to dissolve ultra-high molecular weight polyethylene in a solvent and prepare a uniform dope for molding, and this is an obstacle to industrially applying this processing method. Ta. Polyethylene is a highly crystalline and elutriation-soluble polymer, and there are no solvents that can dissolve it at room temperature.

All aromatic compounds and their halogen derivatives, which are currently known as solvents, have boiling points close to or higher than the melting point of polyethylene, and the polymer molecules dissolve in the form of molten and dispersed particles in the solvent. . There is no particular problem in preparing the solution if the target is ordinary polyethylene with an average molecular weight of several hundred thousand or less.The solution can be prepared by placing the raw material polymer and appropriate solvent in a suitable container, heating it to an appropriate temperature, and then crossing the ocean. Objectives are easily achieved by conventional means. That is, the polyethylene molecules to be dissolved are swollen by solvation and then diffused into the solvent to form a uniform solution. However, when the molecular chain length becomes long, such as ultra-high molecular weight polyethylene, the viscosity is extremely high even in a solvated state, and even if part of the raw material particles are solvated, it is difficult to diffuse into the solvent. Therefore, when dissolution is attempted by the above-mentioned means, even if the surface portion of the polymer particle solvates and swells, this covers the particle surface and prevents the solvent from penetrating into the interior, and furthermore, between the particles and between the particles and the organ. As fusion occurs between the walls,
Uniform dissolution is prevented. This situation becomes more pronounced as the molecular weight of the material increases and as the solute concentration increases. Such troubles related to dissolution of ultra-high molecular weight polyethylene have been pointed out in the literature; for example, Keller (K
Eller (unpublished paper) states that when displaying the concentration of a solution, it is necessary to consider the amount that adheres to and remains on the vessel wall as a liquid bottom. Because of this difficulty in dissolution,
The concentration of ultra-high molecular weight polyethylene solutions achieved by conventional methods is believed to be on the order of 4-5% by weight at most.

For example, Paul Smith, Peter Yarn Lemstra, etc., in ``Tokukan Sho 56-1 Pay 08 concerning filaments with high modulus and tensile strength from high molecular weight polyethylene and their production,'' Although the claimed range is 14yo dissolved in a solvent and its concentration ranges from 1 to 50% by weight, there is no specific description of methods for swelling, dissolving, and dispersing polyethylene. In fact, the upper limit of the polymer concentration stated in the examples is a weight average molecular weight of 8 x 1
For materials with a weight average molecular weight of 1.5 x 1, it is 3%, and for materials with a weight average molecular weight of 1.5 x 1, it is 1%. Examples of high polymer concentrations in the spinning dope have been shown, such as 20% for a weight average molecular weight of 2.8 x 1 pm and 50% for a weight average molecular weight of 6 x 1 pm, but these molecular weights no longer exceed It is not in the range of high molecular weight polyethylene. Several methods have been considered and actually proposed in order to overcome the above-mentioned difficulty in dissolving ultra-high molecular weight polyethylene and to prepare a solution with a sufficient concentration as a molding dope.

One method is to irradiate ultrasonic waves to a polymer swollen by the solvent when heated in the solvent.

However, it is a well-known fact that if a dissolved or swollen polymer is subjected to ultrasound, the polymer molecular chains will be cut and the molecular weight will decrease, and even if a homogeneous solution can be obtained by such means, However, this results in a deviation from the purpose of the molding process, which is to utilize the ultra-long molecular properties of the ultra-high molecular weight polyethylene main pot. Generally, when dissolving polymers, the atmosphere is replaced with an inert gas such as nitrogen in an effort to prevent molecular deterioration and decomposition during the dissolution process, and a decrease in molecular weight due to molecular chain scission is preferable. That's not the point. Furthermore, as a means for promoting the dissolution and dispersion of a polymer in a solvent, there is generally a method of performing a rope bow, shaking a key, etc. when heating a polymer in a solvent, and these methods can be considered. However, in the case of ultra-high molecular weight polyethylene, the viscosity of the polymer is extremely high even in a dissolved or solvated state, so even if it swells, it is not easily dispersed in a solvent.
Therefore, it is necessary to carry out treatment under harsh conditions such as fly-scattering and shaking under high overflow conditions for a long period of time, and as a result, there is an undeniable risk that undesirable effects such as deterioration of molecules and reduction in molecular weight will be brought about. One way to obtain a highly concentrated solution is to condense a dilute solution once prepared, but reducing the solvent by distillation exposes the raw material polyethylene to high temperatures for a long time, resulting in molecular deterioration and molecular weight loss. This is not a realistic method as it will lead to a decrease in

In the literature, after first preparing a 0.5% by weight dope, after precipitating the polyethylene in the dope and filtering the solvent,
A method is described in which a dope is prepared by leaving the solvent at a desired concentration and heating and dissolving it again. [B. Kalb and E. J. Bennings: Journal of Materials Science, Volume 15, Group 2, pp. 4-2590 (198
0), B. Kalb, A. J. Pennin bag; Jou
rnal ofNEterialsScience 1
5,2 songs 4-2590 (1 group 0)]. However, this method has the disadvantage that it is complicated to operate and requires heating twice. Even if the solution concentration is as low as 0.5% by weight, once polyethylene precipitates, it will crystallize, and when it is redissolved, it is difficult for heat to be transferred to the inside of the precipitated souls, so it becomes uniform. It will take a considerable amount of time to do so. Therefore, this method also has the drawback that the concern of molecular weight reduction due to molecular alteration cannot be eliminated. In summary, although it is known that high molecular weight polyethylene exhibits excellent physical properties when processed from a solution, there has been no known method for preparing a dope with a uniform and appropriate concentration that can be applied industrially.

The inventors of the present invention have been conducting intensive research on a method for obtaining high-performance molded products from molding dope containing a relatively high concentration of high-molecular-weight polyethylene. We have discovered a method by which a uniform molding dope of high molecular weight polyethylene can be prepared without worrying about deterioration of the properties of the polyethylene.

Preparation of the molding dope according to the invention is carried out by the following procedure.

First, high molecular weight polyethylene powder is subjected to a wetting process using an organic solvent that can dissolve polyethylene at high temperatures in an amount sufficient to wet the raw material at a temperature range that does not cause the solvent to swell the raw polyethylene. give Next, a required amount of solvent heated to 130 to 180°C is poured into the wet-treated raw material, or the raw material is poured into a solvent heated to the above temperature. The polyethylene molecules are uniformly dissolved in the solvent by either of the following methods: The mechanism of dissolution by this method is interpreted as follows.

First, in the first step, the polyethylene particles pre-wetted with a solvent absorb a portion of the hot solvent and become in a state close to equilibrium swelling, resulting in a state in which the molecules in the swollen particles are extremely easy to disperse. This process is almost instantaneous. Then, in the second step, the molecules are dispersed in the excess hot solvent to form a homogeneous solution. The processing required here is gradual, such as loosening the shape of each sufficiently swollen particle, and a very short time of several minutes is sufficient for the processing. This mechanism can be thought of in exactly the same way as when making r-kuzu-yu in daily life, starch particles are moistened with water in advance and hot water is poured into it to avoid the formation of so-called "mamako". The first feature of this dissolution method as described above is that the operation is performed in an extremely short time, which eliminates the risk of molecular deterioration and molecular weight reduction that can occur when polyethylene is exposed to high temperatures for a long period of time and subjected to mechanical action. One example is that there is no dryness.

Second, according to the present dissolution method, it is possible to prepare a solution with an extremely high concentration, which in principle has a concentration close to the value calculated from the equilibrium swelling ratio between the polyethylene particles and the solvent. Moreover, the entire amount of raw polyethylene is uniformly dissolved without adhesion to the vessel walls, etc., so there is no loss of either the raw polyethylene used or the solvent, and the amount of each used is accurately calculated. It is possible to prepare concentrated doves. There is no particular limit to the average molecular weight range of polyethylene to which the polyethylene dissolution method of the present invention can be applied, but it can be used as a dope for molding, and moreover, in the process of processing into fibers or films, it can be stretched at a high magnification to produce highly elastic products. For the original purpose of obtaining polyethylene, the target is what is called ultra-high molecular weight polyethylene with a weight average molecular weight of 1,000,000 or more, specifically, one with a weight average molecular weight of about 8×1 or more. In addition, as the polyethylene raw material, although commercially available high molecular weight polyethylene powder for molding with a particle size of about 0.1 pores was used as the polyethylene raw material, the particle size does not matter whether the present melting method is applicable or not. The solvent used for preparing the dope of the present invention does not dissolve polyethylene at early temperatures, but dissolves it uniformly at a high temperature of about 130°C or higher,
Any organic material may be used as long as it does not cause deterioration, but since polyethylene is originally a dissociable polymer, its type is naturally limited.

Preferred solvents for this purpose include aromatic compounds such as pure or isomeric paraxylene, decahydronaphthalene, tetrahydronaphthalene, aliphatic compounds such as liquid paraffin, and their halogen derivatives alone or Examples include mixtures of two or more types. The upper limit of the range of the polymer concentration in the solution that can be adjusted by the present invention is, in principle, as stated above (a value close to that calculated from the Heiwei swelling ratio of the polyethylene particles and the solvent; In actual operations, it is impossible to simultaneously and uniformly contact and swell wet-treated particles with a certain amount of a hot solvent, so there is a natural limit.

Practical concentration limits also depend on the weight average molecular weight of the polyethylene and the type of solvent. For example, in the case of polyethylene particles with an extremely large weight average molecular weight of about 3 x 1, even with the swelling and dispersion method of the present invention, it is possible to prepare a uniform solution only at a polymer concentration of about 1% by weight. . If the average molecular weight is smaller than this, it is possible to prepare a uniform solution with a higher concentration than this. but,
The original purpose of using dope in molding processing is not to prepare an extremely highly concentrated or highly viscous solution, but in reality, the molding processability of the dope and the performance of the resulting fibers and films must be considered. must be done. For polyethylene raw materials with weight average molecular weights of 8 x 1 or greater, which are the subject of this invention, a reasonable concentration range is up to approximately 2% by weight. Next, the stability of the molding dope will be discussed.

To put it simply, the polyethylene dope dissolved in the various solvents mentioned above is stable for 2 to 3 hours if kept at 120° C. or higher, which is the approximate crystallization temperature of polyethylene in those solvents. For example, in a test in which the dope was maintained at 130 qo, almost no change was observed in the viscosity and moldability of the dope over a period of 2 to 3 hours, and the subsequent molding operation was not affected at all. On the other hand, when the polymer in the transparent dove is kept at temperature 30 minutes, it begins to crystallize and becomes cloudy, and after a long period of time it solidifies into a white mass, and the solvent is removed and the polymer separates into solid and liquid. did. The dope prepared by the method of the present invention is characterized by excellent moldability in addition to the above-mentioned stability.

For example, when using polyethylene with a weight average molecular weight of 1.9 x 1 as a raw material, it was possible to make continuous gel-like fibers into paper yarn from a dope with a concentration of 0.5 to 1% by weight. These fibers have extremely high drawability, and when hot drawn at 120°C, fibers made from paper yarn made from a dope with a polymer concentration of 2% by weight have a tensile strength of about 3 peas, and fibers made from a 5% dope have a tensile strength of about 2M moss, 1
It was possible to draw the fiber from 0% dope at a high magnification of about 1M sound. As described in the Examples, the products obtained by this processing have excellent performance. Next, the present invention will be explained in more detail with reference to Examples. Note that these do not limit the content of the present invention. Example 1 High molecular weight polyethylene (Million, 24 marks. Weight average molecular weight 1.9 x 1 p) was weighed out to a final concentration of 2% by weight, and 0.5% by weight of the polymer di-tertiarybutyl paracresol was added, a small amount of decalin was added at room temperature, and the mixture was stirred to wet the polyethylene particles.

Meanwhile, in another container, the required amount of decalin was heated until it boiled, and the hot solvent was quickly poured into the container containing the polyethylene particles, which had been moistened earlier, while performing the hawk worship. When the solvent was injected, the polyethylene particles absorbed the hot solvent without aggregating, and swelled as individual particles to approximately the same volume as the solvent, and over time, the polyethylene particles became a sticky solution. The shape of the particles almost completely disappeared approximately 2 minutes after injection of the hot solvent, and when the fly rod was pulled up, the solution flowing down the rod had an extremely uniform starch syrup-like appearance. The temperature of injected decalin is 1 group, which is its boiling point. 3q
The temperature of the solution must be maintained at 13,000 or higher while continuing dissolution while stirring. The time from injection of the solvent to the formation of a uniform polymer dope is sufficient to be within 3 minutes, and at most 5 minutes. In order to evaluate the stability of this molding dope, the dope was stored in a hot oil tank maintained at 130°C, and its viscosity was measured at regular intervals. The results obtained are shown in Table 1 as relative values based on the value after 30 minutes. Example 2 A uniform molding dope having a concentration of 5% by weight was obtained in the same manner as in Example 1 using the same polyethylene as a raw material and xylene as a solvent.

The incubation time required to obtain a uniform dope was approximately 2 minutes. When xylene is used as a solvent, special care must be taken to keep it warm since the boiling point of xylene is as low as about 140° C. and the solution temperature tends to drop below 130° C. while dissolving the polymer. 1 of the dope thus prepared
The viscosity at 30qo was measured over time, and 3
Table 1 shows relative values based on the value after 0 minutes. Table 1 Dove stability (relative value of viscosity based on 30 minutes, 13
0C) Example 3 Using high molecular weight polyethylene (Million, 240M, weight average molecular weight 1.9 x 1) as a raw material, using a xylene-decalin mixture for wet treatment, and using decalin for dissolution, the same procedure as Example 1 was carried out. A dope with a polymer concentration of 1% by weight was prepared in a similar manner.

In this case, due to the high concentration of polyethylene, some non-uniformity appeared in the swelling of the particles, and it took approximately 10 minutes for the surface and interior of the swollen polymer mass to become uniform. The dope prepared in this way had a jelly-like appearance and extremely high viscosity, but it was passed through a 1.0-diameter nozzle from a shark thread tube filled with 13 pips and poured into water, and wound as a continuous fiber onto a bobbin. You can take it. Example 4 Using high molecular weight polyethylene (Million, 24mM, weight average molecular weight 1.6 x 1) as a raw material, using Deca IJin as a solvent, by using the same method as in Example 1, by shaving for 2 minutes,
A uniform dope with a polymer concentration of 5% by weight was prepared.

This dope was spun into water from a paper thread tube kept at 130° C. through a nozzle with a diameter of 1.0 mm, and wound into a bobbin as a continuous fiber. Decalin was extracted and removed from the fibers using methanol to obtain white porous fibers. This fiber can be easily stretched up to 6.7 times even at room temperature;
By stretching at 20°C, it was possible to stretch up to 3 needles. Example 5 Using the same polyethylene and solvent as in Example 4, a dope having a polymer concentration of 2% by weight was obtained in the same manner.

The time required for the rope to be uniformed was about 3 minutes.
Example 4 from a grade yarn tube in which this dope was kept warm at 130 qo.
Continuous fibers were obtained by underwater weaving in the same manner as above. Fibers with decalin extracted and removed from the fibers using methanol have a
．． By stretching at 12,000 times, it was possible to stretch up to 2 tones. Example 6 Using the same polyethylene and solvent as in Example 4, a dope with a polymer concentration of 1% by weight was obtained by the same method.

The time required to homogenize the dope was about 1 minute. Example 4 From a paper thread tube in which this dope was kept at 130°C
Continuous fibers were obtained by underwater spinning in the same manner as above. Fibers from which decalin has been extracted and removed with methanol have a
．． It was possible to stretch up to 2 times the IM sound by stretching at 120qC. Example 7 Regarding the fibers drawn at 120°C obtained in Examples 4.5 and 6, the sample length was 15 m,
Table 2 shows the mechanical performance measured at a stretching speed of 10/min.
Shown below.

Table 2 Mechanical performance of fibers drawn at 120°C Dope concentration:
2 weight co-dope concentration: 5 weight co-dope concentration: 10 weight omitted

Claims (1)

[Claims] 1. A molding dope is prepared using high molecular weight polyethylene with a weight average molecular weight of at least 8 x 10^5 or more as a raw material and using as a solvent an organic solvent with a boiling point of 120°C or higher that can dissolve polyethylene at high temperatures. In doing so, the raw material is subjected to a wetting treatment in advance using a sufficient amount of solvent to wet the raw material within a temperature range in which the solvent does not swell the raw material polyethylene, and then the raw material subjected to the wetting treatment is heated to 130 to 180 ° C. with a solvent. Uniform dissolution of the raw materials can be achieved by either stirring while injecting the raw materials, or by adding the wet-treated raw materials into a solvent heated to the above temperature while stirring. A method for preparing a dope for molding high molecular weight polyethylene. 2 The organic solvent with a boiling point of 120°C or higher is an aliphatic hydrocarbon,
The preparation method according to claim 1, wherein the aromatic hydrocarbon and its halogen derivative are used alone or in a mixture of two or more. 3. The preparation method according to claim 1, wherein the polymer concentration of the dope is 20% by weight or less.