JPH0627224B2 - Ultra high molecular weight polyethylene composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a uniform composition comprising an ultra-high molecular weight polyethylene excellent in moldability and an organic solvent, and an excellent stretchability obtained from the composition. It relates to a crystalline solid of ultra high molecular weight polyethylene.

[Conventional technology]

A substance generally called ultra-high molecular weight polyethylene is a polymer substance having a methylene unit as a repeating unit like ordinary polyethylene, but impact resistance, abrasion resistance, chemical resistance derived from its extremely large average molecular weight. In addition to expanding its applications as engineering plastics, it has recently been clarified that it can exhibit outstanding mechanical performance when given a high degree of molecular orientation. It is also expected to be used as a raw material for new performance materials. However, the feature that the average molecular weight is large is, as described below, linked to processing defects such as extremely high melt viscosity even though it is a thermoplastic linear polymer and extremely low solubility in a solvent, This material makes handling extremely difficult.

That is, ultra-high molecular weight polyethylene as a raw material is produced by polymerization of ethylene using a highly active Ziegler type catalyst and is generally supplied as semi-crystalline white particles having a particle size of about 100 microns. As with ordinary thermoplastic polymers, it loses crystallinity at a specific temperature (melting temperature, about 140 ° C) and becomes translucent, but it shows almost no fluidity and is common to thermoplastic polymers. The melt-molding method based on scriyou extrusion is hardly applicable. Therefore, in actual processing, the inefficient powder molding method is the mainstream in principle, let alone the melt fluidity as in the case of general film production, The application of the concept of providing orientation is extremely impractical only for this polymer.

Although it is not a technique from the viewpoint of overcoming the difficulty of processing ultra-high molecular weight polyethylene in the general sense, a processing method that goes through a solution state is one of the things that has recently been noted for processing the polymer. The potential as a material of high mechanical performance is in this category. Polyethylene has a planar zigzag structure consisting of continuous methylene units in the crystal structure, and the cross-sectional area occupied by the main chain is relatively small.
It has long been expected to have more than 00 GPa), but the experimental proof is that in the latter half of the 1970s, Pennings et al. Of the Netherlands continuously investigated filaments from a dilute solution of ultrahigh molecular weight polyethylene in a rotating double cylinder. This was triggered by the discovery of a method for taking out the above-mentioned fiber and finding that the obtained fiber has excellent mechanical properties based on a highly oriented structure (elastic modulus of 100 GPa level). According to Pennings et al., Such an oriented structure is formed on the surface of the rotating cylinder by successive crystallization. Next, Smith et al. Of the same country suggested that gel polyethylene obtained by quenching a dilute solution in cold water below room temperature could be ultra-stretched at an appropriate temperature, and that the stretched product could also exhibit similar mechanical performance. As a characteristic of such gel-like polyethylene, it is pointed out that the entanglement (entanglement) density between molecules is small. (note:
Super-stretching refers to a deformation in which the stretching ratio in one direction is 16 or more, according to the definition of Professor Ward of Leeds University in the United Kingdom. ) Regarding the processability of such ultra-high molecular weight polyethylene gel-like solids, since then, technical studies have been conducted in addition to academic research. % Or less is targeted, and there is basically no positive reason why it is beyond the scope of Smith's performance.

Naturally, the method of processing a polymer substance with the intervention of a solvent was not a novel one, and the subject of study was regenerated cellulose during the infancy of polymer science.
It has been preferred since 30 years ago, and in that case,
It is common knowledge that the solution concentration is an important factor in connection with the efficiency of workability and productivity. However, when the object is limited to ultra-high molecular weight polyethylene, conventionally, only a solution having a relatively low concentration of several percent or less or a regenerated solid obtained from the solution has been the object of research. The reason is that the polymer is hardly soluble due to its high molecular weight, and there was actually no reliable method for preparing high-concentration solutions, much less knowledge about the properties of high-concentration solutions or solids derived therefrom. Attributed to In fact, when a solvent is added to a raw material powder in a relatively large amount of solvent by a conventional method and heated, only the particle surface is solvated, that is, a so-called fish eye (or “mamako”) is produced and a uniform No solution is obtained. Proposals for obtaining relatively concentrated ultra high molecular weight polyethylene solutions were not without exception. However, the method of concentrating a dilute solution has not found a practical value because it involves complicated operations and also involves a risk that the raw polymer is modified in the process. Further, in the method of performing ultrasonic irradiation when heating the raw material with a solvent, the molecular chain is broken by the action of ultrasonic waves, that is, the reduction of the molecular weight is inevitable, and the solution maintains the original high molecular weight of the raw material. Can't get

[Problems to be solved by the invention]

From this point of view, the present inventors have conducted various studies to develop a method for producing a highly concentrated solution of ultra-high molecular weight polyethylene that has been uniformly dissolved, and as a result, using a solvent capable of dissolving ultra-high molecular weight polyethylene as one method, By heating and mixing the polyethylene and such a solvent, moistening at a specific temperature lower than the melting point of the polyethylene, and further heating and stirring, a highly concentrated and uniform ultra high molecular weight polyethylene solution can be produced. Heading, Japanese Patent Application No. 58-10663
A patent application was filed as Japanese Patent No. 7 and was published as Japanese Patent Publication No. 2-46053, followed by a patent as Japanese Patent No. 1712007. As a result of further studies, it was found that a high-concentration and homogeneous composition including the ultra-high molecular weight polyethylene composition in the specific range obtained by such a method is particularly excellent in molding processability, Since it has come to be acknowledged that a wide range of applications are possible, I claim to be granted a patent here.

[Means for solving problems]

That is, the present invention has at least an intrinsic viscosity [η] of 5d.
/ G or more ultra high molecular weight polyethylene (A) is more than 20% by weight and 75% by weight or less, and the solvent (B) capable of dissolving ultrahigh molecular weight polyethylene (A) is less than 80% by weight to 25% by weight
A composition comprising the above, a melt flow rate of the composition of 1000 to 0.001 g / 10 min, a single melting point (Tm) of the composition within the range defined by the formulas (1) and (2) An ultrahigh molecular weight polyethylene composition excellent in moldability, characterized by: Tm = Tmo-a (1-x) (1) 25 ≦ a ≦ 45 (2) (where Tm is a composition The melting point (° C.) of the product, Tmo is the melting point (° C.) of the ultra high molecular weight polyethylene (A), a is a constant, and x is the weight ratio of the ultra high molecular weight polyethylene (A).

[Action]

The ultrahigh molecular weight polyethylene (A) used in the composition of the present invention has an intrinsic viscosity [η] at 135 ° C. of a decalin solvent of at least 5 d / g or more, preferably 7 to 30 d.
/ G range. When [η] is less than 5 d / g, the melt flow rate (MFR) of the composition is high, and a composition excellent in moldability cannot be obtained. On the other hand, the upper limit of [η] is not particularly limited, but if it exceeds 30 d / g, in order to obtain a composition excellent in moldability with an MFR of 0.001 g / 10 min or more, the ultrahigh molecular weight polyethylene (A) It is necessary to minimize the amount, and there are few practical advantages.
Such ultra-high molecular weight polyethylene can be obtained by polymerizing ethylene or ethylene and a small amount of other α-olefins such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene by so-called Ziegler polymerization. It has a much higher molecular weight in polyethylene.

The solvent (B) used in the composition of the present invention is a solvent capable of dissolving the ultrahigh molecular weight polyethylene (A), preferably the melting point of the polyethylene (A) or more, more preferably the melting point + 20 ℃ or more boiling point It is a solvent having.

As the solvent (B), specifically, n-nonane, n-decane, n-undecane, n-dodecane, n-tetradecane, n-
Octadecane, or liquid paraffin, aliphatic hydrocarbon solvents such as kerosene, xylene, naphthalene, tetralin, butylbenzene, p-cymene, cyclohexylbenzene, diethylbenzene, pentylbenzene, dodecylbenzene, bicyclohexyl, decalin, methylnaphthalene, ethylnaphthalene Aromatic hydrocarbon solvents such as or hydrogenated derivatives thereof, 1,1,2,2-tetrachloroethane,
Halogenated hydrocarbon solvents such as pentachloroethane, hexachloroethane, 1,2,3-trichloropropane, dichlorobenzene, 1,2,4-trichlorobenzene, bromobenzene, paraffin-based process oil, naphthene-based process oil, aromatic system Mineral oil such as process oil may be used.

The ultrahigh molecular weight polyethylene composition of the present invention comprises the above ultrahigh molecular weight polyethylene (A): more than 20% by weight and 75% by weight or less, preferably more than 20% by weight and 60% by weight or less and the solvent (B): 80% by weight. Less than 25% by weight or more, preferably less than 80% by weight to 40% by weight or more, and having an MFR of 1000 to 0.001 g / 1.
0 min, preferably 300 to 0.001 g / 10 min, more preferably 100 to 0.001 g / 10 min and the melting point (Tm) of the composition is single and the formula (1) and the formula (2), preferably the formula (1) ) And the formula (21).

Tm = Tmo-a (1-x) (1) 25 ≤ a ≤ 45 (2) 30 ≤ a ≤ 40 (21) (where Tm is the melting point (° C) of the composition and Tmo is over The melting point (° C) of high molecular weight polyethylene (A), a is a constant, and x is the weight fraction of ultra high molecular weight polyethylene (A).) If the amount of ultra high molecular weight polyethylene (A) is less than 10% by weight, the solvent ( Since the throughput of B) increases, its industrial value is low,
On the other hand, when it exceeds 75% by weight, the MFR is practically 0.001 g.
A composition of / 10 min or more cannot be obtained, resulting in poor moldability.

MFR exceeding 1000g / 10min, and 0.001
If it is less than g / 10 min, the moldability is poor.

The MFR in the present invention is a value measured according to ASTM D1238 under the conditions of a load of 20 kg and a temperature of 160 ° C.

The reason that the Tm of the ultrahigh molecular weight polyethylene composition of the present invention is single and is within the range defined by the above formulas (1) and (2) is to show the homogeneity of the composition. Ie T
Those in which m is not single and those out of the ranges defined by the formulas (1) and (2) are heterogeneous compositions, for example, when the composition is extruded into a filament or a film, the composition is uniform. It is difficult to obtain a good extruded product, and the stretchability is poor, and the moldability is poor.

The ultrahigh molecular weight polyethylene composition of the present invention is a composition having homogeneity at the molecular level, and the preparation method thereof is not particularly limited as long as it has the above characteristics. However, as mentioned above, there has not been a practical method for preparing such a composition in the past, so a plurality of methods found in connection with the present invention will be introduced.

The first method is to disperse a predetermined amount of ultrahigh molecular weight polyethylene (A) powder in the solvent (B), wait for it to swell sufficiently in a certain temperature range, and then further raise the temperature to give an ultrahigh temperature. It is intended to disperse the molecular weight polyethylene molecules in a solvent, and by such a procedure, a target composition having a concentration exceeding 10% by weight can be easily obtained. The method is described in detail in Japanese Patent Publication No. 2-46053 by the applicant.

The second method is an improved method of adjusting the dope for molding high molecular weight polyethylene described in JP-A-59-78238 filed by one of the present applicants. In other words, the original method is to wet the raw material powder of ultra-high molecular weight polyethylene raw material with a necessary and sufficient small amount of a predetermined amount of solvent, and then mix the heated residual amount of solvent. Although the temperature which does not swell the raw material polyethylene is specified as the wet treatment here, only the operation at room temperature was specifically disclosed, but in this case, the polymer concentration is usually as described in the specification. With a high molecular weight of 20% by weight or less, only a solution of about 10% by weight could be obtained. The improved method is to increase the wetting temperature to 70-
Constantly 130 ° C in the operation from raising the temperature to 100 ° C and from the mixing of the wet treated material and the heating solvent to the completion of the dissolution treatment.
By holding the above, it is possible to obtain a solution of higher concentration. Specifically 1
Preheated to about 30 to 150 ° C, and a wettable material of ultra high molecular weight polyethylene in a container capable of supplying heat, and 130 ° C.
A method in which the hot solvent heated above is added at the same time and stirred,
Instead of the hot solvent, a solvent may be added in the form of superheated steam at 140 ° C. or higher.

A common requirement of these two methods is the control of swelling of ultra high molecular weight polyethylene particles. This swelling occurs in a fairly narrow temperature range, and this phenomenon is understood to be “melting of solute in the presence of solvent” due to its concentration dependence, but the swelling state is immediately in the solvent because the solvated molecule has a high molecular weight. It happens because it doesn't spread. According to the method described above, the ultrahigh molecular weight polyethylene can be dissolved in the solvent (B) in principle at any concentration. The composition comprising the ultra high molecular weight polyethylene and the solvent thus obtained is an extremely transparent substance at high temperatures, and can exist as a homogeneous and stable composition even at room temperature.

The ultrahigh molecular weight polyethylene (A) used in the present invention, within the range not impairing the object of the present invention, a heat resistance stabilizer, a weather resistance stabilizer,
You may mix | blend various additives normally used by adding to polyolefin, such as a pigment, a dye, a lubricant, a gelling agent, and an inorganic filler.

The melting points of the ultrahigh molecular weight polyethylene (A) and the composition in the present invention are values measured by a differential scanning calorimeter (DSC) according to ASTM D3418.

The crystalline solid obtained from the composition of the present invention is a lamellar microcrystal having a main constituent of 120 to 250 Å, which is isolated by desolvating a molded product from the ultra high molecular weight polyethylene composition. And is a crystalline solid having an overall crystallinity of 60% or more.

The thickness of the lamellar microcrystals in the present invention is the stacking period measured by the small angle X-ray scattering method, and the crystallinity is the value measured by the X-ray diffraction method.

Isolation of the crystalline solid of the present invention from the ultra high molecular weight polyethylene composition can be carried out in any form, but the purpose of obtaining the crystalline solid is to produce fibers, films and the like from the crystalline solid. Therefore, it is appropriate to preliminarily mold the composition to a desired shape in a high temperature state in which the composition is kept uniform and easily deformed, and then crystallization and precipitation are performed. In fact, this composition has the above-mentioned MFR
Therefore, various processing methods such as spinning, squeeze extrusion, and pressing can be applied. The conditions of crystallization and precipitation have almost no influence on the characteristics of the crystalline solid described later. The reason for this is that, as in the case of solution crystallization of normal polyethylene, the crystallization process is almost nucleation-controlled, so that the crystallization rate after passing through a certain supercooled state is extremely high. Therefore, it does not matter if the work efficiency is rapidly cooled. Desolvation after molding can be performed by various common methods (for example, solvent extraction, vacuum drying, and freeze drying depending on the type of solvent).

〔The invention's effect〕

Unlike the composition obtained by the conventional method, the ultra-high molecular weight polyethylene composition of the present invention does not have an extremely low viscosity at the time of melting, and also has an extremely high melt viscosity such as a melt of ultra-high molecular weight polyethylene. Since it does not exist, it has a feature that extrusion molding using a screw extruder, injection molding, blow molding as well as pressure molding etc. can be easily performed like the melt of general-purpose polyethylene.

The crystalline solid isolated from the ultra-high molecular weight polyethylene composition of the present invention has a feature that, unlike the conventional melt recrystallized product of the ultra-high molecular weight polyethylene, the crystallinity is high and the stretchability is excellent. Further, it may be a crystalline solid having a spherulitic internal structure under quenching conditions.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples without departing from the gist of the present invention.

Example 1 <Determination of low-temperature swelling treatment temperature> Powder of ultrahigh molecular weight polyethylene having an ultimate viscosity of 17 d / g and a melting point of 134 ° C. (trade name: Hi-Zec Million 240M manufactured by Mitsui Petrochemical Industry Co., Ltd.) Mix 10 g with 100 m each of delican (boiling point: 190 ° C.),
After stirring for 15 minutes at each treatment temperature of 0, 90, 100, 110, 120 and 130 ° C., the mixture was allowed to cool to room temperature, and then decalin was removed by decantation. Wg) was measured and the solvent content fraction (S%) was calculated by the following formula.

S (%) = (W-10) / W × 100 Next, the relationship between the solvent content fraction at each treatment temperature and each treatment temperature is plotted as shown in FIG. 1, and the solvent content fraction is 70%.
% Was 105 ° C., and this temperature was used as the low temperature swelling treatment temperature of the ultrahigh molecular weight polyethylene-decalin system.

<Production of Ultra High Molecular Weight Polyethylene Solution> Said ultra high molecular weight polyethylene: 25 g and decalin: 90
After adding g to a glass beaker, the system temperature was heated to 110 ° C. with stirring, and the ultrahigh molecular weight polyethylene powder was swelled while maintaining the temperature. When the state of the inside of the system was continuously observed, the system changed to a roasted egg-like shape after about 6 minutes at 110 ° C., and the swelling was completed. Then the system temperature is increased to 160
When heated to 0 ° C. and continued stirring, a transparent solution was obtained after about 5 minutes, and an ultra high molecular weight polyethylene solution was obtained. The solution was cooled to room temperature and sampled to determine the MFR and Tm
Was a single peak at 85 g / 10 min and 105 ° C., and the composition was uniform.

Examples 2 to 4 The amount of ultra high molecular weight polyethylene of Example 1 was set to 100 each.
90 g, 180 g and 45 g of decalin, respectively.
The same procedure as in Example 1 was carried out except that g was used. Table 1 shows the MFR and Tm of each composition obtained. The Tm was a single peak in all cases.

Comparative Example 1 10 g of ultra-high molecular weight polyethylene used in Example 1 and 90 g of decalin were put into a glass container, then rapidly heated to 160 ° C. with stirring, and after reaching this temperature, kept at this temperature. And continued stirring. However, even after 6 minutes had passed since the temperature was reached, a solution portion diluted to a predetermined concentration in the system and a melted mass of polyethylene powder resulting from the insolubilization were observed. Even if stirring was continued for another 60 minutes, homogenization due to dissolution of the molten polyethylene mass did not occur.

After cooling the solution, MFR and Tm were measured.
In R, the separated decalin flowed out of the nozzle and could not be measured, and Tm was 2 at the main peak at 134 ° C and the minor peak at 100 ° C.
There were two peaks.

Example 5 The homogeneous compositions obtained in Examples 1 to 4 were press-molded at 160 ° C., allowed to cool to room temperature, and decalin was removed under reduced pressure at room temperature to obtain a fine film-like crystalline solid. The structure was investigated as follows.

According to the observation of the surface by scanning electron microscopy, the crystal unit basically has a lamella structure of the order of 100 Å in thickness, which is similar to that usually produced by solution recrystallization of polyethylene, and the size increases as the concentration increases. Although the lamella structure tended to be dense and the lamellas tended to be densely aggregated, the characteristic of this lamella structure was the unclear morphology of the sample surface obtained by melt-forming immediately after the raw powder without using a solvent. Was clearly different from. The lamella thickness (stacking period) measured by the small-angle X-ray scattering method and the crystallinity measured by the X-ray diffraction method are shown in Table 2 and Table 3, respectively.

As a comparative example, the lamella thickness and crystallinity of a film-like crystalline solid obtained from a solution having a concentration of 1% are also shown.

Example 6 5 × 5 each from the film-like crystalline solid obtained in Example 5
A 0 mm test piece was cut out, and the draw ratio until breakage was measured under the conditions of a chuck distance of 20 mm, a drawing speed of 20 mm / min, and a drawing temperature of 120 ° C. (air bath). The results are shown in Table 4. It can be seen from Table 4 that all of them have excellent stretchability as compared with the test pieces of ultra-high molecular weight polyethylene alone (concentration 100%) obtained by melt molding.

Example 7 To 25 g of the ultra high molecular weight polyethylene used in Example 1, 1
A wet-treated product prepared by adding 25 g of decalin at 00 ° C. and 65 g of decalin heated to a boiling point (190 ° C.) were simultaneously charged by an external heater into a enamel beaker preheated to 150 ° C. By stirring, a transparent ultrahigh molecular weight polyethylene solution was obtained. The MFR and Tm measured on the sample obtained by cooling the solution to room temperature were the same as those of the composition obtained in Example 1.
There were single peaks at 85 g / 10 min and 105 ° C, respectively.

[Brief description of drawings]

FIG. 1 shows the relationship between the ultrahigh molecular weight polyethylene-decalin-based solvent content and the processing temperature.

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Claims (1)

[Claims] 1. Ultrahigh molecular weight polyethylene (A) having an intrinsic viscosity [η] of 5 d / g or more exceeds 20% by weight.
A composition comprising 5% by weight or less and a solvent (B) capable of dissolving the ultrahigh molecular weight polyethylene (A) in an amount of less than 80% by weight to 25% by weight or more, and having a melt flow rate of 1000 to 0. 0.001 g / 10 min and the melting point (T _m ) of the composition is single and is in the range defined by the formula (1) and the formula (2). _Tm = _Tmo - _a (1- _x ) ... (1) 25 <= _a <= 45 ... (2) (However, in formula, _Tm is melting _| fusing point (degreeC) of a composition, _Tmo is ultra high molecular weight polyethylene. (A) is the melting point (° C), a is a constant and x is the weight fraction of ultrahigh molecular weight polyethylene (A).)