JPH0641814A - Production of drawn molded body of ultrahigh-molecular weight polypropylene - Google Patents

Abstract

PURPOSE:To obtain the molding excellent in tensile strength by melt mixing an ultrahigh-molecular weight polypropylene with polyethylene and a fluidity improver. CONSTITUTION:The objective method for producing a drawn molding of an ultrahigh-molecular weight polypropylene comprises adding (C) a fluidity improver to a blend of (A) 85-99.5 pts.wt. ultrahigh-molecular weight polypropylene having at least >=5dl/g intrinsic viscosity with (B) 0.5-15 pts.wt. polyethylene having at least >=2dl/g, preferably >=5dl/g intrinsic viscosity, melt mixing the resultant mixture, extruding the mixed blend through a die, molding the melt and drawing the obtained extrude.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an ultra-high molecular weight polypropylene stretch-molded article from an ultra-high-molecular-weight polypropylene stretched article, and more specifically to an ultra-high-molecular-weight polypropylene stretch-molded article having excellent properties. , A method for preparation by a spinning / drawing method.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION By molding ultra-high molecular weight polyethylene into a fiber or a tape and stretching it,
It is already known that a stretched molded product having a high elastic modulus and a high tensile strength can be obtained, and many patents have been published. For example, in Japanese Patent Laid-Open No. 56-15408,
A method relating to a so-called gel spinning / ultra-stretching method, in which a dilute solution of ultra-high molecular weight polyethylene is spun and then the obtained filament is stretched, is shown. Further, in JP-A-58-5228, a dilute solution of an ultrahigh molecular weight thermoplastic crystalline polymer is prepared using a non-volatile solution, and this is spun to form a xerogel fiber.
The method of stretching is shown. This method is basically the same as the above-mentioned gel spinning / ultra-drawing method, but when ultra-high molecular weight polyethylene is used as the ultra-high molecular weight thermoplastic polymer, the elastic modulus is 100 GPa or more, Moreover, it is possible to obtain a stretched molded product having a high elastic modulus and a high strength, which has a tensile strength of 3 GPa or more.

As described above, in the case of ultra-high molecular weight polyethylene, a method for producing a fiber having a high elastic modulus and a high tensile strength is almost established by using a dilute solution as a medium. It is explained in detail in the journal of the Society of Rheology, Japan (Matsuo, Vol.13, No.1, P4-15, 1985). According to this paper, in order for the produced fiber to exhibit high elastic modulus and high tensile strength, its molecular chain must have a so-called "extended chain crystal" in which the molecular chain is fully extended. The "extended chain crystal" is said to be capable of forming ultra-high molecular weight molecular chains by an ultra-stretching method with a stretch ratio much higher than the conventional stretch ratio (6 to 12 times). It is believed that this ultra-stretchability is achieved by the presence of entanglement between molecules existing between undrawn yarn crystals before drawing, that is, between lamellas and adjacent lamellas. .

In the above-mentioned paper, ultra-high-molecular-weight polyethylene cannot form entanglement in an ultra-dilute solution, so that there is no interaction between molecules, and as a result, it does not exhibit stretchability. In the above, since the number of entanglements is too large, the molecules are entangled with each other, and thus the stretchability is not exhibited.The entanglement is the entanglement of the molecules with each other, which controls the stretchability. It has been reported that it becomes a defect when it becomes a "crystal".
Therefore, in order to obtain a fiber having a high elastic modulus and a high tensile strength, it is necessary to minimize the number of this entanglement, and for this purpose, a polymer having an ultrahigh molecular weight is used as a raw material, It is preferred to draw undrawn fibers prepared from a dilute solution of this ultra high molecular weight polymer. Further, it can be said that the use of the ultra-high molecular weight polymer as a raw material is preferable in view of the fact that the resulting high-strength fiber is naturally defective at the molecular end. This principle is supported by the experimental results in this report and the experimental results of many other researchers.

On the other hand, many studies have been conducted to obtain fibers having a high elastic modulus and a high tensile strength even with polypropylene, and various preparation methods which have been successful in the above-mentioned polyethylene are appropriately improved in polypropylene. Has been applied. Here, comparing the theoretical strengths of polypropylene and polyethylene, polypropylene is 1
8 GPa (“Fiber and Industry” Vol. 40, P. 407-418, 1984), while polyethylene is 32 GPa, and polypropylene theoretically has about half the strength of polyethylene. According to the report by Matsuo et al., The ultimate strength of the high-strength fiber of polyethylene has reached about 6 GPa at present, so that about half of polypropylene, that is, about 3 GPa, can be sufficiently reached. Conceivable.

Here, as a conventionally known method for producing high-strength polypropylene fiber, first, as an example of applying the zone drawing method, which was successful in polyethylene, to polypropylene, a report by Kouki et al. (Journal of Applied Polymer Sci.
ence, Vol.28, P179 to 189,1983), which uses a local heating furnace to heat a fiber prepared in advance by a conventional melt spinning method to a portion of 1 to 2 mm and stretch the portion. It is a method of performing ultra-stretching. According to this method, when polypropylene having a molecular weight of 47,000 is used,
A polypropylene fiber having a modulus of elasticity of 6.9 GPa and a tensile strength of 0.74 GPa is obtained.

Further, as an example of applying the above-mentioned gel spinning / super-drawing method to polypropylene, there is a report by Peguy and Manley (Polymer Communications, Vol.25, P39-42, 1984). According to this method, Smith and Lemstra's example for ultra high molecular weight polyethylene (Journal of Polymer Bullet
in, Vol.1,733,1979), 0.75-1.5% W / W
Gel spinning and ultra-stretching were carried out with the solution of 1. to obtain polypropylene fibers having an elastic modulus of 36 GPa and a tensile strength of 1.03 GPa.

Further, the above-mentioned Japanese Patent Application Laid-Open No. 58-5228 discloses an example of polypropylene similar to the example of polyethylene described above.
An elastic modulus of 23.9 GPa from a 6% weight concentration solution of ultra high molecular weight polypropylene of 8 dl / g (molecular weight 3.3 million)
And the polypropylene fiber having a tensile strength of 1.04 GPa has been successfully manufactured.

However, when the conventional methods for preparing high-strength polypropylene fibers are examined, the elastic modulus and tensile strength of polypropylene stretched yarns or tapes are 7-10 GPa and 0.
The value is 5 to 1.04 GPa, and in view of the value of 3 GPa described above, the fact is that the tensile strength is not substantially improved.

As an example of successful improvement of the tensile strength, there is a report by Kanemoto et al. (Proceedings of the Annual Meeting of the Japan Society of Textiles, 1987), which uses ultra-high molecular weight polypropylene with a molecular weight of 3.6 million. And tensile strength 2.3 GP
An ultra-high molecular weight polypropylene stretched molding having a is obtained. This method is roughly divided into the following three steps. [First step]: A so-called solvent cast film is prepared by evaporating and removing the solvent from an ultra high molecular weight polypropylene solution of 1% by weight or less. This is considered to be the same in principle as the above-described gel fiber and xerogel fiber preparation steps. [Second step]: The cast film is sandwiched between polyethylene bullets and solid-phase extruded in a pseudo-melt state. At this time, the cast film is solid-phase stretched by passing through a conical die, and its solid-phase stretch ratio (ED
R) is about 6 times. [Third step]: By subjecting the solid-phase extruded film to ordinary tensile stretching, the solid-phase extruded film is stretched at a solid-phase stretch ratio × tensile stretch ratio = about 72 times to obtain the above-mentioned tensile strength of about 2.3 GPa.
Of high strength polypropylene fiber.

The reason why the ultra-stretched molded article of Kinmoto et al., Which is prepared by the same method as the gel spinning / super-stretching method in principle, remarkably improves the tensile strength, is described above. Process]. That is, passing through a conical die and solid-phase stretching in a burette,
In principle, it is subjected to tensile elongation deformation, so it is the same deformation as the tensile stretching performed in the gel spinning / super stretching method, but the major difference is that the sample is weak and brittle. However, the burette can be stretched in a tough shape from both sides of the sample without damaging and breaking the sample.

In other words, when it is attempted to prepare polypropylene fibers by the gel spinning / super-drawing method, it is considered that the drawn fibers have a fatal defect that affects the high strength during the low-stretching drawing in the tensile drawing operation. . That is, the structure of the gel fiber prepared from polypropylene is fundamentally different from the gel fiber obtained from polyethylene, and it becomes a normal orientation structure to some extent until the fiber strength increases and the stretching operation can be endured. It is not suitable for tensile drawing, and even if the tensile drawing stress exceeds the fiber strength at the initial stage of drawing and the film can be apparently drawn, a fatal defect occurs in at least increasing the strength of the drawn fiber. Is there.

Therefore, it is a rational method to increase the strength of the fiber by sandwiching the ultra high molecular weight polypropylene fiber in the burette and performing solid phase drawing with a conical die as described above. It is extremely disadvantageous in terms of productivity and cost from the standpoint of industrialization to produce a continuous fiber from ultra-high molecular weight polypropylene by sandwiching a polypropylene fiber in a burette and solid-phase stretching with a conical die. I have to say that.

In view of the above points, the present inventors have found that polypropylene fibers having excellent thermal properties, creep resistance and high breaking energy properties are excellent in terms of productivity and cost as a spinning / drawing method. As a result of intensive research to obtain by a method, ultra-high molecular weight polypropylene requires a very long time in comparison with ultra-high molecular weight polyethylene to be cooled and crystallized after discharging the spinning dope from the spinning nozzle. It has been found that the moldability of ultra high molecular weight polypropylene is made extremely difficult.

[0015]

SUMMARY OF THE INVENTION The present invention is intended to solve the problems associated with the prior art as described above, and has the thermal properties, creep resistance and high breaking energy originally possessed by ultrahigh molecular weight polypropylene fibers. It is an object of the present invention to provide a method for producing an ultrahigh molecular weight polypropylene stretched article capable of efficiently producing an ultrahigh molecular weight polypropylene stretched article having excellent tensile properties, particularly tensile strength, without impairing the properties.

[0016]

SUMMARY OF THE INVENTION The method for producing a stretched ultra-high molecular weight polypropylene according to the present invention has an intrinsic viscosity of at least 5 dl.
85 / g or more ultra high molecular weight polypropylene (A)
Melt by adding a fluidity improver (C) to an ultra high molecular weight polypropylene composition consisting of 99.5 parts by weight and 0.5 to 15 parts by weight of polyethylene (B) having an intrinsic viscosity of at least 2 dl / g or more. After mixing, this is extruded from a die and the extrudate obtained is stretched.

Here, polyethylene (B) as described above
Is preferably an ultra high molecular weight polyethylene having an intrinsic viscosity of at least 5 dl / g or more.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The method for producing an ultrahigh molecular weight polypropylene stretch-molded article according to the present invention will be specifically described below.

Ultra High Molecular Weight Polypropylene (A) The ultra high molecular weight polypropylene used in the present invention has an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent.
Is at least 5 dl / g or more, preferably 10 dl / g
That is all. When the intrinsic viscosity [η] is less than 5 dl / g, the molecular chain length becomes insufficient, so that a stretched molded article having excellent tensile strength cannot be obtained, which is not preferable.
On the other hand, the upper limit of the intrinsic viscosity [η] is not particularly limited, but 3
When it exceeds 0 dl / g, the solubility becomes poor, the viscosity of the dope at a high concentration is extremely high, and the spinning stability is poor due to causes such as melt fracture, which is not preferable.

The ultra high molecular weight polypropylene in the present invention is a propylene homopolymer obtained by coordination anionic polymerization, or a small amount of propylene (eg 10
Mol% or less) other α-olefins such as ethylene, 1-butene, 4-methyl-1-pentene, 1-pentene, 1-
A propylene-based copolymer obtained by copolymerizing hexene, 1-octene, 1-decene, or the like is used.

Polyethylene (B) The polyethylene used in the present invention plays a role of promoting the crystallization rate of the ultra high molecular weight polypropylene when the ultra high molecular weight polypropylene is stretched. It is desirable that such polyethylene has an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent of at least 2 dl / g or more, preferably 5 dl / g or more, and more preferably 10 dl / g or more. This intrinsic viscosity [η] is 2 dl
If it is less than / g, the interaction between the molecules of polyethylene and ultra-high molecular weight polypropylene is insufficient, and the effect of promoting the crystallization rate cannot be sufficiently exhibited, which is not preferable.
On the other hand, the upper limit of the intrinsic viscosity [η] of polyethylene is not particularly limited, but if it exceeds 30 dl / g, the solubility is poor and a gelled product is formed in the spinning dope, which is not preferable because the spinning stability is poor.

As the polyethylene in the present invention, ethylene homopolymer obtained by coordination anionic polymerization, or ethylene and a small amount (for example, 10 mol% or less) of other α-olefins such as propylene, 1-butene, 4-
An ethylene-based copolymer obtained by copolymerizing methyl-1-pentene, 1-pentene, 1-hexene, 1-octene, 1-decene and the like is used.

In the present invention, in the ultrahigh molecular weight polypropylene composition comprising the ultrahigh molecular weight polypropylene and polyethylene as described above, polyethylene plays a role of promoting the crystallization rate of the composition, but contains a diluent. The crystallization rate of the ultra high molecular weight polypropylene composition, that is, the spinning dope can be measured using a differential scanning calorimeter as follows.

First, the stock solution for spinning is put into a closed solution cell made of silver in a heated and dissolved state, and this cell is mounted on a sample holder of a high-sensitivity differential scanning calorimeter. As the high sensitivity differential scanning calorimeter, for example, Seiko Denshi Kogyo (manufactured by) High Sensitivity Differential Scanning Calorimeter SS10 type can be used. After mounting the sealed cell on the differential scanning calorimeter, the temperature of the sealed cell is rapidly raised to a spinning temperature of about 130 to 240 ° C. The sealed cell is kept at this temperature for a sufficient time (for example, 15 minutes) to restore the state at the time of preparation of the spinning dope.

Then, this sealed cell was rapidly cooled with liquid nitrogen as a refrigerant, and the time (T) from the start of the rapid cooling to the appearance of an exothermic peak accompanying the crystallization of the ultrahigh molecular weight polypropylene was measured. The rate of conversion is quantitatively evaluated.

For example, when the spinning dope at 150 ° C. is rapidly cooled to a temperature of 60 ° C., the time (T) until the appearance of an exothermic peak due to crystallization is 60 seconds or less, preferably 30 seconds or less, and particularly preferably 10 seconds. It is the following.

The crystallization rate of the ultra-high molecular weight polypropylene composition according to the present invention is visually confirmed at the position of the whitening point (floss point) of the spinning dope when the spinning dope is allowed to flow in a cooling atmosphere or into a refrigerant. By doing so, it is possible to easily and qualitatively measure.

The set in the formed ultra-high molecular weight polypropylene drawn molded body composition according to the present invention, ultra-high molecular weight polypropylene 85-9
9.5 parts by weight, preferably 90 to 99 parts by weight, more preferably 95 to 99 parts by weight, and polyethylene in an amount of 0.5 to 15 parts by weight, preferably 1 to 10 parts by weight, more preferably 1 to Used in an amount of 5 parts by weight.

When the amount of polyethylene exceeds 15% by weight, the mechanical properties of the obtained ultra-high molecular weight polypropylene stretched product (molecular orientation product) tend to deteriorate at high temperature, while it is less than 0.5 part by weight. When the ultra-high molecular weight polypropylene is stretched, the crystallization rate of the ultra-high molecular weight polypropylene is too slow and the moldability tends to be poor. When the melting point of the ultrahigh molecular weight polypropylene stretched molded product (molecular orientation product) obtained from the composition for forming an ultrahigh molecular weight polypropylene stretched molded product according to the present invention is measured, the polyethylene part becomes a relatively low temperature part (around 130 ° C.). It has a peak by itself. From this, it is understood that when the amount of polyethylene is too large, the mechanical properties of the obtained ultra-high molecular weight polypropylene stretch-molded product at high temperature deteriorate.

Fluidity improver (C) The fluidity improver (C) used in the present invention is a low molecular weight compound having a melting point lower than that of the ultrahigh molecular weight polypropylene (A). As such a fluidity improver, a solvent capable of dissolving the ultra high molecular weight polypropylene or various waxes having dispersibility in the ultra high molecular weight polypropylene is used.

As the above-mentioned solvent, a solvent having a boiling point not lower than the melting point of the ultra-high molecular weight polypropylene, more preferably not lower than the melting point of the ultra-high molecular weight polypropylene + 20 ° C. is used.

Specific examples of such a solvent include n-
Aliphatic hydrocarbon solvents such as nonane, n-decane, n-undecane, n-dodecane, n-tetradecane, n-octadecane or liquid paraffin, kerosene; xylene, naphthalene,
Aromatic hydrocarbon solvents such as tetralin, butylbenzene, p-cymene, cyclohexylbenzene, diethylbenzene, pentylbenzene, dodecylbenzene, bicyclohexyl, decalin, methylnaphthalene, ethylnaphthalene or hydrogenated derivatives thereof; 1,1,2, 2-tetrachloroethane, bentachloroethane, hexachloroethane, 1,2,
Halogenated hydrocarbon solvents such as 3-trichloropropane, dichlorobenzene, 1,2,4-trichlorobenzene and bromobenzene; mineral oils such as paraffinic process oil, naphthene type process oil and aromatic process oil are used. .

As the waxes mentioned above, an aliphatic hydrocarbon compound or a derivative thereof is used. Specific examples of the aliphatic hydrocarbon compound as a wax include a saturated aliphatic hydrocarbon compound as a main component, and usually have a molecular weight of 2000 or less, preferably 1000.
Below, more preferably 800 or less paraffin wax is used. Specific examples of these aliphatic hydrocarbon compounds include n-alkanes having 22 or more carbon atoms such as docosane, tricosane, tetracosane, and triacontane, or mixtures with lower n-alkanes containing them as the main component, and separated from petroleum. Purified so-called paraffin wax, low molecular weight polymer obtained by copolymerizing ethylene or ethylene or other α-olefin, medium / lower polyethylene wax, high pressure polyethylene wax, ethylene copolymer wax, or medium / low pressure Waxes obtained by reducing the molecular weight of polyethylene such as high-performance polyethylene and high-pressure polyethylene by thermal degradation, oxides of these waxes, oxidized waxes such as maleic acid-modified waxes, and maleic acid-modified waxes are used.

As the aliphatic hydrocarbon compound derivative, for example, an aliphatic hydrocarbon group (alkyl group, alkenyl group)
Carbon which is a compound having one or more, preferably 1 to 2, particularly preferably 1 carboxyl group, hydroxyl group, carbamoyl group, ester group, mercapto group or carbonyl group at the terminal or inside of Number 8 or more, preferably 12 to 50 carbon atoms or molecular weight 130 to
There may be mentioned 2000, preferably 200 to 800 fatty acids, aliphatic alcohols, aliphatic amides, fatty acid esters, aliphatic mercaptans, aliphatic aldehydes and aliphatic ketones.

Specifically, as the fatty acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, etc., and as the aliphatic alcohol, lauric alcohol, myristyl alcohol, cetyl alcohol,
Examples of the fatty acid amide include stearyl alcohol and the like, and capric amide, laurinamide, palmitin amide, stearyl amide, and the like, and the fatty acid ester include stearyl acetic acid ester and the like.

Among these fluidity improvers, waxes which are solid at room temperature are preferable in terms of storability and transportability. The fluidity improver used in the present invention is a low softening point hydrocarbon polymer having a softening point of 50 to 120 ° C., specifically, a pressure-sensitive adhesive tape as a tackifying resin, as long as the object of the present invention is not impaired. Used in the field of paints and hot melt adhesives, the following resins, for example, C ₄ fraction and C ₅ fraction obtained by decomposition of petroleum, naphtha, etc., depending on the sources of monomers to be polymerized, A mixture of these or any fraction thereof, such as isoprene and 1, in a C ₅ fraction.
Aliphatic hydrocarbon resin mainly composed of 3-pentadiene, aromatic hydrocarbon resin mainly composed of styrene derivative and indene in C ₉ fraction obtained by decomposition of petroleum, naphtha, etc., C ₄ , Any fraction of C ₅ and C ₉
Aliphatic / Aromatic Copolymerized Hydrocarbon Resin Copolymerized Fraction,
Aliphatic hydrocarbon resin obtained by hydrogenation of aromatic hydrocarbon resin, synthetic terpene hydrocarbon resin having a structure containing aliphatic, alicyclic and aromatic, α, β-pinene in terpene oil as raw material Fluidity of terpene-based hydrocarbon resin, indene in coal tar-based naphtha and coumarone-indene-based hydrocarbon resin derived from styrene, low molecular weight styrene-based resin and rosin-based hydrocarbon resin Improvers can also be used.

Manufacturing Method [Dissolution Mixing] In the present invention, first, the above-mentioned ultra-high molecular weight polypropylene, polyethylene and a fluidity improver are mixed into a spinning stock solution to enable spinning.

The compounding ratio of the ultrahigh molecular weight polypropylene composition and the fluidity improver varies depending on the kinds of compounding, but generally speaking, the weight ratio is 1:99 to 1.
It is preferably 5:85, and particularly preferably 3:97 to 10:90. If the amount of the fluidity improver is less than the above range, the viscosity of the spinning dope becomes too high, and not only melt mixing and spinning become difficult, but also the resulting fiber is significantly roughened and stretch breakage easily occurs. Is not preferable. on the other hand,
When the amount of the fluidity improver is more than the above range, the spinnability at the time of spinning and the drawability of the fiber become poor, which is not preferable.

The melt mixing of the composition for forming an ultrahigh molecular weight polypropylene stretched molded product and the fluidity improver is generally 110 ° C. or higher, though it depends on the type of the fluidity improver used.
It is desirable to carry out at a temperature of 300 [deg.] C., preferably 130 [deg.] C. to 240 [deg.] C. When the solution mixing is carried out at a temperature lower than this range, the ultra high molecular weight polypropylene composition and the fluidity improver are not completely dissolved or dispersed. As a result, a uniform unstretched molded article cannot be obtained by spinning, which is not preferable. On the other hand, when melt-mixing is carried out at a temperature higher than the above range, the molecular weight of the ultrahigh molecular weight polypropylene is lowered due to thermal degradation, which makes it difficult to obtain a stretched molded article having high strength, which is not preferable.

Such melt-mixing can be carried out by a mixer equipped with a heatable stirring blade, or can be carried out by using a single-screw or multi-screw extruder. [Spinning] The spinning of the spinning dope is generally performed by extrusion molding. That is, a spinning dope is extruded through a spinneret to obtain a filament for stretching,
By extruding through a flat die, a stretching film, sheet or tape can be obtained, and by extruding through a circular die, a stretched hollow fiber molding pipe can be obtained. The present invention is particularly useful for the production of drawn filaments, in which case the solution extruded from the spinneret is drafted (ie drawn in solution).
Can also be added. The spinning dope extruded in this manner can be cooled by air cooling or by using a forced cooling means such as a refrigerant such as water, methanol, ethanol or acetone to further increase the crystallization rate. [Stretching] The unstretched molded article of ultra-high molecular weight polypropylene thus obtained is stretched. The extent of this stretching treatment may be such that the ultra-high molecular weight polypropylene in the molded body is effectively provided with at least uniaxial molecular orientation.

Stretching of a molded article of ultra-high molecular weight polypropylene is preferably carried out at a temperature of generally 40 ° C. to 230 ° C., particularly 80 ° C. to 200 ° C., and this unstretched molded article is heated and maintained at the above temperature. As the heat medium, any of air, water vapor and liquid medium can be used. Further, prior to stretching, the fluidity improver added in advance can be extracted and removed from the unstretched molded product with a solvent or the like. Further, as a heat medium for heating and holding the unstretched molded article, a solvent capable of extracting and removing the fluidity improver, and having a boiling point higher than the stretching temperature, specifically, decane, decalin, kerosene, etc. When the stretching operation is carried out by using it, the above-mentioned fluidity improver can be extracted and removed, and at the same time, it is possible to eliminate stretching unevenness during stretching and to achieve a high stretching ratio. Even if such a heat medium does not have the effect of removing the fluidity improver, the fluidity improver in the formed article can be removed by treating the stretched article in a solvent, for example. Needless to say.

The stretching operation can be carried out either in one stage or in multiple stages of two or more stages. Further, the draw ratio depends on the desired molecular orientation and the effect of improving the melting temperature associated therewith, but is generally 5 to 200 times, and particularly 1
The stretching operation is preferably performed so that the stretching ratio is 0 to 100 times.

The stretching operation is generally advantageous in multi-stage stretching of two or more stages, and the first stage stretching is preferably performed at a relatively low temperature of 60 ° C to 120 ° C. In the second and subsequent stretching steps, it is preferable to perform the stretching operation of the molded product at a temperature of 120 ° C to 230 ° C and higher than the stretching temperature of the first step. Here, in the second and subsequent stretching steps, at least one step of the stretching operation is preferably performed at a temperature of 165 ° C. or higher. Furthermore, during the stretching operation, some of the polyethylene contained in the unstretched molded product may be removed from the stretched molded product in the form of plaque, but the polyethylene has already promoted crystallization of ultrahigh molecular weight polypropylene. It is preferable that the polyethylene contained in the unstretched molded body be removed since it has performed the function for. Further, when performing the multi-stage stretching as described above, the stretching tension of the n-th stage is 0.01 to 50% of the stretching tension of the preceding stage, and 0.1 to 4
There may also be tension relief zones such as 0 g / filament. When such a tension relaxation zone is provided, the strain at the molecular level generated in the former stretching step is relaxed, the stretching speed can be increased, the stretching ratio can be increased, and the productivity is improved. It will be. [Heat Treatment] The stretch-molded body thus obtained can be heat-treated under a constraint condition or under a slight shrinkage condition, if desired. The shrinking condition mentioned here is the reverse operation of the above-mentioned stretching, but the stretching ratio is 0.92.
It is at least twice, preferably at least 0.95 times. The heat treatment is
It is generally carried out at a temperature of 140 ° C. to 220 ° C., particularly 150 ° C. to 200 ° C., for 0.5 to 10 minutes, preferably 1 to 5 minutes. By this heat treatment, the crystal melting temperature of the stretch-molded body shifts to the high temperature side, and the creep resistance at high temperatures is improved. It is considered that this is because the crystallization of the oriented crystal portion which was previously formed in the stretch-molded body was further promoted by the heat treatment.

Stretch-molded product A stretch-molded product obtained from the above-described ultra-high-molecular-weight polypropylene composition has a composition of 8 ultra-high-molecular-weight polypropylene having an intrinsic viscosity [η] of at least 5 dl / g.
5-99.5% by weight and an intrinsic viscosity [η] of at least 2
Polyethylene of dl / g is composed of 0.5 to 15% by weight, and has a tensile strength of at least 0.8 GPa or more. Further, the melting point of the ultrahigh molecular weight polypropylene stretched molded product obtained by the present invention is 170 ° C. or higher, preferably 180 ° C. or higher, more preferably 190 ° C. or higher, when measured by a differential scanning calorimeter under constrained conditions. It has heat resistance that is not found in conventional polypropylene stretched fibers.

Here, the melting point is measured by the following procedure using a differential scanning calorimeter. That is, the differential scanning calorimeter
Approximately 3m sample using Perkin Elmer DSCII type
The g is wound on an aluminum plate having a size of 4 mm × 4 mm and a thickness of 0.2 mm, thereby constraining the orientation method of the sample. Next, the sample wound around this aluminum plate is enclosed in an aluminum pan, and this is used as a measurement sample. In addition, the same aluminum plate as that used for the sample is enclosed in a normally empty aluminum pan that is placed in a reference holder, which is a sample for comparison, to balance the heat of both. And sample 3
Hold at 0 ° C for about 1 minute, then increase at 2 ° C at a heating rate of 10 ° C / min.
Heat up to 50 ° C. The maximum endothermic peak position determined by this measurement is taken as the melting point of the sample.

When the melting point is measured as described above, the ultrahigh molecular weight polypropylene stretched and molded article according to the present invention does not show a single melting peak of polyethylene, but after the melting point is measured, the temperature is lowered to room temperature and the melting point is measured again. In the case of so-called second run, a single melting peak of polyethylene appears. This is one of the characteristics of the present invention, and shows that polyethylene itself is highly oriented by the spinning / drawing operation, and at least polyethylene is not defective in the fiber.

The degree of molecular orientation of the stretched ultrahigh molecular weight polypropylene according to the present invention can be measured by an X-ray diffraction method, a birefringence method, a fluorescence polarization method or the like. For example, the degree of orientation according to the half width (Industrial Chemistry Magazine, Vol. 39, P.99
2, 1939) F is

[0048]

[Equation 1]

Is represented by In this formula, H ° is the half of the intensity distribution curve along the Debye ring of the strongest paratropic surface on the equator line (generally the (110) surface reflection in the case of polypropylene) of the X-ray diffraction reflections. Price range (°)
Is. The degree of orientation F represented by this formula is 0.90.
From the mechanical properties of the obtained fiber, it is preferable that the molecular orientation is at least 0.95.

[0050]

EFFECT OF THE INVENTION According to the method for producing an ultra-high molecular weight polypropylene stretch-molded product according to the present invention, a polypropylene stretch-molded product having an excellent combination of heat resistance, creep resistance and mechanical properties can be obtained. The molded body is useful as a packaging material such as a packing tape, as well as an industrial textile material such as a high-strength multifilament, a string, a rope, a woven fabric, and a nonwoven fabric. In addition, when a molded product in the form of a filament is used as a reinforcing fiber for various resins such as epoxy resin and unsaturated polyester and synthetic rubber, it has higher heat resistance than conventional ultrahigh molecular weight polyethylene stretched filaments and polypropylene stretched filaments. Significant improvements in terms are achieved. Furthermore, since this filament has high strength and low density, conventional glass fiber, carbon fiber,
It is particularly effective because it can be made lighter than a molded product using boron fiber, aromatic polyamide fiber, aromatic polyimide fiber, or the like. Similar to composite materials using glass fiber etc.,
UD (Unit Directional) laminated board, SMC (Sheet Molding)
Compound), BMC (Bulk Molding Compound), etc. can be molded, and it is expected to be used for various composite materials in the field of light weight and high strength such as automobile parts, boat and yacht structures, electronic circuit boards, etc. To be done.

[0051]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

[0052]

Examples 1 to 5 [Preparation of spinning dope] Ultrahigh molecular weight polypropylene powder, polyethylene powder and decalin in desired mixing ratios are placed in a separable flask equipped with a condenser. At this time, as a process stabilizer, 3,5-di-tert-
Butyl-4-hydroxytoluene was added in an amount of 0.1% by weight based on the total amount of ultra-high molecular weight polypropylene and polyethylene. Then, while stirring, the temperature of the system was kept at room temperature, and nitrogen gas was bubbled for about 30 minutes to remove oxygen dissolved in the system. Further, the temperature of the system is adjusted to 11 with stirring.
The powder was moistened by heating to 0 ° C. When the state of the inside of this system was continuously observed, after about 8 minutes at 110 ° C., it became a porridge-like viscous suspension and the moistening was completed. Next, when the temperature of the system was heated to 140 ° C. and stirring was continued, a transparent solution was formed in about 10 minutes, and a solution of an ultrahigh molecular weight polypropylene-polyethylene composition was obtained.
This solution was allowed to stand at 140 ° C. for about 1 hour to prepare a spinning dope. The crystallization rate measurement sample was sampled from this state. [Spinning] A solution of the ultrahigh molecular weight polypropylene composition prepared as described above was spun under the following conditions to obtain a fiber. That is, the solution was extruded at a temperature of 140 ° C. by a plunger type extruder equipped with a 2 mmφ spinning nozzle. The extruded solution was taken under an air gap of about 30 cm at room temperature and then introduced into an acetone bath to carry out a crystallization operation to obtain a crystallized fiber. At this time, the solution was taken off in a state close to free fall and was not actively drafted. The whitened and crystallized fiber is wound on a bobbin and dried under reduced pressure at room temperature.
It was subjected to the next stretching step. [Drawing] The fiber prepared by the above method was drawn under the following conditions to obtain an oriented drawn yarn. That is, using four godet rolls, n-decane was used for the first stage, and Frusol P (heat medium manufactured by Thermal Chemical Industry) as the heat medium for the second and subsequent stages, and three-stage drawing was performed in a drawing tank. It was At this time, the temperature in the first drawing tank was 110 ° C and the temperature in the second drawing tank was 140 ° C.
C., the temperature in the third stretching tank was 165.degree. C., and the effective length of the tank was 50 cm. At the time of stretching, the rotation speed of the first godet roll was set to 0.5 m / min and the rotation speed of the fourth godet roll was changed to obtain a desired stretch ratio. In addition, the rotation speed of the second and third godet rolls is
It was appropriately selected within the range where stable stretching was possible. However, the stretching ratio was determined by the rotation ratio between the first godet roll and the fourth godet roll. The elastic modulus and the tensile strength were measured at room temperature (23
(° C). The sample length between the clamps at this time is
The pulling speed was 100 mm / min. However, the elastic modulus is the initial elastic modulus and was calculated using the slope of the tangent line. The fiber cross-sectional area required for the calculation was calculated from the weight of the sample with the fiber density of 0.910 g / cc.

Table 1 shows sample numbers, sample compositions, and crystallization rates. The crystallization rates in the table are as described above, when the temperature was rapidly lowered from 140 ° C. to 60 ° C. by the differential scanning calorimeter. It was expressed as the time (sec) from the start to the appearance of the crystallization peak (exothermic). In any case, it can be seen that the crystallization speed is faster and the molding stability during spinning is excellent, as compared with the results of Comparative Examples (Table 3) described later. In addition, Table 2 shows various physical properties of the drawn fiber obtained by drawing each sample having the composition shown in Table 1 under the conditions described above. Results of comparative examples described below (Table 4)
It can be seen that the fiber has a very well-balanced heat resistance and mechanical properties as compared with.

[0054]

Comparative Examples 1 to 5 Stretched fibers were prepared by the same method as described in Example 1. Table 3 shows the sample number, sample composition and crystallization rate. When the crystallization speed is slow (for example, 10 seconds or more), the moldability during spinning is extremely poor,
Further, the uniformity of the diameter of the fiber was poor, and when the crystallization rate was extremely slow, the fiber could not be formed. Also,
Table 4 shows the physical properties of the fibers obtained by drawing the samples shown in Table 3 by the same method as in Example 1 described above. Example 1
It is understood that the heat resistance and mechanical properties are inferior to those of.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

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Claims (2)

[Claims] 1. An intrinsic viscosity [η] of at least 5 dl / g
Ultra high molecular weight polypropylene (A) 85-9
9.5 parts by weight and an intrinsic viscosity [η] of at least 2 dl /
A fluidity improver (C) was added to an ultra high molecular weight polypropylene composition composed of 0.5 to 15 parts by weight of polyethylene (B) of g or more and melt mixed, and then extruded from a die to obtain A method for producing an ultra-high molecular weight polypropylene stretch-molded article, which comprises stretching the extruded product. 2. The production of stretched ultra-high molecular weight polypropylene according to claim 1, wherein the polyethylene (B) is an ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of at least 5 dl / g or more. Method.