JPH06280111A - High strength polyethylene fiber - Google Patents

Abstract

PURPOSE:To obtain a polyethylene fiber excellent in creep elongation resistance and creep breakage resistance and having a high strength and a high elastic modulus by processing ethylenebutene-1 copolymer specified in an intrinsic viscosity and an ethyl-branched degree into the fiber by a gel spinning method, etc. CONSTITUTION:Ethylene-butene-1 copolymer having an ultrahigh mol.wt. represented by an intrinsic viscosity [eta] of >=10, preferably 12-30, in a fiber state and having an average ethyl branching degree B of 5/[eta]<B<150[eta], preferably 6/[eta]/B/127[eta], per 100 skeletal carbon atoms in the ethylene component of the main chain is processed into a fiber to obtain the objective polyethylene fiber having a strength of >=28g/d and an elastic modulus of >=700g/d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength polyethylene fiber having excellent creep elongation resistance and creep rupture resistance.

2. Description of the Related Art Attempts to obtain fibers having high strength and high elastic modulus from a so-called ultra-high molecular weight polyethylene having a viscosity average molecular weight of hundreds of thousands to several millions have been actively conducted in recent years. Therefore, a material having extremely high strength and elastic modulus has been developed (for example, JP-A-56-15408).
JP-A-55-107506, etc.). The reason why ultra-high molecular weight polyethylene was first strengthened as a flexible polymer is that its primary structure is extremely simple. However, since there are no hydrogen bonds between the molecular chains and there is virtually no steric hindrance,
There was a drawback that slippage between molecular chains occurred easily and initial creep elongation was large, that is, creep elongation resistance was low. Such drawbacks have markedly limited the range of use of this material for applications in which a load is applied for a long time, such as mooring ropes and tension members.

Further, in the above-mentioned applications such as high-performance ropes, the time until the break (that is, creep rupture) after applying a load for a long time is also very important,
No material has been known that simultaneously satisfies the above-mentioned reduction in creep elongation and extension of creep rupture time (creep rupture resistance).

Heretofore, in an attempt to improve the creep elongation resistance, a thermal crosslinking agent with or without addition of a crosslinking agent is used.
There are known studies to introduce crosslinks between molecular chains by means such as electron beam irradiation, but it is extremely difficult to introduce crosslinks while maintaining high strength. In addition, JP-A-6
Although the description of 1-289911 discloses that the creep elongation is improved by post-stretching or heat treatment,
There are problems from the viewpoint of economic efficiency and productivity due to extremely slow stretching and complicated processes, and creep rupture resistance cannot be said to have been improved. Furthermore, in recent years, there has been an attempt to introduce a short chain branch into the main chain to improve the creep elongation resistance, but by introducing the branch, there is a problem that the physical properties such as strength are significantly reduced, Although the creep elongation was improved, the creep rupture resistance was not always satisfactory.

[0004]

From the above viewpoint, the present invention simultaneously satisfies unprecedentedly excellent creep elongation resistance and creep rupture resistance without sacrificing high strength and high elastic modulus. It is intended to provide high strength polyethylene fibers.

[0005]

Means for Solving the Problems That is, the present invention comprises an ethylene-butene-1 copolymer having an intrinsic viscosity ([η]) of 10 or more in a fiber state, and its average degree of branching (B).
Relates to a creep-resistant high-strength polyethylene fiber represented by the following formula for 1000 carbon skeleton atoms of the ethylene component forming the main chain and having a strength of at least 28 g / d or more and an elastic modulus of 700 g / d or more. 5 / [η] <B <15 / [η]

The present invention will be described in detail below. The basic concept for molding a material with high strength and high elastic modulus using a flexible polymer such as polyethylene is summarized in the point of how to align molecular chains long and evenly. In practice, since the molecules themselves are flexible, crystallization progresses while the molecules are entangled with each other and the state of folding of the molecular chains is inherent, and thus it is difficult to perform molding by a usual melt extrusion technique.

Such folding of the molecular chain, molecular ends and the like exist as amorphous parts, but if they are taken into the crystal, they become defects in the crystal and become a serious cause of deterioration of creep rupture resistance. . The cause of this is not clear, but the disorder within the crystal causes weaker intermolecular force and promotes slip between molecular chains, or dislocation that causes defects to move together with creep is a dominant factor. I presume it is.

From such a point of view, the present inventors have obtained a proper structure in which the crystal does not lose the integrity and therefore has the creep rupture resistance, by the method which has not been considered so far. That is, they have reached the present invention. It is emphasized here that the fiber according to the present invention has not only a low creep elongation but also a very good creep rupture resistance, which has been difficult in the past, and is not limited to that level. It maintains high strength and high elastic modulus.

The technique for imparting creep rupture resistance will be described below. First of all, one of the raw material polymers
Substructure is one of the most important requirements. That is, the intrinsic viscosity [η] should be 10 or more, and more preferably 12 to 30. This is because if the molecular weight is less than 10, not only the strength and elastic modulus are not improved, but also the creep elongation resistance is significantly reduced. This is because the length less than the molecular chain has a close relationship with creep elongation. Also, it is extremely important that the raw material molecular weight significantly affects creep rupture. This is of course the main reason for the large initial creep elongation, but in addition to this, it is considered that the molecular end is also greatly related to the mechanism at fracture. Specifically, it is considered that the so-called Zhurkov model is such that local stress acts near the ends of molecules to cause molecular breakage at the time of breakage, and a large amount of radicals generated by this breaks adjacent molecules in a chain reaction. But the details are unknown. In the past, the inventors did not know of any reports on the molecular weight, creep elongation, and creep rupture of the ultrahigh molecular weight polyethylene in such a state of yarn, and the molecular weight is actually sufficient to obtain strength. In fact, for the purpose of obtaining high strength, an intrinsic viscosity of about 8-9 was sufficient. Therefore, the molecular weight found by the present inventors significantly affects the creep elongation and the creep rupture resistance, and the higher the molecular weight, the higher the strength and elastic modulus obtained, and the synergistically increased creep elongation and creep rupture resistance. The fact that it also improves is a truly new fact.

Further, the branched structure is important as the primary structure. If a proper amount of branching is introduced, the creep elongation resistance will be good, but on the other hand, the stretchability will decrease and high strength cannot be obtained. In addition, the introduction of branching may disturb the crystals, which may worsen the creep rupture resistance. From this fact, it is important to optimize the crystal disorder to the utmost by minimizing the branch introduction amount and to aim at creep elongation resistance.

Therefore, as a result of intensive studies, the present inventors have found that
With polyethylene of a certain molecular weight or more, if the type and amount of branching are properly selected, it will be introduced into the polyethylene crystal even if it is branched, and therefore it will have relatively good stretchability and creep elongation resistance and creep rupture resistance. It was found that the present invention was reached.

What is particularly emphasized in the present invention is that even if the branching amount is much smaller than what is generally considered, a surprisingly excellent creep elongation resistance can be exhibited due to the synergistic effect with the increase in strength and the branching. It is truly unexpected that the creep rupture resistance can be remarkably improved in the above types. In other words, it has been found that the branching portion is introduced into the crystal in a state with little disorder, if the branching amount is extremely small, without hindering the stretching process. In other words, the introduction of branching into the crystal indicates that slippage between mutual molecular chains during stretching is easy, and once incorporated into the crystal, the movement of the molecular chains within the crystal is significantly restricted. Therefore, it is estimated that intermolecular slip is restricted and creep elongation resistance is improved. At this time, the intrinsic viscosity is 10
The above is important again and again, and the synergistic effect is exerted here as well, because the increase in the molecular weight significantly reduces the number of molecular ends that are considered to be the starting points of slip in the crystal.

From this point of view, the ethyl group is most preferable as the type of branching. Creep elongation is good with methyl group, but creep rupture resistance is insufficient, and if it is a bulkier group than ethyl group, it will not be incorporated into the crystal and there is no effect on creep elongation resistance, as well as markedly poor stretchability. Becomes The reason why the ethyl branch is good in this creep rupture resistance is not clear so far, but it is presumed that the packing property in the crystal is superior to that of the methyl group.

The average degree of branching referred to in the present patent refers to the degree of branching of the ethylene-butene-1 copolymerization simple substance, and in the case of a blend of two or more polymers, the carbon of its main chain. The average value per number is shown. And the average degree of branching (B) must be in the range shown below per 1000 carbons of the main chain. 5 / [η] <B <15 / [η]

In the region where the degree of branching is small, the creep elongation resistance is not sufficient, and when the amount of branching is too large, high strength cannot be obtained due to a decrease in stretchability, and the melting point is lowered, which is an unfavorable result. Becomes Preferably 6 / [η] <B <
It is 12 / [η].

Finally, it is emphasized again that any of the above-mentioned factors of the molecular structure is indispensable for creep elongation resistance and creep rupture resistance, and only in the above range, high strength / high elastic modulus and truly excellent resistance Creep rupture property can be realized.

Next, in order to mold such a raw material into high-strength polyethylene, as mentioned above, it is difficult to carry out ordinary melt molding. The most suitable method is, for example, a method known as a so-called "gel spinning method" for improving moldability by using a solvent, as disclosed in JP-A-55-107506. Examples of the solvent include octene, nonane, decane, liquid paraffin, paraffin waxes, and aliphatic and aromatic hydrocarbons such as isomers thereof, and toluene or xylene, naphthalene, and cyclics such as decalin and tetralin. Examples thereof include aliphatic or aromatic compounds and their derivatives. Here, the solvent used for dissolving the polymer is preferably a volatile solvent that vaporizes at room temperature or in a heated atmosphere. For the mechanical properties such as strength, the volatility of the solvent does not matter in particular, but in the case of the creep properties, non-volatile components such as paraffin remain in the crystals and adversely affect the creep properties, especially creep elongation resistance. Is not preferred.

As described above, the breakage time of the high-strength polyethylene fiber according to the present invention is 20000 hours or more (25 ° C., under a load of 20% of the breaking load), and the creep elongation at 20000 hours is 5% or less, which is extremely excellent. It exhibits creep characteristics.

The measuring method and measuring conditions will be described below. (Creep rate) The creep rate, which represents the initial creep elongation as used herein, is, for example, Journal Polymer Science,
It is calculated by the method described in 22,561 (1984). Specifically, the strain rate when the change in strain rate with time becomes constant after applying a load to the sample, or when the rate of change becomes the minimum, that is, plateau creep (Plateau creep) Deformation speed at. The creep rate (CRV50) in this method means that a load of 9 g / d is applied to a yarn sample adjusted to a temperature of 50 ° C. The length of the original sample is l ₀ (cm), the length after 2 hours is l ₁ (cm),
If the length after 22 hours is l ₂ (cm), CRV50
(Sec ⁻¹ ) is given by the following equation. CRV50 = (l ₂ −l ₁ ) / (20 × 3600 × l
₀ )

(Creep rupture time) The creep rupture time as referred to in the present specification means the time required to cut at 25 ° C. by applying a load corresponding to 20% of the rupture strength of staking.

(Strength / Elastic Modulus) The strength and elastic modulus in the present specification are measured by using Tensilon manufactured by Orientec Co.
The strain-stress curve was measured under the conditions of 0 mm and an elongation rate of 100% / min, and the stress at the breaking point of the curve was strength (g / d), and the initial elastic modulus was calculated from the maximum gradient near the origin of the curve. Each value is an average value of 10 times.

(Intrinsic Viscosity) The viscosity was measured with decalin at 135 ° C. by a capillary viscometer method. Prior to measurement, 1 wt% of antioxidant (trade name (Yoshinox BH
(T; manufactured by Yoshitomi Pharmaceutical Co., Ltd.)) was added and dissolved by stirring for 4 hours.

(Identification of Branches and Quantitative Method) Finely crushed sample was added to orthochlorobenzene so that the concentration of the sample was 13
Melted at 5 ° C., 13 C-NMR at an oscillation frequency of 75 MHz
Was observed. The signal is identified by Makr
omol. Chem. , 184, 569 (1983). Degree of branching is 3 derived from branching
It was calculated by the area ratio of the peak of primary carbon and the peak of methylene of the main chain.

[0024]

EXAMPLES The present invention will be described in the following examples.

[Example 1] Ultra-high molecular weight ethylene-butene copolymer having an intrinsic viscosity of 18.0 and having 0.5 ethyl branches per 1000 main chain carbon atoms 10% by weight and 90% by weight
Of decahydronaphthalene are mixed, kneaded and dissolved by a screw type extruder at a temperature of 210 ° C. and 300 rpm,
It was extruded from an orifice having a diameter of 0.8 and having 30 holes, the temperature of which was adjusted to 190 ° C. The extruded melt was cooled with an air flow, and was taken out at a take-up speed of 50 (m / min), and subsequently drawn 4 times in an air oven at 120 ° C. The yarn was continuously drawn and drawn 5 times in an oven at 150 ° C. The strength of the obtained stretched product is 40 g /
The d and elastic modulus were excellent at 1520 g / d, and the creep rate and creep rupture time were also good as shown in Table 1.

Example 2 Ultra-high molecular weight ethylene-butene copolymer having an intrinsic viscosity of 18.2 and 0.8 ethyl branch per 1000 main chain carbon atoms 10% by weight and 90% by weight
A drawn yarn was prepared under the same conditions as in Example 1 except that decahydronaphthalene was mixed. However, the second draw ratio was only 3 times. The strength of the final drawn yarn is 3
The elastic modulus was 3 g / d and the elastic modulus was 1280 g / d. The creep speed and creep rupture time were extremely good as shown in Table 1.

Example 3 Under the same conditions as in Example 1 except that an ultrahigh molecular weight ethylene-butene copolymer having an intrinsic viscosity of 30.0 and an ethyl branch of 0.2 per 1000 main chain carbon atoms was used. A drawn yarn was created. Two-stage drawing is possible up to 4 times, the intrinsic viscosity of the obtained drawn yarn is 26.1, the strength is 44 g / d, the elastic modulus is 1790 g / d, the creep speed and the creep rupture time are also very good. there were.

Comparative Example 1 Intrinsic viscosity 9.0, main chain carbon 1
The procedure of Example 1 was followed except that an ultra high molecular weight polyethylene-butene copolymer having 0.6 ethyl branches per 000 was used. The stretchability in the two-stage stretching was good, and stable stretching up to 6 times was possible. The physical properties are strength 27g / d,
An elastic modulus of 1002 g / d and a modest value were obtained.
As shown in, the creep rate was extremely high and was not good. It is considered that this is due to the synergistic effect of the low molecular weight and the fact that the strength could not be increased.

Comparative Example 2 Intrinsic viscosity 9.0, main chain carbon 1
The procedure of Example 1 was followed except that an ultra high molecular weight polyethylene-butene copolymer having 2.4 ethyl branches per 000 was used. The stretchability in the two-stage stretching was good, and stable stretching up to 6 times was possible. The physical properties are a strength of 22 g / d,
Although the elastic modulus was low at 715 g / d, the creep rate showed a moderate value. However, the creep rupture time was extremely unsatisfactory.

Comparative Example 3 The procedure of Example 1 was repeated except that an ultrahigh molecular weight polyethylene-butene copolymer having an intrinsic viscosity of 22.3 and an ethyl branch of 0.1 per 1000 carbons in the main chain was used. I wanted to. The two-stage drawing was 6 times, which was very good. As for physical properties, the creep rate and the creep rupture time were unsatisfactory as shown in Table 1, but the strength was good at 45 g / d and the elastic modulus was 1764 g / d.

Comparative Example 4 An ultrahigh molecular weight polyethylene-propylene copolymer having an intrinsic viscosity of 18.0 and having 6.0 methyl branches per 1000 main chain carbon atoms was used.
The method of Example 1 was followed. Two-stage stretching was possible up to 5.5 times. As for the physical properties, the creep rate and the creep rupture time were good as shown in Table 1, and the strength was 40 g / d and the elastic modulus was 1544 g / d, but the creep rupture time was slightly inferior.

[0032]

[Table 1]

[0033]

INDUSTRIAL APPLICABILITY The present invention is extremely excellent without sacrificing strength and elastic modulus due to the synergistic effect of the molecular weight and the degree of branching, which has not been considered so far, by optimizing the primary structure of the polymer molecular chain. Provided is a high strength polyethylene fiber having creep rupture resistance.

Claims (1)

[Claims] 1. The intrinsic viscosity (“η”) in the fiber state is 10
The above ethylene-butene-1 copolymer is used, and the average branching degree (B) of ethyl branches thereof is represented by the following formula for 1000 carbon skeleton atoms of the ethylene component having the main chain, and at least 28 g / d A high-strength polyethylene fiber having creep rupture resistance, which has the above strength and an elastic modulus of 700 g / d or more. 5 / [η] <B <15 / [η]