JPH01162814A - Production of novel polyethylene fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber of high strength and high modulus, low in creep, thus useful as an industrial fibrous material, by spinning a solution of a polymer produced by chemically crosslinking treatment of high-molecular weight polyethylene followed by hot drawing of the resultant undrawn yarn. CONSTITUTION:A solution of a polymer which has been produced by chemically crosslinking treatment, using e.g., di-t-butyl peroxide, of polyethylene with a weight-average molecular weight of >=700,000 (pref. >=2,000,000) is spun and the resultant undrawn yarn is put to hot drawing pref. at 100-160 deg.C by a factor of >=25, thus obtaining the objective fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a novel polyethylene fiber having high strength and high modulus and low creep.

(Prior Art) Polyethylene fibers have excellent properties as industrial fiber materials, such as being light, having excellent chemical resistance, and being relatively inexpensive.

In recent years, fiber materials that are light, strong, and have high modulus of elasticity have been required to meet the demands for energy-saving and high-performance products that use them as industrial fiber materials.As a method for producing polyethylene fibers that meet these demands, Japanese Patent Application Laid-Open No. 55-1075 describes a method of spinning a solution of high molecular weight polyethylene, cooling it, and hot-drawing the resulting gel-like filament to a high magnification.
This method is disclosed in JP-A No. 06, Japanese Unexamined Patent Publication No. 58-5228, and the like.

Due to its characteristics, the high-strength, high-modulus polyethylene fibers obtained by these methods can be used for industrial fiber applications that require particularly high strength and high modulus, such as ropes, slings, various rubber reinforcement materials, and reinforcement materials for various resins. It is expected to be useful as a reinforcement material for concrete and concrete.

However, although the high-strength, high-modulus polyethylene fibers obtained by the above method have high strength, they have the same drawback as ordinary polyethylene fibers of high elongation under load, that is, high creep. Therefore, when these high-strength, high-modulus polyethylene fibers are used as industrial fiber materials, many problems occur. for example,
Lobes using these fibers have the problem of gradually stretching under load. In addition, when these fibers are used as tension members for optical fibers, etc.,
The tension member that is responsible for the tension progresses over time. As a result, tension is applied to the optical fibers and the like that should be supported by the tension members, which may reduce their functionality or cause them to break.

Therefore, if the creep characteristics of high-strength, high-modulus polyethylene fibers as described above can be improved, their use as industrial fiber materials will be greatly expanded.

Crosslinking treatment is known as a method for improving the creep properties of polyethylene.

JP-A No. 60-59172 describes a polyethylene stretching system, and JP-A No. 60-240433 describes a method of subjecting a gel-like film or tape to crosslinking treatment by irradiating radiation before or during stretching. has been done. However, in these methods, when irradiating with radiation, not only crosslinking but also molecular chain scission occurs at the same time, resulting in an unavoidable decrease in strength.

Also, J. DeBoer, H.J. Vandenberg, and A.J. Pennings; Polymer No. 25
Volume 513-519 (1984) [J, d
E. Boer, H. J. van den.
Berg, A. J., Pennings; POLYM
ER, Vol, 25 (1984), P, 513-51
9 pieces are dry gel-like! A method is described in which Li fibers are impregnated with a crosslinking agent dissolved in a solvent, the solvent is blown off, and then a crosslinking treatment is performed at the same time as Nobuoki. Furthermore, JP-A-61-293
No. 229, the purpose of which is to improve heat resistance, describes a method of impregnating a polyethylene gel with a crosslinking agent and molding it. However, in these methods, crosslinking progresses during stretching or molding, which inhibits orientation and crystallization, making it difficult to obtain high strength and high elastic modulus.

Therefore, the mechanical properties of the crosslinked boroethylene fibers obtained by the method described above are generally not sufficient for many industrial fiber applications.

(Problems to be Solved by the Present Invention) An object of the present invention is to provide a method for producing polyethylene fibers that have high strength, high elastic modulus, and low creep and are useful as industrial fiber materials.

(Means for Solving the Problems) The present invention is characterized in that a solution of a polymer obtained by chemically crosslinking polyethylene having a weight average molecular weight of 700,000 or more is spun, and the obtained undrawn yarn is hot stretched. This invention relates to a novel method for producing polyethylene fibers.

The polyethylene used in the present invention includes a small amount of propylene, for example, 10 mol% or less, within a range that does not impair the effects of the present invention.
Other alkenes such as butylene, pentene, hexene, 4-methylpentene, or one or more vinyl monomers copolymerized with ethylene, or a small amount of polypropylene, polybutene-1, etc. It may also be a mixture of polyolefin and polyethylene.

The weight average molecular weight of the polyethylene used in the method of the present invention needs to be 700,000 or more, preferably 1,500,000 or more, and more preferably 2,000,000 or more.

In general, the higher the molecular weight, the fewer defects such as molecular chain ends inside the fiber, and the higher the strength. It is necessary to use polyethylene.

Further, since the higher the molecular weight, the greater the effect of reducing creep, the weight average molecular weight is required to be 700,000 or more.

In the present invention, the chemically crosslinked polymer (hereinafter referred to as crosslinked polyethylene) refers to polyethylene crosslinked using a crosslinking agent, and especially if it contains a substantially crosslinked polymer, Although there is no limitation, it is suitable that the degree of crosslinking is low so that it can be uniformly dissolved in the solvent, and that it is in the form of a powder. Further, it may be a mixture of a chemically crosslinked water lima and an uncrosslinked polymer.

The above crosslinking agent is not particularly limited, but examples include di-L-butyl peroxide, dicumyl peroxide, 2,5-
Dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2゜5-di(t-butylperoxy)hexyne-3, t-butylperoxy-2-ethylhexanoate , 1,1-bis(t-butylperoxy)3゜3.5-1-limethylcyclohexane, t-butylperoxyisopropyl carbonate, organic peroxides such as benzoyl peroxide, t-noir isocyanurate, Organic compounds having two or more vinyl groups such as divinylbenzene, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, α, α′
-A diazo compound such as azobisisobutyronitrile or a mixture of two or more thereof can be used.

The method for preparing the above-mentioned crosslinked polyethylene is not particularly limited, but includes, for example, the following method.

A crosslinking agent capable of crosslinking polyethylene at a temperature below the melting point of polyethylene and polyethylene powder are stirred in a volatile solvent capable of dissolving the crosslinking agent but not polyethylene. Next, the crosslinking agent is uniformly adhered to the surface of each polyethylene particle by evaporating the solvent at a temperature below the melting point of the polyethylene. The polyethylene powder to which this crosslinking agent is attached is heat-treated at a temperature below the melting point of polyethylene to effect crosslinking. Heat treatment at a temperature higher than the melting point of polyethylene may cause fusion between polymer particles, resulting in poor solubility in solvents.

The degree of crosslinking varies depending on the molecular weight of the polyethylene used to prepare crosslinked polyethylene, the type and amount of crosslinking agent, heat treatment temperature, time, etc., but if it is too strong, the molecules of crosslinked polyethylene may not dissolve uniformly in the solvent. If it is too weak, the effect of reducing creep may be reduced. Therefore, the degree of crosslinking must be determined to be an appropriate degree through prior experiments, but this can be easily determined.

Generally, the amount of crosslinking agent used is 0.005wt based on the polymer
% or more and 10wt% or less, and the heat treatment temperature is 80%
The temperature is preferably higher than 0.degree. C. and lower than the melting point of polyethylene.

In the method of the present invention, a solution of crosslinked polyethylene is first prepared.

The solvent used to form the polymer solution is
Examples include, but are not limited to, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and mixtures thereof. Normally, crosslinked polyethylene does not dissolve at temperatures below 60°C even with these solvents, and is often heated to temperatures above 100°C, so solvents with low boiling points are not preferred. Suitable solvents include decalin, xylene, tetralin, nonane, decane, n-paraffin,
Examples include kerosene and paraffin oil.

Moreover, those that are solid at room temperature such as paraffin wax and naphthalene can also be used.

There is no particular limitation on the polymer concentration of the crosslinked polyethylene solution used in the present invention, and it is determined as appropriate from the viewpoints of uniformity during dissolution, ejection stability during spinning, spinnability, thread runnability, and spinnability during drawing. The solution viscosity is selected to be between 1 and 15.
A range of weight percent is suitable.

In the method of the present invention, the above-mentioned crosslinked polyethylene solution is discharged in the form of fibers using an ordinary gear pump and a spinning nozzle, and is cooled and solidified to form fibers. The extruded solution is passed through a gas section and then introduced into a coagulation bath to coagulate the yarn (so-called dry-wet spinning).The extruded solution from the nozzle is cooled and then formed into a rubber-like gel yarn. In gel spinning, the solution extruded from a nozzle is introduced into a bath consisting of a cooling agent and a coagulant to gel and coagulate.
The spinning method described in Japanese Patent No. 1-113813 (hereinafter referred to as gel wet spinning) can be applied, but the method is not particularly limited to these methods. However, it is preferable to apply gel wet spinning because it is easy to obtain polyethylene filaments with high tensile strength and polyethylene multifilaments with less fusion between single filaments. This is because if there is a lot of fusion between single filaments in polyethylene multifilament, problems such as not only the tensile strength of the entire filament will decrease, but also the adhesiveness with the resin will decrease, and the strength utilization rate during heating will decrease. It is from.

When the solvent remains in the yarn spun by the above method, it is preferable to extract the remaining solvent with an extractant. This is because if the residual solvent in the yarn is removed by a method such as drying or hot stretching, fusion between single yarns may occur when the solvent evaporates. If the residual solvent in the yarn is removed using an extractant, drying is possible.
Even if hot stretching is performed, no fusion occurs between single yarns.

Note that it is preferable to remove the extractant from the extracted yarn by drying, since this improves the spinning properties in the subsequent hot stretching step.

The undrawn polyethylene yarn obtained by the above method needs to be subsequently subjected to hot drawing.

This undrawn polyethylene yarn can also be drawn by cold drawing, but in this case, it is not possible to obtain polyethylene fibers with high strength and high elastic modulus that can be used as an industrial fiber material without any problems.

Although there is no particular limitation on the drawing temperature in the hot drawing of this undrawn polyethylene yarn, it is preferably in the range of 80 to 160°C, more preferably 100 to 160°C. In addition,
Examples of the heating medium during stretching include, but are not limited to, heating rolls, hot plates, heated gas baths, heated liquid baths, and U heating pins.

The stretching ratio in hot stretching is suitably set to 10 times or more, preferably 20 times or more, and more preferably 25 times or more so as to obtain high strength and high elastic modulus.

Note that the stretching may be performed in one stage or in multiple stages.

The drawn yarn obtained by the method of the present invention not only has high strength and high elastic modulus, but also contains a crosslinked structure in the fiber, which suppresses the sliding of molecules or fibrils inside the fiber, making it a yarn with low creep. Become.

Therefore, the method of the present invention has a single yarn strength of 30 g/d or more, a single yarn Young's modulus of 1000 g/d or more, and a creep rate of 2.5% when worn for 60 days under a load of 1/10 of the breaking strength at 20°C. The following polyethylene fibers can be easily obtained, and have a single yarn strength of 40 g/d or more, a single yarn Young's modulus of 1400 g/d or more, and when wrapped for 60 days under a load of 1/10 of the breaking strength at 20°C. creep is 2%
It is also possible to obtain polyethylene fibers having:

(Example) Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto. In addition, tensile strength, initial elastic modulus, and creep were measured under the following conditions.

Tensile strength and initial elastic modulus measurement conditions Measurement atmosphere: 20°C, relative humidity 65% Equipment: Tensilon UTM-4 tensile tester manufactured by Toyo Baldwin Co., Ltd. Sample: Single yarn 250 mm Tensile speed: 300 mm/min Initial elastic modulus: Strength and elongation curve It was determined from the slope at the origin.

Creep measurement conditions Measurement atmosphere = 20° C. 1 Relative humidity 65% Load: 1/10 of breaking strength Note that breaking strength here means the product of single yarn tensile strength and fineness. In addition, creep was determined using the following formula.

Ll]: Initial length immediately after applying a load to the sample) L: Length measured with a load applied to the sample for 60 days (Example 1) Straight chain with a weight average molecular weight of 3 million Trichlorotrifluoroethane in which 0.05% by weight of t-butylperoxyisopropyl carbonate was dissolved in the polyethylene was poured into powdered high-density polyethylene, and after stirring, the trichlorotrifluoroethane was evaporated at room temperature. I let it happen.

The polyethylene coated with this crosslinking agent was heat-treated at 125°C for 12 hours and 30 minutes in a nitrogen atmosphere (the half-life of t-butylperoxyisopropyl carbonate at this temperature is about 30 minutes, so the reaction had sufficiently progressed). (It is thought that there is some cross-linking.)

Next, the crosslinked polyethylene was dissolved in kerosene at a temperature of 180°C to prepare a polyethylene solution having a total concentration of 5.0% by weight.

This solution was heated at 170°C and passed through a 5 mm air layer through a nozzle with a hole diameter of 1 mm and 10 holes, and then spun into a two-layer structure with an upper layer of water and a lower layer of trichlorotrifluoroethane. After cooling in a bath, it was coagulated and bundled to obtain a coagulated thread. The temperature of the spinning bath is 10℃, which is above! The thickness of (water) is 80m
m, the thickness of the lower layer (trichloride trifluoride ethane) is 230 mm
And so.

Further, the coagulated yarn was pulled off at a rate of 7.5 m/min.

The coagulated thread is then passed through an extraction bath of trichlorotrifluoroethane at 5°C to extract the kerosene remaining in the thread,
After drying, it was stretched 10 times using a hot plate at 135°C and then wound up with a winder.

6. This one-stage drawn yarn was further heated using a hot plate at 145°C.
As a result of stretching the yarn five times, the physical properties of the yarn were as follows.

Single yarn fineness: 0.86d Single yarn tensile strength: 49g/d Single yarn initial elastic modulus: 1840g/cfAlso, this drawn yarn was loaded and left at 20℃ for 60 days, but the creep was as small as 0.31%. It was something.

(Example 2) The amount of t-butylperoxyisopropyl carbonate was 0. Crosslinked polyethylene and non-crosslinked polyethylene had a weight average molecular weight of 3.
A total of 5.0% by weight polyethylene solution was prepared by mixing 1,000,000 polyethylene at a ratio of 1:9 and dissolving it in kerosene at a temperature of 180°C.

After spinning, extracting and drying this solution in the same manner as in Example 1,
It was stretched 9 times using a 5°C hot plate and then wound up with a winder.

This single-stage drawn yarn was further drawn four times using a hot plate at 145° C., and as a result, the yarn physical properties were as follows.

Single yarn fineness: 1.6d Single yarn tensile strength: 47g/d Single yarn initial elastic modulus: 1460g/d Creep
: 1.62% (Comparative Example 1) Linear high-density polyethylene powder with a weight average molecular weight of 3 million was dissolved in kerosene at a temperature of 180'C to give 5.0% by weight.
A polyethylene solution was prepared.

This solution was spun, extracted and dried in the same manner as in Example 1, and then stretched 10 times to obtain a single-stage drawn yarn.

This one-stage drawn yarn was further drawn 6 times using a hot plate at 145° C. to obtain a drawn yarn 60 times in total.

This drawn yarn has a strength of 56 g/d and a Young's modulus of 1780 g/d.
Although it showed high physical properties, the creep was as high as 4.27%.

(Comparative Example 2) Linear high-density polyethylene with a weight average molecular weight of 150,000 was cross-linked (commonly known as kerosene) in the same manner as in Example 1, and dissolved in kerosene at a temperature of 170°C to prepare a 15% by weight polyethylene solution. .

This solution was spun and extracted in the same manner as in Example 1, and the dried yarn was wound with a winder without stretching).

Next, the obtained undrawn yarn was heated to 36°C using a hot plate at 135°C.
Stretched twice. This drawn yarn had low physical properties such as strength of 12 g/d and Young's modulus of 390 g/d due to the low molecular weight of the polymer. Moreover, the creep exceeded 5%.

(Effects of the Invention) As described above, according to the method of the present invention, it is possible to obtain a novel polyethylene fiber that has high strength and high modulus and has low creep, which is useful as an industrial fiber material.

Claims (1)

[Claims] A novel method for producing polyethylene fibers, which comprises spinning a solution of a polymer obtained by chemically crosslinking polyethylene having a weight average molecular weight of 700,000 or more, and hot drawing the obtained undrawn yarn.