JPH089667B2 - Process for producing polyethylene products of high tensile strength and modulus and low creep and products thus obtained - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides high tensile strength from high molecular weight polyethylene,
Filaments with high modulus and low creep,
It relates to a method for manufacturing products such as tapes, films, tubes, rods and profiles.

It is known to produce high tensile strength and modulus products, especially filaments or tapes, starting from high molecular weight polyethylene solutions. US Patent 434490
No. 8, No. 4411854, No. 4422993, No. 4430383 and No.
See No. 4436689. In these known methods, a semi-dilute solution of linear high molecular weight polyethylene is converted into a solvent-containing substance, for example, filaments, for example, by spinning, which is continuously subjected to high tensile strength by thermoplastic gelation and stretching. And a product of modulus and modulus. Since the tensile strength and modulus of the product has been found to increase with increasing molecular weight of the polyethylene used, it is generally
Starting from polyethylene having a weight average molecular weight of at least ⁴ × 10 ⁵ , even at least ⁶ × 10 ⁵ , preferably 1 × 10 ⁶ or higher.

The products obtained by these known methods have been found to have relatively high creep.

For example, attempts have been made to reduce creep by irradiating it with an electron beam. However, in that case, the tensile strength of the product would be greatly reduced. Further, it is described that post-stretching or heat treatment improves creep resistance. See European Patent Application Publication No. 205960. However, due to very slow stretching and complicated process steps, this does not seem to be a technical or economic solution.

The present invention provides products having high modulus, high tensile strength and low creep, and methods of making such products.

The present invention has a viscosity-average molecular weight of at least 500000 kg /
Mixing kilomoles of polyethylene raw material with a solvent for polyethylene or a solvent mixture, at a temperature above the melting point,
The tangible solvent-containing substance is converted into a solid gel-like substance, which is cooled to form a solid gel-like substance, and the solid substance obtained after cooling with or without complete or partial removal of the solvent is In the method of stretching at 1, a polyethylene raw material containing 2 to 20 alkyl side chains per 1000 carbon atoms is used in this method to obtain a polyethylene product of high tensile strength, high modulus and low creep. It relates to a manufacturing method.

According to one aspect of the practice of the invention, polyethylene copolymers are used. In that case, preferably 6X10 ⁵
Above all, a polyethylene copolymer having a viscosity-average molecular weight of 8 × 10 ⁵ or more, and further 1 × 10 ⁶ kg / kmole or more is used, and it is preferable to contain 3 to 12 alkyl side chains per 1000 carbon atoms. The chains preferably contain up to 2 carbon atoms.

According to another aspect of the practice of the present invention, (A) a polyethylene containing up to 2 alkyl side chains per 1000 carbon atoms and (B) containing at least 4 alkyl side chains per 1000 carbon atoms. A mixture of polyethylene is used,
Both (A) and (B) have a viscosity-average molecular weight of at least 500000 kg / kmole. In this case, both components (A) and (B) are not less than 6X10 ⁵ , especially 8X1.
It is preferable to have a viscosity-average molecular weight of at least ^{5 and} more than 1 × 10 ⁶ kg / kmole, and at the same time, the mixture of (A) and (B) is preferably 2.5 per 1000 carbon atoms.
It is preferred to have -10, more preferably 4-7, alkyl side chains, the side chains containing up to 2 carbon atoms. It has been found that if the side chains are too long, for example 5, 6 or more carbon atoms, the reduction in creep is reduced, as well as the tensile strength and modulus. When using a polyethylene mixture, the number of side chains in the component with the maximum number of side chains should be 100 or less, preferably 20 or less, per 1000 carbon atoms.

The invention further comprises an ethylene polymer containing 2 to 20 side chains per 1000 carbon atoms, the side chains being methyl or ethyl groups and having a viscosity-average molecular weight of at least 500000 kg / kmole, which reduces creep. , A polyethylene product having a modulus of at least 70 GPa and a tensile strength of at least 2.0 GPa. The product according to the invention is
Polymer, Vol. 19, August 1978, pp. 969 (plateus crep rate as defined in Wilding, MA et al.).
eep rate), which is 10-100 more than the creep rate of a product from a similar polyethylene with substantially no side chains.
Twice as small.

The present invention has, inter alia, a creep rate (measured at 50 ° C. and a load of 0.75 GPa) of not more than 3X10 ^-7 sec ^-1 , preferably of not more than 2X10 ^-7 sec ^-1 , and more preferably of not less than 1X10 ^-7 sec ^-1. , A polyethylene product having a tensile strength of in particular 2.5 GPa or more, preferably at least 3 GPa and a modulus of 80 GPa. In particular, in the product of the present invention, the "a" axis of the crystal unit cell measured by wide-angle X-ray at 20 ° C and 65% humidity is not less than 7.45Å. The product is preferably in filament, tape or film form.

Various solvents can be used in the method of the present invention. Suitable solvents are, for example, halogenated or non-halogenated hydrocarbons such as paraffin, paraffin wax, toluene, xylene, tetralin, decalin, monochlorobenzene, nonane, decane or mineral oil fractions. Obviously, mixed solvents can also be used.

The polyethylene concentration in the solution may vary depending on the nature of the solvent and the molecular weight of polyethylene. In particular, when polyethylene having a very high molecular weight, for example, 2 × 10 ⁶ or more is used, a solution having a concentration of 50% by weight or more has a high viscosity, which makes the operation considerably difficult. On the other hand, the disadvantages of using solutions with a concentration of less than 0.5% by weight, for example, are lower yields and higher costs for solvent separation and recovery. Thus, in general, polyethylene solutions with a concentration between 1 and 50% by weight, especially between 3 and 35% by weight, are used.

The solution used can be prepared in various ways, for example by suspending solid polyethylene in a solvent and then stirring it at elevated temperature, or by using a twin-screw extruder equipped with a mixing and conveying section of the suspension. It can be manufactured by changing.

In the present invention, the conversion of the solution into a tangible solvent-containing substance can be carried out in various ways, for example by spinning through spinlets with circular or slit-shaped dies to obtain filaments or tapes respectively, or deformation dies. It can be carried out by extruding with an extruder.

The temperature during the conversion must be chosen above the melting point. This melting point depends, of course, on the selected solvent, concentration,
Depends on the molar weight and chemical composition of polyethylene and the pressure used, at least 90 ° C, especially at least 10
It is preferably 0 ° C. Of course, this temperature is selected below the decomposition temperature of the polyethylene.

If desired, the solvent-containing material may be cooled, for example, from 2 to
It can be stretched at a stretch ratio of 20.

The method according to the invention comprises cooling below the gel point of the tangible solvent-containing substance, such as by quenching with substantially no solvent removal, preferably with air and / or a liquid cooling medium, eg water. The gel point is, of course, somewhat solvent dependent and generally substantially matches the melting point. Preferably, the material is cooled to about room temperature.

The material thus obtained can be continuously stretched. However, it is also possible to remove at least some of the solvent before stretching, for example by extraction with dichloroethane. Of course, it is also possible to carry out the stretching operation under conditions in which all or part of the solvent still present is removed, for example by aeration or in the extractant.

In the method of the present invention, the material is stretched at an elevated temperature, for example above the glass transition temperature and below the decomposition temperature of polyethylene. Preferably, the stretching operation is performed at about 75 ° C. This stretching is preferably carried out in several steps by raising the temperature.

It has been found that high draw ratios can be used in the method of the present invention. Generally, draw ratios of at least 10, preferably at least 20, and even at least 40 are used. Of course, if a high stretch is applied before cooling, the stretch ratio can be lowered.

The products according to the invention are suitable for all technical applications where substantial strength and rigidity are required and weight loss is advantageous.

If desired, small amounts of additives, stabilizers and the like can be applied in or on the product.

The invention is illustrated in the following examples, without being limited thereto.

Each characteristic value used in this specification was measured by the following methods.

Viscosity-Average molecular weight In accordance with ASTM D 2857, the intrinsic viscosity (η) was measured at 135 ° C based on the viscosity dependence of a certain concentration of the decalin solution. The viscosity-average molecular weight was calculated by using the (η) in the following formula.

Mv = 3.64 × 10 ⁴ X (η) 1.39 Measurement of Strength and Elongation The measurement was performed according to JIS-1013. That is, S-S
The curve is drawn under the conditions of a sample length of 200 mm and an elongation rate of 100 mm / min.
The tensile strength and tensile modulus were calculated by using a tensile tester manufactured by Theouldwin Company. The tensile modulus was calculated from the maximum slope around the origin of the SS curve.

Types and number of side chains 10% polyethylene powder or finely crushed molded products
It was dissolved in o-dichlorobenzene at 120 ° C. to obtain a wt% solution. ¹³ CN of this solution at 75 MHz
MR spectra were observed at 120 ° C. Signal identification is performed by Macromolecular Chemie (Makromol.Chem.),
184 , 569 (1983) as a reference. Further, the degree of branching was represented by the ratio of the intensity of one peak derived from the branching point to the intensity of the methylene peak of the main chain.

The size of the "a" axis of the crystal unit cell The measurement of the wide-angle X-ray scattering pattern is performed by, for example, Rigaku
X- manufactured by Rigaku Denki Company
Conduct using a line generator (RU-3H type). For the measurement, a tube voltage of 45 kv and a tube current of 70 were monochromated with a nickel filter.
A copper counter electrode Cu Kα line (λ = 1.5418Å) of mA is used. The filament sample is mounted in the sample holder so that the single yarns are parallel to each other. The thickness is preferably 0.5 to 1.0 mm. The wide-angle X-ray diffraction pattern is obtained by adjusting the fiber axes of the filaments parallel to each other so that they are oriented in the meridian direction, and the size of the "a" axis of the crystal unit cell is determined by measuring the plane of the equatorial diffraction curve (200 ) Can be calculated according to the following formula based on the scattering angle 2α at the diffraction peak position.

λ = 1.5417Å (For correction of scattering angle and other details, see, for example, Nida Isa published by Maruzen Co., Ltd.
See “X-ray Crystallography”, edited by mu). ) Creep rate As used herein, the creep rate is a stage at which the rate of change in elongation with time after a load is applied to a sample is constant or at least the rate of change is minimum, that is, for example, a journal.・ Journal of Polymer Science, 22 , 561 (1984)
Means the rate of deformation in the creep of the flat part. The length of the sample at a certain time (t seconds) is given by l (t) (c
When expressed in m), the creep rate can be calculated by the following formula.

[Wherein l ₀ means the length of the sample without load (cm); and a means any extremely short time (second)] Example 1 Mv is about 1.6 × 10 ⁶ kg / kmole, carbon atom About 1000 pieces
Polyethylene containing 10 methyl side groups was suspended in xylene to a nominal concentration of 2% by weight, stabilizers were added, packaged, degassed and then melted at 130 ° C.
The solution was then poured into a stainless steel container and cooled. The solvent was evaporated at room temperature and the solvent residue was extracted with dichloroethane. The resulting dry gel film is cut into 11
It was stretched to a stretching ratio of 60 in several stages with a temperature gradient of 0 to 130 ° C. The drawn tape has an E-modulus of 84 GPa, 2.0 GPa
Tensile strength and the creep rate (ε) of the flat part at room temperature under a load of 0.9 GPa of 10 ^-8 sec ^-1 .

Example 2 Mv of about 1.5 × 10 ⁶ kg / kmole, 4 per 1000 carbon atoms
The procedure of Example 1 was repeated using polyethylene with methyl side groups. The resulting tape has an E of 88 GPa.
-Modulus, tensile strength of 2.1 GPa and plateau creep rate of 3X10 ^-8 sec ^-1 .

Comparative Example A Example 1 using a polyethylene having an Mv of 1.4 × 10 ⁶ kg / kmole and one methyl side group per 1000 carbon atoms.
The operations of and 2 were repeated. The resulting tape is 90GP
E-modulus of a, tensile strength of 2.2GPa and 8X10 ^-7 seconds
^It had a plateau creep rate of ^-1 .

Example 3 The polyethylene described in Example 1 was suspended at room temperature in decalin to a nominal concentration of 10% by weight.
After degassing, insert nitrogen, add stabilizer, and stir the suspension with co-rotating twin-screw extruder (ZSK of Werner and Pfleiderer).
Mold; diameter 30 mm; L / D ratio = 27). The extruder is equipped with 2 × 30 mm screws consisting of alternating conveying and mixing sections.

At room temperature, supply the suspension to the intake zone (80 ° C),
180 ° C at a screw speed of 200 rpm with a residence time of 3 minutes
I pushed it out.

The obtained solution was spun, cooled in water, extracted with dichloromethane, and then the gel filament was drawn at 120 ° C. and a draw ratio of 30.

The filament obtained has an E-modulus of 95 GPa,
2.7XPa Tensile Strength and 5X10 at 50 ℃ and Load 0.6GPa
^It had a plateau creep rate of ^-8 sec ^-1 .

COMPARATIVE EXAMPLE B The procedure of Example 3 was repeated using a polyethylene having an Mv of 1.6 × 10 ⁶ kg / kmole and also no methyl side groups per 1000 carbon atoms.

The filament obtained has an E-modulus of 110 GPa,
It had a tensile strength of 3 GPa and a plateau creep rate of 10 ^-6 sec ^-1 .

Example 4 Powder of polyethylene (A) having 1.2 methyl side groups per 1000 carbon atoms of the main chain determined by Mv1.9X10 ⁶ and high resolution NMR, and Mv1.9X10 ⁶ and determined by the same NMR Polyethylene (B) having 13.0 methyl side groups per 1000 carbon atoms in the main chain was added in a weight ratio of 10:90.
Mixed in. Decalin (90 parts by weight) was then mixed with this mixture (10 parts by weight) to form a slurry. The substances are mixed and melted in a twin-screw extruder having a temperature of 230 ° C.
Extruded from the m orifice.

The extruded dissolved material was drawn down at a draw down speed of 30 m / min while cooling with an air stream, and then drawn in an air heating oven at a draw ratio of 5 times. That is,
The winding speed of the intermediate stretched material was 150 m / min. The material was then stretched under a heated atmosphere in an oven having a length of 50 m at a maximum stretch ratio of 3.2 (ie, a total stretch ratio of 16.0). The stretching and winding speed at this stage was 100 m / min.

Examples 5, 6, 7 and 8 and Comparative Examples C and D For each example, the polymer mix ratio of branched polymer (B) to polymer (A) was varied as shown in Table 1 and the maximum of two-stage stretching Filaments were prepared using the same polymer as described in Example 4 and following the same procedures and conditions as described in Example 4, except that the draw ratio was changed as shown in Table 1. , Was constant at 100 m / min.). in this way,
There was a difference between the strengths obtained in the final moldings.

Table 2 shows the maximum strength of the products obtained in Examples and Comparative Examples and the creep rate when measured at 50 ° C. under a load of 0.75 GPa. In each example,
The product exhibits excellent high properties and excellent creep resistance.
In particular, in Example 6, when compared with the creep resistance of Comparative Example C, it shows a creep resistance of about 1/20. When using 100% branched polymer as shown in Comparative Example D, high creep and tenacity filaments are not obtained although the creep is small.

 ─────────────────────────────────────────────────── ─── Continued Front Page (56) References European Patent Publication 77590 (EP, A)

Claims (8)

[Claims] 1. A viscosity-average molecular weight of at least 500000 kg /
Mixing kilomoles of polyethylene raw material with a solvent or solvent mixture for polyethylene, converting it to a tangible solvent-containing substance at a temperature above the melting point, cooling this substance, forming a solid gel-like substance, and completely or partially removing the solvent. In a method of stretching at high temperature the material obtained after cooling, with or without removal, to 2 per 1000 carbon atoms.
A method for producing a polyethylene product, wherein a polyethylene raw material having 12 alkyl side chains is used, and the alkyl side chains have a maximum of 2 carbon atoms. 2. The method according to claim 1, wherein a polyethylene copolymer is used as the polyethylene raw material. 3. Polyethylene from 3 to 1000 per 1000 carbon atoms.
A method according to claim 1 or 2 having 12 alkyl side chains. 4. A mixture of polyethylene (A) a polyethylene containing 2 or less alkyl side chains per 1000 carbon atoms and (B) a polyethylene containing at least 4 alkyl side chains per 1000 carbon atoms as raw materials for polyethylene. The method according to claim 1, wherein both (A) and (B) have a viscosity-average molecular weight of at least 500000 kg / kmole. 5. The mixture is from 2.5 to 10 per 1000 carbon atoms.
A method according to claim 4 containing 5 alkyl side chains. 6. An ethylene polymer containing 2 to 12 side chains per 1000 carbon atoms, the side chains being methyl or ethyl groups and consisting of an ethylene polymer having an average molecular weight of at least 500000 kg / kmole and a modulus of at least 70 GPa. And a polyethylene product having a tensile strength of at least 2.0 GPa. 7. A product having a stable creep rate of maximum 3 × 10 ⁻⁷ sec ⁻¹ (measured at 50 ° C. and 0.75 GPa load) and measured by wide-angle X-ray at 20 ° C. and humidity 65%. 7. A product according to claim 6 wherein the "a" axis of the crystal unit cell is at least 7.45Å. 8. The polyethylene polymer is a copolymer or (A) a polyethylene containing up to 2 alkyl side chains per 1000 carbon atoms and (B) a polyethylene containing at least 4 alkyl side chains per 1000 carbon atoms. 8. A product according to claim 6 or 7, wherein both (A) and (B) have a viscosity-average molecular weight of at least 500000 kg / kmole.