JPS60240433A - Manufacture of polyalkene tape and film having high tensile strength, high modulus and low creeping property - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a process for making polyalkene tapes and films having high tensile strength and modulus and low creep properties based on high molecular weight linear polyalkene solutions.

PRIOR ART The production of polyethylene filaments based on dilute solutions of high molecular weight linear polyethylene with very high tensile strength, e.g. 1.2 GPa or more, and high modulus, e.g. 2 Q GPa or more, is known in the art (e.g.
U.S. Pat. No. 4,344,908, No. 4,422,993 and No. 4,430,383), in these known preparations, a weight average molecular weight of at most 20% by weight, in particular from 1 to 5% by weight, of at least 4 x 105, in particular at least 8 x 105
A solution of polyethylene having the following properties is spun through a spinning hole at a temperature higher than the gelling layer tx of the solution to form a filament, and the filament is cooled to a temperature lower than the gelling temperature to completely or partially remove the solvent. Alternatively, the gel filament formed in the step is stretched at an elevated temperature without being removed.

It is also known in such processes to use a spinning head with a slit die instead of a spinning head with an essentially circular die, and to obtain a ribbon instead of a circular filament (for example, see US Pat. No. 4,411,854). No. 4436689).

Although the products obtained by these methods have good mechanical properties in terms of tensile strength and modulus, the creep of these products is relatively high and therefore they are difficult to handle over long periods of loading, especially at elevated temperatures. If exposed, deformation occurs.

Therefore, products obtained in this way are not very preferred in applications where the material is exposed to long-term loads, even under small loads.

Furthermore, it has been found that the resulting product exhibits significant fibrillation, especially at high draw ratios.

SUMMARY OF THE INVENTION The present invention herein provides a method by which tapes and films with high tensile strength and high modulus can be obtained based on high molecular weight linear polyalkene solutions, at the same time the tapes and films have It also has very low creep and low fibrillarity.

Therefore, the present invention involves transforming a linear polyalkene solution having at least 60% by weight of solvent into a film-like or tape-like product at a temperature above the gelling temperature of the solution, and cooling the product below the gelling temperature. , high tensile strength by stretching the resulting gel-like film or tape at elevated temperatures, with or without removal of at least a portion of the solvent;
The present invention relates to a method for producing polyalkene films and tapes having a weight average molecular weight of at least 4X10 and having high modulus and low creep and fibrillarity.

The production method of the present invention involves spraying the gel film obtained after cooling. It is characterized by being attached.

DETAILED DESCRIPTION OF THE INVENTION A film is understood to mean a product in the form of a layer (thin (apparently less than 0.1 ran)) and has a width:thickness ratio of at least 1000. Tape is understood to mean a very thin (<0°1) layer with a width:thickness ratio of at least 50, the length of which is at least several times the width -
In particular, it is more than 10 times as large.

Surprisingly, there is a fundamental correlation between the irradiation of the gel tape or film before or during stretching according to the invention and the irradiation of the tape or film in a state in which the polymer molecules are already substantially oriented, i.e. after stretching. I found out that there is a difference.

Therefore, in the present invention, irradiation of the gel tape or film before or during stretching means irradiation of the gel tape or film in a state where the polymer molecules are still hardly oriented.

Although this theoretical explanation is not intended to limit the present invention, and all related phenomena have not yet been clarified, the basic feature of irradiation before or during stretching is that the molecular chain It is assumed that the irradiation is carried out in a state in which the molecular chains still mostly have a lamellar structure and a cross-linking reaction of the molecular chains occurs mainly in an unoriented state.

By using the process of the present invention, tapes and films exhibit lower creep levels compared to non-irradiated tapes and films, or gel extensibility is reduced or
is hardly affected, and after stretching the tensile strength and modulus remain at a high level. Additionally, the tapes and films exhibit substantially lower fibrillation than their non-irradiated, highly oriented counterparts.

In addition, irradiation of polyethylene itself is known (for example, M. Doll, [Radiochemistry of Polymers J (M, D
ole 5The Radiation Chemises
tyof Macromolecules) Academic Press, New York). here,
For example, it has been described that crosslinking occurs upon irradiation of polyethylene melts with electron beams. However, in such a method, the stretchability of polyethylene, that is,
It is conventionally known that the strength of the obtained filament is greatly reduced (for example, in Volume 1 of the above-mentioned document (1973)).
(see p. 239 and 293).

It is also conventionally known to irradiate polyethylene fibers obtained by drawing. However, it is known that the mechanical properties of the fibers are significantly reduced by such manufacturing methods. After irradiation, the tensile strength therefore decreases, in particular cases up to 40% (see, for example, Polymer Preten, Vol. 5 (1981), pp. 3, 17-324).

In contrast, in the method of the invention, the gel tape or filament obtained by cooling is irradiated. This can be done by passing the tape or film under the radiation source or between two or more radiation sources.

The radiation sources used can initially be electron beam sources, but in principle also r-ray radiation sources are used. A survey of conventional irradiation sources and methods can be found in Rubber Chemistry and
55 (1982), pp. 575-668.

The irradiation intensity applied in the method of the invention may vary depending on the diameter or thickness of the product to be irradiated, with higher intensities generally being applied to products with larger thicknesses or diameters. The selected radiation dose is generally between 1 and 10 megarads, preferably between 3 and 7 megarads.

The radiation irradiation may be carried out under reduced pressure, elevated pressure or atmospheric pressure, and may be carried out with the product at room temperature, high temperature or low temperature. during irradiation and/or between irradiation and stretching,
The tapes and films are preferably kept in an inert atmosphere, especially an oxygen-free atmosphere, so that stretching
Most conveniently, it is carried out during irradiation or immediately after irradiation.

The solvent-containing gel tape or film obtained during cooling is essentially irradiable. However, it is also possible to remove some or almost all the solvent from this gel tape or film and to subject the gel tape or film thus obtained to irradiation. If the solvent is sensitive (to irradiation), removal of such a solvent is essential.

The process of the invention begins with a solution of a high molecular weight linear polyalkene such as polyethylene, polypropylene or mixtures thereof. In this connection, the high molecular weight linear polyethylene contains a small amount, preferably up to 5 mol %, of one or more other alkenes copolymerized therewith, such as propylene, butylene, pentene, hexene, 4-methylpentene. , also refers to polyethylene containing octene, etc.

The polyethylene has 100 or more unbranched carbon atoms, preferably 300 or more unbranched carbon atoms between the carbon atoms having side chains. The polyethylene may also contain small amounts, preferably up to 25% by weight, of one or more polymers, in particular polypropylene, polybutylene or a copolymerization of propylene and small amounts of ethylene.

The polyethylene may contain significant amounts of fillers, such as those described in US Pat. No. 4,411,854. It is also advantageous to use polyethylene having a weight average molecular weight/number average molecular weight ratio of 5 or less, as described in US Pat. No. 4,436,689.

Since the achievable modulus and tensile strength increase with increasing molecular weight, polyethylenes are generally used which have at least a molecule of at least 4X101, preferably at least 8X105.

As the molecular weight increases, polyethylene becomes more difficult to handle. Dissolution in a suitable solvent takes longer and solutions of the same concentration are more viscous, so that lower concentrations must be used and the process is more expensive in terms of efficiency. Therefore, in the method of the present invention, it is possible to handle substances with a higher molecular weight, but with a molecular weight of 15
Polyethylene having an X of 1.0 or more is generally not used. The weight average molecular weight is determined by GPC (gel permi
chromatography) and light scattering method according to known methods.

It is also possible to use solutions of high molecular weight polypropylene, in particular polypropylene having a molecular weight of at least 5.times.10.

The polyalkene concentration in the solution may vary based on the nature of the solvent and the molecular weight of the polyalkene.

Solutions having a concentration of 20% by weight or more are particularly suitable for high molecular weight,
That is, when a polyalkene of 1×10 or more is used, it is considerably difficult to handle due to its high viscosity. On the other hand, for example 0
．． The use of solutions with polyalkene concentrations below 5% by weight is disadvantageous in terms of reduced yields and increased solvent separation and recovery costs.

In general, therefore, the polyalkene solution is started at a concentration of 2 to 20% by weight, in particular 5 to 10% by weight.

The choice of solvent is not critical. Any suitable solvent may be used, such as halogenated or non-halogenated hydrocarbons. In most solvents, polyalkenes can only be dissolved at temperatures of at least 90°C or higher. When solutions are spun into tapes or films, such operations are generally performed in an atmospheric pressure space. Therefore, low boiling point solvents are less preferred. That is, low boiling solvents evaporate very easily from tapes and films, acting somewhat as blowing agents and inhibiting the structure of the film.

The transformation of the solution into tape-like or film-like products can be carried out in various ways, for example through a spinning head with a very wide slit die. Naturally, instead of spinning, it is also possible to spread the solution, for example on a belt or roll, or to extrude, roll or calender.

Upon rapid cooling, the solution of polyalkene material transforms into a gel below a critical temperature (gelling temperature) within the aforementioned concentration range. For example, in spinning a solution must be used and therefore the temperature must be above this gel point.

For example, during spinning, the temperature of the solution is preferably at least 100°C or higher, more preferably at least 120°C, and the boiling point of the solvent is preferably at least 100°C or higher, especially at least the same as the forming temperature, that is, the spinning temperature. It is preferable. The solvent should not have a very high boiling point so that it is difficult to evaporate from the resulting film or tape. Preferred solvents include aliphatic, cycloaliphatic and aromatic hydrocarbons having a boiling point of at least 100° C., such as paraffin, paraffin wax, xylene, tetralin and decalin, and halogenated hydrocarbons or other known Solvents can also be used. For cost reduction, unsubstituted hydrocarbons are most preferred, and may also be halogenated derivatives of aromatic hydrocarbons.

The forming (deformation) and melting temperatures should not be too high so as not to cause substantial thermal decomposition of the polyalkene. Therefore, such a temperature is generally selected to be 240°C or higher. , no tag.

The resulting tape or film product is cooled below the gel point of the solution. Cooling can be accomplished by any suitable method, for example by passing the product through a liquid bath or through a shaft. During cooling of the polyalkene solution below its gelling point, the polyalkene forms a gel. The tape or film made of this polyalkene gel has sufficient mechanical strength for subsequent treatments, such as rolls, guides, etc. that are commonly carried out in spinning technology.

The gel tape or film thus obtained is
Subsequently, it is subjected to radiation irradiation. The gel may still contain a significant amount of solvent, not much lower than the solvent that was present in the polyalkene solution. In such cases, the solution is spun and cooled under conditions that do not promote evaporation of the solvent, for example by passing the film through a water bath.

Next, the irradiated tape or film is uniaxially or biaxially stretched at an elevated temperature, preferably at 75°C or higher. In such methods, stretching is preferably carried out at or below the melting temperature of the polyalkene. That is, at temperatures above this temperature, the mobility of the polymer is too large, and the desired orientation cannot be obtained, resulting in an insufficient blend. It is also necessary to consider the heat generated within the molecules due to the stretching of the film. Therefore, at high draw ratios, the temperature in the film and tape increases significantly and care must be taken not to exceed or approach the melting temperature.

Films and tapes can be brought to the drawing temperature by passing a gaseous or liquid medium maintained at the desired temperature through the containing zone. A tube oven using air as the gaseous medium is highly preferred, but it is also possible to use a liquid bath or any other suitable means.

During stretching, the solvent present is separated from the film or tape. This is preferably facilitated by any suitable method, for example by moving the solvent vapor through a stream of heated gas or air along the film in the stretching zone, or by introducing an extractant for the same or a different solvent. This is done by stretching in a liquid bath containing

The final film or tape must be solvent-free, and conditions are advantageously selected such that this condition is at least virtually achieved already in the stretching zone.

Modulus (E) and tensile strength (σ) were determined using an Instron tensile tester at room temperature and at a test rate of io%.
A strength-elongation curve measured at 1/min is obtained and converted to the original cross-sectional area of the film or tape sample.

In the method of the invention it is possible to apply high draw ratios.

The film or tape should be at least (12X106/M
Preferably, the uniaxial stretching is carried out by a factor of W+1), more preferably at least a factor of (14x 10''7Mw +1), where Mw is the weight average molecular weight of the polyalkene.

The object of the invention is suitable for a wide range of applications. these are,
Can be cut into strong bands, ribbons, and tapes. They can be used for the reinforcement of many known materials to be reinforced with fibers or ribbons, and also for all applications where it is desirable to combine high strength with low weight, e.g. video or magnetic tapes, medical tapes. ,
It can be used for packaging films, protective sheets, adhesive base layers, etc.

If desired, small amounts of conventional additives, stabilizers, fiber treatment agents, etc. may be incorporated in or on the film or tape, ranging from 11 to 10% by weight of O based on the polyalkene.
It is particularly preferable that it be blended.

EXAMPLES Next, the present invention will be explained in more detail based on the following examples, but these are not intended to limit the invention in any way.

Example 1 (comparison) In paraffin at a temperature of about 180°C, weight average molecular weight of about 2
A 5% solution of high molecular weight polyethylene (Hyfax-1900, manufactured by Vercules) having a molecular weight of 10 x 10 is poured onto a cooling conveyor belt to obtain a gel product about 2 m thick and about 100 m wide. The resulting gel film was passed through a trichlorethylene bath to remove the solvent and then subjected to a temperature gradient (12
0-145° C.) in a variable draw ratio oven.

For a film with a stretching ratio of 15 times, an E-modulus (measured at room temperature) of 22 GPa was obtained. Stretch ratio 25x and 3
At 0x, the E-modulus was 4QGPa and 52GPa, respectively.

The creep property of the obtained film was evaluated at approximately 75°C and a load of 0.2.
Measured in GPa. The elongation measured at 100,000 mm was 10-11%.

In said method, the fibrillation tendency increased significantly at high draw ratios.

Example 2 A product was obtained in the same manner as in Example 1. However, after extraction and before stretching, the obtained gel film was subjected to irradiation under the scanner of an electron accelerator (HVE type, high pressure 3MV) in an inert nitrogen atmosphere. In irradiation, the total dose is 3
It's Megarad.

The film had the same modulus as Example 1 after stretching. However, creep was substantially lower. The elongation measured in the same manner as in Example 1 was about 4.5%. Furthermore, the irradiated films had a greatly reduced tendency to fibrillate.

Example 3 High molecular weight polyethylene (Lurhemi/Hoechst, HostalenGur) in Decalin
) 412, weight average molecular weight approximately 1.5 x 106) 2.5
The wt% solution was passed through a slit (1 x 40 m) at 175°C.
The product was spun (formed) in a vacuum cleaner, and then cooled in water. At this time, the gel film obtained releases the solvent through a roller installation in an extraction bath (dichloromethane). The gel film is irradiated as in Example 2 at a dose of 5.5 megarads. The irradiated film is stretched in an oven at 120° C. with stretching ratios of 20x and 33x.

The obtained films each had an E-modulus of 50 GPa.
and 85 GPa. The creep property of the film (expressed as elongation measured in the same manner as in Example 1) is 1.5 to
It was 2.5%. The film showed only a slight tendency to fibrillation.

Example 4 (comparison) High molecular weight polyethylene (Hyfax-1900, manufactured by Vercules, weight average molecular weight Mw approximately 2 x 106, η
(Decalin, 135°C) = 18.5 fluidity, (Flie
A 5% by weight decalin solution of sswert ) N/Id = 0.32) is passed at about 180° C. into a tape through a Ni-Goo equipped with a forming machine having a rectangular sswert) (2x20 mm) at its end. The tape is then passed through a water bath to transform the solution into a gel that is opaque in appearance but has sufficient mechanical hardness for subsequent transport through roller equipment.

The resulting gel remains containing virtually all solvent;
Pre-stretching is carried out in an oven at a temperature of 90° C. and at a stretching ratio of about 10. In such processes, most of the solvent is removed by forced syneresis during the stretching process along with the hot gas stream flowing into the oven during pre-stretching.

Continuing this pre-stretched tape, use Schuber Penta 7 (
Shw2・benthan) Stretching machine (type A
3851). The drawing machine has been modified and is equipped with a temperature controlled hot plate. Post-stretching is carried out under conditions having a temperature gradient with a maximum temperature of 155°C.

At a total stretch (including pre-stretch) of 40 times, the tape exhibits the following physical properties (measured at room temperature):

E-Modular 7 90GPa Tensile strength 2.3GPa The creep properties of the obtained tape/ribbon were evaluated at elevated temperature (75
℃) tr weight 0.2 GPa - tlI city 1? -100,0
The elongation measured after 00 seconds was 12%.

In the method, the fibrillation tendency increased with higher drawing ratios.

Example 5 The same method as Example 4 was repeated. However, the gel tape obtained by cooling and forming in a water bath is first passed through a dichloromethane bath to extract the solvent (decalin), and then the extracted tape is placed in an inert nitrogen atmosphere with H
Irradiation is performed under the scanner of a VE electron accelerator (3MV). In the irradiation step, the total dose is 3 megarads. After irradiation, the tape was post-stretched using a Schwerpentane stretching machine to give a total stretching ratio of 35 times. At this stretching ratio, the mechanical properties obtained were the same as in Example 1, that is, E-modulus was 99 GPa and tensile strength was 2.30 Pa.

However, the creep properties of such pre-irradiated tapes were very different. Measurements were made under the conditions described in Example 4 at a load Q of 2 GPa and a temperature of 75°C.
The elongation after 0,000 seconds was only 4%. Furthermore, the fibrillation tendency of the pre-irradiated tape was also reduced.

Example 6 A tape was obtained in the same manner as in Example 5, except that the irradiation dose was 7 megarads. The creep level of the obtained tape was 1
．． It was 5%.

Example 7 A tape was obtained in the same manner as in Example 5, except that paraffin was used as the solvent and the gel tape was directly irradiated before extraction. The results are shown below.

Example 8 High molecular weight polyethylene (Hostarene Glue 41) having a weight average molecular weight of about 1.5
2. A 4% by weight decalin solution (manufactured by Ruhl Hemi/Hoechst) was added to a 2.5×30
It is extruded through a rectangular slit-like opening with dimensions +a+. The extrudate is passed through a water bath at 50°C, a step that converts the clear, viscous solution into a gel-like material that is sufficiently hard to pass through a roller facility into an extraction bath containing trichlorethylene. Grant. After extraction and pre-drying, the tape was irradiated with electrons according to the method of Example 5 and post-stretched according to the method of Example 4 in a Schwerpentane drawing machine. The results are shown below.

Claims (1)

[Scope of Claims] (1) A linear polyalkene solution containing at least 60% by weight of solvent is transformed into a film-like or tape-like product at a temperature above the gelling temperature of the solution, and the product is transformed into a film-like or tape-like product below the gelling temperature. The resulting gel-like film or tape is stretched at elevated temperatures with or without removal of at least a portion of the solvent to have high tensile strength, high modulus and low creep and low fibrillarity. A process for producing polyalkene films and tapes having a weight average molecular weight of at least 4 x 10'', characterized in that the gel cast product obtained after cooling is subjected to radiation lamination before or during said stretching. Method for producing films and tapes. (2) The method according to item (1) above, wherein the films and tapes are maintained in an oxygen-free atmosphere during radiation irradiation and/or between radiation irradiation and stretching. (3) Gel film or The manufacturing method of item (1) or item (2) above, in which the tape is exposed to electron beam irradiation. (4) Items (1) to (3) above, in which irradiation is performed at an irradiation level of 1 to 10 megarads. (5) The manufacturing method according to any one of paragraphs (1) to (4) above, in which irradiation is carried out at an irradiation level of 3 to 7 megarads;
(6) A polyalkene tape obtained by the method described in any one of items (1) to (5) above. (7) A polyalkene film obtained by the method described in any one of items (1) to (5) above. (8) A product manufactured in whole or in part by the tape or film of item (6) or item (7) above.