POLYETHYLENE MULTIFILAMENT YARN

Abstract

 Novel polyethylene multifilament yarn having high strength and high modulus and being substantially free from cohesion between single yarns is provided by a novel process which comprises employing a dry-wet spinning or gel-wet spinning method, drying single yarns containing an extractant separately from each other by vibrating them using a turbulent air flow, and heat-treating them under tension at temperatures in a specific range before drawing.

Description

Field of the Invention

[0001] The present invention relates to a polyethylene multifilament yarn which has a high tenacity and initial modulus, preferably a high knot strength and is substantially free from cohesion between single filaments.

Description of the Prior Art

[0002] Recently a fiber of light weight having a high tenacity and initial modulus has been desired as fiber materials for various kinds of industrial use in order to impart the product therefrom to an energy saving effect and high level of function.

[0003] As the method for producing such a fiber having a high tenacity and initial modulus there have been proposed, for example, in Japanese Unexamined Patent Publication Nos. 55-107506, 56-15408 and 59-216912 to 216914 the methods which comprise spinning from nozzles and cooling a semi-dilute solution of polyethylene having super-high molecular weight to form gel filaments containing solvent, drying the resulting gel filaments to remove solvent therefrom and heat-drawing them, or, in place of two steps of drying and-heat-drawing, heat-drawing them simultaneously with removing solvent.

[0004] But according to these methods only a multifilament yarn having cohesion between single filaments is obtained because such a cohesion is caused during solvent-removing step.

[0005] Since a multifilament yarn having cohesion between single filaments lacks flexibility and loses its strength to a great degree when being subjected to heat-treatment and is insufficient in adhesion ability with resin when being used for the composite material of yarn and resin, a polyethylene multifilament yarn obtained according to the above-mentioned methods is not suitalbe for a fiber material for industrial applications.

[0006] As a method for prevending this cohesion between single filaments there is described in Japanese Unexamined Patent Publication No. 58-5228 a method which comprises introducing gel filaments containing solvent into the extraction bath and removing solvent therefrom with an extractant, drying them, and heat-drawing them.

[0007] But, even if a polyethylene multifilament yarn is produced according to this method, the resulting multifilament yarn still has cohesion between single filaments though the degree of cohesion can be reduced, because cohesion is caused during drying step. Therefore, also a polyethylene multifilament yarn obtained by this method is not suitable for a fiber material for industrial applications.

[0008] The lower a polymer concentration of spinning solution is, the more frequently this cohesion occurs. And it is necessary so as to enhance a tenacity and initial modulus of the resulting fibers to use polymer with as higher molecular weight as possible and to extrude a spinning solution with as lower polymer concentration as possible. Consequently, this unfabourable cohesion between single filaments is getting more serious when a multifilament yarn having superior physical properties is tried to obtain.

[0009] The cause that this cohesion between single filaments occurs is not certain but may be supposed that each gel single filament obtained by spinning the polymer solution and cooling it is in a swelling state containing a large amount of solvent and, when gathered in the same way as employed in the conventional spinning method, such gel filaments adhere each other intimately to form cohesion between single filaments because of the swelling state mentioned above.

[0010] In fact, a gel single filament, especially in the non-crystallized part, is in such a state that the solvent is super-cooled, which may be supposed to be one cause for the formation of cohesion which takes place in collecting gel single filaments.

[0011] The other possible cause is that since a multifilament to be subjected to drying step contains solvent between single filaments, the single filaments are dissolved in surface portion with the solvent which is heated during the drying step, and a cohesion between single filaments occurs owing to thus dissolved surface portion.

[0012] On the other hand, it may be possible to obtain a multifilament yarn free from cohesion between single filaments by separating physically the multifilament yarn obtained once according to the conventional methods mentioned above into each single filament, that is, by removing out cohesion with a physical power, but such a separating action renders the multifilament yarn free from cohesion to have a much lower tenacity and initial modulus.

[0013] Accordingly, it has been considered to be impossible in this field to obtain a polyethylene multifilament yarn having a high tenacity and initial modulus and being free from cohesion between single filaments.

[0014] Speaking generally about the knot strength of fiber, it is difficult to make the most of the tenacity of fiber in the use for industrial applications wherein the knotting of fiber is necessary, if the fiber has a low knot strength. And it is also difficult to impart a high knot strength to a general high tenacity and modulus fiber.

[0015] For instance, a whole aromatic polyamide fiber has only 6 g/d of knot strength in spite of having a high level of tenacity, e.g. 22 g/d. As for a carbon fiber (for example, having 29 g/d of tenacity), it is impossible to even form a knot.

Disclosure of the Invention

[0016] It is an object of the present invention to provide a polyethylene multifilament yarn suited for use in industrial applications which has a high strength and initial modulus, preferably a high knot strength, and is substantially free from cohesion between single filaments.

[0017] It has been found that the object of the present invention can be attained by a novel polyethylene multifilament yarn from a polyethylene having a weight average molecular weight of 700,000 or more which has a single filament denier of 3 d or less, a single filament tenacity of 40 g/d or more, ... and a single filament initial modulus of 1200 g/d or more, and does not have a structure showing a long period in the small angle X-ray scattering measurement, and has both a γ-dispersion peak height of tan 6 of 0.017 or less in the measurement of dynamic modulus and a dynamic viscoelasticity E' value at 100 °C of 600 g/d or more, and is substantially free from cohesion between single filaments.

[0018] The object of the present invention can be preferably attained by a specific polyethylene multifilament yarn having 15 g/d and more of knot strength in addition to the above-mentioned characteristics or that obtained by a gel-wet spinning method.

Description of the Preferred Embodiment of the Invention

[0019] Polyethylene used in the present invention may include a modified polyethylene obtained by copolymerizing ethylene and at least one other ' monomer, the latter being in not so large amount as impairing a technical effect of the present invention, e.g. 10 mole and less percents and, for example, being selected from the other alkene such as propylene, butylene, pentene, hexene, and 4-methylpentene, and vinyl monomer capable of being copolymerized with ethylene. A polyethylene multifilament yarn of the present invention may consist of a mixture of polyethylene with a small amount of the other polyalkene.

[0020] Molecular weight of a polyethylene used in the present invention is necessary to be weight average molecular weight of 700,000 and more, preferably 2,000,000 and more, preferabley 3,000,000.

[0021] Generally speaking, it can be said that the higher is the average molecular weight of polyethylene, the less becomes an amount of defect found, for example, in the molecular chain end inside of the fiber thereof and the higher tenacity has it, and consequently it is necessary to use a polyethylene having weight average molecular weight of 700,000 and more so as to obtain a polyethylene multifilament yarn consisting of single filaments having a tenacity of 40 g/d or more.

[0022] A denier of a single filament of polyethylene multifilament yarn of the present invention is necessary to be 3 d or less, preferably 1.5 d or less, and more preferably 1 d or less.

[0023] Generally speaking, there is a tendency that the lower is the denier, the higher becomes the tenacity, so it is necessary to make a denier of single filament 3 or less in order to obtain a single filament tenacity of 40 g/d or more.

[0024] In the present invention a single filament tenacity of multifilament is necessary to be 40 g/d or more, preferably 50 g/d or more, more preferably 60 g/d or more, and most preferably 70 g/d or more.

[0025] In case that a single filament tenacity of multifilament is less than 40 g/d, it is necessary to consume more amount of the multifilament for obtaining the same finished product therefrom and, consequently, such a finished product needs more energy for its transportation. That is why such a multifilament is not suited for use in industrial applications.

[0026] An initial modulus of single filament of the present multifilament yarn is necessary to be 1,200 g/d or more, preferably 1,500 g/d or more, more preferably 1,800 g/d, and most preferably 2,000 g/d.

[0027] When an initial modulus of single filament is less than 1,200 g/d, it becomes necessary to use more amount of multifilament yarnfor the same finished product therefrom, and such a finished product needs more energy for its transportation. That is why such a multifilament yarn is not suited for use in industrial applications.

[0028] A multifilament yarn of the present invention does not show a long period structure in the small angle X-ray scattering measurement. A fiber which shows a long period structure in this small angle X-ray scattering measurement has a big structure difference between crystalline region and amorphous region thereof, that is to say, such a fiber has such a structure that a molecular chain inside of fiber is not sufficiently extended.

[0029] For this reason such a fiber neither has a single filament tenacity of 40 g/d or more nor a single filament initial modulus of 1,200 g/d or more.

[0030] The multifilament yarn of the present invention is necessary to have a γ-dispersion peak (peak approximately near -130 °C) height of tan6 in a dynamic viscoelasticity measurement of 0.017 or less, preferably 0.013 or less, more preferably 0.010 or less and to have a dynamic modulus E' value at 100 °C of 600 g/d or more, preferably 1,000 g/d or more. A height of y-dispersion peak of tanδ in a dynamic viscoelasticity measurement represents an amount ratio of the amorphous region and that the higher is this height, the smaller is the amorphous region.

[0031] On the other hand, the value of dynamic modulus E' falls down proportional to a measurement temperature and keeps high even at a high measurement temperature, if a degree of crystallinity and orientation of fiber is high, which means that the fiber has more perfect fibrous structure.

[0032] Accordinly, the fiber of which height of γ-dispersion peak of tan6 in a dynamic viscoelasticity measurement is higher than 0.013 and of which dynamic modulus of elasticity E' at 100 °C is less than 600 g/d has both a low degree of crystallinity of orientation and an insufficient fibrous structure. And such a fiber has neither a single filament tenacity of 40 g/d or more nor a single filament initial modulus of 1,200 g/d or more.

[0033] The multifilament yarn of the present invention should be substantially free from cohesion between single filaments. By the wording "substantially free from cohesion" it is meant that a cohesion portion should be 2 or less per 10 meters of multifilament yarn. If the multifilament yarn is not free from cohesion between single filaments, the multifilament yarn comes to lack flexibility and to lose its tenacity when it is heated and to have a low adhesion force with resin, and consequently is not suited for use in industrial applications.

[0034] The multifilament yarn of the invention preferably has a single filament knot strength of 15 g/d or more. In the use for industrial applications wherein a knotting action is needed, for example, applications for fishing line or rope, it is difficult to make the most of the tenacity of fiber if the fiber has a low knot strength.

[0035] A novel polyethylene multifilament yarn of the present invention can be provided by a novel process described, for example, in the following.

[0036] Polyethylene having a weight average molecular weight of 700,000 or more is dissolved into solvent to prepare 1 to 8 wt% solution of said polyethylene. This solution is extruded from the nozzle having a plurality of holes through the layer of air or inert gaseous atmosphere into a spinning bath consisting of coagulating agent or a spinning bath consisting of cooling agent in the upper layer and coagulating agent in the lower layer, to form a coagulated multifilament. And then the coagulated multifilament is introduced into an extracting bath consisting of extractant to extract solvent therefrom. A multifilament containing an extractant is dried separately from each other of single filament by vibrating it using a turbulent gas flow. And then thus dried multifilament is subjected to heat-treatment under a stretch condition at 70 °C to 130 °C and is drawn at 125 °C to l55 °C in the ratio sufficient to have a single filament denier of 3 d or less, a single filament tenacity of 40 g/d or more and a single filament initial modulus of 1,200 g/d and more.

[0037] The characteristics of such a novel process exist in to employ a dry-wet spinning method (that is, the method wherein a polymer solution is extruded through an air or inert gas atmosphere into a spinning bath consisting of an extractant) or a gel-wet spinning method (that is, the method wherein a polymer solution is extruded through an air or inert gas atmosphere into a spinning bath consisting of a cooling agent in the upper layer and an etractant in the lower layer), to dry a multifilament separately each other of single filament by vibrating it using a turbulent air flow, and to subject a multifilament to a heat-treatment under a stretch condition at a specific temperature before drawing it.

[0038] The process for producing a polyethylene multifilament yarn of the present invention is described in details in the following.

[0039] As a solvent for polyethylene there is preferably used the solvent satisfying to have a good solubility with polyethylene, to be easy to be extracted with an extractant, and to have a boiling point higher than a dissolving temperature or spinning temperature. For example, as such solvents there are preferably employed decaline, paraffin oil, tetraline and kerosene.

[0040] A polyethylene concentration of the solution should be lower as the polyethylene used has a higher molecular weight. -The concentration should be adjusted to provide a solution having a suitable viscosity in light of uniformity in dissolving, stability in extruding, spinnability, and stability in drawing. But the polyethylene concentration should not be lower than one wt. % because not only a productivity of fiber comes down but also the resulting coagulated multifilament becomes so pliant that a running multifilament is unstable and is easy to undergo an unfabourable effect by the outside trubulence, and therefore a multifilament superior in uniformity cannot be obtained.

[0041] Although a productivity of fiber is superior when a higher polyethylene concentration is employed, preferably it should not be higher than 8 wt. % because in such a concentration a viscosity of solution gets too high and an entanglement of polyethylene molecular chain in the polyethylene solution occurs too much, and because, in the concentration too high to be appropriate, not only the dissolving of polyethylene into a solvent cannot be carried out uniformly and the spinnability of polyethylene solution falls down, but also a multifilament obtained after removing out the solvent cannot be drawn at a sufficiently high draw ratio only to provide a multifilament having low physical properties.

[0042] Considering that, for the purpose of attaining an enhanced tenacity and initial molulus, it is necessary to draw a multifilament at a high ratio and it is preferable to spin a dilute solution of polyethylene having a higher molecular weight, it is more preferable to spin a solution having a polyethylene concentration of 1 -- 7 wt. % of polyethylene having a weight average molecular weight of 2,000,000 or more and it is the most preferable to spin a solution having a polyethylene concentration of 2 -- 5 wt. % of polyethylene having a weight average molecular weight of 3,000,000 or more.

[0043] It is preferable that a dissolution temperature of polyethylene and a temperature of the polyethylene solution at the time of spinning are almost the same. The temperature is chosen appropriately from the range of approximately 120 °C to 250 °C. For instance, approximately 170 °C is suitable when a - solution of a polyethylene concentration of 3 % of a weight average molecular weight of 2,000,000 is spun.

[0044] The polyethylene solution is extruded from the nozzle having a plurality of holes through the layer of air or inert gaseous atmosphere into a spinning bath consisting of coagulating agent or a spinning bath consisting of cooling agent in the upper layer and coagulating agent in the lower layer. The inert gas means in the present invention a gaseous material at a normal temperature which does not coagulate a fibrous solution of polyethylene extruded from the nozzle and does not react chemically with the fibrous solution.

[0045] The distance of the layer of gaseous atmosphere is not restricted, but is appropriate to be 3 to 50 mm.

[0046] When this distance is shorter than 3 mm, there is a fear that the nozzle contacts with the solution surface of a spinning bath when the latter happens to vary, which may cause a breakage of fiber.

[0047] In the other hand, when this distance is longer than 50 mm, a safe running of a fibrous solution extruded from the nozzle becomes difficult, which results in the problem that there occurs a cohesion between single filaments in this inert gaseous atmosphere even owing to a slight shaking of them. A small amount of solvent may be evaporated out from a fibrous extruded solution, but almost the all solvents are extracted with a coagulating agent in a spinning bath or an extractant in a extracting bath.

[0048] If a coagulated multifilament is prepared by coagulating the surfaces of single polyethylene filaments to be still in the fibrous solution state while said single polyethylene filaments separate each other in a spinning bath, there cannot occur a cohesion between single filaments even if they are collected in the same manner as in the usual spinning process. That is why a spinning bath consisting of a coagulating agent or consisting of a cooling agent in the upper layer and a coagulating agent in the lower layer is employed in the present invention. When a spinning bath consisting of a coagulating agent is employed, there is employed for prevending a multifilament from cohesion between single filaments such a coagulating agent as neither dissolving nor swelling polyethylene at the coagulating temperature employed and as having a good compatibility with solvent, and as being volatile at a room temperature. For example, there can be used acetones, alcohols such as methanol and ethanol, methylene chloride, trichlorotrifluoroethane and an azeotrope of methylene chloride and trichlorotrifluoroethane.

[0049] When a spinning bath consisting of a cooling agent in the upper layer and a coagulating agent in the lower layer is employed, a cooling agent which has a specific gravity lower than that of a coagulating agent and has no compatibility with solvent is preferably. used. That is because the coagulated fiber becomes coarse in its surface and the drawn fiber obtained therefrom has only poor properties if the extruded fibrous solution is coagulated rapidly. Accordingly it is preferable to form a gel multifilament in advance before contacting the fibrous solution with a coagulating agent so as to prevent a rapid coagulation. For this reason there is preferably used such a cooling agent as having not a compatibility with solvent and as being capable of forming a gel multifilament in the cooling layer.

[0050] As such a cooling agent water is the best in light of safety and economy, but any liquid having the above-mentioned characteristics can be employed.

[0051] A suitable depth and temperature of the cooling layer depends upon a spinning temperature and an amount of output of a spinning solution. It is preferable to adjust the cooling layer to have such depth and temperature that the extruded fibrous solution can be cooled below its gelation temperature there.

[0052] Usually, the range of 3 cm to 30 cm is appropriate as a depth of the cooling layer and the range of 0 °C to 40 °C is appropriate as a temperature thereof.

[0053] The gel multifilament formed in the cooling layer of the upper part is coagulated and a partial extraction of solvent therefrom is carried out both in the coagulating layer of the lower part. Thus a coagulated multifilament is formed. In this coagulating layer, single filaments run separately from each other and a coagulated multifilament is formed by coagulating the surfaces of single filaments while they are kept separate from each other, and therefore a cohesion between single filaments can be prevended.

[0054] In order to have the single filaments run separately from each other in the coagulating layer it is preferable to do the same also in the cooling layer, and for this puopose a depth of the cooling layer should be adjusted to be within a suitable range.

[0055] A coagulating agent used for the coagulating layer in the lower layer is selected from the coagulating agents which have a specific gravity higher than that of the cooling agent and have a good compatibility with solvent, and are volatile at a room temperature.

[0056] For example, there can be used as a coagulating agent methylene chloride, trichlorotrifluoroethane tetrachlorodifluoroethane, and azeotrope of methylene chloride and trichlorotrifluoroethane.

[0057] And there may be also used any mixture of the above-mentioned compound or mixture with the solvent as a coagulating agent.

[0058] The suitable depth and temperature of the coagulating layer vary depending upon a spinning temperature, an amount of output of spinning solution and a coagulating ability of a coagulating agent, but the coagulating layer is preferable to have such depth and temperature that the surfaces of the single filaments can be substantially coagulated while the single filaments are running separately from each other.

[0059] In the ordinary case the range of from 0 °C to 40 °C is suitable as a temperature of the coagulating layer.

[0060] The multifilament coagulated in the spinning bath is then introduced into a extracting bath and, there the residue solvent inside the coagulated multifilament is extracted.

[0061] 'As an extractant, there can be used any that has an ability of extracting the residue solvent inside the coagulated multifilament, and there can be used the same as the coagulating agent discribed above. And there can be used two kinds of extractant in the present invention. For example, the residue solvent inside the coagulated multifilament is extracted with the first extractant, followed by the extraction with the second extractant.

[0062] A multifilament obtained by extracting the residue solvent in the extracting bath is then sent to the drying step and there it is dried while being vibrated using a turbulent gas flow. The single filaments become to be separate from each other by catching the turbulent gas flow and are dried in its state, which can prevend the single filaments from making a cohesion. As this turbulent gas, there can be used any that does not react chemically with the extractant.and is in a gaseous state at a normal temperature. Usually air or nitrogen gas is employed.

[0063] A pressure and flow rate of turbulent gas thus flowed are preferable to be sufficient to render the single filaments to be separate from each other.

[0064] As mentioned above it is important in order to obtain a polyethylene multifilament yarn free from cohesion between single filaments that a polyethylene fibrous solution passing the gas atmosphere layer is coagulated in its surface of each single filament while the single filaments are kept to be separate from each other and the single filaments taken out from the extracting bath are dried while they are kept to be separate from each other by vibrating them using a turbulent gas flow.

[0065] Thus dried multifilament is subjected to a heat-treatment under a stretch condition at 70 °C to 130 °C.

[0066] Within this temperature range of heat-treatment a crystallization of polyethylene is easy to be accelerated and a lamella crystal is formed. It is supposed that at that time the molecules existing in the amorphous region are brought into inside the crystal and, as a result, an amount of entanglement between molecular chains decreases. The molecular chains become easy to be extended by means of having an amount of entaglement between molecular chains decrease by the heat-treatment of the dried multifilament.

[0067] At the next step, the multifilament heat-treated under a stretch condition is drawn at 125 °C to 155 °C in the ratio sufficient to provide a multifilament having a single filament tenacity of 40 g/d or more, and a single filament initial modulus of 1,200 g/d or more. This drawing is carried out in the two stages or more, preferably three stages or more . At the first half of drawing it may be carried out in a high draw velocity, but at the second half of drawing it is preferable to carry out drawing repeatedly in a relatively low draw velocity. And it is preferable to make a draw region as long as possible. For example, when a multifilament is drawn using a hot-plate, the hot-plate having 2 meters or more long is preferably employed.

[0068] As the drawing proceeds, it is carried out slowly and steadily in the lower velocity and along the longer region, whereby the molecular chains are unfolded from lamella crystal and re-crystallized in the extended state.

[0069] As mentioned above, the polyethylene multifilament yarn consists mainly of the extended molecular chain crystal, namely, crystal having a highly completed structure, and therefore it comes to have a single filament tenacity of 40 g/d or more and a single filament initial modulus of 1,200 g/d or more.

[0070] And the preferred polyethylene multifilament yarn of the present invention has a knot strength of 15 g/d or more though its relation with the structure is not clear. Such a fiber having not only a high tenacity and modulus but also a high knot strength can be said to be unique because in general it is difficult to satisfy the both properties at the same time.

[0071] The invention will be further illustrated by the examples below but not be restricted to them.

[0072] Tensile strength, initial modulus, dynamic modulus, and small angle X-ray scattering of the multifilament were measured in the following conditions.

Measurement condition of tensile strength and initial modulus

[0073] Atmosphere: 20°C, relative humidity: 65 %

[0074] Apparatus: "TENSILON-UTM-4" Tensile Tester manufactured by Toyo Baldwin Co. Ltd.

[0075] Sample: single filament (250 mm)

[0076] Pulling speed: 300 mm/minute

[0077] Initial modulus: it was determined from the inclination at the origin of Stress/Strain curve.

Measurement condition of dynamic modulus

[0078] Apparatus: type DDV-II manufactured by Toyo Baldwin Co. Ltd.

[0079] Frequency: 110 Hz

[0080] Heating speed: 3 °C/minute

Measurement condition of small angle X-ray scattering (photographic method)

[0081] Apparatus: type Ru-200 manufactured by Rikagaku Denki Co. Ltd.

[0082] X-ray source: Cu Ka ray (using Ni filter)

[0083] X-ray power: 50 kV, 150mA

[0084] Diameter of slit: 0.3 mmφ

[0085] Radius of lens: 400 mm

[0086] Exposure: 120 minutes

[0087] Film: Kodak "DEF-5"

[0088] A long period was sought using the equation of Bragg based upon the position of the interference spot (or line) on the meridian of small angle X-ray scattering picture. No appearance of the interference spot (or line) on the meridian was judged to mean that there was not recognized a structure showing a long period.

Judgement whether or not there is a cohesion of single filaments

[0089] Non-drawn or drawn multifilament yarn was observed by the naked eye along its length direction. And a multifilament having cohesion only at 2 or less parts per 10 m length was defined to be substantially free from cohesion between single filaments, and an existence of cohesion at the parts more than 2 was judged to mean that the multifilament is not substantially free form cohesion between single filaments.

Examples 1 to 4

[0090] Linear polyethylene having a weight average molecular weight of 3x10⁶ was dissolved Into decaline at 170 °C to prepare a solution having a polyethylene concentration of 3 wt%. This solution of 175 °C was extruded Into a spinning bath consisting of acetone containing 20 % decallne of 20 °C from a nozzle having ₁₅ holes (hole diameter: 1) through the air layer which was 5 long from the nozzle, and thus was coagulated. The flow rate of the solution was 30 cc/minute. The coaoulated multifilament was collected and withdrawn at a speed of 7.5 m/minute.

[0091] Thus obtained multifilament was introduced into the extractino bath consisting of acetone of 20 °C to extract decaline remaining therein and then was dried by vibrating it using a turbulent air of a room temperature. Then the multifilament was heat-treated keeping a constant lenoth by using the heated roll of 90 °C and was wound up. The wound multifilament was substantially free from cohesion between single filaments and was superior in opening. Then the wound multifilament was drawn repeatedly at a low feed speed. Table 1 shows the draw condition used and the properties of the resulting drawn multifilament.

[0092] Also durino the drawing step there happened no consign between single filaments.

Examples 5 to 7

[0093] The same solution as that of the examples 1 to 4 was spun In the same manner as In the examples 1 to 4 except using the nozzle having 30 holes (diameter: 0.5 ) and making the total flow rate 20 cc/minute. The successive treatments of extracting. drying. and heat-treating keeping a constant length were carried out in the same manner as in the examples 1 to 4. The heat-treated multifilament was continuously drawn at one stage at 140 °C and then was wound up. The drawn multifilament was further drawn at a low feed speed. Also in this case there happend no cohesion between single filaments and the drawn multifilament superior in opening was obtained. Table 2 shows the draw condition used and the properties of the resulting drawn multifilament.

Comparative example 1

[0094] Linear polyethylene having a weight average molecular weight of 3x10⁶ was dissolved Into decaline at ₁₇₀'C to prepare a solution having a polyethylene concentration of 3 wt%. This solution of 175°C was extruded into water from the nozzle having 15 holes (diameter of the hole: 1 ) through the air layer of 20 °C which was 5 mm long from the nozzle and thus was gelatinized by cooling it to prepare a gel multifilament. The flow rate of the solution from the nozzle was 30 cc/minute. Thus obtained gel multifilament was collected and withdrawn at a speed of 7. 5 m/minute.

[0095] Said gel multifilament was then introduced into the extracting bath consisting of acetone of 20 °C to extract decaline remaining therein. and then was dried in such a state that the single filaments were collected. and was wound up. This multifilament was drawn at the two stages in the following condition. Thus obtained drawn multifilament had a tenacity of ₄₆ g/d and an initial modulus of 1320 g/d.

[0096] And, the drawn multifilament had a γ-dispersion peak of tan δ of 0.019 and an E- value at 100 °C of 880 9/d.

[0097] The obtained multifilament yarn had a lot of cohesions between single filaments and was difficult to open neatly.

[0098] The gel multifilament taken out from the spinning bath which was obtained accordino to the spinning method mentioned above was dried at 60 °C. but the resulting mulifilament had a lot of cohesions between single filaments and could not be opened at all.

[0099] And the dried multifilament was drawn under the draw condition mentioned above. but the resulting drawn multifilament had a lot of cohesions between single filaments and could not be opened at all.

Example 8

[0100] Linear polyethylene havino a weight average molecular weight of 2.2x10⁶ was dissolved Into decaline of 170°C to prepare a solution having a polyethylene concentration of 3.5 wt.%. This solution was spun. extracted, dried, and heat-treated keeping a constant lenoth in the same manner as In the examples 1 to 4. The resulting multifilament was drawn under the condition described in the following Table 3.

[0101] The drawn multifilament had a sinole filament denier 1.1 d, a tenacity of 63 g/d. and an initial modulus of 2040 g/d. And the drawn multifilament did not show a lono period structure in the small angle X ray scattering. had a γ-dispersion peak of tan δ of 0.009. and had a E value at 100 °C of 1720 9/d. This drawn multifilament yarn was free from cohesion between single filaments and was superior in opening.

Example 9

[0102] The same solution as that of the example 1 was extruded into the air layer from the nozzle having 30 holes (hole diameter: 0.5). and was passed by 5 there, and thereafter was cooled, gelatinized, and coagulated In the spinning bath consisting of water In the upper layer and trichlorotrifluoroethane In the lower layer. The flow rate of the solution from the nozzle was 30cc/minute. The coagulated multifilament was collected and wound up at a speed of 7.5m/minute.

[0103] The depth of water layer was 70 and that of trichlorofluoroethane layer was 250.

[0104] The coagulated multifilament was then Introduced into the extractino bath consisting of trichlorotrifluoroethane of 10 °C to extract decaline remaining therein. and, thereafter, was dried and heat-treated keeping a constant length. After this heat-treatment, the multifilament was continuously drawn In one stage at 130 'C and was wound up.

[0105] This drawn multifilament was further drawn in the same manner as In the example 5. Thus obtained multifilament had a single filament denier of 0. 71 d_. a sigle filament tenacity of 57 g/d and an initial modulus of 1700 g/d. And there was not recoonized a long period structure in the small angle X-ray scattering regarding this multifilament. This multifilament had a γ-dispersion peak of tan δ of 0.01₀ and an E' value at 100 °C of 1250 g/d. and was free from cohesion between single filaments.

Example 10

[0106] Linear polyethylene having a weight average molecular weight of 4 x 10⁶ was dissolved into kerosene at 180 °C to prepare a solution having a polyethylene concentration of 5.0 wt %. This solution was extruded into the air layer from the nozzle having 10 holes (hole diameter: 1 mm), and was passed by 10 mm there, and thereafter was cooled, gelatinized, and coagulated in the spinning bath consisting of water in the upper layer and trichlorotrifluoroethane having 30 % kerosene in the lower layer, and then was collected to obtain a coagulated multifilament. The temperature of the spinning bath was 9 °C. The depth of the upper layer (water) was 100 mm and that of the lower layer (trichlorotrifluoroethane) was 200 mm. The flow rate of the solution from the nozzle was 30 cc/minute and the coagulated multifilament was would up at a speed of 15 m/minute.

[0107] The coagulated multifilament was introduced into the extracting bath consisting of trichlorotrifluoroethane of 5 °C to extract kerosene remaining in the multifilament, and thereafter, was dried and heat-treated keeping a constant length in the same manner as in the example 1. After this heat-treatment, the multifilament was drawn in one stage at a draw ratio of 8 at 130 °C and would up.

[0108] This drawn multifilament was further drawn continuously in two stages at a feed speed of 1 m/minute. (second stage of drawing: temperature 143 °C, draw ratio 3.5, third stage of drawing: temperature ₁₄₅ °C, draw ratio 1.4). Thus obtained drawn multifilament had a single filament denier of 1.5 d, a single filament tenacity of 56 g/d, and an initial modulus of 1600 g/d. And there was not recognized a long period structure in the small angle X-ray scattering regarding this multifilament. This multifilament had a Y-dispersion peak of tan 6 of 0.011, and had an E' value at 100 °C of 1300 g/d. And this multifilament was free from cohesion between single filaments.

Example 11

[0109] The drawn multifilament by the one stage drawing method in the same manner as in the example 9 was drawn by 2.5 times at a feed speed of 1 m/minute at 140 ° C, (total draw ratio: 20).

[0110] Thus drawn multifilament had a single filament denier of 1.0-d, a single filament tenacity of 42 g/d, and an initial modulus of 1230 g/d. And there was not recognized a long period structure in the small angle X-ray scattering regarding this multifilament. This multifilament had a γ-dispersion peak of tan δ of 0.016, and had an E' value at 100 °C of 710 g/d. And this multifilament was free from cohesion between single filaments.

Industrial Utilizability

[0111] The polyethylene multifilament yarn of the present invention has an extremely high tenacity and initial modulus, and is substantially free from cohesion between single filaments. Therefore, the polyethylene multifilament yarn of the present invention is flexible and does not undergo a decrease of strength retention when it is heated. Accordingly, it is extremely suited to use for industrial applicaitons.

Claims

₁. A polyethylene multifilament yarn from a polyethylene having a weight average molecular weight of 700,000 or more which has a single filament denier of 3 d or less, a single filament tenacity of 40 g/d or more and a single filament initial modulus of 1200 g/d or more, and does not have a structure showing a long period in the small angle X-ray scattering measurement, and has both a y-dispersion peak height of tan 6 of 0.017 or less in the measurement of dynamic modulus and a dynamic viscoelasticity E' value at 100 °C of 600 g/d or more, and is substantially free from cohesion between single filaments.

2. A polyethylene multifilament yarn of claim -1 which further has a single filament knot strength of 15 g/d or more.

3. A polyethylene multifilament yarn of claim 1 which has a single filament denier of 1.5 or less, a single filament tenacity of 50 g/d or more, a single filament initial modulus of 1500 g/d or more, a y-dispersion peak height of tan 6 of 0.013 or less in the measurement of dynamic modulus, and a dynamic viscoelasticity E' value at 100 °C of 1000 g/d or more.

₄. A polyethylene multifilament yarn of any of claims 1 to 3 which is obtained according to a get-wet spinning method.