JPH0541723B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing polyolefin fibers that have high strength and high modulus and are free from inter-filament adhesion. The fibers are extruded through a gas atmosphere layer into a two-layer spinning bath where they are cooled in the upper layer and coagulated in the lower layer, and after forming a coagulated thread, the solvent is removed using an extractant, and then hot stretching is performed. The present invention relates to a method for producing a polyolefin fiber having high strength and high modulus without sticking between single filaments. (Prior art) In recent years, fibers with extremely high strength and modulus have been produced by spinning a semi-dilute solution of ultra-high molecular weight polyolefin polymer, cooling it to gel, removing the solvent, and subjecting it to ultra-stretching. (Japanese Unexamined Patent Publication No. 56-15408, Journal of
Materials Science.Vol.15, p505-514 (1980),
JP-A No. 58-5228, etc.), and the polyolefin fibers obtained in this way are used for industrial fibers that require high strength and high modulus, such as ropes, slings, etc. It is expected to be useful in Goss reinforcing materials, various resin reinforcing materials, concrete reinforcing materials, etc. However, the high-strength, high-modulus polyolefin fiber produced by the above method has a problem in that sticking occurs between the single yarns during the production process. This adhesion between single yarns causes problems such as a lack of fiber flexibility, a decrease in the overall strength of the fiber, and a decrease in the strength utilization rate during twisting. Despite the expected usefulness of modular polyolefin fibers as mentioned above, these properties cannot be fully demonstrated, making mass production on an industrial scale extremely difficult. is the reality. Regarding the causes of agglutination between single yarns,
Although the details are not clear, each single fiber spun from a solution using the above method and gelled by cooling is in a swollen state containing a large amount of solvent. It is thought that when the single yarns are bundled together, they come into close contact with each other, resulting in agglomeration between the single yarns. In fact, in the non-crystallized portion of the gelled yarn, the solution is simply supercooled, and there are virtually no boundaries between the single yarns. Even in the above method, it is thought that it is possible to avoid sticking between single yarns by mechanically separating each single yarn until the solvent is removed, but as the number of single yarns increases, the device area becomes too large. Mass production on an industrial scale is virtually impossible because the threading work is complicated. In addition, in the so-called "wet-dry spinning method" (a spinning method in which the solution extruded from a nozzle passes through a gas section and then enters a coagulation bath and is coagulated), the single fibers are bundled in the coagulation bath. Since the surface of the single filaments can be coagulated during this time, agglomeration between single filaments can be avoided. However, from the viewpoint of coagulability, it is preferable to use a liquid with a low boiling point.
If a heated solution of a polymer is directly extruded into such a low boiling point coagulant without being cooled and gelled, the coagulant boils around the extruded solution, resulting in a large amount of coagulant evaporation, which is not economical. Furthermore, since rapid coagulation occurs, the surface structure of the coagulated thread becomes rough, making it impossible to obtain high-strength, high-modulus fibers. (Problems to be solved by the present invention) The present inventors aimed to effectively prevent the above-mentioned sticking between single yarns and to produce a polyolefin fiber with high strength and high modulus. As a result of intensive research, we discovered that the cause of the sticking between single yarns was due to the collection of cooled gel yarns into bundles.
First, while the single fibers of the cooled gel yarn are being separated in a spinning bath, the surface of the single fibers is coagulated with a coagulant, and then the remaining solvent is extracted and removed, thereby effectively preventing sticking between the single fibers. Moreover, the yarn obtained in this way does not stick even during the subsequent drying and hot drawing steps, and the dried yarn is heated between the melting temperature of the yarn and a temperature 70°C lower than the melting temperature. It was discovered that fibers with high strength (20 g/d or more) and high modulus (400 g/d or more) can be obtained by hot drawing 8 times or more, and the present invention has been achieved. (Means for solving the problem) That is, the present invention extrudes a heated solution obtained by dissolving a polyolefin polymer having a weight average molecular weight of 5 x 10 ⁵ or more in a solvent through a nozzle, passes through an inert gas atmosphere layer, It is passed through a bath of two mutually immiscible layers, consisting of an upper layer of low specific gravity and immiscible with the solvent and a lower layer of high specific gravity and miscible with the solvent, cooled in the upper layer in the bath, and then partially drained of the solvent in the lower layer. After extracting and coagulating the thread to form a coagulated thread, the solvent is further extracted and removed, and the obtained thread is hot-stretched 8 times or more between the melting temperature of the thread and a temperature 70°C lower than the melting temperature. The present invention provides a method for producing a high-strength, high-modulus polyolefin fiber characterized by the following. The polyolefin polymer used in the present invention is a polymer represented by polyethylene, polypropylene, polybutene-1, poly(4-methylpentene-1), etc., but a mixture of these or a composition of two or more of these monomers may also be used. It may be a copolymer consisting of units. Alternatively, it may be a copolymer containing these monomers as the main component and copolymerizing a small amount of other non-olefin monomers, or a chemically treated polyolefin. Preferred polymers are polyethylene and polypropylene, more preferably polyethylene. The molecular weight of the polyolefin polymer used in the present invention must be 5 x 10 ⁵ or more in terms of weight average molecular weight, and 1 x 10 ⁶ or more is particularly preferred.
If the weight average molecular weight is less than 5×10 ⁵ , the strength and modulus of the resulting fiber will be low, making it undesirable and lacking in usefulness. Further, examples of the solvent used to form the solution of the polyolefin polymer include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and mixtures thereof. It is not limited. Normally, polyolefin polymers do not dissolve at temperatures below 60°C even with these solvents, so they are often heated to temperatures above 100°C, and therefore low boiling point solvents are not preferred. Suitable solvents include derica, xylene, tetralin, cyclohexane, nonane, decane and paraffin oil. Moreover, those that are solid at room temperature such as paraffin wax and naphthalene may also be used. There is no particular limitation on the polymer concentration of the polyolefin polymer solution, and the higher the molecular weight of the polyolefin polymer, the lower the concentration condition is selected. The concentration is selected so as to provide an appropriate solution viscosity from the viewpoint of silk-spinning properties during stretching. However, if the polymer concentration is less than 0.5% by weight, it is not preferable because not only the productivity is poor but also the coagulated yarn is soft and the yarn runnability becomes unstable and susceptible to external disturbances and lacks uniformity. In addition, the higher the polymer concentration, the higher the productivity, but if it exceeds 15% by weight, the viscosity of the solution increases due to increased entanglement of polymer molecular chains in the solution, and spinning This is not preferable because not only the spinnability during stretching deteriorates, but also the stretching ratio during stretching is not sufficiently increased and only poor physical properties are obtained. Therefore, the appropriate polymer concentration of the polyolefin polymer solution is in the range of 0.5 to 15% by weight. There is no particular limit to the polymer dissolution temperature when creating the solution, and it is approximately the same as the solution temperature during spinning, but it varies depending on the solvent and polymer molecular weight, and approximately
An appropriate temperature is set in the range of 120-250°C. In carrying out the method of the present invention, the polyolefin polymer solution is first heated and extruded from a nozzle through an inert gas atmosphere layer into a spinning bath. The inert gas mentioned here is one that does not cause coagulation or chemical reaction with the fibrous solution extruded from the nozzle, and air or nitrogen is mainly used. There is no particular limit to the distance of this gas atmosphere layer, but a range of 3 to 50 mm is appropriate;
If it greatly exceeds 50 mm, it becomes difficult for the fibrous solution extruded from the nozzle to run stably, and problems such as slight yarn wobbling may easily cause sticking between single yarns in this gas atmosphere layer, which is not preferable. In addition, although a small amount of solvent may evaporate from the extruded fibrous solution in this gas atmosphere layer, most of the solvent is absorbed by the coagulant in the next spinning bath and the extractant in the subsequent extraction bath. Extracted and removed. In the present invention, the spinning bath is composed of a cooling liquid in which the upper layer has a low specific gravity and is immiscible with the solvent, and the lower layer has a coagulant which has a high specific gravity and is miscible with the solvent. This bath has a two-layer structure. This spinning bath has two different functions: cooling of the polymer solution in the upper layer and coagulation of the polymer solution and partial extraction of the solvent in the lower layer. Water is most suitable as a cooling liquid from the viewpoint of safety and economy, but it is a liquid that has the above characteristics, that is, it is immiscible with solvents, is a non-solvent for polymers, and has a specific gravity higher than that of the coagulant in the lower layer. Any small and immiscible liquid can be used. Examples of the coagulant include hydrocarbons or hydrocarbons containing chlorine or fluorine, such as methylene chloride, carbon tetrachloride, chloroform, ethane trichloride trifluoride, and mixtures thereof. The depth and temperature of the spinning bath vary depending on the spinning temperature, discharge rate, coagulating ability of the coagulant, etc. The upper cooling layer should be deep enough to cool the extruded solution below the gelling point. and temperature are preferred, but the entire solution need not necessarily be below the gel point. In addition, in the lower coagulation layer, the depth and temperature should be selected so that the surface layer of the yarn is substantially coagulated while the yarn is separated and running, and all the solvent in the yarn is extracted here. There's no need to worry about it. The coagulated filaments change their running direction using turn guides in the coagulation layer and exit the spinning bath. At this time, the cooling liquid from the upper layer is carried between the bundled single filaments by the turn guides and enters the next extraction bath. go. For this reason, the surfaces of the single yarns inside the yarn bundle are covered with the cooling liquid, preventing extraction.
Therefore, it is desirable to provide a partition wall on the side where the coagulated yarn exits the spinning loop so that the coagulated yarn does not pass through the upper cooling liquid layer. The yarn coagulated by the coagulant in the spinning bath is then sent to an extraction bath, where the remaining solvent is extracted and removed, and then sent to a drying process while still containing the extractant. It is preferable to use the same extractant as the above-mentioned coagulant, but it is also possible to use a different extractant. Drying is carried out by contacting the yarn with drying rolls or by exposing it to a stream of heated air. Also, at this time, the extractant may be replaced with a second extractant and then dried. For example, replacing a flammable first extractant with a second, less flammable extractant. The yarn thus dried is then subjected to a drawing process. There are various means for stretching, such as a hot plate, a heating roll, and a drying tube, and there are no particular limitations. Stretching is performed at a temperature of 70% compared to the melting temperature of the dry yarn.
It is necessary to carry out at a temperature between 15 °C and lower. In order to increase the stretching ratio as high as possible and increase the strength, a temperature between the melting temperature of the dry yarn and a temperature 40° C. lower than the melting temperature is more suitable. If the stretching is carried out at a temperature that is 70°C or more lower than the melting temperature of the dry yarn, the stretching ratio will not be sufficiently increased and only yarn with poor physical properties will be obtained. Furthermore, if the stretching temperature exceeds the melting temperature of the dry yarn, the yarn will be melted and thus cannot be stretched. It is necessary to set the stretching ratio to 8 or more. If the stretching ratio is less than 8, sufficiently high strength and modulus cannot be achieved, resulting in a lack of usefulness. In order to obtain high quality physical properties, it is preferable to use a stretching ratio of 12 or more. Although the method for manufacturing multifilaments has been mainly described above, the present invention can also be applied to manufacturing monofilaments. Next, the present invention will be specifically explained using Examples and Comparative Examples. The yarn physical properties shown below were measured using Tensilon manufactured by Toyo Baldwin Co., Ltd. under the following conditions. Yarn sample: Single yarn (threads that cannot be defibrated are used as multifilament) Trial length: 250mm Pulling speed: 300mm/min Atmosphere: 20℃, 65% relative humidity Also, defibration properties are determined by the naked eye, and the symbols have the following meanings. It shows. ○: Substantially no agglutination between single yarns △: Partially agglutination between single yarns ×: Significant agglutination between single yarns The melting temperature is determined by the following method. (1) Stretch using a 120cm hot plate whose surface temperature is the same as the melting point of the dried yarn measured by DSC, and determine the maximum stretching ratio. (2) When the temperature of the hot plate is raised while stretching at this maximum stretching ratio, the yarn breaks at a certain temperature.
This temperature is defined as the melting temperature. Example 1 Linear high-density polyethylene with a weight average molecular weight of 3.0×10 ⁶ was dissolved in decalin at a temperature of 160°C.
% solution by weight, the solution is extruded into an air layer through a nozzle with a hole diameter of 0.5 mm and a number of holes of 15, and after passing through the air layer for a distance of 8 mm, a two-layer structure is formed in which the upper layer is water and the lower layer is methylene chloride. The structure was solidified after cooling in a spinning bath. The temperature of the spinning bath is 10℃, the thickness of the upper layer (water) is 20 mm, and the distance that the yarn travels in the lower layer (methylene chloride) is 800 mm (300 mm is the part where the single yarn separates and travels). did. The total discharge rate from the nozzle is 10c.c./min, and the coagulated yarn is
It was picked up at a speed of 7.5m/min. The yarn was then passed through an extraction bath of methylene chloride at 10°C to extract the dericane remaining in the yarn, dried with heated rolls at 60°C, and wound up. This dried yarn was drawn at various magnifications shown in Table 1 at a surface temperature of 140° C. and a hot plate having a length of 120 cm. Table 1 also shows the mechanical properties of the drawn yarn. The yarn feeding speed during drawing is 20cm/
It was a minute. As is clear from the results in Table 1, there is no sticking between single yarns in both the yarns that have been dried after solvent removal and the yarns that have been hot-stretched. Further, the strength of the drawn yarn becomes 20 g/d or more only when the drawing ratio becomes 8 times or more, and the modulus also becomes a value exceeding 400 g/d.

[Table] Comparative Example 1 The same spinning dope as in Example 1 was prepared using a spinning dope with a pore diameter of 1 mm and a
A rubber-like thread was obtained by extruding the product from 20 nozzles through an 8 mm air layer into 15°C water and cooling. The total discharge amount from the nozzle and the spinning take-off speed were the same as in Example 1, and after leaving the water cooling bath, it was brought into contact with a heated roll whose surface temperature was 80°C to remove the solvent decalin by drying. The dried yarn thus obtained had significant adhesion between single yarns and was completely impossible to separate into single yarns. In addition, the gel threads that had exited the water cooling bath were subsequently passed through an extraction bath of methylene chloride at 15°C to extract the solvent, and then similarly dried using heated rolls. Although it was mild, it was still insufficient. This state of inter-filament adhesion was not improved even by hot drawing, and compared to Example 1, the fact that the single fibers of the gel yarn were bundled tightly together showed that the single fibers were splittable (decomposable). It is thought that this may be hindering the fiber quality. Since the yarns obtained by the above two methods have poor fibrillation properties and cannot be separated into single filaments, Table 2 lists the yarn physical property values measured as multifilaments.

[Table] Comparative Example 2 Linear high-density polyethylene with a weight average molecular weight of 1.5×10 ⁵ was dissolved in decalin at a temperature of 150°C, and 15
% solution by weight, and this solution was prepared with a pore diameter of 1 mmφ and a number of pores of 20.
from the nozzle into the air layer, and the air layer is
After passing through the same spinning bath as in Example 1, it was cooled and solidified. The total discharge amount from the nozzle is
12 c.c./min, and the coagulated yarn was taken off at 7.5 m/min. This thread was then passed through an extraction bath of methylene chloride at 10°C to extract and remove the derican, and then dried with heated rolls at 60°C and wound up. This dried yarn was drawn using a hot plate with a surface temperature of 130° C. and a length of 120 cm, resulting in the results shown in Table 3. As a result, no stickiness between single yarns was observed, but the strength level of the obtained fibers was as low as about 14 g/d. It is clear that if the molecular weight of the polymer is lower than the range of the present invention, high physical properties cannot be obtained.

[Table] Example 2, Comparative Examples 3 and 4 The desolvation-dried yarn obtained in the same manner as in Example 1 was drawn by changing the drawing temperature conditions as shown in Table 4 to determine the physical properties of the drawn yarn under different temperature conditions. Table 4 also shows the results of investigating the effect on The drawing ratio was the highest at each drawing temperature, that is, the highest yarn physical property values at each drawing temperature are listed in Table 4. As is clear from the results in Table 4, the stretching temperature is 60
When the temperature drops to 0.degree. C., the drawability is extremely reduced, and the strength of the drawn yarn obtained is also low, below 20 g/d. When the stretching temperature reaches 150°C, the thread melts and is cut on a hot plate, and the cut ends of the thread are fused together. In addition, the melting points of the polymer powder and dry thread were measured by DSC.
(Differential thermal analyzer) measured at 135℃, respectively.
The temperature is 137℃, and the melting temperature of the dried yarn is 145℃.
~150°C, and when the stretching temperature reaches 150°C, it melts and flows. Also, when the stretching temperature is 60℃, the melting temperature is 70℃.
Since the conditions are outside the range of the present invention, such as a temperature range of .degree. C. low, a high stretching ratio cannot be achieved and high physical properties cannot be obtained.

[Table] (Effects of the present invention) As explained above, according to the method of the present invention,
Polyolefin fibers with extremely high strength, high modulus, and no stickiness between single yarns can be obtained, and in addition to the above, the obtained fibers are flexible and do not have a decrease in strength utilization during twisting or a decrease in cutting strength during knotting. Therefore, it is extremely useful in various industrial applications, especially in various reinforcing material applications.

Claims (1)

[Claims] 1. A heated solution prepared by dissolving a polyolefin polymer having a weight average molecular weight of 5 x 10 ⁵ or more in a solvent is extruded through a nozzle, passes through an inert gas atmosphere layer, and forms an upper layer with a low specific gravity that is immiscible with the solvent and a high specific gravity layer. It is passed through a bath of two mutually immiscible layers consisting of a lower layer that is miscible with the solvent, cooled in the upper layer of the bath, and then partially extracted in the lower layer to form a coagulated thread. A high-strength, high-modulus polyolefin fiber characterized by extracting and removing the yarn, and then hot-drawing the obtained yarn to 8 times or more between the melting temperature of the yarn and a temperature 70° C. lower than the melting and cutting temperature. manufacturing method.