JPH036246B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyethylene melt extrusion stretching method. More specifically, the present invention relates to a method for producing a stretched polyethylene product having high elastic modulus and high strength. It is well known that by highly stretching and oriented crystallizing crystalline thermoplastic resins such as polyethylene and polypropylene, it is possible to increase the modulus of elasticity and increase the strength. However, the stretching ratio that can be stretched by the usual polyethylene melt extrusion stretching method is about 20 to 30 times at most, and if the stretching ratio is higher than that, so-called stretch breakage occurs and further stretching cannot be performed. As a method for producing a stretched product with a high elastic modulus, for example, a method in which a crystalline polymer is heat treated under conditions to form a specific crystal structure and then stretched under specific conditions (Japanese Patent Publication No. 37454/1983)
However, according to the method specifically disclosed therein, in order to obtain the desired crystal structure, it is necessary to sufficiently control the temperature and time during heat treatment, and also that stretching is necessary. In the case of a sperm, it is usually about 10 to 20 cm per minute, or 30 to 150 cm per minute.
Since it is necessary to draw at a relatively low drawing speed, it is complicated in terms of process control and has low productivity, making it difficult to commercialize. Therefore, the present inventors have conducted various studies on methods of improving the stretchability of polyethylene to obtain a stretched polyethylene product having high elastic modulus and high strength.
By using a composition in which polyethylene is blended with a specific paraffin wax, the objects of the present invention can be achieved and the present invention has been completed. That is, in the present invention, the intrinsic viscosity [η] is 1.5 dl/
Polyethylene (A) of g or more but less than 5 dl/g: 15 or more
97% by weight, a melting point of 40 to 120℃, and a molecular weight of
Paraffin wax (B) below 2000: 85 to 3
% by weight is melt-kneaded at a temperature of 190 to 280°C, the unstretched material is extruded through a die at 210 to 300°C, and after cooling and solidifying, the mixture is then stretched at a temperature of 60 to 140°C with a drawing ratio of at least 20 times or more. The present invention provides a method for producing a stretched polyethylene product having a high elastic modulus and high strength, which is characterized by stretching. Polyethylene (A) used in the method of the present invention has an intrinsic viscosity [η] of 1.5 at 135°C in decalin solvent.
dl/g or more but less than 5.0 dl/g, preferably 2.0 dl/g
It is in the range of above 5.0 dl/g. If [η] is 5 dl/g or more, the stretchability may not be improved if the amount of paraffin wax (B) described below is small. The density of polyethylene (A) is not particularly limited, but is preferably 0.920g/
cm ³ or more, more preferably 0.930 to 0.970 g/cm ³
It is preferable to use a polyurethane resin in the range of 1 to 100% because it results in a stretched product with a high elastic modulus and high strength. Polyethylene (A) within the above range
is not limited to ethylene homopolymers, but also ethylene and small amounts of other α-olefins, such as propylene,
Copolymers with 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, etc., or copolymers with vinyl compounds such as vinyl acetate, vinyl chloride, acrylic acid, etc. It's okay. Paraffin wax (B) used in the method of the present invention
means a melting point of 40 to 120°C, preferably 45 to 110°C, and a molecular weight of 2000 or less, preferably
It is a paraffin wax with a molecular weight of 1000 or less, particularly preferably 800 or less. If a material with a melting point of less than 40°C or liquid paraffin is used, the polyethylene (A) and the screw will rotate together, making uniform melt spinning impossible. On the other hand, even if a material with a melting point exceeding 120°C and a molecular weight exceeding 2000 is used, a drawn product with a high elastic modulus and high tensile strength cannot be obtained at a drawing ratio of about 20 times, and even if the drawing ratio is further increased, a drawn product with high elasticity Even if an attempt is made to obtain a stretched product with a high modulus of elasticity, it is not possible to stretch the material by a factor of 25 times or more, and as a result, a stretched product with a high elastic modulus cannot be obtained.Furthermore, as will be described later, it is not possible to extract excess paraffin wax from the stretched product. do not have. Also, the molecular weight is 800
If the following is used, a stretched product with a sufficiently high elastic modulus can be obtained even at a stretching ratio exceeding 20 times, but the molecular weight is 800
~2000 when using paraffin wax
It is preferable to stretch at a stretching ratio of 25 times or more, preferably 25 times or more. The melting point in the present invention is a value measured using a differential scanning calorimeter (DSC) according to ASTM D 3417. Moreover, the molecular weight is the weight average molecular weight (Mw) measured by GPC method (gel permeation chromatography) under the following conditions. Equipment: Waters Co., Ltd. 150C type column: Toyo Soda Co., Ltd. TSK GMH-6 (6 mmφ x 600 mm) Solvent: Orthodichlorobenzene (ODCB) Temperature: 135°C Flow rate: 1.0 ml/min Injection concentration: 30 mg/20 ml ODCB (injection volume 400μ ) The column elution volume was calibrated by the universal method using standard polystyrene manufactured by Toyo Soda Co., Ltd. and Pressure Chemical Co., Ltd. Further, the density in the present invention is a value measured according to ASTM D 1505. Paraffin wax (B) used in the method of the present invention
is not particularly limited to a compound consisting only of carbon and hydrogen, as long as it has a melting point and molecular weight within the above range, and may contain a small amount of oxygen or other elements. The paraffinic wax (B) is mainly composed of saturated aliphatic hydrocarbon compounds, specifically, n-alkanes having 22 or more carbon atoms such as docosane, tricosane, tetracosane, and triacontane, or n-alkanes containing them as main components. mixtures with lower n-alkanes etc., so-called paraffin waxes separated and refined from petroleum, ethylene or ethylene and other alpha
- Heat degradation of polyethylene such as medium/low pressure polyethylene wax, high pressure polyethylene wax, ethylene copolymer wax, medium/low pressure polyethylene, high pressure polyethylene, etc., which are low molecular weight polymers obtained by copolymerizing with olefin. Oxidized waxes such as waxes whose molecular weights have been lowered by oxidation or maleic acid-modified products of these waxes, maleic acid-modified waxes, and the like. Other hydrocarbon compounds that fall within the melting point and molecular weight range of the paraffinic wax (B) used in the present invention include aromatic hydrocarbon compounds such as naphthalene and dimethylnaphthalene, but unlike the paraffinic wax, polyethylene The compatibility with (A) is poor, and when used in the method of the present invention, aromatic hydrocarbons will be unevenly dispersed in polyethylene (A).
It is difficult to achieve uniform stretching or high stretching ratios. A specific example of a method for examining the compatibility between polyethylene (A) and paraffin wax (B) is the observation of a cross section of an undrawn yarn using a high-magnification scanning electron microscope. That is, a blend of equal amounts of polyethylene (A) and paraffin wax (B), etc. is melt-kneaded and then melt-spun. Next, the obtained undrawn yarn is cut perpendicularly to its longitudinal direction with a sharp blade such as a microtome. A cross section cut out using the same process as the cross section is further immersed in a non-polar solvent such as hexane or heptane at room temperature for at least 1 hour to extract and remove paraffin wax (B), etc. The extracted cross section is at least 3000 times more Comparative observation is made using a scanning electron microscope at a magnification of . The paraffin wax (B) of the present invention is polyethylene (A)
Because it has good compatibility with wax, almost no depressions of 0.1μ or more are observed, and when naphthalene is used instead of paraffin wax (B), poor dispersion occurs, resulting in countless depressions of 0.1μ or more. be observed. The method of the present invention comprises the polyethylene (A): 15 to 97% by weight, preferably 50 to 85% by weight, and the paraffin wax (B): 85 to 3% by weight, preferably 50 to 15% by weight. mixture
Melt kneading at a temperature of 190 to 280°C, preferably 190 to 250°C, and preferably 210 to 300°C.
The unstretched material is extruded through a die at 210 to 270°C, and after cooling and solidifying, it is heated to 60 to 140°C, preferably 100 to 100°C.
This method involves stretching at a temperature of 135° C. at a stretching ratio of at least 20 times, preferably 25 times or more. If the amount of paraffin wax (B) is less than 3% by weight, the stretchability of polyethylene will not be improved and stretching of 20 times or more will not be possible, while if it exceeds 80% by weight, the melt viscosity will be too low and melt-kneading will be difficult. Also, the stretchability of unstretched products is poor, causing breakage during stretching, making it impossible to stretch 20 times or more. It is preferable to melt-knead and extrude the mixture using a conventional single-screw or multi-screw extruder because continuous extrusion can be performed. After melting and kneading, the temperature of the die is 190℃ and 210℃, respectively.
If the temperature is below 280°C or 300°C, the melt viscosity of the mixture is high and melt extrusion is difficult, whereas if the temperature exceeds 280°C or 300°C, the polyethylene will deteriorate severely and the molecular weight will decrease, making it impossible to obtain a drawn product with high strength. In addition, when mixing polyethylene (A) and paraffin wax (B),
The mixture may be directly melt-kneaded and extruded using a Henschel mixer, V-blender, tumbler blender, etc., or it may be melt-kneaded using a single-screw or multi-screw extruder, kneader, Banbury mixer, etc. after pre-mixing. It may be granulated or crushed. After extruding the unstretched material from the die, it is once cooled and solidified, and cooling may be performed by either water cooling or air cooling. Also, until the unstretched material cools and solidifies,
The melt may be drafted. The temperature when stretching the cooled and solidified unstretched material is 60℃.
Below ℃, a stretching ratio of 20 times or more cannot be achieved;
When the temperature exceeds 140°C, polyethylene (A) becomes soft and although it is stretched, a stretched product with a high elastic modulus is obtained. If the above stretching is carried out in an atmosphere within the range of 60 to 140°C, a stretched product with high elastic modulus and high strength can be obtained even if air, water vapor, or a solvent is used as the heating medium.
If a solvent capable of eluting or exuding the paraffinic wax (B), specifically, for example, decalin, decane, or kerosene, is used as a heating medium, the excess paraffinic wax (B) can be extracted or exuded during stretching. This is preferable because it is possible to remove the wax (B) and reduce the unevenness of stretching during stretching. Further, in order to obtain a stretched product in which the wax has been removed or reduced, the method is not limited to the above-mentioned method, but a method in which an unstretched product is treated with a solvent such as hexane or heptane, and then stretched, or a stretched product is treated with a solvent such as hexane or heptane, etc. By performing such treatment, a stretched product with even higher elastic modulus and higher strength can be obtained. If the stretching ratio in the above atmosphere is less than 20 times, the degree of increase in the modulus of elasticity and strength is small, and the drawn product is often accompanied by whitening of the raw yarn, which often impairs the appearance.
The stretching ratio may be as long as the final stretching ratio is 25 times or more, and may be one-stage stretching or multi-stage stretching of two or more stages. Further, the final stretching speed during stretching is not particularly limited, but from the viewpoint of productivity, a speed of 3 m/min or more, preferably 5 m/min or more is preferable. Additives that can be normally added to polyolefins, such as heat stabilizers, weather stabilizers, pigments, dyes, and inorganic fillers, may be added to the polyethylene (A) used in the present invention to the extent that the purpose of the present invention is not impaired. You can leave it there. The drawn polyethylene product obtained by the method of the present invention has high tensile strength and high elastic modulus that cannot be obtained with conventional drawn polyethylene products, so
In addition to the field of conventional drawn yarns such as monofilaments and tapes, it can be used in the field of high-modulus, high-strength fibers, and can be used in various reinforcing materials that require lightness. Furthermore, by blending a paraffin wax, the stretching ratio at which whitening occurs is higher than in conventional stretched products made of polyethylene alone, so there is the advantage that stretched products with better appearance can be obtained. Furthermore, it is suitable for functional materials such as selective membranes and electrets, which utilizes the highly aligned crystal arrangement achieved by ultra-high stretching and the micropores that are generated as a side effect by extracting excess paraffin wax (B). It is also excellent. Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist of the present invention is not exceeded. Example 1 Polyethylene ([η] = 2.47 dl/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 69
℃, molecular weight = 460) was melt-spun and drawn under the following conditions. After mixing the polyethylene granular pellets and the pulverized paraffin wax, they were melt-kneaded at a resin temperature of 190° C. using a screw extruder with a diameter of 20 mm and L/D=20.
The melt was then extruded through a die with an orifice diameter of 1 mm, and solidified with cold water at 20°C in an air gap of 10 cm. Subsequently, using a pair of godet rolls, a drawing tank was drawn using n-decane as a heating medium (temperature inside the tank =
Stretching was carried out at 130°C (tank length = 40cm). At this time, the rotation speed of the first godet roll is set to 0.5
By appropriately changing the rotational speed of the second godet roll (m/min), fibers with different drawing ratios were obtained. However, the stretching ratio was calculated from the rotation ratio of the godet roll. Table 1 shows the elastic modulus and strength at each stretching ratio. It can be seen from Table 1 that a stretched product with high strength can be obtained when the stretching ratio is 20 times or more. The elastic modulus and strength were measured at room temperature (23° C.) using an Instron universal testing machine model 1123 (manufactured by Instron). At this time, the sample length between the clamps was 100 mm, and the tensile speed was 100 mm/min. However, the elastic modulus was calculated using stress at 2% strain. The fiber cross-sectional area required for calculation was determined by measuring the weight and length of the fiber, assuming the density of polyethylene as 0.96 g/cm ³ . The table also shows the presence or absence of whitening of the drawn fibers (〇: no whitening;
×: Whitening).

[Table] Example 2 Polyethylene ([η] = 2.47 dl/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 69
℃, molecular weight = 460) was subjected to melt spinning and drawing under the same conditions as in Example 1. Table 2 shows the elastic modulus and strength at each stretching ratio. Similarly, it can be seen that a stretched product with high strength can be obtained when the stretching ratio is 20 times or more.

【table】

[Table] Example 3 Polyethylene ([η] = 2.47 dl/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 69
℃, molecular weight = 460) was melt-spun and stretched under the same conditions as in Example 1. Table 3 shows the elastic modulus and strength at each stretching ratio. Similarly, it is found that a drawn product with high strength can be obtained when the drawing ratio is 20 times or more, and it is also found that the drawn product does not whiten even at a high drawing ratio of 60 times or more.

[Table] Example 4 Polyethylene ([η] = 2.47 dl/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 69
℃, molecular weight = 460) was formed into a T-die film under the following conditions, and then stretched. After mixing polyethylene powder and pulverized paraffin wax, a 20mmφ, L/D=20 screw with a coat hanger type die (rip length = 300mm, lip thickness = 0.5mm) whose temperature is controlled at 220℃ is used. The mixture was melt-kneaded using an extruder to form a film. At this time, the melt-kneading temperature was 190°C. The extruded molten film was taken off using a cooling roll using cold water at 20°C so that the unstretched film had a width of 300 mm, and was cooled and solidified. Subsequently, using a pair of snack rolls, n-
Stretching tank using decane as a heating medium (tank temperature = 120℃,
The effective length of the tank was 80 cm). At this time, the rotation speed of the first snack roll was set to 0.5 m/min,
Stretched tapes with different stretching ratios were obtained by appropriately changing the rotational speed of the second snap roll. However, the stretching ratio was calculated from the rotation ratio of the Snut roll. Table 5 summarizes the elastic modulus, strength, and appearance of the stretched tape at each stretching ratio.
(However, 〇: Transparent and uniform, ×: Partially fibrillated and whitened)

[Table] Comparative example 1 Polyethylene ([η] = 2.47 dl/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 69
℃, molecular weight = 460) was subjected to melt spinning and drawing under the same conditions as in Example 1. In this yarn, since the raw yarn that had been cooled and solidified was brittle, a continuous raw yarn could not be obtained, and it was not possible to draw the yarn using a godet roll. Comparative example 2 Polyethylene ([η] = 1.24 dl/g, density =
0.965g/cm ³ ) and paraffin wax (melting point = 69
℃, molecular weight = 460) was subjected to melt spinning and drawing under the same conditions as in Example 1. In this system, it was not possible to obtain fibers that could withstand stretching. Comparative example 3 Polyethylene ([η] = 2.47 dl/g, density =
0.964 g/cm ³ ) was melt-spun and stretched under the same conditions as in Example 1. Table 5 shows the elastic modulus and strength at each stretching ratio. From Table 5, it can be seen that with no paraffin wax mixed, whitening already occurs at a drawing ratio of 17 times, and moreover, a drawn product with high strength cannot be obtained.

[Table] In this example, in order to investigate the effect of adding paraffin wax to polyethylene, the elastic modulus and strength were plotted against the stretching ratio in FIGS. 1 and 2. As far as we can see from FIGS. 1 and 2, the elastic modulus and strength are uniquely related to the stretching ratio.
It can be seen that both the elastic modulus and strength increase by increasing the stretching ratio. Furthermore, as shown in Figure 3, the relationship between the amount of paraffin wax added and the ultimate drawing ratio increases markedly by adding paraffin wax. It can be seen that fibers are obtained.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the elastic modulus and the stretching ratio, FIG. 2 shows the relationship between the strength and the stretching ratio, and FIG. 3 shows the relationship between the final stretching ratio and the amount of paraffin wax added.

Claims (1)

[Claims] 1. Polyethylene (A) having an intrinsic viscosity [η] of 1.5 dl/g or more and less than 5.0 dl/g: 15 to 97% by weight and a melting point of
A mixture of paraffin wax (B) with a molecular weight of 2000 or less and 85 to 3% by weight is melt-kneaded at a temperature of 190 to 280°C, and the unstretched product is extruded through a die at 210 to 300°C. , after cooling and solidification, then at a temperature of 60 to 140 °C for at least 20
A method for producing a stretched polyethylene product, which comprises stretching at a stretching ratio of at least twice as high.