JPH0336930B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for melt extrusion and stretching of polyethylene. More specifically, the present invention relates to a method for producing a stretched polyethylene product having high elastic modulus and high strength. [Prior Art] It is well known that a crystalline thermoplastic resin such as polyethylene or polypropylene can be highly stretched and oriented and crystallized to have a high elastic modulus and high 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 most cases, it is usually about 10 to 20 cm per minute, or at most 30 to 150 cm per minute.
Since it is necessary to draw at a relatively low drawing speed of 1 cm, it is complicated in terms of process control and has poor productivity, making it difficult to commercialize. [Problems to be Solved by the Invention] Therefore, the present inventors have investigated various methods for improving the drawability of polyethylene to obtain a drawn polyethylene product having a high modulus of elasticity and high strength. The object of the present invention can be achieved by using a composition containing paraffin wax of
Filed as No. 38273. As a result of further investigation, we found that even if the die temperature of the screw extruder was lowered to below 210℃, the residence time in the die of the screw extruder could be increased, that is, the extrusion speed of the molten resin could be lowered. However, it was found that polyethylene and paraffin wax could be stably and continuously extruded using a screw extruder, leading to the completion of the present invention. [Means for solving the problem] In other words, the present invention has an intrinsic viscosity [η] of 1.5/
Polyethylene (A) of g or more and less than 5/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 a temperature higher than the melting point of the mixture and lower than 210°C, and then stretched at a stretching ratio of at least 20 times or more. The present invention provides a method for producing a stretched polyethylene product having high elastic modulus and high strength. [Function] The polyethylene (A) used in the method of the present invention has an intrinsic viscosity [η] of 1.5 at 135°C as a decalin solvent.
/g or more and less than 5.0/g, preferably 2.0/g
It is in the range of 5.0/g or more. If [η] is 5/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/
A range of cm ³ is preferable because it results in a stretched product with a higher modulus of elasticity and higher 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 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 stretched product with high elastic modulus and high tensile strength cannot be obtained at a stretching ratio of about 20 times, and even if the stretching ratio is further increased, a stretched product with high elasticity Even if you try to obtain a stretched product with a high elastic modulus, you cannot stretch it more than 25 times, and as a result, you cannot obtain a stretched product with a high elastic modulus.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 D3417. Moreover, the molecular weight is the weight average molecular weight ( ) obtained by measuring 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 amount 400 μ) Standards manufactured by Toyo Soda Co., Ltd. and Pressure Chemical Co., Ltd. Column elution volumes were calibrated by the universal method using polystyrene. Further, the density in the present invention is a value measured according to ASTM D1505. 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, triacontane, etc., or n-alkanes containing these 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-reduced 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. Examples include waxes whose molecular weight has been lowered by chemical composition, oxidized waxes such as oxides or maleic acid-modified products of these waxes, and maleic acid-modified waxes. 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 uses the polyethylene (A): 15 to
A mixture consisting of 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,
melt-kneading at a temperature of from 190 to 280°C, preferably from 190 to 250°C, above the melting point of the mixture and below 210°C,
Preferably, the unstretched material is extruded through a die at a temperature higher than the melting point of the mixture +10°C and lower than 210°C, and then stretched 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 85% 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. If the temperatures of the screw extruder and die during melt-kneading are lower than 190° C. and lower than the melting point of the mixture, the melt viscosity of the mixture will be high and melt extrusion will be difficult. The polyethylene (A) and paraffin wax (B) can be mixed using a Henschel mixer, V-blender,
The mixture may be directly melt-kneaded using a tumbler blender or the like and then extruded, or it may be pre-mixed and then melt-kneaded using a single-screw or multi-screw extruder, kneader, Banbury mixer, etc. and then granulated or pulverized. good. 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. In addition, until the unstretched material cools and solidifies,
The melt may be drafted. The temperature when stretching the cooled and solidified unstretched material is usually within the range of 60°C to less than the melting point of the mixture + 20°C, and if it is less than 60°C, a stretching ratio of 20 times or more cannot be achieved; If it exceeds this range, the polyethylene (A) will be softened, and although it can be stretched, there is a risk that a stretched product with a high elastic modulus will not be obtained. A stretched product with high elastic modulus and high strength can be obtained by using air, water vapor, or a solvent as a heating medium during the above-mentioned stretching process. If a solvent with a boiling point higher than the melting point of the mixture, for example, decalin, decane, or kerosene, is used, excess paraffin wax (B) can be extracted or removed during stretching, or exuded wax (B) can be removed during stretching. This is preferable because it makes it possible to reduce unevenness 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. Methods can also be adopted,
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. [Effects of the Invention] 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.
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 that utilize the highly aligned crystalline arrangement achieved by ultra-high stretching and the micropores that are generated as a by-product by extracting excess paraffin wax (B). It is also excellent. [Examples] 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. Experimental example 1 Polyethylene ([η] = 2.47/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 200° 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 2 mm and a die temperature set at 170°C, and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin was 10.0 cm/min, and the withdrawal was performed so that the winding speed was 10.0 cm/min. That is, the draft ratio was set to 1. Here, the draft ratio was defined as the ratio between the winding speed of the molten resin and the extrusion speed. Subsequently, using two pairs of codetrols, a stretching tank was applied using n-decane as a heating medium (tank temperature = 120°C, tank length = 40cm).
Stretching was performed using During stretching, the rotational speed of the first godetroll was set at 0.5 m/min, and the rotational speeds of the second and third godetrolls were appropriately changed to obtain fibers with different drawing ratios. For stretching, the film was first stretched to a stretching ratio of 8.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. However, the stretching ratio was calculated from the rotation ratio of the godet roll. Table 1 shows the dynamic modulus, tensile modulus, tensile strength, and elongation at break at each stretching ratio. The dynamic elastic modulus was measured using a dynamic viscoelasticity measuring device Vibron DDV-type (manufactured by Toyo Baldwin) at a frequency of 110 Hz.
Measured at room temperature (23°C). Further, the tensile modulus, tensile strength, and elongation at break 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 tensile 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 .

[Table] Experimental example 2 Polyethylene ([η] = 2.47/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 Experimental Example 1. However, the melt was extruded through a die with an orifice diameter of 2 mm and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin was 10.0
cm/min, and the withdrawal was performed so that the winding speed was 20.0 cm/min. That is, the draft ratio was set to 2. For stretching, the film was first stretched to a stretching ratio of 8.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. Dynamic modulus, tensile modulus at each stretching ratio,
Table 2 shows the tensile strength and elongation at break.

[Table] Experimental example 3 Polyethylene ([η] = 2.47/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 Experimental Example 1. However, the melt was extruded through a die with an orifice diameter of 2 mm and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin is 10.0
cm/min, and the withdrawal was made so that the winding speed was 50.0 cm/min. That is, the draft ratio was set to 5. For stretching, the film was first stretched to a stretching ratio of 8.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. Dynamic modulus, tensile modulus at each stretching ratio,
Table 3 shows the tensile strength and elongation at break.

[Table] Experimental example 4 Polyethylene ([η] = 2.47/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 52
℃, molecular weight = 340) was subjected to melt spinning and drawing under the same conditions as in Experimental Example 1. However, the melt was extruded through a die with an orifice diameter of 2 mm and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin is 10.0
cm/min, and the withdrawal was performed so that the winding speed was 10.0 cm/min. That is, the draft ratio was set to 1. For stretching, the film was first stretched to a stretching ratio of 8.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. Dynamic modulus, tensile modulus at each stretching ratio,
Table 4 shows the tensile strength and elongation at break.

[Table] Experimental example 5 Polyethylene ([η] = 2.47/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 52
℃, molecular weight = 340) was subjected to melt spinning and drawing under the same conditions as in Experimental Example 1. However, the melt was extruded through a die with an orifice diameter of 2 mm and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin was 10.0
cm/min, and the withdrawal was performed so that the winding speed was 10.0 cm/min. That is, the draft ratio was set to 1. For stretching, the film was first stretched to a stretching ratio of 8.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. Dynamic modulus, tensile modulus at each stretching ratio,
Table 5 shows the tensile strength and elongation at break.

[Table] Experimental example 6 Polyethylene ([μ] = 2.47/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 52
℃, molecular weight = 340) was subjected to melt spinning and drawing under the same conditions as in Experimental Example 1. However, the melt was extruded through a die with an orifice diameter of 2 mm and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin is 10.0
cm/min, and the withdrawal was performed so that the winding speed was 20.0 cm/min. That is, the draft ratio was set to 2. For stretching, the film was first stretched to a stretching ratio of 8.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. Dynamic modulus, tensile modulus at each stretching ratio,
Table 6 shows the tensile strength and elongation at break.

[Table] Comparative example 1 Polyethylene ([η] = 2.47/g, density =
0.964 g/cm ³ ) was melt-spun and stretched under the same conditions as in Experimental Example 1. However, the melt was extruded through a die with an orifice diameter of 2 mm and solidified in air at room temperature with an air gap of 20 cm. At this time, the extrusion speed of the molten resin was 10.0 cm/min, and the withdrawal was performed so that the winding speed was 10.0 cm/min.
That is, the draft ratio was set to 1. For stretching, the film was first stretched to a stretching ratio of 3.0 times using a second godet roll, and then a second stage of stretching was performed to a predetermined stretching ratio using a third godet roll. Table 7 shows the dynamic modulus, tensile modulus, tensile strength, and elongation at break at each stretching ratio. Comparing the results of Experimental Examples 1 to 6, it can be seen that in the present results without adding paraffin wax, a high stretching ratio could not be achieved and a stretched product with high elastic modulus and high strength could not be obtained.

[Table] Comparative example 2 Polyethylene ([η] = 2.47/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 52
℃, molecular weight = 340) was subjected to melt spinning and drawing under the same conditions as in Experimental Example 1. However, extrusion is performed through a die with an orifice diameter of 2 mm and a die temperature set to 100℃, and the air gap is 20 cm.
It was solidified in air at room temperature. At this time, the extrusion speed of the molten resin was 6.0 cm/min, and the strand was wound up so that the winding speed was 6.0 cm/min. However, it was not possible to wind the strands continuously. Furthermore, the obtained strands were brittle and could not withstand stretching even if continuous strands were obtained. Comparative example 3 Polyethylene ([η] = 2.47/g, density =
0.964g/cm ³ ) and paraffin wax (melting point = 64
℃, molecular weight 460) was subjected to melt spinning and drawing under the same conditions as in Experimental Example 1. However, since the mixture co-rotates within the screw extruder, uniform molten strands cannot be obtained, and uniform drawn fibers cannot be obtained.

Claims (1)

[Scope of Claims] 1. Polyethylene (A) having an intrinsic viscosity [η] of 1.5/g or more and less than 5.0/g: 15 to 97% by weight and a melting point of
A mixture with 85 to 3% by weight of paraffin wax (B) having a molecular weight of 2000 or less is melt-kneaded at a temperature of 190 to 280°C, and then heated through a die at a temperature above the melting point of the mixture and below 210°C. 1. A method for producing a stretched polyethylene product, which comprises extruding the stretched product and then stretching it at a stretching ratio of at least 20 times or more.