JPS5889326A - Preparation of high elastic modulus sheet of ultra-high molecular weight polyethylene - Google Patents

Abstract

PURPOSE:To obtain a high density polyethylene sheet having high elastic modulus and high tensile strength by a method wherein a polyethylene sheet is heated and melted, then, stretched at 150 deg.C or below so that the percent of stretch is increased by ten times or more. CONSTITUTION:In preparing a high elastic modulus sheet of ultra-high molecular weight polyethylene having 1.5 millions or more of viscosity average molecular weight, said polyethylene sheet is melted, then, stretched at 150 deg.C or below so that the percent of stretch is increased by ten times or more. In this method, it is possible to obtain a high density polyethylene sheet having excellent high elastic modulus and high tensile strength as well as various characteristics given to common ultra-high molecular weight polyethylene such as high impact resistance, excellent wear resistance, chemical resistance, self-lubricating properties and low water-absorbing properties.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a highly oriented ultra-high molecular weight 1) ethylene sheet having high modulus of elasticity and high tensile strength.

Ultra-high molecular weight polymers with a viscosity average molecular weight of 700,000 or more
Ethylene has extremely different physical properties compared to normal medium-density and high-density polyethylene with a weight average molecular weight of about 100,000, such as high impact strength, good abrasion resistance and chemical resistance, and self-lubricating properties. It has many properties such as high water absorption, low water absorption, and excellent stress cracking properties, and is widely used in industrial parts that require these properties.

However, this ultra-high molecular weight polyethylene has a melt index (load of 2.16 to 4) of 0. It is small (O1 or less), making injection molding difficult, and has the disadvantage of having a small degree of freedom in processing and not being susceptible to plastic deformation such as stretching or extrusion in a solid state.

By the way, in the commonly used high-density polyethylene with a weight average molecular weight of about 100,000, the sheet has a weight average molecular weight of about 70,000.
It is susceptible to plastic deformation at temperatures of ~80° C. and can be stretched to high magnifications in the solid state, thus making it possible to obtain high-density polyethylene sheets with high elastic modulus and high tensile strength.

Ultra-high molecular weight polyethylene sheets with a viscosity average molecular weight of 1,500,000 or more have the above-mentioned drawbacks, and although stretching and solid extrusion have been attempted in the past, the deformation ratio is small and the elastic modulus is No sheet has been obtained that is fully satisfactory in terms of strength and tensile strength.

In view of these circumstances, the inventors of the present invention have conducted intensive research on a method for manufacturing ultra-high molecular weight polyethylene sheets having high elastic modulus and high tensile strength, and have found that ultra-high molecular weight polyethylene sheets with a viscosity average molecular weight of 1.5 million or more have been developed. The sheet has a small melt index (load of 2.16Kg to 21.6Kg) of 0.01 or less, and when melted at a temperature not exceeding 150°C, it becomes rubber elastic and can be stretched to a high ratio. In addition, this ultra-high molecular weight polyethylene has a large number of entangled molecular chains, and as the entangled molecular chains are aligned in the stretching direction by stretching in the molten state, it becomes highly oriented by cooling after stretching. An ultra-high molecular weight polyethylene sheet is obtained,
The inventors have found that it is possible to achieve this objective, and have completed the present invention based on this knowledge.

That is, in producing a high elastic modulus sheet of ultra-high molecular weight polyethylene having a viscosity average molecular weight of 1.5 million or more, the present invention involves melting the polyethylene sheet,
The present invention provides a method for producing a high elastic modulus sheet of ultra-high molecular weight polyethylene, which is characterized by stretching at a stretching ratio of 10 times or more at a temperature not exceeding 50°C.

The ultra-high molecular weight polyethylene used in the method of the present invention has a viscosity average molecular weight of 1.5 million or more.

Such ultra-high molecular weight polyethylene has a sheet of 1
If the stretched sheet is stretched once in a molten state at 50°C or lower, the elastic modulus and tensile strength of the obtained stretched sheet increase as the stretching ratio increases, but those with a viscosity average molecular weight of less than 1.5 million does not exhibit this property. Furthermore, the stretched sheet obtained by stretching to the maximum draw ratio by the method of the present invention has a much higher elastic modulus than the stretched sheet obtained by stretching to the maximum draw ratio by the conventional solid state drawing method. big. For example, in ultra-high molecular weight ethylene with a viscosity average molecular weight of 1.9 million,
By the method of the present invention, it is possible to stretch to a maximum stretching ratio of about 23 times (stretching temperature: 140°C), and the elastic modulus of the stretched sheet obtained in this case reaches about 15 GPa. , maximum stretching ratio approximately 11
It is possible to stretch up to (stretching temperature 130°C),
The elastic modulus of the stretched sheet obtained in this case is about 60 Pa.

In addition, in the stretched sheet obtained by stretching to a high stretching ratio by the method of the present invention, wide-angle X-ray diffraction and birefringence measurements show that both crystalline and amorphous regions are well oriented.
The degree of orientation and crystallinity increase as the stretching ratio increases (and, at the same stretching ratio, the lower the stretching temperature) There exists a long periodic structure of about 400 to 6008 oriented.On the other hand, in a stretched sheet obtained by stretching in a solid state, the small-angle scattering image is a four-point image, and the normal line of the lamella is It has a periodic structure arranged at an angle.

In addition, in the method of the present invention, the melting peak in differential scanning calorimetry shifts to the high temperature side as the stretching ratio increases. it is conceivable that.

In the method of the present invention, it is necessary to stretch an ultra-high molecular weight polyethylene sheet having a viscosity average molecular weight of 1.5 million or more in a molten state of 150°C or less at a stretching ratio of 10 times or more, and this stretching temperature is 150°C or higher. If it exceeds, a high stretching ratio cannot be obtained and a stretched sheet having the desired high elastic modulus and high tensile strength cannot be obtained. In addition, since the polyethylene sheet does not usually melt at temperatures below 130°C,
The preferred stretching temperature is in the range of 136-150°C.

On the other hand, when the method of the present invention is applied to ultra-high molecular weight polyethylene with a viscosity average molecular weight of about 700,000, it is possible to stretch it to a high stretching ratio of 36 times, but the elastic modulus and tensile strength of the obtained stretched sheet are The strength is as thick as expected (in fact, it is better to use the conventional stretching method in the solid state to obtain a stretched sheet with higher elastic modulus and tensile strength than using the method of the present invention.The reason for this is that the viscosity average Molecular weight 7
Ultra-high molecular weight polyethylene of about 0,000 has a viscosity average molecular weight of 1
ii Compared to ultra-high molecular weight polyethylene of 1.5 million or more,
Its melt viscosity is not so high (9).

Next, to give an example of the manufacturing method of the present invention, first, ultra-high molecular weight polyethylene powder with a viscosity average molecular weight of 1.5 million or more is placed in a mold, and the temperature is 220-250°C and the pressure is 60°C.
It is compressed with a hot press under the conditions of ~70 Kg/l; J and formed into a sheet with a thickness of 0.5 to 0.8.

This sheet is then held in a stretching device and stretched to 140-160
After melting at a temperature of 136°C to 150°C, it may be uniaxially stretched at a temperature of 136 to 150°C. It is desirable that this -axis stretching be performed in a free width.

The ultra-high molecular weight polyethylene high modulus sheet obtained by the method of the present invention has various properties that ordinary ultra-high molecular weight polyethylene has, such as high impact strength, excellent abrasion resistance, chemical resistance, self-lubricity, and low In addition to having properties such as water absorption,
Furthermore, it has excellent elastic modulus and tensile strength.

Next, the present invention will be explained in more detail with reference to Examples.

In addition, the elongation, tensile strength, and elastic modulus in each example were measured using a crosshead constant speed tensile tester (manufactured by Toyo Baldwin ■, UTM-1-100), and
Measured according to 1980. The meaning of each measurement value is as follows.

Elongation: Strain value at tensile rupture.

Tensile strength: Stress value at tensile rupture, which is the value obtained by dividing the load at rupture by the original cross-sectional area of the test piece.

Elastic modulus: Ratio of tensile stress to strain at the point where deformation begins.

Furthermore, the solid structure of the stretched sheet was measured according to the following method.

Wide-angle X-ray diffraction was carried out using a Geigerflex xGC-20 diffractometer (manufactured by Rigaku Denki Co., Ltd.), and small-angle X-ray diffraction was carried out using a Rotaflex RU-200ip diffraction device (manufactured by Rigaku Denki Nilmer). Birefringence was Polarizing microscope Toveretsk (
Berθk)# Measured using a compensator. Further, the degree of crystallinity was calculated from the density value measured using a water-ethanol density gradient tube.

Example 1 Ultra-high molecular weight polyethylene powder with a viscosity average molecular weight of 1.9 million (manufactured by Mitsui Petrochemicals, trade name: HIZEX MILLION 24)
0M) into the mold, temperature 240℃, pressure cuff 0Kg/d
It was compressed using a hot press under the following conditions and formed into a sheet with a thickness of 6 mm.

A sample of gauge summary 2 cIn was cut out from this sheet,
It was held in a manual stretching device and placed in a constant temperature air bath, and the temperature was maintained at 140-160°C. The solid sheet, which was initially translucent, gradually became transparent and completely melted after 30 to 60 minutes, turning into a uniformly transparent molten sheet. Then, while keeping it in a molten state, it was heated to 136 to 150
After maintaining a predetermined temperature of .degree. C. for several minutes, free width-axis stretching was carried out at that temperature. After stretching, the stretching device holding the sample was taken out from the constant temperature air bath and allowed to cool, and then the stretched sheet sample was taken out.

The elongation, tensile strength, and elastic modulus of this sample were measured according to the methods described above, and the relationship between these mechanical properties and the stretching ratio is shown in FIG.

In addition, the crystal structure was measured according to the method described above, and the crystal C
The degree of orientation of the axis in the stretching direction, the long period and inclination angle of the lamellar plane determined from the small-angle scattering image, the degree of orientation of the amorphous chains, and the degree of crystallinity were determined, and the results are shown in Table 1.

For comparison, a sheet obtained by compression molding was subjected to free width-axis stretching in a solid state (130° C.), and the mechanical properties and crystal structure of the stretched sheet were measured in the same manner as described above. The σ6 results are shown in Figure 1 and Table 1.

As is clear from FIG. 1, the elastic modulus of the stretched sheet obtained by stretching to the maximum stretching ratio by the method of the present invention (stretching temperature 140°C, stretching ratio 22.7, elastic modulus 15.3 GP
a) is much larger than the elastic modulus of the stretched sheet obtained by stretching to the maximum stretching ratio in the solid state (stretching temperature: 130° C., stretching ratio: 11. Elastic modulus: 5 GPa).

Moreover, as the stretching ratio increases, the elastic modulus and tensile strength increase, and the elongation decreases.

On the other hand, as is clear from Table 1, the crystal C axis and the degree of orientation and crystallinity of amorphous silver increase as the stretching ratio increases, and at the same stretching ratio, the lower the stretching temperature, the lower the big. Further, a stretched sheet obtained by stretching in a molten state has a periodic structure C in which the lamellar plane is oriented perpendicular to the stretching direction, but a stretched sheet obtained by stretching in a solid state has a periodic structure C. It has a periodic structure in which the normal lines of are arranged at an angle from the stretching direction.

Example 2 Ultra-high molecular weight polyethylene powder with a viscosity average molecular weight of 2.7 million (manufactured by Mitsui Petrochemicals, trade name HIZEX MILLION 34)
0M), and each stretching temperature (136°C, 140°C, 150°C in molten state, 130°C in solid state) in the same manner as in Example 1.
) was produced, and its mechanical properties and crystal structure were measured. The results are shown in FIG. 2 and Table 2.

As is clear from FIG. 2, the maximum elastic modulus of the stretched sheet obtained by stretching to the maximum stretching ratio (12,6) in the molten state (136°C) is 7.8 GPa, whereas
Maximum stretching 1 sound rate (8,9
) The maximum elastic modulus of the stretched sheet obtained by stretching it to
, about 8 GPa.

Comparative Example Ultra-high molecular weight polyethylene powder with a viscosity average molecular weight of 700,000 (
Manufactured by Mikata Petrochemical ■, product name: HIZEX MILLION 145
Using M), stretched sheets were prepared at each stretching temperature (136°C, 140"C in the melt state, 130"C in the solid state) in the same manner as in Example 1, and the mechanical properties were measured. The results are shown in Figure 3. Shown below.

As is clear from FIG. 3, when stretching in the molten state, it was possible to stretch to a high stretching ratio of 36 times (136°C), but the elastic modulus of the obtained stretched sheet was 3.
8 GPa, and the tensile strength is as low as Q, 2 GPa. On the other hand, when stretching in the solid state (130°C), the elastic modulus and tensile strength of the obtained stretched sheet increase as the stretching ratio increases, and at the maximum stretching ratio of 12°C, the elastic modulus is 3°C. GPa and tensile strength are Q, 59 GPa. Therefore, in ultra-high molecular weight polyethylene with a molecular weight of this level, it is possible to obtain a stretched sheet with higher elastic modulus and tensile strength when stretched in the solid state rather than in the molten state. It can be seen that the following can be obtained.

[Brief explanation of the drawing]

Figures 1, 2 and 3 show the relationships between the elastic modulus, tensile strength and elongation of stretched sheets obtained using Hisex Million 240M, 340M and 145M, respectively, and the stretching ratio. It is a graph. Patent applicant Makoto Ishizaka, Director of the Agency of Industrial Science and Technology - Figure 1 Figure 2 Stretching Pr* 136°CCΔ) 140'C(0) +50'c(B) 1306c(・)

Claims (1)

[Claims] 1. In producing a high elastic modulus sheet of ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.5 million or more, the polyethylene sheet is heated to a molten state and then stretched at a stretching ratio of 10 times at a temperature not exceeding 150°C. 1. A method for producing a high elastic modulus sheet of ultra-high molecular weight polyethylene, which comprises stretching the sheet to a higher degree.