JPH0358902B2 - - Google Patents

Description

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

Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 700,000 or more exhibits different physical properties compared to ordinary high-density polyethylene with a viscosity average molecular weight of 300,000 or less, such as impact strength, abrasion resistance, chemical resistance, and self-lubricating properties. It has excellent characteristics such as low water absorption and is widely used in various industrial parts by taking advantage of these characteristics.

However, this ultra-high molecular weight polyethylene has a melt index of less than 0.01 (load of 2.16
Kg), so the degree of freedom in processing is small, and it is difficult to undergo plastic deformation such as stretching or rolling in the solid state. For this reason, a method of pulling the material by applying tension while rolling it at a temperature higher than the melting point (Special Publications Publication No. 59)
−215826) has been proposed. However, since a large deformation ratio cannot be obtained by rolling, a high elastic modulus cannot be expected. Furthermore, when a thick sheet is deformed by tensile stretching, it causes uneven stretching and voids, making it difficult to obtain a uniformly stretched sheet. Furthermore, when a thick sheet is deformed by tensile stretching, it causes uneven stretching and voids, making it difficult to obtain a uniformly stretched sheet.

In view of the above circumstances, the inventors of the present invention have deformed a thick sheet of ultra-high molecular weight polyethylene uniformly to a large extent without impairing its properties.
Moreover, in order to develop a method that can form the mold with high precision, we have conducted various studies and found that when this ultra-high molecular weight polyethylene sheet is heated and brought to a molten state, it becomes rubbery elastic while maintaining its shape and melts. We discovered that effective deformation is possible even when the sheet is in a fixed state, and that when a molten sheet is pulled from a fixed curved surface heated under predetermined conditions, it becomes oriented and crystallized and exhibits excellent physical properties.Based on this knowledge, we developed the present invention. I arrived at the eggplant.

That is, in the present invention, an ultra-high molecular weight polyethylene sheet with a viscosity average molecular weight of 1 million or more is heated to a molten state, and then passed between a pair of fixed curved surfaces maintained at a temperature of 135 to 140°C, and then stretched at a stretching ratio of 10 times in one step. The present invention provides a method for producing an ultra-high molecular weight polyethylene sheet, which is characterized by drawing and oriented crystallization as described above.

The ultra-high molecular weight polyethylene used in the method of the present invention has a viscosity average molecular weight of 1 million or more,
This shows the characteristic that when the sheet is brought into a molten state and pulled out under specific conditions, the elastic modulus and tensile strength increase as the drawing ratio increases. However, ordinary high-density polyethylene does not exhibit such properties.

In the method of the present invention, the above-mentioned ultra-high molecular weight polyethylene is formed into a sheet shape, and heated and melted at a temperature of 150° C. or lower while maintaining the sheet shape. The preferred temperature is in the range of 135-150°C, as it will not normally reach a molten state at temperatures below 135°C. Next, the sheet thus molten is
The sheet is drawn through a pair of fixed curved surfaces maintained at a temperature of 135 to 140° C. In this case, the gap between the fixed curved surfaces must be adjusted so that the stretching ratio of the sheet before and after passing through is 10 times or more. The stretching ratio here means the ratio of the length of the sheet after being drawn to the length of the sheet before being drawn.

Further, the drawing speed is preferably 50 mm/min or less. Unlike the case of general rolling, driving power for the fixed curved surface is not required, and the fixed curved surface does not necessarily need to rotate during drawing.

Next, the method of the present invention will be explained with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of the present invention when a roller is used as the fixed curved surface,
The material sheet 2 melted in the preheating section 1 is pulled out by applying tension between a pair of rollers 3 heated to a predetermined temperature, and oriented and crystallized between the rollers and in the space 4 afterward, thereby forming the desired sheet. Manufacture. The spacing between the rollers 3, 3 can be adjusted, so that drawn sheets of various thicknesses can be obtained. The temperature of each roller is set at a temperature slightly above the differential scanning calorimetry melting peak, ie 135-140°C. If the temperature of the roller is lower than this, it will be difficult to obtain a sufficient drawing ratio, and if it is too high, a stick-slip phenomenon will occur, which is unsuitable. In addition, if the drawing speed is too fast, there is a risk that the sheet will break between the rollers, so the drawing speed should be set at 50mm/
It is preferable to make it less than 1 minute. The distance between the rollers is
1/ of the thickness of the material sheet to obtain a given stretch ratio.
It is preferable to set the width to about 3 to 1/12. If it is narrower than that, the sheet will break, and if it is wider than that, it will cause a stick slip phenomenon.

The method of the present invention can be applied to relatively thick material sheets, and it can be said to be superior to rolling or stretching in a fixed state in that it can obtain sheets with high elastic modulus and high strength. . For example, if a 1 mm thick sheet of ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.9 million is used as a material, it can be drawn to a stretching ratio of more than 10 times, which results in a draw of 5 to 8 GPa.
An ultra-high molecular weight polyethylene sheet having an elastic modulus of .

On the other hand, when an ultra-high molecular weight polyethylene sheet is stretched, a sheet with an elastic modulus of about 5.5 GPa can be obtained, but if this is applied to a thick sheet, a uniform stretched sheet cannot be obtained, and ultra-high molecular weight polyethylene When rolled, a large change ratio cannot be obtained. Further, even if the sheet is rolled with rolls and pulled under tension at temperatures above the melting point, only a sheet with a rolling ratio of about 7 times can be obtained.

By the way, in the method of the present invention, a drawn sheet with a uniform thickness and excellent physical properties can only be obtained by applying ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1 million or more as the material sheet. When applied to ultra-high molecular weight polyethylene of less than 10,000 yen, such a drawn sheet cannot be obtained. This is a viscosity average molecular weight of 100
This is thought to be because the melt viscosity of less than 1,000,000 is not as high as that of more than 1,000,000, and a sheet with a uniform thickness cannot be obtained.

If the method of the present invention is carried out in combination with sheet melt extrusion molding, a sheet with high strength and high modulus of elasticity can be obtained continuously, so it is suitable as an industrial method for producing ultra-high molecular weight polyethylene sheets. Furthermore, unlike rolling, the method of the present invention does not require a mechanism or power to drive the rollers, and can be carried out using only a fixed curved surface that can be heated and a mechanism for pulling out the sheet, making it an extremely simple method. be.

Example Using a pair of stainless steel rollers with an outer diameter of 50 mm and a width of 70 mm, ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.9 million (manufactured by Mitsui Petrochemicals, registered trademark name ``Hisex Million 240M'') was pultruded. . That is, a material sheet with a thickness of 1 mm and a width of 30 mm is heated to 150°C to melt it, and each
It was passed through a pair of rollers heated to 100°C, 135°C or 140°C and pulled out at a drawing speed of 50 mm/min. At this time, the difference between the roller interval (tr) and the thickness (to) of the material sheet (tr/to), the thickness of the pulled sheet (t), the pulling stress (pulling tension/cross-sectional area of the material sheet), and the stretching The relationship with the ratio is shown graphically in Figure 2.

The symbol △ in the diagram indicates the roller temperature is 100℃, and the symbol ○ is 135℃.
℃, □ means 140℃.

As is clear from this figure, the roller temperature
When set at 140°C, a draw ratio of 11 to 16 is obtained with tr/to in the range of 0.1 to 0.4. Also, 135℃
In the case of tr/to≧0.2, the stretching ratio is almost constant (6.2 to 7.2), but when tr/to decreases to 0.1 or less, the stretching ratio increases. At 140℃ and 135℃, t/to< in the range of tr/to≧0.15
tr/to, and the sheet is considered to be stretched even after passing the roller. However, when the roller temperature is 100°C, t/to > tr/to, and the thickness returns after passing through the roller, that is, spring back occurs, and the drawing ratio becomes small. It is also observed that the pull-out stress tends to increase as the roller temperature decreases.

Next, Figure 3 is a graph showing the relationship between various physical properties and the stretching ratio of the drawn sheet.As is clear from this, as the stretching ratio increases, the elongation decreases, and the tensile strength and elastic modulus increase. . When the roller temperature was 140°C and 135°C, the tensile strength of the sheet drawn at a stretching ratio of 10 times or more was 0.27 to 0.34 GPa, and the elastic modulus was 5 to 8 GPa. On the other hand, when the roller temperature is 100°C, the elastic modulus is 1 GPa or less, and the tensile strength is also low.

Comparative Example 1 Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.9 million (manufactured by Mitsui Petrochemicals, registered trademark name: Hi-Zex Million 240M) was rolled, that is, a material sheet with a thickness of 1 mm was heated to 150°C. The material was brought into a molten state and rolled between rollers heated to 140°C while taking it back, thereby deforming it to a rolling ratio of 7.4 times.
The elastic modulus and tensile strength of the obtained sheet are respectively
1.0GPa and 0.25GPa, and 10
The elastic modulus remained at a low value compared to the sheet that was pulled out more than twice as much.

Comparative Example 2 Using ultra-high molecular weight polyethylene with a viscosity average molecular weight of 700,000 (manufactured by Mitsui Petrochemicals, registered trade name "Hisex Million 145M"), the roller temperature was 130℃ or
When the sheet was drawn at 135° C. in the same manner as in the example, it was not possible to obtain a sheet with a uniform thickness.

[Brief explanation of drawings]

Figure 1 is a sectional view showing an example of an embodiment of the method of the present invention, and Figure 2 is a cross-sectional view of the method of the present invention when rollers are used as the fixed curved surface, the roller spacing, the thickness of the pulled sheet, the pulling stress, and the stretching ratio. FIG. 3 is a graph showing the relationship between the stretching ratio and various physical properties of the sheet obtained by the method of the present invention.

Claims (1)

[Claims] 1 After heating an ultra-high molecular weight polyethylene sheet with a viscosity average molecular weight of 1 million or more to a molten state,
It is drawn through a pair of fixed curved surfaces maintained at a temperature of 135 to 140°C to a stretching ratio of 10 times or more.
A method for producing an ultra-high molecular weight polyethylene sheet, characterized by oriented crystallization.