JPS60220730A - Stretching method of crystalllne high molecules - Google Patents

Abstract

PURPOSE:To obtain stretched material of high strength and high elastic modulus by stretching crystalline high molecules economically, efficiently and at a high magnification using the external heating method on the first stage and ultrasonic wave or high frequency electric field on the last stage. CONSTITUTION:Crystalline high molecular stretched material such as polyolefin, polyester, fluoropolymer, etc. is stretched on multiple stages. In the first stage of the stretch said material is heated up to an arbitrary temperature in a temperature zone suitable for the stretch of the material to be stretched by means of the external heating method and then strecthed 3-10 times. In the last stage of the stretch said material to be stretched is stretched giving ultrasonic wave or high frequency electric field including the frequency selected from a zone in which of dispersed frequencies based on the amorphous part in the stretching temperature of the material to be stretched dynamic or dielectric loss tandelta is 1/100 of the peak value or more, preferably, 1/10 thereof or more.

Description

[Detailed Description of the Invention] [Technical Field] This invention relates to a method of economically and efficiently stretching a crystalline polymer at a high magnification to obtain a stretched product with high strength and high elastic modulus. .

[Prior art]

It is generally known that when a crystalline polymer is stretched, the elastic modulus and strength in the stretching direction are improved, and the coefficient of linear expansion is decreased. The stretching procedure involves first forming an unstretched material with no or weak orientation by extrusion molding or crystallization from a solution, and then forming an unstretched material that is suitable for stretching as determined by the properties of the polymer and the stretching speed. After raising the temperature to a certain temperature, an external force is applied and the film is stretched to a predetermined magnification.

In the initial stage of this stretching process, the crystals present in the polymer being stretched are oriented in the stretching direction, while the amorphous chains existing between the crystals are also gradually oriented in the stretching direction. Yes, it is called neck stretching process. The later process is
The orientation of the crystals does not change much from the direction they were oriented in the initial process, and the amorphous parts between the crystals become oriented in the stretching direction while being deformed due to slippage within or between the crystals, which is called the super-stretching process. (Shozo Iida, Journal of the Japan Institute of Textile Science, p. 38.245 (1982), Shoji Ichihara, Journal of the Japan Society of Textile Technology, page 38.279 (1982)).

It is believed that the ultimate stretching ratio that can be stretched is determined by the molecular weight between the entanglement points of molecular chains in the sample to be stretched. For example, by crystallizing ultra-high molecular weight polyethylene from a solution, an unstretched material with a large molecular weight between the entanglement points is created, and by super-stretching this,
Uniaxial stretching of 300 times has been achieved (Masaru Matsuo, Pol
ymer Preprints, JAPAN%32, A
4. Page 841 (1983) Demon However, this method is economically disadvantageous because it uses a solvent, and because it takes time to crystallize from the solution, it is also inefficient and has many problems in terms of practicality. .

Methods of applying external force during stretching include changing the speeds on the supply and discharge sides of the object to be stretched, clamping the object to be stretched and mechanically expanding it, and methods for applying external force to tubular objects. There are several methods: a method in which gas, liquid, or a guide body is placed inside and the material is stretched using its pressure or tension; a method in which the film is stretched while applying pressure with rolls; and a method in which a drawing die is provided at the stretching point and the material is stretched while being pulled out. be. These methods can be said to be methods that specify the speed of stretching, but in addition to these methods, there are also methods called constant stress stretching, such as zone stretching and solid phase extrusion.

Heating methods include spraying heated gas or liquid onto the object to be stretched, immersing the object in heated gas or liquid, bringing the object into contact with a heated solid, and using an infrared heater. The so-called external heating method, such as the method used, is common. External heating methods tend to create temperature gradients between the surface and the interior.

In the case of external heating, the surface of the object to be stretched is usually higher in temperature, and by the time the center reaches a temperature suitable for stretching, the surface is already hotter than the temperature suitable for stretching, so the overall temperature is sufficient. The stretched material is oriented to The film often whitens or breaks, which forces the drawing ratio to be kept low, resulting in a disadvantage that a highly drawn and oriented product cannot be obtained.

This phenomenon is particularly noticeable when the object to be stretched is thick or thick.

As a heating method that overcomes these drawbacks of the external heating method, there is a so-called internal heating method in which a high-frequency electric field is applied to the dielectric material of the object to be drawn, which has dielectric loss, to generate heat and heat the object itself. be. Regarding high frequency heating stretching, please refer to JP-A-57-147603, JP-A-57-148616,
JP-A-57-193513, JP-A-57-208212
, Japanese Unexamined Patent Publication No. 58-109651, etc., describe the stretching method and apparatus. In this stretching method, a high-frequency electric field having a frequency within the amorphous fraction frequency band at the stretching temperature is applied to the object to be stretched, thereby selectively heating and stretching the amorphous portion.According to this method, The decrease in strength of the crystalline part during stretching is suppressed, and the stretching stress acts effectively on the amorphous part where molecular chains move easily, so it is possible to stretch at a high magnification and achieve high strength. It is said that

This dielectric heating stretching method is an excellent method in terms of high strength, high modulus of elasticity, and low coefficient of linear expansion, but it is disadvantageous in terms of economy because it requires high equipment costs and processing costs.

[Purpose of the invention]

This invention was made to solve these conventional problems, and involves stretching a crystalline polymer in multiple stages, using an external heating method in the first stage and using ultrasound or ultrasonic waves in at least the final stage. By stretching the crystalline polymer while applying a high-frequency electric field, it is possible to stretch the crystalline polymer economically, efficiently, and at a high magnification, and to obtain a stretched product with high strength and high elastic modulus. A stretching method is provided.

[Structure of the invention]

In the method for stretching a crystalline polymer according to the present invention, when stretching a material to be stretched consisting of a crystalline polymer, the stretching process is divided into at least two stages, and at least in the first stage of stretching, external heating is performed. After heating to any temperature in the temperature range suitable for stretching the object to be stretched using the method, 3 to 10
At least in the final stage of stretching,
This method is characterized by stretching while applying an ultrasonic wave or a high-frequency electric field containing an arbitrary frequency in the amorphous dispersion frequency band at the stretching temperature of the object to be stretched.

The crystalline polymer referred to herein is a so-called crystalline polymer or quasi-crystalline polymer, and examples thereof include polyolefin, polyether, polyester, polyamide, polythioether, polyamideimide, and fluorine-based polymer. It will be done.

Further, the shape of the object to be stretched may be any of a rond shape, a fibrous shape, a film shape, a tape shape, a tube shape, and the like.

As the external heating method that can be used in this invention, any known heating method may be used, and the method of applying external force may also be any of the above-mentioned methods.

The reason why the external heating method is used in the first stage of stretching is that if appropriate improvements are made to this method, it is more cost-effective than the dielectric heating method. That is, although the dielectric heating method is considered to be superior to the above-mentioned known external heating method in terms of temperature uniformity, it is difficult to say that it is advantageous because both equipment costs and processing costs are higher than the external heating method. External heating seems to be disadvantageous in order to uniformly heat the inside of a thick object to the drawing temperature in a short time, but it is important to avoid cooling the extrudate after extrusion more than necessary, or to heat it for a long time in the preheating section. This is because significant improvements can be made by devising a way to retain heat and retain heat.

The reason why the film is stretched while applying ultrasonic waves or a high-frequency electric field in the final stage is as follows.

Crystalline polymers are usually stretched in a temperature range where the frequency of dielectric dispersion or mechanical dispersion peaks based on crystal relaxation and crystal grain boundary relaxation is 10 to 10' Hertz, although it depends on the heating conditions and stretching speed. However, up to about 3 to 10 times,
It is easily stretched even under industrial conditions. Deformation in this range is seen from the relationship between stress and stretching ratio.At the very early stage of stretching, as the strain increases, the stress increases quite rapidly and reaches the yield point, and after exceeding the yield point, the type of polymer A certain stretching ratio, usually 3 to 1, is determined by the molecular weight distribution, crystallinity, degree of orientation of the unstretched material, stretching temperature, stretching speed, etc.
Even if the stretching ratio increases up to 0 times, the stretching is performed almost without an increase in stress or with a relatively small increase in stress.

If the stretching ratio is further increased, the stress will again increase rapidly, except for polyethylene, which can be easily superstretched. Stretching is generally difficult. Normally, in this region, it is thought that the molecular chains of the material to be stretched undergo a kind of sliding deformation while being stretched, but in reality, this deformation does not occur uniformly, but rather locally during the stretching process. This is because the object to be stretched is deformed and broken. Therefore, it is generally difficult to perform superstretching at high speed.

However, in the final stage of stretching in the above region, when stretching is carried out while applying double ultrasonic waves or high-frequency electric fields, a kind of sliding deformation occurs uniformly in the molecular chains, causing stress and stress in this region. As well as causing a change in the relationship between stretching ratios,
It has been found that it becomes possible to stretch to a higher magnification.

From a different perspective, it may be considered that the speed of super-stretching can be increased by stretching while applying ultrasonic waves or high frequencies. Therefore, it is theoretically and economically economical to separate the stretching into regions that can be stretched at high speeds, i.e., regions that can be stretched using normal external heating methods, and regions that must be stretched at low speeds, that is, regions where ultrasonic or high-frequency waves are applied. It is also preferable.

This is the reason why at least the final stage of stretching is performed while applying ultrasonic waves or a high frequency electric field.

In addition, as mentioned above, in the process of stretching while applying ultrasonic waves or high-frequency electric fields, if necessary, the stretched material in the previous steps is kept at the stretching temperature using external heating, or further stretched. If the film is stretched while being externally heated to a temperature suitable for this, the effect of applying ultrasonic waves or a high-frequency electric field can be made more effective.

The ultrasonic waves and high-frequency electric field in the present invention only need to include a wavelength in the amorphous dispersion frequency band at the stretching temperature, and do not need to have a single frequency as in the case where high-frequency heating is intended.

In other words, the frequency of the applied ultrasonic wave or high-frequency electric field is
Among the dispersion frequencies based on the amorphous portion at the stretching temperature of the object to be stretched, it is preferable to select from a region where the magnitude of mechanical or dielectric loss -δ is 1/100 or more of its peak value, and further, It is preferable to select from an area where the ratio is 1/10 or more.

Next, the present invention will be explained in detail.

[Example 1] Polyoxymethylene (density 1.41, melting point 166°C, number average molecular weight 42,000, weight average molecular weight 96,000
, the peak value of dispersion caused by the amorphous part is 2 to 3 x 10?
Hz), the mixture was extruded from an extruder, cooled, and solidified to obtain an unstretched tape.

This was stretched 6 times in the vertical direction using a roll heating type vertical stretching machine (
Stretching speed: 24 m/min, stretching temperature: 155°C), preheat the resulting stretched object to 160°C by external heating, and then use a high-frequency electric field stretching device (oscillation frequency: 2450 MH2-, maximum output: 1!
IKW). The stretching speed at this time was 6 cm.
After 7 minutes, a high-frequency electric field was applied for 5 minutes, and then the high-frequency electric field was applied.

In this way, when the object to be stretched was stretched up to 5 times, that is, up to a total stretching ratio of 30 times, it broke.

FIG. 1 shows the relationship between the stretching ratio and the stretching stress at this time. As is clear from the figure, as the stretching ratio increases, the stress also increases smoothly. this is,
This is thought to be because the object to be stretched is uniformly superstretched.

[Comparative Example 1] The object to be stretched in Example-1 was stretched up to 6 times in the vertical direction using a hot-air heating stretching device (heater capacity I KW ) instead of the high-frequency electric field stretching device in Example-1. Te160
After preheating to .degree. C., stretching was performed (stretching speed: 6 crn/min). The object to be stretched broke when it was stretched exactly 3.3 times, that is, when the total stretching ratio was 20 times.

FIG. 2 shows the relationship between the stretching ratio and the stretching stress at this time. As is clear from the figure, at the initial stage of the second stage of stretching, the stress increases as the stretching ratio increases, but after a certain stage, the increase in stress almost disappears.
On the contrary, stress decreases near the breaking point. This is thought to be due to non-uniform deformation and local stress concentration.

[Example 2] The high-frequency electric field stretching apparatus of Example-1 was modified so that it could be used in combination with the hot air heating of Comparative Example-1, and after sufficient preheating, an experiment similar to Example-1 was conducted (oscillation frequency 2450
MHz, maximum output 19KW, hot air temperature 160℃, stretching speed 6 cm 7 minutes) However, the second stage stretching ratio was 5.5.
The film broke when it was stretched to a total stretching ratio of 33 times.

FIG. 3 shows the relationship between the stretching ratio and the stretching stress at this time. As is clear from the figure, as the stretching ratio increases, the stress also increases smoothly. This is considered to be because the entire stretched object was super-stretched uniformly compared to Comparative Example-1.

[Comparative Example 2] In Example 1, the tape-shaped unstretched material was subjected to a high-frequency electric field stretching device (oscillation frequency 2450 MHz, maximum output
After applying a high-frequency electric field for 5 minutes at KW), stretching was performed while applying the high-frequency electric field (stretching speed: 6 cm, 7 minutes), and the film broke when stretched 28 times.

FIG. 4 shows the relationship between the stretching ratio and the stretching stress at this time. This comparative example is published in Japanese Unexamined Patent Publication No. 57-14861.
This invention is based on the method of applying a high-frequency electric field from the first stage of stretching disclosed in No. 6, and although the stretching method is different from that of the previous invention, it is performed manually. It can be seen that results with the same tendency as Example 1 can be obtained.

[Example 3] Polyvinylidene fluoride (density 1.75, melting point 171°C,
Melt viscosity 9300 Poisel 02/see 23
0℃・Peak value of dispersion caused by amorphous part 2-3X10τ
) lz ) is extruded from an extruder, cooled and solidified,
A monofinment-shaped unstretched product was obtained.

This was vertically stretched by hot air heating (smoked and stretched 5 times in the vertical direction (stretching speed: 40 rn, 7 minutes, stretching temperature: 155°C), and the resulting stretched object was subjected to ultrasonic stretching equipment (firing frequency: 17°C).
MHz, maximum output 50W). The stretching temperature is 6
It was immersed in hot water at a temperature of 60° C. at a speed of m/min and stretched while applying ultrasonic waves.

In this way, when stretched to exactly 2.8 times, that is, when stretched to a total stretching ratio of 14 times,
The object to be stretched was broken.

[Comparative Example 3] The object to be stretched in Example 3, which had been stretched up to 5 mm in the vertical direction, was stretched under the same conditions as in Example 3, except that no ultrasonic waves were oscillated. When it was stretched, that is, when it was stretched to a total stretching ratio of 7 times, it broke.

[Example 4] Polyoxymethylene was stretched according to the method and conditions of Actual Mn Example-2 to a total stretching ratio of 28 times, and the elastic modulus was 48 GPa and the strength was 2.2 GPa.

A consideration of each of the above Examples and Comparative Examples is as follows.

(1) From Example 1 and Comparative Example 1.2, the effect of the high-frequency electric field is good in the range of stretching an unstretched material up to several times, and is effective in the so-called super-stretching range beyond that. , which shows that it can be stretched to a high magnification. Therefore, since the stretching carried out in the first stage is carried out by the usual external heating method, it contributes to the reduction of equipment costs and processing costs, and this shows that stretching can be performed more economically and efficiently. It is something.

(2) Furthermore, if we compare Example 2 with Example 1 and Comparative Example 1, the high-frequency electric field is not only meaningful for simply heating the object to be stretched, but also because of its effect in the above-mentioned super-stretching region. As is clear from the above, there is a meaning in adding it during the super-stretching process of the object to be stretched. It is also found that the effect of the high-frequency electric field in the super-stretching process can be further enhanced by using external heating, if necessary. At the same time, from a comparison with Example 3 and Comparative Example 3, the same can be said even when stretching is performed while applying ultrasonic waves.

(3) From the fourth example, it can be seen that the present invention is effective in increasing the strength and modulus of plastics by increasing the stretching ratio.

(4) In each of the above embodiments, stretching is performed while applying a periodically fluctuating field such as an ultrasonic wave or a high-frequency electric field that directly acts on the polymer chains only in the late stage or final stage of stretching. There is no need to use a high frequency electric field to raise the temperature of the object to be stretched to the initial stretching temperature. Furthermore, even when using a high-frequency electric field, it is economical because the device is small, and ultrasonic waves can be used even for materials that cannot be heated dielectrically, such as polyethylene.
In order to perform dielectric heating as described in No. 7-148616, it is not necessary to add a pond substance, and therefore it is advantageous for increasing the strength.

〔Effect of the invention〕

As explained above, according to the present invention, a crystalline polymer to be stretched is stretched in multiple stages, and in the first stage of stretching, an external heating method is used, and at least in the final stage, an ultrasonic wave or a high-frequency electric field is applied. Since the crystalline polymer is stretched while adding, it is possible to economically and efficiently stretch the crystalline polymer at a high magnification, and to obtain a stretched product having high strength and high elastic modulus.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the drawing ratio and drawing stress of the object to be drawn in Example 1 of the present invention, Fig. 2 is a graph showing the same relationship in Comparative Example 1, and Fig. 3 is a graph showing the relationship between the drawing ratio and the drawing stress in Example 2. FIG. 4 is a graph showing the same relationship as above in Comparative Example 2. Figure 2 Figure 4

Claims (1)

[Claims] When stretching a material to be stretched consisting of a crystalline polymer, the stretching process is divided into at least two stages, and at least the first
In the stretching of the third stage, after heating to an arbitrary temperature in the temperature range suitable for stretching the object to be stretched using an external heating method,
or 10 times, and at least in the final stage of stretching, the stretching is performed while applying an ultrasonic wave or a high-frequency electric field containing an arbitrary frequency in the amorphous dispersion frequency band at the stretching temperature of the object to be stretched. A method for stretching crystalline polymers.