JPS5838302B2 - Polyolefin in film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a uniaxially oriented polyolefin film with improved vertical cracking resistance.

It is well known that conventionally, crystalline polyolefin sheets or films are stretched and oriented several times in one direction to form a stretched film with increased strength, and this is used as slit yarn for manufacturing woven fabrics. be.

Methods for stretching polyolefin inserts or films can be roughly divided into stretching methods using tension and rolling methods using rolls.

The former stretching method generally involves feeding a polyolefin sheet or film to be stretched between a pair of nip rolls that rotate at a low circumferential speed and a pair of nip rolls that rotate at a high circumferential speed. , stretching is carried out by the difference in circumferential speed between two pairs of Nitro rolls.

Further, some kind of heating device is installed between these two pairs of nip rolls to heat the object to be stretched.

This heating device is generally classified into three types as shown below.

That is, (1) the object to be stretched comes into contact with the heated curved surface of the solid phase in the stretching region, such as in the hot plate method in which stretching is performed on a plate having a heated curved surface or in the hot roll stretching method in which stretching is performed on a heated roll surface; A contact-type stretching method that involves stretching while stretching.

(2) A non-contact stretching method in which the object to be stretched is stretched in a gas-phase heating body, such as a hot air oven or an infrared furnace.

(3) An intermediate stretching method in which the heating element is a liquid, such as a hot water bath.

However, with any of these stretching methods, the limit of the stretching ratio is only 8 to 9 times, and even if a higher ratio is obtained, stable operation in the T industry may be difficult or unprofitable. The resulting product does not have desired properties, such as being prone to "vertical cracking," and this tendency becomes more pronounced as the elongation ratio increases.

In addition, when using the rolling method, due to the elastic recovery of the stretched object,
The efficiency of rolling is low, and therefore a multi-step rolling process is required, and it is difficult to obtain a thin molded product with a thickness of several microns.

There is also a method in which a rolling step and a stretching step are combined to orient a polyolefin sheet or film, one example of which is described in, for example, Japanese Patent Publication No. 36-93.

Since the conditions of the rolling process and the stretching process have not been fully elucidated in the various methods, it has been difficult to obtain custom-made products with improved vertical cracking resistance and other properties through stable operations.

In general, crystalline polyolefin films are stretched with a constriction phenomenon (commonly called necking) in which the width or thickness suddenly decreases at a certain point in the stretching region. Approximately 90% of a given elongation
% or more is completed at this deformation point.

Therefore, if fish eyes or foreign matter are mixed into the polyolefin film, the film is likely to break depending on the position and shape of the nesting.

In the present invention, as a result of extensive research to improve these drawbacks, we have discovered a method for producing a polyolefin in-film that enables a high degree of orientation and has excellent longitudinal cracking resistance.

That is, in the present invention, the sheet or film of crystalline polyolefin is stretched 2 to IO times in one direction by roll rolling, and then further stretched to 7 times or less by tensile stretching in the same direction. 8~ in the direction
In the method of stretching 25 times, the roll rolling process is performed between a pair of rolls rotating in opposite directions at different circumferential speeds, the bow stretching process is performed on a heated curved surface of a contact type stretching device, and these steps are performed. The ratio of each elongation magnification is

．． 15<. Elongation magnification by tensile stretching a. This is characterized by regulating the elongation magnification due to rolling.

In the present invention, the extension magnification is expressed by the following formula.

Length after rolling Rolling magnification Length before rolling Length after stretching Length before stretching The reason why the stretching magnification by rolling is limited to 2 to 10 times in the present invention is that at a magnification of less than 2 times This is because necking is likely to occur in the next stretching process as described above.
When the magnification exceeds 10 times, the rolling process is performed one step (once).
This is because, whether it is done in one step or in multiple steps (many times), a huge amount of pressure is required and the expense of multiple dogs is required.

Also, the reason for limiting the elongation ratio by stretching to 7 times or less is 7
If it is carried out at a magnification of more than 2 times, there will be a marked tendency for membrane breakage, making stable operation difficult.

The reason why the ratio of the elongation ratio between rolling and stretching is set to 0.15 or more and 3 or less is because if it is less than 0.15, most of the predetermined elongation ratio will be done by rolling. As a result, the elongation efficiency decreases, making it unsuitable for practical use.

Also, if the product is projected upside down, the vertical cracking resistance of the product will be significantly reduced.

Furthermore, the reason why the method of the present invention is limited to carrying out the stretching step using a contact type stretching device is that when using a non-contact type stretching device such as a hot air oven or an infrared furnace, or an intermediate type stretching device such as a hot water bath, it is difficult to This is also because the maximum stretching ratio is lower than when using a contact type device, and the stretched film has a reduced longitudinal cracking resistance.

In other words, when such a non-contact type device is used for the stretching process, the supply of heat from the heating medium is insufficient, and even if attempts are made to solve this lack of heat by extending the heating area, the length This requires an extremely long length, and in the case of a hot-blast stove, the amount of heated air that must be supplied is necessarily enormous.

Furthermore, since a large-sized device is required, the workability becomes extremely difficult, and this method cannot be considered as a practical method.

Furthermore, when using an intermediate type device that uses a liquid as a heating medium, since the heating medium is usually boiling water, the temperature cannot be raised to 100° C. or higher, and sufficient stretching cannot be achieved.

Although it is conceivable to use a fluid with a high boiling point, it is difficult to wash the polyolefin film in order to completely remove the liquid adhering to it in the stretching machine.

On the other hand, when a contact-type device is used as in the method of the present invention, surface pressure is generated in the region where the polyolefin finolem object to be stretched comes into contact with the heating plate or heating roll that keeps track of the heated curved surface. be.

That is, since surface pressure acts on the object to be stretched, it is possible to prevent the occurrence of longitudinal cracking in the object to be stretched.

In this case, better results can be obtained by contacting the object to be stretched with the heating medium using a method with as little friction as possible.

Accordingly, in the first stage of the rolling process in the present invention, a polyolefin sheet or film to be rolled which is thicker than the gap between the rolls is fed between a pair of conventionally known rolls rotating in opposite directions, and then rolled. By squeezing it, its thickness is reduced and it is expanded in the length direction.

During rolling, a pair of rolling rolls are rotated at different circumferential speeds, and the object to be rolled is taken up at a speed higher than the extrusion speed from the rolling rolls, or the object to be rolled is simultaneously passed through the gap between the rolling rolls and continuously rolled. This is done either by bringing it into close contact with the surface of the rolling roll having a higher circumferential speed and then taking it off.

This method significantly increases the rolling efficiency and is particularly effective for rolling polyolefins with large elastic recovery.

Furthermore, rolling is carried out at a temperature lower than the crystalline melting point or softening point of the polyolefin, but the rolling efficiency increases as the temperature of the rolled object increases. It is preferable to carry out the process between the crystal melting point and a temperature 60'C lower than the crystal melting point.

In terms of efficiency and workability, it is preferable to use rolling rolls with a diameter of 50 to 500 mm, and rolling is carried out by passing between one or several pairs of rolls once or several times.

The crystalline polyolefin resin in the present invention is not particularly limited, but particularly high density polyethylene,
Polypropylene or mixtures and copolymers thereof are preferred.

The polyolefin resin may be blended with additives such as a foaming agent, an anti-aging agent, and an ultraviolet absorber.

Next, the steps of the present invention will be explained with reference to the drawings.

Figures 1 to 3 show an example of the rolling process,
The rolling rolls 2, 2/ are rotated at different circumferential speeds, and the rolled object 1 is brought into close contact with a part of the surface of the rolling roll 20 having a high circumferential speed after passing through the rolling rollers.

In addition, in the figure, 3 is the object to be stretched.

Figures 4 and 5 show the method of the present invention, and in particular, show an example of a contact-type stretching device. In Figure 4, the workpiece 1 to be rolled is preheated by a preheating device 4 to a temperature close to the optimum temperature for rolling. After that, it is rolled by rolling rolls 2 and z.

The rolling rolls 2 and Z must not be bent during rolling, and their surface temperatures must be heated to a predetermined temperature.

The rolling rolls 2, 2' are heated by any suitable means such as circulating a heat medium inside the rolls or heating the roll surfaces with radiant heat.

The object to be stretched that has passed through the rolling rolls 2 and 2 is preheated to a suitable temperature for stretching by a preheating device 5 before entering the second stage stretching process.

In the stretching process, nip roll 6, σ is rolling roll 2,
It is rotationally driven in synchronization with the traveling speed of the object to be stretched which is extruded from 2'.

The object to be stretched slides on the hot plate γ and uniformly reduces its width and thickness over the entire area.

Thereafter, the stretched film passes through nip rolls 8 and 8' which rotate at a higher speed than nip rolls 6 and 6', passes through an annealing tank 9 to remove the shrinkage properties of the stretched film, and is then wound up through take-off nip rolls 10 and 1σ. .

Figure 5 also shows a heating roll 1 as a heating device in the stretching process.
1 a 5 1 1 b t 1 1 c , 1 1
There is no limit to the number of heat rolls that can be installed.

Note that the larger the roll diameter is, the more preferable it is, and it is also preferable that the roll be driven by free rotation.

Further, the temperature of the heating element in the contact type stretching device is preferably as high as possible within a range where the surface of the object to be stretched does not reach the melting point.

That is, preferable results are obtained when the temperature is not lower than 20'C below the melting point of the object to be stretched.

In addition, by reducing the frictional force between the heated body and the stretched body as much as possible, fusion of the stretched body and the heated body can be prevented.

This fusion can be prevented by attaching a fluorinated ethylene resin film or sheet to the surface of the heating element, or by coating it with a fluorinated ethylene resin paint.

In addition, the surface of the object to be stretched may be roughened by increasing the roughness of the surface of the rolling roll.

Furthermore, the method of the present invention is most suitable for obtaining polyolefin stretched tapes having a thickness of 15 to 60 microns.

Next, examples of the present invention will be described.

Examples 1 to 8 and Comparative Examples 1 to 10 Density 0. 9 5 6, melt index 0.3, melting point 129°C commercially available high density polyethylene with a diameter of 100°C.
Using a mm tubular die, the blow-up ratio was set to 1.
Thickness 0.20T by air cooling inflation method as 0.
/Lrn is formed into a film, and this is used as a rolled object,
Stretching was performed by rolling and hot plate stretching or hot roll stretching while changing the rolling ratio and stretching ratio in the rolling step and stretching step, respectively.

In the first stage rolling process, rolling rolls with a diameter of 100 mm and a surface length of 500 mm are arranged diagonally as shown in Figure 3, and the circumferential speed of the rolling rolls is 52 m/min on the high speed side and 13 m/min on the low speed side. (peripheral speed ratio 4:1), and the roll temperature is 12
The object to be rolled is kept at 4±1℃ and rolled at a high speed of 9. After coming into close contact with the character on the *roll side, he was taken in.

In addition, in the second step of stretching, the length is 1 as shown in Fig. 4.
．． 120℃±1℃ heating plate A with 5m gently curved surface
Alternatively, stretching was carried out using a stretching device in which four freely rotating thermal rolls B each having a diameter of 300 mm and a surface temperature of 1 2 Q'C±1° C. were arranged as shown in FIG.

The results of measuring the mechanical properties, longitudinal cracking properties, etc. of the thus obtained highly oriented and elongated polyolefin film are shown in Table 1.

For comparison with the method of the present invention, the same rolled object as in Example 1 was used, the rolling ratio was less than 2 times and the stretching ratio was more than 3, or a non-contact type stretching device was used. Heat oven C with a length of 2 m (temperature 120 ± 0
, 5°C, air flow rate 34m'/min), or a 1.7m long hot water bath D (99-100°C) using an intermediate method.
Stretched polyolefin films were produced using boiling water), and the mechanical performance and longitudinal cracking resistance were measured in the same manner as above, and the results are also listed in Table 1.

Frequency 1) Stretchability: 15 tape-shaped films with a width of 15 mm were simultaneously stretched using the same device and ranked according to the number of films cut during one hour of continuous operation.

5 or more ×, 2 to 4 △, 1 or less ○ (2) Cutting strength and elongation at break meet JIS Z 15
33, using a Tensilon type tester manufactured by Toyo Baldwin Co., Ltd., the tensile speed was 300 mm/min, and the grip interval was 300 mm.
Measured at an environmental temperature of 23±1° C. and 60±1% (relative humidity).

(31 Vertical cracking resistance is determined by the width of 10 m as shown in Figure 6.
A stretched body of 15 mm was passed through a medium-sized round file with a diameter of 15 mm, a load of 1 kg was applied to the file, and the file was heated at 15 o r. p.
After rotating at m for 10 seconds, the stretched products were ranked according to the number of longitudinal cracks that occurred in the stretched products as follows.

Number of cracks 10~fibrillation × 〃 5~9 △〃
0 to 40 Examples 9 to 10 and Comparative Examples 11 to 12 Using the same rolled object made of high-density polyethylene as in Example 1, the rolling process of the first step was carried out in the same manner as in Example 1. It was stretched and its stretchability and longitudinal cracking resistance were measured.

That is, in the first step of rolling, rolling rolls with a diameter of 100 mm and a surface length of 500 mm are arranged vertically as shown in FIG.
1), the rolled body rolled at a speed of 39 m/min from a rolling roll by varying the rolling ratio is rotated at a circumferential speed of 52 m/min without being brought into close contact with the high-speed roll surface. After the film was taken up, all subsequent stretching steps were carried out in the same manner as in Example 1 to obtain a stretched polyolefin film.

Note that the total elongation ratio was 12.

The mechanical properties, longitudinal cracking properties, etc. of the stretched polyolefin film thus obtained were measured, and the results are shown in Table 2.

In addition, in order to compare with the method of the present invention, the performance of a stretched polyolefin film was measured in the same manner as described above using the above-mentioned rolled object at a rolling ratio of less than 2 times and at a stretching ratio of more than 3 times, and is also listed in Table 2. did.

Examples 11 to 18 and Comparative Examples 13 to 20 Air-cooled inflation using a tubular die with a diameter of 100 mm from commercially available polypropylene with a density of 0.898, a melt flow index of 2, and an O melting point of 123°C with a blow-up ratio of 1.0. A film with a thickness of 0.2 mm was obtained by the method.

This film was used as a rolled object and was rolled using rolling rolls having different circumferential speeds in the same manner as in Example 1, and then stretched.

In the second stage stretching process, a heating plate A with a gently curved surface with a length of 1.5 doors and a temperature of 120°C ± 1°C as shown in Fig. 4 or a heating plate A with a surface temperature of 120°C ± 1°C is used. Stretching was carried out using a stretching device in which four hot rolls B each having a roll diameter of 300 mm were arranged as shown in FIG.

In this example, the film temperature during rolling was 150°C for L.
A highly oriented stretched polypropylene film was obtained in the same manner as in Example 1 or Example 7 except that the film temperature during stretching was 145°C±1°C.

Regarding the thus obtained stretched film, the mechanical properties and
Table 3 shows the results of measuring the longitudinal cracking properties.

2. For comparison with the method of the present invention, a rolled object was used and the rolling ratio was less than 2 times and the stretching ratio was more than 3, or a 2 m long hot air oven C using a non-contact method as a stretching device. (Temperature 120±0.5℃, air volume 3
4 m"/min) or an intermediate type method using a 1.7 m long hot water bath D (boiling water at 99-100°C), respectively, to produce stretched polypropylene films. Similar to the above, the mechanical performance and vertical cracking resistance were measured and are also listed in Table 3.

Examples 19-20 and Comparative Examples 21-22 Using the same rolled object made of high-density polyethylene as in Example 1, a rolled film with a rolling ratio of 6 was prepared in the same manner as in Example 1, and this was used as Example 1 and Comparative Examples 21-22. As in Example 7, stretching was performed using a heating plate or heating roll stretching device, and the maximum total stretching ratio was measured.

The results are shown in Table 4.

Note that the maximum total elongation ratio refers to the maximum total elongation ratio in the range where the stretchability measured by the method described in Note (1) of Table 1 is ○.

For comparison with the method of the present invention, Table 4 also shows the results of measuring the maximum total elongation ratio of the above-mentioned rolled film that was stretched using a hot air oven or boiled water as a stretching device.

As described in detail above, the method of the present invention has remarkable effects such as being able to obtain a highly oriented polyolefin stretched tape with excellent stretchability and longitudinal cracking resistance, as well as significantly increasing the stretching ratio.

[Brief explanation of the drawing]

Figures 1 to 3 are explanatory diagrams showing the rolling process in the present invention, Figures 4 and 5 are schematic diagrams showing the method of the present invention, and Figure 6 is an expanded polyolefin film obtained by the method of the present invention. It is an explanatory view for measuring vertical cracking resistance of. 1゜゛゜゜゜Boriorefin film rolled body, 2.
2'...Rolling roll 3...Polyolenoin film to be stretched, 4, 5...Preheating device, 6, 6'...Niso roll ,7...
...Heating plate, 8,8'... Nitsuno roll, 9
...... Annealing tank, 10,10/... Ninoprole, 1 1 a, 1 l b , 1 1 c
, 1 1 d・=-heating roll, 12... Stretched tape (product), 13... Round file, 14...
... Weight.

Claims (1)

[Claims] 1. A sheet or film of crystalline polyolefin is stretched 2 to 10 times in one direction by roll rolling, and then further stretched to 7 times or less by tensile stretching in the same direction, so that the sheet or film is stretched 8 to 25 times in one direction. In the double stretching method, the roll rolling process is performed between a pair of rolls rotating in opposite directions at different circumferential speeds, the tension stretching process is performed on the heated curved surface of a contact type stretching device, and each stretching process in these steps is A method for producing a uniaxially oriented polyolefin film with improved longitudinal cracking resistance, which comprises regulating the magnification so that the ratio thereof is as follows.