JPS5843252B2 - High quality polypropylene film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a high-magnification axially oriented polypropylene film.

Conventionally, many methods of this type of technology have been developed and put into practice, but none are yet satisfactory.

For example, in a low stretching ratio stretching method of 1.1 to 1.6 times, uniaxial longitudinal stretching is carried out at a stretching distance of more than 2000 times the thickness of the unstretched film, but with this method, shrinkage in the width direction (neckdown) is large. There is the disadvantage that the loss at the edges increases, and furthermore, stretching can only be carried out at a low magnification.If you dare to stretch at a high magnification, in addition to the loss at the edges, longitudinal tearing is likely to occur, and "wrinkles" may occur. This also causes the appearance of the film to be seriously damaged.

Therefore, a method has been proposed in which the above-mentioned drawbacks are improved by shortening the distance between the stretches and uniaxial stretching is carried out at a high magnification (for example, Japanese Patent Publication No. 4523438).

However, although this improved method eliminates the above-mentioned shrinkage in the width direction and longitudinal tearing, it also suffers from the disadvantages of minimizing the roll gap, such as loss of film ductility, severe decrease in productivity due to poor operability, and There are drawbacks such as deterioration of the film appearance due to stick and slip phenomena, and since the tension of polypropylene film is very strong during stretching, necking of the film is induced on the roll, resulting in deterioration of the film appearance. The reality is that there has been a strong desire for a high-magnification axial stretching method that eliminates all of these drawbacks.

The present invention was developed under the above circumstances and aims to provide a method for producing a uniaxially oriented polypropylene film with a high magnification, less longitudinal tearing, less shrinkage in the width direction, and excellent film appearance. Specifically, the present invention is a method of axially stretching a polypropylene film by 6 to 10 times in the longitudinal direction, in which an unstretched polypropylene film is stretched 60 to 1000 times the film thickness at the stretching point without contacting a stretching roll. The film is stretched with a distance between stretches of It is an object of the present invention to provide a method for producing a high-magnification axially stretched polypropylene film.

The details will be explained below with reference to drawings and examples.

First, the drawings show an outline of the apparatus used for this stretching process (FIG. 1) and an enlarged schematic view of the stretching section (FIG. 2).

In the figure, 1' and 3' are presser rolls, and the polypropylene resin melted with known extrusion equipment is extruded through an inflation die and a T-die to form an unstretched film 9.
After being sufficiently given the heat necessary for stretching by preheating rolls 1 and 2, it is guided to a stretching roll 3.

The unstretched film 9 of this polypropylene is 0.1
2 to 1.0M is used.

If the thickness is 1.0 mm or more, the mechanical strength of the stretching roll is required at high magnification, and the diameter of the stretching roll 3 must be increased, resulting in an increase in the stretching distance, which is contrary to the intention of the present invention. , and conversely 0.1271#! This is because if the thickness is less than 1,000%, it is easy to cause breakage during stretching at high magnification, and it becomes very difficult to achieve good stretching.

According to various experiments, the thickness of the unstretched film is 0.1
4M to 0.5M was the most preferred.

Next, the unstretched film 9 is stretched between the stretching roll 3 and the take-up roll 4 without contacting the stretching roll 3 due to the difference in circumferential speed between the rolls 3 and 4, and reaches the other take-up roll 5.

5' is a presser roll.

The distance between the stretching roll 3 and the take-up roll 4, that is, the distance between the rolls, which is equal to the tangential distance between the rolls, is the stretching distance, and in the present invention, this distance is adjusted to 60 to 100 times the thickness of the unstretched film 9. The point has one major feature.

In this stretching section, the unstretched film is in contact with the contact points of the stretching rolls 3 and 3' and the take-up roll 4, and does not come into contact with the surface of the stretching roll at all at the stretching points from the start to the end of stretching. .

This is also one of the features of the present invention; if polypropylene comes into contact with a stretching roll, the frictional resistance of polypropylene is large, so a stick phenomenon will occur on the roll surface, causing scratches on the film surface or, in some cases, causing stretching breakage. This is because it will happen.

If the distance is smaller than 60 times, the stretchability of the film will deteriorate, leading to stretch breakage during high-strength stretching, resulting in poor operability and adversely affecting productivity.On the other hand, if the distance is smaller than 100 times, This is because shrinkage in the width direction becomes large, causing vertical tearing or increasing edge loss, making it impossible to demonstrate the features of the present invention.

It has been found through many experiments that the optimum range for the distance between stretches is 100 to 800 times the thickness of the unstretched film.

When stretching at such a stretching distance, it is possible to perform stretching from low to high magnifications, but usually the stretching distance is 6 to 6.
Stretching is performed within a magnification range of 10 times.

This is because if the magnification is less than 6 times, the stretching effect will be left behind and the product will lack strength, and the stretching effect will not be fully exhibited.On the other hand, if the magnification is more than 10 times, stretching will occur and productivity will deteriorate.

There are voids in the stretched film even if it can be stretched on a temporary stand.
) is likely to occur, resulting in a decrease in film strength.

The stretching temperature is within the range of 100-150°C on the roll surface, and most preferably the average temperature of the film is 110-140°C.

If the average temperature of the film is lower than 110°C, the film tends to break easily, and if it is higher than 140°C, the surface of the film becomes rough due to stick-slip, which is undesirable.

The stretching roll 3 used for the above-mentioned stretching has a diameter of 50%φ to 250%φ. It is preferable to set the roll diameter within a range.

Incidentally, a diameter of 250%φ or more is not preferable because the distance between drawings becomes large.

A presser roll 3' is disposed opposite to the stretching roll 3 to bring the stretching roll 3 and the unstretched film 9 into close contact with each other to prevent air from being drawn in, and also to prevent the film from slipping during stretching and preventing uniform stretching. This prevents uneven thickness and poor surface (transparency).

Moreover, it goes without saying that the unstretched film is made to be tensioned or relaxed between the preheating rolls 1 and 2 and the stretching roll 3, so as to adjust the tension to suit the state of the unstretched film.

In this way, the unstretched film 9 is stretched at a magnification of 6 to 10 times and at a distance between stretches of 60 to 1000 times the thickness of the unstretched film, and reaches the take-up roll 4.5. Since the take-up roll 4.5 works as a cooling roll, the film is cooled immediately after stretching, and shrinkage in the radial direction is completely suppressed, resulting in less loss at the edges and a film with good longitudinal tear resistance. It is.

This is also one of the features of the present invention.

However, the stretched film 10 that has passed through the take-up rolls 4 and 5, which serve as cooling rolls, has the property of curling on the cooling surface, which extremely deteriorates the appearance of the film, and furthermore, when this curl occurs, it may be difficult to print or otherwise damage the film. This has the disadvantage that it also has a negative effect on secondary processing.

Therefore, in the present invention, after cooling with the take-up rolls 4 and 5, that is, cooling rolls, this cooling surface is heated, and the surface opposite to the cooling surface is further cooled.

In the figure, 6 and 7 are rolls for this purpose, 6 is an annealing roll, and 7 is a take-up roll for cooling, and such rolls 6.7 perform "annealing" and "reverse cooling" as described above. This is one of the major features of the present invention.

To explain this point in detail, first, the stretched film 10 is guided to the annealing roll 6, and the same surface as the cooled surface of the take-up roll 4 is heated to perform so-called annealing, and here the residual stress of the stretched film 10 is removed. is removed, heat setting (stabilization) is promoted, and the stretched film is produced by relaxing between the heated film surface and a take-up roll 7 that cools the opposite surface.

Therefore, it is necessary to set the roll temperature of the annealing roll 6 at 10 to 30° C. higher than the temperature of the film during stretching, and at 30° C. or higher, the curling phenomenon will occur in the opposite direction of the curling after stretching.

Note that it is also possible to reduce thermal shrinkage by relaxing the film during this annealing step.

Further, the contact time between the annealing roll 6 and the stretched film 10 needs to be 0.1 to 2.5 SeC.

Next, the surface opposite to the cooling surface immediately after the stretching (the heating surface by the annealing roll) is cooled by the take-up roll 7.

By this annealing and cooling of the opposite side, the curl phenomenon that occurs after stretching is completely eliminated, resulting in a film with excellent strength and appearance.

The film is then wound up by a winding machine (not shown) after passing through a take-up roll 8 and a presser roll 8', and the final film has excellent longitudinal and lateral strength, excellent longitudinal tear resistance, and transparency. Because of its good properties, it is used as a general packaging film, particularly in the twist packaging field and other various uses, taking advantage of the characteristics of a -axially stretched film.

Furthermore, if the film obtained according to the present invention is slit to produce flat yarn (stretched tape), the conventional flat yarn can be passed through a loom and turned into flat yarn cloth for a wide range of applications such as cloth bags, civil engineering sheets, cloth sheets, backing cloth, etc. Even when used in looms, longitudinal cracks on the loom significantly reduced the strength of the cloth itself and caused a decrease in productivity due to yarn breakage.However, these drawbacks have been greatly improved and the strength and productivity have been improved. It becomes extremely excellent.

Next, examples will be shown.

Example 1 An unstretched film having a thickness of 0.14 M was extruded from polypropylene having a size of M 4 and a specific gravity of 0.905 using an inflation molding method, and this film was uniaxially stretched in the longitudinal direction using the apparatus shown in FIG.

The extrusion conditions and stretching conditions are as follows.

Extrusion molten resin temperature 200-240°C Preheating roll circumferential speed 8X Preheating o -yv l・2A'''' stretching tension ratio between each 2φ roll 3 Preheating temperature 110-120°C Stretching temperature (film temperature) 120- 140℃ stretching ratio
7 times stretching 0-/L/3 take-off o-yv 4 □.

. . The roll diameter is 130~15.
0°.

Under the above conditions, the stretching stability, operability, and convergence contraction (neckdown) were evaluated when the stretching distance was set at 60, 100, 300, 700, and 1000 times the thickness of the unstretched film. The results shown in Table 1 were obtained.

Example 2 An unstretched film with a thickness of 0.14 m was extruded in the same manner as in Example 1, and the distance between stretching was 70 mm than that of the unstretched film.
0 times, and uniaxial stretching was performed using the apparatus shown in FIG. 1 (extrusion conditions and stretching conditions are the same as in Example 1).At this time, the stretched film was brought into contact with the annealing roll 6 and the cooling roll 7 immediately after annealing. The curling phenomenon and film appearance were determined with respect to the surface, and the results shown in Table 2 were obtained.

(Notes) ×: Poor △: Fairly good ○: Good ◎: Excellent From the table above, the present invention involves annealing the same surface as the cooling surface of the film immediately after stretching, and then cooling the opposite surface to the cooling surface of the film immediately after stretching. It is clear that the method obtained the best results.

Example 3 The stretched film used in Example 1 (distance between stretching is 700 times that of unstretched film) was slit to have a width of 6 mm and a thickness of 21 mm.
A stretched tape of μ, 1000 d was manufactured and woven using a power loom, and the weaving ratio was compared with that of a commercially available cloth woven with a stretched tape of the same shape, and the results shown in Table 3 were obtained.

(Remarks) 4) Strength per stretched film calculated from cross strength As explained above, when a polypropylene film is stretched in the uniaxial direction at a stretching ratio of 6 to 10 times, the stretching roll and take-up By adjusting the stretching distance between rolls to 60 to 1000 times the thickness of the unstretched film, longitudinal tearing and widthwise shrinkage (neckdown) can be prevented.
Stretching is carried out in an optimal state while preventing the occurrence of curls, and the curls that occur due to cooling on a take-up roll are treated by annealing the annealing roll and cooling the surface opposite to the film cooling surface immediately after stretching. Through processing, this problem can be completely resolved and a high-magnification axially stretched polypropylene film with excellent film appearance can be produced. Combined with good operability, productivity is much higher than with conventional methods. It has many excellent effects that can improve your performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an apparatus used in the method of the present invention, and FIG. 2 is an enlarged schematic diagram showing the relationship between a stretching roll and a take-off roll. 1.2...Preheating roll, 3...Stretching roll, 4゜5...Take-off roll (cooling roll)
, 6... Annealing roll, 7...
Take-off roll (cooling roll), 8...Take-off roll, 9...Unstretched film, 10...
・Stretched film, L... Distance between stretches.

Claims (1)

[Claims] 1. In a method of axially stretching a polypropylene film by 6 to 10 times in the longitudinal direction, an unstretched polypropylene film is stretched at a stretching distance of 60 to 1000 times the film thickness without contacting a stretching roll at the stretching point, A high-magnification axially oriented polypropylene characterized in that immediately after stretching, the stretched film is cooled with a take-up roll, the same side as the cooled side of the stretched film immediately after stretching is heated with a heating roll, and the side opposite to the cooling side is further cooled. Film manufacturing method.