JPS58140220A - Heat treatment of polypropylene biaxially oriented film - Google Patents

Abstract

PURPOSE:To obtain a biaxially oriented film which ensures a sufficient effect of heat treatment in both vertical and horizontal ways by a hot air treatment of a biaxially oriented film of polypropylene after the thermal treatment thereof being brought into contact with a heating roll. CONSTITUTION:A polypropylene based biaxially oriented film 1 is heat treated brought into contact with a heating roll 3 and then, introduced into a hot air heating chamber 5 for a hot air treatment. When heat treated being brought into with the heating roll 3, the film 1 adheres to the heating roll 3 by restricting the heat shrinkage thereof 1 on the heating roll 3. The surface temperature of the heating roll immediately before it contacts the film 1 ranges from 50 to 150 deg., preferably 80-130 deg.C. The temperature of the film 1 ranges from 50-150 deg.C immediately after the hot air treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heat treating a biaxially stretched polypropylene film.

The biaxially stretched i-+ polypropylene yarn film has heat shrinkability and shrinkability over time, and after stretching, it undergoes shrinkage heat treatment (herein, heat treatment to promote shrinkage, simply heat treatment). It is well known that these physical properties can be improved in a short period of time by applying the following methods, and several reports have been made regarding this method.

For example, the general method called the tenter method, in which both ends of the film are held with clips and treated with heated air, is put into practical use by making the length of the tank sufficiently long. The mechanism of the stretching process, ``-, *- effect,
Since the equipment is bulky and expensive, it is unsuitable when the I+ of the film is narrow or as a heat treatment method for stretched films using a tubular type. There are also problems with the clipping method and ear loss. A hot air processing device without a clip has a very large film width, making it difficult to transport and use. Tubular biaxially stretched film monthly heat treatment method and 17, there is a duffle bubble method, but it is preferable because the height of the equipment is high and it is difficult to operate. It is true.

The heating roll method is an extremely promising method in terms of being small and inexpensive, as the new equipment is in the cylinder.On the other hand, it has the following drawbacks: If the film is not in close contact with the surface of the heating roll (7), the flat J'F![+ of the film will be extremely deteriorated. By restricting the tension, the necessary tension is obtained to adhere to the heating roll.

On the other hand, the degree of heat shrinkage in the width direction (horizontal) of the film is limited only by the contact friction force with the surface of the heating roll, so it is larger than the degree of shrinkage in the longitudinal direction. As a result, if the physical properties of the stretched film layer 11 after heat treatment have the following formulas in the machine direction and the transverse force direction, -r, and the properties in the machine direction are
14th point C1 of the present invention The disadvantages of the conventional shrink heat treatment method are to be addressed. , (2) Heat treatment for shrinkage while contacting with a heating roll 7. At this time, the film is brought into close contact with the heating roll by limiting the heat shrinkage of the film on a nuclear heating coil, (2) Then, heat treatment is carried out in hot air. : The gist is to perform a 4y heat shrinkage treatment.

The maximum temperature of the film heated by the heating rj-ru (approximately 50 to 150°C) 2 Uruga 80 to
130"'C is preferable 11-V). If this temperature is too low, the heat treatment will be insufficient, and if it is too high, the strength of the film will decrease (-7, or it will become sticky and roll easily!! This is not desirable because the film may shrink abnormally, become unusable, or lose its properties as a biaxially stretched film.The film that has been heat-treated with this heating roll and just before leaving the roll has a surface of the roll. The surface temperature of the roll is approximately 50-150"C, more preferably 80-130"C.

The maximum temperature of the film in the hot air treatment is 50 to 15
(A temperature of about 1"C can be adopted, but preferably 80 to 180'C within this range. For such heating, the temperature of the hot air is 50 to 170 degrees Celsius, preferably 80 to 180'C.
150°C can be adopted. If the maximum temperature of the film in this hot air heating treatment is lower than 50'C, the heat shrinkage treatment will be insufficient, and if it exceeds 150'C, the film will become sticky and tend to wrap around the roll, and it will shrink in the lateral direction. On the other hand, if the maximum temperature of the film in the hot air treatment is too low compared to the maximum temperature of the film heated with a heating roll, the shrinkage in the longitudinal direction will be insufficient, and if the temperature is too high - 5 = Not only the shrinkage in the longitudinal direction but also the shrinkage in the transverse direction is large (7), which is preferable. Therefore, the maximum flow rate of the film in this process is in the range of 50 to 150°C, when the film heated with a heating roll is 20 above the maximum temperature
Temperatures from 0.degree. C. lower to 20.degree. C. higher are preferred.

The present invention will be explained in more detail below with reference to the drawings.

The nip roll 2.4 and the heating roll 8 are used in the heating roll type heat treatment process, and by contacting the surface of the heating roll 3 with one unheated biaxially stretched film, the nip roll 2.4 and the heating roll 8 are used in the running direction (longitudinal) and width direction ( 1. Horizontal) Shrinkage stress occurs in both cases, and if the tension of the film is relaxed, shrinkage will occur.1. The important point in this step is that if the film does not come into close contact with the heating roll 3, the flatness of the film will be extremely poor and a good product will not be obtained. Therefore, tension is required in the film between the nip rolls 2 and 4, and the deceleration e of the circumferential speed of the nip roll 4 relative to the circumferential speed of the nip roll 2 (speed of delivery to the heating roll) 6 - (take-up speed from the heating roll) '', the freedom of the film must be reduced by 11 and the degree of shrinkage must be reduced by 1.

On the other hand, the shrinkage of the film in the lateral direction is suppressed by the contact friction force between the film and the heating roll 3, but the friction force 11 against the shrinkage stress is extremely small, and the film does not shrink sufficiently. Get 2 points.

As a result, the heat-treated film obtained after passing through the nip roll 4 has been heat-treated with sufficient shrinkage in the transverse direction, but this is not sufficient in the longitudinal direction. . It is generally known that this poses a problem in the next process.

In the present invention, a hot air heating chamber 5 is provided immediately after the nip roll 4 in order to solve these problems. The film that has been heat treated by the heating roll 3 is reheated by the hot air heating chamber 5 to generate shrinkage stress again. 1.On the other hand, in the longitudinal direction of the film, the effect of the pretreatment process was small, so large shrinkage stress was generated again in this process, and the nip roll 4
By reducing the circumferential speed of the nip roll 6 relative to the length, shrinkage processing can be performed in the longitudinal direction. Therefore, the heat-treated film 7 obtained through the nip roll 6 has been heat-treated to cause shrinkage in both the longitudinal and transverse directions, and its physical properties are satisfactory.

The heating method for the next step of the heating roll (7) is that the temperature is stable (~ and has a high temperature part like the far infrared leg heating method).
The hot air heating method is most suitable.1.The effective length of the hot air heating chamber 5 should be such that the passage time of the film is 1 second or more in order to obtain the desired effect of the present invention. is preferred.

In this way, according to the present invention, the heating roll method has disadvantages! By providing a simple hot air heating area immediately after the device 11, excellent heat treatment effects can be obtained with the device 1' which is simple, compact and easy to operate.

Examples 1 and 2 A biaxially stretched film of 6 x 6 times was made using the Naubular method using crystalline polypropylene with an MFRl of 0, and this was drawn using a 111 equipment. Shrinkage 1 heat treatment river under 1 of the conditions shown in the table! did. The properties of the obtained film are shown in the same table.

As shown in this table, these films have good properties and have excellent practical evaluations.

Comparative Example 1.2 A biaxially stretched film made in the same manner as in Example 1.2 using the same polypropylene was subjected to shrinkage heat treatment under the conditions shown in Table 2 using only the heating roll shown in FIG. 7ft1.

1 The properties of the obtained fluoro are shown in the same table. The film of Comparative Example 1 showed clearly unbalanced physical properties in the vertical and horizontal directions17, and the film of Comparative Example 2 had poor flatness and could not be put to practical use.

9- Table 1 10- Table 2

[Brief explanation of the drawing]

The drawing is a flow sheet showing an outline of the heat treatment process for a uniaxially stretched film according to the present invention. In this figure, the numbers are shown as follows. 1: Unheated biaxially stretched film. 2: Nitsub roll, 8: Heating roll. 4: Nitsuburol, 5: Hot air heating area. 6: Nip roll. 7: Tokobo (film (product))

Claims (4)

[Claims] (1) A biaxially stretched polypropylene film is q) heat-treated without contacting with a heating roll, and at this time, the film is brought into close contact with the heating roll by limiting the thermal shrinkage of the film on the heating roll. , ■ Polypropylene biaxial 11 [
Method for producing stretched film. (2) In addition to the method described in item 1, the surface temperature of the heating roll is 5.
A pre-nC method characterized in that the temperature is 0.~150''C. (3) The method according to item 1 or 2, wherein the temperature of the film immediately after the hot air treatment is 50 to 150°C. (4) In the method described in item 3, the temperature of the filter immediately after the hot air treatment is 20"(-; lower to 20" C higher than the temperature after the heating roll treatment surface. Characteristic AtJ arrangement method.