JPH10315327A - Heat treating method for heat shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an end slack of a film due to aging and to expedite development of adding effect of various additives by biaxially orienting and winding a crystalline thermoplastic resin, and then heat treating it as remained in a rolled state under specific conditions. SOLUTION: This film is obtained by biaxially orienting and winding crystalline thermoplastic resin and then heat treating it as remained in a rolled state. The treating conditions include 18 to 66 hours at 35 to 55 deg.C, further preferably 24 to 60 hours at 40 to 50 deg.C, and furthermore preferably 24 to 48 hours at 45±2 deg.C. This treatment is executed to set free shrinkage factor at 40 deg.C for 24 hours of the film after the treatment to 0 to -3% in a width direction of the film after the treatment, and bleedout of the additive added to the film can be expedited. The resin used for the film is not particularly limited, and for example uses polyethylene, or polypropylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for heat-treating a heat-shrinkable film obtained by biaxially stretching a crystalline thermoplastic resin.

[0002]

2. Description of the Related Art Conventionally, in a heat-shrinkable film obtained by biaxially stretching, the residual internal stress due to stretching is gradually released after stretching, so that the film can flow over time (MD direction) and width direction (MD direction). It is known that a force returning in the TD direction acts and the film is extremely slack at both ends due to the force in the width direction.

In Japanese Patent Publication No. 55-11495, in order to solve these problems and to improve the smoothness of a film, a 5 to 12% relaxation in the longitudinal and transverse directions in a temperature range of 40 to 80 ° C., respectively. After winding, the roll was left at room temperature for 12 hours, and then again for 40 to 8 hours.
A method of heating to 0 ° C. has been proposed.

[0004]

However, such a conventional method has an effect on the dimensional stability over time, but it is difficult to obtain the effect of adding various additives such as an antistatic agent and a slip agent. There was a problem.

In general, heat-shrinkable films are desired to have excellent slipperiness for printing and automatic packaging. Also, when displayed as a product after shrink wrapping,
In order to avoid the adhesion of dust and the like, it is desired to add an antistatic agent and exhibit an antistatic effect. In the above-mentioned conventional method, there is a problem that the slip property and the antistatic property cannot be sufficiently exhibited by adding such a slip agent or an antistatic agent.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, to suppress the sagging of the film with the passage of time, and to promote the effect of adding various additives to a heat-shrinkable film. It is to provide a method.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for heat-treating a heat-shrinkable film obtained by biaxially stretching a crystalline thermoplastic resin. At 35 to 55 ° C. for 18 to 66 hours.

According to the present invention, after biaxially stretching and winding, heat treatment is performed in a roll state. The heat treatment conditions are 35 to 55 ° C for 18 to 66 hours, more preferably 40 to 50 ° C for 24 to 60 hours, more preferably 40 to 50 ° C for 24 to 48 hours, and even more preferably 45 ± 4 hours. 24-48 hours at 2 ° C.

By performing the heat treatment according to the present invention, the free shrinkage of the heat-treated film at 40 ° C. for 24 hours can be set to 0 to −3% in the width direction of the film. Bleed-out can be promoted.

If the heat treatment temperature is too low, the effect of preventing the film from sagging over time becomes insufficient, and the effect of adding the additive cannot be sufficiently exhibited. On the other hand, if the heat treatment temperature is too high, the bleed out of the additive may proceed too much, and the effect of the additive may be lost. Further, if the heat treatment time is too short, the effect of preventing sagging and the effect of adding the additive become insufficient, and if the heat treatment temperature is too long, the bleed out of the additive proceeds too much, and the effect of the addition disappears. There is a risk that it will. When the heat treatment temperature is about 40 ° C., it is preferably 24 to 60 hours, and when the heat treatment temperature is about 50 ° C., it is preferably about 18 to 48 hours.

The thermoplastic resin used for the heat-shrinkable film of the present invention is not particularly limited, and for example, polyethylene, polypropylene and the like can be used. The film configuration of the heat-shrinkable film is not particularly limited, and for example, a single-layer film or a multilayer film of a thermoplastic resin can be used.

The biaxial stretching method performed in the present invention is not particularly limited, and a conventional biaxial stretching method performed on a heat-shrinkable film can be applied. For example, a tenter method or a tubular method can be used. A biaxial stretching method can be used.

According to the heat treatment method of action the present invention, after heat treatment of the film 4
The free shrinkage in 24 hours at 0 ° C. can be 0 to −3% in the width direction of the film. By performing the heat treatment so as to have such a free shrinkage rate, the sagging of the film due to aging can be suppressed.

Further, according to the heat treatment method of the present invention, bleed out of various additives such as a slip agent and an antistatic agent can be promoted, and the manifestation of the effect of adding these additives can be promoted. . Therefore, for example, the required slipperiness and antistatic property can be imparted to the heat-shrinkable film.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific embodiments according to the present invention. Examples 1 to 5 After a tubular unstretched film made of a polypropylene-based resin was melt-extruded, the film was stretched 5 times in each of the longitudinal and transverse directions by a tubular method, and the obtained 12 μm-thick biaxially stretched film was cut open. Each film was rolled up. The rolled film in a roll state was heat-treated at the heating temperature and heating time shown in Table 1. The sample after the heat treatment was slit into a width of 500 mm and wound up.

The antistatic agent and the slip agent contained 4000 ppm of a polyhydric alcohol ester and 1000 ppm of an erucamide, respectively. The resulting heat-shrinkable film was measured for free shrinkage, surface resistivity, slipperiness, and sag after storage at 40 ° C. for 30 days. The measuring method is as follows.

The film after the heat treatment at 40 ° C. for 24 hours has a width of 40 mm and a length of 50 in each of the machine direction (MD direction) and the transverse direction (TD direction).
It was cut to 0 mm. 45 in the length direction of the obtained test piece
Draw a 0 mm mark, first measure the length between the marks accurately, then let the test piece stand in an oven at 40 ° C. for 24 hours, take it out, measure the length between the marks. , 40 ° C 24
The contraction rate was calculated from the length before and after the marked line at the time of standing by the following equation.

Shrinkage (%) = (starting length−backing length)
/ Starting length × 100 As is clear from the above equation, when the length after 40 hours at 40 ° C. is the same as the previous length, the shrinkage becomes 0%, and when it becomes longer, the shrinkage becomes negative. .

Surface resistivity The surface resistivity was measured according to JIS K6911. Those having a resistance of 10 ¹³ Ω or less were marked with “と し て” as having the effect of adding the antistatic agent. For those exceeding 10 ¹³ Ω, ×
It was evaluated as a mark.

According to JIS K7125, the coefficient of friction was measured.
A rating of 3 or less was evaluated as being good, and a rating of more than 0.3 was evaluated as x.

After storage at 40 ° C. for 30 days, the film after heat treatment was slit into a width of 500 mm with a slitter and wound up, and used as a test film. FIG. 1 is a perspective view showing a sag measuring device. As shown in FIG. 1, the measurement film 3 is hung on the columns 1a and 1b, and weights 2a and 2b are attached to both ends of the measurement film 3. The columns 1a and 1b are arranged such that the film portions to be measured are spaced at 2 m intervals. Also weight 2a
And 2b are 2 kg / c per sectional area of the measurement film 3
The same weight is used so as to obtain m ² .

The measurement of the sag was evaluated by measuring the difference from the height of the columns 1a, 1b at 50 mm intervals in the width direction at the center of the measurement film 3. According to this measurement, the greater the sag, the greater the difference in height from the columns 1a, 1b. Evaluation of the sag is ○ when the difference in height is less than 20 mm.
The marks, 20 to 50 mm, were evaluated as Δ, and those exceeding 50 mm were evaluated as X.

Comparative Examples 1 to 5 In Comparative Example 1, evaluation was made in the same manner as in the above example without performing heat treatment. In Comparative Examples 2 to 5, the heat treatment was performed so that the heating temperature and the heating time shown in Table 1 were obtained, and the other conditions were evaluated in the same manner as in the above Examples. Table 1 shows the evaluation results.

[0024]

[Table 1]

As is evident from Table 1, in Examples 1 to 5 according to the present invention, the sagging of the film over time was suppressed, and the effect of adding the antistatic agent and the slip agent was sufficiently exhibited. . On the other hand, in Comparative Examples 1, 2 and 4, the effect of sagging of the film with the passage of time was little or small, and the effect of adding the antistatic agent and the slip agent was not sufficiently exhibited. I understand. In Comparative Example 3 and Comparative Example 5, although the effect of the sagging of the film was obtained over time, the bleed-out of the antistatic agent and the slip agent progressed too much, so that these effects were not obtained. .

[0026]

According to the present invention, dimensional stability over time,
That is, sagging can be prevented, and the effect of an additive such as an antistatic agent can be sufficiently exhibited.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an apparatus for measuring sag after storage at 40 ° C. for 30 days performed in an example.

[Explanation of symbols]

 1a, 1b ... pillar 2a, 2b ... weight 3 ... measuring film

Claims (1)

[Claims] 1. A method for heat-treating a heat-shrinkable film obtained by biaxially stretching a crystalline thermoplastic resin, comprising the steps of:
A heat treatment method for a heat-shrinkable film, wherein the heat treatment is performed at 55 ° C. for 18 to 66 hours.