JP2003071923A - Method for manufacturing biaxially stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent breaking of a film during an increase in speed at the beginning of molding to prevent the lowering of production efficiency without shortening the speed increase time from a molding start speed to a usual production speed. SOLUTION: At least a part of a circulating preheating fan 11 for preheating the film F before a stretching process is stopped until the moving speed of the film F at the time of stretching reaches a predetermined reference speed at the beginning of molding and, when the moving speed at the time of stretching of the film F becomes the reference speed or more, the stopped circulating preheating fan 11 is started to start the preheating of the film F.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially stretched film by biaxially stretching a plastic unstretched film kneaded by an extruder and extrusion molded from a die.

[0002]

2. Description of the Related Art When a plastic biaxially stretched film is produced by sequentially stretching a plastic unstretched film in the machine and transverse directions, for example, at the start of molding, a molding material extruded from a die is manually operated by an operator. Then, the film is introduced from the longitudinal stretching machine, the transverse stretching machine, and the heat treatment section into the winding machine through the cooling drum and wound up. And about 1/4 to 1/2 of the normal production speed (100 to 300 m / min) during continuous operation 15
The film is wound up at a speed of about 45 m / min to start production, and the winding speed is gradually increased to perform production at a normal production speed.

[0003]

By the way, at the start of molding, a film having a large thickness is used in order to enhance safety and operability, and in order to reduce operational loss, acceleration is completed in the shortest time possible. Is being operated. However, there is a problem that the film often breaks during the acceleration from the molding start speed to the normal production speed, which lowers the production efficiency.

The present invention solves the above problems and prevents the film from being broken during acceleration at the start of molding without shortening the speed-up time from the molding start speed to the normal production speed, thus improving the production efficiency. It is an object of the present invention to provide a method for producing a biaxially stretched film capable of preventing the deterioration of the film.

[0005]

In order to achieve the above object, the invention according to claim 1 stretches an unstretched film in the stretching direction in the longitudinal direction along the transport direction and in the transverse direction orthogonal to the transport direction. When a biaxially stretched film is produced by stretching, at least a part of preheating means for preheating the film before the stretching step is stopped at the start of molding until the moving speed of the film during stretching reaches a predetermined reference speed. When the moving speed of the film at that time reaches or exceeds the reference speed, the stopped preheating means is started.

According to the above construction, at the time of starting the film forming, at least a part of the preheating means is stopped until the reference speed is reached during the acceleration, so that an excessive amount of heat is applied to the film moving at low speed. It is possible to prevent the supply and prevent the breakage in the stretching step. Further, when the reference speed is reached, the preheating means that has been stopped is activated to supply the film with the amount of heat necessary for the stretching process, so that breakage in the stretching process can be prevented. Therefore, it is possible to prevent the film from breaking in the stretching process without shortening the acceleration time from the molding start speed to the normal production speed, and the production efficiency is not lowered.

According to a second aspect of the present invention, the unstretched film is stretched in the machine direction by a longitudinal stretching machine in the machine direction in the machine direction, and then in the transverse stretching process, the film is conveyed in the machine direction by a transverse stretching machine. 2 in the transverse direction orthogonal to
When manufacturing the axially stretched film, at least a part of the preheating means for preheating the film before the transverse stretching step is stopped until the film moving speed at the lateral stretching at the start of molding reaches a predetermined reference speed at the lateral stretching. When the film moving speed during stretching reaches the reference speed, the stopped preheating means is started.

According to the above construction, at the start of film formation, at least a part of the preheating means is stopped until the reference speed is reached during acceleration, whereby an excessive amount of heat is applied to the film moving at low speed. It is possible to prevent the supply and prevent the breakage in the transverse stretching step. Further, when the reference speed is reached, the amount of heat required for the stretching process can be supplied to the film by activating the stopped preheating means, so that breakage in the transverse stretching process can be prevented. Therefore, it is possible to prevent the film from breaking in the transverse stretching step without shortening the acceleration time from the molding start speed to the normal production speed, and the production efficiency does not decrease.

Further, the invention according to claim 3 is the structure according to claim 1 or 2, wherein the reference speed is selected from the range of 1/4 to 1/2 of the normal production speed of the film at the time of stretching and the kind of material. The preheating means is selected by molding conditions and is constituted by a circulating preheating fan.

According to the above construction, the reference speed for activating the preheating means is set to be in the range of 1/4 to 1/2 of the normal production speed, so that an appropriate amount of heat can be supplied.
It is possible to effectively prevent breakage during stretching.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Here, an embodiment of a method for producing a biaxially stretched film according to the present invention will be described with reference to FIGS.

First, a biaxial sequential stretching type film manufacturing facility and its manufacturing procedure will be described. As shown in FIG. 3, this manufacturing facility includes an extruder 1 for heating and kneading a resin raw material,
A die 2 for extruding the film F, a cooling drum (casting roll) 3 for rapidly cooling the extruded film F to produce an unstretched film F, and a hot water tank 4 for controlling the humidity of the unstretched film F (PET resin). However, it is unnecessary), a longitudinal stretching machine 5 for stretching the unstretched film F in the longitudinal direction, a preheating means 6 for preheating the longitudinal stretching film F, a transverse stretching machine 7 for stretching in the lateral direction, and a heat treatment for heat treating the stretched film F. Part 8
And a winding machine 9 for winding the stretched film F.

In the above construction, the resin raw material is heated and kneaded by the extruder 1, extruded from the die 2, and further rapidly cooled by the cooling drum 3 to form the unstretched film F. Then, in the manufacturing process for manufacturing a stretched film from this unstretched film, as shown in FIG. 2, after the unstretched film F is introduced into the hot water tank 4 in the tempering step a to control the humidity, as shown in FIG. In the longitudinal stretching step b, the unstretched film F is stretched by the longitudinal stretching machine 5 at room temperature to about 2 to 5 times in the longitudinal direction. Then, in the preheating step c, the lengthwise stretched film F is 80 to 1 by the preheating means 6.
After preheating to 00 ° C., in the transverse stretching step d, the longitudinal stretching film F is stretched in the transverse direction by about 2 to 4 times by the transverse stretching machine 7 at 100 ° C. to 160 ° C. Further, in the heat treatment step d in the heat treatment section 8, a heat-fixing treatment for surface-fixing the shrinkage characteristics of the film F caused by the stretching action at high temperature, and further reducing or adjusting the shrinking force slightly remaining in the stretched film F, are adjusted. By performing the heat relaxation process for determining the characteristics of the film F with respect to heat and the cooling process for cooling the film to the temperature for winding the film on the winding machine 8, the winding machine 9 performs the winding process e.
Thus, the biaxially stretched film F is manufactured by winding the film F.

At the start of molding by the above-mentioned manufacturing equipment, the worker manually operates the film F from the die 2 to the cooling drum 3, the warm water tank 4, the longitudinal stretching machine 5, the preheating means 6, the transverse stretching machine 7,
The heat treatment section 8 and the winding machine 9 are introduced in this order, and the starting end of the film F is wound onto the reel of the winding machine 9. Then, continuous operation is performed by gradually increasing the forming start speed of the stretched film F wound on the winder 9 to the normal production speed. The molding start speed here is 1 / the normal production speed: 100 to 300 m / min.
It is set in the range of 5 to 1/6, for example, 15 to 45 m / min, and from the molding start speed to the normal production speed, for example, 3 to
The speed is increased over 15 minutes.

By the way, the production temperature condition of the film F at the start of molding (during acceleration) is as short as 3 to 15 minutes from the molding start speed to the normal production speed. Time) and continuous operation are set the same. This is because changing the production temperature condition only for a short time makes it difficult to set and control the equipment and imposes a heavy burden on the cost.

The inventors of the present invention are responsible for a large number of breakages of the film F during acceleration at the start of molding because the amount of heat supplied from the preheating means 6 to the film F moving at a low speed is excessive. Was overheated, which caused the film F to break in the transverse stretching step d. As shown in FIG. 1, the preheating means 6 sucks hot air after heating the film F from the recovery duct 11b and superheats it in the preheater main body 11a. A circulation preheating fan 11 that supplies hot air to each of the lower surfaces is adopted. The present inventors, at the start of molding,
In order to properly control the amount of heat supplied to the film F by the circulating preheating fan 11, the circulating preheating fan 11 should not be started from the beginning, but should be started during acceleration so that the worker can perform it manually. According to the above, it was found that the amount of heat supplied can be easily controlled to prevent the film F from breaking. Then, the time to start the preheating was obtained from the speed of the film F being accelerated, and an appropriate reference speed was determined. This reference speed is based on the type of film F to be molded, molding conditions,
Although it changes depending on the thickness of the film F and the transverse stretching ratio,
0.25 to 0.5 of the normal production rate of the film F at the time of stretching
If it is selected from the range of double (1/4 to 1/2), the breakage of the film F can be prevented. Further, the smaller the thickness of the film F, the easier it is to break due to excessive heat, and the higher the transverse stretching ratio, the easier it is to break due to excessive heat.
It is better not to start the circulation preheating fan 11 until the reference speed approaches 0.5 times the normal production speed and the film F forming speed becomes high.

The operator operates or stops the circulating preheating fan 11 by visually observing the switch 14 of the circulating fan 11.
It may be started and stopped by operating, but here, the circulation preheating fan 11 is automatically operated by the start control unit 13 based on the detection speed of the film speed detector 12 that detects the film speed in the transverse stretching machine 7. Is configured to turn on / off the switch 14.

In the large transverse stretching machine 7, the circulating preheating fans 11 are arranged in a plurality of stages in the moving direction of the film F in order to preheat the film F step by step. The circulation fan 11 is manually operated or the start control unit 13 is used.
May be automatically started by.

(Example) In the manufacturing equipment having the above-mentioned structure,
The PET material was extruded at 280 ° C. with a die 2 and rapidly cooled with a chill roll 3 having a surface temperature of 35 ° C. to obtain a thickness of 160.
An unstretched film F having a thickness of 1 μm and a width of 1400 mm was obtained. This unstretched film F was introduced into the longitudinal stretching machine 5 at a temperature of 88 ° C. and stretched 3.4 times in the longitudinal direction to form a film F having a width of 1100 mm (longitudinal stretching step b). After passing through the preheating means 6 in the stopped state (preheating step c), it is introduced into the flat type horizontal stretching machine 7 and transversely at a temperature of 120 ° C.
235 by the heat treatment part which was stretched to 0 times (transverse stretching step d)
It was heat-treated at 0 ° C., subjected to a relaxation treatment of 3% in the lateral direction, and wound by a winder 9. At this time, the film speed of the transverse stretching machine 7 is 35 m / min (1/5 of the production speed), the circulation preheating fan 11 is stopped and not preheated, and the speed increasing is started to 90 m / min ( When the production speed became 1/2), the circulating preheating fan 11 was started. And when the speed-up time has passed 10 minutes, the production speed is 180 m / mi.
When the speed reaches n, the acceleration is completed and continuous operation is started, and the thickness is 12 μm.
Of the biaxially stretched film F.

According to the above-mentioned embodiment, the film F was not broken during the acceleration at the start of molding, and the film could be operated satisfactorily.
This was the same no matter how many times it was repeated, and the film F could be operated satisfactorily without breakage.

(Comparative Example 1) A biaxially stretched film F was produced in the same manner as in Example 1, but the circulating fan 11 of the preheating means 6 continued to be in an operating (on) state from the beginning.

During the lateral stretching step c during the speed increase, the film F was fractured from the center to the longitudinal direction. Film F
Was re-supplied 4 times, but the same breakage occurred 3 times, and the production rate was not reached.

(Comparative Example 2) A biaxially stretched film F was produced in the same manner as in Example 1, but the circulating fan 11 of the preheating means 6 continued to be stopped (off) from the beginning.

Even when the speed of the film F reached 90 m / min, the circulating fan 11 was not started and the speed was continued, but when the speed reached 120 m / min, the film F broke. Resupply was carried out 4 times, but all 150m / mi
The film F was broken by the time of n, and the production rate was not reached.

The above results are shown in Table 1.

[0026]

[Table 1] In the above embodiment, the biaxial successive stretching type film manufacturing method has been described, but the same applies to the biaxial simultaneous stretching type film manufacturing method in which the preheating means is arranged at the inlet of the biaxial stretching machine.

[0027]

As described above, according to the first aspect of the present invention, at the beginning of film formation, at least a part of the preheating means is stopped until the reference speed is reached during the acceleration. It is possible to prevent an excessive amount of heat from being supplied to the film which is moving at a low speed, and to prevent breakage in the stretching process. Further, when the reference speed is reached, the preheating means that has been stopped is activated to supply the film with the amount of heat necessary for the stretching process, so that breakage in the stretching process can be prevented. Therefore, it is possible to prevent the film from breaking in the stretching process without shortening the acceleration time from the molding start speed to the normal production speed, and the production efficiency is not lowered.

According to the second aspect of the invention, at the start of film forming, until the reference speed is reached during acceleration.
By stopping at least a part of the preheating means, it is possible to prevent an excessive amount of heat from being supplied to the film which is moving at a low speed, and prevent breakage in the transverse stretching step. Further, when the reference speed is reached, the amount of heat required for the stretching process can be supplied to the film by activating the stopped preheating means, so that breakage in the transverse stretching process can be prevented. Therefore, without shortening the acceleration time from the molding start speed to the normal production speed, it is possible to prevent the film from breaking in the transverse stretching step,
There is no reduction in production efficiency.

Further, according to the invention of claim 3, the reference speed for activating the preheating means is 1 / the normal production speed.
By starting from the range of 4 to 1/2, it is possible to supply an appropriate amount of heat, and it is possible to effectively prevent breakage during stretching.

[Brief description of drawings]

FIG. 1 is a front view showing a preheating means, showing an embodiment of a method for producing a biaxially stretched film according to the present invention.

FIG. 2 is an explanatory view showing a manufacturing process for manufacturing a biaxially stretched film from the unstretched film.

FIG. 3 is an overall configuration diagram showing a manufacturing facility for the same biaxially stretched film.

FIG. 4 is a plan view showing a film shape of the film extending portion.

[Explanation of symbols] F film a Humidification process b Vertical stretching process c Preheating process d Horizontal stretching process e Heat treatment process f Winding process 1 extruder Two dies 3 cooling drum 4 hot water tank 5 Vertical stretching machine 6 Preheating means 7 Horizontal stretching machine 8 Heat treatment department 9 Winder 11 Circulation preheating fan 12 film speed detector 13 Start control unit 14 switch

Claims (3)

[Claims] 1. An unstretched film is stretched in a longitudinal direction along the transport direction and in a transverse direction orthogonal to the transport direction in a stretching step to obtain 2
When manufacturing an axially stretched film, at the start of molding, at least a part of preheating means for preheating the film is stopped before the stretching step until the film moving speed during stretching reaches a predetermined reference speed. A method for producing a biaxially stretched film, which comprises activating the stopped preheating means when the film moving speed reaches or exceeds the reference speed. 2. An unstretched film is stretched in a longitudinal direction along a conveying direction by a longitudinal stretching machine in a longitudinal stretching step, and then in a transverse stretching step, a film is stretched in a transverse direction orthogonal to the conveying direction by a transverse stretching machine. In producing the biaxially stretched film, at least a part of preheating means for preheating the film before the transverse stretching step is stopped until the moving speed of the film during transverse stretching reaches a predetermined reference speed at the start of forming. Every time, when the moving speed of the film at the time of transverse stretching reaches the reference speed, the stopped preheating means is started, and the method for producing a biaxially stretched film. 3. The reference speed is selected from the range of 1/4 to 1/2 of the normal production speed of the film at the time of stretching depending on the type of material and the molding conditions, and the preheating means is constituted by a circulating preheating fan. The method for producing a biaxially stretched film according to claim 1 or 2.