JPH043897B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for producing a biaxially stretched thermoplastic resin film, in which a tubular thermoplastic resin film is simultaneously stretched in the feed direction and the width direction. Can be used to stabilize stretch molding.

[Background Art and its Problems] Conventionally, the method for producing biaxially stretched thermoplastic resin films involves stretching the film in one direction with a roll, and then stretching the film with a chuck in a direction perpendicular to the stretching direction. The tenter method and
A tube-shaped film is held between a pair of upper and lower nip rolls having different circumferential speeds, and the tube-shaped film is heated between the nip rolls to a temperature at which it can be stretched. The tube method, which simultaneously stretches in the feeding direction and the width direction using a difference in circumferential speed, is widely known.

In the former tenter method, two-stage biaxial stretching is common, but for example, in the case of resins such as polyamide, the orientation during uniaxial stretching is strong, making two-stage stretching extremely difficult and making it difficult to obtain a uniform stretched film. In addition to the drawbacks of not being able to obtain the desired results, there is also the drawback of high equipment costs.

In the latter tube method, stretching occurs simultaneously;
In addition, it is easy to set the longitudinal and lateral stretching ratios, resulting in a well-balanced film, and has other great features such as low equipment costs. On the other hand, in the tube method, uniform heating of the tube-shaped film in the heating bath is most important, but it is extremely difficult to ensure this. For this reason, the tenter method is currently the predominant method for producing biaxially stretched films, although it has advantages such as low equipment costs.

By the way, in order to eliminate the drawbacks of the tube method, a method (Japanese Patent Publication No. 39-6834) has been proposed in which the front and back of the stretching zone are covered with a cover, and upward air flow prevents the tube from shaking, thereby preventing the influence of outside air. Proposed. However, even with this method, the flow velocity of the air flowing along the film decreases, especially in the bubble neck region, that is, near the stretching start point, and the heat generated between the film in this region and the outside air decreases. As a result of the lack of uniformity in the delivery and reception in the tube circumferential direction, the temperature distribution in the circumferential direction of the tube-shaped film tends to become wide, especially near the stretching start point, resulting in insufficient stretching stability and uniformity.

Therefore, there is a method of blowing air in opposite directions near the stretching start point using two air rings (for example, Japanese Patent Publication No. 45-27480, Japanese Patent Publication No. 46-15439).
No., Special Publication No. 49-47269, etc.) have been proposed.
However, both of these methods require two air rings, and have drawbacks such as the air blown from the air rings colliding with each other, causing turbulence in the air flow, and the need for heated air.

[Object of the Invention] Here, the object of the present invention is to stabilize the stretching start point at a constant position, thereby achieving high stability during stretching and forming, and improving the physical properties of the resulting biaxially stretched film. An object of the present invention is to provide a method for producing a biaxially stretched thermoplastic resin film.

Another object of the present invention is to provide a manufacturing apparatus for carrying out these manufacturing methods at extremely low cost and with ease.

[Means and effects for solving the problems] Therefore, in the manufacturing method of the present invention, after cooling the molten thermoplastic resin extruded into a tube shape from a die, the tube-shaped thermoplastic resin film is heated while being heated. In a method for producing a biaxially stretched film in which the film is fed in one direction and simultaneously stretched in the feeding direction and the width direction by tension and internal pressure in the feeding direction, It is characterized by blowing air directly at a predetermined angle to the film feeding direction.

In addition, the manufacturing apparatus of the present invention includes a cooling means for cooling the molten thermoplastic resin extruded into a tube shape from a die, and a cooling means that cools the tube-shaped thermoplastic resin film while holding it in one direction. Two pairs of nip rolls to send out, a stretching heating section that heats the film to at least a temperature at which it can be stretched between the nip rolls, and a stretching heating section that heats the film at a predetermined angle with respect to the film feeding direction from the upstream side of the stretching start point in the heating stretching zone of the film. Equipped with an air ring device that sprays directly near the stretching start point,
It is characterized by

Here, the thermoplastic resin used in the present invention is a crystalline resin such as polypropylene, polyethylene terephthalate, polyamide, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, or a combination of these crystalline resins or other amorphous resins. A multilayer structure is used.

In addition, as a stretching heating section that heats this thermoplastic resin to a temperature at which it can be stretched between both nip rolls,
For example, it is preferable that the heating source such as an infrared heater be configured in an annular shape, with the upper and lower ends, that is, the upper and lower ends in the feeding direction, open.

In addition, the air ring device has a large number of air outlets such as slits or pores arranged along the inner circumferential surface of the ring body, and the air blown from these air outlets is directed in a predetermined direction with respect to the film feeding direction. angle, preferably in the angular range of 20-60°,
It is configured to spray toward the vicinity of the stretching start point of the film stretching zone. In this case, the blown air is usually at room temperature, but heated air may also be used.

[Example] The figure shows an example of the manufacturing apparatus of the present invention. In the figure, an annular die 2 is produced by an extruder 1.
Compressed air is supplied to the inside of the molten thermoplastic resin extruded downward into a tube shape. The thermoplastic resin supplied with compressed air is air ring 3.
After being cooled through a cooling tank 4, it is taken up by a nip roll 5 and sent to the next process. The air ring 3 is disposed directly below the die 2 and cools the outer surface of the molten thermoplastic resin extruded from the die 2 into a tube shape with air.
The cooling tank 4 is disposed below the air ring 3, and has a hole in the center through which the molten thermoplastic resin extruded from the die 2 passes, and is filled with water. As a result, the molten thermoplastic resin extruded from the die 2 is first air-cooled in the air ring 3, and then further cooled by the water cooling effect in the cooling tank 4.
It is cooled and solidified. Here, the air ring 3 and the cooling tank 4 form a cooling means.

The tubular thermoplastic resin film sent out from the Nippuro roll 5 is passed through two guide rolls 6,
After passing through 7, it passes through an upper nip roll 8 and a lower nip roll 9, and is then wound up, for example, by a winder (not shown). At this time, the circumferential speed of the lower nip roll 9 is higher than the circumferential speed of the upper nip roll 8, and compressed air is injected into the tube-shaped film between the upper nip roll 8 and the lower nip roll 9, so the tube-shaped film is When heated to a temperature at which stretching is possible, the tubular film is simultaneously stretched in the feeding direction and the width direction by the effects of both, namely, the expansion force of the compressed air and the tension in the feeding direction. In this case, the stretching ratio during stretching may be appropriately determined depending on the type of thermoplastic resin, for example, 2.0 to 6.5.
It's about double that.

A stretching heating section 10 is provided between the upper nip roll 8 and the lower nip roll 9 to heat the tubular film to a temperature at which it can be stretched.
The stretching heating section 10 includes a heating source such as an infrared heater arranged in an annular shape along the inner peripheral surface of a cylindrical body whose upper and lower ends are open. Thereby, the tube-shaped film is heated to at least a temperature at which it can be stretched, mainly by radiation heat from the heating source.

On the upstream side of the stretching/heating section 10, that is, on the nip roll 8 side, there is an air ring device 11 that directly blows air at a predetermined angle with respect to the film feeding direction near the stretching start point of the heating stretching zone of the tubular film. It is provided. Air ring device 11
In this case, an air outlet such as a slit or a plurality of pores is provided along the inner peripheral surface of the annular ring body. Therefore, air is blown uniformly in the circumferential direction of the tubular film. In addition, the blowing angle α from these air blowing ports is the angular range in which the air blown from there can smoothly flow from the film stretching start point along the outer surface of the film in the feeding direction, that is, in the film feeding direction. It is set within the angle range of 20 to 60°. In addition, as the blown air,
Room temperature air is usually used, but heated air may also be used.

Further, a preheating section 12 is provided upstream of the air ring device 11, that is, on the nip roll 8 side, if necessary. The preheating section 12 has the same configuration as the stretching heating section 10, and includes an infrared heater and the like arranged along the inner peripheral surface of the cylindrical body.

On the other hand, on the downstream side of the stretching/heating section 10, that is, on the lower nip roll 9 side, guide rollers 13 are provided for sequentially flattening the tube-shaped film after stretching and introducing it into the lower nip roll 9. The guide rollers 13 are arranged in a V-shape such that the width of the plurality of guide rollers becomes gradually narrower as they go downward. As a result, the tube-like film after stretching is moved to the guide roller 13.
After being guided to the lower nip roll 9 while being successively folded into a flat shape, the sheet is heat-fixed if necessary, and then wound onto a winder (not shown), for example.

Next, the operation of this embodiment will be explained. First, a molten thermoplastic resin extruded into a tube shape from a die 2 by an extruder 1 is expanded into a tube shape by compressed air injected inside, and is sequentially expanded by an air ring 3 and a cooling tank 4. After being cooled and solidified into a tube shape, it is sent from the nip roll 5 to the upper nip roll 8 through guide rolls 6 and 7.

The tube-shaped film sent to the upper nip roll 8 is heated in a stretching heating section 10 to a temperature at which it can be stretched. Then, the compressed air injected into the thermoplastic resin film between the upper nip roll 8 and the lower nip roll 9 and the nip rolls 8, 9
The tubular film is simultaneously stretched in the feeding direction and the width direction due to the difference in circumferential speed between the two.

At this time, air is blown from the air ring device 11 near the stretching start point of the stretching zone of the tubular film. The air blown from the air ring device 11 is blown to the stretching start point of the tubular film and then flows in the film feeding direction along the outer surface of the tubular film, so that the film surface becomes a fluidized air film. wrapped. As a result, the temperature distribution at the stretching start point becomes uniform in the circumferential direction of the tubular film, so that the stretching start point is stabilized at a constant position and the film is prevented from shaking after being stretched. Moreover, the air flowing along the outer surface of the tubular film cools the film after passing through the stretching zone.

After that, the tube-shaped film after stretching is
After being folded flat by the guide roller 13,
It is taken up by the lower nip roll 9. The tube-shaped film taken up by the lower nip roller 9 is heat-set if necessary and then wound up.

Therefore, according to this embodiment, air is blown near the stretching start point of the heated stretching zone of the tubular thermoplastic resin film at an angle of 20 to 60 degrees with respect to the film feeding direction. , the stability of stretch molding can be improved.

In other words, the air blown to the starting point of stretching of the tubular film flows along the outer surface of the tubular film in the film feeding direction, creating a fluidized air film on the film surface, which results in the temperature distribution at the starting point of stretching. can be made uniform. Therefore, the stretching start point can be stabilized at a constant position, and the film can be prevented from shaking after stretching. By the way, the blowing angle α from the air blowing port
If it is outside the above range, it is difficult to cause the air blown at the stretching start point to flow smoothly along the outer surface of the tubular film and to form a uniform fluidized air film on the film surface.

As a result, it is possible to obtain a biaxially stretched film that has excellent physical properties such as good orientation balance and high thickness unevenness accuracy.

In addition, as a manufacturing device, it is sufficient to install one air ring device 11 that blows air at a predetermined angle with respect to the film feeding direction near the stretching start point, so two air ring devices can be installed as in the conventional method. Compared to what is required, equipment costs and manufacturing costs are lower, and operation control can be performed extremely easily.

Therefore, the above points will be clarified based on an example in which a biaxially stretched film was manufactured under the following conditions.
This is homopolypropylene (density 0.91g/cm ³ ,
Melt index 10 g/10 minutes, Idemitsu Polypro F900B (manufactured by Idemitsu Petrochemical Co., Ltd.) was extruded to obtain a tubular polypropylene film with a diameter of 60 mmφ and a thickness of 120 μm, and this tubular film was preheated in the preheating section 12. , stretching heating section 1
0 at a speed of 3 m/min, and stretched approximately 4 times in both the feeding direction and the width direction to obtain a biaxially simultaneously stretched polypropylene film. In addition, the preheating section 1
The ambient temperature in the drawing heating section 10 is 140 to 150°C, and the ambient temperature in the drawing heating section 10 is 230 to 240°C. wind of ^10m3 /
It was sprayed with an air volume of min.

As a result, the stretching start point was stabilized at a constant position by the air ring device 11, and stable stretching was performed without shaking of the tube-shaped film after stretching.

[Effects of the Invention] As described above, according to the present invention, since the stretching start point can be stabilized at a constant position, stability during stretch forming is high, and the resulting film has good physical properties. A method for producing a biaxially stretched thermoplastic resin film can be provided. Furthermore, according to the present invention, equipment costs and manufacturing costs are low;
Moreover, it is possible to provide a biaxially stretched film manufacturing apparatus whose operation is easily controlled.

[Brief explanation of drawings]

The figure is an explanatory diagram showing an embodiment of a thermoplastic resin biaxially stretched film manufacturing apparatus according to the present invention. 8... Upper nip roll, 9... Lower nip roll, 10... Stretching heating section, 11... Air ring device.

Claims (1)

[Claims] 1. After cooling the molten thermoplastic resin extruded into a tube shape from a die, the tube-shaped thermoplastic resin film is heated in a heating stretching zone to a temperature at which it can be stretched while being sent in one direction. , in a method for producing a biaxially stretched thermoplastic resin film in which the thermoplastic resin biaxially stretched film is simultaneously stretched in the feed direction and the width direction by tension and internal pressure in the feed direction. A method for producing a biaxially stretched thermoplastic resin film, which comprises directly blowing air at a predetermined angle with respect to the feeding direction. 2. In the method for producing a biaxially stretched thermoplastic resin film according to claim 1, the blowing angle of the air is set to 20 to 20 with respect to the film feeding direction.
A method for producing a biaxially stretched thermoplastic resin film, characterized in that the angle range is 60°. 3. A cooling means for cooling the molten thermoplastic resin extruded into a tube shape from a die, two pairs of nip rolls that hold the tube-shaped thermoplastic resin film cooled by the cooling means and send it out in one direction; a stretching heating section that heats the film to at least a temperature at which it can be stretched between the nip rolls; and a stretching heating section that heats the film to at least a temperature at which it can be stretched; 1. An apparatus for producing a biaxially stretched thermoplastic resin film, comprising a blowing air ring device.