JPS6343216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biaxial stretching apparatus for plastic films.

The term "film" as used herein refers to not only a film in a narrow sense but also a tubular material including a reticulated web.

Stretching is a technology that improves properties such as strength, transparency, and gas barrier properties of plastic films to create high added value and enhance performance. The stretching process is carried out using a tenter method (a clip tenter method in which both edges of the film are held with clips and the film is stretched in the width direction while running in the longitudinal direction).
The simultaneous biaxial stretching process was mainly based on the tubular inflation method in which an expanding force was applied to the tubular film from the inside. However, the former method requires large-scale and expensive heating furnaces, clip running mechanisms, and other equipment, and is uneconomical because it leaves a large amount of unstretched parts on both sides of the film, which are later removed. There were some shortcomings. In addition, although the equipment cost is relatively low in the latter method, it is difficult to control the stretching, and variations in the stretching ratio and film thickness are likely to occur.
Obtaining highly accurate drawn products has been problematic.

In view of these circumstances, the present invention stretches a film using a new method that is different from any of the conventional methods described above. The horizontal stretching mechanism is composed of left and right stretching belts that individually engage within a range of half a circumference or less of each pulley, and a nip roll for film feeding installed on the supply side of the belt, and a film feeding roll installed on the supply side thereof, and a film feeding belt for each of the stretching belts. By performing longitudinal stretching using the peripheral speed difference between the pulley and the pulley, it is possible to efficiently stretch a tubular film biaxially and vertically with a much simpler structure compared to conventional methods. A stretched product can be obtained, and in particular, by imparting an appropriate horizontal orientation effect during longitudinal stretching, longitudinal cracks can be prevented during subsequent horizontal stretching after longitudinal stretching, resulting in good quality biaxial stretching without defects. An object of the present invention is to provide a stretching device that can obtain a film.

Hereinafter, the present invention will be explained with reference to illustrative embodiments.

FIG. 1 shows the overall structure of the apparatus of the present invention, in which 1 and 1' are a pair of left and right stretching pulleys;
2' is a left and right stretching belt individually arranged on each pulley 1, 1', 3, 4, 5, 6 and 3', 4', 5', 6' is a belt for each belt 2, 2'. Guide pulley 7 is a heating chamber that accommodates these. By appropriately supplying heating steam or the like into the heating chamber 7, the film can be heated to a temperature suitable for stretching.

Both stretching pulleys 1 and 1' are mounted on drive shafts 1a and 1'a, respectively, in a state in which they are arranged at a predetermined interval on the left and right within the same plane in the heating chamber 7, and are driven by pulleys (not shown). The pulleys 1 and 1' are connected to the apparatus and are configured to rotate synchronously at a constant rotational speed in opposite directions in the direction in which the original film A fed from above is fed between the two pulleys 1 and 1'. Then, the stretching belts 2, 2' are symmetrically connected to the stretching pulleys 1, 1', respectively.
guide pulleys 3 to 6, 3' so that they engage the lower half of the pulleys 1, 1' in a range less than half the circumference.
~6'. Also, belt 2,
2' is reversed at guide pulleys 3, 4 and 3', 4' located on the left and right above the stretching pulleys 1, 1', and the stretching pulleys 1, 1' are placed outside the circumferential loop of the belts 2, 2'. Both stretching pulleys 1 and 1' are connected from above by forming loops that engage with each other.
For the flat tubular original film A supplied between,
With the belts 2, 2' positioned inside the belts 2, 2', insert the bent edges of the film from the inside and outside.
and extension pulleys 1 and 1'. 8 is a support column for the guide pulleys 3, 3'. Further, 9 and 9' are cutters for lengthwise cutting the film provided near the film take-out point (the point of separation between each stretching pulley 1 and 1' and each belt 2 and 2') on both the left and right sides; Film take-out turn rolls 11, 11, which are arranged horizontally on both front and rear sides corresponding to the point, are nip rolls for taking out stretched film.

In this way, the left and right stretching pulleys 1, 1'
A lateral stretching mechanism is composed of the stretching belts 2 and 2'.

On the other hand, on the raw film supply side to this lateral stretching mechanism, stretching pulleys 1 and 1', a belt 2,
A nip roll 12 for feeding the film is provided above the point at which the film is fed into the film 2' at an appropriate distance. The pair of rolls constituting the nip roll 12 are rotated while being pressed against each other with an appropriate force by a cylinder 13, a spring, etc., so that the film A is sandwiched between the two rolls to prevent the raw film A from slipping. We are trying to send it towards the loading point. This nip roll 12 is rotationally driven by a nip roll drive device 14, and
The driving speed of the nip roll drive device 14 is set so that the peripheral speed of the nip roll 12 is a constant peripheral speed that is slower than the peripheral speed of the stretching pulleys 1, 1' by a predetermined value. As a result, in the section between the nip roll 12 and the film biting point in the lateral stretching mechanism, a longitudinal tension is applied to the film A in accordance with the peripheral speed difference between the stretching pulleys 1, 1' and the nip roll 12. This section becomes the longitudinal stretching section 15 for the film A. This longitudinal stretching section 15 is provided with a film width regulating means for keeping the film during longitudinal stretching at a substantially constant width to prevent shrinkage in the width direction. As a means of regulating the film width,
In the illustrated example, a large number of idling rollers 17..., 17'... are arranged in rows on both left and right sides of a support frame 16 protruding from the upper end of the guide pulley support column 8. These idle rollers 17..., 17'...
With respect to the tubular film A fed through 2, it is located inside the tubular film A and is in contact with the left and right inner surfaces of the film so as to restrict the film A to a constant long circular cross section, and as the film A moves, It guides the film to the biting point while rotating freely. The idle rollers 17..., 17'... are arranged so that they have a predetermined interval on the left and right sides corresponding to the original film A to obtain the above-mentioned regulation state, and in the vertical direction from the nip roll 12 to the guide pulleys 3, 3. Arrange them as densely as possible within the range up to .

The operation of the stretching device constructed in this way will be explained below based on the drawings of FIGS. 2 to 5.

In this stretching apparatus, first, the tubular film A is stretched longitudinally in the longitudinal stretching section 15, and then stretched laterally by a transverse stretching mechanism.For convenience of explanation, the operation of the transverse stretching mechanism will be explained first. The flat tubular film A is sent between the stretching pulleys 1 and 1' via the film feeding nip roll 12 and the longitudinal stretching section 15, and the film A is fed between the stretching pulleys 1 and 1' at the film feeding point, that is, each stretching pulley 1 and 1' and the belt 2. , 2', the bent portions of the film A are gripped from the inside and outside by the belts 2, 2' and the stretching pulleys 1, 1'. While gripped in this manner, as the stretching pulleys 1, 1' rotate, the film is transferred and guided in accordance with the rotational loci of the two pulleys 1, 1', in which the stretching pulleys 1, 1' diverge from each other. Tension is applied to the film, gradually expanding the width of the film and stretching it laterally. In this case, pulley 1,
From the lowest point 1', the film A is turned over and continues to be stretched until it reaches the film take-out point. When the film reaches the film take-out point, the film is separated from between the stretching pulleys 1, 1' and the belts 2, 2', and as the film is moved by the left and right cutters 9, 9', it is longitudinally cut on both left and right sides. ,
The stretched film A′ before and after being divided in this way,
A′ is the turn roll 10 for taking out the film;
10 and Nipprol for film collection 11, 11
It is taken out after passing through.

In the preceding stage of this transverse stretching mechanism, the film A is longitudinally stretched in the longitudinal stretching section 15. That is, by making the circumferential speed of the film feeding nip roll 12 slower than the circumferential speed of the stretching pulleys 1 and 1', the moving speed at which the film A passes through the nip roll 12 and the film feed rate in the lateral stretching mechanism are adjusted. There is a difference in the moving speed when the film A reaches the closing point, and this speed difference causes the film A to
Tension in the longitudinal direction (longitudinal direction) as shown by the wide arrow in FIG. 3 is applied, and the film A is stretched longitudinally. In this case, the stretching ratio of the longitudinal stretching is determined by the above-mentioned moving speed difference, that is, the peripheral speed difference between the film feeding nip roll 12 and the stretching pulleys 1, 1'. Therefore, the above-mentioned circumferential speed difference may be set in advance according to the required longitudinal stretching ratio.

In this longitudinal stretching operation, the film width regulating means such as the idle rollers 17, 17', etc. provided in the longitudinal stretching section 15 shrink the film in the width direction by keeping the film A in a constant cross-sectional shape during longitudinal stretching. This acts to impart appropriate transverse orientation to the film, and as a result, it is possible to prevent vertical cracking of the film during subsequent transverse stretching. In other words, if there is no such film width regulating means in the longitudinal stretching section 15, the film A will shrink in the width direction as shown by the imaginary line in FIG. if you did this,
If the stretching ratio is k, the film will shrink to 1/√ in the width direction, and the thickness will also become 1/√. In this case, since the film is fibrillated in the longitudinal direction, longitudinal cracks are likely to occur in the subsequent transverse stretching process. On the other hand, when a film width regulating means is provided in the longitudinal stretching section 15 as in the present invention, a transverse orientation effect corresponding to 1/√ is produced with respect to the longitudinal stretching ratio k, and fibrillation of the film is prevented. This makes it possible to prevent vertical cracking in the next horizontal stretching process. In particular, if a large number of free rotating rollers 17, 17', etc. arranged in a predetermined arrangement are used as the film width regulating means as in the embodiment, it is possible to move the film as much as possible in the longitudinal stretching section 15 while regulating the film width accurately and constant. directional resistance can be kept small.

Note that the film width regulating means in the longitudinal stretching section 15 is not limited to the above-mentioned embodiments, but may also be, for example, applying an appropriate gas pressure inside the tubular film A to keep the film A in an expanded state. . The pressurized gas in this case is preferably heated steam, since it also has the effect of heating the film A appropriately. It is also possible to use the film width regulating means using gas pressure in combination with the film width regulating means shown in the above embodiments.

As explained above, the apparatus of the present invention employs a lateral stretching mechanism that includes left and right stretching pulleys arranged at a predetermined interval, and left and right stretching belts that engage within a range of half a circumference or less of each pulley. , by gripping the left and right bent portions of the flat tubular film fed between both pulleys from the inside and outside with each belt and each pulley, and transporting and guiding the film to spread outward as both pulleys rotate. At the same time as transverse stretching, in the front stage of the transverse stretching mechanism, the peripheral speed of the film feeding nip roll is made slower than the peripheral speed of the stretching pulley, and the film is stretched by the difference in peripheral speed between the nip roll and the stretching pulley. Since a longitudinal stretching section is provided for longitudinal stretching, the film can be stretched continuously and efficiently in two axes in the longitudinal and lateral directions, and the structure of the apparatus can be made much simpler and more compact, thereby reducing equipment costs. Can be done. In other words, when attempting to perform longitudinal stretching in addition to transverse stretching using the transverse stretching mechanism using the above-mentioned pulleys and belts, the above-mentioned longitudinal stretching device, which is equipped with means for independently applying longitudinal tension to the film, is used. Although it is conceivable that the film feed section is directly connected to the upstream side of the transverse stretching mechanism, compared to such a structure in which the longitudinal stretching device and the transverse stretching mechanism are directly connected, the present invention does not require a unique longitudinal stretching device. Since the stretching pulley and feeding nip roll are commonly used for longitudinal stretching, the structure can be significantly simplified and downsized. Moreover, high quality,
A stretched product with high magnification and high precision can be obtained. Moreover, in particular, a film width regulating means is provided in the longitudinal stretching section to prevent shrinkage in the width direction of the film during longitudinal stretching, so that an appropriate lateral alignment effect can be obtained during longitudinal stretching, and subsequent lateral stretching can be performed. This has excellent effects such as being able to prevent vertical cracking of the film during film, further improving the quality of the stretched product, and increasing the yield.

[Brief explanation of the drawing]

The figures show an embodiment of the device of the present invention, in which FIG. 1 is a perspective view of the entire device, FIG. 2 is a perspective view of the main part of the device in use, and FIG. 3 is a vertical sectional view of the main part of the device. 4 is an enlarged sectional view of a portion taken along the line - in FIG. 3, and FIG. 5 is a sectional view taken along the line - in FIG. 3. 1, 1'...pulley for stretching, 2, 2'... belt for stretching, 7... heating chamber, 12... nip roll for film feeding, 14... nip roll drive device,
15...Longitudinal stretching section, 17, 17'... Idle roller (film width regulating means).

Claims (1)

[Claims] 1. Two left and right stretching pulleys arranged in the same plane at a predetermined interval in the heating chamber and driven by a pulley drive device so as to rotate synchronously in opposite directions at a constant rotation speed, and each of the stretching pulleys. The bent edges of both sides of the flat tubular film sent between the two pulleys are formed by left and right stretching belts that are individually disposed on the pulleys so as to engage within a range of less than half the circumference of each pulley. A lateral stretching mechanism is constructed in which the film is laterally stretched by holding the film between the respective pulleys and each belt and guiding the film to widen as the both stretching pulleys rotate. A film feeding nip roll is provided on the film supply side of the mechanism, and a nip roll driving device that drives the film feeding nip roll at a constant circumferential speed that is slower than the peripheral speed of the stretching pulley is installed to drive the film feeding nip roll and the transverse stretching. A film width regulating means for forming a longitudinal stretching section in which the film is longitudinally stretched by a peripheral speed difference between the nip roll and the stretching pulley between the mechanism and the film width regulating means for preventing the film from shrinking in the width direction in the longitudinal stretching section. A biaxial film stretching device characterized by being provided with.