JP6634207B2 - Longitudinal stretching device - Google Patents

Description

  The present invention relates to a method for producing a thermoplastic film, and more particularly, to a longitudinal stretching apparatus for longitudinally stretching a sheet-like thermoplastic resin into a longitudinally stretched film.

  Films made of thermoplastic resins such as aromatic polyesters, polyolefins and polyamides have excellent properties such as mechanical strength by forming biaxially stretched films that are stretched in two orthogonal directions. Used.

  FIG. 4 shows an example of a manufacturing process of a biaxially stretched film made of a thermoplastic resin. In FIG. 4, the thermoplastic resin is supplied from the hopper 10 to the melt extruder 20 in the form of chips, heated and melted by the melt extruder 20, continuously extruded from the slit die 30, and brought into close contact with the casting roll 40. After being cooled, the unstretched sheet 2 is obtained. The continuous unstretched sheet 2 is stretched in a continuous direction by a longitudinal stretching device 101 to become a longitudinally stretched film 3, and the longitudinally stretched film 3 is stretched in a width direction by a transverse stretching device 102 to become a biaxially stretched film 4. It is wound on a core material by a winding device.

  Among them, as described in Patent Document 1, the longitudinal stretching device 101 is generally configured by a low-speed roll group, a high-speed roll group, and a heating stretching section between both roll groups. An example is shown in FIG. In FIG. 5, a longitudinal stretching device 101 heats an unstretched sheet 2 to a temperature equal to or higher than a softening point temperature (of a thermoplastic resin as a material thereof) in a heating stretching section 6. It has a function of giving a peripheral speed difference between the two and stretching the unstretched sheet 2 by the peripheral speed difference to form a longitudinally stretched film 3. Here, when the unstretched sheet 2 is heated to a temperature equal to or higher than the softening point temperature only by the heating and stretching section 6, uneven heating or the like occurs. It has a preheating function of heating. During preheating, it is desirable to uniformly heat both sides of the unstretched sheet 2. Therefore, the low-speed roll group 5 alternately heats both sides of the unstretched sheet 2 with relatively small rolls 5R (5R1 to 5R4). Configuration.

  As described above, since the unstretched sheet 2 is stretched 2 to 4 times by the longitudinal stretching apparatus 101, the thickness of the longitudinally stretched film 3 becomes 1/2 to 1/4 of that of the unstretched sheet 2. Similarly, since the longitudinally stretched film 3 is stretched 2 to 4 times by the transverse stretching apparatus 102, the thickness of the biaxially stretched film 4 is ２〜 to １ ／ of the longitudinally stretched film 3. Therefore, the thickness of the biaxially stretched film 4 is approximately 1/10 of the unstretched sheet 2. That is, the thickness of the unstretched sheet 2 to be stretched by the longitudinal stretching apparatus 101 is about 10 times the desired thickness of the biaxially stretched film 4.

JP-A-4-282225

  Conventionally, the base film of a recording medium such as a magnetic tape is mainly used as the use of a biaxially stretched film, and the thickness is mostly several tens μm or less.In recent years, for optical use, industrial use, etc., although the thickness exceeds 100 μm, The ratio is increasing, and the demand exceeds 300 μm depending on the application. For this reason, it is necessary to increase the thickness of the unstretched sheet to be stretched by the longitudinal stretching apparatus.

  However, even if the unstretched sheet is made of a relatively flexible thermoplastic resin, it becomes difficult to bend when its thickness increases. As a result, as shown in FIG. 5, when the unstretched sheet 2 is wound around the first low-speed roll 5R1 of the low-speed roll group, the poor adhesion phenomenon that the unstretched sheet 2 does not adhere to the surface of the low-speed roll 5R1 (see FIG. 6). 2d1, 2d2) is more likely to occur. When such a poor adhesion phenomenon occurs, unevenness in preliminary heating occurs, or a scratch occurs on the surface of the unstretched sheet due to slippage between the unstretched sheet and the low-speed roll, which eventually adversely affects the quality of the biaxially stretched film. Exert.

  Corresponding to the increase in the thickness of the unstretched sheet, if the roll diameter of the low-speed roll group can be increased, it becomes easy to adhere to the roll even if it is difficult to bend, but as described above, both sides of the unstretched sheet are heated uniformly. This is disadvantageous from the viewpoint of, in particular, the larger the thickness of the unstretched sheet, the more unsuitable.

  The present invention has been made in view of the above problems, and even if the thickness of an unstretched sheet made of a thermoplastic resin is large, the unstretched sheet can be conveyed in close contact with a low-speed roll in a longitudinal stretching apparatus. It is intended to provide a longitudinal stretching device effective for maintaining the film quality after stretching.

In order to solve the above problem, the invention described in claim 1 is:
A continuous unstretched sheet made of a thermoplastic resin, the unstretched sheet is stretched while running in a continuous direction to form a longitudinally stretched film, a longitudinal stretching apparatus,
Along the downstream from the upstream in the direction in which the unstretched sheet travels, a low-speed roll group, a heating stretching section, and a high-speed roll group,
The low-speed roll group has a function of pre-heating the unstretched sheet to near a softening temperature by contacting and passing through a plurality of low-speed rolls,
Further upstream of the uppermost low-speed roll of the low-speed roll group,
The non-stretched sheet is further provided with a non-contact preheating unit that heats the non-stretched sheet in a non-contact manner such that a temperature of a surface opposite to a surface that first contacts the low-speed roll group is higher .

The invention according to claim 2 is the longitudinal stretching device according to claim 1,
The non-contact preheating unit is characterized in that a heat source is arranged only on a side opposite to a surface where the unstretched sheet first contacts the low-speed roll group.

The invention according to claim 3 is the longitudinal stretching device according to claim 1 or 2,
The non-contact preheating section is made of an infrared heater.

The invention according to claim 4 is the longitudinal stretching device according to claim 3,
The main wavelength of infrared light emitted from the infrared heater is in the range of 0.8 to 1.6 μm.

The longitudinal stretching device of the present invention enables the unstretched sheet to be transported in close contact with a low-speed roll in the longitudinal stretching device, even if the thickness of the unstretched sheet made of a thermoplastic resin is large, and the film quality after stretching. It is effective to maintain.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining one Embodiment of the longitudinal stretching apparatus which has this invention. It is a figure explaining the non-contact preheating part in one embodiment of the longitudinal stretching device which has the present invention. It is a figure explaining the example of composition of the non-contact preheating part in one embodiment of the longitudinal stretching device which has the present invention. It is a figure explaining the manufacturing process of the biaxially stretched film which consists of thermoplastic resins. It is a figure explaining a conventional longitudinal stretching device. It is a figure explaining a problem at the time of handling a thick unstretched sheet with a conventional longitudinal stretching device.

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a longitudinal stretching device 1 for describing an embodiment of the present invention. While running a continuous unstretched sheet 2 supplied from the left side of the drawing in a continuous direction, FIG. The film is stretched and supplied to the next step (generally, a transverse stretching step) on the right side as a longitudinally stretched film 3. The unstretched sheet 2 has a width of about 0.5 to 2.0 m and a thickness of about 1 to 5 mm, and various thermoplastic resins can be used as a material. Generally, polyethylene terephthalate (PET) is used. And an aromatic polyester such as polyethylene naphthalate (PEN). Further, inorganic fine particles or organic fine particles may be dispersed in the thermosetting resin.

  The longitudinal stretching apparatus 1 includes a low-speed roll group 5, a heating stretching section 6, a high-speed roll group 7, and a non-contact preheating section 8 as basic components.

  The low-speed roll group 5 is composed of a plurality of low-speed rolls 5R (symbols when the individual 5R1 to 5R4 are not individually identified), and the unstretched sheets 2 are arranged such that both surfaces are alternately brought into close contact with the surface of the low-speed roll 5R. In FIG. 1, the low-speed roll group 5 includes four low-speed rolls 5R. However, the number of low-speed rolls 5R is not limited to four, and may be more. The low-speed roll 5R is a metal roll having a diameter of 200 to 400 mm, and may have been subjected to surface treatment such as hard chrome plating, tungsten carbide spraying, fluororesin coating, or ceramic coating. Each low-speed roll 5R is provided with a heating unit and a temperature measuring unit for measuring the roll surface temperature, and also has a temperature control function of heating and maintaining the roll surface temperature at a predetermined value. Here, as the heating means, circulation of a heating medium such as hot water, pressurized hot water, or heating oil, induction heating, a cartridge heater with a built-in roll, or the like is used. When controlling the temperature of each of the low-speed rolls 5R, it is desirable to gradually increase the set temperature from the upstream side to the downstream side (toward the heating and stretching unit 6), rather than setting the same set temperature. Although the specific temperature varies depending on the type of thermoplastic resin, in the case of PET resin, the temperature is 60 to 80 ° C. at the most upstream low-speed roll 5R1 of the low-speed roll group 5, and the most downstream side (immediately before the heating stretching section 6; In FIG. 1, the temperature is about 100 to 120 ° C. in 5R4).

  The low-speed rolls 5R of the low-speed roll group 5 rotate at a predetermined peripheral speed so as to convey the unstretched sheet 2 at a predetermined speed. Therefore, all the low-speed rolls 5R are driven at a predetermined rotation speed. It is desirable that only some of the low-speed rolls be used as drive rolls and others as free rolls.

  The heating and stretching unit 6 has a heating function for heating the unstretched sheet 2 to a temperature equal to or higher than the softening point of the thermoplastic resin as the material. The unstretched sheet 2 is stretched in the longitudinal direction, that is, in the running direction by the peripheral speed difference between the low-speed roll group 5 and the high-speed roll group 7 to become the longitudinally stretched film 3. . Therefore, if the heating function is to contact and heat the unstretched sheet 2 (or the longitudinally stretched film 3), there is a concern that the surface of the unstretched sheet 2 (or the longitudinally stretched film 3) may be scratched by friction. . For this reason, the heating function is desirably a non-contact type, and an infrared heater is generally used.

  The high-speed roll group 7 is composed of a plurality of high-speed rolls 7R (symbols when 7R1 and 7R2 are not individually identified), and are arranged such that both surfaces of the longitudinally stretched film 2 alternately adhere to the high-speed roll surface. In FIG. 1, the low-speed roll group includes two high-speed rolls 7R, but the number of high-speed rolls 7R is not limited to two. The high-speed roll 7R is a metal roll having a diameter of 200 to 400 mm like the low-speed roll, and the roll surface may be subjected to surface treatment such as resin coating, ceramic coating, and chrome plating. Further, the high-speed roll 7R is provided with a cooling means for lowering the temperature of the longitudinally stretched film 3 which has been heated to a high temperature by the heating and stretching unit 6 to a temperature equal to or lower than the glass transition point. Here, cooling water circulation is generally used as cooling means.

  The non-contact preheating unit 8 is disposed upstream of the low-speed roll group 5 as shown in FIG. 1 and over the entire width of the unstretched sheet 2 as shown in FIG. have. As a heating means of the non-contact preheating unit 8, a device capable of heating the inside of the unstretched sheet 2 to soften the unstretched sheet 2 having a thickness of several mm is desirable, and an infrared heater or a microwave heater is preferable. It is. In the case of the infrared heater, the wavelength is preferably 0.8 to 1.6 μm, which is easily absorbed by the thermoplastic resin, and more preferably in the range of 1.1 to 1.5 μm.

  Further, when the unstretched sheet 2 comes into contact with the first low-speed roll 5R1 of the low-speed roll group 5, the higher the temperature of the surface that does not come into contact with the roll than the surface that comes into contact with the roll, the more the heat between the two surfaces of the unstretched sheet 2 becomes. The difference in expansion facilitates bending along the roll surface. For this reason, it is preferable to arrange the heat source 81 on the opposite side (the upper side of the unstretched sheet 2 in FIG. 1) of the surface of the low-speed roll group 5 that contacts the first low-speed roll 5R1 (FIG. 3A). However, when the thickness of the unstretched sheet 2 is large, a heat source 82 having a lower heating capacity than the heat source 81 may be arranged on the opposite side of the unstretched sheet 2 (FIG. 3B). Instead, a mirror 8r for reflecting heat rays may be arranged (FIG. 3C). As the mirror 8r, a mirror that effectively reflects heat rays and is less likely to be deformed by thermal distortion is desirable, and a polished stainless steel plate or the like can be used.

  With the above configuration, even if the thickness of the unstretched sheet 2 made of a thermoplastic resin is large, the unstretched sheet 2 adheres to the first low-speed roll 5R1 of the low-speed roll group 5 over the entire width, and closely adheres to the subsequent low-speed roll 5R. Therefore, the unstretched sheet 2 can be stretched longitudinally in a state where both sides are preheated without heating unevenness.

  Although the present invention is suitable for producing a biaxially stretched film, it is also effective in producing a longitudinally stretched film by performing only longitudinal stretching.

  It can be used for producing a stretched film made of a thermoplastic resin, and is particularly suitable for producing a thick film with high quality.

DESCRIPTION OF SYMBOLS 1 Longitudinal stretching apparatus 2 Unstretched sheet 3 Longitudinal stretched film 4 Biaxially stretched film 5 Low-speed roll group 5R Low-speed roll 5R1 Initial low-speed roll 6 Heat stretching section 7 High-speed roll group 7R High-speed roll 8 Non-contact preheating section 81 Heat source 82 Heat source

Claims (4)

A continuous unstretched sheet made of a thermoplastic resin, the unstretched sheet is stretched while running in a continuous direction to form a longitudinally stretched film, a longitudinal stretching apparatus,
Along the downstream from the upstream in the direction in which the unstretched sheet travels, a low-speed roll group, a heating stretching section, and a high-speed roll group,
The low-speed roll group has a function of pre-heating the unstretched sheet to near a softening temperature by contacting and passing through a plurality of low-speed rolls,
Further upstream of the uppermost low-speed roll of the low-speed roll group,
A longitudinal stretching apparatus further comprising a non-contact preheating unit for heating the unstretched sheet in a non-contact manner so that the temperature of the surface opposite to the surface that first comes into contact with the low-speed roll group is higher . The longitudinal stretching device according to claim 1,
The non-contact preheating part arrange | positions a heat source only on the side opposite to the surface where the said unstretched sheet contacts the said low-speed roll group first, The longitudinal stretching apparatus characterized by the above-mentioned. The longitudinal stretching device according to claim 1 or claim 2,
The longitudinal stretching device, wherein the non-contact preheating section comprises an infrared heater. The longitudinal stretching device according to claim 3,
A longitudinal stretching device, wherein a main wavelength of infrared rays emitted from the infrared heater is in a range of 0.8 to 1.6 μm.

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