KR102181046B1 - Method for producing stretched film - Google Patents

Abstract

The process of forming the film 100 before stretching by cooling and solidifying the thermoplastic resin melt-extruded from the molding die 220 by the rolls 230 and 240, and heating and stretching the film 100 before stretching in at least one direction. As a manufacturing method of a stretched film having a step of forming a stretched film, in the step of forming the film 100 before stretching, the central portion of the film 100 before stretching is contracted by plane stretching, and both ends are contracted by uniaxial stretching. by ratio "t _b of a minimum thickness of the boundary formed between the central portion and the both end portions to t _b, and, if the average thickness of the central portion to the t _c, minimum thickness (t _b) and the average thickness (t _c) There is provided a method for producing a stretched film, characterized in that the film 100 is formed before stretching so that /t _c " is 0.75 or more.

Description

Manufacturing method of stretched film {METHOD FOR PRODUCING STRETCHED FILM}

The present invention relates to a method for producing a stretched film.

When manufacturing a stretched film, a method of preparing a film as a material and stretching the prepared film is used, and as a method of stretching the film, the film is conveyed into a heating furnace while holding both ends of the film with a clip, and the film is A simultaneous biaxial stretching method or the like is known in which heating and stretching are performed simultaneously in the longitudinal direction and in the width direction by means of a clip holding both ends of the device.

In this simultaneous biaxial stretching method, by pulling the film in the longitudinal direction and in the width direction in the heating furnace, the film is heated and stretched to the required draw ratio. However, in order to stretch the film, a large stress is applied to both ends of the film, which is the part held by the clip When applied, cracks are formed at both ends of the film or in the thinned portion of the film, and this may cause the entire film to break.

On the other hand, for example, Patent Document 1 discloses a technique for reinforcing the film before heat stretching by making both ends of the film held by the clip thicker than the center in order to prevent the film from breaking during heat stretching by simultaneous biaxial stretching. Has been.

Japanese Patent Application Laid-Open No. Hei 11-105131

However, in the technique of Patent Document 1, since the film for heat stretching is formed by melt extrusion of a thermoplastic resin with a molding die, the thickness of a part of the film becomes thin during melt extrusion, and therefore, heat stretching is performed. When performing, there is a problem that the thinned portion is torn and the entire film is broken.

In other words, in the thermoplastic resin film melt-extruded from the molding die, a phenomenon called neck-in occurs in which the film width becomes narrower while being stretched in the longitudinal direction between the melt-extrusion and being drawn in by a cooling roll or the like. . It is thought that such a neck-in occurs as follows. In other words, since the thermoplastic resin melt-extruded from the molding die exists adjacent to the thermoplastic resins at the center in the width direction of the film, the flow direction of the thermoplastic resin is limited, so that the thermoplastic resin is flatly stretched along a predetermined surface inside the thermoplastic resin. Accordingly, contraction in the width direction is suppressed and contraction is mainly performed in the thickness direction. On the other hand, since the thermoplastic resin melt-extruded from the molding die does not have adjacent thermoplastic resin on the outer side of the film at both ends in the width direction, the thermoplastic resin flows freely, centering on a predetermined axis inside the thermoplastic resin. As a result, it uniaxially expands, and accordingly, contracts in the width direction as well as the thickness direction. Therefore, in the formed film, the boundary portion between the central portion in the width direction and both ends in the width direction is recessed in the thickness direction due to the difference in the shrinkage form of the thermoplastic resin, so that the thickness becomes thin. Thus, when the film is heated and stretched, cracks are generated in the boundary portion having a thin thickness, and thus the entire film is easily broken.

The present invention is in consideration of these facts, and it is an object of the present invention to provide a method for manufacturing a stretched film capable of preventing the breakage of the film when manufacturing a stretched film by heat stretching the film, thereby obtaining a stretched film having excellent productivity and quality. To do.

The present inventors have found that the above object can be achieved by adjusting the thickness of the boundary portion formed between the central portion and both ends of the film with respect to the average thickness of the central portion of the film with respect to the film before heat stretching. Reached.

That is, according to the present invention, after melt-extrusion of a thermoplastic resin from a molding die, it is cooled and solidified by pulling in with a roll to form a film before stretching; And a stretching process of forming a stretched film by heating and stretching the film before stretching in at least one direction, wherein in the film forming process before stretching, a central portion of the film before stretching is a thickness of the film before stretching It contracts toward the specific surface by plane stretching that extends along a specific surface located at the center position or near the center position in the direction, and both ends of the film before stretching are centered on a specific axis passing through the center of the both ends or near the center position. When the minimum thickness of the boundary portion formed between the central portion and the both ends is t _b and the average thickness of the central portion is t _c by contracting around the specific axis by elongating uniaxial elongation, the minimum thickness of the boundary portion There is provided a method for producing a stretched film, characterized in that the pre-stretched film is formed so that the ratio "t _b /t _c "between (t _b ) and the average thickness (t _c ) of the central portion is 0.75 or more.

As the production method of the present invention, it is preferable to use an acrylic resin as the thermoplastic resin.

A manufacturing method of the present invention, comprising: a first thermoplastic resin forming an inner region positioned inside the width direction of the film before stretching; It is preferable to form an outer region located outside the width direction of the film before stretching, and to use a second thermoplastic resin different from the first thermoplastic resin.

As the manufacturing method of the present invention, it is preferable to use an acrylic resin as the first thermoplastic resin.

As the production method of the present invention, it is preferable to use a mixed resin obtained by blending a thermoplastic resin having a glass transition temperature lower than that of the acrylic resin in polycarbonate (PC) as the second thermoplastic resin.

As the manufacturing method of the present invention, it is preferable to use a thermoplastic resin having a difference in glass transition temperature of 10° C. or less as the first thermoplastic resin and the second thermoplastic resin.

As a production method of the present invention, when the maximum thickness of the end portions to t _e, the ratio "t _e / t _c" of the maximum thickness (t _e) and the average thickness (t _c) of the central portion of the both end portions from 1.0 to It is preferable to form the pre-stretching film in the pre-stretching film forming process so that it is in the range of 2.0.

As a production method of the present invention, when the slit width of the outlet of the molding die to t _s, ratio "t of the slit width (t _s) of the outlet of the molding die for the average thickness (t _c) of the central portion It is preferable to form the pre-stretch film in the pre-stretch film forming step so that _s /t _c " is 8.0 or less.

In the manufacturing method of the present invention, in the stretching step, the heat stretching of the pre-stretching film is preferably performed by simultaneous biaxial stretching in which the pre-stretching film is simultaneously stretched in the longitudinal direction and the width direction.

As the manufacturing method of the present invention, in the stretching step, it is preferable that the stretching ratio with respect to the stretching direction of the heat stretching of the pre-stretching film is 3 times or less.

In the manufacturing method of the present invention, in the stretching step, the heat stretching of the film before stretching is preferably performed so that the thickness of the central portion of the stretched film after heat stretching is in the range of 15 to 50 μm.

In addition, as the production method of the present invention, it is preferable to have a smoothing step of smoothing both side surfaces defining the thickness of the film before the stretching step and before the stretching step.

In addition, in the manufacturing method of the present invention, smoothing in the smoothing step is preferably performed by removing regions located at both ends of the film before stretching in the width direction.

ADVANTAGE OF THE INVENTION According to this invention, when heat-stretching a film and manufacturing a stretched film, it can heat-stretch suitably and can provide the manufacturing method of a stretched film which can obtain a stretched film excellent in productivity and quality.

1 is a view for explaining a method of producing a film before stretching.
2 is a view for explaining the neck-in of the melt-extruded thermoplastic resin.
3 is a view for explaining the shrinkage of the melt-extruded thermoplastic resin.
4 is a diagram showing an example of the thickness of the film before stretching in the width direction.
5 is a view for explaining a method of stretching a film before stretching by a simultaneous biaxial stretching method in a stretching step.
6 is a graph showing the results of measuring the thickness of the pre-stretched film and the stretched film produced in Examples and Comparative Examples in the width direction.
7 is a view for explaining a method of manufacturing a pre-stretching film (composite film) composed of a first thermoplastic resin and a second thermoplastic resin.
8 is a view for explaining the neck-in of a thermoplastic resin melt-extruded when manufacturing a composite film.
9 is a diagram for explaining an example of a thermoplastic resin that shrinks immediately after melt extrusion when manufacturing a composite film.
10 is a diagram showing an example of the thickness of a composite film with respect to the position in the width direction.
11 is a view for explaining a method of stretching a composite film by a simultaneous biaxial stretching method in a stretching step.
12 is a graph showing the glass transition temperature of a mixed resin obtained by blending polyethylene terephthalate (PET) with polycarbonate (PC).
13 is a diagram for explaining another example of shrinking immediately after melt extrusion in a composite film.
14 is a graph showing the results of measuring the thickness of the composite film and the stretched film produced in Examples and Comparative Examples in the width direction position.

<<first embodiment>>

Hereinafter, a first embodiment of the present invention will be described based on the drawings.

The manufacturing method of the stretched film according to the first embodiment includes a pre-stretching film forming process in which a thermoplastic resin is melt-extruded with a molding T-die to form a film before stretching, and the film before stretching is heated and stretched in the longitudinal direction and the width direction. A stretching process to be performed is provided.

<film formation process before stretching>

The film forming step before stretching is a step of obtaining the film 100 before stretching by melt-extruding a thermoplastic resin from a T-die. Here, FIG. 1 is a diagram for explaining a film forming process before stretching.

In the film forming process before stretching, first, the thermoplastic resin is supplied to the T-die 220 through the feed block 210 in a heat-melted state.

In this embodiment, a melt extruder (not shown) for melt-extrusion of a thermoplastic resin is connected to the feed block 210. The melt extruder is not particularly limited, and both a single screw extruder and a twin screw extruder can be used. And in this embodiment, the thermoplastic resin is melt-extruded at a temperature equal to or higher than the melting point (melting) temperature by a melt extruder to supply to the feed block 210.

On the other hand, in this embodiment, the thermoplastic resin can be selected according to the application of the stretched film required, etc., for example, acrylic resin (PMMA), cyclic olefin copolymer (COC), polycarbonate (PC), polyester One type of terephthalate (PET) or the like may be used alone, or a mixed resin obtained by mixing two or more types may be used.

And, in the T die 220, the thermoplastic resin supplied from the feed block 210 is expanded in the width direction by the manifold 221 provided in the T die 220, and accordingly, the sheet shape from the die lip 222 Is extruded.

Subsequently, the extruded sheet-shaped thermoplastic resin is continuously pulled in by the touch roll 230 and the cooling roll 240 by the touch roll 230 and the cooling roll 240, pressed, cooled, and solidified to obtain the film 100 before stretching. .

And, in this embodiment, the produced film 100 before extending|stretching is rolled up by a film winding roll (not shown) before extending|stretching, and accordingly, the film 100 before extending|stretching can be continuously obtained.

On the other hand, in the pre-stretching film 100 obtained in this way, it shrinks in the width direction between being melt-extruded from the die lip 222 of the T-die 220 and then drawn in by the cooling roll 240. A phenomenon called neck-in occurs.

Here, FIG. 2 is a view showing a cross section of the die lip 222 of the T die 220 and the film 100 before stretching formed in this embodiment, and the dimensions of the die lip 222 in the width direction and the stretching formed The relationship between the width of the entire film 100 is shown. In the present embodiment, when forming the film 100 before stretching, the thermoplastic resin is melt-extruded by the T-die 220 to the width of the die lip 222, but it is melt-extruded and then pulled by the cooling roll 240. During the indentation, a neck-in that contracts in the width direction as shown by the arrow shown in FIG. 2 is generated, and the width of the resulting film 100 before stretching becomes smaller than the width direction dimension of the die lip 222.

On the other hand, such neck-in occurs when the thermoplastic resin melt-extruded from the T-die 220 shrinks in the direction of the arrow shown in FIG. 2. That is, the center portion of the film 100 before stretching contracts in the direction indicated by the arrow (thickness direction), and the portion at both ends of the film 100 before stretching is in the direction indicated by the arrow (thickness direction and width direction). It occurs by contracting. Then, the thermoplastic resin melt-extruded from the T-die 220 is contracted by the neck-in, so that the cross-sectional shape is as shown in FIG. 2.

Here, FIG. 3 is a diagram for explaining shrinkage of the melt-extruded thermoplastic resin. In this embodiment, the thermoplastic resin melt-extruded from the T-die 220 is formed of the thermoplastic resin due to the presence of the adjacent thermoplastic resin in the portion that becomes the central portion 110 of the film 100 before stretching, as shown in FIG. 3. The flow direction is limited, and accordingly, the thermoplastic resin contracts in the thickness direction as indicated by the arrow by planar elongation extending along a plane α located at or near the center position in the thickness direction. On the other hand, the thermoplastic resin melt-extruded from the T-die 220 is a portion that becomes the both ends 120 of the film 100 before stretching, as shown in FIG. 3, a thermoplastic resin adjacent to the outer side of the both ends 120 Since it does not exist, the thermoplastic resin flows relatively freely, and accordingly, the thickness direction and the thickness direction as indicated by the arrow are uniaxially stretched around the axis β passing through the center of the both ends 120 or near the center position. In addition, it contracts in the width direction. Accordingly, a boundary portion 130 having a concave shape in the thickness direction is formed between the central portion 110 and both ends 120 due to the difference in the shrinkage shape of the thermoplastic resin.

Therefore, in the pre-stretch film 100 formed by the method shown in FIG. 1, as shown in FIG. 4, the boundary portion 130 between the central portion 110 and the both ends 120 becomes particularly thin. On the other hand, FIG. 4 is a diagram showing an example of a result of measuring the thickness of the film 100 before stretching with respect to the position in the width direction.

Here, for the formed film 100 before stretching, if the thickness of the boundary portion 130 becomes too thin relative to the thickness of the central portion 110, when the film 100 is heated and stretched before stretching in the stretching process, the boundary portion having a thin thickness There is a problem that cracks are liable to occur in (130) and it is not possible to appropriately heat-stretch.

On the other hand, in the present embodiment, as shown in FIG. 4, the central portion 110 of the pre-stretched film 100 formed by melt-extruding with the T-die 220 and pulling in with the cooling roll 240 When the average thickness of is t _c and the minimum thickness of the boundary portion 130 is t _b , the ratio of these thicknesses "t _b /t _c "is adjusted to 0.75 or more, as described later, the film 100 before stretching. ) Can be effectively prevented from cracking of the boundary portion 130 when heating and stretching, thereby improving the productivity of the stretched film.

On the other hand, as the average thickness t _c of the central portion 110 shown in FIG. 4, the average thickness of the portion where the thickness of the central portion 110 is stable is used, for example, based on the center of the central portion 110. Thus, it can be set as the average value of the thickness in a region within ±5 to 10% of the thickness. In addition, the minimum thickness (t _b ) of the boundary portion 130 is a thinner thickness among the minimum thicknesses of the boundary portion 130 at two points in the film 100 before stretching.

<stretching process>

The stretching step is a step of heating and stretching the pre-stretching film 100 obtained by the pre-stretching film forming step in the longitudinal direction and the width direction. Here, FIG. 5 is a diagram for explaining a stretching process. In this embodiment, in the stretching process, the pre-stretch film 100 is sent out from the pre-stretch film take-up roll described above, and as shown in FIG. 5, while holding the pre-stretch film 100 with the clip 310, the length direction and width The film 100 is heated and stretched before stretching by a simultaneous biaxial stretching method that simultaneously stretches in the direction.

Specifically, in the stretching process, the pre-stretch film 100 is continuously sent out from the pre-stretch film take-up roll, and the pre-stretch film 100 is gripped at regular intervals using a plurality of clips, and each clip 310 The film 100 before stretching is conveyed into the stretching furnace 320, and the film 100 before stretching is pulled in the length direction and the width direction by each clip 310 in the stretching furnace 320 and stretched. At this time, the film 100 before stretching is conveyed in a state held by the clip 310 to pass through the stretching furnace 320, and in the preheating zone in the stretching furnace 320, the film 100 before stretching Silver is preheated to a temperature about 10 to 30° C. higher than the glass transition temperature of the thermoplastic resin constituting it, and then retained in the drawing zone in the drawing furnace 320 in the longitudinal direction and It is pulled in the width direction and stretched in the length direction and the width direction. And, following this, the stretched film can be obtained by cooling and solidifying in a cooling heat setting zone. Then, by opening the clip 310 and winding it on a roll, a stretched film can be continuously obtained.

On the other hand, in this embodiment, a pair of guide rails for moving the clip 310 are provided so as to pass through the extension path 320. A pair of guide rails are installed at the position of the clip 310 for gripping the upper side of the film 100 before stretching shown in FIG. 5 and the position of the clip 310 for gripping the lower side, respectively, and the drawing furnace 320 In the inner preheating zone, they are parallel to each other, in the stretching zone, they are separated from each other in the width direction of the film 100 before stretching, and in the cooling and heat setting zone, they are parallel to each other again. Alternatively, in the cooling heat setting zone, the distance between the pair of guide rails in the cooling heat setting zone is determined by considering the shrinkage at the time of solidification of the stretched film heated and stretched in the stretching zone. Based on the width, it is possible to approach several percent in the width direction. In this embodiment, the clip 310 holding the film 100 before stretching moves along such a guide rail, so that the film 100 before stretching can be conveyed and stretched.

In the present embodiment, the film 100 before stretching is stretched in the stretching zone in the stretching furnace 320 using the clip 310 moving along the guide rail. That is, in the drawing zone in the drawing furnace 320, the clip 310 holding the film 100 before drawing is moved by expanding it in the width direction along the guide rail, and at the same time, controlling to increase the gap between the clips 310 By performing stretching, the film 100 before stretching is pulled out in the longitudinal direction and the width direction as shown by the arrows shown in FIG. 5. Accordingly, the film 100 before stretching is heated and stretched in the longitudinal direction and in the width direction until the required stretching ratio is achieved. And, after the film 100 before stretching is heated and stretched, it is cooled and solidified in a cooling heat setting zone in the stretching furnace 320, and is wound up by a roll installed outside the stretching furnace 320, thereby continuously obtaining a stretched film. I can.

On the other hand, in this embodiment, a stretched film can also be obtained by making the extending process and the film formation process before extending|stretching into a consistent continuous line (process).

In addition, in the present embodiment, when heat stretching the film 100 before stretching, the draw ratio with respect to the stretching direction is preferably within 3 times, more preferably within 2.5 times, and still more preferably within 2 times. Thereby, fracture of the film 100 before extending|stretching during heat extending|stretching can be prevented more effectively, and heat extending|stretching of the film 100 before extending|stretching can be performed suitably.

In addition, in the present embodiment, in the stretched film obtained by heat stretching the film 100 before stretching, the thickness of the central portion 110 portion is preferably 15 to 50 μm, more preferably 20 to 40 μm. By controlling the thickness of the central portion 110 in the stretched film within the above range, fracture of the film 100 before stretching during heat stretching can be more effectively prevented, and the heat stretching of the film 100 before stretching can be performed appropriately. have.

In addition, in the present embodiment, the stretched film obtained by heat stretching the film 100 before stretching may be removed by cutting the portions of both ends 120 as necessary. Accordingly, in the stretched film, in particular, portions of the both ends 120 having a thick thickness can be removed, thereby making the thickness of the entire stretched film uniform.

As described above, in this embodiment, a stretched film can be obtained by forming the pre-stretching film 100 made of a thermoplastic resin by the pre-stretching film forming step, and heat stretching the pre-stretching film 100 by the stretching step. .

Here, in this embodiment, when forming the pre-stretch film 100 by the pre-stretch film forming process, the ratio of the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 The thickness of the film 100 before stretching is adjusted so that "t _b /t _c "is 0.75 or more. Accordingly, when the film 100 is heated and stretched before stretching in the stretching step, it is possible to effectively prevent the occurrence of cracks in the thin boundary portion 130, thereby improving the productivity of the stretched film.

On the other hand, when the film 100 is heated and stretched before stretching, the boundary portion 130 of the film 100 before stretching has a thin thickness, so that the stretching stress required for stretching is low, and thus, is preferentially stretched. And, as the stretching proceeds at the boundary part 130, the stretching stress of the boundary part 130 gradually increases, and when the stretching stress required for the stretching of the central part 110 is reached, the central part 110 is also stretched following the boundary part 130. . At this time, if the thickness of the boundary portion 130 with respect to the central portion 110 is too thin, while the boundary portion 130 is being stretched, the boundary portion 130 is broken before the stretching of the central portion 110 starts. In addition, if the thickness of the boundary portion 130 with respect to the central portion 110 is too thin, as shown in FIG. 5, after heating and stretching, the impact when the film 100 is released from the clip 310 before stretching, or obtained Cracks also occur in the boundary part 130 due to stress when the stretched film is wound on a roll.

Here, conventionally, as a method of preventing breakage of a film during heat stretching by simultaneous biaxial stretching, a method in which both ends of the film before heat stretching are formed thicker than the central portion has been known. However, in the case of producing a film for stretching by melt extrusion with a T-die 220, even if the both ends of the film are thickened as described above, about the boundary formed between the central part and both ends of the film, Fig. 3 As shown in Fig. 1, the thickness becomes thin, and there is a problem that cracks occur at this boundary when the film is heated and stretched.

On the other hand, according to this embodiment, with respect to the pre-stretching film 100 formed by melt-compressing with the T-die 220 and pulling it with the cooling roll 240, the average thickness of the central portion 110 ( By adjusting the ratio ``t _b /t _c '' of t _c ) and the minimum thickness (t _b ) of the boundary part 130 to the above range, the cracks in the boundary part 130 when the film 100 is heated and stretched before stretching Generation can be effectively prevented, and the productivity of the stretched film can be improved.

On the other hand, in this embodiment, the ratio ``t _b /t _c '' between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 may be 0.75 or more, as described above, It is preferably 0.8 or more, more preferably 0.9 or more.

In addition, in the present embodiment, with respect to the pre-stretch film 100 to be formed, the ratio of the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 described above ``t _b /t Although it is not particularly limited as a method of adjusting " _c " to the above range, for example, a method of using a resin having a lower elongation viscosity as a thermoplastic resin, a method of adjusting the slit width of the die lip 222 of the T die 220 , A method of reducing the distance between the T-die 220 and the cooling roll 240, a method of reducing the drawing speed of the film 100 before stretching by the cooling roll 240, and the like may be used alone or in combination.

On the other hand, in this embodiment, the type of thermoplastic resin applicable among these methods is not limited, and in that it does not decrease the production efficiency of the film 100 before stretching, the slit width of the die lip 222 is adjusted. It is preferred to use the method. At this time, when the slit width of the die lip 222 to t _s, ratio "t _s / t _c" of the slit width (t _s) and the average thickness (t _c) of the central portion 110 of the die lip 222 Is adjusted to be preferably 8.0 or less, more preferably 6.0 or less, and still more preferably 5.0 or less. Accordingly, the thickness of the pre-stretched film 100 obtained by melt-extruding with the T-die 220 can be made more uniform, so that the average thickness of the central portion 110 (t _c ) and the minimum thickness of the boundary portion 130 (t The ratio "t _b /t _c "of _b ) can be appropriately adjusted within the above range.

In addition, in the present embodiment, for the pre-stretch film 100 to be formed, as described above, the ratio of the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 "t _By adjusting _b /t _c ″ to the above range and appropriately adjusting the maximum thickness of the both ends 120, fracture of the film 100 before stretching at the time of heat stretching can be more effectively prevented.

Specifically, in forming the stretch around the film 100, FIG. 4, as shown in, the case where the maximum thickness of the end portions 120 to t _e, the maximum thickness (t _e) and the central portion (110 of each end 120, ) The ratio "t _e /t _c "of the average thickness (t _c ) is adjusted to preferably 1.0 to 3.0, more preferably 1.0 to 2.0, and still more preferably 1.0 to 1.5. Here, as the maximum thickness t _e of the both ends 120, among the thicknesses of the both ends 120 (one end portion and the other end portion in the width direction) of the film 100 before stretching, the thickness is the thicker one. On the other hand, when the maximum thickness (t _e ) of both ends 120 is too thick compared to the average thickness (t _c ) of the central part 110, the film 100 before stretching obtained by melt extrusion with a T die 220 When compressing by the touch roll 230 and the cooling roll 240, the pressure is concentrated on both ends 120 due to the too thick of both ends 120 so that the pressure is not uniformly transmitted to the entire film 100 before stretching. The thickness of the film 100 before stretching becomes non-uniform, and the thickness of the stretched film obtained by heating and stretching the film 100 tends to be non-uniform. On the other hand, when the maximum thickness (t _e ) of both ends 120 is too thin compared to the average thickness (t _c ) of the central part 110, the film 100 before stretching melt-extruded by the T-die 220 is necked. When it is drawn, the force for pulling the thermoplastic resin at both ends 120 tends to be strong, and accordingly, the thickness of the boundary portion 130 becomes thinner, so that the film 100 before stretching is easily broken during heat stretching.

On the other hand, in the present embodiment, with respect to the pre-stretch film 100 formed by the pre-stretch film forming step, it is preferable to smooth the side surfaces of the both ends 120 before heat-stretching. According to the smoothing of the sides of both ends 120 of the film 100 before stretching, when heating and stretching the film 100 before stretching by pulling both ends 120 of the film 100 before stretching in the stretching process, both ends ( It is possible to prevent the occurrence of cracks at both ends 120 by preventing the concentration of local stress caused by the sloppy side of 120), thereby improving the productivity of the stretched film.

A method of smoothing the sides of both ends 120 of the film 100 before stretching is not particularly limited, but a method of trimming a predetermined width from both sides of the both ends 120 with a cutter, and a method of polishing the ends of both ends 120 , A method of heating and pressing the ends of both ends 120 may be used. On the other hand, the smoothing of the sides of both ends 120 reduces the irregularities of the sides of both ends 120, and when the film 100 is pulled in the longitudinal direction before stretching, stress is not concentrated on a part of both ends 120. You just have to do that.

In the case of trimming the both ends 120 of the film 100 before stretching with a cutter, any cutter may be used as long as the sides of both ends 120 can be smoothly smoothed by trimming. For example, a razor blade or , A rotary shear cutter that continuously rotates while crossing the circular upper and lower edges to cut by shear, or a laser cutter using a solid laser, semiconductor laser, liquid laser or gas laser, etc. can be used, but the film before stretching when trimming A laser cutter is preferable in that it is possible to reduce the stress applied to the 100 and prevent the occurrence of cracks in the film 100 before stretching during trimming.

On the other hand, when trimming both ends 120 of the film 100 before stretching, it is preferable to trim while heating both ends 120. Accordingly, it is possible to make the side surfaces of the both ends 120 more smooth, so that fracture of the film 100 before stretching can be prevented more appropriately when the film 100 is heated and stretched before stretching.

In addition, in the above-described example, as a method of heating and stretching the film 100 before stretching, as shown in FIG. 5, a simultaneous biaxial stretching method of heating and stretching the film 100 before stretching in both the length direction and the width direction is used. Although an example has been shown, in this embodiment, a method of uniaxially stretching the film 100 only in the longitudinal direction may be used before stretching.

At this time, heat stretching in the longitudinal direction of the film 100 before stretching can be performed in the same manner as the simultaneous biaxial stretching method as shown in FIG. 5. That is, the film 100 before stretching is conveyed into the drawing furnace 320 while being held by the clip 310, and thereafter, by the clip 310 holding the pre-stretch film 100 in the drawing furnace 320 A method of performing heat stretching only in the longitudinal direction can be used.

In the present embodiment, in both the case where simultaneous biaxial stretching is performed in the longitudinal direction and the width direction, or uniaxial stretching is performed only in the longitudinal direction, while holding the film 100 before stretching with the clip 310 as shown in FIG. By performing stretching, the productivity of a stretched film can be improved as compared with the sequential biaxial stretching method used in the past, and a stretched film having further excellent quality can be obtained.

On the other hand, the conventional sequential biaxial stretching method is a method in which the film 100 before stretching produced by the method shown in FIG. 1 is first heated and stretched in the longitudinal direction, and then heat stretched in the width direction. In the sequential biaxial stretching method, the pre-stretch film 100 is conveyed by a plurality of rolls to heat-stretch in the longitudinal direction, and then, as shown in FIG. 5, while holding the pre-stretch film 100 with the clip 310, the width It is heated and stretched in the direction.

Here, in the sequential biaxial stretching method, stretching in the longitudinal direction of the film 100 before stretching is specifically performed as follows. That is, according to the sequential biaxial stretching method, while conveying the pre-stretch film 100 by a plurality of preheated preheating rolls, preheating is performed to the degree of the glass transition temperature of the thermoplastic resin constituting the pre-stretch film 100, and The heated pre-stretching film 100 is continuously conveyed by a cooling roll while keeping heat by an infrared heater or the like. At this time, by making the conveyance speed by the cooling roll faster than the conveyance speed by the preheating zone roll, tension is generated between the preheating zone roll and the cooling roll, and using this tension, the required draw ratio of the film 100 in the longitudinal direction before stretching Stretch to.

Here, in the sequential biaxial stretching method, when the film 100 before stretching is stretched in the longitudinal direction, the surface of the film 100 before stretching comes into contact with the preheating roll and the cooling roll, so that the surface of the film 100 before stretching There is a fear that scratches may occur in the resulting stretched film and the appearance quality of the resulting stretched film may deteriorate. Further, in the sequential biaxial stretching method, when the film 100 before stretching is heated and stretched in the longitudinal direction, the both ends 120 of the film 100 before stretching are not fixed with a clip or the like, so the film 100 before stretching Due to this heat, there is a fear that the productivity of the stretched film may decrease due to shrinkage in the width direction.

On the other hand, according to this embodiment, by performing stretching in the longitudinal direction with respect to the film 100 before stretching by using the aforementioned simultaneous biaxial stretching method or the aforementioned method of uniaxial stretching only in the longitudinal direction (that is, As shown in Fig. 2, since contact with the roll can be avoided (by using a method of stretching in the longitudinal direction while holding the film 100 before stretching with the clip 310), the film 100 before stretching With respect to a stretched film obtained by stretching by heating, the appearance quality can be improved by reducing scratches on the surface, and in particular, it can be very preferably used for an optical film where the demand for appearance quality is difficult. In addition, according to this embodiment, when stretching the film 100 before stretching in the longitudinal direction, since the film 100 before stretching is held by the clip 310, the width of the film 100 before stretching by heat Shrinkage in the direction can be prevented, and the productivity of the stretched film can be improved.

<<2nd embodiment>>

Subsequently, a second embodiment of the present invention will be described based on the drawings.

The manufacturing method of a stretched film according to the second embodiment is a film before stretching by melt-coextrusioning a first thermoplastic resin (PA) and a second thermoplastic resin (PC) different from the first thermoplastic resin with a molding T-die. A film formation process before extending|stretching which forms (composite film), and the extending process which heat-stretches this film before extending|stretching in a longitudinal direction and a width direction are provided.

<film formation process before stretching>

The film formation step before stretching is a step of forming the film 100 before stretching by melt-coextrusioning the first thermoplastic resin (PA) and the second thermoplastic resin (PC) from a T-die. Here, FIG. 7 is a diagram for explaining a film forming process before stretching. In this embodiment, as the film 100 before stretching, as shown in FIG. 7, the first thermoplastic resin (PA) forming an inner region located inside the width direction of the film 100 before stretching, and the film before stretching ( 100) to obtain a film made of a second thermoplastic resin (PC) forming an outer region located outside the width direction. In this embodiment, the inner region formed by the first thermoplastic resin (PA) coincides with the central portion 110 of the first embodiment described above, and the outer region formed by the second thermoplastic resin (PC) is described above. Although an example consistent with the both ends 120 of the first embodiment is shown, the inner region and the outer region may be inconsistent with the central portion 110 and both ends 120, respectively. For example, as shown in FIG. 13 to be described later, the inner region made of the first thermoplastic resin (PA) becomes a shape covering a part of the outer region made of the second thermoplastic resin (PC), and the inner region and the outer region are It may be inconsistent with the central portion 110 and both ends 120, respectively.

On the other hand, the central part 110 of the film 100 before extending|stretching is a part which becomes a stretched film by heat extending|stretching by the extending process mentioned later. In addition, the both ends 120 of the film 100 before stretching are for reinforcing the central part 110 when heating the film 100 before stretching, and as necessary after heating the film 100 before stretching Can be cut and removed. When cutting the film 100 before stretching, it is preferable to completely remove the both ends 120 by cutting a part of both ends of the central part 110. In this case, a part of both ends of the central portion 110 is also removed, but it is preferable to remove all portions held by the clip 310 to be described later.

In the film formation process before stretching, first, in a state in which the first thermoplastic resin PA and the second thermoplastic resin PC are heated and melted, they are supplied to the T die 220 through the feed block 210.

In this embodiment, the feed block 210 includes a first melt extruder (not shown) for melt-extrusion of the first thermoplastic resin (PA) and a second melt extruder (shown) for melt-extrusion of the second thermoplastic resin (PC). Omitted) are connected respectively. It does not specifically limit as such a melt extruder, and both a single screw extruder and a twin screw extruder can be used. And in this embodiment, the 1st thermoplastic resin (PA) and the 2nd thermoplastic resin (PC) are supplied to the feed block 210 by melt-extruding each at a temperature equal to or higher than the melting point (melting) temperature by each melt extruder.

On the other hand, when supplying the first thermoplastic resin (PA) and the second thermoplastic resin (PC) from the feed block 210 to the T die 220, the pre-stretch film 100 obtained by the T die 220 is As shown in 7, the first thermoplastic resin (PA) and the second thermoplastic resin (PA) and the second end portions 120 are formed at both ends of the central portion 110 made of the first thermoplastic resin (PA). The thermoplastic resin (PC) is supplied.

Specifically, with respect to the inlet for supplying the first thermoplastic resin PA and the inlet for supplying the first thermoplastic resin PA to the feed block 210, on both sides in the width direction of the T-die 220, Each inlet is provided for supplying the second thermoplastic resin (PC). And, in this embodiment, the first thermoplastic resin PA and the second thermoplastic resin PC, respectively introduced from the inlet of the feed block 210, merge in the feed block 210, and the feed block 210 At the outlet, the first thermoplastic resin (PA) flows in the central part with respect to the width direction of the T-die 220, and the second thermoplastic resin (PC) flows through the both ends of the first thermoplastic resin (PA). It is to be supplied to the T-die 220.

Then, in the T die 220, the first thermoplastic resin PA and the second thermoplastic resin PC supplied from the feed block 210 are in the width direction by the manifold 221 provided in the T die 220 ( The first thermoplastic resin (PA) and the second thermoplastic resin (PC) are expanded in the direction in which they are arranged), and accordingly, they are coextruded from the die lip 222 into a sheet shape.

Subsequently, the coextruded sheet-shaped first thermoplastic resin (PA) and the second thermoplastic resin (PC) are continuously drawn in and pressed by the touch roll 230 and the cooling roll 240 as shown in FIG. 7. By cooling and solidifying, the pre-stretch film 100 having a central portion 110 made of a first thermoplastic resin (PA), and both ends 120 made of a second thermoplastic resin (PC) formed at both ends of the central portion 110 ).

And, in this embodiment, the produced film 100 before extending|stretching is wound up by the film take-up roll (not shown) before extending|stretching, and accordingly, the film 100 before extending|stretching can be continuously obtained.

On the other hand, also in the pre-stretch film 100 made of the first thermoplastic resin (PA) and the second thermoplastic resin (PC) obtained in this way, the pre-stretch film 100 made of a single thermoplastic resin in the first embodiment described above. Likewise, a phenomenon called neck-in that contracts in the width direction occurs between melt-extrusion from the die lip 222 of the T-die 220 and then pulled in by the cooling roll 240.

Here, FIG. 8 is a view showing a cross section of the die lip 222 of the T die 220 and the pre-stretched film 100 formed in this embodiment, and the dimensions and formation of the die lip 222 in the width direction The relationship between the width of the film 100 before stretching is shown. In this embodiment, when forming the film 100 before stretching, the first thermoplastic resin (PA) and the second thermoplastic resin (PC) are melt-extruded to the width of the die lip 222 by the T die 220, but , Between being melt-extruded and pulled in by the cooling roll 240, neck-in shrinking in the width direction as shown in the arrow shown in FIG. 8 occurs, and the width of the resulting film 100 before stretching is diced. It becomes smaller than the width direction dimension of 222.

On the other hand, such neck-in occurs when the thermoplastic resin melt-extruded from the T-die 220 shrinks in the direction of the arrow shown in FIG. 8. That is, the portion that becomes the central portion 110 of the film 100 before stretching (that is, the inner region in the width direction of the film 100 before stretching) shrinks in the thickness direction as indicated by the arrow, and the film 100 before stretching It is caused by shrinking in the thickness direction and the width direction as indicated by the arrows (ie, the outer area in the width direction of the film 100 before stretching) that becomes the both ends 120 of the. Then, the first thermoplastic resin PA and the second thermoplastic resin PC melt-extruded from the T-die 220 are contracted by neck-in, so that the cross-sectional shape is as shown in FIG. 8.

Here, FIG. 9 is a view for explaining shrinkage of the melt-extruded first thermoplastic resin PA and the second thermoplastic resin PC. In this embodiment, the first thermoplastic resin (PA) and the second thermoplastic resin (PC) melt-extruded from the T-die 220 become the central part 110 of the film 100 before stretching, as shown in FIG. 9. In the portion (inner region in the width direction), the flow direction of the thermoplastic resin is limited by the presence of the adjacent thermoplastic resin, and accordingly, the thermoplastic resin is located along a surface (α) located at the center position in the thickness direction or near the center position. It contracts in the thickness direction as indicated by the arrow by the extending plane stretching. On the other hand, the thermoplastic resin melt-extruded from the T-die 220 is at the portion (the outer region in the width direction) that becomes the both ends 120 of the film 100 before stretching, as shown in FIG. Since there are no adjacent thermoplastic resins on the side, the thermoplastic resin flows relatively freely, and accordingly, by uniaxial elongation extending around the axis β passing through the center of the both ends 120 or near the center position, the arrow As indicated by, it contracts in the width direction as well as the thickness direction. Accordingly, between the central portion 110 and both ends 120, that is, between the inner region and the outer region in the width direction, the boundary portion 130 having a concave shape in the thickness direction is formed due to the difference in the shrinkage shape of the thermoplastic resin.

Therefore, in the pre-stretch film 100 formed by the method shown in FIG. 7, as shown in FIG. 10, the boundary portion 130 between the central portion 110 and the both ends 120 becomes particularly thin. On the other hand, FIG. 10 is a diagram showing an example of a result of measuring the thickness of the film 100 before stretching with respect to the position in the width direction.

Here, for the formed film 100 before stretching, if the thickness of the boundary portion 130 becomes too thin relative to the thickness of the central portion 110, when the film 100 is heated and stretched before stretching in the stretching process, the boundary portion having a thin thickness There is a problem that cracks are liable to occur in (130), and heat stretching cannot be performed appropriately.

On the other hand, in this embodiment, as shown in FIG. 10, for the pre-stretch film 100 formed by melt-extrusion with the T-die 220 and drawn in by the cooling roll 240, as shown in FIG. When the average thickness is t _c and the minimum thickness of the boundary portion 130 is t _b , the ratio of these thicknesses “t _b /t _c ”is adjusted to 0.75 or more, thereby preparing the film 100 before stretching as described later. During heat stretching, cracks in the boundary portion 130 can be effectively prevented, and the productivity of the stretched film can be improved.

On the other hand, as the average thickness t _c of the central portion 110 shown in FIG. 10, the average thickness of the portion where the thickness of the central portion 110 is stable is used, for example, based on the center of the central portion 110. Thus, it can be set as the average value of the thickness in a region within ±5 to 10% of the thickness. In addition, the minimum thickness t _b of the boundary portion 130 is the thinner of the minimum thicknesses of the boundary portion 130 at two points in the film 100 before stretching.

<stretching process>

The stretching step is a step of heating and stretching the pre-stretching film 100 obtained by the pre-stretching film forming step in the longitudinal direction and the width direction. Here, FIG. 11 is a diagram for explaining an extending process. In the present embodiment, in the stretching process, the pre-stretch film 100 is delivered from the pre-stretch film take-up roll described above, and both ends 120 of the pre-stretch film 100 are held with a clip 310 as shown in FIG. The film 100 before stretching is heated and stretched by a simultaneous biaxial stretching method that simultaneously stretches in the longitudinal direction and the width direction while doing so.

Specifically, in the stretching process, the film 100 before stretching is continuously sent out from the film winding roll before stretching, and both ends 120 of the film 100 before stretching are held at regular intervals by using a plurality of clips. The film 100 before stretching is conveyed into the stretching furnace 320 by the clip 310, and the film 100 before stretching is held in the length direction and the width direction by each clip 310 in the stretching furnace 320. Pull and stretch. At this time, the film 100 before stretching is conveyed in a state held by the clip 310, so that it passes through the stretching furnace 320, and the film 100 before stretching in the preheating zone in the stretching furnace 320 After preheating to a temperature higher than the glass transition temperature of the second thermoplastic resin (PC) at both ends 120 to be 10 to 30° C., in the drawing zone in the drawing furnace 320, the clip 310 is in a heated state. ) Is pulled in the longitudinal direction and the width direction, and is stretched in the longitudinal direction and the width direction. And, following this, the stretched film can be obtained by cooling and solidifying in a cooling heat setting zone. Then, by opening the clip 310 and winding it on a roll, a stretched film can be continuously obtained.

On the other hand, in this embodiment, a pair of guide rails for moving the clip 310 are provided so as to pass through the extension path 320. A pair of guide rails are located at the position of the clip 310 for gripping the upper both ends 120 of the film 100 before stretching shown in FIG. 11 and the position of the clip 310 for gripping the both ends 120 at the lower side. They are installed respectively, and are parallel to each other in the preheating zone in the drawing furnace 320, they are separated from each other in the width direction of the film 100 before drawing in the drawing zone, and are parallel to each other again in the cooling heat setting zone. Alternatively, in the cooling and heat setting zone, the distance between the pair of guide rails in the cooling and heat setting zone is determined by taking into account the shrinkage at the time of solidification of the stretched film heated and stretched in the stretching zone. Based on the width, it is possible to approach several percent in the width direction. In this embodiment, the clip 310 holding the both ends 120 of the film 100 before stretching moves along such a guide rail, so that the film 100 before stretching can be conveyed and stretched.

In the present embodiment, the film 100 before stretching is stretched in the stretching zone in the stretching furnace 320 using the clip 310 moving along the guide rail. That is, in the stretching zone in the stretching furnace 320, the clips 310 holding the both ends 120 of the film 100 before stretching are moved to widen in the width direction along the guide rail, and also between the clips 310 By performing control to increase the gap of the film 100 before stretching, both ends 120 of the film 100 are pulled in the longitudinal direction and the width direction as shown by the arrows shown in FIG. 11. Accordingly, before stretching, the central portion 110 and both ends 120 of the film 100 are heated and stretched until the required stretching ratio is achieved in the length direction and the width direction, respectively. In addition, the heat-stretched pre-stretch film 100 is cooled and solidified in a cooling heat setting zone in the stretching furnace 320 and wound by a roll installed outside the stretching furnace 320, thereby continuously obtaining a stretched film. have.

On the other hand, in this embodiment, a stretched film can also be obtained by making the extending process and the film formation process before extending|stretching into a consistent continuous line (process).

In addition, in the present embodiment, the thickness of the central portion 110 of the film 100 after heat stretching is preferably 15 to 50 μm, more preferably 20 to 40 μm. By controlling the thickness of the central portion 110 of the film 100 after heat stretching within the above range, fracture of the film 100 before stretching during heat stretching can be prevented, and heat stretching of the film 100 before stretching can be appropriately performed. have.

In addition, in the present embodiment, the stretched film obtained by heat stretching the film 100 before stretching may be removed by cutting the portions of both ends 120 as necessary. Accordingly, the stretched film can be made into a film composed of only the central portion 110.

As described above, in the present embodiment, a pre-stretch film having a central portion 110 made of a first thermoplastic resin (PA) and both ends 120 made of a second thermoplastic resin (PC) by a film forming step before stretching. A stretched film can be obtained by forming (100) and heating and stretching the central portion 110 and both ends 120 of the film 100 before stretching by a stretching step.

Here, in this embodiment, when forming the pre-stretch film 100 by the pre-stretch film forming process, the ratio of the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 The thickness of the film 100 before stretching is adjusted so that "t _b /t _c "is 0.75 or more. Accordingly, when the film 100 is heated and stretched before stretching in the stretching process, it is possible to effectively prevent the occurrence of cracks in the thin boundary portion 130, thereby improving the productivity of the stretched film.

On the other hand, when heat stretching the film 100 before stretching, the boundary portion 130 of the film 100 before stretching has a thin thickness, so that the stretching stress required for stretching is low, and thus is preferentially stretched. And, as the stretching proceeds at the boundary portion 130, when the stretching stress of the boundary portion 130 gradually increases to reach the stretching stress required for the stretching of the central portion 110, the central portion 110 is also stretched following the boundary portion 130. . At this time, if the thickness of the boundary portion 130 with respect to the central portion 110 is too thin, while the boundary portion 130 is stretched, the boundary portion 130 is broken before the stretching of the central portion 110 starts. In addition, if the thickness of the boundary portion 130 with respect to the central portion 110 is too thin, as shown in FIG. 11, after heating and stretching, the impact when the film 100 is released from the clip 310 before stretching, or obtained Cracks are also generated in the boundary portion 130 due to stress when the stretched film is wound on a roll.

Here, conventionally, as a method of preventing breakage of a film during heat stretching by simultaneous biaxial stretching, a method in which both ends of the film before heat stretching are formed thicker than the central portion has been known. However, in the case of producing a film for stretching by melt extrusion with a T-die 220, even if both ends of the film are thickened as described above, the boundary formed between the central part and both ends of the film is shown in FIG. 9. As shown, the thickness becomes thin, and there is a problem that a crack occurs at this boundary when the film is heated and stretched. Meanwhile, in FIG. 9 described above, an example of using different thermoplastic resins at the central portion 110 and both ends 120 is shown, but when the central portion 110 and both ends 120 are formed of the same thermoplastic resin (i.e., In the case where the pre-stretching film 100 shown in FIG. 9 is a single film made of one type of resin), similarly, when melt-extruded from the T-die 220, the central portion 110 (inner region in the width direction) and both ends Due to the difference in the shrinkage form of the thermoplastic resin in (120) (the outer region in the width direction), the boundary portion becomes thin.

On the other hand, according to this embodiment, the average thickness of the central portion 110 with respect to the pre-stretched film 100 formed by melt-coextrusion with the T-die 220 and then pulled in with the cooling roll 240 By adjusting the ratio ``t _b /t _c '' of (t _c ) and the minimum thickness (t _b ) of the boundary part 130 to the above range, cracks in the boundary part 130 when the film 100 is heated and stretched before stretching Can be effectively prevented, and the productivity of the stretched film can be improved.

In addition, conventionally, in order to prevent breakage of the film 100 before stretching during heating and stretching, rubber elastic particles are added to both ends 120 of the film 100 before stretching to soften both ends 120 (at room temperature. A method of increasing the elongation at break of) is known. However, in this method, the rubber elastic particles in both ends 120 are liable to be deteriorated by heat, and there are the following problems. That is, when the film 100 before stretching is melt-coextruded from the T-die 220, rubber elastic particles deteriorated by heat are precipitated on the die lip 222 of the T-die 220 to form a sediment. There is a concern that a pressing mark is generated on the film 100 before stretching due to the sediment, or the sediment is mixed in the product winding of the oriented film, thereby deteriorating the quality of the oriented film. In addition, when such a deposit of rubber elastic particles is formed, as shown in FIG. 11, when the film 100 before stretching is heated and stretched using the clip 310, between the film 100 and the clip 310 before stretching There is a concern that sediment enters, and accordingly, the film 100 before stretching may be easily broken.

On the other hand, according to this embodiment, it is not necessary to add these rubber elastic particles to both ends 120 of the film 100 before stretching, or the amount of rubber elastic particles added to both ends 120 can be reduced to a small amount. Therefore, when the film 100 is melt-coextruded before stretching, precipitation of rubber elastic particles can be suppressed, and a stretched film excellent in quality can be obtained.

On the other hand, in this embodiment, the ratio "t _b / t _c" of the average thickness (t _c) and the minimum thickness (t _b) of the boundary 130 of the central portion 110, but can be 0.75 or more, as described above, preferably It is preferably 0.8 or more, more preferably 0.9 or more.

In addition, in the present embodiment, with respect to the pre-stretch film 100 to be formed, the ratio of the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 described above ``t _b /t Although it does not specifically limit as a method of adjusting _c " to the above range, for example, a method of using a resin having a lower elongation viscosity as a thermoplastic resin, a method of adjusting the slit width of the die lip 222 of the T die 220, A method of reducing the distance between the T-die 220 and the cooling roll 240, a method of reducing the drawing speed of the film 100 before stretching by the cooling roll 240, and the like may be used alone or in combination.

On the other hand, in the present embodiment, the type of thermoplastic resin applicable among these methods is not limited, and the method of adjusting the slit width of the die lip 222 in that it does not lower the production efficiency of the film 100 before stretching. It is preferable to use. At this time, when the slit width of the die lip 222 to t _s, ratio "t _s / t _c" of the slit width (t _s) and the average thickness (t _c) of the central portion 110 of the die lip 222 Is adjusted to be preferably 8.0 or less, more preferably 6.0 or less, and still more preferably 5.0 or less. Accordingly, the thickness of the pre-stretched film 100 obtained by melt-extruding with the T-die 220 can be made more uniform, so that the average thickness of the central portion 110 (t _c ) and the minimum thickness of the boundary portion 130 (t The ratio "t _b /t _c "of _b ) can be appropriately adjusted within the above range.

In addition, in the present embodiment, with respect to the pre-stretch film 100 to be formed, the ratio of the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 as described above "t _b /t _c " is adjusted to the above range, and by appropriately adjusting the maximum thickness of the both ends 120, fracture of the film 100 before stretching during heat stretching can be more effectively prevented.

Specifically, in forming the stretch around the film 100, as shown in Fig. 10, the case where the maximum thickness of the end portions 120 to t _e, the maximum thickness (t _e) and the central portion (110 of each end 120, ) The ratio "t _e /t _c "of the average thickness (t _c ) is adjusted to preferably 1.0 to 3.0, more preferably 1.0 to 2.0, and still more preferably 1.0 to 1.5. Here, as the maximum thickness t _e of the both ends 120, among the thicknesses of the both ends 120 (one end portion and the other end portion in the width direction) of the film 100 before stretching, the thickness is the thicker one. On the other hand, when the maximum thickness (te) of both ends 120 is too thick with respect to the average thickness (t _c ) of the central part 110, the film 100 before stretching obtained by melt coextrusion by means of a T-die 220 When pressing by the touch roll 230 and the cooling roll 240, the pressure is concentrated on both ends 120 due to the too thick of both ends 120 so that the pressure is not uniformly transmitted to the entire film 100 before stretching. Accordingly, there is a tendency that the thickness of the film 100 before stretching becomes non-uniform, and the thickness of the stretched film obtained by heating and stretching the film 100 before stretching is also non-uniform. On the other hand, with respect to the average thickness (t _c ) of the central portion 110, when the maximum thickness (t _e ) of both ends 120 is too thin, the pre-stretched film 100 melted and coextruded by the T-die 220 When this neck-in, the force of both ends 120 pulling the thermoplastic resin of the boundary part 130 tends to be strong, and accordingly, the thickness of the boundary part 130 becomes thinner, so that the film 100 before stretching during heating and stretching It becomes easy to break.

On the other hand, in the present embodiment, as the first thermoplastic resin (PA) for forming the central portion 110, it can be selected depending on the application of the stretched film required, etc., for example, acrylic resin (PMMA), cyclic olefin A copolymer (COC) or the like can be used.

In addition, as the second thermoplastic resin (PC) for forming the both ends 120, for example, the glass transition temperature (Tg ₁ ) of the first thermoplastic resin (PA) and the glass transition temperature of the second thermoplastic resin (PC) It is preferable to use a thermoplastic resin having a difference (|Tg ₁ -Tg ₂ |) of (Tg ₂ ) of 10 degrees C or less. Accordingly, in the present embodiment, when the both ends 120 of the film 100 before stretching are gripped with the clip 310 by the stretching process to perform heat stretching, the both ends 120 gripped by the clip 310 By heating by the temporary drawing furnace 320, it is appropriately softened, and it is possible to prevent the clip from being pulled out at the time of heating or stretching, or the rupture of the film 100 before stretching, and thus, the productivity of the stretched film can be improved.

On the other hand, at this time, the difference (|Tg ₁ -Tg ₂ |) of the glass transition temperature of a 1st thermoplastic resin (PA) and a 2nd thermoplastic resin (PC) is preferably 10°C or less, more preferably 5°C Hereinafter, more preferably, it is 3 degreeC or less.

In this embodiment, as the second thermoplastic resin (PC), based on the above-described viewpoint, specifically, the following thermoplastic resins can be used. For example, as the second thermoplastic resin (PC), when an acrylic resin is used for the first thermoplastic resin (PA), one of polyethylene naphthalate (PEN), cyclic olefin polymer (COP), etc. is used alone, or A mixed resin in which two or more kinds are mixed can be used.

Further, as the second thermoplastic resin (PC), a resin obtained by adding a small amount of rubber elastic particles to the above-described first thermoplastic resin (PA) within a range that does not impair the productivity of the stretched film may be used.

Alternatively, as the second thermoplastic resin (PC), the first thermoplastic resin (PA) with respect to a thermoplastic resin (heat-resistant thermoplastic resin) having a higher glass transition temperature than the first thermoplastic resin (PA) and a difference of more than 10°C. A mixed resin obtained by blending a thermoplastic resin having a lower glass transition temperature (low temperature melting thermoplastic resin) can be used. At this time, by adjusting the blending ratio of the heat-resistant thermoplastic resin and the low-temperature melting thermoplastic resin, the glass transition temperature of the obtained mixed resin is the difference between the glass transition temperature of the first thermoplastic resin (PA) (|Tg ₁ -Tg ₂ |) It is preferable to adjust so that is in the above range.

For example, when an acrylic resin having a glass transition temperature (Tg ₁ ) of about 120°C is used as the first thermoplastic resin (PA), a polycarbonate (PC) having a glass transition temperature of about 150°C is used as the second thermoplastic resin (PC). ), polyethylene terephthalate (PET) having a glass transition temperature of about 70° C. is blended to adjust the glass transition temperature to around 120° C., which is the same as the glass transition temperature (Tg ₁ ).

On the other hand, when such a mixed resin is used as the second thermoplastic resin (PC), polycarbonate (PC), cyclic olefin polymer (COP), or the like can be used as the heat-resistant thermoplastic resin. In addition, as low-temperature meltable thermoplastic resins, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylonitrile-butadiene-styrene (ABS), polyethylene (PE), and glass transition than the first thermoplastic resin Low temperature acrylic resin, polyester (PEs), polybutylene terephthalate (PBT), and the like can be used. In this embodiment, it is preferable to use polycarbonate (PC) as a heat-resistant thermoplastic resin and polyethylene terephthalate (PET) as a low-temperature meltable thermoplastic resin from the viewpoint of easy adjustment of the glass transition temperature of the mixed resin obtained among them. Do.

Here, FIG. 12 is a graph showing the results of measuring the glass transition temperature of a mixed resin obtained by blending polyethylene terephthalate (PET) with polycarbonate (PC). On the other hand, in FIG. 12, for a resin in which the content ratio of polyethylene terephthalate (PET) to polycarbonate (PC) is 0%, 25%, 50%, 75%, and 100%, the glass transition temperature is differential scanning calorific value. The result of measurement by measurement (DSC) is shown. Here, in the measurement by differential scanning calorimetry (DSC), even if the content ratio of polyethylene terephthalate (PET) is any value, the glass transition temperature of the mixed resin does not expand, and is determined to be almost one point.

As shown in Fig. 12, the glass transition temperature of the mixed resin in which polycarbonate (PC) is blended with polyethylene terephthalate (PET) can be changed according to the content ratio of polyethylene terephthalate (PET). Accordingly, in the present embodiment, when such a mixed resin is used as the second thermoplastic resin, the glass transition temperature (Tg ₂ ) of the second thermoplastic resin (PC) can be easily adjusted, and the first thermoplastic resin (PA) is The difference (|Tg ₁ -Tg ₂ |) from the glass transition temperature (Tg ₁ ) can be controlled within the above range.

On the other hand, in the present embodiment, with respect to the pre-stretch film 100 formed by the pre-stretch film forming step, it is preferable to smooth the side surfaces of both ends 120 before heating and stretching. According to the smoothing of the sides of both ends 120 of the film 100 before stretching, when heating and stretching the film 100 before stretching by pulling both ends 120 of the film 100 before stretching in the stretching process, both ends ( By preventing the concentration of local stress caused by the sloppy side of 120), it is possible to prevent the occurrence of cracks at both ends 120, thereby improving the productivity of the stretched film.

A method of smoothing the side surfaces of the both ends 120 of the film 100 before stretching is not particularly limited, but a method of trimming a predetermined width from both sides of the both ends 120 with a cutter, and a method of polishing the ends of both ends 120 , A method of heating and pressing the ends of both ends 120 may be used. On the other hand, the smoothing of the sides of both ends 120 reduces the irregularities of the sides of both ends 120, and when the film 100 is pulled in the longitudinal direction before stretching, stress is not concentrated on a part of both ends 120. You just have to do that.

In the case of trimming the both ends 120 of the film 100 before stretching with a cutter, any cutter may be used as long as the sides of both ends 120 can be smoothly smoothed by trimming. For example, a razor blade or , A rotary shear cutter that continuously rotates while crossing the circular upper and lower edges to cut by shear, or a laser cutter using a solid laser, semiconductor laser, liquid laser or gas laser, etc. can be used, but the film before stretching when trimming A laser cutter is preferable in that it is possible to reduce the stress applied to the (100) and to prevent the occurrence of cracks in the film (100) before stretching during trimming.

On the other hand, when trimming both ends 120 of the film 100 before stretching, it is preferable to trim while heating both ends 120. Accordingly, it is possible to make the side surfaces of the both ends 120 more smooth, so that fracture of the film 100 before stretching can be prevented more appropriately when the film 100 is heated and stretched before stretching.

In addition, in the above-described example, as a method of heat stretching the film 100 before stretching, as shown in Fig. 11, a simultaneous biaxial stretching method in which the film 100 before stretching is heated in both directions in the length direction and the width direction is used. Although an example of use has been shown, in this embodiment, a method of uniaxially stretching the film 100 before stretching only in the longitudinal direction may be used.

At this time, heat stretching in the longitudinal direction of the film 100 before stretching can be performed in the same manner as in the simultaneous biaxial stretching method shown in FIG. 11. That is, the both ends 120 of the film 100 before stretching are conveyed into the drawing furnace 320 while being gripped with the clip 310, and thereafter, both ends 120 of the film 100 before stretching in the drawing furnace 320 By increasing the gap between the clips 310 without moving each clip 310 holding the clip 310 in the width direction, a method of performing heat stretching only in the longitudinal direction can be used.

In the present embodiment, both ends 120 of the film 100 before stretching are clipped 310 as shown in Fig. 11 in both the case where simultaneous biaxial stretching is performed in the longitudinal direction and the width direction, or uniaxial stretching is performed only in the longitudinal direction. ), the productivity of the stretched film can be improved as compared with the sequential biaxial stretching method used in the past, and a stretched film having more excellent quality can be obtained.

On the other hand, in the conventional sequential biaxial stretching method, the film 100 before stretching produced by the method shown in FIG. 7 is first heated and stretched in the longitudinal direction, and then heat stretched in the width direction. In the sequential biaxial stretching method, after heat stretching in the longitudinal direction by conveying the film 100 before stretching by a plurality of rolls, as shown in Fig. 11, the both ends 120 of the film 100 before stretching are clipped ( While gripping with 310), it is heated and stretched in the width direction.

Here, in the sequential biaxial stretching method, stretching in the longitudinal direction of the film 100 before stretching is specifically performed as follows. That is, according to the sequential biaxial stretching method, the pre-stretched film 100 is preheated to the glass transition temperature of both ends 120 while conveying the pre-stretched film 100 by a plurality of preheated preheating rolls, and preheated Is conveyed by a cooling roll continuously while further heating to a temperature about 10 to 30° C. higher than the glass transition temperature of both ends 120 by an infrared heater or the like. At this time, by making the conveying speed by the cooling roll faster than the conveying speed by the preheating zone roll, tension is generated between the preheating zone roll and the cooling roll, and the required stretching of the film 100 in the longitudinal direction before stretching by using this tension Stretch to magnification.

Here, in the sequential biaxial stretching method, when the film 100 before stretching is stretched in the longitudinal direction, the surface of the film 100 before stretching comes into contact with the preheating roll and the cooling roll, so that the surface of the film 100 before stretching There is a fear that scratches may occur in the resulting stretched film and the appearance quality of the resulting stretched film may deteriorate. Further, in the sequential biaxial stretching method, when the film 100 before stretching is heated and stretched in the longitudinal direction, the both ends 120 of the film 100 before stretching are not fixed with a clip or the like, so the film 100 before stretching Due to this heat, there is a fear that the productivity of the stretched film is reduced by shrinking in the width direction.

On the other hand, according to this embodiment, by performing stretching in the longitudinal direction with respect to the film 100 before stretching by using the aforementioned simultaneous biaxial stretching method or the aforementioned method of uniaxial stretching only in the longitudinal direction (that is, As shown in Fig. 11, by gripping the both ends 120 of the film 100 before stretching with a clip 310, by using a method of stretching in the longitudinal direction), contact with the roll can be avoided. It is possible to reduce scratches on the surface of the film 100 after stretching and before stretching. Accordingly, for a stretched film obtained by cutting the both ends 120 of the film 100 before stretching, which has been heated and stretched, the appearance quality can be improved, and in particular, it can be very preferably used for an optical film where the demand for appearance quality is difficult. . In addition, according to the present embodiment, when the film 100 before stretching is stretched in the longitudinal direction, the both ends 120 of the film 100 before stretching are held by the clips 310, so that the film 100 before stretching On the other hand, shrinkage in the width direction due to heat can be prevented, so that the productivity of the stretched film can be improved.

In addition, in the above-described example, the pre-stretch film 100 has a central portion 110 made of a first thermoplastic resin (PA) and both ends 120 made of a second thermoplastic resin (PC) as shown in FIG. An example where the boundary is divided by the vicinity of (130) is shown, but in this embodiment, the first thermoplastic resin (PA) and the second thermoplastic resin (PC) may be mixed with each other within a range that does not hinder the manufacture of the stretched film. I can.

For example, as the film 100 before stretching, the viscosity of the second thermoplastic resin (PC) forming the outer region of the film 100 before stretching is a first thermoplastic resin that forms the inner region of the film 100 before stretching. When the viscosity is lower than the viscosity of (PA), as shown in FIG. 13, the central portion 110 may have a shape covering a part of the both ends 120. At this time, the boundary portion 130 of the film 100 before stretching is formed at a position shifted from the boundary between the central portion 110 and both ends 120.

That is, the boundary portion 130 of the film 100 before stretching is, as described above, in the thickness direction due to the difference in the shrinkage shape in the width direction of the thermoplastic resin melt-extruded from the T-die 220. It is concave and formed. Therefore, as shown in FIG. 13, in the pre-stretched film 100 in which the first thermoplastic resin and the second thermoplastic resin are mixed with each other, a boundary portion formed by a difference in shrinkage shape according to a position in the width direction of the film 100 before stretching The 130 is formed at a position deviated from the boundary between the first thermoplastic resin PA and the second thermoplastic resin PC.

On the other hand, when melt-coextrusion is performed with the T-die 220, when the viscosity of the second thermoplastic resin (PC) is higher than that of the first thermoplastic resin (PA), in the film 100 before stretching obtained, Contrary to the pre-stretch film 100 shown in Fig. 13, the second thermoplastic resin PC having a higher viscosity flows to the surface of the central portion 110 to cover a part of the first thermoplastic resin PA.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Example 1>

As a thermoplastic resin for forming the film 100 before stretching, an acrylic resin (glass transition temperature (Tg ₁ ): 123°C, breaking elongation at room temperature: 5%) was prepared.

Here, for the prepared thermoplastic resin, the glass transition temperature was measured by differential scanning calorimetry (DSC), and the elongation at break was measured by a tensile tester (manufactured by Orientech Co., Ltd., product number: RTC-1210A). The same was carried out about the following Example 2 and Comparative Example 1.

Subsequently, using the prepared thermoplastic resin, as shown in Fig. 1, the film 100 before stretching was produced under the following conditions. Here, the produced film 100 before stretching had an overall width of about 310 mm. And, the thickness was measured for the produced film 100 before stretching, the average thickness (t _c ) of the central portion 110 is 160 μm, the minimum thickness (t _b ) of the boundary portion 130 is 128 μm, and both ends 120 ) Had a maximum thickness (t _e ) of 290 μm, a ratio of these thicknesses “t _b /t _c ” of 0.8, “t _e /t _c ” of 1.81, and “t _s /t _c ” of 5.0. The results are shown in Fig. 6A. Here, in FIGS. 6A and 6B and 6C described later, the thickness corresponding to the position in the width direction of the film 100 before stretching is shown. On the other hand, as shown in Fig. 6A, the boundary portion 130 of the film 100 before stretching was formed at a position of about 40 mm from the end portion in the width direction of the film 100 before stretching.

Dimensions in the width direction of the T-Dice 220 outlet: 380mm

Slit width (t _s ) of die lip (222): 0.8mm

Distance between T-die 220 and cooling roll 240: 60mm

The rotational speed of the cooling roll 240: 5mpm

Subsequently, the obtained pre-stretch film 100 is held by a clip 310, and as shown in Fig. 5, it is heated and stretched in the longitudinal direction and the width direction under the following conditions by a simultaneous biaxial stretching method, and then on a roll. By winding up, a stretched film was obtained. On the other hand, in the present embodiment, while the film 100 before stretching was heated and stretched, no fracture of the film 100 before stretching occurred. In addition, when the thickness of the obtained stretched film was measured, the thickness of the portion corresponding to the boundary portion 130 was relatively thick, 30 μm or more, and the effective width of the product (the area of the thickness 40 μm or more in the central portion 110) was relatively wide as 390 mm. The resulting stretched film could be obtained. The results are shown in Fig. 6A.

Inlet speed of drawing machine: 1mpm

Outlet speed of drawing machine: 2mpm

Stretch ratio: 100% in the length direction x 100% in the width direction (2 times in the length direction x 2 times in the width direction)

Clip 310 holding position: 15 mm from the end of the film 100 before stretching

Preheating zone temperature, distance: 140℃, 350mm

Stretching zone temperature, distance: 140℃, 500mm

Cooling and heat setting temperature, distance: 90℃, 700mm

<Example 2>

When producing a stretched film before 100, similarly to the exception of the enlarged slit width (t _s) of the die lip 222 to 1.2mm, Example 1, the obtained stretched film before 100 and the stretched film thickness Was measured. The result of measuring the thickness of the film 100 and the stretched film before stretching is shown in Fig. 6B.

In Example 2, the produced pre-stretch film 100 has an average thickness t _c of the central portion 110 of 160 μm and a minimum thickness t _b of the boundary portion 130 of 120 μm, and the ratio of these thicknesses ``t _b /t _c " was 0.75, and "t _s /t _c " was 7.5. In addition, in Example 2, as compared with Example 1 described above, the boundary portion 130 of the film 100 before stretching before heat stretching is thinner, and accordingly, the stretched film after heating stretching is as shown in FIG. 6B. Likewise, the effective width of the product (a region having a thickness of 40 μm or more in the central portion 110) was reduced.

However, in Example 2, as in Example 1, while the film 100 before stretching was heated and stretched, a stretched film having excellent quality could be continuously produced without fracture of the film 100 before stretching.

<Comparative Example 1>

Except for increasing the extrusion amount of the thermoplastic resin by the T-die 220 and increasing the rotational speed of the cooling roll 240 to 15 mpm, the film 100 and the stretched film before stretching were prepared in the same manner as in Example 1. It was obtained and the thickness was measured. The result of measuring the thickness of the film 100 and the stretched film before stretching is shown in Fig. 6C.

In Comparative Example 1, the produced pre-stretched film 100 has an average thickness (t _c ) of the central portion 110 of 158 μm, a minimum thickness of the boundary portion 130 (t _b ) of 110 μm, and the ratio of these thicknesses “t _b /t _c " was 0.70.

In Comparative Example 1, in the produced film 100 before stretching, since the minimum thickness t _b of the boundary portion 130 was too thin compared to the average thickness t _c of the central portion 110, the film 100 before stretching ) When heated and stretched, cracks were generated in the boundary portion 130 of the film 100 before stretching, causing frequent breakage of the film 100 before stretching, and the productivity of the stretched film decreased. Here, in Comparative Example 1, by changing the temperature of the preheating zone and stretching zone when performing heat stretching from 140° C. to 150° C., the frequency of occurrence of fracture of the film 100 before stretching during heat stretching could be reduced. , The obtained stretched film has a very small thickness of about 8 μm at the portion corresponding to the boundary part 130, and the stress when opening the clip 310 from the stretched film after heat stretching or when winding the obtained stretched film with a roll As a result, a crack was generated in a portion corresponding to the boundary portion 130, and the stretched film was broken.

As described above, with respect to the pre-stretched film 100 before heat stretching, the ratio of the minimum thickness (t _b ) of the boundary portion 130 to the average thickness (t _c ) of the central portion 110 ``t _b / In Examples 1 and 2 in which t _c ′ was 0.75 or more, when the film 100 before stretching was heated and stretched, fracture of the film 100 before stretching could be suppressed, so that a stretched film having excellent quality was obtained. In addition, the productivity of the stretched film could be improved. In particular, Examples 1 and 2 is because the ratio "t _s / t _c" of the slit width (t _s) of the die lip 222 to the average thickness (t _c) of the central portion 110 to less than 8.0 , As shown in FIG. 6A, the obtained stretched film had a uniform thickness and excellent quality.

On the other hand, as described above, the ratio of the minimum thickness (t _b ) of the boundary portion 130 to the average thickness (t _c ) of the central portion 110 with respect to the pre-stretching film 100 before heat stretching is “t _In Comparative Example 1 in which _b /t _c " is less than 0.75, when the film 100 before stretching was heated and stretched, the film 100 before stretching was frequently broken, and the productivity of the stretched film was lowered.

<Example 3>

An acrylic resin (glass transition temperature (Tg ₁ ): 123°C, breaking elongation at room temperature: 5%) as the first thermoplastic resin (PA) for forming the central portion 110 of the film 100 before stretching was prepared, As the second thermoplastic resin (PC) to form both ends 120 of the film 100 before stretching, an acrylic resin containing a small amount of rubber elastic particles (glass transition temperature (Tg ₂ ): 125°C, elongation at break at room temperature) : 7%) was prepared.

Here, for the first thermoplastic resin (PA) and the second thermoplastic resin (PC), the glass transition temperature is measured by differential scanning calorimetry (DSC), and the elongation at break at room temperature is a tensile tester (manufactured by Orientec, Inc., Product number: It measured by RTC-1210A). The same was carried out about the following Example 4 and Comparative Example 2.

Subsequently, the prepared first thermoplastic resin (PA) and the second thermoplastic resin (PC) are respectively supplied to the feed block 210 by a twin-screw extruder, and the film 100 before stretching under the following conditions by the method shown in FIG. 7. ) Was produced. Here, the produced film 100 before stretching had an overall width of about 315 mm. And, a thickness measurement was performed on the produced film 100 before stretching, the average thickness (t _c ) of the central portion 110 is 160 μm, the minimum thickness (t _b ) of the boundary portion 130 is 133 μm, and both ends 120 The maximum thickness (t _e ) of was 270 μm, the ratio of these thicknesses “t _b /t _c ”was 0.83, “t _e / t _c ” was 1.69, and “t _s / t _c ”was 5.0. The results are shown in Fig. 14A. Here, in FIGS. 14A and 14B and 14C described later, the thickness corresponding to the position in the width direction of the film 100 before stretching is shown. On the other hand, as shown in (A) of FIG. 14, the boundary portion 130 of the film 100 before stretching was formed at a position of about 50 mm from the end of the composite film 100 in the width direction. In addition, in this embodiment, acrylic resin to which rubber elastic particles are added was used as the second thermoplastic resin (PC), but since the amount of the rubber elastic particles added was small, the film 100 before stretching was melt-coextruded The precipitation of rubber elastic particles at the time could be suppressed.

Dimensions in the width direction of the T-Dice 220 outlet: 380mm

Slit width (t _s ) of die lip (222): 0.8mm

Distance between T-die 220 and cooling roll 240: 60mm

The rotational speed of the cooling roll 240: 6mpm

Supply of the first thermoplastic resin (PA) to the feed block 210: 15 kg/hr

Supply amount of the second thermoplastic resin (PC) to the feed block 210: 5 kg/hr

Subsequently, the obtained pre-stretch film 100 is gripped by the clips 310 of both ends 120, and heated and stretched in the longitudinal direction and the width direction under the following conditions by the simultaneous biaxial stretching method as shown in FIG. Then, a stretched film was continuously obtained by winding up with a roll. On the other hand, in this embodiment, while the film 100 before stretching was heated and stretched, no fracture of the film 100 before stretching occurred. In addition, when the thickness of the obtained stretched film was measured, the thickness of the portion corresponding to the boundary portion 130 was relatively thick, 30 μm or more, and the effective width of the product (the area of the thickness 40 μm or more in the central portion 110) was relatively wide as 450 mm. A stretched film could be obtained. The results are shown in Fig. 8A.

Inlet speed before heating and stretching: 1mpm

Outlet speed after heating and stretching: 2mpm

Stretch ratio: 100% in the length direction x 100% in the width direction (2 times in the length direction x 2 times in the width direction)

Clip 310 gripping position: 15 mm from the end of the composite film 100

Preheating zone temperature, distance: 140℃, 350mm

Stretching zone temperature, distance: 140℃, 500mm

Cooling and heat setting temperature, distance: 90℃, 700mm

<Example 4>

When producing the film 100 before stretching, except that the slit width (t _s ) of the die lip 222 was enlarged to 1.2 mm, it was carried out in the same manner as in Example 3 to obtain the pre-stretch film 100 and the stretched film, and the thickness Was measured. The result of measuring the thickness of the film 100 and the stretched film before stretching is shown in Fig. 14B.

In Example 4, the produced pre-stretch film 100 has an average thickness t _c of the central portion 110 of 147 μm and a minimum thickness t _b of the boundary portion 130 of 110 μm, and the ratio of these thicknesses ``t _b /t _c " was 0.75. In addition, in Example 4, compared to Example 3 described above, as shown in Fig. 14B, the boundary portion 130 of the film 100 before stretching before heat stretching was slightly thinner, but stretching in the same manner as in Example 1 It is possible to suppress the precipitation of rubber elastic particles when the entire film 100 is melt-coextruded, and also, while the film 100 is heated and stretched before stretching, the film 100 before stretching does not break, so the quality This excellent stretched film could be continuously produced.

<Comparative Example 2>

As the second thermoplastic resin (PC) for forming both ends 120 of the film 100 before stretching, an acrylic resin with an increased amount of rubber elastic particles added (glass transition temperature (Tg ₂ ): 125°C, elongation at break at room temperature) : 28%), it carried out similarly to Example 3, and obtained the film before extending|stretching 100 and a stretched film, and measured the thickness. The result of measuring the thickness of the film 100 and the stretched film before stretching is shown in Fig. 14C.

In Comparative Example 2, the produced film 100 before stretching has an average thickness t _c of the central portion 110 of 155 μm and a minimum thickness t _b of the boundary portion 130 of 102 μm, and the ratio of these thicknesses ``t _b /t _c " was 0.66.

In addition, in Comparative Example 2, in the prepared film 100 before stretching, since the minimum thickness (t _b ) of the boundary portion 130 was too thin compared to the average thickness (t _c ) of the central portion 110, the film before stretching When (100) was heated and stretched, cracks were generated in the boundary portion 130 of the film 100 before stretching, and the film 100 was frequently broken before stretching, resulting in a decrease in productivity of the stretched film.

As described above, with respect to the film 100 before stretching before heating and stretching, the ratio of the minimum thickness t _b of the boundary portion 130 to the average thickness t _c of the central portion 110 ``t <sub>b</sub> /t <sub>c</sub> '' In Example 3 and Example 4 in which was 0.75 or more, when the film 100 before stretching was heated and stretched, fracture of the film 100 before stretching could be suppressed, so that a stretched film having excellent quality can be obtained, In addition, the productivity of the stretched film could be improved. In particular, in Example 3, since the ratio ``t _s / t _c '' of the slit width t _s of the die lip 222 to the average thickness t _c of the central portion 110 was 8.0 or less, As shown in (A), the obtained stretched film had a uniform thickness and excellent quality.

On the other hand, as described above, for the film 100 before stretching before heating and stretching, the ratio of the minimum thickness t _b of the boundary portion 130 to the average thickness t _c of the central portion 110 ``t _b /t _In Comparative Example 2 in which _c " is less than 0.75, when the film 100 before stretching was heated and stretched, the film 100 before stretching was frequently broken, and the productivity of the stretched film was inferior.

100… Film before stretching 110... Central
120... Both ends 130... Border
PA… 1st thermoplastic resin PC... Second thermoplastic resin
210... Feed block 220... T Dice
230... Touch Roll 240... Cooling roll
310... Clip 320... Drawing furnace

Claims (13)

A pre-stretch film forming step of melt-extruding a thermoplastic resin from a molding die and then cooling and solidifying it by drawing it with a roll to form a film before stretching; And
As a method for producing a stretched film having; a stretching step of forming a stretched film by heating and stretching the film before stretching in at least one direction,
In the pre-stretch film forming process, the central portion of the pre-stretch film shrinks toward the specific surface by plane stretching extending along a specific surface located at or near the central position in the thickness direction of the pre-stretch film, The minimum thickness of the boundary portion formed between the central portion and the both ends by contracting about the specific axis by uniaxial stretching of the both ends of the film before stretching is extended around a specific axis passing through the center of the both ends or near the central position, t _b and the average thickness of the central part is t _c ,
The pre-stretch film is formed so that the ratio "t _b /t _c "of the minimum thickness (t _b ) of the boundary part and the average thickness (t _c ) of the central part is 0.75 or more,
If the maximum thickness of the end portions to t _e, the stretching ratio "t _e / t _c" of the maximum thickness (t _e) and the average thickness (t _c) of the central portion of the both end portions are to be in the range of 1.0 to 2.0 A method for producing a stretched film, characterized in that the film before stretching is formed in the entire film forming process. The method of claim 1,
A method for producing a stretched film, characterized in that an acrylic resin is used as the thermoplastic resin. The method of claim 1,
As the thermoplastic resin,
A first thermoplastic resin forming an inner region positioned inside the width direction of the film before stretching;
A method for producing a stretched film, comprising forming an outer region positioned outside the width direction of the film before stretching, and using a second thermoplastic resin different from the first thermoplastic resin. The method of claim 3,
A method for producing a stretched film, wherein an acrylic resin is used as the first thermoplastic resin. The method of claim 4,
A method for producing a stretched film, characterized in that a mixed resin obtained by blending polycarbonate (PC) with a thermoplastic resin having a glass transition temperature lower than that of the acrylic resin is used as the second thermoplastic resin. The method according to any one of claims 3 to 5,
A method for producing a stretched film, characterized in that a thermoplastic resin having a glass transition temperature of 10° C. or less is used as the first thermoplastic resin and the second thermoplastic resin. delete The method according to any one of claims 1 to 5,
If the slit width of the outlet of the molding die to t _s, the ratio "t _s / t _c" of the slit width (t _s) and the average thickness (t _c) of the central portion of the exit of the molding die 8.0 A method for producing a stretched film, characterized in that the pre-stretch film is formed in the pre-stretch film forming step so as to be as follows. The method according to any one of claims 1 to 5,
In the stretching step, the heat stretching of the film before stretching is performed by simultaneous biaxial stretching in which the film before stretching is simultaneously stretched in the longitudinal direction and the width direction. The method according to any one of claims 1 to 5,
In the stretching step, the stretching ratio with respect to the stretching direction of the heat stretching of the film before stretching is 3 times or less. The method according to any one of claims 1 to 5,
In the stretching step, the heat stretching of the film before stretching is performed so that the thickness of the central portion of the stretched film after heat stretching is in a range of 15 to 50 μm. The method according to any one of claims 1 to 5,
A method for producing a stretched film, comprising: a smoothing step of smoothing both side surfaces defining the thickness of the film before the stretching step and before the stretching step. The method of claim 12,
The smoothing in the smoothing step is performed by removing regions located at both ends in the width direction of the film before stretching.

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