JP6338866B2 - Method for producing stretched film - Google Patents

Description

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

  When producing a stretched film, a method of preparing a film as a material and stretching the prepared film is used. As a method of stretching the film, the film is held in a heating furnace while holding both ends of the film with clips. There is known a simultaneous biaxial stretching method in which heating and stretching are simultaneously performed in the length direction and the width direction by clips that are conveyed and gripped at both ends of the film in a heating furnace.

  In such a simultaneous biaxial stretching method, in the heating furnace, the film is stretched by heating to the necessary stretching ratio by pulling the film in the length direction and the width direction. When a large stress is applied to both end portions of the film, which is a portion gripped by the clip, tears are generated at both end portions, and this may cause the entire film to break. For this reason, in order to prevent breakage of the film at the time of heat stretching, a technique is known in which both ends held by the clip are reinforced with a resin having a higher strength than the resin constituting the film to be originally obtained.

  For example, in Patent Document 1, a reinforcing film in which both end portions are formed at both ends in the width direction of the film by a thermoplastic resin having a larger stretching stress value at the time of heat stretching than the thermoplastic resin constituting the central portion of the film. A technique for producing a stretched film by heat-stretching such a reinforcing film is disclosed.

JP 2008-149511 A

  However, in the technique of Patent Document 1, since the stretching stress value at the time of heating and stretching at both ends of the film is too large, the both ends of the film cannot be sufficiently stretched when the both ends are gripped and pulled by the clip. There is a problem that the clip comes off or the film breaks.

  Moreover, in order to increase the stretching stress value at the time of heating and stretching at both ends of the film, the technique of Patent Document 1 is a glass of thermoplastic resin that constitutes the film center as a thermoplastic resin that constitutes both ends of the film. A thermoplastic resin having a glass transition temperature higher than the transition temperature is used. In this case, the difference in glass transition temperature between the thermoplastic resin constituting both ends of the film and the thermoplastic resin constituting the film center is too large (for example, the difference in glass transition temperature is 35 ° C. or more). When heating and stretching, if the heating temperature in the heating furnace is set near the glass transition temperature at the center of the film, the heating temperature in the heating furnace will be lower than the glass transition temperatures at both ends of the film. Therefore, both ends are not sufficiently softened, and there is a problem that when the both ends are gripped and pulled by the clip, the clip comes off or the film is broken.

  The present invention has been made in view of such a situation, and when producing a stretched film by heating and stretching while holding both ends of the film with a clip, it is possible to prevent the clip from coming off and the film from being broken. An object of the present invention is to provide a method for producing a stretched film that can obtain a stretched film having excellent productivity and quality.

  The present inventors form a first end and a second end on one end and the other end in the width direction of the film with a thermoplastic resin different from the thermoplastic resin constituting the central portion of the film, respectively. When producing a stretched film by heating and stretching such a composite film using a composite film, the cross section of the first end and the cross section of the second end of the cross section in the width direction of the composite film before heat stretching Has been found to be able to achieve the above-mentioned object by adjusting to satisfy a predetermined relationship, and the present invention has been completed.

That is, according to the present invention, the first thermoplastic resin and the second thermoplastic resin different from the first thermoplastic resin are melt-coextruded from a molding die and then cooled and solidified. A central portion made of the first thermoplastic resin; a first end portion made of the second thermoplastic resin formed at one end in the width direction of the central portion; and the other end in the width direction of the central portion. A composite film forming step of forming a composite film comprising a second end portion made of the second thermoplastic resin and gripping the composite film using a plurality of gripping members under heating conditions by pulling the grip portion in a state, wherein the stretching step the composite film heating stretched to at least the length direction to form a stretched film, a method for producing a stretched film having the second thermoplastic resin As the second thermoplastic resin, a glass having a higher stretching stress value per unit cross-sectional area at the time of heat stretching than the first thermoplastic resin is used. Using a thermoplastic resin having a high transition temperature , A ₁ [m ² ] is the cross-sectional area of the first end portion of the cut surface in the width direction of the composite film before heat stretching , and the cross-sectional area of the second end portion is A ₂ [m ² ], the coefficient of static friction between the first end and the second end and the gripping member at the time of heat-stretching is μ, and the first end and the second end by the gripping member F [N] is the gripping force of σ [N / m], and the stretching stress value per unit cross-sectional area during the heat stretching of the second thermoplastic resin constituting the first end portion and the second end portion is σ [N / m ² ], the following formulas (1) and (2) are satisfied. A method for producing a stretched film is provided.
A ₁ <μF / σ (1)
A ₂ <μF / σ (2)

In the production method of the present invention, when the composite film is formed by melt coextrusion as the second thermoplastic resin, the first end portion and the second end portion made of the second thermoplastic resin are formed. It is preferable to use a thermoplastic resin such that the elongation at break during heat stretching is larger than the stretch ratio when performing heat stretching in the stretching step .
In the production method of the present invention, it is preferable that the heating temperature at the time of performing the heat stretching in the stretching step is lower than the glass transition temperature of the second thermoplastic resin.
In the production method of the present invention, in the composite film forming step, the second thermoplastic resin is formed by adjusting a melt extrusion amount of the second thermoplastic resin with respect to a melt extrusion amount of the first thermoplastic resin by a molding die. it is preferable to control the size of the cross-sectional area a ₂ of the sectional area a ₁ and the second end of the first end portion of said composite film.
In the manufacturing method of this invention, it has the removal process of removing a part of said 1st edge part and a part of said 2nd edge part in the said composite film formed by the said composite film formation process before the said extending | stretching process. It is preferable.
In the manufacturing method of the present invention, when the composite film is formed by melt coextrusion as the first thermoplastic resin and the second thermoplastic resin, the first end made of the second thermoplastic resin. It is preferable to use a thermoplastic resin such that the elongation at break of the part and the second end portion at room temperature is larger than the break elongation at room temperature of the central portion made of the first thermoplastic resin.
In the manufacturing method of the present invention, when performing heat stretching in the stretching step, it is preferable that the gripping position of each gripping member is a position within 10 mm of the distance from both ends of the central portion in the width direction.
In the production method of the present invention, it is preferable that the heat stretching of the composite film in the stretching step is performed by simultaneous biaxial stretching that extends in the width direction in addition to the length direction of the composite film.
Moreover, in the manufacturing method of this invention, it is preferable to use an acrylic resin as said 1st thermoplastic resin.
Furthermore, in the manufacturing method of this invention, it is preferable to perform the heat stretching of the said composite film in the said extending process so that the thickness of the said center part after the heat stretching of the said composite film may be in the range of 15-50 micrometers.

  According to the present invention, when producing a stretched film by heat-stretching the film, a stretched film production method capable of appropriately performing heat-stretching and obtaining a stretched film excellent in productivity and quality is provided. Can be provided.

FIG. 1 is a diagram for explaining a method of producing a composite film. FIG. 2 is a diagram for explaining a method of stretching a composite film by a simultaneous biaxial stretching method in a stretching step. FIG. 3 is a view for explaining a method of gripping the composite film with clips in the stretching step. FIG. 4 is a diagram for explaining neck-in of the composite film when the composite film is heated and stretched. FIG. 5 is a diagram illustrating an example of a method for trimming a composite film. FIG. 6 is a graph showing the stretching stress value corresponding to the stretching ratio when the thermoplastic resins used in Examples and Comparative Examples are heated and stretched at 140 ° C. FIG. 7 is a graph showing the results of measuring the thicknesses of the composite film and the stretched film prepared in Example 1. FIG. 8 is a graph showing the results of measuring the thicknesses of the composite film and stretched film produced in Example 2. FIG. 9 is a graph showing the results of measuring the thicknesses of the composite film and stretched film produced in Example 3. FIG. 10 is a graph showing the results of measuring the thicknesses of the composite film and the stretched film produced in Example 4. FIG. 11 is a graph showing the results of measuring the thicknesses of the composite film and the stretched film produced in Example 5.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The stretched film manufacturing method according to the present embodiment includes a first thermoplastic resin and a second thermoplastic resin different from the first thermoplastic resin by melt coextrusion using a molding T die. A composite film forming step of forming a film; and a stretching step of heating and stretching the composite film in the length direction and the width direction.

<Composite film formation process>
The composite film forming step is a step of forming the composite film 100 by melt coextruding the first thermoplastic resin and the second thermoplastic resin from a T die. Here, FIG. 1 is a figure for demonstrating a composite film formation process. In the present embodiment, as shown in FIG. 1, the composite film 100 has a central portion 110, an end portion 120 a formed at one end in the width direction of the central portion 110, and the other end in the width direction of the central portion 110. The end portion 120b is formed, the center portion 110 is made of a first thermoplastic resin, and the end portions 120a and 120b are made of a second thermoplastic resin. In addition, the center part 110 of the composite film 100 is a part which becomes a stretched film by being heat-stretched by a stretching process described later. Further, the end portions 120a and 120b of the composite film 100 are for reinforcing the central portion 110 when the composite film 100 is heated and stretched, and are cut as necessary after the composite film 100 is heated and stretched. Can be removed. When cutting the composite film 100, it is desirable to completely remove both end portions 120 by cutting part of both ends of the central portion 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 described later.

  In the composite film forming step, first, the first thermoplastic resin and the second thermoplastic resin are supplied to the T dice 220 through the feed block 210 in a heated and melted state.

  In the present embodiment, the feed block 210 includes a first melt extruder (not shown) for melt-extruding the first thermoplastic resin and a second melt-extruding second thermoplastic resin. These melt extruders (not shown) are connected to each other. These melt extruders are not particularly limited, and any of a single screw extruder and a twin screw extruder can be used. In the present embodiment, the first thermoplastic resin and the second thermoplastic resin are melt-extruded by the respective melt extruders at a temperature equal to or higher than the melting point (melting) temperature. Supply.

  In addition, when supplying the first thermoplastic resin and the second thermoplastic resin from the feed block 210 to the T dice 220, the composite film 100 obtained by the T dice 220 is formed as shown in FIG. 1st thermoplastic resin and 2nd thermoplastic resin so that it may become the structure by which the edge part 120a, 120b which consists of 2nd thermoplastic resin was formed in the both ends of the center part 110 which consists of 1 thermoplastic resin, respectively. Supply resin.

  Specifically, the feed block 210 has both sides in the widening direction of the T-die 220 with respect to the inlet for supplying the first thermoplastic resin and the inlet for supplying the first thermoplastic resin. In addition, an inlet for supplying the second thermoplastic resin is separately provided. In this embodiment, the first thermoplastic resin and the second thermoplastic resin respectively introduced from the inlet of the feed block 210 are merged in the feed block 210, and at the outlet of the feed block 210, the T dice 220 is formed. The first thermoplastic resin flows in the central portion with respect to the widening direction of the first thermoplastic resin, flows out in such a manner that the second thermoplastic resin flows in both end portions of the first thermoplastic resin, and is supplied to the T dice 220. It is supposed to be.

  In the T die 220, the first thermoplastic resin and the second thermoplastic resin supplied from the feed block 210 are fed in the width direction (first thermoplastic resin by the manifold 221 provided in the T die 220. And in the direction in which the second thermoplastic resin is lined up), and thereby co-extruded from the die slip 222 into a sheet shape.

  Next, the co-extruded sheet-like first thermoplastic resin and second thermoplastic resin are continuously taken up by the touch roll 230 and the cooling roll 240 as shown in FIG. By doing so, the composite film 100 including the center portion 110 made of the first thermoplastic resin and the end portions 120a and 120b made of the second thermoplastic resin formed at both ends of the center portion 110 is produced. And the produced composite film 100 is wound up by a composite film winding roll (not shown), and thereby the composite film 100 can be obtained continuously.

<Extension process>
The stretching process is a process in which the composite film 100 obtained by the composite film forming process is heated and stretched in the length direction and the width direction. Here, FIG. 2 is a figure for demonstrating an extending process. In the present embodiment, in the stretching step, the composite film 100 is fed out from the above-described composite film winding roll, and the length direction of the composite film 100 is gripped by the clip 310 as shown in FIG. The composite film 100 is heated and stretched by a simultaneous biaxial stretching method in which stretching is performed simultaneously in the width direction.

  Specifically, in the stretching step, the composite film 100 is continuously fed out from the composite film winding roll, and the ends 120a and 120b of the composite film 100 are held at regular intervals using a plurality of clips. The composite film 100 is conveyed into the stretching furnace 320 by 310, and in the stretching furnace 320, the composite film 100 is stretched by being pulled in the length direction and the width direction by the respective clips 310. In this case, the composite film 100 is conveyed while being held by the clip 310, so that the composite film 100 passes through the stretching furnace 320. 100 is preheated to a temperature higher by about 10 to 30 ° C. than the glass transition temperature of the first thermoplastic resin in the central portion 110 constituting this, and is then kept in the drawing zone in the drawing furnace 320. The clip 310 is pulled in the length direction and the width direction as it is, and is stretched in the length direction and the width direction.

  In this case, it is preferable that the heating temperature in the drawing furnace 320 is lower than the glass transition temperature of the second thermoplastic resin. Thereby, the stretchability of the end portions 120a and 120b made of the second thermoplastic resin can be appropriately reduced, and when the composite film 100 is heated and stretched, a neck-in (end of the composite film 100 described later) Phenomenon in which the portions 120a and 120b contract in the width direction) can be suppressed, and the productivity of the stretched film can be improved.

  In the present embodiment, the stretched film can be obtained by cooling and solidifying the heat-stretched composite film 100 in the cooling heat fixing zone following the stretching zone in the stretching furnace 320. Then, the stretched film can be obtained continuously by opening the clip 310 and winding it with a roll.

  In the present embodiment, as shown in FIG. 3, the clip 310 that grips the end portions 120 a and 120 b of the composite film 100 includes a clip body 311, a lever 312 that can be turned around a pin 313, and a gripping portion. 314. In the clip 310, the position of the grip portion 314 is lowered by moving the lever 312 in the direction indicated by the arrow in FIG. 3 so that the composite film 100 can be gripped.

  Here, for the composite film 100 held by such a clip 310, by adjusting the widths of the end portions 120a and 120b of the composite film 100, surplus portions of the end portions 120a and 120b, that is, broken lines and As indicated by the arrows, it is preferable that the portion on the inner side in the width direction from the grip position of the grip portion 314 at the end portions 120a and 120b is 10 mm or less. Thereby, in the composite film 100 produced in the composite film forming step, the width of the end portions 120a and 120b as the reinforcing members can be reduced, and the use of the second thermoplastic resin constituting the end portions 120a and 120b. Since the amount can be reduced, it is advantageous in cost when producing a stretched film.

  In this case, the boundary portion between the central portion 110 and the end portion 120a or the boundary portion between the central portion 110 and the end portion 120b may be gripped by the grip portion 314 of the clip 310. That is, it is good also as an aspect which hold | grips not only to the edge parts 120a and 120b but to a part of center part 110 with the holding part 314 of the clip 310. FIG.

  In the present embodiment, a pair of guide rails for moving the clip 310 is provided so as to pass through the drawing furnace 320. The pair of guide rails are respectively installed at the position of the clip 310 that holds the end portion 120a of the composite film 100 and the position of the clip 310 that holds the end portion 120b shown in FIG. Are parallel to each other, are separated from each other in the width direction of the composite film 100 in the stretch band, and are parallel to each other in the cooling heat fixing band. Alternatively, in the cooling heat fixing band, the distance between the pair of guide rails in the cooling heat fixing band is determined in consideration of the shrinkage when the stretched film heated and stretched in the stretching band is solidified. On the basis of the width of the stretched film on the side, it may be approximated by several percent in the width direction. In the present embodiment, the clip 310 that grips the end portion 120a of the composite film 100 and the clip 310 that grips the end portion 120b each move along such a guide rail, thereby transporting the composite film 100. And can be stretched.

  In the present embodiment, the composite film 100 is stretched in the stretching zone in the stretching furnace 320 using the clip 310 that moves along such a guide rail. That is, the clip 310 that grips the end portion 120a of the composite film 100 and the clip 310 that grips the end portion 120b are moved so as to spread in the width direction along the guide rails in the stretching band in the stretching furnace 320, respectively. In addition, the end portions 120a and 120b of the composite film 100 are pulled in the length direction and the width direction as indicated by arrows in FIG. Thereby, the center part 110 and edge part 120a, 120b of the composite film 100 are heat-stretched in a length direction and a width direction until it becomes a required draw ratio, respectively. The heat-stretched composite film 100 is cooled and solidified in a cooling heat fixing zone in the stretching furnace 320, and is wound up by a roll installed outside the stretching furnace 320. A stretched film can be obtained.

  In the present embodiment, the stretched film and the composite film forming process can be integrated into a continuous line (process) to obtain a stretched film.

  As described above, in the present embodiment, the composite film 100 including the central portion 110 made of the first thermoplastic resin and the end portions 120a and 120b made of the second thermoplastic resin in the composite film forming step. A stretched film can be obtained by heating and stretching the central portion 110 and the end portions 120a and 120b of the composite film 100 through a stretching step.

  In this embodiment, before heat-stretching the composite film 100 as described above, the cross-sectional areas of the end portions 120a and 120b in the cross-section in the width direction of the composite film 100 before heat-stretching have a predetermined relationship. Adjust to meet the requirements.

That is, in this embodiment, among the cross sections in the width direction of the composite film 100 as shown in FIG. 3, the cross-sectional area of the end 120a is A ₁ [m ² ], and the cross-sectional area of the end 120b is A ₂ [m ² ], the coefficient of static friction between the ends 120a, 120b and the clip 310 at the time of heating and stretching is μ, the gripping force (vertical load) of the ends 120a, 120b by the clip 310 is F [N], and the ends 120a, when the stretching stress value per unit cross-sectional area at the time of heat stretching of the second thermoplastic resin constituting the 120b was σ [N / m ^2], the cross-sectional sectional area a ₁ and the end portion 120b of the end portion 120a an area _{a 2,} is adjusted so as to satisfy the following formula (1) and (2).
A ₁ <μF / σ (1)
A ₂ <μF / σ (2)
Here, the above-described stretching stress value σ indicates the tensile load necessary for heating and stretching the end portions 120a and 120b, and depends on the type of the second thermoplastic resin constituting the end portions 120a and 120b. It is a physical property value.

In the present embodiment, when the heating and drawing the composite film 100, as the cross-sectional area A ₁ and the cross-sectional area A ₂ described above becomes smaller, or per unit sectional area of the second thermoplastic resin at the time of heat stretching As the stretching stress value σ becomes smaller, the end portions 120a and 120b are easily stretched in the length direction, and thereby, the clip 310 is detached from the heat stretching and the composite film 100 is prevented from being broken. Further, when the composite film 100 is heated and stretched, the higher the static friction coefficient μ between the ends 120a and 120b and the clip 310 and the gripping force (vertical load) F by the clip 310, the higher the ends 120a and 120b by the clip 310. Gripping becomes firm, and the clip 310 is prevented from coming off during heating and stretching.

Therefore, according to this embodiment, by adjusting the cross-sectional area A ₂ of the sectional area A ₁ and the end portion 120b of the end portion 120a described above, the cross-sectional area A ₁ and the cross-sectional area A _2, the stretching stress value σ described above In addition, by satisfying the above formulas (1) and (2) in relation to the static friction coefficient μ and the gripping force F, it is possible to effectively prevent the clip 310 from being detached and the composite film 100 from being broken during the heat stretching. And the productivity of the stretched film can be improved.

Further, according to this embodiment, by adjusting the cross-sectional area _{A 2} of the sectional area _{A 1} and the end portion 120b of the end portion 120a so as to satisfy the relationship of the above formula (1) and (2), ends 120a , 120b can be made of a thermoplastic resin having a higher glass transition temperature or the above-described stretching stress value σ, thereby reducing the neck-in of the composite film 100 during heat stretching. It can suppress and can improve the productivity of the stretched film obtained.

  That is, when the composite film 100 is heated and stretched by the simultaneous biaxial stretching method, the end portions 120a and 120b are contracted in the width direction between the clip 310 and the clip 310 as shown in FIG. A phenomenon called neck-in occurs. Here, as the second thermoplastic resin constituting the end portions 120a and 120b of the composite film 100, the glass transition temperature and the above-described stretching stress value σ are the same as those of the first thermoplastic resin constituting the central portion 110. In the case of using a thermoplastic resin of a degree or less, the end portions 120a and 120b are easily contracted in the width direction, and thus such neck-in occurs more remarkably.

  When such a neck-in occurs, as shown in FIG. 4A, in the obtained stretched film, the amount of biting inward in the width direction of the end portions 120a and 120b is increased. Therefore, as will be described later, when cutting and removing the portions of the end portions 120a and 120b in the stretched film to obtain a film consisting only of the central portion 110, the composite film 100 is cut on the inner side in the width direction. As a result, the width of the resulting film (the film consisting only of the central portion 110) is narrowed, and the production yield of the film tends to be reduced. Further, when neck-in occurs, the thickness and orientation of the film consisting only of the central portion 110 vary, and the quality of the obtained film also tends to deteriorate.

  On the other hand, as the second thermoplastic resin constituting the end portions 120a and 120b of the composite film 100, the end portion 120a is obtained by using a thermoplastic resin having a relatively high glass transition temperature and the above-described stretching stress value σ. , 120b is less likely to shrink in the width direction, and therefore, neck-in of the end portions 120a, 120b during heat stretching can be suppressed as shown in FIG. Thereby, when it is going to cut | disconnect and remove the part of edge part 120a, 120b in a stretched film and to obtain the film which consists only of the center part 110, the width | variety to remove can be made small and it consists only of the center part 110 Since the thickness and orientation of the film can be uniform and wide, the quality and production yield of the film can be improved.

  On the other hand, when the thermoplastic resin having a relatively high glass transition temperature or the above-described stretching stress value σ is used as the second thermoplastic resin constituting the end portions 120a and 120b, the composite film 100 is heated and stretched. In this case, since the stretchability of the end portions 120a and 120b is lowered, the clip 310 that grips the end portions 120a and 120b is easily detached, and the end portions 120a and 120b are further torn and the composite film 100 is easily broken. It tends to become.

On the other hand, according to the present embodiment, as the second thermoplastic resin constituting the end portions 120a and 120b, even when a thermoplastic resin having a high glass transition temperature or the above-described stretching stress value σ is used, by adjusting the cross-sectional area _{a 2} of the sectional area _{a 1} and the end portion 120b of the end portion 120a so as to satisfy the relationship of the above formula (1) and (2), be easier to draw the ends 120a, and 120b Therefore, it is possible to appropriately prevent the clip 310 from coming off at the time of heat stretching and the breakage of the composite film 100, thereby reducing the productivity of the stretched film while suppressing the neck-in of the composite film 100 at the time of heat stretching. It can be improved effectively.

Incidentally, the cross-sectional area _{A 2} of the sectional area _{A 1} and the end portion 120b of the end portion 120a as a way to satisfy the above formula (1) and (2) is not particularly limited, for example, T die 220 When the composite film 100 is produced by melt extrusion using the T die 220, the second thermoplastic resin is melt extruded by the T die 220 by adjusting the amount of the second thermoplastic resin supplied from the feed block 210 to the T die 220. A method of adjusting the amount is mentioned. Thus, a simple method of adjusting the melt extrusion amount of the second thermoplastic resin by T die 220, is possible to easily adjust the cross-sectional area A ₁ and the cross-sectional area A ₂ of the end portion 120b of the end portion 120a it can.

Alternatively, the cross-sectional area _{A 2} of the sectional area _{A 1} and the end portion 120b of the end portion 120a as a way to satisfy the above formula (1) and (2), after forming a composite film 100, the composite film A method of removing a part of the end portions 120a and 120b of 100 can also be used. For example, as shown in FIG. 5, by trimming both ends of the produced composite film 100 with a cutter 250, a part of the end portions 120a and 120b can be cut and removed. This makes it possible in a simple method of trimming the composite film 100, easily, and accurately adjust the cross-sectional area A ₂ of the sectional area A ₁ and the end portion 120b of the end portion 120a.

  The cutter 250 is not particularly limited. For example, a laser blade, a rotary shear cutter that continuously rotates while rubbing a circular upper blade and a lower blade, and performs cutting by shearing, a solid laser, a semiconductor laser, Although a laser cutter using a liquid laser or a gas laser can be used, the stress applied to the composite film 100 during trimming can be reduced, and the occurrence of cracks in the composite film 100 during trimming can be prevented. From this viewpoint, a laser cutter is preferable.

  Here, when trimming the composite film 100, it is preferable to trim the composite film 100 while heating the end portions 120a and 120b of the composite film 100. As a result, the side surfaces of the end portions 120a and 120b can be made smooth, and when the composite film 100 is heated and stretched, the side surfaces of the end portions 120a and 120b are roughened. It is possible to prevent the tearing of the end portions 120a and 120b due to the stress concentration on a part of the side surface, and to prevent the composite film 100 from being broken as a result.

  In the present embodiment, the first thermoplastic resin for forming the central portion 110 may be selected according to the intended use of the stretched film. For example, acrylic resin (PMMA), annular An olefin copolymer (COC) or the like can be used.

  In the present embodiment, as the second thermoplastic resin for forming the end portions 120a and 120b, the glass transition temperature and the stretching per unit cross-sectional area at the time of heat stretching are more than the first thermoplastic resin. A thermoplastic resin having a high stress value σ can be used. By using such a second thermoplastic resin, as described above, neck-in of the end portions 120a and 120b when the composite film 100 is heated and stretched can be prevented, and the end portion of the obtained stretched film can be prevented. When manufacturing the film which consists only of the center part 110 by removing the part of 120a, 120b, the quality and manufacturing yield of the film which consist only of the center part 110 can be improved.

  In addition, as a 2nd thermoplastic resin which comprises edge part 120a, 120b, when a thermoplastic resin with comparatively high glass transition temperature and the above-mentioned extending | stretching stress value (sigma) is used, extending | stretching of edge part 120a, 120b Therefore, when the end portions 120a and 120b are gripped and pulled by the clip 310 when the composite film 100 is heated and stretched, there is a problem that the clip is likely to be detached or the film is easily broken.

On the other hand, according to this embodiment, as described above, as the second thermoplastic resin constituting the end portions 120a and 120b, the thermoplastic resin having a relatively high glass transition temperature and the above-described stretching stress value σ. in the case of using the, by adjusting the cross-sectional area a ₂ of the sectional area a ₁ and the end portion 120b of the end portion 120a so as to satisfy the relationship of the above formula (1) and (2), the clip during heating and drawing Detachment 310 and breakage of the composite film 100 can be prevented appropriately. Therefore, according to the present embodiment, it is possible to use a thermoplastic resin having a relatively high glass transition temperature and the above-described stretching stress value σ as the second thermoplastic resin. The neck-in of the film 100 can be appropriately suppressed.

  Further, as the second thermoplastic resin, with respect to the obtained composite film 100, the elongation at break at the time of heat stretching of the end portions 120a and 120b made of the second thermoplastic resin is the heat stretching in the stretching process described above. It is preferable to use a thermoplastic resin that is larger than the draw ratio when performing. In addition, the said breaking elongation rate is a value which shows the elongation rate with respect to the dimension before extending | stretching at the time of extending | stretching until the edge part 120a, 120b is fractured | ruptured. Thereby, when the composite film 100 is heated and stretched, the end portions 120a and 120b can be appropriately stretched, and breakage of the composite film 100 can be more effectively prevented.

  Further, as the second thermoplastic resin, a thermoplastic resin is used in which the end portions 120a and 120b have higher elongation at break at room temperature than the center portion 110 of the obtained composite film 100 before heat stretching. It is preferable. The elongation at break at normal temperature is a value indicating the elongation relative to the dimension before stretching when the center portion 110 and the end portions 120a and 120b are stretched to break in a room temperature environment of about 10 to 30 ° C. . As a result, when the composite film 100 is heated and stretched, the ends 120a and 120b are less likely to break than the center portion 110, and the generation of tears at the ends 120a and 120b is prevented, and the entire composite film 100 is broken. Can be prevented.

  In the present embodiment, as the second thermoplastic resin, specifically, the following thermoplastic resin can be used based on the viewpoint described above. For example, as the second thermoplastic resin, when an acrylic resin is used as the first thermoplastic resin, one kind of polycarbonate (PC), polyethylene naphthalate (PEN), cyclic olefin polymer (COP), and the like is used. Can be used alone, or a mixed resin in which two or more are mixed.

  Further, as the second thermoplastic resin, a resin obtained by adding a small amount of elastic rubber particles to the above-described first thermoplastic resin as long as the productivity of the stretched film is not impaired may be used.

  Alternatively, as the second thermoplastic resin, the glass transition temperature is higher than that of the first thermoplastic resin, and the difference between the thermoplastic resin (heat-resistant thermoplastic resin) having a difference of more than 10 ° C. A mixed resin obtained by blending a thermoplastic resin having a glass transition temperature lower than that of the thermoplastic resin (low temperature meltable thermoplastic resin) can be used.

  When such a mixed resin is used as the second thermoplastic resin, polycarbonate (PC), cyclic olefin polymer (COP), or the like can be used as the heat-resistant thermoplastic resin. Further, as the low-melting thermoplastic resin, polyester such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylonitrile / butadiene / styrene (ABS), polyethylene (PE), glass from the first thermoplastic resin. An acrylic resin, polyester (PEs), polybutylene terephthalate (PBT), or the like having a low transition temperature can be used. In the present embodiment, among these, polycarbonate (PC) is used as a heat-resistant thermoplastic resin and polyethylene terephthalate is used as a low-melting thermoplastic resin from the viewpoint that the glass transition temperature of the resulting mixed resin can be easily adjusted. It is preferable to use (PET).

  Moreover, in the example mentioned above, as shown in FIG. 2, as a method of heating and stretching the composite film 100, an example of using a simultaneous biaxial stretching method in which the composite film 100 is heated and stretched in both the length direction and the width direction is used. In this embodiment, a method of uniaxially stretching the composite film 100 only in the length direction may be used.

  In this case, the heat stretching in the length direction of the composite film 100 can be performed in the same manner as the simultaneous biaxial stretching method shown in FIG. That is, each of the ends 120 a and 120 b of the composite film 100 is conveyed into the heating furnace 320 while being gripped by the clip 310, and then the ends 120 a and 120 b of the composite film 100 are gripped in the heating furnace 320. A method of performing heat stretching only in the length direction can be used by widening the interval between the clips 310 without moving the clips 310 in the width direction.

  In the present embodiment, the end 120a of the composite film 100 is used as shown in FIG. 2 in both the case where simultaneous biaxial stretching is performed in the length direction and the width direction, and the case where uniaxial stretching is performed only in the length direction. , 120b can be stretched while being gripped by the clip 310, so that the productivity of the stretched film can be improved as compared with the conventional sequential biaxial stretching method. It can be made excellent.

  Note that the conventional sequential biaxial stretching method is a method in which the composite film 100 produced by the method shown in FIG. 1 is first heat-stretched in the length direction and then heat-stretched in the width direction. In the sequential biaxial stretching method, the composite film 100 is heated and stretched in the length direction by being conveyed by a plurality of rolls, and then the ends 120a and 120b of the composite film 100 are clipped by clips 310 as shown in FIG. Heat and stretch in the width direction while gripping.

  Here, the stretching in the length direction of the composite film 100 in the sequential biaxial stretching method is specifically performed as follows. That is, according to the sequential biaxial stretching method, the composite film 100 is preheated to about the glass transition temperature of the end portions 120a and 120b while being transported by a plurality of preheated rolls that have been preheated. While being further heated to a temperature about 10 to 30 ° C. higher than the glass transition temperature of the ends 120a and 120b by an infrared heater or the like, it is continuously conveyed by a cooling roll. At this time, by making the transport speed by the cooling roll faster than the transport speed by the pre-tropical roll, a tension is generated between the pre-tropical roll and the cooling roll, and the composite film 100 is formed using this tension. The film is stretched to the necessary stretching ratio in the length direction.

  Here, in the sequential biaxial stretching method, when the composite film 100 is stretched in the length direction, the surface of the composite film 100 comes into contact with the preheating roll and the cooling roll, so that the surface of the composite film 100 is scratched. May occur, and the appearance quality of the obtained stretched film may be deteriorated. Further, in the sequential biaxial stretching method, when the composite film 100 is heated and stretched in the length direction, the end portions 120a and 120b of the composite film 100 are not fixed with clips or the like. There is a concern that the stretched film may be reduced in productivity due to shrinkage in the direction.

  On the other hand, according to the present embodiment, the composite film 100 is stretched in the length direction by using the above-described simultaneous biaxial stretching method or the above-described method of uniaxial stretching only in the length direction. (In other words, as shown in FIG. 2, by using a method of stretching in the length direction while holding the ends 120 a and 120 b of the composite film 100 with the clip 310), contact with the roll is avoided. Therefore, scratches on the surface of the composite film 100 after heat stretching can be reduced. Thereby, about the stretched film obtained by cut | disconnecting edge part 120a, 120b of the composite film 100 heat-stretched, external appearance quality can be improved and it uses suitably especially for an optical film etc. with a severe request | requirement of external appearance quality. be able to. Furthermore, according to this embodiment, when the composite film 100 is stretched in the length direction, the end portions 120a and 120b of the composite film 100 are held by the clip 310. The shrinkage of the film can be prevented, and the productivity of the stretched film can be improved.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

<Example 1>
An acrylic resin (glass transition temperature Tg ₁ : 123 ° C., elongation at break: 5%) is prepared as a first thermoplastic resin for forming the central portion 110 of the composite film 100, and the end of the composite film 100 is prepared. Polycarbonate (PC) (glass transition temperature Tg ₂ : 143 ° C., elongation at break at room temperature: 170%) was prepared as the second thermoplastic resin for forming the portions 120a and 120b.

  Here, for the first thermoplastic resin and the second thermoplastic resin, 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 Co., Ltd.). Model No .: RTC-1210A). The same applies to Examples 2 to 5 and Comparative Example 1 below.

  Moreover, about the 1st thermoplastic resin and the 2nd thermoplastic resin, after producing the single film of thickness 100 micrometers, respectively, the extending | stretching stress at the time of extending | stretching gradually in the state heated to 140 degreeC was measured. The results are shown in FIG. Here, in FIG. 6 (A), with respect to the draw ratio (a value indicating what percentage of the dimension before stretching in one direction based on the dimension of the single film before stretching), The drawing stress values necessary for drawing up to the draw ratio are shown. In FIG. 6A, the measurement result of the first thermoplastic resin is the central portion 110, and the measurement result of the second thermoplastic resin is the end portions 120a and 120b.

Next, the prepared first thermoplastic resin and second thermoplastic resin were respectively supplied to the feed block 210 by a twin screw extruder, and a composite film 100 was produced under the following conditions by the method shown in FIG. . Here, the produced composite film 100 was trimmed at both ends by 30 mm. The overall width of the composite film 100 after trimming was 270 mm, of which the widths of the end portions 120 a and 120 b were 10 mm from both ends of the composite film 100. The observation of the cut surface by cutting the composite film 100 in the width direction, the cross-sectional area _{A 1} of the end portion 120a is 1.78 × ¹⁰ -6 ^{m 2,} the cross-sectional area _{A 2} of the end portion 120b is 1.79 × 10 ⁻⁶ m ² .
T-die 220 outlet width direction dimension: 380mm
Take-up speed of cooling roll 240: 8 mpm
Supply amount of first thermoplastic resin to feed block 210: 20 kg / hr
Supply amount of second thermoplastic resin to feed block 210: 5 kg / hr

  And about the produced composite film 100, distribution of the thickness with respect to the position of the width direction was measured. The results are shown in FIGS. 7 (A) and 7 (B). Note that the graphs of the composite film 100 shown in FIGS. 7A and 7B are the same.

Next, the obtained composite film 100 is gripped by a clip 310 and, as shown in FIG. 2, is heated and stretched in the length direction and the width direction under the following conditions by a simultaneous biaxial stretching method, and then wound by a roll. By taking, a stretched film was obtained continuously. The stretching stress value σ per unit cross-sectional area of the end portions 120a and 120b (second thermoplastic resin) at the time of heat stretching is 23.6 MPa (stretching stress of the end portions 120a and 120b shown in FIG. 6A). Among these, the maximum value at a draw ratio of up to 100%). In this example, while the composite film 100 was heated and stretched, the clip 310 was not detached and the composite film 100 was not broken.
Gripping force (vertical load) by clip 310 F: 200N
Coefficient of static friction μ between the end portions 120a and 120b and the clip 310 at the time of heating and stretching: 0.40
Entry speed before heat drawing: 1 mpm
Outlet speed after heating and stretching: 2 mpm
Stretch ratio: 100% in length direction x 100% in width direction (twice in length direction x double in width direction)
Clip 310 grasping width: 20 mm from the end of the composite film 100 Pre-tropical temperature, distance: 140 ° C., 350 mm
Stretch zone temperature, distance: 140 ° C., 500 mm
Cooling heat fixing temperature, distance: 90 ° C, 700mm

In Example 1, the calculated value of μF / σ shown in the above formulas (1) and (2) was calculated to be 3.39 × 10 ⁻⁶ m ² using the above-described value. Therefore, the cross-sectional area A ₁ (1.78 × 10 ⁻⁶ m ² ) of the end 120a and the cross-sectional area A ₂ (1.79 × 10 ⁻⁶ m ² ) of the end 120b described above are both The value was smaller than μF / σ.

  And the distribution of the thickness of the width direction was measured about the obtained stretched film. The results are shown in FIGS. 7 (A) and 7 (B). Here, FIG. 7A shows a measurement result of a cross section passing through the gripped portion by the clip 310. In FIG. 7 (A), 20 mm each of the both ends of the stretched film (region gripped by the clip 310) is not shown. FIG. 7B shows a measurement result of a cross section passing between gripped portions by adjacent clips 310.

  In Example 1, the cross section passing through the gripping portion by the clip 310 has a width of the stretched film of 527 mm (a value obtained by adding 20 mm of both ends not shown to the width of the stretched film shown in FIG. 7A). As shown in FIG. 7B, the cross-section passing between the gripping portions by the clip 310 has a stretched film width of 509 mm. Therefore, the neck-in width at the time of heat stretching is the difference between the widths of these stretched films. Can be obtained by calculating a value ((527 mm−509 mm) / 2) divided by 2, and the calculated neck-in width is a small value of 8 mm, which indicates that neck-in was suppressed. confirmed.

  Further, in Example 1, as shown in FIGS. 7A and 7B, the stretched film has a uniform thickness over the width of 460 mm at the center, and is excellent in quality. Could get.

<Example 2>
As a second thermoplastic resin for forming the end portions 120a and 120b of the composite film 100, a mixed resin (glass) containing 15% by weight of polyethylene terephthalate (PET) with respect to 85% by weight of polycarbonate (PC). The transition temperature Tg ₂ : 132 ° C., the elongation at break at room temperature: 40%), and the composite film 100 was changed in the same manner as in Example 1 except that the trimming width of the composite film 100 was changed to 5 mm from both ends. And the stretched film was obtained and the thickness was measured similarly. The results of measuring the thickness of the composite film 100 and the stretched film are shown in FIGS. 8 (A) and 8 (B). In FIG. 8A, the 20 mm area (the area gripped by the clip 310) at both ends of the stretched film is not shown. In Example 2, the measurement of the stretching stress value of the single film of the second thermoplastic resin was also performed. The results are shown in FIG.

In Example 2, the produced composite film 100 had an overall width of 315 mm after trimming, and the widths of the end portions 120a and 120b were 30 mm from both ends of the composite film 100, respectively. The observation of the cut surface by cutting the composite film 100 in the width direction, the cross-sectional area _{A 1} of the end portion 120a is 4.44 × ¹⁰ -6 ^{m 2,} the cross-sectional area _{A 2} of the end portion 120b is 4.36 × 10 ⁻⁶ m ² . Further, the stretching stress value σ per unit cross-sectional area of the end portions 120a and 120b (second thermoplastic resin) at the time of heat stretching is 4.4 MPa (stretching stress of the end portions 120a and 120b shown in FIG. 6A). Among them, the maximum value at a draw ratio of up to 100%), and the coefficient of static friction μ between the ends 120a and 120b and the clip 310 at the time of heat drawing was 0.45.

In Example 2, the calculated value of μF / σ shown in the above formulas (1) and (2) could be calculated as 20.45 × 10 ⁻⁶ m ² using the above-described value. Therefore, the cross-sectional area A ₁ (4.44 × 10 ⁻⁶ m ² ) of the end 120a and the cross-sectional area A ₂ (4.36 × 10 ⁻⁶ m ² ) of the end 120b described above are both The value was smaller than μF / σ.

  Further, in the obtained stretched film, the cross section passing through the gripping portion by the clip 310 has a stretched film width of 624 mm (a value obtained by adding 20 mm each of the both ends, not shown, to the stretched film width shown in FIG. 8A). On the other hand, as shown in FIG. 8B, the cross section passing between the gripping portions by the clip 310 has a neck-in width ((624 mm−591 mm) at the time of heat stretching since the width of the stretched film was 591 mm. ) / 2) is a small value of 16.5 mm, which confirmed that neck-in was suppressed.

  Further, in Example 2, the clip 310 was not detached and the composite film 100 was not broken while the composite film 100 was heated and stretched.

  In Example 2, as shown in FIG. 8A, the portion passing through the grip portion by the clip 310 has a uniform thickness over the width of 505 mm at the center portion. ), The portion passing between the gripped portions by the clip 310 had a uniform thickness over a width of 500 mm, and thus a stretched film having excellent quality could be obtained.

<Example 3>
As the second thermoplastic resin for forming the end portions 120a and 120b of the composite film 100, a mixed resin (glass transition temperature Tg ₂ :) obtained by mixing polycarbonate (PC) and acrylonitrile / butadiene / styrene (ABS). The composite film 100 and the stretched film were obtained in the same manner as in Example 1 except that the trimming width of the produced composite film 100 was changed to 10 mm each from both ends. Similarly, the thickness was measured. The results of measuring the thickness of the composite film 100 and the stretched film are shown in FIGS. 9 (A) and 9 (B). Note that in FIG. 9A, the 20 mm regions (regions held by the clips 310) at both ends of the stretched film are not shown. In Example 3, the stretching stress value of the single film of the second thermoplastic resin was also measured. The results are shown in FIG.

In Example 3, the produced composite film 100 had an overall width of 257 mm after trimming, and the widths of the end portions 120a and 120b were 20 mm from both ends of the composite film 100, respectively. Incidentally, observation of the cut surface by cutting the composite film 100 in the width direction, the cross-sectional area _{A 1} of the end portion 120a is 3.59 × ¹⁰ -6 ^{m 2,} the cross-sectional area _{A 2} of the end portion 120b is 3.42 × 10 ⁻⁶ m ² . Furthermore, the stretching stress value σ per unit cross-sectional area of the end portions 120a and 120b (second thermoplastic resin) at the time of heat stretching is 9.6 MPa (the stretching stress of the end portions 120a and 120b shown in FIG. 6A). Among these, the maximum value at a draw ratio of up to 100%), and the coefficient of static friction μ between the ends 120a and 120b and the clip 310 at the time of heat drawing was 0.22.

In Example 3, the calculated value of μF / σ shown in the above formulas (1) and (2) could be calculated as 4.58 × 10 ⁻⁶ m ² using the above-described value. Therefore, the cross-sectional area A ₁ (3.59 × 10 ⁻⁶ m ² ) of the end 120a and the cross-sectional area A ₂ (3.42 × 10 ⁻⁶ m ² ) of the end 120b described above are both The value was smaller than μF / σ.

  Further, in the obtained stretched film, the cross-section passing through the gripping portion by the clip 310 has a width of the stretched film of 507 mm (the value obtained by adding 20 mm each of the both ends not shown to the stretched film width shown in FIG. 9A). On the other hand, as shown in FIG. 9B, the cross-section passing between the gripping portions by the clip 310 has a neck-in width ((507 mm-487 mm) at the time of heat stretching since the width of the stretched film was 487 mm. ) / 2) is a small value of 10 mm, and this confirmed that neck-in was suppressed.

  Furthermore, in Example 3, the clip 310 was not detached and the composite film 100 was not broken while the composite film 100 was heated and stretched.

  In Example 3, as shown in FIG. 9 (A), the thickness of the portion passing through the gripping portion by the clip 310 is uniform over the width of 450 mm. ), The portion passing between the gripped portions by the clip 310 had a uniform thickness over a width of 430 mm. Therefore, a stretched film excellent in quality could be obtained.

<Example 4>
As a second thermoplastic resin for forming the end portions 120a and 120b of the composite film 100, an acrylic resin (glass transition temperature Tg ₂ : 125 ° C., elongation at break at room temperature: 8%) added with rubber elastic particles is used. The composite film 100 and the stretched film were obtained in the same manner as in Example 1 except that the composite film 100 produced was not trimmed, and the thickness was measured in the same manner. The results of measuring the thickness of the composite film 100 and the stretched film are shown in FIGS. 10 (A) and 10 (B). In FIG. 10A, the 20 mm regions (regions held by the clips 310) at both ends of the stretched film are not shown. Moreover, in Example 4, the measurement of the stretching stress value of the single film of the second thermoplastic resin was also performed. The results are shown in FIG. FIG. 6B is a graph showing the measurement results of the stretching stress value of a single film produced using the first thermoplastic resin or the second thermoplastic resin, as in FIG. 6A. The scale of the vertical axis is different from that in FIG.

In Example 4, the produced composite film 100 had an overall width of 301 mm, and the widths of the end portions 120a and 120b were 35 mm from both ends of the composite film 100, respectively. Incidentally, observation of the cut surface by cutting the composite film 100 in the width direction, the cross-sectional area _{A 1} of the end portion 120a is 6.46 × ¹⁰ -6 ^{m 2,} the cross-sectional area _{A 2} of the end portion 120b is 5.99 × 10 ⁻⁶ m ² . Furthermore, the stretching stress value σ per unit cross-sectional area of the end portions 120a and 120b (second thermoplastic resin) at the time of heat stretching is 1.78 MPa (the stretching stress of the end portions 120a and 120b shown in FIG. 6B). Among them, the maximum value at a draw ratio of up to 100%), and the coefficient of static friction μ between the end portions 120a and 120b and the clip 310 at the time of heat drawing was 0.32.

In Example 4, the calculated value of μF / σ shown in the above formulas (1) and (2) could be calculated as 35.96 × 10 ⁻⁶ m ² using the above-described value. Therefore, the cross-sectional area A ₁ (6.46 × 10 ⁻⁶ m ² ) of the end 120a and the cross-sectional area A ₂ (5.99 × 10 ⁻⁶ m ² ) of the end 120b described above are both The value was smaller than μF / σ.

  In Example 4, while the composite film 100 was heated and stretched, the clip 310 was not detached and the composite film 100 was not broken.

  In addition, in the obtained stretched film, the cross section passing through the gripping portion by the clip 310 has a stretched film width of 587 mm (the value obtained by adding 20 mm for each of the two ends, not shown, to the stretched film width shown in FIG. 10A). On the other hand, as shown in FIG. 10 (B), the cross section passing between the gripping portions by the clip 310 has a neck-in width ((587 mm-521 mm) at the time of heat stretching since the stretched film has a width of 521 mm. ) / 2) was 33 mm, and the neck-in width was larger than those of Examples 1 to 3 described above.

<Example 5>
As a second thermoplastic resin for forming the end portions 120a and 120b of the composite film 100, a mixed resin (glass) comprising 75% by weight of polycarbonate (PC) and 25% by weight of polyethylene terephthalate (PET). The composite film 100 and the stretched film were obtained in the same manner as in Example 1 except that the transition temperature Tg ₂ : 125 ° C. and the elongation at break at room temperature: 20% were used, and the produced composite film 100 was not trimmed. Similarly, the thickness was measured. The results of measuring the thickness of the composite film 100 and the stretched film are shown in FIGS. 11 (A) and 11 (B). In FIG. 11A, the 20 mm area (the area gripped by the clip 310) at both ends of the stretched film is not shown. In Example 5, the stretching stress value of the single film of the second thermoplastic resin was also measured. The results are shown in FIG.

In Example 5, the produced composite film 100 had an overall width of 309 mm, of which the widths of the end portions 120a and 120b were 35 mm from both ends of the composite film 100, respectively. Incidentally, observation of the cut surface by cutting the composite film 100 in the width direction, the cross-sectional area _{A 1} of the end portion 120a is 2.47 × ¹⁰ -6 ^{m 2,} the cross-sectional area _{A 2} of the end portion 120b is 2.32 × 10 ⁻⁶ m ² . Furthermore, the stretching stress value σ per unit cross-sectional area of the end portions 120a and 120b (second thermoplastic resin) at the time of heat stretching is 1.87 MPa (stretching stress of the end portions 120a and 120b shown in FIG. 6B). Among them, the maximum value at a draw ratio of up to 100%), and the coefficient of static friction μ between the ends 120a and 120b and the clip 310 at the time of heat drawing was 0.45.

In Example 5, the calculated value of μF / σ shown in the above formulas (1) and (2) could be calculated as 48.13 × 10 ⁻⁶ m ² using the above-described value. The above-described cross-sectional area A ₁ (2.47 × 10 ⁻⁶ m ² ) of the end portion 120a and the cross-sectional area A ₂ (2.32 × 10 ⁻⁶ m ² ) of the end portion 120b are both The value was smaller than μF / σ.

  In Example 5, the clip 310 was not detached and the composite film 100 was not broken while the composite film 100 was heated and stretched.

  In addition, in the obtained stretched film, the cross section passing through the gripping part by the clip 310 has a width of the stretched film of 603 mm (a value obtained by adding 20 mm of each of the both ends not shown to the stretched film width shown in FIG. 11A). On the other hand, as shown in FIG. 11 (B), the cross section passing between the gripping portions by the clip 310 has a neck-in width ((603 mm-544 mm) at the time of heat stretching since the width of the stretched film was 544 mm. ) / 2) was 29.5 mm, and the neck-in width was larger than those of Examples 1 to 3 described above.

<Comparative Example 1>
A composite film 100 was obtained in the same manner as in Example 1 except that the produced composite film 100 was not trimmed.

In Comparative Example 1, the produced composite film 100 had end portions 120 a and 120 b having a width of 40 mm from both ends of the composite film 100. The observation of the cut surface by cutting the composite film 100 in the width direction, the cross-sectional area _{A 1} of the end portion 120a is 12.04 × ¹⁰ -6 ^{m 2,} the cross-sectional area _{A 2} of the end portion 120b is 12.10 × 10 ⁻⁶ m ² . Furthermore, the stretching stress value σ per unit cross-sectional area of the end portions 120a and 120b (second thermoplastic resin) at the time of heat stretching is 23.6 MPa, and the end portions 120a and 120b and the clip 310 at the time of heat stretching The coefficient of static friction μ was 0.40.

In Comparative Example 1, the calculated value of μF / σ shown in the above formulas (1) and (2) could be calculated as 3.39 × 10 ⁻⁶ m ² using the above-described value. The above-described cross-sectional area A ₁ (12.04 × 10 ⁻⁶ m ² ) of the end portion 120a and the cross-sectional area A ₂ (12.10 × 10 ⁻⁶ m ² ) of the end portion 120b are both The value was larger than μF / σ.

In Comparative Example 1, when the composite film 100 was stretched by heating, the composite film 100 was actually stretched in the length direction even though the stretch ratio in the length direction was set to 2 times. It was stretched only 1.6 times. This, at the time of heating and drawing, by the end cross-sectional area _{A 2} of the sectional area _{A 1} and the end portion 120b of 120a in the composite film 100 was too large, the end portion 120a, the stretchability 120b decreases, the composite film This is probably because the clip 310 that grips 100 has slipped. Further, when the film is stretched by heating, the clip 310 is detached and the composite film 100 is broken, and further, the portion of the composite film 100 that is not broken is also whitened by the pulling force of the clip 310, and the stretched film is appropriately formed. Couldn't get.

As described above, the cross-sectional area A ₂ of the sectional area A ₁ and the end portion 120b of the end portion 120a in the composite film 100 before the heat stretching is reduced, and shall meet the relationship of the above formula (1) and (2) In Examples 1 to 5, it was possible to appropriately prevent the clip 310 from coming off and the composite film 100 from being broken, so that a stretched film having excellent quality can be obtained, and the productivity of the stretched film can be improved. It was. In particular, in Examples 1 to 3, heat stretching can be performed using a thermoplastic resin having a relatively high glass transition temperature as the second thermoplastic resin, and the neck-in width of the composite film 100 during heat stretching is reduced. We were able to.

On the other hand, as described above, the cross-sectional area _{A 2} is larger cross-sectional area _{A 1} and the end portion 120b of the end portion 120a in the composite film 100 before heat stretching, did not meet the relation of the above-mentioned formula (1) and (2) In Comparative Example 1, when the composite film 100 is heated and stretched, the clip 310 slips and cannot be properly heated and stretched. Further, the clip 310 is detached and the composite film 100 is broken. The productivity was inferior.

DESCRIPTION OF SYMBOLS 100 ... Composite film 110 ... Center part 120a, 120b ... End part 130 ... Boundary part 210 ... Feed block 220 ... T dice 230 ... Touch roll 240 ... Cooling roll 250 ... Cutter 310 ... Clip 320 ... Stretching furnace

Claims (10)

A first thermoplastic resin and a second thermoplastic resin different from the first thermoplastic resin are melt-coextruded from a molding die and then cooled and solidified, whereby the first thermoplastic resin is obtained. Formed at one end in the width direction of the center portion, formed at the other end in the width direction of the center portion, and formed at the other end in the width direction of the center portion. A composite film forming step of forming a composite film comprising a second end portion made of a thermoplastic resin;
A stretching step of forming a stretched film by heating and stretching the composite film at least in the length direction by pulling a grip portion in a state of gripping the composite film using a plurality of gripping members under heating conditions; A method for producing a stretched film comprising:
As the second thermoplastic resin, a thermoplastic resin having a higher stretching stress value per unit cross-sectional area at the time of heating and stretching than the first thermoplastic resin,
As the second thermoplastic resin, a thermoplastic resin having a glass transition temperature higher than that of the first thermoplastic resin is used.
Of the cut surface in the width direction of the composite film before heat stretching, the cross-sectional area of the first end is A ₁ [m ² ], and the cross-sectional area of the second end is A ₂ [m ² ]. The coefficient of static friction between the first end and the second end and the gripping member at the time is μ, and the gripping force of the first end and the second end by the gripping member is F [N], When the stretching stress value per unit cross-sectional area at the time of heating and stretching of the second thermoplastic resin constituting the first end and the second end is σ [N / m ² ], the following formula ( A method for producing a stretched film, characterized by satisfying 1) and (2).
A ₁ <μF / σ (1)
A ₂ <μF / σ (2) When the composite film is formed by melt coextrusion as the second thermoplastic resin, the elongation at break during the heat stretching of the first end portion and the second end portion made of the second thermoplastic resin. but the production method of the stretched film according to claim 1, characterized in that use larger such thermoplastic resin than the stretch ratio at the time of performing heat stretching at the stretching step. The method for producing a stretched film according to claim 1 or 2 , wherein the heating temperature at the time of performing the heat stretching in the stretching step is lower than the glass transition temperature of the second thermoplastic resin. In the composite film forming step, the first of the composite film to be formed is adjusted by adjusting a melt extrusion amount of the second thermoplastic resin with respect to a melt extrusion amount of the first thermoplastic resin by a molding die. method for producing a stretched film according to any one of claims 1 to 3, wherein the controller controls the magnitude of the cross-sectional area a ₂ of the sectional area a ₁ and the second end of the end portion. 2. The method according to claim 1, further comprising a removing step of removing a part of the first end portion and a part of the second end portion of the composite film formed by the composite film forming step before the stretching step. The manufacturing method of the stretched film in any one of 1-4 . When the composite film is formed by melt coextrusion as the first thermoplastic resin and the second thermoplastic resin, the first end and the second end made of the second thermoplastic resin one of the breaking elongation at normal temperature, the claims 1-5, characterized by using the first thermoplastic the central portion thermoplastic resin, such as larger than the breaking elongation at room temperature consisting of a resin The manufacturing method of the stretched film as described in 2. When performing the heating stretching in the stretching step, the gripping position of each of said gripping members, claim 1-6 in which the distance from the widthwise ends of the central portion, characterized in that a position within 10mm The manufacturing method of the stretched film as described in any one of. Wherein the heating and drawing of the composite film in the stretching step, in addition to the longitudinal direction of the composite film, either of the claims 1 to 7, which comprises carrying out the simultaneous biaxial stretching to be stretched in the width direction A method for producing a stretched film. Wherein the first thermoplastic resin, the manufacturing method of the stretched film according to any one of claims 1 to 8, characterized in that an acrylic resin is used. The heating and drawing of the composite film in the stretching step, to any one of claims 1 to 9, the thickness of the central portion after heat stretching of the composite film and performing to be in the range of 15~50μm The manufacturing method of the stretched film of description.