JP2015134450A - Production method of stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a stretched film by which heating and stretching can be appropriately carried out and a stretched film excellent in productivity and qualities can be obtained.SOLUTION: The production method of a stretched film includes: a composite film forming step of melting and co-extruding a first thermoplastic resin and a second thermoplastic resin different from the first thermoplastic resin through a molding die, then cooling and solidifying to form a composite film having a center part made of the first thermoplastic resin and end parts made of the second thermoplastic resin formed at both ends of the center part in a width direction; and a stretching step of heating and stretching the composite film at least in a longitudinal direction to form a stretched film. The first thermoplastic resin and the second thermoplastic resin used exhibit a difference of 10°C or less between the respective glass transition temperatures.

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, in order to increase the stretching stress value at the time of heating and stretching at both ends of the film, as the thermoplastic resin that configures both ends of the film, the thermoplastic that configures the center of the film. Since a thermoplastic resin having a glass transition temperature higher than the glass transition temperature of the resin (for example, having a glass transition temperature higher than 35 ° C.) is used, the following problems arise.

  That is, in the technique of Patent Document 1, when heating and stretching are performed, if the heating temperature in the heating furnace is set near the glass transition temperature in the center of the film, the heating temperature in the heating furnace is changed to both ends of the film. The glass transition temperature becomes too low, so that both ends are not sufficiently softened, and when the both ends are gripped and pulled by the clip, the clip is detached or the film is broken. There is. On the other hand, in the technique of Patent Document 1, when the heating temperature in the heating furnace is set near the glass transition temperature at both ends of the film, the heating temperature in the heating furnace is set to the glass transition temperature at the center of the film. It becomes too high and the center part is excessively softened, and the problem that the center part cannot be properly stretched or the center part is exposed to high temperature and the molecular orientation becomes non-uniform, There exists a problem that the intensity | strength of the obtained stretched film will fall.

  The present invention has been made in view of such a situation, and is a composite film in which both end portions are formed at both ends in the width direction of the film by a thermoplastic resin different from the thermoplastic resin constituting the central portion of the film. In producing a stretched film by heating and stretching such a composite film, the stretched film can be appropriately stretched and a stretched film excellent in productivity and quality can be obtained. The purpose is to provide.

  When manufacturing the stretched film, the present inventors have a glass transition temperature difference of 10 ° C. or less as the thermoplastic resin constituting the central portion and the thermoplastic resin constituting both ends of the film before heating and stretching. The inventors have found that the above object can be achieved by using a resin, and have completed the present invention.

  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 composite film forming step of forming a composite film comprising a central portion made of the first thermoplastic resin and both end portions made of the second thermoplastic resin formed at both ends of the central portion in the width direction; A stretched film manufacturing method comprising: stretching the composite film by heating and stretching at least in the length direction to form a stretched film, wherein the first thermoplastic resin and the second heat There is provided a method for producing a stretched film, wherein a thermoplastic resin having a glass transition temperature difference of 10 ° C. or less is used as the plastic resin.

In the production method of the present invention, the elongation at break at room temperature of the both end portions made of the second thermoplastic resin in the composite film before being heated and stretched is that of the central portion made of the first thermoplastic resin. It is preferably larger than the elongation at break at room temperature.
In the production method of the present invention, the stretching stress value at the time of heating and stretching at the both end portions made of the second thermoplastic resin is the same as that at the time of heating and stretching at the central portion made of the first thermoplastic resin. It is preferably within 4 times the stretch stress value.
In the production method of the present invention, the viscosity of the second thermoplastic resin when melt coextruded from the molding die is preferably 0.5 to 2 times the viscosity of the first thermoplastic resin. .
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.
In the production method of the present invention, it is preferable that the first thermoplastic resin is an acrylic resin.
Moreover, in the manufacturing method of this invention, it is preferable that the said 2nd thermoplastic resin is a mixed resin formed by mix | blending the thermoplastic resin which has a glass transition temperature lower than the said acrylic resin in a polycarbonate (PC). .
Furthermore, it is preferable that the manufacturing method of this invention performs the heat | fever stretching of the said composite film in the said extending | stretching process so that the thickness of the said center part after the heat | fever stretching of the said composite film may be in the range of 15-50 micrometers.

  According to the present invention, it is possible to prevent breakage during stretching, and to provide a method for producing a stretched film excellent in productivity and yield.

FIG. 1 is a view for explaining a method of producing a composite film in the composite film forming step. 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 graph showing the glass transition temperature of a mixed resin obtained by blending polyethylene terephthalate (PET) with polycarbonate (PC). FIG. 4 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.

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 obtaining the composite film 100 by melt coextruding the first thermoplastic resin and the second thermoplastic resin from the 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 includes a central portion 110 and both end portions 120 formed at both ends in the width direction of the central portion 110, and the central portion 110 is a first portion. A film made of a thermoplastic resin and having both end portions 120 made of a second thermoplastic resin is obtained. 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, both end portions 120 of the composite film 100 are for reinforcing the central portion 110 when the composite film 100 is heat-stretched, and are removed by cutting as necessary after the composite film 100 is heat-stretched. be able to. 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 present embodiment, as the first thermoplastic resin constituting the central portion 110 of the composite film 100 and the second thermoplastic resin constituting both end portions 120, the glass transition temperature Tg of the first thermoplastic resin. _A thermoplastic resin having a difference (| Tg ₁ −Tg ₂ |) between ₁ and the glass transition temperature Tg ₂ of the _second thermoplastic resin of 10 ° C. or less is used. Thereby, in this embodiment, when the composite film 100 is heated and stretched by a stretching process as described later, the composite film 100 can be prevented from being broken and the productivity of the stretched film can be improved.

  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. Supply of the first thermoplastic resin and the second thermoplastic resin so that both end portions 120 made of the second thermoplastic resin are formed at both ends of the central portion 110 made of one thermoplastic resin. I do.

  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 resins are lined up), thereby co-extrusion 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 central portion 110 made of the first thermoplastic resin and the both end portions 120 formed at both ends of the central portion 110 and made of the second thermoplastic resin 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 sent out from the above-described composite film take-up roll, and the length direction and width of the composite film 100 are gripped by the clips 310 as shown in FIG. The composite film 100 is heated and stretched by a simultaneous biaxial stretching method that simultaneously stretches in the direction.

  Specifically, in the stretching step, the composite film 100 is continuously fed out from the composite film winding roll, the both ends 120 of the composite film 100 are held at regular intervals using a plurality of clips, and composited by each clip 310. The film 100 is transported into the stretching furnace 320, and the composite film 100 is stretched in the length direction and the width direction by the respective clips 310 in the stretching furnace 320. 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 second thermoplastic resin at both end portions 120 constituting this, and then is 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. And a stretched film can be obtained by cooling and solidifying in the cooling heat fixed zone following this. And the stretched film can be obtained continuously by opening the clip 310 and winding up with a roll.

  In the present embodiment, a pair of guide rails are provided for moving the clip 310 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 upper ends 120 of the composite film 100 and the position of the clip 310 that holds the lower ends 120 of the composite film 100 shown in FIG. 320 are parallel to each other in the pre-tropical zone, are separated from each other in the width direction of the composite film 100 in the stretch zone, and are parallel to each other in the cooling heat fixing zone. 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 holds the both ends 120 of the composite film 100 moves along such a guide rail so that the composite film 100 can be conveyed and 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 holding the both ends 120 of the composite film 100 is moved in the stretching zone in the stretching furnace 320 so as to spread in the width direction along the guide rail, and the interval between the clips 310 is also expanded. By performing the control, both end portions 120 of the composite film 100 are pulled in the length direction and the width direction as shown by arrows in FIG. Thereby, the center part 110 and the both ends 120 of the composite film 100 are heat-stretched in the length direction and the width direction, respectively, until a necessary stretch ratio is obtained. 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.

  As described above, in the present embodiment, the composite film 100 including the central portion 110 made of the first thermoplastic resin and the both end portions 120 made of the second thermoplastic resin is formed by the composite film forming step. And the stretched film can be obtained by heat-stretching the center part 110 and the both ends 120 of the composite film 100 by a stretching process.

  In this embodiment, it is possible to obtain a stretched film by making the stretching process and the composite film forming process into a continuous line.

  Moreover, in this embodiment, you may cut | disconnect the part of the both ends 120 about the stretched film obtained in this way as needed. Thereby, a stretched film can be made into the film which consists only of the center part 110. FIG.

  Moreover, in this embodiment, the thickness of the center part 110 of the composite film 100 after heat stretching becomes like this. Preferably it is 15-50 micrometers, More preferably, it is 20-40 micrometers. By controlling the thickness of the central portion 110 of the composite film 100 after heat stretching within the above range, breakage of the composite film 100 during heat stretching can be prevented, and the heat stretching of the composite film 100 can be performed appropriately.

Here, in the present embodiment, the first thermoplastic resin constituting the central portion 110 of the composite film 100 and the second thermoplastic resin constituting both end portions 120 are glass of the first thermoplastic resin. A thermoplastic resin having a difference (| Tg ₁ −Tg ₂ |) between the transition temperature Tg ₁ and the glass transition temperature Tg ₂ of the _second thermoplastic resin is 10 ° C. or less is used. Thereby, according to this embodiment, when the composite film 100 is heated and stretched, the clip 310 that holds the composite film 100 is prevented from being detached and the composite film 100 is prevented from being broken, thereby improving the productivity of the stretched film. Can be made.

That is, in the composite film 100, a glass transition temperature Tg ₂ of the both end portions 120, when compared to the glass transition temperature Tg ₁ of the central portion 110 is too high, when the heat-drawing, both ends the heating temperature in the stretching oven 320 The glass transition temperature Tg ₂ of the part 120 is not reached, and the softening of the both ends 120 is insufficient (the stretching stress value necessary for stretching the both ends 120 is high), so as shown in FIG. There is a problem that the clip 310 comes off when the both ends 120 are gripped and pulled using the clip 310. Furthermore, in this case, since the stretching stress value necessary for stretching both end portions 120 is high, the both end portions 120 are not stretched when the both end portions 120 are pulled by the clip 310 as shown in FIG. There is also a problem that the film is torn or a tear is generated at the boundary portion between the central portion 110 and the both end portions 120, thereby breaking the composite film 100. On the other hand, when heating the composite film 100 in the stretching furnace 320, while heating the entire composite film 100, only the both ends 120 are locally heated to a higher temperature to be softened, whereby the both ends 120 are Although a method of facilitating stretching is also conceivable, as shown in FIG. 2, in the stretching furnace 320, the positions of both end portions 120 are sequentially changed as the composite film 100 is transported and stretched. In order to heat to high temperature, there exists a problem that control of the temperature in the drawing furnace 320 will become complicated.

On the other hand, both ends in the composite film 100, a glass transition temperature Tg ₂ of the both end portions 120, when compared to the glass transition temperature Tg ₁ of the central portion 110 is too low, the time of heat-drawing, the heating temperature in the stretching oven 320 Since the glass transition temperature Tg ₂ of the portion 120 is exceeded and the both end portions 120 are excessively softened, when the both end portions 120 of the composite film 100 are pulled in the width direction using the clip 310 as shown in FIG. There is a problem that the portion 120 is preferentially stretched, and the pulling force of the clip 310 is not transmitted to the central portion 110, and the central portion 110 is not sufficiently stretched. Furthermore, both ends 120 are excessively softened during heating and stretching, so that both ends 120 are fused to the clip 310 and both ends 120 are contracted after heating and stretching. There is also a problem that productivity and yield of the product are reduced.

On the other hand, according to the present embodiment, for the composite film 100, the glass transition temperature Tg ₁ of the _first thermoplastic resin that forms the central portion 110 and the glass of the second thermoplastic resin that forms both end portions 120. By making the difference (| Tg ₁ −Tg ₂ |) from the transition temperature Tg ₂ within the above range, it is possible to prevent occurrence of problems such as detachment of the clip 310 and breakage of the composite film 100 when the composite film 100 is heated and stretched. Since the composite film 100 can be appropriately heat-stretched, productivity and yield of the stretched film can be improved.

In the present embodiment, as the first thermoplastic resin and the second thermoplastic resin, as described above, the difference in glass transition temperature (| Tg ₁ −Tg ₂ |) is 10 ° C. or less. A resin may be used, but the difference in glass transition temperature (| Tg ₁ −Tg ₂ |) is preferably 5 ° C. or less, more preferably 3 ° C. or less.

  In addition, conventionally, rubber elastic particles are added to both end portions 120 of the composite film 100 in order to prevent the clip 310 from coming off when the composite film 100 is heated and stretched by the clip 310 and the composite film 100 being broken. A method of softening 120 (increasing the elongation at break at room temperature) is known. However, this method has the following problems because the rubber elastic particles in both end portions 120 are easily deteriorated by heat. That is, when the composite film 100 is melt-coextruded from the T die 220, rubber elastic particles deteriorated by heat are deposited on the die slip 222 of the T die 220 to form a deposit. There is a possibility that the composite film 100 may be imprinted, or a deposit may be mixed into the product roll of the stretched film and deteriorate the quality of the stretched film. Further, when such a deposit of rubber elastic particles is formed, it is deposited between the composite film 100 and the clip 310 when the composite film 100 is heated and stretched using the clip 310 as shown in FIG. There is also a risk that an object will enter and the composite film 100 will be easily broken.

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

  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.

As the second thermoplastic resin for forming the end portions 120, the difference between the glass transition temperature of the first thermoplastic resin as described above such that the above-mentioned range (| | Tg 1 _{-Tg 2)} A thermoplastic resin may be selected.

Further, as the second thermoplastic resin for forming both end portions 120, in addition to the difference in glass transition temperature from the first thermoplastic resin (| Tg ₁ −Tg ₂ |) being in the above range. It can be selected from the following viewpoints.

  For example, as the second thermoplastic resin, it is preferable to use a thermoplastic resin having a viscosity of 0.5 to 2 times that of the first thermoplastic resin when melt coextruded from the T-die 220. Here, the measurement of a viscosity can be obtained by measuring with a capillograph based on JISK7199, for example. Thereby, the difference in viscosity between the first thermoplastic resin and the second thermoplastic resin at the time of melt coextrusion can be reduced, and the center portion 110 of the composite film 100 melt coextruded from the T-die 220 is obtained. And it can prevent that resin which comprises the both ends 120 mixes.

  That is, when the melt coextrusion is performed, if the viscosity of the second thermoplastic resin is too high relative to the viscosity of the first thermoplastic resin, the composite film 100 that is melt coextruded has a higher viscosity. The two end portions 120 made of the thermoplastic resin No. 2 flow to the surface of the central portion 110, cover a part of the central portion 110, and the resins are mixed. On the other hand, when the viscosity of the second thermoplastic resin is too low with respect to the viscosity of the first thermoplastic resin, in the melt-coextruded composite film 100, from the first thermoplastic resin having a higher viscosity. The central portion 110 that covers the ends 120 is partially mixed with the resin.

  Therefore, in this embodiment, by reducing the difference in viscosity between the first thermoplastic resin and the second thermoplastic resin during melt coextrusion to the above range, the composite film 100 that has been heat-stretched is centered. Mixing of the resins constituting the portion 110 and both end portions 120 can be prevented, thereby reducing the portion to be cut when the both end portions 120 are cut as described above when obtaining a stretched film. And the yield of the stretched film can be improved.

  In addition, as the second thermoplastic resin, for the obtained composite film 100, the difference between the stretching stress value of the central portion 110 and the stretching stress value of the both end portions 120 at the time of heat stretching is within a predetermined range. It is preferable to use a thermoplastic resin. Specifically, as the second thermoplastic resin, heat at which the stretching stress value at the time of heating and stretching at the both end portions 120 to be formed is within four times the stretching stress value at the time of heating and stretching at the central portion 110. It is preferable to use a plastic resin. The stretching stress value is a value indicating a tensile load required to stretch the central portion 110 and both end portions 120 when the composite film 100 is stretched to a necessary stretching ratio. Thereby, when the composite film 100 is heated and stretched, the deformation amount with respect to the stretching stress at the center portion 110 and both end portions 120 can be made close, and the breakage of the stretched film and the detachment of the clip at the time of heat stretching are more effective. The productivity of the stretched film can be further improved.

  Furthermore, as the second thermoplastic resin, it is preferable to use a thermoplastic resin that has a higher elongation at break at both ends 120 than at the center 110 in the composite film 100 before heat stretching obtained. 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 both end portions 120 are stretched in a normal temperature environment of about 10 to 30 ° C. Accordingly, when the composite film 100 is heated and stretched, the both end portions 120 are less likely to break than the central portion 110, the generation of a tear at both end portions 120 is prevented, and the entire composite film 100 is prevented from being broken. Can do.

  As the second thermoplastic resin, specifically, the following thermoplastic resin can be used based on the above-described viewpoint. For example, as the second thermoplastic resin, when an acrylic resin is used as the first thermoplastic resin, one of polyethylene naphthalate (PEN) and cyclic olefin polymer (COP) is used alone. Alternatively, a mixed resin in which two or more kinds are mixed can be used.

  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. In this case, the glass transition temperature of the obtained mixed resin is adjusted with the first thermoplastic resin by adjusting the blending ratio of the heat-resistant thermoplastic resin and the low-melting thermoplastic resin. difference in glass transition temperature _(| Tg 1 _-Tg 2 |) is adjusted to the above range.

Here, when an acrylic resin having a glass transition temperature Tg ₁ of about 120 ° C. is used as the first thermoplastic resin, the second thermoplastic resin has a high glass transition temperature of about 150 ° C., for example. Use a mixed resin in which polyethylene terephthalate (PET) with a low glass transition temperature of about 70 ° C. is blended with polycarbonate (PC), and the glass transition temperature is adjusted to around 120 ° C., which is about the same as the glass transition temperature Tg _1. Can do.

  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. Also, low-temperature meltable thermoplastic resins include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylonitrile butadiene styrene (ABS), polyethylene (PE), polyester (PEs), and polybutylene terephthalate. (PBT) or the like 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).

  Here, FIG. 3 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). In FIG. 3, the glass transition temperature of the resin having a polyethylene terephthalate (PET) content of 0%, 25%, 50%, 75%, 100% with respect to polycarbonate (PC) is measured by differential scanning calorimetry ( DSC) shows the measurement results. Here, in the measurement by differential scanning calorimetry (DSC), regardless of the content ratio of polyethylene terephthalate (PET), the glass transition temperature of the mixed resin is determined to be almost one point without becoming broad. Yes.

As shown in FIG. 3, the mixed resin in which polycarbonate (PC) is blended with polyethylene terephthalate (PET) can change the glass transition temperature according to the content ratio of polyethylene terephthalate (PET). Thereby, in this embodiment, when such a mixed resin is used as the second thermoplastic resin, the glass transition temperature Tg ₂ of the _second thermoplastic resin can be easily adjusted. The difference (| Tg ₁ −Tg ₂ |) between the glass transition temperature Tg ₁ and the thermoplastic resin can be controlled within the above range.

  In addition, as a method of heating and stretching the composite film 100 obtained from the first thermoplastic resin and the second thermoplastic resin, in the above-described example, as shown in FIG. Although an example using the simultaneous biaxial stretching method in which the film is heated and stretched in both the length direction and the width direction has been shown, a method of uniaxially stretching the composite film 100 only in the length direction may be used in this embodiment. .

  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, while conveying both ends 120 of the composite film 100 into the heating furnace 320 while gripping with the clips 310, each clip 310 holding the both ends 120 of the composite film 100 in the heating furnace 320 is then A method of heating and stretching only in the length direction can be used by widening the interval between the clips 310 without moving in the width direction.

  In the present embodiment, both the end portions 120 of the composite film 100 are 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. By stretching the film while holding it with the clip 310, the productivity of the stretched film can be improved compared to the conventional sequential biaxial stretching method, and the resulting stretched film is excellent in quality. Can be.

  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 thereafter, both ends 120 of the composite film 100 are held by clips 310 as shown in FIG. While stretching in the width direction.

  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 both end portions 120 while being conveyed by a plurality of preheated rolls preheated, While being further heated to a temperature about 10-30 ° C. higher than the glass transition temperature of both end portions 120 by a 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. In the sequential biaxial stretching method, when the composite film 100 is heated and stretched in the length direction, the both ends 120 of the composite film 100 are not fixed in the width direction. 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 both ends 120 of the composite film 100 with the clip 310), contact with the roll can be 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 the both ends 120 of the composite film 100 heat-stretched, an external appearance quality can be improved and it can use suitably for an optical film etc. with a severe request | requirement of external appearance quality especially. it can. Furthermore, according to the present embodiment, when the composite film 100 is stretched in the length direction, the both ends 120 of the composite film 100 are held by the clips 310, so that the composite film 100 is contracted in the width direction by heat. 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 both ends of the composite film 100 are prepared. As a second thermoplastic resin for forming the portion 120, an acrylic resin (glass transition temperature Tg ₂ : 125 ° C., elongation at break at room temperature: 18%) added with a small amount of rubber elastic particles was prepared.

  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. 4 (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. 4A, the measurement result of the first thermoplastic resin is the central portion 110, and the measurement result of the second thermoplastic resin is the both end portions 120.

Next, using the prepared first thermoplastic resin and second thermoplastic resin, a composite film 100 was produced under the following conditions by the method shown in FIG. Here, the produced composite film 100 had an overall width of about 315 mm, of which the regions having a width of about 50 mm from the end portions at both ends were both end portions 120, and the remaining central region was the central portion 110. In this example, an acrylic resin to which rubber elastic particles were added was used as the second thermoplastic resin. However, since the amount of the rubber elastic particles added was small, when the composite film 100 was melt-coextruded. It was possible to suppress the precipitation of rubber elastic particles.
T dice 220 outlet width: 380mm
Take-up speed of cooling roll 240: 6 mpm
Supply amount of the first thermoplastic resin to the feed block 210: 15 kg / hr
Supply amount of second thermoplastic resin to feed block 210: 5 kg / hr

  Here, about the obtained composite film 100, the boundary of the center part 110 and the both ends 120 can be confirmed clearly visually, and it is confirmed that mixing of resin in the composite film 100 has not generate | occur | produced. It was done.

Next, with respect to the obtained composite film 100, both ends 120 were gripped by clips 310, and as shown in FIG. 2, the film was stretched by heating in the length direction and the width direction under the following conditions by the simultaneous biaxial stretching method. In addition, when the thickness and breaking strength of the heat-stretched central portion 110 were measured in a region having a width of 400 mm in the central portion of the composite film 100 after heat-stretching, the thickness and breaking strength (pulled until it broke at room temperature) (Tensile strength at the time) was within ± 5%.
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 gripping position: 15 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 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, and a stretched film excellent in quality could be continuously produced. .

<Example 2>
As a second thermoplastic resin for forming both end portions 120 of the composite film 100, a mixed resin (glass transition temperature) comprising 75% by weight of polycarbonate (PC) and 25% by weight of polyethylene terephthalate (PET). A stretched film was obtained in the same manner as in Example 1 except that Tg ₂ : 125 ° C., elongation at break at room temperature: 20%), and a single film of both ends 120 (second thermoplastic resin). The stretching stress of was measured. The results are shown in FIG.

  In Example 2, as in Example 1, for the composite film 100 obtained by melt coextrusion, the boundary between the central portion 110 and both end portions 120 can be clearly confirmed by visual observation. In the film 100, it was confirmed that mixing of resin did not generate | occur | produce. Furthermore, while the composite film 100 was heated and stretched, the clip 310 was not detached and the composite film 100 was not broken, and a stretched film excellent in quality could be continuously produced.

<Example 3>
As a second thermoplastic resin for forming both end portions 120 of the composite film 100, a mixed resin (glass transition temperature Tg ₂ : 122 ° C., fracture at normal temperature) obtained by blending acrylic resin (PMMA) with polycarbonate (PC) A stretched film was obtained in the same manner as in Example 1 except that the elongation rate was 25%. Similarly, the stretching stress of the single film at both ends 120 (second thermoplastic resin) was measured. The results are shown in FIG.

  In Example 3, as in Example 1, the boundary between the center part 110 and both end parts 120 can be clearly confirmed visually with respect to the composite film 100 obtained by melt coextrusion. In the film 100, it was confirmed that mixing of resin did not generate | occur | produce. Furthermore, while the composite film 100 was heated and stretched, the clip 310 was not detached and the composite film 100 was not broken, and a stretched film excellent in quality could be continuously produced.

<Example 4>
PC / ABS alloy (glass transition temperature Tg ₂ :) obtained by mixing polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) as the second thermoplastic resin for forming both end portions 120 of the composite film 100. A stretched film was obtained in the same manner as in Example 1, except that the elongation at break at 120 ° C. and room temperature: 180% was used. Similarly, the stretching stress of the single film at both ends 120 (second thermoplastic resin) was obtained. Was measured. The results are shown in FIG. FIG. 4 (B) is a graph showing the measurement results of the stretching stress of a single film produced using the first thermoplastic resin and the second thermoplastic resin, similarly to FIG. 4 (A). The scale of the vertical axis is different from that in FIG.

  Here, in Example 4, as in Example 1, for the composite film 100 obtained by melt coextrusion, the boundary between the central part 110 and both end parts 120 can be clearly confirmed visually, In the composite film 100, it was confirmed that mixing of resin did not generate | occur | produce.

  On the other hand, in Example 4, since the stretching stress at both ends 120 at a stretching ratio of 100% is as high as about 7.7 times the stretching stress at the central portion 110, the composite film 100 is heated and stretched. The both ends 120 became difficult to extend, and the clip 310 was detached rarely. However, in Example 4, since the occurrence frequency of the clip 310 was low, a stretched film excellent in quality could be continuously produced.

<Example 5>
Except for using polyethylene naphthalate (PEN) (glass transition temperature Tg ₂ : 120 ° C., elongation at break at room temperature: 300%) as the second thermoplastic resin for forming both end portions 120 of the composite film 100. In the same manner as in Example 1, a stretched film was obtained, and similarly, the stretching stress of a single film at both ends 120 (second thermoplastic resin) was measured. The results are shown in FIG.

  Here, in Example 5, when the first thermoplastic resin and the second thermoplastic resin are melt-coextruded, the boundary between the central portion 110 and the both end portions 120 is somewhat in the composite film 100 obtained. It was unclear. This is because the central portion 110 and both end portions 120 are slightly mixed because of the large difference in viscosity when melt co-extruding the first thermoplastic resin and the second thermoplastic resin. It is thought that. However, in Example 5, there was no problem in quality with respect to the obtained stretched film.

  In Example 5, as in Example 1, while the composite film 100 was heated and stretched, the clip 310 was not detached and the composite film 100 was not broken, and a stretched film excellent in quality was continuously produced. Could be manufactured.

<Comparative Example 1>
Implementation was performed except that polycarbonate (PC) (glass transition temperature Tg ₂ : 143 ° C., elongation at break at room temperature: 170%) was used as the second thermoplastic resin for forming both end portions 120 of the composite film 100. A stretched film was obtained in the same manner as in Example 1, and the stretch stress of a single film at both ends 120 (second thermoplastic resin) was measured in the same manner. The results are shown in FIG.

  In Comparative Example 1, as in Example 1, the composite film 100 obtained by melt coextrusion can clearly confirm the boundary between the central portion 110 and both end portions 120 by visual observation. In the film 100, it was confirmed that mixing of resin did not generate | occur | produce.

However, in Comparative Example 1, when the composite film 100 is heated and stretched, the temperature of the pre-tropical zone and the stretched zone (140 ° C.) is the glass transition temperature Tg ₂ (143 of the _second thermoplastic resin constituting both ends 120. )), The softening of both end portions 120 became insufficient, and as a result, the clip 310 was frequently detached and a stretched film could not be obtained. On the other hand, in Comparative Example 1, the temperature of the pre-tropical zone and the stretching zone when performing heat stretching by the simultaneous biaxial stretching method is changed from 140 ° C. to 160 ° C., thereby softening both ends 120 and heating. Although the film could be stretched, the obtained stretched film was inferior in quality because it was exposed to a high temperature, the molecular orientation became non-uniform, the strength decreased, and the film thickness also varied.

Example 1 in which the difference (| Tg ₁ −Tg ₂ |) between the glass transition temperature Tg ₁ of the _first thermoplastic resin and the glass transition temperature Tg ₂ of the _second thermoplastic resin was 10 ° C. or less as described above. -5, when the composite film 100 was heated and stretched, the composite film 100 was prevented from being broken and the clip 310 was removed, so that a stretched film with excellent quality could be obtained and the productivity of the stretched film was improved. I was able to.

On the other hand, as described above, the difference (| Tg ₁ −Tg ₂ |) between the glass transition temperature Tg ₁ of the _first thermoplastic resin and the glass transition temperature Tg ₂ of the _second thermoplastic resin was more than 10 ° C. In Comparative Example 1, when the composite film 100 was heated and stretched, the clip 310 was frequently detached, so that a stretched film could not be obtained, and the productivity of the stretched film was inferior.

DESCRIPTION OF SYMBOLS 100 ... Composite film 110 ... Center part 120 ... Both ends 210 ... Feed block 220 ... T dice 230 ... Touch roll 240 ... Cooling roll 310 ... Clip 320 ... Stretching furnace

Claims (8)

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. A composite film forming step of forming a composite film comprising: a central portion made of: and at both ends of the central portion in the width direction; and both ends made of the second thermoplastic resin;
A stretching process for forming a stretched film by heating and stretching the composite film at least in the length direction, and a method for producing a stretched film,
A method for producing a stretched film, wherein a thermoplastic resin having a glass transition temperature difference of 10 ° C. or less is used as the first thermoplastic resin and the second thermoplastic resin.   In the composite film before being heated and stretched, the elongation at break of the both ends made of the second thermoplastic resin at normal temperature is higher than the elongation at break of the central portion made of the first thermoplastic resin at normal temperature. The manufacturing method of the stretched film of Claim 1 characterized by the above-mentioned.   The stretching stress value at the time of heat stretching at the both end portions made of the second thermoplastic resin is within 4 times the stretching stress value at the time of heat stretching at the center portion made of the first thermoplastic resin. The method for producing a stretched film according to claim 1 or 2, wherein:   The viscosity when the second thermoplastic resin is melt-coextruded from the molding die is 0.5 to 2 times the viscosity of the first thermoplastic resin. The manufacturing method of the stretched film in any one of.   The heating and 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. A method for producing a stretched film.   The method for producing a stretched film according to any one of claims 1 to 5, wherein the first thermoplastic resin is an acrylic resin.   The stretch according to claim 6, wherein the second thermoplastic resin is a mixed resin obtained by blending a thermoplastic resin having a glass transition temperature lower than that of the acrylic resin into polycarbonate (PC). A method for producing a film.   8. The heat stretching of the composite film in the stretching step is performed such that the thickness of the central portion after the heat stretching of the composite film is in the range of 15 to 50 μm. The manufacturing method of the stretched film of description.