JP6357838B2 - Multilayer film manufacturing method and retardation film manufacturing method - Google Patents

Description

  The present invention relates to a multilayer film obtained by coextrusion, a method for producing the same, and a retardation film produced from the multilayer film.

  For example, an image display device such as a liquid crystal display device is usually provided with various optical films. An example of the optical film is a retardation film. As such a retardation film, a multilayer film including a plurality of layers formed of different types of resins may be used.

  In general, when thickness unevenness occurs in a layer included in a multilayer film, the optical characteristics of the multilayer film are not uniform in the plane. Therefore, the thickness unevenness of the layer included in the multilayer film may cause, for example, display unevenness and light leakage. Therefore, in the multilayer film, it is required to suppress thickness unevenness by making the layer thickness uniform in the plane.

  One method for producing a multilayer film is a coextrusion method. The coextrusion method is a method of simultaneously extruding a plurality of resins from a die and obtaining a multilayer film having a layer made of each of the extruded resins. In the multilayer film produced by this coextrusion method, the thickness unevenness tends to occur easily in the width direction of the film. On the other hand, Patent Document 1 proposes a technique for suppressing uneven thickness of layers included in the multilayer film in the width direction of the film.

Japanese Patent No. 3564623

  However, in recent years, the required level for optical films has become high. For this reason, it has been difficult to reduce the thickness unevenness of the layers included in the multilayer film by the conventional technique as described in Patent Document 1 to meet the recent high demands. In particular, in a multilayer film including a combination of a thin layer having an average thickness of 5 μm or less and a layer having an average thickness larger than that, it is particularly difficult to reduce the thickness unevenness in the width direction of the film having a thin average thickness. It is. Therefore, in such a multilayer film, development of a technique capable of effectively suppressing thickness unevenness in the width direction of a layer having a thin average thickness has been demanded.

  The present invention was devised in view of the above problems, and is a multilayer film produced by coextrusion, and an average thickness of 5 μm or less and a thin first layer, and a second layer having an average thickness larger than that, A multilayer film having a small thickness unevenness in the first layer; a retardation film produced from the multilayer film; and a production method capable of producing the multilayer film. To do.

As a result of intensive studies to solve the above-mentioned problems, the present inventor, in a die used when producing a multilayer film by a coextrusion method, in the flow path of the molten resin for forming the first layer, the lip portion of the die The present inventors have found that the thickness unevenness of the first layer can be effectively reduced by providing the adjustment flow path portion having a predetermined gap with reference to the size of the gap.
That is, the present invention is as follows.

[1] A multilayer film comprising a first layer and a second layer, obtained by coextrusion,
The average thickness T1 of the first layer is 0.5 μm or more and 5.0 μm or less,
The ratio T1 / T2 between the average thickness T1 of the first layer and the average thickness T2 of the second layer is 1/300 or more and 1/20 or less,
A multilayer film in which the thickness unevenness of the first layer is within ± 5%.
[2] The multilayer film according to [1], further comprising a third layer.
[3] The multilayer film according to [2], wherein a ratio T3 / T2 between the average thickness T3 of the third layer and the average thickness T2 of the second layer is 1/10 or more and 1/3 or less.
[4] A retardation film obtained by subjecting the multilayer film according to any one of [1] to [3] to stretching.
[5] The retardation film according to [4], wherein an average thickness of a layer formed by stretching the first layer is 0.1 μm or more and 3.0 μm or less.
[6] A production method for producing the multilayer film according to [1] using a die,
The die is
A first manifold that can be supplied with a molten resin for forming the first layer;
A first flow path extending downstream from the first manifold;
A second manifold that can be supplied with a molten resin for forming the second layer;
A second flow path extending downstream from the second manifold;
A merge portion where the first flow path and the second flow path merge;
A merge channel extending downstream from the merge section;
A lip portion formed downstream of the merging channel and capable of continuously discharging the molten resin for forming the first layer and the molten resin for forming the second layer merged at the merging portion;
The first channel includes an adjustment channel part,
The ratio of the size of the gap of the adjustment flow path portion to the size of the gap of the lip portion is 3.0 or less,
The manufacturing method is
Supplying molten resin for forming the first layer to the first manifold;
Supplying molten resin for forming the second layer to the second manifold; and
A method for producing a multilayer film, comprising continuously discharging the molten resin for forming the first layer and the molten resin for forming the second layer from the lip portion.
[7] A method for producing a multilayer film according to [2] or [3] using a die,
The die is
A first manifold that can be supplied with a molten resin for forming the first layer;
A first flow path extending downstream from the first manifold;
A second manifold that can be supplied with a molten resin for forming the second layer;
A second flow path extending downstream from the second manifold;
A third manifold capable of supplying a molten resin for forming the third layer;
A third flow path extending downstream from the third manifold;
A merge portion where the first flow path, the second flow path and the third flow path merge;
A merge channel extending downstream from the merge section;
The molten resin for forming the first layer, the molten resin for forming the second layer, and the molten resin for forming the third layer, which are formed downstream of the merging channel and merged at the merging portion, are continuously formed. A lip portion that can be discharged,
The first channel includes an adjustment channel part,
The ratio of the size of the gap of the adjustment flow path portion to the size of the gap of the lip portion is 3.0 or less,
The manufacturing method is
Supplying molten resin for forming the first layer to the first manifold;
Supplying molten resin for forming the second layer to the second manifold;
Supplying molten resin for forming the third layer to the third manifold; and
Continuously discharging the molten resin for forming the first layer, the molten resin for forming the second layer, and the molten resin for forming the third layer from the lip portion, a method for producing a multilayer film .

  According to the present invention, a multilayer film produced by coextrusion, comprising a combination of a thin first layer having an average thickness of 5 μm or less and a second layer having a thicker average thickness, and the first A multilayer film having a small thickness unevenness in the layer; a retardation film produced from the multilayer film; and a production method capable of producing the multilayer film can be realized.

FIG. 1 is a cross-sectional view schematically showing a multilayer film according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a cross section of a die used in the manufacturing method according to one embodiment of the present invention, cut along a plane perpendicular to the width direction of the first flow path. 3 is a cross-sectional view schematically showing a cross section of a die according to an embodiment of the present invention cut along a plane indicated by line III-III in FIG. 4 is a cross-sectional view schematically showing a cross section of a die according to an embodiment of the present invention cut along a plane indicated by line IV-IV in FIG. FIG. 5 is a cross-sectional view schematically showing a cross section of the adjustment bolt according to one embodiment of the present invention cut by a plane parallel to the axial direction of the adjustment bolt.

  Hereinafter, the present invention will be described in detail with reference to examples and embodiments. However, the present invention is not limited to the following examples and embodiments, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

  In the following description, the intrinsic birefringence being positive means that the refractive index in the stretching direction is larger than the refractive index in the direction perpendicular thereto. In addition, negative intrinsic birefringence means that the refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular thereto. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

  Further, the term “long” means that the film has a length of at least 5 times the width, preferably 10 times or more, specifically in a roll shape. It has a length that can be wound and stored or transported.

  Furthermore, the MD direction (machine direction) is a film flow direction in the production line, and is usually parallel to the longitudinal direction and the longitudinal direction of the film. Further, the TD direction (traverse direction) is a direction parallel to the film surface and perpendicular to the MD direction, and is usually parallel to the width direction and the lateral direction of the film.

  In the following description, the in-plane retardation Re of the film is a value represented by Re = (nx−ny) × d unless otherwise specified. The retardation Rth in the thickness direction of the film is a value represented by Rth = {(nx + ny) / 2−nz} × d. Here, nx represents a refractive index in a direction (in-plane direction) perpendicular to the thickness direction of the film and giving the maximum refractive index. ny represents a refractive index in the in-plane direction of the film and in a direction perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the film. d represents the film thickness of the film. Unless otherwise stated, the retardation measurement wavelength is 550 nm. The retardation can be measured using a commercially available phase difference measuring device (for example, “KOBRA-21ADH” manufactured by Oji Scientific Instruments) or the Senarmon method.

[1. Embodiment]
[1.1. (Structure of multilayer film)
FIG. 1 is a cross-sectional view schematically showing a multilayer film 10 according to an embodiment of the present invention.
A multilayer film 10 according to an embodiment of the present invention is a film obtained by coextrusion, and includes a first layer 11, a second layer 12, and a third layer 13 formed in this order. Since the multilayer film 10 is a film obtained by coextrusion, the first layer 11 and the second layer 12 are in direct contact with each other without interposing another layer, and the second layer 12 and the third layer. 13 is in direct contact with no other layer.

  The average thickness T1 of the first layer 11 is usually 0.5 μm or more, preferably 1.0 μm or more, more preferably 1.5 μm or more, and usually 5.0 μm or less, preferably 4.0 μm or less, more preferably 3 0.0 μm or less. In the multilayer film produced by coextrusion, it has been generally difficult to reduce the thickness unevenness in the width direction of the layer having a thin average thickness. However, in the multilayer film 10 according to the present embodiment, the thickness unevenness in the width direction of the first layer 11 having the thin average thickness can be reduced.

  Specifically, the thickness unevenness in the width direction of the first layer 11 is usually within ± 5%, preferably within ± 3%, and more preferably within ± 1%. Here, “thickness unevenness” means the difference between the maximum value and the minimum value of the thickness of the layer in the region of the central part 75% excluding the end in the width direction of the multilayer film 10, and the average thickness of the layer. The value divided by.

  The second layer 12 has an average thickness T2 that allows a ratio T1 / T2 between the average thickness T1 of the first layer 11 and the average thickness T2 of the second layer 12 to fall within a desired range. Specifically, the ratio T1 / T2 is usually 1/300 or more, preferably 1/200 or more, more preferably 1/100 or more, and usually 1/20 or less, preferably 1/25 or less, more Preferably it is 1/30 or less. In a multilayer film produced by coextrusion, it is generally difficult to reduce thickness unevenness in the width direction of a layer having a thin average thickness when a layer having a large difference in average thickness is provided. However, in the multilayer film 10 according to the present embodiment, thickness unevenness in the width direction of the thin first layer 11 is included while including the first layer 11 having a thin average thickness and the layer 12 having a large average thickness in this way. Can be small.

  In the multilayer film 10 according to the present embodiment, the thickness unevenness in the width direction of the second layer 12 can be usually reduced. Specifically, the thickness unevenness in the width direction of the second layer 12 is usually within ± 5%, preferably within ± 3%, and more preferably within ± 1%.

  The average thickness T3 of the third layer 13 can be arbitrarily set according to the use of the multilayer film 10. When the multilayer film 10 is used as an optical film, the average thickness T3 of the third layer 13 is set to a ratio T3 / T2 between the average thickness T3 of the third layer 13 and the average thickness T2 of the second layer 12 within a predetermined range. It is preferable to set so that it can be accommodated. Specifically, the ratio T3 / T2 is preferably 1/10 or more, more preferably 1/8 or more, particularly preferably 1/6 or more, preferably 1/3 or less, more preferably 1 /. 4 or less, particularly preferably 1/5 or less. By setting the average thickness T3 of the third layer 13 as described above, various optical characteristics can be expressed in the third layer 13, and thus a desired optical function can be realized in the multilayer film 10.

  In the multilayer film 10 according to the present embodiment, the thickness unevenness in the width direction of the third layer 13 can be usually reduced. Specifically, the thickness unevenness in the width direction of the third layer 13 is typically within ± 5%, preferably within ± 3%, and more preferably within ± 1%.

  The total thickness of the multilayer film 10 can be arbitrarily set according to the use of the multilayer film 10. The specific range of the total thickness of the multilayer film 10 is preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, preferably 500 μm or less, more preferably 400 μm or less, particularly preferably 300 μm or less. is there.

  The total light transmittance of the multilayer film 10 is preferably 85% or more. Here, the light transmittance can be measured using a spectrophotometer (manufactured by JASCO Corporation, ultraviolet-visible near-infrared spectrophotometer “V-570”) in accordance with JIS K0115.

  The haze of the multilayer film 10 is preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less. Here, according to JIS K7361-1997, haze can measure five places using the Nippon Denshoku Industries Co., Ltd. "turbidimeter NDH-300A", and can employ | adopt the average value calculated | required from it.

  Further, the multilayer film 10 may be an unstretched film that has not been subjected to stretching treatment or a stretched film that has been subjected to stretching treatment. It is preferable that the unstretched film which is the multilayer film 10 provided with the layer 11 is stretched.

[1.2. (Method for producing multilayer film)
As described above, the multilayer film 10 including the first layer 11 with small thickness unevenness can be manufactured by a manufacturing method using a predetermined die 20 described below.

(Composition of dice)
FIG. 2 is a cross-sectional view schematically showing a cross section of the die 20 used in the manufacturing method according to the embodiment of the present invention, taken along a plane perpendicular to the width direction of the first flow path 130.
As shown in FIG. 2, the die 20 includes a die body 100. The die body 100 can be made of, for example, die steel, stainless steel (SUS), or the like. As the die steel, for example, SKD hot die steel (thermal conductivity: about 30 W / m ° C.) or the like can be used. Moreover, as stainless steel, SUS420J2 (thermal conductivity: about 25 W / m ° C.) or the like can be used, for example.

  The die body 100 has a first supply path 110, a first manifold 120, a first flow path 130, a second supply path 210, a second manifold 220, a second flow path 230, and a third flow path through which molten resin can flow. A supply path 310, a third manifold 320, a third flow path 330, a merging portion 410, a merging flow path 420, and a lip portion 430 are formed. Among these, the first supply passage 110, the first manifold 120, and the first flow passage 130 are flow passage portions through which the molten resin for forming the first layer can flow, and the second supply passage 210, the second manifold 220, and the second flow passage. The passage 230 is a flow path portion through which the molten resin for forming the second layer can flow, and the third supply path 310, the third manifold 320, and the third flow path 330 are flow paths through which the molten resin for forming the third layer can flow. Part. In addition, the merging portion 410, the merging channel 420, and the lip portion 430 flow in the form of a layered molten resin for forming the first layer, a molten resin for forming the second layer, and a molten resin for forming the third layer. It is a flow path portion that can be obtained.

(Flow path through which molten resin for forming the first layer can flow)
The first supply path 110 is a flow path portion that opens to the outside of the die body 100. The first supply path 110 is provided so that the molten resin for forming the first layer can be supplied by a resin supply device such as an extruder. The first supply path 110 is provided so as to take in the molten resin supplied from the outside of the die 20 and send the taken-in molten resin to the first manifold 120.

  The first manifold 120 is a flow path portion connected downstream of the first supply path 110. The first manifold 120 is provided so that the molten resin for forming the first layer can be supplied through the first supply path 110.

FIG. 3 is a cross-sectional view schematically showing a cross section of the die 20 according to the embodiment of the present invention taken along the plane indicated by the line III-III in FIG. As shown in FIG. 3, the first manifold 120 is formed so as to extend from the first supply path 110 in the flow path width direction. For this reason, the first manifold 120 has a structure capable of sending the molten resin supplied to the first manifold 120 in the entire flow path width direction. Here, the flow path width direction indicates the normal direction of the paper surface in FIG. 2, and the horizontal direction in FIG.
As shown in FIG. 3, the first manifold 120 is formed so that the position closer to the end in the flow path width direction is lowered downstream. For this reason, the 1st manifold 120 has a structure which can distribute the molten resin supplied to the 1st manifold 120 to the edge part of a flow path width direction efficiently.

  As shown in FIG. 2, a first flow path 130 is connected downstream of the first manifold 120 so as to extend downstream from the first manifold 120. For this reason, the die 20 has a configuration that allows the molten resin supplied to the first manifold 120 to flow into the first flow path 130.

A first preland 131 is formed at a connection portion of the first flow path 130 with the first manifold 120. The gap size A _P1 of the first preland 131 is smaller than the gap size A ₁₃₂ of the portion 132 immediately downstream of the first preland 131 of the first flow path 130. Here, “the size of the gap” of the flow path refers to the size in the depth direction of the flow path unless otherwise specified, and corresponds to the thickness direction of the film or layer. The flow path depth direction indicates the horizontal direction in FIG. 2, and the normal direction of the paper surface in FIG. Thus, in the first preland 131, the flow path cross-sectional area is small. For this reason, the first preland 131 has a configuration capable of applying a large resistance to the molten resin flowing through the first preland 131.

  As shown in FIG. 3, the first pre-land 131 protrudes upstream with the central portion of the first flow passage 130 in the flow passage width direction as a top portion. Therefore, the first preland 131 causes the molten resin flowing through the first preland 131 to flow through the first preland 131 at a long distance in the central portion in the flow path width direction, and the closer to the end in the flow path width direction, the closer the position is. The first pre-land 131 can be circulated within a short distance.

  Since the central portion in the width direction of the first flow path 130 is directly below the first supply path 110, the pressure of the supplied molten resin is large. Moreover, since the width direction edge part of the 1st flow path 130 is far from the 1st supply path 110, the pressure of the molten resin supplied is small. Therefore, since the molten resin tends to flow in the center portion in the width direction of the first flow path 130, the center portion in the width direction tends to be thick in the first layer of the obtained multilayer film when no countermeasure is taken. There is. On the other hand, by providing the first preland 131 as described above, a large resistance is applied to the molten resin flowing in the center portion in the width direction of the first preland 131 by a long distance, and the end portion in the width direction of the first preland 131 is obtained. A large resistance can be applied to the molten resin flowing through the tube only for a short distance. For this reason, the amount of molten resin flowing into the first flow path 130 from the first manifold 120 can be made uniform in the flow path width direction, and the thickness unevenness of the first layer can be reduced in the width direction in the resulting multilayer film.

As shown in FIG. 2, the first flow path 130 includes a first adjustment flow path portion 133. The first adjustment channel portion 133 is a portion having a gap in a predetermined range in the first channel 130. The specific gap size A _C1 of the first adjustment flow path portion 133 is a ratio A _C1 / A of the gap size A _C1 of the first adjustment flow path portion 133 to the gap size A _L of the lip portion 430. _L can be set to fall within a predetermined range. Specific range of the ratio _A C1 / _{A L} of the usually 3.0 or less, preferably 2.0 or less. By providing such a first adjustment flow path portion 133 downstream from the first manifold 120 and upstream from the merge portion 410, thickness unevenness of the first layer can be reduced in the width direction in the obtained multilayer film. Also There is no lower limit value of the ratio _A C1 / _{A L,} and preferably 1.0 or more.

Although it is not clear why the thickness unevenness of the first layer of the multilayer film can be reduced by keeping the size A _C1 of the gap of the first adjustment flow path portion 133 within the above range, according to the study of the present inventors. It is inferred as follows. That is, generally, in which position in the TD direction of the lip portion the molten resin flows in a large amount and in which position the molten resin flows in a small amount, the molten resin at all positions in the TD direction from the supply to the manifold to the discharge from the lip portion. The pressure loss is determined to be constant. In general, the pressure loss related to the die equipment strongly depends on the flow path gap. For this reason, in order to increase the adjustment amount in the first adjustment channel portion 133, it is preferable to narrow the gap of the first adjustment channel portion 133. Usually, in the die design, the gap of the flow path is the narrowest at the lip part. Therefore, by setting A _C1 / _AL to 3 or less, the influence of the first adjustment flow path part 133 in the entire die 20 is large. Therefore, it can be assumed that the thickness unevenness of the first layer can be reduced.

Further, in the present embodiment, the first adjustment channel portion 133 is a portion where the size of the gap is partially reduced in the first channel 130. Therefore, the gap size A _C1 of the first adjustment channel portion 133 is smaller than the gap size A ₁₃₄ of the portion 134 immediately upstream of the first adjustment channel portion 133 of the first channel 130. As a result, the first adjustment flow path portion 133 can function as a throttle whose flow path cross-sectional area is partially reduced in the first flow path 130. For this reason, the pressure of the molten resin in the portion 135 downstream of the first adjustment flow path portion 133 of the first flow path 130 can be stabilized by the action of the restriction. Therefore, in the obtained multilayer film, the thickness unevenness of the first layer can be further reduced in the width direction.

Moreover, the gap size A _C1 of the first adjustment channel 133 is preferably smaller than the gap size A _P1 of the first Purirando 131. Thereby, in the obtained multilayer film, the thickness unevenness of the first layer can be further reduced in the width direction.

  The first flow path 130 is connected to the merging portion 410 at the downstream end thereof. Therefore, the die 20 has a configuration capable of sending the molten resin flowing through the first flow path 130 to the joining portion 410.

(Flow path through which molten resin for forming the second layer can flow)
As shown in FIG. 2, the second supply path 210 is a flow path portion that opens to the outside of the die body 100. The second supply path 210 is provided so that the molten resin for forming the second layer can be supplied by a resin supply device such as an extruder. The second supply path 210 is provided so as to take in the molten resin supplied from the outside of the die 20 and send the taken-in molten resin to the second manifold 220.

  The second manifold 220 is a flow path portion connected downstream of the second supply path 210. The second manifold 220 is provided so that the molten resin for forming the second layer can be supplied through the second supply path 210.

  FIG. 4 is a cross-sectional view schematically showing a cross section of the die 20 according to the embodiment of the present invention taken along the plane indicated by the line IV-IV in FIG. As shown in FIG. 4, like the first manifold 120, the second manifold 220 is formed wider than the second supply path 210 in the flow path width direction. In addition, the second manifold 220 is formed so that the position closer to the end in the flow path width direction is lowered downstream. For this reason, the 2nd manifold 220 has the structure which can send the molten resin supplied to the 2nd manifold 220 to the whole flow path width direction, and can spread efficiently to the edge part of a flow path width direction.

  As shown in FIG. 2, a second flow path 230 is connected downstream of the second manifold 220 so as to extend downstream from the second manifold 220. Therefore, the die 20 has a configuration that allows the molten resin supplied to the second manifold 220 to flow into the second flow path 230.

A second preland 231 is formed at a connection portion of the second flow path 230 with the second manifold 220. Gap size _{A P2} of the second Purirando 231 is smaller than the gap size _{A 232} immediately downstream of the portion 232 of the second Purirando 231 of the second flow path 230. Further, as shown in FIG. 4, the second pre-land 231 protrudes upstream with the central portion of the second flow passage 230 in the flow passage width direction as a top portion. For this reason, similarly to the first preland 131, the second preland 231 can reduce the thickness unevenness of the second layer in the width direction in the obtained multilayer film.

  The second flow path 230 is connected to the merge part 410 at the downstream end thereof. Therefore, the die 20 has a configuration capable of sending the molten resin flowing through the second flow path 230 to the joining portion 410.

(Flow path through which molten resin for forming the third layer can flow)
As shown in FIG. 2, the third supply path 310 is a flow path portion that opens to the outside of the die body 100. The third supply path 310 is provided so that the molten resin for forming the third layer can be supplied by a resin supply device such as an extruder. The third supply path 310 is provided so that the molten resin supplied from the outside of the die 20 can be taken in and the taken molten resin can be sent to the third manifold 320.

  The third manifold 320 is a flow path portion connected downstream of the third supply path 310. The third manifold 320 is provided so that the molten resin for forming the third layer can be supplied through the third supply path 310.

  Similar to the first manifold 120 and the second manifold 220, the third manifold 320 is formed to extend from the third supply path 310 in the flow path width direction. Further, the third manifold 320 is formed so as to be lowered downstream as the position is closer to the end in the flow path width direction. For this reason, the 3rd manifold 320 has the structure which can send the molten resin supplied to the 3rd manifold 320 to the whole flow path width direction, and can spread efficiently to the edge part of a flow path width direction.

  As shown in FIG. 2, a third flow path 330 is connected downstream of the third manifold 320 so as to extend downstream from the third manifold 320. Thereby, the die 20 has a configuration that allows the molten resin supplied to the third manifold 320 to flow into the third flow path 330.

A third preland 331 is formed at a connection portion of the third flow path 330 with the third manifold 320. Size _{A P3} gap of the third Purirando 331 is smaller than the gap size _{A 332} immediately downstream of the portion 332 of the third Purirando 331 of third flow channel 330. Further, the third preland 331 protrudes upstream with the central portion of the third channel 330 in the channel width direction as the top. For this reason, similarly to the first preland 131 and the second preland 231, the third preland 331 can reduce the thickness unevenness of the third layer in the width direction in the obtained multilayer film.

The third flow path 330 includes a third adjustment flow path portion 333. The third adjustment channel portion 333 is a portion having a gap in a predetermined range in the third channel 330. A specific gap size A _C3 of the third adjustment flow path portion 333 is set to fall within a range defined in the same manner as the gap size A _{C1 of} the first adjustment flow path portion 133. By providing such a third adjustment flow path portion 333 downstream of the third manifold 320 and upstream of the merge portion 410, the thickness unevenness of the third layer can be reduced in the width direction in the obtained multilayer film.

The third adjustment flow path portion 333 is a portion where the size of the gap is partially reduced in the third flow path 330, similarly to the first adjustment flow path portion 133. Therefore, the gap size A _C3 of the third adjustment channel portion 333 is smaller than the gap size A ₃₃₄ of the portion 334 immediately upstream of the third adjustment channel portion 333 of the third channel 330. Thereby, in the obtained multilayer film, the thickness unevenness of the third layer can be further reduced in the width direction.

Further, the gap size A _C3 of the third adjustment channel 333 is preferably smaller than the gap size A _P3 of the third Purirando 331. Thereby, in the obtained multilayer film, the thickness unevenness of the third layer can be further reduced in the width direction.

  The third flow path 330 is connected to the merge part 410 at the downstream end thereof. Therefore, the die 20 has a configuration capable of sending the molten resin flowing through the third flow path 330 to the joining portion 410.

(Flow path through which the molten resin for forming the first to third layers can flow)
As shown in FIG. 2, the first flow path 130, the second flow path 230, and the third flow path 330 described above are merged at a merge portion 410. Further, a merging channel 420 is connected downstream of the merging portion 410 so as to extend downstream from the merging portion 410. As a result, the die 20 flows through the first channel 130 through the first layer forming molten resin, through the second channel 230 through the second layer forming molten resin, and through the third channel 330 through the first channel 130. The molten resin for forming the three layers is merged at the merging portion 410, and both have a configuration that can flow through the merging flow path 420 in a layered manner. Moreover, in this embodiment, as shown in FIG. 2, the 1st flow path 130, the 2nd flow path 230, and the 3rd flow path 330 are provided along with this order from the right side in the figure. Therefore, when the die 20 flows through the merged flow path 420, the molten resin for forming the first layer, the molten resin for forming the second layer, and the molten resin for forming the third layer in the flow path depth direction, It has the structure which can be made to flow in the state arranged in this order.

  A lip portion 430 is formed downstream of the merge channel 420. The lip portion 430 opens to the outside of the die body 100 at the downstream end thereof. For this reason, the die 20 continuously discharges the molten resin for forming the first layer, the molten resin for forming the second layer, and the molten resin for forming the third layer, which merged at the merging portion 410, from the lip portion 430. It has a configuration that can be made.

Size A _L of the gap between the lip portion 430 is set smaller than the confluent channel 420 provided upstream of the lip portion 430. Size A specific range _L of the gap between the lip 430 can be arbitrarily set depending on the total thickness of the multilayer film to be produced.

(Adjustment mechanism for the size of the gap in the adjustment channel)
The die 20 according to the present embodiment includes a flow path gap control unit 500 that can adjust the size of the gap of the first adjustment flow path unit 133. The flow path gap control unit 500 includes a choke bar 510 and an adjustment bolt 520.

  The choke bar 510 is a bar-like member that is movably provided. The choke bar 510 has a substantially trapezoidal cross section cut by a plane perpendicular to the channel width direction. In addition, the choke bar 510 continuously extends from one end of the first adjustment channel portion 133 in the channel width direction to the other end. Further, the end of the choke bar 510 on the flow path side faces the first adjustment flow path 133, and the choke bar 510 is provided so as to function as a movable weir. For this reason, the channel clearance control unit 500 has a configuration in which the size of the gap of the first adjustment channel unit 133 can be adjusted by adjusting the position of the choke bar 510.

  The adjustment bolt 520 is provided on the opposite side of the choke bar 510 from the first adjustment flow path portion 133. A plurality of adjustment bolts 520 are provided at predetermined intervals in the longitudinal direction of the choke bar 510 (that is, in the flow channel width direction of the first adjustment flow channel portion 133). The tip of each adjustment bolt 520 is supported by the choke bar 510 so as to freely advance and retract. Thereby, the flow path gap control unit 500 has a configuration in which the choke bar 510 can be moved by moving the adjustment bolt 520 in the axial direction to adjust the size of the gap of the first adjustment flow path 133.

  Specifically, the channel clearance control unit 500 has a configuration capable of adjusting the size of the clearance of the first adjustment channel unit 133 by the following operation. For example, when it is desired to reduce the size of a gap in a portion of the first adjustment flow path portion 133 in the width direction, the adjustment bolt 520 corresponding to the portion is advanced and the choke bar 510 is pushed. Further, when it is desired to increase the size of a gap in a certain portion in the width direction of the first adjustment flow path portion 133, the adjustment bolt 520 corresponding to that portion is retracted and the choke bar 510 is pulled. By performing this operation for each adjustment bolt 520, the size of the gap of the first adjustment channel portion 133 can be adjusted for each position in the channel width direction, and as a result, the first adjustment channel in the channel width direction. The distribution of the size of the gap of the part 133 can be adjusted. For this reason, the die 20 can adjust the flow rate of the molten resin flowing through the first adjustment channel portion 133 for each position in the channel width direction, and can suppress the thickness unevenness of the first layer in the width direction. have.

  The interval between the adjustment bolts 520 is preferably 40 mm or more and 50 mm or less. By setting the distance between the adjustment bolts 520 to be equal to or greater than the lower limit value of the above range, it is possible to suppress the strength reduction of the choke bar 510 due to the bolt holes formed in the choke bar 510. Further, since the number of adjustment bolts 520 can be increased by setting the upper limit value or less, the choke bar 510 can be partially moved in many portions. The size can be adjusted precisely.

FIG. 5 is a cross-sectional view schematically showing a cross section of the adjustment bolt 520 according to an embodiment of the present invention cut by a plane parallel to the axial direction of the adjustment bolt 520.
As shown in FIG. 5, the outer diameter D ₅₂₀ of the adjusting bolt 520 is preferably 10 mm or more, more preferably 14 mm or more, preferably 30 mm or less, more preferably 24 mm or less. The outer shape D ₅₂₀ of the adjustment bolt 520 by more than the lower limit of the range, can be increased bolt strength. Moreover, the intensity | strength of the chalk bar 510 with which the adjustment bolt 520 is screwed can be made high by making it below an upper limit.

  Each adjustment bolt 520 includes a rod-shaped electric heater 530 as a heater that can adjust the temperature of the first adjustment flow path portion 133. The electric heater 530 is embedded in the shaft portion of the adjustment bolt 520. Further, the electric heater 530 is provided so that the amount of heat generated by the electric heater 530 can be adjusted by energizing or interrupting electricity. For this reason, the flow path gap control unit 500 has a configuration capable of heating the choke bar 510 at a desired temperature. Therefore, the die 20 has a configuration in which the choke bar 510 can be adjusted to a desired temperature for each position in the longitudinal direction, and thus the temperature distribution can be precisely adjusted in the flow path width direction of the first adjustment flow path portion 133. Yes.

  Since the temperature distribution can be precisely adjusted in the flow path width direction of the first adjustment flow path portion 133 in this way, in the die 20, the temperature of the molten resin flowing through the first adjustment flow path portion 133 is changed for each position in the flow path width direction. Can be adjusted precisely. Here, the resin viscosity generally changes as the temperature changes. Further, the molten resin tends to flow through the flow path when the viscosity is low, and tends to be difficult to flow through the flow path when the viscosity is high. Therefore, by performing the temperature adjustment as described above, the flow rate of the molten resin flowing through the first adjustment channel portion 133 can be adjusted for each position in the channel width direction. It is possible to adjust the thickness of the first layer of the film more precisely.

  In particular, since the size of the gap of the first adjustment channel portion 133 is small, the temperature adjustment by the electric heater 530 can be performed particularly precisely. Therefore, the thickness unevenness of the first layer of the multilayer film can be remarkably reduced by adjusting the temperature particularly in the first adjustment channel portion 133 in the first channel 130.

  Furthermore, since the size of the gap of the first adjustment flow path portion 133 is small, the temperature of the molten resin in the first adjustment flow path portion 133 can be adjusted precisely and in a wide temperature range by the electric heater 530. Thus, since the temperature of molten resin can be adjusted precisely and within a wide temperature range, the thickness of the first layer can be adjusted precisely and within a wide thickness range. Therefore, by adjusting the temperature in the first adjustment flow path portion 133, the thickness of the first layer can be adjusted precisely in a particularly wide thickness range.

The diameter D ₅₃₀ of the electric heater 530 is preferably 75% or less, more preferably 50% or less, with respect to the outer diameter D ₅₂₀ of the adjusting bolt 520. Thereby, the strength of the adjustment bolt 520 can be increased. Further, There is no limitation on the lower limit of the diameter _{D 530} of the electric heater 530, typically is at least 30% of the outer diameter _{D 520} of the adjustment bolt 520.

  As shown in FIG. 2, the die 20 includes a flow path gap control unit 600 that can adjust the size of the gap of the third adjustment flow path part 333. Similar to the channel clearance control unit 500, the channel clearance control unit 600 includes a choke bar 610 and an adjustment bolt 620. For this reason, the channel clearance control unit 600 can adjust the size of the clearance of the third adjustment channel unit 333 for each position in the channel width direction in the same manner as the first adjustment channel unit 133. Therefore, it has the structure which can suppress the thickness nonuniformity of the 3rd layer in the width direction.

  Each adjustment bolt 620 includes a rod-shaped electric heater 630 similar to the electric heater 530 as a heater that can adjust the temperature of the third adjustment flow path portion 333. For this reason, the flow path gap control unit 600 can adjust the choke bar 610 to a desired temperature for each position in the longitudinal direction, and thus can precisely adjust the temperature distribution in the flow path width direction of the third adjustment flow path unit 333. The composition is being transported. Therefore, since the die 20 can adjust the flow rate of the molten resin flowing through the third adjustment channel portion 333 for each position in the channel width direction, the die 20 has a configuration that can adjust the thickness of the third layer of the multilayer film more precisely. doing.

  Further, as shown in FIG. 2, the die 20 includes a lip adjustment bolt 700 as a flow path gap control unit that can adjust the size of the gap of the lip part 430. The lip adjustment bolt 700 is movably provided. The tip of the lip adjusting bolt 700 is disposed in the vicinity of the lip portion 430. Further, a plurality of lip adjustment bolts 700 are provided at predetermined intervals in the flow path width direction of the lip portion 430. For this reason, the die 20 can adjust the size of the gap of the lip portion 430 for each position in the flow path width direction by moving the lip adjustment bolt 700, and consequently the size of the gap of the lip portion 430 in the flow path width direction. It has the structure which can adjust the distribution of thickness.

  Thus, by adjusting the distribution of the size of the gap between the lip portions 430, the resistance of the molten resin flowing through the lip portion 430 can be adjusted for each position in the flow path width direction. Therefore, in the lip portion 430, the flow rate of the molten resin can be adjusted for each position by adjusting the distribution of the size of the gap. Therefore, the die 20 has a configuration capable of adjusting the thickness of the molten resin discharged from the lip portion 430 and thus adjusting the total thickness of the multilayer film.

(Operation for producing multilayer film)
In the manufacturing method according to an embodiment of the present invention, a multilayer film is manufactured by coextrusion using the die 20.
Specifically, using an extruder (not shown), the first layer forming molten resin, the second layer forming molten resin, and the third layer forming molten resin are respectively supplied to the first supply path 110. The first manifold 120, the second manifold 220 and the third manifold 320 are supplied via the second supply path 210 and the third supply path 310.

The molten resin supplied to the first manifold 120 is expanded in the flow path width direction in the first manifold 120 and then sent to the first flow path 130. The molten resin sent to the first flow path 130 passes through the first flow path 130 including the first preland 131 and the first adjustment flow path portion 133 and is sent to the merge portion 410.
The molten resin supplied to the second manifold 220 is expanded in the flow path width direction in the second manifold 220 and then sent to the second flow path 230. The molten resin sent to the second flow path 230 passes through the second flow path 230 including the second preland 231 and is sent to the junction 410.
Furthermore, the molten resin supplied to the third manifold 320 is expanded in the flow path width direction in the third manifold 320 and then sent to the third flow path 330. The molten resin sent to the third flow path 330 passes through the third flow path 330 including the third pre-land 331 and the third adjustment flow path portion 333 and is sent to the merge portion 410.

The molten resin for forming the first layer, the molten resin for forming the second layer, and the molten resin for forming the third layer that are sent to the merging portion 410 merge at the merging portion 410. The joined molten resin is superposed in layers. Thereafter, these molten resins flow through the merge channel 420 while maintaining the layer state.
The molten resin that has flowed through the merging channel 420 is continuously discharged from the lip portion 430 while maintaining the layer state.
Then, the discharged molten resin is cooled and cured to obtain a multilayer film.

In the manufacturing method described above, the adjustment bolts 520 and 620 allow the gap size A _{C1 of} the first adjustment channel portion 133 and the gap size A _C3 of the third adjustment channel portion 333 to fall within the above ranges. Adjust as follows. Thereby, in the multilayer film manufactured, the thickness nonuniformity of a 1st layer and a 3rd layer can be made small in the width direction.

  Moreover, in the manufacturing method mentioned above, the magnitude | size of the clearance gap in each point of the width direction of the 1st adjustment flow path part 133 and the 3rd adjustment flow path part 333 is adjusted with the some adjustment bolt 520 and 620. FIG. Specifically, in the multilayer film to be manufactured, adjustment is performed so that thickness unevenness in the width direction of the first layer and the third layer is reduced. Thereby, the thickness unevenness of the first layer and the third layer can be further reduced in the width direction.

  Furthermore, in the manufacturing method described above, the electric heaters 530 and 630 adjust the temperature at each point in the width direction of the first adjustment channel portion 133 and the third adjustment channel portion 333. Thereby, the thickness unevenness of the first layer and the third layer of the multilayer film can be particularly effectively reduced in the width direction.

  At this time, the rough adjustment of the thicknesses of the first layer and the third layer is preferably performed by adjusting the size of the gap between the first adjustment channel portion 133 and the third adjustment channel portion 333. Moreover, it is preferable to perform fine adjustment of the thicknesses of the first layer and the third layer by adjusting the temperatures of the first adjustment channel portion 133 and the third adjustment channel portion 333. While precise adjustment of the size of the gap in the flow path is complicated, precise adjustment of the temperature is easy.

  In the manufacturing method described above, the size of the gap at each point in the width direction of the lip portion 430 is adjusted by the lip adjusting bolt 700. Specifically, adjustment is performed so that the total thickness of the multilayer film to be manufactured becomes a desired size. Thereby, the total thickness of a multilayer film can be adjusted easily.

  The multilayer film 10 shown in FIG. 1 can be manufactured by the method as described above. In the manufactured multilayer film 10, the thickness unevenness of the 1st layer 11 and the 3rd layer 13 which are outermost layers can be made small. Further, since the thickness unevenness of the first layer 11 and the third layer 13 is reduced, the thickness unevenness caused by the thickness unevenness of the first layer 11 and the third layer 13 is suppressed in the second layer 12. The thickness unevenness of the second layer 12 sandwiched between the first layer 11 and the third layer 13 is also reduced. Therefore, according to the above-described embodiment, it is possible to obtain the multilayer film 10 having small thickness unevenness and excellent thickness accuracy in any of the first layer 11, the second layer 12, and the third layer 13.

[2. Other Embodiments]
The present invention is not limited to the above-described embodiment, and may be further modified.
For example, in the above-described embodiment, an electric heater provided as a heater along the first supply path 110, the first manifold 120, and the first flow path 130 in the die body 100; the second supply path 210, the second An electric heater provided along the manifold 220 and the second flow path 230; an electric heater provided along the third supply path 310, the third manifold 320, and the third flow path 330 may be provided. The shape of these electric heaters is not particularly limited, and examples thereof include a plate shape and a columnar shape. When a cylindrical electric heater is used, the diameter of the electric heater is preferably 15 mm to 25 mm. Moreover, when using a plate-shaped electric heater, the thickness of the electric heater is preferably 15 mm to 25 mm.

  Further, for example, in addition to the electric heater described above, an electric heater that can adjust the temperature of the entire die body 100 may be provided on the outer periphery of the die body 100.

  Further, for example, an electric heater may be provided in the lip adjustment bolt 700 in the same manner as the electric heater 530. Thereby, the temperature of the molten resin in the lip part 430 can be adjusted. Further, by adjusting the temperature of the lip adjusting bolt 700 with an electric heater, the lip adjusting bolt 700 may be expanded and contracted, and the size of the gap of the lip portion 430 may be adjusted by this expansion and contraction.

  For example, a heater other than an electric heater may be used as the heater. Examples of such a heater include a heat transfer device using oil circulation.

  In addition, for example, surface treatment such as H—Cr plating may be performed on the surfaces of the first flow path 130, the second flow path 230, the third flow path 330, the merge portion 410, and the merge flow path 420. By applying H—Cr plating, the lip portion 430 can be made smooth when the shape of the lip portion 430 is formed by polishing. Therefore, die line can be effectively prevented. Moreover, adhesion of the molten resin to the surfaces of the first flow path 130, the second flow path 230, the third flow path 330, the merging portion 410, and the merging flow path 420 can be suppressed. Thereby, reduction of die line and further reduction of thickness unevenness can be expected. Here, the die line refers to irregularly formed linear recesses and linear projections extending in the MD direction of the manufactured multilayer film.

  Further, for example, the surface of the lip portion 430 may be subjected to a surface treatment such as a ceramic coat. By applying the ceramic coat, adhesion of the molten resin to the surface of the lip portion 430 can be suppressed. Thereby, reduction of die line and further reduction of thickness unevenness can be expected.

  Further, for example, two or more first adjustment flow path portions 133 may be provided in the first flow path 130, and two or more third adjustment flow path portions 333 may be provided in the third flow path 330.

  Further, for example, an adjustment channel portion may be provided in the second channel 230 in the same manner as the first adjustment channel portion 133 and the third adjustment channel portion 333.

  Furthermore, although the example which manufactures the multilayer film 10 which has three layers was shown in embodiment mentioned above, if the multilayer film of this invention is equipped with the 1st layer and the 2nd layer at least, the 3rd layer will be It does not necessarily have to be provided. The multilayer film including only the first layer and the second layer is, for example, the die 20 described in the above-described embodiment except that the third supply path 310, the third manifold 320, and the third flow path 330 are not included. It can be manufactured by using a die having the same configuration. Furthermore, the multilayer film of the present invention may be a multilayer film of four or more layers that further includes layers in addition to the first layer, the second layer, and the third layer.

  Moreover, you may give an arbitrary process further to the multilayer film mentioned above. For example, you may perform the process of providing arbitrary layers on the surface of a multilayer film. Examples of the optional layer include a mat layer, a hard coat layer, an antireflection layer, and an antifouling layer.

  Furthermore, for example, a step of performing a stretching process on the multilayer film may be performed. By performing the stretching treatment, retardation can be expressed in the multilayer film, so that the multilayer film can be used as a retardation film. In this case, as a stretching method, for example, a uniaxial stretching method such as a method of uniaxial stretching in the longitudinal direction using a difference in peripheral speed of a roll, a method of uniaxial stretching in a transverse direction using a tenter stretching machine; Examples thereof include a biaxial stretching method such as a stretching method and a sequential biaxial stretching method; a method of stretching obliquely using a tenter stretching machine. Here, the diagonal direction represents a direction not parallel to both the vertical direction and the horizontal direction.

  In the retardation film obtained by subjecting the multilayer film to stretching, the thickness of the layer included in the retardation film is thinner than the layer included in the multilayer film before stretching, by the stretched amount. . For example, among the layers contained in the retardation film, the average thickness of the layer formed by stretching the first layer is usually 0.1 μm or more, preferably 0.3 μm or more, more preferably 0.5 μm or more. It is 10.0 μm or less, preferably 7.0 μm or less, more preferably 5.0 μm or less. Since the thickness unevenness of the first layer is small in the multilayer film of the present invention, even in such a thin layer obtained by stretching the first layer, the thickness unevenness in the width direction is suppressed to the small range as described above. Is possible.

  The in-plane retardation of the retardation film can be set according to the use of the retardation film. For example, the in-plane retardation of the retardation film may be 50 nm or more, 70 nm or more, or 100 nm or more, or 300 nm or less, 250 nm or less, or 200 nm or less.

[3. Description of resin]
All of the layers such as the first layer, the second layer, and the third layer included in the multilayer film are layers formed of a resin. As such a resin, a thermoplastic resin is usually used.
As the thermoplastic resin, a resin having a positive intrinsic birefringence may be used, a resin having a negative intrinsic birefringence may be used, and a resin having a positive intrinsic birefringence and a resin having a negative intrinsic birefringence are combined. May be used. Among them, from the viewpoint of obtaining various optical characteristics by combining a plurality of layers, one of the first layer and the second layer of the multilayer film is formed of a resin having a positive intrinsic birefringence, and the other has a negative intrinsic birefringence. It is preferable to form with resin. In general, a resin having a positive intrinsic birefringence has a higher mechanical strength than a resin having a negative intrinsic birefringence. Therefore, the first layer having a smaller thickness than the second layer is made of a resin having a positive intrinsic birefringence. It is preferable to form.

  The resin having a positive intrinsic birefringence usually contains a polymer having a positive intrinsic birefringence. Examples of this polymer include olefin polymers such as polyethylene and polypropylene; polyester polymers such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfide polymers such as polyphenylene sulfide; polyvinyl alcohol polymers, polycarbonate polymers, poly Examples include arylate polymers, cellulose ester polymers, polyethersulfone polymers, polysulfone polymers, polyallyl sulfone polymers, polyvinyl chloride polymers, norbornene polymers, and rod-like liquid crystal polymers. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The polymer may be a homopolymer or a copolymer.

  Among these, a polycarbonate polymer is preferable from the viewpoints of retardation development, low-temperature stretchability, and adhesion between a resin layer having positive intrinsic birefringence and other layers. As the polycarbonate polymer, any polymer having a structural unit containing a carbonate bond (—O—C (═O) —O—) can be used. Examples of the polycarbonate polymer include bisphenol A polycarbonate, branched bisphenol A polycarbonate, o, o, o ', o'-tetramethylbisphenol A polycarbonate, and the like.

  The resin having a negative intrinsic birefringence usually includes a polymer having a negative intrinsic birefringence. Examples of this polymer include an aromatic vinyl polymer including a homopolymer of styrene or a styrene derivative, and a copolymer of styrene or a styrene derivative and any other monomer; a polyacrylonitrile polymer; a polymethyl A methacrylate polymer; or a multi-component copolymer thereof. Moreover, as said arbitrary monomer which can be copolymerized with styrene or a styrene derivative, acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene are mentioned as a preferable thing, for example. Moreover, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Among these, an aromatic vinyl polymer is preferable from the viewpoint of high retardation development, and a copolymer of styrene or a styrene derivative and maleic anhydride is particularly preferable from the viewpoint of high heat resistance. In this case, the amount of the structural unit (maleic anhydride unit) having a structure formed by polymerizing maleic anhydride is preferably 5 parts by weight or more, more preferably 100 parts by weight of the aromatic vinyl polymer. It is 10 parts by weight or more, particularly preferably 15 parts by weight or more, preferably 30 parts by weight or less, more preferably 28 parts by weight or less, and particularly preferably 26 parts by weight or less.

  The resin may contain a compounding agent. Examples of compounding agents include anti-blocking agents; layered crystal compounds; antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, UV absorbers, near-infrared absorbers and other stabilizers; plasticizers; dyes and pigments And coloring agents such as antistatic agents. Especially, since an antiblocking agent and an ultraviolet absorber can improve a conveyance property and a weather resistance, they are preferable. Moreover, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the anti-blocking agent include inorganic particles such as silicon dioxide, titanium dioxide, magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, strontium sulfate; polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, cellulose acetate, cellulose Organic particles such as acetate propionate; and the like. Among these, organic particles are preferable as the antiblocking agent.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, acrylonitrile ultraviolet absorbers, triazine compounds, nickel complex compounds. And inorganic powders. Specific examples of suitable UV absorbers include 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) ) Phenol, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone and the like. Particularly suitable is 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol).

  The amount of the compounding agent can be appropriately determined as long as the effects of the present invention are not significantly impaired. For example, the amount of the compounding agent may be within a range in which the total light transmittance in terms of 1 mm thickness of the multilayer film can maintain 80% or more.

  The weight average molecular weight of the resin is preferably adjusted to a range in which the melt extrusion method can be performed with the resin.

  The glass transition temperature Tg of the resin is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, still more preferably 100 ° C. or higher, particularly preferably 110 ° C. or higher, and particularly preferably 120 ° C. or higher. When the glass transition temperature Tg of the resin is thus high, the orientation relaxation of the resin can be reduced when the multilayer film is stretched. Moreover, although there is no restriction | limiting in particular in the upper limit of glass transition temperature Tg, Usually, it is 200 degrees C or less.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. Moreover, the following operation was performed in normal temperature normal pressure atmosphere unless otherwise indicated.

[Evaluation method]
(Measuring method of average thickness of layers contained in multilayer film)
The multilayer film is arranged in a flat state, and the thickness of each layer included in the multilayer film is determined by scanning the interference film thickness meter ("FE-2900" manufactured by Otsuka Electronics Co., Ltd.) in the width direction of the multilayer film. It was measured. The measurement interval in the width direction of the multilayer film was 5 mm. And the average value of the thickness of the layer in each measurement point was made into the average thickness of the layer.

(Measurement method of layer thickness unevenness)
The maximum value and the minimum value were selected from the thicknesses of the plurality of measurement points of each layer measured as described above, and the difference between the maximum value and the minimum value was calculated. The difference between the obtained maximum value and the minimum value was divided by the average thickness of the layer to determine the thickness unevenness in the width direction. The smaller the thickness unevenness, the better the thickness accuracy of the layer.

[Example 1]
As the thermoplastic resin for forming the first layer and the thermoplastic resin for forming the third layer, pellets of polycarbonate resin (“Wonderlite PC-115” manufactured by Chi Mei, glass transition temperature 140 ° C.) were prepared.
Further, as the thermoplastic resin for forming the second layer, styrene-maleic anhydride copolymer resin (Nova Chemicals “Dylark D332”, glass transition temperature 135 ° C.) and polymethyl methacrylate resin (Asahi Kasei “Delpet 80NH”) are used. And pellets having a glass transition temperature of 110 ° C. were mixed at a weight ratio of 85:15.

  A film forming apparatus for three-layer / three-layer coextrusion molding was prepared. This film forming apparatus is a type of apparatus that forms a film composed of three layers with resin extruded by three different extruders. In this film molding apparatus, a die having the same configuration as that described in the above-described embodiment was attached as a die. The surface roughness Ra of the lip portion of this die was 0.1 μm.

For formation of the first layer, the polycarbonate resin pellets were put into a first single screw extruder equipped with a double flight type screw and melted.
In addition, for forming the second layer, the pellet obtained by mixing the pellet of the styrene-maleic anhydride copolymer resin and the pellet of the polymethyl methacrylate resin is put into a second single-screw extruder equipped with a double flight type screw. It was charged and melted.
Further, for forming the third layer, the pellets of the polycarbonate resin were put into a third single screw extruder equipped with a double flight type screw and melted.

  The melted polycarbonate resin for forming the first layer at 260 ° C. was supplied to the first manifold of the die through a leaf filter-shaped polymer filter having an opening of 10 μm. Further, the molten styrene-maleic anhydride copolymer resin for forming the second layer at 260 ° C. and the polymethylmethacrylate resin mixed resin are passed through a polymer filter in the shape of a leaf disk having an opening of 10 μm, and the second of the die. Supplied to the manifold. Further, the molten polycarbonate resin for forming the third layer at 260 ° C. was supplied to the third manifold of the die through the leaf disk-shaped polymer filter having an opening of 10 μm.

A mixed resin of a styrene-maleic anhydride copolymer resin and a polymethyl methacrylate resin and a polycarbonate resin were simultaneously extruded from the aforementioned die at 260 ° C. to obtain “a first layer made of a polycarbonate resin” / “styrene-maleic anhydride malee”. A film-like molten resin having a three-layer structure including a “second layer made of a mixed resin of an acid copolymer resin and a polymethyl methacrylate resin” / “a third layer made of a polycarbonate resin” was obtained. At this time, in the die, the ratio A _C1 / A _L of the gap size A _C1 of the first adjustment flow path portion to the gap size A _L of the lip portion was set to 1.2. The ratio _A C3 / _{A L} of the gap size _{A C3} of the third adjustment channel unit to the size _{A L} of the gap between the lip was set at 1.6.

The film-shaped molten resin is cast on a cooling roll adjusted to a surface temperature of 130 ° C., and then cured by passing between two cooling rolls adjusted to a surface temperature of 120 ° C. Got. The width direction both ends of this multilayer film were removed, and the width was 1400 mm.
The average thickness of the layers contained in the obtained multilayer film and the thickness unevenness in the width direction were measured as described above.

[Example 2]
The extrusion amount of the polycarbonate resin forming the first layer and the third layer was changed.
A multilayer film was produced and evaluated in the same manner as in Example 1 except for the above items.

[Example 3]
The multilayer film obtained in Example 1 was supplied to a tenter transverse uniaxial stretching machine and stretched in the transverse direction at a stretching temperature of 155 ° C. and a stretching ratio of 3.0 times to produce a retardation film. The retardation film thus obtained was evaluated in the same manner as in Example 1.

[Comparative Example 1]
A die having the same configuration as the die used in Example 1 was used except that the first adjustment channel portion and the third adjustment channel portion were not provided. Therefore, the die used in Comparative Example 1, the size of the gap of the first flow path, at any position of the first flow path was greater than 3.0 times the size A _L of the gap of the lip portion. Furthermore, the die used in Comparative Example 1, the size of the gap of the third flow path, at any position of the third flow passage, greater than 3.0 times the size A _L of the gap of the lip portion. Thus, the multilayer film was manufactured and evaluated like Example 1 except having changed the die | dye to be used.

[Comparative Example 2]
The extrusion amount of the polycarbonate resin forming the first layer and the third layer, and the extrusion amount of the mixed resin of the styrene-maleic anhydride copolymer resin and the polymethyl methacrylate resin forming the second layer were respectively changed.
A multilayer film was produced and evaluated in the same manner as Comparative Example 1 except for the above items.

[result]
The results of the examples and comparative examples are shown in Table 1. In Table 1, PC indicates a polycarbonate resin, and St-Ma indicates a mixed resin of a styrene-maleic anhydride copolymer resin and a polymethyl methacrylate resin.

[Consideration]
In the production of a multilayer film by a coextrusion method, it is generally required to precisely control the thickness of each layer. In the conventional extrusion technique, it has been common to try to make the thickness of each layer uniform by designing a die manifold and a preland according to the flow rate and viscosity of each resin. However, in actual industrial production, the resin rarely flows as designed. Further, if there is a slight variation in the temperature of the resin, the layer thickness is often not uniform.

  In the case of a single layer film composed of a single layer, it may be possible to attempt adjustment with the lip portion of the die. However, in a multilayer film having two or more layers, it is possible to increase the accuracy of the total thickness of the multilayer film by adjusting the lip portion, but increase the thickness accuracy of each layer included in the multilayer film. It ’s difficult. Among them, in a multilayer film including a combination of a thin layer having an average thickness of 5 μm or less and a layer having an average thickness larger than that, even when a technique such as Patent Document 1 is used, It was particularly difficult to increase the thickness accuracy.

  On the other hand, from Table 1, if the ratio of the size of the gap of the adjustment flow path portion to the size of the gap of the lip portion in the die is set to a predetermined value or less, the thickness unevenness in the width direction is reduced in the thin layer having the average thickness. You can see that it can be made smaller. From this, according to the present invention, it comprises a first layer having an average thickness T1 of 5 μm or less, and a second layer having an average thickness T2 that satisfies a ratio T1 / T2 of 1/300 or more and 1/20 or less, and It was confirmed that a multilayer film in which the first layer thickness unevenness was within ± 5% could be realized.

DESCRIPTION OF SYMBOLS 10 Multilayer film 11 1st layer 12 2nd layer 13 3rd layer 20 Die 100 Die main body 110 1st supply path 120 1st manifold 130 1st flow path 131 1st preland 132 Immediately downstream of 1st preland of 1st flow path Part 133 First adjustment channel part 134 Part immediately upstream of the first adjustment channel part of the first channel 135 Part downstream of the first adjustment channel part of the first channel 210 Second supply path 220 Second manifold 230 Second flow path 231 Second preland 232 Second downstream area of second preland 310 Third supply path 320 Third manifold 330 Third flow path 331 Third preland 332 Third flow path of third preland Immediately downstream portion 333 Third adjustment flow path portion 334 Third flow adjustment portion of third flow path immediately upstream 410 Merge portion 420 Merge flow channel 430 Lip part 500,600 Channel clearance control part 510,610 Choke bar 520,620 Adjustment bolt 530,630 Electric heater 700 Lip adjustment bolt

Claims (9)

A first manifold that can be supplied with a molten resin for forming the first layer;
A first flow path having an adjustment flow path section extending downstream from the first manifold;
A second manifold that can be supplied with a molten resin for forming the second layer;
A second flow path extending downstream from the second manifold;
A merge portion where the first flow path and the second flow path merge;
A merge channel extending downstream from the merge section;
A lip portion formed downstream of the merging channel and capable of continuously discharging the molten resin for forming the first layer and the molten resin for forming the second layer merged at the merging portion;
By co-extrusion with a die provided with a manufacturing method for manufacturing a multilayer film of Ru with a first layer and a second layer,
The average thickness T1 of the first layer is 0.5 μm or more and 5.0 μm or less,
The ratio T1 / T2 between the average thickness T1 of the first layer and the average thickness T2 of the second layer is 1/300 or more and 1/20 or less,
The thickness unevenness of the first layer state, and are within ± 5%,
The manufacturing method of a multilayer film which can adjust the flow volume of the molten resin for said 1st layer formation in the said adjustment flow path part in the said adjustment flow path part . The method for producing a multilayer film according to claim 1 , wherein the multilayer film further comprises a third layer. The manufacturing method of the multilayer film of Claim 2 whose ratio T3 / T2 of the average thickness T3 of said 3rd layer and the average thickness T2 of said 2nd layer is 1/10 or more and 1/3 or less. The ratio of the adjustment channel section the size of the gap to the size of the gap before Symbol lip portion is 3.0 or less,
The manufacturing method is
Supplying molten resin for forming the first layer to the first manifold;
Supplying molten resin for forming the second layer to the second manifold; and
The multilayer film according to any one of claims 1 to 3, comprising continuously discharging the molten resin for forming the first layer and the molten resin for forming the second layer from the lip portion. Manufacturing method. Before Symbol dice,
A third manifold capable of supplying a molten resin for forming the third layer;
A third flow path extending downstream from the third manifold ,
In the merging section, the first channel, the second channel and the third flow path is merged,
The lip portion can continuously discharge the molten resin for forming the first layer, the molten resin for forming the second layer, and the molten resin for forming the third layer, which merged at the merging portion ,
The ratio of the adjustment channel section the size of the gap to the size of the gap before Symbol lip portion is 3.0 or less,
The manufacturing method is
Supplying molten resin for forming the first layer to the first manifold;
Supplying molten resin for forming the second layer to the second manifold;
Supplying molten resin for forming the third layer to the third manifold; and
Molten resin for the first layer formed from said lip comprises, be continuously discharged molten resin and the molten resin for the third layer forming for the second layer formed, according to claim 2 or 3, wherein A method for producing a multilayer film. The first layer is formed of a resin having a positive intrinsic birefringence.
  The method for producing a multilayer film according to any one of claims 1 to 5, wherein the second layer is formed of a resin having a negative intrinsic birefringence. The method for producing a multilayer film according to claim 2, wherein the third layer is formed of a resin having a positive intrinsic birefringence. Producing a multilayer film by the production method according to any one of claims 1 to 7 ,
It said containing and facilities Succoth stretching treatment in multilayer film, method for producing a retardation film. The method for producing a retardation film according to claim 8 , wherein an average thickness of a layer formed by stretching the first layer is 0.1 μm or more and 3.0 μm or less.

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