Die, multi-layer extrusion molding device, and manufacturing method

Abstract

To provide a die, a multilayer extrusion molding apparatus, and a manufacturing method, for manufacturing a multilayer film, capable of effectively adjusting a thickness-ratio profile, and capable of easily changing a resin material and a thickness ratio.SOLUTION: A die for manufacturing a multilayer film provided with an outermost layer (A), an outermost layer (B), and one or more inner layers (C) provided between the outermost layers (A) and (B) comprises: a manifold (A) for the outermost layer that expands the width of a molten resin material (A); a manifold (B) for the outermost layer that expands the width of a molten resin material (B); a manifold (C) for the inner layer that expands the width of a molten resin material (C); a plurality of heaters (A) positioned at the outer side than the manifold (A); a plurality of heaters (B) positioned at the outer side than the manifold (B); a heat insulator (A) positioned between the manifold (C) and the heaters (A); and a heat insulator (B) positioned between the manifold (C) and the heaters (B).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a die and a multilayer extrusion molding apparatus that can be used in the production of a multilayer film, and to a method for producing a multilayer film and a multilayer stretched film. [Background technology]

[0002] Multilayer extrusion molding devices including a multi-manifold die are known as devices for producing multilayer films. A multi-manifold die is a die having multiple manifolds. In the technical field, a manifold is a structure inside the die that widens the flow path of the molten resin material passing through it. When using a device including a multi-manifold die, multiple types of molten resin materials are supplied from an extruder to each of the multiple manifolds. In each manifold, the flow path of the molten resin material is widened. The multiple flow paths then merge to form a flow in which the multiple molten resin materials form layers. The flow of the molten resin material then reaches the die lip, and the multiple molten resin materials are extruded from the die lip in a layered state. The extruded molten resin material is subjected to any operation such as cooling or stretching, and then becomes a multilayer film.

[0003] When producing a multilayer film using a multi-manifold die, it is necessary to ensure that the thickness ratio of each layer is the desired value and is uniform with little variation. When producing a multilayer film for optical applications, particularly strict control of the thickness ratio is required. Furthermore, when continuously producing a long multilayer film using a die, it is necessary to accurately control the thickness of each layer in the width direction of the film. As a means for controlling the width direction of a film, it has been proposed to independently control the temperature at various locations along the flow path of the molten resin material in the die using multiple heaters (see, for example, Patent Documents 1 and 2). For example, if the thickness of a certain layer in a certain region of the entire width direction of a multilayer film produced on a certain production line is thinner than the desired thickness, the corresponding flow path position can be heated by a heater located near the flow path position. This heating can partially accelerate the flow rate of the molten resin material at that flow path position, thereby controlling the production process to increase the thickness of that region. Such thickness ratio adjustment using a heater can be performed not only at the start-up of the production process using a multilayer extrusion molding device, but also as feedback during the production process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-188018 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-231763 Summary of the Invention [Problem to be solved by the invention]

[0005] While the previously proposed methods of controlling the temperature inside the die using a heater have been effective in reducing thickness variations in a narrow portion of the entire width direction of the multilayer film, they have had difficulty correcting thickness ratio profiles with significant differences in relative thickness across the entire width direction of the multilayer film or across a wide region close to that. For example, in the production of a multilayer film comprising an outermost layer (A), an outermost layer (B), and one or more inner layers (C) disposed between the outermost layers (A) and (B), if a profile is measured in which the thickness of the inner layer (C) is thick in the width direction center and thin at the width direction edges, resulting in a large difference in the thickness ratio between the center and the edges, controlling the heater to increase the thickness of the inner layer(s) over a fairly wide region in the width direction center may not produce the desired results.

[0006] Such thickness ratio profiles, in which the relative thickness varies significantly across a wide region of the multilayer film in the width direction, can be adjusted using other mechanisms provided in the die. For example, adjustments can be made using a mechanism called a choke bar located downstream of the manifold. The choke bar mechanically adjusts the thickness width of the flow channels so that each region in the width direction varies. Adjustments using such a mechanism can be effective at the start-up of the manufacturing process. However, when adjustments are made using a mechanism such as a choke bar that directly and mechanically changes the width of the flow channels as feedback during the manufacturing process, problems such as die lines frequently occur on the film. Therefore, when adjustments are made using a mechanism such as a choke bar, a procedure such as restarting the manufacturing process to stabilize production may be necessary.

[0007] A thickness ratio profile with significant differences in relative thickness across a wide region of a multilayer film's width can occur when the type of resin material used in the film's production is changed. For example, in the production of a multilayer film comprising an outermost layer (A), an outermost layer (B), and an inner layer (C), a certain resin material is used to construct each layer. The thickness ratio profile may be adjusted using a chalk bar, the production process may be started, and the film may then be produced using a different resin material. In such cases, simply changing the resin material can significantly change the thickness ratio profile due to differences in the physical properties of the resin material. In such cases, the chalk bar adjustment must be repeated. This creates the problem of having to restart the process, which involves adjusting using a chalk bar, every time the resin material is changed, making it difficult to produce a wide variety of multilayer films in small quantities.

[0008] Furthermore, due to product design requirements and other circumstances, it may be necessary to change the thickness ratio of a multilayer film from the thickness ratio used in previous production. A slight change in the thickness ratio can be easily achieved by changing production conditions, such as adjusting the pressure ratio of the molten resin material supplied to the die and adjusting the temperature inside the die using a heater. However, a significant change in the thickness ratio may result in a thickness ratio profile with significant differences in relative thickness across a wide region in the width direction of the multilayer film. In such cases, adjustments involving a restart of the process, such as the adjustment using the choke bar described above, may be required. Even in such cases, the problem of difficulty in producing a wide variety of multilayer films in small quantities arises.

[0009] Therefore, an object of the present invention is to provide a die, a multilayer extrusion molding apparatus, and a manufacturing method for producing a multilayer film that can effectively adjust the thickness ratio profile, which has significant relative thickness differences over a wide region in the width direction of the multilayer film, and that can easily change the resin material and thickness ratio. [Means for solving the problem]

[0010] The present inventors have conducted research to solve the above problems, and as a result, have found that the above problems can be solved by placing a heat insulating material at a specific position on the die, and have completed the present invention. That is, the present invention provides the following.

[0011] [1] A die for producing a multilayer film having an outermost layer (A), an outermost layer (B), and one or more inner layers (C) provided between the outermost layers (A) and (B), an outermost layer manifold (A) for expanding and extruding the molten resin material (A) that is the material for the outermost layer (A); an outermost layer manifold (B) for expanding and extruding the molten resin material (B) that is the material for the outermost layer (B); an inner layer manifold (C) positioned inside the manifolds (A) and (B) for expanding and extruding the molten resin material (C) that is the material for the inner layer (C); a plurality of heaters (A) positioned outside the manifold (A) and aligned in the width direction of the die; a plurality of heaters (B) positioned outside the manifold (B) and aligned in the width direction of the die; a heat insulating material (A) located upstream of the manifold (A) and between the manifold (C) and the heater (A) in the thickness direction; and a heat insulating material (B) located upstream of the manifold (B) and between the manifold (C) and the heater (B) in the thickness direction; Equipped with dice. [2] The die comprises a block (A), a block (B), and a block (C), The block (A) has a surface (Ac) facing the block (C), The block (B) has a surface (Bc) facing the block (C), the block (C) has a surface (Ca) facing the block (A) and a surface (Cb) facing the block (B), a part or the whole of the manifold (A) is defined by a recess provided in one or both of the surface (Ac) and the surface (Ca), the manifold (B) is partially or entirely defined by a recess provided in one or both of the surface (Bc) and the surface (Cb), The heat insulating material (A) is provided between the surface (Ac) and the surface (Ca), The die according to [1], wherein the heat insulating material (B) is provided between the surface (Bc) and the surface (Cb). [3] The die according to [1] or [2], a measuring device that measures the thickness of one or more layers of the multilayer film extruded from the die at a plurality of locations aligned in the width direction of the multilayer film; a temperature control device that controls the temperatures of the heaters (A) and (B) based on the thickness measured by the measuring device; A multi-layer extrusion molding apparatus comprising: [4] A method for producing a multilayer film, comprising: A step (I) of supplying each of the molten resin materials (A) to (C) to the manifolds (A) to (C) of the die according to [1] or [2], widening the flow paths of each, and pumping the molten resin materials from each of the manifolds (A) to (C) to a joining position; and a step (II) of joining the molten resin materials (A) to (C) at the joining position and extruding the molten resin materials from the lip of the die as a flat outflow having a plurality of layers; The step (I) further includes a step (I-1) of independently heating a flow path for the molten resin material (A) from outside the manifold (A) using a plurality of the heaters (A), and independently heating a flow path for the molten resin material (B) from outside the manifold (B) using a plurality of the heaters (B). [5] A step (III) of measuring the thickness of one or more layers of the produced multilayer film at multiple locations aligned in the width direction of the multilayer film; and a step (IV) of adjusting heating conditions by the heater (A) and the heater (B) in the step (I-1) based on the thickness of the one or more layers measured in the step (III). [4] A method for producing a multilayer film according to [4]. [6] A step of producing a multilayer film by the method for producing a multilayer film according to [4] or [5]; and stretching the multilayer film A method for producing a multilayer stretched film, comprising: [Effects of the Invention]

[0012] According to the present invention, a die, a multilayer extrusion molding apparatus, and a manufacturing method for producing a multilayer film are provided that can effectively adjust the thickness ratio profile, which has significant relative thickness differences across a wide region in the width direction of the multilayer film, and that can easily change the resin material and thickness ratio. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a die of the present invention. [Figure 2] FIG. 2 is a longitudinal cross-sectional view showing the die shown in FIG. 1 cut along the line 1a. [Figure 3] FIG. 3 is a side view of the sub-block 110C1 shown in FIGS. 1 and 2, observed from the surface facing the block 110A in a state where the sub-block 110C1 is spaced apart from the block 110A. [Figure 4] FIG. 4 is a side view schematically showing an example of a multi-layer extrusion molding apparatus according to the present invention. [Figure 5] FIG. 5 is a longitudinal cross-sectional view schematically showing a cross section of an example of a long multilayer film produced by the multilayer film production method of the present invention, cut along a plane parallel to the film width direction. [Figure 6] FIG. 6 is a longitudinal cross-sectional view schematically showing a cross section of another example of a long multilayer film produced by the multilayer film production method of the present invention, cut along a plane parallel to the film width direction. [Figure 7] FIG. 7 is a longitudinal cross-sectional view schematically showing a cross section of yet another example of a long multilayer film produced by the multilayer film production method of the present invention, cut along a plane parallel to the width direction of the film. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents.

[0015] In the following description, a "long" film refers to a film having a length that is 5 times or more its width, preferably 10 times or more its width, and specifically refers to a film having a length that can be wound into a roll for storage or transportation. There is no particular upper limit to the length of the film, and it can be, for example, 100,000 times or less its width.

[0016] [Dice] The die of the present invention is a die for producing a multilayer film comprising an outermost layer (A), an outermost layer (B), and one or more inner layers (C) disposed between the outermost layers (A) and (B).

[0017] The die of the present invention includes an outermost layer manifold (A) for expanding and extruding a molten resin material (A) that is the material for the outermost layer (A), an outermost layer manifold (B) for expanding and extruding a molten resin material (B) that is the material for the outermost layer (B), and an inner layer manifold (C) that is located inside the manifolds (A) and (B) and that expands and extrudes a molten resin material (C) that is the material for the inner layer (C).

[0018] In a preferred example, the die of the present invention comprises block (A), block (B), and block (C), block (A) has a face (Ac) facing block (C), block (B) has a face (Bc) facing block (C), block (C) has a face (Ca) facing block (A) and a face (Cb) facing block (B), and manifold (A) is defined, in part or in whole, by a recess provided in one or both of faces (Ac) and (Ca), and manifold (B) is defined, in part or in whole, by a recess provided in one or both of faces (Bc) and (Cb).

[0019] An example of the die of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a perspective view schematically showing an example of the die of the present invention. Figure 2 is a longitudinal sectional view showing a cross section of the die shown in Figure 1 taken along line 1a.

[0020] In Figures 1 and 2, the die 100 is illustrated with the upstream end of the flow path of the molten resin material as the upper side and the downstream end as the lower side. Therefore, the upper and lower sides along the Z axis of the coordinate axes in Figure 1 may be referred to as the upstream direction and the downstream direction, respectively. Furthermore, the X-axis and Y-axis directions of the coordinate axes correspond to the width and thickness directions of the film to be produced, and therefore these directions may be referred to as the width and thickness directions of the die. Furthermore, the inner layer (C) and the side closer to the flow path of the molten resin material (C) used to form the inner layer (C) may be referred to as the inside in the thickness direction, and the farther side may be referred to as the outside in the thickness direction. Furthermore, when clear from the context, the inside and outside in the thickness direction may be simply referred to as the "inside" and "outside."

[0021] The die 100 includes blocks 110A to 110C, which correspond to the above-described blocks (A) to (C). Block 110C includes a pair of sub-blocks 110C1 and 110C2. Block 110A is located adjacent to the side of block 110C facing sub-block 110C1. Block 110B is located adjacent to the side of block 110C facing sub-block 110C2. The die 100 further includes block 110D located below block 110A and sub-block 110C1, and block 110E located below block 110B and sub-block 110C2. However, the present invention is not limited to this. For example, block (A) may be formed as a single unit by including a configuration corresponding to block 110D in addition to block 110A, or block (B) may be formed as a single unit by including a configuration corresponding to block 110E in addition to block 110B.

[0022] The die 100 has inlets 121A, 121B, and 121C on its upper surface. The inlets 121A, 121B, and 121C communicate with manifolds 123A, 123B, and 123C via upstream channels 122A, 122B, and 122C, respectively. The manifolds 123A, 123B, and 123C correspond to the manifolds (A) to (C) described above, respectively. Therefore, these correspond to the flow path for the molten resin material (A) that is the material for the outermost layer (A), the flow path for the molten resin material (B) that is the material for the outermost layer (B), and the flow path for the molten resin material (C) that is the material for the inner layer (C), respectively. Each of the manifolds 123A, 123B, and 123C has a shape that widens the flow path, and communicates with a junction position 131 via downstream flow paths 124A, 124B, and 124C, respectively, where these flow paths join together. The flow paths downstream of the junction position 131 communicate with an opening 132 in the die lip.

[0023] The die lip, i.e., the opening 132 of the die 100 and its surrounding area, may be made of any known material. Specific examples of such materials include ceramic coatings and H-Cr plating on the metal surfaces of the blocks 110D and 110E. Ceramic coatings are preferred from the viewpoints of reducing adhesion of molten resin material, reducing the occurrence of die lines on the multilayer film, and reducing thickness variations in the multilayer film. The opening of the die may be appropriately edge-finished. Examples of edge-finishing include sharp edges and R-finishing. Polishing the lip to prevent die lines can smooth the lip, thereby reducing the occurrence of die lines and suppressing thickness variations.

[0024] In this example, choke bars 129A and 129B are provided midway along the downstream flow paths 124A and 124B for the outermost layers. The choke bars 129A and 129B extend across the entire width of the expanded flow paths 124A and 124C, respectively, and are inserted into recesses 129Ac in sub-block 110C1 and 129Bc in sub-block 110C2, occupying a portion of the space within the recesses. A plurality of bolts 128A and 128B are attached to the choke bars 129A and 129B, respectively. By moving these bolts along their axial directions, the position of the choke bars within the die 100 can be adjusted, thereby adjusting the size of gaps 129Ag and 129Bg between the flow paths 124A and 124B near the choke bars.

[0025] For the sake of simplicity, Fig. 1 shows seven bolts 128B arranged in a row in the width direction as bolts for adjusting one choke bar 129B, but the number of bolts per choke bar is not limited to this and may be, for example, more. By independently adjusting these bolts, the width-wise profile of the ratio of each layer thickness to the multilayer film thickness can be easily and significantly adjusted.

[0026] In the example of die 100, the flow paths of the molten resin material are formed at the interface between the blocks (including the sub-blocks) that make up die 100. Specifically, the flow path from inlet 121A to choke bar 129A is formed at the interface between block 110A and sub-block 110C1, the flow path from inlet 121B to choke bar 129B is formed at the interface between block 110B and sub-block 110C2, the flow path from inlet 121C to junction position 131 is formed at the interface between sub-block 110C1 and sub-block 110C2, and the flow path from junction position 131 to opening 132 is formed at the interface between blocks 110D and 110E. The flow paths formed at the interface between the blocks are defined by recesses provided on one or both surfaces of the two blocks that make up the interface. For example, in die 100, manifold 123A is defined by recess 123Aa on the surface of block 110A facing sub-block 110C1 and recess 123Ac on the surface of sub-block 110C1 facing block 110A. Manifold 123B is defined by recess 123Bb on the surface of block 110B facing sub-block 110C2 and recess 123Bc on the surface of sub-block 110C1 facing block 110B. Manifold 123C is defined by recess 123C1 on the surface of sub-block 110C1 facing sub-block 110C2 and recess 123C2 on the surface of sub-block 110C2 facing sub-block 110C1.

[0027] FIG. 3 is a side view of the sub-block 110C1 shown in FIGS. 1 and 2, viewed from the surface facing the block 110A while separated from the block 110A. This surface corresponds to the surface (Ca) described above. In FIG. 3, the sub-block 110C1 has, in addition to the recesses 123Ac and 129Ac described above, a recess 121Ac corresponding to the inlet 121A, a recess 122Ac corresponding to the upstream flow path 122A, and a recess 124Ac corresponding to the downstream flow path 124A. As indicated by the shapes of these recesses, the flow path has a narrow width in the upstream flow path 122A, but is widened by the manifold 123A to a width that spans almost the entire width of the die 100, and becomes a widened flow path in the downstream flow path 124A. Furthermore, the size of the gap 129Ag is adjusted across the entire width of the downstream flow path 124A by a choke bar 129A inserted into the recess 129Ac. Furthermore, the manifolds 123B and 123C may also be shaped to widen the flow paths to the same width as the manifold 123A.

[0028] [Heater (A) (B)] The die of the present invention further includes a plurality of heaters (A) positioned outside the manifold (A) and a plurality of heaters (B) positioned outside the manifold (B). In the example of die 100, heaters 141A and 141B are provided, corresponding to the heaters (A) and (B) described above. As shown in FIG. 2, heater 141A is positioned outside manifold 123A (i.e., on the side farther from the flow path of molten resin material (C)), and heater 141B is positioned outside manifold 123B. Each of heaters 141A and 141B is embedded in a gap provided on the upper surface of the die below recesses 142A and 142B. Each heater is connected to an appropriate energy supply path (not shown in FIGS. 1 and 2) such as an electric wire, and can generate heat by supplying energy such as electricity from the path, in a temperature-controllable manner.

[0029] In the die 100, a plurality of heaters 141A and 141B are provided. Specifically, the heaters 141A and 141B may be arranged in one or more rows aligned in the die width direction. In the example of the die 100, as shown in FIG. 1, the recesses 142A and 142B are arranged in a row in the width direction on the upper surfaces of the blocks 110A and 110B, respectively, and a heater is provided corresponding to each of these recesses. For simplified illustration, FIG. 1 shows seven recesses per row, but the number of heaters per row is not limited to this and may be greater, for example. A path for supplying energy, such as electricity, to each of the multiple heaters may be provided independently. By independently adjusting these heaters via such a path, the width-wise profile of the ratio of each layer thickness to the multilayer film thickness can be easily and significantly adjusted.

[0030] The heating positions on the flow paths of the molten resin materials (A) and (B) heated by the heaters (A) and (B) can be positions that include the portion expanded by the manifold and part or all of the region downstream thereof. By independently heating such regions on the flow paths in the width direction, the profile of the ratio of each layer thickness to the multilayer film thickness across the width direction can be easily and widely adjusted.

[0031] [Insulating material (A) (B)] The die of the present invention further includes thermal insulators (A) and (B). In the example of die 100, thermal insulators 151A and 151B are provided, which correspond to the above-described thermal insulators (A) and (B). In the example of die 100, thermal insulators 151A and 151B are not present on the plane along line 1a in Fig. 1, and therefore in Fig. 2 they are shown by dashed lines at positions corresponding to the internal positions that exist when viewed from the die width direction.

[0032] The insulating material (A) is provided in a position between the manifold (C) and the heater (A) in the thickness direction of the die. The insulating material (B) is provided in a position between the manifold (C) and the heater (B) in the thickness direction of the die. By providing the insulating materials (A) and (B) in such positions, the thickness ratio profile can be effectively adjusted over a wide region in the width direction of the multilayer film, and the resin material can be easily changed. The mechanism by which these effects are obtained will be described in detail in the explanation of the manufacturing method.

[0033] In a preferred example, the insulating material (A) is provided between the surface (Ac) and the surface (Ca), and the insulating material (B) is provided between the surface (Bc) and the surface (Cb). More specifically, the insulating material (A) may be provided in a recess provided in one or both of the surface (Ac) and the surface (Ca). The insulating material (B) may be provided in a recess provided in one or both of the surface (Bc) and the surface (Cb).

[0034] In the example of the die 100, the heat insulator 151A is provided between the heater 141A and the manifold 123C. The heat insulator 151B is provided between the heater 141B and the manifold 123C. The heat insulator 151A is provided between the surface of the block 110A facing the block 110C (corresponding to the surface (Ac)) and the surface of the block 110C facing the block 110A (corresponding to the surface (Ca))), and the heat insulator 151B is provided between the surface of the block 110A facing the block 110C (corresponding to the surface (Ac)) and the surface of the block 110C facing the block 110A (corresponding to the surface (Ca)).

[0035] In this way, by positioning the insulating materials (A) and (B) at the interface of the blocks, it becomes easy to install the insulating materials (A) and (B) in the die. Furthermore, when it becomes necessary to change the type of insulating materials (A) and (B) or when the insulating materials (A) and (B) need to be replaced due to deterioration, the insulating materials (A) and (B) can be easily accessed by separating the blocks.

[0036] However, the present invention is not limited to this, and the heat insulating materials (A) and (B) may be provided in other positions. For example, from the viewpoint of thermally isolating the manifolds (A) and (C) and the manifolds (B) and (C) and more effectively demonstrating the functions of the heat insulating materials (A) and (B), it is preferable to provide them in more inner positions. Specifically, by providing an appropriate recess or split surface in the block (C), the heat insulating material (A) may be provided between the manifolds (A) and (C), and the heat insulating material (B) may be provided between the manifolds (B) and (C).

[0037] The heat insulating materials (A) and (B) are preferably provided over a wide region in the width direction of the die. Referring to Figure 3, taking heat insulating material 151A as an example, heat insulating material 151A is located at the same position as upstream flow path 122A in the thickness direction, and therefore cannot be located at the same position as upstream flow path 122A in the width direction (this position is indicated by recess 122Ac in Figure 3). However, heat insulating material 151A is located in other width direction regions, extending from the vicinity of the center to the ends. By providing heat insulating materials (A) and (B) over such a wide region in the width direction, the functions of heat insulating materials (A) and (B) can be more effectively exhibited.

[0038] The heat insulating material (A) is provided upstream of the manifold (A). The heat insulating material (B) is provided upstream of the manifold (B). By providing the heat insulating material (A) upstream of the manifold (A) and between the manifold (C) and the heater (A), and providing the heat insulating material (B) upstream of the manifold (B) and between the manifold (C) and the heater (B), it is possible to easily install the heat insulating materials at the interface of the blocks.

[0039] The heat insulating materials (A) and (B) may extend only upstream of the manifold, but if possible, their lower ends may extend to a position at the same height as the manifold or to a position downstream of the manifold.

[0040] The heat insulating materials (A) and (B) are preferably provided over a wide area in the upstream-downstream direction of the die. Taking heat insulating material 151A as an example, referring to Figure 3, heat insulating material 151A extends from near the upper end of the die to directly above manifold 123A (this position is indicated by recess 123Ac in Figure 3). By providing heat insulating materials (A) and (B) over such a wide area in the upstream-downstream direction, the functions of heat insulating materials (A) and (B) can be more effectively exhibited.

[0041] Examples of materials constituting the insulating materials (A) and (B) include cement, calcium silicate, inorganic minerals, etc. The preferred thickness of each of the insulating materials (A) and (B) varies depending on various factors such as the type of material used and the desired thermal insulation properties. When a general insulating material is used, the thickness is preferably 5 mm or more, more preferably 10 mm or more, and is preferably 50 mm or less, more preferably 40 mm or less.

[0042] [Optional Component: Additional Heater] The die of the present invention may include optional components in addition to the components described above. For example, the die of the present invention may include additional heaters other than the heaters (A) and (B) described above. Referring to the die 100 shown in FIGS. 1 to 3, an example of an additional heater that the die 100 may include is a heater provided near the upstream flow paths 122A, 122B, and 122C. In the example of the die 100, such heaters are upstream flow path neighboring heaters 143A and 144B. The upstream flow path is required to smoothly flow a relatively large amount of molten resin material at a higher temperature. By including such an upstream flow path neighboring heater, the smooth flow of such a large amount of molten resin material can be easily achieved.

[0043] The upstream flow path vicinity heaters 143A and 143B are embedded in gaps located below the recesses 144A and 144B on the upper surface of the die. They are connected to an appropriate energy supply path (not shown), such as an electric wire, and can generate heat at a temperature-adjustable level by supplying energy such as electricity through the energy supply path. Unlike the heaters 141A and 141B, the upstream flow path vicinity heaters 143A and 143B are provided only for the purpose of heating the upstream flow path, and therefore do not need to be provided in large numbers across the die. In the example of the die 100, only one upstream flow path vicinity heater 143A and 143B are provided, each at a position corresponding to one of the recesses 144A and 144B shown in FIG. 1.

[0044] Another example of an additional heater that can be provided in the die 100 is a choke bar heater (not shown) provided inside or near the choke bars 129A and 129B or the rods 128A and 128B to heat the flow paths at the positions of the choke bars 129A and 129B. Such a choke bar heater allows the thickness ratio profile of the corresponding region in the width direction of the multilayer film to be adjusted by heating each of the multiple choke bars 129A and 129B with independent temperature control.

[0045] Another example of additional heaters that the die 100 may include is inner layer heaters 145A and 145B located near the inner layer manifold. In the example of the die 100, the inner layer heaters 145A and 145B are not located on the plane along line 1a in FIG. 1 , and therefore are shown in FIG. 2 by dashed lines at positions corresponding to their internal positions when viewed from the die width direction. In this example, the inner layer heaters 145A and 145B are arranged in multiples on both sides of the upstream flow path adjacent heaters 143A and 143B in the width direction, aligned across the region from the vicinity of the heaters 143A and 143B to the end of the flow path width widened by the manifold. Independent temperature control of each of the multiple heaters 143A and 143B allows for the adjustment of the thickness ratio profile in the corresponding region in the width direction of the multilayer film.

[0046] When significant thickness variations across the entire width of the multilayer film or across a wide region close to it are corrected by adjusting the temperatures of heaters 141A and 141B, small local variations in thickness ratio may occur in the profile after correction. In such cases, the inner layer heaters 145A and 145B and the choke bar heater described above can be used to further correct the variations in thickness ratio as fine adjustments.

[0047] [Optional Component: Additional Insulation] The die of the present invention may also include additional insulating materials other than the insulating materials (A) and (B) described above. Examples of additional insulating materials include the insulating material 153A that provides insulation between the inner layer heater 145A and the flow path of the molten resin material (A) (particularly the manifold 123A and its vicinity) and the insulating material 153B that provides insulation between the inner layer heater 145B and the flow path of the molten resin material (B) (particularly the manifold 123B and its vicinity). The provision of these insulating materials makes it easier to independently adjust the temperatures of the flow paths of the molten resin materials (A) and (B) and the flow path of the molten resin material (C). The materials constituting these additional insulating materials may be the same as or different from the materials constituting the insulating materials (A) and (B). Specific examples of such materials include the same examples of the materials constituting the insulating materials (A) and (B).

[0048] [Optional components: Other] The die of the present invention may also include various optional components in addition to those described above. An example of an optional component is a temperature sensor for monitoring the temperature of the heater. Specifically, heaters 141A and 141B and other heaters may have a temperature sensor located within or near them for monitoring the temperature within the die controlled by one or more of them. Based on the temperature information obtained from such a temperature sensor, the area heated by each heater can be controlled to maintain a desired temperature.

[0049] Other examples of optional components include various components found in conventional dies. For example, bolts for adjusting the size of the die lip opening can be included. By providing multiple such bolts across the width of the die, the total thickness of the multilayer film can be independently adjusted across the width, allowing the production of a multilayer film with a uniform thickness distribution across the width.

[0050] [Multi-layer extrusion molding device] The multilayer extrusion molding apparatus of the present invention includes the die of the present invention described above, a measuring device, and a temperature control device. The measuring device measures the thickness of one or more layers of the multilayer film extruded from the die at multiple locations aligned in the width direction of the multilayer film. The temperature control device controls the temperatures of heaters (A) and (B) based on the thickness measured by the measuring device.

[0051] The multilayer extrusion molding apparatus of the present invention may further include optional components, such as an extruder that melts a solid resin material, such as pellets, to form a molten resin material and pressure-feeds it to each of the die inlets, a cast roll that cools the molten multilayer film extruded from the die, a conveying device that conveys the cooled multilayer film along a conveying path, a processing device that performs processing such as stretching on the multilayer film, wiring that transmits information obtained by the measuring device to a temperature control device, and wiring that supplies energy, such as electricity, from the temperature control device to a heater in a controlled manner.

[0052] Figure 4 is a side view schematically illustrating an example of a multilayer extrusion molding apparatus according to the present invention. In Figure 4, the multilayer extrusion molding apparatus 10 includes the die 100, measuring device 200, and temperature control device 300 described with reference to Figures 1 to 3. The multilayer extrusion molding apparatus 10 further includes, as optional components, an extruder (not shown) that melts a solid resin material, such as pellets, to produce a molten resin material and pressure-feeds it to the inlets 121A, 121B, and 121C of the die 100; a cast roll 410 that cools the molten multilayer film 11 extruded from the die 100; a conveying device (not shown) that conveys the cooled multilayer film 12 along a conveying path; a processing device 420 that performs processes such as stretching on the multilayer film 12; wiring 201 that transmits information obtained by the measuring device 200 to the temperature control device 300; and wiring 301 that supplies electrical energy from the temperature control device 300 to a heater in the die 100 in a controlled manner.

[0053] The measuring device 200 can be appropriately selected from devices capable of measuring the thickness of each layer constituting the transported multilayer film. Specific examples of measuring devices include infrared thickness gauges, X-ray thickness gauges, and interferometric film thickness gauges. From the viewpoints of high measurement accuracy and adaptability to production lines with high transport speeds, interferometric film thickness gauges are preferred.

[0054] A known appropriate heater control device may be used as the temperature control device 300. Specifically, the temperature control device 300 may include a unit (i) that receives information about the thickness of each layer of the multilayer film 12 obtained by the measurement device 200 and calculates the thickness ratio, a unit (ii) that determines the heating temperature of each heater based on the calculation result of unit (i), and a unit (iii) that supplies energy such as electricity to each heater in a controlled manner so as to maintain the desired heating temperature based on the determination result of unit (ii) and temperature information received from a temperature sensor provided in the die 100. However, the temperature control device 300 is not limited to this, and may be configured, for example, so that an operator can manually perform some of units (i) to (iii).

[0055] [Method for producing multilayer film] The method for producing a multilayer film of the present invention includes the following steps (I) and (II): The method for producing a multilayer film of the present invention may further include the following steps (III) and (IV). Step (I): A step of supplying each of the molten resin materials (A) to (C) to the manifolds (A) to (C) of the die of the present invention described above, widening the respective flow paths, and pumping the materials from each of the manifolds (A) to (C) to a joining position. Step (II): A step of joining the molten resin materials (A) to (C) at a joining position and extruding the mixture from the lip of the die as a flat outflow having multiple layers. Step (III): A step of measuring the thickness of one or more layers of the produced multilayer film at multiple locations aligned in the width direction of the multilayer film. Step (IV): A step of adjusting the heating conditions by the heater (A) and the heater (B) in step (I-1) based on the thickness of one or more layers measured in step (III).

[0056] The step (I) further includes a step (I-1) of independently heating the flow path of the molten resin material (A) from outside the manifold (A) by a plurality of heaters (A), and independently heating the flow path of the molten resin material (B) from outside the manifold (B) by a plurality of heaters (B).

[0057] Steps (I) and (II) are carried out using the die of the present invention, and steps (III) and (IV) can be carried out using the measuring device and temperature control device provided in the multilayer extrusion molding apparatus of the present invention together with the die.

[0058] [Molten resin material] The molten resin materials (A) to (C) may be selected from materials desired for the layers constituting the multilayer film. The molten resin materials (A) to (C) may be different materials from each other, but are not limited to this. For example, the molten resin materials (A) and (B) may be the same material, and the outermost layers (A) and (B) may be layers made of the same material.

[0059] An example of a combination of the molten resin materials (A) to (C) is a combination of a material having a positive intrinsic birefringence (hereinafter sometimes simply referred to as a "positive material") and a material having a negative intrinsic birefringence (hereinafter sometimes simply referred to as a "negative material"). A resin having a positive intrinsic birefringence refers to a resin whose refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to the stretching direction. A resin having a negative intrinsic birefringence refers to a resin whose refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction. The intrinsic birefringence can be calculated from the dielectric constant distribution. More specifically, by using positive materials as the molten resin materials (A) and (B) and a negative material as the molten resin material (C), a multilayer film with optically useful properties can be obtained.

[0060] Examples of polymers that constitute positive materials include polymers of one type of monomer such as olefins (e.g., ethylene, propylene, norbornene, cycloolefin, etc.), esters (e.g., ethylene terephthalate, butylene terephthalate, etc.), arylene sulfides (e.g., phenylene sulfide, etc.), vinyl alcohol, carbonates, arylates, cellulose esters (some of which have negative intrinsic birefringence values), ether sulfone, sulfone, allyl sulfone, vinyl chloride, etc., and multi-component (binary, ternary, etc.) copolymers of the above monomers.

[0061] Examples of polymers that make up negative materials include polymers of one type of monomer, such as styrene, styrene derivatives, acrylonitrile, methyl methacrylate, maleic anhydride, butadiene, and cellulose esters (some of which have positive intrinsic birefringence values), as well as multi-component (binary, ternary, etc.) copolymers of the above monomers.

[0062] Each of the molten resin materials (A) to (C) may contain various additives (for example, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, etc.) as needed.

[0063] In the multilayer film obtained by the production method of the present invention, the average thickness of the inner layer (C) may be, for example, in the range of 10 to 250 μm, while the average thickness of each of the outermost layers (A) and (B) may be in the range of 10 to 200 μm.

[0064] [Specific example of manufacturing method] An example of a method for producing a multilayer film using the apparatus shown in FIGS. 1 to 4 will be specifically described. First, using an appropriate device such as an extruder, a solid resin material in the form of pellets or the like is melted to form molten resin materials (A) to (C), which are then pressurized and introduced into inlets 121A to 121C of die 100. The molten resin materials (A) to (C) pass through upstream flow paths 122A, 122B, and 122C, respectively, and are supplied to manifolds 123A, 123B, and 123C. The flow paths for molten resin materials (A) to (C) are widened here, and the materials flow out of manifolds 123A, 123B, and 123C and are pumped through downstream flow paths 124A, 124B, and 124C, respectively, to a junction position 131 (step (I)). As the molten resin materials (A) to (C) are pumped in this manner, they join at a joining point 131, and the molten multilayer film 11 is extruded from the opening 132 in the die lip as a flat outflow having multiple layers (step (II)).

[0065] In step (I-1), the flow path for molten resin material (A) (i.e., the flow path from inlet 121A to junction 131) is independently heated by heater 141A located outside manifold 123A, and the flow path for molten resin material (B) (i.e., the flow path from inlet 121B to junction 131) is independently heated by heater 141B located outside manifold 123B. Here, "independent heating" refers to independently setting the temperature of each of the aligned heaters 141A and the regions adjacent to each of the aligned heaters 141B to a desired temperature, and controlling the heaters to generate heat at the respective set temperatures. This independent heating allows for independent adjustment of the widthwise temperature distribution in the region expanded by the manifold and in the flow path downstream thereof, thereby making it easy to greatly adjust the widthwise profile of the ratio of each layer thickness to the thickness of the multilayer film.

[0066] Generally, molten resin materials become more fluid as their temperature increases in the molten state. Therefore, if a certain portion of the flow path that is widened in the width direction is locally heated and the temperature of that portion in the width direction is made relatively high, the flow rate of the molten resin material flowing through that portion will be relatively high. Therefore, the thickness ratio profile can be adjusted by independently heating the portion corresponding to the region where a thicker layer is required with multiple heaters so that the temperature is made relatively high.

[0067] The molten multilayer film 11 extruded from the die 100 is cast onto a casting roll 410. The cast multilayer film 11 is cooled by the casting roll 410, and a long, hardened multilayer film 12 is continuously produced. The thickness of each layer of the multilayer film 12 is measured by a measuring device 200 (step (III)). Measurements by the measuring device 200 are performed across the width of the multilayer film 12, thereby obtaining a thickness profile for each layer of the multilayer film 12, consisting of the distance from one end of the film in the width direction and the layer thickness. Based on this, a width-wise profile of the ratio of each layer thickness to the multilayer film thickness is further obtained. The obtained measurements are transmitted to a temperature control device 300 via wiring 201.

[0068] The temperature control device 300 adjusts the heating conditions for heater 141A, heater 141B, and other heaters based on the received profile data of the thickness ratio of each layer (step (IV)). Specifically, it receives information about the thickness of each layer of the multilayer film 12 obtained by the measurement device 200, calculates the multilayer film thickness ratio, determines the heating temperature for each heater based on the calculation result, compares the determined result with temperature information received from a temperature sensor provided in the die 100, and supplies energy such as electricity to each heater in a controlled manner so that the desired heating temperature is maintained, thereby achieving heating under the desired heating conditions.

[0069] [Specific examples of temperature settings] A specific example of setting the heater temperature will be described with reference to FIGS. Figure 5 is a longitudinal cross-sectional view schematically illustrating a cross section of an example of a long multilayer film produced by the multilayer film production method of the present invention, cut along a plane parallel to the film width direction. In Figure 5, multilayer film 500 includes layers 501A and 501B corresponding to the outermost layers (A) and (B), respectively, and layer 501C corresponding to inner layer (C). Regions R1 to R7 in the figure correspond to each of the seven heaters 141A and each of the seven heaters 141B, as schematically shown in Figures 1 and 2.

[0070] In multilayer film 500, layers 501A to 501C are all in an ideal state with no thickness variation. When a multilayer film in such a state is continuously produced by the production method of the present invention, good production can be continued by maintaining the settings of heaters 141A and 141B and other production conditions as they are.

[0071] FIG. 6 is a longitudinal cross-sectional view schematically illustrating a cross section of another example of a long multilayer film produced by the multilayer film production method of the present invention, taken along a plane parallel to the film width direction. In FIG. 6, multilayer film 600 includes layers 601A and 601B corresponding to outermost layers (A) and (B), respectively, and layer 601C corresponding to inner layer (C). In this example, layer 601A has a relatively thin thickness ratio in region R2, resulting in thickness variation. In this state, the set temperature of the heater corresponding to region R among the multiple heaters 141A can be changed to a higher temperature. Since the total thickness of the multilayer film is controlled to a constant value by other factors, such as the size of die lip opening 132, the thickness of layer 601C becomes relatively thin in the region where the flow rate of molten resin material (A) is relatively high. As a result, the thickness ratio is changed, and the thickness ratio variation can be reduced to approach the ideal state of the multilayer film 500 in FIG. 5, where there is no thickness variation among the layers.

[0072] Figure 7 is a longitudinal cross-sectional view schematically illustrating a cross section of yet another example of a long multilayer film produced by the multilayer film production method of the present invention, taken along a plane parallel to the film width direction. In Figure 7, multilayer film 700 includes layers 701A and 701B corresponding to the outermost layers (A) and (B), respectively, and layer 701C corresponding to inner layer (C). In this example, the relative thickness ratio of both layer 701A and layer 701B is significantly reduced in region R4, and the thickness is also reduced in the surrounding regions, resulting in thickness variation with significant thickness differences.

[0073] In such a state, it is expected that thickness variations can be reduced by, for example, setting the temperature of the heaters corresponding to regions R2 and R6 higher than the temperature of the heaters corresponding to regions R1 and R7 among the numerous heaters 141A and 141B, setting the temperature of the heaters corresponding to regions R3 and R5 even higher, and setting the temperature of the heater corresponding to region R4 even higher.

[0074] The inventors discovered that in a conventional die lacking the thermal insulators 151A and 151B, significantly increasing the heater temperature to reduce such significant thickness differences results in difficulty in achieving significant relative thickness changes. While not bound by any particular theory, the reason for this phenomenon is believed to be that significantly increasing the heater temperature within the die allows the heat to propagate widely, reducing the thermal gradient and ultimately hindering the relative thickness change. For example, if the heaters 141A and 141B corresponding to region R4 are set to a significantly higher temperature, the flow paths for the molten resin material (C) for the inner layer are also heated, reducing the thermal gradient between the flow paths, resulting in the desired relative thickness change being unattainable.

[0075] In the die of the present invention, the presence of insulating materials 151A and 151B between the flow path for the molten resin material (C) for the inner layer and heaters 141A and 141B increases the independence between the temperature in block 110A (where heater 141A is located) and block 110B (where heater 141B is located) and the temperature in block 110C (where the flow path for the molten resin material (C) for the inner layer). This makes it easy to adjust the temperature of the flow paths for the molten resin materials (A) and (B) for the outermost layers independently of the temperature of the flow path for the molten resin material (C) for the inner layer. As a result, in the production of multilayer films using die 100 of the present invention, it is easy to correct thickness ratio profiles with significant differences in relative thickness across the entire width of the multilayer film or a wide region close to it.

[0076] As in this example, when significant thickness differences across the entire width of the multilayer film or across a wide region close to it are corrected by setting the temperatures of heaters 141A and 141B, small local variations in thickness ratio may occur in the profile after correction. In such cases, other heaters (e.g., inner layer heaters 145A and 145B near the inner layer manifold, and choke bar heaters that heat choke bars 129A and 129B) can be used to further correct the variations in thickness ratio as fine adjustments.

[0077] The significant thickness difference across the entire width of the multilayer film or a wide region close to it, as illustrated in Figure 7, is particularly likely to occur when the type of resin material used to manufacture the film is changed, or when manufacturing conditions are changed, such as when the thickness ratio of the multilayer film is significantly changed from the thickness ratio used in previous manufacturing due to design requirements or other reasons. The manufacturing method of the present invention can easily correct even such significant thickness differences, making it possible to manufacture multilayer films under significantly changed manufacturing conditions without requiring complicated steps such as restarting the manufacturing process. As a result, a useful effect is achieved in that it is possible to easily produce a wide variety of multilayer films in small quantities.

[0078] When changing the thickness ratio of a multilayer film, for example, when changing the thickness ratio of the inner layers, in one example of a prior art die that does not include the insulating materials 151A and 151B, if the change in the inner layer thickness ratio after the change from the value before the change was 7% or more, adjustment and restart of the equipment was required. However, in production that includes the die of the present invention that has the insulating materials 151A and 151B and other components, even if there is a large change such as 17%, this can be achieved without adjustment and restart of the equipment.

[0079] [Optional step: method for producing multilayer stretched film] The method for producing a multilayer film of the present invention may include any optional steps in addition to the steps described above. For example, the obtained multilayer film may be stretched to produce a multilayer stretched film. The stretching method is not particularly limited, and may be longitudinal stretching (stretching a long film in the longitudinal direction), transverse stretching (stretching in the width direction), oblique stretching, or a combination thereof.

[0080] [Modification] The die, the multilayer extrusion molding apparatus, and the manufacturing method of the present invention are not limited to the examples described above and may include further modifications. For example, the examples described above illustrate methods and apparatus for manufacturing a multilayer film having only one inner layer (C), but the present invention is not limited thereto and may include two or more inner layers.

[0081] [Uses of multilayer film] The multilayer film and multilayer stretched film produced by the die of the present invention, the multilayer extrusion molding apparatus of the present invention, or the production method of the present invention have reduced variation in the thickness ratio of each layer in the width direction, and can therefore be suitably used as materials for optical films such as polarizing plate protective films, retardation films, brightness enhancement films, and transparent conductive films. [Example]

[0082] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents.

[0083] [Evaluation method] [Evaluation of optical properties] The multilayer films obtained in the Examples and Comparative Examples were stretched to obtain multilayer stretched films so that the in-plane retardation Re was 137 nm, which allows the films to function as λ / 4 wavelength plates. The optical properties of the multilayer stretched films were evaluated by measuring them with a retardation meter (Axometrics' "AxoScan"). The optical properties developed by stretching and the evaluation conditions were the same in all Examples and Comparative Examples. The difference between the maximum and minimum values of the many measured Re values was calculated as the variation. The evaluation results were classified into three levels according to the following evaluation index. ◯: The retardation value variation after stretching is less than 5 nm. △: The retardation value variation after stretching is 5 nm or more and less than 15 nm. ×: The retardation value variation after stretching is 15 nm or more.

[0084] [Production Example 1] Pellets of four types of resins (1) to (4) having the physical properties shown in Table 1 below were prepared.

[0085] [Table 1]

[0086] Example 1 A multilayer film was produced and evaluated using a multilayer extrusion molding apparatus 10 including a die 100, as schematically shown in Figures 1 to 4. The width of the die lip opening 132 of the die 100 in the film width direction was 1850 mm. However, as the heat insulating materials, heat insulating materials 151A and 151B were installed in the die 100 and used, while heat insulating materials 153A and 153B were not installed and were not used. Cement boards were used as the material for heat insulating materials 151A and 151B and other heat insulating materials. The thickness of each of heat insulating materials 151A and 151B was 20 mm. As the heaters, heaters 141A and 141B, 143A and 143B, and heaters (not shown) for heating choke bars 129A and 129B were used, while heaters 145A and 145B were not used. In FIG. 1, heaters 141A and 141B are shown as seven heaters each arranged in one row in the width direction, but the device actually used had heaters 141A and 141B each arranged in two rows in the width direction, with 21 heaters. In Figure 1, seven choke bars 129A and seven choke bars 129B are shown in the width direction, but the device actually used had 41 choke bars 129A and 41 choke bars 129B in the width direction. After the thickness of each layer of the cooled multilayer film 12 was measured by the measuring device 200, the film was collected as a product without being subjected to processing by the processing device 420. An interference film thickness meter was used as the measuring device 200. Resin (3) was used as the resin material constituting the outermost layer (A) and the outermost layer (B), and resin (4) was used as the resin material constituting the inner layer (C).

[0087] (1-1. Preliminary adjustment in multilayer film manufacturing before heater adjustment) In the extruder, pellets of resin (3) were melted to form a molten resin material, which was then pumped to inlets 121A and B. Meanwhile, in another extruder, pellets of resin (4) were melted to form a molten resin material, which was then pumped to inlets 121A and B. The resin temperature at the time of extrusion from the extruder was 260°C in all cases. During pumping, upstream flow paths 122A, 122B, and 122C were heated by heaters 143A and 144B near the upstream flow path to ensure smooth flow.

[0088] As a result of the pressure feeding, a molten multilayer film 11 having a layer structure of (molten resin material (A)) / (molten resin material (C)) / (molten resin material (B)) was extruded from the opening 132 of the die lip and cast onto the casting roll 410. The temperature of the molten resin material at the opening 132 was 260°C. The cast multilayer film 11 was cooled by the casting roll 410 to become a hardened multilayer film 12. The total thickness and the thickness of each layer of the multilayer film 12 were measured using the measuring device 200, and the multilayer film 12 was then recovered. Measurements using the measuring device 200 were performed using an interference film thickness meter, and the average thickness, maximum thickness, and minimum thickness were determined. The difference between the maximum thickness and the minimum thickness as a percentage of the average thickness was calculated as the thickness variation.

[0089] The total thickness and the thickness of each layer were adjusted based on the data obtained from the measuring device 200. Thickness adjustment at this stage was performed by adjusting the pumping speed of each molten resin material from the extruder, adjusting the size of gaps 129Ag and 129Bg using choke bars 129A and 129B, adjusting the width of the die lip opening, and adjusting the rotation speed of cast roll 410 to adjust the take-up speed of molten multilayer film 11. At this stage, heaters 141A and 141B and heaters for heating choke bars 129A and 129B were not used. As a result, the device was adjusted to a state where a multilayer film 12 could be produced with a thickness variation of 4.8% for the inner layer (C) when the thicknesses of the outermost layer (A) and the outermost layer (B) were each 40 μm and the thickness of the inner layer (C) was 40 μm.

[0090] (1-2. Manufacturing of multilayer film with heater adjustment) After completing the adjustment of (1-1) and while the multilayer film 12 was being continuously produced, the thickness ratio was adjusted using heaters 141A and 141B. Specifically, the temperature of heater 141A, which corresponds to the thin region of the thickness profile of the outermost layer (A) in the width direction of the multilayer film, was adjusted to a relatively high temperature, and the temperature of heater 141B, which corresponds to the thin region of the thickness profile of the outermost layer (B), was adjusted to a relatively high temperature, thereby adjusting the rough thickness profiles of the outermost layers (A) and (B) to a thickness that is close to flat. Next, in addition to that, the temperature of chalk bar 129A, which corresponds to the thin micro-region of the thickness profile of the outermost layer (A) in the width direction of the multilayer film, was adjusted to a relatively high temperature, and the temperature of chalk bar 129B, which corresponds to the thin micro-region of the thickness profile of the outermost layer (B) in the width direction of the multilayer film, was adjusted to a relatively high temperature, thereby adjusting the local thickness profiles of the outermost layers (A) and (B) to a thickness that is close to flat. These temperature adjustments were performed by receiving information on the thickness measurement results from the measuring device 200 at the temperature control device 300, and adjusting the temperature of a heater connected to the temperature control device 300 based on that information. As a result, it was possible to reduce the thickness variation of the inner layer (C) to 0.4%. The optical properties of the multilayer film obtained under these manufacturing conditions were evaluated.

[0091] Example 2 (2-1. Preliminary adjustment) Using the die 100 adjusted in Example 1 (1-1), a multilayer film was produced by changing the resin material. That is, while the gaps 129Ag and 129Bg and the opening state of the die lip were kept as adjusted in (1-1) of Example 1, resin (1) was used instead of resin (3) as the resin material constituting the outermost layer (A) and the outermost layer (B), and resin (2) was used instead of resin (4) as the resin material constituting the inner layer (C), and a multilayer film was manufactured.

[0092] By adjusting the pumping speed of each molten resin material from the extruder and the rotation speed of the cast roll 410, the thicknesses of the outermost layer (A) and the outermost layer (B) were each set to 32.5 μm, and the thickness of the inner layer (C) was set to 65 μm. At this point, the heaters 141A and 141B and the heaters that heat the chalk bars 129A and 129B were not used. In this state, the thickness variation of the inner layer (C) was 13.9%.

[0093] (2-2. Manufacturing of multilayer film with heater adjustment) After completing the adjustment of (2-1), while the multilayer film 12 was being continuously produced, the thickness ratio was adjusted by the same procedure as in (1-2) of Example 1. As a result, the thickness variation of the inner layer (C) was reduced to 0.5%. The optical properties of the multilayer film produced under these production conditions were evaluated.

[0094] Example 3 (3-1. Preliminary adjustment) Using the die 100 adjusted in Example 1 (1-1), a multilayer film was produced by changing the resin material. That is, while the gaps 129Ag and 129Bg and the opening state of the die lip were kept as adjusted in (1-1) of Example 1, resin (2) was used instead of resin (3) as the resin material constituting the outermost layer (A) and the outermost layer (B) (the resin material constituting the inner layer (C) remained unchanged at resin (4)), and a multilayer film was manufactured.

[0095] By adjusting the pumping speed of each molten resin material from the extruder and the rotation speed of the cast roll 410, the thicknesses of the outermost layer (A) and the outermost layer (B) were each set to 30 μm, and the thickness of the inner layer (C) was set to 210 μm. At this point, the heaters 141A and 141B and the heaters that heat the chalk bars 129A and 129B were not used. In this state, the thickness variation of the inner layer (C) was 17.8%.

[0096] (3-2. Manufacturing of multilayer film with heater adjustment) After completing the adjustment of (3-1), while the multilayer film 12 was being continuously produced, the thickness ratio was adjusted by the same procedure as in (1-2) of Example 1. As a result, the thickness variation of the inner layer (C) was reduced to 0.6%. The optical properties of the multilayer film produced under these production conditions were evaluated.

[0097] Comparative Example 1 A multilayer film was produced and evaluated in the same manner as in Example 1, except for the following changes. Heaters 141A and 141B and heaters for heating choke bars 129A and 129B were not used, while heaters 145A and 145B were used. As for the heat insulating materials, the heat insulating materials 151A and 151B were not installed and were not used, while the heat insulating materials 153A and 153B were installed and used.

[0098] The thickness variation of the inner layer (C) after preliminary adjustment was adjusted to 4.6%. In the production of multilayer film with heater adjustment, the thickness variation of the inner layer (C) could be reduced to 1.2%. The optical properties of the multilayer film obtained under these production conditions were evaluated.

[0099] Comparative Example 2 A multilayer film was produced and evaluated in the same manner as in Example 3, except for the following changes. Heaters 141A and 141B and heaters for heating choke bars 129A and 129B were not used, while heaters 145A and 145B were used. As for the heat insulating materials, the heat insulating materials 151A and 151B were not installed and were not used, while the heat insulating materials 153A and 153B were installed and used.

[0100] The thickness variation of the inner layer (C) after preliminary adjustment was adjusted to 17.2%. In the production of multilayer film with heater adjustment, the thickness variation of the inner layer (C) could be reduced to 13.3%. The optical properties of the multilayer film obtained under these production conditions were evaluated.

[0101] Comparative Example 3 A multilayer film was produced and evaluated in the same manner as in Example 1, except for the following changes. Heaters 141A and 141B were not used (heaters for heating choke bars 129A and 129B were used). -The insulation materials, namely insulation materials 151A and 151B and insulation materials 153A and 153B, were not installed or used.

[0102] The thickness variation of the inner layer (C) after preliminary adjustment was adjusted to 4.5%. In the production of multilayer films involving heater adjustment, the thickness variation of the inner layer (C) could be reduced to 0.5%. The optical properties of the multilayer films produced under these production conditions were evaluated.

[0103] Comparative Example 4 A multilayer film was produced and evaluated in the same manner as in Example 2, except for the following changes. Heaters 141A and 141B were not used (heaters for heating choke bars 129A and 129B were used). -The insulation materials, namely insulation materials 151A and 151B and insulation materials 153A and 153B, were not installed or used.

[0104] The thickness variation of the inner layer (C) after preliminary adjustment was adjusted to 14.1%. In the production of multilayer film with heater adjustment, the thickness variation of the inner layer (C) could be reduced to 7.0%. The optical properties of the multilayer film obtained under these production conditions were evaluated.

[0105] Comparative Example 5 A multilayer film was produced and evaluated in the same manner as in Example 3, except for the following changes. Heaters 141A and 141B were not used (heaters for heating choke bars 129A and 129B were used). -The insulation materials, namely insulation materials 151A and 151B and insulation materials 153A and 153B, were not installed or used.

[0106] The thickness variation of the inner layer (C) after preliminary adjustment was adjusted to 17.4%. In the production of multilayer film with heater adjustment, the thickness variation of the inner layer (C) could be reduced to 10.6%. The optical properties of the multilayer film obtained under these production conditions were evaluated.

[0107] Table 2 shows an outline of the conditions for carrying out the examples and comparative examples, and the results of evaluation of the optical properties.

[0108] [Table 2]

[0109] *1: Types of heat insulating materials used. 151: Heat insulating materials 151A and 151B shown in Figure 2. 153: Heat insulating materials 153A and 153B shown in Figure 2. *2: Types of heaters used. 141: Heaters 141A and 141B shown in Figure 2. 143: Heaters 143A and 143B shown in Figure 2. 145: Heaters 145A and 145B shown in Figure 2. 129: Heater for heating choke bars 129A and 129B shown in Figure 2.

[0110] As is clear from the results of Examples 1 to 3, by using the multilayer extrusion molding apparatus of the present invention equipped with the die of the present invention and carrying out the manufacturing method of the present invention, it is possible to easily change the resins used and the thickness ratio of each layer without making adjustments such as restarting the apparatus or adjusting the choke bar opening, and to easily manufacture a multilayer film with little variation in thickness ratio. In contrast, a comparison of the results of Comparative Examples 1 and 2, and a comparison of Comparative Example 3 with Comparative Example 4 or 5, showed that in production using a die that did not have the components specified in the present invention, the thickness ratio variation of the multilayer film significantly increased in production after changing the resin used and the thickness ratio of each layer (Comparative Example 2, Comparative Example 4, and Comparative Example 5), and the evaluation results of the optical properties of the obtained multilayer film were significantly inferior. [Explanation of symbols]

[0111] 10: Multi-layer extrusion molding equipment 11: Multilayer film in molten state 12: Multilayer film after cooling 100: Dice 110A: Block (Block (A)) 110B: Block (Block (B)) 110C: Block (Block (C)) 110C1: Sub-block 110C2: Sub-block 110D: Block 110E: Block 121A: Inlet 121Ac: Recess 121B: Inlet 121C: Inlet 122A: Upstream flow path 122Ac: Recess 122B: Upstream flow path 122C: Upstream flow path 123A: Manifold (Manifold (A)) 123Aa: Recess 123Ac: Recess 123B: Manifold (Manifold (B)) 123Bb:Concave 123Bc:Concave 123C: Manifold (Manifold (C)) 123C1: Recess 123C2: Recess 124A: Downstream channel 124Ac: Recess 124B: Downstream channel 124C: Downstream channel 128A: Bolt 128B: Bolt 129A: Chalk bar 129Ac: Recess 129Ag: Gap 129B: Chalk bar 129Bc:Concave 129Bg:Gap 131: Merging position 132:Aperture 141A: Heater (Heater (A)) 141B: Heater (Heater (B)) 142A: Invagination 142B: Indentation 143A: Heater near the upstream flow path 144A: Invagination 144B: Heater near the upstream flow path 144B: Indentation 145A: Inner layer heater 145B: Inner layer heater 151A: Insulation material (Insulation material (A)) 151B: Heat insulation material (heat insulation material (B)) 153A: Insulation material 153B:Insulation material 200: Measuring equipment 201: Wiring 300: Temperature control device 301: Wiring 410: Cast Roll 420: Processing device 500: Multilayer film 501A: Layer (outermost layer (A)) 501B: Layer (outermost layer (B)) 501C: Layer (inner layer (C)) 600: Multilayer film 601A: Layer (outermost layer (A)) 601B: Layer (outermost layer (B)) 601C: Layer (inner layer (C)) 700: Multilayer film 701A: Layer (outermost layer (A)) 701B: Layer (outermost layer (B)) 701C: Layer (inner layer (C)) R1: area R2: area R3: area R4: Area R5: Area R6: Area R7: Area

Claims

1. A die for producing a multilayer film comprising an outermost layer (A), an outermost layer (B), and one or more inner layers (C) disposed between the outermost layers (A) and (B), an outermost layer manifold (A) for expanding and extruding the molten resin material (A) that is the material for the outermost layer (A); an outermost layer manifold (B) for expanding and extruding the molten resin material (B) that is the material for the outermost layer (B); an inner layer manifold (C) positioned inside the manifolds (A) and (B) for expanding and extruding a molten resin material (C) that is a material for the inner layer (C); a plurality of heaters (A) positioned outside the manifold (A) and aligned in the width direction of the die; a plurality of heaters (B) positioned outside the manifold (B) and aligned in the width direction of the die; a heat insulating material (A) located upstream of the manifold (A) and between the manifold (C) and the heater (A) in the thickness direction; and a heat insulating material (B) located upstream of the manifold (B) and between the manifold (C) and the heater (B) in the thickness direction; Equipped with The die comprises a block (A), a block (B), and a block (C), The block (A) has a surface (Ac) facing the block (C), The block (B) has a surface (Bc) facing the block (C), the block (C) has a surface (Ca) facing the block (A) and a surface (Cb) facing the block (B), a part or the whole of the manifold (A) is defined by a recess provided in one or both of the surface (Ac) and the surface (Ca), the manifold (B) is partially or entirely defined by a recess provided in one or both of the surface (Bc) and the surface (Cb), The heat insulating material (A) is provided between the surface (Ac) and the surface (Ca), The heat insulating material (B) is provided between the surface (Bc) and the surface (Cb).

2. The die according to claim 1; a measuring device that measures the thickness of one or more layers of the multilayer film extruded from the die at a plurality of locations aligned in the width direction of the multilayer film; a temperature control device that controls the temperatures of the heaters (A) and (B) based on the thickness measured by the measuring device; A multi-layer extrusion molding apparatus comprising:

3. A method for producing a multilayer film, comprising: a step (I) of supplying each of the molten resin materials (A) to (C) to the manifolds (A) to (C) of the die according to claim 1, widening the flow paths of each of the manifolds (A) to (C), and pumping the molten resin materials from each of the manifolds (A) to (C) to a joining position; a step (II) of joining the molten resin materials (A) to (C) at the joining position and extruding the molten resin materials from the lip of the die as a flat outflow having a plurality of layers; The step (I) further includes a step (I-1) of independently heating a flow path for the molten resin material (A) from outside the manifold (A) using a plurality of the heaters (A), and independently heating a flow path for the molten resin material (B) from outside the manifold (B) using a plurality of the heaters (B).

4. a step (III) of measuring the thickness of one or more layers of the produced multilayer film at a plurality of locations aligned in the width direction of the multilayer film; and a step (IV) of adjusting heating conditions by the heater (A) and the heater (B) in the step (I-1) based on the thickness of the one or more layers measured in the step (III). The method for producing the multilayer film according to claim 3 .

5. A step of producing a multilayer film by the method for producing a multilayer film according to claim 3 or 4; and stretching the multilayer film A method for producing a multilayer stretched film, comprising:

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