Method for producing stretched film

Abstract

The present invention provides a method for manufacturing a stretched film with very high productivity by suppressing contamination of a production line and suppressing peeling of an adhesive tape used during manufacturing. A method for manufacturing a stretched film according to an embodiment of the present invention comprises: feeding a preceding elongated raw film to a stretcher for stretching while conveying the film in the longitudinal direction; bonding the rear end part of the preceding long-strip-shaped original film and the front end part of the following long-strip-shaped original film by using an adhesive tape through an intermediate film; and feeding the following long raw film to a stretcher for stretching while conveying the following long raw film in the longitudinal direction. The elongation at break at the stretching temperature of the intermediate film is greater than the stretching ratio of the stretching in the stretching machine.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a stretch film. Background Art

[0002] Stretch films have been widely used for various purposes. Typically, a stretch film can be obtained by stretching a raw film composed of a long strip of resin film through a stretching method and stretching conditions corresponding to target and desired properties. As stretching methods, for example, free-end unidirectional stretching, fixed-end unidirectional stretching, simultaneous biaxial stretching, and sequential biaxial stretching can be cited. As stretching directions, a longitudinal direction (the conveying or supplying direction of the raw film), a transverse direction (a direction substantially orthogonal to the conveying or supplying direction of the raw film), and an oblique direction (a direction forming a given angle with respect to the conveying or supplying direction of the raw film) can be cited.

[0003] On the other hand, when manufacturing a stretch film, from the viewpoint of improving productivity, it has been proposed to supply a new raw film continuously to a processing machine (stretching machine) after a preceding raw film by joining the front end portion of a new raw film to the end portion of the preceding long strip-shaped raw film (so-called splicing). Typically, such joining can be performed using an adhesive tape. However, depending on the stretching method and stretching conditions, etc., the joint between the preceding raw film and the new raw film may sometimes separate, causing the adhesive of the adhesive tape to be exposed and contaminating the production line. In addition, depending on the stretching method and stretching conditions, etc., the adhesive tape may sometimes peel off.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 7-295194 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] The present invention has been completed to solve the above-mentioned existing problems, and its main object is to provide a method for manufacturing a stretch film that can suppress contamination of the production line and can suppress peeling of the adhesive tape used in manufacturing, thereby enabling the stretch film to be manufactured with very high productivity.

[0009] Means for Solving the Problems

[0010] [1] The manufacturing method of the stretch film according to the embodiment of the present invention includes: feeding a preceding long strip-shaped original film to a stretching machine for stretching while transporting it in the length direction; joining the rear end portion of the preceding long strip-shaped original film and the front end portion of a succeeding long strip-shaped original film via an intervening film and using an adhesive tape; and feeding the succeeding long strip-shaped original film to a stretching machine for stretching while transporting it in the length direction, wherein the elongation at break of the intervening film at the stretching temperature is greater than the stretching ratio of the stretching in the stretching machine.

[0011] [2] In the above [1], the elastic modulus of the intervening film is equal to or less than the elastic modulus of the original film.

[0012] [3] In the above [1] or [2], the glass transition temperature (Tg) of the intervening film is equal to or less than the glass transition temperature (Tg) of the original film.

[0013] [4] In any one of the above [1] to [3], the glass transition temperature of the original film is 120 °C or higher.

[0014] [5] In any one of the above [1] to [4], the stretching temperature in the stretching machine is Tg (°C) of the original film to Tg + 15 (°C).

[0015] [6] In any one of the above [1] to [5], the stretching in the stretching machine is performed in a direction substantially orthogonal to the transporting direction of the original film.

[0016] [7] In any one of the above [1] to [6], the stretching ratio in the stretching machine is 1.5 times or more.

[0017] Effects of the Invention

[0018] According to the embodiment of the present invention, it is possible to provide a method for manufacturing a stretch film that can suppress contamination of the production line and peeling of the adhesive tape used during manufacturing, and thus can manufacture the stretch film with very high productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A The drawing is a schematic view for explaining an example of the joining method of the original film in the manufacturing method of the stretch film according to the embodiment of the present invention, and is a schematic view of the joint portion observed from the horizontal direction.

[0020] Figure 1B It is a schematic view of the joint portion observed from above Figure 1A of the joint portion.

[0021] Figure 2A The drawing is a schematic view for explaining one process of the joining of the preceding original film and the succeeding original film in the manufacturing method of the stretch film according to the embodiment of the present invention.

[0022] Figure 2B It is a schematic diagram for explaining another process of joining Figure 2A .

[0023] Figure 2C It is a schematic diagram for explaining yet another process of joining Figure 2A .

[0024] Figure 3A It is a top view schematic diagram for explaining the state where the precursor film has been subjected to transverse stretching in the method for manufacturing a stretched film according to an embodiment of the present invention.

[0025] Figure 3B It is a schematic diagram for explaining Figure 3A the state where the joint portion between the precursor film and the successor film has been subjected to transverse stretching in the manufacturing method.

[0026] Figure 3C It is a schematic diagram for explaining Figure 3A the state where the successor film has been subjected to transverse stretching in the manufacturing method.

[0027] Figure 4 It is a conceptual top view for explaining the possible bending at the joint portion in the method for manufacturing a stretched film according to an embodiment of the present invention.

[0028] Symbol Explanation

[0029] 10a Precursor film

[0030] 10b Successor film

[0031] 12a Precursor stretched film

[0032] 12b Successor stretched film

[0033] 20 Docking portion

[0034] 30 Adhesive tape

[0035] 40 Intervening film

[0036] 50a Bending of the precursor film

[0037] 50b Bending of the successor film

[0038] 60 Joint portion Detailed Description of the Invention

[0039] Hereinafter, representative embodiments of the present invention will be described, but the present invention is not limited to these embodiments. It should be noted that for ease of observation and understanding, the drawings are schematically or conceptually depicted, and there are cases where the length, width, height, thickness, shape, size, ratio, direction, number, etc. are different from the actual ones. In addition, there are parts that do not correspond between the drawings.

[0040] (Meanings of Expressions and Terms)

[0041] (1) Base Film

[0042] When simply referred to as "base film" in this specification, it refers to both the preceding base film and the succeeding base film. When it is necessary to distinguish between the preceding base film and the succeeding base film, "preceding" or "the preceding" or "succeeding" or "the succeeding" is clearly stated.

[0043] (2) Preceding Film or Succeeding Film

[0044] "Preceding film" refers to the preceding base film or the stretched film obtained from the preceding base film; "succeeding film" refers to the succeeding base film or the stretched film obtained from the succeeding base film.

[0045] (3) Joint Portion

[0046] "Joint portion" refers to the portion where an adhesive tape is attached to the rear end portion of the preceding film and the front end portion of the succeeding film.

[0047] (4) Length and Width

[0048] "Length" refers to the length in the conveying direction (length direction) of the base film; "width" refers to the length in the direction orthogonal to the conveying direction (length direction) of the base film.

[0049] A. Outline of the Method for Manufacturing a Stretched Film

[0050] Refer to Figure 1A and Figure 1B The outline of the method for manufacturing a stretched film according to an embodiment of the present invention will be described. As shown in the example figure, the method for manufacturing a stretched film according to an embodiment of the present invention includes: feeding the preceding long strip-shaped base film 10a while conveying it in the length direction to a stretching machine (not shown) for stretching; joining the rear end portion of the preceding long strip-shaped base film 10a and the front end portion of the succeeding long strip-shaped base film 10b via an intermediate film 40 and using an adhesive tape 30; and feeding the succeeding long strip-shaped base film 10b while conveying it in the length direction to a stretching machine for stretching. In the embodiment of the present invention, the elongation at break of the intermediate film at the stretching temperature is greater than the stretching ratio of the stretching in the stretching machine. Hereinafter, the base film, intermediate film, adhesive tape used, and each manufacturing process will be specifically described.

[0051] B. Original film

[0052] As the original film, any suitable resin film corresponding to the purpose can be used. Examples of the resin constituting the original film include: polycarbonate resins or polyester carbonate resins (sometimes collectively abbreviated as polycarbonate resins); polyvinyl acetal resins; polyvinyl alcohol resins; cycloolefin resins such as polynorbornene; acrylic resins such as polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, and polyethyl methacrylate; cellulose resins such as cellulose triacetate; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; olefin resins such as polyethylene and polypropylene; polyurethane resins; vinyl resins such as polyvinyl chloride and polyacrylonitrile; polyamide resins; polyimide resins; polyamideimide resins; fluorine resins such as polytetrafluoroethylene; styrene resins such as polystyrene; polysulfone resins; polyethersulfone resins; polyphenylene sulfide resins; polyetheretherketone resins; and polyarylate resins. These resins can be used alone or in combination of two or more (by blending or copolymerization). In one embodiment, as the original film, a cycloolefin resin or a polycarbonate resin having isosorbide monomer units and fluorene monomer units can be used.

[0053] As described above, the original film is in a long strip shape. Typically, the original film is supplied to a stretching machine while being conveyed by rollers in the length direction on one side.

[0054] The preceding original film and the subsequent original film can be the same or different. It is preferable that the preceding original film and the subsequent original film are the same. With such a configuration, the same stretching conditions can be adopted in the stretching machine, and thus, the same stretched film can be manufactured with extremely excellent productivity.

[0055] The elastic modulus (Young's modulus) of the original film can be appropriately set according to the purpose and the use of the resulting stretched film. For example, the elastic modulus of the original film can be 1800 MPa to 3200 MPa, and for another example, it can be 2000 MPa to 3000 MPa, and for another example, it can be 2100 MPa to 2800 MPa, and for another example, it can be 2200 MPa to 2700 MPa. If the elastic modulus of the original film is in such a range, a stretched film applicable to a wide range of uses can be obtained. If the elastic modulus is too large, shrinkage due to residual stress will occur after stretching, and sometimes this part will be removed from the clamp of the stretching machine. If the elastic modulus is too small, film sagging may occur during stretching, resulting in poor conveyance in the stretching machine. It should be noted that the elastic modulus can be measured according to JIS K 7127.

[0056] The glass transition temperature (Tg) of the original film can be appropriately set according to the purpose and the use of the obtained stretched film, etc. The glass transition temperature (Tg) of the original film can be, for example, 100°C or higher, and can be, for example, 110°C or higher, and can be, for example, 120°C or higher. On the other hand, the glass transition temperature (Tg) of the original film can be, for example, 170°C or lower, and can be, for example, 160°C or lower, and can be, for example, 150°C or lower. If the Tg of the original film is within such a range, a stretched film that can be applied to a wide range of uses can be obtained. If the Tg is too high, it may not be able to adapt to the upper limit temperature of stretching of the stretching machine, and film breakage may occur during stretching. If the Tg is too low, film sagging may occur during stretching, and poor conveyance may occur in the stretching machine.

[0057] The thickness of the original film can be appropriately set according to the purpose and the use of the obtained stretched film, etc. The thickness of the original film can be, for example, 40 μm to 300 μm, and can be, for example, 50 μm to 250 μm, and can be, for example, 60 μm to 200 μm.

[0058] C. Intermediate film

[0059] As described above, the elongation at break of the intermediate film at the stretching temperature of the stretching machine is greater than the stretching ratio of the stretching in the stretching machine. By using such an intermediate film, it is possible to suppress the exposure of the adhesive layer of the adhesive tape at the joint during stretching and / or conveyance of the original film, and to suppress the contamination of the production line. In addition, if the intermediate film has such a structure, it is possible to suppress the peeling of the adhesive tape at the joint during stretching and / or conveyance of the original film. As a result, by using the intermediate film, a stretched film can be manufactured with very high productivity. The ratio of the elongation at break (%) of the intermediate film to the stretching ratio (%) (elongation at break / stretching ratio) is preferably 1.04 or more, more preferably 1.05 to 1.50, further preferably 1.06 to 1.45, and particularly preferably 1.15 to 1.40. The specific elongation at break of the intermediate film can vary according to the stretching ratio. The elongation at break of the intermediate film can be, for example, 270% or more, and can be, for example, 300% or more, and can be, for example, 320% or more, and can be, for example, 330% or more. On the other hand, the elongation at break of the intermediate film can be, for example, 450% or lower, and can be, for example, 430% or lower, and can be, for example, 400% or lower. It should be noted that the elongation at break can be measured in accordance with JIS K 7127.

[0060] The ratio of the elastic modulus of the intervening film to the elastic modulus of the original film (elastic modulus of the intervening film / elastic modulus of the original film) is preferably 0.80 to 1.10, more preferably 0.90 to 1.00, further preferably 0.92 to 1.00, and particularly preferably 0.95 to 1.00. In other words, the elastic modulus of the intervening film is preferably equal to or lower than the elastic modulus of the original film, and the difference from the elastic modulus of the original film is small. With such a configuration, the original film and the intervening film have similar stretching and post-stretching shrinkage behaviors, and have the advantage of being able to maintain transportability and stretchability.

[0061] The Tg of the intervening film is preferably -30°C to +5°C, more preferably -25°C to 0°C, further preferably -20°C to 0°C, and particularly preferably -10°C to 0°C, relative to the Tg of the original film. In other words, the Tg of the intervening film is preferably equal to or lower than the Tg of the original film, and the difference from the Tg of the original film is small. With such a configuration, the original film and the intervening film have similar stretching and post-stretching shrinkage behaviors, and have the advantage of being able to maintain transportability and stretchability.

[0062] The thickness of the intervening film is preferably 20 μm to 300 μm, more preferably 40 μm to 250 μm, and further preferably 60 μm to 200 μm. If the thickness of the intervening film is too large, the adhesive tape may not be able to follow the height difference caused by the thickness of the intervening film, and the adhesive tape is likely to peel off. If the thickness of the intervening film is too small, the effect of using the intervening film may not be obtained sufficiently.

[0063] As long as the elongation at break described above is satisfied, the intervening film can be composed of any suitable resin film. Specific examples of the resin include the resins described in item B above for the original film. For this resin, polymerization conditions (as a result, for example, molecular weight, stereoregularity, etc.) are appropriately set, a variety of resins are blended at an appropriate blending ratio, and / or the types, amounts, combinations, and mixing ratios of monomers are appropriately set for copolymerization, whereby an intervening film having a desired elongation at break can be obtained. For example, the intervening film can be formed of the same resin as the original film or a different resin from the original film. In one embodiment, the intervening film can be formed by cutting out the original film. That is, the intervening film can be formed of the same resin as the original film and can have the same elastic modulus and Tg as the original film.

[0064] D. Adhesive tape

[0065] The elongation at break of the adhesive tape is preferably 200% or more, more preferably 300% or more. If the elongation at break of the adhesive tape is within such a range, breakage of the adhesive tape during stretching can be suppressed. Further, by utilizing the synergistic effect with the effect brought about by using the intervening film, peeling of the adhesive tape at the joint can be suppressed. As a result, contamination of the production line by the adhesive layer of the adhesive tape can be suppressed, and a stretched film can be manufactured with very high productivity. It should be noted that the elongation at break of the adhesive tape can be, for example, 700% or less.

[0066] As long as the elongation at break as described above is satisfied, the adhesive tape can have any suitable configuration. The adhesive tape can be, for example, a single-sided adhesive tape including a base material and an adhesive layer formed on one surface of the base material, or a double-sided adhesive tape including a base material and adhesive layers formed on both surfaces of the base material. In one embodiment, the base material contains an olefin-based thermoplastic elastomer, and the adhesive layer contains a polypropylene-based resin and / or an acrylic resin.

[0067] The tensile strength of the adhesive tape is preferably 10 MPa to 100 MPa, more preferably 40 MPa to 80 MPa. If it has such a configuration, the adhesion to the original film can be maintained during stretching, and it can follow the deformation caused by stretching. It should be noted that the tensile strength can be measured in accordance with JIS K 7127.

[0068] The 10% strain stress relaxation rate of the adhesive tape is preferably 30% or more, more preferably 40% or more. If it has such a configuration, the adhesion and followability to the original film can be made excellent. The 10% strain stress relaxation rate is a value obtained as follows: using an adhesive tape having the same shape and size as the tensile test piece described in JIS K 6732 as the test piece, stretching it by 10% at a test speed of 300 mm / min and then holding it, measuring the initial stress F and the residual stress f after 10 minutes, and obtaining the value by the following formula (1).

[0069] 10% strain stress relaxation rate (%) = (F - f) * 100 / F ··· (1)

[0070] The thickness of the adhesive tape is preferably 20 μm to 300 μm, more preferably 50 to 150 μm. If the thickness of the adhesive tape is within such a range, sufficient adhesion, stretching followability, and strength to the original film can be obtained.

[0071] The specific configuration of the adhesive tape is described, for example, in Japanese Patent Application Laid-Open No. 2017-211580. The description of this publication is incorporated herein by reference.

[0072] The adhesive tape can be a commercially available product. Specific examples of commercially available products include the product names "No. 33T" and "No. 335PE" manufactured by Nitto Denko Corporation.

[0073] E. Tensile of the base film

[0074] E-1. Outline of the stretching machine and stretching method

[0075] As described above, the base film is supplied to a stretching machine (not shown) while being conveyed in the length direction, and is subjected to stretching treatment in the stretching machine. As the stretching method, any appropriate stretching method can be selected according to the purpose and the like. Specific examples of the stretching method include: free-end unidirectional stretching, fixed-end unidirectional stretching, simultaneous biaxial stretching, and progressive biaxial stretching. As the stretching direction, the longitudinal direction (the conveying or supply direction of the base film), the transverse direction (the direction substantially orthogonal to the conveying or supply direction of the base film), and the oblique direction (the direction forming a given angle with respect to the conveying or supply direction of the base film) can be cited. In addition, the stretching can be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching ratio described later is the product of the stretching ratios of each stage.

[0076] As the stretching machine, any appropriate stretching machine can be used according to the target stretching method. For example, a tenter can be used for fixed-end stretching. In addition, for example, a roller stretching machine can be used for free-end stretching. In addition, for example, a simultaneous biaxial stretching machine can be used for simultaneous biaxial stretching.

[0077] The stretching ratio can be appropriately set according to the purpose and the use of the obtained stretched film. The stretching ratio can be, for example, 1.5 times (150%) or more, and can be, for example, 1.8 times (180%) to 4.0 times (400%), and can be, for example, 1.9 times (190%) to 3.5 times (350%), and can be, for example, 2.0 times (200%) to 3.0 times (300%).

[0078] The stretching temperature is preferably Tg (°C) of the base film to Tg + 15 (°C), more preferably Tg + 3 (°C) to Tg + 13 (°C), and further preferably Tg + 5 (°C) to Tg + 10 (°C).

[0079] E-2. Bonding of the preceding base film and the succeeding base film

[0080] Refer again to Figure 1A and Figure 1BThe joining of the leading original film and the trailing original film will be described. The rear end portion of the leading original film and the front end portion of the trailing original film are joined in a state where the original film is not stretched. The intervening film 40 is arranged so as to overlap both the rear end portion of the leading original film and the front end portion of the trailing original film, and the adhesive tape 30 is adhered via the intervening film 40, thereby performing the joining. The arrangement of the intervening film and the adhesion of the adhesive tape can be carried out by any suitable method. As a specific example, manual operation and transfer of a laminate of the intervening film and the adhesive tape can be cited. In this way, the joint portion 60 can be formed.

[0081] The width of the intervening film is preferably equal to or less than the width of the original film ( Figure 1B showing the case where the width of the intervening film is the same as the width of the original film). If such a configuration is adopted, it is possible to suppress poor conveyance of the original film caused by the extending portion (projecting portion) in the width direction of the joint portion.

[0082] The width of the adhesive tape is preferably equal to or less than the width of the intervening film ( Figure 1B showing the case where the width of the adhesive tape is the same as the width of the intervening film). If such a configuration is adopted, the adhesive layer of the adhesive tape will not be exposed in the width direction, and thus it is possible to suppress contamination of the production line caused by the adhesive layer.

[0083] As Figure 1A shown, the adhesive tape 30 extends on both the leading original film 10a side and the trailing original film 10b side of the intervening film 40 and is adhered to both the leading original film 10a and the trailing original film 10b. As a result, the joint portion 60 is formed. The lengths of the extending portions (the adhered portions of the adhesive tape) on the leading original film side and the trailing original film side are each preferably 10 mm to 3000 mm, more preferably 100 mm to 1000 mm. If the lengths of the extending portions are within such a range, the adhesion of the extending portions (the adhesion of the adhesive tape to the original film) can be ensured. The lengths of the extending portions on the leading original film side and the trailing original film side may be the same or different.

[0084] The intervening film 40 and the adhesive tape 30 can be arranged on the lower side of the original film as Figure 1A shown, or can be arranged on the upper side of the original film (not shown). That is, the joint portion 60 can be provided on the lower side of the original film or on the upper side of the original film. Considering the operability, the joint portion can be provided on the upper side of the original film.

[0085] The rear end portion of the leading original film 10a and the front end portion of the trailing original film 10b can be joined together via the intervening film and using the adhesive tape in a state where they are butted to form the butted portion 20 as Figure 1A and Figure 1B shown, or can be joined together via the intervening film and using the adhesive tape in a state where a given interval is provided therebetween.

[0086] The specific order of joining the preceding original film and the succeeding original film will be described. The joining can be performed by any suitable method. Figures 2A - 2C is a schematic diagram showing an example of the joining method. First, as Figure 2A shown, the preceding original film 10a wound in a roll is continuously discharged from the continuous discharge section 1, and is transported in the length direction and supplied to the stretching machine 3 for stretching in a state L with a surplus length more than the length transported within the time required for the joining process. The stretched film 12a is wound into a roll by the winding section 4, for example (in the figure, reference numeral 2 denotes a transport roller). Next, as Figure 2B shown, when all of the preceding original film 10a has been continuously discharged, the succeeding original film 10b is set in the continuous discharge section 1 and continuous discharge is started, and during the period when the rear end portion of the preceding original film 10a in the surplus length portion is being transported, its rear end portion and the front end portion of the succeeding original film 10b are joined via the intervening film 40 using the adhesive tape 30. Next, as Figure 2C shown, the joined preceding original film 10a and succeeding original film 10b are continuously supplied to the stretching machine 3. At this time, by transporting the succeeding original film 10b in the length direction in a state L with a surplus length more than the length transported within the time required for the joining process, it is possible to perform joining with a subsequent original film (not shown) without stopping the transport. According to an embodiment of the present invention, by repeating such joining, it is possible to continuously stretch three or more (for example, three, four, five, six) original films. Further, for example, the preceding original film can be supplied to the stretching machine while being transported in the length direction, temporarily stopped before its rear end portion is supplied to the stretching machine, and joined to the front end portion of the succeeding original film. In the case of such a method, the transport of the original film is resumed after the joining is completed. It should be noted that, as shown in the figure, the stretched film can be directly wound into a roll while maintaining the joined state. In an embodiment of the present invention, by using the intervening film and the adhesive tape in combination, there is an advantage that even when the stretched film including the joined portion is wound into a roll, it is not easily broken.

[0087] E-3. Stretching of the original film

[0088] Next, the stretching of the original film will be specifically described. In one embodiment, the stretching is performed in a direction substantially orthogonal to the transport direction of the original film. That is, the stretching can be transverse stretching. In this case, the stretching machine to which the original film is supplied is typically a tenter stretching machine. The transverse stretching includes, for example: clamping both end portions of the original film with a plurality of clips, and while transporting in the length direction, expanding the distance between the clips in the width direction, thereby performing unidirectional stretching in the width direction.

[0089] Figures 3A - 3C is a top view schematic diagram for explaining a series of processes of the transverse stretching. First, as Figure 3AAs shown, the leading original film 10a is transported while being laterally stretched to obtain a stretched film 12a that has been stretched in the width direction. Next, as Figure 3B shown, the joint portion 60 is laterally stretched. Further, as Figure 3C shown, the trailing original film 10b is transported while being laterally stretched to obtain a stretched film 12b that has been stretched in the width direction. In an embodiment of the present invention, even when the joint portion is laterally stretched as Figures 3A - 3C shown, it is possible to suppress the exposure of the adhesive layer of the adhesive tape and the peeling of the adhesive tape.

[0090] The effect of the embodiment of the present invention is remarkable in the case of lateral stretching. Refer to Figure 4 for explanation. Figure 4 is a conceptual top view for explaining the bending that may occur in the joint portion 60. As Figure 4 shown, in the case of lateral stretching, a convex bend 50a is generated on the transport direction side of the rear end portion of the leading film, and a convex bend 50b is generated on the side opposite to the transport direction of the front end portion of the trailing film. As a result, at the joint portion 60, separation may occur between the rear end portion of the leading film and the front end portion of the trailing film. In this case, if the joint portion is composed only of an adhesive tape, the adhesive layer of the adhesive tape may sometimes be exposed and contaminate the production line. Further / or, the adhesive tape may sometimes peel off. In contrast, according to the embodiment of the present invention, by bonding the adhesive tape via a specific intervening film to form the joint portion, even if bending occurs, it is possible to suppress the exposure of the adhesive layer of the adhesive tape and the peeling of the adhesive tape. It should be noted that in the case of stretching in the transport direction (i.e., longitudinal stretching), both the leading film and the trailing film will shrink in the width direction, so the separation between the rear end portion of the leading film and the front end portion of the trailing film will not substantially occur. Therefore, the possibility of the exposure of the adhesive layer of the adhesive tape is extremely small. However, it should be noted that undoubtedly, even in the case of longitudinal stretching, the effect of the embodiment of the present invention will be obtained.

[0091] F. Use of the stretched film

[0092] The stretched film obtained by the embodiment of the present invention can be widely used for various purposes. As specific examples of the uses, there can be mentioned: food packaging film, food packaging fresh-keeping film, base film of adhesive tape, optical film (for example, retardation film, polarizer), surface protection film, window film (ultraviolet cut-off, heat ray cut-off, anti-scattering, anti-crime, shading, decoration), agricultural film, medical film, insulating film, building material film. In one embodiment, the stretched film can be an optical film, and more specifically, it can be a retardation film.

[0093] The thickness of the obtained stretch film can be appropriately set according to the purpose, use, etc. The thickness of the stretch film can be, for example, 15 μm to 200 μm, and can also be, for example, 20 μm to 150 μm, and can also be, for example, 25 μm to 100 μm.

[0094] Examples

[0095] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0096] [Production Example 1: Base Film]

[0097] 26.2 parts by mass of isosorbide (ISB), 100.5 parts by mass of 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), 10.7 parts by mass of 1,4-cyclohexanedimethanol (1,4-CHDM), 105.1 parts by mass of diphenyl carbonate (DPC), and 0.591 parts by mass of cesium carbonate (0.2 mass% aqueous solution) as a catalyst were respectively charged into a reaction vessel. In a nitrogen atmosphere, as the first stage of the reaction, the temperature of the heat medium in the reaction vessel was 150 °C, and the raw materials were dissolved while stirring as needed (about 15 minutes).

[0098] Next, the pressure in the reaction vessel was changed from normal pressure to 13.3 kPa, and the temperature of the heat medium in the reaction vessel was raised to 190 °C over 1 hour while extracting the generated phenol outside the reaction vessel.

[0099] After maintaining the temperature in the reaction vessel at 190 °C for 15 minutes, as the second stage, the pressure in the reaction vessel was 6.67 kPa, and the temperature of the heat medium in the reaction vessel was raised to 230 °C over 15 minutes while extracting the generated phenol outside the reaction vessel. Since the stirring torque of the stirrer gradually increased, the temperature was raised to 250 °C in 8 minutes. In order to further remove the generated phenol, the pressure in the reaction vessel was reduced to 0.200 kPa or less. After reaching the given stirring torque, the reaction was terminated, and the generated reaction product was extruded into water and then pelletized to obtain a polycarbonate resin with BHEPF / ISB / 1,4-CHDM = 47.4 mol% / 37.1 mol% / 15.5 mol%.

[0100] After subjecting the obtained polycarbonate resin to vacuum drying at 80 °C for 5 hours, a film-forming apparatus equipped with a single-screw extruder (manufactured by ISUZU KAKOKI CO., LTD., screw diameter 25 mm, cylinder set temperature: 220 °C), a T-die (width 200 mm, set temperature: 220 °C), a cooling roll (set temperature: 120 - 130 °C), and a winder was used to produce a strip-shaped polycarbonate resin film (thickness 100 μm). The polycarbonate resin film was slit at the ends in the width direction so that the width reached 150 mm to obtain a base film 1. The Tg of the base film 1 was 140 °C, and the elastic modulus was 2650 MPa.

[0101] [Production Example 2: Base Film]

[0102] Polymerization was carried out using a batch polymerization apparatus composed of two vertical reactors equipped with stirring blades and a reflux condenser controlled at 100 °C. 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of ISB, 42.28 parts by mass (0.139 mol) of SPG, 63.77 parts by mass (0.298 mol) of DPC, and 1.19×10 -2 parts by mass (6.78×10 -5 mol) of calcium acetate monohydrate as a catalyst were added. After replacing the inside of the reactor with nitrogen under reduced pressure, it was heated with a heat medium, and stirring was started when the internal temperature reached 100 °C. Forty minutes after the start of temperature increase, the internal temperature was raised to 220 °C, and while controlling to maintain this temperature, decompression was started, and it reached 13.3 kPa 90 minutes after reaching 220 °C. The phenol vapor by-produced during the polymerization reaction was introduced into a reflux condenser at 100 °C to return a certain amount of monomer components contained in the phenol vapor to the reactor, and the uncondensed phenol vapor was introduced into a condenser at 45 °C for recovery. After introducing nitrogen into the first reactor to temporarily restore it to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Then, the temperature increase and decompression in the second reactor were started, and the internal temperature reached 240 °C and the pressure reached 0.2 kPa in 50 minutes. Then, the polymerization was carried out until a given stirring power was reached. At the moment when the given power was reached, nitrogen was introduced into the reactor to restore the pressure, and the produced polyester carbonate was extruded into water, and the strands were cut to obtain pellets.

[0103] After the obtained polycarbonate resin was vacuum-dried at 80°C for 5 hours, a film-forming apparatus equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-die (width 300 mm, set temperature: 250°C), a cooling roll (set temperature: 120 - 130°C), and a winder was used to produce a strip-shaped polycarbonate resin film (thickness 90 μm). The width-direction ends of the polycarbonate resin film were slit to a width of 150 mm to obtain the original film 2. The Tg of the original film 2 was 120°C, and the elastic modulus was 2521 MPa.

[0104] [Production Example 3: Original Film]

[0105] The width-direction ends of a commercially available cycloolefin resin film (manufactured by Zeon Corporation, product name "ZEONOR ZF14", thickness 100 μm) were slit to a width of 150 mm to obtain the original film 3. The Tg of the original film 3 was 140°C, and the elastic modulus was 2236 MPa.

[0106] [Production Example 4: Intervening Film]

[0107] A commercially available acrylic resin film (manufactured by Mitsubishi Chemical Corporation, product name "ACRYPLEN", thickness 100 μm) was cut into a given shape to obtain the intervening film A. The Tg of the intervening film A was 120°C, and the elastic modulus was 2212 MPa.

[0108] [Production Example 5: Intervening Film]

[0109] A commercially available cycloolefin resin film (manufactured by Zeon Corporation, product name "ZEONOR ZF16", thickness 100 μm) was cut into a given shape to obtain the intervening film B. The Tg of the intervening film B was 155°C, and the elastic modulus was 2392 MPa.

[0110] [Example 1]

[0111] As the leading original film and the trailing original film, the original film 1 of Production Example 1 was used respectively. The respective original films were joined in the order shown in Figures 2A - 2C and stretched in the order shown in Figures 3A - 3C . Specifically, as follows. First, as shown in Figure 2A , the leading original film wound into a roll was continuously discharged from the continuous discharge section, and while having a surplus in a state where the length transported within the time required for the joining process was exceeded, it was transported in the length direction by rollers and supplied to a stretching machine for stretching, and the stretched film was wound into a roll by the winding section. As shown in Figure 3A , a tenter was used as the stretching machine and stretching was performed in the transverse direction. The stretching temperature was 147°C (Tg of the original film + 7°C), and the stretching ratio was 2.85 times.

[0112] Next, as Figure 2B shown, when all of the leading original film is continuously discharged, the trailing original film is set in the continuous discharge section and continuous discharge is started, and the trailing end is docked with the leading end of the trailing original film during the period when the leading original film in the length portion of the remaining paid-out is being transported. An intervening film is disposed at the docking portion, and the adhesive tape extends out on both the leading original film side and the trailing original film side of the intervening film, and the adhesive tape is adhered to both the leading original film and the trailing original film. The intervening film is cut out from the original film 1 and used. The elongation at break of the intervening film at the stretching temperature (147 °C) is 341%. A commercially available product (manufactured by Nitto Denko Corporation, product name “No. 33T”) is used for the adhesive tape. The widths of the intervening film and the adhesive tape are the same as the width of the original film, which is 150 mm. The lengths of the extending portions (the adhered portions of the adhesive tape) on the leading original film side and the trailing original film side are 100 mm each.

[0113] Next, as Figure 2C shown, the joined leading original film and trailing original film are supplied to the stretching machine, and as Figure 3B and Figure 3C shown, the leading original film and the trailing original film are continuously supplied for transverse stretching. The conditions for transverse stretching are the same as above. Thus, a stretched film is continuously produced from the joined leading original film and trailing original film. The obtained stretched film is a long strip-shaped retardation film having a refractive index characteristic of nx > ny = nz, having a slow axis in the width direction, and having an in-plane retardation Re(550) of 144 nm. In a series of manufacturing processes, the following (1) and (2) were evaluated.

[0114] (1) Adhesive tape peeling

[0115] During the joining and stretching of the original film, the state of the adhesive tape at the joined portion was confirmed and evaluated according to the following criteria. The results are shown in Table 1.

[0116] ◎ (excellent): No peeling was confirmed.

[0117] ○ (good): Some peeling was confirmed, but it had no substantial effect on the conveyance of the film.

[0118] △ (not allowable): Peeling that would substantially affect the conveyance of the film was confirmed.

[0119] × (bad): Most of the peeling occurred, having a significant impact on the conveyance of the film.

[0120] (2) Contamination of the production line

[0121] During the joining and stretching of the original film, the states of the conveying equipment and the stretching machine were confirmed and evaluated according to the following criteria. The results are shown in Table 1.

[0122] ◎ (Excellent): No contamination was confirmed.

[0123] ○ (Good): Part of the clamp of the stretching machine was contaminated, but there was no substantial impact.

[0124] △ (Not Permissible): Contamination that necessitated cleaning of the conveying equipment and the stretching machine was confirmed.

[0125] × (Poor): The contamination of the conveying equipment and the stretching machine was significant.

[0126] [Examples 2 - 5 and Comparative Examples 1 - 2]

[0127] The base film, the intervening film, and the adhesive tape were as shown in Table 1. Other than that, a stretched film was continuously produced from the preceding base film and the succeeding base film after bonding in the same manner as in Example 1. Further, the same evaluations as in Example 1 were carried out during the bonding and stretching of the base film. The results are shown in Table 1. It should be noted that in Table 1, for example, "Base Film 1" refers to the base film 1 of Production Example 1, and "Intervening A" refers to the intervening film A of Production Example 4. In addition, "-" in the column of the intervening film means that no intervening film was used.

[0128]

[0129] [Evaluation]

[0130] It can be clearly seen from Table 1 that according to the embodiments of the present invention, during the bonding and stretching of the base film, both the peeling of the adhesive tape and the contamination of the production line were well suppressed. Therefore, it can be known that according to the embodiments of the present invention, a stretched film can be obtained with very high productivity.

[0131] Industrial Applicability

[0132] The stretched film obtained by the manufacturing method of the embodiment of the present invention can be widely used for various purposes.

Claims

1. A method for producing a stretch film, the method comprising: The long original film is fed to a stretching machine for stretching while being conveyed in the length direction; The rear end of the preceding long strip original film and the front end of the succeeding long strip original film are joined via an intervening film and using an adhesive tape; as well as The rear long original film is fed to a stretching machine for stretching while being conveyed in the longitudinal direction. The elongation at break of the intermediate film at the stretching temperature is greater than the stretching ratio in the stretching machine.

2. The manufacturing method according to claim 1, wherein: The elastic modulus of the intervening film is lower than the elastic modulus of the original film.

3. The manufacturing method according to claim 2, wherein: The glass transition temperature (Tg) of the intervening film is lower than the glass transition temperature (Tg) of the original film.

4. The manufacturing method according to claim 3, wherein: The glass transition temperature of the original film is above 120°C.

5. The manufacturing method according to claim 4, wherein: The stretching temperature in the stretching machine is Tg (° C.) to Tg+15 (° C.) of the original film.

6. The production method according to any one of claims 1 to 5, wherein The stretching in the stretching machine is performed in a direction substantially perpendicular to the conveying direction of the original film.

7. The manufacturing method according to claim 6, wherein: The stretching ratio in the stretching machine is 1.5 times or more.

Images