Method for producing acrylic resin-containing film and multi-stage stretched acrylic resin-containing film

Abstract

The problems addressed by the present invention are to provide a method for producing an acrylic resin-containing film which is widened and thinned, does not crack, has high density, and can maintain functionality, and to provide a multi-stage stretched acrylic resin-containing film.　Provided is a method for producing an acrylic resin-containing film characterized by casting a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95:5-30:70, stretching the acrylic resin-containing film in two stages in the widthwise direction, and having the longitudinal expansion / contraction rate A from the detachment position of the acrylic resin-containing film to a position immediately before the second widthwise stretching and the widthwise relaxation rate A after the second widthwise stretching satisfy the relationship -250<(expansion / contraction rate A / relaxation rate A)<550.

Description

Method for producing acrylic resin-containing film and multi-stage stretched acrylic resin-containing film

[0001] The present invention relates to a method for producing an acrylic resin-containing film and a multistage stretched acrylic resin-containing film. More specifically, the present invention relates to a method for producing an acrylic resin-containing film that is wide and thin, crack-free, high-density, and capable of maintaining functionality.

[0002] In recent years, in addition to the trend toward larger TV sizes, there has been a demand for longer and wider films to improve productivity and reduce environmental impact, as well as for thinner films to save resources.

[0003] Here, a widened and thinned film may have a hard coat layer formed as a functional layer on the film before being incorporated into a display device, and the functional layer may be formed through a coating process. In the coating process, a coating solution is first prepared and then allowed to penetrate into the film substrate, but the coating solution may penetrate too much into the substrate, resulting in an insufficient thickness of the hard coat layer.

[0004] This has caused a problem that the function of the functional layer, for example, the function of providing the film with excellent pencil hardness, cannot be fully exerted.

[0005] Furthermore, if the coating liquid penetrates too much into the substrate as described above, cracks may occur in the film substrate, and such problems have arisen, so improvements have been required.

[0006] To address the above-mentioned problems, a method for efficiently producing an acrylic resin-containing film in which an acrylic resin and a cellulose ester resin are mixed in a specific ratio has been disclosed, as in Patent Document 1. The acrylic resin-containing film produced by this production method has excellent flexibility and surface properties, but there is still room for improvement.

[0007] International Publication No. 2009-150910

[0008] The present invention has been made in consideration of the above problems and circumstances, and the problem to be solved is to provide a method for producing an acrylic resin-containing film and a multi-stage stretched acrylic resin-containing film that can be made wider and thinner, is crack-free, has high density, and can maintain functionality.

[0009] In order to solve the above problems, the present inventors have investigated the causes of the above problems and have found that the above problems can be solved by stretching an acrylic resin-containing film in multiple stages and controlling the stretch rate in the longitudinal direction and the relaxation rate in the transverse direction so as to satisfy a specific relationship, thereby arriving at the present invention. That is, the above problems according to the present invention are solved by the following means.

[0010] 1. A method for producing an acrylic resin-containing film, comprising at least a casting step, a first conveying step, a first stretching step, and a second stretching step, in this order, wherein a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast in the casting step, the acrylic resin-containing film is stretched in the width direction in the first stretching step, and the acrylic resin-containing film is further stretched in the width direction in the second stretching step, wherein an expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion rate A / relaxation rate A)<550.

[0011] 2. A second conveying step is provided between the first stretching step and the second stretching step, and a conveying tension T of the acrylic resin-containing film after drying the dope in the first conveying step is １ and the conveying tension T of the acrylic resin-containing film in the second conveying step. ２ and satisfy the relationship of the following formula (2): 1.00<(conveying tension T １ / Transport tension T ２2. The method for producing an acrylic resin-containing film according to claim 1, wherein the viscosity of the film is less than 2.00.

[0012] 3. The method for producing an acrylic resin-containing film according to item 1, wherein the stretch rate A and the relaxation rate A satisfy the relationship of the following formula (3): Relaxation rate A<stretch rate A

[0013] 4. The method for producing an acrylic resin-containing film according to item 1, wherein when the acrylic resin-containing film is transported in the second transport step at an expansion / contraction rate a, the relationship of the following formula (4) is satisfied: 1.25<(expansion / contraction rate a / relaxation rate A)<5.5.

[0014] 5. A multistage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles, wherein the multistage stretched acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70, the total degree of substitution (T) of acyl groups in the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, and the film density of the multistage stretched acrylic resin-containing film is 1.235 to 1.300 g / cm ３ A multi-stage stretched acrylic resin-containing film, characterized in that the film thickness is within the range of

[0015] The above-mentioned means of the present invention can provide a method for producing an acrylic resin-containing film and a multi-stage stretched acrylic resin-containing film that can be made wider and thinner, crack-free, high-density, and maintain functionality. The mechanism by which the effects of the present invention are exerted or acted upon is not clear, but is speculated as follows.

[0016] The method for producing an acrylic resin-containing film of the present invention includes, in this order, at least a casting step, a first conveying step, a first stretching step, and a second stretching step, wherein a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast in the casting step, the acrylic resin-containing film is stretched in the width direction in the first stretching step, and the acrylic resin-containing film is further stretched in the width direction in the second stretching step, and an expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion rate A / relaxation rate A)<550.

[0017] In conventional films, because a wide and thin film is stretched only once, voids are generated in the film due to the influence of the stretch rate, particularly in the longitudinal direction, and the film may not be able to maintain a dense state. This reduces the density of the film, and when a functional layer is formed on the film, the coating liquid for forming the functional layer penetrates excessively, making it difficult to ensure the role of the functional layer.

[0018] The present inventors have controlled the longitudinal stretching rate and the widthwise relaxation rate so as to satisfy the relationship shown in the above-mentioned formula (1) in a method for producing an acrylic resin-containing film, which method includes at least a casting step, a first conveying step, a first stretching step, and a second stretching step in this order.

[0019] Stretching a film at high temperatures improves the mobility of the resin contained in the film, thereby increasing its density. In the above-mentioned manufacturing method, the amount of residual solvent in the film is reduced up to the second stretching step. Here, when the amount of residual solvent is reduced, further stretching in the width direction can increase the density of the film, but at the same time, voids are also generated in the width direction.

[0020] In the present invention, after the film is stretched in the width direction in the second stretching step when the residual solvent is reduced, the film is relaxed in the width direction, thereby filling the voids and increasing the density of the film, thereby maintaining the film in a dense state.

[0021] From the above, it is presumed that the widened and thinned acrylic resin-containing film produced by the production method of the present invention does not develop cracks, has high density, and can maintain functionality.

[0022] Schematic diagram showing the relationship between the state of the resin at the peeling position in the casting process and voids present in the film. Schematic diagram showing the relationship between the state of the resin at a position immediately before stretching in the second stretching process and voids present in the film. Schematic diagram showing the relationship between the state of the resin at a position immediately before stretching in the second stretching process and voids present in the film. Schematic diagram showing the relationship between the state of the resin before relaxation treatment in the second stretching process and voids present in the film. Schematic diagram showing the relationship between the state of the resin after relaxation treatment in the second stretching process and voids present in the film. Flowchart showing the flow of the film manufacturing process according to the present invention. Schematic diagram of a film manufacturing apparatus according to the present invention. Schematic diagram for explaining how a film is stretched by a tenter stretching apparatus.

[0023] The method for producing an acrylic resin-containing film of the present invention includes, in this order, at least a casting step, a first conveying step, a first stretching step, and a second stretching step, wherein a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95:5 to 30:70 is cast in the casting step, the acrylic resin-containing film is stretched in the width direction in the first stretching step, and the acrylic resin-containing film is further stretched in the width direction in the second stretching step, and the longitudinal expansion rate A from the peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step and the width direction relaxation rate A after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship shown in formula (1). This feature is a technical feature common to or corresponding to each of the following embodiments (aspects).

[0024] In one embodiment of the present invention, the conveying tension T １ and the conveying tension T ２ It is preferable that the relationship of the above formula (2) is satisfied from the viewpoint of suppressing the generation of voids in the film and setting the stretchability to an appropriate value.

[0025] It is preferable that the stretch rate A and the relaxation rate A satisfy the relationship of the formula (3) from the viewpoint of further enhancing the effects of the present invention.

[0026] It is preferable that the stretching rate a in the second transport step and the relaxation rate A satisfy the relationship of the above formula (4) from the viewpoint of controlling the film density within an appropriate range.

[0027] The multistage stretched acrylic resin-containing film of the present invention is a multistage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles, wherein the acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70, the total degree of substitution (T) of acyl groups of the cellulose ester resin (B) is in the range of 2.0 to 3.0, the degree of substitution of acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, and the film density of the acrylic resin-containing film is 1.235 to 1.300 g / cm ３ The range is characterized in that:

[0028] The present invention, its components, and embodiments and modes for carrying out the present invention will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0029] However, advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for illustrative purposes only and are not intended to define the limits of the invention.

[0030] 1. Manufacturing Method of Acrylic Resin-Containing Film The manufacturing method of the acrylic resin-containing film of the present invention is a manufacturing method of an acrylic resin-containing film comprising at least a casting step, a first conveying step, a first stretching step, and a second stretching step, in this order, wherein a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast in the casting step, the acrylic resin-containing film is stretched in the width direction in the first stretching step, and the acrylic resin-containing film is further stretched in the width direction in the second stretching step, and an expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion rate A / relaxation rate A)<550.

[0031] From the viewpoint of further enhancing the effects of the present invention, it is preferable that the stretch rate A and the relaxation rate A satisfy the relationship of the following formula (3): Formula (3) Relaxation rate A<stretch rate A.

[0032] If the value of (expansion rate A / relaxation rate A) is −250 or less, the acrylic resin-containing film will shrink too much in the longitudinal direction, and the resin molecules in the acrylic resin-containing film will not be able to maintain a stable arrangement, which will make it easier for voids to form in the acrylic resin-containing film.

[0033] Furthermore, wrinkles occur in the acrylic resin-containing film, and when a hard coat layer or the like is formed on the acrylic resin-containing film, the amount of coating liquid applied when forming the hard coat layer becomes excessive, impairing the functionality of the film.

[0034] To achieve a value of (stretch rate A / relaxation rate A) of 550 or more, the acrylic resin-containing film needs to be stretched excessively, which requires the film to be produced under high temperature and high tension conditions. Films produced under such conditions are prone to breakage. There is also a risk of foaming, which can cause voids in the film.

[0035] (Stretching Ratio A) Hereinafter, the meaning of "stretching ratio A" in the present invention will be conceptually explained with reference to Figs. 1, 2A and 2B.

[0036] Fig. 1 is a schematic diagram showing the relationship between the state of the resin at the peeling position in the casting process and the voids present in the film. Before being stretched in the first stretching step, the relationship between the resin and the voids in the film at the peeling position in the casting process is assumed to be aligned as shown in Fig. 1. (ＭＤ)０ is the length in the machine direction (machine direction, MD) of a specific portion of the film cut out at the peeling position in the casting process.

[0037] 2A and 2B are schematic diagrams showing the relationship between the state of the resin and voids present in the film immediately before stretching in the width direction in the second stretching step. Immediately before stretching in the second stretching step, the relationship between the resin and voids in the film is as shown in FIG. 2A or FIG. 2B. (ＭＤ)Ａ１ is the length of the film in the machine direction (machine direction, MD direction) from the peeling position in the casting process to the position immediately before stretching in the width direction (TD direction) in the second stretching process. (ＭＤ)０ is the length of the extension. (ＭＤ)Ａ２ is the length of the film in the machine direction (machine direction, MD direction) from the peeling position in the casting process to the position immediately before stretching in the width direction (TD direction) in the second stretching process. (ＭＤ)０ is the length that has shrunk.

[0038] If the expansion / contraction rate A is too small, that is, if the film shrinks too much in the longitudinal direction (machine direction, MD), the resin particles will no longer be able to maintain a stable arrangement, and voids will be more likely to form.

[0039] [Calculation of Stretch Rate A] The stretch rate A [%] was calculated using the following formula: Stretch rate A [%] = {(V Ｗ１ -V １ ) / V １}×100+{(V ４ -V ３ ) / V ３} x 100

[0040] The meanings of the symbols in the above formula are as follows: Ｗ１ V: Film winding speed in the second transport step (film winding speed by the winding device 8) １ V: Belt speed in the casting section (speed of the support) ３ V: Film unwinding speed in the second transport step ４ : Film conveying speed in the second stretching step

[0041] (Relaxation Rate A) Hereinafter, the concept of the "relaxation rate A" in the present invention will be explained with reference to FIGS. 3 and 4. FIG.

[0042] 3 is a schematic diagram showing the relationship between the state of the resin before the relaxation treatment in the second stretching step and the voids present in the film. Details of the stretching in the second stretching step will be described later. (ＴＤ)Ａ０ is the length in the width direction (TD direction) of the film before the relaxation treatment in the second stretching step.

[0043] FIG. 4 is a schematic diagram showing the relationship between the state of the resin after the relaxation treatment in the second stretching step and the voids present in the film. (ＴＤ)Ａ１ is the length in the width direction (TD direction) of the film after the relaxation treatment in the second stretching step.

[0044] If the relaxation rate A is small, the film density will be slightly low, but the film density will be extremely good if the film is sufficiently stretched in the longitudinal direction (machine direction, MD direction) and the relaxation rate A is sufficient. Conversely, if the relaxation rate A is too large, the film density will be high, but the film will wrinkle and crack easily, which will result in excessive penetration of the coating liquid when forming a hard coat layer or the like on the film, resulting in poor functionality.

[0045] [Calculation of Relaxation Rate A] The relaxation rate A [%] was calculated by the following formula: Relaxation rate A [%] = (L (ＴＤ)Ａ０ / L (ＴＤ)Ａ１ -1)×100[%] (L (ＴＤ)Ａ１ : Length in the width direction (TD direction) of the film after the relaxation treatment in the second stretching step, L (ＴＤ)Ａ０: length in the width direction (TD direction) of the film before the relaxation treatment in the second stretching step)

[0046] (Types of Film Forming Methods) The acrylic resin-containing film of the present invention can be produced by, for example, a solution casting film forming method or a melt casting film forming method.

[0047] The "solution casting film-forming method" is a film-forming method as follows. First, a dope is cast onto a moving support to form a casting film (web), which is then dried to a degree that allows peeling. Then, the web is peeled off from the support as a film, and the peeled film is dried and stretched while being transported by a transport roller to form a long resin film.

[0048] The "melt casting film-forming method" is a film-forming method in which a composition containing a thermoplastic resin and additives is heated and melted to a temperature at which the composition exhibits fluidity, and then the melt containing the fluid thermoplastic resin is cast.

[0049] 5 is a flowchart showing the flow of the film manufacturing process according to the present invention. This flowchart applies to both the solution casting film-forming method and the melt casting film-forming method, but the following description will be given assuming that the solution casting film-forming method is used.

[0050] (1.1) Casting Step: S1 Fig. 6 is a schematic diagram of a film production apparatus according to the present invention. In the casting step, a dope prepared by stirring at least a resin and a solvent in a stirring tank 1a of a stirring device 1 is sent to a casting die 2 through a conduit via a pressure-type metering gear pump or the like. The dope is cast from the casting die 2 onto a support 3 (casting belt) to form a casting film (web). The casting film (web) is then dried to a peelable degree, and then peeled off as a film from the support 3 (casting belt) by a peeling roller 4.

[0051] In order to increase the film-forming speed of the raw film, two or more casting dies may be provided on the support, and the dope may be divided and layered. It is also preferable to obtain a raw film having a laminated structure by a co-casting method in which a plurality of dopes are simultaneously cast.

[0052] The support 3 is made of, for example, a stainless steel belt and is held by a pair of rollers 3a and 3b and a plurality of rollers positioned between them. In this case, it is preferable that the surface of the support is a mirror finish.

[0053] One or both of the rollers 3a and 3b is provided with a drive device that applies tension to the support 3, so that the support 3 is used in a tensioned state. The support 3 may be a drum.

[0054] (Composition of Resin in Dope) The dope is prepared so as to contain the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70.

[0055] (Peeling of Film and Stretching Ratio A) The position where the film is peeled from the support 3 (casting belt) by the peeling roller 4 is defined as the peeling position, and the stretching ratio in the longitudinal direction (machine direction, MD) of the film from the peeling position to the position immediately before stretching the film in the width direction (TD direction) in the second stretching step described below is the stretching ratio A according to the present invention. The calculation method of the stretching ratio A is as described above.

[0056] (1.2) First conveyance process: S2 (conveyance tension T １ In the first conveying step, the peeled film is conveyed by a conveying roller 4 under a conveying tension T １ [N / m], and the conveying tension T １ [N / m] is the film transport speed in the first transport step and the film winding speed V in the winding device 8. Ｗ１ It is controlled by the speed difference between

[0057] In the first transport step, a drying device 5 may be provided at the position shown in FIG. 6 to dry the film as needed while the film is being transported.

[0058] The above conveying tension T １ The conveying tension T can be measured by installing a tension meter at any position in the first conveying step in FIG. 6 or at both ends of the film.１ For example, a non-contact web tension meter manufactured by Bellmatic may be used, which can measure the conveying tension without contacting the film by air pressure using an air turn bar supplied with air from a blower in the range of minute to low pressure.

[0059] (Temperature during film transport) At this time, the glass transition temperature Tg [°C] of the resin (synthetic resin consisting of acrylic resin and cellulose ester resin) in the dope is calculated from the resin composition, and the temperature during transport is determined to be (Tg-10)°C or less. More preferably, the temperature during transport is determined to be in the range of (Tg-40)°C to (Tg-60)°C.

[0060] (Stretching rate b) The stretching rate b [%] in the first conveying step is also one of the factors that affect the effects of the present invention, and the stretching rate b [%] in the longitudinal direction (conveying direction, MD direction) of the film during conveying is a value calculated by the following formula.

[0061] Formula: Expansion / contraction rate b [%] = {(V ２ -V １ ) / (V １ )×100[%]

[0062] The meanings of the symbols in the above formula are as follows: １ V: Belt speed in the casting section (speed of the support) ２ : Film conveying speed in the first stretching step

[0063] (1.3) First Stretching Step: S3 The first stretching step is a step of stretching the above-mentioned film in the width direction. Examples of the stretching device 6 include a tenter stretching device. Details of the tenter stretching device will be described later in the second stretching step. In this step, the relaxation rate B is calculated.

[0064] (Relaxation Rate B) Hereinafter, the concept of "relaxation rate B" in the present invention is omitted because it is the same as the above-mentioned "relaxation rate A." Therefore, only the method for calculating the relaxation rate B [%] will be described below. Note that if the relaxation rate B is high, the film density will be high. Also, if the relaxation rate B is low, the film density will be slightly low.

[0065] [Calculation of Relaxation Rate B] The relaxation rate B [%] according to the present invention was calculated by the following formula: Relaxation rate B [%] = {(L (ＴＤ)Ｂ０ -L (ＴＤ)Ｂ１ ) / L (ＴＤ)Ｂ１}×100[%] (L (ＴＤ)Ｂ１ : Length in the width direction (TD direction) of the film after the relaxation treatment in the first stretching step, L (ＴＤ)Ｂ０ : length in the width direction (TD direction) of the film before the relaxation treatment in the first stretching step)

[0066] (Second Conveying Step: 2nd MD) In ​​the second conveying step, the film stretched by the stretching device 6 is wound by the winding device 8 to produce a raw film. At this time, the film may be subjected to a drying treatment by providing a drying device 7, for example. Then, both ends of the film in the width direction are cut by a cutting section 13 consisting of a slitter before the film is wound by the winding device 8. In this way, the second conveying step according to the present invention includes a cutting and winding step.

[0067] [Transport tension T ２ The raw film wound by the winding device 8 is fed out from the winding device 8 at a feeding speed V ３ Then, the raw film is fed out at a feeding tension T ２ The conveying tension T ２ [N / m] is the film transport speed in the second transport step and the film winding speed V in the winding device 12. Ｗ２ At this time, the film may be subjected to a drying treatment by providing a drying device 9 or the like.

[0068] Conveying tension T ２ The conveying tension T is measured by installing a tension meter at any position in the second conveying step shown in FIG. 6 or at both ends of the film. １ It can be measured in the same manner as above.

[0069] In the second transport step, the amount of residual solvent is reduced, so if the expansion / contraction ratio a is too high, voids are likely to occur.

[0070] [Temperature and Expansion Ratio a during Film Conveyance] At this time, the glass transition temperature of the resin calculated from the resin composition in the dope as described above is used to determine the temperature during conveyance within the range of (Tg-10)°C to (Tg+20)°C. During conveyance, the expansion ratio a of the film in the longitudinal direction (conveyance direction, MD) is measured.

[0071] [Calculation of the stretch ratio a] The stretch ratio a [%] according to the present invention is a value calculated by the following formula: Ｗ１ -V ２ ) / V ２}×100+{(V ４ -V ３ ) / V ３} x 100

[0072] The meanings of the symbols in the above formula are as follows: Ｗ１ V: Film winding speed in the second transport step (film winding speed by the winding device 8) ２ V: Film conveying speed in the first stretching step ３ V: Film unwinding speed in the second transport step ４ : Film conveying speed in the second stretching step

[0073] [Relationship of conveying tension in conveying process] The conveying tension in the first conveying process is conveying tension T １ The conveying tension in the second conveying step is conveying tension T ２ is.

[0074] Here, the conveying tension T １ and the conveying tension T ２ It is preferable that the relationship of the following formula (2) is satisfied, from the viewpoint of suppressing the generation of voids in the film and setting the stretchability to an appropriate value.

[0075] Formula (2) 1.00<(transport tension T １ / Transport tension T ２ ) <2.00

[0076] Conveying tension T in the first conveying step １ is the conveying tension T in the second conveying step ２By increasing the value, the stretch ratio a in the longitudinal direction (conveying direction, MD direction) of the film in the second conveying step does not become too high.

[0077] In the second conveying step, the amount of residual solvent in the film is also reduced, so that the stretching ratio a does not become too high, and thus the generation of voids in the film can be suppressed. １ is the conveying tension T in the second conveying step ２ If the value is not too large, the stretch ratio a will not be too low, which will prevent the film density from becoming too high.

[0078] (1.4) Second Stretching Step: S4 The second stretching step is a step in which the raw film transported in the second transport step is further stretched in the width direction by a stretching device 10. As the stretching device 10, for example, a tenter stretching device can be used. In this specification, the speed at which the film is transported in the stretching device 10 is referred to as the transport speed V ４ In this step, the raw film may be subjected to a treatment such as drying, if necessary. The relaxation rate A in the width direction of the film is measured during this step.

[0079] (Relaxation Ratio A, Stretch Ratio A, and Stretch Ratio a) The stretch ratio A according to the present invention is the stretch ratio in the longitudinal direction (machine direction, MD) of the film from the peeling position of the film in the casting step to the position immediately before stretching in the width direction in the second stretching step. From the viewpoint of further enhancing the effects of the present invention, it is preferable that the stretch ratio A and the relaxation ratio A satisfy the relationship of the following formula (3): Formula (3) Relaxation ratio A [%] < Stretch ratio A [%]

[0080] In addition to the above relationship, if the relaxation rate A in the width direction of the film is not too small, the generation of voids due to a decrease in the density of the film can be suppressed, and if the relaxation rate A is not too large, the generation of wrinkles and cracks due to an increase in the film density can be suppressed.

[0081] Furthermore, it is preferable that the stretching rate a in the second conveying step and the relaxation rate A satisfy the relationship of the following formula (4): 1.25<(stretching rate a / relaxation rate A)<5.5, from the viewpoint of controlling the film density within an appropriate range.

[0082] (Tenter Stretching Apparatus) FIG. 7 is a schematic diagram for explaining how a film is stretched by a tenter stretching apparatus.

[0083] As shown in Figure 7, the tenter stretching apparatus 14 is mainly divided into a width retention zone A, a stretching zone B, a film width retention zone C, and a stress relaxation zone D. Each zone is described below. Note that the "relaxation treatment" in this specification is carried out in the stress relaxation zone D.

[0084] Width retention zone A: A zone in which the distance between the gripping clips of the film width (both base ends) from the entrance of the tenter stretching device 14 to the stretching start point a of the film is constant. Stretching zone B: A zone in which the distance between the gripping clips of the film width (both base ends) from the stretching start point a to the stretching end point b of the film in the tenter stretching device 14 increases in the traveling direction (transport direction). Film width retention zone C: A zone in which the film width is retained in a stretched state, in which the distance between the gripping clips of the film width (both base ends) after stretching from the stretching end point b of the film in the tenter stretching device 14 to the stress relaxation treatment start point c of the film is constant. Stress relaxation zone D: A zone in which the distance between the gripping clips of the film width (both base ends) from the stress relaxation treatment start point c to the stress relaxation treatment end point d of the tenter stretching device 14 narrows in the traveling direction (transport direction).

[0085] The above-mentioned "relaxation treatment" refers to a gripping pattern that narrows the film width in the direction of travel (conveyance direction, longitudinal direction, MD direction). The process in which the film F is not stretched taut in the width direction, i.e., stress is not applied to the film in the width direction, is called relaxation treatment, and this relaxation treatment is performed while the film ends are being gripped.

[0086] The a, b, c, and d shown between each zone can be summarized as follows:

[0087] a) Starting point of film stretching, entrance of stretching zone b) End point of film stretching, entrance of film width retention zone c) Starting point of film stress relaxation treatment, entrance of stress relaxation zone d) End point of stress relaxation treatment, exit of stress relaxation zone

[0088] 7 are as follows: F film Hc width of film at the entrance of the stress relaxation zone Hd width of film at the exit of the stress relaxation zone 110 housing 111 clip 112 rail

[0089] The relaxation rate A has been explained with reference to FIGS. 3 and 4. (ＴＤ)Ａ０ 4. The "Hc" in FIG. 7 corresponds to the "L" in FIG. 4. (ＴＤ)Ａ１ " corresponds to "Hd" in FIG.

[0090] (1.5) Subsequent Process (Third Conveying Process: 3rd MD) The raw film stretched and relaxed by the stretching device 10 in the second stretching process is conveyed in the third conveying process. At this time, the film may be subjected to a drying treatment by providing a drying device 11, etc., as necessary.

[0091] (Cutting and Winding Process) Thereafter, the film is processed by cutting both ends in the width direction by the cutting unit 13 consisting of a slitter, and is wound by the winding device 12 at a winding speed V Ｗ２ The film is then wound into a roll.

[0092] 2. Multistage Stretched Acrylic Resin-Containing Film The multistage stretched acrylic resin-containing film of the present invention is a multistage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles, wherein the acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70, the total degree of substitution (T) of acyl groups of the cellulose ester resin (B) is in the range of 2.0 to 3.0, the degree of substitution of acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, and the film density of the acrylic resin-containing film is 1.235 to 1.300 g / cm ３ The present invention is characterized in that the content of the polymerizable compound is within the range of 100% by weight. The polymerizable compound can be suitably produced by the above-mentioned production method.

[0093] (2.1) Film Density, Thickness and Length The multistage stretched acrylic resin-containing film of the present invention has a higher film density than the density of conventional stretched films containing acrylic resins, and has a film density of 1.235 to 1.300 g / cm ３ is within the range.

[0094] Here, the term "multi-stage stretching" refers to stretching in multiple stages. The term "single-stage stretching" used below refers to a single stretching. Whether a resin film has been stretched can be confirmed, for example, by checking whether an in-plane slow axis (an axis extending in the direction in which the refractive index is maximized) is present. Whether a resin film has been stretched in multiple stages can be confirmed mainly by checking whether the film density is higher than that of conventional films.

[0095] Conventional stretched films containing acrylic resins are one-stage stretched films, so the film density is 1.180 to 1.235 g / cm ３ However, in the present invention, the film thickness is increased to 1.236 to 1.300 g / cm by multiple stretching. ３ The film density is controlled within the range of .

[0096] The reason why the density of the multi-stage stretched film of the present invention is increased is because the mobility of the resin contained in the film is improved by stretching the film at a high temperature. In addition, the density of the film is further increased by further stretching in the width direction in the second stretching step when the amount of residual solvent in the film production process has been reduced.

[0097] However, since voids are also generated in the width direction at the same time, these voids can be filled by a relaxation treatment in the width direction, allowing stretching without reducing density, which is believed to result in a wide, thin film that can fully exhibit the effects of the functional layer formed on the film.

[0098] Furthermore, the conveying tension T １ The expansion / contraction ratio b in the longitudinal direction in the first conveying step is controlled by controlling the expansion / contraction ratio b in the longitudinal direction in the first conveying step. This further enhances the effects of the present invention.

[0099] Regarding the longitudinal expansion rate b in the first conveying step, since the film contains a large amount of residual solvent, the mobility of the resin is high and the density of the film is likely to increase. Also, by making the longitudinal expansion rate of the film in the first stretching step less than the longitudinal expansion rate in the film peeling process, the film is likely to become denser.

[0100] (Film Density) The density of a film can be measured, for example, by X-ray reflectivity (XRR). X-rays are totally reflected when they are incident on the film surface at a very shallow angle, and when the angle of incidence of the X-rays is equal to or greater than the critical angle of total reflection, the X-rays penetrate into the film, resulting in a decrease in reflectance.

[0101] The reflectance profile measured by the XRR method can be analyzed using dedicated reflectance analysis software. In the present invention, when the angle at which the reflectance starts to decrease is defined as θa, the surface density is defined as the density at which the fitting error between the measurement result and the calculation result is smallest in the range of 2θ from 2θa to 2θa + 0.1°. In this case, the surface roughness is within the range of 0 to 1 nm when performing the fitting.

[0102] The substrate film is cut into a size of 30 mm x 30 mm, fixed to a sample stage, and measured under the following measurement conditions.

[0103] <Measurement conditions> Apparatus: Thin film X-ray diffraction apparatus (ATX-G, manufactured by Rigaku Corporation) Sample size: 30 mm x 30 mm Incident X-ray wavelength: 1.5405 Å Measurement range (θ): 0 to 6° Analysis software: Reflectance analysis software GXRR (manufactured by Rigaku Corporation)

[0104] (Film Thickness) The effect of the present invention is enhanced in the thin film region. The thickness of the film according to the present invention is preferably in the range of 5 to 80 μm, more preferably in the range of 30 to 60 μm.

[0105] Although there is no particular upper limit to the thickness of the film, when the film is produced by a solution casting film-forming method, the upper limit is about 250 μm from the viewpoints of coatability, foaming, solvent drying, etc. The thickness of the film can be appropriately selected depending on the application.

[0106] However, if the film is too thick, the amount of residual solvent is large, and when that amount of solvent evaporates, voids are more likely to occur, so it becomes increasingly necessary to control the range of (stretch rate A / relaxation rate A).

[0107] The thickness of the film can be measured using an in-line retardation / film thickness measuring device RE-200L2T-Rth+film thickness (manufactured by Otsuka Electronics Co., Ltd.).

[0108] (Film Length) The film according to the present invention can be stored by, for example, winding the film in a roll shape in a direction perpendicular to the width direction of the film to form a roll body.

[0109] The length of the film according to the present invention is not particularly limited, but may be, for example, about 100 to 10,000 m. The width of the strip-shaped laminate film is preferably 1 m or more, more preferably in the range of 1.1 to 4 m. From the viewpoint of improving the uniformity of the film, the width is more preferably in the range of 1.3 to 2.5 m.

[0110] (2.2) Resin The film according to the present invention contains at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles. The resin species of the resin composition in the dope used in the casting process for producing this film include at least the acrylic resin (A) and the cellulose ester resin (B). The resin composition may contain other resins besides the above-mentioned resin species, including rubber particles and inorganic particles. The particles may include other particles besides rubber particles and inorganic particles. The resin composition may also contain other components, such as various additives.

[0111] When the film contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), the added resin may be in a compatible state or may be mixed without dissolving. When using a resin or additive other than the acrylic resin (A) and the cellulose ester resin (B), it is preferable to adjust the amount added within a range that does not impair the function of the film.

[0112] The density of the film can be affected by changing the amount of rubber particles or inorganic particles relative to the resin. For example, increasing the amount of rubber particles or inorganic particles relative to the resin promotes solvent diffusion, reducing the difference in density between the front and back of the film.

[0113] (Mass Ratio and Total Mass) In the multistage stretched acrylic resin-containing film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a compatible state at a mass ratio within the range of 95:5 to 30:70. The mass ratio is preferably within the range of 95:5 to 50:50, and more preferably within the range of 90:10 to 60:40.

[0114] If the mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is greater than 95:5, the effect of the cellulose ester resin (B) is insufficient, and if the mass ratio of the acrylic resin (A) is less than 30:70, the moisture resistance is insufficient.

[0115] The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the acrylic resin-containing film is preferably 55% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more of the acrylic resin-containing film.

[0116] In the multistage stretched acrylic resin-containing film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) must be contained in a compatible state. For example, the physical properties and quality required for optical film applications are achieved by mutually compensating for each other through the compatibility of different resins.

[0117] Whether the acrylic resin (A) and the cellulose ester resin (B) are compatible with each other can be determined by the glass transition temperature (Tg).

[0118] When two resins are simply mixed, each resin has its own glass transition temperature, resulting in two glass transition temperatures for the mixture. In contrast, when the two resins are mixed together, the glass transition temperatures specific to each resin disappear, resulting in a single glass transition temperature that becomes the glass transition temperature of the mixed resins.

[0119] From the viewpoint of heat resistance, the film preferably has a glass transition temperature (Tg) of 110°C or higher, more preferably 120°C or higher, and particularly preferably 150°C or higher.

[0120] The glass transition temperature T ｇ１，２ It is known that can be approximated by the Gordon-Taylor equation (M. Gordon and J.S. Taylor, 2 J. of Applied Chem. 493-500 (1952)). The Gordon-Taylor equation is as follows: ｇ１，２ = (w １ T ｇ１ +Kw ２ T ｇ２ ) / (w １ +Kw ２ ) [Here, w １ and w ２is the mass fraction of components 1 (acrylic resin (A)) and 2 (cellulose ester resin (B)). ｇ１ and T ｇ２ are the glass transition temperatures (in degrees Kelvin) of components 1 and 2, respectively. ｇ１，２ is the glass transition temperature of the mixture of components 1 and 2. K is a constant related to the free volume of the two resins.

[0121] The "glass transition temperature" referred to here is that determined using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer). Specifically, a sample is conditioned in advance in an atmosphere of 23°C and 55% RH for 24 hours, and then measured in a nitrogen gas flow at a temperature increase rate of 20°C / min. The midpoint glass transition temperature (Tmg) is determined in accordance with JIS K7121 (1987).

[0122] The acrylic resin (A) and the cellulose ester resin (B) are each preferably an amorphous resin, and either one may be a crystalline polymer or a polymer having partial crystallinity. The acrylic resin (A) and the cellulose ester resin (B) are preferably compatible with each other to form an amorphous resin.

[0123] In the present invention, "containing the acrylic resin (A) and the cellulose ester resin (B) in a compatible state" means that the respective resins (polymers) are mixed together to form a compatible state, and does not include a state in which a precursor of the acrylic resin, such as a monomer, dimer, or oligomer, is mixed with the cellulose ester resin (B) and then polymerized to form a mixed resin.

[0124] For example, the process of obtaining a mixed resin by mixing a precursor of an acrylic resin, such as a monomer, a dimer, or an oligomer, with a cellulose ester resin (B) and then polymerizing the resulting mixture involves a complex polymerization reaction, and the reaction of the resin produced by this method is difficult to control, and the molecular weight is also difficult to adjust.

[0125] Furthermore, when a resin is synthesized by such a method, graft polymerization, crosslinking reaction, or cyclization reaction often occurs, resulting in the resin being insoluble in a solvent or unable to be melted by heating. Furthermore, since it is difficult to measure the weight average molecular weight (Mw) by eluting the acrylic resin in the mixed resin, it is difficult to control the physical properties, and the resin cannot be used to stably produce an acrylic resin-containing film.

[0126] (2.2.1) Acrylic Resin (A) The acrylic resin (A) according to the present invention also includes methacrylic resins. There are no particular limitations on the resin. The acrylic resin (A) is preferably one that contains 50 to 99% by mass of methyl methacrylate units and 1 to 50% by mass of other monomer units copolymerizable therewith.

[0127] Examples of other copolymerizable monomers include alkyl methacrylates having an alkyl group with 2 to 18 carbon atoms, alkyl acrylates having an alkyl group with 1 to 18 carbon atoms, α,β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, etc. These monomers can be used alone or in combination of two or more.

[0128] Among these, from the viewpoint of thermal decomposition resistance and fluidity of the copolymer, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, etc. are preferred, and methyl acrylate and n-butyl acrylate are particularly preferred.

[0129] (Commercially available products) The acrylic resin used in the present invention may be a commercially available product. Examples include Delpet 60N and 80N (manufactured by Asahi Kasei Chemicals Corporation), Dianall BR52, BR80, BR83, BR85, and BR88 (manufactured by Mitsubishi Rayon Co., Ltd.), and KT75 (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha). Two or more types of acrylic resins may also be used in combination.

[0130] (Production Method) The production method of the acrylic resin (A) in the present invention is not particularly limited, and the resin can be produced by a known method, such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization.

[0131] (Weight-average molecular weight) The acrylic resin (A) according to the present invention preferably has a weight-average molecular weight (Mw) in the range of 80,000 to 1,000,000, particularly from the viewpoint of improving brittleness as an acrylic film and improving transparency when it is mixed with the cellulose ester resin (B).

[0132] If the weight average molecular weight (Mw) of the acrylic resin (A) is less than 80,000, sufficient improvement in brittleness cannot be obtained, and compatibility with the cellulose ester resin (B) deteriorates. The weight average molecular weight (Mw) of the acrylic resin (A) is particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000.

[0133] The weight average molecular weight of the acrylic resin according to the present invention can be measured by gel permeation chromatography (GPC) under the following conditions.

[0134] <Measurement conditions> Solvent: methylene chloride Column: Shodex K806, K805, K803G (three columns manufactured by Showa Denko K.K. were connected and used) Column temperature: 25°C Sample concentration: 0.1% by mass Detector: RI Model 504 (manufactured by GL Sciences) Pump: L6000 (manufactured by Hitachi, Ltd.) Flow rate: 1.0 ml / min Calibration curve: A calibration curve was prepared using 13 samples of standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) with Mw = 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

[0135] (2.2.2) Cellulose ester resin (B) The total substitution degree (T) of acyl groups in the cellulose ester resin (B) according to the present invention is in the range of 2.0 to 3.0, and the substitution degree of acyl groups having a carbon number of 3 to 7 is in the range of 1.2 to 3.0. This improves brittleness in particular, and increases transparency when the resin is mixed with the acrylic resin (A).

[0136] If the ratio of structurally bulky cellulose ester resin is too high compared to acrylic resin, the film will assume a three-dimensional and stable arrangement due to hydrogen bonding, making it difficult to increase density even when stretched or relaxed.Furthermore, minute voids are likely to form, which causes excessive penetration of the coating solution when forming a hard coat layer, etc., resulting in reduced functionality.

[0137] The acyl group having 3 to 7 carbon atoms is an aliphatic acyl group having 3 to 7 carbon atoms, and a structure having at least one of the aliphatic acyl groups is preferred as the structure used for the cellulose ester resin (B). Two or more types of cellulose resins can also be used in combination.

[0138] The cellulose ester resin (B) is substituted with an acyl group having a carbon number of 3 to 7. As the acyl group, specifically, a propionyl group, a butyryl group, etc. are preferably used, and a propionyl group is particularly preferably used.

[0139] Specifically, it is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, that is, those having an acyl group having 3 or 4 carbon atoms as a substituent.

[0140] Among the above, cellulose acetate propionate and cellulose propionate are particularly preferred.

[0141] (Total Substitution Degree of Acyl Groups and Carbon Number) The substitution degree of acyl groups can be determined by the method specified in ASTM-D817-96. When the total substitution degree of acyl groups is less than 2.0, that is, when the residual ratio of hydroxyl groups at the 2-, 3-, and 6-positions of the cellulose ester molecule exceeds 1.0, the acrylic resin (A) and the acrylic resin (B) are not sufficiently compatible with each other. This causes haze problems when used as a film. Haze (turbidity) is an index for determining transparency.

[0142] Furthermore, even when the total degree of substitution of the acyl groups is 2.0 or more, if the degree of substitution of acyl groups having 3 to 7 carbon atoms is less than 1.2, sufficient compatibility will not be obtained or brittleness will decrease. For example, even when the total degree of substitution of acyl groups is 2.0 or more, if the degree of substitution of acyl groups having 2 carbon atoms, i.e., acetyl groups, is high and the degree of substitution of acyl groups having 3 to 7 carbon atoms is less than 1.2, compatibility will decrease and haze will increase.

[0143] Furthermore, even when the total degree of substitution of acyl groups is 2.0 or more, if the degree of substitution of acyl groups having 8 or more carbon atoms is high and the degree of substitution of acyl groups having 3 to 7 carbon atoms is less than 1.2, brittleness deteriorates and desired properties cannot be obtained.

[0144] The cellulose ester resin (B) according to the present invention has an acyl substitution degree of 2.0 to 3.0 in total substitution degree (T), and the substitution degree of acyl groups having 3 to 7 carbon atoms is 1.2 to 3.0. However, it is preferable that the total substitution degree of acyl groups having carbon atoms other than 3 to 7, i.e., acetyl groups and acyl groups having 8 or more carbon atoms, is 1.3 or less.

[0145] The total degree of substitution (T) of the acyl groups in the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

[0146] The acyl group may be an aliphatic acyl group or an aromatic acyl group.

[0147] [Aliphatic Acyl Group] When the acyl group is an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms in the acyl group in the present invention includes the number of carbon atoms of the acyl group.

[0148] [Aromatic Acyl Group] When the acyl group is an aromatic acyl group, the number of substituents X substituted on the aromatic ring is 0 to 3. In this case, care must also be taken to ensure that the degree of substitution of an acyl group having 3 to 7 carbon atoms, including the substituent, is 1.2 to 3.0. For example, since a benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the number of carbon atoms as a benzoyl group is 8 or more, and it is not included in the acyl group having 3 to 7 carbon atoms.

[0149] Furthermore, when the number of substituents substituted on an aromatic ring is two or more, they may be the same or different, and may be linked to each other to form a condensed polycyclic compound (e.g., naphthalene, indene, indane, phenanthrene, quinoline, isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

[0150] (Synthesis Method) The portion not substituted with an acyl group is usually present as a hydroxyl group, and can be synthesized by a known method.

[0151] (Weight-average molecular weight) The weight-average molecular weight (Mw) of the cellulose ester resin (B) according to the present invention is preferably in the range of 75,000 to 300,000, particularly from the viewpoint of compatibility with the acrylic resin (A) and improvement of brittleness, more preferably in the range of 100,000 to 240,000, and particularly preferably in the range of 160,000 to 240,000.

[0152] When the weight average molecular weight (Mw) of the cellulose ester resin exceeds 75,000, the effects of improving heat resistance and brittleness are sufficient.

[0153] (2.3) Particles The multistage stretched acrylic resin-containing film of the present invention contains at least rubber particles and inorganic particles. There are no particular restrictions on the particles contained, and particles other than the above-mentioned particles may also be contained.

[0154] (2.3.1) Rubber Particles The multistage stretched acrylic resin-containing film of the present invention contains at least rubber particles. The rubber particles are preferably contained in a range of 40 to 85% by mass, particularly when a (meth)acrylic resin or a styrene-(meth)acrylate copolymer is used. This provides toughness (flexibility) and improves the resistance to creases when the film is folded.

[0155] The rubber particles are particles containing a rubbery polymer. The rubbery polymer is a soft crosslinked polymer having a glass transition temperature (Tg) of 20° C. or less. Examples of the crosslinked polymer include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers.

[0156] Among these, (meth)acrylic crosslinked polymers are preferred, and acrylic crosslinked polymers (acrylic rubbery polymers) are more preferred, from the viewpoint of having a small difference in refractive index from the (meth)acrylic resin and thus preventing the transparency of the film from being impaired. That is, the rubber particles are preferably particles containing the acrylic rubbery polymer [a].

[0157] (Acrylic rubber-like polymer [a]) The acrylic rubber-like polymer [a] is a crosslinked polymer containing structural units derived from an acrylic ester as a main component. Here, "containing structural units derived from an acrylic ester as a main component" means that the content of the structural units derived from an acrylic ester falls within the range described below.

[0158] The acrylic rubber-like polymer [a] is preferably a crosslinked polymer containing the following three structural units (1) to (3): (1) a structural unit derived from an acrylic acid ester, (2) a structural unit derived from another monomer copolymerizable with the structural unit derived from an acrylic acid ester, and (3) a structural unit derived from a polyfunctional monomer having two or more radically polymerizable groups (non-conjugated reactive double bonds) in one molecule.

[0159] Preferred acrylic acid esters include alkyl acrylates in which the alkyl group has 1 to 12 carbon atoms, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and n-octyl acrylate. One type of acrylic acid ester may be used, or two or more types may be used.

[0160] [Structural Units Derived from Acrylic Acid Esters] The content of structural units derived from acrylic acid esters is preferably within a range of 40 to 80 mass % relative to all structural units constituting the acrylic rubber-like polymer [a1]. It is more preferably within a range of 50 to 80 mass %. When the content of acrylic acid esters is within the above range, it is easy to impart sufficient toughness to the film.

[0161] [Other Copolymerizable Monomers] The other monomers copolymerizable with the structural units derived from acrylate esters are monomers copolymerizable with acrylate esters other than polyfunctional monomers, i.e., the copolymerizable monomers do not have two or more radically polymerizable groups.

[0162] Examples of copolymerizable monomers include methacrylic acid esters such as methyl methacrylate; styrenes such as styrene and methylstyrene; (meth)acrylonitriles; (meth)acrylamides; and (meth)acrylic acid. Among these, the copolymerizable other monomer preferably includes a styrene. The copolymerizable other monomer may be one type or two or more types.

[0163] The content of structural units derived from other copolymerizable monomers is preferably within a range of 5 to 55 mass %, more preferably within a range of 10 to 45 mass %, based on the total structural units constituting the acrylic rubber-like polymer [a].

[0164] [Polyfunctional Monomer] Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipropylene glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate.

[0165] The content of the structural units derived from the polyfunctional monomer is preferably within a range of 0.05 to 10% by mass, more preferably within a range of 0.1 to 5% by mass, based on the total structural units constituting the acrylic rubber-like polymer [a].

[0166] When the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the resulting acrylic rubber-like polymer [a] is easily increased, so that the hardness and rigidity of the resulting film are not excessively impaired. When the content is 10% by mass or less, the toughness of the film is less likely to be impaired.

[0167] The monomer composition of the acrylic rubber-like polymer [a] can be measured, for example, by the peak area ratio detected by pyrolysis GC-MS.

[0168] The glass transition temperature (Tg) of the rubbery polymer is preferably 0° C. or lower, and more preferably −10° C. or lower. When the glass transition temperature (Tg) of the rubbery polymer is 0° C. or lower, the film can be imparted with appropriate toughness. The glass transition temperature (Tg) of the rubbery polymer is measured by the same method as described above.

[0169] [Others] The glass transition temperature (Tg) of the rubbery polymer can be adjusted by the composition of the rubbery polymer. For example, in order to lower the glass transition temperature (Tg) of the acrylic rubbery polymer [a], the following is preferable.

[0170] In the acrylic rubber-like polymer [a], it is preferable to increase the mass ratio of the acrylic acid ester having an alkyl group with 3 or more carbon atoms to the other copolymerizable monomer. The number of carbon atoms is preferably within the range of 4 to 10.

[0171] The particles containing the acrylic rubber-like polymer [a] may be particles made of the acrylic rubber-like polymer [a], or may be particles having a hard layer made of a hard crosslinked polymer (c) having a glass transition temperature of 20°C or higher and a soft layer made of the acrylic rubber-like polymer [a] disposed around the hard layer (these are also referred to as "elastomers").

[0172] Furthermore, the particles may be particles made of an acrylic graft copolymer obtained by polymerizing a mixture of monomers such as methacrylic acid esters in at least one stage in the presence of the acrylic rubber-like polymer [a]. The particles made of the acrylic graft copolymer may be core-shell type particles having a core containing the acrylic rubber-like polymer [a] and a shell covering the core.

[0173] In the present embodiment, when the film is not stretched, the shape of the rubber particles may be close to a perfect sphere, i.e., when observing the cross section or surface of the film, the aspect ratio of the rubber particles may be about 1 to 2.

[0174] The average particle size of the rubber particles is preferably in the range of 100 to 400 nm. When the average particle size of the rubber particles is 100 nm or more, sufficient toughness and stress relaxation properties are easily imparted to the substrate film, and when it is 400 nm or less, the transparency of the substrate film is less likely to be impaired. From the same viewpoint, the average particle size of the rubber particles is more preferably in the range of 150 to 300 nm.

[0175] The average primary particle size of the rubber particles can be determined by measuring the dispersed particle size of the rubber particles in the dispersion liquid using a zeta potential / particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

[0176] The content of the rubber particles is not particularly limited, but is preferably in the range of 0.5 to 20% by mass, and more preferably in the range of 0.8 to 15% by mass, based on the film.

[0177] (2.3.2) Inorganic Particles The film of the present invention contains particles of an inorganic compound, i.e., inorganic particles, which improve the transportability of the film. Examples of the inorganic compound in the inorganic particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate.

[0178] (2.3.3) Other Particles The film according to the present invention may contain, in addition to the inorganic particles, particles of organic compounds, i.e., organic particles. Examples of organic compounds that can be used include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene-based resins, silicone-based resins, polycarbonate resins, benzoguanamine-based resins, melamine-based resins, polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyethylene fluoride-based resins, and pulverized fractions of organic polymer compounds such as starch, as well as polymer compounds synthesized by suspension polymerization.

[0179] As the compound, a silicon-containing compound is preferred because it reduces turbidity, and silicon dioxide is particularly preferred. Examples of such commercially available products include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, and TT600 (all manufactured by Nippon Aerosil Co., Ltd.).

[0180] (2.4) Other Components There are no particular limitations on the other components as long as they do not impair the effects of the present invention, and examples thereof include plasticizers, ultraviolet absorbers, antioxidants, and flame retardants.

[0181] (Plasticizer) In the film of the present invention, a plasticizer can be used in combination to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate esters, fatty acid esters, trimellitates, phosphate esters, polyesters, and epoxy plasticizers.

[0182] Among these, polyester and phthalate ester plasticizers are preferred. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are somewhat inferior in plasticizing effect and compatibility. Therefore, by selecting or combining these plasticizers depending on the application, they can be used in a wide range of applications.

[0183] Polyester plasticizers are reaction products of mono- to tetra-carboxylic acids with mono- to hexa-valent alcohols, but those obtained by reacting dicarboxylic acids with glycols are mainly used. Representative dicarboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, and sebacic acid.

[0184] In particular, the use of adipic acid, phthalic acid, etc., results in a composition with excellent plasticizing properties. Examples of glycols include ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, dipropylene, etc. These dicarboxylic acids and glycols may be used alone or in combination.

[0185] The plasticizer is preferably added in an amount of 0.5 to 30 parts by weight per 100 parts by weight of the acrylic film of the present invention. If the amount of plasticizer added exceeds 30 parts by weight, the surface becomes sticky, which is not practically preferable.

[0186] [Commercially Available Products] Examples of commercially available products include Monopet SB (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0187] (Ultraviolet Absorber) The film according to the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber that can be used include benzotriazole-based, 2-hydroxybenzophenone-based, and salicylic acid phenyl ester-based ones.

[0188] Examples of the benzotriazole include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2′-dihydroxy-4-methoxybenzophenone.

[0189] Among the ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize due to their high boiling points and are less likely to scatter even during high-temperature molding, and therefore can effectively improve weather resistance with the addition of a relatively small amount.

[0190] Examples of ultraviolet absorbers having a molecular weight of 400 or more include benzotriazole-based ones such as 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2-benzotriazole and 2,2-methylenebis[4-(1,1,3,3-tetrabutyl)-6-(2H-benzotriazol-2-yl)phenol], and hindered amine-based ones such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate and bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate. Further examples include hybrid systems having both hindered phenol and hindered amine structures in the molecule, such as 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate bis(1,2,2,6,6-pentamethyl-4-piperidyl) and 1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine. These can be used alone or in combination of two or more. Among these, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2-benzotriazole and 2,2-methylenebis[4-(1,1,3,3-tetrabutyl)-6-(2H-benzotriazol-2-yl)phenol] are particularly preferred.

[0191] (Antioxidant) Furthermore, various antioxidants can be added to the film of the present invention in order to improve thermal decomposition and thermal discoloration during molding processing. Also, an antistatic agent can be added to impart antistatic properties to the acrylic film.

[0192] (Flame Retardant) The film according to the present invention may contain a flame-retardant acrylic resin composition containing a phosphorus-based flame retardant. The phosphorus-based flame retardant may be selected from the group consisting of red phosphorus, triaryl phosphate esters, diaryl phosphate esters, monoaryl phosphate esters, aryl phosphonic acid compounds, aryl phosphine oxide compounds, condensed aryl phosphate esters, halogenated alkyl phosphate esters, halogen-containing condensed phosphate esters, halogen-containing condensed phosphonic acid esters, and halogen-containing phosphites, or a mixture of two or more thereof.

[0193] Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris(β-chloroethyl)phosphate, tris(dichloropropyl)phosphate, tris(tribromoneopentyl)phosphate, and the like.

[0194] (2.5) Uses The film according to the present invention can be used in the form of a film for the following uses, such as a liquid crystal display device.

[0195] Specifically, the film may be a polarizing plate protective film for a liquid crystal display device, a retardation film, an anti-reflection film, a brightness enhancing film, a hard coat film, an anti-glare film, an anti-static film, an optical compensation film for widening the viewing angle, or the like.

[0196] Typical uses of the film according to the present invention include polarizing plate protective films, retardation films, and optical compensation films, among the above.

[0197] (2.5.1) Hard Coat Layer The film according to the present invention may have a hard coat layer formed on it in order to enhance functionality such as impact resistance and ease of handling.

[0198] As mentioned above, the film according to the present invention is a multi-stage stretched film, and therefore the film density is 1.235 to 1.300 g / cm ３ This is in the range of 1.180 to 1.235 g / cm3 for conventional film densities. ３Unlike a one-stage stretched film in the range of 100%, when a hard coat layer is formed, the film strength is superior.

[0199] The strength of the film after the hard coat layer is formed can be confirmed by various known methods, for example, by measuring the pencil hardness in accordance with JIS K 5600 5-4 (pencil hardness evaluation method).

[0200] It is more preferable that the hard coat layer contains an ultraviolet curable resin and silica particles from the viewpoint of improving impact resistance, ease of handling, etc. Furthermore, other additives may be further blended as necessary within a range that does not impair the effects of the present invention.

[0201] (UV-curable resin) A component containing a monomer having an ethylenically unsaturated double bond is preferably used as the UV-curable resin. By irradiating with UV light, a hard coat layer having excellent mechanical film strength (scratch resistance, pencil hardness) can be formed.

[0202] Examples of ultraviolet curable resins include organic hard coat materials such as organic silicone, melamine, epoxy, acrylate, and polyfunctional (meth)acrylic compounds, as well as inorganic hard coat materials such as silicon dioxide.

[0203] Among these, (meth)acrylate-based and polyfunctional (meth)acrylic compounds are preferred as hard coat forming materials from the viewpoint of good adhesive strength and excellent productivity. Here, (meth)acrylic refers to acrylic and methacrylic.

[0204] Examples of (meth)acrylates include those having one, two, or three or more polymerizable unsaturated groups in the molecule, and (meth)acrylate oligomers containing three or more polymerizable unsaturated groups in the molecule.

[0205] For example, the polyfunctional acrylate may be a pentaerythritol polyfunctional acrylate, a dipentaerythritol polyfunctional acrylate, a pentaerythritol polyfunctional methacrylate, a dipentaerythritol polyfunctional methacrylate, etc. The (meth)acrylate may be used alone or in combination of two or more.

[0206] (Silica Particles) When the hard coat layer contains an ultraviolet curable resin and silica particles, the mass ratio of the silica particles to the ultraviolet curable resin (silica particles / ultraviolet curable resin) is preferably within the range of 10 / 90 to 50 / 50.

[0207] The above ratio of 10 / 90 or more is preferred in terms of increasing the hardness of the hard coat layer, and the ratio of 50 / 50 or less is preferred in terms of not causing deterioration in haze or scratch resistance.

[0208] In order to achieve both haze and surface hardness, the silica particles preferably have an average primary particle size of 200 nm or less, preferably in the range of 5 to 100 nm, and more preferably in the range of 10 to 50 nm.

[0209] Although the surface hardness of silica particles increases even when the particle surface is untreated, silica particles having a part of the surface coated with an organic component and having reactive polymerizable unsaturated groups introduced by the organic component on the surface are preferred. The average primary particle size of the silica particles preferably used in this embodiment is 5 to 200 nm, and examples of silica particles having such a particle size include silica particles having the above-mentioned reactive polymerizable unsaturated groups on the surface.

[0210] Known silica particles that have not been surface-modified can be used, and their shape may be spherical or irregular. They are not limited to ordinary colloidal silica, but may be hollow particles, porous particles, core / shell type particles, etc., with colloidal silica being preferred.

[0211] [Dispersion medium] The dispersion medium for silica particles is preferably water or an organic solvent, and examples of the organic solvent include organic solvents such as alcohols, ketones, aromatic hydrocarbons, amides, esters, ethers, etc. Among these, alcohols and ketones are preferred, and these organic solvents can be used alone or in combination.

[0212] Examples of alcohols include methanol, isopropyl alcohol, ethylene glycol, butanol, and ethylene glycol monopropyl ether. Examples of ketones include methyl ethyl ketone and methyl isobutyl ketone. Examples of aromatic hydrocarbons include toluene and xylene. Examples of amides include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Examples of esters include ethyl acetate, butyl acetate, and γ-butyrolactone. Examples of ethers include tetrahydrofuran and 1,4-dioxane.

[0213] [Commercially Available Products] Examples of commercially available colloidal silica include IPA-ST, IPA-ST-L, IPA-ST-ZL, MEK-ST-L, and MEK-ST-MS manufactured by Nissan Chemical Industries, Ltd.

[0214] The reactive silica particles are obtained by surface-treating colloidal silica with an organic compound having a reactive polymerizable unsaturated group. That is, the organic component that coats the surface of the silica particles refers to the organic component derived from the organic compound having a reactive polymerizable unsaturated group used in the surface treatment.

[0215] [Organic Compound Used in Surface Treatment] The organic compound used in the surface treatment to coat the surface of silica particles with an organic component is an organic compound having a polymerizable unsaturated group. The polymerizable unsaturated group is preferably any two or more of a hydroxy group, a carboxy group, an amino group, an epoxy group, an isocyanate group, a (meth)acryloyl group, and a vinyl group. In addition, a combination of a hydroxy group, a carboxy group, an isocyanate group, and a (meth)acryloyl group is particularly preferred. In the present invention, (meth)acrylate means methacrylate or acrylate.

[0216] Specific examples of organic compounds having a polymerizable unsaturated group include coupling agents such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, and vinyltriethoxysilane; acrylic acid esters such as methyl acrylate, 2-ethylhexyl acrylate, methoxyethyl acrylate, butoxyethyl acrylate, butyl acrylate, methoxybutyl acrylate, and phenyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, methoxyethyl methacrylate, ethoxymethyl methacrylate, phenyl methacrylate, and lauryl methacrylate; 2-(N,N-diethylamino)ethyl acrylate, 2-(N,N-dimethyl methacrylate), substituted amino alcohol esters of unsaturated substituted acids such as 2-(N,N-dibenzylamino)ethyl acrylate, 2-(N,N-dibenzylamino)methyl acrylate, and 2-(N,N-diethylamino)propyl acrylate; unsaturated carboxylic acid amides such as acrylamide and methacrylamide; compounds such as ethylene glycol diacrylate, propylene glycol diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, and triethylene glycol diacrylate; polyfunctional compounds such as dipropylene glycol diacrylate, ethylene glycol diacrylate, propylene glycol dimethacrylate, and diethylene glycol dimethacrylate; and / or polythiol compounds having two or more thiol groups in the branch (for example, trimethylolpropane trithioglycolate, trimethylolpropane trithiopropylate, and pentaerythritol tetrathioglycol).

[0217] The use of reactive silica particles having polymerizable unsaturated groups in this way leads to crosslinking between the binder resin and the silica particles, as well as between the silica particles themselves, which improves hardness and prevents particle shedding. In addition, the use of modified silica particles can also improve chemical resistance.

[0218] The organic component preferably covers almost the entire particle surface in order to suppress aggregation of the silica particles and to improve the hardness of the hard coating layer by introducing a large number of reactive functional groups onto the silica particle surface. From this viewpoint, the organic component covering the silica particles is present in an amount of 1.00 × 10 －３ g / m ２ It is preferable that the above be included.

[0219] The proportion of the organic component coating can usually be determined as a constant value of the mass loss when the dry powder is completely combusted in air, for example, by thermogravimetric analysis in air from room temperature to usually 800°C.

[0220] The amount of organic compound per unit area can be determined by the following method: First, the value obtained by dividing the mass of the organic component by the mass of the inorganic component (mass of organic component / mass of inorganic component) is measured by differential thermal gravimetric analysis (DTG), and then the volume of the entire inorganic component is calculated from the mass of the inorganic component and the specific gravity of the silica used.

[0221] In addition, assuming that the silica particles before coating are spherical, the volume and surface area per silica particle before coating are calculated from the average particle size of the silica particles before coating, and the number of reactive silica particles is determined by dividing the volume of the entire inorganic component by the volume per silica particle before coating.

[0222] Furthermore, the amount of the organic component per reactive silica particle is calculated by dividing the mass of the organic component by the number of reactive silica particles, and finally, the amount of the organic component per unit area is calculated by dividing the mass of the organic component per reactive silica particle by the surface area of ​​each silica particle before coating.

[0223] As a method for preparing reactive silica particles having at least a portion of their surface coated with an organic component and having polymerizable unsaturated groups introduced onto the surface by the organic component, a conventionally known method can be used as appropriate depending on the type of polymerizable unsaturated group to be introduced into the silica particles.

[0224] The reactive silica particles may be in the form of a powder containing no dispersion medium, but it is preferable to use a solvent-dispersed sol of fine particles, as this allows the dispersion step to be omitted and increases productivity.

[0225] Commercially available reactive silica particles include MIBK-SD, MIBK-SDMS, MIBK-SDL, IPA-ST, and IPA-SDMS manufactured by Nissan Chemical Industries, Ltd.

[0226] The average primary particle size of the silica particles can be determined by measuring the dispersed particle size of the silica particles in the dispersion liquid using a zeta potential / particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

[0227] (Other Additives) Other additives may be blended into the hard coat layer as needed, provided that the effects of the present invention are not impaired, such as a leveling agent, an ultraviolet stabilizer, an ultraviolet absorber, etc. Also, various known additives such as an antioxidant, a surfactant, an antistatic agent, etc. may be used.

[0228] [Leveling Agent] A leveling agent is particularly effective in reducing surface irregularities when applying a coating liquid for forming a hard coat layer. As the leveling agent, for example, a silicone-based leveling agent such as a dimethylpolysiloxane-polyoxyalkylene copolymer is suitable.

[0229] [UV Stabilizer] As the UV stabilizer, for example, a hindered amine UV stabilizer, which has high stability against UV rays, is preferably used. When the hard coat layer contains a UV stabilizer, radicals, active oxygen, etc. generated by UV rays are inactivated, thereby improving UV stability, weather resistance, etc.

[0230] [Ultraviolet absorber] Examples of the ultraviolet absorber include salicylic acid-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, triazine-based ultraviolet absorbers, benzoxazinone-based ultraviolet absorbers, etc. One or more types selected from these groups may be used.

[0231] Among them, triazine-based ultraviolet absorbers and benzoxazinone-based ultraviolet absorbers are preferred from the viewpoint of dispersibility. Furthermore, polymers having ultraviolet absorbing groups in the molecular chain are also preferably used as the ultraviolet absorbers. By using such polymers having ultraviolet absorbing groups in the molecular chain, deterioration of the ultraviolet absorbing function due to bleeding out of the ultraviolet absorber can be prevented.

[0232] Examples of the ultraviolet absorbing group include a benzotriazole group, a benzophenone group, a cyanoacrylate group, a triazine group, a salicylate group, a benzylidene malonate group, etc. Among these, a benzotriazole group, a benzophenone group, and a triazine group are particularly preferred.

[0233] (Method of Forming Hard Coat Layer) As a method of forming a hard coat layer on the film of the present invention in order to enhance functionality, for example, the following method can be mentioned.

[0234] First, a coating liquid for forming an active energy ray-cured material layer, i.e., a coating liquid for forming a hard coat layer, is prepared in advance and applied to the film of the present invention, followed by drying and curing to form a hard coat layer, which is an active energy ray-cured material layer.

[0235] The coating liquid for forming the hard coat layer is preferably a coating liquid containing, for example, an ultraviolet curable resin and silica particles, and the coating liquid is preferably prepared using at least two solvents selected from alcohols, esters, ethers, and ketones in order to reduce drying unevenness.

[0236] Examples of the solvent include chlorine-based solvents such as chloroform and dichloromethane; aromatic solvents such as toluene, xylene, benzene, and mixed solvents thereof; alcohol-based solvents such as methanol, ethanol, isopropanol (IPA), n-butanol, and 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, ethylene glycol monomethyl ether, propylene glycol monomethyl ether (PGME), dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone (MEK), ethyl acetate, and diethyl ether.

[0237] When a solution prepared by dissolving at least two solvents selected from alcohols, esters, ethers, and ketones is cast onto a substrate, one of the solvents is preferably a ketone, and among the ketones, methyl ethyl ketone (MEK) is preferred from the viewpoint of solubility of the UV-curable resin.

[0238] The other type is preferably an ether, and among ethers, propylene glycol monomethyl ether (PGME) is preferred from the viewpoint of its high boiling point, slow drying time, and suppression of unevenness.

[0239] The coating liquid for forming a hard coat layer can be applied to the film of the present invention by any means such as a dipping method, a die coater method, a wire bar method, or a spray method, and the coating liquid can be dried by a known method after application.

[0240] The coating film of the hard coat layer-forming coating liquid can be cured by irradiating it with active energy rays. Examples of light sources for irradiating active energy rays (preferably ultraviolet rays) include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, metal halide lamps, and xenon lamps.

[0241] The irradiation amount of the light source is 20 to 10,000 mJ / cm ２ It is sufficient to have a value of about 50 to 2000 mJ / cm. ２The irradiation time is preferably in the range of 0.5 seconds to 5 minutes, and from the viewpoint of work efficiency, etc., it is more preferably in the range of 3 seconds to 2 minutes.

[0242] The dry thickness of the hard coat layer is preferably in the range of 2 to 15 μm, more preferably in the range of 3 to 8 μm.

[0243] (2.5.2) Antireflection Layer When a functional layer such as the hard coat layer described above is formed on the film of the present invention, an antireflection layer can be coated on the functional layer to form an antireflection film having an external light antireflection function. In this case, the antireflection layer is formed by preparing a coating liquid for forming the antireflection layer using a solvent, applying the coating liquid, and drying and curing the coating liquid.

[0244] If necessary, a method may be applied in which irregularities are formed on the surface of a mold without using a solvent, and the irregularities of the mold are transferred onto a film using an ultraviolet-curable resin or a thermoplastic resin to form an anti-glare (AG) layer or the like (a method for forming an embossed AG layer).

[0245] The layer formed on the functional layer is not limited to the anti-reflection layer described above, and any known layer may be formed according to various applications, and other layers such as a conductive layer may also be formed.

[0246] The antireflection layer is preferably laminated taking into consideration the refractive index, layer thickness, number of layers, layer order, etc. so that the reflectance is reduced by optical interference. The antireflection layer is preferably composed of a low refractive index layer having a lower refractive index than the film used as the support, i.e., the film according to the present invention on which the functional layer is formed, or a combination of a high refractive index layer and a low refractive index layer having a higher refractive index than the film according to the present invention on which the functional layer is formed.

[0247] (Low Refractive Index Layer) The low refractive index layer preferably contains silica-based fine particles, and the refractive index thereof is preferably in the range of 1.30 to 1.45 when measured at 23° C. and a wavelength of 550 nm.

[0248] The thickness of the low refractive index layer is preferably in the range of 5 nm to 0.5 μm, more preferably in the range of 10 nm to 0.3 μm, and most preferably in the range of 30 nm to 0.2 μm.

[0249] The composition for forming a low refractive index layer preferably contains at least one type of silica-based fine particles having an outer shell layer and a porous or hollow interior, and the particles having an outer shell layer and a porous or hollow interior are preferably hollow silica-based fine particles.

[0250] The composition for forming a low refractive index layer may also contain an organosilicon compound represented by the following general formula (OSi-1), or a hydrolyzate thereof, or a polycondensate thereof. General formula (OSi-1): Si(OR) ４ In the above general formula (OSi-1), R represents an alkyl group having 1 to 4 carbon atoms. Specifically, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, etc. are preferably used.

[0251] In addition, a solvent may be added, and if necessary, a silane coupling agent, a curing agent, a surfactant, etc. Furthermore, the composition may contain a thermosetting and / or photocurable compound that contains fluorine atoms in the range of 35 to 80 mass % and is mainly composed of a fluorine-containing compound that contains a crosslinkable or polymerizable functional group.

[0252] Specifically, it is a fluorine-containing polymer, a fluorine-containing sol-gel compound, etc. Examples of the fluorine-containing polymer include a hydrolyzate or dehydration condensate of a perfluoroalkyl group-containing silane compound (for example, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane). Other examples include a fluorine-containing copolymer having a fluorine-containing monomer unit and a crosslinking reactive unit as constituent units.

[0253] (High Refractive Index Layer) The refractive index of the high refractive index layer is preferably adjusted to be in the range of 1.4 to 2.2 when measured at 23° C. and a wavelength of 550 nm. The thickness of the high refractive index layer is preferably in the range of 5 nm to 1 μm, more preferably in the range of 10 nm to 0.2 μm, and most preferably in the range of 30 nm to 0.1 μm.

[0254] The refractive index can be adjusted by adding metal oxide fine particles, etc. The metal oxide fine particles preferably have a refractive index in the range of 1.80 to 2.60, more preferably 1.85 to 2.50.

[0255] The type of metal oxide microparticles is not particularly limited, and metal oxides containing at least one element selected from Ti, Zr, Sn, Sb, Cu, Fe, Mn, Pb, Cd, As, Cr, Hg, Zn, Al, Mg, Si, P, and S can be used.

[0256] (2.5.3) Conductive Layer As a material for forming the conductive layer, a commonly known conductive material can be used, such as a metal oxide such as indium oxide, tin oxide, indium tin oxide, gold, silver, or palladium.

[0257] Using these materials, the conductive layer can be formed as a thin film on the film on which the hard coat layer has been formed by vacuum deposition, sputtering, ion plating, solution coating, etc. Alternatively, the conductive layer can be formed using an organic conductive material that is a π-conjugated conductive polymer.

[0258] In particular, conductive materials containing as a main component any of indium oxide, tin oxide, and indium tin oxide, which are excellent in transparency and conductivity and can be obtained at relatively low cost, can be suitably used.

[0259] The thickness of the conductive layer varies depending on the material used and cannot be generalized, but it is preferable that the thickness be such that the surface resistivity is 1000 Ω or less, preferably 500 Ω or less. Considering economic efficiency, the thickness of the conductive layer is preferably 10 nm or more, more preferably in the range of 20 to 80 nm, and even more preferably 70 nm or less. Furthermore, in such a thin film, interference fringes of visible light caused by uneven thickness of the conductive layer are unlikely to occur.

[0260] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

[0261] [Film Production] Films [1] to

[15] were produced by the solution casting film-forming method according to the following steps.

[0262] [A] Preparation of Film [1] (Preparation of Dope [D-1]) The following dope composition [1] was thoroughly dissolved under heating to prepare dope [D-1]. <Dope composition [1]> Acrylic resin (A) 65 parts by mass Cellulose ester resin (B) 35 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass Rubber particles R1: 1 part by mass

[0263] The "acrylic resin (A)" in the dope composition [1] is "DIANAL BR85" (acrylic resin) manufactured by Mitsubishi Rayon Co., Ltd. The weight average molecular weight (Mw) of the acrylic resin is 280,000, and the proportion of methyl methacrylate (MMA) units in the molecule of the acrylic resin is in the range of 90 to 99% by mass.

[0264] The "cellulose ester resin (B)" in the dope composition [1] has acetyl and propionyl acyl groups, a total substitution degree of the acyl groups is 2.75, a substitution degree of the acetyl group (an acyl group having two carbon atoms) is 0.19, a substitution degree of the propionyl group (an acyl group having three carbon atoms) is 2.56, and a weight average molecular weight (Mw) is 200,000.

[0265] The "rubber particles R1" in the dope composition [1] are "Kane Ace M210" (average primary particle diameter R: 200 nm) manufactured by Kaneka Corporation.

[0266] (Preparation of Dope [D-2]: Preparation of Membrane Dope) Next, the following dope composition [2] containing the dope [D-1] prepared by the above method was charged into a disperser to prepare an inorganic particle dispersion (M-1) as an additive. <Dope composition [2]> Inorganic particles [1] 4 parts by mass Dichloromethane 76 parts by mass Ethanol 10 parts by mass Dope [D-1] 10 parts by mass

[0267] The inorganic particles [1] are "Aerosil R812" (average primary particle size: 7 nm, apparent specific gravity: 50 g / L) manufactured by Nippon Aerosil Co., Ltd.

[0268] 100 parts by mass of the dope solution (D-1) and 0.75 parts by mass of the particle-free dispersion (M-1) were mixed to prepare a dope for film formation [D-2]. The above process was carried out using the stirring device 1 shown in FIG.

[0269] [A-1] Casting step The dope [D-2] was sent to the casting die 2 through a conduit via a pressure type metering gear pump. Then, the dope [D-2] was uniformly cast from the casting die 2 to a casting position on the support 3, which was an endless rotating stainless steel belt, at a temperature of 22°C and in a width of 2 m.

[0270] The dope [D-2] was heated with a stainless steel band support 3 until it became self-supporting, and then the solvent was evaporated by a peeling roller 4 until the residual solvent amount became 40% and the dope [D-2] could be peeled off from the support 3, thereby drying the dope to form a film.

[0271] Thereafter, the film was peeled off from the support by a peeling roller 4 at a peeling tension of 162 N / m while maintaining its self-supporting property. The speed of the support at this time was defined as the casting belt speed V １ and was used to calculate the expansion / contraction ratio A.

[0272] [A-2] First conveying step The solvent was evaporated at 35°C without holding the film widthwise, and the film was slit into a width of 1.6 m. The film was then treated at a high temperature to increase the density of the film while being conveyed. １The film was transported while measuring the tension with the non-contact web tension meter manufactured by Bellmatic.

[0273] (Transport tension T １ , expansion / contraction rate b, temperature during conveyance) conveying tension T in the first conveying step １ The stretch rate b [%] in the longitudinal direction of the film (machine direction, MD direction), and the temperature during transport [°C] are as shown in Table I.

[0274] The stretch rate b [%] in the longitudinal direction (machine direction, MD direction) of the film is a value calculated by the following formula.

[0275] Formula: Expansion / contraction rate b [%] = {(V ２ -V １ ) / (V １ )×100[%]

[0276] The meanings of the symbols in the above formula are as follows: １ V: Belt speed in the casting section (speed of the support) ２ : Film conveying speed in the first stretching step

[0277] [A-3] First Stretching Step Thereafter, the film was stretched in a stretching device 6 while being heated to 140°C. As the stretching device 6, a tenter stretching device 14 as shown in Figure 7 was used, and the film was stretched in the width direction in stretching zone B, and then subjected to relaxation treatment in stress relaxation zone D at 130°C for about 20 seconds at a relaxation rate B [%] (B = 2). The amount of residual solvent at this time was 10%.

[0278] [A-4] Second Conveying Step Thereafter, the film was heated on the drying device 7 while being conveyed, and the solvent was evaporated from the film. Then, both ends of the film in the width direction were cut at the cutting section 13 to produce a raw film, and the raw film was wound by the winding device 8 at a winding speed V Ｗ１ (V Ｗ１ The fiber was wound onto a core at a speed of 30 m / min.

[0279] (Relaxation Rate B) The relaxation rate B [%] in the first stretching step is shown in Table I. The relaxation rate B [%] was calculated by the following formula: Relaxation rate = (L ＴＤＢ０ / L ＴＤＢ１-1)×100[%] (L ＴＤＢ１ : Length in the width direction of the film after the relaxation treatment in the first stretching step, L ＴＤＢ０ : the length in the width direction of the film before the relaxation treatment in the first stretching step)

[0280] The wound raw film is fed from the winding device 8 at a speed V ３ The film was unwound at a speed of 10 m / min and conveyance was started.

[0281] (Transport tension T ２ , expansion / contraction rate a, temperature during transport) Transport tension T in the second transport step ２ The stretch rate a [%] in the longitudinal direction of the film (machine direction, MD direction), and the temperature during transport [°C] are as shown in Table I.

[0282] Conveying tension T ２ is the aforementioned conveying tension T １ The film was transported in the second transport step while measuring the tension with a non-contact web tension meter manufactured by Bellmatic in the same manner as in the first transport step.

[0283] The stretch rate a [%] in the longitudinal direction (machine direction, MD direction) of the film is a value calculated by the following formula.

[0284] Equation: Expansion rate a [%] = [(film winding speed V in the second conveying step) Ｗ１ ) - (film conveying speed V in the first stretching step ２ )} / (film conveying speed V in the first stretching step ２ ) )] × 100 + [{(film conveying speed V in the second stretching step ４ ) - (film unwinding speed V in the second transport step ３ )} / (film payout speed V in the second conveying step ３ ) × 100

[0285] [A-5] Second Stretching Step The unwound raw film was stretched by the stretching device 10. At this time, the stretching device 10 was a tenter stretching device 14 as shown in FIG. 7, and the stretching was performed in the stretching zone B at a conveying speed V ４The raw film was stretched in the width direction while being transported at a speed of 10 m / min, and then subjected to a relaxation treatment at 130°C for about 5 minutes at a relaxation rate A (A = 2 [%]) in stress relaxation zone D. The residual solvent amount at this time was 0.30 mass%.

[0286] [A-6] Third conveying step: The film was then dried in the drying device 11 at 120°C and 140°C while being conveyed by multiple rolls, and the raw film was processed by slitting it into a width of 1.5 m in the cutting section 13 to produce a film.

[0287] The film is wound by the winding device 12 at a winding speed V Ｗ２ (V Ｗ２ The film [1] was then wound around a core at a speed of 10 m / min (=10 m / min) to prepare a film [1]. The thickness of the film [1] at this time was 35 μm.

[0288] The film thickness was measured at 1612 locations using an in-line retardation / film thickness measuring device RE-200L2T-Rth+film thickness (manufactured by Otsuka Electronics Co., Ltd.). The traverse movement speed was 100 mm / sec. The average value of the measured values ​​was taken as the film thickness.

[0289] (Stretch Rate A and Relaxation Rate A) The stretch rate A [%] and relaxation rate A [%] are shown in Table I.

[0290] The stretch rate A [%] was calculated using the following formula: Ｗ１ -V １ ) / V １}×100+{(V ４ -V ３ ) / V ３} x 100

[0291] The meanings of the symbols in the above formula are as follows: Ｗ１ V: Film winding speed in the second transport step １ V: Belt speed in the casting section (speed of the support) ３ V: Film unwinding speed in the second transport step ４ : Film conveying speed in the second stretching step

[0292] The relaxation rate A [%] was calculated by the following formula: Relaxation rate = (L (ＴＤ)Ａ０ / L (ＴＤ)Ａ１ -1)×100[%] (L (ＴＤ)Ａ１ : Length in the width direction of the film after the relaxation treatment in the second stretching step, L (ＴＤ)Ａ０ : the length in the width direction of the film before the relaxation treatment in the second stretching step)

[0293] [B] Preparation of films [2] to

[15] Films [2] to

[15] were prepared in the same manner as in the preparation of film [1], except that the mass ratio of acrylic resin (A) to cellulose ester resin (B) in the preparation of dope and the parameters in the preparation process of film were as shown in Table I.

[0294]

[0295] [Evaluation] Evaluation was carried out by the following methods, and the evaluation results are shown in Table II.

[0296] A hard coat layer was formed on each of the prepared films [1] to

[15] by the following method to form a hard coat film. The pencil hardness of the hard coat layer formed on the hard coat film was measured in accordance with JIS K 5600 5-4 (pencil hardness evaluation method).

[0297] [C] Formation of Hard Coat Layer [C-1] Preparation of Silica-Dispersed Methyl Ethyl Ketone Solution A Before preparing the coating liquid for forming a hard coat layer, a silica-dispersed methyl ethyl ketone solution A to be used in the preparation of the coating liquid for forming a hard coat layer was prepared by the following steps.

[0298] (Surface-adsorbed ion removal step) Water-dispersed colloidal silica "Snowtec N" (average particle size 12 nm, pH 9.0 to 10.0) manufactured by Nissan Chemical Industries, Ltd. was subjected to ion exchange for 3 hours using 500 g of cation exchange resin "Diaion SK1B" manufactured by Mitsubishi Chemical Corporation.

[0299] Next, ion exchange was carried out for 3 hours using 300 g of an anion exchange resin "SA20A" manufactured by Mitsubishi Chemical Corporation, and then the mixture was washed with ion-exchanged water.

[0300] As a result, a silica fine particle water dispersion [a1] having a solid content concentration of 20% by mass was obtained. ２ The O content was 5 ppm.

[0301] (Surface Treatment Step: Introduction of Monomer) 300 ml of isopropanol, 4.0 g of 3,6,9-trioxadecanoic acid, and 4.0 g of methacrylic acid were added to 20 g of the silica fine particle aqueous dispersion [a1] obtained by the surface-adsorbed ion removal step, and the mixture was stirred for 1 hour to prepare a mixed solution [b].

[0302] The mixed solution [b] prepared above was stirred while being heated at 60° C. for 6 hours, thereby obtaining a silica fine particle dispersion [a2] in which methacryloyl groups were introduced into the silica fine particles.

[0303] The obtained silica microparticle dispersion [a2] was evaporated using a rotary evaporator to remove distilled water, isopropanol, and methacrylic acid, and methyl ethyl ketone was added without drying the dispersion, and the same amount (100% by mass) of methacrylic acid used in the surface treatment was added.

[0304] Thus, a silica-dispersed methyl ethyl ketone solution A having a solid content of 40% by mass was prepared.

[0305] The residual water and isopropanol content was set to 0.1% by mass or less.

[0306] The silica fine particles in the silica-dispersed methyl ethyl ketone solution A were measured using a particle size analyzer (Microtrac, manufactured by Nikkiso Co., Ltd.) and the average primary particle size d55 was found to be 13 nm.

[0307] [C-2] Formation of Hard Coat Layer (Preparation of Coating Liquid for Forming Hard Coat Layer) A mixed liquid [c] was prepared by mixing the following ultraviolet-curable resin, surfactant, silica-dispersed methyl ethyl ketone solution A (solid content 40% by mass), and propylene glycol monomethyl ether. Thereafter, the mixed liquid [c] was stirred for 30 minutes to prepare a coating liquid for forming a hard coat layer.

[0308] UV-curable resin "A-DPH" (manufactured by Shin-Nakamura Chemical Co., Ltd.) 60 parts by mass Surfactant "Surflon S-651" (manufactured by AGC Seimi Chemical Co., Ltd.) 0.1 parts by mass Silica dispersion methyl ethyl ketone solution A (solid content 40% by mass) 100 parts by mass Propylene glycol monomethyl ether (PGME) 40 parts by mass

[0309] (Application, drying, and curing of coating liquid for forming hard coat layer) The coating liquid for forming hard coat layer was applied to one side of each of the prepared films [1] to

[15] using a microgravure coating to a dry film thickness of 5 μm, and then dried to form a coating film.

[0310] Next, a high-pressure mercury lamp was used to irradiate the coating film with a light intensity of 270 mJ / cm under atmospheric pressure. ２ The coating was cured by irradiating with ultraviolet light at a temperature of 100° C. to form a hard coat layer on each of the films [1] to

[15] .

[0311] [D] Specific Evaluation Method A dedicated device equipped with a 750 g weight and a test pencil of each hardness specified in JIS S 6006 was run over the hard coating layer formed on each of the films [1] to

[15] at a speed of 0.75 mm / sec for a distance of 7 mm. The angle of the pencil relative to the running surface was 45±1°.

[0312] This operation was repeated five times. The maximum hardness at which there was one or less scratch was determined. A larger maximum value indicates a higher hardness. The hardness was evaluated according to the following evaluation criteria. A, B, and C were considered acceptable, and were evaluated as levels that present no practical problems.

[0313] (Evaluation criteria) A: Pencil hardness is 3H or more (pass). B: Pencil hardness is 2H or more and less than 3H (pass). C: Pencil hardness is H or more and less than 2H (pass). D: Pencil hardness is less than H (fail).

[0314]

[0315] [E] Overall Evaluation From Tables I and II, it can be seen that the examples in which a hard coat layer was formed on the substrate film of the present invention were only rated A, B, and C, and therefore present no practical problems.

[0316] While embodiments of the present invention have been described and illustrated in detail above, the disclosed embodiments are made for purposes of illustration and example only, and not limitation. The scope of the present invention should be construed by the terms of the appended claims.

[0317] It is possible to provide a method for producing an acrylic resin-containing film and a multistage stretched acrylic resin-containing film that can be made wider and thinner, crack-free, have high density, and maintain functionality.

[0318] REFERENCE SIGNS LIST 1 Stirring device 1a Stirring tank 2 Casting die 3 Support (casting belt) 3a, 3b Roller 4 Peeling roller 5, 7, 9, 11 Drying device 6, 10 Stretching device 8 Winding device in second conveying step 12 Winding device in third conveying step 13 Cutting section 14 Tenter stretching device 110 Housing 111 Clip 112 Rail a Starting point of film stretching, entrance of stretching zone b Ending point of film stretching, entrance of film width retention zone c Starting point of film stress relaxation treatment c, entrance of stress relaxation zone d Ending point of stress relaxation treatment, exit of stress relaxation zone F Film Hc Width of film at entrance of stress relaxation zone Hd Width of film at exit of stress relaxation zone L (ＭＤ)０ The length L in the longitudinal direction of a specific portion of the film cut out at the peeling position during the casting process (ＭＤ)Ａ１ The film is stretched in the longitudinal direction L from the peeling position in the casting step to the position immediately before stretching in the width direction in the second stretching step. (ＭＤ)０ The length L (ＴＤ)Ａ０ The length L in the width direction of the film before the relaxation treatment in the second stretching step (ＴＤ)Ａ１ Length in the width direction of the film after the relaxation treatment in the second stretching step F Film S1 Casting step S2 First conveying step S3 First stretching step 2nd MD Second conveying step S4 Second stretching step 3rd MD Third conveying step V Ｗ１ V: Film winding speed in the second transport step (film winding speed by the winding device 8) Ｗ２V: Film winding speed in the third transport step (film winding speed by the winding device 12) １ V: Belt speed in the casting section (speed of the support) ２ V: Film conveying speed in the first stretching step ３ V: Film unwinding speed in the second transport step ４ : Film conveying speed in the second stretching step

Claims

1. A method for producing an acrylic resin-containing film, comprising at least a casting step, a first conveying step, a first stretching step, and a second stretching step, in this order, wherein a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast in the casting step, the acrylic resin-containing film is stretched in the width direction in the first stretching step, and the acrylic resin-containing film is further stretched in the width direction in the second stretching step, wherein an expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion rate A / relaxation rate A)<550.

2. A second conveying step is provided between the first stretching step and the second stretching step, and a conveying tension T of the acrylic resin-containing film after drying the dope in the first conveying step is １ and the conveying tension T of the acrylic resin-containing film in the second conveying step. ２ and satisfy the relationship of the following formula (2): 1.00<(conveying tension T １ / Transport tension T ２ 2. The method for producing an acrylic resin-containing film according to claim 1, wherein the viscosity of the film is less than 2.

00.

3. The method for producing an acrylic resin-containing film according to claim 1, wherein the stretch rate A and the relaxation rate A satisfy the relationship of the following formula (3): Relaxation rate A<stretch rate A.

4. The method for producing an acrylic resin-containing film according to claim 1, characterized in that, when the acrylic resin-containing film is transported in the second transport step at an expansion / contraction rate a, the relationship of the following formula (4) is satisfied: 1.25<(expansion / contraction rate a / relaxation rate A)<5.

5.

5. A multistage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles, wherein the multistage stretched acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70, the total degree of substitution (T) of acyl groups in the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, and the film density of the multistage stretched acrylic resin-containing film is 1.235 to 1.300 g / cm ３ A multi-stage stretched acrylic resin-containing film, characterized in that the film thickness is within the range of

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