JP7644786B2 - Manufacturing method of stretched film - Google Patents

Description

The present invention relates to a method for producing a stretched film.

Stretched films, which are widely used in various industrial products, are produced by stretching a resin film. For example, a method for producing a stretched film has been proposed in which a long resin film is stretched in a direction intersecting the long direction while both ends in the width direction of the film are held by clips (see, for example, Patent Document 1).
In recent years, from the viewpoint of reducing the environmental load, it is desired to reuse waste generated during the manufacture of various industrial products. Therefore, it has been considered to produce a stretched film by forming a resin film using recycled materials regenerated from waste resin products and then stretching the film. However, when a resin film is formed using recycled materials, unevenness (specifically, uneven flow of the resin) occurs in the resin film, and as a result, the stretched film may not have the desired properties.

Patent No. 7096940

The present invention has been made to solve the above-mentioned problems of the conventional art, and its main objective is to provide a method for producing a stretched film that can suppress the occurrence of unevenness in a resin film even when the resin film is produced using recycled materials, and as a result, can produce a stretched film with the desired characteristics.

（式（１）中、Ａはバージン材料の溶融粘度［Ｐａ・ｓ］を表し、Ｃはリサイクル材料の溶融粘度［Ｐａ・ｓ］を表す。）
［２］上記［１］に記載の延伸フィルムの製造方法において、上記バージン材料の溶融粘度および上記リサイクル材料の溶融粘度は、下記式（２）を満たしていてもよい。

（式（２）中、Ａはバージン材料の溶融粘度［Ｐａ・ｓ］を表し、Ｃはリサイクル材料の溶融粘度［Ｐａ・ｓ］を表す。）
［３］上記［１］または［２］に記載の延伸フィルムの製造方法において、上記リサイクル材料は、上記第２樹脂から構成される連続相と、上記混入成分から構成される分散相と、を有していてもよい。該分散相の最大寸法は、５００ｎｍ以下であってもよい。
［４］上記［３］に記載の延伸フィルムの製造方法において、上記分散相の最大寸法は、１０ｎｍ以上２００ｎｍ以下であってもよい。
［５］上記［１］から［４］のいずれかに記載の延伸フィルムの製造方法において、上記混入成分は、樹脂成分と異なる異物を含んでいてもよい。該混入成分に含まれる異物のうち、最も大きい異物の最大寸法は、１ｍｍ未満であってもよい。
［６］上記［５］に記載の延伸フィルムの製造方法において、上記異物は、最大寸法が５００μｍ以上１ｍｍ未満である第１異物と、最大寸法が５００μｍ未満である第２異物と、を含んでいてもよい。上記異物において、該第１異物の含有割合は５体積％以上５０体積％以下であり、前記第２異物の含有割合は５０体積％以上９５体積％以下であってもよい。
［７］上記［１］から［６］のいずれかに記載の延伸フィルムの製造方法は、延伸フィルムの幅方向の両端部のそれぞれを切断して、第２端部フィルムを得る工程を、さらに含んでいてもよい。
［８］上記［１］から［７］のいずれかに記載の延伸フィルムの製造方法は、上記第１端部フィルムおよび／または上記第２端部フィルムを含む再生樹脂材料から、リサイクル材料を調製する工程を、さらに含んでいてもよい。
［９］上記［８］に記載の延伸フィルムの製造方法において、上記再生樹脂材料における水分率は、１．０質量％未満であってもよい。 [1] A method for producing a stretched film according to an embodiment of the present invention includes the steps of: preparing a virgin material containing a first resin and a recycled material containing a second resin and a mixed component; forming a long resin film from the virgin material and the recycled material, in which both ends in the width direction of the resin film are formed from the recycled material and a main body portion located between both ends in the width direction of the resin film is formed from the virgin material; cutting the resin film to separate it into a first end film including the ends in the width direction of the resin film and a film-formed film including the main body portion; and stretching the film-formed film in a direction intersecting the longitudinal direction. The melt viscosity of the virgin material and the melt viscosity of the recycled material satisfy the following formula (1).

(In formula (1), A represents the melt viscosity [Pa·s] of the virgin material, and C represents the melt viscosity [Pa·s] of the recycled material.)
[2] In the method for producing a stretched film described in the above [1], the melt viscosity of the virgin material and the melt viscosity of the recycled material may satisfy the following formula (2):

(In formula (2), A represents the melt viscosity [Pa·s] of the virgin material, and C represents the melt viscosity [Pa·s] of the recycled material.)
[3] In the method for producing a stretched film according to the above [1] or [2], the recycled material may have a continuous phase composed of the second resin and a dispersed phase composed of the mixed component, and the maximum dimension of the dispersed phase may be 500 nm or less.
[4] In the method for producing a stretched film described in [3] above, the maximum dimension of the dispersed phase may be 10 nm or more and 200 nm or less.
[5] In the method for producing a stretched film according to any one of [1] to [4] above, the contaminating components may include foreign matter other than the resin component. The maximum dimension of the largest foreign matter contained in the contaminating components may be less than 1 mm.
[6] In the method for producing a stretched film described in [5] above, the foreign matter may include a first foreign matter having a maximum dimension of 500 μm or more and less than 1 mm, and a second foreign matter having a maximum dimension of less than 500 μm. In the foreign matter, the content of the first foreign matter may be 5 volume % or more and 50 volume % or less, and the content of the second foreign matter may be 50 volume % or more and 95 volume % or less.
[7] The method for producing a stretched film according to any one of [1] to [6] above may further include a step of cutting each of both widthwise ends of the stretched film to obtain a second end film.
[8] The method for producing a stretched film described in any one of [1] to [7] above may further include a step of preparing a recycled material from a recycled resin material including the first end film and/or the second end film.
[9] In the method for producing a stretched film described in [8] above, the recycled resin material may have a moisture content of less than 1.0 mass%.

According to an embodiment of the present invention, even if a resin film is produced using recycled materials, the occurrence of unevenness in the resin film can be suppressed, and a stretched film having the desired characteristics can be produced.

FIG. 1 is a schematic plan view of a resin film in accordance with a method for producing a stretched film according to one embodiment of the present invention. FIG. 2 is a schematic plan view of a stretched film obtained by stretching a film-formed film obtained from the resin film of FIG.

The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. In addition, in order to make the description clearer, the drawings may show the width, thickness, shape, etc. of each part more diagrammatically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

(Definition of terms and symbols)
The definitions of terms and symbols used in this specification are as follows.
(1) Refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
"Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Re(λ) is calculated by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Angles When angles are referred to in this specification, unless otherwise specified, the angles include angles in both clockwise and counterclockwise directions.

A. Overview of the Method for Producing a Stretched Film Fig. 1 is a schematic plan view of a resin film according to a method for producing a stretched film according to one embodiment of the present invention; Fig. 2 is a schematic plan view of a stretched film obtained by stretching a film-formed film obtained from the resin film of Fig. 1 .

（式（１）および（２）中、Ａはバージン材料の溶融粘度［Ｐａ・ｓ］を表し、Ｃはリサイクル材料の溶融粘度［Ｐａ・ｓ］を表す。）
製膜工程では、バージン材料およびリサイクル材料から、長尺状の樹脂フィルム３を製膜する（図１参照）。より詳しくは、樹脂フィルム３の幅方向の両端部３１をリサイクル材料から形成し、樹脂フィルム３の幅方向の両端部３１の間に位置する本体部分３２をバージン材料から形成する。樹脂フィルム３において、本体部分３２は、幅方向の両端部３１と一体的に連続している。第１切断工程では、樹脂フィルム３を切断して、樹脂フィルム３の幅方向の端部３１を含む第１端部フィルム６と、本体部分を含む製膜フィルム４とに分離する。延伸工程では、製膜フィルム４を長尺方向と交差する方向に延伸する（図２参照）。
本発明者らは、リサイクル材料とバージン材料とを併用して樹脂フィルムを製膜し、当該樹脂フィルムを延伸して延伸フィルム（特に光学フィルム）を製造することを検討した。すると、リサイクル材料およびバージン材料から製膜された樹脂フィルムには樹脂の流れムラ（以下、単にムラとする。）が生じる場合があり、樹脂フィルムのムラに起因して、製造される延伸フィルムの外観および／または特性にばらつきが生じる場合があることを発見した。そこで、リサイクル材料とバージン材料との関係について鋭意検討した結果、樹脂フィルムの製膜においてリサイクル材料を樹脂フィルムの幅方向の両端部に利用し、かつ、リサイクル材料の溶融粘度とバージン材料の溶融粘度とが特定の関係にあれば、樹脂フィルムにおけるムラを抑制し得ることを見出した。具体的には、まず、溶融粘度の関係が上記式（１）を満たすバージン材料およびリサイクル材料を準備する。次いで、リサイクル材料から樹脂フィルム３の幅方向の両端部３１を形成し、かつ、バージン材料から樹脂フィルム３の本体部分３２を形成するように、１枚の樹脂フィルム３を製膜する。これによって、リサイクル材料を用いて樹脂フィルム３を製膜しても、樹脂フィルム３にムラが生じることを抑制し得、結果として、所望の特性を有する延伸フィルム５を安定して製造し得る。 A method for producing a stretched film according to an embodiment of the present invention includes a preparation step, a film-forming step, a first cutting step, and a stretching step, in this order.
In the preparation step, a virgin material and a recycled material are prepared. The virgin material includes a first resin. The recycled material includes a second resin and a mixed component. The melt viscosity of the virgin material and the melt viscosity of the recycled material satisfy the following formula (1), and preferably satisfy the following formula (2).

(In formulas (1) and (2), A represents the melt viscosity [Pa·s] of the virgin material, and C represents the melt viscosity [Pa·s] of the recycled material.)
In the film-forming process, a long resin film 3 is formed from virgin material and recycled material (see FIG. 1). More specifically, both widthwise ends 31 of the resin film 3 are formed from recycled material, and a main body portion 32 located between both widthwise ends 31 of the resin film 3 is formed from virgin material. In the resin film 3, the main body portion 32 is integrally continuous with both widthwise ends 31. In the first cutting process, the resin film 3 is cut to separate it into a first end film 6 including the widthwise ends 31 of the resin film 3 and a film-formed film 4 including the main body portion. In the stretching process, the film-formed film 4 is stretched in a direction intersecting the longitudinal direction (see FIG. 2).
The present inventors have studied the use of a combination of recycled and virgin materials to produce a resin film, and stretching the resin film to produce a stretched film (particularly an optical film). As a result, they discovered that resin flow unevenness (hereinafter simply referred to as unevenness) may occur in a resin film produced from recycled and virgin materials, and that the unevenness of the resin film may cause variations in the appearance and/or characteristics of the produced stretched film. As a result of intensively studying the relationship between recycled and virgin materials, they have found that unevenness in the resin film can be suppressed if recycled materials are used at both ends of the resin film in the width direction in the production of the resin film, and if the melt viscosity of the recycled material and the melt viscosity of the virgin material are in a specific relationship. Specifically, first, virgin and recycled materials whose melt viscosity relationship satisfies the above formula (1) are prepared. Next, one resin film 3 is produced so that both ends 31 in the width direction of the resin film 3 are formed from the recycled material, and the main body portion 32 of the resin film 3 is formed from the virgin material. This makes it possible to prevent unevenness from occurring in the resin film 3 even when the resin film 3 is produced using recycled materials, and as a result, it is possible to stably produce a stretched film 5 having the desired properties.

In one embodiment, the recycled material has a continuous phase comprised of the second resin; and a dispersed phase comprised of the entrained components.
The maximum dimension of the dispersed phase is, for example, 1500 nm or less, preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 350 nm or less, particularly preferably 250 nm or less, particularly preferably 200 nm or less, most preferably 100 nm or less, and, for example, 1 nm or more, preferably 10 nm or more, more preferably 30 nm or more, even more preferably 50 nm or more. If the maximum dimension of the dispersed phase is the above upper limit or less, it is possible to stably suppress the occurrence of unevenness in the resin film. If the maximum dimension of the dispersed phase is the above lower limit or more, it is possible to smoothly manufacture the recycled material. The maximum dimension of the dispersed phase can be measured, for example, by cross-sectional observation using a scanning electron microscope.

The contaminating components contained in the recycled material typically include foreign matter. In addition to the foreign matter, the contaminating components may also include a resin component that is different from the second resin. The foreign matter is a solid component that is different from the resin component.

The maximum dimension of the largest foreign object contained in the mixed components is, for example, less than 3 mm, preferably less than 1 mm. If the maximum dimension of the largest foreign object is less than the above upper limit, the occurrence of unevenness in the resin film can be more stably suppressed. The maximum dimension of the foreign object can be measured, for example, by a particle counter.

In one embodiment, the foreign objects include a first foreign object having a maximum dimension of 500 μm or more and less than 1 mm; and a second foreign object having a maximum dimension of less than 500 μm. The foreign objects may include a third foreign object having a maximum dimension of more than 1 mm.
The content of the first foreign matter in the foreign matter contained in the mixed components is, for example, 5 vol. % or more, and, for example, 50 vol. % or less, preferably 40 vol. % or less.
The content of the second foreign matter in the foreign matter contained in the mixed components is, for example, 50 vol. % or more, preferably 60 vol. % or more, and, for example, 95 vol. % or less.
When the content ratio of the first foreign matter and/or the second foreign matter is within the above range, the occurrence of unevenness in the resin film can be more stably suppressed.

Below, we will explain each step of the stretched film manufacturing process in detail.

B. Preparation Step In the preparation step, the virgin material and the recycled material are each prepared as described above.

B-1. Virgin material The virgin material is a synthetic resin material that does not contain recycled resin material. The virgin material may be in the form of, for example, a pellet or a powder. In one embodiment, the virgin material is prepared as a virgin pellet. The following describes in detail the case where the virgin material is a virgin pellet.

The virgin pellets may have any suitable shape and size. The virgin pellets are typically cylindrical. The average maximum length of the virgin pellets is, for example, 1.0 mm or more and 5.0 mm or less. The mass of each virgin pellet is, for example, 5 mg or more and 25 mg or less.

Virgin pellets (virgin material) contain the first resin and are substantially free of other components. The content of the first resin in the virgin pellets is, for example, 99.0% by mass or more, preferably 99.2% by mass or more, more preferably 99.5% by mass or more, and typically 100% by mass or less. In other words, the content of other components in the virgin pellets is, for example, 1.0% by mass or less, preferably 0.8% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.2% by mass or less, particularly preferably 0.09% by mass or less, and particularly preferably 0.05% by mass or less, and typically 0% by mass or more.

The first resin is arbitrarily and appropriately selected depending on the application of the stretched film.
Examples of the first resin include polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, (meth)acrylic resins, cellulose ester resins, cellulose resins, polyester resins, polyester carbonate resins, olefin resins, and polyurethane resins. Note that the (meth)acrylic resin refers to an acrylic resin and/or a methacrylic resin. These first resins may be used alone or in combination.

Among the first resins contained in the virgin pellets, polycarbonate (PC)-based resins, cycloolefin (COP)-based resins, (meth)acrylic-based resins, and polyester-based resins (typically polyethylene terephthalate (PET)) are preferred, and PC-based resins are more preferred. When the first resin is such a resin material, it is possible to stably impart the desired properties to the stretched film (particularly the optical film).

Examples of PC-based resins include PC-based resins that contain structural units derived from dihydroxy compounds. Specific examples of the dihydroxy compound include 9,9-bis(4-hydroxyphenyl)fluorene, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3-ethylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-propylphenyl)fluorene, 9,9-bis(4-hydroxy-3-isopropylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-sec-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-tert-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-cyclohexylphenyl)fluorene, 9,9-bis(4-hydroxy-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, and 9,9-bis( 4-(2-hydroxyethoxy)-3-methylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-isopropylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-isobutylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-cyclohexyl phenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3,5-dimethylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butyl-6-methylphenyl)fluorene, 9,9-bis(4-(3-hydroxy-2,2-dimethylpropoxy)phenyl)fluorene. In addition to the structural units derived from the dihydroxy compounds, the PC resin may contain structural units derived from dihydroxy compounds such as isosorbide, isomannide, isoidet, spiroglycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), cyclohexane dimethanol (CHDM), tricyclodecane dimethanol (TCDDM), and bisphenols.

Details of the above-mentioned PC resins are described, for example, in JP 2012-67300 A and Japanese Patent No. 3325560. The descriptions in these patent documents are incorporated herein by reference.

The melt viscosity A of the virgin pellets (virgin material) is appropriately changed depending on the type of the first resin. The melt viscosity A of the virgin pellets is, for example, 300 Pa·s or more, preferably 500 Pa·s or more, more preferably 1000 Pa·s or more, and is, for example, 3000 Pa·s or less, preferably 2500 Pa·s or less. The melt viscosity of the pellets can be measured, for example, by a method according to JIS K 7199.

Virgin pellets may be prepared by any suitable method. The virgin pellets may be prepared by a strand cut method or a hot cut method. Details of the virgin pellet preparation method are described, for example, in JP 2013-181105 A. The description of this patent document is incorporated herein by reference.

B-2. Recycled material The recycled material is a recycled resin material, which will be described in detail later. The recycled material may be in the form of, for example, a pellet or a powder. In one embodiment, the recycled material is prepared as recycled pellets. The following describes in detail the case where the recycled material is in the form of recycled pellets.

The shape and size of the recycled pellets can be described in the same way as the virgin pellets described above. The recycled pellets contain the second resin described above and the mixed components that are mixed into the second resin. In the recycled pellets, the second resin constitutes a continuous phase as a matrix resin, and the mixed components constitute a dispersed phase that is dispersed in particulate form in the continuous phase. The second resin contained in the recycled pellets (recycled material) and the first resin contained in the virgin pellets (virgin material) are typically the same.

The content of the second resin in the recycled pellets is, for example, 40.0% by mass or more, preferably 50.0% by mass or more, more preferably 70.0% by mass or more, and even more preferably 90.0% by mass or more, and for example, 99.1% by mass or less.
The content of the contaminating components in the recycled pellets is, for example, 60.0% by mass or less, preferably 50.0% by mass or less, more preferably 30.0% by mass or less, and even more preferably 10.0% by mass or less. The lower limit of the content of the contaminating components in the recycled pellets is, for example, 0.3% by mass, for example, 0.5% by mass, or for example, 0.9% by mass.
In the recycled pellets, the mass ratio of the contaminating components to the second resin (contaminating components/second resin) is, for example, 0.01 or more and, for example, 1.5 or less, preferably 1.0 or less. When the contaminating components/second resin is within the above range, unevenness in the resin film can be stably reduced.

The contaminating components typically include the above-mentioned foreign matter. Examples of the foreign matter include amide-based foreign matter, fiber-based foreign matter, etc. The foreign matter may be mixed into the recycled pellets alone or in combination.
The content of foreign matter in the mixed components is, for example, 1 vol % or more and 100 vol % or less, and for example, 10 vol % or more and 50 vol % or less.

The contaminating components may include, in addition to foreign matter, a resin component different from the second resin. Examples of the resin component include those similar to the first resin described above. The contaminating components may include a single resin component or two or more resin components. In one embodiment, the resin component includes an olefin resin (typically polyethylene).
The content of the resin component in the mixed components is, for example, 0 vol % or more and 99 vol % or less, and, for example, 50 vol % or more and 90 vol % or less.

The air bubble content of the recycled pellets is, for example, 10% by volume or less, preferably 3% by volume or less, and more preferably 0% by volume. The air bubble content can be measured by observation and analysis using a microscope. If the air bubble content of the recycled pellets is equal to or less than the above upper limit, the inclusion of air bubbles in the resin film can be suppressed.

The melt viscosity C of the recycled pellets (recycled material) is appropriately changed depending on the type of the second resin and the mixed components. The melt viscosity C of the recycled pellets is, for example, 200 Pa·s or more, preferably 350 Pa·s or more, and, for example, 2800 Pa·s or less, preferably 2300 Pa·s or less.

The melt viscosity A of the virgin pellets and the melt viscosity C of the recycled pellets satisfy the above formula (1). The absolute value of the melt viscosity difference between the virgin pellets and the recycled pellets with respect to the melt viscosity A of the virgin pellets (|(C-A)/A|) is 0 or more, preferably 0.05 or more, more preferably 0.08 or more, and is less than 0.65, preferably 0.60 or less, more preferably 0.55 or less, even more preferably 0.45 or less, particularly preferably 0.35 or less, particularly preferably 0.23 or less, and most preferably 0.20 or less. When |(C-A)/A| is in the above range, unevenness in the resin film can be sufficiently reduced.

B-2-1. Method for Preparing Recycled Pellets Recycled pellets can be prepared from recycled resin materials by any suitable method.
The recycled resin material is obtained by collecting discarded resin products or waste generated during the manufacture of resin products. Examples of resin products include optical films such as retardation films; packaging materials composed of thermoplastic resins such as polyethylene terephthalate (PET) and nylon. Among these resin products, optical films are preferred, and retardation films are more preferred. That is, the recycled pellets are preferably prepared from optical films (typically retardation films) and/or waste generated during the manufacture of optical films. As will be described in detail later, in the manufacturing method of the stretched film according to the embodiment of the present invention, the end film (first end film and/or second end film) generated as a by-product can be suitably used as a recycled resin material for the preparation of recycled pellets. The recycled resin material may be recycled multiple times. That is, the recycled pellets may be prepared from a resin product (typically an optical film) manufactured from a recycled resin material, and/or waste generated during the manufacture of the resin product.

The method for preparing recycled pellets can be, for example, the same method as the method for preparing virgin pellets described above. In one embodiment, the method for preparing recycled pellets includes a process for melting recycled resin material (melting process); and a process for extruding the molten recycled resin material (extrusion process).

The moisture content of the recycled resin material subjected to the melting process is, for example, 2.0% by mass or less, preferably less than 1.0% by mass, more preferably 0.9% by mass or less, and even more preferably 0.8% by mass or less. If the moisture content of the recycled resin material is equal to or less than the above upper limit (less than), the generation of air bubbles in the resin film prepared using the recycled pellets can be suppressed. The lower limit of the moisture content of the recycled resin material is typically 0.01% by mass or more. The moisture content of the recycled resin material can be measured, for example, by the Karl Fischer method.

Any suitable method may be used to adjust the moisture content of the recycled resin material to the above range. For example, the recycled resin material may be stored in a moisture-proof bag.

The moisture-proof bag may have any suitable configuration. For example, a packaging material in which aluminum is fused to an inner bag may be used as the moisture-proof bag. The moisture permeability of the moisture-proof bag is, for example, 10 g/m ² ·24 h or less, preferably 5 g/m ² ·24 h or less, preferably 3 g/m ² ·24 h or less. The moisture permeability may be measured, for example, by a cup method.
The storage time is, for example, 2 hours or more, preferably 12 hours or more, and, for example, 72 hours or less, preferably 36 hours or less. According to such a method, even if the recycled resin material is stored for the above-mentioned time, the moisture content of the recycled resin material can be stably maintained within the above-mentioned range.
The storage temperature is, for example, 0° C. or higher and 30° C. or lower, and the storage humidity is, for example, 0% RH (relative humidity) or higher and 60% RH (relative humidity) or lower.

In the melting process, the recycled resin material is heated and melted. Typically, the recycled resin material is fed into a cylinder housing a screw, where it is heated and melted, and then kneaded by the screw.

The heating temperature and heating time are each set arbitrarily and appropriately depending on the type of recycled resin material. The heating temperature is, for example, 80°C or higher and 150°C or lower. The heating time (residence time) is, for example, 6 hours or higher and 48 hours or lower.

The screw rotation speed is, for example, 5 rpm or more, preferably 10 rpm or more, more preferably 20 rpm or more, and even more preferably 40 rpm or more, and is, for example, 200 rpm or less, preferably 100 rpm or less, and more preferably 80 rpm or less. If the screw rotation speed is equal to or higher than the lower limit, the maximum dimension of the dispersed phase in the recycled pellets can be stably adjusted to be equal to or lower than the upper limit. If the screw rotation speed is equal to or higher than the lower limit, the incorporation of air bubbles into the recycled pellets can be suppressed.

The screw length L relative to the screw diameter D (L/D) is, for example, 15 or more, preferably 20 or more, and, for example, 60 or less, preferably 40 or less.

As a result, a recycled resin material in a molten state (hereinafter referred to as molten resin) is obtained.
In one embodiment, the molten resin is passed through a filter before being subjected to the extrusion molding process, whereby coarse foreign matter contained in the molten resin can be removed from the molten resin.

The filter may have any suitable configuration, and examples of the filter include a screen mesh and a disk filter, and preferably a screen mesh.
The opening of the screen mesh is, for example, 2.6 mm or less (8 mesh), preferably 2.0 mm or less (10 mesh), more preferably 0.60 mm or less (30 mesh), and even more preferably 0.15 mm or less (100 mesh), and is, for example, 0.034 mm or more (400 mesh), preferably 0.045 mm or more (300 mesh), and more preferably 0.060 mm or more (250 mesh). If the opening of the screen mesh is equal to or less than the upper limit, coarse foreign matter can be smoothly removed from the molten resin, and in particular, if the opening is less than 1.0 mm, coarse foreign matter having a maximum dimension exceeding 1 mm can be smoothly removed from the molten resin. If the opening of the screen mesh is equal to or more than the lower limit, the molten resin can be smoothly passed through.

In the extrusion process, the molten resin is discharged from a die and then cooled and solidified, thereby preparing recycled pellets.
When the recycled pellets are prepared by the strand cutting method, the molten resin is discharged from a die in the form of a thread and then cooled to obtain a strand made of the recycled resin material, which is then cut to a predetermined size to obtain the recycled pellets.
When the method for preparing recycled pellets is the hot-cut method, the molten resin is extruded from a die in the form of a thread and immediately thereafter cut to obtain recycled pellets.

1, in the film-forming process, the virgin pellets and recycled pellets are used to form a long resin film 3. More specifically, both end portions 31 in the width direction of the resin film 3 are formed from the recycled pellets, and a main body portion 32 of the resin film 3 is formed from the virgin pellets, thereby forming one sheet of the resin film 3.
Details of the resin film production method are described in, for example, JP 2006-315275 A. The description of this patent document is incorporated herein by reference. More specifically, in the brittle resin film production method described in JP 2006-315275 A, virgin pellets are used as the brittle resin A and recycled pellets are used as the tough resin B, so that the resin film 3 can be produced.

The resin film 3 obtained in the film-forming process may have any appropriate configuration. As described above, the resin film 3 has a long shape. Any appropriate value may be adopted as the dimensions of the resin film 3 in each direction. The width of the resin film 3 (the dimension in the direction perpendicular to the long direction) is, for example, 500 mm or more, preferably 700 mm or more, and, for example, 2500 mm or less, preferably 2000 mm or less. The thickness of the resin film 3 is, for example, 40 μm or more, preferably 60 μm or more, and, for example, 200 μm or less, preferably 180 μm or less.

D. First Cutting Step In the first cutting step, both end portions 31 in the width direction of the resin film 3 are cut.
In the illustrated example, two cutting lines 33 are formed on the resin film 3. The cutting lines 33 extend along the longitudinal direction of the resin film 3. The two cutting lines 33 are formed at a predetermined interval from each other in the width direction of the resin film 3, and each of the two cutting lines 33 is formed at a predetermined interval from an edge of the resin film 3 in the width direction.

As a result, the resin film 3 is separated into two first end films 6 including the widthwise ends 31 of the resin film 3, and the film-forming film 4 including the main body portion 32. Each of the two first end films 6 and the film-forming film 4 has an elongated shape.

When the width of the resin film 3 is taken as 100%, the width of the first end film 6 is, for example, 1% or more, preferably 5% or more, more preferably 10% or more, and for example, 50% or less, preferably 30% or less. The width of the first end film 6 is, for example, 10 mm or more, preferably 50 mm or more, more preferably 100 mm or more, and for example, 1000 mm or less, preferably 600 mm or less. When the width of the first end film is equal to or greater than the above lower limit, the first end film can contain a sufficient portion derived from recycled pellets. When the width of the end film is equal to or less than the above upper limit, the yield of the stretched film can be improved.

The first end film 6 may be recovered by any suitable method. The recovered first end film 6 may be suitably used as a recycled resin material in the above-mentioned method for preparing recycled pellets.

E. Stretching Step As shown in FIG. 2, in the stretching step, the long film-formed film 4 is stretched in a direction intersecting the long direction. Any appropriate stretching method can be adopted. Various stretching methods such as free-end stretching and fixed-end stretching can be used alone, or simultaneously or sequentially. Among the stretching methods, fixed-end uniaxial stretching is preferable.

Fixed-end uniaxial stretching is typically performed by a stretching device equipped with clips capable of gripping the widthwise ends of the film-formed film 4. The stretching device is typically a tenter stretching device. The stretching device stretches the film-formed film 4 in a direction intersecting with the longitudinal direction while each of the widthwise ends of the film-formed film 4 is gripped (typically clamped) by clips. The stretching direction may be substantially perpendicular to the longitudinal direction of the film-formed film 4 (e.g., 90°±1° relative to the longitudinal direction), or may be a direction intersecting both the longitudinal direction and the width direction of the film-formed film 4.

Details of the stretching process are described, for example, in Japanese Patent No. 7096940, Japanese Unexamined Patent Publication No. 2004-226686, and International Publication No. 2007/111313. The descriptions in these patent documents are incorporated herein by reference.

As a result, a long stretched film 5 is produced as shown in FIG. 2. The stretching ratio in the width direction in the stretching process (width of stretched film/width of film-formed film) is, for example, 1.1 or more, preferably 1.5 or more, and, for example, 6.0 or less, preferably 4.0 or less.

The stretched film 5 typically has a slow axis in the stretching direction described above and is configured as a retardation film. The refractive index of the stretched film 5 has the relationship nx>ny.

In one embodiment, the stretched film 5 functions as a λ/4 plate. When the product film functions as a λ/4 plate, the in-plane retardation Re(550) of the stretched film 5 is, for example, 100 nm to 180 nm, and preferably 135 nm to 155 nm.
In another embodiment, the stretched film 5 functions as a λ/2 plate. When the stretched film functions as a λ/2 plate, the in-plane retardation Re(550) of the stretched film is, for example, 230 nm to 310 nm, preferably 250 nm to 290 nm.

The wavelength dependence of the stretched film 5 is not particularly limited. The stretched film 5 preferably exhibits wavelength dependence of reverse dispersion. The Re(450)/Re(550) of the stretched film 5 is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.95. The Re(550)/Re(650) of the stretched film 5 is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.97.

The absolute value of the photoelastic coefficient of the stretched film 5 is, for example, 2×10 ⁻¹² (m ² /N) to 100×10 ⁻¹² (m ² /N), and preferably 5×10 ⁻¹² (m ² /N) to 50×10 ⁻¹² (m ² /N).

F. Second Cutting Step In one embodiment, the production of the stretched film further includes a second cutting step, in which both ends of the stretched film 5 in the width direction are cut.

In the illustrated example, two cutting lines 55 are formed on the stretched film 5. The cutting lines 55 extend along the longitudinal direction of the stretched film 5. The two cutting lines 55 are formed at a predetermined distance from each other in the width direction of the stretched film 5, and each of the two cutting lines 55 is formed at a predetermined distance from the edge of the stretched film 5 in the width direction.

When fixed-end uniaxial stretching is performed in the stretching process, clip marks 51 may be formed on both ends of the stretched film 5 in the width direction. The clip marks 51 are harder and more brittle than the parts of the stretched film 5 other than the grip marks 3.

The slow axis of the stretched film 5 may also be misaligned in the width direction. More specifically, the direction of the slow axis of the stretched film 5 is likely to deviate from the desired angle at the width direction ends. Typically, the misalignment is not substantially evident in the width direction center of the stretched film 5, and becomes greater as it approaches the width direction ends. In the illustrated example of the stretched film 5, the slow axis is substantially parallel to the stretching direction at the width direction center (e.g., the misalignment is less than 0°±1°). Furthermore, at the width direction ends of the stretched film 5, the slow axis may cross the stretching direction (e.g., the misalignment is 1° to 3°).

Therefore, by carrying out the second cutting step, the clip grip marks 51 and/or the portions of the stretched film where the axial misalignment is relatively large can be removed from the stretched film 5. In addition, two second end films 7 corresponding to both ends of the stretched film 5 in the width direction can be obtained from the stretched film 5.

The second end film 7 in the illustrated example includes clip grip marks 51. Furthermore, the stretched film 2 from which the two second end films 7 have been cut is configured as the product film 8. That is, in the second cutting step, the stretched film 5 is typically separated into the two second end films 7 and the product film 8. The product film 8 is typically configured as the retardation film described above.

The width of the second end film 7 is, when the width of the stretched film 5 is taken as 100%, for example, 0.5% or more, preferably 1.0% or more, more preferably 5.0% or more, and even more preferably 10.0% or more, and for example, 30% or less, preferably 25% or less, and more preferably 20% or less. The width of the second end film 7 is, for example, 10 mm or more, preferably 20 mm or more, more preferably 100 mm or more, and even more preferably 200 mm or more, and for example, 600 mm or less, preferably 500 mm or less, and more preferably 300 mm or less.
When the width of the second end film is equal to or greater than the lower limit, the second end film can stably include the entire gripping mark of the clip, and the portion of the stretched film in which the axial misalignment is relatively large can be included in the second end film. As a result, the gripping mark of the clip can be prevented from remaining in the product film, and the axial misalignment in the product film can be reduced. When the width of the second end film is equal to or less than the upper limit, the yield of the product film can be improved.

The second end film 7 may be recovered by any suitable method. The recovered second end film 7 may be suitably used as a recycled resin material in the above-mentioned method for preparing recycled pellets. In other words, the production of the stretched film may further include a step of preparing recycled pellets from the recycled resin material including the first end film 6 and/or the second end film 7.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on mass. The methods for measuring each property in the examples and comparative examples are as follows.

(1) Measurement of Melt Viscosity of Virgin Pellets and Recycled Pellets The melt viscosity of the virgin pellets and recycled pellets used in the examples and comparative examples was measured at a shear rate of 100 sec ^-1 and a measurement temperature of 24°C by a method according to JIS K 7199. The results are shown in Tables 1 to 3.

(2) Measurement of the maximum dimension of the dispersed phase in the recycled pellets The maximum dimension of the dispersed phase in the recycled pellets used in the examples and comparative examples was measured by observation with a scanning electron microscope. The results are shown in Tables 1 to 3.

(3) Measurement of the maximum size of foreign matter contained in recycled pellets, and measurement of the content ratio of each component in the foreign matter The maximum size of the foreign matter in the recycled pellets used in the examples and comparative examples was measured by a particle counter. The foreign matter included a first foreign matter having a maximum dimension x of 500 μm or more and less than 1 mm, and/or a second foreign matter having a maximum dimension x of less than 500 μm. Furthermore, the foreign matter according to Example 14 included a third foreign matter having a maximum dimension x of 1 mm or more in addition to the first foreign matter and the second foreign matter. The content ratio (volume %) of each of the first foreign matter, the second foreign matter, and the third foreign matter was calculated by observation and analysis using an optical microscope. The results are shown in Tables 1 to 3.

(4) Moisture content of end film In the examples and comparative examples, the moisture content of the end film (recycled resin material) immediately before being subjected to the manufacturing process of the recycled pellets was measured by the Karl Fischer method. The results are shown in Tables 1 to 3.

(5) Unevenness in resin film Unevenness (unevenness in resin flow) in the resin films prepared in the examples and comparative examples was confirmed by visually observing the degree of distortion when the film was viewed through a light source, and was evaluated according to the following criteria. The results are shown in Tables 1 to 3.
5: No distortion at all when viewed through transmission.
4: There is some distortion when viewed through a transparent lens.
3: Distortion is present when viewed through a transparent lens.
2: Severe distortion when viewed through transmission (acceptable for practical use).
1: When viewed through a transparent glass, the other side cannot be seen (unacceptable for practical use).

(6) Air bubbles in resin film The presence or absence of air bubbles in the resin films prepared in the examples and comparative examples was confirmed using an optical microscope. The results are shown in Tables 1 to 3.

<<Preparation of Edge Film>>
<Preparation Examples 1 to 6>
In the same manner as in Production Example 9 of JP 2022-150732 A, a resin film made of a PC resin was prepared and stretched to prepare a stretched film made of a PC resin. The thickness of the stretched film was 48 μm.
Next, both ends of the stretched film in the width direction were cut by a slitter (cutting device) to obtain two end films (recycle number: 1). Each of the two end films had a width of 250 mm.
Next, the obtained end film was washed with water, and then dried under conditions of 100° C. and 10 minutes (number of washings: 1).
Next, the end film was placed in a moisture-proof bag (product name: moisture-proof packing bag one-side sewing machine, moisture-proof type, manufactured by Yamaguchi Packaging Industry Co., Ltd.) under the environment shown in Table 1 or 3 and stored for 24 hours.

<Preparation Example 7>
An end film was prepared and stored in the same manner as in Preparation Example 1, except that the moisture-proof bag was changed to a non-moisture-proof bag (product name: Inner Bag Aluminum Bag, manufactured by Yamaguchi Packaging Industry Co., Ltd.).

<Preparation Examples 8 to 13>
Using the end film obtained in Preparation Example 1, recycled pellets were produced in the same manner as in Example 1 described later (preparation step), a resin film was produced from the virgin pellets and the recycled pellets (film production step), the resin film was cut to separate into a first end film and a film-formed film (first cutting step), the film-formed film was then stretched (stretching step), and the obtained stretched film was cut to separate into a second end film and a product film (second cutting step). Next, the preparation step, film-formation step, first cutting step, stretching step, and second cutting step were repeated using the obtained second end film until the recycling number shown in Table 1 or 3 was reached. As a result, an end film (second end film) with the recycling number shown in Table 1 or 3 was prepared. The obtained end film was then stored in the same manner as in Preparation Example 1.

<Preparation Examples 14 to 16>
In the same manner as in Production Example 9 of JP 2022-150732 A, a resin film made of a PC resin was prepared and stretched to prepare a stretched film made of a PC resin. The thickness of the stretched film was 48 μm.
Next, a polyethylene (PE) film (thickness: 48 μm) was attached as a protective film to the surface of the stretched film via an acrylic adhesive layer. Then, both ends of the laminated film of the stretched film and the protective film in the width direction were cut by a slitter (cutting device) to obtain two end films (recycled number: 1 time). The width of each of the two end films was 250 mm.
The obtained end film was then washed with water. Thereafter, the end film was dried under conditions of 100° C. and 10 minutes (number of washings: 1). Thereafter, the end film was stored in the same manner as in Preparation Example 1.

<Preparation Example 17>
An end film was prepared and stored in the same manner as in Preparation Example 14, except that the thickness of the PE film used as the protective film was changed to 96 μm.

<Preparation Example 18>
An edge film was prepared and stored in the same manner as in Preparation Example 1, except that the edge film was washed and dried five times.

<Preparation Examples 19 and 20>
Except for changing the resin film made of PC resin to a resin film made of PET (manufactured by Toray Industries, product number "50U48"), an end film was prepared and stored in the same manner as in Preparation Example 1. The thickness of the stretched film obtained by stretching the resin film was 50 μm.

<Preparation Example 21>
Except for using the end film obtained in Preparation Example 19 instead of the end film obtained in Preparation Example 1, the preparation step, film-forming step, first cutting step, stretching step, and second cutting step were repeated in the same manner as Preparation Example 8 until the recycling number shown in Table 2 was reached. In this way, the end film (second end film) with the recycling number shown in Table 2 was prepared. The obtained end film was then stored in the same manner as Preparation Example 1.

<Preparation Example 22>
Except for changing the resin film made of PC resin to a resin film made of PET (manufactured by Toray Industries, product number "50U48"), an end film containing a PE film was prepared and stored in the same manner as in Preparation Example 14. The thickness of the stretched film obtained by stretching the resin film was 50 μm, and the thickness of the PE film was 50 μm.

<Preparation Examples 23 and 24>
Except for changing the resin film made of PC resin to a resin film made of acrylic resin (manufactured by Kaneka Corporation, product name "HTX-Z"), an end film was prepared and stored in the same manner as in Preparation Example 1. The thickness of the stretched film obtained by stretching the resin film was 40 μm.

<Preparation Example 25>
Except for using the end film obtained in Preparation Example 23 instead of the end film obtained in Preparation Example 1, the preparation step, film-forming step, first cutting step, stretching step, and second cutting step were repeated in the same manner as Preparation Example 8 until the recycling number shown in Table 2 was reached. In this way, the end film (second end film) with the recycling number shown in Table 2 was prepared. The obtained end film was then stored in the same manner as Preparation Example 1.

<Preparation Example 26>
Except for changing the resin film made of PC resin to a resin film made of acrylic resin (manufactured by Kaneka Corporation, product name "HTX-Z"), an end film containing a PE film was prepared and stored in the same manner as in Preparation Example 14. The thickness of the stretched film obtained by stretching the resin film was 80 μm, and the thickness of the PE film as a protective film was 80 μm.

<Preparation Examples 27 and 28>
Except for changing the resin film made of PC resin to a resin film made of COP resin (manufactured by Zeon Corporation, product number "ZF16"), an end film was prepared and stored in the same manner as in Preparation Example 1. The thickness of the stretched film obtained by stretching the resin film was 40 μm.

<Preparation Example 29>
Except for using the end film obtained in Preparation Example 27 instead of the end film obtained in Preparation Example 1, the preparation step, film-forming step, first cutting step, stretching step, and second cutting step were repeated in the same manner as Preparation Example 8 until the recycling number shown in Table 2 was reached. In this way, the end film (second end film) with the recycling number shown in Table 2 was prepared. The obtained end film was then stored in the same manner as Preparation Example 1.

<Preparation Example 30>
Except for changing the resin film made of PC resin to a resin film made of COP resin (manufactured by Zeon Corporation, product number "ZF16"), an end film containing a PE film was prepared and stored in the same manner as in Preparation Example 14. The thickness of the stretched film obtained by stretching the resin film was 40 μm, and the thickness of the PE film as a protective film was 40 μm.

[Examples 1 to 26, Comparative Examples 1 to 7]
The end film after storage obtained in each preparation example was supplied as a recycled resin material to a pellet manufacturing device (strand cut type) equipped with a filter shown in Tables 1 to 3. In the pellet manufacturing device, the end film was heated to 270°C to melt and passed through the filter shown in Tables 1 to 3. Thereafter, recycled pellets were manufactured by extrusion molding under the extrusion conditions (screw rotation speed, compression ratio and effective length) shown in Tables 1 to 3. The mass ratio of the mixed component/second resin in the recycled pellets is shown in Tables 1 to 3.

Separately, virgin pellets were produced by melt extrusion in accordance with the method described in JP 2013-181105 A. The virgin pellets contained the first resins shown in Tables 1 to 3. The content of the first resin in the virgin pellets was 100% by mass.

Next, a resin film was produced from the virgin pellets and the recycled pellets. More specifically, in accordance with the examples of JP 2006-315275 A, both ends in the width direction of the resin film were formed from recycled pellets, and the main body portion located between both ends in the width direction of the resin film was formed from virgin pellets. The width of the resin film was 800 mm. The thickness of the resin film was 200 μm.

Then, the resin film was cut by a slitter (cutting device) to separate it into a first end film including the end in the width direction of the resin film and a film-formed film including the main body portion. The width of each of the two first end films was 60 mm (7.5% when the width of the resin film is 100%).

Then, the film was stretched in the width direction according to Manufacturing Example 9 of JP 2022-150732 A. As a result, a stretched film was obtained. The stretching ratio was 3.0 times. The width of the stretched film was 2000 mm.

The stretched film was then cut by a slitter (cutting device) to separate it into two second end films and a product film. The width of each of the two second end films was 250 mm (12.5% of the width of the stretched film taken as 100%). The width of the product film was 1500 mm.

[evaluation]
As is clear from Tables 1 to 3, when the melt viscosity of the virgin pellets and the melt viscosity of the recycled pellets satisfy the above formula (1), it is possible to suppress unevenness in the resin film. Furthermore, when the maximum dimension of the dispersed phase in the recycled pellets is 500 μm or less and/or the maximum dimension of the foreign matter is less than 1 mm, it is possible to further suppress unevenness in the resin film.

The method for producing a stretched film of the present invention is used to produce stretched films that can be used in various industrial products, and is particularly suitable for producing optical films (specifically, retardation films).

3 Resin film 31 End portion in width direction of resin film 32 Main body portion 4 Film-forming film 5 Stretched film 6 First end film 7 Second end film

Claims (9)

Providing a virgin material comprising a first resin and a recycled material comprising a second resin and contaminant components;
a step of forming a long resin film from the virgin material and the recycled material, wherein both ends in a width direction of the resin film are formed from the recycled material, and a main body portion located between both ends in the width direction of the resin film is formed from the virgin material;
cutting the resin film to separate it into a first end film including an end portion in a width direction of the resin film and a film-forming film including the main body portion;
Stretching the film in a direction intersecting the longitudinal direction;
A method for producing a stretched film, wherein the melt viscosity of the virgin material and the melt viscosity of the recycled material satisfy the following formula (1):

(In formula (1), A represents the melt viscosity [Pa·s] of the virgin material, and C represents the melt viscosity [Pa·s] of the recycled material.) The method for producing a stretched film according to claim 1, wherein the melt viscosity of the virgin material and the melt viscosity of the recycled material satisfy the following formula (2):

(In formula (2), A represents the melt viscosity [Pa·s] of the virgin material, and C represents the melt viscosity [Pa·s] of the recycled material.) the recycled material has a continuous phase comprised of the second resin and a dispersed phase comprised of the contaminant components;
The method for producing a stretched film according to claim 1 or 2, wherein the maximum dimension of the dispersed phase is 500 nm or less. The method for producing a stretched film according to claim 3, wherein the maximum dimension of the dispersed phase is 10 nm or more and 200 nm or less. The contaminating components include foreign matter other than the resin component,
The method for producing a stretched film according to claim 1 or 2, wherein the maximum dimension of the largest foreign particle among the foreign particles contained in the mixed components is less than 1 mm. The foreign matter includes a first foreign matter having a maximum dimension of 500 μm or more and less than 1 mm, and a second foreign matter having a maximum dimension of less than 500 μm,
The method for producing a stretched film according to claim 5 , wherein the content of the first foreign matter is 5 volume % or more and 50 volume % or less, and the content of the second foreign matter is 50 volume % or more and 95 volume % or less. The method for producing a stretched film according to claim 3, further comprising the step of cutting both ends of the stretched film in the width direction to obtain a second end film. The method for producing a stretched film according to claim 7, further comprising a step of preparing a recycled material from a recycled resin material including the first end film and/or the second end film. The method for producing a stretched film according to claim 8, wherein the moisture content of the recycled resin material is less than 1.0% by mass.

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