JP2014083703A - Method for producing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical film, in which an original film comprising an acrylic resin is heated by using a predetermined heating roll and an infrared radiation part and the heated film is stretched vertically.SOLUTION: The method for producing the optical film comprises a step of vertically stretching the heated film by using the heating roll, which is selected from heating rolls contained in a stretch roll group and is adjacent to a cooling roll, and the infrared radiation part from which a predetermined near-infrared ray can be radiated.

Description

  The present invention relates to a method for producing an optical film. More specifically, when a thermoplastic resin film containing an acrylic resin is produced by a process including longitudinal stretching (hereinafter, also referred to as “roll longitudinal stretching”) performed using a roll, the film is stable. The present invention relates to a method for producing an optical film that can be produced.

  Acrylic resins are known to be difficult to handle because they are very brittle (because of low flexibility). For example, when producing a film by longitudinally stretching an acrylic resin roll, due to the brittleness of the acrylic resin, there is a problem that the film is easily broken at the time of stretching, and the film surface is uneven. The problem that the film thickness of the film becomes non-uniform is known.

  Therefore, there is a need for a technique that can stably produce a thermoplastic resin film containing an acrylic resin.

  As a technique for longitudinally stretching an acrylic resin, for example, there is a technique disclosed in Patent Document 1. In the technique disclosed in Patent Document 1, when the roll longitudinal stretching process is performed using the first stretching roll and the first nip roll, and the second stretching roll and the second nip roll, the contact time between the film and the first stretching roll And the method of adjusting the surface temperature of the first stretching roll to a predetermined condition. In the method disclosed in Patent Document 1, the film is heated only by heating a roll.

JP 2011-245624 A (released on December 8, 2011)

  However, the technique disclosed in Patent Document 1 cannot provide a sufficient amount of heat to the film before stretching because the film is only heated by a roll. Therefore, when an acrylic resin having the characteristic of being very brittle is stretched in the roll longitudinal direction by the technique disclosed in Patent Document 1, tensile breakage occurs at the stretched portion, and the thermoplastic resin film containing the acrylic resin is stable. It was found that there was a problem that could not be manufactured.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a film made of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrenic polymer. It is providing the manufacturing method of the optical film stretched longitudinally after heating with a heating roll and an infrared heater (infrared radiation part).

  The present inventor has found the above-mentioned problems and intensively studied the conditions for roll longitudinal stretching that can stably produce the thermoplastic resin film. As a result, it is possible to stably produce the thermoplastic resin film by combining heating with a heating roll and heating with an infrared heater (infrared radiation part) and giving a sufficient amount of heat to the film before stretching. The headline and the present invention were completed.

That is, the method for producing an optical film according to the present invention comprises an optical film comprising a longitudinal stretching step of longitudinally stretching a film made of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer. A manufacturing method comprising:
The longitudinal stretching includes a preheating unit containing one or more heating rolls for preheating the film; one or more heating rolls and one or more cooling rolls for cooling the film, and stretches the film. A drawing roll group; and a cooling part containing one or more cooling rolls for cooling the drawn film, and a longitudinal drawing part provided in this order in the film transport direction,
The longitudinal stretching is a heating roll adjacent to the cooling roll contained in the stretching roll group and a wavelength of 0.8 μm or more and 2 μm or less among the heating rolls contained in the stretching roll group. It is characterized by being performed on the film heated using an infrared radiation part capable of emitting near infrared rays.

  According to the said structure, since the said film is heated using the said heating roll and the said infrared radiation part together, sufficient heat quantity can be given with respect to the said film before extending | stretching. Therefore, even when the acrylic resin having the characteristics of being very brittle and difficult to handle is longitudinally stretched, the film is tension-ruptured at the time of stretching as in the technique disclosed in Patent Document 1 in which heating is performed only with a roll. Therefore, desired longitudinal stretching can be stably performed.

  Therefore, even when an acrylic resin is used, an optical film having desired optical characteristics can be stably supplied.

  In the present specification, “acrylic polymer; or thermoplastic resin containing an acrylic polymer and a styrene polymer” is also referred to as “acrylic resin”.

  The manufacturing method of the optical film concerning this invention is contained in the said extending | stretching roll group, and when connecting between the center of the heating roll and cooling roll which adjoin each other in the conveyance direction of the said film with the straight line, the said straight line and the said heating roll And the distance between the intersection of the straight line and the cooling roll is preferably 50 mm or more and 150 mm or less.

  The present inventor has found that according to the above configuration, the generation of wrinkles accompanying the neck-in of the film during longitudinal stretching and the fluttering of the film can be suppressed. Therefore, occurrence of thickness unevenness (film thickness unevenness) can be suppressed. Moreover, if it is the said structure, it can be set as wide enough to install an infrared radiation part in the space between the heating roll and cooling roll which adjoin each other in the conveyance direction of the said film.

  Therefore, an optical film made of an acrylic resin can be stably supplied with little thickness unevenness.

In the method for producing an optical film according to the present invention, when the output per unit length of the infrared radiation portion in the width direction of the film is W and the transport speed of the film is v, W / v is 800 J. / M ² or more and 3000 J / m ² or less is preferable.

  According to the said structure, sufficient heat quantity can be given with respect to the unstretched acrylic resin film heated with the said heating roll so that a fracture | rupture etc. may not be caused at the time of longitudinal stretching, and avoid excessive heating. Can do.

  Therefore, even when an acrylic resin is used, an optical film having desired optical characteristics can be supplied more stably.

  In the present specification, a film made of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer may be simply referred to as an “acrylic resin film”.

The manufacturing method of the optical film concerning this invention sets temperature of one said heating roll to Tn ₍ degreeC), and sets the temperature of the said other heating roll adjacent to the said heating roll and the conveyance direction of a film to _{Tn-. When the} temperature is ₁ ° C., it is preferable that the relationship shown in the following formula 1 holds.

0 ≦ T _n −T _n−1 ≦ 30 (1)
The present inventor, as shown in the examples described later, when the temperature gradient of the heating roll (T _n -T _n-1 ) exceeds 30, the film suddenly expands between the two corresponding heating rolls, It has been found that the thickness unevenness increases due to loose wrinkles and fluttering of the film caused by the expansion, and at the same time, surface unevenness tends to occur.

According to the above arrangement, since the T n _{-T n-1} is adjusted so as to satisfy the relationship shown in Equation 1, it is possible to suppress an abrupt expansion of the film between the corresponding two rolls. Therefore, stable longitudinal stretching can be performed, and an optical film in which thickness unevenness and surface unevenness are suppressed can be provided.

In the method for producing an optical film according to the present invention, the temperature of one of the cooling rolls is T ′ _n ° C., and the temperature of the cooling roll and the other cooling rolls adjacent in the direction opposite to the film transport direction is T ′. _{When n−1} ° C., it is preferable that the relationship shown in the following formula 2 holds.

−20 ≦ T ′ _n −T ′ _n−1 ≦ 0 (2)
As shown in the examples described later, the present inventor, when the temperature gradient (T ′ _n −T ′ _n−1 ) of the cooling roll is less than −20, the film abruptly changes between the two corresponding cooling rolls. It has been found that shrinkage occurs, the film breaks due to an increase in tension resulting from the shrinkage, and the stretching stability tends to deteriorate.

According to the above arrangement, since the T _'n -T' _n-1 is adjusted so as to satisfy the relationship shown in Equation 2, it is possible to suppress an abrupt contraction of the film between the corresponding two rolls. Therefore, stable longitudinal stretching can be performed while suppressing breakage of the film.

Method for producing an optical film according to the present invention, one of the peripheral speed R _n of the heating _roll, and the heating roll, the peripheral speed of the other of the heating roll adjacent the conveying direction and opposite direction of the film R _n- When it is set to ₁ , it is preferable that the relationship shown in the following formula 3 holds.

1.000 ≦ R _n / R _n−1 ≦ 1.100 (3)
The present inventors, as shown in Examples described later, when the velocity gradient of the heating roll _{(R n / R n-1} ) is less than 1.000, the expansion of the film occurring between corresponding two heating rolls It has been found that the thickness unevenness tends to increase due to slack wrinkles and film fluttering caused by the rotation of the heating roll not catching up, and the surface unevenness tends to occur.

In addition, when the heating roll speed gradient (R _n / R _n-1 ) exceeds 1.100, the film is pulled more than the expansion of the film. It was found that the stability of tended to deteriorate.

According to the above arrangement, since _R n _/ R _n-1 is adjusted so as to satisfy the equation 3, the relationship between the rotation of the expansion and heating roll of film is optimized. Therefore, stable longitudinal stretching can be performed without causing thickness unevenness, surface unevenness, and film breakage.

In the method for producing an optical film according to the present invention, the peripheral speed of one of the cooling rolls is R ′ _n , and the peripheral speed of the other cooling roll adjacent to the cooling roll in the direction opposite to the film transport direction is R ′ _n . _{When n−1} , it is preferable that the relationship shown in the following Expression 4 holds.

0.950 ≦ R ′ _n / R ′ _n−1 ≦ 1.100 (4)
As shown in the examples described later, the present inventor, when the speed gradient (R ′ _n / R ′ _n-1 ) of the cooling roll is less than 0.950, the expansion of the film that occurs between the two corresponding cooling rolls. In addition, the present inventors have found that uneven thickness tends to increase due to slack wrinkles and fluttering of the film due to the rotation of the cooling roll not catching up, and surface unevenness tends to occur.

In addition, when the velocity gradient (R ′ _n / R ′ _n-1 ) exceeds 1.100, the film is pulled more than the expansion of the film. It was found that the stability of tended to deteriorate.

According to the said structure, since _R'n / _R'n-1 is adjusted so that Formula 4 may be satisfy | filled, the relationship between expansion of a film and rotation of a heating roll is optimized. Therefore, stable longitudinal stretching can be performed without causing thickness unevenness, surface unevenness, and film breakage.

  In the manufacturing method of the optical film concerning this invention, the heating roll adjacent to the cooling roll contained in the said extending | stretching roll group in the conveyance direction of the said film among the heating rolls contained in the said extending | stretching roll group, wavelength 0 It is preferable that the surface temperature of the film heated using an infrared radiation portion capable of emitting near infrared rays of 8 μm or more and 2 μm or less is higher than the glass transition temperature of the thermoplastic resin.

  According to the said structure, since sufficient calorie | heat amount is given to the film before extending | stretching, it can prevent that a film fractures | ruptures at the time of extending | stretching. Therefore, even an acrylic resin film that is brittle and difficult to handle can be efficiently and stably subjected to longitudinal stretching.

The method for producing an optical film according to the present invention includes: a melt extrusion step of melt-extruding a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer;
A casting process for forming a film made of the thermoplastic resin by melt-forming the melt-extruded thermoplastic resin;
The longitudinal stretching step of longitudinally stretching a film made of the thermoplastic resin,
A transverse stretching step of transversely stretching a film made of the thermoplastic resin that has been longitudinally stretched;
A winding step of winding the transversely stretched film,
The casting process is performed after the melt extrusion process, the longitudinal stretching process is performed after the casting process, the transverse stretching process is performed after the longitudinal stretching process, and the winding process is performed after the transverse stretching process. Is preferred.

  According to the said structure, when performing from the said melt-extrusion process to the said winding-up process consistently, longitudinal stretch can be performed, after giving sufficient calorie | heat amount with respect to the acrylic resin film before extending | stretching.

  Therefore, while suppressing the occurrence of film breakage, thickness unevenness, and surface unevenness in the longitudinal stretching process, the process from the melt extrusion process to the winding process is smoothly and consistently performed without interrupting the work on the way. Can be done. Therefore, an efficient and stable optical film can be provided.

  In the present invention, even when an acrylic resin that is very fragile and difficult to handle is subjected to longitudinal stretching, the film is not subjected to tensile fracture during stretching, and desired longitudinal stretching can be stably performed. Therefore, even when an acrylic resin is used, there is an effect that an optical film having desired optical characteristics can be stably supplied.

It is a side view which shows an example of the main structures of the biaxial stretching apparatus which can be used by this invention. It is the schematic diagram which showed the film thickness of the part from the right-and-left edge part in the width direction of a film to 100 mm, respectively, and the film thickness of a film center part in the film. It is explanatory drawing for demonstrating the preferable width | variety of an infrared heater (infrared radiation | emission part).

  Hereinafter, embodiments of the present invention will be described in detail. All of the patent documents mentioned in this specification are incorporated herein by reference. In addition, “A to B” indicating a range indicates that the range is A or more and B or less.

  In the present specification, “resin” is a broader concept than “polymer”. The resin may be composed of, for example, one type or two or more types of polymers, and if necessary, materials other than the polymer, for example, additives such as ultraviolet absorbers, antioxidants, fillers, and compatibilizing agents. Further, it may contain a stabilizer and the like.

<1. Manufacturing method of optical film>
The method for producing an optical film according to the present invention includes a longitudinal stretching step of longitudinally stretching a film made of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer. The longitudinal stretching includes a preheating part containing one or more heating rolls for preheating the film; one or more heating rolls and one or more cooling rolls for cooling the film, A stretching roll group that stretches the film; and a cooling section that contains one or more cooling rolls that cool the stretched film, are provided by a longitudinal stretching section that is provided in this order in the transport direction of the film. Of the heating rolls contained in the stretching roll group, adjacent to the cooling roll contained in the stretching roll group in the film transport direction. A heating roll, carried out the following NIR wavelength 0.8μm or 2μm respect to the film that is heated with a radiation capable of infrared radiation unit.

(1-1. Acrylic polymer; or a film made of a thermoplastic resin containing an acrylic polymer and a styrene polymer)
A film made of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer (hereinafter, also referred to as “thermoplastic resin (A)”) is obtained by molding the thermoplastic resin (A). can get.

  The content of the acrylic polymer in the thermoplastic resin (A); or the acrylic polymer and the styrene polymer is usually 30% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, Especially preferably, it is 90 mass% or more, Most preferably, it is 95 mass% or more.

  When the thermoplastic resin (A) contains an acrylic polymer and a styrene polymer, the content of the acrylic polymer is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass. % To 95% by mass. Moreover, it is preferable that content of a styrene-type polymer is 0 to 50 mass%, More preferably, it is 5 to 40 mass%.

  In this specification, the “acrylic polymer” is a polymer having a structural unit ((meth) acrylic acid ester unit) derived from a (meth) acrylic acid ester monomer, Called.

  The content of the (meth) acrylic acid ester unit in the acrylic polymer is usually 10% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more, and particularly preferably 70% by mass or more.

  The acrylic polymer may have a ring structure in the main chain. The ring structure is obtained by, for example, copolymerizing a (meth) acrylate monomer and a monomer having a ring structure, or polymerizing a monomer group including a (meth) acrylate monomer. By proceeding with the cyclization reaction, it is introduced into the main chain of the (meth) acrylic polymer. When the polymer has a ring structure in the main chain, the polymer is a (meth) acrylic polymer if the total content of the (meth) acrylic acid ester unit and the ring structure is 50% by mass or more.

  (Meth) acrylic acid ester units are, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t- (meth) acrylic acid t- Butyl, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxy (meth) acrylate Each of ethyl, 3-hydroxypropyl (meth) acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth) acrylate, and 2,3,4,5-tetrahydroxypentyl (meth) acrylate It is a structural unit derived from a monomer.

  The acrylic polymer preferably has a methyl (meth) acrylate unit, and in this case, the optical properties and thermal stability of the finally obtained optical film are improved. The (meth) acrylic polymer may have two or more (meth) acrylic acid ester units.

  The acrylic polymer may have a structural unit other than the (meth) acrylic acid ester unit. Such structural units include, for example, styrene, vinyl toluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylonitrile, ethylene, propylene, 4-methyl-1-pentene, acetic acid. It is a structural unit derived from each monomer of vinyl, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinyl pyrrolidone, and N-vinyl carbazole.

  The acrylic polymer may have two or more of these structural units. When the acrylic polymer has N-vinylpyrrolidone units or N-vinylcarbazole units, the degree of freedom in controlling the birefringence wavelength dispersion in the optical film is improved. For example, in the visible light region, a retardation film exhibiting wavelength dispersibility (so-called reverse wavelength dispersibility) can be obtained as the birefringence decreases (the absolute value of the phase difference decreases) as the wavelength of light decreases.

  When a cyclic structure is introduced into the main chain by a cyclization reaction after polymerization, the acrylic polymer is preferably formed by copolymerization of a monomer group including a monomer having a hydroxyl group and / or a carboxylic acid group. .

  Examples of the monomer having a hydroxyl group include methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, butyl 2- (hydroxymethyl) acrylate, These are methyl 2- (hydroxyethyl) acrylate, methallyl alcohol, and allyl alcohol. Examples of the monomer having a carboxylic acid group include acrylic acid, methacrylic acid, crotonic acid, 2- (hydroxymethyl) acrylic acid, and 2- (hydroxyethyl) acrylic acid.

  Two or more of these monomers may be used. These monomers become a ring structure located in the main chain of the acrylic polymer by the cyclization reaction, but it is not necessary that all of the monomers change to the ring structure during the cyclization reaction. The acrylic polymer after the chemical reaction may have a structural unit derived from these monomers.

  The weight average molecular weight of the acrylic polymer is preferably 10,000 to 500,000, more preferably 20,000 to 400,000, and still more preferably 30,000 to 300,000.

  The acrylic polymer preferably has a ring structure in the main chain. The film made of the thermoplastic resin used in the present invention preferably contains an acrylic polymer having a ring structure in the main chain. In this case, the heat resistance and hardness of the optical film are improved. In addition, the ring structure of the main chain contributes to the film exhibiting a large retardation by stretching. This feature makes it possible to use the optical film produced by the method according to the present invention as a retardation film or a polarizer protective film having the function of a retardation film.

  The ring structure that the acrylic polymer may have in the main chain is, for example, at least one selected from an N-substituted maleimide structure, a maleic anhydride structure, a glutarimide structure, a glutaric anhydride structure, and a lactone ring structure. is there. The N-substituted maleimide structure is, for example, a cyclohexylmaleimide structure, a methylmaleimide structure, a phenylmaleimide structure, or a benzylmaleimide structure.

  From the viewpoint of the heat resistance of the optical film, the ring structure includes a lactone ring structure, a cyclic imide structure (for example, an N-alkyl-substituted maleimide structure, a glutarimide structure), and a cyclic anhydride structure (for example, a maleic anhydride structure and an anhydrous structure). Glutaric acid structure) is preferred.

  When the optical film produced by the method according to the present invention is a retardation film, from the viewpoint of imparting a positive retardation to the film, the ring structure includes a lactone ring structure, a glutarimide structure, and an anhydrous film. A glutaric acid structure is preferred.

  The following general formula (1) shows a glutaric anhydride structure and a glutarimide structure.

In the general formula (1), R ¹ and R ² are each independently a hydrogen atom or a methyl group, and X ¹ is an oxygen atom or a nitrogen atom. When X ¹ is an oxygen atom, R ³ is not present, and when X ¹ is a nitrogen atom, R ³ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, a benzyl group Or it is a phenyl group.

When X ¹ is an oxygen atom, the ring structure represented by the general formula (1) is a glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by subjecting a copolymer of (meth) acrylic acid ester and (meth) acrylic acid to dealcoholization cyclocondensation in the molecule.

When X ¹ is a nitrogen atom, the ring structure represented by the general formula (1) is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

  The following general formula (2) shows a maleic anhydride structure and an N-substituted maleimide structure.

In the general formula (2), R ⁴ and R ⁵ are each independently a hydrogen atom or a methyl group, and X ² is an oxygen atom or a nitrogen atom. When X ² is an oxygen atom, R ⁶ is not present, and when X ² is a nitrogen atom, R ⁶ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, a benzyl group. Or it is a phenyl group.

When X ² is an oxygen atom, the ring structure represented by the general formula (2) is a maleic anhydride structure. The maleic anhydride structure can be formed, for example, by copolymerizing maleic anhydride and (meth) acrylic acid ester.

When X ² is a nitrogen atom, the ring structure represented by the general formula (2) is an N-substituted maleimide structure. The N-substituted maleimide structure can be formed, for example, by polymerizing an N-substituted maleimide such as phenylmaleimide and a (meth) acrylic acid ester.

  In each method for forming the ring structure exemplified in the description of the general formulas (1) and (2), all the polymers used for forming each ring structure have (meth) acrylate units as constituent units. Therefore, the resin obtained by the method is an acrylic resin.

  The lactone ring structure that the acrylic polymer may have in the main chain is not particularly limited, and may be, for example, a 4- to 8-membered ring. A 6-membered ring is preferable, and a 6-membered ring is more preferable.

  The lactone ring structure which is a 6-membered ring is, for example, the structure disclosed in Japanese Patent Application Laid-Open No. 2004-168882, but the lactone ring structure is high due to the high polymerization yield of the precursor and the cyclization condensation reaction of the precursor. The structure represented by the following general formula (3) is preferable because an acrylic resin having a ring content can be obtained and a polymer having a methyl methacrylate unit as a constituent unit can be used as a precursor.

In the general formula (3), R ⁷ , R ⁸ and R ⁹ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The organic residue in the general formula (3) is, for example, an alkyl group having 1 to 20 carbon atoms, such as a methyl group, an ethyl group, or a propyl group. An aromatic hydrocarbon group having 6 to 20 carbon atoms, such as a saturated aliphatic hydrocarbon group, a phenyl group, or a naphthyl group, and the alkyl group, the unsaturated aliphatic hydrocarbon group, and the aromatic hydrocarbon group are One or more hydrogen atoms may be substituted with at least one group selected from a hydroxyl group, a carboxyl group, an ether group, and an ester group.

  Although the content rate of the said ring structure except the lactone ring structure in the said thermoplastic resin (A) is not specifically limited, For example, it is 5-90 mass%, Preferably it is 10-70 mass%, More preferably, it is 10-70 mass%. It is 60 mass%, More preferably, it is 10-50 mass%.

  When the thermoplastic resin (A) has a lactone ring structure in the main chain, the content of the lactone ring structure in the resin is not particularly limited, but is, for example, 5 to 90% by mass, preferably 10 to 80% by mass. More preferably, it is 10-70 mass%, More preferably, it is 20-60 mass%.

  If the content of the ring structure in the thermoplastic resin (A) becomes transiently small, the heat resistance of the film may be lowered, and the solvent resistance and surface hardness may be insufficient. On the other hand, when the said content rate becomes transiently large, the moldability and mechanical characteristic of a film will fall.

  The acrylic polymer having a ring structure in the main chain can be formed by a known method.

  An acrylic polymer having a glutaric anhydride structure in the main chain is, for example, a polymer described in JP-A-2006-283013, JP-A-2006-335902, JP-A-2006-274118, It can be formed by the method described in the publication.

  Acrylic polymers having a glutarimide structure in the main chain are disclosed in, for example, JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328329, JP-A-2006-328334, and JP-A-2006-328334. JP-A 2006-337491, JP-A 2006-337492, JP-A 2006-337493, JP-A 2006-337469, and JP-A 2007-009182. It can be formed by the methods described.

  An acrylic polymer having a maleic anhydride structure or an N-substituted maleimide structure in the main chain is, for example, a polymer described in JP-A-57-153008 and JP-A-2007-31537. It can be formed by the method described in the publication.

  Examples of the acrylic polymer having a lactone ring structure in the main chain include JP 2000-230016, JP 2001-151814, JP 2002-120326, JP 2002-254544, JP It is a polymer described in 2005-146084, and can be formed by the method described in the publication.

  The thermoplastic resin (A) may contain an acrylic polymer and a styrene polymer.

  Examples of the styrenic polymer include polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer, and the like.

  When the thermoplastic resin (A) contains an acrylic polymer and a styrenic polymer, in the film made of the thermoplastic resin (A), the positive retardation exhibited by the acrylic polymer having a ring structure in the main chain is exhibited. This can be canceled by the negative phase difference exhibited by the styrene polymer. Depending on the content of the styrenic polymer in the film, the optical film produced by the present invention which is a stretched film can be a negative retardation film or a low retardation polarizer protective film.

  When the thermoplastic resin (A) contains an acrylic polymer and a styrene polymer, the styrene polymer is preferably a styrene-acrylonitrile copolymer from the viewpoint of compatibility with the acrylic polymer.

  The thermoplastic resin (A) may contain an acrylic polymer; or a thermoplastic polymer other than the acrylic polymer and the styrene polymer.

  Other thermoplastic polymers include, for example, olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methyl-1-pentene); polyvinyl chloride, polyvinylidene chloride, polyvinyl chloride, etc. Halogenated vinyl polymers; Polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; Cellulose acylates such as cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate; Polyamides such as nylon 6, nylon 66, and nylon 610 Polyacetal; Polycarbonate; Polyphenylene oxide; Polyphenylene sulfide; Polyetheretherketone; Polysulfone; Polyethersulfone; Polyoxyben Ren; polyamideimide; polybutadiene rubber or ABS resin containing an acrylic rubber, rubber-like polymer such as ASA resin; a.

  The content of the other thermoplastic polymer in the thermoplastic resin (A) is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, further preferably 0 to 30% by mass, and particularly preferably 0 to 0% by mass. 20% by mass.

  The film made of the thermoplastic resin (A) may have an ultraviolet absorbing ability as long as the heat resistance, physical properties, and optical properties are not impaired. Specifically, a method of using an ultraviolet absorbing monomer and / or an ultraviolet stabilizing monomer as a monomer component when producing an acrylic polymer, an ultraviolet absorber and / or an ultraviolet stabilizer described above There is a method of blending with an acrylic polymer.

  Examples of the ultraviolet absorbing monomer include benzotriazole compounds, benzophenone compounds or triazine compounds and acrylic monomers having a polymerizable unsaturated group. As the UV-stable monomer, a monomer in which a polymerizable unsaturated group is bonded to a hindered amine compound can be used.

  When such an ultraviolet absorbing monomer and / or an ultraviolet stable monomer is used, the ultraviolet absorbing monomer and / or the ultraviolet stable monomer is 0.1 to 25 of all monomers. The copolymerization is preferably carried out by mass%, more preferably from 1 to 15% by mass.

  Examples of the ultraviolet absorber include benzophenone compounds, salicylate compounds, benzoate compounds, triazole compounds, and triazine compounds.

  Although the compounding quantity of a ultraviolet absorber and / or a ultraviolet stabilizer is not specifically limited, It is preferable that it is 0.01-25 mass% in the film which consists of a thermoplastic resin (A), More preferably, it is 0.05-10. % By mass.

  The film made of the thermoplastic resin (A) may contain other additives. Other additives include, for example, hindered phenol-based, phosphorus-based and sulfur-based antioxidants; light-resistant stabilizers, weather-resistant stabilizers, heat-stabilizers and other stabilizers; glass fibers, carbon fibers and other reinforcing materials; Near-infrared absorbers; flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide; antistatic agents composed of anionic, cationic, and nonionic surfactants; inorganic pigments, organic pigments, dyes Coloring agents such as: organic fillers, inorganic fillers; anti-blocking agents; resin modifiers; organic fillers, inorganic fillers; plasticizers; lubricants;

  The content rate of the other additive in the film which consists of a thermoplastic resin (A) becomes like this. Preferably it is 0-5 mass%, More preferably, it is 0-2 mass%, More preferably, it is 0-1 mass%.

  The glass transition temperature (Tg) of the film made of the thermoplastic resin (A) is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, still more preferably 115 ° C. or higher, and particularly preferably 120 ° C. or higher. Although the upper limit of Tg of the said film is not specifically limited, From a viewpoint of the drawability of the said film, Preferably it is 170 degrees C or less.

  The film made of the thermoplastic resin (A) can be formed by a known film deposition method. Examples of the film forming method include a solution casting method (solution casting method), a melt extrusion method, a calendar method, and a compression molding method. Of these, the solution casting method and the melt extrusion method are preferable.

  The thermoplastic resin (A) used for film formation can be formed by a known method. For example, an acrylic polymer blended according to the composition of the desired thermoplastic resin (A); or an acrylic polymer and a styrene polymer, other thermoplastic polymers and additives, etc., by an appropriate mixing method By thoroughly mixing, the thermoplastic resin (A) is formed.

  The mixing method is, for example, extrusion kneading or mixing in a solution state. A commercially available acrylic resin may be used for film formation. Commercially available acrylic resins are, for example, Acrypet VH and Acrypet VRL20A (both manufactured by Mitsubishi Rayon). Any suitable mixer such as an omni mixer, a single screw extruder, a twin screw extruder, or a pressure kneader can be used for the extrusion kneading.

  An apparatus for performing the solution casting method is, for example, a drum type casting machine, a band type casting machine, or a spin coater.

  The solvent used for the solution casting method is not limited as long as the acrylic resin is dissolved. Examples of the solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as cyclohexane and decalin; esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. Alcohols such as methanol, ethanol, isopropanol, butanol, isobutanol, methyl cellosolve, ethyl cellosolve, butyl cellosolve; ethers such as tetrahydrofuran and dioxane; halogenated hydrocarbons such as dichloromethane, chloroform and carbon tetrachloride; dimethylformamide; dimethyl sulfoxide is there. Two or more of these solvents may be used in combination.

  Examples of the melt extrusion method include a T-die method and an inflation method. The molding temperature during melt extrusion is preferably 150 to 350 ° C, more preferably 200 to 300 ° C. When the T-die method is selected, for example, a belt-like acrylic resin film can be formed by attaching a T-die to the tip of a known extruder. The formed strip-shaped acrylic resin film may be wound on a roll to form a film roll. In the melt extrusion method, from the formation of an acrylic resin by mixing materials to the formation of an acrylic resin film using the resin can be continuously performed.

(1-2. Longitudinal stretching step)
In the present invention, the longitudinal stretching is a preheating part containing one or more heating rolls for preheating the film made of the thermoplastic resin (A); one or more heating rolls and one or more for cooling the film. A longitudinally extending section comprising a cooling roll and a cooling section containing one or more cooling rolls for cooling the stretched film, in this order in the film transport direction. The longitudinal stretching is performed by the heating roll adjacent to the cooling roll contained in the stretching roll group in the transport direction of the film among the heating rolls contained in the stretching roll group, and a wavelength of 0.8 μm. This is performed on the film heated using an infrared radiation portion capable of emitting near infrared rays of 2 μm or less.

  Thus, this invention is equipped with the longitudinal stretch process of longitudinally stretching the film which consists of the said thermoplastic resin (A). Hereinafter, the longitudinal stretching step will be described with reference to the drawings.

  FIG. 1 is a side view showing an example of a main configuration of a biaxial stretching apparatus 100 that can be used in the present invention. In FIG. 1, 1 is a dryer, 2 is an extruder, 3 is a gear pump, 4 is a polymer filter, 5 is a die, 6 is a casting device (casting part), 7 is a roll longitudinal stretching machine (longitudinal stretching part), and 8 is 10 is a shear cutter (trimming section), 10 is a product winding section, 11 and 12 are film winding sections, 13 is a knurling device (knurling section), and 14 is a protective film feeding section. is there. Reference numeral 200 denotes a film made of the thermoplastic resin (A).

  The casting device (casting unit) 6 includes cooling rolls 61, 62, and 63.

  The roll longitudinal stretching machine (longitudinal stretching section) 7 includes a nip roll N2, a preheating section 71 including heating rolls 701 to 705, a stretching roll group 72, a cooling section 73 including cooling rolls 731 to 733, and an infrared ray as a heat retaining heater. A heater (infrared radiation part) 74 and a nip roll N7 are provided.

  In FIG. 1, the transport direction of the film 200 is from the left side to the right side as viewed in the drawing, and the roll longitudinal stretching machine (longitudinal stretching unit) 7 has a preheating unit 71, a stretching roll group 72, and a cooling unit 73 in the film transport direction. In this order.

  “The preheating unit 71, the stretching roll group 72, and the cooling unit 73 are provided in this order in the film conveyance direction” means that the preheating unit 71 is in front of the stretching roll group 72 in the film conveyance direction. Left), indicating that the drawing roll group 72 is arranged in front of the cooling unit 73 (left side in the drawing), and includes a preheating unit 71, a drawing roll group 72, and a cooling unit. A member such as a nip roll that does not participate in the heating and cooling may be further provided between 73 and 73, for example.

  The stretching roll group 72 includes heating rolls 721 and 722 and nip rolls N3 and N4 adjacent to them, and cooling rolls 723 and 724 and nip rolls N5 and N6 adjacent to them.

  The tenter stretching machine (lateral stretching unit) 8 includes a preheating unit 81, a stretching unit 82, and a heat fixing unit 83.

  The film 200 made of the thermoplastic resin (A) that passes through the roll longitudinal stretching machine (longitudinal stretching section) 7 can be manufactured as follows.

  That is, for example, after the pellets made of the thermoplastic resin (A) are put into the dryer 1 and dried, the pellets are put into the extruder (melting extrusion section) 2 and melted at a temperature equal to or higher than the glass transition temperature. The film 200 made of the thermoplastic resin (A) is formed by extruding the thermoplastic resin (A) melted from the die 5 through the polymer filter 4 and the polymer filter 4 and performing melt film formation on a casting device (casting part) 6. Can be obtained.

  As the dryer 1, the extruder (melting extrusion part) 2, the gear pump 3, the polymer filter 4, the die 5, and the casting apparatus (casting part) 6, conventionally known ones can be used.

  Moreover, as drying conditions, for example, the air heated to a temperature of 80 ° C., adjusted to a dew point of −30 ° C., is blown to the pellets (raw material pellets) made of the thermoplastic resin (A) for 4 hours or more. The condition that the moisture content is 200 ppm or less can be preferably used.

  As suitable conditions for melt extrusion, for example, the conditions described in JP-A-2010-82990 can be used. Moreover, as suitable conditions for melt film formation, for example, the conditions described in JP 2012-12704 A and JP 2010-17874 A can be used.

  The film 200 made of the thermoplastic resin (A) is preferably passed through a roll longitudinal stretching machine (longitudinal stretching section) 7 after adjusting the film thickness as described below. That is, the maximum value of the film thickness of the part from the left end in the width direction of the film 200 to 100 mm and the maximum value of the film thickness of the part from the right end to 100 mm in the width direction of the film 200 are respectively It is preferable to pass through a roll longitudinal stretching machine (longitudinal stretching section) 7 after adjusting so as to be 130% or less of the average film thickness of the central portion of the film, which is a portion excluding the portion up to 100 mm.

  In the present specification, the “width direction” means an in-plane direction of the film and a direction perpendicular to the film conveyance direction.

  FIG. 2 is a schematic diagram showing in the film the film thickness of the part from the left and right end parts a and b to 100 mm in the width direction of the film 200 and the film thickness of the film center part c.

  When the maximum film thickness in the part d from the left end a to 100 mm and the maximum film thickness in the part e from the right end b to 100 mm are the film thicknesses shown in FIG. The thickness is preferably adjusted so as to be 130% or less of the average film thickness of the film central portion c (b).

  The film thickness can be adjusted, for example, by adjusting a plurality of adjustment bolts attached to the die 5 in the width direction of the die 5 in the width direction of the die 5.

  When the film thickness exceeds 130% of the average film thickness (b) of the film central portion c, the heating of the portion d and the portion e by the infrared heater (infrared radiation portion) 74 described later is performed at the central portion of the film. Since it becomes inadequate compared with heating, the temperature of the part d and the part e becomes difficult to become a temperature higher than a glass transition temperature. Therefore, the part d and the part e are difficult to be stretched during longitudinal stretching, and cracks are likely to occur. As a result, the part d and the part e can cause the film to break, which is not preferable.

  The film 200 passed through the roll longitudinal stretching machine (longitudinal stretching unit) 7 is preheated by heating rolls 701 to 705 provided in the preheating unit 71 and heating rolls 721 and 722 provided in the stretching roll group 72.

  Although the method of heating the film 200 using the heating roll 701 to the heating roll 722 is not particularly limited, as will be described later, the relationship shown in Formula 1 and / or Formula 3 is established between the heating rolls. It is preferable to heat it.

  The type of the heating roll used in the present invention is not particularly limited. For example, in addition to an electric heating heating roll in which a heater is incorporated in the roll, a heating medium circulation heating method, a steam heating method, a gas heating method, induction A conventionally known heating roll such as a heat generation method can be used.

  Also, the type of the cooling roll used in the present invention is not particularly limited, and the structure is a so-called double pipe structure in which a cooling fluid (refrigerant) flows through the gap between the inner cylinder and the outer cylinder. Etc. can be used suitably.

  The heating rolls 721 and 722 and the cooling rolls 723 and 724 contained in the drawing roll group are respectively heated rolls 701 to 705 included in the preliminary heating unit 71 so as not to excessively heat or cool the film; It is preferable that the temperature can be controlled by the same means as the cooling rolls 731 to 733 provided.

  Each of the heating roll with which the preliminary heating part 71 is equipped, the heating roll contained in the stretching roll group 72, the cooling roll contained in the stretching roll group 72, and the cooling roll with which the cooling part 73 that cools the stretched film 200 is provided. The number of is not particularly limited as long as it is 1 or more, and may be appropriately determined according to the line speed of the biaxial stretching apparatus 100 to be used.

  As will be described later, since it is preferable that the peripheral speeds of the heating roll and the cooling roll satisfy certain requirements (formula 3 and formula 4), the rotation speed of each roll is preferably adjustable individually.

  Among the heating rolls 721 and 722 contained in the drawing roll group 72, when the film 200 is heated by the heating roll 722 adjacent to the cooling roll 723 contained in the drawing roll group 72 in the transport direction of the film, The film 200 is also heated by an infrared heater (infrared radiation portion) 74 capable of emitting near infrared rays having a wavelength of 0.8 μm or more and 2 μm or less. That is, before stretching, the film 200 is heated by using the heating roll 722 and the infrared heater (infrared radiation portion) 74 in combination.

  Here, for example, the heating rolls 722 and 723 in FIG. 1 are separated from each other than the state where they are substantially in contact with each other, for example, the heating rolls 704 and 705, but are adjacent to each other. It can be said that it is in an “adjacent” state.

  The infrared heater (infrared radiation portion) 74 is for radiating infrared rays toward the film 200 from the surface facing the film 200 to heat the film 200. The infrared heater (infrared radiation portion) 74 is not particularly limited as long as it can emit near infrared rays having a wavelength of 0.8 μm or more and 2 μm or less. As the infrared heater (infrared radiation portion) 74, a twin tube quartz glass heater (for example, manufactured by Heraeus), a line condensing type halogen lamp (for example, manufactured by Highbeck) or the like can be used.

  The gap (distance) between the infrared heater (infrared radiation portion) 74 and the film 200 is preferably 10 mm or more and 50 mm or less, more preferably 15 mm or more and 30 mm or less. Among the surfaces of the infrared heater (infrared radiation part) 74, the gap is arranged so that the surface capable of emitting infrared rays is arranged to face the film 200 so as to be parallel to the film 200. Can be obtained by measuring the length of the perpendicular line drawn on the film 200 from the point closest to.

  When the gap between the infrared heater (infrared radiation portion) 74 and the film 200 is smaller than the above range, or when the position of the film 200 fluctuates, the film 200 comes into contact with the infrared heater (infrared radiation portion) 74 and the film 200 is torn. There is a possibility that the infrared heater (infrared radiation part) 74 may be damaged.

  Further, when the gap between the infrared heater (infrared radiation part) 74 and the film 200 is larger than the above range, the heating efficiency of the film 200 by the infrared heater (infrared radiation part) 74 is deteriorated, so that the tension breakage of the film 200 occurs frequently. However, the stretching stability tends to deteriorate.

  FIG. 3 is an explanatory diagram for explaining a preferable width of the infrared heater (infrared radiation portion) 74. In FIG. 3, arrows indicate the conveyance direction of the film 200, and a and b indicate end portions in the width direction of the film 200.

  The width of the infrared heater (infrared radiation part) 74 is 300 mm outward from the left and right end portions a and b when the film 200 and the infrared heater (infrared radiation part) 74 are viewed from vertically above. The width f including the above area is the maximum width, and the width g obtained by subtracting the 200 mm area from the left and right end portions a and b from the width of the film 200 is the minimum width. It is preferable to fit in. More preferably, the width of the film 200 is a width h obtained by adding a region 150 mm outward from the left and right end portions a and b, and a region 100 mm inward from the left and right end portions a and b. It is preferable to fit within the width i subtracted from the width. More preferably, it should be within the range of 150 mm outside to 100 mm inside the film edge.

  If the width of the infrared heater (infrared radiating portion) 74 is longer than the width f, the width of the infrared heater (infrared radiating portion) 74 becomes extremely wider than the width of the film 200, which is not efficient. Further, when the width of the infrared heater (infrared radiation portion) 74 is shortened to be less than the width g, the end of the film 200 is not sufficiently heated, so that the tensile break at the end frequently occurs and the stretching stability is increased. Is not preferred because it tends to deteriorate.

  The surface temperature of the film 200 is the above in the region between the contact region between the film 200 and the heating roll 722 and the contact region between the film 200 and the cooling roll 723, that is, in the region indicated by “L” in FIG. It is preferable to heat with the heating roll 722 and the infrared heater (infrared radiation part) 74 until it becomes higher than the glass transition temperature of a thermoplastic resin (A).

  That is, it is preferable to perform longitudinal stretching after the surface temperature of the film 200 reaches a temperature higher than the glass transition temperature of the thermoplastic resin (A) in the region indicated by “L”. Thereby, since sufficient heat can be given to the film 200 before stretching, stable longitudinal stretching can be performed.

  In addition, the surface temperature of the film 200 is the film surface in the point located in the center in a surface, when the surface of the film 200 straddling the heating roll 722 and the cooling roll 723 in FIG. Temperature.

The heating capacity of the infrared heater (infrared radiation portion) 74 is a unit length of the infrared heater (infrared radiation portion) 74 in the width direction of the film 200 in order to give a sufficient amount of heat to the film 200 and avoid excessive heating. W / v is preferably 800 J / m ² or more and 3000 J / m ² or less, more preferably 900 to 2000 J / m ³ when the output per unit is W and the conveyance speed of the film is v. Preferably, it is 1000-1500 J / m < ³ >.

  The said heating capacity can be calculated | required based on Formula 5 mentioned later. The “output per unit length in the width direction” is a value obtained by dividing the output of the infrared heater (infrared radiation portion) 74 by the above-described width of the infrared heater (infrared radiation portion) 74.

When the heating capacity of the infrared heater (infrared radiation part) 74 is less than 800 J / m ² , the heating efficiency of the film is deteriorated, so that the stretching stability tends to be deteriorated due to the tensile fracture of the film.

On the other hand, when the heating capacity of the infrared heater (infrared radiation part) 74 exceeds 3000 J / m ² , the thickness unevenness tends to increase due to loose wrinkles and fluttering of the film due to excessive heating of the film.

  In the region indicated by “L” in the longitudinal stretching, the heating is performed until the surface temperature of the film 200 becomes higher than the glass transition temperature of the thermoplastic resin (A), and then the circumference of the cooling roll 723 is increased. It is preferable to increase the speed. Even if the film 200 is made of the thermoplastic resin (A) containing a brittle acrylic polymer, it is stable without causing breakage, thickness unevenness, etc. by longitudinally stretching the film 200 after sufficient heat is applied. This is because longitudinal stretching can be performed.

  The longitudinally stretched film 200 is cooled by cooling rolls 723, 724, 731 to 733. Although it does not specifically limit as a cooling method, It is preferable to cool so that the relationship shown in Formula 2 and / or Formula 4 may be materialized between cooling rolls so that it may mention later.

  In the method according to the present invention, when the center of the heating roll and the cooling roll that are contained in the stretching roll group and are adjacent to each other in the transport direction of the film is connected by a straight line, the intersection of the straight line and the heating roll The distance between the straight line and the intersection of the cooling roll is preferably 50 mm or more and 150 mm or less.

  In FIG. 1, when the center of the heating roll 722 and the center of the cooling roll 723 are connected by a straight line, the distance between the intersection of the straight line and the heating roll 722 and the intersection of the straight line and the cooling roll 723 is 50 mm or more. It is preferable that it is 150 mm or less.

  By satisfying this condition, it is possible to suppress the generation of wrinkles associated with the neck-in of the film during longitudinal stretching and the fluttering of the film, and the infrared heater (infrared radiation portion) 74 includes a heating roll 722 and a cooling roll 723. It can be installed easily between.

  When the distance exceeds 150 mm, the thickness unevenness tends to increase due to the generation of wrinkles accompanying the neck-in of the film during stretching and the flapping of the film. If the distance is less than 50 mm, it is difficult to install the infrared heater (infrared radiation portion) 74 between the heating roll 722 and the cooling roll 723, which is not preferable.

In the method according to the present invention, the temperature of one heating roll is set to T _n ° C, and the temperature of the heating roll and the other heating roll adjacent in the direction opposite to the film transport direction is set to T _n-1 ° C. Sometimes, it is preferable that the relationship shown in the following formula 1 holds.

0 ≦ T _n −T _n−1 ≦ 30 (1)
When the temperature gradient of the heating roll (T n _{-T n-1)} satisfies the formula 1, it is possible to suppress an abrupt expansion of the film between the corresponding two rolls, it is possible to perform stable longitudinally stretched The thickness unevenness and the surface unevenness can be suppressed, which is preferable.

When the temperature gradient (T _n −T _n−1 ) exceeds 30, the film suddenly expands between the two corresponding heating rolls (for example, the heating rolls 704 and 703 in FIG. 1), resulting from the expansion. The thickness unevenness increases due to loose wrinkles and fluttering of the film, and at the same time, surface unevenness tends to occur.

  Moreover, if the said temperature gradient is less than 0, the film 200 will be cooled and it will become impossible to longitudinally stretch after giving sufficient heat quantity to the film 200 before extending | stretching, and it is unpreferable.

  The heating roll is heated by, for example, an electromagnetic heater attached to the heating roll (for example, attached to the inside of the heating roll), a heating medium circulating inside or on the surface of the heating roll, and the heat is transmitted to the film 200. In the present specification, the “temperature” of the heating roll refers to a set temperature of means for heating the heating roll (the electromagnetic heater, the heating medium, etc.).

In the method according to the present invention, the temperature of one of the cooling rolls is T ′ _n ° C., and the temperature of the cooling roll and the other cooling rolls adjacent in the direction opposite to the film transport direction is T ′ _n−1 ° C. It is preferable that the relationship shown in the following formula 2 is satisfied.

−20 ≦ T ′ _n −T ′ _n−1 ≦ 0 (2)
When the temperature gradient (T ′ _n −T ′ _n−1 ) of the cooling roll satisfies Expression 2, it is possible to suppress the rapid shrinkage of the film between the two corresponding rolls, and to suppress the breakage of the film and to stabilize the film. It is preferable because the longitudinal stretching can be performed.

When the temperature gradient (T ′ _n −T ′ _n−1 ) is less than −20, the film contracts rapidly between the two corresponding cooling rolls (for example, the cooling rolls 731 and 732 in FIG. 1), The film breaks due to an increase in tension due to shrinkage, and the stretching stability tends to deteriorate.

  Moreover, when the said temperature gradient exceeds 0, since the film 200 will be heated and it will become impossible to cool the film 200 after extending | stretching, it is unpreferable.

  The cooling roll is cooled by, for example, a refrigerant circulating inside or on the surface of the cooling roll to cool the film 200. In the present specification, the “temperature” of the cooling roll refers to a set temperature of means (such as the refrigerant) for cooling the cooling roll.

In the method for producing an optical film according to the present invention, the peripheral speed of one heating roll is R _n , and the peripheral speeds of the heating roll and the other heating roll adjacent in the direction opposite to the film transport direction are R _n−. When it is set to ₁ , it is preferable that the relationship shown in the following formula 3 holds.

1.000 ≦ R _n / R _n−1 ≦ 1.100 (3)
The peripheral speed indicates the rotational speed per unit time of the heating roll or cooling roll, and represents the film conveyance speed on the surface of the heating roll or cooling roll. The peripheral speed can be obtained according to the following Equation 6.

Peripheral speed (m / s) = outer diameter of heating roll or cooling roll (m) × 3.14 × rotational speed (rpm) / 60 (6)
When the velocity gradient (R _n / R _n-1 ) of the heating roll satisfies Equation 3, as shown in the examples described later, stable longitudinal stretching is performed while suppressing thickness unevenness, surface unevenness, and film breakage. Is preferable.

If the velocity gradient of the heating roll _{(R n / R n-1} ) is less than 1.000, the corresponding two heating rolls (e.g., a heating roll 704 heat roll 703) of the heating roll to the expansion of the film occurring between There is a tendency for thickness unevenness to increase due to loose wrinkles and fluttering of the film caused by the fact that rotation cannot catch up, and surface unevenness tends to occur.

In addition, when the heating roll speed gradient (R _n / R _n-1 ) exceeds 1.100, the film is pulled more than the expansion of the film. The stability tends to deteriorate.

In the method for producing an optical film according to the present invention, the peripheral speed of one of the cooling rolls is R ′ _n , and the peripheral speed of the other cooling roll adjacent to the cooling roll and the direction opposite to the film transport direction is R ′. _{When n−1} , it is preferable that the relationship shown in the following Expression 4 holds.

0.950 ≦ R ′ _n / R ′ _n−1 ≦ 1.100 (4)
When the speed gradient (R ′ _n / R ′ _n-1 ) of the cooling roll satisfies Formula 4, as shown in the examples described later, stable longitudinal stretching is achieved by suppressing thickness unevenness, surface unevenness, and film breakage. Since it can be performed, it is preferable.

When the speed gradient (R ′ _n / R ′ _n−1 ) of the cooling roll is less than 0.950, the expansion of the film generated between the two corresponding cooling rolls (for example, the cooling roll 732 and the cooling roll 731) There is a tendency for thickness unevenness to increase due to loose wrinkles and fluttering of the film caused by the fact that rotation cannot catch up, and surface unevenness tends to occur.

In addition, when the speed gradient (R ′ _n / R ′ _n-1 ) of the cooling roll exceeds 1.100, the film is pulled more than the expansion of the film, so that the film frequently breaks due to an increase in tension. , Stretching stability tends to deteriorate.

  As described above, in the longitudinal stretching, among the heating rolls contained in the stretching roll group 72, the heating roll (heating roll 722) adjacent to the cooling roll contained in the stretching roll group in the transport direction of the film. The film 200 is heated using an infrared radiation portion (infrared heater 74) capable of emitting near infrared rays having a wavelength of 0.8 μm or more and 2 μm or less.

  Accordingly, the film 200 to which a sufficient amount of heat is applied from the heating roll 722 and the infrared heater (infrared radiation portion) 74 is stretched before stretching, so that it is very brittle and has low flexibility. With respect to a film made of an acrylic resin having the characteristics described above, it is possible to suppress the occurrence of uneven thickness, breakage, etc., and perform stable longitudinal stretching.

  Furthermore, by adjusting the temperature of the heating roll and the cooling roll and the peripheral speed of the heating roll and the cooling roll so as to satisfy the relationships shown in the above formulas 1 to 4, the occurrence of thickness unevenness, breakage, etc. are further suppressed. Thus, more stable longitudinal stretching can be performed.

(1-3. Other steps)
The film 200 that has been longitudinally stretched in this way may be further stretched laterally.

  A film 200 stretched longitudinally by a roll longitudinal stretching machine (longitudinal stretching section) 7 includes a heating roll (heating rolls 701 to 705, 721, 722) and a cooling roll (cooling roll) provided in the roll longitudinal stretching machine (longitudinal stretching section) 7. 731 to 733) after adjusting the peripheral speed of each roll so that the fluctuation range of the rotational torque is within ± 10% of the average value of the rotational torque of each roll, then the tenter stretching machine (lateral stretching section) 8 It is preferable to carry to.

  As the tenter stretching machine (lateral stretching section) 8, a conventionally known tenter stretching machine can be used. The film 200 preheated in the preheating unit 71 is stretched transversely by the stretching unit 82.

  The conditions for transverse stretching are not particularly limited, and may be determined according to a desired stretching ratio. The laterally stretched film 200 is sent to the heat fixing unit 83 and held at a specific temperature (heat treatment temperature) equal to or lower than the stretching temperature. This heat treatment stabilizes the molecular orientation of the polymer contained in the film, reduces the distortion of the film, and stabilizes the properties exhibited by the finally obtained retardation film, for example, optical properties and mechanical properties. Is achieved.

  The laterally stretched film 200 is preferably trimmed to a desired full width using a shear cutter (trimming section) 9. When lateral stretching is performed, the vicinity of both ends in the width direction of the film 20 is gripped by clips, and therefore the vicinity of the ends is usually removed.

  The trimmed film 200 is preferably knurled at both ends by a knurling device (knurling section) 13. This is to increase the storage stability of the wound optical film roll and to prevent scratches that may occur on the surface that comes into contact with the back surface when wound. As the knurling device (knurling portion) 13, a conventionally known means can be used.

  It is preferable that the knurled film 200 is appropriately wound by the film winding unit 10 to form a roll.

  Instead of the knurling process, when the trimmed film 200 is taken up by the film take-up unit 10, the protective film fed from the protective film feed unit 14 is attached to the back surface of the film 200, and then the film 200 is wound. You may take it. As a result, the storage stability of the wound optical film roll can be improved, and damage that may occur on the surface that comes into contact with the back surface when wound is prevented.

The method for producing an optical film according to the present invention includes: a melt extrusion step of melt-extruding a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer;
A casting process for forming a film composed of the thermoplastic resin by melt-forming the melt-extruded thermoplastic resin;
The longitudinal stretching step of longitudinally stretching a film made of the thermoplastic resin,
A transverse stretching step of transversely stretching a film comprising the thermoplastic resin film which has been longitudinally stretched;
A winding step of winding the transversely stretched film,
The casting process is performed after the melt extrusion process, the longitudinal stretching process is performed after the casting process, the transverse stretching process is performed after the longitudinal stretching process, and the winding process is performed after the transverse stretching process. It may be.

  As described above, in the longitudinal stretching step, the present invention can perform stable longitudinal stretching while suppressing occurrence of thickness unevenness and breakage even for a film made of an acrylic resin. Therefore, the film made of acrylic resin is fragile and has the property of low flexibility, but without causing breakage in the middle, the melt extrusion process, casting process, longitudinal stretching process, The stretching process and the winding process can be performed continuously and consistently.

  The steps to be performed consistently are not limited to these steps. For example, a process of performing the knurling process described above may be further provided between the transverse stretching process and the winding process, and the process from the melt extrusion process to the winding process may be performed consistently and continuously. Or when performing a winding-up process instead of the process of performing a knurling process, you may further provide the process of sticking a protective film on the back surface of a film.

  In carrying out the method according to the present invention, first, the operation of the biaxial stretching apparatus 100 is started by setting the peripheral speed of the first cooling roll 61 of the casting apparatus (casting unit) 6 to 2 to 10 m / min. After the taking process is completed, it is preferable to increase the line speed by increasing the speed of increase for one minute to 5 m / min or less to a predetermined line speed of 10 to 40 m / min.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples.

  First, the manufacture example of the resin pellet which consists of an acrylic resin used in the Example and the comparative example is demonstrated.

[Production Example 1]
In a reaction kettle equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 40 parts by weight of methyl methacrylate (MMA), 10 parts by weight of 2- (hydroxymethyl) methyl acrylate (MHMA), and toluene 50 as a polymerization solvent Part by weight and 0.025 part by weight of an antioxidant (Adeka Stub 2112, manufactured by ADEKA) were charged, and the temperature was raised to 105 ° C. while passing nitrogen through this.

  When the reflux accompanying the temperature rise began, 0.05 parts by weight of t-amylperoxyisononanoate (Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator, and the t-amylperoxyisononoate was added. While 0.10 parts by weight of nanoate was added dropwise over 2 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by further aging for 4 hours.

  Next, 0.05 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry Co., Ltd., Phoslex A-8) is added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst). The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 5 hours under reflux at 110 ° C. Next, the obtained polymerization solution was passed through a heat exchanger and heated to 240 ° C., and the cyclization condensation reaction was further advanced at the temperature.

  Subsequently, the obtained polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 (first and second from the upstream side). 2, a third and a fourth vent), a side feeder provided between the third vent and the fourth vent, and a leaf disk type polymer filter (filtration accuracy 5 μm) disposed at the tip. It was introduced into a type screw twin screw extruder (L / D = 52) at a processing speed of 90 parts by weight / hour (resin amount conversion) and devolatilized.

  At that time, 0.34 parts by weight of ion-exchanged water was added after the first vent at a charging rate of 1.06 parts by weight / hour with a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator. After the second and third vents, the charging was performed at a charging speed of / hour.

  As a mixed solution of the antioxidant / cyclization catalyst deactivator, 50 parts by weight of an antioxidant (manufactured by BASF Japan, Irganox 1010) and 35 parts by weight of zinc octylate as a deactivator (Nippon Chemical Industry) Manufactured by Nikka Octics Zinc (3.6%) was dissolved in 200 parts by weight of toluene.

  In addition, at the time of devolatilization, pellets of styrene-acrylonitrile copolymer (AS resin: ratio of styrene unit / acrylonitrile unit is 73% by weight / 27% by weight, weight average molecular weight is 220,000) from the side feeder. It was charged at a loading speed of 10 parts by weight / hour.

  After completion of devolatilization, the resin in the molten state remaining in the extruder is discharged while filtering through a polymer filter from the tip of the extruder, pelletized by a pelletizer, and has a lactone ring structure in the main chain (meta) An acrylic resin transparent resin pellet (1A) containing an acrylic polymer as a main component (content: 90% by weight) and further containing a styrene-acrylonitrile copolymer at a content of 10% by weight was obtained. The weight average molecular weight of the resin composition constituting the resin pellet (1A) was 132000, and Tg was 125 ° C.

[Production Example 2]
In a reaction kettle equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introduction pipe, 30 parts by weight of methyl methacrylate (MMA), 15 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA), n-butyl methacrylate 5 parts by weight of (BMA), 50 parts by weight of toluene as a polymerization solvent, and 0.025 part by weight of an antioxidant (Adeka Stub 2112, manufactured by ADEKA) were charged, and the temperature was raised to 105 ° C. while passing nitrogen through this.

  When the reflux accompanying the temperature increase started, 0.03 part by weight of t-amylperoxyisononanoate (Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator, and the t-amylperoxyisononoate was added. While 0.06 parts by weight of nanoate was added dropwise over 6 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by aging for 2 hours.

  Next, 0.05 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry Co., Ltd., Phoslex A-8) is added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst). The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 2 hours under reflux at 105 ° C. Next, the obtained polymerization solution was passed through a heat exchanger and heated to 240 ° C., and the cyclization condensation reaction was further advanced at the temperature.

  Subsequently, the obtained polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 (first and second from the upstream side). (Referred to as “second, third, and fourth vents”) and a vent type screw twin screw extruder (L / D = 52) in which a leaf disk type polymer filter (filtration accuracy: 5 μm) is disposed at the tip. Introduced and devolatilized.

  At that time, 0.34 parts by weight of ion-exchanged water was added after the first vent at a charging rate of 1.06 parts by weight / hour with a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator. After the second and third vents, the charging was performed at a charging speed of / hour.

  In the mixed solution of antioxidant / cyclization catalyst deactivator, 50 parts by weight of antioxidant (manufactured by BASF Japan, Irganox 1010) and 35 parts by weight of zinc octylate (manufactured by Nippon Kagaku Sangyo Co., Ltd.) , Nikka octix zinc 3.6%) in toluene 200 parts by weight was used.

  After completion of devolatilization, the resin in the molten state remaining in the extruder is discharged while filtering through a polymer filter from the tip of the extruder, pelletized by a pelletizer, and has a lactone ring structure in the main chain (meta) A transparent resin pellet (2A) of acrylic resin was obtained. The weight average molecular weight of the resin composition constituting the resin pellet (2A) was 128000, and Tg was 133 ° C.

[Production Example 3]
In a reaction kettle equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 40 parts by weight of methyl methacrylate (MMA), 10 parts by weight of 2- (hydroxymethyl) methyl acrylate (MHMA), and toluene 50 as a polymerization solvent Part by weight and 0.025 part by weight of an antioxidant (Adeka Stub 2112, manufactured by ADEKA) were charged, and the temperature was raised to 105 ° C. while passing nitrogen through this.

  When the reflux accompanying the temperature rise began, 0.05 parts by weight of t-amylperoxyisononanoate (Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator, and the t-amylperoxyisononoate was added. While 0.10 parts by weight of nanoate was added dropwise over 2 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by further aging for 4 hours.

  Next, 0.05 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry Co., Ltd., Phoslex A-8) is added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst). The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 5 hours under reflux at 110 ° C. Next, the obtained polymerization solution was passed through a heat exchanger and heated to 240 ° C., and the cyclization condensation reaction was further advanced at the temperature.

  Subsequently, the obtained polymerization solution was passed through a heat exchanger and the temperature was raised to 240 ° C., and the cyclization condensation reaction was further advanced at the temperature, and then the polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 120 rpm, Decompression degree 13.3 to 400 hPa (10 to 300 mmHg), rear vent number 1 and fore vent number 4 (referred to as first, second, third and fourth vents from the upstream side), third vent and fourth vent A side feeder is provided between the two and a bent type screw twin screw extruder (L / D = 52) in which a leaf disk type polymer filter (filtration accuracy 5 μm) is arranged at the tip is converted into a resin amount. It was introduced at a treatment rate of 24 parts by weight / hour and devolatilized.

  At that time, a separately prepared mixed solution of antioxidant / ultraviolet absorber / cyclization catalyst deactivator was added after the first vent at a rate of 0.739 parts by weight / hour. In the mixed solution of antioxidant / ultraviolet absorber / cyclization catalyst deactivator, 0.9 parts by weight of Irganox 1010 (manufactured by BASF Japan) and 0.9 parts by weight of ADK STAB AO-412S were used as antioxidants. (Made by ADEKA), tinuvin 477 (made by BASF, active ingredient 80%, molecular weight 954) as an ultraviolet absorber of 74.8 parts by weight, and 23.4 parts by weight of zinc octylate (Japan) as a cyclization catalyst deactivator Made by Chemical Industry, trade name: Nikka Octix Zinc 18%) A solution dissolved in 10% by weight toluene solution was used.

  In addition to this, pellets of styrene-acrylonitrile copolymer (AS resin: ratio of styrene unit / acrylonitrile unit is 73% by weight / 27% by weight, weight average molecular weight is 220,000) are fed from the side feeder to 3 parts by weight / hour. It was input at the input speed.

  After completion of devolatilization, the resin in the molten state remaining in the extruder is discharged from the tip of the extruder while being filtered through a polymer filter, pelletized by a pelletizer, and an acrylic polymer having a lactone ring structure in the main chain. A transparent resin pellet of the coalescence-containing resin (3A) was obtained. The acrylic polymer-containing resin (3A) had a Tg of 125 ° C. and a weight average molecular weight of 154,000.

[Measurement method]
In the production examples, examples and comparative examples of the present specification, the following methods were used as methods for measuring physical properties.

(1. Film thickness)
The film is cut into three pieces in the width direction at an arbitrary location, and the film thickness in the width direction of the entire width is continuously measured at intervals of 1 mm using an offline contact type thickness measuring device “TOF-5R” manufactured by Yamabun Electric Co., Ltd. The maximum film thickness, the minimum film thickness, the average film thickness, and the thickness unevenness were calculated.

(2. Uneven surface of film)
The surface of the stretched film was visually confirmed, and the number of stripes in the longitudinal direction (film transport direction) that could be confirmed was counted.

(3. Phase difference)
The in-plane retardation value (R0) and thickness retardation (Rth) of the film at a wavelength of 589 nm were measured using KOBRA-WR manufactured by Oji Scientific Instruments.

(4. Temperature of film surface)
Using a radiation thermometer “SK-8110” manufactured by Sato Meter Co., Ltd., the film was measured at one point at the center and at the center of the stretched section. For example, when the surface of the film 200 straddling the heating roll 722 and the cooling roll 723 is viewed from vertically above in FIG.

(5. Glass transition temperature)
The glass transition temperature (Tg) of each sample was determined in accordance with JIS K7121 regulations. Specifically, using a differential scanning calorimeter (manufactured by Rigaku, DSC-8230), a sample of about 10 mg was heated from a normal temperature to 200 ° C. at a heating rate of 20 ° C./min in a nitrogen gas atmosphere. It calculated by the starting point method from the DSC curve. Α-alumina was used as a reference.

(6. Weight average molecular weight)
The weight average molecular weight of the resin pellet was determined by polystyrene conversion of GPC (GPC system manufactured by Tosoh Corporation, chloroform solvent).

(7. Heating capacity of infrared heater (infrared radiation part))
The heating capacity of the infrared heater (infrared radiation part) was determined according to the following formula 5.

[Example 1]
The resin pellet (1A) produced in Production Example 1 was subjected to a biaxial stretching apparatus to produce a biaxially stretched optical film.

  In the present example, using the biaxial stretching apparatus 100 described in FIG. 1, melt film formation, longitudinal stretching, lateral stretching, trimming, and winding are performed on the resin pellet (1A) obtained in Production Example 1. Each step was performed continuously. Hereinafter, each step will be described.

  First, the resin pellet (1A) produced in Production Example 1 was dried by blowing with air heated to a temperature of 80 ° C. adjusted to a dew point of −30 ° C. for 5 hours by the dryer 1, and then an extruder (melt extrusion). Part) 2. Next, the resin pellet (1A) is melted at a temperature equal to or higher than the glass transition temperature, the temperature of the die 5 is set to 282 ° C., and extruded at a condition of an extrusion speed of 100 kg / hr, and the roll of the casting apparatus (casting part) 6 Above, the film was cooled to below the glass transition temperature to perform melt film formation.

  A film 200 was obtained by melt film formation with the peripheral speed of the first cooling roll 61 of the casting device (casting unit) 6 set to 6.0 m / min. Then, while winding the film 200 with the nip roll N1 and the film winding unit 11, the lip interval in the width direction of the die 5 is adjusted with a plurality of adjustment bolts attached in the width direction of the die 5, thereby The film thickness was adjusted.

  The average film thickness of the film central portion (width 330 mm), which is a portion excluding the portion from the left and right ends in the width direction of the melt-formed film 200 to 100 mm, was 515 μm. Moreover, the maximum film thicknesses in the portions from the left and right end portions to 100 mm were 655 μm and 660 μm, respectively.

  Thereafter, the film 200 was passed through the nip roll N2 to the longitudinal stretching device (longitudinal stretching section) 7.

As the infrared heater (infrared radiation part) 74, a twin tube quartz glass heater manufactured by Heraeus was used, and the heating capacity was 950 J / m ³ .

  The gap (distance) between the infrared heater (infrared radiation portion) 74 and the film 200 was 30 mm. That is, among the surfaces of the infrared heater (infrared radiation portion) 74, when a surface capable of emitting infrared rays is arranged to face the film 200 so as to be parallel to the film 200, the surface of the film 200 is the most in the surface. The length of the perpendicular dropped on the film 200 from a close point was 30 mm. Moreover, the width | variety (length in the width direction of the film 200) of the infrared heater (infrared radiation | emission part) 74 was 660 mm.

  The heating roll 722 and the cooling roll 723 are a heating roll and a cooling roll that are adjacent to each other in the transport direction of the film 200 (the direction from the left side to the right side in FIG. 1).

  When the center of the heating roll 722 and the center of the cooling roll 723 are connected by a straight line, the distance between the intersection of the straight line and the heating roll 722 and the intersection of the straight line and the cooling roll 723 (hereinafter, the heating roll 722 and The distance from the cooling roll 723) was 60 mm.

In the heating rolls 701 to 705 and the heating rolls 721 and 722, the temperature of one heating roll is set to T _n ° C., and adjacent to the heating roll and the direction opposite to the film transport direction (in FIG. 1, the left direction toward the paper surface). When the temperature of the other heating roll is set to T _n-1 ° C., as shown in Table 1, the relationship shown in the following formula 1 is established.

0 ≦ T _n −T _n−1 ≦ 30 (1)
Further, in the cooling rolls 723, 724, 731 to 733, the temperature of one cooling roll is set to T ′ _n ° C., and the temperatures of the cooling roll and the other cooling rolls adjacent in the direction opposite to the film transport direction are set to When T ′ _n−1 ° C., as shown in Table 1, the relationship shown in the following formula 2 is established.

−20 ≦ T ′ _n −T ′ _n−1 ≦ 0 (2)
Furthermore, one of the peripheral speed R _n of the heating _roll, when the said heat roll, the peripheral speed of the other of the heating roll adjacent the conveying direction and opposite direction of the film was R _n-1, shown in Table 2 Thus, the relationship shown in the following Expression 3 is established.

1.000 ≦ R _n / R _n−1 ≦ 1.100 (3)
Further, when the peripheral speed of one cooling roll is R ′ _n , and the peripheral speed of the other cooling roll adjacent to the cooling roll and the direction opposite to the film transport direction is R ′ _n−1 , As shown in FIG. 2, the relationship shown in the following Expression 4 is established.

0.950 ≦ R ′ _n / R ′ _n−1 ≦ 1.100 (4)

  Heating rolls 701 to 705, heating while winding the film 200 passed through the film with the film winding unit 12 located on the transport direction side of the film 200 with respect to the longitudinal stretching device (longitudinal stretching unit) 7 under the above conditions. While being heated by the rolls 721 and 722, it was heated by the infrared heater (infrared radiation portion) 74.

  And the surface temperature of the film 200 (in FIG. 1, when the surface of the film 200 straddling the heating roll 723 and the cooling roll 724 is viewed from vertically above, the temperature of the film surface at a point located in the center of the surface. ) Was 140 ° C., and then the circumferential speed of the cooling roll 723 was increased to perform longitudinal stretching. The longitudinal draw ratio was 2.0 times.

  After the end of the longitudinal stretching, the position of 20 mm from both ends in the width direction of the film 200 is gripped by a 2 inch clip, supplied to the tenter stretching machine (lateral stretching section) 8, the oven temperature is set to 140 ° C., and the stretching ratio is 2. Four-fold transverse stretching was performed.

  Thereafter, the film 200 was further trimmed continuously using a shear cutter (trimming portion) 9 so that the total width was 700 mm. Subsequently, the protective film fed out from the protective film feed-out part 14 was pasted on the back surface and wound around the product take-up part 10.

  Thereafter, the peripheral speed of the first cooling roll 61 of the casting device (casting unit) 6 is increased by 4.8 m / min, and finally it is operated at 15 m / min. An optical film was obtained. Table 3 shows the properties of the obtained film (after winding).

[Example 2]
A biaxially stretched optical film was produced in the same manner as in Example 1 except that the resin pellet (2A) obtained in Production Example 2 was used.

  The melt film formation was performed at 280 ° C., and the average film thickness of the film center part (width 330 mm), which is a part obtained by removing the 100 mm part from the left and right ends in the width direction of the film formed by melt film formation, was 450 μm. Moreover, the maximum film thicknesses in the portions from the left and right ends to 100 mm were 580 μm and 565 μm, respectively.

  Further, the longitudinal stretching ratio in the roll longitudinal stretching machine (longitudinal stretching section) 7 is 1.5 times, and the film surface temperature at that time (the surface of the film 200 straddling the heating roll 723 and the cooling roll 724 in FIG. 1). Of the surface at the point located in the center of the surface when viewed from above.

  The temperatures of the heating rolls 701 to 705, 721 and 722, and the cooling rolls 723, 724 and 731 to 733 in the roll longitudinal stretching machine (longitudinal stretching section) 7 were as shown in Table 1. Table 2 shows the peripheral speed ratio of the heating roll and the cooling roll. The transverse stretching in the tenter stretching machine (lateral stretching section) 8 was performed at an oven temperature of 130 ° C. and a stretching ratio of 2.8 times.

  As described in Example 1, after the protective film is pasted on the back surface and wound around the product winding unit 10, the peripheral speed of the first cooling roll 61 of the casting device (casting unit) 6 is set to 3.0 m / min. The speed was increased and the operation was finally carried out at 11 m / min to obtain a continuous 3000 m long biaxially stretched optical film.

In this example, the heating capacity of the infrared heater (infrared radiation part) 74 was 1070 J / m ² . Table 3 shows the properties of the obtained film (after winding).

Example 3
A biaxially stretched optical film was produced in the same manner as in Example 1 except that the resin pellet (3A) obtained in Production Example 3 was used.

  The melt film formation was performed at 282 ° C., and the average film thickness of the film center part (width 330 mm) excluding the 100 mm portions from the left and right ends in the width direction of the film formed by melt film formation was 480 μm. Moreover, the maximum film thicknesses in the portions from the left and right end portions to 100 mm were 612 μm and 620 μm, respectively.

  Further, the longitudinal stretching ratio in the roll longitudinal stretching machine (longitudinal stretching section) 7 is 2.2 times, and the film surface temperature at that time (the surface of the film 200 straddling the heating roll 723 and the cooling roll 724 in FIG. 1). Of the surface at the point located in the center of the surface when viewed from above.

  The temperatures of the heating rolls 701 to 705, 721 and 722, and the cooling rolls 723, 724 and 731 to 733 in the roll longitudinal stretching machine (longitudinal stretching section) 7 were as shown in Table 1. Table 2 shows the peripheral speed ratio of the heating roll and the cooling roll.

  The transverse stretching in the tenter stretching machine (lateral stretching section) 8 was performed at an oven temperature of 140 ° C. and a stretching ratio of 2.8 times.

  As described in Example 1, after the protective film was pasted on the back surface and wound around the product winding portion 10, the peripheral speed of the first cooling roll 61 of the casting device (casting portion) 6 was set to 6.0 m / min. The speed was increased gradually, and finally the operation was performed at 13 m / min to obtain a continuous 3000 m long biaxially stretched optical film.

In this example, the heating capacity of the infrared heater (infrared radiation part) 74 was 830 J / m ² . Table 3 shows the properties of the obtained film (after winding).

[Comparative Example 1]
A biaxially stretched optical film was produced in the same manner as in Example 1 except that the infrared heater (infrared radiation part) 74 was not used in the roll longitudinal stretching machine (longitudinal stretching part) 7.

  The film surface temperature in the roll longitudinal stretching machine (longitudinal stretching section) 7 (in FIG. 1, the surface of the film 200 straddling the heating roll 723 and the cooling roll 724 is located at the center in the plane when viewed from above. The temperature of the surface at the point) was 118 ° C.

  Although the longitudinal stretching was performed by increasing the peripheral speed of the cooling roll 723, when the stretching ratio became 1.3 times, the film could not withstand the tension of stretching, and the film was frequently broken from the stretched portion. As a result, a stretched film could not be obtained.

Example 4
In the roll longitudinal stretching machine (longitudinal stretching section) 7, a biaxially stretched optical film was produced in the same manner as in Example 1 except that the distance between the heating roll 722 and the cooling roll 723 was 160 mm. Table 3 shows the properties of the obtained film (after winding).

Example 5
A biaxially stretched optical film was produced in the same manner as in Example 1 except that the heating capacity of the infrared heater (infrared radiation portion) 74 was changed to 750 J / m ² . In Example 1, it was confirmed that the surface temperature of the film 200 became 140 ° C., and then the peripheral speed of the cooling roll 723 was increased to perform longitudinal stretching. Was 130 ° C.

  Table 3 shows the properties of the obtained film (after winding).

Example 6
A biaxially stretched optical film was produced in the same manner as in Example 1 except that the heating capacity of the infrared heater (infrared radiation portion) 74 was 3200 J / m ² . Table 3 shows the properties of the obtained film (after winding). In Example 1, it was confirmed that the surface temperature of the film 200 became 140 ° C., and then the peripheral speed of the cooling roll 723 was increased to perform longitudinal stretching. Was 150 ° C.

Example 7
Example 1 except that the temperature T _n of the heating roll 704 and the temperature T _n-1 of the heating roll 703 do not satisfy the formula 1 as shown in Table 1 in the roll longitudinal stretching machine (longitudinal stretching section) 7. In the same manner as above, a biaxially stretched optical film was produced. Table 3 shows the properties of the obtained film (after winding).

Example 8
In the roll longitudinal stretching machine (longitudinal stretching section) 7, except that the temperature T ′ _n of the cooling roll 731 and the temperature T ′ _{n−1 of the} cooling roll 724 do not satisfy Formula 2 as shown in Table 1. In the same manner as in Example 1, a biaxially stretched optical film was produced. Table 3 shows the properties of the obtained film (after winding).

Example 9
In the roll longitudinal stretching machine (longitudinal stretching section) 7, except that the circumferential speed R _n of the heating roll 704 and the circumferential speed R _{n-1 of} the heating roll 703 do not satisfy Formula 3 as shown in Table 2, In the same manner as in Example 1, a biaxially stretched optical film was produced. Table 3 shows the properties of the obtained film (after winding).

Example 10
In the roll longitudinal stretching machine (longitudinal stretching section) 7, except that the circumferential speed R _n of the heating roll 704 and the circumferential speed R _{n-1 of} the heating roll 703 do not satisfy Formula 3 as shown in Table 2, In the same manner as in Example 1, a biaxially stretched optical film was produced. Table 3 shows the properties of the obtained film (after winding).

Example 11
In the roll longitudinal stretching machine (longitudinal stretching section) 7, the circumferential speed R ′ _n of the cooling roll 732 and the circumferential speed R ′ _{n−1 of} the cooling roll 731 do not satisfy Expression 4 as shown in Table 2. Except for the above, a biaxially stretched optical film was produced in the same manner as in Example 1. Table 3 shows the properties of the obtained film (after winding).

Example 12
In the roll longitudinal stretching machine (longitudinal stretching section) 7, the circumferential speed R ′ _n of the cooling roll 732 and the circumferential speed R ′ _{n−1 of} the cooling roll 731 do not satisfy Expression 4 as shown in Table 2. Except for the above, a biaxially stretched optical film was produced in the same manner as in Example 1. Table 3 shows the properties of the obtained film (after winding).

(About the results)
The thickness unevenness (%) shown in Table 3 was obtained according to the following formula 7. In the “Evaluation of thickness” column, a circle with a thickness variation of less than 12%, a triangle with a thickness variation of 12% or more and less than 30%, and a cross with a thickness variation of 30% or more are marked with a cross. Expressed and evaluated.

Unevenness of thickness (%) = (maximum film thickness−minimum film thickness) / average film thickness × 100 (7)
The “film streaks (lines / 100 mm)” shown in Table 3 refers to surface unevenness of the film, and the film is rapidly expanded or contracted on the heating roll or the cooling roll, so that the film transport direction is as follows. Is the number of streaks that occur diagonally.

  As for the surface unevenness of the film, in the column of “Evaluation of surface unevenness”, a case where the number of the streaks observed visually per 100 mm in the longitudinal direction (conveying direction) of the film is zero is 1 or more 10 The case of less than this was evaluated as a triangle mark, and the case of 11 or more was evaluated as an x mark.

  The stretching stability shown in Table 3 is the number of breaks in the roll longitudinal stretching machine (longitudinal stretching section) 7 when the roll longitudinal stretching machine (longitudinal stretching section) 7 is continuously operated for 10 hours. In the case of the stretching stability in the column of “Elongation stability evaluation” in Table 3, the case where the number of breaks is 0-5 times is a circle, the case where it is 6-10 times is a triangle, and the case where it is 11 times or more. Was evaluated as a cross.

  Based on the above criteria, the circles and triangles shown in Table 3 were accepted from the standpoint of practical use as a product, and the x marks were rejected from the standpoint of being practically unusable as a product.

In Examples 1 to 3, the heating capacity of the infrared heater (infrared radiation portion) 74 satisfies the condition of “800 J / m ² or more and 3000 J / m ² or less” which is a preferable range in the present invention (hereinafter referred to as Condition 1). ing. Further, the distance between the heating roll 722 and the cooling roll 723 is 60 mm, which satisfies the condition of “50 mm or more and 150 mm or less” (hereinafter referred to as condition 2), which is a preferable range in the present invention. Furthermore, all of the relationships represented by the above-described formulas 1 to 4 (hereinafter referred to as conditions 3 to 6, respectively) are satisfied.

  Therefore, the thickness unevenness, the film surface unevenness, and the stretching stability all show good results. That is, in the method for producing an optical film according to the present invention, it is most preferable that all of the above conditions 1 to 6 are satisfied.

  In each example, the longitudinal stretching ratio is 2.0 times or more, but in Comparative Example 1, the film was broken only by increasing the longitudinal stretching ratio to 1.3 times and could not be stretched. . Therefore, in Table 3, “no data” is described for each characteristic.

  Comparative Example 1 uses the same conditions as in Example 1 except that the infrared heater (infrared radiation part) 74 is not used in the roll longitudinal stretching machine (longitudinal stretching part) 7. Therefore, the result of Comparative Example 1 was that the film 200 was heated only by the heat from the heating roll without using the infrared heater (infrared radiation portion) 74, so that the film 200 before stretching could not be given sufficient heat. It can be said that this is due to this.

  That is, when the acrylic resin is longitudinally stretched, the heating roll 722 adjacent to the cooling roll 723 among the heating rolls 721 and 722 and the cooling rolls 723 and 724 (stretching roll group) shown in FIG. It can be said that it is necessary to longitudinally stretch the heated film 200 using an infrared heater (infrared radiation portion) 74 capable of emitting near infrared rays of 2 μm or less.

  When the set temperature of the heating roll 722 is higher than the glass transition temperature of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer, the film 200 is fused to the surface of the heating roll. Problem occurs.

  Therefore, in the heating roll (heating roll 722) immediately before being heated by the infrared heater (infrared radiation part) 74, the film 200 is heated at a temperature not higher than the glass transition temperature of the thermoplastic resin, and then the infrared heater (infrared ray) (Radiation part) 74 is heated and the surface temperature of the film 200 is heated to a temperature higher than the glass transition temperature (for example, 140 ° C. in Example 1), and then longitudinal stretching is performed.

  That is, in the case of heating only by the heating roll 722, it is difficult to longitudinally stretch the film 200 because of the above problem, and the heating roll 722 and the infrared heater (infrared radiation portion) 74 are heated in combination. It is necessary to stretch the film 200 longitudinally.

  In Example 4, the interval between the heating roll 722 and the cooling roll 723 is 160 mm (described in “Remarks column in Table 3 as“ the interval between the roll 722 and the roll 723: 160 mm ”), and among the above conditions 1 to 6, Condition 2 is not satisfied. In Example 4, since the gap between the heating roll 722 and the cooling roll 723 is wider than Condition 2, the thickness unevenness is larger than those in Examples 1 to 3 due to wrinkles and film fluttering due to the neck-in of the film during stretching. It is thought that it became.

  However, the thickness unevenness was 17.5%, which was practically usable as a product. Therefore, Example 4 is also included in the scope of the present invention.

In Example 5, the heating capacity of the infrared heater (infrared radiation part) 74 is 750 J / m ² (described in the remarks column of Table 3 as heating capacity: 750 J / m ² ), and Example 6 is 3200 J / m ² (Table 3). In the remarks column, the heating capacity is described as 3200 J / m ² ), and among the above conditions 1 to 6, the condition 1 is not satisfied.

  In Example 5, since the heating capacity of the infrared heater (infrared radiation part) 74 is small, the heating efficiency of the film is deteriorated, and the stretching stability is considered to be inferior to those of Examples 1 to 3. In Example 6, the surface unevenness disappears because it is stretched, but since the heating capacity of the infrared heater (infrared radiation portion) 74 is large, the thickness is increased due to loose wrinkles and fluttering of the film caused by excessive heating of the film. It is considered that the unevenness was larger than in Examples 1 to 3.

  However, the number of breaks in Example 5 was 8 per 10 hours, which was practically usable as a product. In addition, the thickness unevenness in Example 6 was 20.8%, which was practically usable as a product. Therefore, Examples 5 and 6 are also included in the scope of the present invention.

In Example 7, the difference between the temperature T _n of the heating roll 704 and the temperature T _n-1 of the heating roll 703 is 35 ° C. (described as “T ₄ −T ₃ = 35 ° C.” in the remarks column of Table 3). The condition 3 is not satisfied. In Example 7, since the condition 3 is not satisfied, the film 200 suddenly expands between the heating rolls 703 and 704, resulting in a thickness unevenness due to slack wrinkles and film fluttering from Examples 1 to 3. At the same time, it is considered that surface irregularities larger than those of Examples 1 to 3 were also generated.

  However, the thickness unevenness in Example 7 was 24.8%, and the number of the streaks was 9, which was practically usable as a product. Therefore, Example 7 is also included in the scope of the present invention.

In Example 8, the difference between the temperature T ′ _n of the cooling roll 731 and the temperature T ′ _n−1 of the cooling roll 724 is −25 ° C. (“T ₁₀ −T ₉ = −25 ° C.” in the remarks column of Table 3). The above condition 4 is not satisfied. In Example 8, since the condition 4 is not satisfied, the stretching stability is inferior to those of Examples 1 to 3 due to the increase in tension caused by the rapid contraction of the film between the cooling roll 731 and the cooling roll 724. Conceivable.

  However, the number of breaks in Example 8 was 7 times per 10 hours, which was practically usable as a product. Therefore, Example 8 is also included in the scope of the present invention.

In Example 9, the peripheral speed _{R n} of the heating roll 704, the ratio of the circumferential speed _{R n-1} of the heating roll 703 is from 0.992 to 0.998 ( _"R 4 / R in the remarks column in Table 3 ₃ = 0.992 to 0.998 "), and the above condition 5 is not satisfied.

  In Example 9, since the ratio is small, loose wrinkles and film fluttering caused by the rotation of the heating roll 704 and the heating roll 703 cannot catch up with the expansion of the film 200 that occurs between the heating roll 704 and the heating roll 703. Therefore, it is considered that the thickness unevenness is larger than those of Examples 1 to 3, and at the same time, the surface unevenness is larger than that of Examples 1 to 3.

  However, the thickness unevenness in Example 9 was 29.4%, and the number of the streaks was 8, which was practically usable as a product. Therefore, Example 9 is also included in the scope of the present invention.

In Example 10, the circumferential speed _{R n} of the heating roll 704, the ratio of the circumferential speed _{R n-1} of the heating roll 703 is from 1.108 to 1.120 ( _"R 4 / R in the remarks column in Table 3 ₃ = 1.108 to 1.120 ”) and the above condition 5 is not satisfied. In Example 10, since the ratio is large, it is considered that the stretching stability was inferior to that of Examples 1 to 3 due to an increase in tension caused by pulling the film beyond the expansion of the film.

  However, the number of breaks in Example 10 was 10 times per 10 hours, which was practically usable as a product. Therefore, Example 10 is also included in the scope of the present invention.

In Example 11, the ratio of the circumferential speed R ′ _n of the cooling roll 732 and the circumferential speed R ′ _n−1 of the cooling roll 731 is 0.915 to 0.940 (see “R” in the remarks column of Table 3). ₁₁ / R ₁₀ = 0.915 to 0.940 ”) and the above condition 6 is not satisfied.

  In Example 11, since the ratio is small, loose wrinkles and film fluttering due to the rotation of the cooling roll 732 and the cooling roll 731 being unable to catch up with the expansion of the film 200 occurring between the cooling roll 732 and the cooling roll 731. Therefore, it is considered that the thickness unevenness is larger than those of Examples 1 to 3, and at the same time, the surface unevenness is larger than that of Examples 1 to 3.

  However, the thickness unevenness in Example 11 was 27.6%, and the number of the streaks was 4, which was practically usable as a product. Therefore, Example 11 is also included in the scope of the present invention.

In Example 12, the ratio of the circumferential speed R ′ _n of the cooling roll 732 and the circumferential speed R ′ _n−1 of the cooling roll 731 is 1.105 to 1.112 (“R” in the remarks column of Table 3) ₁₁ / R ₁₀ = 1.105 to 1.112 ”) and the above condition 6 is not satisfied.

  In Example 12, since the ratio is large, it is considered that the stretching stability was inferior to that of Examples 1 to 3 due to an increase in tension caused by pulling the film beyond the expansion of the film.

  However, the number of breaks in Example 12 was 7 times per 10 hours, which was practically usable as a product. Therefore, Example 12 is also included in the scope of the present invention.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be suitably used for producing a thermoplastic resin film containing an acrylic resin.

6 Casting device (casting part)
7 Roll longitudinal stretching machine (longitudinal stretching section)
8 Tenter stretching machine (transverse section)
71 Preheating part 72 Stretching roll group 73 Cooling part 74 Infrared heater (infrared radiation part)
DESCRIPTION OF SYMBOLS 100 Biaxial stretching apparatus 200 Acrylic polymer; Or the film 61-63 which consists of a thermoplastic resin containing an acryl-type polymer and a styrene-type polymer Cooling roll 701-705 Heating roll 721,722 Heating roll 723,724 Cooling Rolls 731 to 733 Cooling roll

Claims (9)

A method for producing an optical film comprising a longitudinal stretching step of longitudinally stretching a film made of a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrene polymer,
The longitudinal stretching includes a preheating unit containing one or more heating rolls for preheating the film; one or more heating rolls and one or more cooling rolls for cooling the film, and stretches the film. A drawing roll group; and a cooling part containing one or more cooling rolls for cooling the drawn film, and a longitudinal drawing part provided in this order in the film transport direction,
The longitudinal stretching is a heating roll adjacent to the cooling roll contained in the stretching roll group and a wavelength of 0.8 μm or more and 2 μm or less among the heating rolls contained in the stretching roll group. A method for producing an optical film, which is performed on the heated film using an infrared radiation portion capable of emitting near infrared rays.   When the center of the heating roll and the cooling roll adjacent to each other in the transport direction of the film is connected by a straight line, the intersection of the straight line and the heating roll, the straight line and the cooling roll The method for producing an optical film according to claim 1, wherein a distance from the intersection with the optical film is from 50 mm to 150 mm. W / v is 800 J / m ² or more and 3000 J / m ² or less, where W is the output per unit length in the width direction of the film of the infrared radiation portion and v is the transport speed of the film. The method for producing an optical film according to claim 1 or 2. One temperature of the heating roll and T _n ° C., the heating roller, the other temperatures of the heating roll adjacent the conveying direction and opposite direction of the film when formed into a T _n-1 ° C., the following formula 1 4. The method for producing an optical film according to claim 1, wherein the relationship shown in FIG.
0 ≦ T _n −T _n−1 ≦ 30 (1) One temperature of the cooling roll 'and _n ° C., and the cooling roll, the other temperatures of the cooling roll which is adjacent to the conveying direction opposite to the direction of the film T' T when the _n-1 ° C., below 5. The method for producing an optical film according to claim 1, wherein the relationship represented by Formula 2 is satisfied.
−20 ≦ T ′ _n −T ′ _n−1 ≦ 0 (2) When the peripheral speed of one heating roll is R _n and the peripheral speed of the heating roll and the other heating roll adjacent in the direction opposite to the film transport direction is R _n−1 , The optical film manufacturing method according to claim 1, wherein the relationship shown is established.
1.000 ≦ R _n / R _n−1 ≦ 1.100 (3) When the peripheral speed of one cooling roll is R ′ _n , and the peripheral speed of the other cooling roll adjacent to the cooling roll and the direction opposite to the film transport direction is R ′ _n−1 , the following formula: 7. The method for producing an optical film according to claim 1, wherein the relationship shown in FIG.
0.950 ≦ R ′ _n / R ′ _n−1 ≦ 1.100 (4)   Among heating rolls contained in the stretching roll group, in the film transport direction, a heating roll adjacent to the cooling roll contained in the stretching roll group and near infrared rays having a wavelength of 0.8 μm or more and 2 μm or less can be emitted. The optical film according to any one of claims 1 to 7, wherein a surface temperature of the film heated by using an infrared radiation portion is higher than a glass transition temperature of the thermoplastic resin. Method. A melt extrusion step of melt-extruding a thermoplastic resin containing an acrylic polymer; or an acrylic polymer and a styrenic polymer;
A casting process for forming a film made of the thermoplastic resin by melt-forming the melt-extruded thermoplastic resin;
The longitudinal stretching step of longitudinally stretching a film made of the thermoplastic resin,
A transverse stretching step of transversely stretching a film made of the thermoplastic resin that has been longitudinally stretched;
A winding step of winding the transversely stretched film,
The casting process is performed after the melt extrusion process, the longitudinal stretching process is performed after the casting process, the transverse stretching process is performed after the longitudinal stretching process, and the winding process is performed after the transverse stretching process. The method for producing an optical film according to claim 1, wherein:

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