JP2014069436A - Obliquely stretched film and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an obliquely stretched film having an excellent mechanical property with the rupture in the direction of the stretching axis being suppressed, even for the case where a relatively hard and brittle resin such as an acrylic resin is included.SOLUTION: An obliquely stretched film is produced by having: the at least one edge portion with respect to the one direction selected from the width direction and the longitudinal direction, and the portion other than said edge portion composed of thermoplastic resins which are different from each other; the folding endurance exhibited by the thermoplastic resin composing the edge portion being higher compared to the thermoplastic resin composing the portion other than the edge portion; and the stretching axis inclined with respect to the width direction and the longitudinal direction.

Description

  The present invention relates to an obliquely stretched film made of a thermoplastic resin and having a stretched axis inclined with respect to the width direction and the length direction, and a method for producing the same.

  A stretched film composed of a thermoplastic resin (stretched resin film) is known in which the stretch axis is inclined with respect to both the width direction and the length direction of the film. This film is, for example, birefringence exhibited by the thermoplastic resin constituting the film by stretching, more specifically, an optical axis (slow axis or fast axis) generated along or in the vicinity of the stretching axis. Is used as an optical film whose optical axis is inclined with respect to the width direction and the length direction. An example of the use as an optical film is a retardation film whose slow axis is inclined by about 45 ° with respect to the width direction or length direction of the film. Such a stretched film can be produced, for example, by stretching a strip-shaped original film in a direction inclined with respect to its length direction (obliquely stretching) (see Patent Document 1).

  Apart from this, when the original film is stretched to obtain a stretched film, the end in the width direction of the stretched film is removed. For example, Patent Document 2 describes that a cellulose ester film formed by casting is stretched by being gripped by a tenter, and then, in the trimming step after the stretching step, the end in the width direction of the film is cut and removed. Yes. Patent Document 3 describes that after extending a polyethylene naphthalate (PEN) film, the ear portion is removed by trimming. The removal of the end in the width direction in the stretched film is because the trace of gripping by the tenter during stretching remains at the end (Patent Document 2), or the thickness of the ear in the original film before stretching is Since it is larger than the central portion and the difference in thickness becomes larger after stretching (Patent Document 3), the end portion cannot be used as a product, and therefore, the unusable portion is removed from the stretched film. .

  Further, in Patent Document 4, as in Patent Document 3, on the premise of cutting and removing the end portion in the width direction of the stretched film, the thickness deviation of both end portions with respect to the center portion of the stretched film is reduced, For the purpose of reducing the cutting removal width at both ends of an expensive resin film (paragraph 0008), after forming a composite film of two types of thermoplastic resins A and B having different stretching stress values, A method for producing a stretched film in which both end portions in the width direction are cut and removed is disclosed. In the method of Patent Document 4, a part of the main film made of the thermoplastic resin A and the both end film made of the thermoplastic resin B are cut and removed (paragraph 0014). That is, the part that is cut and removed after stretching includes the entire film at both ends and a part of the main film.

  In addition, Patent Documents 2 to 4 do not describe or suggest oblique stretching. The stretched film disclosed in each document is a general uniaxially stretched film or biaxially stretched film having a stretch axis in the width direction or length direction of the film.

International Publication No.2012 / 017639 JP 2010-46932 A Japanese Patent Laid-Open No. 10-315320 JP 2008-149511

  A stretched film (obliquely stretched film) obtained by obliquely stretching an original film and having a stretch axis inclined with respect to the width direction and length direction of the film generally has a stretch axis in the width direction or length direction of the film. Compared to a uniaxially stretched or biaxially stretched film, the film tends to break in a specific direction, more specifically, a direction in which the stretched axis in the film plane extends. This tendency is particularly noticeable when the film is made of a relatively hard and brittle resin such as an acrylic resin.

  One of the objects of the present invention is to provide an obliquely stretched film excellent in mechanical properties in which such breakage is suppressed even when a relatively hard and brittle resin is included.

  Diagonal stretching of the original film is performed, for example, by a moving movement of a clip that grips the end of the strip-shaped original film in the width direction using a heat stretching machine. The portion gripped by the clip at the end portion is deformed at the time of stretching, and the degree of deformation is particularly large in the oblique stretching. For this reason, after stretching, in a route of a stretched film that passes after being discharged from the heat stretching machine, such as a guide roll and a nip roll, the film is caused by cracking or cracking in the portion. It is easy to break. In order to prevent this, it is conceivable to remove the deformed portion with a slit after stretching, but in the case of an obliquely stretched film, the stretch axis is inclined with respect to the length direction and width direction of the film, The film is apt to break due to the slit cut surface extending in the direction of the stretching axis. These breaks are prominent when the original film is made of a relatively hard and brittle resin such as an acrylic resin.

  One of the objects of the present invention is to provide a method for producing an obliquely stretched film in which these breaks are suppressed even when the original film contains a relatively hard and brittle resin.

  The obliquely stretched film of the present invention is composed of thermoplastic resins in which at least one end portion in one direction selected from the width direction and the length direction and portions other than the end portion are different from each other. Compared to the thermoplastic resin constituting the portion, the bending strength exhibited by the thermoplastic resin constituting the end portion is large, and the stretching axis is inclined with respect to the width direction and the length direction.

  The method for producing an obliquely stretched film of the present invention is such that the original film is obliquely stretched by a traveling movement of a clip that holds an end of the strip-shaped original film in the width direction, and the stretching axis is the length direction and width of the original film. This is a method of obtaining an obliquely stretched film inclined with respect to the direction. In this method, after the original film is obliquely stretched, a portion of the end portion of the film that has been stretched is held by the clip so that a part of the end portion remains on the stretched film. A step of removing by an in-line slit at the end. Here, the end portion and the portion other than the end portion in the original film are made of different thermoplastic resins, and the end portion is configured as compared with the thermoplastic resin constituting the portion other than the end portion. The bending strength exhibited by the thermoplastic resin is large.

  The obliquely stretched film of the present invention is an obliquely stretched film excellent in mechanical properties, in which breakage in the direction in which the stretched axis in the film surface after stretching is stretched is suppressed even when a relatively hard and brittle resin is included. .

  In the manufacturing method of the diagonally stretched film of the present invention, even when the original film contains a relatively hard and brittle resin, the deformed portion held by the clip at the time of stretching may be cracked in the film path after stretching. When the film breaks and the slit after stretching, the film breakage due to the slit cut surface extending in the direction of the stretching axis in the film plane is suppressed.

It is a schematic diagram which shows an example of the diagonally stretched film of this invention. It is a schematic diagram which shows another example of the diagonally stretched film of this invention. It is a schematic diagram which shows another example of the diagonally stretched film of this invention. It is a schematic diagram which shows another example of the diagonally stretched film of this invention. It is a schematic diagram which shows an example of the manufacturing method of the diagonally stretched film of this invention. It is the schematic diagram which looked at an example of the manufacturing method of the diagonally stretched film of this invention shown in FIG. 5 from the side surface of the original film and the diagonally stretched film. It is a schematic diagram explaining an example of the diagonal stretch applicable to the manufacturing method of the diagonal stretch film of this invention by the running state of a pair of clip group. It is a schematic diagram explaining another example of diagonal stretch applicable to the manufacturing method of the diagonal stretch film of this invention with the running state of a pair of clip group.

  In the present specification, “thermoplastic resin” (or simply “resin”) is a broader concept than “polymer”. The resin may contain one or more polymers, and if necessary, additives other than the polymer, such as ultraviolet absorbers, antioxidants, fillers, compatibilizers, stabilizers, etc. Can be included.

[Diagonally stretched film]
In FIG. 1, an example of the diagonally stretched film of this invention is shown. The obliquely stretched film 1 shown in FIG. 1 has end portions 2a and 2b in the length direction and portions (center portions) 3 other than the end portions 2a and 2b, and the end portions 2a and 2b and the center portion 3 Are made of different thermoplastic resins. The folding strength exhibited by the thermoplastic resin constituting the end portions 2 a and 2 b is greater than the folding strength exhibited by the thermoplastic resin constituting the center portion 3. The obliquely stretched film 1 has a stretching axis 11 that is inclined with respect to the length direction and the width direction of the film 1. In the present specification, the “width direction” and the “length direction” of the stretched film refer to the “short side (extending) direction” and the “long side (extending) direction” in the rectangular stretched film, respectively. I mean. The same applies to the strip-shaped stretched film.

  The obliquely stretched film is more likely to break in the direction in which the stretch axis extends in the film plane, compared to a general uniaxially stretched or biaxially stretched film having a stretch axis in the width direction or length direction of the film. This breakage typically occurs from the end portion of the obliquely stretched film. However, in the stretched film 1 shown in FIG. 1, the end portions 2 a and 2 b of the film 1 have a higher bending resistance than the center portion 3. It is comprised by. For this reason, such breakage is suppressed. Even when the center portion 3 is made of a relatively hard and brittle resin such as an acrylic resin, such breakage is suppressed by the end portions 2a and 2b. That is, when the center portion 3 is made of a relatively hard and brittle resin such as an acrylic resin, the effect of the present invention becomes more remarkable.

  Except for the mechanical property of preventing the breakage, the properties required for the obliquely stretched film 1, for example, the optical properties when the obliquely stretched film 1 is an optical film, are a center portion with a large area ratio in the film 1 Generally, it is secured by 3 (by the thermoplastic resin constituting the center portion 3). Of course, the characteristics may be realized including the end portions 2a and 2b, and a function different from that of the center portion 3 may be given to the end portions 2a and 2b. For example, the end portions 2a and 2b can be used as a support portion when the obliquely stretched film 1 is transported, thereby suppressing breakage of the obliquely stretched film 1 during transportation.

  The stretching axis 11 of the obliquely stretched film 1 shown in FIG. 1 is a straight line through the end portion 2a and the center portion 3, but the actual obliquely stretched film constitutes the center portion 3 with the thermoplastic resin constituting the end portions 2a and 2b. Since the behavior of molecular orientation at the time of stretching differs from the thermoplastic resin to be used, it does not necessarily become a straight line through both portions. As an example, a configuration in which the extending shaft 11 bends in the vicinity of the boundary between the end 2a or 2b and the center 3 can be considered. Even in this case, the optical characteristics based on the stretching axis 11 are secured by the center portion 3.

  In FIG. 2, another example of the diagonally stretched film of this invention is shown. The obliquely stretched film 1 shown in FIG. 2 has end portions 2a and 2b in the width direction and portions (center portions) 3 other than the end portions 2a and 2b, and the end portions 2a and 2b and the center portion 3 Are made of different thermoplastic resins. The obliquely stretched film 1 shown in FIG. 2 is the same as the obliquely stretched film 1 shown in FIG. 1 except that the positions of the end portions 2a and 2b are the end portions in the width direction of the film.

  In FIG. 3, another example of the diagonally stretched film of this invention is shown. The obliquely stretched film 1 shown in FIG. 3 has a strip shape, and has end portions 2a and 2b in the width direction and portions (center portions) 3 other than the end portions 2a and 2b, and the end portions 2a and 2b and the center. The part 3 is composed of different thermoplastic resins. The obliquely stretched film 1 shown in FIG. 3 is the same as the obliquely stretched film 1 shown in FIG. 1 except that it is strip-shaped and the positions of the end portions 2a and 2b are the end portions in the width direction of the film. .

  In the strip-shaped obliquely stretched film 1 whose end portions in the width direction are the end portions 2a and 2b as shown in FIG. 3, the ratio of the end portions 2a and 2b occupying the sides of the film 1 is large (the center portion 3 is Since the ratio of the exposed side is small), the breakage is more reliably suppressed. Considering that it is common to handle a strip-shaped original film and an obliquely stretched film by roll-to-roll when manufacturing an obliquely stretched film industrially, the obliquely stretched film of the present invention and its production method are For example, the yield is high, and the merit of industrial production is great.

  Whether the end portions 2a and 2b are located at the end portion in the length direction of the obliquely stretched film 1 or the end portion in the width direction depends on the position at which the strip-like obliquely stretched film 1 shown in FIG. You can choose. The strip-shaped obliquely stretched film 1 can be produced, for example, by the production method of the present invention.

  The strip-shaped obliquely stretched film 1 shown in FIG. 3 can be used as a mother film, and the film 1 can be divided in the length direction to obtain two or more obliquely stretched films 1. In this case, the film obtained from the position including the end 2a or 2b in the width direction of the mother film is the obliquely stretched film of the present invention because one end is the end 2a or 2b.

  The obliquely stretched film of the present invention may be a roll (film roll) around which the belt-like obliquely stretched film 1 is wound.

  In FIG. 4, another example of the diagonally stretched film of this invention is shown. The obliquely stretched film 1 shown in FIG. 4 has knurling portions (knurled portions) 12 at the end portions 2a and 2b. The other structure is the same as that of the diagonally stretched film 1 shown in FIG. In the obliquely stretched film 1 shown in FIG. 4, the knurling portion 12 is provided at the end portions 2 a and 2 b, thereby suppressing the occurrence of wrinkles, scratches, and poor winding due to winding of the film when the film roll is formed. Further, since the end portions 2a and 2b are made of a thermoplastic resin having a higher bending strength than the center portion 3, cracking of the knurling portion 12 during formation of the knurling portion 12 and winding around the film roll and Breaking of the stretched film 1 due to the crack is suppressed. Along with this, the degree of freedom of the shape of the knurling portion 12 is increased, for example, the height of the knurling portion 12 can be increased. These effects can also be obtained when the center portion 3 is a relatively hard and brittle resin such as an acrylic resin and is made of a resin having a high surface smoothness as a film.

  In FIG. 4, the knurling portion 12 is shown as a band extending in the longitudinal direction of the obliquely stretched film 1, but the knurling shape itself is not a band shape, and the knurling portion 12 is formed in the obliquely stretched film 1. The region is simply shown as a band extending in the length direction of the stretched film 1.

The height of the unevenness in the knurling portion 12 is, for example, 1 to 30 μm, and preferably 1 to 20 μm. The number of uneven protrusions in the knurling portion 12 is, for example, 10 to 100 per 1 cm ² . The shape of the unevenness in the knurling portion 12 is, for example, a truncated cone, a prismatic column, a cylinder, a prism, a cone, and a pyramid. The irregular shape may be irregular, and the knurling part 12 may be constituted by two or more types of irregularities having different shapes. The width of the knurling part 12 is, for example, 0.3 to 5% of the entire width of the obliquely stretched film 1.

  In the obliquely stretched film 1 of the present invention, the widths of the end portions 2a and 2b differ depending on the type of thermoplastic resin constituting the end portions, but are preferably 5 mm or more in order to suppress the above-described breakage. More preferably, it is 10 mm or more. Although the upper limit of the widths of the end portions 2a and 2b is not particularly limited, the area of the center portion 3 that ensures the properties as the obliquely stretched film 1 is relatively reduced as the width of the end portions 2a and 2b is increased. It is preferably as small as possible within the range where the effects of the invention can be obtained, for example, about 100 mm. The same applies to the case where the end portions 2a and 2b have the knurling portion 12, but in this case, the width of the end portions 2a and 2b is usually greater than or equal to the width of the knurling portion 12.

  The end 2a and the end 2b may be made of the same thermoplastic resin or may be made of different thermoplastic resins. The oblique stretched film 1 in which the end portions 2a and 2b are made of the same thermoplastic resin is generally easier to manufacture.

  The boundary between the end 2a and the center 3 and the boundary between the end 2b and the center 3 are not necessarily straight lines as shown in FIGS. Further, these boundaries are not always visually confirmed. The boundary may be confirmed by the difference in refractive index between the thermoplastic resin constituting the end portions 2 a and 2 b and the thermoplastic resin constituting the center portion 3. When the phase difference is different between the end portions 2a and 2b and the center portion 3, the boundary may be confirmed under polarized light.

  The thermoplastic resin that constitutes the end portions 2 a and 2 b has a higher bending strength than the thermoplastic resin that constitutes the center portion 3. Due to the high strength, breakage of the above-described obliquely stretched film 1 is suppressed.

  The folding strength of the thermoplastic resin is such that a uniaxially stretched film composed of the thermoplastic resin is formed, and a folding resistance tester (MIT tester) is used for the film in accordance with JIS P8115. It can be evaluated by performing a bending strength test. In the bending strength test, the number of bendings (folding times) until the uniaxially stretched film as a test sample is broken is evaluated. The higher the bending strength of the thermoplastic resin, the more the material is composed of the resin. The number of folding times of the film increases. That is, the former has a larger number of folding resistances between the thermoplastic resin constituting the end portions 2 a and 2 b and the thermoplastic resin constituting the center portion 3. In addition, in order to evaluate the resistance against breaking in the direction in which the stretch axis in the film plane extends, the bending strength test was carried out so that the stretch axis direction of the uniaxially stretched film as the test sample was the bending axis. There is a need to.

  The folding endurance number of the thermoplastic resin constituting the end portions 2 a and 2 b only needs to be larger than the folding endurance number of the thermoplastic resin constituting the center portion 3.

  It is considered that the bending strength of the thermoplastic resin has a correlation with the tear strength of the resin. The tear strength refers to the strength of the film against the force of tearing the film in the direction of the stretch axis when a uniaxially stretched film composed of the thermoplastic resin is formed. The oblique stretching is a stretching having a strong uniaxial stretching property.

  Considering the manufacturing process of the obliquely stretched film, the film may be broken even in the stage before stretching, for example, due to the ability to follow a roll when the original film is conveyed. For this reason, in the thermoplastic resin which comprises the edge parts 2a and 2b and the thermoplastic resin which comprises the center part 3, in addition to the frequency | count of folding when the former is used as the uniaxially stretched film mentioned above, an unstretched film It is preferable that the folding endurance is large. The folding endurance of the unstretched film can be evaluated in the same manner as the above-mentioned folding endurance of the uniaxially stretched film except that the test sample is an unstretched film.

  Moreover, it is preferable that the impact strength exhibited by the thermoplastic resin constituting the end portions 2a and 2b is higher than the thermoplastic resin constituting the portion other than the end portions 2a and 2b (center portion 3). In this case, breakage of the film at the time of forming the original film and stretching is further suppressed. The impact strength of a thermoplastic resin refers to the strength exhibited by the unstretched film with respect to an applied impact (impact) when an unstretched film composed of the thermoplastic resin is formed. The unstretched film is used for impact strength. Processes that are likely to break the film due to impact, such as peeling from the cast roll and gripping with a clip for stretching, are concentrated in the state of the unstretched film (original film). Because. The application of impact and the evaluation of impact strength can be performed in accordance with, for example, the regulations of ASTM-D3420.

  The thermoplastic resin constituting the end portions 2a, 2b and the center portion 3 is not particularly limited as long as the above-described magnitude relationship regarding the bending strength is satisfied.

  The thermoplastic resin constituting the center portion 3 is, for example, a resin mainly composed of an amorphous polymer. Amorphous polymers are generally excellent in optical transparency, and thus are preferred when an obliquely stretched film is used as an optical film such as a retardation film or a polarizer protective film. Here, the “main component” refers to a component having the largest content constituting the thermoplastic resin. The content rate of the said component is 50 weight% or more, for example.

  The amorphous polymer is not particularly limited, but the thermoplastic resin constituting the center portion 3 is, for example, at least one selected from an acrylic polymer, a styrene polymer, and a cycloolefin. These polymers are particularly preferable when the obliquely stretched film 1 is used as an optical film because of its high optical transparency. In this specification, a thermoplastic resin mainly composed of an acrylic polymer is an acrylic resin, a thermoplastic resin mainly composed of a styrene polymer is a styrene resin, and a thermoplastic resin mainly composed of a cycloolefin polymer. The resin is a cycloolefin resin. In addition, the amorphous polymer may be a cellulose derivative.

  When the center part 3 is comprised with an acrylic resin or a styrene resin, since the said resin is comparatively hard and brittle, when it is set as the diagonally stretched film 1, it will be easy to produce the fracture | rupture mentioned above. For this reason, when the thermoplastic resin which comprises the center part 3 is an acrylic resin or a styrene resin, the effect of this invention becomes more remarkable.

  The thermoplastic resin constituting the center portion 3 may include a polymer having a ring structure in the main chain. In this case, the glass transition temperature (Tg) of the obliquely stretched film 1 is improved. The obliquely stretched film 1 having a high Tg is used for applications requiring heat resistance, such as a liquid crystal display (LCD) image having a structure in which heating elements such as a power source, a light source, and a circuit board are integrated in a narrow space. It is suitable for use as an optical film for a display device. The optical film is, for example, a retardation film or a polarizer protective film. Further, depending on the type of the ring structure, the optical characteristics of the obliquely stretched film 1, for example, the retardation value is improved.

  The polymer having a ring structure in the main chain may be an acrylic polymer, that is, the center portion 3 may include an acrylic polymer having a ring structure in the main chain, and has a ring structure in the main chain. You may be comprised with the acrylic resin containing an acrylic polymer. An acrylic polymer having a ring structure in the main chain tends to be harder and more brittle than an acrylic polymer having no ring structure in the main chain. For this reason, when it is set as a diagonally stretched film, the fracture | rupture mentioned above tends to arise. That is, in this case, the effect of the present invention becomes more remarkable.

  The acrylic polymer is a polymer having (meth) acrylic acid ester units in an amount of 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more of the total structural units. However, when the acrylic polymer includes a ring structure that is a derivative of a (meth) acrylate unit, the content of the ring structure is also included in the content of the (meth) acrylate unit. The acrylic polymer has high optical transparency and excellent mechanical properties such as surface strength.

  A cycloolefin polymer is a polymer which has a cycloolefin unit 50 mol% or more of all the structural units, Preferably it is 60 mol% or more, More preferably, it is 70 mol% or more. The cellulose derivative is a triacetyl cellulose (TAC) unit, a cellulose acetate propionate unit, a cellulose acetate butyrate unit, a repeating unit such as a cellulose acetate phthalate unit, etc., in an amount of 50 mol% or more, preferably 60 mol% or more, More preferably, it is a polymer having 70 mol% or more. Cycloolefin polymers and cellulose derivatives have a ring structure in the main chain.

  The styrenic polymer is a styrene unit, an α-methyl styrene unit, an α-hydroxymethyl styrene unit, an α-hydroxyethyl styrene unit and other structural units derived from styrene and derivatives thereof, preferably 50 mol% or more of the total structural units. Is a polymer having 60 mol% or more, more preferably 70 mol% or more. Examples of the styrenic polymer include polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene block copolymer.

  The thermoplastic resin constituting the center portion 3 can contain two or more of these polymers. However, when the obliquely stretched film 1 is used as an optical film, it is necessary to consider the compatibility between the polymers in order to obtain an optically transparent film. For example, when the thermoplastic resin constituting the center part 3 includes an acrylic polymer having a ring structure in the main chain, the polymer simultaneously included is a styrene-acrylonitrile copolymer from the viewpoint of compatibility with the acrylic polymer. Preferably there is.

  The acrylic polymer having a ring structure in the main chain includes a structural unit derived from a (meth) acrylic acid ester monomer and a ring structure. The total content of the structural units derived from the (meth) acrylic acid ester monomer and the ring structure in the acrylic polymer is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight. %, Particularly preferably 95% by weight or more, most preferably 99% by weight or more. The content of the ring structure is preferably 5% by weight or more, more preferably 10% by weight or more, and further preferably 15% by weight or more. When the content of the ring structure exceeds 40% by weight, it becomes difficult to form a polymer having such a content of the ring structure (a gel is easily formed when the cyclization reaction proceeds), or the polymer The moldability and handling properties of the thermoplastic resin containing may decrease, and the productivity of the obliquely stretched film 1 may decrease.

  (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, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, (meth) acryl Dicyclopentanyl acid, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, (meth) acrylic acid 2, 3,4,5,6-pentahydroxyhexyl, 2,3,4,5-tetrahydro (meth) acrylic acid Shipenchiru is a structural unit derived from a monomer such as. The acrylic polymer can have two or more of these structural units. The acrylic polymer preferably has methyl methacrylate (MMA) units. In this case, the thermal stability of the obliquely stretched film 1 is improved.

  The acrylic polymer may have a structural unit other than the (meth) acrylic ester unit. The structural unit is, for example, a structural unit having a hydroxyl group and / or a carboxylic acid group. Depending on the type of the structural unit having a hydroxyl group and / or a carboxylic acid group, the structural unit changes to a ring structure located in the main chain of the polymer by a cyclization reaction after polymerization. In the acrylic polymer, these unreacted structural units that have not changed to a ring structure may remain. The structural unit having a hydroxyl group is, for example, a structural unit derived from each monomer of methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, and methyl 2- (hydroxyethyl) acrylate. . The structural unit having a carboxylic acid group is, for example, a structural unit derived from each monomer of acrylic acid, methacrylic acid, crotonic acid, 2- (hydroxymethyl) acrylic acid, and 2- (hydroxyethyl) acrylic acid. The acrylic polymer can have two or more of these structural units.

  Further structural units other than the (meth) acrylic acid ester unit that the acrylic polymer may have include, for example, styrene, vinyltoluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylo Monomers of nitrile, methallyl alcohol, allyl alcohol, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinyl pyrrolidone, N-vinyl carbazole A structural unit derived from the body. The acrylic polymer can have two or more of these structural units.

  The type of the ring structure is not particularly limited, and is, for example, at least one selected from a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, a maleimide structure, and a maleic anhydride structure. Especially, at least 1 sort (s) chosen from a lactone ring structure, a glutarimide structure, and a maleimide structure from a heat resistant viewpoint at the time of the original film shaping | molding before extending | stretching is preferable.

  The lactone ring structure that the acrylic polymer may have in the main chain is not particularly limited. For example, it may be a 4- to 8-membered ring, but it is excellent in the stability of the ring structure. It is preferably a membered ring, more preferably a 6-membered ring. 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 high polymerization yield of the precursor and the high lactone ring due to the cyclization reaction of the precursor. The structure represented by the following formula (1) is preferable because an acrylic polymer having a content rate can be obtained and a polymer having a MMA unit as a constituent unit can be used as a precursor.

In the formula (1), R ¹ , R ² and R ³ 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 formula (1) 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 unsaturated group having 1 to 20 carbon atoms such as an ethenyl group or a propenyl group. An aliphatic hydrocarbon group; an aromatic hydrocarbon group having 1 to 20 carbon atoms such as a phenyl group and a naphthyl group; In the alkyl group, unsaturated aliphatic hydrocarbon group and aromatic hydrocarbon group, one or more hydrogen atoms are substituted by at least one group selected from a hydroxyl group, a carboxyl group, an ether group and an ester group. Also good.

  When the acrylic polymer has a lactone ring structure in the main chain, the content of the lactone ring structure in the polymer is not particularly limited. A content rate is 5-90 weight%, for example, Preferably it is 10-80 weight%, More preferably, it is 10-70 weight%, More preferably, it is 20-60 weight%. When the content of the ring structure in the acrylic polymer is too small, the obliquely stretched film 1 has insufficient properties expected due to the presence of the ring structure, such as heat resistance, solvent resistance, surface hardness, and optical properties. Sometimes. When the content of the ring structure is excessively large, the moldability and handling properties of the acrylic polymer and the thermoplastic resin containing the polymer are lowered, and the productivity of the original film and the obliquely stretched film 1 is lowered.

  The content of the lactone ring structure in the acrylic polymer can be evaluated by a known method. Specifically, for example, dynamic TG measurement is performed on an acrylic polymer, and a weight reduction rate (measured weight reduction rate) when heated from 150 ° C. to 300 ° C. is obtained. This weight reduction rate corresponds to the amount of hydroxyl groups remaining in the acrylic polymer to be evaluated. 150 ° C. is a temperature at which an unreacted (non-cyclized) hydroxyl group remaining in the acrylic polymer starts a cyclization reaction again, and 300 ° C. is a temperature at which the acrylic polymer starts to decompose. From this measured weight loss rate and the theoretical weight loss rate assuming that all the hydroxyl groups (which can be calculated from the precursor composition) of the precursor before the cyclization reaction have undergone dealcoholization cyclization, The content of the structure can be calculated. That is, in the dynamic TG measurement of an acrylic polymer having a lactone ring structure, an actual weight loss rate (X) between 150 ° C. and 300 ° C. is measured. Separately from this, the theoretical weight loss rate (Y) is calculated from the composition of the polymer when it is assumed that all the hydroxyl groups contained in the composition are involved in the formation of the lactone ring (dealcoholization cyclization reaction). More specifically, the theoretical weight reduction rate (Y) is calculated from the molar ratio of the monomer having a structure (hydroxyl group) involved in the dealcoholization cyclization reaction in the polymer, that is, the content of the monomer. sell. By substituting these values X and Y into the formula {1- (actually measured weight reduction rate (X) / theoretical weight reduction rate (Y))} × 100 (%), the dealcoholization reaction rate A is obtained. Next, assuming that the cyclization reaction has proceeded at a rate corresponding to the determined dealcoholization reaction rate A, the content of the lactone ring is determined by the formula B × A × MR / Mm. B is the content of the monomer having a hydroxyl group in the precursor (the polymer before the lactone cyclization reaction proceeds), and MR is the formula weight of the lactone ring structure formed by the cyclization reaction. Yes, Mm is the molecular weight of the monomer having a hydroxyl group, and A is the dealcoholization reaction rate.

  The weight average molecular weight (Mw) of the acrylic polymer having a ring structure in the main chain is preferably 80,000 or more, more preferably 100,000 or more. The molecular weight dispersity is preferably 3.5 or less, more preferably 3 or less. In these cases, there are few branch structures which exist in an acrylic polymer, the thermal stability at the time of a process improves, and the intensity | strength and external appearance of the original film and the diagonally stretched film 1 improve. Mw and dispersity can be determined by polystyrene conversion using GPC (gel permeation chromatograph). The degree of dispersion is the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer. Mn can also be obtained using GPC.

  The glass transition temperature Tg of the acrylic polymer having a ring structure in the main chain is, for example, 110 ° C. or higher, preferably 115 ° C. or higher, and more preferably 120 ° C. or higher. On the other hand, when Tg exceeds 200 ° C., the formability of the original film is deteriorated, for example, it becomes difficult to form a melt film. The general acrylic polymer having no ring structure in the main chain has a Tg of about 100 ° C.

  The acrylic polymer having a ring structure in the main chain can be produced by a known method. An acrylic polymer whose ring structure is a glutaric anhydride structure or a glutarimide structure can be produced, for example, by the method described in WO2007 / 26659 or WO2005 / 108438. An acrylic polymer whose ring structure is a maleic anhydride structure or an N-substituted maleimide structure can be produced, for example, by the method described in JP-A-57-153008 or JP-A-2007-31537. An acrylic polymer having a lactone ring structure as a ring structure can be produced, for example, by the method described in JP-A-2006-96960, JP-A-2006-171464, or JP-A-2007-63541.

  The thermoplastic resin constituting the center portion 3 has a Tg of, for example, 110 ° C. or higher, preferably 115 ° C. or higher, and more preferably 120 ° C. or higher. On the other hand, when Tg exceeds 200 ° C., the formability of the original film is deteriorated, for example, it becomes difficult to form a melt film.

  The thermoplastic resin constituting the center portion 3 can include other polymers than those described above. The content of the polymer in the thermoplastic resin constituting the center part 3 is preferably less than 50% by weight, more preferably 0 to 25% by weight, and still more preferably 0 to 10% by weight. Examples of the polymer include olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl polymers. Biodegradable polyester such as polylactic acid and polybutylene succinate; polyamide such as nylon 6, nylon 66 and nylon 610; polyacetal; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polyether nitrile; Sulphone; polyoxypentylene; polyamideimide; rubbery polymer such as ABS resin or ASA resin blended with polybutadiene rubber or acrylic rubber. However, when using the diagonally stretched film 1 for an optical use, when the diagonally stretched film 1 is an optical film, it is necessary to consider the compatibility between polymers in order to obtain an optically transparent film. When the thermoplastic resin constituting the center part 3 includes an acrylic polymer having a ring structure in the main chain, the rubbery polymer is compatible with the acrylic polymer from the viewpoint of compatibility with the acrylic polymer. It is preferable to have the graft part which has the composition obtained on the surface. In order to obtain an optically transparent film, the average particle size of the rubber polymer is, for example, 400 nm or less, preferably 200 nm or less, more preferably 100 nm or less, and further preferably 70 nm. It is as follows.

  The thermoplastic resin constituting the center part 3 can include a polymer having an α, β-unsaturated monomer unit having a heteroaromatic group as a constituent unit. In this case, depending on the composition of the thermoplastic resin, the degree of freedom in controlling the optical characteristics exhibited by the obliquely stretched film 1, specifically the birefringence wavelength dispersibility, becomes high. For example, an optical film exhibiting reverse wavelength dispersibility can get. Inverse wavelength dispersion is wavelength dispersion in which the birefringence decreases (the phase difference decreases) as the wavelength becomes shorter, at least in the visible light region. The heteroaromatic group is at least one selected from, for example, a carbazole group, a pyridine group, a thiophene group, and an imidazole group. The α, β-unsaturated monomer unit having a heteroaromatic group is, for example, at least one selected from an N-vinylcarbazole unit, a vinylpyridine unit, a vinylthiophene unit, and a vinylimidazole unit. Of these, N-vinylcarbazole units are preferable, and in this case, good reverse wavelength dispersion can be exhibited as an optical film.

  The polymer having an α, β-unsaturated monomer unit having a heteroaromatic group as a constituent unit may be an acrylic polymer having a ring structure in the main chain. The thermoplastic resin constituting the center part 3 is a polymer different from an acrylic polymer having a ring structure in the main chain, and is a polymer having an α, β-unsaturated monomer unit having a heteroaromatic group as a constituent unit. Can include coalescence.

  The thermoplastic resin constituting the end portions 2a and 2b can contain the above-described polymer as a main component. Moreover, since it is excellent in bending strength and excellent in impact strength, the thermoplastic resin constituting the end portions 2a and 2b preferably contains at least one selected from polycarbonate and polyester. It is more preferable that it is contained as a component, and it is more preferable that it is composed of the at least one kind.

  The thermoplastic resin constituting the end portions 2a and 2b and the center portion 3 can contain a known additive. Additives include, for example, UV absorbers; antioxidants; phase difference modifiers such as phase difference increasing agents and phase difference reducing agents; phase difference stabilizers, light resistance stabilizers, weather resistance stabilizers and heat stabilizers, etc. Stabilizers; reinforcements such as glass and carbon fibers; near infrared absorbers; flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate and antimony oxide; anionic, cationic, nonionic Antistatic agents typified by surface active agents; colorants such as inorganic pigments, organic pigments, dyes; organic fillers, inorganic fillers; resin modifiers; matting agents; acid scavengers; Anti-blocking agent; plasticizer; lubricant; flame retardant; rubbery polymer such as ASA and ABS; and other materials that adjust the optical and / or mechanical properties of the obliquely stretched film 1The addition amount of the additive is, for example, 0 to 10% by weight, preferably 0 to 5% by weight, more preferably 0 to 2% by weight, and further preferably 0 to 0.5% by weight. .

  A functional layer that is not a thermoplastic resin layer may be provided on the surface of the obliquely stretched film 1. The functional layer is, for example, a hard coat layer, an easy adhesion layer, an antistatic layer, an antireflection layer, an antiglare layer, an adhesive layer, and an antiblocking layer. Two or more functional layers may be laminated and provided.

  The diagonally stretched film of this invention can be used for the same use as the conventional stretched film containing a uniaxially stretched film and a biaxially stretched film. An example of an application is an optical film. Optical films include, for example, protective films for substrates of various optical disks (VD, CD, DVD, MD, LD, etc.), retardation films and polarizer protective films provided in image display devices such as LCDs, and viewing angle compensation films, A light diffusion film, a reflection film, an antireflection film, an antiglare film, a brightness enhancement film, a conductive film for a touch panel, a polarizing plate, and a circularly polarizing plate.

[Method for producing obliquely stretched film]
5 and 6 show an example of the method for producing the obliquely stretched film of the present invention. FIG. 6 is a schematic view of the example shown in FIG. 5 viewed from the side surfaces (side surfaces of the original film 4 and the obliquely stretched film 1). In the example shown in FIGS. 5 and 6, the belt-shaped resin film (original film) 4 is obliquely stretched in the heat stretching apparatus 21, and the stretched film fed from the heat stretching apparatus 21 is formed into a first roll 23 and a second roll. 24 in order. In the heating and stretching apparatus 21, the original film 4 is stretched obliquely by the traveling movement of a clip (not shown) that holds the end portions 5 a and 5 b in the width direction of the strip-shaped original film 4. The original film 4 stretched by the traveling movement of the clip in the heat stretching apparatus 21 is released from the clip (clipped out) at the clip-out portion 22. In the example shown in FIGS. 5 and 6, after the stretched film is released from the clip, the portions held by the clip at the end portions 2 a and 2 b of the film are part of the end portions 2 a and 2 b. The end portions 2a and 2b are removed by in-line slits so as to remain. Here, the end portions 5a and 5b in the original film 4 and the portions other than the end portions 5a and 5b (center portion 6) are made of different thermoplastic resins, and the thermoplastic resin constituting the center portion 6 is used. Compared to the above, the folding strength of the thermoplastic resin constituting the end portions 5a and 5b is large.

  In the stretching of the resin film by the traveling movement of the clip, the portion of the resin film held by the clip is not stretched and the film thickness remains thick. Further, there is a difference in strength between the stretched portion of the film and the non-stretched portion held by the clip (the grip trace portion). Due to the difference in thickness and / or strength between the thick part and the thinned part due to stretching, the resin film is wrinkled and / or cracked upon contact with the roll after being released from the clip. In this case, the film breaks. This breakage is particularly likely to occur when the original film is stretched obliquely by the moving movement of the clip. This is because, in oblique stretching, a “twist” is added to the portion gripped by the clip, and for example, “swelling wrinkles” are generated in the portion or the entire film is inferior in flatness. This is because wrinkles and / or cracks starting from the portion are more likely to occur due to the contact.

  In the manufacturing method of the present invention, the end portions 5a and 5b of the original film 4 held by the clip at the time of oblique stretching are composed of a thermoplastic resin having a higher folding resistance than the center portion 6. For this reason, after stretching by the heat stretching device, even when it comes into contact with the roll arranged on the film path, the generation of wrinkles and cracks starting from the gripped portion by the clip is suppressed, and the film breakage is suppressed. The

  Further, in the production method of the present invention, in the stretched film, the end portions 2a and 2b made of a thermoplastic resin having a higher folding resistance than the thermoplastic resin constituting the center portion 3 are provided on the end portion. In-line slitting is performed so that the portion remains in the stretched film. That is, the cutting line by the in-line slit passes through the end portions 2a and 2b having a high bending strength, not the center portion 3. Thereby, the fracture | rupture of the film by a slit cut surface extending in the direction of the extending | stretching axis | shaft in the film surface after extending | stretching is suppressed.

  Further, in the manufacturing method of the present invention, the film (obliquely stretched film 1) after the portion gripped by the clip at the time of oblique stretching is removed has a bending strength higher than that of the thermoplastic resin constituting the center portion 3. End portions 2a and 2b made of a large thermoplastic resin are present. Thereby, as described above in the explanation of the obliquely stretched film of the present invention, the breakage of the film in the direction in which the stretch axis in the film plane extends is suppressed.

  These breaks tend to occur when the center portion 6 of the original film 4 (= center portion 3 of the obliquely stretched film 1) contains a relatively hard and brittle resin. In the production method of the present invention, even in such a case, breakage in the stretched film is suppressed. “Relatively hard and brittle resins” are, for example, acrylic resins and styrene resins. That is, the thermoplastic resin constituting the original film 4 and the center portions 3 and 6 of the obliquely stretched film 1 obtained by the production method of the present invention may be an acrylic resin or a styrene resin. The effect by the manufacturing method becomes more remarkable.

  In the present specification, “oblique stretching” means stretching in a direction inclined by less than 90 ° with respect to the longitudinal direction of the belt-shaped resin film (original film), for example, with respect to the length direction (longitudinal direction). 10 ° to 80 °, typically 40 ° to 50 °, preferably 43 ° to 47 °, more preferably 44 ° to 46 °.

  The term “in-line slit” in the present specification does not mean that the stretched film is wound once and then slit (performs a slitting process), but the stretched film is transported while being wound with a winder or the like. It means that a part is cut with a cutter or the like.

<Structure of the original film>
The composition of the original film 4 is such that the end portions 5 a and 5 b and the portions other than the end portions 5 a and 5 b (center portion 6) in the original film 4 are composed of different thermoplastic resins, and the thermoplastic resin constituting the center portion 6. As compared with the above, there is no limitation as long as the folding strength of the thermoplastic resin constituting the end portions 5a and 5b is large.

  The thermoplastic resin constituting the end portions 5a and 5b of the original film 4 may be the same as the thermoplastic resin constituting the end portions 2a and 2b of the obliquely stretched film 1 of the present invention. The thermoplastic resin constituting the center portion 6 of the original film may be the same as the thermoplastic resin constituting the center portion 3 of the obliquely stretched film 1 of the present invention.

  It is preferable that the impact strength exhibited by the thermoplastic resin constituting the end portions 5a and 5b is greater than the thermoplastic resin constituting the portion (center portion 6) other than the end portions 5a and 5b.

  The width of the end portions 5a and 5b varies depending on the type of the thermoplastic resin constituting the end portion, but the melt-extruded original film breaks from the edge beat (the edge beat is thicker than other portions and cracks. In order to suppress (easy), it is preferably at least larger than the edge beat width, preferably 5 mm or more, and more preferably 10 mm or more. The upper limit of the width | variety of edge part 5a, 5b is not specifically limited, It can set suitably with extending | stretching conditions. The widths of the end portions 5a and 5b are preferably set based on the widths of the end portions 2a and 2b after being stretched and slit.

  The end 5a and the end 5b may be made of the same thermoplastic resin or may be made of different thermoplastic resins. The original film 4 in which the end portions 5a and 5b are made of the same thermoplastic resin can stably perform oblique stretching and is generally easier to form.

  The boundary between the end portion 5a and the center portion 6 and the boundary between the end portion 5b and the center portion 6 are not necessarily straight lines as shown in FIG. Further, these boundaries are not always visually confirmed. The boundary may be visible due to the difference in refractive index between the thermoplastic resins constituting both.

  The center part 6 may have a structure in which two or more thermoplastic resin layers are laminated.

  The original film 4 is typically an unstretched film. However, an already stretched film can be used as the original film 4 as long as the effects of the present invention are obtained.

  The end portions 5a and 5b in the width direction of the original film 4 may be subjected to functional processing such as knurling. The strip-shaped original film 4 is generally supplied from a roll, and wrinkles to the film when forming the roll of the original film 4 by forming a knurling portion on the ends 5a and 5b of the original film 4 are performed. The occurrence of scratches and winding defects can be suppressed. In addition, when the knurling part is formed in the end parts 5a and 5b, it is conceivable to hold the knurling part when holding the end part with a clip for oblique stretching. If both end portions 5a and 5b are made of a relatively hard and brittle resin, the knurling portion may break and lead to the film breaking. In the manufacturing method of the present invention, since the folding resistance of the thermoplastic resin constituting the end portions 5a and 5b is larger than that of the center portion 6, the film breaks due to the clip gripping the knurling portion. Is suppressed.

  Functional processing may be affixing of a tape for the purpose of preventing breakage of the original film 4 or imparting anti-blocking property to the original film 4. The tape is, for example, Sekisui Chemical's taffete tape (trade name).

<Formation method of original film>
The method for forming the original film 4 is not particularly limited. The original film 4 can be formed by, for example, melt coextruding a thermoplastic resin that constitutes the end portions 5 a and 5 b and a thermoplastic resin that constitutes the center portion 6. The melt coextrusion method may follow a well-known method, and the strip | belt-shaped original film 4 can be formed by coextruding 2 or more types of thermoplastic resins continuously. The formed strip-shaped original film 4 may be wound to form a roll (original film roll).

  The extrusion molding temperature (molding temperature) is preferably 200 to 350 ° C, more preferably 250 to 300 ° C, still more preferably 255 ° C to 300 ° C, and particularly preferably 260 ° C to 300 ° C.

  The type of the extruder used for extrusion molding is not particularly limited, and any of single-screw, twin-screw, and multi-screw extruders can be used. In order to sufficiently plasticize the thermoplastic resin to obtain a good kneaded state, the L / D value of the extruder (L is the length of the cylinder of the extruder and D is the cylinder inner diameter) is preferably 10 or more and 100 or less. Yes, more preferably from 15 to 80, and even more preferably from 20 to 60. When the L / D value is less than 10, the thermoplastic resin may not be sufficiently plasticized and a good kneaded state may not be obtained. When the L / D value exceeds 100, the polymer in the resin may be thermally decomposed due to excessive generation of shear heat to the thermoplastic resin.

  The set temperature of the cylinder of the extruder is preferably 200 ° C. or higher and 300 ° C. or lower, more preferably 250 ° C. or higher and 300 ° C. or lower. When the set temperature of the cylinder is less than 200 ° C., the melt viscosity of the thermoplastic resin becomes excessively high, and the productivity of the original film 4 tends to decrease. When the set temperature of the cylinder exceeds 300 ° C., the polymer in the resin may be thermally decomposed.

  The shape of the extruder is not particularly limited. The extruder preferably has one or more open vents. In this case, the cracked gas can be sucked from the open vent portion of the extruder, and the amount of volatile components remaining in the obtained original film is reduced. In order to suck the decomposition gas from the open vent portion, for example, the open vent portion may be in a reduced pressure state. 1.3-931 hPa is preferable and, as for the pressure of the open vent part in a pressure reduction state, 13.3-798 hPa is more preferable. If the pressure in the open vent is higher than 931 hPa, the volatile component and the monomer component generated by the decomposition of the polymer are likely to remain in the thermoplastic resin. It is industrially difficult to keep the pressure of the open vent part lower than 1.3 hPa.

  For the production of the original film 4, it is preferable to use a thermoplastic resin filtered through a polymer filter. Filtration using a polymer filter removes foreign substances present in the resin and reduces the defects (optical defects and defects in appearance) of the obtained obliquely stretched film. Filtration is solution filtration or melt filtration.

  During melt filtration, the thermoplastic resin is in a molten state at a high temperature. When the components contained in the resin deteriorate when passing through the polymer filter, the gas components or colored degradation products generated by the deterioration flow out, and defects such as perforations, flow patterns, and flow lines are observed in the resulting original film. May be. These disadvantages are particularly easily observed during continuous forming of the original film. Deterioration of the thermoplastic resin during melt filtration can be prevented by reducing the melt viscosity of the resin and shortening the residence time of the resin in the polymer filter. From this viewpoint, the molding temperature of the resin melt-filtered by the polymer filter is, for example, 255 to 320 ° C, and preferably 260 to 300 ° C.

  The configuration of the polymer filter is not particularly limited. A polymer filter in which a large number of leaf disk filters are arranged in a housing is preferably used. The filter material of the leaf disk type filter may be either a type in which a metal fiber nonwoven fabric is sintered, a type in which metal powder is sintered, a type in which several metal meshes are laminated, or a hybrid type in which they are combined. A type in which a metal fiber nonwoven fabric is sintered is most preferable.

  The filtration accuracy of the polymer filter is not particularly limited, but is usually 15 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the filtration accuracy is 1 μm or less, the residence time of the thermoplastic resin in the polymer filter becomes long, so that the polymer contained in the resin is likely to be thermally deteriorated. Furthermore, the productivity of the original film is also reduced. When the filtration accuracy exceeds 15 μm, it is difficult to remove foreign substances in the resin.

  The shape of the polymer filter is not particularly limited. For example, an inner flow type having a plurality of flow openings and a flow path of a thermoplastic resin in the center pole; An external flow type having a flow path of thermoplastic resin on the outer surface of the center pole. Among these, an external flow type with few resin staying portions is preferable.

  The residence time of the thermoplastic resin in the polymer filter is preferably 20 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less. The filter inlet pressure and the outlet pressure during filtration are, for example, 3 to 15 MPa and 0.3 to 10 MPa, respectively, and the pressure loss (pressure difference between the filter inlet pressure and the outlet pressure) is preferably 1 MPa to 15 MPa. When the pressure loss is 1 MPa or less, the flow path through which the thermoplastic resin passes through the filter tends to be biased, and the quality of the obtained film tends to deteriorate. When the pressure loss exceeds 15 MPa, the polymer filter is easily damaged.

  What is necessary is just to set suitably the temperature of the thermoplastic resin introduce | transduced into a polymer filter according to the melt viscosity, for example, it is 250-300 degreeC, Preferably it is 255-300 degreeC, More preferably, it is 260-300 degreeC. is there.

  The specific procedure for obtaining an original film with few foreign matters and colored substances by melt filtration using a polymer filter is not particularly limited. For example, (1) a process of forming and filtering a thermoplastic resin in a clean environment, followed by molding in a clean environment, (2) a filtration process of a thermoplastic resin having foreign matter or colored substances in a clean environment After that, a process in which molding is performed in a clean environment and (3) a process in which a thermoplastic resin having foreign matters or colored substances is subjected to filtration treatment in a clean environment and molding is adopted at the same time. The filtration treatment can be performed a plurality of times for each step.

  When the thermoplastic resin is melt-filtered by the polymer filter, it is preferable to stabilize the pressure of the resin in the filter by installing a gear pump between the extruder and the polymer filter.

<Original film stretching method>
The stretching of the original film 4 in the production method of the present invention is not limited as long as the stretching is performed by the traveling movement of the clip that holds the end portions 5a and 5b (long edge portions) in the width direction of the strip-shaped original film 4. Specifically, the oblique stretching can be performed as follows, for example.

  A pair of clip groups each composed of a plurality of clips are used to grip both long side edges of the strip-shaped original film 4 (clip-in), and the original clip 4 is held by running the pair of clip groups. The film 4 is stretched, and after the original film 4 is stretched, the original film is released from the pair of clips (clipout) to obtain a strip-shaped stretched film. Here, the stretching of the original film 4 is carried out by the difference in travel speed between one clip group and the other clip group and / or the travel distance difference between one clip group and the other clip group between clip-in and clip-out. The original film 4 is stretched obliquely with respect to the longitudinal direction of the film (stretched obliquely). By such oblique stretching, for example, an obliquely stretched film in which the stretching axis in the film plane is inclined with respect to the length direction (longitudinal direction) of the film is formed. Stretching can be performed two or more times between clip-in and clip-out as necessary.

  When a thermoplastic resin that exhibits birefringence upon stretching is used for the center portion 6 of the original film, such an oblique stretching causes, for example, the optical axis (slow axis or fast axis) in the film plane to be the film. An obliquely stretched optical film (for example, an obliquely stretched retardation film) tilted with respect to the width direction and the length direction is formed. Note that the direction of the stretching axis does not always match the direction of the optical axis. Depending on the type of the thermoplastic resin and the state of stretching, there may be a shift of several degrees to several tens of degrees between the two when viewed from the direction perpendicular to the film surface.

  The specific oblique stretching is performed as follows, for example.

  In one embodiment, the peripheral edges on the left and right sides (left and right when the belt-like original film is viewed in the length direction, the same applies hereinafter) are different from each other while the belt-like original film is uniaxially stretched in the width direction. At a speed, it is stretched in the length direction of the original film.

  This embodiment can be implemented using, for example, a horizontal uniaxial stretching machine such as a tenter lateral stretching machine. Specifically, it can be carried out by driving the left and right clip groups in the stretching machine independently of each other. More specifically, the right and left clip groups improved so as to be independently driven while introducing the strip-shaped original film into the horizontal uniaxial stretching machine in the same manner as before and performing the horizontal uniaxial stretching at different traveling speeds. Drive. The traveling speed difference is a difference in tensile force between the left and right peripheral edge portions of the original film. Thereby, the diagonal stretch of the original film is realized. In this embodiment, the characteristics (for example, optical characteristics such as the optical axis, phase difference, and NZ coefficient) of the obtained obliquely stretched film change depending on the traveling speed difference between the left and right clip groups and / or the stretching ratio of the lateral uniaxial stretching. Can be made.

  This embodiment can also be implemented using a pantograph-type and linear motor-type simultaneous biaxial stretching machine. As in the case of using a tenter transverse stretching machine, while the uniaxial stretching of the strip-shaped original film in the width direction, the traveling speed of the clip group is made different on the left and right, that is, the traveling of the clip group holding the original film The feed speed at the peripheral edge of the original film caused by the above is made different on the left and right. Thereby, the draw ratio in the longitudinal direction of the original film is different between right and left, and the original film is obliquely drawn.

  In another embodiment, the strip-shaped original film is stretched obliquely using a tenter transverse stretching machine having a bent tenter rail. Specifically, when the left and right clip groups travel on the bent inner and outer rails at the same traveling speed, the inner rail clip group advances before the outer rail clip group. At this time, the travel distance from clip-in to clip-out differs between the clip group traveling on the inner rail and the clip group traveling on the outer rail. Thereby, the diagonal stretch of the original film is realized. In this embodiment, the optical properties exhibited by the obtained stretched resin film can be changed depending on the degree of bending of the inner and outer rails.

  Another embodiment is oblique stretching of the original film by the method described in International Publication No. 2012/017639. An example of the method will be described with reference to FIG.

  FIG. 7 schematically shows the running state of the left and right clip groups in an example of the method described in International Publication No. 2012/017639. Reference numeral 21 denotes a heating / stretching apparatus 21 that can implement the example, for example, a simultaneous biaxial stretching machine including a pair of clip groups configured by a plurality of clips that can be accelerated and decelerated independently. In the device 21, clips belonging to each of the left clip group and the right clip group reach the clip-out portion (COL, COR) from the clip-in portion (CIL, CIR) through L1-L10, R1-R9, and the left-side clip rail. The vehicle travels back to the clip-in portion (CIL, CIR) again through the LR and the right clip rail RR. In FIG. 7, the illustration of the original film is omitted, but in the clip-in portions (CIL, CIR), the left and right long edge portions of the strip-shaped original film are gripped by the left clip group and the right clip group, respectively. The original film is guided to the heating and stretching device 21 by the traveling of the left and right clip groups that hold the film, and also passes through the preheating zone Z1, the front stretching zone Z2, the rear stretching zone Z3, and the heat treatment zone Z4 in this order in the device 21. To do.

  In this embodiment, when the clip group grips the strip-shaped original film, that is, in the clip-in portion (CIL, CIR), the traveling speeds of both the left and right clip groups are equal to each other. When the traveling speeds of the left and right clip groups are not equal at the time of clip-in, the original film is pulled toward the clip with a large traveling speed, so that the movement stability of the original film to the heating and stretching apparatus 21 and the heating and stretching apparatus 21 The movement stability of the original film is reduced. For this reason, the diagonally stretched film which has the desired characteristic may not be obtained.

  In reality, the stress generated when the original film is stretched in the oblique direction adds a pulling back force to the relatively preceding clip, and adds a forward force to the relatively delayed clip. For this reason, it is difficult to always control the traveling speed of the left clip group and the traveling speed of the right clip group at the time of clip-in to be completely the same. Considering this, in this embodiment, the ratio v1 / v2 between the traveling speed v1 of the left clip group and the traveling speed v2 of the right clip group at the time of clip-in is maintained at 0.98 or more and 1.02 or less. The ratio v1 / v2 is preferably 0.99 or more and 1.01 or less, more preferably 0.995 or more and 1.005 or less. In the oblique stretching of the original film including the other embodiments described above or later, the traveling speed ratio v1 / v2 of the left and right clip groups at the time of clip-in is set to 0.98 or more and 1.02 or less. It is preferable.

  Similarly, the present invention is not limited to this embodiment, and in the oblique stretching of the original film including the other embodiments described above or later, the running speed ratio v1 / v2 of the left and right clip groups at the time of clip-out is 0.98 or more. It is preferable to set it to 1.02 or less.

  In the preheating zone Z1, the original film supplied to the heating and stretching apparatus 21 is heated to a temperature at which stretching can be performed in the stretching zones (the first stretching zone Z2 and the second stretching zone Z3) that pass later.

  In the preceding drawing zone Z2, the traveling speed v1 of the left clip group that has traveled from the preheating zone Z1 decreases in order. Thereby, in the front | former stage extension zone Z2, the driving | running | working delay of the left side clip group generate | occur | produces with respect to the right side clip group. Then, based on the generated travel delay, the original film is stretched obliquely with respect to the length direction of the film. Unlike the stretching based on the vector sum of the longitudinal stretching (stretching in the film length direction) and the lateral stretching (stretching in the film width direction), this stretching has a strong uniaxial stretching property. Thereby, for example, a stretched film having an NZ coefficient close to 1 and weak biaxial stretchability (strong uniaxial stretchability) can be obtained.

  In the rear stretching zone Z3, the traveling speed of the left clip group that has traveled from the preceding stretching zone Z2 sequentially increases, and the traveling speed v1 of the left clip group and the traveling speed v2 of the right clip group are equal to each other at the exit of the zone. Become. Specifically, the ratio v1 / v2 between the traveling speed v1 of the left clip group and the traveling speed v2 of the right clip group is 0.98 or more and 1.02 or less, preferably 0.99 or more and 1.01 or less. Preferably it becomes 0.995 or more and 1.005 or less. Also in the rear stretching zone Z3, a traveling speed difference occurs between the left and right clip groups until the traveling speeds become equal to each other, and the original film is stretched obliquely based on this speed difference.

  Although not described in International Publication No. 2012/017639, the traveling speed can also be increased by increasing the traveling speed of one clip group in the preceding drawing zone Z2 to give a traveling speed difference between the two clip groups. Based on the difference, the original film can be stretched obliquely. In this case, it is preferable to reduce the traveling speed of the one clip group in the rear-stage stretching zone Z3 and make the traveling speeds of the left and right clip groups equal to each other at the exit of the zone. In either case of reducing or increasing the traveling speed of one clip group in the front drawing zone Z2, the left and right clips generated in the front drawing zone Z2 between the front drawing zone Z2 and the rear drawing zone Z3. There may be further provided a stretching zone for maintaining the traveling speed difference between the groups.

  In the heat treatment zone Z4, the original film stretched in the stretching zone is held at a specific temperature (heat treatment temperature) equal to or lower than the stretching temperature in the stretching zone. This stabilizes the molecular orientation of the resin contained in the film, reduces the distortion of the film, and stabilizes the properties of the finally obtained stretched resin film, for example, optical properties and mechanical properties. Is planned. The original film that has passed through the heat treatment zone Z4 is released from both the left and right clip groups in the clip-out portions (COL, COR).

  FIG. 8 shows another example of the method described in International Publication No. 2012/017639. In the method shown in FIG. 8, in the former drawing zone Z2 and the latter drawing zone Z3, that is, when the original film is drawn, the distance between the left and right clip groups in the width direction of the original film is increased. By such combined use of stretching in the width direction (lateral stretching) by increasing the distance between the pair of clip groups with respect to the width direction of the original film, the degree of freedom in controlling the characteristics of the obtained obliquely stretched film is increased. Get higher. Except for the use of transverse stretching, the running state of the left and right clip groups in the example shown in FIG. 8 is the same as the running state of the left and right clip groups in the example shown in FIG. Moreover, the zones of the preheating zone Z1, the former drawing zone Z2, the latter drawing zone Z3, and the heat treatment zone Z4 are the same as the example shown in FIG. The transverse stretching is not limited to this embodiment, and can be used in combination with the oblique stretching of the original film including the other embodiments described above.

  Each embodiment described above is an example of a method for performing oblique stretching of an original film.

  The NZ coefficient is nx as the refractive index in the slow axis direction in the plane of the stretched film, ny as the refractive index in the fast axis direction in the plane of the film, and nz as the refractive index in the thickness direction of the film. Then, it can be obtained by the equation (nx−nz) / (nx−ny). When the in-plane retardation Re and the thickness direction retardation Rth indicated by the stretched resin film (retardation film) are used, the NZ coefficient can also be obtained by the expression | Rth | / | Re | +0.5. The closer the value of the NZ coefficient is to 1, the lower the biaxial stretchability of the stretched resin film (the stronger the uniaxial stretchability).

<Inline slit method after stretching>
In the in-line slit in the manufacturing method of the present invention, the end portions of the film end portions (end portions in the width direction of the band-shaped film) 2a and 2b after the oblique stretching are gripped by the clips during the oblique stretching. 2a and 2b are removed so as to remain in the stretched film. The width of the portion to be removed from the end portions 2a and 2b is such that the portion gripped by the clip (the portion deformed by gripping the clip during oblique stretching) is removed, and the end portions 2a and 2b are partially stretched films. It can be adjusted within the range that remains. The width of the portion removed from one end 2a and the width of the portion removed from the other end 2b may be the same or different.

  The implementation timing of the in-line slit in the production method of the present invention is not limited as long as it is performed on the stretched film. As shown in FIGS. 5 and 6, after the stretched film is released from the clip of the heat stretching apparatus 21, that is, downstream of the clip-out portion 22, after passing one or more rolls such as a guide roll. You may implement. It may be performed downstream of the clip-out portion 22 and before the stretched film reaches the first roll 23 (the roll through which the stretched film first passes after being clipped out). The term “film after stretching” in the present specification means a film after heating and / or stretching of the original film. For example, in the case where heat treatment (annealing) is performed after stretching. It means the film after the heat treatment.

  In the case where the inline slit is carried out after the stretched film is clipped out and before the film reaches the first roll 23, the conveying tension applied to the stretched film during the inline slit is 5N. / M to 100 N / m is preferable. By controlling the conveyance tension in this way, the portions held by the clips at the end portions 2a and 2b can be stably removed.

  The specific method of removing the portions gripped by the clips at the end portions 2a and 2b by the in-line slit is not limited. For example, as in the example shown in FIGS. The cutter may be of any type, such as one using a metal blade such as a leather blade or a round blade, or one using a high energy beam such as a laser, but a shear cutter that cuts a resin film by shearing is preferred. The position of the cutter may be fixed or movable.

  A part of the end portions 2a and 2b removed by the in-line slit may be discharged from a production line that stretches the original film to obtain an obliquely stretched film. The discharging method can be arbitrarily selected as long as the effect of the present invention is obtained. For example, the portion removed from the end portions 2a and 2b may be discharged from the production line of the obliquely stretched film as it is, or after passing through the same section and the same path as the stretched film, It may be discharged from the production line. In order to prevent the part once removed from coming into contact with the stretched film, the path of the removed part that passes through the in-line slit and the path of the stretched film from which the part has been removed are separated from each other. Is preferred.

  The stretching axis 11 in the obliquely stretched film is inclined with respect to the width direction and the length direction of the film. For this reason, when the film after oblique stretching passes a roll such as a guide roll after clip-out, and when the in-line slit of the portion held by the clip at the end portions 2a and 2b is performed on the film after oblique stretching. The film tends to break from one side of the film because of the relationship between the direction of the stretching axis 11 of the film and the traveling direction. This one side is the side where the stretching axis 11 first reaches the roll or in-line slit, that is, the side where the stretching axis 11 extends in the film traveling direction (for example, the film shown in FIG. Assuming that 1 is traveling above the plane of the paper, the stretching axis 11 extends above the plane of the paper as viewed from the central axis of the film 1 and is the long side on the right side of the plane of the paper. In the manufacturing method of the present invention, such breakage is suppressed by the presence of the end portions 2a and 2b.

  In the production method of the present invention, the obliquely stretched film 1 can be continuously produced by performing the above-described oblique stretching and inline slits on the original film 4 continuously supplied from the original film forming apparatus. The original film forming apparatus is, for example, a melt coextrusion molding machine.

  In the manufacturing method of this invention, the diagonally stretched film 1 can be continuously formed by performing the extending | stretching and in-line slit which were mentioned above with respect to the original film 4 supplied from the roll.

  The obliquely stretched film 1 obtained by the production method of the present invention can be subsequently supplied to any step. For example, the film roll of the obliquely stretched film 1 may be obtained by being wound around a roll. At that time, after the step of removing the gripped portion, a step of forming a knurling portion on the end portions 2a and 2b remaining on the stretched film may be further performed, and then wound on a roll. When winding on a roll, a protective film (interleaf) may be inserted instead of forming the knurling portion. In addition, it may be supplied to a subsequent process such as formation of a coating layer or lamination with another film, or the strip-shaped obliquely stretched film 1 is cut to obtain an obliquely stretched film 1 having an arbitrary size and shape. Also good.

  The knurling process may be performed in the section until the film after stretching in the production line is wound, or without forming the knurling part, once the stretched film roll is formed and the formed roll is rewound. May be.

  The obtained obliquely stretched film 1 can be used as an optical film, for example. Examples of the optical film are as described above.

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

  Initially, the evaluation method of the characteristic of the thermoplastic resin produced in the manufacture example is shown.

[Glass transition temperature (Tg)]
The glass transition temperature (Tg) of the thermoplastic resin was determined in accordance with JIS K7121 regulations. Specifically, a differential scanning calorimeter (manufactured by Rigaku, DSC-8230) is used, and a sample of about 10 mg is heated from normal temperature to 200 ° C. (temperature increase rate: 20 ° C./min) in a nitrogen gas atmosphere. The DSC curve was evaluated by the starting point method. Α-alumina was used as a reference.

[Weight average molecular weight]
The weight average molecular weight of the thermoplastic resin was determined by gel permeation chromatography (GPC) in terms of polystyrene. The apparatus and measurement conditions used for the measurement are as follows.
System: Tosoh GPC system HLC-8220
Measurement side column configuration:
・ Guard column (Tosoh, TSKguardcolumn SuperHZ-L)
-Two separation columns (Tosoh TSKgel SuperHZM-M) connected in series Reference side column configuration:
Reference column (Tosoh, TSKgel SuperH-RC)
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade)
Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Column temperature: 40 ° C

[Melt flow rate (MFR)]
The melt flow rate (MFR) of the thermoplastic resin was determined in accordance with JIS K6874, with a test temperature of 240 ° C. and a test load of 10 kg.

[Intrinsic birefringence]
The positive and negative of the intrinsic birefringence of the thermoplastic resin constituting the film (original film and obliquely stretched film) was evaluated as follows. First, an 80 mm × 50 mm film piece was cut out from the produced unstretched original film, and uniaxially stretched at a stretching ratio of 2 times at Tg + 3 ° C. of the original film using an autograph (manufactured by Shimadzu Corporation) equipped with a heating chamber. Thus, a stretched film for evaluating intrinsic birefringence was obtained. At this time, since 20 mm at both ends in the longitudinal direction of the film piece was used as the allowance for attaching the chuck, the film piece was substantially stretched to a 40 mm × 50 mm portion. Next, the orientation angle of the obtained stretched film for evaluation was determined using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR), and thereby the positive and negative of the intrinsic birefringence of the resin composition constituting the film. It was determined. If the measured orientation angle is near 0 ° (that is, if the orientation direction of the polymer contained in the resin is substantially parallel to the stretching direction), the intrinsic birefringence of the thermoplastic resin constituting the film is positive. . If the measured orientation angle is around 90 ° (that is, if the orientation direction of the polymer contained in the resin is substantially perpendicular to the stretching direction), the intrinsic birefringence of the thermoplastic resin constituting the film is negative. .

(Production Example 1)
In a reaction vessel equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introduction pipe, 40 parts by weight of methyl methacrylate (MMA), 10 parts by weight of 2- (hydroxymethyl) methyl acrylate (MHMA), and ADEKA STAB as an antioxidant 0.025 parts by weight of 2112 (manufactured by ADEKA) and 50 parts by weight of toluene as a polymerization solvent were charged. Next, the temperature was raised to 105 ° C. while introducing nitrogen gas into the reaction vessel, and when refluxing began, tertiary amyl peroxyisononanoate (trade name: Luperox 570, manufactured by Arkema Yoshitomi) was used as a polymerization initiator. 05 parts by weight were added. At the same time, dropwise addition of 0.10 parts by weight of the above-mentioned tertiary amyl peroxyisononanoate was started, and solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C. while dropping over 2 hours. After completion of the dropwise addition, the reaction vessel was kept warm for 4 hours and aged.

  Next, 0.05 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry Co., Ltd., trade name: Phoslex A-8) is added to the polymerization solution thus obtained as a catalyst for the cyclization reaction. 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, heated to 240 ° C., and bent type screw twin screw extrusion in which a leaf disk type polymer filter (filtration accuracy 5 μm) was arranged at the tip via a gear pump. The polymerization solution was devolatilized by introducing into a machine (L / D = 52) at a treatment rate of 70 parts by weight / hour in terms of resin amount. The vent type screw twin screw extruder used had 1 rear vent and 4 fore vents (referred to as the first, second, third and fourth vents from the upstream side), and the third and fourth vents. A side feeder was placed between the barrel temperature of 240 ° C. and the degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg). At the time of devolatilization, 1.05 parts of ion-exchanged water was added from behind the first vent at a charging rate of 1.05 parts by weight / hour with a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator. Charges were made from behind the second and third vents, respectively, at an input speed of parts by weight / hour. As a mixed solution of an antioxidant / cyclization catalyst deactivator, 5 parts by weight of an antioxidant (manufactured by BASF Japan, Irganox 1010) and as a cyclization catalyst deactivator, 55 parts by weight of zinc octylate (Nippon Kagaku) A solution prepared by dissolving 45 parts by weight of toluene with a trade name of Nikka Octics Zinc (3.6%, manufactured by Sangyo) was used. Furthermore, pellets of a styrene-acrylonitrile copolymer (the ratio of styrene units / acrylonitrile units is 73% by weight / 27% by weight, weight average molecular weight 220,000) were charged from the side feeder at a charging rate of 30 parts by weight / hour. .

  Thereafter, the molten resin in the extruder is discharged from the tip of the extruder, pelletized by a pelletizer, containing an acrylic polymer having a lactone ring structure in the main chain, and a styrene-acrylonitrile copolymer, and a negative A pellet of thermoplastic resin (1A) having intrinsic birefringence was obtained. Resin (1A) had a Tg of 122 ° C., a weight average molecular weight of 146000, and an MFR of 13.6 g / 10 min. In the following measurement examples, examples and comparative examples, the pellets were used after being dried in dry air at 60 ° C. for 24 hours.

(Production Example 2)
MHMA 15 parts by weight, MMA 27 parts by weight, methyl acrylate (MA) 10 parts by weight, N-vinylcarbazole (NVCz) 6 parts by weight in a reaction vessel equipped with a stirrer, temperature sensor, cooling pipe, nitrogen introduction pipe and dropping funnel 37 parts by weight of toluene and 2 parts by weight of methanol were charged. Next, the temperature was raised to 95 ° C. while introducing nitrogen gas into the reaction vessel, and when refluxing began, tertiary amyl peroxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, trade name: Luperox) was used as a polymerization initiator. 575) 0.029 parts by weight were added. At the same time, dropping of a mixture of 15 parts by weight of MHMA, 27 parts by weight of MMA, 17 parts by weight of toluene and 0.082 parts by weight of tertiary amyl peroxy-2-ethylhexanoate was started, and this mixture was dropped over 8 hours. However, solution polymerization was allowed to proceed under reflux at about 90 ° C to 100 ° C. Further, after 5 hours from the start of polymerization, 23.3 parts by weight of toluene was dropped into the polymerization system over 3 hours to dilute the polymerization solution.

  Next, 0.24 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry, trade name: Phoslex A-8) as a catalyst for the cyclization reaction was added to the polymerization solution thus obtained, The cyclization condensation reaction 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., barrel temperature 250 ° C., degree of vacuum 13.3 to 400 hPa (10 to 300 mmHg), rear vent number 1 and fore vent number 4 (Referred to as the first, second, third and fourth vents from the upstream side), and a vent type screw twin screw extruder (L / D = 52) was introduced at a treatment rate of 100 parts by weight / hour in terms of resin amount, and the polymerization solution was devolatilized. At the time of devolatilization, a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator is charged with 0.5% by weight of ion exchange water from the back of the second vent at a rate of 1.5 parts by weight / hour. Each was added from behind the third vent at an input speed of parts by weight / hour. In the mixed solution of antioxidant / cyclization catalyst deactivator, 10 parts by weight of antioxidant (5 parts by weight of BASF Japan, Irganox 1010 and 5 parts by weight of ADEKA, ADK STAB AO-412S) A solution obtained by dissolving 80 parts by weight of zinc octylate (manufactured by Nippon Chemical Industry Co., Ltd., trade name: 3.6% of Nikka octix zinc) as a cyclization catalyst deactivator in 65 parts by weight of toluene was used.

  Thereafter, the molten resin in the extruder is discharged from the tip of the extruder, pelletized by a pelletizer, and includes an acrylic polymer having a lactone ring structure in the main chain and an N-vinylcarbazole unit as a structural unit. A pellet of thermoplastic resin (2A) was obtained. The resin (2A) had a Tg of 132 ° C. and a weight average molecular weight of 110,000.

(Production Example 3)
In a pressure-resistant reaction vessel equipped with a stirrer, 70 parts by weight of deionized water, 0.5 parts by weight of sodium pyrophosphate, 0.2 parts by weight of potassium oleate, 0.005 parts by weight of ferrous sulfate, 0.2 parts by weight of dextrose Then, a reaction mixture consisting of 0.1 parts by weight of p-menthane hydroperoxide and 28 parts by weight of 1,3-butadiene was added, the temperature in the container was raised to 65 ° C., and polymerization was allowed to proceed for 2 hours. Next, 0.2 parts by weight of p-hydroperoxide was further added to the mixture in the container obtained by this polymerization, and then 72 parts by weight of 1,3-butadiene, 1.33 parts by weight of potassium oleate and desorption were performed. A mixture of 75 parts by weight of ionic water was continuously added dropwise over 2 hours. Thereafter, the polymerization was allowed to proceed until 21 hours had elapsed from the start of polymerization to obtain a butadiene-based rubber polymer latex having an average particle size of 0.240 μm.

  Next, in a polymerization vessel equipped with a cooler and a stirrer, 120 parts by weight of deionized water, 50 parts by weight of a butadiene rubber polymer latex (in terms of solid content), 1.5 parts by weight of potassium oleate and sodium formaldehyde sulfone. 0.6 parts by weight of xylate (SFS) was added, and the inside of the polymerization vessel was sufficiently replaced with nitrogen gas.

  Next, after raising the temperature in the container to 70 ° C., a mixed monomer solution comprising 36.5 parts by weight of styrene and 13.5 parts by weight of acrylonitrile, 0.27 parts by weight of cumene hydroxyperoxide and 20 deionized water. The polymerization was advanced while continuously dropping dropwise a polymerization initiator solution consisting of 0.0 part by weight over 2 hours. After completion of the dropping, the temperature in the container was set to 80 ° C., and the polymerization was further continued for 2 hours. Next, after the temperature in the container was lowered to 40 ° C., the contents were passed through a 300-mesh wire mesh to obtain an emulsion polymerization liquid of elastic organic fine particles.

  The obtained emulsion polymerization liquid of elastic organic fine particles is salted out and coagulated with calcium chloride, and the solidified product is washed with water and dried to obtain powdered elastic organic fine particles (G1) (average particle size 0.260 μm, soft A refractive index of 1.516) of the polymer layer was obtained.

(Production Example 4)
Pellet of thermoplastic resin (2A) produced in Production Example 2, elastic organic fine particles (G1) produced in Production Example 3 and styrene-acrylonitrile copolymer (the ratio of styrene units / acrylonitrile units is 73% by weight / 27% by weight And a weight average molecular weight of 220,000) were kneaded at a mixing ratio of 81: 14: 5 (weight basis) at 240 ° C. using a twin-screw extruder to obtain transparent thermoplastic resin (3A) pellets. The Tg of resin (3A) was 129 ° C. In the following measurement examples, examples and comparative examples, the pellets were used after being dried in dry air at 60 ° C. for 24 hours.

(Measurement Example 1)
In Measurement Example 1, the impact strength of the thermoplastic resins (1A) and (3A) and polycarbonate (manufactured by Teijin Chemicals, Panlite L-1225Y) produced in Production Examples 1 and 4 was evaluated.

  The evaluation was performed by carrying out an impact test in conformity with the provisions of ASTM-D3420 on unstretched films of each thermoplastic resin (thickness: 250 μm, and for polycarbonate: 250 μm and 20 μm). In the test, an impact (impact) is instantaneously applied to the film, and the strength (impact strength) of the impact at which the film is broken is evaluated. The unstretched film was formed by melt extrusion at 270 ° C. using a single screw extruder equipped with a polymer filter (filtration accuracy: 5 μm) and a 600 mm wide T-die at the tip. Although the width of the formed unstretched film was 520 mm, the impact test was performed at the center in the width direction of the unstretched film.

  The evaluation results are shown in Table 1 below. Regarding polycarbonate, since the film did not break when the thickness was 250 μm, the thickness of the film was set to 20 μm, and the process was repeated.

  As shown in Table 1, the impact strength of the polycarbonate was greater than that of the resin (1A) and the resin (3A).

(Measurement example 2)
The unstretched film having a thickness of 250 μm produced in Measurement Example 1 was uniaxially stretched at a free end at a stretching temperature and a stretching ratio of 2 times higher than the Tg of the thermoplastic resin constituting the film to obtain a uniaxially stretched film. It was. When the obtained stretched film was torn by hand in the stretching direction (direction of the stretching axis), the stretched film composed of the resin (1A) and the stretched film composed of the resin (3A) were torn by hand. I was able to. On the other hand, a stretched film made of polycarbonate could not be torn by hand.

  That is, the tear strength of polycarbonate was higher than that of the resin (1A) and the resin (3A).

(Measurement Example 3)
The unstretched film having a thickness of 250 μm prepared in Measurement Example 1 and the uniaxially stretched film prepared in Measurement Example 2 were allowed to stand for 1 hour or more in an atmosphere having a temperature of 25 ° C. and a relative humidity of 65% RH. A test sample having a width of 15 mm and a length of 60 mm was cut out. For unstretched films, the flow direction during production of the film is the length direction of the test sample, and for uniaxially stretched films, the stretch direction during production is the width direction of the test sample. It was. Using the folding tester (Toyo Seiki Seisakusho, MIT-DA type) for the cut out test samples, each folding resistance was evaluated under the condition of a load of 50 g in accordance with JIS P8115. The evaluation results are shown in Table 2 below. In Table 2, “0 times” indicates that the test sample was broken when the folding clamp was swung up once in order to start the measurement of the folding endurance, and the reciprocal bending could not be performed once. “One time” indicates that the test sample was broken by one reciprocal bending, although it withstood the folding clamp for starting the measurement of the number of folding times. Evaluation was performed 3 times.

  As shown in Table 2, the folding strength of the polycarbonate was larger than that of the resin (1A) and the resin (3A). In addition, about the polycarbonate, since it was confirmed that the bending strength was higher than that of the resin (1A) and the resin (3A), the evaluation was stopped when the number of times exceeded ten.

Example 1
Polycarbonate obtained by drying the thermoplastic resin (1A) produced in Production Example 1 from a single-screw extruder S1 (set temperature 270 ° C.) equipped with a polymer filter (filtering accuracy 5 μm) in dry air at 100 ° C. for 24 hours (Teijin) Kasei, Panlite L-1225Y) is melt-extruded from a single-screw extruder S2 (set temperature: 270 ° C.) equipped with a polymer filter (filtration accuracy 5 μm), and feeds in the width direction as polycarbonate / resin (1A) / polycarbonate. The block was melt-extruded into a film with a T-die through a block to form an unstretched resin film (original film) having a thickness of 150 μm. The formed strip-shaped original film was trimmed in-line at the end in the width direction so as to have a width of 540 mm, and wound on a roll. In addition, each arrangement | positioning and distribution of the resin of the width direction in the original film after trimming are each from single screw extruder S1 and S2 so that it may become polycarbonate (100 mm) / resin (1A); (340 mm) / polycarbonate (100 mm). The amount of resin discharged was adjusted. The polycarbonate portion is the end portions 5a and 5b in the original film 4, and the resin (1A) portion is the center portion 6. The distribution of the resin in the width direction is such that the position where the transmission image of the original film is blurred due to the difference in refractive index between the polycarbonate and the resin (1A) is visually confirmed, and the distance between the position and the long side of the original film is measured with a metal ruler. Measured and confirmed.

  Next, the original film is continuously drawn out from the produced roll, and the drawn-out original film is simultaneously biaxial in which a preheating zone Z1, a front drawing zone Z2, a rear drawing zone Z3, and a heat treatment zone Z4 are set as shown in FIG. Diagonal stretching was performed using a stretching machine.

  The simultaneous biaxial stretching machine used for the oblique stretching is a pair of rails (left clip rail and right clip rail) on which a pair of clips composed of a plurality of clips travels, and from the upstream side to the downstream side of the original film. A heating furnace in which a preheating zone Z1, a front-stage stretching zone Z2, a rear-stage stretching zone Z3, and a heat treatment zone Z4 were set in order was provided. The shape of the left clip rail and the shape of the right clip rail were symmetric with respect to a straight line extending in the longitudinal direction of the original film, which was divided into two in the width direction when viewed from above the simultaneous biaxial stretching machine. In other words, in the left clip rail and the right clip rail, the midpoints of the line segments connecting the points equidistant from the entrance of the preheating zone are always on the straight line (center line). At the boundary between the zones on both the left and right rails, a rail portion was adjusted, and a joint portion was provided to enable combined use of lateral stretching in the front stretching zone and the rear stretching zone. In the front stretching zone Z2, the traveling speed of the clip group (left clip group) traveling on the left rail is decreased, and in the rear stretching zone Z3, the traveling speed of the left clip group decelerated in the preceding stretching zone Z2 is reduced to the traveling speed before deceleration. Recovered. The traveling speed of the left and right clip groups (traveling speed at the left and right clip-in portions) when gripping the belt-shaped original film was set to 2.0 m / min. The position where the clip group grips the original film was 25 mm from the end in the width direction of the film (the grip margin was 25 mm for both the left and right clip groups). The length of each stretching zone (length in the flow direction of the original film) was the same.

  In Example 1, the original film was stretched obliquely according to the stretching conditions shown in Tables 3 and 4 below. As shown in Table 4, in the former drawing zone Z2 and the latter drawing zone Z3, a difference in running speed was given to the left and right clip groups, and the original film was drawn obliquely. Moreover, in the front | former stage extending | stretching zone Z2 and the back | latter stage extending | stretching zone Z3, the horizontal extending | stretching which increases the space | interval between the clip groups on either side with respect to the width direction of an original film was used together. In other sections through which the original film passes from clip-in to clip-out, the traveling speed of the left and right clip groups and the interval are maintained without change. However, in the preheating zone Z1 and heat treatment zone Z4, fine adjustments were made to the running speed of the clip group and the distance between the clip groups for the purpose of eliminating the looseness of the original film due to heating and adjusting the shrinkage stress generated in the film during cooling. did. Moreover, the fluctuation | variation to such an extent that the traveling speed of a clip group usually arises by the stress which arises in the case of diagonal extending | stretching was shown.

  The left (right) clip magnification of each stretching zone shown in Table 4 is an indicator of the change in the running speed of the left (right) clip group in each stretching zone. Specifically, the ratio of the traveling speed of the left (right) clip group at the exit of each stretching zone to the traveling speed of the left (right) clip group at the entrance of each stretching zone is the clip magnification. When the clip magnification is 1, the traveling speed of the clip group in the stretching zone is constant, and when the clip magnification is less than 1, it decreases, and when it exceeds 1, it indicates that it increases. The total clip magnification is a value obtained by multiplying the clip magnification in the former drawing zone by the clip magnification in the latter drawing zone. When this value is 1, the traveling speed of the clip group at the entrance of the former drawing zone and the latter drawing It shows that the traveling speed of the clip group at the exit of the zone is equal. In the example shown in Table 4, since the total clip magnification is 1 in both the left and right clip groups, it indicates that the traveling speed at the time of clip-in was maintained except for each stretching zone. Further, regarding the right clip group, the clip magnification in each stretching zone is also 1, indicating that the traveling speed was constant from clip-in to clip-out. Note that “constant”, “equal”, and “maintained” allow the above-described fine adjustment of the traveling speed and fluctuations in the traveling speed of the clip group due to wobbling.

  In order to carry out the horizontal stretching at a constant ratio, the clip rail was set to be straight through the front stretching zone and the rear stretching zone on both the left and right sides. However, with respect to the transverse stretching, in Table 4, the magnification in each stretching zone is different from each other. This is because the transverse draw ratio in each drawing zone is based on the width of the original film after the transverse drawing in the immediately preceding drawing zone.

  Next, the resin film that has been obliquely stretched in this manner is discharged from the heat-stretching machine, clipped out, passed through the first and second guide rolls, and then the end of the stretched film (polycarbonate) Part) was removed by in-line trimming using a shear cutter so that the end part remained in the center part (resin (1A) part) by a width of 50 mm. Thereafter, the stretched film (the end in the width direction is made of polycarbonate, the portion other than the end is made of resin (1A), and the stretching axis is inclined with respect to the width direction and the length direction. Film) was wound up on a roll after a polyethylene protective film was bonded together.

  In Example 1, it is possible to produce a stable obliquely stretched film without breakage of the original film and the stretched film at the time of stretching and inline slit, and the obliquely stretched film is continuously produced over a length of 500 m. I was able to. Since the supply of the original film was 500 m, the production of the obliquely stretched film was finished at a length of 500 m, but the situation in which the obliquely stretched film having a further length can be continuously produced by supplying a longer original film. Met. Moreover, although the state of generation | occurrence | production of the wrinkles and a crack in the manufactured diagonally stretched film was confirmed visually, generation | occurrence | production of a wrinkle and a crack was not confirmed. The rolled form of the obtained film roll was also good.

(Example 2)
In Example 2, instead of attaching a protective film when winding the film after the in-line slit, a knurling part is formed on the end (polycarbonate part) remaining on the film after the in-line slit, and the film is wound up. It was a roll. The knurling part was formed so that the center line thereof was positioned 10 mm from the long sides of the left and right sides of the film after the inline slit. The height of the knurling part was 24 μm.

  In Example 2, it is possible to produce a stable obliquely stretched film without breakage of the original film and the film after stretching at the time of stretching and inline slit, and the obliquely stretched film is continuously produced over a length of 500 m. I was able to. Since the supply of the original film was 500 m, the production of the obliquely stretched film was finished at a length of 500 m, but the situation in which the obliquely stretched film having a further length can be continuously produced by supplying a longer original film. Met. Moreover, although the state of generation | occurrence | production of the wrinkles and a crack in the manufactured diagonally stretched film was confirmed visually, generation | occurrence | production of a wrinkle and a crack was not confirmed. The rolled form of the obtained film roll was also good.

(Example 3)
A film roll was obtained in the same manner as in Example 2 except that the thermoplastic resin (3A) produced in Production Example 4 was used instead of the thermoplastic resin (1A) produced in Production Example 1.

  In Example 3, it is possible to produce a stable obliquely stretched film without breaking the original film and the film after stretching at the time of stretching and inline slit, and the obliquely stretched film is continuously produced over a length of 500 m. I was able to. Since the supply of the original film was 500 m, the production of the obliquely stretched film was finished at a length of 500 m, but the situation in which the obliquely stretched film having a further length can be continuously produced by supplying a longer original film. Met. Moreover, although the state of generation | occurrence | production of the wrinkles and a crack in the manufactured diagonally stretched film was confirmed visually, generation | occurrence | production of a wrinkle and a crack was not confirmed. The rolled form of the obtained film roll was also good.

(Comparative Example 1)
An unstretched film of the resin (1A) was formed in the same manner as in Example 1 except that the feed block was not used and a single resin film of only the thermoplastic resin (1A) was used. The formed strip-shaped original film was trimmed in-line at the end in the width direction so as to have a width of 540 mm, and wound on a roll.

  Next, production of an obliquely stretched film roll was attempted in the same manner as in Example 1 using the produced roll. However, the stretched film discharged from the heat stretching machine frequently breaks as shown in the following (1) to (3), and only an oblique stretched film having a length of about several meters could be produced.

  (1) When the stretched film passes through the first roll and the guide roll after the roll, the film is present at the end portion in the width direction of the resin film and held by the clip at the time of stretching. The raised wrinkles could not follow the curvature of the roll, and cracks occurred from the wrinkles. In some cases, cracks grew rapidly and the stretched film was broken.

  (2) From the part of the inline slit with respect to the stretched film, the cut surface extended faster than the running speed of the film, and the film was broken. When the rising crease generated in the part held by the clip at the time of stretching exceeds the guide roll, the impact is transmitted to the film, so that the running of the film in the slit part becomes unstable, and the cut surface extends and breaks. Conceivable. Note that when rupture events were observed closely, rupture from the side (R1 to R9 side shown in FIG. 8) on which the right clip was gripped occupied most cases. This is presumably because the breakage from the side easily proceeded from the relationship between the direction of the stretching axis and the traveling direction of the film after stretching.

  (3) A part of the slit end portion was broken, and the film travel in the vicinity of the slit portion was not stabilized by the impact at that time, and wrinkles were generated in some cases. And when the generated wrinkle reached the blade portion of the slit, the film broke. In addition, when the phenomenon which a part of edge part fracture | ruptures was observed closely, the fracture | rupture of the side (L1-L10 side shown in FIG. 8) which the left clip was holding occupied most cases. This is presumably because the breakage from the side easily proceeded from the relationship between the direction of the stretching axis and the traveling direction of the film after stretching.

(Comparative Example 2)
An unstretched film of the resin (3A) was formed in the same manner as in Comparative Example 1 except that the thermoplastic resin (3A) was used instead of the thermoplastic resin (1A). The formed strip-shaped original film was trimmed in-line at the end in the width direction so as to have a width of 540 mm, and wound on a roll.

  Next, production of an obliquely stretched film roll was attempted in the same manner as in Example 3 using the produced roll. However, the stretched film discharged from the heat stretching machine frequently breaks as shown in the following (1) to (3), and only an oblique stretched film having a length of about several meters could be produced.

  (1) When the stretched film passes through the first roll and the guide roll after the roll, the film is present at the end portion in the width direction of the resin film and held by the clip at the time of stretching. The raised wrinkles could not follow the curvature of the roll, and cracks occurred from the wrinkles. In some cases, cracks grew rapidly and the stretched film was broken.

  (2) From the part of the inline slit with respect to the stretched film, the cut surface extended faster than the running speed of the film, and the film was broken. When the rising crease generated in the part held by the clip at the time of stretching exceeds the guide roll, the impact is transmitted to the film, so that the running of the film in the slit part becomes unstable, and the cut surface extends and breaks. Conceivable. In addition, when the event of a fracture | rupture was observed closely, like the comparative example 1, the fracture | rupture from the side which the right side clip was grasping occupied most cases. This is presumably because the breakage from the side easily proceeded from the relationship between the direction of the stretching axis and the traveling direction of the film after stretching.

  (3) A part of the slit end portion was broken, and the film travel in the vicinity of the slit portion was not stabilized by the impact at that time, and wrinkles were generated in some cases. And when the generated wrinkle reached the blade portion of the slit, the film broke. When the phenomenon that a part of the end portion was broken was observed closely, as in Comparative Example 1, the break on the side that was held by the left clip occupied most cases. This is presumably because the breakage from the side easily proceeded from the relationship between the direction of the stretching axis and the traveling direction of the film after stretching.

  Moreover, formation of a knurling part was tried similarly to Example 2 with respect to the edge part of the diagonally stretched film obtained only several meters, However, The crack and perforation occurred frequently in the knurling part formed.

  The diagonally stretched film of this invention can be used for the same use as the conventional stretched film. An example of an application is an optical film.

1 Obliquely stretched film (film after stretching)
2a, 2b (end of the stretched film) 3 (center of the stretched film) 4 original film 5a, 5b (original film) end 6 (original film) center 7 (removed by inline slit) Part 11 Stretching shaft 12 Knurling part 21 Heating and stretching device 22 Clip-out part 23 First roll 24 Second roll 25 Cutter Z1 Preheating zone Z2 Pre-stage stretching zone Z3 Rear-stage stretching zone Z4 Heat treatment zone CIL, CIR Clip-in part COL, COR Clip-out part

Claims (15)

At least one end portion for one direction selected from the width direction and the length direction, and a portion other than the end portion are composed of different thermoplastic resins,
Compared to the thermoplastic resin constituting the portion other than the end portion, the bending strength exhibited by the thermoplastic resin constituting the end portion is large,
An obliquely stretched film in which a stretched axis is inclined with respect to the width direction and the length direction. The obliquely stretched film is strip-shaped,
The said edge part is a diagonally stretched film of Claim 1 which is the edge part of the width direction of the said strip-shaped diagonally stretched film.   The diagonally stretched film according to claim 1 or 2, wherein the impact strength exhibited by the thermoplastic resin constituting the end portion is greater than that of the thermoplastic resin constituting the portion other than the end portion.   The diagonally stretched film according to any one of claims 1 to 3, which has a knurling portion at the end.   The diagonally stretched film according to any one of claims 1 to 4, wherein the thermoplastic resin constituting the portion other than the end portion is an acrylic resin or a styrene resin.   The diagonally stretched film according to any one of claims 1 to 4, wherein the thermoplastic resin constituting the portion other than the end portion is an acrylic resin containing an acrylic polymer having a ring structure in the main chain.   The diagonally stretched film according to any one of claims 1 to 6, wherein the thermoplastic resin constituting the end portion includes at least one selected from polycarbonate and polyester.   The diagonally stretched film according to any one of claims 1 to 7, which is an optical film. The original film is obliquely stretched by a traveling movement of a clip holding the end in the width direction of the belt-shaped original film, thereby obtaining an obliquely stretched film whose stretching axis is inclined with respect to the length direction and the width direction of the original film. A method for producing an obliquely stretched film,
After the original film is obliquely stretched, the end portion of the end portion of the film that has been stretched is held by the clip so that a part of the end portion remains in the film after stretching. Including a step of removing by an in-line slit,
The end portion of the original film and the portion other than the end portion are composed of different thermoplastic resins,
The manufacturing method of the diagonally stretched film whose bending strength which the thermoplastic resin which comprises the said edge part shows compared with the thermoplastic resin which comprises parts other than the said edge part is large.   The manufacturing method of the diagonally stretched film of Claim 9 with which the impact strength which the thermoplastic resin which comprises the said edge part shows compared with the thermoplastic resin which comprises parts other than the said edge part is large. After the step of removing the gripped portion,
The manufacturing method of the diagonally stretched film of Claim 9 or 10 which further includes the process of forming a knurling part in the said edge part which remained in the said film after extending | stretching.   The manufacturing method of the diagonally stretched film in any one of Claims 9-11 whose thermoplastic resin which comprises parts other than the said edge part is an acrylic resin or a styrene resin.   The manufacturing method of the diagonally stretched film in any one of Claims 9-11 whose thermoplastic resin which comprises parts other than the said edge part is an acrylic resin containing the acrylic polymer which has a ring structure in a principal chain.   The manufacturing method of the diagonally stretched film in any one of Claims 9-13 in which the thermoplastic resin which comprises the said edge part contains at least 1 sort (s) chosen from a polycarbonate and polyester.   The manufacturing method of the diagonally stretched film in any one of Claims 9-14 whose said diagonally stretched film is an optical film.

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