JP2008155436A - Biaxially stretched resin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched resin film in which the occurrence of a rainbow pattern is suppressed in the inspection of a cross-Nicols method. <P>SOLUTION: In the biaxially stretched resin film, layers each containing a polyethylene terephthalate based resin (A) and layers each containing a syndiotactic polystyrene based resin (B) are laminated alternately to form at least five layers, the absolute value of retardation measured by a polarization microscope using a Berek compensator is 500 nm or below, and the content of an ethylene terephthalate cyclic trimer as a polyethylene terephthalate oligomer of the polyethylene terephthalate based resin (A) is 0.7 wt.% or below. Preferably, the mass ratio of the polyethylene terephthalate based resin (A) to the syndiotactic polystyrene based resin (B) is 10/90-90/10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biaxially stretched resin film suitable for various uses such as various food packaging, general industrial use, optical use, electric material use, and molding processing.

  Biaxially stretched films made of polyethylene terephthalate (PET) are excellent in mechanical properties, heat resistance, flatness and the like, and thus are used in various fields.

  As one of them, there is a release polyester film used in defect inspection by a crossed Nicols method of a polarizing plate (for example, see Patent Document 1). The crossed Nicols method inspects two polarizing plates so that their orientation principal axes are orthogonal to each other and extinguish them, and if there are foreign objects or defects in the polarizing plates, they will appear as bright spots, so visual defect inspection can be performed. Usually, it is carried out with a release polyester film sandwiched between two polarizing plates. When a biaxially stretched PET film is used as the release film, a rainbow pattern (color stripe that appears with a rainbow-like color) is generated due to the large birefringence of the film, and this is a cross-Nicol method inspection. In some cases, there is a problem that foreign matter in the polarizing plate or defects are easily overlooked.

  In the above crossed Nicols method, foreign objects and defects in the film sandwiched between the polarizing plates are detected as bright spots in the same way as foreign objects in the polarizing plate, so the foreign objects and defects in the film are detected by the crossed Nicols method. There has also been proposed a method (see, for example, Patent Document 2). However, in the case of a biaxially stretched PET film, a rainbow pattern derived from the above-described birefringence is generated, and this rainbow pattern becomes an obstacle to the inspection by the crossed Nicols method.

The generation of the rainbow pattern as described above is not preferable not only in the case of the defect inspection of the polarizing plate and the foreign matter inspection of the film, but also in applications where the film is required to have transparency and transparency, for example. Further, it is desirable that such a rainbow pattern is not easily generated not only when observed from a position perpendicular to the film surface but also when observed from various angles with respect to the normal direction of the film. . In particular, when the release film is used as a protective film for a polarizing plate, the incorporation into various devices is performed with the release film provided on the polarizing plate, but in order to improve the operability of this assembly operation, A film in which the generation of the rainbow pattern as described above is suppressed is desired.
JP-A-2005-15726 JP 2005-49158 A

  An object of the present invention is to provide a biaxially stretched resin film in which generation of a rainbow pattern is suppressed and high transparency is obtained in an inspection by a crossed Nicol method.

  As a result of intensive studies by the present inventors, syndiotactic polystyrene resin was used as a raw material in addition to polyethylene terephthalate resin, and a multilayer structure in which polyethylene terephthalate resin layers and syndiotactic polystyrene resin layers were alternately laminated And the inventors found that the above problem can be solved by making the absolute value of the retardation measured with a polarizing microscope using a Belek compensator below a specific value.

  That is, in the present invention, a layer containing a polyethylene terephthalate resin (A) and a layer containing a syndiotactic polystyrene resin (B) are alternately laminated to form five or more layers, and a Berek compensator is used. The biaxially stretched resin film is characterized in that the absolute value of retardation measured by a polarizing microscope is 500 nm or less.

  The retardation value indicates the degree of the birefringence of the film. In the present invention, the absolute value of the retardation measured by a polarizing microscope using a Belek type compensator is used as the rainbow pattern of the film. Adopted as an indicator of the occurrence of Since the evaluation with the polarizing microscope using the above Belek type Compensator uses white light, it is considered that the evaluation can be more realistic than the evaluation with the Abbe refractometer using light of a specific wavelength. It is done.

  Furthermore, in the film of the present invention, the content of the ethylene terephthalate cyclic trimer as the polyethylene terephthalate oligomer of the polyethylene terephthalate resin (A) is preferably 0.7% by weight or less.

  The mass ratio of the polyethylene terephthalate resin (A) and the syndiotactic polystyrene resin (B) in the film of the present invention is preferably 10/90 to 90/10.

  The film of the present invention preferably has a haze of 2% or less in order to exert the effects of the present invention. From the viewpoint of productivity, the film in the vertical direction and the horizontal direction when heat-treated at 150 ° C. for 30 minutes is preferable. The heat shrinkage rate is preferably 3% or less. Furthermore, it is desirable that the film of the present invention be simultaneously biaxially stretched.

  According to the present invention, since there is almost no rainbow pattern in the cross-Nicol method inspection, when the film of the present invention is used as a release film for the cross-Nicol method inspection of the polarizing plate, foreign matter in the polarizing plate is mixed. And defects can be found easily. In addition, even when foreign matter or a defect in the film of the present invention is detected by the inspection by the crossed Nicols method, since the detection is easy, it is possible to ensure the inspection. Therefore, the film of the present invention can be supplied with high reliability as a film product for various uses such as food packaging, general industrial use, optical use, electric material use, and molding processing. Furthermore, according to the present invention, since the precipitation of the oligomer of the polyethylene terephthalate resin is suppressed, the transparency of the film of the present invention is improved, and the polarizing plate using the film of the present invention as a release film is used in the crossed Nicols method. When subjected to inspection or by inspection by the crossed Nicols method, it is possible to maintain high accuracy of inspection when detecting foreign matter and defects in the film of the present invention, and for various food packaging, molding processing, etc. When used as a film for various applications, contamination of a packaging object or a mold can be reduced.

  The biaxially stretched resin film of the present invention includes a layer containing a polyethylene terephthalate-based resin (A) and a layer containing a syndiotactic polystyrene-based resin (B), which are alternately laminated in five or more layers. It is characterized in that the absolute value of retardation measured by a polarizing microscope using a compensator is 500 nm or less. A biaxially stretched resin film having the above characteristics is less likely to generate a rainbow pattern when observed through a polarizing plate.

  First, the polyethylene terephthalate resin (A) contained in the biaxially stretched film according to the present invention will be described. The polyethylene terephthalate resin (A) (hereinafter also referred to as resin (A)) used in the present invention is composed mainly of polyethylene terephthalate (PET). The polyethylene terephthalate resin (A) may be a homopolymer or a copolymer obtained by copolymerizing other copolymerizable components. Examples of copolymerizable acid components include isophthalic acid, naphthalenedicarboxylic acid, diphenic acid, phthalic acid and other aromatic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids, adipic acid, dimer acid, and sebacin. Examples include acids, aliphatic dicarboxylic acids such as dodecanedioic acid, eicoic acid, polyfunctional acids such as trimellitic acid and pyromellitic acid, polylactic acid, polyglycolic acid, poly (2-oxybutyric acid), and derivatives thereof. . Examples of the copolymerizable alcohol component include propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, and their Derivatives.

  When a copolymer is used as the polyethylene terephthalate resin (A), the copolymerizable acid component is 50 mol% or less, preferably 30 mol% or less, out of 100 mol% of the total acid component of the copolymer. More preferably, it is 10 mol% or less. The copolymerizable alcohol component is 50 mol% or less, preferably 30 mol% or less, more preferably 10 mol% or less, in 100 mol% of all alcohol components of the copolymer.

  The reduced viscosity (ηsp / c) of the resin (A) is preferably 0.55 to 1.10, more preferably 0.58 to 1.00. When the reduced viscosity of the resin (A) is less than 0.55, it becomes difficult to obtain a film having mechanical strength that can be practically used. On the other hand, when the reduced viscosity of the resin (A) exceeds 1.10, The operability during film production may deteriorate.

  In the present invention, in addition to the polyethylene terephthalate resin (A), syndiotactic polystyrene resin (B) is used (hereinafter also referred to as resin (B)). Here, the syndiotactic polystyrene resin is mainly composed of a polystyrene polymer having a syndiotactic structure. Examples of the polystyrene-based polymer include polystyrene, poly (p-, m- or o-methylstyrene), poly (2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene), poly Poly (alkylstyrene) such as (p-tertiarybutylstyrene); poly (p-, m- or o-chlorostyrene), poly (p-, m- or o-bromostyrene), poly (p-, m -Or o-fluorostyrene), poly (halogenated styrene) such as poly (o-methyl-p-fluorostyrene); poly (halogen-substituted alkylstyrene) such as poly (p-, m- or o-chloromethylstyrene) ); Poly (alkoxystyrene) such as poly (p-, m- or o-methoxystyrene), poly (p-, m- or o-ethoxystyrene); poly ( Poly (carboxyalkyl styrene) such as-, m- or o-carboxymethyl styrene); poly (alkyl ether styrene) such as poly (p-vinylbenzylpropyl ether); poly (alkyl such as poly (p-trimethylsilyl styrene) Silyl styrene); and poly (vinyl benzyl dimethoxy phosphide). Of these, polystyrene is preferred.

In the present invention, a polystyrene-based polymer having a syndiotactic structure refers to phenyl groups (in some cases, substituted phenyl groups) that are side chains with respect to the main chain formed from carbon-carbon bonds, which are alternately positioned in opposite directions. It means a polystyrene-based polymer mainly having a three-dimensional structure. The polystyrene-based polymer having a syndiotactic structure used in the film according to the present invention is a value determined by a nuclear magnetic resonance method ( ¹³ C-NMR method), and is a diat (two constituent units) and r (rasemo). Is preferably 85% or more, pentad (5 structural units), and rrrr is 50% or more.

  In the present invention, the polystyrene-based polymer having the syndiotactic structure may be mixed with an isotactic structure polymer or an atactic structure polymer as long as the tacticity of all polymers is within the above range. The polystyrene polymer having the syndiotactic structure may be a resin copolymerized with other types of monomers within a range not impairing the effects of the present invention as long as the tacticity is within the above range.

  The weight average molecular weight of the resin (B) is preferably 10,000 to 1,500,000, more preferably 30,000 to 1,000,000, still more preferably 50,000 to 500,000. If the molecular weight is too large, the workability during film forming may be inferior. If it is too small, it may be difficult to obtain a film having mechanical strength that can be practically used.

In the film of the present invention, the mass ratio of the resin (A) to the resin (B) is preferably 10/90 to 90/10 as resin (A) / resin (B), and 20/80 to 80 / 20 is more preferable, and 30/70 to 70/30 is most preferable.

  Resin (A) and resin (B) may contain particles. By adding the particles, the film of the present invention can be provided with handling properties when the film is produced, when the film is wound into a roll, or when the film is unwound. Examples of particles that can be used include inorganic particles such as silica, kaolin, clay, calcium carbonate, aluminum oxide, barium sulfate, zinc oxide, and zinc sulfide; organic particles such as crosslinked acrylic particles, crosslinked styrene particles, and silicone particles. It is done. Moreover, the particle | grains which have an effect equivalent to what was illustrated can also be used. Of these, silica is preferred.

  For the resin (A) and the resin (B), conventionally known additives such as a lubricant, a stabilizer, a colorant, an antioxidant, an antifoaming agent, an antistatic agent, an ultraviolet absorber, and the like, if necessary. May be blended.

  The film according to the present invention has a structure in which a layer containing a resin (A) and a layer containing a resin (B) are alternately stacked in the thickness direction, and preferably have a structure of 11 layers or more. More preferably, it has a laminated structure of 30 layers or more. If the number of layers is 4 or less, the absolute value of retardation measured by a polarizing microscope using a Belek type compensator may be difficult to be 500 nm or less, and the reduction effect of rainbow pattern generation may be reduced.

  The biaxially stretched resin film according to the present invention has an absolute value of retardation of 500 nm or less as measured by a polarizing microscope using a Berek type compensator. The absolute value of the retardation indicates the degree of birefringence of the film. The smaller the absolute value of retardation, the lower the birefringence of the film. It can be said that the pattern hardly occurs. The absolute value of the retardation is preferably 400 nm or less, more preferably 300 nm or less, and still more preferably 200 nm or less. If the absolute value of retardation is in the above range, the effect of reducing the generation of rainbow patterns is great, and it can be said that the rainbow patterns are hardly generated regardless of the observation position of the film.

  The method for measuring the absolute value of the retardation is also described, for example, in “Introduction to Polarizing Microscopes for Polymer Materials” (authored by Hiroshi Ashiya) published by Agne Technical Center. Is a measured value.

  On the sample stage of a polarizing microscope (for example, ECLIPSE E600 POL manufactured by Nikon Corporation, light source: white light) adjusted so that the polarization axis directions of the polarizer (polarizer) and analyzer (analyzer) are orthogonal to each other (crossed Nicols) Then, a measurement sample having a 1 cm square film sandwiched between the slide glass and the cover glass is placed, and the sample stage is rotated so that the field of view becomes the darkest (quenching position). Next, insert a Belek Compensator (manufactured by Nihon Geoscience) and rotate the sample stage 45 degrees from the extinction position in the + or-direction to change the interference color of the sample film and the rotation direction of the sample stage. From the above, the birefringence of the film is determined.

  Next, the inserted Berek compensator is removed, the sample stage is rotated 45 ° from the extinction position in the direction of the birefringence of the film, and the Berek compensator is inserted again. When the knob of the Berek compensator is turned clockwise and counterclockwise from the 30 ° position, the scale angles when the black band appearing at this time is aligned with the center of the field of view are set as a and b, respectively, and i = (a− b) The compensation value i is calculated by the calculation formula of / 2. From the value of i, a 10000 f (i) value is obtained using a numerical table attached to the Berek compensator, and this is multiplied by a correction constant C / 10000 specific to the Berek compensator to obtain the retardation of the sample film. .

  Further, the biaxially stretched resin film of the present invention has a birefringence index ΔP of 0.05 or less in each direction of 0 °, 45 °, 90 ° and 135 ° of the film as measured by the method described in the examples described later. Preferably, it is 0.01 or less, more preferably 0.005 or less. When the birefringence ΔP exceeds 0.05, a rainbow pattern is observed remarkably. Since the birefringence ΔP is preferably as close to 0 as possible, the lower limit is not particularly limited, and the lower limit is determined by the type of resin constituting the film and the manufacturing method. The minimum value (that is, the lower limit) of the birefringence ΔP of the film of the present invention is considered to be about 0.0001, about 0.0002, or about 0.0005 at the present time.

  In the biaxially stretched resin film of the present invention, the difference between the maximum value and the minimum value among the birefringence ΔP values in the directions of 0 °, 45 °, 90 ° and 135 ° is preferably 0.01 or less. More preferably, it is 0.008 or less, More preferably, it is 0.005 or less. If the difference between the maximum value and the minimum value exceeds 0.01, a rainbow pattern may appear prominently.

  The resin (A) of the present invention is required to have an ethylene terephthalate cyclic trimer content of 0.7% by weight or less as a polyethylene terephthalate oligomer. When the content of the ethylene terephthalate cyclic trimer exceeds 0.7% by weight, the syndiotactic polystyrene resin (adjacent to the film surface or the polyethylene terephthalate resin (A) layer in the film production process or use process) B) Oligomer may precipitate at the interface with the layer, which may contaminate the production line or deteriorate the haze of the film.

  The method of making the content of the ethylene terephthalate cyclic trimer of the resin (A) 0.7% by weight or less is not particularly limited, and a copolymer composition that can suppress the generation amount of the ethylene terephthalate cyclic trimer at the time of polymerization, For example, a method of polymerizing a polyester having a small content of ethylene terephthalate cyclic trimer with a composition in which a part of ethylene glycol used as an alcohol component is replaced with neopentyl glycol; Examples thereof include a method by a solid phase polymerization method for reducing the content of a monomer, a method for removing a cyclic trimer by extraction with water or an organic solvent, and a method in which these methods are combined. In particular, a method by a solid phase polymerization method is preferable.

  The biaxially stretched resin film of the present invention has a haze of 2% or less. It is preferable that the haze is 2% or less because a crossed Nicols method can be performed with a high accuracy that has not been achieved conventionally. More preferably, the haze is 1% or less.

  The film of the present invention preferably has a thermal shrinkage rate of 3% or less in both the vertical and horizontal directions when heat-treated at 150 ° C. for 30 minutes. More preferably, it is 2% or less, and particularly preferably 1.5% or less. If the heat shrinkage rate exceeds 3%, the productivity during post-processing such as mold release processing may decrease. The value of the heat shrinkage rate is a value measured by heating a biaxially stretched resin film under no tension.

  The reduced viscosity (ηsp / c) of the film of the present invention is preferably 0.70 or more, more preferably 0.80 or more, and further preferably 0.85 or more. By setting the reduced viscosity of the film to 0.70 or more, the scratch resistance of the film is improved.

  The film of the present invention preferably has a tensile stress value F-5 of 5 MPa or more and 1000 MPa or less, more preferably 100 MPa or more and 400 MPa or less when stretched 5% in the longitudinal and lateral directions of the film. When the F-5 value is less than 50 MPa, film tearing is likely to occur during mold release processing or when performing defect inspections continuously. In addition, if it exceeds 1000 MPa, the film productivity is poor and the production is difficult.

  The film of the present invention preferably has a thickness of 1 μm to 1000 μm, more preferably 3 μm to 300 μm, and still more preferably 10 μm to 50 μm. A film exceeding the above range is unfavorable because of poor productivity as a biaxially stretched resin film.

  Hereinafter, the production method of the film of the present invention will be specifically described. However, the production method is not limited to the following production method, and the film of the present invention was produced by another production method. May be.

  A polyethylene terephthalate resin (A) chip and a syndiotactic polystyrene resin (B) chip dried by a known method are supplied to separate melt-extrusion apparatuses and heated to a temperature equal to or higher than the melting point of each polymer to be melted. . 260-300 degreeC is suitable for the heating temperature with respect to resin (A), and 270-310 degreeC is suitable with respect to resin (B).

  Next, both resins are introduced into a feed block in a molten state and merged. Then, in order to form a laminated structure in which the layer containing the resin (A) and the layer containing the resin (B) are alternately combined to form five or more layers, the resin is supplied to a laminating apparatus. Examples of the laminating apparatus include a feed block, a multi-manifold die, a static mixer, and the like. Among these, it is preferable to use a static mixer.

The static mixer is, for example, a Noritake Co. static mixer in which a rectangular plate is twisted 180 degrees in a resin flow path and arranged repeatedly. The number of layers is doubled. Therefore, logically, when passing through n elements, it becomes 2 ⁿ layers (or 2 ^{n + 1} layers), but in reality, it may change depending on the flow path diameter, discharge amount, viscosity of each resin, surface tension, etc. . In the present invention, the number n of elements of the static mixer is preferably 2 or more and 10 or less. More preferably, it is 4 or more and 8 or less. By using such a static mixer having the number of elements, an appropriate multilayer structure can be obtained, and an effect of reducing the rainbow pattern can be obtained.

  Subsequently, the resin is guided from the laminating apparatus to the slit die, and extruded from the die onto a rotary cooling drum having a surface temperature of about 20 to 60 ° C. in a molten state. If the extruded resin is rapidly cooled and solidified to a temperature not higher than the glass transition temperature on a rotating cooling drum, a substantially amorphous unoriented sheet can be obtained. In this case, it is preferable to improve the adhesion between the sheet and the rotary cooling drum in order to improve the flatness of the sheet. In the present invention, as means for improving the adhesion between the sheet and the rotary cooling drum, for example, an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed.

  If the unoriented (unstretched) sheet thus obtained is simultaneously stretched in the biaxial direction, the biaxially stretched resin film of the present invention can be obtained. By guiding the non-oriented sheet to a simultaneous biaxial tenter, conveying both ends (width direction) of the sheet with clips, and simultaneously widening the distance between the adjacent clips in the longitudinal direction and the width direction. The longitudinal direction (MD direction) and the width direction (TD direction) are stretched simultaneously. The simultaneous biaxial stretching step may be performed in one stage so as to achieve the final stretching ratio, or may be performed in two or more stages. Examples of the simultaneous biaxial stretching machine include a pantograph system, a screw system, a drive motor system, and a linear motor system. Among these, it is preferable to employ a simultaneous biaxial stretching machine of a drive motor type or a linear motor type that can change the draw ratio and can perform a relaxation treatment at an arbitrary place.

  Specific stretching conditions may be appropriately determined according to the type of resin to be used. Usually, at a temperature of 80 to 130 ° C., the unstretched sheet is 1.3 to 6 times (area) in the longitudinal and lateral directions. It is preferable to stretch at the same time. In order to suppress the in-plane orientation difference of the simultaneous biaxially stretched film, it is recommended that the stretching ratios in the longitudinal direction and the width direction are the same and the stretching speeds are substantially equal.

  In addition, when performing simultaneous biaxial stretching, after applying surface treatment such as corona treatment, flame treatment, plasma treatment, etc. to the unoriented sheet, such as slipperiness, easy adhesion, antistatic properties, etc. The function may be imparted by in-line coating.

  After simultaneous biaxial stretching, the stretched film is preferably subjected to heat treatment at 150 to 240 ° C. for 1 to 600 seconds. Further, at this time, it is preferable to relax in the longitudinal direction and / or the transverse direction by 0.1 to 20% in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet.

  The film of the present invention can be formed into a release film by providing a release layer according to a known method. The material constituting the release layer is not particularly limited as long as it has releasability, and may be a type mainly composed of a curable silicone resin, or an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin. A modified silicone type resin by graft polymerization with a resin or the like may be used. Among these, those containing a curable silicone resin as a main component are preferable because of good release properties. By bonding the release film to a polarizing plate or a polarizing film via an adhesive layer, it can be suitably used for inspection of the polarizing plate by the crossed Nicols method.

  The film of the present invention has excellent mechanical properties, heat resistance, and flatness as a PET film, and also has unique optical properties as a laminated film. And when using the film of this invention, you may provide a coating layer in the surface of the film of this invention according to a well-known method. Further, the film surface can be vapor-deposited with a metal or metal oxide according to a known method. Therefore, the film of the present invention can be suitably used for various uses such as various food packaging, general industrial use, optical use, electric material use, and molding processing.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited by the following examples, and may be appropriately changed within a range that can meet the purpose described above and below. It is also possible to implement them, and they are all included in the technical scope of the present invention.
First, in this example, the film characteristics were evaluated as follows.

(1) Determination of positive / negative of birefringence of film and measurement of retardation A 1 cm square film piece cut out from the films obtained in Examples and Comparative Examples was sandwiched between a slide glass and a cover glass, and used as a measurement sample. The polarizing microscope used ECLIPSE E600 POL (light source: white light) manufactured by Nikon Corporation, and the positive / negative and retardation of the birefringence of the film were measured according to the following procedure.
1. A polarizer (polarizer) is set between the light source and the rotary stage, the scale is set to 0, and an analyzer (analyzer) is set between the objective lens and the eyepiece.
2. Rotate the analyzer and fix it at the position where the field of view is the darkest (crossed Nicols).
3. A sample (10 mm × 10 mm) is set on a slide glass, and a cover glass is placed thereon and fixed, and then set on a rotating stage. At this time, it fixes so that the length direction (MD direction) of a film may become the up-and-down direction (0 degree, parallel to the Y-axis of a rotation stage) of a rotation stage.
4). Pull out the analyzer, focus on the sample, put the analyzer on again, turn the rotary stage, and tighten the rotary stage quick lever at the darkest position (extinction position).
5. From the extinction position, the rotary stage is rotated + 45 ° in the positive direction (counterclockwise) (referred to as a diagonal position of + 45 °).
6). Next, a Berek compensator with a scale of 30 is inserted into the test plate insertion slot and fixed.
7). Turn the knob of the Belek Compensator to the left and right at + 45 ° diagonal position. If a black band appears at this time (in this case, positive birefringence), the center of this band is aligned with the intersection of the cross gauges of the eyepiece, and the Berek compensator scale (a) at this time is read. If a black belt does not appear even if the Berech Compensator knob is turned, turn the rotary stage 90 ° in the negative direction (clockwise), and rotate the Berek Compensator Knob to the −45 ° diagonal position. Then, a black band is developed (in this case, a negative refractive index), and the same operation as in the case of positive birefringence is performed.
In any case, when the black band does not appear only by the change of the interference plate, it indicates that the absolute amount of birefringence is too large. In such a case, it is out of the measurement range.
8). Then turn the knob of the Belek Compensator over 30 scales to the left, align the center of the other black belt with the crossing point of the eyepiece cross gauge, and read the scale (b) of the Belek Compensator at this time. .
9. The above 7. And 8. Repeat the above operation and read 5 points a and b.
10. A compensation value i is obtained from the values of a and b by a calculation formula of i = (ab) / 2. 10000 f (i) value is obtained from the obtained value of i using the numerical table attached to the Berek compensator (Table 1 below), and this is multiplied by a correction constant C / 10000 specific to the Berek compensator. The retardation of the film was determined.
In addition, C is a value peculiar to each Belek-type compensator, and the Belek-type compensator used in this example is No. 1 manufactured by Nihon Geoscience Co., Ltd. 10533 and C = 7520 (see Table 2 below).

(2) Birefringence index ΔP
Samples obtained by cutting out the films obtained in Examples and Comparative Examples so as to have a width of 2 cm and a length of 3 cm were used as samples. At this time, a sample cut out so that the length direction of the sample is parallel to the length direction of the film (0 ° sample), and the relationship between the length direction of the sample and the length direction of the film is 45 °, Samples cut out to be 90 ° and 135 ° (45 ° sample, 90 ° sample, and 135 ° sample, respectively) were prepared.

About each said measurement sample, the refractive index of the length direction (longitudinal stretch direction) of the film, the width direction (lateral stretch direction), and the thickness direction was measured using the Abbe refractometer 4T by an Atago optical company. The solvent used for the measurement was diiodomethane, and the measurement conditions were 23 ° C. and 60 RH%. Measurement was performed at n = 5, and the average value (ΔP) of the refractive indexes of each sample was determined based on the following formula.
ΔP = | 0.5 (Nx + Ny) −Nz |
However, Nx, Ny, and Nz show the refractive index of the length direction of a film, the width direction, and the thickness direction, respectively.

(3) Heat shrinkage rate Ten films were cut into a length of 10 mm and a length of 150 mm, respectively, in the length direction and the width direction as samples, and display lines were provided at intervals of 100 mm in the length direction of the samples.
It heat-processed, holding one side of the length direction of a sample so that it might be in a tension | tensile_strength state for 30 minutes in 150 degreeC oven (The product made by Tabai Espec, model PHH-101).
Thereafter, the film was taken out, and the thermal shrinkage rate was determined according to the following formula.
Thermal contraction rate = (1−interval between display lines after heating / interval between display lines before heating) × 100%

(4) F-5 value Ten films were cut into a length of 10 mm and a length of 150 mm, respectively, in the length direction and the width direction as samples, and display lines were provided at intervals of 100 mm in the length direction of the samples. These samples were subjected to a tensile test according to JIS-K7127 (1999) with a distance between chucks of 100 mm, a temperature of 23 ° C., and a tensile speed of 100 mm / min. The test piece was type 2, and the tensile stress at 5% elongation was F-5.

(5) Rainbow pattern 1
Color of the film surface when the film is rotated with the film placed on a light source (two 10W fluorescent lamps (Toshiba FL100-ELD-56K)) and the film plane is kept parallel to the horizontal plane. Was observed through a polarizing plate from a position parallel to the normal direction of the film, and the case where the film surface was colorless or monochromatic was judged good, and the case where two or more colors were observed was judged as poor. In addition, the evaluation of the rainbow pattern 1 is performed on five films. When all films are judged to be good, ◎, four films are good, and one film is bad. The case where there are two or more films judged to be defective is shown in the table below as x.

(6) Rainbow pattern 2
Color of the film surface when the film is rotated with the film placed on a light source (two 10W fluorescent lamps (Toshiba FL100-ELD-56K)) and the film plane is kept parallel to the horizontal plane. Is observed through a polarizing plate from a position of 20 to 70 ° with respect to the normal direction of the film, and the film surface is colorless or monochromatic, and when two or more colors are observed. Judged as bad. The rainbow pattern 2 was evaluated for 5 films. When all films were judged to be good, ◎, 4 films were good, and 1 film was bad. The case where the number of films judged to be 2 or more was shown as x in the table below.

(7) Haze Based on JIS-K7136, it was determined using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.

(8) Quantitative determination of ethylene terephthalate cyclic trimer The film is immersed in hexafluoroisopropyl alcohol / chloroform = 2/3 (V / V) to dissolve the polyester and remove insoluble matter (syndiotactic polystyrene resin, etc.). Then, the polyester was precipitated with methanol, the precipitated polyester was filtered off, the filtrate was evaporated to dryness, and the evaporated dry matter was dissolved in N, N-dimethylformamide. The solution was developed by a liquid chromatography method, and the content of the ethylene terephthalate cyclic trimer relative to the polyethylene terephthalate resin in the film was quantified.

(9) Measurement of the number of layers The number of layers inside the film was determined by observation using a transmission electron microscope.
1. Preparation of measurement sample First, the film was embedded in an epoxy resin. As the epoxy resin, Luabeck 812, Luavec NMA (manufactured by Nacalai Tesque), and DMP30 (manufactured by TAAB) were mixed well at a ratio of 100: 89: 3 (mass), respectively. After embedding the film in the above-mentioned epoxy resin, the film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedding block.

  The obtained embedding block was attached to Nissan Sangyo Ultracut N, and trimming was performed using a glass knife, and the cross section of the portion to be subjected to film observation was exposed on the resin surface. Subsequently, using a diamond knife (Sumitomo Electric Sumiknife SK2045), an ultrathin section was cut out from the resin surface. The cut out ultrathin sections were collected on a mesh and then stained in a ruthenium tetroxide vapor at room temperature (25 ° C.) for 30 minutes, and then thinly deposited with carbon.

2. Observation with an electron microscope The electron microscope observation was performed using JEM-2010 manufactured by JEOL under conditions of an acceleration voltage of 200 kV and a magnification of 5000 to 20000. The obtained image is recorded on an imaging plate (FDL UR-V manufactured by Fuji Photo Film), and the signal recorded on the imaging plate is read out using digital luminography (Pixsys TEM manufactured by JEOL) and digitally recorded on a Windows personal computer. The number of layers confirmed from the difference in dyeing between the layer containing the resin (A) and the layer containing the resin (B) was counted.

Example 1
As the resin (A), a copolymerized polyester (inherent viscosity 0.62; copolymerized using 100 mol% terephthalic acid as an acid component and 85 mol% ethylene glycol and 15 mol% neopentylglycol as a glycol component) The ethylene terephthalate cyclic trimer content of 0.45 wt% was charged into a 60 mmφ single screw extruder and melted at 285 ° C. Syndiotactic polystyrene (300 zc made by Idemitsu Petrochemical Co., Ltd.) was charged as a resin (B) into a twin screw extruder (22.5 mmφ × 2) and melted at 300 ° C. A static mixer (6-element, manufactured by Noritake Co., Ltd.) was introduced to the feed block so that each resin was in a molten state to form a two-layer laminated structure of resin (A) / resin (B) and then heated to 295 ° C. I let it pass. The ratio of the resin at this time was resin (A) / resin (B) = 40/60 (mass ratio).

  The resin after passing through the static mixer was extruded from a T-die and cooled with a cooling roll at 30 ° C. to obtain an unstretched sheet. This sheet was stretched 3.5 times in the longitudinal and lateral directions simultaneously with a film stretcher (Toyo Seiki, biaxial stretching device No. 586, pantograph method) heated to 110 ° C., and then 220 ° C. for 8 seconds in an oven. By performing heat treatment, a simultaneous biaxially stretched resin film having a thickness of 50 μm was obtained. The obtained film had 64 layers.

Example 2
A simultaneous biaxially stretched resin film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that resin (A) / resin (B) = 50/50 (mass ratio). The obtained film had 64 layers.

Example 3
Polyethylene terephthalate (inherent viscosity of 0.75, ethylene terephthalate) obtained by polymerizing 100 mol% of terephthalic acid as the resin (A) and 100 mol% of ethylene glycol as the glycol component, followed by solid phase polymerization by heat treatment under reduced pressure A biaxially stretched resin film having a thickness direction of 50 μm was obtained in the same manner as in Example 1 except that the cyclic trimer content was 0.55 wt% or less.

Comparative Example 1
The unstretched sheet was stretched 3.3 times in the longitudinal direction on a roll whose surface was heated to 110 ° C, and stretched 3.5 times in the transverse direction with a tenter having a preheating temperature of 110 ° C and a stretching temperature of 120 ° C. A sequential biaxially stretched resin film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that heat treatment was performed at 220 ° C. for 4 seconds in the tenter. The obtained film had 64 layers.

Comparative Example 2
A sequentially biaxially stretched resin film having a thickness of 50 μm was obtained in the same manner as in Comparative Example 1 except that resin (A) / resin (B) = 50/50 (mass ratio). The obtained film had 64 layers.

Comparative Example 3
Resin (A), polyethylene terephthalate polymerized using 100 mol% terephthalic acid as the acid component and 100 mol% ethylene glycol as the glycol component (content of intrinsic viscosity 0.65, ethylene terephthalate cyclic trimer) 0.75 wt%) was charged into a 60 mmφ single screw extruder and melted at 285 ° C. Syndiotactic polystyrene (300 zc made by Idemitsu Petrochemical Co., Ltd.) was charged as a resin (B) into a twin screw extruder (22.5 mmφ × 2) and melted at 300 ° C. A static mixer (6-element, manufactured by Noritake Co., Ltd.) was introduced to the feed block so that each resin was in a molten state to form a two-layer laminated structure of resin (A) / resin (B) and then heated to 295 ° C. I let it pass. The ratio of the resin at this time was resin (A) / resin (B) = 40/60 (mass ratio).

  The resin after passing through the static mixer was extruded from a T-die and cooled with a cooling roll at 30 ° C. to obtain an unstretched sheet. This sheet was stretched 3.5 times in the longitudinal and lateral directions simultaneously with a film stretcher (Toyo Seiki, biaxial stretching device No. 586, pantograph method) heated to 110 ° C., and then 220 ° C. for 8 seconds in an oven. By performing heat treatment, a simultaneous biaxially stretched resin film having a thickness of 50 μm was obtained. The obtained film had 64 layers.

Comparative Example 4
The unstretched sheet was stretched 3.3 times in the longitudinal direction on a roll whose surface was heated to 110 ° C, and stretched 3.5 times in the transverse direction with a tenter having a preheating temperature of 110 ° C and a stretching temperature of 120 ° C. A sequential biaxially stretched resin film having a thickness of 50 μm was obtained in the same manner as in Comparative Example 3 except that heat treatment was performed at 220 ° C. for 4 seconds in the tenter. The obtained film had 64 layers.

Comparative Example 5
A sequential biaxially stretched resin film having a thickness of 50 μm was obtained in the same manner as in Comparative Example 4 except that resin (A) / resin (B) = 50/50 (mass ratio). The obtained film had 64 layers.

Comparative Example 6
In this comparative example, only the resin (A) was used. The resin (A) used in Example 1 was melted at 285 ° C., extruded as it was from a T-die, and cooled with a cooling roll at 25 ° C. to obtain an unstretched sheet. This sheet was stretched 3.3 times in the longitudinal direction on a roll whose surface was heated to 90 ° C., and stretched 3.5 times in the transverse direction with a tenter having a preheating temperature of 110 ° C. and a stretching temperature of 120 ° C. Was subjected to heat treatment at 220 ° C. for 4 seconds to obtain a successively biaxially stretched resin film having a thickness of 50 μm.

  The evaluation results of the biaxially stretched resin films obtained in Examples 1, 2, and 3 and Comparative Examples 1 to 6 are shown in Tables 3 to 12.

  The film of the present invention is suitable for a release film used for inspection of a polarizing plate by the crossed Nicols method. Moreover, the film of this invention can be utilized for various uses, such as various food packaging use, general industrial use, optical use, an electrical material use, and a shaping | molding process.

Claims (5)

  Letters measured with a polarizing microscope using a Belek-type compensator, in which five or more layers including a layer containing polyethylene terephthalate resin (A) and a layer containing syndiotactic polystyrene resin (B) are alternately laminated. Biaxial, characterized in that the absolute value of the foundation is 500 nm or less and the content of the ethylene terephthalate cyclic trimer as the polyethylene terephthalate oligomer of the polyethylene terephthalate resin (A) is 0.7% by weight or less. Stretched resin film.   The biaxially stretched resin film according to claim 1, wherein the mass ratio of the polyethylene terephthalate resin (A) and the syndiotactic polystyrene resin (B) is 10/90 to 90/10.     The biaxially stretched resin film according to claim 1 or 2, wherein the haze is 2% or less.   The biaxially stretched resin film according to any one of claims 1 to 3, which has a thermal shrinkage rate of 3% or less when heat-treated at 150 ° C for 30 minutes.   The biaxially stretched resin film according to any one of claims 1 to 4, which is simultaneously biaxially stretched.