JP5097066B2 - Method for producing crystalline polyolefin resin film - Google Patents

Description

  The present invention relates to a method for producing a crystalline polyolefin resin film.

  A resin film obtained by stretching and molding a thermoplastic resin such as a polycarbonate resin or a polyolefin resin is used as a retardation film for a liquid crystal display device (see Patent Documents 1 to 3). Among these resins, development of a retardation film made of a polyolefin-based resin that is less expensive than a polycarbonate resin has been demanded.

As an example of a polyolefin-based resin film, Patent Document 4 discloses a heat-sealable film made of a polypropylene-based resin whose main component is polypropylene that does not contain an additive that migrates to a contacted object. A heat-sealable polypropylene film characterized in that the thickness unevenness of the film is within 10% is described.
JP-A-6-285848 JP-A-11-166039 JP 2006-103222 A JP 2005-153448 A

  The polyolefin resin film for retardation film as described above is required to have high thickness accuracy such that the thickness tolerance is within about ± 1 μm. However, in the production of a conventional polyolefin resin film, when extruding a molten and kneaded polyolefin resin (hereinafter referred to as melt kneading) into a film shape, the film flow direction (the film is unwound from the T die). In the direction), streaky appearance defects (hereinafter referred to as die lines) and the like occurred in the film, and there was a tendency for thickness unevenness to occur in the film. This die line was thought to be caused by resin sticking (hereinafter referred to as “Meani”) generated at the lip portion of a T die for extrusion molding of a melt-kneaded polyolefin resin. Therefore, in order to suppress the occurrence of the mains, measures have been taken to make the tip of the lip portion of the T die have a unique shape called a sharp edge. However, since the die line cannot be sufficiently suppressed only by measures for improving the shape of the device such as the T-die, a more effective measure has been demanded.

  This invention is made | formed in view of the said subject, and it aims at providing the manufacturing method of the crystalline polyolefin resin film which can suppress the thickness variation of the crystalline polyolefin resin film obtained.

  As a result of diligent research, the present inventor has found that the occurrence of die lines in the crystalline polyolefin resin film is not only due to the resin mess occurring at the lip portion of the T die, but also the crystalline polyolefin resin being melt kneaded. We obtained the knowledge that it was caused by oxygen degradation. Furthermore, the present inventor can suppress the deterioration of the crystalline polyolefin resin during the melt kneading by maintaining the crystalline polyolefin resin before the melt kneading at a predetermined temperature for a predetermined time. It discovered that generation | occurrence | production of the die line in a resin film can be suppressed effectively, and resulted in this invention.

That is, the method for producing a crystalline polyolefin resin film according to the present invention is characterized in that in an inert gas atmosphere having an oxygen partial pressure of 500 Pa or less, the glass transition temperature is T _g ° C and the melting point is T _m ° C. A heat treatment step for maintaining the temperature of the polyolefin resin at T _a ° C. for 2 hours or more, and an extrusion step for extruding the crystalline polyolefin resin after the heat treatment step into a film after melting and kneading. And the temperature T _a ° C of the crystalline polyolefin-based resin is set to _a higher temperature of either 50 ° C or (T _g +50) ° C and not higher than (T _m -10) ° C. The “inert gas atmosphere having an oxygen partial pressure of 500 Pa or less” in the present invention means an inert gas having a purity of 100 mol% or an inert gas containing a trace amount of oxygen to an oxygen partial pressure of 500 Pa or less. means.

  By maintaining the temperature of the crystalline polyolefin resin before melt kneading within the above Ta ° C. for 2 hours or more in the above inert gas atmosphere, oxygen that causes deterioration of the crystalline polyolefin resin is reduced. It can be removed from the crystalline polyolefin resin. In addition, since the crystalline polyolefin-based resin from which oxygen has been removed by the heat treatment step is melt-kneaded, deterioration (oxidative decomposition) of the crystalline polyolefin-based resin is suppressed during the melt-kneading. Thus, by extruding a melt of a crystalline polyolefin resin with suppressed deterioration into a film shape, it is possible to suppress the occurrence of die lines and obtain a crystalline polyolefin resin film with less thickness unevenness. Become.

  The crystalline polyolefin resin in the present invention is a polyolefin resin whose crystal has a calorific value larger than 1 J / g observed in the range of −100 to 300 ° C. in differential scanning calorimetry according to JIS K7122. It is a polyolefin resin having a melting peak or a crystallization peak with a crystallization heat quantity greater than 1 J / g. The crystalline polyolefin resin is a crystalline polyolefin resin film especially for retardation films because a liquid crystal panel in which a film made of the resin is incorporated as a retardation film is excellent in durability and can be used for a long time. It is suitable as a raw material.

  Such a crystalline polyolefin-based resin has a crystal melting peak in which the calorific value of crystals observed in the range of −100 to 300 ° C. is greater than 30 J / g or a crystallization peak in which the calorific value is greater than 30 J / g. Is preferred. Thereby, in the crystalline polyolefin-type resin film obtained, the favorable external appearance without a die line or an unevenness | corrugation is obtained.

Further, in the present invention, the glass transition temperature T _g of the crystalline polyolefin resin is that of the intermediate point glass transition temperature determined in accordance with JIS K7121. Specifically, for example, when the crystalline polyolefin resin is polypropylene, using a differential thermal scanning calorimeter (DSC) or the like, the polypropylene is once heated to the melting point or higher and then cooled to about −30 ° C. at a predetermined rate. Thereafter, the value is obtained from the inflection point of the DSC curve obtained by measuring while raising the temperature at a predetermined speed. Further, the melting point T _m of a crystalline polyolefin-based resin refers to a differential scanning calorimetry definitive melting peak temperature is defined in JIS K7121. Specifically, for example, when the crystalline polyolefin-based resin is polypropylene, 10 mg of the crystalline polypropylene-based press film is heat-treated at 230 ° C. for 5 minutes in a nitrogen atmosphere, and then the temperature drop rate is 10 ° C./min to 30 ° C. This is the melting peak temperature when cooled and kept at 30 ° C. for 5 minutes, and further heated from 30 ° C. to 230 ° C. at a heating rate of 10 ° C./min. Melting point _{T m} of a polypropylene resin which is measured in this way is usually 120 to 170 ° C..

In the present invention, the crystalline polyolefin resin is maintained in the inert gas atmosphere from the heat treatment step to the start of the extrusion molding step, and the surface temperature of the crystalline polyolefin resin is (T _a -20). ) It is preferable that the temperature is maintained at a temperature higher than or equal to 5 ° C. and the fluctuation range of the surface temperature is maintained within 5 ° C.

  By maintaining the crystalline polyolefin-based resin in an inert gas atmosphere and maintaining the surface temperature of the crystalline polyolefin-based resin within the above-mentioned preferred range from the heat treatment step to the start of the extrusion molding step. The crystalline polyolefin-based resin is hardly exposed to oxygen, and oxygen is not easily taken into the crystalline polyolefin-based resin. Therefore, since the crystalline polyolefin resin can be melt-kneaded while oxygen is removed by the heat treatment step, it is possible to reliably suppress the deterioration (oxidative decomposition) of the crystalline polyolefin resin during the melt-kneading. As a result, it is possible to reliably suppress the generation of die lines and obtain a crystalline polyolefin-based resin film with few thickness spots.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the crystalline polyolefin resin film which can suppress the thickness variation of the crystalline polyolefin resin film obtained can be provided.

(Method for producing crystalline polyolefin resin film)
Hereinafter, a method for producing a crystalline polyolefin resin film (retardation film), which is a preferred embodiment of the present invention, will be described in detail with reference to FIG. 1 as appropriate. However, the present invention is not limited to the following embodiments. Further, the dimensional ratio and shape in FIG. 1 do not necessarily match the actual dimensional ratio and shape.

  The method for producing a crystalline polyolefin resin film according to the present embodiment mainly includes a heat treatment step (S1) for maintaining the temperature of the crystalline polyolefin resin at a predetermined value in an inert gas atmosphere, and the crystalline polyolefin after the heat treatment step. After melt-kneading the system resin, it has an extrusion molding step (S2) for extruding into a film to obtain a raw fabric film, and a stretching step (S3) for subjecting the raw fabric film to longitudinal stretching and lateral stretching. Hereinafter, each step will be described.

<S1: Heat treatment step>
First, as a raw material, a crystalline polyolefin resin having a glass transition temperature of T _g ° C and a melting point of T _m ° C is supplied from a raw material inlet 1a of a heater 1 (inert gas reflux dryer) to a raw material tank 1b. Introduce into.

Next, the raw material tank 1b is filled with an inert gas (nitrogen) having an oxygen partial pressure of 500 Pa or less to seal the raw material tank 1b. Preferably, the oxygen partial pressure is maintained at 300 Pa or less. The lower the oxygen partial pressure, the better the effect of suppressing deterioration due to kneading of the crystalline polyolefin resin. As the inert gas, in addition to nitrogen, a rare gas such as argon, carbon dioxide, or the like can be used, but nitrogen is preferably used. When the oxygen partial pressure in the raw material tank 1b is 500 Pa or less, for example, the total pressure of the inert gas in the raw material tank 1b is set to atmospheric pressure (1 × 10 ⁵ Pa), and oxygen content in the inert gas is included. The rate may be 5000 ppm or less.

Nitrogen in the sealed raw material tank 1b is circulated in the nitrogen reflux pipe 1c, and the nitrogen is heated using a nitrogen heater 1d. The crystalline polyolefin resin is heat-treated in the heated atmosphere composed of nitrogen. In the present embodiment, the temperature of the crystalline polyolefin resin during the heat treatment (temperature of the entire resin) T _a ° C. is equal to or higher than the higher one of 50 ° C. and (T _g +50) ° C., and (T _m −10) Maintain for 2 hours or more within the range of not more than ° C. Preferably, the temperature Ta of the crystalline polyolefin resin during the heat treatment is higher than either the higher one of 50 ° C. or (T _g +50) ° C. and within a range of (T _m −30) ° C. or lower. For 2 hours or more.

  Under the above nitrogen atmosphere, by maintaining the temperature of the crystalline polyolefin resin before melt kneading within the range of Ta ° C. for 2 hours or more, oxygen that causes deterioration of the crystalline polyolefin resin is removed. It can be removed from the resin. Therefore, when the crystalline polyolefin resin is melt-kneaded, deterioration (oxidative decomposition) of the crystalline polyolefin resin is suppressed, and generation of low molecular weight resins (resins soluble in normal temperature xylene, etc.) is suppressed. The Oxidation degradation is suppressed, and a melt of crystalline polyolefin resin with a low content of low molecular weight resin is extruded into a film to suppress the occurrence of die lines in the raw film and the completed retardation film It is possible to obtain a film with few thickness spots.

When the temperature Ta of the crystalline polyolefin resin described above is smaller than either the higher temperature of 50 ° C. or (T _g +50) ° C., the mobility of the molecules constituting the crystalline polyolefin resin is reduced, There is a tendency that the effect of substituting oxygen contained in the resin with an inert gas tends to be poor. When the temperature is higher than (T _m −10) ° C., the crystalline polyolefin-based resin adheres and the supply to the extruder is There is a tendency to have adverse effects such as difficulty. In the present embodiment, these tendencies can be suppressed by maintaining the temperature Ta of the crystalline polyolefin-based resin within the above preferred range.

<Transport process>
In the present embodiment, the crystalline polyolefin-based resin after the heat treatment step is held from the inside of the raw material tank 1b through the transport pipe 3 while being held in a nitrogen atmosphere (inert gas atmosphere) having an oxygen partial pressure of 500 Pa or less. It is preferable to transport into the extruder 5. In this embodiment, the surface temperature of the crystalline polyolefin resin during transportation is maintained at (T _a −20) ° C. or higher, preferably (T _a −15) ° C. or higher, and the fluctuation range of the surface temperature is 5 The crystalline polyolefin-based resin is fed into the extruder 5 within a range of ± 2.5 ° C. (within a range of ± 2.5 ° C. with respect to a desired surface temperature), preferably within a range of 3 ° C. It is preferable.

That is, during the period from the heat treatment step to the start of the extrusion molding step, the crystalline polyolefin resin is held in an inert gas atmosphere, and the surface temperature of the crystalline polyolefin resin is (T _a -20) ° C. or higher. It is preferable to maintain the fluctuation range of the surface temperature within 5 ° C.

  During transportation, the crystalline polyolefin resin after the heat treatment step is kept in the nitrogen atmosphere during transportation, and the surface temperature of the crystalline polyolefin resin during transportation is maintained under the above-mentioned suitable conditions. In this case, the crystalline polyolefin resin becomes difficult to be exposed to oxygen, and oxygen is hardly taken into the crystalline polyolefin resin. Therefore, the crystalline polyolefin resin can be supplied into the extruder 5 with the oxygen removed by the heat treatment process, and the deterioration (oxidative decomposition) of the crystalline polyolefin resin melted and kneaded in the extruder 5 is ensured. Can be suppressed. As a result, it is possible to reliably suppress the occurrence of die lines in the original film and the completed retardation film, and it is possible to obtain a film with less thickness unevenness.

When the surface temperature of the crystalline polyolefin resin during transportation is less than (T _a -20) ° C., the crystalline polyolefin resin melts when the crystalline polyolefin resin is melt-kneaded in the extruder 5. When the location is in front of the screw 5b in the extruder 5 (in the direction of the discharge port), the extrusion amount of the resin tends to fluctuate, and when the fluctuation range of the surface temperature exceeds 5 ° C., the solid crystalline polyolefin system There is a distribution in the magnitude of friction between the resin and the screw 5b in the extruder 5, and the extrusion amount of the resin tends to fluctuate. In this embodiment, these tendencies can be suppressed by maintaining the surface temperature of the crystalline polyolefin-based resin during transportation under the above-mentioned suitable conditions.

  The surface temperature of the crystalline polyolefin resin during transportation can be measured by, for example, a thermocouple such as a K thermocouple or an infrared radiation thermometer. As a method for measuring the surface temperature of the crystalline polyolefin resin while forming the film into a film, a thermocouple is attached to the wall surface of the hopper 7 on the extruder 5 or a joint portion connecting the hopper 7 and the extruder 5. And a method of directly measuring the surface temperature of the crystalline polyolefin resin passing through the joint. In addition, the surface temperature of the crystalline polyolefin resin being transported is adjusted by adjusting the temperature of the nitrogen atmosphere supplied together with the resin from the heater side, or a heater for heating is attached to the outer surface of the popper 7 on the extruder 5. By the above, it is possible to control within the preferable range.

<S2: extrusion molding process>
The extruder 5 includes a cylinder 5a and a screw 5b installed in the cylinder 5a, and the crystalline polyolefin resin supplied from the heater 1 is introduced into the hopper 7 or the cylinder 5a. The screw 5b is driven by a motor and a speed reducer (not shown). Further, the extruder 5 includes a heating device (not shown) for melting the crystalline polyolefin resin in the cylinder 5a. The heating device and the screw 5b are operated to melt and knead the crystalline polyolefin resin in the extruder 5.

  When the crystalline polyolefin resin in the cylinder 5a is melt-kneaded, the crystalline polyolefin resin may be melt-kneaded with the crystalline polyolefin resin and nitrogen (inert gas) filled in the cylinder 5a. preferable. Thereby, deterioration (oxidative decomposition) of the crystalline polyolefin resin during melt-kneading can be reliably suppressed. As a result, it is possible to reliably suppress the generation of die lines and obtain a crystalline polyolefin-based resin film with few thickness spots. Moreover, in a nitrogen atmosphere, the production | generation of the carbide | carbonized_material in crystalline polyolefin-type resin is suppressed, and the color tone fluctuation | variation in a film obtained and the effect of preventing a burning can also be anticipated.

  The crystalline polyolefin-based resin melt-kneaded in the cylinder 5 a is, for example, sent out to the leaf disk filter 11 by the gear pump 9 and then extruded from the T die 12 into a film shape. The crystalline polyolefin resin extruded from the T-die 12 is formed into a thinner film while cooling and solidifying to form a raw film.

  The thickness of the original film is preferably small, and the difference between the maximum value and the minimum value of the thickness of the original film is preferably 5 μm or less, and more preferably 2 μm or less. The smaller the thickness unevenness of the original film, the easier it is to obtain a retardation film having excellent optical uniformity. The original film is preferably an optically homogeneous non-oriented film or a non-oriented film, and the in-plane retardation of the original film is preferably 50 nm or less.

  When producing a raw film by the T-die extrusion method as described above, the method of cooling and solidifying the melt of the crystalline polyolefin resin extruded from the T-die is cooling using a casting roll and an air chamber. And a method of clamping between a casting roll and a touch roll, and a method of clamping between the casting roll and a metal endless belt provided so as to be pressed against the casting roll along its circumferential direction. When a casting roll is used for cooling, the surface temperature of the casting roll to be used is preferably 0 to 30 ° C. in order to obtain a retardation film having excellent transparency.

  When manufacturing a raw film by a method of sandwiching between a casting roll and a touch roll, in order to obtain a substantially non-oriented raw film, an outer cylinder made of a rubber roll or an elastically deformable metal endless belt is used as the touch roll. And a roll having a structure in which the outer cylinder and the elastic roll are filled with a temperature adjusting medium. preferable.

  When using a rubber roll as a touch roll, in order to obtain a retardation film having a mirror-like surface, a crystalline polyolefin resin melt extruded from a T-die is supported between the casting roll and the rubber roll. It is preferable to clamp together. As the support, a biaxially stretched film made of a thermoplastic resin having a thickness of 5 to 50 μm is preferable.

  When forming a raw film by a method of pressing between a casting roll and a metal endless belt provided so as to be in pressure contact with the casting roll along the circumferential direction, the endless belt has a circumference of the casting roll. It is preferably held by a plurality of rolls arranged in the direction parallel to the casting roll. More preferably, the endless belt is held by two rolls having a diameter of 100 to 300 mm, and the thickness of the endless belt is 100 to 500 μm.

<S3: Stretching process>
A retardation film (crystalline olefin resin film) is obtained by longitudinally stretching and transversely stretching a raw film obtained by extruding a crystalline polyolefin resin. Examples of the method for stretching the raw film include sequential biaxial stretching in which longitudinal stretching and lateral stretching are individually performed, and simultaneous biaxial stretching in which longitudinal stretching and lateral stretching are simultaneously performed. In the case of sequential biaxial stretching, transverse stretching may be performed after longitudinal stretching of the raw film, or longitudinal stretching may be performed after lateral stretching. Below, the case of sequential biaxial stretching is demonstrated.

Examples of the longitudinal stretching method include a method of stretching a raw film by a difference in rotational speed between two or more rolls, and a long span stretching method. The long span stretching method is a method of stretching using a longitudinal stretching machine having two pairs of nip rolls and an oven between them and heating the raw film in the oven by a difference in rotational speed between the two pairs of nip rolls. In order to obtain a retardation film having high optical uniformity, it is preferable to use a long span longitudinal stretching method, and it is particularly preferable to use an air floating oven. The air floating type oven has a structure that allows hot air to be blown from both the upper nozzle and the lower nozzle onto both sides of the original film when the original film is introduced into the oven. A plurality of upper nozzles and lower nozzles are alternately arranged in the film flow direction. In the oven, the original film is stretched while preventing the original film from coming into contact with either the upper nozzle or the lower nozzle. In this case, the stretching temperature (that is, the temperature of the atmosphere in the oven) is preferably 90 ° C. or higher and (melting point T _m +10 of crystalline polyolefin resin) ° C. or lower. When the oven is divided into two or more zones, the temperature setting of each zone may be the same or different.

  The longitudinal draw ratio is not limited, but is usually 1.01 to 3 times, and preferably 1.5 to 3.0 times in order to obtain a retardation film that is superior in optical uniformity.

  An example of the transverse stretching method is a tenter method. The tenter method is a method in which an original film, which is fixed at both ends in the film width direction with a chuck, is stretched in an oven with an increased chuck interval. In the tenter method, an apparatus that can independently adjust each oven temperature in a zone for performing the preheating step, a zone for performing the stretching step, and a zone for performing the heat setting step is used. The transverse draw ratio is usually 2 to 10 times, and is preferably 4 to 7 times from the viewpoint that the obtained retardation film has high optical uniformity.

The pre-heating step of transverse stretching is a step that is installed before the step of stretching the original film in the width direction, and is a step of heating the original film to a temperature high enough to stretch the original film. is there. Here, the preheating temperature in the preheating step means the temperature of the atmosphere in the zone where the oven preheating step is performed. Usually, in order to improve the retardation uniformity of the obtained retardation film, the preheating temperature is set to (melting point T _m −10 of crystalline polyolefin resin) ° C. to (melting point T _m +10 of crystalline polyolefin resin). ) It is preferable to set within the range of ° C., and it is more preferable to set within the range of (melting point T _m −5 of crystalline polyolefin resin) ° C. to (melting point T _m +5 of crystalline polyolefin resin). .

  The stretching process of transverse stretching is a process of stretching the raw film in the width direction. The stretching temperature in this stretching process (the temperature of the atmosphere in the zone where the oven stretching process is performed) may be lower than the preheating temperature, higher than the preheating temperature, or the same temperature as the preheating temperature. Good. Usually, by stretching a preheated raw film at a temperature lower than that of the preheating step, the original film can be stretched uniformly, and as a result, a retardation film with excellent retardation uniformity can be obtained. Therefore, the stretching temperature is preferably 5 to 20 ° C lower than the preheating temperature in the preheating step, and more preferably 7 to 15 ° C lower.

  The heat setting step of transverse stretching is a step of allowing the raw film to pass through an atmosphere at a predetermined temperature in the oven while maintaining the film width at the end of the stretching step. The heat setting temperature may be lower than the stretching temperature in the stretching step, may be higher than the stretching temperature, or may be the same temperature as the stretching temperature. Usually, in order to effectively improve the stability of optical properties such as retardation and optical axis of the raw film, the heat setting temperature is 10 ° C. lower than the stretching temperature in the stretching step to 30 ° C. lower than the stretching temperature. It is preferable to be within a range up to a high temperature.

  The step of transverse stretching may further include a heat relaxation step. In the tenter method, this step is usually performed between a stretching zone and a heat setting zone, and is performed in a heat relaxation zone where the temperature can be set independently of other zones, or a zone in which a heat setting step is performed. Done. Specifically, the thermal relaxation is performed by stretching the raw film to a predetermined width in the stretching step, and then reducing the chuck interval by several%, preferably 0.1 to 10%, to remove useless distortion. Done.

(Retardation film)
Although the retardation required for the retardation film obtained by the above-described production method varies depending on the type of liquid crystal display device in which the retardation film is incorporated, the in-plane retardation R ₀ is usually 30 to 300 nm. When used in a vertical alignment mode liquid crystal display described later, the in-plane retardation R ₀ is 40 to 70 nm and the thickness direction retardation R _th is 90 to 230 nm from the viewpoint of excellent viewing angle characteristics. preferable. A retardation film having a desired retardation can be obtained by controlling the stretch ratio when producing the retardation film and the thickness of the retardation film to be produced. Moreover, the thickness of a phase difference film is 10-100 micrometers normally, Preferably it is 10-60 micrometers. Further, the thickness of the retardation film preferably has a tolerance with respect to a reference thickness (product specification) within about ± 1 μm.

  The retardation film preferably has a difference between the maximum value and the minimum value of the retardation within the film plane (in the plane of 500 mm width × 500 mm length) of 10 nm or less, and the optical axis in the film width direction of 500 mm. Is measured, the optical axis is preferably −1 ° or more and + 1 ° or less, and a retardation film having high optical uniformity is preferred.

  The above-mentioned retardation film is laminated with various polarizing plates and liquid crystal layers and can be suitably used for liquid crystal display devices such as mobile phones, personal digital assistants (PDAs), personal computers and large-sized televisions. . As a liquid crystal display (LCD) using a laminated retardation film, an optically compensated bend (OCB) mode, a vertical alignment (VA) mode, a lateral electric field (In-Plane Switching: IPS) is used. Examples thereof include liquid crystal display devices in various modes such as a mode, a thin film transistor (TFT) mode, a twisted nematic (TN) mode, and a super twisted nematic (Super Twisted Nematic: STN) mode. In particular, the retardation film obtained by the production method of the present embodiment has an effect of improving the viewing angle dependency when used in a VA mode liquid crystal display device.

  In general, a liquid crystal display device has a polarizing plate disposed on both sides of a liquid crystal cell having two substrates and a liquid crystal layer sandwiched between them, and is disposed on one outer side (back side). Of the light from the backlight, only linearly polarized light parallel to the transmission axis of the polarizing plate between the liquid crystal cell and the backlight is incident on the liquid crystal cell. A retardation film can be arrange | positioned through an adhesive between a back side polarizing plate and a liquid crystal cell and / or between a front side polarizing plate and a liquid crystal cell. Moreover, in order to protect the polarizing film which consists of polyvinyl alcohol normally, a polarizing plate has a structure which clamped the polarizing film through the adhesive with protective films, such as two sheets of triacetyl cellulose (TAC) films. The retardation film is bonded to the polarizing film with an adhesive instead of the protective film on the liquid crystal cell side of the front side polarizing plate and / or the back side polarizing plate. Thus, the retardation film can also serve as both an optical compensation film (retardation film) and a protective film.

(Crystalline polyolefin resin)
The crystalline polyolefin resin that is the raw material of the crystalline polyolefin resin film of the present embodiment has a crystal calorific value observed in the range of −100 to 300 ° C. from 1 J / g in the differential scanning calorimetry according to JIS K7122. It is a polyolefin resin having a large crystal melting peak or a crystallization peak with a crystallization heat quantity greater than 1 J / g. This crystalline polyolefin-based resin may be a mixture of two or more different crystalline polyolefin-based resins, or other resins or additives as long as the calorimetric characteristics of the crystalline polyolefin-based resin described above are not impaired. You may contain an agent suitably.

  Crystalline polyolefin-based resins are cheaper than polycarbonate resins that have been used as materials for conventional retardation films, are excellent in recyclability and solvent resistance, and do not generate dioxins even when incinerated. Is suitable as a material for a retardation film in that it does not worsen.

  As the crystalline polyolefin-based resin, an olefin homopolymer or a copolymer of two or more olefins, a copolymer of one or more olefins and one or more polymerizable monomers that can be polymerized with the olefins, or Examples include modified polymers. The crystalline polyolefin-based resin may be a mixture of two or more different crystalline polyolefin-based resins, or may appropriately contain a resin or additive other than the crystalline polyolefin-based resin.

  Examples of the olefin constituting the crystalline polyolefin-based resin include ethylene, propylene, α-olefins having 4 to 20 carbon atoms, and cyclic olefins.

  Specific examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3- Dimethyl-1-butene, 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2-ethyl-1-pentene, 2-methyl-3-ethyl-1-butene, 1- Octene, 2-ethyl-1-hexene, 3,3-dimethyl-1-hexene, 2-propyl-1-heptene, 2-methyl-3-ethyl-1-heptene, 2,3,4-trimethyl-1- Pentene, 2-propyl-1-pente 2,3-diethyl-1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadacene, 1-octathecene , 1-nonadecene and the like.

Examples of the cyclic olefin include bicyclo [2.2.1] hept-2-ene, which is usually called norbornene, 6-alkylbicyclo [2.2.1] hept-2-ene, 5,6- Of dialkylbicyclo [2.2.1] hept-2-ene, 1-alkylbicyclo [2.2.1] hept-2-ene, and 7-alkylbicyclo [2.2.1] hept-2-ene Such as a norbornene derivative having an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group or a butyl group, or tetracyclo [4.4.0.1 ^2,5 , also called dimethanooctahydronaphthalene. . 1 ^7,10 ] -3-dodecene, 8-alkyltetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene, and 8,9-dialkyltetracyclo [4.4.0.1 ^2,5 . ^{Dimethanooctahydronaphthalene} derivatives in which an alkyl group having 3 or more carbon atoms is introduced at the 8-position and / or 9-position of dimethanooctahydronaphthalene, such as 1 ^7,10 ] -3-dodecene, And a derivative of norbornene into which one or a plurality of halogens are introduced, and a derivative of dimethanooctahydronaphthalene into which halogens are introduced at the 8th and / or 9th positions.

  Examples of one or more polymerizable monomers that can be polymerized with olefins include aromatic vinyl compounds, alicyclic vinyl compounds such as vinylcyclohexane, polar vinyl compounds, and polyene compounds.

  Examples of aromatic vinyl compounds include styrene and derivatives thereof, and examples of styrene derivatives include compounds in which other substituents are bonded to styrene, such as o-methylstyrene, m-methylstyrene, p-methyl. Of styrene, 2,4-dimethyl styrene, o-ethyl styrene, alkyl styrene such as p-ethyl styrene, hydroxy styrene, t-butoxy styrene, vinyl benzoic acid, vinyl benzyl acetate, o-chloro styrene, p-chloro styrene A substituted styrene in which a hydroxyl group, an alkoxy group, a carboxyl group, an acyloxy group, a halogen or the like is introduced into the benzene ring of styrene, a vinylbiphenyl compound such as 4-vinylbiphenyl, 4-hydroxy-4'-vinylbiphenyl, 1-vinyl naphthalene, 2-vinyl Vinyl naphthalene compounds such as phthalene, vinyl anthracene compounds such as 1-vinyl anthracene, 2-vinyl anthracene, vinyl pyridine compounds such as 2-vinyl pyridine and 3-vinyl pyridine, vinyl carbazoles such as 3-vinyl carbazole Further examples include compounds such as acenaphthylene compounds.

  Examples of the polar vinyl compound include acrylic compounds such as methyl acrylate, methyl methacrylate, and ethyl acrylate, vinyl acetate, and vinyl chloride.

  Examples of the polyene compound include conjugated polyene compounds and non-conjugated polyene compounds. Examples of the conjugated polyene compound include an aliphatic conjugated polyene compound and an alicyclic conjugated polyene compound. Examples of the non-conjugated polyene compound include an aliphatic non-conjugated polyene compound, an alicyclic non-conjugated polyene compound, and an aromatic compound. Group non-conjugated polyene compounds and the like. These may be substituted by a substituent such as an alkoxy group, an aryl group, an aryloxy group, an aralkyl group, an aralkyloxy group.

  Specific examples of the crystalline polyolefin resin include polyethylene resins such as low density polyethylene, linear polyethylene (ethylene / α-olefin copolymer) and high density polyethylene, polypropylene, propylene / ethylene copolymer, propylene / 1. -Polypropylene resins such as butene copolymer, ethylene / cyclic olefin copolymer, ethylene / vinylcyclohexane copolymer, poly (4-methylpentene-1), poly (butene-1), ethylene / acrylic Examples include an acid methyl copolymer, an ethylene / methyl methacrylate copolymer, an ethylene / ethyl acrylate copolymer, and an ethylene / vinyl acetate copolymer.

  Examples of the modified product of the crystalline polyolefin resin were modified with a modifying compound such as maleic anhydride, dimethyl maleate, diethyl maleate, acrylic acid, methacrylic acid, tetrahydrophthalic acid, glycidyl methacrylate, and hydroxyethyl methacrylate. Examples thereof include crystalline polyolefin resins.

<Polypropylene resin>
From the viewpoint of easily obtaining the effect of the present invention, among the crystalline polyolefin resins, polyethylene resins or polypropylene resins are preferable, and polypropylene resins are particularly preferable. Examples of polypropylene resins include propylene homopolymers, copolymers of propylene with one or more monomers selected from the group consisting of ethylene and α-olefins having 4 to 20 carbon atoms, and mixtures thereof. Can be mentioned.

  As the α-olefin forming a copolymer with propylene, among the α-olefins described above, α-olefins having 4 to 12 carbon atoms are preferable, for example, 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2- Ethyl-1-pentene, 2,3,4-trimethyl-1-butene, 2-methyl-3-ethyl-1-butene, 1-octene, 5-methyl-1-pentene, 2-ethyl-1-hexene, 3,3-dimethyl -1-hexene, 2-propyl-1-heptene, 2-methyl-3-ethyl-1-heptene, 2,3,4-trimethyl-1-pentene, 2-propyl-1-pentene, 2,3-diethyl -1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene and the like are preferable. Among these, 1-butene, 1-pentene, 1-hexene, and 1-octene are more preferable, and 1-butene and 1-hexene are particularly preferable from the viewpoint of copolymerization.

  From the viewpoint of easily obtaining the effects of the present invention, as a polypropylene resin, a propylene / ethylene copolymer, a propylene / 1-butene copolymer, a propylene / 1-pentene copolymer, a propylene / 1-hexene copolymer, A propylene / 1-octene copolymer is preferred. Further, when the polypropylene resin is a copolymer of propylene and one or more monomers selected from the group consisting of ethylene and an α-olefin having 4 to 20 carbon atoms, it may be a random copolymer. It may be a block copolymer.

  Examples of the random copolymer include a propylene-ethylene random copolymer, a propylene-α-olefin random copolymer, and a propylene-ethylene-α-olefin random copolymer. Specific examples of the propylene-α-olefin random copolymer include a propylene-1-butene random copolymer, a propylene-1-hexene random copolymer, and a propylene-1-octene random copolymer. Examples of the propylene-ethylene-α-olefin random copolymer include propylene-ethylene-1-butene random copolymer, propylene-ethylene-1-hexene random copolymer, and propylene-ethylene-1-octene random copolymer. Examples include coalescence. Among these, propylene-ethylene random copolymer, propylene-1-butene random copolymer, propylene-1-hexene random copolymer, propylene-ethylene-1-butene random copolymer, propylene-ethylene-1- A hexene random copolymer is preferred.

  In the polypropylene resin copolymer described above, the comonomer-derived constituent unit content is preferably more than 0% by weight and less than 40% by weight, more than 0% by weight and less than 30% by weight based on the entire copolymer. More preferably. Further, when the polypropylene resin is a copolymer of two or more kinds of comonomers and propylene, the total content of the constituent units derived from all the comonomers contained in the copolymer is preferably within the above range. . By setting the content of the comonomer-derived constitutional unit within the above-mentioned preferred range, the transparency and heat resistance of the resulting film can be balanced.

  The melt flow rate (MFR) of the polypropylene resin is usually 0.1 to 200 g / 10 minutes as measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K7210, preferably 0.5 to 50 g / 10 min, more preferably 1-10 g / 10 min. By using a propylene polymer having an MFR in such a range, dripping of the original film during longitudinal stretching and lateral stretching is reduced, and uniform stretching is easy.

  The molecular weight distribution of the polypropylene resin is defined by the ratio of the weight average molecular weight Mw to the number average molecular weight Mn, and is usually 1 to 20. Mn and Mw are measured by GPC (gel permeation chromatography) using o-dichlorobenzene at 140 ° C. as a solvent and polystyrene as a standard sample.

  As a method for producing a polypropylene resin, a method of homopolymerizing propylene using a known polymerization catalyst, or one or more monomers selected from the group consisting of ethylene and an α-olefin having 4 to 20 carbon atoms; The method of copolymerizing with propylene is mentioned. As a known polymerization catalyst, for example, a Ti-Mg catalyst comprising a solid catalyst component containing magnesium, titanium and halogen as essential components, a solid catalyst component comprising magnesium, titanium and halogen as essential components, an organoaluminum compound and A catalyst system in combination with a third component such as an electron-donating compound, a metallocene catalyst, or the like, if necessary.

  Among these catalyst systems used for the production of propylene polymers, the catalyst system in which an organic aluminum compound and an electron donating compound are combined with a solid catalyst component containing magnesium, titanium and halogen as the essential components is the most. Can be used generally. More specifically, the organoaluminum compound preferably includes triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride and tetraethyldialumoxane, and the electron donating compound is preferably cyclohexylethyldimethoxy. Examples thereof include silane, tert-butyl-n-propyldimethoxysilane, tert-butylethyldimethoxysilane, and dicyclopentyldimethoxysilane. Examples of solid catalyst components containing magnesium, titanium, and halogen as essential components include catalyst systems described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. Can be mentioned. Examples of the metallocene catalyst include catalyst systems described in Japanese Patent No. 2587251, Japanese Patent No. 2627669, and Japanese Patent No. 2668732.

  Polymerization methods used for the production of polypropylene resins include solvent polymerization using an inert solvent typified by hydrocarbon compounds such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, Examples include a bulk polymerization method using a monomer as a solvent, a gas phase polymerization method performed in a gas monomer, and the like, preferably a bulk polymerization method or a gas phase polymerization method. These polymerization methods may be a batch method or a continuous method.

  The stereoregularity of the polypropylene resin may be any of isotactic, syndiotactic and atactic types. The polypropylene resin is preferably a syndiotactic or isotactic propylene polymer from the viewpoint of heat resistance. The polypropylene-based resin may be a blend of two or more types of polypropylene-based polymers having different molecular weights, proportions of structural units derived from propylene, tacticity, and the like, and may appropriately contain polymers and additives other than the polypropylene-based polymers.

(Additive)
The crystalline polyolefin resin used in the present embodiment may be blended with known additives within a range that does not inhibit the effect of suppressing the occurrence of die lines and suppressing the thickness unevenness of the obtained film.

  Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent. Antioxidants include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, hindered amine antioxidants (HALS), and, for example, phenolic and phosphorus antioxidant mechanisms in one molecule. Examples thereof include a composite type antioxidant having a unit. Examples of the UV absorber include UV absorbers such as 2-hydroxybenzophenone and hydroxytriazole, and UV blockers such as benzoate. Examples of the antistatic agent include a polymer type, an oligomer type, and a monomer type. Examples of the lubricant include higher fatty acid amides such as erucic acid amide and oleic acid amide, higher fatty acids such as stearic acid, and metal salts thereof. Examples of the nucleating agent include sorbitol nucleating agents, organic phosphate nucleating agents, and high molecular nucleating agents such as polyvinylcycloalkane. As the antiblocking agent, fine particles having a spherical shape or a shape close thereto can be used regardless of inorganic or organic. These additives may be used in combination.

  As mentioned above, although preferred embodiment of the manufacturing method of the crystalline polyolefin resin film concerning one embodiment of the present invention was described, the present invention is not necessarily limited to the embodiment mentioned above.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1
In the examples, a propylene-ethylene random copolymer, which is a kind of polypropylene resin, was used as the crystalline polyolefin resin. The glass transition temperature _{T g} of the polypropylene resin is 0 ° C., the melting point _{the T m} was 136 ° C..

  The melt flow rate (MFR), ethylene content, and xylene-soluble component amount (CXS) of this polypropylene resin were measured by the methods shown below.

<Melt flow rate (MFR)>
The melt flow rate of the polypropylene resin was measured according to JIS K7210. The test temperature and nominal load were in accordance with Annex B Table 1 of JIS K7210. The test temperature was 230 ° C. and the load was 21.18 N. As a result of the measurement, the melt flow rate (MFR) of the polypropylene resin was 8 g / 10 minutes.

<Ethylene content>
For the above-mentioned propylene-ethylene random copolymer (polypropylene resin), IR spectrum measurement described in “Polymer Analysis Handbook (1995, published by Kinokuniya Shoten, page 616)” was performed, The content of structural units derived from ethylene was determined. As a result of the measurement, the content of ethylene in the entire polypropylene resin was 5% by weight.

<Amount of xylene soluble component (CXS)>
After 1 g of polypropylene resin was completely dissolved in 100 ml of boiling xylene, the temperature of xylene was lowered to 20 ° C. and left at that temperature for 4 hours. Thereafter, the precipitate was separated into a filtrate and a filtrate, and xylene was distilled off from the filtrate, and the resulting solid was dried at 70 ° C. under reduced pressure to obtain a residue. The percentage of the weight of the obtained residue was obtained with respect to the weight (1 g) of the polypropylene resin, and this value was defined as the xylene-soluble component amount (CXS) of the polypropylene resin. In addition, since the resin component with a small molecular weight is easy to melt | dissolve in xylene, content of the low molecular weight resin component in a polypropylene resin is so large that CXS is large. As a result of the measurement, the CXS of the polypropylene resin was 4.0%.

  A polypropylene resin film (raw film) was prepared from the above-described polypropylene resin as a raw material by the production method shown below. First, an inert gas mainly containing nitrogen, an oxygen content of 800 ppm, and an oxygen partial pressure of 80 Pa and a polypropylene resin were supplied into the raw material tank 1b of FIG. And the raw material tank 1b was sealed in the state which maintained the oxygen partial pressure in the raw material tank 1b at 80 Pa. Next, the nitrogen in the raw material tank 1b is circulated in the nitrogen recirculation pipe 1c, heated with the nitrogen heater 1d, and the temperature of the entire polypropylene resin (hereinafter referred to as the resin temperature) for 3 hours in the heated nitrogen atmosphere. A heat treatment was performed to maintain the temperature at 60 ° C.

  The polypropylene resin after being maintained at 60 ° C. for 3 hours is maintained in an inert gas atmosphere containing nitrogen as a main component, an oxygen content of 800 ppm, and an oxygen partial pressure of 80 Pa, and then into the extruder. Transported. The surface temperature of the polypropylene resin during transportation (hereinafter referred to as resin surface temperature) was maintained at 45 ° C., and the fluctuation range of the surface temperature was maintained within 5 ° C.

  Next, the polypropylene resin was melt kneaded in an extruder. After melt-kneading, the polypropylene resin extruded from the T die into a film was further molded by a molding roll rotating at 100 rpm, and the raw film of Example 1 was obtained. The temperature of the polypropylene resin extruded from the T die (hereinafter referred to as the extrusion temperature) was 250 ° C.

  The amount of xylene-soluble components (CXS) of the obtained raw film was measured by the method described above. CXS was 4.8%.

(Example 2)
The same as in Example 1 except that the time for maintaining the entire polypropylene resin at a resin temperature of 60 ° C. in the heater (hereinafter referred to as heat treatment time), the resin surface temperature, and the extrusion temperature were set to the values shown in Table 1. The raw film of Example 2 was produced by the method. In addition, CXS was measured for the raw film of Example 2 in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Examples 1 and 2)
In Comparative Examples 1 and 2, the atmosphere in the heater was air with an oxygen partial pressure of 20000 Pa (nitrogen volume fraction: about 80%, oxygen volume fraction: about 20% air) and a polypropylene resin. The whole was maintained at a resin temperature of 60 ° C. In Comparative Examples 1 and 2, the heat treatment time, the resin surface temperature, and the extrusion temperature were values shown in Table 1. Except these matters, the raw film of Comparative Examples 1 and 2 was produced in the same manner as in Example 1. In addition, CXS was measured for the raw film of Comparative Examples 1 and 2 in the same manner as in Example 1. The results are shown in Table 1.

  As shown in Table 1, in Examples 1 and 2 in which the temperature of the entire polypropylene resin was maintained at 60 ° C. in a nitrogen atmosphere where the oxygen partial pressure was 80 Pa, the temperature of the entire polypropylene resin was set to 60 ° C. in the air. It was confirmed that CXS was small as compared with Comparative Examples 1 and 2 which were maintained. From this result, in the raw film of Examples 1 and 2, compared with Comparative Examples 1 and 2, deterioration (oxidative decomposition) of the polypropylene-based resin is suppressed, and a low molecular weight resin component (which can be used for xylene) that causes a die line. It was confirmed that the production | generation of (soluble component) was suppressed.

(Example 3)
In Example 3, the following thermogravimetric analysis (Thermo Gravimetric Analysis) was performed on the same polypropylene resin (propylene-ethylene random copolymer) as in Examples 1 and 2. For thermogravimetric analysis, a thermal analysis equipment TG / DTA220 manufactured by SII Nano Technology Co., Ltd. was used.

  In thermogravimetric analysis, the following heat treatment step and the subsequent heating step were carried out continuously.

  First, in the heat treatment step, the polypropylene resin was heated to 60 ° C. at a temperature increase rate of 50 ° C./min. Next, the temperature of the polypropylene resin was maintained at 60 ° C. for 2 hours. In the heat treatment step, nitrogen gas was supplied into the thermal analysis equipment at a flow rate of 500 ml / min, and the polypropylene resin was held in a nitrogen atmosphere.

  In the heat treatment step, the oxygen partial pressure (unit: Pa) in the atmosphere (heat treatment atmosphere) in which the polypropylene resin is held was measured. The results are shown in Table 2. The oxygen partial pressure is a value calculated from the oxygen concentration and atmospheric pressure by analyzing the gas in the heat treatment atmosphere with a “trace oxygen analyzer RO-102” manufactured by Iijima Electronics Co., Ltd. and measuring the oxygen concentration in the heat treatment atmosphere. It is.

  Next, in the heating step, the temperature of the polypropylene resin was changed from 60 ° C. to 550 ° C. at a rate of temperature increase of 20 ° C./min. In the heating step, nitrogen gas was supplied into the thermal analysis equipment at a flow rate of 500 ml / min, and the polypropylene resin was held in a nitrogen atmosphere.

  In the heating step, the weight of the polypropylene resin at each temperature was measured when the temperature of the polypropylene resin was changed from 60 ° C. to 550 ° C. By this measurement, a curve (TG curve) showing the relationship between the temperature of the polypropylene resin and the weight of the polypropylene resin at that temperature was obtained. From this TG curve, the temperature (TG5) of the polypropylene resin when the weight of the polypropylene resin decreased by 5% with respect to the weight of the polypropylene resin at 60 ° C. (initial weight), and the polypropylene resin with respect to the initial weight. The temperature (TG10) of the polypropylene resin at the time when the weight of the resin decreased by 10% was determined. Table 2 shows TG5 and TG10.

  In addition, using the same method as the oxygen partial pressure in the heat treatment atmosphere, the oxygen partial pressure in the atmosphere (heating atmosphere) in which the polypropylene resin is held in the heating step was measured. The oxygen partial pressure of the heating atmosphere in Example 3 was 20 Pa. In Examples 3 to 5 and Comparative Examples 3 to 7 which will be described later, the oxygen partial pressure in the heating atmosphere was 20 Pa.

Example 4
Thermogravimetric analysis of Example 4 was performed in the same manner as in Example 3 except that the time (heat treatment time) for maintaining the temperature of the polypropylene resin at 60 ° C. was 5 hours. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Example 4.

(Example 5)
Thermogravimetric analysis of Example 5 was performed in the same manner as in Example 3 except that the heat treatment atmosphere was a mixed gas in which air and nitrogen were mixed and the oxygen partial pressure was 400 Pa. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Example 5.

(Comparative Example 3)
The thermogravimetric analysis of Comparative Example 3 was performed in the same manner as in Example 3 except that the heat treatment time was 1 hour. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Comparative Example 3.

(Comparative Example 4)
The thermogravimetric analysis of Comparative Example 4 was performed in the same manner as in Example 4 except that the heat treatment atmosphere was air having an oxygen partial pressure of 20900 Pa. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Comparative Example 4.

(Comparative Example 5)
The thermogravimetric analysis of Comparative Example 5 was performed in the same manner as in Example 3 except that the heat treatment atmosphere was a mixed gas in which air and nitrogen were mixed and the oxygen partial pressure was 1000 Pa. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Comparative Example 5.

(Comparative Example 6)
The thermogravimetric analysis of Comparative Example 6 was performed in the same manner as in Example 3 except that the heat treatment atmosphere was a mixed gas in which air and nitrogen were mixed and the oxygen partial pressure was 130 Pa, and the heat treatment time was 0.5 hours. went. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Comparative Example 6.

(Comparative Example 7)
The thermogravimetric analysis of Comparative Example 7 was performed in the same manner as in Example 5 except that the heat treatment time was 1 hour. Table 2 shows the oxygen partial pressure, TG5, and TG10 in the heat treatment atmosphere of Comparative Example 7.

(Technical significance of TG5 and TG10)
In the heating step, when the temperature of the polypropylene resin is changed from 60 ° C. to 550 ° C., the weight of the polypropylene resin decreases. This is because the polypropylene resin is thermally deteriorated (oxidative decomposition) in the heating step, and a low molecular weight resin component that causes die-line formation is generated in the polypropylene resin, and this low molecular weight resin component is released from the polypropylene resin. Due to that. And TG5 and TG10 being low means that the polypropylene resin is likely to be thermally deteriorated, and a die line is likely to occur in a raw film formed from such a resin. Moreover, TG5 and TG10 being high means that polypropylene resin is hard to be thermally deteriorated, and a die line is hardly generated in a raw film formed from such a resin. In other words, the higher the TG5 and TG10, the higher the thermal stability of the polypropylene resin.

  From the above, TG5 and TG10 are preferably as high as possible. Specifically, in Table 2, TG5 is preferably higher than 420 ° C, and TG10 is preferably higher than 430 ° C.

(Evaluation)
As shown in Table 2, in Examples 3-5 in which the temperature of the polypropylene resin was maintained at 60 ° C. for 2 hours or more in an inert gas atmosphere in which the oxygen partial pressure was 500 Pa or less in the heat treatment step, Comparative Examples 4-7 TG5 and TG10 were higher than TG5, TG5 was higher than 420 ° C, and TG10 was higher than 430 ° C. That is, in Examples 3-5, compared with Comparative Examples 4-7, it was confirmed that the thermal deterioration of a polypropylene-type resin is suppressed and it is hard to produce | generate the low molecular weight resin component which causes a die line in a polypropylene-type resin. It was.

It is a schematic sectional drawing of a part of manufacturing apparatus used for the manufacturing method of the crystalline polyolefin resin film which concerns on one Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heater, 3 ... Transport pipe, 5 ... Extruder, 9 ... Gear pump, 11 ... Leaf disk filter, 12 ... T die.

Claims (2)

A heat treatment step for maintaining the temperature of the crystalline polyolefin resin having a glass transition temperature of T _g ° C and a melting point of T _m ° C at T _a ° C for 2 hours or more in an inert gas atmosphere having an oxygen partial pressure of 500 Pa or less When,
An extrusion step of extruding the crystalline polyolefin resin after the heat treatment step into a film after melting and kneading, and
The crystalline polyolefin resin in which the temperature T _a ° C of the crystalline polyolefin resin is set to _a higher one of 50 ° C. and (T _g +50) ° C., and (T _m −10) ° C. or less. A method for producing a resin film. The crystalline polyolefin resin is held in the inert gas atmosphere after the heat treatment step until the extrusion molding step is started, and the surface temperature of the crystalline polyolefin resin is (T _a -20) The method for producing a crystalline polyolefin-based resin film according to claim 1, wherein the surface temperature is maintained at 5 ° C or more and the fluctuation range of the surface temperature is maintained within 5 ° C.

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