JP2021157178A - Film - Google Patents

Abstract

To provide a film with a minimized crystallization rate and enhanced stretchability and heat whitening resistance.SOLUTION: When a heating process and a cooling process are repeated twice in differential scanning calorimetry (DSC), the film provided herein satisfies the following expression 1: Tmc2-Tmc1≥1 ...(1), where Tmc1 (°C) represents a cold crystallization temperature observed in the first cooling process, and Tmc2 (°C) represents a cold crystallization temperature observed in the second cooling process.SELECTED DRAWING: None

Description

The film of the present invention has excellent transparency, surface properties, and mechanical properties as compared with conventional films, and is used for home appliances, mobile phones, automobile interior and exterior materials, packaging materials, building materials, polarizing plate release, FPC. , A film suitable for applications such as membrane switches, coating substrates, and ITO substrates.

Films are used in various applications that take advantage of their transparency, mechanical properties, thermal properties, chemical resistance, electrical properties, moldability, and the like. On the other hand, the thermal properties, stretchability, moldability, etc. of the film differ greatly depending on the resin, and polybutylene terephthalate resin, nylon resin, liquid crystal resin, etc. have high crystallinity, and it is difficult to form a film with stretching. .. For example, Patent Documents 1 and 2 indicate that polybutylene terephthalate and nylon are difficult to sequentially biaxially stretch due to their high crystallinity, and simultaneous biaxial stretching is performed in order to improve stretchability. , Simultaneous biaxial stretching machines have high hurdles for capital investment.

Further, in recent years, in the field of flat panel displays and touch panels, demand for various optical films such as polarizer protective films and transparent conductive films has been increasing. Among them, in the field of polarizer protective films, low moisture permeability, mechanical strength, etc. In addition, replacement of the conventional triacetyl cellulose (TAC) film with a polyester film is being actively studied for the purpose of applying physical properties having excellent thermal dimensional stability and reducing the cost. However, the biaxially stretched polyester film that has been studied conventionally has a higher phase difference than the TAC film due to the orientation of the polymer during stretching, so that interference caused by the phase difference when assembled as a liquid crystal display There is a problem that color is generated (hereinafter, also referred to as rainbow unevenness) and the quality when the image is displayed is deteriorated. Therefore, a film in which the resin is modified to suppress the orientation during stretching has been proposed in order to reduce the phase difference, but there is a problem that crystallization during heating becomes a problem and transparency is impaired.

Further, in the case of an unstretched film that does not involve stretching, crystallization during thermoforming becomes a problem, and the application to which the resin can be applied has been determined. For example, from Patent Document 3, it has been known that when a laminated metal plate is subjected to various molding processes, it crystallizes and whitens.

Japanese Unexamined Patent Publication No. 2014-151567 JP-A-2018-8721 Japanese Unexamined Patent Publication No. 2008-143184

An object of the present invention has been made against the background of the above-mentioned problems of the prior art, and by suppressing the crystallinity of the resin film, it is possible to improve the biaxial stretchability and the high temperature resistance of the unstretched film, which has been difficult in the past. It is an object of the present invention to provide a film having whitening property, good appearance after processing, and productivity.

The film of the present invention has the following structure in order to solve the above problems. That is, the cold crystallization temperature observed in the first temperature lowering process when the temperature raising process and the temperature lowering process are repeated twice by differential scanning calorimetry (DSC) is observed in Tmc1 (° C.) and the second temperature lowering process. The film is characterized in that Tmc1 and Tmc2 satisfy the following formula 1 when the cold crystallization temperature is Tmc2 (° C.).
Equation 1: Tmc2-Tmc1 ≧ 1.

According to the present invention, the biaxial stretchability and the high temperature whitening resistance of the unstretched film are improved, and a film having a good appearance can be obtained. Since the film of the present invention is excellent in transparency, flatness, and mechanical properties, it is used for home appliances, mobile phones, automobile interior and exterior materials, packaging materials, building material members, polarizing plate release, FPC, membrane switch, coating group. It can also be applied to optical applications such as materials and ITO substrates. In particular, since crystallization during heating can be suppressed without stretching orientation, when mounted as a polarizer protective film on a display device of a large-screen liquid crystal display, transparency is maintained and rainbow unevenness is small. It has the effect of being able to display with high quality.

Hereinafter, the present invention will be described.

From the viewpoint of improving stretchability, the film of the present invention has a cold crystallization temperature of Tmc1 which is observed in the first temperature lowering process when the temperature raising process and the temperature lowering process are repeated twice by differential scanning calorimetry (DSC). (° C.) When the cold crystallization temperature observed in the second temperature lowering process is Tmc2 (° C.), Tmc1 and Tmc2 satisfy the following formula 1.
Equation 1: Tmc2-Tmc1 ≧ 1.

The temperature raising process is a process of raising the temperature from 25 ° C. to a temperature of the resin melting point + 35 ° C. or higher at a rate of 20 ° C./min and holding it for 5 minutes, and the temperature lowering process is a process of raising the temperature to 25 ° C. after the temperature raising process of 20 ° C. This is the process of lowering the temperature at a rate of ° C./min. Satisfying this equation 1 means that the cold crystallization temperature is higher in the second temperature lowering process than in the first temperature lowering process. From the above viewpoint, Tmc2-Tmc1 ≧ 2 is preferable, and Tmc2-Tmc1 ≧ 5 is more preferable. Most preferably, Tmc2-Tmc1 ≧ 10.

The higher the value of Tmc2-Tmc1, the more difficult it is to crystallize the film before melting. By using a film satisfying the above formula 1, the biaxial stretchability of the unstretched sheet is improved. Further, the mechanical properties of the film are improved with the improvement of the stretchability. Further, since the melt extrusion temperature can be lowered, the content of decomposition products and oligomers is also reduced, and a film having excellent transparency can be obtained. In addition, whitening of the film during high-temperature heating can also be suppressed (hereinafter, the effect of suppressing whitening of the film during high-temperature heating is also referred to as heat-resistant whitening property).

As one of the preferable methods for obtaining the film of the present invention, there is a method of laminating 100 or more resin layers, more preferably 500 layers or more, still more preferably 2000 layers or more in the thickness direction at the time of melt extrusion. When the number of layers is small, the above-mentioned effect is small, and the effect of lowering the yield stress of the axially stretched film satisfying Equation 1 is reduced. It is considered that this is because the effect of suppressing the crystallization growth at the layer interface by laminating in multiple layers decreases as the number of layers decreases. The mechanism by which the difference between Tmc2 and Tmc1 occurs is that Tmc1 drops significantly because the layer interface remains in the first temperature lowering process, but Tmc2 disappears due to melting in the second temperature lowering process. Is considered to be due to the fact that it does not decrease as much as Tmc1. The upper limit of the number of layers is not particularly limited, but the number of layers is about 10,000 in consideration of the increase in size and feasibility of the device.

In order to satisfy Tmc2-Tmc1 ≧ 1 and obtain the stretchability improving effect, the resin applied to the film usually needs to be a resin that crystallizes by heating, and a resin that does not crystallize (amorphous resin) is used. Even if it is laminated in multiple layers, the above effect is not exhibited. Polyester resin, polyolefin resin, and nylon resin are preferably used because they are highly versatile even for heat-crystallizing resins. The most effective is polyethylene terephthalate resin, and in particular, polyethylene terephthalate in which a copolymerization component is partially introduced has a slow crystallization rate, so that the difference in Tmc2-Tmc1 due to multi-layer lamination can be seen most clearly.

For multi-layer stacking in the thickness direction, a method can be used in which molten resin is fed from different flow paths using two or more extruders and fed to the multi-layer laminating apparatus. As the multi-layer stacking device, a device having independent flow paths such as a multi-manifold die and a feed block, and a combination thereof are preferable. Further, using only one extruder, a device such as a static mixer or a square mixer may be introduced in the melt line from the extruder to the die to divide and re-stack the layers. Lamination by a feed block can be easily realized by applying the method described in steps [0053] to [0063] of JP-A-2007-307893. However, the gap and length of the slit plate need to be adjusted as appropriate because they are design values that determine the layer thickness. The layer thickness may be constant, but an inclined structure may be used in which the layer thickness from the front surface to the back surface changes stepwise according to the purpose.

From the viewpoint of increasing Tmc2-Tmc1, it is preferable to use a multi-layer stacking device having independent flow paths such as the feed block described above. This is thought to be because the crystallization suppression effect of multi-layer lamination largely depends on the layer thickness, so a feed block that can precisely control the layer thickness and increase the number of layers by the number of slits is suitable. Be done. In the case of a method of increasing the number of layers in the melt line via a static mixer or a square mixer, the layer thickness accuracy deteriorates as the number of static mixers and square mixers increases. Therefore, Tmc2-Tmc1 is usually compared with a feed block. Will be low.

On the other hand, it is difficult to increase the number of layers to 1000 or more with only the feed block due to the increase in size of the apparatus. Therefore, when the number of layers is 1000 or more, after forming a layered structure of less than 1000 layers (several hundred layers) with the feed block, 1000 layers or more (number) using a 1 to 3 stage static mixer or a square mixer. It is preferable to increase the number of layers to (thousand layers). When the number of static mixers and square mixers is four or more, the effect of deteriorating layer thickness accuracy is greater than the effect of increasing the number of layers, and the effect of suppressing crystallization may be reduced.

From the viewpoint of heat-resistant whitening, the film of the present invention has a Δ haze of 1 (%) when the film is held at Tmc1 (° C.) for 1 time in the first temperature lowering process and the second temperature lowering process, respectively. And Δ haze 2 (%), it is preferable that Δ haze 1 and Δ haze 2 satisfy the following equation 2.
Equation 2: Δ haze 2-Δ haze 1 ≧ 2.0.

The higher the value of Δhaze 2-Δhaze 1, the more difficult it is for the film before melting to proceed with crystallization even in an atmosphere of crystallization temperature. Excellent heat-resistant whitening property when heated at high temperature. The more preferable range of Δhaze 2-Δhaze 1 is 3.0 or more, and in such an embodiment, it is suitable for a polarizing element protective film in which transparency and heat resistance are required because it is extremely excellent in heat-resistant whitening property. Can be used. On the other hand, in many cases, the film that has undergone the stretching step has already undergone crystallization due to the stretching orientation, so that the effect of heat-resistant whitening is difficult to see. Be done.

The Δ haze shown here is a difference in haze value after heating a film having a thickness of 100 μm gripping the end portion in a hot air oven for 1 minute. The smaller the Δhaze, the more difficult it is for the film before melting to crystallize. In the case of a film having a thickness other than 100 μm, conversion is performed by haze value × film thickness / 100.

The thermoplastic resin constituting the film of the present invention is, for example, polyester resin, polyamide resin, polyacetal resin, polyphenylene sulfide resin, polyether ether ketone resin, liquid crystal polymer, polyethylene resin, polypropylene resin, polyvinyl alcohol resin, polyvinylidene chloride. It is typified by resin, syndiotactic polystyrene resin, and the like.

Among these, from the viewpoints of heat resistance, mechanical strength, transparency, and film-forming property, it is particularly preferable to use a polyester resin as a main component, and more preferably to use a crystalline polyester resin as a main component. Here, the main component means a component contained in an amount of more than 50% by mass and 100% by mass or less when all the components constituting the film are taken as 100% by mass. As the crystalline polyester resin, a polyester obtained by polymerization of a monomer containing an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main constituents is preferable.

Here, as the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyl Examples thereof include a dicarboxylic acid, a 4,4'-diphenyl ether dicarboxylic acid, and a 4,4'-diphenylsulfone dicarboxylic acid. Examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dimer acid, dodecandioic acid, cyclohexanedicarboxylic acid and their ester derivatives. Of these, terephthalic acid and 2,6-naphthalenedicarboxylic acid, which exhibit a high refractive index, are preferable. Only one of these dicarboxylic acid components may be used, two or more of them may be used in combination, and an oxyacid such as hydroxybenzoic acid may be partially copolymerized.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. , 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4-) Hydroxyethoxyphenyl) propane, isosorbate, spiroglycol and the like can be mentioned. Of these, ethylene glycol is preferably used. Only one of these diol components may be used, but two or more of these diol components may be used in combination.

More specifically, as the polyester resin, polyethylene terephthalate, polyethylene-2,6-naphthalate, polymethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene methylene terephthalate and the like are preferably used. These resins such as polyester may be homopolymers or copolymers. In the case of polyesters, the copolymerization components include, for example, diethylene glycol, neopentyl glycol, polyalkylene glycol, bisphenol A ethylene oxide adduct and the like. Dicarboxylic acid components such as diol components, dimer acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and the like are used.

In the film of the present invention, the temperature-increasing crystallization temperature of the polyester resin is preferably 70 ° C. or higher. If the temperature-increasing crystallization temperature is less than 70 ° C., the crystallization rate is too fast, and it becomes difficult to increase the value difference between Δhaze 2-Δhaze1. Therefore, it is difficult to obtain the effects of the above-mentioned improvement in biaxial stretchability, mechanical properties, low oligomer content, and heat-resistant whitening property. The temperature-increasing crystallization temperature of the polyester resin is more preferably 120 ° C. or higher, still more preferably 150 ° C. or higher. The upper limit of the temperature-increasing crystallization temperature is not particularly limited, but is 200 ° C. from the viewpoint of a resin preferably used.

The temperature-increasing crystallization temperature of the polyester resin can be measured by DSC in accordance with JIS K-7121-1987. Specifically, 5 mg of the film is subjected to the following temperature raising process and temperature lowering process twice, and the apex temperature of the endothermic peak observed in the second temperature raising process can be set as the temperature rising crystallization temperature. If multiple endothermic peaks are observed, the peak on the low temperature side shall be adopted.
Heating process: The temperature is raised from 25 ° C. to 20 ° C./min to a melting point of + 35 ° C., and then held for 5 minutes.
Temperature lowering process: After the temperature raising process, the temperature is lowered from the melting point of + 35 ° C to 25 ° C at 20 ° C / min.

In the film of the present invention, the crystal melting enthalpy (ΔHm) of the polyester resin is preferably 1 J / g or more and 30 J / g or less. Even if ΔHm is larger than 30 J / g, the effects of the above-mentioned improvement of biaxial stretchability, mechanical properties, low oligomer content, heat-resistant whitening property, and invisible rainbow unevenness can be obtained, but 1 J / g or more. The effect is more likely to be obtained when the range is 30 J / g or less. From the above viewpoint, ΔHm is more preferably 10 J / g or more and 30 J / g or less. If ΔHm is less than 1 J / g, the resin hardly crystallizes, so Tmc2 and Tmc1 are not observed.

The crystal melting enthalpy (ΔHm) of the polyester resin can be measured by DSC in accordance with JIS K-7122-1987. Specifically, 5 mg of the film was subjected to the following temperature raising process and temperature lowering process twice, and the integrated value obtained by subtracting the baseline from the exothermic peak observed in the second temperature raising process was defined as the crystal melting enthalpy (ΔHm). .. If multiple exothermic peaks are observed, the peak on the low temperature side shall be adopted.
Heating process: After raising the temperature from 25 ° C to 20 ° C / min to a melting point of + 35 ° C, holding for 5 minutes. Temperature lowering process: After the temperature raising process, the temperature is lowered to a temperature from melting point + 35 ° C to 25 ° C at 20 ° C / min.

The polyester resin preferably used in the present invention is preferably composed of one kind of polyester resin. Even when a plurality of polyester resins are used, the effect of suppressing crystallization is obtained, but the transesterification reaction between the polyester resins and the melt-kneading proceed, which may cause problems such as a decrease in mechanical strength and whitening. The term "consisting of one type of polyester resin" as used herein means that one polyester resin accounts for 95% by mass or more of all the resin components constituting the film.

Another preferred embodiment of the film of the present invention is a laminated film of a polyester resin layer and a thermoplastic resin layer incompatible with the polyester resin (hereinafter, may be referred to as an incompatible resin layer). The polyester resin layer is a layer containing more than 50% by mass and 100% by mass or less of polyester resin when all the components constituting the layer are 100% by mass. About a thermoplastic resin layer incompatible with polyester resin. Can be interpreted in the same way. Thermoplastic resins that are incompatible with polyester resins include olefin resins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclic olefins, nylon resins, styrene resins, polyacrylate resins, polycarbonate resins, and polyacrylonitrile resins. Polyphenylene sulfide resin, fluororesin, etc. These may be homopolymers or copolymers. Tmc2-Tmc1 can be made larger by laminating the polyester resin layer and the incompatible resin layer in multiple layers.

In the case of laminating the same resin or laminating polyester resins, the layer interface generated by division disappears during melting, so the longer the melt line, the lower the crystallization suppressing effect. If the polyester resin layer and the incompatible resin layer are laminated, the decrease in the crystallization suppressing effect due to the above mechanism is suppressed, and the crystallization suppressing effect is maintained in a high state. On the other hand, in the case of laminating a polyester resin layer and an incompatible resin layer, as the number of layers increases, flow marks and yuzu skin increase and the appearance is impaired. It is preferable to adopt. From this point of view, it is preferable to use a nylon resin, an olefin resin, or a styrene resin for the incompatible resin layer, and the olefin resin includes polyethylene, polypropylene, an ethylene-propylene copolymer, and ethylene-butene-1. Polymers, cyclic olefins and the like are preferable, and polystyrene, polymethylstyrene, polydimethylstyrene and the like are preferable as the styrene resin.

Further, in the case of a laminated film of a polyester resin layer and an incompatible resin layer, it is also preferable to add a compatibilizer in order to improve the laminating accuracy. Examples of additives include Sanyo Chemicals'Youmex (registered trademark), NOF's “Modiper” (registered trademark), Mitsui Chemicals' “Toughmer” (registered trademark), and Nippon Shokubai's “Epocross” (registered trademark). And so on.

From the viewpoint of application to a film for thermoforming, the film of the present invention preferably has an in-plane refractive index difference of 0.01 or less. The difference in refractive index in the film surface is caused by stretching or compressing the film, and although the mechanical properties of the film are improved, the formability is greatly reduced in applications such as thermoforming through such a process. There is a problem to do. Therefore, it is preferable not to perform a step that causes a difference in refractive index in the film surface, and it is most preferable that the unstretched film is obtained by cooling the melt-extruded film as it is.

The film of the present invention is preferably used as a polarizer protective film. When used as a polarizer protective film, the phase difference is preferably in the range of 0 to 100 nm, and then preferably in the range of 3000 to 30000 nm. When the phase difference is in the above range, when used as a polarizer protective film, rainbow unevenness can be reduced when observed from an oblique direction. This effect is particularly significant when mounted on a display device such as a display device such as a large-screen liquid crystal display in which the area of the display screen is large and rainbow unevenness is likely to occur. The phase difference in the range of 0 to 100 nm can be achieved by using a resin having very low crystallinity or by not performing biaxial stretching, but whitening due to heat crystallization is likely to occur. By applying the technique of the present invention, it is possible to achieve both low phase difference and transparency. Further, in order to make the phase difference in the range of 3000 to 30000 nm, it can be achieved by stretching in the uniaxial direction, but the uniaxial stretching is sufficiently oriented in the range of the stretching magnification of 2.0 to 3.5 times. Therefore, whitening may occur due to heat crystallization. Therefore, by applying the technique of the present invention, it is possible to achieve both high retardation and transparency.

The film of the present invention preferably has a thickness of 10 μm or more and 50 μm or less. In particular, when used as a polarizer protective film, when the thickness is 50 μm or less, the application to a thin film polarizing plate becomes easy, and when the thickness is 10 μm or more, the strength is improved. From the above viewpoint, the thickness is more preferably in the range of 15 μm to 30 μm. Examples of the method of adjusting the thickness include a method of adjusting the film forming speed (for example, the rotation speed of the casting drum), and the film can be thinned by increasing the film forming speed. On the other hand, if the speed is increased too much, defects such as foam biting occur in the film, and it is difficult to reduce the speed to 40 μm or less. In order to reduce the film thickness to 40 μm or less, the film can be further thinned by stretching in the longitudinal direction and / or the width direction. On the other hand, biaxial stretching causes rainbow unevenness, which makes it unsuitable for a polarizer protective film. Therefore, a method of biaxial stretching at a high temperature at which orientation does not occur is preferable.

The film of the present invention preferably has a layer thickness of 1 μm or less per layer. The thinner the layer thickness per layer, the easier it is to adjust the effects of Tmc2-Tmc1 and Δhaze2-Δhaze1 to a desired range. From the above viewpoint, the layer thickness per layer is preferably 0.2 μm or less, more preferably 0.05 or less, more preferably 0.02 μm or less, and most preferably 0.01 μm or less. Although the lower limit of the layer thickness per layer is not particularly limited, no difference in the effect can be seen when the layer thickness per layer is 0.001 μm or less. In order to reduce the layer thickness per layer, it can be adjusted by increasing the number of layers and reducing the film thickness as described above. Further, as a method for confirming the layer thickness per layer, a method of _{dyeing the cross section of the film with known RuO 4} or OsO ₄ and observing with an electron transmission microscope can be mentioned. Further, in this method, since the interface cannot be recognized by laminating the same resin and the layer thickness per layer cannot be confirmed, it can be easily calculated by dividing the film thickness by the number of layers.

Hereinafter, the method for producing the film of the present invention will be specifically described by taking as an example a biaxially oriented multilayer laminated film using polyethylene terephthalate. However, the method for obtaining the film of the present invention is not limited to the following.

First, pre-dried polyethylene terephthalate is supplied to separate extruders and melted at a temperature equal to or higher than its melting point. At this time, at least one of the polyethylene terephthalates supplied to each extruder may contain particles such as aggregated silica. Then, after passing through the gear pump and the filter, 100 or more layers of the resin discharged from each extruder are alternately laminated by the feed block while adjusting the discharge amount, and extruded into a sheet shape from the mouthpiece. While applying this electrostatically, it is rapidly cooled and solidified on a casting drum to obtain an unstretched film, which is heated by a roll group and stretched in the longitudinal direction to obtain a uniaxially oriented film. The obtained uniaxially oriented film can be guided to a tenter, preheated with hot air, stretched laterally, heat-treated in the tenter if necessary, slowly cooled to room temperature, and then wound to obtain a biaxially oriented film. .. The stretching temperature, heat treatment temperature, and the like can be appropriately adjusted according to the resin composition, the intended use of the obtained film, and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In addition, the evaluation of the physical property values in each example was performed by the following method.

(Evaluation method of physical property value)
(1) Using a heated crystallization temperature, a cold crystallization temperature, and a differential scanning calorimeter (manufactured by Seiko Instruments, Inc .: SII robot DSC (model EXSTAR DSC6220, data analysis "Standard Analysis")). Measurements and analyzes were performed in accordance with JIS K-7121-1987 and JIS K-7122-1987. Using 5 mg of a film as a sample, the melting point, which is the temperature of the apex of the endothermic peak obtained from the DSC curve when the temperature was raised from 25 ° C. to 20 ° C./min to 350 ° C., was determined. Next, using a new sample, the following temperature raising process and temperature lowering process were performed twice.
Heating process: The temperature is raised from 25 ° C. to 20 ° C./min to a melting point of + 35 ° C., and then held for 5 minutes.
Temperature lowering process: After the temperature raising process, the temperature is lowered from the melting point of + 35 ° C to 25 ° C at 20 ° C / min.
At this time, the apex temperature of the exothermic peak observed in the first temperature lowering process was defined as Tmc1, and the apex temperature of the exothermic peak observed in the second temperature decreasing process was defined as Tmc2. Further, the peak temperature of the endothermic peak seen in the second temperature raising process was defined as the temperature-increasing crystallization temperature, and the integrated value obtained by subtracting the baseline of the exothermic peak was defined as the crystal melting enthalpy (ΔHm).

(2) With the Δ haze film sandwiched between 25 μm Kapton sheets and fixed to a 150 × 150 mm metal frame, the temperature was raised from 25 ° C. to 20 ° C./min to a melting point of + 35 ° C., held for 5 minutes, and then Tmc1 ( The difference between the absolute values of the haze and the haze before heating when held in a hot air oven heated to a temperature of (° C.) for 5 minutes was defined as Δ haze 2 (%). Similarly, the difference between the absolute values of the haze and the haze before heating when held in a hot air oven heated to a temperature of Tmc2 (° C.) for 5 minutes was defined as Δhaze 1 (%). The haze was measured using a haze meter (HGM-2DP manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K-7136 (2006). The measurement was performed twice, and the average value was adopted.

(3) Difference in refractive index in the film surface Using "Abbe Refractometer 4T type" manufactured by Atago Co., Ltd., methylene iodide was used as the mount liquid and nD1.74 was used as the test piece, and the measurement temperature was 25 ° C., sodium D. The refractive index at the line (wavelength: 589.3 nm) was determined in the main orientation axis direction (TD) of the film, the direction orthogonal to the main orientation axis direction (MD), and the thickness direction (ZD), respectively. The value obtained by subtracting the lowest refractive index from the highest refractive index among MD, TD, and ZD was defined as the "refractive index difference" in the film surface.

(4) Film-forming property (only biaxially stretched film is evaluated)
Under the film-forming conditions shown in the examples, the film-forming property of the biaxially stretched film was judged according to the following criteria.
⊚: There is no film breakage or clip detachment, and there is no problem with film surface quality.
◯: There is no film breakage or clip detachment, but there is slight transparency and uneven stretching.
Δ: A level at which film breakage and clip detachment occur slightly and the continuous productivity is inferior. ×: A level at which film breakage and clip detachment occur frequently and continuous production is not possible.

(5) Heat-resistant whitening property (evaluated only for unstretched film and Example 14)
The degree of whitening when the unstretched film was held in a hot air oven heated to a temperature of Tmc1 (° C.) for 1 minute was visually observed and judged according to the following criteria.
Special ◎: There is no whitening of the film, and it is a level that can be suitably used for a polarizer protective film.
⊚: There is no whitening of the film, and it is a level that can be suitably used for thermoformed films.
◯: There is almost no whitening of the film, and it is a level that can be suitably used for thermoformed films.
Δ: Slightly whitened.
X: Remarkably whitened.

(6) Phase difference Using a phase difference measuring device (KOBRA-21ADH) manufactured by Oji Measuring Instruments Co., Ltd., a film is cut out into a rectangular shape of 4 cm in the width direction x 3 cm in the longitudinal direction, and the width direction is defined by this measuring device. A film was placed on the device so that the angle was 0 °, and the in-plane phase difference at a wavelength of 590 nm was measured.

(7) Rainbow unevenness The orientation axes of the films obtained in each example were bonded together via an adhesive so as to be parallel to the absorption axis of the polarizer. After that, the transmitted light when the white LED backlight was irradiated from the lower surface was visually confirmed at an angle of 60 ° in all directions to observe the presence or absence of rainbow unevenness. It was evaluated according to the following criteria.
⊚: No rainbow unevenness was observed.
◯: Rainbow unevenness was observed to the extent that it could be seen by staring at it.
Δ: Rainbow unevenness was observed to the extent that it could be slightly confirmed without staring.
X: Rainbow unevenness was noticeably observed.

(Example 1)
As the thermoplastic resins A and B, polyethylene terephthalate having an intrinsic viscosity of 0.65 (glass transition temperature 78 ° C., melting point 255 ° C.) plus 0.02% by mass of agglomerated silica (average agglomerated particle size 2.0 μm) was used. .. These thermoplastic resins A and B were dried and then supplied to the extruder. The thermoplastic resins A and B are each melted at 270 ° C. in an extruder, passed through a gear pump and a filter, adjusted so that the discharge rate ratio A / B = 1, and alternately placed in a feed block. 501 layers were laminated. The laminated melt was extruded from the mouthpiece and rapidly cooled and solidified on a casting drum maintained at a surface temperature of 20 ° C. while applying static electricity. The obtained unstretched film was heated in a roll group set at 90 ° C., stretched 3.0 times in the vertical direction, guided to a tenter, preheated with hot air at 100 ° C., and stretched 3.3 times in the horizontal direction. .. The stretched film was directly heat-treated in a tenter with hot air at 230 ° C., slowly cooled to room temperature, and then wound up. The results obtained are shown in Table 1.

(Example 2)
An unstretched film having a thickness of 100 μm was obtained under the film forming conditions of Example 1. The results obtained are shown in Table 1. The thickness was adjusted by adjusting the casting drum speed (the same applies hereinafter).

(Example 3)
Same conditions as in Example 1 except that polyethylene terephthalate (PET / I glass transition temperature 77 ° C., melting point 230 ° C.) copolymerized with 10 mol% of isophthalic acid having an intrinsic viscosity of 0.65 was used as the thermoplastic resins A and B. The film was formed in.

(Example 4)
An unstretched film having a thickness of 100 μm was obtained under the film forming conditions of Example 3. The results obtained are shown in Table 1. The results obtained are shown in Table 1.

(Example 5)
As the thermoplastic resins A and B, Toray nylon 6 (Ny6) "Amylan" (registered trademark) 1021T having a melting point of 226 ° C. was used. These thermoplastic resins A and B are melted at 270 ° C. by separate extruders, and after passing through a gear pump and a filter, they are adjusted so that the discharge rate ratio A / B = 1 and the feed block is used. 501 layers were alternately laminated. The laminated melt was extruded from the mouthpiece and rapidly cooled and solidified on a casting drum maintained at a surface temperature of 20 ° C. while applying static electricity. The obtained unstretched film was heated in a roll group set at 75 ° C., stretched 2.5 times in the vertical direction, guided to a tenter, preheated with hot air at 85 ° C., and stretched 2.7 times in the horizontal direction. .. The stretched film was directly heat-treated in a tenter with hot air at 180 ° C., slowly cooled to room temperature, and then wound up. The thickness of the obtained film was 100 μm. The results obtained are shown in Table 1.

(Example 6)
An unstretched film having a thickness of 100 μm was obtained under the film forming conditions of Example 5. The results obtained are shown in Table 1.

(Examples 7 to 8)
Film formation was carried out in order under the same conditions as in Examples 1 and 2, except that the feed blocks were alternately laminated so as to form 101 layers. The results obtained are shown in Table 1.

(Examples 9 to 10)
The feed blocks were alternately laminated so as to form 501 layers, and then the layers were divided and merged by a two-stage square mixer to obtain the number of layers 2001. Other than that, the film was formed in order under the same conditions as in Examples 1 and 2. The results obtained are shown in Table 1.

(Examples 11-12)
The feed blocks were alternately laminated so as to form 501 layers, and then the layers were divided and merged by a four-stage square mixer to obtain 8001 layers. Other than that, the film was formed in order under the same conditions as in Examples 1 and 2. The results obtained are shown in Tables 1 and 2.

(Example 13)
The film was formed under the same conditions as in Example 10 except that the film forming speed was increased and the thickness was adjusted to 40 μm. The results obtained are shown in Table 2.

(Example 14)
Heat in a roll group set at 105 ° C., stretch 3.0 times in the vertical direction, guide to a tenter, preheat with hot air at 110 ° C. and stretch 3.3 times in the horizontal direction so that the thickness becomes 15 μm. The film was formed under the same conditions as in Example 9 except for the adjustment. The results obtained are shown in Table 2. Since biaxial stretching was performed at a high temperature at which no orientation occurred, the effects of heat-resistant whitening and rainbow unevenness were very high.

(Example 15)
Polyethylene terephthalate (copolymerized PET glass transition temperature 77 ° C., melting point 250 ° C.) obtained by copolymerizing 2 mol% of 5-sodium sulfoisophthalic acid having an inherent viscosity of 0.65 with the thermoplastic resin A was used as the thermoplastic resin B, "Amilan". The procedure was carried out under the same conditions as in Example 6 except that 1021T (registered trademark) was used. The results obtained are shown in Table 2.

(Comparative Examples 1 to 6)
Film formation was carried out in order under the same conditions as in Examples 1 to 6 except that the two layers were laminated with a feed block. The results obtained are shown in Table 2.

According to the present invention, the biaxial stretchability and the high temperature whitening resistance of the unstretched film are improved, and a film having a good appearance can be obtained. Since the film of the present invention is excellent in transparency, flatness, and mechanical properties, it is used for home appliances, mobile phones, automobile interior and exterior materials, packaging materials, building material members, polarizing plate release, FPC, membrane switch, coating group. It can also be applied to optical applications such as materials and ITO substrates.

Claims (8)

When the temperature raising process and the temperature lowering process are repeated twice by differential scanning calorimetry (DSC), the cold crystallization temperature seen in the first temperature lowering process is Tmc1 (° C.), and the coldness seen in the second temperature lowering process. A film characterized in that Tmc1 and Tmc2 satisfy the following formula 1 when the crystallization temperature is Tmc2 (° C.).
Equation 1: Tmc2-Tmc1 ≧ 1 When the Δ haze when the film was held at Tmc1 (° C.) for 1 minute in the first temperature lowering process and the second temperature lowering process was Δ haze 1 (%) and Δ haze 2 (%), respectively, Δ The film according to claim 1, wherein the haze 1 and the Δ haze 2 satisfy the following formula 2.
Equation 2: Δ haze 2-Δ haze 1 ≧ 2.0 The film according to claim 1 or 2, wherein the film contains a polyester resin as a main component. The film according to claim 3, wherein the temperature-increasing crystallization temperature of the polyester resin is 70 ° C. or higher. The film according to claim 3 or 4, wherein the crystal melting enthalpy (ΔHm) of the polyester resin is 1 J / g or more and 30 J / g or less. The film according to any one of claims 1 to 5, wherein the difference in refractive index in the film surface is 0.01 or less. The film according to any one of claims 1 to 6, wherein the film is used as a polarizer protective film. The film according to any one of claims 1 to 7, wherein the film has a thickness of 10 μm or more and 50 μm or less.