JP7205531B2 - biaxially stretched film - Google Patents

Description

The present invention relates to a polyester-based biaxially stretched film.
This application claims priority based on Japanese Patent Application 2018-037857 filed on March 2, 2018, the entire contents of which are incorporated herein by reference.

Polyester resins are excellent in properties such as heat resistance, weather resistance, mechanical strength, transparency, chemical resistance, and gas barrier properties. , beverage and food containers, packaging materials, molded products, films, etc.
Among them, polycyclohexylene dimethylene terephthalate (PCT), which is mainly composed of terephthalic acid as an acid component and 1,4-cyclohexanedimethanol as a diol component, has a high melting point of 290 ° C. and a fast crystallization rate, so it is heat resistant. It is widely used for injection molding applications that require good properties, and various studies are also being conducted for biaxially stretched film applications.

Biaxially stretched film using polycyclohexylene dimethylene terephthalate is expected to be used in applications such as flexible substrates, protective films for ITO, prism sheets for smartphones and tablets, and protective films for liquid crystals, taking advantage of its heat resistance. It is
In these applications, the temperature during use becomes high, so it is necessary to withstand a severe heat resistance test of 80 to 200° C. for several minutes to several days.
For example, Patent Document 1 discloses a biaxially oriented polyester film made of polycyclohexylene dimethylene terephthalate, which is stretched or oriented at a specific draw ratio and draw temperature, and subsequently retains dimensions at temperatures of 260° C. or higher. However, a heat-set film with excellent heat resistance is disclosed.

In addition, in the case of beverage/food packaging and outdoor use, it is assumed to be placed in an environment with high humidity. In these cases, in order to prevent deterioration of mechanical properties due to hydrolysis in a high-humidity environment, moisture resistance and moist heat resistance are required.

On the other hand, in Patent Document 2, (a) a terephthalic acid residue, (b) a 1,4-cyclohexanedimethanol residue, and (c) another dicarboxylic acid or diol residue are produced from a polyester A biaxially stretched polyester film having excellent heat resistance is disclosed.

Further, Patent Document 3 discloses a resin composition excellent in moldability, heat resistance, impact resistance and transparency by adding a polyarylate resin to a polyester composed of terephthalic acid and 1,4-cyclohexanedimethanol. It is

Japanese Patent Application Publication No. 2005-530908 Japanese Patent Application Publication No. 2008-524396 Japanese Patent Application Publication No. 2002-302596

However, the films disclosed in Patent Documents 1 and 2 deteriorate in mechanical properties when used in a high-humidity environment, and problems such as film shrinkage and breakage occur.
Moreover, in Patent Document 3, no examination as a biaxially stretched film is made.
Accordingly, an object of the present invention is to provide a polyester-based biaxially stretched film excellent in transparency, heat resistance, wet heat resistance and stretchability.

The present invention includes the following aspects.

[1] The biaxially stretched film of the present invention is a polycyclohexylene dimethylene terephthalate ( A) contains 1 part by mass or more and 50 parts by mass or less of a polyarylate (B) having a higher glass transition temperature than the polycyclohexylene dimethylene terephthalate (A) with respect to 100 parts by mass, and has a crystal melting enthalpy of 20 J/g or more. 80 J/g or less.
[2] A biaxially stretched film according to a preferred embodiment has a crystal melting enthalpy of 25 J/g or more and 80 J/g or less.
[3] A biaxially stretched film according to a preferred embodiment has a crystal melting temperature of 250°C or higher and 350°C or lower.
[4] A biaxially stretched film according to a preferred embodiment is obtained by heating the resin composition constituting the biaxially stretched film at a heating rate of 10°C/min to a temperature 30°C higher than the crystalline melting temperature, and heating at 10°C/min. When the temperature is lowered, the difference between the crystalline melting temperature and the cooling crystallization temperature is 40° C. or higher and 80° C. or lower.
[5] In a biaxially stretched film according to a preferred embodiment, the polycyclohexylene dimethylene terephthalate (A) has a crystal melting enthalpy of 35 J/g or more and 70°C J/g or less.
[6] In a biaxially stretched film according to a preferred embodiment, the polycyclohexylene dimethylene terephthalate (A) has a crystal melting temperature of 260°C or higher and 340°C or lower.

The biaxially stretched film proposed by the present invention has improved heat resistance, moist heat resistance, and stretching processability without impairing the transparency of polycyclohexylene dimethylene terephthalate, so it is suitable for applications that require heat resistance and optical properties. can also be suitably used.

The present invention will be described in detail below. However, the contents of the present invention are not limited to the embodiments described below.

<Biaxially stretched film>
A biaxially stretched film (hereinafter sometimes referred to as “the present biaxially stretched film”) according to an example of the embodiment of the present invention includes a terephthalic acid unit as a dicarboxylic acid component (a-1), a diol component (a-2 ) contains a polycyclohexylene dimethylene terephthalate (A) containing 1,4-cyclohexanedimethanol units, and the polycyclohexylene dimethylene terephthalate (A ), and the crystal melting enthalpy is 20 J/g or more and 80 J/g or less.

As a method for improving heat resistance and moist heat resistance of polycyclohexylene dimethylene terephthalate, a method of adding a crystal nucleating agent for the purpose of improving crystallinity is known.
However, in this method, the degree of crystallinity is improved by adding a crystal nucleating agent, and the heat resistance is accordingly improved. .

In addition, although the crystal nucleating agent is effective in improving the crystallinity of injection-molded products and unstretched extruded products, it may not always be effective in improving the crystallinity of stretched films.
This is because, in the case of injection-molded products and unstretched extruded products, spherulite crystals grow with the nucleating agent as seeds, whereas the crystals in the stretched film are mainly oriented crystals, and both are crystalline. This is because the growth mode and morphology are different.
Due to the difference in crystal form, the former usually gives an opaque molded product, while the latter (stretched film) gives a transparent molded product.

Also known is a method of promoting crystallization and improving heat resistance by applying heat treatment in an in-line process or an out-line process. However, with this method, there is a limit to the degree of crystallinity that can be finally reached, and the addition of the heat treatment step also poses a problem of reduced productivity.
The present invention finds that polyarylate, which is an amorphous resin having a higher glass transition temperature than polycyclohexylene dimethylene terephthalate, exhibits compatibility with polycyclohexylene dimethylene terephthalate, and polycyclohexylene dimethylene terephthalate and poly The inventors have found that a biaxially stretched film containing an arylate resin exhibits excellent transparency, heat resistance, resistance to moist heat, and stretchability.
The biaxially stretched film can also be suitably used for applications requiring heat resistance and optical properties.

The biaxially stretched film according to one embodiment contains 1 part by mass or more and 50 parts by mass or less of polyarylate (B) with respect to 100 parts by mass of polycyclohexylene dimethylene terephthalate (A).

The content of the polyarylate (B) is preferably 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polycyclohexylene dimethylene terephthalate (A), especially 3 parts by mass or more or 45 parts by mass or less. More preferably, it is 5 parts by mass or more and 40 parts by mass or less, and most preferably 10 parts by mass or more and 35 parts by mass or less.
In other words, the content of the polyarylate (B) is preferably 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polycyclohexylene dimethylene terephthalate (A), and 1 part by mass or more and 45 parts by mass. Below, it is more preferably any of 3 parts by mass to 50 parts by mass and 3 parts by mass to 45 parts by mass, 1 part by mass to 40 parts by mass, 3 parts by mass to 40 parts by mass, 5 parts by mass 50 parts by mass or less, more preferably 5 parts by mass or more and 45 parts by mass or less, or 5 parts by mass or more and 40 parts by mass or less; , 5 parts by mass to 35 parts by mass, 10 parts by mass to 50 parts by mass, 10 parts by mass to 45 parts by mass, 10 parts by mass to 40 parts by mass, and 10 parts by mass to 35 parts by mass. is most preferred.
If the ratio of the polyarylate (B) is 1 part by mass or more with respect to 100 parts by mass of the polycyclohexylene dimethylene terephthalate (A), the crystallization temperature can be slowed down, so the stretching process when stretching the film can be performed. improve sexuality.
On the other hand, if the proportion of polyarylate (B) is 50 parts by mass or less with respect to 100 parts by mass of polycyclohexylene dimethylene terephthalate (A), the crystallinity of the present biaxially stretched film is maintained, and the resulting present The biaxially stretched film has sufficient shrinkage resistance when heated.

(1) Crystal melting enthalpy (Δ (delta) Hm)
The crystal melting enthalpy (ΔHm) of the present biaxially stretched film according to one embodiment is 20 J/g or more and 80 J/g or less.
The crystal melting enthalpy (ΔHm) of the present biaxially stretched film according to one embodiment is preferably 25 J/g or more and 80 J/g or less, more preferably 26 J/g or more or 75 J/g or less, and especially 27 J/g or more. Alternatively, 70 J/g or less is more preferable.
In other words, the crystal melting enthalpy (ΔHm) of the present biaxially stretched film is preferably 25 J/g or more and 80 J/g or less, 25 J/g or more and 75 J/g or less, 26 J/g or more and 80 J/g or less, and 26 J/g or more. more preferably 25 J/g or more and 70 J/g or less, 26 J/g or more and 70 J/g or less, 27 J/g or more and 80 J/g or less, 27 J/g or more and 75 J/g or less or less, or 27 J/g or more and 70 J/g or less.
When the ΔHm is 20 J/g or more, the biaxially stretched film has sufficient crystallinity, and the resulting biaxially stretched film is excellent in heat and humidity resistance during heating.
On the other hand, when the ΔHm is 80 J/g or less, the crystallinity of the biaxially stretched film is suitable for secondary workability.

Since the crystal melting enthalpy (ΔHm) of the present biaxially stretched film is due to the ΔHm of the resin material that constitutes the film, the material is called polycyclohexylene dimethylene terephthalate (A) and polyarylate (B). , can be adjusted within the above range by using two resins having different crystallinities.
In addition, ΔHm of the film can be adjusted by adding a crystal nucleating agent or the like.

In addition, as will be described later, polycyclohexylene dimethylene terephthalate (A) and polyarylate (B) cause transesterification in melt mixing. can be adjusted.
Furthermore, in the production of the biaxially stretched film, the crystalline melting enthalpy (ΔHm) of the biaxially stretched film can be optimized by adjusting the cooling temperature from the molten state, the stretching ratio, the stretching temperature, and the heat treatment conditions after stretching. can be

The crystal melting enthalpy (ΔHm) of this biaxially stretched film is measured at a heating rate of 10° C./min using a differential scanning calorimeter (DSC) according to JIS K7121 (2012).

(2) Crystal melting temperature The crystal melting temperature (Tm) of the biaxially stretched film is preferably 250°C or higher and 350°C or lower, more preferably 255°C or higher and 340°C or lower, and especially 260°C or higher. It is more preferably 330°C or lower, particularly preferably 265°C or higher and 320°C or lower, and most preferably 270°C or higher and 310°C or lower.
If the crystalline melting temperature (Tm) of the biaxially stretched film is in the range, the biaxially stretched film has an excellent balance between heat resistance and melt moldability.

The crystal melting temperature (Tm) of the present biaxially stretched film is the same as the above ΔHm, and the resin material constituting the film is the above polycyclohexylene dimethylene terephthalate (A) and polyarylate (B), which have different crystallinities. By using two resins, it is possible to adjust within the above range.
In the same manner as ΔHm above, in the production of the biaxially stretched film, the crystalline melting temperature ( Tm) can be optimized.

Here, the crystalline melting temperature (Tm) is measured according to JIS K7121 (2012) with a differential scanning calorimeter (DSC) using a differential scanning calorimeter (DSC) at a heating rate of 10°C/min.
When the present biaxially stretched film has two or more crystal melting temperatures (Tm), at least one crystal melting temperature (Tm) may be within the above range.
Moreover, when the present biaxially stretched film has two or more crystal melting temperatures (Tm), the crystal melting enthalpy (ΔHm) is the total value of each crystal melting enthalpy.

(3) The difference between the crystalline melting temperature of the resin composition and the crystallization temperature upon cooling, as a guideline for making the crystallization state of the present biaxially stretched film preferable, the resin composition constituting the biaxially stretched film was heated at a heating rate of 10. C./min using a differential scanning calorimeter (DSC), the temperature at the crystallization peak when the temperature is raised to 30.degree. , the difference between the crystalline melting temperature and the cooling crystallization temperature is used.
The difference between the crystalline melting temperature and the cooling crystallization temperature is preferably 40° C. or higher and 80° C. or lower, more preferably 45° C. or higher or 75° C. or lower, and more preferably 50° C. or higher or 70° C. or lower. More preferred.
If the difference between the crystalline melting temperature and the cooling crystallization temperature is 40° C. or more, the crystallization of the resin composition is not too rapid, and sufficient crystallinity is obtained during the rapid cooling process on the casting rolls in the production process of the biaxially stretched film. Since an amorphous sheet with a low viscosity is obtained, and crystallization is not rapidly promoted in the subsequent stretching process, troubles such as breakage are less likely to occur, and the sheet is excellent in stretchability.
On the other hand, if the difference between the crystal melting temperature and the cooling crystallization temperature is 80° C. or less, the crystallization rate is not too slow, so the crystallization is completed in the heat treatment process after stretching, and a biaxially stretched film with excellent heat resistance is obtained. Obtainable.

The difference between the crystalline melting temperature and the cooling crystallization temperature of the present biaxially stretched film can be obtained by using the above (A) and (B) as the resin material constituting the film, as with the above ΔHm and Tm. can also be optimized by adjusting the film processing conditions as described above.

Here, in order to calculate the difference between the crystalline melting temperature and the cooling crystallization temperature of the resin composition constituting the biaxially stretched film, it is preferable to measure the cast film before stretching using DSC. However, it can also be calculated by heating the stretched film to the melting point or higher to melt the film, preparing a press sample, and performing DSC measurement on the press sample. Any measuring method can be employed in the present invention.

The biaxially stretched film can contain resins other than the polycyclohexylene dimethylene terephthalate (A) and the polyarylate (B) within a range that does not impair the effects of the present invention.
Examples of the other resins include polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins other than polycyclohexylene dimethylene terephthalate (A) (polylactic acid resins, Polybutylene succinate resin), polycarbonate resin, polyamide resin (including aramid resin), polyacetal resin, acrylic resin, ethylene-vinyl acetate copolymer, polymethylpentene resin, polyvinyl alcohol Resins, cyclic olefin resins, polyacrylonitrile resins, polyethylene oxide resins, cellulose resins, polyimide resins, polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins Resins, polyamideimide resins, polyamide bismaleimide resins, polyetherimide resins, polyetheretherketone resins, polyetherketone resins, polyethersulfone resins, polyketone resins, polysulfone resins, and fluorine resins Resin etc. are mentioned.

In addition to the components described above, the present biaxially stretched film can also contain additives that are generally blended within a range that does not impair the effects of the present invention.
Examples of the additives include recycled resin generated from trimming loss such as selvage, silica, talc, kaolin, calcium carbonate, etc., which are added for the purpose of improving and adjusting molding processability, productivity and various physical properties of the film. inorganic particles, pigments such as titanium oxide and carbon black, colorants such as dyes, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, cross-linking agents, lubricants, nucleating agents, plasticizers , anti-aging agents, antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, anti-fogging agents, anti-blocking agents, slip agents, and other additives.

Polycyclohexylene dimethylene terephthalate (A) and polyarylate (B), which are raw materials for the resin composition constituting the present biaxially stretched film, are described below.

<Polycyclohexylene dimethylene terephthalate (A)>
Polycyclohexylene dimethylene terephthalate (A) is a polycyclohexylene dimethylene terephthalate containing a terephthalic acid unit as a dicarboxylic acid component (a-1) and a 1,4-cyclohexanedimethanol unit as a diol component (a-2). . Among them, polycyclohexylene dimethylene terephthalate (A) is a polymer mainly composed of terephthalic acid as the dicarboxylic acid component (a-1) and 1,4-cyclohexanedimethanol as the diol component (a-2). is preferred. In particular, the polycyclohexylene dimethylene terephthalate (A) used in the present invention contains 90 mol% or more of terephthalic acid units as the dicarboxylic acid component (a-1), and 1,4-cyclohexanedimethanol as the diol component (a-2). A polymer containing 90 mol % or more of units is preferable.

In this specification, the term "main component" refers to a component that accounts for the largest mass ratio, preferably 45% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more.
In addition, when described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, "X or more and Y or less", "preferably larger than X" and "preferably smaller than Y" It includes the meaning of

The dicarboxylic acid component (a-1) constituting the polycyclohexylene dimethylene terephthalate (A) preferably contains 90 mol % or more of terephthalic acid.
Among them, in the dicarboxylic acid component (a-1), terephthalic acid is more preferably 92 mol% or more, still more preferably 94 mol% or more, particularly preferably 96 mol% or more, and 98 mol. % or more, and most preferably all (100 mol %) of the dicarboxylic acid component (a-1) is terephthalic acid.
By containing 90 mol% or more of terephthalic acid as the dicarboxylic acid component (a-1), the glass transition temperature, melting point and crystallinity of the polycyclohexylene dimethylene terephthalate (A) are improved, which in turn improves the biaxially stretched film. Improves heat resistance.

The polycyclohexylene dimethylene terephthalate (A) may be copolymerized with an acid component other than terephthalic acid at a rate of less than 10 mol % for the purpose of improving moldability and heat resistance.
Specifically, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid , 3,4-furandicarboxylic acid, benzophenonedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid and other aromatic dicarboxylic acids; cyclohexanedicarboxylic acid, Aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and the like. Among these, isophthalic acid, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, and 3,4-furandicarboxylic acid are preferable from the viewpoint of moldability.

The diol component (a-2) constituting the polycyclohexylene dimethylene terephthalate (A) preferably contains 1,4-cyclohexanedimethanol in an amount of 90 mol % or more.
In the diol component (a-2), 1,4-cyclohexanedimethanol is more preferably 92 mol% or more, still more preferably 94 mol% or more, and particularly preferably 96 mol% or more. , is particularly preferably 98 mol % or more, and most preferably all (100 mol %) of the diol component (a-2) is 1,4-cyclohexanedimethanol.
By 1,4-cyclohexanedimethanol occupying 90 mol% or more as the diol component (a-2), the compatibility with the polyarylate (B) is improved, and furthermore, the polycyclohexylene dimethylene terephthalate (A) This improves the melting point and crystallinity of the biaxially stretched film, thereby improving the heat resistance of the biaxially stretched film.

For the purpose of improving moldability and heat resistance, the polycyclohexylene dimethylene terephthalate (A) may be copolymerized with a diol component other than 1,4-cyclohexanedimethanol at a rate of less than 10 mol %.
Specifically, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, diethylene glycol, tri Ethylene glycol, polyalkylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, hydroquinone, bisphenol, spiroglycol, 2,2,4,4,-tetramethylcyclobutane-1,3-diol, isosorbide etc. Among these, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,3-cyclohexanedimethanol are preferred from the viewpoint of moldability.

The crystal melting enthalpy (ΔHm (A)) of polycyclohexylene dimethylene terephthalate (A) is preferably 35 J/g or more and 70 J/g or less, more preferably 36 J/g or more or 65 J/g or less. preferable.
In other words, the crystalline melting enthalpy (ΔHm(A)) of polycyclohexylene dimethylene terephthalate (A) is preferably 35 J/g or more and 70 J/g or less, 35 J/g or more and 65 J/g or less, 36 J/g. It is more preferably 36/g or more and 65 J/g or less, and 36/g or more and 65 J/g or less.
As long as the ΔHm (A) of the polycyclohexylene dimethylene terephthalate (A) is in the relevant range, the polycyclohexylene dimethylene terephthalate (A) is a moderate crystal that is excellent in heat resistance, heat and humidity resistance, melt moldability and stretching processability. have sex.

Crystal melting enthalpy (ΔHm (A)) of polycyclohexylene dimethylene terephthalate (A) is a constituent unit of (A), acid components other than terephthalic acid and / or 1,4-cyclohexanedimethanol units It can be adjusted within the above range by adjusting the type and blending ratio of other diol components.

Crystal melting enthalpy (ΔHm (A)) of polycyclohexylene dimethylene terephthalate (A) is measured at a heating rate of 10° C./min using a differential scanning calorimeter (DSC) according to JIS K7121 (2012). be able to.

The crystal melting temperature (Tm (A)) of polycyclohexylene dimethylene terephthalate (A) is preferably 260° C. or higher and 340° C. or lower, more preferably 270° C. or higher or 330° C. or lower. C. or more or 310.degree. C. or less is more preferable.
In other words, the crystalline melting temperature (Tm (A)) of polycyclohexylene dimethylene terephthalate (A) is preferably 280°C or higher and 310°C or lower, 260°C or higher and 340°C or lower, 280°C or higher and 340°C or lower, and It is more preferably any of 260° C. or higher and 310° C. or lower, 270° C. or higher and 310° C. or lower, 260° C. or higher and 330° C. or lower, 270° C. or higher and 330° C. or lower, and 280° C. or higher and 330° C. or lower. More preferred.
If the crystal melting temperature (Tm(A)) of the polycyclohexylene dimethylene terephthalate (A) is within the range, the polycyclohexylene dimethylene terephthalate (A) has an excellent balance between heat resistance and melt moldability.

The crystal melting temperature (Tm (A)) of polycyclohexylene dimethylene terephthalate (A) is the same as ΔHm above, and acid components other than terephthalic acid and / or other diols other than 1,4-cyclohexanedimethanol units It can be adjusted within the above range by adjusting the types and blending ratios of the components.

The crystal melting temperature (Tm (A)) of polycyclohexylene dimethylene terephthalate (A) can be measured at a heating rate of 10° C./min using a differential scanning calorimeter (DSC) according to JIS K7121 (2012). .

The glass transition temperature (Tg(A)) of the polycyclohexylene dimethylene terephthalate (A) is more preferably 60°C or higher and 150°C or lower, more preferably 70°C or higher or 120°C or lower.
In other words, the glass transition temperature (Tg(A)) of polycyclohexylene dimethylene terephthalate (A) is preferably 60° C. or higher and 150° C. or lower, 60° C. or higher and 120° C. or lower, 70° C. or higher and 150° C. or lower, and More preferably, the temperature is 70° C. or higher and 120° C. or lower.
If the glass transition temperature (Tg(A)) of the polycyclohexylene dimethylene terephthalate (A) is within such a range, the balance between heat resistance and melt moldability is excellent.

The glass transition temperature (Tg) is determined in accordance with the method specified in JIS K7121, and a straight line equidistant in the vertical axis direction from the straight line extending the low-temperature side baseline and the high-temperature side baseline, respectively, and the glass It is the temperature at the point where the curve of the step change portion of the transition intersects (the midpoint glass transition temperature).

The crystalline melting enthalpy (ΔHm (A)), the crystalline melting temperature (Tm (A)), and the glass transition temperature (Tg (A)) of the polycyclohexylene dimethylene terephthalate (A) are all It is applied not only as a characteristic of the raw material for producing the stretched film, but also as a characteristic of the polycyclohexylene dimethylene terephthalate (A) component constituting the present biaxially stretched film.

Generally, the heat resistance and moist heat resistance of a resin composition can be improved by increasing the glass transition temperature (Tg).
In the present invention, by mixing polyarylate (B) having a higher Tg than polycyclohexylene dimethylene terephthalate (A), a resin composition having a higher glass transition temperature than polycyclohexylene dimethylene terephthalate (A) alone can be obtained. , a biaxially stretched film excellent in heat resistance and wet heat resistance can be obtained.
When different resins are mixed to form a resin composition, a combination of resins having poor compatibility generally forms a phase-separated morphology.
In such a case, the resin composition normally has Tg attributed to each component independently, and thus the effect of increasing the Tg cannot be expected.
In the present invention, if there is a specific combination of polycyclohexylene dimethylene terephthalate (A) and polyarylate (B), the compatibility between the two is high, and the transesterification reaction also occurs (details will be described later), so that uniform It was found that it is possible to make a resin composition.
As a result, the Tg of the resin composition becomes substantially 1, which makes it possible to increase it.

In the present invention according to one embodiment, polycyclohexylene dimethylene terephthalate (A) having a high crystal melting enthalpy (ΔHm) is selected in order to further improve the heat resistance and moist heat resistance of the film.
By using polycyclohexylene dimethylene terephthalate (A) with a high degree of crystallinity, crystallization is promoted during stretching, the crystal melting temperature and crystal melting enthalpy are improved, and the biaxially stretched film has excellent heat resistance and resistance to moist heat. is obtained.
On the other hand, if crystallization during stretching occurs significantly, there is a problem that breakage from the crystal portion tends to occur during stretching.
Therefore, in the present invention, polyarylate (B), which is usually amorphous, relaxes the crystallinity of polycyclohexylene dimethylene terephthalate (A) itself, suppresses breakage during stretching, and improves handleability during processing. I am letting
Furthermore, in the present invention, compatibility between resins to be mixed is important.
That is, since polycyclohexylene dimethylene terephthalate (A) and polyarylate (B) have compatibility as described above, the biaxially stretched film has transparency.

<Polyarylate (B)>
The biaxially stretched film contains a polyarylate (B) having a higher glass transition temperature as measured according to JIS K7198A than the polycyclohexylene dimethylene terephthalate (A).
Polyarylate (B) is a polycondensate of dicarboxylic acid component (b-1) and dihydric phenol component (b-2).
The glass transition temperature of the polyarylate (B) can be adjusted by appropriately selecting the dicarboxylic acid component (b-1) and the dihydric phenol component (b-2). Select is preferred.

The dicarboxylic acid component (b-1) constituting the polyarylate (B) is not particularly limited as long as it is a divalent aromatic carboxylic acid. Among them, a mixture of a terephthalic acid component and an isophthalic acid component is preferred.
The mixing ratio (mol%) of the terephthalic acid component and the isophthalic acid component is preferably terephthalic acid/isophthalic acid = 99/1 to 1/99, more preferably 90/10 to 10/90, and 80/20 to 20/ 80 is more preferred, 70/30 to 30/70 is particularly preferred, and 60/40 to 40/60 is particularly preferred. When the mixing ratio of terephthalic acid and isophthalic acid as the dicarboxylic acid component (b-1) is within the above range, the polyarylate (B) is excellent in heat resistance and melt moldability.

The polyarylate (B) may be obtained by copolymerizing an acid component other than terephthalic acid and isophthalic acid as a dicarboxylic acid component.
Specifically, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, benzophenonedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 3,3′- Aromatic dicarboxylic acids such as diphenyldicarboxylic acid and 4,4'-diphenyletherdicarboxylic acid, cyclohexanedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid and other aliphatic dicarboxylic acids. The copolymerization ratio of acid components other than terephthalic acid and isophthalic acid is preferably less than 10 mol % so as not to impair the heat resistance of the polyarylate resin (B).

The dihydric phenol component (b-2) constituting the polyarylate (B) is not particularly limited as long as it is a dihydric phenol, but bisphenol A component, bisphenol TMC (1,1-bis(4- hydroxyphenyl)-3,3,5-trimethylcyclohexane) component, or both bisphenol A and bisphenol TMC.
In general, containing a bisphenol A component results in a polyarylate having excellent melt moldability (fluidity).
On the other hand, by including the bisphenol TMC component, the polyarylate (B) has an improved glass transition temperature and excellent heat resistance.
Both the bisphenol A component and the bisphenol TMC component are used when it is desired to balance melt moldability and heat resistance.
In this case, the ratio (mol%) of the bisphenol A component and the bisphenol TMC component is preferably bisphenol A/bisphenol TMC = 99/1 to 1/99, more preferably 90/10 to 10/90, and 80/20 to 20. /80 is more preferred, 70/30 to 30/70 is particularly preferred, and 60/40 to 40/60 is particularly preferred. By setting the proportions of the bisphenol A component and the bisphenol TMC component within the range, the polyarylate (B) has an excellent balance between heat resistance and melt moldability.

The polyarylate (B) contains bisphenol A (2,2-bis(4-hydroxyphenyl)propane) and bisphenol TMC (1,1-bis(4-hydroxyphenyl)- 3,3,5-trimethylcyclohexane) may be copolymerized.
Specifically, bisphenol AP (1,1-bis(4-hydroxyphenyl)-1-phenylethane), bisphenol AF (2,2-bis(4-hydroxyphenyl)hexafluoropropane), bisphenol B (2, 2-bis(4-hydroxyphenyl)butane), bisphenol BP (bis(4-hydroxyphenyl)diphenylmethane), bisphenol C (2,2-bis(3-methyl-4-hydroxyphenyl)propane), bisphenol E (1 , 1-bis(4-hydroxyphenyl)ethane), bisphenol F (bis(4-hydroxyphenyl)methane), bisphenol G (2,2-bis(4-hydroxy-3-isopropylphenyl)propane), bisphenol M ( 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene), bisphenol S (bis(4-hydroxyphenyl)sulfone), bisphenol P (1,4-bis(2-(4-hydroxy phenyl)-2-propyl)benzene), bisphenol PH (5,5′-(1-methylethylidene)-bis[1,1′-(bisphenyl)-2-ol]propane), bisphenol Z (1,1 -bis(4-hydroxyphenyl)cyclohexane) and the like.
The copolymerization ratio of the above compounds is preferably less than 10 mol % so as not to impair the heat resistance of the polyarylate (B).

The polyarylate (B) used in the present invention contains a mixture of a terephthalic acid component and an isophthalic acid component as the dicarboxylic acid component (b-1) in order to increase compatibility with polycyclohexylene dimethylene terephthalate, and a divalent phenol component. It is preferable to select either a bisphenol A component, a bisphenol TMC component, or a mixture of bisphenol A and bisphenol TMC as (b-2).

In one embodiment of the present invention, the polyarylate (B) has a higher glass transition temperature than the polycyclohexylene dimethylene terephthalate (A).
Further, the difference in glass transition temperature between the polyarylate (B) and the polycyclohexylene dimethylene terephthalate (A) is preferably 60° C. or higher, more preferably 70° C. or higher. , more preferably 80° C. or higher, particularly preferably 90° C. or higher, and most preferably 100° C. or higher.
Furthermore, the glass transition temperature of the polyarylate (B) is preferably 150° C. or higher and 350° C. or lower, more preferably 160° C. or higher or 340° C. or lower, and especially 170° C. or higher or 330° C. or lower. Among them, a temperature of 180° C. or higher or 320° C. or lower is particularly preferred, and a temperature of 190° C. or higher or 300° C. or lower is most preferred.
In other words, the glass transition temperature of the polyarylate (B) is preferably 150° C. or higher and 350° C. or lower, and is any of 150° C. or higher and 340° C. or lower, 160° C. or higher and 350° C. or lower, and 160° C. or higher and 340° C. or lower. more preferably 150°C or higher and 330°C or lower, 160°C or higher and 330°C or lower, 170°C or higher and 350°C or lower, 170°C or higher and 340°C or lower, and 170°C or higher and 330°C or lower, 150°C to 320°C, 160°C to 320°C, 170°C to 320°C, 180°C to 350°C, 180°C to 340°C, 180°C to 330°C, and 180°C to 320°C It is particularly preferable that the It is most preferably any of 190°C to 330°C, 190°C to 320°C, and 190°C to 300°C.
By satisfying the above difference in glass transition temperature between polycyclohexylene dimethylene terephthalate (A) and polyarylate (B), the glass transition temperature of the biaxially stretched film is improved, and the melt moldability is also excellent. An axially stretched film is obtained.

As the polyarylate (B) used in the present invention, a mixture of polycarbonate may be used to improve melt moldability.
Since polyarylate (B) and polycarbonate are compatible, by mixing polycarbonate with polyarylate (B), the glass transition temperature of polyarylate (B) can be lowered while maintaining transparency and mechanical properties. As a result, the melt moldability can be improved.
When polyarylate (B) and polycarbonate are mixed, the mixing ratio (mass%) is preferably polyarylate (B)/polycarbonate = 99/1 to 50/50, more preferably 98/2 to 60/40, 97 /3 to 70/30 is more preferred, and 96/4 to 80/20 is particularly preferred.
If the mixing ratio of the polyarylate (B) and the polycarbonate is within the range, the melt moldability can be improved while maintaining the heat resistance of the polyarylate (B).
For the mixing of the polyarylate (B) and the polycarbonate, it is preferable to use, as raw materials, a mixture of these two components in advance. However, it is not limited only to this method, and the above structure may be obtained by selecting polycarbonate as the above-mentioned "other resin" and using it as an independent raw material.

<Method for producing the present biaxially stretched film>
A method for producing the biaxially stretched film of the present invention will be described. However, the following description is an example of the method for producing the present biaxially stretched film, and the present biaxially stretched film is not limited to the biaxially stretched film produced by such a production method.

In the method for producing a biaxially stretched film according to an example of the embodiment of the present invention, 1 part by mass or more and 50 parts by mass of the polyarylate (B) is added to 100 parts by mass of the polycyclohexylene dimethylene terephthalate (A). In the following manufacturing method, the resin composition obtained by mixing is formed into a film and then biaxially stretched.

In this method for producing a biaxially stretched film, when the polycyclohexylene dimethylene terephthalate (A) and the polyarylate (B) are melt-mixed, a resin composition having excellent transparency and heat resistance is obtained.
In this resin composition, the polycyclohexylene dimethylene terephthalate (A) and the polyarylate (B) are partially transesterified, and the interfacial tension between the two polymers is greatly reduced, so that they are compatible, It is thought that a polyester resin composition having excellent transparency and heat resistance can be obtained.
Therefore, the polycyclohexylene dimethylene terephthalate (A) also includes a transesterified product obtained by transesterification of part or all of the polycyclohexylene dimethylene terephthalate (A), and the polyarylate (B) is A transesterified product obtained by transesterifying a part or all of a polyarylate is also included.
The degree of transesterification (reaction rate) can be adjusted by melt-mixing conditions such as mixing temperature, shear rate, and residence time, thereby adjusting the crystalline melting enthalpy (ΔHm) of the present biaxially stretched film. can also

The method of kneading the polycyclohexylene dimethylene terephthalate (A) and the polyarylate (B) is not particularly limited, but in order to obtain a resin composition as simply as possible, it is preferable to melt-knead it using an extruder. preferable. Furthermore, in order to uniformly mix the polycyclohexylene dimethylene terephthalate (A) and the polyarylate (B), it is preferable to melt-knead them using a co-rotating twin-screw extruder.
The kneading temperature must be at least the glass transition temperature of all the resins used, and at least the crystal melting temperature of the crystalline resin. If the kneading temperature is as high as possible with respect to the glass transition temperature and crystal melting temperature of the resin used, the transesterification reaction of a part of the resin tends to occur and the compatibility tends to be improved, but the kneading temperature is higher than necessary. Then, decomposition of the resin occurs, which is not preferable. Therefore, the kneading temperature is 260° C. or higher and 350° C. or lower, preferably 270° C. or higher and 340° C. or lower, more preferably 280° C. or higher and 330° C. or lower, and particularly preferably 290° C. or higher and 320° C. or lower. .
If the kneading temperature is within the range, compatibility and melt moldability can be improved without causing decomposition of the resin.
The resin composition may be cooled and solidified once into a shape such as a pellet, and then heated and melted again for molding, or the resin composition obtained in a molten state may be molded as it is. .

A biaxially stretched film can be produced by molding the resin composition obtained above by a general molding method such as extrusion molding, blow molding, vacuum molding, pressure molding, press molding, and the like. In each molding method, the equipment and processing conditions are not particularly limited.
In the present invention, the biaxial stretching means stretching in at least two different directions, but preferably in two orthogonal directions.
The present biaxially stretched film is preferably produced, for example, by the following method.

From the resin composition obtained by mixing polycyclohexylene dimethylene terephthalate (A) and polyarylate (B), a substantially amorphous and non-oriented film (hereinafter sometimes referred to as "unstretched film" ) is produced by extrusion.
The unstretched film is produced by, for example, an extrusion method in which the raw material is melted by an extruder, extruded through a flat die or an annular die, and then quenched to form a flat or annular (cylindrical) unstretched film. can be adopted.
At this time, depending on the case, a laminated structure using a plurality of extruders may be employed.

Next, from the viewpoint of stretching effect, film strength, etc., the unstretched film is stretched in at least one direction out of the flow direction of the film (longitudinal direction) and the direction perpendicular thereto (transverse direction). It is stretched 5.0 times, preferably in the range of 1.1 to 5.0 times in each of the vertical and horizontal directions.

As the biaxial stretching method, any of conventionally known stretching methods such as tenter successive biaxial stretching, tenter simultaneous biaxial stretching, and tubular simultaneous biaxial stretching can be employed. For example, in the case of a tenter-type sequential biaxial stretching method, the glass transition temperature of the resin composition is Tg, the unstretched film is heated to a temperature range of Tg to Tg + 50 ° C., and is stretched in the longitudinal direction by a roll-type longitudinal stretching machine. It can be produced by stretching 1.1 to 5.0 times and then stretching 1.1 to 5.0 times in the lateral direction within a temperature range of Tg to Tg+50° C. using a tenter-type lateral stretching machine.
In the case of tenter type simultaneous biaxial stretching or tubular type simultaneous biaxial stretching method, for example, in the temperature range of Tg to Tg + 50 ° C., by stretching 1.1 to 5.0 times in each axial direction at the same time. can be manufactured.

The biaxially stretched film stretched by the above method is subsequently heat set.
Heat setting can impart dimensional stability at room temperature.
In this case, the treatment temperature is preferably in the range of Tm-1° C. to 50° C., where Tm is the crystal melting temperature of the resin composition.
If the heat setting temperature is within the above range, heat setting is sufficiently performed, the stress during stretching is relieved, sufficient heat resistance and mechanical properties are obtained, and troubles such as breakage and whitening of the film surface are prevented. A good film is obtained.

In the present invention, in order to relax the stress of crystallization shrinkage due to heat setting, relaxation is performed in the width direction during heat setting in the range of 0 to 15%, preferably 3 to 10%, so that the relaxation is sufficiently performed. The film is uniformly relaxed in the width direction, the shrinkage rate in the width direction becomes uniform, and a film excellent in room temperature dimensional stability is obtained.
In addition, since the film is relaxed following the contraction of the film, there is no slackening of the film, no flapping in the tenter, and no breakage of the film.

The thickness of the biaxially stretched film of the present invention is preferably 1 to 300 μm, more preferably 5 μm or more or 200 μm or less. By setting the thickness to 1 μm or more, the film strength can be kept within a practical range.

In one embodiment of the present invention, the tensile strength retention rate of the present biaxially stretched film after performing a pressure cooker test (120° C., 100% RH (relative humidity), 1 atm) for 72 hours is It is preferably 35% or more in both the machine direction (MD) and transverse direction (TD).
If the tensile strength retention rate of the present biaxially stretched film is within the range, it has sufficient moist heat resistance to be used as a film.
The tensile strength retention rate of the present biaxially stretched film can be improved by using two resins having different crystallinities, the polycyclohexylene dimethylene terephthalate (A) and the polyarylate (B), as the resin materials constituting the film. It can be adjusted within the range.
In the same manner as ΔHm above, in the production of the biaxially stretched film, by adjusting the cooling temperature from the molten state, the stretching ratio, the stretching temperature, and the heat treatment conditions after stretching, the tensile strength retention rate of the biaxially stretched film can be optimized.

The haze value of the present biaxially stretched film according to one embodiment is preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, and 2% or less. is particularly preferred, and 1% or less is most preferred.
If the haze value of the biaxially stretched film is within the range, it has sufficient transparency to be used as a film.
Incidentally, the haze value in the present invention can be calculated by the following formula.
[Haze] = ([diffuse transmittance] / [total light transmittance]) x 100

Examples are shown below. However, the present invention is not limited by these.

(1) Crystal melting temperature, crystal melting enthalpy For a biaxially stretched film, using a Diamond DSC (manufactured by PerkinElmer Japan), according to JIS K7121 (2012), at a heating rate of 10 ° C./min in the heating process Crystal melting temperature and crystal melting enthalpy (crystal melting heat) were measured.

(2) Crystallization temperature during cooling
For the cast film before making it into a biaxially stretched film, using a Diamond DSC (manufactured by PerkinElmer Japan), according to JIS K7121 (2012), the temperature was raised to 350 ° C. at a heating rate of 10 ° C./min. After holding for 10 minutes, the crystallization temperature was measured during the cooling process from 350°C to -50°C at a cooling rate of 10°C/min.

(3) Formability
When the cast film was biaxially stretched, the film that could be stretched without breaking was evaluated as pass (○), and the film that fractured was evaluated as disqualified (×).

(4) Humidity and heat resistance test Pressure cooker test (120 ° C., 100% RH (relative humidity), 1 atmosphere) was performed for 0 hours, 24 hours, 48 hours or 72 hours. Tests were performed to measure the tensile strength retention in MD and TD.

(5) Measurement of tensile strength Measured by a method according to JIS K7127:1999. A tensile tester (manufactured by Shimadzu Corporation, tensile tester AG-1kNXplus) was used as a measuring device. As the test piece, a rectangle having a length of 100 mm and a width of 15 mm was cut out from the biaxially stretched polyester film. Both ends in the longitudinal direction of the test piece were chucked at a distance between chucks of 40 mm and pulled at a crosshead speed of 200 mm/min. In the tensile test, the MD tensile strength and the TD tensile strength of the film were measured.

(6) Haze Using a haze meter NDH-5000 (manufactured by Nippon Denshoku Industries Co., Ltd.), the total light transmittance and diffuse transmittance are measured based on JIS K7136 (2000), and the haze is calculated by the following formula. bottom.
[Haze] = ([diffuse transmittance] / [total light transmittance]) x 100

[Polycyclohexylene dimethylene terephthalate (A)]
(A)-1: SKYPURA0502HC
(manufactured by SK Chemicals, dicarboxylic acid component: terephthalic acid = 100 mol%, diol component: 1,4-cyclohexanedimethanol = 100 mol%, Tm = 293°C, ΔHm = 48J/g, Tg = 94°C)

(A)-2: SKYPURA0502
(manufactured by SK Chemicals, dicarboxylic acid component: terephthalic acid = 100 mol%, diol component: 1,4-cyclohexanedimethanol = 100 mol%, Tm = 286°C, ΔHm = 42J/g, Tg = 96°C)

(A)-3: SKYPURA1631
(manufactured by SK Chemicals, dicarboxylic acid component: terephthalic acid = 91.8 mol%, isophthalic acid = 8.2 mol%, diol component: 1,4-cyclohexanedimethanol = 100 mol%, Tm = 274°C, ΔHm = 32J/g, Tg=95°C)

[Polyarylate (B)]
(B)-1: U polymer (registered trademark) U-100
(Manufactured by Unitika Ltd., dicarboxylic acid component: terephthalic acid/isophthalic acid = 50/50 mol%, bisphenol component: bisphenol A = 100 mol%, Tg (B) = 210°C)

(Example 1)
Add pellet-like (B)-1 at a rate of 30 parts by mass to pellet-like (A)-1: 70 parts by mass, dry blend, and then set to 310 ° C. co-rotating twin-screw extruder (manufactured by Toshiba Machine Co., Ltd., barrel inner diameter 40 mm, effective screw length L to outer diameter D ratio L / D = 32), the resulting strand is cooled and solidified in a water tank, cut with a pelletizer, and pelletized. made.
The prepared pellets are melt-kneaded at 310°C using a single screw extruder (manufactured by Mitsubishi Heavy Industries, Ltd.), and then extruded through a T-die at 310°C with a gap of 1.0 mm. It was collected and solidified by cooling to obtain a film-like material having a thickness of about 500 µm.
Subsequently, the obtained cast film was passed through a longitudinal stretching machine and stretched 3 times in the machine direction (MD) at 125°C.
Subsequently, the obtained longitudinally stretched film is passed through a transverse stretching machine (tenter) and stretched 3.5 times in the transverse direction (TD) at a preheating temperature of 130°C, a stretching temperature of 130°C, and a heat setting temperature of 260°C. A 10% relaxation treatment was applied to the film in the tenter.
The obtained biaxially stretched film was evaluated for the above (1) to (6).
Table 1 shows the results.

(Example 2)
Regarding polycyclohexylene dimethylene terephthalate (A), samples were prepared and evaluated in the same manner as in Example 1 except that (A)-2 was used instead of (A)-1. Table 1 shows the results.

(Example 3)
Regarding the polycyclohexylene dimethylene terephthalate resin (A), samples were prepared and evaluated in the same manner as in Example 1, except that (A)-3 was used instead of (A)-1. Table 1 shows the results.

(Comparative example 1)
After obtaining a cast film in the same manner as in Example 1, it was stretched 3.0 times in the machine direction (MD) to obtain a uniaxially stretched film. The uniaxially stretched film was evaluated for the above (1) to (6). Table 1 shows the results.
When the crystal melting temperature and crystal melting enthalpy of the obtained stretched film were measured by DSC, values of 285 (°C) and 33 (J/g) could be read, but at the same time, the temperature was lower than the melting peak. A peak due to crystallization was confirmed at . This is a peak attributed to the fact that crystallization was not sufficiently completed only by longitudinal stretching, and crystallization progressed due to temperature rise during DSC measurement. That is, the crystalline melting temperature and crystalline melting enthalpy obtained by DSC measurement of the uniaxially stretched film obtained in Comparative Example 1 do not reflect the physical properties of the uniaxially stretched film itself. Therefore, it is not shown in Table 1.

(Comparative example 2)
Pellet-shaped (A)-2 alone is melted and kneaded with a Φ25 mm twin-screw extruder set at 300 ° C., extruded as a film from the T die, and rapidly cooled in close contact with a cast roll at 20 ° C. A cast film with a thickness of 450 μm is obtained. Obtained. When an attempt was made to produce a stretched film by setting the resulting cast film to a longitudinal stretching temperature of 104°C, a preheating temperature of 104°C, and a transverse stretching temperature of 114°C, breakage occurred during the transverse stretching process. Table 1 shows the results.

(Comparative Example 3)
Table 1 shows the evaluation results of the cast film obtained in the same manner as in Example 1.
When the crystal melting temperature and crystal melting enthalpy of the obtained cast film were measured by DSC, values of 285 (°C) and 29 (J/g) could be read. A peak due to crystallization was confirmed at . This peak is attributed to the fact that crystallization progressed due to the temperature rise during the DSC measurement because the film did not crystallize when not stretched. That is, the crystal melting temperature and crystal melting enthalpy obtained by DSC measurement of the cast film obtained in Comparative Example 3 do not reflect the physical properties of the cast film itself. Therefore, it is not shown in Table 1.

In Examples 1 and 2, biaxially stretched films could be produced without any particular problems during molding. It can be seen that the crystal melting temperature and the crystal melting enthalpy are high, and the heat and humidity resistance is also excellent.
Further, in comparison with Examples 1 and 2, Example 3 was slightly inferior in wet heat resistance even though it was stretched under the same conditions. This is considered to be caused by the low crystal melting enthalpy (32 J/g) and low crystallinity of polycyclohexylene dimethylene terephthalate.
In Comparative Example 1, in which only uniaxial stretching was performed, the tensile test was impossible because the shrinkage of the film was remarkable after the wet heat test.
From the above, it can be said that the stretched film obtained in Comparative Example 1 is inferior in heat resistance and wet heat resistance.
In Comparative Example 2 in which polycyclohexylene dimethylene terephthalate (A) was used alone, breakage occurred during stretching. The resin used here has a small difference between the crystalline melting temperature and the cooling crystallization temperature, so that it has high crystallinity and a high crystallization rate.
Therefore, it is considered that the breakage occurred because a highly crystalline sheet was obtained in the process of quenching with the casting roll.
In Comparative Example 3 in which stretching was not performed, the tensile strength retention rate after the wet heat test was extremely low, and the wet heat resistance was poor.

Claims (6)

With respect to 100 parts by mass of polycyclohexylene dimethylene terephthalate (A) containing a terephthalic acid unit as a dicarboxylic acid component (a-1) and a 1,4-cyclohexanedimethanol unit as a diol component (a-2), to the polycyclo A biaxially stretched film containing 1 part by mass or more and 50 parts by mass or less of polyarylate (B) having a glass transition temperature higher than that of xylene dimethylene terephthalate (A) and having a crystal melting enthalpy of 20 J/g or more and 80 J/g or less (however , , except for biaxially oriented films containing polyamide) . The biaxially stretched film according to claim 1, which has a crystal melting enthalpy of 25 J/g or more and 80 J/g or less. The biaxially stretched film according to claim 1 or 2, which has a crystal melting temperature of 250°C or higher and 350°C or lower. When the resin composition constituting the biaxially stretched film is heated to a temperature 30° C. higher than the crystalline melting temperature at a heating rate of 10° C./min and then cooled at 10° C./min, the difference between the crystalline melting temperature and the cooling crystallization temperature is is 40° C. or higher and 80° C. or lower. The biaxially stretched film according to any one of claims 1 to 4, wherein the polycyclohexylene dimethylene terephthalate (A) has a crystal melting enthalpy of 35 J/g or more and 70°C J/g or less. The biaxially stretched film according to any one of claims 1 to 5, wherein the polycyclohexylene dimethylene terephthalate (A) has a crystal melting temperature of 260°C or higher and 340°C or lower.