TWI700307B - Two-axis orientation polyester film - Google Patents

Abstract

The present invention utilizes the dimensional stability in the film width direction (TD direction) and the direction perpendicular to it (MD direction) when the temperature is lowered from 150°C to 50°C, which is 50ppm/°C or more and 130ppm/°C or less, and A biaxially oriented polyester film with a surface orientation coefficient (fn) of 0.111 or more and 0.145 or less provides a film with excellent mechanical properties and processability.

Description

Two-axis oriented polyester film

The present invention relates to a biaxially oriented polyester film with excellent mechanical properties and processability.

The mechanical properties of polyester resins, especially polyethylene terephthalate (hereinafter, sometimes referred to as PET), or polyethylene 2,6-naphthalate (hereinafter, sometimes referred to as PEN), It has excellent thermal properties, chemical resistance, electrical properties, and moldability, and is used in various applications. The polyester film formed by thinning the polyester, and the biaxially oriented polyester film is used as a step film to protect the transparent electrode substrate from damage during the processing step due to its excellent mechanical properties and processability .

Generally, in the transparent conductive film substrates (ITO (Indium Tin Oxide) vapor deposition substrates, etc.) used in displays, etc., in order to improve the conductivity of the ITO film, it is necessary to harden the substrate at a certain temperature step. In this step, heat is simultaneously applied to the substrate and the protective film. Therefore, if the thermal characteristics of the transparent conductive film substrate and the protective film are different, especially the dimensional change rate (coefficient of linear expansion (CTE)) when the temperature drops from 150°C to 50°C, there is a difference in the production of transparent conductive film The flatness of the film substrate is deteriorated, or the protective film is peeled off and the protective function is reduced, so it is preferable to take a value close to the dimensional change rate of the film substrate of the transparent conductive film and the protective film. Therefore, conventionally, a biaxially aligned PET film (Patent Document 1) is used in a film-forming substrate of a transparent conductive film, and therefore, a PET film is often used as a protective film.

However, in recent years, from the viewpoint of improving the performance of displays and making thin films, research has been conducted on the use of films containing amorphous resins such as cycloolefin polymers (COP) in transparent conductive film substrates (Patent Document 2 , 3).

[Prior Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2013-093310

Patent Document 2: Japanese Patent Laid-Open No. 2013-114344

Patent Document 3: Japanese Patent Laid-Open No. 2014-112510

When a biaxially aligned PET film is used in the film substrate of the transparent conductive film, the biaxially aligned PET can be preferably used as the protective film of the substrate. However, when a sheet containing COP is used in the film substrate of a transparent conductive film, the COP is usually an amorphous resin, and the dimensional change rate is about 2 to 3 times larger than that of biaxially aligned PET. When the oriented PET film is used as a protective film, the flatness of the film-making substrate of the transparent conductive film will deteriorate, or the protective film will peel off.

On the other hand, if it is considered that reducing the difference in the dimensional change rate between the film-forming substrate of the transparent conductive film and the protective film, a film containing COP is considered as the protective film. However, when a film containing COP is used as a protective film, because COP is an amorphous resin, it has lower toughness and lower flexibility than biaxially oriented PET film, so cracks may occur during processing steps. The problem.

The subject of the present invention is in view of the background of the prior art, and provides a It can be preferably used as a biaxially oriented polyester film for the protective film of COP, which is used as a film substrate for transparent conductive films.

In order to solve the above-mentioned problems, the present invention adopts the following configuration. which is,

[I] A biaxially oriented polyester film whose dimensional change rates in the film width direction (TD direction) and the direction perpendicular to it (MD direction) when the temperature is lowered from 150°C to 50°C are 50 ppm/ °C or higher and 130 ppm/ °C or lower, and the plane alignment coefficient (fn) is 0.111 or higher and 0.145 or lower.

[II] A biaxially oriented polyester film whose dimensional change rate in the film width direction (TD direction) and the direction at right angles to it (MD direction) when the temperature drops from 150°C to 50°C is 50ppm/ The thermal shrinkage rate at 130°C and 30 minutes in the film width direction (TD direction) and the direction perpendicular to it (MD direction) is 1.0% or less, respectively.

[III] The biaxially oriented polyester film as described in [I] or [II], wherein the plane alignment coefficient (fn) is 0.120 or more and 0.140 or less.

[IV] The biaxially oriented polyester film as described in any one of [I] to [III], wherein the width direction of the film (TD direction) and the direction perpendicular to it (MD direction) and the width of the film When the heat shrinkage rate at 130°C and 30 minutes in the direction forming 45° is compared in all directions, the absolute value of the difference is 0% or more and 0.5% or less, and the average value of the same is 0.5 % Or less; and the film width direction (TD direction), the direction at right angles to it (MD direction), and the direction forming 45° with the film width direction when the temperature drops from 150°C to 50°C, the dimensional change rate is each When comparing in the direction, the absolute value of the difference between them is 0 ppm/°C or more and 10 ppm/°C or less.

[V] The biaxially oriented polyester film as described in any one of [I] to [IV], wherein The heat of crystal melting of the polyester resin of the polyester film is 30 J/g or less.

[VI] The biaxially oriented polyester film as described in any one of [I] to [V], wherein the polyester film is a laminated polyester film comprising at least 3 layers, and forms the surface layers on both sides of the film The heat of crystal melting (△HmA) of polyester resin is above 30J/g, and the heat of crystal melting (△HmB) of the polyester resin in layers other than the surface layer on both sides of the film is below 30J/g.

[VII] The biaxially oriented polyester film as described in [VI], wherein the polyester resin constituting the layers other than the surface layers on both sides of the film is a resin with terephthalic acid and ethylene glycol as main constituents, As other constituent units, only one or only two of isophthalic acid and cyclohexylene dimethanol are included.

[VIII] The biaxially oriented polyester film as described in any one of [I] to [V], wherein the polyester film is a laminated polyester film comprising at least 3 layers, and forms the surface layers on both sides of the film The melting point TmA of the polyester resin is above 250°C and below 280°C.

[IX] The biaxially oriented polyester film as described in [IV] to [VIII], wherein the ratio of the sum of the thickness of the surface layer on both sides of the polyester film to the sum of the thickness of the layers other than the surface layer (both sides The sum of the thickness of the surface layer/the thickness of the layers other than the surface layer) is 1/9~1/2.

[X] The biaxially oriented polyester film as described in any one of [I] to [IX], which is used for bonding to a film containing an amorphous resin.

[XI] The biaxially oriented polyester film as described in any one of [I] to [IX], which is used for bonding to a film containing a cycloolefin polymer (COP).

[XII] The biaxially oriented polyester film as described in any one of [I] to [XI], which is used to protect a film containing cycloolefin polymer (COP).

According to the present invention, it is possible to obtain the A biaxially oriented polyester film with excellent mechanical properties and good processability.

Hereinafter, specific examples are given to explain the present invention in detail.

From the viewpoint of mechanical properties, the polyester film of the present invention must be a biaxially oriented polyester film. The polyester referred to here means one having a dicarboxylic acid constituent and a diol constituent. In addition, in this specification, the so-called constituent means the smallest unit that can be obtained by hydrolyzing polyester. From the viewpoint of mechanical properties, the polyester film of the present invention is preferably a copolymer containing polyethylene terephthalate or polyethylene terephthalate.

One aspect of the present invention is that the dimensional change rate of the film width direction (TD direction) and the direction perpendicular to the film width direction (MD direction) from 150°C to 50°C when the temperature drops are 50ppm/°C or more and 130ppm/°C respectively Below, a biaxially oriented polyester film with a plane alignment coefficient (fn) of 0.111 or more and 0.145 or less.

Generally, a transparent conductive film is formed on a substrate at a higher temperature than room temperature, and then cured at a higher temperature than room temperature, and then cooled to room temperature. process. That is, after the formation of the transparent conductive film, in order to prevent the transparent conductive film from being damaged and impairing conductivity, it is important to maintain the flatness of the substrate. The protective film for the substrate also goes through this step. That is, in order to keep the flatness of the substrate good, it is important to set the dimensional change rate of the protective film of the substrate to a value close to that of the substrate when the temperature is lowered.

In recent years, as a transparent conductive film substrate, it has been widely used including As a non-crystalline resin COP film. The dimensional change rate of the film containing COP during cooling from 150°C to 50°C also depends on the molecular framework of the COP, and is above 50ppm/°C and below 150ppm/°C. By setting the dimensional change rate of the polyester film of the present invention from 150°C to 50°C when the temperature is lowered to be close to the range of the above-mentioned COP-containing film, the conductive film can be formed without damage The flatness of the film-making substrate of the transparent conductive film, while maintaining good conductivity. More preferably, it is 60 ppm/°C or more and 110 ppm/°C or less, and more preferably 80 ppm/°C or more and 100 ppm/°C or less.

Furthermore, the dimensional change rate of the biaxially aligned polyester film is determined by the orientation of the molecular chains of the polyester constituting the film. That is, when the molecular chains are aligned, the molecular chains cannot move freely by heat, and as a result, the value of the dimensional change rate decreases. That is, in the case of a normal biaxially oriented polyester film, the value of the dimensional change rate decreases (less than 50ppm/°C) when the alignment degree of the molecular chain with fn exceeding 0.145 is high. On the other hand, when the orientation of the film with fn less than 0.111 is insufficient, the mechanical properties, especially the elongation at break, are poor, resulting in poor workability. In addition, due to the insufficient alignment of the film, the molecular linkages are nearly amorphous, so random coarse crystals are generated when heat is applied to the film, which not only impairs the transparency of the film, but also exists in it by random coarse crystals. The surrounding molecular chains are also fixed, and as a result, the value of the dimensional change rate is also reduced. Therefore, the biaxially oriented polyester film of the present invention can be made into the film width direction (TD direction) and the direction perpendicular to the direction (MD direction) from 150°C to 50°C in terms of dimensional change rate when the temperature is lowered. A biaxially oriented polyester film of 50ppm/°C or more and 130ppm/°C or more, and an area orientation coefficient (fn) of 0.111 or more and 0.145 or less, can be made into a biaxially oriented polyester film with excellent mechanical properties and processability, and maintain a relatively high level even when heated High transparency film. More preferably, fn is 0.120 or more and 0.140 or less.

Another aspect of the present invention is the film width direction (TD direction), and The dimensional change rate from 150°C to 50°C in the right-angled direction (MD direction) is 50ppm/°C or more and 130ppm/°C or less, and the film width direction (TD direction), and the right angle A biaxially oriented polyester film with a thermal shrinkage rate of less than 1.0% at 130°C and 30 minutes in the direction (MD direction). As described above, in the film forming step of the transparent conductive film, the step of forming the transparent conductive film on the substrate in a state where the temperature is higher than room temperature is included. Therefore, when the thermal shrinkage rate of the protective film of the substrate is large, the planarity of the substrate may be damaged. When using a polyester film whose dimensional change rate during cooling from 150°C to 50°C is in the above range and the heat shrinkage rate at 130°C for 30 minutes is in the above range is used as a protective film for COP film, The smoothness of the COP film becomes better, and the adhesion to the COP becomes better. More preferably, the thermal shrinkage rate at 130°C and 30 minutes in the MD direction and TD direction is 0.5% or less. The lower limit of the thermal shrinkage rate is preferably -0.2%. The so-called "-" means expansion. When it swells by exceeding -0.2%, the substrate and the protective film may peel off.

The dimensional change rate and heat shrinkage rate of the polyester film of the present invention preferably satisfy the following requirements. That is, it is preferable that the film width direction (TD direction), the direction at right angles to the film width direction (MD direction), and the direction forming 45° with the film width direction at 130°C and the heat shrinkage rate in 30 minutes are in all directions For comparison, the absolute value of the difference is (the absolute value of the difference between the thermal shrinkage in the TD direction and the MD direction, the absolute value of the difference between the thermal shrinkage in the TD direction and the direction 45° from the TD direction, The absolute value of the difference in the thermal shrinkage between the MD direction and the direction 45° from the TD direction) 0% or more and 0.5% or less, and the average value of the same is 0.5% or less, and the temperature will be lowered from 150°C to 50°C When comparing the dimensional change rate in all directions, the absolute value of the difference is (the absolute value of the difference between the dimensional change rate in the TD direction and the MD direction, the TD direction and the direction forming 45° with the TD direction The absolute value of the difference of the dimensional change rate, MD direction and TD direction The absolute value of the difference in the dimensional change rate in the direction forming 45°) 0 ppm/°C or more and 10 ppm/°C or less.

When a sheet containing amorphous resin is used as a film substrate for a transparent conductive film, it is usually used in a non-stretched state. Therefore, the sheet containing amorphous resin is responsive to heat (dimension change rate, thermal Shrinkage) is isotropic. On the other hand, the biaxially oriented polyester film is between the film width direction (TD direction) as the stretching direction, the direction at right angles to it (MD direction), and the direction that forms 45° with the film width direction in the middle. , The response to heat (dimension change rate, thermal shrinkage rate) is different. If the polyester film with a large difference is used as a laminate by bonding a sheet and film containing an amorphous resin to the polyester film, the laminate may curl. By making a biaxially oriented polyester film that satisfies the above range, even if it is laminated with a sheet containing an amorphous resin to form a laminate, the response to heat is close, and the curl of the laminate is suppressed. Therefore it is better.

In addition, the thermal shrinkage rate of the biaxially oriented polyester film of the present invention at 150°C for 30 minutes is preferably 1.5% or less in both MD and TD directions. More preferably, the heat shrinkage rate at 150°C for 30 minutes is -0.2% or more and 0.5% or less in both MD and TD directions.

In order to set the dimensional change rate, the surface alignment coefficient (fn), and the thermal shrinkage rate of the biaxially oriented polyester film within the above-mentioned ranges, for example, the following method (a) can be adopted.

(a) A method in which the heat of crystal fusion of the polyester resin constituting the biaxially oriented polyester film of the present invention is set to 30 J/g or less, and biaxially stretched by the following method.

The two-axis extension method can adopt the following methods.

First, the polyester resin is heated and melted in an extruder and then discharged from a nozzle to obtain an unstretched sheet.

(1) When the melted polyester is discharged from a nozzle to produce an unstretched sheet, the surface temperature is cooled to 10°C or more and 40°C or less on a rotating drum by static contact cooling and hardening to produce an unstretched sheet.

(2) The unstretched sheet obtained in (1) is set in two axes in the longitudinal direction (MD) of the film and the width direction (TD) of the film by satisfying the temperature T1n (℃) of the following formula (i) The extension is 8.5 times or more and 16.0 times or less in area magnification.

(i)Tg(℃)≦T1n(℃)≦Tg+40(℃)

Tg: The glass transition temperature of the resin constituting the polyester film (℃)

(3) By subjecting the biaxially stretched film obtained in (2) to a temperature (Th0(°C)) that satisfies the following formula (ii), heat-fixing for 1 second to 30 seconds, uniformly After slow cooling, it was cooled to room temperature to obtain a polyester film.

(ii) Tm-60(℃)≦Th0(℃)≦Tm-20(℃)

Tm: the melting point of the resin constituting the film (℃)

By obtaining an unstretched sheet that satisfies the conditions of (1), a substantially amorphous polyester film can be obtained, the film can be easily oriented in the subsequent steps (2), and a film with good mechanical properties can be easily obtained.

By satisfying the condition of (2) to obtain a biaxially stretched film, a proper alignment can be imparted to the film and a film with good mechanical properties can be made.

By ending the crystal alignment according to the conditions of (3), a film with stable structure of aligned polyester molecular chains and good mechanical properties and thermal shrinkage can be made.

Furthermore, in (2), as a biaxial stretching method, it is also possible to use the film in the longitudinal direction (MD) and the film in the width direction (direction perpendicular to the longitudinal direction of the film, TD). In the sequential two-axis extension method where the extension is separated and the extension in the longitudinal direction and the width direction is performed simultaneously Any kind. In addition, when the stretching temperature (T1n) (°C) is less than Tg (°C), stretching is difficult. When T1n (°C) exceeds Tg+40 (°C), the film breaks frequently, and the film cannot be obtained by stretching. More preferably, Tg+10(°C)≦T1n(°C)≦Tg+30(°C).

In the step (3), when Th0 exceeds Tm-20°C, the orientation of the film imparted by stretching may collapse, and the heat shrinkage rate may increase. When Th0 is lower than Tm-60°C, the structure of the molecular chain is unstable, and the flatness or film-forming property is deteriorated. Furthermore, by setting the value of Th0 to Tm-30(°C)≦Th0(°C)≦Tm-20(°C), the stretching of the molecular chain when the film is stretched can be relaxed, and the thermal shrinkage rate is set to be higher. The best range. In the step (3), a relaxation treatment of reducing the distance in the width direction of the film from 2% to 10% can also be implemented.

The heat of crystal fusion of the polyester resin constituting the biaxially oriented polyester film of the present invention is preferably 30 J/g or less. When the heat of crystal melting exceeds 30J/g, the crystallinity of the resin is higher. Even when the above-mentioned method is used for biaxial stretching, the alignment of the molecular chain is enhanced, fn is larger, and the dimensional change rate is reduced. tendency. The lower limit of the heat of crystal fusion is preferably 2 J/g or more. In the case of less than 2J/g, there are cases where the film-forming properties are poor, or the fn is lower than the lower limit of the preferable range. As a method of setting the heat of crystal melting of the polyester resin to 30J/g or less, when the polyester resin is PET, it can be exemplified: a method of copolymerizing phthalic acid as a dicarboxylic acid component, The method of copolymerizing cyclohexane dimethanol as a diol component, etc. These can be copolymerized alone or in several types. The crystallinity of the single copolymer is easier to control, so it is better. In particular, when isophthalic acid is used as a copolymerization component, since the structure is close to terephthalic acid, it is easy to extend and impart alignment and set fn in a preferable range, which is particularly preferred. As the amount of copolymerization, the total amount of copolymerization components is It is preferably 7 mol% or more and 20 mol% or less with respect to the total amount of the constituent components of the polyester.

As a method of a further preferred embodiment, a method of setting the film into the following (b) configuration can be cited.

(b) The polyester film is made into a laminated polyester film containing at least 3 layers, and the crystal melting heat (△HmA) of the polyester resin constituting the surface layers on both sides of the film is set to 30J/g or more, and the composition The heat of crystal fusion (△HmB) of the polyester resin in the layers other than the surface layer on both sides of the film is set to 30J/g or less.

In the case of this structure, the surface layers on both sides of the film have higher crystallinity than the other layers, and the alignment is easier to impart. Therefore, following this layer, the orientation of the other layers is also increased, and the overall orientation of the film is improved. As a result, the mechanical properties are improved and the processability is improved, which is preferable. In addition, as a result of the improved orientation, whitening when heat is applied to the film is suppressed, which is preferable. ΔHmA is preferably 31 J/g or more and 60 J/g or less, and ΔHmB is preferably 2 J/g or more and less than 30 J/g.

In the case of adopting this configuration, the orientation of the resin constituting the surface layers on both sides can be improved, so it is preferable that the elongation temperature satisfies the following formula (iii).

(iii) TgA(℃)≦T1n(℃)≦TgA+40(℃)

TgA indicates the glass transition temperature of the polyester resin constituting the surface layer on both sides of the film. Furthermore, in the case of a film containing polyester resins of different compositions on both sides of the polyester film of the present invention (for example, A/B/C), the polyester resin constituting the two sides of the surface layer is preferred Among the Tg, the higher temperature satisfies formula (iii).

Furthermore, when the polyester film of the present invention is a laminated polyester film comprising at least 3 layers, the melting point TmA of the polyester resin constituting the surface layers on both sides of the film is preferably set to 250°C or higher and 280°C or lower. Implementation form.

When the value of TmA is below 250℃, the heat in film production When receiving heat during processing, etc., the flatness may deteriorate or the film-forming properties may deteriorate. A 3-layer laminated polyester film in which the melting point TmA of the polyester resin forming the surface layers on both sides of the film is 250°C or higher and 280°C or lower will have good flatness and film forming properties, which is particularly preferred.

When the film of the present invention is a laminated polyester film with three or more layers, it is preferably the ratio of the sum of the thickness of the surface layers on both sides of the polyester film to the sum of the thickness of the layers other than the surface layer (the surface layers on both sides The sum of the thickness/the thickness of the layers other than the surface layer) is 1/9~1/2.

When the thickness of the surface layer is thin, and the ratio of the sum of the thickness of the surface layers on both sides to the sum of the thickness of the layers other than the surface layer is less than 1/9, it may not be possible to obtain the improvement of the film forming performance and the improvement of the mechanical properties by the build-up. The effect of the situation. On the other hand, when the thickness of the surface layer is thicker, when the ratio of the sum of the thickness of the surface layer on both sides to the thickness of the layer other than the surface layer exceeds 1/2, it is strongly affected by the orientation of the surface layer and the inner layer is excessive As a result, the film forming properties may deteriorate.

Since the thermal shrinkage rate is set to a more preferable range, the following step (c) is also a preferable embodiment.

(c) The thin film obtained by the method (a) or (b) is annealed at a heat treatment temperature Th1 (°C) satisfying the following formula (iv) for a time of 70 seconds or more and 600 seconds or less. As a method of performing this annealing treatment, a method of heat-treating the film in an oven provided between the film unwinding roll and the film winding roll (off-annealing) can be cited.

(iv)120℃≦Th1(℃)≦Th0(heat-fixing temperature)(℃)

When Th1 (°C) exceeds Th0 (heat fixation temperature) (°C), in step (4), the structure of the molecular chain in the immobilized film in step (3) is destroyed, resulting in As a result, the film may shrink greatly and the flatness may deteriorate. On the other hand, when Th1 (°C) is lower than 120°C, there may be cases where the thermal shrinkage rate at 130°C cannot be set to a better range.

By going through the step (c), the stress remaining in the molecular chains that constitute the film during the steps (a) and (b) can be removed, and the reduction in thermal shrinkage, isotropy, and dimensional change rate can be obtained Therefore, it is the preferred embodiment of the present invention. Especially in the case of the film obtained by the method (b), since the resin with TmA of 250°C or higher and 280°C or lower is arranged on both surface layers, when heat is applied in the step (c), it can be used The alignment of the film is not damaged, but only reduces the heat shrinkage rate, so it is better.

The thickness of the biaxially aligned polyester film of the present invention is preferably 30 μm or more and 150 μm or less. If it is less than 30 μm, it may be easily broken when used as a protective film, and if it exceeds 150 μm, it may have poor handling. More preferably, it is 50 μm or more and 125 μm or less.

The biaxially oriented polyester film of the present invention preferably has a haze change (Δ haze) of 2% or less before and after the treatment at 100°C for 12 hours. By setting the delta haze in the above range, even when the film of the present invention is bonded to a sheet containing an amorphous resin, the sheet containing an amorphous resin can be visually recognized through the film of the present invention , Therefore better. As a factor for increasing the delta haze, it is considered that the amorphous part of the film becomes coarse crystals by heating, or the oligomer is precipitated on the film surface by heating. In the former, the film is oriented and the fn is set to 0.111 or higher, or in the latter, the film is made into a multilayer structure, and the resin constituting the outermost layer is solid-phase polymerized to make the oligomer The content of the resin is reduced, and the precipitation of oligomers is reduced, thereby reducing the delta haze.

The biaxially oriented polyester film of the present invention obtained by the above method is composed of In terms of mechanical properties and processability, the value of the dimensional change rate when the temperature is lowered from 150°C to 50°C is close to that of the film containing the amorphous resin, so it can be preferably used for bonding to the film containing the amorphous resin use. In particular, it can be preferably used as a protective film for films containing COP. In addition, since the transparency is excellent even when heated, it can be preferably used as a protective film for the COP film for forming a transparent conductive film.

[Characteristic evaluation method] A. Melting point (Tm, TmA, TmB) of the film and the resin constituting each layer (℃)

The sample was subjected to a method based on JIS K 7121 (1999), using a differential scanning calorimetry device "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd., and Disk Session "SSC/5200" was used for data analysis. The following methods are used for measurement.

Weigh each 5mg of the sample in the sample pan, heat the sample from 25°C to 300°C (1stRUN) at a heating rate of 20°C/min, keep it in this state for 5 minutes, and then make it below 25°C Perform rapid cooling. Immediately thereafter, the temperature was raised again from 25°C to 300°C at a temperature increase rate of 20°C/min, and the measurement was performed to obtain a differential scanning calorimetry chart of 2ndRUN (the vertical axis is heat energy, and the horizontal axis is temperature). In the differential scanning calorimetry chart of this 2ndRUN, the temperature of the peak top below the crystal melting peak which is the endothermic peak was obtained, and this was set as the melting point (°C). When two or more crystal melting peaks are observed, the temperature of the peak top with the largest peak area is set as the melting point.

When measuring the melting point of the resin constituting each layer of the laminated polyester film, use a microtome to cut off only the resin constituting each layer from the laminated polyester film and use it for measurement.

B. Crystal melting heat of the film and the resin constituting each layer (△Hm, △HmA, △HmB) (J/g)

The sample was used based on JIS K 7121 (1999), using the differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd., and the Disk Session "SSC/5200" was used for data analysis, according to the following The essentials, the implementation of the measurement.

Weigh 5 mg of each sample in the sample pan, heat the sample from 25°C to 300°C (1stRUN) at a temperature rise rate of 20°C/min, keep it in this state for 5 minutes, and then make it below 25°C Way to quench. Immediately thereafter, the temperature was raised again from 25°C to 300°C at a temperature increase rate of 20°C/min, and the measurement was performed to obtain a differential scanning calorimetry chart of 2ndRUN (the vertical axis is heat energy, and the horizontal axis is temperature). In the differential scanning calorimetry chart of the 2ndRUN, the peak area of the endothermic peak was determined and used as the heat of crystal melting. When two or more crystal melting peaks are observed, the area of the highest temperature peak is set as the heat of crystal melting, and when two or more peaks cannot be separated, the two peaks are combined to obtain the peak area.

When measuring the heat of crystallization of the resin constituting each layer of the laminated polyester film, use a microtome to cut off only the resin constituting each layer from the laminated polyester film for measurement.

C. The glass transition temperature (Tg, TgA) of the film and the resin constituting the outermost layer ((℃)

Based on JIS K 7121 (1999), using the differential scanning calorimetry device "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd., and using Disk Session "SSC/5200" for data analysis, the measurement is carried out according to the following procedures .

Weigh 5 mg of each sample in the sample pan, heat the sample from 25°C to 300°C (1stRUN) at a temperature rise rate of 20°C/min, keep it in this state for 5 minutes, and then make it below 25°C Way to quench. Immediately after that, the temperature was increased again from 25°C to 300°C at a temperature increase rate of 20°C/min for measurement to obtain 2ndRUN Differential scanning calorimetry chart (the vertical axis is heat energy, and the horizontal axis is temperature). In the differential scanning calorimetry diagram of the 2ndRUN, in the step-shaped change part of the glass transition, the straight line of each baseline has an equidistant line in the longitudinal axis direction and the curve of the step-shaped change part of the glass transition. Find the point of intersection. When two or more glass transition steps are observed, the glass transition temperature is obtained for these, and the value obtained by averaging the temperature of the same is used as the glass transition temperature (Tg )(℃).

When measuring the glass transition temperature of the resin constituting the outermost layer of the laminated polyester film, use a microtome to cut off only the resin constituting the outermost layer of the laminated polyester film for measurement.

D. Surface orientation coefficient of film (fn)

Based on JIS K 7105 (1999), an Abbe refractometer manufactured by Atago (stock) was used to determine the refractive index at 20°C. The long-side direction refractive index (Nmd), the width direction refractive index (Nd), and the thickness direction refractive index (Nz) of the surface of the film were measured, and the plane alignment coefficient (fn) was calculated. The measurement system was implemented with n=5, and the average value was calculated.

(v)fn=(Nmd十Ntd)/2-Nz

E. Heat shrinkage rate of film (%)

Based on JIS C 2318 (1997), the thermal shrinkage of the film was measured. Cut the film into short strips with a width of 10mm and a length of 150mm. Attach a marking line to the film so that the length measurement part becomes approximately 100 mm, and measure the length of the marking line at 23°C and set it as L0. After that, place a 2g weight in a hot air oven heated to a specific temperature (200°C or 220°C) to lift the film and leave it for 30 minutes. After the film was taken out from the oven and cooled to 23°C, the length of the marking line was measured and set as L1. Calculate by the following formula (vi) The shrinkage rate of the film. The measurement was performed by randomly cutting out 5 locations so that the film longitudinal direction or the film width direction became a length of 150 mm. The average value was calculated for the longitudinal direction and the width direction, and set as the thermal shrinkage rate of the film.

(vi)(Film heat shrinkage rate)=(L0-L1)/L0×100

F. Film thickness (μm)

The thickness of the film is measured using a dial gauge based on the JIS K7130 (1992) A-2 method, and the thickness is measured at five arbitrary locations in the state of overlapping 10 films. The average value is divided by 10 to obtain the film thickness.

G. Thickness of each layer of laminated polyester film (μm)

When the film is a laminated film, the thickness of each layer is obtained by the following method. Cut the cross section of the film in a direction parallel to the width of the film using a slicer. This section was observed with a scanning electron microscope at a magnification of 5000 times, and the thickness ratio of each layer of the build-up layer was determined. The thickness of each layer is calculated from the obtained layer ratio and the above-mentioned film thickness.

H. Film production

The number of times the film ruptured in 1 hour during film formation was counted, and the one with less than one time was designated as A, the one with more than one time and less than 5 times as B, and the one with more than 5 times as C for evaluation. A is the best film forming ability, and C is the worst.

I. Dimensional change rate when the temperature is lowered from 150℃ to 50℃ (ppm/℃)

Based on JIS K7197 (1991), using a thermomechanical measuring device TMA/SS6000 (manufactured by Seiko Instruments), the sample width was set to 4 mm, and the sample length (Distance between chucks) 20mm sample, load 3g. Raise the temperature from room temperature to 160°C at a temperature rise rate of 10°C/min, hold for 10 minutes, and then lower the temperature to 20°C at 10°C/min to obtain the value of the sample size at each temperature (°C). Calculate from the size L (150°C) (mm) of the sample at 150°C and the size L (50°C) (mm) of the sample at 50°C according to the following formula (vii). In addition, the dimensional change rate was implemented with n=5 in the film width direction (TD) and the direction orthogonal to it (MD), and the average value was calculated.

(vii) Size change rate (ppm/℃)=10 ⁶ ×(L(150℃)-L(50℃)))/{20×(150-50)}

J.△Haze (the amount of haze change before and after treatment at 100℃, 12hr) (%)

Cut out the film into a square with a side of 10cm. Use the haze meter NDH-5000 manufactured by Nippon Denshoku Co., Ltd. to randomly measure the haze at 3 locations and calculate the average value. Set the haze before the test as H0 (%). The sample was placed in an oven made by Tabai Espec (stock) in a room maintained at 23°C and 65% RH, and the four sides of the sample were fixed and kept at 100°C and 10% RH or less. Heat treatment for 12 hours under dry heat conditions. In the same way, the haze of the film after the heat treatment is measured to obtain H1 (%). According to the following formula (viii), the Δ haze (ΔH) is obtained.

(viii)△Haze (%)=H1-H0

With the value of △ haze, the judgment is made as follows.

A: △Haze below 1.5%

B: △Haze exceeds 1.5% and 2.0% or less

C: △Haze exceeds 2.0%

A is the best and C is the worst.

K. Processability

Workability is obtained by calculating the elongation at break (%) in the width direction (TD) and the direction perpendicular to the direction (MD) of the film using n5, and judged as follows based on their average value.

A: The elongation at break is above 120%

B: The elongation at break is more than 105% and less than 120%

C: The elongation at break is above 90% and less than 105%

D: The elongation at break is more than 75% and less than 90%

E: The elongation at break is less than 75%

A is the best and E is the worst.

The retention of elongation at break is measured in the following manner. The film is cut out to a size of 1cm×15cm so that the long side is parallel to the MD‧TD of the film. Based on ASTM-D882 (1997), measured when stretched at 5cm between the chucks and at a stretching speed of 300mm/min. The elongation at break. In addition, the number of samples was set to n=5, and the longitudinal direction and the width direction of the film were measured respectively, and the average value of these was calculated, and this was set as the elongation at break of the film.

L. Evaluation of adhesion to COP film

The film of the present invention is cut out to a size of 20cm×20cm, and laminated with the COP film to form a laminate, then placed in an oven at 120°C and allowed to stand for 1 hour. Thereafter, the temperature of the oven was cooled to room temperature at a rate of 20°C/min. After that, the number of wrinkles having a length of 3 cm or more of the laminate formed by bonding the film of the present invention and the COP film was measured, and the judgment was made as follows. The evaluation was carried out with n=5, and the evaluation was carried out based on the average value.

Less than 4 items: S

More than 4 but less than 10: A

More than 10 items but less than 16 items: B

More than 16: C

S is the best and C is the worst.

As the COP film, "ZEONOR ZF14" made by Japan's ZEON company with a thickness of 40μm was used. For bonding, use the toluene solution prepared by adjusting "Rheocoat" R5000 manufactured by Toray Coatex as an adhesive so that the adhesive content becomes 15%, and add Toray to 100 parts by mass of the toluene solution 3 parts by mass of the crosslinking agent "Coronate L" manufactured by Coatex, coated so that the coating thickness after drying becomes 10μm.

M. Curlability of laminate with COP film

Put the laminate made in item L. into an oven at 120°C and let stand for 1 hour. After that, the temperature of the oven was cooled to room temperature at a rate of 20°C/min and left for 1 hour. After that, the film is placed on a horizontal surface, and the COP film is placed on the upper side, and the amount of floating from the horizontal surface of the 4 corners of the laminate is measured, and the average value is obtained as the curl amount (mm), as follows The way to determine. When using the above method to float from the 4 corners of the horizontal area layer body, the curl amount is set to 0 mm.

Above 0mm and less than 10mm: A

Above 10mm and less than 25mm: B

More than 25mm and less than 40mm: C

More than 40mm and less than 55mm: D

Above 55mm: E.

Furthermore, in the above measurement, when the long side direction or the width direction of the film to be measured is unknown, the direction with the largest refractive index in the film is regarded as the long side direction, and the direction parallel to the long side direction Consider the width direction. In addition, the direction of the largest refractive index in the film can also be obtained by measuring the refractive index in all directions of the film with a refractometer. It can be obtained by determining the direction of the slow axis using a retardation measuring device (birefringence measuring device), etc. Out.

[Example]

Hereinafter, the present invention will be explained with examples, but the present invention is not necessarily limited to these.

[Production of PET-1] From terephthalic acid, ethylene glycol, and antimony trioxide as a catalyst, polymerization is carried out by ordinary methods to obtain melt-polymerized PET. The glass transition temperature of the obtained molten polymerized PET was 80°C, the melting point was 255°C, and the intrinsic viscosity was 0.62.

[Production of PET-2] PET-1 is solid-phase polymerized by conventional methods to obtain PET-A. The obtained PET-A has a glass transition temperature of 82°C, a melting point of 255°C, and an inherent viscosity of 0.85.

[Production of PET-A] From terephthalic acid, isophthalic acid and ethylene glycol, using antimony trioxide as a catalyst, the copolymerization amount of isophthalic acid is 7 mol% relative to the total amount of dicarboxylic acid Method: Polymerize by conventional method to obtain copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 77°C, a melting point of 243°C, and an inherent viscosity of 0.62.

[Production of PET-B] From terephthalic acid, isophthalic acid and ethylene glycol, using antimony trioxide as a catalyst, the copolymerization amount of isophthalic acid relative to the total amount of dicarboxylic acid becomes 10mol% Method: Polymerize by conventional method to obtain copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 76°C, a melting point of 235°C, and an inherent viscosity of 0.62.

[Manufacture of PET-C] Made from terephthalic acid, isophthalic acid and ethylene glycol, with O3 Antimony was used as a catalyst, and the copolymerization amount of isophthalic acid was 15 mol% with respect to the total amount of dicarboxylic acid components, and the polymerization was carried out by a conventional method to obtain copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 74°C, a melting point of 230°C, and an inherent viscosity of 0.62.

[Production of PET-D] From terephthalic acid, isophthalic acid and ethylene glycol, using antimony trioxide as a catalyst, the copolymerization amount of isophthalic acid is 20mol% relative to the total amount of dicarboxylic acid Method: Polymerize by conventional method to obtain copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 73°C, a melting point of 220°C, and an inherent viscosity of 0.62.

[Production of PET-E] From terephthalic acid, isophthalic acid and ethylene glycol, using antimony trioxide as a catalyst, the copolymerization amount of isophthalic acid is 25mol% relative to the total amount of dicarboxylic acid Method: Polymerize by conventional method to obtain copolymerized PET. The glass transition temperature of the obtained copolymerized PET was 70°C, and no melting point was observed. The inherent viscosity is 0.62.

[Production of PET-F] From terephthalic acid, cyclohexane dimethanol (CHDM) and ethylene glycol, using antimony trioxide as a catalyst, the copolymerization amount of cyclohexane dimethanol relative to the total glycol component It becomes 10 mol% by conventional polymerization method to obtain copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 72°C, a melting point of 235°C, and an inherent viscosity of 0.62.

[Production of PET-G] From terephthalic acid, cyclohexane dimethanol (CHDM) and ethylene glycol, using antimony trioxide as a catalyst, the copolymerization amount of cyclohexane dimethanol relative to the total glycol component It becomes 20 mol% by conventional polymerization method to obtain copolymerized PET. The obtained copolymerized PET has a glass transition temperature of 70°C, a melting point of 221°C, and an inherent viscosity of 0.62. (Example 1)

The PET-A was vacuum-dried at 160°C for 2 hours and then put into the extruder. It was melted in the machine and extruded onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. Then, the sheet was preheated with a heated roller group, and then stretched 3.1 times in a direction perpendicular to the width direction (MD direction) at a temperature of 90°C, and then stretched using a roller group at a temperature of 25°C. Cool to obtain a uniaxially stretched film. On one side, both ends of the obtained uniaxially stretched film were gripped with a clamp and one side was stretched 3.6 times in the film width direction (TD direction) in a heating zone at a temperature of 100°C in the tenter. Furthermore, the heat treatment area in the tenter is then heat-fixed at a temperature of 210°C for 10 seconds. In the heat-fixing step, a 2% relaxation treatment is performed in the width direction of the film. Then, after uniformly slow cooling in the cooling zone, it is wound up to obtain a biaxially oriented polyester film. The characteristics of the obtained biaxially aligned polyester film are shown in the table. The dimensional change rate is 50 ppm/°C or more and 130 ppm/°C or less in both MD and TD directions. It is a film with excellent adhesion to COP. In addition, it is a film with excellent processability and small haze change due to heating.

(Examples 2-5, Comparative Examples 1, 2)

Except for changing the resin constituting the film as shown in the table, in the same manner as in Example 1, a biaxially oriented polyester film was obtained. The characteristics of the biaxially aligned polyester film are shown in the table. Regarding Examples 2 to 5, they are films with fn, a dimensional change rate in a preferable range, excellent processability, and a small haze change due to heating. In Comparative Example 1, the crystallinity of the resin is higher and the ΔHm is larger. As a result, the fn of the film is increased and the dimensional change rate is smaller. In Comparative Example 2, since ΔHm is not observed and the crystallinity of the resin is lower, it is a film with reduced fn and a smaller rate of dimensional change, and a film with poor adhesion to COP. Furthermore, since fn is small, it is a film with poor processability and large haze change due to heating.

(Example 6)

A three-layer structure of A/B/A, 100 parts by mass of PET-2 as the resin constituting the surface layer, vacuum drying at 160° C. for 2 hours, and input to the extruder 1. In addition, 100 parts by mass of PET-A as the resin constituting the inner layer was vacuum dried at 160° C. for 2 hours, and then put into the extruder 2. The raw materials are melted in the extruder, and the resin fed into the extruder 1 becomes the two surface layers of the film by using the merging device to merge them, and extrude them onto a casting drum with a surface temperature of 25°C. Laminated sheet with 3-layer structure. Then, the sheet was preheated by a group of heated rollers, stretched 3.1 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled by a group of rollers at a temperature of 25°C to obtain a sheet Axis stretch film. While holding both ends of the obtained uniaxially stretched film with clamps, stretch it 3.6 times in the width direction (TD direction) which is a right angle in the longitudinal direction of the heating zone at a temperature of 100°C in the tenter. Furthermore, the heat treatment area in the tenter is then heat-fixed at a temperature of 210°C for 10 seconds. Then, after uniformly slow cooling in the cooling zone, winding was performed to obtain a laminated polyester film. The characteristics of the film are shown in the table. The dimensional change rate is 50 ppm/°C or more and 130 ppm/°C or less in both MD and TD directions. It is a film with excellent adhesion to COP. In addition, it is a film with excellent processability and small haze change due to heating. It can be seen that by using PET-2 for the surface layer, a film with better processability and less haze change due to heating can be made.

(Example 7-21)

The composition of the resin and the film forming conditions were changed as shown in the table, except that the film was formed in the same manner as in Example 6. The characteristics of the film are shown in the table. Dimensional change rate is MD Both the direction and the TD direction are 50 ppm/°C or more and 130 ppm/°C or less. It is a film with excellent adhesion to COP. In addition, it is a film with excellent processability and small haze change due to heating.

(Example 22-24)

The film obtained in Example 6 was used in Example 22, the film obtained in Example 7 was used in Example 23, and the film obtained in Example 8 was used in Example 24, respectively. The film is annealed at a temperature of 140°C in a hot air oven set between the film unwinding roll and the film winding roll so that the heat treatment time of the film becomes 5 minutes to obtain a film with a thickness of 125 μm. The characteristics of the film are shown in the table. The dimensional change rate is 50ppm/°C or more and 130ppm/°C in both MD and TD directions. It is a film with a small heat shrinkage rate at 130°C for 30 minutes, and is particularly excellent in adhesion to COP. In addition, it is a film with excellent processability and small haze change due to heating. In addition, the average value of the thermal shrinkage rate in the MD, TD, and 45° directions is 0.5% or less, and the absolute value of the difference in the thermal shrinkage rate is also 0.5% or less. The difference in the dimensional change rate in these directions The absolute value is also 10 or less, and the curlability of the laminate with COP is also good.

(Comparative example 3-7)

The composition of the resin and the film forming conditions were changed as shown in the table, except that the film was formed in the same manner as in Example 6. The characteristics of the film are shown in the table. In Comparative Examples 3 and 7, the crystallinity of the resin is higher and the ΔHmB is larger. As a result, the fn of the film is increased and the dimensional change rate is also smaller. In Comparative Example 4, the less ΔHm is observed and the lower the crystallinity, it is a thin film with a smaller fn and a smaller dimensional change rate. Furthermore, since fn Smaller, so it is a thin film with poor processability and greater haze changes caused by heating. In Comparative Examples 5 and 6, the heat treatment temperature in the film formation is higher, and the orientation of the film is disordered. As a result, fn is extremely reduced, and the elongation at break is lowered. Not only the workability is poor, but the △ haze caused by heating is also larger. .

(Example 26)

The composition of the resin and the film forming conditions were changed as shown in the table, except that the film was formed in the same manner as in Example 6. The film properties are shown in the table. The dimensional change rate is 50 ppm/°C or more and 130 ppm/°C or less in both MD and TD directions. It is a film with excellent adhesion to COP. In addition, it is a film with excellent processability and small haze change due to heating.

(Example 25, 27-36)

Example 25 uses the film of Example 2, Example 27 uses the film of Example 26, Example 28 uses the film of Example 9, Example 29 uses the film of Example 11, and Example 30 uses the film. For the film of Example 12, Example 31 uses the film of Example 14, Example 32 uses the film of Example 15, Example 33 uses the film of Example 16, and Example 34 uses the film of Example 18. Example 35 used the film of Example 19, and the film of Example 36 used the film of Example 20. The obtained films were placed in a hot air oven between the film unwinding roll and the film winding roll at 140 At a temperature of °C, an annealing treatment is performed so that the time for the heat treatment of the film becomes 5 minutes.

In Examples 29, 30, 31, 34 to 36, the average value of the heat shrinkage rates in the MD, TD, and 45° directions is 0.5% or less, which is The absolute value of the difference is also 0.5% or less, and the absolute value of the difference in the dimensional change rate in these directions is also 10 or less, and the curling property of the laminate with COP is also good.

In Example 25, since it was a single film, the heat shrinkage rate could not be reduced. Although the curling property was slightly inferior, it was at a level without any problems in practical use. In Example 27, since there are several kinds of copolymerization components, the heat shrinkage rate cannot be reduced. Although the curling property is slightly inferior, it is at a level where there is no problem in practical use. In Example 28, since fn is small and amorphous, the heat shrinkage rate cannot be reduced. Although the curling property is slightly worse, it is a level that is not problematic in practical use. In Examples 32 and 33, the difference in the rate of dimensional change in each direction is large, and although the curling property is slightly poor, it is at a level where there is no problem in actual use.

(Industrial availability)

The polyester film of the present invention has excellent mechanical properties and processability, and the dimensional change rate when the temperature is lowered from 150°C to 50°C is close to that of a film containing amorphous resin, so it can be preferably used for lamination containing amorphous resin Use of resin film. In addition, since the transparency is excellent even when heated, it can be particularly preferably used as a protective film for a COP film used for forming a transparent conductive film.

Claims (9)

A biaxially oriented polyester film whose dimensional change rates in the film width direction (TD direction) and the direction perpendicular to it (MD direction) when the temperature drops from 150°C to 50°C are respectively 50ppm/°C or more and 130ppm/°C or less, and the plane orientation coefficient (fn) is 0.111 or more and 0.140 or less, and heat shrinkage at 130°C for 30 minutes in the film width direction (TD direction) and the direction perpendicular to it (MD direction) respectively The rate is 1.0% or less; among them, the biaxially oriented polyester film contains at least 3 layers, and the crystal melting heat (△HmA) of the polyester resin on both sides of the film is above 30J/g, which constitutes the film The heat of crystal fusion (△HmB) of the polyester resin in the layer other than the surface layer on both sides is 30J/g or less. For example, the biaxially oriented polyester film of claim 1, wherein the surface orientation coefficient (fn) is 0.120 or more and 0.140 or less. For example, the biaxially oriented polyester film of claim 1 or 2, wherein the width direction of the film (TD direction), the direction perpendicular to it (MD direction), and the direction forming 45° with the width direction of the film are 130°C, When the heat shrinkage rate under 30 minutes is compared in all directions, the absolute value of the difference between them is 0% or more and 0.5% or less, and the average value of them is 0.5% or less; and the film width direction (TD Direction), and the direction at right angles to the direction (MD direction), and the direction that forms 45° with the width direction of the film when the dimensional change rate from 150°C to 50°C is compared in all directions, the difference between them The absolute value is above 0ppm/℃ and below 10ppm/℃. For example, the biaxially oriented polyester film of claim 1 or 2 has a heat of crystal melting of 30 J/g or less. Such as claim 1 or 2 of the two-axis oriented polyester film, in which both sides of the film are formed The polyester resin of the layer other than the surface layer is a resin with terephthalic acid and ethylene glycol as the main components, and as the other constituent units, it contains only one of isophthalic acid and cyclohexylene dimethanol , Or only two. For example, the biaxially oriented polyester film of claim 1 or 2, wherein the polyester film is a laminated polyester film containing at least 3 layers, and the melting point TmA of the polyester resin constituting the surface layers on both sides of the film is 250°C. Above and below 280°C. For example, the two-axis oriented polyester film of claim 1 or 2, wherein the ratio of the sum of the thickness of the surface layer on both sides of the polyester film to the sum of the thickness of the layer other than the surface layer (the sum of the thickness of the surface layer on both sides/ The sum of the thickness of the layers other than the surface layer) is 1/9~1/2. Such as claim 1 or 2 of the biaxially oriented polyester film, which is used for laminating to a film containing amorphous resin. Such as the biaxially oriented polyester film of claim 1 or 2, which is used for bonding to a film containing cycloolefin polymer (COP).