KR20180018481A - Biaxially oriented polyester film - Google Patents

Abstract

The dimensional stability at a temperature falling from 150 deg. C to 50 deg. C in each of the film width direction (TD direction) and the direction (MD direction) perpendicular to the film width direction is 50 ppm / ° C or more and 130 ppm / (fn) of not less than 0.111 and not more than 0.145 to provide a film excellent in mechanical properties and processability.

Description

Biaxially oriented polyester film

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

Polyester resins, particularly polyethylene terephthalate (hereinafter, sometimes referred to as PET) and polyethylene 2,6-naphthalene dicarboxylate (hereinafter sometimes referred to as PEN) , Electrical properties, and moldability, and is used for various purposes. A polyester film obtained by forming the polyester into a film, particularly a biaxially oriented polyester film, is used as a film for protecting the transparent electrode substrate from scratches and the like due to its excellent mechanical properties and processability.

Generally, in a transparent conductive film formation substrate (ITO (Indium Tin Oxide) deposited substrate or the like) used in a display or the like, a cure process of a substrate at a certain temperature is required in order to increase the conductivity of the ITO film. In this step, the substrate is simultaneously heated to the protective film. Therefore, if there is a difference between the thermal characteristics of the transparent conductive film of the film-forming substrate and the protective film, particularly the dimensional change rate (linear expansion coefficient (CTE)) at 150 ° C to 50 ° C during temperature decrease, the planarity of the transparent conductive film- It is preferable that the rate of dimensional change of the protective film of the transparent conductive film and that of the protective film are close to each other. Therefore, conventionally, a biaxially oriented PET film was used for a film formation substrate of a transparent conductive film (Patent Document 1), and a protective film was also often used a PET film.

In recent years, however, from the viewpoint of improvement in display performance and thinning, a film made of an amorphous resin such as a cycloolefin polymer (COP) is used for a film formation substrate of a transparent conductive film (Patent Documents 2 and 3).

Japanese Patent Application Laid-Open No. 2013-093310 Japanese Patent Application Laid-Open No. 2013-114344 Japanese Patent Application Laid-Open No. 2014-112510

When a biaxially oriented PET film is used for the film formation substrate of the transparent conductive film, biaxially oriented PET can be suitably used for the protective film of the substrate. However, when a COP sheet is used as a film forming substrate of a transparent conductive film, the COP is generally an unmodified resin, and the dimensional change ratio is 2 to 3 times larger than that of the biaxially oriented PET, so that the biaxially oriented PET film is used as a protective film There arises a problem that the flatness of the film-forming substrate of the transparent conductive film is deteriorated or peeling occurs in the protective film.

On the other hand, considering that the difference in the dimensional change rate between the transparent substrate and the protective film of the transparent conductive film is reduced, it is considered to use a film made of COP as a protective film. However, when a film made of COP is used as a protective film, since COP is an unmodified resin, toughness is lower than that of a biaxially oriented PET film, resulting in poor flexibility and a problem of cracking during processing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a biaxially oriented polyester film which is suitably used as a protective film for COP used in applications such as a film forming substrate of a transparent conductive film in view of the background of the prior art.

In order to solve the above problems, the present invention adopts the following configuration. In other words,

[I] The dimensional change ratio at 150 占 폚 to 50 占 폚 during the temperature lowering in each of the film width direction (TD direction) and the direction (MD direction) perpendicular thereto is 50 ppm / 占 폚 or more and 130 ppm / And a biaxial oriented polyester film having a plane orientation coefficient (fn) of 0.111 or more and 0.145 or less.

[II] The dimensional change ratio at 150 ° C to 50 ° C during the temperature lowering in each of the film width direction (TD direction) and the direction (MD direction) perpendicular thereto is 50 ppm / ° C or more and 130 ppm / Wherein the heat shrinkage ratio at 130 占 폚 for 30 minutes in the film width direction (TD direction) and in the direction perpendicular to the film width direction (MD direction) is 1.0% or less, respectively.

[III] A biaxially oriented polyester film having a plane orientation coefficient (fn) of 0.120 or more and 0.140 or less in [I] or [II].

[IV] The film according to any one of [I] to [III], wherein the film has a width direction (TD direction), a direction perpendicular to the film direction (MD direction) (TD direction) and the average value of the heat shrinkage ratio in the film width direction (TD direction) and the heat shrinkage percentage in the film direction (MD direction) perpendicular to the film width direction and the dimensional change rate at 150 deg. C from the film width direction at 45 deg. From the film width direction at the time of decreasing the temperature in the respective directions, / ° C or more and 10 ppm / ° C or less.

[V] A biaxially oriented polyester film according to any one of [I] to [IV], wherein the polyester resin constituting the polyester film has a crystalline melting heat value of 30 J / g or less.

[VI] A laminated polyester film according to any one of [I] to [V], wherein the polyester film is composed of at least three layers, and the crystalline melting heat amount (ΔHmA) of the polyester resin constituting the surface layer on both sides of the film is Is not less than 30 J / g, and the crystal melting heat amount (? HmB) of the polyester resin constituting the layers other than the surface layer on both sides of the film is 30 J / g or less.

[VII] The polyester resin constituting the layers other than the surface layer on both sides of the film is a resin comprising terephthalic acid and ethylene glycol as main constituent components, and the other constituent unit is isophthalic acid, cyclohexylenedimethanol , Or only two types of biaxially oriented polyester films.

[VIII] A laminated polyester film according to any one of [I] to [V], wherein the polyester film has at least three layers, wherein the polyester resin constituting the surface layer on both sides of the film has a melting point TmA of not less than 250 ° C Lt; RTI ID = 0.0 > 280 C. < / RTI >

[IX] A polyester film according to any one of [IV] to [VIII], wherein the sum of the thicknesses of the surface layers on both sides of the polyester film and the sum of the thicknesses of the layers other than the surface layer (sum of thicknesses of both surface layers / Is 1/9 to 1/2 that of the polyester film of the present invention.

[X] A biaxially oriented polyester film for use in any one of [I] to [IX], which is used for bonding to a film made of an amorphous resin.

[XI] A biaxially oriented polyester film to be used in any one of [I] to [IX] for use in bonding to a film comprising a cycloolefin polymer (COP).

[XII] A biaxially oriented polyester film for use in a protective film of a cycloolefin polymer (COP) in any one of [I] to [XI].

(Effects of the Invention)

According to the present invention, it is possible to obtain a biaxially oriented polyester film having a dimensional change ratio close to that of a film made of an amorphous resin such as COP or PC (polycarbonate), excellent mechanical properties and good processability.

Hereinafter, the present invention will be described in detail with specific examples.

The polyester film of the present invention is required to be a biaxially oriented polyester film from the viewpoint of mechanical properties. The polyester referred to herein is composed of a dicarboxylic acid component and a diol component. In the present specification, the constituent component means the minimum unit that can be obtained by hydrolyzing the polyester. The polyester film of the present invention is preferably composed of a copolymer of polyethylene terephthalate or polyethylene terephthalate from the viewpoint of mechanical properties.

In one embodiment of the present invention, the rate of dimensional change at 150 DEG C to 50 DEG C during temperature decrease in the film width direction (TD direction) and the direction (MD direction) perpendicular to the film width direction is 50 ppm / DEG C or more and 130 ppm / ° C or lower and a plane orientation coefficient (fn) of 0.111 or more and 0.145 or less.

In general, the transparent conductive film is formed on a substrate in a state where the temperature is higher than the room temperature, and then is cooled down to room temperature through a curing process in a state where the temperature is higher than the room temperature. That is, maintaining the planarity of the substrate after the formation of the transparent conductive film is important because it prevents the transparent conductive film from being damaged and deteriorating the conductivity. The protective film of the substrate is also subjected to the above process. That is, in order to maintain good planarity of the substrate, it is important that the rate of dimensional change of the protective film of the substrate at the time of temperature decrease is close to the substrate.

In recent years, a film made of COP, which is an amorphous resin, is widely used as a film formation substrate of a transparent conductive film. The dimensional change rate of the film made of this COP at 150 DEG C to 50 DEG C during the temperature lowering is 50 ppm / DEG C or more and 150 ppm / DEG C or less, depending on the molecular skeleton of COP. The dimensional change rate of the polyester film of the present invention at a temperature falling from 150 캜 to 50 캜 at a temperature falling within a range close to the dimensional change rate of the film made of the COP can be obtained without deteriorating the planarity of the film formation substrate of the transparent conductive film after the film formation of the conductive film Can be satisfactorily maintained. Particularly preferably 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.

The dimensional change ratio of the biaxially oriented polyester film is determined by the orientation of the molecular chains of the polyester constituting the film. That is, when the molecular chain is oriented, the molecular chain can not move freely due to heat, and the value of the dimensional change rate is lowered. That is, in the case of a general biaxially oriented polyester film, when the degree of orientation of molecular chains such as fn exceeding 0.145 is high, the value of the dimensional change rate is low (less than 50 ppm / ° C). On the other hand, if the orientation of the film such that the fn is less than 0.111 is insufficient, the mechanical properties, particularly the elongation at break, are poor, resulting in poor processability. In addition, since the orientation of the film is insufficient, the molecular chain is close to the amorphous state, and when heat is applied to the film, random coarse crystals are formed, thereby deteriorating transparency of the film, As a result, the value of the dimensional change rate is also lowered. Therefore, in the biaxially oriented polyester film of the present invention, the dimensional change ratio during cooling at a temperature of from 150 캜 to 50 캜 in the film width direction (TD direction) and the direction (MD direction) perpendicular thereto is 50 ppm / Or more and 130 ppm / ° C or less, and having a plane orientation coefficient (fn) of 0.111 or more and 0.145 or less, can be used as a film having excellent mechanical properties and processability and maintaining high transparency even during heating. have. The fn is more preferably 0.120 or more and 0.140 or less.

In another embodiment of the present invention, the dimensional change ratio at 150 占 폚 to 50 占 폚 during the temperature lowering in the film width direction (TD direction) and in the direction (MD direction) perpendicular to the film width direction is 50 ppm / / ° C and the heat shrinkage rate at 130 ° C for 30 minutes in each of the film width direction (TD direction) and the direction perpendicular to the film width direction (MD direction) is 1.0% or less. As described above, the step of forming the transparent conductive film includes a step of forming a transparent conductive film on the substrate in a state where the temperature is higher than the room temperature. Therefore, when the heat shrinkage ratio of the protective film of the substrate is large, the planarity of the substrate may be impaired. When a polyester film having a dimensional change rate at a temperature falling from 150 deg. C to 50 deg. C falling within the above range and having a heat shrinkage rate at 130 deg. C for 30 min is used as a protective film of a COP film, And good bonding with the COP is obtained. It is more preferable that the heat shrinkage ratio in the MD direction and the TD direction at 130 占 폚 for 30 minutes is 0.5% or less, respectively. The lower limit of the heat shrinkage rate is preferably -0.2%. - means to expand. In the case of expansion exceeding -0.2%, the base material and the protective film may peel off.

It is preferable that the dimensional change rate and heat shrinkage ratio of the polyester film of the present invention satisfy the following requirements. That is, when the heat shrinkage ratios in the film width direction (TD direction), the direction perpendicular to the film width direction (MD direction), and the direction of 45 ° from the film width direction at 130 ° C for 30 minutes (The absolute value of the difference between the TD and MD direction heat shrinkage ratios, the absolute value of the difference between the TD and the TD heat shrinkage ratios at 45 degrees, And the average value thereof is 0.5% or less, and when the dimensional change rate at the time of the temperature drop from 150 DEG C to 50 DEG C in the respective directions is compared with the absolute value of the difference in heat shrinkage ratio in the direction of (The absolute value of the difference between the TD and MD directional change rates, the absolute value of the difference between the TD direction and the dimensional change ratio in the direction of 45 degrees from the TD direction, Of the dimensional change rate in the direction Is the absolute value) less than 0ppm / ℃ 10ppm / ℃ is preferred.

When a sheet made of an amorphous resin is used for a film-forming substrate of a transparent conductive film, the sheet is usually not drawn, and thus the response (dimensional change rate and heat shrinkage rate) of the sheet made of the amorphous resin is isotropic. On the other hand, the biaxially oriented polyester film is excellent in response to heat between the film width direction (TD direction) in the stretching direction and the direction (MD direction) perpendicular to the film width direction, (Dimensional change rate, heat shrinkage ratio). When a polyester film having such a large difference is used as a laminate by bonding a sheet made of an amorphous resin and a film, curling may occur in the laminate. It is preferable to form a biaxially oriented polyester film satisfying the above-mentioned range because it is possible to bond the laminate to a sheet made of an amorphous resin so that the response to heat is close to that of the laminate, thereby suppressing curling of the laminate.

The biaxially oriented polyester film of the present invention preferably has a heat shrinkage ratio of 1.5% or less in both MD and TD directions at 150 DEG C for 30 minutes. More preferably, the heat shrinkage rate at 150 占 폚 for 30 minutes is -0.2% or more and 0.5% or less in both MD and TD directions.

In order to keep the dimensional change rate, the plane orientation coefficient (fn) and the heat shrinkage of the biaxially oriented polyester film within the above-mentioned range, for example, the following method (A) can be adopted.

(A) A method of biaxially stretching the polyester resin constituting the biaxially oriented polyester film of the present invention at a crystal melting heat amount of 30 J / g or less, to be described later.

The biaxial stretching method can be carried out as follows.

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

(1) When an unstretched sheet is produced by discharging melted polyester from a spinneret, it is cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 ° C to 40 ° C to prepare an unoriented sheet.

(2) The unstretched sheet obtained in (1) was stretched at an area ratio 8.5 times or more and 16.0 (mm) in the longitudinal direction (MD) of the film and the width direction (TD) of the film at a temperature Fold or less.

(i) Tg (占 폚)? T1n (占 폚)? Tg + 40 (占 폚)

Tg: glass transition temperature (占 폚) of the resin constituting the polyester film

(3) The biaxially stretched film obtained in (2) was heat-set at a temperature (Th0 (占 폚)) satisfying the following formula (2) for 1 second or more and 30 seconds or less, To obtain a polyester film.

(ii) Tm-60 (占 폚)? Th0 (占 폚)? Tm-20 (占 폚)

Tm: melting point (占 폚) of the resin constituting the film

An amorphous polyester film can be obtained by obtaining an unstretched sheet under the conditions satisfying the following conditions (1), (2) easy orientation of the film can be imparted in subsequent steps, and It is easy to do.

(2), it is possible to obtain a biaxially oriented film, thereby giving an appropriate orientation to the film, thereby obtaining a film having good mechanical properties.

(3), the structure of the polyester molecular chain in which the orientation is formed is stabilized, and a film having good mechanical properties and heat shrinkage can be obtained.

The biaxial stretching method (2) includes a sequential biaxial stretching method in which stretching of the film in the longitudinal direction (MD) and the film width direction (direction perpendicular to the longitudinal direction of the film, TD) And a simultaneous biaxial stretching method in which stretching in the transverse direction and stretching in the transverse direction are performed at the same time. If the stretching temperature T1n (占 폚) is less than Tg (占 폚), stretching is difficult. When T1n (占 폚) exceeds Tg + 40 (占 폚), the film is often cracked and the film can not be obtained by stretching. More preferably, Tg + 10 (占 폚)? T1n (占 폚)? Tg + 30 (占 폚).

In the step (3), when Th0 is higher than Tm-20 占 폚, the orientation of the film given by stretching may collapse and the heat shrinkage may become large. When Th0 is lower than Tm-60 占 폚, the structure of the molecular chain is unstable and the planarity deteriorates or the film-forming property deteriorates. Further, by setting the value of Th0 to Tm-30 (占 폚)? Th0 (占 폚)? Tm-20 (占 폚), strain of the molecular chain at the time of film stretching is relaxed and the heat shrinkage ratio can be set within a preferable range. A relaxation process of shortening the distance in the film width direction from 2% to 10% in the step (3) may be performed.

The heat of crystal melting of the polyester resin constituting the biaxially oriented polyester film of the present invention is preferably 30 J / g or less. When the crystalline melting heat quantity is more than 30 J / g, the crystallinity of the resin is high, and even when the biaxial stretching is carried out by the above-mentioned method, the orientation of the molecular chain becomes strong and fn tends to be large and the rate of dimensional change tends to decrease. The lower limit of the crystal melting heat quantity is preferably 2 J / g or more. If 2 J / g is not satisfied, the film-forming property may be inferior or fn may be lower than the lower limit of the preferable range. As a method of making the crystal melting heat of the polyester resin to be 30 J / g or less, a method of copolymerizing isophthalic acid as the dicarboxylic acid component and a method of copolymerizing cyclohexanedimethanol as the diol component . These may be copolymerized singly or plural types may be copolymerized. The copolymerization by itself is preferable because it is easy to control the crystallinity. Particularly, when isophthalic acid is used as a copolymerization component, the structure is close to that of terephthalic acid, and therefore it is particularly preferable because it is easy to impart orientation by stretching to bring fn to a desired range. As the copolymerization amount, the sum of the copolymerization components is preferably 7 mol% or more and 20 mol% or less based on the total amount of the constituent components of the polyester.

As a method of a more preferred embodiment, the film may be constituted by the following (B).

(B) The polyester film is made of a laminated polyester film composed of at least three layers, and the crystalline melting heat amount (? HmA) of the polyester resin constituting the surface layer on both sides of the film is all 30 J / g or more, (? HmB) of the polyester resin constituting the layer of the thermoplastic resin layer is 30 J / g or less.

In the case of the above structure, the surface layer on both sides of the film has higher crystallinity than the other layers, and is more likely to be oriented. As a result, the orientation of the other layers is increased following the layer, and the orientation of the film as a whole is improved. As a result, mechanical properties are improved and workability is improved. Further, as a result of improving the orientation property, whitening is suppressed when heat is applied to the film, which is preferable. It is preferable that DELTA HmA is not less than 31 J / g and not more than 60 J / g, and DELTA HmB is not less than 2 J / g and not more than 30 J / g.

When this configuration is adopted, it is preferable that the drawing temperature satisfies the following expression (iii) in order to enhance the orientation of the resin constituting the surface layer on both sides.

(iii) TgA (占 폚)? T1n (占 폚)? TgA + 40 (占 폚)

TgA represents the glass transition temperature of the polyester resin constituting the surface layer on both sides of the film. When the surface layer on both sides of the polyester film of the present invention is a film made of a polyester resin having a different composition (for example, A / B / C), the polyester resin having a higher Tg It is preferable that the temperature satisfies the formula (iii).

When the polyester film of the present invention is a laminated polyester film comprising at least three layers, it is also a preferred embodiment that the melting point TmA of the polyester resin constituting the surface layer on both sides of the film is set to 250 deg.

When the value of Tma is 250 DEG C or less, when the heat is applied by heat treatment or the like during the film formation, the planarity may deteriorate or the film formability may deteriorate. When the polyester resin constituting the surface layer on both sides of the film has a melting point Tma of 250 DEG C or more and 280 DEG C or less, the three-layer laminated polyester film is particularly preferable because of its good planarity and film formability.

When the film of the present invention is a laminated polyester film having three or more layers, the sum of the thicknesses of the surface layers on both sides of the polyester film and the sum of the thicknesses of the layers other than the surface layer (sum of thicknesses of both surface layers / Thickness) is preferably 1/9 to 1/2.

If the thickness of the surface layer is so thin that the ratio of the sum of the thicknesses of the surface layers on both sides and the sum of the thicknesses of the layers other than the surface layer is less than 1/9, the effect of improving the film formability and improving the mechanical properties by lamination may not be obtained. On the other hand, when the thickness of the surface layer is too thick and the ratio of the sum of the thicknesses of the surface layers on both sides and the sum of the thicknesses of the layers other than the surface layer exceeds 1/2, the inner layer is stretched forcibly under the influence of the orientation property of the surface layer, There is a case that the sex is bad.

It is also a preferred embodiment to carry out the step (c) below in order to set the heat shrinkage ratio to a more preferable range.

(C) The 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 the method for carrying out the annealing treatment, there is a method of heat-treating the film (off annealing) in an oven provided between a film unwinding roll and a film winding roll.

(iv) 120 占 폚? Th1 (占 폚)? Th0 (Heat fixing temperature) (占 폚)

When the Th1 (占 폚) exceeds the Th0 (heat fixing temperature) (占 폚), the molecular chain structure in the film immobilized in the step (3) in the step (4) is destroyed, So that the planarity may deteriorate. On the other hand, when Th1 (占 폚) is less than 120 占 폚, the heat shrinkage rate at 130 占 폚 may not be within a preferable range.

(A) and (b), the stress remaining in the molecular chains constituting the film can be removed, and the reduction in heat shrinkage, the isotropy and the isotropy of the rate of dimensional change can be obtained Is a preferred embodiment of the present invention. Particularly, in the case of the film obtained by the method (b), since the resin whose Tma is 250 ° C or more and 280 ° C or less is disposed on both surface layers, the orientation of the film is collapsed when heat is applied in the step It is preferable because heat shrinkage can be reduced only without work.

The thickness of the biaxially oriented polyester film of the present invention is preferably 30 占 퐉 to 150 占 퐉. If the thickness is not more than 30 탆, cracking tends to occur when used as a protective film, and if it exceeds 150 탆, handling properties may be poor. More preferably not less than 50 μm and not more than 125 μm.

The biaxially oriented polyester film of the present invention preferably has a haze change (? Haze) before and after treatment at 100 占 폚 for 12 hours of 2% or less. Even when the film of the present invention and the sheet of the amorphous resin are adhered to each other by setting the Δ haze within the above-mentioned range, a sheet made of an amorphous resin can be visually recognized even when passing through the film of the present invention. As factors causing Δ haze, it is considered that the film non-crystallization is coarse by heating, and oligomers are precipitated on the film surface by heating. In the former method, the orientation of the film is made to be fn 0.111 or more. In the latter method, the resin constituting the outermost layer is solid-phase-polymerized by using a film as a laminated structure to reduce oligomer precipitation by reducing the oligomer content. Can be reduced.

The biaxially oriented polyester film of the present invention obtained as described above is excellent in mechanical properties and processability and has a dimensional change rate at a temperature falling from 150 ° C to 50 ° C close to a film made of an amorphous resin, And the like. In particular, it can be suitably used as a protective film for a film made of COP. In addition, since it is excellent in transparency even during heating, it can be suitably used as a protective film of a COP film used for forming a transparent conductive film.

[Evaluation method of characteristics]

A. Melting point (Tm, TmA, TmB) (占 폚) of the film and the resin constituting each layer

The sample was measured using a differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Instruments Inc. according to a method based on JIS K 7121 (1999) and a disk session "SSC / 5200" Conduct.

5 mg of each sample is weighed into a sample pan, and the sample is heated from 25 占 폚 to 300 占 폚 at a heating rate of 20 占 폚 / min (1st RUN), maintained in this state for 5 minutes, and then quenched to 25 占 폚 or lower. Immediately thereafter, the temperature is elevated again from 25 占 폚 to a temperature of 300 占 폚 at a temperature raising rate of 20 占 폚 / minute, and the measurement is carried out to obtain a chart of the 2nd RUN of differential scanning calorimetry (heat energy is plotted on the ordinate axis and temperature is plotted on the abscissa axis). In the differential scanning calorimetry chart of the 2nd run, the peak temperature at the crystal melting peak as the endothermic peak is obtained, and the peak temperature is defined as the melting point (占 폚). When two or more crystal melting peaks are observed, the temperature of the peak top having the largest peak area is set as the melting point.

When the melting point of the resin constituting each layer of the laminated polyester film is measured, only the resin constituting each layer is cut out from the laminated polyester film using a microtome and provided for measurement.

B. Crystalline melting heat amount (? Hm,? HmA,? HmB) (J / g) of the film,

The sample was measured using a differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Instruments Inc. according to a method based on JIS K 7121 (1999) and a disk session "SSC / 5200" Conduct.

5 mg of each sample is weighed into a sample pan, and the sample is heated from 25 占 폚 to 300 占 폚 at a heating rate of 20 占 폚 / min (1st RUN), maintained in this state for 5 minutes, and then quenched to 25 占 폚 or lower. Immediately followed by raising the temperature from 25 占 폚 to 300 占 폚 at a temperature raising rate of 20 占 폚 / minute, and measurement is carried out to obtain a chart of the 2nd RUN differential scanning calorimetry chart (heat energy is plotted on the ordinate axis and temperature is plotted on the abscissa axis). In the differential scanning calorimetry chart of the 2nd run, the peak area of the endothermic peak is determined to be the crystalline melting calorie. When two or more crystal melting peaks are observed, the area of the peak with the highest temperature is determined as the crystal melting heat amount, and when two or more peaks can not be separated, the two peaks are summed to obtain the peak area.

When the crystalline melting heat quantity of the resin constituting each layer of the laminated polyester film is measured, only the resin constituting each layer is cut from the laminated polyester film using a microtome and provided for measurement.

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

The measurement is carried out using the differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Instruments Inc. according to JIS K 7121 (1999) and the disk session "SSC / 5200" for data analysis using the following procedure.

5 mg of a sample is weighed in a sample pan, and the sample is heated from 25 DEG C to 300 DEG C at a temperature raising rate of 20 DEG C / minute (1st run), maintained in this state for 5 minutes, and then quenched to 25 DEG C or lower. Immediately followed by raising the temperature from 25 占 폚 to 300 占 폚 at a temperature raising rate of 20 占 폚 / minute, and measurement is carried out to obtain a chart of the 2nd RUN differential scanning calorimetry chart (heat energy is plotted on the ordinate axis and temperature is plotted on the abscissa axis). In the differential scanning calorimetry chart of the 2nd run, the curves of the straight line extending equidistant from the straight line extending from each base line in the stepped shape of the glass transition and the stepped shape of the glass transition cross each other We obtain from point. When two or more glass transition temperatures are observed, the glass transition temperature is determined for each of them, and the value obtained by averaging these temperatures is taken as the glass transition temperature (Tg) (占 폚) of the sample.

When measuring the glass transition temperature of the resin constituting the outermost layer of the laminated polyester film, only the resin constituting the outermost layer is cut out from the laminated polyester film using a microtome and provided for measurement.

D. Face orientation coefficient (fn)

The refractive index at 20 占 폚 is obtained using an Abbe's type refractive index meter manufactured by ATAGO CO., LTD according to JIS K 7105 (1999). The longitudinal direction refractive index (Nmd), the lateral direction refractive index (Nd), and the thickness direction refractive index (Nz) of the surface of the film are measured and the surface orientation coefficient fn is calculated. The measurement is carried out with n = 5, and the average value is calculated.

(v) fn = (Nmd + Ntd) / 2-Nz

E. Heat shrinkage (%) of film

The heat shrinkage rate of the film is measured in accordance with JIS C 2318 (1997). The film is cut into a strip shape having a width of 10 mm and a length of 150 mm. A mark is drawn on the film so that the measurement length portion is approximately 100 mm, and the length of the mark is measured under conditions of 23 캜 to obtain L0. Thereafter, 2 g of weight is put in a hot air oven heated to a predetermined temperature (200 캜 or 220 캜), the film is hanged and left for 30 minutes. After the film was taken out of the oven and cooled to 23 DEG C, the length of the mark was measured to be L1. The shrinkage ratio of the film is determined by the following formula (vi). The measurement is performed by cutting out five portions randomly so that the film length direction or the film width direction has a length of 150 mm. An average value is calculated for each of the longitudinal direction and the width direction, and is taken as the heat shrinkage rate of the film.

(vi) (film heat shrinkage ratio) = (L0-L1) / L0 100

F. Thickness of film (탆)

The thickness of the film was measured at five arbitrary positions in a state in which ten dials of a film were stacked in accordance with JIS K7130 (1992) A-2 method using a dial gauge. The average value was divided by 10 to obtain a film thickness.

G. Thickness (탆) of each layer of the laminated polyester film

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

H. Castability

The number of times the film is split in one hour during the film formation is evaluated as A, B being less than 5 times and B not less than 5 times, and C being not less than 5 times. A has the best film forming property, and C has the worst shape.

I. Dimensional change rate (ppm / 占 폚) during temperature decrease from 150 占 폚 to 50 占 폚

A sample width of 4 mm was made using a thermomechanical measuring device TMA / SS6000 (manufactured by Seiko Instruments Inc.) in accordance with JIS K7197 (1991), and a load of 3 g was applied to a sample having a sample length (chuck distance) of 20 mm . The temperature is raised from room temperature to 160 ° C at a heating rate of 10 ° C / minute and held for 10 minutes. Thereafter, the temperature is decreased to 20 ° C at 10 ° C / minute to obtain the value of the dimension of the sample at each temperature (° C). Is calculated from the following formula (vii) from the dimension L (150 占 폚) (mm) of the sample at 150 占 폚 and the dimension L (50 占 폚) (mm) of the sample at 50 占 폚. Further, the dimensional change ratio is calculated as n = 5 for each of the film width direction TD and the direction MD perpendicular to the film width direction TD, and the average value is calculated.

(vii) Dimensional change rate (ppm / 占 폚) = 10 ⁶占 (L (150 占 폚 -L (50 占 폚))) / {20 占 (150-50)

J. DELTA haze (haze change before and after treatment at 100 DEG C for 12 hours) (%)

The film was cut into a square of 10 cm on one side, and haze values at three places were measured at random using haze meter NDH-5000 manufactured by NIPPON DENSHOKU INDUSTRIES CO., LTD. ). The four sides of the sample are fixed in a tvevispeople oven in which the sample is kept in a room kept at 23 DEG C and 65% RH, and heat-treated for 12 hours under dry heat at 100 DEG C and 10% RH or less. The haze of the film after the heat treatment is similarly measured to obtain H1 (%). ? Haze (? H) is obtained from the following formula (viii).

(viii) DELTA haze (%) = H1-H0

The value of DELTA haze is determined as follows.

A; Δ Haze 1.5% or less

B; DELTA haze exceeding 1.5% and not exceeding 2.0%

C; DELTA haze exceeds 2.0%

A is the best, and C is the worst.

K. Processability

The workability is determined by n5 as the elongation at break (%) in the direction of the width direction of the film (TD) and the direction (MD) perpendicular to it, and the average value thereof is determined as follows.

A; 120% or more of elongation at break

B; Breaking elongation 105% or more and less than 120%

C; Breaking elongation 90% or more and less than 105%

D; Break elongation 75% or more and less than 90%

E; Less than 75% elongation

A is the best, and E is the least.

The breaking elongation retention is measured as follows. The film was cut into pieces each having a size of 1 cm x 15 cm so as to be parallel to the MD TD of the long-side film. The film was stretched at a stretching speed of 300 mm / min at a chuck interval of 5 cm according to ASTM-D882 (1997) The elongation at break is measured. In addition, the number of samples is n = 5, and the measurement is made for each of the longitudinal direction and the width direction of the film, and the average value thereof is obtained, and this is taken as the elongation at break of the film.

Evaluation of bonding with L. COP film

The film of the present invention was cut into a size of 20 cm x 20 cm and bonded to a COP film to prepare a laminate. The laminate was placed in an oven at 120 캜 for one hour. Thereafter, the temperature of the oven was cooled to room temperature at a rate of 20 DEG C / minute. Then, the number of wrinkles having a length of 3 cm or more of the laminate to which the film of the present invention and the COP film are adhered is measured, and determination is made as follows. The evaluation was carried out with n = 5, and the evaluation was made by the average value thereof.

Less than 4; S

4 or more and less than 10; A

10 to less than 16; B

16 or more; C

S is the most excellent, and C is the least.

As the COP film, "ZEONOR ZF14" manufactured by Zeon Corporation and a film having a thickness of 40 μm are used. To the toluene solution adjusted to have the content of the pressure sensitive adhesive of 15% by TORAY COATEX CO., LTD. "Leo Coat" R5000 made by TORAY COATEX CO., LTD., 100 parts by weight of the above toluene solution was added with a crosslinking agent "Coronate L" Was added so that the coating thickness after drying was 10 占 퐉.

Curl of laminate with M. COP film

The laminate produced in Port L. was placed in an oven at 120 ° C and allowed to stand for one hour. Thereafter, the temperature of the oven was cooled to room temperature at a rate of 20 ° C / minute, and left for 1 hour. Thereafter, the film is placed on the horizontal surface with the COP film on the upper side, and the amount of floating from the horizontal surface at the four corners of the laminate is measured to obtain an average value, and the curl amount (mm) is determined as follows. In the above method, when the four corners of the laminate are not opened from the horizontal plane, the curl amount is set to 0 mm.

0 mm or more and less than 10 mm; A

10 mm or more and less than 25 mm; B

25 mm or more and less than 40 mm; C

40 mm or more and less than 55 mm; D

55 mm or more; E.

When the longitudinal direction and the width direction of the film to be measured are not known in the measurement, the direction having the maximum refractive index in the film is regarded as the longitudinal direction, and the direction perpendicular to the longitudinal direction is regarded as the width direction. Further, the direction of the maximum refractive index in the film may be obtained by measuring the refractive index in all directions of the film by a refractive index meter or by determining the slow axis direction by a phase difference measuring apparatus (birefringence measuring apparatus) or the like.

Example

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

[Production of PET-1] Polymerization was carried out from terephthalic acid and ethylene glycol using antimony trioxide as a catalyst to obtain melt-polymerized PET. The melt-polymerized PET thus obtained had a glass transition temperature of 80 占 폚, a melting point of 255 占 폚, and an intrinsic viscosity of 0.62.

[Production of PET-2] PET-1 was solid-phase polymerized by a conventional method to obtain PET-A. The obtained PET-A had a glass transition temperature of 82 占 폚, a melting point of 255 占 폚, and an intrinsic viscosity of 0.85.

[Production of PET-A] Polymerization was carried out from terephthalic acid, isophthalic acid and ethylene glycol by a conventional method so that antimony trioxide was used as a catalyst and the copolymerization amount of isophthalic acid was 7 mol% based on the total amount of the dicarboxylic acid component to obtain a copolymerized PET . The obtained copolymerized PET had a glass transition temperature of 77 占 폚, a melting point of 243 占 폚, and an intrinsic viscosity of 0.62.

[Production of PET-B] Polymerization was conducted by a conventional method so that the copolymerization amount of isophthalic acid with respect to the total amount of the dicarboxylic acid component was 10 mol% from terephthalic acid, isophthalic acid and ethylene glycol as antimony trioxide catalyst to obtain a copolymerized PET . The obtained copolymerized PET had a glass transition temperature of 76 캜, a melting point of 235 캜, and an intrinsic viscosity of 0.62.

[Production of PET-C] Polymerization was carried out from terephthalic acid, isophthalic acid and ethylene glycol by a conventional method so that the amount of isophthalic acid copolymerized with antimony trioxide was 15 mol% based on the total amount of the dicarboxylic acid component to obtain a copolymerized PET . The obtained copolymerized PET had a glass transition temperature of 74 占 폚, a melting point of 230 占 폚, and an intrinsic viscosity of 0.62.

[Production of PET-D] Polymerization was conducted by a conventional method so that the amount of isophthalic acid copolymerized with terephthalic acid, isophthalic acid and ethylene glycol was 20 mol% based on the total amount of the dicarboxylic acid component, to obtain a copolymerized PET . The obtained copolymerized PET had a glass transition temperature of 73 占 폚, a melting point of 220 占 폚, and an intrinsic viscosity of 0.62.

[Production of PET-E] Polymerization was carried out from terephthalic acid, isophthalic acid and ethylene glycol by a conventional method so that the amount of isophthalic acid copolymerized with antimony trioxide was 25 mol% based on the total amount of the dicarboxylic acid component to obtain a copolymerized PET . The obtained copolymerized PET had a glass transition temperature of 70 캜, and no melting point was observed. The intrinsic viscosity was 0.62.

[Production of PET-F] Polymerization was carried out by a conventional method such that terephthalic acid, cyclohexanedimethanol (CHDM) and ethylene glycol were used as antimony trioxide catalysts and the cyclohexane dimethanol copolymerization amount was 10 mol% based on the whole amount of the diol component Thereby obtaining a copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 72 占 폚, a melting point of 235 占 폚, and an intrinsic viscosity of 0.62.

[Production of PET-G] Polymerization was conducted by a conventional method so that the copolymerization amount of cyclohexane dimethanol was 20 mol% based on the total amount of the diol component, using terephthalic acid, cyclohexanedimethanol (CHDM) and ethylene glycol as antimony trioxide catalyst Thereby obtaining a copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 70 占 폚, a melting point of 221 占 폚, and an intrinsic viscosity of 0.62.

(Example 1)

PET-A was vacuum-dried at 160 DEG C for 2 hours and then put in an extruder, melted in an extruder, and extruded onto a casting drum having a surface temperature of 25 DEG C to prepare an unoriented sheet. Subsequently, the sheet was pre-heated in a heated roll group, and then stretched 3.1 times in a direction (MD direction) perpendicular to the width direction at a temperature of 90 DEG C, and then cooled in a roll group at a temperature of 25 DEG C to obtain a uniaxially stretched film . Both ends of the obtained monoaxially stretched film were held in a clip and stretched 3.6 times in the film width direction (TD direction) in a heating zone at a temperature of 100 캜 in the tenter. Subsequently, heat-setting was performed at a temperature of 210 캜 for 10 seconds in a heat treatment zone in the tenter. In the opening and definition process, a relaxation treatment of 2% in the film width direction was carried out. Subsequently, the film was uniformly cooled in a cooling zone and then taken up to obtain a biaxially oriented polyester film. The properties of the obtained biaxially oriented polyester film are shown in the table. The rate of dimensional change was 50 ppm / ° C or more and 130 ppm / ° C or less in both the MD and TD directions, and the film was excellent in adhesion to COP. In addition, the film had excellent workability and a small haze change due to heating.

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

A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the resin constituting the film was changed as shown in the table. The properties of the biaxially oriented polyester film are shown in the table. In Examples 2 to 5, the fn and the dimensional change ratio were in a suitable range, the workability was excellent, and the haze change due to heating was small. In Comparative Example 1, the crystallinity of the resin was high and ΔHm was large. As a result, the film had a large fn and a small rate of dimensional change. In Comparative Example 2, since the crystallinity of the resin was low to such an extent that? Hm was not observed, the film had a small fn and a small dimensional change rate, and was a film that fell behind the bonding with COP. In addition, since the fn was small, the workability was poor and the haze change due to heating was also great.

(Example 6)

A / B / A, and PET-2 as 100 parts by mass as a resin constituting the surface layer was vacuum-dried at 160 占 폚 for 2 hours, and then charged into an extruder 1. Further, 100 parts by mass of PET-A as a resin constituting the inner layer was vacuum-dried at 160 캜 for 2 hours, and then put in an extruder 2. Each of the raw materials was melted in an extruder, and the resin charged into the extruder 1 by a joining device was joined so as to be a surface layer on both sides of the film and extruded on a casting drum having a surface temperature of 25 캜 to produce a laminated sheet having a three-layer structure. Subsequently, the sheet was preheated in a heated roll group, and then stretched 3.1 times in the longitudinal direction (MD direction) at a temperature of 90 DEG C, and then cooled at a temperature of 25 DEG C to obtain a uniaxially stretched film. Both ends of the obtained monoaxially stretched film were stretched 3.6 times in the transverse direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 100 DEG C in the tenter while gripping both ends with a clip. Subsequently, heat-setting was performed at a temperature of 210 캜 for 10 seconds in a heat treatment zone in the tenter. Then, the film was uniformly cooled in a cooling zone and wound up to obtain a laminated polyester film. Each characteristic of the film is shown in the table. The rate of dimensional change was 50 ppm / ° C or more and 130 ppm / ° C or less in both the MD and TD directions, and the film was excellent in adhesion to COP. In addition, the film had excellent workability and a small haze change due to heating. By using PET-2 in the surface layer, it was found that the film had better workability and had a small haze change due to heating.

(Example 7-21)

Film formation was carried out in the same manner as in Example 6 except that the composition of the resin and the film formation conditions were changed as shown in the table. The characteristics of the film are shown in the table. The rate of dimensional change was 50 ppm / ° C or more and 130 ppm / ° C or less in both the MD and TD directions, and the film was excellent in adhesion to COP. In addition, the film had excellent workability and a small haze change due to heating.

(Examples 22-24)

In Example 22, the film obtained in Example 6, the film obtained in Example 7 in Example 23, and the film obtained in Example 8 in Example 24 were used, respectively, and the obtained film was placed between the film unwinding roll and the film winding roll The film was annealed in an installed hot air oven at a temperature of 140 캜 so that the film was heat-treated for 5 minutes to obtain a film having a thickness of 125 탆. Each characteristic of the film is shown in the table. The dimensional change rate was 50 ppm / ° C or more and 130 ppm / ° C or less in both the MD and TD directions, and the heat shrinkage rate at 130 ° C for 30 minutes was a small film, and the film was particularly excellent in adhesion to COP. In addition, the film had excellent workability and a small haze change due to heating. The average value of the heat shrinkage rate in the MD direction, the TD direction and the 45 ° direction is 0.5% or less, the absolute value of the difference in the respective heat shrinkage rates is 0.5% or less, and the absolute value of the difference in the dimensional change rates in each direction is 10 or less. The laminates with COP also showed good curl.

(Comparative Example 3-7)

Film formation was carried out in the same manner as in Example 6 except that the composition of the resin and the film formation conditions were changed as shown in the table. The characteristics of the film are shown in the table. In Comparative Examples 3 and 7, the crystallinity of the resin was high and ΔHmB was large. As a result, the fn of the film was high and the rate of dimensional change was small. In Comparative Example 4, since the crystallinity was low to such an extent that? Hm was not observed, fn was small and the film exhibited a small rate of dimensional change. In addition, since the fn was small, the workability was poor and the haze change due to heating was also great. In Comparative Examples 5 and 6, the heat treatment temperature in the film formation was high and the orientation of the film was disturbed, resulting in an extremely low fn, resulting in a low elongation at break and poor workability and a large Δ haze due to heating.

(Example 26)

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

(Examples 25, 27-36)

Example 25 is the film of Example 2, Example 27 is the film of Example 26, Example 28 is the film of Example 9, Example 29 is the film of Example 11, Example 30 is Example 12, the film of Example 14 is used for Example 31, the film of Example 15 is used for Example 32, the film of Example 16 is used for Example 33, and the film of Example 18 is used for Example 34 Example 35 is a film obtained by using the film of Example 19, and Example 36 is obtained by using the film of Example 20. The film thus obtained is heat treated in a hot air oven provided between a film take-up roll and a film take- And annealing was performed so that the time was 5 minutes.

In Examples 29, 30, 31 and 34 to 36, the average value of the heat shrinkage rate in the MD direction, the TD direction and the 45 ° direction was 0.5% or less, the absolute value of the difference in the respective heat shrinkage ratios was 0.5% Was also 10 or less, and the laminated body with COP was also excellent in the degree of curl.

In Example 25, the heat shrinkage rate could not be reduced because it was a monolayer film, and the curl was slightly inferior, but there was no problem in practical use. In Example 27, since there are a plurality of kinds of copolymerization components, the heat shrinkage rate could not be reduced and the curl was slightly inferior, but the level was practically free from problems in practical use. In Example 28, since fn is small and amorphous is strong, the heat shrinkage rate can not be reduced, and the curl is slightly inferior, but the level is not problematic in practical use. In Examples 32 and 33, the difference in the dimensional change rate in each direction was large, and the curl was slightly inferior, but there was no problem in actual use.

(Industrial availability)

The polyester film of the present invention is excellent in mechanical properties and processability and is suitable for use in which the film is made of a film made of an amorphous resin in that the dimensional change rate at a temperature falling from 150 캜 to 50 캜 is close to a film made of an amorphous resin Can be used. In addition, since it is excellent in transparency even during heating, it can be suitably used particularly as a protective film for a COP film used for forming a transparent conductive film.

Claims (11)

The dimensional change ratio at 150 DEG C to 50 DEG C during the temperature lowering in each of the film width direction (TD direction) and the direction perpendicular to the film width direction (MD direction) is 50 ppm / DEG C or more and 130 ppm / DEG C or less, (fn) of not less than 0.111 and not more than 0.145. Deg.] C or higher and 150 [deg.] C to 50 [deg.] C in the film width direction (TD direction) and in the direction perpendicular to the film width direction (MD direction) (TD direction) and a thermal shrinkage rate at 130 占 폚 for 30 minutes in a direction perpendicular to the direction (MD direction) of 1.0% or less, respectively. 3. The method according to claim 1 or 2,
And a biaxial oriented polyester film having a plane orientation coefficient (fn) of 0.120 or more and 0.140 or less. 4. The method according to any one of claims 1 to 3,
When the heat shrinkage ratios in the film width direction (TD direction), the direction perpendicular to the film width direction (MD direction), and the direction of 45 DEG from the film width direction at 130 DEG C for 30 minutes were compared in the respective directions, The absolute value of the difference is 0% or more and 0.5% or less, and the average value thereof is 0.5% or less,
Further, the dimensional change rate at the time of temperature decrease from 150 占 폚 to 50 占 폚 in the direction making 45 占 from the film width direction and the direction (MD direction) perpendicular to the film width direction (TD direction) When compared, biaxially oriented polyester films whose absolute values of their differences are all 0 ppm / DEG C or more and 10 ppm / DEG C or less. 5. The method according to any one of claims 1 to 4,
Wherein the polyester resin constituting the polyester film has a crystallization heat of fusion of 30 J / g or less. 6. The method according to any one of claims 1 to 5,
Wherein the polyester resin has at least three layers, wherein the crystalline melting heat amount (? HmA) of the polyester resin constituting the surface layer on both sides of the film is 30 J / g or more, Wherein the heat of crystallization (DELTA HmB) of the polyester resin is 30 J / g or less. The method according to claim 6,
Wherein the polyester resin constituting the layers other than the surface layer on both sides of the film is a resin mainly comprising terephthalic acid and ethylene glycol and only one or two kinds of isophthalic acid and cyclohexylene dimethanol Containing biaxially oriented polyester film. 6. The method according to any one of claims 1 to 5,
Wherein the polyester film comprises at least three layers, wherein the polyester resin constituting the surface layer on both sides of the film has a melting point Tma of 250 DEG C or more and 280 DEG C or less. 9. The method according to any one of claims 6 to 8,
The sum of the thicknesses of the surface layers on both sides of the polyester film and the sum of the thicknesses of the layers other than the surface layer (the sum of the thicknesses of the both surface layers / the thicknesses of the layers other than the surface layer) is 1/9 to 1/2, Oriented polyester film. 10. The method according to any one of claims 1 to 9,
A biaxially oriented polyester film used for bonding to a film made of an amorphous resin. 11. The method according to any one of claims 1 to 10,
A biaxially oriented polyester film used for bonding to a film comprising a cycloolefin polymer (COP).