TWI685510B - Polyester film - Google Patents

Abstract

The present invention is a polyester film whose proportion of polyethylene terephthalate in the polyester resin constituting the film is 60% by weight or more and heat treatment is performed at 200°C for 30 minutes The thermal shrinkage rate of the film in the longitudinal direction and the width direction is 0.5% or less.

The present invention provides a film that achieves heat resistance, especially low thermal shrinkage at high temperatures, and excellent processability.

Description

Polyester film

The invention relates to a polyester film with a low heat shrinkage rate at high temperature.

Mechanical properties, thermal properties, such as polyester resins, especially polyethylene terephthalate (hereinafter sometimes referred to as PET) or polyethylene 2,6-naphthalene dicarboxylate (hereinafter sometimes referred to as PEN) It is excellent in chemical resistance, electrical characteristics, and formability, and is used in various applications. The biaxially oriented polyester film in the polyester film formed from the polyester film has excellent mechanical properties and electrical properties, so it is used as a solar cell bottom sheet, an electric insulating material for water heater motors, or Electrical insulating materials, magnetic recording materials, or capacitor materials, packaging materials, construction materials, and photographic applications, drawing applications, thermal transfer applications, etc. for automotive air-conditioning motors or drive motors used in hybrid vehicles, etc. Various industrial materials, and optical materials such as flexible displays and transparent electrode substrates such as organic electroluminescence (EL, Electro Luminescence).

In these applications, when used for optical materials (such as film-forming substrates of transparent conductive films (ITO, Indium Tin Oxide) substrates, etc.), in order to improve the conductivity of the ITO film, it is necessary Carrying out the curing step at a fixed temperature requires heat resistance, especially a reduction in the thermal shrinkage of the substrate. Therefore, it is known to use a film excellent in low heat shrinkability for this purpose (Patent Documents 1, 2, and 3).

[Prior Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 3-13315

Patent Document 2: Japanese Patent Laid-Open No. 11-165350

Patent Document 3: Japanese Patent Laid-Open No. 2005-216706

However, in order to further improve the conductivity of the ITO film to make high-performance optical devices, it is necessary to increase the temperature of the curing step. Therefore, for the polyester film used for the film-forming substrate of the transparent conductive film, the thermal shrinkage rate of the film at high temperature is required to be further reduced compared to conventional products. In order to reduce the thermal shrinkage of PET film with excellent mechanical properties and heat resistance in polyester film, it is more effective to heat fix the film at a higher temperature. However, in order to reduce the heat shrinkage rate at a higher temperature, if the heat fixing treatment is performed at a high temperature, there is a problem that the flatness of the film is impaired. On the other hand, among the polyester films, the PEN film and the PET film are equally excellent in mechanical properties, and compared with the PET film, the PEN film has more excellent heat resistance. However, it is known that the PEN film has the following problem: since the PEN constituting the film has a rigid molecular structure, the processability is poor, and the film may break during processing.

The object of the present invention is to provide a polyester film with a low heat shrinkage rate under high temperature conditions in view of the background of the conventional technology. In addition, an object is to provide a polyester film having good flatness and excellent processability.

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

[I] A polyester film consisting of polyethylene terephthalate in the polyester constituting the film When the proportion in the resin is 60% by weight or more, the heat shrinkage in the longitudinal direction and the width direction of the film when the heat treatment is performed at 200°C for 30 minutes is 0.5% or less.

[II] The polyester film according to [I], wherein at least one of the heat shrinkage rate in the longitudinal direction and the width direction heat shrinkage rate when the film is heat-treated at 200°C for 30 minutes 0.01% or more.

[III] The polyester film according to [I] or [II], wherein the heat shrinkage rate in the longitudinal direction and the heat shrinkage rate in the width direction of the film when heat-treated at 220°C for 30 minutes are both 0.5% or less, And at least any one has a heat shrinkage rate of 0.01% or more.

[IV] The polyester film according to any one of [I] to [III], wherein, when the unevenness of the film is measured by a non-contact laser microscope, the unevenness of the film is 300 μm or less.

[V] The polyester film according to any one of [I] to [IV], wherein the surface alignment coefficient is 0.145 or more and 0.165 or less.

[VI] The polyester film according to any one of [I] to [V], wherein the polyester resin constituting the film has a melting point (Tmf (°C)) and has at least one minute endothermic peak temperature (Tmeta( ℃)).

[VII] The polyester film as described in [VI], wherein the polyester resin constituting the film has two or more tiny endothermic peaks (Tmeta(℃)), and the lowest temperature Tmeta(Tmeta1)(℃) and the highest temperature Tmeta(Tmeta2)(℃) satisfies the following relationship: Tmf-35(℃)≦Tmeta1(℃)<Tmeta2(℃)≦Tmf(℃).

[VIII] The polyester film according to any one of [I] to [VII], wherein the polyester film is a laminated polyester film including at least 3 layers, and is formed in a layer (layer A) constituting the outermost surface of the film The melting point (Tmo (°C)) of the included polyester resin is 260°C or higher.

[IX] The polyester film according to [VIII], wherein the laminated polyester film contains 3 layers, And the melting point of the polyester resin contained in the layer constituting the surface layer (layer A) (Tmo (℃)), and the melting point of the polyester resin contained in the layer constituting the inner layer (layer B) (Tmi (℃)) The difference is between 5°C and 10°C.

[X] The polyester film as in [IX], wherein the ratio of the sum of the thickness of the layer constituting the surface layer (layer A) and the thickness of the layer constituting the inner layer (layer B) is 1/8 or more and 1/4 or less .

[XI] The polyester film according to any one of [I] to [X], which is a film-forming substrate for a transparent conductive film.

According to the present invention, it is possible to provide a film that achieves heat resistance, particularly low thermal shrinkage at high temperatures, and is excellent in processability.

Specific examples are given below to explain the present invention in detail. The polyester film of the present invention is a polyester film in which the proportion of polyethylene terephthalate in the polyester resin constituting the film is 60% by weight or more.

The polyester described here has a dicarboxylic acid component and a diol component. In addition, in this specification, a component represents the minimum unit which can be obtained by hydrolyzing polyester. The ratio of polyethylene terephthalate is preferably 70% by weight or more, and more preferably 80% by weight or more.

After the polyester film of the present invention is heat-treated at 200°C for 30 minutes, the thermal shrinkage rate in the longitudinal direction and the width direction of the film must be 0.5% or less. More preferably, the film of the present invention has a thermal shrinkage ratio of 0.3% or less in the longitudinal direction and the width direction after treatment at 200°C for 30 minutes.

Generally, when the polyester film is a stretched film, the molecular chain is in a stretched state (aligned state) due to stretching. Therefore, when heated, the stretching of the molecular chain is released, the film shrinks, and the flatness deteriorates. As a method for suppressing this shrinkage due to heat or deterioration in flatness, it is known to use the following method: in order to stabilize the structure of the polyester molecular chain formed by stretching (hereinafter referred to as a film structure), the stretching After the step, a step for performing heat treatment at a predetermined temperature is set (this heat treatment temperature is referred to as a heat fixing temperature). By performing the heat treatment step after the extension step, a film with a certain degree of flatness and good mechanical properties can be obtained. However, even for such a thin film subjected to a heat treatment step, if the thin film is heated at a high temperature, especially at a temperature of 200° C. or higher, the structure of the molecules constituting the thin film is disordered, resulting in deterioration of planarity. That is, in order to reduce the thermal shrinkage rate and improve the flatness of the film, it is necessary to make the structure of the molecules constituting the film strong and become a structure that is stable even at high temperatures, especially at 200°C or higher.

The molecular chains in a stretched state due to extension contract due to heat to different degrees. Therefore, even in the film surface, the thermal shrinkage rate will be different, causing the film to wrinkle and impair the flatness. For example, in the case where a polyester film is used as a substrate for ITO vapor deposition as a film-forming substrate of a transparent conductive film, a heat load is applied to the thin film due to a step (curing step, etc.) after vapor deposition of the ITO film. At this time, if the flatness of the film is impaired due to the thermal shrinkage of the polyester film, the conductivity of the ITO film decreases, which is not good.

In addition, in general, when the curing temperature is high, the crystal size of the ITO film becomes large, and the conductivity of the ITO film increases. However, if the crystal size is large, the followability during deformation such as the bending of the thin film of the substrate becomes poor. ITO film is prone to cracking. The curing temperature of the followability and conductivity when the ITO film is deformed can be achieved at the same time, which is 200°C or higher and 220°C or lower. Therefore, by taking the length of the film at 200°C and 220°C as the temperature The thermal shrinkage in both the direction and the width direction is set to 0.5% or less, and the ITO film can be cured at an appropriate temperature without impairing the planarity of the film, thereby improving the performance as a transparent conductive substrate, which is preferable. More preferably, it is below 0.3%.

As described above, from the viewpoint of the planarity of the polyester film, the thermal shrinkage of the film at 200°C and 220°C is preferably small, but when the polyester film is used as a substrate for ITO vapor deposition If the thermal shrinkage of the film at 200°C and 220°C is greater than 0.01% in either the longitudinal direction or the width direction, the polyester film shrinks due to heat and does not swell, so cracking of the ITO film can be suppressed. It is better to improve the performance as a transparent conductive substrate. More preferably, the thermal shrinkage of the film at 200°C and 220°C is 0.03% or more in either the longitudinal direction or the width direction.

In order to set the heat shrinkage ratio of the polyester film of the present invention to the above range, a method of forming a polyester film under predetermined conditions (method A), and setting the polyester resin constituting the film to a predetermined structure can be cited Method (Method B), and methods combining (Method A) and (Method B).

First, (Method A) will be described. The polyester film of the present invention can be preferably obtained by the following method (Method A): The proportion of polyethylene terephthalate produced in the polyester resin constituting the film by the following method is 60% by weight or more The polyester film is further annealed in the following method.

First, the method of making a film will be described.

After heating and melting polyester containing 60% by weight or more of polyethylene terephthalate in an extruder, it is ejected from a nozzle to obtain an unstretched sheet, and then, biaxial stretching is performed to obtain a biaxially oriented polyester film In this method, the thermal shrinkage rate at 200°C can be reduced by satisfying the following conditions.

(1) When the molten polyester is ejected from the nozzle to produce an unstretched sheet, after cooling to the surface A drum having a surface temperature of 10°C or higher and 40°C or lower is closely cooled and solidified by static electricity to produce an unstretched sheet.

(2) At a temperature T1n (°C) that satisfies the following formula (i), the unstretched sheet obtained in (1) is 10.0 times the area ratio along the length direction (MD) of the film and the width direction (TD) of the film The biaxial extension is performed to the extent of 16.0 times or more.

(i)Tg(℃)≦T1n(℃)≦Tg+40(℃)

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

(3) The temperature (Th0 (°C)) that satisfies the following formula (ii) is performed, and the biaxially stretched film obtained in (2) is subjected to heat fixing treatment for 1 second or more and 30 seconds or less, uniformly slowly cooled, and then cooled To room temperature, thereby obtaining a polyester film.

(ii) Tmf-35(℃)≦Th0(℃)≦Tmf(℃)

Tmf: Melting point of polyester resin constituting polyester film (℃)

By obtaining an unstretched sheet material that satisfies the conditions of (1), a substantially amorphous polyester film can be obtained. In the subsequent steps of (2), the film can be easily oriented to reduce the heat shrinkage, and Films with good mechanical properties can be easily obtained. By obtaining a biaxially stretched film that satisfies the condition of (2), the film can be moderately oriented, and a film with good mechanical properties can be made. By fulfilling the conditions of (3) to complete the crystal alignment, the structure of the aligned polyester molecular chain can be stabilized, the thermal shrinkage rate can be reduced, and the film with good planarity can be made.

In addition, in (2), as a method of performing biaxial stretching, any of the following methods may be used: separately performing the longitudinal direction of the film (MD, Machine Direction) and the width direction of the film (which is perpendicular to the longitudinal direction of the film) Direction, TD (Transverse Direction, horizontal) successive biaxial extension method, or simultaneous biaxial extension method in which the longitudinal direction and the width direction are simultaneously extended. Also, at the extension temperature (T1n) (℃) In the case of less than Tg (°C), it is difficult to extend. In the case where T1n(°C) exceeds Tg+40(°C), there are cases where the film breaks frequently and the film cannot be obtained by stretching. More preferably, Tg+10(°C)≦T1n(°C)≦Tg+30(°C).

Regarding the step (3), from the viewpoint of flatness, it is preferable to perform the method while holding both ends of the film. In addition, from the viewpoint of reducing the thermal shrinkage rate, a method of thermally fixing one side of the film width direction relative to the film width by 1 to 10% shrinkage is also preferable.

In (3), the heat shrinkage generated by the film is generated at a temperature close to the temperature at which the film structure is formed as described above. Therefore, in order to suppress the heat shrinkage rate of the film at a high temperature exceeding 200°C, it is important to make The heat fixing temperature (Th0 (°C)) becomes higher. On the other hand, when heat treatment is performed at a temperature where the heat-fixing temperature (Th0 (°C)) exceeds Tmf (°C), the thin film is melted and the film cannot be formed. In addition, if the heat treatment is performed at a temperature too close to Tmf (°C), the planarity may deteriorate. Therefore, it is more preferable that Tmf-25(°C)≦Th0(°C)≦Tmf-10(°C). When this heat fixing process is performed, the polyester resin constituting the film has a small endothermic peak (Tmeta (°C)) reflecting the heat fixing temperature. Therefore, the polyester resin constituting the polyester film of the present invention preferably has a minute endothermic peak. Moreover, the minute endothermic peak is preferably Tmf-35 (°C) or more and Tmf (°C) or less, and more preferably Tmf-25 (°C) or more and Tmf-10 (°C) or less.

In addition, in order to reduce the heat shrinkage rate at a higher temperature, the structure of the aligned polyester molecular chain in the film becomes stronger, so it is preferable to perform annealing treatment by the following method (4).

(4) At the heat treatment temperature Th1 (°C) satisfying the following formula (iii), the thin film obtained in (3) is annealed for 70 seconds or more and 600 seconds or less. As a method of performing this annealing treatment, there may be mentioned the ones provided on the film take-up roll and the film take-up roll The method of heat treatment (off-annealing) of the film in the oven in between.

(iii) Tmf-35(℃)≦Th1(℃)≦Th0(heat fixing temperature)(℃)

For the film that is thermally fixed to meet the condition of (3), and then anneal to meet the condition of (4), the structure of the aligned polyester molecular chain in the film can be made stronger, which can be greatly reduced For example, the heat shrinkage rate at high temperature exceeding 200℃.

When Th1 (℃) exceeds Th0 (thermal fixation temperature) (℃), in the step (4), the molecular chain structure in the film fixed by the step (3) will be destroyed, resulting in the presence of the film The situation of sharp contraction and worsening flatness. On the other hand, when Th1 (°C) is lower than Tmf-35 (°C), there is a case where the heat shrinkage rate at high temperature cannot be reduced. When Th1 (℃) is lower than Th0 (thermal fixation temperature) (℃), especially when Th1 (℃) is sufficiently smaller than Th0 (thermal fixation temperature) (℃), a small endothermic peak (Tmeta) system is observed Those reflecting the thin film structure formed by the heat fixing process in the step (3), and those reflecting the thin film structure formed by the annealing process in the step (4). In this case, the structure of the film formed by the heat fixing step of (3) will not be destroyed during the annealing process of (4), so that the structure of the aligned polyester molecular chain in the film can be formed Become stronger. In this case, the heat shrinkage rate at a high temperature exceeding 200°C can be greatly reduced, and the flatness of the film becomes good. Therefore, the polyester resin constituting the polyester film of the present invention preferably has two or more Tmeta (°C). Moreover, when there are two or more Tmeta(℃), the low temperature Tmeta(Tmeta1)(℃) and the high temperature Tmeta(Tmeta2)(℃) satisfy Tmf-35(℃)≦Tmeta1(℃)< Tmeta2(°C)≦Tmf(°C). In this case, a thin film with good planarity can be obtained, which is preferable. The heat fixing process of (3) and the annealing process of (4) can be performed multiple times. The film that has undergone the heat-fixing process of (3) multiple times and the annealing process of (4) may have more than 3 Tmeta (°C). Yu has 3 In the case of more than one Tmeta (℃), the lowest temperature Tmeta (℃) is set to Tmeta1 (℃), the highest temperature Tmeta (℃) is set to Tmeta2 (℃), and preferably meets Tmf-35 (℃ )≦Tmeta1(℃)<Tmeta2(℃)≦Tmf(℃).

Next, (Method B) will be described. The polyester film of the present invention can be preferably obtained by the following method (method B): a laminated film comprising at least 3 layers, and the melting point of the resin constituting the layer (layer A) included in the outermost surface of the film ( Tmo) is set to 260°C or higher. By setting the structure of the film as described above, the thermal shrinkage of the film can be reduced and the flatness can be improved, which is preferable. The main component of the polyester film of the present invention, polyethylene terephthalate, has a melting point of about 255°C. That is, the polyester constituting the layer A contains a high melting point component other than polyethylene terephthalate. By having a surface layer (layer A) containing a resin with a high melting point, it can also be heat-fixed or annealed at higher temperatures that cannot be implemented with a thin film containing only the resin constituting the inner layer (layer B) . The reason for this is that the presence of a surface layer (layer A) containing a resin having a high melting point prevents the inner layer (layer B) from melting even if heat fixing treatment or annealing treatment is performed at a relatively high temperature. The results of successful heat fixing treatment or annealing treatment at such higher temperatures can greatly reduce the heat shrinkage rate at high temperatures such as over 200°C.

More preferably, the melting point (Tmo) of the resin constituting the layer (layer A) included on the outermost surface of the film is 262°C or higher. In addition, from the viewpoint of workability and mechanical properties, it is preferable that the inner layer (layer B) that does not constitute the surface layer is polyethylene terephthalate. The melting point Tmf (°C) of the polyester resin constituting the polyester film of the present invention reflects the melting point of polyethylene terephthalate containing 60% by weight or more of the main component.

Examples of the resin used in the layer A include polyethylene naphthalate (hereinafter sometimes referred to as PEN), polycyclohexane terephthalate (hereinafter sometimes referred to as PCHT), and polyphenylene sulfide ( Hereinafter referred to as PPS), or a mixture of these. Also, for In order to improve the adhesion between the A layer and the B layer, within the range that does not impair the effect of the invention of the present invention, it is also a preferred embodiment to add a small amount of the resin constituting the B layer to the resin constituting the A layer. The amount of the resin constituting the layer B added to the resin constituting the layer A is preferably 0.01% by weight or more and less than 15% by weight relative to the total amount of the resin constituting the layer A, and more preferably 0.1% by weight or more and 5% by weight. the following.

Furthermore, it is preferable that the difference between the melting point (Tmo (°C)) of the resin constituting the surface layer (layer A) and the melting point (Tmi (°C)) of the polyester resin constituting the inner layer (layer B) (Tmo-Tmi(C )) is 5°C or higher and 15°C or lower. If the temperature difference exceeds 15°C, the lamination property may be deteriorated during melt extrusion. On the other hand, if it is less than 5°C, it may be difficult to apply a strong alignment to the layer A. More preferably, it is 5°C or higher and 10°C or lower.

The ratio of the sum of the thickness of the layer constituting the surface layer (layer A) and the thickness of the layer constituting the inner layer (layer B) (sum of the thickness of the layer A/thickness of the layer B) is preferably 1/16 to 1/2 . In the case of less than 1/16, the thickness of the surface layer (layer A) becomes thin, and the effect of protecting the layer B is insufficient, and the flatness and heat resistance may deteriorate. When it exceeds 1/2, the extensibility may deteriorate. The ratio of the thickness of the layer constituting the surface layer (layer A) to the thickness of the layer constituting the inner layer (layer B) (the sum of the thickness of the layer A/the thickness of the layer B) is more preferably 1/8 to 1/4 . By setting to this range, a film excellent in flatness, heat resistance, and extensibility can be produced. In addition, the thickness of one side of the layer A is preferably 5 μm or more and 30 μm or less. That is, when it is convenient to satisfy the above-mentioned stacking ratio, when the thickness of one side of the A layer is less than 5 μm, there is also a case where the flatness is deteriorated, and when it exceeds 30 μm, there is also a deterioration in the extensibility and workability. Situation.

When the polyester film of the present invention is a laminate film including at least 3 layers, the following method may be preferably used: the extruder is used for each layer constituting the laminate film, and the raw materials of each layer are melted by Between the extrusion device and the nozzle After the merging device laminates these in a molten state, it is guided to the nozzle, and is extruded from the nozzle onto the casting drum to be processed into a sheet shape. The sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10°C or higher and 40°C or lower to produce an unextended sheet. The unstretched sheet was formed into a film by the methods (2) to (4) above to obtain a polyester film.

In the laminated film of this configuration, since the melting point (Tmo (°C)) of the resin constituting the surface layer is higher than the melting point (Tmi (°C)) of the resin constituting the inner layer of the film, the heat fixation step and the annealing step When the film is heated, the effect of protecting the resin of the inner layer by the surface layer, compared with the single-layer PET film, the structure of the film is not easy to be destroyed. As a result, the flatness of the film becomes better.

In addition, in the laminated film of this configuration, the following embodiment is also preferable: at a heat-fixing temperature (Th0 (°C)) that satisfies formula (iv), heat treatment is performed for 1 second or more and 30 seconds or less to evenly relax After cooling, it is cooled to room temperature to obtain a polyester film, and then annealed at a temperature of Th1 (°C) that satisfies the following formula (v) for 70 seconds to 600 seconds.

(iv) Tmf-10(℃)≦Th0(heat fixing temperature)(℃)≦Tmf(℃)

(v) Tmf-35(℃)≦Th1(℃)≦Th0(heat fix temperature)(℃)

In the laminated film of this constitution, the melting point (Tmo (°C)) of the resin constituting the surface layer is higher than the melting point Tmf (°C) of the polyester resin constituting the film. That is, the surface layer protects the resin of the inner layer as described above, so that the heat fixing temperature can be increased, so that the heat fixing can be performed at a temperature close to Tmf (°C) without melting the film. When the equation (iv) is satisfied, the heat fixing temperature is close to Tmf (°C), so Tmeta (°C) reflecting the heat fixing temperature overlaps with the melting peak and cannot be observed. On the other hand, since the film structure can be formed at a higher temperature after biaxial stretching, the temperature of the annealing step of (4) can be increased without damaging the film structure. As a result, it can be a thin film structure that is stable even at high temperature Heat shrinkage at low temperature.

The film of the present invention obtained in the above-described manner has a low heat shrinkage rate at high temperatures, and is excellent in flatness.

When the film of the present invention is measured by a non-contact laser microscope by the following method, the unevenness of the film is preferably 300 μm or less. If the difference in concavity and convexity is 0 μm, it becomes substantially flat, so the lower limit is 0 μm or more.

When the unevenness of the film surface exceeds 300 μm, there is a case where the processability of the film deteriorates or the conductivity after ITO deposition deteriorates, which may be unsatisfactory. The smaller the unevenness, the higher the conductivity after ITO deposition. In order to set the unevenness of the surface of the film to the above range, a method of providing a heat fixing step after the biaxial stretching of the film, and a step of annealing at a temperature below the heat fixing temperature after the heat fixing step can be cited. It is more preferably 150 μm or less, and particularly preferably 80 μm or less.

In addition, the polyester film of the present invention preferably has a surface alignment coefficient of 0.145 or more and 0.165 or less. The plane alignment coefficient is obtained from the refractive index of the film by the following method. The surface alignment coefficient of a biaxially stretched film including PET, PEN, etc., usually becomes larger because the benzene rings contained in the molecular chain are arranged parallel to the plane of the film. The benzene ring is relatively rigid in the molecular chain, so when the surface alignment coefficient exceeds 0.165, there are many benzene rings and are arranged parallel to the film plane. Therefore, the film is likely to break when the film is bent or cut. situation. In the case where the surface alignment coefficient is less than 0.145, the alignment is not given by biaxial extension, so the mechanical strength may be deteriorated.

In addition, regarding the polyester film of the present invention, if the polyester resin constituting the film contains phosphoric acid and an alkali metal salt of phosphoric acid, it is excellent in moisture resistance and heat resistance, which is preferable. As a method of making the polyester resin contain phosphoric acid and alkali metal phosphate, phosphoric acid and alkali metal phosphate are added during the polymerization of the polyester resin. The polyester film of the present invention has A layer and B In the case of a laminated film of a layer, it is preferable that only layer A contains phosphoric acid and alkali metal phosphate, and that layer A and layer B both contain phosphoric acid and alkali metal phosphate. When the polyester film of the present invention has good moisture and heat resistance, it can be preferably used as an ITO vapor-deposited substrate for displays used in more severe environments, such as displays for car navigation systems.

The film obtained by the present invention has excellent processability, flatness, and a low heat shrinkage rate at high temperature, and therefore can be preferably used as a transparent electrode vapor deposition substrate for ITO or the like.

[Characteristic evaluation method] A. Melting point (Tmo, Tmi) of resin constituting each layer (℃)

For the sample, the differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd. was used by a method based on JIS K 7121 (1999), and the data analysis used DISC Session "SSC/5200", as follows The outline describes the measurement. The 5 mg samples were weighed successively and placed in the sample pan, and the samples were heated from 25°C to 320°C at a temperature increase rate of 20°C/min (1stRUN (first operation)). A differential scanning calorie measurement chart of 1stRUN is obtained (the vertical axis is thermal energy and the horizontal axis is temperature). The temperature of the peak at the end of the crystal melting peak at the endothermic peak, that is, the crystal melting peak of the 1stRUN differential scanning calorimetry chart, was determined 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.

In the sample, only the resin constituting each layer was cut out from the laminated polyester film using a microtome for measurement.

B. Melting point (Tmf) of polyester resin constituting polyester film (℃)

For the sample, the differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd. was used by a method based on JIS K 7121 (1999), and the data analysis used DISC Session "SSC/5200", as follows The outline describes the measurement. The 5 mg samples were weighed successively and placed in the sample pan, and the samples were heated from 25°C to 320°C (1stRUN) at a temperature increase rate of 20°C/min. A differential scanning calorie measurement chart of 1stRUN is obtained (the vertical axis is thermal energy and the horizontal axis is temperature). The temperature at the peak top of the crystal melting peak at the endothermic peak, which is the endothermic peak, of the 1stRUN differential scanning calorimetry chart is obtained and 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.

C. Tiny endothermic peak (Tmeta1, Tmeta2) of polyester resin constituting polyester film (℃)

The small endothermic peak temperature Tmeta (℃) is based on JIS K 7122 (1999), using a differential scanning calorimeter measuring device "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd., and the data analysis is measured using DISC Session "SSC/5200" . A 5 mg sample was weighed and placed in a sample pan, and the sample was heated from 25°C to 320°C (1stRUN) at a temperature increase rate of 20°C/min. A differential scanning calorie measurement chart of 1stRUN is obtained (the vertical axis is thermal energy and the horizontal axis is temperature). The microscopic endothermic peak temperature before the crystal melting peak in the obtained differential scanning calorimetry chart is taken as Tmeta (°C). When it is difficult to observe a small endothermic peak, the data analysis unit amplifies the vicinity of the peak and reads the peak. When there are a plurality of minute endothermic peaks, the highest minute endothermic peak is set to Tmeta1 (°C), and the lowest minute endothermic peak is set to Tmeta2 (°C).

The method of reading the graph of the small endothermic peak is to use the peak detection function of the analysis software, and set the endothermic peak detected at the temperature below the melting point among the temperatures detected as the peak as Tmeta.

D. Glass transition temperature (Tg) (℃) of the polyester resin constituting the polyester film

In accordance with JIS K 7121 (1999), a differential scanning calorimeter measuring device "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd. was used, and data analysis was performed using DISC Session "SSC/5200". The measurement was performed according to the following procedure.

Weigh 5 mg of the sample and place it in the sample tray, heat the sample from 25°C to 300°C (1stRUN) at a temperature increase rate of 20°C/min, hold it for 5 minutes in this state, and then quench it to become below 25°C . Immediately continue to measure again from 25°C to 300°C at a temperature increase rate of 20°C/min to obtain a differential scanning calorimetry chart of 2ndRUN (second operation) (the vertical axis is thermal energy and the horizontal axis is temperature). In the differential scanning calorimetry chart of the 2ndRUN, the step change portion of the glass transition intersects the curve of the step change portion of the glass transition according to a straight line equidistant from a straight line extending from each reference line in the longitudinal axis direction Point. When two or more stepped portions of glass transition are observed, the glass transition temperature is determined for each of them, and the average value of these temperatures is defined as the sample glass transition temperature (Tg) (°C).

D. Film surface alignment coefficient (fn)

According to JIS K 7105 (1999), the refractive index at 20° C. was determined using an Abbe-type refractometer manufactured by Atago Co., Ltd. The refractive index in the longitudinal direction (Nmd), the refractive index in the width direction (Nd), and the refractive index in the thickness direction (Nz) of the surface of the film were measured, and the plane alignment coefficient (fn) was calculated.

fn=(Nmd+Ntd)/2-Nz

E. Thermal shrinkage of the film (%)

According to JIS C 2318 (1997), the thermal shrinkage of the film was measured. The film was cut into elongate strips with a width of 10 mm and a length of 150 mm. A marking line was drawn on the film so that the length measurement part became approximately 100 mm, and the length of the marking line was measured under the condition of 23° C. and set to L0. After that, hang the weight of 2g in a hot air oven heated to a predetermined temperature (200°C or 220°C) to hang the film and leave it for 30 minutes. After removing the film from the oven and cooling to 23°C, the length of the marking line was measured and set to L1. The shrinkage of the film was determined by the following formula (vi). The measurement was performed by randomly cutting out 5 parts so that the length of the film or the width of the film was 150 mm. The average value of the longitudinal direction and the width direction was calculated separately, and set as the thermal shrinkage rate of the film.

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

F. Flatness of the film

Evaluation was performed using a non-contact three-dimensional measuring device NH-SP3 manufactured by Mitaka Koki Co., Ltd. as a non-contact laser microscope. For the analysis, NH soft manufactured by Ryoko Co., Ltd. was used. Cut the film into 120mm×120mm size film. Make each side parallel to the length or width of the film. Fix the 4 sides of the cut film to the horizontally held measuring table with tape. In the three-dimensional shape measurement mode, the surface shape of the film is measured. Let the X-axis direction be the film length direction, and the Y-axis direction be the film width direction. The measurement pitch is set to 100 μm in the X axis direction, 500 μm in the Y axis direction, the measurement range is set to a range of 100 mm×100 mm, and the Z axis magnification is set to 20 times. Calculate the difference between the highest point and the lowest point in the Z-axis direction (height difference H (μm)). Five parts were randomly cut out of the above shape from the film, the average value thereof was calculated, and evaluation was performed as follows.

0≦H<80 evaluation A

80≦H<150 evaluation B

150≦H≦300 evaluation C

300<H evaluation D

Evaluation A was the most excellent in flatness.

G. Thickness of film (μm)

The thickness of the film is measured using a dial gauge, according to JIS K7130 (1992) A-2 method, and measuring the thickness of any 5 locations in a state where 10 films are stacked. The average value is divided by 10 to make the film thickness.

H. Thickness of each layer of laminated film (μm)

When the film is a laminated film, the thickness of each layer is determined according to the following method. Use a microtome to cut out the film cross section parallel to the film width direction. The cross 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 obtained. The thickness of each layer is calculated based on the obtained lamination ratio and the above-mentioned film thickness.

I. Punchability

Using a test piece punching machine manufactured by a polymer meter (unit), the laminated film was punched into the No. 5 dumbbell shape described in JIS K-6251. The number M of the cracks and peeling of the end surface during the punching of 50 overlapping films was counted, and the punchability was evaluated.

0≦M≦9: Punchability A

10≦M≦20: Punchability B

21≦M≦30: Punchability C

31≦M: Punchability D

A is the best and D is the worst.

J. Intrinsic viscosity IV

The polyester composition was dissolved in 100 ml of o-chlorophenol (solution concentration C=1.2 g/dl), and the viscosity of the solution at 25° C. was measured using an Oswald viscometer. In addition, the viscosity of the solvent was measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] (dl/g) was calculated according to the following formula (c), and the obtained value was defined as the intrinsic viscosity (IV).

(c)ηsp/C=[η]+K[η] ² . C

(Here, ηsp=(solution viscosity (dl/g)/solvent viscosity (dl/g))-1, K is the Hekins constant (set to 0.343)).

K. amount of terminal carboxyl group

The amount of terminal carboxyl groups was measured according to the method of Maulice according to the following method (Document: M.J. Maulice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)). Dissolve 2g of the measurement sample (only separated from the polyester resin (raw material) or the P1 layer of the laminate) at a temperature of 80°C in 50mL of o-cresol/chloroform (weight ratio 7/3) by 0.05N The KOH/methanol solution was titrated, and the terminal carboxyl group concentration was measured and expressed as the value of equivalent/polyester 1t (eq./t). Furthermore, phenol red is used as the indicator during the titration, and it is set as the end point of the titration when it changes from yellowish green to light red. In addition, when there is an insoluble matter such as inorganic particles in the solution in which the measurement sample is dissolved, the following correction is implemented: the solution is filtered, the weight of the insoluble matter is measured, and the weight of the insoluble matter is subtracted from the weight of the measurement sample The correction value is set as the measured sample weight.

L. Film making

Count the number of times the film ruptures within 1 hour during the film-making process, set A to less than 1 time, set to B for more than 1 time and less than 3 times, and set to 3 or more and less than 5 times It is C, and the evaluation is made by making D five or more times. A has the best film formation and D has the worst.

Furthermore, in the above measurement, when the length direction or width direction of the film to be measured is not clear, the direction with the largest refractive index in the film is regarded as the length direction, and the direction orthogonal to the length direction is regarded as the width direction. In addition, the direction of the maximum refractive index in the film can be obtained by measuring the refractive index of the film in all directions by a refractometer, or by determining the direction of the slow phase axis using a phase difference measurement device (birefringence measurement device), etc. .

M. Moisture and heat resistance of the film

Cut the laminated film with the long side and the longitudinal direction of the film, and the long side and the width direction parallel to cut out a size of 1cm × 20cm, based on ASTM-D882 (1997), measured with a chuck spacing of 5cm, stretching speed Elongation at break when stretched at 300mm/min. In addition, the number of samples is set to n=5, and after measuring the longitudinal direction and the width direction of the film, respectively, the average value thereof is obtained, and this is taken as the elongation at break E0 of the film.

Next, the film cut out in the same way was processed by a pressure cooker manufactured by Tabai Espec (share) under high humidity and heat conditions at a temperature of 125°C and a relative humidity of 100% RH, and the elongation at break was measured. In addition, the measurement system was set to n=5, and the longitudinal direction and the width direction of the film were respectively measured, and the average value was defined as the elongation at break E1. Using the obtained elongation at break E0 and E1, the elongation retention rate was calculated by the following formula (d). Change the processing time in units of 1 hour to keep the elongation retention rate below 50% The processing time is set as the elongation half-life.

(d) Elongation retention rate (%)=E1/E0×100

Based on the obtained half-life of elongation, the film's moisture and heat resistance was determined in the following manner.

When the elongation half-life is more than 30 hours: A

When the elongation half-life is more than 20 hours and less than 30 hours: B

When the elongation half-life is less than 20 hours: C

[Example]

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

[Manufacture of PET-A] Using antimony trioxide as a catalyst, terephthalic acid and ethylene glycol are polymerized according to a common method to obtain a melt polymerized PET. The glass transition temperature of the resulting melt-polymerized PET was 81°C, the melting point was 255°C, the intrinsic viscosity was 0.62, and the amount of terminal carboxyl groups was 20 eq./t. Next, melt-polymerized PET was subjected to solid-phase polymerization according to a common method to obtain PET-A. The glass transition temperature of the obtained PET-A was 82°C, the melting point was 255°C, the intrinsic viscosity was 0.85, and the amount of terminal carboxyl groups was 11 eq./t.

[Manufacture of PEN-A] Using manganese acetate as a catalyst, a transesterification reaction was carried out from dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol. After the transesterification reaction is completed, antimony trioxide is used as a catalyst to obtain PEN-A according to a common method. The resulting PEN-A had a glass transition temperature of 124°C, a melting point of 265°C, an intrinsic viscosity of 0.62, and a terminal carboxyl group concentration of 25 eq./t.

[Manufacture of PET-B] Polymerization is carried out using terephthalic acid and ethylene glycol as raw materials and antimony trioxide as a catalyst. Simultaneously with the addition of antimony trioxide, a solution prepared by dissolving phosphoric acid and sodium dihydrogen phosphate dihydrate in ethylene glycol is added. Phosphoric acid is added in such a way that it becomes 2.0 mol/t equivalent to PET, and sodium dihydrogen phosphate dihydrate The material system is added so that it becomes 1.7 mol/t equivalent with respect to PET. In addition, in order to suppress the deactivation of the polymerization catalyst due to the phosphorus compound, manganese acetate equivalent to 2.4 mol/t equivalent to PET was added at the same time as the addition of the phosphorus compound to carry out the polymerization reaction to obtain PET-C. The glass transition temperature of the obtained PET-C was 81°C, the melting point was 255°C, the intrinsic viscosity was 0.68, and the amount of terminal carboxyl groups was 20eq./t. Next, PET-C is subjected to solid-phase polymerization according to a common method to obtain PET-B. The glass transition temperature of the obtained PET-B was 82°C, the melting point was 255°C, the intrinsic viscosity was 0.85, and the amount of terminal carboxyl groups was 11 eq./t.

[Production of PEN-B] Using dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol as raw materials, and manganese acetate as a catalyst, a transesterification reaction was carried out. After the transesterification reaction is completed, antimony trioxide is used as a catalyst for polymerization. Simultaneously with the addition of antimony trioxide, a solution prepared by dissolving phosphoric acid and sodium dihydrogen phosphate dihydrate in ethylene glycol is added. Phosphoric acid was added so that it was 2.0 mol/t equivalent to PET, and sodium dihydrogen phosphate dihydrate was added so that it was 1.7 mol/t equivalent to PET, and a polymerization reaction was performed to obtain PEN-B. The glass transition temperature of the obtained PEN-B was 124°C, the melting point was 265°C, the intrinsic viscosity was 0.62, and the terminal carboxyl group concentration was 20 eq./t.

(Example 1)

The resin constituting the surface layer was set to 100 parts by mass of PEN-A, which was vacuum-dried at 160° C. for 2 hours and then put into 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. In the extruder, each raw material is melted at the temperature described in the table, and the resin added to the extruder 1 is merged by a merging device in such a manner that the two layers of the film are extruded and cast to a surface temperature of 25°C. On the drum, a laminated sheet with a 3-layer structure is produced. Then, after preheating the sheet with a heated roller set, it is along the length direction at a temperature of 95°C (MD direction) 3.2 times stretching, and then cooling with a roller set at a temperature of 25°C to obtain a uniaxially stretched film. While holding both ends of the resulting uniaxially stretched film with a jig, the heated area of 110°C in the tenter was extended 3.5 times in the width direction (TD direction) at right angles to the length direction. Furthermore, the heat treatment zone in the tenter was thermally fixed at 240°C for 10 seconds. In the step of heat fixing, the film is shrunk by 5% relative to the film width in the film width direction. Then, after slowly cooling uniformly in the cooling area, winding is performed to obtain a laminated polyester film. Furthermore, the obtained film was annealed by a hot air oven installed between the film take-out roll and the film take-up roll at a temperature of 220° C. so that the time for the film to be subjected to the heat treatment became 5 minutes to obtain A film with a thickness of 100 μm. The characteristics of the film are shown in the table. It is a film with a low thermal shrinkage at 200°C and a particularly good flatness.

(Examples 2 to 4)

The film formation was performed in the same manner as in Example 1 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. It is a film with a low thermal shrinkage at 200°C and a particularly good flatness.

(Example 5)

A thin film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the heat fixing temperature and the re-annealing temperature of the thin film were changed as described in the table. The characteristics of the film are shown in the table. Since the heat fixing temperature is near the melting point of the film, only one Tmeta was observed. It can be seen that the film has a low heat shrinkage rate at 200°C, and a low heat shrinkage rate at 220°C, and is excellent in flatness.

(Examples 6 to 8)

The film formation was performed in the same manner as in Example 5 except that the composition of the resin and the film forming conditions were changed as shown in the table. The characteristics of the film are shown in the table. It is a film with a low heat shrinkage at 220°C and particularly good flatness.

(Examples 9-14, 22)

Except that the lamination ratio of the thin film and the thickness of the thin film were changed as shown in the table, a film was formed in the same manner as in Example 1. The characteristics of the film are shown in the table. In Example 9, since the build-up of the surface layer (layer A) is relatively large, although the film formability and processability are slightly inferior, it is practically resistant. In Example 11, since the buildup of the surface layer (layer A) is relatively small and the thickness is thin, the function of protecting the inner layer (layer B) is reduced, and the planarity is deteriorated. In Example 13, since the thickness of one side of the surface layer (layer A) is thin, although the function of protecting the inner layer (layer B) is reduced, the flatness is slightly poor, but it is practical and durable. In Example 22, since the thickness of one side of the surface layer (layer A) is relatively thick, although the film formability and processability are slightly inferior, it is practically resistant.

(Examples 15-17)

Except that the composition of the resin and the re-annealing temperature of the thin film were changed as described in the table, a film was formed in the same manner as in Example 5. The characteristics of the film are shown in the table. Since the re-annealing temperature is lower than in Example 5, the heat shrinkage at 220°C is slightly inferior, but the flatness shows excellent characteristics.

(Examples 18 and 21)

The resin constituting the film was made of only polyethylene terephthalate, and the film-forming conditions were set as shown in the table to produce a single-film film. The characteristics of the film are shown in the table. in In Example 18, the heat shrinkage rate at 200°C was excellent, and although the flatness was slightly inferior to that in Example 1, it was practically resistant. In Example 21, since the heat fixing temperature is the same as the annealing temperature, the heat shrinkage rate is excellent. Although the flatness is slightly poor, it is practical.

(Example 19)

A film was obtained in the same manner as in Example 1 except that the composition of the resin constituting the layer A was as described in the table. The characteristics of the film are shown in the table. It can be seen that the melting point of layer A is less than 260°C, and the flatness is slightly poor.

(Example 20)

A thin film was obtained in the same manner as in Example 1 except that the resin used in the layer A was PCHT. For PCHT, Copolyester 13319 manufactured by Eastman Chemical Company was used. The characteristics of the film are shown in the table. It is a film with excellent heat shrinkage and flatness.

(Examples 23 to 25)

A film was obtained in the same manner as in Example 1 except that the resin used in layer A was PEN-B and the resin used in layer B was PET-B. The characteristics of the film are shown in the table. It is a film with excellent heat shrinkage, flatness and moisture resistance.

(Comparative examples 1, 2)

The resin constituting the film was made of only polyethylene terephthalate, and the film-forming conditions were set as shown in the table to produce a single-film film. The characteristics of the film are shown in the table. In Comparative Example 1, because the temperature of Tmeta1 is low and it is less than Tmf-35℃, so The heat shrinkage rate becomes worse. In Comparative Example 2, since the heat-fixing temperature is high and the Tmf is the same, the film-forming property is poor and a thin film cannot be obtained.

(Comparative Examples 3 and 4)

The resin constituting the film was made PEN only, and the film was formed under the stretching conditions described in the table. The characteristics of the obtained film are shown in the table. In Comparative Example 3, only heat fixing is performed, and in Comparative Example 4, re-annealing is performed after the heat fixing step. Since the film which is not mainly composed of PET has a large surface alignment coefficient (fn), the processability is greatly deteriorated.

(Comparative Examples 5, 6)

A film was produced in the same manner as in Example 1 except that the composition of the resin constituting the layer A and the film forming conditions were changed as described in the table. The film characteristics are shown in the table.

In Comparative Example 5, since the temperature of Tmeta1 is low and less than Tmf-35°C, the thermal shrinkage rate is greatly deteriorated. In Comparative Example 6, since the re-annealing step was not performed, the thermal shrinkage rate greatly deteriorated.

(Industry availability)

The polyester film of the present invention is not only excellent in flatness and processability, but also excellent in heat resistance. Therefore, the polyester film of the present invention changes little in the shape of the film in the step of high temperature environment such as transparent electrode deposition, and can be preferably used as an optical device substrate.

Claims (7)

A polyester film whose length of polyethylene terephthalate in the polyester resin constituting the film is 60% by weight or more and heat treatment at 220°C for 30 minutes , The thermal shrinkage in the width direction is 0.5% or less, and at least any one has a thermal shrinkage of 0.01% or more; Among them, the polyester resin constituting the film has a melting point (Tmf (℃)), and has more than 2 The small endothermic peak temperature (Tmeta(℃)), and the lowest temperature Tmeta(Tmeta1)(℃) and the highest temperature Tmeta(Tmeta2)(℃) satisfy the following relationship: Tmf-35(℃)≦Tmeta1(℃)< Tmeta2(℃)≦Tmf(℃). The polyester film according to claim 1, wherein, when the unevenness of the film is measured by a non-contact laser microscope, the unevenness of the film is 300 μm or less. The polyester film according to claim 1, wherein the surface alignment coefficient is 0.145 or more and 0.165 or less. The polyester film according to claim 1, wherein the polyester film is a laminated polyester film containing at least 3 layers, and the melting point of the polyester resin included in the layer (layer A) constituting the film surface (Tmo (°C) ) Is above 260℃. The polyester film according to claim 4, wherein the laminated polyester film includes three layers, and the melting point (Tmo (°C)) of the polyester resin included in the layer (A layer) constituting the surface layer and the inner layer The difference in melting point (Tmi (°C)) of the polyester resin included in the layer (layer B) is 5°C or higher and 10°C or lower. The polyester film according to claim 5, wherein the ratio of the sum of the thickness of the layer constituting the surface layer (layer A) and the thickness of the layer constituting the inner layer (layer B) is 1/8 or more and 1/4 or less. The polyester film according to any one of claims 1 to 5, which is used for a film-forming substrate of a transparent conductive film.