Biaxially oriented polyester film roll and method for producing the same

Abstract

To provide a polyester film roll having fewer scratch defects, in response to the advancement of quality enhancement in recent years.SOLUTION: A polyester film roll having 3.0×10-6 or fewer scratches per unit area from the unwound end to the winding core.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyester film roll obtained by winding a biaxially oriented polyester film, and a method for producing the same. [Background technology]

[0002] Polyester film is used in a wide range of industrial applications due to its mechanical and thermal properties, stiffness, and cost. In particular, it has recently been used as a process paper for electronic components, a release film for molding green sheets for multilayer ceramic capacitors, a release film for liquid crystal polarizers, and a substrate for dry film resists.

[0003] However, with the recent trend toward precision in various applications, polyester films are now required to be free of minute defects, which were not a problem in the past, and to have more uniform quality than ever before. The quality of molded articles made from polyester films depends on the precision and quality of the polyester film, particularly the presence or absence of surface defects.

[0004] Patent Document 1 discloses a release polyester film that reduces the number of dent defects and controls the surface roughness to reduce fine defects on the film surface. Patent Document 2 discloses a polyester film that strictly specifies the surface roughness and the number of scratches, thereby reducing the number of scratches transferred to the optical film without deteriorating the transparency of the optical film, thereby improving the yield of the optical film.

[0005] Patent Document 3 discloses a method for preventing defects such as scratches and the possibility of foreign matter occurring during the winding process by controlling the dust level in the atmosphere, the surface pressure during winding, and the tension, thereby achieving excellent winding quality.

[0006] Patent Document 4 discloses a method for producing a release film roll for producing a thin ceramic sheet, which has a uniform surface with little foreign matter mixed in and does not cause defects in the ceramic sheet, by controlling the absolute value of the electrostatic charge of the running take-up roll when winding up a release film having a release layer made of a curable silicone resin formed thereon to 0.5 kV or less.

[0007] Patent Document 5 discloses a polyester film roll that has reduced static charge and fewer protruding defects when unwound by controlling the surface roughness of the polyester film. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-007054 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-109329 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-39590 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-181993 [Patent Document 5] Japanese Patent Application Laid-Open No. 2005-187779 Summary of the Invention [Problem to be solved by the invention]

[0009] However, with these techniques, it is becoming difficult to solve the problem of scratches and other defects in the current situation where density and precision are becoming increasingly important. Therefore, an object of the present invention is to obtain a polyester film roll with fewer scratches and other defects in response to the recent trend toward higher quality. [Means for solving the problem]

[0010] As a result of extensive research, the inventors of the present invention have found that the number of scratches per unit area from the unwinding of a polyester film roll to the core is 3.0 × 10 -6 pieces / m 2It has been found that the above problems can be solved by the following: A preferred embodiment of the present invention has the following configuration. (1) The number of scratches per unit area from the unwinding point of a polyester film roll to the core is 3.0 x 10 -6 pieces / m 2 Below is a roll of polyester film. (2) The polyester film roll according to (1), wherein the absolute value of the charge from the unwinding of the polyester film roll to the core is 1.0 kV or less. (3) Surface resistivity is 10 12 The polyester film roll according to (1) or (2), having a resistance of Ω / □ or less. (4) The polyester film roll according to (1), wherein one surface (side A) has a central surface average roughness SRa of 0.5 nm to 8 nm and a central surface peak height SRp of 50 nm to 500 nm, and the opposite surface has a central surface average roughness SRa of 0.5 nm to 8 nm and a central surface peak height SRp of 1 nm to 300 nm. (5) The polyester film roll according to (1), wherein the coefficient of static friction of the surface opposite to the surface A is 0.5 or more and 2.5 or less. (6) The polyester film roll according to (1), which is used for a dry film resist, has a thickness of 10 μm or more and 50 μm or less and a haze of 0.1% or more and 0.7% or less. (7) The method for producing a polyester film roll according to (1), wherein a touch roll having a static friction coefficient of 0.5 or less is used in winding the polyester film roll. [Effects of the Invention]

[0011] The present invention makes it possible to obtain a polyester film roll with fewer scratches and defects, which meets the recent trend toward higher quality. This also makes it possible to improve the yield in subsequent processes, particularly in the inspection process for dry film resist applications, more than ever before. DETAILED DESCRIPTION OF THE INVENTION

[0012] Representative embodiments of the polyester film and polyester film roll of the present invention will be described below, but the present invention is not limited to the following embodiments and can be practiced with appropriate modifications within the scope of the present invention.

[0013] The polyester in the polyester film of the present invention comprises a dicarboxylic acid component and a diol component. In this specification, the term "component" refers to the smallest unit obtainable by hydrolysis of a polyester. To implement the present invention, it is preferable to use terephthalic acid as the dicarboxylic acid component constituting the polyester in an amount of 30 mol % or more based on the total dicarboxylic acid components. Examples of dicarboxylic acid components other than terephthalic acid include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid; alicyclic dicarboxylic acids such as adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorene acid, or ester derivatives thereof. However, these are not limited thereto.

[0014] Examples of diol constituents constituting such polyesters include, but are not limited to, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol; alicyclic diols such as cyclohexanedimethanol, spiroglycol, and isosorbide; diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis(4-hydroxyphenyl)fluorene, and aromatic diols; and diols in which multiple units of the above-mentioned diols are linked together.

[0015] The polyester of the present invention can be produced by a known method. Specifically, the esterification step can be carried out using one or more esterification reaction vessels with stirring. For example, when a single esterification reaction vessel is used, the reaction temperature is usually 240 to 280°C, the relative pressure to atmospheric pressure is usually 0 to 400 kPa, and the reaction time is usually 1 to 10 hours. The esterification reaction rate of the esterification reaction product obtained in the esterification step is usually 95% or more.

[0016] After the esterification reaction, a melt polycondensation step is preferably performed. This melt polycondensation step can typically be performed continuously or batchwise using one or more polycondensation reaction vessels. The pressure is gradually reduced from atmospheric pressure, and the resulting ethylene glycol is distilled out of the system while the mixture is heated and stirred. For example, in the case of a batch process using a single polycondensation reaction vessel, the reaction temperature is typically 250 to 290°C, the final absolute pressure, gradually reduced from atmospheric pressure, is typically 0.013 to 1.3 kPa (0.1 to 10 Torr), and the reaction time is typically 1 to 20 hours. Furthermore, to improve electrostatic castability during polyester film formation, compounds containing sulfur, phosphorus, calcium, magnesium, or manganese can be added during the polycondensation reaction.

[0017] The intrinsic viscosity of the polyester resin can be determined by the polymerization end point based on the stirring torque of the polymer. High stirring torque results in a high melt viscosity of the polymer, and therefore a high intrinsic viscosity (IV). The stirring torque for determining the end point of the polymerization apparatus can be set to achieve the target intrinsic viscosity. In the present invention, it is preferable to set the stirring torque for determining the end point so that the IV of the film is 0.50 dL / g or more and 0.70 dL / g or less. Setting the torque within this range facilitates control of the surface roughness, which is preferable from the viewpoints of heat shrinkage properties and puncture strength. The obtained polyester resin after polymerization can be discharged in the form of a strand from the bottom of the polymerization apparatus and cut with a cutter while being cooled with water. Since the chip shape can be controlled by cutting, polyester chips with a preferred bulk density can be obtained in the present invention.

[0018] The polycondensation reaction catalyst used in the present invention may be one or more of diantimony trioxide, diantimony pentoxide, antimony acetate, antimony glycolate, germanium dioxide, organotitanium compounds, etc. Among these, diantimony trioxide is preferred from the viewpoints of the transparency of the polyester obtained and availability.

[0019] The polyester film roll of the present invention has a flaw count of 3.0×10 per unit area from the unwinding of the polyester film roll to the winding core. -6 / m 2 Here, the number of scratches per unit area in the present invention refers to the number of periodic scratches per unit area, which indicates light leakage due to scratch defects in the polyester film, and the detected defects are three or more consecutive scratches in the longitudinal direction of the polyester film. As will be explained in the examples, this can be calculated by (number of periodic scratches) = (number of periodic scratches in the width direction) ÷ (inspection area).

[0020] The number of periodic scratches is 3.0 x 10 -6 / m 2 If the number of periodic scratches exceeds 3.0×10, it will cause a decrease in yield in the inspection process for dry film resist applications. -6 / m 2To achieve this, it is preferable to use a touch roll with a surface having a static friction coefficient of 0.5 or less in the winding process.

[0021] The polyester film roll of the present invention preferably has an absolute charge value of 1.0 kV or less from the unwinding to the core. The range of the absolute charge value is determined by the method described in the Examples. By maintaining this range, scratches caused by foreign matter can be suppressed. If the absolute charge value from the unwinding to the core exceeds 1.0 kV, the introduction of foreign matter from the previous process, and the adhesion of floating foreign matter and fine powder generated in the slit to the film or roll tend to increase, resulting in increased scratches. A preferred method for adjusting the absolute charge value of the polyester film roll to satisfy the above range is to adjust the touch roll during winding. More preferably, the material and contact state of the touch roll are adjusted. The charge value of the polyester film roll can also be controlled using a static eliminator. While static eliminators apply a voltage and release positive and negative ions from a static eliminator needle that strike the target for static elimination, this tends to result in uneven static elimination between the vicinity of the static eliminator and a distant location. On the other hand, a touch roll is suitable for controlling the charge distribution because it is in uniform contact with the film.

[0022] The polyester film of the present invention has a surface resistivity of 10 12 It is preferable that the resistance is 10Ω / □ or less. 12 If it exceeds Ω / □, not only will the charge build up due to friction increase, but charge decay will also be difficult, making it easier for foreign matter to adhere during processing, which may lead to an increase in scratches.

[0023] The polyester film roll of the present invention preferably satisfies the requirements that the central surface average roughness (SRa) of one surface is 0.5 nm to 8.0 nm and the central surface peak height (SRp) is 50 nm to 500 nm, more preferably the central surface average roughness (SRa) is 0.7 nm to 7 nm and the central surface peak height (SRp) is 100 nm to 450 nm.

[0024] Furthermore, the opposite surface preferably satisfies the requirements of a central surface average roughness (SRa) of 0.5 nm to 8.0 nm and a central surface peak height (SRp) of 1 nm to 300 nm. The opposite surface more preferably has a central surface average roughness (SRa) of 1.0 nm to 9 nm and a central surface peak height (SRp) of 5 nm to 250 nm. If the central surface average roughness (SRa) of one surface of a polyester film roll is less than 0.5 nm or the central surface peak height (SRp) is less than 50 nm, the film's slipperiness may be significantly impaired, leading to the occurrence of abrasion-like scratches during film formation. On the other hand, if the central surface average roughness (SRa) is greater than 8.0 nm or the central surface peak height is greater than 500 nm, the surface irregularities may be transferred when the polyester film is wound, resulting in a worse surface roughness than that of the film alone.

[0025] The static friction coefficient of the surface opposite to side A of the polyester film roll of the present invention is preferably 0.50 or more and 2.50 or less, more preferably 0.55 or more and 2.4 or less, and even more preferably 0.60 or more and 2.3 or less. By maintaining the static friction coefficient within a suitable range, it is possible to obtain a polyester film that maintains a good winding shape and has few periodic scratches. On the other hand, a static friction coefficient of less than 0.50 means that the friction when left standing is low, which makes it easy for the film to slip during winding, storage, and transportation, making it difficult to achieve a good winding shape. Furthermore, a static friction coefficient of more than 2.50 makes it easy for films to adhere to each other, resulting in blocking, which may cause scratches when the films are peeled off.

[0026] The thickness of the polyester film in the polyester film roll of the present invention is preferably 10 μm or more and 50 μm or less, more preferably 20 μm or more and 45 μm or less, and even more preferably 30 μm or more and 40 μm or less. If the film thickness is less than 10 μm, the film may be easily torn during film formation, resulting in extremely low productivity. Furthermore, the film may lose stiffness and be easily deflected when tension is applied to the film, which may impair the coating suitability when coating the release layer of the release film. On the other hand, if the film thickness is greater than 50 μm, the cost of the polyester film increases due to the increased amount of raw materials used, and the film may become unsuitable for use as a dry film resist.

[0027] Furthermore, the polyester film in the polyester film roll of the present invention preferably has a film haze of 0.1% to 0.7%. By setting the film haze to 0.1% to 0.7%, the polyester film, which serves as a support for the resist layer, will scatter ultraviolet light more effectively when the resist layer is exposed to ultraviolet light after laminating the polyester film. This can prevent distortion, defects, and deterioration of the resist pattern wall surface after development.

[0028] In the method for producing a polyester film roll of the present invention, the static friction coefficient of the touch roll surface is preferably 0.5 or less in the winding step. By making the static friction coefficient of the touch roll surface less than 0.5%, scratches and other defects on the polyester film during winding can be reduced.

[0029] Next, a method for producing the polyester film and film roll of the present invention will be described, but the present invention should not be construed as being limited to such an example.

[0030] (Step 1) Using terephthalic acid or dimethyl terephthalate and ethylene glycol as raw materials, a low polymer such as BHT (bishydroxyethyl terephthalate) is obtained through reactions such as esterification and transesterification. Terephthalic acid, ethylene glycol, and compounds containing sulfur, phosphorus, calcium, magnesium, and manganese are then added, and a polyester resin is obtained through a polycondensation reaction.

[0031] (Step 2) A step of melt-extruding a polyester resin into a sheet, contacting the melt-extruded polyester resin into a sheet on a casting roll at 18 to 50°C for 1 to 15 seconds to cool and solidify it, thereby obtaining an unstretched polyester film having a thickness of 180 to 1400 μm.

[0032] (Step 3) A step of stretching the unstretched polyester film obtained in (Step 2) in the longitudinal direction at a stretching ratio of 2.5 to 5.0, and then cooling to obtain a uniaxially stretched polyester film.

[0033] (Step 4) A step of stretching the uniaxially stretched polyester film obtained in (Step 3) in the width direction at a stretching ratio of 3.0 to 6.0 times, which is higher than the stretching ratio in the longitudinal direction, and then cooling to obtain a biaxially stretched polyester film.

[0034] (Step 5) A step of heat-treating the biaxially stretched polyester film at a heat treatment temperature of 180 to 230°C to obtain a biaxially oriented polyester film.

[0035] (Step 6) A step of winding up the polyester film obtained in Step 5 to obtain an intermediate film roll.

[0036] (Step 7) A step of slitting the intermediate film roll obtained in step 6 to an appropriate width to obtain a polyester film roll.

[0037] Each step will be described in detail below.

[0038] (Step 1) Production of polyester resin A slurry consisting of terephthalic acid and ethylene glycol is gradually added to an esterification reactor charged with dissolved BHT (bishydroxyethyl terephthalate) at 250°C, and the esterification reaction is allowed to proceed while distilling off water. The temperature within the reaction system is controlled to 245-250°C, and the esterification reaction is terminated when the reaction rate reaches 95%, and the resulting esterification reaction product is charged in a molten state into a polymerization reactor equipped with a distillation device.

[0039] Antimony trioxide and a compound containing sulfur and phosphorus are added as an ethylene glycol solution, and the pressure inside the polymerization reactor is gradually reduced to 0.13 kPa or less in 35 minutes. At the same time, the temperature is gradually increased to 279°C, and a polymerization reaction is carried out to obtain a polyester resin.

[0040] (Step 2) Creating unstretched film The polyester resin is dried, if necessary, and fed to an extruder for melt extrusion. A single-screw or twin-screw extruder can be used as the extruder for producing the polyester film and film roll of the present invention. A vented extruder equipped with a vacuum line can also be used to eliminate the pellet drying step. For the intermediate layer, which has the highest extrusion rate in a multilayer film, a so-called tandem extruder can be used, in which each extruder has the function of melting the pellets and the function of maintaining the molten pellets at a constant temperature. To achieve the intrinsic viscosity of the film within the above-mentioned range, the average intrinsic viscosity of the polyester resin fed to the extruder is preferably 0.55 to 0.64 dL / g, more preferably 0.55 to 0.62 dL / g.

[0041] The polyester resin melt-extruded by the extruder is then filtered through a filter. Because even small foreign particles can cause film defects, it is effective to use a high-precision filter that captures, for example, 95% or more of foreign particles 5 μm or larger. The molten polyester resin undergoes thermal decomposition and hydrolysis, which breaks its molecular chains and reduces its intrinsic viscosity. To ensure stable melt extrusion, the temperature and moisture content of the polyester resin during melt extrusion are preferably set to +5 to +40°C above the melting point of the polyester resin, and the moisture content is preferably 300 ppm or less.

[0042] The polyester resin is then formed into a sheet using a T-shaped die or the like, and the sheet-shaped polyester resin is cooled and solidified on a casting roll to obtain an unstretched film. In the case of a three-layer laminate film, three extruders and a three-layer manifold or merging block (e.g., a merging block with a rectangular merging section) are used to laminate the three layers, and the sheet is extruded from the die. In this case, installing a static mixer or gear pump in the polymer flow path is effective from the viewpoint of stabilizing back pressure and suppressing thickness fluctuations. In this case, the casting roll temperature is preferably 18 to 50°C, and the cooling time for the polyester resin formed into a sheet to contact the casting roll is preferably 1 to 15 seconds. If the casting roll temperature is below 18°C, condensation is likely to occur on the casting drum, which may deteriorate film formability. If the casting roll temperature exceeds 50°C, the cooling rate slows, resulting in the formation of microcrystals in the unstretched film, which accelerates crystal orientation during the subsequent stretching process and worsens the orientation angle. Similarly, if the cooling time after contact with the casting roll is less than 1 second, the insufficient cooling time will lead to uneven cooling and stretching, making it difficult to achieve the film thickness, static friction coefficient, and surface roughness within the above-mentioned ranges. The cooling time with the casting roll can be extended by increasing the diameter of the casting roll or reducing the line speed, but in consideration of equipment space and productivity, the upper limit is 15 seconds. More preferably, the temperature of the casting roll is 20 to 30°C, and the cooling time during which the polyester resin formed into a sheet comes into contact with the casting roll is 3 to 12 seconds.

[0043] The thickness of the unstretched film obtained in step 2 is preferably 180 to 1400 μm. If the thickness of the unstretched film is less than 180 μm, the film thickness will be insufficient to achieve the desired orientation angle and heat shrinkage, and film tearing may occur during stretching. On the other hand, if the thickness of the unstretched film exceeds 1400 μm, uneven cooling may occur in the thickness direction when the polyester resin sheet is cooled and solidified on a casting roll, making it difficult to obtain a uniform polyester film. Furthermore, the final thickness of the biaxially oriented polyester film may fall outside the range suitable for use as a release agent for polarizing plates.

[0044] For example, inert particles can be incorporated into polyester by dispersing them in a slurry in a predetermined ratio in ethylene glycol, a diol component, and adding this ethylene glycol slurry at any stage before the completion of polyester polymerization. When adding the particles, for example, adding the aqueous sol or alcohol sol obtained during particle synthesis without first drying it is preferable because this improves particle dispersibility and prevents the formation of coarse protrusions. Another effective method for producing the polyester of the present invention is to directly mix the aqueous slurry of particles with the desired polyester pellets, feed the mixture into a vented twin-screw kneading extruder, and knead the mixture into the polyester.

[0045] (Step 3) Creating uniaxially stretched film The unstretched film obtained in step 2 is stretched in the longitudinal direction at a stretch ratio of 2.5 to 5.0, followed by cooling to obtain a uniaxially stretched polyester film. The longitudinal stretching is preferably performed in one step or multiple steps at a stretching temperature of 90 to 130°C. To prevent bowing and thickness unevenness in the longitudinal direction of the film, the stretching temperature is more preferably 100 to 120°C and the stretching ratio is more preferably 3 to 4 times. To prevent stretching unevenness and scratches, stretching is preferably performed in two or more steps. If the stretching temperature and stretching ratio exceed the aforementioned ranges, it becomes difficult to achieve the puncture strength and heat shrinkage within the aforementioned ranges. Furthermore, although shrinkage in the width direction occurs due to the longitudinal stretching, it is preferable that the width shrinkage of the film from this stretching step to the cooling step be 15% or less. If the film width shrinkage exceeds 15%, the film may meander or vary in width, or the uniformity of the film's plane orientation in the width direction may deteriorate, making it difficult to maintain the orientation angle within the above range. The film width shrinkage can be controlled by adjusting the thickness profile of the film edge before longitudinal stretching or by adjusting the stretching tension using nip rolls, etc.

[0046] The width shrinkage of the film shown here is calculated by dividing the difference between the film width immediately before the longitudinal stretching step and the film width after stretching and cooling by the film width immediately before the longitudinal stretching step. A film temperature of 25 to 45°C in the cooling step in (Step 3) is preferred for stable width stretching in the next (Step 3).

[0047] (Step 4) Creating biaxially stretched film The uniaxially stretched polyester film obtained in the above (step 3) is stretched in the width direction at a stretch ratio of 3.0 to 6.0 times, which is higher than the stretch ratio in the longitudinal direction. The width direction stretching is preferably performed at a stretching temperature of 90 to 130°C. When the stretching temperature is lower than 90°C and the stretch ratio is higher than 6.0 times, the orientation angle tends to decrease and the puncture strength tends to increase, but the film may be more susceptible to breakage and heat shrinkage may be worsened. The stretching temperature is more preferably 100 to 120°C and the stretch ratio is more preferably 4.0 to 5.0 times. Furthermore, to reduce the orientation angle, the stretch ratio in the width direction is preferably higher than the stretch ratio in the longitudinal direction. If the stretch ratio in the longitudinal direction is higher than the stretch ratio in the width direction, the molecular orientation in the film will be tilted toward the longitudinal direction, making it difficult to suppress the orientation angle variation.

[0048] In producing the polyester film of the present invention, the stretching in the longitudinal direction is followed by the stretching in the width direction, because if the stretching in the longitudinal direction is carried out after the stretching in the width direction, the molecules will be strongly oriented mainly in the width direction after the first stretching in the width direction, but if the stretching in the longitudinal direction is carried out thereafter, the molecules will also be oriented in the longitudinal direction, resulting in a high orientation angle.

[0049] The film stretched in the width direction is then cooled at a film temperature of 25 to 45°C and a film width shrinkage rate of 0.1 to 20% / min to obtain a cooled biaxially stretched polyester film. A film temperature of 25 to 45°C in the cooling step is preferred because it suppresses relaxation of orientation in the width direction due to width shrinkage, suppresses bowing, and is also effective in reducing the thermal shrinkage rate. A film temperature of 30 to 40°C is more preferred. If the film temperature in the cooling step is higher than 45°C, the tension caused by the film width shrinkage will affect film formability, and the effect of suppressing relaxation of orientation in the width direction may not be fully achieved. Cooling the film to a temperature below 20°C in the cooling step may result in poor productivity.

[0050] Methods for cooling polyester film include air-cooling using a tenter where heat treatment is performed, air-cooling using aluminum or other shielding plates above and below the heat treatment area to block hot air, and cooling using rolls. In the air-cooling method using a tenter where heat treatment is performed, all zones are connected in the longitudinal direction, so the free flow of hot air, such as accompanying air currents, can cause temperature differences across the top and bottom of the film and across the width, making it difficult to sufficiently cool the film. In such cases, it is possible to address this issue by actively cooling the film by blowing in compressed air or the like.

[0051] In the cooling method using rolls, the number of rolls used and the set temperature are not limited, but it is preferable to use multiple rolls for cooling. In the cooling method using rolls, to keep the film temperature in the above range, the roll temperature is preferably 20 to 45°C, and more preferably 30 to 40°C. In the cooling method using rolls, it is preferable to apply a load to the cooling rolls with nip rolls to make the film tightly contacted with the cooling rolls, as this allows for stable cooling.

[0052] Furthermore, in this cooling step, the width shrinkage rate of the film is preferably 0.1 to 20% / min. If the width shrinkage rate is less than 0.1% / min, the suppression of the width shrinkage of the film affects the film tension, which may result in poor film formability and film tearing. If the width shrinkage rate is faster than 20% / min, the effect of suppressing orientation relaxation due to the width shrinkage of the film is small, and the suppression of the bowing phenomenon may be insufficient. It is more preferable that the width shrinkage rate of the film is 0.2 to 18% / min. The width shrinkage rate can be controlled in various ways by setting it based on the cooling step length and film formation speed. Specifically, in the air-cooling method using a tenter, the width shrinkage rate can be set to the desired value by holding both ends with clips and adjusting the rail width.

[0053] The width shrinkage rate of the film in the cooling process shown here is calculated by formula (1) where W1 (mm) is the film width after the width direction stretching process and immediately before entering the cooling process, W2 (mm) is the film width after the cooling process, and T1 (min) is the time it takes to pass through the cooling process. Film width shrinkage rate = (W1-W2) / W1 × 1 / T1 Equation (1)

[0054] Furthermore, in the cooling step (step 3), it is preferable that the film be left in a cooled state for a certain period of time. The reason for this is presumed to be as follows: As mentioned above, it is thought that orientation relaxation occurs during the cooling step when the film is shrunk in width, and it is presumed that a certain period of time is required to stop the orientation relaxation by cooling the film. Therefore, it is presumed that if the cooling step time is insufficient, orientation relaxation cannot be suppressed, and the effect of suppressing the bowing phenomenon is small. When producing the polyester film of the present invention, the cooling step time is preferably 10 seconds or more, more preferably 15 seconds or more. There is no particular upper limit to the cooling step time, but a time of 60 seconds or less is preferred because it improves productivity.

[0055] The production of biaxially stretched films is not limited to the above-mentioned sequential biaxial stretching, but can also be produced by simultaneous biaxial stretching. In particular, simultaneous biaxial stretching does not involve stretching with rolls, so that localized heating and cooling unevenness on the film surface can be suppressed, resulting in a film of uniform quality, particularly with reduced variations in heat absorption, and is preferable because it can suppress the occurrence of scratches due to speed differences at the contact points between the film and rolls during roll stretching and the transfer of minute scratches from the rolls.

[0056] (Step 5) Heat treatment of biaxially stretched film The biaxially stretched polyester film obtained in step 4 is heat-treated to obtain a biaxially oriented polyester film. The heat treatment temperature is preferably 180 to 230°C, more preferably 180 to 215°C, and particularly preferably 185 to 210°C. If the heat treatment temperature is less than 180°C, the heat treatment will be insufficient, and it may be difficult to achieve a heat shrinkage rate of 2.5 to 7.0% in the longitudinal direction and 2.5 to 8.0% in the transverse direction after heat treatment at 150°C for 30 minutes. If the heat treatment temperature is higher than 230°C, bowing is likely to occur, making it difficult to control the orientation angle within the above range, which may be undesirable.

[0057] In addition, the heat treatment may be followed by a relaxation treatment if necessary. The relaxation treatment may be carried out in either the width direction or the length direction, and may be carried out simultaneously or separately in the width direction and the length direction. A relaxation rate of preferably 1 to 20%, more preferably 1 to 15%, of the total width of the film is effective for obtaining a film with excellent thermal dimensional stability.

[0058] (Step 6) Step of obtaining intermediate film roll The polyester film obtained in step 5 is wound up using a winding device to form an intermediate film roll.

[0059] (Step 7) Step of obtaining polyester film roll The intermediate film roll obtained in step 6 is slit to an appropriate width and length in a slitting process and wound up to obtain the polyester film roll of the present invention. It is preferable to wind the film while maintaining appropriate contact across the entire width with a touch roll having a hardness of 65 to 80 and a friction coefficient of 0.1 to 0.4. This appropriate contact suppresses triboelectric charging of the film and allows for the production of a film roll with a good wound shape without air entrapment. Additionally, suppressing triboelectric charging makes it possible to maintain the charge level within the film roll of the present invention within an appropriate range. Furthermore, a low friction coefficient causes slippage, resulting in a speed difference with the film, leading to the generation of rubbing scratches. A high friction coefficient increases triboelectric charging, which can lead to poor charge distribution within the film roll and increased scratches. [Example]

[0060] The methods for measuring and evaluating the property values in the examples and comparative examples are as follows.

[0061] (1) Charge amount of polyester film roll The amount of charge on the film roll was measured using a static electricity measuring instrument (Keyence SK-H050). The film roll was fixed at an arbitrary position in the circumferential direction, and the width direction was divided into six equal parts. Measurements were taken at three points on the equal parts, excluding both extreme ends of the touch roll, and the absolute values obtained were averaged to determine the charge.

[0062] (2) Charge amount from unwinding of polyester film roll to core Using the measurement data of the charge amount distribution in the width direction described above, the average value of the measurement data at three points in the width direction was calculated, and the absolute value was taken as the absolute value of the charge amount from the unwinding to the core.

[0063] (3)Surface resistivity Under an environment of 23°C x 65% RH, a surface resistance measuring instrument (Nitto Seiko Hirester UX MCP-HT800, upper detection limit 10 14 The surface resistivity of any five points on the surface of the polyester film was measured using a resistivity tester (Ω), and the average value of the five points was taken as the surface resistance value of the polyester film.

[0064] (4) Coefficient of static friction In accordance with JIS-C2151 (2006), the static friction coefficient (μs) between the polyester films of the present invention was measured under the following conditions using a slip tester manufactured by Toray Industries, Inc. The measurement was performed three times, and the average value was taken as the static friction coefficient (μs). Sample size: 75mm (width) x 105mm (length) Sliding speed: 150mm / min Load: 200g Measurement environment: 22°C±2°C, 65%±5%RH (measurement samples are aged in this atmosphere for 24 hours.) The static friction coefficient was calculated as follows: "Static friction coefficient" = "Resistance value when the sample begins to slide" / "Load"

[0065] (5) Surface roughness SRa, SRp Measurements were taken using a three-dimensional micro surface profiler (ET-350K manufactured by Kosaka Laboratory), and the central surface average roughness SRa and central surface peak height SRp, which are three-dimensionally expanded concepts in accordance with JIS-B0601 (2001), were determined from the resulting surface profile curve. The measurement conditions were as follows: X-direction measurement length: 0.5 mm, X-direction feed rate: 0.1 mm / sec Y-direction feed pitch: 5 μm, Y-direction line count: 40 Cutoff: 0.25mm Stylus pressure: 0.02 mN Height (Z direction) magnification: 50,000 times.

[0066] (6)Hardness The measurement was carried out according to the method specified in JIS K 6253 (2012) Type A. Specifically, a JIS spring type hardness tester specified in this standard was placed on a roll with its axial direction turned horizontally, and the hardness reading was read when a load of 9.8 N was applied. The hardness of the touch roll was determined by fixing the circumferential position at an arbitrary position, dividing the width direction into six equal parts, and measuring at seven equal points on the dividing lines excluding both extreme ends of the touch roll, and calculating the average value of the values obtained.

[0067] (7) Static friction coefficient of the touch roll Using a portable tribometer (Type: 94i-I manufactured by Shinto Scientific), the circumferential position of the touch roll was fixed at an arbitrary position, the width direction was divided into six equal parts, and measurements were taken at seven points on the equal dividing lines excluding both extreme ends of the touch roll, and the friction coefficient was determined by averaging the values obtained.

[0068] (8) Thickness Samples were taken from the entire width of the polyester film, 10 of these were stacked together, and the thickness per sheet was measured using a Mitutoyo micrometer. The thickness was calculated by dividing by 10. Sampling was done at 10 locations evenly spaced across the width, and the average value was taken as the average thickness.

[0069] (9) Hayes According to JIS K7105-1981, a sample measuring 4.0 cm in length and 3.5 cm in width is cut out from the center of the film width direction, and the haze is measured using a haze meter (HGM-2DP (for light source C) manufactured by Suga Test Instruments).

[0070] (10) Measurement method for the number of periodic scratches (number of scratches per unit area / m 2 ) Periodic scratches were measured using scratches observed by LED inspection. Scratches refer to light leakage caused by scratches in the film that are visually detected during LED inspection. An LED light (LED Lenser il-7R 360lm) was used to evaluate the defects. Two meters of film were inspected without changing the light intensity of the LED light. Among the defects detected, defects consisting of three or more consecutive strikes in the longitudinal direction, with a constant longitudinal period of ±5mm between the n+1st strike and the nth and n+2nd strikes (i.e., the nth and n+2nd strikes) with a variation of 3mm or less between adjacent scratches, and a variation of 10mm or less in the width direction of the polyester film, were counted as one periodic scratch. The number of periodic scratches in the width direction was calculated using the following formula: (Number of periodic scratches) = (Number of periodic scratches in the width direction) ÷ (Inspection area)

[0071] (11) Evaluation of wiring defects in conductor circuits When the polyester film of the present invention was used as a support for a dry film resist, the wiring defects that contribute to the yield of the conductor circuit were evaluated according to the following procedure. (i) A negative resist "PMER N-HC600" manufactured by Tokyo Ohka Kogyo Co., Ltd. was applied to a 6-inch Si wafer that had been mirror-polished on one side, and a 7 μm thick resist layer was produced by spinning it with a large spinner. Next, a pre-heat treatment was carried out for approximately 20 minutes at a temperature of 70°C using a nitrogen-circulating ventilation oven. (ii) The polyester film was placed so that its surface on the A-side was in contact with the resist layer, and the polyester film was laminated onto the resist layer using a rubber roller. The resist layer side of the dry film resist was then placed in contact with the copper-clad laminate, and a photomask patterned with chromium metal was placed on the A-side surface, and exposure was performed using an I-line stepper. (iii) After peeling off the polyester film from the resist layer, the resist layer was placed in a container containing developer N-A5 and developed for about 1 minute. Then, it was removed from the developer and washed with water for about 1 minute. (iv) The copper-clad laminate with the resist layer remaining after development was immersed in a ferric chloride solution, the exposed copper was etched, and the resist layer was then peeled off to form a conductor circuit with L / S = 10 / 10 μm. The state of the created conductor circuit was examined using an optical microscope (NICON LV-100) at 8.25 mm 2 The area was observed at 500x magnification and the wiring defects of the conductor circuit were evaluated according to the following criteria: A rating of 0 or higher is a practical level, and indicates a polyester film with a good yield. ○: The maximum diameter of the wiring defect is less than 2.4 μm △: The maximum diameter of the wiring defect is less than 3.2 μm ×: The maximum major diameter of the wiring defect is less than 4.0 μm.

[0072] [Raw resin composition] The following materials were used to produce the films of the Examples and Comparative Examples. PET1: Polyethylene terephthalate (manufactured by Toray Industries, Inc.). PET2: PET1 to which 0.1 mass% of synthetic colloidal silica particles with a volume average particle size of 0.06 μm and 0.71 mass% of alumina particles with a volume average particle size of 0.015 μm have been added. PET3: PET1 to which 0.06 mass% of highly cross-linked polystyrene particles with a volume average particle size of 0.3 μm, 0.04 mass% of highly cross-linked polystyrene particles with a volume average particle size of 0.80 μm, and 0.71 mass% of alumina particles with a volume average particle size of 0.015 μm have been added. PET4: PET1 to which 0.71% by mass of alumina particles with a volume average particle size of 0.015 μm, 0.05% by mass of highly cross-linked polystyrene particles with a volume average particle size of 0.3 μm, and 0.01% by mass of highly cross-linked polystyrene particles with a volume average particle size of 0.4 μm have been added.

[0073] Example 1 PET1, PET2, and PET3 were melted and extruded at 285°C in separate extruders. The three layers were laminated in the order PET2 / PET1 / PET3, and then extruded into a sheet from a die. The sheet was then solidified by contact with a rotating cooling drum at 25°C to obtain a non-oriented film. The non-oriented film was then stretched longitudinally at 120°C and a stretch ratio of 5.0x using the difference in peripheral speed of the rolls to obtain a uniaxially oriented film. The uniaxially oriented film was then clamped at both ends with clips and introduced into a tenter oven. It was preheated to 105°C and stretched 4.0x in the width direction. It was then further heat-treated at 230°C, relaxed 3.0% in the width direction at 150°C, and cooled. The three-layer biaxially oriented film was then wound up into an intermediate product roll. The resulting intermediate product roll was slit using a slitter to obtain a polyester film roll with a thickness of 16 μm, a film laminate thickness of PET2 / PET1 / PET3=1 μm / 14 μm / 1 μm, a film width of 1500 mm, and a longitudinal length of 10,000 m. The polyester film roll was wound using a touch roll with a hardness of 73 and a static friction coefficient of 0.23. Table 1 shows the evaluation results along with other examples and comparative examples.

[0074] (Examples 2 and 3) A film roll with controlled charge was obtained by changing the hardness of the touch roll to 73 and the friction coefficient to 0.23, as in Example 1. In Examples 2 and 3, the aim was to control the charge of the film roll by increasing the conductivity of the touch roll, and the charge was reduced by obtaining a film roll that was wound using a touch roll with a conductive layer on its surface.

[0075] (Comparative Examples 1 to 3) A film roll was obtained using a touch roll made of a material with a hardness of 71 and a coefficient of friction of 0.82, characterized by a non-conductive layer on the surface. In most cases, the polyester film of the present invention becomes charged due to frictional charging, which causes variations in charge within the material. Furthermore, since polyester film is an insulator, electricity does not flow easily, and simply contacting the conductive layer was insufficient to remove static electricity. As a result, the film roll's charge value increased, resulting in a large number of scratches and defects.

[0076] (Comparative Examples 4 and 5) A film roll was obtained in the same manner as in Example 1, except that the layer structure was as shown in Table 1. In Comparative Example 4, a film roll was obtained using a touch roll made of a material with a hardness of 73 and a coefficient of friction of 0.23 and featuring a conductive layer on the surface, and the charge amount value was reduced, and the number of scratches and defects was also reduced. A film roll with a good yield during resist coating was obtained. On the other hand, when a film roll was obtained using a touch roll made of a material with a hardness of 72 and a coefficient of friction of 0.60 and featuring a non-conductive layer on the surface, static elimination was insufficient, resulting in a high charge amount value and a large number of scratches and defects. The evaluation results for each item are shown in Table 1.

[0077] [Table 1]

[0078] In the table, P1 to P4 represent PET1 to PET4 in order.

Claims

1. The number of scratches per unit area from the unwinding of the polyester film roll to the core is 3.0 x 10 －６ Below is a roll of polyester film.

2. 2. The polyester film roll according to claim 1, wherein the absolute value of the charge from the unwinding point of the polyester film roll to the core of the roll is 1.0 kV or less.

3. Surface resistivity is 10 １２ 2. The polyester film roll according to claim 1, wherein the stretching strength is Ω / □ or less.

4. 2. The polyester film roll according to claim 1, wherein one surface (side A) has a central surface average roughness SRa of 0.5 nm to 8 nm and a central surface peak height SRp of 50 nm to 500 nm, and the opposite surface has a central surface average roughness SRa of 0.5 nm to 8 nm and a central surface peak height SRp of 1 nm to 300 nm.

5. 2. The polyester film roll according to claim 1, wherein the coefficient of static friction of the surface opposite to the surface A is 0.5 or more and 2.5 or less.

6. 2. The polyester film roll according to claim 1, which is used for a dry film resist, and has a thickness of 10 μm to 50 μm and a haze of 0.1% to 0.7%.

7. 2. The method for producing a polyester film roll according to claim 1, wherein a touch roll having a static friction coefficient of 0.5 or less is used in winding the polyester film roll.

Images