JPWO2019176692A1 - Biaxially oriented polyester film roll for mold release - Google Patents

Abstract

A polyester film for mold release, characterized in that the film width is 400 mm or more, and the variation σ value (σMD) with respect to the average value of the thickness measured continuously in the longitudinal direction of the film is 0.15 μm or less. We provide a biaxially oriented polyester film for mold release that can reduce the rigidity of the support during green sheet molding and the amount of distortion during electrode printing, and is optimized for the coating properties of ceramic slurries during thin film green sheet molding. To do.

Description

The present invention relates to a mold release biaxially oriented polyester film roll in which a mold release biaxially oriented polyester film having excellent film thickness uniformity during thin film slurry coating is wound.

Biaxially oriented polyester films are used in various applications as industrial materials from the viewpoints of mechanical properties, thermal properties, stiffness and cost. In particular, recently, as process papers related to electronic components, mold release films for molding green sheets of multilayer ceramic capacitors, separators for liquid crystal polarizing plates, base materials for dry film resists, base materials for interlayer insulation resin mold release, etc. It is used in.

With the recent sophistication of smartphone functions and the spread of smart watches and wearable devices, the size and capacity of multilayer ceramic capacitors are becoming smaller and higher. With regard to the release film used for manufacturing multilayer ceramic capacitors, the demand for polyester films with high smoothness, no defects on the film surface and inside, and excellent flatness of the film continues to grow as the green sheet becomes thinner. There is. On the other hand, the demand for multilayer ceramic capacitors installed in automobiles is rapidly increasing due to the expansion of production volume of electric vehicles, the conversion of automobiles to IoT (Internet of Things), and the installation of automatic driving functions in automobiles. These monolithic ceramic capacitors for automobiles are required to be more strict and reliable than the conventional requirements. In particular, in the molding of a green sheet, which is a dielectric component of a multilayer ceramic capacitor, the thickness of the slurry laminated on the film when the film is used as a base material due to the uneven thickness of the film and the planar characteristics of the film. Non-uniformity is becoming more tightly controlled.

As shown in Patent Document 1, the film thickness unevenness is determined by performing a measurement of 15 m in the longitudinal direction and determining by measuring a length of 1 m every 5 mm, which is known as a known method. There is. Further, as shown in Patent Document 2, in the cross-nicol method for inspecting a polarizing plate, the unevenness of the intensity of light leaking from the polarizing plate becomes strong, which hinders the inspection. Therefore, it is necessary to set the thickness unevenness within a predetermined range. .. As shown in Patent Document 3, it is known to achieve this by performing simultaneous biaxial stretching and increasing the plane orientation.

Japanese Unexamined Patent Publication No. 2008-2466885 JP-A-2017-007175 Japanese Unexamined Patent Publication No. 2004-291240

In recent years, the demand for capacitors has tended to be high in reliability in addition to miniaturization and large capacity. Miniaturization is achieved by reducing the size of the electrodes. The increase in capacity is achieved by thinning the green sheet, and the increase in reliability is achieved by improving the dimensional accuracy in the width, length, and thickness directions when the electrodes and the green sheet are provided. Among these, the uniformity of the coating thickness at the time of slurry coating is to minimize the distortion and deviation of the electrode pattern because each electrode area is fine in the step of performing electrode printing later. However, it is cited as one of the major factors that determine the variation in the dielectric constant of the capacitor, that is, the variation in the capacitance of the capacitor. For this reason, the demand for the film regarding the minimization of the thickness unevenness is becoming stricter. In particular, in the process of constantly monitoring the slurry thickness during capacitor manufacturing and applying a thin film of slurry while correcting the inclination of the die, it is highly possible that the uneven thickness of the base film in the entire length of the roll contributes. It is known. Therefore, it is an object of the present invention to reduce the thickness unevenness of the film over the entire length of the roll, particularly when it is used as a support during molding of a green sheet.

As a result of diligent studies in view of the above circumstances, the present inventors wound a biaxially oriented polyester film for mold release, which has excellent dimensional stability of the slurry in the longitudinal, width, and thickness directions by optimizing the characteristics of the film. A biaxially oriented polyester film roll for mold release was found, and the present invention was reached. That is, in the present invention, the film width is 400 mm or more, and the variation σ value (σ _MD ) with respect to the average value of the thickness continuously measured 10,000 m in the longitudinal direction of the film is 0.15 μm or less. It features a film roll.

According to the present invention, it is possible to reduce the thickness variation during molding of the green sheet, and the biaxially oriented polyester film for mold release, which is optimized for the coatability of the ceramic slurry during the molding of the ultra-thin green sheet, is wound up. A biaxially oriented polyester film roll for mold release can be provided.

Hereinafter, the present invention will be described in more detail.
The release biaxially oriented polyester film roll of the present invention is obtained by winding a mold release biaxially oriented polyester film (hereinafter, may be simply referred to as a biaxially oriented polyester film) around a core material such as a core. .. Here, the biaxial orientation refers to a state in which an unstretched (unaligned) film is stretched in a two-dimensional direction by a conventional method, and means a film showing a biaxial orientation pattern by wide-angle X-ray diffraction. As the stretching, either a sequential biaxial stretching method or a simultaneous biaxial stretching method can be adopted. In the sequential biaxial stretching, the steps of stretching in the longitudinal direction (vertical) and the width direction (horizontal) can be carried out once in the vertical direction and the horizontal direction, or twice in the vertical direction, the horizontal direction, the vertical direction, and the horizontal direction. You can also do it.

The polyester in the biaxially oriented polyester film of the present invention is a polyester containing dibasic acid and glycol as constituents, and examples of the aromatic dibasic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and diphenylsulfone. Dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylketone dicarboxylic acid, phenylindandandicarboxylic acid, sodium sulfoisophthalic acid, dibromoterephthalic acid and the like can be used. As the alicyclic dibasic acid, oxalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dimer acid and the like can be used. As the glycol, ethylene glycol, propylene glycol, tetramethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, diethylene glycol and the like can be used as the aliphatic diol, and naphthalene diol can be used as the aromatic diol. 2,2 bis (4-hydroxydiphenyl) propane, 2,2-bis (4-hydroxyethoxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, hydroquinone and the like can be used, and as the alicyclic diol, Cyclohexanedimethanol, cyclohexanediol and the like can be used.

The polyester can be produced by a known method, and it is preferable to use one having an intrinsic viscosity of 0.5 at the lower limit and 0.8 at the upper limit. More preferably, the lower limit is 0.55 and the upper limit is 0.70. For the measurement of intrinsic viscosity, the value calculated by the following formula from the solution viscosity measured at 25 ° C. in orthochlorophenol is used.
ηsp / C = [η] + K [η] ²・ C

Here, ηsp = (solution viscosity / solvent viscosity) -1, C is the mass of the dissolved polymer per 100 ml of the solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (0.343). is there. The solution viscosity and solvent viscosity are measured using an Ostwald viscometer. The unit is indicated by [dl / g].

The biaxially oriented polyester film of the present invention may be a single-layer film or may have a laminated structure of two or more layers. When two layers are laminated, it is composed of a polyester A layer and a polyester B layer, and in the case of three layers, it is composed of three layers of polyester A layer, polyester B layer and polyester C layer, or polyester A layer, polyester B layer and polyester A layer. It becomes a laminated film. At this time, by controlling the amount of particles contained in the layer (laminated portion) constituting the surface layer, as long as the inner layer portion does not adversely affect the characteristics of the film surface, the raw material for recovering the edge portion generated in the film forming process, Alternatively, it can be used by mixing recycled materials of other film forming processes in a timely manner, and it is possible to reduce the consumption of petroleum resources and obtain a cost merit. Therefore, it has a layer structure of three or more layers. Is the most preferred embodiment.

Further, the biaxially oriented polyester film of the present invention preferably contains a recovered raw material and / or a recycled raw material in the C layer. For this reason, the C layer is preferably the thickest layer in the layer structure. The melt resistivity of the raw material contained in the A layer (smooth layer) is preferably 1.0 × 10 ⁶ Ω · cm or more and 1.0 × 10 ⁸ Ω · cm or less, and more preferably 5.0. × 10 ⁸ Ω · cm or less is preferable. It is also preferable that the raw material having such a melt resistivity value is a polyester resin. The layer A is preferably a layer constituting a surface in which SRa (A), which will be described later, is 1 nm or more and less than 15 nm. Further, it is also preferable to have the above-mentioned characteristics regarding the raw material composition and thickness of the C layer and the characteristics regarding the raw material and the surface shape of the A layer.

The biaxially oriented polyester film of the present invention has two or more layers, that is, the surfaces of the polyester A layer and the polyester B layer, which form the surface layer, have surface smoothness and handling such as transport and winding. In order to achieve both properties, configurations with different roughness are preferable. That is, it is preferable that the center line roughness SRa (A) of one film surface is 1 nm or more and less than 15 nm, and the center line roughness SRa (B) of the other film surface is 20 nm or more and 40 nm or less. If SRa (A) is less than 1 nm, it may be difficult to peel off in the peeling step after laminating a release layer on the surface and laminating a ceramic slurry on the release layer. Further, when SRa (A) is 15 nm or more, the surface condition of the slurry deteriorates and the thickness becomes uneven, and as a result, the characteristics of the capacitor tend to vary. When SRa (B) is less than 20 nm, blocking is likely to occur in winding after coating the release layer or winding after coating the ceramic slurry, and charging may occur when the SRa (B) is unwound. Regarding the surfaces of the polyester A layer and the polyester B layer, more preferably, the center line roughness SRa (A) of one film surface is 2 nm or more and less than 12 nm, and the center line roughness SRa (B) of the other film surface. Is 25 nm or more and 35 nm or less.

The thickness of the biaxially oriented polyester film of the present invention is preferably 12 μm or more, more preferably 20 μm or more, still more preferably 25 μm or more. Further, it is preferably 188 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less. When the thickness is thinner than 12 μm, there is no waist for holding the ceramic slurry, the ceramic slurry cannot be supported when the ceramic slurry is applied, uniform drying cannot be performed in a subsequent process, and heat wrinkle suppression is insufficient. May be. When the thickness exceeds 188 μm, the durability against heat wrinkles is remarkably excellent, but the unit price per unit area as the base material for forming the ceramic slurry tends to increase as the winding length decreases, and the length is stretched. It is difficult to raise the temperature and stretch in the above, which causes aggravation of thickness unevenness. The preferable range of the thickness is 12 μm or more and 188 μm or less, more preferably 20 μm or more and 50 μm or less, and further preferably 25 μm or more and 40 μm or less.

The biaxially oriented polyester film of the present invention may contain particles. The volume average particle diameter of the particles contained at this time is preferably 1.3 μm or less. If the volume average particle size of the particles exceeds 1.3 μm, there is a high chance that voids, that is, voids, will be generated at the interface between the particles and the polymer during stretching, so that the surface structure may vary, and the slurry may have irregularities. The thickness variation may increase. The ultra-thin green sheet in the present invention refers to a sheet having a thickness of less than 1 μm.

The particles used in the present invention are inorganic particles such as spherical silica, aggregated silica, calcium carbonate, aluminum oxide, barium titanate, titanium oxide, crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, and crosslinked styrene-acrylic resin. Organic particles such as particles, crosslinked polyester particles, polystyrene particles, and melamine resin particles can be used. In addition to the role of forming protrusions on the film surface, these particles can also serve as a core material for forming voids, so it is desirable to select the type as well as the particle size. It is preferable to use organic particles having high elasticity of the particles. As the organic particles, among the above-mentioned organic particles, organic particles selected from crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles are particularly preferable. Among the inorganic particles, spherical silica and aluminum oxide are particularly preferable.

The shape and diameter distribution of the particles are preferably uniform, and the particle shape is particularly preferably close to a sphere. The volume shape coefficient is preferably f = 0.3 to π / 6, and more preferably f = 0.4 to π / 6. The volume shape coefficient f is expressed by the following equation.
f = V / Dm ³

Here, V is the particle volume (μm ³ ), and Dm is the maximum diameter (μm) of the particle on the projection plane.

The volume shape coefficient f takes the maximum value of π / 6 (= 0.52) when the particle is a sphere. In addition, it is preferable to remove aggregated particles, coarse particles, and the like by performing filtration or the like as necessary. Among them, cross-linked polystyrene resin particles, cross-linked silicone resin particles, and cross-linked acrylic resin particles synthesized by an emulsion polymerization method or the like can be preferably used, but in particular, cross-linked polystyrene particles, cross-linked silicone, spherical silica, etc. have a volume shape coefficient. It is preferable from the viewpoint of being close to a true sphere, having an extremely uniform particle size distribution, and uniformly forming film surface protrusions.

The biaxially oriented polyester film of the present invention has a film width of 400 mm or more, and a variation σ value (σ _MD ) with respect to an average value of thickness measured continuously in the longitudinal direction of the film is 0.15 μm or less.

It will be described step by step below.
The biaxially oriented polyester film of the present invention has a film width of 400 mm or more, and a variation σ value (σ _MD ) with respect to an average value of thickness measured continuously in the longitudinal direction of the film is 0.15 μm or less. The thickness continuously measured in the film longitudinal direction of 10,000 m here is the thickness when the film is continuously measured in a non-contact manner. The film width and longitudinal length represent the dimensions of the support required to manufacture multilayer ceramic capacitors in a given lot. That is, it has been found that the moldability of the green sheet can be improved by suppressing the variation in thickness within this dimension. Further, in the following, the σ _MD value may be referred to as film thickness unevenness in the longitudinal direction.

The thickness of a conventional biaxially oriented polyester film is measured by scanning a non-contact thickness gauge in the width direction while the film is being formed, or a sample collected about 20 m in the longitudinal direction from a film roll is a contact type thickness. Although it was measured with a gauge, in the present invention, continuous measurement in the longitudinal direction of 10,000 m as described above revealed a thickness unevenness behavior that could not be confirmed in the past. By reducing the variation in the thickness unevenness behavior, the present invention has the effect of reducing the slurry thickness unevenness at the time of applying the thin film ceramic slurry, reducing the variation in capacitance, and suppressing the probability of short circuit. It is a thing. If σ _MD exceeds 0.15 μm, the thickness unevenness of the slurry becomes large in the coating of the thin film ceramic slurry, and the above-mentioned effect is reduced.

In the biaxially oriented polyester film of the present invention, the center line roughness SRa (A) of one film surface is 1 nm or more and less than 15 nm, and the center line roughness SRa (B) of the other film surface is 20 nm or more and 40 nm or less. It is preferable to have. The biaxially oriented polyester film of the present invention can be subjected to a mold release treatment on either surface in consideration of the balance between the slurry coating thickness and the handleability, and the flattening treatment is performed before the mold release treatment. It is also possible to reduce the roughness of the surface of the release layer.

Next, the method for producing the biaxially oriented polyester film of the present invention will be described, but the present invention is not construed as being limited to such examples.

As a method for incorporating the inert particles into the polyester, for example, the inert particles are dispersed in ethylene glycol which is a diol component at a predetermined ratio in the form of a slurry, and this ethylene glycol slurry is added at an arbitrary step before the completion of the polyester polymerization. .. Here, when adding the particles, for example, if the water sol or alcohol sol obtained during the synthesis of the particles is added without being dried once, the dispersibility of the particles is good and the generation of coarse protrusions can be suppressed, which is preferable. Further, a method in which the aqueous slurry of particles is directly mixed with a predetermined polyester pellet and supplied to a vent type twin-screw kneading extruder and kneaded into the polyester is also effective for the production of the present invention.

In this way, the prepared particle-containing master pellet and the pellet containing substantially no particles or the like are mixed at a predetermined ratio, dried, and then supplied to a known extruder for melt lamination. As the extruder for producing the biaxially oriented polyester film of the present invention, a uniaxial or biaxial extruder can be used. Further, in order to omit the step of drying the pellets, a vent type extruder provided with a vacuum drawing line in the extruder can also be used. Further, for the C layer having the largest extrusion amount, a so-called tandem extruder in which the function of melting the pellets and the function of keeping the melted pellets at a constant temperature are shared by each extruder can be used. The tandem extruder is preferable as a process for reducing thickness unevenness because it can stabilize the polymer temperature at the time of high discharge and as a result, the viscosity variation of the polymer can be reduced.

The polymer melted and extruded by the extruder is filtered through a filter. If even a very small foreign substance enters the film, it becomes a coarse protrusion defect. Therefore, it is effective to use a filter having a high-precision collection efficiency that collects 95% or more of a foreign substance of, for example, 3 μm or more. On the other hand, if the collection efficiency of the filter is too high, the degree of pressure increase may increase. Therefore, a filter with a higher accuracy collection efficiency that collects 95% or more of foreign matter less than 3 μm. Use may be an unfavorable embodiment in controlling thickness unevenness. Subsequently, it is extruded into a sheet from a slit-shaped slit die and cooled and solidified on a casting roll to form an unstretched film. For example, in the case of three-layer lamination, three extruders are used to laminate the three layers using a three-layer manifold or a merging block (for example, a merging block having a rectangular merging portion), and the sheet is extruded from the base. At this time, it is desirable that the gap between the caps can be automatically adjusted by the heater. The sheet extruded from the base is cooled by a casting roll to form an unstretched film. In this case, the method of installing the static mixer and the gear pump in the polymer flow path from the viewpoint of stabilizing the back pressure and suppressing the thickness fluctuation is effective as a means for suppressing the thickness unevenness in the longitudinal direction in the present invention. Since the gear pump has a function of blocking pressure fluctuations in the extrusion process, it is necessary to uniformly control the thickness in the longitudinal direction. By keeping the rotation speed of the gear built in the gear pump constant, the thickness unevenness in the longitudinal direction is uneven. Can be kept small. In the present invention, it is also effective to feed back and control the rotation speed of the gear pump by the weight-equivalent thickness of the wound intermediate product. This is because the discharge decreases as the filter pressure increases, so that the film thickness gradually decreases in the longitudinal direction.

Regarding the rotation accuracy of the casting roll, the speed fluctuation and the unevenness of the surface of the casting roll due to the eccentricity of the casting roll may affect the thickness unevenness in the longitudinal direction. Conventionally, the velocity fluctuation of the casting roll surface has a great influence on the thickness unevenness in the longitudinal direction. In order to reduce this, a balance weight is attached to an arbitrary circumference of the casting roll end face to prevent eccentricity unevenness. Suppression is a preferred embodiment. Further, it is also a preferable embodiment to suppress the thickness unevenness in the longitudinal direction by using two motors for rotating the casting drum and dividing the functions into the drive and the brake. In the present invention, since it is necessary to further improve the accuracy in order to control the σ _MD value, in evaluating the rotation accuracy of the casting roll, it was measured by a sensor installed on the ground where the casting drum is installed. The difference between the maximum value and the minimum value of the uneven state when the distance from the sensor to the cast surface was measured for one round over the circumference of the cast was defined as the runout. The value is preferably 50 μm or less, and more preferably 30 μm or less, which is a desirable form in order to improve the thickness unevenness (σ _MD ) in the longitudinal direction in the present invention. Specifically, the runout of the unevenness on the circumference of the cast at this time is measured by installing a laser displacement meter on the floor on which the cast device is installed and measuring the distance between the casting roll and the measuring unit of the laser displacement meter. ..

The unstretched film landed on the casting roll is brought into close contact with the cast using an electrostatic force using a pinning device. The pinning device applies an electric charge from the electrostatically applied wire to the casting roll over the entire width of the unstretched film, and causes the film and the casting roll to be brought into close contact with each other by static electricity at the interface between the casting roll and the film. At this time, in order to make the charge intensity constant in the width direction, it is desirable that the distance from the electrostatically applied wire to the film is equal to the entire width of the unstretched film. Further, it is desirable to adjust the strength of the electrostatically applied current in order to maintain the adhesion between the casting roll and the film at an appropriate strength.

Further, the edge of the unstretched film is adjusted so that the thickness of the edge is thicker than that of the center in order to increase the gripping force of the clip when stretching by the transverse stretching machine, but the adhesion of the edge is poor and crystallization is performed. As a result of poor cooling efficiency due to the roll, crystallization of the end part progresses, which may cause tearing. Therefore, in addition to the full-width pinning device, an additional pinning device is attached only to the end part, so-called edge pinning device. By attaching, it is also desirable to bring the edge of the unstretched film into close contact with the cast and suppress the cooling unevenness of the edge portion in order to suppress the vibration at the landing point of the cast and to improve the thickness unevenness in the longitudinal direction. It is a process. When the edge pinning device is applied to the unstretched film, effective pinning can be performed by performing the edge pinning device from a portion separated from the edge portion of the unstretched film by 5 mm or more. This is to prevent the leakage current from abnormally discharging to the casting roll when electrostatically applied from the edge pinning device. Further, the processing width of edge pinning is adjusted according to the edge thickness profile of the unstretched film, but it is possible to effectively mold the edge portion by setting the range to 20 mm or more and less than 100 mm.

The film that has been cooled in close contact with the casting roll is peeled from the casting roll by using a pulling roll, and is led to the next stretching step. Water may be passed through the pulling roll at this time to cool the film, or the pulling roll may be driven.

The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. In the simultaneous biaxial stretching, when the vertical and horizontal stretching is performed at the same time, the wind speed unevenness and the airflow flowing along the film (accompanying airflow) are added to the stretching in the width direction and also affect the longitudinal direction as disturbance. It is a form in which stretching is preferably applied.

When the polyester film of the present invention is produced by using sequential stretching, the first stretching in the longitudinal direction is important for suppressing the occurrence of scratches and the thickness unevenness in the longitudinal direction, and the stretching temperature is It is 90 ° C. or higher and 130 ° C. or lower, preferably 100 ° C. or higher and 120 ° C. or lower. When the stretching temperature is lower than 90 ° C., the film is easily broken, and when the stretching temperature is higher than 130 ° C., the film surface is easily damaged by heat. From the viewpoint of preventing uneven stretching and scratches, stretching is preferably performed in two or more stages, and the total magnification is 2.8 times or more and 5.0 times or less, preferably 3.3 times in the length direction. It is 4.0 times or more, 3.5 times or more and 5 times or less in the width direction, preferably 4.0 times or more and 4.5 times or less. When setting the longitudinal stretching ratio to the above-mentioned numerical value, it is desirable to set a plurality of stretching sections so that slipping between the stretching roll and the film is unlikely to occur in order to suppress fluctuations in stretching tension due to slipping. .. At this time, it is preferable that the stretching ratio in one stretching section is 3.0 times or less because an appropriate stretching tension can be ensured. If the temperature and magnification are out of the range, problems such as uneven stretching or film breakage occur, and it is difficult to obtain the film characterized by the present invention.

In the sequential stretching, in the stretching process in the longitudinal direction, the film and the roll come into contact with each other, and due to the difference between the peripheral speed of the roll and the speed of the film, scratches are likely to occur when the film slips, and a factor of thickness unevenness in the longitudinal direction Therefore, a drive system in which the roll peripheral speed can be set individually for each roll is preferable. In the stretching process in the longitudinal direction, the material of the transport roll is such that the unstretched film is heated above the glass transition point before stretching or transported to the stretching zone while being kept at a temperature below the glass transition point, and all at once during stretching. It is selected by heating or either. When the unstretched film is heated to the glass transition point or higher before stretching, the adhesion due to heating induces stretching unevenness. To prevent this, select from non-adhesive silicone rolls, ceramics, and Teflon (registered trademark). It is preferable to do so. Further, the temperature of the transfer roll in the temperature raising process is preferably selected by the combination of the material and the transfer temperature, and in order to suppress the adhesion due to heating until the unstretched film exceeds the glass transition point, the transfer roll It is preferable to set the transport temperature to less than 80 ° C. as a metal roll plated with hard chrome. In this case, it is preferable to supplement the amount of heat by using an infrared heater in the stretching step.

Further, since the stretched roll is a process in which the film is most loaded and the stretched unevenness that causes scratches and thickness unevenness in the longitudinal direction is likely to occur in the process, the surface roughness Ra of the stretched roll is 0.005 μm or more. It is preferably 1.0 μm or less, and more preferably 0.1 μm or more and 0.6 μm or less. If Ra is larger than 1.0 μm, the unevenness of the roll surface during stretching is likely to be transferred to the film surface, while if it is less than 0.005 μm, the roll and the film surface adhere to each other, and the film is susceptible to heat damage. In order to control the surface roughness, it is effective to appropriately adjust the particle size of the abrasive, the number of times of polishing, and the like.

In the sequential stretching, setting the longitudinal stretching ratio lower than the transverse stretching ratio is a preferable stretching condition in order to reduce the thickness unevenness in the longitudinal direction.

Next, the unstretched film was transported to the stretching zone while being kept at a temperature below the glass transition point, but when the unstretched film was heated all at once during stretching, the transport roll in the preheating zone was surface-treated with hard chromium or tungsten carbide. It is preferable to use a metal roll having a surface roughness Ra of 0.2 μm or more and 0.6 μm or less in order to suppress adhesion that causes heat wrinkles and thickness unevenness in the longitudinal direction.

Next, the uniaxially stretched film stretched in the longitudinal direction is heated to 90 ° C. or higher and lower than 120 ° C. by a transverse stretching machine, then stretched in the width direction at 3 times or more and less than 6 times, and biaxially stretched (biaxially stretched). Orientation) Film. This transverse stretching machine performs self-circulation in each oven room and blows warm air onto the film to raise the temperature of the film and perform stretching and heat fixing. At that time, in order to prevent the oligomers precipitated from the film heat-treated in the oven from being cooled and adhering to the oven, it is preferable to supply and exhaust air in the oven to replace the air. At this time, when the air supplied into the oven merges with the circulating air, if the temperature of the air remains close to the outside air, temperature unevenness occurs in the merged air, and the thickness unevenness in the longitudinal direction and the width direction occurs. It is preferable to heat the supply air at the same temperature as the circulating air or at a temperature commensurate with the capacity of the heat exchanger that heats the circulating air.

Further, in adjusting the amount of air supply / exhaust in the oven, it is preferable that the direction of the air flowing above and below the film to be conveyed is the same as the direction of the film flow. In each chamber of the oven, in addition to the self-circulating air, the accompanying airflow flowing from the upstream in the same direction as the film transport direction, and the air supply or exhaust outside the oven change the air flow inside the STN in a complicated manner. .. At this time, due to the pressure difference between the chambers, the air flow between the chambers, for example, the flow from the upstream to the downstream may change to the flow from the downstream to the upstream. The flow of air between chambers can also lead to uneven expansion and contraction of the film when the temperature of the air varies between chambers. Therefore, regarding the conditions of the intake amount and the exhaust amount of the oven, it is possible to induce the air flow in the same direction by increasing the exhaust amount more than the supply air amount.

The biaxially oriented polyester film of the present invention may be re-stretched once or more in each direction, or may be re-stretched in the same biaxial manner. As a method of suppressing the thickness unevenness in the longitudinal direction, it is possible to alleviate the Boeing generated in the previous transverse stretching step in the re-stretching step in the longitudinal direction. At this time, the transport roll before re-longitudinal stretching in the longitudinal direction may be heated at a temperature of 80 ° C. to 100 ° C., or the unheated roll may be used for transport. Further, the re-longitudinal stretching step may be passed without applying the stretching ratio. After the re-longitudinal stretching, the transverse stretching is further performed, and the heat treatment of the film is performed after the stretching. This heat treatment can be performed by any conventionally known method or position such as in an oven or on a heated roll. The heat treatment temperature can be usually any temperature of 150 ° C. or higher and lower than 245 ° C., and the heat treatment time is usually preferably 1 second or longer and 60 seconds or shorter. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction thereof. Further, after the heat treatment, it is preferable to relax at a temperature lower than the heat treatment temperature of 0 ° C. or higher and 150 ° C. or lower and 0% or higher and 10% or lower in the width direction.

The film after the heat treatment can be provided with, for example, an intermediate cooling zone and a cooling zone, and the dimensional change rate and flatness can be adjusted. In particular, in order to impart specific heat shrinkage, it may be relaxed in the vertical direction and / or in the horizontal direction in the intermediate cooling zone or the cooling zone during or after the heat treatment. In this case, it is desirable to control the temperature difference in the width direction inside the oven within 5 ° C. in order to improve the thickness unevenness in the width direction.

The film after biaxial stretching is cooled in a transporting step, and then the edges are cut and then wound to obtain an intermediate product. In this transfer step, the film thickness in the width direction can be measured, the data can be fed back and used to adjust the film thickness by adjusting the die thickness and the like, and foreign matter can be detected by the defect detector. The thickness can be measured by β-ray, X-ray, or optical interference. The measurement is a method of measuring the total width thickness by traversing one measuring device in the width direction, a method of measuring the total width thickness by traversing a plurality of measuring devices within a section divided in the width direction, and measurement. When a wide range can be obtained, a plurality of measuring devices can be fixed in the width direction to measure the thickness of the entire width. Further, the measurement location can be measured in the above-mentioned transfer process, or can be performed offline by using a biaxially oriented polyester film roll after slitting the intermediate product.

The intermediate product is slit to an appropriate width and length by a slitting process and wound around a core to obtain a roll of biaxially oriented polyester film. The core is a cylindrical core made of plastic or paper. Since it is preferable to use a core that expands and contracts less due to temperature and humidity and is less deformed due to winding pressure even for uneven thickness, it is preferable to use a core made of plastic. Furthermore, it is preferable to use a core in which plastic is reinforced with glass fiber or carbon fiber. Further, when paper is used for the core, the strength can be increased by impregnating the surface with a resin. The film cutting step in the slitting step is a step of removing unnecessary portions of the intermediate product to obtain a polyester film roll having a desired product width. In this cutting step, 3 to 10 points are cut at the same time in the width direction of the intermediate product. The method used for this cutting can be selected from a method of cutting by shearing the lower blade and the upper blade and a method of cutting in the air between the pass lines.

The film width is the width of the film after slitting by the slitting step, and by adjusting the cutting place in the cutting step described above in the width direction, a polyester film roll having a desired product width can be obtained. .. Further, the length in the longitudinal direction of the film in the present invention is measured by a length measuring device installed on an arbitrary roll in the slit process. In the present invention, an intermediate product cut in the width direction and wound around a core at an arbitrary length is referred to as a polyester film roll.

Since the biaxially oriented polyester film roll for mold release obtained by the above method winds a film having little thickness unevenness in the longitudinal direction, the film can be used for mold release, especially as a member for molding a multilayer ceramic capacitor. Furthermore, it can be more preferably used as a member for molding a multilayer ceramic capacitor for automobiles. The release application in the present invention refers to an application in which a film obtained from the biaxially oriented polyester film roll of the present invention is used as a base material as a molding member, the member is molded, and the member is peeled off from the molded member. The members referred to here include green sheets in multilayer ceramic capacitors, interlayer insulating resins (electrically insulating resins) in multilayer circuit boards, and polycarbonates in optical-related members (used in solution film formation in this case). Can be mentioned.

Hereinafter, the present invention will be described in detail with reference to Examples.

The measurement method and evaluation method according to the present invention are as follows.

(1) Film thickness unevenness in the longitudinal direction (σ _MD )
Using SI-T80 manufactured by KEYENCE Co., Ltd. installed in the rewinding inspection machine, the thickness in the longitudinal direction of the central portion in the product roll width direction was measured by 10,000 m. The rewinding speed was 50 m / min, the sampling period was 20 msec, and the deviation σ with respect to the average value was obtained based on this thickness data, and this was defined as the film thickness unevenness in the longitudinal direction.

(2) Film surface roughness Surface center line roughness (SRa value)
Measured using a three-dimensional fine surface shape measuring instrument (ET-350K manufactured by Kosaka Seisakusho), and from the obtained surface profile curve, according to JIS B0601 (1994), arithmetic mean roughness (center line roughness) SRa Find the value. The measurement conditions are as follows.
X-direction measurement length: 0.5 mm
X-direction feed rate: 0.1 mm / sec Y-direction feed pitch: 5 μm
Number of lines in Y direction: 40 Cutoff: 0.25 mm
Needle pressure: 0.02 mN
Height (Z direction) Magnification: 50,000 times

The X direction is the width direction of the sample, and the Y direction is the longitudinal direction of the sample.

(3) Melt resistivity of polyester resin 150 g of polyester resin was placed in a 50φ test tube substituted with pure water and dried under reduced pressure at 180 ° C. for 3 hours. Then, it was melted at 290 ° C. for 50 minutes under nitrogen flow, and the electrode was inserted into the molten polymer. The melt resistivity was obtained by calculating the resistance value from the amount of current when a voltage of 5,000 V was applied between the electrodes. The electrodes were prepared by sandwiching a Teflon (registered trademark) spacer between ^two copper plates (22 cm ² ) so that the distance between the copper plates was 9 mm.

(Example 1)
(1) Preparation of polyester pellets (preparation of polyester A)
The esterification reaction is carried out at 255 ° C. with 86.5 parts by mass of terephthalic acid and 37.1 parts by mass of ethylene glycol while distilling water. After completion of the esterification reaction, 0.02 parts by mass of trimethylphosphate, 0.06 parts by mass of magnesium acetate, 0.01 parts by mass of lithium acetate and 0.0085 parts by mass of antimony trioxide were added, and subsequently, under reduced pressure, 290 parts. The polycondensation reaction was carried out by heating to ° C. and raising the temperature to obtain polyester pellet A having an intrinsic mass of 0.63 dl / g. Results The melt specific resistance was measured in this chip was 7.0 × 10 ⁷ Ω · cm.

(Creation of polyester B)
In producing polyester in the same manner as above, after transesterification, spherical silica having a volume average particle size of 0.2 μm, a volume shape coefficient f = 0.51, and a moth hardness of 7 is added and a polycondensation reaction is carried out to obtain the particles of polyester. A silica-containing master pellet containing 1% by volume of the amount was obtained (polyester B).

The spherical silica used in Polyester B is obtained by adding a mixed solution of ethanol, pure water, and aqueous ammonia as a basic catalyst to the mixed solution while stirring the mixed solution of ethanol and ethyl silicate. These are monodisperse silica particles obtained by stirring the reaction solution to carry out a hydrolysis reaction of ethyl silicate and a polycondensation reaction of the hydrolysis product, and then stirring after the reaction.

(Creation of polyesters C and D)
Separately, the volume average particle size of 0.3 μm, the volume shape coefficient f = 0.51, obtained by the method of adsorbing a monomer composed of 80% by mass of divinylbenzene, 15% by mass of ethylvinylbenzene and 5% by mass of styrene by the seed method. A water slurry of divinylbenzene / styrene copolymer crosslinked particles (crosslinking degree 80%) having a moth hardness of 3 was contained in the above-mentioned homopolypoly pellets containing substantially no particles by using a bent twin-screw kneader to add volume. Master pellets containing 1% by mass of divinylbenzene / styrene copolymer crosslinked particles having an average particle size of 0.3 μm and 0.8 μm with respect to polyester were obtained (polyester C, polyester D), respectively.

(Creation of polyester E)
In producing polyester A, after transesterification, 10 parts by mass of calcium carbonate and 90 parts by mass of ethylene glycol prepared by the carbon dioxide gas method (volume average particle size, volume average particle size 1.1 μm, moth hardness 3) were wet-pulverized. , Calcium carbonate / ethylene glycol dispersion slurry was obtained. The volume average particle size of this calcium carbonate was 1.1 μm. On the other hand, 0.04 part by mass of manganese acetate and 0.03 part by mass of antimony trioxide were added as catalysts to 100 parts by mass of dimethyl terephthalate and 64 parts by mass of ethylene glycol to carry out a transesterification reaction, and then trimethyl as a phosphorus compound was added to the reaction product. 0.04 parts by mass of phosphate was added, and then 1 part by mass of the previously prepared slurry was added to carry out a transesterification reaction to obtain a master pellet (polyester E) containing 1% by mass of calcium carbonate with respect to polyester. ..

On the other hand, the film after producing the film having the following formulation was recovered, and the pelletized film was used as the recovery raw material A. The ratio described below is expressed as a mass ratio (mass%) to the mass of the entire film.
Polyester A 93.4
Polyester D: 0.6
Polyester G: 6.0

(2) Preparation of polyester pellets The polyester pellets supplied to the extruders of the A layer, the B layer, and the C layer were prepared in the following ratios. The ratio described below is a mass ratio (unit: mass%) with respect to the polyester pellets constituting each layer.
Layer A polyester A: 87.5
Polyester B: 12.5
Layer B polyester A: 60.0
Recovered raw material A: 40.0
C layer polyester A: 65.0
Polyester C: 30.0
Polyester D: 5.0

(3) Production of Biaxially Oriented Polyester Film After stirring the raw materials prepared for each layer in the blender, the raw materials for layers A and C are the raw materials after stirring, and the raw materials for the A and C layers are vented. The raw material of the B layer was dried under reduced pressure at 160 ° C. for 8 hours, and then supplied to the single-screw extruder for the B layer. Layer B is melt-extruded at 275 ° C. with a tandem extruder, filtered through a high-precision filter that collects 95% or more of foreign matter of 3 μm or more, and then merged and laminated with a rectangular merging block for three different layers. A three-layer laminate consisting of A, layer B, and layer C was used. After that, using an electrostatic application casting method in which electrostatic application is applied to the entire width of the unstretched film through a slit die maintained at 285 ° C., the unstretched laminated film is wound around a casting drum having a surface temperature of 25 ° C. and cooled and solidified. Got At this time, the cast adjusted the alignment, and the runout was 25 μm.

The unstretched laminated film was sequentially stretched (longitudinal direction, width direction). First, the film was stretched in the longitudinal direction, transported at 105 ° C., and then stretched 3.8 times in the longitudinal direction at 120 ° C. to obtain a uniaxially stretched film.

This uniaxially stretched film was stretched 4.0 times in the lateral direction at 115 ° C. in a stenter, subsequently heat-fixed at 230 ° C., relaxed by 5% in the width direction, cooled in a transport step, and then the edges were formed. After cutting, it was wound up to obtain an intermediate product of a biaxially stretched film having a thickness of 31 μm. For the Stentor oven, the air supply and exhaust from outside the oven were adjusted so that the air flowed in a certain direction. This intermediate product was slit with a slitter to obtain a roll of a biaxially stretched film having a thickness of 31 μm. As a result of measuring the laminated thickness of this biaxially stretched film, it was found that the A layer: 6.5 μm, the B layer: 23.5 μm, and the C layer: 1.0 μm. Data were collected from the obtained products, and the characteristics evaluation results are shown in Table 1.

(4) Application of release layer Next, a coating liquid prepared by adjusting a crosslinked primer layer (trade name BY24-846 manufactured by Toray Dow Corning Silicone Co., Ltd.) to a solid content of 1% by mass on a roll of this biaxially stretched film. Was coated / dried, coated with a gravure coater so that the coating thickness after drying was 0.1 μm, and dried and cured at 100 ° C. for 20 seconds. Within 1 hour after that, 100 parts by mass of an addition reaction type silicone resin (trade name: LTC750A manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by mass of a platinum catalyst (trade name: SRX212 manufactured by Toray Dow Corning Silicone Co., Ltd.) were applied. The coating liquid adjusted to a solid content of 5% by mass was coated with a gravure coat so that the coating thickness after drying was 0.1 μm, dried and cured at 120 ° C. for 30 seconds, and then wound to obtain a release film.

(5) Molding and coating of green sheet Barium titanate (trade name HPBT-1 manufactured by Fuji Titanium Industry Co., Ltd.) 100 parts by mass, polyvinyl butyral (trade name BL-1 manufactured by Sekisui Chemical Co., Ltd.) 10 parts by mass, phthalic acid Glass beads having a number average particle size of 2 mm are added to 5 parts by mass of dibutyl and 60 parts by mass of toluene-ethanol (mass ratio 30:30), mixed and dispersed in a jet mill for 20 hours, and then filtered into a paste. The ceramic slurry was prepared. The obtained ceramic slurry is applied onto a release film with a die coater so that the thickness after drying is 0.5 μm and dried, and the thickness of the slurry after drying is determined by a non-contact method at the center of the coating. Continuously measured with. Then it was wound up to obtain a green sheet. At this time, the slurry thickness unevenness σ value was evaluated, and a value of less than 0.13 was regarded as good, a value of 0.13 or more and less than 0.15 was acceptable, and a value of more than 0.15 was regarded as defective. The slurry thickness unevenness in the embodiment of Example 1 was good in moldability of the green sheet. At this time, good is a level at which there is no problem in practical use.

(Examples 2 to 4)
It was carried out in the same manner as in Example 1 except that the stretching ratio and the film forming conditions of the thickness were changed, and the obtained results are shown in Table 1.

(Example 5)
The rotation speed control of the gear pump was lowered in response to the increase in the polymer filter pressure to correct the center value of the thickness. It was carried out in the same manner as in Example 1 except that the stretching ratio and the film forming conditions of the thickness were changed, and the obtained results are shown in Table 1.

(Example 6)
An edge pinning device was applied to the cast sheet. The pinning was electrostatically applied in the range from 5 mm inside to 50 mm inside the unstretched sheet. The film formation was carried out under the same conditions as in Example 1. The results obtained are shown in the table.

(Comparative Examples 1 and 2)
It was carried out in the same manner as in Example 1 except that the stretching ratio and the film forming conditions of the thickness were changed, and the obtained results are shown in Table 2. The unevenness of the slurry thickness was worse than that of Examples 1 to 4, and the evaluation was possible.

(Comparative Example 3)
The same procedure as in Example 1 was carried out except that the longitudinal stretching ratio and the transverse stretching ratio were changed to 4.5 times and 4.5 times, respectively. The purpose was to flatten the unevenness that occurred before the process by setting the magnification high, but as a result, σ _MD deteriorated. As a result of frequency analysis of thickness unevenness of σ _MD, the period of stretching unevenness, which is considered to be derived from longitudinal stretching, was confirmed.

(Comparative Example 4)
The runout of the cast was 50 μm as a result of the deterioration of the cooling water flow path. In this casting, the same procedure as in Example 1 was carried out except that the stretching ratio and the film forming conditions of the thickness were changed, and the obtained results are shown in Table 2. The evaluation of slurry thickness unevenness was poor.

(Comparative Example 5)
The raw material to be contained in the A layer, the melt specific resistance was used for 5.0 × 10 ^8. As a result of observing the sheet after casting with reflected light, there was horizontal stretching unevenness. Film thickness unevenness in the longitudinal direction When σ _MD was measured, periodic thickness unevenness was observed in the waveform of the original data. Since the thickness was significantly uneven, silicone coating and slurry coating were not performed.

(Comparative Example 6)
Although the edge pinning device was applied in the embodiment of Comparative Example 5, there was no improvement effect on the cast defect as seen in Comparative Example 5.

(Comparative Example 7)
In order to increase the ventilation frequency of air in the heat-fixing zone and remove oligomers in the oven, intake and exhaust were performed in each chamber of the heat-fixing zone, and other film forming conditions were the same as in Example 1. As a result, although the cycle was indefinite, the film thickness unevenness was aggravated. The thickness unevenness of the slurry was possible.

Since the biaxially oriented polyester film of the present invention is excellent in planar properties in the longitudinal direction, it can be suitably used for mold release applications. In particular, since the expansion and contraction behavior in the plane is uniform against the tension during processing, it is particularly preferably used for mold release applications in which a green sheet is used as a member in a multilayer ceramic capacitor.

Claims (6)

A biaxially oriented polyester film for mold release, characterized in that the film width is 400 mm or more and the variation σ value (σ _MD ) with respect to the average value of the thickness measured continuously in the longitudinal direction of the film is 0.15 μm or less. roll. The center line roughness SRa (A) of one film surface of the biaxially oriented polyester film for mold release is 1 nm or more and less than 15 nm, and the center line roughness SRa (B) of the other film surface is 20 nm or more and 40 nm or less. , The biaxially oriented polyester film roll for mold release according to claim 1. The biaxially oriented polyester film roll for mold release according to claim 1 or 2, wherein the biaxially oriented polyester film for mold release has a layer structure of three or more layers. The layer (layer A) constituting the film surface having SRa (A) of 1 nm or more and less than 15 nm is a polyester having a melt specific resistance of 1.0 × 10 ⁶ Ω · cm or more and 1.0 × 10 ⁸ Ω · cm or less. The biaxially oriented polyester film roll for mold release according to claim 2 or 3, which contains a resin. The biaxially oriented polyester film roll for mold release according to any one of claims 1 to 4, wherein the biaxially oriented polyester film for mold release is used as a molding member for a laminated ceramic capacitor. The biaxially oriented polyester film roll for mold release according to claim 5, wherein the biaxially oriented polyester film for mold release is used as a member for molding a multilayer ceramic capacitor for automobiles.