WO2019176692A1

WO2019176692A1 - Roll of biaxially oriented release polyester film

Info

Publication number: WO2019176692A1
Application number: PCT/JP2019/008899
Authority: WO
Inventors: 高木順之; 多持洋孝
Original assignee: 東レ株式会社
Priority date: 2018-03-12
Filing date: 2019-03-06
Publication date: 2019-09-19
Also published as: TWI823907B; KR20200131262A; JP7169551B2; CN111868148A; JPWO2019176692A1; TW201945446A

Abstract

A biaxially oriented release polyester film characterized by having a width of 400 mm or greater and a thickness deviation σ (σ_MD) with respect to the average value, determined through a continuous measurement over 10,000 m in the machine direction of the film, of 0.15 μm or less. The release polyester film can give a less rigid support for green sheet forming and can reduce strain amounts during electrode printing. The release polyester film is optimal for ceramic-slurry application in forming thin green sheets.

Description

Biaxially oriented polyester film roll for mold release

The present invention relates to a release biaxially oriented polyester film roll obtained by winding a release biaxially oriented polyester film excellent in film thickness uniformity during thin film slurry coating.

Biaxially oriented polyester films are used in various applications as industrial materials from the viewpoint of mechanical properties, thermal properties, stiffness, and cost. Particularly recently, as process papers related to electronic materials, 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 insulating resin release, etc. It is used for.

】 With the recent advancement of smartphone functions and the spread of smart watches and wearable devices, multilayer ceramic capacitors are becoming increasingly smaller and have higher capacities. With regard to release films used in the production of multilayer ceramic capacitors, the demand for polyester films with high smoothness, no defects in the film surface and inside, and excellent film flatness has continued to grow as green sheets become thinner. Yes. On the other hand, the demand for monolithic ceramic capacitors mounted on automobiles is rapidly expanding due to the expansion of electric vehicle production, IoT (Internet of Things) of automobiles, and the mounting of automatic driving functions on automobiles. For these multilayer ceramic capacitors for automobiles, reliability is demanded more strictly than conventional requirements. In particular, in the molding of a green sheet that is a dielectric part of a multilayer ceramic capacitor, the thickness of the slurry that is laminated on the film when it is used as a base material due to uneven thickness of the film and the planar characteristics of the film Is becoming more strictly managed.

As shown in Patent Document 1, the thickness unevenness of the film is known as a well-known technique in which a measurement is performed by measuring 15 m in the longitudinal direction and a measurement is performed by measuring a 1 m length every 5 mm. Yes. Further, as shown in Patent Document 2, unevenness in the intensity of light leaking from the polarizing plate in the crossed Nicol method for inspecting the polarizing plate becomes strong and obstructs the inspection, so that the unevenness in thickness needs to be within a predetermined range. . As shown in Patent Document 3, it is known that simultaneous biaxial stretching is carried out to enhance the plane orientation.

JP 2008-246665A JP 2017-007175 A JP 2004-291240 A

Demand for capacitors in recent years tends to be high reliability in addition to miniaturization and large capacity. Miniaturization is achieved by reducing the size of the electrode. The increase in capacity is achieved by reducing the thickness of the green sheet, and the increase in reliability is achieved by improving the dimensional accuracy in the width, length, and thickness directions when electrodes and green sheets are provided. Among these, the uniformity of the coating thickness at the time of slurry coating is to minimize the distortion and misalignment 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 request | requirement regarding minimization of the thickness nonuniformity with respect to a film has become severe. In particular, when manufacturing capacitors, the thickness of the base film over the entire roll length is likely to contribute to the process of applying the slurry thin film while constantly monitoring the slurry thickness and correcting the tilt of the die. Is known. For this reason, in this invention, it makes it a subject to reduce the thickness nonuniformity of the film over the full length of a roll especially when it is used as a support body at the time of green sheet molding.

As a result of intensive studies in view of the above circumstances, the present inventors have wound a biaxially oriented polyester film for release having excellent slurry dimensional stability in the longitudinal, width and thickness directions by optimizing the film properties. The obtained biaxially oriented polyester film roll for mold release was found, and the present invention was achieved. That is, the present invention is a biaxially oriented polyester for mold release having a film width of 400 mm or more and a variation σ value (σ _MD ) of 0.15 μm or less with respect to the average value of the thickness measured continuously in the film longitudinal direction of 10,000 m. Features a film roll.

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

Hereinafter, the present invention will be described in more detail.
The biaxially oriented polyester film roll for mold release of the present invention is obtained by winding a biaxially oriented polyester film for mold release (hereinafter sometimes 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 (unoriented) film is stretched in a two-dimensional direction by a conventional method, and indicates a biaxially oriented pattern by wide-angle X-ray diffraction. For stretching, either sequential biaxial stretching or simultaneous biaxial stretching can be employed. In sequential biaxial stretching, the process of stretching in the longitudinal direction (longitudinal) and the width direction (transverse) can be performed once in the length-width direction, or twice in the length-width-length-width direction. You can also

The polyester in the biaxially oriented polyester film of the present invention is a polyester having dibasic acid and glycol as constituent components, and the aromatic dibasic acid is terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenylsulfone. Dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl ketone dicarboxylic acid, phenylindane dicarboxylic 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 naphthalenediol, 2,2-bis (4-hydroxydiphenyl) propane, 2,2-bis (4-hydroxyethoxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, hydroquinone, etc. can be used. As the alicyclic diol, Cyclohexanedimethanol, cyclohexanediol and the like can be used.

The polyester can be produced by a known method, and the intrinsic viscosity preferably has a lower limit of 0.5 and an upper limit of 0.8. More preferably, the lower limit is 0.55 and the upper limit is 0.70. In addition, the measurement of an intrinsic viscosity uses the value calculated by the following Formula from the solution viscosity measured at 25 degreeC in orthochlorophenol.
ηsp / C = [η] + K [η] ² · C

Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the dissolved polymer mass per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assuming 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 a laminated structure of two or more layers. When two layers are laminated, it consists of a polyester A layer and a polyester B layer. In the case of three layers, it consists of a polyester A layer, a polyester B layer and a polyester C layer, or a polyester A layer, a polyester B layer and a polyester A layer. It becomes the laminated film which becomes. In this case, by controlling the amount of particles to be included in the layer constituting the surface layer (lamination part), in the range that does not adversely affect the characteristics of the film surface on the inner layer part, the recovered raw material of the edge part generated in the film forming process, Alternatively, it can be used by mixing recycled raw materials for other film forming processes in a timely manner, and it is possible to reduce the consumption of petroleum resources and to obtain cost merit. This is the most preferred embodiment.

Moreover, it is preferable that the biaxially oriented polyester film of the present invention contains a recovered raw material and / or a recycled raw material in the C layer. Therefore, the C layer is preferably the thickest layer in the layer configuration. The melting specific resistance 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 preferred that the raw material having such a melt specific resistance value is a polyester resin. The A layer is preferably a layer constituting a surface whose SRa (A) described later is 1 nm or more and less than 15 nm. Moreover, the aspect which has the characteristic regarding the raw material composition and thickness of C layer mentioned above, the characteristic regarding the raw material of A layer, and the characteristic regarding a surface shape is also preferable.

In the biaxially oriented polyester film of the present invention, the surface of the two layers constituting the surface layer of the two or more layers, that is, the surface of the polyester A layer and the polyester B layer, the surface smoothness and handling such as conveyance and winding. In order to achieve both properties, a configuration with different roughness is 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. When SRa (A) is less than 1 nm, peeling may be difficult in a peeling step after a release layer is laminated on the surface and a ceramic slurry is laminated thereon. On the other hand, when SRa (A) is 15 nm or more, the surface state of the slurry is deteriorated and the thickness is uneven, and as a result, the characteristics of the capacitor are likely to vary. When SRa (B) is less than 20 nm, blocking is likely to occur during winding after the release layer is applied or winding after applying the ceramic slurry, and charging may occur when it is fed out. For the surfaces of the polyester A layer and the polyester B layer, the center line roughness SRa (A) of one film surface is more preferably 2 nm or more and less than 12 nm, and the center line roughness SRa (B) of the other film surface is more preferably. 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, and further preferably 25 μm or more. Moreover, it is preferable that it is 188 micrometers or less, More preferably, it is 50 micrometers or less, More preferably, it is 40 micrometers or less. When the thickness is less than 12 μm, there is no support for holding the ceramic slurry, and the ceramic slurry cannot be supported in the application of the ceramic slurry, and uniform drying cannot be performed in the subsequent process, and thermal wrinkle is not sufficiently suppressed. It may become. When the thickness exceeds 188 μm, the durability against thermal wrinkles is remarkably excellent, but the unit length per unit area as the base material for forming the ceramic slurry tends to increase as the winding length decreases. It is difficult to raise the temperature and stretch the film, which causes the thickness unevenness to deteriorate. A 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 size of the particles contained at this time is preferably 1.3 μm or less. If the volume average particle diameter of the particles exceeds 1.3 μm, there is a high chance that voids, that is, voids, are generated at the interface between the particles and the polymer at the time of stretching. The thickness variation may increase. In addition, 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, agglomerated silica, calcium carbonate, aluminum oxide, barium titanate, and 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, polyimide 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 of particles together with the particle diameter. Preferably, organic particles having high particle elasticity are used. Among the organic particles described above, the organic particles are particularly preferably 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. In the inorganic particles, spherical silica and aluminum oxide are particularly preferable.

The particle shape and particle size distribution are preferably uniform, and in particular, the particle shape is preferably close to a sphere. The volume shape factor is preferably f = 0.3 to π / 6, more preferably f = 0.4 to π / 6. The volume shape factor 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) on the projection plane of the particles.

The volume shape factor f takes the maximum π / 6 (= 0.52) when the particle is a sphere. Moreover, 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 and the like can be suitably used. Particularly, cross-linked polystyrene particles, cross-linked silicone, and spherical silica have a volume shape factor. It is close to a true sphere, and the particle size distribution is extremely uniform, which is preferable from the viewpoint of 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 ) of 0.15 μm or less with respect to the average value of thicknesses measured continuously in the film longitudinal direction of 10,000 m.

This will be described below in order.
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 ) of 0.15 μm or less with respect to the average value of thicknesses measured continuously in the film longitudinal direction of 10,000 m. 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 the length in the longitudinal direction represent the dimensions of the support necessary for manufacturing the multilayer ceramic capacitor in a certain lot. That is, it has been found that the green sheet moldability can be improved by suppressing variations in thickness within these dimensions. In the following, the σ _MD value is sometimes referred to as uneven film thickness in the longitudinal direction.

The thickness of a conventional biaxially oriented polyester film is measured by scanning a non-contact thickness meter in the width direction while the film is being formed, or by collecting a sample taken about 20 m in the longitudinal direction from a film roll. In the present invention, the thickness unevenness behavior that could not be confirmed in the past was found by continuously measuring in the longitudinal direction of 10,000 m as described above. By reducing the variation with respect to this uneven thickness behavior, the present invention has the effects of reducing the uneven thickness of the slurry when applying the thin film ceramic slurry, reducing the variation in capacitance, and suppressing the probability of short circuit. Is. Incidentally, sigma _MD is more than 0.15 [mu] m, the effect of uneven thickness of the slurry is increased above is reduced in the coating of thin ceramic slurry.

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. Preferably there is. The biaxially oriented polyester film of the present invention can be subjected to mold release treatment on both surfaces in consideration of the balance between slurry coating thickness and handling properties, and can be planarized before mold release treatment. To reduce the roughness of the release layer surface.

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 an example of a method for incorporating inert particles into polyester, for example, inert particles are dispersed in a predetermined proportion in ethylene glycol which is a diol component, and this ethylene glycol slurry is added at an arbitrary stage before completion of polyester polymerization. . Here, when adding the particles, for example, it is preferable to add the water sol or alcohol sol obtained at the time of synthesis without drying once because the dispersibility of the particles is good and the generation of coarse protrusions can be suppressed. In addition, a method in which a water slurry of particles is directly mixed with a predetermined polyester pellet, supplied to a vent type twin-screw kneading extruder, and kneaded into the polyester is also effective for the production of the present invention.

The thus prepared particle-containing master pellets and pellets substantially free of particles and the like are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder. As the extruder for producing the biaxially oriented polyester film of the present invention, a uniaxial or biaxial extruder can be used. Moreover, in order to omit the drying process of a pellet, the vent type extruder which provided the vacuum drawing line in the extruder can also be used. Moreover, what is called a tandem extruder which shares the function which melt | dissolves a pellet, and the function which keeps the fuse | melted pellet at a constant temperature for each C layer can be used for the C layer where extrusion amount increases most. A tandem extruder is preferable as a process for reducing unevenness in thickness because the polymer temperature at the time of high discharge can be stabilized, 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. When 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 collection efficiency that collects 95% or more of a foreign substance having a size of 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 of collection efficiency that collects 95% or more of foreign matters less than 3 μm. Use may be an unfavorable embodiment in reducing thickness unevenness. Subsequently, the sheet is extruded 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, lamination is performed in three layers using three extruders, a three-layer manifold or a merge block (for example, a merge block having a rectangular merge portion), and a sheet is extruded from a die. In this case, it is desirable that the base of the base can be automatically adjusted with a heater. The sheet extruded from the die is cooled by a casting roll to form an unstretched film. In this case, from the viewpoint of stabilization of back pressure and suppression of variation in thickness, a method of installing a static mixer and gear pump in the polymer flow channel is effective as a means for suppressing uneven thickness 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 making the rotational speed of the gear built in the gear pump constant, uneven thickness in the longitudinal direction is required. Can be kept small. In the present invention, it is also effective to control the rotation speed of the gear pump by feeding back the weight-converted thickness of the rolled up intermediate product. This is because the discharge decreases as the filter pressure increases, and the film thickness gradually decreases in the longitudinal direction.

Regarding the rotation accuracy of the casting roll, speed fluctuations on the surface of the casting roll and surface irregularities due to the eccentricity of the casting roll may affect the thickness unevenness in the longitudinal direction. Conventionally, the speed fluctuation of the casting roll surface has a great influence on the thickness unevenness in the longitudinal direction.To reduce this, a balance weight is pasted on an arbitrary circumference of the end face of the casting roll to remove the unevenness of eccentricity. Suppressing is a preferred embodiment. In addition, it is a preferable embodiment in order to suppress the thickness unevenness in the longitudinal direction by using two motors for rotating the casting drum and dividing the function into driving and braking. In the present invention, in order to control the σ _MD value, it was necessary to further improve the accuracy, so when evaluating the rotation accuracy of the casting roll, it was measured by a sensor installed on the ground on which the casting drum was 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 on the cast circumference was defined as a shake. The numerical value is desirably within 50 μm, and further within 30 μm is a desirable form in order to improve the thickness unevenness (σ _MD ) in the longitudinal direction in the present invention. Specifically, the unevenness of the cast circle around the cast circle is measured by installing a laser displacement meter on the floor where the casting device is installed, and measuring the distance between the casting roll and the measurement unit of the laser displacement meter. .

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

In addition, the end of the unstretched film is adjusted so that the thickness of the end becomes thicker than the center in order to increase the gripping force of the clip when stretched by a transverse stretcher, but the end adhesion is poor and casting As a result of poor cooling efficiency due to the roll, crystallization at the end proceeds and may cause breakage.In addition to the full width pinning device, a so-called edge pinning device that additionally attaches a pinning device only to the end is provided. By attaching, the end of the unstretched film is brought into close contact with the cast, and the uneven cooling of the edge part is also suppressed, so that vibration at the landing point of the cast can be suppressed, and desirable in order to improve the uneven thickness in the longitudinal direction. It is a process. In addition, when applying an edge pinning apparatus to an unstretched film, if it implements from the location 5 mm or more away from the edge part edge part of an unstretched film, effective pinning can be performed. This is to prevent the leakage current from being abnormally discharged to the casting roll during the electrostatic application from the edge pinning device. The processing width of edge pinning is adjusted in accordance with the edge thickness profile of the unstretched film, but setting the range to 20 mm or more and less than 100 mm can effectively mold the edge part.

The film that has been in close contact with the casting roll and cooled is peeled off from the casting roll using a pulling roll, and then led to the next stretching step. In this case, the separation roll may be subjected to water for cooling the film, or may be driven.

The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. In simultaneous biaxial stretching, when vertical and horizontal stretching are performed simultaneously, the wind speed variation and the airflow flowing along the film (associated airflow) affect the longitudinal direction as well as the disturbance in the longitudinal direction. This is a form in which stretching is preferably applied.

In producing the polyester film of the present invention using sequential stretching, the first stretching in the longitudinal direction is important for suppressing the occurrence of scratches and for suppressing uneven thickness in the longitudinal direction. 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. Further, from the viewpoint of preventing stretching unevenness and scratches, stretching is preferably performed in two or more stages, and the total magnification is 2.8 times to 5.0 times in the length direction, preferably 3.3 times. It is 4.0 times or less and 3.5 times or more and 5 times or less, preferably 4.0 times or more and 4.5 times or less in the width direction. When setting the longitudinal stretching ratio to the above-mentioned numerical value, it is desirable to set a plurality of stretching sections so that slippage between the stretching roll and the film is less likely to occur due to suppression of 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 secured. If the temperature and magnification range are out of the range, problems such as uneven stretching or film breakage are caused, and it is difficult to obtain a film characterized by the present invention.

In sequential stretching, the stretching process in the longitudinal direction is due to the contact between the film and the roll, and the film is likely to be damaged when the film slips due to the difference between the peripheral speed of the roll and the speed of the film. Therefore, a drive system in which the roll peripheral speed can be individually set for each roll is preferable. In the stretching process in the longitudinal direction, the material of the transport roll is heated to a temperature higher than the glass transition point before stretching or transported to the stretching zone while maintaining the temperature below the glass transition point. Either heating or not is selected. When heating an unstretched film to a temperature above the glass transition point before stretching, adhesiveness 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. Moreover, it is preferable to select the temperature of the conveyance roll in a temperature rising process with the combination of a material and conveyance temperature, and in order to suppress adhesion by heating before an unstretched film exceeds a glass transition point, a conveyance roll As a metal roll plated with hard chrome, it is preferable to set the conveyance temperature to less than 80 ° C. In this case, it is preferable to supplement the amount of heat using an infrared heater in the stretching step.

In addition, since the stretching roll is the process in which the film is most loaded, and stretching unevenness that causes scratches and uneven thickness in the longitudinal direction is likely to occur, the surface roughness Ra of the stretching roll is 0.005 μm or more. The thickness is preferably 1.0 μm or less, more preferably 0.1 μm or more and 0.6 μm or less. When Ra is larger than 1.0 μm, the unevenness of the roll surface during stretching is easily transferred to the film surface, and when it is smaller than 0.005 μm, the roll and the film background adhere to each other, and the film is easily damaged by heat. In order to control the surface roughness, it is effective to appropriately adjust the particle size of the abrasive and the number of polishings.

In the successive 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 is transported to the stretching zone while being kept at a temperature lower than the glass transition point, but when heated at the time of stretching, the preheating zone transport roll was subjected to surface treatment 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 uneven thickness in the longitudinal direction.

Next, the uniaxially stretched film stretched in the longitudinal direction is heated to 90 ° C. or more and less than 120 ° C. with a transverse stretching machine, and then stretched in the width direction at 3 times or more and less than 6 times to obtain biaxial stretching (biaxial stretching) Orientation) film. This horizontal stretching machine performs self-circulation for each room of the oven and blows warm air on the film to raise the temperature of the film and to perform stretching and heat setting. At that time, in order to prevent the oligomer precipitated from the film heat-treated in the oven from being cooled and adhering to the oven, air is preferably supplied and exhausted 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 air after merging, and thickness unevenness in the longitudinal direction and width direction occurs. Therefore, it is preferable to heat the supplied air at the same temperature as the circulating air or at a temperature commensurate with the ability of the heat exchanger for heating the circulating air.

Also, in adjusting the air supply / exhaust amount in the oven, it is preferable that the direction of the air flowing above and below the conveyed film is the same direction as the film flow direction. In each chamber of the oven, in addition to the self-circulating air, the accompanying airflow that flows in the same direction as the film transport direction from the upstream, and air supply or exhaust outside the oven, the air flow inside the STN changes in a complex manner. . At this time, due to the pressure difference between the chambers, the flow of air between the chambers may change from, for example, a flow from upstream to downstream to a flow from downstream to upstream. The air flow between the chambers may lead to uneven stretching of the film when the temperature of the air varies between the chambers. For this reason, regarding the conditions of the intake air amount and the exhaust air amount of the oven, the flow of air in the same direction can be induced by making the exhaust air amount larger than the air supply amount.

The biaxially oriented polyester film of the present invention may be further re-stretched once or more in each direction, or may be re-stretched simultaneously biaxially. As a method for suppressing the thickness unevenness in the longitudinal direction, it is possible to relieve the bowing generated in the previous transverse stretching step in the longitudinal re-stretching step. At this time, it may be heated at a temperature of 80 ° C. to 100 ° C. with a transport roll before re-longitudinal stretching in the longitudinal direction, or may be transported using an unheated roll. Furthermore, you may pass through a re-longitudinal stretch process, without applying a draw ratio. After re-longitudinal stretching, lateral stretching is further performed, and the film is heat-treated after stretching. This heat treatment can be carried out in any conventionally known method or position such as in an oven or on a heated roll. The heat treatment temperature can usually be an arbitrary temperature of 150 ° C. or higher and lower than 245 ° C., and the heat treatment time is 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. Further, after the heat treatment, it is preferable to relax at a temperature lower by 0 ° C. or more and 150 ° C. or less than the heat treatment temperature by 0% or more and 10% or less in the width direction.

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

The film after biaxial stretching is cooled in the conveying process, and then the edge is cut and wound to obtain an intermediate product. In this conveying step, the film thickness in the width direction is measured, the data is fed back and used to adjust the film thickness by adjusting the die thickness and the like, and foreign matter detection by the defect detector can be performed. Thickness can be measured by β-rays, X-rays, or an optical interference method. Measurement is a method of measuring the full width by traversing one measuring device in the width direction, a method of measuring the full thickness by traversing a plurality of measuring devices in the section divided in the width direction, When the range is wide, a plurality of measuring devices can be fixed in the width direction to measure the thickness of the entire width. Moreover, about the place to measure, it can also carry out offline using the measurement in the said conveyance process, or using the biaxially-oriented polyester film roll after slitting an intermediate product.

The intermediate product is slit into an appropriate width and length by a slitting process and wound around a core to obtain a roll of a biaxially oriented polyester film. The core is a cylindrical winding core made of plastic or paper. Since it is preferable to use a core with little expansion and contraction due to temperature and humidity and little deformation due to winding pressure, it is preferable to use a plastic core. Furthermore, it is preferable to use a core in which a plastic is reinforced with glass fiber or carbon fiber. Moreover, when using paper for a core, intensity | strength can also be raised by making the surface impregnate resin. The film cutting step in the slitting step is a step for removing an unnecessary portion of the intermediate product and obtaining a polyester film roll having a desired product width. In this cutting step, 3 to 10 locations are simultaneously cut 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 process, and a polyester film roll having a desired product width can be obtained by adjusting the cutting location in the cutting process described above in the width direction. . Moreover, the length of the film longitudinal direction in this invention is measured with the length measuring device installed on the arbitrary rolls of a slit process. Thus, what cut | interrupted the intermediate product in the width direction and wound up by the core with arbitrary length is called a polyester film roll in this invention.

Since the biaxially oriented polyester film roll for mold release obtained by the above-described method winds up a film with little thickness unevenness in the longitudinal direction, the film is used as a mold member for mold release applications, particularly for multilayer ceramic capacitors. Furthermore, it can be more preferably used as a molding member of a laminated ceramic capacitor for automobiles. In addition, the mold release use in this invention refers to the use which uses the film obtained from the biaxially-oriented polyester film roll of this invention for a base material as a shaping | molding member, shape | molds a member, and peels from the member after shaping | molding. Examples of the member here include a green sheet in a multilayer ceramic capacitor, an interlayer insulating resin (electrical insulating resin) in a multilayer circuit board, and a polycarbonate (in this case, used in solution casting) in an optical member. Can be mentioned.

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

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

(1) Film thickness unevenness in the longitudinal direction (σ _MD )
Using SI-T80 manufactured by Keyence Corporation installed in a rewinding inspection machine, the thickness in the longitudinal direction was measured 10,000 m at the center in the product roll width direction. The winding 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 the thickness data, and this was regarded as the film thickness unevenness in the longitudinal direction.

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

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

(3) Melt specific resistance of polyester resin 150 g of polyester resin was put into a 50φ test tube substituted with pure water, and dried under reduced pressure at 180 ° C. for 3 hours. Then, it melted under nitrogen flow at 290 ° C. for 50 minutes, and the electrode was inserted into the molten polymer. The melt specific resistance was determined 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 such that a Teflon (registered trademark) spacer was sandwiched between ^two copper plates (22 cm ² ) and the distance between the copper plates was 9 mm.

Example 1
(1) Preparation of polyester pellets (Preparation of polyester A)
Esterification reaction is conducted while distilling water at 255 ° C. with 86.5 parts by mass of terephthalic acid and 37.1 parts by mass of ethylene glycol. After completion of the esterification reaction, 0.02 part by weight of trimethyl phosphate, 0.06 part by weight of magnesium acetate, 0.01 part by weight of lithium acetate, and 0.0085 part by weight of antimony trioxide were added. A polycondensation reaction was carried out by heating up to 0 ° C. and a polyester pellet A having an intrinsic viscosity of 0.63 dl / g was obtained. As a result of measuring the melting specific resistance of this chip, it was 7.0 × 10 ⁷ Ω · cm.

(Creation of polyester B)
In producing the polyester in the same manner as described above, after transesterification, spherical silica having a volume average particle size of 0.2 μm, a volume shape factor f = 0.51, and a Mohs hardness of 7 is added, a polycondensation reaction is performed, and the particles are converted into polyester. A silica-containing master pellet containing 1% by mass was obtained (polyester B).

The spherical silica used in polyester B is obtained by adding a mixed solution consisting of ethanol, pure water, and aqueous ammonia as a basic catalyst to this mixed solution while stirring the mixed solution of ethanol and ethyl silicate. The monodispersed silica particles obtained by stirring the reaction solution and conducting a hydrolysis reaction of ethyl silicate and a polycondensation reaction of the hydrolysis product, followed by stirring after the reaction.

(Creation of polyester C and D)
In addition, a volume average particle size of 0.3 μm obtained by a method of adsorbing a monomer comprising 80% by mass of divinylbenzene by a seed method, 15% by mass of ethylvinylbenzene, and 5% by mass of styrene, a volume shape factor f = 0.51, A water slurry of divinylbenzene / styrene copolymer crosslinked particles having a Mohs hardness of 3 (crosslinking degree of 80%) is contained in the above-mentioned homopolyester pellets substantially free of particles using a vented biaxial kneader, and the 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 the polyester were obtained (Polyester C and Polyester D), respectively.

(Creation of polyester E)
In the production of polyester A, after transesterification, 10 parts by mass of calcium carbonate and 90 parts by mass of ethylene glycol prepared by the carbon dioxide method (volume average particle size volume average particle size 1.1 μm, Mohs hardness 3) were wet pulverized. A calcium carbonate / ethylene glycol dispersion slurry was obtained. The volume average particle diameter of this calcium carbonate was 1.1 μm. On the other hand, 0.04 parts by mass of manganese acetate and 0.03 parts by mass of antimony trioxide are added to 100 parts by mass of dimethyl terephthalate and 64 parts by mass of ethylene glycol as a catalyst, and then a transesterification reaction is performed. 0.04 parts by mass of phosphate was added, and then 1 part by mass of the previously prepared slurry was added to perform a polycondensation reaction to obtain a master pellet (polyester E) containing 1% by mass of calcium carbonate relative to the polyester. .

On the other hand, the recovered raw material A was obtained by collecting the film after producing the film having the following formulation and pelletizing it. In addition, the ratio described below is represented by mass ratio (mass%) with respect to the mass of the whole film.
Polyester A 93.4
Polyester D: 0.6
Polyester G: 6.0

(2) Preparation of polyester pellets The polyester pellets to be supplied to the extruders of the respective layers A, B and C were prepared at the following ratio. In addition, the ratio described below is a mass ratio (unit: mass%) with respect to the polyester pellet which comprises each layer.
A layer polyester A: 87.5
Polyester B: 12.5
B layer Polyester A: 60.0
Collected 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 described above in a blender, the raw materials for layer A and C are the raw materials after stirring, and the vents for layer A and layer C. The raw material of the B layer was dried under reduced pressure at 160 ° C. for 8 hours and supplied to the single screw extruder for the B layer. The B layer is melt extruded at 275 ° C. with a tandem extruder, filtered with a high-precision filter that collects 95% or more of foreign matters of 3 μm or more, and then merged and laminated with a rectangular heterogeneous three-layer merge block. A three-layer stack consisting of A, layer B, and layer C was used. Thereafter, the film is wound around a casting drum having a surface temperature of 25 ° C. and cooled and solidified by 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. Got. At this time, the cast was aligned, and the deflection was 25 μm.

¡Sequential stretching (longitudinal direction, width direction) was performed on this unstretched laminated film. First, the film was stretched in the longitudinal direction, conveyed at 105 ° C., and then stretched 3.8 times at 120 ° C. in the longitudinal direction to obtain a uniaxially stretched film.

This uniaxially stretched film was stretched 4.0 times at 115 ° C. in the transverse direction in a stenter, then heat-set at 230 ° C., relaxed by 5% in the width direction, cooled in the conveying process, and then edged. The product was wound up after cutting to obtain an intermediate product of a biaxially stretched film having a thickness of 31 μm. In the oven of the stenter, air supply / exhaust from the outside of the oven was adjusted to allow air to flow in a certain direction. This intermediate product was slit with a slitter to obtain a biaxially stretched film roll having a thickness of 31 μm. As a result of measuring the lamination thickness of this biaxially stretched film, the layer A was 6.5 μm, the layer B was 23.5 μm, and the layer C was 1.0 μm. Data was collected from the obtained products, and the results of characteristic evaluation are shown in Table 1.

(4) Application of Release Layer Next, a coating solution in which a cross-linked primer layer (trade name BY24-846 manufactured by Toray Dow Corning Silicone Co., Ltd.) was adjusted to 1% by mass on the roll of this biaxially stretched film. Was applied 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, 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.) The coating solution adjusted to a solid content of 5% by mass was applied by gravure coating so that the coating thickness after drying was 0.1 μm, dried and cured at 120 ° C. for 30 seconds, and wound up to obtain a release film.

(5) Molding application of green sheet 100 parts by weight of barium titanate (trade name HPBT-1 manufactured by Fuji Titanium Industry Co., Ltd.), 10 parts by weight of polyvinyl butyral (trade name BL-1 manufactured by Sekisui Chemical Co., Ltd.), phthalic acid Glass beads with a number average particle diameter of 2 mm are added to 5 parts by weight of dibutyl and 60 parts by weight of toluene-ethanol (mass ratio 30:30), mixed and dispersed in a jet mill for 20 hours, and then filtered to form a paste A ceramic slurry was prepared. The obtained ceramic slurry is coated on a release film with a die coater so that the thickness after drying is 0.5 μm, and dried, and the slurry thickness after drying is a non-contact method at the center of the coating. Was measured continuously. Thereafter, winding was performed to obtain a green sheet. At this time, the slurry thickness unevenness σ value was evaluated. A value less than 0.13 was good, a value between 0.13 and less than 0.15 was acceptable, and a value exceeding 0.15 was regarded as defective. The slurry thickness unevenness in the embodiment of Example 1 was good in green sheet moldability. At this time, good is at a level where there is no practical problem.

(Examples 2 to 4)
The procedure was the same as in Example 1 except that the film forming conditions such as the draw ratio and thickness were changed. The results obtained are shown in Table 1.

(Example 5)
The center value of the thickness was corrected by decreasing the rotational speed control of the gear pump in accordance with the increase of the polymer filter pressure. The procedure was the same as in Example 1 except that the film forming conditions such as the draw ratio and thickness were changed. The results obtained are shown in Table 1.

(Example 6)
An edge pinning device was applied to the cast sheet. In the pinning, electrostatic application was performed in a range from 5 mm inside to 50 mm inside the unstretched sheet. Film formation was performed under the same conditions as in Example 1. The results obtained are shown in the table.

(Comparative Examples 1 and 2)
The procedure was the same as in Example 1 except that the film forming conditions such as the draw ratio and thickness were changed. The results obtained are shown in Table 2. The slurry thickness unevenness was worse than that of Examples 1 to 4, and the evaluation was acceptable.

(Comparative Example 3)
The same operation as in Example 1 was performed except that the longitudinal draw ratio and the transverse draw ratio were changed to 4.5 times and 4.5 times, respectively. By increasing the magnification, but the purpose of flattening unevenness generated in step earlier, resulting sigma _MD worsened. As a result of performing frequency analysis of thickness unevenness for σ _MD, a period of stretching unevenness that seems to be derived from longitudinal stretching was confirmed.

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

(Comparative Example 5)
A material having a melt specific resistance of 5.0 × 10 ⁸ was used as a raw material to be contained in the A layer. As a result of observing the cast sheet with reflected light, there was horizontal stepwise unevenness. When measuring the film thickness unevenness σ _MD in the longitudinal direction, periodic thickness unevenness was observed in the waveform of the original data. Since the thickness was extremely uneven, silicone application and slurry application were not performed.

(Comparative Example 6)
In the embodiment of Comparative Example 5, the edge pinning device was applied, but there was no improvement effect on the casting failure as seen in Comparative Example 5.

(Comparative Example 7)
In order to remove the oligomers in the oven by increasing the number of times of air ventilation in the heat setting zone, the other film forming conditions were the same as in Example 1 in which intake and exhaust were performed in each chamber of the heat setting zone. As a result, although the cycle was indefinite, the film thickness unevenness was deteriorated. The thickness of the slurry was uneven.

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. Particularly, since the in-plane expansion / contraction behavior is uniformed against the tension at the time of processing, it is particularly suitably used for a mold release application using a green sheet in a multilayer ceramic capacitor as a member.

Claims

A biaxially oriented polyester film for mold release having a film width of 400 mm or more and a variation σ value (σ MD ) of 0.15 μm or less with respect to the average value of thickness obtained by continuously measuring 10,000 m in the film longitudinal direction roll.
The center line roughness SRa (A) of one film surface of the biaxially oriented polyester film for 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 release according to claim 1 or 2, wherein the biaxially oriented polyester film for release has a layer structure of three or more layers.
The layer (A layer) constituting the film surface where SRa (A) is 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, comprising a resin.
The biaxially oriented polyester film roll for release according to any one of claims 1 to 4, wherein the biaxially oriented polyester film for release is used as a molding member for a multilayer 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 molding member of a laminated ceramic capacitor for automobiles.