JP6380104B2 - Biaxially oriented laminated polyester film for mold release - Google Patents

Description

  The present invention relates to a base film for mold release which is based on a biaxially stretched polyester film and has an excellent balance between smoothness and uniform peelability.

  With the recent spread of smartphones, multilayer ceramic capacitors are becoming smaller and higher capacity. With regard to a release film used for manufacturing a multilayer ceramic capacitor, demand for a polyester film film having high smoothness and having no defects on the film surface and inside is rapidly increasing.

  With respect to the polyester film for high-smooth mold release, it is characterized in that the surface on which the ceramic slurry is formed does not substantially contain particles, and the three-dimensional center plane roughness (SRa) is 2 to 7 nm. A base film that generates less pinholes on a green sheet is disclosed (Patent Document 1). Moreover, the technique which improves the coating property of ceramic slurry by suppressing the defect of the green sheet surface formed after ceramic slurry application | coating by reducing the dent defect of a film surface is disclosed (patent document) 2). In addition, there is a method to reduce the occurrence of raised defects by improving the electrostatic charge generated by the smoothing associated with the thinning of the green sheet in the film winding process so that foreign matter attached to the film is caught by static electricity. (Patent Document 3). In addition, a method in which fine particles are not blended in an intermediate layer having a different three-layer structure is disclosed in order to enable high smoothness, foreign matter reduction, and production cost reduction (Patent Document 4). On the other hand, the method of defining and controlling surface protrusions is generally realized by adding particles to the polyester film as the base material, and its evaluation is based on three-dimensional fine surface shape measurement. A method of obtaining from a surface profile obtained from a vessel is known (Patent Documents 5 and 6).

JP 2007-62179 A JP 2007-210226 A JP 2004-196873 A JP 2004-196856 A JP 2009-215350 A JP 2008-239844 A

  In recent years, since high accuracy is required for ceramic capacitors, high release accuracy for ceramic capacitor release films is also required when ceramic green sheets are laminated in a thin film and in multiple layers. However, it has been found that the release film obtained by the above-described conventionally known technique has a problem that the lamination accuracy can be increased to a certain degree, but the variation in the peeling characteristics cannot be suppressed. A release film obtained by a conventionally known technique reduces the number of projections generally called coarse projections present on the surface of the release layer, and makes a highly smooth film. However, in the release film obtained by the above known technique, since the surface of the release layer is too smooth, there is no point (peeling start point) that triggers peeling, and as a result, variation occurs in peeling characteristics. It is thought that. Thus, as a result of intensive studies, the present inventors have clarified that the variation in the peeling characteristics can be suppressed by forming protrusions (large protrusions) having a certain shape on the surface of the release film.

  An object of the present invention is to provide a high-smooth biaxially oriented polyester film for mold release, in which the release properties of the film, in particular, the dispersion of the release is extremely small, after a highly smooth green sheet is laminated in a thin film and in multiple layers. It is in.

As a result of intensive studies in view of the above circumstances, the present inventors have determined that the surface properties, in particular, the number of large protrusions are controlled within an appropriate range, so that the peeling characteristics are good, and particularly the variation in peeling is extremely small and highly smooth. A release polyester film suitable for forming a thin film green sheet has been found, and the present invention has been achieved.
That is,
A biaxially oriented polyester film for mold release that satisfies the following (1) to (3).
(1) The surface roughness SRa (A) of one surface (this surface is the A surface) is 7.0 nm or more and less than 15.0 nm.
(2) The surface roughness SRa (B) of the surface opposite to the A surface (this surface is defined as the B surface) is more than 30 nm and less than 50 nm.
(3) The number of large protrusions present on the A surface is 10 / 5.0 mm ² or more and 20 / 5.0 mm ² or less, and the heights of the large protrusions existing on the A surface are all 800 nm or less. It is.

  According to the present invention, the coating properties of the ceramic slurry during the formation of a highly smooth thin film green sheet and the variation in the peeling characteristics of the green sheet are improved.

  Hereinafter, the present invention will be described in more detail.

  In the biaxially oriented polyester film for mold release according to the present invention, the term “for mold release” refers to a use in which a polyester film substrate is used to mold a member and peel from the molded member. The members referred to here include green sheets in multilayer ceramic capacitors, interlayer insulating resins (electrical insulating resins) in multilayer circuit boards, polycarbonates in optical related members (in this case, used in solution casting), and the like.

  The release-oriented biaxially oriented polyester film of the present invention has good release characteristics, and particularly has very little variation in release. Therefore, it can be suitably used for a release film used for supporting green sheet molding in a process for producing a multilayer ceramic capacitor. The biaxially oriented polyester film for mold release of the present invention is excellent in the coating property of the ceramic slurry at the time of molding even when a highly smooth green sheet is laminated in a thin film and in multiple layers, and the green sheet punching property and green sheet lamination The accuracy is good.

  In the biaxially oriented polyester film for release of the present invention, the biaxial orientation refers to a pattern of biaxial orientation by wide-angle X-ray diffraction. An unstretched (unoriented) film is obtained by stretching in a two-dimensional direction by a conventional method. Stretching can take sequential biaxial stretching. In sequential biaxial stretching, the process of stretching in the longitudinal direction (longitudinal) and the width direction (transverse) can be carried out once in the length-width direction, or in each direction such as length-width-length-width. It can also be carried out once or more.

  In the biaxially oriented polyester film for release of the present invention, the polyester is a polyester comprising dibasic acid and glycol as constituent components, and the aromatic dibasic acid is terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid 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, 2,2bis (4-hydroxydiphenyl) propane, 2,2-bis (4-hydroxyethoxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, hydroquinone and the like 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 dl / g or more and an upper limit of 0.8 dl / g or less. More preferably, the lower limit is 0.55 dl / g or more and the upper limit is 0.70 dl / g or less.

  In the biaxially oriented polyester film for mold release of the present invention, the surface roughness SRa (A) of one surface (the surface is A surface) is 7.0 nm or more and less than 15.0 nm, which is opposite to the A surface. This is a polyester film having a surface roughness SRa (B) of more than 30 nm and less than 50 nm. The biaxially oriented polyester film for mold release of the present invention is a laminated film having a layer A and a layer B (for mold release), comprising at least two layers of an A layer constituting the A surface and a B layer constituting the B surface. A biaxially oriented polyester film) is preferred.

  The A layer is a layer that is excellent in the coating property of the ceramic slurry after providing the release layer and is suitable for constituting the surface on which the ceramic slurry is applied.

  The coating property of the ceramic slurry is a ceramic sheet (molded body) obtained after applying the dielectric material of the ceramic capacitor on the release film made of the biaxially oriented polyester film for release of the present invention and drying it. A so-called green sheet) exhibits the characteristic that it has been obtained without occurrence of pinholes or uneven coating.

  The green sheet peeling property means that the green sheet cut in the above step was peeled without causing damage such as tearing in the step of peeling the release film after being pressed on the substrate by hot pressing. It shows the characteristics. A description of these evaluation methods will be given later.

  The B layer is a surface layer on the opposite side of the A layer forming the release layer, and is a surface in contact with the release layer or the green sheet when the release layer or the green sheet is laminated and wound. .

  The polyester film of this invention may have the intermediate | middle layer which does not have A surface and B surface other than said A layer and B layer. Having an intermediate layer is more preferable because it becomes easy to control the height of the large protrusion.

  The lower limit of the thickness of the biaxially oriented polyester film for release of the present invention is preferably 20 μm or more, more preferably 25 μm or more, and further preferably 31 μm or more. The upper limit is preferably 40 μm or less, and more preferably 38 μm. When the thickness is less than 20 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 may not be possible in the subsequent process. If the thickness exceeds 40 μm, it may be unfavorable because scratches are likely to occur in the transport process during film production.

  In the present invention, the thickness of the layer A is preferably 0.5 μm or more. If the lamination thickness is less than 0.5 μm, the particles may fall off if the A layer contains particles.

  In the intermediate layer in the present invention, only a virgin chip may be used as a raw material, or a recovered raw material may be used. As the recovered raw material, it is preferable to use only the generated waste after biaxial stretching generated in the polyester film manufacturing process. Furthermore, it is preferable to use only the waste generated in the process after winding up the intermediate product because the thermal history received by the recovered raw material can be homogenized and the characteristics of the resulting film can be homogenized. For example, if unoriented film and biaxially stretched film are used together as recovered raw materials, the melt viscosity is not stable due to the difference in crystallinity, resulting in a difference in melting point during remelting, unmelted foreign matter or thermal degradation Foreign matter may be generated. When the foreign matter is larger than the layer thickness of the A layer or the B layer, large protrusions or coarse protrusions may be formed on the A or B surface. At this time, in particular, when a surface protrusion is formed on the A surface side, a pinhole may be generated in the green sheet.

Polyester film of the present invention is a laminated polyester film consisting of three layers, the thickness of the middle-layer is preferably on the whole film is less than 95% more than 25%. By setting the thickness of the intermediate layer in the above range, even if the intermediate layer contains the recovered raw material, the surface shape of the A surface of the film can be a specific shape. When the thickness of the intermediate layer is too thick (95% or more) relative to the entire film, when the recovered raw material is used for the intermediate layer, it is deformed to the surface layer (A, B surface) due to the particle type or foreign matter contained in the recovered raw material (Push-up) may occur, and proper protrusion formation may not be achieved. If the thickness of the intermediate layer is too thin (less than 25%) with respect to the entire film, it may be difficult to include a large amount of recovered material in the intermediate layer.

  The biaxially oriented polyester film for mold release according to the present invention may contain particles for the purpose of improving the handling properties during conveyance and winding. When particles are contained in the A layer and the B layer, fine convex shapes can be formed on the A and B surfaces. When the convex shape is formed, air between the transport roll and the film is easily released during transport, and air between the A surface and the B surface is easily released during winding. It is preferable because it improves.

  The shape and particle size distribution of the particles used in the present invention 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. As the particles used in the present invention, 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 suitably used. In particular, cross-linked polystyrene particles, cross-linked silicone, and spherical silica can be used. The volume shape factor is close to a true sphere, the particle size distribution is extremely uniform, and is preferable from the viewpoint of uniformly forming film surface protrusions.

  Further, the protrusion on the B surface may be caught on the surface of the green sheet when the wound green sheet is unwound, and the green sheet may be shaved off. This catch can also be prevented when the height of the protrusion formed on the flat surface of the B surface is uniform.

  Further, these particles are preferably subjected to a surface treatment with a surfactant or the like to improve the affinity with the polyester, and can form protrusions with less dropout.

  In the biaxially oriented polyester film for mold release of the present invention, the surface roughness (centerline average roughness) SRa (A) of the A surface is 7 nm or more and 15 nm or less, and the surface roughness of the B surface (centerline average roughness). S) SRa (B) needs to be more than 30 nm and 50 nm or less. By achieving a surface roughness in this range, it is possible to obtain appropriate smoothness in forming a thin green sheet having a thickness of 2 μm or less. When the surface roughness (centerline average roughness) SRa (A) of the A surface is less than 7 nm, blocking occurs during storage of the film roll after application of the release layer. It becomes uniform and defects such as pinholes occur in the green sheet.

  Moreover, the green sheet obtained after apply | coating a slurry and drying is hold | maintained and wound up on the release film formed by apply | coating a release layer to the biaxially-oriented polyester film for release of this invention. Therefore, as described above, the shape of the B surface affects the surface form of the green sheet after being wound. When the surface roughness (centerline average roughness) SRa (B) of surface B is 30 nm or less, handling properties deteriorate in the release layer application process and slurry application process, application becomes unstable, and application spots occur. When winding up after application, it becomes difficult for the air that is bitten to escape to cause winding deviation. Further, when the surface roughness (centerline average roughness) SRa (B) of the B surface exceeds 50 nm, the influence of the unevenness formed on the surface being transferred to the surface of the green sheet is increased, and the electrostatic capacity of the ceramic capacitor is increased. Variations in capacity occur. In order to make the surface roughness of the A surface and the B surface within the above range, it can be achieved by containing a specific amount of specific organic particles or inorganic particles in the A layer and the B layer, or by manufacturing with a manufacturing method described later.

In the biaxially oriented polyester film for mold release of the present invention, the number of large protrusions on the A surface is 10 / 5.0 mm ² or more and 20 / 5.0 mm ² or less, and the large protrusions present on the A surface All the heights need to be more than 300 nm and 800 nm or less.

The large protrusion referred to in the present invention is obtained by the following method. That is, the measurement surface of the film is measured under the measurement condition (I) using a three-dimensional structural analysis measuring instrument (New View 7300 manufactured by Zygo) to obtain a differential interference image. In the obtained image, a protrusion satisfying the criterion (II) is determined as a large protrusion. The number of large protrusions is counted, and the value converted per 5.0 mm ^{2 is} defined as the number of large protrusions. Further, the height of the protrusion satisfying the criterion (II) is set as the height of the large protrusion. The above measurement is performed 5 times, and the average value is defined as the number of large protrusions.
(I) Measurement conditions Magnification: 50 times Measurement area: width 0.98 mm, length 5.25 mm
(Measurement of 1 field of view 140 μm × 105 μm is performed for 350 fields of view with 7 fields in the width direction and 50 fields in the length direction.)
Camera Mode: 640x480 210Hz
Scan Length: 10 μm
Min Mod: 15.00%
Min Area Size: 7
Film Min Mod: 4%
(II) Selection criteria Reference Band: 600 nm
Area: 0.25 μm ² or more.

  Here, “Reference Band: 600 nm” is used as a threshold value for determining whether or not the height of the protrusion exceeds 300 nm. The Reference Band value indicates the width that determines the height of the peaks and the depth of the valleys when the average plane is the center. When the Reference Band is 600 nm, the threshold value for the peak / valley is 300 nm, and protrusions exceeding 300 nm in height can be selected. The protrusion determined by the Reference Band is then determined to be a large protrusion at a threshold value of Peak Area.

The Peak Area is the area on the threshold surface of a mountain having a height exceeding the threshold with respect to the mountain exceeding the threshold defined by the Reference Band. That is, in the present invention, a large protrusion means a protrusion having a height exceeding 300 nm and having a cross-sectional area of 0.25 μm ² or more on the threshold surface of 300 nm.

The large protrusion is a protrusion having a broad mountain shape, unlike a coarse protrusion, which is an index of the protrusion that is often used conventionally. Since the large protrusion has a broad mountain shape, it could not be detected by conventional coarse protrusion measurement. When a film having coarse protrusions is brought into close contact with the film surface, in the case of coarse protrusions, the film is peeled off from around the protrusions to generate interference fringes. For this reason, in order to suppress the generation of interference fringes, a method of reducing the coarse protrusions as much as possible has been used in the prior art. However, in a film with fewer coarse protrusions, the film surface is too smooth, so that there is no point (peeling start point) that triggers peeling, and as a result, the peeling characteristics vary. On the other hand, in the film of the present invention having a specific number of large protrusions, unlike the film having coarse protrusions, the film surface is completely adhered and interference fringes are not generated. Further, since the large protrusion can be the peeling start point, the variation in peeling characteristics can be extremely reduced. In other words, if the number of large protrusions on the A surface is less than 10 / 5.0 mm ² , the surface becomes too smooth and the trigger of peeling is difficult to determine, and variations in peeling force are likely to occur, so a stable quality capacitor is produced. Can not. If it exceeds 20 / 5.0 mm ² , many green sheet defects will occur. Further, the height of the large protrusions needs to be controlled, and even if the large protrusions are distributed in the above-mentioned number range, if the height of the large protrusions is 300 nm or less, the peeling is not stable, When it exceeds 800 nm, it leads to a defect of the green sheet. In order to set the number and height of the large protrusions on the A surface within the above ranges, stretching may be performed under the stretching conditions described later.

  In the biaxially oriented polyester film for release of the present invention, the sum of the breaking strengths in the longitudinal direction and the width direction is preferably 500 MPa or more and 600 MPa or less, and more preferably 520 MPa or more and 590 MPa or less. Moreover, it is preferable that the breaking strength in the width direction is equal to or more than the breaking strength in the longitudinal direction, and the difference is 0 MPa or more and 90 MPa or less, and the difference is more preferably 40 MPa or more and 80 MPa or less. When the sum of the breaking strengths in the longitudinal direction and the width direction is less than 500 MPa, a void (void) structure in which the polymer around the particles is peeled off from the particles in the stretching process is difficult to develop, and the desired surface roughness and cushioning properties are obtained. Since it does not express, it is not preferable. In order to achieve a state exceeding 600 MPa, it is necessary to excessively stretch in the longitudinal direction and the width direction, which is not preferable because it may break during stretching.

  Further, the elongation at break is 80% or more and 220% or less, preferably 90% or more and 210% or less in both the longitudinal direction and the width direction. Furthermore, the breaking elongation in the longitudinal direction is preferably equal to or greater than the breaking elongation in the width direction, the difference is more preferably 0% or more and 100% or less, and further, the breaking elongation in the longitudinal direction is 170% or more and 190%. Hereinafter, it is more preferable that the breaking elongation in the width direction is 90% or more and 110% or less, and the breaking elongation in the longitudinal direction is 70% or more and 90% or less larger than the breaking elongation in the width direction. When the elongation at break in at least one of the longitudinal direction and the width direction is less than 80%, it is not preferable because the tension fluctuation cannot be absorbed when the tension in the process is applied at the time of applying the ceramic slurry, resulting in coating unevenness. If the elongation at break in at least one of the longitudinal direction and the width direction exceeds 220%, the flatness deteriorates during storage after applying the release layer, and the flatness of the green sheet is impaired during storage after applying the ceramic slurry. Sometimes, it is not preferable. By controlling the elongation at break within the above-mentioned range, it is possible to control the phenomenon in which the film expands and contracts and the behavior in which the residual stress recovers even after winding by the tension applied in the processing process. The flatness of the green sheet can be kept good. In order to suppress these dimensional changes in the longitudinal and width directions, it is preferable to set the difference in elongation at break between the longitudinal direction and the width direction within the above range.

  The biaxially oriented polyester film for release in the present invention preferably has a haze of 7% or less, more preferably 6% or less. When used as a mold release for multilayer ceramic capacitors, it is possible to put the recovered raw material in the intermediate layer of the three-layer composite layer of the polyester film of the present invention, but if more recovered raw material is added, the haze tends to increase. is there. If the haze exceeds 7%, it may be difficult to confirm the green sheet molding state, particularly the end state.

  Furthermore, the polyester film of the present invention has a thickness variation (thickness variation in the longitudinal direction) that is the difference between the maximum thickness and the minimum thickness obtained by measuring the film thickness in the longitudinal direction of the film by 15 m and obtained from the recorded film thickness chart. ) Is preferably 2 μm or less. Furthermore, it is preferably 1.4 μm or less. Conventionally, reducing the thickness unevenness of the film has been a problem in producing the film. In the release film of the present invention, particularly in the release film applied to the production of thin film ceramic capacitors, the thickness variation in the longitudinal direction is within the above range, so that the electrostatic capacity of the capacitor can be reduced when the thickness of the green sheet is reduced. This is particularly preferable because it does not cause variation in capacity.

The polyester film in the present invention preferably has 5 coarse projections / 100 cm ² or less on the film surface. The coarse protrusions referred to here are protrusions having a reference band of 600 nm and an area of less than 0.25 μm ² (the height of the protrusion exceeds 300 nm and the area of the cross section of the protrusion having a height of 300 nm is less than 0.25 μm ² ). Is expressed. Further, it is preferable that the number of coarse protrusions having a height of 0.54 μm or more is 1/100 cm ² or less. If the number of coarse protrusions exceeds the above value, there may be coating unevenness and pinhole-like coating omission defects when a release agent is applied. Also, when reducing the thickness of the green sheet, Unsatisfactory application of the mold agent causes undesired peeling of the green sheet or coarse protrusions, which may cause dents or pinholes in the green sheet.

  In order to achieve the above-mentioned preferable form in the coarse projection on the film surface, the particle type and the volume average particle diameter should be within the above ranges, and the raw material supply equipment, particularly the raw material storage equipment (silo), the raw material It is desirable to use the piping for conveyance only for the master pellet containing the particles used in the present invention. In order to transport the raw material, it is transported by air using a blower or by free fall. When transporting by air, 95% of dust of 0.3 μm or more is taken in when taking in air. It is preferable to filter the air using a filter that can be cut. Moreover, it can achieve by making the filter used at the time of manufacture of this invention into the highly accurate filter mentioned later.

  In the polyester film of the present invention, it is preferable to appropriately control the dimensional change rate in order to maintain good flatness after post-processing, particularly after the release layer is applied. The rate of dimensional change can be achieved by appropriately adjusting by a known method such as relaxation treatment under film forming conditions. The dimensional change rate at 150 ° C. is preferably 2% or less in the longitudinal direction and 2.5% or less in the width direction, 0.5% or more and 1.7% or less in the longitudinal direction, and 1% or more and 2% or less in the width direction. preferable. The dimensional change rate at 100 ° C. is preferably 1% or less in both the longitudinal direction and the width direction, and more preferably in the range of 0.2% to 0.8%. When the rate of dimensional change is below the lower limit of the above range, poor flatness due to tarmi occurs when the release layer is applied, and when the upper limit is exceeded, shrinkage spots in a tin shape due to shrinkage when the release layer is applied. Is generated, resulting in poor flatness, and in any case, the coating thickness of the thin film green sheet may be uneven.

  Next, the manufacturing method of the biaxially oriented polyester film of this invention is demonstrated. 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 predetermined polyester pellets, supplied to a vent type twin-screw kneading extruder, and kneaded into polyester is also effective for the production of the present invention.

  In this way, the particle-containing master pellets prepared for each layer and the 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 release-oriented 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. In addition, when providing an intermediate layer, since the amount of extrusion is the largest, use a so-called tandem extruder that shares the function of melting the pellets and the function of maintaining the molten pellets at a constant temperature. Can do. In the biaxially oriented polyester film for release according to the present invention, it is preferable to use a biaxial vent type extruder for the A layer and the B layer because the dispersibility of the particles can be kept good.

  The polymer melted and extruded by the extruder is filtered through a filter. Since even a very small foreign substance enters the film and becomes a coarse protrusion defect, it is effective to use a high-accuracy filter that collects 95% or more of a foreign substance of 3 μm or more, for example. Subsequently, the sheet is extruded from a slit-shaped slit die and cooled and solidified on a casting roll to form an unstretched film. That is, three extruders, three layers of manifolds or merging blocks (for example, merging blocks having a rectangular merging portion) are laminated in three layers, a sheet is extruded from a die, cooled by a casting roll, and an unstretched film is formed. create. In this case, a method of installing a static mixer and a gear pump in the polymer flow channel is effective from the viewpoint of stabilizing the back pressure and suppressing thickness fluctuation.

  The stretching method needs to be sequential biaxial stretching.

  Since simultaneous biaxial stretching can carry out longitudinal stretching (hereinafter sometimes referred to as longitudinal stretching) and widthwise stretching (hereinafter sometimes referred to as lateral stretching) in a stenter, a roll in a longitudinal stretching machine While preheating and stretching processes can be omitted, it is difficult to determine the stretching point in the same way as sequential biaxial stretching, which is thought to be due to Poisson deformation during stretching and the accompanying flow in the stenter. .

  When there are multiple stretching in the longitudinal direction, the first stretching in the longitudinal direction is important for suppressing the generation of scratches and forming / controlling large protrusions, and the stretching temperature is 100 ° C. or higher and 120 ° C. or lower. Preferably there is. When the stretching temperature is lower than 100 ° C., the film is easily broken and large protrusions are formed high. If the stretching temperature is higher than 120 ° C., the film surface is easily damaged by heat and it is difficult to form large protrusions. Moreover, from the viewpoint of preventing stretching unevenness and scratches, stretching is preferably performed in two or more stages, and the total magnification is preferably 3.5 times or more and 3.8 times or less in the longitudinal direction.

  In addition, the biaxially oriented polyester film of the present invention has a large protrusion by controlling the output of the infrared heater used to supplement the amount of heat at the time of stretching in an optimal range in order to control the height of the large protrusion. The height can be easily adjusted to a suitable range. That is, the height of the large protrusion of the present application can be controlled by adjusting the output of the infrared heater at a distance of 25 mm to 10 kw or more and less than 13 kw and the processing time to 0.05 second or more and less than 0.3 second. . The biaxially oriented polyester film of the present invention preferably includes a step of heating with an infrared heater under the above conditions in the step of stretching the polyester film. In particular, it is preferable to include a step of heating with an infrared heater in the stretching step in the longitudinal direction because it becomes easy to control the height of the large protrusions to be formed.

  The stretching process in the longitudinal direction is preferably a driving method in which the roll peripheral speed can be individually set for each roll in the process in which the film and the roll are in contact with each other and the scratches easily occur due to the difference between the roll peripheral speed and the film speed. 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. Depending on whether to heat or not, when heating an unstretched film to the glass transition point or higher before stretching, select from non-adhesive silicone rolls, ceramics, and Teflon (registered trademark) to prevent sticking due to heating. it can. In addition, the stretching roll is most burdened on the film, and the surface roughness Ra of the stretching roll is 0.005 μm or more and 1.0 μm or less, preferably 0.1 μm or more for the process in which scratches and stretch spots are likely to occur in the process. 0.6 μm or less. When Ra is larger than 1.0 μm, unevenness on the roll surface during stretching is transferred to the film surface. On the other hand, 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. It is not preferable. In order to control the surface roughness, it is effective to appropriately adjust the particle size of the abrasive and the number of polishings. When the unstretched film is transported to the stretching zone while maintaining the temperature below the glass transition point, and heated at the same time during stretching, the transport roll in the preheating zone is subjected to surface treatment with hard chromium or tungsten carbide. It is preferable to use a metal roll having a thickness Ra of 0.2 μm or more and 0.6 μm or less.

  The film stretched in the longitudinal direction is preferably stretched by 4.0 times to 4.3 times in the width direction. Furthermore, the film is heat-treated after biaxial stretching, and this heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. Heat setting is performed at 205 ° C. to 240 ° C., preferably 210 ° C. to 230 ° C., for 0.5 second to 20 seconds, preferably 1 second to 15 seconds. In particular, when the heat setting temperature is lower than 205 ° C., the crystallization of the film does not proceed, the structure is not stable, and the target characteristics such as the dimensional change rate cannot be obtained. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction. Further, after the heat treatment, the film is relaxed 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 heat treatment can be provided with, for example, an intermediate cooling zone or a cooling zone to adjust the dimensional change rate and flatness. 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.

  After the biaxially stretched film is cooled in the conveying step, the edge is cut and wound to obtain an intermediate product. In this conveying step, the thickness of the film 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 is performed by a defect detector.

  In cutting the edge, it is necessary in the biaxially oriented polyester film for release of the present invention to suppress the generation of chips. Edge cutting is performed using a round blade, a shear blade, and a straight blade, but when using a straight blade, it is preferable not to always make the location where the blade hits the film the same location, because it is possible to suppress wear of the blade. It is. For this reason, it is preferable to have a mechanism for oscillating the upper limit of the blade. Moreover, it is preferable to provide a suction device at a film cutting location to suck generated chips and scraped powder generated by cutting the film ends after cutting.

  The intermediate product is wound into a suitable width and length by a slitting process, and a roll of the biaxially oriented polyester film for mold release according to the present invention is obtained. When cutting the film in the slitting process, it can be selected from the same cutting method as the above-described edge cutting.

  The intermediate product is slit to a desired width to obtain the biaxially oriented polyester film for release of the present invention.

  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) Volume average particle diameter of particles The polymer is removed from the film by a plasma low-temperature ashing method to expose the particles. The processing conditions are selected such that the polymer is ashed but the particles are not damaged as much as possible. The treated sample was observed with a scanning electron microscope (SEM; model S-4000 manufactured by Hitachi, Ltd.), the particle image was taken into an image analyzer (LUZEX_AP manufactured by Nireco Corporation), and the equivalent circle equivalent diameter was measured. Is determined. The SEM magnification is appropriately selected from 5000 to 20000 times depending on the particle size. The observation spot was arbitrarily changed, the equivalent circle equivalent diameter of at least 5000 particles was measured, and the average particle diameter was determined from the average value.

  When the particles are greatly damaged by the plasma low-temperature ashing treatment method, the film cross section is 3000 to 20000 times depending on the particle size using a transmission electron microscope (TEM; H-600 type manufactured by Hitachi, Ltd.). Observe at. The section thickness of TEM is about 100 nm, the equivalent circle diameter of at least 100 particles is measured at different locations, and the volume average particle diameter is obtained from the average value.

  In addition, when measuring the volume average particle diameter of the particles, when observed by SEM and TEM, even when 10 fields of view are confirmed at 5000 times, if no particles are recognized, the particles should be substantially not contained. to decide.

(2) Particle Volume Shape Factor Using a scanning electron microscope, a photograph of a particle is photographed at 10 fields of view, for example, at a magnification of 5000 times, and an image analysis processor is used to calculate the projection surface maximum diameter and the average volume of the particle. The volume shape factor is obtained from the equation.

f = V / Dm ³
Here, V is the average volume (μm ³ ) of the particles, and Dm is the maximum diameter (μm) of the projection surface.

(3) Intrinsic viscosity From the solution viscosity measured at 25 ° C in orthochlorophenol, the value calculated by the following formula is used. That is,
ηsp / C = [η] + K [η] ² · C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer 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 were measured using an Ostwald viscometer. The unit is indicated by [dl / g].

  If there is an insoluble matter in the solution in which the measurement sample is dissolved, the solution is filtered and the weight of the filtrate is measured, and the value obtained by subtracting the weight of the filtrate from the measurement sample weight is measured as the measurement sample weight. .

(4) Film Lamination Thickness Using a transmission electron microscope (TEM; H-600 type manufactured by Hitachi, Ltd.), the cross section of the film is observed with an ultrathin section (RuO ₄ staining) at an acceleration voltage of 100 kV. The total thickness is obtained from the entire cross section. Regarding the lamination thickness, the depth from the surface from the deepest point of the particles observed at the interface, that is, the thickness of the lamination is obtained. The magnification may be appropriately set depending on the total thickness and the layer thickness of the film to be measured. In general, 1000 times is appropriate for measuring the total thickness, and 10,000 to 100,000 times is appropriate for measuring the laminated thickness. In order to presume at what magnification the particle image should be obtained in order to discriminate the laminated interface, such as when there are few particles, it is assumed from the distribution (mapping) of elements in the cross section by SEM-XMA of the cross section It is efficient to estimate the stack thickness and determine the set magnification in TEM.

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

(6) The number of large protrusions and the height are measured under a measurement condition of (I) using a three-dimensional structural analysis measuring instrument (New View 7300 manufactured by Zygo) to obtain a differential interference image. In the obtained image, the number of protrusions satisfying the criterion (II) is counted as a large protrusion, and the value converted per 5.0 mm ^{2 is} defined as the number of large protrusions. Further, the height of the protrusion satisfying the criterion (II) is set as the height of the large protrusion. The above measurement is performed 5 times, and the average value is defined as the number of large protrusions.
(I) Measurement conditions Magnification: 50 times Measurement area: width 0.98 mm, length 5.25 mm
(Measurement of 1 field of view 140 μm × 105 μm is performed for 350 fields of view with 7 fields in the width direction and 50 fields in the length direction.)
Camera Mode: 640x480 210Hz
Scan Length: 10 μm
Min Mod: 15.00%
Min Area Size: 7
Film Min Mod: 4%
(II) Selection criteria Reference Band: 600 nm
Area: 0.25 μm ² or more.

(7) Number of coarse protrusions Measured in the same manner as in (6), and protrusions having a reference band of 600 nm and an area of less than 0.25 μm ² were measured as coarse protrusions.

(8) Application characteristics of release layer A coating solution prepared by adjusting the cross-linking primer layer (trade name BY24-846 manufactured by Toray Dow Corning Silicone Co., Ltd.) to a solid content of 1% is applied to the film roll and dried. It is coated with a gravure coater so that the coating thickness after drying is 0.1 μm, and is dried and cured at 100 ° C. for 20 seconds. Within 1 hour, 100 parts by weight of addition reaction type silicone resin (trade name LTC750A manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by weight of platinum catalyst (trade name SRX212 manufactured by Toray Dow Corning Silicone Co., Ltd.) The coating liquid adjusted to a solid content of 5% by mass is applied by gravure coating so that the coating thickness after drying is 0.1 μm, dried and cured at 120 ° C. for 30 seconds, and then taken up to obtain a release film.
At this time, the application state of the release layer is evaluated by visually observing an area of 1 m ² under a 1000 lux fluorescent lamp.

  S: There are no spots at the coating end, the coating is uniformly applied, and there is no coating omission.

A: The film flutters at the time of application, and there are spots at the application end, but there is no omission. B: There are large spots at the application end. And / or coating omission.

(9) Coating property of ceramic slurry 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 having 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 (weight 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 applied and dried by a die coater on the release film obtained in the examples so that the thickness after drying becomes 2 μm, and wound to obtain a green sheet.

  The green sheet wound up as described above is visually observed in a state where the green sheet is unrolled and not peeled off from the release film, and the presence or absence of pinholes and the coating state of the sheet surface and edges are confirmed. The area to be observed is 300 mm wide and 500 mm long.

a. Presence / absence of pinhole The green sheet molded on the release film is observed from the back with a 1000 lux backlight unit, and the state of the pinhole due to missing coating is observed.

  S: No pinhole or dent.

A: There are no pinholes and 3 or less dents are recognized. B: There are pinholes or 4 or more dents.

b. Application state of sheet surface / edge part About the green sheet molded on the release film, the surface of the sheet is visually observed while illuminating with 1000 lux illumination at an angle of 45 degrees from the front.

  S: Circular marks (transfer marks) are not recognized on the sheet surface.

  A: There are slight circular marks (transfer marks) on the sheet surface.

  B: There are clearly circular marks (transfer marks) on the sheet surface.

(10) Green sheet peeling characteristics After forming an internal electrode pattern in the following steps, punching out and laminating the green sheets, the characteristics are evaluated when peeling is performed.

a. Formation of internal electrode pattern 44.6 parts by weight of Ni particles, 52 parts by weight of terpineol, 3 parts by weight of ethyl cellulose, and 0.4 parts by weight of benzotriazole are kneaded and slurried to obtain a paint for the internal electrode layer. . The internal electrode layer coating material was applied on the green sheet in a predetermined pattern by screen printing to obtain a ceramic green sheet having an internal electrode pattern. The drying temperature is 90 ° C. and the drying time is 5 minutes.

b. Punching of green sheet A ceramic green sheet formed on the above-described release film and provided with an internal electrode pattern is fed out, and 100 green sheets are cut and punched on the release film. A rotary round blade cutter is used for cutting. At this time, the cutting depth of the rotary round blade cutter for cutting the green sheet is set to the thickness of the green sheet plus 2 μm to 3 μm.

c. Green sheet lamination characteristic and peeling characteristic evaluation The green sheet after being punched on the release film is laminated. For the lamination, the green sheet is conveyed while being held on the release film, the green sheet is thermocompression bonded to the laminate, and then the release film is peeled off. This operation is repeated for 100 sheets to obtain a ceramic laminate. The lamination state at this time is visually confirmed, and the green sheet lamination characteristics are evaluated according to the following criteria.

  S: At the time of peeling after sheet lamination, green sheet peeling failure does not occur, and there is no air or foreign matter biting, and the layers are laminated well.

  A: The thermocompression bonding is slightly non-uniform when the sheets are laminated, there is no air biting, and the peeled state is within an allowable range, but the peeled state is occasionally unstable.

  B: Peeling failure occurs during sheet lamination, and the sheet is torn.

[Example 1]
-Preparation of polyester pellets (Preparation of polyester resin composition A)
Esterification reaction is carried out while distilling water at 255 ° C. with 86.5 parts by weight of terephthalic acid and 37.1 parts by weight of ethylene glycol. After completion of the esterification reaction, 0.02 part by weight of trimethyl phosphoric acid, 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. The polycondensation reaction was carried out by heating up to 0 ° C. to obtain polyester pellets having an intrinsic viscosity of 0.63 dl / g.

(Preparation of polyester resin composition B and polyester resin composition C)
In the production of polyester in the same manner as described above, an aqueous slurry of divinylbenzene / styrene copolymer crosslinked particles having a volume average particle size of 0.3 μm and a volume shape factor f = 0.51 obtained by a method of adsorbing a monomer is used as described above. A master containing 2% by weight of divinylbenzene / styrene copolymer crosslinked particles having a volume average particle size of 0.3 μm with respect to the polyester, which is contained in homopolyester pellets substantially free of particles using a vent type biaxial kneader. A pellet is obtained (polyester resin composition B).

  Further, in the production of polyester in the same manner as described above, an aqueous slurry of divinylbenzene / styrene copolymer crosslinked particles having a volume average particle size of 0.8 μm and a volume shape factor f = 0.51 obtained by a method of adsorbing a monomer, The homopolyester pellet containing substantially no particles is contained using a vented twin-screw kneader, and 1% by weight of divinylbenzene / styrene copolymer crosslinked particles having a volume average particle size of 0.8 μm is 1% by weight based on the polyester. The containing master pellet is obtained (polyester resin composition C).

(Preparation of polyester resin composition D)
In the production of polyester in the same manner as described above, after transesterification, the volume average particle size 0.2 μm, the volume shape factor f = 0.51, the volume average particle size 0.06 μm, the volume shape factor f = 0.51, the Mohs hardness No. 7 spherical silica was added and a polycondensation reaction was performed to obtain silica-containing master pellets containing 1% by weight of the particles with respect to the polyester (polyester resin composition D). The spherical silica used in the polyester resin composition D is obtained by adding a mixed solution of ethanol, pure water, and ammonia water as a basic catalyst to this mixed solution while stirring the mixed solution of ethanol and ethyl silicate. The obtained reaction solution was stirred to carry out a hydrolysis reaction of ethyl silicate and a polycondensation reaction of this hydrolysis product, and then stirred after the reaction to obtain monodispersed silica particles.

(Preparation of polyester resin composition E)
In addition, after producing the polyester resin composition A, after transesterification, 1% by weight of calcium carbonate having a volume average particle diameter of 1.1 μm and a Mohs hardness of 3 prepared by the carbon dioxide method is added to the polyester to contain calcium carbonate-containing master pellets. Got.

  On the other hand, the recovered raw material A was obtained by recovering the film after producing the film of Example 1 below and pelletizing it. The ratio described below is expressed as a weight ratio (% by weight) to the weight of each layer.

A layer thickness and composition A layer thickness (μm): 28.0
Polyester resin composition A: 95.0
Polyester resin composition B: 5.0
B layer thickness and composition B layer thickness (μm): 3.0
Polyester resin composition A: 40.0
Polyester resin composition C: 10.0
Polyester resin composition E: 50.0
(2) Preparation of polyester pellets The polyester pellets to be supplied to the extruders of the respective layers A and B are prepared at the following ratio. In addition, the ratio described below is a weight ratio (unit: weight%) with respect to the polyester pellet which comprises each layer.

A layer polyester resin composition A: 95
Polyester resin composition B: 5
B layer polyester resin composition A: 40
Polyester resin composition C: 10
Polyester resin composition E: 50.

(3) Manufacture of biaxially oriented polyester film After the raw materials prepared for each layer described above were stirred in a blender, the raw materials for layer A were fed to the twin-screw extruder with a vent for layer A. 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. After melt extrusion at 275 ° C. and filtration with a high-accuracy filter that collects 95% or more of foreign matters of 3 μm or more, they are joined and laminated by a rectangular two-layer joining block. did. Thereafter, the film is wound around a casting drum having a surface temperature of 25 ° C. by using an electrostatic application casting method on a cooling roll through a slit die maintained at 285 ° C., and solidified by cooling to obtain an unstretched laminated film.

  The unstretched laminated film was sequentially stretched (longitudinal direction and width direction). First, the film was stretched in the longitudinal direction and conveyed with a Teflon (registered trademark) roll at 105 ° C., and then heated in the longitudinal direction at 110 ° C. while being heated by an infrared heater with an output of 11.0 kw for 0.08 seconds. Double stretching is performed to obtain a uniaxially stretched film.

  This uniaxially stretched film was stretched 4.2 times at 100 ° C. in the transverse direction in the stenter, then heat-set at 230 ° C., relaxed by 3.2% in the width direction, and cooled in the conveying step. The edge is wound up and cut to obtain an intermediate product of a biaxially stretched film having a thickness of 31 μm. This intermediate product is slit with a slitter to obtain a roll of a biaxially stretched film having a thickness of 31 μm. The results of measuring the lamination thickness, surface roughness, large protrusions, and coarse protrusions of this biaxially stretched film are shown in the table. The layer thickness was A layer: 28.0 μm and B layer: 3.0 μm.

(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. Is applied / dried, applied with a gravure coater so that the applied thickness after drying is 0.1 μm, and dried and cured at 100 ° C. for 20 seconds. Within 1 hour, 100 parts by weight of addition reaction type silicone resin (trade name LTC750A manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by weight of platinum catalyst (trade name SRX212 manufactured by Toray Dow Corning Silicone Co., Ltd.) The coating liquid adjusted to a solid content of 5% by mass is applied by gravure coating so that the coating thickness after drying is 0.1 μm, dried and cured at 120 ° C. for 30 seconds, and then taken up to obtain a release film.
The obtained release film was evaluated for ceramic slurry coating characteristics and green sheet peeling characteristics.

[Example 2]
In the same layer configuration and formulation as in Example 1, the longitudinal stretching infrared heater output was 12.0 kW, the longitudinal stretching ratio was 3.6 times, the infrared heater treatment time was 0.09 seconds, the transverse stretching ratio was 4.6 times, A biaxially oriented polyester film is obtained under the same film forming conditions as in Example 1 except that the relaxation rate is 2.6%. The release layer coating property, slurry coating property, and green sheet peeling property were also good.

[Example 3]
A biaxially oriented polyester film is obtained under the same film forming conditions as in Example 2 except that in the same layer configuration and formulation as in Example 1, the longitudinal draw ratio was 3.8 times. The release layer coating property, slurry coating property, and green sheet peeling property were also good.

[Example 4]
A biaxially oriented polyester film is obtained under the same film forming conditions as in Example 2 except that in the same layer configuration and formulation as in Example 1, the longitudinally stretched infrared heater output is 10.0 kW. The release layer coating property, slurry coating property, and green sheet peeling property were also good.

[Example 5]
A biaxially oriented polyester film is obtained under the same conditions as in Example 2 with different three-layer configuration (A layer / intermediate layer / B layer).

  The polyester pellets to be fed to the extruder for each of the A layer, the intermediate layer, and the B layer are prepared in the following ratio. In addition, the ratio described below is a weight ratio (unit: weight%) with respect to the polyester pellet which comprises each layer.

Layer A polyester resin composition A: 97
Polyester resin composition D: 3
Intermediate layer polyester resin composition A: 60
Collected raw material A: 40
B layer polyester resin composition A: 45
Polyester resin composition B: 5
Polyester resin composition E: 50.
The release layer coating property, slurry coating property, and green sheet peeling property were also good.

[Comparative Example 1]
A biaxially oriented polyester film was obtained under the same film forming conditions as in Example 1 except that in the same layer configuration and formulation as in Example 1, the output of the longitudinally stretched infrared heater was 9.5 kw. Although there was no problem in the release layer coating, pinholes were found in the slurry coating. Green sheet release characteristics do not cause problems.

[Comparative Example 2]
The polyester pellets supplied to the extruder for the A layer are changed at the following ratios, and a biaxially oriented polyester film is obtained under the same film forming conditions as in Example 1 except that the longitudinal stretching infrared heater output is 9.5 kw. . In addition, the ratio described below is a weight ratio (unit: weight%) with respect to the polyester pellet which comprises each layer.

Layer A polyester resin composition A: 97
Polyester resin composition B: 3
Although there was no problem in the release layer coating, pinholes were found in the slurry coating. The green sheet peeling property is A because the peeling state of the sheet may not be stable.

[Comparative Example 3]
The polyester pellets supplied to the extruder for layer A with the same layer structure and formulation as in Example 1 are polyester A only, and the layer A is a layer containing substantially no particles. Although the number of large protrusions is 0, the roughness exceeds the scope of the present application, and the sheet is broken by peeling, so the evaluation is B.

[Comparative Example 4]
A biaxially oriented polyester film is obtained under the same film forming conditions as in Example 1 except that in the same layer configuration and formulation as in Example 1, the longitudinal draw ratio was changed to 3.3 times. Although there was no problem in the release layer application, pinholes were found in the slurry application. Green sheet release characteristics do not cause problems.

[Comparative Example 5]
A biaxially oriented polyester film is obtained under the same film forming conditions as in Example 1 except that in the same layer configuration and formulation as in Example 1, the longitudinal draw ratio is 3.6 times and the stretched infrared heater output is 14 kW. Although there was no problem in the release layer application, pinholes were found in the slurry application. Since green sheet peeling characteristics are not stable, it is set to A.

[Comparative Example 6]
In the same layer configuration and formulation as in Example 1, the polyester pellets supplied to the extruder for layer A are changed and mixed at the following ratio. In addition, the ratio described below is a weight ratio (unit: weight%) with respect to the polyester pellet which comprises each layer.

A layer polyester resin composition A: 80
Polyester resin composition B: 20
A biaxially oriented polyester film is obtained under the same film forming conditions as in Example 1. The roughness Ra (A) is 20 nm, there are pinholes after slurry application, and the peeling is not stable and the sheet is torn, so the evaluation is B.

[Comparative Example 7]
Under the same conditions as in Comparative Example 1, the additive particles in the B layer were changed to particles having a smaller particle size. Since there is a pinhole after slurry application, the evaluation is B.

[Comparative Example 8]
When the additive particles are adjusted in order to obtain a smooth film in both the A layer and the B layer, and the film forming conditions are the same as in Example 1, the film sometimes meanders when the release layer is applied, resulting in application spots A, Since there is a slight dent in the transfer inspection and the sheet is torn by peeling, the evaluation is B.

[Comparative Example 9]
Under the same conditions as in Example 1, the longitudinal stretching temperature was changed to 90 ° C. Since there is a pinhole after slurry application, the evaluation is B.

  The biaxially stretched polyester film of the present invention has good peeling characteristics, and particularly has very little variation in peeling. Therefore, it can be suitably used for a release film used for supporting green sheet molding in a process for producing a multilayer ceramic capacitor. The biaxially oriented polyester film for mold release of the present invention is excellent in coating properties of ceramic slurry when forming a thin green sheet, even if the green sheets constituting a highly smooth ceramic capacitor are laminated in a thin film and multilayer. The release characteristics of the film become uniform.

Claims (6)

A biaxially oriented polyester film for mold release that satisfies the following (1) to (3).
(1) The surface roughness SRa (A) of one surface (this surface is the A surface) is 7.0 nm or more and less than 15.0 nm.
(2) The surface roughness SRa (B) of the surface opposite to the A surface (this surface is defined as the B surface) is more than 30 nm and less than 50 nm.
(3) The number of large protrusions present on the A surface is 10 / 5.0 mm ² or more and 20 / 5.0 mm ² or less, and the heights of the large protrusions existing on the A surface are all 800 nm or less. It is. (The number and height of the large protrusions are determined by the following measurement method.)
How to measure the number and height of large protrusions:
Using a three-dimensional structural analysis measuring instrument (New View 7300 manufactured by Zygo), measurement is performed under the measurement conditions (I) to obtain a differential interference image. In the obtained image, the number of protrusions satisfying the criterion (II) is counted as a large protrusion, and the value converted per 5.0 mm ^{2 is} defined as the number of large protrusions. Further, the height of the protrusion satisfying the criterion (II) is set as the height of the large protrusion. The above measurement is performed 5 times, and the average value is defined as the number of large protrusions.
(I) Measurement conditions Magnification: 50 times Measurement area: width 0.98 mm, length 5.25 mm
(Measurement of 1 field of view 140 μm × 105 μm is performed for 350 fields of view with 7 fields in the width direction and 50 fields in the length direction.)
Camera Mode: 640x480 210Hz
Scan Length: 10 μm
Min Mod: 15.00%
Min Area Size: 7
Film Min Mod: 4%
(II) Selection criteria Reference Band: 600 nm
Area: 0.25 μm ² or more.   The biaxially oriented polyester film for release according to claim 1, wherein the polyester film is a laminated polyester film composed of at least two layers. A laminated polyester film comprising three layers, the thickness of the middle-layer, releasing biaxially oriented polyester according to claim 1 or 2, characterized in that on the whole the film is less than 95% more than 25% the film.   The biaxially oriented polyester film for mold release according to any one of claims 1 to 3, wherein the biaxially oriented polyester film is used for supporting green sheet molding in a process for producing a multilayer ceramic capacitor. The manufacturing method of the biaxially-oriented polyester film for mold release in any one of Claims 1-4 including the process shown to following (4).
(4) The step of stretching the polyester film includes a step of heating the film with an infrared heater, the output of the infrared heater is 10 kw or more and less than 13 kw, and the heating time is 0.05 second or more and less than 0.3 second There is. The manufacturing method of the biaxially-oriented polyester film for mold release of Claim 5 including the process shown to following (5)-(8).
(5) A step of stretching an unstretched polyester film in the longitudinal direction at a stretch ratio of 3.5 to 3.8 times to obtain a uniaxially oriented polyester film.
(6) In the step of stretching the unstretched polyester film in the longitudinal direction, the step (4) is included.
(7) A step of stretching the uniaxially oriented polyester film obtained in the step (5) in the width direction to obtain a biaxially oriented polyester film.
(8) Including a step of relaxing 0 to 10% in the width direction while heat-treating the biaxially oriented polyester film obtained in the step of (7) at 205 to 240 ° C.