JP2008239843A - Polyester film for mold release - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for mold release, which can form molded articles suitable for downsizing the articles and good in processing characteristics and qualities. <P>SOLUTION: This polyester film for mold release is characterized by containing inactive particles having an average primary particle diameter of 600 to 1,500 nm, and having a center line average roughness SRa of 25 to 35 nm on at least one side surface, a ten point average roughness SRz of ≤1,000 nm, surface protrusions having sizes of 300 nm to <700 nm at a rate of ≥200 protrusions/mm<SP>2</SP>, and surface protrusions having sizes of ≥700 nm at a rate of ≤10 protrusions/mm<SP>2</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to various release polyester films. Specifically, for green sheets, liquid crystal polarizing plates and photoresists used in the production of ceramic capacitors, an epoxy resin or the like is coated on the polyester film. The present invention relates to various release films suitable for multilayer substrates produced by coating.

Conventionally, a release film is formed by applying a resin layer having a releasability, such as a silicone resin or an epoxy resin, using a polyester film as a base material. In particular, it is used for various release applications such as green sheet production, liquid crystal polarizing plate release, liquid crystal protective film release, photoresist, and multilayer substrate. In a polyester film, in order to improve processability, for example, slipperiness and winding characteristics, an appropriate amount of particles is generally blended to form various protrusions on the film surface. Furthermore, in order to ensure the film physical property which can endure processing, it forms into a film by biaxial stretching.
JP-A-11-320524 JP 11-320764 A JP 2001-323079 A JP 2004-323766 A

    However, with the recent refinement of various applications, the release film used has been required to have uniform quality without any fine defects. The quality of the molded product formed from the release film depends on the accuracy and quality of the film used as the substrate, particularly the presence or absence of surface defects. In order to reduce the defects of the film, various improvements have been made, such as reducing the coarse protrusions on the film surface, but it has not been able to sufficiently meet market demands such as downsizing and higher performance.

  In particular, process films used to manufacture ceramic green sheets used for ceramic capacitors and multilayer inductor elements require thinning of the components that make up the recent demands for smaller and lighter electronic devices. It has become. In order to manufacture a ceramic capacitor, an organic solvent slurry containing a high dielectric constant ceramic powder and a binder is applied onto a polyester film and dried to produce a ceramic green sheet. Next, a conductive pattern is formed by screen printing or the like using a conductor paste, and the ceramic green sheet is peeled off. A method is used in which a large number of printed ceramic green sheets are laminated in a predetermined order, and after thermocompression bonding, cut into a predetermined chip, followed by firing and sintering. In such a process, as described above, a ceramic green sheet having a small thickness is required due to a demand for miniaturization. When the thickness of the green sheet is reduced, the polyester film used as the process film is also required to have processing characteristics and excellent surface smoothness. Various studies have been made to reduce the thickness of ceramic green sheets, but it is not possible to reduce the thickness of the ceramic green sheet while maintaining the processing characteristics only by defining the number of particles below a certain number. It was.

    As a result of diligent investigations in view of the above circumstances, the present inventors have found that, as in the prior art, a film that causes problems such as slurry repelling or pinhole generation during ceramic slurry coating, and green sheet breakage during green sheet peeling. In addition to the reduction of coarse protrusions on the surface, it was possible to reduce the film surface roughness while maintaining the processing characteristics by arranging particles on the film surface. Thereby, it discovered that it was suitable as a release film requested | required for size reduction, and came to this invention.

That is, the present invention contains inert particles having an average primary particle size of 600 to 1000 nm, the center line average roughness SRa of at least one surface is 25 to 35 nm, and the ten-point average roughness SRz is 1000 nm or less. A polyester film for release having a number of surface protrusions of 300 nm or more and less than 700 nm of 200 / mm ² or more and a number of surface protrusions of 700 nm or more of 10 / mm ² or less.

  By this invention, the polyester film suitable as a base material for mold release which can shape | mold the molded object with a favorable processing characteristic and good quality suitable for size reduction is obtained. By using this film, it has become possible to provide a release film capable of forming a thin film green sheet having a thickness of 3 μm or less, which was not possible conventionally as a thickness of the ceramic green sheet.

  Hereinafter, the present invention will be described in detail.

    The polyester film in the present invention is not particularly limited as long as it is a polyester that becomes a high-strength film by molecular orientation, but is preferably mainly composed of polyethylene terephthalate and polyethylene-2,6-naphthalate. Particularly preferred is polyethylene terephthalate which is superior in price. Examples of polyester copolymer components other than ethylene terephthalate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, and 1,4-cyclohexanedimethanol, adipic acid, sebacic acid, and phthalate. Dicarboxylic components such as acid, isophthalic acid and 5-sodium sulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, and p-oxyethoxybenzoic acid are used within the range that does not impair the intended film properties. it can.

  The polyester can be produced by a known method, and the intrinsic viscosity is 0.4 to 0.9, preferably 0.5 to 0.7, and more preferably 0.55 to 0.65.

  The biaxially oriented polyester film of the present invention is a laminated film comprising at least a polyester A layer and a polyester B layer. Although it may be A / B which is two layers or three layers of A / C / B having an intermediate layer, a two-layer structure is advantageous from the simplicity of the manufacturing process. On the other hand, in the case of a three-layer structure, the amount of added particles in the laminated part is controlled, so that the inner layer part does not adversely affect the characteristics of the film surface. It is possible to obtain a cost advantage by using a mixture of recycled materials in the film forming process in a timely manner. Moreover, as long as the gist of the present invention is not exceeded, it is not limited to these, and may be a multilayer of four layers or more.

The film of the present invention has a center line roughness SRa of at least one surface of 25 to 35 nm, a ten-point average roughness SRz of 1000 nm or less, and the number of surface protrusions of 300 nm or more and less than 700 nm is 200 pieces / mm ² or more and 700 nm or more. The number of surface protrusions is 10 pieces / mm ² or less, and when it is a laminated film, it contains a specific amount of specific inert particles in the A layer and / or B layer in the surface layer. Can be achieved. Here, SRa and SRz are measured using a three-dimensional fine surface shape measuring instrument (ET-350K manufactured by Kosaka Manufacturing Co., Ltd.), and are obtained from the obtained surface profile curve according to JIS B0601.

  The total thickness of the film of the present invention is preferably 15 to 50 μm, more preferably 25 to 40 μm. In the case of two layers, the B layer in A / B and the three layers having an intermediate layer, the laminated thickness of A and B in A / C / B is 0.3 to 3 μm, preferably 0.8 to The thickness is 2.5 μm, more preferably 0.8 to 2 μm. If the laminated thickness is less than 0.3, the contained particles may fall off in the laminated part. On the other hand, if the laminated thickness exceeds 3 μm, the uniformity of the formed protrusions based on the laminated part-containing particles may be impaired. It is not preferable.

  The surface roughness characteristics of the film can be achieved by containing fine inert particles in the film and controlling the particle size and content of the inert particles. In the layer A, the inert particles having an average particle diameter of preferably 0.5 to 2.0 μm, more preferably 0.8 to 1.3 μm are preferably 0.05 to 0.8% by weight, more preferably 0.3 to It is desirable to contain 0.6% by weight. On the other hand, the B layer can be achieved by containing 0.3 to 0.6% by weight of inert particles having an average particle size of 0.5 to 2.0 μm, preferably 0.8 to 1.3 μm.

  One kind or two or more kinds of particles may be contained, but in the B layer, in particular, fine inert particles I and inert particles II having a particle size larger than the inert particles I are used in combination. Is particularly preferred. 0.05 to 0.2% by weight of inert particles I having an average particle size of 0.2 to 0.4 μm and an average particle size of 0.5 to 2.0 μm, preferably 0.8 to 1.3 μm It can be preferably achieved when 0.05 to 0.8% by weight, preferably 0.3 to 0.6% by weight of inert particles II are contained in combination.

The inert particles I and the inert particles II may be different types of particles or the same type of particles. Further, the inert particles are inorganic particles such as spherical silica, aluminum silicate, titanium dioxide, calcium carbonate, and other organic polymer particles include crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked particles. Styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, melamine resin particles and the like are preferable. For any of the particles, the particle shape and particle size distribution are preferably uniform, particularly the particle shape is preferably close to a sphere, and the volume shape factor is preferably f = 0.3 to π / 6, more preferably. Is f = 0.4-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. In addition to the particle size distribution of inert particles I, which are small particles, even when used as inert particles I and II, which are close to true spheres and have a very uniform particle size distribution and different particle sizes, A particle size distribution having a double existence peak due to the inert particles II that are particles can be formed, which is preferable in terms of film surface protrusion formation.

  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.

  If necessary, an average primary particle size of 0.005 to 0.10 μm, preferably 0.01 to 0.05 μm of α-type alumina, γ-type alumina, δ-type alumina, θ-type alumina, from the viewpoint of reinforcing the background, Inactive particles selected from zirconia, silica, titanium particles, and the like may be contained within a range that does not affect the formation of surface protrusions.

  In the polyester film of the present invention, the sum of the breaking strengths in the longitudinal direction and the transverse direction is preferably 400 to 600 MPa, and more preferably 520 to 580 MPa. Further, the breaking strength in the width direction is preferably equal to or more than the breaking strength in the longitudinal direction, the difference is 0 to 100 MPa, and the difference is more preferably 0 to 70 MPa.

  Further, the breaking elongation is 80 to 220%, preferably 90 to 190%. Further, the breaking elongation in the longitudinal direction is preferably equal to or greater than the breaking elongation in the transverse direction, and the difference is 0 to 70%. More preferably, the longitudinal elongation at break is 150 to 190%, the lateral elongation at break is 90 to 170%, and the longitudinal elongation at break is 10 to 70% larger than the lateral elongation. More preferred is the case.

  In the polyester film of the present invention, the thickness variation in the longitudinal direction of the film is preferably 2 μm or less, more preferably 1.4 μm or less. Conventionally, reducing the thickness unevenness of the film has been a problem in manufacturing the film, but it is applied to the release film of the present invention, particularly to the release film applied to the manufacture of the thin film ceramic capacitor. In order to reduce the thickness of the green sheet, it is preferable to set the thickness variation in the longitudinal direction within the above range.

The polyester film in the present invention is substantially free of coarse protrusions having a height of 0.81 μm or more present on the film surface, and is preferably 1 piece / 100 cm ² or less. If the number of coarse protrusions exceeds the above-mentioned value, it is not preferable because application unevenness and pinhole-like application omission defects may occur when a release agent is applied.

  In the polyester film according to the present invention, it is necessary to appropriately control the heat shrinkage rate, and this can be achieved by appropriately adjusting by a known method such as relaxation treatment under the film forming conditions. The heat shrinkage rate at 150 ° C. is preferably 2.5% or less in the longitudinal direction and 1.5% or less in the width direction, 1.0 to 2.3% in the longitudinal direction, and 0.4 to 1.2% in the width direction. Is more preferable. Further, the heat shrinkage 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 0.0 to 0.6%.

  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. Also effective for the effect of the present invention is 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.

  The particle-containing master pellets prepared in this way and pellets substantially free of particles, etc., are mixed at a predetermined ratio, dried, then supplied to a known melt laminating extruder, and the polymer is filtered through a filter. .

  Further, since a very small foreign matter also becomes a film defect, it is effective to use a high-accuracy filter that collects 95% or more of a foreign matter of 5 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. In other words, 2 to 3 extruders, 2 to 3 layers of manifolds or merging blocks (for example, merging blocks having a rectangular merging section) are used to laminate in two or three layers, the sheet is extruded from the die, and the casting roll Cool to make an unstretched film. 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 may be simultaneous biaxial stretching or sequential biaxial stretching. In particular, since simultaneous biaxial stretching does not involve stretching by a roll, local heating unevenness on the film surface is suppressed, uniform quality is obtained, and at the place of contact between the film and the roll during roll stretching during stretching. In particular, it is possible to suppress the occurrence of dents due to the difference in speed and the transfer of minute scratches on the roll. In simultaneous biaxial stretching, an unstretched film is first stretched simultaneously at a stretching temperature of 80 to 130 ° C., preferably 85 to 110 ° C. in the longitudinal and width directions. When the stretching temperature is lower than 80 ° C., the film is easily broken, and when the stretching temperature is higher than 130 ° C., a sufficient strength cannot be obtained. Further, from the viewpoint of preventing stretching unevenness, the total stretching ratio in the longitudinal direction and the transverse direction is 4 to 20 times, preferably 6 to 15 times. If the total draw ratio is less than 4, it is difficult to obtain a necessary and sufficient strength as an object of the present invention. On the other hand, when the magnification is larger than 20 times, film breakage tends to occur, and it is difficult to produce a stable film. In order to obtain the required strength, the temperature is 140 to 200 ° C., preferably 160 to 190 ° C., and 1.02 to 1.5 times, preferably 1.05 to 1.2 times in the longitudinal direction and / or the width direction. It is preferable to perform the stretching again, and the total stretching ratio is 3 to 4.5 times in the longitudinal direction, preferably 3.2 to 4 times, and 3.2 to 5 times in the width direction, preferably 3.8 to 4. 5 times.

  Thereafter, heat setting is performed at 205 to 240 ° C., preferably 220 to 240 ° C., for 0.5 to 20 seconds, preferably 1 to 15 seconds. When the heat setting temperature is lower than 205 ° C., the crystallization of the film does not proceed, so that the target heat shrinkage rate and the like are difficult to stabilize. Moreover, in order to stabilize film physical properties, the temperature difference between the upper and lower sides of the film is 20 ° C. or less, preferably 10 ° C. or less, more preferably 5 ° C. or less. When the temperature difference between the upper and lower sides of the film is larger than 20 ° C., it is not preferable because the microplanarity tends to be deteriorated during the heat treatment. Thereafter, a relaxation treatment of 0.5 to 7.0% is performed in the longitudinal and / or width direction.

  In simultaneous biaxial stretching, unlike sequential biaxial stretching described later, the film is heated by high-temperature air. Therefore, only the film surface is locally heated and no sticking occurs, and the stretching method is preferable to sequential stretching. On the other hand, the simultaneous biaxial stretching is such that the zones from the initial stretching temperature of about 90 ° C. to the heat setting temperature of about 240 ° C. are all connected in the longitudinal direction. It is also a stretching method in which a temperature difference tends to occur in the vertical and width directions. A method for reducing the temperature difference is not particularly limited, but it is effective to provide a facility such as a shutter for suppressing a free flow of high-temperature air between zones having different temperatures. The gap between the film and the shutter is 1 to 250 mm, preferably 2 to 100 mm, and more preferably 3 to 50 mm. If the gap is less than 1 mm, the film will be in contact with the shutter and easily broken, which makes it difficult to manufacture and is not preferable. However, if it is larger than 250 mm, the variation in thermal characteristics becomes large, and the microplanarity tends to deteriorate, which is not preferable. In order to prevent the film and the shutter from coming into contact with each other, it is effective to appropriately adjust the wind speed blown from the nozzle.

  On the other hand, the polyester film of the present invention can also be produced using sequential stretching. The first longitudinal stretching is important, and the stretching temperature is 90 to 130 ° C, preferably 100 to 120 ° C. 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, which is not preferable. Further, from the viewpoint of preventing stretching unevenness and scratches, stretching is preferably performed in two or more stages, and the total magnification is 3 to 4.5 times, preferably 3.5 to 4.2 times in the length direction. It is 3.2 to 5 times, preferably 3.6 to 4.3 times in the width direction. In order to achieve the target breaking strength of the film, a timely magnification can be selected, but in order to increase the breaking strength in the width direction, it is more preferable to set the stretching ratio in the width direction higher than in the longitudinal direction. If the temperature and magnification range are out of this range, problems such as uneven stretching or film breakage are caused, and it is difficult to obtain a film characterized by the present invention. After re-longitudinal or transverse stretching, heat setting is performed at 205 to 240 ° C., preferably 210 to 230 ° C. for 0.5 to 20 seconds, preferably 1 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 heat shrinkage cannot be obtained.

  In sequential stretching, contact between the film and the roll is unavoidable during the stretching process, and the difference between the peripheral speed of the roll and the speed of the film is suppressed as much as possible, and the surface roughness of the stretching roll is easy to control. Non-stick silicone rolls are preferred. Although it is possible to use ceramics, Teflon (registered trademark) or metal rolls as in the prior art, only the film surface is locally heated, causing stickiness and causing scratches on the film surface. Yes, not preferred.

  Furthermore, the surface roughness Ra of the drawing roll is 0.005 to 1.0 μm, preferably 0.1 to 0.6 μm. When Ra is larger than 1.0 μm, unevenness on the roll surface during stretching is transferred to the film surface, which is not preferable. On the other hand, when it is smaller than 0.005 μm, the roll adheres to the film background, and the film is easily damaged by heat. It is not preferable. In order to control the surface roughness, it is effective to adjust the particle size of the abrasive and the number of times of polishing as appropriate. However, particularly with respect to the stretching roll, avoid the adhesion and accumulation of polyester degradation products and oligomers of concern. Therefore, frequent roll polishing is preferable.

  Further, the total contact time between the roll and the film in the stretching portion is 0.1 seconds or less, preferably 0.08 seconds or less, which is particularly effective in producing the film. When the contact time between the roll and the film is longer than 0.1 seconds, only the film surface is locally heated by the heat of the stretching roll, and in some cases, it may cause micro flatness deterioration at the time of heat load, The film may be scratched, which is not preferable. As a method for shortening the contact time, for example, it is effective to stretch the film in parallel between the nip rolls without winding the film around the stretching roll.

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

  The characteristic value measurement method and effect evaluation method of the present invention are as follows.

(1) 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 particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of SEM is appropriately selected from about 5000 to 20000 times depending on the particle size. The volume average diameter d is obtained by the following formula from the particle diameter and its volume fraction when the number of particles is changed to 5000 or more by changing the observation location. When two or more kinds of particles having different particle diameters were contained, the same measurement was performed for each particle to obtain the particle diameter.
d = Σ (di · Nvi)
Here, di is the particle size, and Nvi is the volume fraction.

  When the particles are significantly damaged by the plasma low-temperature ashing treatment method, the film cross section is observed at 3000 to 20000 times depending on the particle size using a transmission electron microscope (TEM). The section thickness of the TEM is about 100 nm, the location is changed, and 500 fields or more are measured, and the volume average diameter d is obtained from the above formula.

(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 was obtained by the formula.
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 equation was 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].

(4) Film Laminating Thickness The depth profile of the particle concentration is measured with XPS (X-ray photoelectron optical method), IR (infrared spectroscopy) or confocal microscope while etching from the surface. In the surface layer of the film laminated on one side, the particle concentration is low due to the air-resin interface called the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film laminated on one side of the present invention, the particle concentration once reached the maximum value at the depth [I] starts to decrease again. Based on this concentration distribution curve, the depth [II] (here, II> I), which is ½ of the maximum particle concentration, was defined as the lamination thickness. Furthermore, when inorganic particles etc. are contained, using a secondary ion mass spectrometer (SIMS), the concentration ratio of the element resulting from the highest concentration of the particles in the film and the carbon element of the polyester Using (M + / C +) as the particle concentration, analysis in the depth (thickness) direction from the surface of the layer (A) is performed. Then, the laminated thickness is obtained from the same method as described above.

(5) Breaking elongation and breaking strength In accordance with JIS C2151-1990, using an Instron type tensile testing machine (Orientec Co., Ltd. film strong elongation automatic measuring device “Tensilon” universal testing machine RTC-1210). It was measured. A sample film with a width of 10 mm is subjected to a tensile test under the conditions of 100 mm between test lengths and a pulling speed of 200 mm / min. The stress when the film is broken is obtained as the breaking strength, and the strain (elongation) when the film is broken. The elongation at break was determined. The measurement was performed at 23 ° C. and a humidity of 65% RH.

(6) Two lines are drawn on the surface of the heat shrinkage film so that the width is 10 mm and the measurement length is about 100 mm, and the distance between the two lines is accurately measured at 23 ° C., and this is defined as L0. This film sample was left in an oven at 100 ° C. and 150 ° C. for 30 minutes under a load of 1.5 g, and then the distance between the two lines was measured again at 23 ° C., and this was defined as L1. Shrinkage was determined.
Thermal contraction rate (%) = {(L0−L1) / L0] × 100
(7) Film surface roughness (SRa, SRz value), number of surface protrusions Measured using a three-dimensional fine surface shape measuring instrument (ET-350K, manufactured by Kosaka Manufacturing Co., Ltd.), and obtained from the obtained surface profile curve, JIS B0601 According to the above, the arithmetic average roughness SRa value and the ten-point average surface roughness SRz value were determined. The height of the protrusion was calculated based on the cut surface where the area ratio of the cut surface by the cut surface was 70%. With respect to the number of protrusions having a height of 0 nm or more measured under the above conditions, each was converted into pieces / mm ² in increments of 10 nm. 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.

(8) Number of coarse protrusions The number of coarse protrusions is the interference fringes generated by the coarse protrusions on the film surface, with two surfaces for measuring a 10 cm square film superimposed on each other, applied with an applied voltage and brought into close contact with electrostatic force. Estimate the height from The interference fringes were 0.270 μm for a single ring, and the number of coarse protrusions of a double ring of 0.540 μm and a triple ring of 0.810 μm or more was measured. As the light source, a halogen lamp provided with a 564 nm band pulse filter was used.

(9) Longitudinal thickness unevenness Using an Anritsu Electric Film Thickness Continuous Measuring Instrument, measure 15 m in the longitudinal direction, and record the difference between the maximum thickness and the minimum thickness as thickness unevenness (μm) from the recorded film thickness chart. It was measured. The measurement conditions are as follows. In addition, it is not restrict | limited to this apparatus, Other film thickness measuring apparatuses are also possible, and it is obtained by making the difference of the maximum value and minimum value of the film thickness of 15 m of longitudinal directions into thickness spots.
Configuration: K-306C wide range electronic micrometer, K-310C recorder, film feeder.
Film width: 45 mm, measuring length: 15 m, film feeding speed: 3 m / min detector: 3R ruby terminal, measuring force: 15 ± 5 g.

(10) Surface Roughness of Stretching Roll Using a surface roughness meter Surf Test 301 manufactured by Mitutoyo Co., Ltd., the center surface average roughness was measured at three points in the roll width direction at a cutoff of 0.25 mm. The average value was adopted.

Example 1
In dimethyl terephthalate (DMT), 1.9 moles of ethylene glycol and magnesium acetate tetrahydrate with respect to 1 mole of DMT is 0.05 parts by weight with respect to 100 parts by weight of DMT, and phosphoric acid is also 0.015 weight with respect to DMT. Part of the mixture was subjected to transesterification, followed by addition of 0.025 parts by weight of antimony trioxide to DMT, heating and heating to perform a polycondensation reaction by vacuuming, and containing substantially no particles, inherent viscosity 0.63 Homopolyester pellets were obtained.

Further, in producing the polyester in the same manner as described above, 1% calcium carbonate having an average particle diameter of 1.05 μm was added to the polyester after the ester exchange to obtain a master pellet containing calcium carbonate particles having an intrinsic viscosity of 0.6.
Similarly, after the transesterification, an aqueous slurry of divinylbenzene / styrene copolymer crosslinked particles having an average particle size of 0.3 μm and a volume shape factor f = 0.51 is added to the above-mentioned homopolyester pellets substantially free of particles. Master pellets containing 2% by weight of 0.3 μm divinylbenzene / styrene copolymer crosslinked particles with respect to the polyester were obtained even if contained using a bent type twin-screw kneader.

  Next, a master pellet containing calcium carbonate particles, a master pellet containing divinylbenzene / styrene copolymer crosslinked particles, and a homopolyester pellet containing substantially no particles are mixed, and divinylbenzene / styrene having a particle size of 0.3 μm is mixed. A polyester A containing 0.10% by weight of copolymerized crosslinked particles and 0.50% by weight of calcium carbonate having a particle size of 1.05 μm was prepared.

  Furthermore, the polyester film B is prepared by mixing 60% of the recovered film raw material mainly composed of the edge portion generated in the film forming process of the present invention and 40% of the homopolyester pellet containing substantially no particles. did.

  These polyesters A and B were each dried under reduced pressure at 160 ° C. for 8 hours, then supplied to separate extruders, melt-extruded at 275 ° C. and filtered with high precision, and then merged and laminated with a rectangular three-layer merge block. A three-layer laminate composed of A / polyester B / polyester A was used. Thereafter, the film was wound around a casting drum having a surface temperature of 25 ° C. on a cooling roll through a slit die maintained at 285 ° C. by using an electrostatic application casting method, and solidified by cooling to obtain an unstretched laminated film.

This unstretched film was stretched 3.80 times in the longitudinal direction, then stretched 3.93 times in the transverse direction under hot air at 110 ° C. with a stenter, and heat-treated at 230 ° C. with the stenter to obtain a thickness of 38 μm, A biaxially oriented polyester film having a polyester A layer thickness of 1.5 μm and a polyester B layer thickness of 35 μm was obtained. The evaluation results of the obtained film are shown in the table.
Comparative Examples 1-3
Similar to Example 1 except that the particle size and amount of particles added to layer A, and the amount of particles added to layer (B), and the total film thickness, layer (B) thickness, and stretching conditions are changed. Thus, a biaxially oriented polyester film was obtained. The evaluation results of the obtained film are shown in the table.

Claims (6)

Containing inert particles with an average primary particle size of 600-1500 nm,
The center line average roughness SRa of the surface of at least one surface is 25 to 35 nm,
Ten-point average roughness SRz is 1000 nm or less,
The number of surface protrusions of 300 nm or more and less than 700 nm is 200 / mm ² or more,
A release polyester film having a surface protrusion number of 700 nm or more of 10 pieces / mm ² or less. The polyester film for mold release according to claim 1, wherein the polyester film is manufactured by a sequential biaxial stretching method. The polyester film for mold release according to claim 1, wherein the sum of the breaking strengths in the longitudinal direction and the transverse direction is 400 to 600 MPa. The polyester film for mold release of Claim 1 containing the organic particle from which two types of average particle diameters differ at least on one side. The polyester film for mold release according to claim 1, wherein the number of coarse protrusions of 0.8 µm or more is 3 pieces / 100 cm ² or less. 2. The mold release according to claim 1, which has a laminate structure of two or more layers, and the ratio d / t of the average primary particle diameter d of the inert particles to the thickness t of the particle-containing layer is 0.05 or more and 2 or less. Polyester film.