JP2023095425A - Release biaxially oriented polypropylene film and release film - Google Patents

Abstract

To provide a release biaxially oriented polypropylene film that is excellent in rigidity and heat resistance, is easy to peel even if the film thickness is thinner than that of a conventional product, and scarcely causes wrinkles when a release agent is applied for coating.SOLUTION: Provided is a release biaxially oriented polypropylene film that satisfies the following (1) and (2). (1) In the azimuth angle dependence of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray diffraction measurement, the half width of the peak derived from the oriented crystal in the width direction is 26° or less. (2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) as determined by pulse NMR by the solid echo method is 7% or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a release biaxially oriented polypropylene film having excellent rigidity and heat resistance. More particularly, it relates to a release biaxially oriented polypropylene film that exhibits good flatness during release processing even if the film thickness is thinner than conventional products, and is suitable for use as a process release film with little unevenness in thickness.

A biaxially oriented polypropylene film has moisture resistance as well as necessary rigidity and heat resistance, and is therefore used in industrial applications such as packaging, mold release, and adhesive tape. In recent years, in consideration of the environment, release films have been required to be recyclable and to be reduced in volume by thinning. Therefore, it is essential to significantly improve the rigidity of polypropylene films. As a means to improve rigidity, the crystallinity and melting point of the polypropylene resin are improved by improving the catalyst and process technology during the polymerization of polypropylene resin, and the degree of orientation of the film is improved by increasing the draw ratio during the film production process. There was a technology to increase However, there is a problem that the heat resistance is lowered while the rigidity is increased, and there has been no biaxially oriented polypropylene film having sufficient rigidity and heat resistance.

In the manufacturing process of a biaxially oriented polypropylene film, after stretching in the width direction, the first heat treatment is performed while the film is relaxed at a temperature below the temperature during the width direction stretching, and in the second step, the heat treatment is performed at the temperature between the first step and the width direction stretching temperature. (for example, Patent Document 1) and a method for further stretching in the longitudinal direction after stretching in the width direction (for example, Patent Documents 2 and 3) have been proposed. However, the orientation of the film described in Patent Document 1 is low and the rigidity is not sufficient. Although the film described in Patent Document 2 is excellent in rigidity, it is inferior in heat resistance, and there is a problem that wrinkles are generated during mold release processing at 120° C. or higher. In addition, the film described in Patent Document 3 is sequentially biaxially stretched, and the film oriented in the width direction is re-stretched in the longitudinal direction. was low. Moreover, since the relaxation is performed in the width direction, the orientation in the width direction is low and the rigidity is not sufficient.

WO2016/182003 international publication JP 2013-177645 A JP-A-2001-40111

An object of the present invention is to solve the problems described above. That is, it relates to a release biaxially oriented polypropylene film that achieves both film rigidity and heat resistance at temperatures as high as 150°C. The object of the present invention is to solve the above-mentioned conventional problems and to reduce the film waste after use in order to reduce the environmental load. To provide a mold release polypropylene film which does not generate unevenness, has good flatness, and is suitable for a process mold release film with small unevenness in thickness.

The inventors of the present invention made intensive studies to achieve the above object, and as a result, arrived at the following inventions [1] to [10].
[1] A release biaxially oriented polypropylene film that satisfies the following (1) and (2).
(1) In the azimuth angle dependence of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray diffraction measurement, the half width of the peak derived from the oriented crystal in the width direction is 26° or less.
(2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) determined by pulse NMR by the solid echo method is 7% or less. is.
[2] The release biaxially oriented polypropylene film according to [1], which satisfies the following (3), (4) and (5).
(3) Thermal shrinkage at 150° C. is 10% or less in the longitudinal direction and 30% or less in the width direction.
(4) The stress at 5% elongation in the width direction at 23°C is 140 MPa or more.
(5) The thermal contraction rate (%) in the width direction at 150°C and the stress (MPa) at 5% elongation in the width direction at 23°C satisfy the following formulas.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 140
[3] The biaxially oriented polypropylene film for release according to [1] 1 or [2], wherein the biaxially oriented polypropylene film for release satisfies the following (6) and (7).
(6) The heat shrinkage at 120°C is 2.0% or less in the longitudinal direction and 10.0% or less in the width direction.
(7) The thermal shrinkage rate (%) in the width direction at 120°C and the tensile elastic modulus (GPa) in the width direction at 23°C satisfy the following formulas.
Tensile elastic modulus in the width direction at 23°C (GPa) ≥ Heat shrinkage rate in the width direction at 120°C (%) x 0.3 + 7.0
[4] The biaxially oriented polypropylene film for release has a refractive index Ny in the width direction of 1.5250 or more and a ΔNy of 0.0240 or more, according to any one of [1] to [3]. Biaxially oriented polypropylene film for mold release.
[5] The biaxially oriented polypropylene film for release according to any one of [1] to [4], wherein the biaxially oriented polypropylene film for release has a haze of 5.0% or less.
[6] The biaxially oriented polypropylene for release according to any one of [1] to [5], wherein the polypropylene resin constituting the biaxially oriented polypropylene film for release has a mesopentad fraction of 97.0% or more. the film.
[7] The release according to any one of [1] to [6], wherein the polypropylene resin constituting the biaxially oriented polypropylene film for release has a crystallization temperature of 105° C. or higher and a melting point of 160° C. or higher. Biaxially oriented polypropylene film for molds.
[8] The release biaxial according to any one of [1] to [7], wherein the polypropylene resin constituting the release biaxially oriented polypropylene film has a melt flow rate of 4.0 g/10 minutes or more. Oriented polypropylene film.
[9] The release film according to any one of [1] to [8], wherein the content of the polypropylene resin having a molecular weight of 100,000 or less in the release biaxially oriented polypropylene film is 35% by mass or more. Axially oriented polypropylene film.
[10] A release film obtained by laminating a release coating layer on at least one surface of the release biaxially oriented polypropylene film for release according to any one of [1] to [9].
[11] A laminated film comprising a biaxially oriented polypropylene film satisfying the following (1) and (2) and a release coating layer.
(1) In the azimuth angle dependence of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray diffraction measurement, the half width of the peak derived from the oriented crystal in the width direction is 26° or less.
(2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) determined by pulse NMR by the solid echo method is 7% or less. is.

TECHNICAL FIELD The present invention relates to a release biaxially oriented polypropylene film having excellent rigidity and heat resistance. More specifically, even if the film thickness is thinner than conventional products, it is a release biaxially oriented polypropylene film that has good flatness at the time of release processing, has small thickness unevenness, and is suitable for process release films. be.

Schematic illustration of component separation of the spin-spin relaxation time decay curve observed by ¹ H-pulse NMR. Graph comparing Examples and Comparative Examples with respect to F5 in the width direction and 150° C. heat shrinkage

The biaxially oriented polypropylene film for release of the present invention will be described in more detail below.
The release biaxially oriented polypropylene film of the present invention comprises a polypropylene resin composition containing a polypropylene resin as a main component. The "main component" means that the proportion of the polypropylene resin in the polypropylene resin composition is 90% by mass or more, more preferably 93% by mass or more, more preferably 95% by mass or more, and particularly preferably is 97% by mass or more.

(polypropylene resin)
The polypropylene resin used in the present invention may be a polypropylene homopolymer or a copolymer with ethylene and/or an α-olefin having 4 or more carbon atoms. A propylene homopolymer substantially free of ethylene and/or an α-olefin having 4 or more carbon atoms is preferred, and even if it contains ethylene and/or an α-olefin component having 4 or more carbon atoms, ethylene and/or The amount of α-olefin components having 4 or more carbon atoms is preferably 1 mol % or less, more preferably 0.5 mol % or less, still more preferably 0.3 mol % or less, and particularly preferably 0.3 mol % or less. It is 1 mol or less. Within the above range, the crystallinity tends to be improved. Examples of α-olefin components having 4 or more carbon atoms constituting such a copolymer include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methyl Pentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene and the like.
As the polypropylene resin, two or more different polypropylene homopolymers, copolymers with ethylene and/or α-olefins having 4 or more carbon atoms, and mixtures thereof can be used.

(Steric regularity)
The mesopentad fraction (hereinafter sometimes abbreviated as [mmmm]%), which is an index of the stereoregularity of the polypropylene resin used in the present invention, is preferably in the range of 97.0 to 99.9%. , More preferably in the range of 97.5 to 99.7%, more preferably in the range of 98.0 to 99.5%, and in the range of 98.5 to 99.3% Especially preferred.
When it is 97.0% or more, the crystallinity of the polypropylene resin is enhanced, the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, and rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, it is easy to reduce costs in terms of polypropylene production, and it becomes difficult to break during film formation. The mesopentad fraction is measured by a nuclear magnetic resonance method (so-called NMR method).
It is more preferably 99.5% or less. The mesopentad fraction is measured by a nuclear magnetic resonance method (so-called NMR method).
In order to make the mesopentad fraction of the polypropylene resin within the above range, a method of washing the obtained polypropylene resin powder with a solvent such as n-heptane, selection of the catalyst and / or co-catalyst, selection of the polypropylene resin composition A method of appropriately selecting components is preferably adopted.

(melting temperature)
The lower limit of the melting temperature (Tm) measured by DSC of the polypropylene resin constituting the biaxially oriented polypropylene film for release of the present invention is preferably 160°C, more preferably 161°C, and still more preferably 162°C. °C, more preferably 163°C, and even more preferably 164°C. When Tm is 160° C. or higher, rigidity and heat resistance at high temperatures are easily obtained. The upper limit of Tm is preferably 170°C, more preferably 169°C, even more preferably 168°C, still more preferably 167°C, and particularly preferably 166°C. If the Tm is 170° C. or less, it is easy to suppress cost increases in terms of polypropylene production, and it becomes difficult to break during film formation. The melting temperature can be further increased by adding a crystal nucleating agent to the polypropylene resin described above.
Tm is a sample of 1 to 10 mg packed in an aluminum pan, set in a differential scanning calorimeter (DSC), melted at 230 ° C. for 5 minutes under a nitrogen atmosphere, and scanned at a scanning speed of -10 ° C./min to 30 ° C. It is the main peak temperature of the endothermic peak associated with melting observed when the temperature is lowered, held for 5 minutes, and heated at a scanning rate of 10° C./min.

(crystallization temperature)
The lower limit of the crystallization temperature (Tc) measured by DSC of the polypropylene resin constituting the biaxially oriented polypropylene film for release of the present invention is 105°C, preferably 108°C, more preferably 110°C. be. When Tc is 105° C. or more, crystallization is likely to proceed in the width direction stretching and the subsequent cooling step, and rigidity and heat resistance at high temperatures are likely to be obtained. The upper limit of Tc is preferably 135°C, more preferably 133°C, still more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. is. When Tc is 135° C. or less, it is difficult to increase the cost of polypropylene production, and it is difficult to break during film formation. The crystallization temperature can be further increased by adding a crystal nucleating agent to the polypropylene resin described above.
Tc is observed when a sample of 1 to 10 mg is packed in an aluminum pan and set in a DSC, melted at 230 ° C. for 5 minutes under a nitrogen atmosphere, and cooled to 30 ° C. at a scanning speed of -10 ° C./min. is the main peak temperature of the exothermic peak

(melt flow rate)
The melt flow rate (MFR) of the polypropylene resin constituting the biaxially oriented polypropylene film for release of the present invention is measured according to JIS K 7210 (1995) condition M (230 ° C., 2.16 kgf). , preferably 4.0 to 30 g/10 min, more preferably 4.5 to 25 g/10 min, even more preferably 4.8 to 22 g/10 min, and 5.0 to 20 g/10 min. 10 minutes is particularly preferred, and 6.0 to 20 g/10 minutes is most preferred.
When the melt flow rate (MFR) of the polypropylene resin is 4.0 g/10 minutes or more, it is easy to obtain a releasing biaxially oriented polypropylene film with low thermal shrinkage.
Moreover, when the melt flow rate (MFR) of the polypropylene resin is 30 g/10 minutes or less, the film formability of the film is easily maintained.

From the viewpoint of film properties, the lower limit of the melt flow rate (MFR) (230 ° C., 2.16 kgf) of the polypropylene resin constituting the film is preferably 5.0 g / 10 minutes, more preferably 5.5 g / 10 minutes, It is more preferably 6.0 g/10 minutes, particularly preferably 6.3 g/10 minutes, and most preferably 6.5 g/10 minutes.
When the melt flow rate (MFR) of the polypropylene resin is 5.0 g/10 minutes or more, the amount of low-molecular weight components of the polypropylene resin constituting the film increases, so the width direction stretching step in the film forming step described later is performed. By adopting it, in addition to further promoting the oriented crystallization of the polypropylene resin and making it easier to increase the degree of crystallinity in the film, the entanglement between the polypropylene molecular chains in the amorphous portion is reduced, and the heat resistance is improved. It is easy to increase sexuality.
In order to keep the melt flow rate (MFR) of the polypropylene resin within the above range, it is preferable to adopt a method of controlling the average molecular weight and molecular weight distribution of the polypropylene resin.

That is, the lower limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve of the polypropylene resin constituting the film of the present invention is 35% by mass, preferably 38% by mass, more preferably 40% by mass, More preferably 41% by mass, particularly preferably 42% by mass.
The upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% by mass, more preferably 60% by mass, and still more preferably 58% by mass. When the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is 65% by mass or less, the film strength is less likely to decrease.
At this time, if a high-molecular-weight component with a long relaxation time or a long-chain branched component is included, the amount of the component with a molecular weight of 100,000 or less contained in the polypropylene resin can be easily adjusted without significantly changing the overall viscosity, thereby improving the rigidity. It is easy to improve the film formability without significantly affecting the heat shrinkage and heat shrinkage.

(Molecular weight distribution)
In the polypropylene resin used in the present invention, the lower limit of the weight average molecular weight (Mw) / number average molecular weight (Mn), which is an index of the breadth of the molecular weight distribution, is preferably 3.5, more preferably 4, and further 4.5 is preferred, and 5 is particularly preferred. The upper limit of Mw/Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20.
Mw/Mn can be obtained using gel permeation chromatography (GPC). When Mw/Mn is within the above range, it is easy to increase the amount of components having a molecular weight of 100,000 or less.

The molecular weight distribution of polypropylene resin can be determined by polymerizing components with different molecular weights in multiple stages in a series of plants, by blending components with different molecular weights offline using a kneader, or by blending catalysts with different performance. or by using a catalyst capable of realizing a desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC has a single peak in a GPC chart with the logarithm (logM) of the molecular weight (M) on the horizontal axis and the differential distribution value (weight fraction per logM) on the vertical axis. It may have a smooth molecular weight distribution, or may have a molecular weight distribution with multiple peaks or shoulders.

(Method of forming a biaxially oriented polypropylene film for mold release)
The release biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made of the polypropylene resin composition containing the polypropylene resin as a main component, and biaxially stretching the sheet. As the biaxial stretching method, it can be obtained by any of the inflation simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method, and the tenter sequential biaxial stretching method. It is preferable to employ an axial stretching method. In particular, it is preferable to stretch in the width direction after stretching in the longitudinal direction, but it is also possible to stretch in the longitudinal direction after stretching in the width direction.

Next, the method for producing the release biaxially oriented polypropylene film of the present invention will be described below, but the method is not necessarily limited to this. The release biaxially oriented polypropylene film of the present invention may be laminated with a layer having other functions on at least one side thereof. Lamination may be performed on one side or both sides. In such a case, the above-mentioned polypropylene resin composition may be used as the resin composition for the other layer and the center layer. Also, it may be different from the polypropylene resin composition described above.
The number of layers to be laminated may be 1 layer, 2 layers, or 3 layers or more per side, but 1 layer or 2 layers are preferable from the viewpoint of manufacturing. As a lamination method, for example, co-extrusion by a feed block system or a multi-manifold system is preferable. In particular, for the purpose of improving the workability of the release biaxially oriented polypropylene film, a heat-sealable resin layer can be laminated within a range that does not degrade the properties. In addition, one side or both sides can be subjected to corona treatment for imparting printability.

In the following, an example in the case of a single layer will be described in which the tenter sequential biaxial stretching method is employed.
First, a resin composition containing a polypropylene resin is heated and melted with a single-screw or twin-screw extruder, extruded into a sheet form from a T-die, grounded on a cooling roll, and solidified by cooling. For the purpose of promoting the solidification, it is preferable to further cool the sheet cooled by the chill roll by immersing it in a water tank or the like.

Then, the sheet is longitudinally stretched by two pairs of heated stretching rolls by increasing the number of rotations of the rear stretching rolls to obtain a uniaxially stretched film.

Subsequently, after preheating the uniaxially stretched film, it is stretched in the width direction at a specific temperature while gripping the ends of the film with a tenter type stretching machine to obtain a biaxially stretched film. This width direction stretching step will be described later in detail.

After the width direction stretching step is completed, the biaxially stretched film is heat-treated at a specific temperature to obtain a release biaxially oriented film. In the heat treatment step, the film may be relaxed in the width direction.

The biaxially oriented polypropylene film for release thus obtained can be subjected, for example, to a corona discharge treatment on at least one side, if necessary, and then wound up with a winder to obtain a film roll.

Each step will be described in detail below.
(Extrusion process)
First, a polypropylene resin composition containing polypropylene resin as the main component is heated and melted in a single-screw or twin-screw extruder at a temperature in the range of 200 ° C. to 300 ° C., and the sheet-shaped molten polypropylene resin composition coming out of the T die is extruded. , is brought into contact with a metal cooling roll to cool and solidify. The obtained unstretched sheet is preferably put into a water tank.
The temperature of the cooling roll, or the temperature of the cooling roll and the water tank, is preferably in the range of 10°C to Tc. If the transparency of the film is desired to be increased, the cooling roll is cooled and solidified in the temperature range of 10 to 50°C. is preferred. When the cooling temperature is 50°C or lower, the transparency of the unstretched sheet tends to be increased, and the cooling temperature is preferably 40°C or lower, more preferably 30°C or lower. In order to increase the degree of crystal orientation after sequential biaxial stretching, it may be preferable to set the cooling temperature to 40° C. or more, but as described above, a propylene homopolymer having a mesopentat fraction of 97.0% or more is used. In this case, the cooling temperature is preferably 40° C. or lower for facilitating the drawing in the next step and reducing thickness unevenness, and more preferably 30° C. or lower.
The thickness of the unstretched sheet is preferably 3500 μm or less in terms of cooling efficiency, more preferably 3000 μm or less, and can be appropriately adjusted according to the thickness of the film after successive biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition, the lip width of the T-die, and the like.

(Longitudinal stretching process)
The lower limit of the draw ratio in the longitudinal direction is preferably 3.5 times, more preferably 3.8 times, and particularly preferably 4.2 times. Within the above range, the strength can be easily increased, and the film thickness unevenness can be reduced.
The upper limit of the draw ratio in the longitudinal direction is preferably 7.0 times, more preferably 6.0 times, and particularly preferably 7 times. Within the above range, it is easy to stretch in the width direction in the width direction stretching step, and productivity is improved.
The lower limit of the longitudinal stretching temperature is preferably Tm-30°C, more preferably Tm-27°C, still more preferably Tm-25°C. When the thickness is in the above range, subsequent widthwise stretching becomes easier, and thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, still more preferably Tm-12°C. Within the above range, it is easy to reduce the heat shrinkage, and it is less likely that the film will be difficult to be stretched on stretching rolls, or that the quality will be reduced due to the increase in surface roughness.
The longitudinal stretching may be carried out in two or more stages using three or more pairs of stretching rolls.

(Preheating process)
Before the width direction stretching step, it is necessary to heat the uniaxially stretched film after longitudinal stretching in the range of Tm to Tm+25° C. to soften the polypropylene resin composition. By making it Tm or more, softening progresses and stretching in the width direction becomes easy. By adjusting the temperature to Tm+25° C. or lower, the orientation at the time of lateral stretching proceeds, and rigidity is easily exhibited. Tm+2 to Tm+20°C is more preferable, and Tm+3 to Tm+15°C is particularly preferable. Here, the maximum temperature in the preheating step is defined as the preheating temperature.

(Width direction stretching process)
In the width direction stretching step after the preheating step, a preferable method is as follows.

In the width direction stretching step, it is preferable to stretch at a temperature of Tm-10°C or more and a preheating temperature or less. At this time, the stretching in the width direction may be started when the preheating temperature is reached, or when the temperature is lowered after reaching the preheating temperature to reach a temperature lower than the preheating temperature.
The lower limit of the temperature in the width direction stretching step is more preferably Tm-9°C, still more preferably Tm-7°C, and particularly preferably Tm-5°C. When the width direction stretching temperature is within this range, the rigidity of the obtained biaxially oriented film can be easily improved.
The upper limit of the temperature in the width direction stretching step is preferably Tm+10°C, more preferably Tm+7°C, and particularly preferably Tm+5°C. Stretching unevenness is less likely to occur when the width direction stretching temperature is within this range.
In the widthwise stretching step, a late stretching step of stretching at a lower temperature may be added subsequent to the widthwise stretching in the above temperature range.
That is, following the section (previous section) that is drawn at a temperature of Tm-10 ° C. or higher and Tm + 10 ° C. or lower, the temperature is lower than the temperature of the previous section and is drawn at a temperature of Tm-70 ° C. or higher and Tm-5 ° C. or lower. A section (late section) may be provided. By providing the early section and the late section, it is easy to increase the rigidity.
The lower limit of the stretching temperature in the latter period is preferably Tm-65°C, more preferably Tm-60°C, and even more preferably Tm-55°C. When the stretching temperature in the latter period is within this range, film formation tends to be stable.

The lower limit of the final width direction draw ratio in the width direction stretching step is preferably 10 times or more, more preferably 11 times or more, and even more preferably 11.5 times or more. When it is 10 times or more, the rigidity of the film is likely to be increased, and thickness unevenness is likely to be reduced. The upper limit of the width direction draw ratio is preferably 20 times, more preferably 17 times, and still more preferably 15 times. When it is 20 times or less, the heat shrinkage rate is easily reduced, and the film is less likely to break during stretching.
When adding the latter section, the total draw ratio should be within the above range. At this time, the lower limit of the draw ratio in the first drawing step is preferably 4 times, more preferably 5 times, still more preferably 6 times, and particularly preferably 6.5 times. The upper limit of the draw ratio at the end of the previous period is preferably 15 times, more preferably 14 times, and still more preferably 13 times.

It is preferable to cool the film immediately after the completion of stretching in the width direction, that is, immediately after reaching the final stretch ratio in the width direction. The cooling temperature at this time is below the temperature for stretching in the width direction, and is preferably Tm-80 ° C. or higher and Tm-15 ° C. or lower, and Tm-80 ° C. or higher and Tm-20 ° C. or lower. more preferably Tm-80°C or higher and Tm-30°C or lower, and particularly preferably Tm-70°C or higher and Tm-40°C or lower. By adding a cooling step, crystallization occurs and the crystal orientation is fixed. After that, the orientation history is maintained even if the temperature is raised to a temperature higher than the melting point, and as a result, the crystal orientation in the film is increased. can be done.
The temperature can be gradually lowered from the temperature at the end of the width direction stretching to the temperature at the time of cooling, but it can also be lowered stepwise or in one step. Lowering the temperature stepwise or in one step is preferred because it facilitates greater crystal orientation in the film.

After cooling the film, it is preferable to stretch the film again in the width direction at a high temperature (hereinafter also referred to as re-stretching in the width direction). When the film is cooled and then stretched again in the width direction at a high temperature, the crystal orientation of the film is likely to be increased, and the rigidity is likely to be increased. The lower limit of the stretching temperature when stretching in the width direction again is Tm-5°C, preferably Tm°C, more preferably Tm+5°C, still more preferably Tm+7°C, and particularly preferably Tm+9°C. . When the temperature is Tm-5°C or higher, the rigidity tends to be increased, and the heat shrinkage rate tends to decrease.
The upper limit of the re-stretching temperature in the width direction is preferably Tm+20°C, more preferably Tm+18°C, still more preferably Tm+16°C. When the temperature is Tm+20° C. or less, the rigidity tends to be increased.
The lower limit of the re-stretching ratio in the width direction at high temperature is preferably 1.05 times, more preferably 1.1 times, and still more preferably 1.15 times.
The upper limit of the cross-direction re-stretching ratio at high temperature is preferably 2 times, more preferably 1.7 times, and still more preferably 1.5 times. If the re-stretching ratio is too large, the heat shrinkage may become too large, thickness unevenness may occur, or the film may break.

In other words, instead of immediately relaxing at a high temperature after stretching in the width direction as in the past, by stretching again in the width direction at a temperature sufficiently higher than the melting point, the heat shrinkage rate is reduced and the rigidity is further improved. I found that it is possible.
That is, it is preferable to perform the stretching at Tm+5° C. or higher in the step after the initial stretching in the width direction. At Tm + 5 ° C. or higher, the mobility of the molecular chains is sufficiently high, and the effect of entanglement of the molecular chains can be easily eliminated by stretching. , the crystallization also proceeds sufficiently.
By cooling the film to a temperature at which the film can be crystallized after being stretched in the width direction at a high temperature, the crystal orientation is fixed, and a high-melting-point film with a high degree of crystallinity and thick crystal lamellas can be obtained.

In addition, even in portions other than the crystal lamellae, there are few molecular chains with large distortion in molecular orientation constrained by entanglement points, and the film is less likely to shrink even when the crystals begin to melt. Furthermore, when the degree of crystallinity is improved and the crystal lamellae are thick, the melting point tends to be high, and melting below the melting point is difficult to occur. As a result, the heat shrinkage rate tends to decrease.
As a result, it has become possible to reduce the heat shrinkage rate while further improving the rigidity.

In the normal film-making process (extrusion - machine direction stretching - width direction stretching - heat treatment), in order to eliminate the distortion caused by the width direction stretching performed at a temperature lower than the melting point, the film is exposed to a high temperature above the melting point in the heat treatment process. , the heat shrinkage rate is lowered by applying relaxation of several percent to several tens of percent. By relaxing, it is possible to eliminate the difficulty in crystallization due to the restraint of the molecular chains, which contributes to the reduction of the thermal shrinkage rate. Conversely, however, the orientation of the molecular chains generated in the lateral stretching process in the width direction is reduced, and the rigidity is also reduced. In addition, if the temperature is too high, there is also a problem of whitening of the film.
In a normal film-forming process (extrusion-longitudinal stretching-width-direction stretching-heat treatment), by raising the temperature in the width-direction stretching process, the mobility of the molecular chains is high, and when stretching is performed so that no strain remains, The crystal orientation is lowered because the crystals generated by the longitudinal stretching are melted. In the method of the present invention, once the film is stretched in the width direction and sufficiently oriented in the width direction, the film having sufficient tension even if the crystal orientation fixed by cooling is melted is stretched at a high temperature of Tm + 5 ° C. or higher. Since the film is stretched again below the film, there is sufficient tension even when the film is stretched again, and there is little concern that unevenness in thickness will occur or that the film will break.
The draw ratio at a high temperature may be such that the entanglement of the molecular chains can be loosened and aligned, and may be 1.05 times or more. When the draw ratio is 2 times or less, thickness unevenness is less likely to occur.

Thus, by adopting the above-described longitudinal stretching step, width direction stretching step, cooling step, and high temperature stretching step, using a polypropylene resin with high stereoregularity and high melting point and high crystallinity, the polypropylene resin molecules is highly aligned in the main orientation direction (the width direction corresponds to the width direction stretching process described above), so that the crystal orientation in the resulting biaxially oriented film is strong and more crystals with a high melting point are generated. easier.

Further, by increasing the low-molecular-weight component of the polypropylene resin, the entanglement of molecular chains is further reduced, the crystallinity of the film is more likely to be increased, and the portion other than the crystal lamellae is reduced. In addition, by weakening the heat shrinkage stress in portions other than the crystal lamellae, the heat shrinkage rate tends to be further lowered.
In the prior art, it has been difficult to simultaneously reduce the amount of amorphous components that are not bound by crystals while increasing the crystal orientation. In other words, if either the rigidity or the thermal shrinkage rate is improved, the other property tends to be lowered. Considering these, it can be said that the present invention has an epoch-making effect.

(Heat treatment process)
The biaxially stretched film can be heat treated to further reduce heat shrinkage, if desired. The upper limit of the heat treatment temperature is preferably the above-described high temperature re-stretching temperature, more preferably -2°C, and even more preferably -3°C. By keeping the temperature below the high-temperature re-stretching temperature, the rigidity is less likely to decrease, the roughness of the film surface is not excessively increased, and the film is less likely to whiten. The lower limit of the heat treatment temperature is preferably Tm-3°C, more preferably Tm-2°C, and particularly preferably Tm.
For the purpose of adjusting the thermal shrinkage rate, the film may be relaxed (relaxed) in the width direction during the heat treatment. %. Within the above range, the rigidity is less likely to decrease, and film thickness fluctuations are likely to be smaller. When the rigidity is to be further increased, the heat treatment may not be performed.

(Cooling process)
After stretching in the width direction, the film is preferably cooled immediately after stretching in the width direction again at Tm-5° C. or higher, or immediately after the heat treatment step. The cooling temperature at this time is preferably 10° C. or higher and 140° C. or lower, more preferably 20° C. or higher and 120° C. or lower, and further preferably 80° C. or lower. , 50° C. or less is particularly preferred. By providing the cooling process, the state of the film can be fixed.
The biaxially oriented polypropylene film thus obtained is preferably subjected, if necessary, to corona discharge, plasma treatment, flame treatment, or the like.

(film thickness)
The thickness of the biaxially oriented polypropylene film for release of the present invention is set according to each application, but in order to obtain the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, It is more preferably 4 μm, particularly preferably 8 μm, and most preferably 10 μm. When the film thickness is 2 μm or more, it is easy to obtain the rigidity of the film. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, still more preferably 60 μm, particularly preferably 50 μm, most preferably 40 μm. When the film thickness is 100 µm or less, the cooling rate of the unstretched sheet during the extrusion process is difficult to decrease.
The release biaxially oriented polypropylene film of the present invention is usually produced as a roll having a width of about 2000 to 12000 mm and a length of about 1000 to 50000 m, and wound into a film roll. Furthermore, it is slit according to each application and provided as a slit roll having a width of 300 to 2000 mm and a length of about 500 to 5000 m. A longer film roll can be obtained from the biaxially oriented polypropylene film for release of the present invention.

(Thickness uniformity)
The lower limit of the thickness uniformity of the release biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, still more preferably 0.5%, and particularly preferably 1%. is. The upper limit of thickness uniformity is preferably 20%, more preferably 17%, still more preferably 15%, particularly preferably 12%, and most preferably 10%. Within the above range, defects are unlikely to occur during post-processing such as coating and printing, and it is easy to use for applications requiring precision.
The measurement method was as follows. A test piece of 40 mm in the width direction is cut out from the constant region where the film properties are stable in the length direction of the film, and a film feeding device manufactured by Micron Keiseki Co., Ltd. (manufacturing number: A90172 is used) and a film manufactured by Anritsu Co., Ltd. Using a thickness continuous measuring device (product name: K-313A wide-range high-sensitivity electronic micrometer), the film thickness was continuously measured over 20000 mm, and the thickness uniformity was calculated from the following formula.
Thickness uniformity (%) = [(maximum thickness - minimum thickness) / average thickness] x 100

(Film properties)
The release biaxially oriented polypropylene film of the present invention is characterized by the following properties. Here, the "longitudinal direction" in the release biaxially oriented polypropylene film of the present invention is a direction corresponding to the flow direction in the film manufacturing process, and the "width direction" is the flow direction in the film manufacturing process. It is the orthogonal direction. For a polypropylene film in which the flow direction in the film manufacturing process is unknown, a wide-angle X-ray is incident in the direction perpendicular to the film surface, and the scattering peak derived from the (110) plane of the α-type crystal is scanned in the circumferential direction, The direction in which the obtained diffraction intensity distribution has the highest diffraction intensity is defined as the "longitudinal direction", and the direction orthogonal thereto is defined as the "width direction".

The heat shrinkage (%) in the width direction at 150°C and the stress (MPa) at 23°C at 5% elongation in the width direction of the biaxially oriented polypropylene film for release of the present invention satisfy the following formulae.
By satisfying the following formula, the rigidity is higher and the thermal shrinkage rate at high temperatures is smaller, so it is easy to maintain the shape when used as a release film, and deformation during processing such as ceramic capacitors and printed circuit board materials. Because wrinkles are less likely to occur and wrinkles are suppressed, appearance quality is further improved. In addition, it becomes possible to make the film thinner, which contributes to the volume reduction of the release film.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 140
In addition, the heat shrinkage rate (%) in the width direction at 150°C and the stress (MPa) at 5% elongation in the width direction at 23°C of the biaxially oriented polypropylene film for release of the present invention satisfy the following formulas. is preferred.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 150
Furthermore, the heat shrinkage rate (%) in the width direction at 150 ° C. and the stress (MPa) at 5% elongation in the width direction at 23 ° C. of the biaxially oriented polypropylene film for release of the present invention satisfy the following formula. is more preferred.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 160

(Crystalline component (I) determined by pulse NMR, constrained amorphous component (II), unconstrained amorphous component (III))
It is known that the FID (Free Induction Decay) decay time constant of the spin-spin relaxation time T2 observed by ¹ H-pulse NMR is the sum of two or more decay time constants. For example, Polymer Journal, Vol. 3, No. 4, pp. 448-462 (1972) analyzes the attenuation time constant of the relaxation time of a crystalline polymer by the sum of the three components of crystalline component/intermediate phase component/amorphous component by the solid echo method of pulse NMR. .
The spin-spin relaxation time T2 observed by ¹ H-pulse NMR becomes slower in the order of crystalline, mesophase and amorphous. The mesophase has a faster T2 than amorphous and is considered amorphous with constrained mobility. When the film is stretched while loosening the entanglement of the molecular chains, a strongly oriented crystalline component (I) is generated, and an amorphous chain component (II) (corresponding to the above intermediate phase) whose mobility is constrained is generated near the crystals. . On the other hand, if the entanglement is large and the orientation is disturbed during stretching, an amorphous component (III) (corresponding to the above-mentioned amorphous) that is not bound by crystals is likely to occur. The unconstrained amorphous component (III) has high mobility, and at high temperatures, it is likely to move so as to eliminate strain, which is thought to be the cause of shrinkage at high temperatures. On the other hand, it is considered that the bound amorphous chain (II) is less likely to shrink at high temperatures because its movement is suppressed even at high temperatures compared to the amorphous component (III).

The upper limit of the unconstrained amorphous component (III) determined by pulse NMR of the biaxially oriented polypropylene film for release of the present invention is 7%, preferably 6%, more preferably 5%.
When the amorphous component (III) is 7% or less, wrinkles are less likely to occur during drying of the release coating film. In addition, when used as a release film, it is easy to maintain its shape, and deformation is less likely to occur during processing of ceramic capacitors and printed circuit board materials.
In order to reduce the unrestrained amorphous component (III), it is particularly effective to increase the area ratio during film formation, and to stretch the film in the width direction again at a high temperature after successive biaxial stretching.
It is also effective to use a polypropylene raw material with a high mesopentad fraction.
Furthermore, it is effective to set the lower limit of the amount of the component having a molecular weight of 100,000 or less to 35 mass % when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film.
Here, the fact that the unrestrained amorphous component (III) obtained by pulse NMR is 7% or less means that there are few molecular chains with large strain in the molecular orientation constrained by the entanglement points, and even if the crystal starts to melt, This means that the film is less likely to shrink and less likely to wrinkle even when the release coating film is dried at a high temperature.

When the non-constrained amorphous component (III) obtained by pulse NMR exceeds 7%, there are many molecular chains with large distortion in the molecular orientation constrained by the entanglement points, so the crystal melts and shrinks at the same time. , the film tends to wrinkle when the release coating film dries.
Also, the lower limit of the non-restricted amorphous component (III) is not particularly limited, but it is practically 0.1% or more. If the unconstrained amorphous component (III) is to be less than 0.1%, it is necessary to stretch the film in the width direction again at a high temperature after successive biaxial stretching. may occur. In addition, the crystal orientation in the film may be weakened and the rigidity may be lowered.

(Thermal shrinkage at 150°C)
The upper limit of the heat shrinkage rate in the longitudinal direction at 150 ° C. of the biaxially oriented polypropylene film for release of the present invention is 10%, preferably 7.0%, more preferably 6.0%, and more It is more preferably 5.0%, and particularly preferably 4.0% or less. The upper limit of the heat shrinkage rate in the width direction at 150°C is 30%, preferably 20%, more preferably 16%, and particularly preferably 15% or less.
When the heat shrinkage rate in the longitudinal direction is 10% or less and the heat shrinkage rate in the width direction is 30% or less, wrinkles are less likely to occur during mold release processing, and in particular, the heat shrinkage rate in the longitudinal direction at 150 ° C. is 8. When the heat shrinkage ratio in the width direction at 150° C. is 0% or less and 15% or less, the control range of the roll tension during the mold release process is widened, and as a result, wrinkles are less likely to occur, which is preferable. If the heat shrinkage rate in the longitudinal direction is 10% or more and the heat shrinkage rate in the width direction is 30% or more, the shrinkage of the film increases during drying of the release coating film, uneven drying occurs, and separation occurs. The type tends to deteriorate. In order to reduce the heat shrinkage at 150°C, the lower limit of the amount of components having a molecular weight of 100,000 or less when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film is set to 35% by mass. It is effective to

(F5: Stress at 5% elongation at 23°C)
The lower limit of F5 in the width direction at 23° C. of the biaxially oriented polypropylene film for release of the present invention is 140 MPa, preferably 160 MPa, more preferably 180 MPa, and still more preferably 190 MPa. When the pressure is 140 MPa or more, the rigidity is high, so that the shape of the release film can be easily maintained, and deformation of the film hardly occurs during processing of ceramic capacitors, printed circuit board materials, and the like.
The upper limit of F5 in the width direction at 23°C is preferably 300 MPa, more preferably 290 MPa, and even more preferably 280 Pa. When it is 280 MPa or less, realistic manufacturing is easy, and the vertical width balance tends to be improved.
The lower limit of F5 in the longitudinal direction of the release biaxially oriented polypropylene film of the present invention at 23°C is preferably 40 Pa, more preferably 42 Pa, still more preferably 46 Pa, and particularly preferably 48 Pa. When the pressure is 40 MPa or more, the rigidity is high, so that the release film can easily maintain its shape, and the film is less likely to deform during processing of ceramic capacitors, printed circuit board materials, and the like.
The upper limit of F5 in the longitudinal direction at 23° C. is preferably 70 MPa, more preferably 65 MPa, still more preferably 62 MPa, particularly preferably 60 Pa. When the pressure is 70 MPa or less, realistic manufacturing becomes easy, and the vertical width balance tends to be improved.
F5 can be set within the range by adjusting the draw ratio and the relaxation ratio, or by adjusting the temperature during film formation.

The release biaxially oriented polypropylene film of the present invention preferably has the following properties and structure.
(Thermal shrinkage at 120°C)
The upper limit of the longitudinal heat shrinkage at 120° C. of the biaxially oriented polypropylene film for release of the present invention is preferably 2.0%, more preferably 1.5%, and still more preferably 1.2. %, particularly preferably 1.0%. When it is 2.0% or less, appearance defects such as vertical streaks are less likely to occur during mold release processing. The upper limit of the heat shrinkage rate in the width direction at 120°C is 10.0% or less, preferably 5.0%, more preferably 3.5%, and particularly preferably 2.5%. When it is 10.0% or less, wrinkles are less likely to occur in the film after mold release processing.
The heat shrinkage at 120° C. can be controlled within the range by adjusting the draw ratio, draw temperature, and heat setting temperature.

The heat shrinkage (%) in the width direction at 120°C and the tensile modulus (GPa) in the width direction at 23°C of the biaxially oriented polypropylene film for release of the present invention preferably satisfy the following formulae.
By satisfying the following formula, the film has a higher rigidity and a smaller thermal shrinkage rate at high temperatures, so that the film is less likely to wrinkle after release processing when it is used as a bag.
Tensile elastic modulus in the width direction at 23°C (GPa) ≥ Heat shrinkage rate in the width direction at 120°C (%) x 0.3 + 7.0
In addition, the heat shrinkage rate (%) in the width direction at 120 ° C. and the tensile elastic modulus (GPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film for release of the present invention more preferably satisfy the following formula. preferable.
Tensile elastic modulus in the width direction at 23°C (GPa) ≥ Heat shrinkage rate in the width direction at 120°C (%) x 0.3 + 8.0
Furthermore, the heat shrinkage rate (%) in the width direction at 120 ° C. and the tensile elastic modulus (GPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film for release of the present invention further satisfy the following formula. preferable.
Tensile elastic modulus in the width direction at 23°C (GPa) ≥ Heat shrinkage rate in the width direction at 120°C (%) x 0.3 + 9.0

The heat shrinkage (%) in the width direction at 150°C and the stress (MPa) at 23°C at 5% elongation in the width direction of the biaxially oriented polypropylene film for release of the present invention satisfy the following formulae.
By satisfying the following formula, the rigidity is higher and the thermal shrinkage rate at high temperatures is smaller, so that the generation of wrinkles in the film due to heat can be suppressed in the process of drying the release coating film. Wrinkles are caused by shrinkage of the film due to heat and deformation of the film due to tension during roll transport. By optimizing the balance between the two, the occurrence of wrinkles can be suppressed. In addition, when it is used as a release film, it is easy to maintain its shape, and deformation of the film is less likely to occur during processing of ceramic capacitors, printed circuit board materials, etc., and appearance quality such as wrinkles is further improved. Furthermore, it becomes possible to make the film thinner, which contributes to the volume reduction of the release film.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 140
In addition, the heat shrinkage rate (%) in the width direction at 150°C and the stress (MPa) at 5% elongation in the width direction at 23°C of the biaxially oriented polypropylene film for release of the present invention satisfy the following formulas. is preferred.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 150
Furthermore, the heat shrinkage rate (%) in the width direction at 150 ° C. and the stress (MPa) at 5% elongation in the width direction at 23 ° C. of the biaxially oriented polypropylene film for release of the present invention satisfy the following formula. is more preferred.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 160

(tensile modulus at 23°C)
The lower limit of the longitudinal tensile modulus at 23° C. of the biaxially oriented polypropylene film for release of the present invention is 2.0 GPa, preferably 2.1 GPa, more preferably 2.2 GPa, and even more preferably. is 2.3 GPa, particularly preferably 2.4 GPa, most preferably 2.6 GPa. At 2.0 GPa or more, the rigidity is high, so that the shape of the release film can be easily maintained, and deformation of the film hardly occurs during processing of ceramic capacitors, printed circuit board materials, and the like. The upper limit of the longitudinal tensile modulus is preferably 4.0 GPa, more preferably 3.8 GPa, even more preferably 3.7 GPa, particularly preferably 3.6 GPa, and most preferably 3.6 GPa. 5 GPa. At 4.0 GPa or less, realistic production is easy, and the balance of characteristics in the longitudinal direction and the width direction tends to be improved.
The lower limit of the tensile modulus in the width direction at 23° C. of the biaxially oriented polypropylene film for release of the present invention is preferably 6.0 GPa, more preferably 6.5 GPa, and more preferably 6.7 GPa. , more preferably 7.0 GPa, particularly preferably 8.0 GPa, most preferably 8.5 GPa. At 6.0 GPa or more, the rigidity is high, so that the shape of the release film can be easily maintained, and deformation of the film hardly occurs during processing of ceramic capacitors, printed circuit board materials, and the like. The upper limit of the tensile modulus in the width direction is preferably 15 GPa, more preferably 13 GPa, still more preferably 12 GPa. When it is 15 GPa or less, realistic production is easy, and the balance of characteristics in the longitudinal direction and the width direction tends to be improved.
The tensile modulus can be adjusted within the range by adjusting the draw ratio and the relaxation rate, or by adjusting the temperature during film formation.

(Tensile breaking strength at 23°C)
The lower limit of the longitudinal tensile breaking strength at 23° C. of the biaxially oriented polypropylene film for release of the present invention is preferably 90 MPa, more preferably 100 MPa, still more preferably 110 MPa, and particularly preferably 115 MPa. be. When the pressure is 90 MPa or more, wrinkles are less likely to occur during release film processing, and film breakage during release processing is less likely to occur. As a practical value, the upper limit of the tensile strength at break in the longitudinal direction is preferably 200 MPa, more preferably 180 MPa, and even more preferably 160 MPa. If the pressure is 200 MPa or less, the breakage of the film tends to decrease.
The lower limit of the tensile breaking strength in the width direction at 23° C. of the biaxially oriented polypropylene film for release of the present invention is preferably 400 MPa, more preferably 420 MPa, still more preferably 440 MPa, and particularly preferably 450 MPa. is. When the pressure is 400 MPa or more, wrinkles are less likely to occur during release film processing, and film breakage during release processing is less likely to occur. As a realistic value, the upper limit of the tensile strength at break in the width direction is preferably 650 MPa, more preferably 600 MPa, and even more preferably 550 MPa. If the pressure is 650 MPa or less, the breakage of the film tends to decrease.
The tensile strength at break can be adjusted within a range by adjusting the draw ratio, draw temperature, and heat setting temperature.

(Tensile breaking elongation at 23°C)
The lower limit of the longitudinal tensile breaking elongation at 23° C. of the biaxially oriented polypropylene film for release of the present invention is preferably 180%, more preferably 190%, more preferably 200%, Particularly preferably, it is 210% or more. When it is 180% or more, the breakage of the film tends to decrease. The upper limit of the tensile elongation at break in the longitudinal direction at 23° C. is preferably 300%, more preferably 280% as a realistic value.

The lower limit of the tensile breaking elongation in the width direction at 23° C. of the biaxially oriented polypropylene film for release of the present invention is preferably 15%, more preferably 20%, more preferably 30%, When it is 15% or more, breakage of the film tends to decrease. The upper limit of the tensile elongation at break in the width direction at 23°C is preferably 60%, more preferably 55%, and still more preferably 50%. If it is 60% or less, the film is less likely to break during mold release processing.
The tensile elongation at break can be adjusted within a range by adjusting the draw ratio, drawing temperature, and heat setting temperature.

(refractive index)
The lower limit of the refractive index (Nx) in the longitudinal direction of the biaxially oriented polypropylene film for release of the present invention is preferably 1.4950, more preferably 1.4970, still more preferably 1.4980, Particularly preferred is 1.4990, most preferred is 1.5000. When it is 1.4950 or more, it is easy to increase the rigidity of the film. The upper limit of the longitudinal refractive index (Nx) is preferably 1.5100, more preferably 15070, even more preferably 1.5050. If it is 1.5100 or less, the film tends to have an excellent balance of characteristics in the longitudinal direction and the width direction.

The lower limit of the refractive index (Ny) in the width direction of the release biaxially oriented polypropylene film of the present invention is 1.5250, preferably 1.5253, more preferably 1.5255, still more preferably 1 .5260, particularly preferably 1.5265. If it is 1.5250 or more, it is easy to increase the rigidity of the film. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, still more preferably 1.5270. If it is 1.5280 or less, the film tends to have an excellent balance of characteristics in the longitudinal direction and the width direction.

The lower limit of the refractive index (Nz) in the thickness direction of the biaxially oriented polypropylene film for release of the present invention is preferably 1.4960, more preferably 14965, still more preferably 1.4970, and particularly preferably is 1.4980, most preferably 1.4990. When it is 1.4960 or more, it is easy to increase the rigidity of the film. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, still more preferably 1.5010. If it is 1.5020 or less, the heat resistance of the film can be easily improved.
The refractive index can be adjusted within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(ΔNy)
The lower limit of ΔNy of the biaxially oriented polypropylene film for release of the present invention is 0.0240, preferably 0.0245, more preferably 0.0247, still more preferably 0.0250, especially It is preferably 0.0255 and most preferably 0.0260. If it is 0.0240 or more, the rigidity of the film tends to be high. As a realistic value, the upper limit of ΔNy is preferably 0.0280, more preferably 0.0277, even more preferably 0.0273, and particularly preferably 0.0270. If it is 0.0280 or less, thickness unevenness tends to be good. ΔNy can be set within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature of the film.
ΔNy is calculated by the following formula, where Nx, Ny, and Nz are the refractive indices along the longitudinal direction, the width direction, and the thickness direction of the film, respectively. It means the degree of orientation of the direction.
ΔNy=Ny−[(Nx+Nz)/2]

(plane orientation factor)
The lower limit of the plane orientation coefficient (ΔP) of the release biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, still more preferably 0.0140. When it is 0.0135 or more, the balance in the plane direction of the film is good, and the thickness unevenness is also good. As a practical value, the upper limit of the plane orientation coefficient (ΔP) is preferably 0.0155, more preferably 0.0152, and still more preferably 0.0150. If it is 0.0155 or less, it tends to be excellent in heat resistance at high temperatures. The plane orientation coefficient (ΔP) can be set within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.
The plane orientation coefficient (ΔP) was calculated using the formula [(Nx+Ny)/2]-Nz.

(average refractive index)
The lower limit of the average refractive index of the biaxially oriented polypropylene film for release of the present invention is preferably 1.5080, more preferably 1.5081, still more preferably 1.5082, and particularly preferably 1.5083. and most preferably 1.5090. As a practical value, the upper limit of the average refractive index is preferably 1.5150, more preferably 1.5140, even more preferably 1.5135, and particularly preferably 1.5130. When it is 1.5080 or more, wrinkles are less likely to occur in the film when the release coating film is dried at a high temperature. The average refractive index can be adjusted within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature of the film.
The average refractive index is calculated by the following formula, where Nx, Ny, and Nz are the refractive indices along the longitudinal direction, width direction, and thickness direction of the film, respectively.
Average refractive index = (Nx + Ny + Nz)/3

(Haze)
When the biaxially oriented polypropylene film for release of the present invention is required to have transparency, the upper limit of haze of the film is preferably 5.0%, more preferably 4.5%, and still more preferably 4.0%. 0%, particularly preferably 3.5%, most preferably 3.0%. When it is 5.0% or less, it is easy to use in applications where transparency is required. As a practical value, the lower limit of haze is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, and particularly preferably 0.4%. It is easy to manufacture as it is 0.1% or more. Haze is determined by adjusting the cooling roll (CR) temperature, width direction stretching temperature, preheating temperature before stretching in the width direction of the tenter, width direction stretching temperature, or heat setting temperature, or the amount of polypropylene resin having a molecular weight of 100,000 or less. However, the addition of an antiblocking agent or the provision of a seal layer may increase the thickness.

(Half width of diffraction peak derived from oriented crystal)
In the azimuth angle dependence of the scattering peak of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray measurement perpendicularly incident on the film surface of the biaxially oriented polypropylene film for release of the present invention, the width direction of the film The upper limit of the half-value width (Wh) of the diffraction peak derived from the oriented crystal is 26°, preferably 25° or less, more preferably 24° or less, particularly preferably 23° or less, and most preferably is 22.0° or less. When the half width (Wh) is 26° or less, it is easy to increase the rigidity of the film. The lower limit of Wh is preferably 15°, more preferably 16°, still more preferably 17°.

(X-ray orientation degree)
The lower limit of the degree of X-ray orientation calculated by the following formula from Wh of the biaxially oriented polypropylene film for release of the present invention is preferably 0.856, more preferably 0.861, still more preferably 0.861. 867, particularly preferably 0.872, most preferably 0.878. By making it 0.856 or more, it is easy to increase the rigidity.
X-ray orientation = (180-Wh)/180
The upper limit of the degree of X-ray orientation is preferably 0.917, more preferably 0.911, still more preferably 0.906. When the ratio is 0.917 or less, the film formation tends to be stable.

(Biaxially oriented polypropylene film for release having a release coating layer)
The biaxially oriented polypropylene film for release of the present invention may be used as a release film without any particular release processing, but may be used with a release agent such as silicone resin applied to the surface. be.
The wetting tension of the surface of the release biaxially oriented polypropylene film of the present invention is preferably 38 mN/m or more. When the wetting tension is 38 mN/m or more, the adhesion to the release coating layer is improved. In order to obtain a wetting tension of 38 mN/m or more, it is preferable to perform a physicochemical surface treatment such as corona treatment, flame treatment or plasma treatment.
For example, in corona treatment, it is preferable to use a preheated roll and a treatment roll to perform discharge in the air. The wetting tension is preferably 44 mN/m or less, more preferably 43 mN/m or less, and even more preferably 42 mN/m or less.
The release agent to be applied to the release biaxially oriented polypropylene film of the present invention is not particularly limited, and silicone resins, fluororesins, alkyd resins, various waxes, aliphatic olefins, etc. can be used. , can be used in combination of two or more.

As the silicone resin used as a mold release agent in the present invention, a silicone resin generally used as a mold release agent can be used. It can be used by selecting from silicone resins commonly used in the field concerned. In general, thermosetting or ionizing radiation curable silicone resins (including resins and resin compositions) are used. Examples of thermosetting silicone resins that can be used include condensation reaction and addition reaction silicone resins, and ionizing radiation curing silicone resins that can be used include ultraviolet or electron beam curing silicone resins. A release layer is formed by coating these on a film as a substrate and drying or curing them.

The degree of polymerization of the curable silicone resin after curing is preferably about 500,000 to 200,000, particularly preferably about 1000 to 100,000. Specific examples thereof include the following resins: Shin-Etsu Chemical Co., Ltd. ( Co., Ltd. KS-718, KS-774, KS-775, KS-778, KS-779H, KS-830, KS-835, KS-837, KS-838, KS-839, KS-841, KS- 843, KS-847, KS-847H, X-62-2418, X-62-2422, X-62-2125, X-62-2492, X-62-2494, X-62-5048, X-62- 470, X-62-2366, X-62-630, X-92-140, X-92-128, KS-723A/B, KS-705F, KS-708A, KS-883, KS-709, KS- 719; Toshiba Silicon Co., Ltd. TPR-6701, TPR-6702, TPR-6703, TPR-3704, TPR-6705, TPR-6721, TPR-6722, TPR-6700, XSR-7029, YSR-3022, YR -3286; manufactured by Dow Corning Co., Ltd. DK-Q3-202, DK-Q3-203, DK-Q3-204, DK-Q3-205, DK-Q3-210, DK-Q3-240, DK-Q3- 3003, DK-Q3-3057, SFXF-2560; SD-7226, SD-7229, SD-7320, BY-24-900, BY-24-171, BY- manufactured by Dow Corning Toray Silicone Co., Ltd. 24-312, BY-24-374, SRX-375, SYL-OFF23, SRX-244, SEX-290; SILCOLEASE425 manufactured by ICI Japan Co., Ltd.; Furthermore, silicone resins described in JP-A-47-34447 and JP-B-52-40918 can also be used. These curable silicone resins may be used alone or in combination of two or more.

Examples of the addition-reactive silicone resins include those obtained by reacting and curing polydimethylsiloxane having vinyl groups introduced at terminals or side chains thereof and hydrogen siloxane using a platinum catalyst. At this time, it is more preferable to use a resin that can be cured at 120° C. within 30 seconds because processing can be performed at a low temperature. Examples include low temperature addition cure types manufactured by Dow Corning Toray (LTC1006L, LTC1056L, LTC300B, LTC303E, LTC310, LTC314, LTC350G, LTC450A, LTC371G, LTC750A, LTC755, LTC760A, etc.) and thermal UV cure types ( LTC851, BY24 -510, BY24-561, BY24-562, etc.), solvent addition + UV curing type manufactured by Shin-Etsu Chemical Co., Ltd. (X62-5040, X62-5065, X62-5072T, KS5508, etc.), dual cure curing type (X62-2835, X62 -2834, X62-1980, etc.).

As the condensation reaction silicone resin, for example, polydimethylsiloxane having terminal OH groups and polydimethylsiloxane having terminal H groups are condensed using an organic tin catalyst to form a three-dimensional crosslinked structure. is mentioned.

Examples of the above ultraviolet-curing or electron beam-curing silicone resins include, for example, the most basic types of resins that are crosslinked and cured by a radical reaction in the same manner as in ordinary silicone rubber crosslinking, resins that are photocured by introducing acrylic groups, Examples include a resin composition in which an onium salt is decomposed by ultraviolet rays to generate a strong acid, whereby the epoxy ring is cleaved and crosslinked, and a resin composition in which thiol is added to vinylsiloxane for crosslinking. Since the energy of electron beams is stronger than that of ultraviolet rays, a cross-linking reaction by radicals occurs without using an initiator as in the case of ultraviolet curing.

When a release agent is used, one type may be used, or two or more types may be mixed and used. Also, in order to adjust the release force, it is possible to mix additives such as a light release additive and a heavy release additive. The resulting biaxially oriented polypropylene film having a release coating layer is particularly excellent in release properties.

The release coating layer may contain particles having a particle size of 1 μm or less, but from the viewpoint of generating pinholes, it is preferable not to substantially contain particles that form protrusions.
Additives such as an adhesion improver and an antistatic agent may be added to the release coating layer. In addition, in order to improve the adhesion to the substrate, pretreatment such as anchor coating, corona treatment, plasma treatment, atmospheric pressure plasma treatment, etc. is applied to the surface of the release biaxially oriented polypropylene film before providing the release coating layer. It is also preferable to

The thickness of the release coating layer may be set according to the purpose of use, and is not particularly limited, but the thickness of the release coating layer after curing is preferably in the range of 0.005 to 2 μm. It is preferable that the thickness of the release coating layer is 0.005 μm or more because the release performance is maintained. Further, when the thickness of the release coating layer is 2 μm or less, the curing time is not excessively long, and thickness unevenness due to deterioration of the flatness of the release film does not occur, which is preferable. Another layer may be provided between the release biaxially oriented polypropylene film and the release coating layer.

In the present invention, the method for forming the release coating layer is not particularly limited. and the like, and after removing the solvent and the like by drying, a method of heat drying, heat curing, or ultraviolet curing is used. At this time, the drying temperature for solvent drying and heat curing is preferably 100 to 170°C. If the drying temperature is higher than 170° C., wrinkles may occur on the film due to heat. On the other hand, if the drying temperature is too low, the heat curing of the release coating layer may be insufficient and the release property may not be obtained. Since the biaxially oriented polypropylene film has lower thermal dimensional stability at high temperatures than the biaxially oriented polyester film, wrinkles due to heat are likely to occur during drying of the coating film, but the biaxially oriented polypropylene for release of the present invention The film can suppress the occurrence of wrinkles. Incidentally, the heat drying time is generally 10 to 60 seconds.

As a method for applying the coating liquid, any known coating method can be applied, for example, a roll coating method such as a gravure coating method or a reverse coating method, a bar coating method such as a wire bar method, a die coating method, a spray coating method, and an air knife. A conventionally known method such as a coating method can be used.

Hereinafter, the present invention will be described in detail with reference to examples. The properties were measured and evaluated by the following methods.
(1) Melt flow rate Melt flow rate (MFR) was measured according to JISK7210 at a temperature of 230°C and a load of 2.16 kgf.

(2) Mesopentad Fraction The mesopentad fraction ([mmmm]%) of the polypropylene resin was measured using ¹³ C-NMR. The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, 6:925 (1973). ¹³ C-NMR measurement was carried out at 110°C by dissolving 200 mg of a sample in a 8:2 mixture of o-dichlorobenzene and deuterated benzene at 135°C using AVANCE500 manufactured by BRUKER.

(3) Polypropylene Resin Number Average Molecular Weight, Weight Average Molecular Weight, Component Weight with Molecular Weight of 100,000 or Less, and Molecular Weight Distribution Using gel permeation chromatography (GPC), it was determined as PP equivalent molecular weight based on monodisperse polystyrene. When the baseline was not clear, the baseline was set in the range up to the lowest point of the high-molecular-weight elution peak closest to the elution peak of the standard substance.
GPC measurement conditions are as follows.

Device: HLC-8321PC/HT (manufactured by Tosoh Corporation)
Detector: RI
Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%)
Column: TSKgelguard column HHR (30) HT (7.5 mm ID × 7.5 cm) × 1 + TSKgelGMHHR-H (20) HT (7.8 mm ID × 30 cm) × 3 Flow rate: 1.0 mL / min
Injection volume: 0.3 mL
Measurement temperature: 140°C

The number-average molecular weight (Mn) and mass-average molecular weight (Mw) are defined by the following equations according to the number of molecules (N _i ) at each elution position (M _i ) on the GPC curve obtained through the molecular weight calibration curve. be.
Number average molecular weight: Mn = Σ (N _i · M _i ) / ΣN _i
Mass average molecular weight: Mw = Σ (N _i · M _i ² ) / Σ (N _i · M _i )
Here, the molecular weight distribution can be obtained by Mw/Mn.
Also, the ratio of components having a molecular weight of 100,000 or less was obtained from the integral curve of the molecular weight distribution obtained by GPC.

(4) Crystallization temperature (Tc), melting temperature (Tm)
Thermal measurements were performed under a nitrogen atmosphere using a Q1000 Differential Scanning Calorimeter manufactured by TA Instruments. About 5 mg was cut out from the polypropylene resin pellet and enclosed in an aluminum pan for measurement. After raising the temperature to 230° C. and holding it for 5 minutes, it was cooled to 30° C. at a rate of −10° C./min, and the exothermic peak temperature was defined as the crystallization temperature (Tc). The heat of crystallization (ΔHc) was obtained by setting a baseline so that the area of the exothermic peak was smoothly connected from the start of the peak to the end of the peak. The temperature was maintained at 30° C. for 5 minutes, and the temperature was raised to 230° C. at 10° C./min, and the main endothermic peak temperature was defined as the melting temperature (Tm).

(5) Film thickness The thickness of the film was measured using a Seiko EM Millitron 1202D.

(6) Haze Measured according to JIS K7105 at 23° C. using NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd.

(7) Tensile test Based on JISK7127, the tensile strength of the film in the longitudinal direction and the width direction was measured at 23°C. A sample having a size of 15 mm×200 mm was cut from the film, and the chuck width was 100 mm, and the sample was set in a tensile tester (Instron 5965 dual-column desktop tester manufactured by Instron Japan Company Limited). A tensile test was performed at a tensile speed of 200 mm/min. From the obtained strain-stress curve, the tensile modulus was determined from the slope of the straight line portion at the initial stage of elongation, and the stress at 5% elongation was determined as F5.
The tensile strength at break and the tensile elongation at break were the strength and elongation at the time when the sample broke, respectively.

(8) Thermal shrinkage rate It was measured by the following method based on JISZ1712. The film was cut into 20 mm width and 200 mm length in the longitudinal direction and width direction of the film, respectively, and hung in a hot air oven at 120° C. or 150° C. and heated for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the shrinkage length to the original length.

(9) Refractive index, ΔNy, plane orientation coefficient, average refractive index Measured at a wavelength of 589.3 nm and a temperature of 23°C using an Abbe refractometer manufactured by Atago Co., Ltd. Nx and Ny are the refractive indices along the longitudinal and width directions of the film, respectively, and Nz is the refractive index in the thickness direction. ΔNy was obtained using Nx, Ny, and Nz using the formula Ny−[(Nx+Nz)/2]. The plane orientation coefficient (ΔP) was calculated using the formula [(Nx+Ny)/2]-Nz. Also, the average refractive index was calculated using (Nx+Ny+Nz)/3 (formula).

(10) X-ray half width and degree of X-ray orientation Measured by a transmission method using an X-ray diffractometer (SmartLab manufactured by Rigaku Co., Ltd., with αβγ attachment). X-rays with a wavelength of 1.5418 Å were used, and the X-ray output was 45 kV and 200 mA. A hybrid multidimensional pixel detector Hypix-3000 was used as a detector in 0-dimensional mode. As a slit on the incident side in the parallel beam method, a Soller slit of 2.5°, a length limiting slit of 10 mm, and an incident slit width of 1 mm were used. A parallel slit analyzer 0.228° was used as the slit on the light receiving side.
The camera length was 300 mm, and the integration width of the detector was 2 mm.
A sample was prepared by stacking films to a thickness of 400 μm. A detector is placed at the diffraction peak position (diffraction angle 2θ = 14.1°) of the (110) plane of the α-type crystal of the polypropylene resin, and the sample is rotated 360° around the thickness direction of the film to obtain the (110) plane. Azimuth dependence of diffraction intensity is obtained. The step interval was 0.5° and the measurement speed was 60°/min. From this azimuth angle dependence, the half width Wh of the diffraction peak derived from the oriented crystals in the width direction of the film was determined.
Also, using Wh, the degree of X-ray orientation was calculated from the following formula.
X-ray orientation = (180-Wh)/180

(11) Ratio of unconstrained amorphous component (III) determined by pulse NMR The film was cut and packed into a glass tube with an outer diameter of 10 mm to a height of 1 cm. The spin-spin relaxation time T2 of the ¹ H nucleus of the biaxially oriented polypropylene film was measured under the measurement conditions to obtain a decay curve of the magnetization intensity.
Device: Minispec mq20 made by BRUKER
Temperature: 40°C
Observation frequency: 20MHz
90° pulse width: 2.74 μs
Pulse repetition time: 2.0s
Pulse mode: Solido Echo method Accumulation times: 128 times Recycle Delay: 4s
Acquisition Scale: 0.1ms
The measurement was started after the glass tube filled with the biaxially oriented polypropylene film was put into the apparatus and kept warm for 15 minutes. was separated by the least-squares method using the Gaussian function, and the second and third shortest components using the Lorentzian function, and the proportions of each were obtained. The shortest component corresponds to the crystalline component (I), the second and third shortest components correspond to the constrained amorphous component (II) and the unconstrained amorphous component (III), respectively. For the fitting and analysis, the software (TD-NMR Analyzer) attached to the measuring device was used.
The ratio of the unconstrained amorphous component (III) is the crystal component (I) obtained by the above method, the constrained amorphous component (II), and the amorphous component (III) with respect to the total of the unconstrained amorphous component (III). ratio (%)
was calculated by the following formula (1).
Ratio of free amorphous component (III) = M _III /( _MI + M _II + M _III ) (1)
M _I : Component amount of crystalline component (I) M _II : Component amount of restricted amorphous component (II) M _III : Component amount of unrestrained amorphous component (III)

(12) Wetting tension (mN/m)
According to JIS K 6768: 1999, the film was aged at 23°C and 50% relative humidity for 24 hours, and then the corona-treated surface of the film was measured by the following procedure.
Step 1)
The measurement shall be performed in a standard laboratory atmosphere (see JIS K 7100) with a temperature of 23°C and a relative humidity of 50%.
Step 2)
The specimen is placed on the substrate of the hand coater (4.1), a few drops of the test mixture are dropped on the specimen and the wire bar is immediately pulled and spread.
If using a cotton swab or brush to spread the test mixture, spread the liquid quickly over an area of at least 6 cm ² . The amount of liquid should be such that it forms a thin layer without pooling.
The wetting tension is determined by observing the liquid film of the mixed liquid for testing in a bright place and observing the state of the liquid film after 3 seconds. If the applied state is maintained for 3 seconds or more without breaking the liquid film, it means that the liquid is wet. If the wetness is maintained for 3 seconds or more, the mixture proceeds to the next higher surface tension mixture. Conversely, if the liquid film breaks in 3 seconds or less, the mixture proceeds to the next lower surface tension mixture.
This operation is repeated to select a mixed liquid that can wet the surface of the test piece accurately in 3 seconds.

(13) Releasability (tape peeling force)
An acrylic pressure-sensitive adhesive tape No. 50 mm wide was applied to the surface of the release agent layer of the biaxially oriented polypropylene film coated with the release agent described in Examples. 31B (manufactured by Nitto Denko Co., Ltd.) was laminated using a hand roller to prepare a laminate. After storing this laminate at 23 ° C. for 24 hours, it was pulled with a tensile tester at a speed of 300 mm / min by a T-type peeling method such that the release film was downward and the adhesive tape was upward. ℃ atmosphere was measured, and the following evaluation was performed.
○: Peel force is less than 1000 mN/50 mm ×: Peel force is 1000 mN/50 mm or more

(14) Wrinkles on the release film roll The biaxially oriented polypropylene film coated with the release agent was unwound from the roll of the biaxially stretched polypropylene film coated with the release agent described in the example, and wrinkles occurred on the release film. was evaluated by the following method.
That is, a release film having a width of 60 cm was suspended in a room at a temperature of 25° C. and a humidity of 65% so that the longitudinal direction of the film was vertical, and a load of 10 N/m was applied to the release film and allowed to stand still for 30 minutes. A fluorescent lamp is projected onto the film surface from 45° above, 1 m away from the plane for counting the number of corrugated plate-like wrinkles continuous in the longitudinal direction, and the number of wrinkles is projected from below at 45°, 0.5 m away from the plane for counting wrinkles. Numbers were counted and evaluated visually. With respect to wrinkles, the number of wrinkles in the width direction of the film was counted, with one wrinkle being convex in the longitudinal direction of the film with respect to the surface to be observed.
○: The number of wrinkles is 10/m or less. ×: The number of wrinkles is 11/m or more.

(Example 1)
(Manufacturing method of release biaxially oriented polypropylene film)
As a polypropylene resin, propylene homopolymer PP-1 (Sumitomo Chemical Co., Ltd. 80 parts by weight of Sumitomo Noblen FLX80E4), MFR = 11 g/10 min, [mmmm] = 98.8%, Tc = 116.5 ° C., Tm = 161.5 ° C. Propylene homopolymer PP-2 (manufactured by Sumitomo Chemical Co., Ltd., EL80F5) was blended with 20 parts by weight.
The sheet was extruded from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and put into a water bath at 20°C as it was. After that, it was stretched 4.5 times in the longitudinal direction with two pairs of rolls at 142°C, then clipped at both ends, introduced into a hot air oven, preheated at 170°C, and then 162°C as the first stage in the width direction. was stretched 10 times at . Immediately after the film was stretched in the width direction, it was cooled at 120° C. while being held by clips, then re-stretched at 175° C. by 1.2 times in the width direction, and then cooled to room temperature. - Using a corona treatment machine manufactured by Plasma GmbH, the applied current value: 0.75 A, the film was subjected to corona treatment, and then wound up with a winder. The thickness of the film thus obtained was 18.6 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, the film was very excellent in rigidity and had a low thermal shrinkage rate at high temperatures.

(Preparation of biaxially oriented polypropylene film coated with release agent)
A toluene/methyl ethyl ketone = 50/50 solution of a thermosetting silicone compound (manufactured by Shin-Etsu Silicone Co., Ltd., KS-774) (solid concentration: 1 weight %) with a Pt catalyst (PL-50T manufactured by Shin-Etsu Silicone Co., Ltd.) added in ^an amount of 1 part by weight with respect to 100 parts by weight of the solid content of KS-774. The release layer is dried at a transport tension of 2000 kPa and a drying temperature of 150 ° C. for 20 seconds using an air levitation transport type drying device with a distance between the lower and upper air flow outlets of 38 cm. A release film having a weight of 0.03 g/m ² after drying and curing was obtained. After drying, the film was cooled at a rate of 20°C/sec using a cooling roll at 50°C, and wound into a roll to obtain a release film roll. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, its physical properties are very excellent in rigidity, low in heat shrinkage at high temperatures, and a release film coated with a release agent has excellent releasability and is a smooth film without wrinkles. Met.

(Example 2)
The same procedure as in Example 1 was repeated except that the film was re-stretched at 165° C. in the width direction by 1.2 times. The thickness of the resulting film was 18.4 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, its physical properties are very excellent in rigidity, low in heat shrinkage at high temperatures, and a release film coated with a release agent has excellent releasability and is a smooth film without wrinkles. Met.

(Example 3)
Stretched at 147 ° C. in the longitudinal direction, stretched 10 times at 165 ° C. as the first stage in the width direction, immediately after stretching in the width direction, cooled at 120 ° C. while being held by the clip, and then stretched in the width direction at 177 ° C. The same procedure as in Example 1 was repeated except that the film was re-stretched by 1.2 times. The thickness of the resulting film was 18.9 µm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. Its physical properties, as shown in Table 3, were high in rigidity, low in heat shrinkage at high temperatures, and the release film coated with the release agent had excellent releasability and was a smooth film without wrinkles.

(Example 4)
The same procedure as in Example 3 was repeated except that the film was re-stretched 1.1 times in the width direction at 177°C. The thickness of the obtained film was 20.6 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical properties thereof were high in rigidity, low in heat shrinkage at high temperatures, and the release film coated with the release agent had excellent releasability and was a smooth film without wrinkles.

(Comparative example 1)
As the first step in the width direction, the film was stretched 12 times at 162°C, immediately after the film was stretched in the width direction, cooled at 100°C while being held by clips, and then heat-set at 170°C while the width was constant. As in Example 1. The thickness of the obtained film was 20.8 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, its physical properties are high in rigidity, but the heat shrinkage ratio at high temperatures is poor, and the release film coated with the release agent has wrinkles. became.

(Comparative example 2)
It was stretched 12 times at 162 ° C. as the first step in the width direction, and immediately after the width direction stretch, it was not cooled while being held by the clip, and was heat-set at 172 ° C. with a constant width. did the same. The thickness of the obtained film was 23.1 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, the stiffness was poor, and wrinkles occurred in the release film coated with the release agent, resulting in poor processability as a release film.

(Comparative Example 3)
As the first stage in the width direction, it was stretched 12 times at 168 ° C. Immediately after stretching in the width direction, it was cooled at 100 ° C. while being held by a clip, and then heat-fixed at 170 ° C. while the width was constant. As in Example 1. The thickness of the obtained film was 18.7 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, the heat shrinkage rate at high temperatures was high, the rigidity was poor, and wrinkles occurred in the release film coated with the release agent, making it inferior in processability as a release film. .

(Comparative Example 4)
As a polypropylene resin, PP-3 (manufactured by Japan Polypropylene Corporation, FL203D) having MFR = 3 g / 10 minutes, [mmmm] = 94.8%, Tc = 117.2 ° C., Tm = 160.6 ° C. is used. board. The sheet was extruded from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and put into a water bath at 20°C as it was. After that, the film was stretched 4.5 times in the longitudinal direction at 130°C, and in the width direction stretching with a tenter, the preheating temperature was set to 168°C, and the film was stretched 8.2 times at 155°C as the first stage of stretching. Immediately after stretching in the width direction, the film was cooled at 120°C while being held by clips, and then re-stretched at 170°C in the width direction by 1.2 times. Finally, it was cooled at room temperature. The thickness of the resulting film was 18.8 µm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, its physical properties are high in heat shrinkage at high temperatures and poor in rigidity. As a result, it was inferior in processing suitability.

(Comparative Example 5)
Using a blend of PP-1 and PP-2 as the polypropylene resin in the same manner as in Example 1, a film was obtained under the film-forming conditions shown in Table 2 in which the film was heat-treated at 168° C. without being re-stretched in the width direction. The thickness of the obtained film was 20.0 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, the heat shrinkage rate at high temperatures is low, but the rigidity is also poor, and the release film coated with the release agent has wrinkles, so it is inferior in processing suitability as a release film. became a thing.

(Comparative Example 6)
As the polypropylene resin, PP-4 (manufactured by Japan Polypropylene Corporation, SA4L) having MFR = 5 g / 10 minutes, [mmmm] = 97.3%, Tc = 116.8 ° C., Tm = 161.6 ° C. was used. Then, a film was obtained under the film-forming conditions shown in Table 2 in which the film was heat-treated at 168° C. without being re-stretched in the width direction. The thickness of the obtained film was 20.0 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, the heat shrinkage rate at high temperatures is low, but the rigidity is poor, and wrinkles occurred in the release film coated with the release agent, so it is inferior in processing suitability as a release film. became a thing.

The release biaxially oriented polypropylene film of the present invention has high rigidity and can be made into a thin film. Even if the film is thinned, it can be easily peeled off, and wrinkles are less likely to occur during the coating process of the release agent, so that it can be suitably used as a release film.

Claims (11)

A release biaxially oriented polypropylene film satisfying the following (1) and (2).
(1) In the azimuth angle dependence of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray diffraction measurement, the half width of the peak derived from the oriented crystal in the width direction is 26° or less.
(2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) determined by pulse NMR by the solid echo method is 7% or less. is. The biaxially oriented polypropylene film for mold release according to claim 1, which satisfies the following (3), (4) and (5).
(3) Thermal shrinkage at 150° C. is 10% or less in the longitudinal direction and 30% or less in the width direction.
(4) The stress at 5% elongation in the width direction at 23°C is 140 MPa or more.
(5) Heat shrinkage in width direction at 150°C (%) and stress at 5% elongation in width direction at 23°C (MPa)
satisfies the following equation.
Stress at 5% elongation in the width direction at 23 ° C. (MPa) ≥ Heat shrinkage rate in the width direction at 150 ° C. (%) × 4.0 + 140 The biaxially oriented polypropylene film for release according to claim 1 or 2, wherein the biaxially oriented polypropylene film for release satisfies the following (6) and (7).
(6) The heat shrinkage at 120°C is 2.0% or less in the longitudinal direction and 10.0% or less in the width direction.
(7) The thermal shrinkage rate (%) in the width direction at 120°C and the tensile elastic modulus (GPa) in the width direction at 23°C satisfy the following formulas.
Tensile elastic modulus in the width direction at 23°C (GPa) ≥ Heat shrinkage rate in the width direction at 120°C (%) x 0.3 + 7.0 The release biaxial according to any one of claims 1 to 3, wherein the release biaxially oriented polypropylene film has a width-direction refractive index Ny of 1.5250 or more and a ΔNy of 0.0240 or more. Oriented polypropylene film. The biaxially oriented polypropylene film for release according to any one of claims 1 to 4, wherein the biaxially oriented polypropylene film for release has a haze of 5.0% or less. The biaxially oriented polypropylene film for release according to any one of claims 1 to 5, wherein the polypropylene resin constituting the biaxially oriented polypropylene film for release has a mesopentad fraction of 97.0% or more. The biaxially oriented releasing agent according to any one of claims 1 to 6, wherein the polypropylene resin constituting the releasing biaxially oriented polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 160°C or higher. polypropylene film. The biaxially oriented polypropylene film for release according to any one of claims 1 to 7, wherein the polypropylene resin constituting the biaxially oriented polypropylene film for release has a melt flow rate of 4.0 g/10 minutes or more. The biaxially oriented polypropylene film for release according to any one of claims 1 to 8, wherein the polypropylene resin constituting the biaxially oriented polypropylene film for release contains 35% by mass or more of components having a molecular weight of 100,000 or less. A release film obtained by laminating a release coating layer on at least one side of the release biaxially oriented polypropylene film according to any one of claims 1 to 9. A laminated film comprising a biaxially oriented polypropylene film satisfying the following (1) and (2) and a release coating layer.
(1) In the azimuth angle dependence of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray diffraction measurement, the half width of the peak derived from the oriented crystal in the width direction is 26° or less.
(2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) determined by pulse NMR by the solid echo method is 7% or less. is.

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