KR20210086617A - Polypropylene film and release film - Google Patents

Abstract

A polypropylene film having improved surface flexibility, excellent surface smoothness, transparency, and releasability, and suitable for use as a release film is provided. The polypropylene film of the present invention has an elastic modulus of 2.5 GPa or less as measured by the nanoindentation method on at least one surface, and the temperature is increased from 25°C to 250°C by a differential scanning calorimeter DSC at 20°C/min, followed by 250 The crystallization peak temperature (Tc) when the temperature is lowered from °C to 25 °C at 20 °C/min is 110 °C or higher.

Description

Polypropylene film and release film

The present invention relates to a polypropylene film having improved surface flexibility and suitably used as a release film having excellent surface smoothness, transparency and releasability.

Since the polypropylene film is excellent in transparency, mechanical properties, electrical properties, etc., it is used for various uses, such as a packaging use, a mold release use, a tape use, cable wrapping, and electrical uses including a capacitor|condenser. In particular, since it is excellent in surface releasability and mechanical properties, it is used suitably as a release film and process film of various members, such as a plastics product, a building material, and an optical member.

Although the requested|required characteristic with respect to a release film is suitably set by the use use, in recent years, it may be used as a cover film of the resin layer which has adhesiveness, such as a photosensitive resin. In the case of covering a resin layer having adhesiveness, if the releasability of the cover film is poor, it cannot be peeled off cleanly when peeling, the shape of the resin layer as the protective surface changes, or when the transfer marks of slight irregularities of the cover film remain on the protective surface Therefore, a film with a soft surface and low surface elastic modulus is required. Moreover, when the surface smoothness of a cover film is bad, for example, when it uses as a release film of the member for optics, the surface unevenness|corrugation of a film transcribe|transfers to the member for optics, and may affect the visibility of a product. Moreover, when transparency of a cover film is bad, when performing process test|inspection, such as fault observation, after bonding with photosensitive resin, it may become a hindrance. From the above, in order to use it as a release film with high required characteristics, such as an optical member, the film excellent in the release property which combines surface flexibility, surface smoothness, and transparency is calculated|required.

As a means of improving the releasability, for example, in Patent Documents 1 and 2, there is a method of forming a β crystal in the film surface layer, or an example in which the releasability is improved by roughening the surface such as adding particles or polymethylpentene resin to the inner film layer. is described. Moreover, the example which obtains the film which improved transparency is described in patent document 3 by blending polypropylene resin from which molecular weight distribution differs. Moreover, in patent document 4, the example of the release film which made the surface smoothness and slidability compatible by forming microprotrusions on the surface by containing a branched polypropylene resin in one surface of the laminated|multilayer film containing two layers is described. In addition, in order to provide flexibility, for example, in Patent Documents 5 and 6, a release film having flexibility and high transparency is described by adding a low-melting polypropylene to the inner layer portion of a laminated film including three layers.

Japanese Patent Laid-Open No. 2018-127620 Japanese Patent Laid-Open No. 2015-178594 Japanese Patent Laid-Open No. 2014-055283 Japanese Patent Laid-Open No. 2007-126644 International Publication No. 2015/129851 International Publication No. 2018/147335

However, the method described in Patent Documents 1 and 2 lacks surface flexibility, so there is room for improvement. Moreover, in the method of patent document 3, since rigidity became high, the softness|flexibility of the surface was inadequate. Moreover, in the method of patent document 4, the opposite surface was roughened and transparency and surface softness|flexibility were inadequate. Moreover, since the method of patent documents 5 and 6 is a film containing a polypropylene resin in the outermost layer, it cannot be said that the surface softness|flexibility is enough.

Therefore, an object of the present invention is to solve the above problems. That is, to provide a polypropylene film with improved surface flexibility and excellent surface smoothness, transparency, and releasability.

In order to solve the above-mentioned subject and achieve the objective, the polypropylene film of this invention is as follows.

(1) At least one surface of the surface has an elastic modulus of 2.5 GPa or less as measured by the nanoindentation method, and the temperature is increased from 25° C. to 250° C. at 20° C./min using a differential scanning calorimeter DSC, and then from 250° C. to 25° C. The polypropylene film whose crystallization peak temperature (Tc) when temperature-falling at 20 degreeC/min is 110 degreeC or more.

(2) a laminated film of at least three layers, wherein the inner layer (layer B) contains a branched polypropylene resin, and the surface layer (layer A) contains a low-melting polypropylene resin having a melting point of 50°C or more and 135°C or less, poly propylene film.

(3) The crystallization peak temperature (Tc) when the temperature is increased from 25°C to 250°C at 20°C/min with a differential scanning calorimeter DSC and then decreased from 250°C to 25°C at 20°C/min at 20°C/min is 110°C or higher; _{, the maximum height of the surface asperity St x} of the surface X having a small surface asperity St x is 150 nm or less, and the maximum height of the surface asperity St _y of the surface Y having the large maximum height of the surface asperity St y is the maximum height of the surface asperity St _x of the surface X It is 1.3 times or more, and the glossiness of at least one surface is 144 % or more, The polypropylene film.

The polypropylene film of the present invention can be suitably used as a release film from the viewpoint of improving surface flexibility and excellent surface smoothness, transparency, and releasability.

The polypropylene film of the present invention has an elastic modulus measured by the nanoindentation method of at least one surface of 2.5 GPa or less, and the temperature is increased from 25° C. to 250° C. by a differential scanning calorimeter DSC at 20° C./min, followed by 250 It is a film whose crystallization peak temperature (Tc) when temperature-falling from 20 degreeC to 25 degreeC at 20 degreeC/min is 110 degreeC or more. Hereinafter, the polypropylene film of this invention of this aspect is called this invention 1 or the polypropylene film of this invention 1.

Further, the polypropylene film according to another aspect of the present invention is a laminated film of at least three layers or more, the inner layer (layer B) contains a branched polypropylene resin, and the surface layer (layer A) has a melting point of 50°C or more and 135°C or less. A film containing a melting point polypropylene resin. Hereinafter, the polypropylene film of this invention of this aspect is called this invention 2 or the polypropylene film of this invention 2.

In addition, the polypropylene film according to another aspect of the present invention is crystallized when the temperature is increased from 25°C to 250°C at 20°C/min with a differential scanning calorimeter DSC, and then cooled from 250°C to 25°C at 20°C/min. and the peak temperature (Tc) is more than 110 ℃, surface protrusion maximum height St is and is 150nm or less surface protrusion maximum height of the small surface X St _x, surface protrusion maximum height St is a surface protrusion maximum height St _y of large surface Y surface It is a polypropylene film which is 1.3 times or more of surface processus|protrusion maximum height St _x of X, and the glossiness of at least one surface is 144 % or more. Hereinafter, the polypropylene film of this invention of this aspect is called this invention 3 or the polypropylene film of this invention 3. In addition, when it is simply described as the present invention, it is described in a meaning including any of the present invention 1, the present invention 2, and the present invention 3.

In this invention, a polypropylene film means the film which contains 80 mass % or more and 100 mass % or less of polypropylene resin with respect to 100 mass % of total mass of a film. It is preferable that they are 90 mass % or more and 100 mass % or less, and, as for the polypropylene resin in a polypropylene film, it is more preferable that they are 95 mass % or more and 100 mass % or less. In addition, the polypropylene film of this invention means not a microporous film, but a film which does not have many voids, and specifically means the polypropylene film whose porosity is 0% or more and less than 20%. The porosity of the polypropylene film is more preferably 0% or more and less than 10%, and still more preferably 0% or more and less than 5%. The porosity of the polypropylene film can be obtained from the specific gravity (ρ) of the film and the specific gravity (d) of the sheet quenched with water at 25°C after the film is hot-pressed at 280°C and 5 MPa by the following formula.

Porosity (%) = [(d-ρ)/d] × 100

In the polypropylene film of the present invention 1, the elastic modulus of at least one surface measured by the nanoindentation method is 2.5 GPa or less (hereinafter, the elastic modulus measured by the nanoindentation method of at least one surface is simply referred to as the surface elastic modulus) may be described), therefore, when used as a release film for surface protection of a resin layer having surface flexibility and adhesiveness, the shape of the resin layer, which is the protective surface, is not deformed, and slight irregularities of the cover film are applied to the protective surface. It is possible to protect the shape marks without transferring them. On the other hand, when the surface elastic modulus exceeds 2.5 GPa, when used as a release film for surface protection of a resin layer having high rigidity and tackiness, the shape of the resin layer as a protective surface changes when peeling, or a cover film on the protective surface of the uneven warrior marks remain. From the above viewpoint, the surface elastic modulus is preferably 2.3 GPa or less, more preferably 2.1 GPa or less, and most preferably 1.9 GPa or less. The lower limit of the surface elastic modulus is not particularly limited, and although smaller is more preferable, it is not easy to make it smaller than 0.5 GPa in reality, so the realistic lower limit is about 0.5 GPa. In order to make the surface elastic modulus of the polypropylene film of this invention 1 into 2.5 GPa or less, it is set as a laminated film as mentioned later, and a low-melting-point polypropylene resin is added to the film surface layer, and longitudinal stretching and lateral stretching at the time of film forming. It can be achieved by adjusting the relationship between the respective stretching temperatures of , so that the longitudinal stretching temperature becomes high.

In addition, the polypropylene film of the present invention 1 has a crystallization peak temperature when the temperature is increased from 25°C to 250°C at 20°C/min with a differential scanning calorimeter DSC, and then decreased from 250°C to 25°C at 20°C/min ( Tc) is 110°C or higher. The high temperature of Tc means the easiness of spherical crystal formation. As a method of forming the surface unevenness of a polypropylene film, a method using crystal transformation is used. In the film manufacturing process, it is solidified on a cooling drum after melt extrusion to form a β-crystal system spherical crystal, and a thermally unstable β crystal in the stretching process. crystal transformation into α crystals to form irregularities on the surface of the film. When the β crystal is large, the surface unevenness of the film after stretching becomes large, and it tends to be roughened. On the other hand, by making the β crystal small, the surface unevenness of the film after stretching is formed finely. That is, in the polypropylene film of the present invention 1, it is important to form a small spherical crystal size from the viewpoint of obtaining surface smoothness and transparency as a release film for surface protection, and it is important that the crystallization peak temperature (Tc) is 110° C. or higher . For the same reason, that is, from a viewpoint of forming a spherical crystal size small and obtaining surface smoothness and transparency, 112 degreeC or more is preferable, and, as for Tc, 114 degreeC or more is more preferable. On the other hand, when Tc is less than 110 degreeC, a spherical crystal size becomes large, and the film surface unevenness|corrugation after extending|stretching becomes a roughened thing. Although the upper limit of Tc of the polypropylene film of this invention 1 is not specifically limited, Since surface smoothness and transparency will become sufficient values at 125 degreeC, an upper limit shall be 125 degreeC. In order to make Tc into 110 degreeC or more, it can be achieved by setting it as a laminated|multilayer film as mentioned later and adding a branched polypropylene resin to a film inner layer.

The polypropylene raw material used for the polypropylene films of the present inventions 1 to 3 is not particularly limited, but preferably, the cold xylene soluble part (hereinafter CXS) is 4% by mass or less, and the meso pentad fraction is 0.94. It is preferable that it is polypropylene or more, and it is more preferable that it is polypropylene 0.95 or more. When a polypropylene raw material does not satisfy these, film forming stability may fall or the mechanical characteristic of a film may fall.

Here, the cold xylene soluble portion (CXS) refers to a polypropylene component dissolved in xylene when the polypropylene film is completely dissolved in xylene and then precipitated at room temperature, and has low stereoregularity, low molecular weight, etc. It is thought that the component which is difficult to crystallize for the reason of corresponds to the cold xylene soluble part (CXS). When many such components which are difficult to crystallize are contained in resin, the mechanical properties of a polypropylene film may fall. Therefore, although it is preferable that CXS of a polypropylene raw material is 4 mass % or less, More preferably, it is 3 mass % or less, Especially preferably, it is 2 mass % or less. Although it is so preferable that CXS is low, about 0.1 mass % is a minimum. In order to make CXS of a polypropylene resin into the said range, the method of increasing the catalyst activity at the time of obtaining resin, the method of washing|cleaning the obtained resin with a solvent or propylene monomer itself, etc. can be used.

From a similar viewpoint, it is preferable that the mesopentad fraction of a polypropylene raw material is 0.94 or more, More preferably, it is 0.95 or more, More preferably, it is 0.96 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene measured by nuclear magnetic resonance (NMR method), and the higher the value, the higher the crystallinity, the higher the melting point, and the higher the melting point, the more suitable for use at high temperature. It is preferable because There is no particular restriction on the upper limit of the mesopentad fraction. In order to obtain a resin with such high stereoregularity, a method of washing the resin powder obtained with a solvent such as n-heptane, a method of selecting a catalyst and/or a cocatalyst, and a method of appropriately selecting a composition are preferably employed.

Moreover, as a polypropylene raw material, More preferably, a melt flow rate (MFR) is 1-10 g/10min (230 degreeC, 21.18N load), Especially preferably, 2-5 g/10min (230 degreeC, 21.18N load) is 2-5 g/10min (230 degreeC, 21.18N load). ), it is preferable from a viewpoint of film forming property or the mechanical characteristic of a film. In order to make MFR into said value, the method of controlling an average molecular weight, molecular weight distribution, etc. are employ|adopted.

As a polypropylene raw material, the copolymerization component etc. by another unsaturated hydrocarbon may be contained in the range which does not impair the objective of this invention, and the polymer which is not propylene alone may be blended. As a monomer component constituting such a copolymerization component or a blend, for example, ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1,3-methylbutene-1,1 -Hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl- 2-norbornene etc. are mentioned. From the viewpoints of spherical crystal formation and heat resistance, the copolymerization amount or blend amount is preferably less than 1 mol%, and the blend amount is preferably less than 10 mass%.

In the polypropylene raw material used for the polypropylene film of the present inventions 1 to 3, in the range not impairing the effects of the present invention, an antioxidant, a heat stabilizer, an antistatic agent, a lubricant containing inorganic or organic particles, and further You may contain various additives, such as an antiblocking agent, a filler, and an incompatible polymer. In particular, it is preferable to contain an antioxidant for the purpose of suppressing oxidative deterioration of polypropylene or resin having a low surface free energy. It is preferable that content of antioxidant shall be 2 mass % or less with respect to 100 mass % of polypropylene raw materials, More preferably, it is 1 mass % or less, More preferably, it is 0.5 mass % or less.

The polypropylene film of this invention 1 is a laminated|multilayer film of at least 3 layers or more from a viewpoint of improving the surface smoothness, transparency, and releasability of a film, and it is preferable that the inner layer (B layer) contains a branched polypropylene resin. By containing the branched polypropylene resin in the inner layer (layer B), the crystallization peak temperature (Tc) of the polypropylene film is increased, and the spherical crystal size generated in the cooling step of the melt-extruded resin sheet can be easily controlled small. have. In addition, in the present invention 1, by containing a branched polypropylene resin in the inner layer (layer B), the steep height difference of the surface asperity after biaxial stretching using crystal transformation can be reduced, and the surface roughness becomes dense and fine, so smoothness, Transparency and releasability can be improved. Moreover, when the polypropylene film of this invention 1 is a laminated|multilayer film of 4 or more layers, it is preferable that at least one of the inner layers which exist is an inner layer (B layer) containing a branched polypropylene resin.

When content of the branched polypropylene resin which comprises the inner layer (B layer) of the polypropylene film of this invention 1 makes B-layer whole 100 mass %, 0.05-10 mass % is preferable. The crystallization peak temperature (Tc) of the polypropylene film is increased, the spherical crystal size generated in the cooling process of the melt-extruded resin sheet is controlled to be small, and the steep height difference of the surface irregularities of the film after biaxial stretching is reduced. From a viewpoint of forming surface unevenness|corrugation, the minimum of content of branched polypropylene resin becomes like this. More preferably, it is 0.5 mass % or more, More preferably, it is 1 mass % or more. On the other hand, the upper limit of content of branched polypropylene resin becomes like this. More preferably, it is 8 mass % or less, More preferably, it is 5 mass % or less.

The branched polypropylene resin as used herein is a polypropylene having 5 or less internal trisubstituted olefins per 10,000 carbon atoms. And more preferably, the branched polypropylene resin has 1 or more and 5 or less internal trisubstituted olefins with respect to 10,000 carbon atoms. The presence of this internal trisubstituted olefin can be confirmed by the proton ratio of ^{1 H-NMR spectrum.}

The polypropylene film of the present invention 1 is a laminated film of at least three layers or more from the viewpoint of improving the surface smoothness, transparency and releasability of the film, and the surface layer (layer A) is a low-melting polypropylene resin having a melting point of 50°C or more and 135°C or less. It is preferable to contain When the surface layer (layer A) contains a low-melting polypropylene resin having a melting point of 50° C. or more and 135° C. or less, the elastic modulus of the film surface is lowered, and when used as a release film for surface protection of a resin layer having adhesiveness, cover the protective surface It can make it difficult to generate|occur|produce the transfer trace of the surface unevenness|corrugation of a film.

Here, the low-melting polypropylene resin having a melting point of 50°C or more and 135°C or less is preferably a polypropylene resin having low crystallinity in order to improve flexibility. As the low-melting polypropylene resin having such a melting point of 50°C or more and 135°C or less, an amorphous polypropylene resin, a low stereoregular polypropylene resin, a syndiotactic polypropylene resin, an α-olefin copolymer, etc. can be used. An amorphous polypropylene resin or a low stereoregularity polypropylene resin is particularly preferable from the viewpoint of being able to control the excellent transparency and the surface elastic modulus with the added amount. The amorphous polypropylene resin preferably used is preferably a polypropylene polymer mainly having atactic or stereoregularity as a main component, and specific examples thereof include homopolymers and copolymers with α-olefins. In particular, a low stereoregular polypropylene resin produced by a metallocene-based catalyst is preferable because it contains a low molecular weight or amorphous, so-called tackiness component. The melting point of the low stereoregularity polypropylene resin is 50°C or more and 135°C or less, more preferably 60°C or more and 130°C or less, and particularly preferably 65°C or more and 125°C or less. The weight average molecular weight of the low melting point polypropylene resin having a melting point of 50°C or more and 135°C or less is preferably 30,000 to 400,000, more preferably 40,000 to 300,000, still more preferably 40,000 to 200,000, and molecular weight distribution Mw/Mn becomes like this. Preferably it is 1-4, and it is more preferable that it is 1-3 (Mw: weight average molecular weight, Mn: number average molecular weight). Moreover, it is preferable that <2, 1> erythro site defect is 0.01 mol% or more. As the low stereoregularity polypropylene resin having the above characteristics, after appropriately selecting commercially available products such as "Elmodu" manufactured by Idemitsu Kosan Co., Ltd., "WINTEC" manufactured by Nippon Polypro Co., Ltd., "Vistamaxx" manufactured by ExxonChemical, etc. Can be used.

When content of the low-melting-point polypropylene resin contained in the surface layer (A layer) of the polypropylene film of this invention 1 makes A-layer whole 100 mass %, 10-90 mass % is preferable. The content of the low-melting polypropylene resin from the viewpoint of reducing the elastic modulus of the film surface and making it difficult to generate transfer marks of the surface unevenness of the cover film on the protective surface when used as a release film for surface protection of a resin layer having adhesiveness More preferably, it is 15 mass % or more, More preferably, it is 20 mass % or more. On the other hand, the upper limit of content of a low-melting-point polypropylene resin becomes like this. More preferably, it is 70 mass % or less, More preferably, it is 50 mass % or less.

As a method of using the polypropylene films of the present inventions 1 to 3 as a laminated film, a method of bonding the films by lamination, a feed block method or multi-manifold method by co-extrusion, a method by coating, etc. are mentioned, From the viewpoints of production efficiency and cost, the lamination method by melt co-extrusion and the lamination method by coating are preferable. In addition, the lamination|stacking is preferably a structure formed by laminating|stacking three or more layers in the film thickness direction, Specifically, both surface layers are made into A-layer, and it is a three-layer or more structure which has at least B-layer as an inner layer, for example, A-layer/B It is a structure of 5 or more layers, such as three-layer structure of layer/A-layer, and A-layer/B-layer/C-layer/B-layer/A-layer. A layer used as a surface layer here is defined as a layer comprised by melting|fusing point 50 degreeC or more and 135 degrees C or less containing the low-melting-point polypropylene resin. In addition, layer B used as an inner layer is defined as a layer comprised by containing branched polypropylene. In addition, the C layer should just be a polypropylene resin, and is not specifically limited.

As for the polypropylene films of this invention 1-3, it is preferable that the thickness ratio of the surface layer (A layer) with respect to the thickness of the whole film is 1 to 20 %. More preferably, it is 1 to 18 %, More preferably, it is 1 to 15 %. When the ratio of the surface layer (layer A) exceeds 20%, the surface may become too smooth and the releasability may be impaired. If it is less than 1 %, an inner layer (B layer) may affect even the surface, and transparency may be impaired. The thickness of the surface layer (layer A) can be adjusted by the number of screw rotations of the extruder, the width of the unstretched sheet, the film forming speed, the draw ratio, and the like within a range that does not deteriorate other physical properties.

Here, the surface layer (layer A) and the inner layer (layer B) are, for example, by producing a film cross section and performing cross-sectional observation using a scanning electron microscope SEM, etc., the A layer containing the low melting point polypropylene resin and the branched poly It is also possible to determine the resin interface of the layer B containing the propylene resin.

In the polypropylene film of the present invention 1 or 2, from the viewpoint of obtaining appropriate surface smoothness, transparency, and releasability, the maximum height of surface protrusions St _x on the surface X of the surface X having a small surface protrusion maximum height St is 100 nm or less, _{It is preferable that the maximum height St y} of the surface projections on the surface Y having a large maximum height St be 1.5 times or more of the _{maximum height St x} of the surface projections on the surface X. 95 nm or less is more preferable, and, as for surface processus|protrusion maximum height St _{x in surface X, 85 nm or less is still more preferable. On the other hand, the maximum height St y} of the surface projections on the surface Y serving as the opposite surface of the surface X is more preferably 1.6 times or more, and still more preferably 1.7 times or more of the maximum height of the surface projections St _{x of the surface X. Surface X can express surface smoothness and transparency by making the maximum height St x} of the surface protrusion smaller than the surface Y, which is the opposite surface, and surface Y, which is the opposite side, can express releasability by increasing the _{maximum height St y of the surface protrusion.} That is, it is effective to have a front and rear disparity of 1.5 times or more between the _{maximum height of the surface asperity St x} of the surface X and the maximum height of the surface asperity St _{y of the surface Y.}

In addition, when the polypropylene film of the present invention 1 or 2 is used as a release film for surface protection of a resin layer having adhesiveness by controlling the _{maximum height of the surface protrusion St x of the surface X to 100 nm or less, the surface of the cover film on the protective surface} It is preferable because it can make it difficult to generate|occur|produce uneven transfer marks. Although the upper limit of the other surface Y is not specifically limited, From a viewpoint of not impairing transparency and smoothness, _{5 times the maximum height of the surface processus|protrusion St x} of the surface X is made into an upper limit. In the polypropylene films of the present inventions 1 and 2, the maximum height St _x of the surface projections on the surface X is 100 nm or less, and the maximum height of the surface projections St _y of the other surface Y is the maximum height of the surface projections St _x of the surface X In order to make it 1.5 times or more, it is made into a laminated film configuration of three or more layers as described later, and the relationship between the raw material composition of each layer, the casting drum temperature, and each stretching temperature of longitudinal stretching and transverse stretching is adjusted so that the longitudinal stretching temperature becomes high. achievable In particular, it is effective to adjust the low melting point polypropylene resin added to the surface layer (layer A) and the branched polypropylene resin added to the inner layer (layer B) to a preferable range. Here, in general, the surface X is the cast drum mounting surface.

From the viewpoint of obtaining surface smoothness, the polypropylene films of the present inventions 1 to 3 preferably have an arithmetic mean height Sa of at least one surface of 20 nm or less, more preferably 16 nm or less, still more preferably 12 nm or less, most preferably is less than 10 nm. When the arithmetic mean height Sa of both surfaces of the film exceeds 20 nm, since the overall height of the surface convex shape becomes a high film, when used as a release film for surface protection of a resin layer having adhesiveness, the surface of the cover film on the protective surface Concave and convex transfer marks may occur. The lower limit of the surface arithmetic mean height Sa is not particularly limited and is preferably smaller, but in reality, it is about 1 nm. In order to make the arithmetic mean height Sa on at least one surface of the polypropylene films 1 to 3 of the present invention 20 nm or less, a laminated film is prepared as described later, and a low-melting polypropylene resin is used in the surface layer (layer A) in particular. It can be achieved by containing and adjusting the casting drum temperature at the time of film forming, and the relationship between each extending|stretching temperature of longitudinal stretch and transverse stretch so that longitudinal stretch temperature may become high.

It is preferable that the haze of at least one surface of the polypropylene film of this invention 1-3 is 2 % or less. More preferably, it is 1.5 % or less, More preferably, it is 1 % or less. When the haze of both surfaces of a film exceeds 2 %, since transparency of a film is low, after bonding with photosensitive resin, when performing process test|inspections, such as fault observation, it may interfere. The lower limit of the haze is not particularly limited, but substantially about 0.1% is the lower limit. In order to make the haze of at least one surface 2% or less, it is achieved by making a laminated film configuration of three or more layers, and adjusting the raw material composition of each layer and the relationship between the respective stretching temperatures of longitudinal stretching and transverse stretching so that the longitudinal stretching temperature is high. It is possible. In particular, it is effective to adjust the low melting point polypropylene resin added to the surface layer (layer A) and the branched polypropylene resin added to the inner layer (layer B) to a preferable range.

The polypropylene films of the present inventions 1 to 3 preferably have a static friction coefficient µs of 0.8 or less. More preferably, it is 0.75 or less, More preferably, it is 0.65 or less. When the static friction coefficient μs exceeds 0.8, the film has low running properties, so wrinkles and scratches may enter the film when conveying and winding the film by roll-to-roll, or after bonding with a photosensitive resin, when conveying and winding up. . Although the lower limit of the static friction coefficient µs is not particularly limited, substantially about 0.2 is the lower limit. In order to make the static friction coefficient μs or less 0.8, it can be achieved by setting it as a laminated|multilayer film structure of three or more layers, containing a branched polypropylene resin in an inner layer (B layer), and controlling film forming conditions to a preferable range.

It is preferable that the glossiness of at least one surface of the polypropylene film of this invention 1-3 is 145 % or more. More preferably, it is 147 % or more, More preferably, it is 149 % or more. When the glossiness of at least one surface is 145% or more, there are few surface irregularities that optically diffusely reflect light on the surface, and the surface smoothness is high, and when used as a release film for surface protection of a resin layer having adhesion, protection It becomes difficult to generate|occur|produce the transcription|transfer trace of the surface unevenness|corrugation of a cover film on a surface. Although the higher glossiness is preferable, about 155 % is substantially the upper limit. In order to make the glossiness of at least one surface 145% or more, it is set as the laminated|multilayer film structure of three or more layers, and a low-melting-point polypropylene resin is contained in the surface layer (A layer), the casting temperature at the time of film forming, longitudinal stretching and transverse stretching It can be achieved by adjusting the relationship between the respective stretching temperatures of , so that the longitudinal stretching temperature becomes high.

The polypropylene films of the present inventions 1 to 3 are used as a cover film of a resin layer having tackiness such as a photosensitive resin, and from the viewpoint of handling properties in the conveying process during processing, the sticking process to the adhesive layer, and the peeling process, the long side direction It is preferable that the sum of the fracture|rupture elongation in the tensile test of a transverse direction is 200 % or more. As for the sum of elongation at break, 220 % or more is more preferable, and 240 % or more is still more preferable. The upper limit is not particularly limited, but in order to increase the elongation at break, it is necessary to lower the draw ratio at the time of film forming, and it is set to 450% from the viewpoint of poor productivity such as a decrease in the production rate and a decrease in the area of the collected film. In order to make the sum of the elongation at break in the tensile test in the longitudinal direction and the width direction within the above range, it can be achieved by controlling the film forming conditions such as the raw material composition of the film, the lamination structure of the film, and the draw ratio to a preferable range.

The polypropylene films of the present inventions 1 to 3 are used as a cover film of a resin layer having tackiness such as a photosensitive resin, and from the viewpoint of handling properties in the conveying process, sticking and peeling process, in the tensile test in the longitudinal direction and the width direction. It is preferable that the sum of the Young's modulus of is 3.5 GPa or more. As for the sum of Young's modulus, 3.8 GPa or more is more preferable, and 4.0 GPa or more is still more preferable. The upper limit is not particularly limited, but in order to increase the Young's modulus, it is necessary to increase the draw ratio at the time of film forming, and it is set to 7.0 GPa from the viewpoint of film forming properties performed at a draw ratio that does not break the film. In order to make the sum of the Young's modulus in the tensile test in the longitudinal direction and the width direction within the above range, it can be achieved by controlling the film forming conditions such as the raw material composition of the film and the lamination structure of the film to a preferable range.

Here, in the polypropylene film of this invention 1-3, "long side direction" is a direction corresponding to the flow direction in a film manufacturing process (it may be referred to as "MD" hereafter), and "width direction" is , a direction (hereinafter, sometimes referred to as "TD") orthogonal to the flow direction in said film manufacturing process. When a film sample is in the shape of a reel, a roll, etc., it can be said that a film winding direction is a long side direction. On the other hand, in the case of a film in which it is not clear which direction corresponds to the flow direction in the film manufacturing process from the appearance of the film, for example, a line is drawn at 15° intervals based on an arbitrary straight line on the film plane. , a slit-shaped film piece is sampled parallel to each line to obtain the breaking strength with a tensile tester, and the direction giving the maximum breaking strength is regarded as the width direction of the film, and the direction orthogonal to the width direction of the film is considered as the long side direction. Details will be described later, but when the breaking strength cannot be obtained with a tensile tester because the width of the sample is less than 150 mm, the crystal orientation of the α crystal (110) plane of the polypropylene film by wide-angle X-ray is measured as follows, It is set as the film length and width direction based on the following judgment criteria. That is, the X-ray is incident in a direction perpendicular to the film surface, and the crystal peak at 2θ = about 14° (α crystal (110) plane) is scanned in the circumferential direction, and the diffraction intensity distribution of the obtained diffraction intensity distribution is high. Let be the film width direction, and let the direction orthogonal to it be the long side direction.

In the polypropylene films of the present inventions 1 to 3, the temperature at which the thermal contraction force in the film long side direction becomes 20 mN or more is preferably 116°C or higher, more preferably 120°C or higher, still more preferably 124°C or higher, and most preferably It is usually above 128°C. When the temperature when the thermal contraction force in the longitudinal direction of the film becomes 20 mN or more is less than 116 ° C., after bonding to an adherend as a release film, when passing through a high-temperature process such as a heating roll or oven, shrinkage It may peel from a to-be-adhered body, or curl may generate|occur|produce. Although the upper limit of the temperature at which a thermal contraction force becomes 20 mN or more is not specifically limited, About 160 degreeC is an upper limit substantially. In order to make the temperature value when the thermal contraction force is 20 mN or more within the above range, a laminated film configuration of three or more layers is used, and the relationship between the raw material composition of each layer, the casting drum temperature, and each stretching temperature of longitudinal stretching and transverse stretching is vertical. It can be achieved by adjusting so that the stretching temperature becomes high.

The thickness of the polypropylene films of the present inventions 1 to 3 is appropriately adjusted depending on the use and is not particularly limited, but is used as a cover film of a resin layer having adhesiveness such as a photosensitive resin, and is used as a cover film for the conveyance process during processing, for the adhesive layer It is preferable that they are 5 micrometers or more and 100 micrometers or less from a viewpoint of the handling property in a sticking and peeling process. If the thickness is less than 5 µm, handling may become difficult, and if it exceeds 100 µm, the amount of resin may increase and productivity may decrease. The thickness is more preferably 5 µm or more and 80 µm or less, still more preferably 5 µm or more and 60 µm or less, and most preferably 5 µm or more and 40 µm or less. The thickness can be adjusted by the number of rotations of the screw of the extruder, the width of the unstretched sheet, the film forming speed, the draw ratio, and the like within a range that does not deteriorate other physical properties.

The polypropylene film of the present invention 2 is a laminated film of three or more layers including at least a surface layer (layer A) and an inner layer (layer B), and the inner layer (layer B) contains a branched polypropylene resin, and the surface layer (layer A) Silver is a polypropylene film containing the low-melting-point polypropylene resin whose melting|fusing point is 50 degreeC or more and 135 degrees C or less. Here, when a layer containing a low-melting polypropylene resin having a melting point of 50° C. or more and 135° C. or less constituting the layer A is used as the inner layer, the surface elastic modulus of the film cannot be lowered, and the branched polypropylene resin constituting the layer B When the layer containing is made into a surface layer, the steep height difference of the surface asperity after biaxial stretching will generate|occur|produce. The polypropylene film of the present invention 2, by containing branched polypropylene in the inner layer (layer B), reduces the steep height difference of surface asperity after biaxial stretching using crystal transformation, and forms a dense and fine surface asperity and surface layer (A layer) reduces the elastic modulus of the film surface by containing the low-melting-point polypropylene resin whose melting|fusing point is 50 degreeC or more and 135 degrees C or less. In the polypropylene film of the present invention 2, the film structure of the inner layer and the surface layer improves the surface flexibility, and the effect excellent in surface smoothness, transparency, and releasability can be obtained the most, and release for surface protection of the adhesive resin layer When used as a film, it can make it difficult to generate|occur|produce the transfer trace of the surface unevenness|corrugation of a cover film on a protective surface. Moreover, since transparency of a film is high, after bonding with photosensitive resin, when performing process test|inspections, such as fault observation, it can reduce fault erroneous detection by obstruction. In addition, when the polypropylene film of this invention 2 is a laminated|multilayer film of 4 or more layers, what is necessary is just that at least one of the inner layers which exist in multiple numbers contains an inner layer (B layer) containing a branched polypropylene resin.

The polypropylene film of the present invention 3 has a crystallization peak temperature (Tc) when the temperature is increased from 25°C to 250°C at 20°C/min with a differential scanning calorimeter DSC, and then the temperature is lowered from 250°C to 25°C at 20°C/min. ) is 110° C. or higher, the maximum height of the surface asperity St is small on the surface X, the maximum height of St _x is 150 nm or less, and the maximum height of the surface Y of the surface Y with the large maximum height of St _y is the surface asperity of the surface X It is 1.3 times or more of the maximum height St _x , and the glossiness in at least one surface is 144 % or more. Polypropylene film of the present invention 3 is polished in the relationship, the surface of at least one of the surface protrusion maximum height St _x and the surface protrusion maximum height of the surface opposite to the surface Y St _y of the crystallization peak temperature (Tc), the surface X By controlling the degree, the surface flexibility is improved, and the effect excellent in surface smoothness, transparency, and releasability can be obtained most, and when used as a release film for surface protection of a resin layer having adhesiveness, the surface of the cover film on the protective surface It can make it difficult to generate|occur|produce the uneven transfer mark, and since the transparency of a film is high, after bonding with photosensitive resin, when performing process test|inspections, such as fault observation, a fault erroneous detection can be reduced.

Next, although the manufacturing method of the polypropylene film of this invention is demonstrated, it is not necessarily limited to this.

First, each raw material of a surface layer (A) and an inner layer (layer B) is supplied to each single screw extruder, and melt-extrusion is performed at 200-260 degreeC. Then, after removing foreign substances or modified polymers with a filter installed in the middle of the polymer tube, a multi-manifold type A-layer/B-layer/A-layer composite T die, for example, so that the stacking thickness ratio is 1/15/1 It laminates|stacks, and it discharges on a cast drum, and obtains the lamination|stacking unstretched sheet|seat which has the layer structure of A-layer/B-layer/A-layer. At this time, it is preferable that the surface temperature of a cast drum is 15-50 degreeC from a viewpoint of obtaining the smoothness and transparency of the film surface. As a method of adhesion to the casting drum, any of an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. may be used, but the air knife method is preferable from the viewpoint of planarity. The air temperature of the air knife is 20 to 50°C, and the blowing air velocity is preferably 130 to 150 m/s, and in order to improve the uniformity in the width direction, it is preferable to have a double tube structure. Moreover, in order not to generate|occur|produce vibration of a film, it is preferable to adjust the position of an air knife appropriately so that air may flow to a film forming downstream. Here, in the melt-laminated polymer, the surface on the side in contact with the casting drum surface becomes a smooth surface, so the surface X and the opposite surface are referred to as the surface Y.

The obtained unstretched sheet is allowed to cool in the air, and then is introduced into the longitudinal stretching step. In the longitudinal stretching step, the unstretched sheet is first brought into contact with a plurality of metal rolls maintained at 110° C. or higher and 160° C. or lower, preheated to the stretching temperature, stretched 3 to 8 times in the longitudinal direction, and then cooled to room temperature. When extending|stretching temperature is 160 degreeC or more, extending|stretching nonuniformity may generate|occur|produce or a film may fracture|rupture. Moreover, when a draw ratio is less than 3 times, a draw nonuniformity may generate|occur|produce, the orientation of a film may become weak, and a mechanical characteristic may fall.

Subsequently, the longitudinal uniaxially stretched film is guided by a tenter, the end of the film is gripped with a clip, and the transverse stretch is stretched 7 to 13 times in the width direction at less than 100 to 160°C. When the stretching temperature is higher than the longitudinal stretching temperature, the low-melting polypropylene resin contained in the surface layer (layer A) is partially melted and the film is broken, or the film surface after biaxial stretching may be largely roughened even if the film is not broken. However, when extending|stretching temperature is too high, the rigidity of a film may fall.

When the polypropylene film of the present invention contains a low-melting polypropylene resin in the surface layer (layer A), stretching at a temperature lower than the longitudinal stretching temperature for the transverse stretching temperature is suitable for obtaining surface smoothness, transparency, and releasability. easy to obtain It is preferable to make transverse stretching temperature into 100 degreeC or more and less than longitudinal stretching temperature.

In the subsequent heat treatment and relaxation treatment process, while applying relaxation at a relaxation rate of 2 to 20% in the width direction while tensioning in the width direction with a clip, heat fixing at a temperature of 100°C or more and less than 160°C, and then 80-100% It guides to the outside of a tenter through the cooling process at degreeC, the clip of the film edge part is released, the film edge part is slit in a winder process, and the film product roll is wound up. Condition control of the heat treatment and relaxation process is very important to adjust the thermal shrinkage. The relaxation rate is more preferably 5 to 18%, still more preferably 8 to 15%. Further, the heat setting temperature is more preferably 100°C or more and transverse stretching temperature or less, and still more preferably 120°C or more and transverse stretching temperature or less, when the low-melting-point polypropylene resin is contained in the surface layer (layer A).

The laminated polypropylene film of the present invention obtained as described above can be used for various purposes such as packaging films, release films, process films, hygiene products, agricultural products, construction products, medical products, etc. It can be used suitably as a film and a process film. In particular, since it is excellent in transparent smoothness, it is preferably used as a release film, such as a cover film of an adhesive resin layer.

Example

The measuring method of the characteristic value in this invention, and the evaluation method of an effect are as follows.

(1) Film thickness

The thickness of 10 arbitrary places of a polypropylene film was measured using the contact-type Anritsu Co., Ltd. electron micrometer (K-312A type) in the atmosphere of 23 degreeC 65 %RH. The average value of the thickness of the ten places was made into the film thickness of a polypropylene film.

(2) The elastic modulus (surface elastic modulus) measured by the nanoindentation method on the film surface

A nanoindenter "ENT-2100" manufactured by Elionix Co., Ltd. was used for the measurement. To the polypropylene film, apply 1 drop of "Aron Alpha" (registered trademark) Pro impact resistance" manufactured by Toagosei Co., Ltd., and fix the polypropylene film to a dedicated sample holder via an instant adhesive, and Measurement was performed as a measurement surface. For the measurement, a triangular pyramid diamond indenter (Berkovich indenter) having an angle between the edges of 115° was used. The measurement data was processed by the dedicated analysis software (version 6.18) of "ENT-2100", and the indentation modulus EIT (GPa) was measured. The measurement was performed at n=10 for both surfaces of the film, and the average value thereof was obtained, and the value of the smaller one was described in the table among the average values of the measured values of both surfaces.

Measuring Mode: Load-Unload Test

Maximum load: 0.5mN

Holding time at maximum load: 1 second

Loading speed, unloading speed: 0.05mN/sec

(3) crystallization peak temperature (Tc)

Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Co., Ltd.), a 3 mg polypropylene film was heated from 25°C to 250°C at 20°C/min in a nitrogen atmosphere, and held for 5 minutes. Then, it temperature-falls from 250 degreeC to 25 degreeC at 20 degreeC/min. The peak temperature of the exothermic curve obtained at the time of this temperature fall was made into the crystallization temperature (Tc) of a polypropylene film. In addition, when several peak temperatures could be observed, the highest temperature in the area|region of 80 degreeC - 130 degreeC was made into the crystallization temperature (Tc) of a polypropylene film.

(4) surface asperity maximum height (St), arithmetic mean height (Sa)

Measurements were performed using VertScan2.0 R5300GL-Lite-AC of Ryoka Systems Co., Ltd., and the bending component was removed by polynomial fourth-order approximation surface correction of the shooting screen with the supplied analysis software, followed by interpolation (of height data). For pixels that could not be acquired, a process of supplementing them with height data calculated from surrounding pixels) was performed.

St was measured on both surfaces, and the surface of a small value was calculated|required as surface X. In addition, Sa was measured from both surfaces, and the value of the surface from which the small value was obtained was described in the table|surface.

Measurement conditions are as follows.

Manufacturer: Ryoka System Co., Ltd.

Device Name: VertScan2.0 R5300GL-Lite-AC

Measurement conditions: CCD camera SONY HR-57 1/2 inch (1.27 cm)

10x objective lens

Medium Lens 0.5x

Wavelength filter 520nm white

Measurement mode: Phase

Measurement software: VS-Measure Version5.5.1

Analysis software: VS-Viewer Version5.5.1

Measurement area: 1.252×0.939 mm2

(5) Haze

Three (3) square-shaped film samples with a side of 5 cm are prepared. Next, in the state (23 degreeC, 50% of relative humidity), a sample is left to stand for 40 hours. Using a turbidimeter "NDH5000" manufactured by Nippon Denshoku Kogyo Co., Ltd. for each sample, it is carried out in a manner according to JIS "Method for determining haze of transparent material" (K7136 2000 edition). The haze of each of three film samples (three points) was averaged, and it was set as the haze of the film. In addition, the measurement was performed with respect to both surfaces of the film, and the value of the surface from which the small value was obtained was described in the table|surface.

(6) static friction coefficient μs

Using a friction gauge made by Toyo Tester Kogyo, in accordance with ASTM D1894-95 (JIS K 7312-1996), slit-shaped film pieces were sampled at 45° intervals based on an arbitrary straight line on the film plane (width 80 mm, length 200 mm). rectangle), and the initial maximum value of the rising resistance when friction was applied so that one surface and the other surface of the film at the same angle were in contact with each other was taken as the static friction coefficient µs. The measurement was performed 5 times, and the average value was calculated|required. For the static friction coefficient μs of the polypropylene film, the smallest static friction coefficient μs among those measured at 45° intervals was used.

(7) Glossiness

In accordance with JIS K-7105 (1981), using a digital variable angle glossmeter UGV-5D manufactured by Suga Shikekki Co., Ltd., the average value of the data of 5 points measured on the film surface under the condition of 60 degrees of incidence angle and 60 degrees of light reception angle was calculated. It was set as glossiness (%). The measurement was performed with respect to both surfaces of the film, and the value of the surface from which high glossiness was obtained was described in the table|surface.

(8) The sum of the elongation at break in the longitudinal direction and the transverse direction of the film, and the sum of the Young's modulus

The film was cut out into the rectangle of length 150 mm x width direction 10 mm in the test direction, and it was set as the sample. Using a tensile tester (Tensilon AMF/RTA-100 manufactured by Orientec Co., Ltd.), according to the method prescribed in JIS K7161 (1994), measurement was performed 5 times at 25° C. and 65% RH atmosphere, and the average value was obtained. did. However, the point where the load passed through 1N after starting the test at an initial chuck distance of 50 mm and a tensile speed of 300 mm/min was taken as the origin of elongation. In addition, the breaking elongation calculated|required the average value at the time of 5 measurements of the elongation (%) at the time of the breakage of a film.

In addition, the film thickness used for calculation of Young's modulus used the value measured in said (1).

(9) dysplasia

Nitto Denko Co., Ltd. polyester adhesive tape NO.31B was affixed on the surface of the polypropylene film on the side having high gloss obtained in the section of "(7) Glossiness" with a roller, and it was cut to a width of 19 mm. Samples were prepared. The sample was peeled off at a rate of 500 mm/min using a tensile tester, and evaluated on the basis of the following criteria. A and B were passed and C was rejected.

A: The film surface and the adhesive tape can be peeled off at a constant speed

B: The speed is up and down at the time of peeling of a film surface and an adhesive tape

C: At the time of peeling of a film surface and an adhesive tape, a speed|rate goes up and down, and a peeling trace remains on the surface X

(10) Concave-convex transcription inhibitory properties

Polypropylene film and Nippon Zeon Co., Ltd. "Zeonoa Film" (registered trademark) having a thickness of 40 µm were sampled in a square having a width of 100 mm and a length of 100 mm, and obtained in the section of "(7) Glossiness" of the polypropylene film "Zeonoa Film" is superimposed on the side of the low glossiness side so that it contacts, it is sandwiched by two acrylic plates (width 100 mm, length 100 mm), a load of 2.5 kg is applied, 36 in an atmosphere of 23 ° C. time was fixed. After 36 hours, the surface (surface to which the polypropylene film was in contact) of the "Zeonoa film" was visually observed and evaluated according to the following criteria. A and B were passed and C was rejected.

A: Clean, same as before loading

B: Weak irregularities are confirmed

C: Strong unevenness is confirmed

(11) Melting point (Tm) of polypropylene resin

Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Co., Ltd.), 3 mg of a polypropylene resin chip was heated from 25°C to 250°C at 20°C/min in a nitrogen atmosphere, and held for 5 minutes. Subsequently, the temperature was lowered from 250°C to 25°C at 20°C/min to 25°C, the temperature was further increased from 25°C to 250°C at 20°C/min, and held for 5 minutes. The peak temperature of the endothermic curve obtained at the time of this heating up again was made into melting|fusing point (Tm) of polypropylene resin.

(12) The temperature at which the thermal contraction force becomes 20 mN or more

Using TMA (manufactured by SII Nanotechnology Co., Ltd./model TMA/SS6100), the thermal contraction force curve of the film long side direction was measured under the following conditions.

(a) Sample: width 4mm x length 20mm

(b) Temperature program: Raise the temperature from 30°C to a heating rate of 10°C/min

<Heat shrink start temperature>

In the thermal contraction force curve, the temperature at which the thermal contraction force becomes 20 mN during the temperature increase process was read. The measurement was performed 3 times, and the average was calculated|required.

(Example 1)

The whole polypropylene resin for the surface layer (layer A) was 100 mass %, and the polypropylene resin (MFR 3g/10min, melting|fusing point 164 degreeC) made from Co., Ltd. Prime Polymer was 70 mass %, and a low-melting-point polypropylene resin A blend of 30% by mass of "Elmodew" (registered trademark) S901 (melting point 80°C) manufactured by Idemitsu Kosan Co., Ltd. is supplied to a single screw melt extruder for layer A, and polypropylene resin for inner layer (layer B) The whole was 100 mass %, 98 mass % of the polypropylene resin (MFR 3g/10min, melting|fusing point 164 degreeC) manufactured by Prime Polymer Co., Ltd. and the branched polypropylene resin (Profax PF-814) made by Basell were 2 Feed block type A layer / B layer / A layer after the mass % blend is supplied to the single-axis melt extruder for B layer, melt extrusion is performed at 260 ° C., and foreign matter is removed with a sintered filter of 60 μm cut. It is a composite T-die of a three-layer configuration, laminated at a thickness ratio of 1/13/1 (ratio of A-layer on both sides = 13% with respect to the total thickness), and discharged to a cast drum whose surface temperature is controlled at 22° C., and an air knife was in close contact with the casting drum. Thereafter, pneumatic air having a temperature of 25°C and a pressure of 0.3 MPa was blown to the non-cooling drum surface of the sheet on the casting drum, followed by cooling to obtain an unstretched sheet. Subsequently, the sheet was preheated to 148°C using a ceramic roll, and stretched 4.5 times in the longitudinal direction of the film between the rolls at 148°C provided with a circumferential speed difference. Next, the tenter type stretching machine is introduced by gripping the end with a clip, preheated at 168° C. for 3 seconds, stretched 8.0 times in the width direction at 140° C., and heat treatment at 120° C. while giving 12% relaxation in the width direction. After that, it was guided to the outside of the tenter through a 100°C cooling step, the clip at the film edge was released, the film was wound around the core, and a polypropylene film having a thickness of 12 μm was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Example 2)

Except having changed the branched polypropylene resin contained in the inner layer (layer B) to the content shown in Table 1, it carried out similarly to Example 1, and obtained the 11-micrometer-thick polypropylene film. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Examples 3 and 4)

Except having changed the low-melting-point polypropylene resin contained in the surface layer (A layer) into content shown in Table 1, it carried out similarly to Example 1, and obtained the polypropylene film with a thickness of 12 micrometers. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Example 5)

In the same manner as in Example 1, except that the low-melting polypropylene resin contained in the surface layer (layer A) and the branched polypropylene resin contained in the inner layer (layer B) were changed to the contents shown in Table 1, respectively, a thickness of 15 µm A polypropylene film was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Example 6)

In the same manner as in Example 1, an unstretched sheet was obtained in which layer A/layer B/layer A were laminated at a thickness ratio of 1/10/1 (ratio of layer A on both sides to the total thickness = 17%), and then the sheet was It preheated to 148 degreeC using a ceramic roll, and it extended|stretched 4.5 times in the long side direction of the film between the 148 degreeC rolls which provided the circumferential speed difference. Next, the tenter type stretching machine is introduced by gripping the end with a clip, and after preheating at 168° C. for 3 seconds, it is stretched 8.0 times in the width direction at 148° C., which is the same temperature as longitudinal stretching, in the width direction, and 12% relaxation is given in the width direction. While heat-treating at 140 ° C., and then guided to the outside of the tenter through a cooling step of 100 ° C., the clip at the end of the film was released, the film was wound around the core, and a polypropylene film having a thickness of 12 μm was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Example 7)

In the same manner as in Example 1, except that 30% by mass of "WINTEC" (registered trademark) WFX4M (melting point 125°C) manufactured by Nippon Polypro Co., Ltd. was changed as a low-melting-point polypropylene resin contained in the surface layer (layer A). Thus, a polypropylene film having a thickness of 12 µm was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Example 8)

12 µm in thickness in the same manner as in Example 1, except that 2 mass % of "WAYMAX" (registered trademark) MFX6 manufactured by Nippon Polypro Co., Ltd. was changed as a branched polypropylene resin contained in the inner layer (layer B). of polypropylene film was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Comparative Example 1)

As a polypropylene resin, a polypropylene resin made by Prime Polymer Co., Ltd. (MFR 3 g/10 min, melting point 164° C.) is supplied to a 100 mass% single screw melt extruder, melt-extruded at 260° C., and sintered with a 60 μm cut. After removing foreign substances with a filter, it was discharged to a cast drum whose surface temperature was controlled at 25°C with a T-die, and was brought into close contact with the casting drum with an air knife. Thereafter, pneumatic air having a temperature of 25°C and a pressure of 0.3 MPa was blown to the non-cooling drum surface of the sheet on the casting drum, followed by cooling to obtain an unstretched sheet. Subsequently, the sheet was preheated to 148°C using a ceramic roll, and stretched 4.6 times in the longitudinal direction of the film between the 148°C rolls provided with a circumferential speed difference. Next, the tenter-type stretching machine is introduced by gripping the end with a clip, preheated at 168° C. for 3 seconds, stretched 7.8 times in the width direction at 155° C., and heat treatment at 150° C. while giving 12% relaxation in the width direction After that, it was guided to the outside of the tenter through a 100°C cooling step, the clip at the film edge was released, the film was wound around the core, and a polypropylene film having a thickness of 12 μm was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Comparative Example 2)

The whole polypropylene resin was 100 mass %, and 98 mass % of polypropylene resin (MFR 3g/10min, melting|fusing point 164 degreeC) manufactured by Prime Polymer Co., Ltd. and a branched polypropylene resin manufactured by Basell (Profax PF-814) ) is supplied to a single-screw melt extruder, melt-extruded at 260 ° C., and foreign substances are removed with a sintered filter having a cut of 60 µm. Then, a cast drum with a T-die and a surface temperature controlled at 25 ° C. It was discharged to the air knife and adhered to the casting drum with an air knife. Thereafter, pneumatic air having a temperature of 25°C and a pressure of 0.3 MPa was blown to the non-cooling drum surface of the sheet on the casting drum, followed by cooling to obtain an unstretched sheet. Subsequently, the sheet was preheated to 148°C using a ceramic roll, and stretched 4.5 times in the longitudinal direction of the film between the rolls at 148°C provided with a circumferential speed difference. Next, the tenter-type stretching machine is introduced by gripping the end with a clip, preheated at 168° C. for 3 seconds, stretched 8.2 times in the width direction at 155° C., and heat treatment at 140° C. while giving 11% relaxation in the width direction. After that, it was guided to the outside of the tenter through a 100°C cooling step, the clip at the film edge was released, the film was wound around the core, and a polypropylene film having a thickness of 12 μm was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Comparative Example 3)

The whole polypropylene resin is 100 mass %, and 70 mass % of the polypropylene resin (MFR 3g/10min, melting|fusing point 164 degreeC) made from Co., Ltd. Prime Polymer, and Idemitsu Kosan Co., Ltd. as a low melting point polypropylene resin First, a blend of 30% by mass of “Elmodew” (registered trademark) S901 (melting point 80° C.) is fed to a single-screw melt extruder, melt-extruded at 260° C., and after removing foreign substances with a sintered filter having a cut of 60 μm , It was discharged to a cast drum whose surface temperature was controlled at 24°C with a T-die, and was brought into close contact with the casting drum with an air knife. Thereafter, pneumatic air having a temperature of 25°C and a pressure of 0.3 MPa was blown to the non-cooling drum surface of the sheet on the casting drum, followed by cooling to obtain an unstretched sheet. Then, this sheet was preheated to 140 degreeC using a ceramic roll, and it extended|stretched 4.5 times in the long side direction of the film between 140 degreeC rolls provided with a circumferential speed difference. Next, the tenter-type stretching machine is introduced by gripping the end with a clip, preheated at 160°C for 3 seconds, stretched 8.2 times in the width direction at 135°C, and heat treatment at 120°C while giving 11% relaxation in the width direction After that, it was guided to the outside of the tenter through a 100 degreeC cooling process, the clip of the film edge part was released, the film was wound around the core, and the polypropylene film of thickness 12 micrometers was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Comparative Example 4)

In the same manner as in Example 1, with a composite T die, the A layer/B layer/A layer was melt-extruded at a thickness ratio of 1/15/1 (ratio of both-sided layer A with respect to the total thickness = 11.8%), and the surface was heated to 85°C. It was discharged to the cast drum whose temperature was controlled, and it was made to closely_contact|adhere to the casting drum with an air knife. Thereafter, pneumatic air having a temperature of 25°C and a pressure of 0.3 MPa was blown to the non-cooling drum surface of the sheet on the casting drum, followed by cooling to obtain an unstretched sheet. Subsequently, the sheet was preheated to 146°C using a ceramic roll, and stretched 4.6 times in the long side direction of the film between the 146°C rolls provided with a circumferential speed difference. Next, the tenter type stretching machine is introduced by gripping the end with a clip, preheated at 168°C for 3 seconds, stretched 8.0 times in the width direction at 155°C, and heat treatment at 145°C while giving 12% relaxation in the width direction After that, it guided to the outside of the tenter through a 100 degreeC cooling process, the clip of the film edge part was released, the film was wound around the core, and the 18-micrometer-thick polypropylene film was obtained. Table 1 shows the physical properties and evaluation results of the obtained polypropylene film.

(Comparative Example 5)

The whole polypropylene resin for A-layer was 100 mass %, and 70 mass % of polypropylene resin (MFR 3g/10min, melting|fusing point 164 degreeC) made from Co., Ltd. Prime Polymer, and Idemitsu Kosan as low-melting-point polypropylene resin A blend of 30% by mass of "Elmodew" (registered trademark) S901 (melting point 80° C.) manufactured by Co., Ltd. is supplied to a single screw melt extruder for layer A, and a polypropylene resin for layer B manufactured by Prime Polymer Co., Ltd. 100 mass % of polypropylene resin (MFR 3g/10min, melting point 164 degreeC) is supplied to the single-axis melt extruder for B-layer, melt-extrusion is performed at 260 degreeC, After removing foreign material with a sintering filter of 60 micrometers cut, feed A composite T die having a three-layer configuration including a block-type A layer/B layer/A layer, laminated at a thickness ratio of 1/15/1 (ratio of both-sided layer A to total thickness = 11.8%), and 25° C. It was discharged to a cast drum whose surface temperature was controlled with a furnace, and was brought into close contact with the casting drum with an air knife. Thereafter, pneumatic air at a temperature of 25°C and a pressure of 0.3 MPa was blown to the non-cooling drum surface of the sheet on the casting drum, followed by cooling to obtain an unstretched polypropylene film having a thickness of 50 µm. Table 1 shows the physical properties and evaluation results of the unstretched polypropylene film.

As described above, the polypropylene film of the present invention can be used in various applications such as packaging films, release films, process films, hygiene products, agricultural products, construction products, and medical products. In particular, it can be preferably used as a release film or a process film for applications requiring surface smoothness of a product in terms of improving surface flexibility and excellent surface smoothness, transparency, and releasability, and also has excellent releasability, It is preferably used as a release film, such as a cover film of an adhesive resin layer.

Claims (12)

At least one surface has an elastic modulus of 2.5 GPa or less as measured by the nanoindentation method, and the temperature is increased from 25°C to 250°C at 20°C/min using a differential scanning calorimeter DSC, followed by 20°C/min from 250°C to 25°C The polypropylene film whose crystallization peak temperature (Tc) when temperature-falling in min is 110 degreeC or more. The polypropylene film according to claim 1, wherein it is a laminated film of at least three layers or more, and the inner layer (layer B) contains a branched polypropylene resin. The polypropylene film of Claim 1 or 2 which is a laminated|multilayer film of at least 3 layers or more, and the surface layer (A layer) contains the low-melting-point polypropylene resin whose melting|fusing point is 50 degreeC or more and 135 degreeC or less. It is a laminated film of at least three layers or more, wherein the inner layer (layer B) contains a branched polypropylene resin, and the surface layer (layer A) contains a low-melting polypropylene resin having a melting point of 50°C or more and 135°C or less, a polypropylene film . _{The maximum height St of a surface asperity St x} of the surface X with a small surface protrusion maximum height St is 100 nm or less, and the surface asperity maximum height St of the surface Y with a large surface protrusion maximum height St according to any one of claims 1 to 4 _y is 1.5 times or more of the maximum height of the surface asperity St _{x of the surface X, the polypropylene film.} The polypropylene film according to any one of claims 1 to 5, wherein the arithmetic mean height Sa of at least one surface is 20 nm or less. The polypropylene film according to any one of claims 1 to 6, wherein the haze of at least one surface is 2% or less. The polypropylene film according to any one of claims 1 to 7, wherein the coefficient of static friction μs is 0.8 or less. The polypropylene film according to any one of claims 1 to 8, wherein the glossiness of at least one surface is 145% or more. The polypropylene film according to any one of claims 1 to 9, wherein the temperature at which the thermal contraction force in the film longitudinal direction is 20 mN or more is 116°C or more. The crystallization peak temperature (Tc) when the temperature is increased from 25°C to 250°C at 20°C/min with a differential scanning calorimeter DSC and then decreased from 250°C to 25°C at 20°C/min is 110°C or more, and surface protrusions _{The maximum height of the surface asperity St x} of the surface X with a small maximum height St is 150 nm or less, and the maximum height of the surface asperity St _y of the surface Y with the large maximum height of the surface asperity St 1.3 times or more of the maximum height of the surface asperity St _{x of the surface X} and the glossiness of at least one surface is 144% or more, the polypropylene film. The release film using the polypropylene film in any one of Claims 1-11.