TW202024197A - Polyolefin film and release film - Google Patents

Abstract

The present invention addresses the problem of providing a polyolefin film excellent in terms of releasing property and quality. At least one surface (A surface) of the polyolefin film of the present invention has an average roughness Sa of 65-600 nm, and the A surface has a peak height Sp and a valley depth Sv, the ratio Sp/Sv being 2.5 or less. The polyolefin film has a haze of 30% or less.

Description

Polyolefin film and release film

The present invention relates to a polyolefin film that is excellent in release properties and grade and can be applied as a release film.

Polyolefin films have excellent transparency, mechanical properties, electrical properties, etc., so they have been used in various applications such as packaging, release, tape, and electrical applications such as cable wrapping and capacitors. Especially because of its excellent surface release properties and mechanical properties, it is suitable for release films or engineering films for various components such as plastic products, building materials, and optical components.

The properties required for the release film are appropriately set depending on the application. In recent years, it has been used as a cover film for a resin layer with adhesive properties such as photosensitive resin. When covering the adhesive resin layer, if the release property of the cover film is poor, there will be the following situations: it cannot be completely peeled off when peeling off, and the shape of the resin layer for the protection surface changes, or the protection surface Peel marks remain. Therefore, there are cases where the method of improving the release property by roughening the surface of the film and reducing the contact area with the resin layer is used. However, there are situations in which if the surface roughness of the cover film is increased, coarse protrusions are likely to be formed. For example, when the film is used as a release film for an optical member, the surface irregularities of the film will be transferred to the optical member and affect the product. Discrimination affects. From the above, there are the following cases: In order to be used in release films that require high characteristics such as optical components, a film that has not formed coarse protrusions, has been uniformly and finely roughened, and has both releasability and quality is required .

As a means of roughening, for example, Patent Documents 1 and 2 describe that spherulites of β crystals, which are one of the crystal forms of polypropylene, are formed and stretched to form pits on the surface of the film, thereby making the surface rough. An example of improving the transportability of steps. In addition, Patent Document 3 describes an example in which particles are added to the film and uniaxially stretched to roughen the surface to improve step transportability. In addition, Patent Document 4 describes an example of roughening by adding particles to the inner layer of the film and stretching it. [Prior Technical Literature] [Patent Literature]

Patent Document 1: International Publication No. 2016/006578 Patent Document 2: JP 2017-125184 A Patent Document 3: Japanese Patent Application Publication No. 2005-138386 Patent Document 4: Japanese Patent No. 6115687

[The problem to be solved by the invention]

However, the methods described in the aforementioned Patent Documents 1 and 2 have a problem of insufficient surface roughness. In addition, the method described in Patent Document 3 also has insufficient surface roughness. Furthermore, in the method described in Patent Document 4, coarse protrusions are formed from high-hardness particles and the unevenness is transferred to the resin layer of the optical member.

Therefore, the subject of the present invention is to solve the above-mentioned problems. That is to provide a polyolefin film with excellent release properties and grades. [Means to solve the problem]

In order to solve the above-mentioned problems and achieve the objective, the polyolefin film of the present invention is characterized in that at least one side (side A) has an average roughness Sa of 65 to 500 nm, and the ratio of the mountain height Sp and the valley depth Sv of the A side is Sp/Sv The value is 2.5 or less, and the haze of the film is 30% or less. [Effects of Invention]

Since the polyolefin film of the present invention is excellent in release properties, heat resistance, and grade, it can be suitably used as a release film.

[Form to implement the invention]

The polyolefin film of the present invention has an average roughness Sa of at least one side (side A) of 65 to 600 nm, and the value of Sp/Sv of the ratio of the height of the mountain Sp of the A side and the depth of the valley Sv of the A side is 2.5 or less, and The haze is below 30%. The average roughness Sa of at least one side (side A) of the polyolefin film of the present invention is more preferably 150-480 nm, and still more preferably 200-400 nm. When Sa is less than 65nm, when used as a release film for surface protection, the contact area with the adherend is large. When the adherend has strong adhesion, it cannot be peeled off completely, and the shape of the adherend surface changes. Or there are peeling marks on the surface of the adherend. In addition, if Sa exceeds 600nm, when used as a release film for surface protection, the contact area with the adherend may be small, and peeling may occur during lamination transportation. In order to make Sa in the range of 65-600nm, the raw material composition of the film is set to the range described below, and the film forming conditions are set to the range described below. In particular, a low-melting resin is added to the surface of the film and the temperature is higher than its melting point. Stretching is effective to partially melt the surface of the film and roughen it. In addition, from the viewpoint of imprint transfer on the back side or transportability of the film, it is preferable that the Sa on both sides of the film is 65 to 600 nm.

In addition, when the Sa on both sides of the film is 65 to 600 nm, the side with the smaller Sa value is defined as the A side. When the Sa on both sides is the same, the side with the smaller mountain height Sp is defined as the A side. When the Sa and Sp on both sides are the same, the side with the smaller valley depth Sv is defined as the A side.

In the polyolefin film of the present invention, the ratio of Sp/Sv of the mountain height Sp of the A side and the valley depth Sv of the A side is more preferably 2.0 or less, and more preferably 1.5 or less. The value of Sp/Sv is an index indicating the ratio of mountain height to valley depth. A low value of Sp/Sv means that the maximum height in the plane is low and the protrusion height of the coarse protrusion is low. In addition, due to the deep valley depth, the contact area with the adherend to be bonded becomes low, which means that the release property is high. If the value of Sp/Sv exceeds 2.5, for example, when used as a release film for optical components, the releasability will be insufficient, or the surface unevenness of the film will be transferred to the optical component, especially when the adherend is strongly adhered , It cannot be peeled off completely, and the shape of the adherend surface may change, or peeling marks may remain on the adherend surface. The lower limit of the value of Sp/Sv is not particularly limited, but is substantially the lower limit of about 0.05. In addition, from the viewpoint of imprint transfer on the back side or transportability of the film, it is preferable that the Sp/Sv value of both sides of the film is 2.5 or less. In order to make the value of Sp/Sv 2.5 or less, by setting the raw material composition of the film in the range described below, and setting the film forming conditions in the range described below, in particular, the thickness of the surface layer, the ratio of the low melting point resin, and the stretching temperature are controlled. It is effective to stretch the low-melting resin portion on the surface of the film while melting it to uniformly form depressions while suppressing the height of the protrusions to a certain extent.

The haze of the polyolefin film of the present invention is more preferably 20% or less, still more preferably 10% or less, and most preferably 5% or less. If the haze value exceeds 30%, since the transparency of the film is low, it may be hindered during the step inspection such as defect observation after bonding with the photosensitive resin. The lower limit of the haze value is not particularly limited, but is substantially the lower limit of about 0.1%. In order to make the haze value less than 30%, the raw material composition of the film is set to the range described below, and the film forming conditions are set to the range described below, especially to increase the low melting point resin added to the surface layer and the polyolefin resin that constitutes the main component of the film The compatibility is effective.

In the polyolefin film of the present invention, the value of Sp/Sa of the ratio of the mountain height Sp of the A side and the average roughness Sa of the A side is preferably less than 13. The value of Sp/Sa is an index indicating the ratio of mountain height to average roughness. A low value of Sp/Sa means that the maximum height in the plane is low and the projection height of the coarse projections is low. When the value of Sp/Sa is less than 13, for example, when used as a release film for an optical member, the transfer of unevenness on the surface of the film to the optical member is unlikely to occur, and it can achieve good performance even with a highly adhesive adherend. The peelability. The lower limit of the value of Sp/Sa is not particularly limited, but is substantially about 0.1. In addition, from the viewpoint of imprint transfer on the back side or transportability of the film, it is preferable that the value of Sp/Sa on both sides of the film is less than 13. In order to make the value of Sp/Sa less than 13, by setting the raw material composition of the film in the range described below, and setting the film forming conditions in the range described below, in particular, the thickness of the surface layer or the ratio of the low melting point resin is controlled to be uniform The amount of resin partially melted on the surface of the film is effective.

The polyolefin film of the present invention preferably has an elastic modulus in the thickness direction of 2.3 GPa or less. It is more preferably 2.0 GPa or less, and still more preferably 1.8 GPa or less. When the elastic modulus in the thickness direction is 2.3 GPa or less, for example, when it is used as a release film for an optical member, even a low-hardness adherend is not easy to transfer prints, which is preferable from a grade point of view. The lower limit of the elastic modulus in the thickness direction is not particularly limited, but is substantially 0.5 GPa. In order to make the elastic modulus in the thickness direction 2.3 GPa or less, the raw material composition of the film is set in the range described below, and the film forming conditions are set in the range described below. In particular, it is effective to add a low melting point resin to the surface layer to soften the surface.

The polyolefin film of the present invention preferably has a melting peak above 165°C when the temperature is raised from 30°C to 260°C with a differential operating calorimeter DSC. It is more preferably 168°C or higher, and still more preferably 170°C or higher. When the polyolefin film of the present invention has a melting peak above 165°C, for example, when used as a release film, it will not be deformed due to the softening of the film when it passes through a high-temperature heating step after being bonded to the adherend. It is better in terms of level view. The upper limit of the melting peak temperature is not particularly limited, but is substantially 180°C. In order to make the melting peak temperature 165°C or higher, it is effective to set the raw material composition of the film to the range described below, and set the film forming conditions to the range described below. In particular, the use of a high melting point resin for the inner layer of the film is effective to improve the heat resistance of the inner layer of.

The number of fish eyes in the polyolefin film of the present invention is preferably 5.0/m ² or less. It is more preferably 4.0 pieces/m ² or less, and still more preferably 3.0 pieces/m ² or less. When the number of fisheyes is 5.0/m ² or less, when used as a protective film for high-grade products such as display components or as a base film for manufacturing, it can suppress the decrease in yield, and it is from the viewpoint of grade and productivity. The language is better. The number of fish eyes is as small as possible, and the lower limit is 0/m ² . In order to reduce the number of fisheyes to 5.0/m ² or less, the composition or adjustment method of the raw materials, and the layered structure of the film are set within the range described below, and the additive components in the raw materials or thermal degradation caused fisheyes are reduced. The amount of resin is effective. In addition, it is effective to set the conditions at the time of film formation within the range described later, and to remove foreign substances by filtration before melting the raw materials to be thinned, or to reduce the resin retention.

The sum of the thermal shrinkage at 150°C for 15 minutes in the main shrinkage direction and the orthogonal direction of the polyolefin film of the present invention is preferably 8.0% or less, more preferably 6.0% or less, and still more preferably 4.0% or less. In addition, the main shrinkage direction in the present invention refers to the film plane, when an arbitrary direction is set to 0°, it is 15°, 30°, 45°, 60°, 75°, 90°, 105° with the arbitrary direction. °, 120°, 135°, 150°, 165° angle of each direction when measuring the heat shrinkage rate shows the direction of the highest value.

In the present invention, the direction parallel to the direction in which the film is produced is referred to as the film forming direction, the longitudinal direction or the MD direction, and the direction orthogonal to the film forming direction in the film plane is referred to as the width direction or the TD direction. When the sum of the heat shrinkage rate at 150°C for 15 minutes in the main shrinking direction and its orthogonal direction is 8.0% or less, for example, when used as a release film, the film will not be heated after being bonded to the adherend. Deformation occurs, and it is not easy to peel off from the adherend or produce wrinkles, which is preferable. The lower limit of the thermal shrinkage rate is not particularly limited, but the film may expand, and it is substantially the lower limit of about -2.0%. In order to make the sum of the heat shrinkage rate 8.0% or less, the raw material composition of the film is set to the range described below, and the film forming conditions are set to the range described below, especially when the inner layer of the film uses a high melting point resin or after biaxial stretching The thermal fixation and relaxation conditions of is effective in the range described later.

The maximum point strength of the polyolefin film of the present invention in the direction orthogonal to the main shrinkage direction when measured at 130°C is preferably 70 MPa or more, more preferably 75 MPa or more, and still more preferably 80 MPa or more. When the maximum point strength in the direction orthogonal to the main shrinkage direction is less than 70 MPa, for example, when the film is transported in the heating step, the film may break. The upper limit of the breaking strength is not particularly limited, but is substantially about 200 MPa. In order to make the maximum point strength in the orthogonal direction of the main shrinkage direction when measured at 130°C become 70 MPa or more, the raw material composition of the film is set to the range described below, and the film forming conditions are set to the range described below, especially the inner layer of the film It is effective to use a resin with a high melting point, or to set the stretching conditions during biaxial stretching, heat fixation after stretching, and relaxation conditions in the following ranges.

The thickness of the polyolefin film of the present invention may be appropriately adjusted depending on the application and is not particularly limited, but from the viewpoint of handling properties, it is preferably 0.5 μm or more and 100 μm or less. The thickness of the film is more preferably 1 μm or more and 40 μm or less, still more preferably 1 μm or more and 30 μm or less, and particularly preferably 1 μm or more and 15 μm or less. The thickness can be adjusted according to the number of screw rotations of the extruder, the width of the unstretched sheet, the film production speed, the stretching ratio, etc., within a range that does not reduce other physical properties.

Next, the raw material of the polyolefin film of the present invention will be described, but it is not necessarily limited to this. The polyolefin film of the present invention preferably has a laminated structure comprising at least a surface layer and an inner layer, and at least one of the surface layers contains a polypropylene resin with a melting point of 50°C or higher and 135°C or lower (hereinafter also the melting point of 50°C or higher and 135°C or lower) The polypropylene resin is called polypropylene raw material I). It preferably contains: more preferably 60°C or more and 130°C or less, still more preferably 60°C or more and 120°C or less, most preferably 60°C or more and 100°C or less polypropylene resin. During the preheating/stretching roll transportation, the melting point of the polypropylene raw material I is preferably 50° C. or more from the viewpoint that melting of the film surface and adhesion to the roll do not occur. In addition, from the viewpoint of partially melting the surface of the film during stretching to roughen the surface, the melting point of the polypropylene raw material I is preferably 135°C or lower. The content of the polypropylene raw material I, when the surface layer containing the polypropylene raw material I is 100% by mass, is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and still more preferably It is 30% by mass or more and 60% by mass or less.

Furthermore, the polypropylene raw material I is preferably a homopolypropylene resin. That is, the polyolefin film of the present invention preferably contains a homopolypropylene resin as the aforementioned polypropylene resin having a melting point of 50°C or more and 135°C or less. When the polypropylene raw material I contained in at least one of the surface layers is a copolymer such as a random copolymer or a block copolymer, monomer components such as ethylene may sometimes become the main cause of fish eyes.

As far as the homopolypropylene resin is preferably used as the polypropylene raw material I contained in at least one of the surface layers, it is preferably a homopolymer of propylene and is manufactured using a metallocene catalyst as a polymerization catalyst By. The weight average molecular weight of the homopolypropylene resin is preferably 40,000 to 200,000 (Mw: weight average molecular weight, Mn: number average molecular weight). For homopolypropylene resins having the above-mentioned characteristics, commercially available products such as "L-MODU" manufactured by Idemitsu Kosan Co., Ltd., which are polypropylene resins with low stereoregularity, can be used in appropriate selection.

The polyolefin film of the present invention may also have a single-layer structure. The main component of the polyolefin film of the present invention of the single-layer structure and the main component of the inner layer of the polyolefin film of the present invention of the multilayer structure are preferably polyolefin resin (hereinafter also referred to as the main component of the inner layer of the polyolefin film) Polyolefin resin is called polyolefin raw material II). The term "principal component" in the present invention means that the proportion of a specific component in the total components is 50% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and still more preferably 95% by mass Mass% or more and 100 mass% or less, still more preferably 96 mass% or more and 100 mass% or less, particularly preferably 97 mass% or more and 100 mass% or less, and most preferably 98 mass% or more and 100 mass% or less.

From the viewpoint of strength or heat resistance, the polyolefin material II used in the polyolefin film of the present invention is preferably a polypropylene material, and among them, homopolypropylene is preferably used.

The melting point of the polyolefin raw material II is preferably 155°C or higher, more preferably 160°C or higher, and still more preferably 165°C or higher. When the melting point is less than 155°C, it lacks heat resistance. For example, when used as a release film, there are cases where the film will soften and stretch in the direction of tension when it passes through the heating step after being bonded to the adherend. The slime is deformed.

The polyolefin raw material II preferably has a cold xylene soluble portion (hereinafter CXS) of 4% by mass or less, and a mesopentad fraction of 0.90 or more. If these conditions are not met, there are cases where the film formation stability is poor, the strength of the film is reduced, or the dimensional stability and heat resistance are greatly reduced.

The cold xylene soluble portion (CXS, cold xylene soluble portion) here refers to the polyolefin component dissolved in xylene when the sample is completely dissolved with xylene and then precipitated at room temperature. A component that is difficult to crystallize for reasons such as low regularity and low molecular weight. If such a component is contained in a large amount in the resin, the thermal dimensional stability of the film will deteriorate. Therefore, CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. The lower the CXS system, the better, but the lower limit is about 0.1% by mass. In order to become such CXS, a method of increasing the catalyst activity when obtaining a resin, and a method of washing the obtained resin with a solvent or the olefin monomer itself can be used.

When a polypropylene raw material is used as the polyolefin raw material II, the meso pentad fraction is preferably 0.90 or more, more preferably 0.94 or more. The meso pentad fraction is an indicator of the stereoregularity of the polypropylene crystal phase measured by nuclear magnetic resonance (NMR). The higher the value, the higher the crystallinity, the higher the melting point, and the higher the temperature. The higher the dimensional stability, the better. The upper limit of the meso pentad fraction is not specified. In order to obtain a resin with high stereoregularity in this way, it is preferable to use a method of washing the obtained resin powder with a solvent such as n-heptane, or a method of appropriately selecting a catalyst and/or auxiliary catalyst, and selecting a composition.

Moreover, for the polyolefin raw material II, it is more preferable that the melt flow rate (MFR) is 1-10 g/10 minutes (230°C, 21.18N load), and more preferably 1-8 g/10 minutes (230°C, 21.18 N load), especially in the range of 2 to 5 g/10 minutes (230°C, 21.18 N load), is preferable from the viewpoint of film formability or film strength. In order to make the melt flow rate (MFR) the above-mentioned value, a method of controlling the average molecular weight or molecular weight distribution of the polyolefin raw material II, etc. can be adopted.

Regarding the polyolefin raw material II, copolymerization components based on other unsaturated hydrocarbons, etc. may be contained within the scope not to impair the purpose of the present invention, and polymers may also be blended. Examples of monomer components constituting such copolymerization components or blends include ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, and 3-methylpentene. Ene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene Alkenes, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, etc. As for the copolymerization amount or blending amount, from the viewpoint of dimensional stability, the copolymerization amount is preferably less than 1 mol%, and the blending amount is preferably less than 10 mass%.

When the polyolefin raw material II contains an ethylene component, the content of the ethylene component contained in the polyolefin raw material II is preferably 10% by mass or less. It is more preferably 5% by mass or less, and still more preferably 3% by mass or less. The higher the content of the ethylene component, the lower the crystallinity, and the easier it is to improve transparency. When the content of the ethylene component exceeds 10% by mass, there are cases where the strength is reduced or the heat resistance is reduced, resulting in deterioration of heat shrinkage. In addition, there are cases where the resin becomes easy to deteriorate in the extrusion step, and fish eyes in the film become easy to occur.

In the polyolefin film of the present invention, from the viewpoint of transparency and heat resistance, the content of the polypropylene polymer contained in the polymer constituting the film is preferably 95% by mass or more. It is more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more.

The polyethylene material content of the surface layer of the polyolefin film of the present invention is preferably less than 3%. It is more preferably less than 2%, still more preferably less than 1%, and most preferably less than 0.5%. A matte polyolefin film with a rough surface often forms a rough surface by blending a polypropylene material with a polyethylene material. However, with this method, there are cases where there are more fisheyes caused by polyethylene, and there are cases where foreign matter increases due to chipping of the film surface, etc., and the quality is deteriorated, which is not good.

When the polyolefin film of the present invention has a two-layer structure, at least one of the surface layers preferably contains a low-viscosity polyolefin material III. Regarding the polyolefin raw material III, the lower limit of MFR is preferably 5 g/10 min (230° C., 21.18 N load) or more, more preferably 6 g/10 min or more, and still more preferably 10 g/10 min or more. The upper limit of MFR is preferably 60 g/10 minutes or less, more preferably 30 g/10 minutes or less. By blending polypropylene materials with different viscosities, a finely mixed state can be formed, and a uniform and fine rough surface structure can be formed without damaging the grade.

The polyolefin film of the present invention may contain various additives, such as nucleating agents, antioxidants, heat stabilizers, slip agents, antistatic agents, anti-blocking agents, fillers, Viscosity regulator, anti-coloring agent, etc.

Among these, from the viewpoint of the exudation of the antioxidant, it is important to select the type and amount of the antioxidant. The antioxidant is preferably a phenolic compound with steric barrier properties, and when multiple antioxidants are used in combination, at least one of them is preferably a high molecular weight type with a molecular weight of 500 or more. The specific examples may include various ones, but it is preferable to use, for example, 2,6-di-tertiarybutyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4, 6-ginseng (3,5-di-tertiary butyl-4-hydroxybenzyl)benzene (for example, "Irganox" (registered trademark) 1330 manufactured by BASF Corporation: molecular weight 775.2) or four (methylene-3(3) , 5-Di-tertiary butyl-4-hydroxyphenyl) propionate] methane (for example, "Irganox" (registered trademark) 1010 manufactured by BASF Corporation: molecular weight 1177.7). The total content of these antioxidants is preferably in the range of 0.03 to 1.0% by mass relative to the total amount of polyolefin raw materials. If there are too few antioxidants, there are cases where the polymer will deteriorate during the extrusion step, the film will be colored, or the long-term heat resistance will be poor. If there are too many antioxidants, the antioxidants may bleed out and the transparency may decrease. More preferably, the content is 0.05 to 0.9% by mass, and particularly preferably 0.1 to 0.8% by mass.

In the polyolefin raw material I and polyolefin II used in the polyolefin film of the present invention, a nucleating agent may be added in the range that does not violate the purpose of the present invention. In addition, it may also contain branched polypropylene which has the effect of a nucleating agent for α crystals or β crystals, but may also contain other types of α nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.) , Β nucleating agent (potassium 1,2-hydroxystearate, magnesium benzoate, N,N'-dicyclohexyl-2,6-naphthalenedimethamide and other amide compounds, quinacridone compounds and many more. However, excessive addition of the above-mentioned other types of nucleating agents may cause a decrease in film stretchability, or a decrease in transparency and strength due to the formation of voids, so the addition amount is usually 0.5% by mass or less, preferably 0.1% by mass or less , More preferably 0.05% by mass or less.

The polyolefin film of the present invention preferably does not contain organic particles and inorganic particles. The polypropylene used in the polyolefin film of the present invention has a low affinity with organic particles or inorganic particles, and the particles fall off to contaminate the steps or products, or the particles with high hardness form coarse protrusions and have unevenness. When it is transferred to the resin layer of an optical member; when used as a protective film for high-grade products such as display members or a base film for manufacturing, it is better to not contain organic particles or inorganic particles and other lubricants.

The polyolefin film of the present invention is preferably biaxially stretched using the above-mentioned raw materials. As a biaxial stretching method, any of the simultaneous biaxial stretching method, the expansion machine simultaneous biaxial stretching method, and the expansion machine sequential biaxial stretching method can be obtained; among them, the control system In terms of film stability, thickness uniformity, and high rigidity and dimensional stability of the film, it is better to adopt the expansion machine sequential biaxial stretching method.

Next, the same state of the manufacturing method of the polyolefin film of the present invention will be described as an example, but it is not necessarily limited to this.

First, 50 parts by mass of polypropylene material I and 50 parts by mass of polyolefin material II are dry blended and supplied to the uniaxial extruder for layer A (surface layer), and polyolefin material II is supplied to layer B (inner layer). The single-screw extruder used for layer) is used for melt extrusion at 200-280°C, more preferably 220-280°C, and even more preferably 240-270°C. Then, after removing foreign matter or modified polymer with a filter installed in the middle of the polymer tube, it is laminated with a multi-manifold type A-layer/B-layer/A-layer composite T-shaped mold and discharged to a casting drum. On top, a laminated unstretched sheet having a layer structure of A layer/B layer/A layer is obtained. At this time, the thickness of the build-up layer is preferably in the range of 1/8/1 to 1/60/1. By setting it in the above range, the surface layer containing the polypropylene raw material I is uniformly formed on the surface of the film thinly, increasing the uniformity of the height of the protrusions formed during stretching, and suppressing the formation of coarse protrusions.

Moreover, the surface temperature of the casting drum is 40-100 degreeC, Preferably it is 60-100 degreeC, More preferably, it is 75-100 degreeC. Moreover, it can also be made into a two-layer laminated structure of A layer/B layer. In the case of a two-layer laminated structure, the A layer of the surface layer preferably contains a polypropylene resin having a melting point of 50°C or more and 135°C or less. As for the adhesion method to the casting drum, any of the electrostatic application method, the adhesion method using the surface tension of water, the air knife method, the pressure roller method, the underwater casting method, etc. can be used, but the film is preferred. The air knife method has good flatness and can control the surface roughness. The air temperature of the air knife is 40 to 80°C, and the blowing air velocity is preferably 130 to 150 m/s. In addition, in order to prevent vibration of the film, it is preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation.

The obtained unstretched sheet is introduced to 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 80°C or higher and 130°C or lower, preferably 90°C or higher and 120°C or lower, more preferably 100°C or higher and 110°C or lower. It is preheated and stretched 3 to 8 times in the longitudinal direction between rolls provided with a peripheral speed difference, and then cooled to room temperature. The stretching temperature is from 130°C to 160°C, preferably from 140°C to 155°C, and more preferably from 145°C to 150°C. The preheating step of longitudinal stretching is carried out at a low temperature and stretched at a high temperature in one breath. The surface of the uniaxially stretched film can be stretched to form a high melting point and a low melting point on the surface of the film. For the important ones. When the preheating temperature is significantly different from the stretching temperature, the film will shrink in the width direction when it touches the high temperature stretching roll. At this time, the film shrinks unevenly, causing wrinkles in the flow direction. As a solution, ceramic rollers can be used as stretching rollers. We have found that the film is easy to slide on the ceramic roller, and the film can be stretched without wrinkles by shrinking the film uniformly. When the stretching ratio is less than 3 times, the orientation of the film may be weakened and the strength may decrease. Therefore, it is preferably 3 times or more and 6 times or less, and more preferably 4 times or more and 5.5 times or less.

Next, the longitudinally and uniaxially stretched film is guided to a tenter, the end of the film is clamped with a clamp, and preheated, and then stretched 7 to 13 times in the width direction and transverse direction. Stretching is performed while melting the low melting point part of the surface of the longitudinally uniaxially stretched film. The stretching ratio of the low melting point part becomes higher, which causes a difference in the actual stretching ratio of the film surface and roughens the film surface. Therefore, the preheating and stretching temperature is 165 to 180°C, more preferably 170 to 180°C, and even more preferably 173 to 180°C. In this way, transverse stretching at extremely high temperatures can be achieved by making the inner layer mainly composed of high-melting resin and adding only low-melting resin to the surface of the film.

In the subsequent heat treatment and relaxation treatment steps, while the width direction is clamped by the clamp, the relaxation rate is 2-20% in the width direction while the temperature is above 160°C and less than 170°C. Carry out heat fixation, go through a cooling step at 80-100°C in the width direction with the clamp tightened and guide it to the outside of the tenter, loosen the clamp at the end of the film, and cut the edge of the film during the winding step Department, and rolled into a roll of film products. By heat-fixing at high temperature, the residual stress in the film can be relieved and the thermal shrinkage rate can be reduced.

The polyolefin film obtained by the above method can be used in various applications such as packaging film, surface protection film, engineering film, sanitary products, agricultural products, construction products, medical products, etc., especially because of its excellent surface smoothness, it can be applied to As a surface protection film, engineering film, and release film. [Example]

The present invention will be described in detail below based on examples. In addition, the characteristics are measured and evaluated according to the following methods. (1) Film thickness The measurement was performed using a micro thickness meter (manufactured by ANRITSU). Take the film into a square of 10 cm, measure 5 points at random and calculate the average value.

(2) Average roughness (Sa), mountain height (Sp), valley depth (Sv) The measurement was carried out using RYOKA CHEMICAL SYSTEMS (stock) VertScan2.0 R5300GL-Lite-AC, and the surface shape was obtained by performing surface correction on the shooting screen with a polynomial fourth-order approximation using the accompanying analysis software. The measurement conditions are as follows. The measurement was performed on both sides of the film with n=3, and the average value of each surface was calculated and used as Sa, Sp, and Sv of each surface. In addition, Table 1 describes the value of the A side. Manufacturer: RYOKA CHEMICAL SYSTEMS Co., Ltd. Device name: VertScan2.0 R5300GL-Lite-AC Measurement conditions: CCD camera SONY HR-57 1/2 inch Objective lens: 5x Middle lens: 0.5x Wavelength filter: 530nm white (white) Measurement mode: Wave (wave) Measurement software: VS-Measure version 5.5.1 Analysis software: VS-Viewer version 5.5.1 Measuring area: 1.252mm×0.939mm

(3) Haze of film A haze meter (NDH-5000 manufactured by Nippon Denshoku Kogyo Co., Ltd.) was used for the film, and the haze value (%) at 23°C was measured 3 times in accordance with JIS K7136 (2000), and the average value was adopted. (4) Melting point of raw material and film A raw material sheet and 5 mg of a polyolefin film were collected on an aluminum weighing pan as samples, and a differential scanning calorimeter (RDC220 manufactured by SEIKO Electronics Industry) was used for measurement. First, the temperature is increased from room temperature to 260°C at 10°C/min (first run) in a nitrogen atmosphere, and after holding for 10 minutes, it is cooled to 20°C at 10°C/min. After being kept for 5 minutes, the top temperature of the melting curve on the highest temperature side observed when the temperature was raised again at 10°C/min (second round) was taken as the melting peak temperature.

(5) Elastic modulus in the thickness direction The measurement is carried out using the ELIONIX (stock) nanoindentation tester "ENT-2100", following the method specified in ISO 14577 (2002). Apply 1 drop of "Aronalpha" (registered trademark) professional impact resistance made by Toagosei Co., Ltd. to the polyolefin film, and fix the polyolefin film on a dedicated sample holder with instant glue for measurement. The measurement uses a triangular pyramid diamond press (Berkovich press) with an ridge angle of 115°. The measurement data is processed by the dedicated analysis software (version 6.18) of "ENT-2100" to measure the indentation elastic modulus EIT (GPa). The measurement is performed on both sides of the film, each with n=10, the average value is calculated, and the smaller value is used as the elastic modulus in the thickness direction of the film. Therefore, the table records the smaller of the average of the measured values on both sides. Measurement mode: load-unload test Maximum load: 0.5mN Holding time when the maximum load is reached: 1 second Loading speed, unloading speed: 0.05mN/sec

(6) Number of fish eyes Place the polyolefin film cut into A4 size on black paper, and visually mask the part where the light penetration is weaker under a fluorescent lamp. These parts were observed with an optical microscope, the part with a maximum length of 50 μm or more was judged to be fish eyes, and the number of fish eyes was counted. The evaluation system uses A4 specimens for 8 sheets, converted into squares per 1m.

(7) The thermal shrinkage rate at 150°C for 15 minutes in the main shrinkage direction and its orthogonal direction (150°C heat shrinkage rate) For the main shrinkage direction of the polyolefin film and its orthogonal direction, cut out 5 strips with a width of 10mm and a length For a sample of 200 mm (measurement direction), a mark is drawn at a position 25 mm from both ends as a marking, and the distance between the markings is measured by a universal projector as the sample length (l ₀ ). Secondly, sandwich the test piece between papers and under zero load, heat it in an oven with a heat preservation of 150°C for 15 minutes and take it out. After cooling at room temperature, measure the size (l ₁ ) with a universal projector. The following equation is evaluated, and the average value of the five bars is used as the thermal shrinkage rate of each of the main shrinkage direction and the orthogonal direction, and the sum is obtained. Thermal shrinkage={(l ₀ -l ₁ )/l ₀ }×100(%)

(8) Evaluation of releasability from adhesive tape The polyester adhesive tape No. 31B made by Nitto Denko Co., Ltd. was adhered to the polyolefin film of the laminated structure with a roller, and the sample was cut into 19mm width. This sample was peeled off using a tensile testing machine at a speed of 500 mm/min, and evaluated according to the following criteria. ○: There is no delamination between the surface layer and the inner layer, It can be peeled off at a certain speed. △: No delamination occurs between the surface layer and the inner layer, But the peeling resistance is slightly stronger, and the speed fluctuates up and down during peeling. ×: Interlayer peeling occurs between the surface layer and the inner layer, Or the peeling is very serious, leaving peeling marks on the surface of the adherend.

(9) Transfer evaluation of the adherend Cut the polyolefin film and the "ZEONOR film" (registered trademark) made by Japan's ZEON Co., Ltd. (registered trademark) with a thickness of 40 μm into a square with a width of 100 mm and a length of 100 mm, and overlap the polyolefin film so that side A and the "ZEONOR film" are in contact. It was clamped by two acrylic plates (width 100 mm, length 100 mm), a load of 2 kg was applied, and it was allowed to stand for 24 hours in an atmospheric environment at 23°C. After 24 hours, visually observe the surface of the "ZEONOR film" (the surface where the polyolefin film is in contact), and evaluate it based on the following criteria. ○: Clean, same as before load △: Confirm that there are weak irregularities ×: Confirm that there are strong irregularities

(10) Maximum point strength at 130℃ In the direction orthogonal to the main shrinkage direction of the polyolefin film, a sample with a width of 10 mm and a length of 50 mm (measurement direction) was cut out, and the initial distance between the chucks was 20 mm. The sample was installed on a rectangular sample tensile testing machine (TENSILON UCT- manufactured by ORIENTEC) 100), put the chuck into an oven heated to 130°C, and after heating for 1 minute, the film was subjected to a tensile test with a stretching speed of 300 mm/min. Read the maximum load before the sample breaks and calculate the value obtained by dividing it by the cross-sectional area of the sample before the test (film thickness × width (10mm)) as the stress at the maximum point strength. The measurement is performed 5 times for each sample. , To evaluate by its average value. In addition, the film thickness used to calculate the maximum point strength is the value measured in (1) above.

(Example 1) 60 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) used as the material for layer A (surface layer) and polypropylene material I (Idemitsu Kosan ( Stock) manufactured by the company, L-MODU S901, MFR: 50g/10 minutes, melting point: 80°C) 40 parts by mass are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as layer B (inner layer) ) 99.5 parts by mass of the above-mentioned polyolefin material II and 0.5 parts by mass of branched polypropylene resin (manufactured by Basell) used as raw materials were dry blended and supplied to the uniaxial uniaxial melt extruder for the inner layer at 260°C Melt extrusion is performed to remove foreign matter with a sintered filter with a cut-off value of 20μm, and then layer it with a feed block type A/B/A composite T-die with a thickness ratio of 1/34/1 and discharge to surface temperature It is controlled on a casting drum at 90°C, and is closely attached to the casting drum with an air knife. Thereafter, pressurized air is sprayed on the non-cooling drum surface of the sheet on the casting drum to cool it, and an unstretched sheet is obtained. Next, the sheet was preheated to 108°C using ceramic rollers, and stretched 4.5 times in the longitudinal direction of the film between rollers at 148°C with a peripheral speed difference. Next, the ends are clamped with clamps and introduced into a tenter-type stretching machine. After preheating at 180°C for 3 seconds, it is stretched 8.5 times at 176°C while providing 12% slack in the width direction. The heat treatment was performed at 167°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound around the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 2) 50 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) used as the material for layer A (surface layer) and polypropylene material I (Idemitsu Kosan ( Stock) manufactured by the company, L-MODU S901, MFR: 50g/10 minutes, melting point: 80°C) 50 parts by mass are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as layer B (inner layer) ) The above-mentioned polyolefin raw material II used as the raw material is supplied to the uniaxial uniaxial melt extruder for the inner layer, and melt-extruded at 260°C. After removing the foreign matter with a sintered filter with a cut-off value of 20 μm, use the feeding sleeve The type A/B/A composite T-shaped mold is laminated with a thickness ratio of 1/58/1, and is discharged onto a casting drum whose surface temperature is controlled at 70°C, and is attached to the casting drum by an air knife. Thereafter, pressurized air is sprayed on the non-cooling drum surface of the sheet on the casting drum to cool it, and an unstretched sheet is obtained. Next, the sheet was preheated to 112°C using ceramic rolls, and stretched 4.5 times in the longitudinal direction of the film between rolls at 143°C with a peripheral speed difference. Next, the ends are clamped with clamps and introduced into a tenter-type stretching machine. After preheating at 176°C for 3 seconds, it is stretched 9.0 times at 172°C and 9% slack is imparted in the width direction. The heat treatment was performed at 160°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound on the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 3) The polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) used as the material for the A layer (surface layer) and 40 parts by mass of the polypropylene material I (Japan Polypropylene (share) ) Manufactured by the company, Welnex RFX4V, MFR: 6.0g/10 minutes, melting point: 127°C) 60 parts by mass are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as the B layer (inner layer) 99.5 parts by mass of the above-mentioned polypropylene material II and 0.5 parts by mass of branched polypropylene resin (manufactured by Basell) are dry blended and supplied to the uniaxial uniaxial melt extruder for the inner layer, and melted at 260°C Extrusion, after removing the foreign matter with a sintered filter with a cut-off value of 30μm, use the feeding sleeve type A/B/A composite T-shaped mold to laminate with a thickness ratio of 1/58/1, and spit it out until the surface temperature is controlled at 45°C On the casting drum, the air knife is used to make it close to the casting drum. Thereafter, pressurized air is sprayed on the non-cooling drum surface of the sheet on the casting drum to cool it, and an unstretched sheet is obtained. Next, the sheet was preheated to 128°C using ceramic rollers, and stretched 4.1 times in the longitudinal direction of the film between rollers at 132°C with a peripheral speed difference. Next, the end was clamped by a clamp and introduced into a tenter-type stretching machine. After preheating at 179°C for 3 seconds, it was stretched 8.2 times at 177°C, and 13% slack was imparted in the width direction. The heat treatment was performed at 168°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound around the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 4) 80 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) used as the material for layer A (surface layer) and polypropylene material I (Idemitsu Kosan ( Stock) manufactured by the company, L-MODU S901, MFR: 50g/10 minutes, melting point: 80°C) 20 parts by mass are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as layer B (inner layer) ) The above-mentioned polyolefin raw material II used as the raw material is supplied to the uniaxial uniaxial melt extruder for the inner layer, and melt-extruded at 260°C. After removing the foreign matter with a sintered filter with a cut-off value of 20 μm, use the feeding sleeve The A/B/A composite T-shaped mold is laminated with a thickness ratio of 1/58/1, and is discharged onto a casting drum whose surface temperature is controlled at 95°C, and is closely attached to the casting drum by an air knife. Thereafter, pressurized air is sprayed on the non-cooling drum surface of the sheet on the casting drum to cool it, and an unstretched sheet is obtained. Next, the sheet was preheated to 140°C using a ceramic roller, and stretched 4.5 times in the longitudinal direction of the film between rollers at 140°C with a circumferential speed difference. Next, the end was clamped by a clamp and introduced into a tenter-type stretching machine. After preheating at 167°C for 3 seconds, it was stretched 8.0 times at 167°C and 9% slack was imparted in the width direction. The heat treatment was performed at 140°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound on the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 5) 50 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C), and polyolefin material III (manufactured by Sumitomo Chemical Co., Ltd., MFR: 7.5 g/10) Minutes, melting point: 163°C) 45 parts by mass, and 5 parts by mass of branched polypropylene resin (manufactured by Basell) are mixed at this ratio, and the raw materials are supplied to the twin-screw extruder from the measuring hopper, and melt-kneaded at 260°C. It was ejected from a mold into strands, cooled and solidified in a water tank at 25° C. and cut into small pieces to obtain polypropylene raw material IV. 70 parts by mass of the polyolefin material II used as the raw material for the A layer (surface layer) and 30 parts by mass of the above-mentioned polypropylene material IV are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as the B layer ( Inner layer) 80 parts by mass of the above-mentioned polypropylene material II and 20 parts by mass of the above-mentioned polyolefin material III are dry blended and supplied to a uniaxial uniaxial melt extruder for the inner layer, and melt-extruded at 260°C After removing the foreign matter with a sintered filter with a cut-off value of 20μm, use the feeding sleeve type A/B/A composite T-shaped mold to laminate with a thickness ratio of 1/10/1, and spit it out until the surface temperature is controlled at 98℃. On the drum, pressurized air was blown by an air knife to make it closely adhere to the casting drum to obtain an unstretched sheet. Next, the sheet was preheated to 95°C using ceramic rollers, and stretched 5.2 times in the longitudinal direction of the film between rollers at 155°C with a peripheral speed difference. Next, the end was clamped by a clamp and introduced into a tenter-type stretching machine. After preheating at 178°C for 3 seconds, it was stretched 8.8 times at 176°C and 18% slack was imparted in the width direction. The heat treatment was performed at 168°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound around the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative example 1) 50 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) used as the material for layer A (surface layer) and polypropylene material I (Idemitsu Kosan ( Stock) manufactured by the company, L-MODU S901, MFR: 50g/10 minutes, melting point: 80°C) 50 parts by mass are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as layer B (inner layer) ) The above-mentioned polyolefin raw material II used as the raw material is supplied to the uniaxial uniaxial melt extruder for the inner layer, and melt-extruded at 260°C. After removing foreign matter with a sintered filter with a cut-off value of 60μm, use a feeding sleeve The A/B/A composite T-shaped mold is laminated with a thickness ratio of 1/88/1, and is discharged onto a casting drum whose surface temperature is controlled at 30°C, and is closely attached to the casting drum with an air knife. Thereafter, pressurized air is sprayed on the non-cooling drum surface of the sheet on the casting drum to cool it, and an unstretched sheet is obtained. Next, the sheet was preheated to 140°C using a ceramic roller, and stretched 4.6 times in the longitudinal direction of the film between rollers at 140°C with a circumferential speed difference. Next, the end was clamped by a clamp and introduced into a tenter-type stretching machine. After preheating at 160°C for 3 seconds, it was stretched 8.0 times at 155°C and 10% slack was given in the width direction. The heat treatment was carried out at 120°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound on the core to obtain a polyolefin film with a thickness of 12 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative example 2) 93.3 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) as a raw material for the B layer (inner layer), and 80% by mass of calcium carbonate were combined with polyolefin 6.7 parts by mass of the main raw material compounded with 20% by mass of propylene (made by Sankyo Refined Powder, 2480K, calcium carbonate particles: 6μm) is dry blended and supplied to a uniaxial melt extruder for the inner layer, and The above-mentioned polyolefin material II as a raw material for the A layer (surface layer) is supplied to a uniaxial melt extruder for the surface layer, melt-extruded at 240°C, and after removing foreign matter with a sintered filter with a cut-off value of 60 μm, it is used The material-sleeve type A/B composite T-shaped mold is laminated with a thickness ratio of 8/1, and discharged to a casting drum whose surface temperature is controlled at 30°C to obtain a cast sheet. Next, a plurality of ceramic rolls were used for preheating at 125°C, and the film was stretched 4.6 times in the longitudinal direction between the rolls at 125°C. Next, the end part was clamped by a clamp, and it was introduce|transduced into a tenter-type stretching machine, after preheating at 165 degreeC for 3 seconds, it stretched 8.0 times at 160 degreeC. In the subsequent heat treatment step, heat treatment is performed at 160°C while providing 10% relaxation in the width direction. After that, it undergoes a cooling step at 130°C and is guided to the outside of the tenter. The clamp at the end of the film is loosened and the film is rolled. Wound around the core to obtain a polyolefin film with a thickness of 19 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative example 3) The polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C) was supplied to a uniaxial uniaxial melt extruder, and melt-extruded at 240°C with a cut-off value of 60 μm The sintered filter removes the foreign matter, and spit it out onto the casting drum whose surface temperature is controlled at 50°C, and is closely connected to the casting drum with an air knife. Thereafter, pressurized air is sprayed on the non-cooling drum surface of the sheet on the casting drum to cool it, and an unstretched sheet is obtained. Next, the sheet was preheated to 140°C using a ceramic roller, and stretched 4.6 times in the longitudinal direction of the film between rollers at 140°C with a circumferential speed difference. Next, the ends are clamped with clamps and introduced into a tenter-type stretching machine. After preheating at 170°C for 3 seconds, it is stretched 8.0 times at 165°C and 10% slack is provided in the width direction. The heat treatment was performed at 150°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamp at the end of the film was loosened, and the film was wound on the core to obtain a polyolefin film with a thickness of 25 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative Example 4) 50 parts by mass of polyolefin material II (manufactured by PRIME POLYMER Co., Ltd., MFR: 2.9 g/10 min, melting point: 164°C), and polyolefin material III (manufactured by Sumitomo Chemical Co., Ltd., MFR: 7.5 g/10) Minutes, melting point: 163°C) 45 parts by mass, and 5 parts by mass of branched polypropylene resin (manufactured by Basell) are mixed at this ratio, and the raw materials are supplied to the twin-screw extruder from the measuring hopper, and melt-kneaded at 260°C. It was ejected from a mold into strands, cooled and solidified in a water tank at 25° C. and cut into small pieces to obtain polypropylene raw material IV. 70 parts by mass of polyolefin material II as a raw material for the A layer (surface layer) and 30 parts by mass of a polypropylene material IV are dry blended and supplied to the uniaxial uniaxial extruder for the surface layer, and will be used as the B layer (inner Layer) 80 parts by mass of the above-mentioned polyolefin material II and 20 parts by mass of the above-mentioned polyolefin material III, which are the raw materials for the layer, are dry blended and supplied to the uniaxial uniaxial melt extruder for the inner layer, and melt-extruded at 260°C, After removing the foreign matter with a sintered filter with a cut-off value of 20μm, use the feed sleeve type A/B/A composite T mold to laminate with a thickness ratio of 1/34/1, and spit it out to a casting drum whose surface temperature is controlled at 70°C And blow pressurized air with an air knife to make it closely adhere to the casting drum to obtain an unstretched sheet. Next, the sheet was preheated to 133°C using ceramic rollers, and stretched 3.9 times in the longitudinal direction of the film between rollers at 138°C with a peripheral speed difference. Next, the end was clamped with a clamp and introduced into a tenter-type stretching machine. After preheating at 173°C for 3 seconds, it was stretched at 172°C for 7.2 times while providing 4% slack in the width direction. The heat treatment was performed at 145°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound around the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative Example 5) 90 parts by mass of ethylene-propylene copolymer resin (manufactured by Mitsui Chemicals Co., Ltd., MFR: 7g/10min, melting point: 140°C), and high-density polyethylene raw material (manufactured by Nippon Polyethylene Co., Ltd., melting point: 133°C) ) 10 parts by mass are mixed at this ratio and the raw materials are supplied to the twin-screw extruder from the metering hopper, melted and kneaded at 220°C, discharged from the die into strands, cooled and solidified in a water tank at 25°C and cut into small pieces , And obtain polypropylene material V. The above-mentioned polypropylene raw material V as the raw material for the A layer (surface layer) is supplied to the uniaxial uniaxial extruder for the surface layer, and the polyolefin raw material II (PRIME POLYMER ( Stock) manufactured by the company, MFR: 2.9g/10 min, melting point: 164°C) is supplied to the uniaxial uniaxial melt extruder for the inner layer, melt-extruded at 240°C, and removed with a sintered filter with a cutoff value of 20μm After foreign matter, use the feeding sleeve type A/B/A composite T-shaped mold to laminate with a thickness ratio of 1/34/1, and spit it out on a casting drum whose surface temperature is controlled at 90℃, and spray it with an air knife. The compressed air is brought into close contact with the casting drum to obtain an unstretched sheet. Next, the sheet was preheated to 108°C using ceramic rolls, and stretched 4.6 times in the longitudinal direction of the film between rolls at 148°C with a peripheral speed difference. Next, the ends are clamped with clamps and introduced into a tenter-type stretching machine. After preheating at 180°C for 3 seconds, it is stretched 8.5 times at 176°C while providing 12% slack in the width direction. The heat treatment was performed at 167°C, followed by a cooling step at 100°C and guided to the outside of the tenter, the clamps at the ends of the film were loosened, and the film was wound around the core to obtain a polyolefin film with a thickness of 18 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Sa (nm) 350 280 140 220 180 20 430 110 55 700 Sp/Sv (-) 1.2 1.6 1.6 2.3 1.7 2.8 3.0 5.2 1.6 2.6 Sp/Sa (-) 9.7 8.2 4.0 13.3 5.3 14.0 22.3 15.0 5.8 15.7 Haze value (%) 9.6 13.0 2.4 7.0 4.3 1.0 95.0 1.0 2.0 70.0 Modulus of elasticity in thickness direction (GPa) 1.9 2.1 1.7 2.4 2.7 2.1 3.3 2.8 2.5 1.9 Melting point of film (℃) 171 168 169 163 173 159 167 162 166 169 Number of fisheyes (Pcs/m ² ) 3.0 4.0 6.0 2.0 2.0 4.0 - 1.0 2.0 20.0 Thermal shrinkage at 150℃ (%) 2.4 5.3 8.0 13.0 2.8 17.0 8.3 9.2 12.4 2.8 Maximum point strength at 130℃ (MPa) 76 73 65 72 90 63 76 68 58 72 Releasability from adhesive tape ○ ○ △ ○ △ × ○ × × ○ Transfer property to adherend ○ ○ ○ △ ○ ○ × △ ○ × [Possibility of Industrial Use]

As described above, the polyolefin film of the present invention can be used in various applications such as packaging films, release films, engineering films, sanitary products, agricultural products, construction products, and medical products. Especially because of its excellent transparency and smoothness, it can be used as a release film and engineering film for applications that require surface smoothness of the product; even, because of its excellent release property, it is suitable as a cover film for an adhesive resin layer, etc. The release film.

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Claims (10)

A polyolefin film, the average roughness Sa of at least one side (A side) is 65-600nm, The value of Sp/Sv of the ratio of the mountain height Sp of the A side and the valley depth Sv of the A side is 2.5 or less, and the haze is 30% or less. Such as the polyolefin film of claim 1, which has a laminated structure, and at least one of the surface layers contains a polypropylene resin with a melting point of 50°C or more and 135°C or less. The polyolefin film of claim 2, which contains homopolypropylene resin as the polypropylene resin having a melting point of 50°C or more and 135°C or less. The polyolefin film according to any one of claims 1 to 3, wherein the value of Sp/Sa of the ratio of the mountain height Sp of the A side and the average roughness Sa of the A side is less than 13. The polyolefin film according to any one of claims 1 to 3, wherein the elastic modulus in the thickness direction is 2.3 GPa or less. The polyolefin film according to any one of claims 1 to 3, wherein when the temperature is raised from 30°C to 260°C with a differential operating calorimeter DSC, it has a melting peak above 165°C. The polyolefin film according to any one of claims 1 to 3, wherein the number of fish eyes is 5.0/m ² or less. The polyolefin film of any one of claims 1 to 3, wherein the sum of the heat shrinkage rate at 150°C for 15 minutes in the main shrinkage direction and its orthogonal direction is 8.0% or less. The polyolefin film according to any one of claims 1 to 3, wherein the maximum point strength in the direction orthogonal to the main shrinkage direction of the film when measured at 130°C is 70 MPa or more. A release film, which is formed by using the polyolefin film according to any one of claims 1 to 9.