Polyolefin film and release film

Abstract

To provide a polyolefin film having excellent releasability and surface uniformity (quality).SOLUTION: Provided is a polyolefin film which has, when a surface having a surface peak density, Spd, of 100 (1 / mm2) to 1000 (1 / mm2) and an arithmetic average curvature, Spc, of surface peaks of -200 (1 / mm) to -10 (1 / mm) is denoted as Surface A, at least one surface that is the Surface A.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a polyolefin film with excellent release properties and quality, and a release film using the same. [Background technology]

[0002] Polyolefin films are used in a wide range of applications, including packaging, release agents, tapes, cable wrapping, and electrical applications such as capacitors, due to their excellent transparency, mechanical properties, and other characteristics. In particular, their superior surface release properties and mechanical properties make them suitable for use as release films and process films for various materials such as plastic products, building materials, and optical components.

[0003] In recent years, polyolefin films have sometimes been used as cover films for adhesive resin layers, such as photosensitive resin layers. When used as such a cover film, if the release properties are poor, the polyolefin film cannot be cleanly peeled off the substrate, which can alter the shape of the substrate's resin layer or leave peel marks on the resin layer. To solve these problems, a method is used to improve release properties by roughening the film surface to reduce the contact area with the resin layer. On the other hand, increasing the roughness of the cover film surface makes it easier for coarse protrusions to form, and surface irregularities caused by these coarse protrusions can be transferred to the substrate's resin layer, potentially affecting the product's visibility.

[0004] From the above, in fields such as optical components where there are high requirements for characteristics related to release properties and surface uniformity, polyolefin films must have a surface that is uniform and finely roughened with few coarse protrusions in order to be used as release films. As a means of obtaining a polyolefin film having such a dense rough surface, for example, the following method is known.

[0005] Patent documents 1 and 2 describe methods for creating a dense, rough surface on a polypropylene film, a type of polyolefin film. Specifically, they describe an example in which spherulites of β-crystal, one of the crystalline forms of polypropylene, are formed on the film surface by stretching, thereby creating craters and roughening the surface to improve process handling. Patent document 3 describes an example in which particles are added to the film and uniaxially stretched to roughen the surface and improve process handling. Patent document 4 describes an example in which particles are added to the inner layer of the film and stretched to roughen the surface. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2016 / 006578 [Patent Document 2] Japanese Patent Publication No. 2017-125184 [Patent Document 3] Japanese Patent Publication No. 2005-138386 [Patent Document 4] Japanese Patent Publication No. 2017-077752 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the methods described in Patent Documents 1 to 3 mentioned above had the problem of insufficient surface roughness. In addition, the method described in Patent Document 4 resulted in the formation of coarse protrusions by hard particles, and when used as a release film, the irregularities caused by these coarse protrusions were sometimes transferred to the resin layer of the optical component to which it was attached.

[0008] Therefore, the objective of the present invention is to solve the above-mentioned problems. In other words, the objective of the present invention is to provide a polyolefin film with excellent release properties and surface uniformity (quality). [Means for solving the problem]

[0009] To solve the above-mentioned problems, the polyolefin film of the present invention has the following configuration. That is, the polyolefin film of the present invention has a peak density Spd of 100 (1 / mm²). 2 ) or more 1000(1 / mm 2 ) less than or equal to the arithmetic mean curve of the peak. Rate The polyolefin film is characterized in that, when the surface with an Spc of -200 (1 / mm) or more and -10 (1 / mm) or less is designated as surface A, at least one of the surfaces is surface A.

[0010] Furthermore, the polyolefin film of the present invention can be in the following embodiments, and can also be a release film as described below. (1) The peak density Spd of the mountain is 100 (1 / mm 2 ) or more 1000(1 / mm 2 ) less than or equal to the arithmetic mean curve of the peak. Rate A polyolefin film characterized in that, when the surface with Spc between -200 (1 / mm) and -10 (1 / mm) is designated as surface A, at least one of the surfaces is surface A. (2) The polyolefin film according to (1), wherein at least one of the A surfaces has an average roughness Sa of 200 nm or more and 600 nm or less. (3) A polyolefin film according to (1) or (2), wherein the film thickness is t (μm), a polyester adhesive tape is laminated onto surface A, and when peeled at a peeling speed of 300 mm / min and a peeling angle of 180°, the peeling force N (N / 19 mm) is such that N / t is 0.06 or more and 0.20 or less. (4) A polyolefin film according to any one of (1) to (3), having a laminated structure of at least two layers. (5) A release film made using a polyolefin film as described in any of (1) to (4). [Effects of the Invention]

[0011] According to the present invention, a polyolefin film excellent in releasability and quality and suitable for use as a release film can be provided.

Mode for Carrying Out the Invention

[0012] The polyolefin film of the present invention has a peak density Spd of the mountain of 100 (1 / mm 2 ) or more and 1000 (1 / mm 2 ) or less, and when a surface with an arithmetic average curve Rate Spc of the peak of the mountain being -200 (1 / mm) or more and -10 (1 / mm) or less is defined as surface A, at least one surface is the said surface A. Hereinafter, the polyolefin film of the present invention will be specifically described.

[0013] The polyolefin film refers to a sheet-like molded body mainly composed of a polyolefin resin. The main component means a component contained more than 50% by mass and 100% by mass or less when the total constituent components of the object (here, the film) are 100% by mass. Hereinafter, the main component can be interpreted in the same way. When a plurality of components corresponding to the polyolefin resin are contained, if the total amount thereof is more than 50% by mass, it is regarded as a polyolefin resin-based main component. The polyolefin resin refers to a resin whose main structural unit is an olefin unit. The main structural unit means a structural unit contained more than 50 mol% and 100 mol% or less when the total structural units are 100 mol%.

[0014] From the viewpoint of releasability, the polyolefin film of the present invention has a peak density Spd of the mountain of 100 (1 / mm 2 ) or more and 1000 (1 / mm 2 ) or less, and when a surface with an arithmetic average curve Rate Spc of the peak of the mountain being -200 (1 / mm) or more and -10 (1 / mm) or less is defined as surface A, it is important that at least one surface is surface A. The peak density Spd of the mountain is one of the indexes representing the surface roughness and represents the number of peaks of the mountain per unit area. The arithmetic average curve of the peak RateSpc is the average value of the radius of curvature of the peaks of the mountains. Hereinafter, the "peak density Spd of the mountain top" may be simply referred to as "Spd", and the "arithmetic mean curve Rate of the mountain top Spc" may be simply referred to as "Spc". By adopting such a mode, excellent peelability can be realized when the A surface is bonded so as to contact the adherend.

[0015] Spd, Spc, and the average roughness Sa described later can be measured using a known layer cross-sectional shape measuring device. As the measuring device, for example, the non-contact surface / layer cross-sectional shape measuring system "VertScan" (registered trademark) 2.0 manufactured by Rhika System Co., Ltd. can be used. The specific measuring methods of Spd, Spc, and the average roughness Sa (described later) when using this device will be described later.

[0016] When a polyolefin film without an A surface is used as a release film, various problems occur in terms of release properties as described below. When the Spd of the surface to be bonded to the adherend is less than 100 (1 / mm 2 ), the contact area between the adherend and the polyolefin film becomes excessively large, and if the adhesiveness of the adherend is strong, the adhesion between the two becomes excessively strong. Therefore, the polyolefin film cannot be peeled cleanly from the adherend, and the shape of the adherend surface may change or peeling marks may remain on the adherend surface. On the other hand, when the Spd of the surface to be bonded to the adherend exceeds 1000 (1 / mm 2 ), the contact area between the adherend and the polyolefin film is insufficient and the adhesion between the two becomes weak, and the polyolefin film may peel off from the adherend during the conveyance in the bonding process.

[0017] Furthermore, if the Spc of the surface to be bonded to the adherend is less than -200 (1 / mm), the curvature of the protrusions will be insufficient, increasing the contact area between the adherend and the polyolefin film. This can lead to excessively strong adhesion between the two, potentially worsening the peelability of the polyolefin film. On the other hand, if the Spc of the surface to be bonded to the adherend exceeds -10 (1 / mm), the protrusions on the surface of the polyolefin film may become excessively sharp, digging into the adherend and worsening the peelability of the two.

[0018] In other words, the polyolefin film of the present invention has an A-side in which both Spd and Spc are within the above range, which reduces the indentation of protrusions and dents on the adherend when the A-side is bonded to the adherend. As a result, it has excellent release properties and quality, and can be suitably used as a release film.

[0019] From the above viewpoint, the Spd of surface A is preferably 200 (1 / mm 2 ) or more 800 (1 / mm 2 ) or less, more preferably 400 (1 / mm 2 ) or more 600 (1 / mm 2 ) or less. Also, from a similar viewpoint, the Spc of surface A is preferably -100 (1 / mm) or more and -10 (1 / mm) or less, more preferably -80 (1 / mm) or more and -10 (1 / mm) or less. 2 ) are as follows:

[0020] To ensure that at least one side is designated as side A, it is effective to set the raw material composition of the polyolefin film within the range described below and the film-forming conditions within the range described below. More specifically, by using a resin composition containing a preferred amount of branched polypropylene resin described below to form the surface layer (the film itself in the case of a single-layer film), setting the surface temperature of the casting drum within the preferred range described below, and setting the film temperature (preheating temperature) when stretching in the longitudinal direction within the range described below, Spd and Spc can be controlled within the preferred range. Here, the longitudinal direction refers to the direction in which the film travels during the film manufacturing process, and when it becomes a film roll, it refers to its winding direction. The direction perpendicular to the longitudinal direction within the film surface is called the width direction.

[0021] In the polyolefin film of the present invention, at least one side is the A side, and the other side is not particularly limited. However, from the viewpoint of suppressing dent transfer on the back side and improving the transportability and winding properties of the polyolefin film itself, it is preferable that both sides of the polyolefin film are the A side. In a polyolefin film where both sides are the A side, the values ​​of Spd and Spc may be the same or different on both sides.

[0022] The polyolefin film of the present invention preferably has an average roughness Sa of 200 nm to 600 nm, and more preferably 300 nm to 500 nm, on at least one A-side, from the viewpoint of suppressing dent transfer and improving the transportability and winding properties of the film. Here, "at least one A-side" refers to the A-side if only one side is the A-side, and to both sides or one side if both sides are A-sides. Hereinafter, "average roughness Sa" may simply be referred to as "Sa". By having an Sa of 200 nm or more on the A-side, the contact area between the adherend and the polyolefin film (A-side) does not become excessively large, and the adhesion to the adherend can be appropriately suppressed. As a result, the polyolefin film can be cleanly peeled off from the adherend, and changes in the shape of the adherend surface and the occurrence of peel marks on the adherend surface can be reduced. On the other hand, by having an Sa of 600 nm or less on the A-side, the contact area between the adherend and the polyolefin film is not insufficient, and peeling of the polyolefin film from the adherend during transport in the lamination process can be suppressed.

[0023] To set the Sa of side A to the range of 200 nm to 600 nm, it is effective to set the raw material composition of the film to the range described later, and the film formation conditions to the range described later. More specifically, a method similar to the method for controlling Spd and Spc to a preferred range can be used. Furthermore, from the viewpoint of suppressing indentation transfer on the back side and the transportability and winding properties of the film, it is preferable that the Sa of both sides of the polyolefin film be between 200 nm and 600 nm, and more preferably between 300 nm and 500 nm.

[0024] From the viewpoint of achieving appropriate release properties, the polyolefin film of the present invention preferably has a film thickness of t (μm), a peel force N (N / 19mm) when a polyester adhesive tape is laminated to side A and peeled at a peeling speed of 300 mm / min and a peeling angle of 180°, where N / t is 0.06 or more and 0.20 or less. From the above viewpoint, N / t is more preferably 0.08 or more and 0.18 or less, and even more preferably 0.10 or more and 0.16 or less. If both sides are side A, the above requirements are satisfied if N / t is 0.06 or more and 0.20 or less on at least one side. Hereinafter, "the peel force when a polyester adhesive tape is laminated to side A and peeled at a peeling speed of 300 mm / min and a peeling angle of 180°" may simply be referred to as "peel force N". The film thickness t and peel force N can be measured using a known electronic micrometer and a known tensile testing machine, respectively, and the details will be described later.

[0025] When a polyolefin film is used as a release film to adhere an object to its surface, if the N / t of side A is 0.06 or higher, the film thickness will not be excessively large relative to the adhesive strength of the object, thus suppressing the stiffness of the polyolefin film and reducing the risk of unintended peeling. On the other hand, if the N / t of side A is 0.20 or lower, the film thickness will be sufficient relative to the adhesive strength of the object, and enough stiffness will be ensured for easy peeling, resulting in clean peeling and reducing changes in the shape of the object surface and peeling marks.

[0026] The film thickness t of the polyolefin film of the present invention is not particularly limited, but is preferably 1 μm to 100 μm from the viewpoint of handling, more preferably 5 μm to 50 μm, and even more preferably 10 μm to 30 μm. The film thickness t can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film formation speed, the stretching ratio, etc.

[0027] The peeling force N is not particularly limited, but from the viewpoint of handling, it is preferably 0.01 N / 19 mm to 9.0 N / 19 mm, more preferably 0.1 N / 19 mm to 5.0 N / 19 mm, and even more preferably 1.2 N / 19 mm to 2.7 N / 19 mm. The peeling force N can be adjusted by the surface free energy of the release film, and the surface free energy referred to here is the surface tension that acts on a material to reduce its surface area. The surface free energy can be increased by, for example, applying a surface treatment such as corona discharge treatment.

[0028] Furthermore, the polyolefin film of the present invention preferably has a coefficient of friction of 0.20 or more and 1.00 or less, and more preferably 0.40 or more and 0.60 or less, from the viewpoint of reducing problems such as meandering and wrinkles during film transport, winding, and unwinding. The coefficient of friction referred to here is the value calculated by the following formula from the resistance value when two films are stacked so that different surfaces are in contact with each other in an environment with a temperature of 23±3℃ and a humidity of 65±5%, and a load of 200g is applied from above, and the upper film is slid. A coefficient of friction of 0.20 or more ensures a certain amount of frictional force between the film and the roll, thereby reducing film slippage during transport and winding. As a result, it is possible to reduce the occurrence of scratches, wrinkles, winding misalignment, meandering, etc. that occur due to slippage. On the other hand, a coefficient of friction of 1.00 or less prevents excessive frictional force, and it is possible to reduce running problems and scratches caused by friction. Coefficient of friction = resistance (g) / load (g).

[0029] The coefficient of friction can be adjusted, for example, by adjusting the Sa value of surface A. More specifically, the coefficient of friction can be increased by lowering the Sa value of surface A. The method for adjusting the Sa value of surface A is as described above.

[0030] Furthermore, if the coefficient of friction of the polyolefin film of the present invention is within a preferred range, it will possess appropriate friction and slipperiness, making it less likely for scratches to occur on the film surface. Normally, when a stretching method is used that utilizes the difference in peripheral speed of stretching rolls, the film comes into contact with a preheating roll that preheats the film, a stretching roll that stretches the film, and a cooling roll that cools the film, resulting in the problem of scratches occurring on the film surface. The same problem also occurs when the film is transported by rolls, regardless of the stretching process. Films with smooth surfaces have poor slipperiness, resulting in unstable running performance, and scratches are likely to occur due to friction between the film surface and the rolls. Therefore, by setting the coefficient of friction within the preferred range described above, appropriate slipperiness is ensured, making it less likely for scratches to occur on the film surface.

[0031] Next, the layer structure and raw materials of the polyolefin film of the present invention will be described, but the layer structure and raw materials of the polyolefin film of the present invention are not necessarily limited to those described herein.

[0032] The polyolefin film of the present invention is preferably a polypropylene film, with polypropylene resin as the main component, from the viewpoint of transparency and heat resistance. Here, polypropylene resin refers to a resin in which, when the total constituent units of the resin are set to 100 mol%, more than 50 mol% and up to 100 mol% are propylene units (the same interpretation can be applied to other polyolefin resins such as polyethylene). When the polyolefin film of the present invention is a polypropylene film, when the total components constituting the film are set to 100% by mass, the polypropylene resin content is preferably 95% by mass or more and 100% by mass or less, more preferably 96% by mass or more and 100% by mass or less, even more preferably 97% by mass or more and 100% by mass or less, and particularly preferably 98% by mass or more and 100% by mass or less.

[0033] The polyolefin film of the present invention preferably has a laminated structure of at least two layers, from the viewpoint of achieving both heat resistance and release properties. With this configuration, it is possible to provide a layer that plays a role in ensuring the thermal dimensional stability of the polyolefin film (hereinafter sometimes referred to as the base layer (A)) and a layer that plays a role in achieving excellent release properties when bonded to an adherend (hereinafter sometimes referred to as the surface layer (B)), making it easy to produce a polyolefin film that combines both heat resistance and release properties. Furthermore, "a laminated structure of at least two layers" refers to a state in which at least two types of layers are laminated in a total of two or more layers. Specific examples of such configurations include a two-layer configuration of base layer (A) / surface layer (B), a three-layer configuration of surface layer (B) / base layer (A) / surface layer (B), and so on.

[0034] The main component of the base layer (A) of the polyolefin film of the present invention is preferably a polyolefin resin. Hereinafter, the polyolefin resin that is the main component of the base layer (A) of the polyolefin film may be referred to as polyolefin resin I. The polyolefin resin I of the base layer (A) is more preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, even more preferably 96% by mass or more and 100% by mass or less, particularly preferably 97% by mass or more and 100% by mass or less, and most preferably 98% by mass or more and 100% by mass or less.

[0035] In the polyolefin film of the present invention, the polyolefin resin I is preferably a polypropylene resin, and homopolypropylene is preferred from the viewpoint of strength and heat resistance. Homopolypropylene refers to a polypropylene resin in which, when the total constituent units of the resin are set to 100 mol%, 99 mol% to 100 mol% are propylene units.

[0036] The polyolefin resin I preferably has a melting point of 155°C or higher, and more preferably 160°C or higher. A melting point of 155°C or higher improves the heat resistance of the polyolefin film. Therefore, when the polyolefin film is used, for example, as a release film, softening of the polyolefin film and elongation in the tensile direction due to softening during the heat-applied process after lamination with the adherend are suppressed, and deformation of the adherend is reduced. Furthermore, the melting point is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower. A melting point of 200°C or lower for the polyolefin resin I makes it less likely for equipment constraints to occur during melt extrusion.

[0037] When polyolefin resin I is polypropylene resin, its mesopentad fraction is preferably 0.90 or higher, more preferably 0.93 or higher, and even more preferably 0.94 or higher. The mesopentad fraction is an index indicating the stereoregularity of the crystalline phase of polypropylene, as measured by nuclear magnetic resonance (NMR) spectroscopy. Generally, the higher the value, the higher the degree of crystallinity and melting point. Therefore, by using polypropylene with a high mesopentad fraction as polyolefin resin I, the dimensional stability at high temperatures is improved when it is made into a film. There is no particular upper limit specified for the mesopentad fraction, but from the viewpoint of use in film manufacturing, it is set at 0.99.

[0038] To obtain polypropylene with a high mesopentade fraction, methods such as washing the obtained resin powder with a solvent such as n-heptane, or appropriately selecting a catalyst and / or co-catalyst and selecting its composition are preferably employed. Typically, polymerization catalysts containing metallocene compounds having a cyclopentadienyl skeleton in their molecule are preferably used as catalysts.

[0039] Furthermore, when polyolefin resin I is polypropylene resin, its melt flow rate (MFR) is preferably 1 to 10 g / 10 min, more preferably 1 to 8 g / 10 min, and even more preferably 2 to 5 g / 10 min, from the viewpoint of film-forming properties and strength when formed into a film. The MFR referred to here is the MFR measured under conditions of a temperature of 230°C and a load of 21.18 N, and the same applies to the MFR hereafter. In order to achieve the above values ​​for the melt flow rate (MFR) of the polypropylene resin, methods such as controlling the average molecular weight and molecular weight distribution are employed. More specifically, the MFR can be increased by reducing the number average or weight average molecular weight and molecular weight distribution.

[0040] Polyolefin resin I may contain copolymer components made of unsaturated hydrocarbons other than the main constituent units, to the extent that it does not impair the objectives of the present invention. Examples of monomers constituting such copolymer components include ethylene, propylene, 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, and 5-methyl-2-norbornene. The copolymerization amount is preferably less than 1 mol% from the viewpoint of dimensional stability when formed into a film.

[0041] Furthermore, the base layer (A) may contain polyolefin resins other than the main component, polyolefin resin I. Here, polyolefin resins other than polyolefin resin I refer to polyolefin resins whose main constituent units differ from those of polyolefin resin I. Examples of the main constituent units of polyolefin resins other than polyolefin resin I include constituent units derived from ethylene, propylene, 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. Preferably, the content of polyolefin resins other than polyolefin resin I is less than 10% by mass when the total components constituting the base layer (A) are taken as 100% by mass.

[0042] When polyolefin resin I is polypropylene resin and polyethylene is included as a polyolefin resin other than polyolefin resin I, the polyethylene resin contained in the base layer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. The higher the polyethylene resin content, the lower the crystallinity when it is made into a film, making it easier to improve transparency. On the other hand, by limiting the polyethylene resin content to 10% by mass or less, the decrease in strength and heat resistance when it is made into a film can be reduced, as can the degradation of the resin during the extrusion process and the occurrence of fisheye when it is made into a film.

[0043] Next, the polyolefin resin used in the surface layer (B) of the polyolefin film of the present invention will be described. For the surface layer (B) of the present invention, it is preferable to use a resin composition containing branched polypropylene resin in polyolefin resin I. The branched polypropylene resin in the surface layer (B) is preferably 5.0% by mass or more and 30.0% by mass or less, more preferably 10.0% by mass or more and 27.0% by mass or less, and even more preferably 15.0% by mass or more and 24.0% by mass or less, of the total components constituting the layer.

[0044] Since branched polypropylene resin acts as a crystal nucleating agent, a branched polypropylene resin content of 5.0% by mass or more in the surface layer (B) facilitates the formation of polyolefin resin crystals on the surface. On the other hand, a branched polypropylene resin content of 30.0% by mass or less can suppress excessive crystal formation on the surface. In other words, by having a branched polypropylene resin content of 5.0% by mass or more and 30.0% by mass or less in the surface layer (B), the density of protrusions caused by crystal formation on the surface is within an appropriate range, thus allowing the surface Spd to be within a suitable range.

[0045] As the branched-chain polypropylene resin, it is preferable to use a polypropylene resin having a branched structure in its molecular chain. A "polypropylene resin having a branched structure in its molecular chain" is defined as a polypropylene resin having five or fewer internal trisubstituted olefins per 10,000 carbon atoms in the molecular chain, and the presence of these internal trisubstituted olefins is important. 1 This can be confirmed by the proton ratio of the 1H-NMR spectrum. Furthermore, the MFR of the branched polypropylene resin is preferably 1.0 g / 10 min or more and 10.0 g / 10 min or less from the viewpoint of film formation stability.

[0046] Examples of branched polypropylene resins that can be suitably used for the surface layer (B) of the polyolefin film of the present invention include "Profax" (registered trademark) (PF-814, etc.) from Lyondell Basell, "Daploy" (trademark) (WB130HMS, WB135HMS, etc.) from Borealis, and "WAYMAX" (registered trademark) (MFX3, MFX6, MFX8, EX6000, EX8000, etc.) from Nippon Polypropylene Co., Ltd. Although branched polypropylene resin itself has the effect of nucleating α-crystals or β-crystals, other nucleating agents such as α-crystal nucleating agents (e.g., dibenzylidenesorbitol derivatives, sodium benzoate, etc.) and β-crystal nucleating agents (e.g., potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone compounds, etc.) may be added to the extent that it does not contradict the purpose of the present invention. These nucleating agents may be added to either the base layer (A), the surface layer (B), or both.

[0047] However, excessive addition of the above-mentioned other types of nucleating agents may cause a decrease in the stretchability of the film and a decrease in transparency and strength due to void formation, etc. Therefore, the amount added is usually 0.5% by mass or less, preferably 0.1% by mass or less, and more preferably 0.05% by mass or less, when the total components constituting the film are considered to be 100% by mass.

[0048] The polyolefin film of the present invention may contain various additives, such as antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors, as long as the objectives of the present invention are not impaired. Among these, the selection of the type and amount of antioxidant is important from the viewpoint of antioxidant bleed-out. As such antioxidants, sterically hindered phenolic types are preferred, and when multiple types of antioxidants are used in combination, at least one type with a molecular weight of 500 or more is preferred. Various specific examples can be given, but it is preferable to use 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox"® 1010: molecular weight 1177.7) in combination with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4).

[0049] The total content of these antioxidants is preferably in the range of 0.03 to 1.0% by mass, when the total raw materials for obtaining the polyolefin film are considered as 100% by mass, from the viewpoint of reducing discoloration due to polymer degradation and a decrease in transparency due to antioxidant bleed-out. A antioxidant content of 0.03% by mass or more can reduce film discoloration caused by polymer degradation during the extrusion process and a decrease in long-term heat resistance. On the other hand, a antioxidant content of 1.0% by mass or less suppresses a decrease in transparency due to antioxidant bleed-out. From the above viewpoint, a more preferable antioxidant content is 0.05 to 0.9% by mass, and even more preferably 0.1 to 0.8% by mass. These antioxidants may be added to either the base layer (A), the surface layer (B), or both.

[0050] Furthermore, it is preferable that the polyolefin film of the present invention does not contain organic or inorganic particles. For example, polypropylene resins that can be suitably used in the polyolefin film of the present invention have low affinity for organic and inorganic particles, so these particles may fall off during the manufacturing process and contaminate the manufacturing line or the product, or coarse protrusions formed by hard particles may be transferred as unevenness to the resin layer of the adherend. For this reason, when used as a protective film for optical components used in products requiring high quality, such as display components, or as a manufacturing base film, it is preferable that the polyolefin film does not contain lubricants such as organic or inorganic particles.

[0051] The polyolefin film of the present invention is preferably a biaxially oriented film. A biaxially oriented film is a film in which molecules are oriented in two orthogonal directions, and is usually obtained by stretching in two orthogonal directions (for example, the longitudinal direction and the width direction). As for the biaxial stretching method, any of the following methods may be used: simultaneous inflation biaxial stretching, simultaneous stentor biaxial stretching, or sequential stentor biaxial stretching. Among these, sequential stentor biaxial stretching is preferred in terms of controlling film formation stability, thickness uniformity, high rigidity of the film, and dimensional stability. Here, sequential stentor biaxial stretching refers to a method in which stretching in the longitudinal direction and the width direction is performed in separate processes, and at least the stretching in the width direction is performed by a stentor.

[0052] Next, one embodiment of the method for producing the polyolefin film of the present invention will be described using polypropylene film as a specific example, but it is not necessarily limited thereto. First, polypropylene resin is supplied to a single-screw extruder for the base layer (A), and a mixture of polypropylene resin and branched-chain polypropylene resin is supplied to a single-screw extruder for the surface layer (B). Then, melt extrusion is performed at 200 to 280°C, more preferably 220 to 280°C, and even more preferably 240 to 270°C for each. After removing foreign matter and modified polymers using a filter installed in the middle of the polymer tube, the layers are laminated using a multi-manifold type composite T-die to form a surface layer (B) / base layer (A) / surface layer (B) configuration, and then discharged onto a casting drum and cooled and solidified to obtain an unstretched sheet having a layer structure of surface layer (B) / base layer (A) / surface layer (B).

[0053] At this time, the surface temperature of the casting drum is 40 to 100°C, preferably 50 to 100°C, and more preferably 60 to 100°C. Any of the following methods can be used for adhesion to the casting drum: electrostatic application, adhesion using the surface tension of water, air knife method, press roll method, and underwater casting method. However, the air knife method is preferred from the viewpoint of improving the flatness of the film and making it easy to control the surface roughness. The air temperature of the air knife is preferably 40 to 80°C, and the blown air speed is preferably 130 to 150 m / s. It is also preferable to appropriately adjust the position of the air knife so that the air flows to the downstream side of film formation in order to prevent vibration of the sheet. The casting speed is preferably 5 m / min to 16 m / min, and more preferably 8 m / min to 14 m / min. By having a casting speed of 5 m / min or more, the production speed of polyolefin film can be ensured. On the other hand, by keeping the casting speed at 16 m / min or less, sufficient casting time is ensured, which reduces the formation of coarse crystals in the polyolefin resin and the resulting decrease in Spd and Spc, thereby suppressing the increase in peel resistance.

[0054] Next, the obtained unstretched sheet is biaxially stretched and biaxially oriented. Specifically, the stretching conditions are as follows: First, the unstretched sheet is preheated to the temperature required for stretching in the longitudinal direction. Preheating methods include using a temperature-controlled rotary roll, using a hot air oven, etc., either alone or in appropriate combinations. The film temperature (preheating temperature) when stretching in the longitudinal direction is preferably 130°C to 160°C, more preferably 140°C to 160°C, and more preferably 145°C to 154°C, considering the viewpoint of controlling protrusions on the film surface to a desirable range by high-temperature stretching. The stretching ratio is preferably 3.0 to 6.0 times, more preferably 4.0 to 5.7 times, and even more preferably 4.5 to 5.5 times, in order to control the mechanical and thermal properties to a desirable range. When the stretching ratio is 3.0 times or higher, more uniform stretching can be achieved and thickness variations can be suppressed. On the other hand, if the stretching ratio is 6.0 times or less, film breakage in the longitudinal stretching process and the subsequent transverse stretching process is reduced.

[0055] Next, the longitudinally uniaxially oriented film obtained by stretching in the longitudinal direction is cooled to a temperature of 10°C to 70°C. If the cooling temperature is 10°C or higher, curling of the film can be suppressed. On the other hand, if the cooling temperature is 70°C or lower, the promotion of thermal crystallization can be suppressed. After that, it is guided to a tenter, and after preheating by gripping both ends in the width direction with clips, it is transversely stretched to 7.0 to 13 times its original width. Considering the viewpoint of controlling the protrusions on the film surface to a desirable range by high-temperature stretching, the preheating and stretching temperatures are 156 to 166°C, more preferably 159 to 165°C, and even more preferably 160 to 164°C. Furthermore, heat treatment may be performed directly in the tenter, and in this case, in order to control the thermal shrinkage rate in the width direction, the heat treatment temperature is preferably 110°C to less than 170°C, and more preferably 150°C to 165°C. Furthermore, the heat treatment may be carried out while relaxing the film in the width direction. In particular, by setting the relaxation rate in the width direction to 2.0% or more and 20.0% or less, more preferably 7.0% or more and 15.0% or less, the thermal shrinkage rate in the width direction can be set to an appropriate range, and the balance of dimensional stability can be appropriately adjusted.

[0056] The polyolefin film obtained as described above can be used in a variety of applications, including packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, and medical products. However, due to its excellent surface smoothness, it is particularly suitable for use as a surface protection film, process film, and release film. [Examples]

[0057] The polyolefin film of the present invention will be described in more detail below with reference to examples, but the polyolefin film is not limited to these embodiments. The properties were measured and evaluated by the following methods.

[0058] (1) Film thickness, thickness variations Five polyolefin films were stacked to form a measurement sample, and the thickness of the sample was measured using an electronic micrometer (TESA TT80). Next, the obtained value was divided by 5 to calculate the thickness of each polyolefin film. Furthermore, the same measurement was performed at a position shifted by 50 mm in the width direction, and the same measurement was repeated a total of five times. From the obtained measurement results, the maximum, minimum, and average values ​​of the thickness of each polyolefin film were determined, and the average value was taken as the film thickness (t: μm), and the thickness variation (%) was calculated using the following formula. Thickness variation (%) = ((Maximum thickness - Minimum thickness) / Average thickness) × 100.

[0059] (2) Peak density (Spd), arithmetic mean curve of peaks Rate (Spc), mean roughness (Sa) Measurements were taken using the "VertScan" (registered trademark) 2.0 (model: R3300GL-Lite-AC) non-contact surface and layer cross-sectional shape measurement system manufactured by Ryoka Systems Co., Ltd., under the following procedure and conditions. First, polyolefin film was unwound from a film roll, and 10 measurement samples were taken at randomly determined points on a straight line passing through the center in the width direction and parallel to the longitudinal direction. Spd, Spc, and Sa were measured at these 10 points. The average value of each obtained measurement was calculated and used as the Spd, Spc, and Sa of the polyolefin film. Note that one measurement was performed using one field of view (field of view area: 939 μm vertical × 1,252 μm horizontal = 1,175,628 μm). 2 Measurements were taken of the following:

[0060] A. Measurement conditions CCD camera: SONY HR-57 1 / 2 Objective lens: 10X Lens tube: 0.5X BODY Wavelength filter: 530 white Measurement mode: Wave Field of view size: 640 x 480 Scan range: (Start) 5μm, (Stop) -5μm.

[0061] B. Method for fixing the measurement sample A dedicated sample holder was used to secure the measurement samples. The sample holder consisted of two detachable metal plates with a circular hole in the center. The measurement sample was placed between the plates, ensuring there were no wrinkles, and measurements were taken on the sample located within the circular hole.

[0062] C. Analysis method The data obtained from the above measurements was analyzed using the image analysis software VS-Viewer of "VertScan" (registered trademark) 2.0. First, noise was removed using a median filter (5x5), and then undulation components were removed using a Gaussian filter with a cutoff value of 250 μm. Next, Spd, Spc, and Sa, as defined in ISO25178(2012), were measured using the "ISOPara" function. In the "ISOPara" function, the S-Filter was set to 6.0 μm.

[0063] (3) Evaluation of release properties with adhesive tape Polyethylene adhesive tape No. 31B manufactured by Nitto Denko Corporation was applied to a polyolefin film using a roller, and then cut into 19mm wide strips to prepare samples. These samples were peeled using a tensile testing machine under conditions of a peeling speed of 300mm / min and a peeling angle of 180°, and the peeling force N (N / 19mm) was measured. The samples were further evaluated according to the following criteria (○, △1, and △2 indicate that the film can be used without problems as a release film, and these were considered acceptable). The polyester adhesive tape was applied to the inner surface of the film roll. ○: No delamination occurred between the surface and base layers, and delamination was possible at a constant rate. △1: No delamination occurred between the surface and base layers, but the delamination resistance was somewhat strong, and the delamination was unstable. △2: The adhesion between the adhesive tape and the surface layer was insufficient. Although delamination did not occur, the peel resistance was somewhat weak, resulting in unstable peeling. ×: Delamination occurred between the surface layer and the base layer, or the delamination was very severe, leaving delamination marks on the surface of the adherend.

[0064] (4) Coefficient of friction Test specimens (measurement standard length: width 75 mm x length 100 mm), which had been temperature and humidity controlled under specified conditions (temperature: 23±3℃, humidity: 65±5%), were stacked so that different sides were in contact with each other and set in a measuring instrument (slip tester). A 200g load was placed on top of the two stacked test specimens, and the resistance value was measured by sliding the upper test specimen on the measuring instrument. The coefficient of friction was calculated using the following formula. Coefficient of friction = resistance (g) / load (g).

[0065] (5) Product rolled up After winding the product rolls, wrinkles and misalignment were visually inspected and evaluated according to the following criteria. A result of ○ or △ was considered acceptable. ○: No wrinkles or misalignment occurred in the product roll. △: Wrinkles and misalignment occurred in the product rolls, but these were minor and did not cause any actual damage during processing. ×: Wrinkles and misalignment occurred in the product rolls, resulting in an excessive level of damage to the processing.

[0066] (6) Scratches on the film surface First, a film sample was prepared in the shape of a 1m (long side) x 1m (width side) square. Next, in a darkroom, one side (arbitrary) of the film sample was illuminated with 2000lx LED light (OHM EB-10KM) while varying the incident angle within the range of 30° to 90°. While illuminating with the LED light, the film sample was observed from the illuminated side, and scratches that could be visually confirmed were sampled. Subsequently, the sampled scratches were observed under a microscope, and scratches with a length of 1 mm or more and a width of 0.1 mm or less were counted. The same measurement was performed a total of 5 times with different film samples, and the average number of scratches obtained was calculated and evaluated according to the following criteria. ○: Number of scratches ≤ 10 / m 2 . △:10 pieces / m 2 <Number of scratches ≤ 30 / m 2 . ×: Number of scratches > 30 / m 2 .

[0067] (7) N / t The peeling force N (N / 19mm) measured by the method in (3) was calculated by dividing it by the film thickness t (μm) measured by the method in (1).

[0068] [Raw materials] The following raw materials were used to produce the polyolefin films of the examples and comparative examples.

[0069] (1) Resin Polyolefin resin I (homopolypropylene resin): Manufactured by Prime Polymer Co., Ltd., this is a highly stereoregular homopolypropylene resin with an MFR of 2.9 g / 10 min, a melting point of 164 °C, and a mesopentade fraction of 0.94. Branched-chain polypropylene resin: "WAYMAX" (registered trademark) (MFX3) manufactured by Nippon Polypropylene Co., Ltd., with an MFR of 9.0 g / 10 min. Polymethylpentene resin (PMP): Mitsui Chemicals, Inc. "TPX" (registered trademark) MX004 Ethylene-propylene random copolymer: Manufactured by Sumitomo Chemical Co., Ltd., with an MFR of 4.0 g / 10 min and an ethylene content of 1.1% by mass.

[0070] (2) Antioxidants Antioxidant 1: BASF Japan's "Irganox" (registered trademark) 1010. Antioxidant 2: 2,6-di-t-butyl-p-cresol (BHT) manufactured by ADEKA.

[0071] (Example 1) Polyolefin resin I was supplied to a single-screw extruder as the raw material for the base layer (A), and 80 parts by mass of polyolefin resin I and 20 parts by mass of branched polypropylene resin were dry-blended and supplied to another single-screw extruder as the raw material for the surface layer (B), and melt-extruded at 260°C. Next, after removing foreign matter with a 20 μm cut sintered filter, the raw materials were laminated in a feed-block type composite T-die so that the surface layer (B) / base layer (A) / surface layer (B) had a thickness ratio of 1 / 8 / 1 to form a sheet, which was then discharged onto a casting drum with a surface temperature controlled to 90°C and pressed tightly against the casting drum with an air knife. Subsequently, compressed air was injected onto the uncooled drum surface of the sheet on the casting drum to cool it and obtain an unstretched sheet. Next, the unstretched sheet was preheated to 155°C using a conveyor roll, stretched 5.0 times in the longitudinal direction between rolls with a difference in peripheral speed, and after stretching, the uniaxially oriented film was cooled on a roll at 40°C. Next, the uniaxially oriented film was introduced into a tenter stretcher with both ends in the width direction gripped by clips. After preheating at 162°C for 3 seconds, it was stretched to 8.8 times its original length at 162°C, and then heat-treated at 163°C while allowing 10.5% relaxation in the width direction. After a cooling process at 135°C, the film was guided to the outside of the tenter stretcher, the clips at the ends in the width direction were released, and the surface that would become the inner surface of the roll was subjected to corona discharge treatment. Subsequently, the film, with both ends in the width direction (the parts gripped by the clips) cut off by a slitter, was wound up on a winding machine to obtain a biaxially oriented polypropylene film with a thickness of 15 μm. The physical properties and evaluation results of the obtained biaxially oriented polypropylene film are shown in Table 1.

[0072] (Examples 2-8, Comparative Examples 1-5) In Example 1, a biaxially oriented polypropylene film with the thickness shown in Table 1 was obtained using the same method as in Example 1, except that the layer structure, composition of each layer, and film-forming conditions were as shown in Table 1. For the single-film example, a single-screw extruder was used, and the thickness was adjusted by controlling the resin discharge amount by the rotation speed of the extruder, as well as by controlling the casting speed, longitudinal stretching ratio, and transverse stretching ratio. The physical properties of the obtained film and the evaluation results for each item are shown in Table 1.

[0073] [Table 1]

[0074] In Comparative Example 5, since it has a single-layer structure, the layer composition is described assuming that only a base layer exists and there is no surface layer. [Industrial applicability]

[0075] As described above, the polyolefin film of the present invention has excellent release properties and quality, making it suitable for use as a release film or process film, and is particularly suitable as a release film for cover films of adhesive resin layers. Furthermore, since the polyolefin film of the present invention also has excellent surface smoothness, it can be preferably used as a release film or process film in applications where surface smoothness of the product is required. In addition, the polyolefin film of the present invention, possessing the above characteristics, can be used in a variety of applications such as packaging films, process films, sanitary products, agricultural products, construction products, and medical products.

Claims

1. The material has a base layer (A) made of homopolypropylene resin, and on both sides there are surface layers (B) containing homopolypropylene resin and branched-chain polypropylene resin, wherein the amount of branched-chain polypropylene resin in the surface layer (B) is 5.0% by mass or more and 30.0% by mass or less of the total components constituting the layer. The peak density Spd of the mountain is 100 (1 / mm²). ２ ) or more 1000 (1 / mm ２ A biaxially oriented polypropylene film characterized in that, when a surface is defined as surface A, and the surface is less than or equal to the arithmetic mean curvature Spc of the peaks being between -200 (1 / mm) and -10 (1 / mm), at least one of the surfaces is surface A.

2. The biaxially oriented polypropylene film according to claim 1, wherein at least one of the A surfaces has an average roughness Sa of 200 nm or more and 600 nm or less.

3. A biaxially oriented polypropylene film according to claim 1 or 2, wherein the film thickness is t (μm), a polyester adhesive tape is laminated onto surface A, and the peeling force N (N / 19mm) is obtained when peeling is performed at a peeling speed of 300 mm / min and a peeling angle of 180°, and N / t is 0.06 or more and 0.20 or less.

4. A release film made using the biaxially oriented polypropylene film described in claim 1 or 2.

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