JP2016064654A - Biaxial oriented polypropylene film and surface protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxial oriented polypropylene film excellent in productivity, strength and quality and having re-peelable moderate adhesiveness.SOLUTION: There is provided a biaxial oriented polypropylene film comprising at least a substrate layer and an adhesive layer, the substrate layer mainly contains polypropylene, the adhesive layer contains a styrenic thermoplastic elastomer and a crystalline polypropylene, mass percentage (%) of the styrenic thermoplastic elastomer to the total mass of the styrenic thermoplastic elastomer and the crystalline polypropylene is 5 to 45%, and adhesive power is 0.05 N/25 mm to 2.0 N/25 mm.SELECTED DRAWING: None

Description

  The present invention relates to a biaxially oriented polypropylene film that is excellent in productivity, strength, and quality, and has suitable tackiness that can be re-peeled and can be suitably used as a surface protective film.

  Adhesive films that have adhesiveness to the adherend surface and can be peeled off after use without contaminating the adherend are used as packaging films, surface protective films, and process films. Widely used as protective films for products, display panel members, synthetic resin panels, and protective films for processing, storage, transportation, shipping, etc. ing.

  As such an adhesive film, for example, Patent Document 1 describes a film in which an adhesive is applied to the surface of a polyethylene terephthalate film or the like. However, these films are not sufficiently productive because the adhesive layer is applied and dried off-line. In addition, the pressure-sensitive adhesive sometimes remains on the surface of the adherend when it is peeled off.

  As a self-adhesive film without applying an adhesive, for example, Patent Document 2 describes an adhesive film made of an unstretched polyethylene film. Since these films are unstretched, the strength of the film is low, and the adhesive film sometimes stretches or breaks during peeling. In addition, a film made of polyethylene resin is difficult to suppress the generation of polymer gel, and there are cases where defects such as fish eyes occur in the film, and when used as a protective film for members for display panels that are becoming increasingly fine in recent years, In some cases, quality was a problem.

  As means for solving these problems, for example, Patent Documents 3 to 6 describe a self-adhesive film made of a biaxially stretched polypropylene film. However, in the polypropylene film, the crystallization of the polypropylene polymer progresses with the biaxial stretching and the heat treatment, the flexibility of the adhesive layer is lowered, and the adhesiveness is lowered. Therefore, it is necessary to add a large amount of the adhesive component. When a large amount of the adhesive component is added, the material cost is increased, the productivity is lowered, the compatibility with polypropylene is lowered, the defects are increased, and the film quality is sometimes lowered. Moreover, when there are many ratios of the adhesion component of an adhesion layer, when environmental temperature becomes high after bonding with a to-be-adhered body, adhesiveness will increase and it may become difficult to peel. Moreover, as in Patent Documents 3 and 4, when an amorphous polymer is used as the adhesive component, the heat resistance of the amorphous polymer is low, and the film adheres to a roll or the like in a film-forming process such as casting or longitudinal stretching. In some cases, it is difficult to form a film or the film forming speed cannot be increased, resulting in a decrease in productivity.

JP 2007-131661 A WO12 / 128010 JP 2006-299060 A JP 2009-299022 A JP 2008-162059 A JP 2014-24940 A

  An object of the present invention is to solve the above-described problems. That is, an object is to provide a biaxially oriented polypropylene film that has excellent productivity, strength, and quality, and has suitable tackiness that can be removed again.

  In order to solve the above-described problems and achieve the object, the polypropylene film of the present invention is a biaxially oriented polypropylene film including at least a base material layer and an adhesive layer, and the base material layer is mainly composed of polypropylene, The adhesive layer contains a styrene thermoplastic elastomer and crystalline polypropylene, and the mass ratio (%) of the styrene thermoplastic elastomer to the total mass of the styrene thermoplastic elastomer and the crystalline polypropylene is 5 to 45%. The force is 0.05 N / 25 mm or more and 2.0 N / 25 mm or less.

  The biaxially oriented polypropylene film of the present invention is excellent in productivity, strength, and quality, and has an appropriate tackiness that can be re-peeled, so that it can be suitably used as a surface protective film.

  The biaxially oriented polypropylene film of the present invention is a biaxially oriented polypropylene film comprising at least a base material layer and an adhesive layer, the base material layer comprising polypropylene as a main component, and the adhesive layer comprising a styrene-based thermoplastic elastomer and crystallinity. Polypropylene is contained, and the mass ratio (%) of the styrene thermoplastic elastomer to the total mass of the styrene thermoplastic elastomer and the crystalline polypropylene is 5 to 45%. Usually, a self-adhesive film made of a biaxially oriented polypropylene film generally contains an adhesive component such as a styrene thermoplastic elastomer or an amorphous polyolefin in an adhesive layer in a mass ratio of 50% or more. In the invention, even with a small content of 5 to 45%, the present inventors have succeeded in expressing appropriate adhesive strength. Since the content of the adhesive component can be reduced, not only can the cost be reduced, but also the temperature change of the adhesive force can be reduced and the strength of the film can be improved.

  In general, when the temperature of the casting drum is raised in the biaxially oriented polypropylene film, elliptical irregularities are generated on the film surface. Since unevenness on the film surface lowers the adhesive strength, it is common to set the casting drum at a low temperature of 30 ° C. or lower when obtaining a self-adhesive film. In the present invention, the specific polypropylene (polypropylene raw material B), which will be described later, is used as the polypropylene raw material used for the adhesive layer, the casting drum is heated to a high temperature, and the adhesive layer is discharged so that the adhesive layer is in contact with the casting drum. Even if there is little, it became possible to express moderate adhesive force. This is because by using a specific polypropylene for the adhesive layer, the occurrence of elliptical irregularities is reduced even when the casting drum is hot, and the casting drum is heated so that the adhesive layer is in contact with the casting drum. As a result, the adhesion between the casting drum and the film is increased, and the smoothness of the adhesive layer surface is improved. Therefore, it is considered that an appropriate adhesive force can be expressed even with a small addition amount.

Biaxially oriented polypropylene film of the present invention is preferably the longitudinal direction of the Young's modulus E _MD is not less than 1 GPa. When the longitudinal direction of the Young's modulus E _MD of less than 1 GPa, torn stretches the film with a release tension upon the release from the adherend used as a surface protective film, in some cases peeling trace remains on the adherend. In addition, the film may be stretched by the conveyance tension at the time of bonding. E _MD is more preferably 1.2GPa or more, more preferably at least 1.4 GPa. E _MD is preferably as strong, but essentially is the upper limit of about 3 GPa. The value of E _MD to the above range, the range to be described later raw material composition of the film, also a range to be described later deposition conditions, to obtain a polypropylene film film was biaxially stretched at a high magnification preferable.

The biaxially oriented polypropylene film of the present invention preferably has a Young's modulus E _{TD in the} width direction of 1 GPa or more. When E _TD is less than 1 GPa, or become a film easily wrinkles on during transport, wound into a roll is pasted to a film as an adherend, such as wrinkles on the roll by the dimensional change of the film upon storage May occur. E _TD is more preferably 1.5 GPa or more, further preferably 2.0 GPa or more, and most preferably 2.5 GPa or more. The stronger E _TD is, the more preferable, but the upper limit is substantially about 7 GPa. In order to make the value of E _TD within the above range, the raw material composition of the film should be within the range described below, and the film forming conditions should be within the range described below, and the film may be biaxially stretched at a high magnification to obtain a polypropylene film. preferable.

  In the present application, a direction parallel to the film forming direction is referred to as a film forming direction, a longitudinal direction, or an MD direction, and a direction perpendicular to the film forming direction in the film plane is referred to as a width direction or a TD direction.

  The biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage ratio of 1.0% or less after heat treatment at 110 ° C. in the width direction. More preferably, it is 0.8% or less, more preferably 0.5% or less, and most preferably 0.3% or less. When the heat shrinkage rate in the width direction exceeds 1.0%, for example, the film is deformed and peeled off or wrinkled when passing through a drying process where heat is applied after bonding with another material. There is a case. In addition, when the environmental temperature rises when the film is bonded to the adherend film, wound into a roll, and stored, wrinkles or the like may occur on the roll due to a dimensional change of the film. The lower limit of the heat shrinkage rate is not particularly limited, but the film may expand, and the lower limit is substantially about -2.0%. In order to set the heat shrinkage ratio in the above range, the raw material composition of the film is set in the range described later, and the film forming conditions are set in the range described below, and in particular, the heat fixing and relaxation conditions after biaxial stretching are set in the range described below. Is effective.

  The biaxially oriented polypropylene film of the present invention has an adhesive strength of 0.05 N / 25 mm or more and 2.0 N / 25 mm or less. If the adhesive strength is less than 0.05 N / 25 mm, the film may be peeled off during transportation after being bonded to the adherend. If it exceeds 2.0 N / 25 mm, the film may stretch and tear when peeled off from the adherend, or a peeling mark may remain on the adherend. The adhesive force is more preferably 0.1 N / 25 mm or more and 1.5 N / 25 mm or less, still more preferably 0.1 N / 25 mm or more and 1.0 N / 25 mm or less. In order to make the adhesive strength within the above range, it is effective to set the raw material composition of the film in the range described later, and the film forming conditions in the range described below, and in particular, the conditions in the casting step are set in the range described below.

  The biaxially oriented polypropylene film of the present invention preferably has an adhesive strength after treatment at 60 ° C. for 1 hour of 0.05 N / 25 mm or more and 2.0 N / 25 mm or less. If the adhesive strength after treatment at 60 ° C. for 1 hour is less than 0.05 N / 25 mm, the film may be peeled off during transportation after being bonded to the adherend. If the thickness exceeds 2.0 N / 5 mm, the film is bonded to the adherend film, wound up in a roll, and stored at an environmental temperature. When peeled off from the adherend, the film may be stretched and torn. There may be a case where peeling marks remain on the body. The adhesive strength after treatment at 60 ° C. for 1 hour is more preferably 0.05 N / 25 mm or more and 1.5 N / 25 mm or less, still more preferably 0.05 N / 25 mm or more and 1.0 N / 25 mm or less. In order to make the adhesive strength within the above range, it is important that the raw material composition of the film is within the range described below, and the film forming conditions are within the range described below, and particularly the conditions in the casting step are within the range described below. Is effective.

  The thickness of the biaxially oriented polypropylene film of the present invention is appropriately adjusted depending on the application and is not particularly limited, but is preferably 5 μm or more and 100 μm or less. When the thickness is less than 5 μm, handling may be difficult, and when it exceeds 100 μm, the amount of resin may increase and productivity may decrease. Since the biaxially oriented polypropylene film of the present invention is excellent in tensile rigidity even when the thickness is reduced, the handling property can be maintained. In order to make use of such characteristics, the thickness is more preferably 5 μm or more and 40 μm or less, further preferably 5 μm or more and 30 μm or less, and most preferably 5 μm or more and 25 μm or less. The thickness can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, and the like within a range not deteriorating other physical properties.

  Next, the polypropylene raw material preferable for use in the biaxially oriented polypropylene film of the present invention for satisfying the above-described characteristics and the structure of the film using the raw material will be described.

  The biaxially oriented polypropylene film of the present invention is a film including at least a base material layer and an adhesive layer, the base material layer is mainly composed of polypropylene, and the adhesive layer contains a styrenic thermoplastic elastomer and a crystalline polypropylene. The mass ratio (%) of the styrene thermoplastic elastomer to the total mass of the styrene thermoplastic elastomer and the crystalline polypropylene is 5 to 45%. Here, the “main component” in the present application means that the proportion of the specific component in all the components is 50% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, Most preferably, it is 99 mass% or more.

  First, the polypropylene raw material A preferably used for the base material layer of the present invention will be described.

  The polypropylene raw material A is preferably a polypropylene having a cold xylene soluble part (hereinafter referred to as CXS) of 4% by mass or less and a mesopentad fraction of 0.95 or more. If these are not satisfied, the film forming stability may be inferior or the Young's modulus of the film may be reduced.

  Here, the cold xylene-soluble part (CXS) refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene and then deposited at room temperature, and has low stereoregularity. It is considered that it corresponds to a component that is difficult to crystallize due to low molecular weight. If many such components are contained in the resin, the Young's modulus of the film may be inferior. Therefore, CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. CXS is preferably as low as possible, but about 0.1% by mass is the lower limit. In order to obtain such polypropylene having CXS, methods such as a method for increasing the catalytic activity in obtaining a resin and a method for washing the obtained resin with a solvent or propylene monomer itself can be used.

  From the same viewpoint, the mesopentad fraction of the polypropylene raw material A is preferably 0.95 or more, more preferably 0.97 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene measured by a nuclear magnetic resonance method (NMR method). The higher the numerical value, the higher the crystallinity, the higher the melting point, and the higher the temperature. It is preferable because it is suitable for use. The upper limit of the mesopentad fraction is not particularly specified. In order to obtain a resin with high stereoregularity in this way, there are a method of washing resin powder obtained with a solvent such as n-heptane, a method of selecting a catalyst and / or promoter, and a composition as appropriate. Preferably employed.

  Further, as the polypropylene raw material A, the melt flow rate (MFR) is more preferably 1 to 10 g / 10 min (230 ° C., 21.18 N load), particularly preferably 2 to 5 g / 10 min (230 ° C., 21.18 N). The range of (load) is preferable from the viewpoint of film forming properties and tensile rigidity of the film. In order to set the MFR to the above value, a method of controlling the average molecular weight or the molecular weight distribution is employed.

  The polypropylene raw material A is mainly composed of a propylene homopolymer, but may contain other unsaturated hydrocarbon copolymerization components or the like within a range not impairing the object of the present invention. The coalescence may be blended. For example, ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene as monomer components constituting such a copolymer component or blend. 1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- Examples include norbornene. From the viewpoint of tensile rigidity, the copolymerization amount or blend amount is preferably less than 1 mol% in terms of copolymerization amount and less than 10 mass% in terms of blend amount.

  In the above-mentioned polypropylene raw material A, an antioxidant, a heat stabilizer, an antistatic agent, a lubricant composed of inorganic or organic particles, an anti-blocking agent and a filler, and an incompatible material, as long as the effects of the present invention are not impaired. You may contain various additives, such as a polymer. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidative deterioration due to the heat history of the polypropylene raw material A. It is preferable that antioxidant content shall be 2 mass parts or less with respect to 100 mass parts of polypropylene raw materials A, More preferably, it is 1 mass part or less, More preferably, it is 0.5 mass part or less.

  Moreover, the base material layer may contain a styrene-based thermoplastic elastomer described later. However, in this application, content of the styrene-type thermoplastic elastomer in a base material layer shall be less than content of the styrene-type thermoplastic elastomer in an adhesion layer. More preferably, the mass ratio (%) of the styrene thermoplastic elastomer to the total mass of the styrene thermoplastic elastomer and the polypropylene raw material A is 0% or more and less than 5%, more preferably 0% or more and less than 3%. If the content of the styrenic thermoplastic elastomer in the base material layer is large, the Young's modulus of the biaxially oriented polypropylene film may be reduced, the slipping property of the base material layer may be reduced, and handling properties may be deteriorated.

  Next, the raw material preferably used for the adhesive layer of the biaxially oriented polypropylene film of the present invention will be described.

  The adhesive layer contains a styrene thermoplastic elastomer and crystalline polypropylene, and the mass ratio (%) of the styrene thermoplastic elastomer to the total mass of the styrene thermoplastic elastomer and the crystalline polypropylene is 5 to 45%.

  In the present invention, the styrene-based thermoplastic elastomer is not particularly limited as long as it is a raw material that exhibits the above-mentioned adhesive force, and is a styrene / ethylene butylene / styrene copolymer (SEBS), a styrene / butadiene / styrene copolymer ( SBS), styrene / ethylene propylene / styrene copolymer (SEPS), hydrogenated styrene butadiene rubber (HSBR), styrene / ethylene butylene / olefin crystal copolymer (SEBC), and the like can be used. By using a styrene-based thermoplastic elastomer, excellent adhesiveness can be expressed even with a small amount of content, and it is excellent in transportability and the ratio of crystalline polypropylene can be increased, so that fish eyes can be reduced, etc. It is possible to provide a film with excellent quality. Further, among styrene thermoplastic elastomers, a hydrogenated product of a random copolymer synthesized using 1 to 40% by mass of styrene and 99 to 60% by mass of a diene hydrocarbon as a monomer is preferable.

  The crystalline polypropylene raw material B used for the adhesive layer of the biaxially oriented polypropylene film of the present invention will be described. As the crystalline polypropylene raw material B, it is important not to inhibit the adhesiveness of the adhesive layer. For example, if homopolypropylene with Ziegler-Natta catalyst is used, the crystallinity is too high, and after biaxial stretching, elliptical irregularities due to crystals occur on the film surface, the flexibility of the adhesive layer decreases, and adhesiveness is expressed. May not. From the above viewpoint, the crystalline polypropylene raw material B is 10% by mass or less, more preferably 7% by mass or less, and more preferably α-olefin component such as ethylene component, butene, hexene, octene, etc. for the purpose of reducing crystallinity and melting point. It is preferable to use a polypropylene resin copolymerized in a range of preferably 5% by mass or less, most preferably 2.5% by mass or less, or a homopolymer or copolymerized polypropylene polymerized using a metallocene catalyst. As a copolymerization method, either random copolymerization or block copolymerization may be used, but random copolymerization is possible because it is possible to reduce crystallinity and melting point while suppressing deterioration of mechanical properties. Is preferred.

  The melting point of the above-described crystalline polypropylene raw material B is preferably 120 ° C. to 150 ° C., more preferably 125 to 148 ° C., and further preferably 125 to 145 ° C. If the melting point is less than 120 ° C., the crystallinity is too low, the Young's modulus of the film is reduced, the proportion of copolymer components such as ethylene components is too large, and defects such as fish eyes are likely to occur, In some cases, the melting point is too low to adhere to a longitudinal stretching roll or the like, resulting in a decrease in film forming property. When the melting point exceeds 150 ° C., the crystallinity is too high, the flexibility of the adhesive layer is lowered after biaxial stretching, and the adhesiveness may not be expressed. As the crystalline polypropylene raw material B, there can be used polypropylene FS3611 or S131 manufactured by Sumitomo Chemical Co., Ltd., polypropylene PM940M or PB222A manufactured by Sun Allomer, polypropylene B221WA or B241 manufactured by Prime Polymer, or the like.

  The adhesive layer of the biaxially oriented polypropylene film of the present invention contains the above-described thermoplastic elastomer and crystalline polypropylene in a mass ratio of 5 to 45 parts by mass and 95 to 55 parts by mass, respectively. If the content ratio of the thermoplastic elastomer is less than 5 parts by mass, the tackiness may not be exhibited. When the content ratio of the thermoplastic elastomer exceeds 45 parts by mass, the adhesive strength after treatment at 60 ° C. for 1 hour increases, exceeds 2.0 N / 25 mm, and the film stretches and tears when peeled off from the adherend. Or peeling marks may remain on the adherend. Moreover, when there are many content ratios (mass ratio) of a thermoplastic elastomer, the intensity | strength of a film will fall and handling property may fall. The content ratio (mass ratio) of the thermoplastic elastomer when the total amount of the thermoplastic elastomer and the crystalline polypropylene is 100 parts by mass is more preferably 5 to 40 parts by mass, still more preferably 5 to 35 parts by mass. (The content ratios of the corresponding crystalline polypropylene are 95 to 60 parts by mass and 95 to 65 parts by mass, respectively). If the content ratio of the crystalline polypropylene exceeds 95 parts by mass, the tackiness may not be exhibited. When the content ratio of the crystalline polypropylene is less than 55 parts by mass, the Young's modulus of the film may be lowered, or defects such as fish eyes may be easily generated.

  In the adhesive layer of the biaxially oriented polypropylene film of the present invention, the total amount of the thermoplastic elastomer and the crystalline polypropylene described above is preferably 50% by mass or more, and 80% by mass or more with respect to the resin constituting the adhesive layer. More preferably, it is more preferably 90% by mass or more, and most preferably 99% by mass or more. When the total amount of the thermoplastic elastomer and the crystalline polypropylene is less than 50% by mass, the adhesiveness is not exhibited, or the compatibility with the crystalline polypropylene resin is lowered, and the quality is lowered due to the generation of fish eyes and the like. There is a case.

  The pressure-sensitive adhesive layer of the biaxially oriented polypropylene film of the present invention includes an antioxidant, a heat stabilizer, an antistatic agent and an inorganic material as long as the effects of the present invention are not impaired in addition to the thermoplastic elastomer and crystalline polypropylene described above. Alternatively, a lubricant composed of organic particles, and further various additives such as an antiblocking agent, a filler, and an incompatible polymer may be contained. In particular, it is preferable to add an antioxidant for the purpose of suppressing oxidative deterioration due to the thermal history of the polypropylene raw material A and the polypropylene raw material B. The addition amount of the antioxidant is preferably 2 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0.5 parts by mass or less with respect to 100 parts by mass of the polypropylene raw material A and / or the polypropylene raw material B. .

  The biaxially oriented polypropylene film of the present invention is a film including at least a base material layer and an adhesive layer, and the thermoplastic elastomer and the crystalline polypropylene are provided on at least one surface of the base material layer containing the polypropylene raw material A as a main component. It is preferable that the pressure-sensitive adhesive layer containing the raw material B is laminated. At this time, it is preferable that the ratio (%) of the adhesion layer thickness in the thickness of the whole biaxially oriented polypropylene film is 5 to 50%, more preferably 7 to 45%, and still more preferably 10 to 405. When the ratio of the thickness of the adhesive layer exceeds 50%, the strength of the biaxially oriented polypropylene film decreases, and when used as a surface protective film, the film stretches with a peeling tension when the adhesiveness to the adherend is high. May be torn, or peeling marks may remain on the protective surface. If the ratio (%) of the adhesive layer thickness is less than 5%, the adhesiveness may not be exhibited. In order to make a lamination | stacking thickness ratio into the said range, it can adjust with the screw rotation speed of each extruder used for a base material layer and an adhesion layer. However, when the adhesive layer is laminated on both surfaces of the base material layer, the total thickness of the adhesive layer is preferably the above thickness ratio. Further, an intermediate layer may be provided between the base material layer and the pressure-sensitive adhesive layer so as to have a laminated structure of three or more layers.

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

  First, the polypropylene raw material A is supplied to a single screw extruder for the A layer, the thermoplastic elastomer and the crystalline polypropylene raw material B are supplied to a single screw extruder for the B layer, and melt extrusion is performed at 200 to 260 ° C. . After removing foreign substances and modified polymer with a filter installed in the middle of the polymer tube, a multilayer thickness ratio of 1/1 to 19/1 is obtained with a multi-manifold type A / B composite T-die. Are laminated and discharged onto a cast drum to obtain a laminated unstretched sheet having a layer configuration of A layer / B layer. In this case, the surface temperature of the cast drum is preferably 35 to 90 ° C. from the viewpoint of expressing the tackiness of the adhesive layer, and more preferably 40 to 80 ° C. Moreover, it is preferable to discharge the B layer which is an adhesive layer so as to be in contact with the casting drum because a moderate adhesive force can be obtained even with a small amount of adhesive components. By increasing the temperature of the casting drum, the adhesion between the casting drum and the film is improved, and the smoothness of the adhesive layer surface is improved, so that it becomes possible to develop an appropriate adhesive force even with a small content. In addition, it is possible to form a β crystal on the surface of the base material layer to form elliptical irregularities after stretching, thereby improving the slipperiness of the back surface. As an adhesion method to the casting drum, any method among an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. may be used. From the viewpoint, the air knife method is preferable. The air temperature of the air knife is 25 to 100 ° C., preferably 30 to 80 ° C., the blowing air speed is preferably 130 to 150 m / s, and has a double tube structure to improve the width direction uniformity. Is preferred. Further, it is preferable to appropriately adjust the position of the air knife so that air flows downstream of the film formation so as not to cause vibration of the film.

  The obtained unstretched sheet is allowed to cool in air and then introduced into the longitudinal stretching step. In the longitudinal stretching step, an unstretched sheet is first brought into contact with a plurality of metal rolls maintained at 100 ° C. or more and less than 150 ° C., preheated to the stretching temperature, stretched 3 to 8 times in the longitudinal direction, and then cooled to room temperature. If the stretching temperature is less than 100 ° C., the film may be broken, or the crystallinity of the adhesive layer of the resulting biaxially oriented polypropylene film may be too high to exhibit adhesiveness. When the stretching temperature is 150 ° C. or higher, the adhesive layer surface sticks to the heated metal roll, and the film may break. On the other hand, if the draw ratio is less than 3, the orientation of the film becomes weak and the Young's modulus may be lowered. If it exceeds 8 times, the film may be broken or the crystallinity of the adhesive layer of the resulting biaxially oriented polypropylene film may be too high, and the adhesiveness may not be expressed.

  Next, the longitudinally uniaxially stretched film is guided to a tenter, the end of the film is held with a clip, and the transverse stretching is stretched 7 to 13 times in the width direction at a temperature of 120 to 165 ° C. If the stretching temperature is low, the film may be broken, and if the stretching temperature is too high, the film may be melted in the film tenter or the thickness unevenness may be increased. Further, when the magnification is high, the film may be broken, and when the magnification is low, the orientation of the film is weak and the Young's modulus may be lowered.

  In the subsequent heat treatment and relaxation treatment step, the clip is heat-set at a temperature of 100 ° C. or more and less than 165 ° C. while being relaxed at a relaxation rate of 2 to 20% in the width direction while the clip is held in tension in the width direction. The film is guided to the outside of the tenter through a cooling process at 140 ° C., the clip at the film end is released, the film edge is slit in the winder process, and the film product roll is wound up.

  The biaxially oriented polypropylene film of the present invention obtained as described above can be used in various applications such as packaging films, surface protective films, process films, sanitary products, agricultural products, building products, and medical products. Particularly, since it is excellent in adhesiveness, it can be preferably used as a surface protective film and a process film.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) Film thickness Five points were measured using a micro thickness gauge (manufactured by Anritsu), and an average value was obtained.

(2) Young's modulus in the longitudinal direction and width direction (E _MD , E _TD )
A biaxially oriented polypropylene film was cut into a rectangular shape having a length of 150 mm in the test direction and a width of 10 mm as a sample. Using a tensile tester (Tensilon AMF / RTA-100 manufactured by Orientec), measurement was performed 5 times in an atmosphere of 25 ° C. and 65% RH according to the method defined in JIS-K7127 (1999), and the average value was calculated. Asked. However, the distance between the initial chucks was set to 50 mm, the tensile speed was set to 300 mm / min, and the point where the load passed 1 N after the start of the test was used as the origin of elongation.

(3) Heat shrinkage rate Five specimens with a width of 10 mm and a length of 200 mm (measurement direction) are cut out in the width direction of the film, marked as marked lines at 25 mm positions from both ends, and marked with a universal projector. Is measured and set as the test length (l ₀ ). Next, the test piece is sandwiched between papers and taken out after heating for 15 minutes in an oven kept at 110 ° C. with zero load. After cooling at room temperature, the dimension (l ₁ ) is measured with a universal projector and measured as follows. It calculated | required by the type | formula and made the average value of 5 the heat shrinkage rate.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)
(4) Adhesive strength The adhesive strength was measured according to the method specified in JIS Z 0237 (2009), using a mirror-like acrylic resin plate (“Acrylite L001” 3 mm plate manufactured by Mitsubishi Rayon Co., Ltd.) instead of SUS304. It was. About the biaxially oriented polypropylene films of Examples and Comparative Examples, each was cut into a strip shape having a width of 25 mm and a total length of 200 mm, and the adhesive layer side was bonded to the acrylic resin plate and pressed using a rubber roller having a mass of 2 kg. Evenly adhered. After standing for 24 hours in an atmosphere of 25 ° C. and 65% RH, the strength when the acrylic resin plate is fixed and one end of the biaxially oriented polypropylene film is peeled 180 ° at a constant rate of 300 mm / min (N / 25 mm) Was measured as adhesive strength.

(5) Adhesive force after treatment at 60 ° C. for 1 hour A biaxially oriented polypropylene film was bonded to and adhered to an acrylic resin plate by the same method as the measurement method of “(4) Adhesive strength”. Thereafter, the sample was treated in a hot air oven at 60 ° C. for 1 hour, and left to stand in an atmosphere of 25 ° C. and 65% RH for 24 hours. Then, the acrylic resin plate was fixed and one end of the biaxially oriented polypropylene film was 300 mm / The strength (N / 25 mm) when peeling at 180 ° at a constant rate of min was measured and defined as the adhesive strength after treatment at 60 ° C. for 1 hour.

Example 1
First, 99.3 parts by mass of crystalline PP (a) (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min) and surface silane coupling treatment silica particles (manufactured by Denki Kagaku Kogyo Co., Ltd., SFP) -30MHE, average particle size 0.7μm) 0.5 parts by weight, and further, 0.1 parts by weight of IRGANOX 1010 and IRGAFOS 168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at this ratio. The raw material was supplied from the hopper to the twin screw extruder, melt kneaded at 260 ° C., discharged from the die in the form of strands, cooled and solidified in a 25 ° C. water tank, and cut into chips to obtain a polypropylene raw material A. .

  The polypropylene raw material A is supplied as a raw material for the base layer to a uniaxial melt extruder for the A layer, and a hydrogenated styrene elastomer (manufactured by JSR Corp., Dynalon D-1320P) is used as the thermoplastic elastomer for the adhesive layer. ) And 60 parts by mass of crystalline PP (b) (Sumitomo Chemical Co., Ltd., S131, melting point: 132 ° C., MFR: 1.5 g / 10 min) as crystalline polypropylene raw material B And fed to a single-axis melt extruder for layer B, melt extruded at 240 ° C., removed foreign matter with a 60 μm cut sintered filter, and then fed into a feed block type A / B composite T die. The melted sheet is discharged so that the layer B comes into contact with the cast drum, and is brought into close contact with an air knife on the cast drum whose surface temperature is controlled at 80 ° C., and then solidified by cooling and unrolled. To obtain a sheet. Next, preheating was performed to 125 ° C. using a plurality of ceramic rolls, and the film was stretched 4.6 times at 125 ° C. in the longitudinal direction of the film. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment process, heat treatment is performed at 165 ° C. while giving 10% relaxation in the width direction, and then through the cooling process at 130 ° C., the film is guided to the outside of the tenter, the clip at the end of the film is released, and the film is wound around the core. A biaxially oriented polypropylene film having a thickness of 30 μm was obtained. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 2)
The polypropylene raw material A is supplied as a raw material for the base layer to a uniaxial melt extruder for the A layer, and a hydrogenated styrene elastomer (manufactured by JSR Corp., Dynalon D-1320P) is used as the thermoplastic elastomer for the adhesive layer. ) And 70 parts by mass of crystalline PP (b) (Sumitomo Chemical Co., Ltd., S131, melting point: 132 ° C., MFR: 1.5 g / 10 min) as crystalline polypropylene raw material B And fed to a single-axis melt extruder for layer B, melt extruded at 240 ° C., removed foreign matter with a 60 μm cut sintered filter, and then fed with a feed block type A / B composite T die. The melted sheet is discharged so that the B layer is in contact with the cast drum, and is brought into close contact with an air knife on the cast drum whose surface temperature is controlled at 80 ° C., solidified by cooling, and unstretched. It was obtained over door. Next, the film was preheated to 125 ° C. using a plurality of ceramic rolls and stretched 4.6 times in the longitudinal direction of the film. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment process, heat treatment is performed at 165 ° C. while giving 10% relaxation in the width direction, and then through the cooling process at 130 ° C., the film is guided to the outside of the tenter, the clip at the end of the film is released, and the film is wound around the core A biaxially oriented polypropylene film having a thickness of 13 μm was obtained. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 3)
The polypropylene raw material A is supplied as a raw material for the base layer to a uniaxial melt extruder for the A layer, and a hydrogenated styrene elastomer (manufactured by JSR Corp., Dynalon D-1320P) is used as the thermoplastic elastomer for the adhesive layer. 15 parts by weight and 85 parts by weight of crystalline PP (a) (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min) as a crystalline polypropylene raw material B are dry-blended for the B layer To a single-screw melt extruder, melt extruded at 240 ° C., and after removing foreign matter with a 60 μm cut sintered filter, a feed block type A / B composite T die with a thickness ratio of 11/4 The melted sheet was laminated and brought into close contact with an air knife on a cast drum whose surface temperature was controlled at 80 ° C. to cool and solidify to obtain an unstretched sheet. Next, the film was preheated to 125 ° C. using a plurality of ceramic rolls and stretched 4.6 times in the longitudinal direction of the film. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment process, heat treatment is performed at 165 ° C. while giving 10% relaxation in the width direction, and then through the cooling process at 130 ° C., the film is guided to the outside of the tenter, the clip at the end of the film is released, and the film is wound around the core A biaxially oriented polypropylene film having a thickness of 30 μm was obtained. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 1)
In Example 1, 50 parts by mass of hydrogenated styrene-based elastomer (manufactured by JSR Corporation, Dynalon D-1320P) and crystalline PP (b) (manufactured by Sumitomo Chemical Co., Ltd., S131) are used as the adhesive layer resin. A biaxially oriented polypropylene film was obtained in the same manner as in Example 1 except that 50 parts by mass of a melting point of 132 ° C. and an MFR of 1.5 g / 10 minutes were used. The content of the hydrogenated styrene elastomer, which is an adhesive component, was large, the adhesive force increased after treatment at 60 ° C. for 1 hour, and peeling marks were generated. Table 1 shows the physical properties and evaluation results of the polypropylene film.

(Comparative Example 2)
In Example 1, 3 parts by mass of hydrogenated styrene elastomer (manufactured by JSR Corporation, Dynalon D-1320P) as a resin for the adhesive layer and crystalline PP (b) (manufactured by Sumitomo Chemical Co., Ltd., S131) A biaxially oriented polypropylene film was obtained in the same manner as in Example 1 except for using 97 parts by mass of a melting point of 132 ° C. and an MFR of 1.5 g / 10 min. The content of the hydrogenated styrene elastomer, which is an adhesive component, was small, and no tackiness was exhibited. Table 1 shows the physical properties and evaluation results of the polypropylene film.

(Comparative Example 3)
A biaxially oriented polypropylene film was obtained in the same manner as in Example 1 except that the A layer was in contact with the cast drum in Example 1. Table 1 shows the physical properties and evaluation results of the polypropylene film. The smoothness of the adhesive layer surface was lowered, and the adhesive strength became insufficient.

(Comparative Example 4)
In Example 1, a biaxially oriented polypropylene film was obtained in the same manner as in Example 1 except that the surface temperature of the cast drum was controlled at 30 ° C. Table 1 shows the physical properties and evaluation results of the polypropylene film. The adhesiveness with the cast drum was lowered, the smoothness of the adhesive layer surface was lowered, and the adhesive force was insufficient.

(Comparative Example 5)
In Example 1, instead of 60 parts by mass of crystalline PP (b) (manufactured by Sumitomo Chemical Co., Ltd., S131, melting point 132 ° C., MFR: 1.5 g / 10 min) as the crystalline polypropylene raw material B for the adhesive layer A biaxially oriented polypropylene film was obtained in the same manner as in Example 1 except that crystalline PP (a) (Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min) was 60 parts by mass. It was. Table 1 shows the physical properties and evaluation results of the polypropylene film. The obtained film did not develop tackiness.

Claims (7)

A biaxially oriented polypropylene film including at least a base material layer and an adhesive layer, the base material layer comprising polypropylene as a main component, the adhesive layer containing a styrene thermoplastic elastomer and crystalline polypropylene, and a styrenic thermoplastic Biaxial orientation in which the mass ratio (%) of the styrenic thermoplastic elastomer to the total mass of the elastomer and the crystalline polypropylene is 5 to 45%, and the adhesive strength is 0.05 N / 25 mm or more and 2.0 N / 25 mm or less. Polypropylene film. The biaxially oriented polypropylene according to claim 1, wherein the styrenic thermoplastic elastomer is a hydrogenated product of a random copolymer synthesized by using 1 to 40% by mass of styrene and 99 to 60% by mass of a diene hydrocarbon as monomers. the film. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the crystalline polypropylene constituting the adhesive layer has a melting point of 120 to 150 ° C. Longitudinal Young's modulus E _MD is not less than 1 GPa, biaxially oriented polypropylene film according to claim 1. The biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein Young's modulus E _{TD in the} width direction is 1 GPa or more. The biaxially oriented polypropylene film according to any one of claims 1 to 5, wherein a heat shrinkage ratio after heat treatment at 110 ° C in the width direction is 1.0% or less. The surface protection film which uses the biaxially oriented polypropylene film in any one of Claims 1-6.