JP2016043560A - Laminated biaxially-stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated biaxially-stretched film which has good sticking properties and/or followability, is excellent in blocking resistance, and is easy to be unwound from a winding.SOLUTION: A biaxially-stretched film is provided with a core layer, an adhesive layer formed on one surface of the core layer, and a back surface layer formed on the other surface of the core layer. The core layer is formed of a composition (B) containing a high-crystalline polypropylene resin (b1). The adhesive layer is formed of a composition (A) containing a low-crystalline polypropylene resin (a1). The back surface layer is formed of a composition (C) containing a low-density polyethylene resin (c1) and a propylene-based polymer (c2).SELECTED DRAWING: None

Description

  The present invention relates to a biaxially stretched film that has good sticking property and / or followability and is excellent in blocking resistance and easy to unwind from winding. Furthermore, the present invention relates to a biaxially stretched film for re-peeling that has good adhesiveness and / or followability, is excellent in blocking resistance, is easy to unwind from winding, and is excellent in peelability.

  Polypropylene film utilizes its rigidity, heat resistance, oil resistance, chemical resistance, processability, etc., such as optical films, surface protection films, magnetic recording media, thermal transfer films, electrical insulation materials, food packaging materials, etc. Widely used as industrial materials such as packaging materials, adhesive tapes and release materials.

  Polypropylene film, for example, as a surface protection film for preventing the surface of the adherend from being damaged in the manufacturing process, distribution process, etc., optical members such as liquid crystal displays, polarizing plates and retardation films, electronic members, It is used by being attached to the surface of various base materials such as substrates such as semiconductor substrates and electronic substrates, resin plates used in building materials, glass plates, metal plates and the like. Polypropylene films are also used as fixing films when transporting, processing, storing, etc. optical members and electronic members.

  Such a surface protective film and fixing film are required to have good adhesiveness to an adherend. In particular, when the adherend has a curved surface or unevenness, it is required that the adherend has sufficient adhesiveness and / or followability. In addition, while the sticking property and / or followability are required, the surface protective film and the fixing film are re-peeling films that are peeled off from the adherend during the manufacturing process or actual product use. Are required to be easily peeled off, and the phenomenon of “glue residue” in which a part of the pressure-sensitive adhesive layer remains on the adherend is required.

  Furthermore, the polypropylene film is usually stored and distributed in a state of being wound into a roll (the film in this state is also referred to as “winding” in the following), and then the film is unwound from the winding, Further processed or used as a film. For this reason, the polypropylene film is also required to be easily unwound from winding. Especially for a film having an adhesive layer, it is difficult to cause a drawing failure due to blocking between the adhesive layer that is in contact with each other in the state of being wound in a roll and the surface opposite to the adhesive layer. On the other hand, the pressure-sensitive adhesive layer is required to be difficult to deform due to the unevenness of the surface located on the opposite side.

  Patent Document 1 discloses a protective film composed of a single layer of a weak adhesive film containing an amorphous polypropylene resin and a crystalline polypropylene resin, or a film having a laminated structure in which a substrate layer is laminated on the weak adhesive film. Have been described. Patent Document 2 describes a pressure-sensitive adhesive composition containing a resin selected from propylene-based copolymers and ethylene-vinyl acetate copolymers, and the pressure-sensitive adhesive composition is attached to a substrate such as polyester. It can be used. Patent Document 3 describes an adhesive film in which an adhesive layer made of a composition containing an amorphous olefin copolymer, a crystalline olefin polymer, and a thermoplastic elastomer is laminated on a base material layer. The films described in Patent Documents 1 and 2 are unstretched films, and unstretched films are likely to be stretched and deformed, and thus are difficult to unwind from a state of being wound in a roll. Moreover, the film described in patent documents 1-3 is not provided with a back surface layer, and when storing in the state wound up by roll shape, blocking may arise.

  Patent Document 4 discloses an amorphous olefin copolymer, a crystalline olefin polymer, and an olefin (crystalline) / ethylene / butylene / olefin (crystalline) block copolymer or styrene / ethylene-butylene / olefin (crystalline). A pressure-sensitive adhesive film having a pressure-sensitive adhesive layer made of a block copolymer having a crystalline olefin block such as a block copolymer is described. Patent Document 5 describes a self-adhesive protective film having an adhesive layer composed of a hydrogenated styrene elastomer and a propylene / α-olefin random copolymer. However, the pressure-sensitive adhesive layers described in Patent Documents 4 and 5 both contain a very soft resin such as a crystalline olefin block or a hydrogenated styrene-based elastomer, so that the pressure-sensitive adhesive layer is easily deformed. In some cases, the smoothness of the adhesive layer was lowered. When the smoothness of the adhesive layer is reduced, there is a problem that air is included when the film is bonded to the adherend, and it is difficult to uniformly bond the film, and immediately after bonding, the contact area is small and the adhesive force is low. When a long time elapses in the state of bonding, the adhesive layer is smoothed again, the contact area increases, and the problem that the adhesive force increases (adhesion progress) is likely to occur.

Japanese Patent No. 531206 Japanese Patent No. 4781541 JP 2006-188646 A JP 2006-257247 A Japanese Patent No. 4573854

  An object of the present invention is to provide a biaxially stretched film that has a good sticking property and / or followability and is excellent in blocking resistance and easy to unwind from winding.

  In order to solve the above-mentioned problems, the present inventors have made detailed studies on laminated biaxially stretched films, and have completed the present invention.

That is, the present invention includes the following preferred embodiments.
[1] A biaxially stretched film comprising a core layer, an adhesive layer formed on one surface of the core layer, and a back layer formed on the other surface of the core layer,
The core layer is formed from a composition (B) containing a highly crystalline polypropylene resin (b1),
The adhesive layer is formed from a composition (A) containing a low crystalline polypropylene resin (a1),
The back layer is a biaxially stretched film formed from a composition (C) containing a low density polyethylene resin (c1) and a propylene polymer (c2).
[2] The biaxial shaft according to [1], wherein the content of the low crystalline polypropylene resin (a1) in the composition (A) is 50 to 100% by mass based on the total amount of the composition (A). Stretched film.
[3] The biaxially stretched film according to [1] or [2], wherein the mesopentad fraction (mmmm) of the low crystalline polypropylene resin (a1) is 20 to 60 mol%.
[4] The molecular weight distribution (Mw / Mn) calculated as a ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the low crystalline polypropylene resin (a1) is 1.5 to 4, The biaxially stretched film according to any one of 1] to [3].
[5] The content of the low density polyethylene resin (c1) in the composition (C) is 20 to 50% by mass based on the total amount of the composition (C), and any one of the above [1] to [4] 2. A biaxially stretched film described in 1.
[6] The biaxially stretched film according to any one of [1] to [5], wherein the composition (C) contains at least two ethylene-propylene copolymers as the propylene polymer (c2).
[7] The composition (C) includes at least the ethylene-propylene block copolymer (c2-a) and the ethylene-propylene random copolymer (c2-b) as the propylene polymer (c2), 6].
[8] The content of the ethylene-propylene block copolymer (c2-a) in the composition (C) is 30 to 60% by mass, and the content of the ethylene-propylene random copolymer (c2-b) is It is 5-30 mass%, Here, The said content is a biaxially stretched film as described in said [7] based on the total amount of a composition (C), respectively.
[9] The biaxially stretched film according to any one of [1] to [8], wherein the adhesive layer has a thickness of 2 to 10 μm.
[10] The biaxially stretched film according to any one of [1] to [9], wherein the biaxially stretched film is a re-peeling film.

The biaxially stretched film of the present invention has a good sticking property and / or followability, is excellent in blocking resistance, and is easy to unwind from winding.
Further, in one embodiment of the present invention, the biaxially stretched film for re-peeling of the present invention has good sticking property and / or followability, is excellent in blocking resistance, is easy to unwind from winding, and is excellent in peelability. The phenomenon of adhesive residue is less likely to occur.

  The biaxially stretched film of the present invention comprises a core layer, an adhesive layer formed on one surface of the core layer, and a back layer formed on the other surface of the core layer.

  In the biaxially stretched film of the present invention, the core layer is formed from a composition (B) containing a highly crystalline polypropylene resin (b1). By using such a highly crystalline polypropylene resin (b1), the film is excellent in heat resistance, is less prone to partial elongation and deformation of the film, and is easy to unwind from winding during use. Moreover, when using the biaxially stretched film of this invention as a film for re-peeling, it becomes a film excellent in peelability.

  In the present invention, the highly crystalline polypropylene resin (b1) has a mesopentad fraction (mmmm) of preferably 90 mol% or more, more preferably 91 to 99.5 mol%, still more preferably 92 to 99 mol%, particularly Preferably it is 94-99 mol% isotactic polypropylene resin. The composition (B) may contain one kind of highly crystalline polypropylene resin or a combination of two or more kinds of highly crystalline polypropylene resins as the highly crystalline polypropylene resin (b1). .

The mesopentad fraction (mmmm) is an index of stereoregularity that can be obtained by high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) measurement. Specifically, it can be measured using, for example, a high-temperature Fourier transform nuclear magnetic resonance apparatus (for example, “JNM-ECP500” manufactured by JEOL Ltd.). The observation nucleus is ¹³ C (125 MHz). The measurement method by high-temperature FT-NMR is performed with reference to the method described in, for example, “Japan Analytical Chemistry / Polymer Analysis Research Council, New Edition Polymer Analysis Handbook, Kinokuniya, 1995, p. 610”. be able to. For example, measurement can be performed using measurement temperature, solvent, measurement mode, pulse width, pulse interval, number of integrations, and shift reference as described in the examples.

  The pentad fraction representing the degree of stereoregularity is a combination of pentads (mmmm and “meso (m)” arranged in the same direction and “Rasemo (r)” arranged in the opposite direction. calculated as a percentage (%) based on the integrated value of the intensity of each signal derived from mrrm and the like. Each signal derived from mmmm, mrrm and the like can be assigned with reference to, for example, “T. Hayashi et al., Polymer, 29, 138 (1988)”.

  Examples of the highly crystalline polypropylene resin (b1) include a homopolymer of propylene and a copolymer of propylene and an α-olefin having 4 to 20 carbon atoms (for example, ethylene, butene, pentene, hexene, etc.). However, from the viewpoint of heat resistance and ease of unwinding from winding, a homopolymer is preferable. When the highly crystalline polypropylene resin (b1) is a copolymer of propylene and α-olefin, any of a random copolymer and a block copolymer may be used. From the viewpoint of heat resistance and ease of unwinding from winding, The content of monomers other than propylene in the copolymer is preferably 8% by mass or less, more preferably 4% by mass or less, and further preferably 2% by mass or less.

  The melt flow rate (MFR) of the highly crystalline polypropylene resin (b1) is preferably 1 to 10 g / 10 minutes, more preferably 1.5 to 8 g / 10 minutes, from the viewpoint of extrusion moldability and heat resistance. is there. MFR can be measured at 230 ° C. and a load of 21.18 N using a melt flow indexer (for example, a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with JIS K-7210 (1999). . In addition, when temperature is indicated separately in this specification, it measures at the temperature.

  The weight average molecular weight (Mw) of the highly crystalline polypropylene resin (b1) is preferably 200 to 600,000, more preferably 25 to 500,000 from the viewpoints of stretchability and strength.

  The molecular weight distribution (Mw / Mn) calculated as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the highly crystalline polypropylene resin (b1) is used as a stretchable film and a re-peeling film. In view of preventing contamination of the adherend due to the low molecular weight component, it is preferably 3 to 11, more preferably 4 to 10.

  The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polypropylene resin can be measured by a gel permeation chromatography (GPC) method. The GPC apparatus used for the GPC method is not particularly limited, and is a commercially available high-temperature GPC measuring instrument capable of molecular weight analysis of polyolefins (for example, a high-temperature GPC measuring instrument with a built-in differential refractometer (RI) manufactured by Tosoh Corporation). , HLC-8121GPC-HT) or the like. In this case, for example, it can be measured by a GPC column, a column temperature, an eluent, and a flow rate as described in Examples. Usually, a calibration curve is prepared using standard polystyrene, and a weight average molecular weight (Mw) and a number average molecular weight (Mn) are obtained by polystyrene conversion.

  The tensile elastic modulus of the press sheet formed from the highly crystalline polypropylene resin (b1) is preferably 0.5 to 0.5 from the viewpoint that partial elongation and deformation are unlikely to occur, and a film that is easy to unwind from winding during use. 2 GPa, more preferably 0.8 to 1.7 GPa, and even more preferably 1.0 to 1.5 GPa. Here, the details of the conditions for forming the press sheet are as shown in the examples. The tensile modulus of the press sheet is determined using a tensile tester (for example, Universal Tensile Tester Technograph TGI-1kN manufactured by Minebea Co., Ltd.) in accordance with JISK-7127 (1999) using the press sheet as a measurement sample. , 23 ° C., distance between chucks 100 mm, test speed 200 mm / min.

The highly crystalline polypropylene resin (b1) is, for example, a method of polymerizing propylene in a hydrocarbon solvent using a Ziegler-Natta catalyst system made of titanium or an aluminum compound; a method of polymerizing in liquid propylene (bulk polymerization); a gas phase It can be produced by a known method such as:
Moreover, you may use a commercial item as highly crystalline polypropylene resin (b1). Examples of commercially available products include Prime Polypro (registered trademark) series manufactured by Prime Polymer Co., Ltd., PC412A manufactured by Sun Allomer Co., Ltd., Novatec (registered trademark) series manufactured by Nippon Polypro Co., Ltd., and Draploy (registered trademark) manufactured by Borealis. Series, 5014L series manufactured by Korea Oil Chemical Co., Ltd., Sumitomo Nobren (registered trademark) series manufactured by Sumitomo Chemical Co., Ltd., and the like.

  The content of the highly crystalline polypropylene resin (b1) in the composition (B) is such that the composition (B) is easy to obtain a film that is not easily stretched and deformed and is easy to unwind from winding. Preferably, it is 30% by mass or more, more preferably 50% by mass or more based on the total amount, and may be 100% by mass.

  In the biaxially stretched film of the present invention, the composition (B) is added to the high crystalline polypropylene resin (b1) for the purpose of improving the sticking property and / or followability, improving the moldability, reducing costs, etc. Resins (b2) other than the highly crystalline polypropylene resin (b1) may be included.

  The composition (B) may contain a resin other than one kind of highly crystalline polypropylene resin (b1) as the resin (b2), or a resin other than two or more kinds of highly crystalline polypropylene resins (b1). May be contained in combination. In an embodiment in which the composition (B) additionally contains at least one resin (b2), the composition (B) obtains a film that is less prone to partial elongation and deformation and is easy to unwind from winding during use. From the viewpoint of ease, it may contain 90 to 30% by mass of the highly crystalline polypropylene resin (b1) and 10 to 70% by mass of the resin (b2) based on the total amount of the composition (B). Preferably, it contains 85 to 50% by mass of the highly crystalline polypropylene resin (b1) and 15 to 50% by mass of the resin (b2) other than (b1).

  In one embodiment of the present invention, it is preferable that the composition (B) contains a low crystalline polypropylene resin as the resin (b2), particularly from the viewpoint of sticking property and / or followability of the film. . Here, the preferred mesopentad fraction, type, weight average molecular weight (Mw), molecular weight distribution (Mw / Mn) and the like of the low crystalline polypropylene resin as the resin (b2) are described below. The same applies to the description. The melt flow rate (MFR) of the low crystalline polypropylene resin as the resin (b2) is preferably 5 to 400 g / 10 minutes, more preferably 5 to 100 g, from the viewpoint of extrusion moldability, stretchability and heat resistance. / 10 minutes (measured according to JIS K-7210 (1999) at 230 ° C., load 21.18 N). In this embodiment, the composition (B) contains 90 to 50% by mass of the high crystalline polypropylene resin (b1) and 10 to 50% by mass of the low crystalline polypropylene resin based on the total amount of the composition (B). It is preferable to contain 85 to 60% by mass of the high crystalline polypropylene resin (b1) and 15 to 40% by mass of the low crystalline polypropylene resin.

  In another embodiment of the present invention, the composition (B) may contain an ethylene-propylene copolymer containing a trace amount of ethylene of about 0.1 to 1.0% by mass as the resin (b2). When the composition (B) contains an ethylene-propylene copolymer as the resin (b2), it is preferable because the moldability of the film is easily improved.

  In another embodiment of the present invention, the composition (B) may contain a recycled resin as the resin (b2). Recycled resin is a resin obtained by melting and extruding unnecessary portions (for example, ears, start loss, etc.) of the resin of the present invention, cast raw sheet, film, etc., and re-melted into a pellet form. When B) contains a recycled resin of polypropylene as the resin (b2), it is preferable because the cost of the film can be easily reduced.

As a preparation method of the composition (B) when the composition (B) contains a resin (b2) other than the highly crystalline polypropylene resin (b1), polymerized powder or pellets of the highly crystalline polypropylene resin (b1) And a known method such as a method of dry blending the polymer powder or pellets of the resin (b2) with a mixer or the like; a method of melt-kneading with a kneader. There are no particular limitations on the mixer and kneader used, and for example, a single-screw type, a twin-screw type, or a multi-screw type with three or more axes can be used as the kneader. In the case of a screw type having two or more axes, a kneading type kneader of either the same direction rotation or different direction rotation can be used.
In the case of melt kneading, the kneading temperature is not particularly limited as long as kneading can be performed satisfactorily, but is preferably 180 to 300 ° C, more preferably 200 to 260 ° C. If the kneading temperature is too high, the resin may be deteriorated. In order to suppress such deterioration, the kneader may be purged with an inert gas such as nitrogen. A pellet-shaped composition (B) is obtained by pelletizing the melt-kneaded resin to an appropriate size using a generally known granulator.

  In the biaxially stretched film of the present invention, the adhesive layer is formed from a composition (A) containing a low crystalline polypropylene resin (a1). The pressure-sensitive adhesive layer formed from the composition (A) containing such a low crystalline polypropylene resin (a1) becomes a self-adhesive layer having sufficient pressure-sensitive adhesiveness, and sufficient film stickability and / or followability. Is obtained. In addition, since it is not necessary to additionally apply a pressure-sensitive adhesive, the film is excellent in releasability without problems such as adhesive residue. Further, when the film is stored in a roll shape, the smoothness of the pressure-sensitive adhesive layer is not easily lost even if the back layer having irregularities is in contact with the pressure-sensitive adhesive layer. Therefore, when the film is bonded to the adherend, it contains air, and the problem that it becomes difficult to evenly bond, and immediately after bonding, the contact area is small and the adhesive strength is low. After a long time, the pressure-sensitive adhesive layer is smoothed again, the contact area increases, and the problem that the pressure-sensitive adhesive force increases (adhesion progress) is less likely to occur.

  In the present invention, the low crystalline polypropylene resin (a1) is a polypropylene resin having a mesopentad fraction (mmmm) of preferably 60 mol% or less, more preferably 20 to 60 mol%, still more preferably 30 to 55 mol%. is there. The method for measuring the mesopentad fraction is as described above. The composition (A) may contain one kind of low crystalline polypropylene resin or a combination of two or more kinds of low crystalline polypropylene resins as the low crystalline polypropylene resin (a1). .

  Examples of the low crystalline polypropylene resin (a1) include a homopolymer of propylene and a copolymer of propylene and an α-olefin having 4 to 20 carbon atoms (for example, ethylene, butene, pentene, hexene, etc.). When the low crystalline polypropylene resin (a1) is a copolymer of polypropylene and α-olefin, it may be either a random copolymer or a block copolymer, provided that the content of monomers other than propylene in the copolymer is preferably 20 It is at most 10% by mass, more preferably at most 10% by mass. From the viewpoint of improving the miscibility with highly crystalline polypropylene, it is easy to obtain a smooth and highly transparent film, and when used as a film for re-peeling, it suppresses the occurrence of falling off due to poor miscibility. The conductive polypropylene resin (a1) is preferably a homopolymer.

  The melt flow rate (MFR) of the low crystalline polypropylene resin (a1) is preferably from 20 to 500 g / 10 minutes, more preferably from 40 to 500 minutes, from the viewpoint that it is easy to obtain extrudability and suitable tackiness. 400 g / 10 min (measured according to JIS K-7210 (1999) at 230 ° C.). The method for measuring MFR is as described above.

  The weight average molecular weight (Mw) of the low crystalline polypropylene resin (a1) is preferably from the viewpoint of easily obtaining suitable tackiness and from the viewpoint of preventing contamination of the adherend due to low molecular weight components when used as a re-peeling film. Is 40,000 to 150,000, more preferably 60,000 to 140,000.

  The molecular weight distribution (Mw / Mn) calculated as the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the low crystalline polypropylene resin (a1) depends on the low molecular weight component when used as a re-peeling film. From the viewpoint of preventing contamination of the adherend, it is preferably 1.5 to 4, more preferably 1.8 to 3. The method for measuring the weight average molecular weight (Mw) and the number average molecular weight (Mn) is as described above.

  The tensile elastic modulus of the press sheet formed from the low crystalline polypropylene resin (a1) is such that when the film is stored in a roll shape, even if the back layer having unevenness and the adhesive layer are in contact with each other, From the viewpoint that the smoothness is not easily lost, it is preferably 30 MPa or more, more preferably 40 MPa or more. Moreover, from a viewpoint that moderate adhesiveness is easy to be obtained, Preferably it is 130 MPa or less, More preferably, it is 120 MPa or less. Here, the details of the conditions for forming the press sheet are as shown in the examples. The method for measuring the tensile modulus of the press sheet is as described above.

The low crystalline polypropylene resin (a1) is a method of polymerizing propylene in a hydrocarbon solvent using a single site catalyst such as a metallocene catalyst; a method of polymerizing in liquid propylene (bulk polymerization); a method of polymerizing in the gas phase : Can be produced by a known method such as: The low crystalline polypropylene resin (a1) can be produced, for example, by the method described in International Publication No. 2003/087172.
Moreover, as a low crystalline polypropylene resin (a1), you may use a commercial item, for example, "L Modu (registered trademark) S600 and S901" by Idemitsu Kosan Co., Ltd., etc. are mentioned.

  The content of the low crystalline polypropylene resin (a1) in the composition (A) is preferably 50% by mass or more based on the total amount of the composition (A) from the viewpoint that it is easy to obtain suitable tackiness. Preferably it is 60 mass% or more. The content of the low crystalline polypropylene resin (a1) in the composition (A) may be 100% by mass, but from the viewpoint of obtaining suitable tackiness, based on the total amount of the composition (A), Preferably it is 95 mass% or less, More preferably, it is 90 mass% or less.

  In the biaxially stretched film of the present invention, the composition (A) is used in addition to the low crystalline polypropylene resin (a1), in addition to the low crystalline polypropylene resin (a1) for the purpose of obtaining suitable adhesiveness. The resin (a2) may be included. The composition (A) may contain a resin other than one kind of low crystalline polypropylene resin (a1) as (a2), or a resin other than two or more kinds of low crystalline polypropylene resins (a1). You may contain it in combination.

  In one embodiment of the present invention, when the composition (A) contains a highly crystalline polypropylene resin as the resin (a2), when the film is stored in a roll shape, the back layer having an unevenness and an adhesive When the layer of the present invention is used as a re-peeling film, from the viewpoint of making it difficult to lose the smoothness of the pressure-sensitive adhesive layer even when it is in contact with the layer, from the viewpoint of suppressing an increase in adhesive strength over time (adhesion progress) It is preferable from the viewpoint of peelability. Here, the preferred mesopentad fraction, preferred type, preferred melt flow rate, weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), etc. of the highly crystalline polypropylene resin as the resin (a2) are as described above. The same description applies to the conductive polypropylene resin (b1). In this embodiment, the composition (A) comprises 95 to 50% by weight of the low crystalline polypropylene resin (a1) and 5 to 50% by weight of the highly crystalline polypropylene resin (a2) based on the total amount of the composition (A). It is preferable to contain 90-60 mass% low crystalline polypropylene resin (a1), and it is more preferable to contain 10-40 mass% highly crystalline polypropylene resin (a2).

  As a method for preparing the composition (A) when using the resin (a2) other than the highly crystalline polypropylene resin (a1), the same method as described for the composition (B) can be employed.

  The adhesive strength of the biaxially stretched film of the present invention to the acrylic plate is preferably 25 to 500 mN / 25 mm, more preferably 50 to 400 mN / 25 mm, more preferably 75 to 250 mN / 25 mm at a peeling speed of 300 mm / min. More preferably. When the adhesive strength is in the above range, it is preferable to easily obtain a film having a good balance between adhesive strength and blocking resistance. The adhesive strength can be adjusted by adjusting the content of the low crystalline polypropylene resin (a1) in the composition (A) or by adjusting the thickness of the adhesive layer. The adhesive strength can be measured by applying a film to an acrylic plate in accordance with JIS-Z-0237, performing aging, and then performing 180 degree peeling using a tensile tester.

  In the biaxially stretched film of the present invention, the back layer is formed from a composition (C) containing low-density polyethylene (c1) and a propylene-based polymer (c2). When the biaxially stretched film of the present invention is provided with such a back layer, the surface of the back layer and the surface of the above-mentioned pressure-sensitive adhesive layer are difficult to block and become a film excellent in blocking resistance.

The low density polyethylene (c1) preferably has a density of 0.91 to 0.94 g / cm ³ . As the low-density polyethylene (c1), any of those manufactured by a known method and commercially available products may be used. Examples of the low density polyethylene (c1) include high pressure method low density polyethylene and linear low density polyethylene.
In the embodiment in which the high-pressure method low-density polyethylene is used as the low-density polyethylene (c1), the density of the low-density polyethylene (c1) is preferably 0.91 to 0.93 g / cm ³ from the viewpoint of blocking resistance. . In this embodiment, the MFR of the low density polyethylene (c1) is preferably 0.3 to 0.5 g / 10 minutes (however, measured at 190 ° C.) from the viewpoint of moldability. Examples of the low density polyethylene (c1) include “Novatech LD (registered trademark) HE30” manufactured by Japan Polyethylene Corporation, “Novatech LD (registered trademark) LP128” manufactured by Nippon Polyethylene Corporation, and the like.
In an embodiment in which linear low-density polyethylene is used as the low-density polyethylene (c1), the density of the low-density polyethylene (c1) is 0.92 to 0.94 g / cm ³ from the viewpoint of blocking resistance. preferable. In this embodiment, the MFR of the low density polyethylene (c1) is preferably 0.8 to 1.2 g / 10 minutes (however, measured at 190 ° C.) from the viewpoint of moldability. The linear low density polyethylene is a copolymer of ethylene and one or more α-olefins selected from α-olefins having 3 to 20 carbon atoms, and as α-olefins having 3 to 20 carbon atoms. Includes propylene, 1-butene, 1-pentene, 4-methyl 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and the like.
The composition (C) may contain one kind of low density polyethylene as the low density polyethylene (c1), or may contain two or more kinds of low density polyethylene in combination.

  Content of the low density polyethylene (c1) in a composition (C) becomes like this. Preferably it is 20-50 mass% based on the total amount of a composition (C), More preferably, it is 25-40 mass%. When the content of (c1) is in the above range, a back layer having a uniform and moderately rough surface can be formed, and the surface of the pressure-sensitive adhesive layer made of the composition (A) having a specific composition is excessively adhered. Excellent blocking resistance.

  As the propylene polymer (c2), a homopolymer of propylene and a copolymer of propylene and an α-olefin having 4 to 20 carbon atoms (for example, ethylene, butene, pentene, hexene, etc.) (Copolymer). From the viewpoint of blocking resistance, the propylene polymer (c2) is preferably an ethylene-propylene copolymer. As the ethylene-propylene copolymer, an ethylene-propylene block copolymer and an ethylene-propylene random copolymer can be preferably used. The composition (C) may contain one type of propylene polymer as the propylene polymer (c2), or may contain a combination of two or more types of propylene polymers.

  The content of the propylene polymer (c2) in the composition (C) is preferably 80 to 50% by mass, more preferably 75 to 60% by mass, based on the total amount of the composition (C). . When the content of (c2) is in the above range, it becomes easy to obtain a film having excellent blocking resistance.

In one aspect of the present invention in which the composition (C) contains at least the ethylene-propylene block copolymer (c2-a) as the propylene-based polymer (c2), in the ethylene-propylene block copolymer (c2-a) From the viewpoint of blocking resistance, the ethylene content is preferably 5 to 10% by mass, more preferably 8 to 10% by mass, based on the total amount of (c2-a). The MFR of the ethylene-propylene block copolymer (c2-a) is preferably 6 to 10 g / 10 min in terms of moldability.
As such an ethylene-propylene block copolymer (c2-a), you may use what was manufactured by the well-known method, and either a commercial item. As a commercial item, for example, "Nippon Polypro Co., Ltd." Novatec PP (registered trademark) BC4FC ”,“ Novatech PP (registered trademark) BC3HF ”manufactured by Nippon Polypro Co., Ltd., and the like.

In one aspect of the present invention in which the composition (C) contains at least the ethylene-propylene random copolymer (c2-b) as the propylene polymer (c2), in the ethylene-propylene random copolymer (c2-b) From the viewpoint of blocking resistance, the ethylene content is preferably 2 to 5 mass%, more preferably 3 to 4 mass%, based on the total amount of (c2-b). The MFR of the ethylene-propylene random copolymer (c2-b) is preferably 8 to 12 g / 10 minutes in terms of moldability.
As such an ethylene-propylene random copolymer (c2-b), you may use what was manufactured by the well-known method, and a commercial item, for example, Prime Polymer Co., Ltd. " Prime Polypro (registered trademark) S235WC "," Prime Polypro (registered trademark) F129DA "manufactured by Prime Polymer Co., Ltd., and the like.

The composition (C) preferably contains at least two ethylene-propylene copolymers as the propylene polymer (c2) from the viewpoint of blocking resistance, and the ethylene-propylene block copolymer (c2-a). ) And an ethylene-propylene random copolymer (c2-b) are more preferable.
In one aspect of the present invention, the composition (C) contains at least an ethylene-propylene block copolymer (c2-a) and an ethylene-propylene random copolymer (c2-b) as the propylene-based polymer (c2). The content of the ethylene-propylene block copolymer (c2-a) in the composition (C) is preferably 30 to 60% by mass, more preferably 40 to 55% by mass. The content of the ethylene-propylene random copolymer (c2-b) in the composition (C) is preferably 5 to 30% by mass, more preferably 10 to 25% by mass. Here, the content is based on the total amount of the composition (C). When the content of each component is within the above range, a back layer having a uniform and moderately roughened surface can be formed. Such a back layer is composed of a composition (A) having a specific composition due to the fact that the surface is uniformly and appropriately roughened and composed of the composition (C) having a specific composition. It does not excessively adhere to the surface of the adhesive layer and is superior in blocking resistance.

  The composition (C) preferably further contains a resin (c2-c) as the propylene-based polymer (c2) for the purpose of adjusting the blocking resistance and the surface roughness. Examples of the resin (c2-c) include polypropylene homopolymer. The content of the resin (c2-c) in the composition (C) is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass in order to obtain preferable blocking resistance and surface roughness. % Or less.

  The composition (C) is an ethylene-propylene block copolymer (c2-a), an ethylene-propylene random copolymer (c2-b), and a further resin (c2-c) as a propylene-based polymer (c2). In an embodiment of the present invention containing at least, the content of the ethylene-propylene block copolymer (c2-a) in the composition (C) is preferably 30 to 60% by mass, more preferably 40 to 40%. 55% by mass. The content of the ethylene-propylene random copolymer (c2-b) in the composition (C) is preferably 5 to 30% by mass, more preferably 10 to 25% by mass. Content of the further resin (c2-c) in a composition (C) becomes like this. Preferably it is 20-1 mass%, More preferably, it is 10-2 mass%. Here, the content is based on the total amount of the composition (C). When the content of each component is within the above range, the blocking resistance is more excellent.

  As a method for preparing the composition (C), a method similar to the method described for the composition (B) can be employed.

As for the surface roughness of the back layer, the arithmetic average height Sa based on the ISO-25178 standard is preferably 0.3 μm or more, and more preferably 0.5 μm or more. The arithmetic average height Sa is preferably 2 μm or less, and more preferably 1.5 μm or less. When the arithmetic average height Sa of the back layer is not less than the lower limit of the above range, the blocking resistance is excellent, and when it is not more than the upper limit of the above range, the uneven shape on the surface of the back layer is transferred to the surface of the adhesive layer. It is preferable that the smoothness of the adhesive layer is not easily impaired.
The arithmetic average height Sa can be measured by using an optical interference type non-contact surface shape measuring instrument (for example, “VertScan 2.0 (model R5500GML)” manufactured by Ryoka Systems Inc.).

Although the biaxially stretched film of this invention is not limited to the following, it is thought that it is excellent in blocking resistance for the reason shown below.
The composition (C) is considered to have a structure in which the polyethylene (c1) and the propylene polymer (c2) are uniformly dispersed. When an unstretched film made of the composition (C) having such a specific structure is biaxially stretched, the surface thereof is uniformly and moderately roughened. Therefore, it is considered that the back layer formed from the composition (C) has a characteristic that it is difficult to block with the adhesive layer. Furthermore, in the aspect in which the composition (C) contains at least an ethylene-propylene block copolymer (c2-a) and an ethylene-propylene random copolymer (c2-b) as the propylene-based polymer (c2). It is considered that the dispersion state of each resin is easy to make fine and uniform, and a good dispersion structure suitable for roughening is easily formed.
In addition, since the composition (A) has appropriate crystallinity, the adhesive strength of the adhesive layer is in an appropriate range, and since this adhesive strength is unlikely to increase with time, a stable adhesive strength can be obtained. A biaxially stretched film having such an adhesive layer has good blocking resistance. Further, the back layer is formed from the composition (C) having a specific composition, and the adhesive layer is formed from the composition (A) having a specific composition, and the composition (C) and the composition (A) From the viewpoint of composition, the back layer and the adhesive layer are considered to be difficult to block.

  Low crystalline polypropylene resin (a1), high crystalline polypropylene resin (b1), low density polyethylene resin (c1), propylene polymer (c2) (especially ethylene-propylene block copolymer (c2-a) and ethylene- The propylene random copolymer (c2-b)) preferably has an ash content of 100 ppm or less. Ash content is caused by polymerization catalyst residue and the like, and causes fine foreign matters (fish eyes). When the ash content is 100 ppm or less, preferably 50 ppm or less, the generation of fine foreign matters is remarkably reduced, and contamination of the adherend when the biaxially stretched film is used as a re-peeling film can be prevented. Such a biaxially stretched film is suitable as a re-peeling film such as a protective film such as an electronic member or a fixing film. The ash content can be controlled by a method for controlling the type and amount of catalyst used during polymerization.

In this specification, content of ash is measured as follows based on ISO3451-1.
The low crystalline polypropylene resin (a1), the high crystalline polypropylene resin (b1), the low density polyethylene resin (c1), and the propylene polymer (c2) are put in a crucible and heated at 750 ° C. for 1 hour in a muffle furnace. Measure the mass of the residue in the crucible. And the ratio of the mass of the residue in the crucible with respect to the mass of the said resin and / or copolymer thrown into the crucible is calculated, and let this be content of ash.

In addition to the above, in the present invention, the compositions (A) to (C) may be mixed with other polypropylene resins or resins other than polypropylene resins within a range not impairing the effects of the present invention. Here, other than the above-described polypropylene resins or resins other than polypropylene resins, conventionally known resins that are suitable for stretched film applications can be used as appropriate in the present invention.
Examples of such a resin include polyolefins other than polypropylene, such as polyethylene, poly (1-butene), polyisobutene, poly (1-pentene), poly (4-methyl-1-pentene), and ethylene-propylene copolymers. , Propylene-butene copolymer, ethylene-butene copolymer, α-olefin copolymer, vinyl monomer-diene monomer random copolymer, such as styrene-butadiene random copolymer, styrene -Vinyl monomer such as butadiene-styrene block copolymer-Diene monomer-Random copolymer of vinyl monomer.
The blending amount of such other resins is preferably 10% by mass or less, and more preferably 5% by mass or less based on the total amount of each of the compositions (A) to (C).

Compositions (A) to (C) for forming the biaxially stretched film of the present invention may contain at least one additive as required in addition to the resin. In general, the additive is not particularly limited as long as it is an additive used for a polypropylene resin. Such additives include, for example, stabilizers such as antioxidants, chlorine absorbers, ultraviolet absorbers, plasticizers, flame retardants, antistatic agents, colorants, crystal nucleating agents, and the like. You may add such an additive to a resin composition within the range which does not impair the effect of this invention.
However, the resin composition for forming the biaxially stretched film of the present invention preferably does not contain an antiblocking agent or a lubricant in order to prevent adhesion to the adherend. The biaxially stretched film of the present invention has the structure specified in the present invention, so that it has excellent anti-blocking properties even if it does not contain an antiblocking agent, and is partially stretched and deformed when drawn out from winding. It can be pulled out without producing.
In addition, the additive is mainly added to the composition (B) to reduce the amount of the additive added to the composition (A) or (C) as much as possible to prevent contamination of the adherend by the additive. From the viewpoint of

“Antioxidant” has a role as a primary agent blended for the purpose of suppressing deterioration due to heat and oxidation in an extruder during production of a biaxially stretched film, and deterioration over time when used for a long time. There is at least a role as a secondary agent to be blended for the purpose of suppressing the above. Depending on these roles, different types of antioxidants may be used, or one type of antioxidant may have two roles.
When different types of antioxidants are used, for example, 2,6-di-tert-butyl-p-cresol (generic name: BHT) is used as the primary agent for the purpose of suppressing deterioration in the extruder. It is preferable to add about 1000 to 3000 ppm in the resin composition. Most of the antioxidant compounded for this purpose is consumed in the molding process in the extruder, and hardly remains in the biaxially stretched film. Therefore, generally, the residual amount is less than 100 ppm, which is preferable in that the adherend is hardly contaminated by the antioxidant.
As the secondary agent, known antioxidants can be used, and examples thereof include phenol-based, hindered amine-based, phosphite-based, lactone-based, and tocopherol-based thermal stabilizers and antioxidants. Specifically, dibutylhydroxytoluene, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1,3,5-trimethyl-2,4,6-tris ( 3,5-di-t-butyl-4hydroxy) benzene, tris (2,4-di-t-butylphenyl) phosphite and the like can be mentioned. More specifically, Irganox (registered trademark) 1010, Irganox (registered trademark) 1330, and Irgafos (registered trademark) 168, which are antioxidants manufactured by Ciba Specialty Chemicals Co., Ltd., may be mentioned.
Among them, at least one selected from phenolic antioxidants or a combination thereof, a combination of phenolic and phosphite, a combination of phenolic and lactone, a combination of phenolic, phosphite and lactone However, the effect which suppresses deterioration with time at the time of using a film for a long term can be provided, and it is preferable.
Moreover, you may use phosphorus antioxidant as a secondary agent. Examples of phosphorus antioxidants include tris (2,4-di-t-butylphenyl) phosphite (trade name: Irgaphos 168), bis (2,4-di-t-butyl-6-methylphenyl) ethyl. And phosphite (trade name: Irgaphos 38).
The content of the antioxidant as a secondary agent is preferably from 300 ppm to 2500 ppm, more preferably from 500 ppm to 1500 ppm, based on the total amount of each of the compositions (A) to (C). By setting it to 300 ppm or more, it is easy to impart the effect of suppressing deterioration over time when the film is used for a long time, and by setting it to 2500 ppm or less, it is easy to prevent contamination of the adherend with the antioxidant.

  The “chlorine absorbent” is not particularly limited as long as it is normally used for polypropylene. Examples of the chlorine absorbent include metal soaps such as calcium stearate and hydrotalcite.

  The “ultraviolet absorber” is not particularly limited as long as it is usually used for polypropylene. Examples of the ultraviolet absorber include benzotriazole (such as Tinuvin 328 manufactured by BASF), benzophenone (such as Cysorb UV-531 manufactured by Cytec), and hydroxybenzoate (such as UV-CHEK-AM-340 manufactured by Ferro).

  The “plasticizer” is not particularly limited as long as it is one normally used for polypropylene. As a plasticizer, PP random copolymer etc. can be illustrated, for example.

  The “flame retardant” is not particularly limited as long as it is normally used for polypropylene. Examples of the flame retardant include halogen compounds, aluminum hydroxide, magnesium hydroxide, phosphates, borates, and antimony oxides.

  The “antistatic agent” is not particularly limited as long as it is usually used for polypropylene. Examples of the antistatic agent include glycerin monoester (glycerin monostearate, etc.), ethoxylated secondary amine, alkylmethyl dibetaine, alkylamine diethanol and / or alkylamine ethanol ester and / or alkylamine diethanol diester, etc. Can be illustrated.

  The “coloring agent” is not particularly limited as long as it is usually used for polypropylene. Examples of the colorant include cadmium and chromium-containing inorganic compounds to azo and quinacridone organic pigments.

  The “crystal nucleating agent” is not particularly limited as long as it is usually used for polypropylene, and a publicly known fine particle type or dissolution type nucleating agent can be used. For example, examples of the fine particle type include talc-based and aluminum-based inorganic substances, and examples of the dissolution type include amide-based and sorbitol-based organic nucleating agents. Use of the dissolution type is preferred because it is difficult to cause clogging of the filter when the molten resin composition is filtered with a filter in the extrusion / filtration step when forming a film.

The total thickness of the biaxially stretched film of the present invention is preferably 10 to 100 μm, more preferably 15 to 80 μm. If the thickness is not less than the lower limit of the above range, sufficient mechanical properties as a film for re-peeling can be easily obtained, and if it is not more than the upper limit of the above range, the biaxially stretched film can be uniformly stretched in the production process. Biaxially stretched film with stable properties and ease of peeling is easily obtained. The thickness of the film can be measured using a thickness measuring instrument in accordance with JIS-C2330.
In an embodiment where the biaxially stretched film has a total thickness in the above range, the thickness of the adhesive layer is preferably 1 to 10 μm, more preferably 2 to 9 μm, still more preferably 3 to 8 μm, and particularly preferably 3 to 7 μm. . When the thickness of the adhesive layer is not less than the lower limit of the above range, sufficient adhesive strength can be obtained. The thickness of the adhesive layer may exceed the upper limit of the above range, but in this case, the adhesive force is saturated and the material cost increases. The thickness of the back layer is preferably 2 to 10 μm, more preferably 3 to 8 μm, and further preferably 3 to 6 μm. When the thickness of the back layer is in the above range, sufficient blocking resistance can be easily obtained, and the surface roughness of the back layer can be easily set to the above-mentioned preferable range. The thickness of each layer can be measured by cutting the biaxially stretched film and observing the cross section with a microscope.

  In the biaxially stretched film of the present invention, an adhesive layer precursor composed of the composition (A), a core layer precursor composed of the composition (B), and a back layer precursor composed of the composition (C) are sequentially laminated. It can be produced by the step (i) of producing a precursor laminate having a three-layer structure and the step (ii) of biaxially stretching the precursor laminate.

In the step (i), first, each of the composition (A), the composition (B) and the composition (C) is melt-kneaded at 200 to 260 ° C. in an extruder, and then merged with a merging apparatus, and the T-die Extrude from At this time, it is preferable to remove coarse foreign matters from each composition using a polymer filter on the upstream side of the merging device.
Merge is performed in a tube before the T die, a method using a lamination unit provided in the resin introduction part of the T die (feed block method), a method of laminating resin after widening in the T die (manifold lamination method) ) And the like. Among these, the manifold lamination method is excellent in terms of lamination thickness accuracy, but it can be appropriately selected from these in consideration of economics and the like.

  Next, the three-layer laminate thus extruded is brought into close contact with an air knife on at least one metal drum (cooling drum) whose drum surface is controlled at 20 to 60 ° C., and formed into a sheet shape. For example, a precursor laminate (cast raw sheet) having a thickness of 500 to 5000 μm is obtained.

Next, in the step (ii), the biaxially stretched film of the present invention can be produced by performing a stretching treatment on the cast raw sheet before stretching. The stretching treatment is preferably biaxial stretching in the flow (longitudinal, longitudinal, MD) direction and width (transverse, also referred to as TD) direction, but may be biaxial stretching in an oblique direction as necessary. .
Examples of the stretching method include a tubular method, a tenter method, a method of stretching between rolls provided with a peripheral speed difference, and the like. Biaxial stretching can be performed simultaneously, or biaxial stretching can be performed sequentially. Since there is no thickness unevenness and it is easy to obtain a biaxially stretched film with good flatness, between the simultaneous biaxial stretching method by the tenter method, the sequential biaxial stretching method by the tenter method, and the roll provided with a peripheral speed difference A sequential biaxial stretching method of stretching in the flow direction and then stretching in the width direction by a tenter method is preferred.
As the sequential biaxial stretching method, for example, the cast raw sheet is first maintained at a temperature of 100 to 160 ° C. and passed between rolls provided with a speed difference, or led to a tenter and stretched 3 to 8 times in the flow direction. After that, it is relaxed by about 0 to 10% as necessary. Subsequently, the uniaxially stretched film is guided to a tenter and stretched 6 to 12 times in the width direction at a temperature of 120 to 170 ° C., then relaxed by about 0 to 10% as necessary, heat-fixed, and wound up. .
In the simultaneous biaxial stretching method, the cast original fabric sheet is guided to a tenter and stretched at the temperature of 120 to 170 ° C. in the flow direction and the width direction as described above, and then relaxed by about 0 to 10% as necessary. Then, heat set and wind up.
By such a biaxial stretching process, the biaxially stretched film is excellent in mechanical properties such as mechanical strength and rigidity, the surface of the back layer is uniformly and moderately roughened, and is not easily stretched and deformed and is easy to unwind from winding. Is obtained. In addition, when extending | stretching temperature is raised, the arithmetic mean height Sa of a back surface tends to become small.

  The wound film is preferably subjected to an aging treatment in an atmosphere of about 20 to 45 ° C. in order to stabilize the adhesive force. The wound film is wound into a desired size, further cut into a desired product width as necessary, and distributed as a re-peeling film such as a surface protecting film and a fixing film. The biaxially stretched film of the present invention can be subjected to surface treatment such as corona discharge treatment or plasma discharge treatment as necessary. By surface treatment, the adhesive strength of the adhesive layer can be adjusted, coating suitability and printing suitability can be imparted to the back layer, and the like. A known method can be adopted for the surface treatment.

  As described above, the biaxially stretched film of the present invention described above is that the surface of the back layer is uniformly and appropriately roughened, and the back layer is composed of a composition (C) having a specific composition. As a result, it is difficult to block the pressure-sensitive adhesive layer made of the composition (A) having a specific composition and excellent in adhesive strength. Therefore, it can unwind from winding without requiring excessive force. Moreover, since blocking resistance is excellent, it is not necessary to provide a release agent or the like to the back layer. Therefore, contamination of the adhesive layer with a release agent or the like can be prevented. In addition, when the biaxially stretched film of the present invention is stored in a state where the film is wound in a roll shape, even if the back layer having unevenness and the adhesive layer are in contact with each other, the smoothness of the adhesive layer is not easily lost. Since the biaxially stretched film of the present invention has the above properties, it is particularly excellent as a re-peeling film. In the embodiment in which the biaxially stretched film of the present invention is a film for re-peeling, the biaxially stretched film of the present invention has a self-adhesive property, so that it is good for an adherend without applying an adhesive, a tackifier or the like. It has sticking properties and does not cause a problem of adhesive residue at the time of peeling.

The biaxially stretched film of the present invention can be used as an optical film, a surface protecting film, a fixing film, a magnetic recording medium, a thermal transfer film, an electrical insulating material, a packaging material, a release material, an adhesive tape, and the like.
The biaxially stretched film of the present invention particularly has a surface of an optical material or the like such as an electronic component; various substrates such as a semiconductor substrate and an electronic substrate; a liquid crystal display constituent member (polarizing plate, retardation film, display mother glass, etc.) It is suitably used as a film for re-peeling, such as a film for surface protection that protects these manufacturing processes, during transportation and storage, and a fixing film for transporting, processing, and storing optical members and electronic members. The

  EXAMPLES Next, the present invention will be described more specifically with reference to examples, but these examples are for explaining the present invention and do not limit the present invention in any way. Unless otherwise specified, the descriptions “parts” and “%” indicate “parts by mass” and “% by mass”, respectively.

[Measurement of physical properties of resin]
(1) Mesopentad fraction (mmmm)
The polymer was dissolved in a solvent, and the mesopentad fraction (mmmm) was determined under the following conditions using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR).
Measuring instrument: JEOL Ltd., high temperature FT-NMR JNM-ECP500
Observation nucleus: ¹³ C (125 MHz)
Measurement temperature: 135 ° C
Solvent: Ortho-dichlorobenzene [ODCB: Mixed solvent of ODCB and deuterated ODCB (volume ratio = 4/1)]
Measurement mode: Single pulse proton broadband decoupling Pulse width: 9.1 μsec (45 ° pulse)
Pulse interval: 5.5 sec
Integration count: 4500 shift standard: CH ₃ (mmmm) = 21.7 ppm
It calculated by the percentage (%) from the intensity | strength integral value of each signal originating in the combination (mmmm, mrrm, etc.) of a pentad (pentad). Regarding the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of spectra such as “T. Hayashi et al., Polymer, 29, 138 (1988)” was referred to.

(2) Melt flow rate (MFR)
According to JISK-7210 (1999), measurement was performed using a melt indexer manufactured by Toyo Seiki Seisakusho. The measurement conditions were a measurement temperature of 230 ° C. and a load of 21.18N.

(3) Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mn / Mw)
Using GPC (gel permeation chromatography), the average molecular weight of the polypropylene resin and the differential distribution value of the distribution curve were measured under the following conditions.
Measuring instrument: manufactured by Tosoh Corporation, differential refractometer (RI) built-in type high temperature GPC apparatus, HLC-8121GPC-HT type Column: manufactured by Tosoh Corporation, connecting three TSKgel GMHHR-H (20) HT Column temperature: 140 ° C
Eluent: Trichlorobenzene Flow rate: 1.0 ml / min In addition, the measurement result was obtained by polystyrene conversion using the standard polystyrene by Tosoh Corporation for preparation of a calibration curve. However, the molecular weight was converted to the molecular weight of polypropylene using a Q-factor.

(4) Tensile modulus of press sheet A press sheet was prepared by the following procedure using a Toyo Seiki Seisakusho mini test press. 5 g of resin pellets and a 200 μm thick spacer were sandwiched between metal foils and preheated at 200 ° C. for 2 minutes to melt the resin pellets. Next, after pressing for 2 minutes at a press pressure of 2 MPa, the molten resin sheet and the spacer were sandwiched between the metal foil and another mini-test press set at 20 ° C., and pressed for 1 minute at a press pressure of 2 MPa. The obtained sheet was removed from the metal foil and the spacer and subjected to tensile modulus measurement.
The prepared press sheet was used as a sample in accordance with JISK-7127 (1999), and the sample shape was in accordance with test piece type 2 (sample width 15 mm, sample length 190 mm), 23 ° C., test speed 200 mm / min. The tensile elastic modulus and the elongation at break were measured in the MD direction and the TD direction under the condition of a distance between chucks of 100 mm.

Example 1
As the composition (A), a low crystalline polypropylene resin having a stereorandom structure (a1) “El Modue (registered trademark) S901 (mmmm: 45 mol%, MFR: 50 g / 10 min, weight average molecular weight (Mw): 130,000 , Molecular weight distribution (Mn / Mw): 2, tensile modulus: 110 MPa) and homopolypropylene (a2) (mmmm: 93 mol%, MFR: 2.8 g / 10 min, weight average molecular weight (Mw): 35, dry blended with pellets of molecular weight distribution (Mn / Mw): 6, tensile modulus: 1.2 GPa, ash content = 25 ppm) at a compounding ratio shown in Table 1, and a uniaxial made by Ikegai Seisakusho Co., Ltd. with a diameter of 30 mm An extruder FS30 (Satellite A extruder) was charged from a hopper and melted.

  As a composition (B), only a pellet of homopolypropylene as the highly crystalline polypropylene resin (b1) (the same homopolypropylene as used in Example 1 as (a2)) was made by Ikegai Seisakusho Co., Ltd. with a diameter of 30 mm. The single screw extruder FS30 (main B extruder) was charged from a hopper and melted.

As the composition (C), (c1) a low density polyethylene resin “Novatech LD (registered trademark) HE30 (density: 0.92 g / cm ³ , MFR: 0.3 g / 10 min (190 ° C.))”, (c2 -A) ethylene-propylene block copolymer "Novatech PP (registered trademark) BC4FC (MFR = 8 g / 10 min, ethylene content 10% by mass)" and (c2-b) ethylene-propylene random copolymer "Prime" Polypro (registered trademark) S235WC (MFR = 10 g / 10 min, ethylene content 4% by mass) ”was dry blended at the compounding ratio shown in Table 1, and“ Toyo Seiki Co., Ltd. ”“ Labo Plast Mill ” Was melt kneaded at 230 ° C. and pelletized. The pellets were put into another single-screw extruder FS30 (Satellite C extruder) manufactured by Ikegai Seisakusho Co., Ltd. having a diameter of 30 mm from a hopper and melted.

Next, the layers composed of the respective compositions were merged in a feed block as a laminated unit, and extruded from a single-layer die (width 300 mm) as a three-layer sheet. And it cooled and solidified, pressing with air pressure using the air knife on the cooling drum controlled to 30 degreeC, and obtained the precursor laminated body (cast original fabric sheet) about 700 micrometers thick.
The obtained precursor laminate was subjected to sequential biaxial stretching using a batch type biaxial stretching machine “KARO IV” manufactured by Bruckner. The stretching conditions were a preheating temperature of 165 ° C., a preheating time of 2 minutes, a stretching temperature (longitudinal stretching temperature and transverse stretching temperature) of 165 ° C., and a stretching speed of 100% / second. The heat setting conditions were 170 ° C. and 20 seconds. Thus, the precursor laminate was stretched 4.6 times in the vertical direction and 9.3 times in the horizontal direction, the total thickness was about 16 μm, the thickness of the back layer was 4 μm, and the thickness of the adhesive layer was Biaxially stretched films having the values shown in Table 1 were obtained.

Examples 2-8, Comparative Examples 1-7
A biaxially stretched film was obtained in the same manner as in Example 1 except that the type and blending ratio of the resin in each composition and the thickness of the adhesive layer were changed as shown in Table 1.
In Examples 4 to 6, as the low crystalline polypropylene resin (a1) in the composition (A), instead of the above “El Modu (registered trademark) S901”, “El Modu (registered trademark) S600 (mmmm: 45 mol) %, MFR: 350 g / 10 min, weight average molecular weight (Mw): 75,000, molecular weight distribution (Mn / Mw): 2, tensile elastic modulus: 90 MPa).
Further, in Example 7, in addition to the high crystalline polypropylene resin (b1), a low crystalline polypropylene resin “El Modue (registered trademark) S901” was used as the resin (b2).
In Example 8, the low density polyethylene resin “Novatech LD (registered trademark) HE30” as (c1) and the highly crystalline homopolypropylene as (c2) (the same homopolymer used as (a2) in Example 1) The composition (C) containing polypropylene) was used.
In Comparative Examples 2 to 4, the composition (C) having the blending ratio shown in Table 2 was used.
In Comparative Example 1, the same composition (C) containing only the same homopolypropylene as used in Example 1 as (a2) was used.
In Comparative Examples 2-4, the composition (C) which has the compounding ratio shown in Table 1 was used.
In Comparative Example 5, the styrene elastomer “Dynalon (registered trademark) 1320P (styrene elastomer, MFR: 3.5 g / 10 min, tensile elastic modulus: 4.1 MPa)” used in Example 1 as (a2) The composition (A) containing the same homopolypropylene was used.
In Comparative Example 6, the composition (A) containing only the same homopolypropylene as that used in Example 1 as (a2) was used.
In Comparative Example 7, no back layer was provided.

  Each evaluation shown below was performed about the obtained biaxially stretched film. The results are shown in Tables 1 and 2.

[Measurement of each characteristic value of film]
(5) Thickness Based on JIS-C2330, the thickness was measured using a thickness measuring instrument (“MEI-11” manufactured by Citizen Seimitsu Co., Ltd.).
The thicknesses of the adhesive layer, the core layer, and the back layer were measured by cutting the biaxially stretched film and observing the cross section with a microscope.

(6) Arithmetic mean height Sa
The arithmetic average height Sa of each back layer was measured using an optical interference type non-contact surface shape measuring instrument (“VertScan 2.0 (model R5500GML)” manufactured by Ryoka System Co., Ltd.).
Specifically, in the WAVE mode, a measurement of 237 μm × 178 μm per visual field was performed in three visual fields using a 530 white filter and a × 20 objective lens. And this operation was performed about arbitrary 3 places of the surface of the back layer of a film, the wave | undulation component was removed by the 4th-order polynomial approximation about the obtained data, and the average value of Sa by ISO-25178 was calculated | required.

(7) Adhesive strength (adhesive strength against acrylic board)
A film piece having a length (MD direction) of 200 mm and a width (width) of 25 mm was cut out from the biaxially stretched film, and this was pasted on a commercially available acrylic plate (thickness: 2 mm, length: 125 mm, width: 50 mm). The sticking was performed using a rubber roller in accordance with JIS-Z-0237 so that air did not enter between the adhesive layer of the biaxially stretched film and the acrylic plate. This was aged at 40 ° C. for 24 hours under a load of 20 gf / cm ² (0.2 N / cm ² ). Then, after standing at room temperature of 23 ° C. and 50% RH for 2 hours, 180 degree peeling was performed at a speed of 300 mm / min using a tensile tester (Universe Tensile Tester Technograph TGI-1kN manufactured by Minebea Co., Ltd.). The adhesive strength at that time was measured. The measurement was performed 3 times, and the average value was defined as the adhesive strength of the film. In addition, as adhesive force with respect to an acrylic board, 30 mN / 25mm or more is preferable practically.

(8) Blocking resistance A film piece of 200 mm in length (MD direction) and 200 mm in width (width) was cut out from the biaxially stretched film. After 10 sheets were stacked and pasted with a roller, they were aged at 70 ° C. for 60 minutes under a load of 50 gf / cm ² (0.49 N / cm ² ). In addition, when the films cut out from the biaxially stretched film were overlapped, they were overlapped so that the surface of the adhesive layer of one film piece was in contact with the surface of the back layer of another film piece.
This was cut into a width of 50 mm to prepare a measurement sample. In the obtained measurement sample, the blocking state between the surface of the adhesive layer and the surface of the back layer was evaluated. The evaluation was performed by arbitrarily selecting 5 out of 9 interfaces.
The evaluation criteria are as follows.
(Double-circle): In the biaxially stretched film which piled up 10 sheets, both layers are not adhering at all in any of five interfaces of the surface of the adhesion layer and the surface of a back surface layer.
(Circle): In the biaxially stretched film which piled up 10 sheets, both layers can peel easily in any of the interface of five places of the surface of the adhesion layer and the surface of a back surface layer.
(Triangle | delta): Both layers adhere and are hard to peel in any of five interfaces of the surface of the adhesion layer and the surface of a back surface layer in the biaxially stretched film which piled up 10 sheets.
X: Ten layers of the biaxially stretched film are in close contact with each other at the five interfaces of the surface of the adhesive layer and the surface of the back layer, and are extremely difficult to peel off.

(9) Adhesive surface smoothness The biaxially stretched film was wound up and stored for 1 month. The winding after storage was broken, and the adhesive surface of the sample near the winding core was observed using “VertScan 2.0 (model R5500GML)” manufactured by Ryoka System.
Specifically, in the WAVE mode, a measurement of 470.92 μm × 353.16 μm (640 × 480 pixels) per visual field was performed in three visual fields using a 530 white filter and a × 10 objective lens. And this operation was performed about arbitrary 3 places on the surface of the adhesion layer of a film, noise was removed with the median filter of 5x5 pixels about the obtained data, and the wave | undulation component was removed with the 30 micrometer Gaussian filter.
The ratio of the area of the portion of the obtained surface shape data deeper than 0.1 μm to the area of the visual field (the valley area ratio) was determined.
The evaluation criteria are as follows.
◎: Valley area ratio is 0.5% or less, good ○: Valley area ratio is larger than 0.5% and 1% or less, usable △: Valley area ratio is larger than 1%, 2% It is the following, and there is a problem in use. ×: Valley area ratio is larger than 2%, difficult to use

(10) Curved surface adhesiveness From a biaxially stretched film, a film piece having a length (MD direction) of 100 mm and a width (width) of 25 mm was cut out, and this film piece was placed on the outside of a commercially available acrylic pipe (outer diameter 50 mm). It stuck with the roller so that MD direction might become the circumference direction of a pipe, and it aged 24 hours at the temperature of 15 degreeC, and observed the float of the biaxially stretched film edge part.
◎: Lifting at the end is not seen at all, good ○: Lifting at the end is slightly seen, but can be used ×: The end is lifted by 1 cm or more, causing a problem in use

  As shown in Table 2, the biaxially stretched film of the present invention has a good sticking property and / or followability, has a blocking resistance and an adhesive layer smoothness, and is easy to unwind from winding. It turns out that it is a stretched film. Moreover, the biaxially stretched film described in Examples 1 to 8 was a film excellent in peelability without causing any adhesive residue problem. The biaxially stretched film of the present invention can be suitably used as, for example, a re-peeling film because it has good sticking property and / or followability and curved surface sticking property.

  On the other hand, although the films of Comparative Examples 1 to 5 and 7 had stickability, they did not have sufficient blocking resistance and were difficult to unwind from winding. The film of Comparative Example 6 was good in terms of blocking resistance and adhesive layer smoothness, but could not be applied.

Claims (10)

A biaxially stretched film comprising a core layer, an adhesive layer formed on one side of the core layer, and a back layer formed on the other side of the core layer,
The core layer is formed from a composition (B) containing a highly crystalline polypropylene resin (b1),
The adhesive layer is formed from a composition (A) containing a low crystalline polypropylene resin (a1),
The back layer is a biaxially stretched film formed from a composition (C) containing a low density polyethylene resin (c1) and a propylene polymer (c2).   The biaxially stretched film according to claim 1, wherein the content of the low crystalline polypropylene resin (a1) in the composition (A) is 50 to 100% by mass based on the total amount of the composition (A).   The biaxially stretched film according to claim 1 or 2, wherein the mesopentad fraction (mmmm) of the low crystalline polypropylene resin (a1) is 20 to 60 mol%.   The molecular weight distribution (Mw / Mn) calculated as a ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the low crystalline polypropylene resin (a1) is 1.5 to 4. The biaxially stretched film according to any one of the above.   The biaxial stretching according to any one of claims 1 to 4, wherein the content of the low-density polyethylene resin (c1) in the composition (C) is 20 to 50 mass% based on the total amount of the composition (C). the film.   The biaxially stretched film according to any one of claims 1 to 5, wherein the composition (C) contains at least two ethylene-propylene copolymers as the propylene polymer (c2).   The composition (C) contains at least an ethylene-propylene block copolymer (c2-a) and an ethylene-propylene random copolymer (c2-b) as the propylene-based polymer (c2). Biaxially stretched film.   The content of the ethylene-propylene block copolymer (c2-a) in the composition (C) is 30 to 60% by mass, and the content of the ethylene-propylene random copolymer (c2-b) is 5 to 30. The biaxially stretched film according to claim 7, wherein the content is based on the total amount of the composition (C).   The biaxially stretched film according to any one of claims 1 to 8, wherein the adhesive layer has a thickness of 2 to 10 µm.   The biaxially stretched film according to any one of claims 1 to 9, wherein the biaxially stretched film is a re-peeling film.