Adhesive film, adhesive film for adhesive labels, and adhesive labels

Abstract

This adhesive film offers excellent rigidity and heat resistance, and even with a thinner film thickness than conventional products, it is easy to peel, less prone to wrinkling, and less likely to curl. [Solution] An adhesive film comprising an adhesive biaxially oriented polypropylene film and an adhesive coating layer, wherein the adhesive biaxially oriented polypropylene film satisfies the following (1) and (2). (1) When the crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) are separated by pulsed NMR using the solid echo method, the ratio of (III) is 7% or less. (2) The relationship between the loop stiffness stress (S) in the width direction and the thickness (t) satisfies the following equation. S[mN]≧0.0010 × thickness(μm) 3 (3) The mesopentat fraction of the polypropylene resin constituting the film is 97.0% or higher. (4) The melt flow rate of the polypropylene resin constituting the film is 4.0 g / 10% or more.

Description

[Technical Field]

[0001] This invention relates to a biaxially oriented polypropylene film for adhesive applications that exhibits excellent rigidity and heat resistance. More specifically, it relates to a biaxially oriented polypropylene film for adhesive applications that exhibits good flatness during adhesive processing even when the film thickness is thinner than conventional products, and is suitable for process adhesive films with minimal thickness variations. [Background technology]

[0002] Biaxially oriented polypropylene films possess moisture resistance, along with the necessary rigidity and heat resistance, making them suitable for packaging and industrial applications such as adhesives and adhesive tapes. In recent years, due to environmental concerns, there has been a demand for recyclability and volume reduction through thinning of adhesive films, making it essential to significantly improve the rigidity of polypropylene films. As a means of improving rigidity, there have been techniques to improve the crystallinity and melting point of the polypropylene resin by improving the catalyst and process technology during polymerization, and to increase the degree of orientation of the film by increasing the stretching ratio during the film-forming process. However, there is a problem that increasing rigidity simultaneously reduces heat resistance, and until now, there has been no biaxially oriented polypropylene film that possesses sufficient rigidity and heat resistance.

[0003] In the manufacturing process of biaxially oriented polypropylene films, methods have been proposed such as performing a first-stage heat treatment while relaxing the film at a temperature below that of the widthwise stretching, and then performing a second-stage heat treatment at a temperature between the first-stage temperature and the widthwise stretching temperature (e.g., Patent Document 1), or performing further stretching in the longitudinal direction after widthwise stretching (e.g., Patent Documents 2 and 3). However, the orientation of the film described in Patent Document 1 is low and the rigidity is insufficient. The film described in Patent Document 2 has excellent rigidity but poor heat resistance, and there was a problem of wrinkles and curls occurring when adhesive processing was performed at temperatures above 120°C. Furthermore, the film described in Patent Document 3 is sequentially biaxially stretched and oriented in the widthwise direction, and then re-stretched in the longitudinal direction, so the arrangement of molecular chains in the longitudinal direction is not sufficient, resulting in low rigidity in the longitudinal direction. In addition, because relaxation is performed in the widthwise direction, the orientation in the widthwise direction is low and the rigidity is insufficient. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Gazette WO2016 / 182003 [Patent Document 2] Japanese Patent Publication No. 2013-177645 [Patent Document 3] Japanese Patent Publication No. 2001-40111 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to solve the above-mentioned problems. Specifically, it relates to an adhesive biaxially oriented polypropylene film that achieves both film rigidity and heat resistance at high temperatures of 150°C. The objective of the present invention is to solve the above-mentioned conventional problems and to provide an adhesive polypropylene film that is suitable for process adhesive films and the like, which does not wrinkle or curl during adhesive processing, has good flatness, and has small thickness variations, even when the film thickness is thinner than conventional products in order to reduce the amount of film waste after use in order to reduce the environmental impact. [Means for solving the problem]

[0006] As a result of intensive studies by the present inventors to achieve such an object, the inventions of the following [1] to

[12] have been reached. [1] An adhesive film including a biaxially oriented polypropylene film for adhesion and an adhesive coating layer, wherein the biaxially oriented polypropylene film for adhesion satisfies the following (1) and (2). (1) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) determined by pulsed NMR by the solid echo method is 7% or less. (2) The relationship between the loop stiffness stress (S) in the width direction and the thickness (t) satisfies the following formula. S [mN] ≥ 0.0010 × thickness (μm) 3 (3) The meso-pendant fraction of the polypropylene resin constituting the film is 97.0% or more. (4) The melt flow rate of the polypropylene resin constituting the film is 4.0 g / 10 min% or more. [2] The adhesive film according to [1], wherein the heat shrinkage rate of the biaxially oriented polypropylene film for adhesion at 150°C is 10% or less in the longitudinal direction and 30% or less in the width direction. [3] The adhesive film according to [1] or [2], wherein the refractive index Ny in the width direction of the biaxially oriented polypropylene film for adhesion is 1.5250 or more and △Ny is 0.0240 or more. [4] The adhesive film according to [1] or [2], wherein the haze of the biaxially oriented polypropylene film for adhesion is 5.0% or less. [5] The adhesive film according to [1] or [2], wherein the crystallization temperature of the polypropylene resin constituting the biaxially oriented polypropylene film for adhesion is 105°C or more and the melting point is 160°C or more. [6] The adhesive biaxially oriented polypropylene film according to [1] or [2], wherein the amount of components having a molecular weight of 100,000 or less in the polypropylene resin constituting the adhesive biaxially oriented polypropylene film is 35% by mass or more. [7] An adhesive film in which an adhesive coating layer is laminated on at least one surface of the adhesive biaxially oriented polypropylene film according to [1] or [2]. [8] The adhesive film according to [7], wherein the adhesive coating layer contains a silicone rubber and / or an acrylic resin. [9] The adhesive film according to [8], wherein the heat shrinkage rate of the adhesive film after heating at 150°C for 5 minutes is 10% or less in the longitudinal direction and 30% or less in the width direction.

Advantages of the Invention

[0007] The present invention relates to an adhesive biaxially oriented polypropylene film having excellent rigidity and heat resistance. More specifically, even when the film thickness is made thinner than conventional products, the flatness during adhesive processing is good, the thickness unevenness is small, and it is an adhesive biaxially stretched polypropylene film suitable for films for process adhesion and the like.

Brief Description of the Drawings

[0008] [Figure 1] Schematic diagram of component separation of the decay curve of the spin-spin relaxation time observed by 1H-pulse NMR.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the adhesive biaxially oriented polypropylene film of the present invention will be described in more detail. The adhesive biaxially oriented polypropylene film of the present invention is composed of a polypropylene resin composition mainly composed of a polypropylene resin. Note that the "main component" means that the proportion of the polypropylene resin in the polypropylene resin composition is 90% by mass or more, more preferably 93% by mass or more, still more preferably 95% by mass or more, and particularly preferably 97% by mass or more.

[0010] (Polypropylene resin) The polypropylene resin used in the present invention can be a polypropylene homopolymer or a copolymer of ethylene and / or an α-olefin having 4 or more carbon atoms. A propylene homopolymer that is substantially free of ethylene and / or an α-olefin having 4 or more carbon atoms is preferred, and even when it contains an ethylene and / or an α-olefin component having 4 or more carbon atoms, the amount of the ethylene and / or α-olefin component having 4 or more carbon atoms is preferably 1 mol% or less, more preferably 0.5 mol% or less, even more preferably 0.3 mol% or less, and particularly preferably 0.1 mol or less. Crystallinity tends to improve within the above range. Examples of α-olefin components having 4 or more carbon atoms that constitute such a copolymer include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. Polypropylene resins can be made from two or more different polypropylene homopolymers, copolymers with ethylene and / or α-olefins having 4 or more carbon atoms, or mixtures thereof.

[0011] (stereoregularity) The mesopentad fraction (hereinafter sometimes abbreviated as [mmmm]%), which is an indicator of the stereoregularity of the polypropylene resin used in the present invention, is preferably in the range of 97.0 to 99.9%, more preferably in the range of 97.5 to 99.7%, even more preferably in the range of 98.0 to 99.5%, and particularly preferably in the range of 98.5 to 99.3%. A mesopentad fraction of 97.0% or higher enhances the crystallinity of the polypropylene resin, improving the melting point, crystallinity, and crystal orientation of the crystals in the film, resulting in improved rigidity and heat resistance at high temperatures. A fraction of 99.9% or lower helps to reduce costs in polypropylene manufacturing and makes the film less prone to breakage during formation. The mesopentad fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. A concentration of 99.5% or less is more preferable. The mesopentade fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. In order to keep the mesopentade fraction of the polypropylene resin within the above-mentioned range, methods such as washing the obtained polypropylene resin powder with a solvent such as n-heptane, selecting a catalyst and / or co-catalyst, and appropriately selecting the components of the polypropylene resin composition are preferably employed.

[0012] (Melting temperature) The lower limit of the melting temperature (Tm) of the polypropylene resin constituting the adhesive biaxially oriented polypropylene film of the present invention, as measured by DSC, is preferably 160°C, more preferably 161°C, even more preferably 162°C, even more preferably 163°C, and still more preferably 164°C. When Tm is 160°C or higher, rigidity and heat resistance at high temperatures are easily obtained. The upper limit of Tm is preferably 170°C, more preferably 169°C, even more preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. When Tm is 170°C or lower, it is easier to suppress cost increases in terms of polypropylene manufacturing and the film is less likely to break during film formation. The melting temperature can also be further increased by blending a crystal nucleating agent with the aforementioned polypropylene resin. Tm is the primary peak temperature of the endothermic peak observed during melting when a 1-10 mg sample is packed into an aluminum pan, placed in a differential scanning calorimeter (DSC), melted at 230°C for 5 minutes under a nitrogen atmosphere, cooled to 30°C at a scanning rate of -10°C / min, held for 5 minutes, and then heated again at a scanning rate of 10°C / min.

[0013] (crystallization temperature) The lower limit of the crystallization temperature (Tc) of the polypropylene resin constituting the adhesive biaxially oriented polypropylene film of the present invention, as measured by DSC, is 105°C, preferably 108°C, and more preferably 110°C. When Tc is 105°C or higher, crystallization proceeds easily during the widthwise stretching and subsequent cooling process, making it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tc is preferably 135°C, more preferably 133°C, even more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. When Tc is 135°C or lower, it is less likely to increase the cost of polypropylene production and the film is less likely to break during film formation. The crystallization temperature can also be further increased by blending a crystal nucleating agent into the aforementioned polypropylene resin. Tc is the primary peak temperature of the exothermic peak observed when a 1-10 mg sample is packed into an aluminum pan, set in a DSC, melted at 230°C for 5 minutes under a nitrogen atmosphere, and then cooled to 30°C at a scanning rate of -10°C / min.

[0014] (Melt flow rate) The melt flow rate (MFR) of the polypropylene resin constituting the adhesive biaxially oriented polypropylene film of the present invention is preferably 4.0 to 30 g / 10 min, more preferably 4.5 to 25 g / 10 min, even more preferably 4.8 to 22 g / 10 min, particularly preferably 5.0 to 20 g / 10 min, and most preferably 6.0 to 20 g / 10 min, when measured in accordance with the conditions M (230°C, 2.16 kgf) of JIS K 7210 (1995). When the melt flow rate (MFR) of the polypropylene resin is 4.0 g / 10 min or higher, it is easier to obtain a biaxially oriented polypropylene film for adhesive use with low thermal shrinkage. Furthermore, if the melt flow rate (MFR) of the polypropylene resin is 30 g / 10 min or less, it is easier to maintain the film-forming properties.

[0015] From the viewpoint of film properties, it is preferable to set the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the polypropylene resin constituting the film to preferably 5.0 g / 10 min, more preferably 5.5 g / 10 min, even more preferably 6.0 g / 10 min, particularly preferably 6.3 g / 10 min, and most preferably 6.5 g / 10 min. When the melt flow rate (MFR) of the polypropylene resin is 5.0 g / 10 min or higher, the amount of low molecular weight components in the polypropylene resin constituting the film increases. Therefore, by employing the widthwise stretching process in the film manufacturing process described later, the orientation and crystallization of the polypropylene resin are further promoted, and the degree of crystallinity in the film tends to increase. In addition, the entanglement between polypropylene molecular chains in the amorphous portion is reduced, making it easier to improve heat resistance. In order to keep the melt flow rate (MFR) of the polypropylene resin within the above range, it is preferable to employ methods to control the average molecular weight and molecular weight distribution of the polypropylene resin.

[0016] In other words, the lower limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve of the polypropylene resin constituting the film of the present invention is 35% by mass, preferably 38% by mass, more preferably 40% by mass, even more preferably 41% by mass, and particularly preferably 42% by mass. The upper limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is 65% by mass or less, the film strength is less likely to decrease. In this case, including high molecular weight components or long-chain branched components with long relaxation times makes it easier to adjust the amount of components with a molecular weight of 100,000 or less in the polypropylene resin without significantly changing the overall viscosity, thus improving film-forming properties without significantly affecting rigidity or thermal shrinkage.

[0017] (molecular weight distribution) The polypropylene resin used in the present invention has a lower limit of mass-average molecular weight (Mw) / number-average molecular weight (Mn), which is an indicator of the breadth of the molecular weight distribution, preferably 3.5, more preferably 4, even more preferably 4.5, and particularly preferably 5. The upper limit of Mw / Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20. Mw / Mn can be obtained using gel permeation chromatography (GPC). When Mw / Mn is within the above range, it is easy to increase the amount of components with a molecular weight of 100,000 or less.

[0018] Furthermore, the molecular weight distribution of polypropylene resin can be adjusted by polymerizing components of different molecular weights in a multi-stage process in a series of plants, blending components of different molecular weights offline in a kneader, polymerizing with a blend of catalysts having different properties, or using a catalyst capable of achieving the desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC can be a smooth molecular weight distribution with a single peak in a GPC chart where the horizontal axis is the logarithm of molecular weight (logM) and the vertical axis is the differential distribution value (weight fraction per logM), or it can be a molecular weight distribution with multiple peaks or shoulders.

[0019] (Method for manufacturing biaxially oriented polypropylene film for adhesive use) The adhesive biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made from a polypropylene resin composition mainly composed of the polypropylene resin described above, and then biaxially stretching it. The biaxial stretching can be performed by any of the following methods: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential tenter biaxial stretching. However, sequential tenter biaxial stretching is preferred from the viewpoint of film formation stability and thickness uniformity. In particular, it is preferable to stretch in the longitudinal direction first, followed by stretching in the width direction, but a method of stretching in the width direction first, followed by stretching in the longitudinal direction is also acceptable.

[0020] Next, the method for manufacturing the adhesive biaxially oriented polypropylene film of the present invention will be described below, but is not necessarily limited thereto. The adhesive biaxially oriented polypropylene film of the present invention may have layers having other functions laminated on at least one side. Lamination may be on one side or both sides. In that case, the resin composition of the other layer, and the resin composition of the central layer, may be the polypropylene resin composition described above. Alternatively, a different polypropylene resin composition may be used. The number of layers to be laminated may be one, two, or three or more layers per side, but from a manufacturing standpoint, one or two layers are preferred. Preferred lamination methods include, for example, co-extrusion using a feed block system or a multi-manifold system. In particular, to improve the processability of the biaxially oriented polypropylene film for adhesive applications, a heat-sealable resin layer can be laminated to the extent that it does not degrade the properties. Furthermore, corona treatment can be applied to one or both sides to impart printability.

[0021] The following describes an example for a single layer, specifically focusing on the use of the Tenter successive biaxial stretching method. First, a resin composition containing polypropylene resin is heated and melted in a single-screw or twin-screw extruder, extruded into a sheet from a T-die, and cooled and solidified on a cooling roll. To promote solidification, it is preferable to further cool the sheet cooled on the cooling roll by immersing it in a water tank or the like.

[0022] Next, the sheet is stretched longitudinally by increasing the rotation speed of the rear stretching roll using two heated stretching rolls, thereby obtaining a uniaxially oriented film.

[0023] Next, after preheating the uniaxially oriented film, the film is stretched in the width direction at a specific temperature using a tenter-type stretcher while gripping the film edges, thereby obtaining a biaxially oriented film. This width-direction stretching process will be described in detail later.

[0024] After the widthwise stretching process is completed, the biaxially oriented film is heat-treated at a specific temperature to obtain an adhesive biaxially oriented film. During the heat treatment process, the film may be relaxed in the widthwise direction.

[0025] The resulting biaxially oriented polypropylene film for adhesive purposes can be subjected to corona discharge treatment on, for example, at least one side, as needed, and then wound up with a winder to obtain a film roll.

[0026] The following sections will explain each step in detail. (Extrusion process) First, a polypropylene resin composition, mainly composed of polypropylene resin, is heated and melted in a single-screw or twin-screw extruder at a temperature of 200°C to 300°C. The sheet-like molten polypropylene resin composition is then extruded from the T-die and cooled and solidified in contact with a metal cooling roll. Preferably, the resulting unstretched sheet is then placed in a water tank. The temperature of the cooling roll, or the temperature of the cooling roll and water bath, is preferably in the range of 10°C to Tc. If you want to increase the transparency of the film, it is preferable to cool and solidify it with a cooling roll at a temperature in the range of 10 to 50°C. Lowering the cooling temperature to 50°C or below tends to increase the transparency of the unstretched sheet, so it is preferably 40°C or below, and more preferably 30°C or below. In order to increase the degree of crystal orientation after sequential biaxial stretching, it may be preferable to set the cooling temperature to 40°C or below when using a propylene homopolymer with a mesopentat fraction of 97.0% or more, as described above, in order to facilitate the stretching in the next step and reduce thickness variations, it is preferable to set the cooling temperature to 40°C or below, and more preferably 30°C or below. The thickness of the unstretched sheet is preferably 3500 μm or less for optimal cooling efficiency, and more preferably 3000 μm or less. This can be adjusted as appropriate depending on the film thickness after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition and the lip width of the T-die, etc.

[0027] (Longitudinal stretching process) The lower limit of the longitudinal stretching ratio is preferably 3.5 times, more preferably 3.8 times, and particularly preferably 4.2 times. Within this range, it is easier to increase the strength and reduce film thickness unevenness. The upper limit of the longitudinal stretching ratio is preferably 7.0 times, more preferably 6.0 times, and particularly preferably 7 times. Within this range, the widthwise stretching process is easier, and productivity is improved. The lower limit of the longitudinal stretching temperature is preferably Tm-30°C, more preferably Tm-27°C, and even more preferably Tm-25°C. Within this range, subsequent widthwise stretching is facilitated and thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, and even more preferably Tm-12°C. Within this range, the thermal shrinkage rate is easily reduced, making it less difficult to stretch the material by attaching it to the stretching rolls, and reducing the quality by increasing surface roughness. Furthermore, longitudinal stretching may be performed in two or more stages using three or more stretching rolls.

[0028] (Preheating process) Before the widthwise stretching process, the uniaxially oriented film after longitudinal stretching must be heated to a temperature range of Tm to Tm+25°C to soften the polypropylene resin composition. A temperature above Tm promotes softening, facilitating widthwise stretching. A temperature below Tm+25°C promotes orientation during transverse stretching, making it easier to achieve rigidity. More preferably, the temperature is Tm+2 to Tm+20°C, and particularly preferably Tm+3 to Tm+15°C. Here, the highest temperature reached during the preheating process is defined as the preheating temperature.

[0029] (Width direction stretching process) In the widthwise stretching process after the preheating process, the preferred method is as follows:

[0030] In the widthwise stretching process, it is preferable to stretch at a temperature of Tm -10°C or higher and below the preheating temperature. At this time, the widthwise stretching may start when the preheating temperature is reached, or it may start when the temperature is lowered after reaching the preheating temperature and reaches a temperature lower than the preheating temperature. The lower limit of the temperature in the widthwise stretching process is more preferably Tm-9°C, even more preferably Tm-7°C, and particularly preferably Tm-5°C. When the widthwise stretching temperature is within this range, it is easier to improve the rigidity of the resulting biaxially oriented film. The upper limit of the temperature during the widthwise stretching process is preferably Tm+10°C, more preferably Tm+7°C, and particularly preferably Tm+5°C. When the widthwise stretching temperature is within this range, uneven stretching is less likely to occur. In the widthwise stretching process, a later stretching step may be added, in which stretching is performed at a lower temperature, following the widthwise stretching within the above temperature range. In other words, a section (early section) in which stretching occurs at temperatures between Tm-10°C and Tm+10°C may be followed by a section (later section) in which stretching occurs at temperatures lower than those of the early section, but between Tm-70°C and Tm-5°C. By including both an early and a later section, it is easier to increase the rigidity. The lower limit of the stretching temperature in the later stage is preferably Tm-65°C, more preferably Tm-60°C, and even more preferably Tm-55°C. Film formation is more stable when the stretching temperature in the later stage is within this range.

[0031] The lower limit of the final widthwise stretching ratio in the widthwise stretching process is preferably 10 times or more, more preferably 11 times or more, and even more preferably 11.5 times or more. A ratio of 10 times or more makes it easier to increase the rigidity of the film and reduces thickness unevenness. The upper limit of the widthwise stretching ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. A ratio of 20 times or less makes it easier to reduce the thermal shrinkage rate and makes the film less prone to breaking during stretching. When adding a later section, the total stretching ratio should be within the above range. In this case, the lower limit of the stretching ratio for the earlier stretching process is preferably 4 times, more preferably 5 times, even more preferably 6 times, and particularly preferably 6.5 times. The upper limit of the stretching ratio at the end of the earlier section is preferably 15 times, more preferably 14 times, and even more preferably 13 times.

[0032] It is preferable to cool the film immediately after the end of stretching in the width direction, that is, when the final stretching ratio in the width direction is reached. The cooling temperature at this time is preferably below the temperature of stretching in the width direction, and preferably between Tm-80°C and Tm-15°C, more preferably between Tm-80°C and Tm-20°C, even more preferably between Tm-80°C and Tm-30°C, and particularly preferably between Tm-70°C and Tm-40°C. By adding a cooling step, crystallization occurs and the crystal orientation is fixed, and even if the temperature is raised to a temperature above the melting point thereafter, the orientation history is maintained, and as a result the crystal orientation in the film can be greatly increased. The temperature can be gradually lowered from the end of widthwise stretching to the cooling temperature, but it can also be lowered in steps or in a single step. Lowering the temperature in steps or in a single step is preferable because it makes it easier to increase the crystal orientation in the film.

[0033] It is preferable to cool the film and then stretch it again in the width direction at a high temperature (hereinafter also referred to as width direction re-stretching). Stretching the film again in the width direction at a high temperature after cooling makes it easier to increase the crystal orientation of the film, thus making it easier to increase its rigidity. The lower limit of the stretching temperature when stretching again in the width direction is Tm-5°C, preferably Tm°C, more preferably Tm+5°C, even more preferably Tm+7°C, and particularly preferably Tm+9°C. A temperature of Tm-5°C or higher makes it easier to increase rigidity and reduce the thermal shrinkage rate. The upper limit of the re-stretching temperature in the width direction is preferably Tm+20°C, more preferably Tm+18°C, and even more preferably Tm+16°C. A temperature of Tm+20°C or lower makes it easier to increase rigidity. The lower limit of the re-stretching ratio in the width direction at high temperatures is preferably 1.05 times, more preferably 1.1 times, and even more preferably 1.15 times. The upper limit of the re-stretching ratio in the width direction at high temperatures is preferably 2 times, more preferably 1.7 times, and even more preferably 1.5 times. If the re-stretching ratio is too high, the thermal shrinkage rate may become too large, thickness unevenness may occur, or the film may break.

[0034] In other words, instead of immediately relaxing the material at a high temperature after stretching in the width direction, as in the conventional method, we found that stretching it again in the width direction at a temperature sufficiently higher than the melting point makes it possible to reduce the thermal shrinkage rate while further improving rigidity. In other words, it is preferable to perform the stretching at a temperature of Tm+5°C or higher in the step following the initial widthwise stretching. At temperatures of Tm+5°C or higher, the mobility of the molecular chains becomes sufficiently high, making it easier to resolve the effects of molecular chain entanglement during stretching. As a result, the molecular chains are less constrained, making it less likely for disordered molecular orientation to occur, and crystallization proceeds sufficiently. By stretching the film in the width direction at a high temperature and then cooling it to a temperature below which crystallization is possible, the crystal orientation is fixed, resulting in a high-melting-point film with a high degree of crystallinity and thick crystal lamellae.

[0035] Furthermore, even in areas other than the crystalline lamellae, there are fewer molecular chains with large distortions in molecular orientation constrained by entanglement points, and the film is less likely to shrink even when the crystal begins to melt. In addition, as the degree of crystallinity improves and the crystalline lamellae become thicker, the melting point tends to rise, and melting is less likely to occur below the melting point. As a result, the thermal shrinkage rate tends to decrease. As a result, it became possible to further improve rigidity while reducing the thermal shrinkage rate.

[0036] In typical film-forming processes (extrusion - longitudinal stretching - widthwise stretching - heat treatment), to eliminate the strain caused by widthwise stretching, which is performed at a temperature below the melting point, the film is exposed to temperatures above the melting point during the heat treatment process, and a relaxation of several percent to tens of percent is applied to reduce thermal shrinkage. By relaxing the film, the constraint on molecular chains that hinders crystallization can be overcome, contributing to a reduction in thermal shrinkage. However, conversely, the orientation of molecular chains in the widthwise direction generated during the transverse stretching process decreases, reducing rigidity, making it difficult to achieve both low thermal shrinkage and high rigidity. Furthermore, excessively high temperatures can cause the film to whiten. In a typical film formation process (extrusion - longitudinal stretching - widthwise stretching - heat treatment), increasing the temperature during the widthwise stretching step increases the mobility of the molecular chains. However, if stretching is performed in a way that prevents residual strain, the melting of the crystals formed by longitudinal stretching progresses, resulting in a decrease in crystal orientation. In the method of the present invention, after the film is stretched in the width direction and sufficiently oriented in the width direction, the film retains sufficient tension even if the fixed crystal orientation melts due to cooling. Therefore, the film retains sufficient tension even when stretched again, and there is little concern about uneven thickness or film breakage. The stretching ratio at high temperatures should be sufficient to untangle and align the molecular chains; a ratio of 1.05 or higher is acceptable. A stretching ratio of 2 or less minimizes thickness variations.

[0037] Thus, by using a highly crystalline polypropylene resin with high stereoregularity and a high melting point, and employing the aforementioned longitudinal stretching, widthwise stretching, cooling, and high-temperature stretching processes, the molecules of the polypropylene resin align remarkably highly in the main orientation direction (in the widthwise stretching process described above, this corresponds to the widthwise direction). As a result, the resulting biaxially oriented film exhibits strong crystal orientation, and a greater number of crystals with high melting points are more easily formed.

[0038] Furthermore, increasing the low molecular weight components of the polypropylene resin reduces molecular chain entanglement, making it easier to achieve higher crystallinity in the film and reducing the amount of material outside the crystalline lamellae. Additionally, weakening the thermal shrinkage stress in the non-crystalline lamellae areas makes it easier to further reduce the thermal shrinkage rate. Conventional technologies have made it difficult to achieve both strong crystal orientation and a reduction in amorphous components not constrained by the crystal structure. In other words, improving either rigidity or thermal shrinkage tends to degrade the other property. Considering these factors, the present invention can be said to have a groundbreaking effect.

[0039] (Heat treatment process) The biaxially oriented film can be heat-treated as needed to further reduce its thermal shrinkage. The upper limit of the heat treatment temperature is preferably the high-temperature re-stretching temperature described above, more preferably the high-temperature re-stretching temperature -2°C, and even more preferably the high-temperature re-stretching temperature -3°C. By keeping the temperature below the high-temperature re-stretching temperature, the rigidity is less likely to decrease, the film surface roughness does not become too large, and the film is less likely to whiten. The lower limit of the heat treatment temperature is preferably Tm -3°C, more preferably Tm -2°C, and particularly preferably Tm. To adjust the thermal shrinkage rate, the film may be relaxed (relaxed) in the width direction during heat treatment, but the upper limit of the relaxation rate is preferably 5%, more preferably 3%, and even more preferably 1%. Within this range, the rigidity is less likely to decrease, and the variation in film thickness tends to be small. When higher rigidity is desired, heat treatment may be omitted.

[0040] (cooling process) It is preferable to cool the film immediately after stretching it again in the width direction at a temperature of Tm -5°C or higher, or immediately after the heat treatment process. The cooling temperature at this time is preferably 10°C to 140°C, more preferably 20°C to 120°C, even more preferably 80°C or lower, and particularly preferably 50°C or lower. By providing a cooling step, the state of the film can be fixed.

[0041] (Film thickness) The thickness of the adhesive biaxially oriented polypropylene film of the present invention is set according to each application, but in order to obtain the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, even more preferably 4 μm, particularly preferably 8 μm, and most preferably 10 μm. When the film thickness is 2 μm or more, it is easier to obtain the rigidity of the film. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, even more preferably 60 μm, particularly preferably 50 μm, and most preferably 40 μm. When the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion process does not tend to decrease. The adhesive biaxially oriented polypropylene film of the present invention is typically manufactured as a roll with a width of 2,000 to 12,000 mm and a length of 1,000 to 50,000 m, and then wound into a film roll. Furthermore, it is slit according to various applications and supplied as slit rolls with a width of 300 to 2,000 mm and a length of 500 to 5,000 m. The adhesive biaxially oriented polypropylene film of the present invention makes it possible to obtain longer film rolls.

[0042] (Uniformity of thickness) The lower limit of the thickness uniformity of the adhesive biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, even more preferably 0.5%, and particularly preferably 1%. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, even more preferably 15%, particularly preferably 12%, and most preferably 10%. Within the above range, defects are less likely to occur during post-processing such as coating or printing, making it easy to use in applications requiring precision. The measurement method was as follows: A 40 mm wide test piece was cut from the steady-state region where the film properties were stable in the length direction of the film. The film thickness was continuously measured over 20,000 mm using a film feeding device manufactured by Micron Measuring Instruments Co., Ltd. (product number: A90172) and a continuous film thickness measuring instrument manufactured by Anritsu Corporation (product name: K-313A wide-range high-sensitivity electronic micrometer), and the thickness uniformity was calculated from the following formula. Thickness uniformity (%) = [(Maximum thickness - Minimum thickness) / Average thickness] × 100

[0043] (Film characteristics) The adhesive biaxially oriented polypropylene film of the present invention is characterized by the following properties. Here, the "longitudinal direction" in the adhesive biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction in the film manufacturing process, and the "width direction" refers to the direction perpendicular to the flow direction in the film manufacturing process. For polypropylene films in which the flow direction in the film manufacturing process is unknown, wide-angle X-rays are incident perpendicular to the film surface, and the scattering peaks originating from the (110) plane of the α-type crystal are scanned in the circumferential direction. The direction with the largest diffraction intensity in the obtained diffraction intensity distribution is defined as the "longitudinal direction," and the direction perpendicular to it is defined as the "width direction."

[0044] (Crystalline component (I), constrained amorphous component (II), unconstrained amorphous component (III) as determined by pulsed NMR) 1 It is known that the decay time constant of the Free Induction Decay (FID) of the spin-spin relaxation time T2 observed by H-pulsed NMR is observed as the sum of two or more decay time constants. For example, according to Polymer Journal, Vol.3, No.4, pp448-462 (1972), the decay time constant of the relaxation time of crystalline polymers was analyzed as the sum of three components: crystalline component, intermediate phase component, and amorphous component using the solid echo method of pulsed NMR. 1The spin-spin relaxation time T2 observed by H-pulse NMR decreases in the order of crystalline, intermediate phase, and amorphous. The intermediate phase has a faster T2 than the amorphous phase and is considered to be an amorphous material with constrained mobility. When molecular chains are stretched while untangling them, a strongly oriented crystalline component (I) is formed, and an amorphous chain component (II) (corresponding to the intermediate phase above) with constrained mobility is formed near the crystal. On the other hand, when the entanglement is large and the orientation is disordered during stretching, an amorphous component (III) (corresponding to the amorphous material above) that is not constrained by the crystal is more likely to be formed. The unconstrained amorphous component (III) has high mobility and is more likely to move to relieve strain at high temperatures, which is thought to be the cause of shrinkage at high temperatures. On the other hand, the constrained amorphous chain (II) is less likely to shrink at high temperatures because its movement is suppressed even at high temperatures compared to the amorphous component (III).

[0045] The upper limit of the unconstrained amorphous component (III) of the adhesive biaxially oriented polypropylene film of the present invention, as determined by pulsed NMR, is 7%, preferably 6%, and more preferably 5%. When the amorphous component (III) is 7% or less, wrinkles are less likely to occur when the adhesive coating film dries, and curling of the film after adhesive processing is also less likely to occur. To reduce the unconstrained amorphous component (III), it is particularly effective to increase the area ratio during film formation, followed by sequential biaxial stretching and then stretching again in the width direction at high temperature. Furthermore, using polypropylene raw materials with a high mesopentade fraction is effective. Furthermore, it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less, when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film, at 35% by mass. Here, the fact that the unconstrained amorphous component (III) determined by pulsed NMR is 7% or less means that there are few molecular chains with large distortions in molecular orientation constrained by entanglement points, the film is less likely to shrink even when the crystal melting begins, wrinkles are less likely to occur when the adhesive coating is dried at high temperatures, and the film is less likely to curl after adhesive processing.

[0046] If the unconstrained amorphous component (III) determined by pulsed NMR exceeds 7%, it indicates that there are many molecular chains with large distortions in molecular orientation constrained by entanglement points. As a result, shrinkage occurs simultaneously with the start of crystal melting, leading to wrinkles in the film after adhesive processing at high temperatures, and curling in the film after drying of the adhesive coating. Furthermore, while there is no particular lower limit for the unconstrained amorphous component (III), it is practical to have it at 0.1% or higher. If the unconstrained amorphous component (III) is reduced to less than 0.1%, it is necessary to perform sequential biaxial stretching followed by further stretching in the width direction at a higher temperature, which can lead to a decrease in tension during stretching due to melting and potentially cause fracture. In addition, the crystal orientation in the film may weaken, resulting in lower rigidity.

[0047] (Heat shrinkage rate at 150°C) The upper limit of the longitudinal heat shrinkage rate of the adhesive biaxially oriented polypropylene film of the present invention at 150°C is 10%, preferably 7.0%, more preferably 6.0%, even more preferably 5.0%, and particularly preferably 4.0% or less. The upper limit of the widthwise heat shrinkage rate at 150°C is 30%, preferably 20%, more preferably 16%, and particularly preferably 15% or less. When the thermal shrinkage rate in the longitudinal direction is 10% or less and the thermal shrinkage rate in the width direction is 30% or less, wrinkles are less likely to occur when the adhesive coating film dries, and curling of the film after adhesive processing is also less likely. In particular, when the thermal shrinkage rate in the longitudinal direction at 150°C is 8.0% or less and the thermal shrinkage rate in the width direction at 150°C is 15% or less, the range of controllable roll tension during adhesive processing is widened, resulting in fewer wrinkles when the adhesive coating film dries, and further reducing curling of the film after adhesive processing, which is preferable. When the thermal shrinkage rate in the longitudinal direction is 10% or more and the thermal shrinkage rate in the width direction is 30% or more, wrinkles occur when the adhesive coating film dries, and the adhesive-coated film curls, resulting in poor handling. To reduce the thermal shrinkage rate at 150°C, it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less, when the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film is measured, to 35% by mass.

[0048] (Tensile modulus at 23°C) The lower limit of the longitudinal tensile modulus of the adhesive biaxially oriented polypropylene film of the present invention at 23°C is 2.0 GPa, preferably 2.1 GPa, more preferably 2.2 GPa, even more preferably 2.3 GPa, particularly preferably 2.4 GPa, and most preferably 2.6 GPa. Above 2.0 GPa, the rigidity is high, making it less likely for wrinkles to occur when the adhesive coating film dries, and furthermore, less likely for curling to occur in the film after adhesive processing. The upper limit of the longitudinal tensile modulus is preferably 4.0 GPa, more preferably 3.8 GPa, even more preferably 3.7 GPa, particularly preferably 3.6 GPa, and most preferably 3.5 GPa. Below 4.0 GPa, practical manufacturing is easier, and the balance of properties in the longitudinal and width directions tends to improve. The lower limit of the tensile modulus in the width direction at 23°C for the adhesive biaxially oriented polypropylene film of the present invention is preferably 5.5 GPa, more preferably 5.6 GPa, more preferably 5.7 GPa, even more preferably 5.8 GPa, particularly preferably 5.9 GPa, and most preferably 6.0 GPa. Above 5.5 GPa, the rigidity is high, making it less likely for wrinkles to occur when the adhesive coating film dries, and furthermore, less likely for curling to occur in the film after adhesive processing. The upper limit of the tensile modulus in the width direction is preferably 15 GPa, more preferably 13 GPa, and even more preferably 12 GPa. Below 15 GPa, practical manufacturing is easier, and the balance of properties in the longitudinal and width directions tends to improve. The tensile modulus can be kept within a specified range by adjusting the stretch ratio and relaxation rate, or by controlling the temperature during film formation.

[0049] (Tensile breaking strength at 23°C) The lower limit of the longitudinal tensile breaking strength of the biaxially oriented polypropylene adhesive film of the present invention at 23°C is preferably 90 MPa, more preferably 100 MPa, even more preferably 110 MPa, and particularly preferably 115 MPa. If the strength is 90 MPa or higher, curling of the film after adhesive processing becomes less likely, and film breakage during adhesive processing is less likely. The upper limit of the longitudinal tensile breaking strength is preferably 200 MPa, more preferably 180 MPa, and even more preferably 160 MPa as a practical value. If the strength is 200 MPa or lower, film breakage tends to decrease. The lower limit of the tensile breaking strength in the width direction of the adhesive biaxially oriented polypropylene film of the present invention at 23°C is preferably 400 MPa, more preferably 420 MPa, even more preferably 440 MPa, and particularly preferably 450 MPa. If the strength is 400 MPa or higher, curling of the film after adhesive processing becomes less likely, and film breakage during adhesive processing is less likely. The upper limit of the tensile breaking strength in the width direction is preferably 650 MPa as a practical value, more preferably 600 MPa, and even more preferably 550 MPa. If the strength is 650 MPa or lower, film breakage tends to be less frequent. The tensile breaking strength can be kept within a specified range by adjusting the elongation ratio, elongation temperature, and heat-fixing temperature.

[0050] (Tensile elongation at 23°C) The lower limit of the longitudinal tensile elongation at break of the adhesive biaxially oriented polypropylene film of the present invention at 23°C is preferably 180%, more preferably 190%, more preferably 200%, and particularly preferably 210% or more. A value of 180% or more tends to reduce film breakage. The upper limit of the longitudinal tensile elongation at break at 23°C is preferably 300% and more preferably 280% as a practical value.

[0051] The lower limit of the tensile elongation at break in the width direction at 23°C for the adhesive biaxially oriented polypropylene film of the present invention is preferably 15%, more preferably 20%, and more preferably 30%. If it is 15% or higher, film breakage is less likely to occur. The upper limit of the tensile elongation at break in the width direction at 23°C is preferably 60%, more preferably 55%, and even more preferably 50%. If it is 60% or lower, film breakage during adhesive processing is less likely to occur. The tensile elongation at break can be kept within a specified range by adjusting the stretch ratio, stretching temperature, and heat-fixing temperature.

[0052] (Refractive index) The lower limit of the longitudinal refractive index (Nx) of the adhesive biaxially oriented polypropylene film of the present invention is preferably 1.4950, more preferably 1.4970, even more preferably 1.4980, particularly preferably 1.4990, and most preferably 1.5000. A refractive index of 1.4950 or higher tends to increase the rigidity of the film. The upper limit of the longitudinal refractive index (Nx) is preferably 1.5100, more preferably 15070, and even more preferably 1.5050. A refractive index of 1.5100 or lower tends to provide a good balance of longitudinal-width properties of the film.

[0053] The lower limit of the refractive index (Ny) in the width direction of the adhesive biaxially oriented polypropylene film of the present invention is 1.5250, preferably 1.5253, more preferably 1.5255, even more preferably 1.5260, and particularly preferably 1.5265. A refractive index of 1.5250 or higher tends to increase the rigidity of the film. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, and even more preferably 1.5270. A refractive index of 1.5280 or lower tends to provide a good balance of longitudinal-width properties of the film.

[0054] The lower limit of the refractive index (Nz) in the thickness direction of the adhesive biaxially oriented polypropylene film of the present invention is preferably 1.4960, more preferably 14965, even more preferably 1.4970, particularly preferably 1.4980, and most preferably 1.4990. A refractive index of 1.4960 or higher makes it easier to increase the rigidity of the film. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and even more preferably 1.5010. A refractive index of 1.5020 or lower makes it easier to increase the heat resistance of the film. The refractive index can be kept within a specified range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature.

[0055] (△Ny) The lower limit of ΔNy for the adhesive biaxially oriented polypropylene film of the present invention is 0.0240, preferably 0.0245, more preferably 0.0247, even more preferably 0.0250, particularly preferably 0.0255, and most preferably 0.0260. A value of 0.0240 or higher tends to increase the rigidity of the film. The upper limit of ΔNy is preferably 0.0280 as a practical value, more preferably 0.0277, even more preferably 0.0273, and particularly preferably 0.0270. A value of 0.0280 or lower tends to result in good thickness uniformity. ΔNy can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature of the film. △Ny is calculated using the following formula, where Nx, Ny, and Nz are the refractive indices along the longitudinal, width, and thickness directions of the film, respectively. It represents the degree of orientation in the width direction within the overall orientation of the film in the longitudinal, width, and thickness directions. △Ny=Ny-[(Nx+Nz) / 2]

[0056] (Coefficient of surface orientation) The lower limit of the surface orientation coefficient (ΔP) of the adhesive biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and even more preferably 0.0140. A value of 0.0135 or higher indicates good balance in the planar direction of the film and good thickness uniformity. The upper limit of the surface orientation coefficient (ΔP) is preferably 0.0155, more preferably 0.0152, and even more preferably 0.0150 as a practical value. A value of 0.0155 or lower tends to result in excellent heat resistance at high temperatures. The surface orientation coefficient (ΔP) can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature. Furthermore, the surface orientation coefficient (ΔP) was calculated using the formula [(Nx+Ny) / 2]-Nz.

[0057] (Average refractive index) The lower limit of the average refractive index of the biaxially oriented polypropylene film for adhesive purposes of the present invention is preferably 1.5080, more preferably 1.5081, even more preferably 1.5082, particularly preferably 1.5083, and most preferably 1.5090. The upper limit of the average refractive index is preferably 1.5150, more preferably 1.5140, even more preferably 1.5135, and particularly preferably 1.5130 as a practical value. If the average refractive index is 1.5080 or higher, wrinkles are less likely to occur when the adhesive coating film dries, and curling of the film after adhesive processing is less likely to occur. The average refractive index can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature of the film. The average refractive index is calculated using the following formula, where Nx, Ny, and Nz are the refractive indices along the longitudinal, width, and thickness directions of the film, respectively. Average refractive index = (Nx + Ny + Nz) / 3

[0058] (Hayes) When transparency is required for the adhesive biaxially oriented polypropylene film of the present invention, the upper limit of the film's haze is preferably 5.0%, more preferably 4.5%, even more preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. A haze of 5.0% or less makes it easy to use in applications where transparency is required. The lower limit of the haze is preferably 0.1%, more preferably 0.2%, even more preferably 0.3%, and particularly preferably 0.4% as a practical value. A haze of 0.1% or more makes it easy to manufacture. The haze can be kept within range by adjusting the cooling roll (CR) temperature, the widthwise stretching temperature, the tenter preheating temperature before widthwise stretching, the widthwise stretching temperature, or the heat setting temperature, or by adjusting the amount of components with a molecular weight of 100,000 or less in the polypropylene resin. However, it may increase with the addition of anti-blocking agents or the application of a sealing layer.

[0059] (FHAM of diffraction peaks originating from oriented crystals) In the azimuthal angle dependence of the scattering peak of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray measurement perpendicular to the film surface of the adhesive biaxially oriented polypropylene film of the present invention, the upper limit of the full width at half maximum (Wh) of the diffraction peak originating from the orientation crystals in the width direction of the film is 26°, preferably 25° or less, more preferably 24° or less, particularly preferably 23° or less, and most preferably 22.0° or less. A full width at half maximum (Wh) of 26° or less makes it easier to increase the rigidity of the film. The lower limit of Wh is preferably 15°, more preferably 16°, and even more preferably 17°.

[0060] (X-ray orientation degree) The lower limit of the X-ray orientation degree calculated from Wh of the adhesive biaxially oriented polypropylene film of the present invention by the following formula is preferably 0.856, more preferably 0.861, even more preferably 0.867, particularly preferably 0.872, and most preferably 0.878. Setting it to 0.856 or higher makes it easier to increase rigidity. X-ray orientation degree=(180-Wh) / 180 The upper limit of the X-ray orientation degree is preferably 0.917, more preferably 0.911, and even more preferably 0.906. By setting it to 0.917 or less, film formation is likely to be stable.

[0061] (Loop stress) The lower limit of the loop stress S (mN) in the longitudinal direction at 23°C of the biaxially oriented polypropylene film of the present invention is 0.00020×t when the thickness of the biaxially oriented polypropylene film is t (μm). 3 and preferably 0.00025×t 3 and more preferably 0.00030×t 3 and even more preferably 0.00035×t 3 When it is 0.00020×t or more, the film rigidity is high, so wrinkles are less likely to occur during drying of the adhesive coating film, and furthermore, curling is less likely to occur in the film after adhesive processing. Also, when used as an adhesive label, it is easily peeled off from the release paper, and productivity is likely to be improved. The upper limit of the loop stress S (mN) in the longitudinal direction at 23°C is preferably 0.00080×t. 3 and more preferably 0.00075×t, and even more preferably 0.00072×t 3 and particularly preferably 0.00070×t 3 When it is 0.00080×t 3 or less, it is realistically easy to manufacture. The lower limit of the loop stress S (mN) in the width direction at 23°C of the biaxially oriented polypropylene film of the present invention is 0.0010×t when the thickness of the biaxially oriented polypropylene film is t (μm). 3 and preferably 0.0011×t 3 and more preferably 0.0012×t 3 and even more preferably 0.0013×t 3 When it is 0.0010×t 3As a result of the above, the film has high rigidity, making it less likely for wrinkles to form during the drying of the adhesive coating, and further reducing the likelihood of curling in the film after adhesive processing. In addition, when used as an adhesive label, it peels easily from the release paper, improving productivity. The upper limit of the loop stiffness stress S (mN) in the width direction at 23°C is preferably 0.0020 × t 3 Therefore, more preferably 0.0019 × t 3 And more preferably 0.0018 × t 3 And, particularly preferably, 0.0017 × t 3 Therefore, it is practically easier to manufacture if the thickness is 0.0020 × t3 or less.

[0062] Loop stiffness stress is an indicator of the stiffness of a film, but it also depends on the thickness of the film. The measurement method is as follows: Two strips measuring 110 mm x 25.4 mm were cut out, with the longitudinal direction of the film as the major axis of the strip (loop direction), or the width direction of the film as the major axis of the strip (loop direction). These were clipped together to create measurement loops, one where one side of the film is the inner surface of the loop, and the other where the opposite side is the inner surface of the loop, for both the longitudinal and width directions of the strip. The measurement loop with the major axis of the strip being the longitudinal direction of the film was set in the chuck of a Loop Stiffness Tester DA manufactured by Toyo Seiki Co., Ltd. with the width direction perpendicular, the clip was removed, and the loop stiffness stress was measured with a chuck spacing of 50 mm, a compression depth of 15 mm, and a compression speed of 3.3 mm / second.

[0063] The measurements involved measuring the loop stiffness stress and thickness five times with one side of the film facing the inner surface of the loop, and then measuring five more times with the other side facing the inner surface of the loop. Using this total of 10 sets of data, the cube of the thickness of each test specimen was plotted on the x-axis and its loop stiffness stress on the y-axis. The slope 'a' was calculated by approximating the plot with a straight line having an intercept of 0. The slope 'a' value represents a characteristic value inherent to the film that does not depend on the thickness determining the stiffness. Measurement loops with the long axis of the strip aligned with the width direction of the film were measured in the same manner.

[0064] (Adhesive biaxially oriented polypropylene film with an adhesive coating layer (adhesive film)) The biaxially oriented polypropylene film for adhesive use of the present invention is used as an adhesive film by applying an adhesive to its surface. The wettension of the surface of the biaxially oriented polypropylene film to which the adhesive is applied is preferably 38 mN / m or higher. A wettension of 38 mN / m or higher improves adhesion with the adhesive coating layer. To achieve a wettension of 38 mN / m or higher, it is preferable to perform physicochemical surface treatments such as corona treatment, flame treatment, or plasma treatment. For example, in corona treatment, it is preferable to use a preheating roll and a treatment roll and perform discharge in the air. The wettension is preferably 44 mN / m or lower, more preferably 43 mN / m or lower, and even more preferably 42 mN / m or lower.

[0065] Examples of adhesives to be applied to the biaxially oriented polypropylene film for adhesive purposes of the present invention include adhesives composed of components such as acrylic resins, urethane resins, natural and synthetic rubbers (sorbene rubber, butyl rubber, styrene rubber (SEBS, SBS, SIS, etc.)), silicone rubbers, and nitrile rubbers. Silicone rubbers and acrylic resins, which have excellent heat resistance, are particularly preferred.

[0066] Silicone-based rubber is suitable as an adhesive in this invention because it has excellent heat resistance and weather resistance. A platinum group metal catalyst can be used as a crosslinking agent for silicone-based rubber.

[0067] Acrylic resins are suitable as adhesives in the present invention because they have excellent heat resistance, transparency, and weather resistance. Acrylic resins are copolymers of one or more acrylic monomers having functional groups such as hydroxyl groups, tertiary amino groups, carboxyl groups, amide groups, and nitrile groups, and monomers such as alkyl (meth)acrylates, vinyl acetate, vinyl propionate, vinyl ethers, and styrene. Examples of adhesives containing acrylic resins include Olivine BPS3156D, BPS3180-3A, BPS3713, BPS4891, BPW5689J, and BPW5320, all manufactured by Toyo Chem Co., Ltd.

[0068] The adhesive coating layer in the present invention may contain particles with a particle size of 1 μm or less, but from the viewpoint of pinhole generation, it is preferable to substantially omit any particles or other materials that form protrusions. The adhesive coating layer in the present invention may contain additives such as adhesion enhancers and antistatic agents. Furthermore, to improve adhesion to the substrate, it is preferable to pre-treat the surface of the biaxially oriented polypropylene film for adhesion, such as anchor coating, corona treatment, plasma treatment, or atmospheric pressure plasma treatment, before applying the adhesive coating layer. On the other hand, the surface opposite the adhesive-coated layer of the biaxially oriented polypropylene film for adhesive use may be coated with a release agent to facilitate the separation of the adhesive layer from the substrate layer. The release agent to be applied is not particularly limited, and silicone resins, fluororesins, alkyd resins, various waxes, aliphatic olefins, etc., can be used, and each resin can be used alone or in combination of two or more types.

[0069] The thickness of the adhesive coating layer in this invention can be set according to its intended use and is not particularly limited, but preferably, the thickness of the adhesive coating layer after curing is in the range of 1 to 40 μm. A thickness of 1 μm or more of the adhesive coating layer is preferable because it enhances tackiness. Furthermore, a thickness of 40 μm or less of the adhesive coating layer is preferable because it prevents the curing time from becoming too long and allows for the production of a highly adhesive film.

[0070] In the present invention, the method for forming the adhesive coating layer is not particularly limited. A coating solution containing a dissolved or dispersed adhesive resin is applied to one side of an adhesive biaxially oriented polypropylene film substrate. After removing the dissolved resin by drying, the film is heated, heat-cured, or UV-cured. In this case, the drying temperature during solvent drying or heat curing is preferably 100 to 170°C. If the drying temperature is higher than 170°C, wrinkles may occur in the film due to heat. On the other hand, if the drying temperature is low, the adhesive coating layer may not be sufficiently heat-cured, resulting in insufficient adhesion or requiring excessive drying time. Biaxially oriented polypropylene films have lower thermal dimensional stability at high temperatures compared to biaxially oriented polyester films, making them prone to wrinkles during drying of the coating film. However, the adhesive biaxially oriented polypropylene film of the present invention can suppress the occurrence of wrinkles. The heating drying time is generally 10 to 300 seconds.

[0071] Any known coating method can be applied to the above-mentioned adhesive coating liquid. For example, conventional methods such as the comma coating method, gravure coating method, reverse coating method, bar coating method, die coating method, spray coating method, and air knife coating method can be used.

[0072] The adhesive film based on the biaxially oriented polypropylene film for adhesives of the present invention has good heat resistance and can be used at high temperatures. The upper limit of the thermal shrinkage rate in the longitudinal direction of the adhesive film at 150°C is 10%, preferably 7.0%, more preferably 6.0%, even more preferably 5.0%, and particularly preferably 4.0% or less. The upper limit of the thermal shrinkage rate in the width direction at 150°C is 30%, preferably 20%, more preferably 16%, and particularly preferably 15% or less. It is preferable that the above-mentioned adhesive film has a thermal shrinkage rate of 10% or less in the longitudinal direction and 30% or less in the width direction at 150°C, as this makes it less likely for the label to curl, wrinkle, or peel off when the adhesive film is used as an adhesive label in a high-temperature environment.

[0073] The adhesive strength of the above adhesive film can be designed by selecting the adhesive and the thickness of the adhesive layer according to the required adhesive strength. When strong adhesive strength is required, it is preferable that the adhesive strength measured at a peel angle of 180 degrees in accordance with JIS Z0237 be 400 gf / 25 mm or more, and more preferably 700 gf / 25 mm or more. When particularly strong adhesive strength is required, it is preferable to have 2000 gf / 25 mm or more. For adhesive films for low-tack applications, it is preferable that the adhesive strength measured at a peel angle of 180 degrees be 1 to 100 gf / 25 mm, and more preferably 3 to 80 gf / 25 mm. [Examples]

[0074] The present invention will be described in detail below with reference to examples. The characteristics were measured and evaluated by the following methods. (1) Melt flow rate The melt flow rate (MFR) was measured in accordance with JIS K7210, at a temperature of 230°C and a load of 2.16 kgf.

[0075] (2) Mesopentat fraction The measurement of the mesopentad fraction ([mmmm]%) of polypropylene resin is performed as follows: 13 The analysis was performed using 1C-NMR. The mesopentade fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13 ¹

[0076] (3) Number average molecular weight, weight average molecular weight, amount of components with a molecular weight of 100,000 or less, and molecular weight distribution of polypropylene resin Gel permeation chromatography (GPC) was used to determine the molecular weight in terms of PP equivalent, based on monodisperse polystyrene. When the baseline was not clear, the baseline was set within the range from the lowest point of the high molecular weight tail of the elution peak closest to the elution peak of the standard substance. The GPC measurement conditions are as follows: Equipment: HLC-8321PC / HT (manufactured by Tosoh Corporation) Detector: RI Solvent: 1,2,4-Trichlorobenzene + Dibutylhydroxytoluene (0.05%) Column: TSKgelguardcolumnHHR(30)HT (7.5mm I.D. × 7.5cm) × 1 + TSKgelGMHHR-H(20)HT (7.8mm I.D. × 30cm) × 3 Flow rate: 1.0mL / min Injection volume: 0.3mL Measurement temperature: 140℃ The number-average molecular weight (Mn) and mass-average molecular weight (Mw) are obtained by analyzing the molecular weight (M) at each elution position of the GPC curve obtained via the molecular weight calibration curve. i Number of molecules (N) i Defined by the following equation It can be done. Number average molecular weight: Mn=Σ(N i ·M i ) / ΣN i Mass average molecular weight: Mw=Σ(N i ·M i 2 ) / Σ(N i ·M i ) Here, the molecular weight distribution can be obtained as Mw / Mn. Furthermore, the proportion of components with a molecular weight of 100,000 or less was determined from the integral curve of the molecular weight distribution obtained by GPC.

[0077] (4) Crystallization temperature (Tc), melting temperature (Tm) Thermal measurements were performed under a nitrogen atmosphere using a Q1000 differential scanning calorimeter manufactured by T.A. Instruments. Approximately 5 mg of polypropylene resin pellets were cut out and sealed in an aluminum pan for measurement. The temperature was raised to 230°C and held for 5 minutes, then cooled to 3°C at a rate of -10°C / min, and the exothermic peak temperature was defined as the crystallization temperature (Tc). The heat of crystallization (ΔHc) was determined by setting a baseline so that the area of ​​the exothermic peak was smoothly connected from the start to the end of the peak. The temperature was then held at 30°C for 5 minutes, and then raised to 230°C at a rate of 10°C / min, and the main endothermic peak temperature was defined as the melting temperature (Tm).

[0078] (5) Film thickness

[0079] The film thickness was measured using a Seiko EM Miltron 1202D. (6) Hayes Measurements were taken using an NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. at 23°C in accordance with JIS K7105.

[0080] (7) Tensile test The tensile strength in the longitudinal and widthwise directions of the film was measured at 23°C in accordance with JIS K7127. Samples were cut from the film to a size of 15 mm x 200 mm, and the chuck width was 100 mm. The samples were then set on a tensile testing machine (Instron 5965, a dual-column benchtop testing machine manufactured by Instron Japan Company Limited). Tensile tests were performed at a tensile speed of 200 mm / min. The tensile modulus was calculated from the initial slope of the obtained strain-stress curve, and the tensile breaking strength and tensile breaking elongation were determined from the strength and elongation at the time the sample broke.

[0081] (8) Thermal shrinkage The following method was used to measure the film's properties, in accordance with JIS Z1712. The film was cut to a length of 20 mm in width and length, both in the longitudinal and width directions, and then suspended in a hot air oven at 120°C or 150°C for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the length shrunk to the original length.

[0082] (9) Refractive index, ΔNy, surface orientation coefficient, average refractive index Measurements were taken using an Abbe refractometer manufactured by Atago Corporation at a wavelength of 589.3 nm and a temperature of 23°C. The refractive indices along the longitudinal and width directions of the film were denoted as Nx and Ny, respectively, and the refractive index along the thickness direction was denoted as Nz. ΔNy was calculated using Nx, Ny, and Nz with the formula Ny - [(Nx + Nz) / 2]. The surface orientation coefficient (ΔP) was calculated using the formula [(Nx + Ny) / 2] - Nz. The average refractive index was calculated using the formula (Nx + Ny + Nz) / 3.

[0083] (10) X-ray full width at half maximum, X-ray orientation Measurements were performed using the transmission method with an X-ray diffractometer (SmartLab, Rigaku Corporation, with αβγ attachments). X-rays with a wavelength of 1.5418 Å were used, with an X-ray output of 45 kV and 200 mA. A hybrid multidimensional pixel detector, Hypix-3000, was used in 0-dimensional mode. For the parallel beam method, a 2.5° solar slit, a 10 mm longitudinal limiting slit, and a 1 mm wide incident slit were used as the incident slit. A 0.228° parallel slit analyzer was used as the receiving slit. The camera length was 300 mm, and the detector integration width was 2 mm. A sample was prepared by stacking films to a thickness of 400 μm. The detector was placed at the diffraction peak position (diffraction angle 2θ = 14.1°) of the (110) plane of the α-type crystal of polypropylene resin, and the sample was rotated 360° around the thickness direction of the film to obtain the azimuthal angle dependence of the diffraction intensity of the (110) plane. The step interval was 0.5° and the measurement speed was 60° / min. From this azimuthal angle dependence, the full width at half maximum (FWH) of the diffraction peak originating from the oriented crystals in the width direction of the film was determined. Furthermore, the degree of X-ray orientation was calculated using Wh and the following formula. X-ray orientation degree=(180-Wh) / 180

[0084] (11) Ratio of unconstrained amorphous component (III) determined by pulsed NMR The film is cut, and the cut film is packed into a glass tube with an outer diameter of 10 mm until it reaches a height of 1 cm. The biaxially oriented polypropylene film is then measured using the following measuring device and under the following conditions. 1 The spin-spin relaxation time T2 of the H nucleus was measured to obtain a decay curve of the magnetization intensity. Equipment: BRUKER Minispec mq20 Temperature: 40℃ Observation frequency: 20MHz 90° pulse width: 2.74 μs Pulse repetition time: 2.0s Pulse mode: Solido Echo method Total number of times: 128 Recycle Delay: 4s Acquisition Scale: 0.1 ms The measurement began after placing a glass tube filled with biaxially oriented polypropylene film into the apparatus and maintaining the temperature for 15 minutes. The component with the shortest relaxation time was separated using the least squares method with a Gaussian function, and the second and third shortest components with a Lorentz function, so that the resulting magnetization intensity decay curve matched the fitting curve. The proportions of each were obtained. The component with the shortest relaxation time corresponds to the crystalline component (I), and the second and third shortest components correspond to the constrained amorphous component (II) and the unconstrained amorphous component (III), respectively. The fitting and analysis were performed using the software (TD-NMR Analyzer) included with the above-mentioned measurement apparatus. The ratio of the unconstrained amorphous component (III) was calculated using the following formula (1) as the ratio (%) of the amorphous component (III) to the total of the crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) obtained by the above method. Ratio of unconstrained amorphous component (III) = M III / (M I +M II +M III ) ...(1) M I : Amount of crystalline component (I) M II : Amount of constrained amorphous component (II) MIII : Amount of unconstrained amorphous component (III)

[0085] (12) Wetting tension (mN / m) In accordance with JIS K 6768:1999, the film was exposed to air at 23°C and 50% relative humidity for 24 hours. After aging, the corona-treated surface of the film was measured using the following procedure. Step 1) Measurements are performed in a standard test room atmosphere with a temperature of 23°C and a relative humidity of 50% (see JIS K 7100). Step 2) Place the test specimen on the substrate of the hand coater (4.1), drop a few drops of the test mixture onto the specimen, and immediately pull the wire bar to spread it out. When spreading the test mixture using a cotton swab or brush, ensure the liquid is spread to at least 6 cm. 2 Spread it quickly over the area described above. The amount of liquid should be just enough to form a thin layer, without creating any pools. The wetting tension is determined by observing the liquid film of the test mixture in a bright place and checking its condition after 3 seconds. If the liquid film does not break and maintains its state after 3 seconds or more, it is considered wet. If the wettiness is maintained for 3 seconds or more, proceed to the next liquid mixture with higher surface tension. Conversely, if the liquid film breaks in less than 3 seconds, proceed to the next liquid mixture with lower surface tension. Repeat this process to select a mixture that can accurately wet the surface of the test specimen in 3 seconds.

[0086] (13) Evaluation of adhesiveness From a roll of biaxially oriented polypropylene film (adhesive film) coated with the adhesive described in the examples, a piece of adhesive film measuring 25 mm in width and 150 mm in length was cut so that the width direction was the longer side, and this was used as a sample for peel strength measurement. Using a peel tester (Kyowa Interface Science Co., Ltd., VPA-3), the film was peeled at a peel angle of 180 degrees in accordance with JIS Z0237. After adhering the film to a stainless steel plate (SUS304) polished with #280 grit sandpaper and leaving it for 30 minutes, the adhesive strength was measured by peeling it off at 180 degrees at a peel speed of 300 mm / min under conditions of 25°C and 60% relative humidity. The adhesiveness was determined based on the obtained adhesive strength values ​​according to the following criteria. ○:400gf / 25mm or more ×: Less than 400gf / 25mm

[0087] (14) Adhesive film curl A 10cm x 10cm piece of adhesive film was cut from a roll of biaxially oriented polypropylene film (adhesive film) coated with the adhesive described in the examples. The adhesive film sample was placed on a glass plate with the adhesive side facing upwards, and the height of the portion floating above the glass plate was measured. The curl that occurred in the adhesive film was evaluated by the following method. At this time, the height of the part that was most significantly lifted from the glass plate was used as the measurement. The curling properties were evaluated according to the following criteria. ○: Curl is 5mm or less ×: Curl is larger than 5mm

[0088] (15) Wrinkles in adhesive film rolls The biaxially oriented polypropylene film coated with the adhesive described in the example was unwound from a roll, and the wrinkles generated in the adhesive film were evaluated by the following method. Specifically, a 60cm wide adhesive film was suspended in a room at 25°C and 65% humidity with its longitudinal direction perpendicular to the surface, and a load of 10N / m was applied and left undisturbed for 30 minutes. A fluorescent light was projected onto the film surface from 1m away from the surface where the number of continuous corrugated wrinkles in the longitudinal direction was to be counted, at a 45° angle above. The number of wrinkles was then visually counted from 0.5m away from the surface where the wrinkles were to be counted, at a 45° angle below. A wrinkle was defined as one convex wrinkle in the longitudinal direction of the film relative to the surface being observed, and the number of wrinkles in the width direction of the film was counted. ○: Number of wrinkles is 10 or less per meter ×: More than 11 wrinkles per meter.

[0089] (Example 1) (Method for manufacturing biaxially oriented polypropylene film for adhesive use) As the polypropylene resin, 80 parts by weight of propylene homopolymer PP-1 (Sumitomo Noblen FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.), with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C, was blended with 20 parts by weight of propylene homopolymer PP-2 (EL80F5, manufactured by Sumitomo Chemical Co., Ltd.), with MFR = 11 g / 10 min, [mmmm] = 98.8%, Tc = 116.5°C, and Tm = 161.5°C. The material was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then immersed in a 20°C water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction using two pairs of rolls at 142°C, then clipped at both ends and guided into a hot air oven. After preheating to 170°C, it was stretched 10 times in the width direction at 162°C as the first stage. Immediately after the width stretching, it was cooled at 120°C while still held by the clips, and then re-stretched 1.2 times in the width direction at 175°C. After cooling to room temperature, one side surface of the film was treated with corona treatment using a corona treatment machine manufactured by Softal Corona and Plasma GmbH at an applied current of 0.75A, and then wound up with a winder. The thickness of the resulting film was 18.6 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, the resulting film exhibits excellent rigidity and low thermal shrinkage at high temperatures.

[0090] (Preparation of biaxially oriented polypropylene film coated with adhesive) An acrylic adhesive coating solution (100 parts by mass of Olivine BPS3156D acrylic adhesive manufactured by Toyo Chem Co., Ltd., and 3 parts by mass of BHS8515 curing agent) was applied to the corona-treated surface of a roll of biaxially oriented polypropylene film for adhesive use using a coater to achieve a thickness of 25 μm after drying. The adhesive layer was dried for 20 seconds at a conveying tension of 2000 kPa and a drying temperature of 150°C using an air-float conveying dryer with a distance of 38 cm between the lower and upper air outlets, to obtain an adhesive film. After drying, the film was cooled at a rate of 20°C / second using a 50°C cooling roll, and then wound into a roll to obtain an adhesive film roll. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties were excellent in rigidity, with a low thermal shrinkage rate at high temperatures. The adhesive film coated with the adhesive had excellent adhesion and was a smooth film without wrinkles or curls.

[0091] (Example 2) The procedure was the same as in Example 1, except that the film was re-stretched 1.2 times in the width direction at 165°C. The thickness of the obtained film was 18.4 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were excellent, with very good rigidity, low thermal shrinkage at high temperatures, and the adhesive film coated with adhesive had excellent adhesion and was a smooth film without wrinkles or curls.

[0092] (Example 3) The procedure was the same as in Example 1, except that the film was stretched longitudinally at 147°C, then stretched 10 times in the width direction as the first stage at 165°C, cooled at 120°C while still held in clips immediately after the width direction stretching, and then re-stretched 1.2 times in the width direction at 177°C. The thickness of the obtained film was 18.9 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties include high rigidity, low thermal shrinkage at high temperatures, and when an adhesive is applied, the resulting film is highly adhesive, smooth, and free from wrinkles or curls.

[0093] (Example 4) The procedure was the same as in Example 3, except that the film was re-stretched 1.1 times in the width direction at 177°C. The thickness of the obtained film was 20.6 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties include high rigidity, low thermal shrinkage at high temperatures, and when an adhesive is applied to the film, it exhibits excellent adhesion and is a smooth film free from wrinkles and curls.

[0094] (Comparative Example 1) The procedure was the same as in Example 1, except that the first stage involved stretching 12 times in the width direction at 162°C, followed by cooling at 100°C while still held in a clip immediately after stretching in the width direction, and then heat-setting at 170°C while maintaining a constant width. The thickness of the obtained film was 20.8 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, although its physical properties show high rigidity, its thermal shrinkage rate at high temperatures is poor, and wrinkles and curls occurred in the adhesive film when adhesive was applied, resulting in poor processing suitability as an adhesive film.

[0095] (Comparative Example 2) The procedure was the same as in Example 1, except that the first stage of stretching in the width direction was performed at 162°C to a 12-fold increase, and immediately after stretching in the width direction, the film was held in place by clips and heat-set at 172°C while maintaining a constant width without cooling. The thickness of the obtained film was 23.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties were poor, with low rigidity, and the adhesive film coated with adhesive developed wrinkles and curls, resulting in poor processing suitability as an adhesive film.

[0096] (Comparative Example 3) The procedure was the same as in Example 1, except that the first stage involved stretching 12 times in the width direction at 168°C, followed by cooling at 100°C while still held in a clip immediately after stretching in the width direction, and then heat-setting at 170°C while maintaining a constant width. The thickness of the obtained film was 18.7 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties include a high thermal shrinkage rate at high temperatures and poor rigidity. As a result, the adhesive film coated with adhesive developed wrinkles and curls, making it unsuitable for processing as an adhesive film.

[0097] (Comparative Example 4) As the polypropylene resin, PP-3 (manufactured by Nippon Polypropylene Co., Ltd., FL203D) with MFR = 3g / 10 min, [mmmm] = 94.8%, Tc = 117.2℃, and Tm = 160.6℃ was used. It was extruded into a sheet from a T-die at 250℃, brought into contact with a cooling roll at 20℃, and then immediately placed in a 20℃ water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction at 130℃, and in the widthwise stretching on a tenter, the preheating temperature was set to 168℃, and the first stretching stage was performed at 155℃ to a ratio of 8.2 times. Immediately after widthwise stretching, it was cooled at 120℃ while still held in a clip, and then re-stretched 1.2 times in the widthwise direction at 170℃. Finally, it was cooled at room temperature. The thickness of the obtained film was 18.8 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties include a high thermal shrinkage rate at high temperatures and poor rigidity. As a result, wrinkles and curls occurred in the adhesive film when the adhesive was applied, making it unsuitable for processing as an adhesive film.

[0098] (Comparative Example 5) As in Example 1, a blend of PP-1 and PP-2 was used as the polypropylene resin, and a film was obtained under the film-forming conditions shown in Table 2, in which the film was heat-treated at 168°C without re-stretching in the width direction. The thickness of the obtained film was 20.0 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties show that while the thermal shrinkage rate at high temperatures is low, its rigidity is also poor. As a result, the adhesive film coated with adhesive developed wrinkles and curls, making it unsuitable for processing as an adhesive film.

[0099] (Comparative Example 6) Using PP-4 (manufactured by Nippon Polypropylene Co., Ltd., SA4L) as the polypropylene resin, with MFR = 5 g / 10 min, [mmmm] = 97.3%, Tc = 116.8°C, and Tm = 161.6°C, a film was obtained by heat treatment at 168°C without re-stretching in the width direction as shown in Table 2. The thickness of the obtained film was 20.0 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, its physical properties include a high thermal shrinkage rate at high temperatures and poor rigidity. As a result, wrinkles and curls occurred in the adhesive film when the adhesive was applied, making it unsuitable for processing as an adhesive film.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Table 3] [Industrial applicability]

[0103] The biaxially oriented polypropylene film for adhesives of the present invention has high rigidity and can be made into a thin film. Even when the film is made into a thin film, it is easy to peel off, wrinkles do not easily occur when the adhesive dries, and curling occurs little in the film after coating, making it suitable for use as an adhesive film.

Claims

1. A biaxially oriented polypropylene film for adhesive use that satisfies the following conditions (1) to (4). (1) When separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) as determined by pulsed NMR using the solid echo method, the ratio of (III) is 7% or less. (2) The relationship between the loop stiffness stress (S) in the width direction and the thickness (t) satisfies the following equation. S [mN] ≥ 0.0010 × thickness (μm) ３ (3) The mesopentat fraction of the polypropylene resin constituting the film is 97.0% or more. (4) The melt flow rate of the polypropylene resin constituting the film is 4.0 g / 10% or more.

2. The adhesive biaxially oriented polypropylene film according to claim 1, wherein the thermal shrinkage rate of the adhesive biaxially oriented polypropylene film after heating at 150°C for 5 minutes is 10% or less in the longitudinal direction and 30% or less in the width direction.

3. The adhesive biaxially oriented polypropylene film according to claim 1 or 2, wherein the refractive index Ny in the width direction of the adhesive biaxially oriented polypropylene film is 1.5250 or more, and ΔNy is 0.0240 or more.

4. The adhesive biaxially oriented polypropylene film according to claim 1 or 2, wherein the haze of the adhesive biaxially oriented polypropylene film is 5.0% or less.

5. The adhesive biaxially oriented polypropylene film according to claim 1 or 2, wherein the polypropylene resin constituting the adhesive biaxially oriented polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 160°C or higher.

6. The adhesive biaxially oriented polypropylene film according to claim 1 or 2, wherein the amount of polypropylene resin with a molecular weight of 100,000 or less constituting the adhesive biaxially oriented polypropylene film is 35% by mass or more.

7. An adhesive film comprising an adhesive coating layer laminated on at least one side of an adhesive biaxially oriented polypropylene film according to claim 1 or 2.

8. The adhesive film according to claim 7, wherein the adhesive coating layer comprises a silicone rubber and / or an acrylic resin.

9. The adhesive film according to claim 8, wherein the thermal shrinkage rate of the adhesive film after heating at 150°C for 5 minutes is 10% or less in the longitudinal direction and 30% or less in the width direction.

Images