Biaxially oriented polypropylene film, and a label made using the same

Abstract

The object of this invention is to provide a biaxially oriented polypropylene film that has excellent abrasion resistance, prevents printed information from fading easily, and can be suitably used as a label for properly managing components that are exposed to high-temperature environments for long periods of time. [Solution] L in reflective color tone * A biaxially oriented polypropylene film characterized by satisfying the following conditions 1 and 2, where the surface with a value of 50.0 or more and 100 or less is defined as surface A, the direction of the main orientation axis of the film is the X direction, and the direction perpendicular to the X direction within the film surface is the Y direction. Condition 1: At least one side is side A. Condition 2: After heat treatment at 150°C for 30 minutes, the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction is 0.0% or more and 5.0% or less.

Description

Technical Field

[0001] The present invention relates to a biaxially oriented polypropylene film and a label using the same.

Background Art

[0002] A biaxially oriented polypropylene film is excellent in transparency, chemical resistance, and releasability of the polypropylene resin, and also has excellent mechanical properties, moisture resistance, and electrical properties due to the orientation of the polypropylene molecular chains. Therefore, the biaxially oriented polypropylene film is used in various applications such as packaging applications, electrical applications such as cable wrapping and capacitors, tape base material applications, protective cover applications, and label applications.

[0003] Labels are used, for example, for the purpose of attaching a white base film printed with information or a pattern on the surface to an adherend and imparting design properties such as information and patterns to the adherend. In recent years, the information to be printed (hereinafter sometimes referred to as printed information) has shifted to two-dimensional code information typified by character information barcodes and "QR codes" (registered trademarks), and complex pattern printing has become possible due to the improvement of printing technology, and the information value of the label itself has increased. Also, highly functional labels that can be used in harsh environments are required. For example, particularly in a high-temperature environment, a heat-resistant label that can be used without significantly reducing the visibility of the printed information due to peeling or wrinkling deformation of the label is required.

[0004] For example, labels for managing automotive components are exposed to radiant heat from the engine room where the temperature reaches several hundred degrees during driving, high-temperature exhaust gases, and outdoor sunlight, etc., and are thus exposed to a high-temperature environment for a long time. Therefore, labels used for such applications are required to have dimensional stability in a high-temperature environment. Against this background, polyethylene terephthalate (PET) films, which have excellent dimensional stability in a high-temperature environment, have been used for labels used in temperature ranges exceeding 150°C. However, most of the plastic components installed in automobiles are made of polypropylene resin, and due to regulations based on environmental issues and the need to improve the recycling rate of plastic components, the demand for white labels based on biaxially oriented polypropylene films is increasing.

[0005] On the other hand, conventional biaxially oriented polypropylene films begin to shrink significantly from around 120 to 130°C and start to melt around 160°C near the melting point, resulting in a significant decrease in film rigidity. Therefore, when using a biaxially oriented polypropylene film as a label in a high-temperature environment, problems such as label peeling and a decrease in the visibility of printed information due to wrinkle formation become issues.

[0006] As white biaxially oriented polypropylene films, for example, Patent Documents 1 to 3 disclose biaxially oriented polypropylene films containing a large amount of large-diameter inorganic particles such as calcium carbonate, and biaxially oriented polypropylene films in which a void structure (void structure) is formed in the film by adding large-diameter organic particles and applying a stretching process.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0008] However, the biaxially oriented polypropylene films described in Patent Documents 1 to 3 all acquire whiteness by forming a void structure around organic or inorganic particles during the stretching process. Therefore, in order to maintain the formed void structure, a low-temperature stretching process is required, which results in residual stress and strain within the film, making it difficult to apply to components that are exposed to high-temperature environments for extended periods.

[0009] The present invention aims to provide a biaxially oriented polypropylene film that offers excellent abrasion resistance, prevents printed information from easily fading, and can be suitably used as a label for properly managing components exposed to high-temperature environments for extended periods. [Means for solving the problem]

[0010] To solve the above problems, a preferred embodiment of the present invention has the following configuration. [I] L in reflective tones * A biaxially oriented polypropylene film characterized by satisfying the following conditions 1 and 2, where the surface with a value of 50.0 or more and 100 or less is defined as surface A, the direction of the main orientation axis of the film is the X direction, and the direction perpendicular to the X direction within the film surface is the Y direction. Condition 1: At least one side is side A. Condition 2: After heat treatment at 150°C for 30 minutes, the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction is 0.0% or more and 5.0% or less. [II] The biaxially oriented polypropylene film according to [I], wherein when the 60° gloss in the X direction on surface A is GX (%) and the 60° gloss in the Y direction on surface A is GY (%), the average value of GX and GY is 21 or more and 50 or less. [III] A biaxially oriented polypropylene film according to [I] or [II], having a melting point of 176°C or higher and 185°C or lower. [IV] A biaxially oriented polypropylene film according to any one of [I] to [III], wherein at least one of the deformation rate in the X direction and the deformation rate in the Y direction is 0.0% or more and 1.5% or less after heat treatment at 150°C for 30 minutes. [V] A biaxially oriented polypropylene film according to any one of [I] to [IV], wherein the Young's modulus in at least one of the X direction and the Y direction is 1.5 GPa or more and 4.0 GPa or less. [VI] The reflective color of surface A after heat treatment at 150°C for 30 minutes, L * Change in value is ΔL * When this is the case, the ΔL * A biaxially oriented polypropylene film according to any one of [I] to [V], wherein the ratio is between -1.5 and 1.5. [VII] A biaxially oriented polypropylene film according to any one of [I] to [VI], wherein when the layer having surface A is defined as the P1 layer, the amount of white particles in the total constituent components of the P1 layer is 3.0% by mass or more and 30.0% by mass or less. [VIII] A biaxially oriented polypropylene film according to any one of [I] to [VII], wherein the layer having surface A is the P1 layer, and the P1 layer contains white particles having an average secondary particle diameter of 100 nm or more and less than 500 nm. [IX] A biaxially oriented polypropylene film according to any one of [I] to [VIII], wherein the surface free energy of the A surface is 34 mN / m or more and 70 mN / m or less. [X] A biaxially oriented polypropylene film according to any one of [I] to [IX], wherein the layer having surface A is the P1 layer, and the P1 layer contains a polypropylene resin having carboxylic acid terminators. [XI] A biaxially oriented polypropylene film according to any one of [I] to [X], wherein when the layer having surface A is designated as the P1 layer, one of the outermost layers is the P1 layer and the other outermost layer is the adhesive layer. A label made using a biaxially oriented polypropylene film as described in any of [XII] [I] to [XI]. [XIII] A label described in [XII] that is affixed to a polypropylene resin molded body. A polypropylene resin molded body with the labels described in [XIV] and [XII] affixed to it. [Effects of the Invention]

[0011] The present invention provides a biaxially oriented polypropylene film that is highly resistant to abrasion, prevents printed information from fading easily, and can be suitably used as a label for properly managing components that are exposed to high-temperature environments for extended periods. [Modes for carrying out the invention]

[0012] The biaxially oriented polypropylene film of the present invention will be described in detail below. The biaxially oriented polypropylene film of the present invention has L in reflective color tone. * This is a biaxially oriented polypropylene film characterized by satisfying the following conditions 1 and 2, when the surface with a value of 50.0 or more and 100 or less is defined as surface A, the direction of the main orientation axis of the film is the X direction, and the direction perpendicular to the X direction within the film surface is the Y direction. Condition 1: At least one side is side A. Condition 2: After heat treatment at 150°C for 30 minutes, the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction is 0.0% or more and 5.0% or less.

[0013] This embodiment provides a biaxially oriented polypropylene film that is highly abrasion-resistant, prevents printed information from easily fading, and is suitable for use as a label for properly managing components exposed to high-temperature environments for extended periods. In the biaxially oriented polypropylene film of the present invention, side A may be one side or both sides, and each requirement specified for side A only needs to be met on at least one side (it is preferable that both sides be met).

[0014] (Polypropylene film) In this invention, the term "polypropylene film" refers to a film whose main component is polypropylene resin. Here, "main component" refers to a component that is present in greater than 50% by mass and less than or equal to 100% by mass of the total components of the film (100% by mass). Details of the polypropylene resin will be described later.

[0015] (Biaxially oriented polypropylene film) The biaxially oriented polypropylene film of the present invention exhibits improved mechanical strength due to the biaxial orientation of its molecular chains. As a result, it is less prone to wrinkling at room temperature and high temperature environments compared to unoriented polypropylene films. Therefore, when a biaxially oriented polypropylene film is used as a base film for labels, it is less likely to wrinkle when applied to an substrate, and it is also less likely to deform when peeled off, making reapplication easier.

[0016] Furthermore, by increasing the orientation of the molecular chains of the polypropylene resin and thereby improving the overall crystallinity of the film, the thermal dimensional stability of the biaxially oriented polypropylene film can be enhanced. Therefore, by using such a biaxially oriented polypropylene film as a label substrate, it is possible to simultaneously reduce peeling and wrinkling after prolonged exposure to high-temperature environments and reduce the occurrence of reading errors of printed two-dimensional code information.

[0017] In this context, biaxial orientation refers to the appearance of a biaxial orientation pattern in wide-angle X-ray diffraction. Biaxially oriented polypropylene film can generally be obtained by stretching an unstretched polypropylene film sheet in the direction of the film-making machine (hereinafter sometimes referred to as the longitudinal direction) and in a direction perpendicular to the longitudinal direction within the film plane (hereinafter sometimes referred to as the width direction), and then performing heat treatment to complete the crystal orientation. In the state of a film roll, the winding direction is the longitudinal direction, and the axial direction of the core is the width direction.

[0018] In the biaxially oriented polypropylene film of the present invention, when the longitudinal direction is set to 0°, the Young's modulus is measured in each direction parallel to the film surface and at angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° with respect to the longitudinal direction. The direction showing the highest value is defined as the principal orientation axis of the film, and this is referred to as the X direction (hereinafter, this direction may be referred to as the principal orientation axis or the X direction). Furthermore, the direction perpendicular to the principal orientation axis within the film surface is referred to as the Y direction.

[0019] Furthermore, when biaxially oriented polypropylene film is in the form of a reel or roll, the winding direction of the film can be considered the longitudinal direction. On the other hand, if it is unclear from the appearance of the biaxially oriented polypropylene film which direction corresponds to the longitudinal direction, the direction of any straight line on the film surface can be set as 0°, and the principal orientation axis direction (X direction) can be determined using the method described above as a reference. The Young's modulus can be measured using a known tensile tester, and the details of the measurement method will be described later.

[0020] Furthermore, if the width of the polypropylene film is less than 150 mm and the Young's modulus cannot be measured or calculated using a tensile tester, the crystal orientation of the α(110) plane of the polypropylene film is measured using wide-angle X-rays as follows, and the X and Y directions are determined based on the following criteria. Specifically, X-rays are incident perpendicularly to the film surface, and the crystal peak at 2θ = approximately 14° (α(110) plane) is scanned in the circumferential direction. The direction with the highest diffraction intensity in the obtained diffraction intensity distribution is defined as the principal orientation axis direction (X direction), and the direction perpendicular to this within the film plane is defined as the Y direction.

[0021] The biaxially oriented polypropylene film of the present invention may be a single-layer structure or a laminated structure consisting of two or more layers. Specifically, the biaxially oriented polypropylene film of the present invention can be a single-film structure consisting only of the P1 layer, when the layer having surface A (described later) is designated as the P1 layer. Alternatively, the biaxially oriented polypropylene film of the present invention may be a two-layer structure consisting of P1 / P2 layers, where the P1 layer is the surface layer and a P2 layer (hereinafter sometimes referred to as the core layer) is a layer that accounts for more than 50% of the total thickness, separate from the P1 layer, or a two-type three-layer structure consisting of P1 / P2 / P1 layers. Furthermore, the present invention may have a 2-type 2-layer configuration consisting of P1 / P3 layers, which includes a functional layer P3 layer that forms the opposite surface to the A-side of the biaxially oriented polypropylene film of the present invention, separate from the P1 and P2 layers; a 3-type 3-layer configuration consisting of P1 / P2 / P3 layers; a 3-type 4-layer configuration consisting of P1 / P2 / P1 / P3 layers; or a 4-type 4-layer configuration consisting of P1 / P2 / P1' / P3 layers, where a functional layer P3 layer is provided on a P1 / P2 / P1' layer film using a P1' layer different from the P1 layer; or even more types and numbers of layers. Details regarding the P1, P2, and P3 layers will be described later.

[0022] The biaxially oriented polypropylene film of the present invention has a sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction after heat treatment at 150°C for 30 minutes, where the X direction is the principal orientation axis of the film and the Y direction is the direction perpendicular to the X direction within the film plane. This sum is between 0.0% and 5.0%. Hereinafter, the "sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction after heat treatment at 150°C for 30 minutes" is referred to as the 150°C thermal dimensional stability, and details of the method for measuring the deformation rate will be described later. Here, the absolute value of the deformation rate is an index that represents the degree of deformation, without considering deformation in the positive direction (expansion) or deformation in the negative direction (shrinkage).

[0023] The sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction after heat treatment at 150°C for 30 minutes reflects the thermal dimensional stability of the biaxially oriented polypropylene film when exposed to a high-temperature environment for a long period of time. When the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction after heat treatment at 150°C for 30 minutes in the biaxially oriented polypropylene film is 5.0% or less, it is possible to suppress peeling due to thermal deformation of the label in a high-temperature environment, and the reduction in the visibility of printed information on the surface due to heat wrinkles on the label, when the biaxially oriented polypropylene film is used as a label. The sum of the absolute values ​​of the deformation rate is more preferably 3.5% or less, even more preferably 2.5% or less, and particularly preferably 1.7% or less.

[0024] Furthermore, from the above viewpoint, the sum of the absolute values ​​of the deformation rates is ideally 0.0%. On the other hand, considering that the substrate undergoes thermal deformation in a high-temperature environment when a biaxially oriented polypropylene film is used as a label, it is also preferable to have a sum greater than 0.0% for the purpose of following the thermal deformation of the substrate and for causing small wrinkles that accidentally occur during label lamination to disappear over time by being placed in a high-temperature environment. When this effect is expected, the sum of the absolute values ​​of the deformation rates of the biaxially oriented polypropylene film is preferably 0.01% or more, and more preferably 0.05% or more.

[0025] In the biaxially oriented polypropylene film of the present invention, it is preferable that at least one of the deformation rates in the X direction and the Y direction is 0.0% or more and 1.5% or less after heat treatment at 150°C for 30 minutes. With this configuration, when the biaxially oriented polypropylene film is exposed to a high-temperature environment, at least one of the deformation rates will not shrink due to heat, but will either maintain its original size or expand and spread. Therefore, in the process of pressing a label using such a biaxially oriented polypropylene film of the present invention onto an adherend using a heated nip roll or the like, the film expands to release the stress during pressing, and as a result, the occurrence of wrinkles can be suppressed. For the reasons mentioned above, when performing roll-to-roll processing, it is preferable that the deformation rate in the width direction of the biaxially oriented polypropylene film of the present invention is 0.0% or more and 1.5% or less, and more preferably 0.0% or more and 0.7% or less.

[0026] In the biaxially oriented polypropylene film of the present invention, in order to control the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction, and the deformation rates in each direction, to the above-mentioned preferred range after heat treatment at 150°C for 30 minutes, it is important to grow the crystalline domains of polypropylene present in the biaxially oriented polypropylene film and to reduce the stress originating from the stretching process that accumulates in the amorphous polypropylene molecular chains connecting the crystalline domains. These can be achieved, for example, by performing roll-to-roll integrated film manufacturing using a polypropylene resin described later and a film manufacturing process under the conditions described later. Alternatively, these can also be achieved by off-annealing a biaxially oriented polypropylene film manufactured using a polypropylene resin described later, or by laminating another film with a small sum of deformation rates to one side, but the above integrated film manufacturing is preferred from the viewpoint of productivity.

[0027] The biaxially oriented polypropylene film of the present invention preferably has a melting point of 176°C or higher and 185°C or lower. The melting point of the biaxially oriented polypropylene film is a parameter that reflects the size of the crystalline domains of the polypropylene resin formed therein. By using the polypropylene resin described later and applying the film formation conditions described later, the crystal size can be grown beyond the melting point of the polypropylene resin. The melting point can be measured by thermal property analysis using a differential scanning calorimeter (DSC), which will be described in detail later.

[0028] The biaxially oriented polypropylene film of the present invention has a melting point of 176°C or higher, which allows for the formation of a strong crystalline structure within the film. Therefore, when the biaxially oriented polypropylene film is used as a label, it is possible to suppress dimensional changes that cause peeling from the substrate and wrinkles that reduce the visibility of printed information in high-temperature environments such as 150°C. From this viewpoint, 177°C is more preferable as the lower limit of the melting point. On the other hand, the upper limit of the melting point is preferably 185°C, as using a polypropylene resin with excessively high crystallinity can cause film tearing during biaxial stretching, reducing film-forming properties and productivity.

[0029] The biaxially oriented polypropylene film of the present invention preferably has a Young's modulus of 1.5 GPa or more and 4.0 GPa or less in at least one of the X and Y directions (details of the measurement method will be described later). The Young's modulus is a value that reflects the durability of the biaxially oriented polypropylene film against mechanical deformation and can be adjusted mainly by the average secondary particle diameter of the white particles and the film formation conditions (stretching ratio, stretching temperature, and relaxation rate), which will be described later.

[0030] The biaxially oriented polypropylene film of the present invention has a Young's modulus of 1.5 GPa or higher in at least one of the X and Y directions. When used for labels, it can suppress the occurrence of creases and wrinkles during lamination, and the deformation of the label when it is peeled off for re-lamination. Furthermore, when the label is used in a high-temperature environment, it can suppress the occurrence of wrinkles caused by excessive following of the thermal deformation of the substrate, and the reduction in the visibility of printed information.

[0031] On the other hand, the biaxially oriented polypropylene film of the present invention has a Young's modulus of 4.0 GPa or less in at least one of the X and Y directions, which suppresses excessive deformation in high-temperature environments when used for labels, thus preventing peeling from the adherend. From the above viewpoint, a lower limit of 1.7 GPa for Young's modulus is more preferable, and an upper limit of 3.5 GPa is more preferable. A further preferred embodiment is one in which the Young's modulus is 1.5 GPa or more and 4.0 GPa or less in both the X and Y directions, and the preferred upper and lower limits are the same.

[0032] The thickness of the biaxially oriented polypropylene film of the present invention is preferably 15 μm or more and 80 μm or less. A thickness of 15 μm or more of the biaxially oriented polypropylene film prevents the label from sagging under its own weight, causing it to stick unnecessarily, wrinkles to form, and the label's L * Lowering the value helps to suppress the reduction in the visibility of printed information due to the color of the substrate showing through. On the other hand, when the thickness of the biaxially oriented polypropylene film is 80 μm or less, it has appropriate stiffness when used as a label, making it easy to bond to the substrate while pushing out the air. From the above viewpoint, the lower limit of the thickness of the biaxially oriented polypropylene film of the present invention is more preferably 20 μm, and even more preferably 25 μm. Also from the above viewpoint, the upper limit of the thickness of the biaxially oriented polypropylene film of the present invention is more preferably 70 μm, and even more preferably 60 μm.

[0033] (Polypropylene resin) The following describes the polypropylene resin that constitutes the biaxially oriented polypropylene film of the present invention. As the main component of the biaxially oriented polypropylene film of the present invention, homopolypropylene resin is preferably used from the viewpoint of strength and heat resistance. Here, homopolypropylene resin refers to a resin in which, when the total constituent units of the resin are set to 100 mol%, 99 mol% to 100 mol% are propylene units.

[0034] The melting point of the main component, polypropylene resin, is preferably 155°C or higher, more preferably 160°C or higher, and even more preferably 165°C or higher. A melting point of 155°C or higher for the polypropylene resin increases the melting point of the resulting biaxially oriented polypropylene film, thereby improving its thermal dimensional stability. Therefore, when the biaxially oriented polypropylene film is used as a label for components exposed to high-temperature environments for extended periods, it is possible to suppress the label from peeling off the substrate due to thermal shrinkage, or from curling or wrinkling the label.

[0035] A particularly preferred embodiment is that the biaxially oriented polypropylene film of the present invention has at least one polypropylene resin layer having a melting point of 165°C or higher. The melting points of these polypropylene resins and biaxially oriented polypropylene films can be measured in thermal property analysis using a differential scanning calorimeter (DSC), as described later, by completely melting the polypropylene resin, the biaxially oriented polypropylene film, or one of the layers constituting the biaxially oriented polypropylene film, then cooling and reheating it. Further details will be described later.

[0036] The biaxially oriented polypropylene film of the present invention preferably has at least one layer mainly composed of a polypropylene resin having a mesopentad fraction of 0.940 or higher. The mesopentad fraction of the main component polypropylene resin is more preferably 0.970 or higher, and even more preferably 0.980 or higher. The mesopentad fraction is an index indicating the stereoregularity of the crystalline phase of the polypropylene resin measured by nuclear magnetic resonance (NMR) spectroscopy, and a higher value indicates a higher degree of crystallinity. Polypropylene resins with a high mesopentad fraction generally have a higher melting point, and biaxially oriented polypropylene films mainly composed of such polypropylene resins are preferable because they have high thermal dimensional stability at high temperatures. The method for measuring the mesopentad fraction will be described later.

[0037] While there is no specific upper limit for the mesopentade fraction of the main component, polypropylene resin, it is set at 0.995 from a feasibility standpoint. To obtain such a highly stereoregular polypropylene resin, methods such as washing the resin powder obtained with a solvent such as n-heptane, selecting catalysts and / or co-catalysts, and selecting the composition as appropriate are preferably employed.

[0038] Furthermore, the melt viscosity of the main component, polypropylene resin, is such that the melt flow rate (MFR) obtained when a 21.18N load is applied at a temperature of 230°C is 1 g / 10 min or more and 10 g / 10 min or less. A melt flow rate (MFR) of 1.0 g / 10 min or more is preferable from the viewpoint of film formation properties, as it facilitates melt extrusion of the polypropylene resin. From the above viewpoint, a more preferable lower limit for the melt flow rate is 4.0 g / 10 min. Also, by setting the melt flow rate (MFR) to 10 g / 10 min or less, the molecular chain length of the polypropylene resin can be increased, and the mechanical properties of the resulting biaxially oriented polypropylene film can be improved. From the above viewpoint, a more preferable upper limit for the melt flow rate is 8.0 g / 10 min. As a method to set the melt flow rate (MFR) within the above range, for example, methods such as controlling the average molecular weight and molecular weight distribution of the polypropylene resin can be employed. Specifically, by increasing the average molecular weight of the polypropylene resin or increasing the proportion of high-molecular-weight components in the molecular weight distribution, the entanglement between polypropylene molecular chains increases, which can reduce the melt flow rate (MFR).

[0039] The main component polypropylene resin may contain copolymer units made of other unsaturated hydrocarbons, or it may be a blend of polymers, as long as it does not impair the objectives of the present invention. Examples of monomer components that constitute such copolymer units or blends include ethylene, propylene (in the case of copolymerized blends), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and 5-methyl-2-norbornene. From the viewpoint of dimensional stability, the copolymer amount or blend amount is preferably less than 1 mol%, and the blend amount is preferably less than 10% by mass.

[0040] When the main component, polypropylene resin, contains ethylene, the ethylene content is preferably 10 mol% or less. More preferably 5.0 mol% or less, and even more preferably 3.0 mol% or less. By limiting the ethylene content to 10 mol% or less, it is possible to suppress the inhibition of crystallization of the molecular chains of the polypropylene resin by the ethylene component, thereby preventing a decrease in the mechanical strength and thermal dimensional stability of the resulting biaxially oriented polypropylene film. Furthermore, it is possible to suppress thermal degradation of the polypropylene resin during the extrusion process, which can lead to the formation of fish-eye defects in the resulting film.

[0041] Furthermore, it is preferable to use a modified polypropylene resin having hydrophilic functional groups in order to improve the affinity between the label surface and the ink that constitutes the printed information. Examples of modified polypropylene resins include maleic anhydride-modified polypropylene resins having carboxylic acid groups in the side chain, such as Admer from Mitsui Chemicals, Yumex from Sanyo Chemical Industries, and Modic from Mitsubishi Chemicals, as well as Admer from Mitsui Chemicals. TM Examples include imine-modified polypropylene resins, such as IP, which have amino groups in their side chains. Among these, maleic anhydride-modified polypropylene resins are preferred because they have high affinity with many resins and metals, including acrylic resins used in general-purpose inks. More details will be provided later.

[0042] The polypropylene resin used in the biaxially oriented polypropylene film of the present invention may contain various additives, such as nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and anticoloring agents, as long as they do not impair the objectives of the present invention. These may be present individually or in combination.

[0043] Among these, the selection of the type and amount of antioxidant is important from the viewpoint of antioxidant bleed-out. The antioxidant should be a sterically hindered phenol type, and it is preferable that at least one of them be a high molecular weight type with a molecular weight of 500 or more. Various specific examples can be given, but it is preferable to use 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) in combination with 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox"® 1010: molecular weight 1177.7). The total content of antioxidants relative to the total amount of the biaxially oriented polypropylene film of the present invention is preferably in the range of 0.03% by mass or more and 1.0% by mass or less. By setting the total content of antioxidants to 0.03% by mass or more, it is possible to suppress discoloration of the biaxially oriented polypropylene film obtained due to thermal degradation of the polymer during the extrusion process, and to suppress a decrease in thermal dimensional stability when exposed to a high-temperature environment for a long period of time. By setting the total content of antioxidants to 1.0% by mass or less, it is possible to suppress a decrease in the surface quality of the biaxially oriented polypropylene film due to antioxidant bleed-out. From the above viewpoint, a more preferable lower limit for the total content of antioxidants is 0.05% by mass, and even more preferably 0.10% by mass. Also, from the above viewpoint, a more preferable upper limit for the total content of antioxidants is 0.90% by mass, and even more preferably 0.80% by mass.

[0044] Furthermore, it is preferable that the biaxially oriented polypropylene film of the present invention has at least one layer containing branched polypropylene. The branched polypropylene content in the layer containing the branched polypropylene resin is preferably 0.05% by mass or more and 30% by mass or less when the entire layer is considered to be 100% by mass. A more preferable condition is that there is at least one layer containing branched polypropylene, and the branched polypropylene content is 0.05% by mass or more and 10% by mass or less when the entire biaxially oriented polypropylene film is considered to be 100% by mass.

[0045] By setting the branched-chain polypropylene resin content to 0.05% by mass or more, the crystallization of the resulting biaxially oriented polypropylene film is improved, enhancing its thermal dimensional stability. Furthermore, the surface shape of the biaxially oriented polypropylene film becomes dense and fine, suppressing the deterioration of surface quality due to the formation of coarse protrusions with steep height differences. This is because the branched-chain polypropylene resin exhibits an effect similar to that of a crystal nucleating agent in the polypropylene resin, reducing the diameter of the spherulites of the polypropylene resin generated during the cooling process of the melt-extruded resin sheet, thereby reducing the height difference of the film surface irregularities after biaxial stretching. From the above viewpoint, the lower limit of the branched-chain polypropylene resin content is more preferably 0.5% by mass, and even more preferably 1% by mass. On the other hand, from the above viewpoint, the upper limit of the branched-chain polypropylene resin content is more preferably 8.0% by mass, and even more preferably 5.0% by mass.

[0046] In the polypropylene resin used for the polypropylene film of the present invention, a crystal nucleating agent can be added within a range not contrary to the object of the present invention. Examples of α crystal nucleating agents include dibenzylidene sorbitols, sodium benzoate, etc., and examples of β crystal nucleating agents include potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone-based compounds, etc. However, since excessive addition of the above-mentioned different types of nucleating agents may cause a decrease in stretchability and a decrease in transparency and strength due to void formation, etc., the addition amount is usually 0.5% by mass or less, preferably 0.1% by mass or less, and more preferably 0.05% by mass or less.

[0047] (The surface where the L value in the reflected color tone is 50.0 or more and 100 or less: Surface A) * Value is 50.0 or more and 100 or less in the reflected color tone: Surface A) The biaxially oriented polypropylene film of the present invention has at least one surface having Surface A when the surface where the L value is 50.0 or more and 100 or less is defined as Surface A. The method for measuring the L value will be described later. The L value in the reflected color tone is a parameter representing brightness in the color tone of the film. A larger L value in the reflected color tone means that the biaxially oriented polypropylene film has a color closer to white and has high concealability. * When the surface where the L value is 50.0 or more and 100 or less is defined as Surface A, it has Surface A on at least one side. The method for measuring the L value will be described later. The L value in the reflected color tone is a parameter representing brightness in the color tone of the film. A larger L value in the reflected color tone means that the biaxially oriented polypropylene film has a color closer to white and has high concealability. * The method for measuring the L value will be described later. The L value in the reflected color tone is a parameter representing brightness in the color tone of the film. * The L value is a parameter representing brightness in the color tone of the film, and a larger L value in the reflected color tone means that the biaxially oriented polypropylene film has a color closer to white and has high concealability. * A larger L value in the reflected color tone means that the biaxially oriented polypropylene film has a color closer to white and has high concealability.

[0048] When the L value in the reflected color tone of Surface A is 50.0 or more, when the biaxially oriented polypropylene film is used as a label, it is easy to create a contrast difference with the printed information on the surface and improve the visibility of the printed information (improve the appearance). Also, when the label is adhered to an adherend other than white, the color of the adherend is less visible through the label, so the reverse printing is reduced and the visibility of the printed information is improved. From the above viewpoints, the lower limit value of the L value in the reflected color tone of Surface A is preferably 60.0, and more preferably 70.0. * When the L value in the reflected color tone of Surface A is 50.0 or more, when the biaxially oriented polypropylene film is used as a label, it is easy to create a contrast difference with the printed information on the surface and improve the visibility of the printed information (improve the appearance). Also, when the label is adhered to an adherend other than white, the color of the adherend is less visible through the label, so the reverse printing is reduced and the visibility of the printed information is improved. From the above viewpoints, the lower limit value of the L value in the reflected color tone of Surface A is preferably 60.0, and more preferably 70.0. * The lower limit value of the L value is preferably 60.0, and more preferably 70.0.

[0049] On the other hand, the L value in the reflected color tone of Surface A* The upper limit of the value is theoretically 100. However, the L * If large amounts of particles or additives are included as white pigment to increase the value, the mechanical properties of biaxially oriented polypropylene film may deteriorate. Furthermore, when such biaxially oriented polypropylene film is used for labels, the label may not be able to follow the thermal expansion of the substrate in a high-temperature environment, causing it to peel or tear. From the perspective of mitigating these problems, the L of the reflective color tone of side A * The upper limit of the value is preferably 98.0, and more preferably 95.0.

[0050] L in reflective tones * Methods for producing a biaxially oriented polypropylene film having an A-plane with a value between 50.0 and 100 include, for example, a method of incorporating white particles into the biaxially oriented polypropylene film, a method of improving surface light scattering of the biaxially oriented polypropylene film by creating a coarse uneven structure on the film surface using additives, and a method of precisely controlling the degree of crystallinity within the biaxially oriented polypropylene film by incorporating additives that adjust the crystallinity of the polypropylene resin, thereby scattering light transmitted through the film due to the difference in refractive index.

[0051] Among these methods, adding a small amount of L * Because the value can be easily controlled and the influence of film formation conditions is relatively small, the method of incorporating white particles into a biaxially oriented polypropylene film is particularly preferred. When using this method, by increasing the amount of white particles and increasing the particle size of the white particles, L * The value can be increased.

[0052] The white particles contained in the biaxially oriented polypropylene film of the present invention may be inorganic particles or organic particles, or both organic and inorganic particles, L * From the viewpoint of increasing the value, inorganic particles are preferred. Furthermore, the white particles contained in the biaxially oriented polypropylene film of the present invention may be one type or two or more types.

[0053] Examples of inorganic particles include calcium carbonate, magnesium carbonate, zinc carbonate, titanium dioxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, alumina, mica, mica, titanium mica, zeolite, talc, clay, kaolin, lithium fluoride, calcium fluoride, zirconia, and silicates, aluminosilicates, borosilicates, etc. Among these, calcium carbonate, magnesium carbonate, titanium dioxide, zinc oxide, and barium sulfate are preferred from the viewpoint of ease of processing with polypropylene resin, and among these, titanium dioxide, which has a high refractive index, is preferred. * This is preferable from the standpoint of improving the value. Two commonly used types of titanium dioxide are anatase-type titanium dioxide and rutile-type titanium dioxide. * While anatase titanium dioxide is preferable from the standpoint of improving performance, it exhibits photocatalytic activity in response to ultraviolet light contained in sunlight and fluorescent lamps, decomposing polypropylene resin. Therefore, when long-term durability is required, it is preferable to use rutile titanium dioxide. These titanium dioxides can be appropriately selected and used in combination depending on the application.

[0054] The surface of inorganic particles may be modified to improve particle dispersibility within the polypropylene resin or to adjust the particle color. Examples of surface modifications include coating the filler surface with metal oxides such as aluminum dioxide or silicon dioxide, fixing organic compounds to the filler surface via covalent or non-covalent bonds, and methods that combine both.

[0055] Examples of organic particles include granular materials composed of resins incompatible with polypropylene resin. For instance, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, and polyethylene naphthalate; polyamide resins such as nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, nylon 46, nylon MXD6, and nylon 6T; styrene resins such as polystyrene, acrylonitrile-styrene copolymer, and acrylonitrile-butadiene-styrene copolymer; acrylic resins such as polymethyl methacrylate and polybutyl methacrylate; fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride; super engineering plastics such as polyphenylene sulfide, polysulfone, polyethersulfone, polyarylate, and polyetherimide; or polyolefin resins incompatible with the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention. Examples of polyolefin resins include aliphatic polyolefin resins such as polyethylene, high-density polyethylene, low-density polypropylene, ethylene-propylene copolymer, ethylene-propylene-butylene copolymer, and polymethylpentene, as well as cyclic polyolefin resins such as cycloolefin polymers and cycloolefin copolymers. These can also be used in combination with organic particles as appropriate, and can also be used in combination with inorganic particles.

[0056] The shape of the white particles may be spherical, plate-shaped, rod-shaped, needle-shaped, star-shaped, tetrapod-shaped, hollow spherical, or cylindrical, and two or more different shapes may be used in combination.

[0057] In the biaxially oriented polypropylene film of the present invention, it is preferable that the content of white particles is 1.0% by mass or more and 20% by mass or less when the entire biaxially oriented polypropylene film is considered as 100% by mass. When the content of white particles in the biaxially oriented polypropylene film is 1% by mass or more relative to the entire biaxially oriented polypropylene film, its L *The values ​​can be controlled within a desirable range, improving the visibility of printed information when used as a label. Furthermore, by keeping the white particle content in the biaxially oriented polypropylene film at 20% by mass or less relative to the entire biaxially oriented polypropylene film, the mechanical properties of the biaxially oriented polypropylene film are maintained well, preventing peeling or breakage caused by the label being unable to follow the thermal expansion of the substrate in high-temperature environments when used as a label.

[0058] From the above viewpoint, the upper limit of the content of white particles in the biaxially oriented polypropylene film is more preferably 2.0% by mass or more, and even more preferably 3.0% by mass or more, relative to the entire biaxially oriented polypropylene film. On the other hand, from the above viewpoint, the lower limit is more preferably 15% by mass or less, relative to the entire biaxially oriented polypropylene film.

[0059] When the biaxially oriented polypropylene film of the present invention has a laminated structure, the P1 layer (details described later), which is the layer having surface A, contains white particles at the concentration described later, and the L of surface A * The values ​​and glossiness can be adjusted to a desirable range, and the mechanical properties of the biaxially oriented polypropylene film can be controlled to a desirable range.

[0060] Energy-dispersive X-ray spectroscopy can be used to identify inorganic particles in each layer. Furthermore, if determination is difficult based solely on elemental analysis, EELS analysis using GATAN GIF “Tridiem” with a field emission transmission electron microscope (e.g., JEM-2100F (manufactured by JEOL Ltd., accelerating voltage 200kV)) can be performed as elemental state analysis to identify the constituent elements of the particles. The resulting EELS spectrum can then be compared with the EELS spectra of commercially available metal compounds or publicly available EELS spectral data to identify the particles contained in each layer.

[0061] Furthermore, organic particles are identified using X-ray photoelectron spectroscopy (ESCA), Fourier infrared spectrophotometer (FT-IR) ATR method, time-of-flight secondary ion mass spectrometry (TOF-SIMS), or by dissolving and extracting the P2 layer with a solvent and then performing proton nuclear magnetic resonance spectroscopy. 1 H-NMR, carbon nuclear magnetic resonance spectroscopy ( 13 ¹¹-NMR), fluorine nuclear magnetic resonance spectroscopy ( 19 F-NMR), silicon nuclear magnetic resonance spectroscopy ( 29 This can be done by appropriately selecting a method from among Si-NMR, Fourier infrared spectrophotometer (FT-IR), and pyrolysis gas chromatography-mass spectrometry (GC-MS) to analyze the structure.

[0062] Furthermore, known thermogravimetric analyzers (e.g., Shimadzu Corporation, DTG-60, etc.) can be used to quantify inorganic particles in each layer or biaxially oriented polypropylene film, and details of the measurement method when using such an analyzer will be described later. In addition, organic particles in each layer or biaxially oriented polypropylene film can be quantified by dissolving the polypropylene resin components of each layer or biaxially oriented polypropylene film using a solvent (o-dichlorobenzene) heated to 140°C to 150°C, followed by filtration, and then determining the weight of the remaining sediment.

[0063] The biaxially oriented polypropylene film of the present invention, after heat treatment at 150°C for 30 minutes, shows the L of the reflective color of side A. * Change in value is ΔL * When this is the case, ΔL * It is preferable that ΔL is between -1.5 and 1.5. * This value reflects the change in appearance of biaxially oriented polypropylene film when exposed to a high-temperature environment. L in the reflective color tone of surface A. * Change in value is ΔL * By having a value of -1.5 or more and 1.5 or less, when the biaxially oriented polypropylene film of the present invention is used as a label, the change in the appearance of the label when exposed to a high-temperature environment is reduced, and the decrease in the visibility of printed information over time can be suppressed. From the above viewpoint, L in the reflective color tone of surface A *It is preferable that the lower limit of the change in value is -1.0, and the upper limit is 1.0.

[0064] ΔL * As a method to set ΔL to -1.5 or more and 1.5 or less or within the above preferred range, one example is to use white particles having the average secondary particle diameter described later as the raw material for the P1 layer and to produce a biaxially oriented polypropylene film under the film production conditions described later. This is because coarse voids originating from the white particles are formed within the film and collapse under high-temperature conditions, or the entire biaxially oriented polypropylene film shrinks in the planar direction and its thickness increases, resulting in ΔL * This is because it can suppress the increase of [the substance].

[0065] In the biaxially oriented polypropylene film of the present invention, it is preferable that the average value of GX and GY is between 21 and 50, where GX (%) is the 60° gloss in the X direction on surface A and GY (%) is the 60° gloss in the Y direction on surface A. The gloss referred to here is the gloss measured at a light incidence angle of 60° and a detector reception angle of 60°, and details of the measurement method and other measurement conditions will be described later.

[0066] By setting the average value of GX and GY to 50 or less, a matte finish can be imparted to side A, and the light scattering of the label surface helps maintain good visibility of the printed information on the label surface. Furthermore, the moderate roughness of side A improves the abrasion resistance of the label surface, suppressing the loss of printed information due to friction with external objects. Additionally, by setting the average value of GX and GY to 21 or more, the amount of white particles contained in the biaxially oriented polypropylene film becomes appropriate, reducing the decrease in the mechanical strength of the biaxially oriented polypropylene film, and the moderately rough surface makes it less likely for distortion or blurring to occur in printed information such as intricate patterns and small font sizes. From the above viewpoint, the upper limit of the average value of GX and GY is more preferably 45, and even more preferably 40. Also from the above viewpoint, the lower limit of the average value of GX and GY is more preferably 25, and even more preferably 31.

[0067] Methods for controlling the average values ​​of GX and GY include, when the layer having the A-face is designated as the P1 layer, setting the content of white particles and the average secondary particle diameter of the P1 layer within the range described below, and controlling the β-crystal spherulite size and number density of the polypropylene resin constituting the P1 layer in the melt-extruded sheet during the film-forming process described below, thereby controlling the formation of surface irregularities after biaxial stretching. More specifically, the average values ​​of GX and GY can be increased by reducing the content of white particles, reducing their size, reducing the size of the β-crystals in the polypropylene resin constituting the P1 layer in the melt-extruded sheet, and / or reducing the number density to suppress the formation of surface irregularities after biaxial stretching. Methods for reducing the size and number density of β-crystals in the polypropylene resin constituting the P1 layer in the melt-extruded sheet include adding an α-crystal nucleating agent as a raw material for the P1 layer, and, in the film-forming conditions described below, setting the temperature of the cast drum to a low temperature to accelerate the cooling of the melt-extruded sheet, thereby preferentially forming α-crystals over β-crystals.

[0068] The biaxially oriented polypropylene film of the present invention preferably has a static friction coefficient μs of 0.20 or more and 0.70 or less when two A-sides are stacked together (hereinafter sometimes referred to as the static friction coefficient μs of A-side). The method for measuring the static friction coefficient μs of A-side will be described later. A static friction coefficient μs of A-side of 0.70 or less enhances the slipperiness of the biaxially oriented polypropylene film, preventing scratches on A-side due to friction with conveyor rolls during film-making and processing processes, thereby improving quality. Furthermore, since scratches on A-side can be prevented (scratch resistance is increased), when used as a label, the loss of printed information due to friction with disturbances can be suppressed. From the above viewpoint, the upper limit of the static friction coefficient μs of A-side is more preferably 0.60, and even more preferably 0.50. Moreover, a static friction coefficient μs of A-side of 0.20 or more provides appropriate slipperiness, preventing roll misalignment when winding the biaxially oriented polypropylene film onto rolls during film-making and processing processes. From the above viewpoint, the lower limit of the static friction coefficient μs of surface A is more preferably 0.30. Note that the static friction coefficient of surface A can be reduced by increasing the amount of white particles added to the P1 layer.

[0069] The biaxially oriented polypropylene film of the present invention preferably has a surface free energy of A-side of 34 mN / m or more and 70 mN / m or less. By setting the surface free energy of A-side to 34 mN / m or more, the affinity with the ink used to print information on the label surface is improved when the biaxially oriented polypropylene film of the present invention is used as a label. As a result, it is possible to prevent the affinity with the ink from decreasing over time when the label is left in a high-temperature environment, and to prevent the printed information from easily disappearing due to external stress such as wiping with a cloth. Furthermore, by setting the surface free energy of A-side to 70 mN / m or less, when the biaxially oriented polypropylene film of the present invention is used as a label, the surface becomes excessively hydrophilic, which reduces the affinity between the ink and A-side in environments at room temperature or high temperature, and to prevent the printed information from easily disappearing due to external stress such as wiping with a cloth. From the above viewpoint, the lower limit of the surface free energy of A-side is more preferably 36 mN / m, and the upper limit is more preferably 60 mN / m.

[0070] Methods for setting the surface free energy of surface A to a desirable range include applying the following surface treatment to surface A, and incorporating a modified polypropylene resin having hydrophilic functional groups into the P1 layer described later.

[0071] Surface treatments include corona treatment, vacuum plasma treatment, atmospheric pressure plasma treatment, and ozone treatment. From the viewpoint of performing treatment during film formation, corona treatment or atmospheric pressure plasma treatment is preferred. When using atmospheric pressure plasma treatment, it is preferable to fill the processing apparatus with a plasma-excitable gas at atmospheric pressure (in the range of 700 Torr to 780 Torr), apply a high-frequency voltage adjusted to a frequency in the range of 1 kHz to 100 kHz to generate a glow discharge, and perform hydrophilization treatment on surface A. Examples of plasma-excitable gases include noble gases such as argon, helium, neon, krypton, and xenon, nitrogen, carbon dioxide, oxygen, or fluorocarbons such as tetrafluoromethane and mixtures thereof. Furthermore, one type of plasma-excitable gas may be used alone, or two or more types may be combined in any mixing ratio.

[0072] When using corona treatment, a corona discharge is generated by applying a voltage, and surface A is treated to make it hydrophilic. In this case, the apparatus used to generate the corona discharge may be filled with air (atmospheric environment), or it may be filled with nitrogen gas or nitrogen gas mixed with a small amount of carbon dioxide as an inert gas.

[0073] When performing corona treatment or atmospheric pressure plasma treatment, the discharge treatment intensity (E value) calculated using the following formula is 20 W·min / m², from the viewpoint of adjusting the surface free energy of surface A to a suitable range. 2 More than 200W min / m 2 The following is preferable. From the above viewpoint, 30 W·min / m is more preferable. 2 More than 100W min / m 2 The following applies: Formula: E=Vp×Ip / (S×Wt) E: E value (W·min / m) 2) Vp: Application (V) Ip: Applied current (A) S: Processing speed (m / min) Wt: Processing width (m).

[0074] As modified polypropylene resins having hydrophilic functional groups, for example, maleic anhydride-modified polypropylene resins obtained by copolymerizing maleic anhydride with a polypropylene resin using a polymerization catalyst such as a peroxide, or resins obtained by copolymerizing these with ethylene, butene, propylene, etc., can be used.

[0075] In the biaxially oriented polypropylene film of the present invention, when the layer having surface A is designated as layer P1, it is preferable that layer P1 contains a polypropylene resin having carboxylic acid terminals. By containing the polypropylene resin having carboxylic acid terminals in layer P1, the carboxylic acid terminals are exposed on surface A, thereby increasing the affinity with the ink. Alternatively, such carboxylic acid terminals may be formed by hydrolysis of the ester group.

[0076] Methods for incorporating a polypropylene resin having carboxylic acid termini into the P1 layer include forming the P1 layer by melt extrusion using maleic anhydride-modified polypropylene resin or modified polypropylene resin in which ester compounds are chemically modified in the side chains, and forming the P1 layer using a polypropylene resin without functional groups, and then applying a surface treatment to the A surface of the P1 layer to introduce functional groups into the A surface of the P1 layer and the polypropylene resin in its vicinity. These methods may also be combined as appropriate.

[0077] Surface treatments include the aforementioned corona treatment and atmospheric pressure plasma treatment. Among these, corona treatment and atmospheric pressure plasma treatment using nitrogen gas mixed with a small amount of carbon dioxide as the treatment gas are preferred because they allow for efficient introduction of carboxylic acid groups. Whether or not the biaxially oriented polypropylene film P1 layer has carboxylic acid ends can be determined by XPS (X-ray Photoelectron Spectroscopy) measurement, and the details will be described later.

[0078] The adhesion force between side A of the biaxially oriented polypropylene film of the present invention and the acrylic adhesive tape, as measured by the method described later, is preferably 3.5 N / 19 mm or more. The adhesion force between side A and the acrylic adhesive tape is an indicator that reflects the high affinity between side A and the ink, and a value of 3.5 N / 19 mm or more makes it easier for printed information to be retained even when subjected to physical damage such as heat damage or friction when printed information is provided on side A of the biaxially oriented polypropylene film of the present invention. The adhesion force between side A and the acrylic adhesive tape is more preferably 4.0 N / 19 mm or more, and even more preferably 6.0 N / 19 mm or more.

[0079] (Layer with side A: P1 layer) The biaxially oriented polypropylene film of the present invention has a layer having the A-side (P1 layer) since at least one side is the A-side. When the biaxially oriented polypropylene film has a laminated structure, there may be one or two P1 layers. In the former embodiment, the surface layer on one side is the P1 layer, and in the latter embodiment, the surface layers on both sides are the P1 layers. In the latter embodiment, the compositions of the P1 layers on both sides may be the same or different. Furthermore, when the biaxially oriented polypropylene film has a single-layer structure, the biaxially oriented polypropylene film itself becomes the P1 layer.

[0080] In the biaxially oriented polypropylene film of the present invention, it is preferable that the amount of white particles in the total constituent components of the P1 layer is 3.0% by mass or more and 30.0% by mass or less. This configuration is particularly preferable when the surface layer is the P1 layer and the laminated structure has at least a core layer, the P2 layer. Here, white particles refer to particles with a whiteness of 50% or more as defined in JIS K5101-2-2 (2004), and specifically, the inorganic particles and / or organic particles mentioned above can be used.

[0081] The P1 layer contains 3.0% to 30% by mass of white particles, and the L on side A * This makes it easier to set the values ​​and glossiness within desirable ranges. Furthermore, if the biaxially oriented polypropylene film has the above-described laminate structure, the P1 layer can contain 3.0% to 30.0% by mass of white particles, thereby reducing the white particle content in the core layer, P2. Therefore, the degradation of the overall mechanical properties of the biaxially oriented polypropylene film due to white particles can be mitigated. (A-side L) * From the viewpoint of balancing the adjustment of the value and glossiness with mechanical strength, the lower limit of the white particle content in the P1 layer is more preferably 6.0% by mass, the upper limit is more preferably 25.0% by mass, and even more preferably 19.0% by mass. Furthermore, it is preferable that the white particle content (by mass) in the P1 layer is greater than the white particle content (by mass) in the core layer, the P2 layer.

[0082] Furthermore, the white particles contained in the P1 layer can be the aforementioned inorganic particles, organic particles, or both, but L * From the standpoint of controlling the value, it is preferable to use inorganic particles.

[0083] In the biaxially oriented polypropylene film of the present invention, it is preferable that the P1 layer contains white particles with an average secondary particle diameter of 100 nm or more and less than 500 nm. By making the average secondary particle diameter of the white particles 100 nm or more, the visible light incident on the biaxially oriented polypropylene film is efficiently scattered, thereby L on the A surface. *This makes it easier to adjust the values ​​to a desirable range. Furthermore, since surface irregularities originating from the white particles can be formed on surface A, it also becomes easier to control the glossiness of surface A to a desirable range. On the other hand, by setting the average secondary particle diameter of the white particles to less than 500 nm, it is possible to suppress the decrease in the mechanical strength of the resulting film caused by the formation of voids around the white particles during the biaxial stretching process. Furthermore, when exposed to high-temperature environments such as 150°C for a long period of time, the ΔL associated with the collapse of voids around the white particles due to heat is suppressed. * This can mitigate the increase in the value. From the above viewpoint, it is more preferable that the lower limit of the average secondary particle diameter of the white particles be 150 nm and the upper limit be 400 nm or less.

[0084] Here, the average secondary particle diameter is determined by observing a cross-section of a biaxially oriented polypropylene film using the method described later, taking the average diameter of each observed white particle as the secondary particle diameter of the particle, and then calculating the value from the average of these values ​​(details of the measurement method will be described later).

[0085] Furthermore, the P1 layer of the biaxially oriented polypropylene film of the present invention may contain two or more types of white particles of different sizes with an average secondary particle diameter of 100 nm or more and less than 500 nm. In addition, the P1 layer may also contain white particles with an average secondary particle diameter of 100 nm or more and less than 500 nm, as well as white particles with an average secondary particle diameter of 100 nm or more and less than 500 nm.

[0086] In the biaxially oriented polypropylene film of the present invention, the polypropylene resin constituting the surface layer P1 may have the resin properties described in the (Polypropylene Resin) section above. Furthermore, the polypropylene resin constituting the surface layer P1 may be different from the polypropylene resin used in the P2 layer described later.

[0087] In the biaxially oriented polypropylene film of the present invention, the thickness of the P1 layer is preferably 0.5 μm or more and 5.0 μm or less. When the thickness of the P1 layer is 0.5 μm or more, it becomes easy to control the size and content of the white particles contained within to the above preferred range, thereby achieving a preferred gloss level for surface A. Furthermore, when the thickness of the P1 layer is 5.0 μm or less, the proportion of the layer containing a high concentration of white particles within the entire biaxially oriented polypropylene film does not become excessively high. As a result, a decrease in the overall mechanical properties of the biaxially oriented polypropylene film can be suppressed. From the above viewpoint, the lower limit of the thickness of the P1 layer is more preferably 1.0 μm, and even more preferably 1.5 μm. Also from the above viewpoint, the upper limit of the thickness of the P1 layer is more preferably 4.0 μm, and even more preferably 3.5 μm.

[0088] Furthermore, when laminating the P1 layer and the P2 layer described later by melt extrusion, a P1' layer may be provided with modified polypropylene resin composition, white particle content, and lamination thickness within the scope of the P1 layer described above, resulting in a heterogeneous three-layer laminate consisting of P1 / P2 / P1' layers.

[0089] (Core layer: P2 layer) In the case where the biaxially oriented polypropylene film of the present invention has a laminated structure, the P2 layer is responsible for improving the overall mechanical properties of the biaxially oriented polypropylene film, and therefore it is preferable that its thickness relative to the entire biaxially oriented polypropylene film is greater than 50% but less than 100%. From the above viewpoint, it is preferable that the polypropylene resin constituting P2 has the resin properties described in the (Polypropylene Resin) section above.

[0090] In the biaxially oriented polypropylene film of the present invention, the P2 layer preferably contains white particles. As the white particles, the aforementioned inorganic particles, organic particles, or both can be used, but L *From the viewpoint of controlling the values, it is preferable to use inorganic particles. The amount of white particles in the P2 layer is preferably less than that in the P1 layer. This is because keeping the content of white particles in the core layer, P2, relatively low can suppress an excessive decrease in the thermal dimensional stability of the biaxially oriented polypropylene film at 150°C.

[0091] In the biaxially oriented polypropylene film of the present invention, from the viewpoint of improving thermal dimensional stability at 150°C, the P2 layer preferably contains 0.5% to 15% by mass of white particles when the entire P2 layer is considered to be 100% by mass. By limiting the white particle content in the P2 layer to 15% by mass or less, the generation of coarse aggregated particles due to the aggregation of some of the white particles can be reduced. Consequently, the ΔL associated with the formation of voids during the stretching process starting from these aggregated particles is reduced. * This can mitigate the increase in [unclear value] and the deterioration of the mechanical properties of biaxially oriented polypropylene film.

[0092] On the other hand, by setting the content of white particles in the P2 layer to 0.5% by mass or more, the thermal dimensional stability of the biaxially oriented polypropylene film at 150°C can be further improved. This can be explained by the following mechanism: When a small amount of white particles are dispersed in the P2 layer, the polypropylene molecular chains intertwine with the white particles to an appropriate degree, exhibiting a nodal-like effect, and the stress during stretching is efficiently propagated throughout the film, thereby promoting the growth of crystalline domains in polypropylene. In addition, the molecular motion of the amorphous polypropylene molecular chains intertwined with the white particles is suppressed by physical interactions with the white particles or chemical interactions due to surface treatment of the white particles. As a result, thermal shrinkage becomes less likely even in high-temperature environments. Due to these two effects, setting the content of white particles in the P2 layer to 0.5% by mass or more improves the thermal dimensional stability of the biaxially oriented polypropylene film at 150°C. From the above viewpoint, the lower limit of the content of white particles in the P2 layer is more preferably 1.0%, and even more preferably 2.0%. Furthermore, from the above viewpoint, the upper limit of the content of white particles in the P2 layer is more preferably 10% by mass, and even more preferably 6.0% by mass.

[0093] In the P2 layer, it is preferable that the white particles have an average secondary particle diameter of 100 nm or more and less than 500 nm, similar to the P1 layer. This is preferable from the viewpoint of suppressing the reduction in the mechanical strength of the resulting film due to the formation of voids around the white particles during the biaxial stretching process, and from the viewpoint of minimizing changes in the appearance of the biaxially oriented polypropylene film when exposed to high-temperature environments. From the above viewpoint, it is more preferable that the average secondary particle diameter is 100 nm or more and 400 nm. Note that the white particles in the P1 and P2 layers may have the same or different components and average secondary particle diameters.

[0094] Methods for forming the P1 and P2 layers in the biaxially oriented polypropylene film of the present invention include a method of laminating and extruding the molten resin compositions that will be the raw materials for the P1 and P2 layers (co-extrusion method), a method of introducing the raw materials for the other resin layer into the extruder during the film formation process and laminating them while extruding from the die (melt lamination method), a method of laminating the films after film formation with an adhesive layer in between, and a method of coating the surface of the P1 layer with a paint composition during the film formation process (in-line coating method), and a method of coating with a paint composition after film formation (off-coating method). From the viewpoint of productivity, the co-extrusion method is preferred.

[0095] (Layer forming the opposite surface to surface A: Layer P3) When the biaxially oriented polypropylene film of the present invention has a laminated structure, it may have a P3 layer in addition to the P1 layer and P2 layer. Furthermore, the P3 layer may have a different polypropylene resin as its main component than the P1 layer and P2 layer, or it may have a resin other than polypropylene resin as its main component. Note that the P3 layer is "L in reflective color tone * It does not have a face whose value is between 50.0 and 100, i.e., face A.

[0096] From the viewpoint of enabling the biaxially oriented polypropylene film to exhibit desired functions, the P3 layer is preferably a functional layer. Specifically, the P3 layer is preferably an adhesive layer that serves to bond the biaxially oriented polypropylene film to a different material. That is, one preferred embodiment of the biaxially oriented polypropylene film of the present invention is an embodiment in which, when the layer having surface A is designated as the P1 layer, one of the outermost layers is the P1 layer and the other outermost layer is the adhesive layer.

[0097] Examples of adhesive layers include modified olefin adhesives made from modified polypropylene resins or modified polyethylene resins having polar functional groups such as hydroxyl groups, amino groups, and carboxyl groups, as well as rubber adhesives, vinyl polymerization adhesives, condensation polymerization adhesives, thermosetting resin adhesives, silicone adhesives, and acrylic adhesives.

[0098] Examples of rubber-based adhesives include butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, and isobutylene-isoprene copolymers. Examples of vinyl polymerization adhesives include acrylic, styrene, vinyl acetate-ethylene copolymers, and vinyl chloride-vinyl acetate copolymers. Examples of condensation polymerization adhesives include polyester adhesives. Examples of thermosetting resin adhesives include epoxy resins and urethane resins.

[0099] Among these, acrylic adhesives are preferably used, considering weather resistance, heat resistance, humidity resistance, and adhesion to the substrate. Specific examples of such acrylic adhesives include the "SK Dyne" (registered trademark) series manufactured by Soken Chemical Co., Ltd. (1310, 1435, 1811L, 1888, 2094, 2096, 2137, 3096, 1852, SG-50Y, 1717DT, 1259, etc.). In particular, it is preferable to use SG-50Y, 1717DT, and 1259 from the "SK Dyne" (registered trademark) series, which exhibit excellent adhesion to polypropylene.

[0100] Furthermore, it is preferable to use a curing agent together with the acrylic adhesive mentioned above. Specific examples of curing agents include, for example, in the case of isocyanates, toluene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, diphenylmethane-4-4'-diisocyanate, diphenylmethane-2-4'-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4-4'-diisocyanate, disylurohexylmethane-2-4'-diisocyanate, lysine isocyanate, and the like. The mixing ratio of the curing agent is 0.1 parts by mass to 10 parts by mass, preferably 0.5 parts by mass to 5 parts by mass, per 100 parts by mass of the adhesive. By mixing the hardener at a ratio of 0.1 parts by mass or more, the adhesive layer hardens appropriately in the drying oven, which suppresses the backing phenomenon where the adhesive layer is transferred to the opposite surface when wound onto a roll. Furthermore, by mixing the hardener at a ratio of 10 parts by mass or less, it is possible to suppress the decomposition of the hardener, which can gasify and cause contamination when exposed to high-temperature environments.

[0101] Furthermore, depending on the material of the adherend, antioxidants, UV absorbers, silane coupling agents, metal deactivators, etc., may be appropriately added to the acrylic adhesive.

[0102] In the biaxially oriented polypropylene film of the present invention, methods for providing the P3 layer include a method of laminating and extruding together with the molten resin composition for obtaining the P1 and P2 layers (co-extrusion method), a method of introducing other resin layer raw materials into an extruder during film formation and laminating them while extruding from a die (melt lamination method), a method of laminating films together after film formation via an adhesive layer, and a method of coating the surface opposite to the A-side of the P1 layer or the surface of the P2 layer with a paint composition during the film formation process (in-line coating method), and a method of coating with a paint composition after film formation (off-coating method). When the P1 and P2 layers are in contact with the P3 layer in a laminated configuration, the surface on which the P3 layer is laminated may be treated in advance with corona treatment or atmospheric pressure plasma treatment as exemplified in the previous section to improve adhesion with the P3 layer.

[0103] In the biaxially oriented polypropylene film of the present invention, if the P3 layer is an adhesive layer, the thickness of the P3 layer is preferably 0.3 μm or more and 30 μm or less. A P3 layer thickness of 0.3 μm or more allows for good adhesion to the substrate when the biaxially oriented polypropylene film is used as a label. Furthermore, a P3 layer thickness of 30 μm or less prevents the overall label thickness from becoming excessively thick, making it difficult to handle, and also prevents damage to the appearance of the substrate. From this viewpoint, the lower limit of the P3 layer thickness is more preferably 1 μm, and even more preferably 3 μm. Also from this viewpoint, the upper limit of the P3 layer thickness is more preferably 25 μm, and even more preferably 20 μm. Furthermore, the thickness of the P3 layer is smaller than the thickness of the P2 layer.

[0104] (Middle layer: P4 layer) When the biaxially oriented polypropylene film of the present invention has a laminated structure, an intermediate layer P4 may be included between each layer to suppress delamination of the P1, P2, and P3 layers, to the extent that it does not hinder the effects of the present invention. The adhesive exemplified above may be used as the P4 layer. The P4 layer can be applied to the side of the biaxially oriented polypropylene film of the present invention opposite to side A of the P1 layer, or to the surface of either the P2 or P3 layer, using an in-line coating method with a coating composition.

[0105] (Method for manufacturing biaxially oriented polypropylene film) The biaxially oriented polypropylene film of the present invention is obtained by biaxial stretching. Any of the following biaxial stretching methods may be used: simultaneous inflation biaxial stretching, simultaneous stentor biaxial stretching, or sequential stentor biaxial stretching. Among these, sequential stentor biaxial stretching is preferred in terms of controlling film formation stability, thickness uniformity, and film rigidity and dimensional stability.

[0106] Next, the method for producing the polypropylene film of the present invention will be described with examples, but the present invention is not to be interpreted as being limited only to the products obtained by such examples.

[0107] Specifically, one method that can be used is to first heat and melt the raw material in an extruder, then extrude it through a die onto a cooled cast drum to process it into a sheet (melt casting method). Another method that can be used is to dissolve the raw material in a solvent, extrude the solution through a die onto a support such as a cast drum or endless belt to form a film, and then dry and remove the solvent from this film layer to process it into a sheet (solution casting method).

[0108] When manufacturing a biaxially oriented polypropylene film having a laminated structure of two or more layers by the molten casting method, a suitable method is used in which an extruder is used for each layer constituting the biaxially oriented polypropylene film, the raw materials for each layer are melted, and these are laminated in a molten state in a confluence device provided between the extruder and the die, then guided to the die, and extruded from the die onto a casting drum to process into a molten sheet (co-extrusion method). At this time, the melting temperature of the raw materials is preferably 200°C to 280°C.

[0109] Next, the molten sheet is brought into close contact with a cast drum cooled to a surface temperature of 20°C to 80°C and cooled and solidified to produce an unstretched sheet. By keeping the surface temperature of the cast drum between 20°C and 80°C, the excessive formation of β crystals, which have a low melting point among polypropylene crystals, can be suppressed, which favorably increases the proportion of high-melting-point crystals in the film. The upper limit of the surface temperature of the cast drum is more preferably 25°C or higher, and even more preferably 30°C or higher. The lower limit of the surface temperature of the cast drum is 70°C or lower.

[0110] As a method for adhering the molten sheet on the casting drum, any of the following methods may be used: the electrostatic method (electrostatic application method), the water surface tension method, the air knife method, the press roll method, or the underwater casting method. However, the air knife method is preferred because it allows for easy control of surface roughness. When using the air knife method, the air temperature of the air knife is preferably between 20°C and 100°C, and the blown air velocity is preferably 130 to 150 m / s. Furthermore, in order to prevent vibration of the laminated unstretched sheet, it is also preferable to appropriately adjust the position of the air knife so that the air flows to the downstream side of the film formation.

[0111] (Sequential biaxial stretching) The unstretched sheet is introduced into the longitudinal stretching process. In the longitudinal stretching process, the unstretched sheet is preheated by contacting it with multiple metal rolls heated to 80°C to 160°C, preferably 100°C to 158°C, before stretching. When the preheating temperature is within the above range, the structure of the unstretched sheet is softened before proceeding to the longitudinal stretching process, allowing stretching to be performed without applying excessive stress in the longitudinal stretching process, thus reducing the thermal deformation rate in the longitudinal direction. Furthermore, it is possible to reduce the low-melting-point β-crystals contained in the unstretched sheet, promoting crystal growth in the film and leading to an increase in the melting point of the film. As a preliminary preheating before the above preheating, the unstretched sheet may be heated by contacting it with multiple metal rolls maintained at 30°C to 145°C.

[0112] An unstretched sheet immediately after preheating is stretched longitudinally to a length of 4.0 to 8.0 times between heated rolls with a difference in peripheral speed to obtain a longitudinally uniaxially oriented film. The stretching ratio is preferably 4.0 to 7.0 times, and more preferably 4.0 to 6.0 times. The stretching temperature is above 150°C and below 160°C, preferably 152°C to 158°C, and more preferably 154°C to 158°C. By keeping the stretching temperature within the above range, it is possible to suppress the retention of excessive stress and strain in the polypropylene molecular chains within the uniaxially oriented film due to stretching. Furthermore, at the above stretching temperature, the molecular chains incorporated into the crystal undergo thermal motion, disrupting the crystal arrangement and softening. This allows molecular chains to be extracted from crystals that are small in size and have a low melting point due to the stretching, and by incorporating them into another larger crystal, it is possible to promote the growth of high-melting-point crystals with thicker lamellae thickness. These effects allow for a higher melting point of biaxially oriented polypropylene film and a reduction in deformation under high-temperature conditions.

[0113] At the end of the longitudinal stretching process, it is preferable to bring the longitudinally uniaxially stretched film into contact with metal rolls that have a peripheral speed difference as needed and are maintained at 140-160°C, thereby performing a relaxation treatment in the longitudinal direction by more than 0% and less than 10%, and then cooling to room temperature. The relaxation temperature is preferably 145-160°C, more preferably 150-160°C, and even more preferably 154-160°C. Furthermore, the relaxation temperature is preferably between -10°C and +5°C of the stretching temperature, more preferably between -5°C and +5°C of the stretching temperature, and even more preferably between -5°C and the stretching temperature. When the relaxation temperature is within the above range, it promotes the incorporation of molecular chains drawn out from the crystal by longitudinal stretching into other crystals, making it possible to form higher melting point crystals with thicker lamellar thickness. Furthermore, the relaxation treatment in the longitudinal stretching process is more preferably 0.1% to 10%, even more preferably 1.0% to 10%, particularly preferably 3.0% to 10%, and most preferably 5.0% to 10%. By having the relaxation treatment in the longitudinal stretching process within the above range, the stress strain of amorphous molecular chains can be eliminated, reducing the thermal deformation rate. In addition, the mobility of the molecular chains becomes within an appropriate range, and molecular chain rearrangement is also promoted. As a result, the thermal dimensional stability of the biaxially oriented polypropylene film is improved.

[0114] Next, the longitudinally uniaxially oriented film is guided to a transverse stretching process using a tenter device. After preheating with both ends in the width direction of the longitudinally oriented film held by multiple clips, it is stretched (transversely stretched) in the width direction to 7.0 to 13 times, preferably 9.6 to 13 times, to obtain a biaxially oriented polypropylene film. By setting the stretching ratio in the width direction within the above range, the mechanical properties of the resulting biaxially oriented polypropylene film can be improved.

[0115] Here, the temperature of the preheating step in transverse stretching is preferably 170°C to 190°C, more preferably 173°C to 185°C, even more preferably 175°C to 185°C, and particularly preferably 177°C to 185°C. When the preheating temperature is within the above range, the molecular chains incorporated into the crystals formed in the longitudinal stretching step undergo thermal motion, disrupting the crystal arrangement and softening the structure. This suppresses the retention of excessive stress and strain in the polypropylene molecular chains within the longitudinally uniaxially stretched film due to transverse stretching, thereby improving the melting point and thermal dimensional stability of the resulting biaxially oriented polypropylene film.

[0116] Furthermore, the stretching temperature in the transverse stretching step after the preheating step is preferably 170°C to 180°C, more preferably between 170°C and 180°C, even more preferably between 173°C and 180°C, and particularly preferably between 175°C and 180°C. When the transverse stretching temperature is within the above range, similar to the longitudinal stretching step, it becomes possible to extract molecular chains from crystals with relatively low melting points that have been softened by preheating. Together with the subsequent relaxation step, this promotes the formation of high-melting-point crystals with thick lamellar thickness, thereby improving the thermal dimensional stability of the biaxially oriented polypropylene film.

[0117] In the subsequent relaxation process during transverse stretching, it is preferable to perform a relaxation treatment of 5% to 20% in the width direction while maintaining an appropriate tension in the film width direction with clips at a specific heat-fixing temperature. More preferably, the relaxation treatment rate is 6% to 18%, and even more preferably 10% to 15%. By having the relaxation treatment rate after transverse stretching within the above range, residual stress and strain in the amorphous molecular chains can be eliminated, improving thermal dimensional stability. In addition, the mobility of the molecular chains is within an appropriate range, which facilitates the incorporation of molecular chains into the crystal.

[0118] The temperature during the relaxation treatment (heat-fixing temperature) is preferably 168°C to 190°C, more preferably 171°C to 190°C, and even more preferably 173°C to 185°C. When the heat-fixing temperature of this relaxation treatment step is within the above range, it promotes the rearrangement of molecular chains drawn out from the crystal by lateral stretching, making it possible to form a high-melting-point crystal with a thicker lamellar thickness.

[0119] Next, the biaxially oriented film is cooled in a cooling process in which the temperature is gradually lowered in a temperature range of 80°C to 170°C while the width direction is tension-gripped with clips, and then guided to the outside of the tenter. Preferably, the upper limit of the cooling temperature is below the heat-fixing temperature. It is also preferable to perform intermediate cooling at a temperature of 150°C or higher for 5 seconds or more. This is because the stress strain remaining after the formation of the biaxially oriented polypropylene film is removed at the intermediate cooling temperature, thereby improving the thermal dimensional stability of the obtained biaxially oriented propylene film when used at the intermediate cooling temperature.

[0120] Subsequently, the clips at both ends in the width direction that were holding the biaxially oriented film are released and guided to the winder. Here, the biaxially oriented film is cut parallel to the longitudinal direction to remove the edges that were held by the clips, and the film is wound into a roll shape to obtain the biaxially oriented polypropylene film of the present invention. It is preferable that the biaxially oriented polypropylene film of the present invention is corona treated at least on side A during the winder process. By corona treating side A, when the biaxially oriented polypropylene film is used as a label, the adhesion with the printed information printed on side A can be improved, and even when used in a heat-resistant environment, it is possible to prevent the printed information from disappearing and the visibility from decreasing.

[0121] The biaxially oriented polypropylene film of the present invention obtained as described above can be used in a variety of applications, including packaging films, surface protection films, process films, release films, battery films, sanitary products, agricultural products, construction products, and medical products. Furthermore, because the biaxially oriented polypropylene film of the present invention has excellent thermal dimensional stability at 150°C, it can be used as a heat-resistant process film, a heat-resistant release film, and a heat-resistant base film. In particular, because it has excellent whiteness in addition to thermal dimensional stability at 150°C, it is preferable to use it as a label film for properly managing components that are exposed to high-temperature environments for long periods of time, such as automotive labels.

[0122] In the present invention, a release film is a film that is attached to an object such as a molded body or film to protect the object from scratches and contamination during processing and transportation, and that can be easily peeled off and discarded when the final product is ready for use. A process film is a film used in the manufacturing process of an object such as a molded body or film. Examples include films that are attached to an object during the manufacturing process to protect it from scratches and contamination, or films that function as a support when it is difficult to form a film on the object itself due to its thinness or fragility.

[0123] (label) The label of the present invention is made using the biaxially oriented polypropylene film of the present invention. The following describes, with examples, a method for manufacturing the label using the polypropylene film of the present invention, but the present invention is not limited to the products obtained by such examples.

[0124] (Label creation) In the preparation of the label of the present invention, an acrylic adhesive layer is provided on the side opposite to side A of a biaxially oriented polypropylene film using an off-coat method to obtain a biaxially oriented polypropylene film having an adhesive layer (P3 layer). Specific examples of this procedure are as follows: First, an adhesive coating composition liquid is obtained by mixing 100 parts by mass of "SK Dyne" (registered trademark) 1717DT (manufactured by Soken Chemical Co., Ltd.: solid content concentration 43% by mass) as an acrylic adhesive, 5 to 30 parts by mass of toluene as a diluent, and 1 to 5 parts by mass of Coronate L-45E (manufactured by Tosoh Corporation) as an isocyanate-based curing agent. Next, the adhesive coating composition liquid is applied to the surface opposite to side A of the biaxially oriented polypropylene film so that the thickness after drying is 5 μm, and the film is dried in a drying oven at 130°C to form an adhesive layer (P3 layer). Here, it is preferable that the surface opposite to side A is pre-treated with corona. Furthermore, when the biaxially oriented polypropylene film is a single P1 layer or a laminated structure such as P1 / P2 / P1 layers, an acrylic adhesive layer can be provided using the off-coat method, with one side of the P1 layer surface designated as surface A and the opposite side of the P1 layer surface designated as the P3 layer.

[0125] In the production of the labels, a separator film is laminated to the surface of the adhesive layer (P3 layer) provided on the surface opposite to side A of the biaxially oriented polypropylene film of the present invention, for the purpose of protecting the adhesive layer. Examples of separator films include paper coated with a release agent, resin film coated with a release agent, fluororesin film, silicone resin film, and polyolefin film which has excellent release properties from the adhesive layer. Furthermore, a preferred method for laminating the separator film is to sandwich and press it between nip rolls at room temperature or heated.

[0126] Furthermore, printing information is printed on side A of the biaxially oriented polypropylene film of the present invention. Here, it is preferable that side A has been corona treated in advance. As for the printing method, for example, a method is to print on side A of the biaxially oriented polypropylene film using a thermal transfer printer equipped with a black resin-based thermal transfer label. [Examples]

[0127] The present invention will be described below with reference to examples, but the present invention is not necessarily limited to these examples.

[0128] [A. Method for evaluating characteristics] The various properties of biaxially oriented polypropylene films were evaluated using the following methods.

[0129] (A1) Film thickness (A1-1) Total film thickness T The total thickness of the biaxially oriented polypropylene film was measured using the following procedure. First, using a dial gauge, the thickness was measured at five arbitrary points on a stack of 10 films, in accordance with JIS K7130 (1992) A-2 method. The average of these five measurements was divided by 10 to obtain the total film thickness T (μm) of the biaxially oriented polypropylene film.

[0130] (A1-2) Lamination thickness (T P1 , T P2 , T P3 ) A cross-section of a biaxially oriented polypropylene film was cut using a microtome in directions parallel to the width and thickness. After sputtering the surface of the cross-sectional sample with platinum-palladium, the cross-section was observed using a scanning electron microscope (JEOL Ltd., JSM-6700) at a magnification of 2000 to 20000 times under an accelerated voltage of 3 kV, and the thickness ratios of the P1, P2, and P3 layers were determined. The thickness ratios of each layer were determined for five different fields of view, and their average values ​​were taken as the thickness ratio of the biaxially oriented polypropylene film. The thickness of each layer was calculated using the determined thickness ratios and the film thickness obtained in item (A1-1) above, and the stacking thickness of each layer in the biaxially oriented polypropylene film (T P1 , T P2 , T P3 ) was determined. Furthermore, if layers other than P1 to P3 are included in the composition, the lamination of those layers can be determined by the same measurement method.

[0131] (A2) White particle analysis (A2-1) Composition analysis In the same manner as described in section (A1-1) above, cross-sectional samples of biaxially oriented polypropylene film were prepared and their surfaces were sputtered with platinum-palladium. Next, the elements containing the white particles in layers P1 to P3 were identified using a scanning electron microscope (JEOL Ltd., JSM-6700) and its energy-dispersive X-ray spectroscopy (EDX) detector (Oxford Corp., AZtecLiv Standard UltimMax65). Measurements were performed by changing the acceleration voltage from 0.5kV to 30kV, and the detected elements were considered to be the elements constituting the white particles contained in each layer. In this process, platinum and palladium were excluded from the analysis, and if only platinum or palladium was detected through measurements at all acceleration voltages, the identified inorganic particles were judged to contain platinum or palladium.

[0132] (A2-2) Average secondary particle diameter In the same manner as described in section (A1-2) above, cross-sectional images observed at magnifications of 3000 to 20000x using a scanning electron microscope (JEOL Ltd., JSM-6700) were analyzed using image analysis software (Planetron Corporation, Image-Pro Plus Version 4.0 for “Windows” (registered trademark)) to determine the average secondary particle diameter of the white particles.

[0133] (i) Image analysis conditions After capturing the aforementioned cross-sectional image using the software, 8-bit grayscale processing was performed by executing the "Gray Scale 8" command under the "Convert" menu. Next, the width of the captured image was set to 25 μm using the "Spatial Calibration" command under the "Calibration" menu. Subsequently, binarization was performed using the "Binarization" command under the "Processing" menu under the following conditions.

[0134] (Binarization processing conditions) • Select "3x3" • Threshold setting: Press the auto-detection button located to the right of the numerical input field once and use the value obtained. • Preview conditions: The background is displayed in white, and the detected particles are displayed in black. After performing the binarization process, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection conditions, object extraction option conditions, and particle analysis conditions, and then execute "Count" to analyze the detected particles.

[0135] (Particle detection conditions) • Brightness range selection: Select "Automatically extract dark objects". • Check the box for "Measure Object". (Object extraction option conditions) • 4-unit / 8-unit: Select 4-unit • Check only "Pre-select" and "Fill in the gaps". ·Smoothing: 0 • Exclude boundaries: Select 'All boundaries' (Particle analysis conditions) From the "Measurement" tab in the "Count / Size" command screen, select the following: • Count (corrected) ·Diameter (average) Here, "average diameter" refers to the average diameter, which is the average value obtained by measuring the diameter passing through the centroid of the detected object at 2° intervals.

[0136] (ii) Average secondary particle diameter of white particles The same procedure as in item (i) of (A2-2) above was performed in 10 different fields of view of the sample to detect particles. The measurement magnification was set from the range in item (i) above to a magnification where the layer of observation became larger than the field of view size. If the total number of particles detected in all measured fields of view was less than 200, a follow-up measurement was performed on another field of view, and the same measurement was repeated until the number exceeded 200. The average value of the "diameter (average)" of each white particle detected in all measured fields of view was taken as the average secondary particle diameter of the white particles in the sample.

[0137] (A2-3) Content of white particles If the particles identified in item (A2-1) were inorganic particles, the content of white particles in the biaxially oriented polypropylene film was determined using a thermogravimetric analyzer (Shimadzu Corporation, DTG-60) equipped with a gas flow regulator (Shimadzu Corporation, DTG-60) and an attached thermal analysis system (Shimadzu Corporation, TA-60WS). Specifically, the measurement was performed using the following procedure. First, a predetermined weight of biaxially oriented polypropylene film was packed into a metal cell. Then, the metal cell was placed in a heating furnace through which nitrogen gas flowed at a flow rate of 300 mL / min, and the mass data was measured at 1-second intervals while the temperature was raised from 30°C to 600°C at a rate of 20°C / min. The mass of the sample was obtained by subtracting the weight of the empty metal cell from the weight of the metal cell packed with the sample. At this time, the white particle content (mass %) of the sample was obtained by dividing the sample weight at 600°C by the sample mass at 30°C. Similarly, five measurements were performed, and the average value obtained was defined as the content (mass%) of white particles in the biaxially oriented polypropylene film.

[0138] (A3) Thermal property analysis (A3-1) Melting point of film Using a differential scanning calorimeter (Rigaku Corporation, Thermo Plus Evo2 series DSC Vesta), a 3 mg biaxially oriented polypropylene film sample was heated from 25°C to 250°C at a rate of 20°C / min in a nitrogen atmosphere and held for 5 minutes. The highest peak temperature of the endothermic curve obtained during this heating process was defined as the melting point of the sample. Three measurements were taken, and the average value of the obtained values ​​was defined as the melting point (°C) of the biaxially oriented polypropylene film.

[0139] (A3-2) Melting point of polypropylene resin Measurements were performed using a differential scanning calorimeter, similar to the procedure described in item (A3-1) above. After performing the heating procedure described in item (A3-1), the temperature was lowered from 250°C to 25°C at a rate of 20°C / min and held for 2 minutes, and then the temperature was raised again to 250°C at a rate of 20°C / min. The maximum peak temperature of the endothermic curve obtained during this reheating process was taken as the melting point of the polypropylene resin constituting the sample. The average value obtained from three measurements was taken as the melting point (°C) of the polypropylene raw material constituting the biaxially oriented polypropylene film.

[0140] (A4) Mechanical properties (Young's modulus) of biaxially oriented polypropylene film The Young's modulus of a biaxially oriented polypropylene film was measured using the following procedure. First, a rectangular sample measuring 150 mm × 10 mm was cut out so that the longitudinal direction was the longer side of the sample. Following the method specified in ASTM-D882 (2018), an Instron-type tensile testing machine (AMF / RTA-100, manufactured by Orientec Co., Ltd.) was used to set a 10 mm wide sample film with a chuck length of 50 mm, and a tensile test was performed at a tensile speed of 300 mm / min to determine the Young's modulus of the sample. Five measurements were taken, and the average value was taken as the Young's modulus in the longitudinal direction of the biaxially oriented polypropylene film. Furthermore, the Young's modulus in the width direction of the biaxially oriented polypropylene film was also measured in the same manner, with the longer side (measurement direction) being the width direction. Of the Young's moduli obtained from the longitudinal and width directions, the direction showing the larger value was defined as the principal orientation axis direction (X direction), and the direction showing the smaller value was defined as the Y direction.

[0141] (A5) Thermal dimensional stability (A5-1) Deformation rate due to heat treatment For the biaxially oriented polypropylene film, a rectangular sample measuring 150 mm × 10 mm was cut out with the X and Y directions defined in item A4 above as the longer sides. A gauge line (with a gauge interval of 100 mm) was drawn 50 mm from the center of the sample in the direction of the longer side, and the distance between the gauge lines was measured to three decimal places. Next, a 3 g weight was suspended from one end of the rectangular sample in the direction of the longer side, and the sample was placed in a hot air oven heated to 150°C for 30 minutes to perform heat treatment. The distance between the gauge lines of the sample after heat treatment was measured to three decimal places, and the rate of increase in the distance between the gauge lines before and after heating was calculated as the thermal expansion coefficient (%). Here, a positive value was used when the sample expanded, and a negative value was used when it contracted. Five measurements were taken in the X and Y directions, and the average values ​​were taken as the deformation rates in the X and Y directions of the biaxially oriented polypropylene film, respectively.

[0142] (A5-2) Absolute value of deformation rate before and after heat treatment, and sum thereof The absolute value of the thermal expansion coefficient (%) of the biaxially oriented polypropylene film measured in item (A5-1) above was taken as the absolute value of the deformation rate. The sum of the absolute values ​​of the deformation rates (%) in the X and Y directions was taken as the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction of the biaxially oriented polypropylene film after heat treatment at 150°C for 30 minutes.

[0143] (A6) Whiteness (A6-1) L in reflected color tones * Value (whiteness) A 5cm square sample was cut from a biaxially oriented polypropylene film. Then, in accordance with JIS-Z-8781-4 (2013), the reflected color tone (L) of the sample surface was measured using a spectrophotometer SE-2000 (manufactured by Nippon Denshoku Industries, Ltd., light source halogen lamp 12V 4A, 0°~-45° post-spectroscopy method) in the reflectance measurement mode. * The L value was measured. The measurement was performed after calibrating the device using the attached standard plate. Measurements were taken on the same side of three different samples, and the average of these measurements was used to determine the L value on the measurement surface of the biaxially oriented polypropylene film. * This was set as the value. Here, L *Surfaces with values ​​between 50.0 and 100 were designated as surface A, and measurements were performed on those surfaces in the following sections. Both surfaces were L * For surfaces where the value is between 50.0 and 100, the surface opposite to the one where the adhesive layer described later was applied was designated as surface A, and measurements were performed in the following sections.

[0144] (A6-2) L after heat treatment at 150℃ * value A 15cm square sample was cut from a biaxially oriented polypropylene film. Then, 500g / m² was applied to both sides of the sample. 2 Two pieces of cardboard were placed on top of each other, and the sample was sandwiched between them by securing the four corners of the two pieces of cardboard with clips. Next, the sample sandwiched between the two pieces of cardboard was placed in an oven heated to 150°C and subjected to heat treatment for 30 minutes. After heat treatment, the sample was removed from the oven and allowed to return to room temperature. Then, a 5cm square sample was cut from near the center of the sample, and the reflective color of surface A of the sample (L) was measured in the same manner as in section A6-1. * The value was measured.

[0145] (A6-3) L before and after 150℃ heat treatment * Value change (ΔL * value) The reflected color tone (L) of items (A6-1) and (A6-2) above * Using the value, the reflective color tone L of the A-side of the biaxially oriented polypropylene film before and after 150°C heat treatment is calculated according to the following equation (1). * Value change (ΔL * The value was calculated. Equation (1): L before and after heat treatment at 150°C * Value change (ΔL * Value) = L * 1-L * 0 L * 0: Reflective color tone before heat treatment at 150℃ (L * value) L * 1: Reflective color tone after heat treatment at 150℃ (L * value).

[0146] (A7) Glossiness A 5cm square sample was cut from a biaxially oriented polypropylene film. Then, in accordance with JIS Z-8741 (1997), the 60° gloss was measured using a digital angle-bending gloss meter (UGV-5D, manufactured by Suga Test Instruments Co., Ltd.) with the light incidence angle set to 60° and the detector reception angle set to 60°. The measurement was performed after calibration of the instrument using the attached standard plate, and the sample was positioned so that the direction of light incidence matched the X and Y directions of the sample, thereby measuring the 60° gloss in the X direction and the 60° gloss in the Y direction of the sample. Five measurements were performed on the same film sample at arbitrarily changed locations, and the average values ​​obtained were taken as the 60° gloss in the X direction (GX) and the 60° gloss in the Y direction (GY) of the biaxially oriented polypropylene film, respectively. The average of the 60° gloss in the X direction and the 60° gloss in the Y direction of the biaxially oriented polypropylene film was taken as the gloss of the biaxially oriented polypropylene film.

[0147] (A8) Surface free energy Using a contact angle meter (DropMaster DM501, manufactured by Kyowa Interface Chemical Co., Ltd.), four types of measurement liquids—water, ethylene glycol, formamide, and methylene iodide—were dropped onto surface A of a biaxially oriented polypropylene film, and the static contact angle with respect to surface A was determined. The static contact angle was measured 30 seconds after dropping each liquid onto surface A of the film. Substituting the obtained contact angle (θ) for each liquid and the respective components of the surface tension of the measurement liquid into equations (2) to (4) below, the surface free energy γS (mN / m) of the film surface was determined by solving the system of equations (2) to (4) for γSd, γSp, and γSh. Formula (2): (γSd·γLd)1 / 2+(γSp·γLp)1 / 2+(γSh·γLh)1 / 2=γL(1+cosθ) / 2 Equation (3): γS = γSd + γSp + γSh Equation (4): γL = γLd + γLp + γLh γS, γSd, γSp, and γSh represent the surface free energy, dispersion force component, polar force component, and hydrogen bonding component of the film surface, respectively, while γL, γLd, γLp, and γLh represent the surface free energy, dispersion force component, polar force component, and hydrogen bonding component of the measurement liquid used, respectively. Here, the surface tension of each liquid used was the value proposed by Panzer (J. Panzer, J. Colloid Interface Sci., 44, 142 (1973)). Five measurements were performed, and the average value was taken as the surface free energy γS (mN / m) of surface A.

[0148] (A9) Static friction coefficient, kinetic friction coefficient Biaxially oriented polypropylene film was conditioned at 23°C and 65% RH. Two strips measuring 75 mm in width and 100 mm in length were cut from the film, with the longer side being the longer edge, to create strip samples. The coefficient of static friction was measured using a slip coefficient measuring device (model ST-200, manufactured by TechnoNeeds Co., Ltd.) under a 23°C, 65% RH atmosphere using the following procedure. First, one strip sample was fixed on the measuring sample stand of the device with the tension direction of the device being the long direction and side A facing upwards. The other strip sample was then placed on top of it with side A facing downwards and the tension direction being the long direction, so that the sides A of the two strip samples were in contact with each other, and their ends were fixed to the load detection U-gauge of the device. The film was then left to stand, and a 200g weight with a 6.5cm x 6.5cm "Teflon" (registered trademark) sheet attached to the sample contact surface was placed on top of it to bring the samples (sides A together) into close contact. The friction coefficient at the point when the sample began to move (static friction coefficient μs) and the friction coefficient when the sample moved (dynamic friction coefficient μd) were measured when the upper film was pulled under the following conditions. Ten measurements were taken, and the average of the six measurements (excluding the top two and bottom two) was used as the static friction coefficient μs and dynamic friction coefficient μd of the sample. Measurement distance: 12mm Measurement speed: 210mm / min.

[0149] (A10) Mesopentade fraction (mmmm) of biaxially oriented polypropylene film or polypropylene resin (A10-1) A biaxially oriented polypropylene film was freeze-dried into a powder, extracted with n-heptane at 60°C for 2 hours to remove impurities and additives from the biaxially oriented polypropylene film, and then dried under reduced pressure at 130°C for more than 2 hours to obtain the sample. This sample was dissolved in a solvent. 13 The mesopentade fraction (mmmm) was measured and calculated using 1C-NMR under the following measurement and analysis conditions.

[0150] <Measurement conditions> Equipment: Bruker DRX-500 Nucleus for measurement: 13 C nucleus (resonance frequency: 125.8MHz) Measured concentration: 10% by mass Solvent: Benzene: Deuterated orthodichlorobenzene = 1:3 mixed solution (by volume) Measurement temperature: 130℃ Spin speed: 12Hz NMR sample tube: 5mm tube Pulse width: 45° (4.5μs) Pulse repetition time: 10 seconds Data points: 64K Total count: 10,000 times Measurement mode: complete decoupling.

[0151] <Analysis conditions> A Fourier transform was performed with the line broadening factor (LB) set to 1, resulting in a mmmm peak of 21.86 ppm. Peak splitting was performed using WINFIT software (Bruker). During this process, the peak splitting was performed starting from the high-field side as follows, and further automatic fitting by the software was performed to optimize the peak splitting. The sum of the mmmm peak fractions was then taken as the mesopentad fraction (mmmm). (a)mrrm (b)(c)rrrm (split into two peaks) (d)rrrr (e)mrmr (f)mrmm+rmrr (g)mmrr (h)rmmr (i)mmmr (j)mmmm For the same sample, the same measurement was performed 5 times, and the average value of the obtained mesopentad fraction was taken as the mesopentad fraction of the sample.

[0152] (A10-2) Mesopentad fraction of polypropylene resin Regarding the polypropylene resin raw material contained in the biaxially oriented polypropylene film, the same measurement and analysis as in item (A10-1) were performed to measure and calculate the mesopentad fraction.

[0153] (A11) Functional group analysis of the resin constituting the P1 layer (A11-1) XPS measurement Using a photoelectron spectroscopy analyzer (manufactured by ULVAC-PHI, ESCA5700), XPS (X-ray Photoelectron Spectroscopy) measurement on the A side of the biaxially oriented polypropylene film was performed under the following measurement conditions to obtain an XPS spectrum (C1s spectrum) representing the chemical bonding state of carbon present on the A side. <XPS measurement conditions> · X-ray source used: Mg · Number of integrations: 6 times · Element species for narrow scan: C1s · Number of sample measurements: In the same sample, measurements were performed at 5 different locations with an interval of at least 5 μm apart from each other. · X-ray incident angle: 45° · Neutralization: ON.

[0154] (A11-2) Functional group analysis The obtained C1s spectra were processed using the "MultiPak" analysis software (manufactured by ULVAC-FI) included with the photoelectron spectroscopy analyzer, following the procedure below. First, the presence or absence of peaks with peak tops in the bond energy region of 287 eV to 289 eV was checked in the processed C1s spectra. If peaks with peak tops in the 287-289 eV region, where the bond energy originates from a carboxylic acid group or ester group, were confirmed in four or more of the five C1s spectra, it was determined that the P1 layer with A-face contains a polypropylene resin with carboxylic acid termini. Similarly, if peaks with peak tops in the region of 285 to less than 287 eV were confirmed, it was determined that the P1 layer with A-face contains a hydroxyl group. <Data Processing Conditions> • Smoothing correction: Point 9 • Background correction: OFF SET • Shift correction: The binding energy of the maximum peak in the C1s spectrum is corrected to 284 eV.

[0155] (A12) Adhesion strength between acrylic adhesive tape and surface A (affinity with ink) The affinity of the A-side of a biaxially oriented polypropylene film for ink was evaluated by its adhesion to acrylic resin used in general-purpose ink products, based on the adhesion strength between the A-side and the following acrylic adhesive tape.

[0156] (A12-1) Preparation of adhesive tape application samples A strip-shaped sample measuring 100 mm in length and 25 mm in width was prepared from a biaxially oriented polypropylene film. On side A of the strip-shaped sample, a 19 mm wide acrylic adhesive tape No. 31B (manufactured by Nitto Denko, base material: polyester film, adhesive: acrylic resin) was bonded using a roller with a load of 2 kg, ensuring that the long sides were aligned. The adhesive tape was then bonded to the strip-shaped sample. The adhesive tape-bonded sample was then conditioned for 24 hours at a temperature of 23°C and a humidity of 65% RH.

[0157] (A12-2) Measurement of adhesion strength After humidity control, the sample was subjected to a 180° peel test under the following conditions using a Kyowa Interface Science Co., Ltd. adhesive / film peel analyzer (VPA-2). The side of the humidity-controlled sample opposite to the tape-bonded surface was fixed to the apparatus, and then the end of the adhesive tape was fixed to the load cell of the apparatus for measurement. (Peel test conditions) • Peeling angle: 180° • Tape width: 19mm • Peeling speed: 300 mm / min • Initial peeling force: 0N ·Measurement distance: 70mm From the obtained peel force waveforms, the average value of the peel force (N / 19mm) in the travel distance range of 15mm to 60mm was calculated. Similar peel force measurements were performed for three different samples, and their average value was taken as the adhesion force (N / 19mm) between the acrylic adhesive tape and surface A.

[0158] [B. Method for evaluating suitability for use] Next, we will describe a method for evaluating the characteristics of a label made by printing information on side A of a biaxially oriented polypropylene film. Here, the color of the printed information on side A of the label was set to black, and a "QR code" (registered trademark) (Model 1, Version 7, cell size: approximately 0.5 mm) of approximately 22 mm square, created with arbitrary information, and the characters "aiueo" in Gothic font with font sizes of 3pt, 4pt, and 5pt were printed on the label.

[0159] (B1) Visibility of printed information (B1-1) Back-view evaluation (opacity) Labels made from biaxially oriented polypropylene film were laminated onto black paper (AC Card Black #350, manufactured by Oji F-Tex Co., Ltd.), and the visibility of the printed information on the labels was visually checked and evaluated according to the following criteria. A: All the printed information was clearly visible. B: The letters were visible, but the "QR code" (registered trademark) pattern blended in with the background and was not visible. Only the letters "C:5pt" were visible; the other letters, including "QR code" (registered trademark), blended into the background and were not visible. D: All printed information blended into the background and was not visible. For bleed-through, a rating of A to C is preferable, with A being the best among them.

[0160] (B1-2) Text blurring evaluation Labels made of biaxially oriented polypropylene film were attached to white paper with an ISO whiteness of 90% or higher, and the bleeding of printed text was checked and evaluated according to the following criteria. Here, "bleeding" refers to the spreading of ink in printed text, causing white areas within the text or spaces between text parts to appear black, and the overall or partial widening of the line width of the text. A: All sizes of text were printed without blurring. Only the text in B:3pt was blurred. Only the letters in 3pt and 4pt font were blurred. D: All sizes of text were smudged. In terms of text blurring evaluation, A to C are preferable, with A being the best.

[0161] (B1-3) Appearance evaluation The labels obtained in section (B1-2) above, which were attached to the white paper, were illuminated with a light from a direction where the angle with the normal direction of the label surface was 60 ± 10°. The appearance of the illuminated labels was evaluated visually according to the following criteria. A: It had a sufficiently matte finish, and the printed information was clearly visible without any glare from the light. B: It has a matte finish, but the print information sometimes became blurry due to light reflection. C: The matte finish was weak, and the print information was overexposed and difficult to read due to the glare from the light. D: The gloss was so strong that the printed information was completely invisible due to the glare from the light. In terms of appearance evaluation, A to C are preferable, with A being the best among them.

[0162] (B2) Heat resistance (B2-1) Evaluation of appearance change at 150℃ Labels made of biaxially oriented polypropylene film were laminated onto a SUS plate (2 μm thick), and then heat-treated by placing them in an oven heated to 150°C for 30 minutes. After the heat treatment, the labels were removed from the oven and allowed to return to room temperature, and the changes in appearance at 150°C were evaluated visually according to the following criteria. A: There was no dimensional change or surface undulation at all, and the shape was maintained. Or, there was slight dimensional change or slight surface undulation, but the shape was maintained. B: Wrinkles have appeared at the edges of the label, or small wrinkles have appeared on the surface. C: The edges of the label were curled up or warped, or there were large wrinkles on the surface. D: Multiple large wrinkles have appeared across the entire label, or the label has peeled off. For evaluating the change in appearance at 150℃, grades A to C are preferable, with A being the best among them.

[0163] (B2-2) Evaluation of appearance change at 160℃ Except for changing the oven temperature to 160°C, the appearance change at 160°C was evaluated according to the above criteria, in the same manner as in item (B2-1) above.

[0164] (B2-3) Design evaluation The design aesthetics of the labels subjected to the 150°C heat treatment described in (B2-1) above were evaluated based on the change in whiteness according to the following criteria. The change in whiteness was observed visually. A: There was no change in the appearance of the label before and after heat treatment. B: The whiteness of the label changed slightly after heat treatment, but the legibility of the printed information remained unchanged. C: After heat treatment, the whiteness of the label partially changed, and defects occurred in some of the printed information. D: After heat treatment, the whiteness of the label changed overall, resulting in critical defects in the printed information. In terms of design aesthetics, A to C are preferable, with A being the best among them.

[0165] (B2-4) Ink heat resistance and adhesion The heat-resistant adhesion of the ink was evaluated as follows based on the state of the printed information when the labels that had undergone the 150°C heat treatment described in (B2-1) were wiped with gauze and a white cotton cloth for friction (compliant with JIS L 0803 (2011), Kanakin No. 3). The state of the printed information was observed visually. S: The printed information after heat treatment did not disappear even after wiping it repeatedly with gauze and a white cotton cloth for friction. A: The printed information after heat treatment did not disappear even after wiping it multiple times with gauze, but wiping it with a white cotton cloth used for friction left slight scuff marks. B: When the printed information after heat treatment was wiped with gauze, abrasion marks remained. C: When the printed information before and after heat treatment was wiped with gauze, the black ink became lighter. D: The printed information disappeared before or after heat treatment, or the printed information could be easily wiped off with gauze. For evaluating ink heat resistance and adhesion, a rating of S to C is preferable, with S being the best among them.

[0166] (B3) High temperature cycle durability As described in item (B2-1) above, the samples were subjected to a 150°C heat treatment, then allowed to cool to room temperature, and then placed in an oven heated to 150°C for 30 minutes. The 150°C heat treatment and room temperature cooling constituted one cycle, and after repeating this cycle 10 times, the condition of the labels was visually inspected, and the high-temperature cycle durability was evaluated according to the following criteria. A: After 10 heat treatment cycles, no cracks appeared in the label. B: After 10 heat treatment cycles, cracks appeared at the edges of the label. C: After 10 cycles of heat treatment, cracks appeared on the label surface. D: After 10 cycles of heat treatment, the label broke or peeled off. For evaluating high-temperature cycle durability, a rating of A to C is preferable, with A being the best among them.

[0167] (B4) Scratch resistance Labels made of biaxially oriented polypropylene film were slit into strips measuring 12.65 mm in width and 300 mm in length, containing the printed information, to prepare samples. The obtained samples were conditioned at 23°C and 65% RH for more than 24 hours, and then their abrasion resistance was evaluated using a tape running test machine (SFT-700 model, manufactured by Yokohama System Research Institute Co., Ltd.) according to the following procedure. First, one end of the strip-shaped sample was fixed to the machine's drive unit with the label surface, which had the printed information, in contact with the SUS roll fixed to the machine, and a load of 300 g was applied to the opposite end. Then, the tape running test machine was operated and the strip-shaped sample was run back and forth five times in the longitudinal direction under the following conditions. (SUS roll) Roll material: SUS27 (surface roughness 0.2S) Roll diameter: 6mm (Driving conditions) SUS roll and strip sample winding angle: 90° Mileage: 100mm Running speed: 3.3 cm / second The same test was conducted three times, with the strip-shaped samples being replaced. The condition of the printed information was checked by visually observing the label surface of each sample, and the abrasion resistance was evaluated according to the following criteria. S: For the three test samples, the total number of scratches affecting the printed information was 0. A: Across three test samples, the total number of scratches affecting the printed information was one. B: For the three test samples, the total number of scratches affecting the printed information was between 2 and 5. C: For the three test samples, the total number of scratches affecting the printed information was between 6 and 10. D: In all three test samples, the total number of scratches affecting the printed information was 11 or more. For abrasion resistance, a rating of S to C is preferable, with S being the best among them.

[0168] (B5) Recyclability As a polypropylene resin molded body, we evaluated the recyclability using polypropylene resin molded parts (hereinafter sometimes referred to as bumper resin parts) from the genuine front bumper of a Toyota Prius (6AA-ZVW60 model).

[0169] (B5-1) Preparation of recycled resin sheet 1 The aforementioned bumper resin parts were crushed, and 950g of the crushed material was mixed with 50g of biaxially oriented polypropylene film and introduced into an extruder heated to 260°C. After melt-extrusion in the extruder and filtration, the mixture was wound onto a cooling cast roll maintained at 70°C via a T-die using the air knife method (compressed air at 25°C, air velocity 140m / s), cooled and solidified to obtain an unstretched recycled polypropylene resin sheet (hereinafter sometimes referred to as recycled resin sheet 1).

[0170] (B5-2) Preparation of recycled resin sheet 2 In the same manner as in the previous section (B5-1), a polypropylene resin sheet (hereinafter sometimes referred to as recycled resin sheet 2) was obtained using 1000g of crushed bumper resin parts.

[0171] (B5-3) Evaluation of the breaking strength of recycled resin sheets Mechanical properties tests were performed on recycled resin sheets 1 and 2 obtained in the previous sections (B5-1) and (B5-2) using the method described in the previous section (A4). More specifically, samples were cut into 50 mm x 10 mm rectangular shapes so that the longer side was the winding direction of the cast roll. Then, following the method specified in ASTM-D882 (2018), an Instron-type tensile testing machine (AMF / RTA-100, manufactured by Orientec Co., Ltd.) was used to set a 10 mm wide sample with a chuck length of 50 mm, and a tensile test was performed at a tensile speed of 300 mm / min to determine the breaking strength of the sample. Five measurements were taken, and the average value was taken as the breaking strength (MPa) of the recycled resin sheet.

[0172] (B5-4) Strength retention rate of recycled resin sheets (recyclability evaluation) From the breaking strengths (MPa) of recycled resin sheets 1 and 2 obtained in the previous section (B5-3), the strength retention rate of the recycled resin sheets was obtained using the following formula (5). Equation (5): (Strength retention rate of recycled resin sheet (%)) = (Breaking strength of recycled resin sheet 1) / (Breaking strength of recycled resin sheet 2) × 100 The recyclability of the obtained recycled resin sheets was evaluated based on the strength retention rate according to the following criteria. A: The strength retention rate of the recycled resin sheet is 95% or higher. B: The strength retention rate of the recycled resin sheet is between 92% and 95%. C: The strength retention rate of the recycled resin sheet is 90% or more but less than 92%. D: The strength retention rate of the recycled resin sheet is less than 90%. For recyclability, a rating of A to C is preferable, with A being the best among them.

[0173] (B6) High temperature lamination properties Labels made of biaxially oriented polypropylene film were laminated onto a SUS plate (2 μm thick) using a thermal laminating machine equipped with two heating rolls under the following conditions. (Thermal lamination conditions) Roll temperature: 150℃ Roll material: Silicone resin Laminating speed: 2m / min Lamination pressure: 0.4 MPa The above lamination procedure was performed on 10 labels, and the high-temperature lamination properties were evaluated as follows by checking for wrinkle formation in the laminated labels. A: Less than one out of ten labels had wrinkles. B: Two to three out of ten labels were wrinkled. C: Between 4 and 6 out of 10 labels had wrinkles. D: More than 7 out of 10 labels were wrinkled. For evaluating high-temperature lamination properties, A to C are preferred, with A being the best among them.

[0174] [Resins, etc., used in the manufacture of biaxially oriented polypropylene film] (Polypropylene resin) The raw materials and their properties used in the biaxially oriented polypropylene films of the examples and comparative examples are shown in Table 1 below. These property values ​​were evaluated in the form of resin pellets. Four types of polypropylene raw materials (PP-1 to PP-4) were prepared. All of PP-1 to PP-4 contained BASF's "Irganox" (registered trademark) 1010 as an antioxidant in the range of 1000 ppm to 5000 ppm. The resin properties were as described in Table 1. Homopolypropylene resin 1 (PP-1): Manufactured by Sumitomo Chemical Co., Ltd. Homopolypropylene resin 2 (PP-2): Manufactured by Prime Polymer Co., Ltd. Branched-chain polypropylene resin 3 (PP-3): Manufactured by Borealis. Random polypropylene resin 4 (PP-4): Manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 1.8-2.3 mol%. (Polypropylene resin blend pellets) Furthermore, in order to improve the dispersibility of branched polypropylene resin (PP-3) in biaxially oriented polypropylene film, pre-mixing was performed with homopolypropylene resin 2. Specifically, homopolypropylene resin 2 (PP-2) and branched polypropylene resin 3 (PP-3) were dry-blended to the composition shown in Table 1, fed into a twin-screw compounding extruder, melt-mixed at 260°C, extruded into a gut-like form, and cut after cooling to obtain chip-shaped blend pellet raw material. The resin properties were as shown in Table 1. Polypropylene resin blend pellets (PP-5): Polypropylene resin blend pellets obtained by pre-mixing PP-2 and PP-3 in the composition shown in Table 1 using the method described above.

[0175] (Acid-modified polypropylene resin) As the acid-modified polypropylene resin, we used "Admer" (registered trademark) QF500, a maleic anhydride-modified polypropylene resin manufactured by Mitsui Chemicals, Inc. The resin properties are as shown in Table 1. Acid-modified polypropylene resin (PP-6): Manufactured by Mitsui Chemicals, Inc., "Admer" (registered trademark) QF500.

[0176] (White particle master pellets) Four types of white particle master pellets (MB-A to MB-D) based on polypropylene resin were prepared as white particle raw materials by pre-mixing them to the following compositions. For pre-mixing, each raw material was dry-blended to the composition shown in Table 1, fed into a twin-screw extruder, melt-mixed at 260°C, extruded into a gut-like form, and then cut after cooling to obtain chip-shaped white particle master pellets (MB-A to MB-D). The resin properties were as shown in the table. The titanium dioxide contained in each master pellet all had a whiteness of 50% or more as specified in JIS K5101-2-2 (2004). Titanium dioxide-containing master pellet A (MB-A): PP-4 based rutile-type titanium dioxide (titanium dioxide-1, average secondary particle size: 200 nm) containing 60% by mass master Titanium dioxide-containing master pellet B (MB-B): PP-4 based rutile-type titanium dioxide (titanium dioxide-2, average secondary particle size: 500 nm) containing 60% by mass master Titanium dioxide-containing master pellet C (MB-C): PP-4 based rutile-type titanium dioxide (titanium dioxide-3, average secondary particle size: 80 nm) containing 60% by mass master Calcium carbonate-containing master pellet B (MB-D): A master containing 30% by mass of spherical calcium carbonate (calcium carbonate-1, average secondary particle size: 2.8 μm) based on PP-1.

[0177] [Table 1]

[0178] [Adhesive paint composition liquid] As an acrylic adhesive, 100 parts by mass of "SK Dyne" (registered trademark) 1717DT (manufactured by Soken Chemical Co., Ltd.: solid content concentration 43% by mass) was mixed with 10 parts by mass of toluene as a diluent and 2.1 parts by mass of Coronate L-45E (manufactured by Tosoh Corporation) as an isocyanate-based curing agent to obtain an adhesive coating liquid.

[0179] (Example 1) Homopolypropylene resin PP-1, titanium dioxide-containing master pellet A (MB-A), and polypropylene resin blend pellets (PP-5) were blended so that the final content ratio was the composition of the P1 and P2 layers as shown in Table 2, and the mixture was supplied to two separate extruders. After melt-extrusion in each extruder and filtration, the mixture was combined in a feed block to form a three-layer structure (P1 layer / P2 layer / P1 layer structure, laminate thickness: 2 μm / 21 μm / 2 μm). The mixture was then wound onto a cooling cast roll maintained at 70°C via a T-die using the air knife method (compressed air at 25°C, air velocity 140 m / s), cooled and solidified to obtain an unstretched polypropylene sheet.

[0180] Next, the unstretched polypropylene sheet was sequentially biaxially stretched under the conditions described in Table 3. First, the unstretched sheet was guided to a group of preheating rolls heated to 100°C to 150°C in the longitudinal direction and heated. Then, a uniaxially oriented film was obtained by longitudinal stretching to a total of 4.0 times using the peripheral speed difference of a group of stretching rolls heated to 154°C. Next, the film was guided to a tenter, preheated to 180°C, stretched to 10 times its width in the width direction at 175°C, then heat-set at 173°C while allowing 11% relaxation in the width direction, and intermediate cooling at a temperature of 150°C to 170°C. The obtained biaxially oriented polypropylene film was guided to a winder, corona treated at the strength described in Table 3 with air filling both sides of the film (in an atmospheric environment), and then wound up to obtain a biaxially oriented polypropylene film with a thickness of 25 μm. The composition and properties of the obtained biaxially oriented polypropylene film are shown in Tables 4 to 6.

[0181] Subsequently, using the off-coat method, an adhesive coating liquid was applied to the surface opposite side A of the biaxially oriented polypropylene film so that the laminate structure was as shown in Table 7 and the thickness after drying was 5 μm. The adhesive layer (P3 layer) was then formed by drying at 130°C in a drying oven. Next, a PET film (Toray Industries, Inc., "Therapeuil" (registered trademark) BX8A) coated with a silicone release agent was laminated to the surface of the adhesive layer (P3 layer) by sandwiching it between nip rolls at room temperature. Print information was then printed on the side A of the biaxially oriented polypropylene film with the resulting adhesive layer using a thermal transfer printer equipped with a black resin-based thermal transfer label, according to the method described in section [B. Evaluation Method for Suitability for Application]. The evaluation results are shown in Table 8.

[0182] (Examples 2-9, 11, Comparative Examples 1, 2) As shown in Tables 2 and 3, biaxially oriented polypropylene films for Examples 2-9, 11, and Comparative Examples 1 and 2 were obtained by sequential biaxial stretching and film formation in the same manner as in Example 1, except that the raw material composition and film formation conditions were changed. Labels were then prepared in the same manner as in Example 1. The evaluation results of the biaxially oriented polypropylene films and labels are shown in Tables 4-6 and 8.

[0183] (Example 10) Homopolypropylene resin PP-1, acid-modified polypropylene resin PP-6, titanium oxide-containing master pellet A (MB-A), and polypropylene resin blend pellet PP-5 were blended so that the final content ratios were the compositions of the P1 layer, P2 layer, and P1' layer described in Table 2, and supplied to each of the three extruders. After melting and extruding this with each extruder and filtering with a filter, it was combined so as to be laminated in a three-layer structure (P1 layer / P2 layer / P1' layer structure, lamination thickness: 2 μm / 22 μm / 1 μm) using a feed block, and then wound and cooled and solidified on a cooling cast roll maintained at 70 °C via a T-die using an air knife method (25 °C compressed air, wind speed 140 m / s) to obtain an unstretched polypropylene sheet. Thereafter, except for changing the film-forming conditions described in Table 3, sequential biaxial stretching film formation was carried out in the same manner as in Example 1 to obtain a biaxially oriented polypropylene film of Example 10, and labels were produced in the same manner as in Example 1. The evaluation results of the biaxially oriented polypropylene film and the labels are shown in Tables 4 to 6 and 8.

[0184] (Comparative Example 3) As described in Tables 2 and 3, the raw material composition and film-forming conditions were changed, and an unstretched sheet was obtained by the method described in Example 1. Thereafter, without performing biaxial stretching film formation, a corona treatment was performed on both sides of the unstretched sheet at the strength described in the table to obtain a polypropylene film, and a label was obtained in the same manner as in Example 1. The evaluation results of the biaxially oriented polypropylene film and the labels are shown in Tables 4 to 6 and 8.

[0185] [Table 2]

[0186] [Table 3]

[0187] [Table 4]

[0188] [Table 5]

[0189] [Table 6]

[0190] [Table 7]

[0191] [Table 8] [Industrial applicability]

[0192] The present invention provides a biaxially oriented polypropylene film that is highly resistant to abrasion, prevents printed information from fading easily, and can be suitably used as a label for properly managing components that are exposed to high-temperature environments for extended periods. The biaxially oriented polypropylene film of the present invention can be suitably used for managing components that are exposed to high-temperature environments for extended periods, such as components in the engine compartment of an automobile.

Claims

1. L in reflective color tones ＊ A biaxially oriented polypropylene film characterized by satisfying the following conditions 1 and 2, where the surface with a value of 50.0 or more and 100 or less is defined as surface A, the direction of the main orientation axis of the film is the X direction, and the direction perpendicular to the X direction within the film surface is the Y direction. Condition 1: At least one side is side A. Condition 2: After heat treatment at 150°C for 30 minutes, the sum of the absolute values ​​of the deformation rate in the X direction and the absolute values ​​of the deformation rate in the Y direction is 0.0% or more and 5.0% or less.

2. The biaxially oriented polypropylene film according to claim 1, wherein when the glossiness of the surface A at 60° in the X direction is GX (%) and the glossiness of the surface A at 60° in the Y direction is GY (%), the average value of GX and GY is 21 or more and 50 or less.

3. A biaxially oriented polypropylene film according to claim 1 or 2, wherein the melting point is 176°C or higher and 185°C or lower.

4. The biaxially oriented polypropylene film according to claim 1 or 2, wherein at least one of the deformation rate in the X direction and the deformation rate in the Y direction after heat treatment at 150°C for 30 minutes is 0.0% or more and 1.5% or less.

5. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the Young's modulus is 1.5 GPa or more and 4.0 GPa or less in at least one of the X direction and the Y direction.

6. The L of the reflective color tone of surface A after heat treatment at 150°C for 30 minutes. ＊ Change in value is ΔL ＊ When this is done, the ΔL ＊ A biaxially oriented polypropylene film according to claim 1 or 2, wherein the coefficient of gravity is -1.5 or greater and 1.5 or less.

7. The biaxially oriented polypropylene film according to claim 1 or 2, wherein when the layer having surface A is defined as layer P1, the amount of white particles in the total constituent components of layer P1 is 3.0% by mass or more and 30.0% by mass or less.

8. The biaxially oriented polypropylene film according to claim 1 or 2, wherein when the layer having surface A is defined as the P1 layer, the P1 layer contains white particles with an average secondary particle diameter of 100 nm or more and less than 500 nm.

9. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the surface free energy of surface A is 34 mN / m or more and 70 mN / m or less.

10. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the layer having surface A is defined as layer P1, and the layer P1 contains a polypropylene resin having carboxylic acid terminus.

11. The biaxially oriented polypropylene film according to claim 1 or 2, wherein when the layer having surface A is designated as the P1 layer, one of the outermost layers is the P1 layer and the other outermost layer is the adhesive layer.

12. A label made using the biaxially oriented polypropylene film according to claim 1 or 2.

13. A label according to claim 12, which is affixed to a polypropylene resin molded body.

14. A polypropylene resin molded body having the label described in claim 12 affixed to it.

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