Surface protective film

Abstract

To provide a surface protective film good in releasability of a release layer from an adhesive layer, little in fish eye, and capable of suppressing end part over-adhesion after a punching process after pasting to adherends of various shapes.SOLUTION: A surface protective film has a three layer constitution of an adhesive layer, a substrate layer, and a release layer, where the arithmetic average roughness Ra of the release layer is 0.1 μm or more and 0.45 μm or less, the ten point average roughness (Rz) is 1.0 μm or more and 4.5 μm or less, and the thickness ratio of the release layer is 2% or more and 12% or less of the total film thickness.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface protection film that has good peelability between the adhesive layer and the release layer, has few fish eyes, and can suppress excessive adhesion at the edges after the die-cutting process following lamination to various shapes of substrates. [Background technology]

[0002] In recent years, liquid crystal displays and touch panel devices have become widespread, and these are composed of numerous optical sheets, optical films, and other components made of synthetic resin. Since it is necessary to minimize defects such as optical distortion in these optical components, surface protective films are frequently used to prevent scratches and dirt that could cause defects.

[0003] Among the optical components mentioned above, substrates with uneven surfaces, such as diffusers and prism sheets, are available on the market with a variety of surface shapes. Surface protection films used in the manufacture of small devices such as smartphones and tablets require particular protection against damage to the substrate caused by dents from fisheye lenses, etc. Adhesion strength is sometimes adjusted depending on the size of the surface irregularities.

[0004] Furthermore, this type of surface protection film is manufactured as a long roll by co-extruding multiple layers, including an adhesive layer, a base layer, and a release layer. Therefore, an antiblocking agent is added to the release layer to prevent blocking between the adhesive layer and the release layer. Since irregularities are formed on the surface of the release layer to which the antiblocking agent is added, the coefficient of friction between the adhesive layer and the release layer can be reduced when forming the long roll, thus enabling stable production.

[0005] However, as in Patent Document 1, if the elastic modulus of the film is lowered to improve conformability with the adherend, the adhesive layer component may protrude outside the adherend during the cutting process after lamination, making it difficult to peel off the film at the cut portion. Patent Document 2 uses a design with a high elastic modulus of the film, but if the elastic modulus of the film is too high, it may tear during processing or use. Also, in Patent Document 3, aluminosilicate is added as an antiblocking agent to reduce the coefficient of friction, but if the particle size is large, the particles may aggregate and increase the number of fish eyes. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 110361 [Patent Document 2] Japanese Patent Publication No. 2021-138834 [Patent Document 3] Japanese Patent Publication No. 2008-150623 [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is the above-mentioned problem. That is, to provide a surface protective film that has good peelability between the adhesive layer and the release layer, has few fish eyes, and can suppress excessive adhesion at the edges after the die-cutting process following bonding with the adherend. [Means for solving the problem]

[0008] In other words, the present invention is as follows:

[0009] This surface protection film has a three-layer structure consisting of an adhesive layer, a base layer, and a release layer, characterized in that the arithmetic mean roughness (Ra) of the release layer is 0.1 μm or more and 0.45 μm or less, the ten-point mean roughness (Rz) is 1.0 μm or more and 4.5 μm or less, and the thickness ratio of the release layer is 2% or more and 12% or less of the total thickness of the surface protection film. [Effects of the Invention]

[0010] The surface protection film of the present invention has good peelability between the adhesive layer and the release layer, has fewer fish eyes, and can suppress excessive adhesion at the edges after the die-cutting process following lamination with the adherend. [Modes for carrying out the invention]

[0011] The present invention will be described below. However, the present invention is not limited to the following embodiments.

[0012] The present invention relates to a surface protection film having three layers: an adhesive layer, a base layer, and a release layer, wherein the adhesive layer and the release layer are arranged on opposite sides of the base layer, the release layer contains a polyolefin resin, the arithmetic mean roughness (Ra) is 0.1 μm or more and 0.45 μm or less, the ten-point mean roughness (Rz) is 1.0 μm or more and 4.5 μm or less, and the thickness ratio of the release layer is 2% or more and 12% or less of the total surface protection film.

[0013] The release layer in the present invention is designed to improve peelability from the adhesive layer and prevent blocking, and is preferably made of at least one polyolefin resin selected from polyethylene, polypropylene, and polybutene.

[0014] Examples of polyethylene include high-pressure low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). Examples of polypropylene include homopolypropylene (hereinafter sometimes referred to as homopolypropylene PP; propylene is sometimes referred to as PP), random polypropylene, and block polypropylene. Examples of polybutene include homopolybutene, butene-ethylene copolymer, and butene-propylene copolymer. These polyolefin resins may be crosslinked to improve heat resistance and mold release properties. As the crosslinking method, known crosslinking methods such as electron beam crosslinking and dynamic crosslinking in the presence of peroxides can be adopted. In the release layer of the present invention, it is most preferable to use block polypropylene in which an uncrosslinked rubber component is present in homopolypropylene to form a sea-island structure. The release layer is preferably a mixture composition of block polypropylene (hereinafter sometimes referred to as block PP) of 97% by mass or more and ultra-high molecular weight polyethylene described below.

[0015] The arithmetic mean roughness (Ra) of the release layer in the present invention is 0.1 μm or more and 0.45 μm or less. Ra is more preferably 0.2 μm or more and 0.40 μm or less, still more preferably 0.25 μm or more and 0.40 μm or less, and particularly preferably 0.3 μm or more and 0.40 μm or less. When Ra is less than 0.1 μm, the surface unevenness of the release layer is not large, so the peelability between the adhesive layer and the release layer deteriorates, and film blocking causes process troubles. When the Ra of the release layer exceeds 0.45 μm, there is a risk that the rubber component contained in the raw material aggregates into fish eyes, or the haze of the surface protective film increases and the visibility deteriorates, so there is a risk of overlooking defects after bonding to the adherend. The evaluation of visibility is performed by the method described below. The Ra of the release layer can be controlled by the type and addition amount of the above polyolefin used for the release layer.

[0016] The ten-point average roughness (Rz) of the release layer in the present invention is 1.0 μm or more and 4.5 μm or less. Rz is more preferably 1.5 μm or more and 4.5 μm or less, still more preferably 2.0 μm or more and 4.5 μm or less, and particularly preferably 2.5 μm or more and 4.0 μm or less. If the Rz of the release layer is less than 1.0 μm, many irregularities cannot be formed on the surface, resulting in deterioration of the peelability between the adhesive layer and the release layer, and process troubles due to blocking of the film. If the Rz of the release layer exceeds 4.5 μm, irregularities are generated in the adhesive layer when it comes into contact with the adhesive layer, and the contact area with the adherend decreases, resulting in non-expression of adhesive force.

[0017] The arithmetic mean roughness Ra and the ten-point average roughness (Rz) of the release layer of the surface protection film described above can be calculated by the method described below.

[0018] The thickness ratio of the release layer in the present invention is 2% or more and 12% or less of the entire surface protection film. The thickness ratio of the release layer is preferably 3% or more and 12% or less, and more preferably 4% or more and 10% or less. If the thickness ratio of the release layer exceeds 12%, the thickness ratio of the base material layer decreases, so the film elastic modulus does not increase, and end over-adhesion occurs in the cutting process after bonding to the adherend. On the other hand, if it is less than 2%, the surface roughness of the release layer is insufficient, blocking occurs when contacting the adhesive layer of the laminated film, and the laminated film becomes difficult to peel off.

[0019] The release layer in the present invention may contain particles. For example, inorganic particles, organic particles, etc. can be used, and it is preferably organic particles with less concern about damaging the adherend when bonded to the adherend. Examples of the organic particles include acrylic resin particles, styrene resin particles, polyolefin resin particles, polyester resin particles, polyurethane resin particles, polycarbonate resin particles, polyamide resin particles, silicone resin particles, fluororesin particles, or copolymer resin particles of two or more monomers used in the synthesis of the above resins, and these may be used alone or in combination.

[0020] In one preferred embodiment of the present invention, a composition comprising the polyolefin resin and ultra-high molecular weight polyethylene can be used as a release layer. The intrinsic viscosity [η] of the ultra-high molecular weight polyethylene is 3.5 dl / g or more and 35 dl / g or less, preferably 5 dl / g or more and 30 dl / g or less. If ultra-high molecular weight polyethylene with a viscosity of less than 3.5 dl / g is formulated as the release layer, surface irregularities may not be formed, the peelability between the adhesive layer and the release layer may deteriorate, and blocking may occur, potentially preventing the film from peeling off. If ultra-high molecular weight polyethylene with a viscosity exceeding 35 dl / g is formulated as the release layer, the particles may aggregate and form a fish-eye pattern. As the ultra-high molecular weight polyethylene, for example, fine particulate ultra-high molecular weight polyethylene with excellent heat resistance and sliding properties, as described in Japanese Patent Application Publication No. 2015-48384, is suitable. Furthermore, the average particle size of the fine particulate polyethylene is preferably in the range of 5 μm or more and 20 μm or less, preferably 7 μm or more and 15 μm or less. If the average particle size of the particulate ultra-high molecular weight polyethylene is less than 5 μm, sufficient irregularities may not be formed in the release layer, resulting in insufficient release properties, which is undesirable. If it exceeds 20 μm, the particles may aggregate, causing fish-eye patterns and clogging of the filters used in the extrusion process, which can lead to production problems. The ultra-high molecular weight polyethylene used in this invention may be crosslinked to improve heat resistance and release properties. Known crosslinking methods such as electron beam crosslinking and dynamic crosslinking in the presence of peroxides can be employed.

[0021] In the present invention, the release layer is preferably a mixed composition in which block PP accounts for 97% by mass or more, the average dispersion diameter of island-like particles of ultra-high molecular weight polyethylene in the block PP is 5 μm or more and less than 20 μm, and the amount of ultra-high molecular weight polyethylene added is 0.05% by mass or more and 0.5% by mass or less.

[0022] As the above block PP is 97% by mass or more, the arithmetic mean roughness (Ra) of the release layer is between 0.1 μm and 0.45 μm.

[0023] Furthermore, when the average particle size of ultra-high molecular weight polyethylene is less than 5 μm, the ten-point average roughness Rz may be less than 1 μm, and when it exceeds 20 μm, the ten-point average roughness Rz may exceed 4.5 μm.

[0024] The amount of ultra-high molecular weight polyethylene added is preferably 0.05% by mass or more and 0.5% by mass or less, more preferably 0.1% by mass or more and 0.5% by mass or less, and even more preferably 0.3% by mass or more and 0.5% by mass or less. If the amount of ultra-high molecular weight polyethylene is less than 0.05% by mass, the ten-point average roughness (Rz) of the release layer may be less than 1.0 μm, which may worsen the peelability between the adhesive layer and the release layer, and blocking may occur. If it exceeds 0.5% by mass, the particles may aggregate and form a fisheye pattern.

[0025] The surface protective film of the present invention has a base layer. The mechanical properties of the film (breaking strength, elongation at break, modulus of elasticity, etc.) can be adjusted depending on the type of resin used in the base layer. Here, the base layer refers to a layer having a finite thickness. The material of the base layer is not particularly limited, but for example, polyolefin resins and polyester resins can be used, and among these, polyolefin resin is preferred as the main component from the viewpoint of productivity and processability. The main component referred to here is the component with the highest mass percentage (highest content) among all the components constituting the base layer.

[0026] Examples of polyolefin resins included as the main component in the substrate layer include low-crystallinity or amorphous ethylene-α-olefin copolymers, homopolypropylene, propylene-ethylene copolymers (random copolymers and / or block copolymers), propylene-α-olefin copolymers, propylene-ethylene-α-olefin copolymers, ethylene-ethyl (meth)acrylate copolymers, ethylene-methyl (meth)acrylate copolymers, ethylene-n-butyl (meth)acrylate copolymers, and ethylene-vinyl acetate copolymers. These may be used alone or in combination. The α-olefin is not particularly limited as long as it can be copolymerized with propylene or ethylene, and examples include 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, and 1-heptene.

[0027] In the present invention, it is preferable to use homopolypropylene for the base layer in order to improve excessive adhesion at the edges during the cutting process after lamination of the adherend and the surface protective film.

[0028] The elastic modulus of the surface protective film of the present invention is the average value of the elastic modulus measured parallel to the resin flow during film formation (hereinafter sometimes referred to as MD elastic modulus) and the elastic modulus measured perpendicular to the resin flow (hereinafter sometimes referred to as TD elastic modulus), and is preferably 900 MPa to 1300 MPa, and more preferably 1000 MPa to 1200 MPa. If the elastic modulus of the film is less than 900 MPa, the adhesive layer component may protrude outside the adherend during the cutting process after lamination to the adherend, causing excessive adhesion at the cut edges and making it difficult to peel off the film. If the elastic modulus of the film exceeds 1300 MPa, the elongation of the film is considerably reduced, which may cause it to tear during processing or use.

[0029] Homopolypropylene is a resin that is preferably used in the base layer in the present invention. The melt flow rate (MFR, measured under the conditions of 230°C and 2.16 kg) of the resin used is preferably 3 g / 10 min to 20 g / 10 min, more preferably 4 g / 10 min to 15 g / 10 min, and even more preferably 5 g / 10 min to 10 g / 10 min. If the MFR of the resin in the base layer is less than 3 g / 10 min, the melt viscosity may be too high, which may reduce productivity. Also, if the MFR of the resin in the base layer is greater than 20 g / 10 min, the shape of the lamination interface with the adhesive layer may become unstable.

[0030] The number of fisheyes in the surface protective film of the present invention, with a major axis of 80 μm or more and less than 200 μm, is 75 per square meter. 2 Preferably, the following: 75 pieces / m 2 If the following limits are exceeded, there is a risk that dents will occur when the material is bonded to the substrate, potentially damaging the substrate.

[0031] In the present invention, it is preferable that the substrate layer contains a nucleating agent for the purpose of achieving the elastic modulus specified in this application. By containing a nucleating agent in the substrate, the rigidity of the surface protective film can be increased and the heat resistance can be improved.

[0032] As the aforementioned nucleating agent, sorbitol compounds, nonitol compounds, phosphate ester compounds, rosin compounds, carboxylate metal salt compounds, amide compounds, aromatic sulfonic acid compounds, quinacridone compounds, and high-density polyethylene can be used. However, high-density polyethylene is preferred because it is less likely to cause clogging of the filter in the substrate layer and is used from the viewpoint of suppressing fisheye formation in the film.

[0033] The density of the aforementioned high-density polyethylene is 0.93 g / cm³. 3 More than 0.97g / cm 3 The following is preferable: 0.93 g / cm³ 3 Below this level, the molecular weight is small and the crystallization temperature is low, so the effect as a crystal nucleating agent may be small, and the density is 0.97 g / cm³. 3If the size is larger, the high molecular weight of the high-density polyethylene can impair fluidity, and gelation can result in a fish-eye appearance.

[0034] In the present invention, various additives such as lubricants, antioxidants, weathering agents, antistatic agents, and pigments may be appropriately added to the substrate layer, as long as they do not impair its properties.

[0035] In the present invention, the amount of nucleating agent added to the substrate layer is preferably 0.1% by mass or more and 7.0% by mass or less, more preferably 0.5% by mass or more and 6.0% by mass or less, and particularly preferably 1.0% by mass or more and 5.0% by mass or less. If the amount of nucleating agent in the substrate layer is less than 0.1% by mass, the crystallization temperature of the surface protective film of the present invention may not rise, and the elastic modulus of the surface protective film of the present invention may not be satisfied. On the other hand, if the amount of nucleating agent in the substrate layer exceeds 7.0% by mass, dispersion problems may occur within the substrate layer, and the number of fisheyes may increase.

[0036] In the present invention, the base layer preferably contains a styrene-based elastomer having a melt flow rate of 5 g / 10 min to 50 g / 10 min at 230°C and 2.16 kg, and / or a polypropylene-based resin having a melt flow rate of 1 g / 10 min to 20 g / 10 min at 230°C and 2.16 kg. It is preferable that the base layer contains, as a component other than the main component, a styrene-based elastomer having a melt flow rate of 5 g / 10 min to 50 g / 10 min at 230°C and 2.16 kg, and / or a polypropylene-based resin having a melt flow rate of 1 g / 10 min to 20 g / 10 min at 230°C and 2.16 kg, which can improve the affinity between the adhesive layer and the base layer and enhance interfacial adhesion.

[0037] As a method for incorporating a styrene-based elastomer having a melt flow rate of 5 g / 10 min to 50 g / 10 min at 230°C and 2.16 kg, or a polypropylene-based resin having a melt flow rate of 1 g / 10 min to 20 g / 10 min at 230°C and 2.16 kg, into the base layer, one example is to use a method in which the surface protective film of the present invention is recovered and recycled as raw material, and this method is preferable from the viewpoint of resin recycling and reduction of production costs.

[0038] In this invention, the adhesive layer is laminated on the opposite side of the release layer and is designed to adhere to the substrate. The components constituting the adhesive layer are not particularly specified, but from the viewpoint of adhesion during lamination, suppression of contamination after heating, recyclability, and film formation, it is preferable to use a thermoplastic synthetic rubber-based adhesive, and among these, a styrene-based thermoplastic elastomer is more preferable.

[0039] Suitable styrene-based thermoplastic elastomers for the adhesive layer in the present invention include, for example, styrene-conjugated diene copolymers such as styrene-butadiene copolymer (SBR), styrene-isoprene-styrene copolymer (SIS), and styrene-butadiene-styrene copolymer (SBS), and their hydrogenated derivatives (e.g., hydrogenated styrene-butadiene copolymer (HSBR), styrene-ethylenebutylene-styrene triblock copolymer (SEBS), styrene-ethylenebutylene diblock copolymer (SEB)), and styrene-isobutylene copolymers (e.g., styrene-isobutylene-styrene triblock copolymer (SIBS), styrene-isobutylene diblock copolymer (SIB), or mixtures thereof). Among these, styrene-conjugated diene copolymers such as styrene-butadiene-styrene copolymer (SBS) and their hydrogenated derivatives, and styrene-isobutylene copolymers are preferably used. Only one type of styrene-based elastomer may be used, or two or more types may be used in combination. Furthermore, materials other than styrene-based elastomers may be used as needed.

[0040] In the adhesive layer of the present invention, polyolefin resins can be formulated for the purpose of adjusting the adhesive strength. Specifically, examples include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, low-crystalline or amorphous ethylene-α-olefin copolymers, crystalline polypropylene, low-crystalline polypropylene, amorphous polypropylene, propylene-ethylene copolymer (random copolymer and / or block copolymer), propylene-α-olefin copolymer, propylene-ethylene-α-olefin copolymer, polybutene, 4-methyl-1-pentene-α-olefin copolymer, ethylene-ethyl (meth)acrylate copolymer, ethylene-methyl (meth)acrylate copolymer, ethylene-n-butyl (meth)acrylate copolymer, and ethylene-vinyl acetate copolymer. Among these, polypropylene resins such as crystalline polypropylene, low-crystalline polypropylene, amorphous polypropylene, propylene-ethylene copolymer (random copolymer and / or block copolymer), propylene-α-olefin copolymer, and propylene-ethylene-α-olefin copolymer are preferably used. These polyolefin resins may be used alone or in combination. The α-olefin is not particularly limited as long as it can copolymerize with ethylene, propylene, and 4-methyl-1-pentene. Examples include ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, and 1-heptene.

[0041] In the adhesive layer of the present invention, tackifiers can be added to increase tackiness. Specifically, examples include terpene phenols, styrene-α-methylstyrene systems, aromatic hydrocarbon systems, and aliphatic / aromatic copolymer systems. These can be formulated considering adhesion to the substrate and contamination. These tackifiers can be used individually or in combination of two or more types.

[0042] In the present invention, known additives such as UV absorbers, antioxidants, and fatty acid amides may be appropriately incorporated into the adhesive layer for the purpose of improving adhesive strength and preventing blocking with the release layer.

[0043] The surface protection film of the present invention described above is used as a surface protection film for a large number of optical sheets, optical films, and other components made of synthetic resin, particularly optical components with surfaces having an uneven shape, such as diffusers and prism sheets.

[0044] Next, the method for manufacturing the surface protective film of the present invention will be described.

[0045] The method for manufacturing the surface protective film of the present invention is not particularly limited. For example, in the case of a three-layer laminated structure having an adhesive layer, a base layer, and a release layer in that order, examples include a so-called co-extrusion method in which the resin compositions constituting each layer are melt-extruded from separate extruders and laminated together in a die, or a method in which the adhesive layer, base layer, and release layer are melt-extruded individually and then laminated by a lamination method. However, from the viewpoint of productivity, it is preferable to manufacture by co-extrusion. The materials constituting each layer may be mixed separately using a Henschel mixer or the like, or all or part of the materials for each layer may be kneaded in advance. As for the co-extrusion method, known methods such as the inflation method and the T-die method can be used, but from the viewpoint of excellent thickness accuracy and surface shape control, the hot-melt co-extrusion method using the T-die method is particularly preferred.

[0046] When manufactured by co-extrusion, the components of the adhesive layer, base layer, and release layer are each extruded from a melt extruder. At this time, the extrusion temperature of the base layer and release layer is preferably between 180°C and 250°C, and more preferably between 200°C and 230°C, depending on the resin used. If the extrusion temperature exceeds 250°C, the melt viscosity decreases, which may cause uneven thickness and result in a film with non-uniform thickness. If the resin temperature is below 180°C, the melt viscosity is too high, which may reduce productivity.

[0047] The extrusion temperature of the adhesive layer is preferably in the range of 120°C to 230°C, and more preferably 150°C to 200°C, although this depends on the resin used. If the extrusion temperature is below 120°C, the melt viscosity is high, which may reduce productivity. On the other hand, if the temperature exceeds 230°C, the viscosity of each raw material in the adhesive layer decreases, and pressure fluctuations during extrusion may reduce productivity.

[0048] It is preferable to laminate and integrate the adhesive layer, base material layer, and release layer inside the T-die and perform co-extrusion. Then, the material is cooled and solidified with a metal cooling roll, formed into a film, and wound into a roll to obtain a surface protection film. In the surface protection film of the present invention, it is preferable to add an antiblocking agent to the release layer laminated on the opposite side of the adhesive layer. In this case, the coefficient of friction is reduced, and winding during production can be carried out without problems.

[0049] The total thickness of the surface protection film of the present invention is preferably 10 μm or more and 200 μm or less, more preferably 20 μm or more and 150 μm or less, and particularly preferably 25 μm or more and 100 μm or less. If it is less than 10 μm, the elastic modulus of the film will not increase, and it may tear during processing or use. If it exceeds 200 μm, the thickness variation during the production of the surface protection film will become large, which is undesirable.

[0050] The ratio of the adhesive strength at the edges of the substrate after lamination and die-cutting of the surface protective film of the present invention to the adhesive strength of the normal portion of the surface protective film (edge ​​over-adhesion index) is 1.0 or more and 1.5 or less, more preferably 1.0 or more and less than 1.3. If the edge over-adhesion index is less than 1.0, it is lower than the adhesive strength of the normal portion, which may cause lifting at the cut area. If the edge over-adhesion index exceeds 1.5, it may be difficult to get a starting point when trying to peel off the cut portion, which may make it impossible to peel off.

[0051] The surface protection film of the present invention can be used as a surface protection film to prevent scratches and dirt from adhering during the manufacturing, processing, and transportation of synthetic resin plates, metal plates, glass plates, etc., but is preferably used as a surface protection film for optical applications, such as diffusers and prism sheets, which have uneven surfaces. In other words, the surface protection film of the present invention can be bonded to substrates such as synthetic resin plates, metal plates, and glass plates. [Examples]

[0052] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. The measurement and evaluation of various physical properties were carried out by the following methods.

[0053] (1) Arithmetic surface roughness (Ra) The arithmetic mean roughness (Ra) of the release layer of the surface protective film, the ten-point mean roughness (Rz) of the release layer, and the arithmetic mean roughness Ra of resin layer B were determined using a shape measuring laser microscope (VK-X100) manufactured by Keyence Corporation, in accordance with JIS B0601-1994, by taking measurements of 21 samples within a 1.5 mm x 1.5 mm area of ​​the surface protective film and calculating the average values ​​of each.

[0054] (2) Number of fish eyes After cutting the surface protective film to A4 size, three A4-cut sheets were visually inspected under fluorescent light reflection, and the fisheye areas were marked. Then, using a Keyence microscope, only fisheyes with a major axis of 80 μm or more and less than 200 μm were extracted. This process was repeated for all three A4 sheets, and then 1 m 2 It was converted to [a certain value].

[0055] (3) Thickness ratio of the release layer Five samples were randomly taken from the laminated film, embedded in epoxy resin, and the film cross-sections were cut out with a microtome. These cross-sections were observed with a scanning electron microscope at 3,000x magnification to calculate the thickness of each layer, and the thickness ratio of the release layer was calculated from the average of the five samples.

[0056] (4) Island dispersion diameter From the surface of the release layer of the surface protection film, 10 particles were randomly collected from around 1 cm 2 on each side, and the major diameter of the particle size was measured, and the average value was taken as the island dispersion diameter.

[0057] (5) Haze The haze of the surface protection film was measured in accordance with JIS K7136 using a haze meter HM-150 manufactured by Murakami Color Technology Research Institute Co., Ltd. The measurement was carried out 3 times, and the average value of the total haze for the 3 times was taken as the measured value.

[0058] (6) Visibility It is determined based on the relationship between the evaluation result of the number of fish eyes measured by the method described in (2) above and the total haze described by the method described in (3) above. The evaluation method for visibility is as follows. A. Visibility "〇": When both the total haze of the surface protection film is less than 55% and the number of fish eyes is less than 75 per m 2 . B: Visibility "△": When both the total haze of the surface protection film is 55% or more and the number of fish eyes is less than 75 per m 2 . C: Visibility "×": Regardless of the total haze of the surface protection film, when the number of fish eyes is 75 per m 2 or more.

[0059] (7) Film elastic modulus The film elastic modulus was taken as the average value of the MD elastic modulus and the TD elastic modulus. Specifically, after cutting the surface protection film stored and adjusted for 24 hours under the conditions of a temperature of 23 °C and a relative humidity of 50% to 125 mm in the MD direction and 50 mm in the TD direction, the measurement was carried out in accordance with JIS K-7161. The MD elastic modulus and the TD elastic modulus were taken as the average values obtained when measured 3 times each.

[0060] (8) Measurement of end adhesion Each surface protective film, which had been temperature and humidity controlled for 24 hours under conditions of 23°C and 50% relative humidity, was bonded to the prism surface of the prism sheet to the substrate using a roll press (special pressure roller manufactured by Yasuda Seiki Seisakusho Co., Ltd. (hardness A80, weight 2kg)) at a bonding pressure of 0.10 MPa and bonding speed of 3 m / min. After that, the films were stored at 23°C and 50% relative humidity for 24 hours, and then cut into pieces 25 mm wide and 150 mm long using a Thomson die cutter to create test pieces, which were used for peel tests.

[0061] Adhesion strength was evaluated using a tensile testing machine (Orientec universal testing machine Tensilon) at a peeling speed of 300 mm / min and a peeling angle of 180°. The adhesive strength in the central 70 mm of the test specimen, excluding the 25 mm at both ends, was defined as the normal adhesive strength, and the maximum adhesive strength near the end of the test specimen just before the peeling of the surface protective film was completed was defined as the end adhesive strength. The ratio of the end adhesive strength to the adhesive strength in the normal portion was defined as the end over-adhesion index.

[0062] (9) Peelability of the adhesive layer and the release layer Each surface protection film was rolled up to 100m in length, and after being controlled temperature and humidity for 24 hours under conditions of 23°C and 50% relative humidity, the adhesive layer and release layer were peeled off smoothly without any peeling noise. Those that peeled off smoothly without any noise and left peeling marks on the adhesive layer were marked with a "○" (good).

[0063] (10) Melt Flow Rate (MFR) The melt flow rate (MFR) of the resin used in surface protective films is measured using a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd., in accordance with JIS K7210-1997. When measuring the melt flow rate of styrene-based thermoplastic elastomers and polypropylene-based resins, the temperature is 230°C and the load is 2.16 kg / cm². 2 When measuring the melt flow rate of polyethylene resin under these conditions, use a temperature of 190°C and a load of 2.16 kg / cm². 2 The measurements were taken under the following conditions. All units are in g / 10 min.

[0064] (Example 1) The constituent resins for each layer were prepared as follows.

[0065] Release layer: Block PP-A (MFR = 5g / 10 min (230℃, 2.16kg / cm²) 2 The mixture used consisted of 99.7% by mass of (measured using [method]) and 0.3% by mass of ultra-high molecular weight polyethylene ("Mipelon®", PM200, average particle size 10 μm) manufactured by Mitsui Chemicals, Inc.

[0066] Adhesive layer: JSR HSBR ("Dynalon®") 1321P, MFR 10g / 10min (230℃, 2.16kg / cm²) 2 (Measured at 230℃, 2.16 kg / cm²) 80% by mass of (aromatic hydrocarbon tackifier manufactured by Mitsui Chemicals, Inc. "FTR (registered trademark)" FTR8100), 10% by mass of (4-methyl-1-pentene ("absortomer (registered trademark)" EP1013) manufactured by Mitsui Chemicals, Inc. 2 (Measured using)) 10% by mass was used.

[0067] Base layer: 95% by mass of homo-PP ("Novatec" PP FL4, MFR 5g / 10 min (measured at 230℃, 2.16kg) manufactured by Nippon Polypropylene Co., Ltd., and commercially available high-density polyethylene (density 0.96g / cm³). 3 , MFR10g / 10min (190℃, 2.16kg / cm 2 (Measured using)) 5% by mass was used.

[0068] Next, the constituent resins for each layer were fed into the extruders of a T-die composite film-making machine, which has three extruders. The discharge rate of each extruder was adjusted so that the release layer was 3.0 μm thick (10% of the total film thickness), the base layer was 25 μm thick, and the adhesive layer was 2.0 μm thick. The layers were then stacked in this order and extruded from the composite T-die at an extrusion temperature of 230°C. The resulting film was cast onto a casting drum roll with a surface temperature controlled to 40°C, and the formed film was wound around the drum roll to obtain a surface protective film.

[0069] Subsequently, the obtained surface protective film was evaluated using the method described above.

[0070] (Example 2) A surface protective film was obtained in the same manner as in Example 1, except that the composition constituting the release layer was changed from 99.7% by mass of block PP-A to 99.5% by mass, and from 0.3% by mass of ultra-high molecular weight polyethylene ("Mipelon®", PM200) manufactured by Mitsui Chemicals, Inc. to 0.5% by mass.

[0071] (Example 3) A surface protective film was obtained in the same manner as in Example 1, except that the composition constituting the release layer described in Example 2 was changed to Block PP ("Topylene" J640F) manufactured by Gyosei Chemical Co., Ltd., with an MFR of 9 g / 10 min (measured at 230°C and 2.16 kg).

[0072] The surface protection films produced in Examples 1 to 3 satisfy all the claims of the present application, have few fisheyes, offer good visibility, can suppress excessive adhesion at the edges after the die-cutting process following lamination to various shapes of substrates, and also provide excellent surface protection for the substrates.

[0073] (Example 4) A surface protection film was obtained in the same manner as in Example 1, except that the composition constituting the release layer consisted of 99.9% by mass of block PP-A and 0.1% by mass of ultra-high molecular weight polyethylene ("Mipelon®", PM200) manufactured by Mitsui Chemicals, Inc. The surface protection film produced by this method satisfies all the claims of the present application, has few fisheyes, good visibility, can suppress excessive adhesion at the edges after the die-cutting process following lamination to various shapes of substrates, and also exhibits excellent surface protection of the substrate.

[0074] (Example 5) A surface protection film was obtained in the same manner as in Example 1, except that the high-density polyethylene content of the base layer was set to 0.5% by mass. The surface protection film produced by this method satisfies all the claims of the present application, has few fisheyes, good visibility, can suppress excessive adhesion at the edges after the die-cutting process following lamination to various shapes of substrates, and also exhibits excellent surface protection of the substrate.

[0075] (Comparative Example 1) A surface protective film was obtained in the same manner as in Example 1, except that the composition constituting the release layer was 100% by mass of block PP-A. Because the surface protective film produced by this method did not contain ultra-high molecular weight polyethylene, the ten-point average roughness (Rz) of the release layer was less than 1 μm, so no irregularities were formed on the surface, and the peelability of the adhesive layer and release layer was inferior to that of the surface protective film produced in the example.

[0076] (Comparative Example 2) A surface protection film was obtained in the same manner as in Example 1, except that the composition constituting the release layer consisted of 99% by mass of block PP-A and 1% by mass of ultra-high molecular weight polyethylene ("Mipelon®", PM200) manufactured by Mitsui Chemicals, Inc. The surface protection film produced by this method had too much ultra-high molecular weight polyethylene added, resulting in a ten-point average roughness (Rz) of 4.5 μm or more in the release layer and a haze of 55% or more in the surface protection film, making it difficult to observe fish eyes.

[0077] (Comparative Example 3) A surface protective film was obtained in the same manner as in Example 1, except that the composition constituting the release layer was changed to 99.5% by mass of block PP ("Novatec" PP BC4FC, MFR of 9 g / 10 min (measured at 230°C, 2.16 kg) manufactured by Nippon Polypropylene Co., Ltd., which has a high haze as a raw material, and 0.5% by mass of ultra-high molecular weight polyethylene ("Mipelon®", PM200) manufactured by Mitsui Chemicals, Inc. The surface protective film produced by this method had an arithmetic mean roughness (Ra) of 0.45 μm or more in the release layer and a haze of 55% or more in the surface protective film, making it difficult to observe fish eyes.

[0078] (Comparative Example 4) A surface protective film was obtained in the same manner as in Example 1, except that the thickness of the adhesive layer in the surface protective film was fixed, the thickness of the release layer was changed from 3.0 μm to 4.5 μm (the thickness ratio of the release layer from 10% to 15%), and the thickness of the base layer was changed from 25 μm to 23.5 μm. In the surface protective film produced by this method, the elastic modulus of the surface protective film did not increase due to the reduced thickness ratio of the base layer, resulting in excessive adhesion at the edges.

[0079] (Comparative Example 5) A surface protective film was obtained in the same manner as in Example 1, except that the composition constituting the release layer was changed from 0.3% by mass of ultra-high molecular weight polyethylene ("Mipelon®", PM200) to 0.3% by mass of amorphous silica with an average particle size of 10 μm. The surface protective film produced by this method had 75 fisheyes / m². 2 The value exceeded the limit, and dents occurred after the surface protective film was bonded to the substrate.

[0080] [Table 1]

Claims

1. This surface protection film has a three-layer structure consisting of an adhesive layer, a base layer, and a release layer. The release layer contains 97% by mass or more of block polypropylene relative to the release layer, and 0.05% by mass or more and 0.5% by mass or less of ultra-high molecular weight polyethylene relative to the release layer. The intrinsic viscosity [η] of the aforementioned ultra-high molecular weight polyethylene is 3.5 dl / g or more and 35 dl / g or less. The ultra-high molecular weight polyethylene has a particulate shape, and the average particle diameter, which is the arithmetic mean of the major axes of 10 points of the particulate matter observed from the surface of the release layer, is 5 μm or more and less than 20 μm. A surface protective film characterized in that the release layer has an arithmetic mean roughness (Ra) of 0.1 μm or more and 0.45 μm or less, a ten-point mean roughness (Rz) of 1.0 μm or more and 4.5 μm or less, and the thickness ratio of the release layer is 2% or more and 12% or less of the total thickness of the surface protective film.

2. The surface protective film according to claim 1, wherein the surface protective film is laminated to a substrate, and the ratio of the adhesive strength of the edges of the substrate after punching to the adhesive strength of the normal portion of the surface protective film (edge ​​over-adhesion index) is 1.0 or more and 1.5 or less.

3. The surface protective film according to claim 1 or 2, wherein the adhesive layer comprises a styrene-based thermoplastic elastomer.

4. The surface protective film according to any one of claims 1 to 3, wherein the adhesive layer comprises a polyolefin resin.

5. A surface protective film according to any one of claims 1 to 4, wherein the film elastic modulus is 900 MPa or more and 1300 MPa or less.

6. The surface protective film according to any one of claims 1 to 5, wherein the base layer contains 50% by mass or more and 99% by mass or less of homopolypropylene, and the MFR of said homopolypropylene is 3 g / 10 min or more and 20 g / 10 min or less.

7. The number of fisheyes on the film with a major axis of 80 μm or more and less than 200 μm is 75 per meter. ２ A surface protective film according to any one of claims 1 to 6, which is less than [amount missing].

8. The aforementioned substrate layer acts as a crystal nucleating agent with a density of 0.93 g / cm³. ３ 0.97g / cm or more ３ A surface protective film according to any one of claims 1 to 7, containing 0.1 to 7.0% by mass of the following polyethylene.

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