Oriented polyolefin film

Abstract

To provide a polyolefin film capable of suppressing roll wrinkles and having higher strength for suppressing film breakage.SOLUTION: The stretched polyolefin film is stretched in at least one axial direction of the MD direction and the TD direction and has a coefficient of variation of the thickness in the TD direction of 0.200 or less, a tensile strength in the MD direction of 30MPa or more and a tensile strength in the TD direction of 50MPa or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a stretched polyolefin film and the like. [Background technology]

[0002] Polyolefin films, such as polyethylene films and polypropylene films, are widely used in a variety of fields, including as protective films for electronic devices, packaging films, and optical films, and are highly valuable materials.

[0003] For example, polyolefin films are known to be suitable as protective films for build-up films used in build-up processes (see, for example, Patent Document 1). The build-up process is an essential technology for achieving high integration of printed wiring boards. In this build-up process, a build-up film is attached to a circuit board, the resin in the build-up film is cured by heat, vias are formed by laser processing, and any resulting resin residue is removed, followed by copper plating and patterning. High integration of printed wiring boards is achieved by repeating this process.

[0004] The build-up film used in the build-up method is formed of an adhesive layer containing a thermosetting resin such as an epoxy resin, and is an insulating material. One side of the adhesive layer is provided with a base film made of polyethylene terephthalate (PET), and the other side is provided with a protective film made of the aforementioned polyolefin film or the like.

[0005] Patent Document 1 also discloses a protective film used for dry film resist. Dry film resist is used to produce circuit boards, but the resist layer (photosensitive resin layer) of dry film resist is adhesive, so a cover film is required to cover it and protect the surface. For such cover films for surface protection, the use of polyethylene-based films is being considered from the standpoints of flexibility and cost. In the examples of Patent Document 1, an inflation method is used as a film manufacturing method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6905640 Summary of the Invention [Problem to be solved by the invention]

[0007] When using polyolefin films, the films are sometimes transported through film rolls and subjected to surface treatment, lamination of other layers, etc. In this case, roll wrinkles and film breakage may occur, which may reduce roll quality and production efficiency.

[0008] Furthermore, heat treatment may be performed when laminating other layers, and in this case, the film may curl, leading to a decrease in yield.

[0009] An object of the present invention is to provide a polyolefin film that can suppress roll wrinkles and has higher strength to suppress film breakage. In a preferred embodiment, in addition to the above object (i.e., as an object that is not essential), an object of the present invention is to provide a polyolefin film that can further suppress curling due to heat. [Means for solving the problem]

[0010]

[0006] In view of the above problems, the present inventors have conducted extensive research and have succeeded in obtaining a stretched polyolefin film containing a polyolefin resin, which is stretched at least uniaxially in the MD and TD directions, has a coefficient of variation of film thickness distribution in the TD direction of 0.200 or less, and has a tensile strength in the MD direction of 30 MPa or more and a tensile strength in the TD direction of 50 MPa or more, and have found that this film can solve the above essential problems. Based on this finding, the present inventors have conducted further research and have completed the present invention. That is, the present invention encompasses the following aspects.

[0011] Item 1. A stretched polyolefin film containing a polyolefin resin, stretched at least uniaxially in the MD direction and the TD direction, The coefficient of variation of the film thickness distribution in the TD direction is 0.200 or less, The tensile strength in the MD direction is 30 MPa or more, and the tensile strength in the TD direction is 50 MPa or more. Oriented polyolefin film.

[0012] Item 2. The stretched polyolefin film according to Item 1, having a heat shrinkage rate in the MD direction at 100°C of 7.0% or less and a heat shrinkage rate in the TD direction at 100°C of 7.0% or less.

[0013] Item 3. The stretched polyolefin film according to Item 1 or 2, wherein the polyolefin resin contains a polyethylene resin.

[0014] Item 4. The stretched polyolefin film according to any one of Items 1 to 3, which is a biaxially stretched film stretched in both the MD and TD directions.

[0015] Item 5. A protective film comprising the stretched polyolefin film according to any one of items 1 to 4.

[0016] Item 6. A protective film for electronic devices, comprising the stretched polyolefin film according to any one of items 1 to 4.

[0017] Item 7. A release film comprising the stretched polyolefin film according to any one of items 1 to 4.

[0018] Item 8. A packaging film comprising the stretched polyolefin film according to any one of items 1 to 4. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a polyolefin film which can suppress roll wrinkles and has higher strength because film breakage is suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0020] In this specification, the expressions "contain" and "comprise" include the concepts of "contain", "include", "consist essentially of" and "consist only of".

[0021] 1. Stretched polyolefin film In one aspect, the present invention relates to a stretched polyolefin film containing a polyolefin resin, which is stretched at least uniaxially in the MD and TD directions, and which has a coefficient of variation of film thickness distribution in the TD direction of 0.200 or less, a tensile strength in the MD direction of 30 MPa or more, and a tensile strength in the TD direction of 50 MPa or more (herein, this may be referred to as the "stretched polyolefin film of the present invention"). This will be described below.

[0022] The stretched polyolefin film of the present invention can suppress roll wrinkles and has higher strength to suppress film breakage. In the present invention, the inventors focused on the film thickness distribution in the TD direction and found that by adjusting this, roll wrinkles can be effectively suppressed. Then, they focused on tensile strength as the strength for suppressing film breakage, and succeeded in obtaining a stretched polyolefin film in which the film thickness distribution in the TD direction and tensile strength are well controlled, leading to the completion of the present invention.

[0023] The stretched polyolefin film of the present invention contains a polyolefin resin. Specifically, the stretched polyolefin film of the present invention is a stretched film formed from a resin containing a polyolefin resin as a main component.

[0024] The polyolefin resin may be, for example, a wide variety of polyolefin resins used for producing stretched films. For example, the polyolefin resin may be a polymer obtained by polymerizing an olefin compound. Such an olefin compound preferably has 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 3 to 6 carbon atoms. Specific examples of the polyolefin resin include polyethylene resin, polypropylene resin, poly(1-butene) resin, polyisobutene resin, poly(1-pentene) resin, and poly(4-methylpentene-1) resin. Furthermore, the polyolefin resin may be a copolymer containing two or more structural units derived from different olefin compounds, such as an ethylene-propylene copolymer.

[0025] Among these, the polyolefin resin preferably contains at least one selected from the group consisting of polyethylene resins and polypropylene resins, and more preferably contains a polyethylene resin, since the coefficient of variation of the thickness distribution in the TD direction and the tensile strength of the stretched polyolefin film can be easily adjusted to desired ranges. Among the polyethylene resins, low-density polyethylene or high-density polyethylene is preferred, and linear low-density polyethylene, or LLDPE, is more preferred.

[0026] The polyolefin resin contained in the stretched polyolefin film of the present invention may contain other resins as long as the effects of the present invention are not impaired.

[0027] The polyolefin resin preferably contains 80% by mass or more of the polyethylene resin, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. The polyolefin resin may consist solely of polyethylene resin.

[0028] The stretched polyolefin film of the present invention may contain other components in addition to the polyolefin resin, as long as the effects of the present invention are not impaired. Examples of other components include a wide range of additives contained in known stretched films, such as heat stabilizers, antioxidants, organic and inorganic lubricants, antiblocking agents, chlorine scavengers, antistatic agents, antifogging agents, and hydrolysis inhibitors. When the stretched polyolefin film of the present invention contains the other components, the content of the other components is 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.5% by mass, based on the total mass of the stretched polyolefin film.

[0029] As described above, the stretched polyolefin film of the present invention is stretched at least uniaxially in the MD direction and the TD direction, and is preferably stretched at least in the TD direction.

[0030] The stretched polyolefin film of the present invention may be a uniaxially stretched film obtained by stretching in one direction, or a biaxially stretched film obtained by stretching in two directions. When the stretched polyolefin film of the present invention is a biaxially stretched film, it is preferably a biaxially stretched film stretched in both the MD and TD directions.

[0031] The stretched polyolefin film of the present invention can have a single-layer structure or a multi-layer structure. The stretched polyolefin film of the present invention is preferably a single-layer structure. When the stretched polyolefin film of the present invention has a multi-layer structure, each layer contains the above-mentioned polyolefin resin. In this case, the polyolefin resins contained in each layer may be the same, or at least one or all of them may be different.

[0032] The polyolefin film of the present invention has a coefficient of variation of film thickness distribution in the TD direction of 0.200 or less, which can suppress roll wrinkles.

[0033] The coefficient of variation of the film thickness distribution in the TD direction can be measured according to the method described in the section (Measurement of the coefficient of variation of the film thickness distribution in the TD direction) in the Examples below.

[0034] The coefficient of variation of the film thickness distribution in the TD direction is preferably as low as possible to further suppress roll wrinkles. The coefficient of variation is preferably 0.180 or less, more preferably 0.170 or less, even more preferably 0.160 or less, and even more preferably 0.150 or less. From the viewpoint of particularly significantly suppressing roll wrinkles, the coefficient of variation is particularly preferably 0.140 or less, even more preferably 0.100 or less, even more preferably 0.080 or less, and even more preferably 0.050 or less. The lower limit of the coefficient of variation is not particularly limited and is, for example, 0.001, 0.002, or 0.005.

[0035] The polyolefin film of the present invention has a tensile strength of 30 MPa or more in the MD direction and a tensile strength of 50 MPa or more in the TD direction, which ensures a high strength that prevents the film from breaking.

[0036] The tensile strength in the MD direction / TD direction can be measured according to the method described in the section (Measurement of tensile strength in the MD direction / TD direction) in the Examples below.

[0037] The tensile strength in the MD direction is preferably 40 MPa or more, more preferably 50 MPa or more, even more preferably 60 MPa or more, still more preferably 70 MPa or more, and particularly preferably 80 MPa or more. The upper limit of the tensile strength is not particularly limited, and is, for example, 300 MPa, 200 MPa, or 150 MPa.

[0038] The tensile strength in the TD direction is preferably 70 MPa or more, more preferably 80 MPa or more, even more preferably 90 MPa or more, still more preferably 100 MPa or more, and particularly preferably 120 MPa or more. There is no particular upper limit to the tensile strength, and it is, for example, 400 MPa, 350 MPa, or 300 MPa.

[0039] The polyolefin film of the present invention preferably has a heat shrinkage rate of 7.0% or less in the MD direction at 100° C. and a heat shrinkage rate of 7.0% or less in the TD direction at 100° C. This makes it possible to suppress curling due to heat.

[0040] The heat shrinkage in the MD direction at 100°C can be measured according to the method described later in the Examples (Measurement of heat shrinkage in the MD direction at 100°C). The heat shrinkage in the TD direction at 100°C can be measured according to the method described later in the Examples (Measurement of heat shrinkage in the TD direction at 100°C).

[0041] From the viewpoint of further suppressing curling, the heat shrinkage rate in the MD direction at 100°C is preferably 6.0% or less, more preferably 5.0% or less, even more preferably 4.0% or less, still more preferably 3.0% or less, particularly preferably 2.5% or less, especially more preferably 2.0% or less, especially more preferably 1.5% or less, and particularly preferably 1.2% or less.

[0042] From the viewpoint of further suppressing curling, the heat shrinkage rate in the TD direction at 100°C is preferably 6.0% or less, more preferably 5.0% or less, even more preferably 4.0% or less, still more preferably 3.0% or less, particularly preferably 2.5% or less, especially more preferably 2.0% or less, and particularly preferably 1.7% or less.

[0043] The thickness of the stretched polyolefin film of the present invention is not particularly limited and can be set to a desired thickness depending on the intended use. For example, the thickness of the stretched polyolefin film can be set to 5 to 100 μm, preferably 10 to 50 μm, and more preferably 15 to 30 μm. When the stretched polyolefin film has the above-mentioned multilayer structure, the thickness of the stretched polyolefin film means the total thickness of each layer.

[0044] The stretched polyolefin film of the present invention can be used in various applications. Among them, the stretched polyolefin film of the present invention is particularly suitable as a protective film for electronic components. The stretched polyolefin film of the present invention can also be used as a protective film, release film, or packaging film other than those mentioned above.

[0045] The stretched polyolefin film of the present invention can be used as a protective film for buildup films. The type of buildup film is not particularly limited, and for example, it can be widely applied to known buildup films. Such a protective film is provided to protect the adhesive layer of the buildup film. In one embodiment, the buildup film can be a film obtained by laminating the stretched polyolefin film of the present invention, an adhesive layer (e.g., an adhesive layer containing a thermosetting resin such as an epoxy resin), and a base film (e.g., a film containing polyethylene terephthalate (PET)) in this order.

[0046] The stretched polyolefin film of the present invention can be used for various applications by disposing other layers on one or both sides as needed. For example, the stretched polyolefin film of the present invention can be used as the above-mentioned protective film, release film, etc. by disposing a release layer containing a release agent (such as a silicone coating) on ​​one or both sides as needed. As another example, the stretched polyolefin film of the present invention can be used as a packaging film, etc. by disposing a coating layer (such as a gas barrier layer) on one or both sides as needed.

[0047] 2. Manufacturing method of stretched polyolefin film The method for producing the stretched polyolefin film of the present invention is not particularly limited, and for example, the same methods as those for known stretched films can be widely adopted. Specifically, the stretched polyolefin film of the present invention can be produced by a production method including a step of stretching a raw sheet containing the polyolefin resin at least uniaxially in the MD direction and the TD direction.

[0048] The method for producing the raw sheet is not particularly limited, and the raw sheet can be obtained by a method similar to a known method. Specifically, the raw sheet can be formed by extrusion molding a raw material containing the polyolefin resin using an extruder.

[0049] The raw sheet is stretched under appropriate conditions to obtain the desired stretched polyolefin film. The stretching method is not particularly limited, and a wide variety of known methods can be used. For example, known methods such as stretching between rolls with different peripheral speeds, a tenter method, and a tubular method can be used as the stretching method.

[0050] The stretching direction can be uniaxial or biaxial. The stretching direction is preferably at least uniaxial in the MD and TD directions. When the stretched polyolefin film is a uniaxially stretched film, it is more preferable to stretch the raw sheet in the TD direction, and when it is a biaxially stretched film, it is preferable to stretch the raw sheet in both the MD and TD directions.

[0051] When the stretching treatment is the biaxial stretching described above, for example, both sequential stretching and simultaneous stretching can be applied as the biaxial stretching method. Among these, simultaneous biaxial stretching by a tenter method, sequential biaxial stretching by a tenter method, and sequential biaxial stretching in which longitudinal (flow, MD) stretching is performed between rolls with different peripheral speeds and then transverse (width, TD) stretching is performed by a tenter method are preferred, as they are easier to obtain the desired stretched film.

[0052] The raw sheet is preheated before stretching. By setting the preheating temperature for uniaxial stretching (preferably in the TD direction) or for at least uniaxial stretching (preferably only in the TD direction) in biaxial stretching to 147 to 163°C (preferably 150 to 160°C, more preferably 152 to 158°C, and particularly preferably 153 to 157°C), the desired film thickness distribution can be easily achieved. This also makes it easy to obtain the desired heat shrinkage. The preheating temperature for stretching in the MD direction in biaxial stretching is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. There is no particular upper limit to the preheating temperature for stretching in the MD direction in biaxial stretching. However, from the viewpoint of suppressing adhesion to the metal roll by keeping the preheating temperature low, it is preferably 120°C or lower, more preferably 115°C or lower, and even more preferably 110°C or lower.

[0053] The raw sheet can be preheated by a variety of known methods, including preheating the raw sheet at a predetermined temperature using hot air from an oven heated to a predetermined temperature by a tenter, or preheating the raw sheet at a predetermined temperature using an IR heater installed between metal rolls. After this preheating, the raw sheet is stretched in a stretching zone. The temperature of the stretching zone is not limited and is, for example, 110 to 130°C.

[0054] The stretching ratio of the raw sheet by biaxial stretching is not particularly limited, and for example, the stretching ratio in the MD direction can be 2 to 10, and the stretching ratio in the TD direction can be 2 to 15. The stretching ratio of the raw sheet by uniaxial stretching is not particularly limited, and for example, the stretching ratio can be 1.1 to 15.

[0055] After stretching the raw sheet, it is preferable to subject the resulting stretched film to a relaxation treatment, which can control the film thickness distribution and heat shrinkage rate within better ranges, particularly by relaxation in the MD direction (and in the TD direction in the case of biaxial stretching).

[0056] As the relaxation treatment method, a wide variety of known methods can be adopted, and specifically, the stretched film can be relaxed by hot air from an oven heated to a predetermined temperature in a tenter. In the case of biaxial stretching, the relaxation treatment is carried out after stretching in the MD direction and / or after stretching in the TD direction.

[0057] The relaxation rate is not particularly limited, and for example, the relaxation rate in the MD direction can be, for example, 2 to 10%, preferably 5 to 8%, and the relaxation rate in the TD direction can be, for example, 2 to 20%, preferably 7 to 15%.

[0058] The stretched film obtained by uniaxial or biaxial stretching is wound up, and then subjected to an aging treatment, and can be cut to a desired product width.

[0059] In one aspect, the present invention relates to a method for producing a stretched polyolefin film, comprising a step of stretching a raw sheet containing the polyolefin resin at least uniaxially in either the MD or TD direction, wherein the preheating temperature for uniaxial stretching (preferably in the TD direction) or for at least uniaxial stretching (preferably only in the TD direction) in the case of biaxial stretching is 147 to 163° C. This allows the stretched polyolefin film of the present invention to be easily obtained.

[0060] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described herein. [Example]

[0061] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0062] The polyolefin resins used in the examples and comparative examples are as follows. PE-1: Dow Chemical Company's "INNATE™ TF80" (LLDPE) PE-2: SABIC "BX202" (LLDPE)

[0063] Example 1 100 parts by mass of PE-1 pellets and 0.3 parts by mass of an antiblocking agent (Sylysia 430, Fuji Silysia Chemical Co., Ltd.) were fed from a hopper to a single-screw extruder, melt-kneaded, and extruded through a single-layer die. The extruded resin layer was cooled and solidified while being pressed onto a cooling drum by air pressure using an air knife, to obtain a raw sheet.

[0064] Next, the raw sheet was stretched using a tenter-type sequential biaxial stretching machine. Specifically, the raw sheet was preheated at 100°C with a longitudinal stretching roll and stretched in the MD direction at a stretch ratio of 6.0 at 100°C. This stretched raw sheet was preheated in a tenter oven at 155°C, and then stretched in the TD direction at a stretch ratio of 7.8 in a stretching zone at 125°C. The stretched film obtained was then relaxed 10% in the TD direction to obtain a stretched polyolefin film with a thickness of 20 μm.

[0065] Example 2 A stretched polyolefin film was obtained in the same manner as in Example 1, except that the preheating temperature during stretching in the TD direction was changed to 150°C.

[0066] Example 3 A stretched polyolefin film was obtained in the same manner as in Example 1, except that the preheating temperature during stretching in the TD direction was changed to 160°C.

[0067] Example 4 A stretched polyolefin film was obtained in the same manner as in Example 1, except that the polyolefin resin was changed to PE-2.

[0068] Example 5 A stretched polyolefin film was obtained in the same manner as in Example 1, except that the stretching method was changed to simultaneous biaxial stretching (preheating temperature during stretching: 155°C, stretching temperature: 125°C).

[0069] Example 6 A stretched polyolefin film was obtained in the same manner as in Example 1, except that immediately after the relaxation treatment in the TD direction, the clips were released after the oven exit and the winding draw ratio was reduced to perform 5% MD relaxation.

[0070] Example 7 A stretched polyolefin film was obtained in the same manner as in Example 1, except that immediately after the relaxation treatment in the TD direction, the clips were released after the oven exit and the winding draw ratio was reduced to perform 8% MD relaxation.

[0071] Example 8 A stretched polyolefin film was obtained in the same manner as in Example 4, except that immediately after the relaxation treatment in the TD direction, the clips were released after the oven exit and the winding draw ratio was reduced to perform 5% MD relaxation.

[0072] Example 9 Immediately after the relaxation treatment in the TD direction, the temperature inside the oven was set to 25°C, and while the film was rapidly cooled, the vertical distance between the holding clips was narrowed, and a stretched polyolefin film was obtained in the same manner as in Example 5, except that 5% MD relaxation was performed.

[0073] (Comparative Example 1) A stretched polyolefin film was obtained in the same manner as in Example 1, except that the preheating temperature during stretching in the TD direction was changed to 145°C.

[0074] (Comparative Example 2) A stretched polyolefin film was obtained in the same manner as in Example 1, except that the preheating temperature during stretching in the TD direction was changed to 165°C.

[0075] (Comparative Example 3) 100 parts by mass of PE-1 pellets and 0.3 parts by mass of an antiblocking agent (Sylysia 430, manufactured by Fuji Silysia Chemical Co., Ltd.) were melt-kneaded and formed into a film by a casting method to obtain a polyolefin film having a thickness of 20 μm.

[0076] Comparative Example 4 A polyolefin film was obtained in the same manner as in Comparative Example 3, except that the polyolefin resin was changed to PE-2.

[0077] (Comparative Example 5) 100 parts by mass of PE-1 pellets and 0.3 parts by mass of an antiblocking agent (Sylysia 430, manufactured by Fuji Silysia Chemical Co., Ltd.) were melt-kneaded and formed into a film by an inflation method to obtain a polyolefin film having a thickness of 20 μm.

[0078] (Comparative Example 6) A polyolefin film was obtained in the same manner as in Comparative Example 5, except that the polyolefin resin was changed to PE-2.

[0079] (Measurement of tensile strength in MD and TD directions) The tensile strength in the MD and TD directions of the stretched polyolefin films of the Examples and Comparative Examples was measured using a Tensilon universal material testing machine RTG-1210 (trade name) manufactured by A&D Co., Ltd. Specifically, the stretched polyolefin film was cut into a size of 15 x 150 mm with the long sides in the MD and TD directions, and the tensile strength was measured under conditions of a chuck distance of 100 mm and a pulling speed of 200 mm / min, and the strength at the breaking point (unit: MPa) was determined.

[0080] (Measurement of the coefficient of variation of the film thickness distribution in the TD direction) The thickness distribution in the TD direction of the stretched polyolefin films of the Examples and Comparative Examples was measured using a tabletop offline contact-type thickness measurement device TOF-5R (product name) manufactured by Yamabun Electric Co., Ltd. Specifically, the stretched polyolefin film was cut into a size of 50 x 600 mm with the long side in the TD direction, and the thickness was measured over a 600 mm full width area at 1 mm intervals. The average thickness (unit: μm) and standard deviation of thickness (unit: μm) were calculated from the thickness data obtained at 600 locations. The value obtained by dividing the standard deviation of thickness by the average thickness was used as the coefficient of variation of the thickness distribution in the TD direction.

[0081] (Measurement of heat shrinkage rate at 100℃ in MD direction) The heat shrinkage in the MD direction of the stretched polyolefin films of the Examples and Comparative Examples at 100°C was calculated by marking a film cut from a roll, heat-treating it, and then calculating the change in the distance between the marks before and after the heat treatment. Specifically, the measurement was performed using the following method. A 20 mm wide, 150 mm long rectangular test piece was prepared so that the length of the film coincided with the MD direction of the film. Markings were made at intervals of 100 mm on each piece, and the distance between the marks was measured with an accuracy of 0.1 mm using a glass scale. The test piece was suspended in a thermostatic chamber set at 100°C for 15 minutes without load, removed, and allowed to cool at room temperature for at least 15 minutes. The distance between the previously read marks was then measured. The rate of change in the distance between the marks before and after heating was calculated using the formula: Heat shrinkage = [(length before treatment - length after treatment) / length before treatment] × 100 (%).

[0082] (Measurement of thermal shrinkage at 100°C in the TD direction) The thermal shrinkage in the TD direction of the stretched polyolefin films of the Examples and Comparative Examples at 100°C was calculated by marking a film cut from a roll, heat-treating it, and then calculating the change in the distance between the marks before and after the heat treatment. Specifically, the measurement was performed using the following method. A 20 mm wide, 150 mm long strip-shaped test piece was prepared so that the length of the film coincided with the TD direction of the film. Markings were made at intervals of 100 mm on each piece, and the distance between the marks was measured using a glass scale to an accuracy of 0.1 mm. The test piece was suspended in a thermostatic chamber set at 100°C for 15 minutes without load, removed, and allowed to cool at room temperature for at least 15 minutes. The distance between the previously read marks was then measured. The rate of change in the distance between the marks before and after heating was calculated using the formula: Thermal shrinkage = [(length before treatment - length after treatment) / length before treatment] × 100 (%).

[0083] (Evaluation of roll wrinkles) The stretched polyolefin films of the Examples and Comparative Examples were rolled into a shape of 600 mm wide x 5000 m long, and the rolls were wound up at a speed of 50 m / min using a winding machine. The appearance of the wound rolls was visually inspected and evaluated according to the following criteria. ⊚: There were no wrinkles on the sides of the stretched polyolefin film. ◯: There were 1-2 small wrinkles less than 2 mm wide on the side of the stretched polyolefin film. ×: The stretched polyolefin film had three or more small wrinkles less than 2 mm wide or large wrinkles 2 mm wide or more.

[0084] (Curl evaluation) The curl of the stretched polyolefin films of the Examples and Comparative Examples was measured by cutting the stretched polyolefin film from the roll, heat-treating it, and then placing it on a glass plate to measure the height of the part floating above the glass plate. Specifically, the measurement was performed using the following method. Five pieces of stretched polyolefin film cut to a size of 5 cm x 5 cm were prepared and suspended in a thermostatic chamber set to 100°C under no load for one hour. After removal, they were allowed to cool at room temperature for 15 minutes or more, placed on the glass plate with the convex side down, and the heights of the four corners were measured with a tape measure. The maximum value was taken as the curl value. The curl was evaluated using the following criteria. ⊚: Curl is 3 mm or less. Good: Curl is greater than 3 mm and less than 5 mm. ×: Curl is greater than 5 mm.

[0085] (Measurement and evaluation results) Table 1 shows the production conditions and measurement and evaluation results of the stretched polyolefin films obtained in each of the Examples and Comparative Examples.

[0086] [Table 1]

Claims

1. A stretched polyolefin film containing a polyolefin resin, stretched at least uniaxially in the MD direction and the TD direction, The coefficient of variation of the film thickness distribution in the TD direction is 0.200 or less, The tensile strength in the MD direction is 30 MPa or more, and the tensile strength in the TD direction is 50 MPa or more. Oriented polyolefin film.

2. 2. The stretched polyolefin film according to claim 1, which has a heat shrinkage rate of 7.0% or less at 100°C in the MD direction and a heat shrinkage rate of 7.0% or less at 100°C in the TD direction.

3. The stretched polyolefin film according to claim 1 , wherein the polyolefin resin comprises a polyethylene resin.

4. 2. The stretched polyolefin film according to claim 1, which is a biaxially stretched film stretched in both the MD and TD directions.

5. A protective film comprising the stretched polyolefin film according to any one of claims 1 to 4.

6. A protective film for electronic components, comprising the stretched polyolefin film according to any one of claims 1 to 4.

7. A release film comprising the stretched polyolefin film according to any one of claims 1 to 4.

8. A packaging film comprising the stretched polyolefin film according to any one of claims 1 to 4.

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