JP6988981B2 - Biaxially stretched polypropylene film - Google Patents

Description

The present invention relates to a biaxially stretched polypropylene film having excellent adhesion and peelability and reducing foreign matter contamination, voids and air voids when bonded. In particular, it relates to protective films and release materials used in the manufacturing process of electronic parts and electronic substrates, the manufacturing process of thermosetting resin members such as fiber-reinforced plastics, the manufacturing process of photosensitive films, and the like. The present invention relates to a biaxially stretched polypropylene film having excellent peelability, which is particularly useful for a release film, a release liner, a carrier or a protective material at the time of material production, a separator film thereof, and the like.

Biaxially stretched polypropylene film is excellent in light weight, thermal stability, and mechanical properties, and is therefore widely used as an industrial material film including packaging. Particularly in recent years, it has been used as a non-silicone mold release material by utilizing the low surface energy of polypropylene film in the manufacturing process of electronic parts and electronic substrates, and the manufacturing process of thermosetting resin members such as fiber-reinforced plastics. Widely used as a protective material and a mold release material.

As a technique for improving mold release performance while maintaining the thermal stability and mechanical properties of a polypropylene film, for example, a technique of applying a silicone-based mold release agent to a polypropylene film having a low heat shrinkage is generally widely known (). For example, Patent Document 1). As a technique for improving the thermal stability of a polypropylene film, for example, the crystallinity of the polypropylene film may be improved (Patent Document 2), or a film using crystalline polypropylene having a specific molecular weight and stereoregularity may be used (Patent Document 3). ) Etc. are disclosed. However, when a film coated with a silicone-based mold release agent is used as a mold release material (separator film) for a protective film for electronic devices or the like, silicone transfer occurs, which is not preferable for electronic components. Therefore, in recent years, a non-silicone (coated) film has been strongly demanded as a separator for a protective film used in a manufacturing process of electronic parts and electronic substrates.

As a protective film used in the manufacturing process of electronic parts, electronic substrates, photosensitive materials, etc., it is also necessary that there is little foreign matter contamination, voids, and air voids when bonded.
As a polypropylene protective film having excellent thermal stability and few fish eyes (microforeign substances), for example, a non-stretched film containing an α-olefin copolymer elastomer in a polypropylene resin and having a specific physical property value is proposed. (Patent Document 4). Further, Japanese Patent Application Laid-Open No. 2002-40667 (Patent Document 5) discloses a photoresist cover film having a specific surface, and Japanese Patent Application Laid-Open No. 2003-62954 (Patent Document 6) further discloses. Matte films for overlamination that have a specific range of surfaces are disclosed.

Since the films produced by these techniques are substantially free of lubricant and have a small amount of ash in the film, the amount of minute foreign substances (fish eyes) is less than that of the conventional level, and the film can be used as a protective film. However, in the recent market for electronic parts, photosensitive materials, etc., there is a demand for a protective film having an even lower level of foreign matter, and it cannot be said that the level required by the market is satisfied. In addition, it does not always meet the demands of the market in terms of peelability and film windability. The surface roughness of the film has a great influence on the peelability of the non-silicone film. Since the surface roughened film disclosed in the above-mentioned Patent Documents 5 and 6 has a sufficiently high protrusion height on the surface, high peelability can be obtained and no winding deviation or the like occurs. However, it tends to be an over-roughened surface, and therefore, when it is attached to a protective body as a protective film or a release film, it has a drawback that air or the like is easily sandwiched and an (air) void is easily formed.

On the other hand, in the technical field of photosensitive films and photosensitive elements, techniques for protective films that form a specific surface property and reduce fish eyes have been developed (Patent Documents 7 and 8). However, even with these technologies, biaxially stretched polypropylene films with excellent adhesion and peelability while reducing foreign matter contamination, voids, and air voids when bonded so that the market can be fully satisfied are still available. Not obtained.

Japanese Patent Application Laid-Open No. 10-226781 (Claims) JP-A-11-279497 (Claims, [0006] to [0007]) Japanese Unexamined Patent Publication No. 2001-146536 (Claims, [0007] to [0010]) JP-A-2010-184990 (Claims) JP-A-2002-40667 (Claims) JP-A-2003-62954 (Claims) Japanese Unexamined Patent Publication No. 2000-330291 (Claims, [0041] to [0045]) JP-A-2002-229200 (Claims, [0036] to [0038])

An object of the present invention is to provide a biaxially stretched polypropylene film having excellent peelability, which is useful as a protective film and / or a non-silicone separator film thereof.

The present invention includes aspects described below.
(1) Formed from a polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less.
The surface roughness of at least one surface
(A) Center line roughness (Ra) of 0.03 to 0.10 μm,
(B) Maximum height (Rmax) of 0.3 μm to 1.0 μm,
The biaxial feature is that the film has a layer having a size (major axis) of 50 μm or more and a number of fish eyes of 100 pieces / m ² or less, and a thickness of 5 μm or more and 60 μm or less. Stretched polypropylene film.
(2) The polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less is made of an isotactic polypropylene homopolymer having an isotactic mesopentad fraction of 93% or more. The biaxially stretched polypropylene film according to the above item (1).
(3) A polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less is biaxially stretched from a cast raw sheet formed by passing it through a sintered metal non-woven fabric filter having a filtration accuracy of 10 μm or less. The biaxially stretched polypropylene film according to the above item (1) or (2), characterized in that the film is made of.
(4) Any of the above items (1) to (3), wherein the polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less has an ash content of 200 ppm or less. The biaxially stretched polypropylene film according to item 1.
(5) Both surface layers (skin layers) composed of polypropylene resin layers having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less, and a core layer whose resin component is polypropylene resin are provided between the two surface layers. The biaxially stretched polypropylene film according to any one of the above items (1) to (4), which comprises a three-layered biaxially stretched film.
(6) The biaxially stretched polypropylene film according to item (5) above, wherein the core layer in which the resin component is a polypropylene resin contains the same polypropylene resin as the surface layer.
(7) The core layer in which the resin component is a polypropylene resin is different from a polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less on the surface layer, and a polypropylene resin having a melt flow rate of the surface layer. The biaxially stretched polypropylene film according to the above item (5) or (6), which is a layer containing polypropylene resin as a resin component.
(8) The biaxially stretched polypropylene film according to any one of the above items (5) to (7), wherein the core layer is a layer containing fine particles of an inorganic substance.
(9) The biaxially stretched polypropylene film according to item (8) above, wherein the fine particles of the inorganic substance are at least one fine particle selected from the group consisting of talc and calcium carbonate.

The biaxially stretched polypropylene film according to the present invention has few fish eyes (microforeign substances) and is extremely excellent in releasability. Therefore, it is a thermosetting resin such as an electronic component, an electronic substrate manufacturing process, and a fiber-reinforced plastic. It is suitable as a protective film used in a member manufacturing process, a photosensitive film manufacturing process, and / or a non-silicone separator film thereof.

The figure which shows an example of the size distribution (occurrence frequency) of a fish eye (small foreign substance).

The biaxially stretched polypropylene film of the present invention is formed of a polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less, and has a surface roughness of at least one surface.
(A) Center line roughness (Ra) of 0.03 to 0.10 μm,
(B) Maximum height (Rmax) of 0.3 μm to 1.0 μm,
A biaxially stretched film having a layer having a size (major axis) of 50 μm or more and a number of fish eyes of 100 pieces / m ² or less and a thickness of 5 μm or more and 60 μm or less. It is a polypropylene film.

The surface roughness of the biaxially stretched polypropylene film on at least one surface is 0.03 μm or more and 0.10 μm or less in the center line average roughness (Ra), and 0.3 μm in the maximum height (Rmax). It is preferable that the surface is finely roughened to 1.0 μm or less.
If Ra or Rmax is a large value to some extent, the film will slip appropriately due to the formation of appropriate voids between the films during processing such as winding and rewinding, and wrinkles will occur during laminating and winding. It is preferable because it is difficult to enter, it is difficult for lateral displacement to occur, and it has good peelability. However, if these values are too large, when they are bonded as a protective film or a release film, unevenness is transferred between the protective film and a large void, which is not preferable because it causes voids and air voids. On the other hand, if the surface roughness is too low, the film is not slippery, wrinkles are likely to occur during laminating or winding, and peeling is also difficult, which is not suitable for practical use.

Ra and Rmax are measured by a method defined in, for example, JIS-B0601, using a generally widely used stylus type or non-contact type surface roughness meter. There are no restrictions on the manufacturers or models of equipment that can be used.
In the study of the present invention, Ra and Rmax were determined according to the method specified in JIS-B0601 ・ 1982 using the surface roughness / contour shape measuring instrument Surfcom 1400D manufactured by Tokyo Seimitsu Co., Ltd.
Measurement can be performed by either a contact method (a stylus type using a diamond needle or the like) or a non-contact method (non-contact detection using a laser beam or the like), but in the study of the present invention, the measurement was performed by the contact method with a measured load of 750 μN.

Various known roughening methods such as an embossing method and an etching method can be adopted as a method for giving fine irregularities to the film surface, but among them, β crystals, which are not likely to be mixed with impurities, are used. The roughened surface method is preferable. The formation rate of β crystals can generally be controlled by the cast temperature and the cast speed. In addition, the melting / transition ratio of β crystals can be controlled by the roll temperature in the longitudinal stretching step, and fine rough surfaces can be selected by selecting the optimum production conditions for these two parameters of β crystal formation and its melting / transition. You can get sex. The cast temperature for controlling β crystals is generally 30 to 120 ° C., and is preferably in the range of 30 ° C. to 90 ° C., preferably 30 ° C. to 80 ° C. in order to have the surface property of the present invention. It is more preferable to adjust to the range.

The number of fish eyes with a size (major axis) of 50 μm or more is 100 / m ² or less.
The fisheye, which is a minute foreign substance or insoluble matter, should have a size (major axis) of 50 μm or more and 100 pieces / m ² or less. It is preferably 80 pieces / m ² or less, and more preferably 70 pieces / m ² or less.
Further, the number of fish eyes (microforeign substances) having a size (major axis) of 150 μm or more is preferably 5% or less as a ratio to the whole.
The term “fish eye” as used herein refers to foreign substances, unmelted substances, oxidative deterioration substances, etc. in the material used for producing a film by thermally melting the material resin, extruding, and stretching the film product. It is the one that was taken in.
If the number of fish eyes is large, it may cause foreign matter contamination, voids, and air voids when bonded as a protective film used in the manufacturing process of electronic parts, electronic boards, and photosensitive materials, so it is not suitable for practical use. I can say.

As a means for reducing fish eyes (fine foreign substances), it is preferable to reduce the ash content caused by the polymerization catalyst residue and the like contained in the polypropylene resin which is the material. The ash content of the resin is preferably 200 ppm or less, more preferably 100 ppm or less.
Further, as another means for reducing fish eyes (fine foreign substances), it is preferable to use a filter having high filtration accuracy as a so-called polymer filter installed between the extruder and the T die.

The filtration accuracy is preferably as small as 10 μm (98% cut size) or less, and preferably as small as 5 μm or less. If the accuracy is too high (size is small) (for example, 1 μm or less), the removal rate of fish eyes (micro foreign matter) will be high, but the resin differential pressure between the polymer filter will be too large, and extrusion molding (casting) will be performed. Production (resin discharge) at the time of raw fabric production) tends to be unstable, which is not preferable in practical use. On the other hand, when the filtration accuracy is made larger than 10 μm (the accuracy is made lower), the mesh of the filter becomes large, so that the removal rate of fish eyes (fine foreign substances) becomes poor, and the fish eyes (small foreign substances) which is the object of the present invention is deteriorated. ) Cannot be reduced, which is not preferable.

As the filter medium used for the polymer filter, a generally known filter medium can be used without limitation. Examples of such a filter medium include a sintered metal non-woven fabric (fiber sintered body), a laminated sintered wire mesh, and a powder sintered body.
As the filter type, a leaf disc filter, a candle filter, a pack filter, etc. can be used without limitation.
Above all, for the molding of polypropylene resin with reduced fish eyes (microforeign matter) according to the present invention, a leaf disk type filter using a sintered metal non-woven fabric (fiber sintered body) can be used if the differential pressure (pressure loss) is large. It can be preferably used because stable discharge can be obtained and the service life is long.

Either the reduction of the ash content of the resin or the improvement of the filtration accuracy of the polymer filter may be used, but it is preferable to carry out both of them because the fish eyes (microforeign substances) can be reduced more effectively.

The number of fish eyes (microforeign substances) can be measured visually or by using an industrial optical microscope such as a digital microscope using a counter or the like. Of course, generally known techniques can be adopted without limitation as long as the measurement can be performed with high accuracy.
As for the method of measuring the size of fish eyes (small foreign substances), generally known techniques can be adopted without limitation, but a method of analyzing an image with a computer or the like using an industrial optical microscope such as a digital microscope, or a laser. A method of measuring using a non-contact surface shape measuring machine (laser microscope) using light, a non-contact surface / layer cross-sectional shape measuring machine by an optical interference method, a scanning electron microscope, or the like can be preferably adopted.
The size of the fish eye (micro foreign matter) is measured by measuring the major axis diameter (maximum diameter).

The thickness of the film of the present invention is preferably 5 μm or more and 60 μm or less, more preferably 10 to 50 μm, and even more preferably 20 to 50 μm. If the thickness of the film is less than 5 μm, it is not suitable for use as a protective film or a release material, which is not preferable. Further, if the thickness of the film exceeds 60 μm, the film cannot be uniformly stretched, and the film may not be practically used.

The polypropylene resin used in the biaxially stretched polypropylene film of the present invention is a crystalline isotactic polypropylene resin and is a homopolymer of propylene.
The film of the present invention has a mesopentad fraction ([mm mm]), which is a stereoregularity determined by high temperature nuclear magnetic resonance (NMR) measurement, of 93% or more, more preferably 93% or more and 97% or less. A biaxially stretched polypropylene film suitable for condenser applications, which is characterized by having molecular properties.

When the mesopentad fraction [mm mm] = 93% or more, the crystallinity of the resin is improved due to the high stereoregularity component, and high thermal stability and mechanical properties are exhibited. When the isotactic mesopentad fraction [mm mm] = less than 93%, the thermal stability and the mechanical heat resistance tend to be inferior. On the other hand, if the mesopentad fraction [mm mm] is too high, the speed of solidification (crystallization) during molding of the cast raw sheet becomes too fast, and peeling from the metal drum for sheet molding tends to occur. Stretchability is reduced.

The high-temperature NMR apparatus for measuring the mesopentad fraction ([mm mm]) is not particularly limited, and is a generally commercially available high-temperature nuclear magnetic resonance (NMR) apparatus capable of measuring the stereoregularity of polyolefins. For example, a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) manufactured by JEOL Ltd., JNM-ECP500 can be used. The observation nucleus is ¹³ C (125 MHz), the measurement temperature is 135 ° C, and ortho-dichlorobenzene (ODCB: mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4/1)) is used as the solvent. Be done. The method by high temperature NMR can be carried out by a known method, for example, the method described in "Japan Analytical Chemistry / Polymer Analysis Research Council, New Edition Polymer Analysis Handbook, Kinokuniya Bookstore, 1995, p. 610". ..
The measurement mode is single pulse proton broadband decoupling, the pulse width is 9.1 μsec (45 ° pulse), the pulse interval is 5.5 sec, the number of integrations is 4500, and the shift reference is CH ₃ (mm mm) = 21.7 ppm. To.

The pentad fraction, which represents the degree of stereoregularity, is a combination (mmmm or mrrm) of a 5-series (pentad) of a series "meso (m)" arranged in the same direction and a mixture "racemo (r)" arranged in a different direction. Etc.), calculated as a percentage from the integrated intensity of each signal. Regarding the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of the spectrum such as "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" is referred to.
The mesopentad fraction ([mm mm]) can be controlled by appropriately adjusting the polymerization conditions of the polypropylene resin, the type of catalyst, the amount of catalyst, and the like.

The melt flow rate of the isotactic polypropylene homopolymer according to the present invention at 230 ° C. is 1.5 g / 10 min or more and 6.0 g / 10 min or less. It is preferably 2.0 g / 10 min or more and 4.0 g / 10 min or less. When the melt flow rate is lower than 1.5 g / 10 min, the resin fluidity is remarkably lowered, it becomes difficult to control the thickness of the cast raw sheet, and the stretched film cannot be accurately produced in the width direction. Practically unfavorable. Further, when the melt flow rate is higher than 6.0 g / 10 min, the extrudability is excellent, but the stretchability is remarkably lowered as the mechanical properties of the finished sheet are deteriorated, and biaxial stretch molding cannot be performed. It is not preferable because it causes difficulties.

The ash content caused by the polymerization catalyst residue and the like contained in the polypropylene resin used in the present invention is preferably small, preferably 200 ppm or less, and preferably 100 ppm or less in order to reduce minute foreign substances (fish eyes). be. When the amount is 200 ppm or less, minute foreign substances are remarkably reduced, and contamination when used for electronic component applications can be reduced, which is preferable.

The biaxially stretched polypropylene film of the present invention may be a film obtained by extruding a polypropylene resin from a single-layer die and subjecting it to biaxially stretched, but a multilayer die is used to form a surface layer (skin layer: layer A). A three-layer structure of layer A / layer B / layer A, which is composed of a core layer (layer B), may be used.
In the case of a three-layer structure, the resin compositions of the layers A and B may be changed. For example, the core layer of the layer B is added to the polypropylene resin of the layer A with a core material such as fine particles of an inorganic substance (from the layer A). For the purpose of forming a resin layer (increased amount) or for the purpose of nucleation or the like, a resin layer obtained by blending a polypropylene resin of layer A with a resin having a melt flow rate different from that of the resin of layer A as a nucleating agent may be used.

By adding a nucleating material, a nucleating agent, or the like to the core layer (layer B), it is possible to improve or maintain the thermal stability and / or the mechanical properties of the polypropylene film, which is preferable.
As the fine particles of the inorganic substance as the core material, talc, calcium carbonate and the like can be used. As the resin component as the nucleating agent, a long-chain branched polymer, an ultra-high molecular weight polypropylene resin, or the like can be used, but a polypropylene resin having a melt flow rate different from that of the polypropylene resin on the surface layer A is preferable.

In the layer B (core layer), the content of different resins blended with the resin of the surface layer A for the purpose of nucleation or the like is 1% by mass or more and less than 30% by mass. It is preferably 1 to 10% by mass. More preferably, it is 1 to 5% by mass. If the content is less than 1% by mass, the desired effect such as nucleation cannot be obtained. Further, if the content exceeds 30% by mass, delamination or the like in which the skin layer and the core layer are peeled off may occur, which is not preferable.

On the other hand, the layer A is a skin layer composed of an isotactic polypropylene resin alone. The polypropylene resin used for layer A has a desired surface according to the present invention in order to reduce minute foreign substances (fish eyes) and while maintaining the high thermal and mechanical stability inherent in isotactic polypropylene. In order to obtain the properties, the isotactic polypropylene homopolymer having the above-mentioned molecular properties according to the present invention is preferable.
There is no particular deadline for the layer structure in the case of multiple layers, but in the case of the layer structure of layer A / layer B / layer A, there is no problem such as thermal curl of the film, and the film has excellent flatness. preferable. The thickness of the skin layer (layer A × 1/2) is preferably 2% to 20%, more preferably 2% to 10% with respect to the thickness of the core layer.

A heat stabilizer and an antioxidant may be added to the film of the present invention for the purpose of imparting chemical stability to the polypropylene resin and the polypropylene resin composition. Specific examples thereof include phenol-based, hindered amine-based, phosphite-based, lactone-based, and tocopherol-based heat stabilizers and antioxidants. More specifically, dibutylhydroxytoluene and pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (Ciba Specialty Chemicals Co., Ltd .: "Irganox®" 1010 "), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4hydroxy) benzene (Ciba Specialty Chemicals Co., Ltd .:" Irganox® 1330 ”), Tris (2,4-di-t-butylphenyl) phosphite (Ciba Specialty Chemicals Co., Ltd .:“ Irgafos® 168 ”). Among them, at least one selected from phenol-based antioxidants or a combination thereof, or a combination of phenol-based and phosphite-based, and phenol-based and lactone-based, phenol-based and phosphite-based and lactone-based. Is preferable from the viewpoint of imparting the chemical stability of the polypropylene resin.

The film of the present invention may contain an organic and / or an inorganic slip agent, a chlorine trapping agent, and an antistatic agent as long as the object of the present invention is not violated. Examples of the slip agent include stearic acid amides, erucic acid amides and other aliphatic amides, lauric acid diethanolamides, alkyldiethanolamines, aliphatic monoglycerides, aliphatic diglycerides, silica, alumina, silicone crosslinked polymers and the like. Examples of the chlorine trapping agent include calcium stearate and hydrotalcite. Examples of the antistatic agent include alkylmethyldibetaine, alkylamine diethanol and / or alkylamine ethanol ester and / or alkylamine diethanol diester.

The polypropylene resin can be obtained by a known method. Examples of the production method include a method of polymerizing propylene in a hydrocarbon solvent using a Ziegler catalyst system composed of a titanium and an aluminum compound, a method of polymerizing in liquid propylene (bulk polymerization), and a method of polymerizing in a gas phase.

The method for mixing the resin for obtaining the composition of the layer B composed of polypropylene and the added polymer (for example, polypropylene resin for nucleation) is not particularly limited, but the polymer powder or pellets are dry-blended using a mixer or the like. A method of supplying a polypropylene resin and a polymer powder or pellet of an added polymer (for example, a polypropylene resin for nucleation) to a kneader and melt-kneading to obtain a blended resin may be used.
The mixer and the kneader are not particularly limited, and the kneader may be either a 1-axis screw type, a 2-axis screw type, or a multi-axis screw type having more than that, and in the case of a screw type having 2 or more axes. , Either the same direction rotation or the different direction rotation may be used.

In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as good kneading is obtained, but generally, it is in the range of 200 ° C. to 300 ° C., preferably 230 ° C. to 270 ° C. A kneading temperature that is too high is not preferable because it causes deterioration of the resin. In order to suppress deterioration during kneading and mixing of the resin, the kneader may be purged with an inert gas such as nitrogen.
The melt-kneaded resin can be pelletized to an appropriate size using a generally known granulator to obtain a mixed polypropylene resin composition.

As the biaxial stretching method for obtaining the film of the present invention, the tenter method having good thickness unevenness and flatness is preferable. The tenter method also includes a simultaneous biaxial stretching method and a sequential biaxial stretching method, and either method may be used. Hereinafter, a method for obtaining the film of the present invention by a sequential biaxial stretching method will be described, but the present invention is not limited thereto.

The resin and / or the resin and the resin composition prepared as described above are melted at 230 to 270 ° C. by an extruder, fine foreign substances and the like are removed by the above-mentioned polymer filter, and then melted into a sheet from a T-die. Extrude.
In order to obtain a film of layer A / layer B / layer A, the resins of layer A and layer B are melt-kneaded in an extruder, and after removing minute foreign substances and the like with the above-mentioned polymer filter, the resins merge. Using the device, a three-layer resin layer composed of a layer A and a layer B is configured. The merging device includes a method of merging resins in a polymer tube in front of the mouthpiece, a feed block method of merging with a laminating unit provided in the resin introduction portion of the mouthpiece, a manifold laminating method of laminating both resins after widening in the mouthpiece, and the like. Is exemplified, but is not particularly limited. Although the manifold method is excellent in terms of stacking thickness accuracy, it can be appropriately selected in consideration of economic efficiency.

The single layer or the laminated sheet composed of layer A / layer B / layer A obtained as described above is formed into a sheet by being brought into close contact with at least one metal drum controlled at 30 to 90 ° C. with an air knife. It is molded and becomes a cast raw sheet.

The stretching is preferably biaxial stretching in which the orientation is biaxially oriented vertically and horizontally. As a sequential biaxial stretching method, first, the cast raw sheet is kept at a temperature of 100 to 160 ° C., passed between rolls provided with a speed difference, stretched 4 to 5 times in the flow direction, and immediately cooled to room temperature. Subsequently, the stretched film is guided to a tenter and stretched 8 to 10 times in the width direction at a temperature of 160 ° C. or higher, and then relaxed and heat-fixed to be wound. The wound film can be aged in an atmosphere of about 20 to 45 ° C. and then cut to a desired product width. By such a stretching step, a stretched film having excellent mechanical strength and rigidity can be obtained.
The film thus obtained has few fish eyes (microforeign substances) and is extremely excellent in adhesion and mold release property, and is therefore suitable as a protective material film and / or a non-silicone separator film thereof. ..

Next, the present invention will be described in more detail by way of examples, but of course, the scope of the present invention is not limited thereto. Unless otherwise specified, parts and% in the example indicate "parts by mass" and "% by mass", respectively.
Further, the method for measuring the characteristic value and the method for evaluating the effect in the examples are as follows.

[Measurement method of characteristic value and evaluation method of effect]
(1) Melt flow rate (MFR) of polypropylene resin at 230 ° C.
The MFR of polypropylene resin at 230 ° C. was determined by JIS K-7210 (1999).

(2) Isotactic mesopentad fraction ([mmmm]) measurement Isotactic by dissolving polypropylene resin in a solvent and using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) under the following conditions. The tick mesopentad fraction ([mm mm]) was determined.
Measuring machine: High temperature FT-NMR JNM-ECP500 manufactured by JEOL Ltd.
Observation nucleus: ¹³ C (125 MHz)
Measurement temperature: 135 ° C
Solvent: Ortho-dichlorobenzene [ODCB: Mixed solvent of ODCB and deuterated ODCB (
4/1)]
Measurement mode: Single pulse Proton broadband decoupling Pulse width: 9.1 μsec (45 ° pulse)
Pulse interval: 5.5 sec
Accumulation number: 4500 times
Shift reference: CH ₃ (mmmm) = 21.7ppm
It was calculated as a percentage (%) from the integrated intensity value of each signal derived from the combination of quintuplets (pentads) (mm mm, mrrm, etc.). Regarding the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of the spectrum such as "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" was referred to.

(3) Measurement of surface roughness The center line average roughness (Ra) and maximum height (Rmax) of the biaxially stretched polypropylene film are measured by Tokyo Seimitsu Co., Ltd., Surface Roughness / Contour Shape Measuring Instrument Surfcom 1400D. It was obtained by using a mold and according to the method specified in JIS-B0601 ・ 1982. The number of measurements was 3 times, and the average value was used for evaluation. In this evaluation, it was measured by the contact method, and the measured load was measured at 750 μN.

(4) Evaluation of fish eyes (small foreign substances) The number of fish eyes (micro foreign substances) was visually measured using a counter. For the size, use a digital microscope VHX-200 / 100F type manufactured by KEYENCE, observe (reflected light) each of the visually confirmed fish eyes at an appropriate magnification, and use a measurement tool to fish. The major axis diameter (maximum diameter) of the eye (small foreign substance) was measured.

(5) Evaluation of film thickness The thickness of the biaxially stretched polypropylene film was measured using a micrometer (JIS-B7502) in accordance with JIS-C2151.
(6) Mechanical properties The tensile strength of the biaxially stretched polypropylene film was measured according to JIS-C2151. The measurement directions were MD (flow direction) and TD (width direction).
(7) Heat shrinkage rate The heat shrinkage rate of the biaxially stretched polypropylene film was measured according to JIS-C2151. The measurement directions were MD (flow direction) and TD (width direction).

(8) Adhesion / peelability evaluation Nitto Denko Corporation polyester adhesive tape NO. 31B is attached with a roller and aged for 30 minutes under the conditions of ^{load: 5 g / mm 2 and temperature: 100 ° C.} It was cut to a width of 25 mm to prepare a sample. The obtained sample was qualitatively evaluated for its close contact state (whether it contained air, etc.) and the peeled state when it was peeled off by hand.
◯: Good adhesion and light peeling ×: Poor adhesion and / or heavy peeling

(9) Comprehensive evaluation It was comprehensively judged whether fish eyes (small foreign substances) were reduced and adhesion / peelability was improved while maintaining thermal stability and mechanical properties.
○: Improved ×: Same as or inferior to the conventional one

[Example 1]
As a polypropylene resin, resin A (MFR = 2.8 g / 10 min, [mm mm] = 93%, total ash content = 25 ppm) pellets manufactured by Prime Polymer Co., Ltd. were prepared.
The above resin pellets are put into a single-screw extruder manufactured by Mitsubishi Heavy Industries, Ltd. from a hopper, the filtration accuracy is 10 μm, and the filter medium is a sintered metal non-woven fabric (fiber sintered body) manufactured by Nagase Sangyo Co., Ltd. After extruding as a sheet from a single-layer die at 230 ° C via a filter, it is cooled and solidified while being pressed with air pressure using an air knife on a cooling drum whose surface temperature has been adjusted to 60 ° C. I got a sheet.
Subsequently, the sheet was heated to 140 ° C. while in contact with the metal rolls, and then stretched about 4.5 times in the bending direction between the rolls having different peripheral speeds. Next, the uniaxially stretched film was introduced into a hot air oven while being sandwiched between clips, preheated to 160 ° C., then stretched about 9 times in the width direction, and subsequently heat-fixed at 160 ° C. while relaxing 5% in the width direction. A biaxially stretched polypropylene film having a thickness of about 50 μm was continuously obtained. The obtained biaxially stretched polypropylene film was wound after trimming the end portion.
The film thickness, surface roughness, fisheye evaluation, tensile strength, heat shrinkage rate, and adhesion / peelability of the obtained biaxially stretched polypropylene film were evaluated. The film and the evaluation results are shown in Table 1.

[Example 2]
As a polypropylene resin, resin B (MFR = 4.0 g / 10 min, [mm mm] = 94%, total ash content = 25 ppm) pellets manufactured by Prime Polymer Co., Ltd. were prepared.
A biaxially stretched polypropylene film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the thickness of the cast raw sheet was adjusted to about 400 μm.
Table 1 shows the evaluation results of the obtained biaxially stretched polypropylene film.

[Example 3]
As the polypropylene resin for the skin layer A, resin A (MFR = 2.8 g / 10 min, [mm mm] = 93%, total ash = 25 ppm) pellets manufactured by Prime Polymer Co., Ltd. were prepared.
Further, as the resin of the core layer B, the polypropylene resin A (MFR = 2.8 g / 10 min, [mm mm] = 93%, total ash content = 25 ppm) pellets manufactured by Prime Polymer Co., Ltd. was used as an additive resin, and the polypropylene resin manufactured by SunAllomer Ltd. was used. C (MFR = 7.5 g / 10 min, [mm mm] = 93%, talc 1000 ppm as a nucleating agent) was prepared. 3% by mass of the added resin C pellet was added to the polypropylene resin A pellet, and dry blending was performed. The total ash content of the obtained blended resin was 80 ppm.
Next, the mixed pellet was charged into a single-screw extruder I manufactured by Mitsubishi Heavy Industries as a core layer B from a hopper, while an extruder manufactured by Mitsubishi Heavy Industries, in which only polypropylene resin A was prepared in series as a skin layer A. Leading to II, the filtration accuracy is 10 μm, and the filter medium is made of sintered metal non-woven fabric (fiber sintered body) manufactured by Nagase Sangyo Co., Ltd. After extruding as a three-layer (layer A / layer B / layer A configuration) sheet, it is cooled and solidified while being pressed with air pressure using an air knife on a cooling drum whose surface temperature is adjusted to 60 ° C. I got an anti-sheet.
Subsequently, the sheet was heated to 140 ° C. while in contact with the metal rolls, and then stretched about 4.5 times in the bending direction between the rolls having different peripheral speeds. Next, the uniaxially stretched film was introduced into a hot air oven while being sandwiched between clips, preheated to 160 ° C., then stretched about 9 times in the width direction, and subsequently heat-fixed at 160 ° C. while relaxing 5% in the width direction. A biaxially stretched polypropylene film having a thickness of about 30 μm was continuously obtained. The obtained biaxially stretched polypropylene film was wound after trimming the end portion.
Table 1 shows the evaluation results of the obtained biaxially stretched polypropylene film.

[Comparative Example 1]
Same as Example 1 except that the filtration accuracy is 20 μm, the filter medium is a polymer filter using a laminated sintered wire mesh manufactured by Nagase & Co., Ltd., and a disc filter is used, and the thickness of the cast raw sheet is adjusted to about 1200 μm. A biaxially stretched polypropylene film having a thickness of 30 μm was obtained.
Table 1 shows the evaluation results of the obtained biaxially stretched polypropylene film.

[Comparative Example 2]
As a polypropylene resin, Prime Polymer Co., Ltd. resin D (MFR = 5.5 g / 10)
min, [mm mm] = 97%, total ash content = 25 ppm) Pellets were prepared.
A biaxially stretched polypropylene film having a thickness of 30 μm was obtained in the same manner as in Example 1 except that the surface temperature of the cooling drum was adjusted to 80 ° C. and the thickness of the cast raw sheet was adjusted to about 1200 μm.
Table 1 shows the evaluation results of the obtained biaxially stretched polypropylene film.

[Comparative Example 3]
As the polypropylene resin of the skin layer A, resin E (MFR = 3.0 g / 10 min, [mm mm] = 92%, total ash content = 25 ppm) pellets manufactured by Prime Polymer Co., Ltd. were prepared.
Further, as the resin of the core layer B, polypropylene resin E (MFR = 3.0 g / 10 min, [mm mm] = 92%, total ash content = 25 ppm) pellets manufactured by Prime Polymer Co., Ltd. was used as an additive resin, and manufactured by SunAllomer Ltd. Polypropylene resin C (MFR = 7.5g /
10 min, [mm mm] = 93%, containing 1000 ppm of talc as a nucleating agent) was prepared. 3% by mass of the added resin C pellet was added to the polypropylene resin E pellet, and dry blending was performed. The total ash content of the obtained blended resin was 80 ppm.
The same as in Example 3 except that the filtration accuracy is 20 μm, the filter medium is a polymer filter using a laminated sintered wire mesh manufactured by Nagase Sangyo Co., Ltd., and a disc filter is used, and the surface temperature of the cooling drum is adjusted to 30 ° C. , A biaxially stretched polypropylene film having a thickness of 30 μm was obtained. Table 1 shows the obtained biaxially stretched polypropylene film and the evaluation results.

As is apparent from Examples 1, 2 and 3, the biaxially stretched polypropylene film of the present invention is
Since it has an appropriate surface property as the object of the present invention, it is excellent in adhesion and peelability, has few fish eyes (small foreign substances), reduces the possibility of foreign substance contamination, and is an electronic component. It was extremely suitable as a protective film for a manufacturing process of an electronic substrate, a photosensitive film, a non-silicone type release film, a release liner, and a separator film for a protective material.
However, when a polymer filter having low filtration accuracy is used, fish eyes (fine foreign substances) cannot be reduced (Comparative Example 1), and when the surface roughness is higher than the range according to the present invention, the adhesion is high. It was inferior to the above and could not withstand practical use (Comparative Example 2).
Furthermore, if the polypropylene resin has a low isotactic mesopentad fraction and a low surface roughness based on the prior art, it is inferior in mechanical properties and thermal stability (high heat shrinkage rate) and peels off. The performance was poor. Moreover, due to the use of a polymer filter having low filtration accuracy, fish eyes (fine foreign substances) could not be reduced, and it was not practically usable (Comparative Example 3).

FIG. 1 shows the distribution of the sizes of fish eyes (microforeign substances) of Example 3 and Comparative Example 1. Not only the number of fish eyes (small foreign substances) of the biaxially stretched polypropylene film according to the present invention is reduced, but also the size is reduced, and the manufacturing process of electronic parts and electronic substrates and the protective film of the photosensitive film are reduced. It can be seen that it is preferable as a non-silicone type release film, a release liner, and a separator film as a protective material.

The biaxially stretched polypropylene film of the present invention has excellent peelability and reduces foreign matter contamination, voids, and air voids when bonded, so that electronic parts, electronic substrate manufacturing processes, fiber-reinforced plastics, etc. Protective films and release materials used in the manufacturing process of thermosetting resin members, photosensitive film manufacturing processes, etc., more specifically, release films and release liners, carriers and protective materials during material manufacturing, and / Alternatively, it can be used for the non-silicone-based separator film and the like.

Claims (7)

The surface roughness of at least one surface formed from a polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less is determined.
(A) Center line roughness (Ra) of 0.03 to 0.10 μm,
(B) Maximum height (Rmax) of 0.3 μm to 1.0 μm,
A biaxially stretched polypropylene film having a layer having a major axis of 50 μm or more and a number of fish eyes of 100 pieces / m ² or less, a thickness of 5 μm or more and 60 μm or less, and a major axis of 150 μm in the layer. A biaxially stretched polypropylene film for a protective film or a separator film, characterized in that the number of the above fish eyes is 5% or less as a ratio to the whole. The polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less is biaxially stretched from a cast raw sheet formed by passing it through a sintered metal non-woven fabric filter having a filtration accuracy of 10 μm or less. The biaxially stretched polypropylene film according to claim 1, characterized in that. The biaxially stretched polypropylene film according to claim 1 or 2, wherein the polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 6.0 g / 10 min or less has an ash content of 200 ppm or less. 2. According to any one of claims 1 to 3, the heat shrinkage rate measured in accordance with JIS-C2151 in the width direction (TD) is 0.5 to 1.0%. Axial stretch polypropylene film. 2. According to any one of claims 1 to 4, the heat shrinkage rate measured according to JIS-C2151 in the flow direction (MD) is 1.8 to 2.0%. Axial stretch polypropylene film. The tensile strength in the flow direction (MD) is 156 to 162 MPa.
The biaxially stretched polypropylene film according to any one of claims 1 to 5. The biaxially stretched polypropylene film according to any one of claims 1 to 6, wherein the tensile strength in the width direction (TD) is 326 to 341 MPa.

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