JP2007003975A - Polypropylene film for light reflection board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene film for a light reflection board having characteristics such as high porosity, whiteness degree, optical density and reflectance, preferable mechanical strength and smoothness, and low rate of thermal shrinkage. <P>SOLUTION: The polypropylene film for a light reflection board has substantially coreless voids and shows 25 to 75% porosity, ≥70% whiteness degree and ≥80% reflectance at 560 nm wavelength. A laminated polypropylene film for light reflection board is also provided which comprises the above polypropylene film as a core layer (A), and a skin layer (B) of a polypropylene resin having a porosity of 0.1% or more and less than 25%, laminated on at least one surface of the core layer, and which shows ≥70% whiteness degree on the surface of the skin layer (B) and ≥80% reflectance at 560 nm wavelength. The obtained polypropylene film for a light reflection board is suitable as a reflection board or a reflector in a surface light source which is bright and excellent in illumination efficiency and processability. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polypropylene film for a light reflecting plate. More specifically, the present invention is a polypropylene film for a light reflecting plate suitable as a reflecting plate or reflector of a surface light source, and can obtain a surface light source that is bright and excellent in illumination efficiency and excellent in workability. The present invention relates to a polypropylene film for a light reflector.

  In recent years, many displays using liquid crystals have been used as display devices for personal computers, televisions, mobile phones, and the like. Since these liquid crystal displays are not themselves light bodies, display is possible by installing a surface light source called a backlight on the back side and irradiating light from the backlight. Further, the backlight has a structure of a surface light source called a side light type or a direct type in order to meet the requirement that the entire screen should be irradiated uniformly, not just light.

  In particular, for a thin liquid crystal display used for a notebook type personal computer or the like for which a thin and small size is desired, a side light type, that is, a backlight of a type that irradiates light from the side of the screen is applied (for example, , See Patent Document 1).

  In general, this sidelight type backlight uses a cold cathode ray tube as an illumination light source from the edge of the light guide plate and uses a light guide plate that uniformly propagates and diffuses light to uniformly illuminate the entire liquid crystal display. Is adopted. In this illumination method, in order to use light more efficiently, a reflector is provided around the cold cathode ray tube, and further under the light guide plate in order to efficiently reflect the light diffused from the light guide plate to the screen side. A reflector is provided. Thereby, the loss of light from the cold cathode ray tube is reduced, and the function of brightening the liquid crystal screen is provided.

  On the other hand, for large screens such as liquid crystal televisions, since the edge light method cannot be expected to increase the screen brightness, the direct light method has been adopted. In this method, a cold cathode ray tube is provided in parallel at the lower part of the liquid crystal screen, and the cold cathode ray tubes are arranged in parallel on the reflector. The reflecting plate may be a flat plate or a cold cathode ray tube formed into a semicircular concave shape.

  Reflectors and reflectors used for such surface light sources for liquid crystal screens (hereinafter collectively referred to as surface light source reflecting members) are required to have a high reflection function as well as a thin film. Conventionally, white pigments have been added. A film or a film in which fine particles are contained inside by adding inorganic particles or the like has been used.

  For example, a white polyethylene terephthalate film in which 5 to 30% by weight of calcium carbonate as inorganic particles is contained in polyethylene terephthalate resin, melt extruded, and biaxially stretched to form voids therein is known (see Patent Document 2). . Also, as a film with increased light reflectance, a polyethylene terephthalate resin containing 5 to 25% by weight of inorganic particles is laminated on both sides of a layer containing 2 to 25% by weight of a polyolefin resin in a polyethylene terephthalate resin, and biaxially stretched. A white polyester film is known (see Patent Document 3). All of these films have a high specific gravity and are difficult to process because the strength at 5% elongation is too high, and the reflection and absorption of light is caused by irregular reflection or absorption of light by the void-forming resin and inorganic particles. In some cases, the void-forming resin and inorganic particles are yellowed by irradiation with ultraviolet rays or the like, and the whiteness of the film is lowered. Furthermore, there is a drawback that the void-forming resin and inorganic particles drop off in the film forming process and the light reflecting plate manufacturing process, thereby contaminating the process.

  In addition, as a light reflector of the polyolefin resin sheet, 100 parts by weight of the polyolefin resin includes 100 to 300 parts by weight of a fine powdery inorganic filler, and is stretched by 1.5 to 20 times in area magnification. A light reflector having a light reflectance of 95% or more at a wavelength of 550 nm and a rigidity of the reflector of at least 50 mm is known (see Patent Document 4). In order to make this film porous, it is necessary to add a large amount of inorganic particles, resulting in inferior film formation stability, and the film surface has projections due to particles, resulting in increased surface roughness, and the film forming process and light reflector There was a defect that the inorganic particles dropped off during the manufacturing process and contaminated the process. Further, since the rigidity is low, it is necessary to supplement the rigidity by laminating other resins.

  Further, as a synthetic paper for printing, a synthetic paper of a polypropylene microporous film to which a β crystal nucleating agent is added is known (see Patent Document 5). This synthetic paper is a synthetic paper for printing by adding a layer in which a β crystal nucleating agent is added and voids are formed in a polypropylene film on the surface of another base material layer film. Micropores were formed and the irregularities were large, so that the glossiness was low and the mechanical strength was also low. This synthetic paper was developed as a printing paper, and its diversion to a light reflecting member has not been studied.

JP 63-62104 A (Claim 1) JP 63-161029 A (Claim 1, Example 1) Japanese Patent Publication No. 8-16175 (Claims 2, 4, and 7) JP-A-8-262208 (Claim 1, Examples 4 and 5) JP-A-8-1845 (Claim 1, Example 1)

  The present invention has a high porosity, high whiteness, high optical density (that is, low light transmittance), excellent concealability, and is a thin film required for a surface light source reflecting member and at the same time has a high reflecting function. An object of the present invention is to provide a polypropylene film for a light reflecting plate that satisfies the above requirements and has excellent film forming properties and processability to a surface light source reflecting member.

  In order to achieve the above object, the present invention has the following configuration.

  That is, the polypropylene film for a light reflecting plate of the present invention has a substantially non-nucleated void, a porosity of 25 to 75%, a whiteness of 70% or more, and light at a wavelength of 560 nm. A polypropylene film characterized by having a reflectance of 80% or more. Further, a polypropylene film having a substantially non-nucleated void and having a porosity of 25 to 75% is used as the core layer (A), and at least one surface thereof has a porosity of 0.1% or more and less than 25%. A laminated film formed by laminating a resin skin layer (B), wherein the whiteness on the surface of the skin layer (B) is 70% or more, and the light reflectance at a wavelength of 560 nm is 80% or more. It is what.

  As a preferred embodiment, at least one surface has an average surface roughness Ra of 0.02 to 0.5 μm, a glossiness of 30 to 150%, a specific gravity of 0.18 to 0.8, and optical. The concentration is in the range of 0.5 to 1.5, and the sum of the strength when the film is stretched 5% in the longitudinal direction and the width direction is in the range of 50 to 200 MPa, and the film is stretched 5% in the longitudinal direction and the width direction. The strength ratio at the time is in the range of 5: 1 to 1: 5, the thermal shrinkage at 120 ° C. is 5% or less in the longitudinal direction and 5% or less in the width direction, and the thickness of the film is 20 to 300 μm. It is a polypropylene film for light reflecting plates satisfying that the thickness is within the range and the thickness of the skin layer (B) of the laminate is 1 to 50 μm.

  Moreover, it is a polypropylene film for light reflection boards which satisfies that the polypropylene which comprises a film has (beta) crystal activity, and provided the coating layer containing a light stabilizer on the at least single side | surface of a film.

The polypropylene film for a light reflecting plate according to the present invention has characteristics suitable for a reflecting member of a surface light source as described below.
(1) Having a large number of fine coreless voids, high porosity, high whiteness, optical density, and high light reflectivity, it has a high reflection function when used as a surface light source reflecting member of a liquid crystal display device. And the efficiency of the backlight is improved.
(2) By setting the strength at 5% elongation and the average surface roughness Ra within a specific range, the mechanical strength is high, the slipperiness is good, and the processability to the surface light source reflecting member is excellent.
(3) Since the voids are non-nucleated and fine, and the heat shrinkage rate is low, the process passability in the film forming process and the processing process is excellent.
(4) Even if it is used for a long time as a reflector, the film is less yellowed, the reflectance is less lowered, and a high-quality image can be maintained.

  Hereinafter, the case where the polypropylene for a light reflecting plate of the present invention and the polypropylene film for a light reflecting plate of the present invention are applied to a surface light source reflecting member will be described.

  The polypropylene film for a light reflecting plate of the present invention needs to have a substantially nucleus-free void. By having a substantially nucleus-free void, a film with high reflectance and high whiteness can be obtained even with a thin film. On the other hand, as in the past, a film in which a void was formed by adding a large amount of incompatible resin or inorganic or organic particles as a void forming agent to a polypropylene resin, the dispersibility of the void forming agent when stretched There may be cases where huge holes are formed due to defects or agglomeration and the light reflectivity is deteriorated, and the void forming agent may fall off in the film forming process and the secondary processing process, and the film may be broken or the process may be soiled.

Here, having a substantially nucleus-free void is defined as follows. That is, the cross section of the film was photographed by magnifying and observing 1500 times using a scanning electron microscope S-2100A type (manufactured by Hitachi, Ltd.), and the total number of voids per 1000 μm ² using this cross-sectional photograph. When the number of voids having nuclei (single bubbles having a boundary line) and the number of voids having nuclei divided by the total number of voids is 5% or less, and having substantially non-nuclear voids To do. In addition, when observing voids in the cross section of the film, a total of 10 cross-sectional photometers selected from 10 different measurement fields are used.

  The porosity of the polypropylene film needs to be in the range of 25 to 75%. Preferably it is 30 to 70%. When the porosity is less than 25%, the light reflectivity at a wavelength of 560 nm is insufficient with less than 80%, and the sum of the strengths when stretched by 5% in the longitudinal and width directions of the film exceeds 200 MPa. It may be inferior in bending workability when assembled in a light. When the porosity exceeds 75%, the film formation stability is inferior, and when processing into a light reflecting member, the film is easily torn (cut) due to tension or rubbing, and there may be a problem in process passability.

  The whiteness of the film of the present invention needs to be 70% or more, more preferably 75% or more. If the whiteness is less than 70%, the image becomes dark as a whole, and the reflected light is colored (yellow, red), which may affect the color of the screen.

As described in JIS Z8722 and Z8730, the whiteness is determined according to Richard S. Using a spectroscopic color meter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd. designed based on Hunter's color difference formula, XYZ values indicating tristimulus values of the color of the sample are measured by the reflection method. Is required.
Whiteness = 4 × 0.847 × Z-3 × Y (%)

  At this time, the L value indicating the color difference of the film simultaneously obtained is 50 or more, the a value is 3 to -3, and the b value is in the range of -0.01 to -6. As preferred.

  The larger the L value, the higher the brightness, that is, the brighter. a indicates that the larger the numerical value is on the (+) side, the greater the degree of red, and the greater the degree of green is on the (−) side. b indicates that the degree of yellow is large on the (+) side and that the degree of blue is large on the (−) side. When the L value of the film of the present invention is less than 50, the color developability of the screen becomes unclear when used as a light reflecting material for backlight. An L value of 60 or more is preferable because the image becomes clearer.

  Moreover, it is preferable that a value is the range of 3--3, More preferably, it is the range of 2--2. If the a value exceeds 3, the screen looks reddish as a whole, and if it is less than -3, the green color becomes strong. The b value is preferably in the range of -0.01 to -6, more preferably in the range of -0.2 to -5. If the b value exceeds -0.01, that is, on the + side, the screen looks yellowish as a whole, and it is not preferable if it is less than -6 because the blue color becomes strong.

  The light reflectance at a wavelength of 560 nm of the film of the present invention is 80% or more, more preferably 90% or more, and still more preferably 95% or more. If the light reflectance is less than 80%, the illumination efficiency of the illumination light source is inferior and the liquid crystal screen becomes dark.

The voids present in the film of the present invention preferably have an average major axis of 1 to 7 μm and an average minor axis (diameter in the film thickness direction) of 0.1 to 0.7 μm. Further, the number of voids is 2/10 μm ² or more, and even a thin film has high reflectivity, whiteness indicating color, a. It is preferable for the value of b to fall within the scope of the present invention.

  The polypropylene film of the present invention having a substantially non-nucleated void, having a porosity of 25 to 75%, a whiteness of 70% or more, and a light reflectance at a wavelength of 560 nm of 80% or more is a polypropylene film. In the film-forming method, which is melt-extruded, cooled and solidified on a metal drum, and then stretched at least uniaxially, the following specific polypropylene and additives are used, and the film-forming conditions are specified as described later Can be manufactured.

  In order to obtain a polypropylene film having a nucleus-free void of the present invention, a method of forming pores by mixing and extruding polypropylene and a solvent and extracting the solvent contained in the extruded sheet before or after stretching. , A method of forming a high density, high elastic recovery rate elastic structure in polypropylene and deforming the elastic structure by stretching to form pores, using the polymorph of polypropylene, and crystal transition from β to α crystal There is a method of forming a hole by using a crystal, but from the viewpoint of economic efficiency and a nucleus, a method using a crystal transition from a β crystal to an α crystal in order to generate a large number of fine voids and increase reflectance. It is preferable to form a hole.

  The polypropylene constituting the polypropylene film of the present invention has β crystal activity, a melt flow rate (MFR) in the range of 1 to 30 g / 10 min, and an isotactic index (II) of 92 to 99.8%. It is preferred to use a range of polypropylene.

  If the MFR of the polypropylene constituting the polypropylene film of the present invention is less than the above range, melt extrusion becomes unstable or it becomes difficult to form a film having a uniform thickness, and the diameter of voids in the film also increases. There is a case where problems such as non-uniformity and deterioration of film forming property occur. When the MFR exceeds the above range, the polymer viscosity at the time of melt extrusion becomes too low, and the molten polymer discharged from the slit-shaped die in the casting process is wound around a metal drum and formed into a sheet shape. Since the landing point on the drum fluctuates greatly, it becomes difficult to produce uniform β crystals in the unstretched sheet, and the sheet has defects such as waviness, resulting in increased thickness unevenness of the resulting film. In some cases, void formation unevenness increases. MFR is more preferably 1 to 20 g / 10 min.

  Moreover, when the II of polypropylene is less than the above range, there are cases where the strength at the time of 5% elongation of the film is lowered and the heat shrinkage rate is increased. As II increases, rigidity, dimensional stability and the like tend to improve. However, when the above range is exceeded, the film forming property itself may become unstable. II is more preferably 94 to 99.5%.

  Here, it is desirable to determine the characteristic values of polypropylene such as MFR and II described above using raw material chips before film formation. However, the film after film formation is left as it is or the film is kept at 60 ° C. or lower. Extraction with n-heptane at a temperature for 2 hours, removal of impurities and additives, and vacuum drying at 130 ° C. for 2 hours or more can be used as a sample for measurement.

  Moreover, the polypropylene which comprises the polypropylene film of this invention is a waste film produced when manufacturing the polypropylene film of this invention, and other polypropylene films in the range which does not impair the characteristic of this invention from viewpoints, such as economical efficiency. It may be used by blending scrap film and other resins produced during the production. In this case, it is necessary that the polypropylene constituting the polypropylene film of the present invention satisfies MFR and II and has β-crystal activity.

  The polypropylene as referred to in the present invention is mainly composed of a homopolymer of propylene, but a polymer in which other unsaturated hydrocarbon monomer components are copolymerized with polypropylene within a range not to impair the purpose of the present invention. Or a copolymer obtained by copolymerizing monomer components other than propylene and propylene may be blended, or a (co) polymer of an unsaturated hydrocarbon monomer component other than propylene may be used. May be blended. Examples of the monomer component constituting such a copolymer component or blend include, for example, ethylene, propylene (in the case of a copolymer blend), 1-butene, 1-pentene, 3-methylpentene-1, 3 -Methylbutene-1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl Examples include, but are not limited to, 2-norbornene, acrylic acid and derivatives thereof.

  In addition, it is preferable to add and mix 1 to 15% by weight of the following polyolefin resin because fine void formation, film-forming stability and flexibility are improved, and surface glossiness and whiteness are improved.

  As the polyolefin resin, for example, homopolypropylene, homopropylene and a second component other than propylene, such as ethylene or α-olefin, copolymerized with random or block such as ethylene, butene, hexene, octene are preferable. . Moreover, the following elastomer component can also be added to the polyolefin resin. Linear low density polyethylene (LLDPE), linear low density polyethylene (m-LLDPE) by metallocene catalyst method, low density polyethylene (LDPE), very low density polyethylene (V-LDPE) by metallocene catalyst method, propylene-butene rubber (PBR), ethylene-α-olefin copolymer, ethylene-propylene rubber (EPR), ethylene-butadiene rubber (EBR), ethylene vinyl acetate (EVA), ethylene-ethacrylate (EEA), ethylene-methyl methacrylate (EMMA), ethylene -Propylene-diene copolymer (EPDM), isoprene rubber (IR), styrene copolymer, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber (H-SBR), styrene-butylene- Ren copolymer (SBS), styrene - ethylene - butylene - at least one of such styrene copolymer (SEBS). Among these, linear low-density polyethylene (m-LLDPE) or ultra-low-density polyethylene (V-LDPE) produced by a metallocene catalyst method is particularly preferable because many fine voids are formed and film formation stability is improved.

  Moreover, the polypropylene which comprises the polypropylene film of this invention may add at least 1 type chosen from other polymers other than the above-mentioned polyolefin resin at 5% or less. Examples of polymers other than polyolefin resins include, but are not limited to, so-called vinyl polymer resins, polyester resins, polyamide resins, polyphenylene sulfide resins, and polyimide resins. Examples of polymers other than polyolefin resins include, for example, polybutylene terephthalate, polycarbonate, syndiotactic polystyrene, etc., from the viewpoint of fine dispersion in polypropylene in the melt extrusion process and the effect of assisting pore formation in the subsequent stretching process. However, it is not necessarily limited to these.

  Next, “having β crystal activity” of the polypropylene for obtaining the polypropylene film of the present invention means that a 5 mg sample is obtained under a nitrogen atmosphere according to JIS K 7122 (1987) using a differential scanning calorimeter (DSC). Obtained when the temperature is raised to 280 ° C. at a rate of 10 ° C./min, then held for 5 minutes, then cooled to 30 ° C. at a cooling rate of 10 ° C./min, and then heated again at a rate of 10 ° C./min. In the caloric curve (hereinafter sometimes referred to as the second run caloric curve), there is an endothermic peak accompanying melting of the β crystal at 140 to 160 ° C., and the calorific value calculated from the peak area of the endothermic peak is 10 mJ / mg. That's it. In addition, when there is an endothermic peak in the above temperature range but it is unclear whether it is caused by melting of the β crystal, a wide angle X-ray diffraction method is performed on the sample crystallized under the conditions described later together with the DSC result. The presence of a diffraction peak on the (300) plane observed near 2θ = 16 ° due to the β crystal may be confirmed, and the presence of this diffraction peak may be determined as “having β crystal activity”.

  The presence of a diffraction peak on the (300) plane of the polypropylene constituting the polypropylene film of the present invention was confirmed. Propylene of this diffraction peak has β crystal activity, so that β crystal in the unstretched sheet in the production process. In the subsequent stretching step, the β crystal is transformed into the α crystal, and a void can be formed by the difference in crystal density. Here, in order to form more uniform and a large number of holes, the β crystal fraction of the polypropylene film of the present invention is preferably 30% or more.

The β crystal fraction is a melting calculated from the peak area of the endothermic peak (one or more peaks) accompanying the melting of the polypropylene-derived β crystal observed at 140 ° C. or higher and lower than 160 ° C. in the second run caloric curve. Peak area of calorific value (ΔHβ) and endothermic peak accompanying melting of polypropylene-derived crystals other than β crystals (peak exceeding the baseline due to melting of polypropylene-derived crystals other than β crystals observed at 160 ° C. or higher) From the heat of fusion (ΔHα) calculated from the above, the following equation is used.
β crystal fraction (%) = {ΔHβ / (ΔHβ + ΔHα)} × 100 (1)

  In addition, when there is an endothermic peak at 140 to 160 ° C., but it is unclear whether it is a peak due to melting of β crystal, it is caused by β crystal by wide-angle X-ray diffraction method on a sample crystallized under the conditions described later. The existence of a (300) plane diffraction peak observed near 2θ = 16 ° may be confirmed, and the presence of this diffraction peak may be determined to be due to the melting of the β crystal.

  When the β crystal fraction of the polypropylene film of the present invention is less than the above range, the resulting film may have a low porosity or inferior light reflectance. The β crystal fraction of the polypropylene film of the present invention is more preferably 35% or more, further preferably 40% or more, and most preferably 50% or more.

  In order to obtain a polypropylene having such a high β crystal activity, it is preferable to add a so-called β crystal nucleating agent to the polypropylene. When such a β crystal nucleating agent is not added, the above high β crystal fraction may not be obtained. Examples of the β crystal nucleating agent that can be preferably added to the polypropylene constituting the polypropylene film of the present invention include carboxylic acids represented by potassium 1,2-hydroxystearate, magnesium benzoate, magnesium succinate, magnesium phthalate and the like. Alkali or alkaline earth metal salt; N, N′-dicyclohexyl-2,6-naphthalene Amide compound represented by dicarboxamide, etc .; Aromatic sulfonic acid compound represented by sodium benzenesulfonate, sodium naphthalenesulfonate, etc. Di- or triesters of di- or tribasic carboxylic acids; tetraoxaspiro compounds; imide carboxylic acid derivatives; phthalocyanine pigments typified by phthalocyanine blue; typified by quinacridone, quinacridone quinone, etc. Quinacridone pigments include, but are not limited to, binary compounds comprising component A which is an organic dibasic acid and component B which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table. However, only one type may be used, or two or more types may be mixed and used.

  In the present invention, the β crystal nucleating agent to be added to polypropylene is represented by the following chemical formulas (i) and (ii), and is represented by N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, among others. Pores of the film obtained by the amide compound or the binary compound comprising component A which is an organic dibasic acid and component B which is an oxide, hydroxide or salt of Group IIA metal of the periodic table It is particularly preferable because the rate can be increased and the permeability can be improved.

_{R 2 -NHCO-R 1 -CONH-} R 3 ··· (i)
[Wherein R ₁ represents a saturated or unsaturated aliphatic dicarboxylic acid residue having 1 to 24 carbon atoms, a saturated or unsaturated alicyclic dicarboxylic acid residue having 4 to 28 carbon atoms, or a carbon number. Represents an aromatic dicarboxylic acid residue having 6 to 28, and R ₂ and R ₃ are the same or different cycloalkyl groups having 3 to 18 carbon atoms, cycloalkenyl groups having 3 to 12 carbon atoms, or derivatives thereof. ]

R ₅ —CONH—R ₄ —NHCO—R ₆ (ii)
[Wherein R ₄ represents a saturated or unsaturated aliphatic diamine residue having 1 to 24 carbon atoms, a saturated or unsaturated alicyclic diamine residue having 4 to 28 carbon atoms, or 6 to 6 carbon atoms. 12 heterocyclic diamine residues or aromatic diamine residues having ₆ to 28 carbon atoms, wherein R ₅ and R ₆ are the same or different cycloalkyl groups having 3 to 12 carbon atoms and cycloalkenyl groups having 3 to 12 carbon atoms. A group or a derivative thereof. ]

  Specific examples of such particularly preferable β crystal nucleating agent or β crystal nucleating agent-added polypropylene include β crystal nucleating agent “NJESTER” (type name: NU-100, etc.) manufactured by Shin Nippon Rika Co., Ltd., β crystal manufactured by SUNOCO. Examples include nucleating agent-added polypropylene “BEPOL” (type name: B022-SP and the like).

  The addition amount of the β crystal nucleating agent is preferably 0.001 to 1% by weight based on the total amount of polypropylene, although it depends on the β crystal forming ability of the β crystal nucleating agent to be used. When the added amount of the β crystal nucleating agent is less than the above range, the β crystal fraction of the obtained film may be insufficient, the porosity may be lowered, or the reflectance and whiteness may be inferior. If the amount of β-crystal nucleating agent exceeds the above range, the β-crystal fraction of the resulting film will not improve even if it is added more than that, the economic efficiency will be inferior, and the dispersibility of the nucleating agent itself will deteriorate, conversely The β crystal fraction may be reduced. The addition amount of the β crystal nucleating agent is more preferably 0.005 to 0.5% by weight, still more preferably 0.05 to 0.2% by weight.

  Here, the β crystal nucleating agent described above is preferably dispersed in a needle shape in polypropylene. As shown below, the dispersion form of the nucleating agent is observed with an optical microscope for the raw material chip or unstretched sheet or stretched film heated and melted, and the average value of the ratio of the minor axis to the major axis of the nucleating agent shape confirmed at that time is If it is 10 or more, it is defined as being dispersed in a needle shape. When the β crystal nucleating agent is dispersed in a needle shape, the porosity may be increased or the reflectance may be increased.

  Moreover, high melt tension polypropylene (High Melt Strength-PP: hereinafter abbreviated as HMS-PP) is added to and mixed with the polypropylene constituting the polypropylene film of the present invention to increase the melt tension (hereinafter abbreviated as MS). And, it is preferable because tearing at the time of stretching is reduced and film forming properties are improved. Furthermore, for example, in the process of biaxial stretching, even if the film is stretched in the longitudinal direction after being stretched at a low temperature and a high magnification, the film can be formed without tearing during transverse stretching. Can be increased. Further, when the porosity is increased by stretching at a high magnification in the longitudinal direction, the strength and dimensional stability at 5% elongation can be improved. This is because the inclusion of the HMS-PP promotes the entanglement of the amorphous tie molecules penetrating through the microcrystals in the polypropylene system from the casting stage, and thereby the stretching stress is applied to the entire system in the subsequent stretching process. It is estimated that it is transmitted uniformly.

  Here, with MS, a sample was heated to 230 ° C. using a melt tension tester manufactured by Toyo Seiki Co., Ltd., and the molten polypropylene was extruded at an extrusion speed of 20 mm / min to form a strand, and this strand was 15.7 m / min. (Unit: cN).

  The HMS-PP as described above is, for example, a method of blending polypropylene containing a large amount of high molecular weight components, a method of blending oligomers or polymers having a branched structure, as described in JP-A-62-1121704. A method of introducing a long-chain branched structure into a polypropylene molecule, or a melt tension and intrinsic viscosity, a crystallization temperature and a melting point are not specified without introducing long-chain branches as described in Japanese Patent No. 2869606, respectively. It can be prepared by a method of satisfying the relationship and obtaining a linear crystalline polypropylene having a boiling xylene extraction residual ratio in a specific range.

  The HMS-PP contained in the polypropylene film of the present invention tends to have a large effect of improving the stability of melt extrusion, the above-described effect of improving the film-forming property, and the accompanying improvement in porosity and permeability. Particularly preferred is HMS-PP having long chain branches in the case.

  Here, HMS-PP having a long chain branch in the main chain skeleton is a polypropylene having a polypropylene chain branched from the polypropylene main chain skeleton. The large effect obtained as described above with polypropylene having a long chain branch in the main chain skeleton is that the long chain branch acts as a tie molecule that pseudo-crosslinks between microcrystals from the casting stage, and in the subsequent stretching step It is estimated that the stretching stress is uniformly transmitted to the entire system.

  Specific examples of HMS-PP having a long chain branch in the main chain skeleton include HMS-PP (type names: PF-814, PF-633, PF-611, SD-632, etc.) manufactured by Basell, Borealis HMS-PP (type name: WB130HMS, etc.) manufactured by Dow, HMS-PP (type names: D114, D201, D206, etc.) manufactured by Dow, and the like can be mentioned.

As an index value indicating the degree of long-chain branching of polypropylene, there is a branching index g represented by the following formula (2).
g = [η] _LB / [η] _Lin (2)

Here, [η] _LB is the intrinsic viscosity of polypropylene having long chain branches, and [η] _Lin is a linear crystalline polypropylene having substantially the same weight average molecular weight as polypropylene having long chain branches. Intrinsic viscosity. In addition, the intrinsic viscosity shown here is measured at 135 ° C. by a usual method for a sample dissolved in tetralin. In addition, the weight average molecular weight at the time of g value measurement was determined by the method published by “American Laboratory”, May, 63-75 (1978) by McConnell, ie, low angle. Measured by laser light scattering photometry.

  The branching index g of HMS-PP contained in the polypropylene film of the present invention is preferably 0.95 or less. When the branching index g exceeds the above range, the effect of adding HMS-PP is lowered, the film forming property is deteriorated, the porosity of the microporous film obtained by stretching at a high longitudinal magnification is lowered, or the transmission May be inferior. The branching index g of HMS-PP is more preferably 0.9 or less.

  The MS of HMS-PP contained in the polypropylene film of the present invention is preferably 3 to 100 cN. If the MS is less than the above range, the effect of adding the above-mentioned HMS-PP cannot be obtained, the film forming property is deteriorated, and in particular, the lateral stretchability at the time of longitudinal high magnification stretching may be degraded, or the longitudinal high magnification The porosity of the film obtained by stretching may be low. If the above range is exceeded, the film formability deteriorates, and in particular, the longitudinal stretchability at the time of longitudinal high magnification stretching may deteriorate, or the stable extrudability of the molten polymer at the time of melt extrusion and the impact resistance of the film deteriorate. There is a case. MS of said HMS-PP becomes like this. More preferably, it is 4-80 cN, More preferably, it is 5-60 cN.

  The mixing amount of HMS-PP contained in the polypropylene film of the present invention is not particularly limited, but is preferably 1 to 10% by weight, and an effect is seen even when added in a small amount. If the mixing amount is less than the above range, the effect of addition is not observed, and if it exceeds the above range, the film-forming property is deteriorated, and particularly the longitudinal stretchability at the time of stretching at a high longitudinal magnification may be deteriorated, or melt extrusion In some cases, the stable extrudability of the molten polymer and the impact resistance of the film may deteriorate, and the β crystal fraction may decrease more than necessary. The mixing amount of HMS-PP is more preferably 1 to 7% by weight, and most preferably 2 to 5% by weight.

In the polypropylene film of the present invention, the relationship between the melt tension (MS) and the melt flow rate (MFR) measured at 230 ° C. preferably satisfies the following formula (3).
log (MS)> − 0.91 log (MFR) +0.6 (3)

  Here, the MS of the film is less than 5 cN, and the relationship between MS and MFR satisfies the above formula (3) is that the MS obtained for the entire polypropylene forming the film of the present invention is less than 5 cN, and It means that MFR satisfies the above formula (3). At this time, when an additive or the like is contained in polypropylene, it is preferable to extract and measure this, but the relationship between MS and MFR measured in the pre-extraction situation where the additive or the like was present is the above. You may satisfy | fill Formula (3).

  When MS is less than 5 cN and the relationship between MS and MFR satisfies the above formula (3), tearing during stretching is reduced, and film forming properties are improved. Furthermore, for example, in order to increase the porosity of the film, the film can be formed without tearing the film at the time of transverse stretching even if the film is stretched at a low temperature and a high magnification in the longitudinal direction and then stretched in the longitudinal direction. By increasing it, the film forming speed can be increased, and the production amount per unit time can be increased. Thus, since the film forming property can be improved and the production amount can be increased, the productivity can be remarkably improved. This is presumably because the entanglement of the amorphous tie molecules penetrating the microcrystals in the system is promoted from the casting stage, whereby the stretching stress is uniformly transmitted to the entire system in the subsequent stretching process.

  In addition, as described above, when MS is less than 5 cN and the relationship between MS and MFR is made of polypropylene satisfying the above formula (3), and stretching in the longitudinal and high magnification ratio, the area ratio after stretching (= the effective stretching ratio in the longitudinal direction) And the effective draw ratio in the width direction) can be increased, and void formation is promoted, so that the porosity can be increased.

  The MS of the polypropylene film of the present invention is more preferably less than 4 cN, even more preferably less than 3 cN, and most preferably less than 2.5 cN.

  In the polypropylene constituting the polypropylene film of the present invention, for example, an antioxidant, a heat stabilizer, a chlorine scavenger, an antistatic agent, a lubricant, an antiblocking agent, a viscosity modifier, within a range not impairing the object of the present invention. You may mix well-known additives, such as a copper damage inhibitor, a light stabilizer, and an ultraviolet absorber. At this time, it is preferable that the β crystal fraction of the obtained microporous film is substantially the same when added and not added.

  Among these, selection of the kind and addition amount of the antioxidant and the heat stabilizer is important for the long-term heat resistance of the film. Examples of the antioxidant and heat stabilizer that are preferably added to the polypropylene used in the microporous polypropylene film of the present invention include various compounds. Examples of the antioxidant include 2,6-di-tert-butyl. -P-cresol (BHT); 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri -P-cresol (for example, “IRGANOX” 1330 manufactured by Ciba Geigy Co., Ltd.); pentaerythrole tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (for example, Ciba Geigy ( "IRGANOX" 1010, etc.) and the like, and examples of the heat stabilizer include tris (2,4-di-tert-butylpheny). ) Phosphite (for example, “IRGAFOS” 168 manufactured by Ciba Geigy Co., Ltd.); reaction product of 3-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene (for example, Ciba Geigy ( However, it is not limited to these.

  These antioxidants and heat stabilizers are preferably used in combination of two or more, and the addition amount thereof is preferably 0.03 to 1 part by weight with respect to the total amount of polypropylene. When the addition amount of each of the antioxidant and the heat stabilizer is less than the above range, the long-term heat resistance may be inferior in the production process until the microporous film is obtained from the initial raw material and the subsequent secondary processing process. Moreover, when the addition amount of each of the antioxidant and the heat stabilizer exceeds the above range, the long-term heat resistance of the resulting film is not improved even if it is further added, and the economy may be inferior. The addition amount of each of the antioxidant and the heat stabilizer is more preferably 0.05 to 0.9 parts by weight, still more preferably 0.1 to 0.8 parts by weight with respect to the total amount of polypropylene.

  In addition, an antistatic agent may be added to the polypropylene constituting the polypropylene film of the present invention in order to prevent electrostatic damage due to charging of the film. Examples of the antistatic agent added to the polypropylene constituting the polypropylene film of the present invention include ethylene oxide adducts of betaine derivatives, quaternary amine compounds, alkyldiethanolamine fatty acid esters, glycerin fatty acid esters, stearic acid glycerides, or Examples thereof include, but are not limited to, mixtures thereof.

  Moreover, you may add a lubricant to the polypropylene film of this invention. This is added to improve fluidity and releasability during thermoforming of thermoplastic resins expressed in JIS terms, and adjusts the friction force between the processing machine and the film surface or between films. To be added. Examples of the lubricant added to the polypropylene constituting the polypropylene film of the present invention include, but are not limited to, amide compounds such as stearamide, erucamide, and oleic amide, or mixtures thereof. It is not something.

  The amount of the antistatic agent added to the polypropylene film of the present invention is preferably 0.3 parts by weight or more, more preferably 0.4 to 1.5 parts by weight with respect to the total amount of polypropylene. is there. Further, the total addition amount of the antistatic agent and the lubricant is more preferably 0.5 to 2.0 parts by weight in terms of antistatic property and slipperiness. Furthermore, as described above, when the β crystal fraction is reduced by adding them, it is preferable not to add them substantially, and the addition amount may be appropriately selected.

  In the polypropylene constituting the polypropylene film of the present invention, inorganic particles and / or crosslinked organic particles may be added for imparting slipperiness, preventing blocking (antiblocking agent), assisting pore formation, and the like.

  In the present invention, the inorganic particles are inorganic particles of a metal compound, such as zeolite, calcium carbonate, magnesium carbonate, alumina, silica, aluminum silicate, kaolin, kaolinite, talc, clay, diatomaceous earth, montmorillonite, titanium oxide and the like. Examples thereof include, but are not limited to, particles or a mixture thereof.

  In the present invention, the crosslinked organic particles are particles obtained by crosslinking a polymer compound using a crosslinking agent. For example, crosslinked particles of a polymethoxysilane compound, crosslinked particles of a polystyrene compound, crosslinked particles of an acrylic compound, Examples include, but are not limited to, polyurethane-based compound crosslinked particles, polyester-based compound crosslinked particles, fluorine-based compound crosslinked particles, or a mixture thereof.

  Moreover, when using these as an antiblocking agent, it is preferable that the average particle diameter of an inorganic particle and bridge | crosslinking organic particle is 0.5-5 micrometers. If the average particle size is less than the above range, the resulting microporous film may be inferior in slipperiness, and if it exceeds the above range, the particles may fall off. Moreover, when adding hole formation assistance as the main objective, it is preferable that it is 0.05-1 micrometer. When the average particle size is less than the above range, the effect of addition may not be exhibited. When the average particle size is exceeded, the particles may fall off or coarse pores may be formed.

  The amount of inorganic particles and / or crosslinked organic particles added is preferably 0.02 to 0.5% by weight, more preferably 0.05 to 0.2%, when these are used only as an antiblocking agent. The weight percentage is preferred from the viewpoints of antiblocking properties, slipperiness and the like.

  Further, when pore formation assistance is added as the main purpose, it depends largely on the average particle diameter, but it is within a range that does not hinder the requirement of “having substantially non-nuclear voids” of the present invention. For example, 0.1 to 5% by weight, particularly 0.5 to 2% by weight is preferable from the viewpoints of particle dispersibility and pore formation. Furthermore, as described above, when the β crystal fraction is reduced by adding particles, or when the particles drop off and tend to foul the process, it is better not to add them substantially.

  In addition, when the film of the present invention is used as a light reflecting material, it is preferable to add a hindered amine light stabilizer in order to impart resistance to light. The addition amount is 0.01 to 1% by weight, preferably 0.05 to 0.5% by weight with respect to the polypropylene resin, and does not affect the void formation or whiteness reduction of the film. It is preferable because resistance to light is improved.

  The polypropylene film for light reflection of the present invention has a substantially non-nucleated void and a polypropylene film having a porosity of 25 to 75% as a core layer (A), and at least one surface thereof has a porosity of 0.00. It may be a laminated polypropylene film obtained by laminating a skin layer (B) of 1 to 25% polypropylene resin. In the case of this laminated film, it is necessary that the whiteness on the surface of the skin layer (B) is 70% or more and the light reflectance at a wavelength of 560 nm is 80% or more.

  In this laminated polypropylene film, the laminated thickness of the skin layer (B) laminated on at least one side of the core layer (A) is in the range of 1 to 50 μm, and is laminated on both sides of the core layer (A). The smoothness and flatness are improved, and the running property in the film forming process and the reflective material processing process is good and the production yield is improved.

  The porosity of the skin layer needs to be 0.1% or more and less than 25%, preferably in the range of 0.5 to 20%, more preferably in the range of 2 to 10%. By setting it as this range, glossiness and light reflectance are increased, and the production yield is improved. When the porosity exceeds 25%, there is no difference from the single core layer film, and there is no effect of skin layer lamination.

  A film cross-sectional photograph showing an example of this laminated polypropylene film is shown in FIG. FIG. 1A is an electron micrograph at a magnification of 1500 times mainly showing a core layer (A) portion, and it is shown that many coreless voids exist in the core layer (A). FIG. 1B is an electron micrograph mainly showing the skin layer (B) at 8000 times magnification, and it is shown that some voids are also present in the skin layer (B).

  As for the surface roughness of the single-layer polypropylene film of the present invention or the surface of the laminated polypropylene film, at least on one side, the average surface roughness Ra is preferably in the range of 0.02 to 0.5 μm, and at least gloss on one side. The degree is preferably in the range of 30 to 150%. If the average surface roughness Ra is less than 0.02 μm, the runnability in the film forming process and the reflector processing process is poor, and the production yield is unfavorable. If it exceeds 0.5 μm, the surface protrusions are scraped off. Therefore, it is not preferable.

  The glossiness of at least one surface of the surface of the single-layer polypropylene film or the laminated polypropylene film of the present invention is preferably in the range of 30 to 150%. If the glossiness is less than 30%, it is difficult to achieve a light reflectance of 80% or more. On the other hand, in order to achieve a glossiness of more than 150% with a polypropylene film, it is not stretched by adding a low temperature cast or an α crystal nucleating agent. Since a large amount of α crystals are generated in the sheet and the average surface roughness Ra needs to be less than 0.02 μm, the running property in the film forming process and the reflector processing process is poor, and the production yield is low. Since it falls, it is not preferable.

  The specific gravity of the single-layer polypropylene film or laminated polypropylene film of the present invention is preferably in the range of 0.18 to 0.8. More preferably, in the case of a single-layer polypropylene film, the range is from 0.20 to 0.65, and in the case of a laminated polypropylene film, the range is from 0.25 to 0.70.

  If the specific gravity is less than 0.18, the porosity is too high, the mechanical strength is lowered, and tearing tends to occur in the film forming process and the processing process, which is not preferable. On the other hand, if the specific gravity exceeds 0.8, the light reflectivity at a wavelength of 560 nm is less than 80%, which is not preferable, and the sum of the strength at the time of 5% elongation in the longitudinal direction and the width direction exceeds 200 MPa. Bending workability may be inferior. In order to set the specific gravity of the laminated polypropylene film in the range of 0.25 to 0.70, a polypropylene film having a specific gravity within the above range is used as the core layer (A), and the skin layer (B) is provided on at least one side thereof. What is necessary is just to adjust suitably the skin layer thickness at the time of laminating | stacking, and the porosity of a skin layer.

  The optical density (hereinafter abbreviated as OD) of the single-layer polypropylene film or laminated polypropylene film of the present invention is preferably in the range of 0.5 to 1.5. If the OD is less than 0.5, most of the light from the light source is transmitted through the film, the reflection efficiency is lowered, and the liquid crystal screen becomes dark. When OD exceeds 1.5, the reflection efficiency reaches equilibrium, and an increase in reflection efficiency cannot be expected. Rather, when the OD exceeds 1.5, the porosity, specific gravity, and thickness are outside the scope of the present invention, which is not preferable because the mechanical strength is reduced and the film thickness is increased.

  Sum of strength (hereinafter abbreviated as F5 value) at 5% elongation in the longitudinal direction (hereinafter abbreviated as MD) and width direction (hereinafter abbreviated as TD) of the single-layer polypropylene film or laminated polypropylene film of the present invention Is in the range of 50 to 200 MPa, and the ratio of F5 values of MD and TD is preferably in the range of 5: 1 to 1: 5.

  In general, the porosity and F5 value are contradictory properties, and when the porosity is increased, the F5 value decreases. However, the film of the present invention has a high F5 value despite the high porosity. It is. The reason is presumed to be that the voids of the film of the present invention are very fine and large in number compared to known void-containing films.

  If the sum of the F5 values of MD and TD is less than 50 MPa, the film formation stability is inferior, and the film is stretched due to the tension at the time of processing into a light reflecting member, and the flatness deteriorates or is torn (cut). This is not preferable because it is easy to cause a problem in process passability. On the other hand, if the sum of the MD and TD F5 values exceeds 200 MPa, bending workability may be inferior when incorporated into a backlight member of a liquid crystal screen such as a notebook computer. Moreover, when the ratio of F5 values of MD and TD is out of the range of 5: 1 to 1: 5, it is not preferable because the film may be warped or distorted after being processed as a reflecting member.

  The heat shrinkage rate after heating at 120 ° C. for 15 minutes in the single-layer polypropylene or laminated polypropylene film of the present invention is preferably 5% or less in both the MD and TD directions. When the thermal shrinkage rate exceeds 5% in both the MD and TD directions, the film shrinks greatly due to the heat of the backlight, and the reflectance may decrease when used for a long time, which is not preferable.

  The thickness of the single-layer polypropylene or laminated polypropylene film of the present invention is preferably in the range of 20 to 300 μm. When the film thickness is too thin and less than 20 μm, it becomes difficult to ensure the flatness of the film, and unevenness in brightness tends to occur when used as a reflecting member. On the other hand, when it is thicker than 300 μm, as described above, the liquid crystal display member has been made thinner and lighter, and the increase in the film thickness is hardly practical. Since a higher reflectance is required as the reflecting material, the film thickness is in the range of 50 to 250 μm, more preferably 100 to 200 μm.

  In addition, when setting it as a light reflection board with a thickness of 100 micrometers or more, according to the shape of a reflection member, the polypropylene film of this invention with a thickness of 20 micrometers-100 micrometers may be used, and a reflectance may be adjusted.

  In the laminated polypropylene film of the present invention, the laminated thickness of the skin layer (B) is preferably 1 to 50 μm. When the thickness of the skin layer is less than 1 μm, there is no lamination effect, and when it exceeds 50 μm, the reflectance is lowered and the bending workability may be lowered. The difference in thickness between the core layer (A) and the skin layer (B) is that the core layer (A): skin layer (B) = 2: 1 to 50: 1. It is preferable because both mechanical strength can be easily achieved.

  In the laminated polypropylene film of the present invention, as the polypropylene resin constituting the skin layer (B), homopolypropylene or a second component other than propylene and propylene (for example, ethylene, α-olefin, ethylene, butene, hexene, There is a propylene copolymer obtained by copolymerizing 1 to 15% by weight of octene or the like randomly or in blocks. Moreover, you may add and mix 1-5 weight% of elastomer components with the said polypropylene resin. As this elastomer component, linear low density polyethylene (m-LLDPE) by the metallocene catalyst method, ethylene-α-olefin copolymer, ethylene-butene rubber (EBR), ethylene-propylene rubber (EPR), propylene-butene rubber (PBR) ), Ethylene vinyl acetate (EVA), ethylene-ethacrylate (EEA), ethylene-methyl methacrylate (EMMA), ethylene-propylene-diene copolymer (EPDM), isoprene rubber (IR), styrene copolymer, styrene -Butadiene rubber (SBR), hydrogenated polystyrene butadiene rubber (H-SBR), styrene-butylene-styrene copolymer (SBS), styrene-ethylene-butylene-styrene copolymer (SEBS) and the like. The addition and mixing of the elastomer component is preferable because flexibility is imparted to the film, and slipperiness and moldability are improved. When the addition amount is less than 1% by weight, the effect of addition is not observed, and when it exceeds 5% by weight, dispersion failure occurs, gel-like protrusions may be formed, and heat resistance may be lowered.

  The isotactic index (II) of the polypropylene resin constituting the skin layer (B) is 90% or more, preferably 95% or more, more preferably 98%. Value) is preferable. The melt flow rate (MFR) is preferably in the range of 1 to 30 g / 10 min (230 ° C., 2.16 kg) in terms of extrusion moldability and void formation on the skin layer.

  The polypropylene resin may contain known additives such as antioxidants, heat stabilizers, antistatic agents, slip agents, antiblocking agents, light stabilizers, ultraviolet absorbers, fillers, etc. You may make it contain to such an extent that it is not made. Among them, it is preferable to contain a small amount of at least one kind of inorganic particles and organic particles in order to impart easy slipping and improve process passability. However, the addition amount at this time is preferably 2% by weight or less, and more preferably in the range of 0.02 to 1% by weight. If the added amount exceeds 2% by weight, the resin and particles may fall off in the film forming process and the laminating process, and the process may be soiled. Further, the porosity may exceed 25%, which is not preferable.

  Examples of inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc white), antimony oxide, and oxidation. Cerium, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, Kaolin, lithium fluoride, calcium fluoride, and the like can be used.

  Organic particles are particles obtained by crosslinking a polymer compound using a crosslinking agent. For example, crosslinked particles of polymethoxysilane compounds, crosslinked particles of polystyrene compounds, crosslinked particles of acrylic compounds, crosslinked particles of polyurethane compounds, crosslinked particles of polyester compounds, crosslinked particles of fluorine compounds, or a mixture thereof Can be mentioned.

  It is preferable that the inorganic particles and the crosslinked organic particles have a spherical shape and have an average particle diameter in the range of 0.1 to 2 μm because the aggregation of the particles is small and the slipperiness effect is high. If the average particle size is less than 0.1 μm, the slippery effect is low, and if it exceeds 2 μm, the film surface tends to be damaged when the particles fall off or when the films are rubbed together.

When the film of the present invention is used as a light reflecting material, it is preferable to add a hindered amine light stabilizer as a light stabilizer to the skin layer (B) in order to improve the light resistance. The amount added is 0.01 to 1% by weight, preferably 0.05 to 0.5% by weight.
It is preferable to add the β crystal nucleating agent to the skin layer (B) because the adjustment of the porosity becomes easy. At this time, the content of the β crystal nucleating agent is preferably 0.01 to 0.05% because both the porosity and the glossiness can be achieved.

  Further, when an α crystal nucleating agent and HMS-PP are added to the skin layer (B) in addition to the β crystal nucleating agent, the crystallization temperature is increased. This is preferable because it prevents sticking to the surface and increases the speed.

  The polypropylene resin constituting the skin layer (B) preferably has a melting temperature of 145 to 175 ° C. If this melting temperature is less than 145 ° C., the film may shrink and curl due to the heat of the backlight when used as a reflecting member. If it exceeds 175 ° C., film tearing frequently occurs during biaxial stretching. The film-forming property is deteriorated, and the glossiness and average surface roughness may be out of the preferred range of the present invention.

  When distinguishing the β crystal fraction of the core layer (A) and the skin layer (B) in the laminated polypropylene film of the present invention, first, a scanning electron microscope (S-2100A type, manufactured by Hitachi, Ltd., hereinafter SEM) The thickness of the skin layer (B) is scraped or sliced and only the core layer (A) is taken out and the melting peak is measured.

  The whiteness of the laminated polypropylene film of the present invention is 70% or more, preferably 75% or more, as in the case of the single-layer polypropylene film. If the whiteness is less than 70%, the image becomes dark as a whole, and the reflected light is colored (yellow, red), which may affect the color of the screen. This whiteness is a measured value on the surface of the skin layer (B).

  Similarly, the light reflectance at a wavelength of 560 nm on the surface of the skin layer (B) is 80% or more, and more preferably 90% or more. If the light reflectance is less than 80%, the illumination efficiency of the illumination light source is inferior, and the liquid crystal screen becomes dark, which is not preferable. It is preferable that L value which shows the color difference of a laminated polypropylene film is 50 or more, a value is 3--3, and b value is the range of -0.01--6.

  The single-layer polypropylene film and the laminated polypropylene film of the present invention have high porosity, low specific gravity, high whiteness, surface smoothness, high glossiness, and high reflectivity. The film is preferably uniaxially stretched, more preferably biaxially stretched in order to balance the F5 value of MD and TD and the heat shrinkage rate. The longitudinal stretching conditions in the biaxial stretching step are preferably 3 to 7 times at 100 to 140 ° C, and the transverse stretching conditions are preferably 3 to 12 times at 125 to 160 ° C.

  Since the polypropylene film for light reflectors of the present invention has voids that are substantially non-nuclear, the yellowing due to light is less and the reflectance is less than that of a void-forming film obtained by adding conventional inorganic particles or incompatible resin. However, in order to meet the demands of long-time use on large screens such as LCD TVs in recent years, higher brightness and durability are required. In the case of use, since light emitted from the light source directly hits and a higher level of durability of the reflector is required, a coating layer containing a light stabilizer may be provided on at least one side of the film. preferable.

  As the light stabilizer, organic light stabilizers such as hindered amine, salicylic acid, benzophenone, benzotriazole, cyanoacrylate, triazine, benzoate, oxalic anilide, or inorganic light stabilizer such as sol-gel An agent can be used. Specific examples of the light stabilizer suitably used are shown below, but of course not limited thereto.

  Hindered amines: bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine Polycondensate, salicylic acid series: pt-butylphenyl salicylate, p-octylphenyl salicylate, benzophenone series: 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5 Sulfobenzophenone, 2,2′-4,4′-tetrahydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, bis (2-methoxy- 4-hydroxy-5-benzoylphenyl) methane Benzotriazole series: 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-5′-t-butylphenyl) benzotriazole, 2- (2′-hydroxy-3) ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy) -3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-5'-t-octylphenol) benzotriazole, 2- (2'-hydroxy-3', 5'-di-t-amylphenyl) benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-be Zotriazol-2-yl) phenol], 2 (2′hydroxy-5′-methacryloxyphenyl) -2H-benzotriazole, 2- [2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″) , 6 "-tetrahydrophthalimidomethyl) -5'-methylphenyl] benzotriazole, 2- (2'-hydroxy-5-acryloyloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-5'- Methacryloxyethylphenyl) -2H-benzotriazole, 2- (2′-hydroxy-3′-t-butyl-5′-acryloylethylphenyl) -5-chloro-2H-benzotriazole cyanoacrylate series: ethyl-2- Cyano-3,3′-diphenyl acrylate, other than above: nickel bis (octylphenyl) Sulfide, [2,2′-thiobis (4-tert-octylphenolate)]-n-butylamine nickel, nickel complex-3,5-di-t-butyl-4-hydroxybenzyl phosphate monoethylate, nickel dibutyl Dithiocarbamate, 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl-4′-hydroxybenzoate, 2,4-di-t-butylphenyl-3 ′, 5′-di T-Butyl-4′-hydroxybenzoate, 2-ethoxy-2′-ethyl oxazac acid bisanilide, 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5- [ (Hexyl) oxy] -phenol,

  In the present invention, it is preferable to use at least one of a hindered amine type, a benzophenone type, and a benzotriazole type among the above specific examples, and it is more preferable to use these in combination.

  In the present invention, in order to make the formation of the coating layer easier, it is preferable to appropriately mix other resin components with the light stabilizer in the coating layer. That is, an organic solvent capable of dissolving the resin component and the light stabilizer, water, a mixed solution of two or more organic solvents, or a resin solution and a light stabilizer dissolved or dispersed in an organic solvent / water mixed solution. It is a preferred embodiment to use in a state. Of course, resin components and light stabilizers separately dissolved or dispersed in an organic solvent, water, an organic solvent mixed solution, or an organic solvent / water mixed solution may be arbitrarily mixed and used. It is also a preferred embodiment that a copolymer of a light stabilizer component and a resin component is used as it is as a coating material. Of course, the copolymer may be dissolved in an organic solvent, water, a mixture of two or more organic solvents, or an organic solvent / water mixture. The resin component to be mixed or copolymerized is not particularly limited. For example, polyester resin, polyurethane resin, acrylic resin, methacrylic resin, polyamide resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, Examples thereof include polystyrene resin, polyvinyl acetate resin, and fluorine resin. These resins may be used alone or in the form of two or more copolymers or a mixture.

  Among the above resin components, it is preferable to select and use an acrylic resin or a methacrylic resin, and it is more preferable to use an acrylic resin or a methacrylic resin copolymerized with a light stabilizer component for the coating layer. In the case of copolymerization, it is preferable to copolymerize an acrylic monomer component or a methacryl monomer component with respect to the light stabilizer monomer component.

  As the light stabilizer monomer component, for example, a benzotriazole-based reactive monomer, a hindered amine-based reactive monomer, a benzophenone-based reactive monomer, or the like can be preferably used. The benzotriazole-based monomer is not particularly limited as long as it is a monomer having benzotriazole in the substrate skeleton and an unsaturated bond. For example, 2- (2′-hydroxy-5-acryloyloxyethylphenyl)- 2H-benzotriazole, 2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-acryloylethylphenyl)- 5-chloro-2H-benzotriazole and the like can be mentioned. Similarly, the hindered amine-based reactive monomer and the benzophenone-based reactive monomer may be any monomer having hindered amine and benzophenone on the substrate skeleton and having an unsaturated bond, respectively. Examples of the hindered amine-based reactive monomer include bis (2,2,6,6-tetramethyl-4-piperidyl-5-acryloyloxyethylphenyl) sebacate, dimethyl succinate, 1- (2-hydroxyethyl) -4- Hydroxy-2,2,6,6-tetramethyl-5-acryloyloxyethylphenylpiperidine polycondensate, bis (2,2,6,6-tetramethyl-4-piperidyl-5-methacryloxyethylphenyl) sebacate, Dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl-5-methacryloxyethylphenylpiperidine polycondensate, bis (2,2,6,6-tetra Methyl-4-piperidyl-5-acryloylethylphenyl) sebacate, dimethyl succinate 1- (2 Hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl-5-acryloylethyl phenylpiperidine polycondensates, and the like. Examples of the benzophenone-based reactive monomer include 2-hydroxy-4-methoxy-5-acryloyloxyethylphenylbenzophenone, 2,2′-4,4′-tetrahydroxy-5-acryloyloxyethylphenylbenzophenone, 2, 2'-dihydroxy-4-methoxy-5-acryloyloxyethylphenylbenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-acryloyloxyethylphenylbenzophenone, 2-hydroxy-4-methoxy-5-methacryl Loxyethylphenylbenzophenone, 2,2′-4,4′-tetrahydroxy-5-methacryloxyethylphenylbenzophenone, 2,2′-dihydroxy-4-methoxy-5-acryloylethylphenylbenzophenone, 2,2 -, and the like-dihydroxy-4,4'-dimethoxy-5-acryloyl ethyl phenyl benzophenone.

  As the acrylic monomer component or methacryl monomer component copolymerized with these light stabilizer monomer components, or oligomer components thereof, alkyl acrylate, alkyl methacrylate (the alkyl group is methyl group, ethyl group, n-propyl group, isopropyl group) , N-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, lauryl group, stearyl group, cyclohexyl group, and the like), and monomers having a crosslinkable functional group, such as carboxyl group, methylol group, acid anhydride group Examples thereof include monomers having a sulfonic acid group, an amide group, a methylolated amide group, an amino group, an alkylolated amino group, a hydroxyl group, and an epoxy group. Furthermore, acrylonitrile, methacrylonitrile, styrene, butyl vinyl ether, maleic acid, itaconic acid and dialkyl esters thereof, methyl vinyl ketone, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl pyridine, vinyl pyrrolidone, alkoxysilane having a vinyl group, It is good also as a copolymer with saturated polyester.

  The copolymerization ratio of these light stabilizer monomer components to the monomers to be copolymerized is not particularly limited, and one or more of each can be copolymerized at an arbitrary ratio, Most preferably, the proportion of the stabilizer monomer component is 10% by weight or more, more preferably 20% by weight or more, and even more preferably 35% by weight or more. Of course, it may be a homopolymer of a light stabilizer monomer component. The molecular weight of these polymers is not particularly limited, but is usually 5,000 or more, preferably 10,000 or more, and more preferably 20,000 or more in terms of toughness of the coating layer. These polymers are used in a state dissolved or dispersed in an organic solvent, water, or an organic solvent / water mixture. In addition to these, commercially available hybrid light-stable polymers such as “Udouble” (manufactured by Nippon Shokubai Co., Ltd.) can also be used.

  The thickness of the coating layer containing the light stabilizer is not particularly limited, but is preferably 0.5 to 15 μm, more preferably 1 to 10 μm, and most preferably 2 to 7 μm. When the thickness is less than 0.5 μm, the durability of the coating layer is insufficient, and conversely, when it exceeds 15 μm, the luminance may be lowered.

  The coating layer containing the light stabilizer may be provided directly on the polypropylene film for a reflector of the base material. However, when the adhesiveness is insufficient, it is preferable to provide a subbing treatment.

  The subbing treatment may be a method provided in the process for producing a polypropylene film for a reflector (inline coating method), or may be a method in which a film is separately applied and provided (offline coating method). The material to be applied to the subbing treatment is not particularly limited and may be appropriately selected. Suitable examples thereof include copolymer polyester resin, polyurethane resin, acrylic resin, methacrylic resin, and various coupling agents. .

  The coating layer containing the light stabilizer can be applied by any method. For example, methods such as gravure coating, roll coating, spin coating, reverse coating, bar coating, screen coating, blade coating, air knife coating, and dipping can be used.

  Moreover, when hardening an application layer after application | coating, the hardening method can take a well-known method. For example, thermosetting, a method using active rays such as ultraviolet rays, electron beams, radiation, or a combination of these methods can be applied. At this time, it is preferable to use a curing agent such as a crosslinking agent in combination. Moreover, as a method of providing an application layer, it may be applied at the time of manufacturing a white film of a substrate (in-line coating), or may be applied on a white film after completion of crystal orientation (off-line coating).

  Moreover, various additives can be added to the coating layer containing the light stabilizer within a range that does not impair the effects of the present invention. As additives, for example, organic and / or inorganic fine particles, optical brighteners, crosslinking agents, heat stabilizers, oxidation stabilizers, organic lubricants, antistatic agents, nucleating agents, coupling agents, and the like are used. Can do.

  The film for a light reflecting plate of the present invention preferably has an average reflectance at a wavelength of 560 nm measured from a surface provided with a coating layer containing a light stabilizer of 80% or more, more preferably 85% or more, particularly preferably. Is desirably 90% or more. When the average reflectance is less than 80%, the luminance may be insufficient depending on the applied liquid crystal display.

  In the present invention, the whiteness measured from the surface provided with the coating layer containing the light stabilizer is preferably 70% or more, more preferably 80% or less, and further preferably 90% or less. Most preferred. When the whiteness is lower than 80%, the image becomes dark when applied to a liquid crystal display, which is not preferable.

  When using the polypropylene film of the present invention as a reflecting member, it may be used alone or in combination with other materials. At this time, in order to adhere to another base material, corona discharge treatment is performed on the surface on one side in air or in one or more atmospheres of nitrogen gas and carbon dioxide gas, and the surface wetting tension is 35 mN / m or more is preferable.

  Examples of the other materials include plain paper, fine paper, medium paper, coated paper, art paper, cast coated paper, resin-impregnated paper, emulsion-impregnated paper, latex-impregnated paper, synthetic resin internal paper, glassine paper, and laminate. Paper such as paper, synthetic paper, non-woven fabric, or other types of film can be used.

  Next, although an example is demonstrated about the manufacturing method of the polypropylene film for light reflection plates of this invention, this invention is not limited only to this example.

  In the case of the single layer polypropylene film of the present invention, it can be produced by the following method.

  β crystal nucleating agent is added to polypropylene, mixed and supplied to a twin-screw extruder, melted and kneaded at 280-300 ° C, then extruded into a gut shape, cooled through a 20 ° C water bath, and 5 mm with a chip cutter. After being cut into long pieces, it is dried at 120 ° C. for 2 hours. Next, the mixed chip is supplied to an extruder heated to 180 to 280 ° C., melted, and extruded by a T die die to obtain a molten sheet. This molten sheet is extruded and adhered onto a drum maintained at a surface temperature of 70 to 130 ° C., and 10 to 120 ° C. wind is blown onto the film surface not adhered to the drum to cool and solidify the unstretched sheet. Is made. At this time, by cooling the polypropylene melt sheet containing the β crystal nucleating agent with the above-described high temperature drum, the β crystal fraction of the unstretched sheet can be increased to 30% or more, and the voids of the film after stretching The rate can be increased. That is, holding the unstretched sheet from melt extrusion to the longitudinal stretching preheating oven at 120 ° C. for 5 seconds or more and increasing the β crystal fraction and then biaxially stretching can reduce the porosity of the film. Is important to enhance. Further, the surface glossiness can be improved by blowing air to bring the film into close contact with the drum. Furthermore, you may add the process made to pass, making it immerse in a 10-80 degreeC water tank for cooling of this unstretched sheet | seat.

  Subsequently, the unstretched sheet is led to a roll group or oven heated to 100 to 150 ° C., and after the film temperature is set to 100 to 140 ° C., the hard chrome plated metal roll and rubber roll whose surface temperature is maintained at 80 to 140 ° C. Between a pair of nip rolls (stretching rolls) and a pair of nip rolls (cooling rolls) of a metal roll and a rubber roll with a hard chrome plating maintained at a surface temperature of 30 to 100 ° C. Then, the film is stretched 3 to 7 times in the longitudinal direction (longitudinal direction, i.e., the traveling direction of the film), and cooled by a roll group of 30 to 100C.

  Subsequently, the both ends of the film stretched in the longitudinal direction are guided to a tenter while being gripped by clips, and are perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 to 190 ° C. (film temperature: 125 to 160 ° C.). To 3 to 12 times. The area magnification (= longitudinal stretching magnification × lateral stretching magnification) is preferably 9 to 84 times, and particularly preferably 30 to 50 times from the viewpoint of film formation stability. When the area magnification is less than 9 times, the surface glossiness of the obtained film is low, and void formation is insufficient, so that the characteristics of the film of the present invention cannot be obtained. Conversely, if the area magnification exceeds 84 times, there is a tendency for tearing to occur during stretching.

  In order to complete the crystal orientation of the biaxially stretched film thus obtained and to impart flatness and dimensional stability, it is subsequently subjected to heat treatment at 140 to 170 ° C. for 1 to 30 seconds in the tenter, and thereafter The film of the present invention can be obtained by uniform cooling and then cooling to room temperature and winding. In addition, in the said heat processing process, you may perform a 3-12% relaxation process in a horizontal direction or a vertical direction as needed. Biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching, and may be re-stretched in either the longitudinal or lateral direction after biaxial stretching.

  Moreover, in the case of the laminated polypropylene film which laminated | stacked the skin layer, it can manufacture with the following method.

  In a composite film forming apparatus having an extruder (a) and an extruder (b), in order to form the core layer (A), a mixed resin (a ) Is fed to an extruder (a) heated to 180 to 280 ° C., melted, and introduced into a T-die composite die. On the other hand, as a polypropylene for laminating the skin layer (B), an inorganic or organic material having an average particle diameter of 0.1 to 2 μm is formed on homopolypropylene or polypropylene obtained by copolymerizing 1 to 5% by weight of ethylene or α-olefin. A mixed resin (b) to which particles are added at 2% by weight or less is prepared. This mixed resin (b) is supplied to an extruder (b) heated to 180 to 280 ° C., melted, and introduced into a T-die composite die. The polymer in the extruder (b) is laminated so as to be on one surface layer (one surface) or both surface layers (both surfaces) of the polymer in the extruder (a), and is coextruded into a sheet to obtain a melt-laminated sheet. This melt-laminated sheet is biaxially stretched under the same film-forming conditions as in the production of the single-layer film described above to produce a light reflecting plate polypropylene film.

  In addition, as a method for laminating the skin layer, it is also possible to adopt a method of performing lateral stretching after extrusion lamination on a longitudinally stretched film.

The surface of the monolayer film or laminated film of the present invention thus produced is subjected to corona discharge treatment in air or in one or more atmospheres of nitrogen gas and carbon dioxide gas in order to be bonded to another substrate. It is preferable that the surface is wound with a surface wetting tension of 35 mN / m or more.
Next, as a coating layer containing a light stabilizer, a resin containing a binder amine light stabilizer is applied to the surface subjected to corona discharge treatment, dried at 100 to 140 ° C. and wound up.

[Measurement and evaluation method of characteristics]
The characteristic value in this invention is calculated | required with the following evaluation method and evaluation criteria.

(1) Film Using a dial gauge thickness gauge (JIS B-7509, measuring element 5 mmφ flat type), 10 points were measured at 10 cm intervals in the longitudinal direction and the width direction of the film, and the average value was defined as the film thickness. .

(2) Thickness of core layer (A) and skin layer (B) constituting film The cross section of the film was magnified 1500 times using a scanning electron microscope S-2100A type (manufactured by Hitachi, Ltd.). Using this cross-sectional photograph, the length in the thickness direction of each layer was measured, and the thickness of each layer was determined by calculating backward from the magnification. In determining the thickness of each layer, a total of five cross-sectional photometers arbitrarily selected from different measurement visual fields were used, and the average value thereof was calculated.

(3) Specific gravity The specific gravity of the film was measured using a JIS K 7112 (1999) A method (underwater) for a sample cut into a 30 × 40 mm size using a high-precision electronic hydrometer (SD-120L) manufactured by Mirage Trading Co., Ltd. It was determined by measurement at 23 ° C. and 65% RH according to the substitution method.

(4) Porosity The porosity of the single-layer film is determined according to JIS K 7112 (1999) for a sample cut into a size of 30 × 40 mm using a high-precision electronic hydrometer (SD-120L) manufactured by Mirage Trading Co., Ltd. A specific gravity (d1) measured at 23 ° C. and 65% RH in accordance with Method A (substitution method in water) and the sample are sandwiched between 0.5 mm thick aluminum plates and hot-pressed at 280 ° C. to melt and compress Then, the obtained sheet was obtained by using the following formula from the specific gravity (d0) measured by the same method as above for the sheet that was immersed in water at 30 ° C. and rapidly cooled with the aluminum plate (unit:%). ).
Porosity (%) = {1- (d1 / d0)} × 100

  In addition, in order to obtain the porosity of the skin layer of the laminated film, the cross section of the film was magnified and photographed 1500 times using a scanning electron microscope S-2100A type (manufactured by Hitachi, Ltd.). In the cross-sectional photograph, all the boundary lines that form the cross section of the bubble are marked, and if there is a nucleus inside the bubble, all the boundary lines of the cross section of the nucleus are also marked, and the marking portion is marked with the high vision image analysis apparatus PIAS- The bubble area was calculated by performing image processing using IV (made by Pierce Co., Ltd.), and the value obtained by dividing the bubble area by the total cross-sectional area was taken as the porosity. In determining the bubble area, a total of five cross-sectional photometers arbitrarily selected from different measurement fields were used, and the average value was calculated.

(5) Reflectance A reflectance of 560 nm was measured with a spectrophotometer U-3410 (manufactured by Hitachi, Ltd.) and a φ60 integrating sphere 130-0632 (manufactured by Hitachi, Ltd.) and a 10 ° inclined spacer attached. It was measured. In addition, the same measurement was performed about the same sample 5 times arbitrarily changing places, and the average value obtained was taken as the reflectance. Moreover, in the laminated film, since the skin layer surface is the reflective surface side, the reflectance of the skin layer surface of the film in which the skin layer is laminated on one side or both sides is measured.

(6) Whiteness (%), L, a, b values Using a spectroscopic colorimeter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd., the values of L, a, b of the sample and XYZ Measure the value. The whiteness was determined by the following formula using the value of XY.
Whiteness = 4 × 0.847 × Z-3 × Y (%)

  In addition, the same measurement was performed 5 times by changing a place arbitrarily about the same sample, and the obtained average value was made into the value of L, a, b, and the value of XYZ. Moreover, in the laminated film, since the skin layer surface is the reflective surface side, the skin layer surface of the film in which the skin layer is laminated on one side or both sides is measured.

(7) Surface glossiness (%)
Based on JIS Z-8741, the glossiness at an input / output angle of 60 ° was determined using a digital variable angle glossiness meter UGV-5D manufactured by Suga Test Instruments Co., Ltd.
In addition, the same measurement was performed 5 times by changing a place arbitrarily about the same sample, and the obtained average value was made into surface glossiness. Moreover, in the laminated film, since the skin layer surface is the reflective surface side, the skin layer surface of the film in which the skin layer is laminated on one side or both sides is measured.

(8) Optical density OD
Measurement was performed using an optical densitometer TR-927 manufactured by Macbeth.
In addition, the same measurement was performed 5 times by changing a place arbitrarily about the same sample, and the obtained average value was made into optical density OD.

(9) Average surface roughness Ra
In accordance with JIS B0601, measurement was performed using a stylus type surface roughness meter (manufactured by Kosaka Laboratory Ltd., high-precision thin film level difference measuring instrument, type ET30HK). The conditions at this time were a stylus diameter cone type of 0.5 μmR, a load of 16 mg, and a cutoff of 0.08 mm. When the portion of the measurement length L is extracted from the roughness curve in the direction of the center line, the center line of the extracted portion is the X axis, the vertical direction is the Y axis, and the roughness curve is expressed by y = f (X) The value (μm) obtained by the following formula is defined as the center line average surface roughness Ra.
Ra = (1 / L) ∫ | f (X) | dx.

  In addition, the same measurement was performed 5 times by changing a place arbitrarily about the same sample, and the obtained average value was made into surface roughness Ra. Moreover, in the laminated film, since the skin layer surface is the reflective surface side, the skin layer surface of the film in which the skin layer is laminated on one side or both sides is measured.

(10) Strength at 5% elongation in the longitudinal direction (MD) and width direction (TD) (F5 value)
In accordance with JIS K 7127 (1999, test piece type 2), it was measured at 25 ° C. and 65% RH using a film strong elongation measuring device (AMF / RTA-100) manufactured by Orientec Co., Ltd. A sample cut into a size of 15 cm in the longitudinal direction and 1 cm in the width direction is stretched at an original length of 50 mm and a pulling speed of 300 mm / min, and MD and TD are each 5% stretch strength (F5 value) (unit: MPa). Asked. In addition, the same measurement was performed 5 times and the obtained average value was made into F5 value.

(11) Thermal shrinkage rate Marks are placed at both end positions at intervals of 200 mm (L ₀ ) in the longitudinal direction of a sample cut into a size of longitudinal direction: 260 mm and width direction: 10 mm. A load of 3 g is applied to the lower end of the sample, heat treated for 15 minutes in a 120 ° C. hot air circulating oven, then taken out to room temperature, and the length (L ₁ ) between the marks on the sample is measured. At this time, the thermal shrinkage rate was determined by the following formula (unit:%).
Thermal contraction rate (%) = 100 × (L ₀ −L ₁ ) / L ₀
In addition, the same measurement was performed 5 times and the average value of the obtained heat shrinkage rate was made into heat shrinkage rate.

(12) Wetting tension (mN / m)
It measured based on the measuring method prescribed | regulated to JISK6768 using the liquid mixture of formamide and ethylene glycol monoethyl ether.
In addition, the same measurement was performed 5 times about the same sample, and the obtained average value was made into the wetting tension.

(13) Average particle diameter of particles The volume average diameter measured by centrifugal sedimentation (using CAPA500 manufactured by Horiba, Ltd.) was defined as the average particle diameter (μm).

(14) Melt tension (MS)
It measured at the temperature of 230 degreeC using the apparatus according to the melt flow rate measuring apparatus shown by JISK7210 (1999). Using a melt tension tester manufactured by Toyo Seiki Co., Ltd., a 5 g sample was set in a cylinder heated to 230 ° C., held and melted for 5 minutes, and the molten polymer was discharged from the capillary at an extrusion speed of 20 mm / min by a piston. The strand was discharged to take out the strand at a speed of 15.7 m / min. The tension during the take-up was measured with a stress gauge via a pulley on the way. The melt tension (MS) is an average value of tension between 120 and 180 seconds from the start of measurement (unit: cN). The same measurement was performed 5 times for the same sample, and the average value of the obtained MS was used.

(15) Confirmation of β-crystal activity Measurement was performed according to JIS K 7122 (1987) using a scanning differential calorimeter (DSC) (thermal analyzer RDC220 type manufactured by Seiko Instruments). A polypropylene film sample of 5 mg was enclosed in an aluminum pan, loaded, set in the apparatus, heated from 30 ° C. to 280 ° C. at a rate of 10 ° C./min in a nitrogen atmosphere, and after completion of the temperature rising, at 280 ° C. for 5 minutes. Then, the cooling is continued to 30 ° C. at a rate of 10 ° C./min. After completion of the cooling, the system is allowed to stand at 30 ° C. for 5 minutes, and then heated again to 280 ° C. at a rate of 10 ° C./min. When the endothermic peak accompanying the melting of the β crystal was observed at 140 ° C. or more and less than 160 ° C. in the caloric curve obtained at the time of the temperature increase, the sample film was determined to have β crystal activity.

  In addition, the endothermic peak here means that whose heat of fusion is 10 mJ / mg or more. The heat of fusion is the area enclosed by the baseline and the calorific curve until the heat curve is shifted from the baseline to the endothermic side as the temperature rises and then returns to the baseline position. A straight line was drawn on the high temperature side to the intersection of the calorific curves, and this area was determined by computer processing.

  For example, in the case of the heat quantity curve 1 shown in FIGS. 2 and 3 as a model, of the area surrounded by the baseline and the heat quantity curve, the area portion below 160 ° C. is the heat of fusion ΔHβ of the β crystal portion (reference numeral 2 in FIG. 3). The area portion of 160 ° C. or higher is the heat of fusion ΔHα of the α crystal portion (reference numeral 3 in FIG. 3).

  In addition, although a melting peak exists at 140 to 160 ° C. by the above method, if it is unclear whether it is caused by the melting of the β crystal, the presence of a melting peak at 140 to 160 ° C. and wide-angle X-ray diffraction The presence of a diffraction peak due to the β crystal in the diffraction profile obtained by the method may be determined as having β crystal activity.

The measurement conditions of the wide angle X-ray diffraction method are shown below.
・ Measurement sample: After aligning the direction of the film so that the thickness of the sample after hot press adjustment is about 1 mm, the sample is sandwiched between aluminum plates of 0.5 mm thickness and melted by hot pressing at 280 ° C. -Compressed. The obtained compressed sheet was crystallized by being immersed in boiling water at 100 ° C. for 5 minutes together with the aluminum plate, and then cooled in an atmosphere at 25 ° C. A sample obtained by cutting the obtained sheet into a width of 1 mm was used as a measurement sample.

-X-ray diffractometer: 4036A2 manufactured by Rigaku Corporation
・ X-ray source: CuKα ray (using Ni filter)
・ Output: 40kV, 20mA
・ Slit system: 2mmφ-1 ° -1 °
Detector: Scintillation counter Counting recording device: RAD-C type manufactured by Rigaku Corporation Co. Measurement method: 2θ / θ scan (step scan, 2θ range 10-55 °, 0.05 ° step, integration time 2 Seconds)

  If the strongest diffraction peak due to the (300) plane of the β crystal is observed in the vicinity of 2θ = 16.1 to 16.4 ° in the obtained diffraction profile, it is determined that a diffraction peak due to the β crystal exists. The structure of the polypropylene crystal type (α crystal, β crystal), the obtained wide-angle X-ray diffraction profile, etc. are described in, for example, Edward P. Moore Jr. Written by "Polypropylene Handbook", Industrial Research Committee (1998), p. 135-163; Hiroyuki Tadokoro, “Structure of Polymer”, Kagaku Dojin (1976), p. 393; A. Turner-Jones et al., “Macromolecular Chem.”, 75, p. There are a number of reports including 134-158 and references cited in these documents, which can be referred to.

(16) β crystal fraction It measured according to JIS K7122 (1987) using DSC (Thermo-analyzer RDC220 type | mold by Seiko Instruments). 5 mg of sample was sealed in an aluminum pan, loaded, set in the apparatus, heated from 30 ° C. to 280 ° C. at a rate of 10 ° C./min in a nitrogen atmosphere, and waited at 280 ° C. for 5 minutes after the completion of the heating. Subsequently, it is cooled to 30 ° C. at a rate of 10 ° C./minute, and after completion of the cooling, it is allowed to stand at 30 ° C. for 5 minutes, and then heated again to 280 ° C. at a rate of 10 ° C./minute. In the caloric curve obtained at the time of temperature rise, the heat of fusion (ΔHβ) calculated from one or more endothermic peaks accompanying melting of β crystal observed at 140 ° C. or higher and lower than 160 ° C. and observed at 160 ° C. or higher It calculated | required using the following formula from the calorie | heat amount of fusion ((DELTA) H (alpha)) calculated from the endothermic peak accompanying the melt | dissolution of the crystal | crystallization derived from polypropylene other than (beta) crystal | crystallization. At this time, a slight exothermic or endothermic peak may be observed between the melting peak of ΔHβ and the melting peak of ΔHα, but this peak may be deleted.

β crystal fraction (%) = {ΔHβ / (ΔHβ + ΔHα)} × 100
In addition, although a melting peak exists at 140 to 160 ° C. by the above method, if it is unclear whether it is caused by the melting of the β crystal, the presence of a melting peak at 140 to 160 ° C. and wide-angle X-ray diffraction The presence of a diffraction peak due to the β crystal in the diffraction profile obtained by the method may be determined to be a melting peak due to the melting of the β crystal. The measurement conditions of the wide-angle X-ray diffraction method are the same as those in the confirmation of the β crystal activity in (15) above.

  Moreover, since it is difficult to measure the β crystal fraction of the laminated unstretched sheet of the core layer (A) and the skin layer (B) for each layer, in the following examples, the β crystal fraction of the total laminated unstretched sheet Was measured.

  In addition, when distinguishing and measuring the β crystal ratio of the core layer (A) and the skin layer (B) of the stretched film, the cross-sectional observation is performed by SEM, and after confirming the thickness configuration, the skin layer (B) is removed. What is necessary is just to scrape and measure a melting peak about each. At this time, the skin layer (B) and the core layer (A) can be prepared as follows. After putting a single blade on the surface of the film, after sticking an adhesive tape on the film surface, the skin layer (B) is peeled off by rapidly peeling along the film. Next, from the thickness obtained by SEM observation, up to 80% from the surface of the peeled skin layer (B) portion is used as a skin layer (B) sample. Similarly, a single blade is put in the central part of the film thickness, an adhesive tape is applied to both sides of the film, and the film is pulled at the same time, and the film is cut in half at the central part of the film. The center portion of the half-cut film is scraped off with a single blade to obtain a core layer (A) sample.

(17) Confirmation of dispersion state of β crystal nucleating agent Using an optical microscope equipped with a heating device, a sample (chip-shaped raw material is used as it is and a film / sheet-shaped material is cut into a 10 mm square is used) Matsunami Glass Co., Ltd. ) It was put on a cover glass (18 × 18 mm, No. 1) manufactured by the company, heated at 200 ° C. and melted. After melting, it was directly covered with another cover glass and compressed to obtain a 0.03 mm thick melt. The dispersion state of all the nucleating agents in the thickness direction was observed by changing the depth of focus at a magnification of 400 times at any five points of the sample, and the major axis and the minor axis were measured for all the observed nucleating agents, and the ratio (= The average value of the major axis / minor axis was calculated. The same measurement was performed 5 times on the same sample, and the average value of the ratio of the major axis to the minor axis was obtained as the ratio of major axis to minor axis. In the present invention, a material having a major axis / minor axis ratio of 10 or more is defined as a nucleating agent dispersed in a needle shape.

(18) Isotactic index (II)
The sample is extracted with boiling n-heptane for a certain period of time, and the weight (%) of the portion not extracted (boiling n-heptane extraction residue) is obtained to calculate the isotactic index.

  Specifically, after drying the cylindrical filter paper at 110 ± 5 ° C. for 2 hours and leaving it in a constant temperature and humidity room for 2 hours or more, put 10 g of the sample (powder or flakes) in the cylindrical filter paper, weighing cup, tweezers Measure the balance with a direct balance (up to 4 decimal places).

This is set on the top of the extractor containing 80 cc of heptane, and the extractor and the cooler are assembled. This is heated with an oil bath or an electric heater and extracted for 12 hours. Heating is adjusted so that the number of drops from the cooler is 130 drops or more per minute. The cylindrical filter paper containing the extraction residue is taken out, put in a vacuum dryer, and dried at 80 ° C. and a vacuum degree of 100 mmHg or less for 5 hours. After drying, the sample is allowed to stand for 2 hours in constant temperature and humidity, and then precisely weighed and calculated by the following formula.
Isotactic index (II) (%) = (P / Po) × 100
However, Po is the sample weight (g) before extraction, P is the sample weight (g) after extraction.

(19) MFR (melt flow rate)
Crystalline polypropylene measures MFR according to condition 14 of JIS K 7210 (230 ° C., 2.16 kg). The ethylene-based resin measures MFR in accordance with JIS K 7210 condition 4 (190 ° C., 2.16 kg).

(20) Process passability in film forming process The number of tears of the film when the film was wound up by 5 m width and 10,000 m was obtained. Moreover, the process passability was evaluated as follows from the number of times of film breakage and the adhesion state of white powder to a metal roll, particularly a stretching roll, arranged in a film forming machine.

(Double-circle): The film was not broken once, no white powder adhered to the metal stretching roll, and the film formation was stable.
○: The film was broken once or less, no white powder adhered to the metal stretching roll, and the film formation was stable.
X: The film was torn twice or more, and particles or resin adhered to the metal product roll to contaminate the process.

(21) Light resistance A forced ultraviolet ray irradiation test was performed under the following conditions using an ultraviolet deterioration accelerating tester iSuper UV Tester SUV-W131 (manufactured by Iwasaki Electric Co., Ltd.).
"UV irradiation conditions"
Illuminance: 100 mW / cm 2, temperature: 60 ° C., relative humidity: 50% RH, irradiation time: 8 hours The reflectance and whiteness of the sample after irradiation were measured according to the methods (5) and (6) above. Compared with before ultraviolet irradiation, the reflectance and whiteness were decreased and evaluated as follows.

A: Decrease rates of both reflectance and whiteness are less than 10%.
○: Both the reflectance and the whiteness are reduced by 10% or more and less than 20%.
X: Decrease rate of both reflectance and whiteness is 20% or more.

  The present invention will be described with reference to the following examples, but the present invention is not limited thereto.

Example 1
As polypropylene (hereinafter abbreviated as homo-PP), FSX81E4 (melt flow rate (MFR): 6 g / 10 min) manufactured by Sumitomo Chemical Co., Ltd. is 96.9% by weight, and has a long chain branching with a melt tension of 20 cN. As a melt tension polypropylene (hereinafter abbreviated as HMS-PP), 3% by weight of HMS-PP PF-814 (MFR: 3 g / 10 min) manufactured by Basell, and N, N′-dicyclohexyl-2 as a β crystal nucleating agent , 6-Naphthalene dicarboxamide (NU-100 manufactured by Shin Nippon Rika Co., Ltd., hereinafter abbreviated as NU-100) was added and mixed at a ratio of 0.1 wt% to 100 parts by weight of a polypropylene resin composition, and an antioxidant. As a heat stabilizer, 0.15 parts by weight of “IRGANOX” 1010 manufactured by Ciba Geigy Co. “IRGAFOS” 168 manufactured by Ciba Geigy Co., Ltd. 0.1 part by weight was added, and this was supplied to a twin-screw extruder, melted and kneaded at 300 ° C., then extruded into a gut shape, cooled through a 20 ° C. water tank, and cut into a 5 mm length with a chip cutter. Thereafter, it was dried at 120 ° C. for 2 hours. The resulting β crystal nucleating agent-added PP resin composition (hereinafter abbreviated as β crystal PP) had a β crystal fraction of 75%.

  Next, β-crystal PP is supplied to a single screw extruder, melted and kneaded at 220 ° C., passed through a multi-layer filtration filter in which four 250 meshes are stacked, and then extruded from a slit-shaped base heated to 200 ° C. It is wound around a metal drum (= casting drum, cast drum) heated to a temperature of 120 ° C., and hot air heated to 120 ° C. is blown from the non-drum surface side of the film using an air knife to form a sheet. Molded. At this time, the retention time at 120 ° C. of the unstretched sheet from the melt extrusion to the longitudinally stretched preheating oven was 15 seconds, and the β crystal fraction of the unstretched sheet was 85%.

  The obtained unstretched sheet was passed through an oven maintained at 135 ° C. to set the film temperature to 125 ° C., then passed between rolls maintained at 120 ° C. and provided with a peripheral speed difference, and stretched 5 times in the longitudinal direction (MD). And cool to 100 ° C. Subsequently, both ends of this longitudinally stretched film were introduced into a tenter while being held by clips, preheated at 155 ° C., and stretched 10 times in the transverse direction (width direction, TD) at 145 ° C. (area ratio: longitudinal stretch ratio × width) Next, in order to complete the crystal orientation of the film and impart flatness and dimensional stability, a relaxation heat treatment of 3% in the transverse direction at 162 ° C. is performed in the tenter, and the film is gradually and gradually cooled. Then, it cooled to room temperature. Further, in order to apply the adhesive to the surface of the obtained film or to bond it to another substrate, both surfaces are subjected to corona discharge treatment in air, the surface has a wetting tension of 37 mN / m, and a film having a thickness of 40 μm is formed. Winded up.

  The raw material composition and film characteristic evaluation results of the obtained polypropylene film are shown in Tables 1 to 3, respectively. The obtained film was excellent in film formability, had many non-nucleated fine voids, had high porosity, and had high whiteness and optical density. Moreover, since the F5 value of the longitudinal direction (MD) and the width direction (TD) is in the range of the present invention and the heat shrinkage rate is low, the film forming property is excellent and the process passability is excellent. When five films were laminated to a thickness of 200 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited.

(Example 2)
A polypropylene film having a thickness of 100 μm was produced under the same conditions as in Example 1, except that the stretching ratio in the longitudinal direction was 4 times and the stretching ratio in the transverse direction was 6 times. The results are shown in Tables 1-3. The obtained film has a high porosity, whiteness, optical density, and light reflectance, and the F5 value in the longitudinal direction (MD) and the width direction (TD) is within the range of the present invention, and the heat shrinkage rate. Therefore, the film-forming property was excellent and the process passability was excellent. When two films were stacked and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited.

(Example 3)
A polypropylene film having a thickness of 200 μm was produced under the same conditions as in Example 1, except that the stretching ratio in the longitudinal direction was 6 times and the stretching ratio in the transverse direction was 6 times. The results are shown in Tables 1-3. The obtained film exhibited a high reflection function when used as a surface light source reflecting member of a liquid crystal display device due to its high porosity, whiteness, optical density, and high light reflectance. Moreover, since the F5 value of the longitudinal direction (MD) and the width direction (TD) is in the range of the present invention and the heat shrinkage rate is low, the film forming property is excellent and the process passability is excellent.

Example 4
Homo PP (manufactured by Mitsui Sumitomo Chemical Co., Ltd., WF836DG3) (MFR: 7 g / 10 min, II: 96%) 93.8 wt% and Basell HMS-PP PF-814 (MFR: 3 g / 10 min) 3% by weight, 3% by weight of ultra-low density polyethylene (“Engege” 8411 manufactured by Mitsui DuPont Co., Ltd., specific gravity 0.88, hereinafter abbreviated as V-LDPE) and β-nucleating agent NU-100 0.15 parts by weight of “IRGANOX” 1010 manufactured by Ciba Geigy Co., Ltd. as an antioxidant, and “IRGAFOS” 168 manufactured by Ciba Geigy Co., Ltd. as a thermal stabilizer were added to 100 parts by weight of a polypropylene resin composition added with 0.2% by weight. 0.1 parts by weight was added, and β-crystal PP was prepared in the same manner as in Example 1. An unstretched sheet was produced in the same manner as in Example 1 except that this β-crystal PP was used as the resin for the core layer (A). Thereafter, the film was stretched at the same longitudinal-lateral stretching temperature as in Example 1 at a stretching ratio of 5 times in length and 9 times in width to produce a polypropylene film having a thickness of 50 μm.

  The results are shown in Tables 1-3. The obtained film was excellent in film formability, had many non-nucleated fine voids, had high porosity, and had high whiteness and optical density. Moreover, since the F5 value of the longitudinal direction (MD) and the width direction (TD) is in the range of the present invention and the heat shrinkage rate is low, the film forming property is excellent and the process passability is excellent.

  Further, when five of the obtained polypropylene films were laminated to a thickness of 250 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited.

(Example 5)
Homo PP (Mitsui Chemicals Co., Ltd. J3H) (Melt Flow Rate (MFR): 18 g / 10 min, II: 96%) 50 wt% Homo PP “BEPOL” (manufactured by SUNOCO) , Type: B022-SP, MFR: 1.8 g / 10 min) was added and mixed 50 wt% of the mixed homo PP and melt extruded as in Example 1 and heated to a surface temperature of 110 ° C. = Casting drum, cast drum), and after forming into a sheet shape by blowing hot air heated to 120 ° C. using an air knife from the non-drum surface side of the film and then closely contacting it, the same longitudinal direction as in Example 1− The film was stretched at a stretching ratio of 4.5 times longitudinal and 9 times transverse at the transverse stretching temperature. Other than that was carried out similarly to Example 1, and produced the 25-micrometer-thick polypropylene film.

  The results are shown in Tables 1-3. The obtained film was excellent in film formability, had many non-nucleated fine voids, had high porosity, and had high whiteness and optical density. Moreover, since the F5 value of the longitudinal direction (MD) and the width direction (TD) is in the range of the present invention and the heat shrinkage rate is low, the film forming property is excellent and the process passability is excellent. When the obtained eight films were laminated to a thickness of 200 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited.

(Example 6)
The β-crystal PP prepared in Example 4 was used as the resin for the core layer (A), which was supplied to the extruder (a) heated to 200 ° C., melted, and introduced into the T-die composite die. On the other hand, as the resin for the skin layer (B), Homo PP, F107BV (MFR: 7 g / 10 min, II = 98%) 99.8% by weight made by Mitsui Chemical Co., Ltd. 0.2% by weight) is added and mixed, fed to a twin-screw extruder, extruded in a gut shape at 260 ° C, cooled through a 20 ° C water bath, and cut to 3 mm length with a chip cutter. Then, a mixed resin obtained by drying at 100 ° C. for 2 hours was used. Next, the mixed resin was supplied to an extruder (b) heated to 240 ° C., melted in the same manner, and introduced into a T-die composite die. The polymer of the extruder (b) was laminated so as to be on both surface layers of the polymer of the extruder (a) and coextruded into a sheet. Other than that was carried out similarly to Example 1, and produced the biaxially stretched film.

  The cross-section of the obtained laminated film was magnified and observed 1500 times with an SEM, so that the thickness structure was B layer / A layer / B layer = 3/44/3 (μm), and the inside of the skin layer (B) There were fine voids, and the porosity was 10%.

  The results are shown in Tables 1-3. The obtained film was excellent in film formability, had many non-nucleated fine voids, had high porosity, and had high whiteness and optical density. Moreover, since the F5 value of the longitudinal direction (MD) and the width direction (TD) is in the range of the present invention and the heat shrinkage rate is low, the film forming property is excellent and the process passability is excellent. When three of the obtained films were laminated to a thickness of 150 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited.

(Example 7)
As a resin for the skin layer (B), Homo PP manufactured by Sumitomo Chemical Co., Ltd., WF836DG3 (MFR: 7 g / 10 min) 99.8% by weight, and crosslinked polystyrene particles (hereinafter abbreviated as PS) by 0.2 wt. % And mixed resin prepared in the same manner as in Example 6 was used. Other than that was carried out similarly to Example 6, and produced the laminated polypropylene film of thickness structure, B layer / A layer / B layer = 3/29/3 (micrometer).

  The results are shown in Tables 1-3. The obtained laminated film has excellent film forming properties, and the core layer (B) has a large number of fine coreless voids and has a high porosity, and the voids inside the skin layer (B) are fine. It was confirmed that the porosity was 5% and had high whiteness and optical density. Moreover, since the F5 value of the longitudinal direction (MD) and the width direction (TD) is in the range of the present invention and the heat shrinkage rate is low, the film forming property is excellent and the process passability is excellent. When five of the obtained films were stacked to a thickness of 175 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited.

(Example 8)
As a coating layer containing a light stabilizer on the corona discharge treated surface of the skin layer (B) of Example 6, 100 parts of “Utable” UV714 (manufactured by Nippon Shokubai Co., Ltd.), “Sumijoule” N3200 (curing agent) A mixed solution of 5 parts of Sumitomo Bayern Urethane Co., Ltd. and 120 parts of ethyl acetate / toluene (weight ratio 1/1) was applied off-line with a gravure coater so that the thickness after drying was 5 μm. Drying was performed with hot air at 120 ° C. for 2 minutes. As shown in Table 1, the thus-obtained polypropylene film for reflectors was hardly yellowed in the light resistance test, and had a small decrease in reflectance and whiteness.

(Comparative Example 1)
100 parts by weight of a polypropylene resin composition in which 80% by weight of the same homo-PP used in Example 1 and 20% by weight of calcium carbonate (hereinafter abbreviated as CaCO ₃ ) having an average particle diameter of 2 μm manufactured by Shiraishi Calcium Co., Ltd. were added and mixed. In addition, 0.15 parts by weight of Ciba Geigy “IRGANOX” 1010 as an antioxidant and 0.1 part by weight of “IRGAFOS” 168 from Ciba Geigy as a heat stabilizer are added to a twin screw extruder. Then, after melting and kneading at 280 ° C., it was extruded into a gut shape, cooled by passing through a 20 ° C. water tank, cut to a length of 5 mm with a chip cutter, and then dried at 120 ° C. for 2 hours.

  The obtained polypropylene chip is supplied to a single screw extruder, melted and kneaded at 280 ° C., passed through a 200 mesh single filter, extruded from a slit-shaped base heated to 260 ° C., and heated to a surface temperature of 50 ° C. The film was wound around a metal drum (= casting drum, cast drum) and formed into a sheet from the non-drum surface side of the film by blowing cold air using an air knife to bring it into close contact.

  The obtained unstretched sheet was preheated through a roll group maintained at 140 ° C., passed between rolls maintained at 135 ° C. and provided with a peripheral speed difference, and stretched 5 times in the longitudinal direction (MD), and then 30 ° C. Cooled to. Subsequently, both ends of this longitudinally stretched film were introduced into a tenter while being gripped with clips, preheated at 165 ° C., and stretched 9 times in the direction (width direction, TD) at 155 ° C. (area ratio: longitudinal stretch ratio × width) Next, in order to complete the crystal orientation of the film and impart flatness and dimensional stability, a relaxation heat treatment of 3% in the transverse direction is performed at 160 ° C. in the tenter, and the film is gradually cooled gradually. Then, it cooled to room temperature. Further, in order to apply the adhesive to the surface of the obtained film or to bond it to another substrate, both surfaces are subjected to corona discharge treatment in the air so that the surface wetting tension is 37 mN / m and a film having a thickness of 40 μm is wound. I took it.

The raw material composition and film characteristic evaluation results of the obtained polypropylene film are shown in Tables 1 to 3, respectively. The resulting film had inferior film-forming properties due to CaCO ₃ falling off and adhering to the longitudinal stretching roll during film formation, and having low whiteness and optical density. Moreover, since the F5 value in the longitudinal direction (MD) and the width direction (TD) was low, tearing occurred frequently during film formation, and the process passability was poor. When five sheets of this film are overlapped to have a thickness of 200 μm and used as a surface light source reflecting member of a liquid crystal display device, the reflectance is low, and the a value and b value of the Lab value of the film are high. The yellow color became strong and the light resistance was inferior, making it unsuitable as a surface light source reflecting member.

(Comparative Example 2)
Resin composition obtained by adding NU-100, a β crystal nucleating agent, at a ratio of 0.1% by weight to 99.9% by weight of Homo PP, FS2011C (MFR: 1.3 g / 10 min) manufactured by Sumitomo Chemical Co., Ltd. 0.15 parts by weight of Ciba Geigy “IRGANOX” 1010 as an antioxidant and 0.1 part by weight of “IRGAFOS” 168 by Ciba Geigy as a heat stabilizer are added to 100 parts by weight of the product. The mixture was supplied to an extruder and melted and kneaded at 280 ° C., then extruded into a gut shape, cooled by passing through a 20 ° C. water tank, cut to a length of 5 mm with a chip cutter, and then dried at 100 ° C. for 2 hours.

  Uniaxial extrusion of a resin composition obtained by adding 15 wt% of Idemitsu Chemical Co., Ltd. Syndiotactic Polystyrene (“Zarek”, S100, hereinafter abbreviated as SPS) as a void-forming agent to 85 wt% of the obtained raw material chip It is fed to a machine, melted and kneaded at 300 ° C, passed through a 200-mesh single plate filter, extruded from a slit-shaped base heated to 270 ° C, wound around a cast drum heated to a surface temperature of 60 ° C, The sheet was formed into a sheet shape while being in close contact with a 40 ° C. cold air blow from the non-drum surface side using an air knife.

  The obtained unstretched sheet is preheated through a group of rolls maintained at 140 ° C., passed between rolls maintained at 135 ° C. and provided with a peripheral speed difference, stretched 5 times in the longitudinal direction, and immediately cooled to room temperature. Subsequently, both ends of this longitudinally stretched film were introduced into a tenter while being gripped by clips, preheated at 165 ° C., stretched 9 times in the width direction at 150 ° C., and then given a relaxation of 8% in the width direction, After heat-fixing, the film was cooled and wound up to produce a void-containing polypropylene film having a thickness of 25 μm.

  The results are shown in Tables 1-3. This film was inferior in film formation stability due to SPS dropping during film formation, and the obtained film had a low porosity, a high specific gravity, a low whiteness and an optical density. Moreover, when 8 sheets of this film were laminated | stacked and it was set as 200 micrometers in thickness, and it was used for the surface light source reflective member of a liquid crystal display device, the reflectance was low and it was inferior in light resistance, and was not suitable as a surface light source reflective member.

(Comparative Example 3)
In Example 1, the temperature of the single screw extruder and the die is 260 ° C., the casting temperature is 30 ° C., the longitudinal preheating temperature and the stretching temperature are 142 ° C., respectively, the stretching is 5 times, the transverse stretching ratio, the preheating temperature. A biaxially stretched polypropylene film having a thickness of 40 μm was produced under the same conditions as in Example 1 except that the stretching temperature / heat setting temperature were 10 times and 165 ° C./160° C./160° C., respectively.

  The results are shown in Tables 1-3. Although the film-forming property was excellent, the porosity was substantially 0, and it was estimated from the value that substantially no void was formed, and the whiteness and optical density were extremely low, making it suitable as a reflector. It was not.

(Comparative Example 4)
In Example 6, as a resin for the skin layer (B), Homo PP manufactured by Sumitomo Mitsui Chemicals Co., Ltd., WF836DG3 (MFR: 7 g / 10 min, II: 96%) 90% by weight, and a melting temperature of 240 ° C. An extruder in which 10% by weight of polymethylpentene resin (manufactured by Mitsui Chemicals, “TPX” MX-004, hereinafter abbreviated as PMP) is added and mixed, and this mixed resin is heated to 290 ° C. ( b), melted in the same manner as in Example 6, and introduced into the T-die composite die. Lamination was performed such that the polymer of the extruder (b) was on both surfaces of the polymer of the extruder (a). Other than that was carried out similarly to Example 6, and produced the polypropylene film of thickness 50 micrometers.

  The results are shown in Tables 1-3. The obtained film had a high porosity of the skin layer and high whiteness and optical density. Further, when four films were laminated to a thickness of 200 μm and used for a surface light source reflecting member of a liquid crystal display device, the reflectance was high and the surface light source reflecting member was excellent. However, the surface roughness Ra was increased, PMP was dropped during film formation, process passability was deteriorated, and productivity was inferior.

(Comparative Example 5)
In Example 1, the casting temperature was 125 ° C., the unstretched sheet was held at 125 ° C. for 50 seconds, the β crystal fraction was 87%, the longitudinal preheating temperature and the stretching temperature were 115 ° C., respectively, and stretched 6 times. The stretching ratio in the transverse direction and the preheating temperature / stretching temperature / heat setting temperature were 10 times and 125 ° C / 125 ° C / 130 ° C, respectively. Otherwise, a biaxially stretched polypropylene film having a thickness of 25 μm was produced under the same conditions as in Example 1.

  The results are shown in Tables 1-3. The obtained film had a very high porosity of 85%, a low specific gravity, and a high whiteness and optical density. In addition, eight films were stacked to have a thickness of 200 μm, and when used as a surface light source reflecting member of a liquid crystal display device, the reflectance was high, and the surface light source reflecting member was excellent. However, because the porosity is too high, the sum of F5 values of MD and TD is as low as 40 MPa, the surface roughness Ra exceeds 0.3, the glossiness is low, and the stretching and heat setting temperature is low. The film-forming stability was inferior, the heat shrinkage rate was high, and it was not suitable for productivity and practicality.

(Comparative Example 6)
In Example 6, a mixed resin obtained by adding 1% by weight of α-crystal nucleating agent (NA-11, manufactured by Denki Kagaku Kogyo Co., Ltd.) to 99% by weight of the homo-PP used as the resin for the skin layer (B). The mixed resin was supplied to an extruder (b) heated to 240 ° C., melted in the same manner as in Example 6, and introduced into a T-die composite die. One area layer was formed so that the polymer of the extruder (b) was on one surface layer (non-drum side) of the polymer of the extruder (a). The sheet is then co-extruded and wound around a metal drum (= casting drum, cast drum) heated to a surface temperature of 90 ° C., and cooled from the non-drum surface side of the film to 15 ° C. using an air knife. Was formed into a sheet shape by spraying. Other than that was carried out similarly to Example 1, and produced the biaxially stretched film.

  When the cross section of the obtained laminated film was magnified 1500 times with an SEM, the thickness configuration was A layer / B layer = 47/3 (μm). The porosity inside the skin layer (B) was 0%.

  The results are shown in Tables 1-3. The obtained film had many non-nucleated fine voids, high porosity, and high whiteness and optical density. Further, the F5 value in the longitudinal direction (MD) and the width direction (TD) is within the range of the present invention, the thermal shrinkage rate is low, the dimensional stability is excellent, and the surface gloss of the skin layer is as high as 153%. When four sheets were stacked to a thickness of 200 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function was exhibited. However, this film is inferior in slipperiness because the average surface roughness Ra of the skin layer is as small as 0.01 μm, the running property in the film forming process and the reflector processing process is poor, and wrinkles and tears are likely to occur. The production yield is greatly reduced, which is not preferable for industrial production.

(Comparative Example 7)
A polypropylene film having a thickness of 400 μm was produced in the same manner as in Example 1 except that the longitudinal uniaxial stretching in which the stretching ratio in the longitudinal direction in Example 1 was 10 times.

  The results are shown in Tables 1-3. The obtained film had a low porosity and a low reflectance, and the film was liable to be longitudinally torn and inferior in film forming stability, and was not suitable for productivity and practicality. Further, when used in a surface light source reflecting member of a liquid crystal display device, the reflectance is low and the surface light source reflecting member becomes thick, so that it is not suitable for practical use.

(Comparative Example 8)
A polypropylene film having a thickness of 15 μm was produced under the same conditions as in Example 1 except that the draw ratio in the longitudinal direction in Example 1 was 6 times and the draw ratio in the transverse direction was 12 times.

  The results are shown in Tables 1-3. The resulting film has a high porosity, high whiteness, optical density, and light reflectance. When 14 films are laminated to a thickness of 210 μm and used as a surface light source reflecting member of a liquid crystal display device, a high reflecting function is obtained. Demonstrated. However, this film has a porosity too high and the sum of the MD and TD F5 values is as low as 20 MPa, is too thin, frequently breaks the film, has poor film formation stability, and is not suitable for productivity and practicality. Met.

  The polypropylene film of the present invention is suitable as a reflecting plate or reflector for a surface light source, and particularly suitable as a surface light source reflecting member for a liquid crystal display device.

It is an electron microscope (SEM) photograph which shows the cross section of the lamination | stacking polypropylene film of this invention. (A) is a 1500 times enlarged photograph showing a core layer part, and (b) is an 8000 times enlarged photograph showing a skin layer part. It is a figure which shows typically the caloric curve at the time of temperature rising of polypropylene obtained using a scanning differential calorimeter (DSC) for explanation of a method for obtaining an endothermic peak accompanying melting of polypropylene. In the calorific curve of FIG. 2, it is a figure which shows the heat of fusion of the endothermic peak (ΔHβ) accompanying melting of β crystal and the heat of fusion of the endothermic peak (ΔHα) accompanying melting of crystals other than β crystal.

Explanation of symbols

1. Total heat of fusion curve in β crystal containing PP or β crystal containing film 2. Heat of fusion ΔHβ of β crystal part
3. Heat of fusion of α crystal part ΔHα

Claims (10)

It has substantially non-nucleated voids, has a porosity of 25 to 75%, a whiteness of 70% or more, and a light reflectance at a wavelength of 560 nm of 80% or more. Polypropylene film for light reflectors. A polypropylene film having a substantially nucleus-free void and having a porosity of 25 to 75% is used as the core layer (A), and a polypropylene resin having a porosity of 0.1% or more and less than 25% is formed on at least one surface thereof. A laminated film obtained by laminating a skin layer (B), wherein the whiteness on the surface of the skin layer (B) is 70% or more, and the light reflectance at a wavelength of 560 nm is 80% or more. Polypropylene film for light reflectors. 3. The polypropylene film for a light reflector according to claim 1, wherein the average surface roughness Ra of at least one surface is in the range of 0.02 to 0.5 [mu] m and the glossiness is in the range of 30 to 150%. . The polypropylene film for a light reflecting plate according to any one of claims 1 to 3, wherein the specific gravity is in the range of 0.18 to 0.8 and the optical density is in the range of 0.5 to 1.5. The sum of the strengths at the time of 5% elongation in the longitudinal direction and the width direction of the film is in the range of 50 to 200 MPa, and the ratio of the strength at the time of 5% elongation in the longitudinal direction and the width direction of the film is 5: 1 to 1: 5. It is a range, The polypropylene film for light reflecting plates in any one of Claims 1-4 characterized by the above-mentioned. The polypropylene film for a light reflecting plate according to any one of claims 1 to 5, wherein the film has a heat shrinkage rate of 120% at 15 ° C for 15 minutes and 5% or less in both the longitudinal direction and the width direction. The thickness of a film is the range of 20-300 micrometers, The polypropylene film for light reflecting plates in any one of Claims 1-6 characterized by the above-mentioned. The polypropylene film for a light reflecting plate according to claim 2, wherein the thickness of the skin layer (B) is 1 to 50 µm. The polypropylene which comprises a film has (beta) crystal activity, The polypropylene film for light reflecting plates in any one of Claims 1-8 characterized by the above-mentioned. A polypropylene film for a light reflecting plate, wherein a coating layer containing a light stabilizer is provided on at least one surface of the film.