JP3641877B2 - White film and method for producing the same - Google Patents

Description

【００７８】
【実施例】
以下、本発明を実施例に基づいて説明する。
【００７９】
実施例１
平均粒径１．４μｍの炭酸カルシウム２０重量％、ポリエチレンテレフタレート（ＰＥＴ）８０重量％およびリン酸トリメチル（ＴＭＰＡ）１０００ｐｐｍを混合し、２７０〜３００℃に加熱された２軸ベント付き押出機からベント圧力が５（ｍｍＨｇ）となるように真空ポンプで脱気乾燥させながら押出を行ない、Ｔダイよりシート状に形成した。このとき静電印加キャスト法を用いた。電極として直径０．５ｍｍのタングステンワイヤーに＋電荷、キャスティングドラムをアース（０電位）とし７ｋＶの直流電界をかけた。このとき溶融フィルムのキャスティングドラムとの接地点とタングステンワイヤーとの距離は１ｃｍであった。なお炭酸カルシウムの５００ｎｍ〜６００ｎｍにおける平均反射率は９０％であり、溶融時の比抵抗は１×１０⁸ Ω・ｃｍであった。さらにこのフィルムを表面温度２５℃の冷却ドラムで冷却固化させ、１００℃に加熱されたロール群に導き、機械軸方向に３倍縦延伸し、２５℃のロール群で冷却した。続いて、この縦延伸したフィルムの両端をクリップで把持しながらテンタに導き、１２５℃に加熱された雰囲気中で機械軸方向に垂直な方向に３．６倍横延伸した。その後テンタ内で２２０℃の熱固定を行ない、均一に徐冷後室温まで冷却して巻取り厚み１００μｍのフィルムを得た。得られたフィルムのについては表１に示したように、印字品質が最高レベルにあり、輝度が大きく白色で明るい画面が得られた。
【００８０】
比較例１
実施例１において使用したリン酸トリメチル（ＴＭＰＡ）を添加せず、炭酸カルシウム添加量を１０ｗｔ％とした以外は実施例１と同様の方法でフィルムを得た。得られたフィルムの物性は表１のとおりであった。フィルムのＲ×ＯＤの値が５０を下回っており、画面の明るさが十分でなく印字品質も劣っていた。
【００８１】
実施例２
平均粒径０．１μｍの二酸化チタン２０重量％、ポリエチレンテレフタレート（ＰＥＴ）８０重量％およびリン酸トリメチル（ＴＭＰＡ）１０００ｐｐｍを混合し、２７０〜３００℃に加熱された２軸ベント付き押出機よりベント圧力が１０（ｍｍＨｇ）となるように真空ポンプで脱気乾燥させながら押出し、Ｔダイよりシート状に形成し、以降は実施例１と同様の方法でフィルムを得た。得られたフィルムについては表１に示したように、印字品質レベルが高く、輝度が大きく明るい画面が得られた。
【００８２】
比較例２
ＴＭＰＡ無添加とした以外は実施例２と同様の方法でフィルムを得た。得られたフィルムの物性は表１のとおりであった。
【００８３】
ＴＭＰＡが添加されていないために平均反射率の低いフィルムとなり、このフィルムを用いた画面は十分明るいものとはならなかった。また印字品質も若干低下していた。
【００８４】
実施例３
平均粒径０．８μｍの炭酸カルシウム１０重量％、ポリエチレンテレフタレート（ＰＥＴ）９０重量％を混合し、２７０〜３００℃に加熱された２軸ベント付き押出機Ａよりベント圧力が５（ｍｍＨｇ）となるように真空ポンプで脱気乾燥させながら押出し、ＰＥＴ８０重量％、平均粒径１．４μｍの炭酸カルシウム２０重量％およびリン酸トリメチル（ＴＭＰＡ）１０００ｐｐｍを１８０℃で３時間真空乾燥し押出機Ｂより押出し、押出機Ａが内層、押出機Ｂが外層の３層構成（Ｂ／Ａ／Ｂ）となるように共押出を行ない、Ｔダイよりシート状に形成し、以降は実施例１と同様の方法でフィルムを得た。なお用いた炭酸カルシウムの５００ｎｍ〜６００ｎｍにおける平均反射率は９０％であった。得られたフィルムについては表１に示したように、印字品質レベルが高く、輝度が大きく明るい画面が得られた。
【００８５】
【表１】

【００８６】
【発明の効果】
本発明によれば、平均反射率および隠蔽性を掛け合わせた値が大きい白色フィルムが得られる。かかる白色フィルムの使用により、液晶ディスプレイ反射板用基材など面光源用反射板基材に用いて、より高反射率で明るい画面が得られると同時に印字品質にも優れるという効果が得られる。また、受容紙または印字基材として使用した場合、印字のコントラストがよく高級感を与える。
【図面の簡単な説明】
【図１】図１は、反射板をサイドライト式面発光体に組み込んだ際の概略断面図である。
【符号の説明】
１・・・画面
２・・・反射板
３・・・網点印刷
４・・・透明導光板
５・・・拡散板
６・・・冷陰極管（蛍光灯）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a white film and a method for producing the same. More specifically, the present invention relates to a receiving paper for bar code printers, a receiving paper for match printing, a receiving paper for video printers, and a printing substrate, packaging paper, copying paper, poster, home delivery slip, card, label, White film used as a substrate for photographic paper, display board, white board, magnetic card, receiving sheet and prepaid card for thermal recording, reflector for liquid crystal display, etc., particularly preferably used for reflector for surface light source The present invention relates to a brightening white film and a method for producing the same.
[0002]
[Prior art]
Conventionally, when illuminating a liquid crystal display, a backlight system that applies light from the back of the display has been adopted, but in recent years, the sidelight system as disclosed in JP-A-63-62104 is thin, It has come to be widely used because of its ability to illuminate uniformly.
[0003]
As shown in FIG. 1, the sidelight method is a method in which halftone dot printing 3 is performed on one side of a transparent light guide plate (base material) 4 such as an acrylic plate having a certain thickness, the reflection plate 2 is provided on one side, and the other side is provided. A diffusion plate 5 and a screen 1 are installed, and illumination light is uniformly distributed for halftone printing 3 by applying illumination such as a cold cathode tube 6 from the edge of the transparent light guide plate 4 and the like. The feature is that a bright screen can be obtained. In addition, since the illumination is installed not at the back of the screen but at the edge portion, there is an advantage that it can be made thinner than the backlight method. However, in order to prevent the escape of the illumination light to the back of the screen, it is necessary to install the reflector 2 on the screen. However, since the reflector 2 is required to be thin and highly reflective to light, titanium oxide is required. A film to which a white pigment such as is added is used.
[0004]
[Problems to be solved by the invention]
However, although the film whitened by adding titanium oxide or the like as described above can increase the reflectance of light to a certain level, there is a limit to improving the reflectance, and the brightness of the screen is still insufficient. There was a problem.
[0005]
As a result of intensive studies on such problems, the present inventors have absorbed light of a specific wavelength due to the mixing of specific impurities in the manufacturing process, and the overall reflectivity is lowered in a certain wavelength range, so that it is sufficient. It has been found that this is due to the reason that a bright screen cannot be obtained and the reason that the concealability is insufficient due to the inappropriate particle size distribution of particles such as titanium oxide. As market demand, there is a tendency to desire a brighter screen, and there is a strong demand for a reflector having a higher reflectivity over a wide wavelength range. In addition, when used in the market as workability to be incorporated into a liquid crystal display panel and a reflector substrate for a surface light source, it has been found that the value obtained by multiplying the reflectance and concealability of the front and back is preferably a certain value or more.
[0006]
An object of the present invention is to solve such problems, and to produce a white film optimal for use in a reflector for a surface light source such as a reflector for a liquid crystal display that provides a higher reflectance and a brighter screen. It is to provide a method.
[0007]
Other objects of the present invention include receiving paper for bar code printers, receiving paper for match prints, receiving paper for video printers and printing substrates, packaging, copying paper, posters, home delivery slips, cards, labels, An object of the present invention is to provide a high brightness white film preferably used for photographic paper, a display board, a white board, a magnetic card, a thermal recording receiving sheet, a prepaid card, and the like, and a method for producing the same.
[0008]
[Means for Solving the Problems]
The white film of the present invention that achieves the above object,A white film comprising polyester and white particles,A white film whose at least one surface (A surface) satisfies the following formula (1) is used as the gist thereof.
[0009]
      300 ≧ (R) × (OD) ≧63・ ・ ・ ・ ・ Formula (1)
(However, R is the average reflectance (%) in the light wavelength region of 500 to 600 nm when the white film is converted to 100 μm, and OD is the optical density when the white film is converted to 100 μm.)
Further, the present invention provides the following a todOf preferred embodiments.
[0011]
a. The light average reflectance of the white particles in the light wavelength region of 500 to 600 nm is 80% or more.
[0012]
b. It contains 100 ppm or more of a phosphorus compound and is at least uniaxially stretched to contain voids.
[0013]
c. Specific resistance when the white film is melted is 1 × 10⁷~ 1.9 × 10¹²Must be Ω · cm.
[0014]
d. The white film is used as a reflector substrate for a surface light source.
[0015]
  In addition, the white film of the present invention is applied to an unstretched film made of a polyester composition containing 5 to 30% by volume of white particles with a direct current of 1 kV / cm or more.electric fieldBy applying a strong electrostatic charge and then stretching at least in a uniaxial direction, it can be preferably produced by causing interfacial peeling at the white particle interface and forming voids.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, it is necessary to satisfy the above formula (1), but a more preferable range of (R) × (OD) value is 100 or more, and a more preferable range is 110 or more. In the present invention, this value is preferably as large as 1000 or 500. However, considering the ease of manufacturing in the actual industry, about 300 is practical and the effect is sufficient. When the white film of the present invention is used for a liquid crystal display reflector substrate, if the (R) × (OD) value is too low, the concealability is insufficient, the back side is transparent, and the reflectance is low, which is sufficiently bright. The screen cannot be obtained.
[0017]
A method for measuring the average reflectance (R) and optical density (OD) will be described later. In the present invention, the higher the value of R at 500 to 600 nm, the more preferable. This wavelength region corresponds to yellow, and is the wavelength region with the highest sensitivity for the human eye. That is, in the present invention, the white film is intended to be a white film with a concealing property that satisfies the above formula (1), and may be slightly colored. In the case of such coloring, the color is not limited, but a preferable color is blue to yellowish white in terms of a color ring.
[0018]
In the white film of the present invention, if necessary, a fluorescent whitening agent containing an organic and / or inorganic fluorescent agent can be added to enhance whiteness and give a high-class feeling. In particular, in order to obtain these preferred whitenesses, in the case of a composite film, at least a part of the outermost layer or the like may contain a fluorescent whitening agent. You may make it contain. In this case, it is desirable that the content of the fluorescent whitening agent in the outermost layer is larger than the content in the other layers.
[0019]
The fluorescent brightening agent may be any one that can be added to the film or can be laminated and / or coated on the film using various binders, but those developed especially for polyesters have good durability. It tends to be optimal. Examples of product names include “Uvitex” OB, MD (manufactured by Ciba-Geigy), “Mikawhite” (manufactured by Nippon Kayaku-Mitsubishi Chemical), “OB-1” (manufactured by Eastman Chemical Japan), and the like. It is done. The addition amount of the optical brightener is preferably 100 to 10,000 ppm, more preferably 200 to 5000 ppm with respect to the film substrate. If it is less than 100 ppm, the yellowness due to the particles may be strong and undesirable, and if the amount of the fluorescent brightener added is too large, the reflectance may decrease.
[0020]
  The material of the white film of the present invention isGoodPolyester is particularly preferred because it can provide good dimensional stability and planarity.
[0021]
Here, the polyester is a polymer obtained by condensation polymerization from a diol and a dicarboxylic acid, and the dicarboxylic acid is represented by terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid phthalate, adipic acid, sebacic acid, etc. It is. The diol is represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Specifically, for example, polyethylene terephthalate (PET), polytetramethylene terephthalate (PBT), polyethylene-p-oxybenzoate, poly-1,4-cyclohexylenedimethylene terephthalate (PCHDMT), polyethylene-2, 6-naphthalene Carboxylate (PEN) or the like can be used.
[0022]
In the film of the present invention, the polyester is particularly preferably PET or PEN. Various additives such as an antioxidant and an antistatic agent may be added to the polyester as long as the effects of the present invention are not impaired.
[0023]
Further, in order to obtain a preferable whiteness of the film, it is preferable to add an antioxidant, a light-resistant stabilizer and / or a heat-resistant additive, particularly in order to make it difficult to form a colored product during extrusion. The preferable content of these additives is 10 to 20000 ppm with respect to the film substrate. If it is less than 10 ppm, it may be colored with light such as a fluorescent lamp, and if it exceeds 20000 ppm, it may bleed out and contaminate the surface. Among these additives, phosphorus compounds, hindered amine-based or phenol-based antioxidants are particularly preferable. In particular, a high molecular weight phenol type is particularly preferable because it is difficult to bleed and the effect is stable.
[0024]
As content of a phosphorus compound, 100 ppm or more is preferable as a phosphorus element. More preferably, it is 200-20000 ppm, More preferably, it is 300-10000 ppm. Especially preferably, it is 400-8000 ppm.
[0025]
If the phosphorus compound content exceeds 20000 ppm, the surface may be contaminated by bleed-out. On the other hand, when the phosphorus element content in the film is less than 100 ppm, the dispersibility of the white inorganic particles is inferior, or when the resin composition is retained at a high temperature, foreign matter is generated and foamed, and the preferred whiteness cannot be obtained. May not be preferable. Although the kind of phosphorus compound is not specifically limited, For example, phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid, derivatives thereof, or metal phosphates can be used. Specifically, phosphoric acid, phosphorous acid, phosphoric acid trimethyl ester, phosphoric acid tributyl ester, phosphoric acid mono- or dimethyl ester, dimethylphosphinic acid, finylphosphinic acid, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, etc. Further, metal phosphates such as calcium phosphate, sodium phosphate, magnesium phosphate and manganese phosphate, and phosphorus compounds such as ammonium phosphate can be used.
[0026]
From the viewpoint of the dispersibility of the inorganic particles in the obtained polyester and the composition, the quality stability of the polyester composition, the foamability of the polymer when the polyester composition stays at a high temperature, the generation of foreign matter due to the inorganic particles, etc. As the above-mentioned phosphorus compound, phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid and derivatives thereof or metal phosphates are preferable, and phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid or carbon thereof is more preferable. It is an alkyl ester compound having a number of 3 or less. Two or more of these phosphorus compounds may be used in combination.
[0027]
In the production of the white film of the present invention, it is desirable to use a high-molecular-weight phenolic antioxidant, particularly those listed in the positive list added to FDA (FOOD AND DRUG AD-MINISTRATION) polyester or olefin. Is preferably used. In particular, tetrakis- [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane is preferred. As addition amount of antioxidant, 10 ppm-20000 ppm are preferable with respect to a film base material. More preferably, it is 200 ppm-20000 ppm, More preferably, it is 300 ppm or more and 10000 ppm. Especially preferably, it is 400-8000 ppm.
[0028]
If the content of the antioxidant exceeds 20000 ppm, the surface may be contaminated by bleed out. On the other hand, if the content of the phenolic antioxidant in the film is less than 10 ppm, the dispersibility of the white inorganic particles may be inferior, and foreign matter generation and foaming may occur during high-temperature residence of the resin composition, which may be undesirable. is there.
[0029]
The white film of the present invention preferably contains voids and / or white particles. Conventionally, in order to whiten the film, inorganic particles such as titanium oxide have been added without particularly examining the particle size and the light average reflectance (R). There is a limit to improving the rate, and it has been difficult to obtain a brighter liquid crystal screen.
[0030]
In the present invention, white particles having a light average reflectance (R) in the light wavelength region of 500 to 600 nm of 80% or more are preferably used as the white particles. The higher the (R) of the white particles, the better, but the upper limit is about 150%. A more preferable range is 95 to 120%. When the (R) is less than 80%, a white film having a preferable high reflectance may not be obtained. The white particles having a high reflectance can be obtained by removing a coloring compound having light absorption at a wavelength of 500 to 600 nm. Specifically, there is a method in which particles are dissolved, removed by a column that adsorbs a colored compound, and formed into particles while being precipitated.
[0031]
The white particles referred to in the present invention are inorganic white particles and / or organic white particles. Inorganic white particles include calcium carbonate, alumina, magnesium oxide, barium sulfate, silica and the like. In the case of the present invention, it is particularly preferable to use calcium carbonate. Further, it is more preferable that 50% by weight or more of the crystal form of calcium carbonate is a calcite type because impurities can be reduced and a product having less impurities can be easily obtained.
[0032]
The organic white particles can be obtained by, for example, melting and mixing a thermoplastic resin having a parallel light transmittance of 80% or more with polyester to form dispersed particles. In this case, a compatibilizing agent for reducing the dispersed particle size is also preferably used. The compatibilizing agent has an effect of reducing the dispersed particle size of the incompatible resin by adding it compared to the case where it is not added.
[0033]
In obtaining the film of the present invention, the film is preferably stretched in at least a uniaxial direction in a subsequent step. In this stretching step, voids (bubbles) are generated by interfacial peeling at the white particle interface, and light is scattered by the voids, thereby improving the reflectance. The amount of white particles used is preferably 5 to 30% by volume, more preferably 4 to 15% by volume, based on the film substrate. If the amount of white particles added is less than 5% by volume, it may be difficult for the reflectance and optical density of the white film of the present invention to fall within the scope of the present invention. Conversely, when the amount of white particles added exceeds 30% by volume, the mechanical properties of the white film of the present invention are not only inferior, but tearing during film formation occurs frequently, and thermal dimensional stability is also improved. Problems such as inferiority may occur.
[0034]
In the present invention, the average particle size of the white particles preferably used is 0.01 to 20 μm, more preferably 0.1 to 10 μm, and most preferably 0.4 to 5 μm. Here, the average particle diameter means the “equivalent spherical diameter” of the particles at a point of 50% by weight of the measured total particles. Here, the “equivalent sphere diameter” means an imaginary sphere having the same volume as the particle, and can be calculated from measurement by a normal sedimentation method or the like. When the average particle size is larger than 20 μm, there are generally many coarse particles and the optical density is lowered, which is not preferable. If the average particle size is smaller than 0.01 μm, it may be difficult to make the value of R × OD within the range of the present invention.
[0035]
Various methods can be used to cause the film to contain white particles, an antioxidant, and various additives. In the case of polyester preferably used, the following methods (1) to (3) can be used as typical methods.
[0036]
(1) A method of adding before transesterification or esterification reaction at the time of polyester synthesis or before polycondensation reaction.
[0037]
(2) A method of adding to polyester and melt-kneading.
[0038]
(3) In the above methods (1) and (2), a large amount of additives are added to produce a master batch, or white inorganic particles, antioxidants, and various additives are added in one or two kinds respectively. A method for producing a master batch, kneading with a polyester not containing particles, and adding a predetermined amount of additive.
[0039]
In addition, as a method for adding the antioxidant, a method in which the antioxidant is adsorbed on the inorganic particles in advance and then added together with the inorganic particles is also preferably used.
[0040]
When the white film of the present invention is made of polyester, the specific gravity is preferably 0.5 or more and 1.3 or less. If the specific gravity is greater than 1.3, the softness and flexibility of the film tend to be poor, and the thermal conductivity does not decrease sufficiently, so that high-quality printing cannot be performed when used as a receiving paper for thermal transfer. This is because there are cases. On the other hand, if the specific gravity is lower than 0.5, the mechanical strength as a film is generally low, and handling may be difficult.
[0041]
The excellent flexibility of the white film of the present invention is preferable because, for example, an image can be clearly transferred even when the pressure of the thermal recording head is lowered when used as a receiving paper for a video printer or the like. It is. Of course, touch feeling is also an important factor. For this reason, it is also important that cocoons are difficult to enter during handling.
[0042]
While not limiting the present invention, a suitably made white film of the present invention generally exhibits a value of 4% or greater in cushioning ratio. Preferably it is 10%-40%, More preferably, it is 20%-40%. When the cushion rate is less than 4%, for example, when used as a receiving paper for a video printer, when the pressure of the thermal recording head is lowered, the head hits hard and missing dots occur to transfer a clear image. This is not preferable because it may not be able to be performed and the touch when touched may be deteriorated.
[0043]
In the present invention, it is also a preferable production method to efficiently generate voids (bubbles) by injecting an electrostatic charge in advance to the interface of the dispersed particles and then stretching, but since static electricity can be injected particularly during melting. A production method using an electrostatic application casting method is preferred. This electrostatic application casting method is a preferable means because it can rapidly cool the front and back, and has the effect of reducing the difference of (R) × (OD) between the front and back of the film. Further, the difference between (R) × (OD) on the front and back of the film is preferably 10 or less, more preferably 5 or less, and most preferably 2 or less.
[0044]
The specific resistance at the time of melting of the white film of the present invention is 1 × 10⁶~ 1.9 × 10¹²It is preferably Ω · cm. More preferably 1 × 10⁷~ 1.9 × 10^TenΩ · cm. 1 × 10⁶If it is less than Ω · cm, the thermal stability at the time of melting may be inferior, which may be undesirable. 1.9 × 10¹²If it exceeds Ω · cm, adhesion to the cast drum is inferior, which may be undesirable.
[0045]
Further, the color tone b value obtained with a color difference meter is preferably -20 or more and 4 or less. The smaller the b value, the better the apparent whiteness of the film, giving a high-quality image, and it is also preferable for a reflector for a liquid crystal display.
[0046]
In order to improve the winding property at the time of film production and to improve the glossiness of the surface, it may be further laminated and used.
[0047]
The preferred surface roughness (Ra) of the white film in the present invention is 1 μm or less. More preferably, it is 0.5 micrometer or less, Most preferably, it is 0.2 micrometer or less. If the surface roughness is larger than this value, the printability may be poor when used as a printing substrate. In addition, a magnetic card or the like has a poor electromagnetic conversion characteristic and may not be preferable. However, if (Ra) is less than 0.01 μm or the like, the slipperiness of the film is deteriorated and handling becomes difficult, and glossy light is generated, and it may be felt cheap and the commercial value may be lowered.
[0048]
In the present invention, the void shape resulting from the white particles in the film preferably has a shape factor of 10 or more and 100 or less. Outside this range, folds are likely to occur during use, and it may be difficult to use with a magnetic card or the like.
[0049]
Next, although the manufacturing method of the white film of this invention is described, this invention is not limited to this method.
[0050]
Antioxidant is coated on white particles in advance and mixed well with resin to make a resin composition, which is then fed into an extruder heated to a temperature equal to or higher than the melting point of the resin, extruded from a die, and formed into a film on a drum. To do. Here, the resin composition can be extruded by removing moisture during the extrusion by a twin screw extruder with a vent. At this time, it is possible to pass through a filter in order to obtain a film having preferable surface characteristics. At this time, the film extruded from the die can be tightly cooled and solidified by static electricity on the drum. The surface of the drum is preferably a smooth surface plated with metal.
[0051]
Next, the unstretched film thus cooled and solidified is longitudinally stretched in the machine axis direction at the stretching temperature of the resin, and then guided to a tenter while holding both ends of the uniaxially stretched film with clips. Stretch in the direction perpendicular to the direction. At this time, a void is generated by stretching, and a desired white film can be obtained.
[0052]
The method for producing a white film in the case of using polyester that is more preferably implemented will be described more specifically.
[0053]
Calcium carbonate, which is synthesized by carbon dioxide gas compound method as white particles and from which impurities have been sufficiently removed, and trimethyl phosphoric acid as an antioxidant are blended in polyethylene terephthalate, mixed thoroughly and dried, Supply to an extruder heated to a temperature of 300 ° C. and extrude. Here, the polyester composition can be extruded by removing moisture during the extrusion by a twin screw extruder with a vent. At this time, in order to obtain a film having preferable surface characteristics, it is desirable to pass through the filter in a molten state at least once before forming the film for the purpose of removing coarse foreign matters. The filtration accuracy of the filter used is 400 μm or less. Preferably it is 100 micrometers or less, More preferably, it is 50 micrometers or less.
[0054]
The sheet thus melt-extruded is then tightly cooled and solidified by static electricity on a drum cooled to a drum surface temperature of 10 to 60 ° C. In the present invention, it is preferable to inject static electricity since interfacial peeling occurs effectively when static electricity is previously injected into the interface of the dispersed particles and then stretched. The injection of static electricity may be performed before longitudinal stretching and before lateral stretching, but electrostatic application casting that adds an electrostatic charge during melting is particularly preferable. The load electrolysis strength is direct current electrolysis of 1 kV / cm or more, preferably 1 kV / cm or more. If it is 20 kV / cm or more, corona discharge may occur, which may be undesirable.
[0055]
The surface of the drum is preferably a smooth surface plated with metal. It is preferable to use a drum surface roughness of 1S or less. More preferably 0.5S or less, still more preferably 0.3S or less. If the surface of the drum is rough, the drum surface roughness is transferred and the film surface becomes rough.
[0056]
Next, for example, the unstretched film thus cooled and solidified is led to a roll group heated to 75 to 120 ° C., stretched 2 to 5 in the machine axis direction, and cooled with a roll group of 20 to 50 ° C. At this time, the inside of the film has a structure containing voids. In order to obtain the target white film, it is preferable to generate voids in this step.
[0057]
Furthermore, the uniaxially stretched film obtained at this time can be subjected to a corona discharge treatment and coated. Next, the both ends of this uniaxially stretched film are guided to a tenter while being gripped by clips, and are stretched in the direction perpendicular to the machine direction in an atmosphere heated to 90 to 140 ° C. The stretching ratio is 2 to 5 times in the vertical and horizontal directions, and the area ratio is preferably 6 to 15 times. When the area magnification is less than 6 times, the whiteness is insufficient. Conversely, when the area magnification exceeds 15 times, the film tends to be broken during stretching and the film forming property tends to be poor.
[0058]
The biaxially stretched film is heat-fixed at 150 to 230 ° C. in a tenter to provide flatness and dimensional stability, and after uniform cooling, it is cooled to room temperature and wound. . In order to reduce the heat shrinkage rate during the heat setting, it is possible to add a relaxation of 10% or less. Thus, the white polyester film of the present invention can be obtained.
[0059]
Alternatively, as described above, a white film made of polyester can be first produced under the above conditions, and a coating layer can be separately melt-extruded thereon or laminated by coating.
[0060]
In the white film made of the polyester of the present invention, fine particles such as calcium carbonate, amorphous zeolite particles, calcium phosphate, silica, kaolin, talc and clay may be used in combination. These addition amounts are preferably 0.005 to 1 part by weight with respect to 100 parts by weight of the polyester composition. In addition to such fine particles, fine particles precipitated by the reaction between the catalyst residue and the phosphorus compound in a polyester polycondensation reaction system can be used in combination. As the precipitated particles, for example, those made of calcium, lithium and a phosphorus compound, or those made of calcium, magnesium and a phosphorus compound can be used, and the content of these particles in the polyester is 100 parts by weight of the polyester. The amount is preferably 0.05 to 1 part by weight.
[0061]
The white film of the present invention is a receiving paper for bar code printers, a receiving paper for match printing, a receiving paper for video printers, and a printing substrate, packaging paper, copying paper, poster, home delivery slip, card, label, and printing. It is preferably used for a reflector for a surface light source, such as a substrate for paper, a display board, a white board, a magnetic card, a heat-sensitive recording receiving sheet and a prepaid card, and a reflector for a liquid crystal display.
[0062]
In the present invention, a method for measuring physical properties and a method for evaluating effects are as follows.
[0063]
1. specific gravity
The film was cut into 100 × 100 mm squares, and a thickness of 10 points at least was measured with a dial gauge (No. 2109-10, manufactured by Mitoyo Seisakusho) with a 10 mm diameter probe (No. 7002). The value d (μm) is calculated. Further, this film was weighed with a direct balance, and the weight w (g) was 10.^FourRead up to g. At this time, the specific gravity is set to w / d × 100.
[0064]
2. Optical density
One or several films are stacked, and the transmission density is measured using an optical densitometer (TR927, manufactured by Macbeth). The thickness of the film and the optical density were plotted, and the optical density corresponding to a thickness of 100 μm was determined by interpolation or extrapolation.
[0065]
3. Cushion rate (%)
Mitutoyo Manufacturing Co., Ltd. Dial Gauge No. Standard gauge 900030 was used for 2109-10, and dial gauge stand No. Thickness of each film when dial gauge pressing part load 50g and 500g is applied using 7001DGS-M₅₀, D₅₀₀From the following equation.
[0066]
Cushion rate = 100 × (d₅₀−d₅₀₀) / D₅₀
4). Surface roughness Ra, Rt
According to JIS B-0601, it measured with the stylus type surface roughness meter (Kosaka Laboratory make ET-10).
[0067]
5). Average particle size of inorganic particles
The inorganic particles were dispersed in ethanol and measured using a centrifugal sedimentation type particle size distribution measuring device (Horiba Seisakusho CAPA500), and the volume average diameter was calculated to obtain the average particle diameter.
[0068]
6). Light transmittance
It is melted to the melting point or higher with an extruder and extruded. The test piece is adjusted to a thickness of 1 mm with a T-die and measured according to JIS-7105 measuring method A. The total light transmittance and the amount of scattered light were measured using an integrating sphere light transmittance measuring device, and the total light transmittance, the diffuse transmittance, and the parallel light transmittance were determined as the difference therebetween.
[0069]
7). Light average reflectance of white particles
After adjusting 100% with a spectrophotometer U-3410 manufactured by Hitachi, Ltd. using an MgO white plate as a standard plate, white particles are put into an optical quartz glass (cell optical path length 1 cm) and measured.
[0070]
The collection of the white particles in the film is performed by dissolving the matrix resin and dissolving the matrix resin in a solvent that does not affect the white particles, and separating and drying the matrix resin and the white particles by centrifugation and washing. Particularly in the case of a polyethylene terephthalate film, an orthochlorophenol / chloroform mixed solution is preferable as a solvent.
[0071]
8). Light average reflectance of film
An integrating sphere is attached to a spectrophotometer U-3410 manufactured by Hitachi, Ltd., and 100% is adjusted using a MgO white plate as a standard plate, and then measured over 500 to 600 nm. The reflectance is read from the obtained chart at intervals of 5 nm, and the average value is calculated to obtain the average reflectance. The film thickness and the light average reflectance were plotted, and the light average reflectance corresponding to a thickness of 100 μm was determined by interpolation or extrapolation.
[0072]
9. Measurement of resistivity during film melting
The method described in BRITISH JOURNAL OF APPLIED PHYSICS Vol. 17, pp. 1491-1154 (1966) was followed. However, in this case, the temperature at the time of melting of the polymer composition is 300 ° C., and the value immediately after applying DC 3000 V is the specific resistance at the time of melting.
[0073]
10. Screen brightness and color eye
In the apparatus shown in FIG. 1, halftone printing was performed on an acrylic plate having a thickness of 3 mm, a film was set as the reflecting plate 2, and illumination was performed with a 6 W fluorescent lamp from one end face. Illuminance is measured on the screen 1 with an illuminance meter (manufactured by Hioki Electric Co., Ltd. 3421) to obtain the brightness of the screen. The illuminance is measured by attaching a 20 mm wide black paper sheet to the size of the photoreceiver to form a cylinder and setting the distance between the screen 1 and the photoreceiver to 20 mm. The thing of 1000 (Lx) or more was set as the pass.
[0074]
Also, the screen is judged visually. White light is white, yellow is yellow, red is red, blue is blue. It was.
[0075]
11. Screen brightness
In FIG. 1, 15 points of luminance were measured on the screen 1 with a luminance meter (LS-110 manufactured by Minolta), and the average value was taken as the luminance of the screen. 200 (cd / m²) The above was accepted.
[0076]
12 Print quality
The resulting white film was coated with a heat-sensitive transfer receiving layer and cut into 4 plates. The film was subjected to thermal transfer recording using a CX-5000 color printer manufactured by Sharp Corporation, and the obtained hard copy was visually evaluated in terms of printing density, printing unevenness and contrast in the following five stages, and an average value was obtained. Four or more were accepted.
[0077]

[0078]
【Example】
Hereinafter, the present invention will be described based on examples.
[0079]
Example 1
Vent pressure from a twin-screw vented extruder mixed with 20% by weight of calcium carbonate having an average particle size of 1.4 μm, 80% by weight of polyethylene terephthalate (PET) and 1000 ppm of trimethyl phosphate (TMPA) and heated to 270 to 300 ° C. Extrusion was carried out while degassing and drying with a vacuum pump so that the thickness became 5 (mmHg), and a sheet was formed from a T-die. At this time, an electrostatic application casting method was used. A direct electric field of 7 kV was applied to a tungsten wire having a diameter of 0.5 mm as an electrode with a + charge and a casting drum as ground (0 potential). At this time, the distance between the contact point of the molten film with the casting drum and the tungsten wire was 1 cm. The average reflectance of calcium carbonate at 500 nm to 600 nm is 90%, and the specific resistance during melting is 1 × 10.⁸  It was Ω · cm. Further, this film was cooled and solidified by a cooling drum having a surface temperature of 25 ° C., led to a roll group heated to 100 ° C., stretched three times in the machine axis direction, and cooled by a roll group at 25 ° C. Subsequently, both ends of the longitudinally stretched film were guided to a tenter while being held by clips, and stretched 3.6 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 125 ° C. Thereafter, the film was heat-set at 220 ° C. in a tenter, uniformly cooled and then cooled to room temperature to obtain a film having a winding thickness of 100 μm. As shown in Table 1, the obtained film had the highest printing quality, a white screen with a large brightness, and a bright screen.
[0080]
Comparative Example 1
A film was obtained in the same manner as in Example 1 except that trimethyl phosphate (TMPA) used in Example 1 was not added and the amount of calcium carbonate added was 10 wt%. Table 1 shows the physical properties of the obtained film. The R × OD value of the film was less than 50, the screen was not bright enough, and the print quality was poor.
[0081]
Example 2
Vent pressure from a twin-screw vented extruder mixed with 20% by weight of titanium dioxide having an average particle size of 0.1 μm, 80% by weight of polyethylene terephthalate (PET) and 1000 ppm of trimethyl phosphate (TMPA) and heated to 270 to 300 ° C. Was extruded while being deaerated and dried with a vacuum pump so as to be 10 (mmHg), formed into a sheet form from a T-die, and thereafter a film was obtained in the same manner as in Example 1. As shown in Table 1, the obtained film had a high print quality level, a large brightness and a bright screen.
[0082]
Comparative Example 2
A film was obtained in the same manner as in Example 2 except that TMPA was not added. Table 1 shows the physical properties of the obtained film.
[0083]
Since TMPA was not added, the film had a low average reflectance, and the screen using this film was not sufficiently bright. Also, the print quality was slightly degraded.
[0084]
Example 3
10% by weight of calcium carbonate having an average particle size of 0.8 μm and 90% by weight of polyethylene terephthalate (PET) are mixed, and the vent pressure becomes 5 (mmHg) from the extruder A with a biaxial vent heated to 270 to 300 ° C. Extruded while being degassed and dried with a vacuum pump, 80% by weight of PET, 20% by weight of calcium carbonate with an average particle size of 1.4 μm and 1000 ppm of trimethyl phosphate (TMPA) were vacuum dried at 180 ° C. for 3 hours and extruded from Extruder B , Coextrusion is performed so that the extruder A has an inner layer and the extruder B has a three-layer structure (B / A / B), and a sheet is formed from a T-die. Thereafter, the same method as in Example 1 A film was obtained. The average reflectance of the used calcium carbonate at 500 nm to 600 nm was 90%. As shown in Table 1, the obtained film had a high print quality level, a large brightness and a bright screen.
[0085]
[Table 1]

[0086]
【The invention's effect】
According to the present invention, a white film having a large value obtained by multiplying the average reflectance and the concealability can be obtained. By using such a white film, it is possible to obtain a bright screen with a higher reflectivity and an excellent print quality at the same time as a reflector for a surface light source such as a reflector for a liquid crystal display. Further, when used as a receiving paper or a printing substrate, the printing contrast is good and gives a high-class feeling.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view when a reflector is incorporated in a sidelight type surface light emitter.
[Explanation of symbols]
1 ... screen
2 ... Reflector
3 ... halftone printing
4 ... Transparent light guide plate
5 ... Diffuser
6. Cold cathode tube (fluorescent lamp)

Claims (6)

A white film made of polyester and white particles, wherein at least one surface (A surface) satisfies the following formula (1).
300 ≧ (R) × (OD) ≧ 63 Expression (1)
(However, R is the average reflectance (%) in the light wavelength region of 500 to 600 nm when the white film is converted to 100 μm, and OD is the optical density when the white film is converted to 100 μm.) White film of claim 1, wherein the light average reflectivity in the optical wavelength region 500~600nm of the white particles is 80% or more. A phosphorus compound containing more than 100 ppm, is stretched in at least one direction, the white film according to claim 1 or 2, wherein the containing voids. White film according to any one of claims 1 to 3, the specific resistance at the time of melting, characterized in that a ^{1 × 10 7 ~1.9 × 10 12} Ω · cm of the white film. The white film in any one of Claims 1-4 used for the reflecting plate base material for surface light sources. By applying an electrostatic charge having a DC electric field strength of 1 kV / cm or more to an unstretched film comprising a polyester composition containing 5 to 30% by volume of white particles, the white particle interface is stretched at least in a uniaxial direction. The method for producing a white film according to claim 1 , wherein interfacial peeling is caused to form voids.

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