JP2013202960A - White polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film excellent in hue depending on an angle of visual recognition especially when used as a base material of an internal illumination signboard of an advertisement, and also having optical characteristics satisfying a resolution property with sufficient balance.SOLUTION: In a white polyester film, a coating layer containing polyester is provided on one side of the white polyester film, two dimensional arithmetic average roughness (Ra) of the coating layer surface is within a range of 21-50 nm, and a coating layer containing an antistatic agent is provided on the other side, and the total light transmittance of the film is within a range of 30-50%, and a b-value in Lab color system is within a range of -4 to 5.

Description

  The present invention relates to a white polyester film that can be used publicly as a base material for internally illuminated signboards for advertisements, for example.

  In recent years, the technology of inkjet printers has advanced rapidly, and it has become possible to obtain recorded matter having image quality equivalent to or higher than that obtained by a general silver salt photography method. Accordingly, ink jet recording materials having a texture equivalent to that used in silver salt photography are required. As an ink jet recording material that satisfies such requirements, a recording material in which a porous ink absorbing layer is provided on a substrate such as paper or a plastic film is used.

  On the other hand, large-scale inkjet printers using solvent ink (hereinafter referred to as solvent ink printers) have also appeared, and those recorded on polymer film sheets such as vinyl chloride films and tarpaulins require water resistance and weather resistance. It has been used as an outdoor display material for billboards and banner advertisements. The solvent ink is obtained by dispersing a colorant pigment in an organic solvent. Initially, a solvent with a low boiling point and high solubility was used to shorten the drying time after recording and to secure the adhesion to the vinyl chloride recording material. In recent years, the use of solvent ink printers has been expanded with the introduction of solvent inks that have very little odor and skin irritation and reduced environmental impact.

  Under such circumstances, a recording material using a paper support is being recorded by a solvent ink printer. This is considered to be because there is a movement to avoid this because the environmental load of the vinyl chloride film is large.

JP-A-8-197839 JP 2001-341262 A JP 2003-175579 A JP 2003-291509 A JP 2001-341262 A JP 2004-223714 A JP 2010-89304 A JP-A-8-36746 JP 2004-160867 A JP 2002-137350 A JP-A-7-304224

  The present invention has been made in view of the above circumstances, and the solution to the problem is, for example, excellent hue according to the angle visually recognized when used for a base material of an internally illuminated signboard for advertising, and resolution. An object of the present invention is to provide a white polyester film having optical properties satisfying the above in a well-balanced manner.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is to have a coating layer containing polyester on one side of a white polyester film, the two-dimensional arithmetic average roughness (Ra) of the coating layer surface is in the range of 21 to 50 nm, the other It is a film having a coating layer containing an antistatic agent on its surface, the total light transmittance of the film is in the range of 30 to 50%, and the b value in the Lab color system is in the range of -4 to 5. It exists in the white polyester fill characterized by.

  According to the present invention, there is provided a white polyester film having an excellent hue depending on an angle to be visually recognized when used as a base material for an internally-illuminated electric signboard for advertising, and also having optical characteristics that satisfy a good balance of resolution. The industrial value of the present invention is high.

  As the polyester constituting the white polyester film of the present invention, typically, for example, polyethylene terephthalate in which 80 mol% or more of the structural unit is ethylene terephthalate, and 80 mol% or more of the structural unit is ethylene-2,6-naphthalate. Polyethylene-2,6-naphthalate, and poly-1,4-cyclohexanedimethylene terephthalate in which 80 mol% or more of the structural unit is 1,4-cyclohexanedimethylene terephthalate. Other examples include polyethylene isophthalate and polybutylene terephthalate.

  Examples of copolymer components other than the above-described dominant components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, and polytetramethylene glycol, isophthalic acid, 2,7-naphthalenedicarboxylic acid, and 5-sodium dicarboxylic acid. Ester-forming derivatives such as diasulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid and oxymonocarboxylic acid can be used. Further, as the polyester, in addition to a homopolymer or a copolymer, a small proportion of a blend with another resin can also be used.

  For the white polyester film of the present invention, a method in which inorganic pigment particles are contained in the film is preferably used in order to exhibit whiteness and concealment. As the particles, conventionally known particles can be used, and examples thereof include titanium dioxide, calcium carbonate, barium sulfate, zinc oxide, silicon dioxide, etc., but the types of particles used are limited to the above examples. is not.

  The average particle diameter of the inorganic pigment used in the present invention is usually in the range of 0.1 to 1.0 μm, more preferably in the range of 0.2 to 0.6 μm. If the average particle size of the inorganic pigment is too small, the concealability of the polyester film may be insufficient. On the other hand, if the average particle size of the inorganic pigment is too large, the particles tend to fall off from the surface of the polyester film. Here, an inorganic pigment may be used individually by 1 type, and may use 2 or more types together.

  You may mix | blend particle | grains in the polyester layer in this invention with the main objective of providing lubricity. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium, silicon oxide, kaolin, aluminum oxide, and titanium oxide. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  The polyester used in the present invention may be chipped after melt polymerization, and may be further subjected to solid phase polymerization under reduced pressure by heating or in an inert gas stream such as nitrogen as necessary. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and more preferably 0.40 to 0.90 dl / g. If the intrinsic viscosity is too low, the mechanical strength of the film tends to decrease. Moreover, when intrinsic viscosity is too high, the load in the melt extrusion process at the time of film formation will be large, and there exists a tendency for productivity to fall.

  In the present invention, in order to obtain an excellent hue depending on the viewing angle, particularly when used as a base material for advertising interior lighting signs for advertisements, and to satisfy a good balance of resolution, a fluorescent enhancement is added to the film. Whitening agents can be included. When the content of the optical brightener is less than 0.01% by weight, the effect of improving the brightness may be insufficient. On the other hand, when the content exceeds 1.0% by weight, the effect is saturated, Problems such as changes in color tone and bleed out on the surface of the film may adversely affect use.

Examples of fluorescent brighteners that can be suitably used in the present invention include a product “Ubitec” manufactured by Ciba Specialty Chemicals, a product “OB-1” manufactured by Eastman, and the like.
The white polyester film of the present invention has a coating layer formed by coating a coating solution containing polyester on one side and a coating layer obtained by coating a coating solution containing an antistatic agent on the opposite side. Is.

  The total light transmittance of the polyester film of the present invention is in the range of 30 to 50%, more preferably in the range of 35 to 45%, and the b value in the Lab color system is in the range of -4 to 5. is necessary. When the total light transmittance is less than 30%, the resolution of the recording material as a base material in the present invention is low, and the brightness of the optical characteristics is low, which is inappropriate. When used as a base material for recording materials, the color tone of the image is inferior. When the b value is less than -4, the blueness of the film as the base material is strong, and when it exceeds 5, the yellowish color of the film as the base material becomes strong and balances the resolution when used as the base material. I can't meet well.

Furthermore, in the present invention, from the viewpoint of antistatic properties in the film forming process and the processing process, the surface specific resistance value of the surface of the coating layer at 25 ° C. and 65% RH is 1 × 10 ⁶ to 1 × 10 ¹³ Ω / □. Preferably there is. Since the surface specific resistance value is low, when a film roll is unwound and a printing layer is provided, adhesion of foreign matters due to static electricity can be prevented, so that defects such as printing omission can be eliminated.

Moreover, although the said polyester film may be a single layer or a multilayer, in this invention, a white pigment is contained in the polyester film which consists of a single layer. Examples of white pigments include anatase type titanium oxide, rutile type titanium oxide, barium sulfate and the like, and among these, anatase type titanium oxide is preferable. Here, the white pigment has an average particle size in the range of usually 0.1 to 1.0 μm, and the content is usually 1 to 35% by weight.
If the average particle size is less than 0.1 μm, the film concealing property tends to be inferior. On the other hand, if it exceeds 1.0 μm, the film forming continuity may be inferior. On the other hand, if the content is less than 1% by weight, the whiteness and hiding property of the film tend to be inferior. On the other hand, if the content exceeds 35% by weight, the film forming continuity tends to be poor.

  In addition to the above components, the polyester film of the present invention preferably contains 0.01 to 1.0% by weight of amorphous silica particles having an average particle size of 0.1 to 5.0 μm. When the average particle size is less than 0.1 μm or the content is less than 0.01% by weight, the film transportability tends to be inferior. On the other hand, when the average particle diameter exceeds 5.0 μm or the content exceeds 1.0% by weight, the film formation continuity is lowered, and the two-dimensional arithmetic average roughness (Ra) of the film is preferably increased. Absent.

  The two-dimensional arithmetic average roughness (Ra) of the surface of the coating layer containing the polyester of the film of the present invention is in the range of 21 to 50 nm. When the two-dimensional arithmetic average roughness (Ra) is less than 19 nm, the glossiness increases and the visibility is inferior. On the other hand, when the two-dimensional arithmetic average roughness (Ra) exceeds 50 nm, the surface properties become rough, the printing resolution is lowered, and the visibility is inferior.

  In addition to the pigment and silica particles described above, the polyester film of the present invention may include conventionally known antioxidants, heat stabilizers, lubricants, fluorescent brighteners, dyes, ultraviolet absorbers, and near infrared absorption as necessary. Additives such as agents can be added.

  Although the thickness of the polyester film of the present invention is not particularly limited, it preferably has an appropriate waist strength as the processability of the film, usually in the range of 50 to 200 μm, preferably in the range of 75 to 175 μm. Is within. If the thickness is less than 50 μm, the recording material may be stiff and the desired concealing property may not be ensured. On the other hand, if the thickness exceeds 200 μm, the cost per area increases.

  Hereinafter, although the manufacturing method of the polyester film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not limited to the following illustrations.

  First, a dried or undried polyester chip by a known method is supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then at 90 to 160 ° C. in the lateral direction. It is preferable to perform 2-6 times stretching and to heat-process at 150-240 degreeC for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  The polyester film may be a single layer or a multilayer.

In particular, the film of the present invention has an easy adhesion treatment layer having polyester on one side for improving adhesion to a printed layer when used as a recording material, and prevents adhesion of foreign matters due to static electricity on the opposite side. It is necessary to provide an antistatic treatment layer.
In forming such a coating layer, the method of forming a film, in particular, after stretching in the longitudinal direction and before stretching in the lateral direction can form a very thin coating layer, and the coating solution drying and curing reaction Is preferable in that it can be carried out in the film forming process.

  The easy adhesion treatment of the present invention preferably comprises a combination of a crosslinking agent and various binder resins, and as the binder resin, a polymer usually selected from polyester, acrylic polymer and polyurethane is adopted from the viewpoint of adhesiveness. To do. Each of the above polymers shall also include derivatives thereof. The derivative here refers to a polymer obtained by reacting a reactive compound with a copolymer or a functional group with another polymer.

  Among the polyesters, acrylic polymers, and polyurethanes that are used as coating agents in the present invention, particularly preferred polymers have a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher. It is a polyurethane having a carboxylic acid residue, at least a part of which is made water-based using an amine or ammonia.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine-based resin may be either a monomer, a condensate composed of a dimer or higher multimer, or a mixture thereof.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipperiness, stickiness and the like. The amount of the particles in the coating agent is usually 0.5% by weight or more, preferably 1% by weight or more. When the amount is less than 0.5% by weight, the blocking resistance may be insufficient.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon oxide is easy to use because it is inexpensive and has various particle sizes. On the other hand, examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound containing two or more carbon-carbon double bonds in one molecule (for example, divinylbenzene).

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like. Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned.
These organic solvents may be used in combination of two or more as required.

  If you do not apply a polyester-containing coating solution on one side, the adhesion to the film will be insufficient, resulting in poor ink adhesion in the next process, or the interface peeling between the film surface and the ink surface will cause the product appearance Will be damaged.

  The antistatic treatment layer of the present invention preferably contains a sulfonate salt, an alkyl sulfate ester salt, a cationic compound, or the like.

  The alkyl group of the sulfonate or alkyl sulfate ester salt used in the present invention preferably has 8 to 30 carbon atoms. When the number of carbon atoms is small, the compatibility with the resin to be applied is poor, and when the number of carbon atoms is large, the effect of the antistatic property is deteriorated, and when a film roll is unwound and a printing layer is provided, adhesion of foreign matters due to static electricity cannot be prevented. . Examples of the cationic antistatic agent used in the present invention include compounds having a quaternary ammonium base.

  This refers to a compound having a component containing a quaternary ammonium base in the main chain or side chain in the molecule. Examples of such constituents include pyrrolidinium ring, quaternized alkylamine, copolymerized with acrylic acid or methacrylic acid, quaternized N-alkylaminoacrylamide, vinylbenzyltrimethylammonium salt, 2 -Hydroxy 3-methacryloxypropyltrimethylammonium salt etc. can be mentioned.

  Further, these may be combined or copolymerized with other resins. In addition, examples of anions that serve as counter ions for these quaternary ammonium salts include ions such as halogen, alkyl sulfate, alkyl sulfonate, and nitric acid.

  In the present invention, the compound having a quaternary ammonium base is preferably a polymer compound, and the number average molecular weight thereof is usually 1000 or more, more preferably 2000 or more, and particularly preferably 5000 or more and 500,000 or less. . If the molecular weight is too low, the antistatic agent may bleed out and cause troubles that transfer to the contacting surface. If the molecular weight is too high, the viscosity of the coating solution may become too high, and troubles may occur in which the coating properties become poor.

  The average particle size of the particles to be contained in the antistatic layer in the present invention is 0.01 to 5 μm, preferably 0.02 to 2 μm. When the average particle diameter exceeds 5 μm, a coating defect may occur, or when a high-definition circuit pattern is formed, transmission of ultraviolet rays may be shielded to cause a defect in the circuit pattern. On the other hand, when the thickness is less than 0.01 μm, handling properties such as film slipperiness and winding property tend to be lowered.

  Examples of the particles to be included in the antistatic layer include wet and dry silica, colloidal silk, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay, hydroxyapatite, and the like. Organic particles containing styrene, silicone, acrylic acid, or the like as constituent components can be used. Two or more kinds of these particles may be used in combination as long as the characteristics defined in the present invention are not impaired.

  Furthermore, the particles contained in the antistatic layer are preferably in the range of 0.01 to 25% by mass. When the content is less than 0.01% by mass, handling properties such as deterioration of the slipperiness of the film and difficulty in winding are likely to be deteriorated. On the other hand, if it exceeds 25% by weight, transparency and coating properties tend to deteriorate.

  The antistatic layer has a dry thickness of usually 0.003 to 1.5 μm, preferably 0.005 to 0.5 μm. If the thickness of the antistatic layer is less than 0.003 μm, sufficient performance may not be obtained, and if it exceeds 1.5 μm, blocking between films tends to occur.

  When an antistatic treatment layer is not provided on the surface opposite to the easy-contact treatment layer of the white polyester film of the present invention, foreign matter due to static electricity adheres when the surface roll has a high surface resistivity and a printed layer is provided. Defects such as missing prints occur.

As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used.
The coating layer may be formed only on one side of the polyester film or on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually 0.01 to 0.5 μm, preferably 0.015 to 0.3 μm as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  The film of the present invention exhibits its particularly excellent effect when used as a recording material, but has an excellent hue depending on the angle visually recognized when used as a base material for a recording material of an internally illuminated electric signboard. Polyester film.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measuring method used in the present invention is as follows.

(1) Film thickness Ten-point thickness was measured for the film with an electronic micrometer (K-402B manufactured by Anritsu), and the average value was taken as the thickness of the film.

(2) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measurement was performed at 30 ° C.

(3) Measurement of average particle size (d ₅₀ : μm) of added particles The size of particles was measured by a sedimentation method based on Stokes' resistance law using Shimadzu Corporation centrifugal sedimentation type particle size distribution analyzer SA-CP3 type. Was measured. The average particle diameter was determined by using a value of 50% of integration (volume basis) in the equivalent spherical distribution of particles obtained by measurement.

(4) Color tone measurement (L value, a value, b value)
Using Nippon Denshoku Industries Co., Ltd.'s colorimetric color difference meter DN-300A, the printing surface was measured according to the method of JIS Z-8722, with the color tone set to L value, a value, and b value. In addition, it measured with C light source and a 2 degree | time visual field.

(5) Total light transmittance The total light transmittance was measured according to JIS-K7136 using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.

(6) Surface roughness of the film (two-dimensional arithmetic average roughness: Ra)
Surface roughness measuring machine (SE3500, manufactured by Kosaka Laboratory Co., Ltd.) on the surface of the coating layer containing polyester (the surface of the polyester when there is no coating layer, or the surface of the coating layer when the coating layer contains an antistatic agent on both sides). ) And the printed surface was measured according to JIS-B-0601-1994. The cut-off value was 0.08 mm.

(7) Glossiness Using a gloss meter VG-2000 manufactured by Nippon Denshoku Industries Co., Ltd., the printed surface was measured with a specular glossiness and an incident angle and a light receiving angle of 60 degrees according to JIS-Z8741.

(8) Blocking property The printed surface of the product roll and the opposite surface are overlapped, and the pressure of 1 kgf / cm ² is adhered to this in an atmosphere of 50 ° C. and 60% RH for 24 hours, and then peeled off. Was determined according to the following criteria.
○: Lightly peelable without transfer of coating layer Δ: Peeling sound is generated, but the coating layer is not transferred to the mating surface ×: The coating layer is transferred to the mating surface, two films Is fixed and cannot be peeled off, or the base polyester film is cleaved even if it can be peeled off

(9) Image Visibility An image of a check pattern is output by an ink-jet printer PM-700C manufactured by Seiko Epson Corporation, and the image visibility from the transparent support side is visually observed by reflected light and transmitted light, according to the following criteria: evaluated.
◎: Visibility with reflected light and visibility with transmitted light are good and balanced ○: Visibility with reflected light and visibility with transmitted light are good, but balance is slightly inferior × : Visibility with reflected light or visibility with transmitted light is not good The visibility of reflected light here refers to the image readability from the front of the print when there is no light from the back of the film in the daytime. Visibility with transmitted light refers to image readability from the front of printing when the light source is transmitted from the back of the night film.

(10) Normal adhesion (23 ° C., 50% RH)
Cross-cut cross cut (25 squares of 2 mm ² ) reaching the base film on the printed surface, and 18 mm wide tape (Cello Tape (registered trademark) CT-18 manufactured by Nichiban Co., Ltd.) is pasted on it. After peeling off rapidly at a peeling angle of 180 degrees, the peeling surface was observed, the number of peelings in 25 squares was counted, and classified into the following standard ranks. In addition, ○ or more is a practical limit.
○: The number of peeled is 0. Δ: The number of peeled is 1 or more and less than 10. ×: The peeled area is 10 or more.

(11) Defects of the coating layer (foreign matter)
Black solid printing is performed in an area of 1 m ² , and the printed layer is visually observed for defects such as repellency and foreign matter. If there are defects, the printed layer is subjected to a laser optical microscope (VF-750) manufactured by Keyence Corporation. Measure the size with. The number of defects of the coating layer having a maximum diameter of 0.5 mm or more is obtained.
○: Less than 3 defects of coating layer with a maximum diameter of 0.5 mm or more are good. ×: 3 defects or more of coating layer with a maximum diameter of 0.5 mm or more are defective.

Examples and Comparative Examples are shown below, and the method for producing the polyester used in the Examples and Comparative Examples is as follows.
<Manufacture of polyester>
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.01 part of antimony trioxide was added and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.71 and a diethylene glycol content of 1.0 mol%.

<Method for producing polyester (B)>
In the method for producing polyester A, after the transesterification reaction was completed, ethylene glycol slurry containing 1.6 parts by weight of silica particles having an average particle size of 3.5 μm was added to the reaction system, and ethyl acid phosphate 0. After adding 04 parts and 0.04 part of antimony trioxide, the temperature was 280 ° C. and the pressure was 15 mmHg in 100 minutes, and thereafter the pressure was gradually reduced to finally 0.3 mmHg. After 4 hours, the system was returned to normal pressure to obtain polyester B. The resulting polyester B had a silica particle content of 1.0% by weight. The intrinsic viscosity of this polyester was 0.64.

<Production method of polyester (C)> TiO ₂
50 parts by weight of polyester (A) was mixed with 50 parts by weight of anatase-type titanium dioxide having an average particle size of 0.3 μm, and the mixture was supplied to a vent type twin screw extruder and pre-kneaded. Next, the molten polymer was continuously supplied to a vent type single-screw kneader and then sufficiently kneaded to obtain polyester (C) as a titanium oxide-containing master pellet. The obtained polyester (C) had an intrinsic viscosity of 0.49.

Example 1:
The above-mentioned polyester (A) / polyester (B) / polyester (C) were mixed at a ratio of 90/6/4 (parts by weight), respectively, and each was supplied to a vent type twin screw extruder and melted at 280 ° C. Then, it was co-extruded, extruded from the die, and cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched sheet. Next, the film was stretched 3.1 times in the machine direction at a film temperature of 85 ° C. using the difference in roll peripheral speed, and then the coating agent [I] having the composition shown below and [II] on the opposite surface were coated. Then, the film was stretched 3.4 times at 110 ° C. in the transverse direction, heat treated at 230 ° C., and then relaxed 2% in the transverse direction to obtain a single-layer polyester film having a thickness of 100 μm. Both coating layers had a thickness of 0.04 μm.

(Coating agent composition: weight ratio)
[I]
A coating layer formed by mixing a coating solution in which the following coating agent is mixed at a non-volatile component ratio of a / b / c / d = 35/30/30/5 so that the film thickness after drying becomes 0.04 μm. The compounds constituting each coating layer are as follows.
・ Polyester resin a
Monomer composition: (acid component) terephthalic acid / isophthalic acid / (diol component) diethylene glycol / neopentyl glycol / dimethylolpropionic acid = 20/80/72/20/8 (mol%)
・ Polyvinyl alcohol b
Polyvinyl alcohol / epoxy compound c having a saponification degree of 88 mol% and a polymerization degree of 500
Polyglycerol polyglycidyl ether / particles d
Colloidal silica fine particles (average particle size 0.07μm)

[II]
A coating layer formed by mixing a coating solution in which the following coating agent is mixed at a non-volatile component ratio of e / f / g / d = 42/28/24/6 so that the film thickness after drying is 0.04 μm. Yes, the compounds constituting each coating layer are as follows.
・ Polyurethane resin e
76.7 parts by weight of a polycarbonate polyol (number average molecular weight of about 1000 by GCP) obtained by the reaction of 6-hexanediol and diethyl carbonate, 6.4 parts by weight of polyethylene glycol (molecular weight 600), and trimethylolpropane 2.0 parts by weight, 19.9 parts by weight of N-methyl-N, N-diethanolamine, 84.0 parts by weight of 4,4′-diphenylmethane diisocyanate, and 87 parts by weight of MEK in a reaction vessel. Reaction was performed at ˜75 ° C. to obtain a urethane prepolymer. To this urethane prepolymer, 16.8 parts by weight of dimethyl sulfate was added and reacted at 50 to 60 ° C. to obtain a cationic urethane polymer. After 623 parts by weight of water was added and emulsified, MEK was recovered to obtain an aqueous dispersion of polyurethane resin 3.
・ Cationic polymer antistatic agent f
Quaternary ammonium salt-containing cationic polymer using diallyldimethylammonium chloride (pyrrolidinium ring-containing polymer of formula (I)) Average molecular weight of about 30,000
・ Crosslinking agent g
Copolymer-type crosslinking agent aqueous solution of 2-isopropenyl-2-oxazoline and acrylic monomer, oxazoline group amount = 4.5 mmol / g
・ Fine particle d
Colloidal silica fine particles (average particle size 0.07μm)

Example 2:
A monolayer polyester film was obtained in the same manner as in Example 1 except that the above-mentioned polyester (A) / polyester (B) / polyester (C) were mixed at a ratio of 95/2/3 (parts by weight).

Example 3:
A monolayer polyester film was obtained in the same manner as in Example 1 except that the above-mentioned polyester (A) / polyester (B) / polyester (C) were mixed in a ratio of 91/3/6 (parts by weight).

Example 4:
In the same manner as in Example 1 described above, polyester (A) / polyester (B) / polyester (C) were mixed in a ratio of 94.4 / 3 / 32.6 (parts by weight), respectively, and a single layer polyester having a thickness of 150 μm. A film was obtained.

Comparative Example 1:
After stretching in the longitudinal direction, a single-layer polyester film was obtained in the same manner as in Example 1 except that the coating agent was not applied.

Comparative Example 2:
After stretching in the longitudinal direction, a single-layer polyester film was obtained in the same manner as in Example 1 except that the coating agent [I] was coated on one side. In addition, the film of Comparative Example 2 had adhesion of foreign matters due to static electricity, and had a defect of missing printing.

Comparative Example 3:
After stretching in the longitudinal direction, a single layer polyester film was obtained in the same manner as in Example 1 except that the coating agent [II] was coated on one side. In addition, when the film of Comparative Example 3 was used as an ink jet recording material, sufficient adhesion of the printing coating material was not obtained.

Comparative Example 4: (based on the formulation of Patent Document 4 Example 27)
The above-mentioned polyester (A) / polyester (B) / polyester (C) were mixed at a ratio of 77/3/20 (parts by weight) and stretched in the longitudinal direction, and then the coating agent [II] was applied to one side. Otherwise, a single-layer polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1. In addition, when the film of Comparative Example 1 was used as an ink jet recording material, sufficient adhesion of the printing coating material was not obtained.

Comparative Example 5:
After stretching in the longitudinal direction, a single layer polyester film was obtained in the same manner as in Example 1 except that the coating agent [II] was applied on both sides. In addition, the film of the comparative example 5 produced blocking on the overlapping surface when wound up, and it was difficult to convey the product.

Comparative Example 6:
After stretching in the longitudinal direction, a single-layer polyester film was obtained in the same manner as in Example 1 except that the coating agent [I] was applied on both sides. In the film of Comparative Example 6, blocking occurred on the overlapping surface when wound up. The production of polyester film due to blocking was greatly inhibited.

Comparative Example 7:
A single-layer polyester film was obtained in the same manner as in Example 1 except that the polyester (A) / polyester (B) / polyester (C) were mixed at a ratio of 14/55/31 (parts by weight). In addition, the film of Comparative Example 7 could not satisfy the resolution as a base material of the recording material.

Comparative Example 8:
A single-layer polyester film was obtained in the same manner as in Example 1 except that the polyester (A) / polyester (B) / polyester (C) were mixed at a ratio of 87/13/0 (parts by weight). Note that the film of Comparative Example 8 had a strong brightness as a base material of the recording material and could not satisfy a sufficient color tone.

Comparative Example 9:
A single-layer polyester film was obtained in the same manner as in Example 1 except that the above-mentioned polyester (A) / polyester (B) / polyester (C) were mixed at a ratio of 86/6/8 (parts by weight). Incidentally, the film of Comparative Example 4 was not able to sufficiently satisfy the resolution as the base material of the recording material.

Comparative Example 10:
A monolayer polyester film was obtained in the same manner as in Example 1 except that the above-mentioned polyester (A) / polyester (B) / polyester (C) were mixed in a ratio of 93/6/1 (parts by weight). Note that the film of Comparative Example 5 was strong in brightness as a base material of the recording material and could not satisfy a sufficient color tone.

  The physical properties and the suitability of the ink jet recording material member of the obtained film are summarized in Table 2 below. It can be seen that a film satisfying the requirements of the present invention has high suitability when used as a base material for internally illuminated signboards for advertisements.

  The film of the present invention is used for recording materials when used as a base material for internally illuminated signboards for advertisements, paper substitutes, image paper for video printers, ink jet, image paper for barcode printers, posters, displays It can be used as a base material for a receiving sheet used for various printing records such as a plate, a white plate, and offset printing.

Claims (1)

The white polyester film has a coating layer containing polyester on one side, the two-dimensional arithmetic mean roughness (Ra) of the coating layer surface is in the range of 21 to 50 nm, and the other side contains an antistatic agent. A white polyester film having a coating layer, wherein the total light transmittance of the film is in the range of 30 to 50%, and the b value in the Lab color system is in the range of -4 to 5.