JP2013226724A - Polyester film for protective base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a protective base material, which has hydrolysis resistance, weather resistance, UV barrier properties and design properties, has few visible interference fringes that are visible at a short distance, and is excellent in visibility.SOLUTION: A polyester film for a protective base material has a layer composed of a polyester having ≤170 ppm phosphorus element content as one of the outermost layers, has ≤26 equivalent/ton terminal carboxyl group amount, and satisfies the following inequalities (1) to (4) at the same time. The inequality (1) is T380≤5.0%, the inequality (2) is T400≥80%, the inequality (3) is ΔD≤60 and the inequality (4) is H≤1.0 [wherein T380 denotes a transmittance of light having 380 nm wavelength; T400 denotes a transmittance of light having 400 nm wavelength; ΔD is a value obtained by using thicknesses d, dmeasured by a continuous thickness gauge at two optional points separated by 10 mm and calculating by using formula (5): ΔD=(d-d)×1,000].

Description

  TECHNICAL FIELD The present invention relates to a polyester film for a protective substrate, and more specifically, hydrolysis resistance when used as a protection for display members such as electronic paper, protection for decoration on a housing such as a slate personal computer, and protection of building materials. In particular, the present invention relates to a polyester film for a protective substrate that has excellent visibility, weather resistance, and ultraviolet shielding properties, and suppresses interference fringes and has excellent visibility without impairing the display color of the material to be protected.

  Maintains hydrolysis resistance, weather resistance, UV shielding, design, and visibility on display materials such as electronic paper, decorative surfaces of slate PC and smartphone housings, and building materials such as system kitchens. For this purpose, many protective films are used.

  Patent Document 1 discloses a technique related to a polyester film for electronic paper having high durability against ultraviolet rays, but the use and usage environment of electronic paper are widened, and durability regarding hydrolysis resistance is highly required. It has become like this.

  Polyester films are excellent in mechanical properties, thermal properties, and chemical resistance, and are used in various applications. In particular, films mainly composed of polyethylene terephthalate are used in various applications such as industrial applications, packaging applications, and printing applications.

  However, it is known that when a polyester film is used in a high-temperature and high-humidity environment, the ester bond site in the molecular chain is hydrolyzed, causing delamination. Therefore, various studies have been made to suppress hydrolysis, assuming that the polyester film is used outdoors, for example, or used in a high humidity environment.

  It is known that the hydrolysis of polyester is faster as the amount of terminal carboxyl groups in the polyester molecular chain is higher.

  Therefore, Patent Document 2 discloses a technique for improving hydrolysis resistance by esterifying a carboxylic acid at the end of a molecular chain by using an epoxy compound and reducing the amount of terminal carboxyl groups. However, an epoxy compound is highly undesirable in terms of environment and cost because it has a high possibility of inducing gelation and generating foreign substances in the melt extrusion process or the material recycling process in the film forming process.

  Patent Document 3 discloses a technique for reducing the amount of terminal carboxyl groups by adding a carbodiimide such as polycarbodiimide. However, carbodiimide tends to undergo thermal transformation itself, and the physical properties of the polyester film are lowered depending on reaction conditions. In some cases, the odor may be caused by a carbodiimide volatile component at the outlet of the tenter during film formation.

  In addition, it is known that hydrolysis of polyester is promoted in an acidic or alkaline environment (Non-patent Document 1). Therefore, phosphorous compounds such as phosphoric acid and phosphorous acid, which are added for the purpose of preventing undesirable coloring in the polymerization reaction, are considered to have an adverse effect on hydrolyzability because they make the system acidic. .

  In order to solve this problem, Patent Document 4 discloses a technique for improving hydrolysis resistance by suppressing the terminal carboxylic acid to a specified amount and containing a specific amount of a specific phosphate ester. Yes. However, since the phosphate ester in the said technique has the characteristic structure, the process and cost which adjust phosphate ester are needed. Therefore, it is not suitable for providing a polyester film that is inexpensive and can be used outdoors.

In order to suppress the interference fringes related to visibility, the spectrum intensity sum ΔPw of 0.01 to 0.3 m when the waveform of the uneven thickness of the polyester film is Fourier-analyzed Δ 0.01 to 1 m of intensity Δ There is also a method for specifying a ratio to Pw ₀ (see, for example, Patent Document 5). Moreover, there exists what has an easily bonding layer on both surfaces of the polyester film, and specified the spectral reflectance in the wavelength of 550 nm (for example, refer patent document 6).

  In recent years, display devices such as electronic paper, mobile devices such as slate PCs and smartphones have been used more frequently outdoors, and there has been an increase in the number of buildings such as system kitchens in houses where external light has been taken in. In addition, hydrolysis resistance, weather resistance, and ultraviolet shielding properties have been highly demanded.

  In addition, the surface electronic paper has become more detailed, and the number of screens and housings such as slate PCs and smartphones that can be viewed at a short distance has increased, and building materials such as system kitchens are preferred to have a rich glossy color. Therefore, not only long-period interference fringes but also narrow interference fringes that are visually recognized at a short distance are required to be highly advanced.

JP-A-2007-183423 JP-A-9-227767 JP-A-8-73719 JP-A-8-3428 JP 2004-160774 A JP 2011-93290 A

Kazuo Yuki Saturated Polyester Resin Handbook published by Kosaido 1989

  The present invention has been made in view of the above-mentioned circumstances, and the problem to be solved is hydrolysis resistance, weather resistance, ultraviolet shielding properties, design properties, and excellent visibility with few interference fringes even at a short distance. The object is to provide a protective base film.

  As a result of intensive studies in view of the above problems, the present inventor has adjusted both light resistance and weather resistance, UV shielding ability and visibility, and further controls minute unevenness of the thickness profile of the base film. As a result, the inventors have found that the above-described problems can be easily solved, and have completed the present invention.

  That is, the gist of the present invention is a polyester film having a layer made of polyester having a phosphorus element content of 170 ppm or less as one of the outermost layers, and the terminal carboxyl group content of the film is 26 equivalents / ton or less, It exists in the polyester film for protective base materials characterized by satisfy | filling following (1)-(4) Formula simultaneously.

T380 ≦ 5.0% (1)
T400 ≧ 80% (2)
ΔD ≦ 60 (3)
H ₀ ≦ 1.0 (4)
(In the above formula, T380 represents the light transmittance at a wavelength of 380 nm, T400 represents the light transmittance at a wavelength of 400 nm, and ΔD represents a thickness d _n0 and a thickness d at two points 10 mm apart measured by a continuous thickness meter. (It is a value calculated from _n10 by the following formula (5))
ΔD = (d _n0 −d _n10 ) ² × 1000 (5)

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film for protective base materials which is excellent in hydrolysis resistance, a weather resistance, and the ultraviolet-ray shielding property, and was excellent in visibility and the designability can be provided, The industrial value is very high.

  In the present invention, the polyester used for the polyester film may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. On the other hand, in the case of a copolymerized polyester, a copolymer containing 30 mol% or less of the third component is preferable. Examples of the dicarboxylic acid component of the copolyester include one or two of isophthalic acid, terephthalic acid phthalate, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, P-oxybenzoic acid). The glycol component includes one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

  In any case, the polyester referred to in the present invention is usually 80 mol% or more, preferably 90 mol% or more of polyethylene terephthalate in which ethylene terephthalate units are formed, or polyethylene-2,6- in which ethylene-2,6-naphthalate units are formed. Refers to polyester such as naphthalate.

  The equivalent ratio (P / M) of the equivalent (P) of the phosphorus element to the equivalent (M) of all elements of Group 2 of the periodic table contained in the polyester in the present invention is preferably 0.4 to 1.0. More preferably, it is preferably 0.5 to 0.9. When the polyester is 0.4 or less, the casting of melt extrusion becomes unstable, and the interval between the peaks and valleys of the film thickness profile is narrow, and interference unevenness is likely to occur. If it exceeds 1.0, the polyester resin tends to be thermally deteriorated, and the resulting film may be yellowed to cause defects. Therefore, the amount of change ΔD in film thickness tends to be able to obtain a desired low value by controlling P / M within the aforementioned range.

  The phosphorus element contained in the polyester in the present invention is 170 ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less. If it exceeds 170 ppm, it is necessary to increase the total amount of elements belonging to Group 2 of the periodic table contained in the polyester in order to achieve both casting stability and weather resistance deteriorates.

  Also, the internal haze tends to yield a film having a low internal haze by controlling the amount of phosphorus element in the polyester and the total amount of elements belonging to Group 2 of the periodic rule within the above-mentioned range so that the change in film thickness is small. .

  The terminal carboxyl group amount of the polyester in the present invention is 26 equivalent / ton or less, preferably 20 equivalent / ton or less. When it exceeds 26 equivalents / ton, the weather resistance is impaired. In the polyester layer in the present invention, it is preferable to blend particles for the main purpose of imparting slipperiness. 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 magnesium phosphate. , Particles of kaolin, aluminum oxide, titanium oxide and the like. 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 if necessary.

  Moreover, it is preferable that the average particle diameter of the particle | grains contained in a polyester film in this invention satisfies 0.1-5 micrometers, More preferably, it is 0.5-3 micrometers, Most preferably, it is the range of 0.5-2 micrometers. . If the average particle size is less than 0.1 μm, the particles tend to aggregate and the dispersibility tends to be insufficient. On the other hand, if it exceeds 5 μm, the surface roughness of the film becomes too rough, Problems may occur when a release layer is provided in a subsequent process.

  Furthermore, the particle content in the polyester preferably satisfies 0.01 to 5% by weight, more preferably 0.01 to 3% by weight. When the particle content is less than 0.01% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the smoothness of the film surface is insufficient. It may become.

  In addition, conventionally known antioxidants, heat stabilizers, lubricants, dyes, pigments and the like can be added to the polyester film in the present invention within the range not impairing the gist of the present invention in addition to the above-mentioned particles.

  The light transmittance at a wavelength of 380 nm of the polyester film for protective substrate in the present invention is 5.0% or less, preferably 3.0% or less, more preferably 1.0 or less. When it exceeds 5.0%, the display color of the material to be protected is likely to be discolored, and the design is impaired. The light transmittance at a wavelength of 380 nm can be lowered by adding an ultraviolet absorber.

  The light transmittance at a wavelength of 400 nm of the polyester film for protective substrate in the present invention is 80% or more, preferably 87% or more. If it is less than 80%, the vividness of the display color of the protected material is impaired. The light transmittance at a wavelength of 400 nm can be lowered by lowering the addition amount of the phosphorus element in the polyester, all elements of Group 2 of the periodic table, and particles.

  The internal haze of the polyester film for protective substrate in the present invention is 1.0% or less, preferably 0.8% or less, and more preferably 0.5%. If it exceeds 1.0%, the display precision of the protected material is impaired.

  The change amount ΔD of the film thickness of the protective base polyester film in the present invention is 60 or less, preferably 30 or less, and more preferably 20. When it exceeds 60%, interference fringes with a narrow interval are likely to occur, and the visibility of display contents is impaired.

  The thickness of the polyester film constituting the protective film of the present invention is preferably a thin film in order to increase transparency, but on the other hand, the film needs to be high in order to improve film processing suitability. When the thickness of the polyester film constituting the protective film is too thin, wrinkles or the like may easily occur during bonding. From this viewpoint, the thickness of the polyester film constituting the release film in the present invention is preferably 12 to 188 μm, more preferably 25 to 130 μm.

The volume resistivity value at 285 ° C. of the polyester film constituting the protective film of the present invention is preferably 50 × 10 ⁷ Ω · cm or less, more preferably 20 × 10 ⁷ Ω · cm or less, most preferably 10 × 10 ⁷ Ω · cm or less. When the volume resistivity exceeds 50 × 10 ⁷ Ω · cm, the thickness unevenness of the film is deteriorated, and interference fringes with a narrow interval are easily generated. In addition, casting after melt extrusion may become unstable and productivity may deteriorate.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.

  That is, a method of using the polyester raw material described above and cooling and solidifying the molten sheet extruded from the die with a cooling roll to obtain an unstretched sheet is preferable. The edge of the lip used for the base is preferably a straight corner like the cutting edge of a cutter. If there is a chipped portion or a corner portion, streaky thickness unevenness occurs in the longitudinal direction of the film, and interference fringes may be a problem due to the uneven thickness. Further, when the film is rolled up, the winding hardness of the roll becomes uneven and the flatness of the film may be deteriorated. In order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction.

  In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the extending | stretching temperature orthogonal to the extending | stretching direction of the 1st step is 130-170 degreeC normally, and a draw ratio is 3.0-7 times normally, Preferably it is 3.5-6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges. It is also possible to perform simultaneous biaxial stretching. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is as follows. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film.

As for the simultaneous biaxial stretching apparatus using the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, a linear drive method, or the like can be adopted. The “screw method” is a method in which a clip is placed in the groove of the screw to increase the clip interval.
The “pantograph method” is a method of expanding the clip interval using a pantograph. The “linear motor system” has an advantage that the clip interval can be arbitrarily adjusted by applying the linear motor principle and controlling the clips individually.

  Further, simultaneous biaxial stretching may be performed in two or more stages. In that case, stretching may be performed in one tenter or a plurality of tenters may be used in combination.

  In the present invention, by stretching the polyester film constituting the protective film by simultaneous biaxial stretching, conventionally, in the case where the area magnification becomes larger in sequential biaxial stretching, there may be a problem such as breaking during stretching. However, since the stretching followability is good in simultaneous biaxial stretching, the area magnification can be further increased in the film longitudinal direction and width direction compared to sequential biaxial stretching. A small polyester film with suppressed interference fringes can be produced, which is preferable.

  In addition, a so-called coating stretching method (in-line coating) for treating the film surface during the above-described stretching process of the polyester film can be performed.

  Although it is not limited to the following, for example, in the sequential biaxial stretching, in particular, the first-stage stretching is completed, and the coating treatment can be performed before the second-stage stretching.

  The coating layer constituting the protective film of the present invention preferably contains a metal organic compound (A). The metal organic compound (A) contains a metal element and has no metal-carbon bond in the structure. Compounds are preferred. For example, an organic compound having a titanium element, an organic compound having a zirconium element, an organic compound having an aluminum element, and the like can be given.

  Only one kind of these metal organic compounds (A) may be used, or two or more kinds may be appropriately mixed and used.

  Specific examples of the organic compound having a titanium element include titanium orthoesters such as tetranormal butyl titanate, tetraisopropyl titanate, butyl titanate dimer, tetra (2-ethylhexyl) titanate, tetramethyl titanate; titanium acetylacetonate, Examples thereof include titanium chelates such as titanium tetraacetylacetonate, polytitanium acetylacetonate, titanium octylene glycolate, titanium lactate, titanium triethanolamate, and titanium ethylacetoacetate.

  Specific examples of the organic compound having a zirconium element include zirconium acetate, zirconium normal propyrate, zirconium normal butyrate, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium bisacetylacetonate and the like.

Specific examples of the organic compound having an aluminum element include, for example, aluminum alcoholates such as (CH ₃ O) ₃ Al and (C ₂ H ₅ O) ₃ Al, aluminum salts such as stearic acid, octylic acid and benzoic acid, aluminum Tris (acetylacetonate), aluminum monoacetylacetonate bis (ethylacetoacetate), aluminum-di-n-butoxide-monoethylacetoacetate, aluminum-di-iso-propoxide-monomethylacetoacetate, aluminum organic acid Aluminum chelates such as chelates are exemplified.

  Among the metal organic compounds (A), an organic compound having a titanium element having a chelate structure, an organic compound having a zirconium element, and an organic compound having an aluminum element are more preferable, and more preferably, in that the oligomer precipitation preventing performance is particularly good. In consideration of application to the coating stretching method (in-line coating), a water-soluble titanium chelate compound, a water-soluble zirconium chelate compound, and a water-soluble aluminum chelate compound are preferably used. It is also described in detail in the “Crosslinking agent handbook” (Yamashita Shinzo, Kaneko East Assistant Editor, Taiseisha, 1990 edition).

  Moreover, the silane coupling agent which has a metal element substantially is not contained regarding the metal organic compound (A) in this invention.

  Furthermore, it is preferable to use a binder polymer (B) in combination in the coating layer in the present invention.

  The “binder polymer (B)” used in the present invention is a number average measured by gel permeation chromatography (GPC) according to a polymer compound safety evaluation flow scheme (sponsored by the Chemical Substances Council in November 1985). It is defined as a polymer compound having a molecular weight (Mn) of 1000 or more and having a film-forming property.

  Specific examples of the binder polymer (B) include polyvinyl alcohol, polyacrylamide, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches, polyurethane, polyacrylate, and chlorinated polymers (both polyvinyl chloride and vinyl chloride vinyl acetate). Polymer, etc.).

  Among the above-mentioned binder polymers (B), it is preferable to contain polyvinyl alcohol in the coating layer because the oligomer precipitation preventing performance is further improved.

The content of polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) contained in the coating layer is not particularly limited, but is preferably in the range of 10% by weight or more. If the PVA content is less than 10% by weight, the oligomer precipitation preventing effect may be insufficient.

  Further, the degree of polymerization of PVA is not particularly limited, but usually 100 or more, preferably 300 to 40,000 is suitably used for applications.

  On the other hand, the saponification degree of PVA is not particularly limited, but 70 mol% or more, preferably 80 mol% or more and 99.9 mol% or less is suitably used. As a specific example, saponified vinyl acetate is used. Etc.

The coating amount (after drying) of the coating layer is usually 0.01 to 1 g / m ² , preferably 0.04 to 0.5 g / m ² , more preferably 0.06 to 0.3 g / m ² . It is.

  In the present invention, conventionally known coating methods such as multi-roll coating, reverse gravure coating, direct gravure coating, bar coating, and die coating can be used as a method for providing the coating layer on the polyester film. Regarding the coating method, there is a description example in Yuji Harasaki's “Coating Method”, published in 1979.

  Moreover, you may give surface treatments, such as a corona treatment and a plasma treatment, to the polyester film which comprises the protective film in this invention previously.

  In addition, the coating layer which comprises the protective film in this invention may be provided on a polyester film by the above-mentioned coating extending | stretching method (in-line coating).

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 measurement method used in the present invention is as follows.
(1) Content of metal atom A polyester film sample of 2.5 g is ashed and completely aged by heating it for about 1 hour at about 150 ° C. in the presence of sulfuric acid and then gradually adding hydrogen peroxide water and holding it for about 30 minutes. After the decomposition, the sample was made up to a volume of 50 ml with distilled water and quantified using a plasma emission spectrometer (ICP-AES “JY46P type” manufactured by JOBIN YVON). In the case where a lubricant was contained in the film, the film was dissolved in a solvent in advance, the undissolved lubricant was centrifuged, and then the solvent in the supernatant was evaporated and dried.
(2) Intrinsic Viscosity 1 g of polyester from which other polymer components and pigments incompatible with polyester were removed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved. Measured at ° C.
(3) Measurement of average particle diameter (d50: μm) 50% integrated (weight basis) in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) The value was defined as the average particle size.
(4) Volume resistivity value of 285 ° C. 20 g of a film sample is put into a test tube with a branch having an inner diameter of 20 mm and a length of 180 mm, and the inside of the tube is sufficiently purged with nitrogen, and then immersed in an oil bath at 160 ° C. After vacuum drying with a vacuum pump at 1 Torr or lower for 4 hours, the oil bath temperature was raised to 285 ° C. to melt the resin sample, air bubbles mixed together were removed by repeating nitrogen re-pressure and pressure reduction. Two stainless steel electrodes with an area of 1 cm 2 were inserted into the melt in parallel at an interval of 5 mm (non-opposite back surface covered with an insulator), and after the temperature was stabilized, an ohmmeter (manufactured by Hewlett-Packard Company “ A direct voltage of 100 V was applied between the electrodes by MODEL HP4339B "), and a volume specific resistance value (Ω · cm) was determined from the resistance value at that time.
(5) Amount of terminal carboxyl group (equivalent / ton)
The amount of terminal carboxyl groups was measured by a so-called titration method. That is, polyester was dissolved in benzyl alcohol, phenol red indicator was added, and titrated with a water / methanol / benzyl alcohol solution of sodium hydroxide. If there is a coating layer on the film, in order to eliminate this effect, wash the coating layer with water using an abrasive cleanser, rinse thoroughly with ion-exchanged water, and dry, then measure in the same way. went.
(6) Film thickness change ΔD
The film thickness is measured in units of 0.5 mm using a film thickness tester KG601A / wide-range electronic micrometer K306C manufactured by Anritsu Electric Co., Ltd., at a measurement point 10.0 mm away from the thickness d ₀ of any measurement point. It _{calculated |} required by the following formula from thickness _dn10 .

ΔD = (d ₀ −d _n10 ) ² × 10 ³
Thickness meter measurement conditions Feeding speed: 1.5m / min Measuring pressure: 30 ± 5g
Probe: tip R3 ruby probe (7) Internal haze H ₀
A film test piece obtained by immersing a sample film in a quartz cell filled with ethanol was used as a sample for measuring internal haze. Moreover, what filled the ethanol into the quartz cell before putting a film test piece was made into the blank sample. In accordance with JIS-K-7136, a value measured with a haze meter “HZ-2” manufactured by Suga Test Co., Ltd. is defined as internal haze.
(8) Light transmittance The light transmittance at a wavelength of 380 nm and a wavelength of 400 nm was measured with a spectrophotometer (UV3100PC, manufactured by Shimadzu Corporation) using a halogen lamp light source.
(9) Hydrolysis resistance The film is allowed to stand for 35 hours in an atmosphere at a temperature of 120 ° C. and a relative humidity of 100%. It is pasted to a length of 7 cm, and a constant load is given thereon by a 3 kg manual load roll. The film is fixed, one end of the cellophane tape is connected to a 500 g weight, and a distance of 45 cm is evaluated by a method in which a peel test in a 180 ° direction is started after a natural fall. Hydrolysis resistance was evaluated according to the following five-step criteria.

A: Polyester does not peel at all on the cellophane tape surface O: Polyester does not peel off on the cellophane tape surface less than 10% Δ: 10 to 50% of the polyester peels to the cellophane tape side ×: 50% or more of the portion Polyester peels to the cellophane tape side Practically, it can be used without any problem if the evaluation is ◯ or higher.
(10) Evaluation of weather resistance A weather resistance test was conducted under the following conditions based on JIS-B-7753 (2007) standard.
Equipment: Sunshine weather meter (Model: WEL-SUN-HCH-B Manufacturer: Suga Test Instruments Co., Ltd.)
Discharge voltage / current: 50V, 60A
Filter: Glass filter type A Black panel temperature: 63 ° C
Processing time: 1000 hours Spray cycle (120 minutes): 102 minutes of irradiation, followed by 18 minutes of irradiation and measurement of the intrinsic viscosity of the outermost layer of the film before and after the spray weather resistance test, and evaluation of weather resistance by the intrinsic viscosity maintenance rate Went.

Intrinsic viscosity maintenance rate = Intrinsic viscosity after weather resistance test / Intrinsic viscosity before weather resistance test × 100 (%)
○: Intrinsic viscosity maintenance ratio is 70% or more ×: Intrinsic viscosity maintenance ratio is less than 70% (11) Interference fringes A film sample is placed on a matte black film, and a Panasonic three-wavelength fluorescent lamp FPL27EX-N is used. Then, the interference fringes were observed from the vertical direction and judged according to the following criteria.

◎: Interference fringe spacing exceeds 10 mm or not visible ○: Interference fringe spacing is 6-10 mm, can be used as a display screen without any problem Δ: Interference fringe spacing is 3-5 mm, usable as a display screen × : Interference fringe spacing is less than 3 mm and cannot be used as a display screen <Method of producing polyester raw material (1)>
A slurry is prepared using a continuous polymerization apparatus comprising a slurry preparation tank, a two-stage esterification reaction tank connected in series to the slurry preparation tank, and a three-stage melt polycondensation tank connected in series to the second-stage esterification reaction tank. While continuously supplying 865 parts by weight and 485 parts by weight of terephthalic acid and ethylene glycol, respectively, to the preparation tank, a 0.3 wt% ethylene glycol solution of ethyl acid phosphate was added to the resulting polyester resin per ton of phosphorus. A slurry was prepared by continuously adding the content as an atom so as to be 0.130 mol / ton of resin, stirring and mixing. This slurry was subjected to a first-stage esterification reaction tank set at 260 ° C. in a nitrogen atmosphere, a relative pressure of 50 kPa (0.5 kg / cm 2) and an average residence time of 4 hours, and then at 260 ° C. in a nitrogen atmosphere. The mixture was continuously transferred to a second stage esterification reaction tank set at a relative pressure of 5 kPa (0.05 kg / cm 2) and an average residence time of 1.5 hours to cause an esterification reaction. At that time, a 0.6 wt% ethylene glycol solution of magnesium acetate tetrahydrate was added as magnesium atoms per ton of the obtained polyester resin through an upper pipe provided in the second stage esterification reaction tank. Continuously added at an amount of 0.350 mol / ton of resin, and continuously added 60 parts by weight of ethylene glycol per hour through another upper pipe provided in the second stage esterification reaction tank did. Subsequently, when the esterification reaction product obtained above is continuously transferred to the melt polycondensation tank, tetra-n-butyl titanate is added to the esterification reaction product in the transfer pipe with a concentration of titanium atoms. As an ethylene glycol solution having a water concentration of 0.15 wt% and a water concentration of 0.5 wt%, the content as titanium atoms per ton of the resulting polyester resin is continuously 0.085 mol / ton of resin. While adding, the first stage melt polycondensation tank set at 270 ° C. and absolute pressure 2.6 kPa, then the second stage melt polycondensation tank set at 278 ° C. and absolute pressure 0.5 kPa, Next, the polyester resin is continuously transferred to a third-stage melt polycondensation tank set at 280 ° C. and an absolute pressure of 0.3 kPa so that the intrinsic viscosity of the resulting polyester resin is 0.63 (dl / g). Each heavy Polyester which is melt polycondensed by adjusting the residence time in the combined tank, is continuously extracted in the form of a strand from the outlet provided at the bottom of the polycondensation tank, cooled with water, and then cut with a cutter to form a chip-like granule Raw material (1) was produced. The amount of terminal carboxyl groups was 13 (equivalent / ton).
<Method for producing polyester raw material (2)>
The polyester raw material (1) is used as a starting raw material, and continuously fed into a stirring crystallizer maintained at about 160 ° C. in a nitrogen atmosphere so that the residence time is about 60 minutes. Is continuously supplied to the solid phase polycondensation apparatus, and at 215 ° C. in a nitrogen atmosphere, the residence time is adjusted so that the intrinsic viscosity of the obtained polyester resin is 0.79 (dl / g), and the solid phase polycondensation is performed. To obtain a polyester raw material (2). The amount of terminal carboxyl groups was 9 (equivalent / ton), and the volume resistivity (ρv) was 16 × 10 ⁷ Ω · cm.
<Method for producing polyester raw material (3)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, tetra-n-butyl titanate can be obtained as a catalyst. Content as titanium atoms per ton of polyester resin is 0.104 mol / ton of resin. The reaction start temperature was 150 ° C., and the reaction temperature was gradually increased as methanol was distilled off. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank, and an ethylene glycol slurry of silica particles having an average particle diameter of 2.5 μm was added so that the content of the particles with respect to the polyester would be 0.3% by weight. went. 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 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester raw material (3). The intrinsic viscosity was 0.63 dl / g, and the amount of terminal carboxyl groups was 21 equivalents / ton.
<Method for producing polyester raw material (4)>
In the production method of the polyester resin (1), the addition amount of 0.3% by weight ethylene glycol solution of ethyl acid phosphate is 0.453 mol / ton of resin as a phosphorus atom per ton of the obtained polyester resin. As a result, a polyester resin (4) was obtained. The intrinsic viscosity was 0.63 dl / g, the amount of terminal carboxyl groups was 17 equivalents / ton, and the volume resistivity (ρv) was 12 × 10 ⁷ Ω · cm.
<Method for producing polyester raw material (5)>
A slurry is prepared using a continuous polymerization apparatus comprising a slurry preparation tank, a two-stage esterification reaction tank connected in series to the slurry preparation tank, and a three-stage melt polycondensation tank connected in series to the second-stage esterification reaction tank. To the preparation tank, terephthalic acid and ethylene glycol were continuously fed at a weight ratio of 865: 485, and a 0.3 wt% ethylene glycol solution of ethyl acid phosphate was added to the phosphorus atom per ton of the resulting polyester resin. Is added continuously in such an amount that the content P becomes 3.229 mol / ton of resin, and a slurry is prepared by stirring and mixing. The slurry is 260 ° C. under a nitrogen atmosphere, a relative pressure of 50 kPaG, First stage esterification reactor set at an average residence time of 4 hours, then at 260 ° C. under a nitrogen atmosphere, a relative pressure of 5 kPaG, And continuously transferred to the esterification reaction tank of the second stage which is set in the dwell time of 1.5 hours to an esterification reaction. At that time, the esterification reaction rate was 85% in the first stage and 95% in the second stage. Subsequently, when the oligomer obtained above is continuously transferred to the melt polycondensation tank, an ethylene glycol solution of antimony trioxide (concentration 1.9% by weight) is continuously added to the oligomer in the transfer pipe. did. The first stage melt weight set to 270 ° C. and 2.6 kPa while continuously adding the content S as antimony atoms per ton of the obtained polyester resin in an amount of 2.464 mol / ton. Continuously into the condensation tank, then the second stage melt polycondensation tank set at 278 ° C. and pressure 0.5 kPa, then the third stage melt polycondensation tank set at 280 ° C. and 0.3 kPa The extraction port provided at the bottom of the polycondensation tank is adjusted so that the residence time in each polycondensation tank is adjusted so that the intrinsic viscosity IV of the resulting polyester resin is 0.65 dL / g. The polyester resin (5) was obtained as a pellet by continuously taking out a strand from the substrate, cooling with water, and cutting with a cutter. The amount of terminal carboxyl groups was 50 equivalent / ton, and the volume resistivity (ρv) was 200 × 10 ⁷ Ω · cm.
<Production method of UV absorber masterbatch 1 (MB1)>
The polyester resin (2) was subjected to a twin screw extruder with a vent, and 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] (CYTEC Co., Ltd.) as an ultraviolet absorber. CYASORBUV-3638 (Molecular weight 369 benzoxazine system) manufactured was made into chips by chipping to obtain an ultraviolet absorber master batch (MB1).
Example 1:
The mixed raw materials obtained by mixing the above polyester resins (2) and (3) in proportions of 92% and 8%, respectively, are used as the raw material for the a layer, and the raw materials for the b layer are polyester (1) and MB1 of 90% and 10%, respectively. As a mixed raw material mixed at a ratio of 2, each is supplied to two vent type twin screw extruders and melted at 285 ° C., respectively, and the a layer is the outermost layer (surface layer) and the b layer is the intermediate layer. It was coextruded with a layer structure of layers (a / b / a), extruded from a die, and cooled and solidified on a cooling roll set at a surface temperature of 18 ° 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 83 ° C. by utilizing the difference in peripheral speed of the roll, and after applying a coating agent having the composition shown below, it was led to a tenter and 4 ° C. at 130 ° C. in the transverse direction. .2 times stretching, heat treatment was performed at a zone temperature of 212 ° C. and a main crystallization zone temperature of 230 ° C. in the previous step of the main crystallization zone, and then relaxed by 5% in the transverse direction. A slitting process was performed on a film roll having a product width of 1500 mm and a winding length of 2000 m to obtain a laminated biaxially stretched polyester film roll having a thickness of 125 μm. The thickness of each layer of the obtained film was 3/119/3 μm. The thickness of the coating layer was 0.09 μm on one side.

(Coating agent composition: weight ratio)
a / b / c / d = 47/20/30/3
Here, a is a polyester dispersion of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / diethylene glycol / triethylene glycol = 31/16/3/22/21 (molar ratio); b is Methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio) emulsion polymer (emulsifier: anionic surfactant); c is hexamethoxymethylmelamine (melamine type) D) is an aqueous dispersion (inorganic particles) of silicon oxide having a particle size of 0.06 μm.
Example 2:
A polyester film roll having a thickness of 125 μm was obtained in the same manner as in Example 1 except that the blending and thickness ratio of the polyester resin in Example 1 were changed.
Comparative Example 1:
A polyester film roll having a thickness of 125 μm was obtained in the same manner as in Example 1 except that the composition and thickness ratio of the polyester resin of Example 1 were changed and the lateral draw ratio was 3.6 times.
Comparative Example 2:
A polyester film roll having a thickness of 125 μm was obtained in the same manner as in Example 1 except that the composition and thickness ratio of the polyester resin of Example 1 were changed and the transverse draw ratio was increased to 3.9 times.

  Comparative Example 1 The durability was poor, the thickness profile had a large difference between the peaks and valleys, the interference fringe spacing was narrow, and the overall transparency was poor. In Comparative Example 2, there was a portion where the durability was poor and the thickness profile in the width direction was specifically thickened at one place, and a contrast difference was observed in a narrow space between the interference fringes and streaks.

  The polyester film for a protective substrate of the present invention is, for example, for protection of display members such as electronic paper, protection of decoration on a housing such as a slate personal computer, hydrolysis resistance when used as a protection of building materials, weather resistance It can be suitably used as a polyester film for a base material of a protective film excellent in visibility and ultraviolet shielding properties and suppressing interference fringes and having excellent visibility without impairing the display color of the material to be protected.

Claims (1)

A polyester film having a layer made of polyester having a phosphorus element content of 170 ppm or less as one of the outermost layers, the terminal carboxyl group content of the film is 26 equivalents / ton or less, and the following (1) to (4) A polyester film for a protective substrate characterized by satisfying the formula simultaneously.
T380 ≦ 5.0% (1)
T400 ≧ 80% (2)
ΔD ≦ 60 (3)
H ₀ ≦ 1.0 (4)
(In the above formula, T380 represents the light transmittance at a wavelength of 380 nm, T400 represents the light transmittance at a wavelength of 400 nm, and ΔD represents a thickness d _n0 and a thickness d at two points 10 mm apart measured by a continuous thickness meter. (It is a value calculated from _n10 by the following formula (5))
ΔD = (d _n0 −d _n10 ) ² × 1000 (5)