Polyester resin composition, and film and laminate film produced using the same

Abstract

To provide a polyester resin composition having superior electrostatic application characteristics, being suitable for biaxially oriented films, particularly laminate films; and also to provide films and laminate films produced using the polyester resin composition.SOLUTION: A polyester resin composition comprises a naphthalenedicarboxylic acid component and an ethylene glycol component as main components, the polyester resin composition comprising 3 wt.% or more and 15 wt.% or less of a polyalkylene glycol having a number-average molecular weight of less than 1000. The polyester resin composition has a melt resistivity of 10 MΩ cm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a polyester resin composition, and a film and a laminate film made using the same. [Background technology]

[0002] Polyethylene naphthalate has excellent mechanical properties and heat resistance and is used for a variety of purposes.

[0003] However, polyethylene naphthalate has poorer electrostatic application characteristics than polyethylene terephthalate, and uneven application of electrostatic charges during film production can lead to defects on the film surface, and increased film production speeds can result in reduced adhesion to the casting drum, resulting in uneven thickness.

[0004] For example, Patent Document 1 discloses a technology for improving electrostatic applicability by incorporating a specific sulfonic acid compound into polyester. However, the examples only describe polyethylene terephthalate, and do not disclose polyethylene naphthalate, which has poorer electrostatic applicability.

[0005] Furthermore, Patent Document 2 discloses a polyester containing an organic salt compound consisting of a combination of a quaternary ammonium cation and / or a quaternary phosphonium cation and an organic acid ion having a positive pKa, with the aim of reducing the melt resistivity required for electrostatic application film formation. However, the examples only describe polyethylene terephthalate, and do not disclose polyethylene naphthalate, which has poorer electrostatic application characteristics and higher melt resistivity.

[0006] Patent Document 3 discloses polyethylene naphthalate containing polyalkylene glycol, but there is no description of a technique for improving static electricity application characteristics.

[0007] Therefore, these techniques are insufficient for improving the static electricity application characteristics of polyester resins containing polyethylene naphthalate as a main component. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2022-89784 A [Patent Document 2] JP 2020-7542 A [Patent Document 3] JP 2020-117575 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a polyester resin composition having excellent heat resistance and suitable for biaxially oriented films, particularly laminate films, and a film and laminate film made using the same. [Means for solving the problem]

[0010] That is, the object of the present invention is achieved by a polyester resin composition comprising a naphthalenedicarboxylic acid component and an ethylene glycol component as main components, containing 3% by weight or more and 15% by weight or less of a polyalkylene glycol having a number average molecular weight of less than 1,000, and having a melt resistivity of 10 MΩ cm or less. Effect of the Invention

[0011] According to the present invention, it is possible to provide a polyester resin composition having excellent electrostatic application characteristics, and further to provide a film and a laminated film using the same. These films can be applied to optical applications such as liquid crystal displays, and in particular, by forming the multi-layer laminated film with a controlled refractive index distribution, they can be used for applications such as a total light reflection film and a heat reflection film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The polyester resin composition in the present invention must contain 3% by weight or more and 15% by weight or less of polyalkylene glycol having a number average molecular weight of less than 1,000 relative to the polyester resin composition mainly composed of a naphthalenedicarboxylic acid component and an ethylene glycol component.

[0013] In the polyester resin of the present invention, the naphthalenedicarboxylic acid component and the ethylene glycol component must be the main components. The term "main components" means that the naphthalenedicarboxylic acid component accounts for 90 mol% or more of the total dicarboxylic acid components, and that the ethylene glycol component accounts for 90 mol% or more of the total diol components.

[0014] The content of the naphthalenedicarboxylic acid component is preferably 95 mol% or more, more preferably 98 mol% or more, based on the total dicarboxylic acid components, from the viewpoint of increasing the refractive index. In addition, other dicarboxylic acid components can be used within a range of 5 mol% or less, and examples of such components include terephthalic acid components, isophthalic acid components, cyclohexanedicarboxylic acid components, decacarboxylic acid components, adipic acid components, and sebacic acid components. Among these, aromatic compounds such as terephthalic acid components, isophthalic acid components, cyclohexanedicarboxylic acid components, and decacarboxylic acid components, and alicyclic compounds are preferred from the viewpoints of increasing the refractive index and heat resistance.

[0015] The content of the ethylene glycol component in the polyester resin composition of the present invention is preferably 95 mol % or more of ethylene glycol based on the total diol components in terms of high refractive index, crystallinity, melt viscosity, and film formability. In addition, other diol components can be used within a range of 5 mol % or less, such as diethylene glycol, 1,3-propanediol, 1,4-butanediol, and neopentyl glycol.

[0016] The polyester resin composition of the present invention must contain 3% by weight or more and 15% by weight or less, more preferably 3% by weight or more and 10% by weight or less, of polyalkylene glycol having a number average molecular weight of less than 1000. If the content of polyalkylene glycol is less than 3% by weight, the polyester resin composition may become brittle and film formability may decrease, whereas if it exceeds 15% by weight, heat resistance and orientation during film stretching may decrease, making it difficult to obtain the desired optical properties.

[0017] Examples of such polyalkylene glycols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc., from the viewpoints of heat resistance and film-forming properties, with polyethylene glycol being preferred from the viewpoints of glass transition temperature design and heat resistance.

[0018] The number average molecular weight of the polyalkylene glycol must be less than 1,000, and is preferably 200 or more and 600 or less, from the standpoints of reactivity and optical properties.

[0019] The timing of addition of such polyalkylene glycol may be any stage from before the ester exchange reaction, which is a process for producing a polyester resin, to before the start of the polycondensation reaction. From the viewpoint of reactivity, however, it is preferable to add it before the ester exchange reaction.

[0020] The glass transition temperature of the polyester resin composition of the present invention (midpoint glass transition temperature: the temperature at the point where a line equidistant in the vertical direction from the extended straight line of each baseline intersects with the curve of the stepwise change part of the glass transition) is preferably 80° C. or more and 110° C. or less from the viewpoint of film formability. Specifically, the midpoint glass transition temperature is the temperature obtained when 10 mg of the polyester resin composition is melted at 300° C., held for 5 minutes, rapidly cooled to room temperature, and then heated at a heating rate of 16° C. / min.

[0021] In the polyester resin composition of the present invention, the content of alkaline earth metal elements is preferably 10 ppm or less based on the weight of the polyester resin composition in terms of heat resistance.

[0022] The alkaline earth metals of the present invention are beryllium, magnesium, calcium, strontium, barium, and radium, which are elements of Group 2 of the periodic table. Among them, acetates of magnesium and calcium that can be used as transesterification reaction catalysts are preferred, and magnesium compounds that are soluble in ethylene glycol and have the effect of lowering the melt resistivity are more preferred.

[0023] The alkaline earth metal compound can be added at any stage from the start of the transesterification reaction or esterification reaction to the discharge of the polyester, and when it is added immediately after the target viscosity during the polymerization reaction is reached, it is recommended to stir for about 30 minutes after the addition before discharging. The alkaline earth metal compound may be added as a powder, an ethylene glycol solution, or a mixed solution of water and ethylene glycol.

[0024] The polyester resin composition of the present invention preferably contains an ionic salt in an amount of 40 ppm or more and 10,000 ppm or less by weight based on the polyester resin composition from the viewpoint of electrostatic application characteristics, and further, the upper limit is preferably 1,000 ppm or less from the viewpoint of heat resistance.

[0025] From the viewpoint of electrostatic application characteristics, the ionic salt of the present invention preferably contains one or more of a sulfide compound, a thiophene compound, a thiol compound, a sulfonic acid compound, and a sulfonyl compound, and one or more of an alkali metal, a quaternary phosphonium, and a quaternary ammonium, and among these, a mixture of a sulfonic acid compound and a quaternary phosphonium which is a phosphorus compound is preferable.

[0026] Examples of the sulfonic acid compound include sulfonic acid compounds that do not have an ester-forming functional group, such as methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 1-butanesulfonic acid, 1-pentanesulfonic acid, trifluoromethanesulfonic acid, tetrafluoroethanesulfonic acid, nonafluorobutanesulfonic acid, benzenesulfonic acid, o-toluenesulfonic acid, m-toluenesulfonic acid, p-toluenesulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, styrenesulfonic acid, perfluorooctane sulfonic acid, and heptadecafluorooctane sulfonic acid, and sulfonic acid compounds that have two or more ester-forming functional groups, such as 3,5-dicarboxybenzenesulfonic acid. Of these, benzenesulfonic acid, o-toluenesulfonic acid, m-toluenesulfonic acid, and p-toluenesulfonic acid are preferred.

[0027] Examples of the quaternary phosphonium, which is a phosphorus compound to be mixed with the sulfonic acid compound, include tetraethylphosphonium cation, tetrabutylphosphonium cation, tetrahexylphosphonium cation, methyltributylphosphonium cation, ethyltributylphosphonium cation, octyltributylphosphonium cation, hexadecyltributylphosphonium cation, benzyltrimethylphosphonium cation, benzyltriethylphosphonium cation, and 3-(trifluoromethyl)phenyltrimethylphosphonium cation.

[0028] In the present invention, the content of the sulfur element is preferably 2 ppm or more and 50 pm or less in terms of weight with respect to the polyester resin composition from the viewpoint of electrostatic application characteristics.

[0029] The polyester resin composition of the present invention can be produced by a conventionally known method.

[0030] A specific production example will be shown below, but the present invention is not limited thereto.

[0031] 95.5 parts by weight of dimethyl naphthalenedicarboxylate, 47.6 parts by weight of ethylene glycol, and 6.3 parts by weight of polyethylene glycol (number average molecular weight 400) are charged into a reaction vessel and dissolved at 180° C., and then an ester exchange reaction catalyst is added with stirring.

[0032] The polyalkylene glycol of the present invention can be added at any stage from before the ester exchange reaction to before the start of the polycondensation reaction. From the viewpoint of reactivity, however, it is preferably added before the ester exchange reaction.

[0033] As the transesterification reaction catalyst, a compound having a known transesterification ability, such as a titanium alkoxide, a titanium chelate compound, or a metal acetate such as manganese acetate, magnesium acetate, or calcium acetate, can be used. In the case of manganese acetate tetrahydrate, the reaction proceeds sufficiently when 0.05 to 0.06 parts by weight is added as an ethylene glycol solution.

[0034] When using alkaline earth metal compounds such as calcium acetate and magnesium acetate as the transesterification catalyst, it is necessary to keep the total amount of alkaline earth metal elements to 10 ppm or less by weight based on the polyester resin composition and to use them in combination with other transesterification catalysts.

[0035] After the addition of the transesterification catalyst, the temperature is raised to 240°C over 3 to 4 hours while distilling off the by-product methanol. The target for the completion of the transesterification reaction is preferably 90% or more of the theoretical amount (when 100% reaction occurs, twice the molar amount of methanol as dimethyl naphthalenedicarboxylate is generated). After the completion of the transesterification reaction, various phosphorus compounds as heat resistant stabilizers, antioxidants, antifoaming agents, etc. can be added.

[0036] Examples of phosphorus compounds as heat resistance stabilizers include phosphoric acid, phosphorous acid, phosphonic acid, and phosphinic acid compounds, and known phosphorus compounds such as phosphoric acid, phosphorous acid, trimethylphosphate, and ethyl diethylphosphonoacetate can be used. In this case, it is preferable to use an alkali metal phosphate in combination in terms of improving heat resistance. The amount of such phosphorus compounds to be added is 0.022 parts by weight of phosphoric acid and 0.026 parts by weight of sodium dihydrogen phosphate dihydrate per 100 parts by weight of the polyester resin composition, and the molar ratio of manganese element to phosphorus element is about 1.0, resulting in good heat resistance.

[0037] After the addition of additives such as phosphorus compounds is completed, the reaction product is transferred to a polycondensation apparatus, and a polycondensation catalyst is added. Known compounds can be used as the polycondensation catalyst, and examples of such compounds include titanium chelate compounds, titanium alkoxides, germanium dioxide, antimony trioxide, antimony acetate, and aluminum catalysts. In the case of antimony trioxide, an amount of about 0.015 parts by weight of the polycondensation catalyst is sufficient.

[0038] As the ion salt, p-toluenesulfonic acid and tetrabutylphosphonium hydroxide as a tetrabutylphosphonium cation are mixed in a molar ratio of 1:1, and 0.01 parts by weight of the mixture is added before the polycondensation reaction.

[0039] After adding the polycondensation catalyst, the pressure inside the device is reduced to 133 Pa or less, and the temperature is raised to 290°C over 3 to 4 hours. The polycondensation reaction is carried out while distilling off by-products. When the reactant reaches a specified viscosity, the reaction is stopped and the molten polyester is discharged into a water tank. The discharged polyester is quenched in the water tank and cut into chips with a cutter.

[0040] In this manner, a polyester resin composition can be obtained, but the above is merely an example, and the raw materials, catalysts, and polymerization conditions are not limited to those described above.

[0041] The polyester film of the present invention is made using the polyester resin composition of the present invention, and preferably contains 80% by weight or more of the polyester resin composition of the present invention from the viewpoints of heat resistance and optical properties.

[0042] In the laminated film of the present invention, it is preferable that at least one of the polyester resin layers constituting the laminated film contains 80% by weight or more of the polyester resin composition of the present invention, and it is preferable that the other polyester resin layer is composed of an amorphous polyester resin. The layer containing 80% by weight or more of the polyester resin composition of the present invention can have a higher in-plane refractive index in the stretching and heat treatment process than that in the amorphous state before stretching. On the other hand, in the case of an amorphous polyester resin, by performing heat treatment at a temperature far exceeding the glass transition temperature in the heat treatment process, it is possible to completely relax any slight orientation caused in the stretching process, and to maintain the low refractive index of the amorphous state. In this way, a refractive index difference can be easily provided between the layer containing 80% by weight or more of the polyester resin composition of the present invention and the layer made of an amorphous polyester resin in the stretching and heat treatment processes in the production of the film.

[0043] Next, a preferred method for producing the laminated film of the present invention will be described below using the polyester resin composition and the amorphous polyester resin of the present invention, but the method is not limited thereto. The laminated film can be produced according to paragraphs

[0053] to

[0063] of JP-A-2007-307893.

[0044] In addition, when preparing a laminated film made of a plurality of polyester resins, a plurality of resins such as the polyester resin composition of the present invention and the amorphous polyester resin are fed from different flow paths using two or more extruders and fed into a lamination device. As the lamination device, a multi-manifold die, a feed block, a static mixer, etc. can be used, but in particular, in order to efficiently obtain the configuration of the present invention, it is preferable to use a feed block that includes at least two or more separate members having a large number of fine slits. When such a feed block is used, the device does not become extremely large, so that there is little foreign matter due to thermal degradation, and even if the number of layers is extremely large, high-precision lamination is possible. In addition, the lamination accuracy in the width direction is also significantly improved compared to the conventional technology. In addition, it is also possible to form an arbitrary layer thickness configuration.

[0045] The molten multilayer laminate thus formed in the desired layer structure is guided to a die, extruded onto a cooling body such as a casting drum, and cooled and solidified to obtain a casting film. In this case, it is preferable to use a wire-shaped, tape-shaped, needle-shaped, or knife-shaped electrode to rapidly solidify the laminate by electrostatic force against a cooling body such as a casting drum. In addition, a method of blowing air from a slit-shaped, spot-shaped, or planar device to rapidly solidify the laminate by closely contacting the cooling body such as a casting drum, or a method of rapidly solidifying the laminate by closely contacting the cooling body with a nip roll, is also preferable. The casting film thus obtained is preferably biaxially stretched. Here, biaxial stretching refers to stretching in the longitudinal direction and the width direction. Stretching may be performed in two directions successively, or may be performed in two directions simultaneously. In addition, re-stretching may be performed in the longitudinal direction and / or the width direction.

[0046] First, the case of sequential biaxial stretching will be described. Here, stretching in the longitudinal direction refers to stretching for giving the film molecular orientation in the longitudinal direction, and is usually performed by the difference in peripheral speed of rolls. This stretching may be performed in one stage, or may be performed in multiple stages using a pair of rolls. The stretching ratio varies depending on the type of resin, but is usually preferably 2 to 15 times, and when the polyester composition of the present invention is used as one of the resins constituting the laminated film, it is particularly preferably 2 to 7 times. In addition, the stretching temperature is preferably in the range of the glass transition temperature of the resin constituting the multi-layer laminated film to the glass transition temperature + 100°C.

[0047] The uniaxially stretched film thus obtained may be subjected to a surface treatment such as corona treatment, frame treatment, or plasma treatment as necessary, and then may be imparted with properties such as easy slippage, easy adhesion, and antistatic properties by in-line coating.

[0048] The stretching in the width direction means stretching for giving the film a width direction orientation, and is usually performed by conveying the film while holding both ends with clips using a tenter to stretch it in the width direction. The stretching ratio varies depending on the type of resin, but is usually preferably 2 to 15 times, and when the polyester resin composition of the present invention is used as one of the resins constituting the laminated film, it is particularly preferably 2 to 7 times. The stretching temperature is preferably in the range of the glass transition temperature of the resin constituting the multi-layer laminated film to the glass transition temperature + 120°C.

[0049] The biaxially stretched film is preferably heat-treated in a tenter at a temperature equal to or higher than the stretching temperature and equal to or lower than the melting point in order to impart flatness and dimensional stability. By carrying out heat treatment, the dimensional stability of the film is improved. After being heat-treated in this manner, the film is uniformly cooled slowly, cooled to room temperature, and wound up. If necessary, a relaxation treatment or the like may be carried out in combination with the heat treatment and the slow cooling.

[0050] After being heat-treated in this manner, the sheet is gradually cooled uniformly, cooled to room temperature, and wound up.

[0051] In the multilayer laminate film of the present invention having 50 or more layers laminated therein, the molar ratio of the naphthalenedicarboxylic acid component to the terephthalic acid component (naphthalenedicarboxylic acid component / terephthalic acid component) is preferably 0.85 or more as the composition of the entire multilayer laminate film, and is preferably 0.90 or more from the viewpoint of reflection characteristics. The naphthalenedicarboxylic acid component is a component that greatly contributes to a high refractive index, and a high content means that one of the polyester layers (polyester layer A) has a higher refractive index. A low content of the terephthalic acid component contributes to a low refractive index, and means that the refractive index of the other polyester layer (polyester layer B) is reduced. Therefore, an increase in the molar ratio of the naphthalenedicarboxylic acid component to the terephthalic acid component indicates that the refractive index difference between the high refractive index layer and the low refractive index layer is large, and optical characteristics such as reflection characteristics are improved. EXAMPLES

[0052] The present invention will be described in more detail below with reference to examples.

[0053] The physical properties were measured and the effects were evaluated according to the following methods.

[0054] (1) Composition analysis of polyester resin composition The film was dissolved in HFIP-d2 (hexafluoro-2-propanol dideuterated) and 1H-NMR was measured. From the spectrum obtained, the area of ​​the signal with a peak at a chemical shift of 8.7 ppm was determined as the naphthalene dicarboxylic acid component, the area of ​​the signal with a peak at a chemical shift of 4.9 ppm as the ethylene glycol component, the area of ​​the signal with a peak at a chemical shift of 3.9 ppm as the polyethylene glycol component, the area of ​​the signal with a peak at a chemical shift of 1.9 ppm as the polytetramethylene glycol component, and the area of ​​the signal with a peak at a chemical shift of 4.1 ppm as the diethylene glycol component. The molar ratio of each component and the content of polyalkylene glycol were calculated from the area ratio of each component.

[0055] The molecular weight of polyethylene glycol was calculated by calculating n from (4×(n-2)) / 4=S2 / S1, where S1 is the area of ​​the signal having a peak at a chemical shift of 3.9 ppm (proton number: 4) and S2 is the area of ​​the signal having a peak at a chemical shift of 3.8 ppm (proton number: 4), and n is calculated as n×44+16 (44: formula weight of the repeating unit of ethylene glycol).

[0056] If the signal area of ​​the peak (proton number 8) of polytetramethylene glycol having a chemical shift of 1.9 is S3 and the signal area of ​​the peak (proton number 4) having a chemical shift of 1.7 ppm is S4, n was calculated from (4 × (n-2)) / 8 = S4 / S3, and the molecular weight of polytetramethylene glycol was calculated as n × 72 + 16 (72: formula weight of the repeating unit of tetramethylene glycol).

[0057] (2) Thermal properties of polyester resin composition (glass transition temperature) Approximately 10 mg of the sample to be measured was weighed out, sealed in an aluminum pan and pan cover, and measured using a differential scanning calorimeter (Q2000 type, manufactured by TA Instruments). In the measurement, the sample was heated to 300°C in a nitrogen atmosphere, held for 5 minutes, then removed and rapidly cooled to room temperature on an iron plate, and again heated from 20°C to 300°C at a rate of 16°C / min in a nitrogen atmosphere and held for 5 minutes. The midpoint glass transition temperature (the temperature at the point where the straight line equidistant in the vertical direction from the extended straight line of each baseline intersects with the curve of the step-like change part of the glass transition) when the temperature was raised at a rate of 16°C / min, and the peak temperature (crystallization temperature) due to crystallization observed when the temperature was raised at 16°C / min were measured.

[0058] (3) Determination of alkaline earth metal elements and sulfur element in polyester composition The intensity of the fluorescent X-rays of the polymer was measured using a fluorescent X-ray analyzer (model number MESA-500W) manufactured by Horiba, Ltd. This value was converted into the metal content using a calibration curve previously prepared using samples with known metal content.

[0059] (4) Melt resistivity of polyester resin composition The polyester resin composition was melted at 290°C and then cut into a 0.5 cm 2 Two stainless steel electrodes were inserted in parallel with an interval of 8 mm, and after the temperature stabilized, the resistance value (R) was measured using a resistance meter (HIOKI EE: Resistance Meter RM3545). The melt resistivity value (ρ) was then calculated using the formula ρ (Ω cm) = R × 0.5 / 0.8.

[0060] (5) Refractive index (optical properties) The polyester resin composition was molten at 280°C in a vented twin-screw extruder, and then passed through a gear pump and a filter into a T-die to be molded into a sheet. The sheet was then rapidly cooled and solidified on a casting drum whose surface temperature was kept at 25°C by applying static electricity, to obtain an unstretched sheet having a thickness of 100 μm.

[0061] The refractive index of the obtained unstretched sheet was measured according to JIS K7142 (1996) Method A.

[0062] (6) Solution haze (optical properties) 2 g of the polyester resin composition was dissolved in 20 mL of a 3 / 2 (volume ratio) mixed solution of orthochlorophenol / 1,1,2,2-tetrachloroethane, and the haze was measured by integrating sphere photoelectric photometry using a cell with an optical path length of 20 mm and a haze meter (HZ-1 manufactured by Suga Test Instruments Co., Ltd.).

[0063] The solution haze is an index that indicates that the lower the value, the more excellent the transparency, and a value of 1.0% or less (◯, △) was considered to be acceptable. 0.5% or less... ○ Over 0.5% and 1.0% or less... △ Above 1.0%... ×.

[0064] (7)ΔIV (heat resistance) 7 g of the polyester resin composition was weighed into a test tube and vacuum dried for 8 hours at 160° C. The dried polyester resin composition was melt-treated at 290° C. for 1 hour in a nitrogen atmosphere, and the difference between the intrinsic viscosity (IV) before drying and the intrinsic viscosity after the melt-treatment was calculated as ΔIV.

[0065] The intrinsic viscosity (IV) was measured at 25°C by preparing a calibration curve according to JIS K7367-5:2000 (ISO 1628-5:1998) and dissolving 0.1 g of polymer in 10 ml of o-chlorophenol at 160°C for 20 minutes.

[0066] The smaller the difference in ΔIV, the better the heat resistance during melting. A ΔIV of 0.5 or less was considered acceptable. Less than 0.30... ○ Over 0.30 and 0.50 or less... △ Above 0.50... ×

[0067] (8) Film forming properties The film formability was judged based on the presence or absence of horizontal dents (stripes in the width direction) in the obtained laminated film, and films without horizontal dents as observed under a polarizing microscope were rated as acceptable.

[0068] (9) Reflectance (optical properties) The laminated film cut to 5cm x 5cm was used to measure the reflectance and transmittance using a Hitachi spectrophotometer (U-4100 Spectrophotometer) with an integrating sphere attached to the basic configuration. The reflectance measurement was performed using the aluminum oxide secondary white plate attached to the device as a reference. The reflectance measurement was performed with the sample's longitudinal direction facing up and down and placed behind the integrating sphere. The transmittance measurement was performed with the sample's longitudinal direction facing up and down and placed in front of the integrating sphere. Measurement conditions: The slit was set to 2nm (visible) / automatic control (infrared), the gain was set to 2, and the measurement was performed at a scanning speed of 600nm / min to obtain the reflectance at an azimuth angle of 0 degrees.

[0069] Example 1 95.5 parts by weight of dimethyl naphthalenedicarboxylate, 47.6 parts by weight of ethylene glycol, and 6.7 parts by weight of polyethylene glycol (Sanyo Chemical Industries, Ltd.: PEG400) were charged into a reaction vessel and dissolved at 180°C, and then 0.055 parts by weight of manganese acetate tetrahydrate and 0.015 parts by weight of antimony trioxide were added while stirring to start the transesterification reaction. The temperature was raised to 235°C while distilling off methanol over 3.5 hours, and the transesterification reaction was completed. 0.011 parts by weight of phosphoric acid, 0.013 parts by weight of sodium dihydrogen phosphate dihydrate, and 0.1 parts by weight of IRGANOX1010 were added, and the excess ethylene glycol was distilled off.

[0070] After transferring the reactants to a polycondensation reaction vessel, 0.01 parts by weight of ion salt A, which was a mixture of p-toluenesulfonic acid and tetrabutylphosphonium hydroxide in a molar ratio of 1:1, was added, and the pressure was reduced to 133 Pa or less while increasing the temperature from 240°C, and the temperature was increased to 290°C while distilling off excess ethylene glycol. When the desired melt viscosity was reached, the mixture was discharged into a water tank and chipped with a strand cutter.

[0071] The resulting polyester composition had a thermal loss of 0.09% by weight, a glass transition temperature (Tg) of 100.7° C., and a solution haze of 0.2%. The 1.9 mol % diethylene glycol content is believed to be the result of a side reaction during the polymerization reaction and the conversion of some of the decomposition products of polyethylene glycol to diethylene glycol.

[0072] The obtained polyester composition (hereinafter referred to as polyester A) and a non-crystalline (no melting point) PET resin (hereinafter referred to as polyester B) having a glass transition temperature of 79°C and copolymerized with 30 mol% of cyclohexane dimethanol with respect to the total diol components were each melted at 280°C in a vented twin-screw extruder, and then merged in a 201-layer feed block through a gear pump and a filter. Both surface layers of the laminated film were made of polyester A, and the layer thickness of the B layer mainly composed of polyester B adjacent to the A layer mainly composed of polyester A was made to be almost the same. After being merged in the 201-layer feed block, the mixture was introduced into a T-die and formed into a sheet, and then rapidly cooled and solidified on a casting drum whose surface temperature was kept at 25°C by applying electrostatic force to obtain a cast film. The discharge amount was adjusted so that the weight ratio of polyester A to polyester B was about 1:1, and the thickness ratio of adjacent layers was about 1.

[0073] The obtained cast film was heated with a group of rolls set at a temperature of 10°C above the glass transition temperature of Polyester A, and then stretched 4.0 times in the longitudinal direction while being rapidly heated from both sides of the film with a radiation heater within a stretching section length of 100 mm, and then cooled once.

[0074] Next, this uniaxially stretched film was introduced into a tenter, preheated with hot air at 100°C, and then stretched 4.0 times at a uniform stretching speed in the transverse direction at a temperature of 20°C above the glass transition temperature of Polyester A. The stretched film was heat-treated in the tenter with hot air at 235°C, then relaxed in the transverse direction by 2% at the same temperature, and then gradually cooled to room temperature and wound up. The thickness of the resulting laminated film was 40 μm.

[0075] The obtained laminated film had good performance as a laminated film reflecting a specific wavelength. The results are shown in Table 1.

[0076] The glass transition temperature of the film was measured by scraping off the surface layer (polyester A layer) as a sample and following the method for measuring thermal properties (glass transition temperature) of (2) polyester resin composition.

[0077] Examples 2 to 8, Comparative Examples 1 to 3 Except for changing the type, amount added, and molecular weight of polyalkylene glycol, the content of alkaline earth metal element, and the type and amount added of ion salt, a polyester composition and a laminated film were obtained in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0078] In Example 2, the content of polyethylene glycol was reduced, resulting in an increase in the glass temperature, while the amount of ionic salt A was increased, resulting in a tendency for the melt resistivity to decrease, and the performance was satisfactory as a laminated film that reflects specific wavelengths.

[0079] In Example 3, when the amount of polyethylene glycol added was increased and the amount of ionic salt A added was decreased, the refractive index and the glass transition temperature decreased, but the melt resistivity was almost the same as in Example 1. This is considered to be because the effect of decreasing the melt resistivity by increasing the amount of polyethylene glycol compared to Example 1 was offset by the increase in the melt resistivity by decreasing the amount of ionic salt A added. The refractive index of the obtained film decreased, so the reflective properties tended to decrease, but the performance was satisfactory as a laminated film that reflects a specific wavelength.

[0080] In Example 4, the sulfonic acid compound of the ionic salt was changed to 3,5-dicarboxybenzenesulfonic acid, and the amount of ionic salt B added was increased. As a result, the melt resistivity decreased, and the solution haze and ΔIV tended to deteriorate, but the obtained film had satisfactory performance as a laminated film that reflects specific wavelengths.

[0081] In Example 5, polytetramethylene glycol with a large molecular weight was used instead of polyethylene glycol, and as a result, the melt resistivity was equivalent to that of Example 1, and the obtained film had satisfactory performance as a laminated film that reflects specific wavelengths. It is believed that diethylene glycol was contained due to a side reaction during the polymerization reaction.

[0082] In Example 6, magnesium acetate was added instead of the ion salt, resulting in an increase in solution haze and ΔIV, and a quality inferior to that of Example 1, but the performance was satisfactory as a laminated film that reflects specific wavelengths.

[0083] In Example 7, the amount of polyethylene glycol added was increased, and as a result, the refractive index tended to decrease and the reflective properties also tended to decrease, but the performance was not problematic as a laminated film that reflects specific wavelengths.

[0084] In Example 8, polyethylene glycol having a large molecular weight was added, resulting in an increase in solution haze and a lower quality than in Example 1, but the performance was satisfactory as a laminated film that reflects specific wavelengths.

[0085] In Comparative Example 1, since polyethylene glycol and ionic salt were not added, the melt resistivity was high and the obtained film had poor film formability.

[0086] In Comparative Example 2, the amount of polyalkylene glycol added was increased, and a laminated film was obtained in the same manner as in Example 1, except that no ionic salt was added. As a result, the melt resistivity was high, ΔIV tended to deteriorate, and the obtained film had poor film formability.

[0087] In Comparative Example 3, a laminated film was obtained in the same manner as in Example 1, except that a polyalkylene glycol having a large molecular weight was added and no ionic salt was added. As a result, the melt resistivity was high, and the obtained film had poor film formability.

[0088] Example 9 A polyester resin composition (resin A) was obtained in the same manner as in Example 1, except that the amount of ion salt A added was increased.

[0089] Further, a polyester resin composition (resin B) was obtained in the same manner as in Example 1, except that ionic salt A was not added.

[0090] Next, resin A and resin B were kneaded at 290° C. in a vented twin-screw extruder in a weight ratio of resin A / resin B=1 / 9 to obtain a polyester resin composition (resin C).

[0091] The obtained resin C was used as polyester A, and a laminated film was obtained in the same manner as in Example 1. The obtained film had the same performance as in Example 1, and had satisfactory performance as a laminated film that reflects a specific wavelength.

[0092] [Table 1]

[0093] [Table 2]

Claims

1. A polyester resin composition comprising a naphthalenedicarboxylic acid component and an ethylene glycol component as main components, the polyester resin composition containing 3% by weight or more and 15% by weight or less of a polyalkylene glycol having a number average molecular weight of less than 1,000, and having a melt resistivity of 10 MΩ·cm or less.

2. 2. The polyester resin composition according to claim 1, having a midpoint glass transition temperature of 80°C or higher and 110°C or lower.

3. 2. The polyester resin composition according to claim 1, wherein the content of alkaline earth metal elements is 10 ppm or less by weight.

4. 2. The polyester resin composition according to claim 1, which contains the ionic salt in an amount of 40 ppm or more and 10,000 ppm or less by weight based on the polyester resin composition.

5. 5. The polyester resin composition according to claim 4, wherein the ionic salt is a mixture of a sulfonic acid compound and a phosphorus compound.

6. 6. The polyester resin composition according to claim 5, wherein the sulfonic acid compound is at least one selected from the group consisting of benzenesulfonic acid, o-toluenesulfonic acid, m-toluenesulfonic acid and p-toluenesulfonic acid.

7. 6. The polyester resin composition according to claim 5, wherein the phosphorus compound is at least one selected from quaternary phosphonium compounds.

8. 2. The polyester resin composition according to claim 1, wherein the content of elemental sulfur is from 2 ppm to 50 ppm by weight based on the weight of the polyester resin composition.

9. 2. The polyester resin composition according to claim 1, which contains an alkali metal phosphate.

10. A polyester film comprising at least 80% by weight of the polyester resin composition according to claim 1.

11. A laminated polyester film comprising a layer made of the polyester film according to claim 10.

12. A multi-layer laminate film comprising 50 or more laminated layers of the laminated polyester according to claim 11.

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