JP2014193953A - Void-containing film, back sheet for solar cell, electronic device and solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light void-containing film which has a high reflectance with variation of the reflectance reduced.SOLUTION: A void-containing film comprises a polymer and particles containing a metal and phosphate, and the average length (Lma) in the longitudinal direction and the average length (Lta) in the direction perpendicular to the longitudinal direction of voids present within the film, in a plane view, meet the conditions 2 μm≤Lma≤1000 μm and 2 μm≤Lta≤500 μm, respectively. When the reflectance (R) to the light of the 550-nm wavelength is measured at 10 positions along either of the longitudinal direction and the direction perpendicular to the longitudinal direction, the average value (Ra) is 60-100%, and all the reflectances meet the condition 0.85Ra≤R≤1.15Ra.

Description

  The present invention relates to a cavity-containing film, a solar cell backsheet, an electronic device, and a solar cell module.

As a method for increasing the reflectance of the film, a method for generating a cavity in the film and a method for providing a coating layer having a high reflectance are known.
For example, a method of providing a coating layer with high reflectivity is known (see Patent Documents 1 and 2). However, in order to produce a coating layer with high reflectivity, various additives are required and a coating process is required, which increases the manufacturing cost.

In addition, a method is known in which the reflectivity is increased by creating a cavity in the film.
For example, in order to produce a film having high reflectivity, there is a method of generating a cavity by containing an incompatible resin (see Patent Document 3). However, since the incompatible resin is mixed in the melt extrusion process, it is easy to agglomerate or disperse in the dispersion state, and the variation in the cavity size becomes large, which tends to cause the reflectance variation and breakage. In addition, the cost is likely to increase due to an increase in the number of processes.

  In addition, a method has been proposed in which a stretched film is impregnated with supercritical carbon dioxide and then foamed to form independent voids (see Patent Document 4). However, in this method, the equipment cost for impregnating the stretched film with the supercritical carbon dioxide gas is high and the cost is high.

JP 2012-137618 A Japanese Patent No. 4576687 JP 2012-207153 A JP 2001-114923 A

  A film having a cavity in the film has a high reflectance, and has applications such as a reflector for a liquid crystal monitor and a back sheet for a solar cell.

An object of the present invention is to provide a lightweight cavity-containing film that has a high reflectance and a small variation in reflectance.
Moreover, an object of this invention is to provide the solar cell backsheet, electronic device, and solar cell module which were provided with the said cavity containing film.

In order to achieve the above object, the following invention is provided.
<1> including a polymer and particles containing metal and phosphorus,
The average length (Lma) in the longitudinal direction and the average length (Lta) in the direction orthogonal to the longitudinal direction in the plan view of the cavities existing in the film are 2 μm ≦ Lma ≦ 1000 μm and 2 μm ≦ Lta ≦ 500 μm, respectively. And satisfy
The average value (Ra) when measuring the reflectance (R) for light having a wavelength of 550 nm at 10 locations along any one of the longitudinal direction and the direction orthogonal to the longitudinal direction is 60% or more and 100% or less, And all of reflectance satisfy | fills 0.85Ra <= R <= 1.15Ra,
Cavity-containing film.
Void containing film according to <2> an apparent specific gravity of ^{0.7g / cm 3 ~1.2g / cm 3} <1>.
<3> The polyester void-containing film according to <1> or <2>, wherein the void ratio represented by the following formula is 5% or more and 60% or less.
Cavity (%) = Cavity area / (Cavity area + Polymer area) × 100
<4> The void-containing film according to any one of <1> to <3>, wherein the particles containing metal and phosphorus are particles precipitated internally during the melt polymerization of the polymer.
<5> The void-containing film according to any one of <1> to <4>, which contains polyester as a polymer.
<6> The void-containing film according to any one of <1> to <5>, wherein all of the reflectances satisfy 0.85Ra ≦ R ≦ 1.15Ra.
<7> A solar cell backsheet comprising the void-containing film according to any one of <1> to <6>.
<8> A solar cell module comprising a transparent substrate on which sunlight is incident, a solar cell element, and the solar cell backsheet according to <7>.
<9> An electronic device comprising the cavity-containing film according to any one of <1> to <6>.

  According to the present invention, it is possible to provide a lightweight cavity-containing film with high reflectivity and small variation in reflectivity.

It is a schematic block diagram which shows an example of the biaxial stretching machine which can be used for manufacture of the cavity containing film of this invention.

<Cavity-containing film>
The void-containing film of the present invention includes a polymer and particles containing metal and phosphorus (hereinafter sometimes referred to as “metal-phosphorous particles”), and has a longitudinal direction in plan view of the voids present in the film. The average length (Lma) and the average length (Lta) in the direction orthogonal to the longitudinal direction satisfy 2 μm ≦ Lma ≦ 1000 μm and 2 μm ≦ Lta ≦ 500 μm, respectively, and are orthogonal to the longitudinal direction and the longitudinal direction. The average value (Ra) when the reflectance (R) for 550 nm wavelength light is measured at 10 locations along any one of the directions is 60% or more and 100% or less, and all of the reflectance is 0. It is a cavity-containing film satisfying .85Ra ≦ R ≦ 1.15Ra.

The method for producing the void-containing film of the present invention is not particularly limited, but the void-containing film of the present invention can be suitably produced by a method comprising a polymer melt polymerization step, a melt extrusion step, and a stretching step. .
The inventor deposits a certain amount of nano-order size particles (less than 1 μm) inside the film by an additive in the melt polymerization step of a polymer such as a polyester resin, and generates cavities in the stretching step. It has been found that a void-containing film that is dispersed with high uniformity in size, has a small variation in reflectance, and is difficult to break in the stretching process can be produced. Moreover, in such a method for producing a void-containing film, since the void ratio can be stably increased, a lightweight film having a small apparent specific gravity can be produced.

(polymer)
What is necessary is just to select the polymer contained in the cavity containing film of this invention according to the use of a film. Examples thereof include polyester resins and polyolefin resins, and polyester resins are preferable.

(Particles containing metal and phosphorus)
The void-containing film of the present invention includes particles containing metal and phosphorus (metal-phosphorous particles). In the present invention, for example, nano-sized particles of a metal-phosphorus compound can be precipitated inside the film by an additive in the polymer melt polymerization step, and it is considered that cavities are generated by using the nano-sized particles as a trigger.

  The metal-phosphorus particles contained in the void-containing film of the present invention preferably contain at least one metal selected from Sb, Li, Zn, Mn, Co and Mg. In the polymer melt polymerization step, at least one compound containing the above metal and at least one compound containing phosphorus such as phenylphosphonic acid, dimethylphosphonic acid, phosphoric acid, phosphorous acid, etc. are added to form metal-phosphorus It is preferable to internally precipitate the system particles.

  A film with a small reflectance distribution can be produced by generating cavities triggered by nano-sized metal-phosphorous particles. In addition, the nano-sized metal-phosphorous particles can increase the crystallization speed and form cavities more stably. This is because, in the method in which the incompatible material is mixed in the extrusion process, the incompatible material is aggregated and the dispersibility is lowered, whereas the internal precipitate is uniformly precipitated.

(cavity)
The void-containing film of the present invention includes voids, and the average length (Lma) in the longitudinal direction and the average length (Lta) in the direction perpendicular to the longitudinal direction in the plan view of the cavities existing in the film are 2 μm, respectively. ≦ Lma ≦ 1000 μm and 2 μm ≦ Lta ≦ 500 μm are satisfied. In addition, the size (length) of each direction of the cavity in the film in the present invention is observed by observing a cross section in the plane direction of the film (direction perpendicular to the thickness direction) with a scanning electron microscope, and magnifying the image by 100 times. It is a value obtained by measuring all the cavities in one image (corresponding to a film area of about 1.2 mm ² ), and Lma and Lta are calculated as an average of measured values of the length in each direction of the cavities.

After a certain amount of nano-order sized metal-phosphorous particles are precipitated inside the film by an additive in the polymer melt polymerization step, cavities are generated by uniaxial stretching or biaxial stretching.
The size of the cavity in the film can be adjusted by, for example, the draw ratio. When uniaxial stretching is performed, the stretching direction is the longitudinal direction of the cavity. On the other hand, in the case of biaxial stretching, the cavity usually has a direction in which the stretching ratio is high as the longitudinal direction, but the direction in which the stretching ratio is low may be the longitudinal direction.

When the cavity size in the film is too large, the cavities are easily connected to each other, which causes breakage. On the other hand, when the cavity size is too small, the amount of the cavity is reduced, and the amount of the interface between the resin and air is reduced, so that the reflectance is lowered.
When the average lengths (Lma, Lta) of the cavities are within the above ranges, the high reflectance can be more stably achieved. More preferably, the average length of each direction of the cavity satisfies 10 μm ≦ Lta ≦ 300 μm and 10 μm ≦ Lma ≦ 500 μm.

(Cavity ratio)
The void-containing film of the present invention preferably has a void ratio of 5% to 60%.
Here, the void ratio (%) is a value calculated from the following equation by measuring a cross-sectional image of the film.
Cavity (%) = Cavity area / (Cavity area + Polymer area) × 100
The reflectance of a film can be made high because a cavity rate is 5% or more. On the other hand, if the void ratio is 60% or less, the cavities are hardly connected to each other, and breakage can be effectively prevented from occurring in the stretching and winding processes after the generation of the cavities. The void-containing film of the present invention preferably has a void ratio of 30% to 55%.

(Apparent specific gravity)
The void-containing film of the present invention is lightweight because it contains voids with high uniformity. The smaller the specific gravity of the film, the lighter the liquid crystal monitor or solar cell using this film is. On the other hand, if there are too many cavities, the film tends to break. From this point of view, void containing film of the present invention, the apparent specific gravity of preferably 0.7 to 1.2 g / cm ^3, more preferably 0.7~1.0g / cm ^3, 0.7~0. 9 g / cm ³ is more preferable. The specific gravity of the film of polyester containing no cavities are 1.3~1.4g / cm ^3, it can be said that 1.2 g / cm ³ or less is sufficiently lightweight.

  Cavity ratio and apparent specific gravity are highly dependent on the size and number of cavities. Since metal-phosphorous particles trigger the formation of cavities, the porosity and apparent specific gravity of the film are adjusted by the amount of additive that contributes to the formation of metal-phosphorous particles and the stretching conditions that have a large effect on the cavity size. can do.

(Reflectance)
The void-containing film of the present invention measures the reflectance (R) with respect to light having a wavelength of 550 nm at 10 locations along one of the longitudinal direction and the direction orthogonal to the longitudinal direction in a plan view of the cavity existing in the film. The average value (Ra) is 60% or more and 100% or less, and all the reflectances satisfy 0.85Ra ≦ R ≦ 1.15Ra.
The reflectance is a value measured with a spectrophotometer by irradiating one side of the film with light having a wavelength of 550 nm.

  When the reflectance is less than 60%, for example, when used as a reflection plate for a liquid crystal monitor, a back sheet for a solar cell, or the like, the reflectance is insufficient. The reflectance is preferably 75% or more and 100% or less, and more preferably 85% or more and 100% or less.

  Further, when the reflectance unevenness is reduced, the brightness unevenness is reduced when used for a liquid crystal monitor or the like. The reflectance R at the ten locations preferably satisfies 0.90Ra ≦ R ≦ 1.10Ra, and more preferably satisfies 0.95Ra ≦ R ≦ 1.05Ra.

  The reflectance of the void-containing film of the present invention is due to reflection at the interface between the resin and the cavity, and it is preferable that the difference in refractive index between the resin and the cavity is large. If this difference in refractive index is small, the reflection at the interface becomes small, and as a result, the target reflectance cannot be obtained. Since the refractive index of gas (air) is substantially 1.0, the refractive index of the cavity in the film is 1.0, and the refractive index of the resin component is preferably higher and is preferably 1.4 or more. Examples of the resin that satisfies the condition that the refractive index is 1.4 or more include polyester.

(Thickness)
What is necessary is just to select the thickness of the hollow image milk film of this invention according to a use. From the viewpoint of achieving a high reflectance and reducing the weight, it is preferably 50 μm or more and 300 μm or less, and more preferably 100 μm or more and 250 μm or less.

  Hereinafter, the case where a polyester resin is used will be described as an example of the method for producing the void-containing film of the present invention.

[Melt polymerization]
The polyester resin used in the present invention is a step of obtaining a polycondensate by subjecting an esterification reaction product obtained by reacting (A) a dicarboxylic acid component and (B) a diol component by an esterification reaction to a polycondensation reaction. It can be synthesized through (melt polymerization step).
In the present invention, it is preferable to deposit metal-phosphorous particles for depositing particles inside the film with an additive such as a catalyst added in melt polymerization when synthesizing the polymer. Such metal-phosphorous particles tend to precipitate particularly when the metal and the phosphorus compound are separately added, that is, after one of them is added and then dispersed, the other is added.

-Esterification reaction-
Examples of the dicarboxylic acid component (A) used as a raw material for the polyester resin include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, Aliphatic dicarboxylic acids such as azelaic acid, methylmalonic acid and ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalate Acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid Acid, 5-Natri Arm sulfoisophthalic acid, phenyl ene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) a dicarboxylic acid or its ester derivatives such as aromatic dicarboxylic acids such as fluorene acid.
(A) As a dicarboxylic acid component, the case where at least 1 sort of aromatic dicarboxylic acid is used is preferable. More preferably, the dicarboxylic acid component contains an aromatic dicarboxylic acid as a main component. The “main component” means that the proportion of aromatic dicarboxylic acid in the dicarboxylic acid component is 80% by mass or more. A dicarboxylic acid component other than the aromatic dicarboxylic acid may be included. Examples of such a dicarboxylic acid component include ester derivatives such as aromatic dicarboxylic acids.

  (B) Examples of the diol component include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. , Cycloaliphatic dimethanol, spiroglycol, isosorbide and other alicyclic diols, bisphenol A, 1,3-benzenedimethanol, 1,4-benzendimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene And diol compounds such as aromatic diols.

  (B) As a diol component, the case where at least 1 sort of aliphatic diol is used is preferable. The aliphatic diol can contain ethylene glycol, and preferably contains ethylene glycol as a main component. The main component means that the proportion of ethylene glycol in the diol component is 80% by mass or more.

  The amount of the aliphatic diol (for example, ethylene glycol) used is in the range of 1.015 to 1.50 mol with respect to 1 mol of the aromatic dicarboxylic acid (for example, terephthalic acid) and, if necessary, its ester derivative. preferable. The amount used is more preferably in the range of 1.02 to 1.30 mol, and still more preferably in the range of 1.025 to 1.10 mol. If the amount used is in the range of 1.015 or more, the esterification reaction proceeds favorably, and if it is in the range of 1.50 mol or less, for example, by-production of diethylene glycol due to dimerization of ethylene glycol is suppressed, and the melting point In addition, many properties such as glass transition temperature, crystallinity, heat resistance, hydrolysis resistance, and weather resistance can be kept good.

  A known reaction catalyst can be used for the esterification reaction. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and phosphorus compounds. Usually, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at an arbitrary stage before the polyester production method is completed. As such a method, for example, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is.

  For example, in the esterification reaction, an aromatic dicarboxylic acid and an aliphatic diol are polymerized in the presence of a catalyst containing a titanium compound. In this esterification reaction, an organic chelate titanium complex having an organic acid as a ligand is used as a catalyst titanium compound, and at least an organic chelate titanium complex, a magnesium compound, and an aromatic ring as a substituent are used in the process. It is preferable to provide a process of adding a pentavalent phosphate ester not included in this order.

  First, an aromatic dicarboxylic acid and an aliphatic diol are mixed with a catalyst containing an organic chelate titanium complex, which is a titanium compound, prior to the addition of the magnesium compound and the phosphorus compound. Titanium compounds such as organic chelate titanium complexes have high catalytic activity for esterification reactions, so that esterification reactions can be performed satisfactorily. At this time, the titanium compound may be added to the mixture of the dicarboxylic acid component and the diol component, or after mixing the dicarboxylic acid component (or diol component) and the titanium compound, the diol component (or dicarboxylic acid component) is mixed. May be. Further, the dicarboxylic acid component, the diol component, and the titanium compound may be mixed at the same time. The mixing is not particularly limited, and can be performed by a conventionally known method.

  More preferable polyesters are polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN), and still more preferable is PET. Further, PET is polymerized using one or more selected from a germanium (Ge) -based catalyst, an antimony (Sb) -based catalyst, an aluminum (Al) -based catalyst, and a titanium (Ti) -based catalyst. A Ti-based catalyst is more preferable.

  Ti-based catalysts have high reaction activity and can lower the polymerization temperature. Therefore, in particular, it is possible to suppress the thermal decomposition of PET during the polymerization reaction and the generation of COOH. In the void-containing polyester film obtained by the present invention, the amount of terminal COOH is adjusted to a predetermined range. Is preferred.

Examples of the Ti-based catalyst include oxides, hydroxides, alkoxides, carboxylates, carbonates, oxalates, organic chelate titanium complexes, and halides. The Ti-based catalyst may be used in combination of two or more titanium compounds as long as the effects of the present invention are not impaired.
Examples of Ti-based catalysts include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, tetraphenyl Titanium alkoxide such as titanate and tetrabenzyl titanate, titanium oxide obtained by hydrolysis of titanium alkoxide, titanium-silicon or zirconium composite oxide obtained by hydrolysis of a mixture of titanium alkoxide and silicon alkoxide or zirconium alkoxide, titanium acetate , Titanium oxalate, potassium potassium oxalate, sodium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride-aluminum chloride Miniumu mixture, titanium acetylacetonate, an organic chelate titanium complex having an organic acid as a ligand, and the like.

  For production of a Ti catalyst PET obtained by polymerization using a Ti catalyst, for example, JP 2005-340616 A, JP 2005-239940 A, JP 2004-319444 A, Patent 3436268, The polymerization methods described in Japanese Patent No. 3978666, Japanese Patent No. 3780137, Japanese Patent Application Laid-Open No. 2007-204538, and the like can be used.

When the polyester is polymerized, it is preferable to perform the polymerization using a titanium (Ti) compound as a catalyst in the range of 1 ppm to 30 ppm, more preferably 2 ppm to 20 ppm, and even more preferably 3 ppm to 15 ppm. In this case, the polyester film of the present invention contains 1 ppm to 30 ppm of titanium.
When the amount of the Ti compound is 1 ppm or more, a preferable intrinsic viscosity IV (Intrinsic Viscosity) is obtained, and when it is 30 ppm or less, the terminal COOH can be adjusted so as to satisfy the above range.

  To synthesize a Ti-based polyester polymerized using such a Ti-based compound, for example, Japanese Patent Publication No. 8-30119, Patent 2543624, Patent 3335683, Patent 3717380, Patent 3897756, Patent 396226, The methods described in Japanese Patent No. 3997866, Japanese Patent No. 39996871, Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269704, Japanese Patent No. 4313538, and the like can be applied.

<Titanium compound>
As the titanium compound as the catalyst component, at least one kind of organic chelate titanium complex having an organic acid as a ligand is used. Examples of the organic acid include citric acid, lactic acid, trimellitic acid, malic acid and the like. Among them, an organic chelate complex having citric acid or citrate as a ligand is preferable.

For example, when a chelate titanium complex having citric acid as a ligand is used, a polyester resin having better polymerization activity and color tone than other titanium compounds can be obtained. Furthermore, even when using a citric acid chelate titanium complex, by adding it at the stage of the esterification reaction, a polyester resin having better polymerization activity and color tone and less terminal carboxyl groups can be obtained compared to the case where it is added after the esterification reaction. It is done. In this regard, the titanium catalyst also has a catalytic effect of the esterification reaction. By adding it at the esterification stage, the oligomer acid value at the end of the esterification reaction is lowered, and the subsequent polycondensation reaction is performed more efficiently. In addition, complexes with citric acid as a ligand are more resistant to hydrolysis than titanium alkoxides, etc., and do not hydrolyze in the esterification reaction process, while maintaining the original activity and catalyzing the esterification and polycondensation reactions It is estimated to function effectively as
In general, it is known that as the amount of terminal COOH increases, the hydrolysis resistance deteriorates. By reducing the amount of terminal carboxyl groups, the hydrolysis resistance is expected to be improved.

  As a citric acid chelate titanium complex, for example, VERTEC AC-420 manufactured by Johnson Matthey is easily available as a commercial product.

  The aromatic dicarboxylic acid and the aliphatic diol can be introduced by preparing a slurry containing them and continuously supplying it to the esterification reaction step.

  In the esterification reaction, a titanium compound is used as a catalyst, and the amount of Ti added is 1 ppm or more and 30 ppm or less, more preferably 3 ppm or more and 20 ppm or less, more preferably 5 ppm or more and 15 ppm or less in terms of element. Is preferred. If the amount of titanium added is 1 ppm or more, it is advantageous in that the polymerization rate is increased, and if it is 30 ppm or less, it is advantageous in that a good color tone is obtained.

In addition to the organic chelate titanium complex, examples of the titanium compound generally include oxides, hydroxides, alkoxides, carboxylates, carbonates, oxalates, and halides. Other titanium compounds may be used in combination with the organic chelate titanium complex as long as the effects of the present invention are not impaired.
Examples of such titanium compounds include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, Titanium alkoxide such as tetraphenyl titanate, tetrabenzyl titanate, titanium oxide obtained by hydrolysis of titanium alkoxide, titanium-silicon or zirconium composite oxide obtained by hydrolysis of a mixture of titanium alkoxide and silicon alkoxide or zirconium alkoxide, Titanium acetate, titanium oxalate, potassium potassium oxalate, sodium titanium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride Down - aluminum chloride mixture, and titanium acetylacetonate.

  For synthesis of Ti-based polyester using such a titanium compound, for example, Japanese Patent Publication No. 8-30119, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 3897756, Japanese Patent No. 396226, Japanese Patent No. 3978666, The methods described in Japanese Patent No. 3,996,871, Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269704, Japanese Patent No. 431538, and the like can be applied.

  In the present invention, an aromatic dicarboxylic acid and an aliphatic diol are polymerized in the presence of a catalyst containing a titanium compound, and at least one of the titanium compounds is an organic chelate titanium complex having an organic acid as a ligand. An esterification reaction step including at least a step of adding an organic chelate titanium complex, a magnesium compound, and a pentavalent phosphate ester having no aromatic ring as a substituent in this order, and an ester formed in the esterification reaction step And a polycondensation step in which a polycondensation product is produced by a polycondensation reaction of the polymerization reaction product, and is preferably produced by a method for producing a polyester resin.

In this case, in the course of the esterification reaction, the addition of a magnesium compound to the presence of an organic chelate titanium complex as a titanium compound, followed by the addition order of adding a specific pentavalent phosphorus compound, thereby providing a titanium catalyst. It is possible to effectively suppress the decomposition reaction in the polycondensation while keeping the reaction activity of the compound moderately high, imparting electrostatic application characteristics with magnesium. As a result, it is possible to obtain a polyester resin that is less colored, has high electrostatic application characteristics, and has improved yellowing when exposed to high temperatures.
As a result, coloring during polymerization and subsequent coloring during melt film formation are reduced, and yellowishness is reduced compared to conventional antimony (Sb) catalyst-based polyester resins, and germanium catalysts having a relatively high transparency are also obtained. It is possible to provide a polyester resin having a color tone and transparency comparable to a polyester resin and having excellent heat resistance. Further, a polyester resin having high transparency and less yellowness can be obtained without using a color tone adjusting material such as a cobalt compound or a pigment.

  This polyester resin can be used for applications requiring high transparency (for example, optical film, industrial squirrel, etc.), and it is not necessary to use an expensive germanium-based catalyst, so that the cost can be greatly reduced. In addition, since foreign matters caused by the catalyst that are likely to occur in the Sb catalyst system are also avoided, the occurrence of failures and quality defects in the film forming process can be reduced, and the cost can be reduced by improving the yield.

  In the esterification reaction, a process of adding an organic chelate titanium complex which is a titanium compound and a magnesium compound and a pentavalent phosphorus compound as additives in this order is provided. At this time, the esterification reaction proceeds in the presence of the organic chelate titanium complex, and thereafter, the addition of the magnesium compound is started before the addition of the phosphorus compound.

<Phosphorus compound>
As the pentavalent phosphorus compound, it is preferable to use at least one pentavalent phosphate having no aromatic ring as a substituent. Examples of the pentavalent phosphate in the present invention include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris phosphate (triethylene glycol), methyl acid phosphate, and ethyl acid phosphate. Isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, triethylene glycol acid phosphate and the like.

Among pentavalent phosphates, phosphates having a lower alkyl group having 2 or less carbon atoms as a substituent [(RO) ₃ P═O; R = alkyl group having 1 or 2 carbon atoms] are preferable. In particular, trimethyl phosphate and triethyl phosphate are particularly preferable.

  In particular, when a chelate titanium complex coordinated with citric acid or a salt thereof is used as a catalyst as the titanium compound, the pentavalent phosphate ester has better polymerization activity and color tone than the trivalent phosphate ester, Furthermore, in the case of adding a pentavalent phosphate having 2 or less carbon atoms, the balance of polymerization activity, color tone, and heat resistance can be particularly improved.

  The addition amount of the phosphorus compound is preferably such that the P element conversion value is in the range of 50 ppm to 90 ppm. The amount of the phosphorus compound is more preferably 60 ppm to 80 ppm, and still more preferably 65 ppm to 75 ppm.

<Magnesium compound>
Inclusion of the magnesium compound improves electrostatic applicability. In this case, coloring is likely to occur, but in the present invention, coloring is suppressed and excellent color tone and heat resistance are obtained.
Examples of the magnesium compound include magnesium salts such as magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, and magnesium carbonate. Among these, magnesium acetate is most preferable from the viewpoint of solubility in ethylene glycol.

  The amount of magnesium compound added is preferably such that the Mg element conversion value is 50 ppm or more, more preferably 50 ppm or more and 100 ppm or less in order to impart high electrostatic applicability. The addition amount of the magnesium compound is preferably an amount that is in the range of 60 ppm to 90 ppm, more preferably 70 ppm to 80 ppm in terms of imparting electrostatic applicability.

In the esterification reaction step, the titanium compound as the catalyst component and the magnesium compound and the phosphorus compound as the additive are set so that the value Z calculated from the following formula (i) satisfies the following relational expression (ii): Particularly preferred is the case of adding and melt polymerizing. Here, the P content is the amount of phosphorus derived from the entire phosphorus compound including the pentavalent phosphate ester having no aromatic ring, and the Ti content is the amount of titanium derived from the entire Ti compound including the organic chelate titanium complex. It is. As described above, by selecting the combined use of the magnesium compound and the phosphorus compound in the catalyst system containing the titanium compound and controlling the addition timing and the addition ratio, while maintaining the catalyst activity of the titanium compound moderately high, yellow A color tone with less taste can be obtained, and heat resistance that hardly causes yellowing can be imparted even when exposed to high temperatures during polymerization reaction or subsequent film formation (melting).
(I) Z = 5 × (P content [ppm] / P atomic weight) −2 × (Mg content [ppm] / Mg atomic weight) −4 × (Ti content [ppm] / Ti atomic weight)
(Ii) + 0 ≦ Z ≦ + 5.0
This is an index for quantitatively expressing the balance between the three because the phosphorus compound not only acts on titanium but also interacts with the magnesium compound.
Formula (i) expresses the amount of phosphorus that can act on titanium by excluding the phosphorus content that acts on magnesium from the total amount of phosphorus that can be reacted. When the value Z is positive, it can be said that there is an excess of phosphorus that inhibits titanium, and conversely, when it is negative, there is a shortage of phosphorus necessary to inhibit titanium. In the reaction, since each atom of Ti, Mg, and P is not equivalent, each mole number in the formula is weighted by multiplying by a valence.

  In the present invention, no special synthesis or the like is required, and the titanium compound, phosphorus compound, and magnesium compound, which are inexpensive and easily available, are used for color tone and heat while having the reaction activity required for the reaction. A polyester resin excellent in coloring resistance can be obtained.

  In the formula (ii), it is preferable to satisfy + 1.0 ≦ Z ≦ + 4.0 from the viewpoint of further increasing the color tone and coloring resistance to heat while maintaining the polymerization reactivity, and + 1.5 ≦ Z ≦ + 3 Is more preferable.

  As a preferred embodiment in the present invention, before the esterification reaction is completed, after adding a chelate titanium complex having 1 ppm or more and 30 ppm or less of citric acid or citrate as a ligand to the aromatic dicarboxylic acid and the aliphatic diol, In the presence of the chelate titanium complex, a magnesium salt of a weak acid of 60 ppm or more and 90 ppm or less (more preferably 70 ppm or more and 80 ppm or less) is added, and after the addition, a fragrance of 60 ppm or more and 80 ppm or less (more preferably 65 ppm or more and 75 ppm or less). The aspect which adds the pentavalent phosphate which does not have a ring as a substituent is mentioned.

  The esterification reaction may be carried out using a multistage apparatus in which at least two reactors are connected in series under conditions where ethylene glycol is refluxed while removing water or alcohol produced by the reaction from the system. it can.

Further, the esterification reaction may be performed in one stage or may be performed in multiple stages.
When the esterification reaction is performed in one step, the esterification reaction temperature is preferably 230 to 260 ° C, more preferably 240 to 250 ° C.
When the esterification reaction is performed in multiple stages, the temperature of the esterification reaction in the first reaction tank is preferably 230 to 260 ° C, more preferably 240 to 250 ° C, and the pressure is 1.0 to 5.0 kg / cm ² is preferable, and 2.0 to 3.0 kg / cm ² is more preferable. Temperature of the esterification reaction of the second reaction vessel is preferably from 230 to 260 ° C., more preferably from 245 to 255 ° C., the pressure is 0.5~5.0kg / cm ^2, more preferably 1.0 to 3. 0 kg / cm ² . Furthermore, when carrying out by dividing into three or more stages, it is preferable to set the conditions for the esterification reaction in the intermediate stage to the conditions between the first reaction tank and the final reaction tank.

-Polycondensation-
In polycondensation, a polycondensation product is produced by subjecting an esterification reaction product produced by the esterification reaction to a polycondensation reaction. The polycondensation reaction may be performed in one stage or may be performed in multiple stages.

  The esterification reaction product such as an oligomer generated by the esterification reaction is subsequently subjected to a polycondensation reaction. This polycondensation reaction can be suitably performed by supplying it to a multistage polycondensation reaction tank.

For example, as for the polycondensation reaction conditions in the case of carrying out in a three-stage reaction vessel, the reaction temperature of the first reaction vessel is 255 to 280 ° C., more preferably 265 to 275 ° C., and the pressure is 100 to 10 torr (13.3). × 10 ^{−3 to} 1.3 × 10 ⁻³ MPa), more preferably 50 to 20 torr (6.67 × 10 ^{−3 to} 2.67 × 10 ⁻³ MPa), and the second reaction tank is a reaction The temperature is 265 to 285 ° C., more preferably 270 to 280 ° C., and the pressure is 20 to 1 torr (2.67 × 10 ^{−3 to} 1.33 × 10 ⁻⁴ MPa), more preferably 10 to ³ torr (1. 33 × 10 ^{−3 to} 4.0 × 10 ⁻⁴ MPa), and the third reaction vessel in the final reaction vessel has a reaction temperature of 270 to 290 ° C., more preferably 275 to 285 ° C., and a pressure of 10-0.1tor ^{(1.33 × 10 -3 ~1.33 × 10} -5 MPa), is a preferred embodiment more preferably ^{5~0.5torr (6.67 × 10 -4 ~6.67 ×} 10 -5 MPa) .

The polycondensate obtained in the polycondensation is formed into small pieces such as pellets.
In the melt polymerization step of the polyester resin obtained as described above, the metal and the phosphorus compound are added to precipitate the nano-sized particles inside the polyester while the transesterification reaction is changed to a pellet shape. At this time, the metal and phosphorus compounds are added simultaneously or individually. However, after the polycondensation, the dispersibility of the nano-sized particles is deteriorated, and breakage at the time of stretching tends to occur.

Mg, Li, Mn, etc. are more preferable because the metal is easy to produce minute nano-sized particles and has good stretchability.
Examples of phosphorus compounds include monoethyl phenylphosphonate, phenylphosphonic acid, monomethyl phenylphosphonate, monopropyl phenylphosphonate, propyl phenylphosphinate, monobenzyl phenylphosphonate, 2-naphthylphosphonic acid, 1-naphthylphosphonic. Acid, 2-anthrylphosphonic acid, phenylphosphinic acid, 1-anthrylphosphonic acid and the like. Of these, phenylphosphonic acid, dimethylphosphonic acid, phosphoric acid, and phosphorous acid are more preferable.
It should be noted that the addition of a metal-containing compound and a phosphorus-containing compound does not necessarily cause the metal-phosphorous particles to be precipitated, and it is preferable to select a combination in which nano-order size metal-phosphorous particles are likely to precipitate. . For example, when “magnesium acetate” and “trimethyl phosphate” are added, no precipitated particles are observed, but when “manganese acetate tetrahydrate” and “phenylphosphonic acid” are added, metal-phosphorous precipitated particles Is observed.

  The polyester resin obtained as described above contains additives such as light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, lubricants (fine particles), nucleating agents (crystallization agents), crystallization inhibitors and the like. Can further be contained.

[Melting extrusion]
The void-containing film of the present invention is formed by melt-extruding a polyester resin (raw material polyester) obtained by melt polymerization as described above and further cooling to form an unstretched polyester film.
The raw material polyester is melt-extruded by, for example, using an extruder equipped with one or two or more screws, heating to a temperature not lower than the melting point of the raw material polyester, and rotating the screw. The raw material polyester is melted into a melt in the extruder by heating and kneading with a screw. Further, from the viewpoint of suppressing thermal decomposition (polyester hydrolysis) in the extruder, it is preferable to perform melt extrusion of the raw material polyester by replacing the inside of the extruder with nitrogen.
The melted raw material polyester (melt) is extruded from an extrusion die through a gear pump, a filter or the like. The extrusion die is also simply referred to as “die”.
At this time, the melt may be extruded as a single layer or may be extruded as a multilayer.

By extruding the melt from the die onto a casting drum (cooling roll), it can be formed into a film (cast process).
The thickness of the film-like molded body obtained by the cast treatment is preferably 0.1 mm to 4 mm, more preferably 0.2 mm to 3.5 mm, and more preferably 0.3 mm to 2.5 mm. Further preferred.
By setting the thickness of the film-like polyester molded body to 4.0 mm or less, cooling delay due to heat accumulation of the melt and cavity size distribution in the thickness direction are avoided, and by setting the thickness to 0.1 mm or more, stretching or winding Wrinkles and breakage during removal can be suppressed.

The means for cooling the melt extruded from the extrusion die is not particularly limited, and it is sufficient to apply cold air to the melt, contact the melt with a cast drum (cooled cast drum), or spray water. Only one cooling means may be performed, or two or more cooling means may be combined.
Among the above, the cooling means is preferably at least one of cooling by cold air and cooling using a cast drum from the viewpoint of preventing oligomer adhesion to the film surface during continuous operation. Further, it is particularly preferable that the melt extruded from the extruder is cooled with cold air and the melt is brought into contact with the cast drum and cooled.

  The molded body cooled using a cast drum or the like is peeled off from a cooling member such as a cast drum using a peeling member such as a peeling roll.

[Stretching]
Stretching is performed by uniaxial stretching of longitudinal stretching or lateral stretching, or longitudinal and transverse biaxial stretching of longitudinal stretching and lateral stretching. Biaxial stretching may be sequential stretching or simultaneous biaxial stretching. In addition, the longitudinal stretching and the lateral stretching at the time of sequential stretching may be independently performed twice or more, and the order of the longitudinal stretching and the lateral stretching is not limited. For example, stretching modes such as longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, transverse stretching → longitudinal stretching can be mentioned. Of these, longitudinal stretching → transverse stretching is preferred.
In the present invention, it is considered that cavities are generated in the stretching process starting from the nano-sized particles of the metal-phosphorus compound deposited inside the film in the polymer melt polymerization process. Cavities starting from such metal-phosphorous particles are likely to be generated by stretching at a high stretching stress in the stretching process, and the size of the cavity can be adjusted by the stretching direction and the stretching ratio.

The longitudinal stretching process of the present invention is a process in which an unstretched polyester film obtained by a melt extrusion process is longitudinally stretched in the longitudinal direction (flow direction) of the film.
The longitudinal stretching of the film can be performed, for example, using two or more pairs of nip rolls arranged in the film transport direction while passing the film through a pair of nip rolls sandwiching the film and transporting the film in the longitudinal direction of the film.

Specifically, for example, when a pair of nip rolls A is installed on the upstream side in the film conveyance direction and a pair of nip rolls B is installed on the downstream side, when the film is conveyed, the rotational speed of the nip roll B on the downstream side is By making it faster than the rotational speed of the nip roll A on the upstream side, the film is stretched in the transport direction (MD).
Two or more pairs of nip rolls may be installed independently on the upstream side and the downstream side, respectively.
Moreover, you may perform the longitudinal stretch of a polyester film using the longitudinal stretch apparatus provided with the said nip roll.

  In addition, as a means to heat at the time of extending | stretching a polyester film, when extending | stretching using rolls, such as a nip roll, the polyester film which touches a roll is provided by providing piping which can flow a heater and a warm solvent inside a roll. Can be heated. Moreover, even when not using a roll, a polyester film can be heated by spraying warm air on a polyester film, making it contact with heat sources, such as a heater, or allowing the vicinity of a heat source to pass through.

In the transverse stretching process of the present invention, the polyester film is stretched by applying tension to the preheating portion for preheating the polyester film, and at least in the direction (TD; Transverse Direction) perpendicular to the longitudinal direction of the polyester film. Conveying the polyester film in this order to the stretching section, the heat fixing section for heating and fixing the tensioned polyester film, and the heat relaxation section for heating and relaxing the heat-fixed polyester film, at least This is a step of transverse stretching.
As long as the polyester film is at least laterally stretched in the above configuration, the means for realizing the lateral stretching step is not limited.
In the transverse stretching step, it is further preferable to cool the polyester film that has passed through the thermal relaxation portion.

The stretching ratio in the longitudinal or lateral stretching step is preferably 3.5 times or more and 6.5 times or less, more preferably 4.5 times or more and 6.2 times or less, and further more preferably 5.2 times or more and 6.0 times or less. preferable. By setting the draw ratio to 3.5 times or more, a highly reflective film can be obtained, and when it is more than 6.5 times, breakage tends to occur.
At the time of biaxial stretching, the product of the draw ratio is preferably 5 to 24 times, more preferably 6 to 22 times. Cavity is likely to occur at 5 times or more. If it is larger than 24 times, breakage tends to occur.

  In the case of uniaxial stretching, the longitudinal or lateral stretching ratio is preferably 3.5 times or more and 6.5 times or less. It is more preferably 4.5 times or more and 6.2 times or less, and further preferably 5.2 times or more and 6.0 times or less.

  The longitudinal stretching temperature is preferably Tg-10 ° C. or higher and Tg + 30 ° C. or lower, and more preferably Tg−5 ° C. or higher and Tg + 25 ° C. or lower, where Tg is the glass transition temperature of the raw material polyester. By being Tg-10 ° C or higher, breakage can be suppressed, and cavities can be generated more uniformly at Tg + 30 ° C or lower. This stretching temperature is a film temperature when stretching is started, that is, when a change in thickness is started, and does not include heat generated by stretching.

In the case of biaxial stretching, the stretching ratio in the first stage is preferably 3.5 times or more and 6.5 times or less. It is more preferably 4.5 times or more and 6.2 times or less, and further preferably 5.2 times or more and 6.0 times or less.
The stretching temperature is preferably Tg-10 ° C or higher and Tg + 30 ° C or lower, more preferably Tg-5 ° C or higher and Tg + 25 ° C or lower. By being Tg-10 ° C or higher, breakage can be suppressed, and cavities can be generated more uniformly at Tg + 30 ° C or lower.
The product of the draw ratio is preferably 5 to 24 times. 6 times or more and 22 times or less are more preferable.

  The stretching temperature after the second stage is preferably Tg-10 ° C or higher and Tg + 100 ° C or lower. Tg ° C. or higher and Tg + 90 ° C. or lower is more preferable, and Tg + 10 ° C. or higher and Tg + 80 ° C. or lower is still more preferable. By setting the temperature to Tg-10 ° C. or higher and Tg + 100 ° C. or lower, uniform stretching can be performed and uneven thickness can be suppressed.

Here, the details of the transverse stretching process will be described in line with the description of the biaxial stretching machine.
FIG. 1 schematically shows an example of the configuration of a biaxial stretching machine. FIG. 1 shows a biaxial stretching machine 100 and a polyester film 200 attached to the biaxial stretching machine 100. The biaxial stretching machine 100 includes a pair of annular rails 60a and 60b, and is arranged symmetrically with the polyester film 200 in between.
The biaxial stretching machine 100 includes a preheating unit 10 that preheats the polyester film 200, a stretching unit 20 that stretches the polyester film 200 in an arrow TD direction that is a direction orthogonal to the arrow MD direction, and applies tension to the polyester film, The heat fixing part 30 that heats the polyester film to which the tension is applied is heated, the heat relaxation part 40 that relaxes the tension of the polyester film that is heat-fixed by heating the heat-fixed polyester film, and the heat relaxation part. And a cooling unit 50 for cooling the polyester film.

The annular rail 60a includes at least gripping members 2a, 2b, 2e, 2f, 2i, and 2j that can move the edge of the annular rail 60a. The annular rail 60b is a gripping member 2c that can move the edge of the annular rail 60b. 2d, 2g, 2h, 2k, and 2l. The gripping members 2a, 2b, 2e, 2f, 2i, and 2j grip one end of the polyester film 200 in the TD direction, and the gripping members 2c, 2d, 2g, 2h, 2k, and 2l are polyesters The other end of the film 200 in the TD direction is gripped. The holding members 2a to 2l are generally referred to as chucks, clips, and the like.
The gripping members 2a, 2b, 2e, 2f, 2i, and 2j move counterclockwise along the edge of the annular rail 60a, and the gripping members 2c, 2d, 2g, 2h, 2k, and 2l are annular It moves clockwise along the edge of the rail 60b.

The holding members 2a to 2d hold the end portion of the polyester film 200 in the preheating unit 10 and move the edge of the annular rail 60a or 60b as it is, and the thermal relaxation unit in which the extending unit 20 and the holding members 2e to 2h are shown. After 40, the process proceeds to the cooling unit 50 where the gripping members 2i to 2l are shown. Thereafter, the gripping members 2a and 2b and the gripping members 2c and 2d are separated from the end of the polyester film 200 at the end of the cooling unit 50 on the downstream side in the MD direction in the conveying direction, and the annular rail 60a or 60b is left as it is. It advances along an edge and returns to the preheating part 10.
As a result, the polyester film 200 moves in the direction of the arrow MD in FIG. 1 and is sequentially conveyed to the preheating unit 10, the stretching unit 20, the heat fixing unit 30, the heat relaxation unit 40, and the cooling unit 50. .
The moving speed of the gripping members 2a to 2l is the transport speed at the gripping portion of the polyester film 200.

The gripping members 2a to 2l can change the moving speeds independently.
Accordingly, the biaxial stretching machine 100 enables lateral stretching in which the polyester film 200 is stretched in the TD direction in the stretching unit 20, but the polyester film can be changed by changing the moving speed of the gripping members 2a to 2l. 200 can also be stretched in the MD direction.
That is, simultaneous biaxial stretching can be performed using the biaxial stretching machine 100.

In FIG. 1, only twelve gripping members 2a to 2l are shown as gripping members for gripping the end portion of the polyester film 200 in the TD direction. However, in order to support the polyester film 200, the biaxial stretching machine 100 is In addition to 2l, it has a gripping member (not shown).
Hereinafter, the gripping members 2a to 2l may be collectively referred to as “grip member 2”.

(Preheating part)
In the preheating part 10, the polyester film 200 is preheated. Before the polyester film 200 is stretched, it is preheated to facilitate the lateral stretching of the polyester film 200.
The film surface temperature at the end point of the preheating part (hereinafter also referred to as “preheating temperature”) is preferably Tg−10 ° C. to Tg + 60 ° C., where Tg is the glass transition temperature of the polyester film 200, and Tg ° C. to Tg + 50. More preferably, it is ° C. The end point of the preheating portion refers to the time when the preheating of the polyester film 200 is finished, that is, the position where the polyester film 200 is separated from the region of the preheating portion 10.

(Extension part)
In the stretching unit 20, the preheated polyester film 200 is laterally stretched at least in the direction (TD) perpendicular to the longitudinal direction (conveying direction, MD) of the polyester film 200 to give tension to the polyester film 200.
Stretching (transverse stretching) in the direction (TD) perpendicular to the longitudinal direction (conveying direction, MD) of the polyester film 200 is perpendicular to the longitudinal direction (conveying direction, MD) of the polyester film 200 (90) as described above. Is intended to be stretched in the direction of the angle (°), but may be in the direction of a range of mechanical errors. The range of the mechanical error is a direction at an angle (90 ° ± 5 °) that can be regarded as perpendicular to the longitudinal direction (conveying direction, MD) of the polyester.

In the stretched portion 20, the tension (stretching tension) for lateral stretching applied to the polyester film 200 is 0.1 t / m to 6.0 t / m.
Further, the area stretch ratio (product of each stretch ratio) of the polyester film 200 is preferably 5 to 24 times the area of the polyester film 200 before stretching, and more preferably 6 to 22 times.
Moreover, the film surface temperature at the time of lateral stretching of the polyester film 200 (hereinafter also referred to as “lateral stretching temperature”) is Tg−10 ° C. or higher and Tg + 100 ° C. or lower when the glass transition temperature of the polyester film 200 is Tg. More preferably, it is Tg ° C. or more and Tg + 90 ° C. or less, and further preferably Tg + 10 ° C. or more and Tg + 80 ° C. or less.

As described above, the gripping members 2 (grip members 2a to 2l) can independently change the moving speed. For example, the extending portion 20, the moving speed of the gripping member 2 in the preheating unit 10 can be changed. By increasing the moving speed of the gripping member 2 on the downstream side in the MD 20 MD direction such as the heat fixing unit 30, it is also possible to perform longitudinal stretching for stretching the polyester film 200 in the transport direction (MD).
The longitudinal stretching of the polyester film 200 in the transverse stretching step may be performed only by the stretching unit 20, or may be performed by the heat fixing unit 30, the heat relaxation unit 40, or the cooling unit 50 described later. You may longitudinally stretch in several places.

(Heat fixing part)
In the heat fixing part 30, the polyester film 200 to which tension is applied is heated and heat fixed. At this time, it is preferable to heat the polyester film 200 so that the highest surface temperature of the polyester film 200 is 90 ° C to 230 ° C, more preferably 100 ° C to 220 ° C, and still more preferably 120 ° C to 215 ° C.
Heat setting refers to heating at a specific temperature while applying tension to the polyester film 200 in the stretched portion 20, and in the present invention, the maximum surface temperature of the polyester film 200 is 90 ° C to 230 ° C. It is preferable to heat so that.
Heating the polyester film 200 to which the tension is applied so that the highest surface temperature of the surface becomes 90 ° C. to 230 ° C., thereby reducing the heat shrinkage rate when heat is applied while maintaining the cavity. Can do.

When the maximum film surface temperature of the surface of the polyester film 200 at the time of heat setting (hereinafter also referred to as “ _heat setting temperature” or “T _heat setting”) is 90 ° C. or more, the polyester molecules can be moderately relaxed, It can suppress that it aligns too lamellarly. Further, when the heat setting temperature is 230 ° C. or lower, the polyester molecules can be restrained from being extremely relaxed, and the polyester molecules can be fixed in a relatively stretched state, and the cavity can be maintained.

(Heat relaxation part)
In the thermal relaxation part 40, the polyester film 200 is heated and the tension | tensile_strength given to the polyester film 200 is loosened.
Heating is preferably performed so that the maximum film surface temperature on the surface of the polyester film 200 is 100 ° C. or higher and not higher than the maximum film surface temperature (T _heat setting) of the polyester film 200 in the heat fixing unit 30.
Hereinafter, the highest reached film surface temperature of the surface of the polyester film 200 during _{thermal relaxation} is also referred to as “thermal relaxation temperature” (T _{thermal relaxation} ).
In the thermal relaxation part 40, the thermal relaxation temperature (T _{thermal relaxation} ) is heated at a temperature not lower than 100 ° C. and not higher than the heat fixing temperature (T _{heat fixing} ) (100 ° C. ≦ T _{heat relaxation} ≦ T _{heat fixing} [° C.]). By making (drawing tension small), it can suppress that the polyester base material surface of a polyester film destroys, or the layer adjacent to a polyester base material peels from a polyester base material.

(Cooling section)
In the cooling part 50, the polyester film 200 which passed through the heat relaxation part 40 is cooled.
By cooling the polyester film 200 heated by the heat fixing unit 30 or the heat relaxation unit 40, the shape of the polyester film 200 can be fixed.
The film surface temperature (hereinafter also referred to as “cooling temperature”) of the cooling part outlet of the polyester 200 in the cooling part 50 is preferably lower than the glass transition temperature Tg + 50 ° C. of the polyester film 200. Specifically, it is preferably 25 ° C to 110 ° C, more preferably 25 ° C to 95 ° C, and further preferably 25 ° C to 80 ° C.
By being in the above range, it is possible to prevent the film from shrinking unevenly after releasing the clip.
Here, the cooling unit outlet refers to an end portion of the cooling unit 50 when the polyester 200 is separated from the cooling unit 50, and the gripping member 2 (the gripping members 2j and 2l in FIG. 1) grips the polyester film 200. The position when releasing the polyester film 200 is said.

  In addition, as the temperature control means for heating or cooling the polyester film 200 in preheating, stretching, heat setting, thermal relaxation, and cooling in the transverse stretching step, hot or cold air is blown on the polyester film 200, or the polyester film For example, 200 may be brought into contact with the surface of a metal plate whose temperature can be controlled, or the vicinity of the metal plate may be passed.

  Through the above steps, the void-containing polyester film according to the present invention, that is, the polymer and particles containing metal and phosphorus, the average length in the longitudinal direction (Lma) and the length in the plan view of the voids present in the film The average length (Lta) in the direction orthogonal to the direction satisfies 2 μm ≦ Lma ≦ 1000 μm and 2 μm ≦ Lta ≦ 500 μm, respectively, and is along one of the longitudinal direction and the direction orthogonal to the longitudinal direction In addition, the average value (Ra) when the reflectance (R) with respect to light having a wavelength of 550 nm was measured at 10 locations was 60% or more and 100% or less, and all of the reflectances were 0.85Ra ≦ R ≦ 1.15Ra. A void-containing polyester film that satisfies the above can be obtained.

<Back sheet for solar cell>
The solar cell backsheet of the present invention comprises the above-described void-containing film of the present invention.
The void-containing film of the present invention is a back surface protection sheet disposed on the back surface opposite to the sunlight incident side of the solar cell power generation module because the reflectance is high and the variation in reflectance on the film surface is small. It is suitable for use as a solar cell backsheet.

<Solar cell module>
The solar cell module of the present invention includes a transparent substrate on which sunlight is incident, a solar cell element, and the solar cell backsheet of the present invention.
In the application of the solar cell power generation module, the power generation element (solar cell element) connected by the lead wiring for taking out electricity is sealed with a sealing agent such as ethylene / vinyl acetate copolymer system (EVA system) resin, The aspect comprised by sticking together between transparent substrates, such as glass, and the polyester film (back sheet | seat) of this invention is mentioned. Examples of solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, and copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenic, and other III- Various known solar cell elements such as V group and II-VI compound semiconductor systems can be applied.

<Electronic device>
The electronic device of the present invention includes the above-described void-containing film of the present invention. Since the void-containing film of the present invention has a high reflectance and a small variation in reflectance on the film surface, it can be suitably applied, for example, as a reflector. Therefore, for example, it is possible to provide an electronic device including the void-containing film of the present invention, such as a liquid crystal display device having the void-containing film of the present invention as a reflector of a liquid crystal monitor and having excellent visibility.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. “Parts” and “%” are based on mass unless otherwise specified.

<Example 1>
(Synthesis of raw material polyester 1)
As shown below, by directly reacting terephthalic acid and ethylene glycol to distill off water, esterify, and then use a direct esterification method in which polycondensation is performed under reduced pressure, polyester (Ti catalyst) by a continuous polymerization apparatus. System PET) was obtained.

(1) Esterification reaction In a first esterification reaction tank, 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed for 90 minutes to form a slurry, and 3800 kg / manganese together with manganese acetate tetrahydrate. The flow rate of h was continuously supplied to the first esterification reaction tank. Further, an ethylene glycol solution of a citric acid chelate titanium complex (VERTEC AC-420, manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal is continuously supplied, and the average residence time is maintained at 250 ° C. in the reaction vessel with stirring. The reaction was carried out for about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. At this time, the acid value of the obtained oligomer was 600 equivalent / ton.

  This reaction product was transferred to a second esterification reaction vessel, and reacted under stirring at a reaction vessel temperature of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 200 equivalents / ton. The inside of the second esterification reaction tank is partitioned into three zones, and an ethylene glycol solution of magnesium acetate is continuously supplied from the second zone so that the amount of Mg added is 75 ppm in terms of element, From the third zone, 0.05 part of phenylphosphonic acid was added, and then an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the added amount of P was 65 ppm in terms of element.

(2) the polycondensation reaction above-obtained esterification reaction product supplied to the first polycondensation reaction vessel continuously stirring, the reaction temperature 270 ° C., the reaction vessel pressure 20 torr (2.67 × 10 ^{- 3} MPa) and polycondensation with an average residence time of about 1.8 hours.

Further, it was transferred to the second double condensation reaction tank, and while stirring in this reaction tank, the reaction tank temperature was 276 ° C., the reaction tank pressure was 5 torr (6.67 × 10 ⁻⁴ MPa), and the residence time was about 1.2 hours. The reaction (polycondensation) was performed under the conditions.

Subsequently, it was further transferred to the third triple condensation reaction tank. In this reaction tank, the reaction tank temperature was 278 ° C., the reaction tank internal pressure was 1.5 torr (2.0 × 10 ⁻⁴ MPa), and the residence time was 1.5 hours. The reaction product (polycondensation) was obtained under the following conditions to obtain a reaction product (polyethylene terephthalate (PET)).

  Next, the obtained reaction product was discharged into cold water in a strand shape and immediately cut to prepare polyester pellets (cross section: major axis: about 4 mm, minor axis: about 2 mm, length: about 3 mm).

  About the obtained polyester (raw material polyester 1), as a result of using high resolution type high frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology), Ti = 9 ppm, Mg = 75 ppm, P = 60 ppm. P is slightly reduced with respect to the initial addition amount, but is estimated to have volatilized during the polymerization process.

The obtained polymer (raw polyester 1) has an intrinsic viscosity IV = 0.65, a terminal carboxyl group concentration AV = 22 equivalent / ton, a melting point = 257 ° C., a solution haze = 0.3%, and a glass transition temperature Tg = It was 73 ° C.
The intrinsic viscosity and the terminal carboxy group concentration were determined as follows.

Intrinsic viscosity (IV)
The intrinsic viscosity (IV) of the polyester is a specific viscosity (η _sp = η _r −1) obtained by subtracting 1 from the ratio η _r (= η / η ₀ ; relative viscosity) of the solution viscosity (η) and the solvent viscosity (η ₀ ). ) Divided by the density is extrapolated to a density zero state. The IV of the polyester is obtained from a solution viscosity at 25 ° C. by dissolving the polyester in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent using an Ubbelohde viscometer. It was.

Terminal carboxy group concentration (AV)
The terminal carboxyl group concentration (AV) of the polyester was determined by dissolving the polyester completely in a mixed solution of benzyl alcohol / chloroform (= 2/3; volume ratio), using phenol red as an indicator, and using this as a standard solution (0.01 N KOH). -Benzyl alcohol mixed solution) and calculated from the titer.

-Film forming process-
The raw material polyester 1 (PET1) was dried to a moisture content of 20 ppm or less and then charged into a hopper of a single-screw kneading extruder having a diameter of 50 mm. The raw material polyester 1 was melted at 300 ° C. and extruded from a die through a gear pump and a filter (pore diameter: 20 μm) under the following extrusion conditions. In addition, the dimension of the slit of die | dye was adjusted so that the thickness of a polyester sheet might be 4 mm. The thickness of the polyester sheet was measured by an automatic thickness meter installed at the exit of the cast drum.

The molten resin was extruded from the die under the conditions that the pressure fluctuation was 1% and the temperature distribution of the molten resin was 2%. Specifically, the back pressure was increased by 1% with respect to the average pressure in the barrel of the extruder, and the piping temperature of the extruder was heated at a temperature 2% higher than the average temperature in the barrel of the extruder.
The molten resin extruded from the die was extruded onto a cooling cast drum and adhered to the cooling cast drum using an electrostatic application method.

  For cooling the molten resin, the temperature of the cooling cast drum was set to 25 ° C., and cold air of 25 ° C. was blown from a cold air generator installed facing the cooling cast drum and applied to the molten resin. The unstretched polyester film (unstretched polyester film 1) was peeled off from the cooling cast drum using the peeling roll disposed opposite to the cooling cast drum.

  The obtained unstretched polyester film 1 had an intrinsic viscosity IV = 0.72, a terminal carboxyl group concentration AV = 15 equivalent / ton, a glass transition temperature Tg = 73 ° C., and a thickness of 1.2 mm. Tg was determined by measurement according to JIS K7121.

-Manufacture of Axial Stretched Polyester Film-
The obtained unstretched polyester film 1 was sequentially biaxially stretched by the following method and stretched as follows to obtain a biaxially stretched polyester film 1 having a thickness of 80 μm.

-Longitudinal stretching process-
The unstretched polyester film 1 was passed between two pairs of nip rolls having different peripheral speeds and stretched 5.5 times in the longitudinal direction (conveying direction).

-Transverse stretching process-
The stretched polyester film 1 (longitudinal stretched polyester film 1) was stretched 3.2 times using a tenter (biaxial stretching machine) having the structure shown in FIG.
Thereafter, heat setting was performed at 200 ° C., heat relaxation was performed at 180 ° C., and cooling was performed to 65 ° C. As a result, a biaxially stretched polyester film 1 was obtained.

<Measurement of evaluation items>
(1) Confirmation of presence / absence of particles The biaxially stretched film 1 produced as described above was observed with a transmission electron microscope to confirm the presence / absence of particles inside the film.

(2) Presence / absence of cavities and cavity size / cavity ratio The presence or absence of cavities was confirmed from a cross-sectional image in the in-plane direction of the biaxially stretched film 1 with a Hitachi scanning electron microscope. Moreover, the size of the cavity in the width direction (lateral direction) and the flow direction (longitudinal direction) during film stretching was calculated from the obtained image.
Further, the void ratio (%) was calculated from the area ratio of the cavity portion in the image and the area ratio of the polymer portion by the following formula.
Cavity (%) = Cavity area / (Cavity area + Polymer area) × 100

(3) Reflectance Samples were cut into 50 mm × 50 mm, and the reflectance at 550 nm was measured with a spectrophotometer manufactured by Shimadzu Corporation. The reflectance was measured at 10 points in the width direction (lateral direction) during film stretching, and the minimum value, maximum value, and average value Ra were determined.

The uniformity of the reflectance R was evaluated according to the following criteria.
A: All the reflectances R satisfy 0.90Ra ≦ R ≦ 1.10Ra.
B: All the reflectances R satisfy 0.85Ra ≦ R ≦ 1.15Ra.
C: There is a portion where the reflectance R does not satisfy 0.85Ra ≦ R ≦ 1.15Ra.

Further, the reflectance was comprehensively evaluated as A when both of the following (I) and (II) were satisfied, and as B when neither was satisfied.
(I) The average value Ra of the reflectance R is 60% or more and 100% or less. (II) All the reflectances R are 0.85 Ra ≦ R ≦ 1.15 Ra.

(4) Apparent specific gravity A sample was cut into 100 mm x 50 mm and measured with an automatic specific gravity measuring device manufactured by Kanto Major Co., Ltd. (ASG-320K).

(5) Film forming property The film forming property was evaluated according to the following criteria.
A: No film breakage B: Film breakage occurred

<Examples 2 to 29 and Comparative Example 1-7>
A stretched polyester film was produced in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.
In Examples 23-26, only longitudinal stretching was performed, and in Examples 27-28, only uniaxial stretching was performed.

  Table 1 shows the presence / absence of nano-sized particles and cavities in the films produced in each Example and Comparative Example, film forming conditions, and Table 2 shows the results of reflectance, apparent specific gravity, cavity size, void ratio, and film forming property. Show.

  From Table 2, the void-containing films of the examples had a high average reflectance Ra of 70% or more and a small variation in reflectance.

2 Gripping member
DESCRIPTION OF SYMBOLS 10 Preheating part 20 Extending part 30 Heat fixing part 40 Thermal relaxation part 50 Cooling part 60 Annular rail 100 Biaxial stretching machine 200 Polyester sheet

Claims (9)

Comprising a polymer and particles comprising metal and phosphorus;
The average length (Lma) in the longitudinal direction and the average length (Lta) in the direction perpendicular to the longitudinal direction in plan view of the cavities existing in the film are 2 μm ≦ Lma ≦ 1000 μm and 2 μm ≦ Lta ≦, respectively. Satisfies 500 μm, and
The average value (Ra) when measuring the reflectance (R) with respect to light having a wavelength of 550 nm at 10 locations along any one of the longitudinal direction and the direction orthogonal to the longitudinal direction is 60% or more and 100% or less. And all of the reflectances satisfy 0.85Ra ≦ R ≦ 1.15Ra,
Cavity-containing film. Void containing film according to claim 1 apparent specific gravity of ^{0.7g / cm 3 ~1.2g / cm 3} . The polyester void-containing film according to claim 1 or 2, wherein a void ratio represented by the following formula is 5% or more and 60% or less.
Cavity (%) = Cavity area / (Cavity area + Polymer area) × 100   The void-containing film according to any one of claims 1 to 3, wherein the particles containing metal and phosphorus are particles that are internally precipitated during the melt polymerization of the polymer.   The void-containing film according to any one of claims 1 to 4, comprising polyester as the polymer.   All the said reflectances satisfy | fill 0.85Ra <= R <= 1.15Ra, The cavity containing film as described in any one of Claims 1-5.   The solar cell backsheet containing the cavity containing film of any one of Claims 1-6.   The solar cell module provided with the transparent board | substrate with which sunlight injects, a solar cell element, and the solar cell backsheet of Claim 7.   The electronic device provided with the cavity containing film of any one of Claims 1-6.