JP2013231195A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film having low melt resistivity and high clarity.SOLUTION: A polyester film is produced using a polyester resin obtained by adding a polycondensation catalyst, a magnesium compound, a potassium compound, and a phosphorus compound. The polyester film has melt resistivity at 275°C of 0.15-0.30×10Ωcm and satisfies the following conditions (1) to (3): (1) a content of Mg is 15-35 ppm based on the polyester film; (2) a content of K is 5-20 ppm based on the polyester film; and (3) a content of P is 5-15 ppm based on the polyester film.

Description

  The present invention relates to a polyester film. Specifically, it relates to a polyester film having good electrostatic adhesion and a high degree of clarity.

  Polyester films are widely used as base materials for various optical functional films from the viewpoint of excellent transparency, dimensional stability, and chemical resistance. In recent years, polyester films having weather resistance have been frequently used as back sheets for solar cell panels.

  Usually, a polyester film is obtained by biaxial stretching after melt extrusion of polyester. That is, the sheet-like material melt-extruded by the extruder is brought into close contact with the surface of the rotating cooling drum and then taken, and then the sheet-like material is guided to a drawing roll disposed at the subsequent stage of the cooling drum, and longitudinally drawn. Furthermore, after transverse stretching with a tenter, heat setting treatment (heat setting) is performed. Here, in order to increase the uniformity of the thickness of the film and increase the casting speed, when the sheet-like material melt-extruded from the extrusion die is cooled on the surface of the rotary cooling drum, the sheet-like material and the drum surface Must be in close contact with sufficiently high adhesion. For this reason, as a method for increasing the adhesion between the sheet-like material and the surface of the rotating drum, a wire-like electrode is provided between the extrusion die and the cooling rotating drum, and a high voltage is applied to the unsolidified sheet. A so-called electrostatic contact casting method is often used in which static electricity is deposited on the surface of an object, and the sheet-like object is electrostatically attached to the surface of a cooling drum and rapidly cooled. That is, by electrostatically adhering a sheet-like object to the cooling drum, the sheet-like object adheres to the surface of the drum with high adhesion without forming a gap between the surface and the rotation speed of the cooling rotating drum is increased. Even if the speed is increased, the sheet-like material is taken out without being displaced and uniformly cast, and a film having excellent thickness uniformity is efficiently manufactured. In recent years, the electrostatic adhesion has been demanded even in the production of a relatively thick film having a thickness of 50 μm or more for cost reduction.

  In the electrostatic adhesion casting method, it is effective to increase the amount of charge on the surface of the sheet-like material in order to improve the electrostatic adhesion of the sheet-like material to the cooling drum. It is known that it is effective to modify the resulting polyester (hereinafter referred to as raw material polyester) to lower its melt specific resistance. As a method of reducing the melt specific resistance, an alkali metal and / or alkaline earth metal compound is converted into a phosphorus compound during the esterification or transesterification reaction or after the completion of the reaction and before the polycondensation reaction in the raw material polyester production stage. Addition is performed together (see, for example, Patent Documents 1 and 2).

  However, although Patent Documents 1 and 2 are improved in terms of lowering the melt specific resistance, foreign substances formed by aggregation of alkali metal and / or alkaline earth metal compound and phosphorus compound added to the polyester are likely to occur. There was a trend. Therefore, in terms of suppressing foreign matter in the polymer, it is not sufficient depending on the application, and it is necessary to reduce the pore size of the filter after synthesizing the polyester or after the melting / extrusion process, resulting in decreased productivity and increased cost. It was.

  In particular, in an optical film, it is necessary to reduce the amount of foreign matter in the film and minimize defects such as fish eyes. That is, clarity is required for the polyester film. Therefore, a high degree of clarity is required for the raw material polyester, and measures are taken to increase the clarity (Patent Document 3). However, in recent years, full-high-definition displays have become mainstream for displays exceeding 40 inches, and higher definition is being advanced. Therefore, it is expected that the demand for higher clarity of polyester film will increase further in the future.

  Furthermore, high moisture-proof properties are required for solar cell backsheets (Patent Document 4). However, if protrusions due to foreign matters are present on the polyester film used for the backsheet, scratches and dents are generated in the metal thin film layer and the highly durable moisture-proof layer, which are the water vapor barrier layers to be laminated. For this reason, when a polyester film having many protrusions is used in a backsheet that has a locally reduced moisture resistance and requires a high level of moisture resistance, the deterioration of the solar cell element due to the occasional decrease in moisture resistance is slight. Even in use exceeding 10 years, the life of the solar cell may be greatly affected.

JP-A-4-345617 JP 2006-249213 A JP 2003-341000 A JP 2007-70430 A

  In view of the above circumstances, an object of the present invention is to provide a polyester film that has good electrostatic adhesion, has a very small amount of foreign matter, and has a higher degree of clarity than before.

  As a result of intensive research to achieve the above object, the present inventor uses a magnesium compound as a resistance adjusting agent (low resistance agent) in addition to a polycondensation catalyst in order to achieve good electrostatic adhesion. In addition, a polyester film having a sufficiently low melting specific resistance and a very small amount of insoluble foreign matter in the film can be obtained by adding and using a predetermined amount of three types of compounds of potassium compound and phosphorus compound. It was found that it can be obtained. Furthermore, the inventors have found that the method of adding a resistance modifier greatly affects the performance of the polyester film, and completed the present invention.

The present invention is characterized by the following configuration.
1st invention of this application is a polyester film containing a polycondensation catalyst, a magnesium compound, a potassium compound, and a phosphorus compound, Comprising: The melt specific resistance in 275 degreeC of the said polyester film is 0.15-0.30 * 10 < ⁸ >. Further, the polyester film satisfies the following conditions (1) to (3).
(1) Mg content: 15 to 35 ppm with respect to the polyester film
(2) K content: 5 to 20 ppm relative to the polyester film
(3) P content: 5 to 15 ppm relative to the polyester film
2nd invention of this application is the said polyester film whose main repeating unit is ethylene terephthalate and whose main phosphorus compound is diethylphosphono ethyl acetate.
A third invention of the present invention is a laminated polyester film having an adhesive modification layer on at least one surface of the polyester film.
A third invention of the present application is an optical polyester film comprising the laminated polyester film.
4th invention of this application is the polyester film for solar cells which consists of the said polyester film.

  According to the present invention, a polyester film having a low melt specific resistance and a high clarity can be obtained. Furthermore, the polyester film of the present invention has high heat resistance while having a low melt specific resistance. for that reason. It can be suitably used as an optical polyester film that requires a high degree of clarity, or a polyester film for solar cells with little protrusion generation due to foreign matter.

  In the following description of the present specification, the “esterification reaction” means a reaction that forms a dicarboxylic acid-glycol diester and / or an oligomer thereof, and unless otherwise specified, is not limited to a direct esterification reaction, This concept includes exchange reactions. Further, “esterification reaction can” means a reaction can in which such “esterification reaction” is mainly performed.

The melt specific resistance (specific resistance value Si (Ω · cm)) at 275 ° C. of the polyester film is used as an index of electrostatic adhesion when the polyester film is formed by the electrostatic adhesion casting method. In the range of 0.15 to 0.30 × 10 ⁸ Ω · cm, good electrostatic adhesion can be obtained, and a film having excellent thickness uniformity can be stably formed. When the melt specific resistance is less than 0.15 × 10 ⁸ Ω · cm, such a polyester composition generally has an excessive amount of resistance adjusting agent (low resistance agent) and a large amount of insoluble foreign matter is present. High clarity cannot be obtained. On the other hand, when it exceeds 0.30 × 10 ⁸ Ω · cm, static electricity is not sufficiently deposited on the surface of the sheet (film), and good electrostatic adhesion cannot be obtained. Since air bubbles are trapped between the sheet and a defect (abbreviated as pinner bubble) due to local deformation that can be easily visually recognized (size of 3 mm or more) is likely to occur. Failures such as the need to decrease occur. The lower limit of the melting specific resistance is more preferably 0.16 × 10 ⁸ Ω · cm or more, and further preferably 0.17 × 10 ⁸ Ω · cm or more. Moreover, the upper limit of the melting specific resistance is more preferably 0.28 × 10 ⁸ Ω · cm or less, and further preferably 0.26 × 10 ⁸ Ω · cm or less.

  The clarity of the polyester film can be evaluated also by observing coarse particles (particles of 5 μm or more) contained in the polyester film with a microscope. That is, in this method, a pulverized polyester film is sandwiched between two cover glasses, melt-pressed at 280 ° C., rapidly cooled, then observed in 20 fields of view with a 100 × phase contrast microscope, and 5 μm or more using an image analyzer. This is a method of counting and evaluating the number of coarse particles. If the total number of coarse particles of 5 μm or more measured by this method is 15 or less, such a polyester film is insoluble foreign matter (coarse particles) such as magnesium salt (Mg salt) or potassium salt (K salt). There are few metallized polycondensation catalysts, etc., and it has a high degree of clarity. Therefore, it can be suitably used in applications where high transparency is required as an optical film, and in applications where high flatness is required as a film for solar cells. On the other hand, when the total number of particles of 5 μm or more exceeds 15, such a polyester film does not have a high degree of clarity. The upper limit of the number of coarse particles per 20 fields of view is more preferably 10 or less, still more preferably 8 or less, and still more preferably 5 or less.

  The polyester polycondensation catalyst used in the polycondensation of the polyester composition used in the present invention can be selected from antimony compounds, aluminum compounds, titanium compounds, and germanium compounds. Further, the polycondensation catalyst may be one kind or a combination of two or more kinds of catalysts.

  The polyester composition used for the polyester film of the present invention is produced by adding a magnesium compound, a potassium compound and a phosphorus compound to the same reaction vessel in addition to the polycondensation catalyst. Details thereof will be described later. In the following, a case where an antimony compound is used as the polycondensation catalyst will be described as an example, but the present invention is not limited to this.

  The polyester film of the present invention is preferably composed of ethylene terephthalate as the main ester unit (repeating unit) from the viewpoint of having a desired high degree of clarity, and specifically, preferably all ester units (repeating units). Is preferably 80 mol% or more, more preferably 90 to 97 mol% of ethylene terephthalate. As the copolymerization component, as the dicarboxylic acid component, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and dimer acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid; And aromatic dicarboxylic acids such as acid, naphthalenedicarboxylic acid, and 4,4′-biphenyldicarboxylic acid. In addition, as glycol components, aliphatic glycols such as diethylene glycol, triethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, pentamethylene glycol, hexamethylene glycol; 1,4-cyclohexanedimethanol, 1,3- Examples include alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as p-xylylene glycol and m-xylylene glycol. In order to suppress the crystallization rate, in addition to diethylene glycol (1 to 2 mol% to ethylene glycol) by-produced in the reaction, 1 to 4 mol% (ethylene glycol) of diethylene glycol may be added. As a component, it is preferable that it is the said range. Moreover, in any of the dicarboxylic acid component and the glycol component, any one of them may be used alone, or two or more of them may be used in combination at any ratio.

  When using an antimony compound as a polycondensation catalyst for the polyester composition used in the polyester film of the present invention, for example, antimony trioxide, antimony pentoxide, antimony acetate, antimony glycoxide, etc. may be mentioned, and any one of these may be used. May be used alone or in combination of two or more. Antimony trioxide is particularly preferable.

  The antimony compound is preferably added in an amount such that the content of antimony atoms with respect to the amount of the polyester composition substance finally obtained is 100 to 200 ppm. If it is less than 100 ppm, the polymerization productivity is lowered, and conversely, 200 ppm is reduced. When it exceeds, it becomes easy to produce an insoluble foreign material. A more preferable content of antimony atoms is 130 to 170 ppm.

  In the present invention, a magnesium compound is used as a resistance adjuster. Examples of the magnesium compound used in the present invention include lower fatty acid salts such as magnesium acetate, alkoxides such as magnesium methoxide, etc., and these may be used alone or in combination of two kinds. You may use the above together. Magnesium acetate is particularly preferable.

  The said magnesium compound needs to add the quantity from which the content of magnesium atom with respect to the polyester film mass finally obtained will be 15-35 ppm. When the content of magnesium atoms is less than 15 ppm, such a polyester film does not sufficiently lower the melt specific resistance, and it is difficult to obtain sufficient electrostatic adhesion during film formation. Conversely, when it exceeds 35 ppm, Such a polyester film increases the amount of insoluble foreign matter (Mg salt) produced. Moreover, when a magnesium compound exists in polyester, the decomposition reaction of polyester is easily promoted. Therefore, if the content of magnesium atoms exceeds 35 ppm, the heat resistance may be lowered, and the film may be severely colored, which may not be preferable. A more preferable magnesium atom content is 20 to 30 ppm.

  In the present invention, a potassium compound is used as a resistance adjusting agent. Conventionally, a commonly used sodium compound has been used as the alkali metal compound. In the present invention, while using a potassium compound at a specific composition ratio, the content of the magnesium compound is within the above range. Thus, a low melting specific resistance has been realized. I'm not sure why this effect is produced by using a potassium compound, but the inclusion of a specific metal ion species at a specific concentration ratio may form a more stable complex state in the polyester. thinking.

  Examples of the potassium compound used in the present invention include lower fatty acid salts such as potassium acetate, alkoxides such as potassium methoxide, etc., and these may be used alone or in combination of two kinds. You may use the above together. In particular, potassium acetate is preferred.

The potassium compound needs to be added in such an amount that the content of potassium atoms is 5 to 20 ppm relative to the amount of the polyester film substance finally obtained. When the content of potassium atoms is less than 5 ppm, such a polyester composition does not sufficiently reduce the melt specific resistance, and it is difficult to obtain sufficient electrostatic adhesion during film formation. Conversely, when the content exceeds 20 ppm. Such a polyester composition is not preferable because the amount of insoluble foreign matter (K salt) is increased, and the heat resistance is lowered, and the film is severely colored. A more preferable potassium atom content is 7 to 15 ppm.

  Examples of the phosphorus compound used in the present invention include phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples include phosphoric acid, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, Monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphorous acid, trimethyl phosphite, tributyl phosphite, methylphosphonic acid, dimethyl methylphosphonate, dimethyl ethylphosphonate, ethyl diethylphosphonoacetate, phenylphosphone Examples include dimethyl acid, phenyl phosphonate diethyl, and phenyl phosphonate diphenyl. Any of these may be used alone or in combination of two or more. Of these, ethyl diethylphosphonoacetate, trimethyl phosphate and phosphoric acid are preferred, and ethyl diethylphosphonoacetate is particularly preferred because of its difficulty in scattering and ease of lowering the melt resistivity.

  In the present invention, it is preferable to add ethyl diethylphosphonoacetate as the main phosphorus compound. In this case, ethyl diethylphosphonoacetate is preferably 70 mol% or more of the total phosphorus compound, and 90 mol% or more. More preferably, it is more preferably 100 mol%.

The phosphorus compound needs to be added in an amount such that the content of phosphorus atoms with respect to the mass of the finally obtained polyester film is 5 to 15 ppm. If the content is less than 5 ppm, the heat resistance of such a polyester film is lowered. On the other hand, if it exceeds 15 ppm, the decrease in melting specific resistance is insufficient, and the amount of insoluble foreign matter (Mg salt and K salt) generated is undesirably increased. A more preferable phosphorus atom content is 7 to 12 ppm.
Yes.

  In order to improve the effect of reducing the amount of insoluble foreign matter (Mg salt and K salt) generated, the content of magnesium atoms, the content of potassium atoms, and the content of phosphorus atoms with respect to the mass of the finally obtained polyester film The total amount is preferably 60 ppm or less, and more preferably 50 ppm or less.

  The range of preferable intrinsic viscosity when the polyester film of the present invention is used for an optical film is 0.580 to 0.650 dl / g from the viewpoints of physical properties and productivity. It is also preferable to use a polyester having a high molecular weight by solid phase polymerization or a low acid value polyester. When the polyester is made to have a high molecular weight by solid phase polymerization, the intrinsic viscosity is preferably 0.65 to 0.80 dl / g in order to obtain high heat resistance and hydrolysis resistance, and more preferably 0.70. ~ 0.75 dl / g. The intrinsic viscosity of polyester can be measured by dissolving polyester in a mixed solvent of parachlorophenol (6 parts by mass) and 1,1,2,2-tetrachloroethane (4 parts by mass) at 30 ° C. it can. Moreover, the preferable acid value of the polyester film of this invention is 25 eq / ton or less.

The polyester composition used for the polyester film of the present invention can be produced by using the polycondensation catalyst and adding a magnesium compound, a potassium compound and a phosphorus compound. In order for these metal ions to exist in a stable state in the polyester, the method of adding these three types of compounds is also important. When the magnesium atom content, the potassium atom content, and the phosphorus atom content are in the ranges specified above, the melt specific resistance at 275 ° C. of the polyester composition is 0.15 to 0.30 × 10 ⁸ Ω · In order to satisfy cm, it is desirable that the following conditions (a) to (b) are satisfied during the production.
(A) The esterification reaction is carried out using at least three or more cans of the esterification reaction in which the inside of the can is at or above normal pressure.
(B) Magnesium compound, potassium compound, and phosphorus compound are added in the same amount to the third and subsequent esterification reaction cans among the three or more esterification reaction cans.

That is, satisfying the above conditions (a) to (b) means the following technical contents.
When the inside of the can of the esterification reaction can is in a reduced pressure state, not only the phosphorus compound but also a magnesium compound or a potassium compound may be scattered, making it difficult to manage the remaining amount. Therefore, in order to avoid this, the pressure of the esterification reaction vessel is set to a normal pressure or higher. The upper limit of the pressure is preferably 29.4 kPa. If it exceeds 29.4 kPa, the by-product amount of diethylene glycol (DEG) is increased, the softening point of the polyester is lowered, the film is broken at the time of film formation, and the film forming workability is deteriorated.

  When dicarboxylic acid (or its dialkyl ester) and glycol are supplied into the esterification reaction can, dicarboxylic acid-glycol diester and / or its oligomer are produced by the esterification reaction (for example, terephthalic acid and ethylene glycol are supplied). In this case, bis- (β-hydroxyethyl terephthalate) and / or its oligomer is produced.) In the first and second esterification reaction cans, the acid value of the produced oligomer is still large. When a compound is added, insoluble foreign matter (Mg salt and K salt) is easily generated between the magnesium compound or potassium compound and the dicarboxylic acid. Accordingly, the magnesium compound and potassium compound are supplied to the esterification reaction can where the acid value of the third and subsequent oligomers is small.

  In addition, many phosphorous compounds are in a liquid state and are particularly prone to scatter. When phosphorus compounds are added to a reaction can that does not contain magnesium or potassium compounds, the amount of phosphorous compounds scattered outside the system increases and is effectively incorporated into the reaction system. A polyester composition having the target quality cannot be obtained. Therefore, it is preferable to add in the presence of a magnesium compound or a potassium compound, and for this purpose, it is preferable to add the phosphorus compound to the same reaction vessel to which the magnesium compound and the potassium compound are added.

  In addition, in the manufacturing method of the polyester composition used for this polyester film of this invention, the addition time in particular of a polycondensation catalyst is not restrict | limited. That is, it may be added at an initial stage in the esterification reaction or may be added thereafter. Moreover, it is preferable to add a magnesium compound, a potassium compound, and a phosphorus compound as an ethylene glycol solution from the point of supply precision. Also. The temperature in the can (reaction system) in the esterification reaction can is generally 240 to 280 ° C, preferably 255 to 265 ° C. If it is less than 240 ° C., the oligomer tends to solidify and the reaction rate decreases, which is not preferable. On the other hand, if it exceeds 280 ° C., the amount of DEG by-product increases and the hue of the produced polymer tends to deteriorate. This is not preferable. The esterification reaction can is preferably 5 cans or less from the viewpoint of polyester production efficiency.

  The final product (polymer) is preferably filtered before being chipped. For such filtration, a filter having an opening of about 3 to 20 μm is usually used.

  The polyester film of the present invention may be a single layer polyester film or a polyester film having at least three layers having an outermost layer and a center layer.

  In the case of the three-layer structure in the present invention, particles are contained in the outermost layer (A layer in the case of the above-mentioned two types and three layers), and particles are substantially contained in the central layer (B layer in the case of the above two types and three layers). May not be included. The reason why it is preferable to include particles in the A layer is that when the polyester film of the present invention is used as a member for a solar cell, a moisture-proof functional layer such as a metal or metal oxide thin film layer or a coating layer is laminated. This is to improve the adhesion with the functional layer by imparting handling properties and increasing the surface area in the post-processing step. When particles are added to the outermost layer, sufficient handling properties suitable for processability can be obtained. The handling property of the film of the present invention can be evaluated by the dynamic friction coefficient (μd) between the laminated film surfaces. In this case, the dynamic friction coefficient (μd) is preferably 0.7 or less from the viewpoint of workability.

  The reason why it is preferable that the B layer substantially does not contain particles is to reduce the probability of formation of protrusions due to aggregates of lubricant particles, particularly inorganic particles. Further, by adopting such a configuration, a highly transparent film can be obtained, which is suitable for a field requiring transparency, such as a see-through solar cell.

  Note that “substantially free of inert particles” means, for example, in the case of inorganic particles, when the element derived from the particles is quantitatively analyzed by fluorescent X-ray analysis, it is less than 50 ppm, preferably less than 10 ppm. Preferably, the content is below the detection limit. This means that even if particles are not actively added to the base film, contaminants derived from foreign substances and raw material resin or dirt adhering to the line or equipment in the film manufacturing process will be peeled off and mixed into the film. It is because there is a case to do.

  These layers may contain various additives in the polyester as necessary. Examples of the additive include an antioxidant, a light resistance agent, an antigelling agent, an organic wetting agent, an antistatic agent, an ultraviolet absorber, and a surfactant.

  The type and content of the particles contained in the outermost layer may be inorganic particles or organic particles, and are not particularly limited, but include metal oxidation such as silica, titanium dioxide, talc, and kaolinite. Examples thereof include inorganic particles that are inert to polyesters such as products, calcium carbonate, calcium phosphate, and barium sulfate. Any one of these inert inorganic particles may be used alone, or two or more thereof may be used in combination.

  The particles preferably have an average particle size of 0.1 to 3.5 μm. The lower limit of the average particle diameter is more preferably 0.5 μm, further preferably 0.8 μm, and still more preferably 1.0 μm. Further, the upper limit of the average particle is more preferably 3.0 μm, still more preferably 2.8 μm. If the average particle size is less than 0.1 μm, sufficient handling properties cannot be obtained. When it exceeds 3.5 μm, coarse protrusions are likely to be generated.

  These particles are preferably porous particles, particularly porous silica. The porous particles are particularly preferable for optical applications because they are easily deformed into a flat shape when stretched in the film-forming process and the decrease in transparency is small.

  When the film of the present invention is used for optical applications, it is necessary to ensure high transparency. Therefore, the entire film preferably has a haze of 2.0% or less, more preferably 1.0% or less. . By setting the haze of the film to 2.0% or less, it can be suitably used for display applications that require high transparency. Furthermore, when using for an optical use, it is preferable that the total light transmittance of the film of this invention is 85% or more, More preferably, it is 88% or more. When the total light transmittance of the film is 85% or more, high luminance can be obtained even when used as a display member.

  The content of inorganic particles in the outermost layer is preferably 0.01 to 0.20 mass% with respect to the polyester constituting the outermost layer. The lower limit of the concentration is more preferably 0.02% by mass, and further preferably 0.03% by mass. Further, the upper limit of the concentration is more preferably 0.15% by mass, and further preferably 0.10% by mass. If it is less than 0.01% by mass, sufficient handling properties cannot be obtained. If it exceeds 0.2% by mass, the transparency is lowered, which is not preferable for optical applications.

The average particle diameter of the particles can be measured by the following method.
The particles are photographed with an electron microscope or an optical microscope, and the maximum diameter of 300-500 particles (in the case of porous silica, the aggregate size) is such that the size of one smallest particle is 2-5 mm. Particle diameter) is measured, and the average value is taken as the average particle diameter. Moreover, when calculating | requiring the average particle diameter of the particle | grains in the coating layer of a laminated film, the cross section of a laminated film is image | photographed by 120,000 times magnification using a transmission electron microscope (TEM), and the largest diameter of a particle | grain is calculated | required. Can do.

  A known method can be adopted as a method of blending the above-mentioned particles with polyester. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the end of the ester exchange reaction and before the start of the polycondensation reaction. The polycondensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder It can be carried out.

  As the polyester film of the present invention, an unoriented sheet obtained by melt extrusion or solution extrusion of the polyester is stretched in a uniaxial direction in the longitudinal direction or the width direction as necessary, or sequentially biaxially stretched in a biaxial direction. Alternatively, a biaxially oriented polyester film that is simultaneously biaxially stretched and heat-set is suitable.

  After sufficiently drying the polyester resin pellets in a vacuum, each polyester constituting the outermost layer and the central layer is supplied to a co-extrusion machine, melt-extruded into a sheet at 270 to 295 ° C., cooled and solidified, and uncast. Get a film. The obtained cast film is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially oriented polyester film.

Then, the both ends of a film are hold | gripped with a clip, are guide | induced to the hot air zone heated at 80-180 degreeC, and are extended | stretched 2.5 to 5.0 times in the width direction. Subsequently, it is guided to a heat treatment zone at 220 to 240 ° C., heat setting treatment and cooling are performed to complete crystal orientation. In this heat treatment step, a relaxation treatment of 1 to 12% may be performed in the width direction or the longitudinal direction as necessary.

  Moreover, it is good also as a laminated polyester film which formed the adhesive property modification layer in the at least single side | surface of the polyester film of this invention for adhesive property modification. As the coating solution used for forming the adhesion modified layer, an aqueous coating solution containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, acrylic resin and polyurethane resin is suitable. . Examples of these coating liquids include water-soluble or water-dispersible copolyester solutions, acrylic solutions, polyurethane solutions and the like disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, and the like.

  Furthermore, it is preferable that the adhesion modified layer has a cross-linked structure in order to impart necessary and sufficient heat and heat resistance. Examples of the crosslinking agent for obtaining a crosslinked structure include isocyanate, melamine, oxazoolin and the like.

The adhesive modification layer can be obtained by applying these coating solutions on one or both sides of a uniaxially stretched polyester film in the longitudinal direction, drying at 100 to 150 ° C., and further stretching in the lateral direction. You may apply | coat to a non-orientation sheet | seat and may extend | stretch longitudinally and transversely by the simultaneous biaxial stretching method. It is preferable to manage the final coating amount of the adhesion modified layer at 0.05 to 0.20 g / m ² . If the coating amount is less than 0.05 g / m ² , the resulting laminated film and adhesion may be insufficient. On the other hand, when the coating amount exceeds 0.20 g / m ² , blocking resistance may be lowered. When the adhesive modified layer is provided on both sides of the polyester film, the coating amount of the adhesive modified layer on both sides may be the same or different, and depending on the required performance, each of the above ranges. Can be set within.

  It is preferable to add fine particles to the adhesion modified layer in order to impart easy slipping. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle diameter of the particles exceeds 2 μm, the transparency of the particles, which makes it easy for the particles to fall off from the adhesive modified layer, is lowered. Particles to be included in the adhesive modification layer include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide, barium sulfate, calcium fluoride. Inorganic particles such as lithium fluoride, zeolite, molybdenum sulfide, mica, crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate resin particles, benzoguanamine / formaldehyde condensate particles, melamine / formaldehyde condensate particles, polytetra Examples thereof include heat-resistant polymer particles such as fluoroethylene particles. Among these particles, silica particles are preferable because the refractive index is relatively close to the resin component of the adhesive modification layer, and thus a film having high transparency can be easily obtained. Moreover, a well-known method can be used as a method of apply | coating a coating liquid. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, etc. can be mentioned. Or it can carry out in combination.

  The polyester film of the present invention has high clarity and can be suitably used as an optical film such as a display. In particular, the laminated polyester film having the above-described adhesion modified layer is preferable because of high adhesion to the optical functional layer. That is, the laminated polyester film of the present invention can be suitably used for a PDP panel, a liquid crystal display, a solar cell, an organic EL, etc. as an optical functional film or a base film of an optical functional sheet. In particular, it is suitable as a prism sheet used in a display panel or the like. A prism sheet is an optical film in which a prism pattern made of acrylic resin having a relatively high refractive index of 1.55 to 1.60 is uniformly formed on the surface of a transparent resin film, and is incorporated into the front surface of the backlight. Therefore, of the light emitted from the light source, the light that is not used outside the viewing angle is recycled by reflection and refraction, and is condensed in the direction of the user at the optimum angle, thereby improving the front brightness. It is an important member.

  In addition, the polyester film of the present invention can be suitably used as a polyester film for solar cells in which foreign matter protrusions due to coarse particles are few and high moisture-proofing is required. The polyester film for solar cells of the present invention can be used as a base film (base film) for the surface protective sheet, the back sheet, or a laminate of flexible electronic members. In particular, it is suitable as a base film for a solar cell backsheet that requires high durability and long-term thermal stability. A solar cell backsheet protects the solar cell module on the back side of the solar cell.

  The polyester film for solar cells of the present invention can be used as a solar cell back sheet, alone or in combination of two or more. The polyester film for solar cells of the present invention can be laminated with a coating or film having a water vapor barrier property, an inorganic oxide layer, an aluminum foil or the like for the purpose of imparting a water vapor barrier property.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited at all by these Examples. In the following Examples and Comparative Examples, TPA means terephthalic acid, EG means ethylene glycol, DEPA means diethylphosphonoethyl acetate, and TMPA means trimethyl phosphate. Each characteristic and physical property value were measured by the following test methods.

(1) Acid value of polyester film The polyester film was pulverized using a freeze pulverizer (SPEX 6700) so that no foreign matter such as dust was mixed, then dried, and 0.2 g of the dried product was heated with 10 ml of benzyl alcohol. Dissolved. Subsequently, it is obtained by titration with 0.04 mol / L potassium hydroxide ethanol solution (80 mL of 0.5 mol / L potassium hydroxide aqueous solution diluted to 1 L with ethanol) using phenol red as an indicator. In addition, when there existed an adhesive modification layer in the polyester film, it removed beforehand and used for the sample.

(2) Intrinsic viscosity A polyester film is dissolved in a mixed solvent of parachlorophenol (6 parts by weight) and 1,1,2,2-tetrachloroethane (4 parts by weight) and measured at 30 ° C. In addition, when there existed an adhesive property modification layer, it removed beforehand and used for the sample.

(3) Melt specific resistance at 275 ° C. The polyester film obtained in Example or Comparative Example was melted at 275 ° C., two electrodes (stainless steel wire with a diameter of 0.6 mm) were placed, and a voltage of 120 V was applied. The specific resistance value Si (Ω · cm) obtained by measuring the current (i _o ) at the time and applying this to the following equation.
Si (Ω · cm) = (A / L) × (V / i _o )
[A: Area between electrodes (cm ² ), L = Distance between electrodes (cm), V = Voltage (V)]
In addition, when there existed an adhesive property modification layer, it removed beforehand and used for the sample.

(4) Content of Mg (magnesium), K (potassium), Na (sodium), and P (phosphorus) in the film A polyester film is formed into a disk shape with a thickness of about 5 mm on a smooth metal plate, and a smooth surface Was measured with a fluorescent X-ray analyzer. In addition, when there existed an adhesive property modification layer, it removed beforehand and used for the sample. The calibration curve was prepared using a standard sample whose concentration was previously confirmed by a light emission plasma analysis method.

(5) Number of coarse particles in the polyester film (number of particles having a particle size of 5 μm or more)
The polyester film from which the adhesive reforming layer has been removed was pulverized using a freeze pulverizer (6700, manufactured by SPEX) so that no foreign matter such as dust was mixed in, and then 30 mg of the pulverized product was weighed and heated to 270 ° C. on the cover glass. Melt. Press from above with the same cover glass and quench. Using a NIRECO image analyzer (Luzex-Fs), the number of foreign matters having a size of 5 μm or more was measured with a microscope by a transmission dark field method. The number of foreign matters was measured for 20 fields of view, and the total number was defined as the number of coarse particles. At this time, CF Plan DM 40X was used as an objective lens.

(6) Heat resistance of polymer After pulverizing the polyester film and putting it in a glass ampoule, and replacing with nitrogen, 13.3 kP
The glass ampoule is sealed under reduced pressure (nitrogen atmosphere) of a, and the change in intrinsic viscosity when heated at 300 ° C. for 2 hours is measured. The heat resistance is expressed as a decrease in intrinsic viscosity (ΔIV) due to heat treatment. The smaller ΔIV, the better the heat resistance.

(7) Haze and total light transmittance The haze and total light transmittance of the film were measured using a turbidimeter (NHD2000, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS-K7105.
A sample having a haze of 2% or less was rated as ○, and a sample having a haze exceeding 2% was rated as ×. In addition, the total light transmittance of 85% or more was evaluated as ◯, and the total light transmittance of less than 85% was evaluated as ×.

(8) Adhesiveness 50 mass parts of photocurable acrylic resin (manufactured by Dainichi Seika, Seika Beam EXF01 (B)), 25 mass parts of toluene, and 25 mass parts of methyl ethyl ketone are mixed well on the surface of the adhesive modified layer of the film sample. The stirred coating agent was applied with a wire bar, dried at 70 ° C. for 1 minute to remove the solvent, and then an acrylic with a thickness of 3 μm under the conditions of 200 mJ / cm ² , irradiation distance 15 cm, and traveling speed 5 m / min with a high-pressure mercury lamp. A resin layer was laminated.

A surface opposite to the acrylic resin layer of the obtained laminated film was attached to a glass plate having a thickness of 5 mm to which a double-sided tape was attached. Next, 100 grid-like cuts that penetrated through the acrylic resin layer and the adhesion modified layer to reach the base film were made using a cutter guide having a gap interval of 2 mm. Next, an adhesive tape (manufactured by Nichiban Co., Ltd., No. 405; 24 mm width) was attached to the cut-like cut surface. The air remaining on the interface at the time of pasting was pushed with an eraser to bring it into close contact, and then the adhesive tape was peeled off vigorously and vertically. The adhesion was visually determined from the following formula. In addition, what is partially peeled within one square is also included in the number of peeled.
Those with less than 20 peeled off ○
Those with more than 20 peeled pieces ×
Judged as.

(9) Detection of pinner bubble About the obtained polyester film, the film was pulled out from the film roll of width 1m and length 100m, and it hung in the perpendicular direction. At this time, the surface layer 100m of the film roll was removed, and 100 m was used as a sample. Next, a glossy black cloth was placed on the entire back surface of the film, and observed from the front surface to detect and mark a defect (locally shining point). Next, the size of the major axis of the marked part was measured using a magnifying glass with a magnification of 10 times (SCALE LUPE × 10 manufactured by PEAK). The determination was made according to the following criteria.
○ The number of optical defects with a size of 3 mm or more is 0 / m ²
Δ 1-3 optical defects with a size of 3 mm or more / m ²
× The number of optical defects with a size of 3 mm or more is 3 / m ² or more

Example 1
(Polymerization of polyester composition)
As the esterification reaction apparatus, a continuous esterification reaction apparatus comprising a three-stage complete mixing tank having a stirrer, a distillation column, a partial condenser, a raw material charging port and a product discharge port is used, and the TPA is set to 2 ton / hr. EG is 2 moles relative to 1 mole of TPA, antimony trioxide is in an amount such that Sb atoms are 160 ppm with respect to the produced PET, and these slurries are continuously supplied to the first esterification reactor of the esterification reactor, The reaction was conducted at 255 ° C. with an average residence time of 4 hours at normal pressure.

  Next, the reaction product in the first esterification reaction can is continuously taken out of the system and supplied to the second esterification reaction can, and the second esterification reaction can is distilled from the first esterification reaction can. The EG to be removed was added at 8% by weight to the produced PET and reacted at 260 ° C. at an average residence time of 1.5 hours at normal pressure.

  Next, the reaction product in the second esterification reaction can is continuously taken out of the system and supplied to the third esterification reaction can, and magnesium acetate in an amount of 25 ppm of Mg atoms to the generated PET is added. An EG solution containing, an EG solution containing potassium acetate in an amount of 10 ppm K atoms relative to the generated PET, and an EG solution containing DEPA in an amount of 9 ppm P atoms relative to the generated PET, and normal pressure At 260 ° C. with an average residence time of 0.5 hours. The additive amount was determined assuming that the yield of the additive was 100%.

  The esterification reaction product generated in the third esterification reaction can is continuously supplied to a three-stage continuous polycondensation reaction apparatus to perform polycondensation, and after filtration through a sintered fiber filter having an opening of 5 μm, A pelletized PET (A) (polyester composition A) having a viscosity of 0.620 dl / g was obtained.

(Polyester film production)
After pelletized PET (A) as a raw material for the base film was dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours, it was supplied to an extruder and dissolved at 285 ° C. It is filtered with a filter material of stainless steel sintered body (nominal filtration accuracy 10 μm particles 95% cut), extruded into a sheet form from the die, and then wound around a casting drum having a surface temperature of 30 ° C. by using an electrostatic application casting method and cooled. Solidified to make an unstretched film. Next, this unstretched film was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a peripheral speed difference to obtain a uniaxially oriented PET film.

Next, a coating solution shown below was applied to one side of the uniaxially stretched polyester film so that the final coating layer thickness was 0.08 g / m ^2, and then dried at 135 ° C.

  Subsequently, while holding the edge of the film with a clip, the film was guided to a hot air zone at a temperature of 120 ° C. and stretched 4.3 times in the width direction. Next, while maintaining the width stretched in the width direction, after heat-fixing at a maximum temperature of 235 ° C., 3% relaxation treatment is performed at 150 ° C. in the width direction, both ends are trimmed, and a winding device is used. The polyester film having a film thickness of 50 μm was obtained by winding.

(Coating solution adjustment)
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component (based on the entire glycol component) was prepared. Next, 51.4 parts by weight of water, 38 parts by weight of isopropyl alcohol, 5 parts by weight of n-butyl cellosolve, 0.06 parts by weight of a nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by weight of the water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer solidified, the resin water dispersion is cooled to room temperature, and the solid content concentration is 5.0% by weight. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Further, after 3 parts by weight of silica particles having an average particle diameter of 2.5 μm were dispersed in 50 parts by weight of water, 99.46 parts by weight of the water-dispersible copolymerized polyester resin liquid was mixed with 0.54 parts of the above-mentioned aqueous dispersion of silica particles. Part by weight was added, and 20 parts by weight of water was added with stirring to obtain a coating solution (A).

Example 2
In Example 1, the type of the phosphorus compound was changed from DEPA to TMPA, and the amount of the phosphorus compound added was 85%, and the pelletized PET (B) was changed to 10.6 ppm as the phosphorus atom as the phosphorus atom. A polyester film was obtained in the same manner as in Example 1 except that it was used.

Example 3
In the production of pelletized PET, as an esterification reaction apparatus, a continuous esterification reaction apparatus comprising a four-stage complete mixing tank having a stirrer, a distillation column, a partial condenser, a raw material charging port and a product take-out port is used. Pellet PET (C) was obtained in the same manner as in Example 1 except that the addition location of magnesium acetate, potassium acetate and DEPA was changed to the fourth esterification reaction can. A polyester film was obtained in the same manner as in Example 1 except that pellet-like PET (C) was used.

Example 4
In the production of pelletized PET of Example 1, pelletized PET (D) was obtained in the same manner as in Example 1 except that the addition amounts of magnesium acetate, potassium acetate, and DEPA were changed to the amounts shown in Table 1. Got. A polyester film was obtained in the same manner as in Example 1 except that pellet-like PET (D) was used.

Example 5
In the production of pelletized PET of Example 1, pelletized PET (E) was obtained in the same manner as in Example 1 except that the addition amounts of magnesium acetate, potassium acetate, and DEPA were changed to the amounts shown in Table 1. Got. A polyester film was obtained in the same manner as in Example 1 except that pelletized PET (E) was used.

Example 6
In the third esterification reaction can in the production of pelletized PET of Example 1, in addition to magnesium acetate, potassium acetate, and DEPA, an EG dispersion of silica particles having an average particle size of 2.5 μm is 20000 ppm relative to the produced PET. A pellet-like PET (F) was obtained in the same manner as in Example 1 except that the amount was added.

  After pelletized PET (A) was dried at 135 ° C. under reduced pressure (1 Torr) for 6 hours as a raw material for the intermediate layer of the base film, the pelletized PET (A) and the pelleted PET (A) were fed into the extruder 2 (for the intermediate layer B layer). PET (F) was blended so that the concentration of silica particles having an average particle diameter of 2.5 μm was 0.06% by mass, supplied to the extruder 1 (for outer layer A layer), and dissolved at 285 ° C. These two polyester resins are filtered through a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles, 95% cut), laminated in a three-layer confluence block, extruded into a sheet form from a die, and then electrostatically The film was wound around a casting drum having a surface temperature of 30 ° C. using an applied casting method and solidified by cooling to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the ratio of the thicknesses of the A layer, the B layer, and the A layer was 1.5: 7: 1.5. Next, this unstretched film was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a peripheral speed difference to obtain a uniaxially oriented PET film. Subsequently, the coating layer was provided similarly to Example 1, the width direction extending | stretching, heat setting, and the relaxation process were performed, and the polyester film was obtained.

Example 7
The pelletized PET (A) obtained in Example 1 was subjected to solid phase polymerization at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus, and pelletized PET (with an intrinsic viscosity of 0.73 dl / g) ( G) was obtained.
Next, a polyester film was obtained in the same manner as in Example 1 except that pellet-like PET (G) was used, the adhesive modified layer was not provided, and corona treatment was performed.

Example 8
In Example 1, the polyester film was obtained like Example 1 except having used the following coating liquid (B).
(Preparation of coating solution B)
Mixing polyurethane resin (trade name Takelac W511, manufactured by Mitsui Takeda Chemical Co., Ltd.) and polyurethane resin 100 parts by mass so that the content of regenerated isocyanate is 20 parts by mass with 5.4% by mass, Silica particles having a total resin solid content concentration of 3.8% by mass and a silica particle average particle size of 1.0 μm as particles are 0.44% by mass with respect to the total resin and silica particles having an average particle size of 0.1 μm are based on the total resin The solution was diluted with a mixed solvent of water / isopropyl alcohol (= 65/35: mass ratio) so as to contain 10% by mass to obtain a coating solution (B).

Comparative Example 1
In the production of the pelletized PET of Example 1, pelletized PET (H) was obtained in the same manner as in Example 1 except that the addition amounts of the magnesium compound, potassium compound, and phosphorus compound were changed to 65 ppm, 30 ppm, and 30 ppm, respectively. . A polyester film was obtained in the same manner as in Example 1 except that pellet-like PET (H) was used.

Comparative Example 2
In the production of pelletized PET in Example 1, pelletized PET (I) was obtained in the same manner as in Example 1 except that the addition of the potassium compound was stopped. A polyester film was obtained in the same manner as in Example 1 except that pellet-like PET (I) was used.

Comparative Example 3
In the production of the pelletized PET of Example 1, the addition of potassium acetate was stopped, and pelletized PET (J) was obtained in the same manner as in Example 1 except that 10 ppm of sodium acetate as a sodium atom was added to the resulting polyester composition. Got. A polyester film was obtained in the same manner as in Example 1 except that pellet-shaped PET (J) was used.

Comparative Example 4
In the production of pelletized PET of Example 1, two esterification reaction cans were used, and EG distilled from the first esterification reaction can was added to the second esterification reaction can by 8% by weight with respect to the produced PET. In addition, pellet-like PET (K) was obtained in the same manner as in Example 1 except that the same amounts of magnesium acetate, potassium acetate and DEPA as in Example 1 were added. A polyester film was obtained in the same manner as in Example 1 except that pelletized PET (K) was used.

  As is apparent from the above description, according to the present invention, a polyester film having a low melting specific resistance, a high clarity, and a high heat resistance can be provided.

Claims (5)

A polyester film comprising a polycondensation catalyst, a magnesium compound, a potassium compound and a phosphorus compound, wherein the polyester film has a melt specific resistance at 275 ° C. of 0.15 to 0.30 × 10 ⁸ Ω · cm, and A polyester film that satisfies the conditions (1) to (3).
(1) Mg content: 15 to 35 ppm with respect to the polyester film
(2) K content: 5 to 20 ppm relative to the polyester film
(3) P content: 5 to 15 ppm relative to the polyester film   The polyester film according to claim 1, wherein the main repeating unit is ethylene terephthalate, and the main phosphorus compound is ethyl diethylphosphonoacetate.   A laminated polyester film having an adhesive modification layer on at least one side of the polyester film according to claim 1.   An optical polyester film comprising the laminated polyester film according to claim 3.   The polyester film for solar cells which consists of a polyester film of Claim 1 or 2.