JP2011006659A - Polyester film for sealing material for back of solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film for sealing material for back of solar battery which has an excellent hydrolysis resistance and weather resistance with little oligomer, in particular, to provide the biaxially oriented polyester film which prevents the occurrence of poor appearance due to embrittlement and delamination possibly developed under a high temperature high humidity environment or outdoors, and which has good mechanical performance.SOLUTION: The polyester film for sealing material for back of solar battery comprises a polyester having a phosphor element content of ≤170 ppm, and has an amount of terminal carboxylic acid of ≤26 equivalent/ton, contains a white pigment of 3-50 wt.%, and an amount of oligomers on a film surface which was heat-treated for 30 minutes at 150°C is ≤0.8 mg/m.

Description

  This invention provides the biaxially-oriented polyester film for solar cell backside sealing materials which is excellent in hydrolysis resistance and a weather resistance, and has little surface oligomer amount. More specifically, the present invention relates to a biaxially oriented polyester film having good mechanical performance and preventing appearance defects due to embrittlement and delamination that can occur during high-temperature and high-humidity environments and long-term use outdoors.

  The solar cell back surface sealing material is a member for the purpose of preventing moisture permeation from the back side of the solar cell, and required physical properties include gas barrier properties, hydrolysis resistance, and dielectric breakdown resistance. Furthermore, the weather resistance with respect to the leak light from between photovoltaic cells is also requested | required. Although a glass plate is generally used as the solar cell back surface sealing material, it is light and flexible from the viewpoints of lack of flexibility and increase in the total weight of the solar cell. Substitution with filled materials is demanded, such as a laminate film of vinyl fluoride resin film and polyester film, a polyester film coated with fluororesin, a laminate film of gas barrier polyester film and hydrolysis resistant polyester film, etc. Has been. The polyester film of this invention belongs to the structural member of the said solar cell back surface sealing material.

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

  However, when a polyester film is used in a high-temperature and high-humidity environment, hydrolysis of the ester bond site in the molecular chain occurs and mechanical properties deteriorate, and when a laminated laminated film is configured as a solar cell back surface sealing material In addition, it is known that oligomers are deposited on the bonding interface and cause delamination. Therefore, various studies have been conducted to suppress hydrolysis, assuming that the polyester film is used outdoors for a long period (20 years) or used in a high humidity environment.

  It is known that the hydrolysis of polyester is faster as the amount of terminal carboxyl groups in the polyester molecular chain is higher. Therefore, Patent Document 1 discloses a technique for improving hydrolysis resistance by esterifying a carboxylic acid at the end of a molecular chain by using an epoxy compound and reducing the amount of terminal carboxyl groups. However, an epoxy compound is highly undesirable in terms of environment and cost because it has a high possibility of inducing gelation and generating foreign substances in the melt extrusion process or the material recycling process in the film forming process.

  Patent Document 2 discloses a technique for reducing the amount of terminal carboxyl groups by adding a carbodiimide such as polycarbodiimide. However, carbodiimide tends to undergo thermal transformation itself, and the physical properties of the polyester film are lowered depending on reaction conditions. In some cases, the odor may be caused by a carbodiimide volatile component at the outlet of the tenter during film formation.

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

  In order to solve this problem, Patent Document 3 discloses a technique for improving hydrolysis resistance by suppressing the terminal carboxylic acid to a specified amount and containing a specific amount of a specific phosphate ester. Yes. However, since the phosphate ester in the said technique has the characteristic structure, the process and cost which adjust phosphate ester are needed. Therefore, it is not suitable for providing a polyester film that is inexpensive and can be used outdoors for a long period (20 years).

Moreover, although the leak light from between the photovoltaic cells is incident on the solar cell back surface sealing material, weather resistance is required for outdoor use over a long period (20 years). Patent Document 4 introduces that weather resistance is improved by adding a titanium dioxide pigment to polyester. However, this technique is not fully satisfactory with respect to the hydrolysis resistance most required in the field of films for solar cell backside sealing materials, and the use in this field is limited.

JP-A-9-227767 JP-A-8-73719 JP-A-8-3428 Japanese Patent Laid-Open No. 2001-10002

Kazuo Yuki Saturated Polyester Resin Handbook published by Kosaido 1989

  This invention is made | formed in view of the said actual condition, Comprising: The solution subject is the hydrolysis resistance and the weather resistance, and the biaxially-oriented polyester film for solar cell backside sealing materials with little surface oligomer amount. Is to provide.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above-mentioned problems can be easily solved by using a polyester film having a specific configuration, and the present invention has been completed.

That is, the present inventors are a polyester film comprising a polyester having a phosphorus element content of 170 ppm or less, a terminal carboxyl group content of 26 equivalents / ton or less, and a white pigment content of 3 wt% to 50 wt%. Then, by using a polyester film for solar cell backside sealing material, the amount of oligomer present on the film surface heat-treated at 150 ° C. for 30 minutes is 0.8 mg / m ² or less. I found that it can be solved.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in hydrolysis resistance and a weather resistance, and can provide the biaxially-oriented polyester film for solar cell backside sealing materials with little surface oligomer amount.

  In the present invention, the polyester used for the polyester film refers to a polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid. Examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like.

  In the polyester film of the present invention, the amount of phosphorus element detected by analysis using a fluorescent X-ray analyzer, which will be described later, is in a specific range. It is derived from a compound. In the present invention, the amount of phosphorus element needs to be in the range of 0 to 170 ppm, preferably in the range of 0 to 150 ppm, and more preferably in the range of 1 to 150 ppm. By satisfying a specific amount of phosphorus element, hydrolysis resistance can be highly imparted to the film. If the amount of phosphorus element is too large, hydrolysis is accelerated, which is not preferable.

Examples of phosphoric acid compounds include known ones such as phosphoric acid, phosphorous acid or ester phosphonic acid compounds, phosphinic acid compounds, phosphonous acid compounds, phosphinic acid compounds, and specific examples include regular phosphoric acid. , Dimethyl phosphate, trimethyl phosphate, diethyl phosphate, triethyl phosphate, dipropyl phosphate, tripropyl phosphate, dibutyl phosphate, tributyl phosphate, diamyl phosphate, triamyl phosphate, dihexyl phosphate, tri Examples include hexyl phosphate, diphenyl phosphate, triphenyl phosphate, and ethyl acid phosphate.

In addition, it is preferable not to contain as much as possible a metal compound that can act as a catalyst in order to suppress thermal decomposition and hydrolysis, but in order to reduce the volume resistivity at the time of melting in order to improve the productivity of the film, magnesium, Metals such as calcium, lithium, and manganese can be contained in the polyester component, usually at 300 ppm or less, preferably 250 ppm or less. In addition, in the case of using a method such as a master batch method for blending particles and various additives described later, antimony can be contained as a metal component of the polymerization catalyst, but the present invention is excellent. In order to obtain hydrolysis resistance and weather resistance, the content of antimony with respect to the entire polyester component is preferably 400 ppm or less as an antimony element. In addition, the metal compound referred to here does not include particles to be blended in the polyester described later.

In order to prevent deterioration of the solar cell back surface sealing material due to incident light leaked from between the solar cells, the solar cell back surface sealing material preferably has high concealing properties. In this invention, a white pigment is added to the polyester component which comprises the polyester film for solar cell backside sealing materials, and it is set as a white film. Examples of white pigments include titanium dioxide, zinc oxide, zinc sulfide, barium sulfate, and the like, preferably titanium dioxide, barium sulfate, and particularly preferably titanium dioxide.

The average particle diameter of the white pigment is preferably 0.25 μm or more, more preferably 0.28 μm or more, and particularly preferably 0.30 μm or more. If the average particle size is less than 0.25 μm, the wavelength of light that can be efficiently scattered shifts to the lower wavelength side, and thus the reflectance in the near-infrared light region may decrease. If the average particle size of the white pigment exceeds 10 μm, the white pigment contains coarse particles depending on the particle size distribution, which may cause problems such as pinholes in the film. Therefore, the white pigment has an average particle size of 10 μm or less. It is preferable that

  The content of the white pigment is 3 to 50% by weight, preferably 5 to 30% by weight, and more preferably 7 to 20% by weight. When the content of the white pigment is less than 3% by weight, the weather resistance is low, and the mechanical strength tends to decrease with time when it is left outdoors for a long time. On the other hand, if the content of the white pigment exceeds 50% by weight, the concealing property is saturated, so that the effect cannot be obtained and the cost is not practical.

  The method for incorporating a white pigment in the polyester film is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester component, but it may preferably be added at the stage of esterification or after completion of the transesterification reaction to advance the polycondensation reaction. Alternatively, a white pigment slurry dispersed in ethylene glycol or water and a polyester raw material may be blended using a kneading extruder with a vent. Moreover, the method of blending the dried white pigment and the polyester raw material using a kneading extruder may be used. In addition, a so-called master batch chip containing a high concentration of white pigment is produced using a kneading extruder, and if necessary, this master batch chip may contain a polyester raw material containing no white pigment or a small amount. A polyester film having a predetermined blending amount can also be produced by mixing using a kneading extruder.

In addition to the above-mentioned particles, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, fluorescent whitening agents, dyes, and UV absorbers are added to the polyester film of the present invention as necessary. can do.

  The thickness of the polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 20 to 250 μm, preferably 25 to 200 μm.

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

  That is, dried or undried polyester chips by a known method are supplied to a kneading extruder and heated to a temperature equal to or higher than the melting point of each polymer to melt. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed. Even in the melt extrusion process, the amount of terminal carboxylic acid increases depending on the conditions. Therefore, in the present invention, the residence time of the polyester in the extruder in the extrusion process is shortened. Dry sufficiently so that the amount is 50 ppm or less, preferably 30 ppm or less. When a twin screw extruder is used, a vent port is provided, and the pressure is reduced to 40 hectopascals, preferably 30 hectopascals or less, more preferably 20 hectopascals or less. A method such as maintaining the above is adopted.

In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. It is preferable to perform ~ 6 times stretching and heat treatment at 160 to 220 ° C for 1 to 600 seconds.
Further, at this time, it is preferable to relax 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.
In the present invention, as described above, two or three or more polyester melt extruders can be used to form a laminated film of two layers or three or more layers by a so-called coextrusion method. The layer structure is A / B structure using A raw material and B raw material, or A / B / A structure, and further C film is used for A / B / C structure or other structure. Can do.

  In the film of the present invention thus obtained, the amount of terminal carboxylic acid of the polyester component constituting the film is 26 equivalent / ton or less, preferably 24 equivalent / ton or less. If the amount of terminal carboxylic acid exceeds 26 equivalents / ton, the hydrolysis resistance of the polyester is poor. On the other hand, in view of the hydrolysis resistance of the present invention, there is no lower limit of the amount of terminal carboxylic acid of the polyester, but it is usually about 10 equivalents / ton from the viewpoint of the efficiency of the polycondensation reaction, thermal decomposition in the melt extrusion process, and the like. is there.

  The hydrolysis resistance of the polyester film is a property related to the entire film. In the present invention, in the case of a film having a laminated structure by coextrusion, the amount of terminal carboxylic acid as the entire polyester constituting the film is in the above-described range. It is necessary to be. Similarly, in the case of a film having a laminated structure by coextrusion, the content of phosphorus contained as a catalyst required in the present invention needs to be within the above-mentioned range as the entire polyester constituting the film. is there.

  In addition, in imparting hydrolysis resistance to the polyester film, the intrinsic viscosity of the film is 0.65 or more, preferably 0.68 or more, in addition to setting the phosphorus element content and the terminal carboxylic acid content within the above ranges. It is desirable. When the intrinsic viscosity of the film is less than 0.65, the hydrolysis resistance of the polyester film is inferior, and high-temperature and high-humidity environments and outdoor long-term use are difficult. On the other hand, considering the hydrolysis resistance of the present invention, there is no upper limit of the intrinsic viscosity of the polyester, but it is usually about 0.90 from the viewpoint of thermal decomposition in the melt extrusion process.

  In the present invention, in order to set the terminal carboxylic acid amount and the intrinsic viscosity of the polyester within a specific range, for example, a method of shortening the residence time of the polyester in the extruder in the extrusion process of the polyester chip is used. Alternatively, a polyester film having a specific amount of terminal carboxylic acid may be obtained by forming a polyester chip having a low terminal carboxylic acid amount. Conventional methods for reducing the amount of terminal carboxylic acid in polyester chips include solid-phase polymerization of chips obtained by melt polymerization, methods for increasing polymerization efficiency, methods for increasing the polymerization rate, and methods for suppressing the degradation rate. A known method may be employed. For example, it is carried out by a method of shortening the melt polymerization time, a method of increasing the amount of polymerization catalyst, a method of using a highly active polymerization catalyst, a method of lowering the polymerization temperature, or the like. Further, in the production of a film, since the amount of terminal carboxylic acid increases when a regenerated raw material that has undergone a melting step is added, it is preferable not to add such a regenerated raw material in the present invention. preferable.

In the polyester film of the present invention, the amount of oligomer on the film surface after heat treatment at 150 ° C. for 30 minutes is 0.8 mg / m ² or less, preferably 0.4 mg / m ² or less. The amount of oligomer here refers to the amount of cyclic trimer (polyester-derived oligomer) measured by the method described later. When the amount of oligomer present on the surface of the film exceeds 0.8 mg / m ² , when used outdoors over a long period (20 years), the bonded interface of the laminated laminated film configured as a solar cell backside sealing material Delamination occurs due to the precipitation of the oligomer. When delamination occurs, moisture permeates into the solar cell from the location where delamination occurs, causing problems such as short-circuiting the power generation element. In addition, the oligomer amount on the film surface as used in the field of this invention means the quantity calculated by the measuring method of the oligomer amount on the film surface described later.

  The polyester of the present invention may be a product obtained by a melt polymerization reaction, but after melt polymerization, the amount of oligomers contained in the raw material can be reduced by solid-phase polymerization of the chipped polyester. A method using the product obtained by the polymerization reaction is preferably used. Moreover, you may form an oligomer precipitation prevention layer in the film surface by application | coating, such as polyvinyl alcohol and curable silicone.

  In the present invention, a coating layer is formed on one side or both sides of the film in order to impart adhesiveness, antistatic property, slipperiness, releasability, etc. to the film in or after the stretching step, or corona treatment. It is also possible to perform a discharge treatment such as.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist of the present invention. In addition, the measurement and evaluation method of various physical properties of a film are shown below.

(1) Amount of terminal carboxylic acid (equivalent / ton)
The amount of terminal carboxyl groups was measured by a so-called titration method. That is, the polyester film was dissolved in benzyl alcohol, added with phenol red indicator, and titrated with a water / methanol / benzyl alcohol solution of sodium hydroxide. In addition, when a white pigment such as titanium dioxide or barium sulfate is contained in the polyester film, the white pigment that is an insoluble component with respect to benzyl alcohol is appropriately determined by removing it by centrifugal sedimentation, The terminal carboxyl group amount (equivalent / ton) relative to the polyester component was determined.

(2) Determination of catalyst-derived elements Using a fluorescent X-ray analyzer (model “XRF-1500” manufactured by Shimadzu Corporation), the amount of elements in the film was determined by single sheet measurement under the conditions shown in Table 1 below. . In the case of a laminated film, the content of the film as a whole was measured by melting the film, molding it into a disk shape, and measuring it. In addition, when a white pigment is contained in the polyester film, a peak derived from the white pigment is detected. Therefore, the white pigment is excluded from the whole, and the catalyst-derived element of the polyester component is quantified.

(3) Hydrolysis resistance The film was allowed to stand for 35 hours in an atmosphere at a temperature of 120 ° C. and a relative humidity of 100%, and the elongation at break was measured as the mechanical properties of the film. The retention rate (%) of elongation at break before and after the treatment was calculated by the following formula and judged according to the following criteria.
Breaking elongation retention rate = breaking elongation after treatment ÷ breaking elongation before treatment × 100
◎: Retention rate is 80% or more ○: Retention rate is 60-80%
Δ: Retention rate is 30 to 60%
X: Retention rate is less than 30%

(4) Intrinsic Viscosity 1 g of a measurement sample is precisely weighed and dissolved in a solvent of phenol / tetrachloroethane = 50/50 (parts by weight) to prepare a solution having a concentration c = 0.01 g / cm ³ at 30 ° C. Relative viscosity η _r with the solvent was measured to determine the intrinsic viscosity [η].

(5) Evaluation of accelerated weather resistance (A) Weather resistance test A weather resistance test was conducted under the following conditions based on the JIS-B-7753 (2007) standard.
Equipment: Sunshine weather meter (Model: WEL-SUN-HCH-B Manufacturer: Suga Test Instruments Co., Ltd.)
Discharge voltage / current: 50V / 60A
Filter: Glass filter type A Black panel temperature: 63 ° C
Treatment time: 1000 hours Spray cycle (120 minutes): 102 minutes of irradiation, followed by 18 minutes of irradiation and spraying (B) Weather resistance evaluation method The intrinsic viscosity of the film before and after the weather resistance test is measured, and the intrinsic viscosity maintenance rate The weather resistance was evaluated.
Intrinsic viscosity maintenance rate = Intrinsic viscosity after weather resistance test / Intrinsic viscosity before weather resistance test × 100 (%)
○: Intrinsic viscosity maintenance ratio is 70% or more ×: Intrinsic viscosity maintenance ratio is less than 70%

(6) Heat treatment of film A4 size Kent paper and heat-treated polyester film are combined, clipped at the four corners with a Zem clip or the like, and Kent paper and polyester film are stopped. At that time, if an oligomer precipitation preventing layer is provided, the surface with the coating layer is arranged outside. In a nitrogen atmosphere, the polyester film is left in an oven at 150 ° C. for 30 minutes for heat treatment.

(7) Amount of oligomer on film surface Fold the heat-treated polyester film so that the top is open and the bottom area is 250 cm ² to create a square box. When the coating layer is provided, the coating layer surface is set to the inside. Next, 10 ml of DMF (dimethylformamide) is placed in the box prepared by the above method, and the DMF is recovered after being left for 3 minutes. The recovered DMF is supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer in DMF, and this value is divided by the film area in contact with DMF to determine the amount of oligomer on the film surface (mg / m ² ). And

Next, the polyester raw material used for an Example is demonstrated.
<Method for producing polyester (1)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of calcium acetate as a catalyst is placed in the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours.
After 4 hours, the transesterification reaction was substantially terminated. To this reaction mixture, 0.04 part of antimony trioxide and 0.08 part by weight of silica particles having an average particle diameter of 2.6 μm dispersed in ethylene glycol were added, and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 40 pascals. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.60 due to a change in the stirring power of the reaction vessel, and the polyester was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (1) was 0.60, and the amount of terminal carboxyl groups of the polymer was 35 equivalents / ton.

<Method for producing polyester (2)>
Polyester (1) was used as a starting material, and solid phase polymerization was performed at 220 ° C. under vacuum to obtain polyester (2). The intrinsic viscosity of the polyester (2) was 0.74, and the amount of terminal carboxyl groups of the polymer was 9 equivalents / ton.

<Method for producing polyester (3)>
In the production of polyester (1), 0.094 part of orthophosphoric acid (0.03 part as phosphorus element) was added after the transesterification, and then 0.04 part of antimony trioxide and the average particle diameter dispersed in ethylene glycol A polyester (3) was obtained in the same manner except that 0.08 part by weight of 2.6 μm silica particles was added. The intrinsic viscosity of the obtained polyester (3) was 0.63, and the amount of terminal carboxyl groups of the polymer was 14 equivalents / ton.

<Method for producing polyester (4)>
Polyester (3) was used as a starting material, and solid phase polymerization was performed at 220 ° C. under vacuum to obtain polyester (4). The intrinsic viscosity of the polyester (4) was 0.69, and the amount of terminal carboxyl groups of the polymer was 12 equivalents / ton.

<Method for producing polyester (5)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, adding 0.02 part of magnesium acetate tetrahydrate as a catalyst, taking it into the reactor, setting the reaction start temperature to 150 ° C., and gradually distilling off methanol. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.136 parts of ethyl acid phosphate (0.03 parts as phosphorus element) was added to the reaction mixture, the mixture was transferred to a polycondensation tank, and 0.04 part of antimony trioxide was added to carry out a polycondensation reaction for 4 hours. . That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg.
After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (5). The intrinsic viscosity of this polyester was 0.63, and the amount of terminal carboxyl groups of the polymer was 51 equivalents / ton.

<Manufacture of polyester (6)>
Polyester (5) was used as a starting material, and solid phase polymerization was performed at 220 ° C. under vacuum to obtain polyester (6). The intrinsic viscosity of the polyester (6) was 0.85, and the amount of terminal carboxyl groups of the polymer was 45 equivalents / ton.

<Method for producing white masterbatch 1 (WMB1)>
The polyester (2) was subjected to a twin screw extruder with a vent and supplied so that the titanium dioxide particles became 50% by weight to form chips, thereby obtaining a white master batch (WMB1).

<Method for producing white masterbatch 2 (WMB2)>
The polyester (5) was subjected to a twin screw extruder with a vent and supplied so that the titanium dioxide particles were 50% by weight to form chips, and a white masterbatch (WMB1) was obtained.

<Method for producing white masterbatch 3 (WMB3)>
The polyester (2) was subjected to a twin screw extruder with a vent and supplied so that the barium sulfate particles were 50% by weight to form chips, thereby obtaining a white masterbatch (WMB3).

Example 1:
A mixture of polyester (2) and polyester (3) mixed at a ratio of 80:20 as a raw material and 43 parts by weight of white masterbatch 1 (WMB1) added thereto is a single twin-screw extruder with a vent. Then, it was melt-extruded at 290 ° C. and rapidly cooled and solidified on a casting drum whose surface temperature was set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched single layer sheet. The obtained sheet was stretched 3.7 times in the longitudinal direction at 83 ° C., led to a tenter, stretched 3.9 times in the lateral direction at 110 ° C., and further heat-treated at 220 ° C. The average thickness of the obtained film was 50 μm. The properties and evaluation results of the obtained film are shown in Table 2 below. When creating a solar cell backside sealing material using the obtained film, strength degradation due to hydrolysis can be suppressed, weather resistance is also good, delamination due to oligomers generated on the film surface during bonding does not occur frequently, The period which can be used as a solar cell back surface sealing material was a satisfactory level.

Example 2:
In Example 1, a film was obtained in the same manner as in Example 1 except that the polyester raw material in the mixture was changed to the above polyester (2). The properties and evaluation results of the obtained film are shown in Table 2 below. When creating a solar cell backside sealing material using the obtained film, strength degradation due to hydrolysis can be suppressed, weather resistance is also good, delamination due to oligomers generated on the film surface during bonding does not occur frequently, The period which can be used as a solar cell back surface sealing material was a satisfactory level.

Example 3:
In Example 1, with respect to the polyester raw material in the mixture, the polyester obtained by mixing the polyester (2) and the polyester (3) at a ratio of 60:40 was changed to the raw material, and the white masterbatch 1 (WMB1) was 20 weights. A film was obtained in the same manner as in Example 1 except that the part was changed. The properties and evaluation results of the obtained film are shown in Table 2 below. When creating a solar cell backside sealing material using the obtained film, strength degradation due to hydrolysis can be suppressed, weather resistance is also good, delamination due to oligomers generated on the film surface during bonding does not occur frequently, The period which can be used as a solar cell back surface sealing material was a satisfactory level.

Example 4:
In Example 1, with respect to the polyester raw material in the mixture, the polyester obtained by mixing the polyester (2) and the polyester (3) at a ratio of 80:20 was changed to the raw material, and the white masterbatch 1 (WMB1) was 20 weights. A film was obtained in the same manner as in Example 1 except that the part was changed. The properties and evaluation results of the obtained film are shown in Table 2 below. When creating a solar cell backside sealing material using the obtained film, strength degradation due to hydrolysis can be suppressed, weather resistance is also good, delamination due to oligomers generated on the film surface during bonding does not occur frequently, The period which can be used as a solar cell back surface sealing material was a satisfactory level.

Example 5:
A mixture obtained by adding 43 parts by weight of the white masterbatch 1 (WMB1) to the polyester obtained by mixing the polyester (2) and the polyester (3) in a ratio of 80:20 is directly fed to the vented twin-screw extruder A (sub). A mixture obtained by adding 15 parts by weight of the white masterbatch (WMB1) to the polyester obtained by mixing the polyester (2) and the polyester (3) at a ratio of 80:20 was added to the vented twin-screw extruder B (main) Directly into Both raw materials were melted and kneaded in a twin-screw extruder at 290 ° C., and the resulting melt was merged into a multilayer T-die so as to have an A / B / A configuration and extruded into a slit shape. Then, it was rapidly cooled and solidified on a casting drum set to 2 to obtain an unstretched two-layered three-layer sheet. The obtained unstretched sheet was stretched 3.7 times in the longitudinal direction at 83 ° C., led to a tenter, stretched 3.9 times in the lateral direction at 110 ° C., and further heat treated at 220 ° C. The average thickness of the obtained film was 250 μm, and the layer composition ratio of A / B / A was 25/200/25. The properties and evaluation results of the obtained film are shown in Table 2 below. When creating a solar cell backside sealing material using the obtained film, strength degradation due to hydrolysis can be suppressed, weather resistance is also good, delamination due to oligomers generated on the film surface during bonding does not occur frequently, The period which can be used as a solar cell back surface sealing material was a satisfactory level.

Example 6:
In Example 1, regarding the polyester raw material in the mixture, the polyester obtained by mixing the polyester (2) and the polyester (3) in a ratio of 80:20 with respect to the polyester raw material in the mixture was changed to the raw material, and the white master batch was further changed. A film was obtained in the same manner as in Example 1 except that the type of the white master batch 3 (WMB3) was changed and the addition amount was changed to 43 parts by weight. The properties and evaluation results of the obtained film are shown in Table 2 below. When creating a solar cell backside sealing material using the obtained film, strength degradation due to hydrolysis can be suppressed, weather resistance is also good, delamination due to oligomers generated on the film surface during bonding does not occur frequently, The period which can be used as a solar cell back surface sealing material was a satisfactory level.

Comparative Example 1:
In Example 1, the polyester raw material in the mixture was changed to the above polyester (1), and the same method as in Example 1 except that the addition amount of the above white masterbatch 1 (WMB1) was changed to 20 parts by weight. A film was obtained. The properties and evaluation results of the obtained film are shown in Table 3 below. When the solar cell backside sealing material was made using the obtained film, the weather resistance was good, but the strength degradation due to hydrolysis was severe, and delamination due to oligomers that occurred on the film surface during lamination also occurred frequently. The period that can be used as the solar cell back surface sealing material was at an unsatisfactory level.

Comparative Example 2
In Example 1, the polyester raw material in the mixture was changed to the polyester (6), the white masterbatch type was changed to white masterbatch 2 (WMB2), and the addition amount was changed to 43 parts by weight. A film was obtained in the same manner as in Example 1. The properties and evaluation results of the obtained film are shown in Table 3 below. When the solar cell backside sealing material was created using the obtained film, the weather resistance was good, and delamination due to oligomers generated on the film surface during lamination did not occur frequently, but strength degradation due to hydrolysis The period when it can be used as a solar cell back surface sealing material was unsatisfactory.

Comparative Example 3:
In Example 1, with respect to the polyester raw material in the mixture, the polyester (2) and the polyester (4) were changed to a polyester mixed at a ratio of 10:90, and the addition amount of the white masterbatch 1 (WMB1) was 20 A film was obtained in the same manner as in Example 1 except that the weight was changed. The properties and evaluation results of the obtained film are shown in Table 3 below. When the solar cell backside sealing material was created using the obtained film, the weather resistance was good, and delamination due to oligomers generated on the film surface during lamination did not occur frequently, but strength degradation due to hydrolysis It was not sufficient, and the period during which it could be used as a solar cell back surface sealing material was at an unsatisfactory level.

Comparative Example 4:
In Example 1, the polyester raw material in the mixture was obtained in the same manner as in Example 1, except that the polyester (1) and the polyester (3) were changed to a polyester mixed at a ratio of 10:90. . The properties and evaluation results of the obtained film are shown in Table 3 below. When the solar cell backside sealing material was created using the obtained film, the weather resistance was good, but delamination due to oligomers generated on the film surface during lamination frequently occurred, and strength deterioration due to hydrolysis was sufficient However, the period that can be used as the solar cell back surface sealing material was unsatisfactory.

Comparative Example 5:
A film was obtained in the same manner as in Example 1 except that the amount of white master batch 1 (WMB1) added was changed to 5.0 parts by weight in Example 1. The properties and evaluation results of the obtained film are shown in Table 3 below. When a solar cell back surface sealing material was created using the obtained film, delamination due to oligomers generated on the film surface during lamination did not occur frequently, and strength deterioration due to hydrolysis did not occur, but weather resistance was poor Therefore, the period that can be used as the solar cell back surface sealing material was at an unsatisfactory level.

  In the said Table 2 and Table 3, the amount of terminal carboxylic acids and the amount of catalysts show the value in a polyester component.

  The film of this invention can be utilized suitably in the polyester film use for solar cell backside sealing materials.

Claims (1)

It is a polyester film comprising a polyester having a phosphorus element content of 170 ppm or less, a terminal carboxyl group content of 26 equivalents / ton or less, a white pigment content of 3% to 50% by weight, and heat treatment at 150 ° C. for 30 minutes. The polyester film for solar cell backside sealing materials, wherein the amount of oligomer present on the surface of the film is 0.8 mg / m ² or less.