JP2011189560A - Molten film-forming method for polyester film and polyester film for solar battery member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molten film-forming method for a polyester film suppressing effects by thermal history during melting and obtaining the polyester film having excellent hydrolytic resistance. <P>SOLUTION: Material resin including polyester resin and 30 eq/t or less of terminal carboxylic acid groups is input to a single-spindle extruding machine. Then, on the condition that a maximum temperature Tmax[°C] and a melting point Tm[°C] of the material resin in the melting process satisfy a relationship of Tm≤Tmax≤Tm+30 and a filling factor of the material resin in a screw compression part 4 is 50-80%, melting and extrusion are performed and molding is performed to form a film shape. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for melt-casting a polyester film having weather resistance and a polyester film for a solar cell member.

  In recent years, resin materials such as polyester have been used for backsheets arranged on the side opposite to the sunlight incident side of the solar cell module. Polyester usually has many carboxyl groups and hydroxyl groups on its surface, and tends to undergo hydrolysis in an environment where moisture exists, and tends to deteriorate over time. For this reason, polyesters used in solar cell modules and the like that are constantly exposed to wind and rain, such as outdoors, are required to have reduced hydrolyzability.

  In order to impart hydrolysis resistance to the polyester resin, it is conceivable to reduce terminal COOH serving as a catalyst for the hydrolysis reaction. Since terminal COOH is generated by heating at the time of melting, it is important to alleviate the thermal history at the time of melting when melt-forming with a plasticizing melt extruder.

  In relation to the above situation, a technique is disclosed in which the thermal history is reduced by placing the extruder in a tandem arrangement and cooling the resin with a second-stage extruder (see, for example, Patent Document 1). In addition, there is a document describing that plasticization exotherm is suppressed by the bulk specific gravity of the raw material (for example, see Patent Document 2).

  On the other hand, in order to suppress heat generation and achieve mass production, it is disclosed to use a vent type twin screw extruder (see, for example, Patent Document 3).

JP-A-10-119112 JP 11-43588 A Japanese Patent No. 3577178

  However, among the conventional technologies described above, in the extruder arranged in tandem, the heat generation of plasticization cannot be suppressed in the first-stage extruder, and the temperature rises locally, so that sufficient hydrolysis resistance is achieved. It cannot be granted.

  In addition, in the above-described technology that attempts to suppress the plasticization heat generation by the bulk specific gravity of the raw material, the heat generation when mass production is performed using a large extruder cannot be suppressed, and it is difficult to provide sufficient hydrolysis resistance. It is.

  Twin-screw extruders have equipment costs that are significantly higher than those of single-screw machines, and there are equipment incompatibilities such as increasing the number of places where resin may accumulate. ing.

  The present invention has been made in view of the above, suppresses the influence of heat history at the time of melting, and is excellent in hydrolysis resistance and hydrolysis resistance of a polyester film from which a polyester film excellent in hydrolysis resistance can be obtained. It aims at providing the polyester film for solar cell members with high durability, and makes it a subject to achieve this objective.

Specific means for achieving the above object are as follows.
<1> The maximum temperature Tmax [° C.] and the melting point of the raw material resin in the melting process after the raw material resin having an amount of terminal carboxylic acid groups of 30 eq / t (tons; the same applies hereinafter) is introduced into a single screw extruder. Tm [° C.] satisfies the relationship of Tm ≦ Tmax ≦ Tm + 30, and is melt-extruded under the condition that the filling ratio of the raw material resin in the screw compression portion is 50 to 80%, and is formed into a film. Is the method.

  <2> The method for melt film formation of a polyester film according to <1>, wherein the bulk specific gravity of the raw material resin is 0.6 to 0.8.

  <3> A pulverized piece of a resin film is used as a part of the raw material resin, and the mass ratio of the crushed piece in the raw material resin is 50% or less. It is a membrane method.

  <4> The melt film-forming method for a polyester film according to any one of <1> to <3>, wherein an average residence time in the screw compression section is 15 to 40 seconds.

  <5> The method according to <3> or <4>, wherein the crushed pieces have a thickness of 20 to 5000 μm.

  <6> The melt film-forming method for a polyester film according to any one of <3> to <5>, wherein the pulverized piece has a bulk specific gravity of 0.30 to 0.70.

  <7> The method for melt-forming a polyester film according to any one of <1> to <6>, wherein the amount of terminal carboxylic acid groups of the film after melt extrusion is 30 eq / t or less.

  <8> A solar cell member polyester film produced by the method for melt-forming a polyester film according to any one of <1> to <7>.

ADVANTAGE OF THE INVENTION According to this invention, the melt film forming method of the polyester film from which the influence of the heat history at the time of a fusion | melting can be suppressed, and the polyester film excellent in hydrolysis resistance can be obtained can be provided. Also,
ADVANTAGE OF THE INVENTION According to this invention, it is excellent in hydrolysis resistance and can provide the polyester film for solar cell members with high durability.

It is a schematic sectional drawing which shows the structural example of the single screw extruder for implementing the melt film-forming method of the polyester film of this invention. It is a schematic diagram which expands and shows the part of the broken-line circle | round | yen 4 of FIG.

  Hereinafter, the method for melting and forming a polyester film of the present invention will be described in detail, and the polyester film for a solar cell member formed by the melting and forming method will be described in detail through the description.

  In the melt film-forming method of a polyester film of the present invention, a raw material resin containing a polyester resin and having an amount of terminal carboxylic acid groups (hereinafter also referred to as terminal COOH) of 30 eq / t or less is charged into a single-screw extruder, Conditions in which the maximum temperature Tmax [° C.] and the melting point Tm [° C.] of the raw material resin in the melting process satisfy the relationship of Tm ≦ Tmax ≦ Tm + 30, and the filling rate of the raw material resin in the screw compression portion is 50 to 80% The composition is melt extruded and formed into a film.

In the present invention, the amount of heat in the melting process given to the raw resin during melt extrusion is in a range in which the increase in terminal COOH can be suppressed, and a filling rate that balances insufficient melting at the screw compression part and exothermic relaxation is achieved. By selecting, since the amount of terminal COOH of the formed film can be reduced, hydrolysis resistance can be improved, and long-term durability performance can be enhanced.
Even when film forming is performed using an extruder equipped with a large screw, shear heat generation is suppressed so that carboxylic acid groups do not increase, and deterioration of hydrolysis resistance due to the thermal history can be suppressed.

  The melt extrusion can be performed using a conventionally known extruder equipped with a single screw for extruding a molten resin. The extruder may be a small or large apparatus. In the present invention, the screw outer diameter is φ150 mm or more (more preferably φ200 to 400 mm) from the viewpoint that the effect of improving the hydrolysis resistance of the polyester film can be further expected while suppressing shearing heat generation that is likely to occur in mass production. A single screw extruder is preferred.

The raw material resin to be used has a terminal COOH amount of 30 eq / t (tons) or less. When the amount of terminal COOH exceeds 30 eq / t, hydrolysis resistance of the resulting polyester film becomes insufficient.
The terminal COOH amount of the raw material resin represents the amount in a mixed state when a plurality of types of resins are mixed and used. For example, when polyethylene terephthalate (PET) is mixed with one or more kinds of pellets or chip material that is crushed waste of PET film, the total amount of terminal COOH of pellets, or the amount of terminal COOH of pellets and chips And the total amount of terminal COOH.

  The terminal COOH amount of the raw material resin is preferably 25 eq / t or less. Further, the lower limit of the amount of terminal COOH is preferably 2 eq / t, for example, from the viewpoint of obtaining adhesion with the adherend.

The amount of terminal COOH is a value measured by the following method. That is,
After 0.1 g of the raw material resin is dissolved in 10 ml of benzyl alcohol, chloroform is further added to obtain a mixed solution, and a phenol red indicator is added dropwise thereto. This solution is titrated with a standard solution (0.01N KOH-benzyl alcohol mixed solution), and the amount of terminal carboxyl groups is determined from the amount added.

The raw material resin has a relationship of Tm ≦ Tmax ≦ Tm + 30 between the maximum temperature Tmax [° C.] when heated in the melting process and the melting point Tm [° C.]. When Tmax is less than Tm, melting at the time of melt extrusion becomes insufficient, and discharge from the die becomes impossible. Also. When Tmax exceeds “Tm + 30”, the terminal COOH significantly increases.
Among these, the range of Tmax is more preferably Tm + 10 ≦ Tmax ≦ Tm + 20.

  The maximum temperature Tmax in the melting process is the temperature of the raw material resin heated in the cylinder in which the screw of the single screw extruder is arranged. When there is shearing heat generation, the temperature including the local high temperature portion due to the heat generation It is. Tmax is obtained by measuring the resin temperature in the cylinder. In the relational expression of Tm and Tmax, Tmax [° C.] is preferably 290 ° C. or less, and more preferably 280 ° C. or less from the viewpoint of suppressing increase in terminal COOH. The lower limit temperature of Tmax is 260 ° C. from the viewpoint of preventing insufficient melting of the resin.

The melting point Tm of the raw material resin is an average value of melting points when it is a mixture of a plurality of resins, and is preferably in the range of 250 ° C to 260 ° C. In this case, it is more preferable to satisfy the relationship of Tm ≦ Tmax ≦ Tm + 30.
The melting point Tm is a value obtained by differential scanning calorimetry.

  Melt extrusion is performed under the condition that the filling rate of the raw material resin (vs. the cylinder void volume) in the screw compression part of the cylinder of the extruder is 50 to 80%. Here, the filling rate is an average filling rate in the screw compression part in the cylinder, and since the resin is almost completely melted at the outlet of the compression part, the filling rate at the compression part outlet is 100%. The screw compression portion refers to a region in the cylinder where the screw groove depth is smaller than the screw groove depth of the supply portion (for example, the screw groove depth gradually decreases from the screw groove depth of the supply portion). In the cylinder in which the screw groove depth decreases in this way, the volume in which the resin can move (cylinder gap volume) decreases toward the resin extrusion direction, and the shear stress applied to the resin gradually increases, so it is extremely easy to generate heat. Tend.

The average filling rate in the present invention uses an estimated value obtained as follows based on the result of pressure measurement.
First, the pressure in the longitudinal direction of the screw groove is measured with a pressure gauge. Since the screw is rotating at the time of extrusion, the pressure gauge apparently scans (measures) the screw groove width direction (the shortest distance direction between screw flights). From the waveform (value) indicating the maximum and minimum pressures obtained by measurement, the filling rate in the screw groove width direction (the shortest distance direction between screw flights) is obtained, and the average filling rate is obtained by the following equation (1). In addition, the filling rate [%] at the inlet of the compression unit is obtained from the following formula (2).
In the formula, the filling rate [%] in the screw groove width direction shows the maximum peak in the pressure waveform in the screw groove width direction, considering the groove width position where the pressure is halfway between the maximum and minimum values as the full / unfilled boundary. This is a value obtained by the ratio of the width on the side shown to the overall length of the groove.
Average filling rate [%] = (compression unit outlet filling rate + compression unit inlet filling rate) / 2 (1)
Compression section outlet filling rate = 100%
Compression unit inlet filling rate [%] = screw groove width direction filling rate [%] × raw material bulk specific gravity (2)

  At the compression section outlet, the resin is almost completely melted, so the filling rate becomes 100%. However, on the compression section inlet side where the screw groove depth starts to decrease, the melting is still insufficient, so the bulk density of the resin and Since the bulk specific gravity decreases due to the start of melting, when the amount of resin is schematically shown as shown in FIG. 2, the full length d in the groove width direction of the screw groove of the raw resin 8 becomes small. FIG. 2 is a schematic diagram showing an enlarged view of the broken-line circle 4 in FIG.

  If the filling rate of the raw material resin is less than 50%, the resin will be insufficiently melted. If it exceeds 80%, the terminal COOH will increase due to the temperature rise due to shearing heat generation, and the hydrolysis resistance will be significantly reduced. As a range of a filling rate, the range of 65 to 80% is preferable, and the range of 70 to 80% is more preferable.

  The above filling rate can be adjusted by increasing or decreasing the bulk of the raw material resin. In the present invention, for example, two or more kinds of pellets having different sizes are mixed, or one or two or more kinds of pellets are mixed with a film pulverizing material (e.g., pulverized waste such as film crushed chips). The filling rate can be adjusted by adjusting the bulk of the raw material resin by the method.

  The bulk specific gravity of the raw material resin refers to the specific gravity (per unit volume) obtained by dividing the mass of the powder into a predetermined shape by dividing the powder into a predetermined volume in a constant volume container. Mass), the smaller the bulk specific gravity, the larger the bulk.

The bulk specific gravity of the raw material resin is preferably in the range of 0.6 to 0.8. When the bulk specific gravity is 0.6 or more, extrusion can be performed more stably. When the bulk specific gravity is 0.8 or less, local heat generation can be effectively suppressed.
Among the above, the bulk specific gravity of the raw material resin is particularly preferably in the range of 0.7 to 0.75 in that the increase in terminal COOH is further suppressed by suppressing heat generation during extrusion.

The polyester resin constituting the raw material resin can be obtained by subjecting dicarboxylic acid or an ester derivative thereof and a diol compound to an esterification reaction and / or an ester exchange reaction by a known method.
Examples of the dicarboxylic acid or ester derivative thereof include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalon. Aliphatic dicarboxylic acids such as acid, ethylmalonic acid and the like, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4 -Naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylether dicarboxylic acid, 5-sodium Sulfoisophthalate Acid, phenyl ene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic, 9,9'-bis (4-carboxyphenyl) a dicarboxylic acid or an ester derivative such as an aromatic dicarboxylic acid such as fluorene acid.
Examples of the diol compound include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. , Cycloaliphatic dimethanol, spiroglycol, isosorbide and other alicyclic diols, bisphenol A, 1,3-benzenedimethanol, 1,4-benzendimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene And aromatic diols such as.

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

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

  The Ti-based catalyst has high reaction activity and can lower the polymerization temperature. Therefore, it is possible to suppress the thermal decomposition of PET and the generation of COOH particularly during the polymerization reaction. In the present invention, it is suitable for adjusting the terminal COOH amount of the polyester film to a range of 30 eq / ton or less.

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

Polymerization is preferably performed using a titanium (Ti) -based compound in the range of 1 ppm to 30 ppm, more preferably 2 ppm to 20 ppm, and even more preferably 3 ppm to 15 ppm. In this case, the polyester film of the present invention contains 1 ppm to 30 ppm of titanium.
When the amount of the Ti-based catalyst is 1 ppm or more, preferable IV is obtained, and when it is 30 ppm or less, the terminal COOH can be kept low, which is advantageous in improving the hydrolysis resistance.

  The raw material resin is preferably prepared by mixing pulverized pieces of a resin film. As the resin film, a polyester film is preferable, and a polyester film of the same type as the polyester resin in the raw resin is preferable. The pulverized piece of the resin film is a pulverized product obtained by pulverizing an unnecessary film into small pieces (so-called chips), scrap pieces, etc., giving a bulkiness and lowering the bulk specific gravity, for example, compared to the case of only a pellet. be able to.

  The size of the crushed pieces is not limited as long as the bulk change is given, but those having a thickness of 20 μm to 5000 μm are preferable. Among these, from the viewpoint of preventing the filling ratio from excessively decreasing due to excessive bulk specific gravity and avoiding insufficient melting, the range of 100 to 1000 μm, more preferably the range of 100 to 500 μm is more preferable.

  Further, in terms of further reducing the amount of terminal COOH of the polyester film to be formed, it is preferable that the variation in the size of the crushed pieces is smaller, for example, in the thickness of the crushed pieces, the variation is preferably within ± 100%, More preferably, it is within ± 50%, and further within ± 10%. When using the pulverized pieces, it is possible to suppress the variation in the amount of terminal COOH of the obtained polyester film by suppressing the size variation such as thickness.

  The mass ratio of the crushed pieces in the raw resin is preferably 50% or less with respect to the total mass of the raw resin, and the lower limit of the mass ratio is preferably 10%. By setting the proportion of the crushed pieces to 50% by mass or less, the fluctuation range of the terminal COOH amount of the obtained polyester film can be further reduced. Among these, for the same reason, the mass ratio of the crushed pieces is more preferably 10 to 30%, and particularly preferably 20 to 30%.

  The bulk specific gravity of the crushed pieces is preferably in the range of 0.3 to 0.7 in the range where the bulk specific gravity of the raw material resin satisfies the above range. The bulk specific gravity is synonymous with the bulk specific gravity of the raw material resin described above, and is measured in the same manner as described above.

The method for producing a polyester film of the present invention includes a step of drying a prepared raw resin or each resin component constituting the prepared raw resin in advance, and then charging the dried raw resin into a hopper of a single screw extruder. After melt-kneading at a temperature of, a melt extrusion step of extruding this from a die (for example, to a cooling roll) is provided, and the film can be formed by forming into a film shape.
In addition, when performing the drying process with respect to each resin component etc. which prepare raw material resin, the process of preparing raw material resin by mixing a resin component etc. can be provided after a drying process.

  As a single screw extruder, it can select and use from the single screw kneading extruder provided with the cylinder by which the screw was distribute | arranged. Specifically, for example, as shown in FIG. 1, a cylinder 6 in which a screw 5 having a desired outer diameter is disposed, and a hopper that is attached to the cylinder wall and supplies raw material resin 8 into the cylinder. 7 can be used. The cylinder 6 includes a supply portion having a supply port to which a hopper 7 is attached and a raw material resin is supplied, and a screw compression portion in which the groove depth of the screw gradually decreases from the supply portion side toward the resin extrusion direction (also simply referred to as a compression portion). And a weighing unit that measures a predetermined amount of the molten resin in a kneaded state, and the molten resin measured by the weighing unit is provided downstream of the metering unit in the resin extrusion direction. Extruded from a die (not shown).

When the raw material resin is extruded while being melt-kneaded as described above, in the screw compression portion, the shear stress increases as the groove depth of the groove portion decreases, and locally generates heat. By suppressing the heat generation at this time, the hydrolysis resistance of the formed polyester film can be enhanced. The shear rate during extrusion is preferably from 1 s ^{−1 to} 300 s ⁻¹ , more preferably from 10 s ^{−1 to} 200 s ⁻¹ , and even more preferably from 30 s ^{−1 to} 150 s ⁻¹ .

In the present invention, it is particularly preferred that the kneading is carried out with the average residence time in the screw compression section being 15-40 seconds. As described above, in the melting process, the raw material resin satisfies the relationship of Tm ≦ Tmax ≦ Tm + 30, and the filling rate of the raw material resin in the screw compression part is 50 to 80%, so that the average residence time is 15 seconds or more. In this case, melt kneading can be performed satisfactorily and an increase in terminal COOH can be suppressed. Further, when the average residence time is 40 seconds or less, the terminal COOH can be kept lower.
Among these, the average residence time is preferably in the range of 15 to 30 seconds for the same reason as described above.
Here, the average residence time of the screw compression section is defined by the following formula.
Average residence time [sec] = screw compression section length [mm] / screw diameter [mm] / screw rotation speed [r.p.m.] × 60

  It is preferable to adjust the humidity to 5% RH or more and 60% RH or less after extruding the melt (molten resin) from the die and bringing it into contact with the cooling roll (air gap), and 15% RH or more and 50% RH or less. It is more preferable to adjust to the following. By adjusting the humidity in the air gap to the above range, it is possible to adjust the amount of COOH and OH on the film surface, and by adjusting to low humidity, the amount of carboxylic acid on the film surface can be reduced. .

  In the melt film-forming method of the polyester film of the present invention, the screw groove depth of φ150 mm or more is gradually reduced by 30 to 70% (compression rate is 2.0 to 4.0). The range of 80%, the maximum temperature of the resin is Tm to Tm + 30 ° C. or less, and the mode of melt kneading with an average residence time in the screw compression part of 15 to 30 seconds is the terminal COOH while maintaining productivity. This is preferable in that the increase in hydrolysis resistance is suppressed and the effect of improving hydrolysis resistance is large.

After the melt extrusion, a polyester film (polyester film for solar cell member of the present invention) having a terminal COOH amount of 30 eq / t (tons) or less can be obtained. When the terminal COOH amount is 30 eq / ton or less, the hydrolysis resistance is excellent, and long-term durability is obtained. The amount of terminal COOH is desirably low in terms of hydrolysis resistance, but is preferably 2 eq / ton or more from the viewpoint of improving adhesion when the film is adhered to an adherend. Especially, the range of 10-30 eq / ton is more preferable.
The terminal COOH amount can be measured in the same manner as described above.

  The polyester film for solar cell members of the present invention is formed by the above-described method for melt-forming the polyester film of the present invention, and is suitable for producing a solar cell excellent in long-term durability performance.

  The film thickness is preferably 2 mm or more and 8 mm or less, more preferably 2.5 mm or more and 7 mm or less, and further preferably 3 mm or more and 6 mm or less. By increasing the thickness, the time required for the extruded melt to cool below the glass transition temperature (Tg) can be increased. During this time, COOH groups on the film surface are diffused into the polyester, and the amount of surface COOH can be reduced.

  The polyester film of the present invention can further contain additives such as a light stabilizer and an antioxidant.

  When a light stabilizer is contained, UV degradation can be prevented. Examples of the light stabilizer include a compound that absorbs light such as ultraviolet rays and converts it into heat energy, and a material that captures radicals generated by light absorption and decomposition of the resin and suppresses the decomposition chain reaction. The light stabilizer is preferably a compound that absorbs light such as ultraviolet rays and converts it into heat energy. By containing such a light stabilizer, the effect of improving the partial discharge voltage can be kept high for a long period of time even if it is irradiated with ultraviolet rays continuously for a long period of time. Change, strength deterioration, etc. are prevented.

  For example, if an ultraviolet absorber is a range in which other properties of the polyester are not impaired, any of organic ultraviolet absorbers, inorganic ultraviolet absorbers, and combinations thereof are preferably used without particular limitation. Can do. On the other hand, it is desired that the ultraviolet absorber is excellent in moisture and heat resistance and can be uniformly dispersed in the resin.

Examples of ultraviolet absorbers include, for example, salicylic acid-based, benzophenone-based, benzotriazole-based, cyanoacrylate-based ultraviolet absorbers, hindered amine-based ultraviolet stabilizers, and the like as organic ultraviolet absorbers. Specifically, for example, salicylic acid-based pt-butylphenyl salicylate, p-octylphenyl salicylate, benzophenone-based 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy -5-sulfobenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenyl) methane, benzotriazole 2- (2'-hydroxy-5) '-Methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6 (2H benzotriazol-2-yl) phenol], a cyanoacrylate Ethyl-2-cyano-3,3′-diphenylacrylate), 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol as triazine system Hindered amine-based bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl Piperidine polycondensate, in addition, nickel bis (octylphenyl) sulfide, 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl-4′-hydroxybenzoate, and the like .
Of these ultraviolet absorbers, triazine-based ultraviolet absorbers are more preferable in that they have high resistance to repeated ultraviolet absorption. In addition, these ultraviolet absorbers may be added to the above-mentioned ultraviolet absorber alone, or a form in which an organic conductive material or a water-insoluble resin is copolymerized with a monomer having an ultraviolet absorber ability. May be introduced.

  The content of the light stabilizer in the polyester film is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.3% by mass or more and 7% by mass or less with respect to the total mass of the polyester film. More preferably, it is 0.7 mass% or more and 4 mass% or less. Thereby, the molecular weight fall of the polyester by the photodegradation over a long time can be suppressed, and the adhesive force fall resulting from the cohesive failure in the film which arises as a result can be suppressed.

  In addition to the light stabilizer, the polyester film of the present invention contains, for example, a lubricant (fine particles), an ultraviolet absorber, a colorant, a nucleating agent (crystallization agent), a flame retardant, and the like. It can contain as.

  The polyester film of this invention is suitable for uses, such as a back surface protection sheet (what is called a back sheet) arrange | positioned at the back surface on the opposite side to the sunlight incident side of a solar cell power generation module, a barrier film base material.

  For solar cell power generation module applications, the power generation elements (solar cell elements) connected by lead wires (not shown) for extracting electricity are sealed with a sealant such as ethylene / vinyl acetate copolymer (EVA) resin. The aspect comprised by sticking together this between the transparent substrates, such as glass, and the polyester film (back sheet | seat) of this invention is mentioned. Examples of solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, and copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenic, and other III- Various known solar cell elements such as V group and II-VI compound semiconductor systems can be applied.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1
-Preparation of molding equipment-
As an extrusion molding machine, as shown in FIG. 1, a uniaxial kneading extruder provided with the following screw 5 inside a cylinder 6 (screw outer diameter D = 250 mm, length L [mm] / D [mm] = 30, cylinder Temperature setting = 275 ° C.) was prepared. In addition, the length of each part of a screw is supply part: compression part: measurement part = 10D: 10D: 10D.
<Screw part>
・ Full flight ・ Supply part groove depth: 20mm
・ Measurement groove depth: 6.1mm
・ Compression rate: 3.1

As shown in FIG. 2, a pressure gauge P1 is attached to the outer wall of the cylinder 6 of this kneading extruder on the downstream side of the compression portion where the groove depth of the screw 5 becomes small, and the screw 5 is rotating. At the time of extrusion, the longitudinal direction of the screw groove is scanned by the pressure gauge P1, and the internal pressure of the groove portion can be measured.
The pressure gauge P1 also has a temperature detection function, and can detect the local heat generation temperature of the wall surface resin.

-Preparation of raw materials-
Next, the following PET pellets and PET chips (melting point Tm = 257 ° C., intrinsic viscosity IV = 0.65, terminal COOH amount = 25 eq / ton, crystallized at 160 ° C. with a Henschel mixer) were prepared as raw materials.
PET pellets having an average major axis: 4.5 mm, an average minor axis: 1.8 mm, and an average length: 4.0 mm were used. Further, the PET chip is a crushed scrap of a PET film, and the size is 80 to 180 μm in thickness and 0.40 to 0.55 in bulk specific gravity.

-Film production-
PET chips were mixed with PET pellets at the ratios shown in Table 1 below to prepare raw materials with bulk specific gravity and terminal COOH content shown in Table 1 below. This raw material was dried by heating to a moisture content of 50 ppm or less, and then charged into a hopper of a single-screw kneading extruder, melted at 275 ° C., and extruded. At this time, the discharge pressure was kept constant by controlling the rotational speed of the screw.

At this time, the pressure in the longitudinal direction of the screw groove was measured by a pressure gauge P1 attached to the cylinder wall in the compression portion of the cylinder 6. Since the screw 5 is rotating at the time of extrusion, the pressure gauge P1 apparently scans and measures the screw groove width direction (the shortest distance direction between screw flights). From the measured waveform (value), the average filling rate was obtained as the compression portion filling rate by the following formula. The average filling rate is shown in Table 1 below.
Average filling rate [%] of compression part = (100 + filling rate [%] of compression part inlet) / 2
In addition, the filling rate of a compression part inlet_port | entrance is calculated | required from a following formula.
Filling rate at compression section inlet [%] = Filling rate in screw groove width direction [%] x raw material bulk specific gravity

The melt (melt) was passed through a gear pump and a filter (pore diameter 20 μm), and then extruded from a die to a cooling (chill) roll under the following conditions. The extruded melt was brought into close contact with the cooling roll using an electrostatic application method. As the cooling roll, a hollow chill roll is used, and the temperature of the cooling roll can be controlled through water as a heating medium.
The conveyance area (air gap) from the die exit to the cooling roll surrounds this conveyance area, and humidity is adjusted to 30% RH by introducing humidity-conditioned air therein. Further, the melt thickness was set to 1000 μm by adjusting the discharge amount of the extruder and the slit width of the die.
As described above, a PET film was melt-formed.

-Measurement of terminal COOH amount-
About the obtained PET film, after dissolving 0.1 g of PET film in 10 ml of benzyl alcohol, chloroform was further added, the mixed solution was obtained, and the phenol red indicator was dripped at this. This solution was titrated with a standard solution (0.01 N KOH-benzyl alcohol mixed solution), and the amount of terminal carboxyl groups was determined from the amount added dropwise. The results are shown in Table 1 below.

(Examples 2 to 7)
In Example 1, except that the conditions such as the bulk specific gravity, the chip ratio, and the residence time were changed as shown in Table 1 below, a film was formed in the same manner as in Example 1, and the amount of terminal COOH was measured. . The results are shown in Table 1 below.

(Example 8)
In Example 1, PET pellets having a terminal COOH amount of 18 eq / ton (melting point Tm = 257 ° C., intrinsic viscosity IV = 0.65, crystallized at 160 ° C. with a Henschel mixer) were prepared, and used as a raw material resin A film was formed in the same manner as in Example 1 except that the terminal COOH amount was changed from 25 eq / ton to 18 eq / ton, and the terminal COOH amount was measured. The results are shown in Table 1 below.

Example 9
In Example 8, a film was formed in the same manner as in Example 8 except that the conditions such as residence time and screw rotation number were changed as shown in Table 1 below, and the amount of terminal COOH was measured. The results are shown in Table 1 below.

(Example 10)
A film was formed in the same manner as in Example 1 except that the cylinder temperature was lowered to 270 ° C. in Example 1 (resin temperature at the exit of the extruder = 271 ° C.), and the amount of terminal COOH was measured. The results are shown in Table 1 below.

(Examples 11 to 12)
In Example 10, a film was formed in the same manner as in Example 10 except that the conditions such as temperature, residence time, screw rotation speed, and the like were changed as shown in Table 1 below, and the amount of terminal COOH was measured. . The results are shown in Table 1 below.

(Comparative Examples 1-5)
In Example 1, a comparative film was formed in the same manner as in Example 1 except that the conditions such as the filling rate, temperature, bulk specific gravity, and chip ratio were changed as shown in Table 1 below. The amount of COOH was measured. The results are shown in Table 1 below.

(Comparative Examples 6-7)
In Example 1, except that the cylinder temperature was changed from 275 ° C. to 295 ° C. (resin temperature at the exit of the extruder = 293 ° C., Comparative Example 6) or 255 ° C. (Comparative Example 7). In the same manner as in Example 1, a comparative film was formed, and the amount of terminal COOH was measured. The results are shown in Table 1 below.

As shown in Table 1, in the examples, the amount of terminal COOH was kept low, and a PET film excellent in hydrolysis resistance could be obtained.
On the other hand, in Comparative Example 1 in which the amount of terminal COOH of the raw material is large, a PET film capable of suppressing hydrolyzability was not obtained, which greatly affected the provision of wet heat resistance. Further, in Comparative Examples 2 and 3 in which the filling rate in the compressed portion was too low or too high, the increase in terminal COOH was remarkable, and in Comparative Example 2 with a low filling rate, the melting was insufficient. In Comparative Examples 4 to 7 not satisfying the relationship of Tm ≦ Tmax ≦ Tm + 30, the lower limit side caused insufficient melting, and the upper limit side could not prevent an increase in terminal COOH.

Claims (8)

  A raw material resin containing a polyester resin and having an amount of terminal carboxylic acid groups of 30 eq / t or less is charged into a single screw extruder, and then the maximum temperature Tmax [° C.] and melting point Tm [° C.] of the raw material resin in the melting process Is a melt film-forming method of a polyester film, which satisfies the relationship of Tm ≦ Tmax ≦ Tm + 30 and is melt-extruded under the condition that the filling rate of the raw material resin in the screw compression part is 50 to 80% and molded into a film shape.   The method for melt film formation of a polyester film according to claim 1, wherein the bulk specific gravity of the raw material resin is 0.6 to 0.8.   The method for melting and forming a polyester film according to claim 1 or 2, wherein a pulverized piece of a resin film is used as a part of the raw resin, and a mass ratio of the pulverized piece in the raw resin is 50% or less.   The average residence time in the said screw compression part is 15 to 40 second, The melt film-forming method of the polyester film of any one of Claims 1-3.   The method for melting and forming a polyester film according to claim 3 or 4, wherein the crushed pieces have a thickness of 20 to 5000 µm.   The method for melting and forming a polyester film according to any one of claims 3 to 5, wherein the pulverized piece has a bulk specific gravity of 0.3 to 0.7.   The amount of terminal carboxylic acid groups of the film after melt extrusion is 30 eq / t or less, The melt film-forming method of the polyester film of any one of Claims 1-6.   The polyester film for solar cell members produced by the melt film-forming method of the polyester film of any one of Claims 1-7.