JP6199198B2 - Laminated film, back sheet for solar cell module, and solar cell module - Google Patents

Description

  The present invention relates to a laminated film, a back sheet for a solar cell module, and a solar cell module.

  Polyester films are used in various fields because they are inexpensive and have excellent characteristics. The performance required for polyester films is diverse. For example, when a polyester film is used for a long-term outdoor use such as a protective film for a solar cell, it is visible from the viewpoint of high hydrolysis resistance and designability in order to maintain strength over a long period of time. It is required that the light concealment is high.

  For this reason, for example, Patent Document 1 includes a surface layer containing 10 to 30% by weight of titanium oxide particles and a base material layer containing 0.1 to 4% by weight of titanium oxide particles. A laminated polyester film is described which is 3-8% by weight. Moreover, in patent document 2, it has the multilayer structure by which the inorganic fine particle concentration containing layer containing an inorganic fine particle was arrange | positioned in at least one outermost layer, and content of the inorganic fine particle in the whole polyester film is 2-10 mass%. A polyester film is described.

International Publication 2010/113920 Pamphlet Japanese Patent No. 5288068

  The visible light hiding property of the polyester film can be improved by adding a white pigment to the polyester film. However, in the process of kneading the white pigment into the polyester during the production of the polyester film, the polyester may be hydrolyzed due to moisture contained in the white pigment, and the heat generated by shearing of the white pigment particles may cause thermal degradation of the polyester. May occur. For this reason, there is a problem that the molecular weight of the polyester decreases and the hydrolysis resistance decreases as the white pigment concentration is increased for the purpose of improving the visible light hiding property. For these reasons, it is difficult to produce a polyester film having both hydrolysis resistance and visible light hiding properties.

  The polyester film of Patent Document 1 achieves both hydrolysis resistance and visible light hiding properties by increasing the visible light hiding property by the surface layer and enhancing the hydrolysis resistance by the base material layer. However, since the titanium oxide concentration of the entire film is as high as 3 to 8% by weight, the visible light hiding property is excellent, but the hydrolysis resistance is not sufficient. The polyester film of patent document 2 is aiming at coexistence of light reflectivity and hydrolysis resistance by making content of the inorganic fine particles of the whole film into 2-10 mass%. However, since the content of the inorganic fine particles in the entire film is as high as 2 to 10% by mass, the visible light hiding property is excellent, but the hydrolysis resistance is not sufficient.

  This invention is made | formed in order to solve said subject, and makes it the subject which should be solved to provide the laminated | multilayer film which has the property of both hydrolysis resistance and visible-light hiding property. Furthermore, this invention makes it the problem which should be solved to provide the solar cell module backsheet and solar cell module containing said laminated | multilayer film.

As a result of intensive studies to solve the above problems, the present inventors have at least a first layer containing polyester and a white pigment, and a second layer containing polyester, and the first layer In the laminated film in contact with at least one surface of the second layer, the white pigment density of the first layer, the thickness of the second layer, the white pigment concentration of the whole laminated film, and the terminal carboxyl group of the whole laminated film It has been found that excellent hydrolysis resistance and excellent visible light hiding property can be achieved by satisfying predetermined conditions for the respective concentrations. The present invention has been completed based on these findings.
Specifically, the present invention has the following configuration.

<1> A laminated film having at least a first layer containing a polyester and a white pigment and a second layer containing a polyester,
The first layer is in contact with at least one surface of the second layer;
The white pigment density of the first layer is 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻³ g / cm ² ,
The thickness of the second layer is 100-300 μm,
The white pigment concentration of the entire laminated film is greater than 0% by mass and less than 2% by mass,
The laminated film whose terminal carboxyl group density | concentration of the whole laminated film is 6-30 equivalent / ton.
<2> The laminated film according to <1>, wherein the white pigment concentration of the first layer is 5 to 20% by mass.
<3> The film according to <1> or <2>, wherein the first layer has a thickness of 5 to 50 μm.
<4> The laminated film according to any one of <1> to <3> 3, wherein the white pigment concentration of the second layer is 0 to 1.5% by mass.
<5> The second layer contains 60% by mass or less of recycled chips obtained by trimming and crushing the widthwise end of the laminated film as a raw material, and the first layer substantially does not contain recycled chips, <1> The laminated film according to any one of to <4>.
<6> The laminated film according to any one of <1> to <5>, which is for a solar cell module.
<7><1>-<6> The solar cell module backsheet containing the laminated | multilayer film in any one of.
<8> A solar cell module including the back sheet for a solar cell module according to <7>.

  According to the present invention, a laminated film having both hydrolysis resistance and visible light hiding properties is provided. Furthermore, according to this invention, the solar cell module backsheet which has the property of both hydrolysis resistance and visible-light concealment property is provided. Furthermore, according to this invention, the solar cell module containing the laminated film or solar cell module backsheet of this invention is provided.

FIG. 1 is a cross-sectional view showing an example of the configuration of the laminated film of the present invention. FIG. 2 is a cross-sectional view showing another example of the configuration of the laminated film of the present invention.

  Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

<Laminated film>
The laminated film of the present invention is a laminated film having at least a first layer containing polyester and a white pigment, and a second layer containing polyester, wherein the first layer is the second layer. The white pigment density of the first layer is 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻³ g / cm ² , and the thickness of the second layer is in contact with at least one surface of Is 100 to 300 μm, the white pigment concentration of the whole laminated film is more than 0% by mass and less than 2% by mass, and the terminal carboxyl group concentration of the whole laminated film is 6 to 30 equivalent / ton. And

By setting it as such a structure, the property of both hydrolysis resistance and visible-light hiding property can be achieved. About the mechanism which comes to have the property of both hydrolysis resistance and visible light hiding property, it estimates as follows. That is, a layer having a low white pigment concentration is used as the second layer to impart high hydrolysis resistance to the second layer, and a layer having a high white pigment concentration is used as the first layer. It is presumed that both the hydrolysis resistance and the visible light hiding property can be realized by giving a high visible light hiding property to a layer structure in which the first layer and the second layer are laminated. Specifically, by setting the white pigment density of the first layer to 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻³ g / cm ² , a good visible light hiding property is achieved, and the second layer The layer has a thickness of 100 to 300 μm, the white pigment concentration of the entire laminated film is less than 2% by mass, and the terminal carboxyl group concentration of the entire laminated film is 6 to 30 equivalents / ton. Presumed to be achieved.

  The laminated film of the present invention has at least a first layer containing polyester and a white pigment and a second layer containing polyester, and the first layer has at least one surface of the second layer. It touches.

An example of the laminated film of the present invention is shown in FIG. The laminated film shown in FIG. 1 is a laminated film having a two-layer structure including a first layer 12 and a second layer 10, and the first layer is in contact with one surface of the second layer. Further, the laminated film of the present invention is not limited to the laminated film having a two-layer structure as shown in FIG. 1, and as shown in FIG. 2, the first layer 12 and the second layer 10. And the laminated film of the 3 layer structure laminated | stacked in order of the 1st layer 12 may be sufficient. Furthermore, the laminated film of the present invention may be a laminated film in which the first layer, the second layer, and other layers are laminated in this order.
When a laminated film is used in an application used by being bonded to a different material such as a solar battery back sheet, the adhesive layer is poor and easily peels off when the white pigment concentration on the bonded surface is large. A two-layer structure consisting of these layers is preferred.

Hereinafter, each layer of the laminated film of the present invention will be described.
<First layer>
The first layer contains polyester and a white pigment, and the white pigment density is 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻³ g / cm ² . The first layer is in contact with at least one surface of the second layer.

The white pigment density of the first layer is 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻³ g / cm ² , and 1.0 × 10 ^{−4 to} 7.0 × 10 ⁻⁴ g / cm 2. ² is preferable, and 1.5 × 10 ^{−4 to} 6.0 × 10 ⁻⁴ g / cm ² is more preferable. Visible light concealability can be improved by setting the white pigment density of the first layer to 1.0 × 10 ⁻⁴ g / cm ² or more, and 1.0 × 10 ⁻³ g / cm ² or less. Thereby, hydrolysis resistance can be improved.

The white pigment density of the first layer is a parameter determined by the thickness of the first layer and the concentration of the white pigment contained in the first layer, and can be specifically calculated by the following equation.
D = t × ρ × C × 10 ⁻⁶
here,
White pigment density: D g / cm ²
White pigment concentration: C mass%
The thickness of the first layer: t μm
Density of the first layer: ρ g / cm ³
It is.

The concentration of the white pigment contained in the first layer is preferably 5 to 20% by mass, more preferably 5 to 15% by mass, and further preferably 6 to 12% by mass. When the content is 5% by mass or more, sufficient visible light hiding property can be obtained, and when the content is 20% by mass or less, hydrolysis resistance can be improved.
The concentration of the white pigment in the first layer is a parameter representing the percentage of the mass of the white pigment in the mass of the entire first layer, and can be specifically measured by the following method. . That is, 3 g of the laminated film as a measurement sample was taken in a crucible and heated in an electric oven at 900 ° C. for 120 minutes. Then, after the electric oven has cooled, the crucible is taken out and the mass of ash remaining in the crucible is measured. This ash content is the white pigment content, the mass of the ash content is divided by the mass of the measurement sample, and a value multiplied by 100 is taken as the white pigment concentration.

  The thickness of the first layer is not particularly limited, and is, for example, 1 to 100 μm, preferably 5 to 50 μm, more preferably 10 to 50 μm, and further preferably 30 to 50 μm. When the thickness of the first layer is 5 μm or more, the visible light hiding property can be improved, and when it is 50 μm or less, the hydrolysis resistance can be improved.

<Second layer>
The second layer contains polyester. The thickness of the second layer is 100 to 300 μm, more preferably 200 to 300 μm, and further preferably 200 to 250 μm. When the thickness is 100 μm or more, sufficient hydrolysis resistance is obtained, and when the thickness is 300 μm or less, productivity is improved and economical.

  Regarding the polyester contained in the second layer, the polyester contained in the first layer and the polyester contained in the second layer may be the same or different.

The second layer may or may not contain a white pigment. When a white pigment is included in the second layer, the white pigment contained in the first layer and the white pigment contained in the second layer may be the same or different.
When the white pigment is contained in the second layer, the white pigment concentration is preferably 0 to 1.5% by mass, more preferably 0 to 1% by mass, and still more preferably substantially not contained. “Substantially not contained” means that it is not contained within a range that does not affect the effect of the present invention, and represents 0.1% by mass or less, for example.

<Polyester>
The polyester used in the first layer and the second layer is not particularly limited. For example, a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof is used. Can be mentioned.
Specific examples of the polyester include polyethylene terephthalate (PET), polyethylene isophthalate, polybutylene terephthalate (PBT), poly (1,4-cyclohexylenedimethylene terephthalate), polyethylene-2,6-naphthalate and the like. . Of these, polyethylene terephthalate or polyethylene-2,6-naphthalate is more preferable, and polyethylene terephthalate is particularly preferable in terms of the balance between mechanical properties and cost.

  The polyester may be a homopolymer or a copolymer. Further, the polyester may be blended with a small amount of another type of resin such as polyimide.

  When the polyester is polymerized, from the viewpoint of keeping the carboxy group content below a predetermined range, Sb-based, Ge-based, and Ti-based compounds are preferably used as catalysts, and among these, Ti-based compounds are particularly preferable. In the case of using a Ti-based compound, an embodiment in which polymerization is performed by using the Ti-based compound as a catalyst in a range of 1 ppm to 30 ppm, more preferably 3 ppm to 15 ppm is preferable. When the proportion of the Ti-based compound is within the above range, the terminal carboxyl group content can be adjusted to the range described later, and the hydrolysis resistance of the polymer can be kept low.

  For the synthesis of polyester using a Ti-based compound, for example, Japanese Patent Publication No. 8-301198, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 397756, Japanese Patent No. 39622626, Japanese Patent No. 39786666 No. 3, Patent No. 3,996,871, Patent No. 4000086, Patent No. 4053837, Patent No. 4,127,119, Patent No. 4,134,710, Patent No. 4,159,154, Patent No. 4,269,704, Patent No. 4,313,538 and the like can be applied.

The carboxyl group content of each polyester in the first layer and the second layer is preferably 35 equivalents / ton or less, more preferably 20 equivalents / ton or less, and particularly preferably 17 equivalents / ton or less.
When the carboxyl group content of the polyester is 35 equivalents / ton or less, hydrolysis resistance can be maintained, and a decrease in strength when subjected to wet heat aging can be suppressed to be small. The lower limit of the carboxyl group content is preferably 2 equivalents / ton in terms of maintaining adhesiveness. In this specification, “equivalent / ton” represents a molar equivalent per ton (1000 kg).

The carboxyl group content (AV) is a value measured by the following method. That is,
After 0.1 g of polyester is dissolved in 5 ml of benzyl alcohol, phenol red indicator is added dropwise to a mixed solution containing 5 ml of chloroform, and this is titrated with a standard solution (0.01 N KOH-benzyl alcohol mixed solution). The concentration [equivalent / ton] of the terminal carboxyl group is calculated from this dripping amount.

  The carboxyl group content in the polyester can be adjusted by the polymerization catalyst species and the film forming conditions (film forming temperature and time).

  The polyester constituting the first layer or the second layer is preferably solid-phase polymerized after polymerization. Thereby, a preferable carboxyl group content can be achieved. Solid-phase polymerization may be a continuous method (a method in which a tower is filled with a resin, which is slowly heated for a predetermined time and then sent out), or a batch method (a resin is charged into a container). , A method of heating for a predetermined time). Specifically, for solid phase polymerization, Japanese Patent No. 2621563, Japanese Patent No. 3121876, Japanese Patent No. 3136774, Japanese Patent No. 3603585, Japanese Patent No. 3616522, Japanese Patent No. 3617340, Japanese Patent No. 3680523, Japanese Patent No. 3717392 are disclosed. The method described in Japanese Patent No. 4167159 can be applied.

  The temperature of the solid phase polymerization is preferably 170 ° C. or higher and 240 ° C. or lower, more preferably 180 ° C. or higher and 230 ° C. or lower, and further preferably 190 ° C. or higher and 220 ° C. or lower. The solid phase polymerization time is preferably 5 hours to 100 hours, more preferably 10 hours to 75 hours, and still more preferably 15 hours to 50 hours. The solid phase polymerization is preferably performed in a vacuum or in a nitrogen atmosphere.

The first layer or the second layer is obtained by, for example, melt-extruding the polyester into a film and then cooling and solidifying it with a casting drum to form an unstretched film. The unstretched film is Tg to (Tg + 60) ° C. The biaxially stretched so that the total magnification becomes 3 to 6 times in the longitudinal direction once or twice, and then stretched so that the magnification becomes 3 to 5 times in the width direction at Tg to (Tg + 60) ° C. A stretched film is preferred.
Furthermore, what was heat-processed for 1 to 60 second at 180-230 degreeC as needed may be used.

The first layer may be subjected to a surface treatment such as corona treatment, flame treatment, glow discharge treatment on at least the surface opposite to the surface on which the second layer is provided, if necessary. Good. Corona discharge treatment is usually performed by applying high frequency and high voltage between a metal roll (dielectric roll) coated with a derivative and an insulated electrode to cause dielectric breakdown of the air between the electrodes. Is ionized to generate a corona discharge between the electrodes. And it performs by passing a polymer base material between this corona discharge.
Preferable treatment conditions include an electrode-dielectric roll gap clearance of 1 to 3 mm, a frequency of 1 to 100 kHz, and an applied energy of about 0.2 to 5 kV · A · min / m ² .

  The glow discharge treatment is a method called vacuum plasma treatment or low-pressure plasma treatment, and is a method in which plasma is generated by discharge in a gas (plasma gas) in a low-pressure atmosphere to treat the substrate surface. The low-pressure plasma used in the process of the present invention is a non-equilibrium plasma generated under conditions where the plasma gas pressure is low. The treatment of the present invention is performed by placing a film to be treated (polymer substrate) in this low-pressure plasma atmosphere.

  In the glow discharge treatment, methods such as direct current glow discharge, high frequency discharge, and microwave discharge can be used as a method for generating plasma. The power source used for discharging may be direct current or alternating current. When alternating current is used, a range of about 30 Hz to 20 MHz is preferable. When alternating current is used, a commercial frequency of 50 or 60 Hz may be used, or a high frequency of about 10 to 50 kHz may be used. A method using a high frequency of 13.56 MHz is also preferable.

  As the plasma gas used in the glow discharge treatment, an inorganic gas such as oxygen gas, nitrogen gas, water vapor gas, argon gas, and helium gas can be used. In particular, oxygen gas or a mixed gas of oxygen gas and argon gas can be used. Is preferred. Specifically, it is desirable to use a mixed gas of oxygen gas and argon gas. When a mixed gas of oxygen gas and argon gas is used, the ratio between the two is oxygen gas: argon gas = 100: 0 to 30:70, more preferably 90:10 to 70:30, as a partial pressure ratio. preferable. In addition, a method in which a gas such as water entering the processing container due to a leak or water vapor coming out of the object to be processed is used as the plasma gas without introducing a gas into the processing container.

  As the pressure of the plasma gas, a low pressure at which non-equilibrium plasma conditions are achieved is necessary. The specific pressure of the plasma gas is preferably in the range of about 0.005 to 10 Torr (0.666 to 1333 Pa), more preferably about 0.008 to 3 Torr (1.067 to 400 Pa). If the pressure of the plasma gas is 0.666 Pa or more, the effect of improving the adhesiveness is sufficient, and if it is 1333 Pa or less, the current is increased and the discharge is suppressed from becoming unstable.

The plasma output cannot be generally specified depending on the shape and size of the processing vessel, the shape of the electrode, and the like, but is preferably about 100 to 2500 W, more preferably about 500 to 1500 W.
The treatment time of the glow discharge treatment is preferably 0.05 to 100 seconds, more preferably about 0.5 to 30 seconds. If the treatment time is 0.05 seconds or longer, the effect of improving adhesiveness is sufficiently obtained, and if it is 100 seconds or less, deformation or coloring of the film to be treated can be prevented.

Discharge treatment intensity of the glow discharge treatment depends on the plasma power and treatment time, preferably in the range of 0.01~10kV · A · min / ^{m 2,} 0.1~7kV · A · min / ^{m 2} is more preferable.
Discharge treatment intensity that is sufficient adhesion improving effect of the 0.01 kV · A · min / m ² or more is obtained, and such deformation and coloration of the processed film by a 10 kV · A · min / m ² or less You can avoid problems.

In the glow discharge treatment, it is also preferable to heat the film to be treated in advance. By this method, better adhesiveness can be obtained in a shorter time than when heating is not performed. The heating temperature is preferably in the range of 40 ° C. to the softening temperature of the film to be processed + 20 ° C., more preferably in the range of 70 ° C. to the softening temperature of the film to be processed. By setting the heating temperature to 40 ° C. or higher, a sufficient adhesive improvement effect can be obtained. Moreover, the handleability of a favorable film can be ensured during a process by making heating temperature below into the softening temperature of a to-be-processed film.
Specific methods for raising the temperature of the film to be treated in vacuum include heating with an infrared heater, heating by contacting with a hot roll, and the like.

  Examples of the flame treatment include flame treatment using a flame introduced with a silane compound.

  As the form of the raw material resin for the polyester of the second layer, pellets, fluffs, mixtures thereof, and the like can be used, and those in which the fluff mass ratio is 60% or less and mixed with the pellets are preferable. By using a mixture of pellets and fluffs in this way, the melting method and heat history of the raw resin can be adjusted. The fluff is, for example, a pulverized product obtained by pulverizing an unnecessary film into small pieces (so-called chips), scrap pieces, or the like, that is, a recycled chip obtained by trimming and crushing the end portion in the width direction of the laminated film. Increasing the fluff ratio has a high recycling ratio and can reduce the cost of raw materials. On the other hand, an increase in the fluff ratio gives a bulkiness, and the bulk specific gravity can be lowered as compared with, for example, a pellet alone. As the resin film for obtaining the fluff, a polyester film is preferable, and a polyester film of the same type as the polyester resin in the raw resin is preferable. By setting the fluff ratio to 60% by mass or less, the fluctuation range of the terminal COOH amount of the obtained polyester film can be kept low. Among these, for the same reason, the mass ratio of the fluff is preferably 60% by mass or less, more preferably 10 to 50% by mass, and particularly preferably 30 to 50% by mass.

  The fluff size is not limited as long as the bulk change is given, but a fluff thickness of 20 to 5000 μm is preferable. Among them, from the viewpoint of preventing the bulk density from becoming too small and reducing the filling rate too much and avoiding insufficient melting, the thickness of the fluff is preferably in the range of 100 to 1000 μm, more preferably in the range of 100 to 500 μm.

  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 fluff is smaller, for example, the variation in the thickness of the fluff is preferably within ± 100%, more preferably It is within ± 50%, and further within ± 10%. In the case of using a fluff, variation in the terminal COOH amount of the obtained polyester film can be suppressed low by suppressing size variation such as thickness.

  The bulk specific gravity of the fluff is preferably in the range of 0.3 to 0.7 as long as the bulk specific gravity of the raw material resin satisfies the above range. 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.

  In addition, it is preferable that a 1st layer does not contain a recycling chip substantially. “Substantially not contained” means that it is not contained within a range that does not affect the effect of the present invention, and represents 0.1% by mass or less, for example.

<White pigment>
The first layer contains a white pigment. Further, the second layer may or may not contain a white pigment. By including a white pigment in the first layer, the reflectance (whiteness) of light is improved, and the design property can be imparted by improving the visible light hiding property. Moreover, the reflectance (whiteness) of light can be improved and the power generation efficiency of a solar cell can be raised.

  The average particle diameter of the particles constituting the white pigment (hereinafter simply referred to as “particles”) is not particularly limited, but is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm, still more preferably 0.15 to 1 μm. Particles. If the average particle diameter of the particles is 0.1 to 10 μm, the whiteness of the film can be 50 or more even with a small addition amount.

The average particle diameter of the particles can be obtained by an electron microscope method, and specifically, can be obtained by the following method.
The particles are observed with a scanning electron microscope, the magnification is appropriately changed according to the size of the particles, and the photographed image is enlarged and copied. Next, the circumference of each particle is traced for at least 200 particles selected at random. The equivalent circle diameter of the particles is measured from these trace images with an image analysis apparatus, and the average value of these is taken as the average particle diameter.

  The particles may be either inorganic particles or organic particles, or a combination of both. Thereby, the reflectance of light can be improved and the power generation efficiency of a solar cell can be raised. Suitable inorganic particles include, for example, wet and dry silica, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc white), antimony oxide, oxidation Cerium, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, Kaolin, lithium fluoride, calcium fluoride, and the like can be used, and titanium dioxide and barium sulfate are particularly preferable. The titanium oxide may be either anatase type or rutile type. The particle surface may be subjected to inorganic treatment such as alumina or silica, or may be subjected to organic treatment such as silicon or alcohol.

Among these particles, titanium dioxide is preferable, and thereby excellent durability can be achieved even under light irradiation. Specifically, when UV irradiation is performed at 63 ° C., 50% Rh, irradiation intensity of 100 mW / cm ² for 100 hours, the elongation at break is preferably 35% or more, more preferably 40% or more. As described above, polyester is more suitable as a back surface protective film for a solar cell used outdoors because the photodegradation and deterioration are suppressed by light irradiation.

  There are rutile type and anatase type in titanium dioxide, but it is preferable to add titanium dioxide particles mainly composed of rutile type to polyester. The anatase type has a very high spectral reflectance of ultraviolet rays, whereas the rutile type has a characteristic that the absorption rate of ultraviolet rays is large (spectral reflectance is small). The present inventor pays attention to such a difference in spectral characteristics in the crystal form of titanium dioxide, and uses a rutile-type ultraviolet absorption performance, so that the polyester film for protecting the back surface of a solar cell (back sheet for solar cell) has light resistance. It was found that can be improved. Thereby, it is excellent in the film durability under light irradiation, even if it does not add another ultraviolet absorber substantially. For this reason, it is difficult for the ultraviolet absorber to bleed out and to reduce contamination and adhesion.

As described above, the titanium dioxide particles are preferably mainly composed of rutile type, but the term “main body” as used herein means that the amount of rutile type titanium dioxide in all titanium dioxide particles exceeds 50% by mass. Means that
Moreover, it is preferable that the amount of anatase type titanium dioxide in all the titanium dioxide particles is 10 mass% or less. More preferably, it is 5 mass% or less, Most preferably, it is 0 mass%. If the content of anatase type titanium dioxide exceeds the above upper limit, the amount of rutile type titanium dioxide in the total titanium dioxide particles may be reduced, resulting in insufficient ultraviolet absorption performance. Since the photocatalytic action is strong, the light resistance tends to be lowered by this action. Rutile titanium dioxide and anatase titanium dioxide can be distinguished by X-ray structure diffraction and spectral absorption characteristics.

  The rutile titanium dioxide particles may be subjected to inorganic treatment such as alumina or silica on the particle surface, or may be subjected to organic treatment such as silicon or alcohol. Rutile titanium dioxide may be subjected to particle size adjustment and coarse particle removal using a purification process before blending with the polyester composition. As industrial means of the purification process, for example, a jet mill or a ball mill can be applied as a pulverizing means, and as a classification means, for example, dry or wet centrifugation can be applied.

In the present invention, organic particles can also be used as the white pigment. Those that can withstand the heat in the polyester film are preferable, for example, those made of a cross-linkable resin are used, and specifically, polystyrene cross-linked with divinylbenzene is used. The size and addition amount of particles are the same as in the case of inorganic particles.
Various known methods can be used to add particles to the polyester film as a method using a known method. The following method can be mentioned as the typical method.

(A) A method of adding particles before the end of the ester exchange reaction or esterification reaction during the synthesis of polyethylene terephthalate, or adding particles before the start of the polycondensation reaction.
(B) A method in which particles are added to polyethylene terephthalate and melt kneaded.
(C) Producing master pellets (or master batch (MB)) in which a large amount of particles are added in the methods (A) and (B), kneading these and polyethylene terephthalate containing no particles, A method of containing a predetermined amount of particles.
(D) The method of using the master pellet of said (C) as it is.

  Of these, the master batch method (MB method: (C) above) in which polyester and particles are mixed in advance by an extruder is preferred. Further, it is possible to adopt a method in which a polyester resin and particles that have not been dried in advance are put into an extruder and MB is produced while moisture and air are deaerated. Furthermore, it is preferable to prepare an MB using a polyester resin that has been slightly dried in advance to suppress an increase in the acid value of the polyester. In this case, a method of extruding while degassing, a method of extruding without deaeration with a sufficiently dried polyester resin, and the like can be mentioned.

  For example, when preparing MB, it is preferable to reduce the moisture content of the polyester to be added in advance by drying. Drying conditions are preferably 100 to 200 ° C., more preferably 120 to 180 ° C., for 1 hour or longer, more preferably 3 hours or longer, and even more preferably 6 hours or longer. Thereby, it is sufficiently dried so that the moisture content of the polyester resin is preferably 50 ppm or less, more preferably 30 ppm or less. The premixing method is not particularly limited, and may be a batch method or a single-screw or twin-screw kneading extruder. When producing MB while degassing, melt the polyester resin at a temperature of 250 ° C to 300 ° C, preferably 270 ° C to 280 ° C, and provide one, preferably two or more degassing ports in the pre-kneader. It is preferable to adopt a method such as performing continuous suction deaeration of 0.05 MPa or more, more preferably 0.1 MPa or more, and maintaining the reduced pressure in the mixer.

<Other materials>
In addition to polyester and white pigment for the first layer, and in addition to polyester for the second layer, an end-capping agent may be added to improve hydrolysis resistance (weather resistance). good. Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, heat, and the like may be added to the first layer and / or the second layer as long as the effects of the present invention are not impaired. Stabilizers, lubricants, antistatic agents, brighteners, colorants, conductive agents, ultraviolet absorbers, flame retardants, flame retardant aids and dyes may be added.

(End sealant)
A 1st layer and / or a 2nd layer can contain 0.1-10 mass% terminal blocker with respect to the total mass of a polyester resin and a polyester resin. The added amount of the end-capping agent with respect to the total mass of the polyester resin constituting the polyester is more preferably 0.2 to 5% by mass, and still more preferably 0.3 to 2% by mass.

Since the hydrolysis of the polyester is accelerated by the catalytic effect of H ⁺ (proton) generated from the terminal carboxylic acid or the like, the end-capping agent that reacts with the terminal carboxylic acid is used to improve the hydrolysis resistance (weather resistance). It is effective to add.
If the added amount of the end-capping agent is 0.1% by mass or more with respect to the total mass of the polyester resin, the effect of improving the weather resistance is easily exhibited. The action is suppressed, and the decrease in mechanical strength and heat resistance is suppressed.

  Examples of the end capping agent include an epoxy compound, a carbodiimide compound, an oxazoline compound, and a carbonate compound, and carbodiimide having high affinity with polyethylene terephthalate (PET) and high end capping ability is preferable.

It is preferable that terminal blocker (especially carbodiimide terminal blocker) is high molecular weight. This can reduce volatilization during melt film formation. The molecular weight is preferably 200 to 100,000, more preferably 2000 to 80,000, and still more preferably 10,000 to 50,000. If the molecular weight of the end-capping agent (especially carbodiimide end-capping agent) is within the above range, it is easy to uniformly disperse in the polyester, and it is easy to fully express the effect of improving weather resistance, and it is volatilized during extrusion and film formation. It is difficult and it becomes easy to express an effect of improving weather resistance.
In addition, the molecular weight of terminal blocker means a weight average molecular weight.

(Carbodiimide-based end-capping agent)
The carbodiimide compound having a carbodiimide group includes a monofunctional carbodiimide and a polyfunctional carbodiimide. Examples of the monofunctional carbodiimide include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, and diphenylcarbodiimide. , Di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, and the like. Particularly preferred are dicyclohexylcarbodiimide and diisopropylcarbodiimide.

  As the polyfunctional carbodiimide, carbodiimide having a polymerization degree of 3 to 15 is preferably used. Specifically, 1,5-naphthalene carbodiimide, 4,4′-diphenylmethane carbodiimide, 4,4′-diphenyldimethylmethane carbodiimide, 1,3-phenylene carbodiimide, 1,4-phenylene diisocyanate, 2,4-tolylene Carbodiimide, 2,6-tolylene carbodiimide, mixture of 2,4-tolylene carbodiimide and 2,6-tolylene carbodiimide, hexamethylene carbodiimide, cyclohexane-1,4-carbodiimide, xylylene carbodiimide, isophorone carbodiimide, isophorone carbodiimide, Dicyclohexylmethane-4,4′-carbodiimide, methylcyclohexanecarbodiimide, tetramethylxylylene carbodiimide, 2,6-diisopropylphenylcarbodiimide and , And the like can be exemplified 3,5-triisopropyl-2,4-carbodiimide.

  The carbodiimide compound is preferably a carbodiimide compound having high heat resistance because an isocyanate gas is generated by thermal decomposition. In order to improve heat resistance, it is preferable that the molecular weight (degree of polymerization) is high, and it is more preferable that the terminal of the carbodiimide compound has a structure with high heat resistance. Further, once thermal decomposition occurs, further thermal decomposition is likely to occur. Therefore, it is necessary to devise measures such as setting the extrusion temperature of the polyester as low as possible.

  A carbodiimide as a terminal blocking agent preferably has a cyclic structure (for example, those described in JP2011-153209A). These exhibit the same effect as the above high molecular weight carbodiimide even at low molecular weight. This is because the terminal carboxylic acid of the polyester and the cyclic carbodiimide undergo a ring-opening reaction, one reacts with this polyester, and the other with the ring-opening reacts with another polyester to increase the molecular weight, thus suppressing the generation of isocyanate gas. It is to do.

Among those having a cyclic structure, in the present invention, the terminal blocking agent is a carbodiimide compound having a carbodiimide group and a cyclic structure in which the first nitrogen and the second nitrogen are bonded by a bonding group. It is preferable. Further, the end capping agent has a cyclic structure in which at least one carbodiimide group adjacent to the aromatic ring is present, and the first nitrogen and the second nitrogen of the carbodiimide group adjacent to the aromatic ring are bonded by a bonding group. More preferred is carbodiimide (also referred to as aromatic cyclic carbodiimide).
The aromatic cyclic carbodiimide may have a plurality of cyclic structures.
The aromatic cyclic carbodiimide is preferably an aromatic carbodiimide having no ring structure in which the first nitrogen and the second nitrogen of two or more carbodiimide groups are bonded by a linking group in the molecule, that is, a monocyclic ring. Can be used.

  The cyclic structure has one carbodiimide group (—N═C═N—), and the first nitrogen and the second nitrogen are bonded by a bonding group. One cyclic structure has only one carbodiimide group. For example, when there are a plurality of cyclic structures in the molecule, such as a spiro ring, one cyclic structure bonded to a spiro atom is included in each cyclic structure. Needless to say, the compound may have a plurality of carbodiimide groups as long as it has a carbodiimide group. The number of atoms in the cyclic structure is preferably 8 to 50, more preferably 10 to 30, further preferably 10 to 20, and particularly preferably 10 to 15.

  Here, the number of atoms in the cyclic structure means the number of atoms that directly constitute the cyclic structure. For example, it is 8 for an 8-membered ring and 50 for a 50-membered ring. This is because if the number of atoms in the cyclic structure is smaller than 8, the stability of the cyclic carbodiimide compound is lowered, and it may be difficult to store and use. From the standpoint of reactivity, the upper limit of the number of ring members is not particularly limited, but a cyclic carbodiimide compound having 50 or less atoms is less difficult to synthesize, and the cost can be kept low. From this viewpoint, the number of atoms in the cyclic structure is preferably 10-30, more preferably 10-20, and particularly preferably 10-15.

Specific examples of the carbodiimide-based end capping agent having a cyclic structure include the following compounds. However, the present invention is not limited to the following specific examples.

(Epoxy end sealant)
Preferable examples of the epoxy compound include glycidyl ester compounds and glycidyl ether compounds.

  Specific examples of the glycidyl ester compound include benzoic acid glycidyl ester, t-butyl-benzoic acid glycidyl ester, P-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, and lauric acid glycidyl ester. , Glycidyl palmitate, glycidyl behenate, glycidyl versatate, glycidyl oleate, glycidyl linoleate, glycidyl linolein, glycidyl behenol, glycidyl stearol, diglycidyl terephthalate, isophthalic acid Diglycidyl ester, diglycidyl phthalate, diglycidyl naphthalene dicarboxylate Stell, methyl terephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexanedicarboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecane Examples thereof include diglycidyl diacid, octadecanedicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester. These may be used alone or in combination of two or more.

  Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (β, γ-epoxypropoxy) butane, 1,6-bis (β, γ- Epoxypropoxy) hexane, 1,4-bis (β, γ-epoxypropoxy) benzene, 1- (β, γ-epoxypropoxy) -2-ethoxyethane, 1- (β, γ-epoxypropoxy) -2-benzyl Oxyethane, 2,2-bis- [р- (β, γ-epoxypropoxy) phenyl] propane and 2,2-bis- (4-hydroxyphenyl) propane and 2,2-bis- (4-hydroxyphenyl) Examples include bisglycidyl polyether obtained by reaction of bisphenol such as methane and epichlorohydrin, and these include one or more. It can be used.

(Oxazoline-based end-capping agent)
As the oxazoline compound, a bisoxazoline compound is preferable, and specifically, 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline), and 2,2′-bis. (4,4-dimethyl-2-oxazoline), 2,2′-bis (4-ethyl-2-oxazoline), 2,2′-bis (4,4′-diethyl-2-oxazoline), 2,2 '-Bis (4-propyl-2-oxazoline), 2,2'-bis (4-butyl-2-oxazoline), 2,2'-bis (4-hexyl-2-oxazoline), 2,2'- Bis (4-phenyl-2-oxazoline), 2,2'-bis (4-cyclohexyl-2-oxazoline), 2,2'-bis (4-benzyl-2-oxazoline), 2,2'-p- Phenylenebis (2-oxazoline), 2,2'-m- Enylene bis (2-oxazoline), 2,2'-o-phenylene bis (2-oxazoline), 2,2'-p-phenylene bis (4-methyl-2-oxazoline), 2,2'-p-phenylene bis (4,4-dimethyl-2-oxazoline), 2,2′-m-phenylenebis (4-methyl-2-oxazoline), 2,2′-m-phenylenebis (4,4-dimethyl-2-oxazoline) ), 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2-oxazoline), 2,2′-octamethylene Bis (2-oxazoline), 2,2′-decamethylenebis (2-oxazoline), 2,2′-ethylenebis (4-methyl-2-oxazoline), 2,2′-tetramethylenebis (4,4 - Methyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis (2-oxazoline), 2,2′-cyclohexylenebis (2-oxazoline) and 2,2′-diphenylenebis ( 2-oxazoline) and the like. Among these, 2,2′-bis (2-oxazoline) is most preferably used from the viewpoint of reactivity with polyester. Furthermore, as long as the objective of this invention is achieved, the bisoxazoline compound mentioned above may be used individually by 1 type, or may use 2 or more types together.

  Such an end-capping agent needs to be kneaded into the polyester film. That is, the above-described effect cannot be obtained unless the polyester molecule is directly reacted. This is because the polyester and the end-capping agent do not react even when added to the coating layer on PET.

<Other layers>
In the laminated film of the present invention, other layers may be laminated in addition to the first layer and the second layer. Examples of other layers include a layer with high whiteness (a layer with a lot of voids and particles), a layer with low whiteness (a layer with a small amount of voids and particles), etc. Examples of other layers include JP2013-65846A. The descriptions in paragraphs 0065 to 0066 of the publication can be referred to, and the contents thereof are incorporated in the present specification.

<Physical properties of laminated film>
In the laminated film of the present invention, the white pigment concentration of the whole laminated film is greater than 0% by mass and less than 2% by mass, preferably 0.5% by mass or more and less than 2% by mass, and more preferably 1.5% by mass or more and 2% by mass. Less than is more preferable. Visible light shielding property can be improved by making the white pigment concentration of the whole film larger than 0 mass%, and hydrolysis resistance can be improved by making it less than 2 mass%.
The concentration of the white pigment in the entire film is a parameter representing the percentage of the mass of the white pigment in the mass of the entire laminated film, and can be specifically measured by the following method. That is, 3 g of the laminated film as a measurement sample is taken in a crucible and heated at 900 ° C. for 120 minutes in an electric oven. Then, after the electric oven has cooled, the crucible is taken out and the mass of ash remaining in the crucible is measured. This ash content is the white pigment content, the mass of the ash content is divided by the mass of the measurement sample, and a value multiplied by 100 is taken as the white pigment concentration.

Hydrolysis resistance is improved by the amount of terminal carboxyl groups (terminal carboxyl group concentration; AV). For this reason, the terminal carboxyl group density | concentration of the whole laminated film is 6-30 equivalent / ton, 10-25 equivalent / ton is preferable and 10-20 equivalent / ton is more preferable.
When the terminal carboxyl group concentration is less than 6 equivalents / ton, the surface carboxyl groups (COOH groups) become too small (polarity becomes too low), and adhesive adhesion to different materials may be lowered. On the other hand, when the terminal carboxyl group concentration exceeds 30 equivalents / ton, H ⁺ of the COOH group at the end of the polyester molecule serves as a catalyst to promote hydrolysis, which may reduce hydrolysis resistance.
The terminal carboxyl group concentration was determined by dissolving 0.1 g of polyester in 5 ml of benzyl alcohol and then adding a phenol red indicator dropwise to a mixed solution containing 5 ml of chloroform. This was used as a reference solution (0.01 N KOH-benzyl alcohol mixed solution). It is a value calculated from the amount of dripping.

The thickness of the entire laminated film is preferably 100 to 400 μm, more preferably 100 to 300 μm, still more preferably 100 to 250 μm, and particularly preferably 110 to 250 μm.
The ratio of the thickness of the first layer to the thickness of the entire laminated film (the thickness of the first layer / the thickness of the entire laminated film) is preferably 0.01 to 0.30, and preferably 0.02 to 0.25. More preferred.

  The laminated film of the present invention can be used for various applications, but can be used for films for solar cell modules (for example, protective films for solar cells), films for building materials, films for outdoor advertising, and the like. .

<Method for producing laminated film>
Although the manufacturing method of the laminated film of the present invention is not particularly limited, it is preferably manufactured by a coextrusion method from the viewpoint of interlayer adhesion and productivity. In the case of a two-layer configuration of a first layer and a second layer, two extruders are prepared, and a composition that constitutes the first layer on one side and a composition that constitutes the second layer on the other side. The melt (melt) extruded from each extruder is merged using a two-layer feed block device and extruded from a die while maintaining the laminated state to obtain an unstretched laminated film (coextrusion step) ). The laminated film can be biaxially stretched (stretching step) to obtain the laminated film of the present invention.

  The polyester used for the first and second layers is preferably subjected to solid phase polymerization after polycondensation. Solid phase polymerization is as described above, and the preferred embodiment is also the same.

  In the coextrusion step, the polyester after undergoing solid-phase polymerization is melt-kneaded, a composition constituting the first layer for forming the first layer, and a second for forming the second layer The composition constituting the layer is melted by two extruders, and the melt (melt) is merged by the two-layer feed block device to form a laminated state, and then extruded from the die to constitute the second layer. A laminated film is formed by laminating the composition constituting the first layer on at least one surface of the composition.

For example, the polyester that has undergone the above solid-phase polymerization is dried, the residual moisture is reduced to 100 ppm or less, and then melted using an extruder. The melting temperature is preferably 250 ° C. or higher and 320 ° C. or lower, more preferably 260 ° C. or higher and 310 ° C. or lower, and further preferably 270 ° C. or higher and 300 ° C. or lower.
It is more preferable that the inside of the extruder is replaced with nitrogen from the viewpoint that generation of terminal COOH due to thermal decomposition can be further suppressed.
The melt (melt) melted in the extruder is extruded from a die through a gear pump, a filter and the like. At this time, the composition constituting the second layer for forming the second layer and the first layer for forming the first layer on at least one side of the composition constituting the second layer After the composition which comprises is made into a lamination | stacking state using a feed block apparatus, it extrudes from a die | dye and it is set as a laminated | multilayer film.
The composition constituting the first layer may be laminated on one side of the composition constituting the second layer, or may be laminated on both sides.

The melt coextruded from each extrusion die is cooled and solidified using a chill roll (cooling roll). At this time, the temperature of the chill roll is preferably 10 ° C. or higher and 80 ° C. or lower, more preferably 15 ° C. or higher and 70 ° C. or lower, and further preferably 20 ° C. or higher and 60 ° C. or lower. Furthermore, from the viewpoint of improving the adhesion between the melt and the chill roll and increasing the cooling efficiency, it is preferable to apply static electricity before the melt contacts the chill roll. Furthermore, it is also preferable to apply cooling air from the opposite surface of the chill roll or to contact a cooling roll to promote cooling. Thereby, even a thick film (specifically, a film having a thickness after stretching of 250 μm or more, and further 300 μm or more) can be effectively cooled.
In addition, when the cooling is insufficient, spherulites are likely to be generated, which may cause uneven stretching and uneven thickness.

  In the stretching step, the unstretched laminated film produced in the coextrusion step is subjected to longitudinal stretching and lateral stretching, and the film surface temperature during longitudinal stretching and lateral stretching is controlled to (Tg1 + 10) ° C. or more and (Tg1 + 35) ° C. or less. (Tg1 represents the glass transition temperature of the first layer). If the film surface temperature during longitudinal stretching and lateral stretching is (Tg1 + 10) ° C. or higher, the stress during stretching can be reduced, so stretching at a stretching ratio necessary for imparting hydrolysis resistance becomes possible. If it is Tg1 + 35) ° C. or lower, it becomes possible to impart the orientation necessary for improving the hydrolysis resistance. The film surface temperature during biaxial stretching (longitudinal stretching and transverse stretching) is more preferably (Tg1 + 12) ° C. or higher and (Tg1 + 30) ° C. or lower.

  For example, an unstretched laminated film is led to a group of rolls heated to a temperature of 70 ° C. or more and 140 ° C. or less, and stretched at a stretching ratio of 3 to 5 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film). And it cools with the roll group of the temperature of 20 to 50 degreeC. Subsequently, the film is guided to a tenter while gripping both ends of the film with a clip, and in an atmosphere heated to a temperature of 80 ° C. or higher and 150 ° C. or lower, the direction perpendicular to the longitudinal direction (width direction) is 3 to 5 times. Stretch at a stretch ratio.

  The stretching ratio is preferably 3 to 5 times in each of the longitudinal direction and the width direction. Moreover, it is preferable that the area magnification (longitudinal stretch magnification x lateral stretch magnification) is 9 times or more and 15 times or less. When the area magnification is 9 times or more, the reflectivity, concealability and film strength of the obtained biaxially stretched laminated film are good, and when the area magnification is 15 times or less, tearing during stretching should be avoided. Can do.

  As the biaxial stretching method, as described above, in addition to the sequential biaxial stretching method in which the longitudinal direction and the width direction are separated separately, the simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched. Either may be sufficient.

  In order to complete the crystal orientation of the obtained biaxially stretched film and to give flatness and dimensional stability, the biaxially stretched film was heat-set in the tenter, and after uniform cooling, You may cool to room temperature. In general, when the heat setting treatment temperature (Ts) is low, the heat shrinkage of the film is large. Therefore, in order to impart high thermal dimensional stability, the heat treatment temperature is preferably high. However, if the heat treatment temperature is too high, the orientation crystallinity is lowered, and as a result, the formed film may be inferior in hydrolysis resistance.

In the present invention, when the heat setting treatment of the biaxially stretched film is performed, when the crystal melting peak of the second layer is Tm2 (° C.), the film surface temperature at the time of heat setting is (Tm2-40) ° C. or higher. Control below ℃. If the film surface temperature at the time of heat setting is (Tm2-40) ° C. or higher, the effect of removing residual strain by heat setting will be sufficient, and heat shrinkage will be within an acceptable range, and if it is Tm 2 ° C. or lower, the second layer It is possible to prevent deterioration of hydrolysis resistance due to relaxation of orientation.
In addition, although the laminated | multilayer film of this invention can be used as a back seat | sheet which comprises a solar cell module, atmospheric temperature may rise to about 100 degreeC at the time of module use. Therefore, the film surface temperature during heat setting is more preferably (Tm2-30) ° C. or higher and (Tm2-10) ° C. or lower.

Moreover, you may perform a 1-12% relaxation process in the width direction or a longitudinal direction as needed. The heat-set polyester film is usually cooled to Tg or less, and the clip gripping portions at both ends of the polyester film are cut and wound into a roll. At this time, it is preferable to perform a relaxation treatment of 1 to 12% in the width direction and / or the longitudinal direction within a temperature range of not more than the final heat setting treatment temperature and not less than Tg.
In terms of dimensional stability, the cooling is preferably performed by gradually cooling from the final heat setting temperature to room temperature at a cooling rate of 1 ° C. to 100 ° C. per second. In particular, it is preferable to slowly cool Tg + 50 ° C. to Tg at a cooling rate of 1 ° C. or more and 100 ° C. or less per second. The means for cooling and relaxation treatment is not particularly limited and can be performed by a conventionally known means. However, it is preferable to perform these treatments while sequentially cooling in a plurality of temperature ranges, in view of improving the dimensional stability of the laminated film. .
Further, in the production of the laminated film, for the purpose of improving the strength of the laminated film, stretching used for known stretched films such as multistage longitudinal stretching, re-longitudinal stretching, re-longitudinal and transverse stretching, and transverse / longitudinal stretching may be performed. The order of longitudinal stretching and lateral stretching may be reversed.

  Details of the method for producing the laminated film can be referred to, for example, paragraphs 0098 to 0110 of JP2011-211087, and the contents thereof are incorporated in the present specification.

<Back sheet for solar cell module>
The solar cell backsheet of the present invention includes the laminated film of the present invention. The back sheet for a solar cell of the present invention is formed by providing the laminated film of the present invention, and has an easy-adhesive easy-adhesive layer, an ultraviolet-absorbing layer, and a light-reflecting property on the adherend, if necessary. It can be configured by providing at least one functional layer such as a white layer. Since the laminated film of the present invention is provided, stable durability performance is exhibited during long-term use.

In the solar cell backsheet of the present invention, for example, the following functional layer may be applied to the laminated film after uniaxial stretching and / or biaxial stretching. For coating, a known coating technique such as a roll coating method, a knife edge coating method, a gravure coating method, or a curtain coating method can be used.
Further, surface treatment (flame treatment, corona treatment, plasma treatment, ultraviolet treatment, etc.) may be performed before the coating. Furthermore, it is also preferable to bond together using an adhesive.

(Easily adhesive layer)
When a solar cell module is configured using the laminated film of the present invention, the solar cell element has an easy-adhesive layer on the side facing the sealing material of the battery side substrate sealed with a sealing agent. Is preferred. Easy adhesion showing adhesion to an adherend containing a sealing agent (particularly ethylene-vinyl acetate copolymer) (for example, the surface of the sealing agent on the battery side substrate in which the solar cell element is sealed with the sealing material). By providing the adhesive layer, the back sheet and the sealant can be firmly bonded. Specifically, it is preferable that the easy-adhesive layer has an adhesive force of 10 N / cm or more, preferably 20 N / cm or more, particularly with EVA (ethylene-vinyl acetate copolymer) used as a sealing material.
Further, the easy-adhesive layer needs to prevent the backsheet from peeling off during use of the solar cell module, and therefore, the easy-adhesive layer desirably has high moisture and heat resistance.

(binder)
The easy-adhesion layer can contain at least one binder. As the binder, for example, polyester, polyurethane, acrylic resin, polyolefin, or the like can be used. Among these, acrylic resins and polyolefins are preferable from the viewpoint of durability. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. The following can be mentioned as an example of a preferable binder.
Examples of the polyolefin include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals, Inc.). Examples of the acrylic resin include Julimer ET-410 and SEK-301 (both manufactured by Nippon Pure Chemical Industries, Ltd.). Examples of the composite resin of acrylic and silicone include Ceranate WSA 1060 and WSA 1070 (both manufactured by DIC Corporation), and H7620, H7630, and H7650 (both manufactured by Asahi Kasei Chemicals Corporation).
The amount of the binder is preferably in the range of 0.05-5 g / m ^2, the range of 0.08~3g / m ² is particularly preferred. The binder amount is more good adhesion is obtained by at 0.05 g / m ² or more, a better surface is obtained by at 5 g / m ² or less.

(Fine particles)
The easily adhesive layer can contain at least one kind of fine particles. The easy-adhesive layer preferably contains 5% by mass or more of fine particles with respect to the mass of the entire layer.
As the fine particles, inorganic fine particles such as silica, calcium carbonate, magnesium oxide, magnesium carbonate, tin oxide and the like are preferably exemplified. Among these, fine particles of tin oxide and silica are preferable in that the decrease in adhesiveness when exposed to a humid heat atmosphere is small.
The particle size of the fine particles is preferably about 10 to 700 nm, more preferably about 20 to 300 nm. By using fine particles having a particle diameter in the above range, good easy adhesion can be obtained. The shape of the fine particles is not particularly limited, and those having a spherical shape, an indefinite shape, a needle shape, or the like can be used.
The addition amount of the fine particles in the easy-adhesive layer is preferably 5 to 400% by mass, more preferably 50 to 300% by mass per binder in the easy-adhesive layer. When the addition amount of the fine particles is 5% by mass or more, the adhesiveness when exposed to a moist heat atmosphere is excellent, and when it is 1000% by mass or less, the surface state of the easy-adhesive layer is better.

(Crosslinking agent)
The easy-adhesion layer can contain at least one crosslinking agent.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, an oxazoline-based cross-linking agent is particularly preferable from the viewpoint of securing adhesiveness after wet heat aging.
Specific examples of the oxazoline-based crosslinking agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline. 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2′-bis- (2-oxazoline), 2,2′-methylene-bis- ( 2-oxazoline), 2,2′-ethylene-bis- (2-oxazoline), 2,2′-trimethylene-bis- (2-oxazoline), 2,2′-tetramethylene-bis- (2-oxazoline) 2,2′-hexamethylene-bis- (2-oxazoline), 2,2′-octamethylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (4,4′- Methyl-2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene- Bis- (4,4′-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinylnorbornane) sulfide and the like can be mentioned. Furthermore, (co) polymers of these compounds can also be preferably used.

Further, as a compound having an oxazoline group, Epocros K2010E, K2020E, K2030E, WS500, WS700 (all manufactured by Nippon Shokubai Chemical Co., Ltd.) and the like can be used.
The preferable addition amount of the crosslinking agent in the easy-adhesive layer is preferably 5 to 50% by mass, more preferably 20 to 40% by mass per binder of the easy-adhesive layer. When the addition amount of the crosslinking agent is 5% by mass or more, a good crosslinking effect is obtained, and the strength of the reflective layer is not reduced and adhesion failure hardly occurs, and when it is 50% by mass or less, the pot life of the coating liquid is further increased. I can keep it long.

(Additive)
If necessary, the easily adhesive layer may further contain a known matting agent such as polystyrene, polymethyl methacrylate, silica, or the like, or a known surfactant such as an anionic or nonionic surfactant.

(Method for forming easy-adhesive layer)
As a method for forming the easy-adhesive layer, there are a method of pasting a polymer sheet having easy adhesion to a polyester film and a method by coating, but the method by coating is simple and highly uniform. This is preferable because it is possible. As a coating method, for example, a known method such as a gravure coater or a bar coater can be used. The solvent of the coating solution used for coating may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.
Moreover, when forming an easily-adhesive layer by application | coating, as described in the manufacturing method of this invention, it is preferable to combine the drying and heat processing of an application layer in the drying zone after heat processing. The same applies to the case where a colored layer and other functional layers described later are formed by coating.

(Physical properties)
Although there is no restriction | limiting in particular in the thickness of an easily-adhesive layer, Usually, 0.05-8 micrometers is preferable, More preferably, it is the range of 0.1-5 micrometers. When the thickness of the easy-adhesive layer is 0.05 μm or more, the required easy adhesion can be easily obtained, and when the thickness is 8 μm or less, the planar shape can be maintained better.
The easy-adhesion layer preferably has transparency from the viewpoint of not impairing the effect of the colored layer when a colored layer (particularly a reflective layer) is disposed between the polyester film.

<Solar cell module>
The solar cell module of the present invention includes the laminated film of the present invention or the back sheet of the present invention.
The solar cell module of the present invention comprises a solar cell element that converts light energy of sunlight into electrical energy, a transparent substrate on which sunlight is incident, and the laminated film (back sheet for solar cell) of the present invention described above. It is arranged and arranged between. A space between the substrate and the laminated film can be constituted by sealing with a resin (so-called sealing material) such as an ethylene-vinyl acetate copolymer.

  The members other than the solar cell module, the solar cell, and the back sheet are described in detail in, for example, “Photovoltaic power generation system constituent material” (supervised by Eiichi Sugimoto, Kogyo Kenkyukai, published in 2008).

  The transparent substrate only needs to have a light-transmitting property through which sunlight can pass, and can be appropriately selected from base materials that transmit light. From the viewpoint of power generation efficiency, the higher the light transmittance, the better. For such a substrate, for example, a glass substrate, a transparent resin such as an acrylic resin, or the like can be suitably used.

  Examples of solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, and group III-V such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenide, and II. Various known solar cell elements such as a group VI compound semiconductor can be applied.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1: Production of laminated film <Synthesis of polyester>
-Esterification-
In the first esterification reactor, 4.7 tons (4700 kg) of high-purity terephthalic acid and 1.8 tons (1800 kg) of ethylene glycol are mixed over 90 minutes to form a slurry, and continuously at a flow rate of 3800 kg / h. To the first esterification reactor. Further, an ethylene glycol solution of a citric acid chelate titanium complex (VERTEC AC-420, manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal is continuously supplied, and the average residence time is maintained at 250 ° C. in the reaction vessel with stirring. The reaction was carried out for about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of Ti element. At this time, the acid value of the obtained oligomer was 600 equivalent / ton.
This reaction product was transferred to a second esterification reaction vessel, and reacted under stirring at a reaction vessel temperature of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 200 equivalents / ton. The inside of the second esterification reaction tank is partitioned into three zones, and an ethylene glycol solution of magnesium acetate is continuously supplied from the second zone so that the amount of Mg added is 67 ppm in terms of element, From the third zone, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the added amount of P was 65 ppm in terms of element.

-Polycondensation reaction-
The esterification reaction product obtained above was continuously supplied to the first polycondensation reaction tank, and with stirring, the reaction temperature was 270 ° C., the reaction tank internal pressure was 2.67 × 10 ⁻³ MPa (20 torr), and the average The polycondensation was carried out with a residence time of about 1.8 hours.
Further, the mixture was transferred to the second double condensation reaction tank, and in this reaction tank, the temperature in the reaction tank was 276 ° C., the pressure in the reaction tank was 6.67 × 10 ⁻⁴ MPa (5 torr), and the residence time was about 1.2 hours. The reaction (polycondensation) was performed under the conditions.

Subsequently, it was further transferred to the third triple condensation reaction tank, in which the temperature in the reaction tank was 278 ° C., the pressure in the reaction tank was 2.0 × 10 ⁻⁴ MPa (1.5 torr), and the residence time was 1.5 hours. The reaction product (polyethylene terephthalate; hereinafter abbreviated as PET) was obtained by reaction (polycondensation) under the following conditions.
The obtained PET (reaction product) was measured using high resolution high frequency inductively coupled plasma mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology). As a result, Ti = 9 ppm, Mg = 67 ppm, and P = 58 ppm. P is slightly reduced with respect to the initial addition amount, but is estimated to have volatilized during the polymerization process.

-Solid-state polymerization process-
The above polymerized PET was pelletized (diameter 3 mm, length 7 mm), and the resulting resin pellet (inherent viscosity IV = 0.60 dl / g, terminal carboxyl group concentration = 25 eq / ton) was obtained as follows. The solid phase polymerization was carried out.
The intrinsic viscosity (IV) of the polyester can be calculated from the following equation based on the solution viscosity measured at 25 ° C. by dissolving the polyester in orthochlorophenol.
ηsp / C = [η] + K [η] ² · C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the dissolved polymer weight per 100 ml of solvent (in this measurement, 1 g / 100 ml), and K is the Huggins constant (0.343). The solution viscosity and the solvent viscosity can be measured using an Ostwald viscometer.

In the solid phase polymerization, the polyester polymerized by the above-described esterification reaction was heated at 140 ° C. for 7 minutes with nitrogen having a dew point temperature of −30 ° C., and pre-crystallization was performed for the purpose of preventing sticking during the solid phase polymerization.
Next, it was dried at 165 ° C. for 4 hours using heated nitrogen having a dew point temperature of −30 ° C., and the water content in the resin was adjusted to 50 ppm or less.

Next, after the dried polyester resin was preheated to 205 ° C., solid-state polymerization was advanced by circulating nitrogen at 207 ° C. for 25 hours. As nitrogen circulation conditions, the gas ratio (the amount of nitrogen gas circulated with respect to the amount of discharged resin) is 1.5 m ³ / kg, the superficial velocity is 0.08 m / sec, the ethylene glycol concentration is 240 ppm, the water concentration is 12 ppm, the ethylene glycol and water The solid phase polymerization was allowed to proceed by using nitrogen having a molar partial pressure ratio of 20 (methylene partial pressure of ethylene glycol / molar partial pressure of water) of 20. In order to obtain the above mixed gas composition, high purity ethylene glycol having a water content of 100 ppm was used for the ethylene glycol scrubber, and the scrubber temperature was set to 35 ° C. The pressure in the scrubber was in the range of 0.1 MPa to 0.11 MPa.
Next, the resin (500 kg / h) discharged from the reaction step was cooled to 60 ° C. The obtained resin had an intrinsic viscosity IV = 0.78 dl / g and a terminal carboxyl group concentration = 9 equivalents / ton.

<Preparation of master pellet>
Master pellets were prepared by kneading the PET pellets so that titanium oxide was 40 to 60% by mass.

<Extrusion film formation>
In the first layer, the PET and the master pellet are mixed so that the titanium oxide concentration becomes 12% by mass, dried to a moisture content of 100 ppm or less, and then supplied to the extruder 1 and melted at 285 ° C. Extruded. As the extruder 1, a double vent type co-rotating and meshing twin screw extruder having two vents was used.
The second layer is a mixture of the above PET and a recycled chip produced by trimming and crushing the end in the width direction of the obtained laminated film so that the titanium oxide concentration is 0.2% by mass. Was dried to a water content of 100 ppm or less, then supplied to the extruder 2 and melt-extruded at 285 ° C. As the extruder 2, a double vent type co-rotating mesh type twin screw extruder provided with two vents was used like the extruder 1.
The melts (melts) extruded from the outlets of the respective extruders are passed through a gear pump and a metal fiber filter (pore diameter: 20 μm), and then merged using a two-layer feed block device, and from the die while maintaining the laminated state. Extruded into a cooling roll. The extruded melt was brought into close contact with the cooling roll using an electrostatic application method. As the cooling roll, a hollow cast roll is used, and the temperature can be adjusted by passing water as a heating medium.

<Extension / winding>
The unstretched film extruded and solidified by the above method was sequentially biaxially stretched by the following method to obtain a film having a thickness of 250 μm. The stretching was performed in the order of longitudinal stretching at 95 ° C. and transverse stretching at 140 ° C. in the order of longitudinal stretching and transverse stretching. Then, after heat-fixing at 210 ° C. for 12 seconds, it was relaxed by 3% in the lateral direction at 205 ° C. After stretching, both ends were trimmed by 10 cm, and after thicknessing was applied to both ends, 3000 m was wound around a resin core having a diameter of 30 cm. The width was 1.5 m. The thickness of the first layer was 10 μm, and the thickness of the second layer was 240 μm.
When the white pigment density of the first layer was calculated from the product of the thickness of the first layer, the density of the first layer, and the white pigment concentration, it was 1.8 × 10 ⁻⁴ g / cm ² .

-Longitudinal stretching-
The unstretched film was passed between two pairs of nip rolls having different peripheral speeds, and stretched in the longitudinal direction (conveying direction) under the following conditions.
・ Preheating temperature: 95 ℃
-Stretching temperature: 95 ° C
-Stretching ratio: 3.5 times-Stretching speed: 3000% / second

-Horizontal stretching-
The film stretched longitudinally was stretched transversely under the following conditions using a tenter.
-Preheating temperature: 110 ° C
-Stretching temperature: 120 ° C
-Stretch ratio: 3.9 times-Stretch speed: 70% / second

<Measurement / Evaluation>
The following measurements and evaluations were performed on the PET obtained before and after solid phase polymerization.

-Terminal carboxyl group concentration-
After 0.1 g of polyester was dissolved in 5 ml of benzyl alcohol, phenol red indicator was added dropwise to a mixed solution containing 5 ml of chloroform, and this was titrated with a standard solution (0.01 N KOH-benzyl alcohol mixed solution). The concentration of the terminal carboxyl group [equivalent / ton] was calculated from the amount dropped.

-White pigment concentration-
The concentration of the white pigment in the entire film is a parameter representing the percentage of the mass of the white pigment in the mass of the entire laminated film, and can be specifically measured by the following method. That is, 3 g of the laminated film as a measurement sample is taken in a crucible and heated at 900 ° C. for 120 minutes in an electric oven. Then, after the electric oven has cooled, the crucible is taken out and the mass of ash remaining in the crucible is measured. This ash content is the white pigment content, and the value obtained by dividing the mass of the ash content by the mass of the measurement sample and multiplying by 100 was defined as the white pigment concentration of the entire laminated film.
The white pigment concentration of the first layer was measured in the same manner by using 3 g of the first layer of the laminated film as a measurement sample in the above measurement method.
The white pigment concentration of the second layer was measured in the same manner by using 3 g of the second layer of the laminated film as a measurement sample in the above measurement method.

Examples 2 to 11 and Comparative Examples 1 to 11: Production of Laminated Films The white pigment density and thickness of the first and second layers in Example 1, the white pigment concentration of the entire film, the terminal carboxyl group concentration, and the like are shown in the following table. The laminated films of other examples and comparative examples were produced in the same manner except that the film was changed to that described in 1.

-Hydrolysis resistance-
About the film obtained by film forming-extending | stretching process, a predetermined time process was performed on the wet heat conditions of 100% at 120 degreeC, break elongation measurement was performed by JIS-K7127 method after that, and it evaluated according to the following evaluation criteria. . A and B are practically acceptable standards.
A: Time when the elongation at break decreases to 50% of the untreated film exceeds 90 hours and 100 hours or less B: Time when the elongation at break decreases to 50% of the untreated film exceeds 80 hours 90 Less than time C: Time when the breaking elongation is reduced to 50% of the untreated film exceeds 70 hours and less than 80 hours D: Time when the breaking elongation is reduced to 50% of the untreated film is 70 Less than hours

-Visible light concealment-
The optical density (OD) in the visible light region (380-700 nm) was measured with a Macbeth light densitometer, and evaluated according to the following evaluation criteria. A, B and C are practically acceptable standards.
A: Optical density is 0.6 [O.D. D. ]: Exceeding B: Optical density is 0.5 [O. D. ] And 0.6 [O. D. ] The following C: The optical density exceeds 0.4 [OD] and 0.5 [O.D.]. D. ] The following D: Optical density is 0.4 [O.D. D. ] The following

  From the said table | surface, it turns out that Examples 1-11 with which the 1st layer, the 2nd layer, and the whole laminated film satisfy | fill all predetermined requirements are excellent in hydrolysis resistance and visible light shielding property. On the other hand, Comparative Examples 1 to 11 in which any of the first layer, the second layer, and the entire laminated film does not satisfy the predetermined requirements cannot satisfy both the hydrolysis resistance and the visible light shielding property. I understand that.

  The laminated film of the present invention can maintain strength for a long time outdoors by being excellent in hydrolysis resistance, and is also excellent in design by being excellent in visible light hiding property. By using the laminated film of the present invention, a solar cell module backsheet and a solar cell module can be obtained. Furthermore, the laminated film of the present invention has high industrial applicability, which can be used for a film for building materials, a film for outdoor advertising, and the like.

10 Second layer 12 First layer

Claims (6)

A laminated film having at least a first layer containing polyester and a white pigment and a second layer containing polyester,
The first layer is in contact with at least one surface of the second layer;
The white pigment density of the first layer is 4.3 × 10 ^{−4 to} 5.4 × 10 ⁻⁴ g / cm ² ,
The white pigment concentration of the first layer is 6-12% by mass ,
The thickness of the first layer is 30 to 50 μm,
The thickness of the second layer is 100 to 300 μm,
The white pigment concentration of the entire laminated film is 1.58% by mass or more and less than 2% by mass,
A laminated film having a terminal carboxyl group concentration of 6 to 17 equivalents / ton in the whole laminated film. The laminated film according to claim 1, wherein the concentration of white pigment in the second layer is 0 to 1.5 mass%. The second layer includes 60% by mass or less of a recycled chip obtained by trimming and crushing an end portion in the width direction of the laminated film as a raw material, and the first layer substantially does not include the recycled chip. The laminated film according to 1 or 2. The laminated film according to any one of claims 1 to 3, which is for a solar cell module. The solar cell module backsheet containing the laminated | multilayer film of any one of Claims 1-4. A solar cell module comprising the back sheet for a solar cell module according to claim 5.

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