KR20160111428A - Multilayer film, back sheet for solar cell modules, and solar cell module - Google Patents

Abstract

A problem to be solved by the present invention is to provide a laminated film having both properties of hydrolysis resistance and visible light hiding ability, a back sheet for a solar cell module, and a solar cell module. According to the present invention, there is provided a laminated film having at least a first layer containing a polyester and a white pigment, and a second layer containing a polyester, wherein the first layer is in contact with at least one side 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 to 300 μm, the white pigment concentration of the entire laminated film is , More than 0 mass% and less than 2 mass%, and a terminal carboxyl group concentration in the entire laminated film is 6 to 30 equivalents / ton.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a laminated film, a back sheet for a solar cell module, and a solar cell module,

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 properties. The performance required for polyester films varies. For example, when a polyester film is used for a long-term use in an outdoor environment such as a protective film for a solar cell, it is required that the hydrolysis property is high to maintain the strength for a long period of time, Is required.

Thus, for example, Patent Document 1 discloses a film comprising a surface layer containing 10 to 30 wt% of titanium oxide particles and a base layer containing 0.1 to 4 wt% of titanium oxide particles, And a content of particles of 3 to 8% by weight. Patent Document 2 discloses a polyester film in which the inorganic fine particle concentration-containing layer containing inorganic fine particles has a multilayer structure in which at least one outermost layer is disposed, and the content of the inorganic fine particles in the polyester film as a whole is 2 to 10% Film is described.

Patent Document 1: International Publication No. 2010/113920 Patent Document 2: Japanese Patent Publication 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 step of putting the white pigment into the polyester at the time of producing the polyester film, hydrolysis of the polyester may occur due to the water contained in the white pigment, and the shearing of the white pigment particles may occur, There is a case where the polyester is thermally decomposed due to the heat generated by the polyester resin. For this reason, there is a problem that the higher the white pigment concentration is, the lower the molecular weight of the polyester and the lower the hydrolysis resistance, for the purpose of improving visible light hiding ability. For these reasons, it is difficult to produce a polyester film having both properties of hydrolysis resistance and visible light hiding ability.

The polyester film of Patent Document 1 enhances the visible light hiding ability by the surface layer and enhances the hydrolysis resistance by the base layer, thereby achieving compatibility between the hydrolysis resistance and the visible light hiding ability. However, since the titanium dioxide concentration of the whole film is as high as 3 to 8% by weight, the visible light hiding ability is excellent, but the hydrolysis resistance is not sufficient. In the polyester film of Patent Document 2, both the light reflectance and the hydrolysis resistance are achieved by setting the content of the inorganic fine particles in the film as a whole to 2 to 10 mass%. However, since the content of the inorganic fine particles in the whole film is as high as 2 to 10 mass%, the visible light hiding property is excellent, but the hydrolysis property is not sufficient.

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a laminated film having both properties of hydrolysis resistance and visible light hiding ability. It is another object of the present invention to provide a back sheet for a solar cell module and a solar cell module including the above laminated film.

Means for Solving the Problems As a result of intensive investigations to solve the above problems, the present inventors have found that a polyester resin composition having at least a first layer containing a polyester and a white pigment and a second layer containing a polyester, The white pigment density of the first layer, the thickness of the second layer, the white pigment concentration of the entire laminated film, and the terminal carboxyl group concentration of the entire laminated film satisfy the predetermined conditions, respectively, It has been found that both hydrolysis resistance and excellent visible light hiding ability can be achieved. The present invention has been completed on the basis of these discoveries.

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 side of the second layer,

The white pigment density of the first layer is 1.0 x 10 ^-4 to 1.0 x 10 ^-3 g / cm ² ,

The thickness of the second layer is 100 to 300 mu m,

The white pigment concentration of the whole laminated film is more than 0 mass% and less than 2 mass%

Wherein the terminal carboxyl group concentration of the whole laminated film is 6 to 30 equivalents / ton.

&Lt; 2 > The laminated film according to < 1 >, wherein the white pigment concentration of the first layer is 5 to 20 mass%.

<3> The laminated film according to <1> or <2>, wherein the thickness of the first layer is 5 to 50 μm.

<4> The laminated film according to any one of <1> to <3>, wherein the second layer has a white pigment concentration of 0 to 1.5% by mass.

<5> The second layer contains recycled chips obtained by trimming and crushing the end portions in the width direction of the laminated film in an amount of 60% by mass or less as a raw material, and the first layer contains substantially no recycled chips, Lt; 4 &gt;.

&Lt; 6 > A laminated film according to any one of < 1 > to < 5 >

<7> A back sheet for a solar cell module, comprising a laminated film according to any one of <1> to <6>.

&Lt; 8 > A solar cell module comprising a back sheet for a solar cell module according to < 7 >.

According to the present invention, there is provided a laminated film having properties of both hydrolysis resistance and visible light hiding ability. According to the present invention, there is also provided a back sheet for a solar cell module having both hydrolysis resistance and visible light hiding properties. According to the present invention, there is also provided a solar cell module comprising the laminated film of the present invention or a back sheet for a solar cell module.

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

Hereinafter, the present invention will be described in detail. Descriptions of the constituent elements described below are based on representative embodiments and concrete examples, but the present invention is not limited to such embodiments. In the present specification, the numerical range indicated by "to" means a range including numerical values written 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 a polyester and a white pigment and a second layer containing a polyester, wherein the first layer is a laminated film comprising at least one surface of the second layer Wherein the first layer has a white pigment density of 1.0 × 10 ^-4 to 1.0 × 10 ^-3 g / cm ² , the second layer has a thickness of 100 to 300 μm, and the white pigment concentration of the entire laminated film Is more than 0 mass% and less than 2 mass%, and the terminal carboxyl group concentration of the whole laminated film is 6 to 30 equivalents / ton.

By such a constitution, both properties of hydrolysis resistance and visible light hiding ability can be achieved. The mechanism by which both the hydrolysis property and the visible light hiding property are obtained is presumed as follows. That is, the layer having a low white pigment concentration is made into a second layer, thereby imparting high hydrolysis resistance to the second layer, and a layer having a high white pigment concentration as a first layer, thereby imparting high visible light hiding properties to the first layer, It is presumed that both of the hydrolysis resistance and the visible light hiding ability can be realized by forming the layer constituted by laminating the first layer and the second layer. Specifically, it is preferable that the white pigment density of the first layer is 1.0 × 10 ^-4 to 1.0 × 10 ^-3 g / cm ² to achieve good visible light hiding performance, the thickness of the second layer is 100 to 300 μm, It is presumed that the white pigment concentration of the whole film is less than 2 mass% and the end carboxyl group concentration of the entire laminated film is 6 to 30 equivalents / ton, thereby achieving good hydrolysis resistance.

The laminated film of the present invention has at least a first layer containing a polyester and a white pigment and a second layer containing a polyester, wherein the first layer is in contact with at least one side of the second layer.

An example of the laminated film of the present invention is shown in Fig. The laminated film shown in Fig. 1 is a two-layer laminated film composed of a first layer 12 and a second layer 10, and the first layer is in contact with one surface of the second layer. The laminated film of the present invention is not limited to a laminated film having a two-layer structure as shown in Fig. 1, but may be a laminated film of a first layer 12, a second layer 10, And the first layer 12 may be laminated in this order. The laminated film of the present invention may be a laminated film in which the first layer, the second layer, and the other layers are laminated in this order.

When a laminated film is used for the purpose of being used in conjunction with a different material such as a solar cell back sheet, if the concentration of the white pigment in the conjugated joint surface is large, It is preferable to use a two-layer structure.

Each layer of the laminated film of the present invention will be described below.

&Lt; First Layer >

The first layer, containing a polyester and a white pigment, a white pigment density is ^{1.0 × 10 -4 ~ 1.0 × 10} -3 g / cm 2. The first layer is in contact with at least one surface of the second layer.

White pigment density of the first layer ^{is, 1.0 × 10 -4 ~ 1.0 ×} 10 -3 and ^{g / cm 2, 1.0 × 10} -4 ~ 7.0 × 10 -4 ~ g / cm 2 is preferred and, 1.5 × 10 ^{- 4} to 6.0 x 10 &lt; ^-4 &gt; g / cm &lt; ² &gt; The white pigment by the density of the first layer to less than 1.0 × 10 ^-4 g / cm ² or ^higher, can be enhanced by the visible light ^{hiding, 1.0 × 10 -3 g / cm} 2 it is possible to improve the I-hydrolyzable.

The white pigment density of the first layer is determined from the thickness of the first layer and the white pigment concentration contained in the first layer. Specifically, the white pigment density can be calculated by the following formula.

D = t x p x C x 10 ^-6

From here,

White pigment density: Dg / cm ²

White pigment concentration: C mass%

Thickness of the first layer: tμm

Density of the first layer: ρg / cm ³

to be.

The concentration of the white pigment contained in the first layer is preferably 5 to 20 mass%, more preferably 5 to 15 mass%, and still more preferably 6 to 12 mass%. When the content is 5% by mass or more, sufficient visible light hiding properties can be obtained. When the content is 20% by mass or less, the hydrolysis resistance can be improved.

The white pigment concentration of the first layer is a parameter indicating the ratio of the mass of the white pigment to the mass of the entire first layer as a percentage. Specifically, the white pigment concentration can be measured by the following method. That is, 3 g of the first layer as a measurement sample in the laminated film was taken out from the crucible and heated in an electric oven at 900 DEG C for 120 minutes. Then, when the electric oven is cooled, take out the crucible and measure the mass of the ash remaining in the crucible. This ash is white pigment powder, and the mass of the ash is divided by the mass of the sample to be measured, and multiplied by 100 is used as the white pigment concentration.

The thickness of the first layer is not particularly limited and is, for example, 1 to 100 占 퐉, preferably 5 to 50 占 퐉, more preferably 10 to 50 占 퐉, and still more preferably 30 to 50 占 퐉. If the thickness of the first layer is 5 탆 or more, the visible light hiding ability can be improved, and if it is 50 탆 or less, the hydrolysis resistance can be improved.

&Lt; Second Layer >

The second layer contains polyester. The thickness of the second layer is 100 to 300 占 퐉, more preferably 200 to 300 占 퐉, and further preferably 200 to 250 占 퐉. When the thickness is 100 占 퐉 or more, sufficient hydrolysis resistance can be obtained, and when the thickness is 300 占 퐉 or less, productivity is improved and it is economical.

The polyester contained in the second layer may be the same as or different from the polyester contained in the first layer.

The second layer may or may not contain a white pigment. When the second layer contains a white pigment, 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, still more preferably substantially not. The term "substantially not containing" means a substance which does not affect the effect of the present invention and indicates, for example, not more than 0.1% by mass.

<Polyester>

The polyester used for the first layer and the second layer is not particularly limited, and for example, linear saturated polyesters synthesized from aromatic dibasic acids or ester-forming derivatives thereof and diols or ester-forming derivatives thereof have.

Specific examples of the polyester include polyethylene terephthalate (PET), polyethylene isophthalate, polybutylene terephthalate (PBT), poly (1,4-cyclohexylene dimethylene terephthalate), polyethylene-2,6- . Of these, polyethylene terephthalate or polyethylene-2,6-naphthalate is more preferable, and polyethylene terephthalate is particularly preferable in view of mechanical properties and cost balance.

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

When the polyester is polymerized, Sb-based, Ge-based and Ti-based compounds are preferably used as the catalyst from the viewpoint of suppressing the content of the carboxy group to a predetermined range or less. In the case of using a Ti-based compound, it is preferable to polymerize the Ti-based compound by using the Ti-based compound as a catalyst in the range of 1 ppm to 30 ppm, more preferably 3 ppm to 15 ppm. When the proportion of the Ti-based compound is within the above range, the content of the terminal carboxyl group can be adjusted to the range described below, 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 Publication No. 2543624, Japanese Patent Publication No. 3335683, Japanese Patent Publication No. 3717380, Japanese Patent Publication No. 3897756 Japanese Patent Publication No. 3962226, Japanese Patent Publication No. 3979866, Japanese Patent Publication No. 3996871, Japanese Patent Publication No. 4000867, Japanese Patent Publication No. 4053837, Japanese Patent Publication No. 4127119, Japanese Patent Publication No. 4134710 , Japanese Patent Publication No. 4159154, Japanese Patent Publication No. 4269704, Japanese Patent Publication No. 4313538, and the like can be applied.

The carboxyl group content of each polyester in the first layer and the second layer is preferably not more than 35 equivalents / ton, more preferably not more than 20 equivalents / ton, particularly preferably not more than 17 equivalents / ton .

When the carboxyl group content of the polyester is 35 equivalents / ton or less, the hydrolysis resistance is maintained and the decrease in the strength when the wet heat is aged can be suppressed to be small. The lower limit of the carboxyl group content is preferably 2 equivalents / ton in view of maintaining the adhesiveness. In this specification, "equivalent amount / ton" means the molar equivalent per 1 ton (1000 kg).

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

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

The polyester constituting the first layer or the second layer is preferably solid-phase polymerized after polymerization. As a result, a desired carboxyl group content can be achieved. The solid phase polymerization may be a continuous method (a method in which a resin is filled in a tower and the resin is allowed to slowly stay for a predetermined time while heating it, and then the resin is fed), or a batch method (a method in which a resin is charged into a container and heated for a predetermined time) . Concretely, the solid-state polymerization is carried out in the following manner: Japanese Patent Publication No. 2621563, Japanese Patent Publication No. 3121876, Japanese Patent Publication No. 3136774, Japanese Patent Publication No. 3603585, Japanese Patent Publication No. 3616522, Japanese Patent Publication No. 3617340, Japanese Patent Publication No. 3680523, Japanese Patent Publication No. 3717392, Japanese Patent Publication No. 4167159, and the like can be applied.

The solid phase polymerization is preferably carried out at a temperature of 170 占 폚 to 240 占 폚, more preferably 180 占 폚 to 230 占 폚, and still more preferably 190 占 폚 to 220 占 폚. The solid phase polymerization time is preferably 5 hours or more and 100 hours or less, more preferably 10 hours or more and 75 hours or less, and still more preferably 15 hours or more and 50 hours or less. The solid phase polymerization is preferably carried out in a vacuum or under a nitrogen atmosphere.

The first layer or the second layer can be obtained by, for example, melt-extruding the above-mentioned polyester in a film form, cooling and solidifying it by a casting drum to form an unstretched film, ) At a temperature of Tg to (Tg + 60) ° C, and then stretched so as to have a magnification of 3 to 5 times in the width direction at a temperature of Tg to (Tg + 60) It is preferably a stretched film.

If necessary, it may be subjected to a heat treatment at 180 to 230 ° C for 1 to 60 seconds.

The first layer may be subjected to a surface treatment such as a corona treatment, a flame treatment, and a glow discharge treatment on a surface opposite to the surface on the side where at least the second layer is provided, if necessary. In the corona discharge treatment, high-frequency and high-voltage are applied between a metal roll (dielectric roll) coated with a derivative and an insulated electrode to cause insulation breakdown of air between the electrodes, ionizing the air between the electrodes to corona discharge . Then, during this corona discharge, the polymer substrate is passed.

The preferable treatment conditions are a gap clearance of 1 to 3 mm between the electrode and the dielectric roll, 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 of treating the substrate surface by generating a plasma by discharge in a gas (plasma gas) in a low-pressure atmosphere by a method called a vacuum plasma treatment or a low-pressure plasma treatment. The low-pressure plasma used in the process of the present invention is a non-equilibrium plasma generated under a low plasma gas pressure. The treatment of the present invention is carried out by placing a film to be treated (polymer substrate) in this low-pressure plasma atmosphere.

As a method of generating plasma in the glow discharge processing, methods such as direct current glow discharge, high frequency discharge, and microwave discharge can be used. The power source used for discharging may be DC 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 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 an oxygen gas, a nitrogen gas, a steam gas, an argon gas or a helium gas can be used, and an oxygen gas or a mixed gas of an oxygen gas and an argon gas is particularly preferable. Concretely, it is preferable to use a mixed gas of oxygen gas and argon gas. When a mixed gas of an oxygen gas and an argon gas is used, the ratio of the oxygen gas and the argon gas is preferably about 100: 0 to 30:70, and more preferably about 90:10 to 70:30, . It is also preferable to use a gas such as water vapor that comes from the atmosphere or the object to be processed into the processing vessel by leaking, as the plasma gas, without introducing the gas into the processing vessel.

As the pressure of the plasma gas, a low pressure is required at which the non-equilibrium plasma condition is achieved. The pressure of the specific plasma gas is preferably in the range of about 0.005 to 10 Torr (0.666 to 1333 Pa), and 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 becomes sufficient. If the pressure of the plasma gas is 1333 Pa or less, the electric current increases and the discharge becomes unstable.

The plasma output is not limited by the shape and size of the processing container, the shape of the electrode, etc., but is preferably about 100 to 2500 W, and more preferably about 500 to 1500 W.

The treatment time of the glow discharge treatment is preferably about 0.05 to 100 seconds, and more preferably about 0.5 to 30 seconds. When the treatment time is 0.05 seconds or more, the adhesion improving effect is sufficiently obtained. When the treatment time is 100 seconds or less, deformation and coloring of the film to be treated can be prevented.

The discharge intensity of the glow discharge treatment varies depending on the plasma output and the treatment time, but is preferably in the range of 0.01 to 10 kVA · min / m ² , more preferably in the range of 0.1 to 7 kV · A · min / m ² .

When the discharge treatment strength is set to 0.01 kV · A · min / m ² or more, a satisfactory improvement in adhesiveness can be obtained. By setting the discharge treatment strength to 10 kV · A · min / m ² or less, problems such as deformation and coloring of the film to be treated can be avoided .

In the glow discharge treatment, it is also preferable to heat the film to be treated in advance. According to this method, good adhesion can be obtained in a short period of time as compared with the case where heating is not performed. The heating temperature is preferably in the range of 40 ° C to the softening temperature of the film to be treated + 20 ° C, and more preferably 70 ° C to the softening temperature of the film to be treated. When the heating temperature is 40 占 폚 or higher, a sufficient improving effect of adhesiveness can be obtained. By setting the heating temperature at or below the softening temperature of the film to be treated, good handling properties of the film can be ensured during the treatment.

Specific examples of the method for raising the temperature of the film to be treated in a vacuum include heating with an infrared heater, heating with contact with a heat roll, and the like.

As the flame treatment, for example, a flame treatment using a flame into which a silane compound is introduced can be mentioned.

As the form of the raw resin for the polyester of the second layer, pellets, fluffs, a mixture thereof and the like can be used, and it is preferable that the weight ratio of fluff is set to 60% or less and mixed with the pallet. By using the mixture of the pellets and the fluff as described above, the melting method and the thermal history of the raw resin can be adjusted. The fluff is, for example, a recycled chip obtained by crushing a film that has become unnecessary and being a crushed material such as a small piece (so-called chip) or debris, that is, trimming and crushing the end portion in the width direction of the laminated film. Increasing the fluff ratio enables a cost reduction of the raw material because of a high recycling ratio. On the other hand, the increase in the fluff ratio can give a bulky property, and the bulk specific gravity can be lowered than, for example, only the pallet. As the resin film for obtaining fluff, a polyester film is preferable, and a polyester film of the same kind as the polyester resin in the raw resin is preferable. When the proportion of the fluff is set to 60% by mass or less, the fluctuation range of the terminal COOH amount of the obtained polyester film can be suppressed to a low level. Among them, from the same reason, the mass ratio of fluff is preferably 60% by mass or less, more preferably from 10 to 50% by mass, and particularly preferably from 30 to 50% by mass.

The size of the fluff is not particularly limited as long as it is within a range in which a change in volume is given, but it is preferable that the thickness of the fluff is 20 to 5000 占 퐉. Among them, the thickness of the fluff is preferably in the range of 100 to 1000 占 퐉, more preferably in the range of 100 to 500 占 퐉, from the viewpoint that the bulk specific gravity becomes so small that the filling rate is not lowered too much and the insufficient melting is avoided.

In view of further reducing the amount of terminal COOH of the polyester film to be formed, it is preferable that the variation of the size of the fluff is small. For example, the variation of the thickness of the fluff is preferably within ± 100% Preferably within ± 50%, and further within ± 10%. In the case of using a fluff, fluctuation in the amount of terminal COOH of the obtained polyester film can be suppressed to be low by suppressing the size deviation such as the thickness to be small.

The volume specific gravity of the fluff is preferably in the range of 0.3 to 0.7 in the range in which the volume specific gravity of the raw material resin satisfies the above range. The volume specific gravity of the raw material resin refers to a specific gravity (mass per unit volume) obtained by dividing the mass of a powder in a predetermined shape by a volume in such a manner that the powder is placed in a constant volume in a constant volume container, The smaller the volume, the larger the volume.

Further, it is preferable that the first layer does not substantially contain a recycled chip. The term "substantially not containing" means a substance which does not affect the effect of the present invention and indicates, for example, not more than 0.1% by mass.

<White pigment>

The first layer contains a white pigment. The second layer may or may not contain a white pigment. By including the white pigment in the first layer, it is possible to improve the reflectance (whiteness degree) of light and increase the visible light hiding ability, thereby giving designability. In addition, the reflectance (whiteness) of light can be improved and the power generation efficiency of the solar cell can be increased.

The average particle diameter of the particles constituting the white pigment (hereinafter simply referred to as "particles") is not particularly limited, but is preferably from 0.1 to 10 μm, more preferably from 0.1 to 5 μm, still more preferably from 0.15 to 1 μm. When the average particle size of the particles is 0.1 to 10 占 퐉, the whiteness degree of the film can be made 50 or more even with a small addition amount.

The average particle diameter of the particles can be determined according to the electrodeposition method, and specifically, it can be obtained by the following method.

The particles are observed with a scanning electron microscope, and the magnification is appropriately changed according to the size of the particles. Then, for at least 200 or more randomly selected particles, the outer circumference of each particle is traced. The particle diameter of the particles from these traces is measured by an image analyzer, and the average value of these particles is taken as the average particle diameter.

The particles may be either inorganic particles or organic particles, or they may be used in combination. As a result, the reflectance of light can be improved and the power generation efficiency of the solar cell can be increased. Examples of the inorganic particles suitably used include inorganic particles such as wet and dry silica, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide , Cerium oxide, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, basic carbonates, barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, mica titanium, talc, clay, kaolin, Lithium fluoride, and calcium fluoride. Of these, titanium dioxide and barium sulfate are particularly preferable. Further, the titanium oxide may be any of anatase type and rutile type. The surface of the particles may be treated with an inorganic substance such as alumina or silica, or an organic treatment such as a silicon-based or alcohol-based treatment may be carried out.

Of these particles, titanium dioxide is preferable, and thus excellent durability can be achieved even under light irradiation. Concretely, when UV irradiation is conducted at 100 캜 for 100 hours at 63 캜, 50% Rh and an irradiation intensity of 100 mW / cm ² , the elongation at break is preferably 35% or more, more preferably 40% or more. As described above, polyester is more suitable as a back protection film for solar cells used outdoors because light decomposition and deterioration are suppressed by light irradiation.

There are rutile type and anatase type in titanium dioxide, and 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 high absorption rate of ultraviolet rays (a small spectral reflectance). The present inventors paid attention to the difference in spectral characteristics in the crystal form of titanium dioxide and found that by using the rutile type ultraviolet ray absorbing property, the light resistance can be improved in a polyester film for protection (back sheet for a solar cell) I found that I can improve. As a result, the film durability under light irradiation is excellent even if substantially no other ultraviolet absorber is added. As a result, the ultraviolet absorber is less prone to contamination or deterioration in adhesion due to bleed-out.

As described above, preferably, the titanium dioxide particles are based on a rutile type. Here, the term "subject" means that the amount of the rutile type titanium dioxide in the overall titanium dioxide particles exceeds 50 mass%.

It is also preferable that the amount of the anatase type titanium dioxide in the entire titanium dioxide particles is 10 mass% or less. More preferably 5% by mass or less, and particularly preferably 0% by mass. When the content of the anatase type titanium dioxide exceeds the upper limit value, the amount of the rutile type titanium dioxide occupied in the total titanium dioxide particles becomes small, so that the ultraviolet ray absorption performance may become insufficient. Besides, since the anatase type titanium dioxide has a strong photocatalytic action, This action also tends to lower the light resistance. Rutile-type titanium dioxide and anatase-type titanium dioxide can be distinguished by X-ray diffraction and spectroscopic absorption characteristics.

The rutile titanium dioxide particles may be subjected to an inorganic treatment such as alumina or silica on the surface of the particles, or may be subjected to an organic treatment such as a silicone treatment or an alcohol treatment. The rutile type titanium dioxide may be subjected to particle size adjustment and coarse particle removal using a purification process before being blended into the polyester composition. As an industrial means of the purification process, for example, a jet mill or a ball mill can be used as the crushing means, and as the classification means, for example, dry or wet centrifugal separation can be applied.

In the present invention, organic particles may also be used as a white pigment. It is preferable to withstand the heat in the polyester film, and for example, those made of a crosslinkable resin are used, and specifically polystyrene crosslinked with divinylbenzene is used. The size and addition amount of the particles are the same as those of the inorganic particles.

The addition of the particles to the polyester film is a known method, and various methods known in the art can be used. As a representative method thereof, the following methods can be mentioned.

(A) adding particles before completion of an ester exchange reaction or esterification reaction in the synthesis of polyethylene terephthalate, or adding particles before the initiation of the polycondensation reaction.

(B) a method in which particles are added to polyethylene terephthalate and melt-kneaded.

(C) A master pallet (also referred to as a master batch (MB)) to which a large amount of particles have been added in the methods (A) and (B) is prepared and polyethylene terephthalate containing no particles is kneaded , And a predetermined amount of particles are contained.

(D) The master pallet of (C) is used as it is.

Among them, the master batch method (MB method: (C) above) in which the polyester and the particles are mixed in advance by an extruder is preferable. It is also possible to adopt a method in which an un-dried polyester resin and particles are put into an extruder and the MB is produced by degassing water or air. Preferably, the increase in the acid value of the polyester can be suppressed by preparing the MB using a polyester resin that has been previously dried. In this case, a method of extruding while degassing or a method of extruding without deaeration by a sufficiently dried polyester resin can be given.

For example, in the case of producing an MB, it is preferable to reduce the water content by preliminarily drying the polyester to be added. The drying is preferably carried out at a temperature of 100 to 200 ° C, more preferably 120 to 180 ° C for 1 hour or more, more preferably 3 hours or more, further preferably 6 hours or more. Thus, the polyester resin is sufficiently dried so that the water content thereof is preferably 50 ppm or less, more preferably 30 ppm or less. The method of preliminary mixing is not particularly limited and may be a batch method or a single-shaft or two-shaft or more-kneading extruder. When the MB is produced by degassing, the polyester resin is melted at a temperature of 250 ° C to 300 ° C, preferably 270 ° C to 280 ° C, and one, preferably two or more degreasing mechanisms are provided in the preliminary kneader, It is preferable to adopt a method in which continuous suction and deaeration of 0.05 MPa or more, more preferably 0.1 MPa or more, is carried out to maintain the reduced pressure in the mixer.

<Other materials>

In addition to the polyester and the white pigment in the first layer, and in the second layer in addition to the polyester, an end sealant may be added to improve the hydrolysis resistance (weather resistance) . If the effect of the present invention is not impaired, the first layer and / or the second layer may contain various additives such as a compatibilizer, a plasticizer, a lubricant, an antioxidant, a heat stabilizer, a lubricant, , A brightener, a colorant, a conductive agent, an ultraviolet absorber, a flame retardant, a flame retarder, and a dye may be added.

(Terminal sealing agent)

The first layer and / or the second layer may contain 0.1 to 10% by mass of a terminal sealing agent based on the total mass of the polyester resin and the polyester resin. The addition amount of the terminal endblock agent to the total mass of the polyester resin constituting the polyester is more preferably from 0.2 to 5 mass%, and still more preferably from 0.3 to 2 mass%.

Hydrolysis of polyester is accelerated by the catalytic effect of H ⁺ (proton) generated from a terminal carboxylic acid or the like. Therefore, in order to improve the hydrolysis resistance (weather resistance), it is necessary to add a terminal endblock which reacts with a terminal carboxylic acid Valid.

If the addition amount of the terminal endblock agent is 0.1 mass% or more based on the total mass of the polyester resin, the effect of improving the weatherability is easy to manifest. If the amount is 10 mass% or less, the polyester resin is inhibited from acting as a plasticizer, Is suppressed.

As the end-capping agent, an epoxy compound, a carbodiimide compound, an oxazoline compound, a carbonate compound and the like can be mentioned, but a carbodiimide having high affinity with polyethylene terephthalate (PET) and high terminal capping ability is preferable.

The terminal endblock (particularly the carbodiimide endblock) preferably has a high molecular weight. As a result, it is possible to reduce the amount of volatile acid in the molten film. The molecular weight is preferably 200 to 100,000, more preferably 2000 to 80,000, and even more preferably 10,000 to 50,000. When the molecular weight of the terminal endblock (particularly the carbodiimide endblocker) is within the above range, it is easy to uniformly disperse in the polyester, so that the effect of improving the weatherability can be sufficiently manifested and the effect of extrusion, It becomes easier to do.

The molecular weight of the end-capping agent means the weight average molecular weight.

(Carbodiimide-based end encapsulant)

The carbodiimide compound having a carbodiimide group includes a monofunctional carbodiimide and a multifunctional carbodiimide. Examples of the monofunctional carbodiimide include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethyl Carbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide and di-beta-naphthylcarbodiimide And the like. Particularly preferred are dicyclohexylcarbodiimide and diisopropylcarbodiimide.

As the multifunctional carbodiimide, a carbodiimide having a degree of polymerization of 3 to 15 is preferably used. Specific examples thereof include 1,5-naphthalene carbodiimide, 4,4'-diphenylmethanecarbodiimide, 4,4'-diphenyldimethylmethanecarbodiimide, 1,3-phenylenecarbodiimide , 1,4-phenylene diisocyanate, 2,4-tolylene carbodiimide, 2,6-tolylene carbodiimide, 2,4-tolylene carbodiimide and 2,6- A mixture of diimides, hexamethylene carbodiimide, cyclohexane-1,4-carbodiimide, xylylene carbodiimide, isophorone carbodiimide, dicyclohexylmethane-4,4'-carbodiimide, Methyl cyclohexane carbodiimide, tetramethyl xylylene carbodiimide, 2,6-diisopropylphenyl carbodiimide, and 1,3,5-triisopropylbenzene-2,4-carbodiimide .

The carbodiimide compound is preferably a carbodiimide compound having high heat resistance because an isocyanate-based gas is generated by thermal decomposition. In order to enhance the heat resistance, the higher the molecular weight (degree of polymerization), the better, and more preferably the end of the carbodiimide compound has a structure with a high heat resistance. In addition, since pyrolysis once is likely to cause additional pyrolysis, it is necessary to design the extrusion temperature of the polyester to be as low as possible.

The carbodiimide of the end-capping agent is also preferably one having a cyclic structure (for example, those described in JP-A No. 2011-153209). Even if they have a low molecular weight, they exhibit an effect equivalent to that of the high molecular weight carbodiimide. This is because the terminal carboxylic acid of the polyester and the cyclic carbodiimide undergo ring-opening reaction, one of them reacts with the polyester, and the other terminal reacts with the other polyester to have a high molecular weight. Thus, an isocyanate- And the like.

Among these cyclic structures, in the present invention, it is preferable that the end-capping agent is a carbodiimide compound having a cyclic structure having a carbodiimide group and the first nitrogen and the second nitrogen bonded by a bonding group . Also, the end-capping agent may be a carbodiimide containing at least one carbodiimide group adjacent to the aromatic ring and having a cyclic structure in which the first nitrogen and the second nitrogen of the carbodiimide group adjacent to the aromatic ring are bonded by a bonding group (Also referred to as an 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 at least two of the carbodiimide groups in the molecule have the first nitrogen and the second nitrogen bonded by a linking group, that is, a monocyclic ring.

The cyclic structure has one carbodiimide group (-N═C═N-) and the first nitrogen and the second nitrogen are bonded by a bonding group. Among the one cyclic structure, only one carbodiimide group is present, but in the case of having a plurality of cyclic structures in the molecule, such as a spirocyclic ring, one carbodiimide It is needless to say that the compound may have a plurality of carbodiimide groups as a compound. The number of atoms in the cyclic structure is preferably 8 to 50, more preferably 10 to 30, still more preferably 10 to 20, and particularly preferably 10 to 15.

Here, the number of atoms in the cyclic structure means the number of atoms constituting the cyclic structure directly. For example, when it is an 8-membered ring, it is 50 when it is an 8- or 50-membered ring. When the number of atoms in the cyclic structure is less than 8, the stability of the cyclic carbodiimide compound decreases, which makes storage and use difficult. From the viewpoint of the reactivity, there is no particular limitation on the upper limit of the number of rings, but the cyclic carbodiimide compound having an atomic number of 50 or less 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 selected in the range of 10 to 30, more preferably 10 to 20, and particularly preferably 10 to 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.

[Chemical Formula 1]

(Epoxy-based end encapsulant)

Preferable examples of the epoxy compound include a glycidyl ester compound and a glycidyl ether compound.

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, stearic acid glycidyl ester, lauric acid glycidyl ester, palmitic acid glycidyl ester, behenic acid glycidyl ester, bissate glycidyl ester, oleic acid glycidyl ester, linolic acid glycidyl ester, linoleic acid Glycidyl ester, behenic acid glycidyl ester, stearoyl glycidyl ester, terephthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, phthalic acid diglycidyl ester, naphthalenedicarboxylic acid diglycidyl ester, Methyl terephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, cyclohexane The carboxylic acid diglycidyl ester, adipic acid diglycidyl ester, succinic acid diglycidyl ester, sebacic acid diglycidyl ester, dodecanedioic acid diglycidyl ester, octadecane dicarboxylic acid diglycidyl ether, A trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester. These may be used singly or in combination of two or more kinds.

Specific examples of the glycidyl ether compound include phenyl glycidyl ether, O-phenyl glycidyl ether, 1,4-bis (?,? - epoxypropoxy) (?,? - epoxypropoxy) hexane, 1,4-bis (?,? - epoxypropoxy) benzene, 1- (?,? - epoxypropoxy) phenyl] propane and 2,2-bis- (4-hydroxyphenyl) Bisglycidyl polyethers obtained by reaction of bisphenol such as propane or 2,2-bis (4-hydroxyphenyl) methane with epichlorohydrin, etc. These may be used alone or in combination of two or more Can be used.

(Oxazoline-based end-sealing agent)

As the oxazoline compound, a bisoxazoline compound is preferable, and specific examples thereof include 2,2'-bis (2-oxazoline), 2,2'-bis (4-methyl- Bis (4,4-dimethyl-2-oxazoline), 2,2'-bis (4-ethyl-2-oxazoline), 2,2'- 2-oxazoline), 2,2'-bis (4-hexyl-oxazoline), 2,2'- 2-oxazoline), 2,2'-bis (4-phenyl-2-oxazoline), 2,2'- (2-oxazoline), 2,2'-p-phenylenebis (2-oxazoline), 2,2'- Phenylenebis (4-methyl-2-oxazoline), 2,2'-p-phenylenebis (4,4- 2-oxazoline), 2,2'-m-phenylenebis (4,4-dimethyl-2-oxazoline), 2 , 2'-ethylene bis (2-oxazoline), 2,2'-tetramethylene bis (2-oxazoline), 2,2'-hexamethylene bis ), 2,2'-octamethylene bis (2-oxazoline), 2,2'-decamethylene bis (2-oxazoline), 2,2'- 2,2'-tetramethylenebis (4,4-dimethyl-2-oxazoline), 2,2'-9,9'-diphenoxyethanebis (2-oxazoline) Hexylene bis (2-oxazoline) and 2,2'-diphenylene bis (2-oxazoline). Of these, 2,2'-bis (2-oxazoline) is most preferably used from the viewpoint of reactivity with polyester. The above-mentioned bisoxazoline compounds may be used singly or in combination of two or more as long as the objects of the present invention are attained.

Such an end encapsulant needs to be contained in a polyester film. That is, the above effect can not be obtained unless it is directly reacted with the polyester molecule. This is because polyester and end-capping agent do not react even when added to a coating layer on PET.

<Other layers>

In the laminated film of the present invention, other layers besides the first layer and the second layer may be laminated. Examples of other layers include a layer having a high degree of whiteness (a layer having a large degree of whiteness) and a layer having a low degree of whiteness (a layer having a small degree of void or particle). As other layers, reference may be made, for example, to paragraphs 0065 to 0066 of Japanese Laid-Open Patent Publication No. 2013-65846, the contents of which are incorporated herein by reference.

&Lt; Property of laminated film &

The laminated film of the present invention preferably has a white pigment concentration of more than 0 mass% and less than 2 mass%, preferably 0.5 mass% or more and less than 2 mass%, more preferably 1.5 mass% or more and less than 2 mass% Do. By making the white pigment concentration of the whole film larger than 0 mass%, the visible light shielding property can be improved, and when it is less than 2 mass%, the hydrolysis property can be improved.

The white pigment concentration of the entire film is a parameter indicating the ratio of the mass of the white pigment occupying in the mass of the entire laminated film as a percentage. Specifically, the white pigment concentration can be measured by the following method. That is, 3 g of the laminated film was taken as a measurement sample in the crucible, and heating was performed at 900 캜 for 120 minutes in an electric oven. Then, when the electric oven cools down, take out the crucible and measure the mass of the ash remaining in the crucible. This ash is white pigment powder, and the mass of the ash is divided by the mass of the sample to be measured, and multiplied by 100 is used as the white pigment concentration.

The hydrolysis resistance is improved by the amount of the terminal carboxyl group (terminal carboxyl group concentration: AV). Due to this, the terminal carboxyl group concentration in the entire laminated film is 6 to 30 equivalents / ton, preferably 10 to 25 equivalents / ton, and more preferably 10 to 20 equivalents / ton.

If the terminal carboxyl group concentration is less than 6 equivalents / ton, the carboxyl group (COOH group) on the surface becomes too small (the polarity becomes too low) and the adhesion property with the isotactic material may be lowered. When the terminal carboxyl group concentration is more than 30 equivalents / ton, H ⁺ of the COOH group at the molecular terminal of the polyester is catalyzed to accelerate the hydrolysis, and the hydrolysis resistance may be lowered.

The terminal carboxyl group concentration was determined by dropping a phenol red indicator into a mixed solution obtained by dissolving 0.1 g of polyester in 5 ml of benzyl alcohol and adding 5 ml of chloroform to this solution and adding this solution to a reference solution (0.01 N KOH-benzyl alcohol mixed solution) And is a value calculated from the drop amount.

The thickness of the entire laminated film is preferably 100 to 400 占 퐉, more preferably 100 to 300 占 퐉, further preferably 100 to 250 占 퐉, and particularly preferably 110 to 250 占 퐉.

The ratio of the thickness of the first layer to the total thickness of the laminated film (thickness of the first layer / thickness of the entire laminated film) is preferably 0.01 to 0.30, more preferably 0.02 to 0.25.

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

&Lt; Method of producing laminated film &

The method for producing the laminated film of the present invention is not particularly limited, but from the viewpoint of adhesion between layers and productivity, it is preferable that the laminated film is produced by a co-extrusion method. In the case of the two-layer structure of the first layer and the second layer, two extruders are prepared, a composition constituting the first layer on one side and a composition constituting the second layer on the other side are introduced, (Melts) are joined together using a two-layer feed block device and extruded from the die while maintaining the laminated state to obtain an unstretched laminated film (co-extrusion step). The laminated film is 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 preferred embodiments are also the same.

In the co-extrusion step, the polyester after the solid-phase polymerization is melt-kneaded to form a composition constituting the first layer for forming the first layer and a composition constituting the second layer for forming the second layer, (Melts) are merged in a two-layer feed block device to form a laminated state, and then extruded from the die to form a composition constituting the first layer on at least one side of the composition constituting the second layer Thereby forming a laminated film.

For example, the above-mentioned solid-phase-polymerized polyester is dried to make the residual moisture to be 100 ppm or less, and then melted using an extruder. The melting temperature is preferably 250 占 폚 or higher and 320 占 폚 or lower, more preferably 260 占 폚 or higher and 310 占 폚 or lower, and still more preferably 270 占 폚 or higher and 300 占 폚 or lower.

It is more preferable to perform nitrogen substitution in the extruder in that the generation of terminal COOH by thermal decomposition can be further suppressed.

In the extruder, the melted molten material (melt) is extruded from the 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 composition constituting the first layer for forming the first layer on at least one side of the composition constituting the second layer were fed by a feed block device To form a laminated state, and then extruded from a die to form a laminated 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 co-extruded 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 more and 80 ° C or less, more preferably 15 ° C or more and 70 ° C or less, and further preferably 20 ° C or more and 60 ° C or less. From the viewpoint of enhancing the adhesion between the melt and the chill roll and increasing the cooling efficiency, it is preferable to apply the static electricity before the melt touches the chill roll. It is also preferable to apply cold air from the opposite side of the chill roll or bring the cooling roll into contact to promote cooling. Thus, even if a thick film (concretely, a film having a thickness after stretching of 250 占 퐉 or more, or 300 占 퐉 or more) can be effectively cooled.

In addition, when the cooling is insufficient, spherical crystals are likely to be generated, which may cause uneven stretching, resulting in a thickness variation.

In the stretching step, longitudinal stretching and transverse stretching of the unstretched laminated film produced by the co-extrusion process are performed so that the film surface temperature during longitudinal stretching and transverse stretching is (Tg1 + 10) DEG C or more and (Tg1 + 35) (Tg1 represents the glass transition temperature of the first layer). When the film surface temperature at the time of the vertical stretching and the transverse stretching is not less than (Tg1 + 10) DEG C, the stress at the time of stretching can be reduced, so that stretching at the stretching magnification necessary for imparting hydrolysis resistance becomes possible, ° C., it is possible to impart the orientation necessary for improving the hydrolysis resistance. More preferably, the film surface temperature at the time of biaxial stretching (at the time of longitudinal stretching and at the time of transverse stretching) is (Tg1 + 12) DEG C or more and (Tg1 + 30) DEG C or less.

For example, an unstretched laminated film is led to a roll group heated to a temperature of 70 ° C or more and 140 ° C or less and stretched at an elongation rate of 3 to 5 times in the longitudinal direction (longitudinal direction, that is, the film advancing direction) , And cooled in a roll group at a temperature of 20 ° C or more and 50 ° C or less. Subsequently, both ends of the film were gripped with a clip while being guided by a tenter, and the film was stretched at a stretching rate of 3 to 5 times in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 80 DEG C to 150 DEG C .

The elongation is preferably 3 to 5 times in both the longitudinal direction and the width direction. The area ratio (longitudinal stretching magnification x transverse stretching magnification) is preferably 9 times or more and 15 times or less. If the area multiplication factor is 9 or more, the reflectance, hiding property and film strength of the obtained biaxially oriented laminated film are good, and if the area multiplication factor is 15 times or less, breaking at the time of stretching can be avoided.

As a biaxial stretching method, it is possible to use either a sequential biaxial stretching method in which the stretching in the longitudinal direction and the transverse direction is separated as described above, or a simultaneous biaxial stretching method in which the stretching in the longitudinal direction and the transverse direction are simultaneously performed.

In order to complete the crystal orientation of the obtained biaxially stretched film and to impart planarity and dimensional stability, the biaxially stretched film was successively heat-fixed in a tenter, uniformly cooled (cooled) to room temperature You can. In general, since the heat shrinkage of the film is large when the heat fixing treatment temperature (Ts) is low, the heat treatment temperature is preferably high in order to impart high thermal dimensional stability. However, if the heat treatment temperature is too high, the crystallinity of the orientation is lowered, and as a result, the hydrolysis resistance of the formed film may be poor.

In the present invention, when the heat-setting treatment of the biaxially oriented film is carried out, the surface temperature of the film at the time of heat fixation is preferably (Tm2-40) DEG C or higher and Tm2 DEG C or lower when the crystal melting peak of the second layer is Tm2 . When the surface temperature of the film at the time of heat fixation is (Tm2-40) DEG C or more, the effect of removing the residual strain by the heat fixation becomes sufficient, the heat shrinkage becomes the level within the allowable range, Deterioration of the hydrolysis resistance can be prevented.

Further, the laminated film of the present invention can be used as a back sheet constituting a solar cell module, but when the module is used, the atmospheric temperature may rise up to about 100 캜. Therefore, the film surface temperature at the time of heat setting is more preferably (Tm2-30) DEG C or higher and (Tm2-10) DEG C or lower.

If necessary, a relaxation treatment of 1 to 12% in the width direction or the longitudinal direction may be carried out. The heat-set polyester film is usually cooled to below Tg, and the clip holding portions at both ends of the polyester film are cut, and wound in a roll shape. At this time, it is preferable to relax 1 to 12% in the width direction and / or the length direction within the temperature range of the final heat fixing treatment temperature or lower and Tg or higher.

It is preferable that the cooling be carried out at a cooling rate of 1 ° C or more and 100 ° C or less per second from the final heat fixing temperature to the room temperature in view of dimensional stability. In particular, it is preferable that the temperature from Tg + 50 deg. C to Tg is cooled at a cooling rate of 1 deg. C or more and 100 deg. C or less every second. The means for cooling and relaxing is not particularly limited and can be carried out by a conventionally known means. In particular, it is preferable to perform these treatments while sequentially cooling in a plurality of temperature ranges from the viewpoint of improving the dimensional stability of the laminated film.

For the purpose of improving the strength of the laminated film in the production of the laminated film, the laminated film is used in a known stretching film such as multistage longitudinal stretching, re-stretching, re-stretching, transverse stretching or the like It may be stretched. The order of longitudinal stretching and transverse stretching may be reversed.

For details of the production method of the laminated film, reference can be made to, for example, paragraphs 0098 to 0110 of Japanese Laid-Open Patent Publication No. 2011-211087, the contents of which are incorporated herein by reference.

<Back Sheet for Solar Module>

The back sheet for a solar cell of the present invention includes the laminated film of the present invention. The back sheet for a solar cell of the present invention is constituted by providing the laminated film of the present invention and a functional layer such as an adhesive layer, an ultraviolet absorbing layer and a light reflecting white layer which is adhered to the adherend, if necessary, At least one layer may be provided. Since the laminated film of the present invention is provided, it exhibits stable durability performance for a long term use.

In the back sheet for a solar cell of the present invention, for example, the following functional layer may be applied (laminated) to the laminated film after uniaxial stretching and / or biaxial stretching. For coating, known coating techniques such as roll coating, knife edge coating, gravure coating, and curtain coating may be used.

Further, surface treatment (flame treatment, corona treatment, plasma treatment, ultraviolet ray treatment, or the like) may be carried out before the application thereof. It is also preferable to use a pressure-sensitive adhesive.

(This adhesive layer)

In the case of constructing the solar cell module using the laminated film of the present invention, it is preferable that the solar cell element has the adhesive layer on the side opposite to the sealing material of the battery side substrate sealed with the sealing agent. By providing this adhesive layer exhibiting adhesiveness to an adherend including an encapsulant (in particular, an ethylene-vinyl acetate copolymer) (for example, a surface of an encapsulant of a battery-side substrate sealed with a sealing material for a solar cell element) , The back sheet and the sealing agent can be firmly adhered to each other. Specifically, the adhesive layer has an adhesive strength of 10 N / cm or more, preferably 20 N / cm or more, particularly to EVA (ethylene-vinyl acetate copolymer) used as an encapsulating material.

In addition, this adhesive layer is required to prevent peeling of the back sheet during use of the solar cell module, so that the adhesive layer preferably has high humidity and humidity resistance.

(bookbinder)

The adhesive layer may contain at least one kind of binder. As the binder, for example, polyester, polyurethane, acrylic resin, polyolefin and the like can be used. Among them, an acrylic resin and a polyolefin are preferable from the viewpoint of durability. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. Examples of preferable binders include the following.

Examples of the polyolefin include Chemipearl S-120 and S-75N (all manufactured by Mitsui Chemicals, Inc.). As examples of the acrylic resin, there can be mentioned Main Reimer ET-410 and SEK-301 (both manufactured by Nihon Junyaku Kogyo Co., Ltd.). Examples of the composite resin of acrylic and silicon include Ceranate WSA1060, WSA1070 (all manufactured by DIC), and H7620, H7630, and H7650 (all available from Asahi Kasei Chemicals Co., Ltd.).

The amount of the binder is preferably in the range of 0.05 to 5 g / m ² , and particularly preferably in the range of 0.08 to 3 g / m ² . The amount of the binder is 0.05 g / m ² or more, so that a better adhesive force is obtained, and it is 5 g / m ² or less, whereby a better surface shape can be obtained.

(Fine particles)

The adhesive layer may contain at least one kind of fine particles. The adhesive layer preferably contains fine particles in an amount of 5% by mass or more based on the total mass of the layer.

As the fine particles, inorganic fine particles such as silica, calcium carbonate, magnesium oxide, magnesium carbonate, tin oxide and the like are suitably used. Particularly, fine particles of tin oxide or silica are preferred because of a small decrease in the adhesiveness when exposed to a humid atmosphere.

The particle size of the fine particles is preferably about 10 to 700 nm, and more preferably about 20 to 300 nm. Good adhesion can be obtained by using fine particles having a particle diameter in the above range. The shape of the fine particles is not particularly limited, and spherical, irregular, needle-shaped, or the like can be used.

The amount of the fine particles to be added in the adhesive layer is preferably 5 to 400 mass%, more preferably 50 to 300 mass%, per binder in the adhesive layer. The addition amount of the fine particles is 5% by mass or more, and the adhesive property when exposed to a moist heat atmosphere is excellent. When the amount is 1000% by mass or less, the adhesive layer has a better surface shape.

(Crosslinking agent)

The adhesive layer may contain at least one of crosslinking agents.

Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among them, an oxazoline crosslinking agent is particularly preferable from the viewpoint of securing the adhesiveness after the lapse of the wet heat.

Specific examples of the oxazoline crosslinking agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, (2-oxazoline), 2,2'-ethylene- bis- (2-oxazoline), 2,2'-trimethylene- bis- , 2'-tetramethylene-bis- (2-oxazoline), 2,2'-hexamethylene-bis- (2-oxazoline), 2,2'-octamethylene- 2,2'-ethylene- bis- (4,4'-dimethyl-2-oxazoline), 2,2'-p- phenylene- bis- (2- oxazoline) Phenylene-bis- (4,4'-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane ) Sulfide, bis- (2-oxazolylinobonane) sulfide, and the like. Also, (co) polymers of these compounds can be preferably used.

As the compound having an oxazoline group, EPOKROS K2010E, copper K2020E, copper K2030E, copper WS500 and copper WS700 (both manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) and the like can also be used.

The amount of the crosslinking agent to be added in the adhesive layer is preferably from 5 to 50% by mass, more preferably from 20 to 40% by mass, based on the binder of the adhesive layer. The amount of the crosslinking agent to be added is 5% by mass or more, and a good crosslinking effect is obtained. The strength of the reflective layer is poor and the adhesion failure is difficult to occur. The amount of the crosslinking agent is 50% by mass or less.

(additive)

To the adhesive layer, a known matting agent such as polystyrene, polymethylmethacrylate, and silica, and a known surfactant such as anionic or nonionic surfactant may be further added, if necessary.

(Method of forming this adhesive layer)

As a method of forming the adhesive layer, there is a method of applying a polymer sheet having the adhesive property to a polyester film or a method of coating, and the method by coating is a method of forming a film with a simple and high uniformity . 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 liquid used for coating may be water or an organic solvent such as toluene or methyl ethyl ketone. One solvent may be used alone, or two or more solvents may be mixed and used.

In the case of forming the adhesive layer by coating, it is preferable to combine the drying of the coating layer and the heat treatment in the drying zone after the heat treatment, as described in the production method of the present invention. The same applies to the case where a colored layer or other functional layer described later is formed by coating.

(Properties)

The thickness of the adhesive layer is not particularly limited, but is usually 0.05 to 8 탆, more preferably 0.1 to 5 탆. The thickness of the adhesive layer is 0.05 占 퐉 or more, which is easy to obtain the necessary adhesiveness, and is 8 占 퐉 or less, so that the surface shape can be kept better.

The adhesive layer preferably has transparency from the viewpoint of not hindering the effect of the colored layer when a colored layer (in particular, a reflective layer) is disposed between the adhesive layer and the polyester film.

<Solar cell module>

The solar cell module of the present invention is characterized by comprising the laminated film of the present invention or the back sheet of the present invention.

The solar cell module of the present invention is a solar cell module in which a solar cell element that converts the optical energy of solar light into electric energy is disposed between a transparent substrate on which sunlight is incident and a laminated film (back sheet for a solar cell) Consists of. The space between the substrate and the laminated film can be formed by sealing with a resin such as an ethylene-vinyl acetate copolymer (so-called sealing material).

For example, a member other than the solar cell module, the solar cell, and the back sheet is described in detail in, for example, "Photovoltaic power generation system constituent material" (issued by Sugimoto Aichi Co., Ltd., Sakai, have.

The substrate having transparency needs only to have light transmittance capable of transmitting sunlight, and can be appropriately selected from a substrate through which light is transmitted. From the viewpoint of power generation efficiency, it is preferable that the light transmittance is higher. As 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 the solar cell element include silicon such as single crystal silicon, polycrystalline silicon and amorphous silicon, group III-V such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium- Various compound solar cell devices such as compound semiconductors can be used.

Example

Hereinafter, the features of the present invention will be described in more detail with reference to Examples and Comparative Examples. The materials, the amounts used, the ratios, the processing contents, the processing procedures, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the following specific examples.

Example 1: Fabrication of laminated film

<Synthesis of Polyester>

- Esterification -

4.7 tons (4700 kg) of high-purity terephthalic acid and 1.8 tons (1.800 kg) of ethylene glycol were mixed in the first esterification reactor for 90 minutes to form a slurry and continuously fed to the first esterification reactor at a flow rate of 3800 kg / h did. Further, an ethylene glycol solution of citric acid chelate titanium complex (VERTEC AC-420, manufactured by Johnson &amp; Matthey) for citric acid to Ti metal was continuously supplied to the reaction tank at an internal temperature of 250 ° C and an average residence time of about 4.3 hours Lt; / RTI &gt; At this time, the citrate 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 equivalents / ton.

This reaction product was transferred to a second esterification reaction tank and reacted with stirring at an internal retention time of 1.2 hours at a temperature of 250 DEG C in the reaction tank to obtain an oligomer having an acid value of 200 equivalents / ton. The inside of the second esterification tank was partitioned into three zones and an ethylene glycol solution of magnesium acetate was continuously supplied from the second zone so that the Mg addition amount was 67 ppm in terms of the element, And ethylene glycol solution of trimethyl phosphate were continuously supplied so that the amount of P added 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 subjected to polycondensation under stirring at a reaction temperature of 270 ° C and a pressure of 2.67 × 10 ^-3 MPa (20 torr) in the reaction tank for an average residence time of about 1.8 hours .

The reaction was carried out in the second polycondensation reaction tank and the reaction (polycondensation) was carried out under the conditions of a temperature of 276 ° C in the reaction tank and a residence time of about 1.2 hours at a pressure of 6.67 × 10 ^-4 MPa (5 torr) .

Subsequently, the resultant was transferred to the third polycondensation reaction tank. In this reaction tank, the reaction (polycondensation) was carried out under the conditions of a temperature of 278 ° C in the reactor, a pressure of 2.0 × 10 ^-4 MPa (1.5 torr) To give a reaction product (polyethylene terephthalate; hereinafter abbreviated as PET).

The obtained PET (reaction product) was subjected to measurement using a high-resolution type 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 was slightly decreased with respect to the original amount of addition, but it is presumed that P was volatilized during the polymerization process.

- Solid phase polymerization process -

The resin pellets (intrinsic viscosity IV = 0.60 dl / g, terminal carboxyl group concentration = 25 equivalents / ton) were subjected to solid phase polymerization in the following manner, and the thus obtained PET was palletized (diameter: 3 mm, length: did.

The intrinsic viscosity (IV) of the polyester can be calculated from the following equation at the solution viscosity measured at 25 DEG C by dissolving the polyester in the orthochlorophenol.

? sp / C = [?] + K [?] ² ? C

Where C is the dissolved polymer weight per 100 ml of solvent (in this case 1 g / 100 ml), K is the Huggins constant (0.343) ), And solution viscosity and solvent viscosity can be measured using an Ostwald viscometer.

In the solid phase polymerization, the polyester polymerized by the above-described esterification reaction was preliminarily crystallized by heating at 140 DEG C for 7 minutes by nitrogen at a dew point temperature of -30 DEG C to prevent sticking during solid phase polymerization.

Next, it was dried at 165 DEG C for 4 hours by using heated nitrogen at a dew point temperature of -30 DEG C, and the water content in the resin was made to be 50 ppm or less.

Next, the dried polyester resin was preliminarily heated to 205 占 폚 and then nitrogen circulated at 207 占 폚 for 25 hours to proceed solid-state polymerization. As the nitrogen circulation conditions, the gas ratio (the amount of nitrogen gas circulated with respect to the discharged resin amount) was 1.5 m ³ / kg, the superficial velocity was 0.08 m / sec, the ethylene glycol concentration was 240 ppm, the water concentration was 12 ppm, Solid phase polymerization was carried out by using nitrogen having a partial pressure ratio (molar partial pressure of ethylene glycol / molar partial pressure of water) of 20. In order to make the composition of the mixed gas, ethylene glycol scrubber was made of high purity ethylene glycol having a water content of 100 ppm and the temperature of the scrubber was set at 35 캜. The pressure in the scrubber was set in the range of 0.1 MPa to 0.11 MPa.

Next, the resin (500 kg / h) discharged from the reaction process was cooled to 60 占 폚. The obtained resin had an intrinsic viscosity IV = 0.78 dl / g and a terminal carboxyl group concentration = 9 equivalents / ton.

<Production of master pallet>

The master pallet was produced by kneading the PET pallet so that the amount of the titanium oxide was 40 to 60% by mass.

&Lt; Extrusion film forming &

In the first layer, the PET and the master pallet were mixed so as to have a titanium oxide concentration of 12 mass%, dried at a water content of 100 ppm or less, and then fed to an extruder 1 and melt-extruded at 285 deg. As the extruder 1, a twin-screw extruder of the double-vent type in the co-rotating direction with two vents was used.

The second layer was obtained by mixing the PET and the recycled chips produced by trimming and crushing the end portions in the width direction of the obtained laminated film so as to have a titanium dioxide concentration of 0.2% by mass, drying the mixture at a water content of 100 ppm or less, And melt-extruded at 285 ° C. As in the case of the extruder 1, the extruder 2 was a double-vent type twin-screw extruder having two vents in the same direction.

The melts (melts) extruded from the respective extruder outlets were passed through a gear pump and a metal fiber filter (pore diameter: 20 m), joined together using a two-layer feed block device, . The extruded melt was brought into close contact with the cooling roll using an electrostatic application method. The cooling roll can be controlled in temperature through water as a heat medium by using a hollow cast roll.

<Stretching and winding>

The thus obtained unstretched film was extruded on a cooling roll in the above manner and subjected to biaxial stretching in succession in the following manner to obtain a film having a thickness of 250 mu m. The stretching was performed in the order of longitudinal stretching at 95 캜 and transverse stretching at 140 캜 in the order of longitudinal stretching and transverse stretching. Thereafter, it was opened and fixed at 210 캜 for 12 seconds, and then relaxed by 3% in the transverse direction at 205 캜. After stretching, the both ends were trimmed by 10 cm, and both ends were subjected to a thickness treatment. Thereafter, a resin winding core having a diameter of 30 cm was wound at a winding rate of 3000 m. The width was 1.5 m. The thickness of the first layer was 10 mu m and the thickness of the second layer was 240 mu m.

The hanba calculating the white pigment density of the first layer, from the density, the product of the white pigment concentration in the thickness of the first layer, the first layer, 1.8 × 10 ^-4 was g / cm ^2.

- longitudinal stretching -

The unstretched film was passed between two pairs of nip rolls having different peripheral speeds, and was stretched in the longitudinal direction (transport direction) under the following conditions.

· Preheating temperature: 95 ℃

Draw temperature: 95 ° C

· Drawing magnification: 3.5 times

· Drawing speed: 3000% / second

- Horizontal stretching -

The longitudinally stretched film was transversely stretched using a tenter under the following conditions.

· Preheating temperature: 110 ℃

Stretching temperature: 120 ° C

· Drawing magnification: 3.9 times

· Drawing speed: 70% / second

<Measurement and evaluation>

The PET obtained before and after the solid-state polymerization was subjected to the following measurement and evaluation.

- terminal carboxyl group concentration -

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

- White pigment concentration -

The white pigment concentration of the entire film is a parameter indicating the ratio of the mass of the white pigment occupying in the mass of the entire laminated film as a percentage. Specifically, the white pigment concentration can be measured by the following method. That is, 3 g of the laminated film was taken as a measurement sample in the crucible, and heating was performed at 900 캜 for 120 minutes in an electric oven. Then, when the electric oven cools down, take out the crucible and measure the mass of the ash remaining in the crucible. This ash was white pigment powder, and the mass of the ash was divided by the mass of the sample to be measured and multiplied by 100 to obtain 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 in the laminated film as the measurement sample.

The white pigment concentration of the second layer was measured in the same manner by using 3 g of the second layer in the laminated film as the measurement sample.

Examples 2 to 11 and Comparative Examples 1 to 11: Production of a laminated film

Except that the white pigment density and thickness of the first and second layers in Example 1, the white pigment concentration of the entire film, and the terminal carboxyl group concentration were changed to those described in the following table, A laminated film of Comparative Example was produced.

- I hydrolyse -

The film obtained by the film-forming process was subjected to a treatment at a temperature of 120 ° C under a humid condition of 100% for a predetermined time, and thereafter, the breaking elongation was measured according to the JIS-K7127 method and evaluated according to the following evaluation criteria. A and B are practically acceptable standards.

A: The breaking elongation is reduced to 50% of the untreated film by more than 90 hours and less than 100 hours

B: The elongation at break is reduced to 50% of the untreated film by more than 80 hours and less than 90 hours

C: The time at which the elongation at break is reduced to 50% of the untreated film is more than 70 hours but less than 80 hours

D: The time at which the elongation at break decreases to 50% of the untreated film is 70 hours or less

- Visibility of visible light -

The optical density (OD) in the visible range (380-700 nm) was measured by a Macbeth optical densitometer and evaluated according to the following evaluation criteria. A, B and C are practically acceptable standards.

A: Optical density exceeding 0.6 [OD]

B: Optical density exceeding 0.5 [OD] and 0.6 [OD] or less

C: Optical density exceeding 0.4 [OD] and not more than 0.5 [OD]

D: Optical density of 0.4 [OD] or less

[Table 1]

From the above table, it can be seen that Examples 1 to 11, in which all of the first layer, the second layer and the laminated film satisfy predetermined requirements, are excellent in hydrolysis resistance and visible light shielding property. On the other hand, in Comparative Examples 1 to 11 in which any one of the first layer, the second layer and the laminated film did not satisfy the predetermined requirements, it was found that neither the hydrolysis decomposability nor the visible light shielding property could be satisfied have.

Industrial availability

INDUSTRIAL APPLICABILITY The laminated film of the present invention has excellent hydrolysis resistance, so that it can maintain its strength for a long period of time outdoors, and is also excellent in designability because of its excellent visibility hiding ability. By using the laminated film of the present invention, a back sheet for a solar cell module and a solar cell module can be obtained. Further, the laminated film of the present invention can be used for a film for building materials, a film for outdoor advertisement, and the like, which is highly industrially applicable.

10 Second Floor
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Claims (8)

1. A laminated film having at least a first layer containing a polyester and a white pigment, and a second layer containing a polyester,
Wherein 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 to 300 mu m,
The white pigment concentration of the whole laminated film is more than 0 mass% and less than 2 mass%
Wherein a terminal carboxyl group concentration of the whole laminated film is 6 to 30 equivalents / ton. The method according to claim 1,
And the white pigment concentration of the first layer is 5 to 20 mass%. The method according to claim 1 or 2,
Wherein the thickness of the first layer is 5 to 50 占 퐉. The method according to any one of claims 1 to 3,
And the white pigment concentration of the second layer is 0 to 1.5% by mass. The method according to any one of claims 1 to 4,
Wherein the second layer includes recycled chips obtained by trimming and crushing the end portions in the width direction of the laminated film in an amount of 60 mass% or less as a raw material, and the first layer does not substantially contain the recycled chips. The method according to any one of claims 1 to 5,
Laminated film for solar cell module. A backsheet for a solar cell module, comprising the laminated film according to any one of claims 1 to 6. A solar cell module comprising a back sheet for a solar cell module according to claim 7.

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