JP6096135B2 - White polyester film and method for producing the same, solar cell module and method for producing the same - Google Patents

Description

  The present invention relates to a white polyester film and a manufacturing method thereof, and a solar cell module and a manufacturing method thereof.

Polyester is used for various applications such as electrical insulation and optical applications. In recent years, solar cell applications such as solar cell backsheets have attracted attention as electrical insulation applications.
The solar cell has a structure in which a power generating element sealed with a sealing material such as ethylene-vinyl acetate copolymer (EVA) is attached to a glass plate. A sheet material for protecting the back surface (so-called back sheet (back surface protection member)) is disposed on the back surface opposite to the surface in order to prevent deterioration due to wind and rain.

  In recent years, resin materials have been used for such solar cell backsheets, and polyester films are being used as an example of resin materials. As a polyester film constituting the back sheet, a whitened polyester film including fine particles is known from the viewpoint of increasing light reflectivity and improving power generation efficiency. However, when fine particles are added, the polyester is embrittled and tends to be inferior in weather resistance. As a technique for improving such a decrease in weather resistance, a polyester film having a multilayer structure has been proposed (see, for example, Patent Documents 1 and 2).

In general, the back sheet is often used in close contact with a sealing material for sealing the power generating element. Therefore, the polyester film which comprises a back sheet is normally provided with the easily bonding layer for making it closely_contact | adhere with EVA.
As a polyester film showing good adhesion to a sealing material, an easily adhesive polyester film for a solar cell using a urethane resin having an aliphatic constituent component has been proposed (for example, Patent Documents 3 to 4). reference).

Japanese Patent No. 5288068 Japanese Patent No. 5102392 International Publication No. 2011/068132 Pamphlet JP 2011-142128 A

  However, the easily-adhesive polyester film proposed heretofore has a problem that it is inferior in weather resistance in the long term, and particularly the adhesion is greatly lowered when exposed to light or heat for a long time. If the adhesion between the polyester film of the back sheet and the sealing material is reduced, or if the adhesion between the polyester film and the adjacent layer is reduced in the back sheet, a decrease in the durability performance of the solar cell is noticeable. It becomes.

  The present invention has been made in view of the above circumstances, a white polyester film exhibiting excellent adhesion even under an environment exposed to heat and light for a long period of time, a method for producing the same, and heat for a long period of time. It aims at providing the solar cell module excellent in the durability in the environment exposed to a light, and its manufacturing method, and makes it a subject to achieve this objective.

Specific means for achieving the object are as follows.
<1> A polyester film containing fine particles, and an easy-adhesion layer having at least one surface of the polyester film, having a thickness of 0.01 μm to 1 μm, and a thickness distribution of 1% to 30%. and, a polyester film containing fine particles contain 5% by weight to 30% by weight of particles relative to the weight of the polyester, and saw including a first layer dispersion degree is less than 100% to 10% of the fine particles The easy-adhesion layer is a white polyester film having a surface haze of 0.01% to 3% and an in-plane distribution of the surface haze of 0.1% to 30% .
<2> The film according to <1>, wherein an easy-adhesion layer is formed on at least one surface of the polyester film during film formation, and the film is formed by performing at least one of the following steps (1) and (2): It is a white polyester film.
(1) A drying step in which the formed easy-adhesion layer is dried by applying a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the plane of the easy-adhesion layer. (2) A polyester film on which the easy-adhesion layer is formed. , by applying a temperature difference 0.5 ℃ above 10 ° C. or less in the plane of the polyester film, as stretching Engineering stretching
<3 > The polyester film containing fine particles further includes 0.06% by mass to 10% by mass of fine particles with respect to the mass of the polyester, and the degree of dispersion of the fine particles is 10% to 100%. It is a white polyester film as described in <1> or <2> containing at least 1 layer of these layers.
< 4 > The first layer has a thickness of 5 μm or more and 80 μm or less and a thickness distribution of 1% or more and 20% or less, and the total thickness of the polyester film containing fine particles is 40 μm or more and 350 μm or less <1 It is a white polyester film as described in any one of>-< 3 >.
< 5 > As a polyester film containing fine particles, the first layer and the second layer are laminated, and an easy adhesion layer is laminated on at least one surface of the first layer and the second layer. It is a white polyester film as described in < 3 > or < 4 >.
< 6 > As a polyester film containing fine particles, it includes a first layer and a second layer, and has a structure in which a first layer, a second layer, and an easy-adhesion layer are laminated in this order < It is a white polyester film as described in any one of 3 >-< 5 >.
< 7 > Any one of <1> to < 6 >, wherein the half elongation at break when exposed to an environmental condition of a temperature of 120 ° C. and a humidity of 100% RH for 60 hours is 70 hours to 200 hours It is a white polyester film of description.

< 8 > A bonding step of bonding an ethylene-vinyl acetate resin having a thermal dimensional change distribution of 1% to 40% and the white polyester film according to any one of <1> to < 7 >. It is a manufacturing method of a solar cell module.
< 9 > The bonding step is performed by using a heater having an average temperature of 40 ° C. or higher and 70 ° C. or lower and a temperature distribution of 0.5 ° C. or higher and 8 ° C. or lower before bonding the ethylene-vinyl acetate resin. It is a manufacturing method of the solar cell module as described in < 8 > including the process of heat-processing in the range for more than 10 minutes.

< 10 > A step of forming an easy-adhesion layer by coating on at least one surface of a polyester film in the course of film formation containing fine particles, at least one of the following steps (1) and (2), a resin material and fine particles, Alternatively, a resin material in which fine particles are dispersed is charged into a melt extruder, melt-extruded with a fluctuation of 0.5% or more and 20% or less applied to the torque of the screw of the melt extruder, so that the total mass is 5 Forming a first layer containing fine particles of not less than 30% by weight and not more than 30% by weight and having a fine particle dispersity of not less than 10% and not more than 100%, and the polyester film comprises at least the first layer It is a manufacturing method of the white polyester film containing.
(1) A drying step in which the formed easy-adhesion layer is dried by applying a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the plane of the easy-adhesion layer, and a dried easy-adhesion layer after the drying step. And a step of cooling the polyester film having a temperature difference of 0.1 ° C. or more and 10 ° C. or less between the one side and the other side of the polyester film . a polyester film, by applying a temperature difference 0.5 ℃ above 10 ° C. or less in the plane of the polyester film, as stretching Engineering stretching
<11 > When the step (1) is included, after the drying step, the polyester film having the dried easy-adhesion layer is cooled by providing a temperature difference of 0.1 ° C. or more and 10 ° C. or less in the plane of the polyester film. It is a manufacturing method of the white polyester film as described in < 10> which further has a process to do.
< 12 > A resin material and fine particles, or a resin material in which fine particles are dispersed, are charged into a melt extruder, and melt extrusion is performed by imparting a variation of 0.5% to 20% to the screw torque of the melt extruder. The method further comprises the step of forming a second layer containing 0.06% by mass or more and 10% by mass or less of fine particles with respect to the total mass and having a fine particle dispersity of 10% or more and 100% or less. And a polyester film is a manufacturing method of the white polyester film as described in < 10 > or <11> containing a 1st layer and a 2nd layer at least.
< 13 > When the molten resin melt-kneaded by a melt extruder is melt-extruded from a die to form the first layer, a temperature variation of 0.5 ° C. or more and 10 ° C. or less is imparted to the die < 10 > to < 12 > The method for producing a white polyester film according to any one of 12 >.
< 14 > When the step (1) described above is included, the step of longitudinally stretching an unstretched polyester film, the step of laterally stretching the longitudinally stretched polyester film, the step of longitudinally stretching, and the step of laterally stretching The white polyester film according to any one of < 10 > to < 13 >, further comprising a step of cooling the polyester film after longitudinal stretching at a cooling rate of 5 ° C / second or more and 100 ° C / second or less. It is a manufacturing method.
< 15 > When the step (2) is included, the stretching step includes a step of longitudinally stretching an unstretched polyester film and a step of laterally stretching the longitudinally stretched polyester film, and a step of longitudinally stretching. < 10 > to < 14 >, further comprising a step of cooling the polyester film after longitudinal stretching at a cooling rate of 5 ° C./second or more and 100 ° C./second or less between the step of stretching and the step of transverse stretching. Is a method for producing a white polyester film.
< 16 > A transparent base material on which sunlight enters, an element structure portion provided on the base material and having a solar cell element and a sealing material for sealing the solar cell element, and a base material for the element structure portion. It is a solar cell module provided with the white polyester film as described in any one of <1>-< 7 > arrange | positioned on the opposite side to the located side.

ADVANTAGE OF THE INVENTION According to this invention, the white polyester film which shows the outstanding adhesiveness in the environment exposed to a heat | fever and light over a long period of time, and its manufacturing method are provided. Also,
ADVANTAGE OF THE INVENTION According to this invention, the solar cell module excellent in the durability in the environment exposed to heat and light over a long period of time and its manufacturing method are provided.

  Hereinafter, the white polyester film of the present invention and the production method thereof, the solar cell module using the same, and the production method thereof will be described in detail.

<White polyester film>
The white polyester film of the present invention has a polyester resin film containing a white pigment and at least one surface of the polyester resin film, has a thickness of 0.01 μm to 1 μm, and a thickness distribution of 1% to 30%. And an easy-adhesion layer.

  In the present specification, a numerical range may be indicated by using a notation of “to”, but a numerical range indicated by using “to” indicates a numerical value described before and after “to” as a minimum value and a numerical value range, respectively. Indicates the range to include as the maximum value.

In the present invention, when an easy-adhesion layer is provided on a polyester resin film colored in white, the easy-adhesion layer is configured to have a thin thickness in the range of 0.01 μm to 1 μm, and the thickness distribution is deliberately made thin. Is adjusted to a relatively large range of 1% or more. Thereby, the thick part and the thin part will exist in the surface of an easily bonding layer, and the adhesive force between the adjacent layers which contact | connect an easily bonding layer can be improved. That is, by providing both thick and thin portions in the surface and providing uneven thickness of a waveform having a relatively large period, the adhesion with the layers in contact with each other is improved.
Presumed that the thick part of the easy-adhesion layer is deformed by the peeling stress at the adhesion interface and absorbs the peeling energy, thereby suppressing cohesive failure in the polyester and interfacial peeling between the polyester and the easy-adhesion layer. Is done. Moreover, since the thin part of an easily bonding layer is a thin film, it is easy to contact | adhere with the surface of a polyester film, and it is estimated that it is working advantageously in ensuring adhesive force.
As described later, such thickness unevenness can be caused by (1) drying the applied easy-adhesion layer by applying a predetermined temperature difference, or (2) applying a predetermined polyester resin film to the predetermined adhesive layer. It is preferably applied by stretching by giving a temperature difference.

-Easy adhesion layer-
The white polyester film of the present invention has an easy-adhesion layer having a thickness of 0.01 μm or more and 1 μm or less and a thickness distribution of 1% or more and 30% or less on one surface or both surfaces of the polyester film. . The easy-adhesion layer has a function of improving the adhesion between the sealing material, and according to the easy-adhesion layer in the present invention, excellent adhesion over a long period of time even in an environment exposed to heat or light for a long period of time. Indicates. Therefore, the promotion of deterioration due to peeling in the solar cell is suppressed, and the long-term durability is excellent.

(Thickness)
The thickness of the easy adhesion layer is 0.01 μm or more and 1 μm or less. When the thickness of the easy-adhesion layer is less than 0.01 μm, a region where the easy-adhesion layer is not formed occurs in a thin portion, and the adhesion is reduced. Moreover, when the thickness of an easily bonding layer exceeds 1 micrometer, destruction in the easily bonding layer by peeling stress will generate | occur | produce in a thick location, and adhesive force will fall.
The thickness of the easy adhesion layer is preferably 0.02 μm or more and 0.5 μm or less, and more preferably 0.04 μm or more and 0.2 μm or less.
The thickness of the easy-adhesion layer is extremely thin compared to the thickness of the second layer constituting the polyester film described later being 16 μm to 332.5 μm (40% to 95% of the total thickness (40 μm to 350 μm)). Are distinguished as separate functional layers.

  The thickness of the easy adhesion layer is an average of a total of 40 points including a thickness of 20 points along the MD and a thickness of 20 points along the TD when measuring the “thickness distribution of the easy adhesion layer” described later. This is a value obtained as a value.

The easy-adhesion layer may be formed by either the WET method (coating method) or the DRY method (coextrusion method). However, the easy-adhesion layer can be easily made thin and impart a thickness distribution by the WET method. This is preferable. Formation of the easy-adhesion layer (for example, application of the coating solution for the easy-adhesion layer) may be carried out after completion of the polyester film formation (that is, after the end of longitudinal stretching and transverse stretching), or during the formation of the polyester film For example, after one of the longitudinal stretching and the lateral stretching of the polyester film during film formation (and before the other), or in the case of multi-stage stretching, it may be performed in the middle.
In the present invention, as will be described later, from the viewpoint of easily imparting a thickness distribution, a molten resin is extruded to form a polyester film, and the film is longitudinally stretched. A mode in which the film is further stretched in the transverse direction in a state where an easy-adhesion layer is formed by coating and drying is preferred.

The easy-adhesion layer is preferably thinned by stretching the polyester film after it is formed on the polyester film during film formation. Thereby, interface mixing arises between an easily bonding layer and a polyester film, and adhesive force can be improved more.
Here, the stretching ratio when stretching the polyester film in the middle of film formation is preferably 2 to 5 times. The stretching temperature is preferably “polyester glass transition temperature (Tg) −10 ° C.” or higher and “Tg + 50 ° C.” or lower.
The stretching after providing the easy-adhesion layer may be performed in either the longitudinal direction or the transverse direction, or may be performed in both directions. In the present invention, it is more preferable to stretch the polyester film in the middle of film formation in advance in the longitudinal direction, then form an easy-adhesion layer, and laterally stretch in a state where the easy-adhesion layer is formed. This is because the transverse stretching is often performed using a tenter and is transported in a non-contact manner, so that the easy-adhesion layer softened by the heat during stretching does not stick to a roll or the like.

(Thickness distribution)
The thickness distribution of the easy-adhesion layer in the white polyester film of the present invention is in the range of 1% to 30%.
In the present invention, the thin portion of the easy-adhesion layer easily diffuses into the polyester because it is a thin film, enters the gap in the surface of the polyester film, causes interfacial mixing with the polyester film, and as a result, improves the adhesion itself It is presumed that it works favorably. Such interfacial mixing is further promoted by stretching after providing an easy-adhesion layer on the polyester film. This is because a new surface is formed on the polyester film by stretching, and at this time, it is considered that the easy adhesion molecules diffuse into the film.
Therefore, if the thickness distribution is less than 1%, a synergistic effect due to the provision of the thick portion and the thin portion cannot be obtained, and the effect of improving the adhesion is poor. If the thickness distribution exceeds 30%, extremely thick portions and thin portions are formed, and as a result, the adhesion is lowered. This is because the peeling stress is concentrated at the boundary between the thick part and the thin part, and the easy-adhesion layer is easily broken to cause adhesion failure.

The thickness distribution of the easy-adhesion layer is determined as follows.
A 20 cm square polyester film is prepared, and any 10 points are selected from them, and 10 1 cm square samples having sides parallel to MD and TD are cut out. And the cross section of the center part of each 2 sides of 2 sides along MD of each sample and 2 sides along TD is observed with a microscope, and the thickness of the easily bonding layer in MD and TD is calculated | required. The same operation is performed on 10 samples, and the thickness of the easy-adhesion layer of 20 points in total in each of MD and TD is obtained. From the obtained thickness, the difference between the maximum value and the minimum value of the measured values at 20 points of MD is divided by the average value of 20 points, and the value expressed as a percentage is taken as the thickness distribution of the easily adhesive layer of MD. Also for TD, the difference between the maximum value and the minimum value of the 20 measured values of TD is divided by the average value of 20 points, and the value expressed as a percentage is used as the thickness distribution of the TD easy-adhesion layer. The average value of the thickness distribution in MD and the thickness distribution in TD in the easy adhesion layer is defined as the thickness distribution of the easy adhesion layer.

The thickness distribution of the easy-adhesion layer is imparted by forming an easy-adhesion layer on at least one surface of the polyester film in the middle of film formation, and applying at least one of the following (1) and (2) to form a film. can do.
(1) Drying time distribution after coating the easy-adhesion layer Specifically, the thickness distribution of the easy-adhesion layer is 0.5% within the plane of the polyester film in the middle of film formation. It can adjust by providing the drying process dried in the state which provided the temperature difference (degreeC or more and 10 degrees C or less).
Drying is fast at the high temperature part, and the coating liquid tends to flow into the high temperature part at a low temperature, so the high temperature part tends to be thick. Therefore, thickness distribution can be given to an easily bonding layer by providing distribution to the drying time after application | coating. For example, it is possible to give a thickness distribution to the easy-adhesion layer by giving a distribution of the amount of blown air to the slit part of the nozzle that blows dry air such as hot air, so that the amount of dry air corresponding to the easy-adhesion layer can be distributed. it can. Moreover, the heater installed in the drying zone may be divided so that the output of each heater has a distribution.

(2) Temperature distribution in stretching Specifically, the thickness distribution of the easy-adhesion layer is such that the polyester film on which the easy-adhesion layer is formed has a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the plane of the polyester film. It can adjust by providing the extending | stretching process which provides and extends | stretches.

When extending | stretching after application | coating, a draw ratio can be locally changed by providing temperature distribution to the film in extending | stretching. That is, the higher the temperature, the higher the draw ratio, and the lower the temperature, the lower the draw ratio. Therefore, the easy-adhesion layer becomes thin in the high-temperature part, and the easy-adhesion layer becomes thick in the low-temperature part, whereby a thickness distribution can be imparted to the easy-adhesion layer.
In this case, a preferable temperature distribution is 0.5 ° C. or higher and 10 ° C. or lower, more preferably 1 ° C. or higher and 8 ° C. or lower, and further preferably 1.5 ° C. or higher and 6 ° C. or lower.

  The thickness distribution of the easy adhesion layer is preferably in the range of 2% to 25%, more preferably in the range of 3% to 20%.

(Surface haze)
The easy-adhesion layer formed on the polyester film preferably has a surface haze of 0.01% to 3%. The surface haze here is the haze value obtained by subtracting the internal haze (the haze value measured by applying silicone oil on both sides of the film and removing the surface irregularities) from the total haze (the haze value of the film measured in the air), Haze value derived from surface irregularities.
When laminating a solar cell and a white polyester film, it is possible to improve the adhesion by providing an easy adhesion layer, but by roughening the surface of the easy adhesion layer and providing irregularities on the surface, the adhesion is improved. The power can be further improved. This is presumably because the contact area with EVA increased, and EVA entered into the recesses of the easy-adhesion layer and the anchoring effect appeared. “Surface haze” is effective as an index of such surface irregularities.

Therefore, when the surface haze is 0.01% or more, it is easy to obtain a throwing effect, which is advantageous for improving the adhesion. In addition, when the surface haze is 3% or less, the unevenness does not become excessively large, and it is difficult to form, for example, a thin portion that causes stress concentration on the easy-adhesion layer at the interface, and is excellent in preventing cohesive failure due to peeling stress. This is advantageous for achieving adhesion.
Especially, as surface haze of an easily bonding layer, 0.03% or more and 2.5% or less are more preferable, More preferably, they are 0.05% or more and 2% or less.

The surface haze is a value obtained by measuring internal haze and total haze and calculating from the following formula.
Surface haze = (all haze)-(inside haze)
Here, the internal haze is obtained by dropping several drops of silicone oil on the front and back surfaces of the polyester film, and using two glass plates (micro slide glass product number S 9111, manufactured by MATSUNAMI) with a thickness of 1 mm. A value measured in a state where two glass plates and a polyester film are optically brought into close contact with each other and the surface haze is removed. This internal haze is measured using a haze meter NDH2000 (Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K-7136.
The total haze is a value measured by sandwiching a polyester film between only two glass plates, and is measured using a haze meter NDH2000 (Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K-7136. .

Examples of the method for adjusting the surface haze to the above range by making irregularities on the surface of the easy-adhesion layer in the present invention include the following methods.
(A) When forming an easy-adhesion layer by a coating method -a) Formation by cooling-
After the drying step of drying the easy-adhesion layer formed on the polyester film, the polyester film having the dried easy-adhesion layer is 0.1 ° C. or more and 10 ° C. or less between the one side and the other side of the polyester film. Surface haze can be adjusted to the said range by providing the process of providing a temperature difference and cooling.
When cooling after coating and drying, the surface roughness, that is, the surface haze can be adjusted to the above range by giving a temperature difference between the coated surface side and the surface opposite to the coated surface side. When extending | stretching and heat setting are combined after application | coating, what is necessary is just to provide such a front-back temperature difference after these. This is presumed to be due to the following mechanism. That is, when the coating surface side becomes high temperature, the coating surface is stretched and the easy adhesion layer as the coating layer is stretched. Then, when it cools to room temperature and the temperature of both surfaces becomes the same, the extended easily bonding layer loosens, a micro unevenness | corrugation is formed, and surface roughness (surface haze) expresses. On the other hand, when the temperature of the coated surface becomes low, the coated surface tends to shrink, and the easy-adhesion layer that is the coated layer is pulled to generate minute cracks. Due to the occurrence of minute cracks, minute irregularities are formed and surface roughness (surface haze) is manifested. Temperature application to the front and back of such a film is done by arranging blowing nozzles on both sides of the polyester film. This can be done by changing the temperature of the blown drying air. The preferable temperature difference between the one surface and the other surface of the polyester film is more preferably 0.3 ° C. or more and 8 ° C. or less, and further preferably 0.5 ° C. or more and 6 ° C. or less.

(B) When forming an easy-adhesion layer by melt lamination After laminating (laminating) a melt-extruded resin on a polyester film, for example, the following method can be used.
-B) Formation by cooling-
When rapidly cooling after laminating, the surface haze can be adjusted to the above range by imparting a temperature difference between the front and back of the film in the same manner as in “a) Formation by cooling”.
-C) Formation by embossing-
A surface haze can be adjusted to the said range by making the roll (embossing roll) which roughened the surface contact an easily bonding layer, and transferring an unevenness | corrugation to an easily bonding layer.
At this time, the temperature of the easy adhesion layer is preferably 100 ° C. or higher and 300 ° C. or lower, more preferably 120 ° C. or higher and 280 ° C. or lower, and further preferably 150 ° C. or higher and 250 ° C. or lower.

(In-plane distribution of surface haze)
The in-plane distribution of the surface haze of the easy-adhesion layer is preferably in the range of 0.1% to 30%. A portion having a large surface roughness and a portion having a small surface roughness in the same plane have the following advantages and disadvantages.
Where the surface roughness is large, it is easy to obtain a throwing effect on EVA, but the peeling stress tends to concentrate on the convex portions. On the other hand, the portion having a small surface roughness has a poor anchoring effect on EVA, but the peeling stress at the convex portion is difficult to concentrate. Therefore, by adjusting the portion having a large surface roughness and the portion having a small surface roughness within a predetermined range and coexisting with each other, a synergistic effect is obtained at the same time as a complementary action, and the adhesion is greatly improved. By providing such a surface roughness distribution, surface haze distribution is caused.

If the in-plane distribution of the surface haze is 0.1% or more, it contributes further by improving the adhesion. Further, when the in-plane distribution of the surface haze is 30% or less, the effect of hindering adhesion by a portion having a large surface roughness and a portion having a small surface roughness (stress concentration of convex portions at a portion having a large surface roughness, and surface roughness) Insufficient anchoring effect at a small part) is suppressed, and a part having a large surface roughness and a part having a small surface roughness act in a complementary manner, and a better adhesion force appears as a synergistic effect.
The in-plane distribution of surface haze is more preferably from 0.5% to 20%, and even more preferably from 1% to 10%.

The in-plane distribution of surface haze is determined as follows.
The surface haze was measured according to the above method for 10 points arbitrarily selected on the surface of the 20 cm square easy-adhesion layer, and the difference between the maximum value and the minimum value was divided by the average value of the surface haze of 10 points and expressed as a percentage. The value is the in-plane distribution of surface haze.

In-plane distribution of surface haze can be imparted to the above methods a) to c) for adjusting surface haze by the following.
(I) Case of “a) Formation by cooling” (coating method)
In-plane distribution can be imparted to the surface roughness by providing a distribution of the cooling air blowing temperature and imparting a temperature difference in the plane during cooling after coating and drying. This is because a plurality of blowing nozzles are provided, and a temperature distribution can be formed in the surface by giving a difference in the ejection temperature of each nozzle. At this time, the temperature distribution may be imparted to either the coated surface, the surface opposite to the coated surface, or both surfaces. The temperature difference is preferably 0.1 ° C. or higher and 10 ° C. or lower, more preferably 0.3 ° C. or higher and 8 ° C. or lower, and still more preferably 0.5 ° C. or higher and 6 ° C. or lower. Case of “Formation by cooling” (melt lamination)
As in the case of (a) above, when drying is performed after coating, an in-plane distribution can be imparted to the surface roughness by imparting a distribution to the blowing air blowing temperature and imparting a temperature difference in the surface.
(C) Case of “c) Formation by embossing” (melt lamination)
You may provide distribution to the surface unevenness | corrugation of an embossing roll. A difference may be given to the surface unevenness by giving a distribution to the heating temperature of the embossing roll or film and giving a difference to the ease of deformation of the resin. In this case, the temperature distribution is preferably 1 ° C. or more and 50 ° C. or less, more preferably 2 ° C. or more and 40 ° C. or less, and further preferably 3 ° C. or more and 30 ° C. or less.
As for the temperature distribution of the resin, for example, temperature modulation may be applied to an IR heater or a heating roll for heating. In the case of using an IR heater, this can be achieved by using a plurality of heaters and changing the output for each heater. In the case of a heating roll, this can be achieved by installing a baffle plate in the flow path through which the heat medium in the roll flows and modulating the flow.

Next, the preferable composition of an easily bonding layer is demonstrated.
The easy-adhesion layer provided on the polyester film depends on the use of the polyester film, but an easy-adhesion layer containing an acrylic, urethane, polyester, or polyamide resin is preferred. These resins have a polarity close to that of polyester and are easy to obtain adhesion.
Examples of the resin constituting the easy-adhesion layer include, for example, JP-A-2006-152013, JP-A-2006-332091, JP-A-4457322, JP-A-2006-175564, JP-A-2006-253565, Application formation on the surface of a polyester film substrate such as an easy adhesion layer described in Japanese Patent No. 4547644, Japanese Patent No. 3777725, Japanese Patent No. 3731286, Japanese Patent Application Laid-Open No. 2009-269301, Japanese Patent Application Laid-Open No. 2006-335853, etc. Examples of the resin used in the coating solution for the purpose of the treatment are as follows. More specifically, for example, the following resins may be mentioned.

-Urethane resin-
Examples of the resin include a resin having a blocked isocyanate group, and a thermally reactive water-soluble urethane in which a terminal isocyanate group is blocked with a hydrophilic group (hereinafter also referred to as a block). Blocking agents for blocking isocyanate groups with hydrophilic groups include bisulfites and phenols containing sulfonic acid groups, alcohols containing sulfonic acid groups, lactams containing sulfonic acid groups, sulfonic acids And oximes containing a group and active methylene compounds containing a sulfonic acid group. The blocked isocyanate group makes the urethane prepolymer hydrophilic or water-soluble. When thermal energy is applied to the polyurethane resin, the blocking agent deviates from the isocyanate group, so that the polyurethane resin immobilizes the mixed water-dispersible copolymer polyester resin on the self-crosslinked stitch, and the copolymer polyester. It also reacts with the terminal groups of the resin. The resin during the preparation of the coating solution is poor in water resistance because it is hydrophilic. A coating film is obtained. Among the above blocking agents, bisulfites are most preferable from the viewpoint that the blocking agent is removed from the isocyanate group at the heat treatment temperature and heat treatment time in the film production process, and from the viewpoint of being industrially available.

  The chemical composition of the urethane prepolymer used in the resin includes (1) an organic polyisocyanate having two or more active hydrogen atoms in the molecule, or a molecular weight having at least two active hydrogen atoms in the molecule. ˜20,000 compounds, (2) obtained by reacting an organic polyisocyanate having two or more isocyanate groups in the molecule, or (3) a chain extender having at least two active hydrogen atoms in the molecule. And a compound having a terminal isocyanate group.

  The compound (1) generally known is a compound containing two or more hydroxyl groups, carboxyl groups, amino groups or mercapto groups in the terminal or molecule, and particularly preferred compounds include polyether polyols. , Polyester polyol, polyether ester polyol and the like. Examples of the polyether polyol include compounds obtained by polymerizing alkylene oxides such as ethylene oxide and propylene oxide, styrene oxide, epichlorohydrin, and the like, compounds obtained by random copolymerization or block copolymerization of two or more thereof, or polyhydric alcohols thereof. There are compounds obtained by performing addition polymerization.

-Polyester resin-
Polyester resins are formed from the following polybasic acids or ester-forming derivatives of polybasic acids and polyols or ester-forming derivatives of polyols. That is, as the polybasic acid component, terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic An acid, a dimer acid, 5-sodium sulfo isophthalic acid, etc. are mentioned. A copolymer polyester resin is synthesized using preferably two or more of these acid components. Moreover, if it is a slight amount, a hydroxycarboxylic acid such as maleic acid, itaconic acid, or p-hydroxybenzoic acid can be used in combination as the unsaturated polybasic acid component. The polyol component includes ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, and poly (ethylene oxide) glycol. , Poly (tetramethylene oxide) glycol and the like.

-Acrylic resin-
As acrylic resin, the acrylic resin formed by superposing | polymerizing the acrylic monomer which is illustrated below is mentioned. Examples of the acrylic monomer include alkyl acrylate and alkyl methacrylate (the alkyl group includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group). Groups); hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether; Acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.), etc. Monomers containing a carboxy group, a sulfoxy group or a salt thereof; acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N, N-dialkylacrylamide, N, N-dialkylmethacrylamide (the alkyl group is methyl Group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N -Dialkoxyacrylamide, N, N-dialkoxymethacrylamide (alkoxy groups include methoxy, ethoxy, butoxy, isobutoxy, etc.), acryloylmorpholine, N-methylolacrylamide, N-methylolmethacrylate Monomers containing amide groups such as luamide, N-phenylacrylamide and N-phenylmethacrylamide; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinyl Methyl ether, vinyl ethyl ether, vinyl trialkoxysilane, alkyl maleic acid monoester, alkyl fumaric acid monoester, alkyl itaconic acid monoester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, butadiene And the like.

  Among these, monomers containing a hydroxyl group such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-methylol acrylamide, N-methylol methacrylamide and the like are 2-20. It is preferably contained in a mol%, preferably 4 to 15 mol%.

  The coating liquid for forming the easy-adhesion layer may further contain a wetting agent, an antistatic agent, a colorant, a surfactant, an ultraviolet absorber and the like. When it contains a wetting agent, the content is 1 mass%-20 mass% with respect to solid content, for example.

  The easy adhesion layer is also preferably a polyolefin-based, for example, a rubber-based resin such as SBR. With such an easy-adhesion layer containing a polyolefin, it is easy to absorb peeling stress due to its flexible structure, and the adhesion can be increased. For example, those described in JP-A-61-60424, Japanese Patent No. 2583455, Japanese Patent No. 3626305, Japanese Patent No. 3783989, Japanese Patent No. 4041784, and Japanese Patent No. 4505402 can be used.

  Moreover, it is also preferable to use polyvinyl alcohol (PVA) resin as the polyolefin resin. This is because when the polyester film produced according to the present invention is used as a solar battery backsheet, if an easy-adhesion layer containing a PVA-based resin is provided, it has a high affinity with the polyvinyl alcohol resin laminated on the easy-adhesion layer. Because.

It is also preferable that a crosslinkable compound (crosslinking agent) coexist in the easy adhesion layer. Thereby, a crosslink can be formed in the easy-adhesion layer or the polyester, and the adhesion strength can be further increased. Examples of the crosslinkable compound include an epoxy compound, a glycidyl compound, a melamine compound, and an oxazoline compound.
Moreover, moisture resistance can be improved further by containing a crosslinking agent in an easily bonding layer. In addition, when using a crosslinking agent, if the content is less than 5% by mass, the effect of improving the moisture resistance is hardly exhibited. This is not preferable because the adhesiveness of the resin may deteriorate.

  In addition to the crosslinking agent, other compounds having an epoxy group may be used in combination. Examples of these compounds include sorbitol tol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, Polyepoxy compounds such as methylolpropane polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether , Polypropylene glycol diglycidyl ether, polytetramethylene Diepoxy compounds such as recall diglycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and monoepoxy compounds such as phenyl glycidyl ether.

  When using these epoxy compounds together with a crosslinking agent, it is preferable to use the total amount of a crosslinking agent and these epoxy compounds in 5-20 mass% with respect to solid content of a coating liquid.

  In addition, when the fine particles and the crosslinking agent contained in the coating liquid, and in some cases further containing a relatively large amount of wetting agent, the total amount of solids becomes 100% by mass by relatively reducing the amount of the polymer binder. What should I do?

  Prior to the application of the easy-adhesion layer, it is also preferable to subject the polyester film substrate to a surface treatment, and examples thereof include corona treatment, flame treatment, ultraviolet treatment, glow treatment, and atmospheric pressure plasma treatment.

  The thickness of the easy adhesion layer (the easy adhesion layer after stretching when stretched together with the polyester film) in the white polyester film of the present invention is preferably 0.05 μm or more and 1.5 μm or less, and preferably 0.1 μm or more and 1.0 μm or less. More preferably, it is 0.2 μm or more and 0.7 μm or less. When the thickness of the easy adhesion layer is 0.05 μm or more, good adhesion with the polyester film can be maintained. In addition, when the thickness of the easy-adhesion layer is 1.5 μm or less, deterioration of the easy-adhesion layer over time is suppressed even in a relatively hot and humid environment (thermo environment), and damage within the easy-adhesion layer is prevented. Can be prevented. Thereby, it will become the thing excellent in contact | adhesion power over the long term.

-Polyester film-
The white polyester film of the present invention has a polyester film containing fine particles together with the substantially contained polyester, and the above-mentioned easy adhesion layer is provided on this film. The easy-adhesion layer in the present invention has good adhesion with the white polyester film, and can prevent deterioration in durability due to poor adhesion and poor adhesion between the white polyester film and the solar cell body over a long period of time.

(polyester)
The type of polyester is not limited, and known polyesters can be used. As polyester used as raw material resin, you may synthesize | combine using a dicarboxylic acid component and a diol component, and may use commercially available polyester.
Specific examples, preferred embodiments, usage amounts, and the like of the (A) dicarboxylic acid component and (B) diol component that can be used in the present invention are described in paragraphs [0036] to [0039] of JP 2012-197432 A. Can be referred to.

  When the polyester is synthesized, for example, it can be obtained by subjecting (A) a dicarboxylic acid component and (B) a diol component to an esterification reaction and / or a transesterification reaction by a well-known method. Conventionally known reaction catalysts can be used for the esterification reaction and / or the transesterification reaction. Regarding specific examples of reaction catalysts and esterification reaction steps that can be used in the present invention, the description in paragraphs [0040] to [0042] of JP 2012-197432 A can be referred to.

  In the polymerization of the polyester, it is also preferable to add a phosphorus compound, a magnesium compound or the like. Specific examples and addition rates of the phosphorus compound and the magnesium compound are described in paragraphs [0071] to [0077] of JP 2012-197432 A. Can be referred to. For the preferable conditions of the esterification reaction step, usable additives, and the like, the description in paragraphs [0078] to [0085] of JP 2012-197432 A can be referred to.

The polyester film may contain a component derived from a trifunctional monomer in which the total (a + b) of the carboxylic acid group (a) and the hydroxyl group (b) is 3 or more. Among the constituents having a total of 3 or more carboxylic acid groups and hydroxyl groups, the carboxylic acid constituents having 3 or more carboxylic acid groups (a) are trimesic acid, trimethyl as trifunctional aromatic carboxylic acid constituents. Mellitic acid, pyromellitic acid, naphthalenetricarboxylic acid, anthracentricarboxylic acid and the like are listed, and trifunctional aliphatic carboxylic acid components include methanetricarboxylic acid, ethanetricarboxylic acid, propanetricarboxylic acid, butanetricarboxylic acid, and the like. Examples of tetrafunctional aromatic carboxylic acid components include benzenetetracarboxylic acid, benzophenonetetracarboxylic acid, naphthalenetetracarboxylic acid, anthracenetetracarboxylic acid, and berylenetetracarboxylic acid. Ethanetetracarboxylic acid Examples include ethylene tetracarboxylic acid, butane tetracarboxylic acid, cyclopentane tetracarboxylic acid, cyclohexane tetracarboxylic acid, adamantane tetracarboxylic acid, etc., and pentafunctional or higher functional aromatic carboxylic acid constituents include benzene pentacarboxylic acid, benzene hexacarboxylic acid Acid, naphthalene pentacarboxylic acid, naphthalene hexacarboxylic acid, naphthalene heptacarboxylic acid, naphthalene octacarboxylic acid, anthracene pentacarboxylic acid, anthracene hexacarboxylic acid, anthracene heptacarboxylic acid, anthracene octacarboxylic acid, etc. Aliphatic carboxylic acid constituents include ethanepentacarboxylic acid, ethaneheptacarboxylic acid, butanepentacarboxylic acid, butaneheptacarboxylic acid, cyclopentanepentacarboxylic acid Cyclohexane penta carboxylic acid, cyclohexanehexacarboxylic acid, adamantane penta carboxylic acid, include such as adamantane hexacarboxylic acid, and the like ester derivatives thereof and acid anhydrides thereof as examples.
Further, those obtained by adding oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, derivatives thereof, and a combination of a plurality of oxyacids to the carboxy terminal of the carboxylic acid component are also preferably used.

  In addition, for examples of components having 3 or more hydroxyl groups (b), trihydroxybenzene, trihydroxynaphthalene, trihydroxyanthracene, trihydroxychalcone, trihydroxyflavone, trihydroxycoumarin as trifunctional aromatic components. Examples of the trifunctional aliphatic alcohol component include glycerin, trimethylolpropane, and propanetriol, and examples of the tetrafunctional aliphatic alcohol component include compounds such as pentaerythritol. Moreover, the structural component (p) which added diol to the hydroxyl terminal of the above-mentioned compound is also preferable.

  As other constituent components, among oxyacids having both a hydroxyl group and a carboxylic acid group in one molecule such as hydroxyisophthalic acid, hydroxyterephthalic acid, dihydroxyterephthalic acid, etc., and the number of carboxylic acid groups (a) and the number of hydroxyl groups (b) And the total (a + b) is 3 or more. In addition, oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, and derivatives thereof, in which a plurality of the oxyacids are connected to the carboxy terminus of the above-described constituents are also preferably used. .

  In the polyester film, the content of the constituent components in which the total of carboxylic acid groups and hydroxyl groups is 3 or more is preferably 0.005 mol% or more and 2.5 mol% or less with respect to all the constituent components in the polyester film. More preferably, it is 0.020 mol% or more and 1 mol% or less. A component having a total of 3 or more of carboxylic acid groups and hydroxyl groups is present in the polyester film, so that functional groups not used for polycondensation are hydrogen bonded or covalently bonded to the components in the coating layer. Adhesion can be further improved.

  The polyester film constituting the white polyester film of the present invention can contain a carbodiimide compound and / or a ketene imine compound. A carbodiimide compound or a ketene imine compound may be used alone or in combination.

  The terminal carboxylic acid and hydroxyl group of polyester have high polarity, tend to adsorb water, and partial discharge tends to decrease. When the polyester film contains a carbodiimide compound and / or a ketene imine compound, these compounds react with a terminal carboxylic acid group and a hydroxyl group of the polyester to function as a terminal blocking agent. Thereby, it can suppress that partial discharge falls. In particular, a high partial discharge voltage can be maintained even after a thermo treatment in which the partial discharge voltage is likely to be lowered, and insulation can be exhibited.

The content of the carbodiimide compound and / or ketenimine compound is preferably 0.1% by mass to 10% by mass, more preferably 0.1% by mass to 4% by mass, and more preferably 0.1% by mass to 2% by mass with respect to the polyester. % Is more preferable. When the content of the cyclic carbodiimide compound is within the above range, the adhesion between the layers of the polyester film and the adhesion between the polyester film and the easy adhesion layer can be enhanced. Moreover, the heat resistance of the polyester film is enhanced.
In addition, when a carbodiimide compound and a ketene imine compound are used together, it is preferable that the sum total of the content rate of two types of compounds exists in the said range.

Examples of the carbodiimide compound include compounds having one or more carbodiimide groups in the molecule (including polycarbodiimide compounds). Examples of the monocarbodiimide compound include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t- Examples include butyl isopropyl carbodiimide, diphenyl carbodiimide, di-t-butyl carbodiimide, di-β-naphthyl carbodiimide, N, N′-di-2,6-diisopropylphenyl carbodiimide, and the like. Examples of the polycarbodiimide compound include U.S. Pat. No. 2,941,956, Japanese Patent Publication No. 47-33279, Org. Chem. 28, p2069-2075 (1963), and Chemical Review 1981, 81, No. 4, p. And those produced by the method described in 619-621 and the like.
Specific examples of industrially available polycarbodiimides include carbodilite HMV-8CA (manufactured by Nisshinbo), carbodilite LA-1 (manufactured by Nisshinbo), Starbazole P (manufactured by Rhein Chemie), starbactol P100 (manufactured by Rhein Chemie), and starbactol P400. (Product made by Rhein Chemie), Stabilizer 9000 (made by Rashihi Chemi), etc. are illustrated.
In addition, a cyclic carbodiimide compound including one carbodiimide group in the ring skeleton and having in the molecule at least one cyclic structure in which the first nitrogen and the second nitrogen are bonded by a bonding group can also be used. Examples of the cyclic carbodiimide compound include those prepared by the method described in International Publication 2011/093478.

The polyester used as the raw material resin for the polyester film is preferably subjected to solid phase polymerization after polymerization by an esterification reaction.
By solid-phase polymerization, it is possible to control the moisture content of the polyester, the crystallinity, the acid value of the polyester, that is, the concentration of the terminal carboxyl group of the polyester, and the intrinsic viscosity. When the solid phase polymerization time is lengthened, the carboxylic acid value decreases, and when the solid phase polymerization time is shortened, the carboxylic acid value increases.
In particular, the ethylene glycol (EG) gas concentration at the start of solid phase polymerization is preferably higher in the range of 200 ppm to 1000 ppm than the EG gas concentration at the end of solid phase polymerization, more preferably 250 ppm to 800 ppm, and even more preferably 300 ppm. It is preferable to carry out solid phase polymerization by increasing the concentration in the range of ˜700 ppm. At this time, the amount of carboxylic acid (AV) can be controlled by changing the average EG gas concentration (average value of gas concentration at the start and end of the solid-phase polymerization reaction). That is, AV can be reduced by reacting with a terminal COOH group by adding EG. The EG is preferably 100 ppm to 500 ppm, more preferably 150 ppm to 450 ppm, and still more preferably 200 ppm to 400 ppm.

  The temperature of the solid phase polymerization is preferably 180 ° C to 230 ° C, more preferably 190 ° C to 215 ° C, and still more preferably 195 ° C to 209 ° C. The solid phase polymerization time is preferably 10 hours to 40 hours, more preferably 14 hours to 35 hours, and still more preferably 18 hours to 30 hours.

  Preferred polyesters are polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN), with PET being more preferred.

  The polyester film constituting the white polyester film of the present invention may be a single layer film made of a single polyester film or a laminated film in which a plurality of polyester films are laminated. When the polyester film is a single layer film, the single layer film includes at least polyester and fine particles. When the polyester film is a laminated film, the plurality of polyester films include at least polyester, and at least one layer of the polyester film further includes fine particles. The laminated film may have an aspect in which all of the plurality of polyester films contain fine particles, or may have an aspect in which the content of the fine particles contained in the plurality of polyester films differs from film to film. The plurality of polyester films may include different kinds of fine particles.

~ First layer ~
The polyester film constituting the white polyester film of the present invention contains 5% by mass or more and 30% by mass or less of fine particles relative to the mass of the polyester, and the degree of dispersion of the fine particles is 10% or more and 100% or less An embodiment including a layer is preferred.

When the content of the fine particles is 5% by mass or more, the reflectance of light becomes better and the power generation efficiency is improved. Further, when the content of the fine particles is 30% by mass or less, brittle fracture hardly occurs and the adhesion improving effect is excellent.
As content of microparticles | fine-particles, 7 mass% or more and 25 mass% or less are preferable with respect to the mass of polyester, More preferably, they are 9 mass% or more and 20 mass% or less.

The measurement of the content of fine particles in the first layer can be performed as follows.
The content of fine particles is expressed as a ratio of the mass of fine particles to the total amount of polyester. Specifically, the content of fine particles can be calculated by precisely weighing the weight of the polyester film before and after firing. Specifically, a polyester film is put in a crucible and precisely weighed (Xg), and then the film is baked in air at 800 ° C. for 3 hours. Weigh (Yg).
The content (% by mass) of the inorganic fine particles is calculated as 100 × Y / X.
Here, when the polyester film is a laminated film having a second layer, which will be described later, the second layer is scraped off with a razor, and the film is placed in a crucible and weighed (Xg).

  When the fine particles are organic fine particles, the content of the organic fine particles can be calculated by dissolving the polyester film, collecting the organic fine particles contained in the solution, and accurately weighing them. Specifically, the polyester film is precisely weighed (Pg) and dissolved in 50 ml of HFIP (hexafluoroisopropanol). The obtained lysate is centrifuged at 14000 rpm for 30 minutes to collect organic fine particles. The collected organic fine particles are filtered through a precisely weighed Teflon (registered trademark) filter (Qg) having a pore diameter of 0.2 μm, dried while being washed with HFIP, and precisely weighed (Rg). The content (% by mass) of the organic fine particles can be calculated by 100 × (R−Q) / P.

When fine particles are present, peeling is likely to occur between the fine particles and the polyester, and the brittle fracture in the polyester film occurs due to the peeling force at the time of adhesion evaluation starting from here, resulting in poor adhesion. This becomes apparent after a long period of time because the polyester molecules are cleaved by photolysis and hydrolysis over time to lower the molecular weight and more easily cause cohesive failure.
In general, the fine particles are uniformly dispersed. However, in the present invention, the non-uniform dispersion (non-uniform dispersion) suppresses the cohesive failure over a long period of time, and provides stable adhesion over a long period of time. Can be secured.

The fine particle dispersity in the present invention is measured as follows.
First, a cross section of the polyester film is taken with a microscope along the longitudinal direction (MD), and L is set so that 10 to 50 fine particles can be contained in the film surrounded by the thickness (T) and the measurement length (L) in the film surface direction. Determine. Subsequently, the number of fine particles is measured while shifting 20 times by L in the film surface direction, and the difference between the maximum number and the minimum number is divided by the average value, and the calculated value is defined as “MD dispersity”. . Next, the same measurement is performed in the width direction (TD) to obtain “TD dispersion”.
Then, an average of the obtained MD dispersity and TD dispersity is obtained and set as “dispersion”.

It is presumed that the degree of dispersion is defined by the following mechanism.
Low molecular weight components decomposed over a long period of time are easily extruded from the polyester and collected at the interface with the fine particles. As a result, cohesive failure is further facilitated. Cohesive failure is likely to occur at locations where there are many fine particles, but cohesive failure is unlikely to occur at locations where there are few fine particles. For this reason, if the strength of the “parts with few fine particles” that hardly cause cohesive failure works more preferentially than the “parts with many fine particles”, a decrease in the strength of the entire film is suppressed, and adhesion becomes difficult to break due to peeling stress. Therefore, when compared with the same amount of fine particles, the adhesion strength is improved.
Furthermore, light resistance tends to decrease because the light is scattered multiple times in places where there are many fine particles (that is, the molecular cleavage of polyester due to light is likely to occur), but in places where there are few fine particles, there is little multiple scattering of light, Light resistance is unlikely to decrease. Therefore, as described above, the effect of suppressing cohesive failure at “locations with few fine particles” works more preferentially than “location with high fine particles”, and the effect of suppressing cohesive failure of the entire film is obtained.

From the above points, the polyester film constituting the white polyester film of the present invention preferably includes a first layer having a fine particle dispersity of 10% or more and 100% or less. When the degree of dispersion of the fine particles is 10% or more, the adhesion is further improved. In addition, when the degree of dispersion of the fine particles is 100% or less, the strength reduction of the portion having a lot of fine particles is suppressed, and the strength of the whole film is improved in combination with the high strength of the portion having a small amount of fine particles, and the adhesion is further improved. To do.
The degree of dispersion of fine particles is more preferably 20% or more and 90% or less, and further preferably 25% or more and 85% or less.

The degree of dispersion of the fine particles in the first layer can be imparted as follows.
Feeding raw materials into the extruder, extruding the melt melted and kneaded between the barrel and screw of the extruder from the die, cooling and solidifying this melt on a chill roll, and changing the torque of the screw Thus, the degree of dispersion of the fine particles can be adjusted to the above range. As raw materials, resin pellets (mainly polyester pellets) and fine particles, or resin pellets in which fine particles are dispersed (for example, master pellets containing polyester) are used.
The screw torque is preferably given a fluctuation of 0.5% to 20%, more preferably a fluctuation of 1% to 15%, and still more preferably a fluctuation of 1.5% to 10%.
Here, the torque fluctuation is a value obtained by dividing the difference between the maximum value and the minimum value of the torque measured for one minute by the average value of the torque.

The degree of dispersion of the fine particles is so-called non-uniformity of dispersion, and can be achieved by reducing the degree of melt-kneading the resin in the extruder. The reduction in the degree of melt kneading is achieved by reducing the degree of resin filling between the barrel and the screw, that is, by creating a gap between the barrel and the screw. At the time of melt-kneading, kneading is generally carried out by friction between the resin and the screw and the barrel. However, if a gap is generated between the barrel and the screw, the friction is lowered and the degree of kneading is lowered.
In the present invention, by giving fluctuations to the torque of the screw, the bite of the pellet in the extruder becomes unstable, and a gap is generated between the barrel and the screw. Torque variation is achieved by varying the current value of the motor that moves the screw.
The torque fluctuation period is preferably 1/10 to 10 times the time required for one screw rotation.

(Fine particles)
Examples of the fine particles include inorganic fine particles and organic fine particles. The fine particles are not particularly limited, but can be used singly or in combination of two or more.
Examples of the inorganic fine particles include zinc carbonate, calcium carbonate, magnesium carbonate, titanium oxide, magnesium oxide, zinc oxide, silica, talc, kaolin, lithium fluoride, calcium fluoride, barium sulfate, zinc sulfide, alumina, calcium phosphate, mica. Etc. Examples of the organic fine particles include polystyrene, polymethylstyrene, polymethoxystyrene, polyethylene, polypropylene, polymethacrylate, polymethyl methacrylate, crosslinked polydivinylbenzene particles, crosslinked polystyrene particles, crosslinked polyester particles, crosslinked polyimide particles, and crosslinked polycrystals. Ether sulfone particles, silicone particles and the like can be used.

  From the viewpoints of the whiteness of the polyester film and its color, inorganic fine particles are preferable. Among these, titanium oxide, calcium carbonate, barium sulfate and the like are preferable, and titanium oxide is more preferable. Various production methods and the like of titanium oxide are disclosed. For example, rutile type and anatase type fine particles described in, for example, Chemical Dictionary (Kyoritsu Shuppan Co., Ltd.) can be used. Among them, it is preferable to use a material suitable for whiteness, dispersibility, concealment and the like. The fine particles may be in the form of a porous or hollow porous material. Further, in order to improve the dispersibility with respect to polyester, the surface is made of an organic acid, a salt thereof, a polymer having a functional group, an inorganic acid, or the like. Processing may be performed. In addition, it is desirable to use a dispersing agent together with the fine particles because the aggregation of the particles can be prevented and the scratch resistance becomes better.

  The average particle diameter of the fine particles is preferably in the range of 0.1 μm to 10 μm, more preferably in the range of 0.2 μm to 5 μm, and even more preferably in the range of 0.3 μm to 2 μm in both organic fine particles and inorganic fine particles. is there. When the average particle diameter is within the above range, the light reflectance is excellent.

  The method for adding the fine particles is not particularly limited. For example, after the fine particles are kneaded with polyester to form a master pellet, the master pellet may be put into an extruder and melt-kneaded to form a film. Further, fine particle powder may be directly fed into an extruder.

  The white polyester film may be whitened by voids (bubbles). The partial discharge voltage can be increased by dispersing the electric field at the interface between the polyester and the void. Although there is no restriction | limiting in particular in the formation method of a void, For example, it can form by making the polyester resin contain the inorganic fine particle, incompatible resin, or inert gas with low affinity of polyester resin, and extending | stretching. Especially, a void can be formed suitably by mixing incompatible resin with a polyester resin and extending | stretching the extruded raw material.

  In the present invention, it is preferable that the incompatible resin is finely dispersed in a particulate form in the polyester and contained in large numbers. The incompatible resin is preferably a thermoplastic resin that is incompatible with polyester, and is not particularly limited as long as it is incompatible with polyester. Specifically, examples of incompatible resins include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, polystyrene resins or polyolefin resins such as polymethylpentene and polypropylene are suitable.

  The mixing amount of the incompatible resin with respect to the polyester varies depending on the desired amount of voids (bubbles), but is preferably in the range of 3% by mass to 20% by mass, and more preferably 5% by mass to 18% with respect to the entire film. A range of mass% is more preferred. When the mixing amount of the incompatible resin is 3% by mass or more, there is a limit to the amount of voids generated. Further, when the mixing amount of the incompatible resin is 20% by mass or less, heat resistance, strength, and waist strength are not impaired.

The thickness of the first layer is preferably in the range of 5 μm to 80 μm.
When the thickness of the first layer is 5 μm or more, the reflectance is higher and the power generation efficiency in the solar cell can be further improved. Moreover, the effect at the time of laminating | stacking the 2nd layer mentioned later on a 1st layer as the thickness of a 1st layer is 80 micrometers or less becomes higher. In other words, the second layer maintains weather resistance to light and heat, but the first layer is in a range that does not become too thick, so that the second layer retains strength when the first layer deteriorates. In addition, the adhesion can be maintained well over a long period of time.
The thickness of the first layer is preferably 10 μm or more and 70 μm or less, and more preferably 15 μm or more and 65 μm or less.

When the molten resin is formed into a film, the thickness of the first layer can be adjusted, for example, by the following method.
(1) It adjusts to desired thickness by adjusting the extrusion amount of resin. For example, when the amount of extrusion is increased, the film thickness can be increased.
(2) The thickness is adjusted to a desired thickness by adjusting the peripheral speed of the cast drum. For example, when the molten resin (melt) extruded from the extruder is solidified on a cast drum, the film thickness can be increased by reducing the peripheral speed of the drum.

At this time, the thickness distribution of the first layer is preferably in the range of 1% to 20%.
The presence of the thickness distribution in the first layer increases the boundary length between adjacent layers (for example, a second layer described later). As a result, the effect due to the distribution of fine particles at the interface is easily exhibited, and the adhesion is more effectively improved.
When the thickness distribution is 1% or more, the effect due to the distribution of fine particles at the interface tends to appear, and the adhesion is improved. Further, when the thickness distribution is 20% or less, a part of the first layer does not become too thick. As a result, it is possible to prevent the thickness of the adjacent layer (for example, a second layer described later) from decreasing relatively, and it is difficult for partial stress concentration or peeling stress to break, resulting in better adhesion. It will be.
The thickness distribution of the first layer is more preferably 2% or more and 18% or less, and further preferably 3% or more and 15% or less.

The thickness and thickness distribution of the first layer are determined by the following method.
The thickness distribution of the first layer is as follows. A 1 cm long sample of 10 points is made at 2 cm intervals along the MD of the polyester film, and the cross section of each sample is observed with a scanning electron microscope (SEM). The thickness of the layer is measured. Among the measured values, the difference between the maximum value and the minimum value is obtained, and the value obtained by dividing the difference by the average value of the measured values is shown as a percentage, and is defined as the MD thickness distribution. As for TD, 10 cm 1 cm long samples are prepared at intervals of 2 cm along the TD and measured in the same manner as in MD to obtain the TD thickness distribution.
And the average of thickness distribution of obtained MD and thickness distribution of TD is calculated | required, and it is set as the thickness distribution of a 1st layer.
Moreover, the average thickness of MD in the 1st layer and the average thickness of TD are averaged, and let this average value be the thickness of a 1st layer.

Molten resin (melt) is laminated inside the die. At that time, by varying the melt viscosity, a difference occurs in the fluidity in the die, and a thickness distribution is formed.
The fluctuation of the melt viscosity is achieved by modulating the output of the heater installed in the die. At this time, it is preferable to modulate the heater output so that the temperature fluctuation of the die is 0.5 ° C. or more and 10 ° C. or less. The temperature fluctuation of the die is more preferably 0.7 ° C. or more and 8 ° C. or less, and further preferably 1 ° C. or more and 5 ° C. or less.
Further, the period of temperature modulation is preferably 0.05 seconds or more and 1 second or less, more preferably 0.1 seconds or more and 0.8 seconds or less, and further preferably 0.2 seconds or more and 0.7 seconds or less. is there.

When it has said 1st layer, it is preferable that it is 40 micrometers or more and 350 micrometers or less as total thickness of the polyester film which comprises a white polyester film.
When the total thickness is 40 μm or more, the light reflection efficiency is excellent. Further, when the total thickness is 350 μm or less, the adhesiveness is more excellent. This is due to the following reason. That is, after laminating a white polyester film on a solar cell and peeling it to evaluate adhesion, the white polyester film is usually peeled while being bent in a U shape, so that the inner and outer sides of the U-shaped part In this case, a difference in circumference occurs, and as a result, distortion occurs in the film. The difference between the inner periphery and the outer periphery is larger as the film is thicker, and adhesion failure due to cohesive failure in the film due to distortion tends to be caused. Therefore, the total thickness is preferably 350 μm or less.
The total thickness is more preferably 45 μm or more and 330 μm or less, and still more preferably 50 μm or more and 300 μm or less.

  When the molten resin is formed into a film, the total thickness of the first layer can be adjusted, for example, in the same manner as the method of adjusting the thickness of the first layer as described above.

~ Second layer ~
The polyester film constituting the white polyester film of the present invention contains 0.06% by mass or more and 10% by mass or less of fine particles in addition to the first layer described above, and the dispersion of fine particles. The aspect containing at least 1 layer of the 2nd layer whose degree is 10% or more and 100% or less is preferable.

The polyester film constituting the white polyester film of the present invention is configured in a mode in which a second layer is further provided in addition to the first layer described above, so that the degree of dispersion of fine particles is within a predetermined range. The effect by this is promoted, and the adhesion when exposed to light, heat, etc. for a long time is further improved. This is presumed to be due to the following mechanism.
That is, the concentration of fine particles is different at the interface between the first layer and the second layer, and a dispersed state of the fine particles is formed at this interface. The improvement effect is exhibited.

It is preferable that at least one second layer is provided on the first layer. The second layer may be provided on one side of the first layer or on both sides. As for the polyester film which comprises the white polyester film of this invention, 1st layer and 2nd layer are laminated | stacked, and also the surface of 1st layer or 2nd layer, or 1st layer and 2nd layer An embodiment having a structure in which an easy adhesion layer is laminated on both surfaces is preferable. Furthermore, the aspect which has the structure where the 1st layer, the 2nd layer, and the easily bonding layer were laminated | stacked in this order including the 1st layer and the 2nd layer is preferable.
The number of second layers is preferably 1 or more and 5 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or more and 2 or less. When the number of layers of the multilayer structure is in the above range, an effect commensurate with the number of layers can be expected without saturating the effect, and the equipment is not enlarged.

  The second layer can be formed by using an extruder capable of co-extrusion of a plurality of layers and introducing and laminating the extruded molten resin into a multi-manifold die, a feed block die or the like. When there are a plurality of second layers, the composition of each layer may be the same or different.

In the second layer, the content of the fine particles is in the range of 0.06% by mass to 10% by mass with respect to the mass of the polyester, and is different from the content of the fine particles in the first layer described above. preferable. When the fine particle concentration in the second layer is different from the fine particle content in the first layer, the adhesion at the interface with the first layer can be further improved.
In addition, since the fine particle concentration in the second layer is lower than the fine particle concentration in the first layer, the second layer has an effect of maintaining the strength even when the first layer is deteriorated. The weather resistance to light and heat is further improved. As a result, even if the first layer is about to break due to peeling stress, the second layer suppresses cohesive failure and improves adhesion.

  Further, in the second layer, the same effect as that of the first layer can be obtained by providing the fine particle dispersity in the same manner as in the first layer. That is, adhesion is improved by the same action mechanism as that of the first layer. This effect is that, by laminating the second layer and the first layer, the adhesive force is synergistically improved, and the light reflection efficiency is also improved. Therefore, the light leaked from the first layer is reflected by the second layer and returned to the first layer, thereby increasing the reflection efficiency and contributing to the improvement of the power generation efficiency.

The dispersion degree of the fine particles in the second layer is synonymous with the dispersion degree of the fine particles in the first layer, and the preferable range of the dispersion degree is also the same. That is,
When the degree of dispersion of the fine particles is 10% or more, the adhesion is further improved. In addition, when the degree of dispersion of the fine particles is 100% or less, the strength reduction of the portion having a lot of fine particles is suppressed, and the strength of the whole film is improved in combination with the high strength of the portion having a small amount of fine particles, and the adhesion is further improved. To do.
The degree of dispersion of fine particles is more preferably 20% or more and 90% or less, and further preferably 25% or more and 85% or less.

The degree of dispersion of the fine particles in the second layer can be measured in the same manner as the method for measuring the degree of dispersion of the fine particles in the first layer.
Further, the degree of dispersion of the fine particles in the second layer is the dispersion non-uniformity as in the case of the first layer, and is achieved by reducing the degree of melt kneading of the resin in the extruder. Can do. The detailed achievement method is the same as that in the first layer.

When the content of the fine particles in the second layer is 0.06% by mass or more, the reflectance of light becomes better, and the power generation efficiency is improved. Further, when the content of the fine particles is 10% by mass or less, the weather resistance is excellent, and even when the first layer described above is deteriorated, the effect of maintaining the strength of the second layer is exerted, and the adhesion is further improved. It can be maintained for a long time.
As content of microparticles | fine-particles, 0.1 mass% or more and 5 mass% or less are preferable with respect to the mass of polyester, More preferably, they are 0.2 mass% or more and 2 mass% or less.

The measurement of the content of fine particles in the second layer can be performed as follows.
Similar to the first layer, the content of the fine particles can be calculated by accurately weighing the weight of the polyester film before and after firing. Specifically, the second layer of the polyester film is scraped off and placed in a crucible and precisely weighed (Xg). Next, the second layer placed in the crucible is fired in air at 800 ° C. for 3 hours. After firing, the sample is allowed to stand at room temperature overnight and then weighed (Yg).
The content (% by mass) of the inorganic fine particles is calculated as 100 × Y / X.
In addition, when there are a plurality of second layers, each layer is measured by the above method.

  The method for adding the fine particles to the second layer is not particularly limited, but the fine particles may be added to the polyester that forms the second layer during coextrusion. For example, fine particles may be kneaded with polyester to form a master pellet, and then the master pellet may be put into an extruder, melt-kneaded to form a film. Further, fine particle powder may be directly fed into an extruder.

In the case of having the second layer, the thickness of the second layer is preferably 40% or more and 95% or less, more preferably 45% or more and 90% or less, more preferably the total thickness of the polyester film constituting the white polyester film. It is 50% or more and 85% or less.
When the thickness of the second layer is 40% or more, the adhesion improving effect by providing the second layer is further exhibited. Further, when the thickness of the second layer is 95% or less, the light reflectance is more excellent.

The white elongation at break of the white polyester film of the present invention when exposed to environmental conditions of a temperature of 120 ° C. and a humidity of 100% RH for 60 hours is preferably from 70 hours to 200 hours.
When the rupture elongation half time is 70 hours or more, it is advantageous for improving the adhesion and the generation of cutting waste is suppressed. Moreover, when the elongation at break half time is 200 hours or less, the mobility of the polyester molecules is maintained, embrittlement is suppressed, and as a result, cracking during cutting is less likely to occur, and generation of cutting waste is also suppressed.
The breaking elongation half time is more preferably 80 hours or more and 170 hours or less, and further preferably 90 hours or more and 150 hours or less.

When the breaking elongation half time is within the above range, in addition to the effect (a) below, the effect (b) is exhibited as a unique effect that cannot be predicted.
(A) Adhesion improvement effect When wet heat treatment is performed under the environmental conditions of a temperature of 120 ° C. and a humidity of 100% RH, the polyester is hydrolyzed to lower the molecular weight. When is added, cohesive failure occurs in the polyester, and the adhesion is reduced. When the breaking elongation half time is within the above range, hydrolysis of the polyester is suppressed, and the adhesion strength after wet heat aging is improved.
(B) Cutting waste reduction Cutting fines are likely to be generated during cutting due to the inclusion of fine particles, and particularly when there is a concentration distribution in the fine particles as in the present invention, cutting waste is likely to be generated at a location where the fine particle concentration is high. Cutting scraps are reduced when the half elongation at break is within the above range. This is presumably due to the following mechanism. That is,
Polyesters having a long half elongation at break as described above (usually 30 to 50 hours), that is, polyesters that are difficult to hydrolyze, can be obtained by suppressing the mobility of polyester molecules. Reactivity with water is suppressed due to the decrease in mobility, and polyester with low mobility is difficult to move through the film, and deformation (creep) of the polyester film is suppressed. Cutting waste is generated when cutting stress concentrates on the interface between the fine particles and the polyester, and the polyester is deformed (stretched) and cut. Therefore, cutting waste is reduced by increasing the hydrolyzability of the polyester to reduce the mobility.

The measurement of the elongation at break half time can be performed by the following method.
While increasing the sample film in 100% at 120 ° C. for 50 hours, 60 hours, 70 hours and 10 hours, the measurement is performed until the breaking elongation retention rate becomes 10% by the following method. The time for the thermo treatment is plotted on the horizontal axis and the breaking elongation retention is plotted on the vertical axis, and the time at which the breaking elongation retention is 50% is interpolated. The breaking elongation retention is determined according to the following formula from the breaking elongation (S0) before the thermo treatment and the breaking elongation (St) after the thermo treatment for a certain time.
Breaking elongation retention rate (%) = 100 × (St) / (S0)

Normally, the elongation at break of polyester can be improved by solid phase polymerization or the like, but this method cannot be expected to be sufficiently effective for white polyester. In particular, the effect of suppressing cutting waste cannot be obtained.
In the case of white polyester (for example, white PET), in addition to normal hydrolysis, the polyester is easily crystallized around fine particles, and this is promoted under high temperature and high humidity. Therefore, polyester tends to be more brittle and the elongation at break tends to decrease. By suppressing the generation of spherulites as crystal nuclei when forming a white polyester film, it is possible to suppress the formation of crystals around the fine particles and to easily improve the elongation at break. In the polyester film-forming process, spherulites are most easily formed by longitudinal stretching, and this can be achieved by rapidly cooling after stretching and rapidly cooling the temperature range in which spherulites are formed. That is, it is preferable that the cooling rate after longitudinal stretching is 5 ° C./second or more and 100 ° C./second or less.
The cooling rate is more preferably 10 ° C./second to 90 ° C./second, and further preferably 15 ° C./second to 80 ° C./second. When the cooling rate is 5 ° C./second or more, it is difficult to produce crystals around the fine particles, and generation of cutting waste is suppressed. Further, when the cooling rate is 100 ° C./second or less, the residual strain in the polyester film accompanying rapid cooling is reduced, cracks generated from the residual strain at the time of cutting are suppressed, and generation of cutting waste is also suppressed.
The method of cooling at a predetermined cooling rate after the longitudinal stretching can be performed by bringing the polyester film into contact with a cooling roll or blowing cold air.

<Method for producing white polyester film>
The method for producing a white polyester film of the present invention comprises a step of forming an easy-adhesion layer on at least one surface of a polyester film in the middle of film formation, and at least one of the following steps (1) and (2): Have at least.
(1) Drying step of drying the applied easy-adhesion layer by applying a temperature difference of 0.5 ° C. or more and 10 ° C. or less within the surface of the easy-adhesion layer (2) Polyester film on which the easy-adhesion layer is formed Stretching step in which a temperature difference of 0.5 ° C. or more and 10 ° C. or less is applied to the surface of the polyester film.

(Formation of easy adhesion layer)
The manufacturing method of the white polyester film of this invention has the process (henceforth an easy-adhesion layer formation process) of forming an easily bonding layer by application | coating at least one surface of the polyester film in the middle of film forming. In the present invention, the easy-adhesion layer is formed on a polyester film in the middle of film formation in which processing such as stretching after film formation has not been completed, so that the thickness is 0.01 μm or more and 1 μm or less, and the thickness distribution A white polyester film in which an easy-adhesion layer having a thickness of 1% or more and 30% or less is formed on the polyester film is obtained.

  The polyester film in the middle of film formation refers to a polyester film in which the melt-extruded molten resin is formed into a film, but the stretching process, the heat setting process after stretching, and the heat relaxation process are not completed.

In the easy-adhesion layer forming process of the present invention, in particular, as a polyester film in the middle of film formation, the easy-adhesion layer coating solution is applied and dried on a polyester film that has been longitudinally stretched and not laterally stretched after film formation. It is preferable to form an easy adhesion layer. Thereby, by extending | stretching the polyester film in which the easily bonding layer was formed, interfacial mixing arises between an easily bonding layer and a polyester film, and adhesive force can be improved more.
Details of the easy-adhesion layer are as described above.

As a method of providing an easy-adhesion layer on the surface of the polyester film, for example, a known coating technique such as a bar coating method, a roll coating method, a knife edge coating method, a gravure coating method, or a curtain coating method can be used.
Moreover, you may perform surface treatment (a flame treatment, a corona treatment, a plasma treatment, an ultraviolet treatment, etc.) with respect to the easily bonding layer formation surface of a polyester film before formation of an easily bonding layer.

  The coating liquid for forming the easy-adhesion layer (coating liquid for easy-adhesion layer) contains at least an acrylic, urethane-based, polyester-based, or polyamide-based resin, depending on the use of the polyester film. Details of the resin are as described above.

(Film forming process)
The polyester film provided with the easy-adhesion layer can be obtained by mixing polyester as a raw material together with fine particles and other resins, melting and kneading with an extruder, and forming an extruded molten resin (melt).

In melt-kneading the resin, a master pellet in which polyester, fine particles or incompatible resin is melt-kneaded and fine particles or incompatible resin is dispersed at a high concentration may be prepared in advance.
The polyester resin used for the preparation of the master pellet is preferably used after polycondensation of diol and dicarboxylic acid according to a conventional method and then processing into a pellet. End-capping agents such as carbodiimides and ketene imine compounds may be added directly to the extruder, but mixing with polyester in advance to form a masterbatch, and this masterbatch is put into the extruder, extrusion stability From the viewpoint of
The concentration of the fine particles or incompatible resin and end-capping agent in the master pellet is preferably 1.5 to 20 times, more preferably 2 to 15 times, and even more preferably 3 times the concentration used in the film. 10 times. The reason why the content concentration is made higher than the target concentration is that the concentration is diluted with the polyester pellets in the next film-forming step to reach the target concentration.

For kneading, various kneaders such as a single screw extruder, a twin screw extruder, a Banbury mixer, and a Brabender can be used. Among these, it is preferable to use a twin screw extruder.
The kneading temperature is preferably from the crystal melting temperature (Tm) of the polyester to Tm + 80 ° C., more preferably Tm + 10 to Tm + 70 ° C., and even more preferably Tm + 20 to Tm + 60 ° C.
The kneading atmosphere may be in air, in a vacuum, or in an inert stream, but more preferably in a vacuum or an inert stream.
The kneading time is preferably from 1 minute to 20 minutes, more preferably from 2 minutes to 18 minutes, and even more preferably from 3 minutes to 15 minutes.
The kneaded resin is extruded into strands, cooled and solidified in air or water, and then cut into pellets.

  Drying is performed by drying a composition such as fine particles or incompatible resin, polyester, and terminal blocker in vacuum or hot air so that the water content is 100 ppm or less, more preferably 80 ppm or less, and even more preferably 60 ppm or less. To be done. The drying temperature at this time is preferably 80 ° C to 200 ° C, more preferably 100 ° C to 180 ° C, and further preferably 110 ° C to 170 ° C. The drying time can be appropriately adjusted so as to achieve the above moisture content.

  In the film forming process, molten resins having different contents of fine particles and incompatible resin are extruded through a die onto a cast drum. When laminating, it is coextruded on a cast drum through a multilayer die. The molten resin is solidified on a cast, formed into a film, and obtained as a cast film (unstretched original fabric). As the multi-layer die system, either a multi-manifold die or a feed block die can be suitably used. The shape of the die can be a T-die, a hanger coat die, a fish tail, or the like. The molten resin (melt) is preferably passed through a melt pipe, a gear pump, and a filter. The opening of the filter is preferably 1 μm to 50 μm, more preferably 5 μm to 40 μm, and even more preferably 10 μm to 30 μm. It is also preferable to provide a static mixer in the melt pipe to promote mixing of the resin and the additive.

  The temperature of the cast drum is preferably 0 ° C to 60 ° C, more preferably 5 ° C to 55 ° C, and further preferably 10 ° C to 50 ° C. At this time, in order to improve the adhesion between the molten resin and the cast drum and improve the flatness, it is also preferable to use an electrostatic application method, an air knife method, water coating on the cast drum, or the like. Furthermore, in order to perform cooling efficiently, cold air may be blown from the cast drum.

Extrusion is preferably performed under vacuum exhaust or an inert gas atmosphere. Thereby, decomposition | disassembly of a ketene imine, a carbodiimide compound, etc. can be suppressed. The temperature of the extruder is preferably in the temperature range from the melting point of the polyester used to the melting point + 80 ° C or less, more preferably in the range of melting point + 10 ° C or more, melting point + 70 ° C or less, more preferably melting point + 20 ° C or more. , Melting point + 60 ° C. or less. If the temperature of the extruder is higher than the melting point of the polyester, the resin will melt better. Conversely, if the temperature of the extruder is lower than the "melting point + 80 ° C", decomposition of the polyester, ketene imine compound, carbodiimide compound, etc. will be suppressed. It is done.
In addition, it is preferable to dry masterbatches, such as polyester, a ketene imine compound, a carbodiimide compound, before extrusion. The preferable water content in this case is 10 ppm to 300 ppm, more preferably 20 ppm to 150 ppm.

The film forming process for forming the polyester film constituting the white polyester film is a process in which the resin material and the fine particles or the resin material in which the fine particles are dispersed are charged into the melt extruder, and the torque of the screw of the melt extruder is 0.5%. It can be configured by providing a step of melting and extruding with a variation of 20% or less.
In this step, the aforementioned “first layer” constituting the polyester film is formed. When a polyester film consists of a single layer, the polyester film which comprises a white polyester film is obtained by forming a 1st layer.
As a raw material charged into the melt extruder, a resin material (mainly polyester) and a mixed material of fine particles, or a resin material (for example, a polyester material) in which fine particles are dispersed in a resin (mainly polyester) are used.
When melt extrusion is performed with an extruder in which raw materials are charged, a fluctuation of 0.5% or more and 20% or less is applied to the torque of the rotating screw, whereby a gap is generated between the barrel and the screw, and dispersion is not achieved. As a result, the dispersion degree of the fine particles can be adjusted within a range where good adhesion can be obtained. A preferable degree of dispersion of the fine particles is 10% or more and 100% or less as described above.

  In the film forming step, when the molten resin melt-kneaded by a melt extruder is extruded from the die to form the first layer, it is preferable to give the die a temperature variation of 0.5 ° C. or more and 10 ° C. or less. As the temperature of the die fluctuates, the viscosity of the molten resin (melt) fluctuates, resulting in a difference in fluidity within the die and the formation of a thickness distribution. As a result, a thickness distribution can be imparted to the first layer. By doing in this way, a white polyester film becomes the thing excellent by adhesive force.

Further, in the film forming process for forming the polyester film constituting the white polyester film, the resin material and the fine particles or the resin material in which the fine particles are dispersed are charged into the melt extruder, and the torque of the screw of the melt extruder is set to 0.00. A step of melt-extrusion with a variation of 5% or more and 20% or less can be provided.
In this step, the aforementioned “second layer” constituting the polyester film is formed. By forming a second layer in addition to the first layer, a multilayer polyester film constituting the white polyester film can be obtained.
The raw material charged into the melt extruder is the same as that for forming the “first layer”.
When melt extrusion is performed with an extruder in which raw materials are charged, a fluctuation of 0.5% or more and 20% or less is applied to the torque of the rotating screw, whereby a gap is generated between the barrel and the screw, and dispersion is not achieved. As a result, the dispersion degree of the fine particles can be adjusted within a range where good adhesion can be obtained. A preferable degree of dispersion of the fine particles is 10% or more and 100% or less as described above.

Further, after the easy adhesion layer forming step, the following steps (1) or (2) or (1) and (2) are performed.
(1) Drying step In the drying step, the easy-adhesion layer formed by coating is dried by imparting a temperature difference of 0.5 ° C. or more and 10 ° C. or less to the surface of the polyester film during film formation. At the time of drying, since the drying is fast in the high temperature part and the coating liquid tends to flow into the high temperature part at a low temperature, the high temperature part tends to be thick. From this, thickness distribution can be given to an easily bonding layer by providing distribution to the drying time after application | coating.
The significance of the temperature difference between 0.5 ° C. and 10 ° C. is as described above, and the preferable range of the temperature difference is also as described above.

In the drying step, for example, the distribution of the amount of blown air that hits the easy-adhesion layer can be achieved by providing the distribution of the amount of blown air to the slit portion of the nozzle that blows out the dry air such as hot air. Thereby, thickness distribution can be given to an easily bonding layer.
Moreover, the heater installed in the drying zone may be divided so that the output of each heater has a distribution.

  In the drying step, it is preferable to perform drying by giving a temperature difference of 0.1 ° C. or more and 10 ° C. or less in the surface. When drying is performed with a temperature difference in the plane, the in-plane distribution of surface haze can be given to the easy-adhesion layer. As the in-plane distribution of the surface haze, as described above, an in-plane distribution in the range of 0.1% to 30% can be given. As a temperature difference here, 0.3 degreeC or more and 8 degrees C or less are more preferable, More preferably, they are 0.5 degreeC or more and 6 degrees C or less.

After the drying step, a cooling step of cooling the polyester film having the dried easy-adhesion layer by imparting a temperature difference of 0.1 ° C. or more and 10 ° C. or less between one side and the other side of the polyester film. Can be provided. When cooling after coating and drying the easy-adhesion layer coating solution, the surface roughness, i.e., surface haze, can be adjusted by giving a temperature difference between the coated surface side and the coated surface side opposite to the coated surface side. it can. The adjustment of the surface haze is preferably in the range of 0.01% to 3%.
The temperature difference is more preferably 0.3 ° C. or more and 8 ° C. or less, and further preferably 0.5 ° C. or more and 6 ° C. or less.

(2) Stretching step In the stretching step here, the polyester film on which the easy-adhesion layer is formed is stretched by applying a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the plane of the polyester film. When extending | stretching after application | coating, a draw ratio can be locally changed by providing temperature distribution to the film in extending | stretching. That is, the higher the temperature, the higher the draw ratio, and the lower the temperature, the lower the draw ratio. Therefore, the easy-adhesion layer becomes thin in the high-temperature part, and the easy-adhesion layer becomes thick in the low-temperature part, whereby a thickness distribution can be imparted to the easy-adhesion layer.
The significance of the temperature difference between 0.5 ° C. and 10 ° C. is as described above, and the preferable range of the temperature difference is also as described above.

The unstretched film formed in the film forming process can be subjected to a stretching process in the stretching process. Stretching is preferably performed in at least one of the machine direction (MD) and the transverse direction (TD), and is preferably stretched in both the MD and TD directions in terms of a good balance of film properties. Such stretching in two directions may be performed sequentially in the vertical and horizontal directions, or may be performed simultaneously. In the stretching step, the unstretched film cooled and solidified with a cooling roll is preferably stretched in one or two directions, and more preferably stretched in two directions. Stretching in two directions (biaxial stretching) includes stretching in the longitudinal direction (MD) (hereinafter also referred to as “longitudinal stretching”) and stretching in the width direction (TD) (hereinafter referred to as “lateral stretching”). It is also preferred that Each of the longitudinal stretching and the lateral stretching may be performed once or a plurality of times. At the same time, it may be stretched both vertically and horizontally.
The stretching treatment is preferably performed in the range of the glass temperature (Tg; ° C.) to (Tg + 60) ° C. of the film, more preferably (Tg + 3) ° C. to (Tg + 40) ° C., and further preferably (Tg + 5) ° C. (Tg + 30) ° C. At this time, it is preferable to provide a temperature distribution as described above.

A preferred draw ratio is 280% to 500%, more preferably 300% to 480%, and still more preferably 320% to 460% on at least one side. In the case of biaxial stretching, the film may be stretched evenly in the vertical and horizontal directions, but it is more preferable to stretch one of the stretch ratios more than the other and unevenly stretch. The draw ratio may be increased in either the machine direction (MD) or the transverse direction (TD).
A draw ratio is calculated | required using the following formula | equation.
Stretch ratio (%) = 100 × {(Length after stretching) / (Length before stretching)}

  The biaxial stretching treatment is performed once in the machine direction (MD), for example, in the range of (Tg1) ° C to (Tg1 + 60) ° C, which is the glass transition temperature of the film, so that the total magnification becomes 3 to 6 times. After extending | stretching 2 times or more, it can extend | stretch in the width direction so that magnification may become 3-5 times in the range of (Tg1) degreeC-(Tg + 60) degreeC.

The biaxial stretching process can be stretched (longitudinal stretch) in the longitudinal direction (MD) using two or more pairs of nip rolls with increased peripheral speed on the outlet side, and is held in the width direction (TD) with a chuck. Thereafter, stretching may be performed by widening the distance between the chucks in the longitudinal direction. The transverse stretching can be performed by holding both ends of the film with a chuck and spreading the chuck in an orthogonal direction (a direction perpendicular to the longitudinal direction).
The simultaneous stretching can be performed by combining an operation of expanding the chuck interval in the longitudinal direction and an operation of expanding the chuck interval in the width direction after being held by the chuck.

It is preferable to combine the stretching process with a coating process for coating and forming an easy-adhesion layer.
The easy adhesion layer is preferably formed on the surface of the polyester film by coating before the stretching step or in the middle of the stretching step. That is, in this invention, it is preferable to extend | stretch the polyester film in which the easily bonding layer was formed by apply | coating a coating liquid at least once.
For example, the stretching process and the coating process can be performed in the following combinations.
(A) Longitudinal stretching → Coating → Horizontal stretching (b) Coating → Longitudinal stretching → Horizontal stretching (c) Coating → Vertical and transverse simultaneous stretching (d) Longitudinal stretching → Horizontal stretching → Coating → Vertical stretching (e) Longitudinal stretching → Horizontal Stretch->application-> lateral stretch Among these, preferred methods are (a), (b), and (c), and a more preferred method is (a). In this case, it is preferable because it has the highest adhesion and the equipment is compact.

When the stretching step includes a step of longitudinal stretching and a step of lateral stretching, the polyester film after longitudinal stretching is stretched between 5 ° C./second and 100 ° C./second between the step of longitudinal stretching and the step of lateral stretching. It is preferable to provide a step of cooling at a cooling rate of. By cooling (rapid cooling) the polyester film after longitudinal stretching at a predetermined cooling rate, the elongation at break half-life is long and the adhesiveness is excellent.
The rapid cooling can be performed by, for example, a method of bringing a polyester film into contact with a cooling roll, a method of blowing cool air, or the like.

In the stretching step, the film can be subjected to heat treatment before or after the stretching treatment, preferably after the stretching treatment. By performing heat treatment, microcrystals can be generated, and mechanical properties and durability can be improved. About 180-225 ° C. (more preferably, 185-21
The film may be subjected to heat treatment at 0 ° C. for 1 to 60 seconds (more preferably 2 to 30 seconds).

In the stretching step, a thermal relaxation treatment can be performed after the heat treatment.
The thermal relaxation treatment is a treatment for shrinking the film by applying heat to the film for stress relaxation. The thermal relaxation treatment is preferably performed in both the MD and TD directions of the polyester film. The various conditions in the thermal relaxation treatment are preferably a treatment at a temperature lower than the heat treatment temperature, and preferably 130 to 220 ° C. In the heat relaxation treatment, the thermal shrinkage of the film is preferably 1% to 12% for both MD and TD, and more preferably 1% to 10%.
For the heat shrinkage rate, a sample with a measurement direction of 350 mm and a width of 50 mm was cut out, marked at 300 mm intervals near both ends in the longitudinal direction of the sample, one end was fixed to an oven adjusted to a temperature of 150 ° C., and the other end was free. After being allowed to stand for 30 minutes, the distance between the gauge points is measured at room temperature. The measured length is L (mm), and the thermal contraction rate is obtained by applying the measured value to the following equation.
Thermal shrinkage at 150 ° C. (%) = 100 × (300−L) / 300
Further, when the heat shrinkage rate is positive, it indicates shrinkage, and when the heat shrinkage rate is negative, it indicates elongation.

Although the use of the white polyester film of this invention is not specifically limited, It is suitable for uses, such as a solar cell module backsheet and a barrier film base material. When using a white polyester film for a solar cell module backsheet, an easy-adhesion layer may be provided on the white polyester film, and the following layers may be provided.
1. Colored layer A colored layer can be provided in the white polyester film of the present invention. The colored layer is a layer arranged in contact with the surface of the polyester film or through another layer, and can be constituted using a pigment or a binder. Specifically, the description of paragraphs [0126] to [0138] of JP2012-166354A can be referred to.
2. Undercoat layer The white polyester film of the present invention may be provided with an undercoat layer. For example, when a colored layer is provided, the undercoat layer may be provided between the colored layer and the polyester film. The undercoat layer can be formed using a binder, a crosslinking agent, a surfactant, and the like. Specifically, reference can be made to the descriptions in paragraphs [0139] to [0142] of JP2012-166354A.
3. Antifouling layer (fluorine resin layer / silicon resin layer)
The white polyester film of the present invention is preferably provided with at least one of a fluorine-based resin layer and a silicon-based (Si-based) resin layer as an antifouling layer. By providing the fluorine-based resin layer or the Si-based resin layer, it is possible to prevent contamination of the polyester surface and improve weather resistance. Specifically, reference can be made to the descriptions in paragraphs [0143] to [0144] of JP2012-166354A.

<Solar cell module and manufacturing method thereof>
The solar cell module of the present invention is configured by providing the above-described white polyester film of the present invention as a solar cell backsheet. The solar cell module of the present invention is stable for a long period of time because the white polyester film of the present invention described above provided in the solar cell module of the present invention has excellent long-term adhesion to the adjacent layer. It becomes possible to maintain a typical power generation performance.

  Specifically, the solar cell module of the present invention is provided on a transparent base material (a front base material such as a glass substrate) on which sunlight enters and the base material, and seals the solar cell element and the solar cell element. An element structure portion having a sealing material to be stopped, and a white polyester film (back sheet for solar cell) disposed on a side opposite to a side where a substrate such as a glass substrate of the element structure portion is located, and transparent It has a laminated structure of a front substrate / element structure portion / back sheet. Specifically, an element structure portion in which a solar cell element that converts light energy of sunlight into electric energy is disposed on a transparent front base material disposed on a side where sunlight directly enters, and Sealing material such as an ethylene-vinyl acetate (EVA) system that is arranged between a white polyester film and an element structure portion (for example, a solar battery cell) including a solar battery element between the front substrate and the white polyester film. It is the structure which sealed and adhere | attached using. The white polyester film of the present invention is particularly excellent in adhesiveness with EVA and can improve long-term durability.

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 base material should just have the light transmittance which sunlight can permeate | transmit, and can be suitably selected from the base materials which permeate | 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, and gallium-arsenic. Various known solar cell elements such as II-VI group compound semiconductor systems can be applied. A space between the substrate and the polyester film can be configured by sealing with a resin (so-called sealing material) such as an ethylene-vinyl acetate copolymer.

(Bonding process)
The manufacturing method of the solar cell module of the present invention includes a bonding step of bonding an ethylene-vinyl acetate resin having a thermal dimensional change distribution of 1% to 40% and the white polyester film of the present invention described above. It is configured. Adhesion is further improved by bonding with EVA having a heat shrinkage distribution of 1% to 40%.

The ethylene-vinyl acetate resin is used as a sealing material for sealing the solar cell element provided in the solar cell, and in the bonding step of the present invention, a white polyester film is applied to the sealing material. Laminate as a back sheet to make a solar cell module.
About manufacture of the element structure part which has a sealing material which seals a solar cell element and a solar cell element, it can carry out by selecting a well-known method suitably.

  When the white polyester film and EVA are bonded together by heat, EVA tends to thermally shrink, but since it is bonded to polyester, it cannot shrink and becomes a residual stress. This residual stress promotes peeling in combination with the force when the peeling stress is applied, and the adhesion force is reduced. If there are large and small portions of heat shrinkage in the EVA, the portions with small heat shrinkage suppress the heat shrinkage of the whole EVA, and the thermal dimensional change distribution of EVA is in the range of 1% to 40%. As a result, the average heat shrinkage rate becomes approximately the same, and the adhesion can be improved more effectively.

  The thermal dimensional change distribution of EVA is more preferably 2% or more and 30% or less, and further preferably 3% or more and 20% or less. If the thermal dimensional change distribution is within this range, the locations where the thermal dimensional change is large are reduced and the residual stress is also suppressed, so that the occurrence of peeling that tends to occur from the residual stress is suppressed. As a result, the effect of improving the adhesion is excellent.

The thermal dimensional change distribution of EVA is measured by the following method.
a) After conditioning the EVA overnight in an environment of 25 ° C. and 60% RH, reference points are set at intervals of 20 cm and measured (L1).
b) This EVA sheet is heat-treated at 60 ° C. for 1 hour in an air thermostatic chamber. c) Thereafter, humidity is adjusted overnight in an environment of 25 ° C. and 60% RH, and then the length is measured (L2).
d) Calculate the thermal dimensional change from the following formula: Thermal dimensional change (%) = 100 × | L1-L2 | / L1
Note that “| L1−L2 |” in the formula represents the absolute value of the difference between L1 and L2.
e) This measurement is repeated for 10 sheets of 30 cm square cut out from the raw fabric roll, and the thermal dimensional change of each sheet is measured by the above method along MD and TD. f) Each of 10 points along MD and TD The difference between the maximum value and the minimum value of the thermal dimensional change is divided by the average value of the thermal dimensional change at 10 points for each of MD and TD and expressed as a percentage to obtain the thermal dimensional change distribution of MD and TD. Then, an average of the thermal dimensional change distribution of MD and the thermal dimensional change distribution of TD is obtained to obtain the thermal dimensional change distribution.

  The average value of EVA thermal dimensional change is preferably 0.1% to 5%, more preferably 0.3% to 4%, and still more preferably 0.5% to 3%.

The thermal dimensional change distribution can be adjusted by relaxing a part of the thermal shrinkage generated during film formation.
Specifically, the average temperature of EVA is 40 ° C to 70 ° C, more preferably 45 ° C to 65 ° C, still more preferably 50 ° C to 60 ° C, and the temperature distribution of EVA is more preferably 0.5 to 8 ° C. Is 1 to 7 ° C, more preferably 1.5 to 6 ° C, and heating is performed for 1 minute to 10 minutes, more preferably 1.5 minutes to 9 minutes, and further preferably 2 minutes to 8 minutes.

The period of the temperature distribution is preferably 5 cm to 1 m, more preferably 10 cm to 80 cm, and still more preferably 15 cm to 60 cm. Although the heating method which has such a temperature distribution is not specifically limited, For example, the following method is mentioned.
B) Using a panel heater divided vertically and horizontally with the above period, set these temperatures to have the above temperature distribution, and bring EVA into contact with this. B) Hot air from divided nozzles from one or both sides of EVA. The above temperature distribution is given to the temperature of each nozzle.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.
The present invention 16, the present invention 22, the present invention 23, the present invention 29, the present invention 30, the present invention 37, and the present invention 43 are reference examples of the present invention.

(1) Preparation of polyester (1-1) pellets-A. Ti catalyst PET (Ti-PET)-
Polyester (polyethylene terephthalate; hereinafter abbreviated as Ti catalyst PET or Ti-PET) is produced using a titanium catalyst in the same manner as in Example 1 described in paragraphs 0098 to 0104 of JP-A-2007-70462. A pellet was obtained.

-B. Sb catalyst PET (Sb-PET)-
According to “Raw material PET-1” described in paragraph 0054 of WO 2010/110119 pamphlet, polyester was obtained as follows.
A mixture of 100% by mass of dimethyl terephthalate and 60% by mass of ethylene glycol was added with 0.08% by mass of calcium acetate and 0.03% by mass of antimony trioxide, and heated to increase the temperature by a conventional method to conduct a transesterification reaction. It was. After adding lithium acetate 0.16 mass% and trimethyl phosphate 0.11 mass% to the transesterification product obtained here, it moved to the polymerization reaction tank. The reaction system was gradually depressurized while being heated and heated, and polymerization was performed at 290 ° C. under a reduced pressure of 1 mmHg by a conventional method to obtain a polyester (polyethylene terephthalate) having an intrinsic viscosity of 0.52, which was made into pellets.

-C. Al catalyst PET (Al-PET)-
To a heat medium circulation type (2 liter) stainless steel autoclave with a stirrer, high-purity terephthalic acid and its 2-fold molar amount of ethylene glycol and triethylamine are added so as to be 0.3 mol% with respect to the acid component. The esterification reaction was carried out for 120 minutes while distilling water out of the system at 245 ° C. under a pressure of 25 MPa to obtain an oligomer mixture. To this oligomer mixture, an ethylene glycol solution of 15 g / l basic aluminum acetate as a polycondensation catalyst was 0.014 mol% in terms of aluminum atom with respect to the acid component in the polyester, and Irganox 1425 (Ciba Specialty Chemicals) as the phosphorus compound. 10 g / l ethylene glycol solution, 0.02 mol% in terms of solid content of Irganox 1425, relative to the acid component in the polyester was added.
At this time, the basic aluminum acetate added as a polycondensation catalyst was used as an ethylene glycol solution of 15 g / l basic aluminum acetate obtained by returning a basic aluminum acetate (Aldrich) aqueous solution and ethylene glycol.
Subsequently, it stirred at 245 degreeC for 10 minutes by the normal pressure in nitrogen atmosphere. Thereafter, while raising the temperature to 275 ° C. over 60 minutes, the pressure of the reaction system is gradually reduced to 13.3 Pa (0.1 Torr) until a desired IV is obtained at 275 ° C. and 13.3 Pa. A polycondensation reaction was performed. When a predetermined stirring torque was reached, nitrogen was introduced into the autoclave to return to normal pressure, and the polycondensation reaction was stopped.
In this way, Al catalyst PET (Al-PET) was obtained and formed into pellets.

-D. PEN-
Polyethylene-2,6-naphthalate (PEN) resin was produced by the same method as in Example 3 described in paragraph 0120 of JP2011-258641, and pelletized.

(1-2) Solid Phase Polymerization Each of the above resins (pellets) was dried at 180 ° C. for 5 hours and crystallized. In addition, the pellet size used was a cylindrical shape having a diameter of 3 mm and a length of 5 mm.
After drying, the pellets were transferred to a 205 ° C. solid phase polymerization tank, and a solid phase polymerization reaction was performed by flowing nitrogen gas into the solid phase polymerization tank at 1 Nm ³ / hr per kg of resin. Solid phase polymerization was carried out at 205 ° C. for 24 hours.

(2) Preparation of fine particles (whitening material, etc.) The following inorganic fine particles and incompatible resin were prepared as whitening materials. In addition, the average particle diameter was measured using the LA-750 particle size analyzer (Particle Size Analyzer) made from HORIBA. The particle diameter of each particle corresponding to 50% by mass of the entire particle was read, and the average value of these values was taken as the average particle diameter.
<I. Inorganic fine particles (white particles)>
TiO ₂ −1: Rutile type titanium dioxide particles (surface coated with alumina, average particle size: 0.2 μm)
TiO ₂ -2: Rutile-type titanium dioxide particles (surface coated with alumina and trimethylolpropane, average particle size: 0.3 μm)
BaSO ₄ -1: barium sulfate particles (barium sulfate simple substance; average particle size: 1 μm)
BaSO ₄ -2: barium sulfate particles (surface coated with silica (average particle size: 3 μm)

<B. Incompatible resin>
-TPX: Polymethylpentene (TPX DX820, manufactured by Mitsui Chemicals)

(3) Production of polyester film-Film production (extrusion, casting)-
The pellets (polyester), fine particles, and incompatible resin that had been subjected to solid phase polymerization as described above were mixed as shown in Tables 1 and 2 below. At this time, the mixing ratio of the fine particles was the ratio shown in Tables 1 and 2 below (addition amount [mass basis]).
When forming a film, a master batch in which polyester, fine particles, and an incompatible resin are blended in advance using a biaxial kneader is prepared, and this master batch and pellets made of the same polyester alone as used in the master batch, Were mixed, put into a hopper of a twin-screw kneading extruder having a screw diameter of 200 mm, melt-kneaded at 290 ° C. under vacuum, and extruded. At this time, the rotation direction of the screw was the same direction rotation, and the dispersion of fine particles was changed by applying the torque fluctuation described in Tables 1 and 2 to the screw of the extruder. In the case of forming a polyester film having a two-layer structure, the film formation was performed by coextrusion. The pellets were dried to a water content of 50 ppm or less before the hopper was charged.
The extruded molten resin (melt) was filtered through a gear pump (pore diameter: 20 μm), laminated using a feed block die, and extruded from a die lip onto a cast drum to form a film. At this time, thickness distribution was provided to the polyester film (1st layer) which comprises a polyester film by providing the temperature distribution of Table 1-Table 2 to the division | segmentation heater attached to die | dye.
When casting, electrostatic application was performed under the following conditions.
・ Cast drum: 3m in diameter
・ Cast drum temperature: 25 ℃
・ Cast drum speed: 10m / min

-Longitudinal stretching and application-
The resin (unstretched polyester film) cooled and solidified on the cast drum as described above was preheated to 70 ° C. after being peeled off from the cast drum. And this unstretched polyester film was longitudinally stretched 3.5 times at 90 degreeC using the nip roll from which a peripheral speed difference differs, and it cooled to 30 degreeC with the cooling rate shown in the following Table 1-2. At this time, by blowing cold air after longitudinal stretching, the temperature distributions shown in Tables 1 and 2 below were given, and the elongation at break half time was achieved.

Next, corona treatment was performed on one side of the unstretched polyester film under the following conditions.
<Condition>
・ Electrode and dielectric roll gap clearance: 1.6mm
・ Processing frequency: 9.6 kHz
Processing speed: 20 m / min Processing strength: 0.375 kV A / min / m ²

  Then, the following coating liquid for easy-adhesion layers was applied to the corona-treated surface of the unstretched polyester film as shown in Tables 1 and 2 below, and an easy-adhesion layer as an application layer was formed. The details of the coating solution for the easy adhesion layer are as follows. The thickness of the coating layer was achieved by changing the bar count.

  In addition, the easy-adhesion layer was formed on the first layer side and the second layer side as shown in Tables 1 and 2 below in order to confirm the degree of adhesion. In the column of “application surface” of the easy-adhesion layer in Tables 1 and 2, “first layer” means that the easy-adhesion layer was formed on the surface of the first layer. "" Indicates that an easy-adhesion layer was formed on both surfaces of the first layer and the second layer.

(Preparation of coating solution for easy adhesion layer)
Solutions of resins (A) to (V) having the following compositions were used as the easy-adhesion layer coating solutions, respectively.
(A) Acrylic resin: A-1
・ Methyl methacrylate: 55 mol%
・ Ethyl acrylate: 40 mol%
・ N-methylolacrylamide: 3 mol%
・ 2-hydroxyethyl methacrylate 2 mol%
Tg of acrylic resin composed of the above components = 27 ° C.

(B) Urethane resin: U-1
-Urethane resin A-1 below

(C) Urethane resin: U-2
・ Water: 51.00% by mass
・ Isopropanol: 30.00% by mass
・ The following polyurethane resin: 12.58% by mass
-Resin having the following oxazoline group: 4.72% by mass
・ Particle: 1.57 mass%
(Silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass)
・ Particles: 0.08% by mass
(Silica sol with an average particle size of 450 nm, solid content concentration of 40% by mass)
・ Surfactant ... 0.05% by mass
(KF6011, manufactured by Shin-Etsu Silicone, silicone surfactant, solid concentration 100% by mass)

-Preparation of polyurethane resin-
In a four-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 43.75% by mass of 4,4-diphenylmethane diisocyanate, 12.85% by mass of dimethylolbutanoic acid, several An average molecular weight of 2000 polyhexamethylene carbonate diol 153.41% by mass, dibutyltin dilaurate 0.03% by mass, and 84.00% by mass of acetone as a solvent were added, and the mixture was stirred at 75 ° C. for 3 hours in a nitrogen atmosphere. It was confirmed that had reached the predetermined amine equivalent. Next, after the temperature of this reaction liquid was lowered to 40 ° C., 8.77 mass% of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring and adjusted to 25 ° C., while stirring and mixing at 2000 min ⁻¹ , the polyurethane prepolymer solution was added and dispersed in water. . Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin having a solid content of 35%. The glass transition temperature of the obtained polyurethane resin was −30 ° C.

-Preparation of resin having oxazoline group-
A flask equipped with a thermometer, a nitrogen gas inlet tube, a reflux condenser, a dropping funnel, and a stirrer, a mixture of 58% by mass of ion-exchanged water and 58% by mass of isopropanol as an aqueous medium, and a polymerization initiator (2, 2 4% by mass of '-azobis (2-amidinopropane) dihydrochloride) was added. On the other hand, in a dropping funnel, 16% by mass of 2-isopropenyl-2-oxazoline as a polymerizable unsaturated monomer having an oxazoline group, methoxypolyethylene glycol acrylate (average added mole number of ethylene glycol, 9 mol, Shin-Nakamura Chemical) A mixture of 32% by mass and 32% by mass of methyl methacrylate was added, and the mixture was added dropwise at 70 ° C. for 1 hour in a nitrogen atmosphere. After completion of the dropwise addition, the reaction solution was stirred for 9 hours and cooled to obtain a water-soluble resin having an oxazoline group having a solid concentration of 40% by mass.

(D) Urethane resin: U-3
Coating liquid / polyurethane with a concentration of 10% by mass prepared by adding water so that the solid content of each component is the following ratio: 60% by mass
(Hydran AP-40 manufactured by Dainippon Ink & Chemicals, Inc.)
・ Polyurethane ... 10% by mass
(Permarin UA310 manufactured by Sanyo Chemical Industries, Ltd.
・ Polyester: 20% by mass
(Finetex ES-670 manufactured by Dainippon Ink & Chemicals, Inc.)
・ Alkyrol melamine: 10% by mass

(E) Urethane resin: U-4
・ Water: 55.86% by mass
・ Isopropanol: 30.00% by mass
・ The following polyurethane resin solution (A-1): 13.52% by mass
・ Particle: 0.59 mass%
(Silica sol with an average particle diameter of 40 nm, solid content concentration: 40% by mass)
・ Surfactant ... 0.03% by mass
(Silicone-based, solid content concentration: 100% by mass)

-Preparation of urethane resin solution (A-1)-
In a four-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 43.75 parts by mass of 4,4-diphenylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, several 153.41 parts by mass of polyhexamethylene carbonate diol having an average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were added and stirred at 75 ° C. for 3 hours in a nitrogen atmosphere. It was confirmed that had reached the predetermined amine equivalent. Next, after the temperature of this reaction liquid was lowered to 40 ° C., 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the polyurethane prepolymer solution was added and dispersed in water while adjusting to 25 ° C. and stirring and mixing at 2000 min ⁻¹ . Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution (A-1) having a solid content of 35% by mass. The obtained polyurethane resin (A-1) had a glass transition temperature of -30 ° C.

(F) Polyester resin: E-1
・ Crosslinking agent ... 15% by mass
(Methyl methacrylate 30 mol% / 2-isopropenyl-2-oxazoline 30 mol% / polyethylene oxide (n = 10) methacrylate 10 mol% / acrylamide 30 mol% polymer having oxazoline group (Tg = 50 ℃))
・ Resin component: 75% by mass
(Copolymerized polyester composed of 80 mol% terephthalic acid / 15 mol% isophthalic acid / 5 mol% 5-sodium sulfoisophthalic acid as the acid component and 60 mol% ethylene glycol / 40 mol% diethylene glycol as the glycol component (Tg = 43 ℃))
・ Filler (silica particles having an average particle diameter of 60 nm): 4% by mass
・ Wetting agent (polyoxyethylene (n = 7) lauryl ether) 6 mass%

(G) Polyester resin: E-2
・ Water: 40.16% by mass
・ Isopropanol: 30.00% by mass
・ The following polyester aqueous dispersion: 18.19% by mass
・ Block polyisocyanate aqueous dispersion: 2.08% by mass
(Elastoron E-37 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
・ Particle A: 9.37% by mass
(Cerames S-8 manufactured by Taki Chemical Co., Ltd., solid content concentration: 8% by mass)
-Particle B: 0.17% by mass
(Sea Catalyst KEW50 manufactured by Nippon Shokubai Co., Ltd., solid content concentration: 15% by mass)
・ Silicone-based surfactant 0.03% by mass
(DC57 manufactured by Toray Dow Corning, solid content concentration: 100% by mass)
The particle A is SnO ₂ having a refractive index of 2.1, and the particle B is a silica particle having an average primary particle size of about 500 nm.

-Preparation of aqueous polyester dispersion-
30% by mass of the following polyester resin (a-1) and 15% by mass of ethylene glycol n-butyl ether were placed in a reactor equipped with a stirrer, a thermometer and a reflux device, and heated and stirred at 110 ° C. to dissolve the resin. After the resin was completely dissolved, 55% by mass of water was gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester aqueous dispersion having a solid content of 30% by mass.

-Preparation of polyester resin (a-1)-
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, dimethyl terephthalate 194.2% by mass, dimethyl isophthalate 184.5% by mass, dimethyl-5-sodium sulfoisophthalate 14.8% by mass Then, 233.5% by mass of diethylene glycol, 136.6% by mass of ethylene glycol, and 0.2% by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was performed from 160 ° C. to 220 ° C. over 4 hours. Next, the temperature was raised to 255 ° C., the pressure of the reaction system was gradually reduced, and the mixture was reacted for 1 hour 30 minutes under a reduced pressure of 30 Pa to obtain a copolymerized polyester resin (a-1). The obtained copolyester resin (a-1) was light yellow and transparent. Moreover, it was 0.70 dl / g when the reduced viscosity of the obtained copolyester resin (a-1) was measured. The glass transition temperature by DSC was 40 ° C.

(H) Polyester resin: E-3
・ Modified polyester polymer binder: 80% by mass
(FS-44, manufactured by Nippon Kakko Paint Co., Ltd.)
・ Isocyanate-based crosslinking agent (TD curing agent) ... 19.9% by mass
・ Lubricant MP-300 (Soken Chemical Co., Ltd.) ... 0.1% by mass

(I) Polyester resin: E-4
-Acid component-
・ Terephthalic acid 32.8% by mass
・ Isophthalic acid: 10.5% by mass
・ Trimellitic acid: 14.7% by mass
-Sebacic acid: 4.3% by mass
-Glycol component-
・ Ethylene glycol: 6.5% by mass
・ Neopentyl glycol: 13.1% by mass
・ 1,4-Butanediol: 18.1% by mass
Here, an ammonium salt type aqueous dispersion of a polyester resin (Tg: 20 ° C.) composed of an acid component and a glycol component was obtained.

(Nu) Polyester resin: E-5
・ Water-based polyester: 30% by mass
(Baironal, manufactured by Toyobo Co., Ltd.)
・ Water-based polyblock isocyanate compound B: 33% by mass
(Daiichi Kogyo Seiyaku, sulfite block type)
・ Water-based polyblock isocyanate compound C: 3% by mass
(Eastron BN11, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
・ Semipolar organoboron compound as antistatic agent: 34% by mass
(Boron International, High Boron)
Here, a coating solution having a solid content concentration of 14.6% by mass was obtained from the acid component and the solvent having a mass ratio of water / isopropanol = 93/7.

(L) PVA resin: V-1
・ Polyvinyl alcohol (polyvinyl alcohol having a saponification degree of 86 to 89 mol%): 20% by mass
・ Fine particles (spherical silica particles having an average particle diameter of 100 nm)...
・ Crosslinking agent (compound with the following structure): 1% by mass
Here, an aqueous coating solution having the above composition was obtained.

(Wo) Polyolefin resin: O-1
・ Polyolefin binder: 24.12% by mass
(Arrow Base SE-1013N, manufactured by Unitika Ltd., solid content concentration: 20% by mass)
・ Oxazoline-based crosslinking agent: 3.90% by mass
(Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content concentration: 25% by mass)
・ Fluorine-based surfactant: 0.19% by mass
(Sodium = bis (3,3,4,4,5,5,6,6-nonafluoro) = 2-sulfonite oxysuccinate, manufactured by Sankyo Chemical Co., Ltd., solid content concentration: 1% by mass)
・ Distilled water ... 71.80 mass%

<Drying, transverse stretching>
Subsequently, after applying the coating solution for the easy-adhesion layer on the unstretched polyester film, as shown in Tables 1 and 2 below, the distribution is given to the air volume of the drying air given to the coating surface, thereby increasing the drying speed. Distribution was given and thickness distribution was given to the easily bonding layer. At this time, the distribution of the drying air was formed by providing a distribution in the opening degree of the blowing nozzle of the drying air. Further, as shown in Tables 1 and 2 below, dry air is blown on both sides of the polyester film so that there is a temperature difference between the coated surface side and the non-coated surface side. The thickness distribution was given.

Next, an unstretched polyester film on which an easy-adhesion layer was formed was passed through a tenter, and both ends were gripped by a chuck, and then widened while being exposed to hot air at an average of 120 ° C. to be stretched 4 times in the width direction. Thereafter, the film was heat-fixed at 210 ° C. for 30 seconds, relaxed by 5% in each of the vertical and horizontal directions at 205 ° C., and then cooled to 70 ° C. At this time, by blowing cold air so that a temperature difference as shown in Tables 1 and 2 below can be made on the front and back of the film, and by giving a temperature difference to the front and back of the film, the surface as shown in Tables 1 and 2 Adjusted the haze. Furthermore, the in-plane distribution of the surface haze was adjusted by dividing the blowing nozzle on the application surface side and providing a temperature distribution on the application surface side.
Then, after trimming both ends of the film by 10 cm, the chuck was removed and knurling was applied. Thereafter, it was wound up to 2000 m with a width of 2 m.

  As described above, the white polyester film of the present invention having an easy-adhesion layer on the polyester film was produced.

<Evaluation>
Using the white polyester film obtained from the above, adhesion and cutting waste were evaluated by the following methods. The evaluation results are shown in Tables 1 and 2 below.
Note that the thickness and thickness distribution of the easy-adhesion layer, the surface haze and in-plane distribution of the easy-adhesion layer, the amount and dispersion of fine particles, the thickness and thickness distribution of the first layer, and EVA heat shrinkage (thermal dimensional change and its The measurement method of (distribution) is as described above.

  In this example, the EVA sheet to be attached to the white polyester film was subjected to heat treatment under the conditions described in Tables 1 and 2 below and provided with a heat shrinkage distribution.

(1) Adhesiveness The obtained white polyester film was cut into a size of 100 mm length × 100 mm width to prepare a PET sample. Moreover, the EVA sheet | seat was cut out to length 90mm x width 70mm, and the EVA sample was prepared.
Using these samples, a PET sample (easy-adhesive layer surface) / EVA sample / (easy-adhesive layer surface) PET sample was layered in this order, and thermocompression bonded under the following adhesion conditions with a vacuum laminator to prepare a laminate. The PET sample is disposed so as to be in contact with the EVA sample on the surface of the easy adhesion layer. The obtained laminate was thermo-treated under the following conditions, then cut into a length of 100 mm × 20 mm, attached to a SUS plate, and peel strength between a PET sample and an EVA sample under the following conditions using a tensile tester Was measured. The peel strength was determined as the average value of the portions that peeled stably after exceeding the maximum point.
<Types of EVA sheet>
A. Standard cure type Ultra Pearl PV (thickness: 0.4 μm), B. Fast cure type Solar EVA RC02B (thickness: 0.45μm), manufactured by Mitsui Fabro
<Adhesion conditions>
・ Equipment: Vacuum Laminator NP-30 type LM-30 × 30 ・ Pressurization: 1 atm ・ When using Ultra Pearl PV for EVA sheet,
Lamination process: 100 ° C. (vacuum 5 minutes, vacuum pressurization 5 minutes)
Cure process: Heat treatment 150 ° C (normal pressure 45 minutes)
When using EVA EVA RC02B for EVA sheet Laminating process: 150 ° C (vacuum 5 minutes, vacuum pressurization 15 minutes)
<Thermo conditions>
-Temperature: 120 ° C, Humidity: 100% RH
・ Processing time: 70 hours
<Measurement conditions>
The peel strength was measured by the following method after leaving the thermo-treated laminate in an atmosphere of 25 ° C. and 60% RH for 1 day.
・ Device: Tensilon RTM-100 manufactured by Toyo BALDWIN
・ Peeling speed: 200 mm / min ・ Peeling angle: 180 degrees

(2) Cutting waste (chip)
Ten pieces of film were punched out of the white polyester film on the black paper using a square Thomson blade having a side of 10 cm, and the white scraps scattered on the black paper were counted.

(3) Light reflectance A spectrophotometer (manufactured by Shimadzu Corp., self-recording spectrophotometer "UV-3150") is mounted with an integrating sphere, and a standard white plate (Sphere Optics, white standard plate "ZRS-99-010-"). W ") was calibrated with a reflectance of 100%, light was incident on the white polyester film from the easy-adhesion layer side, and the spectral reflectance (%) was measured. The measurement was performed in 1 nm increments in the wavelength region of 400 nm to 800 nm, and the average value was obtained.

(4) Breaking elongation half-life The white polyester film was allowed to stand in an environment of 120 ° C. and 100% RH and increased by 50 hours, 60 hours, 70 hours and 10 hours, respectively, and the breaking elongation retention rate was as follows. Was measured until 10%.
At this time, the time for the thermo treatment was plotted on the horizontal axis, and the breaking elongation retention was plotted on the vertical axis, and the time at which the breaking elongation retention was 50% was interpolated. The breaking elongation retention was determined according to the following formula from the breaking elongation (S0) before the thermo treatment and the breaking elongation (St) after the thermo treatment for a certain time.
Breaking elongation retention rate (%) = 100 × (St) / (S0)

  As shown in Tables 1 and 2, the easy adhesion layer provided on the white polyester film with a thickness of 0.01 μm or more and 1 μm or less has a thickness distribution in the range of 1% or more and 30% or less. Thus, excellent adhesion with EVA was shown. Moreover, the light reflectance was also good and the generation of chips was kept low.

Claims (16)

A polyester film containing fine particles;
An easy-adhesion layer having at least one surface of the polyester film, having a thickness of 0.01 μm to 1 μm, and a thickness distribution of 1% to 30%;
Have
Polyester film containing the fine particles, containing 5% by weight to 30% by weight of particles relative to the weight of the polyester, and saw including a first layer dispersion degree is less than 100% to 10% of the fine particles ,
The easy adhesion layer is a white polyester film having a surface haze of 0.01% to 3% and an in-plane distribution of the surface haze of 0.1% to 30% . The white polyester according to claim 1, wherein the easy-adhesion layer is formed on at least one surface of a polyester film in the middle of film formation, and is formed by performing at least one of the following steps (1) and (2). the film.
(1) A drying step in which the formed easy-adhesion layer is dried by applying a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the plane of the easy-adhesion layer. Stretching step in which a temperature difference of 0.5 ° C. or more and 10 ° C. or less is applied in the plane of the polyester film. The polyester film containing the fine particles further includes 0.06% by mass to 10% by mass of fine particles with respect to the mass of the polyester, and the degree of dispersion of the fine particles is 10% to 100%. The white polyester film according to claim 1, comprising at least one layer. 2. The first layer has a thickness of 5 μm or more and 80 μm or less, a thickness distribution of 1% or more and 20% or less, and a total thickness of the polyester film containing the fine particles is 40 μm or more and 350 μm or less. The white polyester film according to claim 3 . The polyester film containing the fine particles has a structure in which the first layer and the second layer are laminated, and the easy adhesion layer is laminated on at least one surface of the first layer and the second layer. The white polyester film according to claim 3 or 4 which has. The polyester film containing the fine particles includes the first layer and the second layer, and has a structure in which the first layer, the second layer, and the easy adhesion layer are laminated in this order. The white polyester film according to any one of Items 3 to 5 . The white according to any one of claims 1 to 6 , wherein the half elongation at break when exposed to an environmental condition of a temperature of 120 ° C and a humidity of 100% RH for 60 hours is from 70 hours to 200 hours. Polyester film. Solar cell module comprising a vinyl acetate resin, a white polyester film according to any one of claims 1 to 7, the be bonded bonding step of - thermal dimensional change distribution is less than 40% 1% of ethylene Manufacturing method. In the pasting step, the ethylene-vinyl acetate resin is bonded to the ethylene-vinyl acetate resin for 1 minute or more using a heater having an average temperature of 40 ° C. or higher and 70 ° C. or lower and a temperature distribution of 0.5 ° C. or higher and 8 ° C. or lower. The manufacturing method of the solar cell module of Claim 8 including the process of heat-processing in the range for 10 minutes or less. Forming an easy-adhesion layer by coating on at least one surface of the polyester film in the middle of film formation containing fine particles;
At least one of the following steps (1) and (2);
A resin material and fine particles, or a resin material in which fine particles are dispersed are charged into a melt extruder, and melt extrusion is performed by giving a variation of 0.5% to 20% to the screw torque of the melt extruder. Forming a first layer containing fine particles of 5% by mass or more and 30% by mass or less with respect to the mass and having a fine particle dispersity of 10% or more and 100% or less;
Have
The method for producing a white polyester film, wherein the polyester film includes at least a first layer.
(1) A drying step in which the formed easy-adhesion layer is dried by applying a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the surface of the easy-adhesion layer, and an easy adhesion dried after the drying step A step (2) having an easy-adhesion layer comprising: cooling a polyester film having a layer by applying a temperature difference of 0.1 ° C. or more and 10 ° C. or less between one surface and the other surface of the polyester film. A stretching process in which the formed polyester film is stretched by giving a temperature difference of 0.5 ° C. or more and 10 ° C. or less in the plane of the polyester film. When the step (1) is included, after the drying step, the polyester film having the dried easy-adhesion layer is cooled by providing a temperature difference of 0.1 ° C. or more and 10 ° C. or less in the plane of the polyester film. The manufacturing method of the white polyester film of Claim 10 which further has the process to do. A resin material and fine particles, or a resin material in which fine particles are dispersed are charged into a melt extruder, and melt extrusion is performed by imparting a variation of 0.5% to 20% to the screw torque of the melt extruder. , Further comprising a step of forming a second layer containing 0.06% by mass or more and 10% by mass or less of fine particles with respect to the total mass and having a fine particle dispersity of 10% or more and 100% or less, The method for producing a white polyester film according to claim 10 or 11 , wherein the polyester film comprises at least a first layer and a second layer. When forming a film of the first layer is melt-extruded melt-kneaded molten resin in the melt extruder through a die, according to claim 10 to claim 12 for imparting the temperature change of 10 ° C. below 0.5 ℃ above the die The manufacturing method of the white polyester film of any one of these. When having the step (1),
A step of longitudinally stretching the unstretched polyester film;
A step of transversely stretching the longitudinally stretched polyester film;
Between the step of longitudinal stretching and the step of lateral stretching, a step of cooling the polyester film after longitudinal stretching at a cooling rate of 5 ° C./second to 100 ° C./second,
The method for producing a white polyester film according to any one of claims 10 to 13 , further comprising: When having the step (2), the stretching step includes a step of longitudinally stretching the unstretched polyester film and a step of laterally stretching the longitudinally stretched polyester film,
Between the step of the step and the transverse stretching of longitudinal stretching, further comprising the step of cooling the polyester film after longitudinal stretching at 5 ° C. / sec or higher 100 ° C. / sec cooling rate, according to claim 10 to claim 14 The manufacturing method of the white polyester film of any one. A transparent base material on which sunlight is incident, an element structure portion provided on the base material and having a solar cell element and a sealing material for sealing the solar cell element, and the base material of the element structure portion solar cell module comprising but a white polyester film according to any one of claims 1 to 7 disposed on the side opposite to the side on which is located.